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- An Interview with Reason at Undoing Aging 2019
- The Potential of Senolytic Therapies to Treat Chronic Kidney Disease
- The Implications of Greater Amounts of Remnant Cholesterol in the Bloodstream
- Reviewing Progress Towards Regenerative Therapies for Age-Related Hearing Loss
- The Present Popularity of Epigenetic Reprogramming to Treat Aging
- An Interview with Daniel Ives of Shift Bioscience
- The Gut Microbiome Changes Over the Course of Aging
- MicroRNA miR-122 is Important in Improved Mitochondrial Function Resulting from Calorie Restriction
- Increasing NAD+ to Improve Mitochondrial Function Slows Age-Related Hearing Loss in Mice
- Comparing the Metabolomic Signature of Aging in Mice and Naked Mole-Rats
- The Inflammatory Feedback Loop Produced by Senescent Cells in the Aging Heart
- DGCR8 Overexpression Attenuates the Accumulation of Senescent Cells with Age
- Cytomegalovirus in the Immunology of Aging
- Even Low Levels of Infection Can Cause Cardiac Dysfunction in Older Individuals
- A Comparatively Simple Approach to Improve Engraftment of Transplanted Cells
An Interview with Reason at Undoing Aging 2019
Much of the proceedings at Undoing Aging in Berlin earlier this year were recorded, but of course it takes a few months for everything to process through the queue. I briefly escaped from the conference for an ad hoc, unstructured discussion with Adam Ford of Science, Technology, and the Future, who, like the Life Extension Advocacy Foundation folk, was interviewing as many people as he could during the event. It wound up a monologue on topics that were at the top of my mind at the time, particularly the present state of funding and the transformation of our community from a primary focus on advocacy and academic research to one in which a great deal of important work is now carried out in startup companies, and the utilitarian ethics of treating aging as a medical condition. The resulting video is now up at YouTube, and is here accompanied by a transcript for those who prefer text.
I’m Reason. I’ve been around in this community for quite the long time, going on I guess twenty years now, rather shockingly. I seem to have become old in my own lifetime; I’m not as young as I look, unfortunately. I run Fight Aging!, the blog, which I’ve used as a platform for advocacy for some time, the aforementioned going on twenty years, though more like fifteen now for that site. Recently, last year, I cofounded Repair Biotechnologies with Bill Cherman to actually jump into the industry and do some things. Prior to that I was investing as an angel in a few biotech startups focused on aging, where I felt it was a better choice than giving to the SENS Research Foundation or other groups to do the research, because companies have the chance to attract a great deal more funding more rapidly than non-profits do, unfortunately – that is just the way of the world.
That is very much the transition of our community right now. And as that happens, I think it becomes much more important to think about why the hell are we doing this thing? Sudden influxes of vast amounts of funding are consequential. There are several hundred million funds right now, focused on longevity, and there will be more next year, because it is a land rush right now. If you lose sight of why you are doing this, and thus what is the most effective approach, then you wind up with a bunch of idiots doing stupid things that won’t work, and the upshot of that is that funding will be wasted. It is to a certain degree unavoidable, I mean look at the dot com era; every new industry has its peak of hype, a bunch of stupid things happen, a bunch of charlatans come in and take funding from investors who don’t know any better. It will happen, but I think that those of us who are here now, and have been here in this community, have something of a duty to try to reduce the size of that problem, down to some nominal minimum, to the degree that that is possible to achieve.
So why do we do this? The fundamental philosophy of the problem is that death is bad. Suffering is bad. That death is bad is the more debatable of those two. It is quite possible to construct an ethical position in which we say it is fine to be dead, you didn’t exist for quite a long time prior to existing, and you will not exist for quite a long time after you cease to exist. That is the way of the universe; the Stoics were good with this position. But I think it is very hard to argue that suffering is acceptable, at least above the sort of “maybe I should get out of bed and do something today” level of suffering needed to motivate the human animal to go and do something constructive. Anything much more than that level of angst I think should go away – and certainly that includes the level of pain, physical decrepitude, loss of function, and horrible things happening to the people around you that comes with aging. That should go away.
The world just hasn’t quite got there yet in terms of thinking about this in the right way. People think about malaria in the right way. Malaria is something like one six hundredth of the cost to humanity of aging, depending on how you want to measure all the little fripperies around the edges. So if we really feel up in arms about malaria, willing to spend billions on getting rid of it, which some people clearly are, then we should be spending trillions on getting rid of aging. We should be, but we are not, and that is why the advocacy community came into being. We have this weird mismatch between our capabilities and our goals. The world is a crazy place, I think everyone acknowledges that; there are many, many insanities that the human condition contains, be that politics, be that the way that some people like peanut butter, pick your poison. The present relationship with aging is just another one of these insanities: the world is insane with respect to aging, because accepting aging is insane. Why would anybody accept that he or she is going to crumble and die, and not want to do something about it? Plain, basic utilitarianism says that we should do something about it if we can do something about it. And we can do something about it!
So is the population of the world asleep at the switch because next to no-one realizes that we can do something about it? That will change pretty soon. Senolytics will wake up everybody. What if you can take one pill that makes your arthritis go away? That is basically what senolytics will do, when they are truly effective. The ones we have right now, that are available right now, appear to be fairly good at getting rid of arthritis, based on the results of trials yet to be published. Once this realization happens, I think there will be an interesting phase change. People will start to somewhat wake up from this business of “oh well, aging is just a fact of life, wherein we’re all going to die horribly, let’s just get on and try to paper over that.” So no, instead let us go full on utilitarian and try to do something about it. That is essentially the philosophy of action here. It is that aging is so terrible that there is really no amount of effort that humanity could spend on this problem that would be too great. Of course we’re so far away from anything that even approaches a reasonable amount of effort, given the level of death and suffering caused by aging, that for the foreseeable future we can keep on advocating and building hundred million funds. If investors build another hundred of those hundred million funds, that would be a nice start, but by no means the right amount of funding in order to reasonably address the problem, given what it actually costs.
The cost is enormous, and, sadly, most discussions about aging, when they do get going, really skate over the utilitarianism of it in favor of “wow, we’re spending a lot of money on entitlements, we need to do something about this.” That latter expression seems to be what passes for ethical thought in policy circles these days. It is a matter of “well, we’re spending a bunch of funds, we should find a way to stop doing that.” Then of course, the nihilists seems to be mostly in charge now, because their idea of spending less is to not treat old people for their conditions, rather than building rejuvenation therapies that stop old people from getting those conditions. As I said, it is insanity. This really just needs to change. So this is why the advocacy, and now that we’re at the point at which funding can be raised for startup companies working on rejuvenation biotechnologies, these startups are just another form of advocacy, really, if you look at the bigger picture. We’re not building therapies because we can do something with our small slice of the pie of aging, we’re building therapies because if we show people that we can do something with our small slice of the pie of aging, then soon enough there will be another hundred companies over the next decade, working on their small slices. People will see success and attempt to replicate it themselves.
There are a hundred, two hundred, three hundred programs out there languishing in the research community that could be turned into companies, turned into therapies, doing useful things in and around aging. As you know, the research community is just not good at raising funding. They are not good at translating their research to the clinic. They are poor at a lot of things other than just advancing the science. I think it falls to the rest of us, where “the rest of us” means anyone who might be an entrepreneur, or in venture capital, or an advocate, to set forth and sift through these programs, the output of the scientific community, and say “look, we should do something with these things.” If the research community isn’t pushing a program forward, well, this is a time in which anyone can wrap a company around a project, say “I think we can do something with this,” go to venture capital and get a few million in seed funding.
That will be the case for the next twenty years, on and off, as the market cycles up and down. So we should have a thousand startup companies working on a thousand projects related to aging. While there are only seven categories of fundamental causative damage, per SENS, some of those categories are very, very broad in terms of their little individual components. We have to fix all of lipofuscin, and we don’t even have a good catalog of everything that is in lipofuscin, just the major pieces of it. We have to get rid of all the amyloids, and that is a good few dozen projects right there. Replacing aged stem cells: a different cell population, different recipes for therapy for every tissue. And so on and so forth all the way down the list.
Then after we’ve worked through the SENS list of causative damage as it exists today, there will be all the things about aging that are problematic but are hidden by the fact that people presently die before they become problematic. Such as nuclear pore proteins in long-lived neurons. Some of those molecules never change after they are initially created. It is the same molecule for your entire life, and if it gets damaged, well, that is kind of a problem. How do we build the nanotechnology to go fix our nuclear pore proteins? That is a problem that no-one should much care about today, because there are fifty other things that will kill you before that will become an issue. But it will become an issue, eventually. If we come to live to 150, I’m willing to believe that your nuclear pore proteins becoming corroded and corrupted and reacted with is actually a serious issue, at least in neurons.
We can in principle replace everything except the brain. So the worst case scenario for the ultimate future is that they open your skull, take out your brain, and put it into a new body. I’m sure it will actually be somewhat more sophisticated than that, but this is just a thought experiment – what is the most radical thing you can make work in terms of replacement, in principle? That is moving the brain to a new body. What will probably happen instead is that your new body will be rebuilt from your old body: regeneration and rejuvenation by delivery of cells and therapies and control over cell behavior. But the brain itself? A really challenging problem, because you have to fix it without breaking it. I think we are along the way towards understanding the mechanisms to target for the early, preventative reductions in inflammation, to avoid supporting cells in the brain going crazy, to get rid of the protein aggregates. To try to keep things the way they were during your 30s. But that is just a starting point. There is so much to do after that. It is a big project. When I say trillions in funding, I’m serious. This is a very big thing, this is reinventing architecture when you are a caveman, going all the way up to the Renaissance, and building huge palaces. That is the scope of the project for us. I don’t think it will take as long as it took the cavemen, but I think that we’re definitely in for the long haul. To the extent that we can incrementally build meaningful rejuvenation therapies along the way, then many of us will also be in for the long haul, and this turns into someone’s life’s work. That life might be rather long.
I don’t know how long people will live. I am a late 40s individual, and if you can just run the thought experiment of the biotechnologies that will be available to me in my 80s, I won’t look anything like an 80 year old person today. I will have no chronic inflammation; no senescent cells; probably no cross-links in my body; my stem cells will have been replaced; my immune system gardened; and so on and so forth through a long list of treatments that are going to happen in the next few decades, and are very plausible right now. So you can add these things up and say, right, if an 80 year old has no inflammation, no senescent cells, no cross-links, no atherosclerosis, what does that do to health? Do you still look like an 80 year old? Can you go run a mile? No-one knows, and we get to find out by doing it. That is the great adventure.
The big problems in aging are all comparatively simple to solve, and it is all benchwork in the lab to get your programs going. You don’t need the massive computational, big data, machine learning projects that are popular right now. The only place where present artificial intelligence might be useful is in improving the state of small molecule drug discovery, and my belief is that small molecule drug discovery will go away, largely, in favor of gene therapy. So maybe your AI is looking for genes or proteins that are of useful effect, but the present process of finding genes that have useful effects is not terrible. It is having good results. The upshot is, ok, where do you use AI in this process outside of small molecule development? And I don’t see anything in which AI is absolutely necessary, useful in any way other than incrementally improving the infrastructure, reducing costs. Targeting senescent cells with senolytics, that is where small molecules might be useful, but the best projects there don’t involve small molecules. Dealing with mitochondrial DNA damage? No, that is benchwork, and it seems unlikely that small molecules can do anything meaningful there – that is gene therapy territory. Stem cells? Again, it is just a matter of developing the methodologies that can lead to successful therapies, and deep down under that development, you find a role for AI in anything where there is a lot of data to be analyzed, but it is only incremental improvement in cost and efficacy.
Infrastructure makes the world turn, and incremental improvement is not to be sneezed at, but it is just a part of the technology background. You can’t just jump up and say “we’re going to do AI for longevity”, no. You are going to do AI for biotechnology in general, and biotechnology is then applied to longevity. So AI will vanish into the tool space. It won’t be a major category that is up there on its own in the fight against aging. Right now it is because it is novel and because investors throw funding at AI like there’s no tomorrow, and entrepreneurs and scientists follow the funding. So you get In Silico Medicine, for example, and they are doing small molecule discovery AI, which is what most other people are now following on to do nowadays, because that is where the funding is in the present phase. But I think this will just fade into the background, it will be another tool in the toolkit. It isn’t exciting, it is not category changing. It is an incremental advance, using computers a little bit more to help you do things when there is a lot of data involved.
Let’s talk about Effective Altruism. That community is doing smart things, in the sense that Big Philanthropy is thoroughly corrupt, and one should ask the question: if I want to do good in the world, versus conning myself into thinking that I did good in the world, what should I in fact do? You don’t give to the Red Cross, because the Red Cross is a thoroughly corrupt organization. The same for most large entities in philanthropy; they have enormous overheads, and most donated funding doesn’t go to the projects you would want it to go to. The Effective Altruism movement in that sense is great, and a very overdue examination and critique of philanthropy as a whole. Secondly, if the effective altruists can find convincing ways to convince high net worth individuals to actually give sensibly, this will be a good thing. I suspect that reason many of high net worth individuals don’t give sensibly is because they have absolutely no idea how to do good, and it is a big project to figure out how to do good at scale. If Effective Altruism can lead to more people in the high net worth category putting their funds into projects that actually have a good chance of improving the human condition, then that is a public good.
The third strand is obviously that the Effective Altruism community includes people who are quite concerned about which projects to fund from a utilitarian point of view, and to the extent that anyone takes even a cursory look at aging, it is obviously the case that aging is far worse than anything else that happens anywhere. Pick your favorite cause in the third world, and I can tell you that those people are suffering more from aging than from the target of your favored cause. Even for war, even for famine, it is still the case that aging is much, much worse. This is a sad thing, because we could be dealing with all of these issues, but when it comes to prioritization, yes, if you want to solve famine because it is terrible and causes people to suffer, then you also be willing to work on solving aging in that same population, because it causes a far worse outcome to far more people. So the Effective Altruism community should logically work its way to advocacy for the treatment of aging as a medical condition, because it is undeniably the case that it is the worst problem facing humanity, and it is the most cost effective point of intervention to reduce suffering and death in the world. Even when intervening in tiny ways, the outcome is an enormous return on philanthropic investment in the cause.
So I think that the effective altruists do good, and I think that there are not enough of them, and I think that they are not talking about aging to the degree that they should. But they are coming at it largely from an outsider perspective, and except for a few, they don’t understand the science, they don’t understand the degree to which rejuvenation is possible. Effective Altruism is a young movement, it has a way to go yet, but it has the potential to be very important. We shall see how it develops. In terms of our community engaging with effective altruists, it is all just advocacy at the end of the day. To the extent that the aging research and development community needs funding, then we set forth and engage the effective altruists to the extent that they have funds, or can influence sources of funding. If it is more effective to talk to effective altruists, then we aging advocates will do that, trust me.
That might be challenging as an argument right now, as right now it is clearly more effective to talk to venture capitalists, because they are very incentivized to put funding into these projects. Very large amounts of funding, in fact, to the point at which it would be very hard to raise that level of funding through any sort of philanthropic program. Unless of course you are talking to high net worth individuals. But convincing high net worth individuals to go and put funds into work on treating aging is Effective Altruism, whether or not you are cloaking it in that name. Certainly, I and others are guilty of poking high net worth individuals to say “have you thought about this a little bit? Do you want to get old? You can do something about it. So go do something about it.” But it is an incremental process. You can’t just flip a switch and have all of the trooping masses of the Effective Altruism community go off and spread the desired message. So we shall see. It will go where it goes.
There is an enormous waste right now in development and deployment of ineffective ways to treat age-related disease, those that don’t target the causes of aging. Further it will cost a great deal to develop functional rejuvenation therapies that do target causes of aging. But if you look at the enormous amounts that are spent on merely coping with the consequences of aging, then making it go away is highly efficient. But of course it is not just about funding and cost, it is about effective reduction of suffering. Funding spent on anti-aging research is an enormously cost-effective way to reduce suffering, providing it is spent on the right anti-aging research, rather than the programs that are not likely to produce more than a small effect. So mTOR inhibitors are great compared to previous technologies for dealing with age-related diseases, because they influence a lot of processes, but the effect size is really not large in the grand scheme of things. If you are going to put funding into developing mTOR inhibitors, then fine, that is happening, then you should spend that same level of funding on aspects of the SENS program that can actually repair underlying damage, rather than trying to tweak the body to be a little more resilient to damage. People taking mTOR inhibitors are still going to die on the same schedule as the rest of us. That aren’t that much more resilient. People with senescent cells removed, on the other hand, well, who knows. We will see what that does to life span. I think that the pensions and insurance companies are going to be in for a rude awakening. Personally, I think that five years of additional life is not an unreasonable guess, and that will break a lot of insurance companies if they haven’t prepared successfully.
Regarding what will convince the world that meaningful progress is happening and further meaningful progress is possible, I think that recent developments in the laboratory, particularly around senolytics, are convincing to scientists. That is helpful. But I don’t think that it convinces the world at large in a useful way. Things have to leave the lab for that to happen. The thing about senolytics is that even those initial compounds available now seem to be quite good at making a sizable impact on quality of life in older people, and possibly for autoimmune diseases, and a bunch of other things. To the degree that we can say “guys, we’re giving you a rejuvenation pill, your arthritis is probably going to go away” and then if even half of the patients lose their arthritis, or their symptoms are greatly minimized, and they lose their other inflammatory conditions, and we turn back early Alzheimer’s disease – and all of these are plausible things that senolytics should accomplish, based on the mouse studies – then if that happens, then suddenly rejuvenation therapies are a real thing, and people can stop saying it is impossible to rejuvenate humans. Then we can go from there to explain that this is just one part of a larger program. We’re just doing one tiny thing, and not even that well, and look how good it is.
Senolytics will be the point at which an awful lot of things change. The early stages are happening right now. The self-experimentation community is doing interesting things with senolytics. Once the first studies that actually have large effects are published, it will be hard for regulators to keep these early senolytic drugs out of peoples’ hands. There are 60 million people in the US alone who would benefit from senolytics because they are old enough to have conditions that are inflammatory. This should happen. It will happen. And that would be the moment, I think. Senolytics, not anything else. Aging is a huge burden. Effectively treating aging will solve many problems. Old people are old people because they are aged. If you rejuvenate them, then they are no longer old. They will have a better time of it, and if you have an aging population of 80 year olds who are physiologically like 65 year olds, then you have an aging population of 65 year olds, effectively. After that it is very easy.
The Potential of Senolytic Therapies to Treat Chronic Kidney Disease
Senescent cells are a cause of aging. While near all senescent cells are destroyed shortly after entering that state, either by their own programmed cell death processes or by the immune system, the few that linger accumulate over the years to cause considerable harm. While it is true that even in late life senescent cells are far outnumbered by non-senescent, functional cells, senescent cells secrete a potent mix of inflammatory and other signals known as the senescence-associated secretory phenotype (SASP). The SASP disrupts tissue function, encourages nearby cells to also become senescent, and produce a state of chronic inflammation that accelerates many age-related conditions.
On the bright side, this means that near all age-related conditions can be turned back to some degree by the targeted removal of senescent cells, using senolytic therapies. The more such cells that are destroyed by a treatment, the larger the benefit. Since this produces such a broad range of beneficial effects, and there are only so many scientists in the world, the research community has yet to fully investigate even all of the most compelling, urgent uses of senolytic treatments to reverse specific age-related disease, let alone all of the other, lesser opportunities.
Today’s open access paper on the prospects for senolytic therapies to effectively treat chronic kidney disease is an example of the sort of work we’ll be seeing on a regular basis in the years ahead. Research teams will make slow inroads on assessing the use of senolytics as a rejuvenation therapy that can benefit patients with age-related condition A, B, or C, and so forth through a long, long list of diseases. It is a measure of just how new this field is, assessed in the grand scheme of things, that even the most widespread and severe conditions such as chronic kidney disease, those with no good therapeutic options at present, and wherein senolytic treatments might plausibly turn back much of the disease, are still not well investigated.
Cellular Senescence and the Kidney: Potential Therapeutic Targets and Tools
Chronic kidney disease (CKD) is defined by the persistent loss of kidney function and currently affects approximately 13.4% of the global population. The progressive nature of CKD often leads to end-stage renal disease (ESRD), requiring renal replacement therapy. To date, there are no curative therapeutic options for CKD/ESRD. An as yet untreatable final common pathway irrespective of the etiology in CKD is kidney fibrosis, characterized histologically by glomerulosclerosis, tubular atrophy, and interstitial fibrosis. Numerous compounds directly targeting factors involved in fibrosis driving pathways are currently being studied with varying results. Apart from the use of the renin-angiotensin-aldosteron pathway interfering agents such as ACE inhibitors or angiotensin receptor blockers to reduce the progressive remodeling of renal parenchyma, no therapeutics that can address the pathophysiological mechanisms underlying CKD are used clinically. However, increasing effort is currently put into investigating the efficacy of targeting senescent cells during renal disease.
Aging is associated with the decline of kidney function. During aging, increased renal p16 expression is most notably seen in tubular epithelium and to a lesser extent in glomerular (podocytes and parietal epithelium) and interstitial cells. Changes in p16 were more pronounced in the cortex compared to the medulla. In rodents, the amount of senescent proximal tubular cells increases with age, whereas no increase of senescent cells is seen in the glomeruli. Renal tubular cell senescence correlates with tubular atrophy, interstitial fibrosis, and glomerulosclerosis. Furthermore, the removal of senescent tubular cells leads to decreased glomerulosclerosis.
Eliminating senescent cells through transgenic depletion and pharmaceutical inhibition reduces kidney dysfunction and long-term kidney injury in experimental models of kidney damage, obesity-induced metabolic dysfunction, and during aging. These promising results have spurred interest in the development of clinically applicable therapeutic compounds that target senescence-associated pathways. Eliminating senescent cells (dubbed as senolysis) is just one of the various potential interventional approaches to target the adverse effects of cellular senescence (so-called “senotherapy”), including the prevention of senescence, modulation of SASP (termed senomorphics), and stimulation of immune system-mediated clearance of senescent cells.
The removal of senescent cells with so-called “senolytics” may be the most feasible and most attractive approach for clinical application, as the prevention of senescence and modulation of SASP would require chronic treatment with prolonged exposure to therapeutics. Several chemotherapeutics and checkpoint inhibitors currently used in daily oncological practice show senolytic properties. However, the applicability of such senolytic compounds for the treatment of renal diseases has hardly been investigated.
Research regarding senescence in the kidney has pointed to the proximal tubular epithelium as the culprit, and the removal of senescent tubular epithelial cells is therefore a promising approach to the attenuation of fibrosis in CKD. Due to the specific nature of proximal tubular epithelium, several specific targeting options are available, by which therapeutic drug efficacy can be potentiated and side effects can be reduced. Repurposing senolytic drugs that have been tested in clinical trials for other, mostly oncological, indications by functionalization for targeted delivery is a promising method to make a fast translation to clinical nephrology practice.
The Implications of Greater Amounts of Remnant Cholesterol in the Bloodstream
Atherosclerosis is a condition in which fatty lesions form to narrow and weaken blood vessels. It causes a sizable percentage of all deaths in old age, via stroke or heart attack when lesions rupture. Much of the focus in the medical and research communities is on cholesterol in the bloodstream as a contributing factor to the condition, but atherosclerosis should be thought of as being primarily caused by the dysfunction of the macrophage cells responsible for removing cholesterol from blood vessel tissues, handing it off to HDL particles to return to the liver. In youth these cells function just fine, and young people don’t develop lesions. In old age, however, it is a different story.
Macrophages are vulnerable to oxidized cholesterol and to the signaling of chronic inflammation. Both can degrade their ability to transport cholesterol, and they can develop into senescent foam cells that make the local environment even more inflammatory. They also die in large numbers, overwhelmed by cholesterol, and the debris of cell death expands the lesion that the macrophages should be helping to remove. It is because oxidized cholesterol is important in this process that reductions in overall cholesterol in the bloodstream can slow the progression of atherosclerosis. Treatments such as statins have become widely used as a result, but they do not lead to significant reversal of existing lesions.
Scientists here note that most of the work on atherosclerosis to date focuses on reducing LDL cholesterol in the bloodstream, which is to say cholesterol attached to an LDL particle. But other forms of cholesterol are also present in the blood stream, the so-called remnant cholesterol, and the research community has underestimated its presence and contribution to atherosclerosis. This has implications for the various approaches taken to try to control the condition, and further demonstrates that perhaps it is a better idea to focus on the macrophages rather than on the cholesterol. If macrophages can be made resilient to oxidized cholesterol, either by removing that cholesterol in a targeted way, by preventing it from being created in the first place, or by giving the macrophages additional capabilities, as we’re working on at Repair Biotechnologies, then this should go a long way towards the goal of reversal of atherosclerosis.
Levels of ‘Ugly Cholesterol’ in the Blood are Much Higher than Previously Imagined
Three quarters of the Danish population have moderately elevated levels of cholesterol. If cholesterol levels are too high, risk of cardiovascular disease is increased. Often, LDL cholesterol, the so-called bad cholesterol, is considered the culprit. However, new research shows that a completely different type of cholesterol may be more responsible than previously assumed. What we are talking about is remnant cholesterol To their surprise, the researchers have discovered that the amount of remnant cholesterol in the blood of adult Danes is much higher than previously believed. From the age of 20 until the age of 60, the amount in the blood is constantly increasing, and for many people it remains at a high level for the rest of their lives.
“Our results show that the amount of remnant cholesterol in the blood of adult Danes is just as high as the amount of the bad LDL cholesterol. We have previously shown that remnant cholesterol is at least as critical as LDL cholesterol in relation to an increased risk of myocardial infarction and stroke, and it is therefore a disturbing development.” The results are based on data from people from the Copenhagen General Population Study. A total of 9,000 individuals had cholesterol in their fat particles in the blood measured by metabolomic techniques. “Previous studies from the Copenhagen General Population Study show that overweight and obesity are the main cause of the very high amount of remnant cholesterol in the blood of adult Danes. In addition, diabetes, hereditary genes and lack of exercise play a part.”
In 2018, a large international, controlled clinical trial was published that clearly showed that when triglycerides and thus remnant cholesterol were reduced by the help of medication in people with elevated levels in the blood, the risk of cardiovascular disease was reduced by 25%. “Our findings point to the fact that prevention of myocardial infarction and stroke should not just focus on reducing the bad LDL cholesterol, but also on reducing remnant cholesterol and triglycerides. So far, both cardiologists and GPs have focused mostly on reducing LDL cholesterol, but in the future, the focus will also be on reducing triglycerides and remnant cholesterol.”
A third of nonfasting plasma cholesterol is in remnant lipoproteins: Lipoprotein subclass profiling in 9293 individuals
Increased concentrations of calculated remnant cholesterol in triglyceride-rich lipoproteins are observationally and genetically, causally associated with increased risk of ischemic heart disease; however, when measured directly, the fraction of plasma cholesterol present in remnant particles is unclear. We tested the hypothesis that a major fraction of plasma cholesterol is present in remnant lipoproteins in individuals in the general population.
We examined 9293 individuals from the Copenhagen General Population Study using nuclear magnetic resonance spectroscopy measurements of total cholesterol, free- and esterified cholesterol, triglycerides, phospholipids, and particle concentration. Fourteen subclasses of decreasing size and their lipid constituents were analysed: six subclasses were very low-density lipoprotein (VLDL), one intermediate-density lipoprotein (IDL), three low-density lipoprotein (LDL), and four subclasses were high-density lipoprotein (HDL). Remnant lipoproteins were VLDL and IDL combined.
Mean nonfasting cholesterol concentration was 72 mg/dL for remnants, 78 mg/dL for LDL, and 71 mg/dL for HDL, equivalent to remnants containing 32% of plasma total cholesterol. Of 14 lipoprotein subclasses, large LDL and IDL were the ones containing most of plasma cholesterol. The plasma concentration of remnant cholesterol was from 54 mg/dL at age 20 to 74 mg/dL at age 60. Corresponding values for LDL cholesterol were from 58 mg/dL to 81 mg/dL. Thus, using direct measurements, one third of total cholesterol in plasma was present in remnant lipoproteins, that is, in the triglyceride-rich lipoproteins IDL and VLDL.
Reviewing Progress Towards Regenerative Therapies for Age-Related Hearing Loss
Today’s open access paper is a review of present progress towards regenerative therapies that can reverse hearing loss. Progressive hearing loss is pervasive in old age, and accelerates considerable in the later stages of life. Hearing loss correlates with cognitive decline, and while it is plausible that this is because of degeneration of central nervous system function, there is also the consideration that loss of hearing isolates people and deprives them of interactions that stimulate brain activity. It is well demonstrated in mice that environment richness has a strong impact on the brain and its pace of aging.
Much of the research into age-related hearing loss is focused on the sensory hair cells of the inner ear. These detect the pressure waves of sound and in response pass impulses into nervous system connections leading to the brain. There is some evidence for loss of these cells to be the problem, and some evidence for the cells to survive in sufficient numbers, but lose their connections to the brain. Numerous research teams over the past decade or more have worked on producing regenerative therapies to regrow functional hair cells in the aged inner ear. Numerous strategies have been attempted, such as adapting mechanisms from regenerative species that can regrow hair cells as adults, or direct stimulation of pathways such as Notch that are associated with growth. Varying degrees of success have been demonstrated in mice, but as is often the case, progress towards the clinic remains frustratingly slow.
Hearing regeneration and regenerative medicine: present and future approaches
More than 5% of the world population lives with some degree of hearing impairment. The main factors behind hearing degeneration are ototoxic drugs, aging, continued exposure to excessive noise and infections. After an injury, the auditory system is damaged irreversibly, because the regeneration system is inhibited or deactivated in higher mammals, oppositely to other non-mammalian vertebrates. The pool of adult stem cells in the inner ear drops dramatically after birth. Therefore, an endogenous cellular source for regeneration is absent. In mammals, hair cells (HCs) are only generated during a short embryonic period; hence, their loss in adults produces an irreversible hearing defect. Similarly, the spiral ganglion neurons (SGNs) degeneration is unrecoverable and in the case of synaptic loss, recovery has been shown to be limited.
Because of the drastic reduction in the number of stem cells in the inner ear after the neonatal period, the autonomous regenerating capacity is almost depleted. Therefore, many research groups have focused their efforts on developing stem cell-based treatments to restore HC, SGN, and SC populations. The auditory regeneration field is mainly focus on embryonic stem cells, adult stem cells, or induced pluripotent stem cells (iPSCs). However, nowadays the main issues to be solved are the obtaining of a proper efficiency in the production of auditory stem cells and to demonstrate the utility and safety of these cells in a clinical context. Experimentation in animal models with regenerative capacity, such as zebrafish or avian models, has shown that their auditory regeneration is guided by the same genetic pathways activated during embryonic development. That mechanism leads to HC or stereocilia regeneration by different mechanisms, that have aroused great interest for the development of novel therapies that can reconstruct these pathways in humans.
In our opinion, the important discoveries in this area are mainly focused on the development of methods for stem cell transplantation, improving migration, survival, and new genetic systems for cell fate monitoring. Different routes for stem cell transplantation to the cochlea have been tested, such as through the perilymph or the endolymph. Although these techniques are promising, their results show a low cell survival rate, with only small populations of new cells at the target tissue. Transplantation of cells into the modiolus (bone lamina inside the cochlea) or in the cochlear nerve, showed a higher cell survival rate and increased migration to the target. However, the transplantation process involves potential hearing damage. The direct transplantation of stem cells on the side wall tissue of the cochlea seems to achieve efficient results. The abundance of tissue and blood supply to the area, may be responsible for the increased survival of grafted cells in the wall.
In our opinion, hearing regeneration should be considered from a multidisciplinary point of view, not only focused on stem cells, but also considering molecular mediators as a strategy to improve the outcome. Some combined therapies have been shown to be a better approach to treat some diseases than singular therapies, for instance, stem cell delivery with gene therapy to treat critical limb ischemia. The transplantation of stem cell-derived otic progenitors or adult stem cells (as neural stem cells), results in a significant improvement in hearing, which is especially noticeable in neuronal regeneration. However, the cells have to properly migrate to the damaged area and promote the establishment of functional synaptic connections between HCs and SGNs, which could be improved with molecular mediators or genetic engineering.
The Present Popularity of Epigenetic Reprogramming to Treat Aging
A fair number of research groups are presently working on ways to force large numbers of cells in the body to adopt more youthful epigenetic profiles. Much of this research is an outgrowth of the discovery of induced pluripotency, the ability to reprogram any cell into a pluripotent stem cell that is largely indistinguishable from an embryonic stem cell, capable of generating any of the cell types in the body. This process also happens to reset many of the epigenetic markers of age that are found in cells in old tissues, alongside restoring mitochondrial function by clearing out damaged mitochondria, and a few other interesting changes. The article here focuses on one representative project, but readers here might be more familiar with the work of Turn.bio in the same space, since it was covered recently.
The important question to be addressed here is this, since it is frequently mentioned: are epigenetic changes a cause of aging? To my eyes the answer is no, a thousand times no. They are – they must be – a downstream consequence of the true cause, which is the molecular damage that accumulates with age as a normal side-effect of the operation of cellular metabolism. However, since these epigenetic changes themselves cause further harm, one can, in principle and in animal studies, produce benefits by forcing cells to adopt a more youthful epigenetic profile for various genes of interest. But this does nothing to address the cause of aging, the underlying damage.
Without repair, the underlying causative damage of aging will continue to cause all of the problems that cannot be ameliorated by forcing a mass change in epigenetic programming and consequent cellular behavior. Consider the presence of molecular waste that the body cannot effectively clear, such as persistent cross links degrading extracellular matrix elasticity, or hardy constituents of lipofuscin making autophagy inefficient in long-lived cells, or potentially cancerous nuclear DNA damage. I predict that epigenetic reprogramming is not going to meaningfully address these line items, because youthful cells and tissues cannot meaningfully address these forms of damage if present. Reprogramming may well turn out to be as useful a tool as stem cell therapies for the purpose of regeneration of functional tissues, though with a very different focus on the type of functional improvement obtained. But be wary of those who claim that epigenetic change is the cause of aging, and that turning it back will fix all issues.
Has this scientist finally found the fountain of youth?
Izpisúa Belmonte, a shrewd and soft-spoken scientist, has access to an inconceivable power. These mice, it seems, have sipped from a fountain of youth. Izpisúa Belmonte can rejuvenate aging, dying animals. He can rewind time. But just as quickly as he blows my mind, he puts a damper on the excitement. So potent was the rejuvenating treatment used on the mice that they either died after three or four days from cell malfunction or developed tumors that killed them later.
The powerful tool that the researchers applied to the mouse is called “reprogramming.” It’s a way to reset the body’s so-called epigenetic marks: chemical switches in a cell that determine which of its genes are turned on and which are off. Erase these marks and a cell can forget if it was ever a skin or a bone cell, and revert to a much more primitive, embryonic state. The technique is frequently used by laboratories to manufacture stem cells. But Izpisúa Belmonte is in a vanguard of scientists who want to apply reprogramming to whole animals and, if they can control it precisely, to human bodies.
Izpisúa Belmonte believes epigenetic reprogramming may prove to be an “elixir of life” that will extend human life span significantly. Life expectancy has increased more than twofold in the developed world over the past two centuries. Thanks to childhood vaccines, seat belts, and so on, more people than ever reach natural old age. But there is a limit to how long anyone lives, which Izpisúa Belmonte says is because our bodies wear down through inevitable decay and deterioration. “Aging is nothing other than molecular aberrations that occur at the cellular level.” It is, he says, a war with entropy that no individual has ever won.
The treatment Izpisúa Belmonte gave his mice is based on a Nobel-winning discovery by the Japanese stem-cell scientist Shinya Yamanaka. Starting in 2006, Yamanaka demonstrated how adding just four proteins to human adult cells could reprogram them so that they look and act like those in a newly formed embryo. To many scientists, Yamanaka’s discovery was promising mainly as a way to manufacture replacement tissue for use in new types of transplant treatments. Researchers at the Spanish National Cancer Research Centre took the technology in a new direction when they studied mice whose genomes harbored extra copies of the Yamanaka factors. Turning these on, they demonstrated that cell reprogramming could actually occur inside an adult animal body, not only in a laboratory dish. The experiment suggested an entirely new form of medicine. You could potentially rejuvenate a person’s entire body. But it also underscored the dangers. Clear away too many of the methylation marks and other footprints of the epigenome and “your cells basically lose their identity.”
To others, however, the evidence for rejuvenation is plainly in its infancy. Jan Vijg, chair of the genetics department at the Albert Einstein College of Medicine in New York City, says aging consists of “hundreds of different processes” to which simple solutions are unlikely. Theoretically, he believes, science can “create processes that are so powerful they could override all of the other ones. We don’t know that right now.” An even broader doubt is whether the epigenetic changes that Izpisúa Belmonte is reversing in his lab are really the cause of aging or just a sign of it – the equivalent of wrinkles in aging skin. If so, Izpisúa Belmonte’s treatment might be like smoothing out wrinkles, a purely cosmetic effect. “We have no way of knowing, and there is really no evidence, that says the DNA methylation is causing these cells to age,” says John Greally, another professor at Einstein. The notion that “if I change those DNA methylations, I will be influencing aging has red flags all over it.”
An Interview with Daniel Ives of Shift Bioscience
Shift Bioscience is working on a way to improve mitochondrial function in old tissues. Mitochondria, as you might recall, are the power plants of the cell, responsible for producing chemical energy store molecules used to power cellular processes. Every cell has a herd of hundreds of mitochondria that replicate like bacteria and are culled when damaged by the quality control process of mitophagy. Mitochondrial function nonetheless declines with age, and this affects all cell activities. It is particularly relevant to age-related disease in energy hungry tissues such as the brain and muscles, but the detrimental effects are global throughout the body.
Aging degrades mitochondrial function via several mechanisms, and an important one is the loss of quality control, allowing broken mitochondria to overtake cells. Systematically removing those broken mitochondria on a consistent, ongoing basis should be beneficial, but the question has always been how to manage this feat. The present Shift Bioscience candidate small molecule drug enables functional, undamaged mitochondria to better outcompete their damaged peers for the limited supply of proteins needed to function. This can in principle tip the balance back towards healthy rather than dysfunctional mitochondria in a tissue.
You are proposing to search for small molecules that could potentially slow down progression of the epigenetic clock. Can you tell us a little bit more about your drug screening process?
It is very difficult to implement high-throughput drug screening for biological aging, since contemporary assays of biological age are cell based and can take months to complete. This would require millions of cell lines to be maintained in parallel for months, and this is simply too cost prohibitive. To overcome this challenge, we plan to utilize an approach called ‘protein interference’, where a library of protein fragments is delivered by virus to a population of cells containing a biological age-reporter. Each cell receives a unique protein fragment that may bind to any protein at any position, and through this binding, we could discover peptides that slow down, stop, or reverse biological aging. These protein fragments could be used as therapeutics or guide the design of small molecules.
Many of the hallmarks of aging influence the epigenetic aging clocks; what makes you consider the mitochondria the optimal target for therapeutic interventions?
The discovery of epigenetic aging clocks had particular significance to our company, as they provided the opportunity to audit our key hypothesis (e.g. mitochondrial dysfunction is an important part of aging). To do this, we measured the clock in human cells without a functional citric acid cycle, which severely reduces energy production by mitochondria. This caused a 16-year acceleration of the clock compared to control cells, which, to our knowledge, is the largest acceleration reported.
So far you claim to have identified one family of small molecules that appear to slow the epigenetic clock by at least 50% by restoring mitochondrial function in aged cells. Does this mean that the mitochondria are being repaired or replaced?
In mice, we have preliminary data indicating a deceleration of biological aging by 40% in the brain and 60% in the heart due to the small molecules (as defined by the epigenetic clock). Current evidence suggests that under such conditions, functional mitochondria are able to ‘outbreed’ dysfunctional mitochondria and become the dominant population. This is an example of overcoming damage by dilution, in contrast to conventional repair.
Cells have the unfortunate habit of favoring mutated mitochondria over healthy ones, and these damaged mitochondria can take over a cell in a relatively short time. How might we prevent the cells from making this poor choice so that they retain their healthy mitochondria?
Though our small molecule approach is closest to clinical development, there are other exciting approaches to combating mutated mitochondria in development. Aubrey de Grey has proposed transferring the mitochondrial DNA to the safety of the nucleus, an approach called ‘allotopic expression’. This is not as far-fetched as it might seem, since evolution has already encouraged the vast majority of mitochondrial DNA to transfer to the relative safety of the nucleus. Why not finish off the job that evolution started? The second approach is to deliver endonucleases to mitochondria that specifically target and digest mutated mitochondrial DNA. Researchers have recently validated this approach in mouse models of mitochondrial disease.
So where are you now in terms of development of a therapy and potential human trials?
We are currently creating an enhanced molecule that overcomes some of the limitations of this small molecule family (e.g. they are quickly cleared out of the bloodstream). Once validated in cellular and animal models, we plan to target rare inherited mitochondrial diseases with this enhanced molecule because they provide the fastest route to the clinic.
The Gut Microbiome Changes Over the Course of Aging
This short open access review is a good introduction to what is known of the changes to the microbial population of the gut that take place over the course of aging. Collectively, the activity of gut microbes is influential on health, arguably to a similar degree as exercise, though far less well quantified at this time. Altering the distribution of bacterial populations in older animals, to better resemble what is observed in young animals, leads to benefits to health, for example. Some of the specific mechanisms by which beneficial gut microbes improve health are being uncovered, such as the secretion of propionate, a compound now being developed as a dietary supplement. Much more remains to be established, of course; this is a part of the broader field still in its comparative infancy.
Dwelling at the interface between host epithelia and the external environment, commensal microbes actively modulate development, nutrient absorption, and disease onset in the host. Host metabolism is significantly modulated by commensal microbes, and the gut microbial composition significantly affects blood metabolite composition. Just as the composition of the microbiota varies within and between tissues, microbial consortia do also vary through time within individual tissues. Although individual gut microbiota are largely unstable in the first years of life, they become more stable during adulthood and undergo dramatic changes in richness and composition upon onset of disease and frailty. The onset of specific diseases, such as cancer, obesity, diabetes, or inflammatory bowel disease, is associated with specific microbial signatures.
Studies in humans and laboratory model organisms, such as flies, fish, and mice, have additionally shown that the composition of the gut microbiota dramatically changes during aging and is associated with host health and life span. In mice, e.g., lipopolysaccharide (LPS) from gut microbiota can accelerate age-dependent inflammation (“inflammaging”), and mice lacking Toll-Like receptor 4 (TLR4), which is the LPS receptor, are protected from age-dependent inflammation, showing that a microbial-specific substrate induces aging-specific phenotypes. Inflammaging can be further exacerbated in germ-free mice by gut microbiota transfers from aged donor mice, showing a direct causal relation between age-specific microbial communities and host aging.
Using deep learning to analyze human microbiome data helped build a human microbiome aging clock, which predicts host age with an accuracy of about four years. While during adulthood microbial composition contributes to cellular and tissue homeostasis, age-dependent changes in the microbial composition may contribute to increasing frailty and disease onset in later life. The causes leading to the changes in microbiota composition and function during host aging are still poorly understood and possibly include direct or indirect microbial selection by the host and microbe-microbe interactions, as well as microbial evolution.
MicroRNA miR-122 is Important in Improved Mitochondrial Function Resulting from Calorie Restriction
Calorie restriction improves near all measures of metabolic health, mitochondrial function included. Mitochondria are the power plants of the cell, and they accumulate damage and dysfunction with age, in part because the processes of quality control intended to remove worn and broken mitochondria falter. Calorie restriction improves the situation, but, characteristically, does so in a very broad way that makes it challenging to pick out the important mechanisms from the many other sweeping changes in cellular activity. Researchers here suggest that upregulation of miR-122 is noteworthy, but it is just one of many changes noted in the paper.
Both caloric restriction (CR) and mitochondrial proteostasis are linked to longevity, but how CR maintains mitochondrial proteostasis in mammals remains elusive. MicroRNAs (miRNAs) are well known for gene silencing in cytoplasm and have recently been identified in mitochondria, but knowledge regarding their influence on mitochondrial function is limited.
Here, we report that CR increases miRNAs, which are required for the CR-induced activation of mitochondrial translation, in mouse liver. The ablation of miR-122, the most abundant miRNA induced by CR, or the retardation of miRNA biogenesis via Drosha knockdown significantly reduces the CR-induced activation of mitochondrial translation. Importantly, CR-induced miRNAs cause the overproduction of mitochondrial DNA encoded proteins, which induces the mitochondrial unfolded protein response (UPRmt), and consequently improves mitochondrial proteostasis and function.
These findings establish a physiological role of miRNA-enhanced mitochondrial function during CR and reveal miRNAs as critical mediators of CR in inducing UPRmt to improve mitochondrial proteostasis.
Increasing NAD+ to Improve Mitochondrial Function Slows Age-Related Hearing Loss in Mice
There is a great deal of hype surrounding the use of compounds that increase NAD+ levels in mitochondria, thereby improving the function of old tissue. This doesn’t address the underlying molecular damage that leads to reduced NAD+ levels in later life, and thus might be thought of as something akin to pressing the accelerator harder in a car with a worn engine, but there is a slow accumulation of evidence for some degree of benefit to result. For example, reduced blood pressure in older hypertensive individuals, suggesting improved function of smooth muscle tissue in blood vessel walls. The example today is quite different, as the focus is on the function of cochlear tissue of the inner ear that is vital to hearing, and which suffers the loss of cells and cell function with age.
Age-related hearing loss (ARHL) or presbycusis is the most common cause of hearing loss and sensory disability, characterized by gradual deterioration of auditory sensitivity at all frequencies, with increasing age. ARHL still remains largely untreated. Despite the fact that the mechanism of ARHL has remained elusive, multiple studies have demonstrated that age-dependent oxidative stress, reactive oxygen species (ROS) metabolism, up-regulation of inflammatory responses, and mitochondrial dysfunction in parallel with cellular signaling and gene expression changes are implicated in this process. Particularly, structural changes and degeneration of inner ear cells, such as sensory hair cells, spiral ganglion neurons, and stria vascularis, are characteristics of aged mammals.
NAD+ and NADH are crucial mediators of energy metabolism and cellular homeostasis, as they act as cofactors for NAD+-dependent enzymes, including sirtuins (SIRTs), histones, and poly (ADP-ribose) polymerases (PARPs). Notably, cytosolic-free NAD+ levels decrease under various pathological conditions, including aging. There is strong evidence to support a role for SIRT1 in the process of aging and cell death, through deacetylation of targets such as NF-κB and p53. In addition, it has been proven that SIRT3 plays key roles in mitochondrial functions through deacetylation of mitochondrial proteins. Therefore, we hypothesize that long-term induction of high cellular NAD+ levels may produce protective effects against ARHL.
We investigated the effect of β-lapachone (β-lap), a known plant-derived metabolite that modulates cellular NAD+, on ARHL in C57BL/6 mice. We elucidated that the reduction of cellular NAD+ during the aging process was an important contributor for ARHL; it facilitated oxidative stress and pro-inflammatory responses in the cochlear tissue through regulating sirtuins that alter various signaling pathways, such as NF-κB, p53, and IDH2. However, augmentation of NAD+ by β-lap effectively prevented ARHL and accompanying deleterious effects through reducing inflammation and oxidative stress, sustaining mitochondrial function, and promoting mitochondrial biogenesis in rodents. These results suggest that direct regulation of cellular NAD+ levels by pharmacological agents may be a tangible therapeutic option for treating various age-related diseases, including ARHL.
Comparing the Metabolomic Signature of Aging in Mice and Naked Mole-Rats
Naked mole-rats live something like ten times longer than similarly sized mice, show few signs of aging until very late life, and are near immune to cancer. These two species are used as models by researchers to try to understand how, in detail, differences in metabolism can lead to the observed large differences in life span across mammalian species. Since metabolism is ferociously complex, this is very much a work in progress; in the grand scheme of things, only small inroads and starting points have been established. I fully expect investigations of the detailed interactions of metabolism and aging to be ongoing and nowhere near complete thirty years from now, when rejuvenation therapies based on repair of the well-known root causes of aging are a going concern. While it is of course the right thing to do to attempt to fully understand metabolism, this work is not the fast path to new medical technologies that will have significant impacts on human health and longevity.
Although biological and chronological time can be dissociated to some extent by experimental manipulation, aging appears to be the most important risk factor for the deterioration of normal physiological functions. One species that – to a certain degree – escapes from the rule that natural life expectancy declines with body mass is the naked mole-rat (Heterocephalus glaber). Although this rodent has a similar size as the laboratory mouse (Mus musculus), it lives 10-20 times longer without showing any visible signs of aging. Furthermore, the naked mole-rat can live for over 32 years in captivity, without facing any increased age-related risk of mortality, challenging Gompertz’s mortality law, and thus establishing the naked mole-rat as a non-aging mammal.
Not only naked mole-rats can live an extremely long life, but they also show a remarkably long healthspan associated with almost no decline in physiological or biochemical functions for more than 20 years. For example, cardiac functions are well preserved in aged naked mole-rats, cognitive functions do not decline with age and the naked mole-rat brain seems to be naturally protected from neurodegenerative processes, and also very little pathologic alterations have been found in the kidneys of aged naked mole-rats. In addition, typical signs of aging, such as loss of fertility, muscle atrophy, bone loss, changes in body composition or metabolism are mostly absent in the naked mole-rats. Finally, the incidence of age-related diseases such as cancers or metabolic disorders is extremely low in the naked mole-rat.
We used mass spectrometric metabolomics to analyze circulating plasma metabolites in both species at different ages. Interspecies differences were much more pronounced than age-associated alterations in the metabolome. Such interspecies divergences were found to affect multiple metabolic pathways that involve amino, bile, and fatty acids as well as monosaccharides and nucleotides.
The most intriguing metabolites were those that had previously been linked to pro-health and antiaging effects in mice and that were significantly increased in the long-lived rodent compared to its short-lived counterpart. This pattern applies to α-tocopherol and polyamines (in particular cadaverine, N8-acetylspermidine and N1,N8-diacetylspermidine), all of which were more abundant in naked mole-rats than in mice. Moreover, the age-associated decline in spermidine and N1-acetylspermidine levels observed in mice did not occur, or is even reversed (in the case of N1-acetylspermidine) in naked mole-rats. In short, the present metabolomics analysis provides a series of testable hypotheses to explain the exceptional longevity of naked mole-rats.
The Inflammatory Feedback Loop Produced by Senescent Cells in the Aging Heart
Senescent cells are an important cause of degenerative aging. Lingering senescent cells accumulate over time and disrupt tissue function and immune function via their secretions. An insidious part of this is that the signals secreted by senescent cells cause other nearby cells to be more likely to become senescent. Thus once they start to accumulate the result is an accelerating feedback loop of dysfunction and degeneration. There are many such feedback loops in aging, which is why the process starts slow and then speeds up considerably in later life.
Aging is a major risk factor in the development of chronic diseases, especially cardiovascular diseases. Age-related organ dysfunction is strongly associated with the accumulation of senescent cells. Cardiac mesenchymal stromal cells (cMSCs), deemed part of the microenvironment, modulate cardiac homeostasis through their vascular differentiation potential and paracrine activity. Transcriptomic analysis of cMSCs identified age-dependent biological pathways regulating immune responses and angiogenesis. Aged cMSCs displayed a senescence program characterized by Cdkn2a expression, decreased proliferation and clonogenicity, and acquisition of a senescence-associated secretory phenotype (SASP).
Increased CCR2-dependent monocyte recruitment by aged cMSCs was associated with increased IL-1ß production by inflammatory macrophages in the aging heart. In turn, IL-1ß induced senescence in cMSCs and mimicked age-related phenotypic changes such as decreased CD90 expression. The CD90+ and CD90- cMSC subsets had biased vascular differentiation potentials, and CD90+ cMSCs were more prone to acquire markers of the endothelial lineage with aging. These features were related to the emergence of a new cMSC subset in the aging heart, expressing CD31 and endothelial genes.
These results demonstrate that cMSC senescence and SASP production are supported by the installation of an inflammatory amplification loop, which could sustain cMSC senescence and interfere with their vascular differentiation potentials.
DGCR8 Overexpression Attenuates the Accumulation of Senescent Cells with Age
Given the newfound acceptance of cellular senescence as an important cause of aging, many more research groups are assessing the impact of senescent cells in their research into aging. Here, the focus is on chromatin organization, a collection of nuclear structures and processes in the cell that appear to have some influence over the pace of aging over a lifetime. The researchers discover that the gene DGCR8 accelerates the appearance of senescent cells and dysfunction when mutated, and thus producing broken protein machinery, but slows the accumulation of lingering senescent cells when overexpressed in its correct form. This touches on some of the same machinery of the cell as the mir-122 findings discussed a few days ago, and that work is worth comparing with the notes here, as an example of just how complicated this all is.
Stem cell aging is newly recognized as an important culprit in organismal aging. For example, aging of mesenchymal stem cells (MSCs) has been shown to drive aging-associated tissue degeneration. MSCs, which have the potential to differentiate into mesodermal lineages like osteoblasts, chondrocytes, and adipocytes, can be isolated from various tissues including bone marrow, cord blood, adipose tissue, and dental pulp. Premature depletion of MSCs is observed in patients with Hutchinson-Gilford progeria syndrome (HGPS) and Werner syndrome (WS), two premature aging diseases that are associated with accelerated atherosclerosis, osteoporosis, and osteoarthritis. Despite numerous studies showing that MSCs play pivotal roles in tissue rejuvenation, regeneration, and repair by differentiating into various somatic cell types, little is known about the key regulators of MSC aging.
Aging-associated declines in stem cell functionality are often accompanied by epigenetic changes, such as changes in genomic DNA methylation, histone modifications, and chromatin remodeling enzymes. Heterochromatin domains are structurally inaccessible and usually transcriptionally inactive. These domains are established during early stages of embryogenesis and are gradually lost with aging, resulting in the de-repression of normally silenced genes. Whereas heterochromatin loss drives human MSC (hMSC) aging, the re-establishment of heterochromatin alleviates premature aging and promotes longevity in Drosophila and human cells, suggesting that the maintenance of heterochromatin organization could be an effective therapeutic intervention against aging.
DiGeorge syndrome critical region 8 (DGCR8) is a critical component of the canonical microprocessor complex for microRNA biogenesis. Here, we demonstrate that DGCR8 plays an important role in maintaining heterochromatin organization and attenuating aging. A truncated version of DGCR8 accelerated senescence in human mesenchymal stem cells (hMSCs) independent of its microRNA-processing activity. Further studies revealed that DGCR8 maintained heterochromatin organization. DGCR8 was downregulated in pathologically and naturally aged hMSCs, whereas DGCR8 overexpression alleviated hMSC aging and mouse osteoarthritis. Taken together, these analyses uncovered a novel, microRNA processing-independent role in maintaining heterochromatin organization and attenuating cellular senescence by DGCR8, thus representing a new therapeutic target for alleviating human aging-related disorders.
Cytomegalovirus in the Immunology of Aging
The open access editorial noted here serves as an introduction to some of the current thinking on the role of cytomegalovirus (CMV) in the age-related decline of the immune system. CMV infection is pervasive throughout the population, particularly in the old. This persistent viral infection cannot be effectively cleared by the immune system, and an ever greater percentage of immune cells become uselessly specialized to fight CMV. This leaves ever fewer immune cells ready to tackle other threats. This seems an important component of immune dysfunction, one that can perhaps be addressed by selectively destroying these immune cells to free up space for replacements. The research community is by no means unified on this view of CMV, however, as illustrated here.
Aging represents a paradox of immunodeficiency and inflammation (inflammaging) and autoimmunity. Over the lifespan there are changes in the architecture and functioning of the immune system, often termed immunosenescence. Recently, there have been major developments in understanding the cellular and molecular bases, and genetic and epigenetic changes, in the innate and the adaptive immune system during aging, and the interactions between these separate arms of vertebrate immunity. Limited longitudinal studies have begun to reveal biomarkers of immune aging, which may be considered to constitute an “immune risk profile” (IRP) predicting mortality and frailty in the very elderly. Hallmark parameters of the IRP may also be associated with poorer responses to vaccination.
The usually asymptomatic infection with the widespread persistent cytomegalovirus, CMV, has an enormous impact on immune biomarkers, but according to the circumstances and depending on what is measured, this can translate into a detrimental or a beneficial effect. The prevalence of CMV infection in populations in industrialized countries increases with age, and within individuals the degree of immune commitment to anti-CMV responses also increases with age. This may cause pathology by maintaining higher systemic levels of inflammatory mediators (“inflammaging”) and decreasing the “immunological space” available for immune cells with other specificities, or it may exert beneficial “adjuvant-like” effects. Modalities to prevent or reverse immunosenescence may therefore need to include targeting infectious agents such as CMV in a robustly personalized manner.
Because of the increasing recognition that CMV has a marked impact on immune parameters commonly associated with age, it is crucial to dissect out whether age or CMV is responsible for altering biomarkers predictive of health status (e.g., frailty) or other important parameters such as response to vaccination (especially seasonal influenza). Researchers have investigated whether T cell responsiveness to a range of CMV proteins is different in younger and older healthy people and whether relaxation of anti-CMV immunosurveillance in later life could contribute to disease. They found that CMV-specific CD4+ T cells secreting the anti-inflammatory cytokine IL 10 were predominantly directed to latency-associated CMV proteins and that these responses were not greater in the elderly than the young. However, the frequency of IFN-γ-secreting CD4+ T cells correlated with latent viral genome copy number in monocytes. They conclude that viremia is rare in the elderly due to the maintenance of T cell responsiveness but that CMV can be an important comorbidity factor in people who are not perfectly healthy.
Further complications in analyzing the impact of CMV may arise because most human data are derived from studies using peripheral blood. However, the bone marrow harbors large amounts of late-stage differentiated CD8 T cells possibly because the production of IL 15 is greater in CMV-infected individuals. Also, expression of the NK-associated receptor CD161 is similar in CMV-seropositive and seronegative young subjects but is different in the elderly, illustrating that CMV effects may be different at different ages. The large accumulations of CMV-specific T cells, also in the bone marrow, may contribute to the state of inflammaging, but it is likely that other immune (and non-immune) cells are also major contributors. Cells of the innate immune system far outnumber those of adaptive immunity and may also be heavily influenced by the presence of CMV, contributing to inflammaging.
Even Low Levels of Infection Can Cause Cardiac Dysfunction in Older Individuals
Researchers here suggest that infection plays an important role in cardiovascular disease in later life, and that the chronic inflammation of aging is a factor in allowing infection to cause significant harm to the heart. This is one of countless issues that could be mitigated through rejuvenation of the aging immune system, fixing the underlying issues that cause the immune system to become less functional and more inflammatory. These include atrophy of the thymus, the loss of thymic tissue where T cells of the adaptive immune system mature, loss of hematopoietic stem cell capacity, leading to reduced generation of new immune cells, the structural aging of lymph nodes, preventing immune cells from efficiently coordinating with one another, and the accumulation of senescent and otherwise dysfunctional immune cells.
Infection and infectious disease associated pathologies are often complicated by delays in immune response generation and excess inflammation that impact infection resolution. The term “inflammaging” was coined to denote the multifaceted dysregulation of homeostatic processes that over time culminates in quantifiable, organism-wide shifts towards inflammation in old age. As we shift our focus towards understanding the impact of inflammaging, we have recently determined that inflammaging may also accelerate the decline in cardiovascular fitness.
Age is a major prognostic factor for the development of non-tuberculous mycobacteria (NTM) disease, with recent clinical data reflecting increased incidence of NTM infection in elderly individuals. It is also known that tuberculosis (TB) caused by Mycobacterium tuberculosis (M.tb) can cause pericarditis, endocarditis, and myocarditis leading to sudden deaths. TB is a major global killer and it is estimated that 57% of all TB deaths globally occur in individuals older than 65. Based upon abundant circumstantial evidence, a direct link between mycobacterial infections, aging, and cardiac dysfunction was hypothesized by our group.
We examined how mycobacterial infection and inflammaging catalyze the decline in cardiovascular function in the elderly. Young (3 months) and old (18 month) female C57BL/6 mice were infected with a sub-lethal dose of Mycobacterium avium (M. avium), an NTM. We observed no differences in the M. avium bacterial numbers in the lung, liver, or spleen between young and old M. avium infected mice. However, through the course of M. avium infection, old mice developed severe dysrhythmia and developed pericarditis. Moreover, the hearts of M. avium infected old mice had increased cardiac hypertrophy, fibrosis, expression of pro-inflammatory genes, and infiltration of immune cells, which are hallmarks of myocarditis.
Since these cardiac abnormalities only manifested in old mice, we investigated several factors that contribute to this form of age dependent infectious myocarditis. Independent of M. avium infection, old mice had increased levels of pro-inflammatory cytokines in their serum, which may have predisposed old mice to infectious myocarditis. The reasons for increased inflammation in old age are multifaceted, and future studies will be needed to identify the principal sources of increased inflammation and whether ameliorating inflammation prevents NTM associated cardiac complications in old mice. This highlights how even low or what we may generally consider as insignificant bacterial loads can profoundly impact cardiovascular health.
A Comparatively Simple Approach to Improve Engraftment of Transplanted Cells
The issue with first generation cell therapies for regenerative medicine is that transplanted cells near entirely fail to engraft into tissue. There are exceptions, but for the most part, the cells used in therapy die rather than take up productive work to enhance tissue function. Where benefits occur, they are mediated by the signals secreted by the transplanted cells in the brief period they remain alive. Mesenchymal stem cell therapies that reduce chronic inflammation for some period of time are an example of the type. They are good at that outcome of reduced inflammation, but highly unreliable when it comes to any other desired result, such as increased regeneration.
Thus an important goal in regenerative medicine and tissue engineering circles is to solve the issue of engraftment, and enable the reliable delivery of cells that survive to participate in improving tissue function. Numerous strategies have been tried, with varying degrees of success. The best to date is to provide cells with a surrounding biodegradable scaffold that incorporates supporting nutrients and signals. This can work quite well when cells are allowed to form a pseudo-normal tissue like structure prior to transplantation, for example in heart patches or retina patches. The research noted here offers quite a different and much simpler strategy to improve engraftment rates, the removal of lower quality cells from the cell population created for transplantation.
Biomedical engineers believe they can aid the failing heart by using pluripotent stem cells to grow heart muscle cells outside of the body, and then injecting those muscle cells or adding a patch made from those cells, at or near the site of the dead heart tissue. Experimental and clinical trial evidence with this approach has shown moderate improvement of the pumping ability of the heart’s left ventricle. However, the ability of the delivered cells to remuscularize the heart and improve cardiac function depends on the quality of those cells. A challenge has been low rates of engraftment by the transplanted cells.
Researchers now report a simple method to improve the quality of the delivered cells, and they found that this method – tested in a mouse heart attack model – doubled the engraftment rate of the injected stem cell-derived cardiomyocytes. The robust approach to select functionally competent, intact-DNA cells from a heterogeneous population can be easily adopted in clinical settings to yield cells that are better able to repopulate the ischemic myocardium and improve the performance of a failing heart.
Cardiac cell transplantation requires millions of stem cells or their differentiated derivatives. Cell propagation under accelerated growth conditions is a common way to get these large numbers of cells; but accelerated growth causes culture stress, including lethal DNA damage. These DNA-damaged cells are not suitable for cell transplantation and have to be removed from cell preparations. The researchers found they could activate transcription factor p53 in induced pluripotent stem cells to selectively induce programmed cell death, or apoptosis, specifically in DNA-damaged cells, while sparing DNA damage-free cells. They used Nutlin-3a, an MDM2 inhibitor, to activate the p53. After Nutlin-3a treatment, the dead cells were washed from the culture, and the remaining DNA damage-free cells were cultured normally and differentiated into cardiomyocytes.
The researchers then injected 900,000 of the derived cardiomyocytes into the border zone in the left ventricle of the mouse heart attack model. Four weeks later, the researchers found a significantly higher engraftment rate, about 14 percent, in hearts that received the DNA damage-free cardiomyocytes. Engraftment of the control derived cardiomyocytes was about 7 percent. “As this is a small molecule based approach to select DNA damage-free cells, it can be applied to any type of stem cells, though selection conditions would need to be optimized and evaluated. Other stem cell approaches for diseases such as neurodegenerative diseases, brain and spinal cord injuries, and diabetes might benefit by adopting our method.”