Fight Aging! Newsletter, October 30th 2023

Galectin-3 (Gal-3, also known as Mac-2), a β-galactoside binding lectin, is widely expressed in human tissues, including all types of immune cells, epithelial cells, endothelial cells, stem cells, and sensory neurons. Furthermore, it is highly expressed and secreted by macrophages. As a specific regulator of many biological systems, Gal-3 is highly promiscuous and localized within the tissue micro-environment, including extracellular, cytoplasmic, and nuclear. The different locations of Gal-3 contribute to its various functions.

Secreted Gal-3 is pivotal in numerous biological activities including cell growth, differentiation, transformation, apoptosis, angiogenesis, inflammation, fibrosis, and host defense. Also, it is able to cross-link surface glycoproteins and stimulate important pathways involved in the innate immune response such as the oxidative burst in neutrophils, alternative macrophage (M2) activation, and mast-cell degranulation.

Previous studies have reported that elevated blood Gal-3 level in humans was related to exacerbating disease in inflammatory, metabolic, and malignant diseases. Elevated serum Gal-3 levels have been detected in almost all types of cardiovascular disease. However, little is known about the function of Gal-3 in frailty. Moreover, the physiological relevance of whole-blood Gal-3 to predict aging-associated conditions clearly needs further investigation. Thus, monitoring circulating Gal-3 levels in humans could help us understand the mechanism of aging and frailty, leading the way to finding potential treatments.

A chronic state of low-grade inflammation, accompanied by a dysregulation of the inflammatory cytokine network, has been indicated as a major driver of age-associated conditions. A previous study also proposed that the association of inflammatory factors such as C-reactive protein (CRP), interleukin (IL)-6, tumor necrosis factor (TNF)-α, and IL-10 levels with frailty may reflect the phenotype of inflammaging. Hence, we speculated that the association of frailty and Gal-3 might also be mediated by inflammatory cytokine networks.

Nevertheless, up to now, there is very limited evidence on the frailty status in human Gal-3-related studies. In this study, we aimed to address the change of Gal-3 levels in human whole blood with frailty. We performed serum biochemical and peripheral blood mononuclear cells (PBMC) microarray analyses in humans to determine the secretory phenotype characteristics of frailty. Furthermore, we used the frail mouse model to study the significantly altered behavioral phenotype and associated secreted Gal-3 levels in blood samples to reveal the Gal-3-dependent inflammatory dysregulation of frailty.

Natural selection has shaped a wide range of lifespans across mammals, with a few long-lived species showing negligible signs of ageing. Approaches used to elucidate the genetic mechanisms that underlie mammalian longevity tend to involve phylogenetic selection tests on candidate genes, detections of convergent amino acid changes in long-lived lineages, analyses of differential gene expression between age cohorts or species, and measurements of age-related epigenetic changes. However, the link between gene duplication and evolution of mammalian longevity has not been widely investigated.

Here, we explored the association between gene duplication and mammalian lifespan by analysing 287 human longevity-associated genes across 37 placental mammals. We estimated that the expansion rate of these genes is eight times higher than their contraction rate across these 37 species. Using phylogenetic approaches, we identified 43 genes whose duplication levels are significantly correlated with longevity quotients. In particular, the strong correlation observed for four genes (CREBBP, PIK3R1, HELLS, FOXM1) appears to be driven mainly by their high duplication levels in two ageing extremists, the naked mole rat (Heterocephalus glaber) and the greater mouse-eared bat (Myotis myotis). Further sequence and expression analyses suggest that the gene PIK3R1 may have undergone a convergent duplication event, whereby the similar region of its coding sequence was independently duplicated multiple times in both of these long-lived species.

Collectively, this study identified several candidate genes whose duplications may underlie the extreme longevity in mammals, and highlighted the potential role of gene duplication in the evolution of mammalian long lifespans.

During DNA methylation, a methyl group (-CH3) is added to a specific nucleobase, cytosine or adenine, primarily converting the former to 5-methylcytosine (5mC) and the latter to N6-methyladenine (6mA). These modified nucleobases often alter the activity of the affected genetic locus (in general, 5mC represses, while 6mA promotes, gene expression), and the new DNA methylation pattern can be inherited by daughter cells and offspring for certain generations. Efforts to understand the relationship between 5mC and aging have reached such an advanced stage in the last 10 years that several research groups have managed to set up a so-called epigenetic clock to estimate an individual's age based on CpG methylation distributions in the genome. Although relatively good results have been obtained by predicting biological age from 5-cytosine methylation, the method still relies on a genome-wide methylation profile for which the 5mC pattern of the whole genome or at least significant parts of the genome has to be revealed, and this makes the method cumbersome, costly and slow.

DNA methylation at the N6 position of adenine is the other major type of epigenetic modification, which has been widely recognized in bacteria and plants. A few years ago, DNA 6mA modification was also identified in the genome of a diverse range of animal taxa ranging from worms to mammals. Furthermore, the presence of 6mA was recently detected in mammalian mitochondrial DNA (mtDNA). The mitochondrion, a membrane-bound, energy-converting organelle of eukaryotic cells, is known to be involved in the regulation of the aging process across a wide variety of animal species; Caenorhabditis elegans (nematode), Drosophila melanogaster (insect) and mouse (mammalian) strains with decreased mitochondrial activity exhibit a long-lived phenotype.

Because there is a strong association between the epigenetic modifications of genomic DNA and biological age, epigenetic modifications in the mitochondrial genome may be similarly related to the age of the organism, but this has not yet been investigated and explored. In this study, we present a novel, reliable, PCR-based (i.e., sequence-specific) 6mA detection method that is free of technological artifacts and show in several genetic models that relative 6mA levels at different mtDNA sites (these levels actually show that how many percent of the individual mitochondrial genomes present in a given tissue sample are methylated at a selected adenine nucleobase) are significantly related to the age of the organism. Thus, N6-adenine methylation is an inherent process in the organization of mitochondrial genomes too.

These results suggest that the widely observed age-related decline in mitochondrial function is strongly associated with changing 6mA levels and that biological age can be accurately determined from 6mA levels at certain mtDNA sites in a reliable, fast and cost-effective way. Furthermore, we reveal the enzymatic pathways of the mtDNA N6-adenine methylation and demethylation processes in C. elegans and Drosophila, showing the involvement of DNA N6-adenine methyltransferases and N6-methyladenine demethylases mediating 6mA metabolism in the nuclear genome. Together, these results suggest a fundamental role for mtDNA N6-adenine methylation in aging and reveal an efficient diagnostic technique to determine age using DNA.

For the first time, researchers have found that Alzheimer's symptoms can be transferred to a healthy young organism via the gut microbiota, confirming its role in the disease. The study shows that that the memory impairments in people with Alzheimer's could be transferred to young rats through transplant of gut microbiota. The study supports the emergence of the gut microbiome as a key target for investigation in Alzheimer's disease due to its particular susceptibility to lifestyle and environmental influences. Alzheimer's patients had a higher abundance of inflammation-promoting bacteria in faecal samples, and these changes were directly associated with their cognitive status.

To understand the involvement of Alzheimer's patient gut microbiota in host physiology and behaviour, we transplanted faecal microbiota from Alzheimer's patients and age-matched healthy controls into microbiota-depleted young adult rats. We found impairments in behaviours reliant on adult hippocampal neurogenesis, an essential process for certain memory functions and mood, resulting from Alzheimer's patient transplants. Notably, the severity of impairments correlated with clinical cognitive scores in donor patients. Discrete changes in the rat caecal and hippocampal metabolome were also evident. As hippocampal neurogenesis cannot be measured in living humans but is modulated by the circulatory systemic environment, we assessed the impact of the Alzheimer's systemic environment on proxy neurogenesis readouts. Serum from Alzheimer's patients decreased neurogenesis in human cells in vitro and were associated with cognitive scores and key microbial genera.

Our findings reveal for the first time, that Alzheimer's symptoms can be transferred to a healthy young organism via the gut microbiota, confirming a causal role of gut microbiota in Alzheimer's disease, and highlight hippocampal neurogenesis as a converging central cellular process regulating systemic circulatory and gut-mediated factors in Alzheimer's.

As we get older, more cells in healthy tissues become senescent. Senescent cells (SCs) are inactive in terms of reproduction, but extremely active in terms of metabolism and potentially inflame the milieu by producing thousands of bioactive molecules. Growth and development are not possible without the presence of SCs due to the critical role of SCs in a variety of biological processes such as embryogenesis, limb generation, wound healing, host immunity, and tumor suppression. However, due to the proinflammatory entity of senescent cells, their chronic accumulation is associated with a gradual decline in tissue function and age-related disorders.

Diseased blood vessels are a common feature in many eye disorders including retinopathy of prematurity, diabetic retinopathy, and age-related macular degeneration. Mounting recent evidence has discovered the accumulation of senescent neurons and blood vessels in the retina. However, the underlying mechanisms of senescent cell contribution in retinal vasculopathies are not well defined yet. Here, we reviewed dichotomous implications of SCs at the onset and severity of proliferative retinopathies with a specific focus on the retinal vascular system. In a retinal blood vessel, the senescence phenotype in endothelial cells is associated with lower barrier integrity and increased permeability probably due to the impairment of both adherence and tight junctions.

In retinopathies, the hypoxic/oxidative stress induces cellular senescence in retinal neuronal cells that reside predominantly in the avascular zone. The inflammatory secretome of the cell cycle arrested cell boosts and propagates the senescence phenotype to the surrounding tissues in a paracrine and autocrine manner. Dysregulated angiogenesis is another feature of proliferative retinopathies in which SCs play a role. The presence of angiogenic factors, as a part of the SASP secretome, attracts tip cells of retinal blood vessels to the ischemic area and leads to excessive uncontrolled vascularization in the retina. The newly formed blood vessels are leaky, tortuous, and misdirected and do not properly supply the high energy-demanding tissues of the retina and stimulate the senescence phenotype in surrounding retinal cells.

In the retina, it is vital to bear in mind that all implications of SCs are not detrimental. Immune-mediated clearance of senescent endothelial cells in proliferative retinopathies promotes regression of the pathological neovascular tufts and prepares the retina for reparative vascular regression. Recruited mechanisms by retinal immune cells for eliminating stressed endothelial cells are comprehensively described in this review. Finally, senolytics and senomorphics are discussed as two main available therapeutic strategies for eliminating retinal SCs in proliferative retinopathies.

Skeletal muscles are organized into long fibers composed of many nuclei, and when a fiber is damaged, the entire fiber is often lost. It seems that if any one of these nuclei were in a senescent state and were hit by a senolytic therapy, it might result in a fiber break and pull down the entire muscle fiber with it. And muscle fibers aren't easily replaced, and loss of muscle mass and function is already a major problem in aging, so the drug-induced destruction of muscle fibers could accelerate an aging person's slide into disability. Is this a real risk, and if so, does it make senolytic therapies a non-starter?

That's a worrying scenario for those of us who are excited by the promise of senolytic therapies. Fortunately, all the animal data refute it. When we get to the bottom-line question of what senolytic treatment did to the mass and function of muscle in old mice, we see good news all around. Not only did the senolytic-treated old mice not lose muscle, the treated animals actually sustained or restored the distribution of their muscle fiber sizes to the same distribution seen in young mice. Senolytic-treated mice also either gained more strength or suffered less age-related loss of strength than the untreated aging animals, leaving their muscle power partway between that of old and young untreated mice. And senolytic treatment also reduced the amount of dysfunctional repair activity in their muscles.

Klotho is an antiaging protein, and its levels decline with age and chronic stress. The exogenous administration of Klotho can enhance cognitive performance in mice and negatively modulate the Insulin/IGF1/PI3K/AKT pathway in terms of metabolism. In humans, insulin sensitivity is a hallmark of healthy longevity. Therefore, this study aimed to determine if exogenous Klotho, when added to neuronal and astrocytic cell cultures, could reduce the phosphorylation levels of certain insulin signaling effectors and enhance antioxidant strategies in these cells.

Primary cell cultures of cortical astrocytes and neurons from mice were exposed to 1 nM Klotho for 24 hours, with or without glucose. Klotho decreased phosphorylated AKT and mTOR levels. However, in astrocytes, Klotho increased FOXO-3a activity and catalase levels, shielding them from intermediate oxidative stress. In neurons, Klotho did not alter FOXO-3 phosphorylation levels but increased proteasome activity, maintaining lower levels of PFKFB3. This study offers new insights into the roles of Klotho in regulating energy metabolism and the redox state in the brain.

The global burden of age-related cognitive decline is increasing, with the number of people aged 60 and over expected to double by 2050. This study compares the acute effects of age-appropriate cognitively demanding aerobic exercises involving walking, on cognitive functions and exerkine responses such as brain-derived neurotrophic factor (BDNF) and cathepsin B (CTSB) in older, healthy adults. Healthy older golfers (n=25, 16 male and 9 female, 69±4 years) were enrolled in a 5-day randomised cross-over study and completed three different exercise trials (18-hole golf round, 6 km Nordic walking, 6 km walking) in a real-life environment, in random order and at a self-selected pace. Differences in cognition (the Trail-Making Test (TMT) AB) and exerkines (BDNF and CTSB) were analysed within groups and between groups.

All exercise types resulted in a significant decrease in the TMT A-test (golf: -4.43±1.5 s, Nordic walking: -4.63±1.6 s, walking: -6.75±2.26 s), where Nordic walking and walking demonstrated a decrease in the TMT B-test (Nordic walking: -9.62±7.2 s, walking: -7.55±3.2 s). In addition, all exercise types produced significant decreases in the TMT AB test scores, and Nordic walking showed decreases in the TMTB-TMTA-test. There were no immediate postexercise changes in the levels of BDNF or CTSB.

Acute bouts of golf, Nordic walking and walking improved cognitive functions irrespective of exerkines in healthy older adults. In addition, Nordic walking and walking in general enhanced executive functions. No significant effects were seen on the levels of BDNF and CTSB.

Several studies in mouse models of Alzheimer's disease (AD) and in cognitively normal older adults at risk for AD have consistently pointed to the selective vulnerability of cholinergic neurons to amyloid pathology as an early and critical component of presymptomatic disease which predicts subsequent neurodegenerative progression. Indeed, basal forebrain cholinergic neurons dysfunction and degeneration are early pathological events in AD that precede and predict cortical degeneration, clinical onset, and dementia severity.

There is also a close relationship between early dysfunctions in cholinergic signaling and amyloid β (Aβ) pathology. Decreased cholinergic signaling is associated with increased Aβ levels in the brain of mouse models and human patients. Furthermore, Aβ reduces acetylcholine (ACh) synthesis and release both in vitro and in vivo. Given that the brain cholinergic system of males and females show subtle functional differences and that sex hormones exert trophic effects on the cholinergic system, we hypothesized that biological sex may causally influence the relationship between cholinergic tone and amyloid pathology.

We quantified amyloid beta (Aβ) in male and female App-mutant mice with either decreased or increased cholinergic tone and examined the impact of ovariectomy and estradiol replacement in this relationship. We also investigated longitudinal changes in basal forebrain cholinergic function and Aβ in elderly individuals. We show a causal relationship between cholinergic tone and amyloid pathology in males and ovariectomized female mice, which is decoupled in ovary-intact and ovariectomized females receiving estradiol. In elderly humans, cholinergic loss exacerbates Aβ. Our findings emphasize the importance of reflecting human menopause in mouse models. They also support a role for therapies targeting estradiol and cholinergic signaling to reduce Aβ.

There is a major challenge for discovering and developing anti-aging drugs. How does one design a clinical trial to convince patients, physicians, payers and, especially, the FDA that a drug actually works? To do this, a company would have to prove that its drug extends lives. You can't test such a drug in young or even middle-aged people, as these groups still have considerable life left - assuming a life expectancy of 80 years. Thus, you would probably need to study the drug in healthy 70-year-olds (with a placebo control group as comparator) and then follow these subjects for a decade or more to see if those on the drug live meaningfully longer than those in the placebo group. In order to see a statistically meaningful longevity effect, however, the study would need a minimum of 20,000 subjects. This "outcomes" trial would be similar to what is now done for new drugs to treat heart disease, in which a drug's efficacy is determined by whether it reduced heart attacks and strokes. Such studies are not cheap. The costs can be on the order of 2 billion.

The FDA would likely set a very high bar for safety and efficacy for such a study. Unlike studying patients with heart disease, here you would be testing your drug on 70-year-olds who are relatively healthy. Yet, these patients are entering a decade when they become more susceptible to various cancers, neurological disorders, cardiovascular diseases, etc. You would have to be certain that your drug was no different from placebo when studying these safety parameters. The FDA's caution would be well justified. Such a drug would be in tremendous demand should it actually work. Should such a drug be approved and then later shown to increase major side effects, the fallout would be unprecedented.

Given these enormous challenges, why would anyone actually engage in research and development to produce anti-aging drugs? After all, the people investing in these field are accomplished scientists and investors. They are aware of these challenges. Despite the hype around extending the human life span by 10 to 20 years, these companies will not look to conduct life extension studies right out of the gate. Rather, the first drugs will be tested against age-related diseases.

Telomere length is a good index of cellular aging. Longer telomeres are predictive of longer life, and healthy lifestyles are associated with longer telomeres. This study explored the relationship between time spent jogging or running each week and leukocyte telomere length (LTL) in 4,458 randomly selected U.S. adults. The association was studied using data collected by the National Health and Nutrition Examination Survey (NHANES), and a cross-sectional design. Total weekly jog/run time was calculated from survey responses. From the minute totals, three categories were formed: <10 minutes/week, 10-74 minuntes/week, and ≥75 minutes/week. Adults in the third category met the U.S. guidelines.

Data were analyzed using one-way ANOVA. Partial correlation was used to adjust for differences in potential mediating factors, including demographic and lifestyle/medical factors. In the total sample, after adjusting for all the potential covariates, mean LTL significantly differed across the three jog/run categories. Specifically, adults who met the guidelines via jogging and/or running had significantly longer telomeres than adults who performed no jogging/running. Adults in the middle category did not differ from the other two categories. A minimum of 75 minutes of jogging/running weekly is predictive of longer telomeres when compared to adults who do not jog or run regularly.

To map protein production by different types of cells within the eye, researchers used a high-resolution method to characterize proteins in 120 liquid biopsies taken from the aqueous or vitreous humor of patients undergoing eye surgery. Altogether, they identified 5,953 proteins and were able to trace each protein back to specific cell types.

To investigate the relationship between disease and molecular aging, the researchers built a machine learning model that can predict the molecular age of the eye based on a subset of 26 proteins. The model was able to accurately predict the age of healthy eyes but showed that diseases were associated with significant molecular aging. For diabetic retinopathy, the degree of aging increased with disease progression and this aging was accelerated by as much as 30 years for individuals with severe (proliferative) diabetic retinopathy. These signs of aging were sometimes observable before the patient displayed clinical symptoms of the underlying disease and lingered in patients who had been successfully treated.

The researchers also detected several proteins that are associated with Parkinson's disease. These proteins are usually identified postmortem and current diagnostic methods aren't capable of testing for them, which is one reason Parkinson's diagnoses are so difficult. Screening for these markers in eye fluid could enable earlier diagnosis of Parkinson's disease and later therapeutic monitoring.

The alpha-Klotho gene is responsible for encoding a transmembrane protein that is predominantly found in renal tubules. This protein is known as alpha-Klotho and its extracellular domain can be shed to form a soluble variant known as S-Klotho. Studies have shown that S-Klotho has the ability to protect against a range of systemic diseases, such as chronic kidney disease, interstitial lung disease, and cardiovascular events. Furthermore, investigations have demonstrated that S-Klotho plays a pivotal role in modulating oxidative stress, apoptosis, cellular senescence, and endothelial function, positioning it as a promising target in the development of treatments for aging-related diseases. There is a growing body of evidence that suggests a relationship between S-Klotho levels and inflammation. Reduced levels of S-Klotho have been associated with a heightened risk of chronic inflammation, whereas increased levels of Klotho have been shown to possess anti-inflammatory effects.

The Systemic Immune-Inflammation Index (SII) is a measure obtained by dividing the product of neutrophil counts (N) and platelet counts (P) by lymphocyte counts (L). Compared with other inflammatory biomarkers, SII provides a more comprehensive evaluation of the systemic immune-inflammatory status by incorporating multiple components. The objective of this research is to determine the linkage between soluble Klotho (S-Klotho) level and systemic immune-inflammation index (SII).

Eligible participants with complete information of S-Klotho level and SII were selected from the National Health and Nutrition Examination Surveys (NHANES). Subsequently, weighted multivariate linear regression and subgroup analysis were carried out to evaluate the association. Totally, 11,108 adults with complete data on S-Klotho level, SII and other important covariates were included in final analysis. Multivariate liner regression revealed that high level of S-Klotho was associated with low level of SII after multivariate adjustments. When classifying S-Klotho into tertiles, participants in the highest tertile showed a decrease in SII level compared with those in the lowest tertile. The negative associations remained significant regardless of age and gender, and varied depending on smoking status and BMI subgroups.

Most Alzheimer's disease research on human brain tissue has studied postmortem samples, making it difficult for scientists to discern the earliest events in the brain that might have triggered the buildup of plaques and the death of neurons. Knowing the molecular changes in neurons, glia, and other brain cells around plaques during the early phases of the disease could help scientists design treatments that work best when given early.

Researchers have now analyzed an assembly of rare brain tissue samples from 52 living patients with varying degrees of other Alzheimer's-related changes in the brain - including 17 individuals who were later clinically diagnosed with the disease. The brain tissue samples were obtained from normal pressure hydrocephalus (NPH) patients during routine surgeries to reduce excess brain fluid. The scientists identified a suite of changes in cells unique to the early stages of Alzheimer's, including some not seen before in animal studies.

The team discovered a brief hyperactive state in a specific group of neurons that was associated with their death in later stages of the disease, and also increased inflammatory processes in immune cells called microglia as the disease progressed. Neurons are thought to produce the plaque-forming protein called amyloid beta, and the researchers found evidence for this in their data. They also found for the first time that another brain cell type, oligodendrocytes, which produce insulating sheaths around nerve fibers in the brain, may also contribute to plaque formation. A better understanding of how these cells spur the growth of plaques could one day help researchers identify new targets for Alzheimer's drugs.

Unhealthy lifestyle behaviours such as smoking, high alcohol consumption, poor diet, or low physical activity are associated with morbidity and mortality. Public health guidelines provide recommendations for adherence to these four factors, however, their relationship to the health of older people is less certain. This study involved 11,340 Australian participants (median age 73.9) from the Aspirin in Reducing Events in the Elderly (ASPREE) study, followed for a median of 6.8 years. We investigated whether a point-based lifestyle score based on adherence to guidelines for a healthy diet, physical activity, non-smoking and moderate alcohol consumption was associated with subsequent all-cause and cause-specific mortality.

In multivariable adjusted models, compared to those in the unfavourable lifestyle group, individuals in the moderate lifestyle group (Hazard Ratio 0.73) and favourable lifestyle group (Hazard Ratio 0.68) had lower risk of all-cause mortality. A similar pattern was observed for cardiovascular related mortality and non-cancer/non-cardiovascular related mortality. There was no association of lifestyle with cancer-related mortality. In conclusion, reported adherence to a healthy lifestyle is associated with reduced risk of all-cause and cause-specific mortality. Adherence to all four lifestyle factors resulted in the strongest protection.