Reviewing the State of Gene Editing to Make Cells Compatible Between Donor and Recipient

A sizable level of funding in academia and industry is devoted to the goal of enabling cell transplants between different individuals, with large and well funded pharma companies such as Astellas, Sana, and others involved. This would allow for the creation of cost-effective cell therapies of all sorts, in which the donor cells used in every patient originate from the same few well-vetted and well-controlled cell lines.

Logistics is everything in the realm of cell therapies, and the reason why autologous cell therapies, such as CAR-T treatments for cancer, are so expensive is that every treatment site must have the ability to extract cells from the patient, engineer them, slowly expand their numbers over weeks in carefully monitored culture conditions, and then perform quality control before use. Compare this with a universal cell line that is manufactured in one central location, with cells frozen down in a standardized way for storage, transport, and then use by any clinic capable of performing an infusion. It is a very different picture of cost and difficulty.

Regenerative medicine has come a long way since the derivation of the first human pluripotent stem cells (hPSC). As a community, we have become better at sourcing stem cells, differentiating them into therapeutic cell types and transplanting them to cure different diseases. To unlock the full potential of stem cell therapies, we need to overcome the immune barrier to transplantation. The human immune system is incredibly discerning in distinguishing between self and non-self, which could be viral or bacterial proteins, malignant cells, and, of course, cells from a genetically non-identical donor. Genetic differences between the donor and the recipient are recognized as alloantigens if they have never been encountered by the host's immune system before (as opposed to autoantigens) and may prompt allograft rejection.

Based on the nature of the genetic polymorphism and how/when they present themselves to the immune system, three types of alloantigens can be distinguished that, together, define the immune barrier. Human leukocyte antigens (HLA) are the immunodominant barrier to cell and tissue transplantation. Minor histocompatibility antigens (miHA) can vary in their expression from cell type to cell type. Neoantigens (NA) can accumulate during prolonged culture and pose a risk of rejection even of cells of autologous origin.

Initial attempts have focused primarily on the major histocompatibility barrier that is formed by the human leukocyte antigens (HLA). More recently, immune checkpoint inhibitors, such as PD-L1, CD47, or HLA-G, are being explored both, in the presence or absence of HLA, to mitigate immune rejection by the various cellular components of the immune system. In this review, we discuss progress in surmounting immune barriers to cell transplantation, with a particular focus on genetic engineering of human pluripotent stem cells and progenitor cells and the therapeutic cell types derived from them.

Link: https://doi.org/10.1007/s40778-022-00221-0

Making Senescent Cells Glow In Vivo

Currently there is some debate over whether the initial markers used to detect senescent cells, such as as senescence-associated β-galactosidase and P16 expression, are general enough across cell types and specific enough to senescent cells for all uses in research and clinical development. Nonetheless, these markers are well known and the efficiency of senolytic treatments that clear senescent cells does appear to be measurable this way. Greater convenience in that measurement is always useful: at present, the state of the art involves biopsies and post-mortem tissue histology. Here researchers take a step forward by producing a mouse lineage in which senescence-associated β-galactosidase expression is associated with fluorescence, allowing for more cost-effective investigation of cellular senescence and its treatment.

The progressive decline of physiological function and the increased risk of age-related diseases challenge healthy aging. Multiple anti-aging manipulations, such as senolytics, have proven beneficial for health; however, the biomarkers that label in vivo senescence at systemic levels are lacking, thus hindering anti-aging applications. In this study, we generate a Glb1+/m-Glb1-2A-mCherry (GAC) reporter allele at the Glb1 gene locus, which encodes lysosomal β-galactosidase - an enzyme elevated in tissues of old mice.

A linear correlation between GAC signal and chronological age is established in a cohort of middle-aged (9 to 13 months) Glb1+/m mice. The high GAC signal is closely associated with cardiac hypertrophy and a shortened lifespan. Moreover, the GAC signal is exponentially increased in pathological senescence induced by bleomycin in the lung. Senolytic dasatinib and quercetin (D + Q) reduce GAC signal in bleomycin treated mice. Thus, the Glb1-2A-mCherry reporter mice monitors systemic aging and function decline, predicts lifespan, and may facilitate the understanding of aging mechanisms and help in the development of anti-aging interventions.

Link: https://doi.org/10.1038/s41467-022-34801-9

Arguing for Well Explored Approaches to Slow Aging to Not In Fact Slow Aging

Today's open access paper mounts an interesting argument, based on the use of a large data set for phenotypic aging in mice. They looked at transcriptomic and proteomic data for a sizable number of genes in a variety of different tissues, then grouping these into phenotypes by related function, or relation to specific age-related declines. Differences in expression by age in these phenotypic groups of genes were observed directly in mice and in human data sets.

The researchers then looked the effects on phenotypes of a few very well studied interventions widely thought to slow aging in mice: growth hormone signaling inhibition, mTOR inhibition, and intermittent fasting. The authors argue, based on their data, that these interventions are essentially compensatory rather than age-slowing, in that they appear to be changing phenotypes (mostly for the better) in a similar way in youth and old age, but they are not slowing the age-related change in those phenotypes. At least insofar as those phenotypes are assessed by the selected transcriptomic and proteomic data.

This is a very interesting view, given the present consensus that, yes, these interventions genuinely slow aging, setting aside some arguments as to whether mTOR is extending life in animal models only because it reduces cancer risk. It is a good illustration of the state of the present debate over strategies for intervention in aging, shaped by the lack of a strong consensus on how to define aging in a way that is useful for the assessment of therapies in animal models or human trials. One can always look at obvious external signs of dysfunction, such as grip strength, but it will never be completely clear, given only those biomarkers, as to whether a therapy helps because it is compensating, or because it legitimately does in fact address mechanisms of aging.

It is a reasonable supposition that better therapies will be better because they reverse underlying mechanisms of aging, and therefore will produce lasting benefits to patients in many aspects of health. As a strategy, this is the right way forward, but the expectation of better outcomes for aging-targeting therapies is by no means a given for any specific therapy and specific age-related condition. If we can point to interventions such as mTOR inhibition that appear to slow the age-related decline of a great many of those aspects of health, and show that they are in fact only broadly compensatory instead, it muddies the waters considerably when it comes to steering the research and development communities towards better approaches to therapy.

Deep phenotyping and lifetime trajectories reveal limited effects of longevity regulators on the aging process in C57BL/6J mice

A large body of work, carried out over the past decades in a range of model organisms including yeast, worms, flies and mice, has identified hundreds of genetic variants as well as numerous dietary factors, pharmacological treatments, and other environmental variables that can increase the length of life in animals. Current concepts regarding the biology of aging4 are in large part based on results from these lifespan studies. Much fewer data, however, are available to address the question of whether these factors, besides extending lifespan, in fact also slow aging, particularly in the context of mammalian models.

It is important to distinguish lifespan vs. aging because it is well known that lifespan can be restricted by specific sets of pathologies associated with old age, rather than being directly limited by a general decline in physiological systems. In various rodent species, for instance, the natural end of life is frequently due to the development of lethal neoplastic disorders: Cancers have been shown to account for ca. 70-90% of natural age-related deaths in a range of mouse strains. Accordingly, there is a strong need to study aging more directly, rather than to rely on lifespan as the sole proxy measure for aging.

Deep phenotyping represents a powerful approach to capture a wide range of aging-associated phenotypic changes, since it takes into account alterations at molecular, cellular, physiological, and pathological levels of analysis, thereby providing a very fine-grained view of the consequences of aging as they develop across tissues and organs. The approach is therefore ideally suited to assess genetic variants, pathways, dietary or pharmacological factors previously linked to lifespan extension and, potentially, delayed aging. Deep phenotyping examines hundreds of parameters, many of which are expected to differ between young and old animals (hereafter called age-sensitive phenotypes; ASPs); these can be collectively used to address if and how a given intervention interacts with the biological processes underlying the signs and symptoms of aging.

We here refer to the mechanisms of aging as the sets of processes that underlie age-dependent phenotypic change. Accordingly, an intervention that targets the mechanisms underlying aging should slow the transformation of a phenotypically young to a phenotypically aged organism. In other words, the intervention should attenuate the age-dependent change in ASPs (the delta in phenotype between young and old). For instance, a specific intervention or genotype could ameliorate the age-dependent loss of neurons by promoting processes concerned with maintaining the integrity of neurons over time.

An intervention could mimic a targeting of age-dependent change by affecting ASPs directly (i.e., independently of age-dependent change in these phenotypes). For instance, a specific genetic variant may increase the number of neurons by promoting neurogenesis during brain development, without affecting the rate of subsequent age-dependent neuron loss. This variant would regulate neurodevelopmental processes but would not affect the mechanisms underlying age-dependent change. Although this would also result in increased neuronal numbers in old age, it cannot be taken as evidence of a slowed progression of aging because the rate of age-dependent change remains unaltered

Here, we employ large-scale phenotyping to analyze hundreds of markers in aging male C57BL/6J mice. For each phenotype, we establish lifetime profiles to determine when age-dependent change is first detectable relative to the young adult baseline. To cover key genetic longevity interventions and study their effects on aging in mice, we here chose genetic models targeting the mTOR pathway as well as growth hormone signaling. In parallel to our studies in mice, we applied multi-dimensional phenotyping combined with stratification based on genetic expression variants in GHRHR and MTOR in a human population across a wide age range, spanning from 30 to 95 years. The analyses in humans complement our work in animal models and allowed us to address, in parallel to the work in mice, whether or not a potential genetic modification of human ASPs occurs in an age-independent fashion or not.

We examine these key lifespan regulators (putative anti-aging interventions; PAAIs) for a possible countering of aging. Importantly, unlike most previous studies, we include in our study design young treated groups of animals, subjected to PAAIs prior to the onset of detectable age-dependent phenotypic change. Many PAAI effects influence phenotypes long before the onset of detectable age-dependent change, but, importantly, do not alter the rate of phenotypic change. Contrary to a general expectation that 'anti-aging' treatments should produce a broad change in aging rate across many phenotypes, our study shows that the PAAIs we examined - that are concerned with some of the very core mechanisms proposed to be involved in aging - often did not seem to work through targeting age-dependent change.

In conclusion, the PAAIs examined (i.e. mTOR loss of function, Ghrhr loss of function, intermittent fasting-based version of dietary restriction) often influenced age-sensitive traits in a direct way and not by slowing age-dependent change. Previous studies often failed to include young animals subjected to PAAI to account for age-independent PAAI effects. However, any study not accounting for such age-independent intervention effects will be prone to overestimate the extent to which an intervention delays the effects of aging on the phenotypes studied. This can result in a considerable bias of our view on how modifiable aging-related changes are.

Advocating for Glutathione Upregulation as a Basis for Therapy

You might recall a recent small clinical trial in which oral supplementation with large amounts of glutathione precursors produced improvements in health in older adults, the size of the outcome surprisingly large for a treatment based on supplements. Here, researchers enthusiastically advocate for glutathione upregulation, reversing the normal age-related decline in glutathione levels, as a basis for improving the health of older people and slowing the onset of age-related degeneration.

Many local and systemic diseases especially diseases that are leading causes of death globally like chronic obstructive pulmonary disease, atherosclerosis with ischemic heart disease and stroke, cancer, and COVID-19, involve both, (1) oxidative stress with excessive production of reactive oxygen species (ROS) that lower glutathione (GSH) levels, and (2) inflammation. The GSH tripeptide, the most abundant water-soluble non-protein thiol in the cell, is fundamental for life by (a) sustaining the adequate redox cell signaling needed to maintain physiologic levels of oxidative stress fundamental to control life processes, and (b) limiting excessive oxidative stress that causes cell and tissue damage.

GSH activity is facilitated by activation of the Keap1-Nrf2-antioxidant response element (ARE) redox regulator pathway, releasing Nrf2 that regulates expression of genes controlling antioxidant, inflammatory, and immune system responses. GSH exists in the thiol-reduced (98%+ of total GSH) and disulfide-oxidized (GSSG) forms, and the concentrations of GSH and GSSG are indicators of the functionality of the cell. GSH depletion may play a central role in inflammatory diseases and COVID-19 pathophysiology, host immune response, and disease severity and mortality.

Therapies enhancing GSH could become a cornerstone to reduce severity and fatal outcomes of inflammatory diseases and COVID-19 and increasing GSH levels may prevent and subdue these diseases. The life value of GSH makes for a paramount research field in biology and medicine and may be key against systemic inflammation and COVID-19 disease. In this review, we emphasize (1) GSH depletion as a fundamental risk factor for diseases like chronic obstructive pulmonary disease and atherosclerosis (ischemic heart disease and stroke), (2) importance of oxidative stress and antioxidants in COVID-19 disease, (3) significance of GSH to counteract persistent damaging inflammation, inflammaging, and early (premature) inflammaging associated with cell and tissue damage caused by excessive oxidative stress and lack of adequate antioxidant defenses in younger individuals, and (4) new therapies that include antioxidant defenses restoration.

Link: https://doi.org/10.3389/fnut.2022.1007816

Interactions Between the Aging Immune System and Aging Kidney

Researchers here discuss the ways in which the aging of the immune system influences the aging of the kidney, such as through disruption of the normal participation of immune cells in tissue maintenance and repair. With age the immune system falls into a state of chronic inflammation, and unresolved inflammatory signaling is disruptive to the structure and operation of tissues throughout the body. The kidney is but one example of how this contributes to the declines of aging.

With the steady increase in the number of elderly individuals globally, age-related diseases emerge as a major challenge to health care workers. Apart from functional and structural changes in the kidneys introduced by aging, immune system decline also significantly increases the risk of age-related kidney diseases. Immunosenescence is a loose definition of age-related changes in the innate and adaptive immune responses, which is characterized by shrinkage of naïve immune cell reservoirs, accumulation of late-stage differentiated cells with a senescent phenotype, and immunoglobulin class switching. These changes in the immune system result in two seemingly incompatible aspects: diminished immune response and increased inflammatory response, also known as inflammaging.

Tubular epithelial cells (TECs) senescence and tertiary lymphoid tissue formation occur following acute kidney injury. Senescent kidney cells promote a chronic inflammatory microenvironment, which can subsequently cause local tissue damage, hinder tissue repair, and promote immune system senescence. Intrarenal inflammation underlies the development of renal fibrosis and chronic kidney disease (CKD) later in life. Immunosenescence is exaggerated in patients with CKD and end-stage renal disease (ESRD). Hallmarks of immunosenescence, including decreased naïve T cells, reduced CD28 expression, and increased proinflammatory macrophages, are convincing predictors of mortality in patients with CKD and ESRD. Renal replacement therapy for old patients with ESRD results in a lower acute rejection rate after the kidney transplantation. However, immunosenescence may increase the risk of chronic, but severe, graft failure. In addition, immunosenescence has been reported to speed up during kidney transplantation and immunosuppressive treatment.

Link: https://doi.org/10.1186/s12979-022-00313-9

Studying the Trajectory of Exercise Across Life Suggests that It is Never Too Late to Undertake More Of It

You may recall a study from a few years back suggesting that increasing level of exercise in later life, after a low level of exercise in earlier life, removes a perhaps surprisingly large fraction of the negative consequences of that low level of exercise. This is at least the case when it comes to age-related mortality. Nonetheless, in that study, maintaining a high level of exercise across life was still shown to be much better for health than only beginning high levels of exercise in later life.

Today's open access paper reports on a similar study, but here the metrics are specifically focused on measurements of frailty, such as grip strength. The interesting portion of the outcome is that the people who moved from low levels of exercise to greater exercise look similar to those that always maintained that higher level of exercise. The conclusion that one could make from this is that frailty as presently observed in the wealthier parts of the world is a large part a consequence of inactivity, and that at least that portion of the problem is reversible given sufficient effort.

Associations of physical activity participation trajectories with subsequent motor function declines and incident frailty: A population-based cohort study

Increasing evidence reports the benefits yielded by regular physical activity (PA) on the motor function in older people by preserving mobility, muscle strength, and balance. However, there is a methodological limitation that PA are evaluated at single time-point (primarily the baseline level) or short time-scales without considering the long-term dynamic nature of PA behavior. Group-based trajectory modeling (GBTM) allows grouping of subjects presenting with similar baseline values and longitudinal patterns of change according to their direction and magnitude. Using this method, some studies have detected different PA trajectories among older adult cohorts. Three studies examined the association of PA trajectories with mortality in older adults. But, there isn't an investigation of the temporal association of long-term PA participation trajectories with subsequent motor function changes and incident frailty.

Therefore, the main objectives of this study were to investigate different trajectories of long-term PA participation over a 6-year span by the GBTM and evaluate their associations with subsequent motor function decline and incident frailty in middle-aged and elderly adults. Our hypotheses are that older adults maintaining PA over time will have a slower motor function decline and a lower risk of incident frailty compared with persistently inactive subjects or those reducing PA levels, and that increasing PA even at older ages promotes healthy aging characterized by reduced motor function decline and incident frailty.

Five distinct trajectories of long-term PA participation were identified in the aging cohort, including persistently low-active trajectory (N = 2,039), increasing active trajectory (N = 1,711), declining active trajectory (N = 216), persistently moderate-active trajectory (N = 2,254), and persistently high-active trajectory (N = 2,007). Compared with the persistently low-active group, the participants in persistently moderate- and high-active groups experienced significantly decelerated grip strength decline, decreased gait speed decline, and faster chair rises after multiple-adjustment. Similarly, participants maintaining moderate- and high-active PA were also associated with a lower risk of incident frailty (multiple-adjusted hazard ratio 0.70 and 0.42 respectively), compared with those with persistently low PA. Notably, the participants with the increasing active trajectory got similar health benefits as those with persistently moderate and high levels of PA.

Thus in conclusion, in addition to persistent PA, increasing PA was linked to a slower decline in motor function and lower risk of incident frailty in the cohort. Our findings suggest that regular PA is never too late.

Targeting the Aging of the Immune System in the Context of Frailty

The immune system declines into a state of incapacity (immunosenescence) and chronic inflammation (inflammaging) with advancing age. Unresolved inflammatory signaling is disruptive of tissue function in many ways, from reduced stem cell activity to pathologically altered somatic cell behavior. It is thought to be important in the declining muscle mass and strength that contributes to age-related frailty. Thus addressing immune aging is a significant and important target in the treatment of aging as a whole.

Frailty is a highly prevalent geriatric syndrome that has attracted significant attention from physicians and researchers due to its associated increase in vulnerability and healthcare costs, especially in the elderly population. Generally, frail patients suffer from multiple chronic diseases, with comorbidities and polypharmacy greatly challenging their health management. Gerontologists suggest that targeting the common pathogenesis of comorbidities rather than a single disease is probably a better solution for older people. Multiple factors contribute to development of frailty with advancing age, thus the therapeutic target is diversed depends on specific condition. Nutrition supplements and physical exercise are proved to be helpful in preventing and treatment of frailty, however, valid pharmaceutical intervention is scarce.

Mesenchymal stem cells (MSCs) can exert regenerative effects and possess anti-inflammatory properties, offering a promising therapeutic strategy to address the pathophysiologic problems of frail syndrome. Currently, MSC therapy is undergoing phase I and II trials in human subjects to endorse the safety and efficacy of MSCs for aging frailty.

Numerous studies have shown that rapamycin and rapalogs, considered novel and promising longevity agents, can extend lifespan. Interestingly, these agents showed an immunosuppressive effect at high doses and an immune stimulatory effect at low doses. However, the reason for these immunity-boosting effects is unclear. The inhibition of mammalian target of rapamycin (mTORC1) is a possible explanation, as mTOR can regulate the STAT signaling pathway. A study showed a significant difference in STAT phosphorylation levels in the T cells of healthy people compared with unhealthy senescent people.

Senolytics are a novel type of agent. The interference of stem cell signaling pathways temporarily disables senescent cell anti-apoptotic pathway (SCAP), thus targeting selectively senescent cells. In addition to its main effect on clearing senescent cells, senolytics can also eliminate pro-inflammatory cytokines. According to the study, inflammation symptoms are relieved after the administration of senolytics. A recent study found reduced SASP and coronavirus-related mortality in old mice after the administration of senolytics.

A low level of nicotinamide adenine dinucleotide (NAD)+ is reportedly associated with the poor function of mitochondria and metabolic reprogramming of immune cells; therefore, NAD+ is also recognized as a therapeutic target for aging immunity. Promising data has demonstrated that administrating nicotinamide mononucleotide, the NAD+ precursor, into mice could maintain NAD+ levels and mitochondrial function, with the mitochondrial function of immunocytes being essential for controlling virus propagation.

A centenarian study revealed that longevity is associated with gut microbial structures, making individuals more potent against age-associated disorders and leading to a longer life. The microbiota-targeting probiotic and dietary interventions affect natural aging by enhancing oxidation resistance, regulating metabolism, suppressing chronic inflammation, and promoting immune homeostasis. Immunosenescence may have a certain influence on human microbial composition, function, and diversity. In addition, fecal microbiota transplantation or prebiotic/probiotic/synbiotic supplementation in the diet is beneficial for restoring active microbiota and extending a healthy lifespan. Thus, there are multiple ongoing developments in this field to ease the process of aging and reduce the risk of potential disabilities that could lead to a significant decrease in the quality of life of elderly individuals.

Link: https://doi.org/10.21037/atm-22-4405

mTOR in the Enhancement of Cancer Treatment Outcomes via Calorie Restriction

Calorie restriction, and related approaches such as protein restriction, tend to improve the outcomes for cancer patients, making cancers more vulnerable to therapies by reducing the normally rampant replication of cancer cells. Here, researchers explore the role of mTOR signaling in the mechanisms underlying this effect, finding the link between dietary intake of amino acids and mTOR activity in cell growth. Manipulating these mechanisms isn't enough on its own to deal with cancer, but there is a lot to be said for low cost improvements to the odds of success for patients undertaking any form of cancer therapy.

Researchers found in cells and in mice that a low-protein diet blocked the nutrient signaling pathway that fires up a master regulator of cancer growth. The regulator, mTORC1, controls how cells use nutritional signals to grow and multiply. It's highly active in cancers with certain mutations and is known to cause cancer to become resistant to standard treatments. A low-protein diet, and specifically a reduction in two key amino acids, changed the nutritional signals through a complex called GATOR.

GATOR1 and GATOR2 work together to keep mTORC1 in business. When a cell has plenty of nutrients, GATOR2 activates mTORC1. When nutrients are low, GATOR1 deactivates mTORC1. Limiting certain amino acids blocks this nutrient signaling. Previous efforts to block mTORC1 have focused on inhibiting its cancer-causing signals. But these inhibitors cause significant side effects - and when patients stop taking it, the cancer comes back. The study suggests that blocking the nutrient pathway by limiting amino acids through a low-protein diet offers an alternative way to shut down mTORC1.

Researchers confirmed their findings in cells and mice, where they saw that limiting amino acids stopped the cancer from growing and led to increased cell death. They also looked at tissue biopsies from patients with colon cancer, which confirmed high markers of mTORC correlated with more resistance to chemotherapy and worse outcomes.

Link: https://labblog.uofmhealth.org/lab-report/dietary-change-starves-cancer-cells-overcoming-treatment-resistance

First Generation Stem Cell and Exosome Therapies Promote Neurogenesis

First generation stem cell transplants have not as yet produced the reliably improved regeneration that was hoped for, but they do suppress chronic inflammation for some months. This effect is mediated by cell signaling on the part of the transplanted cells in the short time that they survive after transplantation. Much of that signaling is carried by exosomes and other classes of extracellular vesicle, and hence similar outcomes result from therapies based on delivery of exosomes harvested from cultured stem cells.

One of the effects of the unresolved inflammatory signaling characteristic of aging is a suppression of stem cell activity, such as in the cell populations responsible for producing new neurons in the brain. Neurogenesis is essential to brain maintenance, as well as memory and learning. From what is known to date, greater neurogenesis appears to be beneficial at any age. Thus one of the ways in which first generation stem cell and exosome therapies might act to improve cognitive function in older people is via suppression of inflammation leading to improved neurogenesis in the aging brain.

Mesenchymal stem cells and exosomes improve cognitive function in the aging brain by promoting neurogenesis

Brain aging is a significant cause of most neurodegenerative diseases and is often irreversible and lacks an effective treatment, leading to a dramatic decline in quality of life. As with other organ systems, brain function gradually declines during the aging, mainly in learning and memory functions. Some studies point out that age-related cognitive decline is characterized by a considerable reduction or even death of neurons in the brain. In the hippocampus (and perhaps in other brain areas), neuronal death can partially compensated by neuronal generation. However, neuronal production is significantly impaired with age. In the adult mammalian hippocampus, new neurons are derived from the stem cell and progenitor cell divisions, a process known as adult neurogenesis.

In recent years, evidence has accumulated that neurogenesis can restore a more youthful state during aging. In addition, increased adult neurogenesis contributes to a variety of human diseases, including cognitive impairment and neurodegenerative diseases. Neuroinflammation has been shown to alter neurogenesis in adults. Various inflammatory components, such as immune cells, cytokines, or chemokines, regulate neural stem cells' survival, proliferation, and maturation. During normal brain aging, increased inflammatory activity is caused by the activation of glial cells.

It has been shown that mesenchymal stem cells (MSCs) can stimulate neurogenesis and angiogenesis and delay neuronal cell death. At the same time, their secreted exosomes are smaller in size and cause less immune response in the body, which is a hot topic of current research. This manuscript describes how MSCs and their derived exosomes promote brain neurogenesis and thereby delay aging by improving brain inflammation.

Further Discussion of the Poor Evidence For Metformin to Even Mildly Slow Aging`

The problem with metformin as a drug to slow aging is that the evidece to support that use is very poor. In animal studies, the results are very unreliable, and the Interventions Testing Program found no effect in its highly overengineered studies. Further, the existing human data is not supportive, taken as a whole. Even if we did want to cherry pick the better data and be hopeful, the effect size compares unfavorably with that achieved through regular exercise, and further appears to be only achieved in people with the abnormal metabolism associated with obesity and diabetes. All of the work that was done to convince the FDA to endorse the TAME human clinical trial to test the ability of metformin to slow aging is useful, but the resulting agreement on trial structure should be applied to an intervention more likely to produce an outcome that is worth the effort, such as senolytic therapies.

The study that is most often cited as evidence that metformin slows the aging process in humans was released with a press release misleadingly titled "Type 2 diabetics can live longer than people without the disease." But the underlying study had a design flaw that first unintentionally selected only the healthiest diabetic patients (those on metformin) and compared them to patients with poorer glycemic control (those on other drugs) and a random assortment of the nondiabetic population - and then systematically pushed subjects on metformin "off the books" as soon as their diabetes progressed.

The same problem (or related ones) have plagued most of the observational studies that you may have heard cited as showing that metformin lowers the risk of atherosclerosis, total mortality, and especially cancer. Drawing inferences from such studies about effects on aging in otherwise-healthy people would thus be misguided even if these studies didn't share this design flaw, since none of these other studies include a separate group of people without diabetes. Rather, such studies have compared metformin-taking diabetic people to other people with diabetes taking other diabetic drugs. But actually, even in such diabetics-only studies, the apparent benefits of metformin vanish when the studies are designed to avoid survivorship bias and selection bias.

When put to the test in human trials, metformin has no effect on blood sugar control in obese women with normal glucose tolerance and only modest effects on fasting glucose in normal-weight, nondiabetic men. Similarly, exercise but not metformin tames glycemic variability (dangerously wide swings in blood sugar over the course of the day) in prediabetic people. And importantly, adding metformin to such lifestyle interventions doesn't lower the risk of developing diabetes any more than lifestyle all by itself.

You may be surprised to learn that there has already been a trial with followup that gives fairly long-term human data on mortality in a group of people who were not yet diabetic - and again, metformin came up short. This was report from the long-term follow-up of the Diabetes Prevention Program (DPP). The volunteers in the DPP were on average 50 years old, and all had prediabetes. The DPP itself lasted only 2.8 years, but the researchers followed up with the participants at 10, 15, and as much as 20 years later. And to get to the punchline, people who had been taking metformin lived no longer than people in the control group.

Link: https://www.sens.org/tame-attempt-slow-aging-part-2-human-studies-survival-risk-of-diabetes/

Gain or Loss of Specific Microbial Species May Be a Better Measure of Gut Microbiome Aging

It now costs little to determine the contents of the gut microbiome, producing a list of microbial species and their prevalence. Numerous companies offer this service. This data can be sliced in numerous ways, but as researchers note here, it is the gain and loss of specific populations with advancing age that produces contributions to aging. More general measures of diversity or change, those that give little to no weight to which specific microbial populations alter in abundance, do not produce good correlations with degenerative aging. It is important to consider the actions and mechanisms of specific microbes: are they causing chronic inflammation, are they generating beneficial or harmful metabolites, and so forth.

The gut microbiome is a modifier of disease risk because it interacts with nutrition, metabolism, immunity, and infection. Aging-related health loss has been correlated with transition to different microbiome states. There is broad consensus how the microbiome changes with age, but specific intervention targets are less clear. Moreover, terms like diversity, assumed by many to be desirable, and 'uniqueness', which has been cast as a marker of healthy aging, need greater precision and should not be used agnostic of the loss or gain of specific taxa in aging. Other summary statistics include different measures of uniqueness that capture specific aspects of gut microbiome variability and are calculated using different distance measures.

This study explored whether determining the gain or loss of specific taxa represent a more precise metric of healthy/unhealthy aging than summary microbiome statistics, such as diversity and uniqueness. We analyzed microbiome diversity and four measures of microbiome uniqueness in 21,000 gut microbiomes for their relationship with aging and health. We show that diversity and uniqueness measures are not synonymous; uniqueness is not a uniformly desirable feature of the aging microbiome, nor is it an accurate biomarker of healthy aging. Different measures of uniqueness show different associations with diversity and with markers of health and disease.

The study identifies that the gut microbiome alterations associated with both aging in general and unhealthy aging are characterized by a common theme: loss of the core microbiome structure (specifically a coabundant species-level guild of the core microbiome) and concomitant increase of a specific guild of disease-associated taxa.

Link: https://doi.org/10.1038/s43587-022-00306-9

Prodrugs As a Useful Approach to Targeting Distinctive Aspects of Cancer Metabolism

The goal of cancer research should be to produce a robust, highly effective universal cancer therapy, or as close to universal as possible. One treatment that can be deployed for every type of cancer, with a very good chance of inducing remission. Attempting to tackle cancer subtypes one by one based on their genetic peculiarities is simply not efficient enough to produce meaningful progress in our lifetimes. Further, most cancers are subject to high mutation rates, and in a sizable fraction of patients will prove to be quite capable of evolving immunity to any therapy that targets a non-essential aspect of cancer biochemistry.

Cancer cells as a class are metabolically very different from normal cells; they have to be in order to power the rampant growth characteristic of tumor tissue. This presents a broad area of discovery for the development of prodrugs, molecules in which a toxic drug is amended to become non-toxic in a way that can be reversed by the activity of enzymes present only in the the targeted cell populations. This in principle allows for any usefully toxic chemotherapeutic drug, of which there are many, to be amended into a non-toxic form that will be near entirely processed back into the original toxic drug only by cancer cells. Importantly, at least some prodrug strategies of this nature might be applicable to a broad range of cancers.

Researchers Design 'Prodrug' That Targets Cancer Cells' Big Appetite for Glutamine, Leaving Healthy Cells Unharmed

"Our goal was to modify an old cancer drug that had shown robust efficacy but was too toxic, especially to the gut, to be developed clinically. To do this, we used a prodrug approach." The newly modified prodrug takes advantage of a common property of cancer cells: a voracious appetite for an amino acid called glutamine, which is a critical building block for proteins, lipids, and nucleotides, as well as for energy formation. Rapidly growing cancer cells use a tremendous amount of glutamine, a phenomenon called "glutamine addiction," but other healthy cells with rapid turnover, like those lining the gut, also rely on glutamine.

"DRP-104 is a tumor-targeted prodrug of the glutamine mimic drug called DON (6-Diazo-5-Oxo-L-norleucine), which inhibits multiple glutamine-utilizing enzymes in cancer cells. Many early studies of DON showed it was robustly efficacious in people and mice, but its development was halted due to its toxicity to normal tissues, especially the gut. We added chemical groups, called promoieties, to DON that rendered it inactive in the body until it reached the tumor, where the promoieties were clipped off by enzymes that are abundant in the tumor but not in the gut."

Discovery of DRP-104, a tumor-targeted metabolic inhibitor prodrug

6-Diazo-5-oxo-l-norleucine (DON) is a glutamine antagonist that suppresses cancer cell metabolism but concurrently enhances the metabolic fitness of tumor CD8+ T cells. DON showed promising efficacy in clinical trials; however, its development was halted by dose-limiting gastrointestinal (GI) toxicities. Given its clinical potential, we designed DON peptide prodrugs and found DRP-104 [isopropyl(S)-2-((S)-2-acetamido-3-(1H-indol-3-yl)-propanamido)-6-diazo-5-oxo-hexanoate] that was preferentially bioactivated to DON in tumor while bioinactivated to an inert metabolite in GI tissues.

In drug distribution studies, DRP-104 delivered a prodigious 11-fold greater exposure of DON to tumor versus GI tissues. DRP-104 affected multiple metabolic pathways in tumor, including decreased glutamine flux into the TCA cycle. In efficacy studies, both DRP-104 and DON caused complete tumor regression; however, DRP-104 had a markedly improved tolerability profile. DRP-104's effect was CD8+ T cell dependent and resulted in robust immunologic memory. DRP-104 represents a first-in-class prodrug with differential metabolism in target versus toxicity tissue. DRP-104 is now in clinical trials under the FDA Fast Track designation.

Medin Amyloid May Be Important in Alzheimer's Disease

There are a score or so of proteins in the human body capable of producing amyloid when they misfold, by encouraging other molecules of the same protein to misfold in the same way, linking together to produce solid deposits in and around cells. Only those amyloids for which there is clear evidence of disease association or toxicity to cells have been well studied, unfortunately. That doesn't mean that the others are harmless! As demonstrated here, it may just be the case that researchers have to look a little harder to find the ways in which these amyloids are causing pathology in older people.

Medin belongs to the group of amyloids. Of these proteins, amyloid-β is best known because it clumps together in the brains of Alzheimer's patients. These aggregates then deposit both as so-called plaques directly in the brain tissue, but also in its blood vessels, thereby damaging the nerve cells and the blood vessels, respectively. But while many studies have focused on amyloid-β, medin has not been a focus of interest.

However, medin is actually found in the blood vessels of almost everybody over 50 years of age, making it the most common amyloid known. Medin even develops in aging mice. The older the mice get, the more medin accumulates in the blood vessels of their brains. What's more, when the brain becomes active and triggers an increase in blood supply, vessels with medin deposits expand more slowly than those without medin. This ability of blood vessels to expand, however, is important to optimally supply the brain with oxygen and nutrients.

Now researchers were able to show in Alzheimer's mouse models that medin accumulates even more strongly in the brain's blood vessels if amyloid-β deposits are also present. Importantly, these findings were confirmed when brain tissue from organ donors with Alzheimer's dementia was analysed. However, when mice were genetically modified to prevent medin formation, significantly fewer amyloid-β deposits developed, and as a result, less damage to blood vessels occurred. "There are only a handful of research groups worldwide working on medin at all. We have now been able to show through many experiments that medin actually promotes vascular pathology in Alzheimer's models, and this indicates that medin is one of the causes of the disease."

Link: https://www.dzne.de/en/news/press-releases/press/new-target-for-alzheimers-therapies-found/

IGF1 Gene Therapy as a Neuroprotective Treatment, Slowing Female Reproductive Aging

Researchers here describe an interesting approach to slowing aspects of neurodegeneration that contribute to, among other things, female reproductive aging. That is the focus of this paper, but numerous other aspects of the aging brain are also involved. IGF1 is well studied in the context of aging, and manipulation of the signaling pathways linking insulin, IGF1, and growth hormone has been shown to extend life span in a number of species. Where we can make direct comparisons between mice and humans, such as between growth hormone receptor knockout mice and humans with Laron syndrome, the effects are nowhere near as large. Suppression of growth hormone signaling can extend life by 70% or so in mice, but Laron syndrome doesn't appear to make humans live meaningfully longer. Many approaches to slowing aging have much larger effects in short-lived mammals than they do in long-lived mammals.

The inflammatory environment characteristic of the aged brain is caused by activation of glial cells, mainly microglia. Several studies report that neuroinflammation leads to reduced gonadotropin-releasing hormone (GnRH) secretion, which is associated with multiple aging-related physiological changes, including bone loss, skin atrophy, muscle weakness, and memory loss. Indeed, GnRH administration amend aging-impaired neurogenesis and decelerates aging in mice. In addition, the same authors also describe that inhibition of NF-κB-directed immunity, specifically in hypothalamic microglia cells, has an anti-aging effect.

GnRH secretion is regulated by hormonal and environmental signals such as kisspeptin. This peptide plays a critical role in controlling the onset of puberty and reproductive function in adulthood. There are two populations of kisspeptin neurons, one in the anteroventral periventricular nucleus (AVPV) and one in the arcuate nucleus (Arc), that are targets of positive and negative feedback regulation of estrogen, respectively. Aging female rats transition from regular to irregular estrus cycles, constant estrus, and finally to an anestrus stage. Changes within the hypothalamic-pituitary-ovarian axis, manifested by altered secretion of neurotransmitters, altered secretion of pituitary hormones and altered follicular development and steroid content, lead to the final cessation of reproductive cycles. These processes that lead to reproductive senescence are associated with an increase in circulating cytokines and proinflammatory markers produced by microglial cells. Indeed, several studies describe that hypothalamic and systemic inflammation affect kisspeptin neurons, which are responsible for regulating GnRH neurons.

IGF1 is a neurotrophic factor with an outstanding neuroprotective action in the central nervous system. Previous studies of our group showed that intraparenchymal hypothalamic IGF1 gene therapy was capable to prolong the operation of reproductive cycles in rats. Indeed, we have demonstrated that intracerebroventricular IGF1 gene therapy restores motor performance and generates cognitive and morphological changes in the dorsal hippocampus in senile rats. In addition, we have reported that IGF1 gene therapy modifies microglia number and phenotype in senile rats and decreases astrocytic inflammatory response in vitro, supporting the extensive idea that IGF1 plays a potent anti-inflammatory effect.

The aim of the present study is to investigate the effect of IGF1 gene therapy on estrous cycle, kisspeptin, and GnRH neurons, and microglial cells in middle-aged female rats. Our data indicate that IGF1 gene therapy prolongs the operation of reproductive cycles in middle-aged rats by modulating kisspeptin/GnRH secretion in the hypothalamus and altering microglial cell number and reactivity. Based on our findings, we propose IGF1 gene therapy to delay reproductive senescence as a potential strategy to optimize lifespan and combat age-related health problems in women.

Link: https://doi.org/10.18632/aging.204360

The Realization that Developing Rejuvenation Therapies is the Most Useful Thing One Can Do with Great Wealth

A core point regarding wealth, realized by many but only acted on by a few to date, is that being the wealthiest individual in the graveyard begins to look very foolish in an era in which research and development is producing the basis for rejuvenation therapies. Historically, people traded time for wealth. Now, we enter the start of the era in which people can trade wealth for time. Fortunately, this is a collaborative venture: no-one wins on their own. Either sufficient funding is devoted to the right projects in rejuvenation biotechnology, and all humanity benefits as a result, or we as a society collectively fail to achieve that goal.

Another important point made in this article is that it is challenging for outsiders to make sense of a field of endeavor in which half of the participants appear, on the surface at least, to be modernized versions of 1970s snake oil supplement salespeople, along with a good scattering of eccentric or fraudulent larger than life characters, as well as unhelpful ventures that are clearly chasing or talking up the hype of a longevity industry while providing nothing of any great value.

How does a layperson pick out the legitimate, exciting science of rejuvenation, such as senolytic therapies, or epigenetic reprogramming, from the garbage that is discussed and marketed in exactly the same terms? Eventually the good drives out the bad, but for now we're still stuck with a mess of alchemists pretending to be scientists, alongside supplement salespeople making hay while the sun shines, siphoning attention and funding away from actually valuable projects.

Inside the billion-dollar meeting for the mega-rich who want to live forever

The super-rich eventually reach a point where having more money doesn't improve their lives very much. "If you buy a yacht, you can always get a bigger yacht; if you buy a plane, you can always get a bigger plane. But the extent to which your life is changing with more money is actually very minimal." It makes more sense to direct funds to being healthier and living longer. Such deep-pocketed individuals and groups are looking to be the biggest investors in longevity research. Most of the $4.4 billion invested over the last five years into understanding whether or not reprogramming our cells might help us live longer has gone into Altos Labs, a biotech company whose funders are thought to include Jeff Bezos and Yuri Milner.

A sense of hope and optimism was palpable at the Longevity Investors Conference. I got the impression that most people believed that, with enough funding, positive scientific results were just a few years away. And with that, we'd be on the road to reliably extending human healthspan. The presenters were a mix of longtime academics, biotech startups, and people selling the idea of longevity as a high-end luxury good for those who frequent spas and lavish retreats. Some have been studying the biology of aging for decades, and are well-respected among their peers. But I also met a young man who told me that breathing low-oxygen air could benefit multiple aspects of my health - and who then commented that he "didn't believe" in covid vaccines. A 67-year-old man took to the stage to tell us that, since he'd been taking his own supplement, his biological age had reversed, and he was now biologically only 49 years old.

How is an investor - or anyone else, for that matter - meant to make sense of all these claims? Ask an academic, and they'll tell you that the answer is education-the more people know about the biology of aging and how clinical trials work, the better placed they are to work out how much faith to put in any claim. Many agree that it's the wild claims made by some - claims that we could live to be a thousand years old, or avoid death entirely - that have helped bring attention and investment to the field. But they have also tarnished its reputation as a scientific discipline.

Others say that while there's more hype in biotech than academia, they thinks that any hype tends to be short-lived. "If you're selling hot air, you can't get away with doing that for very long." I've been writing about the science of aging for over a decade myself, and I'm not sure I fully agree with him. I've seen shoddy science get plenty of press attention. I've seen smart scientists fall prey to flimsy claims about health-extending supplements. But I've also seen some fascinating and tantalizing research - enough to want to follow it through and find out if these approaches really will be as beneficial for people as they are for lab animals.