Fight Aging!

Senescent cells accumulate with age in tissues throughout the body. Cells enter a senescent state constantly throughout life, largely the result of cells reaching the Hayflick limit on replication, but also due to stress, injury, and damage. A senescent cell ceases replication and instead produces a potent mix of pro-growth, pro-inflammatory signals. The primary purpose of senescence in an adult is to signal to the immune system that a cell needs to be removed, and potentially that the surrounding region of tissue requires further attention, such as in the case of an injury or toxic environment that is damaging other cells. Unfortunately, the immune system becomes progressively incapable with advancing age, and clearance of senescent cells falters and slows. The burden of senescent cells grows, and their signaling turns from helpful to harmful when sustained constantly, disrupting tissue structure and function.

The heart is one of the least regenerative organs, and also one of the most vital. What limited capacity for regeneration that it does have is diminished with age, in part because of a growing burden of senescent cells. Thus among the many potential uses for senolytic therapies capable of selectively clearing senescent cells from tissues, we might consider treatment to improve outcomes following heart attack, or in a more preventative sense to reverse the harmful remodeling of heart muscle that occurs in response to hypertension, changes in the systemic environment, and narrowed blood vessels.

Targeting Cell Senescence to Improve Cardiac Regeneration

Aging impairs the heart's ability to repair and regenerate. As people age, their cardiac stem cells, i.e. cardiac progenitor cells (CPCs), become senescent, upregulating key markers of senescence, such as p16Ink4a and senescence-associated β-galactosidase, and markers of DNA damage, such phosphorylated histone 2AX. Senescent CPCs also possess critically short telomeres and a senescence-associated secretory phenotype (SASP). Indeed, by the time a person is 75 years old, approximately 50% of their CPCs are senescent. Cardiac progenitor cells from older patients are dysfunctional, showing impaired growth, clonogenicity, and cardiomyogenic differentiation potential. When senescent human CPCs were transplanted into a myocardial-infarcted mouse heart, there was decreased cardiac regeneration and cardiac function compared with when non-senescent CPCs were transplanted.

Next, the effects of senolytics and global senescent cell removal on the aged heart were determined. In this experiment, 24- to 32-month-old wild-type mice were randomly assigned to vehicle or senolytic dasatinib and quercetin (D+Q) treatment, administered in 4 cycles at 3 consecutive days per cycle, with the cycles occurring 12 days apart. P16Ink4a messenger RNA expression decreased in the heart following D+Q treatment in older mice. Morphometric analysis of heart sections showed that D+Q-treated mice had decreased fibrosis and hypertrophy and that senolytic treatment had induced compensatory cardiomyocyte renewal and replacement. An increased number of smaller ventricular 5-ethynyl-2ʹ-deoxyuridine-positive or Ki-67-positive cardiomyocytes were found, suggesting that these mice had cardiomyocytes that were immature and newly formed compared with vehicle-treated mice, which exhibited only rare, small 5-ethynyl-2ʹ-deoxyuridine-positive or Ki-67-positive cardiomyocytes but a greater proportion of hypertrophied myocytes. Finally, D+Q treatment rejuvenated the heart's regenerative potential, activating and increasing the number of CPCs.

The present findings support targeting senescence using senolytics to prevent, delay, and treat multiple age-related heart disorders as well as the toxic and senescence-inducing effects of cancer chemotherapy on the heart. Clinical trials on senolytics are already underway. The Translational Geroscience Network in the United States is conducting 15 clinical studies on senolytics for age-related conditions. They have developed assays for measuring biomarkers in the blood and tissues that can be used to test the efficacy of senolytics in the proposed trials and to identify people who are most likely to benefit from senolytic therapy. Research into understanding how senolytics act on the human heart, in clearing senescent cells, or whether they have any off-target side effects is greatly needed.

The relationship between insulin metabolism and aging is one of the most studied areas of the field, with decades of researchers putting in time to deepen the understanding of the web of interactions surrounding insulin. Yet this has failed to lead to any practical outcome when it comes to slowing or reversing aging. Researchers now have an incrementally better idea as to why obesity, metabolic syndrome, and type 2 diabetes shorten life and worsen health, but that was well understood to be the case well prior to the advent of modern biotechnology.

Experimental studies in animal models of aging such as nematodes, fruit flies, or mice have observed that decreased levels of insulin or insulin signaling promotes longevity. In humans, hyperinsulinemia and concomitant insulin resistance are associated with an elevated risk of age-related diseases suggestive of a shortened healthspan. Age-related disorders include neurodegenerative diseases, hypertension, cardiovascular disease, and type 2 diabetes. High ambient insulin concentrations promote increased lipogenesis and fat storage, heightened protein synthesis, and accumulation of non-functional polypeptides due to limited turnover capacity. Moreover, there is impaired autophagy activity, and less endothelial NO synthase activity. These changes are associated with mitochondrial dysfunction and oxidative stress.

The cellular stress induced by anabolic activity of insulin initiates an adaptive response aiming at maintaining homeostasis, characterized by activation of the transcription factor Nrf2, of AMP activated kinase, and an unfolded protein response. This protective response is more potent in the long-lived human species than in short-lived models of aging research resulting in a stronger pro-aging impact of insulin in nematodes and fruit flies. In humans, resistance to insulin-induced cell stress decreases with age, because of an increase of insulin and insulin resistance levels but less Nrf2 activation. These detrimental changes might be contained by adopting a lifestyle that promotes low insulin/insulin resistance levels and enhances an adaptive response to cellular stress, as observed with dietary restriction or exercise.

Link: https://doi.org/10.3389/fendo.2023.1261298

The gut microbiome appears important to health, as judged by the changes in relative population sizes between species that take place across the course of aging, and the ability of reversing those changes to improve health and extend life in old animals. If the near future is restoration of a more youthful balance of microbial populations in the aged gut microbiome, to produce more beneficial metabolites and reduce inflammation, then the next step after that is to start engineering gut microbes to produce even greater effects. The example here produces poor, sex-specific effects in rats, but it is one example of a thousand different possibilities, many of which will turn out to be far more impressive.

Engineered gut microbiota represents a new frontier in medicine, in part serving as a vehicle for the delivery of therapeutic biologics to treat a range of host conditions. The gut microbiota plays a significant role in blood pressure regulation; thus, manipulation of gut microbiota is a promising avenue for hypertension treatment. In this study, we tested the potential of Lactobacillus paracasei, genetically engineered to produce and deliver human angiotensin converting enzyme 2 (Lacto-hACE2), to regulate blood pressure in a rat model of hypertension with genetic ablation of endogenous Ace2 (Ace2-/- and Ace2-/y).

Our findings reveal a sex-specific reduction in blood pressure in female (Ace2-/-) but not male (Ace2-/y) rats following colonization with the Lacto-hACE2. This beneficial effect of lowering blood pressure was aligned with a specific reduction in colonic angiotensin II, but not renal angiotensin II, suggesting the importance of colonic Ace2 in the regulation of blood pressure. We conclude that this approach of targeting the colon with engineered bacteria for delivery of ACE2 represents a promising new paradigm in the development of antihypertensive therapeutics.

Link: https://doi.org/10.1016/j.phrs.2023.106920

Glia of various sorts are supporting cells in the brain, assisting the function of neurons. Dysfunction and stress in glial cells is nonetheless important. A growing body of evidence suggests that cellular senescence in astrocytes and microglia contribute to age-related neurodegenerative conditions, for example. Further, stress of various forms in these cells may be provoking both inflammation and altered signaling throughout the brain and body. Overly active, pro-inflammatory astrocytes and microglia are implicated in neurodegeneration, even when these cells are not senescent. It isn't clear as to how much of this is a reaction to damage in the environment, such as the presence of protein aggregates, versus harmful changes that are intrinsic to cells, such as altered epigenetics and mitochondrial dysfunction.

In today's open access paper, researchers report on a study of the way in which mitochondrial stress in glial cells can result in signaling to provoke compensatory responses throughout the organism. The study involved nematode worms, a much simpler organism than mammals, but one might expect much of this process to be similar in humans nonetheless. It suggests that novel ways to induce greater cell maintenance in the whole body might start by manipulating astrocytes and microglia. So far, little headway has been made in producing therapies to meaningfully slow aging by boosting cell stress responses. The research community has so far collectively failed to much improve on the effects of exercise in this regard. Is this a limitation of this class of therapy, or do greater gains lie in the future? Time will tell.

Glial-derived mitochondrial signals affect neuronal proteostasis and aging

Historically, much scientific work interrogating the homeostatic roles of the nervous system focused on neurons. While it is clear that glia, the other main cell type of the nervous system, can serve many roles in neuronal development and function, these roles are normally associated with support roles, including regulating cell number, neuronal migration, axon specification and growth, synapse formation and pruning, ion homeostasis, and synaptic plasticity and providing metabolic support for neurons. However, in recent years, it has become increasingly clear that glial health can affect aging and progression of neurodegenerative diseases, like Alzheimer's disease (AD).

For example, expression of apolipoprotein E4 (ApoE4), one of the strongest risk factors for AD, specifically in astrocytes resulted in increased neuronal tau aggregation. Moreover, hyperactivation of the unfolded protein response of the endoplasmic reticulum (UPRER), which drives ER stress resilience, solely in astrocyte-like glial cells resulted in a significant life-span extension in Caenorhabditis elegans. While these studies show the importance of glial function in organismal health, what they lacked is an active function of glia in promoting these beneficial effects.

To uncover an active role for glia in stress signaling and longevity, we aimed to determine whether glial cells can sense mitochondrial stress and initiate an organism-wide response to promote mitochondrial stress resilience and longevity. We used multiple genetic methods to activate the mitochondrial unfolded protein response (UPRMT) in nonneuronal cells, including cell-type-specific application of mitochondrial stress and direct activation of the UPRMT in the absence of stress.

We found that, regardless of method, activation of UPRMT in a small subset of glial cells, the cephalic sheath glia, provided robust organismal benefits, including prolonged life span and increased resistance to oxidative stress. Perhaps most unique in this model is that UPRMT activation in cephalic sheath glia promotes neuronal health by alleviating protein aggregation in neurons of a Huntington's disease (HD) model. Cephalic sheath glia directly communicate with neurons through the release of small clear vesicles (SCVs) and relay the coordination to the periphery via downstream neuronal mechanisms. This glia to neuron signal results in induction of the UPRMT in distal tissues, through a cell nonautonomous mechanism, which is dependent on the canonical UPRMT pathway, yet unexpectedly distinct from paradigms where UPRMT is directly activated in neurons.

Collectively, these results reveal a previously unknown function for cephalic sheath glia in sensing mitochondrial stress, which initiates a signal to promote protein homeostasis in neurons and ultimately prolongs longevity. Therefore, glial cells serve as one of the upstream mediators of mitochondrial stress and its coordination across the entire organism.

A number of vertebrate species exhibit negligible senescence, meaning little to no functional degeneration over the course of their lives. Usually they also exhibit very long life spans for their size, and in comparison to near relative species that do exhibit evident aging. Researchers study these species in order to (a) identify important mechanisms of degenerative aging as targets for further research, as well as to (b) potentially find adjustments to cellular biochemistry that might stop a given mechanism from contributing to aging in our species. The first goal is much more feasible in the near term; it remains to be seen as to whether the second is even plausible to engineer in our lifetimes. A necessary first step in this field of research is to identify which vertebrate species are in fact negligibly senescent. Less is known about life spans and life histories in the wild than one might think, and so one should expect the research community to continue to identify new examples as time goes on.

During the 1910s three buffalofish species (Catostomidae: Ictiobus cyprinellus, I. bubalus, I. niger) were reared in ponds along the Mississippi River. Individuals of these buffalofishes were transported to locations across the United States to support or establish commercial fisheries, including Roosevelt Lake, Arizona in 1918. During the 1930s-1960s a commercial fishery existed on Roosevelt Lake, ending by 1970. Scarce information exists on Arizona buffalofishes since.

From 2018 to 2023 we studied buffalofishes from nearby Apache Lake (adjacent and downstream of Roosevelt Lake) in collaboration with anglers. Here we show that more than 90% of buffalofishes captured from Apache Lake are more than 80 years old and that some of the original buffalofishes from the Arizona stocking in 1918 are likely still alive. Using unique markings on old-age buffalofishes, we demonstrate how individuals are identified and inform dozens of recaptures. With a sample size of only 23 individuals across the three species of buffalofishes at Apache Lake, we found direct evidence of centenarian longevity for black buffalo (108 years), bigmouth buffalo (105 years), and smallmouth buffalo (101 years).

We now know all species of USA Ictiobus can live more than 100 years, making it the only genus of animal besides marine rockfishes (Sebastes) for which three or more species have been shown to live more than 100 years. Our citizen-science collaboration has revealed remarkable longevity for freshwater fishes and has fundamentally redefined our understanding of the genus Ictiobus itself.

Link: https://doi.org/10.1038/s41598-023-44328-8

Inflammatory periodontal disease is caused by a specific bacterial species. The bacteria can use damaged gums to enter the bloodstream. It is thought that its ability to provoke inflammation can then contribute to cardiovascular disease and dementia, though the size of the effect is up for debate. Along these lines, researchers here show that periodontal bacteria can worsen the consequences of a heart attack, impairing the already limited ability of the heart to regenerate and restore function following injury.

Heart attacks occur when blood flow in the coronary arteries is blocked, resulting in an inadequate supply of nutrients and oxygen to the heart muscle, and ultimately death of cardiac myocytes. To prevent this, cardiac myocytes use a process known as autophagy to dispose of damaged cellular components, keeping them from causing cardiac dysfunction. Previous studies have shown that the periodontal pathogen Porphyromonas gingivalis, which has been detected at the site of occlusion in myocardial infarction, can exacerbate post-infarction myocardial fragility. However, the mechanisms underlying this effect remained unknown.

To investigate this, researchers created a version of P. gingivalis that does not express gingipain, its most potent virulence factor, which an earlier study showed can inhibit cells from undergoing programmed cell death in response to injury. They then used this bacterium to infect cardiac myocytes or mice. "The results were very clear. The viability of cells infected with the mutant bacterium lacking gingipain was much higher than that of cells infected with the wild-type bacterium. In addition, the effects of myocardial infarction were significantly more severe in mice infected with wild-type P. gingivalis than in those infected with the mutant P. gingivalis lacking gingipain."

More detailed investigation of this effect showed that gingipain interferes with fusion of two cell components known as autophagosomes and lysosomes, a process that is crucial to autophagy. In mice, this resulted in an increase in the size of cardiac myocytes and accumulation of proteins that would normally be cleared out of the cells to protect the cardiac muscle. "Our findings suggest that infection with P. gingivalis producing gingipain results in excessive autophagosome accumulation, which can lead to cellular dysfunction, cell death, and ultimately cardiac rupture."

Span: https://www.tmd.ac.jp/english/press-release/20230921-1/

Senescent cells accumulate with age throughout the body. While their numbers remain a small fraction of all cells in a tissue, even in late life, senescent cells produce an outsized harm to tissue structure and function via a continual, disruptive, pro-growth, pro-inflammatory signaling, the senescence-associated secretory phenotype (SASP). Researchers have demonstrated, in animal models, that senescent cells directly contribute to the onset and progression of many distinct age-related conditions. Further, it has been shown in animal models that clearing senescent cells throughout the body can rapidly reverse pathology in these conditions.

Degeneration of the vasculature is involved in retinopathies, forms of degenerative blindness. In today's open access review, researchers outline what is known of the way in which senescent cells contribute to the degenerative aging of the retina. That senescent cells are involved offers the prospect of using senolytic therapies to selectively remove these cells and their contribution to the disease state. Sadly, few groups are making use of existing low-cost senolytic small molecules in human clinical trials, so while treatments such as the dasatinib and quercetin combination are known to clear senescent cells in humans to about the same degree as in mice, they are not yet widely used. Scores of age-related conditions might be treated or slowed via this approach, but the focus of the industry is on the production and regulatory approval of new senolytics over the years ahead.

Senescent Cells: Dual Implications on the Retinal Vascular System

As we get older, more cells in healthy tissues become senescent. Senescent cells (SCs) are inactive in terms of reproduction, but extremely active in terms of metabolism and potentially inflame the milieu by producing thousands of bioactive molecules. Growth and development are not possible without the presence of SCs due to the critical role of SCs in a variety of biological processes such as embryogenesis, limb generation, wound healing, host immunity, and tumor suppression. However, due to the proinflammatory entity of senescent cells, their chronic accumulation is associated with a gradual decline in tissue function and age-related disorders.

Diseased blood vessels are a common feature in many eye disorders including retinopathy of prematurity, diabetic retinopathy, and age-related macular degeneration. Mounting recent evidence has discovered the accumulation of senescent neurons and blood vessels in the retina. However, the underlying mechanisms of senescent cell contribution in retinal vasculopathies are not well defined yet. Here, we reviewed dichotomous implications of SCs at the onset and severity of proliferative retinopathies with a specific focus on the retinal vascular system. In a retinal blood vessel, the senescence phenotype in endothelial cells is associated with lower barrier integrity and increased permeability probably due to the impairment of both adherence and tight junctions.

In retinopathies, the hypoxic/oxidative stress induces cellular senescence in retinal neuronal cells that reside predominantly in the avascular zone. The inflammatory secretome of the cell cycle arrested cell boosts and propagates the senescence phenotype to the surrounding tissues in a paracrine and autocrine manner. Dysregulated angiogenesis is another feature of proliferative retinopathies in which SCs play a role. The presence of angiogenic factors, as a part of the SASP secretome, attracts tip cells of retinal blood vessels to the ischemic area and leads to excessive uncontrolled vascularization in the retina. The newly formed blood vessels are leaky, tortuous, and misdirected and do not properly supply the high energy-demanding tissues of the retina and stimulate the senescence phenotype in surrounding retinal cells.

In the retina, it is vital to bear in mind that all implications of SCs are not detrimental. Immune-mediated clearance of senescent endothelial cells at the late stage of proliferative retinopathies promotes regression of the pathological neovascular tufts and prepares the retina for reparative vascular regression. Recruited mechanisms by retinal immune cells for eliminating stressed endothelial cells are comprehensively described in this review. Finally, senolytics and senomorphics are discussed as two main available therapeutic strategies for eliminating retinal SCs in proliferative retinopathies.

Researchers here look at a sizable set of epidemiological data for people in their 70s, and note that the difference in outcomes between healthy and unhealthy lifestyles is sizable. This is much as one might expect from other studies of late life mortality and its relationship with lifestyle choices. It is certainly possible that the next few decades will see the advent of first generation age-slowing and rejuvenation therapies that will add a decade to human life span, but why make it harder to achieve additional years of good health?

Unhealthy lifestyle behaviours such as smoking, high alcohol consumption, poor diet, or low physical activity are associated with morbidity and mortality. Public health guidelines provide recommendations for adherence to these four factors, however, their relationship to the health of older people is less certain. This study involved 11,340 Australian participants (median age 73.9) from the Aspirin in Reducing Events in the Elderly (ASPREE) study, followed for a median of 6.8 years. We investigated whether a point-based lifestyle score based on adherence to guidelines for a healthy diet, physical activity, non-smoking and moderate alcohol consumption was associated with subsequent all-cause and cause-specific mortality.

In multivariable adjusted models, compared to those in the unfavourable lifestyle group, individuals in the moderate lifestyle group (Hazard Ratio 0.73) and favourable lifestyle group (Hazard Ratio 0.68) had lower risk of all-cause mortality. A similar pattern was observed for cardiovascular related mortality and non-cancer/non-cardiovascular related mortality. There was no association of lifestyle with cancer-related mortality. In conclusion, reported adherence to a healthy lifestyle is associated with reduced risk of all-cause and cause-specific mortality. Adherence to all four lifestyle factors resulted in the strongest protection.

Link: https://doi.org/10.1186/s12877-023-04247-9

Prevention is both better than a cure and easier to achieve than a cure. Intervening early, prior to evident clinical symptoms of disease, is always desirable. This is challenging in the case of Alzheimer's disease because (a) there is little access to human brain tissue from people in the early stages of the condition, for ethical and regulatory reasons, and (b) Alzheimer's doesn't naturally occur in mice and other readily available mammalian species, so animal models of Alzheimer's are highly artificial, embodying assumptions about which disease processes are important. In this context, one can only learn from human brains. Here, researchers report on the results of a rare opportunity to study brain tissue samples from patients with early stage Alzheimer's disease.

Most Alzheimer's disease research on human brain tissue has studied postmortem samples, making it difficult for scientists to discern the earliest events in the brain that might have triggered the buildup of plaques and the death of neurons. Knowing the molecular changes in neurons, glia, and other brain cells around plaques during the early phases of the disease could help scientists design treatments that work best when given early.

Researchers have now analyzed an assembly of rare brain tissue samples from 52 living patients with varying degrees of other Alzheimer's-related changes in the brain - including 17 individuals who were later clinically diagnosed with the disease. The brain tissue samples were obtained from normal pressure hydrocephalus (NPH) patients during routine surgeries to reduce excess brain fluid. The scientists identified a suite of changes in cells unique to the early stages of Alzheimer's, including some not seen before in animal studies.

The team discovered a brief hyperactive state in a specific group of neurons that was associated with their death in later stages of the disease, and also increased inflammatory processes in immune cells called microglia as the disease progressed. Neurons are thought to produce the plaque-forming protein called amyloid beta, and the researchers found evidence for this in their data. They also found for the first time that another brain cell type, oligodendrocytes, which produce insulating sheaths around nerve fibers in the brain, may also contribute to plaque formation. A better understanding of how these cells spur the growth of plaques could one day help researchers identify new targets for Alzheimer's drugs.

Link: https://www.broadinstitute.org/news/scientists-reveal-cellular-changes-unique-early-alzheimers-disease

The gut microbiome changes with age, the relative population sizes of the many distinct microbial species altering to provoke chronic inflammation and potentially other, more complex issues driven by changes in the production of beneficial and harmful metabolites. With the advent of ways to cheaply assess the contents of the gut microbiome, researchers are finding that a number of age-related conditions appear characterized by dysbiosis, growth in the population of specific harmful microbial species. One of those conditions is Alzheimer's disease, which has a puzzling incidence that doesn't track well with the well established lifestyle risk factors for inflammatory disease. If it is instead primarily driven by specific alterations to the gut microbiome, that might go some way towards explaining why only some people progress from mild cognitive impairment to Alzheimer's disease.

The study reported in today's research materials is intended to extend existing correlational data in humans to demonstrate whether or not an Alzheimer's-like gut microbiome can produce pathology when introduced into animal models, rats in this case. As such, the usual caveats to apply, in that rodents do not normally develop anything resembling Alzheimer's disease. Nonetheless, it is intriguing to see that Alzheimer's patient microbiomes cause cognitive issues in rats when compared to the effects of a non-Alzheimer's aged human microbiome. The observed effects are likely a matter of a greater induction of chronic inflammation in the rats by the Alzheimer's microbiome, but it is plausible that other microbiome-related mechanisms operate in humans to contribute to the risk of Alzheimer's disease, but not in rats because rats cannot naturally develop Alzheimer's disease. If it were only a matter of risk scaling with chronic inflammation, then being overweight or obese would have a far greater correlation with Alzheimer's disease risk than is actually the case.

Scientists discover links between Alzheimer's disease and gut microbiota

For the first time, researchers have found that Alzheimer's symptoms can be transferred to a healthy young organism via the gut microbiota, confirming its role in the disease. The study shows that that the memory impairments in people with Alzheimer's could be transferred to young rats through transplant of gut microbiota. The study supports the emergence of the gut microbiome as a key target for investigation in Alzheimer's disease due to its particular susceptibility to lifestyle and environmental influences. Alzheimer's patients had a higher abundance of inflammation-promoting bacteria in faecal samples, and these changes were directly associated with their cognitive status.

Microbiota from Alzheimer's patients induce deficits in cognition and hippocampal neurogenesis

To understand the involvement of Alzheimer's patient gut microbiota in host physiology and behaviour, we transplanted faecal microbiota from Alzheimer's patients and age-matched healthy controls into microbiota-depleted young adult rats. We found impairments in behaviours reliant on adult hippocampal neurogenesis, an essential process for certain memory functions and mood, resulting from Alzheimer's patient transplants. Notably, the severity of impairments correlated with clinical cognitive scores in donor patients. Discrete changes in the rat caecal and hippocampal metabolome were also evident. As hippocampal neurogenesis cannot be measured in living humans but is modulated by the circulatory systemic environment, we assessed the impact of the Alzheimer's systemic environment on proxy neurogenesis readouts. Serum from Alzheimer's patients decreased neurogenesis in human cells in vitro and were associated with cognitive scores and key microbial genera.

Our findings reveal for the first time, that Alzheimer's symptoms can be transferred to a healthy young organism via the gut microbiota, confirming a causal role of gut microbiota in Alzheimer's disease, and highlight hippocampal neurogenesis as a converging central cellular process regulating systemic circulatory and gut-mediated factors in Alzheimer's.

Klotho is a longevity-associated protein. More of it extends life span in mice, and higher levels correlate with human health in later life. Klotho improves kidney function in older individuals, and improves cognitive function at any age, but it is far from clear as to which of the many aspects of cellular biochemistry and systemic function affected by klotho are most important in longevity, and how they interact. It may be the case that a reduced level of chronic inflammation is an important effect that helps to improve tissue function throughout the body, but it will take more than a single correlation study to make a compelling case for that to be true.

The alpha-Klotho gene is responsible for encoding a transmembrane protein that is predominantly found in renal tubules. This protein is known as alpha-Klotho and its extracellular domain can be shed to form a soluble variant known as S-Klotho. Studies have shown that S-Klotho has the ability to protect against a range of systemic diseases, such as chronic kidney disease, interstitial lung disease, and cardiovascular events. Furthermore, investigations have demonstrated that S-Klotho plays a pivotal role in modulating oxidative stress, apoptosis, cellular senescence, and endothelial function, positioning it as a promising target in the development of treatments for aging-related diseases. There is a growing body of evidence that suggests a relationship between S-Klotho levels and inflammation. Reduced levels of S-Klotho have been associated with a heightened risk of chronic inflammation, whereas increased levels of Klotho have been shown to possess anti-inflammatory effects.

The Systemic Immune-Inflammation Index (SII) is a measure obtained by dividing the product of neutrophil counts (N) and platelet counts (P) by lymphocyte counts (L). Compared with other inflammatory biomarkers, SII provides a more comprehensive evaluation of the systemic immune-inflammatory status by incorporating multiple components. The objective of this research is to determine the linkage between soluble Klotho (S-Klotho) level and systemic immune-inflammation index (SII).

Eligible participants with complete information of S-Klotho level and SII were selected from the National Health and Nutrition Examination Surveys (NHANES). Subsequently, weighted multivariate linear regression and subgroup analysis were carried out to evaluate the association. Totally, 11,108 adults with complete data on S-Klotho level, SII and other important covariates were included in final analysis. Multivariate liner regression revealed that high level of S-Klotho was associated with low level of SII after multivariate adjustments. When classifying S-Klotho into tertiles, participants in the highest tertile showed a decrease in SII level compared with those in the lowest tertile. The negative associations remained significant regardless of age and gender, and varied depending on smoking status and BMI subgroups.

Link: https://doi.org/10.1186/s12877-023-04349-4

Our biochemistry changes with age in ways that are broadly similar from person to person, occurring due to the same underlying mechanisms of aging. Any sufficiently large set of biological data can in principle be used to find an aging clock, some combination of weighted measures that assesses biological age or chronological age. As an illustration of that point, researchers here use the contents of aqueous humor from the eye to do just that. This approach is unlikely to be widely used, given that clocks based on blood samples or other more easily accessible data work just as well when it comes to determining biological age, but researchers note the possibility of assessing risk or progression of neurodegenerative conditions based on this approach.

To map protein production by different types of cells within the eye, researchers used a high-resolution method to characterize proteins in 120 liquid biopsies taken from the aqueous or vitreous humor of patients undergoing eye surgery. Altogether, they identified 5,953 proteins and were able to trace each protein back to specific cell types.

To investigate the relationship between disease and molecular aging, the researchers built a machine learning model that can predict the molecular age of the eye based on a subset of 26 proteins. The model was able to accurately predict the age of healthy eyes but showed that diseases were associated with significant molecular aging. For diabetic retinopathy, the degree of aging increased with disease progression and this aging was accelerated by as much as 30 years for individuals with severe (proliferative) diabetic retinopathy. These signs of aging were sometimes observable before the patient displayed clinical symptoms of the underlying disease and lingered in patients who had been successfully treated.

The researchers also detected several proteins that are associated with Parkinson's disease. These proteins are usually identified postmortem and current diagnostic methods aren't capable of testing for them, which is one reason Parkinson's diagnoses are so difficult. Screening for these markers in eye fluid could enable earlier diagnosis of Parkinson's disease and later therapeutic monitoring.

Link: https://www.eurekalert.org/news-releases/1004571

Epigenetic clocks to measure biological age are near all based on the analysis of DNA methylation of the nuclear genome. Epigenetic changes to the nuclear genome, such as whether or not a particular CpG site is decorated with a methyl group, adjust gene expression by altering the structure of packaged DNA, hiding or exposing sequences. The genes in exposed sequences can be transcribed into RNA, those in hidden reaches of the genome cannot. Epigenetic marks are in constant flux, driven by the surrounding environment within and outside the cell. Some of these marks are characteristic of age, however, and in some way reflect specific changes in the cell and its environment that tend to occur with aging. Thus it is possible to construct epigenetic clocks, though it remains a topic for discussion and further research as to exactly which processes of aging give rise to which epigenetic changes.

In today's open access paper, researchers report on progress in understanding DNA methylation of the mitochondrial genome. Mitochondria, the power plants of the cell, are the descendants of ancient symbiotic bacteria, and bear a remnant circular genome. Epigenetics works quite differently in a circular genome, but at the high level, the concept is similar: it adjusts expression of genes. The researchers show that, once more accurately measured than has been possible in the past, a common form of DNA methylation of the mitochondrial genome correlates with the age of the individual bearing that mitochondrion, at least in the laboratory species tested.

N6-Methyladenine Progressively Accumulates in Mitochondrial DNA during Aging

During DNA methylation, a methyl group (-CH3) is added to a specific nucleobase, cytosine or adenine, primarily converting the former to 5-methylcytosine (5mC) and the latter to N6-methyladenine (6mA). These modified nucleobases often alter the activity of the affected genetic locus (in general, 5mC represses, while 6mA promotes, gene expression), and the new DNA methylation pattern can be inherited by daughter cells and offspring for certain generations. Efforts to understand the relationship between 5mC and aging have reached such an advanced stage in the last 10 years that several research groups have managed to set up a so-called epigenetic clock to estimate an individual's age based on CpG methylation distributions in the genome. Although relatively good results have been obtained by predicting biological age from 5-cytosine methylation, the method still relies on a genome-wide methylation profile for which the 5mC pattern of the whole genome or at least significant parts of the genome has to be revealed, and this makes the method cumbersome, costly and slow.

DNA methylation at the N6 position of adenine is the other major type of epigenetic modification, which has been widely recognized in bacteria and plants. A few years ago, DNA 6mA modification was also identified in the genome of a diverse range of animal taxa ranging from worms to mammals. Furthermore, the presence of 6mA was recently detected in mammalian mitochondrial DNA (mtDNA). The mitochondrion, a membrane-bound, energy-converting organelle of eukaryotic cells, is known to be involved in the regulation of the aging process across a wide variety of animal species; Caenorhabditis elegans (nematode), Drosophila melanogaster (insect) and mouse (mammalian) strains with decreased mitochondrial activity exhibit a long-lived phenotype.

Because there is a strong association between the epigenetic modifications of genomic DNA and biological age, epigenetic modifications in the mitochondrial genome may be similarly related to the age of the organism, but this has not yet been investigated and explored. In this study, we present a novel, reliable, PCR-based (i.e., sequence-specific) 6mA detection method that is free of technological artifacts and show in several genetic models that relative 6mA levels at different mtDNA sites (these levels actually show that how many percent of the individual mitochondrial genomes present in a given tissue sample are methylated at a selected adenine nucleobase) are significantly related to the age of the organism. Thus, N6-adenine methylation is an inherent process in the organization of mitochondrial genomes too.

These results suggest that the widely observed age-related decline in mitochondrial function is strongly associated with changing 6mA levels and that biological age can be accurately determined from 6mA levels at certain mtDNA sites in a reliable, fast and cost-effective way. Furthermore, we reveal the enzymatic pathways of the mtDNA N6-adenine methylation and demethylation processes in C. elegans and Drosophila, showing the involvement of DNA N6-adenine methyltransferases and N6-methyladenine demethylases mediating 6mA metabolism in the nuclear genome. Together, these results suggest a fundamental role for mtDNA N6-adenine methylation in aging and reveal an efficient diagnostic technique to determine age using DNA.

Average telomere length measured in immune cells from a blood sample is a terrible measure of biological age. Trends only appear in large study populations, and the measure can move up and down with transient changes in health, such as infections. It is as much a measure of momentary pressure on the immune system and increased immune cell replication as it is a measure of longer term trends in health due to underlying mechanisms of aging. Still, while much of the world has moved on to epigenetic clocks, some groups still insist on using telomere length in their studies of the pace of aging. In large study populations, one would expect to see good lifestyle choices correlating with a slower erosion of telomeres, as occurs here.

Telomere length is a good index of cellular aging. Longer telomeres are predictive of longer life, and healthy lifestyles are associated with longer telomeres. This study explored the relationship between time spent jogging or running each week and leukocyte telomere length (LTL) in 4,458 randomly selected U.S. adults. The association was studied using data collected by the National Health and Nutrition Examination Survey (NHANES), and a cross-sectional design. Total weekly jog/run time was calculated from survey responses. From the minute totals, three categories were formed: <10 minutes/week, 10-74 minuntes/week, and ≥75 minutes/week. Adults in the third category met the U.S. guidelines.

Data were analyzed using one-way ANOVA. Partial correlation was used to adjust for differences in potential mediating factors, including demographic and lifestyle/medical factors. In the total sample, after adjusting for all the potential covariates, mean LTL significantly differed across the three jog/run categories. Specifically, adults who met the guidelines via jogging and/or running had significantly longer telomeres than adults who performed no jogging/running. Adults in the middle category did not differ from the other two categories. A minimum of 75 minutes of jogging/running weekly is predictive of longer telomeres when compared to adults who do not jog or run regularly.

Link: https://doi.org/10.3390/ijerph20196872

It is the nature of regulators at the FDA to aim for zero risk at any cost, and this is particularly apparent in the case of preventative therapies intended to be deployed widely in comparatively healthy people. Absent unusual political pressure, any number of ongoing deaths while therapies are assessed is treated as an acceptable cost to avoid even small numbers of deaths that may occur due to use of a new therapy. Thus even after aging is recognized as a medical condition by regulators, it is likely that they will make it too expensive to assess potential therapies. Instead, companies will gain clinical approval for treatment of specific age-related conditions, and widespread off-label use will become a political battle, clinics and physicians versus regulators. The result of this will be the usual consequence of heavy regulation: a dramatic slowing of progress, and increased cost to patients.

There is a major challenge for discovering and developing anti-aging drugs. How does one design a clinical trial to convince patients, physicians, payers and, especially, the FDA that a drug actually works? To do this, a company would have to prove that its drug extends lives. You can't test such a drug in young or even middle-aged people, as these groups still have considerable life left - assuming a life expectancy of 80 years. Thus, you would probably need to study the drug in healthy 70-year-olds (with a placebo control group as comparator) and then follow these subjects for a decade or more to see if those on the drug live meaningfully longer than those in the placebo group. In order to see a statistically meaningful longevity effect, however, the study would need a minimum of 20,000 subjects. This "outcomes" trial would be similar to what is now done for new drugs to treat heart disease, in which a drug's efficacy is determined by whether it reduced heart attacks and strokes. Such studies are not cheap. The costs can be on the order of $2 billion.

The FDA would likely set a very high bar for safety and efficacy for such a study. Unlike studying patients with heart disease, here you would be testing your drug on 70-year-olds who are relatively healthy. Yet, these patients are entering a decade when they become more susceptible to various cancers, neurological disorders, cardiovascular diseases, etc. You would have to be certain that your drug was no different from placebo when studying these safety parameters. The FDA's caution would be well justified. Such a drug would be in tremendous demand should it actually work. Should such a drug be approved and then later shown to increase major side effects, the fallout would be unprecedented.

Given these enormous challenges, why would anyone actually engage in research and development to produce anti-aging drugs? After all, the people investing in these field are accomplished scientists and investors. They are aware of these challenges. Despite the hype around extending the human life span by 10 to 20 years, these companies will not look to conduct life extension studies right out of the gate. Rather, the first drugs will be tested against age-related diseases.

Link: https://www.forbes.com/sites/johnlamattina/2023/10/17/companies-seek-to-increase-life-span-by-a-decade-or-more/

Duplication of a genetic sequence is a common occurrence over evolutionary time, one of the mechanisms by which species evolve. Noteworthy duplications include the many versions of cancer suppressor gene TP53 that are observed in the elephant genome. Large animals have many more cells than small animals, and so the evolution of greater size must be accompanied by the evolution of ways to greatly reduce cancer risk per cell.

Researchers here report on the results of searching for specific gene duplications in mammalian species that correlate with species longevity. This provides starting points for further study of the mechanisms that determine sizable differences in mammalian life spans, at present a poorly understood area of biochemistry. Whether or not such mechanisms can provide a basis for therapies to slow or reverse degenerative aging in humans in the near term of the next few decades remains a question mark.

Duplications of human longevity-associated genes across placental mammals

Natural selection has shaped a wide range of lifespans across mammals, with a few long-lived species showing negligible signs of ageing. Approaches used to elucidate the genetic mechanisms underlying mammalian longevity usually involve phylogenetic selection tests on candidate genes, detections of convergent amino acid changes in long-lived lineages, analyses of differential gene expression between age cohorts or species, and measurements of age-related epigenetic changes. However, the link between gene duplication and evolution of mammalian longevity has not been widely investigated.

Here, we explored the association between gene duplication and mammalian lifespan by analysing 287 human longevity-associated genes across 37 placental mammals. We estimated that the expansion rate of these genes is eight times higher than their contraction rate across these 37 species. Using phylogenetic approaches, we identified 43 genes whose duplication levels are significantly correlated with longevity quotients. In particular, the strong correlation observed for four genes (CREBBP, PIK3R1, HELLS, FOXM1) appears to be driven mainly by their high duplication levels in two ageing extremists, the naked mole rat (Heterocephalus glaber) and the greater mouse-eared bat (Myotis myotis). Further sequence and expression analyses suggest that the gene PIK3R1 may have undergone a convergent duplication event, whereby the similar region of its coding sequence was independently duplicated multiple times in both of these long-lived species.

Collectively, this study identified several candidate genes whose duplications may underlie the extreme longevity in mammals, and highlighted the potential role of gene duplication in the evolution of mammalian long lifespans.

Why are most Alzheimer's disease patients women? The longer female life expectancy is not enough to explain all of this difference, so researchers investigate the underlying biochemical differences between sexes in search of an explanation. The goal is to use this difference in outcomes to identify mechanisms that are important to disease progression in all humans. One might look at a recent paper on microglial biochemistry, for example, and compare with this examination of the activity of cholinergic neurons. It is worth noting that the two are linked, with cholinergic neurons likely regulating microglial behavior to some degree.

Several studies in mouse models of Alzheimer's disease (AD) and in cognitively normal older adults at risk for AD have consistently pointed to the selective vulnerability of cholinergic neurons to amyloid pathology as an early and critical component of presymptomatic disease which predicts subsequent neurodegenerative progression. Indeed, basal forebrain cholinergic neurons dysfunction and degeneration are early pathological events in AD that precede and predict cortical degeneration, clinical onset, and dementia severity.

There is also a close relationship between early dysfunctions in cholinergic signaling and amyloid β (Aβ) pathology. Decreased cholinergic signaling is associated with increased Aβ levels in the brain of mouse models and human patients. Furthermore, Aβ reduces acetylcholine (ACh) synthesis and release both in vitro and in vivo. Given that the brain cholinergic system of males and females show subtle functional differences and that sex hormones exert trophic effects on the cholinergic system, we hypothesized that biological sex may causally influence the relationship between cholinergic tone and amyloid pathology.

We quantified amyloid beta (Aβ) in male and female App-mutant mice with either decreased or increased cholinergic tone and examined the impact of ovariectomy and estradiol replacement in this relationship. We also investigated longitudinal changes in basal forebrain cholinergic function and Aβ in elderly individuals. We show a causal relationship between cholinergic tone and amyloid pathology in males and ovariectomized female mice, which is decoupled in ovary-intact and ovariectomized females receiving estradiol. In elderly humans, cholinergic loss exacerbates Aβ. Our findings emphasize the importance of reflecting human menopause in mouse models. They also support a role for therapies targeting estradiol and cholinergic signaling to reduce Aβ.

Link: https://doi.org/10.1002/alz.13481

Some parts of the brain appear to be operating beneath their capacity while provided with the baseline, resting supply of nutrients from the bloodstream. Exercise produces short-term gains in cognitive function, perhaps in a very direct way by increasing cerebral blood flow and thus the capacity of neurons for activity. Researchers here provide evidence for even comparatively modest activity to have this effect in older people, though interestingly some of the candidate signal molecules thought to mediate these effects did not appear to be involved.

The global burden of age-related cognitive decline is increasing, with the number of people aged 60 and over expected to double by 2050. This study compares the acute effects of age-appropriate cognitively demanding aerobic exercises involving walking, on cognitive functions and exerkine responses such as brain-derived neurotrophic factor (BDNF) and cathepsin B (CTSB) in older, healthy adults. Healthy older golfers (n=25, 16 male and 9 female, 69±4 years) were enrolled in a 5-day randomised cross-over study and completed three different exercise trials (18-hole golf round, 6 km Nordic walking, 6 km walking) in a real-life environment, in random order and at a self-selected pace. Differences in cognition (the Trail-Making Test (TMT) AB) and exerkines (BDNF and CTSB) were analysed within groups and between groups.

All exercise types resulted in a significant decrease in the TMT A-test (golf: -4.43±1.5 s, Nordic walking: -4.63±1.6 s, walking: -6.75±2.26 s), where Nordic walking and walking demonstrated a decrease in the TMT B-test (Nordic walking: -9.62±7.2 s, walking: -7.55±3.2 s). In addition, all exercise types produced significant decreases in the TMT AB test scores, and Nordic walking showed decreases in the TMTB-TMTA-test. There were no immediate postexercise changes in the levels of BDNF or CTSB.

Acute bouts of golf, Nordic walking and walking improved cognitive functions irrespective of exerkines in healthy older adults. In addition, Nordic walking and walking in general enhanced executive functions. No significant effects were seen on the levels of BDNF and CTSB.

Link: https://doi.org/10.1136/bmjsem-2023-001629

Galectin-3 is very broadly expressed in the body, but its connection to immune function leads to raised levels of galectin-3 in the bloodstream of patients suffering from any one of a number of inflammatory conditions that are associated with obesity, aging, or both. Consider nonalcoholic steatohepatitis (NASH), for example, where some groups are trying to inhibit galectin-3 or its interactions in order to treat the condition. It isn't clear as to where exactly galactin-3 lies in the complex web of cause and effect taking place in the liver in this condition - the only way to find out is to inhibit it and see what happens.

Frailty is an age-related condition strongly associated with chronic inflammation. In today's open access paper, researchers show that is also associated with raised galectin-3 levels. As for NASH, it is unclear as to whether galectin-3 could be targeted to reduce the burden of inflammation and dysfunction in patients with frailty, or whether it is too far downstream in the web of cause and consequence to be useful in any way other than as a marker of risk and severity.

High blood galectin-3 level associated with risk of frailty in aging

Galectin-3 (Gal-3, also known as Mac-2), a β-galactoside binding lectin, is widely expressed in human tissues, including all types of immune cells, epithelial cells, endothelial cells, stem cells, and sensory neurons. Furthermore, it is highly expressed and secreted by macrophages. As a specific regulator of many biological systems, Gal-3 is highly promiscuous and localized within the tissue micro-environment, including extracellular, cytoplasmic, and nuclear. The different locations of Gal-3 contribute to its various functions.

Secreted Gal-3 is pivotal in numerous biological activities including cell growth, differentiation, transformation, apoptosis, angiogenesis, inflammation, fibrosis, and host defense. Also, it is able to cross-link surface glycoproteins and stimulate important pathways involved in the innate immune response such as the oxidative burst in neutrophils, alternative macrophage (M2) activation, and mast-cell degranulation.

Previous studies have reported that elevated blood Gal-3 level in humans was related to exacerbating disease in inflammatory, metabolic, and malignant diseases. Elevated serum Gal-3 levels have been detected in almost all types of cardiovascular disease. However, little is known about the function of Gal-3 in frailty. Moreover, the physiological relevance of whole-blood Gal-3 to predict aging-associated conditions clearly needs further investigation. Thus, monitoring circulating Gal-3 levels in humans could help us understand the mechanism of aging and frailty, leading the way to finding potential treatments.

A chronic state of low-grade inflammation, accompanied by a dysregulation of the inflammatory cytokine network, has been indicated as a major driver of age-associated conditions. A previous study also proposed that the association of inflammatory factors such as C-reactive protein (CRP), interleukin (IL)-6, tumor necrosis factor (TNF)-α, and IL-10 levels with frailty may reflect the phenotype of inflammaging. Hence, we speculated that the association of frailty and Gal-3 might also be mediated by inflammatory cytokine networks.

Nevertheless, up to now, there is very limited evidence on the frailty status in human Gal-3-related studies. In this study, we aimed to address the change of Gal-3 levels in human whole blood with frailty. We performed serum biochemical and peripheral blood mononuclear cells (PBMC) microarray analyses in humans to determine the secretory phenotype characteristics of frailty. Furthermore, we used the frail mouse model to study the significantly altered behavioral phenotype and associated secreted Gal-3 levels in blood samples to reveal the Gal-3-dependent inflammatory dysregulation of frailty.

Klotho is a longevity-associated protein; more of it produces life extension in mice, while less of it shortens life span. Separately, why does increased expression of circulating klotho protein produce cognitive benefits? Klotho appears to operate functionally in the kidney, given what is known of the protein, and there has been some thought that it is kidney function that is important to the effects of klotho on tissues elsewhere in the body, that protecting the kidney from age-related decline will naturally improve function everywhere else. However, that doesn't explain why klotho can increase cognitive function in young mice; that strongly suggests that there must be effects on cells in the brain.

Klotho is an antiaging protein, and its levels decline with age and chronic stress. The exogenous administration of Klotho can enhance cognitive performance in mice and negatively modulate the Insulin/IGF1/PI3K/AKT pathway in terms of metabolism. In humans, insulin sensitivity is a hallmark of healthy longevity. Therefore, this study aimed to determine if exogenous Klotho, when added to neuronal and astrocytic cell cultures, could reduce the phosphorylation levels of certain insulin signaling effectors and enhance antioxidant strategies in these cells.

Primary cell cultures of cortical astrocytes and neurons from mice were exposed to 1 nM Klotho for 24 hours, with or without glucose. Klotho decreased phosphorylated AKT and mTOR levels. However, in astrocytes, Klotho increased FOXO-3a activity and catalase levels, shielding them from intermediate oxidative stress. In neurons, Klotho did not alter FOXO-3 phosphorylation levels but increased proteasome activity, maintaining lower levels of PFKFB3. This study offers new insights into the roles of Klotho in regulating energy metabolism and the redox state in the brain.

Link: https://doi.org/10.1038/s41598-023-41166-6

Senescent cells accumulate with age to cause harm via their pro-inflammatory secretions. Senolytic therapies can selectively destroy these cells, to benefit the patient quite rapidly. Hypothesized harms that might be caused by senolytics generally revolve around the idea that some senescent cells might be structurally useful and hard to replace, so while having those senescent cells is bad, getting rid of them could be worse. The response to these concerns is to point to the mouse studies, in which no such problems appear to occur. The article here is a lengthy examination of this sort of argument of hypothetical concern versus actual mouse data in the specific case of muscle tissue.

Skeletal muscles are organized into long fibers composed of many nuclei, and when a fiber is damaged, the entire fiber is often lost. It seems that if any one of these nuclei were in a senescent state and were hit by a senolytic therapy, it might result in a fiber break and pull down the entire muscle fiber with it. And muscle fibers aren't easily replaced, and loss of muscle mass and function is already a major problem in aging, so the drug-induced destruction of muscle fibers could accelerate an aging person's slide into disability. Is this a real risk, and if so, does it make senolytic therapies a non-starter?

That's a worrying scenario for those of us who are excited by the promise of senolytic therapies. Fortunately, all the animal data refute it. When we get to the bottom-line question of what senolytic treatment did to the mass and function of muscle in old mice, we see good news all around. Not only did the senolytic-treated old mice not lose muscle, the treated animals actually sustained or restored the distribution of their muscle fiber sizes to the same distribution seen in young mice. Senolytic-treated mice also either gained more strength or suffered less age-related loss of strength than the untreated aging animals, leaving their muscle power partway between that of old and young untreated mice. And senolytic treatment also reduced the amount of dysfunctional repair activity in their muscles.

Link: https://www.sens.org/senolytics-muscle-cure-worse-than-disease/

Human life expectancy has been trending upwards, slowly, for a very long time. Life expectancy at birth is influenced by a great many factors that have little to do with aging, and so is much less interesting than, say, life expectancy at 60. At present, that number increases by one year with every passing decade. This has been the case in an environment in which essentially nothing was being done to deliberately target underlying mechanisms of aging. The trend is an incidental side-effect of, most likely, (a) better life-long control over the burden of infectious disease, and (b) general improvements in the ability to treat age-related conditions without addressing their deeper causes, the mechanisms of aging.

The outcome of a modest slowing of aging across the life span coupled with better medicines for age-related diseases that fail to target mechanisms of aging is the situation that we find ourselves in, in which all three of (a) time spent in health, (b) time spent in ill health, and (c) overall life span are increasing over time. Near all of the furor over the burden of healthcare spending in overly centralized medical systems derives from the increase in time spent in ill health. It is expensive and difficult to keep someone going when the therapies to hand do not address the actual causes of ill health, meaning the specific forms of cell and tissue damage that cause aging.

All of this will change dramatically with the advent of rejuvenation therapies that deliberately target that underlying cell and tissue damage. The point of the exercise is to both greatly extend time spent in health and make it possible to take people in late-life disease states and fix their issues, restoring them to health. This won't happen overnight, it will be an incremental progression of ever better partial successes that add up over time, but it will happen.

Long-term Trends in Healthy and Unhealthy Life Expectancy Among Adults Aged 60 - A Global Perspective, 1990-2019

Although life expectancy has been a crucial health population metric, distinguishing between "healthy" and "unhealthy" years lived gains heightened significance, particularly in the face of medical advancements that prolong life. Despite extensive research on life expectancy and healthy life expectancy (HALE), a noticeable gap prevails in concurrent investigations of healthy and unhealthy life expectancies in the older demographic.

Using data derived from the Global Burden of Disease Study 2019 (GBD 2019), our research provides an in-depth analysis of global trends in these three metrics from 1990 to 2019 for older adults. For the study, Life Expectancy at age 60 (LE-60), constructed based on age-specific mortality rates from all locations and estimations years across all populations by sex, and the HALE at age 60 (HALE-60) were employed to assess "healthy" years. Proportion of Years in Ill Health at age 60 (PYIH-60), meaning (LE-60 - HALE-60) / LE-60, has been used to calculate the "unhealthy" years proportion in life expectancy.

The study yields several critical observations. First, the disparity between global life expectancy, which has been on a steady rise, and HALE, suggests a prolonged period of morbidity or disability for older adults. This emphasizes the need for health systems to shift focus from extending life to prioritizing quality of the extended years. Unlike unhealthy life expectancy, augmenting the health life expectancy of a population results in higher per capita output levels and improved labor productivity. This also allows for the reduction of social and medical security costs for older adults. Future research assessing the impact of specific.

Attention must also be paid to regional variations. The swift increase in life expectancy in regions like South Asia and East Asia may be attributed to economic growth, enhancements in healthcare infrastructure, and successful public health interventions. Yet, the concurrent enlargement of unhealthy life expectancy in certain regions underlines the urgency for interventions targeted at addressing health challenges unique to specific regions. The significant increase in China's life expectancy warrants special attention. This progress may be attributed to the country's strategic health reforms, economic growth, and public health initiatives. However, the rise in PYIH-60 among older adults in China indicates an area of concern, suggesting potential areas for targeted healthcare interventions and policy implementation.

The correlation between HALE-60 and various sociodemographic and health system indicators illuminates the interaction between social determinants and health outcomes. The observed positive relationship, showing that an increase in sociodemographic index (SDI), universal health coverage (UHC), healthcare access and quality index (HAQ), and healthcare expenditure leads to an improvement in HALE-60, suggests that comprehensive socio-economic development paired with accessible, high-quality healthcare yields measurable benefits for the aging population.

First generation stem cell therapies, in which cells near entirely die following transplantation, cause benefits via changes in native cell behavior resulting from the signaling produced by the transplanted cells. Much of cell signaling is carried in extracellular vesicles, membrane-bound packages of various molecules. The types, contents, and circumstances of creation of extracellular vesicles are not fully understood, a work in progress. Harvesting these vesicles from specific cell types known to be beneficial when transplanted is a way to circumvent this lack of knowledge in the near term.

Degenerative bone disorders, encompassing conditions such as intervertebral disc degeneration (IVDD), osteoarthritis (OA), and osteoporosis (OP), exert a profound impact on the well-being of individuals. In recent years, the landscape of regenerative medicine has been transformed by the emergence of stem cell-derived extracellular vesicles (EVs) therapies, presenting a promising approach for improving degenerative bone disorders.

These diminutive yet potent membrane-enclosed vesicles, released by stem cells, have emerged as the effective factors responsible for the regenerative outcomes witnessed in stem cell therapies. With their bioactive cargo, these EVs derived from stem cells release a complex of regenerative signals, directing a coordinated interaction within the complicated microenvironment of deteriorating bone. This captivating phenomenon has captured the attention of both researchers and clinicians, as stem cell-derived EVs show their remarkable potential in reshaping the landscape of regenerative medicine.

By harnessing the inherent regenerative attributes of stem cells and utilizing the distinctive cargo encapsulated within their secreted EVs, researchers, and clinicians aspire to surmount the constraints frequently linked to conventional therapeutic modalities. In contrast to conventional methods primarily centered on symptom management, this pioneering strategy aims to exploit the innate healing potential of the human body. In this extensive review, we perform an intriguing exploration to investigate the captivating domain of therapies involving EVs derived from stem cells, with a particular emphasis on their prospective applications in revitalizing degenerated bone tissues.

Link: https://doi.org/10.2147/IJN.S424731

The practice of calorie restriction is known to improve health in many ways. Researchers continue to perform analyses on the samples taken from the human CALERIE study that was conducted some years ago, in which comparatively mild calorie restriction produced worthwhile results in the study participants. Here, researchers note improvements in markers of muscle quality, as one might expect given the animal studies of calorie restriction in which similar improvements were observed in skeletal muscle.

The lifespan extension induced by 40% caloric restriction (CR) in rodents is accompanied by postponement of disease, preservation of function, and increased stress resistance. Whether CR elicits the same physiological and molecular responses in humans remains mostly unexplored. In the CALERIE study, 12% CR for 2 years in healthy humans induced minor losses of muscle mass (leg lean mass) without changes of muscle strength, but mechanisms for muscle quality preservation remained unclear.

We performed high-depth RNA-Seq (387-618 million paired reads) on human vastus lateralis muscle biopsies collected from the CALERIE participants at baseline, 12- and 24-month follow-up from the 90 CALERIE participants randomized to CR and "ad libitum" control. Using linear mixed effect model, we identified protein-coding genes and splicing variants whose expression was significantly changed in the CR group compared to controls, including genes related to proteostasis, circadian rhythm regulation, DNA repair, mitochondrial biogenesis, mRNA processing/splicing, FOXO3 metabolism, apoptosis, and inflammation.

Changes in some of these biological pathways mediated part of the positive effect of CR on muscle quality. Differentially expressed splicing variants were associated with change in pathways shown to be affected by CR in model organisms. Two years of sustained CR in humans positively affected skeletal muscle quality, and impacted gene expression and splicing profiles of biological pathways affected by CR in model organisms, suggesting that attainable levels of CR in a lifestyle intervention can benefit muscle health in humans.

Link: https://doi.org/10.1111/acel.13963

T cells engineered to express a chimeric antigen receptor (CAR) aggressively attack other cells bearing surface markers that match that receptor. This approach is expensive, as it requires engineering cells taken from a patient, and developing CARs specific to each cancer subtype, but has so far proven effective against a number of forms of cancer. Not all cancers are consistent in markers expressed by cancer cells, however, and many cancers exhibit rapid evolution of tumor cell characteristics - only a marginal slowing of progress is achieved when much of the cancer can quickly become immune to a therapeutic approach.

In today's research materials, scientist report on an interesting and novel way to make CAR-T therapies both more effective and logistically efficient. The researchers used engineered, tumor-seeking bacteria to introduce consistency into the markers found on cancerous cells, allowing engineered immune cells to more efficiently destroy tumor tissue. Targeting different cancers then becomes a matter of picking the right bacterial species to engineer, most of which are quite capable of seeking out many different types of cancer, as well as adapting to the evolution of a tumor, rather than having to develop new CARs.

Engineered Bacteria Paint Targets on Tumors for Cancer-killing T Cells to See

For several years, researchers have been successfully using chimeric antigen receptor (CAR) T cells to target specific antigens found on blood cells as a cure for patients with leukemia and lymphoma. But solid tumors, like breast and colon cancers, have proven to be more difficult to home in on. Solid tumors contain a mix of cells that display different antigens on their surface - often shared with healthy cells in the body. Thus, identifying a consistent and safe target has impeded the success of most CAR-T cell therapy for solid tumors at the first phase of development.

Researchers have now engineered tumor-colonizing bacteria (probiotics) to produce synthetic targets in tumors that direct CAR-T cells to destroy the newly highlighted cancer cells. "Traditional CAR-T therapies have relied on targeting natural tumor antigens. This is the first example of pairing engineered T cells with engineered bacteria to deliver synthetic antigens safely, systemically, and effectively to solid tumors. This could have a significant impact on the treatment of many cancers."

This probiotic-guided CAR-T cell (ProCAR) platform is the first time that scientists have not only successfully combined engineered probiotics with CAR-T cells, but have also demonstrated the first evidence of CARs responding to synthetic antigens produced directly within the tumor. "Combining the advantages of tumor-homing bacteria and CAR-T cells provides a new strategy for tumor recognition, and this builds the foundation for engineered communities of living therapies. We chose to bridge the individual limitations of these two cell therapies by combining the best features of each - using bacteria to place the targets, and T cells to destroy the malignant cells."

Probiotic-guided CAR-T cells for solid tumor targeting

A major challenge facing tumor-antigen targeting therapies such as chimeric antigen receptor (CAR)-T cells is the identification of suitable targets that are specifically and uniformly expressed on heterogeneous solid tumors. By contrast, certain species of bacteria selectively colonize immune-privileged tumor cores and can be engineered as antigen-independent platforms for therapeutic delivery.

To bridge these approaches, we developed a platform of probiotic-guided CAR-T cells (ProCARs), in which tumor-colonizing probiotics release synthetic targets that label tumor tissue for CAR-mediated lysis in situ. This system demonstrated CAR-T cell activation and antigen-agnostic cell lysis that was safe and effective in multiple xenograft and syngeneic models of human and mouse cancers. We further engineered multifunctional probiotics that co-release chemokines to enhance CAR-T cell recruitment and therapeutic response.

Aggrephagy is a comparatively poorly understood cell maintenance mechanism that targets aggregated proteins, distinct from the ubiquitin-proteasome system that disposes of misfolded or otherwise problematic proteins. Alterations to protein structure break the proper function of the protein, and damaged machinery causes problems to a cell. Protein aggregation is a feature of neurodegenerative conditions, and scientists are in search of ways to encourage cells to more rapidly and efficiently remove these aggregates before they accumulate to pathological levels.

The ubiquitin-proteasome system (UPS) and autophagy are the two primary cellular pathways of misfolded or damaged protein degradation that maintain cellular proteostasis. When the proteasome is dysfunctional, cells compensate for impaired protein clearance by activating aggrephagy, a type of selective autophagy, to eliminate ubiquitinated protein aggregates; however, the molecular mechanisms by which impaired proteasome function activates aggrephagy remain poorly understood.

Here, we demonstrate that activation of aggrephagy is transcriptionally induced by the transcription factor NRF1 in response to proteasome dysfunction. Although NRF1 has been previously shown to induce the expression of proteasome genes after proteasome inhibition (i.e., the proteasome bounce-back response), our genome-wide transcriptome analyses identified autophagy-related p62 and GABARAPL1 as genes directly targeted by NRF1. Intriguingly, NRF1 was also found to be indispensable for the formation of p62-positive puncta and their colocalization with ULK1 and TBK1, which play roles in p62 activation via phosphorylation. Consistently, NRF1 knockdown substantially reduced the phosphorylation rate of p62.

Finally, NRF1 selectively upregulated the expression of GABARAPL1, an ATG8 family gene, to induce the clearance of ubiquitinated proteins. Our findings highlight the discovery of an activation mechanism underlying NRF1-mediated aggrephagy through gene regulation when proteasome activity is impaired.

Link: https://doi.org/10.1038/s41598-023-41492-9

The presence of lingering senescent cells characteristic of aged tissues is harmful due to the pro-inflammatory signaling produced by these cells, the senescence-associated secretory phenotype (SASP). Researchers here show that mitochondrial stress leading to mislocalization of mitochondrial DNA and a consequent inflammatory response is important in the generation of the SASP. Mammalian cells have evolved an innate immune response to the presence of foreign DNA, but mitochondrial DNA is sufficiently bacteria-like that it can trigger this response. Thus the mitochondrial stress and dysfunction that takes place in aged tissues can provoke some fraction of the chronic inflammation of aging. This process appears to be particularly pronounced in senescent cells.

Senescent cells drive age-related tissue dysfunction partially through the induction of a chronic senescence-associated secretory phenotype (SASP). Mitochondria are major regulators of the SASP; however, the underlying mechanisms have not been elucidated.

Mitochondria are often essential for apoptosis, a cell fate distinct from cellular senescence. During apoptosis, widespread mitochondrial outer membrane permeabilization (MOMP) commits a cell to die. Here we find that MOMP occurring in a subset of mitochondria is a feature of cellular senescence. This process, called minority MOMP (miMOMP), requires BAX and BAK macropores enabling the release of mitochondrial DNA (mtDNA) into the cytosol. Cytosolic mtDNA in turn activates the cGAS-STING pathway, a major regulator of the SASP.

We find that inhibition of MOMP in vivo decreases inflammatory markers and improves healthspan in aged mice. Our results reveal that apoptosis and senescence are regulated by similar mitochondria-dependent mechanisms and that sublethal mitochondrial apoptotic stress is a major driver of the SASP. We provide proof-of-concept that inhibition of miMOMP-induced inflammation may be a therapeutic route to improve healthspan.

Link: https://doi.org/10.1038/s41586-023-06621-4

A small number of the thousands of different proteins in the body are capable of misfolding in ways that encourage other molecules of the same protein to misfold in the same way. These misfolded proteins spread, multiply, and form solid aggregates. The surrounding halo of altered biochemistry that attends these aggregates is harmful to cells, leading to dysfunction, inflammation, and even cell death. Many neurodegenerative conditions involve protein aggregation, of amyloid-β, α-synuclein, and tau, among others. Aggregation of misfolded transthyretin, meanwhile, contributes to cardiovascular disease and other conditions.

The dominant therapeutic approach for most of the protein aggregates in the brain is clearance via immunotherapy. For transthyretin, the research and development community has focused on use of small molecules that inhibit the misfolding and aggregation process, allowing cellular quality control mechanisms to catch up with the task of degrading aggregates. This inhibition approach could be applied to other protein aggregates as well, as illustrated by today's research materials focused on α-synuclein.

"Anti-tangle" molecule could aid search for new dementia treatments

Alpha-synuclein, a protein found in brain cells, is commonly associated with neurodegenerative diseases such as Parkinson's, a debilitating neurological disorder affecting millions worldwide. In healthy individuals, alpha-synuclein interacts with cell membranes where it plays a role in how brain cells (neurons) communicate with each other, but as a person ages, the 3D shape of the protein can malform, or "misfold", causing it to start sticking together to form toxic clumps in the brain. Over time these clumps continue to stack, forming fibres that can interfere with the protein's normal role, eventually killing brain cells, contributing to the development of Parkinson's and related dementia diseases.

A team of scientists took a protein fragment, or peptide, from one end of the alpha-synuclein protein strand and mixed it with samples of the full-length alpha-synuclein protein. They found that the fragment prevented misfolding in vitro, by stabilising its normal structure to prevent it from tangling, forming clumps and disrupting the cell membrane. This research opens up new avenues for therapeutic development, potentially in the future leading to drugs that can target and disrupt alpha-synuclein misfolding, ultimately preventing or slowing down the progression of diseases like Parkinson's.

An N-terminal alpha-synuclein fragment binds lipid vesicles to modulate lipid-induced aggregation

Misfolding and aggregation of alpha-synuclein (αS) into toxic conformations is involved in numerous neurodegenerative diseases. In Parkinson's disease (PD), this occurs within dopaminergic neurons, causing cell death and disease symptoms. During αS aggregation, many protein-protein interactions (PPIs) form over broad and flat protein surfaces, limiting potential for small-molecule intervention. Peptides, however, harbor great therapeutic promise since they can selectively engage with and modulate the large surface areas involved yet are small enough to function as druggable agents if suitably structured.

Here, we explore the first 25 residues of αS (αS1-25) as a template for peptide-based αS aggregation antagonists. We report that αS1-25 inhibits lipid-induced αS aggregation in a dose-dependent manner. αS1-25 functions by binding to lipids to prevent αS binding, with both αS and peptide requiring lipid for inhibition to occur. These findings present a potential mechanistic route for the treatment or prevention of PD.

The scientific community seeks a complete understanding of the progression of degenerative aging, at the fine-grained level of environmental influences on specific molecular machinery in the cell, by cell type, by cell status, and then how all of those mechanisms interact with one another as they change. It is a vast project, and may well be largely irrelevant to the task of building a first generation of rejuvenation therapies based on what we presently know of the forms of damage and dysfunction that accumulate in cells and tissues with age. If damage can be periodically repaired, then it isn't so important to know what that damage does in fine detail when it is left to accumulate.

Aging and cellular senescence are characterized by a progressive loss of physiological integrity, which could be triggered by aging factors such as physiological, pathological and external factors. Numerous studies have shown that gene regulatory events play crucial roles in aging, increasing the need for a comprehensive repository of regulatory relationships during aging. Here, we established a manually curated database of aging factors (AgingReG), focusing on the regulatory relationships during aging with experimental evidence in humans. By curating thousands of published items in the literature, 2157 aging factor entries (1345 aging gene entries, 804 external factor entries and eight aging-related pathway entries) and related regulatory information were manually curated.

The regulatory relationships were classified into four types according to their functions: (i) upregulation, which indicates that aging factors upregulate the expression of target genes during aging; (ii) downregulation, which indicates that aging factors downregulate the expression of target genes during aging; (iii) activation, which indicates that aging factors influence the activity of target genes during aging and (iv) inhibition, which indicates that aging factors inhibit the activation of target molecule activity, leading to declined or lost target activity. AgingReG involves 651 upregulating pairs, 632 downregulating pairs, 330 activation-regulating pairs and 34 inhibition-regulating pairs, covering 195 disease types and more than 800 kinds of cells and tissues from 1784 published literature studies. AgingReG provides a user-friendly interface to query, browse and visualize detailed information about the regulatory relationships during aging. We believe that AgingReG will serve as a valuable resource database in the field of aging research.

Link: https://doi.org/10.1093/database/baad064

The standard view of Parkinson's disease is that misfolding of α-synuclein occurs in the gut or brain, and then spreads in a prion-like manner to cause widespread dysfunction and cell death throughout the brain. The most vulnerable cells are dopaminergic neurons, and their destruction causes the most evident symptoms of the disease. Some people have a greater risk of Parkinson's disease than others. The most studied vulnerabilities are genetic variants that appear to make dopaminergic neurons even more vulnerable to stress. Environmental factors may also attack this population of neurons: here, researchers note that a soil bacteria sometimes found in the gut microbiome can produce a metabolite that is toxic to dopaminergic neurons.

The causes of nigrostriatal cell death in idiopathic Parkinson's disease are unknown, but exposure to toxic chemicals may play some role. We followed up here on suggestions that bacterial secondary metabolites might be selectively cytotoxic to dopaminergic neurons. Extracts from Streptomyces venezuelae were found to kill human dopaminergic neurons in vitro. Utilizing this model system as a bioassay, we identified a bacterial metabolite known as aerugine and confirmed this finding by chemical re-synthesis.

This compound was previously shown to be a product of a wide-spread biosynthetic cluster also found in the human microbiome and in several pathogens. Aerugine triggered half-maximal dopaminergic neurotoxicity at 3-4 µM. It was less toxic for other neurons (10-20 µM), and non-toxic (at <100 µM) for common human cell lines. Neurotoxicity was completely prevented by several iron chelators, by distinct anti-oxidants and by a caspase inhibitor.

In the Caenorhabditis elegans model organism, general survival was not affected by aerugine concentrations up to 100 µM. When transgenic worms, expressing green fluorescent protein only in their dopamine neurons, were exposed to aerugine, specific neurodegeneration was observed. The toxicant also exerted functional dopaminergic toxicity in nematodes as determined by the "basal slowing response" assay.

Thus, our research has unveiled a bacterial metabolite with a remarkably selective toxicity toward human dopaminergic neurons in vitro and for the dopaminergic nervous system of Caenorhabditis elegans in vivo. These findings suggest that microbe-derived environmental chemicals should be further investigated for their role in the pathogenesis of Parkinson's disease.

Link: https://doi.org/10.1016/j.envint.2023.108229

Since the advent of very large databases of combined human genetic and epidemiological information, the evidence has increasingly leaned to support only a modest effect of genetic variation on human life span variation. Setting aside small populations with rare mutations, lifestyle has a much greater effect on life expectancy than one's genes. Even cases of familial longevity might largely result from transmission of culture, and thus lifestyle choices, rather than transmission of genetic variants.

Today's open access paper reports on data in which both genetic risk and lifestyle risk can be assessed. It is worth noting that the genetic risk is here limited to a consideration of only a few genes, but equally only a small number of genetic variants have been shown to robustly correlate with human life span. The thing to take away from the results is the degree to which the effects of a healthy lifestyle on life expectancy are similar for the high genetic risk and low genetic risk cohorts. In other words, the high genetic risk as assessed here isn't doing all that much to life expectancy when compared to the consequences of lifestyle choices.

Healthy lifestyle in late-life, longevity genes, and life expectancy among older adults: a 20-year, population-based, prospective cohort study

Lifestyle and longevity genes have different and important roles in the human lifespan; however, the association between a healthy lifestyle in late-life and life expectancy mediated by genetic risk is yet to be elucidated. We aimed to investigate the associations of healthy lifestyle in late-life and genetic risk with life expectancy among older adults.

A weighted healthy lifestyle score was constructed from the following variables: current non-smoking, non-harmful alcohol consumption, regular physical activity, and a healthy diet. Participants were recruited from the Chinese Longitudinal Healthy Longevity Survey, a prospective community-based cohort study that took place between 1998 and 2018. Eligible participants were aged 65 years and older with available information on lifestyle factors at baseline, and then were categorised into unhealthy (bottom tertile of the weighted healthy lifestyle score), intermediate (middle tertile), and healthy (top tertile) lifestyle groups. A genetic risk score was constructed based on 11 lifespan loci among 9,633 participants, divided by the median and classified into low and high genetic risk groups. Stratified Cox proportional hazard regression was used to estimate the interaction between genetic and lifestyle factors on all-cause mortality risk.

36,164 adults aged 65 years and older were recruited, among whom a total of 27 ,462 deaths were documented during a median follow-up of 3.12 years and included in the lifestyle association analysis. Compared with the unhealthy lifestyle category, participants in the healthy lifestyle group had a lower all-cause mortality risk (hazard ratio 0.56). The highest mortality risk was observed in individuals in the high genetic risk and unhealthy lifestyle group (hazard ratio 1.80). The absolute risk reduction was greater for participants in the high genetic risk group. A healthy lifestyle was associated with a gain of 3.84 years at the age of 65 years in the low genetic risk group, and 4.35 years in the high genetic risk group.

A healthy lifestyle, even in late-life, was associated with lower mortality risk and longer life expectancy among Chinese older adults, highlighting the importance of a healthy lifestyle in extending the lifespan, especially for individuals with high genetic risk.

The ovaries, like the thymus, undergo a form of degenerative aging that occurs somewhat in advance of the aging of other parts of the body. It leads to the phenomenon of menopause and subsequent consequences to health and function, which, interestingly, is a feature of aging that is shared with only a few other mammalian species. That makes the ovaries and their surrounding tissues an interesting target for the development of ways to slow or reverse loss of function. Maintained ovarian function may prove to modestly slow aging in older women; it is a reasonable hypothesis and goal to pursue given what is known of the interaction of ovarian aging with other aspects of aging in humans.

Ovarian reserve is essential for fertility and influences healthy aging in women. Advanced maternal age correlates with the progressive loss of both the quantity and quality of oocytes. The molecular mechanisms and various contributing factors underlying ovarian aging have been uncovered.

In this review, we highlight some of critical factors that impact oocyte quantity and quality during aging. Germ cell and follicle reserve at birth determines reproductive lifespan and timing the menopause in female mammals. Accelerated diminishing ovarian reserve leads to premature ovarian aging or insufficiency. Poor oocyte quality with increasing age could result from chromosomal cohesion deterioration and misaligned chromosomes, telomere shortening, DNA damage and associated genetic mutations, oxidative stress, mitochondrial dysfunction, and epigenetic alteration.

We also discuss the intervention strategies to delay ovarian aging. Both the efficacy of senotherapies by antioxidants against reproductive aging and mitochondrial therapy are discussed. Functional oocytes and ovarioids could be rejuvenated from pluripotent stem cells or somatic cells. We propose directions for future interventions. As couples increasingly begin delaying parenthood in life worldwide, understanding the molecular mechanisms during female reproductive aging and potential intervention strategies could benefit women in making earlier choices about their reproductive health.

Link: https://doi.org/10.1515/mr-2022-0031

The consensus on iron is that higher levels become an issue in the context of aging, contributing to a number of issues such as raised oxidative stress and creation of the metabolic waste known as lipofuscin. Researchers here provide evidence for increased iron levels to correlate with epigenetic age acceleration, a measure of biological age. This is an expected result, given all of the other data on the possible role of dysfunctional iron metabolism in degenerative aging.

Iron is one of the most essential transition metals in the human body. The balance of iron metabolism, also known as iron homeostasis, is strictly regulated due to its crucial role in erythropoiesis, oxidative phosphorylation, and redox reaction. Evidence has connected altered iron homeostasis with biological aging. For example, epidemiological research reported that over 10% of both men and women aged 65 years or older were anemic in the US, in which iron deficiency made up approximately 20% of all anemia cases. Chronic inflammation of the elder people might also contribute to the alteration of serum iron biomarkers, causing iron deficiency and impaired iron mobilization. On the other hand, cellular iron accumulation in older individuals was observed. Serum level of ferritin, which reflected the storage of iron, was reported to be increasing with age and negatively associated with telomere length. Iron overload in cell induced the accumulation of lipofuscin, which was considered one of the hallmarks of aging and could be cytotoxic.

Epigenetic clocks based on DNA methylation status and chronological age and health-related outcomes were built to discover the impact of both genetic and environmental factors on human aging. Epigenetic age acceleration (EAA) was used to describe individuals with greater epigenetic-clock-estimated age than their true chronological age, indicating worse health outcome. Although iron homeostasis is connected with aging, no research regarding the relationship between epigenetic clocks or EAA and iron homeostasis has been conducted.

Utilizing outcomes from genome-wide association studies (GWAS), Mendelian randomization (MR) has been widely used in discovering causality between exposure factors and outcomes. Researchers have conducted a GWAS of four epigenetic clocks, and subsequent MR analysis identified several risk factors of EAAs. In this study, we conducted a two-sample MR analyses with summarized GWAS data mentioned above to investigate the causal relationship between iron homeostasis and EAAs. Each standard deviation (SD) increase in genetically predicted serum iron was associated with increased GrimAge acceleration (GrimAA), HannumAge acceleration (HannumAA), and Intrinsic epigenetic age acceleration (IEAA). Similar results were also observed in transferrin saturation. Transferrin carries and transports most of the serum iron to organs and tissues.

In conclusion, the results of the present investigation unveiled the causality of iron overload on acceleration of epigenetic clocks. Researches are warranted to illuminate the underlying mechanisms and formulate strategies for potential interventions.

Link: https://doi.org/10.1186/s13148-023-01575-w

There is some debate over the mechanisms involved in the bidirectional relationship between hearing loss and cognitive decline in aging. While both must, logically, arise from the same underlying causes of aging, the increased burden of a variety of forms of cell and tissue damage that produce many different forms of dysfunction, it appears that (a) loss of function in the brain can itself contribute to hearing loss, while (b) hearing loss can in and of itself accelerate the pace of cognitive decline.

Thanks to the existence of electromechanical means of improving hearing, meaning hearing aids, cochlear implants, and the like, there is a growing body of evidence to show that people with these devices suffer a slower pace of cognitive decline than those without, at a given level of age-related hearing loss. This is a strong argument for portions of the brain to require the exercise of processing sound in order to better resist decline. "Use it or lose it" isn't just for muscles, and this isn't the only line of evidence to suggest that a well exercised mind will lose functional capacity more slowly in later life. Similar effects are observed for blindness and cognitive decline, for example, implying that the exercise of processing of visual information helps to resist loss of brain function.

Interestingly, the study noted in today's open access paper suggests that the effect of maintained processing of audio information only goes so far. It only helps for a few years. More is needed if we are to be the masters of our own destiny when it comes to the aging of the brain. Rejuvenation therapies must directly address the underlying mechanisms of cell and tissue damage, and the research community must aim at greater goals than a mere slowing of aging.

Longitudinal trajectories of memory among middle-aged and older people with hearing loss: the influence of cochlear implant use on cognitive functioning

Cochlear implants (CI) are the gold standard intervention for severe to profound hearing loss, a known modifiable risk factor for dementia. However, it remains unknown whether CI use might prevent the age-related cognitive decline. Recent studies are encouraging but are limited, mainly by short follow-up periods and, for ethical reasons, lack of appropriate control groups. Further, as age-related cognitive decline is multifaceted and not linear, other statistical approaches have to be evaluated.

Immediate and delayed recall as measures of cognitive function were assessed in 75 newly implanted CI users (mean age 65.41 years ± 9.19) for up to 5 years (mean 4.5 ± 0.5) of CI use and compared to 8,077 subjects of the same age range from two longitudinal cohort studies, the Health and Retirement Study (HRS) and the English Longitudinal Study of Aging (ELSA). Linear and quadratic changes in cognitive trajectories were analyzed in detail using mixed growth models, considering possible confounders.

For CI users, the linear time slope showed a significant improvement in the specific domains (recall and delayed recall) over time. The quadratic time slope clearly indicated that the predicted change after CI provision followed an inverted U-shape with a predicted decline 2 years after CI provision. In the hearing-impaired group, a significant decline over time was found, with steeper declines early on and the tendency to flatten out in the follow-up. In conclusion, cochlear implant use seems to boost cognitive trajectories in the first years after implantation. However, long-term prevention of dementia seems to need far more than restoration of hearing loss.

Beta cells in the pancreas produce insulin and are essential to the regulation of glucose metabolism. Dysfunction in this cell population causes diabetes, whether the origin is autoimmune destruction of beta cells (type 1 diabetes) or senescence of beta cells brought on by obesity (type 2 diabetes). Aging also impairs beta cell function through some of the same mechanisms, such as cellular senescence and constant, unresolved inflammatory signaling. The practice of calorie restriction slows aging, albeit to a greater degree in short-lived species than in long-lived species, and so it is not surprising to see that calorie restriction attenuates this aspect of degenerative aging.

Caloric restriction (CR) extends organismal lifespan and health span by improving glucose homeostasis mechanisms. How CR affects organellar structure and function of pancreatic beta cells over the lifetime of the animal remains unknown. Here, we used single nucleus transcriptomics to show that CR increases the expression of genes for beta cell identity, protein processing, and organelle homeostasis. Gene regulatory network analysis link this transcriptional phenotype to transcription factors involved in beta cell identity (Mafa) and homeostasis (Atf6). Imaging metabolomics further demonstrates that CR beta cells are more energetically competent.

In fact, high-resolution light and electron microscopy indicates that CR reduces beta cell mitophagy and increases mitochondria mass, increasing mitochondrial ATP generation. Finally, we show that long-term CR delays the onset of beta cell aging and senescence to promote longevity by reducing beta cell turnover. Therefore, CR could be a feasible approach to preserve compromised beta cells during aging and diabetes.

Link: https://doi.org/10.21203/rs.3.rs-3311459/v1

Researchers here report a novel approach to building an aging clock, a system that can usefully measure biological age, the growing burden of damage and dysfunction. Epigenetic data, usually the status of DNA methylation at various sites on the genome, has been used to construct aging clocks in the past. Epigenetic changes of all sorts alter gene expression by altering the structure of chromatin, folded DNA in the cell nucleus, determining which regions and genes are exposed to transcriptional machinery. Thus why not directly assess changes in the structure of chromatin via microscopy imaging approaches? Researchers have now tried that, and it seems to work.

Biomarkers of biological age that predict the risk of disease and expected lifespan better than chronological age are key to efficient and cost-effective healthcare. Several years ago, we pioneered microscopic imaging of epigenetic landscapes rooted in the analysis of chromatin topography in single cells. We employed immunolabeling with antibodies specific for histone modifications (e.g. acetylation and methylation marks) and automated microscopy to capture cell-specific patterns using image texture analysis, resulting in multiparametric signatures of cellular states. Here, we took advantage of this technique to develop an image-based chromatin and epigenetic age (ImAge), a fundamentally different approach to studying aging compared to DNA methylation clocks.

We observed the emergence of intrinsic trajectories of ImAge using dimensionality reduction without regression on chronological age. ImAge was correlated with chronological age in all tissues and organs examined and was consistent with the expected acceleration and/or deceleration of biological age in chronologically identical mice treated with chemotherapy or following a caloric restriction regimen, respectively. ImAge from chronologically identical mice inversely correlated with their locomotor activity (greater activity for younger ImAge), consistent with the essential role of locomotion as an aging biomarker. Finally, we demonstrated that ImAge is reduced upon partial reprogramming in vivo following transient expression of OSKM in the liver and skeletal muscles of old mice and validated the power of ImAge to assess the heterogeneity of reprogramming.

We propose that ImAge represents the first-in-class individual-level biomarker of aging and rejuvenation with single-cell resolution.

Link: https://doi.org/10.1101/2022.10.16.512441

The gut microbiome changes with age for reasons yet to be fully explored, but which most likely involves the age-related decline of the immune system. Research suggests a bidirectional relationship between immune aging and changes in the balance of microbial populations found in the intestines. The immune system is responsible for gardening the gut microbiome, removing unwanted microbes, but its capacity to do so declines with age. A growth in problematic microbial populations can produce disruptive, pro-inflammatory metabolites that provoke the immune system into a state of chronic inflammation, as well as invasion of tissue and bloodstream by microbes as the intestinal barrier becomes leaky.

Given that there are ways to adjust the microbial populations of the intestine into a more youthful configuration, well-established in animal models, this seems a very feasible approach to improve late life health. The treatment with the greatest amount of data is fecal microbiota transplantation from a young individual to an old individual. This class of therapy is already used in the clinic to treat severe forms of dysbiosis, and some data exists for use in old humans, in addition to the sizable body of work in old animals. Self-experimenters can readily source stool samples from young donors, and many do so. Bringing this to the clinic and widespread use would be comparatively straightforward, other than the usual problem in such cases, which is that none of the entities with deep enough pockets to fund the necessary clinical trials for FDA approval have any interest in treatments that cannot be restricted, patented, and monopolized.

Still, research continues. Beyond the existing approaches such as fecal microbiota transplant, it may be that research will give rise to much more sophisticated forms of probiotic treatment that can be restricted, patented, and monopolized, given the complexity involved. One can imagine a probiotic equivalent of fecal microbiota transplantation, in which the necessary mix of microbes is cultured rather than harvested. That would likely require advances in the process technologies involved in producing microbes in bulk quantities in order to be cost effective for mixes of hundreds of different species. Those advances could form the basis for a business funded to the level needed to conduct clinical trials and gain approval for use.

Multi-omics analysis reveals substantial linkages between the oral-gut microbiomes and inflamm-aging molecules in elderly pigs

Altered gut microbiome and host metabolism have been implicated in the process of aging. Aging is associated with changes in the gut microbiota, which in turn can affect host metabolism. The gut microbiota is a complex community of microorganisms that live in the gastrointestinal tract and play an important role in maintaining human health. As we age, the diversity and composition of the gut microbiota can change, with a decrease in beneficial bacteria and an increase in harmful bacteria. These changes in the gut microbiota can contribute to a number of age-related health problems, such as impaired immune function, inflammation, and metabolic dysfunction. For example, alterations in the gut microbiota have been linked to age-related diseases such as type 2 diabetes, cardiovascular disease, and cognitive decline.

The gut microbiome plays a critical role in host metabolism through a variety of mechanisms, including fermentation of dietary fibers, regulation of intestinal barrier function, regulation of immune function and bile acid metabolism, for instance, microbial derived short-chain fatty acids (SCFAs) can modulate various metabolic pathways in the host, including glucose metabolism and lipid metabolism, and can also affect immune function and inflammation. Overall, the relationship between the gut microbiota and host metabolism is complex and their joint action on aging still not fully understood. However, there is growing evidence to suggest that interventions aimed at modulating the gut microbiota, such as dietary changes or probiotics, may have potential therapeutic benefits for age-related metabolic disorders.

Hence, a well-controlled model system that reproduces faithfully the trajectories in the oral and gut microbiota with age is warranted and will provide a better understanding of the role played by them in the healthy development and aging of the host. Pigs are used as an excellent model to study the interaction between host microbiome and aging by combining multi-omics, because pigs share many similarities with humans in terms of their anatomy, physiology, and nutritional requirements. For example, the structure and function of the pig gut is similar to that of humans, as well as in organ development and disease progression. In addition, swine can be raised in a controlled environment and are readily available and relatively inexpensive compared to other animal models, which allows researchers to manipulate their diet and other environmental factors that may influence the host microbiome and aging process. Previous research has also been identified that pigs have a gut microbiome that is similar in composition to that of humans, with a high degree of microbial diversity and similar microbial taxa.

This study employed a comprehensive metagenomic analysis encompassing saliva and stool samples obtained from 45 pigs representing three distinct age groups, alongside serum metabolomics and lipidomics profiling. Our findings unveiled discernible modifications in the gut and oral microbiomes, serum metabolome, and lipidome at each age stage. Specifically, we identified 87 microbial species in stool samples and 68 in saliva samples that demonstrated significant age-related changes. Notably, 13 species in stool, including Clostridiales bacterium, Lactobacillus johnsonii, and Oscillibacter spp., exhibited age-dependent alterations, while 15 salivary species, such as Corynebacterium xerosis, Staphylococcus sciuri, and Prevotella intermedia, displayed an increase with senescence, accompanied by a notable enrichment of pathogenic organisms. Concomitant with these gut-oral microbiota changes were functional modifications observed in pathways such as cell growth and death (necroptosis), bacterial infection disease, and aging (longevity regulating pathway) throughout the aging process. Moreover, our metabolomics and lipidomics analyses unveiled the accumulation of inflammatory metabolites or the depletion of beneficial metabolites and lipids as aging progressed.

Control of chronic inflammation may turn out to be one of the more important themes in the treatment of aging as a medical condition. Senescent cells generate inflammatory signaling, but removing that contribution is likely the easiest aspect of the problem. Many forms of age-related cellular damage and dysfunction generate constant, unwanted, excess inflammation through interactions and signals that are used during a normal, desirable inflammatory reaction, such as to injury or infection. Thus interfering in these mechanisms must be very selective; simply blockading a given signal has undesirable side-effects, such as a weakening of the immune response. A fair amount of the research aimed at producing more selective anti-inflammatory treatments is focused on STING, as many pro-inflammatory mechanisms associated with age and disease involve this protein, and it can act in many different ways. As researchers note here, perhaps this is a place to start in the search for better approaches to dampening the chronic inflammation of aging.

A type of T cell known as an effector memory T cell (Tem) can become a critical driver of cytokine storms. The chain reaction appears to start when Tem cells interact with dendritic cells, which serve as the immune system's primary detector of viral and bacterial invasions. When the immune system wins the battle, most of the custom T cells stand down. But a few guards linger in the blood and other body tissues to be ready to "effect" a rapid response should the same type on infection occur again. Hence the name effector memory T cells.

However, ongoing encounters with Tem cells, such as those occurring when people have autoimmunity or live in a state of chronic inflammation, actually cause DNA strands within dendritic cells to break. This, in turn, prompts a DNA repair pathway that rapidly generates large numbers of inflammatory cytokines, including IL-1b, IL-6, and IL-12. This flood, or storm, of cytokines causes the tissue damage that occurs in autoinflammatory diseases including type 1 diabetes, multiple sclerosis, rheumatoid arthritis, and inflammatory bowel diseases like Crohn's disease. For some people with these conditions, ongoing inflammation also increases their risk of developing cancer.

Researchers detected upregulation of expression of Tmem173 in dendritic cells following interactions with Tem cells. Tmem173 which encodes for stimulator of interferon genes (STING). The STING pathway has been described in previous research as being important to detect viral infections. But when Tem cells harm dendritic cells, the STING pathway does not follow the same route that it typically does when directly responding to viral infections. In this situation, STING teams up with the gene TRAF6 and the transcription factor NFkB to form an "axis" of activity that drives runaway production of innate inflammatory cytokines.

The researchers further reasoned that if they could prevent STING and TRAF6 from working together, they could cut off the inflammation chain reaction at an early stage. In mice gene-edited to lack the STING pathway, that's exactly what they found. When treated with a drug known to induce an intense T cell-mediated inflammatory response, these mice did not produce a flood of innate cytokines. The mouse study involved a whole-body elimination of STING. Attempting the same in humans would not be advisable because STING is used by a number of cell types outside the immune system in necessary ways. "Our goal will be to develop a highly focused method or methods for blocking STING within targeted immune cells, without disrupting its other important functions. If we can achieve that, we may have a powerful new tool for controlling hyper-inflammation."

Link: https://www.eurekalert.org/news-releases/1003174

Type 2 diabetes is near entirely a lifestyle condition, and can be reversed even in later stages via suitably aggressive dietary and weight loss interventions. Obesity in early adult life is sufficient to cause type 2 diabetes via some combination of mechanisms involving excess fat in the pancreas and increased stress put upon insulin-generating beta cells resident in the pancreas, leading to greater cellular senescence and altered cell behavior. Excess visceral fat is in general harmful to the body via its metabolic activity. There are a range of ways beyond an increased burden of senescent cells by which it can produce chronic inflammation, disruptive to cell function and tissue function throughout the body. As noted here, the consequences of type 2 diabetes and the lifestyle required to sustain it are sizable.

The prevalence of type 2 diabetes is increasing rapidly, particularly among younger age groups. Estimates suggest that people with diabetes die, on average, 6 years earlier than people without diabetes. We aimed to provide reliable estimates of the associations between age at diagnosis of diabetes and all-cause mortality, cause-specific mortality, and reductions in life expectancy. For this observational study, we conducted a combined analysis of individual-participant data from 19 high-income countries using two large-scale data sources: the Emerging Risk Factors Collaboration (96 cohorts, median baseline years 1961-2007, median latest follow-up years 1980-2013) and the UK Biobank (median baseline year 2006, median latest follow-up year 2020). We calculated age-adjusted and sex-adjusted hazard ratios (HRs) for all-cause mortality according to age at diagnosis of diabetes using data from 1,515,718 participants.

For participants with diabetes, we observed a linear dose-response association between earlier age at diagnosis and higher risk of all-cause mortality compared with participants without diabetes. HRs were 2.69 when diagnosed at 30-39 years, 2.26 at 40-49 years, 1.84 at 50-59 years, 1.57 at 60-69 years, and 1.39 at 70 years and older. HRs per decade of earlier diagnosis were similar for men and women. Using death rates from the USA, a 50-year-old individual with diabetes died on average 14 years earlier when diagnosed aged 30 years, 10 years earlier when diagnosed aged 40 years, or 6 years earlier when diagnosed aged 50 years than an individual without diabetes. Using EU death rates, the corresponding estimates were 13, 9, or 5 years earlier.

Link: https://doi.org/10.1016/S2213-8587(23)00223-1

Cells become senescent in response to stress and damage, and there is a great deal of stress and damage taking place in the toxic environment of an atherosclerotic plaque. These fatty plaques develop with age in blood vessel walls throughout the body. Many contributing factors determine the age of onset and pace of progression of atherosclerosis, but at the center of it all, atherosclerotic plaques form and grow because macrophage cells of the innate immune system fail to keep up with clearance of excess cholesterol delivered from the bloodstream into blood vessel walls. After a plaque becomes established, it contains toxic altered forms of cholesterol, stressed and dying cells, and certainly a fair number of senescent cells.

Senescent cells are actively harmful to surrounding tissue via the secretion of pro-inflammatory factors. Researchers have in the past shown that removing senescent cells via senolytic treatments can improve the pathology of atherosclerosis in mice, and that cellular senescence is pronounced in cell populations surrounding and involved in an atherosclerotic plaque, such as smooth muscle and endothelium. In today's open access paper, researchers report on a novel way to use nanoparticles to deliver a senolytic payload to atherosclerotic plaques in mice. They employ magnetic guidance as a strategy for localization of nanoparticles via the bloodstream to areas such as the vasculature close to the heart. Unlike some localized senolytic treatments, this does appear beneficial, suggesting the influence of local senescent cells is dominant over the influence of distant senescent cells - at least in this disease and this model. The story might be different in older mice with a greater prevalence of senescent cells throughout the body.

Targeted elimination of senescent cells by engineered extracellular vesicles attenuates atherosclerosis in ApoE-/- mice with minimal side effects

Atherosclerosis (AS) is a prevalent vascular disease characterized by dyslipidemia and chronic inflammation. Despite the use of preventive lipid-lowering and anti-inflammatory therapeutic strategies, there is still a critical need for more effective treatment options. Recent research has revealed a significant accumulation of senescent cells in plaques positively correlated with plaque instability. Senescent cells in plaques aggravate chronic inflammation and accelerate AS progression generating a senescence-associated secretory phenotype (SASP) consisting of matrix remodeling proteases, chemokines, cytokines, growth factors, and lipids. Therefore, the targeted removal of senescent cells in plaques presents a promising therapeutic strategy for treating AS.

BCL-2 associated X protein (BAX), a natural inhibitor of the pro-survival protein, is a key pro-apoptotic protein and plays an essential role in regulating the mitochondrial apoptotic pathway. Increasing the intracellular active BAX level may trigger apoptosis in broad-spectrum senescent cells regardless of origin. Therefore, delivering Bax messenger RNA (mRNA) and the BAX activator BTSA1 to senescent cells may represent a novel approach for clearing senescent cells ("activate the activator").

Superparamagnetic iron oxide nanoparticles (SMN) have recently gained significant attention for targeted drug delivery due to their advanced targeting capacity, biodegradability, biological compatibility, and low toxicity. The ability for magnetic targeting is not dependent on cell types but on the recognition of the spatial location of the affected tissue, rendering it a suitable method for delivering drugs to senescent cells in plaques. Furthermore, small extracellular vesicles (EVs) with a diameter ranging from 30 to 150 nm exhibit favorable biocompatibility and cycling stability, and are well-suited for carrying protein and nucleic acid-based drugs. Thus, Bax mRNA-loaded EVs modified with SMN (EVSMN) hold significant potential as drug carriers for treating AS.

Even for targeted delivery, nanoparticles, including EVs, are accumulated in the liver, causing liver injury when Bax mRNA is excessively delivered. Therefore, repressing Bax translation in liver cells is imperative to avoid potential toxicity. MicroRNAs are key regulators of gene expression that destabilize target mRNAs or inhibit their translation. miR-122-5p (miR-122), is a liver-specific molecule with an estimated cellular abundance of 50,000-82,000 copies in adult liver cells, suggesting that Bax mRNA harboring miR-122 recognition sites in the 3'-untranslated region (3'-UTR) (termed as iBax) could be translationally repressed in liver cells.

Herein, a therapeutic EV (EViTx) was engineered with SMN conjugated on the surface, iBax mRNA encapsulated inside and BAX activator BTSA1 incorporated into the membrane. With external magnetic field (MF) navigation, EViTx, when targeted to atherosclerotic plaques, induced significant apoptosis in senescent cells regardless of origin. Notably, when delivered into liver cells, iBax mRNA was translationally repressed by miR-122 endogenously expressed in liver cells and thus had minimal hepatotoxicity. Repeated delivery of EViTx via tail vein injection achieved high therapeutic efficacy and low side effects in ApoE-/- mice. Hence, the EViTx-based strategy offers a promising treatment approach for AS and other age-related diseases.

Senescent cells accumulate in tissues throughout the body, and their collective signaling is pro-inflammatory to a significant degree. Focusing on cellular senescence in specific cell populations, such as stem cells or other critical cells in joint tissues, is a popular area of study. Adding senescent cells to a joint in mice produces degeneration, but specifically removing senescent cells from a joint using a locally injected senolytic drug doesn't reverse degeneration in humans. This suggests that the rest of the senescent cell population in the body can continue to provide enough signaling to the joint to maintain dysfunction. Nonetheless, a fair number of papers continue to look at the contribution of cells local to the issue in joint tissue.

Mesenchymal/medicinal stem/signaling cells (MSCs), well known for regenerative potential, have been involved in hundreds of clinical trials. Even if equipped with reparative properties, aging significantly decreases their biological activity, representing a major challenge for MSC-based therapies. Age-related joint diseases, such as osteoarthritis, are associated with the accumulation of senescent cells, including synovial MSCs. An impaired ability of MSCs to self-renew and differentiate is one of the main contributors to the human aging process.

Moreover, senescent MSCs (sMSCs) are characterized by the senescence-messaging secretome (SMS), which is typically manifested by the release of molecules with an adverse effect. Many factors, from genetic and metabolic pathways to environmental stressors, participate in the regulation of the senescent phenotype of MSCs. To better understand cellular senescence in MSCs, this review discusses the characteristics of sMSCs, their role in cartilage and synovial joint aging, and current rejuvenation approaches to delay/reverse age-related pathological changes, providing evidence from in vivo experiments as well.

Link: https://doi.org/10.1177/09636897231200065

Setting aside the movements of the broader market from year to year, and noting that this past year has been a poor time for venture funding, we should expect the funding available for biotech companies in the longevity industry to continue to increase in the years ahead. The fundamental reasons for this trend appear at the end of this article: the science looks very promising, there are many good projects sitting on the sidelines waiting for a champion to take them forward, and the upside for investors seems high. A therapy that targets one or more underlying mechanisms of aging will likely be applicable to a long list of age-related conditions.

While the wonders of modern medicine helped to double global life expectancy between 1920 and 2020, human health span has not followed the upward trend. Today, more than ever, people are living more years in poor health. The call to develop therapeutics that interfere with aging, helping people live not only longer but healthier lives, is increasing. So it isn't surprising that, even in the current economy, some up-and-coming longevity-focused biotech companies are managing to snag funds to push closer to the clinic with therapeutics that have the potential to transform how we age.

Rejuvenation Technologies posted $10.6 million in seed financing, led by Khosla Ventures, a firm headed by businessman and entrepreneur Vinod Khosla. Rejuvenation is looking to rewind the body's molecular aging clock by targeting telomere shortening. The biotech's platform is built around optimized telomerase mRNA encapsulated in custom tissue-targeted lipid nanoparticles. Khosla Ventures was a driving factor in the company's successful seed round. Vinod Khosla has been a name in the longevity space - and telomeres - since his involvement in funding Geron in the 1990s, when it was focused on modifying human aging by way of telomerase activity. As a leader in the space, his participation means something to other investors.

For Rejuvenation, the time was right to enter this space due to the convergence of knowledge and tools. The knowledge around the effect of telomere shortening on aging and age-related disease is not new. However, the mRNA technology the company will utilize has finally had its kinks worked out. "The challenge is delivery and that was what held us up for a few years. It was breakthroughs in 2019 and 2021 that brought ways to deliver messenger RNA with this efficiency and tolerability that it is now ready for the clinic."

In the current economy, attracting investors is no small feat. Yet progress in the longevity field is vital not only for society but also for the global financial burden, according to a cost-benefit analysis which suggests that aging research could be comparable or superior in cost-effectiveness to the most cost-effective global health interventions. Perhaps reflecting this need, the longevity sector is projected to be worth at least $600 billion by 2025, according to analysts.

Over the past five years, investors have shown an increased interest in the longevity space, with investment peaking in 2021 at a record-breaking $7.65 billion. 2022 financing came close to that high at $6.94 billion, pumped up from a $3 billion investment in Altos Labs. It can be hard to pinpoint the potential market size for a successful longevity therapeutic. "Studies are all over the map. One solid way to look at this is to see the statins market since it is effectively used as a longevity drug, namely for reducing cardiac risk. Most of them are off-patent, but it's still $15 billion a year in sales. If you like high-risk, high-return, cost-effective lifesaving projects, then aging research is an especially good investment because the level of existing funding is so low, and the size of the impact of success is so high."

Link: https://www.biospace.com/article/investors-fuel-fountain-of-youth-research-with-longevity-company-investments/

Atherosclerosis is a universal age-related condition in which fatty plaques grow in blood vessel walls, eventually rupturing to produce a heart attack or stroke. Even prior to that, reduced blood flow due to narrowed arteries contributes to heart failure and numerous other age-related conditions. The chronic inflammation that accompanies aging is a contributing factor in the development of atherosclerosis, but efforts to suppress inflammation have so far produced results that are only in the same ballpark as the effects of statins and similar approaches to lower LDL cholesterol in the bloodstream. This is to say a modest slowing of atherosclerosis, but no great reversal of existing plaque.

This may be the case because present anti-inflammatory strategies are relatively crude, while inflammatory signaling is a complex process spanning hundreds to thousands of proteins and other molecules inside cells and passing between cells of many different types and function. Or it could be because targeting the state of inflammation isn't the most effective way forward. It seems like a compelling target, however, given that the progression of atherosclerosis, the formation of fatty plaques, comes down to the dysfunction of macrophage cells. It is macrophages of the innate immune system that are responsible for clearing cholesterol from blood vessel walls, and inflammatory signaling can (a) cause macrophages to focus instead on other tasks, making them less effective when it comes to cholesterol clearance, and (b) attract more macrophages to existing plaque environments. Large plaques are packed with a toxic mix of cholesterol and altered cholesterols that is capable of overwhelming and killing even larger than usual numbers of macrophages, adding their mass to the plaque.

In today's open access paper, researchers discuss a more sophisticated approach to suppression of inflammation, employing regulatory T cells that are normally responsible for resolving inflammation after its purpose is complete. Using cells in principle allows the full spectrum of inflammation resolving mechanisms to be employed, even those that are poorly understood at the present time. On the other hand, using cells introduces a great deal of complexity and cost into any potential therapy. Cell therapies that work in animal studies in the academic environment remain very challenging to develop into a reliable treatment that will satisfy regulators, and the same goes for attempts manipulate the immune system in this way.

Regulatory T Cells in Atherosclerosis: Is Adoptive Cell Therapy Possible?

Atherosclerosis is an insidious vascular disease with an asymptomatic debut and development over decades. The aetiology and pathogenesis of atherosclerosis are not completely clear. However, chronic inflammation and autoimmune reactions play a significant role in the natural course of atherosclerosis. The pathogenesis of atherosclerosis involves damage to the intima, immune cell recruitment and infiltration of cells such as monocytes/macrophages, neutrophils, and lymphocytes into the inner layer of vessel walls, and the accumulation of lipids, leading to vascular inflammation. The recruited immune cells mainly have a pro-atherogenic effect, whereas CD4+ regulatory T (Treg) cells are another heterogeneous group of cells with opposite functions that suppress the pathogenic immune responses. Present in low numbers in atherosclerotic plaques, Tregs serve a protective role, maintaining immune homeostasis and tolerance by suppressing pro-inflammatory immune cell subsets.

The development of atherosclerosis and the stability of atherosclerotic plaques are directly related to changes in the balance of the effector and suppressor populations of the immune system. Treg cells are key immunocytes that control immune responses and maintain tissue homeostasis. Therefore, manipulations aimed at regulating Treg cells are of interest for considering the development of personalised treatments for atherosclerosis. There are several general approaches to modulating Treg activity and Treg numbers in atherosclerosis, but promising preclinical and several clinical studies have suggested that adoptive Treg transfer may be a treatment option for atherosclerosis. For therapies based on adoptive cell transfer, two kinds of Treg cells can be used: polyclonally expanded Treg cells or antigen-specific Treg cells.

In early and ongoing studies of Treg-based adoptive therapies, a general ineffective approach is used: peripheral Treg cells are sorted, polyclonally expanded ex vivo, and infused in certain quantities into the bloodstream. However, this approach does not take into account a number of key factors. First, this approach ignores the functional state of Treg cells. Currently, Treg cells are isolated from peripheral blood mononuclear cells (PBMCs) and expanded ex vivo. Treg cells isolated from PBMCs are heterogeneous and largely represented by cells with induced FOXP3 expression. The lack of potent and stable FOXP3 expression and steady suppressive activity are the common problems in this approach to cell therapy. Second, it is important to increase the specificity of Treg-based adoptive therapy. Antigen-specific Treg cells have been shown to be more powerful in suppressing alloimmune responses in vitro and in vivo compared to polyclonally expanded Treg cells. Thereby, infusions of polyclonally expanded Treg cells with unknown antigen specificity cannot effectively inhibit the target cells and suppress undesirable immune responses and can lead to unwanted side effects.

Recently, new highly effective therapeutic approaches based on adoptive therapy with genetically engineered Treg cells have emerged, which can overcome the barriers to the use of Treg cells for immunotherapy of atherosclerosis and other immune-inflammatory diseases. These approaches include the application of cells with genetically modified T-cell receptors or with the expression of highly specific chimeric antigen receptors (CARs), as well as the use of genome editing techniques such as CRISPR/Cas9. CAR technology is a very promising tool, allowing T cells to be reprogrammed to overcome the limitations of native T cells. CAR-modified T cells have already been successfully applied for the treatment of certain types of cancer. Therefore, this technology can also be effective in the case of Treg cells.

In conclusion, a number of studies have shown that CD4+ Treg cells are crucial in the maintenance of peripheral tolerance and have an important role in the control of atherosclerosis-related inflammation. Therefore, Treg cells are a promising target of major research efforts focused on immune-modulating therapies against atherosclerosis. Developing anti-atherosclerotic Treg-based therapies faces challenges. However, rapid progress in genetic, epigenetic, and molecular aspects of cellular immunology gives hope for a fast-track solution.

Senolytic drugs selectively destroy senescent cells. First generation senolytic drugs generally target apoptosis-resistance mechanisms and have off-target effects, though these appear quite acceptable in the case of dasatinib and quercetin, given the potential benefits. Nonetheless, researchers are expending a great deal of effort to search for ways to produce far more selective targeting of senescent cells. One example is the category of prodrugs that are only transformed into their cytotoxic form via the activity of β-galactosidase, upregulated in senescent cells. Another type of prodrug employs iron metabolism peculiar to senescent cells. Today's example is more complex than either of those, and quite interesting.

Senolytics, which eliminate senescent cells from tissues, represent an emerging therapeutic strategy for various age-related diseases. Most senolytics target antiapoptotic proteins, which are overexpressed in senescent cells, limiting specificity and inducing severe side effects. To overcome these limitations, we constructed self-assembling senolytics targeting senescent cells with an intracellular oligomerization system. Intracellular aryl-dithiol-containing peptide oligomerization occurred only inside the mitochondria of senescent cells due to selective localization of the peptides by RGD-mediated cellular uptake into integrin αvβ3-overexpressed senescent cells and elevated levels of reactive oxygen species (ROS), which can be used as a chemical fuel for disulfide formation.

This oligomerization results in an artificial protein-like nanoassembly with a stable α-helix secondary structure, which can disrupt the mitochondrial membrane via multivalent interactions because the mitochondrial membrane of senescent cells has weaker integity than that of normal cells.

These three specificities (integrin αvβ3, high ROS, and weak mitochondrial membrane integrity) of senescent cells work in combination; therefore, this intramitochondrial oligomerization system can selectively induce apoptosis of senescent cells without side effects on normal cells. Significant reductions in key senescence markers and amelioration of retinal degeneration were observed after elimination of the senescent retinal pigment epithelium by this peptide senolytic in an age-related macular degeneration mouse model and in aged mice, and this effect was accompanied by improved visual function. This system provides a strategy for the treatment of age-related diseases using supramolecular senolytics.

Link: https://doi.org/10.1021/jacs.3c06898

This review paper covers both genetic and epigenetic changes that occur with age, taking a broad look at everything from telomere length to stochastic mutational damage to alterations in chromatin structure. As for all aspects of aging at the level of cellular biochemistry, it is easier to catalog than it is to determine relationships between these items, or to determine whether one characteristic of aging cellular biochemistry is more or less important than another when it comes to age-related disease and loss of function. Greater funding for the field would allow researchers to take the best of brute force approaches, which is to find ways to reverse each specific form of change observed in cells, and then compare the results. This is also the most likely way forward to discovering novel rejuvenation therapies.

Aging is considered the deterioration of physiological functions along with an increased mortality rate. This scientific review focuses on the central importance of genomic instability during the aging process, encompassing a range of cellular and molecular changes that occur with advancing age. In particular, this review addresses the genetic and epigenetic alterations that contribute to genomic instability, such as telomere shortening, DNA damage accumulation, and decreased DNA repair capacity. Furthermore, the review explores the epigenetic changes that occur with aging, including modifications to histones, DNA methylation patterns, and the role of non-coding RNAs. Finally, the review discusses the organization of chromatin and its contribution to genomic instability, including heterochromatin loss, chromatin remodeling, and changes in nucleosome and histone abundance.

The simultaneous occurrence of these alterations, each with its activating or inhibiting role, affects DNA availability and contributes to genomic instability, overall decline in cellular function, and organismal dysregulation. Consequently, there is an increased susceptibility to age-related diseases such as cancer, cardiovascular diseases, and inflammation. Since the initial suggestion that DNA damage and genome instability are primary drivers and DNA repair is a key factor in aging, followed by the finding that defects in DNA repair can hasten the progression of various age-related diseases, significant progress has been made in understanding the detailed connections between genome instability and every facet of the aging process. Exploring the specific mechanisms by which DNA damage impacts each major process contributing to age-related diseases offers promising avenues to address aging at its fundamental causes, thereby mitigating diseases associated with aging.

Link: https://doi.org/10.3390/ijms241814279

Is Alzheimer's disease the result of persistent infection, or the interaction of several different persistent infections? If a long-term burden of infection is a primary driver of the development of the condition, it would help to explain why lifestyle factors strongly associated with other age-related conditions, such as obesity and lack of exercise, don't correlate anywhere near as well with Alzheimer's incidence. Given the apparent importance of chronic inflammation in Alzheimer's pathology, one might expect it to be more of a lifestyle condition than is in fact the case. But chronic infection has a different, overlapping incidence, and this may better fit the observed pattern of disease.

Researchers here discuss this view of Alzheimer's disease in the context of their analysis of immune cell populations, finding that T cell exhaustion tends to correlate with the severity of Alzheimer's symptoms. T cell exhaustion is a complex, loosely defined, and not fully understood phenomenon in which an increasing number of T cells respond poorly to antigen presentation. They don't react as aggressively as they should, and immune function is compromised as a consequence. This is distinct from T cell senescence, also a feature of aging. Exhaustion is a state that appears to be reversible, given the right changes in regulatory systems.

T cell exhaustion is associated with cognitive status and amyloid accumulation in Alzheimer's disease

In this study we examined immune system alterations early in the progression to Alzheimer's disease (AD). We observed multiple changes across the peripheral innate and adaptive immune systems associated with amyloid and cognitive status within our aging cohort. In the innate immune system, we observed increased plasmacytoid and myeloid dendritic cells in amyloid positive participants, but these changes were particularly pronounced in those with mild cognitive impairment. We also observed a decrease in total natural killer cells with amyloid positivity. When the adaptive immune system was examined, we observed increases in total T cells and B cells in amyloid positive participants.

To further understand alterations in the T cell pool we used flow cytometry to interrogate T cell differentiation and function. We observed an increase in differentiated CD4+ and CD8+ T cell phenotypes in amyloid positive participants with mild cognitive impairment. Surprisingly, we observed an increase in functional CD4+ and CD8+ T cells in amyloid positive cognitively normal participants, while those from amyloid positive mild cognitive impairment subjects had a dramatic increase in exhausted T cells. Importantly when T cell function was compared to cognitive status as determined by mini-mental state examination (MMSE), patients with the lowest score had the highest number of exhausted cells.

Understanding how inflammation and the immune response control the development of AD is critical to develop new treatments. While AD is a disease of the brain, our results demonstrate changes of the immune system in the blood. The increases in both plasmacytoid and myeloid dendritic cells are suggestive of an ongoing response in amyloid positive participants regardless of cognitive status that precedes dementia.

Given the numerous links between infection, inflammation, and AD our results suggest two models where T cells may be the nexus for disease. In the first, amyloid production is a response to simmering infections in periphery and brain with the multiple chronic pathogens all humans carry. Individuals who have strong T cell function control the replication of these pathogens and remain cognitively normal. This would explain why particpants who have the most functional T cells still have the highest MMSE score. But in individuals who lose T cell function, chronic pathogens reactivate, overstimulate innate responses, particularly type I interferon production, potentially leading to cognitive impairment. This is the model we favor and suggests rejuvenation of T cells by immune checkpoint inhibitors and other treatments may be a plausible ex vivo therapy for AD.

An alternative model posits that the cytokine production by the T cells while participants are cognitively normal drives the development of cognitive impairment. Support for this idea is provided by a recent study that used in vitro cultured stem cell derived neurons, astrocytes, and microglia incubated with healthy peripheral blood mononuclear cells (PBMCs) that showed increased microglial activation and inflammation driven by CD8+ T cells mediated by CXCR3 driven infiltration. While these are important and interesting results there are two reasons that a protective rather than pathogenic role for T cells may be warranted. First, from a teleological point of view the increased function may be a form of resilience helping to stave off disease from chronic innate inflammation as we described earlier. The second, is that several studies have observed an increase in IFNγ that is associated with slower symptomatic progression in AD. Discerning between these two models will require a longitudinal study to understand the exact temporal relationship between T cell function, exhaustion, and cognitive function.

A range of evidence points to degeneration of neuromuscular junctions as an important contribution to the characteristic loss of muscle mass and strength that takes place with age, leading to sarcopenia. Neuromuscular junctions are the structurally complex link between muscle fibers and the nervous system. While the fine details are not well understood at this time, it seems plausible that some downstream effect of neuromuscular junction activity is necessary for tissue maintenance in muscles to function correctly. When neuromuscular junctions suffer dysfunction due to the underlying molecular damage of aging, muscles suffer as well.

Age-induced degeneration of the neuromuscular junction (NMJ) is associated with motor dysfunction and muscle atrophy. While the impact of aging on the NMJ presynapse and postsynapse is well-documented, little is known about the changes perisynaptic Schwann cells (PSCs), the synaptic glia of the NMJ, undergo during aging. Here, we examined PSCs in young, middle-aged, and old mice in three muscles with different susceptibility to aging. Using light microscopy and electron microscopy, we found that PSCs acquire age-associated cellular features either prior to or at the same time as the onset of NMJ degeneration. Notably, we found that aged PSCs fail to completely cap the NMJ even though they are more abundant in old compared with young mice. We also found that aging PSCs form processes that either intrude into the synaptic cleft or guide axonal sprouts to innervate other NMJs.

We next profiled the transcriptome of PSCs and other Schwann cells (SCs) to identify mechanisms altered in aged PSCs. This analysis revealed that aged PSCs acquire a transcriptional pattern previously shown to promote phagocytosis that is absent in other SCs. It also showed that aged PSCs upregulate unique pro-inflammatory molecules compared to other aged SCs. Interestingly, neither synaptogenesis genes nor genes that are typically upregulated by repair SCs were induced in aged PSCs or other SCs. These findings provide insights into cellular and molecular mechanisms that could be targeted in PSCs to stave off the deleterious effects of aging on NMJs.

Link: https://doi.org/10.1111/acel.13981

Given the importance of lingering senescent cells in the progression of degenerative aging, researchers continue to dig deeper into the biochemistry of these errant cells and their disruptive influence on tissue function. Here find a representative example of this work, in which the senescence-associated secretory phenotype is analyzed, in part to find better universal markers of senescence, and in part to find better therapeutic targets that are common across different cell types and causes of senescence.

DNA damage resulting from genotoxic injury can initiate cellular senescence, a state characterized by alterations in cellular metabolism, lysosomal activity, and the secretion of factors collectively known as the senescence-associated secretory phenotype (SASP). Senescence can have beneficial effects on our bodies, such as anti-cancer properties, wound healing, and tissue development, which are attributed to the SASP produced by senescent cells in their intermediate stages. However, senescence can also promote cancer and aging, primarily due to the pro-inflammatory activity of SASP.

Studying senescence is complex due to various factors involved. Genotoxic stimuli cause random damage to cellular macromolecules, leading to variations in the senescent phenotype from cell to cell, despite a shared program. Furthermore, senescence is a dynamic process that cannot be analyzed as a static endpoint, adding further complexity. Investigating SASP is particularly intriguing as it reveals how a senescence process triggered in a few cells can spread to many others, resulting in either positive or negative consequences for health.

Senescence is a dynamic process influenced by a variety of factors, which greatly affects SASP composition and functions. However, to our knowledge, there is no comprehensive secretome analysis that considers these influences. In this study, we performed a meta-analysis of 70 protein lists from 20 studies to clarify the induction process of senescence. The analysis revealed the following points: I) The IGF and IGFBP signaling pathways are representative common factors in senescent cells. II) The RUNX1 and UCH deubiquitination that regulates proteasome activity were enriched at the very early stage (1-3 days). III) SASP of the middle stage and late stage were enriched inflammatory pathway related protein, including IL-1, IL-4, IL-12, IL-13, and NF-kb. IV) There is a change in carbohydrate metabolism towards glycolysis during senescence induction. V) Senescent fibroblasts subjected to oncogene-induced senescence were found to be distinct from other senescent cells.

IGFBPs have been extensively linked to senescent cells. Studies have demonstrated that these IGFBPs can induce senescence at both the cellular and individual levels when administered to either the culture medium or living organisms. In our analysis, we consistently detected IGFBP4 and IGFBP7 in all datasets at the late stage. Furthermore, the IGF and IGFBP signaling pathway emerged as a common pathway in both the middle and late stages, irrespective of the type of stressor. These findings align with previous analyses and underscore the significant role of the IGF and IGFBP pathway in senescence. They suggest that factors associated with this pathway could serve as a universal marker for identifying senescent cells.

Link: https://doi.org/10.1186/s12964-023-01280-4

The most noticeable symptoms of Parkinson's disease occur because of the loss of a small but vital population of dopamine-generating neurons in the brain. The condition is associated with the spread of misfolded, aggregated α-synuclein throughout brain tissue. α-synuclein is one of the few molecules in the body capable of misfolding in ways that encourage other molecules o α-synuclein to also misfold in the same way. It can thus spread from cell to cell, perhaps carried in extracellular vesicles. It is thought that misfolding of α-synuclein often first occurs in the intestines, and only then spreads to the brain through the nervous system.

Dopaminergenic neurons are in some way more vulnerable than other cells to the pathological biochemistry that accompanies the presence of misfolded α-synuclein. This vulnerability also appears strongly connected to the function of mitochondria, the power plants of the cell, hundreds found in every neuron. Genetic variants that increase the risk of suffering Parkinson's disease are connected to loss of mitochondrial function and loss of mitochondrial quality control, suggesting that mitochondrial dysfunction is important to the death of neurons in this condition.

One of the mechanisms thought to cause age-related declines in mitochondrial function is mitochondrial DNA damage. Mitochondria are the descendants of ancient symbiotic bacteria, and they still carry their own circular genome. In today's open access paper, the authors provide evidence to suggest that mitochondrial DNA damage can spread from cell to cell in the Parkinson's brain. In addition to an investigation of the biochemistry involved in this transmission of damage, the researchers demonstrate that introducing damaged mitochondrial DNA into the brains of mice produces symptoms that mimic those of Parkinson's disease.

One does have to be careful when looking at studies in which researchers damage the biochemistry of mice in some way and thereafter draw conclusions about aspects of aging and disease. Age-related diseases emerge from damage and dysfunction, so many different forms of damage and dysfunction can mimic specific aspects of aging to some degree, even if they are not all that important in normal aging, even if they are not operating in any meaningful way in normal aging. Whether or not any given study is usefully taking this approach of applying a specific form of damage to mice depends on the details. Here it seems that one can argue that the approach is more rather than less compelling, but it still leaves open the question of the degree to which the mechanism of transmission of damaged mitochondrial DNA is important in the condition.

Mitochondrial DNA damage triggers spread of Parkinson's disease-like pathology

In the field of neurodegenerative diseases, especially sporadic Parkinson's disease (sPD) with dementia (sPDD), the question of how the disease starts and spreads in the brain remains central. While the prion-like proteins resulting from misfolding of α-synuclein have been designated as a culprit, recent studies suggest the involvement of additional factors. We found that oxidative stress, damaged DNA binding, cytosolic DNA sensing, and Toll-Like Receptor (TLR)4/9 activation pathways are strongly associated with the sPDD transcriptome, which has dysregulated type I Interferon (IFN) signaling. In sPD patients, we confirmed deletions of mitochondrial DNA (mtDNA) in the medial frontal gyrus, suggesting a potential role of damaged mtDNA in the disease pathophysiology.

To explore its contribution to pathology, we used spontaneous models of sPDD caused by deletion of type I IFN signaling (Ifnb-/-/Ifnar-/- mice). We found that the lack of neuronal IFNβ/IFNAR leads to oxidization, mutation, and deletion in mtDNA, which is subsequently released outside the neurons. Injecting damaged mtDNA into mouse brain induced PDD-like behavioral symptoms, including neuropsychiatric, motor, and cognitive impairments. Furthermore, it caused neurodegeneration in brain regions distant from the injection site, suggesting that damaged mtDNA triggers spread of PDD characteristics in an "infectious-like" manner.

We also discovered that the mechanism through which damaged mtDNA causes pathology in healthy neurons is independent of Cyclic GMP-AMP synthase and IFNβ/IFNAR, but rather involves the dual activation of TLR9/4 pathways, resulting in increased oxidative stress and neuronal cell death, respectively. Our proteomic analysis of extracellular vesicles containing damaged mtDNA identified the TLR4 activator Ribosomal Protein S3 as a key protein involved in recognizing and extruding damaged mtDNA.

These findings might shed light on new molecular pathways through which damaged mtDNA initiates and spreads PD-like disease, potentially opening new avenues for therapeutic interventions or disease monitoring.

The intestinal barrier becomes leaky with age, allowing microbes and unwanted metabolites in the gut access to the body, where they will produce chronic inflammation and other harmful consequences. Ironically, it may be increased inflammatory signaling in the intestinal epithelium that causes dysfunction of the intestinal barrier and then later widespread, greater inflammation. Researchers here explore some of this inflammatory signaling and its downstream consequences, focusing in on IFNγ and its effects on a variety of mechanisms relevant to tissue dysfunction in the intestine.

The influence of aging on intestinal stem cells and their niche can explain underlying causes for perturbation in their function observed during aging. Molecular mechanisms for such a decrease in the functionality of intestinal stem cells during aging remain largely undetermined. Using transcriptome-wide approaches, our study demonstrates that aging intestinal stem cells strongly upregulate antigen presenting pathway genes and over-express secretory lineage marker genes resulting in lineage skewed differentiation into the secretory lineage and strong upregulation of MHC class II antigens in the aged intestinal epithelium.

Mechanistically, we identified an increase in proinflammatory cells in the lamina propria as the main source of elevated interferon gamma (IFNγ) in the aged intestine, that leads to the induction of Stat1 activity in intestinal stem cells thus priming the aberrant differentiation and elevated antigen presentation in epithelial cells. Of note, systemic inhibition of IFNγ signaling completely reverses these aging phenotypes and restores the regenerative capacity of the aged intestinal epithelium.

Link: https://doi.org/10.1038/s41467-023-41683-y

Skeletal stem cells in the bone marrow produce cells responsible for creating bone tissue. Researchers here show that disabling the well-known notch pathway in these cells leads to a considerable increase in bone mineral density with age. This is a desirable outcome, slowing the onset of osteoporosis, a widespread condition of old age. Better ways to encourage greater deposition of bone extracellular matrix are much needed, given the only modest efficacy of present drugs used in the treatment of osteoporosis.

Skeletal stem and progenitor cells (SSPCs) perform bone maintenance and repair. With age, they produce fewer osteoblasts and more adipocytes leading to a loss of skeletal integrity. The molecular mechanisms that underlie this detrimental transformation are largely unknown. Single-cell RNA sequencing revealed that Notch signaling becomes elevated in SSPCs during aging.

To examine the role of increased Notch activity, we deleted Nicastrin, an essential Notch pathway component, in SSPCs in vivo. Middle-aged conditional knockout mice displayed elevated SSPC osteo-lineage gene expression, increased trabecular bone mass, reduced bone marrow adiposity, and enhanced bone repair. Thus, Notch regulates SSPC cell fate decisions, and moderating Notch signaling ameliorates the skeletal aging phenotype, increasing bone mass even beyond that of young mice. Finally, we identified the transcription factor Ebf3 as a downstream mediator of Notch signaling in SSPCs that is dysregulated with aging, highlighting it as a promising therapeutic target to rejuvenate the aged skeleton.

Link: https://doi.org/10.1038/s41413-023-00283-8

Microglia are innate immune cells of the central nervous system, analogous to macrophages elsewhere in the body. In addition to mounting a defense against pathogens and cleaning up metabolic waste, these cells are involved in maintenance of neural connections. Ever more attention is given of late to chronic inflammation in the aging of the brain, and microglia are known to become more active and inflammatory with advancing age, amplifying inflammatory signaling in ways that are disruptive to tissue function.

Some of this microglial inflammatory signaling is due to a growing fraction of senescent microglia, one facet of the rising numbers of senescent cells of many different types throughout the body with age, but the rest is a mixed bag of reactions to damage and dysfunction in brain tissue. This includes issues internal to cells, such as mitochondrial dysfunction that leads to mislocated mitochondrial DNA fragments and an inflammatory reaction to that DNA, issues external to cells, such as the growing presence of misfolded amyloid-β associated with Alzheimer's disease, and structural problems such as leakage of the blood brain barrier that allows inappropriate cells and molecules to pass into the brain and provoke an immune response.

It is possible to clear the entire population of microglia from the brain using CSF1R inhibitors such as pexidartinib. New microglia repopulate the brain within a few weeks. Some researchers have considered this as a way to reset some of the excessive inflammatory activity. It produces benefits in mice, but too little work has been carried out to date to determine just how long such a respite might last in humans. Other researchers are interested in finding ways to adjust the state of microglia from pro-inflammatory M1 to anti-inflammatory M2, analogous to the established research into manipulation of macrophage state. This is also promising, and something that could be achieved with existing drugs. It is also not very far advanced towards the clinic, however.

The role of signaling crosstalk of microglia in hippocampus on progression of ageing and Alzheimer's disease

Microglial-related neuroinflammation affects the trajectory of Alzheimer's disease (AD), and an individual's susceptibility to AD may depend in part on the behavioral phenotype of microglia. Understanding the immune response patterns of microglia and the behavioral interaction mode of microglia with other cell types allows for the accurate targeting of microglia with impaired or abnormal responses, which has great potential for developing effective tools to delay aging and avoid neurodegenerative diseases.

In the present study, scRNA-seq analysis was performed on hippocampal samples from wide type (WT) and 5× familiar Alzheimer's disease (5× FAD) mice at 2-, 12-, and 24-month of age to map the clustering of hippocampal cells during aging and AD. We focused on the immune behavior and phenotypic characteristics of microglia. The outside and inside signal flow in the population of microglia reveals the crosstalk between neuroinflammatory pathways and cell behavior interactions guided by immune responses in the hippocampus. Our study found that blood-brain barrier (BBB) injury may increase the percentage of microglia during the progression of aging and AD.

In rodents, microglia account for 5%-12% of all central nervous system (CNS) cells and are distributed throughout the parenchyma. We found that microglia made up over 12% of the total hippocampal cells, about 45%-55% in WT mice and 45%-78% in 5× FAD mice. Maintenance of the brain microglial population is independent of circulating monocytes generated in the bone marrow and depends primarily on the self-renewal of microglia. Our scRNA-seq results showed that in WT mice, the number of microglia increased significantly at 24 months, but the fraction of microglia in the total hippocampal cells remained stable.

In the hippocampus of 5× FAD mice, the number and proportion of microglia increased abnormally at 12 months, and at 24 months, the number of microglia tended to level off compared with the 12-month of age. The accumulation of amyloid-β also showed a similar trend. This may be one of the reasons for the induction of microglial activation and proliferation. In addition, from 2 to 24 months, the PTN growth signal received by microglia in WT mice tended to decrease, suggesting that excessive growth of microglia was continuously suppressed. In 5× FAD mice, the growth and development signals were significantly enhanced at 12 months compared to those at 2 months. The uncontrolled proliferation of microglia is clearly not spontaneous but arises from environmental stimuli.

The challenge with most identified mechanisms of disease is that they are not close enough to root causes to be highly influential on the progression of the condition. Particularly in the case of neurodegenerative diseases such as Alzheimer's disease, the condition is very complex, and there is much to be discovered about how dysfunction progresses. That doesn't mean that any given aspect of that progression will prove to be useful enough to make the jump from improvements shown in animal models to a basis for therapy in humans. There are many discoveries in the history of Alzheimer's research that have appeared to be as interesting as the work noted here.

Studies have shown that even before Alzheimer's symptoms appear, brain activity is disrupted in people who go on to develop the disease. There is neuronal hyperactivity and signal disorganization in the brain. The main inhibitor of neuronal signals in the human brain is the neurotransmitter GABA. It works in close collaboration with a cotransporter, KCC2. This is an ion pump, located in the cell membrane, which circulates chloride and potassium ions between the inside and outside of neurons. "A loss of KCC2 in the cell membrane can lead to neuronal hyperactivity. One study has already shown that KCC2 levels were reduced in the brains of deceased Alzheimer's patients. This gave us the idea of examining the role of KCC2 in an animal model of Alzheimer's disease."

Scientists used mice expressing a manifestation of Alzheimer's disease. The researchers found that when these mice reached the age of four months, KCC2 levels decreased in two regions of their brains: the hippocampus and the prefrontal cortex. These two regions are also affected in people suffering from Alzheimer's disease. In light of these results, the researchers turned to a molecule developed in their laboratory, CLP290, a KCC2 activator that prevents its depletion. In the short term, the administration of this molecule to mice that already had reduced KCC2 levels improved their spatial memory and social behaviour. In the long term, CLP290 protected them against cognitive decline and neuronal hyperactivity. "Our results do not imply that the loss of KCC2 causes Alzheimer's disease. On the other hand, it does appear to cause an ionic imbalance leading to neuronal hyperactivity that can lead to neuronal death. This suggests that by preventing the loss of KCC2, we could slow down and perhaps even reverse certain manifestations of the disease."

Link: https://www.eurekalert.org/news-releases/998174

General inhibition of mTOR slows aging, a calorie restriction mimetic effect, but comes with a range of side-effects, given that mTOR is a regulator of growth and development. mTOR forms two different protein complexes, mTORC1 and mTORC2. In recent years, work to produce drugs based on mTOR inhibition has focused on selectively inhibiting mTORC1 in order to reduce side-effects. Researchers here report further reduction in side-effects in short-lived nematode worms by restricting mTORC1 inhibition to neurons only.

mTORC1 (mechanistic target of rapamycin complex 1) is a metabolic sensor that promotes growth when nutrients are abundant. Ubiquitous inhibition of mTORC1 extends lifespan in multiple organisms but also disrupts several anabolic processes resulting in stunted growth, slowed development, reduced fertility, and disrupted metabolism. However, it is unclear if these pleiotropic effects of mTORC1 inhibition can be uncoupled from longevity. Here, we utilize the auxin-inducible degradation (AID) system to restrict mTORC1 inhibition to C. elegans neurons. We find that neuron-specific degradation of RAGA-1, an upstream activator of mTORC1, or LET-363, the ortholog of mammalian mTOR, is sufficient to extend lifespan in C. elegans.

Unlike raga-1 loss of function genetic mutations or somatic AID of RAGA-1, neuronal AID of RAGA-1 robustly extends lifespan without impairing body size, developmental rate, brood size, or neuronal function. Moreover, while degradation of RAGA-1 in all somatic tissues alters the expression of thousands of genes, demonstrating the widespread effects of mTORC1 inhibition, degradation of RAGA-1 in neurons only results in around 200 differentially expressed genes with a specific enrichment in metabolism and stress response. Notably, our work demonstrates that targeting mTORC1 specifically in the nervous system in C. elegans uncouples longevity from growth and reproductive impairments, and that many canonical effects of low mTORC1 activity are not required to promote healthy aging. This data challenges previously held ideas about the mechanisms of mTORC1 lifespan extension and underscore the potential of promoting longevity by neuron-specific mTORC1 modulation.

Link: https://doi.org/10.1371/journal.pgen.1010938

In today's open access review paper, researchers lay out summarize hypotheses and evidence for there to be a bidirectional relationship between age-related hearing loss and loss of cognitive function. Their summary is informative, but in their view the present literature is too sparse to be conclusive, and further studies are needed to provide a greater breadth of human data.

There is good reason to think that hearing loss contributes directly to a more rapid pace of cognitive decline. The brain is very much a "use it or lose it" organ, and lacking use in later life, it declines more rapidly. Evidence from study populations with age-related hearing loss have compared the trajectories of those fitted with hearing aids versus those who were not, showing a greater incidence of dementia in those without augmented hearing.

When it comes to causation in the other direction, much of the thinking centers around common cause mechanisms of neurodegeneration. The same issues of chronic inflammation and cellular dysfunction that harm the brain also harm the sensory hair cells of the inner ear and their connections to the brain. It is also possible that complex issues situated entirely in the aging brain may contribute to difficulties in processing of auditory information that appear very similar to hearing loss.

Which Came First, Age-Related Hearing Loss with Tinnitus or Cognitive Impairment? What are the Potential Pathways?

Age-related hearing loss (ARHL), caused by peripheral hearing loss or central auditory processing disorder (CAPD), is the third leading cause of chronic disability in the older population. ARHL is one of the most important modifiable risk factors for dementia. Cumulative evidence links peripheral ARHL and cognitive decline with impaired performance across multiple cognitive domains, including episodic memory and processing speed. An independent association was also observed between subclinical hearing loss and cognitive impairment in a cross-sectional population study. A longitudinal cohort study further indicated that subjects with worse subclinical hearing loss have a steeper cognitive decline, as measured by the Digit Symbol Substitution Test over a mean follow-up of 9.1 years. However, a direct causal effect of peripheral hearing loss on dementia with hearing alterations is not defined. In a large cohort of cognitively healthy older people, peripheral hearing dysfunction was not associated with the pathological hallmark brain amyloid deposition of Alzheimer's disease (AD), the main phenotype of dementia. Age-related CAPD may precede the onset of clinical dementia in people with probable AD and might be an early marker of mild cognitive impairment (MCI) and AD. Older individuals with CAPD had a high risk for the subsequent onset of probable AD, and CAPD was independently associated with cognitive frailty, a frailty phenotype defined by coexisting physical frailty and MCI.

Accumulating evidence suggests that neurodegenerative pathologies add disproportionate central hearing deficits to any already existing peripheral hearing loss. Clinical findings have indicated that central auditory processing is impaired in people diagnosed with AD and its preclinical stages and may manifest many years before clinical diagnosis. Patients with semantic dementia frequently reported tinnitus and hyperacusis and were found to have abnormal neuroanatomical alterations in cortico-subcortical auditory network and limbic network. The prevalence of auditory hallucinations in Parkinson's disease and in dementia with Lewy bodies is estimated to be 8.9% and 30.8%, respectively. Neuropathological findings have indicated that AD pathological hallmarks, i.e., amyloid plaques and neurofibrillary tangles (NFTs), presented in the higher structures of the central auditory pathways and primary and secondary auditory cortical areas, but did not in the cochlea and cochlear nucleus. CAPD was persistently associated with cerebrospinal-fluid (CSF) tau levels, entorhinal and hippocampal cortex volumes, cortical thickness, and cognitive deficits in cognitively and physically healthy individuals with positive AD family history. These neuropathological alterations suggest that AD-related CAPD might not have resulted from peripheral hearing loss and induced maladaptive plastic changes.

Several hypotheses of possible etiological mechanisms have been proposed that elucidate these relationships. The common-cause hypothesis involves neurodegenerative, metabolic, and vascular pathophysiological alterations and chronic systemic inflammation during aging. The cognitive-reserve depletion or cascade hypothesis is based on brain experience-dependent neuroplasticity, cognitive reserve, and brain reserve, which refer to individual differences in the functionality and structure of the brain. The cognitive-load hypothesis proposes that individuals with hearing loss use greater cognitive resources for listening to degraded auditory signals and auditory perceptual processing, which makes these resources unavailable for other cognitive tasks, eventually leading to cognitive reserve depletion. Another hypothesis is proposed to further explain the neuropathological basis of cognitive load resulting in a vicious cycle of brain structure alterations, cognitive reserve and auditory reserve depletion. The hypothesis proposes a mechanism for the interaction between the medial temporal lobe related to auditory processing and dementia pathology, which could explain the association between hearing loss and cognitive impairment.

The brain is immune privileged and has its own immune system separated from that of the rest of the body by the blood-brain barrier. It isn't true that T cells of the adaptive immune system are never found in the brain, however. There are ways in, and as researchers show here, T cells do play a role in coordinating the immune defense against issues such the excessive protein aggregation characteristic of neurodegenerative conditions such as Alzheimer's disease. There is an increasing focus on immune system dysfunction and chronic inflammation in the aging of the brain and onset of neurodegeneration. Exerting greater control over cells that have become overly inflammatory is an important goal in the research community, and hence the interest in finding existing mechanisms whereby that might be occurring.

Microglia are immune cells in the brain responsible for clearing beta-amyloid plaques. As Alzheimer's disease progresses, microglia can lose their capacity to remove these plaques and instead produce inflammatory mediators that may accelerate beta-amyloid plaque progression. Researchers have found that accumulating another subtype of immune cells, called CD8+ T cells, is essential to slow this process by interacting with microglia. This interaction, in turn, was important to limit beta-amyloid burden and preserve memory capabilities in a mouse model of the disease.

To understand how T cells were delaying symptom progression in their Alzheimer's disease model, researchers searched for the most abundant molecular interaction between CD8+ T cells and the microglia. They found a protein on the surface of CD8+ T cells, CXCR6, interacts with the protein CXCL16 expressed by microglia. The two surface proteins, CXCR6 and CXCL16, essentially performed a handshake between the two cells, communicating in both directions. Just like the firmness of a human handshake can convey information, so can the interaction of these two proteins on the outside of their respective cells.

The scientists determined how the handshake occurs and delays the onset of Alzheimer's disease-related pathologies. The CD8+ T cells first move next to the microglia, which are localized next to the beta-amyloid plaques. Then, the CD8+ T cells use the handshake to signal to the microglia to stop causing uncontrolled inflammation, which, in turn, slows plaque growth and symptoms in the mouse models. When the scientists deleted the gene for the CD8+ T cell's protein CXCR6, the mice developed worse Alzheimer's disease-related symptoms. This effect was partially because the CD8+ T cells without CXCR6 failed to accumulate in the brain near the microglia or plaque site. These cells also did not acquire the appropriate suppressive function. Thus, disrupting the CD8+ T cell's ability to perform the handshake prevented its protective effect against Alzheimer's disease symptoms.

Link: https://www.stjude.org/media-resources/news-releases/2023-medicine-science-news/t-cells-in-brain-slow-progression-of-alzheimers-disease.html

The heart is one of the least regenerative organs in the adult body, and this makes the lasting consequences of a heart attack that much worse. While the best approach to the challenge of cardiovascular disease is to find a way to reverse atheroslerosis, and thus prevent heart attacks from ever occurring, much of the focus of the research community is on improving the regenerative capacity of heart tissue. Here, researcher find a comparatively straightforward way to make cardiomyocyte cells in the heart behave more like those in developing tissue, increasing their regenerative capacity. Since the target is well defined, this may well lead to drugs that can recapture some of the effect.

Postnatal maturation of cardiomyocytes is characterized by a metabolic switch from glycolysis to fatty acid oxidation, chromatin reconfiguration and exit from the cell cycle, instating a barrier for adult heart regeneration. Here, to explore whether metabolic reprogramming can overcome this barrier and enable heart regeneration, we abrogate fatty acid oxidation in cardiomyocytes by inactivation of Cpt1b. We find that disablement of fatty acid oxidation in cardiomyocytes improves resistance to hypoxia and stimulates cardiomyocyte proliferation, allowing heart regeneration after ischaemia-reperfusion injury.

Metabolic studies reveal profound changes in energy metabolism and accumulation of α-ketoglutarate in Cpt1b-mutant cardiomyocytes, leading to activation of the α-ketoglutarate-dependent lysine demethylase KDM5. Activated KDM5 demethylates broad H3K4me3 domains in genes that drive cardiomyocyte maturation, lowering their transcription levels and shifting cardiomyocytes into a less mature state, thereby promoting proliferation. We conclude that metabolic maturation shapes the epigenetic landscape of cardiomyocytes, creating a roadblock for further cell divisions. Reversal of this process allows repair of damaged hearts.

Link: https://doi.org/10.1038/s41586-023-06585-5

Cells enter a senescent state constantly throughout life, largely as a result of reaching the Hayflick limit on cellular replication, but also due to damage and stress. Senescent cells cease to replicate and begin to secrete pro-inflammatory, pro-growth signals. This attracts the immune system to sites of potential concern, and in the case of physical injuries to tissue the signaling of senescent cells helps to coordinate repair. Senescent cells are normally cleared from tissues fairly quickly, being destroyed either by immune cells, or via programmed cell death mechanisms. With age, however, the pace of clearance slows and the pace of creation picks up as the body becomes more inflamed, stressed, and damaged.

Studies in mice make it clear that a burden of lingering senescent cells grows with age throughout the body, and that their secreted signals actively disrupt tissue structure and function when maintained for the long term, changing the behavior of other cells for the worse. Targeted destruction of senescent cells by first generation senolytic drugs, or the genetic engineering techniques that preceded those drugs, produces rapid rejuvenation. Life span is extended, measures of many different age-related diseases are reversed. This happens quite quickly. As one might expect, a great deal of attention is now focused on refining strategies for clearing senescent cells, both in academia and in biotech companies.

While the research and development communities are focused on working towards new, more selective senolytics, I think it worth noting that the cheap, safe senolytics that already exist receive far less attention than they should. The combination of dasatinib and quercetin has a good safety profile in clinical trials, and has been shown to clear senescent cells in humans to about the same degree as it does in mice. It can be prescribed off-label by physicians. One might expect a good deal more ongoing effort to prove that this is in fact reversing aging in humans than is actually taking place: only a few, slow academic clinical trials and little exploration of dosing. This is an area in which philanthropists might do a great deal of good by sponsoring low-cost, well-managed trials that are intended to prove that off-label approaches of this nature are actually as good as the animal data might indicate.

Senescent cells at the crossroads of aging, disease, and tissue homeostasis

The variation in senescent cell phenotypes creates some challenges in their elimination, as not every pathway may be shared between senescent cells, as is often observed during cancer. Furthermore, beneficial aspects of senescent cells create caveats for when and how they should be eliminated, as disruption of healing, developmental, or regenerative processes in pursuit of prevention or treatment of chronic diseases is less desirable. Thus, development of next-generation precision senolytic therapies that take advantage of potential distinctions between beneficial and detrimental senescent cells might improve safety by allowing selective clearance of those that drive the condition being treated.

Since current strategies focus on targeting pathways that promote cell survival, collateral damage to other cell types, as observed in the case of thrombocytopenia with the BCL-2 family inhibitor ABT-263, are a current target for improvement. Indeed, a modified version of ABT-263 that cannot be activated by platelets has removed one form of collateral damage, and others are currently in development.

One aspect of senescence that might be amenable to precision targeting is the temporal nature of acute vs. chronic senescence. Many beneficial aspects of senescence described thus far are transient in nature, and typically occur within a few days following induction/initiation of senescence, while chronic accumulation of senescent cells has been linked to interferon activation and age-related chronic disease. Therefore, perhaps the simplest way differentiating between beneficial and deleterious senescent cells may be by targeting effects that occur in chronic senescence and not during the more transient early response. This approach may improve outcomes in the future by improving the safety of senolytic use and more selectively only targeting those senescent cells that drive more degenerative chronic pathology.

Overall, identification of senescent cell types and their role in causing human disease will be invaluable in the creation of new senotherapeutics that might allow these contrasting phenotypes to be selectively targeted. This is a major potential benefit of the recently announced SenNet Consortium, which will map senescent cells in both murine and human tissues and help to catalog the diversity, abundance, spatial localization, and secretome of senescent cells in human and murine conditions. Beyond identification of senescent cell heterogeneity, these data will also help answer questions about translatability of findings between species, identify new biomarkers of senescence, and give indications about the origins of senescent cells across the lifespan.

Researchers here show that the burden of white matter hyperintensities in the brain correlates with both age and with loss of cognitive function. A white matter hyperintensity is named for its appearance in MRI images of the brain, and is an area of damaged tissue. The cause can include rupture of small blood vessels, which is increasingly common with advancing age, particularly in patients with hypertension, or forms of inflammation and scarring, often associated with leakage of the blood-brain barrier, another issue that becomes prevalent with age. These incidences of damage to the brain are individually minor, but collectively add up over time.

To elucidate the relationship between aging and cognitive decline, it is important to understand the structural changes in the brain that occur throughout aging as a potential mechanistic explanation. One example of structural changes that are typically associated with older age is the presence of white matter hyperintensities (WMHs). WMHs are a neuroimaging marker of small vessel disease and are often indicative of chronic, insufficient cerebrovascular supply.

The accrual of WMHs is a subtle, progressive process typically associated with cardiovascular risk factors (e.g., body mass index, hypertension, or diabetes) and aging. There is also evidence that both age and cardiovascular risk factors predict increasing WMH load over time. This is supported by findings suggesting that increasing physical activity or controlling vascular risk factors such as blood pressure can slow the progression of WMHs.

We aimed to investigate if WMH load is a mediator of the relationship between age and cognitive decline. Healthy participants (N = 166, 20-80 years) completed the Montreal Cognitive Assessment (MoCA). WMHs were manually delineated on fluid-attenuated inversion recovery (FLAIR) scans. Mediation analysis was conducted to determine if WMH load mediates the relationship between age and cognition. Older age was associated with worse cognition, but this was an indirect effect: older participants had more WMHs, and, in turn, increased WMH load was associated with worse MoCA scores. Thus WMH load mediates the relationship between age and cognitive decline. Importantly, this relationship was not moderated by age, i.e., increased WMH severity is associated with poorer MoCA scores irrespective of age.

Link: https://doi.org/10.1016/j.neurobiolaging.2023.08.007

Hearing loss is prevalent in older individuals, either involving the destruction of sensory hair cells in the inner ear, or the axonal connections between those hair cells and the brain, or both. Hair cells do not normally regenerate to any great degree in adults, which has led to efforts to grow patient matched replacement cells, or reprogram native cells to convince them to produce new hair cells. Despite promising advances, it is not as yet a solved problem.

Age-related hearing loss, or presbycusis, is a common cause of hearing loss in elderly people worldwide. It typically presents as progressive, irreversible, and usually affects the high frequencies of hearing, with a tremendous impact on the quality of life. Presbycusis is a complex multidimensional disorder, in addition to aging, multiple factors including exposure to noise, or ototoxic agents, genetic susceptibility, metabolic diseases, and lifestyle can influence the onset and severity of presbycusis.

With the aging of the body, its ability to clean up deleterious substances produced in the metabolic process is weakened, and the self-protection and repair function of the body is reduced, which in turn leads to irreversible damage to the cochlear tissue, resulting in the occurrence of presbycusis. Presently, oxidative stress (OS), mitochondrial DNA damage, low-grade inflammation, decreased immune function, and stem cell depletion have been demonstrated to play a critical role in developing presbycusis. The purpose of this review is to illuminate the various mechanisms underlying this age-related hearing loss, with the goal of advancing our understanding, prevention, and treatment of presbycusis.

Link: https://doi.org/10.3389/fnins.2023.1253574

Aubrey de Grey and Brian Kennedy are prominent scientists in the longevity community who take very different approaches to the problem of human aging. They recently collaborated to write the Dublin Longevity Declaration, now posted online and signed by some of the leading figures in the aging research field, as well as fellow travelers in the longevity industry, founders of biotech companies attempting to implement interventions to treat aging. We live in a world in which the opportunity to produce actual, real, working rejuvenation therapies exists, but too few people believe this to be true. There is too little funding devoted to this goal. Declarations signed by prominent scientists, patient advocates, and biotechnology industry executives are one part of a broad range of advocacy that is still needed if we are to live in a world in which the treatment of aging stands alongside the treatment of cancer as a broadly supported goal.

Dublin Longevity Declaration: Consensus Recommendation to Immediately Expand Research on Extending Healthy Human Lifespans

For most of our history, even getting to old age was a significant accomplishment - and while centenarians have been around at least since the time of the Greeks, aging was never of major interest to medicine. That has changed. Longevity medicine has entered the mainstream. First, evidence accumulated that lifestyle modifications prevent chronic diseases of aging and extend healthspan, the healthy and highly functional period of life. More recently, longevity research has made great progress - aging has been found to be malleable and hundreds of interventional strategies have been identified that extend lifespan and healthspan in animal models. Human clinical studies are underway, and already early results suggest that the biological age of an individual is modifiable.

A concerted effort has been made in the longevity field to institutionalize the word "healthspan". Why healthspan (how long we stay healthy) and not its side-effect of lifespan (how long we live)? The reasons are linked more to perception than reality. Fundamental to this need to highlight healthspan is the idea that individuals get when they are asked if they want to live longer. Many imagine their parents or grandparents at the end of their lives when they often have major health issues and low quality of life. Then they conclude that they would not choose to live longer in that condition. This is counter to longevity research findings, which show that it is possible to intervene in late middle life and extend both healthspan and lifespan simultaneously. Emphasizing healthspan also reduces concerns of some individuals about whether it is ethical to live longer.

A drawback of this strategy exists, though: many current longevity interventions may extend healthspan more than lifespan. Lifestyle interventions such as exercise probably fit this mold. Many interventions that have dramatic health-extending effects in invertebrate models have more modest effects in mice, and there is a concern that they will be further reduced in humans. In other words, the drugs and small molecules that we are excited about today may, despite their hefty development costs and lengthy approval processes, only extend average healthspan by five or ten years and may not extend maximum lifespan at all.

Most experts in the field now acknowledge that this is a likely outcome in the near future and one focus of longevity medicine is now on achieving it. But far more is possible. Arguably, the avoidance of an emphasis on lifespan is a consequence of an overly pragmatic approach to two fundamental questions: Why do humans age and what can we do about it? These are surely two of the biggest questions in human biology. Although we try our best to ignore it, the prospect of an inevitable decline in health leading to mortality shapes our thoughts and actions. Despite the incredible advances in longevity research, these questions remain unanswered. What biological processes bring about the aged state? Can aging not just be significantly slowed, but more and more thoroughly reversed? How would humans, and their societies, be different if we achieve these goals?

It will cost billions of dollars in research and significant time to answer such questions, but we assert that it would undoubtedly pay for itself many times over. What cards need to be turned over to answer the longevity question? What interventional strategies are likely to take us beyond modest healthspan effects, and toward radical change in the rate of biological aging? Most of the lifestyle or small-molecule interventions that are currently being tested target pathways affecting longevity. These include those designed to improve metabolism, restore youthful immune function, maintain youthful body composition, eliminate deleterious cells, or improve cellular stress responses. But there are strategies on (and just over) the horizon that may have much bigger impact. These need to be seriously interrogated and resources need to be devoted to these big questions. There needs to be an acceptance and tolerance of significantly higher levels of failure in longevity research, knowing that big ideas are sometimes wrong and that the ones that are right will far outweigh the setbacks. Is radical lifespan extension foreseeable? No one can answer that question with certainty. But there are certainly enough tantalizing clues suggesting that aging is sufficiently malleable to warrant the allocation of very substantial resources.

The difference between lesser and greater degrees of modest exercise is sizable when it comes to effects on measures of cardiovascular health, such as blood pressure. The raised blood pressure characteristic of aging and a lack of physical fitness is damaging to delicate tissues, speeds the development of atherosclerosis, and is associated with a raised risk of mortality. A sizable proportion of the mortality reduction that attends greater physical activity in later life may be mediated via effects such as lowered blood pressure.

A study sought to determine if older adults with hypertension could receive these benefits by moderately increasing their daily walking, which is one of the easiest and most popular forms of physical activity for this population. The study focused on a group of sedentary older adults between ages 68 and 78 who walked an average of about 4,000 steps per day before the study. After consulting existing studies, researchers determined that 3,000 steps would be a reasonable goal. This would also put most participants at 7,000 daily steps, in line with the American College of Sports Medicine's recommendation.

The team conducted the study during the height of the COVID-19 pandemic, which meant they had to do everything remotely. The researchers sent participants a kit with pedometers, blood pressure monitors, and step diaries for participants to log how much they were walking each day. On average, participants' systolic and diastolic blood pressure decreased by an average of seven and four points, respectively, after the intervention. Other studies suggest decreases of these magnitudes correspond to a relative risk reduction of all-cause mortality by 11%, and 16% for cardiovascular mortality, an 18% reduction in the risk of heart disease, and a 36% risk reduction of stroke.

The findings suggest that the 7,000-step regimen the participants in the study achieved is on-par with reductions seen with anti-hypertensive medications. Eight of the 21 participants were already on anti-hypertensive medications. Those participants still saw improvements in systolic blood pressure from increasing their daily activity.

Link: https://today.uconn.edu/2023/09/increasing-steps-by-3000-per-day-can-lower-blood-pressure-in-older-adults/

Researchers here demonstrate in mice an effective approach to mimicking some of the adaptive responses to exercise, and sustaining those responses over time. Exercise mimetics have undergone a sedate pace of development in comparison to the larger body of work on calorie restriction mimetics, intended to mimick some of the sweeping changes to metabolism that occur at low nutrient levels, and the field isn't yet as well established. Still, some interesting lines of work have emerged, such as the program noted here.

The new drug, known as SLU-PP-332, doesn't affect appetite or food intake. Nor does it cause mice to exercise more. Instead, the drug boosts a natural metabolic pathway that typically responds to exercise. In effect, the drug makes the body act like it is training for a marathon, leading to increased energy expenditure and faster metabolism of fat in the body. The drug leads obese mice to lose weight by convincing the body's muscles that they are exercising more than they really are, boosting the animals' metabolism. It also increases endurance, helping mice run nearly 50% further than they could before. All without the mice lifting a paw.

"This compound is basically telling skeletal muscle to make the same changes you see during endurance training. When you treat mice with the drug, you can see that their whole body metabolism turns to using fatty acids, which is very similar to what people use when they are fasting or exercising. And the animals start losing weight."

The new drug targets a group of proteins in the body known as estrogen-related receptors (ERRs), which are responsible for activating some of the most important metabolic pathways in energy-gobbling tissues like muscles, the heart, and the brain. The ERRs are more active when people exercise, but they have proven difficult to activate with drugs. In another paper published in March, the researchers reported that they had successfully designed SLU-PP-332 to boost activity of the ERRs. They also observed that the compound allowed normal-weight mice to run for 70% longer and 45% further than mice not receiving the drug. In their latest research, the team tested the drug on obese mice. Treating obese mice twice a day for a month caused them to gain 10 times less fat than untreated mice and lose 12% of their body weight. Yet the mice kept eating the same amount of food and didn't exercise any more.

Link: https://www.eurekalert.org/news-releases/1002687

A brace of popular science articles on aging research were recently published at the Economist. Like many of these views from a distance written by journalists on the outside, peering into the field, one must assume that its existence is largely the result of the sizable investments made over the last two years into the development of therapies based on partial reprogramming. The Altos Labs funding in particular represented a meaningful fraction of all investment into biotech made that year. That tends to attract attention. From there, an investigator would notice an additional broad focus on cellular senescence, many companies and research groups working towards the development of senolytic therapies to clear senescent cells from aged tissues.

After that, however, there are few obvious high points for the outside observer to focus on. Epigenetic clocks, perhaps. The relentless self-promoters such as David Sinclair. But it quickly starts to become harder to figure out what is going on, which of the hundreds of small biotech companies and research groups in the field, trying to treat age-related disease by focusing on mechanisms of aging, are important. It is certainly the case that theories of aging abound, and researchers disagree on which paths are best. A sizable fraction of the progress of the next twenty years in the matter of treating aging as a medical condition will arise not because of the where the mainstream is focused, but will occur because a few small biotech companies tried something and it turned out to be far more useful than most of the community expected it to be.

There are advantages and disadvantages to the way in which distribution of funding tends to follow a power law. The projects at the top of the list, such as partial reprogramming, will definitely have enough funds to determine whether or not these are good approaches to rejuvenation. If they fail, then on to the next. Something will be accomplished, one way or another. But aging is a complex process of many different mechanisms, and many different approaches to therapy will be needed, not just one. Exploring the potential of the rest of the projects, underneath those at the top of the list, is just as necessary in the long run.

In search of forever

Slowing, let alone reversing, the process of ageing was once alchemical fantasy. Now it is a subject of serious research and investment. Peter Thiel, a co-founder of PayPal, Larry Page and Sergey Brin, co-founders of Google, and Jeff Bezos, founder of Amazon, have all invested in, and often been instrumental in the creation of, firms trying to prolong lifespan and healthspan. In March Sam Altman, the head of OpenAI, revealed that two years ago he had invested $180m in Retro Biosciences, a Silicon Valley firm founded with the goal of adding ten years to healthy human lifespans.

Beneath the forest canopy of firms backed by tech royalty an undergrowth of more conventionally financed startups is working on drugs that might slow or stall some aspects of ageing. Even closer to the ground, the idea is catching on of prolonging lifespan and healthspan using pills and potions that are already available, in addition to (and sometimes instead of) the conventional approach of diet, exercise, and early-to-bed. A culture of do-it-yourself lifespan extension is emerging, at least in affluent places endowed with the sort of technical expertise and technological hubris identified with Silicon Valley.

Many in mainstream science and medicine look at all this slightly askance. That is understandable. It is an area which attracts chancers and charlatans as well as those with more decent motives, and its history is littered with "breakthroughs" that have led more or less nowhere. America's Food and Drug Administration does not recognise "old age" as a disease state, and thus as a suitable target for therapy. Nevertheless, evidence has been accumulating that such research might have something to offer.

Some established drugs really do seem to extend life, at least in mice. That offers both the possibility that they might do so in people and some insight into the processes involved. The ever-greater ease with which genes can be edited helps such investigations, as does access to large amounts of gene-sequence data. The ability to produce personalised stem cells, which stay forever young, has opened up new therapeutic options. And new diagnostic tools are now offering scientists means to calculate the "biological ages" of bodies and organs and compare them with actual calendar ages. In principle this allows longevity studies to achieve convincing results in less than a lifetime.

Another reason for hope is that the physiological details of ageing are becoming clearer. In particular, those researching the question have been able to divide the problem into bite-sized chunks that can, to some extent, be tackled individually. Researchers have proposed 12 hallmarks of ageing chosen on the basis that they are all things which typically get worse with age, which accelerate ageing if stimulated and which seem to slow it down if treated. Some of these smaller (if often still huge) problems are attractive targets for intervention in their own right; chronic inflammation, for example, or the build-up of aberrant proteins seen in Alzheimer's disease. George Church of Harvard University, a biotech guru unafraid of the unorthodox, thinks the approach could offer more than that: identify and deal with each of the components separately and you may find you have solved the problem in its entirety.

Urolithin A is one of a number of compounds available as supplements that can improve mitochondrial function in older individuals. Like others, urolithin A may function by improving the mitochondrial quality control process of mitophagy, responsible for removing damaged and worn mitochondria. Mitophagy becomes less efficient with age, and this is one of the contributing factors to age-related loss of mitochondrial function and its harmful impact on tissues. Like other supplement based approaches to improving mitochondrial function, it is likely that regular exercise delivers larger gains than those demonstrated for supplementation with urolithin A. Whether exercise and supplementation produce greater gains when undertaken in combination is poorly studied, unfortunately.

Cardiovascular diseases remain the primary cause of global mortality, necessitating effective strategies to alleviate their burden. Mitochondrial dysfunction is a driving force behind aging and chronic conditions, including heart disease. Here, we investigate the potential of Urolithin A (UA), a gut microbiome-derived postbiotic that enhances mitophagy, to ameliorate both age-related decline in cardiac function and cardiac failure.

We highlight the significance of targeting mitochondria, by comparing gene expression changes in aging human hearts and cardiomyopathies. UA oral administration successfully counteracts mitochondrial and cardiac dysfunctions in preclinical mouse models of aging and heart failure. In mice, UA improves both systolic and diastolic heart functions, distinguishing it from other mitochondrial interventions. In cardiomyocytes, UA recovers mitochondrial ultrastructural defects and decline in mitochondrial biomarkers occurring with aging and disease. These findings extend UA's benefits to heart health, making UA a promising nutritional intervention to evaluate in the clinic to promote healthy cardiovascular function as we age.

Link: https://doi.org/10.1101/2023.08.22.554375

When senescent cells linger in significant numbers in aged tissues, they cause harm via the senescence-associated secretory phenotype (SASP), a potent mix of pro-growth, pro-inflammatory signals. In the short term, this is necessary to draw the attention of the immune system to potentially cancerous cells, and helps to coordinate wound healing, among other activities. When sustained for the long term, it is increasingly disruptive to normal tissue structure and function, however.

If the desire is to remove the contribution of senescent cells to degenerative aging, suppressing the SASP seems a poor choice when compared to periodic destruction of senescent cells via senolytic drugs. As researchers here note, disabling the SASP over the long term has the effect of increasing cancer risk, even as it reduces other aspects of aging. Periodic destruction of senescent cells, however, allows one to both have the cake and eat it, still gaining the benefits of cellular senescence while reducing the burden of senescent cells.

Cellular senescence is a stress-induced, permanent cell cycle arrest involved in tumor suppression and aging. Senescent cells secrete bioactive molecules such as pro-inflammatory cytokines and chemokines. This senescence-associated secretory phenotype (SASP) has been implicated in immune-mediated elimination of senescent cells and age-associated chronic inflammation. However, the mechanisms regulating the SASP are incompletely understood.

Here, we show that the stress-responsive kinase ASK1 promotes inflammation in senescence and aging. ASK1 is activated during senescence and increases the expression of pro-inflammatory cytokines and chemokines by activating p38, a kinase critical for the SASP. ASK1-deficient mice show impaired elimination of oncogene-induced senescent cells and an increased rate of tumorigenesis. Furthermore, ASK1 deficiency prevents age-associated p38 activation and inflammation and attenuates glomerulosclerosis. Our results suggest that ASK1 is a driver of the SASP and age-associated chronic inflammation and represents a potential therapeutic target for age-related diseases.

Link: https://doi.org/10.1101/2023.09.20.558729