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- Impaired Monocyte to Macrophage Transition Implicated in Cardiovascular Disease
- Overexpression of Proteasome β5 Subunit in Neurons Slows Aging in Flies
- Cells with Stem Cell Properties Identified in the Adult Liver
- ATGL-1 is a Central Regulator of Life Span in Nematode Worms
- Garfish as a Model for Limb Regeneration
- Being Overweight Correlates with Faster Brain Aging
- Physical Exercise Reduces Brain Inflammation and Microglial Dysfunction
- Xenobiotic Detoxifying Enzymes are Critical to the Hormetic Increase in Life Span via Mitochondrial Oxidative Stress
- Older Adults Should Undertake Resistance Training
- A Discussion of the Role of Inflammaging in Age-Related Frailty
- An Age-Related Epigenetic Change that Degrades Muscle Stem Cell Function
- UNITY Biotechnology Scheduling Phase II Senolytics Trial for Late 2019
- Oxidative and Inflammatory Markers in Immune Cells as Predictors of Lifespan
- In Vivo Reprogramming of Cells to a Pluripotent, Partially Rejuvenated State Continues to Forge Ahead in the Lab
- The GENtervention Database: Gene Expression Profiles for Interventions that Slow Aging
Impaired Monocyte to Macrophage Transition Implicated in Cardiovascular Disease
The innate immune cells called macrophages are vitally important to the health and function of tissues. They help to coordinate the intricate dance of stem cells, somatic cells, and immune cells that produces tissue regrowth and tissue maintenance. They destroy errant cells and pathogens. They have a variety of other roles as well. But where do macrophages come from? While some macrophages are generated within tissues, it is generally the case that in damaged or diseased tissues, most macrophages were originally monocytes. Circulating monocytes in the bloodstream enter tissues in response to chemical cues and then transform into macrophages that set to work to try to aid in repair and regeneration. Monocytes themselves are generated by cell populations in the bone marrow that descend from hematopoietic stem cells. At any given time about half of the monocytes in the body reside in the spleen, acting as a reserve that can leap into action when required.
Thus in any given situation of injury or disease in which the presence of macrophages would be beneficial, any process that prevents monocytes from arriving and transforming into macrophages will make things worse. Interestingly, it isn't always the case that more macrophages will improve the situation. Atherosclerosis, for example, is a condition in which fatty lesions that narrow and weaken blood vessels form because the macrophages responsible for repairing the problem become overwhelmed by cholesterol and die, adding their debris to the lesion. Adding more macrophages accelerates the process, which is why animal models of atherosclerosis often use angiotensin II to cause monocytes to leave the spleen and enter the bloodstream, to make lesions form faster.
In today's open access research materials, the authors report on a mechanism operating in heart tissue that impairs the ability of monocytes to become macrophages of a type and behavior suitable for tissue regeneration. Blocking this mechanism improves tissue maintenance, heart structure, and heart function. It is a recent example of many research results published over the past few years that, collectively, demonstrate the great importance of macrophage dynamics to normal tissue function. Macrophages have several phenotypes or polarizations, states distinguished by different markers and behaviors. The ones of interest are M1, inflammatory and aggressive, versus M2, anti-inflammatory and regenerative. A lot of issues in aging are marked by the presence of too many M1 macrophages, and there is considerable interest in the research community regarding the development of means to alter this balance.
Disrupting immune cell behavior may contribute to heart disease and failure
A new study provides evidence that when circulating anti-inflammatory white blood cells known as monocytes fail to properly differentiate into macrophages - the cells that engulf and digest cellular debris, bacteria and viruses - certain forms of heart disease may result. The research shows the presence of a specific protein prevents this monocyte-to-macrophage transition from occurring in the heart. This triggers a cascade of events that can cause heart muscle inflammation, or myocarditis; remodeling of the cardiac muscle structure; enlargement of the heart, or dilated cardiomyopathy; and weakening of the organ's ability to pump blood. Eventually, this can result in heart failure.
In previous live mouse and "test-tube" laboratory studies, researchers determined that IL-17A stimulates spindle-shaped cardiac cells called fibroblasts to release a mediator that causes one type of monocyte, an inflammatory cell known as Ly6Chi to accumulate in greater numbers in the heart than the anti-inflammatory type known as Ly6Clo.
"The good news, also shown by our study, is that blocking a key protein, known as interleukin-17A or IL-17A, permits the differentiation of anti-inflammatory monocytes, promotes healthy cardiac function, and allows the newly created macrophages to protect, rather than attack, cardiac muscle. We knew that cardiac fibroblasts stimulated by IL-17A are potent producers of a protein, granulocyte-macrophage colony-stimulating factor, or GM-CSF, that is a cytokine, a molecule that evokes an immune response and inflammation in tissues. So, thinking that GM-CSF might be the key to why differentiation is disrupted, we added antibodies against GM-CSF to a mix of cardiac fibroblasts, IL-17A, and Ly6Clo and found that we could counter IL-17A's influence on the fibroblasts, and in turn, restore normal Ly6Clo monocyte-to-macrophage differentiation,"
The Cardiac Microenvironment Instructs Divergent Monocyte Fates and Functions in Myocarditis
Two types of monocytes, Ly6Chi and Ly6Clo, infiltrate the heart in murine experimental autoimmune myocarditis (EAM). We discovered a role for cardiac fibroblasts in facilitating monocyte-to-macrophage differentiation of both Ly6Chi and Ly6Clo cells, allowing these macrophages to perform divergent functions in myocarditis progression. During the acute phase of EAM, IL-17A is highly abundant. It signals through cardiac fibroblasts to attenuate efferocytosis of Ly6Chi monocyte-derived macrophages (MDMs) and simultaneously prevents Ly6Clo monocyte-to-macrophage differentiation.
We demonstrated an inverse clinical correlation between heart IL-17A levels and efferocytic receptor expressions in humans with heart failure (HF). In the absence of IL-17A signaling, Ly6Chi MDMs act as robust phagocytes and are less pro-inflammatory, whereas Ly6Clo monocytes resume their differentiation into MHCII+ macrophages. We propose that MHCII+Ly6Clo MDMs are associated with the reduction of cardiac fibrosis and prevention of the myocarditis sequalae.
Overexpression of Proteasome β5 Subunit in Neurons Slows Aging in Flies
The proteasome is just one part of the extensive cellular maintenance apparatus, many systems operating to keep a cell functioning correctly in the face of inappropriate chemical reactions, broken molecules, damaged cellular structures, and the like. Each proteasome is a very complex assembly of proteins that, collectively, are responsible for shredding excess or damaged or otherwise unwanted proteins into component parts that will be recycled into new proteins. Cellular processes identify unwanted proteins and tag them with ubiquitin, and this chemical change allows the proteasome to engage with and break down the tagged protein.
As is the case for other cellular maintenance processes, particularly autophagy, changes in proteasomal activity can influence the pace of aging and length of life in short-lived species. Further, proteasomal activity declines with age, impairing cells. Cellular stress produced via a range of approaches, including the restricted nutrient availability of calorie restriction, causes increased and more efficient proteasomal activity. Cells become less cluttered with unwanted proteins, and are more efficient and functional as a result. Scaled up, this leads to slowed aging. Unfortunately this is nowhere near as effective as a strategy in long-lived species such as our own. While calorie restriction allows mice to live 40% longer, it only adds a few years at most to human life span. Nonetheless, the research community is interested in establishing ways to upregulate proteasomal activity as a potential basis for therapies.
In recent years, researchers have shown that causing cells to produce more of the proteasomal β5 subunit protein has the effect of improving proteasomal function and extending life in nematode worms and flies. In effect, a similar outcome to stress response is being produced without the actual stress response. A paper published earlier this year demonstrated that global overexpression of the β5 subunit can slow aging in flies. Here, a different research group shows that only overexpressing the β5 subunit in neurons also extends life in flies, but their data shows no effect on lifespan for global overexpression. This sort of conflicting data is often an issue with mechanisms producing modest effect sizes.
Neuronal-specific proteasome augmentation via Prosβ5 overexpression extends lifespan and reduces age-related cognitive decline
With age, there is a progressive decline in 26S proteasome function in the nervous system of mammals as well as flies, with a corresponding increase in 20S proteasome levels but not activity, which either declines or is unchanged. These changes likely result from reduced capacity of the existing proteasome, diminished 26S assembly and disassembly of the 26S proteasome into free 20S to compensate for reduced 20S functionality. It has been shown that proteasome depletion and inhibition in mice can mirror brain aging phenotypes, producing neurodegeneration, cognitive deficits, and formation of Lewy-like bodies. The goal of this study is to establish whether age-related cognitive decline can be ameliorated by augmenting proteasome function.
The size and complexity of the proteasome has made manipulating its expression a challenge. Elevating the proteasome β5 subunit increases both expression of other subunits and whole proteasome assembly in mammalian cell cultures and Caenorhabditis elegans. We used the same approach in Drosophila melanogaster, utilizing UAS-Prosβ5 (fly ortholog of the β5 subunit). We used an inducible driver system to limit gene overexpression to adulthood, thereby removing developmental artifacts and allowing experiment and control animals to be genetically identical siblings.
We report that overexpression of the proteasome β5 subunit enhances proteasome assembly and function. Significantly, we go on to show that neuronal-specific proteasome augmentation slows age-related declines in measures of learning, memory, and circadian rhythmicity. Surprisingly, neuronal-specific augmentation of proteasome function also produces a robust increase of lifespan in Drosophila melanogaster. Our findings appear specific to the nervous system; ubiquitous proteasome overexpression acts to increase oxidative stress resistance but does not impact lifespan and is detrimental to some healthspan measures. These findings demonstrate a key role of the proteasome system in brain aging.
Cells with Stem Cell Properties Identified in the Adult Liver
The liver is the most regenerative organ in adult mammals. Unlike any other organ, it is possible to cut out sections and the liver will regrow the lost tissue. The regrowth isn't perfect, unlike the case in highly regenerative species such as salamanders and zebrafish, but it does produce functional liver tissue. What makes the liver different? Despite a great deal of interest and activity in the research community, that question is nowhere near being comprehensively answered. Will practical regenerative therapies for the liver emerge before regenerative therapies for other organs? Maybe, maybe not. So far there is little sign that work on the liver is racing ahead of work on the rest of the portfolio of internal organs.
Today's open access paper is a recent output from just one line of investigation into liver regeneration, among the many lines that are presently ongoing. While the search for stem cell like populations in adult liver tissue is the focus here, with hybrid hepatocytes as the starting point, other research groups are looking into alternative splicing and the Hippo pathway that influences regeneration in a number of organs, or the subset of liver cells that express telomerase, behavior usually reserved for stem cells in the human body. It remains to be seen which lines of work will give rise to the next generation of regenerative medicine for the liver.
Liver transplants could be redundant with discovery of new liver cell
Scientists have identified a new type of cell called a hepatobiliary hybrid progenitor (HHyP), that forms during our early development in the womb. Surprisingly, HHyP also persists in small quantities in adults and these cells can grow into the two main cell types of the adult liver (Hepatocytes and Cholangiocytes) giving HHyPs stem cell-like properties. The team examined HHyPs and found that they resemble mouse stem cells which have been found to rapidly repair mice liver following major injury, such as occurs in cirrhosis.
"For the first time, we have found that cells with true stem cell-like properties may well exist in the human liver. This, in turn, could provide a wide range of regenerative medicine applications for treating liver disease, including the possibility of bypassing the need for liver transplants. We now need to work quickly to unlock the recipe for converting pluripotent stem cells into HHyPs so that we could transplant those cells into patients at will. In the longer term, we will also be working to see if we can reprogramme HHyPs within the body using traditional pharmacological drugs to repair diseased livers without either cell or organ transplantation."
Single cell analysis of human foetal liver captures the transcriptional profile of hepatobiliary hybrid progenitors
In rodents both hepatocytes and biliary epithelial cells (BECs) are derived from a common bi-potent hepatoblast population during liver development. In adult mice, conflicting evidence exists regarding the presence of a distinct bi-potent progenitor capable of regenerating both hepatocytes and BECs. The regenerative potential of the rodent liver has been attributed to hepatocytes, BECs, biliary-like progenitor cells or 'oval cells' arising in the ductal region, stem cells located around the central vein and hepatocyte or cholangiocyte de-differentiation into a hybrid bi-potent progenitor.
In comparison, the mechanisms of human liver regeneration are poorly characterised, and the existence of a bi-potent human liver 'progenitor' cell remains unclear. This issue is in part due to a substantial overlap in markers between potential progenitor populations, hepatic precursors and mature BECs, challenging the field to define the true transcriptional nature of a bi-potent progenitor phenotype that can be replicated for clinical use. Several recent studies have captured a bi-potent progenitor-like state via small molecule-reprogramming of primary hepatocytes, capable of in vitro hepatic and biliary maturation, imitating a process that has been observed during chronic mouse liver injury. Despite several well-established phenotypic criteria for liver progenitor cells, no benchmark exits that truly distinguishes them from other human hepatic and biliary cells. To facilitate the in vitro development of cell-based therapies for treating liver disease, it is critical to precisely define a liver progenitor cell that accurately captures the developmental origin of human liver parenchyma.
In this study we utilise single-cell RNA sequencing (scRNA-seq) to interrogate the transcriptome of human foetal and adult liver at single-cell resolution. In recent years scRNA-seq has helped identify unreported cell types within populations previously defined as homogenous. Here, we report the transcriptional signature of distinct hepatic cell types in foetal and adult human liver, including a foetal hepatobiliary hybrid progenitor (HHyP) population. We identify a gene expression profile that can distinguish between foetal HHyPs, foetal hepatocytes, and mature BECs. We further identify HHyP-like cells maintained in uninjured adult primary liver tissue. Finally, we sorted HHyPs from freshly isolated human foetal liver and show evidence of hepatic and biliary phenotypes in vivo. Our in depth profiling of previously undefined HHyPs finally provides an accurate template for the human liver progenitor phenotype that will be a valuable roadmap for translating ex vivo hepatic progenitor studies into successful cell-based liver disease therapies.
ATGL-1 is a Central Regulator of Life Span in Nematode Worms
Most of the interventions and genetic alterations shown to slow aging in laboratory species are operating through some combination of the same set of underlying stress response mechanisms, the quality control and repair systems that step up their operation in response to nutrient deprivation and other stresses. Therefore is isn't surprising that the research community continues to discover shared mechanisms and regulators that, if disabled, will prevent numerous interventions from working to extend life in animal studies.
The research here, in which the gene ATGL-1 is identified as vital to such a shared mechanism, is interesting from a pure science perspective. It is another step forward in understanding how stress responses systems interact with the pace of aging. It isn't, however, going to be all that useful in the process of building therapies to extend human life. In our species, unlike short-lived species such as flies, worms, and mice, greater activity of stress response mechanisms does not greatly alter length of life. That said, the data obtained from the practice of calorie restriction shows that it has a large enough positive impact on health to be well worth considering as a lifestyle choice - larger than near any medical technology is so far proven to provide to basically healthy individuals.
Still, even given sizable health benefits, relative to the present bounds of the possible, producing therapies that mimic the response to calorie restriction or other stresses is not the path forward to meaningful rejuvenation of the old. These approaches do not do enough to address the underlying damage that causes aging. They don't reverse it to a great enough degree, and they don't slow it down enough to escape the current limits on the human life span. We need means of deliberate repair of the underlying damage that causes aging in order to produce rejuvenation, not means of adjusting metabolism into a somewhat more resilient state, that little more able to resist the damage.
ATGL-1 mediates the effect of dietary restriction and the insulin/IGF-1 signaling pathway on longevity in C. elegans
In metazoans, the insulin/IGF1 signaling pathway (IIS) coordinates nutrient and energy availability with growth, metabolism, and longevity. Two major "signaling nodes", FoxO- and TORC1-centered, are responsible for the effect of nutrients and IIS on the lifespan. Transcription factor FoxO1 that adapts mammalian organisms to starvation is negatively regulated by IIS via Akt-mediated phosphorylation and nuclear exclusion. At the same time, TORC1 (Target Of Rapamycin Complex 1) is activated by Akt and nutrients and promotes anabolic processes while inhibiting catabolism.
The downstream targets of FoxO and TORC1 that transmit longevity signals remain largely unknown. Given that both FoxO and TORC1 are ubiquitously expressed and regulate a plethora of important biological responses, investigation of the specific pathways that control longevity is challenging. In fact, we do not even know whether FoxO and mTORC1 are involved in the same pathway or mediate different pathways of the longevity control.
We have recently found that FoxO1 and mTORC1 control the rates of lipolysis in mammalian cells by regulating expression of adipose triglyceride lipase (ATGL). Although complete hydrolysis of triglycerides to glycerol and fatty acids is performed jointly by tri-, di-, and monoacylglyceride lipases, ATGL represents the rate-limiting lipolytic enzyme. In other words, in every mammalian experimental system tested thus far, elevated ATGL expression increases, while attenuated ATGL expression decreases, lipolysis.
Since known biochemical pathways that control longevity converge on the regulation of ATGL expression, we have hypothesized that ATGL may represent the long sought after target of the nutrient and insulin/IGF1 signaling pathways that regulate life span. Here, we utilize the nematode C. elegans, a well-characterized and widely used model for longevity studies, and show that expression of the C. elegans ATGL homologue ATGL-1 is controlled by nutrients and the DAF-2/DAF-16 pathway. Moreover, we find that the partial loss-of-function ATGL-1 mutant blocks the life-extending effects of dietary restriction (in the eat-2 loss-of-function model) and DAF-2 deficiency, whereas over-expression of ATGL-1 increases C. elegans lifespan.
Garfish as a Model for Limb Regeneration
Exceptional regeneration can be found in some higher animals, such as zebrafish and salamanders. These species are capable of completely regenerating non-lethal injuries and large loss of tissue from internal organs and limbs, producing an organ that is indistinguishable in function from the original, and doing so repeatedly. In mammals, with very few exceptions that occur in only a few species and a few tissues, such injuries only scar with no proficient regeneration. Why is this case? That is the question that many research groups seek to answer, as finding a way to spur regeneration of organs and limbs in our species is obviously a very desirable goal.
The authors of today's paper argue for the use of garfish as an animal model for the investigation of regeneration, based on the fact that they can regrow fins and have a genome that is closer to that of humans than is the case for zebrafish. The question all along regarding proficient regeneration is whether all of the relevant mechanisms are still in place in humans, just dormant and waiting for the right cues to be activated. Some research makes this seem plausible, but the scientific community is still some unknown distance from a definitive understanding of what needs to be accomplished in human biochemistry to allow limb or organ regrowth. It seems likely that cellular senescence and macrophage function are quite different in highly regenerative species, and some cancer suppression genes are similarly important. We can only speculate at this point as to whether any of these items can be safely changed in human biochemistry.
Fish Reveal Limb-Regeneration Secrets
Researchers have studies how gar and other fish regenerate entire fins. More importantly, the researchers focused on how they rebuild the endochondral bones within their fins, which are the equivalents of human arms and legs. Garfish has been called a "bridge species," as its genome is similar to both zebrafish - often used as a genetic model for human medical advances - and humans. Gar evolve slowly and have kept more ancestral elements in their genome than other fish. This means that along with serving as a bridge species to people, gar also are great connectors to the deep past.
So, by studying how fish regenerate fins, researchers pinpointed the genes and the mechanisms responsible that drive the regrowth. When they compared their findings to the human genome, they made an interesting observation. "The genes responsible for this action in fish also are largely present in humans. What's missing, though, are the genetic mechanisms that activate these genes in humans. It is likely that the genetic switches that activate the genes have been lost or altered during the evolution of mammals, including humans."
Evolutionary speaking, this suggests that the last common ancestor of fish and tetrapods, or four-legged vertebrates, had already acquired a specialized response for appendage regeneration, and that this program has been maintained during evolution in many fish species as well as salamanders. Continuing research into these key genes and missing mechanisms could eventually lead to some revolutionary medical advances. "The more we study these commonalities among vertebrates, the more we can home in on prime targets for awakening this program for regenerative therapies in humans."
Deep evolutionary origin of limb and fin regeneration
Salamanders and lungfishes are the only sarcopterygians (lobe-finned vertebrates) capable of paired appendage regeneration, regardless of the amputation level. Among actinopterygians (ray-finned fishes), regeneration after amputation at the fin endoskeleton has only been demonstrated in polypterid fishes (Cladistia). Whether this ability evolved independently in sarcopterygians and actinopterygians or has a common origin remains unknown. Here we combine fin regeneration assays and comparative RNA-sequencing (RNA-seq) analysis of Polypterus and axolotl blastemas to provide support for a common origin of paired appendage regeneration in Osteichthyes (bony vertebrates).
We show that, in addition to polypterids, regeneration after fin endoskeleton amputation occurs in extant representatives of 2 other non-teleost actinopterygians: the American paddlefish (Chondrostei) and the spotted gar (Holostei). Furthermore, we assessed regeneration in 4 teleost species and show that, with the exception of the blue gourami (Anabantidae), three species were capable of regenerating fins after endoskeleton amputation: the white convict and the oscar (Cichlidae), and the goldfish (Cyprinidae).
Our comparative RNA-seq analysis of regenerating blastemas of axolotl and Polypterus reveals the activation of common genetic pathways and expression profiles, consistent with a shared genetic program of appendage regeneration. Comparison of RNA-seq data from early Polypterus blastema to single-cell RNA-seq data from axolotl limb bud and limb regeneration stages shows that Polypterus and axolotl share a regeneration-specific genetic program. Collectively, our findings support a deep evolutionary origin of paired appendage regeneration in Osteichthyes and provide an evolutionary framework for studies on the genetic basis of appendage regeneration.
Being Overweight Correlates with Faster Brain Aging
Does carrying excess body weight, meaning inflammatory visceral fat tissue that distorts metabolism in many ways, actually accelerate the processes of aging, or just make all later life health issues worse and shorten life expectancy via unrelated mechanisms? The evidence leans in the direction of actually accelerating aging. Regardless, by now we should all be used to the headlines announcing that yet another aspect of age-related degeneration proceeds faster in overweight individuals.
Having a bigger waistline and a high body mass index (BMI) in your 60s may be linked with greater signs of brain aging years later, according to a new study that suggests that these factors may accelerate brain aging by at least a decade. "People with bigger waists and higher BMI were more likely to have thinning in the cortex area of the brain, which implies that obesity is associated with reduced gray matter of the brain. These associations were especially strong in those who were younger than 65, which adds weight to the theory that having poor health indicators in mid-life may increase the risk for brain aging and problems with memory and thinking skills in later life."
The study involved 1,289 people with an average age of 64. Participants' BMI and waist circumference were measured at the beginning of the study. An average of six years later, participants had MRI brain scans to measure the thickness of the cortex area of the brain, overall brain volume and other factors. Having a higher BMI was associated with having a thinner cortex, even after researchers adjusted for other factors that could affect the cortex, such as high blood pressure, alcohol use, and smoking. In overweight people, every unit increase in BMI was associated with a 0.098 millimeter thinner cortex and in obese people with a 0.207 mm thinner cortex. Having a thinner cortex has been tied to an increased risk of Alzheimer's disease. Having a bigger waist was also associated with a thinner cortex after adjusting for other factors.
"In normal aging adults, the overall thinning rate of the cortical mantle is between 0.01 and 0.10 mm per decade, and our results would indicate that being overweight or obese may accelerate aging in the brain by at least a decade. These results are exciting because they raise the possibility that by losing weight, people may be able to stave off aging of their brains and potentially the memory and thinking problems that can come along with brain aging. However, with the rising number of people globally who are overweight or obese and the difficulty many experience with losing weight, obviously this is a concern for public health in the future as these people age."
Physical Exercise Reduces Brain Inflammation and Microglial Dysfunction
Regular exercise has many beneficial effects on health because it triggers stress response mechanisms that work to maintain cell quality and function. It is worth noting that it isn't as good at this as the practice of calorie restriction, however. This might be expected from the differing effects of exercise and calorie restriction on life span in short lived species such as laboratory mice. Calorie restriction can improve maximum life span by as much as 40%, while exercise can only improve healthy life span. This isn't a case of do one or the other, of course. Do both.
Age is associated with rising levels of chronic inflammation, and in the brain this correlates with the dysfunction of microglia, supporting immune cells with a range of important roles. They don't just clear up debris, but also participate in many of the functions of neurons and neural connections. Needless to say, when they start to be inflammatory and overactive, this is not good for brain health. It is connected to the progression of all of the most common neurodegenerative conditions. Exercise is well known to reduce inflammation, and the research here adds to the existing mountain of data on this front.
Exercise impacts our body at multiple levels, including the central nervous system (CNS). In responding to exercise-related stress (e.g., hypoxia, heat, free radicals, etc.) and injuries, the body launches multiple endogenous protective and repair systems by altering gene expression and releasing a range of factors that prepare the body for the next challenge. These factors, amongst others, involve trophic effects, anti-oxidation, energy metabolism, and anti-inflammation.
Some of these factors enhance brain function and ameliorate brain disorders by inducing neuroplasticity, increasing metabolic efficiency, and improving anti-oxidative capacity. Others maintain brain homeostasis and protect brain from pathological insults by regulating glial activation and neuroinflammation. Activated microglia and several pro-inflammatory cytokines play active roles in the pathogenesis of neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD). It has been well-documented that although acute, high-intensity exercise may cause muscle injury and induce inflammation, long-term exercise at low-to-moderate intensity negatively regulates the inflammatory response.
Considerable evidence also suggests that exercise may inhibit microglial activation by downregulation of the levels of pro-inflammatory factors. However, the mechanism for the exercise-related downregulation of pro-inflammatory factors is less clear, as pro-inflammatory cytokines can be secreted from various sources (e.g., injured neurons, astrocytes, and microglia). Thus, the anti-microglial activation effect of exercise can be interpreted indirectly by upregulating the levels of trophic factors, which then lead to reduced neuronal injury and degrees of microglial activation.
Furthermore, there are a few reports suggesting that physical exercise can shift the composition of the gut microbiome, which then affects both peripheral and central inflammation, including microglial activation in the CNS. Although some mechanisms are still waiting to be determined, it should be emphasized that physical activity represents a natural strong anti-inflammatory strategy to improve brain function.
Xenobiotic Detoxifying Enzymes are Critical to the Hormetic Increase in Life Span via Mitochondrial Oxidative Stress
Researchers have for many years demonstrated that short-lived organisms such as the nematode worms C. elegans live longer when there is some increase in damaging reactive oxygen species released by mitochondria. This is a hormetic mechanism: processes of cell maintenance are triggered into greater activity, and the net result is improved tissue function and increased longevity. Unfortunately we know that these mechanisms do not have the same sizable effect on life span in long-lived species such as our own, even though they appear quite beneficial to short term measures of health.
Establishing the fine details of exactly which stress responses are important, and to what degree, is a work in progress. Metabolism is enormously complex, and there are only so many scientists and so much funding for ongoing investigations. Researchers here identify xenobiotic detoxifying enzymes as an important component of stress responses, and in this context it is interesting to look back at other recent research showing correlation between genetic variants of xenobiotic metabolizing enzymes and human longevity.
Lifespan extension in different species can be achieved by various genetic manipulations and treatments, such as disruption of insulin/IGF1 signalling, decrease in mitochondrial respiration, suppression of translation or caloric restriction. Despite very different origins of these longevity programmes, they all warrant increased resistance to various stresses like heat, oxidative stress or radiation. Although the concept that lifespan might depend on the capacity to withstand external stress cues is very old, little is currently known about signalling pathways underlying these cytoprotective responses and their ability to affect lifespan. Furthermore, how much an individual cytoprotective mechanism contributes to the lifespan extension induced by different manipulations is a key question that remains to be answered.
Transcription profiling of many long-lived mutants from worm to mouse has recently revealed that upregulation of a number of genes involved in xenobiotic detoxification is common to longevity-assurance pathways across different phyla. Xenobiotic detoxification includes activation of drug-metabolizing enzymes (DMEs), which are classified in two main groups: phase I, mainly cytochrome P450 oxidases (CYPs), and phase II, mainly UDP-glucuronosyltransferases (UGTs), glutathione-S-transferases (GSTs), sulfotransferases, and acetyltransferases, coupled to the activity of phase III transporters that mediate the efflux of metabolic end products out of the cells after the completion of phase II.
Interestingly, analyses of expression profiles from long-lived mice, including calorically restricted mice, different dwarf mice, or mice treated with rapamycin, revealed that many CYPs are upregulated and positively correlate with increased longevity. Moreover, increased expression of multiple cyp genes was reported in diverse long-lived C. elegans models, including mitochondrial mutants. Although interesting, these findings provided just a correlative connection to longevity.
Here we identify Krüppel-like factor 1 (KLF-1) as a mediator of a cytoprotective response that dictates longevity induced by reduced mitochondrial function. A redox-regulated KLF-1 activation and transfer to the nucleus coincides with the peak of somatic mitochondrial biogenesis that occurs around a transition from larval stage. We further show that KLF-1 activates genes involved in the xenobiotic detoxification programme and identified cytochrome P450 oxidases, the KLF-1 main effectors, as longevity-assurance factors of mitochondrial mutants. Collectively, these findings underline the importance of the xenobiotic detoxification in the mitohormetic, longevity assurance pathway and identify KLF-1 as a central factor in orchestrating this response.
Older Adults Should Undertake Resistance Training
The evidence from numerous studies of recent years makes it clear that resistance training can produce significant benefits to the health and remaining life expectancy of older adults. To put it another way, most people do too little to maintain strength and their health suffers for it. The effects here seem to partially overlap with and partially be distinct from the benefits of aerobic exercise. But the benefits are broad, as indicated in this open access position paper on the subject.
Age-related loss of muscle mass (originally termed sarcopenia) has an estimated prevalence of 10% in adults older than 60 years (538), rising to greater than 50% in adults older than 80 years. Prevalence rates are lower in community-dwelling older adults than those residing in assisted living and skilled nursing facilities. Loss of muscle mass is generally gradual, beginning after age 30 and accelerating after age 60. Previous longitudinal studies have suggested that muscle mass decreases by 1.0-1.4% per year in the lower limbs, which is more than the rate of loss reported in upper-limb muscles. Sarcopenia is considered part of the causal pathway for strength loss, disability, and morbidity in older adult populations. Yet, muscle weakness is highly associated with both mortality and physical disability, even when adjusting for sarcopenia, indicating that muscle mass loss may be secondary to the effects of strength loss.
The rate of decline in muscle strength with age is two to five times greater than declines in muscle size. As such, thresholds of clinically relevant muscle weakness have been established as a biomarker of age-related disability and early mortality. These thresholds have been shown to be strongly related to incident mobility limitations and mortality. Given these links, grip strength (a robust proxy indicator of overall strength) has been labeled a "biomarker of aging". Losses in strength may translate to functional challenges because decreases in specific force and power are observed. Declines in muscle power have been shown to be more important than muscle strength in the ability to perform daily activities. Moreover, a large body of evidence links muscular weakness to a host of negative age-related health outcomes including type 2 diabetes, disability, cognitive decline, osteoporosis, and early all-cause mortality.
Resistance training is considered an important component of a complete exercise program to complement the widely known positive effects of aerobic training on health and physical capacities. There is strong evidence that resistance training can mitigate the effects of aging on neuromuscular function and functional capacity. Various forms of resistance training have potential to improve muscle strength, mass, and power output. Evidence reveals a dose-response relationship where volume and intensity are strongly associated with adaptations to resistance exercise.
Despite the known benefits of resistance training, only 8.7% of older adults (older than 75 years of age) in the United States participate in muscle-strengthening activities as part of their leisure time. When performed regularly (2-3 days per week), and achieving an adequate intensity and volume (2-3 sets per exercise) through periodization, resistance exercise results in favorable neuromuscular adaptations in both healthy older adults and those with chronic conditions. These adaptations translate to functional improvements of daily living activities, especially when power training exercise is included. In addition, resistance training may improve balance, preserve bone density, independence, and vitality, reduce risk of numerous chronic diseases such as heart disease, arthritis, type 2 diabetes, and osteoporosis, while also improving psychological and cognitive benefits.
A Discussion of the Role of Inflammaging in Age-Related Frailty
Immune system dysfunction is an important component of age-related frailty, not just because of an increased vulnerability to infection and cancer, but also because the immune system falls into a state of chronic inflammation. It is overactive and ineffective at the same time, and this inflammation produces widespread dysfunction in tissues and processes throughout the body. This state has been given the name inflammaging. Here, researchers discuss inflammaging in the context of frailty in older individuals. It should go without saying that new therapeutic approaches that are able to restore correct immune function in the elderly will go a long way towards improving health and extending healthy life span. Developing such therapies, such as regrowth of the thymus, restoration of hematopoietic stem cells, regeneration of lymph nodes, and clearance of damaged immune cells, should be a higher priority than is presently the case.
Increasing attention has been paid to frailty as a potential explanation of the health diversity found in the elderly. Although a clear definition is still lacking, frailty is commonly understood as a geriatric state associated with increased vulnerability to internal and external stressors resulting from a significant loss of physiological reserve. Described as a disorder of multiple inter-related physiological systems, frailty is characterized by sedentariness, fatigue, weight loss, and poor muscle strength, and it increases the risk of adverse outcomes. However, frailty is a dynamic process that may be delayed or even reversed.
Several pathophysiological factors, including dysregulation of inflammatory processes, oxidative stress, mitochondrial dysfunction, and cellular senescence, underlie the frailty syndrome, and it is also influenced by many other factors, such as sociodemographic characteristics, psychological conditions, nutritional status, lack of physical activity, and comorbidities. However, is not clear what drives frailty and little is known about the risk factors that contribute to the development of the syndrome. Genetic differences together with environmental factors can contribute to the dysfunction of physiological mechanisms associated with frailty, leading, in turn, to the dysregulation of multiple systems, including the immune system. Furthermore, diet has been proposed to be a key element in the development frailty. Low intake of certain micronutrients and protein is associated with a higher risk of developing frailty.
Aging of the immune system leads to a low grade, chronic systemic inflammatory state, dubbed InflammAging, and it has been suggested that there exists a relationship between changes in inflammatory molecule levels and diseases and syndromes typical of old age. The InflammAging inflammatory phenotype is characterized by elevated inflammatory molecule levels, and associated with increased morbidity and mortality in older adults. It is suggested that InflammAging is a systemic physiological process that may involve one or several organs, leading to an increased risk of age-related chronic diseases and frailty. More recently it has been speculated that InflammAging is a dynamic auto-inflammatory process that can be amplified and propagated to neighbouring and distant cells and organs, thus accelerating and expanding aging processes both locally and systemically.
Furthermore, the concept of anti-inflammation, understood as an active phenomenon, has also been introduced. The rising levels of pro-inflammatory molecules in aging stimulate an increase in levels of anti-inflammatory mediators, serving to neutralize the dangerous inflammatory processes. The balance between inflammation and anti-inflammation has been suggested to determine the rate of aging, the onset and severity of age-associated disorders, and the individual's ability to achieve extreme longevity.
In conclusion, with study of the frailty syndrome still in its infancy, frailty analysis remains a major challenge. It is a challenge that needs to be overcome in order to shed light on the multiple mechanisms involved in the pathogenesis of this syndrome. Although several mechanisms contribute to frailty, immune system alteration seems to play a central role: this syndrome is characterized by increased levels of pro-inflammatory markers and the resulting pro-inflammatory status can have negative effects on various organs. Future studies should aim to better clarify the immune system alteration in frailty, and seek to establish exactly when the inflammation appears.
An Age-Related Epigenetic Change that Degrades Muscle Stem Cell Function
Stem cells support their tissues by generating daughter somatic cells and various forms of pro-regenerative signaling. Unfortunately, this activity declines with age. In the better studied stem cell populations, such as those in muscle tissue, this appears to be more a matter of signaling changes in the local environment than intrinsic damage to the stem cells themselves. The stem cells spend ever more time in a quiescent state, emerging ever more rarely to generate new daughter cells. At the high level, these changes must be a reaction to rising levels of molecular damage and its consequences such as chronic inflammation, but most of the research community is more interesting in finding proximate causes than in tackling root causes. The research here is an example of the type, in which scientists identify a specific epigenetic change that alters the muscle stem cell niche to suppress stem cell activity.
Muscle possesses remarkable regenerative capacity that is mediated by adult muscle stem cells, also called satellite cells (SCs) that reside in close association with individual myofibers, underneath the fiber's basal lamina. Responding to muscle injury, SCs will be activated and proliferate, differentiate, and fuse to existing damaged fibers or fuse with one another to form myofibers de novo. Meanwhile, a subpopulation of SCs returns to quiescence to replenish the stem cell pool. As we age, the mass, function, and regenerating capacity of muscle gradually decline, affecting mobility, voluntary function, and quality of life. It is thus imperative to investigate mechanisms accounting for the age-related muscle loss and functional decline.
Changes at all levels, including gene expression, histone modification, DNA methylation, and physical changes in muscle stem cell environment, or niche, have been found to be associated with aging. For instance, one of the studies of gene expression in aging muscle revealed that mitochondrial dysfunction is a major age-related phenomenon and highlighted the beneficial effects of maintaining a high physical capacity in the prevention of age-related muscle function decline. In another report, transcriptome-wide analysis demonstrated that the expression of extracellular matrix (ECM) genes is up-regulated during muscle aging. The myofiber basal lamina is comprised of an ECM network that is in direct contact with SCs and ECM plays an essential role in maintaining microenvironment homeostasis and SC function; the increased ECM levels in aging niche thus lead to deregulated behaviors of SCs. Specifically, SCs displayed decreased myogenic potential but increased expression of fibrogenic genes in aged muscle.
Alterations at epigenetic levels are also known to be associated with aging. For example, DNA hypermethylation at gene regions is associated with aging muscle. However, potential alterations of histone marks in aging muscle have not been investigated. For example, H3K27ac enrichment is a hallmark of enhancers. Several studies have shown the deregulation of H3K27ac and enhancers in aging tissues/cell types. In this study, we examined the changes of a panel of histone marks and found H3K27ac is markedly increased during aging in human skeletal muscle tissues. We next identified aging-related enhancer alterations and found them associated with the up-regulation of ECM genes. Furthermore, comparison of transcriptomes in young and aged SCs demonstrated that an age-related fibrogenic conversion of SCs. In mice, treatment of aging muscles with JQ1, an inhibitor of enhancer activation, reverted the ECM up-regulation and fibrogenic conversion of SCs, thus restored myogenic potential of SCs, suggesting that ECM increase in aging muscle is a result of enhancer activation and JQ1 can be a potential treatment approach for restoring SC function in aging muscle.
UNITY Biotechnology Scheduling Phase II Senolytics Trial for Late 2019
UNITY Biotechnologies is the furthest ahead of the growing number of companies working on the development of senolytic therapies capable of selectively destroying senescent cells in old tissues. Senescent cells are generated constantly in the body, but are near all destroyed by programmed cell death processes or by the immune system. The few that linger, however, accumulate to cause serious issues via their inflammatory secretions. They disrupt tissue structure and function and provoke a sizable fraction of the chronic inflammation of aging.
Because senescent cells have systemic effects throughout the body, not just local effects in the tissue they reside in, and because the whole point of the exercise is to produce therapies that can be used off-label to produce rejuvenation for all aspects of aging, not just the very narrow aspect being trialed, the UNITY Biotechnology principals are thought by many in the community to be taking a poor approach to their first trials. They are using local injections to target arthritic joints, while it has already been shown that systemic administration in animal models is beneficial to not just arthritis but also near all other aspects of aging physiology. Nonetheless, the effect size for removal of senescent cells is so large that even this technically worse approach produced decent results in an earlier trial.
UNITY Biotechnology, Inc., a biotechnology company developing therapeutics to extend healthspan by slowing, halting or reversing diseases of aging, today announced details for the planned Phase 2 study of UBX0101 in patients with osteoarthritis (OA) of the knee. "In June, we announced promising results from our Phase 1 study of UBX0101 in patients with OA of the knee showing that our senolytic molecule had a dose-dependent response across multiple clinical endpoints. We look forward to substantiating the promising results we observed in Phase 1 in a larger Phase 2 study. We will also be gathering additional information on duration of effect out to 24 weeks, validating early safety and dose-finding, and characterizing potential disease-modifying effects on bone and cartilage."
In June 2019, UNITY announced results from its first-in-human Phase 1 study of UBX0101 in patients with moderate-to-severe OA of the knee. In this study, UBX0101 was well-tolerated. Improvement in several clinical outcomes, including pain and function, as well as modulation of certain senescence-associated secretory phenotype (SASP) factors and disease-related biomarkers was observed after a single dose of UBX0101.
UNITY plans to initiate a Phase 2 study of UBX0101 in patients with painful, moderate-to-severe OA of the knee. The study is expected to enroll approximately 180 patients with initiation expected in the fourth quarter of 2019 and initial 12-week results expected in the second half of 2020. This will be a randomized, double-blind, placebo-controlled study evaluating three doses (0.5mg, 2mg and 4mg) of UBX0101 administered via a single intra-articular injection. The primary measure will be an assessment of pain at 12 weeks using the WOMAC-A instrument. Secondary measures will include safety and tolerability, pain (by 10 point Numerical Rating Scale, or NRS) and function (by WOMAC-C) at 12 weeks, as well as similar measures at 24 weeks.
Oxidative and Inflammatory Markers in Immune Cells as Predictors of Lifespan
Researchers here analyze markers in mice that are reflective of the decline of the immune system into the state of inflammaging, in which chronic inflammation disrupts normal cell and tissue function throughout the body. Unsurprisingly, some of these markers are predictive of life span. A faster decline of the immune system, for whatever underlying reason, will tend to lead to a shorter life expectancy. The immune system is vital in defense against pathogens, destruction of cancerous cells, and clearance of senescent cells. When these functions decline, the result is increased risk of age-related disease and mortality.
Several theories have been proposed to explain the aging process. The oxidative-inflammatory theory of aging links the age-related increase in oxidative stress with the chronic low-grade inflammation, the so-called "inflammaging", through the interplay of the immune system. It is known that the age-related increase in oxidative stress impairs the correct functioning of cells. Given that oxidation and inflammation are interlinked processes, the increase in oxidative stress in immune cells results in an increased release of proinflammatory mediators, giving as a result the age-related establishment of a chronic oxidative and inflammatory stress.
According to this theory, a relationship has been found between the oxidative and inflammatory states of immune cells, their functional capacity, and the lifespan of a subject. In this regard, it has been demonstrated that centenarians have immune cell function and redox parameters similar to those in adults, despite their advanced age. However, if they maintain this optimal functionality during their whole lifespan or they undergo some remodelling of these parameters during aging is unknown. Therefore, a deep understanding of these subjects would require their follow-up throughout the aging process to shed light into which changes or adaptations are the "successful ones." Since a longitudinal study is impossible to carry out in human subjects throughout the whole aging process, mice, which have a mean longevity of two years, were used for this work.
Thus, a longitudinal study was performed analysing several functions (macrophage chemotaxis and phagocytosis, natural killer activity, lymphocyte chemotaxis, and lymphoproliferation capacity), redox parameters (catalase, glutathione peroxidase, and glutathione reductase activities, reduced and oxidized glutathione, and superoxide anion and malondialdehyde concentrations), and inflammatory mediators (basal release of IL-6, IL-1β, TNF-α, and IL-10) in peritoneal leukocytes throughout the aging process of mice. This approach allowed us to address three important questions: (i) which markers are the most important predictors of remaining longevity in adult or middle life? (ii) Are the same parameters predictive of successful aging at very advanced age? (iii) Which changes or adaptations an individual experiences throughout his/her lifetime that allow the attainment of extreme longevity?
The results reveal that some of the investigated parameters are determinants of longevity at the adult age (lymphoproliferative capacity, lymphocyte chemotaxis, macrophage chemotaxis and phagocytosis, glutathione peroxidase activity, and glutathione, malondialdehyde, IL-6, TNF-α, and IL-10 concentrations), and therefore, they could be proposed as markers of the rate of aging. However, other parameters are predictive of extreme longevity only at the very old age (natural killer activity, catalase, and glutathione reductase activities, and IL-6 and IL-1β concentrations), and as such, they could reflect some of the adaptive mechanisms underlying the achievement of high longevity.
In Vivo Reprogramming of Cells to a Pluripotent, Partially Rejuvenated State Continues to Forge Ahead in the Lab
It has for some years now been possible to reprogram adult somatic cells into pluripotent stem cells that are functionally equivalent to embryonic stem cells. This is achieved by overexpressing some or all of the Yamanaka transcription factors, Oct4, Sox2, Klf4, and c-Myc (OSKM) proteins. One of the most interesting outcomes of this process is that cells so treated reverse epigenetic markers of aging to some degree, and repair their mitochondrial damage. Thus the research community has started to induce this same reprogramming in living animals to observe the results. If done haphazardly, the outcome is unrestrained cancer and tissue dysfunction, as one might expect. The surprise is that there are approaches that can lead to benefits with no such issues.
The discoveries of recent years in this part of the field have given rise to the company Turn.bio, who are attempting an implementation of transient partial reprogramming to rejuvenate cells throughout the body, as well as numerous research groups working on their own approaches to a basis for therapies capable of enhancing regeneration and function in old tissues. The work noted here is an example of the type, and is quite interesting for the further evidence that it is possible, given suitable methodologies, to deliver reprogramming factors to mice over a long period of time without causing noticeable harm.
Reversal of ageing- and injury-induced vision loss by Tet-dependent epigenetic reprogramming
In mammals, progressive DNA methylation changes serve as an epigenetic clock, but whether they are merely an effect or a driver of ageing is not known. In cell culture, the ectopic expression of the four Yamanaka transcription factors, namely Oct4, Sox2, Klf4, and c-Myc (OSKM), can reprogram somatic cells to become pluripotent stem cells, a process that erases most DNA methylation marks and leads to the loss of cellular identity. In vivo, ectopic, transgene-mediated expression of these four genes alleviates progeroid symptoms in a mouse model of Hutchison-Guilford Syndrome, indicating that OSKM might counteract normal ageing. Continual expression of all four factors, however, induces teratomas or causes death within days, ostensibly due to tissue dysplasia.
Ageing is generally considered a unidirectional process akin an increase in entropy, but living systems are open, not closed, and in some cases can fully reset biological age, examples being "immortal" cnidarians and the cloning of animals by nuclear transfer. Having previously found evidence for epigenetic noise as an underlying cause of ageing, we wondered whether mammalian cells might retain a faithful copy of epigenetic information from earlier in life, essentially a back-up copy of the original signal to allow for its reconstitution at the receiving end if information is lost or noise is introduced during transmission.
To test this hypothesis, we introduced the expression of three-gene OSK combination in fibroblasts from old mice and measured its effect on RNA levels of genes known to be altered with age, including H2A, H2B, LaminB1, and Chaf1b. We excluded the c-Myc gene from these experiments because it is an oncogene that reduces lifespan. OSK-treated old fibroblasts promoted youthful gene expression patterns, with no apparent loss of cellular identity or the induction of Nanog, an early embryonic transcription factor that can induce teratomas.
Next, we tested if a similar restoration was possible in mice. To deliver and control OSK expression in vivo, we engineered a tightly regulated adeno-associated viral (AAV) vector under the control of tetracycline response element (TRE) promoter. To test if ectopic OSK expression was toxic in vivo, we infected 5 month-old C57BL/6J mice with the vector delivered intravenously, then induced OSK expression by providing doxycycline in the drinking water. Surprisingly, continuous induction of OSK for over a year had no discernable negative effect on the mice, ostensibly because we avoided high-level expression in the intestine, thus avoiding the dysplasia and weight loss seen in other studies.
Post-mitotic neurons in the central nervous system are some of the first cells in the body to lose their ability to regenerate. Using the eye as a model tissue, we have shown that expression of OSK in mice resets youthful gene expression patterns and the DNA methylation age of retinal ganglion cells, promotes axon regeneration after optic nerve crush injury, and restores vision in a mouse model of glaucoma and in normal old mice. Thus we have shown that in vivo reprogramming of aged neurons can reverse DNA methylation age and allow them to regenerate and function as though they were young again.
The requirement of the DNA demethylases Tet1 and Tet2 for this process indicates that altered DNA methylation patterns may not just a measure of age but participants in ageing. How cells are able to mark and retain youthful DNA methylation patterns, then in late adulthood OSK can instruct the removal of deleterious marks is unknown. Youthful epigenetic modifications may be resistant to removal by the Tets by the presence of a specific protein or DNA modification that inhibits the reprogramming machinery. Even in the absence of this knowledge, these data indicate that the reversal of DNA methylation age and the restoration of a youthful epigenome could be an effective strategy, not just to restore vision, but to give complex tissues the ability to recover from injury and resist age-related decline.
The GENtervention Database: Gene Expression Profiles for Interventions that Slow Aging
Vadim Gladyshev's team has put online the new GENtervention database that shows gene expression profile data for mouse livers, assessed across a range of interventions known to slow aging in that species. Since many or even near all these interventions work through a similar collection of stress response and cellular maintenance mechanisms, such as macroautophagy, proteasomal function, and so forth, there are many commonalities in the profiles. The paper is not open access, though the usual approaches work if you want to read it, but the database is freely available.
We collected and characterized RNA-seq data on several lifespan-extending interventions, including three that had never been analyzed at the level of gene expression, across sexes, doses, and age groups. We observed a significant feminizing pattern of gene expression changes in males in response to genetic and dietary interventions at both transcriptomic and metabolomic levels. This effect was associated with perturbations of common genes and molecular pathways including those regulated by growth hormone. The feminizing effect could not explain lifespan extension but was associated with the diminution of sex-associated differences pointing to the converging effect of lifespan-extending interventions on hepatic transcriptome and metabolome across sexes.
Expanding this analysis with available microarray data allowed us to define gene expression signatures associated with individual interventions (rapamycin, calorie restriction, and growth hormone deficiency) as well as shared across longevity interventions. We observed that despite some differences, most of them perturb similar genes and pathways, including upregulation of xenobiotic metabolizing enzymes regulated by NRF2, TCA cycle, oxidative phosphorylation, and ribosome protein genes and downregulation of complement and coagulation cascades. Many of these functions turned out to be affected across tissues. Moreover, some genes involved in stress response, apoptosis, glucose metabolism, and immune response, as well as certain pathways, such as oxidative phosphorylation, were found to be commonly perturbed across interventions and, at the same time, associated with the degree of lifespan extension effect, serving as both qualitative and quantitative predictors of longevity. These genes and processes seem to be most persistent and reliable determinants of longevity in mice and deserve further exploration. We further developed a publicly available web application GENtervention that can be used to interrogate this dataset.
Finally, we employed gene expression signatures to identify new lifespan-extending interventions based on gene expression data. Here, our algorithm could distinguish two mouse strains of the same age with different expected lifespans. We have also found that hypoxia and hepatocyte-specific Keap1 knockout are positively associated with longevity signatures at the level of gene expression, and therefore appear to be strong candidates for experimental validation. In addition, we demonstrated the applicability of this method to predict new candidate lifespan-extending compounds and validated the detected positive association of gene expression induced by mTOR inhibitor KU-0063794 and ascorbyl-palmitate, making them appealing candidates for further investigation and survival studies.