Fight Aging! Newsletter, December 25th 2023

Aging is an uncontrolled biological process that poses challenges to human health and becomes a social problem that can't be ignored. Aging is regarded as a common risk factor for various human diseases and by reducing sensory, motor, circadian rhythms, and cognitive functions, aging affects the brain morphologically and functionally, resulting in neurological diseases. Importantly, circadian rhythms disruption, characterized by phase shifts and reduced expression of many genes and proteins involved in circadian rhythms greatly impacts aging and longevity in many ways. Disturbances in the circadian rhythms induce disorders of cognitive function, metabolism, mental function, motor control, alertness, blood-brain barrier (BBB) damage, and sleep/wake cycles.

A prospective cohort study of 72,242 participants further supported that disturbances of circadian rhythm are a risk factor for the development of common neurodegenerative and psychiatric disorders. Interestingly, the amount and function of different microbial species fluctuate over time during aging, leading to gut microbiota dysbiosis. The gut microbiota continuously exchanges nutrients, genetic material, and metabolites with the host throughout its life cycle which regulates the homeostasis in the host, including brain function and blood-brain barrier (BBB) integrity. In individuals with neurological disorders, including Alzheimer's disease (AD), Parkinson's disease (PD), stroke, and multiple sclerosis (MS), circadian rhythm disturbances and gut microbiota dysbiosis are common symptoms. Accumulating data suggest that either circadian rhythms or gut dysbiosis contribute to aging-accompanied neurological diseases (AAND). Notably, the disruption of the circadian system can alter microbiome communities and perturb host metabolism, energy homeostasis, and inflammatory pathways, and gut microbiota can regulate host circadian rhythms and metabolism as a transducer of dietary cues. Genetic defects of a biological clock, timing or restriction of food availability, and light/dark phase changes can significantly affect microbial oscillations, leading to a reduction in microbial abundance and species. In addition, gut microbiota-derived metabolites, including short-chain fatty acids (SCFAs) and bile acids (BA), can alter circadian rhythms, indicating that circadian rhythms and gut microbiota can affect each other, and their interplays can induce subsequent effects.

The BBB provides nutrients to the central nervous system (CNS), maintains homeostasis, and regulates its communication with the periphery, forming a protective barrier for the CNS. The changes and destruction of the structure and functional components of the BBB could occur naturally with the aging process. Aging itself may worsen the disruption of different components of the BBB, thus accelerating the progression of brain damage and an ever-increasing global aging population has stimulated the exploration of the relationship between AAND and BBB, to prevent or delay the prevalence of AAND.

Therefore, there is an urgent need to further investigate the role of the BBB in AAND and the underlying mechanisms of BBB damage induced by aging-accompanied circadian rhythms disruption and dysbiosis of gut microbiota which play important roles in regulating BBB integrity. Further elucidation of the interplay of gut microbiota with circadian rhythms could also shed light on the systemic regulatory mechanisms of aging and the BBB. Here, in this review, we first describe how BBB, circadian rhythms, and gut microbiota are altered during the aging process and how these alterations are exacerbated in AAND. We then discuss the effect of the interplay between circadian rhythms disruption and dysbiosis of gut microbiota on BBB integrity. We then discuss and propose potential mechanisms underlying BBB damage induced by dysregulated circadian rhythms and gut microbiota, which could serve as the basis for developing potential interventions to protect the BBB in the aging population through targeting the BBB by exploiting its links with gut microbiota and circadian rhythms for treating AAND.

An aging drug is a drug that has been rigorously shown to increase healthy lifespan in people, with emphasis on the ability of such an intervention to extend quality of life. It could allow older adults to enjoy a higher quality of life, for longer. The economics of delivering such value to human health at scale are unprecedented - we found that a drug approved and labeled for aging would conservatively have a peak global market size in the range of 150-200 billion annually. This size is ~4x the peak projected annual revenue of GLP-1 receptor agonists at 50 billion by 2030, ~6x the peak projected revenue of America's soon-to-be best-selling drug, Keytruda (PD-1 cancer immunotherapy) at 30 billion annually by 2028, ~10x current bestseller Humira's peak annual revenue (anti-TNF) at 21.2 billion in 2022, and ~15x the peak annual revenue of enormous blockbuster Lipitor (a statin) at 13 billion in 2013.

It's also promising that the clinical trial to get this drug approved for aging and age-related disease on the label could potentially be as short as 3-6 years in length and cost 50-100 million, within an order of magnitude of most Phase III clinical trials. Furthermore, just in the past month, we learned it was possible to get a drug approved and labeled for healthy lifespan extension in dogs by the FDA. In this piece, we walk through an estimate of the market potential of an aging drug.

To build a financial model for an aging drug, we need to answer: 1) How big is the market? 2) Who will pay for it? 3) What is the price of the drug? 4) What does adoption look like? The total addressable market (TAM) for an aging drug refers to the entire potential customer base that could generate revenue for the drug, encompassing all individuals who might benefit from or be interested in using it. We based our foundational TAM size on the total number of adults aged 65 or older in the US from the 2017 US census data. To know how much a drug is worth, we need to start with understanding who will pay for it. In the US, the majority of prescription medication costs are paid for by commercial health insurers and Medicare Part D. There is the potential for direct to consumer (DTC) brands to obtain a significant slice of this pie, however. If a drug designed to slow down the aging process receives FDA approval, it could initially pursue a DTC route, especially before long-term health outcomes and economics research can show financial benefits for insurers and other payers.

To predict the price of an aging drug, we estimated the monthly list price for a cash-pay model and the monthly net price for a reimbursement model. The list price is what the manufacturer sets for a drug before negotiations or discounts, which might reflect DTC market prices. In reality, a consumer pays something closer to the net price after discounts and rebates, determined via negotiations between pharma industry stakeholders. Currently, the reduction from the monthly list price ranges between 40-60%. What does adoption over time look like? For the maximum penetration rate (percentage of the TAM captured), we considered the following patient adherence numbers to approximate a range of 25% to 50%: half of all American adults get the flu vaccine every year; patient adherence to chronic medications is about 50%; patient adherence to cardiovascular medication (treatment dependent) ranges from 25-50%; in one study, of 400,000 people eligible to take statins, about 20% were chronically taking them. What is the adoption of an aging drug over time? Assuming a 25% penetration rate, the numbers range from 0.006% in 2030 to 25% in 2045. Assuming a 50% penetration rate the numbers range from 0.012% in 2030 to 50% in 2045.

The approval of a drug targeting the aging process could lead to a seismic shift in healthcare. The potential long-term healthcare savings are vast, as was with statins, which significantly reduced expenditure for inpatient care from hospitalization. With the potential to yield conservatively up to 200 billion annually, a company that owned only this drug would be more valuable than the top two big pharma companies (J&J and Pfizer) in terms of revenue... combined. We believe that this drug has the potential to become the largest product in human history.

Age-related hearing loss (ARHL) is one of the most common health disorders in the aging population, affecting over a third of adults over age 65. Recently, dysregulation of the immune system has come into light as a major pathological driver of ARHL. The term "inflammaging" describes the low-grade, sterile, chronic inflammatory state in the body's tissues with age. Chronic inflammation plays a role in multiple systemic diseases such as diabetes, as well as neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis, and retinal degeneration.

During aging, immune cells undergo senescence, a process in which they lose the ability both to mount the normal immune response and to resolve inflammation after acute insults. Increased systemic levels of inflammatory markers, including C-reactive protein, interleukin-6 (IL-6), and white blood cell counts, are observed in neurodegenerative processes and ARHL, suggesting that inflammation is a hallmark of the aging brain and inner ear. Newer studies are exploring the role of gut microbiota in inflammaging, noting how pro-inflammatory diets such as foods high in sugar correlate with systemic inflammatory markers and severity of hearing loss. Conversely, long-term exercise is thought to delay progression of neurodegenerative processes and ARHL through the dampening of inflammation. Inflammaging can impair neural and sensory networks through several interrelated processes, many of which have been well-characterized in neurodegenerative diseases. Similar mechanisms are now being elucidated in ARHL as well.

This brief review summarizes current research on the cellular and molecular components of the innate immune system in ARHL, including the role of inflammatory cytokines, chemokines, inflammasomes, the classical complement pathway, and macrophages, as well as the interactions of each of these players with inner ear sensory structures. It also discusses emerging research of the involvement of the adaptive immune system in ARHL which thus far has largely been overlooked. A better understanding of immunosenescence in ARHL can elucidate future therapeutic avenues for a very prevalent and debilitating condition that currently has no preventative medicines or molecular treatments that target its underlying pathology.

Functional parameters such as cardiorespiratory fitness (CRF), daily steps, gait speed, and skeletal muscle mass, strength, and power predict the risk of morbidity and mortality in humans. Exercise has wide-reaching systemic effects impacting nearly every tissue and intervenes on multiple biological pathways that become impaired with age, including senescence, proteostasis, mitochondrial function/quality, nutrient signaling, DNA damage, and inflammation. Through repeated exercise, these cellular and molecular changes facilitate increasing CRF, muscle mass, strength, and power while also decreasing established risk factors for cardiometabolic diseases and thereby lowering the risk of type 2 diabetes mellitus (T2DM), dementia, Alzheimer's, cardiovascular disease (CVD), atherosclerosis, frailty, and improving cancer survival/remission. Despite extensive research and commercial investment, a pharmacological agent that captures the numerous pleotropic health benefits of exercise has yet to be identified; thus, efforts to increase adherence to regular exercise continues.

Increased adherence to exercise over a lifetime has remarkable health benefits. At the musculoskeletal level, lifelong exercise delays age-related declines in functional metrics while extending a more youthful molecular phenotype later in life. However, with increasing age, sedentary behavior and cardiometabolic risk factors (hyperglycemia, hyperlipidemia, etc.) may contribute to delayed or diminished whole body and skeletal muscle adaptive potential to exercise, which is often referred to as anabolic resistance. Many of the proposed cellular and biological hallmarks of aging are implicated in blunting the responsiveness of skeleteal muscle to a bout of exercise. However, consistent exercise can still elicit robust adaptations in older adults. One year of endurance training can improve CRF by ~ 5 ml kg-1 min-1 in previously untrained 65-year-old or older individuals. Importantly, in healthy individuals, a 3.5-ml kg-1 min-1 greater CRF was associated with a 11% reduction in all-cause mortality.

Intervening on conserved underlying mechanisms of aging before the development of disease could postpone the onset, slow the progression, or perhaps ameliorate multi-morbidity and extend healthy longevity. Numerous dietary, lifestyle, pharmacological, and genetic approaches have identified that lifespan is modifiable in model systems. The mTOR inhibitor rapamycin is the most ubiquitous intervention thus far to extend lifespan in diverse species. The glucose-lowering medications metformin, sodium-glucose transporter 2 inhibitors (SGLT2i), acarbose, senolytics, and estrogenic agonists (17 estradiol) have also been demonstrated to extend lifespan.

Positive results from preclinical models have spurred large-scale public interest in gerotherapeutics, prompting some self-motivated individuals to take one or more putative geroprotective drugs and supplements off-label with the idea of further extending healthy longevity. Several telehealth companies have begun supplying these proposed geroprotectors to thousands of people across the globe. Importantly, it remains unclear whether the benefits of these pharmacologic approaches observed in pre-clinical models or in-patient populations extend to individuals free from overt disease who may also engage in other bona fide health-extending interventions such as exercise. Current dogma suggests combining geroprotectors with concurrent exercise blunts hallmarks of exercise that are associated with healthy longevity. Frequent (daily) dosing of leading geroprotectors blunts clinically relevant improvements to cardiorespiratory fitness, muscle size/strength/power, and insulin sensitivity.

In the past, we showed that autophagy inducers can prevent or mitigate cardiovascular diseases, including myocardium infarction and heart failure. Due to their galenic properties and reduced cost, small molecules are particularly interesting for the prevention or treatment of cardiovascular diseases. Thus, high nutritional spermidine uptake is associated with reduced cardiovascular morbidity and mortality in humans and spermidine supplementation reduces the severity of atherosclerosis in mice. Spermidine acts against normal cardiac aging, as well as against high-salt diet-induced cardiac insufficiency. The copper-chelating agent triethylenetetramine (TETA) improves cardiovascular function and can induce the regression of pressure overload-induced cardiac hypertrophy. Another autophagy inducer, 4,4'-dimethoxychalcone (4,4'-DC) prevents myocardial necrosis after ligation of the left coronary artery. Furthermore, another, structurally related chalcone, 3,4-dimethoxychalcone (3,4-DC), prevents myocardial necrosis and induces autophagy in multiple mouse organs.

Atherosclerosis is the most prevalent aging-associated cardiovascular disease, providing the pathogenic substratum of most cases of myocardial infarction, stroke, aortic aneurysm, and arterial occlusion affecting internal organs or the femoral artery. The etiology of atherosclerosis appears complex but involves an important dysfunction of innate and cognate immune effectors, with macrophage-mediated inflammatory responses and the formation of foam cells (macrophages exhibiting the accumulation of lipid droplets in their cytoplasm) as prominent elements of the disease process. Given the anti-inflammatory effects of autophagy and the important anti-atherosclerotic role of lipophagy (a subtype of autophagy causing the removal of lipid droplets), we wondered whether the administration of pharmacological autophagy inducers might protect against the development of atherosclerosis.

Based on these premises, we attempted to identify the best strategy to prevent atherosclerosis by searching for agents among the aforementioned compounds that would induce autophagy in all cardiovascular disease-relevant cell types, i.e., cardiomyocytes, endothelial cells, and macrophages. As we report here, 3,4-DC stood out as a broad autophagy inducer. In a series of in vivo experiments involving two distinct mouse models of atherosclerosis, we obtained preclinical evidence indicating that 3,4-DC can efficiently slow the onset of this condition.

Proteins floating in the cerebrospinal fluid (CSF) might do more than diagnose Alzheimer's disease (AD) - they may identify different subtypes. Of the 3,863 proteins measured, 1,058 were either more or less abundant in people with AD. Researches clustered these by whether they were upregulated or downregulated in sync, then used gene ontology to identify biological pathways associated with each cluster. Proteomic profiles suggested five subtypes based on cellular processes predicted to be dysfunctional: the three previously identified - neuronal hyperplasticity, innate immune activation, and blood-brain barrier (BBB) dysregulation - and two new ones, dubbed choroid plexus dysfunction and RNA dysregulation.

Among the 419 people with AD, 137 fell into the neuronal hyperplasticity subtype. Upregulation of proteins involved in synapse assembly, axon guidance, and neurogenesis and gliogenesis suggested overactive neuron signaling and possibly an overabundance of neurons. Indeed, MRI scans showed the least atrophy in this subtype. Only the hippocampus and temporal and parietal lobes shrank. Prevalence of the TREM2 R47H variant was highest in this group. This hypofunctional TREM2 hobbles microglial pruning of synapses in mouse models of amyloidosis and was recently linked to cortical synapse growth. This subtype represented the mildest disease, with people living nine years, on average, after being clinically diagnosed with dementia.

Fifty-six people fit the BBB dysfunction criteria, having blood proteins, such as albumin, fibrinogens, and plasminogen, show up in the CSF. In contrast, there was a dearth of proteins made by brain vascular cells that typically leach into the CSF, such as platelet-derived growth factor receptor β and the cell adhesion proteins cadherin and laminin, suggesting disrupted brain tissue around blood vessels. Along these lines, people with the BBB dysfunction subtype had more microbleeds on MRI than people in other subtypes. In contrast, microglia may be overactive in the second of the three previously identified subtypes, innate immune activation. Among the 124 people in this group, complement components, regulators of cytokine production, and microglial proteins were overrepresented. Researchers saw severe and widespread cortical atrophy in this group, perhaps because microglia prune synapses too vigorously, she speculated. People with this subtype progressed the quickest from mild cognitive impairment to dementia.

As for the two new subtypes, molecules from the extracellular matrix and the choroid plexus (CP), including transthyretin, wound up in the CSF of 78 people with the CP subtype. MRI scans showed that the CP, a network of extracellular matrix and blood vessels, was enlarged. Large CPs associate with inflammation and cortical atrophy in multiple sclerosis, and in this fourth AD subtype, researchers detected elevated cytokines and severe, widespread cortical thinning. The other new subtype, RNA dysregulation, comprised just 24 people. They had high levels of chaperones and RNA-binding proteins in their CSF. Intriguingly, they had little of the microtubule-binding protein stathmin-2 (STMN2). Correct splicing and translation of STMN2 requires the RNA-binding protein TDP-43, best known for its role in frontotemporal dementia. This RNA dysregulation subtype seems the most aggressive. People had the most total tau and neurofilament light in their CSF, both signs of neuron damage, and they died soonest, about 5.5 years on average, after a clinical dementia diagnosis.

Cellular senescence and the senescence-associated secretory phenotype (SASP) contribute to age-related arterial dysfunction, in part, by promoting oxidative stress and inflammation, which reduce the bioavailability of the vasodilatory molecule nitric oxide (NO). In the present study, we assessed the efficacy of fisetin, a natural compound, as a senolytic to reduce vascular cell senescence and SASP factors and improve arterial function in old mice. We found that fisetin decreased cellular senescence in human endothelial cell culture.

In old mice, vascular cell senescence and SASP-related inflammation were lower 1 week after the final dose of oral intermittent (1 week on-2 weeks off-1 weeks on dosing) fisetin supplementation. Old fisetin-supplemented mice had higher endothelial function. Leveraging old p16-3MR mice, a transgenic model allowing genetic clearance of p16INK4A-positive senescent cells, we found that ex vivo removal of senescent cells from arteries isolated from controls but not fisetin-treated mice increased endothelium-dependent dilation, demonstrating that fisetin improved endothelial function through senolysis. Enhanced endothelial function with fisetin was mediated by increased NO bioavailability and reduced cellular- and mitochondrial-related oxidative stress.

Arterial stiffness was lower in fisetin-treated mice. Ex vivo genetic senolysis in aorta rings from p16-3MR mice did not further reduce mechanical wall stiffness in fisetin-treated mice, demonstrating lower arterial stiffness after fisetin was due to senolysis. Lower arterial stiffness with fisetin was accompanied by favorable arterial wall remodeling. The findings from this study identify fisetin as promising therapy for clinical translation to target excess cell senescence to treat age-related arterial dysfunction.

Cardiovascular diseases (CVDs), such as coronary artery disease (CAD), are the leading global causes of mortality and morbidity. The pathological hallmark of CAD is atherosclerosis, a chronic build-up of plaque inside arterial walls, which can lead to thrombus formation and myocardial infarction (MI) or stroke. This process involves a complex interplay of both immune and vascular cell types and cell state transitions along a continuum. In response to injury of the inner vessel wall layer, contractile smooth muscle cells (SMCs) transition to a more proliferative and migratory state and endothelial cells to a mesenchymal state in early and advanced atherosclerosis. Thus, a thorough assessment of cell heterogeneity and plasticity within the vessel wall is paramount to uncover new knowledge regarding atherosclerosis development and progression.

This study generates a comprehensive single-cell transcriptomic atlas of human atherosclerosis including 118,578 high-quality cells from atherosclerotic coronary and carotid arteries. By performing systematic benchmarking of integration methods, we mitigated data overcorrection while separating major cell lineages. Notably, we define cell subtypes that have not been previously identified from individual human atherosclerosis scRNA-seq studies.

Besides characterizing granular cell-type diversity and communication, we leverage this atlas to provide insights into smooth muscle cell (SMC) modulation. We integrate genome-wide association study data and uncover a critical role for modulated SMC phenotypes in CAD, myocardial infarction, and coronary calcification. Finally, we identify fibromyocyte/fibrochondrogenic SMC markers (LTBP1 and CRTAC1) as proxies of atherosclerosis progression and validate these through omics and spatial imaging analyses. Altogether, we create a unified atlas of human atherosclerosis informing cell state-specific mechanistic and translational studies of cardiovascular diseases.

Patients undergoing total thyroidectomy typically require lifelong oral levothyroxine sodium (L-T4) treatment. While effective in maintaining basic serum hormone levels, this treatment falls short in restoring the dynamic responsive regulatory capacity of triiodothyronine (T3), essential for critical physiologic regulatory functions. Clinical data indicates that T3 deficiency can elevate the risk of hypertension, cardiac dysfunction, and other metabolic or mental health conditions.

Researchers have proposed an innovative solution to thyroid transplantation challenges by growing the thyroid in the spleen. Leveraging the spleen's unique properties, characterized by a loose structure and rich blood supply, the team explored a new strategy for thyroid regeneration. Intrasplenic thyroid transplantation was performed without compromising the structure and function of the spleen. Mice with total thyroidectomy were transplanted with thyroid glands in the spleen, featuring intact follicles and reconstructed vascular networks. This approach successfully recapitulated the angio-follicular unit (AFU), leading to the full restoration of hormone levels in mice.

Furthermore, studies have demonstrated that this method is more effective in responding to physiological signals than hormone replacement therapy. Moreover, long-term evaluation of the effects with that of hormone replacement therapy proved that the regenerated thyroid glands in the spleen completely restored the physiological homeostasis in the mice after total thyroidectomy without any negative side effects, indicating significant potential for clinical applications.

The population around the world is graying, and as many of these individuals will spend years suffering from the burdens of age associated diseases, understanding how to increase healthspan, defined as the period of life free from disease and disability, is an urgent priority of geroscience research. The lack of agreed-upon quantitative metrics for measuring healthspan in aging mice has slowed progress in identifying interventions that do not simply increase lifespan, but also healthspan.

Here, we define FAMY (Frailty-Adjusted Mouse Years) and GRAIL (Gauging Robust Aging when Increasing Lifespan) as new summary statistics for quantifying healthspan in mice. FAMY is based entirely on a widely utilized clinical frailty index, while GRAIL incorporates frailty, widely utilized healthspan assays, and information about the hallmarks of aging. Both metrics are conceptually similar to quality-adjusted life years (QALY), a widely-utilized measure of disease burden in humans, and can be readily calculated from data acquired during longitudinal and cross-sectional studies of mouse aging.

We find that interventions generally thought to promote health, including calorie restriction, robustly improve healthspan as measured by FAMY and GRAIL. Finally, we show that use of GRAIL provides new insights, and identify dietary restriction of protein or isoleucine as an intervention that promotes healthspan but not longevity in female HET3 mice. We suggest that the routine integration of these measures into studies of aging in mice will allow the identification and development of interventions that promote healthy aging even in the absence of increased lifespan.

In a prior study researchers showed that blocking the consequences of PU.1 protein activity helps to reduce Alzheimer's disease-related neuroinflammation and pathology. The simplest way to test whether siRNA could therapeutically suppress PU.1 expression in microglia would have been to make use of an already available delivery device, but one of the first discoveries in the study is that none of eight commercially available reagents could safely and effectively transfect cultured human microglia-like cells in the lab.

Instead the team had to optimize a lipid nanoparticle (LNP) to do the job. LNPs have four main components and by changing the structures of two of them, and by varying the ratio of lipids to RNA, the researchers were able to come up with seven formulations to try. Among the seven candidates, one the team named "MG-LNP" stood out for its especially high delivery efficiency and safety of a test RNA cargo. What works in a dish sometimes doesn't work in a living organism, so the team next tested their LNP formulations' effectiveness and safety in mice. Testing two different methods of injection, into the body or into the cerebrospinal fluid (CSF), they found that injection into the CSF ensured much greater efficacy in targeting microglia without affecting cells in other organs. Among the seven formulations, MG-LNP again proved the most effective at transfecting microglia.

Once they knew MG-LNP could deliver a test cargo to microglia both in human cell cultures and mice, the scientists then tested whether using it to deliver a PU.1-suppressing siRNA could reduce inflammation in microglia. In the cell cultures, a relatively low dose achieved a 42 percent reduction of PU.1 expression (which is good because microglia need at least some PU.1 to live). Indeed MG-LNP transfection did not cause the cells any harm. It also significantly reduced the transcription of the genes that PU.1 expression increases in microglia, indicating that it can reduce multiple inflammatory markers.

The final set of tests evaluated MG-LNP's performance delivering the siRNA in two mouse models of inflammation in the brain. In one, mice were exposed to LPS, a molecule that simulates infection and stimulates a systemic inflammation response. In the other model, mice exhibit severe neurodegeneration and inflammation when an enzyme called CDK5 becomes hyperactivated by a protein called p25. In both models, injection of MG-LNPs carrying the anti-PU.1 siRNA reduced expression of PU.1 and inflammatory markers, much like in the cultured human cells.

Aging poses a number of challenges to the body's well-being, one of the most important being an increased susceptibility to multiple diseases, including urinary tract infections (UTIs). Researchers have now shown that, compared to the younger counterpart, the aging urinary tract in animal models changes how it functions at the cellular level in ways that seem to favor the establishment and recurrence of UTIs. The researchers investigated a process called autophagy that all cells naturally use to clean up old or defective cellular materials by digesting and recycling them in structures called lysosomes. "We found that the recycling process naturally slows down as urothelial cells age. Older cells accumulate larger lysosomes that are less effective at degrading cellular materials, which leads to their toxic accumulation inside the cell."

Aged urothelial cells also accumulate more damaging reactive oxygen species (ROS) than younger tissues. "ROS are molecules that can harm tissues, and the redox response that normally neutralizes ROS in younger cells is dampened in aging urothelial cells. Consequently, an inflammatory process builds up, leading to cell death. Dead urothelial cells leave their location, exfoliating the bladder and disrupting its integrity, which further exacerbates age-related dysfunction."

Importantly, researchers also discovered that treating aged mice with D-Mannose, a natural sugar, restores autophagy and mitigates ROS and urothelial cell shedding, suggesting that mannose supplementation could counter age-associated human urothelial dysfunction. Researchers then compared bacterial UTIs in older animals versus younger animals. "We found that aged mice have more bacterial reservoirs in the urinary tract and are more prone to spontaneous recurrent UTI than younger mice, suggesting that the age-related dysfunction of the tissue could explain the higher recurrence of UTIs observed in older age. Collectively, our results demonstrate that normal aging affects bladder physiology, with aging alone increasing baseline cellular stress and susceptibility to infection. We suggest that mannose supplementation could counter age-associated urothelial dysfunction in addition to limiting recurring UTIs."

While looking at previous lifespan and healthspan extension studies may seem an obvious place to start when seeking new gene therapies, the Rejuvenate Bio founders explain that there is more to it than just the results. "These studies are essentially long-term safety experiments where they showed durable safety, coupled with an ability to treat multiple different issues with the animal or at least prevent age related conditions. Our focus was on how to turn transgenic interventions into therapies that would be safe and relevant for human patients. That is where we started."

The team studied those successful genetic interventions and how to "therapize" them - selecting the genetic or transgenic interventions that best lent themselves to becoming a gene therapy. In the end, the company arrived at three key longevity genes with proven efficacy and validated safety profiles, each associated with either an upward or downward trajectory through age: FGF21, which regulates important metabolic and immune pathways; TGFβ-1, which is a known driver of fibrosis and several cancers; and α-klotho, which is associated with cognitive performance as well as protection against heart and kidney diseases.

The Rejuvenate Bio founders explain how the company's FGF21 gene therapy is delivered via a strain of adeno-associated virus that targets liver tissue. "Even if our FGF21 gene therapy is only infecting liver tissue, we can actually see systemic effects throughout the body. What we're doing is turning the liver into a therapeutic bio factory, and then overexpressing this key signaling protein that then goes out through the blood stream and does its work across the body." This approach has advantages over gene replacement therapies, as evidenced by the company's recent success targeting arrhythmogenic cardiomyopathy in mice. "Because we're utilizing a secreted protein for our delivery, we've shown that we're able to hit large amounts of the cardiac tissue. Compare that to these groups who are trying to get the gene therapy to infect every cardiomyocyte that they'd like to change. That's a key difference."

Phytochemicals are increasingly recognized in the field of healthy aging as potential therapeutics against various aging-related diseases. Nutmeg, derived from the Myristica fragrans tree, is an example. Nutmeg has been extensively studied and proven to possess antioxidant properties that protect against aging and alleviate serious diseases such as cancer, heart disease, and liver disease. However, the specific active ingredient in nutmeg responsible for these health benefits has not been identified thus far.

In this study, we present evidence that Nectandrin B (NecB), a bioactive lignan compound isolated from nutmeg, significantly extended the lifespan of the fruit fly Drosophila melanogaster by as much as 42.6% compared to the control group. NecB also improved age-related symptoms including locomotive deterioration, body weight gain, eye degeneration, and neurodegeneration in aging D. melanogaster. This result represents the most substantial improvement in lifespan observed in animal experiments to date, suggesting that NecB may hold promise as a potential therapeutic agent for promoting longevity and addressing age-related degeneration.

Age-related immunosenescence is characterized by changes in immune cell subsets and is associated with mortality. In this study, we found that T cells and natural killer (NK) cells with low expression of CD56 were inversely associated with mortality while neutrophils were positively associated with mortality. In addition, we found myeloid dendritic cells to be nominally associated with a reduced odds of mortality, and CD4+ effector memory T cells and IgD- memory B cells to be nominally associated with increased mortality odds.

Several previous studies have shown a positive association between neutrophils and mortality and our study confirmed these previous findings. The number of neutrophils are preserved in older adults though their phagocytic ability is impaired. Furthermore, since neutrophils are pro-inflammatory, higher numbers of neutrophils in older adults may increase the odds of mortality. NK cells cytotoxicity and IFN-γ production decreases in old age, and low cytotoxicity is associated with increased morbidity and mortality. NK LO cells have significantly higher cytotoxicity than NK Hi cells. Hence, the observed inverse association with mortality was consistent with the biological activity of this NK cell subtype.

A higher percentage of myeloid subset of dendritic cells was associated with reduced mortality, which was consistent with previous studies showing that dendritic cells mediate antitumor immune responses, and were used in immunotherapies and vaccinations that resulted in improved survival of cancer patients. The absolute count of T cells decreases with age, and this decrease especially affects naïve subset (Tn). This alters the T cell repertoire, compromising their ability to mediate effective immune responses, and thus increasing the odds of mortality. The inverse association seen for total T cells in this study was in line with a previous study on hemodialysis patients.

As immunosenescence is characterized by accumulation of memory and effector T cells, a positive association between CD4+ effector memory T subset and mortality was consistent with the known distribution of this immune subset in older adults. Of note, we have previously shown that CMV seropositivity and not age was the predominant determinant of CD4+ effector memory T levels suggesting that the association between some of the immune cell subsets and mortality may be primarily driven by environmental exposures as compared to age-related processes.