17α-Estradiol Alleviates Age-related Metabolic and Inflammatory Dysfunction in Male Mice Without Inducing Feminization

A pilot study evaluating dosing tolerability of 17α-estradiol in male common marmosets (Callithrix jacchus)

17α-estradiol extends healthspan and lifespan in male mice without significant feminization or deleterious effects on reproductive function, making it a candidate for human translation. However, studies in animal models that more accurately replicate human physiology are necessary to establish 17α-estradiol dosing standards for clinical trials. This study evaluated the tolerability of 17α-estradiol treatment in the common marmoset over a short treatment duration. We found that male marmosets tolerated two dosing regimens (0.37-0.47 or 0.62-0.72 mg/kg/day) as evidenced by the absence of gastrointestinal distress, changes in vital signs, or overall health conditions. 17α-estradiol treatment mildly decreased body mass, adiposity, and glycosylated hemoglobin, although these changes were not statistically significant in most instances. However, neither dose of 17α-estradiol elicited feminization in our study, thereby suggesting that optimized dosing regimens may provide health benefits without feminization in primates. Additional studies are needed to determine if longer duration treatments would also be nonfeminizing and elicit significant health benefits, which would aid in developing dosing regimens targeting healthy aging in humans.

Chronic β3 adrenergic agonist treatment improves brain microvascular endothelial function and cognition in aged mice

Microvascular endothelial dysfunction, characterized by impaired neurovascular coupling, reduced glucose uptake, blood-brain barrier disruption, and microvascular rarefaction, plays a critical role in the pathogenesis of age-related vascular cognitive impairment (VCI). Emerging evidence points to non-cell autonomous mechanisms mediated by adverse circulating milieu (an increased ratio of pro-geronic to anti-geronic circulating factors) in the pathogenesis of endothelial dysfunction leading to impaired cerebral blood flow and cognitive decline in the aging population. In particular, age-related adipose dysfunction contributes, at least in part, to an unfavorable systemic milieu characterized by chronic hyperglycemia, hyperinsulinemia, dyslipidemia, and altered adipokine profile, which together contribute to microvascular endothelial dysfunction. Hence, in the present study, we aimed to test whether thermogenic stimulation, an intervention known to improve adipose and systemic metabolism by increasing cellular energy expenditure, could mitigate brain endothelial dysfunction and improve cognition in the aging population. Eighteen-month-old old C57BL/6J mice were treated with saline or CL (β3-adrenergic agonist) for 6 weeks followed by functional analysis to assess endothelial function and cognition. CL treatment improved neurovascular coupling responses and rescued brain glucose uptake in aged animals. In addition, CL treatment also attenuated blood-brain barrier leakage and associated neuroinflammation in the cortex of aged animals. More importantly, these beneficial changes in microvascular function translated to improved cognitive performance in radial arm water maze and Y-maze tests. Our results suggest that β3-adrenergic agonist treatment improves multiple aspects of brain microvascular endothelial function and can be potentially repurposed for treating age-associated cognitive decline.

Metformin treatment results in distinctive skeletal muscle mitochondrial remodeling in rats with different intrinsic aerobic capacities

The rationale for the use of metformin as a treatment to slow aging was largely based on data collected from metabolically unhealthy individuals. For healthspan extension metformin will also be used in periods of good health. To understand the potential context specificity of metformin treatment on skeletal muscle, we used a rat model (high-capacity runner/low-capacity runner [HCR/LCR]) with a divide in intrinsic aerobic capacity. Outcomes of metformin treatment differed based on baseline intrinsic mitochondrial function, oxidative capacity of the muscle (gastroc vs soleus), and the mitochondrial population (intermyofibrillar vs. subsarcolemmal). Metformin caused lower ADP-stimulated respiration in LCRs, with less of a change in HCRs. However, a washout of metformin resulted in an unexpected doubling of respiratory capacity in HCRs. These improvements in respiratory capacity were accompanied by mitochondrial remodeling that included increases in protein synthesis and changes in morphology. Our findings raise questions about whether the positive findings of metformin treatment are broadly applicable.

The killifish germline regulates longevity and somatic repair in a sex-specific manner

Classical evolutionary theories propose tradeoffs among reproduction, damage repair and lifespan. However, the specific role of the germline in shaping vertebrate aging remains largely unknown. In this study, we used the turquoise killifish (Nothobranchius furzeri) to genetically arrest germline development at discrete stages and examine how different modes of infertility impact life history. We first constructed a comprehensive single-cell gonadal atlas, providing cell-type-specific markers for downstream phenotypic analysis. We show here that germline depletion-but not arresting germline differentiation-enhances damage repair in female killifish. Conversely, germline-depleted males instead showed an extension in lifespan and rejuvenated metabolic functions. Through further transcriptomic analysis, we highlight enrichment of pro-longevity pathways and genes in germline-depleted male killifish and demonstrate functional conservation of how these factors may regulate longevity in germline-depleted Caenorhabditis elegans. Our results, therefore, demonstrate that different germline manipulation paradigms can yield pronounced sexually dimorphic phenotypes, implying alternative responses to classical evolutionary tradeoffs.

The killifish germline regulates longevity and somatic repair in a sex-specific manner

Classical evolutionary theories propose tradeoffs between reproduction, damage repair, and lifespan. However, the specific role of the germline in shaping vertebrate aging remains largely unknown. Here, we use the turquoise killifish ( N. furzeri ) to genetically arrest germline development at discrete stages, and examine how different modes of infertility impact life-history. We first construct a comprehensive single-cell gonadal atlas, providing cell-type-specific markers for downstream phenotypic analysis. Next, we show that germline depletion - but not arresting germline differentiation - enhances damage repair in female killifish. Conversely, germline-depleted males instead showed an extension in lifespan and rejuvenated metabolic functions. Through further transcriptomic analysis, we highlight enrichment of pro-longevity pathways and genes in germline-depleted male killifish and demonstrate functional conservation of how these factors may regulate longevity in germline-depleted C. elegans . Our results therefore demonstrate that different germline manipulation paradigms can yield pronounced sexually dimorphic phenotypes, implying alternative responses to classical evolutionary tradeoffs.

Disruption of NMDA receptor-mediated regulation of PPI in the maternal immune activation model of schizophrenia is restored by 17β-estradiol and raloxifene

Maternal immune activation (MIA) during pregnancy is known to increase the risk of development of schizophrenia in the offspring. Sex steroid hormone analogues have been proposed as potential antipsychotic treatments but the mechanisms of action involved remain unclear. Estrogen has been shown to alter N-methyl-d-aspartate (NMDA) receptor binding in the brain. We therefore studied the effect of chronic treatment with 17β-estradiol, its isomer, 17α-estradiol, and the selective estrogen receptor modulator, raloxifene, on MIA-induced psychosis-like behaviour and the effect of the NMDA receptor antagonist, MK-801. Pregnant rats were treated with saline or the viral mimetic, poly(I:C), on gestational day 15. Adult female offspring were tested for changes in baseline prepulse inhibition (PPI) and the effects of acute treatment with MK-801 on PPI and locomotor activity. Poly(I:C) offspring had significantly lower baseline PPI compared to control offspring, and this effect was prevented by 17β-estradiol and raloxifene, but not 17α-estradiol. MK-801 reduced PPI in control offspring but had no effect in poly(I:C) offspring treated with vehicle. Chronic treatment with 17β-estradiol and raloxifene restored the effect of MK-801 on PPI. There were no effects of MIA or estrogenic treatment on MK-801 induced locomotor hyperactivity. These results show that MIA affects baseline PPI as well as NMDA receptor-mediated regulation of PPI in female rats, and strengthen the view that estrogenic treatment may have antipsychotic effects.

Antioxidants green tea extract and nordihydroguaiaretic acid confer species and strain-specific lifespan and health effects in Caenorhabditis nematodes

The Caenorhabditis Intervention Testing Program (CITP) is an NIH-funded research consortium of investigators who conduct analyses at three independent sites to identify chemical interventions that reproducibly promote health and lifespan in a robust manner. The founding principle of the CITP is that compounds with positive effects across a genetically diverse panel of Caenorhabditis species and strains are likely engaging conserved biochemical pathways to exert their effects. As such, interventions that are broadly efficacious might be considered prominent compounds for translation for pre-clinical research and human clinical applications. Here, we report results generated using a recently streamlined pipeline approach for the evaluation of the effects of chemical compounds on lifespan and health. We studied five compounds previously shown to extend C. elegans lifespan or thought to promote mammalian health: 17α-estradiol, acarbose, green tea extract, nordihydroguaiaretic acid, and rapamycin. We found that green tea extract and nordihydroguaiaretic acid extend Caenorhabditis lifespan in a species-specific manner. Additionally, these two antioxidants conferred assay-specific effects in some studies-for example, decreasing survival for certain genetic backgrounds in manual survival assays in contrast with extended lifespan as assayed using automated C. elegans Lifespan Machines. We also observed that GTE and NDGA impact on older adult mobility capacity is dependent on genetic background, and that GTE reduces oxidative stress resistance in some Caenorhabditis strains. Overall, our analysis of the five compounds supports the general idea that genetic background and assay type can influence lifespan and health effects of compounds, and underscores that lifespan and health can be uncoupled by chemical interventions.

Ablation of skeletal muscle estrogen receptor alpha impairs contractility in male mice

Estradiol and estrogen receptor α (ERα) have been shown to be important for the maintenance of skeletal muscle strength in females; however, little is known about the roles of estradiol and ERα in male muscle. The purpose of this study was to determine if skeletal muscle ERα is required for optimal contractility in male mice. We hypothesize that reduced ERα in skeletal muscle impairs contractility in male mice. Skeletal muscle-specific knockout (skmERαKO) male mice exhibited reduced strength across multiple muscles and several contractile parameters related to force generation and kinetics compared with wild-type littermates (skmERαWT). Isolated EDL muscle-specific isometric tetanic force, peak twitch force, peak concentric and peak eccentric forces, as well as the maximal rates of force development and relaxation were 11%-21% lower in skmERαKO compared with skmERαWT mice. In contrast, isolated soleus muscles from skmERαKO mice were not affected. In vivo peak torque of the anterior crural muscles was 20% lower in skmERαKO compared with skmERαWT mice. Muscle masses, contractile protein contents, fiber types, phosphorylation of the myosin regulatory light chain, and caffeine-elicited force did not differ between muscles of skmERαKO and skmERαWT mice, suggesting that strength deficits were not due to size, composition, or calcium release components of muscle contraction. These results indicate that in male mice, reduced skeletal muscle ERα blunts contractility to a magnitude similar to that previously reported in females; however, the mechanism may be sexually dimorphic.NEW & NOTEWORTHY We comprehensively measured in vitro and in vivo contractility of leg muscles with reduced estrogen receptor α (ERα) in male mice and reported that force generation and contraction kinetics are impaired. In contrast to findings in females, phosphorylation of myosin regulatory light chain cannot account for low force production in male skeletal muscle ERα knockout mice. These results indicate that ERα is required for optimal contractility in males and females but via sexually dimorphic means.

Insights into targeting cellular senescence with senolytic therapy: The journey from preclinical trials to clinical practice

Interconnected, fundamental aging processes are central to many illnesses and diseases. Cellular senescence is a mechanism that halts the cell cycle in response to harmful stimuli. Senescent cells (SnCs) can emerge at any point in life, and their persistence, along with the numerous proteins they secrete, can negatively affect tissue function. Interventions aimed at combating persistent SnCs, which can destroy tissues, have been used in preclinical models to delay, halt, or even reverse various diseases. Consequently, the development of small-molecule senolytic medicines designed to specifically eliminate SnCs has opened potential avenues for the prevention or treatment of multiple diseases and age-related issues in humans. In this review, we explore the most promising approaches for translating small-molecule senolytics and other interventions targeting senescence in clinical practice. This discussion highlights the rationale for considering SnCs as therapeutic targets for diseases affecting individuals of all ages.

Protection against APOE4 -associated aging phenotypes with the longevity-promoting intervention 17α-estradiol in male mice

The apolipoprotein ε4 allele ( APOE4 ) is associated with decreased longevity, increased vulnerability to age-related declines, and disorders across multiple systems. Interventions that promote healthspan and lifespan represent a promising strategy to attenuate the development of APOE4 -associated aging phenotypes. Here we studied the ability of the longevity-promoting intervention 17α-estradiol (17αE2) to protect against age-related impairments in APOE4 versus the predominant APOE3 genotype using early middle-aged mice with knock-in of human APOE alleles. Beginning at age 10 months, male APOE3 or APOE4 mice were treated for 20 weeks with 17αE2 or vehicle then compared for indices of aging phenotypes body-wide. Across peripheral and neural measures, APOE4 was associated with poorer outcomes. Notably, 17αE2 treatment improved outcomes in a genotype-dependent manner favoring APOE4 mice. These data demonstrate a positive APOE4 bias in 17αE2-mediated healthspan actions, suggesting that longevity-promoting interventions may be useful in mitigating deleterious age-related risks associated with APOE4 genotype.

Metformin treatment results in distinctive skeletal muscle mitochondrial remodeling in rats with different intrinsic aerobic capacities

The rationale for the use of metformin as a treatment to slow aging was largely based on data collected from metabolically unhealthy individuals. For healthspan extension metformin will also be used in periods of good health. To understand potential context specificity of metformin treatment on skeletal muscle, we used a rat model (HCR/LCR) with a divide in intrinsic aerobic capacity. Outcomes of metformin treatment differed based on baseline intrinsic mitochondrial function, oxidative capacity of the muscle (gastroc vs soleus), and the mitochondrial population (IMF vs SS). Metformin caused lower ADP-stimulated respiration in LCRs, with less of a change in HCRs. However, a washout of metformin resulted in an unexpected doubling of respiratory capacity in HCRs. These improvements in respiratory capacity were accompanied by mitochondrial remodeling that included increases in protein synthesis and changes in morphology. Our findings raise questions about whether the positive findings of metformin treatment are broadly applicable.

17α-Estradiol alleviates high-fat diet-induced inflammatory and metabolic dysfunction in skeletal muscle of male and female mice

17α-estradiol (17α-E2) is a naturally occurring nonfeminizing diastereomer of 17β-estradiol that has life span-extending effects in rodent models. To date, studies of the systemic and tissue-specific benefits of 17α-E2 have largely focused on the liver, brain, and white adipose tissue with far less focus on skeletal muscle. Skeletal muscle has an important role in metabolic and age-related disease. Therefore, this study aimed to determine whether 17α-E2 treatment has positive, tissue-specific effects on skeletal muscle during a high-fat feeding. We hypothesized that male, but not female, mice, would benefit from 17α-E2 treatment during a high-fat diet (HFD) with changes in the mitochondrial proteome to support lipid oxidation and subsequent reductions in diacylglycerol (DAG) and ceramide content. To test this hypothesis, we used a multiomics approach to determine changes in lipotoxic lipid intermediates, metabolites, and proteins related to metabolic homeostasis. Unexpectedly, we found that 17α-E2 had marked, but different, beneficial effects within each sex. In male mice, we show that 17α-E2 alleviates HFD-induced metabolic detriments of skeletal muscle by reducing the accumulation of diacylglycerol (DAG), and inflammatory cytokine levels, and altered the abundance of most of the proteins related to lipolysis and β-oxidation. Similar to male mice, 17α-E2 treatment reduced fat mass while protecting muscle mass in female mice but had little muscle inflammatory cytokine levels. Although female mice were resistant to HFD-induced changes in DAGs, 17α-E2 treatment induced the upregulation of six DAG species. In female mice, 17α-E2 treatment changed the relative abundance of proteins involved in lipolysis, β-oxidation, as well as structural and contractile proteins but to a smaller extent than male mice. These data demonstrate the metabolic benefits of 17α-E2 in skeletal muscle of male and female mice and contribute to the growing literature of the use of 17α-E2 for multi tissue health span benefits.NEW & NOTEWORTHY Using a multiomics approach, we show that 17α-E2 alleviates HFD-induced metabolic detriments in skeletal muscle by altering bioactive lipid intermediates, inflammatory cytokines, and the abundance of proteins related to lipolysis and muscle contraction. The positive effects of 17α-E2 in skeletal muscle occur in both sexes but differ in their outcome.

Role of estrogen in treatment of female depression

Depression is a neurological disorder that profoundly affects human physical and mental health, resulting in various changes in the central nervous system. Despite several prominent hypotheses, such as the monoaminergic theory, hypothalamic-pituitary-adrenal (HPA) axis theory, neuroinflammation, and neuroplasticity, the current understanding of depression's pathogenesis remains incomplete. Importantly, depression is a gender-dimorphic disorder, with women exhibiting higher incidence rates than men. Given estrogen's pivotal role in the menstrual cycle, it is reasonable to postulate that its fluctuating levels could contribute to the pathogenesis of depression. Estrogen acts by binding to a diversity of receptors, which are widely distributed in the central nervous system. An abundance of research has established that estrogen and its receptors play a crucial role in depression, spanning pathogenesis and treatment. In this comprehensive review, we provide an in-depth analysis of the fundamental role of estrogen and its receptors in depression, with a focus on neuroinflammation, neuroendocrinology, and neuroplasticity. Furthermore, we discuss potential mechanisms underlying the therapeutic effects of estrogen in the treatment of depression, which may pave the way for new antidepressant drug development and alternative treatment options.

Geroprotector drugs and exercise: friends or foes on healthy longevity?

Physical activity and several pharmacological approaches individually combat age-associated conditions and extend healthy longevity in model systems. It is tantalizing to extrapolate that combining geroprotector drugs with exercise could extend healthy longevity beyond any individual treatment. However, the current dogma suggests that taking leading geroprotector drugs on the same day as exercise may limit several health benefits. Here, we review leading candidate geroprotector drugs and their interactions with exercise and highlight salient gaps in knowledge that need to be addressed to identify if geroprotector drugs can have a harmonious relationship with exercise.

Telomere Checkpoint in Development and Aging

The maintenance of genome integrity through generations is largely determined by the stability of telomeres. Increasing evidence suggests that telomere dysfunction may trigger changes in cell fate, independently of telomere length. Telomeric multiple tandem repeats are potentially highly recombinogenic. Heterochromatin formation, transcriptional repression, the suppression of homologous recombination and chromosome end protection are all required for telomere stability. Genetic and epigenetic defects affecting telomere homeostasis may cause length-independent internal telomeric DNA damage. Growing evidence, including that based on Drosophila research, points to a telomere checkpoint mechanism that coordinates cell fate with telomere state. According to this scenario, telomeres, irrespective of their length, serve as a primary sensor of genome instability that is capable of triggering cell death or developmental arrest. Telomeric factors released from shortened or dysfunctional telomeres are thought to mediate these processes. Here, we discuss a novel signaling role for telomeric RNAs in cell fate and early development. Telomere checkpoint ensures genome stability in multicellular organisms but aggravates the aging process, promoting the accumulation of damaged and senescent cells.

Assessing tolerability and physiological responses to 17α-estradiol administration in male rhesus macaques

17α-estradiol has recently been shown to extend healthspan and lifespan in male mice through multiple mechanisms. These benefits occur in the absence of significant feminization or deleterious effects on reproductive function, which makes 17α-estradiol a candidate for translation into humans. However, human dosing paradigms for the treatment of aging and chronic disease are yet to be established. Therefore, the goals of the current studies were to assess tolerability of 17α-estradiol treatment, in addition to evaluating metabolic and endocrine responses in male rhesus macaque monkeys during a relatively short treatment period. We found that our dosing regimens (0.30 and 0.20 mg/kg/day) were tolerable as evidenced by a lack of GI distress, changes in blood chemistry or complete blood counts, and unaffected vital signs. We also found that the higher dose did elicit mild benefits on metabolic parameters including body mass, adiposity, and glycosylated hemoglobin. However, both of our 17α-estradiol trial doses elicited significant feminization to include testicular atrophy, increased circulating estrogens, and suppressed circulating androgens and gonadotropins. We suspect that the observed level of feminization results from a saturation of the endogenous conjugation enzymes, thereby promoting a greater concentration of unconjugated 17α-estradiol in serum, which has more biological activity. We also surmise that the elevated level of unconjugated 17α-estradiol was subjected to a greater degree of isomerization to 17β-estradiol, which is aligned with the sevenfold increase in serum 17β-estradiol in 17α-estradiol treated animals in our first trial. Future studies in monkeys, and certainly humans, would likely benefit from the development and implementation of 17α-estradiol transdermal patches, which are commonly prescribed in humans and would circumvent potential issues with bolus dosing effects.

17α-estradiol does not adversely affect sperm parameters or fertility in male mice: implications for reproduction-longevity trade-offs

17α-estradiol (17α-E2) is referred to as a nonfeminizing estrogen that was recently found to extend healthspan and lifespan in male, but not female, mice. Despite an abundance of data indicating that 17α-E2 attenuates several hallmarks of aging in male rodents, very little is known with regard to its effects on feminization and fertility. In these studies, we evaluated the effects of 17α-E2 on several markers of male reproductive health in two independent cohorts of mice. In alignment with our previous reports, chronic 17α-E2 treatment prevented gains in body mass, but did not adversely affect testes mass or seminiferous tubule morphology. We subsequently determined that chronic 17α-E2 treatment also did not alter plasma 17β-estradiol or estrone concentrations, while mildly increasing plasma testosterone levels. We also determined that chronic 17α-E2 treatment did not alter plasma follicle-stimulating hormone or luteinizing hormone concentrations, which suggests 17α-E2 treatment does not alter gonadotropin-releasing hormone neuronal function. Sperm quantity, morphology, membrane integrity, and various motility measures were also unaffected by chronic 17α-E2 treatment in our studies. Lastly, two different approaches were used to evaluate male fertility in these studies. We found that chronic 17α-E2 treatment did not diminish the ability of male mice to impregnate female mice, or to generate successfully implanted embryos in the uterus. We conclude that chronic treatment with 17α-E2 at the dose most commonly employed in aging research does not adversely affect reproductive fitness in male mice, which suggests 17α-E2 does not extend lifespan or curtail disease parameters through tradeoff effects with reproduction.

Metabolic benefits of 17α-estradiol in liver are partially mediated by ERβ in male mice

Metabolic dysfunction underlies several chronic diseases. Dietary interventions can reverse metabolic declines and slow aging but remaining compliant is difficult. 17α-estradiol (17α-E2) treatment improves metabolic parameters and slows aging in male mice without inducing significant feminization. We recently reported that estrogen receptor α is required for the majority of 17α-E2-mediated benefits in male mice, but that 17α-E2 also attenuates fibrogenesis in liver, which is regulated by estrogen receptor β (ERβ)-expressing hepatic stellate cells (HSC). The current studies sought to determine if 17α-E2-mediated benefits on systemic and hepatic metabolism are ERβ-dependent. We found that 17α-E2 treatment reversed obesity and related systemic metabolic sequela in both male and female mice, but this was partially blocked in female, but not male, ERβKO mice. ERβ ablation in male mice attenuated 17α-E2-mediated benefits on hepatic stearoyl-coenyzme A desaturase 1 (SCD1) and transforming growth factor β1 (TGF-β1) production, which play critical roles in HSC activation and liver fibrosis. We also found that 17α-E2 treatment suppresses SCD1 production in cultured hepatocytes and hepatic stellate cells, indicating that 17α-E2 directly signals in both cell-types to suppress drivers of steatosis and fibrosis. We conclude that ERβ partially controls 17α-E2-mediated benefits on systemic metabolic regulation in female, but not male, mice, and that 17α-E2 likely signals through ERβ in HSCs to attenuate pro-fibrotic mechanisms.

17α-estradiol Alleviates High-Fat Diet-Induced Inflammatory and Metabolic Dysfunction in Skeletal Muscle of Male and Female Mice

Skeletal muscle has a central role in maintaining metabolic homeostasis. 17α-estradiol (17α-E2), a naturally-occurring non-feminizing diastereomer of 17β-estradiol that demonstrates efficacy for improving metabolic outcomes in male, but not female, mice. Despite several lines of evidence showing that 17α-E2 treatment improves metabolic parameters in middle-aged obese and old male mice through effects in brain, liver, and white adipose tissue little is known about how 17α-E2 alters skeletal muscle metabolism, and what role this may play in mitigating metabolic declines. Therefore, this study aimed to determine if 17α-E2 treatment improves metabolic outcomes in skeletal muscle from obese male and female mice following chronic high fat diet (HFD) administration. We hypothesized that male, but not female, mice, would benefit from 17α-E2 treatment during HFD. To test this hypothesis, we used a multi-omics approach to determine changes in lipotoxic lipid intermediates, metabolites, and proteins related to metabolic homeostasis. In male mice, we show that 17α-E2 alleviates HFD-induced metabolic detriments of skeletal muscle by reducing the accumulation of diacylglycerol (DAGs) and ceramides, inflammatory cytokine levels, and reduced the abundance of most of the proteins related to lipolysis and beta-oxidation. In contrast to males, 17α-E2 treatment in female mice had little effect on the DAGs and ceramides content, muscle inflammatory cytokine levels, or changes to the relative abundance of proteins involved in beta-oxidation. These data support to the growing evidence that 17α-E2 treatment could be beneficial for overall metabolic health in male mammals.

Role of Estrogen Receptor α in Aging and Chronic Disease

Estrogen receptor alpha (ERα) plays a crucial role in reproductive function in both sexes. It also mediates cellular responses to estrogens in multiple nonreproductive organ systems, many of which regulate systemic metabolic homeostasis and inflammatory processes in mammals. The loss of estrogens and/or ERα agonism during aging is associated with the emergence of several comorbid conditions, particularly in females undergoing the menopausal transition. Emerging data also suggests that male mammals likely benefit from ERα agonism if done in a way that circumvents feminizing characteristics. This has led us, and others, to speculate that tissue-specific ERα agonism may hold therapeutic potential for curtailing aging and chronic disease burden in males and females that are at high-risk of cancer and/or cardiovascular events with traditional estrogen replacement therapies. In this mini-review, we emphasize the role of ERα in the brain and liver, summarizing recent evidence that indicates these two organs systems mediate the beneficial effects of estrogens on metabolism and inflammation during aging. We also discuss how 17α-estradiol administration elicits health benefits in an ERα-dependent manner, which provides proof-of-concept that ERα may be a druggable target for attenuating aging and age-related disease burden.

Revisiting adipose thermogenesis for delaying aging and age-related diseases: Opportunities and challenges

Adipose tissue undergoes significant changes in structure, composition, and function with age including altered adipokine secretion, decreased adipogenesis, altered immune cell profile and increased inflammation. Considering the role of adipose tissue in whole-body energy homeostasis, age-related dysfunction in adipose metabolism could potentially contribute to an increased risk for metabolic diseases and accelerate the onset of other age-related diseases. Increasing cellular energy expenditure in adipose tissue, also referred to as thermogenesis, has emerged as a promising strategy to improve adipose metabolism and treat obesity-related metabolic disorders. However, translating this strategy to the aged population comes with several challenges such as decreased thermogenic response and the paucity of safe pharmacological agents to activate thermogenesis. This mini-review aims to discuss the current body of knowledge on aging and thermogenesis and highlight the unexplored opportunities (cellular mechanisms and secreted factors) to target thermogenic mechanisms for delaying aging and age-related diseases. Finally, we also discuss the emerging role of thermogenic adipocytes in healthspan and lifespan extension.

A Genetically Heterogeneous Rat Model with Divergent Mitochondrial Genomes

We generated a genetically heterogenous rat model by a 4-way cross strategy using 4 inbred strains (Brown Norway [BN], Fischer 344 [F344], Lewis [LEW], and Wistar Kyoto [KY]) to provide investigators with a highly genetically diverse rat model from commercially available inbred rats. We made reciprocal crosses between males and females from the 2 F1 hybrids to generate genetically heterogeneous rats with mitochondrial genomes from either the BN (OKC-HETB, a.k.a "B" genotype) or WKY (OKC-HETW a.k.a "W" genotype) parental strains. These two mitochondrial genomes differ at 94 nucleotides, more akin to human mitochondrial genome diversity than that available in classical laboratory mouse strains. Body weights of the B and W genotypes were similar. However, mitochondrial genotype antagonistically affected grip strength and treadmill endurance in females only. In addition, mitochondrial genotype significantly affected multiple responses to a high-fat diet (HFD) and treatment with 17α-estradiol. Contrary to findings in mice in which males only are affected by 17α-estradiol supplementation, female rats fed a HFD beneficially responded to 17α-estradiol treatment as evidenced by declines in body mass, adiposity, and liver mass. Male rats, by contrast, differed in a mitochondrial genotype-specific manner, with only B males responding to 17α-estradiol treatment. Mitochondrial genotype and sex differences were also observed in features of brain-specific antioxidant response to a HFD and 17α-estradiol as shown by hippocampal levels of Sod2 acetylation, JNK, and FoxO3a. These results emphasize the importance of mitochondrial genotype in assessing responses to putative interventions in aging processes.

Metabolic benefits of 17α-estradiol in liver are partially mediated by ERβ in male mice

Metabolic dysfunction underlies several chronic diseases. Dietary interventions can reverse metabolic declines and slow aging but remaining compliant is difficult. 17α-estradiol (17α-E2) treatment improves metabolic parameters and slows aging in male mice without inducing significant feminization. We recently reported that estrogen receptor α is required for the majority of 17α-E2-mediated benefits in male mice, but that 17α-E2 also attenuates fibrogenesis in liver, which is regulated by estrogen receptor β (ERβ)-expressing hepatic stellate cells (HSC). The current studies sought to determine if 17α-E2-mediated benefits on systemic and hepatic metabolism are ERβ-dependent. We found that 17α-E2 treatment reversed obesity and related systemic metabolic sequela in both male and female mice, but this was partially blocked in female, but not male, ERβKO mice. ERβ ablation in male mice attenuated 17α-E2-mediated benefits on hepatic stearoyl-coenyzme A desaturase 1 (SCD1) and transforming growth factor β1 (TGF-β1) production, which play critical roles in HSC activation and liver fibrosis. We also found that 17α-E2 treatment suppresses SCD1 production in cultured hepatocytes and hepatic stellate cells, indicating that 17α-E2 directly signals in both cell-types to suppress drivers of steatosis and fibrosis. We conclude that ERβ partially controls 17α-E2-mediated benefits on systemic metabolic regulation in female, but not male, mice, and that 17α-E2 likely signals through ERβ in HSCs to attenuate pro-fibrotic mechanisms.

Sex differences in neuroimmunoendocrine communication. Involvement on longevity

Endocrine, nervous, and immune systems work coordinately to maintain the global homeostasis of the organism. They show sex differences in their functions that, in turn, contribute to sex differences beyond reproductive function. Females display a better control of the energetic metabolism and improved neuroprotection and have more antioxidant defenses and a better inflammatory status than males, which is associated with a more robust immune response than that of males. These differences are present from the early stages of life, being more relevant in adulthood and influencing the aging trajectory in each sex and may contribute to the different life lifespan between sexes.

17α-estradiol, a lifespan-extending compound, attenuates liver fibrosis by modulating collagen turnover rates in male mice

Estrogen signaling is protective against chronic liver diseases, although men and a subset of women are contraindicated for chronic treatment with 17β-estradiol (17β-E2) or combination hormone replacement therapies. We sought to determine if 17α-estradiol (17α-E2), a naturally occurring diastereomer of 17β-E2, could attenuate liver fibrosis. We evaluated the effects of 17α-E2 treatment on collagen synthesis and degradation rates using tracer-based labeling approaches in male mice subjected to carbon tetrachloride (CCl4)-induced liver fibrosis. We also assessed the effects of 17α-E2 on markers of hepatic stellate cell (HSC) activation, collagen cross-linking, collagen degradation, and liver macrophage content and polarity. We found that 17α-E2 significantly reduced collagen synthesis rates and increased collagen degradation rates, which was mirrored by declines in transforming growth factor β1 (TGF-β1) and lysyl oxidase-like 2 (LOXL2) protein content in liver. These improvements were associated with increased matrix metalloproteinase 2 (MMP2) activity and suppressed stearoyl-coenzyme A desaturase 1 (SCD1) protein levels, the latter of which has been linked to the resolution of liver fibrosis. We also found that 17α-E2 increased liver fetuin-A protein, a strong inhibitor of TGF-β1 signaling, and reduced proinflammatory macrophage activation and cytokines expression in the liver. We conclude that 17α-E2 reduces fibrotic burden by suppressing HSC activation and enhancing collagen degradation mechanisms. Future studies will be needed to determine if 17α-E2 acts directly in hepatocytes, HSCs, and/or immune cells to elicit these benefits.

Human cell-based estrogen receptor beta dimerization assay

Estrogen is not only responsible for important functions in the human body, such as cell growth, reproduction, differentiation, and development, but it is also deeply related to pathological processes, such as cancer, metabolic and cardiovascular diseases, and neurodegeneration. Estrogens and other estrogenic compounds have transcriptional activities through binding with the estrogen receptor (ER) to induce ER dimerization. The two estrogen receptor subtypes, estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ), show structural differences and have different expression ratios in specific cells and tissues. Currently, the methods for confirming the estrogenic properties of compounds are the binding (Test guideline no. 493) and transactivation (Test guideline no. 455) assays provided by the Organization for Economic Co-operation and Development (OECD). In a previous study, we developed an ERα dimerization assay based on the bioluminescence resonance energy transfer (BRET) system, but there are currently no available tests that can confirm the effect of estrogenic compounds on ERβ. Therefore, in this study, we developed a BRET-based ERβ dimerization assay to confirm the estrogenic prosperities of compounds. The BRET-based ERβ dimerization assay was verified using nine representative ER ligands and the results were compared with the dimerization activity of ERα. In conclusion, our BRET-based ERβ dimerization assay can provide information on the ERβ dimerization potential of estrogenic compounds.

Three Tiers to biological escape velocity: The quest to outwit aging

As longevity companies emerge with new products and the fields of anti-aging research develop new cutting-edge therapies, three distinct classes of longevity methodologies emerge. This discussion finds that there are three clear classes (Tiers) of longevity systems that are currently under development, and all three will be paramount to achieve biological escape velocity (where tissues can be repaired faster than aging can damage them). These classes are referred to as Tier 1, Tier 2, and Tier 3 treatments and are described in detail below. These three Tiers are required for easy identification for pharmaceutical companies and research companies to determine the type of therapy they may choose to deliver being noninvasive, invasive, time consuming, or simple end user products. Specific targets and goals need to be defined clearly from an early perspective in the development of these technologies for future precision medicines. This allows consumers of future anti-aging technologies to consider which Tier a particular therapy may be, delivering a more informed choice.

Cellular senescence and senolytics: the path to the clinic

Interlinked and fundamental aging processes appear to be a root-cause contributor to many disorders and diseases. One such process is cellular senescence, which entails a state of cell cycle arrest in response to damaging stimuli. Senescent cells can arise throughout the lifespan and, if persistent, can have deleterious effects on tissue function due to the many proteins they secrete. In preclinical models, interventions targeting those senescent cells that are persistent and cause tissue damage have been shown to delay, prevent or alleviate multiple disorders. In line with this, the discovery of small-molecule senolytic drugs that selectively clear senescent cells has led to promising strategies for preventing or treating multiple diseases and age-related conditions in humans. In this Review, we outline the rationale for senescent cells as a therapeutic target for disorders across the lifespan and discuss the most promising strategies-including recent and ongoing clinical trials-for translating small-molecule senolytics and other senescence-targeting interventions into clinical use.

17α-Estradiol, an ignored endogenous natural estrogen in human: Updated estrogen metabolism pathways and its environmental risk analysis

E1 and E2 are considered as the parent natural estrogens (NEs) in human metabolism pathways of NEs, while the enantiomer of E2, αE2 was not included and ignored. In this study, αE2 along with the other eleven NEs with estrogenic activities were found in six healthy human urines with the total concentration levels of 62.9-99.3 μg/L. The concentration contributed ratios (CCRs) of αE2 to the total twelve NEs ranged from 4.7% to 11.0% with an average CCR of 7.0%. On the basis of the average CCR, αE2 was 1.5 times that of E2, which suggested that αE2 was one important NE in humans. As the main source of NEs in municipal wastewater was derived from human urine, αE2 should also be an important NE in municipal wastewater that can be proven by previous limited studies, in which the municipal effluent concentrations of αE2 ranged from not detection to 144.2 ng/L with an average concentration of 11.9 ng/L, indicating αE2 in municipal effluent was an important source to the natural environment. Although αE2 is a NE with weak estrogenic potency, the estrogenic effect of αE2 via municipal effluent to its receiving water body cannot be ignored because it can be bio-transformed into E2 under aerobic environment. This work is the first to indicate that αE2 is an ignored NE in human and its environmental risk via municipal effluent discharging cannot be ignored, which should be paid with attention.

Physiological Systems in Promoting Frailty

Frailty is a complex syndrome affecting a growing sector of the global population as medical developments have advanced human mortality rates across the world. Our current understanding of frailty is derived from studies conducted in the laboratory as well as the clinic, which have generated largely phenotypic information. Far fewer studies have uncovered biological underpinnings driving the onset and progression of frailty, but the stage is set to advance the field with preclinical and clinical assessment tools, multiomics approaches together with physiological and biochemical methodologies. In this article, we provide comprehensive coverage of topics regarding frailty assessment, preclinical models, interventions, and challenges as well as clinical frameworks and prevalence. We also identify central biological mechanisms that may be at play including mitochondrial dysfunction, epigenetic alterations, and oxidative stress that in turn, affect metabolism, stress responses, and endocrine and neuromuscular systems. We review the role of metabolic syndrome, insulin resistance and visceral obesity, focusing on glucose homeostasis, adenosine monophosphate-activated protein kinase (AMPK), mammalian target of rapamycin (mTOR), and nicotinamide adenine dinucleotide (NAD⁺ ) as critical players influencing the age-related loss of health. We further focus on how immunometabolic dysfunction associates with oxidative stress in promoting sarcopenia, a key contributor to slowness, weakness, and fatigue. We explore the biological mechanisms involved in stem cell exhaustion that affect regeneration and may contribute to the frailty-associated decline in resilience and adaptation to stress. Together, an overview of the interplay of aging biology with genetic, lifestyle, and environmental factors that contribute to frailty, as well as potential therapeutic targets to lower risk and slow the progression of ongoing disease is covered. © 2022 American Physiological Society. Compr Physiol 12:1-46, 2022.

Role of senescence in the chronic health consequences of COVID-19

While the full impact of COVID-19 is not yet clear, early studies have indicated that upwards of 10% of patients experience COVID-19 symptoms longer than 3 weeks, known as Long-Hauler's Syndrome or PACS (postacute sequelae of SARS-CoV-2 infection). There is little known about risk factors or predictors of susceptibility for Long-Hauler's Syndrome, but older adults are at greater risk for severe outcomes and mortality from COVID-19. The pillars of aging (including cellular senescence, telomere dysfunction, impaired proteostasis, mitochondrial dysfunction, deregulated nutrient sensing, genomic instability, progenitor cell exhaustion, altered intercellular communication, and epigenetic alterations) that contribute to age-related dysfunction and chronic diseases (the "Geroscience Hypothesis") may interfere with defenses against viral infection and consequences of these infections. Heightening of the low-grade inflammation that is associated with aging may generate an exaggerated response to an acute COVID-19 infection. Innate immune system dysfunction that leads to decreased senescent cell removal and/or increased senescent cell formation could contribute to accumulation of senescent cells with both aging and viral infections. These processes may contribute to increased risk for long-term COVID-19 sequelae in older or chronically ill patients. Hence, senolytics and other geroscience interventions that may prolong healthspan and alleviate chronic diseases and multimorbidity linked to fundamental aging processes might be an option for delaying, preventing, or alleviating Long-Hauler's Syndrome.

The Unfolded Protein Responses in Health, Aging, and Neurodegeneration: Recent Advances and Future Considerations

Aging and age-related neurodegeneration are both associated with the accumulation of unfolded and abnormally folded proteins, highlighting the importance of protein homeostasis (termed proteostasis) in maintaining organismal health. To this end, two cellular compartments with essential protein folding functions, the endoplasmic reticulum (ER) and the mitochondria, are equipped with unique protein stress responses, known as the ER unfolded protein response (UPR ER ) and the mitochondrial UPR (UPR mt ), respectively. These organellar UPRs play roles in shaping the cellular responses to proteostatic stress that occurs in aging and age-related neurodegeneration. The loss of adaptive UPR ER and UPR mt signaling potency with age contributes to a feed-forward cycle of increasing protein stress and cellular dysfunction. Likewise, UPR ER and UPR mt signaling is often altered in age-related neurodegenerative diseases; however, whether these changes counteract or contribute to the disease pathology appears to be context dependent. Intriguingly, altering organellar UPR signaling in animal models can reduce the pathological consequences of aging and neurodegeneration which has prompted clinical investigations of UPR signaling modulators as therapeutics. Here, we review the physiology of both the UPR ER and the UPR mt , discuss how UPR ER and UPR mt signaling changes in the context of aging and neurodegeneration, and highlight therapeutic strategies targeting the UPR ER and UPR mt that may improve human health.

Geroprotectors and Skeletal Health: Beyond the Headlines

Osteoporosis and osteoarthritis are the most common age-related diseases of the musculoskeletal system. They are responsible for high level of healthcare use and are often associated with comorbidities. Mechanisms of ageing such as senescence, inflammation and autophagy are common drivers for both diseases and molecules targeting those mechanisms (geroprotectors) have potential to prevent both diseases and their co-morbidities. However, studies to test the efficacy of geroprotectors on bone and joints are scant. The limited studies available show promising results to prevent and reverse Osteoporosis-like disease. In contrast, the effects on the development of Osteoarthritis-like disease in ageing mice has been disappointing thus far. Here we review the literature and report novel data on the effect of geroprotectors for Osteoporosis and Osteoarthritis, we challenge the notion that extension of lifespan correlates with extension of healthspan in all tissues and we highlight the need for more thorough studies to test the effects of geroprotectors on skeletal health in ageing organisms.

Chronic HIV Infection and Aging: Application of a Geroscience-Guided Approach

ABSTRACT

The ability of virally suppressive antiretroviral therapy use to extend the life span of people with HIV (PWH) implies that the age of PWH will also increase. Among PWH, extended survival comes at a cost of earlier onset and increased rates of aging-associated comorbidities and geriatric syndromes, with persistent inflammation and immune dysregulation consequent to chronic HIV infection and to antiretroviral therapy use contributing to an overall decrease in health span. The geroscience hypothesis proposes that the root causes of most aging-related chronic diseases and conditions is the aging process itself. Hence, therapeutically targeting fundamental aging processes could have a greater impact on alleviating or delaying aging-associated comorbidities than addressing each disease individually. Extending the geroscience hypothesis to PWH, we speculate that targeting basic mechanisms of aging will improve overall health with age. Clinical features and pathophysiologic mechanisms of chronic diseases in PWH qualitatively resemble those seen in older adults without HIV. Therefore, drugs that target any of the pillars of aging, including metformin, rapamycin, and nicotinamide adenine dinucleotide precursors, may also slow the rate of onset of age-associated comorbidities and geriatric syndromes in PWH. Drugs that selectively induce apoptosis of senescent cells, termed senolytics, may also improve health span among PWH. Preliminary evidence suggests that senescent cell burden is increased in PWH, implying that senescent cells are an excellent therapeutic target for extending health span. Recently initiated clinical trials evaluating senolytics in age-related diseases offer insights into the design and potential implementation of similar trials for PWH.

Rapamycin, Acarbose and 17α-estradiol share common mechanisms regulating the MAPK pathways involved in intracellular signaling and inflammation

BACKGROUND

Rapamycin (Rapa), acarbose (ACA), and 17α-estradiol (17aE2, males only) have health benefits that increase lifespan of mice. Little is known about how these three agents alter the network of pathways downstream of insulin/IGF1 signals as well as inflammatory/stress responses.

RESULTS

ACA, Rapa, and 17aE2 (in males, but not in females) oppose age-related increases in the MEK1- ERK1/2-MNK1/2 cascade, and thus reduce phosphorylation of eIF4E, a key component of cap-dependent translation. In parallel, these treatments (in both sexes) reduce age-related increases in the MEK3-p38MAPK-MK2 pathway, to decrease levels of the acute phase response proteins involved in inflammation.

CONCLUSION

Each of three drugs converges on the regulation of both the ERK1/2 signaling pathway and the p38-MAPK pathway. The changes induced by treatments in ERK1/2 signaling are seen in both sexes, but the 17aE2 effects are male-specific, consistent with the effects on lifespan. However, the inhibition of age-dependent p38MAPK pathways and acute phase responses is triggered in both sexes by all three drugs, suggesting new approaches to prevention or reversal of age-related inflammatory changes in a clinical setting independent of lifespan effects.

Telomere dysfunction in ageing and age-related diseases

Ageing organisms accumulate senescent cells that are thought to contribute to body dysfunction. Telomere shortening and damage are recognized causes of cellular senescence and ageing. Several human conditions associated with normal ageing are precipitated by accelerated telomere dysfunction. Here, we systematize a large body of evidence and propose a coherent perspective to recognize the broad contribution of telomeric dysfunction to human pathologies.

Mild calorie restriction, but not 17α-estradiol, extends ovarian reserve and fertility in female mice

Calorie restriction (CR) (25-40%) is the most commonly studied strategy for curtailing age-related disease and has also been found to extend reproductive lifespan in female mice. However, the effects of mild CR (10%), which is sustainable, on ovarian aging has not yet been addressed. 17α-estradiol (17α-E2) is another intervention shown to positively modulate healthspan and lifespan in mice but its effects on female reproduction remain unclear. We evaluated the effects of mild CR (10%) and 17α-E2 treatment on ovarian reserve and female fertility over a 24-week period, and compared these effects with the more commonly employed 30% CR regimen. Both 10% and 30% CR elicited positive effects on the preservation of ovarian reserve, whereas 17α-E2 did not alter parameters associated with ovarian function. Following refeeding, both 10% and 30% increased fertility as evidenced by greater pregnancy rates. In aligned with the ovarian reserve data, 17α-E2 also failed to improve fertility. Collectively, these data indicate that 10% CR is effective in preserving ovarian function and fertility, while 17α-E2 does not appear to have therapeutic potential for delaying ovarian aging.

Endolysosome Localization of ERα Is Involved in the Protective Effect of 17α-Estradiol against HIV-1 gp120-Induced Neuronal Injury

Neurotoxic HIV-1 viral proteins contribute to the development of HIV-associated neurocognitive disorder (HAND), the prevalence of which remains high (30-50%) with no effective treatment available. Estrogen is a known neuroprotective agent; however, the diverse mechanisms of estrogen action on the different types of estrogen receptors is not completely understood. In this study, we determined the extent to which and mechanisms by which 17α-estradiol (17αE2), a natural less-feminizing estrogen, offers neuroprotection against HIV-1 gp120-induced neuronal injury. Endolysosomes are important for neuronal function, and endolysosomal dysfunction contributes to HAND and other neurodegenerative disorders. In hippocampal neurons, estrogen receptor α (ERα) is localized to endolysosomes and 17αE2 acidifies endolysosomes. ERα knockdown or overexpressing an ERα mutant that is deficient in endolysosome localization prevents 17αE2-induced endolysosome acidification. Furthermore, 17αE2-induced increases in dendritic spine density depend on endolysosome localization of ERα. Pretreatment with 17αE2 protected against HIV-1 gp120-induced endolysosome deacidification and reductions in dendritic spines; such protective effects depended on endolysosome localization of ERα. In male HIV-1 transgenic rats, we show that 17αE2 treatment prevents the development of enlarged endolysosomes and reduction in dendritic spines. Our findings demonstrate a novel endolysosome-dependent pathway that governs the ERα-mediated neuroprotective actions of 17αE2, findings that might lead to the development of novel therapeutic strategies against HAND.SIGNIFICANCE STATEMENT Extranuclear presence of membrane-bound estrogen receptors (ERs) underlie the enhancing effect of estrogen on cognition and synaptic function. The estrogen receptor subtype ERα is present on endolysosomes and plays a critical role in the enhancing effects of 17αE2 on endolysosomes and dendritic spines. These findings provide novel insight into the neuroprotective actions of estrogen. Furthermore, 17αE2 protected against HIV-1 gp120-induced endolysosome dysfunction and reductions in dendritic spines, and these protective effects of 17αE2 were mediated via endolysosome localization of ERα. Such findings provide a rationale for developing 17αE2 as a therapeutic strategy against HIV-associated neurocognitive disorders.

Litter expansion alters metabolic homeostasis in a sex specific manner

Nutritional manipulations early in life have been shown to influence growth rate and elicit long lasting effects which in turn has been found to impact lifespan. Therefore, we studied the long-term effects of pre-weaning dietary restriction implemented by litter expansion (4, 6, 8, 10, and 12 pups per dam: LS4, LS6, LS8, LS10, LS12) on male and female C57BL/6J mice. After weaning, these mice were fed ad libitum a commercial lab chow for the 15-month duration of the study. The male mice from large litter size (LS12) were significantly leaner and had reduced total fat mass compared to the normal size litters (LS 6) starting from weaning through to 15 months of age. Male LS10 & 12 mice also showed significant reduction in their fat depot masses at 15 months of age: gonadal, subcutaneous, and brown fat whereas the females did not mimic these findings. At 9 months of age, only male LS12 mice showed improved glucose tolerance and male LS12 mice also showed improved insulin tolerance starting at 5 months of age. In addition, we found that the male LS8, 10 & 12 mice at 15 months of age showed significantly reduced IGF-1 levels in the serum and various other organs (liver, gastrocnemius and brain cortex). Interestingly, the female LS8, 10, 12 mice showed a different pattern with reduced IGF-1 levels in serum, liver and gastrocnemius but not in the brain cortex. Similarly, the litter expanded mice showed sex specific response to levels of FGF21 and adiponectin with only the male mice showing increased FGF21 and adiponectin levels at 15 months of age. In summary, our data show that, litter expansion results in long-lasting metabolic changes that are age and sex dependent with the male mice showing an early and robust response compared to female mice.

17-a-estradiol has sex-specific effects on neuroinflammation that are partly reversed by gonadectomy

17-α-estradiol (17aE2) treatment from 4-months of age extends lifespan in male mice and can reduce neuroinflammatory responses in the hypothalamus of 12-month-old males. Although 17aE2 improves longevity in males, female mice are unaffected, suggesting a sexually dimorphic pattern of lifespan regulation. We tested whether the sex-specific effects of 17aE2 on neuroinflammatory responses are affected by gonadal removal and whether hypothalamic changes extend to other brain regions in old age. We show that sex-specific effects of 17aE2 on age-associated gliosis are brain region-specific and are partially dependent on gonadectomy. 17aE2 treatment started at 4 months of age protected 25-month-old males from hypothalamic inflammation. Castration before 17aE2 exposure reduced the effect of 17aE2 on hypothalamic astrogliosis in males. By contrast, sex-specific inhibition of microgliosis generated by 17aE2 was not significantly affected by castration. In the hippocampus, gonadectomy influenced the severity of gliosis and the responsiveness to 17aE2 in a region-dependent manner. The male-specific effects of 17aE2 correlate with increases in hypothalamic ERα expression, specifically in gonadally intact males, consistent with the idea that 17aE2 might act through this receptor. Our results indicate that neuroinflammatory responses to 17aE2 are partially controlled by the presence of sex-specific gonads. Loss of gonadal function and age-associated neuroinflammation could, therefore, influence late-life health and disease onset, leading to sexual dimorphism in both aging and in response to drugs that modify the pace of aging.

Cell-Free Culture Supernatant of Probiotic Lactobacillus fermentum Protects Against H2O2-Induced Premature Senescence by Suppressing ROS-Akt-mTOR Axis in Murine Preadipocytes

Information regarding cellular anti-senescence attributes of probiotic bacteria vis-à-vis modulation of senescence-associated secretory phenotype (SASP) and mTOR signaling is very limited. The present study assessed anti-senescence potential of secretory metabolites of probiotic Lactobacillus fermentum (Lact. fermentum) using H₂O₂-induced model of senescence in 3T3-L1 preadipocytes. Application of H₂O₂-induced cellular senescence characterized by increased cell size and SA-β-gal activity, activation of SASP and reactive oxygen species (ROS), DNA damage response and induction of cell cycle inhibitors (p53/p21^WAF1/p16^INK4a). Further, a robust stimulation of the PI3K/Akt/mTOR pathway and AMPK signaling was also observed in H₂O₂-treated cells. However, exposure of cells to cell-free supernatant of Lact. fermentum significantly attenuated phosphorylation of PI3K/Akt/mTOR pathway and alleviated senescence markers p53, p21^WAF1, SA-β-gal, p38MAPK, iNOS, cox-2, ROS, NF-κB, and DNA damage response. These results provide evidence that secretory metabolites of Lact. fermentum can mitigate the development as well as severity of stress-induced senescence thereby indicating its utility for use as anti-aging or age-delaying agent.

Sex differences and aging: Is there a role of brown adipose tissue?

In every population across the world, women live significantly longer than men; however, the underlying physiological processes that drive these sex differences in age-specific mortality are largely unknown. Recently, the role of adipose tissue in aging and longevity has been a focus of biomedical research in both humans and rodent models. Specifically, brown adipose tissue, a thermoregulatory tissue originally thought to not exist past infancy in humans, has been shown to potentially play a role in health throughout the lifespan. Females have larger adult brown adipose depots that are not just larger in size but also more efficient in non-shivering thermogenesis. This improved functioning of the brown adipose tissue may potentially lead to improved female health, and we hypothesize that this advantage may be of even bigger significance in the older population. Here, we briefly review what is known about sex differences in aging and how sex differences in brown adipose tissue may be contributing to the female lifespan advantage. These questions have usually been addressed in large experimental studies in rodents as a translational model of human aging. Overall, we propose that a better understanding of the thermogenesis-metabolism nexus is necessary in biomedical research, and sex differences in these factors may contribute to the female longevity bias seen in human populations.

Frailty and HIV: Moving from Characterization to Intervention

PURPOSE OF REVIEW

While the characteristics associated with frailty in people with HIV (PWH) have been well described, little is known regarding interventions to slow or reverse frailty. Here we review interventions to prevent or treat frailty in the general population and in people with HIV (PWH).

RECENT FINDINGS

Frailty interventions have primarily relied on nonpharmacologic interventions (e.g., exercise and nutrition). Although few have addressed frailty, many of these therapies have shown benefit on components of frailty including gait speed, strength, and low activity among PWH. When nonpharmacologic interventions are insufficient, pharmacologic interventions may be necessary. Many interventions have been tested in preclinical models, but few have been tested or shown benefit among older adults with or without HIV. Ultimately, pharmacologic and nonpharmacologic interventions have the potential to improve vulnerability that underlies frailty in PWH, though clinical data is currently sparse.

Kinetic Study of 17α-Estradiol Activity in Comparison with 17β-Estradiol and 17α-Ethynylestradiol

17α-estradiol (αE2), an endogenous stereoisomer of the hormone 17β-estradiol (E2), is capable of binding to estrogen receptors (ER). We aimed to mathematically describe, using experimental data, the possible interactions between αE2 and sperm ER during the process of sperm capacitation and to develop a kinetic model. The goal was to compare the suggested kinetic model with previously published results of ER interactions with E2 and 17α-ethynylestradiol (EE2). The HPLC-MS/MS method was developed to monitor the changes of αE2 concentration during capacitation. The calculated relative concentrations Bt were used for kinetic analysis. Rate constants k and molar ratio n were optimized and used for the construction of theoretical B(t) curves. Modifications in αE2–ER interactions were discovered during comparison with models for E2 and EE2. These new interactions displayed autocatalytic formation of an unstable adduct between the hormone and the cytoplasmic receptors. αE2 accumulates between the plasma membrane lipid bilayer with increasing potential, and when the critical level is reached, αE2 penetrates through the inner layer of the plasma membrane into the cytoplasm. It then rapidly reacts with the ER and creates an unstable adduct. The revealed dynamics of αE2–ER action may contribute to understanding tissue rejuvenation and the cancer-related physiology of αE2 signaling.

17-a-estradiol late in life extends lifespan in aging UM-HET3 male mice; nicotinamide riboside and three other drugs do not affect lifespan in either sex

In genetically heterogeneous mice produced by the CByB6F1 x C3D2F1 cross, the "non-feminizing" estrogen, 17-α-estradiol (17aE2), extended median male lifespan by 19% (p < 0.0001, log-rank test) and 11% (p = 0.007) when fed at 14.4 ppm starting at 16 and 20 months, respectively. 90th percentile lifespans were extended 7% (p = 0.004, Wang-Allison test) and 5% (p = 0.17). Body weights were reduced about 20% after starting the 17aE2 diets. Four other interventions were tested in males and females: nicotinamide riboside, candesartan cilexetil, geranylgeranylacetone, and MIF098. Despite some data suggesting that nicotinamide riboside would be effective, neither it nor the other three increased lifespans significantly at the doses tested. The 17aE2 results confirm and extend our original reports, with very similar results when started at 16 months compared with mice started at 10 months of age in a prior study. The consistently large lifespan benefit in males, even when treatment is started late in life, may provide information on sex-specific aspects of aging.

17α-Estradiol Modulates IGF1 and Hepatic Gene Expression in a Sex-Specific Manner

Aging is the greatest risk factor for most chronic diseases. The somatotropic axis is one of the most conserved biological pathways that regulates aging across species. 17α-Estradiol (17α-E2), a diastereomer of 17β-estradiol (17β-E2), was recently found to elicit health benefits, including improved insulin sensitivity and extend longevity exclusively in male mice. Given that 17β-E2 is known to modulate somatotropic signaling in females through actions in the pituitary and liver, we hypothesized that 17α-E2 may be modulating the somatotropic axis in males, thereby contributing to health benefits. Herein, we demonstrate that 17α-E2 increases hepatic insulin-like growth factor 1 (IGF1) production in male mice without inducing any changes in pulsatile growth hormone (GH) secretion. Using growth hormone receptor knockout (GHRKO) mice, we subsequently determined that the induction of hepatic IGF1 by 17α-E2 is dependent upon GH signaling in male mice, and that 17α-E2 elicits no effects on IGF1 production in female mice. We also determined that 17α-E2 failed to feminize the hepatic transcriptional profile in normal (N) male mice, as evidenced by a clear divergence between the sexes, regardless of treatment. Conversely, significant overlap in transcriptional profiles was observed between sexes in GHRKO mice, and this was unaffected by 17α-E2 treatment. Based on these findings, we propose that 17α-E2 acts as a pleiotropic pathway modulator in male mice by uncoupling IGF1 production from insulin sensitivity. In summary, 17α-E2 treatment upregulates IGF1 production in wild-type (and N) male mice in what appears to be a GH-dependent fashion, while no effects in female IGF1 production are observed following 17α-E2 treatment.

Short-term Calorie Restriction and 17α-Estradiol Administration Elicit Divergent Effects on Proteostatic Processes and Protein Content in Metabolically Active Tissues

17α-Estradiol (17α-E2) is a "non-feminizing" estrogen that extends life span in male, but not female, mice. We recently reported that 17α-E2 had robust beneficial effects on metabolic and inflammatory parameters in aged male mice. However, it remains unclear if 17α-E2 also delays other "hallmarks" of aging, particularly maintaining proteostasis. Here, we used isotope labeling methods in older mice to examine proteostatic mechanisms. We compared weight-matched mild calorie restricted (CR) and 17α-E2 treated male mice with the hypothesis that 17α-E2 would increase protein synthesis for somatic maintenance. 17α-E2 had no effect on protein synthesis or DNA synthesis in multiple tissues, including white adipose tissue. Conversely, mild short-term CR decreased DNA synthesis and increased the protein to DNA synthesis ratio in multiple tissues. Examination of individual protein synthesis and content did not differentiate treatments, although it provided insight into the regulation of protein content between tissues. Contrary to our hypothesis, we did not see the predicted differences in protein to DNA synthesis following 17α-E2 treatment. However, mild short-term CR elicited differences consistent with both lifelong CR and other treatments that curtail aging processes. These data indicated that despite similar maintenance of body mass, 17α-E2 and CR treatments elicit distinctly different proteostatic outcomes.

Does Diet Have a Role in the Treatment of Alzheimer's Disease?

The aging process causes many changes to the brain and is a major risk factor for the development of neurodegenerative diseases such as Alzheimer's Disease (AD). Despite an already vast amount of research on AD, a greater understanding of the disease's pathology and therapeutic options are desperately needed. One important distinction that is also in need of further study is the ability to distinguish changes to the brain observed in early stages of AD vs. changes that occur with normal aging. Current FDA-approved therapeutic options for AD patients have proven to be ineffective and indicate the need for alternative therapies. Aging interventions including alterations in diet (such as caloric restriction, fasting, or methionine restriction) have been shown to be effective in mediating increased health and lifespan in mice and other model organisms. Because aging is the greatest risk factor for the development of neurodegenerative diseases, certain dietary interventions should be explored as they have the potential to act as a future treatment option for AD patients.

Health benefits attributed to 17α-estradiol, a lifespan-extending compound, are mediated through estrogen receptor α

Metabolic dysfunction underlies several chronic diseases, many of which are exacerbated by obesity. Dietary interventions can reverse metabolic declines and slow aging, although compliance issues remain paramount. 17α-estradiol treatment improves metabolic parameters and slows aging in male mice. The mechanisms by which 17α-estradiol elicits these benefits remain unresolved. Herein, we show that 17α-estradiol elicits similar genomic binding and transcriptional activation through estrogen receptor α (ERα) to that of 17β-estradiol. In addition, we show that the ablation of ERα completely attenuates the beneficial metabolic effects of 17α-E2 in male mice. Our findings suggest that 17α-E2 may act through the liver and hypothalamus to improve metabolic parameters in male mice. Lastly, we also determined that 17α-E2 improves metabolic parameters in male rats, thereby proving that the beneficial effects of 17α-E2 are not limited to mice. Collectively, these studies suggest ERα may be a drug target for mitigating chronic diseases in male mammals.

17α-Estradiol prevents ovariectomy-mediated obesity and bone loss

Menopause is a natural physiological process in older women that is associated with reduced estrogen production and results in increased risk for obesity, diabetes, and osteoporosis. 17α-estradiol (17α-E2) treatment in males, but not females, reverses several metabolic conditions associated with advancing age, highlighting sexually dimorphic actions on age-related pathologies. In this study we sought to determine if 17α-E2 could prevent ovariectomy (OVX)-mediated detriments on adiposity and bone parameters in females. Eight-week-old female C57BL/6J mice were subjected to SHAM or OVX surgery and received dietary 17α-E2 during a six-week intervention period. We observed that 17α-E2 prevented OVX-induced increases in body weight and adiposity. Similarly, uterine weight and luminal cell thickness were decreased by OVX and prevented by 17α-E2 treatment. Interestingly, 17α-E2 prevented OVX-induced declines in tibial metaphysis cancellous bone. And similarly, 17α-E2 improved bone density parameters in both tibia and femur cancellous bone, primarily in OVX mice. In contrast, to the effects on cancellous bone, cortical bone parameters were largely unaffected by OVX or 17α-E2. In the non-weight bearing lumbar vertebrae, OVX reduced trabecular thickness but not spacing, while 17α-E2 increased trabecular thickness and reduced spacing. Despite this, 17α-E2 did improve bone volume/tissue volume in lumbar vertebrae. Overall, we found that 17α-E2 prevented OVX-induced increases in adiposity and changes in bone mass and architecture, with minimal effects in SHAM-operated mice. We also observed that 17α-E2 rescued uterine tissue mass and lining morphology to control levels without inducing hypertrophy, suggesting that 17α-E2 could be considered as an adjunct to traditional hormone replacement therapies.