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- Planning a Single Person Trial of Senolytic Drug Candidates
- Are there Commonalities Between Neurodegenerative Conditions that can be Targeted to Produce General Therapies?
- In Essence, All Aging Research Revolves around the Science and Advocacy of SENS, the Strategies for Engineered Negligible Senescence
- Patterns of Aging in Both Normal and Longevity Mutant Nematodes
- The Problem with Focusing on Healthspan
- Latest Headlines from Fight Aging!
- The Basis for a Skin Sample Test of Level of Cellular Senescence
- SIWA Therapeutics Obtains Funding to Continue with an Immunotherapy Approach to Clearance of Senescent Cells
- Why is the Postfertile Longevity Exhibited by Humans so Unusual?
- Complicating the Bigger Picture of Protein Aggregation in Aging
- A View of How Senescent Cells Disrupt Tissue Regeneration
- Assessing the Prevalence of Sarcopenia
- Speculation on a Role for ATP in Age-Related Protein Aggregation
- Stem Cells versus Inflammation in Tendon Regeneration
- Another Example of a Human Genetic Variant that Lowers Blood Lipids and thus Reduces Heart Disease Risk
- It Might be Possible to Prevent Cellular Senescence from Occurring at All
Planning a Single Person Trial of Senolytic Drug Candidates
This post should be considered as part of an ongoing and yet to be concluded process of thinking out loud on the topic of self-experimentation with senolytic drug candidates. These are compounds that to some degree selectively destroy senescent cells in animal studies. Some have been shown to have positive effects in animal studies of various sorts in the years prior to the present wave of interest in senescent cell clearance, and some of those effects might be plausibly linked to removal of senescent cells. Some were tested as cancer therapeutics, or analgesics, or for other uses. Some have serious and harmful side effects, as is the case for most prospective chemotherapeutics. They are intended to destroy cells, and they are nowhere near as discriminating as we'd all like them to be. Nonetheless, all of these drug candidates are to varying degrees available for purchase, and thus available for self-experimentation.
Now, self-experimentation has a long and storied history in the scientific community. Many noted researchers at some point obtained the first human data from their own bodies, and that seems to me the most ethical of approaches: the researcher assumes the risks. Setting aside for a moment the question of risk, the point to take away from this history is that there is absolutely no point in doing this unless you measure and publish what you did and what happened. Guessing at outcomes or using drug candidates merely in the hope that effects will carry over from studies in mice helps no-one. The same goes for picking easily measured outcomes just because they are easy to measure. The objective here is to learn something and transmit that learning, which is possible even in an environment of single person tests without controls, provided we are seeking effects that are both large and reliable, and provided we go about this is a sensible manner. In this context, self-experimentation can help to point the way for those with the resources to run more rigorous experiments capable of better quantifying effect size, optimal dosage, and the like.
Obtain a Cooperative Physician
The first step is to ensure that you have a physician who understands what you are intending to do and achieve, and is willing to order up the required tests. You will need an interface and guide to the local medical establishment, especially for the more expensive scanning and testing. This usually isn't all that hard to obtain, since you'll be paying.
Obtain a Cooperative Laboratory Company
You will need a company to act as an interface with suppliers, as many of them will not accept orders for senolytics from individuals. In this age of drug prohibition, it also smooths the way for biochemical deliveries across national borders for them to be between laboratory companies. You will also need a company with laboratory resources, or that can act as an interface to laboratory services for some of the work you might want carried out. The ideal situation here is to work with someone within the community, via your connections, as it would otherwise require some legwork to find a company willing to work with you.
Determine the Health Metrics to be Assessed
The ideal set of data desired at the end of a short test of senolytics includes (a) the degree to which senescent cells were removed, and (b) the degree to which relevant measures of aging were reversed. The reality is that both require some compromises given the current state of medical testing. After some reading around and thinking on what would likely be affected by cellular senescence, given what is presently known, I settled on the following tests for consideration. One important item is that the normal values obtained from healthy individuals for a given test must vary to a large enough degree across the age range of 30 to 60 to make it useful to run the test if you are something other than very old. This is definitely not true for as many of the available tests as you might think would be the case.
Firstly, there is standard bloodwork and urinalysis. This is actually not all that likely show anything interesting if comparing before and after measures, especially in people who are not in their 60s or later, but it is cheap and a useful demonstration to show that nothing terrible took place. Further, some of the measures in bloodwork are needed for other parts of the testing. In particular, it is possible to see indications of tumor lysis syndrome resulting from senescent cell destruction. If there is a characteristic change in such measures immediately following use of a senolytic drug, it is an indication that something is happening, which is useful evidence.
When looking at liver function, none of the values obtained from normal bloodwork are particularly helpful. The numbers for normal function don't vary enough with age, and do vary a fair amount with circumstances and lifestyle choices. However, hepatobiliary scintigraphy results do change characteristically with age. This is a nuclear medicine procedure involving use of a radioactive tracer, so expect to pay accordingly.
For kidney function, the desired measure is glomular filtration rate. Now there are numerous ways of obtaining this result. There is the direct and expensive nuclear medicine approach with tracers, but also estimated approaches using data obtained from standard bloodwork. There are a number of resources that explain the differences in some detail, such as a PDF from the National Kidney Foundation. The estimated approaches suffer from various degrees of inaccuracy for the levels one would expect to find in a healthy individual, sad to say. The MDRD Study equation method should not be used, but the alternative CKD-EPI equation seems worth trying.
Given the evidence for a relationship between cellular senescence and calcification of blood vessels, calcium scans and scoring at first seem interesting. This is especially the case since it is apparently very hard to reduce a calcium score; it is something achieved only gradually over years, and with great attention to lifestyle changes. Calcium scans are just a standard CT scan followed by semi-automated analysis, producing an Agatston score or lesion-specific calcium score. Unfortunately, even later in life a large percentage of people score zero - as many as half or more in the late 40s and early 50s, for example. There is an online calculator from one of the research groups involved in this work if you are interested in exploring the numbers. All of this makes calcium scoring nowhere near as helpful as it might be, given the cost of a CT scan. It is probably only worth trying for people in their 70s and later, or who already have a score to hand and know it is non-zero.
Tests in lung tissue suggest that removal of senescent cells can somewhat reverse loss of tissue elasticity. So it seems worth looking at measures of skin elasticity. These can be obtained using cutometer or ballistometer commercial devices, with a number of papers commenting on reliability of the results. You might have to find a plastic surgeon or one of those dubious anti-aging clinics, however, rather than a standard dermatology practice. Possibly more useful is the indirect measure of blood vessel elasticity via pulse wave velocity, which is an easy test to arrange, and which does have a significant degree of change over the middle years of life. The question there, as with all matters cardiovascular, is the degree to which normal readings change because of primary (including the effects of senescent cells) versus secondary (weight gain and lack of exercise) causes of aging. The testing that is being accomplished here is as much of the relevance of the tests as it is of the effects of senolytic therapies. For that and other reasons, you can't just pick one test.
Another cardiovascular measure with a useful profile of changes over time is heart rate variabilility. Measurement here is also easily arranged. Of note, the Palo Alto Prize founders chose heart rate variability as their measure of aging for the interventions produced by competing teams.
Biomarkers of aging based on DNA methylation are well on the way towards becoming a practical possibility these days, though there is as yet no one consensus approach that everyone agrees upon. Nonetheless, Osiris Green is offering a DNA methylation biomarker of aging implementation at an affordable price. This is cheap enough to put into contention, even though there is as much validation of the test needed as validation of senolytics.
If you can stretch to custom lab work, then it is worth looking into the existing cellular senescence tests, or the skin sample test noted this morning, both of which require a biopsy. In the former case there are kits and the tests are well established, at least in the research community, with a question mark on how the biopsy process will interact with the role of cellular senescence in wound healing to make the results unhelpful. In the latter case, the paper provides enough details for someone to repeat the protocol, but it is anyone's guess as to how useful it will be in practice. This is another case where calibrating the test is as much the goal as calibrating the effects of a senolytic.
Pick the Senolytic Drug Candidates
Right at the start, let us throw out dasanitib, navitoclax, and similar items targeting the Bcl-2 family. They are comparatively indiscriminate chemotherapeutics, and almost everything else that the research community has identified as a potential senolytic drug is better, judging from the animal data: either more discriminating, less harmful, or both. Of the remaining compounds, it makes sense to try a combination, as some studies have suggested synergies exist between drug candidates, or that different senolytics work on different types of senescent cell. Also, the academic and corporate studies will not at the outset tend to run trials for drug combinations. It is better to raise the odds of finding interesting new data.
The compounds that seem worth looking into fall into two categories. The first are easily obtained supplement-like items that are comparatively cheap, taken orally, and well characterized for safety. In this category are fisetin and quercetin, though there is some debate over whether or not the latter is in fact senolytic. The second are more recently identified senolytics that are less easily obtained and used, in some cases with little to no human data on safety and usage, but that seem promising given recent research. Here, I'd include piperlongumine and FOXO4-DRI. In each case, you would want to read around on what is known of the pharmacology, the studies that used the compound, current thinking on how it works, and make a call on whether or not you are willing to take the risk of trying it. This will certainly involve digging through research papers, and will certainly be an individual choice. Don't blindly follow anyone's recommendations: choose for yourself.
Establish Dosage and Schedule
Figuring the likely dose for a human study involves reading the existing literature on animal studies to find the most relevant dose used there, usually expressed in mg/kg, and then multiply accordingly. You will quickly find that for most senolytics there is no easy way to come to a recommended dose, and you'll be forced to use your best judgement. For example, piperlongumine has so far only been studied in cell cultures for its effects on senescent cells. Looking at the literature, it was tested as an analgesic at levels of 1-250 mg/kg, for cancer suppression at 2.5-5 mg/kg, for sensitizing cancer to other treatments at 1 mg/kg, and for more direct cancer ablation at 2.5 mg/kg. In some cases these were single doses followed by an assessment, in others they continued for weeks.
Similarly for fisetin, there are no published animal studies for effects on senescent cells. For other purposes in past years, however, you'll find data on the pharmacokinetics for doses of 10-250 mg/kg, another study providing 10-45 mg/kg, twice a day for weeks, and yet another for cancer suppression at 5 mg/kg twice over a period of a few weeks.
For quercetin, one can look at the original study identifying it as senolytic to see that the researchers used a single dose of 50 mg/kg. For FOXO4-DRI, there is a very little data beyond the one recent study announcing its effects and another equally recent focused on cancer. Both are paywalled and unfortunately the details of the dosage are not in the main body of the original paper, but rather in the supplemental materials that I've yet to obtain. Still, it is there for consideration when I get to it.
Bear in mind that you are certainly going to want to try a very tiny dose at the outset, and then work your way up to the final dose. This precaution is only sensible and is done for a variety of reasons. In some cases these senolytic compounds are poorly or not at all tested in humans. Secondly, how certain are you that the suppliers did everything absolutely correctly, and that the testing of their compounds worked as desired? Further, if trying combinations yet to be tested in any published paper, there is always the possibility of unforeseen interactions. Lastly, if things actually work well and you started out with a high load of senescent cells, you do have to worry about the possibility of tumor lysis syndrome due to too many cells dying at once. All of these are very good reasons to ease into the desired dosage over time.
There is very definitely a spectrum of safety in the compounds I've mentioned here, from quercetin (sold in stores, manufactured by many supplement companies, in existence for years) through to FOXO4-DRI (comparatively new, barely manufactured at all, must be custom ordered, with no published human data, and only a couple of papers for animal studies). When you pick your poison, do so in full knowledge of the level of risk you undertake.
Figure out the Logistics
Quercetin and fisetin are things you put in bottles on a shelf and can leave there for months. You take the pills orally. That is all pretty easy. Piperlongumine requires freezer storage, and possibly powering or compounding to be taken orally. FOXO4-DRI is a short lifespan protein, must be keep in freezer storage, then reconstituted and given via injection: intraperitoneal injection in mice, but most likely intravenous injection would be the most desirable option in humans. If you are familiar at all with how diabetics manage their insulin supplies, the situation is very similar.
Management of injection logistics is something that you want a lab company and probably a physician to help with, rather than embark upon it alone. In this context it is very much worth noting that, given the drug war nonsense that has gripped the world these past few decades, you want to be careful as to how you go about obtaining needles for any compounds that must be injected. This is another good reason to arrange everything in conjunction with a friendly lab company and physician.
Determine Suppliers and Order Products
Finding suppliers for the chosen senolytics varies considerably in difficulty. For quercetin, you walk across the street to pick up a few bottles from the nearest supplement store, and by going with a trusted brand can probably feel good about skipping the step of validating that the contents are what they say they are. Or you may be able to find an existing review of the supplier's products online. Fisetin can still be ordered in bottles, but here the number and quality of suppliers is more of an unknown, so the need to test the product comes into play.
For piperlongumine, you will be ordering from a chemical supplier and paying a considerable amount - hundreds for a single dose, going by the levels used in animal studies. For FOXO4-DRI, it is likely that the best course, given the very small number of suppliers, is to have it synthesized as a custom batch by a company that specializes in protein synthesis. This is expensive, and is where you will need the lab company. In both cases, suppliers will be reluctant to supply anyone they think is going to use it for human testing outside the formal trial system or a research institution.
Test the Products
You will also need the friendly lab company for the task of determining how to validate the quality of products when they arrive from the suppliers. Validation of quality is not a completely straightforward process, and may require digging up specialist services, which is better done through a company already in that ecosystem than to try it yourself. It is a matter of great importance to establish that you are getting what you pay for, both to avoid wasting the time and resources spent on the exercise of self-experimentation, as well as for reasons of personal safety. Even with the best of intentions, compounds that are not mass manufactured can have bad batches.
Run the Experiment
The first step is to run all the desired tests to obtain a set of initial baseline values. For many of these, such as standard bloodwork, it makes sense to run them twice, perhaps a few weeks apart, since numbers tend to vary with circumstances. Then follow the dosage schedule. Then run two more sets of tests, one a few days after the end of dosage, and one a month later. Precisely because many of the measures can vary with lifestyle, it is important to be consistent in your diet, exercise, and so forth across this period of time.
Then, once done, wrap it all up by publishing the data online for the community to look over.
Considering the Easy versus the Not So Easy Options
It should be apparent from reading the above notes and the linked materials that the choice of candidate senolytics and assays makes a big difference to the amount of work required to run a useful exercise in self-experimentation. It also makes a big difference to the level of personal risk undertaken. I picked the senolytics discussed in this post in part to make this point. To cut down to the easiest and safest level of self-experimentation, it would be possible to try only fisetin and quercetin and largely avoid the need for laboratory services, just relying upon a friendly physician to order bloodwork, cardiovascular, and other established tests. One could also be fairly confident that the risk of adverse effects in that scenario is lower than it is in the others. Sadly these are also the more dubious senolytic candidates; there is no such thing as a free lunch, it seems.
Are there Commonalities Between Neurodegenerative Conditions that can be Targeted to Produce General Therapies?
Cancer research will only progress meaningfully towards control of all cancer when the research community puts significant time and effort into finding common mechanisms shared by many or all cancers - or better still, attacking the one known mechanism shared by all cancers, which is abuse of telomere lengthening. The reason that the cancer community struggles with progress is that there are hundreds of forms of cancer, and researchers largely continue to try to address them one by one. There is a lot of cancer, but only so much funding and only so many scientists. A better way forward is needed. The question for today, however, is whether or not this principle of action extends to another broad class of widely varied conditions, the neurodegenerative diseases that corrode the aging brain. Are there faster paths forward here as well, built on common mechanisms? I'm on the fence on this topic. I think it easy to argue that any two different forms of neurodegeneration are far more distinct from one another than any two types of cancer; they involve completely different ways to disrupt cellular activity in the brain or kill brain cells. There is no one mechanism with a clear analogy to the central role of abuse of telomere lengthening in cancer when it comes to neurodegenerative disease.
Still, it is tempting to speculate on mechanisms that might be shared between many different types of neurodegenerative disease, because if they do exist, that offers the same prospect of faster progress, if only the research community better directed its efforts. Obviously, at root, many layers of cause and consequence removed from the disease state, we can look to the forms of tissue and cell damage outlined in the SENS rejuvenation research proposals - the root causes of aging. Most neurodegeration is age-related because it is caused by aging, and thus the first resort should probably be attempts at first principles rejuvenation, therapies based on repair of root cause damage. Sadly, few in the research community agree with that statement; persuading them to see the light is an ongoing project. Further along the chain of damage and dysfunction can be found other examples. We might, for example, consider the failure of cerebral spinal fluid drainage channels as a possible common factor in all conditions involving the build-up of aggregates and other unwanted molecular waste in the brain. Equally, there may be other, more esoteric points at which intervention is possible, though in general the later in the disease process the intervention occurs, the less likely it is to produce more than marginal benefits, if the past century of medicine is any guide to what the future holds. You might look at this work as an example of the type:
Alzheimer's, Parkinson's, and Huntington's diseases share common crucial feature
Abnormal proteins found in Alzheimer's disease, Parkinson's disease, and Huntington's disease all share a similar ability to cause damage when they invade brain cells. The finding potentially could explain the mechanism by which Alzheimer's, Parkinson's, Huntington's, and other neurodegenerative diseases spread within the brain and disrupt normal brain functions. The finding also suggests that an effective treatment for one neurodegenerative disease might work for other neurodegenerative diseases as well. "A possible therapy would involve boosting a brain cell's ability to degrade a clump of proteins and damaged vesicles. If we could do this in one disease, it's a good bet the therapy would be effective in the other two diseases."
Previous research has suggested that in all three diseases, proteins that are folded abnormally form clumps inside brain cells. These clumps spread from cell to cell, eventually leading to cell deaths. Different proteins are implicated in each disease: tau in Alzheimer's, alpha-synuclein in Parkinson's and huntingtin in Huntington's disease. The new study focused on how these misfolded protein clumps invade a healthy brain cell. The authors observed that once proteins get inside the cell, they enter vesicles (small compartments that are encased in membranes). The proteins damage or rupture the vesicle membranes, allowing the proteins to then invade the cytoplasm and cause additional dysfunction. When protein clumps invade vesicles the cell gathers the ruptured vesicles and protein clumps together so the vesicles and proteins can be destroyed. However, the proteins are resistant to degradation. "The cell's attempt to degrade the proteins is somewhat like a stomach trying to digest a clump of nails."
Endocytic vesicle rupture is a conserved mechanism of cellular invasion by amyloid proteins
Numerous pathological amyloid proteins spread from cell to cell during neurodegenerative disease, facilitating the propagation of cellular pathology and disease progression. Understanding the mechanism by which disease-associated amyloid protein assemblies enter target cells and induce cellular dysfunction is, therefore, key to understanding the progressive nature of such neurodegenerative diseases. In this study, we utilized an imaging-based assay to monitor the ability of disease-associated amyloid assemblies to rupture intracellular vesicles following endocytosis. We observe that the ability to induce vesicle rupture is a common feature of α-synuclein (α-syn) assemblies, as assemblies derived from wild type (WT) or familial disease-associated mutant α-syn all exhibited the ability to induce vesicle rupture. Similarly, different conformational strains of WT α-syn assemblies, but not monomeric or oligomeric forms, efficiently induced vesicle rupture following endocytosis.
The ability to induce vesicle rupture was not specific to α-syn, as amyloid assemblies of tau and huntingtin Exon1 with pathologic polyglutamine repeats also exhibited the ability to induce vesicle rupture. We also observe that vesicles ruptured by α-syn are positive for the autophagic marker LC3 and can accumulate and fuse into large, intracellular structures resembling Lewy bodies in vitro. Finally, we show that the same markers of vesicle rupture surround Lewy bodies in brain sections from PD patients. These data underscore the importance of this conserved endocytic vesicle rupture event as a damaging mechanism of cellular invasion by amyloid assemblies of multiple neurodegenerative disease-associated proteins, and suggest that proteinaceous inclusions such as Lewy bodies form as a consequence of continued fusion of autophagic vesicles in cells unable to degrade ruptured vesicles and their amyloid contents.
In Essence, All Aging Research Revolves around the Science and Advocacy of SENS, the Strategies for Engineered Negligible Senescence
Today's popular science article for consideration is the usual mix of frustrating and interesting remarks that result when various researchers are convinced to talk to the press on the subject of SENS rejuvenation research. I in no way exaggerate when I say that all approaches to the research of aging, all of the intent in aging research, all of the fundamental disagreements in the field, ultimately revolve around SENS, the Strategies for Engineered Negligible Senescence. The advocacy and the science of SENS are the moral and technological sun in this solar system, for all that many of those orbiting it apparently would rather things were otherwise. Is the point of aging research to cure aging, rejuvenate the old, and greatly extend healthy human life spans? Is the point of aging research to move as rapidly as possible to this goal? In the SENS view, yes, and with specific plans for how the medical control of aging can be realized. Everyone else in the field must be defined by their answers to these questions, and thus by their position on SENS, their differences from the SENS view.
When looking in on this situation from the outside, it is important to realize that (a) more than fifteen years after its introduction, SENS research still represents only a tiny fraction of the research field, (b) that its origins are as an outsider group, its founders entering the research community because they were sufficiently outraged by its lack of action with regard to aging to put aside their own plans, and (c) that only SENS and SENS-like research appears to be producing the basis for cost-effective interventions to address aging as a medical condition. Given this situation, no-one in the field can really ignore SENS, but there are nonetheless a great many who would prefer to.
In one sense, the SENS approach to aging, considering it as the downstream consequence of fundamental damage that should be repaired, has already won the war of ideas: establishment research groups have taken up their own SENS-like agendas based on identifying damage and addressing it in order to turn back aspects of aging. Researchers now argue over how to effectively treat aging rather than remaining silent. Senescent cell clearance, on the SENS list for more than fifteen years on this basis of many lines of research from the past few decades, has in recent years been proven to be a reliable means of reversing numerous aspects of aging in animal studies. It is well on the way to the clinic, under development by a number of funded startup companies. This significant progress has required a fraction of the expenditure to date on, say, calorie restriction mimetic drugs or other ways to slightly slow aging that are diametrically opposed to the SENS philosophy. These are approaches that do not repair root cause damage, but rather try to alter metabolism to slow down accumulation of damage. Senescent cell clearance therapies to date demonstrate very well the point that SENS approaches are cheaper and better, as we should expect of any attempt to repair damage rather than just slow it down.
Yet in another sense, SENS has barely touched on the bigger picture of research and development. It is a tiny fraction of the ongoing work in the field. The vast majority of aging research remains investigative only, with no intention of producing therapies. Only a couple of the characteristically SENS approaches have made it into the mainstream in a big way, senescent cells and amyloid clearance. The first working, real rejuvenation therapies are not yet available in the nearest clinic. Yet tiny fraction as it is, it is the fraction that matters when it comes to results, as the past few years of work on senescent cell clearance has demonstrated. When the only thing that really matters is results, given that the successful treatment of aging is a matter of life and death for all of us, that puts SENS firmly at the center of the field.
SENS as a line of advocacy and set of specific research programs to achieve rejuvenation has helped to fundamentally change the research community since the turn of the century, from one in which no-one could talk about treating aging as a medical condition, to one in which young researchers publish openly on this topic and the first therapies are moving towards the clinic. Yet the researchers whose field has been changed remain on the whole remarkably unwilling to credit any of this to the small community of advocates and researchers who have occupied the central point of strategy and intent in their field. Even those researchers who ten years ago penned a letter dismissing all of SENS as something other than science, the presented evidence for the merits of senescence cell clearance included, find it hard today to admit outright that they were completely wrong. But everything of importance in aging research comes back down to SENS in the end: are research groups working on meaningful ways to turn back aging, or are they just wasting time and funding? What matters more than saving all of the lives lost to degenerative aging? Than preventing all of the suffering caused by degenerative aging? This is a meaningful question in a field that is still in the ragged process of a slow - and apparently sometimes reluctant - change from pure research to applied research, and whose members often seem quite hostile to the SENS advocates who ask these and other pointed questions.
Can Human Mortality Really Be Hacked?
It's just after 10:30 a.m. on a pleasant weekday morning at the SENS Research Foundation, a biotech lab in Mountain View, California. I've come to speak to its chief science officer, Aubrey de Grey. The 54-year-old's long hair, tied back in a ponytail, is turning gray, a change that would be unremarkable if he weren't one of the world's most outspoken proponents of the idea that aging can be completely eradicated. Unlike most scientists, he isn't shy about making bold speculations. He believes, for example, that the first person who will live to be 1,000 years old has most likely already been born. In 2009, de Grey founded the nonprofit SENS Research Foundation, the world's first organization dedicated to "curing" human aging, not just age-related diseases. The organization, which conducts its own research and funds studies by other scientists, occupies an unassuming space in a small industrial park. Its walls are affixed with large, colorful posters illustrating human anatomy and the inner workings of cells.
The basic vision behind SENS is that aging isn't an inevitable process by which your body just happens to wear out over time. Rather, it's the result of specific biological mechanisms that damage molecules or cells. Some elements of this idea date back to 1972, when the biogerontologist Denham Harman noted that free radicals cause chemical reactions, and that these reactions can damage the mitochondria, the powerhouses within cells. De Grey takes this concept further than most scientists are willing to go. His 1999 book argued that there could be a way to obviate mitochondrial damage, slowing the process of aging itself. Now SENS is working to prove this. Its scientists are also studying other potential aging culprits, such as the cross-links that form between proteins and cause problems like arteriosclerosis, and senescent cells that stop dividing but accumulate inside us, secreting proteins that contribute to inflammation. They're looking at damage to chromosomal DNA, and at "junk" materials that accumulate inside and outside cells (such as the plaques found in the brains of Alzheimer's patients). As de Grey's thinking goes, if we could figure out how to remove senescent cells and other damage using approaches like drugs or gene therapy, along with other types of repair, we could potentially keep our bodies vital forever.
This desire to eradicate aging has, in the last decade, inspired a mini-boom of private investment in Silicon Valley, where a handful of labs have sprung up in SENS' shadow, funded most notably by tech magnates. It's this influx of wealth that has brought novel anti-aging theories out of the scientific fringes and into gleaming Silicon Valley labs. De Grey notes that developing the means to make everyone live forever is not cheap. Further, immortality, it turns out, is not such an easy sell: Most people don't like the idea of living forever. "I find it frustrating that people are so fixated on the longevity side effects," de Grey says, clearly irritated. "And they're constantly thinking about how society would change in the context of everyone being 1,000 years old or whatever. The single thing that makes people's lives most miserable is chronic disease, staying sick and being sick. And I'm about alleviating suffering."
Judy Campisi works in Novato at the Buck Institute for Research on Aging, a gleaming profit research institution. "For 99.9 percent of our human history as a species, there was no aging," she says. Humans were very likely to die by our 30s from predation, starvation, disease, childbirth or any number of violent events. Life spans in the developed world have more than doubled over the past century or so, but this hasn't happened through any interventions against aging itself. Rather, it's a byproduct of innovations such as clean water, medication, vaccinations, surgery, dentistry, sanitation, shelter, a regular food supply and methods of defending against predators. A biochemist and professor of biogerontology, Campisi has spent her career studying aging and cancer, and the role senescent cells play in both. She has researched these cells in her lab and published widely on the possible evolutionary reasons they remain in our bodies. She posits that for most of human history, natural selection didn't favor living to old age. Evolution protected younger people so they could pass along their genes, and senescent cells play a very important role.
"One thing evolution had to select for was protection from cancer," she says. "Because we are complex organisms, we have lots of cells in our body that divide, and cell division is a very risky time for a cell because it's easy to pick up a mutation when you are replicating three billion base pairs of DNA." If a cell doesn't divide, there are fewer chances for such a mutation to creep in. "So evolution put into place these very powerful tumor suppressant mechanisms - senescent cells - but they only had to last for 40 years at the most." Senescent cells contribute to inflammation, and "inflammation is the number one risk factor for all diseases of aging, including cancer." The idea that senescent cells contribute to aging was first postulated in the 1960s. Yet 50 years later, scientists still don't entirely understand the role they play. All Campisi can say definitively is that, for most of human history, there was "no evolutionary pressure to make that system better because everybody died young."
When I ask Campisi why some scientists talk about "curing" aging, she says it comes down to getting interventions approved. "There are people who want to consider aging a disease for the purposes of going to regulatory agencies and having a specific drug able to treat a specific symptom, which you can only do if it's recognized as a disease." But Campisi stresses that living forever is not the goal of most research on aging. Instead, she says it's primarily aimed not at life span but "health span" - increasing the number of years that people can remain physically and mentally agile. Campisi has known de Grey for years, collaborates with SENS and even serves on the organization's advisory board. I ask what she makes of his assertion that someone alive today will reach the age of 1,000. "I have to tell you Aubrey has two hats," she says, smiling. "One he wears for the public when he's raising funds. The other hat is when he talks to a scientist like me, where he doesn't really believe that anyone will live to 1,000 years old. No."
In 2006, the magazine MIT Technology Review published a paper called "Life Extension Pseudoscience and the SENS Plan." The nine co-authors, all senior gerontologists, took stern issue with de Grey's position. "He's brilliant, but he had no experience in aging research," says Heidi Tissenbaum, one of the paper's signatories and a professor of molecular, cell and cancer biology at the University of Massachusetts Medical School. "We were alarmed, since he claimed to know how to prevent aging based on ideas, not on rigorous scientific experimental results."
More than a decade later, Tissenbaum now sees SENS in a more positive light. "Kudos to Aubrey," she says diplomatically. "The more people talking about aging research, the better. I give him a lot of credit for bringing attention and money to the field. When we wrote that paper, it was just him and his ideas, no research, nothing. But now they are doing a lot of basic, fundamental research, like any other lab." In marked contrast with de Grey, however, Tissenbaum doesn't see aging itself as the problem. "I don't think it's a disease," she says. "I think it's a natural process. Life and death are a part of the same coin." Meanwhile, scientists are trying to understand why the brain deteriorates over time, losing mass and neural circuitry. Tissenbaum and others are trying to understand these mechanisms, hoping to find new treatments for neurodegenerative diseases. But she doesn't expect any intervention to keep humans healthy forever. "It may be that the brain has a finite life span," she says.
Patterns of Aging in Both Normal and Longevity Mutant Nematodes
If you've been following efforts to slow aging in laboratory animals for any great length of time, then you should find the open access paper I'll point out today to be quite interesting - though note that the full text is PDF only at the time of writing. As a general rule, it is a lot harder to dissect the statistical shape of aging for a population than it is to just put numbers to mean and maximum life span. Measuring health to any useful level of detail is far more labor intensive than counting the study animals who are still alive. This means that there is actually comparatively little information on the numerous methods of slightly slowing aging when it comes to what exactly that means in various species: a longer span of health, a longer span of ill health, slower aging at the outset, slower aging at the end, the development of plateaus in which little aging takes place, and so forth.
For smaller and shorter-lived species such as nematodes, there is the potential to solve this problem with automation, however. In the past few years researchers have made considerable progress in automating lifespan and healthspan studies of nematodes, with one group constructing a Lifespan Machine that enables data mining of the health and longevity across tens of thousands of individuals. The authors of the paper quoted below have built what they call the WorMotel, serving a similar function. This new data is enabling a variety of novel insights.
What does this tell us about slowing aging? Judging from this latest set of results, it looks like yet another illustration to show that everything in the intersection of cellular metabolism and aging is more complex than we'd like it to be. More data is needed, and in gathering that data there continues to be some debate over the sort of outcome that is produced by any specific intervention: extended youth or extended decline. Do these interventions increase resistance to the consequences of damage, which seems the likely cause of an extended period of decline, or postpone damage, which seems the likely cause of extended youth? It would be very interesting to see what an analogous Lifespan Machine or WorMotel would find in flies, or in mice - though the cost would be prohibitive for mouse studies in the current model of automation.
For further consideration, bear in mind that slowing aging is itself a completely different mode of intervention from that of rejuvenation produced by repair of damage - the SENS approach. We don't yet have much to go on when it comes to how repair therapies differ in outcomes between species, or between individuals, or between approaches. Only one such class of therapy has any life span studies to reference, those for senescent cell clearance. Even there only a couple of studies exist and only a comparatively small number of animal subjects have undergone the therapies. There is every reason to expect that repair therapies will look very different from methods of slowing aging in the results produced, but we won't know the full details across populations and species for years yet, even for removal of senescent cells. Still, the sort of analysis in the paper below is exactly the sort of thing we'd like to see applied to rejuvenation therapies as they emerge from the laboratory.
Longitudinal imaging of Caenorhabditis elegans in a microfabricated device reveals variation in behavioral decline during aging
Here we describe the WorMotel, a microfabricated device for long-term cultivation and automated longitudinal imaging of large numbers of C. elegans confined to individual wells. Using the WorMotel, we find that short-lived and long-lived strains exhibit patterns of behavioral decline that do not temporally scale between individuals or populations, but rather resemble the shortest and longest lived individuals in a wild type population.
While many factors are known to modulate the mean lifespan of a population, less is known about how these factors alter the aging process on an individual level. It was recently shown that within a wild-type population, long-lived and short-lived animals differed in two ways. First, the rate of physiological decline was slower in long-lived individuals, as might be expected. The second, however, was counter-intuitive: the additional lifespan of longer-lived individuals was primarily due to differences toward the end of the lifespan. That is, long-lived animals exhibited longer periods of low physiological function, or 'extended twilight'. A different picture was suggested by a study using automated assays of lifespan in the 'Lifespan machine'. In this study it was reported that various genetic and environmental perturbations do not fundamentally change the shape of the survival curve, but rather only compress or dilate it in time. This result was interpreted as suggesting that the aging process in C. elegans is, at least at some point in its pathway, controlled by a single process describable by a single variable corresponding to the rate of aging.
We sought to determine to what extent, 'extended twilight' and/or scaling effects apply at the behavioral level in mutants with altered aging. The concept of a universal scaling parameter in aging would suggest that the short and long-lived individuals within any strain (whether with normal, short, or long mean lifespan) would resemble their short and long-lived counterparts in the reference strain, but with a temporal scaling. If the variations in aging rate among individuals in any isogenic strain are governed by similar factors, we would expect that long and short lived individuals would display similar late-life characteristics as their wild type counterparts. If, on the other hand, short-lived strains as a whole physiologically more closely resemble short-lived individuals of a wild type population, we might expect them to display late-life characteristics similar to these short lived individuals. Similarly, long-lived strains might display a range of late-life decays or alternatively collectively resemble long-lived worms in the reference strain.
Wild-type strain N2 worms exhibited an initial decline followed by a 'plateau' period of nearly constant spontaneous and stimulated activity and response duration and latency. When we compared the behavior of the shortest-lived and longest-lived quartile of N2 worms, we found that their behavioral declines were qualitatively different. The longest-lived animals exhibited a "decline and plateau" phenotype, in which an initial rapid decline in behavioral capacity is later replaced by a very gradual decline for the remainder of life. By contrast, the shortest-lived animals showed only the rapid decline in behavior before dying. The result that long-lived animals experience a long period of low behavior are consistent with the 'extended twlight' reported by other researchers.
Short-lived daf-16 mutants declined at a similar rate to N2, but did not exhibit any plateau phase; instead, daf-16 worms die after their initial behavioral decline. A similar effect was seen in daf-16 response duration and response latency, which do not level off but decrease or increase, respectively, at a similar rate until the time of death. Comparing the activity history of the shortest-lived N2 worms to that of daf-16 as a whole, we found a striking correspondence between the behavioral decline of the two groups. These results show that the behavioral decline of daf-16 animals is not a scaled version of the wild type distribution of decline, but instead resembles the short-lived individuals in a wild-type population.
Long-lived daf-2 mutants, in which behavioral quiescence has been previously reported, exhibited a decline in stimulated activity akin to that observed in N2 and daf-16 followed by a nearly constant low level of stimulated activity and response behaviors for the remainder of life. Spontaneous activity in daf-2, on the other hand, declined to near zero within 10 days of adulthood, where it remained until death. Long-lived strains age-1, tax-4, and unc-31 also exhibited the "decline and plateau" phenotype. These results show that aging behavior of daf-2 and other long-lived animals, like that of daf-16 animals, does not resemble a scaled version of wild type. Instead, they resemble the longest-lived individuals in a wild-type population, in that they exhibit a long plateau period of low locomotory function during late life.
These results suggest that the sources of variability in lifespan in individuals also impact functional decline in a corresponding manner. For example, the N2 worm that survives 15 days due to stochastic factors will decline in a similar manner to the daf-16 worm that survives 15 days. Furthemore, individuals with a 30-day lifespan will exhibit a different shape of functional decline, but this shape is dictated by the confluence of genetic and stochastic factors that result in the lifespan of 30 days.
The Problem with Focusing on Healthspan
There are numerous ways to go about advocacy for the cause of treating aging as a medical condition, for the production of therapies to address the aging process. One might focus on talking about extended health, or the goal of greatly increased longevity, or the details of aging as a novel target for medicine, or discard aging as a topic in favor of the development of cures for common, well-recognized age-related diseases - something that can only be achieved through addressing the causes of aging, but many people are more receptive to treating age-related disease rather than treating aging, no matter that these must be one and the same in the end.
The advocates, researchers, and supporters in our small community are largely here because of the possibility of radical life extension and working rejuvenation therapies, especially those who were involved early on. The SENS rejuvenation research programs were initially supported because they are the most viable path forward towards the long-term goal of escaping the bounds of aging. SENS is the best of current plans for aging research because it aims to fundamentally change the human condition by bringing aging under control. Those who have over the years materially supported SENS to the greatest degree are also doing so precisely because the project aims high, not just because it is credible, but also because it isn't just another group of aging researchers talking about small changes to the aging process.
Once engaging with the broader community of larger, more conservative funding bodies, and scientific institutions, and high net worth individuals, however, these are near entirely people who either do not subscribe to transhumanist views of what is possible to achieve through medical science in our lifetimes, or who are not willing to be seen to adopt that minority viewpoint, or to espouse any viewpoint significantly different from those of their peers. Even when it is correct. Even when it is useful. Even when it is the only practical way forward to address aging and age-related disease. This is politics in all its prosaic ugliness. So as advocacy for the treatment of aging as a medical condition has spread over the years, the message has been watered down. We go from the goals of radical life extension and rejuvenation to a focus on modest increases in healthspan with no mention of longevity.
There is a faction in our core community that believes we should go along with this, and dial back our public positions. Talk about healthspan and only healthspan, because it will pull in more supporters and more conservative funding, those who are not comfortable with the topic of greatly extending longevity. Or at least we can point to aging research institutions much larger than the SENS community, who only talk about healthspan, and seem to do quite well on the funding front - the Buck Institute is a good example. Why can't we do that? If we did, the funds will still go to the same projects that are the foundation of rejuvenation therapies, stepping closer to an end to degenerative aging. Those projects will certainly do a good job of increasing healthspan: the only way to achieve radical life extension is to maintain youth, after all. Why care if goals are misaligned, if the funding sources think they are helping to achieve marginal, tiny gains in healthspan, because that is all they believe to be possible, and instead the result is large gains in both health and longevity?
I think that this argument misses the reality of what will happen in an environment where the rejuvenation research message is the same as that of people pushing supplements, trials of metformin, calorie restriction mimetics, boosted autophagy, cholesterol-lowering drugs, and so forth. When the greater conversation surrounding aging research is that it is a way to extend healthspan, and no-one talks about longevity, then the existing well-connected research groups that only work on slightly slowing aging will trample all over more radical groups like SENS researchers, by weight of numbers if nothing else. Those involved in research that aims to slightly slow aging can set a target of adding five years via some form of metabolic adjustment, and when it is achieved present the outcome as a great victory, task accomplished.
They will say that most people die by 90, with the unspoken assumption that this is set in stone. By adding five years of health, they can claim to have removed 20%-30% of the period of significant decline at the end of life, and isn't that amazing progress? Armed with this message of compression of morbidity, such marginal strategies will continue to dominate the research community, just as they do today. Those of us who see further and want the implementation of rejuvenation to significantly extend both health and life, not just a slight slowing of the aging process, will continue to struggle to move the field of aging research beyond paltry efforts. So much of what goes on in the field today is near meaningless, a waste of effort when considered against what is possible to achieve through rejuvenation: additional decades and then centuries and longer of health and vigor.
The problem is that this field of research already spends near all of its time on marginal, unambitious goals. The problem is that the vast majority of advocacy and public engagement is focused on painting tiny gains as large gains, via the vision of compression of morbidity that talks only of healthspan. When longevity is not open to improvement, small increases in healthspan can be made to look large. But it is an illusion. These increases are not large, vastly greater gains are possible, and this present state of affairs must change. Creating that change requires that we distinguish ourselves and our message. All of the progress to date in establishing SENS rejuvenation research as an important part of the field has been achieved by distinguishing ourselves, by talking about greatly increased health and longevity and an end to aging, rather than hiding that view simply because some people would rather not engage with it. Further progress requires that we persuade more people to the goal of radical life extension, not that we make ourselves look just like the many other groups whose research strategies cannot possibly do more than add a couple of years to health or life span.
If you are running with the one viable, best, most effective way forward, then the worst thing you can do is to make your efforts, your plan for the future, look like the initiatives undertaken by everyone else. The point is to upend the world, revolutionize the research community, drag the field kicking and screaming into this 21st century of endless potential in biotechnology, to defeat aging and all of the death and suffering it creates completely and comprehensively. Aim high. Do what the others are not doing. Bring the world to your point of view. You can't do that in camouflage, with the light under the bushel.
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The Basis for a Skin Sample Test of Level of Cellular Senescence
Researchers here set forth the basis for a novel approach to assessing the level of cellular senescence present in a patient, using a skin sample as a starting point. The current situation for assays of cellular senescence is very biased towards laboratory research needs, with little innovation over the past twenty years. The present standard assays are unfortunately not a suitable basis for the efficient, discriminating, and above all easy and low-cost clinical tests that will be needed in the years ahread. Senolytic therapies capable of clearing senescent cells as a form of rejuvenation treatment will become available in the next few years, and adventurous souls can already self-experiment with some of the drug candidates. Tests capable of clearly establishing the results of such experimentation are much needed.
Fibroblasts form one the most important cellular components of the skin derma. During aging, skin fibroblasts undergo substantial changes in their functional activity, morphology and proliferative potential. The number of dermal fibroblasts decreases with aging, along with their ability to synthesize active soluble factors and to maintain proteostasis of components of the intercellular dermal matrix. The skin thinning, the loss of skin flexibility and elasticity, and wrinkle formation are natural consequences of such a decline. Therefore, we suggested that evaluating the proliferative potential of dermal fibroblasts is of great significance.
Measuring the ability to form colonies in vitro represents one of the "gold standard" methods for the assessment of the clonogenic survival of cells. The method was initially developed to evaluate the loss of reproductive capacity (reproductive death) of cells after exposure to damaging agents, particularly ionizing radiation. Later it was shown that cells isolated from biopsy material from different patients had varying ability for colony formation. This allows for comparative assessment of different patient's cell capacity to proliferate and may represent a promising avenue for personalized medicine.
Beside a colony-forming efficiency of fibroblasts, defined as percentage of plated cells that are able to form colonies, the evaluation of colony size/type distribution provides additional important information especially for heterogenic cell populations such as primary fibroblasts. In this case, the size of the colony depends directly on the proliferative capacity of cell-precursors: cells can form morphologically distinct colonies that can be broken down into the following three types: dense (or compact), diffuse and mixed colonies. If the fractions of each of these colony phenotypes are known, one can evaluate the proliferative potential of the entire fibroblasts culture. Cellular aging, traditionally assessed by the fraction of senescence associated β-galactosidase (SA-βgal) positive cells, along with the degree of differentiation are closely associated with the proliferative capacity of cells. With aging, intracellular β-galactosidase accumulates in lysosomes and a sharp increase in the β-galactosidase activity in older cells is traditionally considered to be a classic marker of cellular aging. Therefore, it could be anticipated that the fraction of aging cells in colonies of the diffuse phenotype would be larger than that in the colonies of the dense phenotype.
The aim of this work was to verify the assumptions regarding the relationship of cellular aging with the formation of fibroblast colonies of different phenotypes, and to examine whether such enriched analysis of colony formation may be used for evaluating the degree of cellular senescence. To this end, we measured the fraction of SA-βgal positive cells (SA-βgal+) in the three types of colonies (dense, mixed and diffuse) of human skin fibroblasts from donors of various ages. Although the donors were chosen to be within the same age group (33-54 years), the colony forming efficiency of their fibroblasts (ECO-f) and the percentage of dense, mixed and diffuse colonies varied greatly among the donors. We showed, for the first time, that the SA-βgal positive fraction was the largest in diffuse colonies, confirming that they originated from cells with the least proliferative capacity. The percentage of diffuse colonies was also found to correlate with the SA-βgal positive cells in mass culture. Moreover, a significant inverse correlation between the percentage of diffuse colonies and ECO-f was found. Our data indicate that quantification of a fraction of diffuse colonies may provide a simple and useful method to evaluate the extent of cellular senescence in human skin fibroblasts.
SIWA Therapeutics Obtains Funding to Continue with an Immunotherapy Approach to Clearance of Senescent Cells
SIWA Therapeutics is one of the older companies in the field of cellular senescence, among the small number of ventures that made an attempt to target senescent cells for destruction a decade ago and didn't really get all that far before funding ran out. Times have changed, however, and these groups have now been invigorated by progress in the science of cellular senescence and demonstrations of turning back aging and age-related disease in animal studies. One of these older ventures transformed into Unity Biotechnology, and Unity's success in raising a very large amount of venture funding has made it that much easier for everyone else with a credible approach to find backers. Between the established groups and newer ventures like Oisin Biotechnologies a wide range of potential approaches to senescent cell destruction are covered. It remains to be seen how well they all do on the later stages of the path to the clinic.
SIWA Therapeutics announced that it has successfully humanized its SIWA 318 monoclonal antibody, a significant milestone in the race to treat cancer and numerous other diseases by removing senescent cells, which become increasingly problematic as humans age. Senescent cells lose their ability to divide or replicate for a variety of reasons and also secrete chemicals which interfere with the normal functions of other cells as well as contribute to inflammation. When too many senescent cells accumulate, they can cause or exacerbate a variety of age-related and degenerative diseases.
In previous research in mice, SIWA 318 has targeted and successfully removed senescent cells, and it also increased muscle mass. Other testing showed that mice treated with SIWA 318 had fewer metastatic lung cancer occurrences as well as possible suppression of tumor growth. No adverse effects were observed from the antibody treatment in either study. The humanized form of SIWA 318 has demonstrated strong and significant binding to senescent cells in preclinical studies, critical to accurately targeting and removing them. SIWA Therapeutics just completed a new round of funding and is planning to submit an IND to the FDA, with the ultimate goal of conducting the first human clinical trials for senescent cell removal. Based on initial results, the primary focus likely will be pancreatic cancer metastasis.
"With SIWA 318 now available in humanized form, we have moved closer to determining if removing senescent cells could become a common therapeutic approach in the fight against metastatic cancers. Based on data that we and others in the scientific community have generated over the last few years, evidence is clearly mounting that many diseases, including cancer metastasis, will be treatable through senescent cell removal."
Why is the Postfertile Longevity Exhibited by Humans so Unusual?
Humans are an unusually long-lived species when compared to other mammals of a similar size, and even in comparison to our near relative primates. Further, we exhibit an extended period of life following loss of fertility, a rare form of life history that is only observed in a few other species. The grandmother hypothesis is one of the possible explanations for the evolution of extended longevity without fertility; it is a selection effect based on the ability of older individuals to assist in the survival of their descendants. Given the existence of such a mechanism, however, why is it not more widespread?
Data on historical agricultural populations and modern hunter-gatherers show that these groups enjoy significant postfertile periods. Taking an evolutionary approach, the Grandmother Hypothesis proposes that this reproductive inactivity is in fact adaptive. With the sacrifice of continued reproduction, an individual may increase their inclusive fitness by decreasing the interbirth intervals of their offspring. The care that would otherwise be put into one's own children can now be put into weaned (and increasingly independent) grandchildren, allowing their own offspring to reproduce again sooner. Otherwise put, the cost of a reduced relatedness coefficient may be outweighed by an increase in total number of grandchildren resulting from the diverted care.
A valid objection to the Grandmother Hypothesis, however, is if grandmothering can result in a higher fitness, why are significant postfertile life stages so rare? Among vertebrates in the wild, only humans, Globicephala macrorhynchus (pilot whales) and Orcinus orca (resident killer whales), have a significant proportion of individuals with such a life history. In this study, we present a model to investigate this objection. Our model assumes only that individuals transition through various life stages and that there is an average time to conception and gestation. In one of those stages, individuals have the option to provide care for a certain number of their grandchildren thereby allowing their own offspring to reproduce again sooner.
By comparing inclusive fitnesses of individuals that provide intergenerational care with those that instead continue to reproduce into old age, we arrive at a necessary condition for grandmothering to be an evolutionarily stable strategy (ESS). This condition, or stability threshold, relates the number of grandchildren that care must be given to with the ratio of the length of the first two life stages. It tells us nothing about when or how grandmothering may arise initially in a population, but places restrictions on when it will persist. We then make the observation that if a grandmother is to provide care for even one set of grandchildren, their expected postfertile stage must be sufficiently long. More precisely, for grandmothering to be adaptive, it must be the case that postfertile life exceeds the time taken to raise a weaned child to independence. If this were not the case, grandmothers would not be able to shorten their offspring's time between births by caring for some infants themselves. In this way, we derive an eligibility threshold that tells us when grandmothering is a strategy with any possible evolutionary advantage. These eligibility and stability criteria must both be satisfied for grandmothering to evolve and then, most importantly for our purposes, to persist.
Our analyses show that there is conflict between the stability and eligibility thresholds. As it becomes increasingly easier to meet one of them, it becomes increasingly harder to fulfill the other and vice versa. This conflict is, at its core, a grandparent-grandoffspring conflict analogous to parent-offspring conflicts. The result of this is that there is a narrow range over which we should expect grandmothering to evolve and then to persist. In other words, we should in fact expect grandmothering to be rare.
Complicating the Bigger Picture of Protein Aggregation in Aging
A number of different proteins can misfold or otherwise be altered in ways that cause them to precipitate into solid deposits. The best known of these are best known because they are are a contributing cause of age-related disease, through their disruption of normal tissue function or via a surrounding halo of biochemistry that is in some way toxic to cells. There are twenty or so forms of amyloid deposits, for example, and of these the most attention is given to the amyloid-β involved in Alzheimer's disease - though transthyretin amyloid is catching up, given the growing evidence for its role in heart failure. In the paper here, the authors suggest that the way in which amyloids and other similar deposits get started involves interactions between the aggregation of potentially many other proteins: in other words that proteins A and B might aggregate without any great evidence for a link to resulting harm, but their aggregation acts to seed the aggregation of protein C that is very definitely harmful to health over the years.
A variety of neurodegenerative diseases are associated with the misfolding and aggregation of specific proteins. In Alzheimer's disease (AD), amyloid-β (Aβ) peptides and tau proteins aggregate and ultimately form the characteristic pathological hallmarks: amyloid plaques and neurofibrillary tangles (NTFs) respectively. In recent years, understanding the initiation and spread of these hallmark protein aggregates has become a central area of investigation. The current model stipulates that aggregation in disease is initiated by a protein seed that forms a template for further protein aggregation. Support for this model comes from research showing that the exogenous addition of minute amounts of Aβ or tau seeds greatly accelerates the onset of aggregation both in vitro and in vivo. An important and currently understudied question is how aging influences protein aggregation in neurodegeneration. Recently, physiological protein insolubility in the context of aging has become a hot topic of research. Indeed, numerous publications demonstrate that protein aggregation is not restricted to disease but a normal consequence and possibly cause of aging.
Until now, it remains unclear whether and how age-dependent protein aggregation and disease-associated protein aggregation influence each other. One possibility is that age-dependent aggregates indirectly accelerate disease-associated protein aggregation by stressing the cell and/or titrating away anti-aggregation factors. Another possibility is a direct interaction whereby disease-associated proteins and age-dependent aggregation-prone proteins co-aggregate. In support of this latter hypothesis, proteins prone to aggregate during normal aging are significantly overrepresented as minor protein components in amyloid plaques and NFTs. Recent research reveals that the sequestration of these age-dependent aggregation-prone proteins in the disease aggregates is a source of toxicity. However, whether misfolded proteins aggregating with age can form heterologous seeds that initiate Aβ aggregation has not been investigated.
Although current research focuses on homologous seeding, there are a few examples of cross-seeding (or heterologous seeding) mostly between different disease-aggregating proteins. For instance, Aβ is a potent seed for the aggregation of human islet amyloid polypeptide (hIAPP) involved in type II diabetes; Aβ and prion protein PrPSc cross-seed each other and accelerate neuropathology; and both α-synuclein and Aβ co-aggregate with tau and enhance tau pathology in vivo. Finally, we recently showed that cross-seeding between different age-dependent aggregating proteins is possible in the absence of disease. Here, we demonstrate that cross-seeding during aging is likely to be an important mechanism underlying protein aggregation in AD.
We show for the first time that highly insoluble proteins from aged Caenorhabditis elegans or aged mouse brains, but not from young individuals, can initiate amyloid-β aggregation in vitro. We tested the seeding potential at four different ages across the adult lifespan of C. elegans. Significantly, protein aggregates formed during the early stages of aging did not act as seeds for amyloid-β aggregation. Instead, we found that changes in protein aggregation occurring during middle-age initiated amyloid-β aggregation. Mass spectrometry analysis revealed several late-aggregating proteins that were previously identified as minor components of amyloid-β plaques and neurofibrillary tangles such as 14-3-3, Ubiquitin-like modifier-activating enzyme 1 and Lamin A/C, highlighting these as strong candidates for cross-seeding. Overall, we demonstrate that widespread protein misfolding and aggregation with age could be critical for the initiation of pathogenesis, and thus should be targeted by therapeutic strategies to alleviate neurodegenerative diseases.
A View of How Senescent Cells Disrupt Tissue Regeneration
Normal tissue regeneration is disrupted in various ways in later life, such as the tendency for increased fibrosis, scar tissue formation rather than normal regrowth. Researchers here theorize on the role of growing numbers of lingering senescent cells in this age-related loss of function, a complex situation because the transient creation of senescent cells, soon destroyed, is an important part of the normal wound healing process. Despite their positive function in that scenario, the accumulation of long-lasting senescent cells is nonetheless one of the root causes of aging. These cells produce a harmful effect on surrounding tissue through the potent mix of signals they generate, known as the senescence-associated secretory phenotype (SASP), which drives chronic inflammation, among other items.
The inability of adult tissues to transitorily generate cells with functional stem cell-like properties is a major obstacle to tissue self-repair. Nuclear reprogramming-like phenomena that induce a transient acquisition of epigenetic plasticity and phenotype malleability may constitute a reparative route through which human tissues respond to injury, stress, and disease. However, tissue rejuvenation should involve not only the transient epigenetic reprogramming of differentiated cells, but also the committed re-acquisition of the original or alternative committed cell fate. Chronic or unrestrained epigenetic plasticity would drive aging phenotypes by impairing the repair or the replacement of damaged cells; such uncontrolled phenomena of in vivo reprogramming might also generate cancer-like cellular states. We herein propose that the ability of senescence-associated inflammatory signaling to regulate in vivo reprogramming cycles of tissue repair outlines a threshold model of aging and cancer.
The degree of senescence/inflammation-associated deviation from the homeostatic state may delineate a type of thresholding algorithm distinguishing beneficial from deleterious effects of in vivo reprogramming. First, transient activation of NF-κB-related innate immunity and senescence-associated inflammatory components (e.g., IL-6) might facilitate reparative cellular reprogramming in response to acute inflammatory events. Second, para-inflammation switches might promote long-lasting but reversible refractoriness to reparative cellular reprogramming. Third, chronic senescence-associated inflammatory signaling might lock cells in highly plastic epigenetic states disabled for reparative differentiation. The consideration of a cellular reprogramming-centered view of epigenetic plasticity as a fundamental element of a tissue's capacity to undergo successful repair, aging degeneration or malignant transformation should provide challenging stochastic insights into the current deterministic genetic paradigm for most chronic diseases, thereby increasing the spectrum of therapeutic approaches for physiological aging and cancer.
If the loss of differentiation features following reprogramming is not accompanied by re-acquisition of the original or alternative differentiated cell fate, the resulting tissue plasticity might impair the repair or replacement of damaged cells. The ability of SASP-associated pro-inflammatory cytokines to regulate stemness and nuclear reprogramming raises the notion that a SASP-impaired local environment could interfere with tissue rejuvenation by imposing the so-called "stem-lock" state. Chronic inflammatory conditions via exposure to IL-1, which normally functions as a key "emergency" signal and a master regulator of SASP by inducing downstream effectors such as IL-6, has been shown to impair tissue homeostasis and to induce an aged appearance of the hematopoietic system by restricting stem cell differentiation.
While counterintuitive, given the ability of SASP factors including IL-6 to transiently create a permissive environment for in vivo reprogramming capable of inducing cellular plasticity and tissue regeneration, a prolonged promotion of such progenerative response might reduce tissue rejuvenation and promote aging by self-enhancing futile cycles of SASP/IL-6-driven reparative cellular reprogramming. Compared with young tissues containing few senescent cells where transient creation of senescent cells might cause temporary reprogramming and differentiation/proliferation to replenish cells, the prolonged accumulation of senescent cells in tissues that are old or under high levels of stress (e.g., following medical procedures such as chemotherapy) might be accompanied by a defective clearance of damaged, senescent cells, which can promote further SASP accumulation. A situation of chronic SASP secretion might not only counter the continued regenerative stimuli by promoting cell-intrinsic senescence arrest in single damaged cells but also paradoxically impose a permanent, locked gain of stem cell-like cellular states with blocked differentiation capabilities in surrounding cells.
Assessing the Prevalence of Sarcopenia
Sarcopenia is the name given to the characteristic loss of muscle mass and strength that accompanies aging, though formal definitions under development tend towards including only those with the greatest degree of loss. This is something of a political problem in the research and medical community; the tendency to describe some level of aging as normal and therefore not treatable, while classifying greater degrees of exactly the same process and symptoms as a disease. Along with the failure of the immune system and loss of bone strength, sarcopenia is one of the most evident forms of age-related frailty. A good many research groups are involved in the attempt to find ways to slow or reverse this decline, most of which are focused on mechanisms of stem cell activity and tissue regeneration rather than fundamental damage after the SENS model of aging. Of the present options outside the SENS portfolio, gene therapies or antibody therapies that target the muscle growth regulators of myostatin and follistatin appear most promising in the short term, given the rapid progress taking place in the broader field of genetic editing.
Sarcopenia, an age-related decline in muscle mass and function, is one of the most important health problems in elderly with a high rate of adverse outcomes. However, several studies have investigated the prevalence of sarcopenia in the world, the results have been inconsistent. The current systematic review and meta- analysis study was conducted to estimate the overall prevalence of sarcopenia in both genders in different regions of the world.
Electronic databases were searched between January 2009 and December 2016. The population- based studies that reported the prevalence of sarcopenia in healthy adults aged ≥ 60 years using the European Working Group on Sarcopenia in Older People (EWGSOP), the International Working Group on Sarcopenia (IWGS) and Asian Working Group for Sarcopenia (AWGS) definitions, were selected. According to these consensual definitions, sarcopenia was defined by presence of low muscle mass (adjusted appendicular muscle mass for height) and muscle strength (handgrip strength) or physical performance (the usual gait speed). The random effect model was used for estimation the prevalence of sarcopenia.
Thirty-five articles met our inclusion criteria, with a total of 58,404 individuals. The overall estimates of prevalence was 10% in men and 10% in women, respectively. The prevalence was higher among non-Asian than Asian individuals in both genders especially, when the Bio-electrical Impedance Analysis (BIA) was used to measure muscle mass (19% vs 10% in men; 20% vs 11% in women). Despite the differences encountered between the studies, regarding diagnostic tools used to measure of muscle mass and different regions of the world for estimating parameters of sarcopenia, present systematic review revealed that a substantial proportion of the old people has sarcopenia, even in healthy populations. However, despite sarcopenia being a consequence of the aging progress, early diagnosis can prevent some adverse outcomes.
Speculation on a Role for ATP in Age-Related Protein Aggregation
Researchers here suggest that ATP, the chemical energy store molecule produced by mitochondria, also serves to keep proteins soluble in the cell. This might help to explain the well known correlation between age-related mitochondrial dysfunction and age-related neurodegenerative diseases involving protein aggregates that build up in brain tissue. If mitochondria are producing less ATP, that may in turn accelerate the seeding of solid aggregates, and the consequent harm they produce. At this stage, the research is interesting but still fairly speculative when it comes to the degree to which this chemistry is relevant in disease states, however.
Adenosine triphosphate (ATP) performs many jobs in a cell. It carries energy, serves as a signaling molecule, and is the source of adenosine in DNA and RNA. But cells contain far more ATP than these known uses seem to require. That might be because ATP also can solubilize proteins, suggests a new study.
ATP has the general characteristics of a hydrotrope, an amphiphilic molecule that has both a hydrophilic and a hydrophobic component but does not assemble into structures such as micelles. Hydrotropes are used industrially to solubilize hydrophobic species in aqueous solution. The hydrophobic portion of hydrotropes - such as ATP's adenosine - likely interacts with the hydrophobic species, while the hydrophilic part - such as ATP's triphosphate - allows the species to stay in solution.
In the new work, a team investigated the effects of ATP on the aggregation of several proteins. They found that ATP could prevent the aggregation of two proteins known to form amyloid clumps. For a third protein, ATP was further able to dissolve fibers of already aggregated protein. And ATP kept proteins in boiled egg white from aggregating. "Most healthy cell functions require that proteins remain soluble at enormous intracellular concentrations, without aggregating into pathogenic deposits. The cell may exploit a natural hydrotrope to keep itself in a functioning, dynamic state."
Stem Cells versus Inflammation in Tendon Regeneration
Tendon tissue is one of many tissue types in mammals that is reluctant to heal completely following injury. Better methods of regeneration are desired, here as elsewhere in the body, and stem cell therapies show a great deal of promise in this regard. The most reliable of current stem cell therapy approaches, those with the greatest expectation of benefits to result for the patient, appear to work largely through a reduction in chronic inflammation. It is interesting to see that hold up in the case of tendons and their supporting stem cell populations.
New research suggests that tendon stem cells (TSCs) may be able to significantly improve tendon healing by regulating inflammation, which contributes to scar-like tendon healing and chronic matrix degradation. This has implications for the treatment of acute tendon injuries and chronic tendon disease. "Inflammation plays a critical role in acute and chronic tendon injuries and healing. Our findings represent an important foundation for the development of a new treatment that would regulate overwhelmed inflammation for tendon ruptures and tears, tendonitis, tendinopathy, and other tendon injuries and diseases."
In their study, the researchers used both in vitro human models and in vivo rat models. In vitro, isolated TSCs were stimulated with proinflammatory cytokines (proteins that can influence interactions between cells), and the expression of genes involved in inflammatory regulation was measured. In vivo, the researchers evaluated inflammatory responses by TSCs, including infiltration of macrophages (white blood cells that consume damaged or dead cells) and expression of anti-/proinflammatory cytokines, at different time points. Connective tissue growth factor (CTGF) was used in both models to stimulate the anti-inflammatory roles of TSCs. The researchers found that CTGF stimulation induced TSCs' production of anti-inflammatory cytokines, consequently leading to improved tendon healing and matrix remodeling. "Many would have predicted that tendon healing is inflammation-linked, but that the anti-inflammatory roles of TSCs could be so potent, and so amplifiable, is a striking finding."
Another Example of a Human Genetic Variant that Lowers Blood Lipids and thus Reduces Heart Disease Risk
In recent years researchers have discovered a couple of human gene variants that dramatically reduce blood lipid levels, in ANGPTL4 and ASGR1, which in turn reduces the risk of cardiovascular disease by slowing the development of atherosclerosis. The atherosclerotic lesions that form in blood vessel walls are seeded by oxidatively damaged blood lipids, and so lower lipid levels mean less seeding, all other things being equal. The research here presents another such gene variant, though by the sound of it one that has a lesser effect and isn't as widespread across populations.
A genetic variant that protects the heart against cardiovascular disease has been discovered in an isolated Greek population, who are known to live long and healthy lives despite having a diet rich in animal fat. In Mylopotamos in northern Crete the population are unusual as they have a diet that is rich in animal fat and should cause health complications, yet they have good health and live to an old age. In an attempt to solve the puzzle, scientists made a genetic portrait of the population by sequencing the entire genome of 250 individuals to get an in-depth view. This was the first time Mylopotamos villagers had their whole genome sequenced. The team then used the results to give a more detailed view of approximately 3,200 people for whom previous genetic information was known.
Scientists discovered a new genetic variant that was not previously known to have cardioprotective qualities. The variant, rs145556679, was associated with lower levels of both 'bad' natural fats - triglycerides - and 'bad' cholesterol - very low density lipoprotein cholesterol (VLDL). These factors lower the risk of cardiovascular disease. The cardioprotective variant may be almost unique to the Mylopotamos population. rs145556679 resides within an intron of the Down syndrome cell adhesion molecule like 1 (DSCAML1) gene, which is involved in cell adhesion in neuronal processes and is expressed in heart, liver, pancreas, skeletal muscle, kidney and brain. The genome sequencing results of a few thousand Europeans has only revealed one copy of this variant in a single individual in Tuscany, Italy. A separate variant in the same gene has also been found to be associated with lower levels of triglycerides in the Amish founder population in the United States.
It Might be Possible to Prevent Cellular Senescence from Occurring at All
Cellular senescence is a cause of aging. Enormous numbers of cells become senescent day in and day out, entering a state in which they secrete damaging signals that disrupt surrounding tissue. Near all self-destruct or are quickly destroyed by the immune system. It is the very few that linger and build up in tissues over the years that act to produce chronic inflammation, fibrosis, and ultimately age-related disease. Current approaches to the problem aim at killing these errant cells, finishing the job that was left uncompleted by natural processes, and turning back this aspect of aging.
As this research makes apparent, it may be possible in the near term to take the alternative approach of completely preventing senescence from occurring in the first place. Is this a good idea, however? My first reaction would be to say "no, absolutely not"; senescent cells play a role in in wound healing, as well as in cancer suppression, at least in small numbers. Also, and perhaps more importantly, what happens to the enormous number of somatic cells that reach the end of their replicative life span if they don't then become senescent and self-destruct? How would this disrupt the normal balance of tissue regeneration and maintenance? But the researchers here are maintaining a genetically altered lineage of mice in which cGAS, a controlling gene for senescence, is deleted. So far the mice appear largely normal, though deficient in the innate immune response to cancer due to loss of other functions of cGAS. So perhaps this does bear further investigation from a therapeutic point of view despite all the obvious objections that might be mounted.
Since its formal description more than 50 years ago, cellular senescence has been extensively studied and found to play a critical role in cancer, aging, and age-related diseases. Cellular senescence can be induced by DNA damage, telomere shortening, oxidative stress, and oncogenes. Interestingly, all of these senescence-inducing conditions impinge on DNA directly or indirectly. The DNA damage response is a key event leading to senescence, which is characterized by the senescence-associated secretory phenotype (SASP) that includes expression of inflammatory cytokines. Here we show that cGMP-AMP (cGAMP) synthase (cGAS), a cytosolic DNA sensor that activates innate immunity, is essential for senescence. We found that damaged DNA is associated with cGAS in the cytoplasm and that deletion of cGAS abrogated SASP gene expression and other markers of cellular senescence. These results reveal cGAS as an important molecular link between DNA damage, SASP gene expression, and senescence.
Whereas cGAS clearly plays an important role in cellular senescence, it should be noted that cGas-deficient mice appear to be healthy. We have not observed a significant increase in spontaneous tumors in our cGas-/- mice even though some of these mice are more than 20 months old. Because there are multiple barriers for a cell to become a malignant cancer cell, removal of cGAS alone may not be sufficient to cause spontaneous tumors. However, it will be very interesting to test whether cGAS deletion promotes tumor development driven by oncogenes such as Ras, which is known to induce senescence. In this context, we recently reported that cGas-deficient mice are refractory to the antitumor effect of immune checkpoint blockade, indicating that cGAS is required for generating intrinsic antitumor immunity. It remains to be determined whether cGAS has a cell-autonomous function in impeding the transformation of a normal cell into a cancer cell.
Recent studies have provided strong evidence that senescence has a causal role in aging and age-related diseases and that genetic deletion of senescent cells increases the lifespan and ameliorates age-related pathologies in mice. It would be very interesting to determine whether cGAS plays a role in normal aging as well as age-related diseases in animal models. If so, cGAS inhibitors may be used for treating not only autoimmune diseases but also a variety of age-related diseases.