Reducing LDL Cholesterol is the Wrong Target for Cardiovascular Disease

When people say "cardiovascular disease" in the context of blood cholesterol, they mean atherosclerosis. This is the name given to the build up of fatty deposits that narrow and weaken blood vessels, leading to heart failure and ultimately some form of disabling or fatal rupture - a stroke or heart attack. The primary approach to treatment is the use of lifestyle choices and drugs such as statins to lower cholesterol carried by LDL particles in the blood. Unfortunately, the evidence strongly suggests that this is the wrong approach, in that the benefits are small and unreliable.

Atherosclerosis does occur more readily with very high levels of LDL cholesterol, as illustrated by the early onset of the condition in patients with genetic disorders such as homozygous familial hypercholesterolemia, in which blood cholesterol can be as high as ten times normal. Yet reducing LDL cholesterol levels, even to as much as ten times lower than normal, does very little for patients with established atherosclerotic lesions. One has to look at the mechanisms of the disease in more detail to (a) see why this is the case, and (b) identify which classes of therapy should be attempted instead.

Atherosclerosis is essentially a consequence of the failure of a process called reverse cholesterol transport. When cholesterol becomes stuck in excessive amounts in blood vessel walls, macrophage cells of the innate immune system are called to the site. The macrophages ingest cholesterol and then hand it off to HDL particles. The HDL cholesterol is then carried to the liver to be excreted. This all works just fine in young people. Older people, however, exhibit growing levels of oxidized cholesterols such as the toxic 7-ketocholesterol. Even small amounts of these oxidized cholesterols disrupt macrophage function in ways that are otherwise only achievable through very sizable amounts of cholesterol. The macrophages become inflammatory, cease their work, become loaded down with cholesterol, and die. An atherosclerotic lesion is essentially a self-sustaining macrophage graveyard that will keep pulling in and destroying ever more cells, growing larger as it does so.

The right point of intervention in atherosclerosis is therefore macrophage function. Make macrophages resistant to oxidative cholesterol and cholesterol overload, as Repair Biotechnologies is doing. Or remove oxidized cholesterols from the body, as Underdog Pharmaceuticals is doing. The crucial goal is to allow macrophages to operate normally in the toxic environment of the atherosclerotic lesion; given enough time, it is in principle possible for these cells to dismantle even advanced and sizable lesions. That they do not normally do this is because of oxidized cholesterols or sheer amount of cholesterol, not any other inherent limit.

Doubt cast on wisdom of targeting 'bad' cholesterol to curb heart disease risk

Setting targets for 'bad' (LDL) cholesterol levels to ward off heart disease and death in those at risk might seem intuitive, but decades of research have failed to show any consistent benefit for this approach, reveals a new analysis. If anything, it is failing to identify many of those at high risk while most likely including those at low risk, who don't need treatment, say the researchers, who call into question the validity of this strategy.

Cholesterol-lowering drugs are now prescribed to millions of people around the world in line with clinical guidelines. Those with poor cardiovascular health; those with LDL cholesterol levels of 190 mg/dl or higher; adults with diabetes; and those whose estimated risk is 7.5% or more over the next 10 years, based on various contributory factors, such as age and family history, are all considered to be at moderate to high risk of future cardiovascular disease. But although lowering LDL cholesterol is an established part of preventive treatment, and backed up by a substantial body of evidence, the approach has never been properly validated, say the researchers.

Hit or miss: the new cholesterol targets

This analysis highlights the discordance between a well-researched clinical guideline written by experts and empirical evidence gleaned from dozens of clinical trials of cholesterol reduction. It further underscores the ongoing debate about lowering cholesterol in general and the use of statins in particular. In this analysis over three-quarters of the cholesterol lowering trials reported no mortality benefit and nearly half reported no cardiovascular benefit at all.

The widely held theory that there is a linear relationship between the degree of LDL-C reduction and the degree of cardiovascular risk reduction is undermined by the fact that some randomized controlled trials with very modest reductions of LDL-C reported cardiovascular benefits while others with much greater degrees of LDL-C reduction did not. This lack of exposure-response relationship suggests there is no correlation between the percent reduction in LDL-C and the absolute risk reduction in cardiovascular events.

Moreover, consider that the Minnesota Coronary Experiment, a 4-year long randomized controlled trial of a low-fat diet involving 9423 subjects, actually reported an increase in mortality and cardiovascular events despite a 13% reduction in total cholesterol. What is clear is the lack of clarity of these issues. In most fields of science the existence of contradictory evidence usually leads to a paradigm shift or modification of the theory in question, but in this case the contradictory evidence has been largely ignored simply because it doesn't fit the prevailing paradigm.

Considering the Use of Lasers to Break Down Harmful Protein Aggregates

It is possible to tailor the frequency of laser light to selectively disrupt the bonds or structure of particular arrangements of molecules - such as, say, the harmful protein aggregates found in neurodegenerative and other age-related conditions. Researchers here showcase early work into the disruption of amyloids, a class of altered of proteins that feature prominently in numerous conditions. The challenge in this sort of approach is usually not that of achieving the desired disruption, but rather doing so without the delivery of so much energy, released as heat, that the process kills surrounding cells and tissues. Past early stage efforts have floundered on that problem.

A notable characteristic of several neurodegenerative diseases, such as Alzheimer's and Parkinson's, is the formation of harmful plaques that contain aggregates - also known as fibrils - of amyloid proteins. Unfortunately, even after decades of research, getting rid of these plaques has remained a herculean challenge. Thus, the treatment options available to patients with these disorders are limited and not very effective.

In recent years, instead of going down the chemical route using drugs, some scientists have turned to alternative approaches, such as ultrasound, to destroy amyloid fibrils and halt the progression of Alzheimer's disease. Now, a research team has used novel methods to show how infrared-laser irradiation can destroy amyloid fibrils. While laser experiments coupled with various microscopy methods can provide information about the morphology and structural evolution of amyloid fibrils after laser irradiation, these experiments have limited spatial and temporal resolutions, thus preventing a full understanding of the underlying molecular mechanisms. On the other hand, though this information can be obtained from molecular simulations, the laser intensity and irradiation time used in simulations are very different from those used in actual experiments. It is therefore important to determine whether the process of laser-induced fibril dissociation obtained through experiments and simulations is similar."

The scientists used a portion of a yeast protein that is known to form amyloid fibrils on its own. In their laser experiments, they tuned the frequency of an infrared laser beam to that of the "amide I band" of the fibril, creating resonance. Scanning electron microscopy images confirmed that the amyloid fibrils disassembled upon laser irradiation at the resonance frequency, and a combination of spectroscopy techniques revealed details about the final structure after fibril dissociation. For the simulations, the researchers employed a technique that a few members of the current team had previously developed, called "nonequilibrium molecular dynamics (NEMD) simulations." Its results corroborated those of the experiment and additionally clarified the entire amyloid dissociation process down to very specific details. Through the simulations, the scientists observed that the process begins at the core of the fibril where the resonance breaks intermolecular hydrogen bonds and thus separates the proteins in the aggregate. The disruption to this structure then spreads outward to the extremities of the fibril.

Link: https://www.tus.ac.jp/en/mediarelations/archive/20200804_0101.html

A Fisetin Variant, CMS121, Slows Disease Progress in an Alzheimer's Mouse Model

The research materials here are of interest because fisetin has been shown to be a senolytic compound in mice, capable of selectively destroying harmful senescent cells. Other senolytics have reversed the progression of Alzheimer's disease pathology in mouse models of the condition. Destroying senescent cells in the brain reduces inflammatory signaling, and chronic inflammation is a significant mechanism in neurodegenerative conditions such as Alzheimer's disease. Whether this compound works well as a senolytic in humans has yet to be established - a clinical trial is underway, so hopefully we'll find out in the next year or two.

The researchers here are not interested in cellular senescence at all, however, and instead base their work on the effects of fisetin and fisetin-like molecules on lipid metabolism in the brain. Back in 2014, they showed that fisetin slowed the onset of Alzheimer's like symptoms in mice. The present work is much the same, except with an improved version of fisetin called CMS121. This all raises the question of whether their approach is working for the reasons that they think it is working.

Over the last few decades, researchers have studied how a chemical called fisetin, found in fruits and vegetables, can improve memory and even prevent Alzheimer's-like disease in mice. More recently, the team synthesized different variants of fisetin and found that one, called CMS121, was especially effective at improving the animals' memory, and slowing the degeneration of brain cells.

In the new study, researchers tested the effect of CMS121 on mice that develop the equivalent of Alzheimer's disease. The team gave a subset of the mice daily doses of CMS121 beginning at 9 months old - the equivalent of middle age in people, and after the mice have already begun to show learning and memory problems. The timing of the lab's treatment is akin to how a patient who visits the doctor for cognitive problems might be treated, the researchers say. After three months on CMS121, at 12 months old, the mice were given a battery of memory and behavior tests. In both types of tests, mice with Alzheimer's-like disease that had received the drug performed equally well as healthy control animals, while untreated mice with the disease performed more poorly.

To better understand the impact of CMS121, the team compared the levels of different molecules within the brains of the three groups of mice. They discovered that when it came to levels of lipids - fatty molecules that play key roles in cells throughout the body - mice with the disease had several differences compared to both healthy mice and those treated with CMS121. In particular, the researchers pinpointed differences in something known as lipid peroxidation - the degradation of lipids that produces free radical molecules that can go on to cause cell damage. Mice with Alzheimer's-like disease had higher levels of lipid peroxidation than either healthy mice or those treated with CMS121.

Link: https://www.salk.edu/news-release/new-molecule-reverses-alzheimers-like-memory-decline/

Telomerase Gene Therapy May Treat Fibrosis via a Reduced Burden of Cellular Senescence

A number of research groups are quite enthusiastic about the prospects for telomerase gene therapy as a treatment for aging and numerous age-related diseases. This is based on more than a decade of work in mice, showing extended life spans and improved metabolism. Over the past few years, reversal of fibrosis via telomerase gene therapy has been demonstrated in mice. The evidence for this to be an approach worth bringing to the clinic continues to accumulate. Fibrosis is a disruption of tissue maintenance, associated with chronic inflammation, in which an inappropriate deposition of scar-like collagen takes place, degrading normal tissue structure and function. Today's research materials are the latest on this topic, in which scientists dig deeper into the mechanisms by which telomerase upregulation might be acting on fibrosis in the lung.

The primary function of telomerase is to extend telomeres, caps of repeated DNA at the ends of chromosomes. Telomere length shortens with every cell division, but only stem cells normally express telomerase and thus have the capability to maintain long telomeres. The vast majority of somatic cells in the body lose their telomere length until hitting the Hayflick limit, at which point their shortened telomeres trigger cell death or cellular senescence. All tissues are in a state of turnover, losing cells to the Hayflick limit, while replacements with long telomeres are generated by stem cells.

Telomerase upregulation might produce benefits in a number of ways. Firstly, if all cells express telomerase, then there will tend to be more functional cells in any given tissue, postponing age-related declines in function that occur due to a slowing of stem cell activity. A concern here is that this will allow damaged cells to function for longer, and thus raise cancer risk. That raised risk doesn't occur in mice with upregulated telomerase, possibly because immune system function is improved by telomerase gene therapy in the same way as other tissue function, and improved cancer suppression by immune cells outweighs the increased risk due to lengthening the telomeres of damaged and potentially cancerous cells. Whether or not the same balance of factors will occur in humans is still to be determined.

Secondly, telomerase upregulation may reduce the burden of senescent cells in tissues, both by preventing cells from replicative senescence, and by improving the operation of mechanisms that clear senescent cells. Senescent cells are important in aging, as demonstrated by the extension of life and reversal of age-related disease produced in mice via senolytic therapies that selectively remove these errant cells. Interestingly, senescent cells are strongly implicated in the progression of fibrosis, and their removal has been shown to reverse the condition in mice. In the research noted here, telomerase gene therapy reduces measures of senescence in fibrotic lungs. It is entirely plausible that this is the primary mechanism by which increased telomerase activity reverses fibrosis.

Researchers pave the way for a future gene therapy to reverse pulmonary fibrosis associated with ageing

Idiopathic pulmonary fibrosis is a potentially lethal disease for which there is currently no cure and that is associated with certain mutations or advanced age. Resesarchers had previously developed an effective therapy for mice with fibrosis caused by genetic defects. Now they show that the same therapy can successfully be used to treat mice with age-related fibrosis. The treatment tested in mice is a gene therapy that activates the production of telomerase in the body. Telomerase is an enzyme that repairs the telomeres at the end of chromosomes.

The new study describes the effects of ageing on lung tissue in detail. One such effect is that alveolar type II cells stop doing their job. In addition to regenerating tissue, these cells produce and release a lipid-protein complex called pulmonary surfactant that facilitates the mechanical work done by the lungs. "Lung tissue must expand when we breathe in, six to ten times per minute, which means a great deal of physical effort. Pulmonary surfactant plays an important role in lubricating lung tissue, retaining its elasticity, and reducing the amount of work required to expand and contract it. If type II pneumocytes fail to regenerate, the surfactant is not produced, which results in lung stiffness and fibrosis."

In 2018, researchers developed a gene therapy that reversed pulmonary fibrosis in mice lacking the telomerase gene. This therapy was based on activating telomerase expression temporarily. A virus used as a telomerase gene carrier was injected intravenously into the mice. The effect - alveolar type II cells with long telomeres - was temporary, but lung tissue regeneration was successfully induced. The same therapy was now used in aging mice. And it worked in them too. "The telomerase-activating gene therapy prevented the development of fibrosis in all mice, including the ones without genetic alterations that only underwent physiological ageing."

Telomerase treatment prevents lung profibrotic pathologies associated with physiological aging

We determined the impact of AAV9-Tert gene therapy in rescuing DNA damage, apoptosis, and senescence in Tert+/+ and Tert-/- lungs treated with either AAV9-Tert or AAV9-null virus particles. We found that both Tert+/+ and Tert-/- mice treated with AAV9-Tert showed significantly decreased numbers of γ-H2AX-positive cells in the lung parenchyma compared with the corresponding cohorts treated with the null vector, indicating decreased DNA damage upon telomerase treatment. Similarly, we detected significantly decreased numbers of activated caspase3-positive cells in the alveolar parenchyma of both Tert+/+ and Tert-/- lungs treated with AAV9-Tert compared with those treated with the null vector. Interestingly, increased senescence as detected by p16-positive cells specifically in the case of aveolar macrophages was also rescued in both Tert+/+ and Tert-/- lungs treated with AAV9-Tert compared with those treated with the null vector.

Finally, by performing double immunostainings with the proliferation marker Ki67 and the specific markers for alveolar type II cells, club cells, and aveolar macrophages, we observed that proliferation of alveolar type II cells, club cells, and aveolar macrophages was significantly increased in both Tert+/+ and Tert-/- lungs treated with AAV9-Tert compared with those treated with the null vector. Interestingly, the number of SOX2-positive differentiating club cells was also significantly reduced in Tert+/+ and Tert-/- lungs upon telomerase gene therapy.

Finally, to address whether treatment with telomerase gene therapy also prevented expression of proinflammatory and anti-inflammatory markers, we determined mRNA expression of Tnf, Il1b, Il6, Il4, Il10, and Il13 in total lung extracts from Tert+/+ and Tert-/- mice. We observed significantly decreased expression of these markers in both Tert+/+ andTert-/- mice treated with AAV9-Tert compared with those treated with the null vector.

Overexpression of VRK-1 Extends Life Span in Nematode Worms

A great many approaches exist to slow aging in short-lived laboratory species such as nematodes, flies, and mice. The example here is an illustrative example, similar to dozens of other discoveries regarding life span and upregulation or downregulation of the expression of specific proteins. Since cellular biochemistry is a connected web of interactions, most such methods involve adjusting different parts of the same underlying system of regulation. An increased operation of cellular stress responses is the most common such regulator of the pace of aging. Unfortunately this type of intervention has much larger effects on life span in short-lived species than it does in long-lived species. This has led to much of the field of aging research focusing on projects that appear interesting in mice, but cannot possibly produce large gains in human life span.

Mitochondria are essential subcellular organelles for cellular energy production. Mitochondria also play important functions in a wide array of other cellular processes, ranging from cellular signaling to apoptosis. In addition, mitochondria play crucial roles in organismal aging, and functional declines in mitochondria are associated with age-related diseases. However, mild inhibition of mitochondrial respiration has been shown to promote longevity in multiple species. In Caenorhabditis elegans, the genetic inhibition of mitochondrial respiration genes prolongs life span. Inhibition of mitochondrial respiration also increases life span in Drosophila and mammals.

Adenosine 5′-monophosphate (AMP)-activated protein kinase (AMPK), a critical cellular energy sensor that increases life span in multiple species, is one of the factors required for the enhanced longevity caused by inhibition of mitochondrial respiration in C. elegans. The vaccinia virus-related kinase (VRK) family consists of three serine-threonine protein kinases (VRK1 to VRK3) in mammals, which are related to casein kinases. Among these three, the best characterized is VRK1, a cell cycle regulator that is abundant in proliferative tissues. Unlike mammals, C. elegans has a single VRK ortholog, VRK-1, whose function in cell proliferation is relatively well established. However, it remains unknown whether VRK-1 acts in postmitotic cells or has a role in adult life span.

In this study, we sought to elucidate the role of VRK-1 in regulation of adult life span in C. elegans. We found that overexpression of VRK-1::GFP (green fluorescent protein), which was detected in the nuclei of cells in multiple somatic tissues, including the intestine, increased life span. Conversely, genetic inhibition of vrk-1 decreased life span. We further showed that vrk-1 was essential for the increased life span of mitochondrial respiratory mutants. We demonstrated that VRK-1 was responsible for increasing the level of active and phosphorylated form of AMPK, thus promoting longevity.

Link: https://doi.org/10.1126/sciadv.aaw7824

The Gut Microbiome Changes Shortly Before Death in Centenarians

Extremely old people have such high mortality rates that studies such as this one here become practical, answering the question of how the gut microbiome changes in the final decline into death. It is well established that the gut microbiome is influential on health, and undergoes detrimental changes across the course of adult life, although it remains to be determined as to which of the possible mechanisms are most important. In particular, it is unclear as to whether gut microbiome changes provoke inflammatory immune dysfunction or whether age-related immune dysfunction allows more inflammatory microbes to prosper. Or whether both directions of causation are relevant.

Several studies have revealed certain unique characteristics of gut microbiome in centenarians. We established a prospective cohort of fecal microbiota and conducted the first metagenomics-based study among centenarians. The objective was to explore the dynamic changes of gut microbiota in healthy centenarians and centenarians approaching end of life and to unravel the characteristics of aging-associated microbiome. Seventy-five healthy centenarians participated in follow-up surveys and collection of fecal samples at intervals of 3 months. Data pertaining to dietary status, health status scores, cause of disease and death, and fecal specimens were collected for 15 months.

Twenty participants died within 20 months during the follow-up period. The median survival time was 8-9 months and the mortality rate was 14.7% per year. The health status scores before death were significantly lower than those at 3 months before the end of the follow-up period. At this time, the participants mainly exhibited symptoms of anorexia and reduced dietary intake and physical activity. Metagenomics sequencing and analysis were carried out to characterize the gut microbiota changes in the centenarians during their transition from healthy status to death.

Analysis showed a significant change in gut microbiota from 7 months prior to death. All participants were grouped with 7 months before death as cut-off; no significant difference in α diversity was found between the two groups. Analysis revealed significant changes in the abundance of ten bacterial species before death; of these, eight species were significantly reduced (Akkermansia muciniphila, Alistipes finegoldii, Alistipes shahii, Bacteroides faecis, Bacteroides intestinalis, Butyrivibrio crossotus, Bacteroides stercoris, and Prevotella stercorea) while two were significantly increased before death (Bifidobacterium longum and Ruminococcus bromii). We speculate that these changes might occur before the clinical symptoms of deterioration in health status.

Link: https://doi.org/10.3389/fmicb.2020.01474

30% to 40% of Dementia Might be Avoided via Lifestyle Choices

Today's open access research materials present a statistical exercise that uses broad epidemiological data to determine the impact of individual lifestyle choices and environmental factors to the incidence of dementia. The results are not declaring that, say, particulate air pollution is responsible for 2% of dementias. Rather if the statistics point out that particulate air pollution is associated with 2% of cases, smoking with 5%, and hearing loss with 8%, then one starts to see priorities in the choices that people should be making to better manage their health over the long term.

Summing all of the impacts together - to see a 30-40% contribution of lifestyle and environment to incidence of dementia - also provides an assessment of the degree to which dementia is a lifestyle disease. To which it is avoidable with sensible choices regarding health and surrounding environment. Alzheimer's disease in particular involves a number of mechanisms that look suspiciously like those involved in type 2 diabetes, a condition that is near entirely a lifestyle issue resulting from excess fat tissue. Nonetheless, Alzheimer's disease and other dementias are clearly not determined by obesity to the same degree. The risk spreads out over choices and influences that touch on chronic inflammation (fat, smoking, air pollution), cognitive reserve (education), physical damage to brain tissue and surrounding channels for cerebrospinal fluid drainage (hypertension, head injury). It is a matter of many smaller contributions that cause harm through a range of quite different mechanisms.

While senolytic drugs that remove senescent cells in the brain will probably make a sizable difference to dementia incidence, via greatly reducing inflammation in brain tissue, it remains the case that comparatively little else can be done at present other than slowing the decline through better life-long health. More and better regenerative therapies, and more and better therapies that target the underlying molecular damage of brain aging are needed.

Dementia prevention, intervention, and care: 2020 report of the Lancet Commission

Overall, a growing body of evidence supports the nine potentially modifiable risk factors for dementia modelled by the 2017 Lancet Commission on dementia prevention, intervention, and care: less education, hypertension, hearing impairment, smoking, obesity, depression, physical inactivity, diabetes, and low social contact. We now add three more risk factors for dementia with newer, convincing evidence. These factors are excessive alcohol consumption, traumatic brain injury, and air pollution. We have completed new reviews and meta-analyses and incorporated these into an updated 12 risk factor life-course model of dementia prevention. Together the 12 modifiable risk factors account for around 40% of worldwide dementias, which consequently could theoretically be prevented or delayed. The potential for prevention is high and might be higher in low-income and middle-income countries (LMIC) where more dementias occur.

The number of people with dementia is rising. Predictions about future trends in dementia prevalence vary depending on the underlying assumptions and geographical region, but generally suggest substantial increases in overall prevalence related to an ageing population. For example, according to the Global Burden of Diseases, Injuries, and Risk Factors Study, the global age-standardised prevalence of dementia between 1990 and 2016 was relatively stable, but with an ageing and bigger population the number of people with dementia has more than doubled since 1990.

However, in many high income countries (HIC) such as the USA, the UK, and France, age-specific incidence rates are lower in more recent cohorts compared with cohorts from previous decades collected using similar methods and target populations and the age-specific incidence of dementia appears to decrease. All-cause dementia incidence is lower in people born more recently, probably due to educational, socio-economic, health care, and lifestyle changes. However, in these countries increasing obesity and diabetes and declining physical activity might reverse this trajectory. In contrast, age-specific dementia prevalence in Japan, South Korea, Hong Kong, and Taiwan looks as if it is increasing, as is Alzheimer's in LMIC, although whether diagnostic methods are always the same in comparison studies is unclear.

Cognitive reserve is a concept accounting for the difference between an individual's clinical picture and their neuropathology. It is divided into neurobiological brain reserve (eg, numbers of neurons and synapses at a given timepoint), brain maintenance (as neurobiological capital at any timepoint, based on genetics or lifestyle reducing brain changes and pathology development over time) and cognitive reserve as adaptability enabling preservation of cognition or everyday functioning in spite of brain pathology. Early-life factors, such as less education, affect the resulting cognitive reserve. Midlife and old-age risk factors influence age-related cognitive decline and triggering of neuropathological developments. Consistent with the hypothesis of cognitive reserve is that older women are more likely to develop dementia than men of the same age, probably partly because on average older women have had less education than older men. Cognitive reserve mechanisms might include preserved metabolism or increased connectivity in temporal and frontal brain areas.

Risk factors in early life (education), midlife (hypertension, obesity, hearing loss, traumatic brain injury, and alcohol misuse) and later life (smoking, depression, physical inactivity, social isolation, diabetes, and air pollution) can contribute to increased dementia risk. Good evidence exists for all these risk factors although some late-life factors, such as depression, possibly have a bidirectional impact and are also part of the dementia prodrome. Our new life-course model and evidence synthesis has paramount worldwide policy implications. It is never too early and never too late in the life course for dementia prevention. Early-life (younger than 45 years) risks, such as less education, affect cognitive reserve; midlife (45-65 years), and later-life (older than 65 years) risk factors influence reserve and triggering of neuropathological developments.

IGF-1R Inhibition Reduces Neuroinflammation in an Alzheimer's Mouse Model

Chronic inflammation in brain tissue is an important component of the progression of neurodegenerative conditions such as Alzheimer's disease. It is important enough that some researchers propose inflammation resulting from persistent infection and cellular senescence to be the primary mechanism in Alzheimer's disease, and the characteristic accumulation of amyloid-β deposits only a side-effect. Given the failure to achieve meaningful benefits in patients through removal of amyloid-β, researchers are turning their eyes towards ways to suppress inflammatory signaling in the brain. Removal of senescent cells, the source of a great deal of that inflammatory signaling, is one promising avenue, but other efforts focus on interference in specific signaling pathways, as is the case here.

Extracellular amyloid β (Aβ) plaques and intracellular neurofibrillary tangles are Alzheimer's disease (AD) pathological features hypothesized to lead to neuronal death and cognitive dysfunction. Since aging is the main risk factor for AD, slowing down this process may delay disease onset or progression. The growth hormone (GH)/insulin-like growth factor (IGF-1) signaling pathway is hypothesized to be one of the primary pathways regulating lifespan in general. Partial inactivation of the IGF-1 receptor (IGF-1R) gene or insulin-like signaling extends longevity and postpones age-related dysfunction in nematodes, flies, and rodents.

The role of IGF-1 in regulating age-associated AD remains unclear. For instance, lower serum IGF-1 levels correlate with increased cognitive decline and risk of AD. Also, patients with familial AD demonstrate lower levels of circulating IGF-1 compared to controls. An ex vivo study revealed IGF-1 resistance along with insulin resistance through the PI3K pathway in AD patient brains. Finally, IGF-1 treatment diminished Aβ accumulation by improving its transportation out of the brains of AD mouse models while IGF-1R inhibition aggravated both behavioral and pathological AD symptoms in mice. On the other hand, the administration of a potent inducer of circulating IGF-1 levels failed to delay AD progression in a randomized trial. Also, acute or chronic delivery of IGF-1 exerted no beneficial effect on AD pathological hallmarks in rodent models in vivo. Moreover, high levels of serum IGF-1 were detected in individuals diagnosed with AD or other forms of dementia in one study.

Presumably, this dichotomy of effects is, in part, mediated through the effects of IGF-1 on its receptor. The IGF-1R and the insulin receptor (IR) are homologous tyrosine kinase proteins with remarkably different functions. In our previous work, AβPP/PS1 transgenic mice, which express human mutant amyloid precursor protein (APP) and presenilin-1 (PS-1), demonstrated a decrease in brain IGF-1 levels when they were crossed with IGF-1 deficient Ames dwarf mice. Subsequently, a reduction in gliosis and amyloid-β (Aβ) plaque deposition were observed in this mouse model. This supported the hypothesis that IGF-1 may contribute to the progression of the disease.

To assess the role of IGF-1 in AD, 9-10-month-old male littermate control wild type and AβPP/PS1 mice were randomly divided into two treatment groups: control and picropodophyllin (PPP), a selective, competitive, and reversible IGF-1R inhibitor. Mice were sacrificed after 7 days of daily injection and the brains, spleens, and livers were collected to quantify histologic and biochemical changes. The PPP-treated AβPP/PS1 mice demonstrated attenuated insoluble amyloid-β. Additionally, an attenuation in microgliosis and protein p-tyrosine levels was observed due to drug treatment in the hippocampus. Our data suggest IGF-1R signaling is associated with disease progression in this mouse model. More importantly, modulation of the brain IGF-1R signaling pathway, even at mid-life, was enough to attenuate aspects of the disease phenotype. This suggests that small molecule therapy targeting the IGF-1R pathway may be viable for late-stage disease treatment.

Link: https://doi.org/10.3389/fncel.2020.00200

Arguing for DNA Methylation Changes to be a Contributing Cause of Aging

Contributing mechanisms of aging form an interconnected network of cause and consequence. For most such mechanisms there is considerable debate over relative importance to the manifestations of aging, as well as over whether a mechanism is upstream or downstream of its peers. The step by step "A causes B causes C causes D" view of aging and age-related disease is very unclear in the middle reaches of the chain of cause and effect, despite a good list of first causes and a growing understanding of proximate causes for many age-related conditions. Progress is slow, as no biochemical mechanism exists in isolation, and it is a challenge to pick apart the complexities of cellular metabolism to find the important relationships.

Thus for DNA methylation, epigenetic changes that alter expression of proteins, at the high level one can argue that this is downstream of forms of damage and dysfunction, a response on the part of cells. One can also argue that some of these changes are harmful and cause further issues. Connecting DNA methylation to causes and consequences is an enormous undertaking, given the number of methylation sites that are now connected to aging as a result of work on epigenetic clocks. Nonetheless, some inroads are being made.

During aging, predefined genes constantly undergo epigenetic modifications and exhibit altered expression in response to internal and external environmental stress. Changes in DNA methylation may occur hundreds of times over the lifespan of an individual in the form of a fully adaptive response. However, in some cases, this methylation acts as a switch for the acceleration of pathological aging, resulting in negative consequences. Thus, global fluctuations in DNA methylation are not only a consequence but also a cause of aging. Understanding the biological mechanisms underlying the observed associations may reveal novel targets for reversing aging-related phenotypes and ultimately prolonging lifespan.

Evidence has emerged showing that decreased autophagic activity is involved in DNA methylation. DNA methylation inhibits autophagy processes in two ways, one of which is the direct modification and silencing of autophagy-related genes by DNA methyltransferases. The promoter regions of Atg5 and LC3 are hypermethylated in aged mice, which suppresses gene expression and disrupts the completion of autophagosomes. Whole-body overexpression of Atg5 results in antiaging phenotypes, extending the median lifespan of mice by 17.2%. Furthermore, researchers have recently shown that DNA methylation inhibitors can rescue phenotypic changes associated with aging by reactivating autophagy-related genes.

Identification of the target genes modified by DNA methylation-related regulatory elements in aging individuals is highly informative to figure out the hormone-like effectors and signal pathways that mediate these alterations as well as related diseases. The interaction among epigenetic regulators during aging should also be highly valued. Further studies should focus on the cross-talk among these epigenetic regulators, such as DNA methylation, RNA methylation, histone methylation, and noncoding RNAs, which will aid in providing a full picture of epigenetics and aging. The results of such studies may pave the way for antiaging interventions as well as treatments for related diseases, enabling human life extension.

Link: https://doi.org/10.1155/2020/1047896

Short Term Cdc42 Inhibition In Middle Aged Mice Extends Median and Maximum Life Span

An interesting study of mouse life span extension via a novel methodology was recently published. The researchers developed a small molecule approach to inhibition of Cdc42, a protein with numerous functions throughout the cell. This is a target for intervention because - at least in cell cultures - loss of Cdc42 activity appears to restore youthful function to aged hematopoietic stem cells. This is the cell population responsible for producing blood and immune cells, and declining immune function with age is driven at least in part by dysfunction in hematopoietic stem cells. Ways to restore immune function in older individuals should prove to be broadly beneficial to health in later life, given that the immune system has roles in tissue maintenance and function that extend far beyond merely defending against pathogens.

The effect size in mice for Cdc42 inhibition is here shown to be somewhere in the range of a 12-16% gain in median and maximum life spans, along with a reversal of age-related changes in some inflammatory cytokine levels. This gain in life span isn't large in the grand scheme of things, given that lifelong calorie restriction can result in a 40% increase in mouse life span, but the point of interest here is that this result was achieved with a single four day treatment carried out in middle aged mice, already well on the way towards being aged. Only rapamycin and senolytics have robustly achieved similar outcomes based on short term late life treatment.

We might hypothesize that, in these aging mice, the generation of new immune cells by hematopoietic stem cells was increased for long enough via this intervention to provide the lasting benefits of a renewed and bolstered immune system. Even if raised rates of immune cell generation don't last, the additional cells created will last. An aging immune system should be in an incrementally better state going forward as the result of any intervention capable of providing more new immune cells for a time. Unfortunately a full assessment of immune cell populations wasn't carried out in this study; only proximate measures of immune system activity such as cytokine levels were assessed.

Inhibition of Cdc42 activity extends lifespan and decreases circulating inflammatory cytokines in aged female C57BL/6 mice

Cdc42 is involved in multiple and diverse functions of eukaryotic cells, including actin cytoskeleton reorganization, cell polarity, and cell growth. The activity of Cdc42 is significantly elevated in blood of elderly humans and in several tissues of aged C57BL/6 mice. We recently identified a specific small-molecule inhibitor of Cdc42 activity termed CASIN. Administration of CASIN in vivo did not show signs of toxicity. Previously, we reported that a brief ex vivo exposure of aged hematopoietic stem cells (HSCs) to CASIN that reduced the activity of Cdc42 in aged cells to the level found in young cells resulted in long-lasting youthful function of HSCs in vivo, likely due to epigenetic remodeling of aged cells upon modulation of Cdc42 activity. Consequently, we hypothesized that maybe a short-term systemic reduction of Cdc42 activity in aged animals in vivo might be also beneficial for lifespan, as an elevated activity of Cdc42 upon aging is causatively linked to a shorter lifespan in mice.

To determine whether a short-term systemic CASIN treatment of aged animals might indeed influence lifespan, we administered CASIN via intraperitoneal injection every 24 hours for 4 consecutive days to 75-week-old female C57BL/6 mice. 4 days of consecutive injections did not induce acute toxicity, and as well, none of the treated mice died within 4 weeks after CASIN injections, rendering chronic toxicity issues unlikely. Quantification of Cdc42 activity 24 hours after the last injection on day 5 demonstrated a reduction of Cdc42 activity in aged bone marrow cells to the level seen in young, confirming that CASIN is indeed reducing Cdc42 activity after a systemic in vivo treatment. Notably, aged mice treated with CASIN for only 4 consecutive days showed extension of their average and also maximum lifespan.

We performed analyses to investigate the extent to which aging-associated inflammatory cytokines in serum of aged mice were affected by CASIN treatment. Data showed a marked increase in the concentrations of INFγ, IL-1β, and IL-1α on aging and the concentrations for these cytokines were similar to concentrations in young animals upon CASIN treatment of aged mice. It is thus a possibility that a reduction in the concentrations of these cytokines upon CASIN treatment might contribute to the increase in lifespan observed in these animals.

Previously, the methylation status of CpG sites within the genes Prima1, Hsf4, and Kcns1 was shown to qualify as likely predictor of biological age of C57BL/6 mice. Applying this C57BL/6-trained DNA methylation marker panel to blood cells from aged animals treated with CASIN 9 weeks after treatment, we observed that epigenetic age predictions did not correlate anymore to the chronological age as in aged control animals, but resulted in a biological age prediction that was on average 9 weeks younger than their chronological age. These data imply that epigenetic changes underlie the extended longevity of aged CASIN-treated mice, while reinforcing the necessity to mechanistically validate tissues, cells, and biological pathways involved in the extension of longevity.

Accelerated Osteoporosis in Mitochondrial Mutator Mice

Mitochondria are the power plants of the cell, the evolved descendants of ancient symbiotic bacteria. They generate the chemical energy store molecules needed to power cellular processes. The herd of hundreds of mitochondria in every cell replicate like bacteria, and carry a small remnant circular genome, the mitochondrial DNA. Mice engineered to lack a functional PolgA gene exhibit defective mitochondrial DNA repair, and as a consequence accumulate mutations in their mitochondrial DNA at a rapid pace. Random mutation and declining mitochondrial function is a feature of aging, and these mitochondrial mutator mice exhibit accelerated aging as a consequence of the more rapid damage they suffer to this vital cell component.

Here, researchers examine just one feature of this accelerated aging, the more rapid onset of osteoporosis, the characteristic loss of bone mass and strength that occurs with age. Bone is a dynamic tissue, constantly remodeled by osteoblasts that create bone and osteoclasts that break it down. Damage to mitochondrial function causes a decline in osteoblast activity, favoring bone destruction over bone creation. Over time this leads to osteporosis and all of its consequences.

The pathogenesis of declining bone mineral density, a universal feature of ageing, is not fully understood. Somatic mitochondrial DNA (mtDNA) mutations accumulate with age in human tissues and mounting evidence suggests that they may be integral to the ageing process. To explore the potential effects of mtDNA mutations on bone biology, we compared bone microarchitecture and turnover in an ageing series of wild type mice with that of the PolgA mitochondrial DNA 'mutator' mouse.

In vivo analyses showed an age-related loss of bone in both groups of mice; however, it was significantly accelerated in the PolgA mice. This accelerated rate of bone loss is associated with significantly reduced bone formation rate, reduced osteoblast population densities, increased osteoclast population densities, and mitochondrial respiratory chain deficiency in osteoblasts and osteoclasts in PolgA mice compared with wild-type mice. In vitro assays demonstrated severely impaired mineralised matrix formation and increased osteoclast resorption by PolgA cells.

Finally, application of an exercise intervention to a subset of PolgA mice showed no effect on bone mass or mineralised matrix formation in vitro. Our data demonstrate that mitochondrial dysfunction, a universal feature of human ageing, impairs osteogenesis and is associated with accelerated bone loss.

Link: https://doi.org/10.1038/s41598-020-68566-2

Too Much Mitochondrial Fission in the Aging Germline Stem Cells of Flies

Mitochondria are bacteria-like organelles responsible for producing chemical energy store molecules to power cellular processes. Hundreds of them exist in every cell, constantly undergoing fusion and fission, swapping component parts with one another, and being culled when damaged by the quality control mechanism of mitophagy. Past work has indicated that there is too little mitochondrial fission in old cells, leading to mitochondria that are too large to be effectively removed when damaged. The research here suggests that there is instead too much mitochondrial fission in stem cells, though it is focused specifically on germline stem cells in flies. Mitochondrial dynamics is a balance, and disruption in either direction is problematic. Age-related disruption may well be different in different species and cell types, so it is a little early to say whether or not the work here is relevant to mammals.

Mitochondria frequently undergo coordinated cycles of fusion and fission (known as mitochondrial dynamics) to properly adjust the shape, size, and cellular distribution of the organelle to meet specific cellular requirements. Fusion produces elongated mitochondria by respectively joining the outer and inner membranes of two mitochondria. The closely related Dynamin-related GTPases, Mfn1 and Mfn2, mediate outer membrane fusion, while Opa1 is integral for fusion of the inner membrane. On the other hand, excessive mitochondrial fission produces fragmented mitochondria and is mediated by another Dynamin-related GTPase, called Drp1. Drp1 is recruited by its receptors on the outer membrane and oligomerizes along the mitochondrial constriction site to constrict the organelle and induce scission.

Mitochondrial dynamics are known to influence several mitochondria-dependent biological processes, such as lipid homeostasis, calcium homeostasis, and ATP production. Recent studies have also proposed a role for mitochondrial fusion and fission in regulating stem cell fate. In one interesting example, murine neural stem cells were shown to exhibit elongated mitochondria, and depletion of Mfn1 or Opa1 impaired their self-renewal. Despite tantalizing observations such as these, the overall impact of mitochondrial dynamics in aging stem cells and the mechanisms by which mitochondrial dynamics might affect stem cell function remain unclear.

Here, we report that mitochondrial dynamics are shifted toward fission during aging of Drosophila ovarian germline stem cells (GSCs), and this shift contributes to aging-related GSC loss. We found that as GSCs age, mitochondrial fragmentation and expression of the mitochondrial fission regulator Drp1 are both increased, while mitochondrial membrane potential is reduced. Moreover, preventing mitochondrial fusion in GSCs results in highly fragmented depolarized mitochondria, decreased BMP stemness signaling, impaired fatty acid metabolism, and GSC loss. Conversely, forcing mitochondrial elongation promotes GSC attachment to the niche. Importantly, maintenance of aging GSCs can be enhanced by suppressing Drp1 expression to prevent mitochondrial fission or treating with rapamycin, which is known to promote autophagy via TOR inhibition.

Link: https://doi.org/10.1111/acel.13191

Delivery of BDNF Reverses Inflammatory Microglial Activation in Old Mice

Brain-derived neurotrophic factor (BDNF) shows up in many aspects of the interaction between health practices, mechanisms of aging, and mechanisms of neurodegeneration. Most research is focused on the effects of BDNF on neural plasticity, meaning the generation of new neurons from neural stem cell populations, followed by the integration of those new neurons into neural networks, such that they participate in the functioning of the brain. Plasticity is necessary for memory, learning, and maintenance and repair of brain tissue, and in this context the presence of higher levels of BDNF appears to be entirely beneficial.

Unfortunately, BDNF levels decline with age, for reasons that are yet to be fully explored. Exercise is known to improve memory function in older individuals, and there is good evidence for increased BDNF to be an important mechanism in this effect. Similarly, gut microbes generate butyrate, which increases BDNF, establishing a link between changes in the gut microbiome and age-related cognitive decline. Various interventions that improve memory in old mice, such as upregulation of osteocalcin or RbAp48 have also been shown to produce their effects via increased expression of BDNF.

So why not just delivery BDNF as a therapy to improve cognitive function in later life? This does indeed work, as illustrated in today's open access research materials. Interestingly, the authors are focused on the effects of BDNF on inflammatory behavior in the immune cells of the brain rather than on neuroplasticity. It is becoming clear that chronic inflammation in brain tissue is an important contributing cause of neurodegenerative conditions. Among other process, chronic inflammation in the brain involves the inappropriate inflammatory activation of microglia, a specialized type of innate immune cell resident to the brain. Beyond the usual functions one would expect for such cells - chasing down pathogens, destroying errant cells, and so forth - microglia also aid in the maintenance of synaptic connections in various ways. So it is entirely plausible that more inflammatory microglia could mean a greater disruption of neural function in numerous ways, both via inflammatory signaling that changes cell behavior for the worse, and through neglect of normal microglial duties.

BDNF reverses aging-related microglial activation

Microglial activation is implicated in the pathogenesis of multiple neurodegenerative diseases. Under physiological conditions, microglia are in a resting state characterized by ramified morphology, and they function as homeostatic keepers of the central nervous system. Resting microglia are not dormant; their processes are constantly and actively scanning a defined territory of brain parenchyma. After they have been exposed to stimulatory signals, microglia undergo various degrees of activation, such as changing their morphology, gene expression, and functional behavior. Depending upon the type, intensity, and duration of the exposure to the stimuli, activated microglia can be neuroprotective or neurotoxic. Activated microglia can release various inflammatory cytokines and toxins that together might injure or even cause neuronal death.

Brain-derived neurotrophic factor (BDNF), a versatile member of the neurotrophin family, is widely and highly expressed in the brain and is a chief regulator of axonal growth, neuronal differentiation, survival, and synaptic plasticity. In the central nervous system, BDNF and downstream prosurvival pathways have been demonstrated to protect neurons from damage and enhance neuronal network reorganization after injury. It has also been reported that BDNF treatment could reduce degrees of microglial activation in certain brain injury models, albeit these responses were considered a consequence of reduced neuronal injury and death elicited by BDNF. The direct effect of BDNF on microglia has rarely been explored.

This study aimed to characterize the role of BDNF in age-related microglial activation. Initially, we found that degrees of microglial activation were especially evident in the substantia nigra (SN) across different brain regions of aged mice. The levels of BDNF and TrkB in microglia decreased with age and negatively correlated with their activation statuses in mice during aging. Interestingly, aging-related microglial activation could be reversed by chronic, subcutaneous perfusion of BDNF. Peripheral lipopolysaccharide (LPS) injection-induced microglial activation could be reduced by local supplement of BDNF, while shTrkB induced local microglial activation in naïve mice. Thus in conclusion, decreasing BDNF-TrkB signaling during aging favors microglial activation, while upregulation BDNF signaling inhibits microglial activation via the TrkB-Erk-CREB pathway.

An Update on Single Issue Political Advocacy for Longevity in Europe

In most European countries, electoral rules are such that it is possible to conduct effective advocacy for a cause via a single issue political party. Successful examples include the Green Party and the Pirate Party, but there are many others. In the matter of patient advocacy for investment into rejuvenation research, to treat aging as a medical condition and greatly reduce the suffering that occurs in old age, a number of European advocates have formed single issue political parties to raise awareness. The Party for Health Research in Germany is one such initiative. Here, the European Longevity Initiative is discussed, an alliance of single-issue parties and non-profits across Europe.

There is ample need to communicate fresh facts, principles and arguments around aging research and longevity technology opportunities within the European Union, with the single message that only these new technologies will provide a long-term solution to the problems presented by aging and general health. The last decade yielded a complete change of the paradigm around the understanding of the main hallmarks of aging and the malleability of the overall aging process. Building upon accumulating research in the previous decades, aging research has gone completely mainstream, and the paradigm of translational geroscience has gained strong supporters working on interventions directly targeting the root causes of biological aging to prevent - the biggest killer - age-associated diseases, and to extend healthy lifespan, aka healthspan, significantly.

Cross-European single issue longevity politics has an actual birth date, or rather period, the Members of the European Parliament elections of 2019. That is when multiple actors, in different countries stood at the elections focusing on the issue of working towards preventing age-associated diseases with healthy longevity technologies. Let me highlight here a dedicated, single-issue, one of its kind, political party, the German Party for Health Research and myself who stood as an independent candidate in the East of England Region. We got 0.2% of the votes with an almost zero budget, virtually unknown, meaning 1 in 500 voters thought the mission and programme are worth their votes.

The European Longevity Initiative (ELI) is a loose association of mainly EU citizens and residents coming together to form a healthy longevity advocacy group particularly targeting EU level legislation and EU wide public. Its associates are currently covering the following EU countries: Germany, Slovenia, France, Czech Republic, Belgium, Hungary, Greece, Austria, Poland. Moreover, current ELI associates are representatives of at least six existing European longevity advocacy groups. (1) The already-mentioned German The Partei für Gesundheitsforschung - The Party for Health Research; (2) LongevityForum.eu, funded by longevity supporters in the Czech Republic; (3) UK-based Longevity International running the pioneering All Party Parliamentary Group (APPG) for Longevity in the UK; (4) International Institute of Longevity based in Poland and Liechtenstein; (5) Društvo za vitalno podaljševanje življenja Slovenije - Slovenian society for vital life extension; (6) Heales Société pour l'Extension de la Vie - The Healthy Life Extension Society, based in Belgium.

Link: https://www.longevity.technology/european-longevity-initiative-single-issue-healthy-longevity/

The Reasons to Study Aging

I point out this open access paper not for the content, but for the preamble, in which the author offers a view on why the research community should study aging. Not to learn how it works, but to learn how to intervene in order to make the world a better place, in which people suffer less than is presently the case. This, at root, is why we work on treating aging as a medical condition - because it is by far the greatest source of suffering and death in the world.

Aging is characterized by the progressive deterioration of the body's physiological function, which leads to decreased health, increased incidence of degenerative diseases and, finally, a progressive increase in the risk of death. Aging is classically approached as an inevitable phenomenon whose problems are treated in a timely and palliative way, aiming only to minimize the suffering of the elderly or extend their life span. In addition, these illnesses, usually manifested by chronic diseases associated with aging, tend to be treated individually. That is, individuals with cancer will be treated to eliminate the tumor, while diabetics will be treated with drugs to lower blood glucose levels. As much as it is obvious that these people should be treated, these treatments are still palliative, since even with the cure of one of these diseases, the elderly individual continues to be at an increased risk for other diseases that will inevitably kill them. That is why the main health agencies in the world started to approach aging itself as a clinical entity that deserves to be treated as such. Not by chance, the first clinical study that aims to delay aging itself has recently started.

The impact of having aging as a target for treatment is enormous, not only because aging is the main risk factor for death among humans, but also because it tends to be one of the main expenses of elderly individuals and governments, and it is potentially a major cause of social inequality. If health systems maintain their current policy, public health costs are expected to double by 2050, creating a burden that many countries will not be able to sustain. In addition to health gains, intervening with aging would represent savings of approximately 7 trillion US dollars over 50 years in the US alone, while disease retardation scenarios would lead to minimal savings, since the risk of individuals acquiring other chronic disabling diseases remain.

But is it even possible to delay the aging process itself, or even reverse it as some propose? In 2016, it was suggested that there is a maximum limit to human life span, and that this limit is around 115 years old. This article, however, has been challenged in regard to the statistical analysis, and some are convinced that the proposed limit on human longevity proposed is not real. In fact, a more recent study of Italian centenarians showed that, surprisingly, the risk of death stops increasing with time when individuals reach the age of 105 years. The progressive increase in the risk of death is what characterizes the aging process in living beings. Thus, eliminating this increase means, in practice, that aging stops happening after a certain age. According to the study, at 105 years of age, the chance of death remains fixed at around 50% per year. This leads to the conclusion that at a given moment the balance between damage and repair stabilizes, preserving vital functions as they are, ceasing, however without reversing, the aging process. Although the estimates are still up for debate, the question remains: if it is possible to stabilize and mitigate the aging process at some point in life, why wouldn't it be possible to do it at a younger age?

Evidence that indicates this is possible is abundant in nature. There are several species that show negligible aging, i.e. which do not present an increased risk of death (or hazard rate) with age. For example, some species of turtles live for decades and show no signs of senescence. The Greenland shark is yet another vertebrate of extreme longevity and can live more than 400 years. Even among closer species and with similar habits, the lifespan can vary greatly. The naked mole-rat is a rodent that lives up to 30 years and practically does not develop cancer, unlike other rats and rodents that live a maximum of 5 years. Some species, such as the hydra, are even considered "immortal", or "amortal", because they do not die from causes related to aging. Even in humans, there are cells that can be considered amortal, such as germline cells. In other words, nature offers us examples of how aging and lifespan can be controlled. Looking at these examples, understanding how individual's senescence rate is determined, and proposing strategies to delay aging are the goals of a growing field called biogerontology.

Link: https://doi.org/10.1590/0001-3765202020200437