Cardiovascular diseases are responsible for the majority of deaths in western countries and age has been identified as a main risk factor. Vascular tissue biomarkers such as arterial stiffness (AST) provide a means of optimized risk assessment to detect individual subclinical organ damage. Commonly measured as central pulse wave velocity (PWV), AST has gained clinical importance and has been proven to be a reliable predictor for cardiovascular (CV) risk in the general population. Altered PWV indicates subclinical target organ damage and may be used to quantify cumulative damaging effects of CV risk factors on the aging arterial wall integrity.

Previous studies on the effect of regular physical activity and exercise on indices of AST in the elderly have reported conflicting results. High-intensity interval training (HIIT) is an exercise modality that has attracted attention for its potency to increase cardiorespiratory fitness and reduce CV risk in patients, for example, with metabolic syndrome. Data on HIIT and its effects on PWV are scarce. Previous evidence suggests that HIIT may be superior regarding reductions in AST compared to moderate aerobic training in young patients with increased CV risk. However, a recent meta-analysis could not detect differences in AST reduction between the two training regimens.=

Our aim was to investigate the associations between long-term physical activity and central PWV in healthy and diseased elderly. Our study results demonstrate the importance of long-term physical activity and the limited impact of short-term exercise training on large artery stiffness in an older population. Long-term physical activity was associated with lower central PWV even in the absence of CV risk factors. Most importantly, 12-weeks of HIIT did not reduce PWV in elderly at increased CV risk.

Aging is characterized by continuous remodeling of the arterial wall, and higher cardiorespiratory fitness may mitigate stiffening of the aging arterial tree. In our study, with every 10 ml/min/kg increase in VO2max, PWV dropped by 0.8 m/s. Active participants presented with 0.5 m/s lower central PWV than their sedentary counterparts. An increase of 1 m/s in central PWV has been associated with a 15% risk increase in CV and all-cause mortality. Thus, our cross-sectional findings indicate an 8% risk increase attributable to a sedentary lifestyle even in healthy elderly.

Our results demonstrate that long-term active compared to sedentary lifestyle is associated with lower AST even in healthy elderly. This suggests that age- and disease-related vascular stiffening and the associated worse CV outcome can be postponed by long-term regular physical exercise. Short-term exercise, even at higher intensities, cannot improve arterial stiffening in sedentary elderly with increased CV risk. Exercise-induced reductions of AST seem to depend on a concomitant decrease of blood pressure.

Cellular senescence is a form of permanent cell cycle arrest that can be induced in primary cells in response to a variety of stimuli. Senescence was first discovered in primary cells that were grown for extended periods in culture, reaching what became known as a state of replicative senescence, the cellular equivalent of old age. Subsequently, it was shown that cells exhibiting markers of senescence accumulate in aging tissues, further linking the senescence process with aging. Later, a landmark study identified that the expression of active oncogenes (such as those encoding mutant Ras) in primary cells could induce senescence prematurely, in a process now known as oncogene-induced senescence (OIS). This introduced the concept that senescence might function as a tumor-suppressive mechanism to block the aberrant proliferative effects of oncogenic mutations in cells.

Following on from this, many diverse stress-inducing stimuli including irradiation, chemotherapy, cytokine treatment and even induced pluripotent stem cell(iPSC) reprogramming have been shown to induce a senescent response in a variety of cell types. In summary, senescence functions as a cellular process that prevents the proliferation of old, damaged and potentially tumorigenic cells, but the consequence of which is increased aging at the organismal level. Although the regulated induction of senescence is beneficial in preventing tumor formation, prolonged aberrant persistence of senescent cells can have detrimental effects in promoting cancer. For example, if the timely clearance of OIS cells by the immune system is perturbed, this leads directly to tumor formation. Similarly, although chemotherapy can, in part, exert beneficial effects by inducing tumor-cell senescence, the persistence of therapy-induced senescent cells can, via the SASP, promote tumor recurrence and metastasis.

The senescence process has long been linked to aging, including in the original study demonstrating that aging human skin has increased numbers of cells that are positive for the senescence marker senescence-associated beta-galactosidase (SA-ß-gal). In recent years, perhaps the most conclusive data linking senescence with organismal aging has come from the use of senescence 'deletor' mouse models, in which cells expressing p16INK4A are selectively targeted for elimination. In such models, the removal of senescent cells results in significant improvements in health and vigor, and also in lifespan. These studies unequivocally demonstrate how the accumulation of senescent cells during aging can have a negative impact on health and lifespan.

Much of what we understand about senescence has been extrapolated from studies of disease or aging. However, more recent discoveries of beneficial roles for senescence in non-disease conditions has helped to create a clearer understanding of the physiological function of senescence. Beneficial roles for senescent cells have been described in various conditions of wound repair. After wounding, the deposition of extracellular matrix (ECM) aids the repair process but, if excessive, can result in fibrosis, which subsequently impairs proper repair. Senescence has been demonstrated to have a role in wound repair and the fibrotic response in a number of tissues.

The discovery of cells exhibiting markers and features of senescence in developing embryos was an exciting finding. This was primarily based on studies describing senescent cells in mouse embryos. However, cells bearing some or many features of senescence have also been described in human embryos. Interestingly, in many cases, senescent cells were found in signaling centres, with the secretory function of these structures contributing to cell fate specification and tissue patterning. The emerging details suggest that senescent cells may have multiple functions in the embryo. Senescent cells that appear in the embryo arise in very precise patterns in time and space, appearing during specific time windows, before subsequently disappearing, demonstrating that the induction, presence and removal of these cells is a tightly controlled programmed cellular process.

Senescence is also intricately linked with cellular reprogramming, with studies of iPSCs providing key clues. Indeed, expression of the four reprogramming factors Oct4, Sox2, Klf4, and Myc (OSKM) causes widespread induction of senescence markers in cells that ultimately do not undergo reprogramming, whereas those that successfully reprogram manage to silence key senescence mediators. Interestingly, induction of reprogramming in tissues also activates a senescence response, but in cells adjacent to those that undergo reprogramming. It appears that the SASP, and in particular IL6 from the senescent cells, enhances OSKM activity and reprogramming in nearby cells.

This month's question from the community: when senolytic drugs cause senescent cells to die, other (younger) cells need to divide and take the place of the dead cells. This cell division causes telomere shortening, thus possibly creating new senescent cells. How is it that the process of killing senescent cells is not self-defeating if new senescent cells are being created?

There are a couple of ways to come at this question. The first is to just look at the astonishing beneficial effects of senolytic drugs or gene therapies in aging mice and mouse models of age-related disease. In these studies, senolytic drugs have restored exercise capacity and capacity to form new blood and immune precursor cells in aging mice to near youthful norms, while preventing age-related lung hypofunction, fatty infiltration into the liver, weakening or failure of the heart, osteoporosis, and hair loss. These treatments have also prevented or treated mouse models of diseases of aging like osteoarthritis, fibrotic lung disease, nonalcoholic fatty liver disease, atherosclerosis, cancer and the side-effects of conventional chemotherapy, as well as neurodegenerative diseases of aging like Parkinson's and Alzheimer's diseases ... and on and on! So whatever collateral damage might ensue from ablating senescent cells, it's pretty clear that senolytic treatments are doing a lot more good than harm.

But let's drill down on the underlying reasoning of the question a little more. Suppose (as the question posits) that every time you destroy a senescent cell, a progenitor cell (one of the partly-specialized tissue-specific cells that repopulate a tissue with mature cells specific to that tissue) replicates to create a new cell to take its place. In fact, studies do show that when senescent cells are killed in a tissue, the progenitor cells begin to multiply and/or to function better as stem cells. This benefit is not due to the progenitor cells automatically replicating themselves and taking the place of the senescent cell, but because the baleful secretions spewed out of senescent cells inhibit the progenitor cells' regenerative function, such that destroying senescent cells allows the progenitor cells to begin working properly again. This is observed in blood-cell-forming cells, cardiac progenitor cells, bone-forming cells, and the cells that form new fat cells - in both mice and now (in a small, short-term clinical trial) even in humans!

So does this support the worry behind the question? Not really. It just takes a moment's thought to realize that just one such replication can't possibly be enough to drive a stem/progenitor cell into senescence. Still, even if a single round of senolytics isn't enough to drive your stem cells senescent, what if you turn one tissue stem cell senescent for every two times they are triggered to proliferate by senolytic therapy - or every three, or four, or ten? Might a single round of senolytic drugs be a net benefit, whereas repeated treatments over a lifetime would deplete tissue stem cells step by step, eventually riddling the body with senescent cells and leaving the patient (murine or human) worse off over the long term? Fortunately, we have long-term studies to address that question - and they tell us again that the answer is "no."

Due to the sheer amount of time and cost required to validate a study in humans, the bulk of our aging and lifespan data come from shorter-lived yeast, worms, flies, and rodents. With the exception of research showing that caloric restriction improves health and survival in rhesus monkeys, little aging work has been done in longer-lived organisms. The bulk of our understanding regarding aging comes from genetic experiments in model organisms, and we do not yet know how similar or dissimilar human aging is. Rather than screen every lifespan-extending intervention in humans to better understand how human aging works, another approach would be to utilize aging biomarkers.

Biomarkers that strongly correlate with aging, lifespan, and healthspan can teach us about which processes are involved in human aging. Ideally, a robust and practical biomarker would be one that incurs a low monetary cost and can be measured safely, repeatedly, and easily. Blood draws are especially appealing because they are inexpensive, simple, low risk, and can be taken as needed throughout a patient's lifetime. While several biomarker studies have focused on protein-based markers, the advancement of metabolomic techniques has made it feasible to look closely into a large array of metabolites. Metabolomic lipids and lipid-related proteins represent a large, rich source of potential biomarkers that are easily measured in the blood. Compounds in lipid metabolism can take many forms, such as phospholipids, triglycerides, waxes, steroids, and fatty acids. They also play diverse physiological roles, such as forming cell membranes and exerting powerful cell signaling effects. Lipids are perhaps the most well-known for the paramount roles they play in both the storage and mobilization of energy.

Although lipids have been traditionally treated as detrimental and as simply associated with age-related diseases, numerous studies have shown that lipid metabolism potently regulates aging and lifespan. For example, researchers assessed the plasma lipidomic profiles of 11 different mammalian species with longevities varying from 3.5 to 120 years. They found that a lipidomic profile could accurately predict an animal's lifespan and that, in particular, plasma long-chain free fatty acids, peroxidizability index, and lipid peroxidation-derived product content are inversely correlated with longevity. Evidence from animals with extreme longevity also links lipid metabolism to aging. The ocean quahog clam Arctica islandica, an exceptionally long-lived animal that can survive for more than 500 years, exhibits a unique resistance to lipid peroxidation in mitochondrial membranes. Naked mole rats, which enjoy remarkably long lifespans and healthspans for rodents, have a unique membrane phospholipid composition that has been theorized to contribute to their exceptional longevity.

A plethora of dietary, pharmacological, genetic, and surgical lipid-related interventions extend lifespan in nematodes, fruit flies, mice, and rats. For example, the impairment of genes involved in ceramide and sphingolipid synthesis extends lifespan in both worms and flies. The overexpression of fatty acid amide hydrolase or lysosomal lipase prolongs life in Caenorhabditis elegans, while the overexpression of diacylglycerol lipase enhances longevity in both C. elegans and Drosophila melanogaster. The surgical removal of adipose tissue extends lifespan in rats, and increased expression of apolipoprotein D enhances survival in both flies and mice. Mouse lifespan can be additionally extended by the genetic deletion of diacylglycerol acyltransferase 1, treatment with the steroid 17-α-estradiol, or a ketogenic diet.

In humans, blood triglyceride levels tend to increase, while blood lysophosphatidylcholine levels tend to decrease with age. Specific sphingolipid and phospholipid blood profiles have also been shown to change with age and are associated with exceptional human longevity. These data suggest that lipid-related interventions may improve human healthspan and that blood lipids likely represent a rich source of human aging biomarkers.

Subclinical but heightened inflammation in the absence of infection is a key feature of aging, and includes senescent cells that secrete cytokines. Yet, what are the intrinsic processes that initiate 'inflammaging', and possibly other forms of sterile inflammation, like autoimmunity? Self-DNA has long been suspected as trigger and target of autoimmunity, as anti-nuclear antibodies, anti-dsDNA (double-stranded DNA) antibodies and plasma DNA are observed in autoimmune patients of lupus and rheumatoid arthritis.

In studying the initiating events leading to autoimmune arthritis in mice deficient for the lysosomal nuclease DNASE2A, we revealed an unexpected 'hidden' source of this inflammatory DNA - the cell's own nucleus. In healthy cells, damaged and irreparable nuclear DNA fragments are trafficked to the cytosol, enclosed by autophagosomes, and delivered to the lysosomes for degradation by DNASE2A. Lacking DNASE2A, extranuclear DNA accumulates in cells and induces inflammation via innate DNA sensing. Cytosolic DNA sensing is activated when dsDNA binds the DNA sensor enzyme cGAS (cyclic GMP-AMP synthase), converting GTP and ATP into the endogenous second messenger cGAMP, which in turns activates the adaptor protein STING (stimulator of interferon genes) and induces innate immune responses and inflammation. Nuclear DNA as a trigger of immunity could help explain a range of inflammatory conditions.

As cells age, damaged DNA accumulates over time. As an interesting aside, anti-dsDNA antibodies are also found at higher levels in older adults. Could damaged DNA march out of the nucleus of an old cell to set off inflammaging? Indeed, in replicative and oncogene-induced senescent cells, damaged nuclear DNA is exported. Clearing DNA is perhaps the most effective way to eliminate its inflammatory danger. As the only known acidic DNA endonuclease, DNASE2A preferentially degrades dsDNA. It resides with the lysosome, where intracellular and extracellular DNA cargoes converge for degradative digestion. In mice, Dnase2a-deficient cells exhibits the typical senescent phenotype of enlarged cells, slow cell growth, and increased expression of aging markers (senescence-associated β-gal activity, p16 and HP1β expression). Indeed, ectopic expression of DNASE2A substantially reduces cytosolic DNA abundance, innate immune activation and cellular aging phenotype in old cells, thus confirming the protective role of enzymatic DNA degradation in limiting inflammation.

Growing evidence now supports a unifying theory that damaged or irreparable DNA leaves the nucleus to drive aging-related inflammation via innate DNA sensing. Where DNA damage is increased (aging), DNA repair inhibited (ataxia), or nuclear barrier compromised (progeria), DNA load may be not reduced promptly or sufficiently, leading to inflammation. So how far can this DNA theory help to understand the cellular immune mechanisms underlying aging? Each nucleus holds a massive reservoir of endogenous DNA that can trigger local and systemic immunity if there are internal abnormalities such as DNA damage. How nuclear DNA export, trafficking, sensing, and degradation is coordinated to maintain cellular homeostasis is largely unknown. DNA danger coming from within generates exciting questions that probe into the basic life cycle of broken DNA fragments, and suggest ways of treating self-DNA-mediated sterile inflammation (autoimmunity, cancer, neurodegeneration, and chemotherapy) by regulating the abundance of mis-localized DNA.

There so many things that make longevity investment risky. Not only is it subject to all of the translational risks seen in more traditional biotech investing, but we're also so early on in the game that its hard to tell if any of it will live up to its promise. Let's say I'm a nervous first-time investor in longevity - you run one of the biggest funds in this space, give me some tips on how you assess risk.

Longevity is a new and exciting field, which does bring certain risks - but at the same time, the potential is unmatched. We are currently undergoing a massive Longevity Revolution, where how medicine is practiced, drugs are developed, is changing. Tech giants are becoming our new healthcare providers. Medicine is becoming more personalized. I am often invited to speak at longevity and private wealth conferences, where investors ask me the same question. I start by explaining my personal "3 Horizons" framework to help map the longevity space: Horizon 1: technology currently available that has the potential to expand our lifespans to 100 years, such as DIY diagnostics, wearables, digital healthcare delivery, medical software and apps; Horizon 2: emerging technology with the potential to expand our lifespans to 150 years, such as genome therapy and editing, stem cell therapy, nano-robots, AI-based diagnostics and drug discovery, smart hospitals; Horizon 3: age reversal, brain-computer integration, avatars, Internet of the Body.

We invest across all three Horizons, but new investors may want to focus on the first two: early diagnostics, AI in healthcare, life extension technologies in general, and therapies addressing age-related diseases. As for dealing with investment risks, it is really important to have access to the scientific and medical expertise in this field, because scientific due diligence is a key part of the investment decision-making.

You've recently set up the Longevity Vision Fund. How do you hope to differentiate it from others (Juvenescence has a strong focus on regenerative medicine, for instance)?

Longevity is such a new field for investment that there is room for everybody, which inspires collaboration and exchange of knowledge. As such, we don't tend to compete or actively differentiate ourselves from others in this field - ultimately, we are all in this together with the same goal of improving health and longevity for humanity. We also love what Juvenescence does in the field - especially their collaborations with the world's leading scientific hubs. Apart from Juvenescence, we also have other investments, including Life Biosciences and more - and we all share the same vision of extending healthy human lifespans and making the world a better place.

In your upcoming book you're set to cover the ethical 'trade-offs' of extended lifespans. What do you think could be the biggest benefit and the biggest detriment to us all living to 200?

I think the goal is not just to have "extended lifespans" or "to live to 200" (although this is my personal aspiration!) but the improved healthspan, the energy and the wellbeing that we could enjoy into the longer years of our lives. If we look from the perspective of healthy longevity, many detriments commonly associated with longer lifespans, such as an aging population, overburdening the economy, excessive medical costs become irrelevant. Extended healthy longevity means healthier populations, lower medical costs, a more productive workforce, a later retirement. In fact, as an investor, I consider longevity to be the biggest economic opportunity of the century.

As we age, the innate immune system becomes dysregulated and is characterized by persistent inflammatory responses, and the chronic inflammation mediated by inflammatory receptors represents a key mechanism by which amyloid-beta (Aβ) drives the development of cognitive decline in Alzheimer's disease (AD). A crucial aspect of this process is a failure to resolve inflammation, which involves the suppression of inflammatory cell influx and the endocytosis of inflammatory receptors.

To decipher the mechanism associated with its pathogenesis, we investigated the molecular events associated with the termination of IL-1β inflammatory responses by focusing on the role played by the target of Myb1 (TOM1), a negative regulator of the interleukin-1β receptor-1 (IL-1R1). We first show that TOM1 steady-state levels are reduced in human AD hippocampi and in the brain of an AD mouse model versus respective controls. Experimentally reducing TOM1 affected microglia activity, substantially increased amyloid-beta levels, and impaired cognition, whereas enhancing its levels was therapeutic.

This data shows that reparation of the TOM1-signaling pathway represents a therapeutic target for brain inflammatory disorders such as AD. A better understanding of the age-related changes in the immune system will allow us to craft therapies to limit detrimental aspects of inflammation, with the broader purpose of sharply reducing the number of people afflicted by AD.

Scientists initially used parabiosis to investigate how conjoined organisms, like some twins, affect each other. After a period of declining interest in the method starting in the 1970s, parabiosis returned to the scene in 2005, when scientists decided to use the approach to answer questions about tissue regeneration in older organisms. After the release of the 2005 study and other work showing that young blood could seemingly rejuvenate old mice, scientists and the public alike seized on the alluring notion of an elixir of youth.

In February, concerned about premature application in humans based on findings in mice, the US Food and Drug Administration cautioned against young plasma transfusions, noting that they have "no proven clinical benefit" for age-related or other diseases in humans. In the wake of the initial fervor surrounding young blood, researchers are taking a more measured approach. Rather than trying to reverse aging, they're identifying the molecular factors responsible for the changes seen in parabiosis experiments in hopes of targeting specific diseases associated with aging.

The relative abundance of aging and regenerative factors in our bodies shifts as we age. At birth, our blood contains more regenerative factors - like oxytocin, which has been shown to rejuvenate skeletal muscle stem cells in mice - than aging factors. But as we get older, that balance gradually tips in favor of aging factors, like the protein eotaxin, thought to play a role in age-related diseases in which systemic inflammation occurs. Aging factors lower our ability to maintain and repair tissue structure and function, while regenerative factors raise it.

Some researchers who study aging think that young blood could point us to more than just regenerative factors for treating disease. Research to slow or halt aging is more complex than searching for regenerative factors in blood. In parabiosis, animals share not only a circulatory system but also their immune and organ systems, making it difficult to rule out these systems' influence on aging or rejuvenation. Researchers developed a parabiosis-like technique that allows mice to exchange only blood. When the researchers used the technique to connect young and old mice, they found that after each mouse had equal parts old blood and young blood circulating through it, the young mouse displayed negative effects. Old blood drastically decreased hippocampal neuron generation, learning and agility, and liver regeneration in young mice.

Young blood, on the other hand, showed no significant benefits for cognition, agility, or the generation of hippocampal neurons in old mice. In other words, the secret to stalling aging may not lie in boosting rejuvenating factors but instead in blocking factors in old blood that promote aging - ones that hinder tissue maintenance and repair. Researchers have turned their focus to TGF-β, a protein that increases with age. A recent study showed that pharmacologically normalizing the activity of the TGF-β pathway, which is elevated in old age, while adding the rejuvenating factor oxytocin improves muscle regeneration, enhances hippocampal neuron growth, and boosts cognition.

Increasing life expectancy is causing the prevalence of age-related diseases to rise, and there is an urgent need for new strategies to improve health at older ages. In organisms ranging from invertebrates to mammals, reducing the activity of the nutrient-sensing mechanistic target of rapamycin (mTOR) and insulin/insulin-like growth factor signaling (IIS) network can promote longevity and health during aging. Lowering network activity can also protect against the pathology associated with genetic models of age-related diseases. The network contains many drug targets, including mTOR, mitogen-activated protein kinase kinase (MEK), and glycogen synthase kinase-3 (GSK-3). Down-regulation of mTOR activity by rapamycin, GSK-3 by lithium, or MEK by trametinib can each individually extend lifespan in laboratory organisms, and brief inhibition of mTOR has recently been shown to increase the response of elderly people to immunization against influenza.

An advantage of pharmacological interventions is that the timing and dose of drug administration are relatively simple to optimize, and drugs can be easily combined. Here we show that trametinib, rapamycin, and lithium act additively to increase longevity in Drosophila. Because rapamycin, lithium, and trametinib extend lifespan by at least partially independent mechanisms, we investigated the effects on lifespan of their double and triple combinations.

Double combinations of lithium and rapamycin, lithium and trametinib, or rapamycin and trametinib produced a reproducibly greater lifespan extension than controls, on average 30%, compared to each compound alone, which extended lifespan by an average of 11%. Remarkably, the triple drug combination increased lifespan by 48%. Furthermore, the combination of lithium with rapamycin cancelled the latter's effects on lipid metabolism. In conclusion, a polypharmacology approach of combining established, prolongevity drug inhibitors of specific nodes may be the most effective way to target the nutrient-sensing network to improve late-life health.

Neurogenesis occurs in the subgranular zone of the dentate gyrus (DG) in the hippocampus and the subventricular zone (SVZ) of the lateral ventricle in the adult mammalian brain. Adult hippocampal neurogenesis arises from neural stem cells (NSCs) within the DG. NSCs give rise to intermediate progenitor cells, which divide generating immature neurons that subsequently integrate into the local neural network as granule cells. Accumulating evidence suggests that adult-born neurons may play distinct physiological roles in hippocampus-dependent functions such as memory encoding and mood regulation. Age induces a decline in adult NSC activity and neuronal plasticity, which could partially explain some age-related cognitive deficit symptoms. Neuronal loss or dysfunction also contributes to the onset of age-related neurodegenerative pathologies.

Increasing evidence reveals that NSC activity is regulated by intrinsic and extrinsic factors. Among the latter, it has been recently shown that neuronal activity controls NSC quiescence and subsequently neurogenesis in the hippocampus. The molecular mechanism by which neuronal activity contributes to the regulation of NSCs, and whether this decreases with aging, remains unknown.

p38 mitogen-activated protein kinase (p38MAPK) is an important sensor of intrinsic and extrinsic stresses and consequently controls key processes of mammalian cell homeostasis such as self-renewal, differentiation, proliferation, and death. In the brain, p38MAPK signalling is activated during neurodegenerative diseases and in response to brain injury. Its genetic or pharmacological inhibition ameliorates symptoms of neurodegenerative diseases and protects against ischemia. The p38MAPK family comprises four members, with p38α and p38β being expressed at high levels in the brain. p38α has been involved in inflammation and environmental stresses, and there is evidence implicating p38α in neuronal function and cognitive activity with contradictory results.

Using mice, we demonstrate that genetic deletion of p38α in neurons suffices to reduce age-associated elevation of p38MAPK activity, neuronal loss and cognitive decline. Moreover, aged mice with genetic deletion of p38α present elevated numbers of NSCs in the hippocampus and the subventricular zone. These results reveal novel roles for neuronal p38MAPK in age-associated NSC exhaustion and cognitive decline.

Mitochondria are small powerhouse organelles that have their own DNA, the mitochondrial DNA (mtDNA). For almost half a century, mitochondrial DNA mutations and oxidative stress have been asserted as major contributors to aging, as postulated in the mitochondrial theory of aging published in the 1970s. The theory has been tested on the mtDNA Mutator mice that have an inactive DNA repair mechanism. These mice accumulate mtDNA mutations and present with accelerated aging, which has led scientists to believe that mtDNA mutagenesis drives aging. However, despite rigorous studies by several groups, no one has been able to show that the Mutator mice would present elevated oxidative stress.

The prematurely-ageing Mutator mice harbour a defective polymerase-gamma enzyme and present with pronounced mtDNA mutagenesis. Despite the existence of other mouse models with equivalent mtDNA mutagenic propensity, the Mutator mouse model is the only one manifesting accelerated aging. Furthermore, progeria is not a clinical feature of mitochondrial disease patients, not even in those with the most severe mtDNA mutagenic profiles. Rather, the clinical picture of the mtDNA Mutator mice is remarkably similar to that of other mouse progeria models and human progeric syndromes with nuclear genome instability, with the most prominent defects in proliferating cells, and especially in stem cells and progenitor cells important for tissue regeneration.

The new study shows that in addition to the mtDNA maintenance defects, the Mutator mice also manifest nuclear DNA defects, including replication fork stalling, increased DNA-breaks and activation of DNA damage response pathways. So, how can a primary mitochondrial DNA maintenance defect affect the maintenance of nuclear genome? Nucleotides are the building blocks of DNA, and proper cellular nucleotide levels are critical for genome maintenance. Moreover, the cytoplasmic and mitochondrial nucleotide pools are interconnected. The researchers show that in the Mutator mice, the total cellular nucleotide levels are decreased, while the mitochondrial nucleotide pools are increased, suggesting preferential usage of nucleotides in the mitochondria. Indeed, the replication of mtDNA is drastically accelerated in the cells of the Mutator mice.

Your research group started developing an improved method for allotopic expression of mitochondrial DNA in 2015 that has already shown very promising results?

The major hurdle that we have overcome is, at least, showing protein products for all the 13 genes. We made some fundamental changes to all 13 genes with a uniform approach, but that approach may not work equally well for all of them. We may have to engineer each one of them for specific properties. So, all of these 13 genes differ with respect to their length, their hydrophobicity, and the complexes that they target. The main hurdle is actually the hydrophobicity factor. These 13 proteins are normally synthesized within the mitochondrial matrix, and they are inserted into their complexes. But, in allotopic expression, they are synthesized in the cytosol and have to traverse two membranes and then go to the right location. We will have to engineer them one after the other or modify them in such a way that it recognizes the right pathway. So, like I said, we are causing global changes to all 13 genes, and we will cause specific changes to each one of them to make it functional as a whole. The first step is to at least see a product, and that's what we've overcome now.

What have been the criteria for selecting mitochondrial DNA genes to work on for allotopic expression?

One of the other hurdles is proving that your technology actually works, and for that, you need model systems. The reason we were able to show that ATP8 really works is because we were able to get a patient cell line with a severe mutation that's null for the ATP8 protein. Usually, in humans, mutations to mitochondrial genes manifest in various levels, but it is unusual that the protein is completely absent in the patient. It's a rare event. But mitochondrial DNA exists in heteroplasmy. There are wild type and mutant levels, both present continuously, and it's the tipping factor that causes a disease phenotype to ensue. The one reason we were able to really convincingly show ATP8 works is because we were able to get the null cell line and show that the exogenous protein goes into the right location and regains many of the functions that were absent before. Basically, you have the cell line available, which is really rare. So, let's make use of it.

What do you think will be a realistic timeframe for therapies targeting mitochondrial DNA mutations to reach humans?

They are actually already doing that but with the recoded version. That means we already have a precedent. All we have to show is that our version of it is better and that ours has a better immune profile. That's also why we want to do it in animal models, so we can actually show how it's better. I don't know about the timeframe; that's a very difficult question. If the animal studies go well, I want to say five years. Not five years before it reaches people, but five years to establish enough proof of principle that we can start to develop this for people.

In your view, what does aging research need most right now to ensure it can make the most significant leaps that the field is capable of in the coming 10 years?

I think you need good biomarkers. That's lacking in the field. Everybody wants to have a quick fix. They have all these different areas that they think are very important to aging, but I don't think that's the way it is. I think it's more like a general breakdown of everything with time. So you need better markers, and maybe even a better mindset where it's okay to be healthy in old age. People shouldn't be resigned to the fact that they will age with time and that they are going to die. Maybe a little more public education is needed to accept that it's okay to want and to have a healthy lifespan.

I was wondering if you could briefly explain how BioAge verifies whether the aging targets they identify are valid?

BioAge begins with human data. We find human cohorts that have banked blood samples from decades ago, coupled with electronic health records that have followed those people ever since, in some cases, until their deaths. We send these blood samples for deep omics profiling: proteomics, metabolomics, transcriptomics, stuff like that. From that, we can find what's in the blood, for instance, the transcription profiles of the blood cells and soluble protein metabolites, which is correlated with age-related diseases and mortality. That's only part of the picture, of course, because that doesn't tell you what's causal, it only tells you what's correlational. So, from there, we adopt a systems biology approach where we connect the results to whatever datasets we can find out in the world or among those we generate ourselves, which gives us a few extra clues. However, ultimately, the only way we can really verify if a target is valid is by testing it experimentally, and so that's what we do. After we pull everything together data-wise, that only gives us so much. We really need to test these targets in animal models as well as cell models, but we prefer to test in vivo.

Since research budgets are limited, what is your view on how these budgets should be allocated across these differing priorities, i.e. should the discovery of biomarkers for more diseases or the development of interventions take precedence if we need to choose, and why?

That's how BioAge started: the whole point was to generate biomarkers. At the same time, these so-called biomarkers are often themselves druggable targets. Part of the evolution of BioAge as a company is that first we find these biomarkers, and then we turn them into drugs. In terms of how society should allocate resources (biomarker research versus the development of interventions), we personally don't have to consider that as much, seeing as we're doing both in-house. I can't really say what anyone else should do, but I think we found something that works for us.

Aubrey de Grey's idea is that if we develop a therapy for one subtype of causative damage of aging, it will be much easier to extend that therapy to similar types of damage. Since BioAge is working on using computational approaches to find the molecular pathways that drive aging, I was wondering if you are using a similar type of clustering approach to facilitate faster intervention development?

To some extent, because I love Aubrey's integrated approach. For me, personally, his 'seven deadly things' talk was kind of my introduction into the field back in 2004/2005. But BioAge, at least initially, takes an opposite approach in the sense that we don't cluster things. We look for mortality as our first differentiating factor. Any target that we look at as something that we might want to pursue must be associated with mortality, and mortality is really as broad as it gets. That being said, once we've screened for mortality, we then examine what specific disease indications would make the most sense. I can't really get into detail about what those are. But I like the way we look broadly at the data first, in a kind of "hypothesis-free" sense, with an open mind, letting the data speak for itself.

In the last five years, as several large clinical trials testing drugs for Alzheimer's disease failed, the field came to a stark conclusion: These approaches did nothing to slow down - let alone reverse - the course of the disease once patients already exhibited symptoms of early dementia. The failed trials, along with the dawning realization that the disease unfolds over decades, have put the entire field on a reset-to develop and test interventions that can be used much earlier, to discover new targets beyond misfolded amyloid and tau proteins, and to fund large, interdisciplinary, big data collaborations.

Aging is by far the biggest risk factor for developing Alzheimer's - if everyone lived to be 85, one in two people would develop dementia. The lion's share of Alzheimer's research and drug discovery to date has focused on misfolded amyloid and tau proteins, which aggregate to form plaques (amyloid) and tangles (tau) in the brain. But the body's attempt to clear the sticky proteins might also be contributing to or causing the neurodegeneration. Drug trials have almost exclusively sought to use antibodies targeted toward these two proteins to try to attack and clear the misfolded forms or mop up soluble forms, or to inhibit enzymes responsible for generating the miscreant peptides.

New areas being explored include the vascular system, epigenetics, neuroprotection, synaptic health, immunity and inflammation, and metabolic dysfunction, among others. Neuroinflammation and proteostasis, or the management of proteins within cells, are trending areas of research. Another booming area of Alzheimer's research is the development of biomarkers and diagnostic tests to monitor disease presence and progression. Radioactive positron emission tomography (PET) tracers enable physicians to image and measure amyloid and tau proteins in the brains of living patients. Other biomarkers can be measured precisely from collecting cerebral spinal fluid. However, both types of tests are invasive, and PET scans are expensive. "We need a blood test like the one we have for cholesterol that can be done in any doctor's office quickly and inexpensively."

Tardigrades, which are also known as water bears or moss piglets, are small invertebrate animals that are found in marine, freshwater, and terrestrial habitats throughout the Earth. Terrestrial tardigrades require a thin film of water to remain active. In the absence of water, they undergo anhydrobiosis into a dormant dehydrated state from which they can be rehydrated to an active form. In the anhydrobiotic state, tardigrades are resistant to extreme conditions of heat, cold, vacuum, pressure, radiation, and chemical treatments. Remarkably, they have been found to survive exposure to the vacuum and radiation of outer space.

The tardigrade Ramazzottius varieornatus contains a unique nuclear protein termed Dsup, for damage suppressor, which can increase the resistance of human cells to DNA damage under conditions, such as ionizing radiation or hydrogen peroxide treatment, that generate hydroxyl radicals. Here we find that R. varieornatus Dsup is a nucleosome-binding protein that protects chromatin from hydroxyl radicals. Moreover, a Dsup ortholog from the tardigrade Hypsibius exemplaris similarly binds to nucleosomes and protects DNA from hydroxyl radicals.

Strikingly, a conserved region in Dsup proteins exhibits sequence similarity to the nucleosome-binding domain of vertebrate HMGN proteins and is functionally important for nucleosome binding and hydroxyl radical protection. These findings suggest that Dsup promotes the survival of tardigrades under diverse conditions by a direct mechanism that involves binding to nucleosomes and protecting chromosomal DNA from hydroxyl radicals.