A Research Agenda for Aging in China

Today's review paper is a look at views on aging on the other side of the world, a counterpoint to commentaries from US and European sources. It is interesting to compare the intersection between science and policy in different regions of the world, when it comes to perspectives on degenerative aging, the enormous costs of age-related disease, and what is to be done about it. It is only comparatively recently that scientific advances have offered the potential for aging to become anything other than an inevitable, enormous cost to be suffered. Governments with entrenched and growing entitlement programs (such as the US Social Security) or command and control health systems (such as the UK NHS) - both transfers of wealth to the old - face insolvency and collapse as the fraction of the population that is old and expecting not to work expands over time.

Regardless of entitlement programs, everyone in every country faces a future of personal decline, pain, loss, and death. While much of the literature is focused on funding and the collapse of government programs, the real reason to make progress is this point about individual suffering. A world in which people did not decline with age would be a world in which people can support themselves through multiple careers and a life worth living. It is a goal to aim for, step by step, via the development of new medical technologies.

Still, few government bodies have waded in to talk in earnest about funding research to prevent and reverse degenerative aging. Where discussion takes place, it is largely focused on approaches such as calorie restriction mimetic drugs, unlikely to do much more than very modestly slow aging in humans. Policy is stuck in the era of aging as a costly inevitability, and the cause of a future collapse due to unsustainable entitlements. There is always considerable lag between an expansion of the bounds of the possible, driven by new technology, and policy white papers, of course. But still, the first rejuvenation therapies exist, in the form of first generation senolytic drugs, and it won't be too many years before their use becomes widespread. The world at large has a great deal of catching up to do in present thinking on the future of aging and its treatment.

A research agenda for ageing in China in the 21st century (2nd edition): Focusing on basic and translational research, long-term care, policy and social networks

One of the key issues facing public healthcare is the global trend of an increasingly ageing society which continues to present policy makers and caregivers with formidable healthcare and socio-economic challenges. Ageing is the primary contributor to a broad spectrum of chronic disorders all associated with a lower quality of life in the elderly. In 2019, the Chinese population constituted 18% of the world population, with 164.5 million Chinese citizens aged 65 and above (65+), and 26 million aged 80 or above (80+). China has become an ageing society, and as it continues to age it will continue to exacerbate the burden borne by current family and public healthcare systems.

Europe is characterized by three types of care provision: 1) 'crowding out', whereby the state largely replaces family care; 2) 'crowding in', whereby the state promotes family care; 3) 'mixed responsibility', whereby both the state and the family take a joint responsibility for care, yet have separate functions. In China, family is still the traditional provider for elderly care. In order to deal with the ongoing boom in the elderly population, the Chinese government has put more effort into funding research on ageing and its related diseases in recent decades. More attention has been placed on the development of pharmacological strategies against ageing, organ degeneration and major ageing-related diseases.

Targeting classic longevity pathways

Calorie restriction (CR) was first demonstrated as an effective way to extend lifespan in rodents, however the physiological mechanisms behind its anti-ageing effectiveness were not fully understood at the time, and remain uncertain. Later studies have suggested that CR might extend lifespan by regulating insulin-like growth factor (IGF) and mammalian target of rapamycin (mTOR) pathways. Metformin is primarily known for treating type 2 diabetes, with its underlying molecular mechanisms leading to the to down-regulation of IGF-1 signaling, and the inhibition of cellular proliferation, mitochondrial biogenesis, reactive oxygen species (ROS) production, DNA damage, activity of the mTOR pathway, etc. Acarbose has been shown to partially mimic the effects of CR and extend lifespan in mice by controlling blood sugar and slowing carbohydrate digestion. Rapamycin, a well-known inhibitor of mTOR, has shown life-extending effects in all model organisms and postpones the onset of age-associated diseases.

NAD+ boosters

Nicotinamide adenine dinucleotide (NAD+) is a fundamental molecule in human life and health; while there is an age-dependent reduction of NAD+, NAD+ augmentation extends lifespan and improves healthspan in different animal models as well as shows potential to treat different neurodegenerative diseases based on phase I clinical trials. NAD+ precursors such as nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN) have emerged as promising approaches for intervention against ageing phenotypes and age-related diseases. Supplementation via these precursors can elevate NAD+ level in vivo and improve glucose metabolism, mitochondria biogenesis, DNA repair, neovascularization, and neuroprotection.


Senescent cells accumulate in aged tissues and this accumulation is considered one of the driving forces of ageing. Senolytics are a class of molecules specifically designed to induce apoptosis of these senescent cells. Clearing senescent cells in mice has been shown to substantially alleviate ageing phenotypes, producing potent therapeutic effects in ageing-related diseases such as Alzheimer's disease, atherosclerosis, and osteoarthritis. The senolytic cocktail of dasatinib plus quercetin (DQ) decreased naturally occurring senescent cells, improved mobility, and reduced the risk of mortality. While clinical trials on senolytic drugs are mainly conducted in the USA, the concept of reducing senescent cells to delay the ageing progress has attracted interest from all over the world. Since 2016, the National Natural Science Foundation of China (NSFC) has set up special programs, providing millions to support research on cellular senescence and organ degeneration.

Cellular Senescence as a Mediator of Age-Related COVID-19 Severity

Wherever we find the intersection of inflammation and aging, important in many age-related conditions, it has become the case that attention is drawn to the role of senescent cells. Senescent cells cease replication, grow in size, and secrete a potent mix of inflammatory signals. Usually they self-destruct or are destroyed by the immune system shortly after entering a senescent state. Cells become senescent constantly throughout life, and for a variety of reasons, but only with advancing age do these cells linger and build up in number. Senescent cells serve a number of useful purposes when present in the short term, assisting in cancer suppression and wound healing, for example. When senescent cell signaling continues unabated, however, it disrupts tissue structure and function, and rouses the immune system to a state of chronic inflammation. This is an important contributing cause of degenerative aging.

SARS-CoV-2 is a novel betacoronavirus which infects the lower respiratory tract and can cause coronavirus disease 2019 (COVID-19), a complex respiratory distress syndrome. Epidemiological data show that COVID-19 has a rising mortality particularly in individuals with advanced age. Identifying a functional association between SARS-CoV-2 infection and the process of biological aging may provide a tractable avenue for therapy to prevent acute and long-term disease.

Here, we discuss how cellular senescence - a state of stable growth arrest characterized by pro-inflammatory and pro-disease functions - can hypothetically be a contributor to COVID-19 pathogenesis, and a potential pharmaceutical target to alleviate disease severity. First, we define why older COVID-19 patients are more likely to accumulate high levels of cellular senescence. Second, we describe how senescent cells can contribute to an uncontrolled SARS-CoV-2-mediated cytokine storm and an excessive inflammatory reaction during the early phase of the disease. Third, we discuss the various mechanisms by which senescent cells promote tissue damage leading to lung failure and multi-tissue dysfunctions. Fourth, we argue that a high senescence burst might negatively impact on vaccine efficacy.

Measuring the burst of cellular senescence could hypothetically serve as a predictor of COVID-19 severity, and targeting senescence-associated mechanisms prior and after SARS-CoV-2 infection might have the potential to limit a number of severe damages and to improve the efficacy of vaccinations.

Link: https://doi.org/10.1111/acel.13237

Learning is Damaged Before Memory in the Progression to Clinical Alzheimer's

Researchers searching for better ways to assess the early progression towards clinical Alzheimer's disease have established what looks like a decent way to measure loss of learning capability, a decline that occurs well before loss of memory function. This sort of approach compares poorly with a hypothetical blood biomarker or other non-invasive, low-cost assay, but while there are a few promising inroads towards the development of such a test, none have yet emerged into clinical practice.

As amyloid-β (Aβ) accumulates in a person's brain during the long preclinical stage of Alzheimer's disease, deficits in learning emerge prior to impairments in episodic memory, according to a new study. Cognitively normal people who tested positive for brain amyloid learned fewer Chinese characters over a six-day period than their amyloid-negative peers. Their learning deficit was more pronounced than any form of memory impairment, and it correlated with smaller hippocampi.

In public parlance, memory loss has become almost synonymous with AD. Alas, during the disease's preclinical stage-which scientists are trying to target for intervention - memory loss creeps up slowly and varies from person to person. Hence trials enrolling people at those stages struggle to assess clinical efficacy of the drug under investigation. New tests are sorely needed.

The new study tested 80 cognitively normal participants - 42 amyloid-negative, 38 amyloid-positive - and included other cognitive and neuroimaging measures. As had been seen in the previous cohort, amyloid-negative participants learned the meaning of Chinese characters faster, with accuracy differences between the groups emerging on day one and growing in each session. The two groups' average rate of learning over the entire six days differed by more than two standard deviations. In contrast, the groups barely differed on their most recent scores on any test of episodic memory. Among Aβ-positive participants only, those who learned the Chinese characters more slowly had smaller hippocampi and larger brain ventricles, suggesting less gray-matter volume.

Link: https://www.alzforum.org/news/research-news/preclinical-alzheimers-learning-falters-memory

The Aging of Chimpanzees versus that of Humans

We humans are unusually long-lived in comparison to our near primate cousins, and also compared to other mammals of similar body mass. We also exhibit menopause, an end to reproductive capability well before the end of life, which occurs in only a small number of other mammalian species. With a few noteworthy exceptions, such as naked mole-rats, some bats, and we humans, mammalian lifespan correlates quite well with some combination of body mass and resting metabolic rate. So why are the outliers long-lived?

Evolutionary theorists consider longer human life spans to be a consequence of our intelligence and culture. Once it became possible for grandparents to meaningfully contribute to the fitness of their grandchildren, a selection pressure for longer lives came into being. Unfortunately that selection pressure was not necessarily for anything other than an extended decline, given that the role of grandparents in the success of grandchildren is more intellectual and cultural than physical. At that point, we diverge from other primate species over time by gaining a much longer life span.

Today's research materials are an interesting look at some of the differences between humans and chimpanzees, the latter living a little more than half as long as we do. The effects of a sedentary lifestyle are clearly quite similar at the end of the day, despite the faster process of aging that occurs in our primate relatives. The pace of aging can be measured by an epigenetic clock that assesses characteristic changes in DNA methylation that take place with age, and researchers have recently extended that line of work into a number of species, chimpanzees the latest addition.

Evolution of the primate ageing process

The world's population is ageing rapidly, presenting an urgency to address the health problems of the aged. Critical insights on these problems can be gained by examining how the ageing process has been shaped over evolutionary time, and how it is influenced by different environments and lifestyles. In this issue, we feature research conducted on humans in small-scale societies and on our closest primate relatives to ask how bodies, minds, and behaviour age outside of the usual research settings. These contributions shed light on the complex relationship between ageing and disease and offer clues to the social and ecological predictors of successful ageing.

Researchers find cardiovascular health similarities between chimpanzees, humans

Researchers examined cardiovascular profiles in chimpanzees living in African sanctuaries. These chimpanzees occupy large rainforest enclosures, consume a diet of fruits and vegetables, and generally experience conditions more similar to a wild chimpanzee lifestyle. They measured blood lipids, body weight and body fat in 75 sanctuary chimpanzees during annual veterinary health check-ups, and then compared them to published data from laboratory-living chimpanzees. Free-ranging chimpanzees in sanctuaries exhibited lower body weight and lower levels of lipids, both risk factors for human cardiovascular disease. Some of these disparities increased with age, indicating that the free-ranging chimpanzees stayed healthy as they got older.

Prior work suggested that chimpanzees have very high levels of blood lipids that are cardiovascular risk factors - higher than humans in post-industrial societies in some cases. The work also showed that chimpanzees living a naturalistic life have much lower levels even as they age, providing a new reference for understanding human health. In biomedical research labs, chimpanzees have more limited space and often consume a processed diet (food such as primate chow), unlike wild chimpanzees.

Your Cells Look Young for Their Age, Compared to a Chimp's

Many humans live to see their 70s and 80s, some even reach 100 years old. But life is much shorter for our closest animal relatives. Chimpanzees, for example, rarely make it past age 50, despite sharing almost 99% of our genetic code. While advances in medicine and nutrition in the last 200 years have added years to human lifespans, a new study suggests there could be a more ancient explanation why humans are the long-lived primate.

Studies have shown that certain sites along our DNA gain or lose chemical tags called methyl groups in a way that marks time, like a metronome. The changes are so consistent that they can be used as an "aging clock" to tell a person's age to within less than four years. The new study marks the first time such age-related changes have been analyzed in chimpanzees. Researchers analyzed some 850,000 of these sites in blood from 83 chimpanzees aged 1 to 59. Sure enough, they found that aging leaves its mark on the chimpanzee genome, just as it does in humans. More than 65,000 of the DNA sites the scientists scrutinized changed in a clock-like way across the lifespan, with some gaining methylation and others losing it.

The pattern was so reliable that the researchers were able to use DNA methylation levels to tell a chimpanzee's age to within 2.5 years, which is much more accurate than current methods for estimating a wild animal's age by the amount of wear on their molars. When the researchers compared the rates of change they found in chimps with published data for humans, the epigenetic aging clock ticked faster for chimpanzees.

Exosome Therapy Appears as Effective as Cell Therapy for Cardiac Regeneration

Cells are logistically challenging and more expensive to work with in comparison to components of cell signaling such as proteins or extracellular vesicles. In cell therapies wherein the bulk of the benefit is due to signaling by the transplanted cells - which is the case for near all first generation stem cell therapies, in which the newly introduced cells have a very low survival rate - it makes a lot of sense to isolate the relevant signals and deliver those instead of cells. Since a majority of signaling is transported via classes of extracellular vesicle, such as exosomes, many development programs now focus on the delivery of harvested exosomes rather than cultured cells, well in advance of a full understanding of the beneficial signals involved.

Cell transplant has been an attractive potential therapy for cardiovascular disease; however, poor cell engraftment limits efficacy of the approach. We here compared transplanting a mixture of human induced pluripotent stem cell-derived cardiomyocytes, endothelial cells, and smooth muscle cells to transplant of exosomes produced by these cells in a pig model of myocardial infarction. They saw similar improvements in cardiac function in cell, cell fragment, and exosome transplant groups without evidence of increased arrhythmogenicity.

We compared the efficacy of treatment with a mixture of cardiomyocytes (CMs; 10 million), endothelial cells (ECs; 5 million), and smooth muscle cells (SMCs; 5 million) derived from human induced pluripotent stem cells (hiPSCs), or with exosomes extracted from the three cell types, in pigs after myocardial infarction (MI). Female pigs received sham surgery; infarction without treatment (MI group); or infarction and treatment with hiPSC-CMs, hiPSC-ECs, and hiPSC-SMCs (MI + Cell group); with homogenized fragments from the same dose of cells administered to the MI + Cell group (MI + Fra group); or with exosomes (7.5 mg) extracted from a 2:1:1 mixture of hiPSC-CMs:hiPSC-ECs:hiPSC-SMCs (MI + Exo group). Cells and exosomes were injected into the injured myocardium.

In vitro, exosomes promoted EC tube formation and microvessel sprouting from mouse aortic rings and protected hiPSC-CMs by reducing apoptosis, maintaining intracellular calcium homeostasis, and increasing adenosine 5′-triphosphate. In vivo, measurements of left ventricular ejection fraction, wall stress, myocardial bioenergetics, cardiac hypertrophy, scar size, cell apoptosis, and angiogenesis in the infarcted region were better in the MI + Cell, MI + Fra, and MI + Exo groups than in the MI group 4 weeks after infarction. The frequencies of arrhythmic events in animals from the MI, MI + Cell, and MI + Exo groups were similar. Thus, exosomes secreted by hiPSC-derived cardiac cells improved myocardial recovery without increasing the frequency of arrhythmogenic complications and may provide an acellular therapeutic option for myocardial injury.

Link: https://doi.org/10.1126/scitranslmed.aay1318

Parkinson's Disease is Two Distinct Conditions with a Similar Outcome

Some age-related and other diseases with formal definitions based on symptoms and late stage mechanisms are likely several distinct conditions that happen to converge on a similar end result. This is particularly true of conditions of the brain and the immune system, where there is a great deal of biochemistry yet to map and fully understand. While Parkinson's disease in the late stages uniformly involves α-synuclein aggregation and loss of dopaminergenic neurons, the research community has in recent years gathered the data needed to make a clear distinction between cases that start in the brain and cases that start in the intestines. Thus Parkinson's disease is in fact two distinct diseases that will likely require different approaches to prevention and early stage diagnosis and treatment.

Researchers around the world have been puzzled by the different symptoms and varied disease pathways of Parkinson's patients. A major study has now identified that there are actually two types of the disease. Although the name may suggest otherwise, Parkinson's disease is not one but two diseases, starting either in the brain or in the intestines, which explains why patients with Parkinson's describe widely differing symptoms. "With the help of advanced scanning techniques, we've shown that Parkinson's disease can be divided into two variants, which start in different places in the body. For some patients, the disease starts in the intestines and spreads from there to the brain through neural connections. For others, the disease starts in the brain and spreads to the intestines and other organs such as the heart."

Parkinson's disease is characterised by slow deterioration of the brain due to accumulated alpha-synuclein, a protein that damages nerve cells. This leads to the slow, stiff movements which many people associate with the disease. In the study, the researchers have used advanced PET and MRI imaging techniques to examine people with Parkinson's disease. People who have not yet been diagnosed but have a high risk of developing the disease are also included in the study. The study showed that some patients had damage to the brain's dopamine system before damage in the intestines and heart occurred. In other patients, scans revealed damage to the nervous systems of the intestines and heart before the damage in the brain's dopamine system was visible.

"It has long since been demonstrated that Parkinson's patients have a different microbiome in the intestines than healthy people, without us truly understanding the significance of this. Now that we're able to identify the two types of Parkinson's disease, we can examine the risk factors and possible genetic factors that may be different for the two types. The next step is to examine whether, for example, body-first Parkinson's disease can be treated by treating the intestines with fecal microbiota transplantation or in other ways that affect the microbiome. The discovery of brain-first Parkinson's is a bigger challenge. This variant of the disease is probably relatively symptom-free until the movement disorder symptoms appear and the patient is diagnosed with Parkinson's. By then the patient has already lost more than half of the dopamine system, and it will therefore be more difficult to find patients early enough to be able to slow the disease."

Link: https://newsroom.au.dk/en/news/show/artikel/parkinsons-disease-is-not-one-but-two-diseases/

The Old are Becoming Functionally Younger

Today's research materials cover one of a number of studies to suggest that older people are becoming functionally younger over time, comparing the capabilities of age-matched cohorts of old people in past decades with old people of the same age today. Being 70 or 80 in 1990 was accompanied by greater loss of physical capabilities, such as walking speed or grip strength, than is the case at those ages today. This is what one would expect given the slow upward trend in life expectancy that has continued year after year for more than a century now, driven by a shifting combination of better lifestyle choices, greater control over medical issues throughout life, and slow improvements in treating age-related disease.

It is interesting to see just how much has been achieved without undertaking direct efforts to target the mechanisms of aging. While the reasons for a lesser burden of frailty and mortality in late life have changed over time, from a reduction in the burden of infectious disease across the 20th century to a lessening of cardiovascular disease over the last few decades, the theme remains an incidental reduction in the level of accumulated damage and dysfunction at a given age. Now that we are moving into an era in which the research and development community is actively and deliberately targeting underlying causes of aging, we might expect to see a considerable increase in the upward trend of vigor, health, and longevity in old age.

Older people have become younger: physical and cognitive function have improved meaningfully in 30 years

Among men and women between the ages of 75 and 80, muscle strength, walking speed, reaction speed, verbal fluency, reasoning and working memory are nowadays significantly better than they were in people at the same age born earlier. In lung function tests, however, differences between cohorts were not observed. "The cohort of 75- and 80-year-olds born later has grown up and lived in a different world than did their counterparts born three decades ago. There have been many favourable changes. These include better nutrition and hygiene, improvements in health care and the school system, better accessibility to education and improved working life."

The results suggest that increased life expectancy is accompanied by an increased number of years lived with good functional ability in later life. The observation can be explained by slower rate-of-change with increasing age, a higher lifetime maximum in physical performance, or a combination of the two. "The results suggest that our understanding of older age is old-fashioned. From an aging researcher's point of view, more years are added to midlife, and not so much to the utmost end of life. Increased life expectancy provides us with more non-disabled years, but at the same time, the last years of life comes at higher and higher ages, increasing the need for care. Among the ageing population, two simultaneous changes are happening: continuation of healthy years to higher ages and an increased number of very old people who need external care."

Cohort differences in maximal physical performance: a comparison of 75- and 80-year-old men and women born 28 years apart

Whether increased life expectancy is accompanied by increased functional capacity in older people at specific ages is unclear. We compared similar validated measures of maximal physical performance in two population-based older cohorts born and assessed 28 years apart. Participants in the first cohort were born in 1910 and 1914 and were assessed at age 75 and 80 years, respectively (N=500, participation rate 77%). Participants in the second cohort were born in 1938 or 1939 and 1942 or 1943 and were assessed at age 75 and 80 years, respectively (N=726, participation rate 40%). Maximal walking speed, maximal isometric grip strength and knee extension strength, lung function measurements; forced vital capacity (FVC) and forced expiratory volume in 1 second (FEV1) were assessed. Data on non-participation were systematically collected.

Walking speed was on average 0.2-0.4 m/s faster in the later than earlier cohort. In grip strength, the improvements were 5-25%, and in knee extension strength 20-47%. In FVC, the improvements were 14-21% and in FEV1 0-14%. The later cohort showed markedly and meaningfully higher results in the maximal functional capacity tests, suggesting that currently 75- and 80-year old people are living to older ages nowadays with better physical functioning.

Injection of Metformin Improves Cognitive Function in Old Mice to a Greater Degree than Oral Administration

Researchers here note that delivering metformin via injection rather than the usual oral administration removes unwanted side-effects and better improves cognitive function in old mice. Near all testing of metformin has used oral administration, and the effects on pace of aging and life span are, frankly, too unreliable and too small to justify the present level of interest in the drug on the part of the longevity community. Administration by injection might be a different story, but waiting on further research and confirming data would be a wiser course of action than immediate excitement. Even then, this is tinkering with the damaged state of metabolism, not a form of repair. The upside is always going to be more limited than that of approaches that address underlying causes of aging.

Many studies have shown that in patients with type 2 diabetes, chronic administration of metformin causes side effects such as abdominal or stomach pain, diarrhea, early satiety, decreased appetite, risk of vitamin B-12 deficiency, and lactic acidosis. In the current study, we treated non-diabetic mice with metformin for 10 months. Unequivocally, our results show that chronic metformin treatment may lead to severe disabilities, including cancer, cataracts, and dermatitis. Studies in nematodes and other smaller organisms suggest that the side effects of chronic metformin treatment may be caused by changes in the gut microbiome.

To avoid the side effects of metformin, we treated mice with metformin by tail vein injection, which is believed to have little effect on the composition of gut microbes. Interestingly, it appears that metformin treatment by tail vein injection results in better cognitive function performance than oral administration. Consequently, we speculate that gut microbes may play an important role in mediating the side effects of metformin, and this potential role needs to be further explored. The beneficial effects of metformin on cognitive function are associated with the restoration of vascular integrity, producing a richer cerebral blood flow, as well as activation of neurogenesis in the subventricular zone. The mechanism of metformin administration enhanced glycolysis through increased mRNA expression of GAPDH, which ultimately increased angiogenesis and neurogenic potential of neural stem cells.

To avoid the side effects of metformin, our study proposes careful reconsideration of lower doses of metformin treatment by tail vein injection for translational research. Altogether, our study shows an improved method for metformin treatment, which might contribute to a reduction in the side effects of metformin and lead to better therapeutic value for anti-aging in humans.

Link: https://doi.org/10.18632/aging.103693

Upregulation of Mitophagy as an Approach to Treat Age-Related Disease

Mitophagy is a cellular housekeeping process that removes damaged mitochondria. Mitochondria are the power plants of the cell, crucial in all tissues, but particularly so in the energy-hungry brain and muscles. Mitochondrial function declines with age throughout the body, and failing mitophagy is a proximate contributing cause of this issue, allowing dysfunctional mitochondria to accumulate in cells. Why this happens is a topic for study; various important genes relating to mitochondrial structure and mitophagy have alterations in expression levels, a maladaptive reaction to the damaged environment of aged tissues, perhaps. But it is not well understood. Boosting the operation of mitophagy in old tissues may be a useful approach to therapy for age-related conditions, and may also be an important mechanism by which exercise can improve health and reduce mortality older individuals.

Macroautophagy, hereafter referred to as "autophagy," is an evolutionarily conserved pathway involving the engulfment of cytosolic contents by a lipid membrane for recycling of nutrients or removal of harmful aggregates, microbes, and organelles. Mitophagy is one form of macroautophagy that involves selectively targeting and engulfing mitochondria for removal through lysosomal degradation. Activation of this pathway is a result of mitochondria being damaged beyond the capabilities of other quality control methods or in instances in which the cell needs to get rid of mitochondria for metabolic or developmental purposes.

Mitophagy is important for any cell that contains mitochondria. When moving from this idea of a nondescript eukaryotic cell to differentiated, specific cells that make up our body's organs, certain tissues become focal points for discussion. These include muscle cells and neurons because of their specific functions, metabolism, and energy requirements. These cells make up organs with high energy consumption and vulnerability, and slight perturbations in homeostasis can lead to pronounced effects. Although we focus on these two cell types, mitophagy is important in all organs where mitochondria play important roles.

The deep molecular understanding of mitophagy we have stems from the thorough investigation into PINK1 and Parkin, which are both major recessive risk factors for developing early onset Parkinson's disease (PD). The unique structure of the neuron creates an environment where not only does the mitochondrial pool have to be healthy, but it also must be properly transported down the axon to quite distant sites where ATP production and calcium buffering are its two most important functions. An aged nervous system coupled with a decline in mitophagy leads to accumulation of bad mitochondria and is a hallmark of neurodegeneration.

Until recently, surprisingly little evidence directly linked mitophagy to the most common neurodegenerative disease, Alzheimer's disease (AD). Historically, PD etiology was more focused on defective mitophagy, whereas investigation of AD has focused on accumulation of amyloid-β (Aβ) plaques and phospho-tau neurofibrillary tangles. Recent studies have shown that mitophagy is, in fact, affected in AD and, more important, that inducing mitophagy could benefit the pathological and cognitive outcomes. Models of toxic Aβ and tau were shown to impair mitophagy, and increasing mitophagy helped to reduce the plaque and neurofibrillary tangle burden in Caenorhabditis elegans and mouse models.

As with most therapeutics that control a biological process, increasing levels of mitophagy must be carefully controlled because passing an upper limit would induce cell death, so careful modulation rather than constitutive activation would be ideal for this style of treatment. Physiologically relevant stimulation through NAD+ supplementation has been effective in mouse and C. elegans studies in AD. By supplementing with a molecule that is already present in the body, the safety concerns are greatly reduced. Alternatively, by removing the brakes on the mitophagy system, such as the deubiquitinating enzymes, we would also increase levels of basal mitophagy. Regardless of the treatment approach, the ideal therapy will be targeted to the dysfunctional organ because affecting the balance of mitophagy in off-target organs that do not have mitochondrial dysfunction will create additional problems.

Link: https://doi.org/10.1083/jcb.202004029

Amyloid Precursor Protein Glycosylation is Different in the Alzheimer's Brain

The puzzle of Alzheimer's disease is why it only occurs in some people. Unlike other common age-related diseases, such as atherosclerosis, it isn't universal, even in groups exhibiting all of the lifestyle risk factors. Thus a strong theme in the Alzheimer's research community is the search for clear and robust differences in cellular biochemistry between people with and without the condition, in an attempt to shed more light on how and why Alzheimer's arises.

In the absence of a complete understanding of how and why Alzheimer's disease begins, the strategy for developing effective therapies is haphazard. Perhaps the obvious points of intervention based on today's knowledge are good, perhaps not. The history of this research and development is not encouraging. Most past work has focused on clearance of amyloid-β aggregates, an obvious point of difference between diseased and normal brains, informed by the amyloid cascade hypothesis. Unfortunately, lowering amyloid-β levels in the brain has failed to produce improvements in patients.

Back to the question of why only some people suffer Alzheimer's disease: a good deal of theorizing has taken place to try to explain this observation. For example, perhaps Alzheimer's disease is primarily driven by maladaptive responses to persistent infection, such as by herpesviruses. This is a state that occurs in a sizable fraction of the population, but not in everyone. There is as much digging into cellular biochemistry as theorizing, however. Today's open access research materials are a good example of this part of the search for differences between Alzheimer's patients and healthier old individuals, in that the focus is on cellular biochemistry. Only later would there be efforts to try to connect this difference to causative mechanisms.

New alteration in the brain of people with Alzheimer's discovered

Despite the important advances in research in recent years, the etiopathogenesis of Alzheimer's disease is still not fully clarified. One of the key questions is to decipher why the production of beta amyloid, the protein that produces the toxic effect and triggers the pathology, increases in the brain of people with Alzheimer's. The research has focused on the different fragments of the Amyloid Precursor Protein (APP) until now, but the results have been inconclusive, because this protein is processed so quickly that its levels in the cerebrospinal fluid or in the plasma do not reflect what is really happening in the brain.

Glycosylation consists of adding carbohydrates to a protein. This process determines the destiny of the proteins to which a sugar chain (glycoproteins) has been added, which will be secreted or will form part of the cellular surface, as in the case of the Amyloid Precursor Protein (APP). The alteration of this glycosylation process is related with the origin of various pathologies. In the specific case of Alzheimer's, the results of the study suggest that the altered glycosylation could determine that the APP is processed by the amyloidogenic (pathological) pathway, giving rise to the production of the beta-amyloid, a small protein with a tendency to cluster forming the amyloid plaques characteristic of Alzheimer's disease.

The fact that the glycosylation of the amyloid precursor is altered indicates that this amyloid precursor may be located into areas of the cell membrane that are different from the usual, interacting with other proteins and therefore probably being processed in a pathological way.

Amyloid precursor protein glycosylation is altered in the brain of patients with Alzheimer's disease

In this study, elevated APP mRNA expression was found in the brain of Alzheimer's disease (AD) subjects when compared to non-demented controls (NDC) individuals. Several studies have already reported increases in expression of total APP mRNA, both considered as a whole. However, there is contradictory data regarding APP mRNA expression in the brain of AD patients, with several reports indicating no change or weaker expression. In conclusion, it remains unclear if brain-specific regional and temporal changes occur in the expression of the different APP variants during AD progression. Since APP is also found in blood cells, assessing the changes in APP mRNA expression in peripheral blood cells from AD patients has been considering an alternative. However, again the quantification of APP mRNA in peripheral blood cells has generated controversial results.

Brain APP protein has been analyzed in only a few studies, probably as it is difficult to interpret the complex pattern of APP variants and fragments. We previously characterized the soluable APP (sAPP) species present in the cerebrospinal fluid (CSF), which form heteromers involving sAPPα, sAPPβ, and also soluble full-length forms of APP. Our approach allows the sAPPα and sAPPβ species derived from APP695 and APP-KPI to be studied separately. Here, we found a similar balance of sAPPα and sAPPβ protein, and of that between C-terminal fragments CTFα and CTFβ, in brain extracts from AD and NDC subjects. Interestingly, despite the lack of any differences between NDC and AD patients, the ratio of APP695/APP-KPI species was associated with very different profiles of sAPPα and sAPPβ. Our results indicate that relevant amounts of sAPPβ are likely to be generated in non-neuronal cells and that their pattern of glycosylation may serve to characterize changes in AD.

Moderate changes in the glycosylation of key brain proteins may critically affect their behavior. Alterations to the glycosylation of specific glycoproteins may alter the contribution of different cell types to the protein pool, producing an imbalance in protein glycoforms, and such altered glycosylation may reflect changes in metabolism or in differentiation states. In this context, the altered glycosylation of APP in AD warrants further study, particularly as we assume that APP glycosylation determines its proteolytic processing. As such, alterations to its glycosylation may have pathophysiological consequences in terms of the generation of the diverse APP fragments.

Naringenin is a Senotherapeutic that Enhances Neurogenesis in Mice

Researchers here evaluate the flavonoid naringenin for its ability to dampen the inflammatory signaling of senescent neural cells, particularly levels of TNF-α, and increase neurogenesis in mice. This increased neurogenesis is likely a result of reduced inflammation in brain tissue, but possibly due to other, distinct mechanisms. Neurogenesis is the name given to the generation of new neurons in the brain, and their integration into existing neural circuits. Evidence suggests that increased neurogenesis is a good thing at any age, improving cognitive function and making the brain more resilient to injury. Now that the research community is paying attention to senescent cells and their signaling in the context of aging, we'll no doubt see a great many compounds classified or reclassified as senotherapeutics in the years ahead.

The use of metabolomic analysis to investigate the specific composition of Ribes meyeri anthocyanins revealed that naringenin (Nar) may be an important flavonoid metabolite. Nar has previously been reported to ameliorate myocardial cell senescence, improve the metabolic capacity of the intestinal tract, and exert anti-inflammatory and anti-cancer effects. However, the effects of Nar on neural stem cells (NSCs) during aging remains unknown.

To explore the anti-aging effects of R. meyeri anthocyanins, we conducted further studies using Nar. Treatment with 6.8 μg/mL Nar increased cell viability, reduced P16ink4a gene expression, lengthened telomeres, and promoted mouse NSC differentiation into neurons in vitro. To further assess the effects of Nar on cell proliferation, we performed immunofluorescence studies. Results indicated that Nar treatment increased both the number of Ki67-positive cells and the proportion of MAP2-positive cells, suggesting that Nar may promote neurogenesis.

Furthermore, the effects of Nar on learning and memory were also evaluated in aging mice. Morris water maze test results consistently demonstrated that Nar treatment enhances spatial learning in aging mice. Interestingly, RNA-seq analysis revealed that Nar may affect senescence via the TNF signaling pathway, especially by downregulating TNF-α expression in the blood of aging mice. ELISA assays also indicated that Nar treatment reduced plasma TNF-α levels compared with control aging mice. TNF-α is a key factor in the TNF signaling pathway and is closely related to cognitive aging. Its functions include the promotion of pathological changes in hippocampal synapses and the inhibition of precursor cell proliferation. Altered TNF levels are associated with cognitive impairment in depression, schizophrenia, bipolar disorder, and Alzheimer's disease. More specifically, TNF-α is upregulated in patients with Alzheimer's disease.

In summary, our study demonstrates that R. meyeri anthocyanins improve the effects of aging in NSCs via Nar, which downregulates TNF-α levels in vivo and improves cognition in aging mice. Collectively, our findings provide a novel strategy for the development of clinical treatments, aimed at greater realization of the medicinal value of R. meyeri anthocyanins.

Link: https://doi.org/10.18632/aging.103955

A Discussion of Targeting the Mechanisms of Cardiovascular Aging

This very readable open access paper discusses some of the mechanisms involved in cardiovascular aging. As for many such publications, and to my eyes at least, it leans too much towards the details of the aged metabolism rather than towards the underlying causes that make the cells of an aged cardiovascular system behave differently. Near all medicine for age-related disease has so far focused on trying to change the way in which cells behave in response to the causes of aging, without addressing those causes, and, as a result, beneficial outcomes have been marginal at best. It is somewhere between very hard and impossible to make a damaged machine run well without actually repairing the damage. The approach we take to aging, cardiovascular or otherwise, should be one of periodic repair of root causes.

All around the world, scientists are trying to beat age-related diseases, such as heart attacks, cancer, and dementia; stop people getting ill is an obvious goal to aid the individual wellbeing and reduce pressure on society. At the whole organism level, aging has been defined as the time-related deterioration of the physiological functions necessary for survival and fertility. This definition applies to all the individuals of a species and overlaps with disease-related aging. Aging of the vasculature plays a key role in morbidity and mortality of older people. It is often assimilated with endothelial dysfunction, that is, the failure of vascular endothelial cells to respond to vasoactive stimuli and mount reparative transformation upon tissue damage. Zooming into the molecular level, aging of the vasculature consists in small, incremental amounts of damage that spreads to all vascular cells, including vascular smooth muscle cells and pericytes, and, owing to the system dependency on vascular homeostasis, to tissues and organs; eventually, the whole organism will suffer from this accumulation of damage.

The development of novel treatments targeting vascular aging and prevention of age-related vascular pathologies requires a better knowledge of the cellular and functional changes that occur in the vasculature during aging. These include oxidative stress, mitochondrial dysfunction, susceptibility to molecular stressors, chronic low-grade inflammation, genomic instability, cellular senescence, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, and stem cell dysfunction. Senescent cells secrete autocrine or paracrine factors, including cytokines, growth factors, proteases, and soluble receptors called senescence-associated secretory phenotype (SASP).

The capacity to repair and regenerate empowers living organisms with resilience to natural fluctuations and events that cause disturbance or damage. Aging and regeneration are two sides of the same coin and this has been confirmed through the examination of species with extreme regenerative capabilities, such as planarians and salamanders, which show no signs of aging or quantifiable age-associated functional decline. In contrast, in complex organisms like humans, aging is characterized by a decay in the regenerative capacity and reparative activities. Tissue-specific stem cells and progenitor cells incur in age-related defects, such as the loss of self-renewal capacities and proliferative activity and the deterioration in functionality and potency. Likewise, differentiated cells become progressively uncapable of regulating protein synthesis and metabolism, especially under stress conditions, eventually undergoing irreversible proteotoxic damage. Exhaustion of compensatory mechanisms increases the susceptibility to risk factors and diseases and results in excess morbidity and mortality.

Prolonged survival, as in supercentenarians, denotes an exceptional capacity to repair and cope with risk factors and diseases. These characteristics are shared with offspring, suggesting that the regenerative phenotype is heritable. New evidence indicates that genetic traits responsible for prolongation of health span in humans can be passed to and benefit the outcomes of animal models of cardiovascular disease. Genetic studies have also focused on determinants of accelerated senescence and related druggable targets. Evolutionary genetics assessing the genetic basis of adaptation and comparing successful and unsuccessful genetic changes in response to selection within populations represent a powerful basis to develop novel therapies aiming to prolong cardiovascular and whole organism health.

Link: https://doi.org/10.1530/VB-19-0029

Rescuing Senescent Cells by Delivering New Mitochondria Sounds Like a Risky Proposition

Mitochondria are effectively power plants, hundreds of these organelles per cell working to create the chemical energy store molecule adenosine triphosphate. Mitochondria are the descendants of ancient symbiotic bacteria, and retain many bacterial characteristics, including a small genome, the mitochondrial DNA, and the ability to replicate. Mitochondrial dysfunction is one of the paths by which cells can become senescent, entering a state of growth arrest while secreting an inflammatory set of signals, but mitochondria are in any case involved in the transition to senescence in response to other forms of damage or dysfunction. In youth, senescent cells are quickly destroyed by their own programmed cell death processes or by the immune system. In older people, these cells accumulate, contributing to tissue dysfunction and the chronic inflammation of age.

In today's open access paper, the authors propose treating skin aging by delivering whole mitochondria into senescent cells, thereby rescuing their function. In recent years, various approaches to introducing mitochondria into target cells have been demonstrated. It also appears to be the case that cells naturally transfer, eject, and ingest mitochondria under a range of circumstances. Is rescuing the usual forms of senescent cells found in old tissues a good idea, however? If cellular senescence is largely due to mitochondrial dysfunction, which it may be under some circumstances, then the proposal here isn't completely unreasonable. But cells become senescent for a variety of good reasons, including nuclear DNA damage that is potentially cancerous, and which can occur in skin as the result of exposure to UV radiation. Selectively destroying senescent cells in skin sounds like a safer approach than attempting to rehabilitate them.

For what it is worth, delivering functional and undamaged mitochondria appears best targeted to normal cells in the aging body, to boost their function in an environment of damaged and dysfunctional mitochondria. Indeed, that has been attempted. Mitochondrial function does decline with age in tissues throughout the body. Perhaps something should be done about that. While it is unclear as to whether newly introduced mitochondria would remain functional for long in the aged environment, the strategy sounds worth a try, given the evidence to date for it to enhance tissue function in the short term.

Bases for Treating Skin Aging With Artificial Mitochondrial Transfer/Transplant (AMT/T)

The perception of mitochondria as only the powerhouse of the cell has dramatically changed in the last decade. It is now accepted that in addition to being essential intracellularly, mitochondria can promote cellular repair when transferred from healthy to damaged cells. The artificial mitochondria transfer/transplant (AMT/T) group of techniques emulate this naturally occurring process and have been used to develop therapies to treat a range of diseases including cardiac and neurodegenerative. Mitochondria accumulate damage with time, resulting in cellular senescence. Skin cells and its mitochondria are profoundly affected by ultraviolet radiation and other factors that induce premature and accelerated aging. In this article, we propose the basis to use AMT/T to treat skin aging by transferring healthy mitochondria to senescent cells, possibly revitalizing them.

Mutations related to monogenic mitochondrial disorders can cause fragmentation of the mitochondrial network in the cell. Affecting this network hampers its capacity to maintain mitochondrial DNA (mtDNA) stability. When good and damaged mitochondria are unable to fuse within networks, they can't exchange healthy mtDNA or get rid of damaged DNA copies. This ultimately leads to dysfunctions in the cell and premature senescence. For instance, patients with fibromyalgia suffer from oxidative stress and inflammation of the skin which has been linked to mitochondrial dysfunction. Healthy skin depends on the maintenance of functional mitochondria, which could be a target for the development of medical and cosmetic anti-aging treatments.

To our knowledge, there is no effective treatment available to the public to reverse skin aging by targeting mitochondria. The few existing therapeutic options focused on the mitochondria are under development and still, need further in vitro assays and clinical validation. In addition, no available products, including topical application of natural substances and antioxidants, offer a substantial recovery from many skin aging symptoms such as mtDNA instability, respiration, collagen production, neovascularization, and localized inflammation.

In this hypothesis article we present the idea and arguments of using the artificial mitochondria transfer/transplant (AMT/T) technique as a possible skin anti-aging therapeutic. It has been observed previously that the use of AMT/T in vitro, in vivo, and clinically promotes cell and tissue recovery in different diseases, with effects that could be used to repair skin damage. For example, MitoCeption, one of many AMT/T techniques, induces cell proliferation, migration, and increased respiratory ATP production, processes needed to repair the damage in aged skin. PAMM MitoCeption (Primary Allogeneic Mitochondria Mix Transfer by MitoCeption) repaired UV radiation damaged cells by recovering the loss of metabolic activity, mitochondrial mass, mtDNA sequence stability in addition to decreasing p53 expression. Beyond in vitro applications, AMT/T showed to have regenerative effects in vivo, in diseases such as heart and brain ischemia. AMT/T applied clinically to pediatric patients with myocardial dysfunction has also shown positive results on ischemic injured tissues.

Our hypothesis regarding AMT/T as an antiaging skin therapeutic could be tested in vitro, in vivo, and clinically, to promote the applications of this technique. The possibility to transfer new mitochondria to senescent or age-induced harmed cells in the skin could represent a plausible option to treat the effects of aging.

Theorizing on Cosmic Radiation as an Accelerator of Aging via Cellular Senescence

Researchers here suggest that some of the detrimental effects of prolonged space missions are mediated by an increased burden of senescent cells resulting from cosmic radiation exposure. Senescent cell accumulation is a feature of aging and cancer treatments such as chemotherapy, and contributes to the progression of age-related dysfunction and disease. Senescent cells secrete an inflammatory mix of signal molecules that disrupt nearby tissue structure, alter cell behavior, and rouse the immune system into a state of chronic inflammation. Even a small number of senescent cells can have outsized effects on tissue function due to this signaling.

The increasing duration of space missions involves a progressively higher exposure of astronauts to cosmic rays, whose most hazardous component is made up of High-Atomic number and High-Energy (HZE) ions. HZE ions interact along their tracks with biological molecules inducing changes on living material qualitatively different from that observed after irradiation for therapeutic purposes or following nuclear accidents. HZE ions trigger in cells different responses initialized by DNA damage and mitochondria dysregulation, which cause a prolonged state of sterile inflammation in the tissues. These cellular phenomena may explain why spending time in space was found to cause the onset of a series of diseases normally related to aging.

Despite their concentration in the cosmic rays being around 1%, HZE ions due to their high penetration and strong oxidizing power have been proven to induce permanent damage. The direct or indirect damage through radiolysis of mitochondria has as a consequence not only failure of its metabolic role but also establishment of a persistent oxidative imbalance. Once damaged, mitochondrial DNA may insert in nuclear chromosomes perpetuating genomic instability. The cells bearing DNA damage that cannot be quickly repaired with the DNA damage response system enter into apoptosis or the quiescent state typical of senescence. The final result is a decrease in the tissue functionality as is occurring in aging. Therefore, cosmic rays would mimic the effect of aging, inducing a persistent state of sterile inflammation damaging DNA, proteins, and lipids the consequences of which are aging-related disease such as cardiovascular diseases, neurocognitive impairment, and increase of cancer occurrence.

Link: https://doi.org/10.3389/fphys.2020.00955

Activated and Senescent Microglia as a Contributing Cause of Neurodegeneration

Microglia are innate immune cells of the brain, responsible not just for destroying pathogens and errant cells, but also for clearing debris and assisting neurons in managing the connections of neural circuits. With age, microglia become ever more inflammatory and dysfunctional. This is most likely a reaction to the accumulating damage of aging brain tissue, but in addition a significant number of microglia become senescent. Senescent cells are now well known to be harmful if not quickly destroyed by their own programmed cell death processes or by other immune cells; they secrete a potent inflammatory mix of signals that degrade tissue function when present for an extended period of time. Targeted clearance of senescent microglia has been shown to reduce chronic inflammation in brain tissue and reverse processes of neurodegeneration in animal models. It is plausible that addressing the excessive inflammatory activation of non-senescence microglia may be similarly beneficial, if a suitable approach can be found.

Age-related chronic inflammatory activation of microglia and their dysfunction are observed in many neurodegenerative diseases, and the potential contributions of these dysfunctional cells to neurodegeneration have been demonstrated recently. The housekeeping and defensive functions of microglia, such as surveying the brain parenchyma and phagocytosis of neuronal debris after injury, are important for brain homeostasis and immunity. During neurodegenerative diseases, loss of these functions can promote disease pathology by producing proinflammatory cytokines and increasing oxidative stress, which can exaggerate the ongoing neuroinflammation.

A recent surge in microglial research has unraveled myriads of microglial phenotypes associated with aging and neurodegenerative diseases, in addition to the conventional M1/M2 paradigm. Each of these phenotypes can be characterized by distinct transcriptional profiles as well as altered metabolism, migration, and phagocytosis characteristics. Mutations in triggering receptor expressed on myeloid cells 2 (Trem2) and granulin (GRN) are associated with various neurodegenerative diseases, and these genes are dysregulated in the majority of recently identified microglial phenotypes. These genes act as checkpoint regulators and maintain microglial inflammatory fitness, principally through metabolic modulation. Dysfunctional microglia typically show mitochondrial deficits, glycolysis elevation, and lipid droplet accumulation, which results in reduced migration and phagocytosis and increased proinflammatory cytokine secretion and reactive oxygen species release.

Here we discuss the existing data regarding metabolic perturbations in dysfunctional microglia and their documented associations with neurodegeneration, highlighting how aging-induced chronic microglial activation alters microglial bioenergetics, leading to impaired homeostatic and housekeeping functions. Dysfunctional microglia initiate or exacerbate neurodegeneration, and key pathways involved in the dysfunctional processes, including metabolism, may represent potential intervention targets for correcting imbalances.

Link: https://doi.org/10.3389/fncel.2020.00246

Medin Amyloid Aggregation with Age Causes Cerebral Vascular Dysfunction

There are twenty or so different proteins in the body that can become altered in ways that cause them to aggregate into solid deposits known as amyloids, spreading and encouraging other molecules of the same protein to do likewise. Amyloids are a phenomenon of old individuals and old tissues, for reasons that are much debated and no doubt quite complex.

Some of these amyloids are well studied and well known to be harmful, such as the amyloid-β involved in Alzheimer's disease. Others are known but less well studied, and whether or not they are harmful is a question mark. The progression of knowledge over the past decade regarding the damage done by transthyretin amyloid, with new associations with disease states emerging every few years, suggests that looking more closely at any amyloid will turn up ways in which it contributes to age-related tissue dysfunction and disease. The SENS proposals for rejuvenation therapies suggest that all amyloids should be targeted for removal by approaches such as catabodies, firstly on the basis that they are a feature of aging, a distinguishing difference between young and old tissues, and secondly that the amyloids that have been carefully investigated all turned out to be harmful.

Today's research materials are an example of looking more closely at the biochemistry of one specific amyloid, and as a result finding out that it isn't innocuous. Medin is the most common human amyloid, which makes it interesting that there has been just about as little investigation of its role in age-related disease as was the case for transthyretin amyloid until quite recently. Researchers have published evidence for medin to be involved in aortic anyeurism and of late vascular dysfunction in the brain. That latter finding is echoed in the research noted below.

Lumpy proteins stiffen blood vessels of the brain

Nearly all people over the age of 50 are known to have tiny lumps of the protein Medin in the walls of their blood vessels. "These deposits are apparently a side effect of the aging process. They are predominantly found in the aorta and in blood vessels of the upper body, including those of the brain. Most surprisingly, in our study we could not only detect Medin particles in brain tissue samples from deceased individuals but also in old mice - despite the limited lifespan of these animals. It has been assumed for quite some time that Medin aggregates have an unfavorable effect on blood vessels and can contribute to vascular diseases. Recent studies support this hypothesis. According to these previous findings, older adults with vascular dementia show increased amounts of Medin deposits compared to healthy individuals."

However, despite these suspicious signs, there has not yet been conclusive evidence that the protein lumps are actually harmful. A research team has now succeeded in proving this - enabled by their finding that Medin deposits also form in aging mice. In mice, when the brain is active and a higher blood supply is needed, blood vessels with Medin deposits expand more slowly than those without Medin. However, the ability of the vessels to expand rapidly is important for regulating blood flow and providing the brain with an optimal supply of oxygen and nutrients. If this ability is impaired, it can have far-reaching consequences for the functioning of organs. Medin deposits therefore seem to contribute to the deterioration of blood vessel function at an advanced age, and this is probably not only the case in the brain, because the deposits also occur in other blood vessels and could therefore lead not only to vascular dementia but also to cardiovascular disease.

Medin aggregation causes cerebrovascular dysfunction in aging wild-type mice

Vascular dysfunction, as it develops either during normal aging or vascular disease, remains a major medical problem. The amyloid Medin, which is derived from its precursor protein MFG-E8 (through unknown mechanisms), forms insoluble aggregates in the vasculature of virtually anybody over 50 years of age, and it has been hypothesized that Medin aggregation could contribute to age-associated vascular decline; however, mechanistic analyses have so far been lacking. Our data now demonstrate that reminiscent of humans, mice also develop Medin deposits in an age-dependent manner. Importantly, mice that genetically lack Medin show reduced vascular dysfunction in the aged brain. Therefore, the prevention of Medin accumulation should be investigated as a novel therapeutic approach to preserve vascular health in the aging population.

miR-192 in Extracellular Vesicles as a Negative Regulator of Inflammation in Old Tissues

Chronic inflammation is a feature of aging; the immune system is persistently overactive, and this disrupts tissue function in numerous ways, contributing to the progression of age-related disease. There are still anti-inflammatory mechanisms operating in old people, but these mechanisms are washed out by excessive pro-inflammatory signaling, the response to an age-damaged environment. Scientists here identify one such anti-inflammatory mechanism, an increased presence of microRNA-192 (miR-192) in the extracellular vesicles that pass between cells. Research of this nature may offer a basis for interventions that dial back age-related inflammation with fewer side-effects, in this case via upregulation of miR-192, an important goal in the treatment of aging.

A hyperinflammatory state has been observed in elderly humans and animals, wherein levels of IL-6 and several other pro-inflammatory cytokines in the blood are elevated. Inflammation itself is a necessary part of immune cell-mediated host protection, with pro-inflammatory cytokines mainly produced by innate immune cells, including macrophages, which are essential components for counteracting viral infections before the development of acquired immunity. However, the onset and termination of inflammatory responses must be tightly regulated because excessive inflammation or unbalanced production of inflammatory cytokines and chemokines can be detrimental to the organism.

Recent studies have revealed that small extracellular vesicles (EVs) mediate intercellular communications and influence our immune system. Aging and senescence have been found to modulate EV function, but it remains unclear whether aging affects EV-mediated immune regulation. EVs consisting of 30- to 150-nm lipid bilayer vesicles are the potent systemically circulating factors that regulate immune responses, including inflammation. These vesicles are secreted by many types of cells throughout the body for local or remote cell-to-cell communication, and they contain functional proteins and RNAs, such as microRNAs (miRNAs), which modulate cellular responses. Recent studies have shown that EVs deliver several immune regulatory miRNAs suited to different tasks.

This study found that the microRNA-192 (miR-192) is an aging-associated immune regulatory microRNA whose concentration was significantly increased in aged EVs due to the hyperinflammatory state of aged mice. Interestingly, EV miR-192 exhibited anti-inflammatory effects on macrophages. In our aged mouse model, aging was associated with prolonged inflammation in the lung upon stimulation with inactivated influenza whole virus particles (WVP), whereas EV miR-192 alleviated the prolonged inflammation associated with aging. The hyperinflammatory state of aged mice resulted in reduced production of specific antibodies and efficacy of vaccination with WVP; however, EV miR-192 attenuated this hyperinflammatory state and improved vaccination efficacy in aged mice. Our data indicate that aged EVs constitute a negative feedback loop that alleviates aging-associated immune dysfunction.

Link: https://doi.org/10.1016/j.isci.2020.101520

Proposing an Approach to Obtain Human Data on Combined Interventions and Effects on Aging

With the advent of epigenetic clocks that appear able to measure biological age, researchers are interested in putting these clocks to work on the assessment of interventions that might affect the pace and state of aging. It is the case, of course, that today there are all too few interventions that can reliably affect the pace and state of aging. But, arguably, the research community shouldn't let that get in the way of generating data with the interventions that do exist, such as exercise, calorie restriction, or senolytics, even though the effects on longevity in humans are either small or unknown.

The most important challenge in the use of epigenetic clocks is that it remains somewhat unclear as to what exactly it is that these clocks are measuring. In other words which of the underlying mechanisms of aging contribute to the observed epigenetic changes that are characteristic of aging, and the relative size of their contributions. Some researchers, on the other hand, and as is the case here, think that epigenetic changes are an underlying cause of aging, and that puts a different spin on assessing these changes. To some extent the motivation doesn't matter in this case: gathering more data, and particularly data on combinations of interventions, may be a decent first step towards making better use of epigenetic age assessments.

Josh Mitteldorf's latest initiative, The Data-BETA Project, is a bold attempt to learn how a wide range of supplements, dietary changes, and exercise regimes are actually impacting our biological age. "Up until a few years ago, we really only had animal studies to go on for life extension. And then it was a major revolution when Horvath came out with his first methylation clock. The second generation of that clock called the PhenoAge clock came out two years ago and that is what inspired me to think about this study. The crucial point is that the methylation profile derived from PhenoAge is an even better predictor of when you're going to die than PhenoAge itself. So, and this is a theme that I've been putting out there, that's a deep indication that methylation is a driver of aging, and potentially a deeper cause of aging than things like autoimmunity, inflammation, blood pressure, blood sugar, and so on."

As a result, Mitteldorf believes that time is now right to start using methylation clocks to start evaluating anti-aging programs to see what works - and what doesn't. This belief led him to the creation of the Data-BETA Project - a proposed 5,000 person study that will use methylation clocks to measure the anti-aging impact of a wide range of interventions. Importantly, the study will also explore the potential impact of combinations of interventions to produce a bigger anti-aging benefit than the sum of their separate effects. "People have been caught up in this model of studying one intervention at a time, but I think biology doesn't work that way. Biology really is much more holistic than that. We should be looking at combinations of treatments and not expect that there's going to be a single chemical and that's going to solve aging for us. We're much more likely to make progress if we look at combinations of treatments and the interactions from the get-go - not just what the treatment does separately."

Link: https://www.longevity.technology/longevity-interventions-find-out-whats-working-and-what-isnt/

Reviewing the Clinical Evidence for NAD+ Upregulation

I recently collaborated on a review paper covering the history of clinical work on upregulation of nicotinamide adenine dinucleotide (NAD) as an approach to therapy. This is of interest to the aging research community because NAD is important to mitochondrial function. NAD levels diminish with age, alongside a loss of mitochondrial function that is known to contribute to the onset and progression of many age-related conditions. Animal studies and a few clinical trials have indicated that increased NAD levels may improve, for example, cardiovascular function in older individuals, as a result of improved mitochondrial function in important cell populations.

The most common approaches to increasing NAD levels involve compounds derived from vitamin B3 - niacin, nicotinamide riboside, nicotinamide mononucleotide, and so forth. These are involved in the mechanisms of NAD synthesis or recovery. In that sense research into NAD upregulation has been taking place for a century or more, somewhat unknowingly, as researchers characterized the use of high doses of vitamin B3 as an intervention. The more modern phase of this work, deliberately targeting NAD with methodologies that move beyond the use of vitamin B3, has less of a history, but it is nonetheless interesting to note just how far back it goes.

It is also interesting to note the ragged and haphazard character of the clinical work on NAD upregulation, taken as a whole over the past few decades. Many approaches and indications have been tested, but few more than once, and few in large study populations. Further, the studies that used exercise as an intervention show effect sizes on NAD levels that are comparable or better than those that used other approaches. That, to me, raises the question of just how much effort is actually worth putting into NAD-based approaches to the treatment of age-related declines.

Clinical Evidence for Targeting NAD Therapeutically

A number of clinical trials have been conducted recently, with more underway, to rigorously assess NAD pharmacology in the context of aging and metabolic and age-related disease. We have conducted a review of the literature in an attempt to determine whether or not the present human evidence for the potential benefits from NAD pharmacology supports an expansion of efforts to assess this approach to age-related conditions. Of the 36 human trials with published results identified in our literature review, 18 reported on oral administration of NAD precursors, such as nicotinamide, nicotinamide mononucleotide, or nicotinamide riboside, while 8 employed oral administration of NAD. The remainder used an eclectic mix of exercise programs, antioxidants, forms of topical, intravenous, or intramuscular administration of NAD, as well as compounds targeting NQO1 activity. Of the 36 trials, 7 assessed only pharmacokinetics, safety, or biomarkers, and 17 reported beneficial outcomes. The remaining 12 reported no benefits to patients.

Our review reveals that the upregulation of NAD has been studied for a wide range of medical conditions, only a few of which are addressed by more than one study. These conditions include acute kidney injury, Alzheimer's disease, chronic fatigue syndrome, dementia, hyperphosphatemia, hypertension, obesity, Parkinson's disease, photoaging of skin, psoriasis, skin cancers, type 1 diabetes mellitus, type 2 diabetes mellitus, and schizophrenia. NAD levels after intervention were measured in only 11 trials, in blood samples or tissues. In all cases, increased NAD was observed, but the size of the effect varied widely. These changes were almost incomparable due to the current lack of standardization, as variance may be due to differences in methodology of measurement, in interventions, or other factors.

The earliest deliberate attempts at NAD pharmacology, as distinct from the extensive study of vitamin B3, involved the delivery of niacin or formulations of NAD in the treatment of schizophrenia, beginning in the 1960s. This intervention was based on a variety of hypotheses linking NAD biochemistry to the neurobiological changes thought to be involved in schizophrenia. More modern hypotheses of NAD-related redox dysfunction in schizophrenia continue to be debated today; mitochondrial dysfunction and oxidative stress are thought to contribute to the pathogenesis of the condition. Available reports refer to positive results in earlier studies, but the authors reported no benefits to patients resulting from their small clinical trials. Beginning in the 1990s, NAD pharmacology was assessed as a basis for the treatment of Parkinson's disease and Alzheimer's disease, efforts that have since expanded to other forms of dementia. To date, the results of clinical trials have been mixed for Parkinson's disease and largely negative for Alzheimer's disease. Further trials are in progress.

NAD upregulation prevents actinic keratosis and improves some measures of photoaging. While the mechanisms of action are not fully understood, NAD is a co-factor for the PARP enzymes that play a key role in DNA repair. Skin is exposed to UV damage, causing frequent DNA breaks. Improving PARP function, and thus improving DNA repair, might protect from precancerous skin lesions and other consequences of photoaging. This mechanism may also influence the skin pathology associated with dysregulated skin cell division in conditions, such as psoriasis.

Only limited data is available for the use of NAD boosters in the treatment of metabolic conditions, such as obesity and metabolic syndrome. While some studies report improvement in lipid profile, exercise capacity, and muscle fiber composition despite a sedentary lifestyle, others show no benefit of supplementation in the prevention of type 1 diabetes, and no improvements in insulin resistance.

Based on the human trials conducted to date, NAD pharmacology is a promising treatment strategy that is likely to be safe for human use. However, despite several decades of active investigation, there is still only suggestive evidence, in the form of a few successful and sufficiently powered clinical trials, for NAD upregulation to be effective for any of the many potential indications where it may benefit patients. More and larger studies are required to produce robust data in support of NAD pharmacology. This includes in particular studies in which different forms of NAD upregulation are compared consistently with one another. For example, exercise programs tailored to older individuals may be more effective than all of the existing approaches to NAD pharmacology. Whether or not this is the case is one of the more important questions for the research community to answer.

Reducing Chronic Inflammation as Effective as Reducing Blood Cholesterol in Producing a Small Reversal of Atherosclerotic Lesions

The study results here provide an interesting comparison between the strategies of lowering inflammation and lowering blood cholesterol for the treatment of atherosclerosis. Atherosclerosis is the name given to the buildup of fatty lesions in blood vessel walls, a process that occurs in all of us with advancing age. These deposits narrow and weaken blood vessels, ultimately leading to a fatal rupture or blockage. This is one of the largest causes of human mortality. Unfortunately the present dominant approach of reducing blood cholesterol - via statins and similar therapies - doesn't do more than modestly slow the condition, and only slightly diminishes the size of existing lesions. While atherosclerosis appears to have a strong inflammatory component, in that it progresses more rapidly in the presence of greater age-related chronic inflammation, dampening that inflammation doesn't appear to do any better than reducing blood cholesterol when it comes to turning back the condition and reducing lesion size. Different approaches are going to be needed, perhaps along the lines of removing the lipids present in lesions more directly.

Chronic inflammation in people with psoriasis is associated with a higher risk of developing coronary artery disease. Biologic therapy medications are proteins that are given by injection or infusion and suppress the inflammation process by blocking the action of cytokines, which are proteins that promote systemic inflammation. Previous research has shown a clear link between psoriasis and the development of high-risk coronary plaque. This study provides characterization of a lipid-rich necrotic core, a dangerous type of coronary plaque made up of dead cells and cell debris that is prone to rupture. Ruptured plaque can lead to a heart attack or stroke.

The analysis involved 209 middle-aged patients (ages 37-62) with psoriasis who participated in the Psoriasis Atherosclerosis Cardiometabolic Initiative at the National Institutes of Health, an ongoing observational study. Of these participants, 124 received biologic therapy, and 85 were in the control group, treated only with topical creams and light therapy. To measure the effects of biologic therapy on arteries of the heart, the researchers performed cardiac computed tomography (CT) scans on all study participants before they started therapy and one year later. The CT results between the two groups were then compared.

Biologic therapy was associated with an 8% reduction in coronary plaque. In contrast, those in the control group experienced slightly increased coronary plaque progression. Even after adjusting for cardiovascular risk factors and psoriasis severity, patients treated with biologic therapy had reduced coronary plaque. "There is approximately 6-8% reduction in coronary plaque following therapy with statins. Similarly, our treatment with biologic therapy reduced coronary plaque by the same amount after one year. These findings suggest that biologic therapy to treat psoriasis may be just as beneficial as statin therapy on heart arteries."

Link: https://newsroom.heart.org/news/biologic-therapy-for-psoriasis-may-reduce-heart-disease

Fasting Mimicking Diet Improves Chemotherapy Effectiveness and Reduces Side Effects

The fasting mimicking diet emerged from efforts to better define the dose-response curve for beneficial effects resulting from a reduced calorie intake. Fasting is beneficial, calorie restriction is beneficial, but where are the dividing lines? How much food can one eat and still obtain near all of the benefits of fasting? As a result of this work, the fasting mimicking diet has undergone clinical testing in cancer patients. Numerous benefits have been demonstrated, and the paper here is an example of the type. In this human trial, fasting mimicking reduced the negative short term impact of chemotherapy on health, and, further, three to four times as many patients experienced a strongly beneficial response to the chemotherapeutic treatment.

Extensive preclinical evidence suggests that short-term fasting and fasting mimicking diets (FMDs) can protect healthy cells against the perils of a wide variety of stressors, including chemotherapy, simultaneously rendering cancer cells more vulnerable to chemotherapy and other therapies. Essentially, fasting causes a switch in healthy cells from a proliferative state towards a maintenance and repair state. Malignant cells, in contrast, seem to be unable to enter this protective state because of oncoprotein activity, and therefore fail to adapt to nutrient scarce conditions. Instead, fasting deprives proliferating cancer cells of nutrients and growth factors, which renders them more sensitive to cancer therapy and increases cell death. The phenomenon by which normal but not cancer cells become protected to toxins is termed differential stress resistance (DSR) whereas the specific sensitization of cancer cells to stress is called Differential Stress Sensitization (DSS).

Declines of plasma levels of insulin like growth factor-1 (IGF-1), insulin, and glucose are among the mediators of the effects of fasting on cancer cells, as these factors can promote growth and prevent apoptosis. Fasting periods of at least 48 hours are required to induce a robust decrease in circulating glucose, IGF-1, and insulin levels. A very low calorie, low protein FMD was developed for its ability to cause metabolic effects on various starvation response markers similar to those caused by water-only fasting, while reducing the burden associated with a water only fast.

In the DIRECT trial, we randomized 131 patients with HER2-negative stage II/III breast cancer, without diabetes and a BMI over 18 kg/m2, to receive either FMD or their regular diet for 3 days prior to and during neoadjuvant chemotherapy. Here we show that there was no difference in toxicity between both groups, despite the fact that dexamethasone was omitted in the FMD group. A radiologically complete or partial response occurs more often in patients using the FMD (odds ratio 3.168). Moreover, per-protocol analysis reveals that the 90-100% tumor-cell loss is more likely to occur in patients using the FMD (odds ratio 4.109). Also, the FMD significantly curtails chemotherapy-induced DNA damage in T-lymphocytes. These positive findings encourage further exploration of the benefits of fasting and FMD in cancer therapy.

Link: https://doi.org/10.1038/s41467-020-16138-3

Mitochondrial Point Mutations Contribute to Female Reproductive Aging, and NAD+ Upregulation Attenuates These Consequences in Mice

Today's open access paper discusses the impact of mitochondrial DNA damage on female reproductive capabilities. Mitochondria are the power plants of the cell, a herd of hundreds of organelles responsible for packaging the chemical energy store molecule ATP, used to power cellular processes. They are additionally deeply integrated into many core cellular processes. Mitochondria are the evolved descendants of ancient symbiotic bacteria: they carry their own small genome, the mitochondrial DNA, and replicate like bacteria. Unfortunately this mitochondrial DNA is more vulnerable and less proficiently repaired than the nuclear DNA in the cell nucleus, and it accumulates mutational damage. Most is washed out by cell turnover in the body, but this damage nonetheless adds up over a lifetime.

Some rare forms of mitochondrial DNA mutation, such as large deletions, can give rise to dysfunctional mitochondria that overtake their cells. The cell itself becomes dysfunction, exporting damaging reactive molecules into the surrounding tissue. This happens infrequently, but is sufficiently problematic when it does occur for it to contribute to aging. Other forms of mitochondrial mutation, such as point mutations, can also be a problem via a more subtle degradation of mitochondrial function. Mutator mice that accumulate this form of damage much more rapidly than their peers exhibit accelerated age-related degeneration, however. This is driven by the progressively greater dysfunction of mitochondria throughout the body.

Researchers here note that the dysfunction of mitochondria produced by point mutations in mutator mice causes a disruption in NAD metabolism. NAD in aging and mitochondrial function has been a topic of growing interest for some years now. NAD levels decline with age, but the cycling of NADH to NAD+ and back again is a central portion of the processes by which mitochondria produce ATP. There are a variety of ways in which NAD levels can be increased, primarily compounds vitamin B3 and related compounds: niacin, nicotinamide riboside, nicotinamide mononucleotide, and so forth. It is unclear than any of these produce better results than exercise programs when it comes to increasing NAD+ levels, but they can be convenient tools for animal studies. That is the case here, where nicotinamide mononucleotide is used to reverse some of the imbalance in mitochondrial function caused by point mutations, and thus restore some lost ovarian function.

On the whole, it seems surprising that stochastic mitochondrial DNA point mutations could be responsible for meaningful age-related degeneration in humans (the sizeable loss of fertility) by age 40, given that a 40 year old human is still in fairly good physical shape, looking at mortality and disease risk across the board. Why just this ovarian loss of function and not a much larger general decline, if there are point mutations degrading mitochondrial function everywhere? It may be the case that critical ovarian tissue is especially sensitive to this particular mechanism of aging, but more research is needed on that topic.

Mitochondrial DNA mutation exacerbates female reproductive aging via impairment of the NADH/NAD+ redox

Aging is one of the key factors in both male fertility and female fertility. Indeed, female fertility normally peaks at age 24 and diminishes after 30, with pregnancy occurring rarely after 50. Mitochondrial malfunction has been hypothesized to play important roles in age- and environment-induced infertility. For instance, mitochondrial DNA (mtDNA) deletions were reported to accumulate in human ovarian aging. However, the links among aging, mtDNA mutations, and infertility remain not fully understood.

mtDNA-mutator (PolgAMut/Mut) mice are widely used as an experimental model to study the roles of mtDNA mutations in aging process. The PolgAMut/Mut mice harbor a mutation in the nuclear DNA-encoded mitochondrial polymerase PolgA, leading to the inactivation of its proofreading function. As compared to wild-type (WT) mice, the PolgAMut/Mut mice exhibited a ~10-fold higher mtDNA mutation frequency, eventually leading to a progressive decline in the function of mtDNA-encoded respiratory complexes. PolgAMut/Mut mice were reported to show a reduced life span that is limited to 13-15 months. Consistently, aging-associated disorders occurred approximately 6-8 months after the birth of the PolgAMut/Mut mice.

In the present study, we first determined how mtDNA mutations in human female oocytes changed with age. We analyzed oocyte quality of young (≤30 years old) and elder (≥38 years old) female patients and show the elder group had lower blastocyst formation rate and more mtDNA point mutations in oocytes. Using the PolgAMut/Mut mouse model, we demonstrate mtDNA mutations decrease the fertility of females, but not males, via reducing ovarian primordial and mature follicles. We further show that accumulation of mtDNA mutations decreases female fertility by reducing oocyte's NADH/NAD+ ratio and that nicotinamide mononucleotide (NMN) is remarkably capable of ameliorating infertility in female PolgAMut/Mut mice.

Evidence for Chronic Inflammation to be a Significant Factor in Age-Related Hearing Loss

Hearing loss is a prevalent problem with age, the result of loss of sensory hair cells of the inner ear, or as seems more likely in recent years, damage to those parts of the peripheral nervous system connecting hair cells to the brain. Chronic inflammation is a noted aspect of aging, excessive activity of the immune system, and is very disruptive to tissue function and maintenance throughout the body. Researchers here provide evidence to suggest that this persistent inflammation in older individuals is an important factor in age-related hearing loss.

Age-related hearing loss (AHL) or presbycusis is a universal sensory disorder in modern society and affects about 25-40% of people over 65 years. The underlying mechanisms of AHL include oxidative stress, mitochondrial DNA mutations, autophagy impairment, and non-coding RNA disorders. However, the mechanism of cochlear degeneration during aging is still not fully understood. In recent years, the effects of inflammation on aging-related disorders have been extensively investigated. During aging, the body suffers from chronic low-grade inflammation, a phenomenon also referred to as "inflammaging". Chronic inflammation is a consequence of immunosenescence, the aging of the immune system, and is primarily characterized by increased levels of proinflammatory cytokines in response to various stressors. However, only little research on the potential role of inflammation in AHL has been reported.

The current study was designed to determine the transcriptional changes of cochlear genes and the most significantly affected functions and pathways during aging in C57BL/6 mice using next generation sequencing. Our RNA-sequencing data revealed that transcripts associated with aging, apoptosis, and necroptosis were significantly modulated in aged cochleae. Importantly, numerous genes related to immune responses and inflammation were differentially expressed during aging. Bioinformatics analysis of the upregulated genes also revealed that a large portion of biological processes and pathways are related to immune and inflammatory pathways, such as complement system and macrophage activation. Whereas, lots of the downregulated genes are involved in biological processes and pathways associated with ion channel function and neuronal signaling. These findings suggest chronic inflammation may be associated with aging-related cochlear degeneration.

Link: https://doi.org/10.7717/peerj.9737

Calorie Restriction Improves Intestinal Stem Cell and Barrier Function in Old Mice

The practice of calorie restriction improves many measures of health, and extends life meaningfully in short lived species such as mice. Unfortunately, while calorie restriction improves health in much the same way in humans, the effects on longevity are much smaller in long-lived species than is the case for short-lived species. Nonetheless, given that it is an intervention that requires no great effort or cost to carry out, it is well worth it for the health benefits that it does provide, such as a reduced risk of suffering age-related conditions, and a postponement of many of the more evident declines of age. One has to be realistic about the modest effects on life span in our species, but it remains interesting to see papers such as the one here, examining just one of the many ways in which calorie restriction is beneficial.

This study aimed to reveal the impact of calorie restriction on the intestine via structural and molecular changes in terms of intestinal stem cell (ISC) function, ISC niche, intestinal epithelial barrier function, and intestinal immune function. Female C57BL/6J mice, aged 12 months, fed a commercial chow were used in this study. The ISC function, ISC niche, intestinal epithelial barrier function, and intestinal immune function were assessed.

Calorie restriction reversed aging-induced intestinal shortening and made the crypts shallower. The intestinal epithelial cells isolated from the intestine showed a significant increase in the expression levels of stem cell-associated genes in small intestinal epithelial cells as detected by flow cytometry. Despite the increase in the number of stem cells and the expression levels of markers, no increase or decrease was found in the enteroid complexity of the small intestine and colonic enteroid formation in vitro.

The colonic mucous layer was measured in mice of the calorie restricted (CR)-treated group to investigate the epithelial barrier function in the colon. The results revealed that the barrier was more complete. The fluorescence intensity of tight junction markers claudin-2 and zonula occludens-1 increased and the mRNA expression profiles of monocyte chemotactic protein 1 and interleukin-6 decreased in the colon of mice in the CR-treated group. The beneficial effects of CR on the colon in terms of the integrity of the mucosal barrier and alleviation of inflammation were confirmed, thus highlighting the importance of modulating the intestinal function in developing effective antiaging dietary interventions.

Link: https://doi.org/10.1016/j.nutres.2020.06.015

Higher Temperature Slows Osteoporosis, an Effect Mediated by Polyamine Produced by Gut Microbes

Osteoporosis is the name given to the characteristic age-related loss of bone mass and strength. The extracellular matrix of bone tissue is constantly remodeled, created by osteoblasts and broken down by osteoclasts. The proximate cause of osteoporosis is a tilt in the balance of these processes, favoring osteoclast activity and thus slow loss of bone structure.

Today's research materials discuss a most intriguing result: in mice, maintaining a higher environmental temperature slows the progression of osteoporosis. Interesting, but is it a path to therapy? As is always the case when looking at metabolic responses to environmental differences in mice, there is the question of whether similar effects in humans are anywhere near as large All too many examples of this sort of thing are, unfortunately, clearly of little interest as a basis for human therapies because larger mammals respond less strongly. Here, however, a range of epidemiological data from hotter versus colder regions of the world suggests that, yes, the effect of temperature on osteoporosis in humans may be large enough to care about.

Perhaps the most interesting part of this work is the investigation into underlying mechanisms. It appears that the effect of temperature on osteoporosis is mediated by differences in the gut microbiome. In hotter climates, there is a greater microbial production of the metabolite polyamine, known to beneficially affect bone tissue maintenance. Transplanting gut microbes from high temperature environment mice to mice with osteoporosis modestly reverses the progression of the condition, improving bone density, but this benefit is not realized in mice in which polyamine production is inhibited.

Stronger bones thanks to heat and microbiota

Many biologists are familiar with Allen's Rule, according to which animals living in warm areas have a larger surface area in relation to their volume than animals living in colder environment. Indeed, a larger skin surface allows better evacuation of body heat. By placing several groups of adult mice in a warm environment, scientists observed that while bone size remained unchanged, bone strength and density were largely improved.

What about human beings? The research team analysed global epidemiological data on the incidence of osteoporosis in relation to the average temperature, latitude, calcium consumption, and vitamin D levels. Interestingly, they found that the higher the temperature, the fewer hip fractures - one of the main consequences of osteoporosis - regardless of other factors.

Scientists wanted to understand the role of the gut microbiome in these metabolic modifications. To this end, they transplanted the microbiota of mice living in a 34°C environment to osteoporotic mice, whose bone quality was rapidly improved. Thanks to the state-of-the-art metagenomic tools developed in their laboratory, the scientists then succeeded in understanding the role played by microbiota. When adapts to heat, it leads to a disruption in the synthesis and degradation of polyamines, molecules that are involved in ageing, and in particular in bone health.

Warmth Prevents Bone Loss Through the Gut Microbiota

Osteoporosis is the most prevalent metabolic bone disease, characterized by low bone mass and microarchitectural deterioration. Here, we show that warmth exposure (34°C) protects against ovariectomy-induced bone loss by increasing trabecular bone volume, connectivity density, and thickness, leading to improved biomechanical bone strength in adult female, as well as in young male mice. Transplantation of the warm-adapted microbiota phenocopies the warmth-induced bone effects. Both warmth and warm microbiota transplantation revert the ovariectomy-induced transcriptomics changes of the tibia and increase periosteal bone formation.

Combinatorial metagenomics / metabolomics analysis shows that warmth enhances bacterial polyamine biosynthesis, resulting in higher total polyamine levels in vivo. Spermine and spermidine supplementation increases bone strength, while inhibiting polyamine biosynthesis in vivo limits the beneficial warmth effects on the bone. Our data suggest warmth exposure as a potential treatment option for osteoporosis while providing a mechanistic framework for its benefits in bone disease.

Long Term mTORC1 Inhibition Slows Muscle Aging in Mice via Preservation of Neuromuscular Junctions

Sarcopenia is the name given to the characteristic loss of muscle mass and strength that occurs in later life, the result of numerous contributing processes of damage and decline. Researchers here find that long-term treatment with rapamycin, and thus likely other more targeted approaches to mTORC1 inhibition, slows the onset of sarcopenia in mice by preserving the function of neuromuscular junctions, the links between nerves and muscles. The most important contributing cause of sarcopenia is likely to be a slowdown in muscle stem cell activity. Interestingly, these stem cell populations appear to remain viable, but are increasingly quiescent in response to the damaged and inflammatory environment of aged tissues. This work suggests that damage and declining function of neuromuscular junctions should be given a greater weight than previously considered, however.

Recently, nine processes involved in aging were proposed, namely cellular senescence, stem cell exhaustion, genomic instability, telomere attrition, loss of proteostasis, deregulation of nutrient sensing, epigenetic alterations, mitochondrial dysfunction, and altered intracellular communication. Each biological process fulfils three hallmark criteria: (1) it occurs during normal aging, (2) intensifying the process accelerates aging, and (3) dampening the process delays aging. Overactivity of the mammalian (or mechanistic) target of rapamycin complex 1 (mTORC1) is central to many of these processes, and dampening mTORC1 activity by its allosteric inhibitor rapamycin is one of the most effective interventions to prolong life. However, mTORC1 activity is also required for muscle hypertrophy. Therefore, there is concern that suppressing mTORC1 to extend lifespan could be at the expense of skeletal muscle function, thereby extending the "poor-quality" period of life.

In previous work, we have shown that mTORC1 activity must be finely balanced in skeletal muscle. Here, we demonstrate that long-term rapamycin treatment is overwhelmingly positive in aging skeletal muscle, preserving muscle size, function, and neuromuscular junction (NMJ) integrity. Interestingly, responsiveness to rapamycin differs between muscles, suggesting that the primary drivers of age-related muscle loss may differ between muscles. To dissect the key signaling nodes associated with mTORC1-driven sarcopenia, we create a comprehensive multimuscle gene expression atlas from (1) adult (10-months old), (2) geriatric (30-months old), and (3) geriatric, rapamycin-treated mice using mRNA-seq. Our data point to age-related NMJ instability as a focal point of mTORC1-driven sarcopenia. Maintenance of NMJ structure and transmission efficiency is crucial for preserving muscle function at high age.

Link: https://doi.org/10.1038/s41467-020-18140-1

Geroscience and Ovarian Aging

The geroscience view of the treatment of aging isn't limited to the reuse of existing drugs that happen to upregulate stress responses in ways that modestly slow aging, but this is the near entirely the focus of those researchers who publish on the topic. Unfortunately the effect size of this approach to aging is small, and diminishes as species life span increases. We know the upper limits of what can be achieved with the beneficial stress response induced by calorie restriction in humans, and we know that it won't really add more than a couple of years to human life spans. Better strategies exist, based on the development of biotechnologies that repair the underlying cell and tissue damage that causes aging. Repair can in principle achieve rejuvenation, not just a modest slowing of aging, and that rejuvenation has already been demonstrated in animal models for the repair-based approach of removing senescent cells from old tissues.

In women 35 years and older the incidences of infertility, aneuploidy, and birth defects dramatically increase. These outcomes are a result of age-related declines in both ovarian reserve and oocyte quality. In addition to waning reproductive function, the decline in estrogen secretion at menopause contributes to multi-system aging and the initiation of frailty. Both reproductive and hormonal ovarian function are limited by the primordial follicle pool (PFP), which is established in utero and declines irreversibly until menopause. Because ovarian function is dependent on the PFP, an understanding of the mechanisms that regulate follicular growth and maintenance of the PFP is critical for the development of interventions to prolong the reproductive lifespan.

Manipulating the rate of aging and delaying the onset of aging-related diseases have been the makeup of medical, scientific, and pseudo-scientific pursuits throughout history. However, it is not until relatively recently, in the later part of the 20th and early 21st centuries, that the molecular targets and geroscience approaches needed to make this a reality have been elucidated. For example, improvements in reproductive function after rapamycin treatment are evident in studies of physiologic murine aging. A 2-week course of rapamycin in healthy mice improved primordial follicle count, oocyte morphology, and mitochondrial activity. In mating studies, after 12 months of age, when the control mice began to experience age-related infertility, the rapamycin-treated mice retained fertility and continued to have pups. Equally, a 12-month course of resveratrol in mice increased primordial follicle counts, litter size, and oocyte quality at advanced ages. Additionally, a specific SIRT1 activator SRT1720 administered to mice suppressed the activation of primordial follicles and increased the ovarian reserve by activating SIRT1 and inhibiting mTOR signaling.

Multiple pathways, many of them nutrient-sensing, converge in the mammalian ovary to regulate the quiescence and activation of primordial follicles. The PI3K/PTEN/AKT/FOXO3 and mTOR pathways appear to be central to the regulation of the primordial follicle pool; however, GH/IGF-1 and H2S may also play a role. A delicate balance of primordial follicle activators and suppressors must be maintained in order to allow for continued ovulation while preventing rapid depletion of the ovarian reserve. The behavioral and pharmacologic interventions that prevent primordial follicle activation, including DR and rapamycin, cause infertility for the duration of the intervention. In order for these interventions to be useful clinically, the resulting period of infertility must be reversible, and the treatments must confer long-term benefits after a relatively short duration of use.

Link: https://doi.org/10.1093/gerona/glaa204

Recent Studies on the Changing Gut Microbiome in Aging

Today's research materials are a selection of recent studies on the gut microbiome and its relationship to the aging process. The scientific community has in recent years uncovered a great deal of new information regarding the way in which the gut microbiome both influences health and exhibits detrimental changes with age. Some of the microbes of the digestive tract are responsible for the generation of beneficial metabolites such as butyrate, indoles, and propionate. Unfortunately these populations decline in number with advancing age, and this negatively impacts tissue function throughout the body. Additionally, harmful inflammatory species increase in number. This contributes to the state of chronic inflammation that characterizes old age and accelerates the progression of all of the common age-related conditions.

The causes of age-related shifts in these microbial populations are not well understood, particular recently discovered changes that take place in earlier life. There is evidence for dietary changes to be involved, as well as the decline of the immune system's ability to suppress harmful microbes, and the loss of integrity of intestinal barrier tissue. Which of these are more significant or less significant is an open question, however. It is also an open question as to how great an influence this has on long-term health and longevity; it wouldn't be surprising to find it in the same ballpark as that of exercise.

This is an age-related change that is amenable to reversal in the near term. Animal studies show that fecal microbiota transplant from young animals to old animals resets the gut microbiome to a more youthful distribution of species, and results in improved health and extended life spans. This procedure is already carried out in human medicine for certain conditions, and could thus be expanded to other uses. Other potential approaches also exist, such as inoculation with bacterial proteins to encourage the immune systems to suppress harmful species, or sizable sustained dosage with a suitable mix of probiotics. We'll likely see many such initiatives in the years ahead.

Relationship between Diet, Microbiota, and Healthy Aging

The gastrointestinal tract is colonized by a set of microorganisms that include not only bacteria but also viruses, fungi, and protozoa. Unlike other microorganisms, these are not identified as pathogens by our immune system, but rather coexist symbiotically with the enterocytes. So far, it is known that its composition contains a total of 52 different phyla and up to 35,000 different bacterial species, the large majority being Firmicutes, Bacteroidetes, Actinobacteria, and Proteobacteria.

As we age, progressive changes are produced in the morphology and function of the microbiota - a decrease in Firmicutes and Bifidobacterium, with diversity in the patterns of abundance for Clostridium. The mechanism by which the microbiota changes with age is not yet fully understood. Lifestyle changes, and particularly diet, play an important role. As aging is often accompanied by a reduction in quantity and variety of aliments containing fiber, it often leads to a risk of malnourishment. This could alter its diversity and provoke inflammatory and metabolic disruption, causing inflammatory diseases in the intestine, such as irritable bowel, obesity, etc. Additionally, the microbiota can modulate changes in aging related to innate immunity, sarcopenia, and cognitive function, which are essential components of the frailty syndrome.

Gut Microbiome Composition is Associated with Age and Memory Performance in Pet Dogs

Gut microbiota can crucially influence behavior and neurodevelopment. Dogs show unique similarities to humans in their physiology and may naturally develop dementia-like cognitive decline. We assessed 29 pet dogs' cognitive performance in a memory test and analyzed the bacterial 16S rRNA gene from fecal samples collected right after the behavioral tests. The major phyla identified in the dog microbiomes were Bacteroidetes, Firmicutes, and Fusobacteria, each represented by more than 20% of the total bacterial community. Fewer Fusobacteria were found in older dogs and better memory performance was associated with a lower proportion of Actinobacteria. Our preliminary findings support the existence of links between gut microbiota, age, and cognitive performance in pet dogs.

Gut microbes could unlock the secret to healthy ageing

The study included 422,417 unrelated individuals in the UK Biobank who had undergone genotyping to identify their genetic make-up. Information was also collected on a wide range of diseases and other characteristics including BMI and blood pressure. The average age of participants was 57 years and 54% were women. The researchers found that higher levels of eleven bacteria (estimated from genetic data) were associated with a total of 28 health and disease outcomes. These included chronic obstructive pulmonary disease (COPD), atopy (a genetic tendency to develop allergic diseases like asthma and eczema), frequency of alcohol intake, high blood pressure, high blood lipids, and BMI. To take one example, higher levels of the genus Ruminococcus were linked with increased risk of high blood pressure.

Metformin Found to Reduce Liver Inflammation

Metformin produces a modest and unreliable extension of life in animal models, and human data shows a small increase in life span in diabetic patients. This is thought to work as a calorie restriction mimetic drug, triggering one slice of the beneficial response to a reduced nutrient intake. Researchers here dig further in the biochemistry of the drug, and find that it reduces liver inflammation in addition to other, known effects. This is interesting, and suggestive that any benefits it produces are going to be much smaller in healthier older adults with lower levels of chronic inflammation. It doesn't change the fact that metformin does have only a small and unreliable effect on life span per the existing data, and is thus not where we should be focusing our attention.

Researchers have known for 20 years that metformin activates a metabolic master switch, a protein called AMPK, which conserves a cell's energy under low nutrient conditions, and which is activated naturally in the body following exercise. Twelve years ago, researchers discovered that in healthy cells, AMPK starts a cascade effect, regulating two proteins called Raptor and TSC2, which results in a block of the central pro-growth protein complex called mTORC1 (mammalian target of rapamycin complex 1). These findings helped explain the ability of metformin to inhibit the growth of tumor cells.

But in the intervening years, many additional proteins and pathways that metformin regulates have been discovered, drawing into question which of the targets of metformin are most important for different beneficial consequences of metformin treatment. Indeed, metformin is currently entering clinical trials in the United States as a general anti-aging treatment because it is effects are so well established from millions of patients and its side effects are minimal. But whether AMPK or its targets Raptor or TSC2 are important for different effects of metformin remains poorly understood.

In the new work, in mice, researchers genetically disconnected the master protein, AMPK, from the other proteins, so they could not receive signals from AMPK, but were able to otherwise function normally and receive input from other proteins. When these mice were put on a high-fat diet triggering diabetes and then treated with metformin, the drug no longer had the same effects on liver cells as it did in normally diabetic animals, suggesting that communication between AMPK and mTORC1 is crucial for metformin to work. By looking at genes regulated in the liver, the researchers found that when AMPK couldn't communicate with Raptor or TSC2, metformin's effect on hundreds of genes was blocked. Some of these genes were related to lipid metabolism, helping explain some of metformin's beneficial effects. But surprisingly, many others were linked to inflammation. Metformin, the genetic data showed, normally turned on anti-inflammatory pathways and these effects required AMPK, TSC2, and Raptor.

Metformin and exercise elicit similar beneficial outcomes, and research has previously shown that AMPK helps mediate some of the positive effects of exercise on the body. "If turning on AMPK and shutting off mTORC1 are responsible for some of the systemic benefits of exercise, that means we might be able to better mimic this with new therapeutics designed to mimic some of those effects."

Link: https://www.salk.edu/news-release/common-diabetes-drug-reverses-inflammation-in-the-liver/

Lowered Body Temperature is Important in the Beneficial Calorie Restriction Response

Calorie restriction lowers body temperature in mammals, but most research on how reduced calorie intake produces benefits to long-term health and longevity has focused on nutrient sensing as the primary trigger for the upregulation of stress responses and other helpful changes to cellular metabolism. Here, researchers demonstrate that reduced body temperature is in fact an important trigger mechanism, possible more so than nutrient sensing, as keeping calorie restricted mice warm eliminates much of the beneficial metabolic adaptation to reduced nutrient levels.

Cutting calories significantly may not be an easy task for most, but it's tied to a host of health benefits ranging from longer lifespan to a much lower chance of developing cancer, heart disease, diabetes, and neurodegenerative conditions such as Alzheimer's. One consistent observation is that when mammals consume less food, their body temperature drops. It's evolution's way of helping us conserve energy until food is available again. It makes sense, considering that up to half of what we eat every day is turned into energy simply to maintain our core body temperature.

Previous work showed that temperature reduction can increase lifespan independently of calorie restriction - and that these effects involve activation of certain cellular processes, most of which remain to be identified. On the flip side, studies have shown that preventing body temperature from dropping can actually counteract positive effects of calorie restriction. Notably, in an experiment involving calorie-restricted mice, anti-cancer benefits were diminished when core body temperature remained the same. "It's not easy to discern what's driving the beneficial changes of calorie restriction. Is it the reduced calories on their own, or the change in body temperature that typically happens when one consumes fewer calories? Or is it a combination of both?"

In the new research, scientists compared one group of calorie-restricted mice housed at room temperature, about 68 degrees Fahrenheit (22 degrees Celsius), to another group housed at 86 degrees (30 degrees Celsius). The warmer environment invoked "thermoneutrality," a state at which most animals cannot easily reduce their body temperature. The team evaluated the mice by measuring their metabolites, or chemicals released by the animals' metabolism. Through this, they were able to look for molecules in the bloodstream and in the brain that are changed by the reduction of either nutrients or body temperature. "The data we collected showed that temperature has an equal or greater effect than nutrients on metabolism during calorie restriction."

Link: https://www.scripps.edu/news-and-events/press-room/2020/20200908-conti-temperature.html

SENS Research Foundation Issues 2020 Annual Report

The SENS Research Foundation, like the Methuselah Foundation it emerged from, is one of the more important organizations involved in the creation and shaping of the present R&D communities focused on treating aging as a medical condition. In earlier days, advocates and philanthropic programs were attempting to sway the research community (and the world at large) into taking intervention in aging seriously at all. In other words to accept that the evidence was strongly in favor of the plausibility of rejuvenation therapies, that the evidence had been strongly in favor for a long time, and that the long-standing reluctance of researchers and developers to engage in this work was entirely irrational.

That battle was in essence won a decade ago, all over bar the shouting. The research community is now wholeheartedly in favor of the treatment of aging, albeit in a wide variety of ways, not all of which are likely to work. Now advocates and philanthropic programs focus on helping the best and most promising research programs to achieve meaningful progress: provision of funding at early stages, removing roadblocks such as a lack of tooling in the space, giving them the publicity they need, persuading researchers to work on better rather than worse approaches, and so forth.

The best and most promising programs are those that can in principle produce rejuvenation in old people, and the SENS Research Foundation approach to identifying such programs has always been that they must result in periodic repair of the forms of cell and tissue damage that lie at the root of aging. It remains the case that most researchers in the field are not working on potential rejuvenation technologies, but rather on ways to tinker with metabolism in late stage aging that might make it slightly more resilient to damage. Thus there remains a great deal of work to be undertaken by advocates and philanthropists, or indeed anyone who would like to see sizable gains in human longevity sooner rather than later.

SENS Research Foundation 2020 Annual Report (PDF)

At our 2013 conference at Queens College, Cambridge, I closed my talk by saying, "We should not rest until we make aging an absurdity." We are now in a very different place. After a lot of patient explanation, publication of scientific results, conferences, and time, our community persuaded enough scientists of the feasibility of the damage repair approach to move SENS and SENS Research Foundation from the fringes of scientific respectability to the vanguard of a mainstream community of scientists developing medical therapies to tackle human aging.

Then we made the same case to investors and entrepreneurs; now, rejuvenation companies built on or inspired by our research are part of a robust ecosystem of basic science and biotech venture capitalists advancing the mission. After serving on the board for ten years, it was great to join the team full time last fall. While resources affect the pace of our progress, so do regulations and other government policies. So we began a lively dialogue with policymakers by inviting discussions of regulatory reform at our conferences and by hosting the Deputy Secretary of Health and Human Services, Eric Hargan, at our January health care event in San Francisco. More and more influential people consider aging an absurdity. Now we need to make it one.

Stepwise Visualization of Autophagy for Screening Remediation of Intraneuronal Aggregates

People often assume that an increase in autophagy automatically results in an increase in the ultimate degradation of unwanted molecular waste, but in fact the word only refers to the delivery process: it's possible to have an increase in autophagy (or in markers of autophagy) that is ultimately futile. Typical methods of testing autophagy activity can fool investigators into thinking that the affected cells are engaged in robust and successful autophagy, when instead they are signs of futile autophagy and associated with cellular dysfunction. To sort out this confusion, determine what's really being delivered to the lysosome, and pinpoint disruptions in the autophagy process, Dr. Andersen's team team has been developing a system to visualize each of the key steps along the way.

Retrolytic Therapy to Destroy Cells with Reactivated "Jumping Genes"

With SRF sponsorship, Dr. Gudkov's lab is developing a proof of concept for future rejuvenation biotechnologies that will ablate cells with active retrotransposon activity. For this initial demonstration, Gudkov will use a transgenic "suicide gene" system similar to the INK-ATTAC system that first demonstrated the rejuvenating effects of destroying senescent cells in aging mammals. In this case, the suicide gene system will be triggered by the activation of the interferon response to retroviral reactivation instead of a senescence-associated gene. Just as INK-ATTAC paved the way to the development of today's senolytic therapies (drugs and other approaches that destroy senescent cells), this suicide gene system for the elimination of cells harboring reactivated retrotransposons holds the promise of paving the way for similarly-powerful future "retrolytic" therapies.

Functional Neuron Replacement to Rejuvenate the Neocortex

The maintenance of the brain against degenerative aging processes poses extreme challenges. Only recently have researchers succeeded in integrating new neurons into areas of the brain involved in cognitive functions. Surgically transplanting a small number of neuronal progenitors into a local brain structure has been done to date but cannot realistically scale to the sheer size of the brain, or keep up with the rate of age-related neuronal loss. Therefore, maintenance of the aging brain requires a system for ongoing dispersal of neuronal precursor cells across the brain. To accomplish this goal, SENS Research Foundation is supporting Dr. Jean Hébert's innovative strategies to overcome these critical challenges. To enable the dispersal of replacement neurons noninvasively and throughout the brain, Dr. Hébert's team will next take advantage of the unique properties of microglia, the specialized macrophage immune cells of the brain. Unlike neurons and their precursors, microglia are highly motile cells, able to disperse widely throughout the brain. Hébert's strategy is to transplant microglia into the brains of mice and then reprogram the new microglia into cortical projection neurons after they disperse throughout the brain.

Engineering cyclodextrins for the Removal of Toxic Oxysterols as a Treatment For Atherosclerosis and other diseases of aging

Dr. O'Connor's team has created a family of novel cyclodextrins that are able to selectively remove toxic forms of cholesterol from early foam cells and other cells in the blood, thus forming a potential treatment for atherosclerosis. In 2019, SENS Research Foundation announced the launch of Underdog Pharmaceuticals, Inc. (Underdog), a pharmaceutical company focused on the development of this program for disease-modifying treatments for atherosclerosis and other age-related diseases. Its co-founders are Matthew O'Connor, Ph.D., and Michael Kope, formerly the Vice President of Research and the founding Chief Executive Officer, respectively, of SRF. Mike and Oki have worked incredibly hard to transition a piece of SRF's basic research to the next level, stepping into the private sector and creating a treatment for age-related disease based on one of SRF's successful proof-of-concept programs. Ten or twenty years ago, cardiovascular disease research meant developing better stents or bypass techniques; Underdog aims to ensure that atherosclerosis won't even exist in the future. All of us at SRF wish Mike and Oki success in this endeavor.

Targeting Secondary Senescence

Scientists have relatively recently discovered the phenomenon of secondary senescence. For reasons which we are only beginning to understand, existing senescent cells can cause other cells in the body to become senescent. Although this research is still in an early stage, it is beginning to appear that secondary senescent cells behave differently from primary senescent cells: they produce less SASP, but more fibrillar collagens - something that is normally suppressed in primary senescent cells. Granted their differences in origin and function, might secondary senescent cells also be differentially susceptible to senolytic therapies? For instance, might they be resistant to senolytic drugs that are effective against primary senescent cells, requiring a new generation of targeted "secondary senolytics" to eliminate - or might they be exceptionally susceptible to particular such treatments? SENS Research Foundation Forever Healthy Postdoctoral Fellow Tesfahun Admasu's work seeks to find answers to these questions.

Target Prioritization of Tissue Crosslinking

One cause of stiffening in long-lived tissues is crosslinking, where one strand of structural protein becomes chemically bound to an adjacent strand, limiting the range of motion of both strands. Prior SRF-funded work in Dr. David Spiegel's lab at Yale paved the way to the discovery of the therapeutic glucosepane-cleaving enzyme candidates that our startup company Revel Pharmaceuticals is now working to advance into functional rejuvenation biotechnologies. However, AGEs are not the only cause of crosslinking in aging tissues. The sheer number of a given type of crosslink is moreover not necessarily a good parameter for determining how we should prioritize that crosslink type as a rejuvenation target. Recognizing the importance of prioritizing our targets, SRF is funding a systematic study in "normally"-aging, nondiabetic mice by Dr. Jonathan Clark at the Babraham Institute in Cambridge. These mice are fed diets containing labeled amino acids, which are then incorporated into extracellular matrix proteins during synthesis. This allows Dr. Clark's group to track the rate at which proteins are synthesized, crosslinked, and replaced over time.

The Aging of Macrophages Impairs Peripheral Nerve Regeneration

Macrophages of the innate immune system, cells derived from monocytes, are involved in many processes in tissue beyond merely hunting down invading pathogens. They are also important to the processes of tissue maintenance regeneration following injury. Like all aspects of the immune system, macrophage behavior becomes dysregulated with age, a consequence of changes in the signaling environment that result from the accumulation of molecular damage that causes aging. Here, researchers demonstrate that this aging of the immune system degrades the ability of the peripheral nervous system to regenerate, and that exposing macrophages to a more youthful tissue environment reverses some of this lost regenerative capacity. Further, they identify a little of the regulatory biochemistry involved in this aspect of degenerative aging.

The regenerative capacity of injured peripheral nerves is diminished with aging. To identify factors that contribute to this impairment, we compared the immune cell response in young versus aged animals following nerve injury. First, we confirmed that macrophage accumulation is delayed in aged injured nerves which is due to defects in monocyte migration as a result of defects in site-specific recruitment signals in the aged nerve. Interestingly, impairment in both macrophage accumulation and functional recovery could be overcome by transplanting bone marrow from aged animals into young mice. That is, upon exposure to a youthful environment, monocytes/macrophages originating from the aged bone marrow behaved similarly to young cells.

Transcriptional profiling of aged macrophages following nerve injury revealed that both pro- and anti-inflammatory genes were largely downregulated in aged compared to young macrophages. One ligand of particular interest was macrophage-associated secreted protein (MCP1), which exhibited a potent role in regulating aged axonal regrowth in vitro. Given that macrophage-derived MCP1 is significantly diminished in the aged injured nerve, our data suggest that age-associated defects in MCP1 signaling could contribute to the regenerative deficits that occur in the aged nervous system.

Link: https://doi.org/10.3389/fnagi.2020.00174

Targeting Inflammatory Microglia in the Treatment of Neurodegenerative Disease

The immune cells of the central nervous system are distinct from those of the rest of the body. Innate immune cells such as microglia become increasingly inflammatory with advancing age, and this is very disruptive of tissue function in the brain. This progression into a state of chronic inflammation is an important component of many neurodegenerative conditions. Some of this is due to growing levels of cellular senescence in these cell populations, and with the advent of senolytic therapies to selectively destroy senescent cells, some reversal of neurodegeneration has been demonstrated in animal models. Not all inflammatory microglia are senescent, however, and it seems likely that the causes of the more general overactivation of such cells will also need to be addressed.

Advances in nanotechnology have enabled the design of nanotherapeutic platforms that could address the challenges of targeted delivery of active therapeutic agents to the central nervous system (CNS). While the majority of previous research studies on CNS nanotherapeutics have focused on neurons and endothelial cells, the predominant resident immune cells of the CNS, microglia, are also emerging as a promising cellular target for neurodegeneration considering their prominent role in neuroinflammation. Under normal physiological conditions, microglia protect neurons by removing pathological agents. However, long-term exposure of microglia to stimulants will cause sustained activation and lead to neuronal damage due to the release of pro-inflammatory agents, resulting in neuroinflammation and neurodegeneration.

This perspective highlights criteria to be considered when designing microglia-targeting nanotherapeutics for the treatment of neurodegenerative disorders. These criteria include conjugating specific microglial receptor-targeting ligands or peptides to the nanoparticle surface to achieve targeted delivery, leveraging microglial phagocytic properties, and utilizing biocompatible and biodegradable nanomaterials with low immune reactivity and neurotoxicity. In addition, certain therapeutic agents for the controlled inhibition of toxic protein aggregation and for modulation of microglial activation pathways can also be incorporated within the nanoparticle structure without compromising stability. Overall, considering the multifaceted disease mechanisms of neurodegeneration, microglia-targeted nanodrugs and nanotherapeutic particles may have the potential to resolve multiple pathological determinants of the disease and to guide a shift in the microglial phenotype spectrum toward a more neuroprotective state.

Link: https://doi.org/10.1063/5.0013178

Alpha-Ketoglutarate Supplementation Modestly Increases Life Span in Mice

Alpha-ketoglutarate supplementation has been shown to modestly extend life span and improve measures of health in old mice; the publicity materials here accompany the formal release of that paper. Recently, a novel epigenetic clock was used to suggest that alpha-ketoglutarate supplementation in old humans can reduce epigenetic measures of aging, though since this was a novel epigenetic clock, those results should not yet be taken too seriously. Confirming studies are needed, assessing other metrics.

Alpha-ketoglutarate supplementation may act to produce benefits via reductions in excessive inflammatory signaling. Given the sizable influence that the chronic inflammation of aging has on the development of disease and dysfunction, any approach to achieve that goal should be at least in principle interesting. Effect size matters, of course, and here in mice it is both modest and gender-specific, usually signs that effects in humans will be small at best.

A metabolite produced by the body increases lifespan and dramatically compresses late-life morbidity in mice

Studies show that blood plasma levels of alpha-ketaglutarate (AKG) can drop up to 10-fold as we age. Fasting and exercise, already shown to promote longevity, increase the production of AKG. AKG is not found in the normal diet, making supplementation the only feasible way to restore its levels. AKG is involved in many fundamental physiological processes. It contributes to metabolism, providing energy for cellular processes. It helps stimulate collagen and protein synthesis and influences age-related processes including stem cell proliferation. AKG inhibits the breakdown of protein in muscles, making it a popular supplement among athletes. It also has been used to treat osteoporosis and kidney diseases.

Middle-aged mice that had AKG added to their chow were healthier as they aged and experienced a dramatically shorter time of disease and disability before they died. "The mice that were fed AKG showed a decrease in levels of systemic inflammatory cytokines. Treatment with AKG promoted the production of Interleukin 10 (IL-10) which has anti-inflammatory properties and helps maintain normal tissue homeostasis. Chronic inflammation is a huge driver of aging. We think suppression of inflammation could be the basis for the extension of lifespan and probably healthspan, and are looking forward to more follow up in this regard. We observed no significant adverse effects upon chronic administration of the metabolite, which is very important."

Many of the study results were sex specific, with female mice generally faring better than males. Fur color and coat condition were dramatically improved in the treated females; the animals also saw improvement in gait and kyphosis, a curvature of the spine often seen in aging. The females also saw improvements in piloerection, which involves involuntary contraction of small muscles at the base of hair follicles. Male mice treated with AKG were better able to maintain muscle mass as they aged, had improvements in gait and grip strength, less kyphosis and exhibited fewer tumors and better eye health.

Alpha-ketoglutarate, an endogenous metabolite, extends lifespan and compresses morbidity in aging mice

Here we show that alpha-ketoglutarate (delivered in the form of a Calcium salt, CaAKG), a key metabolite in tricarboxylic (TCA) cycle that is reported to extend lifespan in worms, can significantly extend lifespan and healthspan in mice. AKG is involved in various fundamental processes including collagen synthesis and epigenetic changes. Due to its broad roles in multiple biological processes, AKG has been a subject of interest for researchers in various fields. AKG also influences several age-related processes, including stem cell proliferation and osteoporosis. To determine its role in mammalian aging, we administered CaAKG in 18 months old mice and determined its effect on the onset of frailty and survival, discovering that the metabolite promotes longer, healthier life associated with a decrease in levels of inflammatory factors. Interestingly the reduction in frailty was more dramatic than the increase in lifespan, leading us to propose that CaAKG compresses morbidity.

Using Direct Conversion of Cells to Investigate the Behavior of Aging Tissues

The process of reprogramming used to produce induced pluripotent stem cells erases many of the marks of aging in cells taken from old tissues, such as epigenetic changes and declining mitochondrial function. This may prove to be the basis for therapies based on reprogramming, but it is also very inconvenient for researchers who want to study how old cells and tissues behave in detail. Thus scientists here use a process of direct conversion, programming one cell type to become another without inducing a stem cell state, in order to retain the features of old tissue. That allows the identification of differences between old and young cellular metabolism, and run initial tests of potential interventions in cell cultures.

Research into aging vasculature has been hampered by the fact that collecting blood vessel cells from patients is invasive, but when blood vessel cells are created from special stem cells called induced pluripotent stem cells, age-related molecular changes are wiped clean. In 2015, however, researchers showed that fibroblasts could be directly reprogrammed into neurons, skipping the induced pluripotent stem cell stage that erased the cells' aging signatures. The resulting brain cells retained their markers of age, letting researchers study how neurons change with age. In new work, researchers applied the same direct-conversion approach to create two types of vasculature cells: vascular endothelial cells, which make up the inner lining of blood vessels, and the smooth muscle cells that surround these endothelial cells.

The researchers used skin cells collected from three young donors, aged 19 to 30 years old, three older donors, 62 to 87 years old, and 8 patients with Hutchinson-Gilford progeria syndrome (HGPS), a disorder of accelerated, premature aging often used to study aging. The resulting induced vascular endothelial cells (iVECs) and induced smooth muscle cells (iSMCs) showed clear signatures of age. 21 genes were expressed at different levels in the iSMCs from old and young people, including genes related to the calcification of blood vessels. 9 genes were expressed differently according to age in the iVECs, including genes related to inflammation.

To test the utility of the new observations, the researchers tested whether blocking BMP4 - which had been present at higher levels in smooth muscle cells developed from people with HGPS - could help treat aging blood vessels. In smooth muscle cells from donors with vascular disease, antibodies blocking BMP4 lowered levels of vascular leakiness - one of the changes that occurs in vessels with aging. The findings point toward new therapeutic targets for treating both progeria and the normal age-related changes that can occur in the human vascular system.

Link: https://www.salk.edu/news-release/method-to-derive-blood-vessel-cells-from-skin-cells-suggests-ways-to-slow-aging/

Upregulation of Unacetylated Ghrelin Slows Age-Related Muscle Loss in Mice

Ghrelin is best known for its role in the mechanisms of hunger, but it has two different forms, only one of which induces hunger. Both forms are known to affect muscle tissue metabolism, and this may be one of the ways in which calorie restriction slows the onset of muscle loss with age, a condition known as sarcopenia. Researchers here increase levels of the non-hunger-inducing ghrelin in mice and show that this does indeed slow the onset and progression of sarcopenia, and thus might be a basis for therapy.

Sarcopenia, the decline in muscle mass and functionality during aging, might arise from age-associated endocrine dysfunction. Indeed, muscle wasting follows the general decline in trophic hormones and the establishment of a chronic mild inflammatory status characteristic of aging. Ghrelin is a gastric hormone peptide circulating in both acylated (AG) and unacylated (UnAG) forms that have anti-atrophic activity on skeletal muscle. AG is the endogenous ligand of the growth hormone secretagogue receptor (GHSR-1a), and it is involved in metabolic regulation and energetic balance through induction of appetite, food intake, and adiposity. UnAG does not induce GH release and has no direct effects on food intake, but it shares with AG several biological activities on cell types lacking AG receptor.

In particular, both AG and UnAG have direct biological activities on skeletal muscle, including promotion of myoblast differentiation and protection from atrophy, in all likelihood by activating a common receptor. Also, UnAG promotes muscle regeneration, stimulation of muscle satellite cell activity, and activates autophagy and mitophagy at higher extent than AG. Age-dependent hypoghrelinemia could participate in the establishment of sarcopenia by facilitating the progression of muscle atrophy and limiting skeletal muscle regeneration capability.

Here, we show that both the deletion of the ghrelin gene (Ghrl KO) and the lifelong overexpression of UnAG (Tg) in mice attenuated the age-associated decline in muscle mass and functionality, seen as larger myofiber areas, lower levels of Atrogin-1, and increased mitochondrial functionality compared to old wild type (WT) animals. Also, both Ghrl KO and Tg animals displayed reduced systemic inflammation and maintenance of brown adipose tissue functionality. While old Tg mice apparently preserved the characteristics of young animals, Ghrl KO mice features deteriorate with aging. However, young Ghrl KO mice show more favorable features compared to WT animals that result, on the whole, in better performances in aged Ghrl KO mice. Altogether, the data collected suggest that, in Ghrl KO mice, it is the lack of AG that is the major determinant factor of their overall better conditions and advocate for the design of analogs to UnAG rather than AG to therapeutically treat sarcopenia in humans.

Link: https://www.eurekalert.org/pub_releases/2020-09/esoe-gmb090320.php

Clearance of Senescent Cells Reverses the Peripheral Neuropathy Caused by Chemotherapy

A primary goal of chemotherapy is to force cancerous cells into programmed cell death or cellular senescence. Cellular senescence is a state of growth arrest that should normally be triggered by exactly the sort of damage and dysfunction exhibited by cancer cells, but cancer is characterized by a mutation-induced ability to bypass those restrictions. Chemotherapy remains the primary approach to cancer therapy, but chemotherapeutic agents are still at best only marginally discriminating. Treating cancer with chemotherapy has always been a fine balance between harming the cancer and harming the patient. Even in the best of outcomes, it is well established that chemotherapy causes lasting damage. There are many unpleasant, lingering side-effects, and in fact chemotherapy lowers remaining life expectancy significantly. It is about as bad as a smoking habit when it comes to its effects on later mortality.

With the growing understanding of the role of senescent cells in aging, it has become clear that much of the long-term harm that results from chemotherapy results from the greatly increased burden of senescent cells that it produces. This is obviously a better outcome than dying from cancer, but it is nonetheless a problem that should be addressed. Senescent cells secrete a potent mix of inflammatory signals known as the senescence-associated secretory phenotype. This is highly disruptive to tissue function when sustained over the long term, even given a comparatively small number of senescent cells in comparison to normal cells in a tissue. Cellular senescence directly contributes to near all of the common, ultimately fatal age-related conditions.

Fortunately, the research community is developing a variety of senolytic therapies: drugs, gene therapies, immunotherapies and others, all capable of selectively destroying senescent cells. These have proven able to reverse many aspects of aging and the progression of numerous age-related diseases in animal models, and are presently undergoing human trials. It seems clear that the first senolytic therapies should be capable of reversing many of the long-term consequences of chemotherapy as well, a point well illustrated by today's open access paper.

Depletion of senescent-like neuronal cells alleviates cisplatin-induced peripheral neuropathy in mice

Chemotherapy-induced peripheral neuropathy, a common dose-limiting toxicity of many chemotherapy regimens, limits the potentially curative effects of systemic chemotherapy. Particularly, platinum-based chemotherapeutics, such as cisplatin, are known to cause systemic neuronal toxicity. Clinically, cisplatin-induced peripheral neuropathy (CIPN) presents as burning, shooting or electric-shock-like pain affecting the feet and hands, for which no effective treatments or preventive measures are available.

An important senescence phenotype, termed therapy-induced senescence (TIS), can be induced by DNA damage-based chemotherapeutics. The genotoxic stress caused by these agents induces senescence during cancer treatment and has been shown to promote the adverse effects of chemotherapy. Cellular senescence, a conserved response to stress, results in a stable cell cycle arrest while maintaining cell viability and metabolic activity. The distinct metabolic and signaling features of senescent cells include a senescence-associated secretory phenotype (SASP). The expression of SASP includes the secretion of numerous molecules, including growth factors, proteases, cytokines, chemokines, and extracellular matrix components, which mediate the paracrine activities of senescent cells. Despite the relatively low proportion of senescent cells in tissues, the SASP allows these cells to generate durable local and systemic deleterious effects in most tissues, which contribute to the pathogenesis of a variety of diseases including chemotherapy toxicity.

We hypothesized that senescence and the SASP might also play a role in CIPN following neuronal DNA damage, and the depletion of senescent cells may be an effective treatment of peripheral neuropathy induced by cisplatin. We showed that cisplatin induces peripheral neuropathy, as confirmed by mechanical and thermal pain assessment, and was associated with the accumulation of senescent-like neuronal cells in the dorsal root ganglia (DRG) using immunostaining and qPCR for senescence biomarkers. Furthermore, we provided genetic and pharmacologic evidence that selective clearance of senescent-like DRG neurons alleviates CIPN.

To determine if depletion of senescent-like neuronal cells may effectively mitigate CIPN, we used a pharmacological senolytic agent, ABT263, which inhibits the anti-apoptotic proteins BCL-2 and BCL-xL and selectively kills senescent cells. Our results demonstrated that clearance of DRG senescent neuronal cells reverses CIPN, suggesting that senescent-like neurons play a role in CIPN pathogenesis. This finding was further validated using transgenic p16-3MR mice, which permit ganciclovir to selectively kill senescent cells. We showed that CIPN was alleviated upon GCV administration to p16-3MR mice. Together, the results suggest that clearance of senescent DRG neuronal cells following chemotherapeutic cancer treatment might be an effective therapy for the debilitating side effect of CIPN.

Increased Insulin Receptor Expression Improves Memory in Old Rats

This is a interesting example of modulating the metabolism of the aging brain in order to improve its function, without any attempt to address the underlying cell and tissue damage that causes loss of function. Researchers delivered recombinant insulin receptor protein to the hippocampus of old rats, and demonstrated improved memory function as an outcome of this intervention. An age-related decline in insulin metabolism has been implicated in neurodegenerative conditions, but it is somewhat hard to pick this apart from reduced blood flow, blood-brain barrier dysfunction, and other related issues that contribute to the declining function of the brain. Hence this effort to attempt to modify insulin metabolism somewhat distinctly from other mechanisms.

As demonstrated by increased hippocampal insulin receptor density following learning in animal models and decreased insulin signaling, receptor density, and memory decline in aging and Alzheimer's disease, numerous studies have emphasized the importance of insulin in learning and memory processes. This has been further supported by work showing that intranasal delivery of insulin can enhance insulin receptor signaling, alter cerebral blood flow, and improve memory recall. Additionally, inhibition of insulin receptor function or expression using molecular techniques has been associated with reduced learning.

Here, we sought a different approach to increase insulin receptor activity without the need for administering the ligand. A constitutively active, modified human insulin receptor (IRβ) was delivered to the hippocampus of young (2 months) and aged (18 months) male Fischer 344 rats in vivo. The impact of increasing hippocampal insulin receptor expression was investigated using several outcome measures, including Morris water maze and ambulatory gait performance, immunofluorescence, immunohistochemistry, and Western immunoblotting.

In aged animals, the IRβ construct was associated with enhanced performance on the Morris water maze task, suggesting that this receptor was able to improve memory recall. Additionally, in both age-groups, a reduced stride length was noted in IRβ-treated animals along with elevated hippocampal insulin receptor levels. These results provide new insights into the potential impact of increasing neuronal insulin signaling in the hippocampus of aged animals and support the efficacy of molecularly elevating insulin receptor activity in vivo in the absence of the ligand to directly study this process.

Link: https://doi.org/10.1111/acel.13220

Evidence for Familial Longevity to be Largely Cultural Rather than Genetic

It is certainly possible that a small number of people have mutations or genetic variants that confer notable longevity. The small lineage exhibiting a PAI-1 loss of function mutation springs to mind as an example of this sort of thing. But for the overwhelming majority of long-lived lineages, the evidence on genetic contributions to longevity tends to support the hypothesis that familial longevity arises much more from lifestyle and environment than from inherited genetics. The data from very large genetic databases points to genetic variants contributing little to variation in human life span. The data on exercise, diet, and environmental factors such as particulate air pollution and persistent viral infection regularly results in larger effect sizes for late life mortality.

The familial resemblance in length of adult life is very modest. Studies of parent-offspring and twins suggest that exceptional health and survival have a stronger genetic component than lifespan generally. To shed light on the underlying mechanisms, we collected information on Danish long-lived siblings (born 1886-1938) from 659 families, their 5379 offspring (born 1917-1982), and 10,398 grandchildren (born 1950-2010) and matched background population controls through the Danish 1916 Census, the Civil Registration System, the National Patient Register, and the Register of Causes of Death.

Comparison with the background, population revealed consistently lower occurrence of almost all disease groups and causes of death in the offspring and the grandchildren. The expected incidence of hospitalization for mental and behavioral disorders was reduced by half in the offspring (hazard ratio 0.53) and by one-third in the grandchildren (0.69), while the numbers for tobacco-related cancer were 0.60 and 0.71, respectively. Within-family analyses showed a general, as opposed to specific, lowering of disease risk. Early parenthood and divorce were markedly less frequent in the longevity-enriched families, while economic and educational differences were small to moderate.

The longevity-enriched families in this study have a general health advantage spanning three generations. Having a long-lived parent or grandparent who had at least one long-lived sibling is associated with a substantial health and survival advantage in our study. Most notable is the strength of the associations, and that these are found for a wide range of diseases and causes of death, suggesting a fundamentally slower aging in these families and not just avoidance of specific diseases.

The combination of a particularly low incidence of mental and behavioral disorders and tobacco-related cancers combined with demographic characteristics such as low occurrence of teenage parenthood and early marriage and divorce implicate behavior as a key mechanism underlying the three-generation health and survival advantage observed. We found no evidence that the associations were driven by socioeconomic advantages in the longevity-enriched families either in the 1916 census or in the civil registration system over the last half-century.

Link: https://doi.org/10.1111/acel.13228

Hormone Therapy in Postmenopausal Women Correlates with Lesser Senescent Cell Signaling

Beyond their use for conditions of severe hormone deficiency, hormone therapies are one of the higher profile approaches taken by the less rigorous, more dubious end of the "anti-aging" medical community. An interesting consequence of the greater focus on underlying mechanisms of aging in the research and development community, particularly senescent cell accumulation at the present time, is that scientists and physicians now have access to a novel set of measurements that are definitively connected to aging, and can use those measurements to try to figure out whether any of the overhyped, dubious strategies in the "anti-aging" marketplace are actually doing something useful (even if marginal) under the hood.

Senescent cells secrete a potent mix of inflammatory and other molecules, the senescence-associated secretory phenotype (SASP). This is how a comparatively small number of lingering senescent cells in aged tissues cause harm: their signaling disrupts tissue structure and maintenance, and produces a state of chronic inflammation that drives the onset and progression of many age-related conditions. Over the past few years, the SASP has been far more extensively mapped than was previously the case. Measuring circulating levels of the more prominent SASP molecules is a way to assess the burden of aging, or at least that due to this particular aspect of age.

That is the approach taken in today's open access paper, in which the authors report that hormone treatment of postmenopausal women is associated with lower levels of some of the SASP factors known to be involved in inflammatory signaling. Whether this reflects a lesser burden of senescent cells, or a reduced signaling of such cells is an open question, though the authors here seem to lean towards the latter possibility, given what is known of the way which estrogen regulates metabolism. In general, hormones have extremely broad effects on metabolism, and it is certainly the case that their use comes with many caveats.

Effect of menopausal hormone therapy on proteins associated with senescence and inflammation

Cell senescence, a state of cell cycle arrest due to the finite capacity of cells to proliferate, also occurs as a result of the accumulation of molecular and cellular damage. Senescent cells secrete an array of cytokines, chemokines, growth factors, and proteases collectively referred to as the senescence-associated secretory phenotype (SASP). The array of SASP proteins includes many proteins that have been shown to be regulated by estrogen and to be secreted by platelets, leukocytes, and vascular endothelium including the metalloproteins (MMPs), tumor necrosis factor-α (TNF-α), ecosinoids, and serotonin. However, other proteins considered to be part of the SASP array (e.g., GDF15, Fas, MIP1α, and TNFR1) may be more specific indicators of the systemic senescent cell burden.

In response to DNA damage, senescence serves as an anticancer mechanism and may also have beneficial functions in embryogenesis, parturition, and tissue repair. However, senescent cells that are not cleared efficiently by the immune system disrupt tissue function, which increases the vulnerability to the onset and progression of a host of age-related diseases, including pulmonary dysfunction, cardiovascular disorders, osteoporosis, neurodegeneration, and diabetes. In part, the deleterious effects of senescent cells are mediated by the SASP. Strategies to remove senescent cells and suppress the SASP are now being pursued as a means to counter age-related diseases and geriatric syndromes.

Estrogen is a steroid hormone implicated in modulating cell senescence. For example, estrogen decreases cell senescence in endothelial progenitor cells, and activates estrogen receptor alpha (ERα) to inhibit cell senescence-like phenotypes in human epithelial cells. Estrogen also slows deficits associated with aging and cell senescence in bone, such as declining bone density. However, little is known regarding how cell senescence might be modified by natural changes in hormone concentrations, such as those that occur during menopause, and how this might be modulated by hormone therapies. This study examined whether menopausal hormone therapies, in the form of oral conjugated equine estrogens (oCEE) and transdermal 17β-estradiol (tE2), altered the circulating levels of a specific set of SASP proteins in women who had undergone natural menopause.

Growth differentiation factor 15 (GDF15), tumor necrosis factor receptor 1 (TNFR1), FAS, and macrophage inflammatory protein 1α (MIP1α) were measured in serum. Results were compared among menopausal women participating in the Kronos Early Estrogen Prevention Study randomized to either placebo (n = 38), oral conjugated equine estrogen (oCEE, n = 37), or transdermal 17β-estradiol (tE2, n = 34). Serum levels of the senescent markers for each treatment were compared to placebo 36 months after randomization. We found that serum levels of GDF15, TNFR1, and FAS, but not MIP1α, were lower in both the oCEE and tE2 groups compared to placebo. Differences in the magnitude of effect of the two active treatments may reflect the differences in circulating levels of estrogen metabolites due to formulation and mode of delivery.

Dysfunction of the Blood-Brain Barrier as an Early Stage in the Progression to Dementia

The blood-brain barrier is a lining of specialized cells that surrounds blood vessels passing through the brain. The barrier permits only certain molecules and cells to pass, isolating the tissue environment of the brain from that of the result of the body. When the blood-brain barrier leaks, an immediate consequence is inflammation in brain tissue, the result of the brain's immune cells reacting to the presence of inappropriate molecules. Unfortunately the integrity of the blood-brain barrier degrades with age and the accumulation of molecular damage, as is the case for all other tissues. The resulting inflammation is an important mechanism in the progression towards neurodegenerative disease and dementia. As noted here, degradation of the blood-brain barrier may also prevent necessary molecules from being transported into the brain in sufficient amounts. That also may be an important early determinant of loss of function in brain tissue.

The vascular endothelium in the brain is an essential part of the blood-brain-barrier (BBB) because of its very tight structure to secure a functional and molecular separation of the brain from the rest of the body and to protect neurons from pathogens and toxins. Impaired transport of metabolites across the BBB due to its increasing dysfunction affects brain health and cognitive functioning, thus providing a starting point of neurodegenerative diseases.

The term "cerebral metabolic syndrome" is proposed to highlight the importance of lifestyle factors in neurodegeneration and to describe the impact of increasing BBB dysfunction on neurodegeneration and dementia, especially in elderly patients. If untreated, the cerebral metabolic syndrome may evolve into dementia. Due to the high energy demand of the brain, impaired glucose transport across the BBB via glucose transporters as GLUT1 renders the brain increasingly susceptible to neurodegeneration. Apoptotic processes are further supported by the lack of essential metabolites of the phosphocholine synthesis.

In Alzheimer's disease, inflammatory and infectious processes at the BBB increase the dysfunction and might be pace-making events. Chronic inflammatory processes of the BBB transmitted to an increasing number of brain areas might cause a lasting build-up of spreading, pore-forming β-amyloid fragments explaining the dramatic progression of the disease.

Link: https://doi.org/10.3389/fnagi.2020.00185

Greater Fitness Correlates with Lower White Matter Hyperintensity Volume in the Aging Brain

White matter hyperintensities in the brain are small areas of damage most likely produced by the rupture or other loss of integrity of tiny blood vessels. In effect they are miniscule strokes, individually unnoticed, but collectively a form of damage to the brain that adds up over time. Since white matter hyperintensities are connected to vascular health, it isn't too surprising to see that old people possessed of better vascular function, as a consequence of maintaining physical fitness into later life, exhibit a lower burden of this form of damage in the brain. It should be expected that this lesser degree of structural damage contributes to the slower cognitive decline that accompanies higher levels of fitness in later life.

White matter (WM) hyperintensities (WMHs) are one of the most ubiquitous age-related structural changes observed via MRI, yet they are of unknown etiology. WMHs are presumed to be a consequence of age-related vascular changes. Arterial stiffness is associated with WMHs and is the most influential hemodynamic factor in individuals over the age of 60. Age-related arterial dysfunction is the result of a variety of deleterious changes that include intimal remodeling, increased arterial stiffness, and endothelial dysfunction. Age-related changes in the physical properties of, and the interaction between, macrovasculature and microvasculature contribute to the development of WMHs. For example, large artery stiffening transmits increases in pulsatility, the variation of blood pressure throughout the cardiac cycle, to small cerebral vessels. Excessive pulsatility to small cerebral vessels is associated with WMHs.

While cerebrovascular changes are endemic to aging, older adults show considerable variability in vascular brain health. One variable known to positively impact the brain's vascular health is cardiorespiratory fitness (CRF), a product of regular exercise. However, little is known about the effects of CRF on WMH volume per se. In contrast, higher CRF has been linked to higher WM microstructure in older adults. Since low WM microstructure in normal appearing WM precedes conversion to WMHs, WMHs may also be positively influenced by high CRF. If so, CRF may attenuate the development of WMHs in older adults.

This study explored the effects of CRF on WMH volume in community-dwelling older adults. We further tested the possibility of an interaction between CRF and age on WMH volume. Participants were 76 adults between the ages of 59 and 77 who underwent a maximal graded exercise test and structural brain imaging. Results indicated that age was a predictor of WMH volume. However, an age-by-CRF interaction was observed such that higher CRF was associated with lower WMH volume in older participants. Our findings suggest that higher levels of aerobic fitness may protect cerebrovascular health in older adults.

Link: https://doi.org/10.1371/journal.pone.0236986

Targeting Cellular Senescence to Heal Non-Healing Wounds

An accumulation of senescent cells takes place throughout the body with age. Cells become senescent constantly, the vast majority as a consequence of hitting the Hayflick limit on replication of somatic cells. In youth, these cells are efficiently removed, either via programmed cell death, or destroyed by the immune system. In later life, removal processes slow down, while the damaged state of tissue provokes ever more cells into becoming senescent. In older people, this imbalance leads to a state in which a few percent of all cells in tissues are senescent at any given time. This is, unfortunately, more than enough to produce sizable consequences to health and mortality. Senescent cells secrete a potent mix of inflammatory and growth signals that disrupt tissue function when present consistently.

Senescent cells do conduct useful, necessary activities in an environment in which they are quickly removed, and their signaling is beneficial in the short term. They assist in aspects of embryonic development, for example. The senescence of damaged and potentially cancerous cells suppresses cancer risk by efficiently removing these errant cells. Then there is the role of senescent cells in wound healing, which is the topic of today's open access paper. Wound healing captures the two-edged nature of cellular senescence in and of itself: wounds heal more rapidly in young individuals due to the presence of senescent cells. But when senescent cells are present in too great a number, they disrupt the processes of wound healing, and can give rise to non-healing wounds.

Fortunately, advances are being made in the development of therapies to selectively destroy senescent cells, or to suppress at least some of their secreted signals. I think that the former is a better strategy, as cell signaling is a very complex, poorly understood environment with many possible targets. Periodically destroying some fraction of senescent cells in a tissue reduces all of the harmful signaling, not just the part that the research community has mapped and understood. When this approach is applied to non-healing wounds, we might hope to see favorable outcomes.

Senescence in Wound Repair: Emerging Strategies to Target Chronic Healing Wounds

The widespread causative biological effects of cellular senescence in tissue ageing pathology make the therapeutic modulation of senescence an attractive target for a plethora of age-related diseases. Genetic studies positively support this idea, with inducible knockdown of p16 alleviating hallmark features of ageing in progeroid murine models. In fact, the well-documented effects of caloric restriction, which both extends mammalian lifespan and delays the onset of age-related disease, may be a physical manifestation of tissue senescence modulation. Caloric restriction has been shown to reduce cardiac senescence, and senescence in hepatocytes and intestinal crypt cells in vivo.

A considerably more attractive proposition is the use of senescence-targeted drugs, otherwise known as senolytics. These drugs affect unique features of senescent cells, such as resistance to apoptosis. Senescent cells upregulate prosurvival pathways, particularly BCL-2. This opens up drug repurposing opportunities around the numerous BCL-2 inhibitors that were developed for the treatment of cancer. Results have been promising. Targeting BCL-2 in vivo induces apoptosis and thus eliminates senescent cells in the lung following irradiation and throughout the body following irradiation or natural ageing.

Other senolytics that have demonstrated experimental efficacy include the tyrosine kinase inhibitor, Dasatinib, used to treat leukaemia, and the flavonoid p53 activator, Quercetin. Combinatorial treatment with Dasatinib and Quercetin extends lifespan, alleviates frailty, and improves vasomotor function in aged mice. Dasatinib and Quercetin have also shown promise in a phase I trial in diabetic kidney disease patients, where reduced senescent cells and circulating SASP factors were observed following administration. Alternative flavonoids are now being tested for their potential senolytic effects, such as Fisetin, which is able to eliminate senescent cells and, crucially, restore tissue function in aged mice.

The importance of transient senescence for effective healing should not be underestimated. As noted previously, temporary induction of senescence aids rapid tissue reformation. During a normal damage response, these senescent cells are effectively cleared by natural killer cells and macrophages. Nevertheless, in chronic situations, senescent cells persist, likely due to elevated immunosenescence and resulting impaired immunological functions. It follows that treatments to boost immune system function, for instance by aiding senescent cell recognition, could be beneficial in the context of transient senescence and tissue repair. Generally, senescent cells express stimulatory ligands that bind to NK2GD receptors on natural killer cells, thus initiating a killing response. However, senescent fibroblasts in aged skin have recently been shown to express HLA-E, which bypasses recognition and clearance by natural killer and T cells. Here, approaches developed in the cancer field may also be useful, for example engineering T cells to express receptors that target specific cellular (tumour) proteins. Studies to identify and validate new senescent cell receptors will be essential to the development and clinical application of such immune-regulated approaches.

We remain a long way from implementing senescence-targeted treatments for pathological wound healing, yet it is reassuring to see that current senolytic drugs display efficacy across a wide range of tissues and pathologies. In a number of studies, systemic senolytic treatments have been shown to have clear effects in peripheral target tissues across a range of treatment regimens. For example, a single dose of BCL inhibitor, and dosing over consecutive days, was able to reverse irradiation-induced senescence in different tissues. In other work, aged mice showed improved physical performance following biweekly oral treatments of Dasatinib and Quercetin for 4 months, yet reduced SASP was observed in human ex vivo cultured adipose tissue within 48 h of treatment. Moreover, a single 3 day oral treatment of Dasatinib and Quercetin was able to reduce senescence in the adipose tissue of diabetic patients in a phase I trial. These studies therefore suggest that senolytic treatments not only have rapid effects in target peripheral tissues, but can overcome established tissue senescence.

Experimental studies do show beneficial effects of modulating senescence in the skin. For example, elimination of senescent cells from the epidermis restored proliferative capacity in hair follicle stem cells, known to participate in wound healing. Further, blockade of the potential senescence receptor, CXCR2, directly accelerated healing in human ex vivo skin wounds and diabetic murine wounds in vivo. Here, a CXCR2 antagonist was administered to wounds topically (ex vivo) and subcutaneously (in vivo), suggesting direct delivery to the wound site as a viable administration route. Indeed, elevated CXCR2 has previously been observed in diabetic wounds, and more recently in T cells from human diabetic patients. We note with interest that pharmacological inhibition of CXCR1/2 additionally prevents inflammation-mediated damage to pancreatic islets, thus prohibiting streptozocin-induced diabetes in mice. Therefore, CXCR2 appears a common factor in both the ontology and local pathology of diabetes. Senolytics should certainly be considered for the treatment of human chronic wounds characterised by high levels of senescence. However, given that knockdown of CXCR2 and ablation of senescent cells actually delays acute wound healing, future senescence-targeted therapies should be reserved for the treatment of chronic conditions.

A Damage-Based View of Aging, Offering the Hope of Rejuvenation through Repair

This paper, published earlier in the year, is a reaffirmation of the consensus position that aging is caused by the accumulation of cell and tissue damage, made at a time in which programmed aging theories are becoming more popular. Initiatives such as those of Turn.bio and other groups, in which cells are at least partially reprogrammed towards a pluripotent state in living animals, have spurred greater interest in the characteristic epigenetic changes that take place with aging. That reversing those epigenetic changes produces rejuvenation by many measures is interesting and promising, but it isn't clear that it can be taken as evidence that epigenetic programs of change are at the root of aging. We might look instead at the evidence for detrimental epigenetic change in cells throughout the body to be an unfortunate consequence of the processes of DNA double strand break repair, for example. If confirmed, that puts age-related epigenetic change firmly in the category of damage, not a program that exists independently of damage as a root cause of aging.

Aging is an irreversible process, and most organisms can never escape the diversity and accumulation of damage that their own functions generate. To reduce damage, species with a simple organization may opt to discard some damage with a part of the cytoplasm, but this mechanism needs to be investigated in more complex species. Interventions such as parabiosis may partially restore aged organ functions through transfusion of young blood to an old organism. This may be considered as a damage dilution process, where the old blood is diluted by the less damaged young blood. It was shown that, following hematopoietic stem cell transfer, the blood of the recipient follows the epigenomic age of the donor, suggesting a possibility to consistently generate younger blood than the actual age of the organism, if the source of hematopoietic stem cells is a young donor. It is important to emphasize that the transition to a younger age, based on one or more tissues being younger than the rest and younger than the chronological age, does not necessarily mean a longer lifespan for the subject, particularly if the lifespan is limited by a particular dysfunction or disorder that causes death.

Although somatic aging appears at first sight irreversible, we cannot bypass the fact that it is successfully reset to zero from generation to generation, suggesting that, during germline development, embryonic development, or some other phases of life there is a process that rewinds the aging clock. Somatic cell nuclear transfer shows that this rewinding process can be also induced in differentiated cell nuclei. These mechanisms of dilution or repair of damage are currently unclear, although evidence suggests that they may involve a combination of cell division, cell selection, epigenetic remodeling, and global activation of genes, especially those genes for controlling DNA damage. These mechanisms allow cells to dilute even the scarcest molecular species such as functionally abnormal RNA, proteins, harmful metabolites, and those that would not be sensed by a cell. Thus, a combination of cell growth, selection, and proliferation dilutes mild damage, in addition to the removal of damage through specialized detoxification, repair, excretion, preemption, and other approaches. These mechanisms together allow the cells to keep the damage in control.

It should be noted that division and dilution are not necessarily related in the context of proliferation of differentiated somatic cells, as, unlike germ cells or stem cells, these cells may undergo senescence or tumor transformation when proliferating in culture. This suggests that there is a particular relationship between cell division and damage dilution, whose mechanism is not yet understood. We think that this relationship is reflected, for instance, in the differences between early embryonic and aged cells, partially due to their different differentiation states. The former may stay in quiescent stage to avoid further damage or proliferate to select the cells with less damage. Compared to adult cells, embryonic cells specifically experience two waves of global demethylation and re-methylation, establishing the same DNA methylation pattern for every generation. These differences suggest a possibility that certain embryonic cells and somatic cells have different modes and rate of damage accumulation and dilution through proliferation. From the damage perspective, the proliferation of cells with more specialized functions bears higher damage, as more specialized molecules are produced, allowing more side-products to be generated. Furthermore, adult stem cells may overcome the proliferation limit when exposed to a mixed pro-stemness signal. This shows that the combined effect of niche pathways that promote the stemness of the adult stem cells may act similarly to reprogramming. Thus, the difference in the damage accumulation between somatic cells and stem cells may lie, at least in part, in the cell matrix environment in which cells reside. Moreover, the environment may undergo a transition to sacrifice stemness for specific biological functions.

To visualize this stage-shifting concept, we advance a weight-scale metaphor, which we call a "stemness-function" model. We designate the two states as "pro-stemness" and "pro-function" based on the balance between damage production and its removal by proliferation and apoptosis. During early life, organisms remain in a "pro-stemness" state, encouraging cells to proliferate and grow so that the damage is unchecked and does not cause cell cycle arrest. In that state, although stem cells exhibit a limited intrinsic immune function, the function to recognize "self" and "nonself" is not yet fully developed, allowing a lower level of inflammation and an increased potential for regeneration. In contrast, in somatic cells, the damage generation can be sensed easier, triggering the reactions such as the DNA damage repair process, growth arrest, apoptosis, and immune responses. Therefore, organisms must undergo a transition from the "pro-stemness" to "pro-function" states, wherein differentiation and specification of cells are supported. Following this transition, the cells enhance their function in reproduction, damage sensing and apoptosis pathway, complete the immune function, and increase fitness by generating specific biological products related to their functions, while adult stem cells at this stage undergo gradual exhaustion. At this stage, damage accumulation is spontaneous while damage dilution via proliferation is not supported in most cell types. During the process of fertilization or before/after it, this damage gets thoroughly checked, cleared and diluted by the transition to the "pro-stemness" state.

What perturbations might then be expected to delay or reverse aging? If a mild "pro-function" feature is induced in the cells with the "pro-stemness" state, it may extend lifespan as we learn from mild overexpression of certain tumor suppressors. Similarly, the weakened immune system upon rapamycin treatment provides an example that the opposite may also work. On the other hand, if a specific function (supported by a certain gene) that shifts the system toward the "pro-function" state is introduced, it may lead to death or premature aging, caused by a sudden increase in function and damage. This might be the case when tumor-suppressor Tp53 is overexpressed in mice, and the animals show a significantly shorter lifespan. It should be noted, however, that similar cases of Tp53 overexpression in mouse models show an indistinguishable lifespan. Nevertheless, considering that cancer-related deaths are more common in lab mice than in humans and that these risks are limited in these cancer-resistant mouse models, there is still a possibility that the overexpression accelerates aging. Conversely, if a "pro-stemness" signal introduced to cells in the "pro-function" state, it may also cause deleterious effects, resulting in cell death or aberrant immortality. For instance, forcing cell proliferation by expressing oncogenes in fibroblasts promotes tumor transformation.

Link: https://doi.org/10.1002/ggn2.10025

A Meta-Analysis of the Ability of Exercise to Reduce Age-Related Mortality

Exercise improves health, and that statement continues to be the case throughout life, even into late old age, and while suffering from age-related conditions that impact the ability to exercise. Exercise exhibits a dose-response curve, just like any other intervention to improve health. More is better for near all people: one has to undertake a great deal of physical activity indeed to come to the point of diminishing returns or self harm. One of the interesting findings of the past twenty years, achieved after it became cost-effective to measure activity more precisely via the use of wearable accelerometers, is that even very modest levels of exercise make a sizable difference to mortality rates in older people. Becoming sedentary is a fate to be avoided.

The current evidence for the general population regarding physical activity and mortality is comprehensive and unambiguous. Numerous large cohort studies have consistently demonstrated an inverse relationship between physical activity levels and mortality. Compared with the lower physical activity groups, the risk of premature death was remarkably reduced in the higher physical activity groups. One meta-analysis revealed that per 1 hour increment of moderate-intensity physical activity per week, the relative risk of mortality was reduced by 4%.

In the updated physical activity guidelines for healthy adults from the U.S. Department of Health and Human Services, a clear dose-response association between the volume of physical activity and mortality rates has been shown. The shape of the dose-response curve is characterized by a regressive, non-linear effect, where the greatest difference in mortality rates occurs among inactive and minimally active individuals. For higher physical activity levels, the dose-response curve flattens out. This means that the relative risk of mortality continues to decline with higher volumes of physical activity with no adverse effects on mortality, even at very high levels of physical activity.

The objective of this study was to conduct a systematic review and dose-response meta-analysis of physical activity and mortality in people with selected non-communicable diseases (NCDs). We aimed to define the dose-response relationship between post-diagnosis physical activity and mortality rates for nine NCDs with a high global burden of disease, including low back pain, type 2 diabetes (T2D), osteoarthritis, depressive disorder, chronic obstructive pulmonary disease (COPD), breast cancer, lung cancer, stroke, and ischemic heart disease (IHD).

In total, 28 studies were included in the meta-analysis: 12 for breast cancer, 6 for type 2 diabetes, 8 for ischemic heart disease and 2 for COPD. The linear meta-analysis revealed that each 10 metabolic equivalent task hours increase of physical activity per week was associated with a 22% lower mortality rate in breast cancer patients, 12% in ischemic heart disease patients, 30% in COPD patients, and 4% in type 2 diabetes patients. There was indication of a non-linear association with mortality risk reductions even for low levels of activity, as well as a flattening of the curve at higher levels of activity. Thus higher levels of post-diagnosis physical activity are associated with lower mortality rates in breast cancer, type 2 diabetes, ischemic heart disease, and COPD patients, with indication of a no-threshold and non-linear dose-response pattern.

Link: https://doi.org/10.1186/s12966-020-01007-5

Connecting the Immune Response to Amyloid-β Aggregation in Alzheimer's Disease via IFITM3

It is well established that chronic inflammation in brain tissue contributes to the onset and progression of neurodegenerative conditions such as Alzheimer's disease. Short-term inflammation is a necessary part of the response to injury and infection, required to mobilize immune cells. Inflammation that fails to resolve and continues unabated for the long term is disruptive to tissue function, however, and very definitely harmful. Unfortunately, aging is characterized by progressively increasing chronic inflammation, the result of processes such as accumulation of senescent cells and harmful metabolic byproducts.

Alzheimer's is a complicated condition. It is thought to begin with a slow aggregation of amyloid-β deposits over the course of years. This produces mild cognitive impairment and a state of chronic inflammation sufficient to trigger a later, much more harmful aggregation of altered tau protein. This later stage leads to dementia and death. Clearing amyloid-β from the brain hasn't produced meaningful benefits to patients, however, suggesting that it is not the key process in the development of the condition.

An alternative view of Alzheimer's disease is that persistent infection causes both chronic inflammation and amyloid-β aggregation, as amyloid-β is actually a part of the innate immune system - an anti-microbial peptide. In this view the more important problem is the chronic inflammation of aging, the constant over-activation of the immune system in brain tissue. The best targets for treatment are thus the set of mechanisms that produce that inflammation, such as senescent cell accumulation, the presence of persistent pathogens such as herpesviruses, and so forth. Supporting evidence is emerging for this position, such as today's research materials, in which the immune response is linked to amyloid-β production.

Study Links Inflammation to Alzheimer's Disease Development

Recent studies have found that beta-amyloid has antiviral and antimicrobial properties, suggesting a possible link between the immune response against infections and the development of Alzheimer's disease. Researchers have now discovered clear evidence of this link: A protein called IFITM3 that is involved in the immune response to pathogens also plays a key role in the accumulation of beta-amyloid in plaques. IFITM3 alters the activity of an enzyme called gamma-secretase, which chops up precursor proteins into the fragments of beta-amyloid that make up plaques. Researchers found that removing IFITM3 decreased the activity of the gamma-secretase enzyme and, as a result, reduced that number of amyloid plaques that formed in a mouse model of the disease.

Neuroinflammation (inflammation in the brain) has emerged as an important line of inquiry in Alzheimer's disease research. Markers of inflammation, such as certain immune molecules called cytokines, are boosted in Alzheimer's disease mouse models and in the brains of people with Alzheimer's disease. This study is the first to provide a direct link between this inflammation and plaque development - by way of IFITM3.

Scientists know that the production of IFITM3 starts in response to activation of the immune system by invading viruses and bacteria. These observations, combined with the new findings that IFITM3 directly contributes to plaque formation, suggest that viral and bacterial infections could increase the risk of Alzheimer's disease development. Indeed, researchers found that the level of IFITM3 in human brain samples correlated with levels of certain viral infections as well as with gamma-secretase activity and beta-amyloid production. Age is the number one risk factor for Alzheimer's, and the levels of both inflammatory markers and IFITM3 increased with advancing age in mice, the researchers found.

The innate immunity protein IFITM3 modulates γ-secretase in Alzheimer's disease

Innate immunity is associated with Alzheimer's disease1, but the influence of immune activation on the production of amyloid-β is unknown. Here we identify interferon-induced transmembrane protein 3 (IFITM3) as a γ-secretase modulatory protein, and establish a mechanism by which inflammation affects the generation of amyloid-β.

Inflammatory cytokines induce the expression of IFITM3 in neurons and astrocytes, which binds to γ-secretase and upregulates its activity, thereby increasing the production of amyloid-β. The expression of IFITM3 is increased with ageing and in mouse models that express familial Alzheimer's disease genes. Furthermore, knockout of IFITM3 reduces γ-secretase activity and the formation of amyloid plaques in a transgenic mouse model (5xFAD) of early amyloid deposition. IFITM3 protein is upregulated in tissue samples from a subset of patients with late-onset Alzheimer's disease that exhibit higher γ-secretase activity. The amount of IFITM3 in the γ-secretase complex has a strong and positive correlation with γ-secretase activity in samples from patients with late-onset Alzheimer's disease. These findings reveal a mechanism in which γ-secretase is modulated by neuroinflammation via IFITM3 and the risk of Alzheimer's disease is thereby increased.

Long Lived Humans Do Not Exhibit Fewer Harmful Gene Variants

Why are long lived humans long lived? Why does this trait often run in families? One of the few firm advances in answering these questions is to rule out the hypothesis that long-lived lineages bear fewer detrimental gene variants. Several studies and study populations have indicated that there are just as many harmful variants present in the genomes of exceptionally long-lived people as are present in the rest of us. Beyond that, it remains to be seen as to just how much of exceptional longevity is in fact genetic. Broader genetic studies have in recent years continued to revise downward the contribution of genetics to variation in human life span. At the present time, it appears to be almost entirely a matter of lifestyle choice and environmental exposures to infectious disease, particulate air pollution, and so forth.

Centenarians (exceptionally long-lived individuals - ELLI) are a unique segment of the population, exhibiting long human lifespan and healthspan, despite generally practicing similar lifestyle habits as their peers. We tested disease-associated mutation burden in ELLI genomes by determining the burden of pathogenic variants reported in the ClinVar and HGMD databases using data from whole exome sequencing (WES) conducted in a cohort of ELLI, their offspring, and control individuals without antecedents of familial longevity (n = 1879), all descendent from the founder population of Ashkenazi Jews.

The burden of pathogenic variants did not differ between the three groups. Additional analyses of variants subtypes and variant effect predictor (VEP) biotype frequencies did not reveal a decrease of pathogenic or loss-of-function (LoF) variants in ELLI and offspring compared to the control group. Case-control pathogenic variants enrichment analyses conducted in ELLI and controls also did not identify significant differences in any of the variants between the groups and polygenic risk scores failed to provide a predictive model. Interestingly, cancer and Alzheimer's disease-associated variants were significantly depleted in ELLI compared to controls, suggesting slower accumulation of mutation. That said, polygenic risk score analysis failed to find any predictive variants among the functional variants tested.

The high similarity in the burden of pathogenic variation between ELLI and individuals without familial longevity supports the notion that extension of lifespan and healthspan in ELLI is not a consequence of pathogenic variant depletion but rather a result of other genomic, epigenomic, or potentially nongenomic properties.

Link: https://doi.org/10.1111/acel.13216

An Interview with a Principal Investigator at Calico

Calico is Google's venture into aging research. It has, in general, been a disappointment to the community - though I suspect that this is a matter of unrealistic expectations as to the path that any new, large deployment of capital is likely to follow. Rather than taking on any of the approaches to rejuvenation that might plausibly produce sizable gains in life span, such as those of the SENS portfolio, Calico has focused on very staid, long-standing metabolic manipulations derived from the study of calorie restriction and growth hormone loss of function mutants. These lines of research are highly unlikely to produce sizable gains in health and longevity in humans, as the calorie restriction response and disruption of growth hormone metabolism are known to produce only modest gains in our species. Calico, like the Ellison Medical Foundation that preceded it, has in essence become a small arm of the National Institute on Aging, characterized by conducting fundamental rather than translational research, and in areas of the field that won't do much for human health and life span at the end of the day.

What area of aging and age-related diseases has Calico's biggest focus at the moment?

Our top-level goal is to develop interventions that delay aging, but to test such interventions, we have to be able to measure aging. This is easier said than done - the gold standard, lifespan, takes a long time and is relatively information-poor. There are molecular and cellular changes that occur with age, but it's not always clear which are the most relevant readouts. We'd like to measure aspects of physiological decline, but current healthspan assays take a lot of time and effort, and even then tend to be pretty noisy. To address those limitations, we've spent a lot of time developing innovative tools and novel analyses for quantifying physiological decline in mouse models. We emphasize automated, longitudinal monitoring and multi-dimensional time-series analysis.

On the intervention side, one area of focus for my lab is IGF signaling. This was a pretty straightforward choice - reduced IGF signaling is the most validated anti-aging intervention known (slows aging from worms to mammals, with the largest effect sizes ever reported). There are challenges with targeting this pathway, of course - dose-limiting toxicity, endocrine feedback, lack of biomarkers, just to name a few - but we think we've identified a viable therapeutic strategy.

What emerging discoveries and techniques is Calico utilising?

I'm excited about using outbred mice for intervention testing. We're clearly not the first people to think of this, but we've embraced the concept. Outbred mice are somewhat more resource-intensive than inbred mice because they have more variability, but we think they're worth it. As we're all painfully aware, many published results fail to replicate. I think that a big fraction of what's being called irreproducibility is actually a lack of generalizability. In other words, the results might repeat under the exact same conditions, but alter those conditions just a little and it's a different answer. For mouse studies, strain background is an important condition, and we worry about results from a single, homozygous-at-all-loci genotypes not being generalizable. Outbred mice help us avoid this

What do you think is the best way to quantify longitudinal decline - are there key biomarkers that you're addressing?

Aging manifests at all levels of biological organization (i.e. molecules, cells, tissues, organs, organ-systems, and whole organisms), and measuring aging at each level has pros and cons. Molecular and cellular data provide mechanistic insight and can point to new therapeutic targets, but it can be hard to know if effects are truly relevant to the organism (e.g. does delaying mutation accumulation delay decline in organ function)? Organ-level and physiological data provide health relevance, but it can be hard to tease out mechanism - good for testing putative targets, less good for target discovery. My lab focuses on developing tools for measuring organism-level decline because we think the state of the art is lacking and robustly testing putative targets is rate-limiting in the field.

Link: https://www.longevity.technology/ardd-2020-exclusive-interiew-with-calicos-pi/

We Should Actually Try to Treat Aging for a Change

I am generally in favor of the sentiment offered in this commentary on recent clinical trial failures for the first attempts to guide anti-aging technologies through the FDA gauntlet, which is that researchers and developers should be aiming to treat aging, not specific age-related diseases. There is likely to be a greater incidence of failure on the way to the clinic, and for entirely avoidable reasons, if everyone is attempting to force a more or less square peg into a more or less round hole.

Longevity trials: time to change the approach?

Following the recent clinical trial failures by Unity Biotechnology and resTORbio, Buck Institute professor Brian Kennedy feels that a change in approach is potentially needed. "I get the idea that you target aging pathways, but then you try to treat disease because you need to get FDA approval and reimbursement from insurance companies - but if that strategy doesn't work, we've got to stop doing it. I think we should actually try to treat aging for a change."

While Kennedy agrees that effort needs to continue to convince the FDA to recognise aging as a treatable disease, Kennedy also believes that there are alternative approaches that can be employed. "You don't need the FDA to approve your trial, you need an institutional review board to approve your trial. From an academic standpoint, as long as you can convince people that the trial is safe, you can use biomarkers and study the effects of these drugs. So I think if we start generating that kind of data, then it'll be a lot easier to get the FDA on board, and hopefully the rest of the world on board. We need to nail down the foundation here and stop giving people excuses why this won't work. I'm still optimistic about drugs, but if you develop a drug for A and try to treat B, and then you wonder why it doesn't work - I'm starting to feel like the strategy may not work that well."

Of course, if companies are going to run trials on aging, then a clearer consensus is needed on the definition of aging, and Kennedy is encouraged by developments in the various clocks that measure biological age. "There's a bunch of clocks and we don't really know how they relate to each other yet, and how specific clocks relate to specific kinds of age-related disease. There are a lot of questions to answer, but I think that the most advanced clocks are starting to look like good biomarkers. Some may be better than others but I'm very optimistic about these biomarkers."

At present the FDA doesn't recognize aging as a condition that can be treated, so the first generation of companies working on therapies that target mechanisms of aging will all attempt to apply their approach to specific age-related conditions. If successful, the vast majority of usage will then be off-label, as physician networks apply the therapy at their judgement, based upon the extensive literature suggesting that it will be effective for many age-related conditions. It is in the arena of widespread off-label use that the real battle to lighten the regulatory burden will take place. While off-label use is entirely legal, the FDA will likely attempt to shut down providers and manufacturers, in order to force further trials when a therapy becomes widely used in this way.

It would be much easier if we could all just obtain clinical approval by directly assessing the impact of a potential rejuvenation therapy on aging. Or better, obtain clinical approval by demonstrating safety only, rather than safety and efficacy as presently required by the FDA, and letting later studies, reviews, and the marketplace sort out what actually works. It would also be much easier if the FDA was not the bureaucratic monstrosity that it presently is, operating under perverse incentives that cause regulators to have more than doubled the cost of compliance in the past twenty years, at the same time as reducing the number of new therapies that arrive on the marketplace. I don't see any of this changing any time soon, however. Which is why we will continue to see companies in the longevity industry applying their therapies to specific age-related conditions in order to obtain regulatory approval.

As a sidebar, the trial failures in question were those of UNITY Biotechnology, for senolytics versus knee osteoarthritis, and resTORbio, for an mTORC1 inhibitor versus influenza risk in the elderly. In the former case, the present consensus among observers is that UNITY took a risk on localized senolytic treatment being good enough, and has demonstrated that it isn't. Senescent cells are present throughout the body, and the inflammatory signals that they generate circulate widely. For an inflammatory joint disease, the background inflammation may well be more relevant in many individuals than the local inflammatory process of joint tissue. In the case of resTORbio, the whisper mill suggests that they were tripped up by a change to the trial endpoint forced on them by the FDA between phase 2 (successful) and phase 3 (failure). Equally, one might suspect that the effect sizes for mTOR inhibition on the immune system are just not that large or that reliable in a general population of humans - this may well be the case for all approaches derived from calorie restriction and stress response upregulation research. We shall see.

Mechanisms by which Hearing Loss Might Contribute to the Onset of Dementia

There is a correlation between age-related hearing loss and cognitive decline. Is this because similar mechanisms of cell and tissue damage disrupt both the function of the brain and nerve cells in the ears, or is this because hearing is important in the ongoing operation of the brain? Supporting evidence exists for both options. Here, researchers discuss ways in which loss of hearing might disrupt brain function.

Hearing loss in midlife has been estimated to account for 9% of cases of dementia. Acquired hearing loss is most commonly caused by cochlear damage, while dementia is due to cortical degeneration that typically begins in multimodal cortex. This immediately begs the question of how the two are linked. This is a crucial question from a theoretical perspective, as there are multiple biological and psychological pathways that may link peripheral auditory function to broad-based cortical changes associated with dementia. It also has critical practical implications because while it is difficult, if not impossible, to remediate cortical degradation, hearing loss is widely treatable with hearing aids or cochlear implants. Thus, an understanding of the mechanisms linking the two could have wide-ranging public health importance.

There are a number of possible mechanisms for the relationship between hearing loss and dementia. A first possible mechanism is common pathology affecting the cochlea and ascending auditory pathway (causing hearing loss) and the cortex (causing dementia). Alzheimer's disease (AD)-related pathology has been observed in the retina, but it is not well established as occurring in the cochlea. Transgenic mouse models of AD suggest that AD may be associated with cochlear pathology and hearing loss, but the loss is early onset, unlike the midlife impairment in humans. Vascular pathology can also occur in the cochlea, and this is one of the factors implicated in typical acquired hearing loss. It can also affect the ascending auditory pathway and auditory cortex. Vascular mechanisms are therefore potential contributors to the hearing loss associated with cases of vascular dementia.

A second possible mechanism is that hearing loss leads to the decreased stimulation of cognitive processing. The idea is that auditory deprivation creates an impoverished environment, particularly with the diminishment of speech and language input, that negatively affects brain structure and function. This change in brain structure and function is a risk factor for the subsequent development of dementia. A variety of lines of evidence suggest that listening experience may have a direct impact on the human brain. In parallel to the enriched environment studies with mice, the active listening experience of musicians is associated with positive effects on the structure of auditory cortex and the hippocampus and functional changes in the hippocampus. Piano tuners, expert listeners who spend large amounts of time carrying out a highly specialized form of selective listening, demonstrate hippocampal structural correlates of that experience.

A third mechanism is based on the idea that people with hearing impairment use greater cognitive resources for listening, making these resources unavailable for other aspects of higher cognition when they are "occupied" during listening. "Resources" refers here to the means for cognitive tasks such as attention, working memory, or language processing. There is debate about how cognitive resources are allocated, and the corresponding neural bases. With respect to working memory, for example, there is a question about the extent to which resources may be specifically allocated to objects or represent a distributed resource. Further debate concerns the extent to which working memory resources reflect neuronal or synaptic mechanisms, or both. What is important here, however, is that there is a fixed capacity for many general cognitive operations. These resources may be absorbed when listening becomes challenging, reducing their availability for other aspects of cognition.

A fourth possible explanation focuses on auditory cognitive mechanisms in the medial temporal lobe (MTL) that may be specifically linked to AD pathology in the same region. Although MTL structures are not classically regarded as part of the auditory system, animal models support their role in auditory processing. This mechanism starts from the same idea as the prior mechanism, that hearing loss alters cortical activity, including in the MTL. The critical difference is the incorporation of an interaction between that altered activity and AD pathology. The AD pathology that best correlates with the cognitive phenotype is neurofibrillary change related to tau pathology. The earliest neurofibrillary changes in typical AD are found in MTL structures, particularly the perirhinal cortex, which has a strong functional relationship to the hippocampus. This raises the possibility of an interaction between this pathological process and changes in neuronal activity in MTL structures that occur in hearing impaired individuals.

Link: https://doi.org/10.1016/j.neuron.2020.08.003

Raised Blood Pressure is So Harmful that Reductions are Beneficial Even Without Addressing Underlying Causes

The raised blood pressure of hypertension causes harm throughout the body, raising mortality risk and accelerating the onset and progression of numerous forms of ultimately fatal age-related disease. It accelerates atherosclerosis, and raises the risk of a fatal rupture of blood vessels weakened by atherosclerotic lesions. It causes pressure damage to delicate tissues throughout the body. It leads to detrimental remodeling of heart tissue and the onset of heart failure. Thus forcing a reduction in blood pressure is quite beneficial in later life, even when it is achieved - as is presently the case - by overriding regulatory mechanisms, without addressing any of the underlying forms of cell and tissue damage that produce hypertension. Imagine how much better the outcomes could be if those forms of damage were addressed, reducing not only hypertension but many other forms of downstream harm.

Blood pressure medication can prevent heart attacks and strokes - even in people with normal blood pressure. "Greater drops in blood pressure with medication lead to greater reductions in the risk of heart attacks and strokes. This holds true regardless of the starting blood pressure level, in people who previously had a heart attack or stroke, and in people who have never had heart disease."

There has been controversy about whether pharmacological blood pressure lowering is equally beneficial in people with versus without a prior heart attack or stroke, and when blood pressure is below the threshold for hypertension (typically 140/90 mmHg). Evidence from previous studies has been inconclusive, leading to contradictory treatment recommendations around the world. This was the largest - and most detailed - study ever conducted to examine these questions. The researchers combined data on individuals who had participated in a randomised clinical trial and conducted a meta-analysis. The study included 348,854 participants from 48 trials.

Participants were divided into two groups: those with a prior diagnosis of cardiovascular disease and those without. Each group was divided into seven subgroups based on systolic blood pressure at study entry (less than 120, 120-129, 130-139, 140-149, 150-159, 160-169, 170 and above mmHg). Over an average four years of follow-up, each 5 mmHg reduction in systolic blood pressure lowered the relative risk of major cardiovascular events by about 10%. The risks for stroke, ischaemic heart disease, heart failure, and death from cardiovascular disease were reduced by 13%, 7% and 14% and 5%, respectively. Neither the presence of cardiovascular disease nor the level of blood pressure at study entry modified the effect of treatment.

Link: https://www.escardio.org/The-ESC/Press-Office/Press-releases/Blood-pressure-lowering-is-even-more-beneficial-than-previously-thought

Kimer Med Founded to Develop the DRACO Antiviral Strategy

Today's good news is that a biotech startup, Kimer Med, has been founded to develop the DRACO approach to defeating viral infections. Those of us who have been following developments in antiviral technologies that might be applied to persistent infections relevant to aging, such as cytomegalovirus (CMV) and other herpesviruses, may recall a burst of interest in DRACO some years ago, particularly the research crowdfunding efforts in 2015 and 2016.

DRACO (Double-stranded RNA Activated Caspase Oligomerizer) works by selectively killing cells that exhibit one of the distinctive signs of viral replication. This replication produces long double-stranded RNA, whereas mammalian cells only produce short double-stranded RNA in the normal course of events. It is possible to deliver a form of molecule into the cell that interacts with only long double-stranded RNA and triggers cell death via caspase induced apoptosis as a result, depriving the viral particles of their factory. The fine details of the approach are outlined in the original 2011 paper, and DRACO has been proven to do quite well by a few different research groups in several different animal models of viral infection.

There are two reasons as why this is interesting. Firstly, it can be applied, with little additional work on a per-case basis, to a broad range of virus types, becoming a potentially near-universal antiviral platform. The economics of such a technology look very good in comparison to most other antiviral approaches. Secondly, it has the potential to clear the body of persistent viruses such as CMV. CMV causes great harm to the immune system over a lifetime because it can only be suppressed by present strategies, never fully cleared from the body. The evidence strongly suggests that it is one of the major causes of age-related immunosenescence.

Unfortunately, DRACO went the way of all too many novel research initiatives. It was a struggle to obtain following grants for such a radical departure from the established approaches, the research crowdfunding efforts didn't go that well (as is usually the case - it is very hard to crowdfund scientific research), the researchers involved moved on, the institutions involved abandoned any effort to maintain and license the intellectual property. All of this happens to many projects in the research community, year after year, regardless of their scientific merits and potential to produce viable, useful therapies.

Sadly, intellectual property is such a linchpin in the standard approach to biotechnology investment, as well as in Big Pharma business models, that technologies in the public domain tend to be left for dead. The view is that no-one can monopolize them, own that whole part of the field, which is seen as necessary in order to justify the enormous resources needed to push a therapy through the present heavy-handed regulatory system. Yet it is nonsense to think that any approach to therapy can in practice be monopolized. Every successful development program quickly results in other organizations putting significant efforts into finding ways to achieve a similar result via the same mechanism that nonetheless bypass existing patents. Still, near all investors and institutions in the commercial space steer clear of public domain science until such time as someone produces clinical success by doing otherwise.

Thankfully, the Kimer Med team are willing to be outliers in this matter. They have picked DRACO as their cause to champion, and intend to raise funds to replicate the work, expand it, and bring this radical new approach to antiviral therapy to the clinic. To the degree that they achieve success, others will follow.

HDAC9 Inhibition Slows the Progression of Osteoporosis in Old Mice

Researchers here explore a role for HDAC9 in the progression of osteoporosis, the progressive loss of bone density with age. The signs suggest that age-related upregulation of HDAC9 is involved in cellular senescence and the disruption of cell populations responsible for creating bone tissue. Bone tissue is constantly remodeled, created by osteoblast cells and destroyed by osteoclast cells. The proximate cause of osteoporosis is that the activity of osteoclasts comes to outweigh that of osteoblasts, removing bone structure faster than it is deposited. Many mechanisms that might contribute to this imbalance have been investigated over the years, but it remains unclear as to how exactly they all fit together, and which are the most important.

Osteoporosis is a common aged-related disease and is characterized by decrease bone mass and bone mineral density, leading to bone fragility and a higher risk of fractures. Researchers have discovered several risk factors associated with osteoporosis, including genetic and epigenetic factors, hormone imbalance, and stem cell senescence. Bone marrow mesenchymal stem cells (BMMSCs) are a group of cell residual in the bone marrow. They have self-renewal capacity and multilineage differentiation potential. There is considerable data showing that BMMSCs play crucial roles in maintaining bone remodeling, reparation, and regeneration. Importantly, the number of BMMSCs declines and their lineage commitment shifts from osteoblasts to adipocytes with aging leading to an imbalance between bone mass and bone marrow fat. This imbalance is considered to be a hallmark of aged-related bone loss disorder, osteoporosis.

During senescence, mesenchymal stem cells (MSCs) undergo epigenetic and transcriptional changes, including decreased expression of stemness genes, Oct4 and Nanog, and increased age-related genes, p16 and p53. Some adverse factors that trigger MSC senescence have been identified, such as reactive oxygen species (ROS) accumulation, telomere shortening, and epigenetic effectors, including histone deacetylases (HDACs) and DNA methyltransferases (DNMTs). However, the details of the epigenetic regulation network remain elusive and its roles in BMMSCs during aged-related bone loss remain to be established.

HDACs are important epigenetic regulators that control gene transcription by removing acetyl groups. In this study, we report that HDAC9 plays an important role in maintaining the balance between osteogenesis and adipogenesis of BMMSCs during aged-related bone mass loss. Furthermore, we found that the downregulation of HDAC9 could partially reverse the differentiation of aging BMMSCs and bone loss in mice by regulating autophagy. These results suggest that aged-related bone mass loss may be partially controlled by the HDAC9-meditated autophagy of BMMSCs.

Link: https://doi.org/10.1186/s13287-020-01785-6

Approaches to Optimize Growth of Muscles in Response to Resistance Training in Old People

Muscle growth in response to resistance exercise is attenuated in older individuals, the result of much the same set of processes that lead to sarcopenia, the name given to the characteristic loss of muscle mass and strength that occurs with age. Resistance exercise is clearly still beneficial in later life, judging by the reduction in mortality risk that results, but can it be made more beneficial? Undoubtedly yes, given the appropriate technology to address the underlying root causes of degenerative aging, but all too few such technologies exist at the present time. The use of senolytic therapies to destroy harmful, inflammatory senescent cells is one of the few such technologies, and a plausible approach to improving muscle function in older people, but alas is not mentioned in this paper. The focus here is instead on established ways to tinker with the operation of metabolism in muscle tissue, with results on muscle growth in response to exercise that tend to be modest at best.

The acute anabolic responses to feeding and exercise were found to be dampened in old subjects compared to their young counterparts, thus limiting their recovery and muscle growth. It has been hypothesized that the blunted increase in protein synthesis following acute muscle loading may influence the smaller gains in lean tissue following resistance exercise training in older adults. As such, supplementation of high-quality protein may improve anabolic response to a single bout of exercise. Specific amino acid supplements are available, in the forms of essential amino acids (EAAs), branched-chain amino acids (BCAAs), and leucine. Leucine-rich EAA supplementation enhanced muscle strength following exercise. It is important to note, however, that prolonged protein supplementation with whey or casein, in the setting of a training program, does not appear to improve the exercise response in elderly patients. β-hydroxy-β-methylbutyrate (HMB), a metabolite of leucine which directly activates mTOR, has also been investigated and increased lean muscle mass and strength in sarcopenic individuals.

Chronic, age-related inflammation in skeletal muscle may play a role in aging-associated muscle loss. NF-κB, a master transcriptional regulator of inflammation, becomes upregulated in skeletal muscle with aging. This has led to investigations of whether NF-κB inhibition using commercially available NSAIDs can improve the maintenance of muscle mass. The efficacy of NF-κB inhibition, using commercially available NSAIDs, on the maintenance of muscle mass and strength in response to exercise has been explored in many clinical studies in elderly patients. A 3-month bout of resistance exercise in elderly patients with knee osteoarthritis, NSAIDs therapy resulted in a mild improvement in muscle strength, however, without hypertrophy. Other studies found that NSAID treatment augmented training-induced improvement in strength with associated muscle hypertrophy and limited muscle catabolism. Others have instead shown that NSAID supplementation does not improve skeletal muscle strength or function during physical training. As such, the use of NSAIDs during exercise remains controversial.

Testosterone has emerged as another potential supplement to exercise for the elderly population. Multiple studies have demonstrated that testosterone levels decrease with age. Testosterone administration to elderly patients increases both muscle mass and maximal voluntary strength in a dose-dependent fashion, possibly by the induction of myogenic gene expression. Despite this assertion, the additional benefits of physiological testosterone replacement in elderly patients remains unclear. A prospective study demonstrated increased upper body strength following testosterone treatment of elderly patients with low to normal serum testosterone, but this treatment did not offer any benefit beyond resistance exercise alone.

The growth hormone (GH) axis is another area that has received attention as a potential supplement for exercise therapy for the elderly. GH is made in the pituitary gland and promotes IGF-1 expression in skeletal muscle. IGF-1, in turn, stimulates the Akt/mTOR pathway which promotes muscle anabolism and protein synthesis in response to exercise. In elderly patients, GH treatment increases lean body mass and decreases fat-to-muscle ratio from baseline, although it is unclear as to whether this was attributable to increased skeletal muscle mass. However, multiple studies have shown that healthy elderly patients do not see any additional benefit in strength or muscle hypertrophy with GH supplementation as compared to exercise alone, even at 6-month follow-up. Despite the integral role of the GH/IGF axis on muscle development or hypertrophy, it does not appear to have a therapeutic benefit in physical training in healthy individuals.

Link: https://doi.org/10.3389/fphys.2020.00874

Assessing the Utility of Six of the Better Known Epigenetic Clocks in a Large Study Population

Epigenetic clocks to measure age emerged from the ability to cost-effectively obtain the moment to moment epigenome of an individual, the distribution of epigenetic marks on nuclear DNA that control gene expression. Cells react to their environment, and some of those reactions are characteristic of the ways in which the cellular environment changes with age. Given this data and ample computational power, it is possible to find weighted combinations of, for example, DNA methylation status at specific CpG sites that fairly accurately correlate with age. More interestingly, this appears to be a measure of biological age rather than chronological age, in that people with a higher epigenetic age than chronological age tend to have a higher incidence and later risk of age-related disease and dysfunction - and vice versa.

It remains unclear is what exactly it is that is being measured by an epigenetic clock. Which processes of aging, the accumulation of damage and downstream change, actually cause these characteristic epigenetic changes across all individuals? Is it all of them? Or only some of them? Researchers have produced clocks based on patterns of transcription and protein levels in addition to epigenetic marks, and some of these later clocks use only a handful of transcripts, proteins, or marks. It seems unlikely that the more abbreviated clocks measure more than a fraction of the causative processes of aging. Since these processes interact, and all of the facets of aging proceed at much the same pace in most people, then a clock that measures, say, only chronic inflammation, might be just as good today as a clock that is affected by all mechanisms of aging.

This is true, at least, until we start being able to repair specific forms of underlying cell and tissue damage, such as the presence of senescent cells. Some clocks will stop working usefully, and we don't really know which ones are vulnerable to the deployment of any given approach to rejuvenation. Which is a challenge, because assessing the results of therapies that repair specific forms of underlying cell and tissue damage is exactly how we'd like to use these clocks. As things stand, no clock, epigenetic or otherwise, can be trusted for such a task until it is fairly well calibrated against a class of rejuvenation therapy via multiple life span studies.

Epigenetic measures of ageing predict the prevalence and incidence of leading causes of death and disease burden

Individuals of the same chronological age display different rates of biological ageing. A number of measures of biological age have been proposed which harness age-related changes in DNA methylation profiles. These measures include five 'epigenetic clocks' which provide an index of how much an individual's biological age differs from their chronological age at the time of measurement. The five clocks encompass methylation-based predictors of chronological age (HorvathAge, HannumAge), all-cause mortality (DNAm PhenoAge, DNAm GrimAge) and telomere length (DNAm Telomere Length). A sixth epigenetic measure of ageing differs from these clocks in that it acts as a speedometer providing a single time-point measurement of the pace of an individual's biological ageing. This measure of ageing is termed DunedinPoAm.

In this study, we examined associations between six major epigenetic measures of ageing and the prevalence and incidence of the leading causes of mortality and disease burden in high-income countries. DNAm GrimAge, a predictor of mortality, associated with the prevalence of COPD and incidence of various disease states, including COPD, type 2 diabetes, and cardiovascular disease. It was associated with death due to all-cause mortality and outperformed competitor epigenetic measures of ageing in capturing variability across clinically associated continuous traits. Higher values for DunedinPoAm, which captures faster rates of biological ageing, associated with the incidence of COPD and lung cancer. Higher-than-expected DNAm PhenoAge predicted the incidence of type 2 diabetes in the present study. Age-adjusted measures of DNAm Telomere Length associated with the incidence of ischemic heart disease. Our results replicate previous cross-sectional findings between DNAm PhenoAge and body mass index, diabetes, and socioeconomic position (in a basic model). We also replicated associations between DNAm GrimAge and heart disease.

In conclusion, using a large cohort with rich health and DNA methylation data, we provide the first comparison of six major epigenetic measures of biological ageing with respect to their associations with leading causes of mortality and disease burden. DNAm GrimAge outperformed the other measures in its associations with disease data and associated clinical traits. This may suggest that predicting mortality, rather than age or homeostatic characteristics, may be more informative for common disease prediction. Thus, proteomic-based methods (as utilised by DNAm GrimAge) using large, physiologically diverse protein sets for predicting ageing and health may be of particular interest in future studies. Our results may help to refine the future use and development of biological age estimators, particularly in studies which aim to comprehensively examine their ability to predict stringent clinically defined outcomes. Our analyses suggest that epigenetic measures of ageing can predict the incidence of common disease states, even after accounting for major confounding risk factors. This may have significant implications for their potential utility in clinical settings to complement gold-standard methods of clinical disease assessment and management.

Much Faster Peripheral Nerve Regrowth with Electrical Stimulation

Researchers here produce faster nerve regrowth following injury via the use of electrical stimulation of tissue. This is an interesting companion piece to a recent paper that reported on the use of electrical stimulation to produce greater degrees of neurogenesis in the brain. Applying electromagnetic fields to the body with the goal of beneficially changing the behavior of cells is a poorly explored facet of medical technology, when compared to the effort put into pharmacology. In part this may be because it appears more challenging to achieve success and reliability of outcomes in research. The fine technical details of the methodology used appear to matter greatly: field character, strength, frequency, time and repetition of application, and so forth.

Researchers have found a treatment that increases the speed of nerve regeneration by three to five times, which may one day lead to much better outcomes for trauma surgery patients. Peripheral nerve injury occurs in about three per cent of trauma victims. The slow nature of nerve regeneration means that often muscles atrophy before the nerve has a chance to grow and reconnect. That's where conditioning electrical stimulation (CES) comes in. The process involves electrically stimulating a nerve at the fairly low rate of 20 hertz for one hour. A week after the CES treatment, nerve surgery is done, and the nerves grow back three to five times faster than if the surgery was done without CES.

In their latest work on CES, researchers examined animal models with foot drop, a common injury that affects patients' quality of life by impeding their ability to walk normally. Previously, the only treatments for foot drop were orthotics, that affect a patient's gait, or surgery. Researchers performed a distal nerve transfer in which a nerve near the damaged one was electrically stimulated, then a week later a branch of the nerve was cut and placed near the target of the non-functioning nerve. The newly transferred nerve would then be primed and ready to regrow, at a much faster rate, into the muscles that lift the foot. Researchers hopes to bring the information gained from examining nerve transfers in the leg - a difficult body part for nerve regrowth due to the vast area the nerve must cover - to clinical trials within the next year or two.

Link: https://www.folio.ca/u-of-a-researchers-find-way-to-speed-up-nerve-regrowth-for-trauma-patients/

Reviewing the Role of miR-181a in Sarcopenia

A great many research groups investigate the mechanisms and biochemistry of sarcopenia, the characteristic age-related loss of muscle mass and strength. The most compelling evidence points of a loss of stem cell activity in muscle tissue as the dominant cause, but numerous other mechanisms may contribute. Many researchers are more interested in proximate causes, age-related changes in muscle cell biochemistry, than in deeper causes of the condition. In this context, the review here examines the role of one microRNA out of a number of microRNAs that are of interest in the pathogenesis of sarcopenia.

Frailty is largely associated with sarcopenia, aging-related loss of muscle mass and function, characterised by a progressive and degenerative loss of skeletal muscle mass, quality, and strength during aging. Sarcopenia affects 5-13% of 60-70 year olds and up to 50% of people over 80. The role of microRNAs (miRNAs, miRs) as epigenetic modifiers in regulating loss of muscle mass and function has become increasingly recognised. miRs are short, non-coding RNAs which regulate the expression of approximately two thirds of human genes.

In skeletal muscle, miRs have been demonstrated to control multiple biological processes, including development, regeneration, and aging. A number of miRs are involved in the regulation of muscle protein synthesis, that target regulators involved maintaining the balance between muscle atrophy and hypertrophy, and including regeneration of skeletal muscle. Early studies in humans demonstrated differential expression of miRs in skeletal muscle during aging. We and others have demonstrated the role of miRs in aging-associated processes in skeletal muscle, such as satellite cell senescence and inflammation.

Bioinformatic analyses of non-coding RNAs and transcripts in human and rodent muscle during aging have identified miR-181a as a potentially key regulator of muscle mass and function during aging. In skeletal muscle, miR-181a appears to be the predominant miR-181 family member in skeletal muscle affected by aging and has been suggested as biomarker of muscular health. miR-181 has also been demonstrated to be upregulated in muscle during exercise and predicted to regulate transcription factors and co-activators involved in the adaptive response of muscle to exercise. Based on computer simulation models, miR-181a was predicted to regulate muscle atrophy and hypertrophy through its target genes: HOXA11 by inhibiting MYOD, and SIRT1, through regulating FoxO3 signalling. Indeed, we and others confirmed these as miR-181a direct targets.

More recently, miR-181 family of miRs gained more attention due to their regulation of processes associated with mitochondrial dynamics. Mitochondrial dysfunction is one of the hallmarks of aging. During aging, skeletal muscle is characterised by a loss of mitochondrial content and disrupted mitochondrial turnover, particularly in sedentary individuals. A number of studies to date suggest that miR-181a may be a global regulator of mitochondrial dynamics, redox homeostasis, and potentially energy balance of the whole organism.

Link: https://doi.org/10.1016/j.tma.2020.07.001

Stress Granules as a Therapeutic Target

Stress granules are a comparatively poorly understood portion of the processes that a cell uses to maintain its protein machinery and component structures. When cells are subject to mild stress or damage, whether it is due to radiation, heat, lack of nutrients, or other challenges, they upregulate the activity of both autophagy and the ubuiquitin-proteasome system. Autophagy involves flagging proteins and structures for disassembly, followed by transport to a lysosome packed with enzymes to break down molecules into component parts that can be reused. The ubuiquitin-proteasome system tags proteins with ubiquitin, allowing them to be drawn into a proteasome for disassembly into raw materials. In addition, cells also form stress granules, carefully packed assemblies of RNA that are presently thought to act as stockpiles that prevent vital molecules from being recycled too aggressively.

Upregulation of autophagy and proteasomal activity are both known to improve health and extend life in short-lived laboratory species. Functional autophagy in particularly is necessary for the life extension produced by calorie restriction. Recently, it was established that the existence of stress granules is also necessary in order for the mild nutrient stress of calorie restriction to extend healthy life span. Further, abnormal stress granule formation is observed in older individuals. This makes stress granules a target of interest in the development of therapies for a range of conditions. That said, as is the case for calorie restriction mimetic drugs, it seems unlikely that very large benefits for patients can be engineered atop this foundation. We know the outcome of calorie restriction in humans: health benefits, but no great extension of life span. Better and more direct strategies to address the cell and tissue damage of aging are needed.

Targeting stress granules: A novel therapeutic strategy for human diseases

A large portion of mRNA in mammalian eukaryotic cells completes transcription in the nucleus and is then transported to the cytoplasm for translation and expression. When eukaryotic cells are stimulated or disturbed, the mature mRNA in cells cannot be translated into proteins immediately. These temporarily untranslated mRNA or translation-stalled mRNA then polymerize with RNA-binding proteins (RBPs) to form messenger ribonucleoprotein (mRNP) granules without a membrane structure, known as Cajal bodies, stress granules (SGs), processing bodies (P-bodies), RNA transport granules, or germ granules.

While mRNP granule types are complex and diverse, there are three commonalities between mRNP granules: first, mRNP granules usually contain non-translated or poorly translated mRNA, and these mRNA can re-enter polysome for translation after cellular adaption or environmental recovery. Second, different mRNP granules may contain the same mRNA or RBP and these components can be relocated from one mRNP granule to another granule. Third, different mRNP granules can interact dynamically, involving docking, fusion, and becoming another mRNP granule after maturation.

mRNP granules have a very important effect on mRNA function and cell signalling, and are also closely related to diseases. One of the most studied mRNP granules is SGs. SGs are a type of dynamic granular substance formed of mRNA of stagnant translation and RBPs in the cytoplasm of eukaryotic cells, the formation of which is stimulated by various stresses including oxidative stress, heat shock, hypoxia, or viral infection. It is an adaptive regulatory mechanism that protects cells from apoptosis under adverse conditions.

SGs have been identified in many biological processes and diseases. The assembly and disassembly of SGs determine further storage, translation remodelling, or degradation of untranslated mRNA, which affect cell death or survival under specific conditions. In cancer treatment, on the one hand, the formation of SGs can lead to cell survival and increase cell resistance to chemotherapeutic drugs. The combined use of drugs that inhibit SG formation or promote SG disassembly with chemotherapeutic drugs may alleviate drug resistance. On the other hand, some drugs may enhance the effects of chemotherapy by inducing SG-mediated cell apoptosis. Furthermore, the persistence of stress particles leads to chronic SG formation and irreversible pathogenesis, for example in neurodegeneration and aging.

It is therefore possible that targeting chronic SGs that inhibit the abnormal aggregation of related SGs or promote SG clearance may be a novel therapeutic strategy in neurodegenerative diseases and other chronic diseases. The formation and the biological functions of SGs are complex. Many questions need to be answered by research and the development of SG-targeting drugs. (1) Studies on SGs are largely confined to cell culture and C. elegans because of the absence of a suitable in vivo mammalian model. Ideally, a mouse model will be developed that can directly assess stress particles in living animals and more intuitively present direct associations between SGs, drugs, and diseases. (2) The side effects of the long-term administration of SG-interfering agents remain unclear. (3) Most SG contents are not the direct target of small molecules. So, the identification of druggable targets in SGs will reveal new biological functions and mechanisms of SG biology. Thus, SGs deserve more in-depth research.

Longevity-Risk-Adjusted Global Age, by Country

People tend to live longer in some parts of the world than in others, the result of a cultural distribution of lifestyle choices such as smoking and becoming overweight, environmental exposure to, say, particulate air pollution and infectious disease, and access to medical technology. One can use the worldwide statistics of life expectancy to produce a "longevity-risk-adjusted global age" to compare with chronological age: longevity-risk-adjusted global age is higher than chronological age in countries with a higher late-life mortality rate and shorter life expectancy. What happens at the population level says very little about individual life expectancy, of course, as that is a matter of one's own personal lifestyle choices, exposures, and access to medical technology, none of which necessarily have to bear any relation to the local median. This is nonetheless an interesting way to present the existing data on human life expectancy.

The boxer Muhammad Ali is quoted as saying that: Age is whatever you think it is. You are as old as you think you are. Similarly, author Mark Twain joked that: Age is just a state of mind. I say it is more about the state of your body. Clearly, there is a wide divergence of opinions about the proper definition of true age, all of which are quite distinct from the number of times you circled the sun. In fact, recent work indicates that economic behavior is highly correlated with how old people feel versus their chronological age. The pertinent question here is whether actuarial science can contribute yet another age metric, one that is consistent with heterogeneous mortality and known mathematical theories of aging. This paper argues that the answer is yes.

This paper develops a computational framework for inverting Gompertz-Makeham mortality hazard rates, consistent with compensation laws of mortality for heterogeneous populations, to define a longevity-risk-adjusted global (L-RaG) age. To illustrate its salience and possible applications, the paper calibrates and presents L-RaG values using country data from the Human Mortality Database (HMD). Under this approach, the data indicate that for a male at chronological age 55, the gap in L-RaG ages between high-mortality (e.g. Russia) and low-mortality countries (e.g. Sweden), can be as high as 20 years: a 55-year-old Swedish male has an L-RaG age of 48, whereas a 55-year-old Russian male is closer in L-RaG age to 67. Stated differently, using the language of risk-adjusted benchmarks, your true age depends on where you live.

Link: https://doi.org/10.1016/j.insmatheco.2020.03.009

Clearance of Senescent Cells as a Way to Expand the Donor Organ Supply

Researchers here provide a proof of principle to suggest that the presence of senescent cells in older organs contributes meaningfully to transplant rejection, via mechanisms that spur greater immune activity. This is of course only one of the ways in which senescent cell accumulation with age contributes to degenerative aging, the dysfunction of cells and tissues throughout the body. It may be possible to apply senolytic treatments that clear senescent cells to donor organs prior to transplantation (preferably), or to the patient immediately following transplantation (with the risk that it will suppress regeneration for a short time, as senescent cells are involved in the wound healing process), in order to allow greater viability of those organs and fewer complications in the transplantation process. It is worth noting that a sizable fraction of organ donors are older people, old enough to have a meaningful increase in the senescent cell burden.

The world population is aging rapidly. Organ transplantation is the treatment of choice for patients with irreversible end-stage organ failure. The supply of organs, however, is limited, resulting in prolonged waiting times with many patients dying or becoming too ill to be eligible for transplantation. Currently, the most obvious strategy with potential for closing the gap between demand and supply would be to enable the use of organs from older deceased donors that currently are frequently discarded.

Aging is associated with increased senescent cell burden that is linked to chronic, low grade, sterile inflammation. Increased levels of cytokines, including IL-6, IFN-γ, and TNF-α, contribute to the pro-inflammatory secretome of senescent cells, termed the senescence-associated secretory phenotype or SASP. Damage-associated molecular patterns (DAMPs), which include mitochondrial DNA (mt-DNA), also increase with aging. Relationships among senescent cell accumulation, mt-DNA, the SASP, outcomes of transplantation in clinically relevant disease models, and the potential to mitigate injury and augmented immunogenicity of older organs by targeting senescent cells have so far not been tested. However, recent studies propose that circulating mitochondria and mt-DNA might mediate early allograft dysfunction.

Ischemia and reperfusion injury (IRI) is characterized by initial tissue hypoxia with metabolic changes and subsequent further damage with the reintroduction of oxygen and elevated shear forces during reperfusion. Local tissue injury is followed by a systemic sterile inflammatory response, mediated by DAMPs including mt-DNA.

Here we show that cell-free mitochondrial DNA (cf-mt-DNA) released by senescent cells accumulates with aging and augments immunogenicity. IRI induces a systemic increase of cf-mt-DNA that promotes dendritic cell-mediated, age-specific inflammatory responses. Comparable events are observed clinically, with the levels of cf-mt-DNA elevated in older deceased organ donors, and with the isolated cf-mt-DNA capable of activating human dendritic cells. In experimental models, treatment of old donor animals with senolytics clear senescent cells and diminish cf-mt-DNA release, thereby dampening age-specific immune responses and prolonging the survival of old cardiac allografts comparable to young donor organs. Collectively, we identify accumulating cf-mt-DNA as a key factor in inflammaging and present senolytics as a potential approach to improve transplant outcomes and availability.

Link: https://doi.org/10.1038/s41467-020-18039-x

A Bidirectional Relationship Between the Gut Microbiome and Aging

The gut microbiome is influential on health over the long term, possible as much so as exercise. That said, research related to aging in this part of the field is comparatively recent, and consequently is far less developed than the long-standing evidence for the effects of exercise on mortality and risk of age-related disease. It seems fairly clear that the gut microbiome changes in characteristic ways with age, becoming less helpful and more harmful. Species that produce beneficial metabolites decline in number and activity, while inflammatory microbial populations grow in size, contributing the state of chronic inflammation found in older individuals. Equally, the immune system plays a role in gardening the gut microbiome, and as the immune system declines with age, this gardening fails, allowing detrimental changes to take place. This is a two-way relationship.

There is good evidence in short-lived animal models for fecal microbiota transplant from young individuals to old individuals to reverse age-related changes in the gut microbiome and consequently improve health and life span. It is unknown as to how well such a strategy would work in long-lived humans, meaning how long the beneficial changes last. That said, fecal microbiota transplant is a proven therapy in human medicine, used to cure conditions in which pathological bacteria have overtaken the gut. It is not a stretch to consider expanding on this approach to favorably readjust the aging gut microbiome as a preventative measure to improve health and extend health life expectancy across the population as a whole.

The microbiome: An emerging key player in aging and longevity

During the past two decades, studies have provided evidence that age-associated shifts in the gut microbiome contributes to increased predisposition of aged individuals to certain diseases, including cardiovascular diseases, cancer, obesity, cancers, diabetes, and neurodegenerative diseases. Aging is a complicated process that affects physiological, metabolic, and immunological functions of the organism and thus is accompanied by inflammation and metabolic dysfunctions. The overall age-related increase in chronic inflammation and deterioration of systemic immune system led to coining the term "inflammaging". A direct causal role of the gut microbiome on host aging has been suggested by a number of studies using various experimental models.

The symbiotic co-existence between the host and microbiota is feasible due to the anatomical separation of microbial species from the host by a physical barrier. The intestinal barrier is responsible for adjusting metabolic homeostasis and systemic antimicrobial responses by detecting microbial-cell components and metabolites through its extensive repertoire of innate immune receptors. Relevant to aging, decline of the immune system in the aged intestinal epithelium have been suggested to contribute to age-onset dysbiosis. An important characteristic of age-onset dysbiosis is reduced microbiota diversity, which is suggested to lead to an expansion of distinct groups of bacteria. Concurrently, bacteria that is reported to be involved in maintenance of immune tolerance in the gut, such as Bifidobacteria and Lactobacilli, are found in reduced level in aged groups, whereas those that are found in increased levels, such as Enterobacteriaceae and Clostridium, are involved in infection and intestinal inflammation stimulation. Together, these studies suggest that the host immune system shapes not only the host's immune response to microbiome changes, but also the structure of the microbiome itself.

Cumulative evidence has implicated a close functional relationship between the immune system of the host and the microbiome, to an extent that the gut microbiome is important for proper development and expansion of intestinal mucosal and systemic immune system. Supporting the notion that the microbiome can directly shape the immune states of the host, the transcriptomic profile of African turquoise killifish guts derived from animals that received young or old gut microbiota transplants showed clear differences, especially in expression of immune-related genes.

Increased permeability of the intestinal barrier with age has been described across animal species, including worms, flies, mice and rats. Age-related deterioration of intestinal barrier function has been proposed to result in leakage of gut microbes into the systemic circulation, and ultimately lead to increased antigenic load and systemic immune activation. For example, age-associated remodeling of the gut microbiome in mice was shown to result in increased production of pro-inflammatory cytokines and intestinal barrier failure. In Drosophila, the age-related increase in Gammaproteobacteria was suggested to lead to increased intestinal permeability, inflammation, and mortality. The study showed that regardless of chronological age, intestinal dysbiosis serves as an indicator of age-onset mortality in flies.

Microbiome-derived short-chain fatty acids (SCFAs), including butyrate, propionate, acetate, and valerate, are important energy source for the epithelium and ultimately affects hypoxia-inducible factor-mediated fortification of the epithelial barrier. Interestingly, a decline in SCFA levels, including that of butyrate, were observed in aged humans, whereas centenarians presented with a rearrangement in the population of specific butyrate-producing bacteria. Microbiota-derived metabolites has also been reported to play a role in intestinal epithelial stem cell proliferation. For example, butyrate and nicotinic acid, both by-products of the gut microbiota, are involved in suppression and promotion of stem cell proliferation in the colon, respectively. In addition, microbiota-derived neurostimulators, including serotonin, glutamate, gamma-aminobutyric acid, have been reported to regulate proliferation of intestinal epithelial stem cells through the enteric nervous system. Other microbiota-derived metabolites have been shown to directly affect numerous systems of the host, although their functions in relation to host aging is in need of further investigation.

Is Age-Related Polyploidy a Beneficial Adaptation to a Damaged Environment?

Cells with abnormal chromosome counts, a state known as aneuploidy, are considered to be a problem. The evidence suggests that such cells accumulate with age, a form of damage and dysfunction that is associated with cellular senescence, and is expected to contribute to age-related degeneration and disease. Here, researchers argue that having duplicate chromosomes, polypoidy, might actually be protective, a beneficial adaptation that emerges in the damaged environment of aged tissues. This may be the case, and it may also be true that it is both protective and harmful. The weight of evidence to date continues to point to aneuploidy as an undesirable state regardless of whether there are more or fewer chromosomes in a cell.

Terminally differentiated postmitotic cells such as mature neurons and glia are long-lived and must cope with the accumulation of damage over the course of an animal's lifespan. The mechanisms used by such long-lived cells to deal with aging-related damage are poorly understood. The brain of the fruit fly Drosophila melanogaster is an ideal context to examine this since the fly has a relatively short lifespan and the adult fly brain is nearly entirely postmitotic with well understood development and excellent tools for genetic manipulations.

Polyploidy can confer an increased biosynthetic capacity to cells and resistance to DNA damage induced cell death. Several studies have noted neurons and glia in the adult fly brain with large nuclei and in some cases neurons and glia of other insect species in the adult central nervous system (CNS) are known to be polyploid. Rare instances of neuronal polyploidy have been reported in vertebrates under normal conditions and even in the CNS of mammals.

Polyploidization is employed in response to tissue damage and helps maintain organ size. Therefore, polyploidy may be a strategy to deal with damage accumulated with age in the brain, a tissue with very limited cell division potential. Here we show that polyploid cells accumulate in the adult fly brain and that this proportion of polyploidy increases as the animals approach middle-age. We show that multiple types of neurons and glia which are diploid at eclosion which become polyploid specifically in the adult brain. We have found that the optic lobes of the brain contribute to most of the observed polyploidy. We also observe increased DNA damage with age, and show that inducing oxidative stress and exogenous DNA damage can lead to increased levels of polyploidy. We find that polyploid cells in the adult brain are resistant to DNA damage-induced cell death and propose a potentially protective role for polyploidy in neurons and glia in adult Drosophila melanogaster brains.

Link: https://doi.org/10.7554/eLife.54385

mTOR in the Cerebrovascular Dysfunction that Contributes to Neurodegenerative Disease

Aging brings considerable disruption to the vascular system: stiffening of blood vessels; hypertension that damages delicate tissues; a loss of capillary density resulting in reduced delivery of nutrients and oxygen; failure of the blood-brain barrier that keeps unwanted cells and molecules from vulnerable brain tissue; and more. All of this contributes to the onset and progression of neurodegenerative diseases through mechanisms that include increased inflammation in the brain and structural pressure damage to brain tissues.

Impaired cerebrovascular function, a universal feature of aging, is a biomarker for increased risk of Alzheimer's disease (AD), and is one of the earliest detectable changes in the pathogenesis of AD. Indeed, chronic cerebral hypoperfusion typically develops nearly a decade prior to cognitive decline and precedes the presence of pathological hallmarks of AD, including brain atrophy and accumulation of β-amyloid and pathogenic tau. In accordance with the two-hit vascular hypothesis of AD, these observations suggest that early age-associated cerebrovascular dysfunction may trigger the development of cerebrovascular pathology, driving cognitive impairment and accelerating the pathogenesis of neurological diseases of aging, including AD. Thus, cerebrovascular dysfunction may represent one of the earliest and most therapeutically addressable biological pathways under-lying age-related cognitive impairment and neurological disease.

Research from our lab and others showed that the mechanistic/mammalian target of rapamycin (mTOR) drives several different aspects of cerebrovascular dysfunction in models of AD and vascular cognitive impairment and dementia (VCID), including blood-brain barrier (BBB) breakdown, cerebral hypoperfusion, reduced cerebrovascular reactivity, and impaired neurovascular coupling. We recently established that mTOR drives age-related cerebrovascular dysfunction in 34-month-old aged rats devoid of overt pathology or disease. Cerebral blood flow deficits in aged rats were associated with microvascular rarefaction, synaptic loss, impaired neuronal network activation, and spatial learning and memory impairments. Chronic mTOR attenuation via rapamycin preserved cerebrovascular function and microvascular integrity, improved synaptic integrity and neuronal network activation throughout aging, and negated age-related cognitive decline in aged rats. These recent results indicate that in addition to driving cognitive and cerebrovascular deficits in models of AD and VCID, mTOR underlies the etiology of age-associated cerebrovascular and neuronal dysfunction during normative aging.

Link: https://doi.org/10.18632/aging.103854

An Update on Lygenesis: Functional Liver Organoids in the Lymph Nodes of Pigs

Lygenesis is the company founded to conduct the clinical development of research into the use of lymph nodes to support the growth and function of organoids. Lymph nodes are found in the lymphatic system, places where immune cells can coordinate with one another in order to produce an immune response. Mammals have more lymph nodes than they need, and so it is possible to insert small pieces of organ tissue into a few lymph nodes, transforming them into miniature organs, without harming the immune system. This can in principle work well for factory organs like the liver and thymus, which carry out functions that do not have a strong dependency on structure or location in the body.

The primary thrust of the work at Lygenesis is to provide a way to support failing liver function, but the company intends to do the same for the thymus. The latter is perhaps more interesting a line of work, given that loss of thymus tissue occurs early in life, and the thymus is responsible for the maturation of T cells of the adaptive immune system. Thymic atrophy is an important contributing factor in the age-related loss of immune function, as the supply of replacement immune cells diminishes over time. Today's news is focused on the liver, however. Here, researchers show that their approach works in a large animal model, specifically pigs.

Pigs Grow New Liver in Lymph Nodes, Study Shows

The cells of the liver normally replenish themselves, but need a healthy, nurturing environment to regenerate. However, in end-stage liver disease, the liver is bound up by scar tissue and too toxic for the cells to make a comeback. Nearly a decade ago, researchers noticed that if they injected healthy liver cells into the lymph nodes of a mouse, they would flourish, forming an auxiliary liver to take over the tasks of the animals' genetically induced malfunctioning liver. But mice are small. Researchers needed to show that a large animal could grow a meaningful mass of secondary liver tissue to overcome liver disease.

To mimic human liver disease in pigs, the researchers diverted the main blood supply from the liver, and at the same time, they removed a piece of healthy liver tissue and extracted the hepatocytes. Those liver cells were then injected into the abdominal lymph nodes of the same animal they came from. All six pigs showed a recovery of liver function, and close examination of their lymph nodes revealed not only thriving hepatocytes, but also a network of bile ducts and vasculature that spontaneously formed among the transplanted liver cells. The auxiliary livers grew bigger when the damaged tissue in the animals' native liver was more severe, indicating that the animals' bodies are maintaining an equilibrium of liver mass, rather than having runaway growth akin to cancer.

Development of Ectopic Livers by Hepatocyte Transplantation into Swine Lymph Nodes

Orthotopic liver transplantation continues to be the only effective therapy for patients with end-stage liver disease. Unfortunately, many of these patients are not considered transplant candidates, lacking effective therapeutic options that would address both the irreversible progression of their hepatic failure and the control of their portal hypertension. In this prospective study, a swine model was exploited to induce sub-acute liver failure. Autologous hepatocytes, isolated from the left hepatic lobe, were transplanted into the mesenteric lymph nodes by direct cell injection.

30 to 60 days after transplantation, hepatocyte engraftment in lymph nodes was successfully identified in all transplanted animals with the degree of ectopic liver mass detected being proportional to the induced native liver injury. These ectopic livers developed within the lymph nodes showed remarkable histologic features of swine hepatic lobules, including the formation of sinusoids and bile ducts. Based on our previous mouse model and the present pig models of induced sub-acute liver failure, the generation of auxiliary liver tissue using the lymph nodes as hepatocyte engraftment sites represents a potential therapeutic approach to supplement declining hepatic function in the treatment of liver disease.

A Better Chondroitinase ABC to Break Down Nerve Tissue Scarring

Researchers here report on their successful redesign of the chondroitinase ABC enzyme, capable of degrading a form of scarring that forms following nervous system injury. This scarring inhibits regrowth of nerves, and thus suppressing or removing it may be beneficial. Chondroitinase ABC achieves this goal to some degree, but is impractical to use because of its instability in the body. This redesign may have improved stability to a large enough degree to make the enzyme a practical basis for therapies that improve nerve regrowth.

One of the major challenges to healing after the kind of nerve injury resulting from stroke or spinal cord damage is the formation of a glial scar. A glial scar is formed by cells and biochemicals that knit together tightly around the damaged nerve. In the short term, this protective environment shields the nerve cells from further injury, but in the long term it can inhibit nerve repair.

About two decades ago, scientists discovered that a natural enzyme known as chondroitinase ABC - produced by a bacterium called Proteus vulgaris - can selectively degrade some of the biomolecules that make up the glial scar. By changing the environment around the damaged nerve, chondroitinase ABC has been shown to promote regrowth of nerve cells. In animal models, it can even lead to regaining some lost function. But progress has been limited by the fact that chondroitinase ABC is not very stable in the places where researchers want to use it. "It aggregates, or clumps together, which causes it to lose activity. This happens faster at body temperature than at room temperature. It is also difficult to deliver chondroitinase ABC because it is susceptible to chemical degradation and shear forces typically used in formulations."

Various teams have experimented with techniques to overcome this instability. Some have tried wrapping the enzyme in biocompatible polymers or attaching it to nanoparticles to prevent it from aggregating. Others have tried infusing it into damaged tissue slowly and gradually, in order to ensure a consistent concentration at the injury site. But all of these approaches fail to address the fundamental problem of instability. Now researchers tried a new approach: they altered the biochemical structure of the enzyme in order to create a more stable version. In the end, the team ended up with three new candidate forms of the enzyme that were then produced and tested in the lab. All three were more stable than the wild type, but only one, which had 37 amino acid substitutions out of more than 1,000 possible substitution locations, was both more stable and more active.

"The wild type chondroitinase ABC loses most of its activity within 24 hours, whereas our re-engineered enzyme is active for seven days. This is a huge difference. Our improved enzyme is expected to even more effectively degrade the glial scar than the version commonly used by other research groups." The next step will be to deploy the enzyme in the same kinds of experiments where the wild type was previously used.

Link: https://news.engineering.utoronto.ca/re-engineered-enzyme-could-help-reverse-damage-from-spinal-cord-injury-and-stroke/

Theophylline Produces Accelerated Remyelination in the Central Nervous System of Mice

The myelin sheathing around axons is necessary for the proper function of nervous system tissue. Demyelinating conditions such as multiple sclerosis, an autoimmune disease in which the immune system attacks myelin, well illustrate the severe consequences that result from a sizable loss of myelin. Unfortunately, the integrity of myelin sheathing declines with age for everyone, most likely the result of disruption and damage in the oligodendrocyte cell population responsible for maintaining these structures. Evidence suggests that this contributes to cognitive decline and other issues. Thus it is worth keeping an eye on progress towards therapies that might enhance the generation and repair of myelin sheathing. The work noted here is an example of the type, in which the drug theophylline is shown to improve recovery from myelin loss in mice.

Neurons are composed of axons, i.e., long fiber-like extensions that transmit signals to other cells. Many of them are surrounded by a myelin sheath, a thick fatty layer that protects them and helps to transfer stimuli rapidly. Without myelin, the functional capacity of neurons - and therefore of the whole nervous system - is limited and neurons can easily degenerate. Multiple sclerosis (MS) is one of the diseases associated with myelin sheath degradation. MS patients suffer successive episodes of demyelination resulting in a progressive loss of function of their nervous system. Remyelination of the axons can prevent this.

Intact myelin sheaths are a prerequisite for the healthy functioning of the peripheral and central nervous systems. If the peripheral nervous system (PNS) is damaged, in an accident involving injury to the arms or legs for example, the axons and their myelin sheaths can recover relatively well. However, the central nervous system (CNS) is completely different in this regard as there is no efficient restoration of the axons and therefore of the myelin sheath after a lesion. This means that CNS injuries usually result in permanent paralysis - as in the case of MS when loss of myelin leads to axon degeneration. Further, the capacity of the body to remyelinate decreases dramatically with age.

Researchers recently investigated how remyelination occurs in both peripheral and central nervous systems of mice. The neuroscientists identified a protein called eEF1A1 as a key factor in the process and found that eEF1A1 activated by acetylation prevents the remyelination process, but if eEF1A1 is deactivated by deacetylation, myelin sheaths can be rebuilt. The protein that deacetylates eEF1A1 is the enzyme called histone deacetylase 2 (HDAC2).

The researchers decided to try to control this process by boosting HDAC2 activity and its synthesis in cells. This was achieved by using the active substance theophylline, which has long been used in the treatment of asthma. In a mouse model, the use of theophylline over a period of four days resulted in significant recovery. Restoration of myelin sheaths was particularly impressive in the PNS, where they recovered completely. Regeneration also improved in the CNS, as there was rapid and efficient rebuilding of myelin sheaths in both young and old mice. A low dose of the active substance was sufficient to trigger the improvements - a big plus with regard to the known side effects of theophylline, which occur at higher doses.

Link: https://www.uni-mainz.de/presse/aktuell/11912_ENG_HTML.php