MicroRNA in Macrophage Exosomes Mediates Harms Done by Visceral Fat Tissue

Enough excess visceral fat tissue will kill you. It causes chronic inflammation that accelerates all of the common fatal age-related diseases, and further produces disarray in metabolism leading to metabolic syndrome and then type 2 diabetes. Considering that type 2 diabetes can, for the vast majority of patients, be turned back even in the later stages through a sustained low calorie diet, it is quite amazing the amount of funding present in the field chasing pharmaceutical solutions to this condition. A sizable fraction of medical researchers are working on this problem rather than others precisely because that is where the funding is. Like the rest of us, scientists need to earn a living. Looking at the situation from a glass half full perspective, this work should inform work on the interaction of aging with normal levels of fat tissue in later life, a point when fat starts to produce a number of similar problems to those exhibited by young, obese individuals.

In the recent past, researchers have made some progress on determining the mechanisms by which excess fat produces inflammation: fat cells can act in similar ways to infected cells, rousing the immune system; in addition, the debris from dying fat cells produces similar results. A sizable proportion of fat tissue in obese individuals is composed of the immune cells called macrophages, and in the research noted below, it is signaling by these immune cells that links the presence of excess fat tissue to some of the consequences of excess fat tissue. It is possible to envisage a chain of consequences involving fat dysfunction and the immune system that initially directly produces inflammation, and then the progressively larger number of immune cells that become involved in the tissue themselves cause further dysfunction in metabolic processes.

It is also worth considering the evidence for deposits of visceral fat tissue to produce harmful effects through the creation of a larger than usual level of cellular senescence. Senescent cells cause problems through altered signaling, the senescence-associated secretory phenotype. It will be interesting to see the degree to which the signaling mechanisms examined in the paper below are produced by senescent versus normal macrophage cells. This is all fairly speculative: researchers have found macrophages showing signs of senescence in older individuals, but there is currently some debate as to whether or not these are actually senescent cells. This part of the field is moving fairly rapidly, so answers may well emerge over the next few years, especially given the deployment of senolytic therapies to clear senescent cells into human trials.

Exosomes are the missing link to insulin resistance in diabetes

Chronic tissue inflammation resulting from obesity is an underlying cause of insulin resistance and type 2 diabetes. But the mechanism by which this occurs has remained cloaked. Researchers have now identified exosomes - extremely small vesicles or sacs secreted from most cell types - as the missing link. "The actions induced by exosomes as they move between tissues are likely to be an underlying cause of intercellular communication causing metabolic derangements of diabetes. By fluorescently labeling cells, we could see exosomes and the microRNA they carry moving from adipose tissue through the blood and infiltrating muscle and liver tissues."

During chronic inflammation, the primary tissue to become inflamed is adipose. Forty percent of adipose tissue in obesity is comprised of macrophages - specialized immune cells that promote tissue inflammation. Macrophages in turn create and secrete exosomes. When exosomes get into other tissues, they use the microRNA (miRNA) they carry to induce actions in the recipient cells. The macrophage-secreted miRNAs are on the hunt for messenger RNAs. When the miRNA finds a target in RNA, it binds to it, rendering the messenger RNA inactive. The protein that would have been encoded by the messenger RNA is no longer made. Thus, the miRNAs are a way to inhibit the production of key proteins.

Researchers took macrophages found in adipose tissue of obese mice and harvested their exosomes. Lean, healthy mouse models were treated with these "obese" exosomes and once-normal mice began exhibiting obesity-induced insulin resistance despite not being overweight. When reversing the process, the team found that they could restore insulin sensitivity to obese mice by treating them with exosomes from lean mice. The obese mice remained overweight, but were metabolically healthy. Similarly, during an in vitro study, when human liver and fat cells were treated with "obese" exosomes, these cells became insulin resistant. Conversely, when they were treated with "lean" macrophage exosomes, they became highly sensitive to insulin. "This is a key mechanism of how diabetes works. This is important because it pins the pathophysiology of the disease in inflamed adipose tissue macrophages which are making these exosomes. If we can find out which of the microRNAs in those exosomes cause the phenotype of diabetes, we can find drug targets."

Adipose Tissue Macrophage-Derived Exosomal miRNAs Can Modulate In Vivo and In Vitro Insulin Sensitivity

MiRNAs are regulatory molecules that can be packaged into exosomes and secreted from cells. Here, we show that adipose tissue macrophages (ATMs) in obese mice secrete miRNA-containing exosomes (Exos), which cause glucose intolerance and insulin resistance when administered to lean mice. Conversely, ATM Exos obtained from lean mice improve glucose tolerance and insulin sensitivity when administered to obese recipients.

miR-155 is one of the miRNAs overexpressed in obese ATM Exos, and earlier studies have shown that knock out animals are insulin sensitive and glucose tolerant compared to controls. Furthermore, transplantation of wild type bone marrow into miR-15 knock out mice mitigated this phenotype. Taken together, these studies show that ATMs secrete exosomes containing miRNA cargo. These miRNAs can be transferred to insulin target cell types through mechanisms of paracrine or endocrine regulation with robust effects on cellular insulin action, in vivo insulin sensitivity, and overall glucose homeostasis.

Adjusting Neutrophil Behavior to Enhance Stroke Recovery

An emerging theme in regenerative research is the importance of the innate immune system to the mechanisms of tissue maintenance, and researchers have so far found a number of ways in which the behavior of these immune cells might potentially be adjusted in order to enhance healing. The scientific community has made initial strides with macrophages and microglia, shifting the balance of pro-inflammatory versus pro-regenerative cells, and here some of the same high level themes are observed in the response to injury of the innate immune cells known as neutrophils. It matters greatly as to whether these immune cells turn up at the point of injury in the mode of defending against intruding pathogens, or in the mode of assisting with repair; they are capable of both, but individual cells tend to be focused only on one of these at a given time.

White blood cells called neutrophils are like soldiers in your body that form in the bone marrow and at the first sign of microbial attack, head for the site of injury just as fast as they can to neutralize invading bacteria or fungi using an armament of chemical weapons. But when that injury is an intracerebral hemorrhage, which releases blood into the brain, neutrophils arrive at the point of battle only to discover that there's no infection to attack. Unless immediately removed from the brain by other immune cells, they actually cause damage and deploy an array of toxic chemicals into the brain that worsen injury.

Now researchers have discovered a way to temporarily suppress these soldiers' pro-killing effect and turn them into beneficial weapons that scavenge for toxins, potentially opening a door for a therapeutic approach to hemorrhagic stroke treatment. A hemorrhagic stroke occurs when an artery inside the brain leaks or ruptures. It is the second-most common form of stroke after ischemic stroke, has a 30 to 67 percent mortality rate and is the main cause of disabilities among adults. Because half of hemorrhagic stroke victims die within the first two days, researchers believe that deadly secondary damage, including through toxicity of iron from the breakdown of red blood cells, leads to an excess in free radicals and inflammation.

Along with carrying chemicals that could aggravate injury, neutrophils produce and release potentially beneficial molecules including lactoferrin, an iron-binding protein. At the same time the neutrophils are getting ready to attack inside the brain, the brain and spleen are releasing interleukin-27 molecules, which can signal to the neutrophils to produce more lactoferrin and thus benefit the brain as it recovers from the stroke injury. "This is one of the first discoveries showing that you can train neutrophils to act as friendly cells. We've adapted how the body already responds naturally, but it can take 12 to 18 hours for the signal to turn them from damaging neutrophils to the beneficial cells that release lactoferrin and by then, it can be too late. Treatment with lactoferrin in our models is effective in reducing brain damage after hemorrhage and we are working on a modified form of lactoferrin that could penetrate the brain better and quicker."

Link: https://www.uth.edu/media/story.htm?id=caf2ac24-bf5a-433e-aa00-e0d22ba0209b

Frailty is Not Entirely Irreversible, Even Now

The research materials here fit nicely with a recent post in which the degree to which frailty is self-inflicted was discussed. In this age of comfort and technology, people eat too much and exercise too little. The latter point is demonstrated in the numerous studies that show benefits in older individuals arising from structured exercise programs, a turning back of some of the advance of age-related disability. Thus the progression of frailty is not inexorable for those who choose to exercise more frequently in later years, a small example of the point that our choices do make a difference.

As we age, we may be less able to perform daily activities because we may feel frail, or weaker than we have in the past. Frailer older adults may walk more slowly and have less energy. Frailty also raises a person's risks for falling, breaking a bone, becoming hospitalized, developing delirium, and dying. No one knows exactly how many older adults are frail - estimates range from 4 percent to 59 percent of the older adult population. Researchers say that frailty seems to increase with age, and is more common among women than men and in people with lower education and income. Being in poorer health and having several chronic illnesses also have links to being frail.

Frailty also tends to worsen over time, but in at least two studies, a small number (9 percent to 14 percent) of frail older adults became stronger and less frail as they aged. The researchers examined information gathered from more than 5,000 men aged 65 or older (average age was about 73) who had volunteered for a study about bone fractures caused by osteoporosis. At the start of the study, between 2000 and 2002, the men all lived independently and could walk; none had had hip replacements. Most of the men participated in a second examination about four years after the study began.

At the start of the study, the researchers determined the participants' frailty status by measuring levels of weakness, exhaustion, lean muscle mass, walking speed, and physical activity. The men were categorized as frail, pre-frail (had one or more signs of frailty, such as low grip strength, low energy, slow walking speed, low activity level or unintentional weight loss), or robust (showing no signs of frailty). At the start of the study, nearly 8 percent of the men were frail and 46 percent were pre-frail. The most common problems for the frail men were weakness, slowness, and low activity.

Over four and a half years, the number of frail men increased while the proportion of robust men decreased. Among the men who were frail at both visits: 56 percent had no change in frailty status, 35 percent had become frailer or had died, 15 percent of pre-frail or frail men improved. Having greater leg power, being married, and reporting good or excellent health were linked to improvements in frailty status.

Link: http://www.healthinaging.org/blog/frailty-and-older-men-study-identifies-factors-that-speed-or-slow-progression/

Evidence Accumulates for Macrophages to be Central to Exceptional Regeneration

The immune system participates in regeneration, particularly the innate immune cells called macrophages. The behavior of these cells also appears to be an important part of the differences between (a) proficient regeneration, exhibited by salamanders, zebrafish, and to a lesser degree by a few mammals such as spiny mice, and (b) the limited regenerative capacities of the rest of the vertebrate kingdom. Cut off a finger or an arm, and we do not regrow that limb. Our hearts do not regenerate well from damage. Our nerves do not restore themselves from injury. Salamanders accomplish all of these things, and a number of groups in the life science research community are working towards an explanation for that difference. The research results noted here represent the latest incremental gain in understanding, one of many such steps since the turn of the century.

The presently emerging picture of regeneration is one of a coordinated dance of biochemistry involving temporarily present senescent cells, macrophages, and the various populations of cells and stem cells resident in a tissue. Take away the macrophages and it all falls apart; that much has been demonstrated in the studies of recent years. When researchers look at aspects of this dance in salamanders, it appears to be a lot more efficient than is the case in most mammals - but still, as demonstrated in the research here, take away the macrophages and salamanders heal as poorly as we do. Further, spiny mice, that unlike other mammals can regenerate several tissue types without scarring, have salamander-like macrophage behavior during regeneration.

Despite the intriguing examples of tissue regeneration in spiny mice and engineered MRL mice, there is more going on in salamanders and zebrafish than just greater efficiency in the activities of senescent cells and macrophages in tissue regrowth. Salamander and zebrafish cells reprogram themselves into pluripotent states in response to injury, building a blastema, a mass of cells capable of generating all of the necessary replacement parts. Limb regeneration in those species bears a great deal of resemblance to embryonic development. Mammals do not do this, and it seems quite plausible that the reasons why mammals do not do this go far beyond macrophage behavior. One plausible theory is that most species lost the ability to regenerate in this way due to the evolution of cancer suppression mechanisms: inserting the human tumor suppressor gene ARF into zebrafish shuts down their ability to regrow fins and organs, for example.

So it seems very plausible at this point that adjusting macrophage activity is a path to some degree of enhanced human regeneration. Indeed, simple demonstrations in mammals have been carried out involving alterations of macrophage polarization, the balance between pro-inflammatory and pro-regeneration populations of these cells. However, the full salamander package with cellular reprogramming and blastemas recapitulating embryonic development seems likely to require an earnest reengineering of mammalian cellular biochemistry, and as such is probably not a near-term prospect. In the near term, the plausible goal is the enhanced regeneration of MRL and spiny mice, not the limb regrowth of salamanders and zebrafish. In the long term, of course, everything is possible, but we have other battles to fight before that comes to pass.

Study Finds Immune System is Critical to Regeneration

The answer to regenerative medicine's most compelling question - why some organisms can regenerate major body parts such as hearts and limbs while others, such as humans, cannot - may lie with the body's innate immune system, according to a new study of heart regeneration in the axolotl, or Mexican salamander. Researchers found that the formation of new heart muscle tissue in the adult axolotl after an artificially induced heart attack is dependent on the presence of macrophages, a type of white blood cell. When macrophages were depleted, the salamanders formed permanent scar tissue that blocked regeneration.

The goal is to activate regeneration in humans through the use of drug therapies derived from macrophages that would promote scar-free healing directly, or those that would trigger the genetic programs controlling the formation of macrophages, which in turn could promote scar-free healing. The team is already looking at molecular targets for drug therapies to influence these genetic programs. "If humans could get over the fibrosis hurdle in the same way that salamanders do, the system that blocks regeneration in humans could potentially be broken. We don't know yet if it's only scarring that prevents regeneration or if other factors are involved. But if we're really lucky, we might find that the suppression of scarring is sufficient in and of itself to unlock our endogenous ability to regenerate."

The prevailing view in regenerative biology has been that the major obstacle to heart regeneration in mammals is insufficient proliferation of cardiomyocytes, or heart muscle cells. But researchers found that cardiomyocyte proliferation is not the only driver of effective heart regeneration. The findings suggest that research efforts should pay more attention to the genetic signals controlling scarring. When a human experiences a heart attack, scar tissue forms at the site of the injury. While the scar limits further tissue damage in the short term, over time its stiffness interferes with the heart's ability to pump, leading to disability and ultimately to terminal heart failure. The next step is to study the function of macrophages in salamanders and compare them with their human and mouse counterparts. Ultimately, researchers would like to understand why macrophages produced by adult mice and humans don't suppress scarring in the same way as in axolotls and then identify molecules and pathways that could be exploited for human therapies.

Heart regeneration in the salamander relies on macrophage-mediated control of fibroblast activation and the extracellular landscape

In dramatic contrast to the poor repair outcomes for humans and rodent models such as mice, salamanders, and some fish species are able to completely regenerate heart tissue following tissue injury, at any life stage. This capacity for complete cardiac repair provides a template for understanding the process of regeneration and for developing strategies to improve human cardiac repair outcomes. Using a cardiac cryo-injury model we show that heart regeneration is dependent on the innate immune system, as macrophage depletion during early time points post-injury results in regeneration failure.

In contrast to the transient extracellular matrix that normally accompanies regeneration, this intervention resulted in a permanent, highly cross-linked extracellular matrix scar derived from alternative fibroblast activation and lysyl-oxidase enzyme synthesis. The activation of cardiomyocyte proliferation was not affected by macrophage depletion, indicating that cardiomyocyte replacement is an independent feature of the regenerative process, and is not sufficient to prevent fibrotic progression. These findings highlight the interplay between macrophages and fibroblasts as an important component of cardiac regeneration, and the prevention of fibrosis as a key therapeutic target in the promotion of cardiac repair in mammals.

RIPK1 as a Target to Reduce Microglial Dysfunction in Alzheimer's Disease

One component of most neurodegenerative diseases is that classes of immune cells resident in the brain adopt disruptive, inflammatory behaviors. This is a reaction in some way to growing levels of damage in the form of aggregated proteins, such as amyloid-β and tau in Alzheimer's disease, but it isn't a helpful reaction. It makes the overall situation worse, producing greater dysfunction in the necessary operations of brain cells. Reducing this immune failure should help to slow disease progression even in the absence of effective ways to remove the protein aggregates - though that will have to happen as well in order to produce some form of cure. The research here ties into SENS views of the causes of aging and age-related disease, in that failure of lysosomes in immune cells is implicated: lysosomes are responsible for recycling cellular waste and damaged components, but with age they become dysfunctional for various reasons. That is problematic in any cell, but particularly so in immune cells that are responsible for gathering and destroying metabolic waste materials from the cellular environment.

Microglia normally gobble up and break down amyloid-β (Aβ). However, in Alzheimer's disease (AD), an altered inflammatory state causes them to stop clearing the aggregated peptide. How does this happen, and can it be stopped? Researchers blame the microglial enzyme RIPK1, and believes that blocking it may help return microglia to their normal state. The kinase appears to set off transcriptional changes that cripple the microglial lysosome system. The cells start producing new gene products, some characteristic of the recently identified disease-associated microglia (DAM) surrounding plaques in AD model mice. Genetically deleting or pharmacologically inhibiting RIPK1 both sped up Aβ clearance and improved memory in an AD mouse model. The findings lay the groundwork for a new treatment for AD, and, since RIPK1 has been implicated in amyotrophic lateral sclerosis (ALS) and multiple sclerosis (MS), for those diseases as well.

"It's the first paper that shows blocking RIPK1 alleviates the inflammatory response, reduces plaque, and improves behavior in AD mice. It points out directly the beneficial effects of inhibiting RIPK1 for the treatment of multiple diseases characterized by inflammation and cell death. Microglial lysosome biology is poised to become the next hot topic in Alzheimer's research. A lot of recent data are pointing to failure of the lysosome in microglia and other innate immune cells as the problem in AD, and rebalancing that as the way forward."

RIPK1, short for Receptor-interacting protein 1 kinase, gets induced in response to the inflammatory signals tumor necrosis factor (TNFa) and ligands of the toll-like receptor (TLR) family. It causes an inflammatory response, controls inflammation-induced cell death (necroptosis), and leads to some forms of apoptosis. The researchers first peered into postmortem human brains and found more phosphorylated RIPK1 in slices from AD patients than controls. This implied that the kinase was activated in the disease. That RIPK1 co-localized with microglial markers suggested that it was expressed primarily in these cells.

What did the kinase do? The authors tested this in APP/PS1 mice by adding to their drinking water a RIPK1 inhibitor the group had previously developed called necrostatin-1 (Nec-1s). After a month, the treated mice had fewer plaques and less soluble and insoluble Aβ in the brain. What's more, whereas five-month-old APP/PS1 mice scurried around an open field in a hyperactive state, a month of Nec-1s treatment calmed them down. The researchers also examined spatial memory with a T-shaped water maze, where mice are trained to find a hidden platform at the end of one arm, then retrained to find it in another. At five months, APP/PS1 mice had trouble learning a new platform location, but a month of Nec-1s restored their performances to match those of wild-type mice.

How does a microglial kinase do this? The researchers added Aβ1-42 to microglia isolated from wild-type mice and mice lacking the kinase. Wild-type cells bumped up production of the inflammatory cytokines TNFa and IL6, mutant cells less so. Wild-type microglia pretreated with Nec-1s also produced less TNFα and IL6. Intriguingly, microglia lacking RIPK1 action better digested synthetic Aβ1-42 oligomers. What whetted their appetites? Analyzing the microglial transcriptomes, reserchers found that one of the proteins upregulated by RIPK1 was cystatin F. Encoded by the Cst7 gene, cystatin F inhibits the endosomal/lysosomal system responsible for breaking down unwanted proteins and other metabolic waste.

Link: http://www.alzforum.org/news/research-news/microglial-kinase-promotes-dam-blocks-lysosomal-av-digestion

Encapsulated Stem Cells Improve Heart Regeneration

Researchers here report on a cheaper implementation of encapsulation for transplanted stem cells, preventing the recipient's immune system from attacking cells originating from a different individual or even different species. Since the stem cells produce improvement in regeneration in heart tissue via signaling, there is no need to expose the cells themselves to the local environment - the cells are only needed at all because the signaling environment is not yet fully mapped and understood. Encapsulating transplanted cells in a nanogel extends their lifetime and thus the therapeutic effect.

As a promising approach to tissue repair, multiple types of stem cells have entered the stage of clinical testing. However, their efficacy is limited by low retention and engraftment of transplanted cells, together with the potential risk of inflammation and immunoreaction when allogeneic or xenogeneic cells are used. Heart diseases including myocardial infarction (MI) and heart failure remain the leading cause of death worldwide. Even with the most advanced pharmacological and medical device treatment methods, mortality and morbidity of heart disease stay high. Cardiac tissue engineering and stem cell transplantation approaches aim at de novo cardiac regeneration after injury. Clinical outcomes of cardiac stem cell (CSC) therapy are hampered by low cell retention rate and side effects associated with immune rejection if allogeneic cells are used.

Injectable hydrogels have been used to treat MI, and the studies have been demonstrated to improve cardiac function via increased heart wall thickness and reduced wall stress. Various natural polymers such as fibrin, collagen, Matrigel, chitosan, keratin, and hyaluronic acid have been investigated as injectable hydrogels to treat MI. They have excellent biocompatibility and can promote cell migration, proliferation, and/or differentiation, leading to ultimate heart regeneration/repair. However, the drawbacks of natural polymers hampering their clinical applications are their batch-to-batch variation and expensive cost.

Synthetic polymers hold the potential to replace natural polymers as injectable hydrogels to treat MI. One appealing regenerative medicine strategy for MI is encapsulating stem cells such as CSCs inside the hydrogels and deliver the cell-laden hydrogels into the damage tissues. Here, we propose the use of P(NIPAM-AA) nanogel, a synthetic injectable carrier to encapsulate human CSCs in mouse and pig models of MI. The nanogel serves as a scaffolding material to enhance cell retention and as a barrier to prevent T cells from entering and attacking the encapsulated CSCs. The treatment ultimately resulted in augmented cardiac function and stimulation of endogenous regeneration.

The mechanisms underlying the therapeutic benefits of nanogel-encapsulated CSC therapy are likely to be complicated. Our findings indicated that the P(NIPAM-AA) nanogel-encapsulated hCSCs promoted post-MI cardiac repair by the inhibition of apoptosis and promotion of angiomyogenesis. Collectively, these favorable actions lead to reduced fibrosis and improved cardiac function. Fast degrading natural polymers do not support long-term support to the heart. In contrast, synthetic polymers cannot be quickly removed by enzyme activities. In real scenarios, we expect the nanogel will provide a shield for allogeneic stem cells or induced pluripotent cells, which are likely to trigger immune reaction in the host tissue. In addition, the polymer carrier can drastically improve cell retention rate.

Link: https://doi.org/10.1021/acsnano.7b01008

An Introduction to DAF-16 and FOXO in the Context of Aging and Longevity

In the early 1990s Cynthia Kenyon and others produced the first C. elegans nematode worms to exhibit significantly extended longevity through a single gene mutation, in daf-2, the nematode version of the insulin-like growth factor 1 (IGF-1) receptor, and went on to map the relevant nearby biochemical landscape of these mutants. It is perhaps overly simplistic to mark this as the dividing line between a research mainstream whose members believed aging to be an intractably complex process, and a research mainstream increasingly interested in slowing aging through adjustment of metabolism, but that is the story as it is commonly told these days.

The mechanisms of longevity enhancement in daf-2 mutants depend on daf-16, a FOXO family transcription factor. The roles of these and other related proteins have been studied intensively in nematodes and other species since the first discoveries. Insulin metabolism - involving insulin, IGF-1, growth hormone, and their cell surface receptors - has emerged as one of the more influential means by which cellular mechanisms determine variations in longevity, both in response to circumstances for individuals within the same species, and to some degree between species. The record for mouse longevity is still held by growth hormone receptor loss of function mutants, for example. These proteins and their relationships are tied to cell growth, nutrient sensing, the calorie restriction response, temperature regulation, autophagy, and many other fundamental aspects of biochemistry.

From a historical perspective, to understand how the research community came to its present distribution of attitudes and focus, it helps to know something about this body of research and its central position in the modern study of aging. It has progressed and grown alongside the slow awakening to view aging as a treatable medical condition. If reliable changes of any sort can be achieved, so the thinking goes, then in principle something can be done to reduce the terrible toll of suffering, pain, and death that accompanies aging. The ability make even small changes means that aging is not intractable. Manipulating insulin metabolism and its surrounding mechanisms, such as through the development of calorie restriction mimetic drugs, is not the future of longevity science, however. It is not a road to rejuvenation, because rejuvenation can only occur when the causes of aging are reversed. All that can be done with the manipulation of insulin metabolism is to modestly slow down aging.

Thus the future of the field, for the treatment of aging at least, will involve a transition away from the study of processes that explain natural variations in longevity between individuals, or due to environmental factors such as calorie intake. A transition away from the work that awoke the possibility of influencing aging, and towards effective means of turning back aging. Since tinkering with insulin metabolism, or any similar approach, cannot produce rejuvenation, other methods must be adopted. This future is best represented by the SENS portfolio, the strategies for engineered negligible senescence, and similar programs focused on repairing the cell and tissue damage that causes aging. This is an entirely distinct focus, orthogonal to topics such as the way in which insulin metabolism functions to adjust the pace of aging. Metabolism generates various forms of damage even when operating normally, and that damage accumulates over time to cause age-related dysfunction, disease, and death. Removing this damage will turn back the state of aging, and thus be a form of rejuvenation.

DAF-16/FOXO Transcription Factor in Aging and Longevity

The genetic pathways and biochemical processes that modulate aging and longevity are well conserved from budding yeast to the nematode worm Caenorhabditis elegans and mammals. The forkhead transcription factor FOXO as the key downstream regulator that integrates different signals from these pathways plays a crucial role in aging and longevity. The roundworm C. elegans has been considered to be an excellent system for studying molecular mechanisms in regulating animal aging and longevity. Here we discuss the evidence for the role of DAF-16/FOXO in aging and longevity, especially the data in C. elegans, which could give clues to the further studies for human aging and longevity.

FOXOs belong to the class O of the Forkhead transcription factors, which is featured by a conserved DNA-binding domain that participates a wide range of important cellular processes such as cell cycle arrest, apoptosis, and metabolism besides its function in stress resistance and longevity. There are four FOXO genes in mammals: FOXO1 (FKHR), FOXO3 (FKHRL1), FOXO4 (AFX), and FOXO6 sharing high similarity in their structure and function as well as regulation with each other, while invertebrates have only one FOXO gene, named daf-16 in C. elegans.

"Deregulated nutrient sensing" as one of the aging hallmarks to be firstly described to influence longevity, is mainly regulated by the insulin and IGF-1 signaling (IIS) pathway. And this pathway is so highly conserved to modulate aging and longevity across a great evolutionary distance from invertebrates to mammals that the components in every step found in C. elegans could be corresponded to the homologs in mice or human. Any conditions that cause inner stress to block the IIS pathway, like in the presence of food restriction or signals failing to be transduced to DAF-16/FOXO, would increase the transcriptional activity of DAF-16/FOXO by inducing the translocation of DAF-16/FOXO to the cell nucleus, which could subsequently promote or repress the expression of downstream targets to trigger the resistance to different kinds of stress and prolong the lifespan of the organisms.

Another pathway correlated with nutrition affecting longevity is the TOR (target of rapamycin) pathway, which was firstly described in C. elegans and was proved evolutionarily conserved later in other organisms. Various dietary interventions such as caloric restriction may inactivate TOR pathway to promote lifespan extension. The TOR kinase exists in two distinct complexes, TORC1 and TORC2. TORC1-mediated longevity is dependent on DAF-16/FOXO.

AMPK pathway as an energy-sensing signaling pathway responses to stimuli of decreased energy as well as reduced glucose or leptin levels, and it is the theoretical basis of dietary restriction regimen that is considered to extend both the mean and maximal lifespan in a wide range of species. DAF-16 is necessary for AMPK function in oxidative stress resistance and longevity, as the increased longevity caused by overexpression of AMPK was reverted when DAF-16 was inhibited.

The JNK (Jun N-terminal kinase) family, a subgroup of MAPK (mitogen-activated protein kinase) superfamily, as a part of a signal transduction cascade that is activated by cytokines such as TNF and IL-1, serves as a molecular sensor for various stresses including UV irradiation, ROS (reactive oxygen species), DNA damage, heat, and inflammatory cytokines. In C. elegans, overexpression of JNK showed extension lifespan and resistance to heavy metal toxicity, which may function through phosphorylation of DAF-16.

A reproductive system that may integrate nutrient signaling and communicate with other tissues through germline to affect aging has been observed in C. elegans, flies, and mice, indicating a conserved regulation mechanism across different organisms. And it has been reported that lifespan could be extended by 40-60% if the germline precursor cells were removed or the germline stem cell division were prevented in C. elegans. A steroid hormone pathway that includes the key components DAF-36/NVD, DAF-9/CYP27 as well as DAF-12/NHR is required for lifespan extension in response to germline loss, and DAF-12/NHR and DAF-9/CYP27 probably form a complex with DAF-16/FOXO to function, although the detailed mechanisms remain to be further determined.

Thus multiple signaling pathways such as the insulin/IGF-1 signaling pathway, TOR signaling, AMPK pathway, JNK pathway, and germline signaling have been found to be involved in aging and longevity. DAF-16/FOXO, as a key transcription factor, could integrate different signals from these pathways to modulate aging, and longevity via shuttling from cytoplasm to nucleus. Hence, understanding how DAF-16/FOXO functions will be pivotal to illustrate the processes of aging and longevity.

Aiming to Develop Monoclonal Antibodies for Glucosepane

Funded by the SENS Research Foundation and allied philanthropists, the researchers at the Spiegel Lab are working on the tools needed to build the means to remove glucosepane cross-links from aged tissue. Like clearance of senescent cells, this is one of the more promising near-term approaches to rejuvenation therapies because it is just the single, narrow problem, rather an enormous range of compounds and mechanisms grouped into a category, as is the case for amyloids, lipofusin, and other forms of damaging metabolic waste. It should be possible to develop and deploy working approaches to glucosepane cross-link breaking in a much shorter period of time, once the initial hurdles are overcome.

Persistent sugary cross-links form in the extracellular matrix as a side-effect of the normal operation of cellular metabolism. In humans the vast majority of lasting, problematic cross-links involve glucospane. These cross-links alter and corrode the structural properties of tissue, making bone and cartilage fragile, and producing loss of elasticity in skin and blood vessels. While all of these are bad, the loss of blood vessel elasticity is probably the most important of these consequences, as increased vascular stiffness with advancing age drives the progression of hypertension, cardiac hypertrophy, and fatal cardiovascular disease. The sooner the research community makes the leap to far greater funding and interest in cross-link breaking, the better. This requires better tools, such as those planned in this new research project.

SENS Research Foundation (SRF) has launched a new research program focused on developing monoclonal antibodies against glucosepane. David A. Spiegel will be running the project in his laboratory, which focuses on developing new methods and molecules that will facilitate our understanding and treatment of human disease.

Glucosepane is the most prevalent crosslink found in collagen in people over 65 years of age, and its presence has been correlated to age-related tissue damage through various mechanisms. Understanding of glucosepane has been hampered by the molecule's complex and sensitive chemical structure; it can only be isolated from human samples in minute quantities and in an impure form. To enable these advances in both basic and therapeutic science, the Spiegel laboratory has recently accomplished the first total synthesis of glucosepane.

The lab is now utilizing its novel synthetic glucosepane derivatives to generate the first monoclonal anti-glucosepane antibodies. Access to these antibodies would profoundly accelerate the goal of developing the first discrete, specific reagents for labeling, studying, and perhaps also cleaving glucosepane in vivo. Such tools have tremendous potential to help illuminate, and reverse, age-related damage as it occurs in human tissues.

This research has been made possible through the generous support of Michael Antonov and the Forever Healthy Foundation and its founder Michael Greve. The Forever Healthy Foundation is a private nonprofit initiative whose mission is to enable people to vastly extend their healthy lifespans and be part of the first generation to cure aging. In order to accelerate the development of therapies to bring aging under full medical control, the Forever Healthy Foundation directly supports cutting-edge research aimed at the molecular and cellular repair of damage caused by the aging process.

Link: http://www.sens.org/outreach/press-releases/srf-and-spiegel-lab-to-collaborate-on-antibodies-to-glucosepane

Is Dementia Incidence in Decline?

When the population as a whole is aging because of historical changes in birth and mortality rates, meaning that an increasing percentage of people are older rather than younger with each passing year, it is perfectly possible to observe both a growth in the total number of cases of age-related disease and at the same time a reduction in the rate at which individuals develop age-related disease. Both of these trends are underway at the present time. In this context, the short article noted here reviews some of the epidemiological research that indicates the risk of suffering dementia is falling.

Numerous studies have reported a dip in dementia incidence in the developed world. When did this trend begin? Researchers analyzed birth cohort data from the Einstein Aging Study, which enrolls cognitively healthy older adults living in the Bronx. Surprisingly, people born after 1928 were 85 percent less likely to develop dementia than those born before that year. The reason for such a stark drop in incidence is unclear. Neither better education nor improved cardiovascular health accounted for the effect. "The birth cohort effect is intriguing but will need replication in other populations. This important insight compels us to search for novel social and environmental factors that may have impacted this birth cohort. Changes in nutrition, education, pollutants, and infections all occurred and would be worth examining."

A growing number of studies have reported a drop in dementia incidence in the U.S. and Europe over the last two or three decades. Researchers have speculated that this may be due to better public health, particularly cardiovascular health. The finding is not uniform, however, with a handful of studies reporting higher dementia incidence that may be due to greater recognition of the disease or a larger number of people reaching old age.

To try to clarify the picture, researchers examined data from participants who enrolled in the Einstein Aging Study between 1993 and 2015. The cohort comprised 1,348 participants who had completed at least one annual follow-up visit, with an average follow-up time of four years. All participants were older than 70, and about two-thirds were non-Hispanic white. The researchers diagnosed dementia by a clinical exam. A subset of participants donated their brains after death, and 96 percent of those with a dementia diagnosis had some type of extensive brain pathology. For example, in a subgroup diagnosed with Alzheimer's disease, 79 percent had plaques and tangles.

Within each age group, the researchers saw a steady drop in dementia incidence for those born in later years. Among people born before 1920 there were 5.09 cases per 100 person-years. This dropped to 3.11 for people born in the early 1920s, and 1.73 for those born in the late 1920s. The most dramatic shift occurred right at the turn of that decade, when the rate fell to 0.23. Mathematical modeling pegged the best estimate for the change point to July 1929. While the model suggests an abrupt change in dementia rates, the researchers noted that this might partly be the result of small sample size; the post-1929 cohorts totaled only 350 people, with just three cases of dementia among them. "If there were more people in the analysis, the trend might be smoother." Nonetheless, the findings were statistically significant, and the researchers believe the data are picking up a real decline in dementia risk at around this time point.

What might explain it? The researchers found marked decreases in the rates of heart attack and stroke in later birth cohorts, but after adjusting the model to account for this, the drop in dementia incidence in those born after 1929 remained unchanged. While previous epidemiological studies did not specifically examine birth years, those older findings are roughly congruent with the Einstein Aging Study data, reporting the greatest drop in dementia cases after 1990, the authors noted. People born after 1929 would have entered their 60s in that decade. Most cases of late-onset dementia occur after age 60. The Rotterdam Study found a 25 percent decrease in dementia incidence in the 1990s, while the Framingham Heart Study recently reported that incidence dropped starting in the late 1980s and continued to decline into the 2010s.

Link: http://www.alzforum.org/news/research-news/more-evidence-dementia-case-numbers-are-falling

HSP90 Inhibitors as Another New Class of Potential Senolytic Drug Compounds

The increasing number of senescent cells present in older tissues is one of the root causes of degenerative aging. It is also the closest to being effectively reversed. An open access paper describing the evidence for HSP90 inibitors to selectively destroy senescent cells was published earlier this month. I had half missed it in passing and half skipped over it in favor of a more general review of the current state of senolytic drug development, pharmaceuticals capable of clearing senescent cells, but on reflection I think it is worth pointing out. The number of senolytic drug candidates has not yet reached a count of twenty, and some of them are probably not all that great, such as quercetin and fisetin, while others are chemotherapeutics with enough in the way of ugly side-effects to be avoided if there is a choice in the matter. So new categories of potential senolytics are worth noting.

Like many classes of drug candidates, HSP90 inhibitors have been considered for use against cancer. There is a strong connection between the phenomenon of cellular senescence and cancer research, through scientists in that field have generally been interested in generating more senescent cells rather than fewer of them. They are trying to push tumor cells and potentially cancerous cells into becoming senescent rather than replicating rampantly, enhancing the natural function of of cellular senescence as a means to reduce cancer risk. Unfortunately, the fact that chemotherapeutics generate a high load of senescent cells in patients, either intentionally or because they are toxic to cells in general, is one of the reasons why chemotherapy is so damaging to long term health even when successful. There are other points of connection as well: cancer researchers are also interested in pushing abnormal cells into programmed cell death processes such as apoptosis, and selectively triggering apoptosis in senescent cells is the goal of all senolytic drug candidates to date. So we should certainly expect to see new senolytic pharmaceuticals to have been evaluated as cancer therapies at some point in the past.

Are HSP90 inhibitors any good in comparison to the other types of senolytic discovered to date? I'd say it is far too early to do any more than handwave this sort of comparison. The results from animal studies to date suggest that candidate senolytics fall into one of two broad categories: they either do little to senescent cells, or they clear up to 50% of these cells, that effectiveness varying by tissue type, drug candidate, and dosage. Different drugs in the same general category of senolytics can have very different outcomes. This sort of variation is in evidence in the data from progeroid mice in this study, which at least puts a few HSP90 inhibitors, geldanamycin and 17-AAG / tanespimycin, into the category of "clears senescent cells" rather than "does nothing" - the results in mice look something like 50% clearance in the kidney versus 25% in the liver, on a par with the best of the other present drug candidates with published animal data.

Identification of HSP90 inhibitors as a novel class of senolytics

Replicative senescence is a cellular program preventing further cell divisions once telomeres become critically short. Senescence also can be induced by cellular stress, including oxidative and genotoxic stresses, or by activation of certain oncogenes. Senescent cells secrete pro-inflammatory factors, metalloproteinases, and other proteins, collectively termed the senescence-associated secretory phenotype (SASP). With chronological aging, there is an accumulation of senescent cells in mammals. This is thought to drive senescence of neighboring cells via the SASP and the functional decline of tissues.

Clearance of senescent cells rodent models restored vascular reactivity, stabilized atherosclerotic plaques, improved pulmonary function, alleviated osteoarthritis, and improved fatty liver disease. Thus, the increase in cellular senescence that occurs with aging appears to play a major role in driving life-limiting age-related diseases. Therefore, therapeutic approaches to specifically kill senescent cells have the potential to extend healthspan and lifespan.

Using a bioinformatics approach, we recently identified several pro-survival pathways, including the Bcl-2/Bcl-XL, p53/p21, PI3K/AKT, and serpine anti-apoptotic pathways that, when inhibited, result in death of senescent murine and human cells. A combination of the drugs dasatinib and quercetin, which target several of these pro-survival pathways, induce death specifically in senescent murine and human cells. Similarly, we and others also demonstrated that several inhibitors of Bcl-2 family members like navitoclax (ABT263), A1331852 and A1155463 are senolytic in some, but not all cell types. In addition, a FOXO4-interacting peptide that blocks an association with p53 recently was demonstrated to induce apoptosis in senescent cells.

Here, we describe the development of a novel screening platform to identify senotherapeutics, drugs that either suppress senescence (senomorphics) or selectively kill senescent cells (senolytics). The screen utilizes DNA repair deficient Ercc1-/- primary murine embryonic fibroblasts (MEFs), which senesce rapidly when grown at atmospheric oxygen, and detection of senescence-associated β-galactosidase (SA-β-gal). Using this platform to screen a library of autophagy regulators, a process known to influence the senescence phenotype of different cell types, we identified HSP90 inhibitors as a novel class of senolytic agents, able to induce apoptosis of senescent cells specifically.

To validate the platform, HSP90 inhibitors were tested for senolytic activity in human cells in culture and in a progeroid mouse model of accelerated aging, where the intervention delayed multiple age-related comorbidities. These results demonstrate the utility of the screening platform for identifying novel classes of senotherapeutics. Furthermore, the results demonstrate that an HSP90 inhibitor used clinically is senolytic and could be potentially repurposed to extend healthspan.

Reviewing the Effects of Exercise on Mitophagy and Mitochondrial Function

Mitochondrial damage is important in aging, and many of the means shown to modestly slow aging in various species involve increased cellular maintenance activities directed towards mitochondria. One of these is mitophagy, a specialized form of autophagy that recycles damaged mitochondria. There is plenty of evidence to suggest that more efficient mitophagy is good for long-term health. There is also plenty of evidence for increased autophagy of all sorts to be one of the more important mediating mechanisms in many of the interventions shown to slow aging in laboratory species, including the long-studied and simple approaches of calorie restriction and exercise. In this paper, the authors review what is known of the effects of exercise on mitophagy and mitochondrial function in older individuals. We all know the rough boundaries of the benefits that can be produced by exercise; the open question for researchers is the degree to which various specific mechanisms contribute to those benefits.

The maintenance of mitochondrial structural integrity, biogenesis, and function is essential to cells, since mitochondrial dysfunction can induce disturbances in energy metabolism, increase reactive oxygen species (ROS) production and, consequently, trigger mechanisms of apoptotic cell death. Moreover, during the last decades, multiple lines of evidence in model organisms and humans have demonstrated that impaired mitochondrial function can contribute to the aging process, as well as age-associated diseases. In fact, it has been shown that decreased mitochondrial performance is a hallmark of aging possibly due to the central role of mitochondria in metabolism and cellular function. Thus, the potential toxicity of mitochondrial ROS (mtROS), originating from the mitochondrial respiratory chain, led to the formulation of the oxidative stress theory of aging, which suggested that the accumulation of oxidative damage to macromolecules is an important point in the aging process.

Mitochondrial DNA has two characteristics that make it a key target of mtROS: on the one hand, its proximity to the respiratory chain and, on the other, the lack of protective histones. Damaged mitochondrial DNA alters the respiratory chain, increasing the free radical generation and triggering a vicious cycle. These changes result in organic dysfunction and aging phenotype. Recently, however, in contrast to the original theory favoring oxidative damage as a cause for mtDNA mutations and corresponding declines in mitochondrial function, there are strong data arguing that most mammalian mtDNA mutations originate as replication errors made by the mitochondrial DNA polymerase.

Since mitochondria are involved in both adaptive metabolism and survival in response to cellular stress, it is necessary to maintain good mitochondrial functioning through a tight mitochondrial quality control. Recently, mitophagy has gained importance because the damage accumulated in the mitochondria may result in a large number of cell consequences. This process of dysfunctional mitochondria removal occurs by two major pathways, damage-induced mitophagy and developmental-induced mitophagy. Mitophagy not only clears dysfunctional mitochondria but also participates in adaptive response to nutrient deprivation, hypoxia, or developmental signals, promoting a reduction in the overall mitochondrial mass.

Physical exercise has been proposed as a nondrug treatment against different diseases for people of all ages. In addition, it is suggested that regular exercise could promote an increase in mitophagy capacity and produce effects on the mitochondrial life cycle. Theoretically, physical exercise could also have effects on the major signaling pathways that are involved in the quality and quantity control of mitochondria during the aging process, such as mitophagy. Mitochondria produce ROS that can act as signaling molecules, inducing a survival response or causing damage to cellular components. However, contraction of the skeletal muscle during physical exercise can activate a mitochondrial response that improves the quality of mitochondria in different ways: (1) increasing biogenesis; (2) enhancing the expression and action of the proteins involved in mitochondrial dynamics; (3) raising mitochondrial turnover by the action of mitophagy proteins; and (4) increasing the quality control of mitochondria through the degradation of damaged or dysfunctional mitochondria.

Although the studies analyzed do not exhibit a general consensus, it seems that aging impairs mitochondrial biogenesis and dynamics and decreases the mitophagic capacity of the organism. Several interventions, such as any type of physical exercise, are able to affect the activity and turnover of mitochondria by increasing biogenesis. In addition to the changes detected in the biogenesis, aerobic exercise or combined long-term training also seem to produce increases in several markers of mitochondrial dynamics and mitophagy.

Link: https://doi.org/10.1155/2017/2012798

The First Practical Means of Human Rejuvenation are Not Distant

The first, narrowly focused rejuvenation therapies based on repair of the cell and tissue damage that causes aging already exist. They are entering trials, they are under development in companies. Senolytic therapies to clear senescent cells will be a going concern in just a few years: the drug candidates are cheap, people are running small trials funded by philanthropists, and others are self-experimenting. The first forms of treatment capable of turning back numerous aspects of aging in humans to a large enough degree to be worth it are nearly here. Unless your remaining life expectancy is in fact only a few years, then you have every chance of being able to benefit from at least the first generation of these treatments. There is no excuse for turning away and shrugging, telling yourself that this is science fiction, the medicine of the next generation, out of reach and therefore not worth your support. That is all false.

Given that up to the beginning of the twentieth century many of us succumbed to disease at an early age, it should be no surprise that living a long life is still seen today as something akin to winning the lottery. Even when confronted with the galloping pace of scientific advances in human longevity, our historical sensibilities have led us to take a defeatist stance towards the subject: "Even if longevity interventions become available during my lifetime, I am already too late to take advantage of them, so why bother?" Indeed, for so long as tangible rejuvenation therapies do not become available, we will feel validated in our pragmatism.

Today, however, rejuvenation biotechnology is far from a fictional dream: it is a quickly growing field in which advances which may increase the lifespan of you and your children to well over a hundred years are already making their way to the clinic, and this is something we can no longer ignore. Every reality begins with a dream. Only 114 years ago, the Wright brothers made the first powered flight a reality, and since then we have taken to the skies, orbited the earth, and landed a man on the moon. Today, most of us will have flown in an airplane, and have ceased to see this as exceptional. It would be short-sighted to think that the same will not happen with new technologies such as cryonics or rejuvenation.

In the last year alone, we have seen a rapid rise in the number of senolytic drugs, that aim at clearing senescent cells, under development, with companies such as Unity Biotechnology recently raising more than 100 million dollars to push these therapies through the US regulatory process and into the clinic. Last year, scientists found a way to cheaply synthesize glucosepane, a key molecule thought to be a crucial factor in aging. A drug which clears glucosepane from the body is now being developed by the Spiegel Lab at Yale University, among others, and the first potential drug candidates are projected to be available within the next 10 years. And this is only the tip of the iceberg. At this point, it is indeed challenging to continue to pull the wool over our eyes. Not only are these therapies likely to become available in our lifetime, but it seems many of them will be reaching the market within the next decade.

However, reflecting on the feasibility and the desirability of bringing aging under comprehensive medical control inevitably demands us to question many of our preconceived assumptions regarding what is possible, what is or isn't good for us, and what is acceptable. Disputing what one had long thought to be true - or at least learned to accept - is never without effort or discomfort, and this is especially true when we consider that many of us still see aging as an inevitable, perhaps even necessary, fact of life. It should thus come as no surprise that one of the most common responses to the thought of robust rejuvenation is that of neglect; in other words: why concern ourselves with something that might come to pass only after we are long gone?

Yet our actions today have the possibility, for the first time in history, to bring a profound change to the number of people who may live long enough to benefit from rejuvenation. By acting to speed up the development of the first therapies in the coming years, we ensure that a large majority of people alive today are granted the opportunity to take advantage of them; conversely, our inaction will lead to a slowing down of the pace of progress, making the impossibility of robust rejuvenation a self-fulfilling prophecy.

Link: http://www.leafscience.org/not-in-my-lifetime/

Cellular Biochemistry is Never Simple: an Example Involving Autophagy and Aging

Nothing in cellular biology is any way straightforward. All rules have exceptions, enormous complexity is the norm, and old understandings are consistently overturned with the arrival of new data: what was thought to be simple turns out to be anything but simple. Even something like the cellular maintenance processes of autophagy, universally demonstrated to be a good thing in laboratory species, to slow aging when more active, and to accelerate aging when disabled via genetic engineering, are no exception. As demonstrated here, researchers have found that selectively disabling autophagy can actually extend life in nematode worms, possibly because the operation of age-damaged autophagy in some important tissues is actually worse than the absence of running autophagy.

In the publicity materials, this is all wrapped in considerations of antagonistic pleiotropy in the evolution of aging, but I think the mechanics of the thing are more interesting in this case. In lower species like worms and flies there is a fair amount of evidence for some tissues to be especially influential over aging: the intestines, some groupings of neurons in the brain, for example. It is very unclear as to the degree to which this is still the case in mammals. Certainly most things demonstrated to slow aging in short-lived species have far less of an effect in long-lived species such as our own. Nonetheless, this research can be taken as an example of the importance of neurons in the pace of aging in nematodes.

Why we did not evolve to live forever: Unveiling the mystery of why we age

Natural selection results in the fittest individuals for a given environment surviving to breed and pass on their genes to the next generation. The more fruitful a trait is at promoting reproductive success, the stronger the selection for that trait will be. In theory, this should give rise to individuals with traits which prevent ageing as their genes could be passed on nearly continuously. Thus, despite the obvious facts to the contrary, from the point of evolution ageing should never have happened. This evolutionary contradiction has been debated and theorised on since the 1800s. It was only in 1953 with his hypothesis of antagonistic pleiotropy that George C. Williams gave us a rational explanation for how ageing can arise in a population through evolution.

Williams proposed that natural selection enriches genes promoting reproductive success but consequently ignores their negative effects on longevity. Importantly, this is only true when those negative effects occur after the onset of reproduction. Essentially, if a gene mutation results in more offspring but shortens life that's fine. This is because there can be more descendants carrying on the parent's genes in a shorter time to compensate. Accordingly, over time, these pro-fitness, pro-ageing mutations are actively selected for and the ageing process becomes hard-wired into our DNA. While this theory has been proven mathematically and its implications demonstrated in the real world, actual evidence for genes behaving in such as fashion has been lacking.

Now researchers have identified that genes belonging to a process called autophagy - one of the cells most critical survival processes - promote health and fitness in young worms but drive the process of ageing later in life. "These genes haven't been found before because it's incredibly difficult to work with already old animals, we were the first to figure out how to do this on a large scale. From a relatively small screen, we found a surprisingly large number of genes, 30, that seem to operate in an antagonistic fashion. Previous studies had found genes that encourage ageing while still being essential for development, but these 30 genes represent some of the first found promoting ageing specifically only in old worms. Considering we tested only 0.05% of all the genes in a worm this suggests there could be many more of these genes out there to find."

The researchers also found a series of genes involved in regulating autophagy which accelerate the ageing process. These results are surprising indeed, the process of autophagy is a critical recycling process in the cell, and is usually required to live a normal full lifetime. Autophagy is known to become slower with age and the authors of this paper show that it appears to completely deteriorate in older worms. They demonstrate that shutting down key genes in the initiation of the process allows the worms to live longer compared with leaving it running crippled. "Autophagy is nearly always thought of as beneficial even if it's barely working. We instead show that there are severe negative consequences when it breaks down and then you are better off bypassing it all together. It's classic antagonistic pleiotrophy. In young worms, autophagy is working properly and is essential to reach maturity but after reproduction, it starts to malfunction causing the worms to age."

In a final revelation, the team were able to track the source of the pro-longevity signals to a specific tissue, namely the neurons. By inactivating autophagy in the neurons of old worms they were not only able to prolong the worms life but they increased the total health of the worms dramatically. "We turn autophagy off only in one tissue and the whole animal gets a boost. The neurons are much healthier in the treated worms and we think this is what keeps the muscles and the rest of the body in good shape. The net result is a 50% extension of life."

Neuronal inhibition of the autophagy nucleation complex extends life span in post-reproductive C. elegans

Autophagy is a ubiquitous catabolic process that causes cellular bulk degradation of cytoplasmic components and is generally associated with positive effects on health and longevity. Inactivation of autophagy has been linked with detrimental effects on cells and organisms. The antagonistic pleiotropy theory postulates that some fitness-promoting genes during youth are harmful during aging. On this basis, we examined genes mediating post-reproductive longevity using an RNAi screen.

From this screen, we identified 30 novel regulators of post-reproductive longevity, including pha-4. Through downstream analysis of pha-4, we identified that the inactivation of genes governing the early stages of autophagy up until the stage of vesicle nucleation, such as bec-1, strongly extend both life span and health span. Furthermore, our data demonstrate that the improvements in health and longevity are mediated through the neurons, resulting in reduced neurodegeneration and sarcopenia. We propose that autophagy switches from advantageous to harmful in the context of an age-associated dysfunction.

Can the Age-Related Harm Done by Fat Tissue be Prevented?

The way to avoid the harms done to long-term health and life expectancy by excess visceral fat tissue is not to gain that fat, or to lose it if you have it. This is not the path pursued by that part of the research community interested following the large-scale funding associated with the metabolic diseases of obesity, of course. There is comparatively little profit to be made in telling people to lose weight, versus selling them compensatory pharmaceuticals for a lifetime. However, even with normal, healthy levels of fat tissue, as aging progresses that tissue starts to cause similar issues to those produced by excess fat in earlier life: chronic inflammation, metabolic disruption leading to type 2 diabetes, and so forth. The changes of aging include processes that introduce dysfunction into the relationship between fat and the immune system, one of which is examined here.

Adipose tissue inflammation has become widely accepted as a major contributor to metabolic dysfunction and disorders. Previous studies on diet induced obesity mice have shown that adipose tissue is primed for inflammatory changes prior to other metabolic organs. There is a plethora of research investigating factors in obese adipose tissue inflammation to identify valuable therapeutic targets for metabolic dysfunction. However, much less is understood about age-related adipose tissue inflammation and dysfunction. A better understanding of the cellular and molecular mechanisms of adipose tissue inflammation in aging will be crucial in the development of therapeutics for metabolic diseases beyond cases of diet-induced adipose tissue inflammation and insulin resistance.

Both age-related adiposity and diet-induced obesity are characterized by immune cell infiltration and a sustained inflammatory cycle. Among these various immune cells, adipose tissue macrophage (ATM) accumulation, proliferation, and polarization are major contributors to adipose tissue inflammation and dysfunction. Interestingly, recent studies suggest that changes in preadipocyte function during aging also lead to dysfunctional adipose tissue, eventually progressing to chronic inflammation. Our group have recently shown that elevated endoplasmic reticulum (ER) stress response in aging contributes to greater inflammatory responses, in part due to compromised autophagy activity in the aging adipose tissue. Recent studies have also indicated that with aging there is increased accumulation of senescent cells in many organs including fat depots, which contributes to aging pathologies. However, the detailed molecular mechanisms that lead to increased inflammation in aging adipose tissue are poorly defined.

During the last decade, major advances were made in identifying the molecular mechanisms by which lipid-derived products promote inflammation in different cell types. One type of lipid-derived product, non-esterified fatty acids (NEFA), elevates tissue inflammation through interaction with the pattern recognition receptor Toll-like receptor 4 (TLR4) via its endogenous ligand Fetuin-A (Fet A), a liver derived glycoprotein. Fet A is considered a biomarker of chronic inflammation due to its ability to stimulate the production of inflammatory mediators from both adipocytes and macrophages. Interestingly, Fet-A null mice were protected against obesity and insulin resistance with aging.

The involvement of Fet A-mediated activation of TLR4 pathway in adipose tissue inflammation in diet-induced obesity is well explored. However, the role of this pathway in age-associated adipose tissue inflammation is unknown. We undertook this study to test the hypothesis that age-related adipose tissue inflammation is dependent on the Fet A-mediated TLR4 signaling pathway. We first evaluated the expression of Tlr4 and Fet A gene products in adipose tissue, liver, and plasma samples derived from young and old mice. We then exploited the TLR4-deficient mice to investigate the role of TLR4 in age-associated adipose tissue inflammation, ER stress response, autophagy activity, cellular senescence, and metabolic status (glucose tolerance).

We found that, in contrast to data from diet-induced obesity models, adipose tissue from aged mice have normal Fet A and TLR4 expression. Interestingly, aged TLR4-deficient mice have diminished adipose tissue inflammation compared to normal controls. We further demonstrated that reduced adipose tissue inflammation in old TLR4-deficient mice is linked to impaired ER stress, augmented autophagy activity, and diminished cellular senescence. Importantly, old TLR4-deficient mice have improved glucose tolerance compared to age-matched wild type mice, suggesting that the observed reduced adipose tissue inflammation in aged TLR4-deficient mice has important physiological consequences. Taken together, our present study establishes novel aspect of aging-associated adipose tissue inflammation that is distinct from diet-induced adipose tissue inflammation. Our results also provide strong evidence that TLR4 plays a significant role in promoting aging adipose tissue inflammation.

Link: https://doi.org/10.18632/aging.101288

Protein Posttranslational Modifications in Aging

This very readable review paper walks through what is known of modifications to proteins that occur after their creation, and the role these modifications play in aging. If you are familiar with the SENS view of aging as an accumulation of damage, you'll recall that this damage includes the buildup of numerous forms of metabolic waste, and many of these items are modified proteins. Equally, the vast majority of other age-related changes in modified proteins are downstream consequences of the damage of aging or reactions to the damage of aging, not root causes - the details matter on a case by case, per-protein and per-modification basis.

From a biodemographic point of view, aging is defined as an exponential increase in mortality with time, sometimes accompanied by a deceleration or plateau at later ages. Although the changes that underlie aging are complex, it is characterized by the gradual accumulation of a wide variety of molecular and cellular damage throughout the lifespan. The nine proposed hallmarks of aging in mammals are genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication. However, the connections between these hallmarks, their contributions to aging, and their links with frailty and disease remain incompletely understood. In fact, uncovering the biological basis of aging is one of the greatest contemporary challenges in science.

Interestingly, epigenetics plays a crucial role in aging. While there are several different types of epigenetic mechanisms, protein posttranslational modifications (PTM) are intriguing contributors in regulating aging. Proteins are the basis of cellular and physiological functioning in living organisms, and the physical and chemical properties of proteins dictate their activities and functions. The primary sequence of a protein is a main determinant of protein folding and final conformation as well as biochemical activity, stability, and half-life. However, at any given moment in the life of an individual, its proteome is up to two or three orders of magnitude more complex than the encoding genomes would predict. One of the main routes of proteome expansion is through posttranslational modifications (PTM) of proteins.

Protein PTM results from enzymatic or nonenzymatic attachment of specific chemical groups to amino acid side chains. Such modifications occur either following protein translation or concomitant with translation. PTM influences both protein structure and physiological and cellular functions. Examples of enzymatic PTMs include phosphorylation, glycosylation, acetylation, methylation, sumoylation, palmitoylation, biotinylation, ubiquitination, nitration, chlorination, and oxidation/reduction. Nonenzymatic PTMs include glycation, nitrosylation, oxidation/reduction, acetylation, and succination. Some rare and unconventional PTMs, such as glypiation, neddylation, siderophorylation, AMPylation, and cholesteroylation, are also known to influence protein structure and function.

Generally, protein PTMs occur as a result of either modifying enzymes related to posttranslational processing (such as glycosylation) or signaling pathway activation (such as phosphorylation). Moreover, PTM patterns are known to be affected by disease conditions. Similarly, the dysregulation of PTM is associated with the aging process. In this context, both enzymatic and nonenzymatic PTMs can undergo age-related alterations. Alteration in the pattern of nonenzymatic PTMs depends mainly on the nature of the modifying substances, such as metabolites and free radicals. For instance, reactive oxygen species can lead to oxidation of amino acid side chains (oxidation of thiols to different forms, oxidation of methionine, formation of carbonyl groups, etc.), modification by-products of glycoxidation and lipoxidation, and formation of protein-protein cross-links as well as oxidation of the protein backbone, resulting in protein fragmentation. In contrast, changes in the nature of enzymatic PTMs rely primarily on the activities of modifying enzymes.

As awareness of the role of PTMs in aging and aging-related diseases grows, there is an urgent need for the development of methods to detect protein PTMs more rapidly and accurately. Furthermore, the recent finding of rare and unconventional modifications in age-related pathologies calls for the development of more specific and sensitive methods to detect such modifications. The recent rapid progress in large-scale genomics and proteomics technologies is likely to be a catalyzing factor for such studies. Drugs that target PTMs, such as phosphorylation, acetylation, methylation, and ubiquitination, will serve as useful tools in exploring the basic mechanism of PTM modulation and provide a pharmacological platform to combat the detrimental effects of aging.

Link: https://doi.org/10.1155/2017/5716409