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- Conversion of Glial Cells into Neurons as an Approach to Regeneration in the Brain
- RAGE and Chronic Inflammation in Aging
- Senescent Cells Implicated in Age-Related Changes in Blood Clotting
- ApoE Levels Rise with Age and Degrade the Ability to Regenerate Bone
- Alzheimer’s Disease as a Condition of Many Subtypes and Contributing Causes
- ADRB1 Mutation Grants a Lesser Need for Sleep, and thus a Longer Subjective Life
- Aging Biotech Info is a Curated List of Companies in the Longevity Industry
- Exosomes Improve Collagen Production in Aged Skin
- Fitter, Thinner Older Adults Have a Measurably Different Gut Microbiome
- Risk Factors versus Lifestyle Choices in the Mortality of Old Age
- An Interview with Tristan Edwards of Life Biosciences
- The Boost to the Unfolded Protein Response Achieved via Exercise Declines with Age
- Altered Calcium Transport in Aging Mitochondria is Maladaptive
- A Skeptical Review of the Evidence for Metformin
- A Non-Invasive Approach to Measuring Cellular Senescence in the Kidney
Conversion of Glial Cells into Neurons as an Approach to Regeneration in the Brain
The authors of today’s research report on success in use of a gene therapy to convert glial cells into neurons in a living mouse brain, and thereby improve the normally limited recovery that takes place following brain injury, such as that caused by a stroke. A number of research groups are investigating this class of approach to enhance regeneration in the brain, an organ that has little capacity to repair itself. The capacity that does exist is generated by neural stem cells that, arguably, continue to produce new neurons at some pace throughout life. As for all stem cell populations, activity declines with age, however. An increased supply of new neurons, provided that they are capable of correctly maturing and integrating into neural circuits, should prove beneficial.
Interestingly, increasing the supply of neurons is not just relevant to regeneration in the brain. Functions such as memory rely on changes in neural networks, and in turn on a supply of new neurons. It is possible that increasing the pace at which new neurons emerge could improve cognitive function even in younger people. We are a long way removed from that sort of application of new biotechnology, however – the focus today is very much on addressing age-related conditions.
Gene therapy helps functional recovery after stroke
Researchers have pioneered a new approach to regenerate functional neurons using glial cells, a group of cells surrounding every single neuron in the brain that provide essential support to neurons. Unlike neurons, glial cells can divide and regenerate themselves, especially after brain injury. Researchers previously reported that a single genetic neural factor, NeuroD1, could directly convert glial cells into functional neurons inside mouse brains with Alzheimer’s disease, but the total number of neurons generated was limited. The research team believed that this limited regeneration was due to the retroviral system used to deliver NeuroD1 to the brain. In the current study, the research team used the AAV viral system, which is now the first choice for gene therapy in the nervous system, to deliver NeuroD1 into mouse motor cortex that had suffered from stroke.
Many neurons die after stroke but surviving glial cells can proliferate and form a glial scar in the stroke areas. The AAV system was designed to express NeuroD1 preferentially in the glial cells that form these scars, turning them directly into neuronal cells. Such direct glia-to-neuron conversion technology not only increased neuronal density in the stroke areas, but also significantly reduced brain tissue loss caused by the stroke.
“The most exciting finding of this study is to see the newly converted neurons being fully functional in firing repetitive action potentials and forming synaptic networks with other preexisting neurons. They also send out long-range axonal projections to the right targets and facilitate motor functional recovery. “Because glial cells are everywhere in the brain and can divide to regenerate themselves, our study provides the proof-of-concept that glial cells in the brain can be tapped as a fountain of youth to regenerate functional new neurons for brain repair not only for stroke but also for many other neurological disorders that result in neuronal loss.”
A NeuroD1 AAV-Based Gene Therapy For Functional Brain Repair After Ischemic Injury Through In Vivo Astrocyte-To-Neuron Conversion
Adult mammalian brains have largely lost neuroregeneration capability except for a few niches. Previous studies have converted glial cells into neurons, but the total number of neurons generated is limited and the therapeutic potential is unclear. Here, we demonstrate that NeuroD1-mediated in situ astrocyte-to-neuron conversion can regenerate a large number of functional new neurons after ischemic injury. Specifically, using NeuroD1 AAV-based gene therapy, we were able to regenerate one third of the total lost neurons caused by ischemic injury and simultaneously protect another one third of injured neurons, leading to a significant neuronal recovery. RNA-sequencing and immunostaining confirmed neuronal recovery after cell conversion at both the mRNA level and protein level.
Brain slice recordings found that the astrocyte-converted neurons showed robust action potentials and synaptic responses at 2 months after NeuroD1 expression. Tracing revealed long-range axonal projections from astrocyte-converted neurons to their target regions in a time-dependent manner. Behavioral analyses showed a significant improvement of both motor and cognitive functions after cell conversion. Together, these results demonstrate that in vivo cell conversion technology through NeuroD1-based gene therapy can regenerate a large number of functional new neurons to restore lost neuronal functions after injury.
RAGE and Chronic Inflammation in Aging
Chronic inflammation is a very important downstream consequence of molecular damage in the progression of aging, arising from numerous causes. The past decade of work on the presence of lingering senescent cells in old tissues indicates that their signaling is significant cause. In animal studies, removing senescent cells can reverse the course of many age-related and other conditions that are primarily inflammatory in nature. Visceral fat tissue in excess amounts can accelerate the production of senescent cells, but it also generates inflammation through other mechanisms, such as debris from dead cells, signaling by non-senescent fat cells that resembles the signaling of infected cells, and so forth.
There are also numerous other contributing factors relating to the growing dysfunction of the immune system, or some of the metabolic issues that accompany excess fat tissue. The one examined in today’s open access paper is the interaction of advanced glycation end-products (AGEs) with the receptor for AGEs (RAGE). There are a couple of different issues in aging, type 2 diabetes, and obesity relating to AGEs. The more interesting one for the SENS rejuvenation research community is the accumulation of persistent cross-links in the extracellular matrix formed from glucosepane; these cross-links degrade tissue elasticity, which in turn contributes to hypertension via arterial stiffening, among many other issues. However, there are many other short-lived AGEs that arise from the diet and from cellular metabolism, and which are particularly prevalent in the distorted metabolism of obese and diabetic patients.
These short-lived AGEs produce inflammation by overactivating RAGE; this mechanism has been fairly well studied in past years, particularly in diabetic patients. As the authors of this paper note, however, even well studied parts of human biochemistry have plenty of unanswered questions left for researchers to work on. As for a number of processes that may operate to a significant degree in both diabetes and aging, it is an open question as to the degree to which RAGE is important in purely age-related dysfunction, versus other mechanisms such as the accumulation of senescent cells. Older people tend to have more fat tissue, which obscures the matter.
Is RAGE the receptor for inflammaging?
In its full-length form the receptor for advanced glycation end products, RAGE, is a multi-ligand, transmembrane receptor promoting activation of key pro-inflammatory and pro-oxidative pathways. The deleterious effects of its activation via the binding of AGEs (the advanced glycation end products after which it is named) are widely reported, especially in diabetes mellitus. Indeed, our current understanding of RAGE relies heavily upon research on this metabolic disorder, but it is simplistic to apprehend this receptor solely within a diabetic context or through its interactions with AGEs. RAGE is more broadly implicated in both immunity and inflammation: more than 28 RAGE ligands are known, many of which are damage-associated molecular patterns (DAMPs) or pathogen-associated molecular patterns (PAMPs).
RAGE can thus be more accurately considered a pattern recognition receptor (PRR), and has been labelled a “noncanonical Toll-like receptor (TLR)” by some authors. This wider involvement of RAGE signalling nevertheless remains poorly-studied relative to research involving diabetes and AGEs, but evidence is accumulating of its role in what has come to be known as “inflammaging”. RAGE deletion has been shown to be protective against both cardiovascular disease and Alzheimer’s disease in RAGE-/- mice, and while the impact of anti-RAGE therapeutics remains to be demonstrated in humans, laboratory results highlight the potential of targeting this receptor to address multiple public health issues.
RAGE has obvious similarities with other PRRs and there are acknowledged pro-aging mechanisms such as oxidative stress, mitochondrial dysfunction or inflammasome activation resulting from its interaction with several of its ligands. The concomitant, age-related increase of circulating DAMPs, and the expression of RAGE on many cell membranes, even in the absence of a pathological event, could favour low-grade, persistent, pro-inflammatory processes which in turn could drive increased production of DAMPs and expression of RAGE. This pro-aging vicious circle of events places RAGE firmly in the spotlight as a key-actor in inﬂammaging, not least because senescent cells also produce RAGE ligands like HMGB1 and S100s.
This hypothesis is attractive and opens up significant possibilities in the development of anti-RAGE therapeutics, but many questions remain. To what extent do the different RAGE ligands compete for binding, and how does this competition modulate its activation? Are the activated signalling pathways ligand-specific, or perhaps specific to the configuration of RAGE in its various forms? Are there negative effects to RAGE inhibition?
Senescent Cells Implicated in Age-Related Changes in Blood Clotting
Senescent cells are created constantly in the body as the result of a number of processes: the Hayflick limit, wound healing, a toxic local environment, DNA damage, and so forth. Near all are destroyed quite quickly, either via programmed cell death or by the immune system. Some few linger, however, and secrete a potent mix of molecules known as the senescence-associated secretory phenotype (SASP). The SASP produces wide-ranging damage and dysfunction in tissues, causing issues such as chronic inflammation, fibrosis, and harmful behavior or increased senescence in nearby cells. Thus senescent cell burden is one of the important causes of aging, and efforts to produce senolytic therapies capable of selectively destroying these cells are a very important new branch of medicine.
As noted in today’s scientific materials, researchers have recently provided data to associate the burden of senescent cells in older individuals with detrimental changes in blood clotting. This adds one more item to a very long list of harmful effects resulting the SASP. With age, blood clots form more readily, and in inappropriate circumstances, such as inside major blood vessels. This can cause serious issues such as thrombosis, the blocking of blood vessels and consequent ischemia, or worse, such as a stroke or heart attack should a sizable clot fragment and the fragments block a more vital blood vessel elsewhere.
The data here associating components of the SASP with increased susceptibility to blood clotting is interesting to compare with a recent review paper on changes in platelet function with age. The biochemistry of the age-related hyperactivity of platelets, leading to increased clotting, has been examined in a proximate sense, but reaching backwards to root causes is something that the research community has never been all that good at following through on. The work here is a good example of starting with a known cause of aging and working forwards, a much more efficient approach, and one that must become more widespread in the research community if we are to see meaningful progress in treatments for age-related conditions in the years ahead.
Cellular senescence is associated with age-related blood clots
Cells that become senescent irrevocably stop dividing under stress, spewing out a mix of inflammatory proteins that lead to chronic inflammation as more and more of the cells accumulate over time. Researchers have identified 44 specific senescence-associated proteins that are involved in blood clotting, marking the first time that cellular senescence has been associated with age-related blood clots. “The incidence of venous thrombosis, which includes deep vein thrombosis and pulmonary embolism is extremely low until the age of 45, when it begins to rise rapidly. Over time it becomes a major risk factor for death. By 80, the condition affects five to six people per thousand individuals. Blood clots are also a serious side effect of chemotherapy, which sets off a cascade of senescence in those undergoing treatment. That’s why blood thinners, which carry their own risks, are often included in treatment protocols.”
In this study, researchers validated the expression of some of the specific factors in cultured cells and in mice, which were treated with doxorubicin, a widely-used chemotherapy drug which induces widespread senescence. Those mice showed increased blood clotting, similar to what happens in humans who undergo chemotherapy. “Conversely, when we selectively removed senescent cells in specially bred transgenic mice, the increased clotting caused by doxorubicin went away.”
SILAC Analysis Reveals Increased Secretion of Hemostasis-Related Factors by Senescent Cells
Cellular senescence irreversibly arrests cell proliferation, accompanied by a multi-component senescence-associated secretory phenotype (SASP) that participates in several age-related diseases. Using stable isotope labeling with amino acids (SILACs) and cultured cells, we identify 343 SASP proteins that senescent human fibroblasts secrete at 2-fold or higher levels compared with quiescent cell counterparts. Bioinformatic analysis reveals that 44 of these proteins participate in hemostasis, a process not previously linked with cellular senescence.
We validated the expression of some of these SASP factors in cultured cells and in vivo. Mice treated with the chemotherapeutic agent doxorubicin, which induces widespread cellular senescence in vivo, show increased blood clotting. Conversely, selective removal of senescent cells using transgenic p16-3MR mice showed that clearing senescent cells attenuates the increased clotting caused by doxorubicin. Our study provides an in-depth, unbiased analysis of the SASP and unveils a function for cellular senescence in hemostasis.
ApoE Levels Rise with Age and Degrade the Ability to Regenerate Bone
ApoE is a important protein in lipid metabolism, one of those responsible for transporting cholesterols and other lipids around the body. In today’s open access research, the authors present evidence for rising levels of ApoE with aging to degrade the ability of bone to regenerate. This is unfortunate, because it will not be straightforward to just reduce ApoE levels. The protein is vital; a number of serious inherited conditions involve ApoE mutation that leads to greatly increased lipid levels on the bloodstream and organs.
Bone regeneration, and normal tissue maintenance of bone for that matter, is a balance between constant creation and destruction of extracellular matrix structures. Osteoblast cells build bone, and osteoclasts tear it down. Age-related loss of bone density and strength is the result of a growing imbalance that favors osteoclast activity. There is good evidence for numerous mechanisms to be important here, including the usual suspects such as the inflammatory signaling produced by senescent cells. The data here for reversal of loss of regenerative capacity via reduced ApoE levels is quite compelling as an argument for this to be an important proximate mechanism, however.
Protein prevalent in older people could be key to healing bones
Researchers confirmed that older people have more Apolipoprotein E, ApoE for short, than younger people. (If that protein name rings a bell, it’s because ApoE is also implicated in Alzheimer’s and heart disease). The team found that 75-85 year olds had twice as much ApoE in their bloodstreams as 35-45 year olds, then found the same was true for 24-month-old mice versus 4-month-old mice, which approximate the same human age ranges. Next, they wanted to figure out if and how ApoE affects the multi-step process of bone healing. When you break a bone, your body sends signals through the bloodstream to recruit cells to fix it. Some of those recruits, specifically skeletal stem cells, build up cartilage as a temporary scaffolding to hold the fracture together.
In the next step, more recruited cells mature into osteoblasts, bone-building cells, which lay strong, dense bone cells on top of the cartilage scaffolding. Finally, a different kind of cell eats up the cartilage scaffolds and osteoblasts fill those holes with bone. That’s if the bone healing process works perfectly. But the researchers found that if they added ApoE to a petri dish with skeletal stem cells, fewer cells developed into osteoblasts and the osteoblasts were worse at building bones. Next, the researchers created an intervention by injecting a virus which keeps mice from making ApoE protein. Circulating ApoE levels dropped by 75 percent and the healed bones contained one and a half-times more strong, hard bone tissue than bones of untreated mice.
Lowering circulating apolipoprotein E levels improves aged bone fracture healing
In our previous work investigating aged bone regeneration, we identified apolipoprotein E (ApoE) to be one of many candidates potentially involved in aged bone fracture healing. ApoE is a widely expressed lipoprotein classically associated with lipid metabolism and fatty acid transport. ApoE polymorphisms are present in 20% of the population and are associated with hypercholesterolemia, atherosclerosis, and Alzheimer’s disease. More recently, clinical evidence has revealed that these ApoE polymorphisms are also associated with decreased bone mineral density and increased risk of hip and vertebral fracture. Mouse models lacking ApoE expression display increased cortical thickness, trabecular number, and bone mineral density. However, a role for ApoE in fracture healing and musculoskeletal aging remains to be investigated.
Here, we sought to understand the role of ApoE in age-associated deficiencies in bone fracture healing. Our previous work has established the importance of circulating factors in the age-associated impairment of bone regeneration. Here, we use our established tibial fracture model coupled with μCT and histological analysis as well as our parabiosis models to identify a role for circulating ApoE in bone fracture healing. We identify ApoE as a negative regulator of osteoblast differentiation and combine this work with functional metabolic assessment and transcript analysis to identify the mechanism by which ApoE influences osteoblast differentiation. Finally, we identify that lowering circulating ApoE levels, using siRNA strategies, in aged mouse models leads to improved bone fracture healing. Collectively, our findings demonstrate that ApoE impairs bone fracture healing in an age-dependent manner by decreasing osteoblast differentiation.
Alzheimer’s Disease as a Condition of Many Subtypes and Contributing Causes
Neurodegeneration in late life is a very complex phenomenon, and its complexity strains against the nice neat clinical definitions of disease found in the textbooks. Different patients with Alzheimer’s disease can exhibit quite different mixes of various forms of pathology, developing at different paces and times: aggregates of amyloid-β, tau, and α-synuclein; vascular degeneration; markers of neuroinflammation; metabolic disruption similar to that of diabetes, and so forth. One case of Alzheimer’s might be different enough from another to require a different designation. Thus researchers talk about defining subtypes of Alzheimer’s disease, or that individual patients have Alzheimer’s that is exacerbated by a comorbidity arising from other neurodegenerative processes.
Another way of looking at this is to categorize mechanisms that contribute to Alzheimer’s. To what degree is a given set of mechanisms important in a given patient? A sizable amount of work has gone into investigation of processes and feedback loops other than the primary amyloid cascade hypothesis of the condition. It is an open question as to where all of these contributing aspects of the condition fit into a chain of cause and consequence, or whether the ordering of that chain is similar from patient to patient. Alzheimer’s disease may well be a collection of distinct conditions that all happen to wind up in a similar end state.
The authors of this paper draw the gloomy conclusion that this complexity, and continued failures in the development of therapies based on the amyloid cascade hypothesis, imply that there are no silver bullets. I would argue otherwise, and say that instead comparatively simple points of intervention have not yet been developed fully. Senolytic therapies that clear senescent glial cells from the brain seem quite effective in animal models, for example. The approach of restoring lost drainage of cerebrospinal fluid, to clear out aggregates from the brain, also looks promising. There will be others. The complexity of aging emerges from simpler root causes, and there will always be some clever way to intervene at a point of maximum leverage.
Multi-Loop Model of Alzheimer Disease: An Integrated Perspective on the Wnt/GSK3β, α-Synuclein, and Type 3 Diabetes Hypotheses
Alzheimer’s disease (AD) is among the most ominous of modern health epidemics. AD is not alone in its ascent. Other chronic diseases, particularly Parkinson’s disease (PD), a neurodegenerative disorder associated with the build-up of α-synuclein protein and death of dopaminergic neurons, and type 2 diabetes mellitus (T2DM) are increasing in prevalence at similarly alarming rates. Although AD, PD, and T2DM share common risk factors, chief among these being age, there is more to their relationship. Evidence suggests that the pathophysiological mechanisms underlying AD, PD, and T2DM interact synergistically.
In addition to the well-known amyloid cascade hypothesis of AD, other hypotheses have been proposed that include: (1) the Wnt/Glycogen Synthase Kinase 3β (GSK3β) hypothesis, (2) the α-synuclein hypothesis, and (3) the type 3 diabetes hypothesis. Dsfunctional Wnt-signaling can contribute to the development of AD and its two pathological hallmarks, Aβ plaques and p-tau tangles. The canonical PD-associated protein α-synuclein may be locked in pathological positive feedback loops with Aβ and tau. Finally, insulin resistance in the brain, “type 3 diabetes,” may contribute to development and exacerbation of AD. Each model interacts with the others. These interrelationships, make it clear that the pathology of AD is not a linear cascade, nor a simple feedback loop, but rather a network of cross-talking models and overlapping vicious cycles.
Given the cooperative and reinforced nature of this complex network, it is no surprise that the prototypical monotherapeutic approach to AD has reliably failed. Certainly, drugs that target key nodes within the network, such as GSK3β inhibitors or AKT activators, have shown promise in animal models, and this important work affords us valuable mechanistic insights. However, these pre-clinical successes generally have not translated into clinical success, at least not with the same degree of efficacy. This is likely because animal models harboring distinct AD-causing mutations and dysfunctions in particular linear pathways do not accurately recapitulate the complex pathologies underlying sporadic human AD. In brief, we are proposing that the single-target silver-bullet approach to AD drug discovery is doomed to fail and that we may only be able to treat or prevent AD by developing new multifaceted treatment options.
ADRB1 Mutation Grants a Lesser Need for Sleep, and thus a Longer Subjective Life
We lose a third of our life to sleep. If we didn’t need to sleep at all, then we would have the experience of living 50% longer, considered subjectively. We would accomplish much more, experience much more. There are, unfortunately, few useful ways to safely reduce the amount of time spent asleep, without reductions in the quality of life while awake. Here, researchers report on a rare human genetic variant that manifests itself in a family whose members with the mutation need comparatively little sleep to be fully rested, and who appear to be otherwise unaffected by this genetic difference.
This discovery may well prove to be the basis for enhancement treatments to reduce required sleep time in the years ahead. We should consider the caveats, however: sleep appears to be important in clearance of some aggregates from the brain, and it could be the case that individuals who sleep less have raised rates of neurodegenerative disease in late life, but these possible risks and associations have not yet been evaluated.
An understanding of the regulatory mechanism for sleep lays at the foundation for healthy living and aging. Sleep behavior has long been thought to be regulated by the interactions of circadian clock and sleep homeostasis pathways. In humans, variations of genetically inherited sleep features in the population have been recognized for a long time. Importantly, human sleep has unique features that are different from that of animal models. For example, human sleep is usually consolidated, whereas mice sleep throughout the 24 hour day. Drosophila sleep-like behavior is consolidated into one long period, but the level of similarity between the Drosophila and human molecular regulatory mechanisms remains unclear.
Previously, we identified a series of genetic variations that influence the timing of sleep in humans, and mouse models of these mutations mostly recapitulate the phenotypes. Timing of sleep is heavily influenced by the circadian clock, which has been intensely studied, and we now have a large and growing body of knowledge on how the clock is regulated at the molecular level. On the other hand, our understanding of sleep homeostasis regulation for human lags behind. We reported a mutation in the human DEC2 gene that causes mutation carriers to sleep 6 hours nightly for their entire lives without apparent negative effects. Another mutation in DEC2 was later reported in a single individual who is a short sleeper and resistant to sleep deprivation. Identification of additional genes participating in modulation of human sleep duration provides a unique way to expand our knowledge of genes and pathways critical for human sleep homeostasis regulation.
Noradrenergic signaling in the central nervous system (CNS) has long been known to regulate sleep. The network involving the noradrenergic neurons has been extensively studied, and most of the receptor subtypes have been genetically defined. In contrast to α1 and α2 adrenergic receptors (ARs), relatively little is known about the function of β receptors in the CNS. βARs within the brain were previously suggested to mediate the effect of norepinephrine (NE) for alert waking and rapid eye movement (REM) sleep. Clinically, β-blockers are widely used and can be associated with difficulty falling asleep and staying asleep, possibly due to reduced production and release of melatonin.
We report here a rare mutation in the β1AR gene (ADRB1) found in humans with natural short sleep. Engineering the human mutation into mice resulted in a sleep phenotype similar to that seen in familial natural short sleepers. We show that β1AR is expressed at high levels in the dorsal pons (DP). Neuronal activity measured by calcium imaging in this region demonstrated that ADRB1+ neurons in DP are wake and REM sleep active. Manipulating the activity of these ADRB1+ neurons changes sleep/wake patterns. Also, the activity of these neurons was altered in mice harboring the mutation. Together, these results not only support the causative role of this ADRB1 mutation in the human subjects but also provide a mechanism for investigating noradrenaline and β1AR in sleep regulation at the circuit level.
Aging Biotech Info is a Curated List of Companies in the Longevity Industry
Karl Pfleger is one of the small community of angel investors and philanthropists who collectively initially supported the first rejuvenation biotechnology companies to emerge in this present generation of the longevity industry. Here he is performing the public service of publishing a curated list of biotechnology companies in the industry, startups that are either definitively or at least arguably working on a means to intervene in important mechanisms of aging, along with their targets and progress to date. That there are still fewer than 100 such companies indicates that this is very much an industry in its initial growth phase – but growth is certainly happening. The sizable pools of venture funding dedicated to the longevity industry, such as Juvenescence and Life Biosciences are attracting new entrepreneurs, and the scientific community is starting to realize that the prospects for advancing their research programs into clinical translation have greatly improved these past few years.
Chronic diseases of aging have over the past century taken over from infectious diseases as the predominant causes of death and suffering. The science of aging has shown over the past few decades that certain slow biological changes collectively underlie most (if not all) chronic diseases. The aging and longevity field, the understanding of these slow changes and how to interfere with them, is currently a small part of the overall medical, healthcare, and biotech spaces, but the efficiency of targeting the underlying causes of multiple diseases will rapidly cause aging to grow to become a much larger portion.
The aging and longevity field has recently grown to the point where it is difficult to follow important developments, even for insiders. There are books, journals, and blogs, but few sources of structured information to refer to for broader context or to consult for targeted inquiries, particularly few focused narrowly on aging defined as the underlying molecular causes of multiple age-related diseases.
As an especially important example, the internet previously had no reasonably comprehensive and precise list of companies with therapies or diagnostics for underlying aging in the above sense. Some argue that aging will be a scientific, commercial, and cultural revolution to rival any others. What is even more certain is that the field is important and of interest to many, so concise ways to pay attention will be useful. This will be a living site with ongoing updates. Focus will be on content, not flashiness, with the goal being utility for the community, those interacting with it, and the wider interested public.
Exosomes Improve Collagen Production in Aged Skin
Loss of collagen in the extracellular matrix is one of the manifestations of aging in skin. There are any number of very marginal approaches intended to improve matters presently available in clinics and stores, very few of which in any way address the underlying causes, or in only very minor ways if they do. Delivery of signals generated by healthy skin cells is an approach that might be more effective, but again this doesn’t address the underlying causes of skin aging – it is an attempt to override cellular reactions to the aged environment. In this vein, researchers here demonstrate the harvesting of exosomes, small membrane bound packages that carry signals between cells, from cell cultures, and their delivery to aged skin as a possible therapy.
Researchers have shown that exosomes harvested from human skin cells are more effective at repairing sun-damaged skin cells in mice than popular retinol or stem cell-based treatments currently in use. Additionally, the nanometer-sized exosomes can be delivered to the target cells via needle-free injections. Exosomes are tiny sacs (30 – 150 nanometers across) that are excreted and taken up by cells. They can transfer DNA, RNA, or proteins from cell to cell, affecting the function of the recipient cell. In the regenerative medicine field, exosomes are being tested as carriers of stem cell-based treatments for diseases ranging from heart disease to respiratory disorders.
To test whether exosomes could be effective for skin repair, researchers first grew and harvested exosomes from skin cells. They used commercially available human dermal fibroblast cells, expanding them in a suspension culture that allowed the cells to adhere to one another, forming spheroids. The spheroids then excreted exosomes into the media. “These 3D structures generate more procollagen – more potent exosomes – than you get with 2D cell expansion.”
In a photoaged, nude mouse model, the researches tested the 3D spheroid-grown exosomes against three other treatments: retinoid cream; 2D-grown exosomes; and bone marrow derived mesenchymal stem cells (MSCs) exosomes, a popular stem cell-based anti-aging treatment currently in use. The team compared improvements in skin thickness and collagen production after treatment. They found that skin thickness in 3D exosome treated mice was 20% better than in the untreated and 5% better than in the MSC-treated mouse. Additionally, they found 30% more collagen production in skin treated with the 3D exosomes than in the MSC treated skin, which was the second most effective treatment.
Fitter, Thinner Older Adults Have a Measurably Different Gut Microbiome
In recent years, researchers have demonstrated that the microbiome of the gut is influential over the pace of aging. Dietary changes, immune system changes, tissue changes, and microbiome population changes all take place and interact with one another with advancing age. There is evidence for changes in the microbiome to aggravate the immune system into chronic inflammation, and evidence for declining immune function to lead to unhelpful changes in the balance of microbes. Some people have better microbiomes, such as athletes tending to have microbes that secrete compounds such as proprionate that can incrementally improve health. In animal models, transplanting gut microbes from young to old animals improves the health and longevity of the older animals.
In this broader context, we should probably expect fitter adults to have a measurably different gut microbiome in comparison to their less fit and overweight peers. Are those different bacteria helping to maintain fitness? The evidence here suggests that they are, but questions of causation remain: is it diet, weight, and inflammation that determines whether or not helpful bacteria are present, or do natural variations in bacterial populations between individuals make it easier or harder to maintain fitness?
The gut-muscle axis, or the relationship between gut microbiota and muscle mass and physical function, has gained momentum as a research topic in the last few years as studies have established that gut microbiota influences many aspects of health. While researchers have begun exploring the connection between the gut microbiome, muscle, and physical function in mice and younger adults, few studies have been conducted with older adults. To gain insight into this population, the researchers compared bacteria from the gut microbiomes of 18 older adults with high-physical function and a favorable body composition (higher percentage of lean mass, lower percentage of fat mass) with 11 older adults with low-physical function and a less favorable body composition. The small study identified differences in the bacterial profiles between the two groups.
Similar bacterial differences were present when mice were colonized with fecal samples from the two human groups, and grip strength was increased in mice colonized with samples from the high-functioning older adults, suggesting a role for the gut microbiome in mechanisms related to muscle strength in older adults. Specifically, when compared to the low-functioning older adult group, the researchers found higher levels of Prevotellaceae, Prevotella, Barnesiella, and Barnesiella intestinihominis – all potentially good bacteria – in the high-functioning older adults and in the mice that were colonized with fecal samples from the high-functioning older adults.
“While we were surprised that we didn’t identify a role for the gut microbiome on the maintenance of body composition, with these results we now start to understand the role of gut bacteria in the maintenance of muscle strength in older adults. For example, if we were to conduct an intervention to increase Prevotella levels in the gut microbiome, we would expect to see an increase in muscle strength if these bacteria are involved. Prevotella’s role in the maintenance of muscle strength in older adults is one area we expect to continue to explore.”
Risk Factors versus Lifestyle Choices in the Mortality of Old Age
Environmental and lifestyle choices, as numerous epidemiological studies have demonstrated, have considerable influence over health and mortality in late life. This open access paper balances lifestyle choices against a range of environmental factors and measures of the progression of aging. The authors find that a healthy lifestyle can only partially offset the effects of having a greater burden of age-related damage and its consequences, or, separately, the impact of low socioeconomic status. The former makes a great deal of sense, given the inevitability of aging as matters currently stand, with even the healthiest succumbing, while the latter is an interesting finding. It remains unclear as to the mechanisms linking socioeconomic status to aging: wealth, education, intelligence, stress, access to medical services, and other factors are closely tied and hard to pick apart in the human data.
Annual mortality among oldest-old individuals was reduced by somewhere between 0.2% and 1.3% from 1998 to 2008 in China. Impaired cognitive functions were independent predictors of all-cause mortality in very old people. Moreover, the risk of mortality is very high for the oldest-old with disabilities. Additionally, socioeconomic inequalities, obesity, cardiovascular factors, and chronic diseases are associated with mortality in the oldest-old. Conversely, healthy lifestyle practices, such as consumption of fruits and vegetables, social participation, and maintaining a normal weight, are associated with lower mortality. The question remains as to whether a healthy lifestyle and behavioral factors (e.g., never smoking and physical training) can somehow compensate for the harmful effects of the risk factors on mortality.
In this large, nationwide cohort study of Chinese oldest-old (80 years of age and older), we found that rural residence, not in marriage, lower economic level, physical disability, impaired cognitive function, and comorbidity are independent risk factors for mortality. Using these factors, we computed a weighted “risk score.” Because never smoking, never drinking, doing physical exercise, having an ideal diet, and a normal weight were independently associated with lower mortality, we also combined them to compute a weighted “protection score.” Both scores were divided into lowest, middle, and highest groups using their tertiles.
In joint effect analyses, participants with the combined highest-risk score and lowest-protection score profile had a nearly threefold higher joint death risk. These analyses show that adherence to a healthy lifestyle counteracts the negative effect of risk factors on all-cause mortality in the oldest-old by more than 20%.
An Interview with Tristan Edwards of Life Biosciences
Alongside Juvenescence, Life Biosciences is one of the first large investment concerns wholly dedicated to the growing longevity industry. The Life Biosciences principals take the approach of providing the extensive supporting infrastructure needed to wrap a company around a senior scientist in the field of aging research, and then guide their work towards commercialization. Most scientists have very little interest in founding a company, and in any case lack the skills needed to do so. This approach of providing an environment that operates in much the same way as academia from the perspective of the researcher, in which the business side of things is handled, is a good way to accelerate progress in a field that presently lacks a sufficiently large population of entrepreneurs for companies to emerge naturally at a good pace.
How far along is longevity in becoming a defined category for investors? Put it on a scale of 0-10 for us. If fintech has developed to a nine or a ten, where would you score longevity?
From an investment perspective I would say it’s a one or a two. But I believe that will change very quickly. I think the scale will go from a two to an eight in the next four to five years. Like the Internet of Things, or Artificial Intelligence before it, in the next few years I can’t imagine a single person on the planet not being aware of the ability to extend lifespan and healthspan, both as an industry and as a benefit to humankind.
So, a major shift in our thinking is on the way?
In 1903, the Wright brothers defied expectation and took their first flight. We have the photo of this on our office wall, to remind us of who we are. The idea of humans being able to fly back then was crazy; most people were saying it couldn’t be done. Yet after they left the earth’s gravity, it didn’t take mankind years to accept it. We immediately forgot that it was crazy. All we needed was proof that it could be done, and we never looked back. That’s exactly where we are with longevity sciences. Longevity research has been evolving as a legitimate science for many years. But I think we are at the cusp of dramatic change. We’ll see more and more bright young minds focusing on longevity, and we will soon treat aging. Eventually, we’re talking about adding another 20 – 30 years to the average lifespan with none of the diseases of aging: Parkinson’s, Alzheimer’s, type 2 diabetes, etc. In other words, not only expanding lifespan but what we call “healthspan,” the period during which the individual can live a healthy, productive life.
Does all this development mean big institutional investors will soon be paying attention?
Plenty already are. The science, however, has to build to a point where the rounds are large enough for them to get involved. Once you start raising $100m to $200m rounds, they’ll start paying real attention and investing. The rounds must be large enough for the mandates to allow and value checks must be in place in new areas; this can be tough to do. As the science progresses, we see the investment interest ramping up, with bigger contributors stepping in. A lot also depends on how quickly some institutions learn to adapt. By “adapt” I mean simply this: There’s a long-held understanding that Big Pharma relies on illness for profits. But if they reframe their mission as being in the healthspan business, then the longevity revolution is valuable for them. It’s my hope that Pharma embraces this change as a wonderful and necessary way for them to evolve their business in a much more effective way.
The Boost to the Unfolded Protein Response Achieved via Exercise Declines with Age
Exercise achieves benefits to health in large part through upregulation of cellular maintenance processes. In this way it is similar to the practice of calorie restriction, but the outcome is of a lesser degree – exercise does not extend life span in laboratory species, while calorie restriction does. Nonetheless, exercise is certainly beneficial. One of the cellular maintenance processes involved is the unfolded protein response, which, as the name might suggest, clears out proteins that are improperly folded, or have otherwise become stuck at the folding stage of protein manufacture, in the endoplasmic reticulum structure of the cell. Like other maintenance processes, the unfolded protein response becomes less effective with age, for reasons that are far from fully explored. Here, researchers demonstrate this diminished effectiveness in the context of the response to exercise.
Aging is associated with the loss of skeletal muscle mass, quality, and function; decrements that have a negative influence on health span. Resistance exercise improves muscle mass and function, but there is emerging evidence that the molecular and cellular responses to anabolic stimuli (e.g., exercise and nutrition) are attenuated in older adults; a phenomenon termed anabolic resistance. The unfolded protein response (UPR) has emerged as a key regulatory pathway in skeletal muscle protein quality control and adaptations to exercise. Early evidence points to altered UPR as an explanation for age and disease related changes in protein folding and accumulation and aggregation of proteins within the endoplasmic reticulum (ER).
The influence of age on skeletal muscle adaptive UPR in response to exercise, and the relationship to other key exercise-responsive regulatory pathways is not well-understood. We evaluated age-related changes in transcriptional markers of UPR activation following a single bout of resistance exercise in 12 young (27 ± 5yrs) and 12 older (75 ± 5yrs) healthy men and women. At baseline, there were modest differences in expression of UPR-related genes in young and older adults. Following exercise, transcriptional markers of UPR pathway activation were attenuated in older adults compared to young based on specific salient UPR-related genes and gene set enrichment analysis. The coordination of post-exercise transcriptional patterns between the UPR pathway, p53/p21 axis of autophagy, and satellite cell (SC) differentiation were less evident in older compared to young adults.
In conclusion, older adults exhibited decreased markers of UPR activation and reduced coordination with autophagy and SC-associated gene transcripts following a single bout of unaccustomed resistance exercise. In contrast, young adults demonstrated strong coordination between UPR genes and key regulatory gene transcripts associated with autophagy and SC differentiation in skeletal muscle post-exercise. Taken together, the present findings suggest a potential age-related impairment in the post-exercise transcriptional response that supports activation of the UPR and coordination with other exercise responsive pathways (i.e., autophagy, SC differentiation) in skeletal muscle that is likely to contribute to sarcopenia and age-related attenuation of adaptive responses to exercise.
Altered Calcium Transport in Aging Mitochondria is Maladaptive
Mitochondria are the power plants of the cell, responsible for packaging energy store molecules used to power cellular processes. There are hundreds of them in any given cell, the descendants of ancient symbiotic bacteria. They replicate by fission, like bacteria, and carry a remnant of their original DNA. Mitochondrial function declines with age, a problem that appears to stem from an imbalance in mitochondrial fission that in turn impairs the ability of the cell to clear out worn and malfunctioning mitochondria via the process of autophagy. Exactly why this imbalance arises is poorly understood, but it can be added to the long, long list of maladaptive processes that emerge in response to the underlying molecular damage of aging.
Researchers here focus on another maladaptive aspect of mitochondrial function in aging cells: they exhibit altered calcium transport, which may initially compensate for other shortfalls, but then ultimately further contributes to the faltering of mitochondrial function. This is very much a downstream consequence of deeper problems.
Sometimes the more a person tries to fix a seemingly minor problem, the worse things become. Cells are no different, it turns out, though attempting to compensate for what begins as a minor deficiency or dysfunction can be dire. In the case of Alzheimer’s disease, researchers now show that mitochondrial calcium transport remodeling – what appears to be an attempt by cells to compensate for flagging energy production and metabolic dysfunction – while initially beneficial, ultimately becomes maladaptive, fueling declines in mitochondrial function, memory, and learning.
Altered calcium regulation and metabolic dysfunction have been suspected of contributing to neuronal dysfunction and Alzheimer’s development. Calcium transport into mitochondria plays an important part in many cellular functions and requires the involvement of multiple proteins to be carried out effectively. Among the key regulators of this process is a protein known as NCLX, which previously was discovered to mediate calcium efflux from heart cells. NCLX expression is also important in mitochondrial calcium efflux in neurons.
In a new study, researchers examined the role of mitochondrial calcium uptake by neurons in Alzheimer’s disease. To do so, the team used a mouse model of familial Alzheimer’s disease in which animals harbored three gene mutations that give rise to age-progressive pathology comparable to Alzheimer’s progression in human patients. As mice carrying the three mutations aged, the researchers observed a steady reduction in NCLX expression. This reduction was accompanied by decreases in the expression of proteins that limit mitochondrial calcium uptake, resulting in damaging calcium overload. NCLX loss was further linked to increases in the production of cell-damaging oxidants. When NCLX expression was restored, levels of harmful protein aggregates declined, neuronal mitochondrial calcium homeostasis was reestablished, and mice were rescued from cognitive decline.
“Our findings indicate that maladaptive remodeling of pathways to compensate for abnormalities in calcium regulation, which perhaps are meant to maintain energy production in cells, lead to neuronal dysfunction and Alzheimer’s pathology. Moreover, our data suggest that amyloid beta and tau pathology actually lie downstream of mitochondrial dysfunction in the progression of Alzheimer’s disease, which opens up a new therapeutic angle.”
A Skeptical Review of the Evidence for Metformin
This review paper more or less leans towards my thoughts on metformin as a treatment to slow aging: the animal data is not great, the human data is a single study, the effect size on life span is far too small to care about, and the detrimental side effects are large in comparison to that effect size. The strategy of upregulating stress response mechanisms via drugs such as metformin is a poor strategy for long-lived species, as we clearly don’t exhibit the sizable gains in life span that occur in short lived species such as mice under these circumstances. Metformin, in turn, is a low performance example of this strategy, much worse than, say, the practice of calorie restriction or mTOR inhibitors.
Metformin is sometimes proposed to be an “anti-aging” drug, based on preclinical experiments with lower-order organisms and numerous retrospective data on beneficial health outcomes for type 2 diabetics. Large prospective, placebo-controlled trials are planned, in pilot stage, or running, to find a new use (or indication) for an aging population. In 2015, Nir Barzilai met with regulators from the FDA to discuss the now famous phase III multi-site TAME (Targeting Aging with Metformin) trial. The acronym chosen and the intention behind it – namely, that aging is a “disorder” that can be treated like any other disease – was a clear provocation. The FDA’s mandate is to regulate medications and devices to cure diseases or aid in their diagnosis, but aging is not (yet) an indication. Interestingly, frailty is missing from the proposed composite outcome. Other ongoing trials (e.g., NCT02570672) with metformin provide arguments that frailty may be an important endpoint. It will be interesting to compare the results with the ongoing fisetin trial (NCT03675724).
Although widely cited as evidence for the small effects of 0.1% metformin in the diet on the lifespan of older male inbred mice, earlier results obtained by researchers should be dismissed: the National Institute on Aging Interventions Testing Program could not replicate the findings regarding an extension of the lifespan with 0.1% metformin. The negative results were obtained at three different locations using genetically heterogeneous female and male mice.
The rationale for the ongoing or planned metformin trials is almost exclusively based on observations (associations) of potential benefits in a diabetic (or prediabetic) population. Its efficacy even in an at-risk cohort of aged people has not yet been proven. Metformin is associated with a higher risk of vitamin B12 and vitamin B6 deficiency, which may result in an increased risk of cognitive dysfunction. Supplementation is strongly recommended to metformin users.
Of greater concern are the results of small trials in which the effects of metformin on metabolic responses to exercise or on cardiorespiratory fitness were tested. In a placebo-controlled, double-blind, crossover trial with healthy young subjects, metformin caused a small but significant decline in maximal aerobic capacity. A double-blind, placebo-controlled landmark trial with older adults with one risk factor for type 2 diabetes investigated the effects of metformin and 12 weeks of aerobic exercise. Contrary to expectations – namely, that the effects of exercise and the drug would be additive – “metformin attenuated the increase in whole-body insulin sensitivity and abrogated the exercise-mediated increase in skeletal muscle mitochondrial respiration.”
A Non-Invasive Approach to Measuring Cellular Senescence in the Kidney
Researchers here provide evidence that the presence in the urine of extracellular vesicles carrying p16 as a part of their cargo might be used as a way to assess cellular senescence levels in the kidney. The presence of lingering senescent cells increases with age, and these cells cause chronic inflammation and tissue dysfunction in proportion to their numbers. With rapid growth in the clinical development of senolytic drugs capable of clearing senescent cells from aged tissues, and the present availability of a few proven and potential senolytic treatments such as the dasatinib and quercetin combination, there is a strong need for ways to quantify the burden of senescent cells in humans. Simple, low-cost tests that can run before and after a senolytic treatment would go a long way towards quantifying the degree to which the presently available approaches actually work.
Hypertension may be associated with renal cellular injury. Cells in distress release extracellular vesicles (EVs), and their numbers in urine may reflect renal injury. Cellular senescence, an irreversible growth arrest in response to a noxious milieu, is characterized by release of proinflammatory cytokines. We hypothesized that EVs released by senescent nephron cells can be identified in urine of patients with hypertension.
We recruited patients with essential hypertension (EH) or renovascular hypertension and healthy volunteers. Renal oxygenation was assessed using magnetic resonance imaging and blood samples collected from both renal veins for cytokine-level measurements. EVs isolated from urine samples were characterized by imaging flow cytometry based on specific markers, including p16 (senescence marker), calyxin (podocytes), urate transporter 1 (proximal tubules), uromodulin (ascending limb of Henle’s loop), and prominin-2 (distal tubules).
Overall percentage of urinary p16+ EVs was elevated in EH and renovascular hypertension patients compared with healthy volunteers and correlated inversely with renal function and directly with renal vein cytokine levels. Urinary levels of p16+/urate transporter 1+ were elevated in all hypertensive subjects compared with healthy volunteers, whereas p16+/prominin-2+ levels were elevated only in EH versus healthy volunteers and p16+/uromodulin+ in renovascular hypertension versus EH.
In conclusion, levels of p16+ EVs are elevated in urine of hypertensive patients and may reflect increased proximal tubular cellular senescence. In EH, EVs originate also from distal tubules and in renovascular hypertension from Henle’s loop. Hence, urinary EVs levels may be useful to identify intrarenal sites of cellular senescence.