Mitochondrially Targeted Hydrogen Sulfide Delivery Molecules Slow Photoaging

Researchers here demonstrate that molecules designed to supply hydrogen sulfide to mitochondria in skin cells can slow the progression of photoaging, the damage done to skin tissue by UV radiation. This offers some insight into the role of mitochondria in the reaction to UV radiation that produces lasting structural damage in skin. The publicity materials speculate on the ability to reverse existing photoaging damage, but that is unsupported by the work presented in the paper, which only shows the outcome of the topical application of the treatment to skin prior to exposure to ultraviolet radiation.

Two new molecules, AP39 and AP123, that generate minute amounts of the gas hydrogen sulfide have been found to prevent skin from ageing after being exposed to ultraviolet light found in sunlight. Researchers exposed adult human skin cells and the skin of mice to ultraviolet radiation (UVA). UVA is the part of natural sunlight which damages unprotected skin and can penetrate through windows, and even through some clothes. It causes skin to age prematurely by turning on skin digesting enzymes called collagenases. These enzymes eat away at the natural collagen, causing the skin to lose elasticity and sag, resulting in wrinkles

In the experiments, the compounds AP39 and AP123 did not protect the skin in the same way traditional sun creams prevent sunburn, but instead penetrated the skin to correct how skin cells' energy production and usage was turned off by UVA exposure. This then prevented the activation of skin-degrading collagenase enzymes and subsequent skin damage.

The compounds AP39 and AP123 specifically target the energy generating machinery inside our cells, the mitochondria, and supply them with minute quantities of alternative fuel, hydrogen sulfide, to use when skin cells are stressed by UVA. The direct result of this was the activation of two protective mechanisms. One is a protein call PGC-1α, which controls mitochondria number inside cells and regulates energy balance. The other is Nrf2, which turns on a set of protective genes that mitigate UVA damage to skin and turn off the production of collagenase, the main enzyme that breaks down collagen in damaged skin tissue and causes skin to look significantly more "aged".

Link: https://www.exeter.ac.uk/research/news/articles/newdrugmoleculescouldprev.html

Reviewing What is Known of the Biochemistry of Blood-Brain Barrier Dysfunction in Aging

Blood vessels passing through the central nervous system are sheathed by specialized cells that form the blood-brain barrier. The barrier controls the passage of cells and molecules into the brain. This protection is essential to the normal function of the brain, which operates in a biological environment that is very different to that of the result of the body. Unfortunately, and like all systems in the body, the blood-brain barrier deteriorates with age. This allows harmful molecules and cells to leak into the brain, provoking a damaging state of chronic inflammation in brain tissue. Inflammation is thought to be an important component of age-related neurodegenerative conditions, and to the degree that blood-brain barrier dysfunction contributes to the overall state of inflammation in brain tissue, it can be considered one of the important causes of neurodegeneration.

What to do about this problem? There is the question. The blood-brain barrier is a complex system, and thus its failure is also complex, when considered in detail. As is the case for much of aging, it is presently somewhere between challenging and impossible to accurately assess the relative importance of the many changes, failures, and forms of damage that can be measured in the cells of the blood-brain barrier. Even determining the direction of cause and effect for a few of these line items can be a hard task, an undertaking of years for teams of scientists. This is why the easier path to knowledge is to start with what is known of the root causes of aging, attempt to repair those causes one by one, and then observe the results on the dysfunction of critical biological systems such as the blood-brain barrier.

For example, senescent cells that accumulate in old tissues can now be cleared to a sizable degree via the application of senolytic therapies. Will this help to restore lost blood-brain barrier integrity? If so, it is then possible to look at specific differences before and after treatment in order to ask why this outcome the case. That may then inform researchers about the arrangement and relationships of blood-brain barrier pathologies in a more general sense. A working, narrowly focused rejuvenation therapy is the best of tools with which to explore the details of the aging process.

Blood-Brain Barrier Breakdown: An Emerging Biomarker of Cognitive Impairment in Normal Aging and Dementia

Blood vessels are essential to transport oxygen and nutrients, remove CO2 and other waste products, and, thus, maintain homeostasis in the body. Blood vessels that vascularize the central nervous system (CNS) acquire specific anatomical and functional characteristics that collectively form the blood-brain barrier (BBB). At the cellular level, the BBB is developed by continuous non-fenestrated endothelial cells (ECs) encompassed by pericytes, smooth muscle cells, astrocytes, microglia, oligodendroglia, and neurons that are altogether called the neurovascular unit (NVU). At the molecular level, the BBB ECs are compacted by claudins, occludins, and ZO-1 [tight junction (TJ) proteins] and junction adhesion molecule (JAM) proteins to restrict the paracellular and transcellular diffusion of molecules in the CNS.

In addition, the BBB ECs mediate influx transporters to select metabolite uptake from the blood and efflux transporters to remove toxins and waste products from the brain into the blood. In BBB ECs, leukocyte adhesion molecules (LAMs) express very low to suppress immune surveillance in the brain. Thus, the BBB confines the access of neurotoxic compounds, blood cells, and pathogens to the brain. In addition, the BBB sustains the homeostasis of the brain through tight regulation of the transport of molecules between the brain parenchyma and peripheral circulation.

Hence, the BBB is a fundamental and crucial element of normal and healthy brain function. Any impairment in the cellular or molecular components causes BBB breakdown that results in BBB dysfunction. Aging is one of several factors involved in the breaking of the BBB and was first observed in aged patients reported in the 1970s. In dysfunctional BBBs, the possibility of permeability increases; thus, toxic and blood-borne inflammatory substances that infiltrate the brain could change the biochemical microenvironment of the neurons, thus leading to neurodegenerative diseases and dementia. It has been reported that BBB disruption in aged people is strongly related to Alzheimer's disease (AD) and cognitive impairment.

Although researchers have reported the contributions of BBB disruption to the pathogenesis of cognitive impairment associated with normal aging and dementia, more research is needed to elucidate the precisely causing factors and the cellular and molecular mechanisms of BBB maintenance, breakdown, and repair correlated with neurodegeneration and cognition decline. In the future, how aging and dementia affect BBB function in health and disease state, thus leading to neurodegeneration and cognitive impairment, should be explored in living organisms. Clinical research pertaining to this will boost our knowledge and help us better understand the association between BBB breakdown and cognitive decline. Such studies pave the way for the use of the BBB as a novel biomarker and therapeutic target to treat dementia and other neurological diseases associated with cognitive impairment.

Identifying Age-Related Epigenetic Changes Related to Reduced Function in Mesenchymal Stem Cells

Stem cells maintain tissue by providing a supply of daughter somatic cells to replace losses. This stem cell activity declines with age, and a sizable fraction of that decline in the most studied populations appears to be a reaction to the aged signaling environment rather than intrinsic dysfunction, at least in earlier old age. The behavior of cells lacking damage is controlled by their epigenetic state, alterations to the genomic machinery that governs the production of specific proteins. Could long term health be significantly improved by altering the epigenetic state of old stem cells, overriding their reaction to the aged tissue environment, and maintaining function at youthful levels? The consensus view of stem cell aging is that loss of function is an evolved response that serves to minimize cancer risk, but equally the evidence to date from animal studies suggests that there is considerable room to improve stem cell function and tissue maintenance in later life without greatly raising cancer risk.

Researchers have been looking at epigenetics as a cause of ageing processes for some time. Epigenetics looks at changes in genetic information and chromosomes that do not alter the sequence of the genes themselves, but do affect their activity. One possibility is changes in proteins called histones, which package the DNA in our cells and thus control access to DNA. A research group has now studied the epigenome of mesenchymal stem cells. These stem cells are found in bone marrow and can give rise to different types of cells such as cartilage, bone, and fat cells.

"We wanted to know why these stem cells produce less material for the development and maintenance of bones as we age, causing more and more fat to accumulate in the bone marrow. To do this, we compared the epigenome of stem cells from young and old mice. We could see that the epigenome changes significantly with age. Genes that are important for bone production are particularly affected."

The researchers then investigated whether the epigenome of stem cells could be rejuvenated. To do this, they treated isolated stem cells from mouse bone marrow with a nutrient solution which contained sodium acetate. The cell converts the acetate into a building block that enzymes can attach to histones to increase access to genes, thereby boosting their activity. The treatment caused the epigenome to rejuvenate, improving stem cell activity and leading to higher production of bone cells. To clarify whether this change in the epigenome could also be the cause of the increased risk in old age for bone fractures or osteoporosis in humans, the researchers studied human mesenchymal stem cells from patients after hip surgery. The cells from elderly patients who also suffered from osteoporosis showed the same epigenetic changes as previously observed in the mice.

Link: https://www.mpg.de/17468019/fountain-of-youth-for-ageing-stem-cells-in-bone-marrow

A Demonstration of Artificial Mitochondria Capable of Generating Adenosine Triphosphate to Support Cell Function

Researchers here demonstrate the creation of artificial pseudo-organelles capable of generating adenosine triphosphate (ATP). ATP is a chemical energy store molecule that is produced by mitochondria. It is vital to cell function. Mitochondrial production of ATP falters with age, as well as in tissues that become poorly supplied with nutrients. Finding a way to provide additional ATP could be quite helpful as a compensatory therapy, though whether or not a constant oversupply of ATP has meaningful negative consequences will have to be explored in greater detail than has been the case to date.

Cells have small compartments known as organelles to perform complex biochemical reactions. These compartments have multiple enzymes that work together to execute important cellular functions. Research have now successfully mimicked these nano spatial compartments to create 'artificial mitochondria'. This was achieved through reprogramming of 'exosomes', which are small vesicles (diameter ~120 nm) that cells use for intercellular signaling. The researchers carried out the experiments using microfluidic droplet reactors, which generated small droplets that were of similar size as typical cells. The researchers first aimed to facilitate controlled fusion of these exosomes within the droplets while preventing unwanted fusions.

These customized exosomes were then preloaded with different reactants and enzymes, which turned them into biomimetic nano factories. The team demonstrated this multienzyme biocatalytic cascade function by encapsulating glucose oxidase (GOx) and horseradish peroxidase (HRP) inside the exosomes. The GOx first converts glucose into gluconic acid and hydrogen peroxide. The HRP in turn uses the hydrogen peroxide generated in the first reaction to oxidize Amplex Red to a fluorescent product, resorufin. Next, the researchers wanted to know exactly how well these mini reactors can be uptaken and internalized by the cells. The cells derived from human breast tissues were fed with fused exosome nanoreactors, and their internalization over the next 48 hours was observed. It was found that cells were able to uptake these customized exosomes primarily through endocytosis, along with multiple other mechanisms.

Armed with this knowledge, the team sought to create functional artificial mitochondria that are capable of producing energy inside the cells. To achieve this, ATP synthase and bo3 oxidase were reconstituted into the earlier exosomes containing GOx and HRP, respectively. These exosomes were in turn fused to create nanoreactors that can produce ATP using glucose and dithiothreitol (DTT). It was found that the fused exosomes were capable of penetrating deep into the core part of a solid spheroid tissue and produce ATP in its hypoxic environment.

Link: https://www.ibs.re.kr/cop/bbs/BBSMSTR_000000000738/selectBoardArticle.do?nttId=20413

Hyperbaric Oxygen Treatment Improves Cerebral Blood Flow and Cognitive Function in Old People

In today's open access paper, researchers report a modest improvement in cerebral blood flow and cognitive performance in a small study of older individuals suffering cognitive impairment as a result of sustained hyperbaric oxygen treatment over a period of months. This seems a compensatory approach to therapy, in that improvements in cerebral blood flow should be expected to improve cognitive function at any age. This is the mechanism by which exercise rapidly improves memory function, for example. A direct comparison of hyperbaric oxygen treatment and exercise would be interesting.

This result might help to inform discussions of the degree to which loss of blood supply to the brain contributes to cognitive decline in patients diagnosed with neurodegenerative conditions. Vascular dementia is an acknowledged and well-researched condition, but to what degree is the impairment of Alzheimer's patients at various stages due to vascular aging and consequent reduced blood flow to the brain, versus the harmful protein aggregation and neuroinflammation characteristic of Alzheimer's? Absent a way to remove just one of these pathologies, it is hard to answer that question.

It is worth noting that this study was conducted and published by the same groups who put together the poor study and accompanying overhyped media materials regarding the effects of hyperbaric oxygen treatment on measures of metabolism related to aging. It is most likely a good idea to treat this and any future work conducted by these researchers with an appropriately greater level of scrutiny and skepticism.

Hyperbaric oxygen therapy alleviates vascular dysfunction and amyloid burden in an Alzheimer's disease mouse model and in elderly patients

Vascular dysfunction is entwined with aging and the pathogenesis of Alzheimer's disease (AD), and contributes to reduced cerebral blood flow (CBF) and consequently, hypoxia. Hyperbaric oxygen therapy (HBOT) is in clinical use for a wide range of medical conditions. In the current study, we exposed 5XFAD mice, a well-studied AD model that presents impaired cognitive abilities, to HBOT and then investigated the therapeutical effects. HBOT increased arteriolar luminal diameter and elevated CBF, thus contributing to reduced hypoxia. Furthermore, HBOT reduced amyloid burden by reducing the volume of pre-existing plaques and attenuating the formation of new ones. This was associated with changes in amyloid precursor protein processing, elevated degradation and clearance of amyloid-ß protein and improved behavior of 5XFAD mice. Hence, our findings are consistent with the effects of HBOT being mediated partially through a persistent structural change in blood vessels that reduces brain hypoxia.

To understand whether the ability of HBOT to change CBF and affect cognitive function also applied to elderly people, we performed a human study in which six elderly patients (age 70.00 ± 2.68 years) with significant memory loss at baseline (memory domain score < 100) were treated with HBOT (60 daily HBOT sessions within 3 months). CBF and cognitive function were evaluated before and after HBOT. CBF was measured by MRI, while cognitive functions were evaluated using computerized cognitive tests. Following HBOT, there were significant CBF increases in several brain areas.

At baseline, patients attained a mean global cognitive score (102.4±7.3) similar to the average score in the general population normalized for age and education level (100), while memory scores were significantly lower (86.6 ± 9.2). Cognitive assessment following HBOT revealed a significant increase in the global cognitive score (102.4 ± 7.3 to 109.5 ± 5.8), where memory, attention and information processing speed domain scores were the most ameliorated. Moreover, post-HBOT mean memory scores improved to the mean score (100.9 ± 7.8), normalized per age and education level (100). The improvements in these scores correlate with improved short and working memory, and reduced times of calculation and response, as well as increased capacity to choose and concentrate on a relevant stimulus.

Are Gene Variant Interactions a Better Approach to Determining the Contribution of Genetics to Longevity?

The analysis of the effects of genetic variants on human life expectancy has employed ever large databases in recent years: more genes, more sequences, more people. As the data grows, the likely size of the effect of genetic variation on human longevity has become smaller. Outside of a few interesting genes, such as those relating to blood cholesterol levels and cardiovascular disease risk, he picture is one of countless variants with small, interacting, environment-dependent effects, different in every study population.

How much of this picture is a true assessment versus a consequence of larger effects being hidden in the interactions between gene variants? Past studies have near all focused on a variant by variant analysis, considering each variant alone - and so this is an interesting question. Interesting or not, it remains the case that there may be no practical application here, however. Old people are still aged, damaged, and increasingly frail, whether or not they carry rare gene variants associated with longevity. Finding ways to emulate survivors to old age is an inherently poor approach to the treatment of aging, at least in comparison to working towards the repair of the underlying molecular damage that causes aging, in order to produce rejuvenation.

A major goal of aging research is identifying genetic targets that could be used to slow or reverse aging - changes in the body and extend limits of human lifespan. However, the majority of genes that showed the anti-aging and pro-survival effects in animal models were not replicated in humans, with few exceptions. Potential reasons for this lack of translation include a highly conditional character of genetic influence on lifespan, and its heterogeneity, meaning that better survival may be result of not only activity of individual genes, but also gene-environment and gene-gene interactions, among other factors.

In this paper, we explored associations of genetic interactions with human lifespan. We selected candidate genes from well-known aging pathways (IGF1/FOXO growth signaling, P53/P16 apoptosis/senescence, and mTOR/SK6 autophagy and survival) that jointly decide on outcomes of cell responses to stress and damage, and so could be prone to interactions. We estimated associations of pairwise statistical epistasis between SNPs in these genes with survival to age 85+ in the Atherosclerosis Risk in Communities study, and found significant effects of interactions between SNPs in IGF1R, TGFBR2, and BCL2 on survival to age 85 and older. We validated these findings in the Cardiovascular Health Study sample, using survival to age 85+, and to the 90th percentile, as outcomes.

Our results show that interactions between SNPs in genes from the aging pathways influence survival more significantly than individual SNPs in the same genes, which may contribute to heterogeneity of lifespan, and to lack of animal to human translation in aging research.

Link: https://doi.org/10.3389/fcell.2021.692020

A Trend Towards Increased Proteostasis in Longer-Lived Mammalian Species

Researchers here report on a broad comparison of protein sequences across many mammalian species, conducted in order to search for small differences between individual proteins that correlate with species life span. They find that humans, as one of the longer-lived mammals, already have most of these differences present across most of the the population. Further, the nature of these differences between proteins, meaning the specific functions of differing proteins in cell metabolism, is argued to support the hypothesis that quality control processes responsible for maintaining protein structure and removing damaged proteins make a sizable contribution to species differences in life span.

A key mechanism that may contribute to differences in lifespan between species is the maintenance of the proteostasis network. Protein stability or proteostasis refers to the capacity to protect protein structures and functions against environmental stressors, including aging. In fact, dysfunction of the protein quality control mechanisms is a hallmark of aging and there is substantial evidence linking proteostasis and longevity. For instance, improved protein stability is determinant for longevity in exceptionally long-lived mollusks and in the naked mole-rat, the longest-living rodent. In addition, interventions that enhance proteome stability can improve health or increase lifespan in model organisms, such as pharmacological chaperones that have been investigated as potential therapeutic targets to reduce the adverse effects of misfolding of aging-related proteins.

A mammalian-wide study of the genomic underpinnings of lifespan has never been carried out with the combined goals of identifying individual mutations linked to longevity; analyzing the functional properties of their genes and the pathways in which they take part; and studying how the stability of proteins coded by these genes may differentiate long- and short-lived species. Here, we performed the largest phylogeny-based genome-phenotype analysis to date, focusing on the detection of individual mutations and genes that underlie the enormous variation of lifespan in mammals. We report the discovery of more than 2,000 longevity-related genes and show that, overall, they present a trend towards increased protein stability in long-lived organisms. In addition, we successfully show that our findings enhance the interpretation of the results of longevity genome-wide association studies that have been carried out in humans.

We discovered a total of 2,737 single amino acid differences (AA) in 2,004 genes that distinguish long- and short-lived mammals, significantly more than expected by chance. These genes belong to pathways involved in regulating lifespan, such as inflammatory response and hemostasis. Among them, a total 1,157 AA showed a significant association with maximum lifespan in a phylogenetic test. Interestingly, most of the detected AA positions do not vary in extant human populations (81.2%) or have allele frequencies below 1% (99.78%). Consequently, almost none of these putatively important variants could have been detected by genome-wide association studies. Additionally, we identified four more genes whose rate of protein evolution correlated with longevity in mammals. Crucially, SNPs located in the detected genes explain a larger fraction of human lifespan heritability than expected, successfully demonstrating for the first time that comparative genomics can be used to enhance interpretation of human genome-wide association studies. Finally, we show that the human longevity-associated proteins are significantly more stable than the orthologous proteins from short-lived mammals, strongly suggesting that general protein stability is linked to increased lifespan.

Link: https://doi.org/10.1093/molbev/msab219

Cellular Reprogramming, and the Goal of Separating Dedifferentiation from Epigenetic Rejuvenation

Rejuvenation takes place very early in embryonic development. The germline cells that go into the creation of an embryo are well protected and maintained in comparison to the average somatic cell in the adult body. Nonetheless, there is an accumulation of age-related epigenetic changes and molecular damage. Cells purge themselves of as much of this change and damage as possible, in order to ensure that the young are born with young somatic cells and tissues. This is primarily a resetting of epigenetic controls over gene expression, decorations on the structure of the genome that control shape and access to specific genes by the molecular machinery responsible for producing proteins from genetic blueprints.

A cell is a state machine, largely governed in operation by the matter of which proteins are produced, and in what quantities. Not completely governed: some damage, such as mutations to nuclear DNA, is irreversible. Some molecular waste cannot be managed even by cells in a youthful epigenetic state, and will degrade normal function. In a collection of replicating cells, that waste can be diluted via cell division, or even passed off entirely to a sacrificial daughter cell in a process of asymmetric division. So long as no one cell or small number of cells are vital, even serious mutation can be evaded by replication, provided that mutated cells are rejected. This is how single celled life, such as bacteria, can continue indefinitely. Further, a few lower organisms, such as the hydra, essentially a tiny bundle of stem cells in which every structure is replaceable, use this strategy in order to achieve individual immortality. Higher animals, with complex central nervous systems that include many non-replicating cells that cannot be sacrificed, cannot use this strategy, and so suffer from degenerative aging.

Embryonic rejuvenation is a process that can be understood, induced, and manipulated. The creation of induced pluripotent stem cells from normal adult somatic cells via reprogramming is one example of what becomes possible given sufficient knowledge and technical aptitude. This combines, in the same way as occurs in the early embryo, both an epigenetic reset and loss of somatic cell state, such as the shape and function of a skin cell or a brain cell, producing dedifferentiation into a pluripotent stem cell state. Researchers are presently looking beyond experiments in cell cultures towards the application of reprogramming in living animals. An epigenetic reset is a desirable outcome for somatic tissues throughout the aged body, likely able to reverse to some degree many age-related issues, such as loss of mitochondrial function. Dedifferentiation of somatic cells in an adult individual, on the other hand, is a roadblock and a challenge. It will lead to cancer where it occurs to a lesser degree, and it will cause pathology and death if prevalent. Differentiated cell state is vital to normal tissue function.

Thus an important question currently under investigation is whether or not these two aspects of reprogramming are inseparable. Is there an approach to reprogramming that will produce maximal epigenetic rejuvenation with minimal dedifferentiation? If so, that could prove to the the basis for a very useful approach to the treatment of aging. It likely cannot help much in the case of stochastic nuclear DNA damage leading to somatic mosaicism, and it cannot help with the accumulation of some forms of persistent molecular waste in long-lived cells, but it could nonetheless be beneficial enough to be interesting.

Cellular reprogramming and epigenetic rejuvenation

A recent addition to the anti-ageing strategies being developed comes from cellular reprogramming approaches. Induced pluripotency studies provided evidence that age-related cellular phenotypes such as mitochondrial morphology, function and number, as well as nuclear envelope integrity, are not irreversible. However, developmental cellular reprogramming turns a cell to a pluripotent state, where it has the potential to generate any somatic cell type. This process is not appropriate for an anti-ageing therapy in vivo because it requires not only the loss of the original cellular identity, but also the re-establishment of self-renewal capabilities. Therefore, induction of pluripotency or the direct injection of pluripotent cells in vivo, invariably lead to cancer in mice. For a cellular reprogramming-based intervention to be considered rejuvenative (turning an old cell into a younger cell), we need to uncouple its effects from dedifferentiation (loss of somatic cell identity).

Cellular reprogramming has demonstrated potential not only in regenerative medicine, but also in the ageing field through the amelioration of both physiological and cellular ageing hallmarks. While partial reprogramming might be used as a catch-all term to describe this type of rejuvenation, it does not reflect the fact that the described interrupted cellular reprogramming techniques are applied with the aim of (epigenetic) rejuvenation as opposed to inducing pluripotency (loss of cell identity). Reprogramming-induced rejuvenation (RIR) is a better term, capturing the nature of the utilised process and final aim of the interventions.

RIR has shown promise as a treatment to safely reverse ageing whilst retaining the ability to revert to or maintain original cell identity, both in vivo and in vitro. However, the precise nature of RIR still needs to be fully understood before it can be safely implemented as an anti-ageing treatment. For example, tracking any traces of pluripotency in partially reprogrammed cells (particularly in vivo) is a necessary precaution to minimise long-term cancer risk. Additionally, can rejuvenated partially reprogrammed cells be cultured long-term? The rejuvenated phenotype of some OSKM-treated cells lasts at least four weeks, but does this phenotype remain stable or eventually start to deteriorate at a rate faster than normal ageing?

Other important RIR safety concerns include how the reprogramming factors are introduced in vivo. Retroviruses are commonly used to integrate reprogramming factors into the genome. However, this method bears risks, such as insertional mutagenesis, residual expression and re-activation of reprogramming factors, and retrotransposon activation, all of which could increase cancer risk in vivo. Non-integrative delivery methods, such as transient transfection, non-integrating viral vectors, and RNA transfection are safer alternatives. For example, researchers have successfully used mRNA transfection to non-integratively conduct RIR. Another safe alternative is chemical-based reprogramming, which involves direct conversion of a somatic cell to a pluripotent state by use of small molecules and growth factors. It is conceivable that, in the future, chemical-based reprogramming could be adapted to achieve rejuvenation, however, this reprogramming approach currently only works for mice.

While RIR applied to skeletal muscle stem cells appears effective in improving regenerative capacity and muscle function in immunocompromised mice, further analysis is required regarding the somatic mosaicism of partially reprogrammed stem cells. Somatic variants at a stem or early progenitor cell level in turn can cause lineage bias, reduced stem cell function, and increased risk of developing haematologic cancer (e.g. age-related clonal haematopoesis). This can lead to the development of pre-malignant cells, which have a higher propensity to transform to a malignant state, the effect of which could be attenuated or exacerbated by RIR.

It also remains to be further explored whether and how RIR would work on post-mitotic terminally differentiated cells, such as neurons, cardiomyocytes, or adipocytes, but also other non-dividing cells such as quiescent or senescent cells. Pilot work has been done in the latter two states, demonstrating that a rejuvenated phenotype is achievable after restoration of cell division. These results may point to a scenario where proliferation is an essential requirement for rejuvenation. Indeed, induced pluripotency of postnatal neurons was only possible after forced cell proliferation via p53 expression. Coincidentally, the natural rejuvenation event in the early mouse embryo spans over stages of very active cell proliferation.

Overall, RIR is currently the best prospect to achieve epigenetic rejuvenation. Further studies are required to fully determine its limitations and efficacy.

Towards the Regeneration of Hair Cells to Restore Lost Hearing

Loss of hair cells in the inner ear is thought to be the primary mechanism behind the progression of age-related hearing loss, though there is some debate over whether it is in fact loss of cells versus loss of the connections that link hair cells to the brain. For some years, the research community has investigated whether or not it is possible to generate new hair cells in a living animal, bypassing the usual inability to replace losses in this cell population. Various approaches to signaling and cell therapy have been attempted, but despite interesting technology demonstrations, there is as yet little progress towards clinical translation of this research.

Various mechanisms can cause sensorineural hearing loss, among which irreversible damage to inner ear hair cells is the main cause. Although the commonly used hearing aids and cochlear implants in clinical practice improve the hearing of patients, their effect depends on the quantity and quality of residual hair cells and spiral neurons. Therefore, the ideal way to treat sensorineural hearing loss is to regenerate hair cells, through the use of stem cells to repair the structure and function of the cochlea, so as to fundamentally restore hearing.

Stem cell therapy in the auditory field has been a research hotspot in recent years. Although some progress has been made, almost all are results at the animal level, and there is still a long way to go before clinical transformation. The microenvironment of inner ear stem cells and the interaction with neighboring cells are very important for inner ear stem cells or sensory precursor cells to induce differentiation into mature inner ear hair cells. In the reported studies, the efficiency of differentiation of inner ear stem cells or sensory precursor cells into hair cells is still low. An insufficient number of new hair cells, immature new hair cells without the function of mature hair cells, and long-term survival of new hair cells are all key problems and difficulties that need to be solved urgently.

These results indicate that it is more difficult to regulate a single signal pathway to regenerate functional hair cells, and it may require coordinated regulation of multiple genes to effectively promote hair cell regeneration and the functional maturity and survival of new hair cells. Still, inducing the committed differentiation of stem cells into hair cells or nerve cells, the exploration of the methods of stem cell transplantation into the inner ear, and the safety research of stem cell transplantation have collectively laid the foundation for the transplantation of stem cells in vivo.

Link: https://doi.org/10.3389/fncel.2021.732507

The Benefits of Calorie Restriction are Based on Calorie Intake, not Food Quantity

Researchers here note that reduction in the calorie content in the diet is the important trigger for the benefits of calorie restriction, not reductions in the quantity of food ingested. The practice of calorie restriction, reducing calorie intake while still obtaining optimal micronutrient intake, has been shown to extend life span in near all species and lineages tested to date. Firm data on human life span has yet to be obtained, and is expected to be modest, on the order of a few years only, but short-term beneficial changes to the operation of metabolism are quite similar between mice and humans. Research into calorie restriction has given rise to a broad field of development of calorie restriction mimetic drugs, targeting many of the same cellular stress response mechanisms that are triggered by a low calorie intake. One shouldn't expect miracles from this line of work: we know the limits of calorie restriction in humans, and while it is certainly beneficial, it doesn't greatly change the duration of a human life.

Although calorie restriction has been reported to extend lifespan in several organisms, animals subjected to calorie restriction consume not only fewer calories but also smaller quantities of food. Whether it is the overall restriction of calories or the coincidental reduction in the quantity of food consumed that mediates the anti-aging effects is unclear. Here, we subjected mice to five dietary interventions. We showed that both calorie and quantity restriction could improve early survival, but no maximum lifespan extension was observed in the mice fed isocaloric diet in which food quantity was reduced.

Mice fed isoquant diet with fewer calories showed maximum lifespan extension and improved health among all the groups, suggesting that calorie intake rather than food quantity consumed is the key factor for the anti-aging effect of calorie restriction. Midlife liver gene expression correlations with lifespan revealed that calorie restriction raised fatty acid biosynthesis and metabolism and biosynthesis of amino acids but inhibited carbon metabolism, indicating different effects on fatty acid metabolism and carbohydrate metabolism. Our data illustrate the effects of calories and food quantity on the lifespan extension by calorie restriction and their potential mechanisms, which will provide guidance on the application of calorie restriction to humans.

Link: https://doi.org/10.18632/aging.203493

Restoration of Autophagy as a Goal in the Treatment of Aging

The processes of autophagy act to remove damaged molecular machinery and structures in the cell. Autophagy becomes dysfunctional with age, however. This is likely downstream of underlying causes of aging that cause changes in gene expression that degrade the function of autophagic processes in one way or another. For example mitophagy, the clearance of damaged mitochondria by autophagy, is indirectly negatively impacted by changes in mitochondrial dynamics resulting from altered gene expression. Equally, age-related changes in gene expression produce defects in the formation of autophagosomes, and this affects all aspects of autophagy.

Many of the known interventions that slow aging in animal models appear to improve the efficiency of autophagy, and functional autophagy is required for the extension of healthy life span via calorie restriction to take place. While improvement of autophagy has been a goal in the research community for quite some time, surprisingly little concrete progress has been made towards the development of therapies that specifically target dysfunction in autophagic processes.

Calorie restriction mimetics such as mTOR inhibitors improve autophagy, and mitochondrially targeted antioxidants and NAD+ upregulation may act to restore mitophagy. These were not designed with the enhancement of autophagy in mind; rather, it has been found to be one of their outcomes. The research and development communities have yet to see success in the development of narrowly targeted means of restoring a youthful function of autophagy in old tissues, though a few groups, such as the startup Selphagy Therapeutics that emerged from work on LAMP2A upregulation in the liver, are working in that area.

Selective Autophagy as a Potential Therapeutic Target in Age-Associated Pathologies

Cellular garbage disposal is critical for recycling defective cell constituents, such as proteins and organelles, towards the maintenance of cellular homeostasis. One of the main degradative molecule pathways is autophagy, which is a physiological catabolic process shared by all eukaryotes. Derived from the Greek words 'auto' meaning self, and 'phagy', meaning eating, autophagy, it was initially considered to be a bulk degradation process, while now its highly selective nature is increasingly appreciated. This self-digestive mechanism relieves the cell from proteotoxic, genotoxic, oxidative, and nutrient stress. It is accomplished in an intricate stepwise manner, which leads to clearance of damaged cell constituents, in the degradative organelle, the lysosome. Failure to complete this procedure has been implicated in many age-related diseases.

Homeostatic mechanisms that respond to mitochondrial damage are less efficient during aging. Mitophagy is a physiological eukaryotic pathway, which involves the degradation of superfluous or damaged mitochondria. When perturbed, normal mitochondrial function is hindered, resulting in the production of excessive reactive oxygen species (ROS). This ultimately leads to cellular dysfunction and tissue damage. Defective mitophagy is evident in a variety of age-related pathologies such as neurodegeneration, metabolic syndromes, and myopathies.

Aggrephagy degrades aggregation-prone proteins via targeted macroautophagy, in addition to chaperone-mediated autophagy and the proteasomal pathway. These proteins typically form aggresomes near the nucleus, which are surrounded by intermediate filament cytoskeleton, and are further processed to be degraded by autophagy. Protein aggregation usually occurs due to misfolding and can cause, among others, dysregulation of calcium homeostasis, inflammation, neurotoxicity.

Recycling of peroxisomes is also regulated by autophagy. These small dynamic single membrane organelles regulate fatty acid oxidation, production of bile acid and other lipids, while also producing ROS, which is neutralized by catalase. Moreover, peroxisomes interact with a multitude of other cellular constituents, such as lipids, the endoplasmic reticulum (ER), and mitochondria. Pexophagy and peroxisome biogenesis have recently been implicated with disease. During aging, peroxisomal targeting signal 1 (PTS1) protein import deteriorates and catalase function is diminished. Peroxisomes become more abundant and PEX5 accumulates on their membranes. This causes increased production of ROS, which further blocks peroxisomal protein import and contributes to aging.

With regard to therapeutic intervention, several pharmacological compounds have been shown to activate mitophagy and alleviate symptoms of age-related diseases, dependent on dysfunctional mitochondria. Rapamycin activates AMPK, while blocking mTOR, maintaining energetic demands and preventing neurological symptoms, such as neuroinflammation. Metformin and pifithrin induce Parkin by inhibiting p53 activity and alleviating diabetic phenotypes. Resveratrol, mainly found in grape skin, as well as, NAD+ precursors found in natural compounds activate mitophagy and mitochondrial biogenesis through the sirtuin 1 (SIRT1)-PGC-1α axis. Urolithin A, an intestinal microbiome-derived metabolite from dietary intake, induces both mitochondrial degradation and biogenesis, and increases health span of model organisms such as C. elegans and mice.

Selective autophagic induction by genetic intervention or chemical compound administration is currently being investigated in multiple diseases as potential therapeutic approach, although no drug has reached the clinic yet. Indeed, clinical studies concerning druggable autophagy targets remains limited. This highlights the complexity and intricacies of selective autophagic pathways, which in humans, cannot be easily targeted due to context-dependence and extensive crosstalk with other functional networks. Thus, initial optimism has subsided, with research now focusing on specific compounds that could target specific aspects of selective autophagy. An important objective of the collective efforts of the research community and pharmaceutical companies is to achieve targeting selective autophagy mediators, while not affecting other cellular processes.

NANOG Expression versus Cellular Senescence

Are there many strategies that can reverse cellular senescence? There are certainly strategies that can lower levels of cellular senescence over time, both in cell cultures and in living animals, but very few are actually reprogramming senescent cells into normal cells. It isn't clear that this reversal of the senescent state is a good idea, given that there is usually a good reason for at least some of such cells to be senescent, such as potentially cancerous mutations. The strategy described here is probably not causing senescent cells to become normal cells in any great number, but rather lowering the rate at which cells become senescent or encouraging senescent cells to self-destruct more rapidly, as well as encouraging normal cells to replicate more rapidly, thus diluting the senescent fraction of the population.

Cellular rejuvenation occurs naturally in embryonic development when sperm and egg (each having a certain chronological age) fuse to each other to form an embryo of age zero. Similarly, reprogramming of somatic cells to pluripotency, producing induced pluripotent stem cells (iPSCs), resets their biological clock as well. At this stage, a core network of transcription factors including NANOG, OCT4, and SOX2 maintains pluripotency in embryonic stem cells (ESCs) and iPSCs. In particular, the pluripotency factor NANOG is essential for maintaining the self-renewal of ESCs over many population doublings.

Although overexpression of NANOG does not confer pluripotency to somatic cells, it has been shown to restore several cellular functions that are compromised by aging including proliferation and differentiation of senescent fibroblasts and mesenchymal stem cells. In vivo endogenous expression of this transcription factor in stratified epithelia of adult mice showed that systemic overexpression of NANOG induces hyperplasia without initiating tumors.

Recently, we discovered that expression of NANOG in myoblasts restored their myogenic differentiation potential, as evidenced by expression of myogenic regulatory factors and the ability to form myotubes, which was impaired by replicative senescence. This result prompted us to investigate the anti-aging effects of NANOG on primary human myoblasts and in skeletal muscle tissue in vivo. Here, we show that overexpression of NANOG reversed the hallmarks of cellular senescence in muscle progenitors in vitro and restored the satellite cell abundance in the skeletal muscle of progeroid mice.

Link: https://doi.org/10.1126/sciadv.abe5671

Antioxidants to Prevent LDL Oxidation Act to Restore Macrophage Function and Reverse Atherosclerosis in Mice

Researchers here demonstrate that introducing an antioxidant into the diet, one that accumulates in cell lysosomes, helps to prevent macrophage dysfunction and thus reverse atherosclerotic plaque in an animal model of atherosclerosis. The hypothesis is that oxidized LDL particles, ingested and carried to lysosomes for degradation, are an important component of dysfunction in the macrophage cells responsible for clearing out lipid accumulations in blood vessel walls. Macrophages function well in youth, but are challenged and made dysfunctional in later life by the age-related increase in levels of oxidation of lipids and lipid carriers such as LDL particles. Strategies in clinical use to slow atherosclerosis have so far not directly targeted this challenge of oxidation and macrophage function, which may well be why they are of only limited benefit.

Multiple studies suggest that the presence of lysosomal cholesterol accumulation in macrophages, and not the total amount of intracellular lipids, is critical for the observed inflammatory response. We have shown that lysosomes in macrophages are a site of low-density lipoprotein (LDL) oxidation. Seven days after taking up mechanically aggregated LDL or sphingomyelinase aggregated LDL, mouse or human macrophage-like cells and human monocyte-derived macrophages generated ceroid in their lysosomes. Ceroid (lipofuscin) is a polymerized product of lipid oxidation found within foam cells in atherosclerotic lesions.

The lysosomal oxidation of LDL is catalyzed by oxidation-reduction active iron present in the lysosomes of macrophages through the generation of hydroperoxyl radicals at the lysosomal pH of 4.5. This oxidation is inhibited by cysteamine (2-aminoethanethiol), an antioxidant that accumulates in lysosomes. Cysteamine is used in patients for the lysosomal storage disease cystinosis, caused by the absence of the lysosomal cystine transporter cystinosin. Recently, we have shown that cysteamine reduces atherogenic conditions caused by lysosomal LDL oxidation, such as lysosomal dysfunction, cellular senescence, and secretion of various proinflammatory cytokines, such as interleukin-1β, TNF-α, and interleukin-6, and chemokines, such as CCL2, in human macrophages.

LDL receptor-deficient mice were fed a high-fat diet to induce atherosclerotic lesions. They were then reared on chow diet and drinking water containing cysteamine or plain drinking water. Aortic atherosclerosis was assessed, and samples of liver and skeletal muscle were analyzed. There was no regression of atherosclerosis in the control mice, but cysteamine caused regression of between 32% and 56% compared with the control group, depending on the site of the lesions. Cysteamine substantially increased markers of lesion stability, decreased ceroid, and greatly decreased oxidized phospholipids in the lesions. The liver lipid levels and expression of cluster of differentiation 68, acetyl-coenzyme A acetyltransferase 2, cytochromes P450 (CYP)27, and proinflammatory cytokines and chemokines were decreased by cysteamine. Skeletal muscle function and oxidative fibers were increased by cysteamine. There were no changes in the plasma total cholesterol, LDL cholesterol, high-density lipoprotein cholesterol, or triacylglycerol concentrations attributable to cysteamine.

In conclusion, inhibiting the lysosomal oxidation of LDL in atherosclerotic lesions by antioxidants targeted at lysosomes causes the regression of atherosclerosis and improves liver and muscle characteristics in mice and might be a promising novel therapy for atherosclerosis in patients.

Link: https://doi.org/10.1161/JAHA.120.017524

Looking at the Effects of Hyperbaric Oxygen Treatment on Aging: Revisiting a Problematic Study and Ridiculous Claims

The scientific community is very broad, and there are many groups within that community whose members intermittently produce studies that are either poorly designed, poorly conducted, or poorly presented and explained. Or all three, for all of the usual reasons. Constraints of time and funding, institutional pressure to publish, the involvement of external interests, and so forth. Bad papers do get published, provided that the authors are subtle enough. This does tend to be a self-correcting problem, when considered over a sufficiently long span of time to allow errant individuals and institutions to blacken their reputations with the community at large. Still, at any given moment, one should expect to see that some small fraction of published scientific papers are problematic, rather than merely incorrect.

The problematic paper for today's discussion was published last year, reporting on a study of the effects of hyperbaric oxygen treatment on areas of metabolism that are connected to the study of aging. At the time, claims of reversal of aging were circulating in the media. The paper itself was of poor quality, but far less offensive than the related and entirely unfounded hype. It was the usual circus of ignorant commentary, yes, but also a matter of hyperbaric oxygen treatment providers pushing claims that were completely unsupported by the evidence. Serious researchers will think twice about working with anyone who was involved in this exercise. I talked about this a little at the time, focusing as much on the ridiculous claims being made by institutions involved in the work, and by the media at large, as on issues with the study and interpretation of data. Relatedly, I see that the SENS Research Foundation team have chosen to pick apart the scientific details in a recent article. A little more shaming can't hurt in this case!

Hyperbolic Hyperbaric "Age Reversal"

Lower-quality, clickbait-hungry media outlets love sensationalist claims, but one does expect better from the public relations department of an internationally-respected research university. And it was an easy jump from the already-overstated "In First, Aging Stopped in Humans" and "treatments can reverse two processes associated with aging and its illnesses" to saying that a treatment "can reverse aging process" - and to then land in a mud-pit of self-parody with "Human ageing reversed in 'Holy Grail' study, scientists say."

The actual findings of a recent study on hyperbaric oxygen treatment (HBOT) were much more limited. Despite some intriguing indicators, the actual impact of HBOT on aging based on this study is entirely unclear, quite plausibly negligible, and in any case objectively less impressive than that of (say) regular exercise, which certainly does not "reverse aging."

The actual details of the study show that even the narrow claims of the study abstract aren't fully justified. It's not clear that blood-cell telomeres were lengthened any more than they would have been without HBOT; it's not clear that "senescent" T-cells were reduced in numbers, let alone actually destroyed; and if "senescent" T-cells had been destroyed, it would not demonstrate a senolytic effect of HBOT. Despite the fact that it's standard terminology in the immunology world, "senescent" T-cells aren't actually "senescent cells" in the sense usually used in the geroscience world. Jumping from post-HBOT reductions in the number of these "senescent" T-cells to potential effects on classical senescent cells is really just a misunderstanding of what kinds of cells are involved in each case.

Even if the study had robustly demonstrated that every one of the points above really did occur, it would not constitute "reversing aging" - or even justify the more restrained claims that "blood cells actually grow younger as the treatments progress" or "that the aging process can in fact be reversed at the basic cellular-molecular level."

The Detailed Progression of Aging is Always More Complex than Previously Suspected

Aging has comparatively simple root causes, forms of cell and tissue damage that accumulate as a side-effect of the normal operation of metabolism. These comparatively simple causes take effect on a very, very complex system, however. The result is an intricate web of interacting consequences, and ultimately a dysfunctional, failing mess in which it is very hard to pinpoint which of the countless observed mechanisms are actually important. The complexity of the outcome is a result of the complexity of a living organism, not of the complexity of the root causes of aging. Metabolism is incompletely understood, and for so long as that is the case, inspecting the progression of aging will continue to reveal new subtleties. This is why interventions should focus on the causes of aging, far better understood at the present time, and not on manipulating later stages of the process, much of which remains a dark forest.

Researchers have made a surprising discovery about the connection between protein shape and mitochondrial health, providing a piece of evidence for yet another theme in aging research: it's always more complicated than we thought. Proteins within the mitochondria are intricately involved in mitochondrial function, and are protected by the mitochondrial unfolded protein response (UPRmt). When proteins misfold in the mitochondria, which can be caused by external threats like pathogens or mitochondrial toxins, the UPRmt gets activated which helps restore protein shape and function. Past research on the microscopic worm C. elegans has demonstrated that boosting the UPRmt during development contributes to better mitochondrial health and a longer lifespan for the worms.

Consistently, pharmacologically boosting UPRmt has been shown to slow down diseases with mitochondrial dysfunction, such as Alzheimer's. The new research has found that activating the UPRmt in adult worms has the opposite effect: adult worms with a boosted unfolded protein response have worse health and a shorter lifespan. Digging into the details of this surprising outcome led the team to examine the mitochondrial permeability transition pore. Most of the time this pore is closed, keeping the interior of the mitochondria separate from the rest of the cell. Under stress, though, it opens to release calcium into the rest of the cell, signaling that it's time to cut its losses and induce cell death. It turns out that methods to boost the UPRmt in adult C. elegans are caused indirectly - the UPRmt is initiated in response to the opening of the transition pore. While the UPRmt is busy trying to clean things up, the signals coming from the opened pore are too strong for the cell to ignore and result in cell death. Researchers think this is what contributes to the early death of the adult worms.

Research in C. elegans forms the basis of much aging research, but what does this mean for efforts to boost health and prevent disease in people? While the mitochondrial permeability transition pore is already implicated in conditions like stroke and heart attack, the role of the UPRmt is not as well understood. Researchers liken the UPRmt to inflammation, which has a specific purpose and is useful under some conditions, but causes damage under others. One possibility is that, in a stressed cell, the UPRmt uses valuable cellular resources, hastening the already inevitable cell death.

Link: https://www.buckinstitute.org/news/aging-its-more-complicated-than-we-thought/