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- Applying Proteomics to the Development of Senolytic Therapies
- Assessing Markers of Cellular Senescence in the CALERIE Study of Calorie Restriction
- Intestinal Inflammation Increases with Age, and is Greater Still in Patients with Alzheimer's Disease
- XPRIZE Healthspan, 101 Million to Incentivize Rejuvenation in Old People
- The Effects of Diet on Life Expectancy
- Visceral Fat Increases Brain Inflammation and Amyloid Aggregation
- The Amaranth Foundation on Bottlenecks in Aging Research
- Associations Between Gut Microbiome and Risk of Age-Related Neurodegenerative Disease
- Using Explainable AI in the Production of Biological Age Measures
- Arguing for SGLT2 Inhibitors to be Senomorphic Drugs
- Age-Related Hearing Loss Correlates with Microstructural Change in the Brain
- Frailty Correlates with Hearing Loss in Later Life
- Mild Mitochondrial Inhibition Slows Aging in Nematode Worms
- Inflammatory Mid-Old Cells in Tissues are Restored to More Youthful Function by Recombinant SLIT2
- IsoDGR as a Form of Molecular Damage Contributing to Degenerative Aging
Applying Proteomics to the Development of Senolytic Therapies
A cell can enter a senescent state in response to various forms of damage and stress, including the short telomeres that occur when reaching the Hayflick limit on cellular replication. A senescent cell ceases to replicate and secretes pro-inflammatory signals, attracting the attention of the immune system. Senescent cells help to suppress cancer by pointing the immune system to areas of potential risk in tissue, and are a part of the response to injury, aiding in regeneration. Senescent cells are normally destroyed by the immune system shortly after creation, but the pace of destruction slows down with age, allowing the number of lingering senescent cells to increase over time. The signals that are helpful in the short term become harmful when present constantly for the long term, disrupting tissue function.
Senolytic therapies are those that can selectively destroy senescent cells, and seem the most straightforward approach to treating this contribution to degenerative aging. Animal studies in which senescent cells are destroyed have demonstrated a rapid, sizable reversal of many measures of aging and age-related disease. The data is impressive. Researchers are looking into other approaches, though, such as suppression of inflammatory signaling or prevention of the senescent state, under the general heading of senotherapeutics. Proteomic analysis plays a sizable role in this area of research and development, as noted in today's open access paper. While first generation senolytic drugs are being tested at some pace in the clinic, largely the dasatinib and quercetin combination, readily available to many via off-label prescriptions, very little effort is spend on that in comparison to the search for novel ways to destroy or change the behavior of senescent cells. This is unfortunate; more of an effort should be made to determine whether existing, low-cost senolytics could be highly beneficial in human patients.
Translating Senotherapeutic Interventions into the Clinic with Emerging Proteomic Technologies
Aging comprises a cascade of underlying cellular and molecular processes, commonly referred to as the hallmarks of aging, that lead to a gradual loss of function and increased susceptibility to diseases. One of the most studied hallmarks of aging, cellular senescence, is a key driver of aging and age-related diseases. Cellular senescence is a complex stress response resulting from a variety of sub-lethal stresses that permanently alter the state of a cell. Three of the defining features of senescence are a permanent arrest of cell proliferation, an increased secretion of a variety of bioactive molecules known as the senescence-associated secretory phenotype (SASP), and a resistance to apoptosis. Despite an arrest of cell growth, senescent cells remain metabolically active and secrete a robust SASP that comprises bioactive molecules, including metabolites, proteins, and lipids. The chronic presence of senescent cells and the SASP are connected to various age-related disorders such as cancer, diabetes, neurodegeneration, osteoarthritis, and cardiovascular disease. Therefore, the elimination of senescent cells and the SASP are promising approaches for combating age-related diseases and improving healthspan.
Causal linkage among aging, cellular senescence, and age-related diseases has caused the emergence of 'senotherapeutics', a catch-all term that refers to therapeutic interventions that target senescent cells. Two common classes of pharmacological senotherapeutics include senolytics and senomorphics. Senolytics are chemical compounds that selectively kill senescent cells. Non-pharmacological senotherapeutic approaches, such as vaccines or immunotherapies, are also proposed options for the selective elimination of senescent cells. Interventions that reduce the upstream inducers of senescence, such as DNA damage, ROS, inflammation, or metabolic imbalance, likely confer senotherapeutic benefits by reducing the initiation of senescence. Additionally, targeting cell populations that drive senescence, such as aged immune cells, may reduce senescent cell burden. Senomorphics are the agents that can block or otherwise modulate the SASP to reduce its detrimental activity and mitigate aging phenotypes. The discovery of the SASP and its potency as a driver of aging have greatly increased interest in its comprehensive characterization, both to explore new mechanisms of aging and identify new biomarkers that indicate 'senescence burden', a useful metric for the clinical translation of senotherapeutic approaches.
Protein biomarkers are essential due to their diagnostic, prognostic, and predictive power, as well as identifying and stratifying patients for treatment and measuring the efficacy of therapies. Mass spectrometry-based proteomics is a powerful, versatile, and robust technology used for comprehensively quantifying and discovering proteins with unrivaled specificity. Given the robust and heterogeneous proteomic phenotypes associated with senescence and the SASP, the discovery and profiling of their proteomic signatures require the large-scale, unbiased, and quantitative abilities that mass spectrometry can provide. The presence of senescence-associated proteins in circulation in recent studies also suggests the use of proteomic technologies will be required for the detection and quantification of senescence biomarkers in blood. Numerous innovations in mass spectrometry workflows for biomarker and drug discovery have been made in recent years, opening new opportunities to accelerate the development of senotherapeutics.
Here, we review the available technologies for identifying, validating, and prioritizing protein biomarkers and therapeutic targets identified via mass spectrometry and how these technologies may be leveraged for the clinical translation of senotherapeutics. We describe the technological advancements that have enabled researchers to address challenges inherent to the proteomic analysis of blood, such as the wide dynamic range of protein concentrations, and discuss multiple workflows that can be leveraged for the discovery of senescence biomarkers, senolytic targets, and cell-surface proteins. We also highlight how modern mass spectrometry-based technologies will open the door for future clinical applications, develop translationally relevant approaches to quantify aging and cellular senescence, and develop therapeutics for enhancing human healthspan.
Assessing Markers of Cellular Senescence in the CALERIE Study of Calorie Restriction
The practice of calorie restriction, eating up to 40% fewer calories while structuring the diet to continue to obtain sufficient micronutrients, is well demonstrated to slow aging and extend life in short-lived species. It is thought that the primary mechanism for this effect is upregulation of the cellular maintenance process of autophagy, given that sabotaging autophagy prevents extension of life span resulting from calorie restriction. Calorie restriction produces such sweeping changes in cell and tissue function that there remains plenty of room to argue for other mechanisms to be important, however. For example, we might consider the loss of visceral fat mass as likely a sizable contribution, given that visceral fat promotes chronic inflammation, and surgically removing visceral fat from mice produces significant benefits.
Calorie restriction is thought unlikely to produce sizable gains in human life span, on the grounds that this would have become well known in ancient times if it was the case. Calorie restriction has been formally assessed in humans in recent years. In the short-term, health benefits look quite similar to those produced in mice. Over the longer term, data is lacking. The longest and largest formal study today was the second phase of the CALERIE trial, in which 128 participants underwent two years of an average 12% calorie restriction compared to the 71 control participants. This study produced a great deal of data that continues to be mined for insights into human aging and effects of calorie restriction in a long-lived species such as our own, to contrast with the sizable effects on health and longevity in short-lived species such as mice.
In particular, and the topic for today, cellular senescence and its role in degenerative aging has garnered far greater interest in the research community in the years since the CALERIE study took place. Thus in today's open access paper, scientists examine CALERIE study data to find evidence for calorie restriction to reduce the burden of cellular senescence that is characteristic of aging. It is known that calorie restriction reduces the burden of senescent cells in mice. The CALERIE data is not as convincing, however. This is probably because the participants were largely not old enough to have a sizable number of senescent cells present in their tissues. It is also the case that other researchers have found it hard to correlate levels of circulating proteins known to be generated by senescent cells with senescent cell burden, for reasons yet to be fully explored.
Calorie restriction reduces biomarkers of cellular senescence in humans
Compelling evidence from a wide range of animal studies suggests that calorie restriction (CR) with adequate nutrient intake is a promising strategy to extend lifespan and delay the onset of several age-related chronic diseases. In humans, the Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy (CALERIE) has been the most rigorous study to investigate the effects of CR. Phase 2 of CALERIE was a 2-year, multicenter, randomized controlled trial in healthy non-obese young-to-middle-aged individuals to examine the safety and effects of moderate CR compared to an ad libitum (AL) diet on predictors of longevity, disease risk factors, and quality of life. Although the average CR attained over the 2 years was ~12% rather than the prescribed 25%, the intervention was deemed safe and effective in promoting cardiometabolic risk reduction. The long-term implications of the intervention on healthspan and longevity remain to be established, but the biospecimens collected during the CALERIE study represent a unique resource to explore the influence of CR on the biology of aging in humans.
In this study we found that 2 years of moderate CR with adequate nutrient intake compared to AL significantly decreased the circulating levels of several senescence-associated biomarkers in healthy, young to middle-aged individuals without obesity. A greater number of biomarkers were modulated at 12 months than at 24 months, but PAI1, PARC, TARC, and TNFR1 were lower in CR participants at both timepoints. Using a machine learning approach, we observed that the changes in several biomarkers were important predictors of the change in CALERIE metabolic outcomes, including HOMA-IR, insulin sensitivity index, and resting metabolic rate residual. Our results advance the mechanistic understanding of CR and suggest a potential link between cellular senescence and metabolic health in humans.
Previous findings from the CALERIE study evidenced a reduction in systemic markers of inflammation, such as C-reactive protein, in participants randomized to the CR intervention. Low grade "sterile" systemic inflammation is considered a risk factor for several age-related chronic diseases and, although its pathogenesis is multifactorial, senescent cells through their senescence-associated secretory phenotype (SASP) are a plausible source of proinflammatory molecules. Unfortunately, none of the SASP components studied to date is unique to senescent cells and, certainly, the secretome of other cell types may be affected by CR. At this time, however, we cannot disentangle whether the reduced levels in circulating senescence-related biomarkers observed in response to CR reflect reduced senescent cell accumulation, increased clearance, or inhibition of their SASP. It is also not clear what organs are the main targets of the intervention. Results from our in silico analysis would suggest that CR may target senescent cells in adipose tissue, but the small sample size limits the generalizability of these results.
To corroborate our data demonstrating a reduction in circulating senescence biomarkers in response to CR, we examined tissue-level changes in a recently defined gene set of 125 secreted factors, transmembrane proteins, and intracellular proteins centered on cellular senescence and the SASP, named SenMayo. Through gene set enrichment analysis we observed a significant reduction in SenMayo in response to CR, which is reflected by an enrichment at baseline compared to 12 months. We note that we did not detect a significant change by RNA sequencing in expression of CDKN1A (P21) or CDKN2A (P16), two prototypical markers of cellular senescence. This may be related to their variable and low levels of expression, particularly in younger and healthier adults.
Intestinal Inflammation Increases with Age, and is Greater Still in Patients with Alzheimer's Disease
16s rRNA sequencing allows the microbial populations resident in the gut to be catalogued in detail: which species are present, and relative numbers by species. In the years since this assay became cheap, reliable, and readily available, researchers have built increasingly large human gut microbiome databases from samples obtained over the course of epidemiological studies. The research community has found that the gut microbiome exhibits characteristic differences in older people, marked by a growth in populations of inflammatory microbes and a loss of those species that produce beneficial metabolites. Further, some age-related conditions appear to be strongly correlated with an altered gut microbiome, particularly with the presence of increased numbers of inflammatory microbes.
Alzheimer's disease is one of the conditions for which a growing body of evidence indicates that an altered gut microbiome plays a role in the onset and progression of pathology. The most likely mechanism by which the gut microbiome can contribute to disease is via provoking an increase level of chronic inflammatory signaling. Unresolved, continual inflammation is a characteristic of aging. It is disruptive of cell and tissue function, and contributes to many different age-related conditions. This doesn't rule out other possibilities, as biology is complex, and the gut microbiome can generate harmful metabolites as well as beneficial ones, but as today's open access paper indicates, inflammation is the first place to look.
Gut inflammation associated with age and Alzheimer's disease pathology: a human cohort study
Age-related disease may be mediated by low levels of chronic inflammation ("inflammaging"). Recent work suggests that gut microbes can contribute to inflammation via degradation of the intestinal barrier. While aging and age-related diseases including Alzheimer's disease (AD) are linked to altered microbiome composition and higher levels of gut microbial components in systemic circulation, the role of intestinal inflammation remains unclear. To investigate whether greater gut inflammation is associated with advanced age and AD pathology, we assessed fecal samples from older adults to measure calprotectin, an established marker of intestinal inflammation which is elevated in diseases of gut barrier integrity.
Multiple regression with maximum likelihood estimation and Satorra-Bentler corrections were used to test relationships between fecal calprotectin and clinical diagnosis, participant age, cerebrospinal fluid biomarkers of AD pathology, amyloid burden measured using 11C-Pittsburgh compound B positron emission tomography (PiB PET) imaging, and performance on cognitive tests measuring executive function and verbal learning and recall. Calprotectin levels were elevated in advanced age and were higher in participants diagnosed with amyloid-confirmed AD dementia. Additionally, among individuals with AD dementia, higher calprotectin was associated with greater amyloid burden as measured with PiB PET. Exploratory analyses indicated that calprotectin levels were also associated with cerebrospinal fluid markers of AD, and with lower verbal memory function even among cognitively unimpaired participants.
Taken together, these findings suggest that intestinal inflammation is linked with brain pathology even in the earliest disease stages. Moreover, intestinal inflammation may exacerbate the progression toward AD.
XPRIZE Healthspan, 101 Million to Incentivize Rejuvenation in Old People
Prizes for success in research and development can work well, if coupled with suitable publicity and activism. Such efforts have a long history, going back to the well-documented longitude rewards offered by the British government in the 1700s. More recently, the original Ansari X Prize for suborbital flight was a very successful example of this sort of initiative, and was launched around the same time as the Methuselah Mouse Prize to spur greater efforts to extend life in animal models. The Palo Alto Longevity Prize followed later with similar goals. Unfortunately for the ability of longevity-focused prizes to generate ongoing publicity, it has turned out to be hard to beat the 60-70% extension of life of mice lacking functional growth hormone signaling. That was not anticipated.
XPRIZE is the foundation that emerged from the original Ansari X Prize, set up to run further incentive prizes for research and development. After a few years of recent interest in involving XPRIZE to in some way help to accelerate the ongoing development of means to treat aging, organizers have now found the sizable funding needed for such an effort, and launched the XPRIZE Healthspan initiative. Development of medical interventions and clinical trials to prove their efficacy are expensive propositions, and a prize to incentivize more activity in this arena must be correspondingly large - and so it is.
XPRIZE Launches Larges Competition in History - 101M XPRIZE Healthspan to Drive Healthier Aging for All
XPRIZE, the world's leader in designing and operating large-scale incentive competitions to solve humanity's grand challenges, today launches 101M XPRIZE Healthspan. This 7-year global competition is the largest competition in history and the largest XPRIZE to date, offering 111 million total between the prize purse and a bonus award. XPRIZE Healthspan will award 101 million in prize funding to the team who successfully develops a proactive, accessible therapeutic that restores muscle, cognition, and immune function by a minimum of 10 years, with a goal of 20 years, in persons aged 65-80 years, in one year or less. An additional 10M FSHD Bonus Prize will be awarded to a team that demonstrates the ability to restore lost muscular function due to Facioscapulohumeral Muscular Dystrophy (FSHD) in one year or less.
XPRIZE Healthspan is the first health-focused competition of its kind, incentivizing competing teams to develop a single or combination of therapeutic treatments that will restore muscle, brain, and immune function lost to age-related degradation by at least 10 years, with a goal of 20 years. The finalist teams competing for XPRIZE Healthspan will conduct 1-year clinical trials. These trials will include persons who are aged 65-80 years who are generally healthy and free of major chronic disease or disability but who are experiencing mild age-related declines in function. For example, slowing walk speed, ability to rise from a chair, or mild changes in memory or cognition. The specific criteria are based on data from multiple sources, and indicate higher risk for future mobility disability, Alzheimer's disease, and related dementias, and multiple age-related diseases such as cardiovascular disease and cancer.
Focusing on multiple measures of healthspan rather than the one absolute measure of life span, and focusing on people rather than mice, is a logical reaction to what has been learned in the past few decades about mouse aging and a greater appreciation of the differences in the response to interventions targeting metabolism in mice and humans. Short-lived species exhibit a much greater extension of life span from calorie restriction and loss of growth hormone signaling than is the case in long-lived species, but the short-term improvements in health and metabolism appear much the same.
By the way functions are commonly measured, it might be possible to hit the prize minimum threshold of a 10 year reversion of measures of aging in at least muscle function via resistance exercise. If one starts with sedentary older people, much more likely! This may be intentional, in the sense that trying to improve on the size of the benefits produced by exercise should be a focus for the research and development community, but many of the interventions currently under development do not outperform exercise, and nobody is really holding anyone's feet to the fire on that topic.
The XPRIZE site does not appear to yet include a description of the specific measures they wish to use to assess the quality of an intervention in each of muscle function, cognitive function, and immune function, but a variety of different measures exist, some standardized, some not. It is unclear as to whether the prize organizers will leave it to the teams to pick their own measures. There is certainly a lot of room to argue over which measures are most appropriate.
The Effects of Diet on Life Expectancy
It is somewhat interesting to see a careful analysis of diet and life expectancy, using the sizable UK Biobank population, that does not contain any of the words "calorie", "weight", or "obesity". The effects of calorie intake on health over the long-term are sizable, even if we focus only on mechanisms associated with the gain of weight. Visceral fat is metabolically active, generates an increased burden of senescent cells, and contributes to the chronic inflammation of aging via a range of different mechanisms.
Thus one would assume that buried underneath this set of data on what it is that people eat is a more relevant and useful set of data that incorporates both dietary components and calorie intake, and which is only mentioned in passing in this paper. Certainly, it is the case that people who eat more processed and less healthy foods are usually consuming significantly more calories than the few who put in an effort to garden their diet, and are usually going to carry a greater burden of visceral fat.
Life expectancy can increase by up to 10 years following sustained shifts towards healthier diets in the United Kingdom
In this paper, we present a method for estimating changes in life expectancy following changes in food choices, considering correlation between mortality and food group intakes, and effect delay. Such estimates may be useful particularly for policy purposes and for underpinning both guidance and interventions for improving public health. Our results indicate that UK adults aged 40 years with median dietary patterns can expect to gain approximately 3 years in life expectancy from sustained changes to the longevity-associated dietary patterns. Importantly, the estimated gain in life expectancy is approximately a decade for those shifting from the unhealthiest to the longevity-associated dietary patterns. Overall, the bigger the changes made towards healthier dietary patterns, the larger the expected gains in life expectancy are.
Consuming less sugar-sweetened beverages and processed meats and eating more whole grains and nuts were estimated to result in the biggest improvements in life expectancy. Sensitivity analysis also adjusting for body mass index and energy consumption indicated that body mass index and energy consumption might partially mediate and/or confound a possible beneficial effect between life expectancy and whole grains, vegetables and fruits, and inversely for red meat and eggs. For white meat, associations were stronger when adjusting for energy intake and body mass index, while the situation was mixed for legumes. These estimates correspond well with meta-analyses on associations between intakes of food groups and mortality.
Unsurprisingly, predicted gains in life expectancy are lower when the dietary change is initiated at older ages, but these remain substantial. For example, we estimated that people at the age of 70 years could expect to benefit from about half of the life expectancy gain predicted for adults at the age of 40 years, equivalent to a gain in 1.5 years when optimizing median dietary patterns and 4-5 years for those shifting from the unhealthiest dietary patterns. The UK population currently has a life expectancy at birth of 83.6 years for females and 79.9 years for males, and a 3 year gain in life expectancy associated with changes from median to longevity-optimized dietary patterns from the age of 40 years. Life expectancies have steadily increased over time, and the observed increase is parallel to the changes in life expectancy observed in the United Kingdom over the past 15 years. A large shift towards healthy dietary patterns could contribute substantially to meeting the Sustainable Development Goal target 3.4 that aims to cut premature mortality by one-third.
Visceral Fat Increases Brain Inflammation and Amyloid Aggregation
The correlation between being overweight and risk of developing Alzheimer's disease is nowhere near as strong as, say, between being overweight and risk of developing type 2 diabetes. Given the evidence for chronic inflammation to be important in the development of Alzheimer's disease, and the many ways in which excess visceral fat tissue promotes chronic inflammation, it is somewhat puzzling that Alzheimer's isn't more of a lifestyle disease, similar to the way in which type 2 diabetes derives from lifestyle choices. That said, there is a contribution to Alzheimer's risk, and carrying excess weight is unwise, for this and many other reasons.
To try and identify Alzheimer's risks earlier, researchers assessed the association between brain MRI volumes, as well as amyloid and tau uptake on positron emission tomography (PET) scans, with body mass index (BMI), obesity, insulin resistance, and abdominal adipose (fatty) tissue in a cognitively normal midlife population. Amyloid and tau are proteins thought to interfere with the communication between brain cells. "Even though there have been other studies linking BMI with brain atrophy or even a higher dementia risk, no prior study has linked a specific type of fat to the actual Alzheimer's disease protein in cognitively normal people. Similar studies have not investigated the differential role of visceral and subcutaneous fat, especially in terms of Alzheimer's amyloid pathology, as early as midlife."
For this cross-sectional study, researchers analyzed data from 54 cognitively healthy participants, ranging in age from 40 to 60 years old, with an average BMI of 32. The participants underwent glucose and insulin measurements, as well as glucose tolerance tests. The volume of subcutaneous fat (fat under the skin) and visceral fat were measured using abdominal MRI. Brain MRI measured the cortical thickness of brain regions that are affected in Alzheimer's disease. PET was used to examine disease pathology in a subset of 32 participants, focusing on amyloid plaques and tau tangles that accumulate in Alzheimer's disease.
The researchers found that a higher visceral to subcutaneous fat ratio was associated with higher amyloid PET tracer uptake in the precuneus cortex, the region known to be affected early by amyloid pathology in Alzheimer's disease. This relationship was worse in men than in women. The researchers also found that higher visceral fat measurements are related to an increased burden of inflammation in the brain. "Several pathways are suggested to play a role. Inflammatory secretions of visceral fat - as opposed to potentially protective effects of subcutaneous fat - may lead to inflammation in the brain, one of the main mechanisms contributing to Alzheimer's disease."
The Amaranth Foundation on Bottlenecks in Aging Research
The Amaranth Foundation is one of a small number of organizations created by high net worth individuals to accelerate progress towards the development of therapies to treat aging, picking and choosing research programs and biotech startups to fund based on the founders' understanding of the science and favored goals. Amaranth has a strong focus on neuroscience, for example. The Amaranth pitch on the importance of focusing on bottlenecks in the research and development process is a more general call to action, however, and an interesting take on how best philanthropic organizations should direct their efforts in order to speed up the advent of human rejuvenation.
By 2029, the United States will spend 3 trillion every year - half its federal budget - on adults aged 65 and older. By the same year, nearly 20 million Americans will die from age-related illnesses. Yet research on the biology of aging remains overlooked. Despite a 70-fold increase in funding for aging research since the last decade, the incentives of governments and for-profit investment do not always lend themselves to early bets on ambitious science or field-building. Amaranth is committed to filling this gap by funding moonshot approaches to longevity while expanding the field's talent pool.
In 2022, the Amaranth Advisory Board - a group of leading experts in longevity and neuroscience - convened to address the bottlenecks hindering progress in extending healthy human lifespan. During the meeting, the group enumerated focus areas that require philanthropic investment. Over the last two years (2021-2023), we've directed over 30M of funding to scientific labs, policy-makers, educational initiatives, and prize funding to further the most promising research in these overlooked areas.
Here, we outline initiatives which, if executed, could meaningfully accelerate the advancement of aging science and other life-extending technologies. The resulting document is a philanthropic menu, for which Amaranth is seeking both talent to execute on and co-funders.
Associations Between Gut Microbiome and Risk of Age-Related Neurodegenerative Disease
It is becoming clear that there are correlations between the composition of the gut microbiome and risk of suffering neurodegenerative conditions such as Parkinson's disease and Alzheimer's disease. The gut microbiome changes with age, the populations of inflammatory microbes growing in size, while microbes that create beneficial metabolites are diminished in number. Even only considering the effects of additional chronic inflammation in later life, it is clear that a more inflammatory gut microbiome is harmful. There may be other ways in which gut-resident microbes can contribute to neurodegenerative conditions, however. Finding associations is just the start of the research process, but it does indicate that greater emphasis should be placed on the known ways to restore a youthful balance of microbes in the gut, such as fecal microbiota transplantation.
Researchers conducted a comprehensive analysis of all of the genetic material found in the gut of 420 participants from two large epidemiological studies - the Nurses' Health Study and the Health Professionals Follow-Up Study. They found a consistently lower abundance of certain types of anti-inflammatory, anaerobic bacteria in people with Parkinson's disease. This change was also noticeable among study participants who experienced early signs of Parkinson's disease, which can predate the onset of the classic motor symptoms by many years.
"These species of bacteria are known for their role in reducing inflammation in the gut. This depletion supports a potential link between gut inflammation and Parkinson's disease (PD). The fact that we see these changes before a PD diagnosis suggests that, in the future, the gut microbiome may serve as a biomarker for identifying the earliest phases of PD. This has the potential to revolutionize the diagnosis and treatment, as early detection is often key to developing new therapies."
Researchers are now turning their attention to new research that examines the connection between the microbiome and Alzheimer's disease. The brain disorder slowly destroys memory, thinking skills and, eventually, the ability to carry out the simplest tasks. Researchers are conducting the largest comprehensive study of the microbiome in Latinos to better understand the link between the gut microbiome and Alzheimer's disease. The researchers will study participants in the ongoing Boston Puerto Rican Health Study (BPRHS), a long-term research project launched in 2004. With updated cognitive assessments and the analysis of MRI brain scans and blood and stool samples, the research team will identify the gut composition in each participant, the function of each species of bacteria, and any harmful molecules that could cause disruption in the brain.
Using Explainable AI in the Production of Biological Age Measures
Standard approaches to generating aging clocks from biological data produce algorithmic combinations of factors that are opaque. It is entirely unclear as to how they relate to underlying mechanisms of damage and dysfunction that produce degenerative aging, and thus hard to use them as a tool to assess ways to modify those mechanisms. Explainable artificial intelligence is a term of art used to describe approaches to machine learning that produce more insight into how the final product actually works, what factors went into its construction, how it relates to underlying processes. Given that the primary challenge in the field of measuring biological age, such as via epigenetic clocks, is that we don't understand how these clocks relate to specific causes and processes of aging, it seems sensible to make more of an effort to produce aging clocks that are comprehensible from the outset. The work here is a step in that direction.
Existing biological age clocks have three main limitations. First, they necessitate a trade-off between accuracy (ie, predictive performance for chronological age or mortality) and interpretability (ie, understanding each feature's contribution to the prediction). Most of them use linear models that offer interpretability but weaker predictive power for mortality prediction than complex machine-learning models. This choice is natural given that interpretability is a key goal of biological age clocks: identifying biomarkers of biological age can improve our understanding of the ageing process and help develop drugs that target ageing-related dysfunction. Although advanced machine-learning models have created first-generation biological age models using diverse data types such as epigenetic features, blood markers, electrocardiogram features, brain MRI features, and transcriptomic features, these models are hard to interpret and do not have individualised explanations. To build models that are both accurate and interpretable, we turn to the emerging area of explainable artificial intelligence (XAI).
The second limitation is that interpretations of previous biological age clocks might not address important scientific questions. Previous biological age studies primarily explain the model as a whole (global explanation). However, given the substantial variations in ageing processes among individuals, individualised explanations are crucial for comprehending complex ageing mechanisms. We leveraged recent XAI methods to provide principled individualised (local) explanations on the basis of feature attributions. Typically, feature attributions can be difficult to understand for non-machine-learning practitioners because they are usually in units of predicted probability or logits units. To make our biological age explanations more accessible, we rescaled our attributions to the age scale in units of years so that the rescaled attributions sum to the biological age acceleration (AgeAccel) of an individual.
The third limitation of current biological age clocks is their inability to incorporate several age-related outcomes, such as cause-specific mortalities. Their inability to account for these factors restricts our understanding of important features for different ageing processes. This shortcoming is problematic because biological ageing is enormously complex and thought to be driven by many biological processes. Previous studies noted low agreement between biological age clocks in terms of their correlations with each other and associations with ageing traits, implying that they measure different aspects of biological age. To solve this, we developed our biological age clocks by predicting diverse age-related outcomes, such as specific mortalities and morbidities, allowing us to target and specify particular underlying ageing mechanisms that our clocks capture.
Here we introduce ExplaiNAble BioLogical Age (ENABL Age), a new approach to estimate and interpret biological age that combines complex machine learning and XAI methods. We performed a comprehensive validation of ENABL Age using the UK Biobank and National Health and Nutrition Examination Survey (NHANES) datasets, assessing its ability to capture ageing mechanisms and offering concrete examples of its interpretability.
Arguing for SGLT2 Inhibitors to be Senomorphic Drugs
The incentives placed upon medical development ensure that far too much attention is given to ways in which established, existing drugs can be reused in other contexts, even given marginal effect sizes. It is much cheaper to repurpose an existing drug to a marginal new use than it is to build an actually effective new drug. To the extent that aging becomes a popular target for drug development, and one might argue that this is in the process of happening, every existing drug is going to be scrutinized in this context. Anti-diabetic drugs in particular seem to receive a lot of attention for potential marginal ability to slow aging in some way.
Here we propose that SGLT2 inhibitors (SGLT2i), a class of drugs primarily used to treat type 2 diabetes, could also be repositioned as anti-aging senomorphic drugs (agents that prevent the extrinsic harmful effects of senescent cells). As observed for metformin, another anti-diabetic drug with established anti-aging potential, increasing evidence suggests that SGLT2i can modulate some relevant pathways associated with the aging process, such as free radical production, cellular energy regulation through AMP-activated protein kinase (AMPK), autophagy, and the activation of nuclear factor (NF)-kB/inflammasome. Some interesting pro-healthy effects were also observed on human microbiota.
All these mechanisms converge on fueling a systemic proinflammatory condition called inflammaging, now recognized as the main risk factor for accelerated aging and increased risk of age-related disease development and progression. Inflammaging can be worsened by cellular senescence and immunosenescence, which contributes to the increased burden of senescent cells during aging, perpetuating the proinflammatory condition. Interestingly, increasing evidence suggested the direct effects of SGLT-2i against senescent cells, chronic activation of immune cells, and metabolic alterations induced by overnutrition (meta-inflammation). In this framework, we analyzed and discussed the multifaceted impact of SGLT2i, compared with metformin effects, as a potential anti-aging drug beyond diabetes management. Despite promising results in experimental studies, rigorous investigations with well-designed cellular and clinical investigations will need to validate SGLT2 inhibitors' anti-aging effects.
Age-Related Hearing Loss Correlates with Microstructural Change in the Brain
Researchers here note correlations between hearing loss and specific microstructural changes in the brain indicative of loss of function. Evidence from studies involving patients with and without hearing aids suggests that hearing loss accelerates age-related neurodegeneration. Depriving the brain of sensory processing activity may produce maladaptive compensatory changes, or may simply be a case of "use it or lose it", as is the case for muscle tissue. The mechanisms involved are not yet fully understood, and the situation is complicated by underlying processes of aging that contribute separately to dysfunction in both the brain and the auditory system.
Hearing loss affects more than 60 percent of adults aged 70 and older in the United States and is known to be related to an increased risk of dementia. Researchers employed hearing tests and magnetic resonance imaging (MRI) to determine whether hearing impairment is associated with differences in specific brain regions. Individuals enrolled in this observational study who had hearing impairment exhibited microstructural differences in the auditory areas of the temporal lobe and in areas of the frontal cortex involved with speech and language processing, as well as areas involved with executive function.
"These results suggest that hearing impairment may lead to changes in brain areas related to processing of sounds, as well as in areas of the brain that are related to attention. The extra effort involved with trying to understand sounds may produce changes in the brain that lead to increased risk of dementia. If so, interventions that help reduce the cognitive effort required to understand speech - such as the use of subtitles on television and movies, live captioning or speech-to-text apps, hearing aids, and visiting with people in quiet environments instead of noisy spaces - could be important for protecting the brain and reduce the risk of dementia."
Frailty Correlates with Hearing Loss in Later Life
Many seemingly unrelated aspects of aging correlate with one another in incidence and progression. All of the myriad manifestations of degeneration aging arise from the same small set of underlying processes of cell and tissue damage, so such correlations are perhaps unsurprising. There are cases in which a direct causal connection is found, as in the case of hearing loss contributing to dementia, but in the case of hearing loss and frailty we might expect correlation to arise from shared underlying mechanisms, such as the chronic inflammation that is characteristic of later life.
In a nationally representative sample of older adults in the U.S., worse hearing continuously was associated with greater odds of being frail and pre-frail versus robust after adjusting for sociodemographic and health characteristics. Across hearing categories, those with moderate or greater hearing loss had 84% and 46% greater odds of being frail and pre-frail versus robust, respectively, compared to those with no hearing loss. In age-stratified analyses, the association of worse hearing with being frail versus robust remained significant among older adults aged 71-80 only. Furthermore, lack of hearing aid use was associated with greater odds of being frail and pre-frail versus robust, and frail versus pre-frail.
How hearing loss may be linked to frailty in older adults is not clear. Hearing loss impairs encoding of sound resulting in difficulty with communication and hinders spatial awareness. This may eventually lead to cognitive and physical decline via constantly high cognitive load due to effortful listening, greater risk for social isolation, and depression, and a poorer physical function profile including slower gait speed, lower levels of physical activity, and more falls. Furthermore, these manifestations may negatively impact and reinforce one another in a vicious cycle. For example, hearing loss may cause social withdrawal which in turn may contribute to physical decline and more social withdrawal. Therefore, the underlying mechanisms potentially linking hearing loss to frailty may be related to cognitive and physical decline. Interestingly, we found that the studied associations were stronger among participants ages 71-80 years, suggesting that hearing loss at a relatively younger age may have a greater impact on frailty risk.
Mild Mitochondrial Inhibition Slows Aging in Nematode Worms
Researchers here demonstrate that means of mildly inhibiting the production of some of the protein machinery used to generate chemical energy store molecules, adenosine triphosphate, in mitochondria can extend life by 50-70% in nematode worms - a species in which much larger life extension is possible, so this might be viewed as a moderate effect size. Many different approaches to adjusting mitochondrial function can slow aging and extend life in short-lived species. In some cases this works by provoking mitochondria into an alternative pathway for ATP generation that produces a little more oxidative stress than usual, triggering greater cell maintenance activities. The details and dosing matter, however, and there is a fine line between lesser disruption that slows aging versus greater disruption that causes cell and tissue dysfunction to accelerate aging.
Aging is a continuous degenerative process caused by a progressive decline of cell and tissue functions in an organism. It is induced by the accumulation of damage that affects normal cellular processes, ultimately leading to cell death. It has been speculated for many years that mitochondria play a key role in the aging process. In the aim of characterizing the implications of mitochondria in aging, here we used Caenorhabditis elegans (C. elegans) as an organismal model treated a panel of mitochondrial inhibitors and assessed for survival. In our study, we assessed survival by evaluating worm lifespan, and we assessed aging markers by evaluating the pharyngeal muscle contraction, the accumulation of lipofuscin pigment, and ATP levels.
Our results show that treatment of worms with either doxycycline, azithromycin (inhibitors of the small and the large mitochondrial ribosomes, respectively), or a combination of both, significantly extended median lifespan of C. elegans, enhanced their pharyngeal pumping rate, reduced their lipofuscin content and their energy consumption (ATP levels), as compared to control untreated worms, suggesting an aging-abrogating effect for these drugs. Similarly, diphenyleneiodonium chloride (DPI), an inhibitor of mitochondrial complex I and complex II, was capable of prolonging the median lifespan of treated worms. On the other hand, subjecting worms to vitamin C, a pro-oxidant, failed to extend C. elegans lifespan and upregulated its energy consumption, revealing an increase in ATP level. Therefore, our longevity study reveals that mitochondrial inhibitors (i.e., mitochondria-targeting antibiotics) could abrogate aging and extend lifespan in C. elegans.
Inflammatory Mid-Old Cells in Tissues are Restored to More Youthful Function by Recombinant SLIT2
Researchers here note the existence of what they call "mid-old" cells, cells in tissue stroma that are on the path to becoming senescent, are not yet entered into the senescent state, but nonetheless produce constant inflammatory signaling that is disruptive to tissue structure and function. The researchers find that these cells respond positively to delivery of recombinant SLIT2, diminishing their bad behavior. In very old mice, this treatment resulted in improved muscle mass and function and greater animal activity. This is an interesting finding, and will need further investigation and replication to rule out other mechanisms resulting from SLIT2 delivery. For example, this behavior of mid-old cells could be a bystander effect of senescent cells, and SLIT2 is in some way removing those.
Senescent cell accumulation in tissues is a well-known driver of organ aging and the overall aging process. Multiple studies have consistently revealed the accumulation of senescent cells with the progression of aging. Accumulated senescent cells play a significant role as they cause a halt in the proliferation of functional cells, ultimately resulting in organic dysfunction. Moreover, senescent cells significantly affect the surrounding microenvironment by inducing sterile chronic inflammation through the secretion of senescence-associated secretory phenotypes (SASPs), which are known as "inflammaging" phenomena.
While it has been known that the accumulation of senescent cells in the tissues of the elderly is related to tissue aging, it does not constitute the majority of cells within the tissue. Moreover, it is understood that non-senescent cells within the elderly tissue still proliferate. However, the reason for the decline in organic function in the elderly as they age remains unclear. Therefore, we hypothesized that there might be a subset of cells in an intermediate stage of the cellular senescence process within the tissue, significantly impacting and ultimately leading to organic dysfunction in the elderly. Here, we propose the existence of intermediate stage cells that are neither youthful nor senescent. We termed these cells as "mid-old cells."
Here, we found that the major population of stroma fibroblasts or smooth muscle cells are mid-old status. Moreover, we investigated the cellular characteristics of mid-old fibroblasts and smooth muscle cells in vitro and in vivo, leading us to propose mid-old cells as a new potential target for anti-aging therapy. Upregulation of pro-inflammatory genes (IL1B and SAA1) and downregulation of anti-inflammatory genes (SLIT2 and CXCL12) were detected in mid-old cells. n the stroma, SAA1 promotes development of the inflammatory microenvironment via upregulation of MMP9, which decreases the stability of epithelial cells present on the basement membrane, decreasing epithelial cell function. Remarkably, the microenvironmental change and the functional decline of mid-old cells could be reversed by a young cell-originated protein, SLIT2. Our data identify functional reversion of mid-old cells as a potential method to prevent or ameliorate aspects of aging-related tissue dysfunction.
IsoDGR as a Form of Molecular Damage Contributing to Degenerative Aging
Proteins can become modified in a wide range of ways via addition or removal of various motifs. This is a necessary part of our biochemistry, but some modifications are harmful rather than useful. The pattern of protein modifications present in cells changes with age, and some pathological modifications begin to appear more often. The underlying reasons for these changes are usually poorly understood, at least once stepping beyond the immediate causal chemical reactions, as cellular biochemistry is very complex. As researchers here demonstrate, given a problematic modified protein that exists outside cells, it is possible to target it for removal and thereby produce benefits.
At a molecular level, aging is thought to be underpinned by progressive biomolecular damage caused by degenerative protein modifications (DPMs), including oxidation, deamidation, glycation, and a range of other non-enzymatic structural changes. We now recognize that aging is a consequence of deleterious chemical processes that damage biomolecules and impair the homeostatic functions programmed by our genomes. The functional impact of DPMs depends on the mode of modification and the target molecule involved. For example, deamidation leads to the accumulation of isoaspartate residues that progressively disrupt protein integrity and alter biological activity. However, "gain of function" structural changes caused by DPMs may play equally important roles in human pathology. DPMs greatly increase the diversity of biomolecules present in body tissues, with a high probability of generating proteoforms capable of interacting with or binding to key biomolecules in novel ways.
Indeed, we recently reported that deamidation of the amino acid sequence NGR (Asn-Gly-Arg) in extracellular matrix (ECM) proteins results in "gain-of-function" conformational switching to isoDGR (isoAsp-Gly-Arg) motifs that can bind to integrins and promote immune cell activation. Unlike isoaspartate-modified proteins within cells that can be repaired by the Pcmt1 enzyme, long-lived ECM proteins cannot be repaired by intracellular mechanisms and are thus susceptible to progressive damage over time. Accordingly, age-linked isoDGR modifications have previously been detected in several ECM proteins derived from human carotid plaque tissues, suggesting that these molecules may be capable of enhancing leukocyte binding to the atherosclerotic matrix, thereby accelerating progression of atherosclerosis.
We now report that anti-isoDGR immunotherapy mitigates lifespan reduction of Pcmt1-/- mouse. We observed extensive accumulation of isoDGR and inflammatory cytokine expression in multiple tissues from Pcmt1-/- and naturally aged wild type (WT) animals, which could also be induced via injection of isoDGR-modified plasma proteins or synthetic peptides into young WT animals. However, weekly injection of anti-isoDGR monoclonal antibody was sufficient to significantly reduce isoDGR-protein levels in body tissues, decreased pro-inflammatory cytokine concentrations in blood plasma, improved cognition/coordination metrics, and extended the average lifespan of Pcmt1-/- mice. Mechanistically, isoDGR-mAb mediated immune clearance of damaged isoDGR-proteins via antibody-dependent cellular phagocytosis. These results indicate that immunotherapy targeting age-linked protein damage may represent an effective intervention strategy in a range of human degenerative disorders.