Fight Aging! Newsletter, August 7th 2023

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Examining the Details of Mitochondrial Dysfunction in the Aging Mouse Heart

Every cell contains hundreds of mitochondria, hard at work to produce the chemical energy store molecule adenosine triphosphate (ATP), used to power cellular activities. Mitochondria are complex structures, the evolved descendants of ancient symbiotic bacteria that are now integrated into the cell. At their center is the electron transport chain, a collection of protein complexes that conducts the energetic chemical reactions needed to make ATP. Mitochondria bear copies of a remnant circular genome, DNA distinct from that in the cell nucleus, which encodes some of the mitochondrial proteins necessary for mitochondrial function. The sequences for other mitochondrial proteins have migrated over time into the nuclear DNA.

A great deal of evidence points to a significant role for mitochondrial dysfunction in degenerative aging. This arises in part due to damage to mitochondrial DNA, which is less well protected and maintained than is the case for nuclear DNA. It is also a matter of age-related changes in the expression of mitochondrial genes in the cell nucleus, which appear to affect both function of mitochondria and the clearance of damaged mitochondria via mitophagy, a form of selective autophagy. Mitochondria are dynamic organelles, constantly dividing and fusing together, and imbalances in this behavior can impair mitophagy, as well as lead to smaller numbers of mitochondria than would be optimal.

Today's open access paper takes a look at the proximate outcomes rather than the proximate causes of mitochondrial dysfunction. Firstly a loss of ATP production, and secondly an increase in the production of oxidative molecules as a side-effect of the energetic activities of the electron transport chain. Too much oxidative stress on cells is damaging to their function, and dysfunctional mitochondria are the primary culprit when it comes to producing that oxidative stress.

Aging Triggers Mitochondrial Dysfunction in Mice

The current study sought to investigate the effects of aging on cardiac mitochondrial function by examining various parameters of mitochondrial respiration, ROS production, ATP production, mitochondrial membrane potential, mitochondrial swelling, and proton leakage. The findings of this study suggest that the aging process has a significant impact on cardiac mitochondrial function.

One of the most important findings of this study was that cardiac mitochondrial oxygen consumption was significantly lower in old mice than in young mice. Besides showing a slight reduction in oxygen consumption by complex I under the phosphorylative state (state 3), we observed a strong reduction in oxygen consumption by complex II state 3. This finding suggests that aging reduces mitochondrial respiratory capacity. Furthermore, this dysfunction in the complex II state 3 may indicate a characteristic failure of oxidative phosphorylation during aging. The decreased respiratory capacity in old mice could be attributed to an age-related decline in the expression and activity of electron transport chain complexes or a decrease in the number of functional mitochondria.

Additionally, our study demonstrated that under complex I and complex II state 3 stimulation, the production of mitochondrial reactive oxygen species (ROS) was higher in the hearts of older animals than in younger animals. This finding raises the possibility that the age-related decline in the antioxidant defense system, which lead to results in oxidative stress and cellular damage and may be the cause of the increased ROS production. These results are in agreement with the previously published studies that describe transcriptional changes in pathways related to ROS in the heart. Our study also showed that the mitochondrial ATP production under stimulation of complex I and complex II state 3 was significantly lower in the hearts of old versus young mice. This finding suggests that the production of mitochondrial ATP declines with age. The reduction in the number of functional mitochondria or the age-related decline in the activity of the electron transport chain complexes, which produce the proton gradient for ATP synthesis, may be the cause of this decline in ATP production

Interesting data, in particular, are the significantly depolarized mitochondrial membrane potential in the hearts of old versus young mice. This result explains the increase in mitochondrial ROS production in old mice once a membrane depolarization reduces the rate of electron flow, increasing the degree of electronic reduction in the phosphorylative chain and generating more ROS. Additionally, it explains the reduction in the production of ATP because the membrane depolarization also reduces the proton gradient, reducing the proton driving force through the ATP-synthase and impairing its functioning. The age-related changes in the expression and activity of the electron transport chain complexes or the mitochondrial uncoupling proteins may be the cause of the elevated mitochondrial membrane potential. Finally, the study showed that under complex I and II state 3 stimulation, the mitochondrial proton leakage was significantly higher in old mice compared to young mice hearts. This finding indicates that the mitochondrial proton leakage increases with aging, possibly as a result of the aging-related decline in activity of the electron transport chain complexes or the mitochondrial uncoupling proteins.

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Extracellular Vesicles from Embryonic Stem Cells Reduce Cellular Senescence

Much of the communication between cells passes back and forth in the form of extracellular vesicles, membrane-wrappd packages of molecules that are presently far from completely cataloged or understood. This lack of full understanding hasn't stopped the growth of an industry seeking to replace stem cell therapies with vesicles harvested from those stem cells. It seems clear from the evidence to date that most stem cell therapies produce benefits via signaling, and not because transplanted cells survive to engraft in any meaningful numbers. In principle, use of vesicles allows for less expensive, more logistically practical forms of treatment, as vesicles can be indefinitely stored, and their production involves far fewer of the challenges of quality and consistency found in stem cell manufacture. In practice, this is a still a work in progress in the world of regulated medicine, even given that extracellular vesicle treatments are readily available in the world of medical tourism.

In today's open access paper, researchers discuss the mechanisms by which delivery of extracellular vesicles harvested from embryonic stem cells reduces measures of aging in animal studies and reduces incidence of cellular senescence in cell cultures. It may or may not be a good idea to prevent or reverse cellular senescence, as some cells become senescent for good reason, being damaged in ways that might provoke cancerous behavior if not stopped. Further, some senescent cells exhibit sizable amounts of DNA damage that is induced on the transition into a senescent state. On the other hand, in aged tissues many cells may become senescent only in response to the signaling of other senescent cells, or due to stress that is survivable given a little more resilience or support. Some of the better-studied approaches to slowing aging clearly prevent cellular senescence to some degree, such as mTOR inhibition. One suspects that when it comes to risk, the details of the biochemistry matter greatly for any novel approach to rescuing cells from the senescent state.

Embryonic stem cell-derived extracellular vesicles rejuvenate senescent cells and antagonize aging in mice

A few decades ago, rejuvenation or amelioration of aging seemed impossible. However, in the last decades, the concept of parabiosis and partial reprogramming with pluripotency-related factors has changed our view on the subject, indicating that factors derived from young cells prevent senescence. Researchers found that young circulating extracellular vesicles (EVs) can regenerate aged muscle. Previously, we found that EVs derived from embryonic stem cells (ESCs) could rejuvenate the aged MSCs (mesenchymal stem cells) and rescue their regenerative capacity. Recently, several rejuvenation factors enriched in ESC-EVs or ESC-CM (conditioned medium) have been identified, such as TGF-β, Smad2, PDGF-BB (platelet-derived growth factor-BB), miR-291a-3p, miR-294, and miR-200a. However, the roles and mechanisms of ESC-EVs in vivo are unknown.

Here, we investigate the anti-senescence effects of ESC-EVs in vivo using aged mice. Our data show that ESC-EVs treatment rescues the transcriptome profile of aged mice and ameliorates the senescence status of several aged organs, providing evidence that ESC-EVs may be candidates for the therapy of various age-related diseases. Others have found that EVs from young adipose-derived stem cells improved motor coordination, grip strength, fatigue resistance, and significantly reduced frailty in aged mice. However, the effects of ESC-EVs treatment on cognitive function and motor activity in aged mice remain unclear and require further investigation.

Furthermore, we identify miR-15b-5p and miR-290a-5p, which are enriched in ESC-EVs and exert rejuvenating effects by silencing of the Ccn2-mediated AKT signaling pathway. miR-15b-5p and miR-290a-5p are crucial for ESC-EVs rejuvenation. Their target gene of Ccn2 is upregulated in aged cells and can be rescued by ESC-EVs treatment. Several studies have shown that Ccn2 induces cellular senescence and activates the PI3K/AKT signaling pathway, suggesting that Ccn2 may be a potential target for anti-aging. We found that miR-15b-5p and miR-290a-5p silenced Ccn2, thereby inhibiting the Ccn2-dependent AKT signaling pathway and ameliorating the senescence.

In conclusion, here, we demonstrate a novel mechanism for ESC-EVs to protect cells from senescence. However, whether ESC-EVs rejuvenate aged mice via miR-15b-5p and miR-290a-5p remains unknown. Next, we plan to use miR-15b-5p and miR-290a-5p antagonists while treating aged mice with ESC-EVs to further investigate the mechanism by which ESC-EVs resist aging in vivo.

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Fatty Acid Metabolism as a Commonality in Different Approaches to Slowing Aging

It seems clear that many of the varied approaches to adjusting the operation of metabolism in ways that (usually modestly) slow aging in animal models achieve this outcome by acting on a set of common underlying mechanisms. For example, a great deal of effort has gone towards the study of autophagy in this context, a response to mild stress that improves cell function by recycling damaged molecular machinery. Upregulation of autophagy appears to be a feature of most of the better studied approaches to slowing aging, and certainly those derived from investigations of calorie restriction.

What do more sophisticated efforts to find commonalities between age-slowing interventions look like? Today's open access paper offers some insight into that question. The authors report on an approach to the analysis of omics data from biological samples taken from mice following intervention, in search of a greater understanding of the resulting changes in metabolism. This is potentially a vast amount of data, and the exercise is narrowed by considering only liver tissue samples. Even so, the researchers identify changes in the operation of fatty acid metabolism as a common feature of several quite diverse approaches shown to slow aging in short-lived species. The idea is that this sort of analysis will aid in the more deliberate design of different, better interventions in the future.

Lifespan-extending interventions induce consistent patterns of fatty acid oxidation in mouse livers

Some nutritional and pharmacological interventions consistently extend lifespan and healthspan (i.e., the period free from age-associated diseases and disabilities) in mouse and other animal models. Nutritional interventions include calorie restriction (CR), methionine restriction, and ketogenic diet. While the number of possible geroprotectors (i.e., drugs aiming to prevent, slow, or reverse aging process) has been growing, pharmacological interventions whose effects on lifespan extension have been documented by the National Institute on Aging (NIA) Interventions Testing Program (ITP) include acarbose (ACA), canagliflozin, 17α-estradiol (17aE2), glycine, nordihydroguaiaretic acid, Protandim (a Nrf2 inducer), and rapamycin (Rapa).

Rapa modulates nutrient-sensing pathways by inhibiting the activity of mTOR through complex formation with FK506-binding protein 12, which globally attenuates protein translation via mTOR complex 1 (mTORC1) and ultimately reduces inflammation, increases autophagy, and improves stem cell maintenance. ACA could share some aspects of CR; it is an oral antidiabetic drug which competitively inhibits the activity of α-glucosidase enzymes to digest polysaccharides, resulting in the delay of sugar uptake in the gastrointestinal tract. ACA treatment has been shown to extend lifespan in male mice more than in female mice, possibly related to sex-dependent differences observed in heart, liver, and gut metabolite profiles. 17aE2 is a stereoisomer of the dominant female sex hormone 17β-estradiol, having much weaker binding affinity to the classical estrogen receptors, stronger affinity to the brain estrogen receptor, and neuroprotective properties. 17aE2 treatment extends lifespan in male but not in female mice, potentially related to male-specific reduction of age-associated neuroinflammation and sex-specific metabolomic responses observed in liver and plasma metabolite profiles. Because these lifespan-extending drugs were tested with standardized protocols in the NIA ITP and because they have differences in primary mode of action, comparisons of their effects on molecular regulation are valuable for our understanding of common, fundamental, or core aging and longevity mechanisms.

A module of a biological system can be represented as a molecular network where nodes and edges correspond to biomolecules (e.g., gene transcripts, proteins, and metabolites) and relationships (e.g., physical interactions, chemical reactions), respectively. For each sample, ranks of biomolecules can be obtained from experimental data by ordering the values of interest (e.g., abundances, levels of specific post-translational modification) between the biomolecules within a module. When these ranks are highly conserved among the samples within a population of a specific phenotype, the module is considered tightly regulated in the population, because biological regulatory mechanisms or pressures must act consistently across the samples to produce this high conservation pattern. In contrast, low rank conservation among the samples within a phenotype indicates loose module regulation in the population.

In this study, we report systemic changes in the molecular regulation of biological processes under multiple lifespan-extending interventions, by jointly leveraging systems-level analyses on two mouse liver proteomic datasets, which were generated in the NIA Longevity Consortium, and a previously published mouse liver transcriptomic dataset. Differential Rank Conservation (DIRAC) analyses of mouse liver proteomics and transcriptomics data show that mechanistically distinct lifespan-extending interventions (acarbose, 17α-estradiol, rapamycin, and calorie restriction) generally tighten the regulation of biological modules. These tightening patterns are similar across the interventions, particularly in processes such as fatty acid oxidation, immune response, and stress response.

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Mitochondrial Transplantation as a Treatment for Kidney Damage

It is interesting see an increased focus on assessing the ability of mitochondrial transplantation to be useful in a variety of circumstances, not just as a treatment to reduce the mitochondrial dysfunction that occurs with aging. The limiting factor in bringing mitochondrial transplantation to the clinic is chiefly the speed at which the research and development communities can achieve the logistical advances needed to reliably produce enough mitochondria to deliver to an entire organ (at first), and the whole body (later). It is likely the case that mitochondria will have to be patient-matched by haplotype of mitochondrial DNA, which further multiplies the size of the necessary infrastructure. Several biotech startups are working on this challenge, and the research community anticipates that present small tests will point the way to later clinical trials, once it is possible to manufacture sufficient mitochondria in a cost-effective way.

Today's research materials provide an example of one such small test of mitochondrial transplantation, focused on the treatment of kidney damage in the context of disease and transplantation. It is possible that mitochondrial transplantation can be used to greatly improve the quality of donor organs, reducing the cell death and damage resulting from the stresses of the transplantation process. Though not the focus of the research here, good results in this context also suggest that mitochondrial transplantation would be useful as a treatment for acute kidney injury.

Study Shows Mitochondrial Transplantation Effective in Reversing Damage to Kidneys and Kidney Cells

Mitochondrial transplantation is a regenerative medicine technology where healthy mitochondria are taken from cultured cells or tissue from organ donors and then injected into a diseased or damaged tissue or organ. Mitochondria produce the energy needed for a cell to function. "Here, we provide evidence that mitochondrial transfer lessens the damage that renal cells or the kidneys may suffer from disease or injury." For the study, the research team conducted preliminary tests in cultures of human proximal tubular cells, which are found in the kidneys and play an important in removing toxins. When the damaged cells were exposed to healthy mitochondria, cellular energy increased, and toxicity decreased.

Additional research found that kidneys injected with healthy mitochondria showed signs of recovery. These results are significant because in the U.S., 20% of the kidneys procured for transplantation are eventually discarded because they are too damaged, and this potential new treatment may help. This is especially true in a new type of organ donation called "uncontrolled donation after cardiac death," an area of active research. In this setting, the kidneys do not receive adequate blood supply, and mitochondria and the kidneys are damaged.

Mitochondria Transplantation Mitigates Damage in an In Vitro Model of Renal Tubular Injury and in an Ex Vivo Model of DCD Renal Transplantation

Mitochondrial transplantation (MITO) is a process where exogenous isolated mitochondria are taken up by cells. As virtually any morbid clinical condition is characterized by mitochondrial distress, MITO may find a role as a treatment modality in numerous clinical scenarios including acute kidney injury (AKI).

In vitro, cells treated with MITO showed higher proliferative capacity and ATP production, preservation of physiological polarization of the organelles and lower toxicity and reactive oxygen species production. Ex vivo, kidneys treated with MITO shed fewer molecular species, indicating stability. In these kidneys, pathology showed less damage while RNAseq analysis showed modulation of genes and pathways most consistent with mitochondrial biogenesis and energy metabolism and downregulation of genes involved in neutrophil recruitment

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Extracellular Vesicles from Young Cardiac Progenitor Cells Produce Benefits in Old Mice

The signaling environment in the body is generated by cells, communication mediated by the molecules that cells release and take up, many of which are packaged into extracellular vesicles. This signaling changes profoundly between development and adult life, and then again in important ways with advancing age. In principle, providing aged tissues with the signals passed back and forth during embryonic development will spur greater maintenance and regeneration. In practice, tissues are systems of great and only partially understood complexity, and attempts to beneficially manipulate signaling in this way are still very much a work in progress, even after decades of effort.

The transplantation of forms of stem cell is perhaps the most successful approach to date when it comes to manipulation of cell signaling for benefit. Stem cells die off following transplantation, but while they survive, their signals influence surrounding tissues. Yet these therapies are as yet nowhere near as reliable or successful as desired, again a matter of complexity: which cells; how to culture them; how to deliver them; how to replicate winning strategies. Deriving extracellular vesicles from stem cell populations will likely run into many of the same issues, but this approach is at least less logistically complex, and thus less costly. Just as researchers produce evidence for benefits in animal models derived from transplantation of embryonic stem cells, they also demonstrate that extracellular vesicles can produce interesting results. This remains some way from clinical application in the mainstream, though increasingly available via medical tourism.

Today's open access paper is an example of the transition from cell therapy to extracellular vesicle therapy. The authors use a population of progenitor cells derived from the embryonic heart to produce vesicles, and demonstrate positive results in old rats following injection of these vesicles into the heart. This delivery of embryonic signaling may or may not be reducing harmful cellular senescence via reprogramming; it is a little early to say whether or not the reduction in senescence results from that mechanism. It is, however, quite interesting to see benefits throughout the body resulting from an injection of vesicles into the heart.

Rejuvenating effects of young extracellular vesicles in aged rats and in cellular models of human senescence

Cardiosphere-derived cells (CDCs) are cardiac progenitor cells with broad-ranging bioactivity in preclinical and clinical studies. Recently, we found that transplantation of young CDCs exerts anti-aging effects in old rodents, improving heart function. Although we specifically targeted the heart in that study, multiple systemic benefits were evident, hinting that soluble factors might play a prominent role. In vitro experiments revealed that extracellular vesicles (EVs) from CDCs (CDC-EVs) mimicked the anti-senescent effects of CDCs, at least partially through activation of the telomerase-telomere axis. Together with the anti-tumorigenic effects of CDC-EVs in old rats with spontaneous leukemia, it seems reasonable to hypothesize that anti-senescent properties of CDC-EVs may underlie the benefits. If so, EVs might be logical therapeutic candidates for a variety of aging-related diseases.

Treatment with young CDC-EVs induce structural and functional improvements in the heart, lungs, skeletal muscle, and kidneys of old rats, while favorably modulating glucose metabolism and anti-senescence pathways. Repeated systemic administration of young CDC-EVs in aged rodents triggered broad-ranging functional improvements, with concordant structural changes in different organs and associated evidence of tissue rejuvenation. The beneficial effects of CDC-EVs were maintained over mid-term follow-up, with prolongation of survival of treated animals. But, beyond longevity, the changes we observed in heart and kidney function, glucose metabolism, and exercise tolerance have the potential to improve quality of life, which is an important goal of anti-aging therapies.

Using a single cell-free therapeutic agent, young CDC-EVs, we demonstrated that multiple pathologies can be favorably modulated. Moreover, tissue fibrosis contributing to organ dysfunction was broadly ameliorated (heart, lungs, skeletal muscle, and kidneys exhibited less interstitial fibrosis) in CDC-EV treated rats. Based on these findings, CDC-EVs emerge as a strategy capable of targeting pathophysiologic mechanisms underlying many age-related chronic conditions. Both MiR-146 and miR-92a highly enriched in CDC-EVs known to be implicated in aging-related pathways may have played a role in rejuvenating effects observed in our study.

Cellular senescence is thought to contribute to progressive age-related organ dysfunction. Previously, we described an anti-senescent effect of young CDC-EVs in vitro. Here, we confirm that cellular rejuvenation, conceived as partial or total reversal of senescence, can be also achieved in vivo in old animals injected with young CDC-EVs. Benefits include telomere elongation in heart cells, less-active DNA damage response (represented by phosphorylated γH2AX), lower IL-6 levels, and changes in protein levels suggestive of enhanced mitochondrial biogenesis in skeletal muscle. Extensive transcriptomic differences in treated versus control groups were consistent with the observed upregulation of the transcription factor NANOG and extracellular signal-regulated kinase ERK 1/2. Both are recognized regulators and stabilizers of the pluripotency gene regulatory network. Accordingly, we speculate that the mechanism of action of young CDC-EVs is related in part to the control of the dynamic state of pluripotency and reprogramming, a strategy that has been touted in pursuit of rejuvenation.

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Postmenopausal Hormone Treatment Correlates with Increased Dementia Risk

Researchers here report on a large study showing that an increased risk of dementia is correlated with postmenopausal hormone treatment in women. It may well be the case that the people who opt into this form of treatment are doing so because they tend to be more burdened by the processes of aging, and are thus more likely to develop later dementia regardless of the therapy. Under the hood, a range of possibly relevant mechanisms can be used to argue for protective or harmful effects of increased levels of the hormones used in these therapies; the biochemistry is complex and there is a lack satisfactory answers as to whether long term use is in fact harmful in this way.

Dementia affects more women than men worldwide. Even when controlling for differences in survival rates, the incidence of dementia among women is higher compared with that of men, suggestive of risk factors related to the female sex. Oestrogen is known to have both neuroprotective and neurodamaging properties. Exogenous systemic oestrogen is used in the management of menopausal vasomotor symptoms. The effect of menopausal hormone therapy on the risk of dementia is uncertain.

Recent, large scale observational studies have reported a positive association between use of menopausal hormone therapy and Alzheimer's disease in long term users who initiated treatment before age 60 years. However, the studies were not able to obtain full exposure history of hormone treatment for most of their study population, especially short term use (e.g. up to five years) around the age of menopause. We report a nationwide study on the association between menopausal hormone therapy and development of dementia. 5,589 incident cases of dementia and 55,890 age matched controls were identified between 2000 and 2018 from a population of all Danish women aged 50-60 years in 2000 with no history of dementia or contraindications for use of menopausal hormone therapy.

Compared with people who had never used treatment, people who had received oestrogen-progestin therapy had an increased rate of all cause dementia (hazard ratio 1.24). Increasing durations of use yielded higher hazard ratios, ranging from 1.21 for one year or less of use to 1.74 for more than 12 years of use. Oestrogen-progestin therapy was positively associated with development of dementia for both continuous (hazard ratio 1.31) and cyclic (hazard ratio 1.24) regimens. Associations persisted in women who received treatment at the age 55 years or younger (hazard ratio 1.24). Findings persisted when restricted to late onset dementia (hazard ratio 1.21) and Alzheimer's disease (hazard ratio 1.22).

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Removing AGEs from the Lens of the Eye to Treat Presbyopia

A few different approaches have been proposed to clear advanced glycation endproducts (AGEs) from the lens of the eye, where they build up with age to make the lens stiffer. That stiffness results from cross-linking of extracellular matrix molecules by AGEs, restricting their ability to move relative to one another, and thus changing the structural properties of thetissue. That in turn leads to presbyopia as the muscles of the eye can no longer produce the desired changes to the lens needed to focus on near objects. Sadly, the most advanced program of cross-link breaking for the eye, a formulation of lipoic acid choline ester, failed in its phase IIb clinical trial after promising earlier results. We might hope that other, similar approaches to lens cross-linking have a larger effect size, such as the work of Lento Bio, and the project noted here.

Presbyopia is an age-related vision disorder that is a global public health problem. Up to 85% of people aged ≥40 years develop presbyopia. In 2015, 1.8 billion people globally had presbyopia. Of those with significant near vision disabilities due to uncorrected presbyopia, 94% live in developing countries. Presbyopia is undercorrected in many countries, with reading glasses available for only 6-45% of patients living in developing countries. The high prevalence of uncorrected presbyopia in these parts of the world is due to the lack of adequate diagnosis and affordable treatment.

The formation of advanced glycation end products (AGEs) is a non-enzymatic process known as the Maillard reaction. The accumulation of AGEs in the lens contributes to lens aging (leading to presbyopia and cataract formation). Non-enzymatic lens protein glycation induces the gradual accumulation of AGEs in aging lenses. AGE-reducing compounds may be effective at preventing and treating AGE-related processes.

Fructosyl-amino acid oxidase (FAOD) is active on both fructosyl lysine and fructosyl valine. As the crosslinks encountered in presbyopia are mainly non-disulfide bridges, and based on the positive results of deglycating enzymes in cataracts (another disease caused by glycation of lens proteins), we studied the ex vivo effects of topical FAOD treatment on the power of human lenses as a new potential non-invasive treatment for presbyopia.

This study demonstrated that topical FAOD treatment resulted in an increase in lens power, which is approximately equivalent to the correction obtained by most reading glasses. The best results were obtained for the newer lenses. Simultaneously, a decrease in lens opacity was observed, which improved lens quality. We also demonstrated that topical FAOD treatment results in a breakdown of AGEs, as evidenced by gel permeation chromatography and a marked reduction in autofluorescence. This study demonstrated the therapeutic potential of topical FAOD treatment in presbyopia.

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Altered Mitochondrial Calcium Metabolism is a Major Factor in Inflammaging

Researchers here report that an overlooked aspect of mitochondrial dysfunction with age, the ability of these organelles to take up calcium ions, provides an important contribution to age-related chronic inflammation when it occurs in the innate immune cells known as macrophages. With advancing age, the immune system falls into a harmful state of overactivation, often referred to as inflammaging. A range of different mechanisms have been shown to contribute to imflammaging, such as the pro-inflammatory secretions of senescent cells, persistent viral infection, mislocated mitochondrial DNA, excess visceral fat tissue, and so forth. Altered mitochondrial calcium metabolism makes an interesting addition to the list; it remains to be seen as to how this issue might be best targeted for therapy.

In this study, we report a surprising discovery that mitochondrial Ca2+ (mCa2+) uptake capacity in macrophages drops significantly with age. This amplifies cytosolic Ca2+ (cCa2+) signaling and promotes NF-κB activation, rendering the macrophages prone to chronic low-grade inflammatory output at baseline and hyper-inflammatory when stimulated. Although mitochondrial dysfunction has long been a suspected driver of aging, our study pinpoints the mitochondrial calcium uniporter (MCU) complex as a keystone molecular apparatus that links age-related changes in mitochondrial physiology to macrophage-mediated inflammation.

Both chronic low-grade inflammation and mitochondrial dysfunction are known hallmarks of aging, but mechanistic links between these two processes have not been defined with clear links to human biology. For example, defective mitophagy in Prkn-/- mice may contribute to inflammaging by shedding mitochondrial DNA as an inflammatory stimulus in senescent cells. Although a progressive age-associated decline in mitophagy is not evident in human myeloid cells, if one supposes that there is a steady age-associated shedding of inflammatory mediators from other senescent cells, our findings predict that the decreased mCa2+-uptake capacity will render the macrophages hyper-responsive to such inflammatory stimuli from senescent cells and thereby drive inflammaging.

A recent study performed a comprehensive analysis of mitochondrial phenotypes in purified human cell types and mixtures but omitted mCa2+ uptake as a marker of mitochondrial fitness. Interestingly, the authors found that their mitochondrial health index was most impaired in monocytes isolated from aged human donors. Although we chose to focus on macrophage-mediated inflammation, the broad outlines of the mechanistic model are likely applicable to other myeloid cells such as neutrophils and mast cells too, and that is an important line for our future investigations.

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NRF2 in the Oxidative Stress of Alzheimer's Disease

There are many ways of looking at the pathology of Alzheimer's disease, as it is very complex, layered condition. One of these viewpoints is to note that levels of oxidative stress increase in the Alzheimer's brain, stressing and killing cells. Researchers here report on their investigation of changes in the NRF2-centered regulation of cellular antioxidant systems that take pace in the Alzheimer's brain. A decline in antoxidants accelerates the progression of cell death and dysfunction, but this can be slowed or prevented by suitably targeted intervention aimed at maintaining NRF2 activity. Whether or not this is too far downstream of the causes of Alzheimer's disease to be useful in human patients remains to be seen, but there is enough of a benefit in animal models to ensure continued efforts to build drugs that target this mechanism.

A protein called Nuclear factor erythroid 2-related factor 2 (Nrf2) is regularly activated in response to oxidative stress to protect the brain from oxidative damage. But in the brain of someone with Alzheimer's disease (AD), Nrf2 defense against oxidative stress declines. How that occurs in AD was unknown. A new study found that a protein called Slingshot Homolog-1, or SSH1, stops Nrf2 from carrying out its protective biological activity.

Genetically eliminating SSH1 in mouse models of AD increases Nrf2 activation and slows the development of oxidative damage and buildup of toxic plaques and tangles in the brain - both risk factors for AD. As a result, the regular connections between brain cells are maintained and degeneration of brain nerve cells is avoided.

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VEGF and Runx2 mRNA Delivered by Nanomicelle Accelerate Bone Regeneration

Researchers here report on progress in their program of demonstrating that upregulation of VEGF and Runx2 in combination can accelerate bone regrowth. In this animal study the researchers employed a therapy based on delivery of messenger RNA (mRNA) encapsulated in nanomicelle carrier particles formed from polyethylene glycol and polyamino acid. This produces short-term, localized expression of VEGF and Runx2 in the injured bone tissue when injected directly, and is a suitable basis for translation to clinical use, where the carrier might be swapped out for one of the more established lipid nanoparticle carriers.

Bone defects remain a challenge today. In addition to osteogenic activation, the crucial role of angiogenesis has also gained attention. In particular, vascular endothelial growth factor (VEGF) is likely to play a significant role in bone regeneration, not only to restore blood supply but also to be directly involved in the osteogenic differentiation of mesenchymal stem cells. In this study, to produce additive angiogenic-osteogenic effects in the process of bone regeneration, VEGF and Runt-related transcription factor 2 (Runx2), an essential transcription factor for osteogenic differentiation, were coadministered with messenger RNAs (mRNAs) to bone defects in the rat mandible.

The mRNAs were administered to a bone defect prepared in the rat mandible using our original cationic polymer-based carrier, the polyplex nanomicelle. The bone regeneration was evaluated by micro-computerized tomography (μCT) imaging, and histologic analyses.

Osteogenic markers such as osteocalcin (Ocn) and osteopontin (Opn) were significantly upregulated after mRNA transfection. VEGF mRNA was revealed to have a distinct osteoblastic function similar to that of Runx2 mRNA, and the combined use of the two mRNAs resulted in further upregulation of the markers. After in vivo administration into the bone defect, the two mRNAs induced significant enhancement of bone regeneration with increased bone mineralization. Histological analyses using antibodies against CD31, ALP, or OCN revealed that the mRNAs induced the upregulation of osteogenic markers in the defect, together with increased vessel formation, leading to rapid bone formation.

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Rutin Suppresses the SASP of Senescent Cells

Senescent cells accumulate with age and cause harm via a sustained, energetic production of signal molecules, the senescence-associated secretory phenotype (SASP), that disrupts tissue structure and function. In addition to the search for senolytic drugs that can selectively destroy senescent cells by pushing them into programmed cell death, researchers are also looking for senomorphic drugs that can suppress some or most of the SASP by interfering in its regulatory mechanisms. This seems to me a poor alternative to clearance of senescent cells, as a senomorphic drug must be taken continually, but nonetheless a great many such research programs are underway.

Aging is a major risk factor for most chronic disorders, for which cellular senescence is one of the central hallmarks. Senescent cells develop the pro-inflammatory senescence-associated secretory phenotype (SASP), which significantly contributes to organismal aging and age-related disorders. Development of senotherapeutics, an emerging class of therapeutic agents to target senescent cells, allows to effectively delay aging and alleviate chronic pathologies. Here we report preliminary outputs from screening of a natural medicinal agent library for senotherapeutic candidates and validated several agents with prominent potential as senomorphics.

Rutin, a phytochemical constituent found in a number of plants, showed remarkable capacity in targeting senescent cells by dampening expression of the full spectrum SASP. Further analysis indicated that rutin restrains the acute stress-associated phenotype (ASAP) by specifically interfering with the interactions of ATM with HIF1α, a master regulator of cellular and systemic homeostasis activated during senescence, and of ATM with TRAF6, part of a key signaling axis supporting the ASAP development toward the SASP. Conditioned media produced by senescent stromal cells enhanced the malignant phenotypes of prostate cancer cells, including in vitro proliferation, migration, invasion, and more importantly, chemoresistance, while rutin remarkably downregulated these gain-of-functions. Although classic chemotherapy reduced tumor progression, the treatment outcome was substantially improved upon combination of a chemotherapeutic agent with rutin.

Our study provides a proof of concept for rutin as an emerging natural senomorphic agent, and presents an effective therapeutic avenue for alleviating age-related pathologies including cancer.

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Heterochronic Parabiosis Produces Modest Extension of Life in the Older Paired Mouse

Heterochronic parabiosis is the surgical joining of the circulatory systems of an old and young mouse, both of the same genetic background. The younger mouse shows signs of accelerated aging, while the old mouse shows signs of rejuvenation. This has led to a broad range of research and development focused on age-related changes in levels of various signal molecules in the bloodstream. Some groups continue to look at declining levels of specific molecules such as GDF11 and oxytocin that might be boosted in old mice, but at present the consensus appears to be that old blood contains damaging signals, changing cell behavior for the worse. Thus any dilution of those signals is beneficial, whether achieved with young blood or with saline. Here, researchers demonstrate that a few weeks to a few months of parabiosis is enough to modestly extend life span in old mice.

A process of surgically joining the circulatory systems of a young and old mouse slows the aging process at the cellular level and lengthens the lifespan of the older animal by up to 10%. Researchers found that the longer the animals shared circulation, the longer the anti-aging benefits lasted once the two were no longer connected. The findings suggest that the young benefit from a cocktail of components and chemicals in their blood that contributes to vitality, and these factors could potentially be isolated as therapies to speed healing, rejuvenate the body, and add years to an older individual's life.

Earlier studies documented anti-aging benefits in tissues and cells of the older mice after three weeks of parabiosis. These studies found that the older mice became more active and animated, and their tissue showed evidence of rejuvenation. "Our thought was, if we see these anti-aging effects in three weeks of parabiosis, what happens if you bring that out to 12 weeks. That's about 10% of a mouse's lifespan of three years." The ages of the mice were also important, with the young mouse aged four months, and the older mouse aged two years. With follow-up during a two-month detachment period, the older animals exhibited improved physiological abilities and lived 10% longer than animals that had not undergone the procedure.

At the cellular level, parabiosis drastically reduced the epigenetic age of blood and liver tissue, and showed gene expression changes opposite to aging, but akin to several lifespan-extending interventions such as calorie restriction. The rejuvenation effect persisted even after two months of detachment. "The elements that are driving this are what's important, and they are not yet known. Are they proteins or metabolites? Is it new cells that the young mouse is providing, or does the young mouse simply buffer the old, pro-aging blood? This is what we hope to learn next."

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Complement-Producing Macrophages in Atherosclerosis

Atherosclerosis is, fundamentally, a condition centered around the function, capabilities, and age-related dysfunction of macrophage cells. These innate immune cells are responsible for clearing excess cholesterol, transported via LDL particles, from blood vessel walls. As macrophages become more dysfunctional with age, or otherwise shift in their activities due to rising inflammatory signaling, deposits of cholesterol can reach a tipping point at which they can no longer be cleared and turn into atherosclerotic lesions. Macrophages in the lesions are overwhelmed by the excess of cholesterol, become inflammatory, and die, adding their mass to the growing lesion while also calling in more macrophages to suffer the same fate.

Researchers have identified a specific subtype of complement-producing macrophages that are present in both mouse as well as human atherosclerotic plaques. The complement system is a family of blood-borne proteins with crucial importance in host defense from pathogens. In addition, complement exerts critical housekeeping functions by aiding the removal of damaged and dying cells by macrophages. Part of the complement is continuously active by the generation of cleavage products of the central component C3 - a process that is highly regulated by CFH. Complement activation has long been implicated in human atherosclerosis - however, the pathologic importance of cellular versus systemic complement activation in lesion progression has not been appreciated.

"In contrast to the conventional understanding that the role of complement in atherosclerosis is primarily driven by liver-derived complement via the circulation, there has been increasing evidence that immune cells can also produce a defined set of complement components. However, if and how complement is controlled within these cells has been unknown. We were able to demonstrate that inflammatory monocyte-derived macrophages accumulate complement C3, the central complement component during inflammation with a concomitant increase in the production of its master regulator, CFH."

"First, we made the surprising observation that global lack of CFH displays an overall beneficial impact on plaque progression, which is dependent on its interaction with C3. Building on these data, we were able pinpoint, that the protective effect is exerted on the cellular level, as selective deletion of CFH in monocytes and macrophages led to a robust decrease in both atherosclerotic lesion size and necrotic area due to an improved capacity to ingest and clear dying cells. Importantly, we identified a distinct inflammatory macrophage subset in human coronary artery plaques that is specifically enriched for C3 and CFH. Based on their gene expression profile, these cells are wired to respond to inflammation and appear to be critical for the engulfment of dying cells in human plaques."

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A Glimpse at the Future of Preventative Treatment for Aging

At some point, the various measures of biological age currently under development and assessment will coalesce into some form of consensus measurement, largely agreed upon, the objections to its use minimal and circumstantial. At that point, a great deal of effort will go into assessing established and new interventions that might decrease or slow the progression of that consensus measure of biological age. It will likely take some decades for the back and forth of real time validation of interventions to treat aging to progress thereafter, but things will certainly become a great deal more heated once the research community agrees on how to best measure biological age. Meanwhile, it is certainly possible today for anyone to propose a measure and demonstrate that some interventions affect it, but unlikely that any great number of other people will agree that this is the right, useful, or in any way proven measure of aging.

Clinical healthy aging recommendations are disease-centric and reactive rather than focusing on holistic, organismal aging. In contrast, biological age (BA) estimation informs risk stratification by predicting all-cause mortality, however current BA clocks are not connected to underlying aging mechanisms, making it difficult to intervene clinically.

To generate actionable BA clocks, we developed and validated a principal component (PC)-based clinical aging clock (PCAge) that identifies signatures (PCs) associated with healthy and unhealthy aging trajectories. We observed that by intervening in PC-specific space, angiotensin-converting-enzyme inhibitors (ACE-Is) or angiotensin receptor blockers (ARBs) normalize several modifiable clinical parameters, involved in renal and cardiac function as well as inflammation. Proactive treatment with ACE-I/ARBs appeared to significantly reduce future mortality risk and prevented BA acceleration.

Finally, we developed a reduced BA clock (PC_mAge), based directly on PCAge, which has equivalent predictive power, but is optimized for immediate application in clinical practice. Our geroscience approach points to mechanisms associated with BA providing targets for preventative medicine to modulate biological processes that drive the shift from healthy functioning toward aging and the eventual manifestations of age-related diseases.

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Hoping for Gut Microbiome Rejuvenation to Reduce the Incidence of Alzheimer's Disease

It has only comparatively recently become widely understood that the microbial populations making up the gut microbiome change in abundance in characteristic ways with age. Similarly, that the gut microbiome tends to be different in characteristic ways in older people who go on to develop Alzheimer's disease. It remains to be seen as to whether an altered gut microbiome is a meaningful contributing cause to Alzheimer's disease, such as via increased chronic inflammation, or a side effect of some other meaningful contribution, such as the aging of the immune system. At the least, it presents a novel way to assess risk in older people. We might hope that it will be more than that, and that means of rejuvenating the gut microbiome, such as fecal microbiota transplantation using young donors, will significantly reduce the incidence of Alzheimer's disease.

Studies have shown that the gut microbiomes of people with symptomatic Alzheimer's differ from those of healthy people with normal cognition. Now, new work shows that these differences arise early on in people who will develop Alzheimer's, even before any obvious symptoms appear. The science still has a way to go before we'll know if specific dietary changes can alter the gut microbiome and modify its influence on the brain in the right ways. But what's exciting about this finding is it raises the possibility that doctors one day could test a patient's stool sample to determine if what's present from their gut microbiome correlates with greater early risk for Alzheimer's dementia. Such a test would help doctors detect Alzheimer's earlier and intervene sooner to slow or ideally even halt its advance.

Researchers enrolled 164 healthy volunteers, age 68 to 94, who performed normally on standard tests of cognition. They also collected stool samples from each volunteer and thoroughly analyzed all the microbes from their gut microbiome. Study participants also kept food diaries and underwent extensive testing, including two types of brain scans, to look for signs of beta-amyloid plaques and tau protein accumulation that precede the onset of Alzheimer's symptoms.

Among the volunteers, about a third (49 individuals) unfortunately had signs of early Alzheimer's. And, as it turned out, their microbiomes showed differences, too. The researchers found that those with preclinical Alzheimer's had markedly different assemblages of gut bacteria. Their microbiomes differed in many of the bacterial species present. Those species-level differences also point to differences in the way their microbiomes would be expected to function at a metabolic level. These microbiome changes were observed even though the individuals didn't seem to have any apparent differences in their diets.

The team is now conducting a five-year study that will follow volunteers to get a better handle on whether the differences observed in the gut microbiome are a cause or a consequence of the brain changes seen in Alzheimer's. If it's a cause, this discovery would raise the tantalizing possibility that specially formulated probiotics or fecal transplants that promote the growth of "good" bacteria over "bad" bacteria in the gut might slow the development of Alzheimer's and its most devastating symptoms.

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