Growth curves and survival characteristics of the animals used in the Biomarkers of Aging Program

The essential role of magnesium in immunity and gut health: Impacts of dietary magnesium restriction on peritoneal cells and intestinal microbiome

Magnesium (Mg2+) is essential for life, and low levels impair immune function, promote chronic inflammation, and influence the intestinal microbiome, with the peritoneal cavity serving as a site for direct interaction between the cavity and intestinal contents, including the microbiota. This study investigates the effects of a Mg2+-restricted diet on peritoneal immune cells and its interplay with the intestinal microbiome. Male C57BL/6NTaq mice were divided into three groups: control, restricted, and restored. The control group received a diet containing 500 mg Mg2+/kg, the restricted group received a diet with 50 mg Mg2+/kg for four weeks, and the restored group first received the restricted diet for four weeks, followed by the control diet supplemented with 0.5 g MgCl₂ per liter of water for an additional four weeks. Results showed Mg2+ restriction did not affect body weight, food intake, or water consumption but induced hypomagnesemia, reversible upon dietary restoration. Mg2+ deficiency increased in neutrophils numbers in the blood and peritoneal cavity, indicating an inflammatory response. Gene expression analysis in peritoneal mononuclear cells revealed elevated levels of Nfkb, Stat1 and Stat3, suggesting heightened inflammatory signaling. Additionally, cytokine expression analysis showed increased levels of Tnfa, Il1b and Il10, but not Il6, in Mg2+-restricted group. The intestinal microbiome of Mg2+-restricted mice exhibited increased alpha diversity, with changes in taxa abundance, including an increase in Romboutsia ilealis and a decrease in the Oscillospiraceae and Lachnospiraceae. Mg2+ deficiency significantly affects some immune functions and gut microbiota, highlighting the importance of Mg²+ in maintaining the gut health.

Protocol to study inter-tissue communication between the hypothalamus and white adipose tissue and lifespan using a chemogenetic approach in aged mice

Here, we present a protocol for assessing the impact of a chemogenetic manipulation in a subpopulation of the hypothalamic neurons on aging and lifespan control using a mouse model developed specifically for this purpose. We describe steps for stereotaxic viral injection and assess inter-tissue communication between protein phosphatase 1 regulatory subunit 17 (Ppp1r17)-expressing neurons in the dorsomedial hypothalamus and white adipose tissue. We then detail procedures for lifespan measurements following chemogenetic manipulation in aged mice. For complete details on the use and execution of this protocol, please refer to Tokizane et al.1.

Dendritic alterations precede age-related dysphagia and nucleus ambiguus motor neuron death

Motor neurons (MNs) within the nucleus ambiguus innervate the skeletal muscles of the larynx, pharynx and oesophagus, which are essential for swallow. Disordered swallow (dysphagia) is a serious problem in elderly humans, increasing the risk of aspiration, a key contributor to mortality. Despite this importance, very little is known about the pathophysiology of ageing dysphagia and the relative importance of frank muscle weakness compared to timing/activation abnormalities. In elderly humans and in aged Fisher 344 (F344) rats, a variety of motor pools exhibit weakness and atrophy (sarcopenia), contemporaneous to MN death. Synchronisation of swallow is dependent on the stability of MN dendrites, which integrate neural circuits. Dendritic derangement occurs in many neuromotor degenerative conditions prior to MN death. We hypothesise behavioural weakness and death of nucleus ambiguus MNs will occur by age 24 months in F344 rats and that this will be preceded by swallow-respiration dyscoordination and dendritic arbour degenerations from 18 months compared to controls at 6 months. Using pressure catheters to estimate laryngeal and diaphragm function during naturalistic water bolus applications, we show that swallow number and post-swallow apnoeas are altered from 18 months. Swallow pressure (weakness) and nucleus ambiguus MN numbers (evaluated via stereological assessments of Nissl staining) were reduced at 24 months. Dendritic lengths, surface areas and dendritic spines were reduced in nucleus ambiguus MNs from 18 months (evaluated by confocal imaging of Golgi-Cox impregnated brainstem). These results show that synapse loss occurs prior to MN death and behavioural weakness. Strategies to preserve synapses may be of utility in ameliorating sarcopenia. KEY POINTS: Dysphagia is a major contributor to ageing morbidity and mortality, but the underling pathophysiology is unexplored. Here, in Fischer 344 rats, we use pressure and timing evaluations of swallow-respiration, showing timing impairments occur prior to frank pressure defects. In nucleus ambiguus motor neurons, dendritic defects were apparent with the onset of swallow-respiration dyscoordination, with frank motor neuron loss occurring subsequently to synapse loss. Our results show that synapse loss occurs prior to motor neuron death and behavioural impairments. Strategies to preserve synapses may be of utility in ameliorating sarcopaenia.

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.

Age-induced changes in skeletal muscle mitochondrial DNA synthesis, quantity, and quality in genetically unique rats

Mitochondrial genomic integrity is a key element of physiological processes and health. Changes in the half-life of the mitochondrial genome are implicated in the generation and accumulation of age-induced mitochondrial DNA (mtDNA) mutations, which are implicated in skeletal muscle aging and sarcopenia. There are conflicting data on the half-life of mtDNA, and there is limited information on how aging affects half-life in skeletal muscle. We hypothesized that skeletal muscle mtDNA synthesis rates would decrease with age in both female and male rats concomitant with changes in mtDNA integrity reflected in mtDNA copy number and mutation frequency. We measured mitochondrial genome half-life using stable isotope labeling over a period of 14 days and assessed mtDNA copy number and deletion mutation frequency using digital PCR in the quadriceps muscle of 9-month-old and 26-month-old male and female OKC-HET rats. We found a significant age-related increase in mtDNA half-life, from 132 days at 9 months to 216 days at 26 months of age in OKC-HET quadriceps. Concomitant with the increase in mtDNA half-life, we found an age-related increase in mtDNA deletion mutation frequency in both male and female rats. Notably, 26-month-old female rats had a lower mutation frequency than male rats, and there were no changes in mtDNA copy number with sex, age, or mitochondrial genotype. These data reveal several key findings: (1) mtDNA turnover in rat skeletal muscle decreases with age, (2) mtDNA half-lives in skeletal muscle are approximately an order of magnitude longer than what is reported for other tissues, and (3) muscle mtDNA turnover differs significantly from the turnover of other mitochondrial macromolecules including components of the mitochondrial nucleoid. These findings provide insight into the factors driving age-induced mtDNA mutation accumulation, which contribute to losses of mitochondrial genomic integrity and may play a role in skeletal muscle dysfunction.

Anti-aging properties of the aminosterols of the dogfish shark

The development of anti-aging drugs is challenged by both the apparent complexity of the physiological mechanisms involved in aging and the likelihood that many of these mechanisms remain unknown. As a consequence, the development of anti-aging compounds based on the rational targeting of specific pathways has fallen short of the goal. To date, the most impressive compound is rapamycin, a natural bacterial product initially identified as an antifungal, and only subsequently discovered to have anti-aging properties. In this review, we focus on two aminosterols from the dogfish shark, Squalus acanthias, that we discovered initially as broad-spectrum anti-microbial agents. This review is the first to gather together published studies conducted both in vitro and in numerous vertebrate species to demonstrate that these compounds target aging pathways at the cellular level and provide benefits in multiple aging-associated conditions in relevant animal models and in humans. The dogfish aminosterols should be recognized as potential anti-aging drugs.

Liver iron stores and effectors of ferroptosis are dependent on age and sex

Ferroptosis is a form of cell death characterized by a pro-oxidative cellular milieu and iron-dependent lipid peroxidation. Ferroptosis has been implicated in various forms of liver injury, in keeping with the major role of the liver in iron metabolism. Limited research has addressed potential differences in ferroptosis mediators with age and sex, especially in an in vivo model. The goal of this investigation was to evaluate hepatic labile iron and mediators of ferroptosis with ageing in both sexes. Because female animals generally display greater antioxidant defences than males, we hypothesized that females would display a phenotype resistant to ferroptosis. Here, we determined iron contents, protein expression of ferroptosis mediators and measures of oxidative injury in liver samples from 12- and 24-month-old male and female Fischer 344 rats. In comparison to males, the livers of female rats at both ages contained more non-haem iron, which was associated with greater ferritin heavy chain expression and attenuated expression of transferrin receptor-1. In female rats, the 24-month-old group had higher contents of thiobarbituric acid reactive substances compared with their 12-month-old counterparts, yet similar contents of labile iron. These results suggest a disconnect between labile iron contents and oxidative injury with age. Female animals also displayed greater expression of acyl-CoA synthetase long-chain family member 4 (ACSL4), a modulator of ferroptosis, and greater abundance of high molecular weight 4-hydroxnonenal-modified proteins. These results demonstrate clear differences in iron and ferroptosis mediators between sexes and suggest that female rats of this strain might be more susceptible to ferroptosis.

Systemic metabolic benefits of 17α-estradiol are not exclusively mediated by ERα in glutamatergic or GABAergic neurons

17α-Estradiol (17αE2), a less-feminising enantiomer of 17β-estradiol, has been shown to prolong lifespan and improve metabolic health in a sex-specific manner in male, but not in female mice. Recent studies have demonstrated the pivotal role of estrogen receptor α (ERα) in mediating the effects of 17αE2 on metabolic health. However, the specific tissues and/or neuronal signalling pathways that 17αE2 acts through remain to be elucidated. ERα expression in glutamatergic and GABAergic neurons (principal excitatory and inhibitory neurons respectively) in the hypothalamus is essential for estradiol signalling. Therefore, we hypothesised that knocking out ERα from one of these neuronal populations would attenuate the established beneficial metabolic effects of 17αE2 in male mice exposed to a high fat diet. To test this hypothesis we used two established brain specific ERα KO models, targeting either glutamatergic or GABAergic neurons (Vglut2/Vgat-ERαKO). We show that both of these ERα KO models exhibit a strong reduction in ERα expression in the arcuate nucleus of the hypothalamus, a control centre for metabolic regulation. Deletion of ERα from GABAergic neurons significantly diminished the effect of 17αE2 on body weight relative to controls, although these animals still show metabolic benefits with 17αE2 treatment. The response to 17αE2 was unaffected by ERα deletion in glutamatergic neurons. Our results support a benefit of 17αE2 treatment in protection against metabolic dysfunction, but these effects do not depend on exclusive ERα expression in glutamatergic and GABAergic neurons and persist when ERα expression is strongly reduced in the arcuate nucleus of the hypothalamus.

Negative effects of lifespan extending intervention on resilience in mice

One key goal of basic aging research is the development of reliable assays of both current and future health. These assays could dramatically accelerate progress toward developing health-extending interventions by obviating the need for full lifespan studies, especially if they were informative relatively early in life. One potential approach is the assessment of physiological resilience, defined as the ability to recover from an adverse event. Here, using CB6F1 mice, we evaluated four potential resilience assays, each quantifying recovery from a physiological challenge with clear relevance to humans. The challenges were: (1) anesthesia recovery, (2) restoration of hemoglobin levels after a blood draw, (3) speed of wound healing, and (4) survival after pathogen exposure. We evaluated how each changed with age and with interventions known to extend health in males only (17α-estradiol) or both sexes (calorie restriction). We found that three of the four (recovery from anesthesia, blood draw, and pathogen exposure) showed significant and expected age effects, but wound healing did not. None of the three age-sensitive assays responded to the health-extending interventions in the way we expected, and for some assays, including anesthesia response, interventions actually worsened outcomes. Possible explanations are: (1) our interventions were too brief, (2) the ages we evaluated were too young, (3) our assays did not capture important features of organismal resilience, or (4) organismal resilience is not as clearly related to current or future health as hypothesized. Future studies are needed to determine which of these interpretations is valid and to determine whether other resilience metrics may be more informative about current and future health.

The dietary exposome: a brief history of diet, longevity, and age-related health in rodents

It has been recognized for over a century that feeding animals less food than they would normally eat increases lifespan and leads to broad-spectrum improvements in age-related health. A significant number of studies have subsequently shown that restricting total protein, branched chain amino acids or individual amino acids in the diet, as well as ketogenic diets, can elicit similar effects. In addition, it is becoming clear that fasting protocols, such as time-restricted-feeding or every-other-day feeding, without changes in overall energy intake can also profoundly affect rodent longevity and late-life health. In this review, I will provide a historical perspective on various dietary interventions that modulate ageing in rodents and discuss how this understanding of the dietary exposome may help identify future strategies to maintain late-life health and wellbeing in humans.

Cellular and transcriptomic changes by the supplementation of aged rat serum in human pluripotent stem cell-derived myogenic progenitors

Introduction

The changing composition of non-cell autonomous circulating factors in blood as humans age is believed to play a role in muscle mass and strength loss. The mechanisms through which these circulating factors act in age-related skeletal muscle changes is not fully understood. In this study, we used human myogenic progenitors derived from human pluripotent stem cells to study non-cell autonomous roles of circulating factors during the process of myogenic differentiation.

Methods

Myogenic progenitors from human embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) were supplemented with serum samples from aged or young Fischer 344 × Brown Norway F1-hybrid rats. The effect of aged or young serum supplementation on myogenic progenitor proliferation, myotube formation capacity, differentiation, and early transcriptomic profiles were analyzed.

Results

We found that aged rat serum supplementation significantly reduced cell proliferation and increased cell death in both ESC- and iPSC-derived myogenic progenitors. Next, we found that the supplementation of aged rat serum inhibited myotube formation and maturation during terminal differentiation from progenitors to skeletal myocytes when compared to the cells treated with young adult rat serum. Lastly, we identified that gene expression profiles were affected following serum supplementation in culture.

Discussion

Together, aged serum supplementation caused cellular and transcriptomic changes in human myogenic progenitors. The current data from our in vitro model possibly simulate non-cell autonomous contributions of blood composition to age-related processes in human skeletal muscle.

Late-life dietary folate restriction reduces biosynthesis without compromising healthspan in mice

Folate is a vitamin required for cell growth and is present in fortified foods in the form of folic acid to prevent congenital abnormalities. The impact of low-folate status on life-long health is poorly understood. We found that limiting folate levels with the folate antagonist methotrexate increased the lifespan of yeast and worms. We then restricted folate intake in aged mice and measured various health metrics, metabolites, and gene expression signatures. Limiting folate intake decreased anabolic biosynthetic processes in mice and enhanced metabolic plasticity. Despite reduced serum folate levels in mice with limited folic acid intake, these animals maintained their weight and adiposity late in life, and we did not observe adverse health outcomes. These results argue that the effectiveness of folate dietary interventions may vary depending on an individual's age and sex. A higher folate intake is advantageous during the early stages of life to support cell divisions needed for proper development. However, a lower folate intake later in life may result in healthier aging.

Non-canonical metabolic and molecular effects of calorie restriction are revealed by varying temporal conditions

Calorie restriction (CR) extends lifespan and healthspan in diverse species. Comparing ad libitum- and CR-fed mice is challenging due to their significantly different feeding patterns, with CR-fed mice consuming their daily meal in 2 h and then subjecting themselves to a prolonged daily fast. Here, we examine how ad libitum- and CR-fed mice respond to tests performed at various times and fasting durations and find that the effects of CR-insulin sensitivity, circulating metabolite levels, and mechanistic target of rapamycin 1 (mTORC1) activity-result from the specific temporal conditions chosen, with CR-induced improvements in insulin sensitivity observed only after a prolonged fast, and the observed differences in mTORC1 activity between ad libitum- and CR-fed mice dependent upon both fasting duration and the specific tissue examined. Our results demonstrate that much of our understanding of the effects of CR are related to when, relative to feeding, we choose to examine the mice.

Effect of Age at Time of Irradiation, Sex, Genetic Diversity, and Granulopoietic Cytokine Radiomitigation on Lifespan and Lymphoma Development in Murine H-ARS Survivors

Acute, high-dose radiation exposure results in life-threatening acute radiation syndrome (ARS) and debilitating delayed effects of acute radiation exposure (DEARE). The DEARE are a set of chronic multi-organ illnesses that can result in early death due to malignancy and other diseases. Animal models have proven essential in understanding the natural history of ARS and DEARE and licensure of medical countermeasures (MCM) according to the FDA Animal Rule. Our lab has developed models of hematopoietic (H)-ARS and DEARE in inbred C57BL/6J and Jackson Diversity Outbred (JDO) mice of both sexes and various ages and have used these models to identify mechanisms of radiation damage and effective MCMs. Herein, aggregate data from studies conducted over decades in our lab, consisting of 3,250 total-body lethally irradiated C57BL/6J young adult mice and 1,188 H-ARS survivors from these studies, along with smaller datasets in C57BL/6J pediatric and geriatric mice and JDO mice, were examined for lifespan and development of thymic lymphoma in survivors up to 3 years of age. Lifespan was found to be significantly shortened in H-ARS survivors compared to age-matched nonirradiated controls in all four models. Males and females exhibited similar lifespans except in the young adult C57BL/6J model where males survived longer than females after 16 months of age. The incidence of thymic lymphoma was increased in H-ARS survivors from the young adult and pediatric C57BL/6J models. Consistent with our findings in H-ARS, geriatric mice appeared more radioresistant than other models, with a lifespan and thymic lymphoma incidence more similar to nonirradiated controls than other models. Increased levels of multiple pro-inflammatory cytokines in DEARE bone marrow and serum correlated with shortened lifespan and malignancy, consistent with other animal models and human data. Of interest, G-CSF levels in bone marrow and serum 8-11 months after irradiation were significantly increased in females. Importantly, treatment with granulopoietic cytokine MCM for radiomitigation of H-ARS did not influence the long-term survival rate or incidence of thymic lymphoma in any model. Taken together, these findings indicate that the lifespan of H-ARS survivors was significantly decreased regardless of age at time of exposure or genetic diversity, and was unaffected by earlier treatment with granulopoietic cytokines for radiomitigation of H-ARS.

Long-term NMN treatment increases lifespan and healthspan in mice in a sex dependent manner

Nicotinamide adenine dinucleotide (NAD) is essential for many enzymatic reactions, including those involved in energy metabolism, DNA repair and the activity of sirtuins, a family of defensive deacylases. During aging, levels of NAD + can decrease by up to 50% in some tissues, the repletion of which provides a range of health benefits in both mice and humans. Whether or not the NAD + precursor nicotinamide mononucleotide (NMN) extends lifespan in mammals is not known. Here we investigate the effect of long-term administration of NMN on the health, cancer burden, frailty and lifespan of male and female mice. Without increasing tumor counts or severity in any tissue, NMN treatment of males and females increased activity, maintained more youthful gene expression patterns, and reduced overall frailty. Reduced frailty with NMN treatment was associated with increases in levels of Anerotruncus colihominis, a gut bacterium associated with lower inflammation in mice and increased longevity in humans. NMN slowed the accumulation of adipose tissue later in life and improved metabolic health in male but not female mice, while in females but not males, NMN increased median lifespan by 8.5%, possible due to sex-specific effects of NMN on NAD + metabolism. Together, these data show that chronic NMN treatment delays frailty, alters the microbiome, improves male metabolic health, and increases female mouse lifespan, without increasing cancer burden. These results highlight the potential of NAD + boosters for treating age-related conditions and the importance of using both sexes for interventional lifespan studies.

Caloric restriction reduces trabecular bone loss during aging and improves bone marrow adipocyte endocrine function in male mice

Introduction

Caloric restriction (CR) is a nutritional intervention that increases life expectancy while lowering the risk for cardio-metabolic disease. Its effects on bone health, however, remain controversial. For instance, CR has been linked to increased accumulation of bone marrow adipose tissue (BMAT) in long bones, a process thought to elicit detrimental effects on bone. Qualitative differences have been reported in BMAT in relation to its specific anatomical localization, subdividing it into physiological and potentially pathological BMAT. We here examine the local impact of CR on bone composition, microstructure and its endocrine profile in the context of aging.

Methods

Young and aged male C57Bl6J mice were subjected to CR for 8 weeks and were compared to age-matched littermates with free food access. We assessed bone microstructure and BMAT by micro-CT, bone fatty acid and transcriptomic profiles, and bone healing.

Results

CR increased tibial BMAT accumulation and adipogenic gene expression. CR also resulted in elevated fatty acid desaturation in the proximal and mid-shaft regions of the tibia, thus more closely resembling the biochemical lipid profile of the distally located, physiological BMAT. In aged mice, CR attenuated trabecular bone loss, suggesting that CR may revert some aspects of age-related bone dysfunction. Cortical bone, however, was decreased in young mice on CR and remained reduced in aged mice, irrespective of dietary intervention. No negative effects of CR on bone regeneration were evident in either young or aged mice.

Discussion

Our findings indicate that the timing of CR is critical and may exert detrimental effects on bone biology if administered during a phase of active skeletal growth. Conversely, CR exerts positive effects on trabecular bone structure in the context of aging, which occurs despite substantial accumulation of BMAT. These data suggest that the endocrine profile of BMAT, rather than its fatty acid composition, contributes to healthy bone maintenance in aged mice.

In the land of not-unhappiness: On the state-of-the-art of targeting aging and age-related diseases by biomedical research

The concept of the Land of Not-Unhappiness refers to the potential achievement of eliminating the pathologies of the aging process. To inform of how close we are to settling in the land, we summarize and review the achievements of research on anti-aging interventions over the last hundred years with a specific focus on strategies that slow down metabolism, compensate for aging-related losses, and target a broad range of age-related diseases. We critically evaluate the existing interventions labeled as "anti-aging," such as calorie restriction, exercise, stem cell administration, and senolytics, to provide a down-to-earth evaluation of their current applicability in counteracting aging. Throughout the text, we have maintained a light tone to make it accessible to non-experts in biogerontology, and provide a broad overview for those considering conducting studies, research, or seeking to understand the scientific basis of anti-aging medicine.

Failure of senolytic treatment to prevent cognitive decline in a female rodent model of aging

There are sex differences in vulnerability and resilience to the stressors of aging and subsequent age-related cognitive decline. Cellular senescence occurs as a response to damaging or stress-inducing stimuli. The response includes a state of irreversible growth arrest, the development of a senescence-associated secretory phenotype, and the release of pro-inflammatory cytokines associated with aging and age-related diseases. Senolytics are compounds designed to eliminate senescent cells. Our recent work indicates that senolytic treatment preserves cognitive function in aging male F344 rats. The current study examined the effect of senolytic treatment on cognitive function in aging female rats. Female F344 rats (12 months) were treated with dasatinib (1.2 mg/kg) + quercetin (12 mg/kg) or ABT-263 (12 mg/kg) or vehicle for 7 months. Examination of the estrus cycle indicated that females had undergone estropause during treatment. Senolytic treatment may have increased sex differences in behavioral stress responsivity, particularly for the initial training on the cued version of the watermaze. However, pre-training on the cue task reduced stress responsivity for subsequent spatial training and all groups learned the spatial discrimination. In contrast to preserved memory observed in senolytic-treated males, all older females exhibited impaired episodic memory relative to young (6-month) females. We suggest that the senolytic treatment may not have been able to compensate for the loss of estradiol, which can act on aging mechanisms for anxiety and memory independent of cellular senescence.

Caloric restriction mitigates age-associated senescence characteristics in subcutaneous adipose tissue-derived stem cells

Adipose tissue regulates metabolic balance, but aging disrupts it, shifting fat from insulin-sensitive subcutaneous to insulin-resistant visceral depots, impacting overall metabolic health. Adipose-derived stem cells (ASCs) are crucial for tissue regeneration, but aging diminishes their stemness and regeneration potential. Our findings reveal that aging is associated with a decrease in subcutaneous adipose tissue mass and an increase in the visceral fat depots mass. Aging is associated with increase in adipose tissue fibrosis but no significant change in adipocyte size was observed with age. Long term caloric restriction failed to prevent fibrotic changes but resulted in significant decrease in adipocytes size. Aged subcutaneous ASCs displayed an increased production of ROS. Using mitochondrial membrane activity as an indicator of stem cell quiescence and senescence, we observed a significant decrease in quiescence ASCs with age exclusively in subcutaneous adipose depot. In addition, aged subcutaneous adipose tissue accumulated more senescent ASCs having defective autophagy activity. However, long-term caloric restriction leads to a reduction in mitochondrial activity in ASCs. Furthermore, caloric restriction prevents the accumulation of senescent cells and helps retain autophagy activity in aging ASCs. These results suggest that caloric restriction and caloric restriction mimetics hold promise as a potential strategy to rejuvenate the stemness of aged ASCs. Further investigations, including in vivo evaluations using controlled interventions in animals and human studies, will be necessary to validate these findings and establish the clinical potential of this well-established approach for enhancing the stemness of aged stem cells.

Amino acid restriction, aging, and longevity: an update

Various so-called dietary restriction paradigms have shown promise for extending health and life. All such paradigms rely on ad libitum (hereafter ad lib) feeding, something virtually never employed in animals whose long-term health we value, either as a control or, except for food restriction itself, for both control and treatment arms of the experiment. Even though the mechanism(s) remain only vaguely understood, compared to ad lib-fed animals a host of dietary manipulations, including calorie restriction, low protein, methionine, branched-chain amino acids, and even low isoleucine have demonstrable health benefits in laboratory species in a standard laboratory environment. The remaining challenge is to determine whether these health benefits remain in more realistic environments and how they interact with other health enhancing treatments such as exercise or emerging geroprotective drugs. Here we review the current state of the field of amino acid restriction on longevity of animal models and evaluate its translational potential.

Daily fluctuations in blood glucose with normal aging are inversely related to hippocampal synaptic mitochondrial proteins

Defective brain glucose utilization is a hallmark of Alzheimer's disease (AD) while Type II diabetes and elevated blood glucose escalate the risk for AD in later life. Isolating contributions of normal aging from coincident metabolic or brain diseases could lead to refined approaches to manage specific health risks and optimize treatments targeted to susceptible older individuals. We evaluated metabolic, neuroendocrine, and neurobiological differences between young adult (6 months) and aged (24 months) male rats. Compared to young adults, blood glucose was significantly greater in aged rats at the start of the dark phase of the day but not during the light phase. When challenged with physical restraint, a potent stressor, aged rats effected no change in blood glucose whereas blood glucose increased in young adults. Tissues were evaluated for markers of oxidative phosphorylation (OXPHOS), neuronal glucose transport, and synapses. Outright differences in protein levels between age groups were not evident, but circadian blood glucose was inversely related to OXPHOS proteins in hippocampal synaptosomes, independent of age. The neuronal glucose transporter, GLUT3, was positively associated with circadian blood glucose in young adults whereas aged rats tended to show the opposite trend. Our data demonstrate aging increases daily fluctuations in blood glucose and, at the level of individual differences, negatively associates with proteins related to synaptic OXPHOS. Our findings imply that glucose dyshomeostasis may exacerbate metabolic aspects of synaptic dysfunction that contribute to risk for age-related brain disorders.

Differential impact of unilateral stroke on the bihemispheric motor cortex representation of the jaw and tongue muscles in young and aged rats

Introduction

Dysphagia commonly occurs after stroke, yet the mechanisms of post-stroke corticobulbar plasticity are not well understood. While cortical activity associated with swallowing actions is bihemispheric, prior research has suggested that plasticity of the intact cortex may drive recovery of swallowing after unilateral stroke. Age may be an important factor as it is an independent predictor of dysphagia after stroke and neuroplasticity may be reduced with age. Based on previous clinical studies, we hypothesized that cranial muscle activating volumes may be expanded in the intact hemisphere and would contribute to swallowing function. We also hypothesized that older age would be associated with limited map expansion and reduced function. As such, our goal was to determine the impact of stroke and age on corticobulbar plasticity by examining the jaw and tongue muscle activating volumes within the bilateral sensorimotor cortices.

Methods

Using the middle cerebral artery occlusion rat stroke model, intracortical microstimulation (ICMS) was used to map regions of sensorimotor cortex that activate tongue and jaw muscles in both hemispheres. Young adult (7 months) and aged (30 months) male F344 × BN rats underwent a stroke or sham-control surgery, followed by ICMS mapping 8 weeks later. Videofluoroscopy was used to assess oral-motor functions.

Results

Increased activating volume of the sensorimotor cortex within the intact hemisphere was found only for jaw muscles, whereas significant stroke-related differences in tongue activating cortical volume were limited to the infarcted hemisphere. These stroke-related differences were correlated with infarct size, such that larger infarcts were associated with increased jaw representation in the intact hemisphere and decreased tongue representation in the infarcted hemisphere. We found that both age and stroke were independently associated with swallowing differences, weight loss, and increased corticomotor thresholds. Laterality of tongue and jaw representations in the sham-control group revealed variability between individuals and between muscles within individuals.

Conclusion

Our findings suggest the role of the intact and infarcted hemispheres in the recovery of oral motor function may differ between the tongue and jaw muscles, which may have important implications for rehabilitation, especially hemisphere-specific neuromodulatory approaches. This study addressed the natural course of recovery after stroke; future work should expand to focus on rehabilitation.

How are APOE4, changes in body weight, and longevity related? Insights from a causal mediation analysis

The ε4 allele of the APOE gene (APOE4) is known for its negative association with human longevity; however, the mechanism is unclear. APOE4 is also linked to changes in body weight, and the latter changes were associated with survival in some studies. Here, we explore the role of aging changes in weight in the connection between APOE4 and longevity using the causal mediation analysis (CMA) approach to uncover the mechanisms of genetic associations. Using the Health and Retirement Study (HRS) data, we tested a hypothesis of whether the association of APOE4 with reduced survival to age 85+ is mediated by key characteristics of age trajectories of weight, such as the age at reaching peak values and the slope of the decline in weight afterward. Mediation effects were evaluated by the total effect (TE), natural indirect effect, and percentage mediated. The controlled direct effect and natural direct effect are also reported. The CMA results suggest that APOE4 carriers have 19%-22% (TE p = 0.020-0.039) lower chances of surviving to age 85 and beyond, in part, because they reach peak values of weight at younger ages, and their weight declines faster afterward compared to non-carriers. This finding is in line with the idea that the detrimental effect of APOE4 on longevity is, in part, related to the accelerated physical aging of ε4 carriers.

BIO101 stimulates myoblast differentiation and improves muscle function in adult and old mice

BACKGROUND

Muscle aging is associated with a consistent decrease in the ability of muscle tissue to regenerate following intrinsic muscle degradation, injury or overuse. Age-related imbalance of protein synthesis and degradation, mainly regulated by AKT/mTOR pathway, leads to progressive loss of muscle mass. Maintenance of anabolic and regenerative capacities of skeletal muscles may be regarded as a therapeutic option for sarcopenia and other muscle wasting diseases. Our previous studies have demonstrated that BIO101, a pharmaceutical grade 20-hydroxyecdysone, increases protein synthesis through the activation of MAS receptor involved in the protective arm of renin-angiotensin-aldosterone system. The purpose of the present study was to assess the anabolic and pro-differentiating properties of BIO101 on C2C12 muscle cells in vitro and to investigate its effects on adult and old mice models in vivo.

METHODS

The effects of BIO101 on C2C12 differentiation were assessed using myogenic transcription factors and protein expression of major kinases of AKT/mTOR pathway by Western blot. The in vivo effects of BIO101 have been investigated in BIO101 orally-treated (50 mg/kg/day) adult mice (3 months) for 28 days. To demonstrate potential beneficial effect of BIO101 treatment in a sarcopenic mouse model, we use orally treated 22-month-old C57Bl6/J mice, for 14 weeks with vehicle or BIO101. Mice body and muscle weight were recorded. Physical performances were assessed using running capacity and muscle contractility tests.

RESULTS

Anabolic properties of BIO101 were confirmed by the rapid activation of AKT/mTOR, leading to an increase of C2C12 myotubes diameters (+26%, P < 0.001). Pro-differentiating effects of BIO101 on C2C12 myoblasts were revealed by increased expression of muscle-specific differentiation transcription factors (MyoD, myogenin), resulting in increased fusion index and number of nuclei per myotube (+39% and +53%, respectively, at day 6). These effects of BIO101 were like those of angiotensin (1-7) and were abolished with the use of A779, a MAS receptor specific antagonist. Chronic BIO101 oral treatment induced AKT/mTOR activation and anabolic effects accompanied with improved physical performances in adult and old animals (maximal running distance and maximal running velocity).

CONCLUSIONS

Our data suggest beneficial anabolic and pro-differentiating effects of BIO101 rendering BIO101 a potent drug candidate for treating sarcopenia and possibly other muscle wasting disorders.

Late-life dietary folate restriction reduces biosynthetic processes without compromising healthspan in mice

Folate is a vitamin required for cell growth and is present in fortified foods in the form of folic acid to prevent congenital abnormalities. The impact of low folate status on life-long health is poorly understood. We found that limiting folate levels with the folate antagonist methotrexate increased the lifespan of yeast and worms. We then restricted folate intake in aged mice and measured various health metrics, metabolites, and gene expression signatures. Limiting folate intake decreased anabolic biosynthetic processes in mice and enhanced metabolic plasticity. Despite reduced serum folate levels in mice with limited folic acid intake, these animals maintained their weight and adiposity late in life, and we did not observe adverse health outcomes. These results argue that the effectiveness of folate dietary interventions may vary depending on an individual's age and sex. A higher folate intake is advantageous during the early stages of life to support cell divisions needed for proper development. However, a lower folate intake later in life may result in healthier aging.

Carnosine supplementation and retinal oxidative parameters in a high-calorie diet rat model

BACKGROUND

To assess oxidative effects induced by a high-calorie diet on the retina of Wistar rats and test the antioxidative effects of carnosine supplementation.

METHODS

Wistar rats were randomly divided into the following groups: standard diet (SD), high-calorie diet (HcD), standard diet + carnosine (SD + Car), and high-calorie diet + carnosine (HcD + Car). The body weight, adiposity index, plasma glucose, total lipids, high-density lipoprotein (HDL), low-density lipoprotein (LDL), uric acid, creatinine, and triglycerides of the animals were evaluated. The retinas were analyzed for markers of oxidative stress. Hydrogen peroxide production was assessed by 2',7'-dichlorodihydrofluorescein diacetate (DCF) oxidation. The total glutathione (tGSH), total antioxidant capacity (TAC), protein carbonyl, and sulfhydryl groups of the antioxidant system were analyzed.

RESULTS

TAC levels increased in the retinas of the SD + Car group compared to the SD group (p < 0.05) and in the HcD + Car group compared to the HcD group (p < 0.05). The levels of GSH and the GSSH:GSSG ratio were increased in the HcD + Car group compared to the SD + Car group (p < 0.05). An increase in the retinal carbonyl content was observed in the HcD group compared to the SD group (p < 0.05) and in the HcD + Car group compared to the SD + Car group (p < 0.05). A high-calorie diet (HcD) was also associated with a decrease in retinal sulfhydryl-type levels compared to the SD group (p < 0.05).

CONCLUSION

The results suggest that feeding a high-calorie diet to rats can promote an increase in carbonyl content and a reduction in sulfhydryl groups in their retinas. The administration of carnosine was not effective in attenuating these oxidative markers.

TRIAL REGISTRATION

Animal Ethics Committee of Botucatu Medical School - Certificate number 1292/2019.

SIRT2 transgenic over-expression does not impact lifespan in mice

The NAD+ -dependent deacylase family of sirtuin enzymes have been implicated in biological ageing, late-life health and overall lifespan, though of these members, a role for sirtuin-2 (SIRT2) is less clear. Transgenic overexpression of SIRT2 in the BubR1 hypomorph model of progeria can rescue many aspects of health and increase overall lifespan, due to a specific interaction between SIRT2 and BubR1 that improves the stability of this protein. It is less clear whether SIRT2 is relevant to biological ageing outside of a model where BubR1 is under-expressed. Here, we sought to test whether SIRT2 over-expression would impact the overall health and lifespan of mice on a nonprogeroid, wild-type background. While we previously found that SIRT2 transgenic overexpression prolonged female fertility, here, we did not observe any additional impact on health or lifespan, which was measured in both male and female mice on standard chow diets, and in males challenged with a high-fat diet. At the biochemical level, NMR studies revealed an increase in total levels of a number of metabolites in the brain of SIRT2-Tg animals, pointing to a potential impact in cell composition; however, this did not translate into functional differences. Overall, we conclude that strategies to enhance SIRT2 protein levels may not lead to increased longevity.

Polymethylmethacrylate Microspheres are Immunologically Inert in Mouse Tissues

Nowadays, aesthetic concerns have gained attention, especially by patients looking for a less invasive alternative to minor facial corrections. Polymethylmethacrylate (PMMA) is widely used as a soft tissue filler; the demand for this polymer has increased, and along with it, there are some reports of adverse reactions. Such adverse reactions stem from consequences of immune and inflammatory reactions to PMMA. Some animal models have been used to unravel the causes of these reactions, among other factors involving the management of PMMA. The aim of this study was to determine the immunogenic profile of PMMA implantation in different anatomical planes of mice, over up to 360 experimental days. In this study, BALB/c mice were divided into 30 groups for immune evaluation of the interaction between the organism and the polymer; 2% PMMA was implanted subcutaneously, 10% intramuscularly and 30% in periosteal juxtaposition and followed during five experimental days (7, 30, 90, 180 and 360 days after implantation-DAI). Pro- and anti-inflammatory cytokines (IL-2, IL-4, IL-6, IFN-gamma, TNF, IL-17A, IL-10 and TGF-beta) were quantified in all experimental days. There was no statistical difference between the groups analyzed considering the evaluated parameters. Therefore, at all implanted depths, PMMA behaved inertly in a murine model.No Level Assigned This journal requires that authors assign a level of evidence to each submission to which Evidence-Based Medicine rankings are applicable. This excludes Review Articles, Book Reviews, and manuscripts that concern Basic Science, Animal Studies, Cadaver Studies, and Experimental Studies. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Effects and possible mechanisms of intermittent fasting on health and disease: a narrative review

The imbalance between energy intake and expenditure in an environment of continuous food availability can lead to metabolic disturbances in the body and increase the risk of obesity and a range of chronic noncommunicable diseases. Intermittent fasting (IF) is one of the most popular nonpharmacological interventions to combat obesity and chronic noncommunicable diseases. The 3 most widely studied IF regimens are alternate-day fasting, time-restricted feeding, and the 5:2 diet. In rodents, IF helps optimize energy metabolism, prevent obesity, promote brain health, improve immune and reproductive function, and delay aging. In humans, IF's benefits are relevant for the aging global population and for increasing human life expectancy. However, the optimal model of IF remains unclear. In this review, the possible mechanisms of IF are summarized and its possible drawbacks are discussed on the basis of the results of existing research, which provide a new idea for nonpharmaceutical dietary intervention of chronic noncommunicable diseases.

Age-related sex differences in tongue strength and muscle morphometry in a rat model

OBJECTIVE

To investigate potential effects of sex on voluntary tongue strength, evoked twitch and tetanic tension, speed of contraction, and muscle fiber cross-sectional area in the muscles of the rat tongue. Additionally, we aimed to determine whether estrous cycle stage impacts any of the dependent variables as a pilot investigation into the use of female rats in a model of tongue exercise and aging.

DESIGN

Fischer 344-Brown Norway male and female rats in two age groups (16 middle-aged, 16 young-adult) were trained to use a tongue force operandum. Tongue muscle contraction, myosin heavy chain (MyHC) composition, and cross section area of the genioglossus and styloglossus muscles were examined. Vaginal lavage determined estrous cycle stage of the female rats daily.

RESULTS

The female group had significantly lower evoked twitch and tetanic tension, longer contraction times, and a smaller proportion of MyHC type IIa and MyHC type IIx in the styloglossus muscle. There was no significant sex effect in maximal voluntary tongue force (MVTF) despite a significant weight difference between the male and female groups. There were no significant age or sex effects in the genioglossus. Estrous cycle stage did not have a significant effect on any of the dependent variables.

CONCLUSIONS

Sex and age both have a significant effect on tongue muscle structure and physiology. While the female group showed reduced contraction speed and maximal twitch and tetanic tension relative to the male group, differences in muscle morphology appeared to vary by muscle.

The Effects of Graded Levels of Calorie Restriction: XX. Impact of Long-Term Graded Calorie Restriction on Survival and Body Mass Dynamics in Male C57BL/6J Mice

Calorie restriction (CR) typically promotes a reduction in body mass, which correlates with increased lifespan. We evaluated the overall changes in survival, body mass dynamics, and body composition following long-term graded CR (580 days/19 months) in male C57BL/6J mice. Control mice (0% restriction) were fed ad libitum in the dark phase only (12-hour ad libitum [12AL]). CR groups were restricted by 10%-40% of their baseline food intake (10CR, 20CR, 30CR, and 40CR). Body mass was recorded daily, and body composition was measured at 8 time points. At 728 days/24 months, all surviving mice were culled. A gradation in survival rate over the CR groups was found. The pattern of body mass loss differed over the graded CR groups. Whereas the lower CR groups rapidly resumed an energy balance with no significant loss of fat or fat-free mass, changes in the 30 and 40CR groups were attributed to higher fat-free mass loss and protection of fat mass. Day-to-day changes in body mass were less variable under CR than for the 12AL group. There was no indication that body mass was influenced by external factors. Partial autocorrelation analysis examined the relationship between daily changes in body masses. A negative correlation between mass on Day 0 and Day +1 declined with age in the 12AL but not the CR groups. A reduction in the correlation with age suggested body mass homeostasis is a marker of aging that declines at the end of life and is protected by CR.

Assessing Optimal Cell Counts in Sperm Shape Abnormality Assays in Rodents

Rodents have been the preferred models for the evaluation of the toxicity of pollutants and drugs and their genotoxic effects, including sperm shape abnormalities. The scientific literature is dominated by studies conducted with model animals in laboratory conditions, but a generally accepted and standardized protocol addressing the optimal number of sperm cells to count is still lacking. In this study, we reviewed the literature regarding the number of counted sperm cells in such assessments, published from 1969 to 2023. To infer the number of counts providing the best cost/benefit regarding the robustness of the assay results, a new dataset involving the analysis of two populations of wild rodents was produced. We evaluated the frequency of sperm shape abnormalities in a total of 50 wild brown rats (Rattus norvegicus) captured in two port cities, aiming to detect the impact of differential sperm cell counts in the obtained results. During necropsy, the fresh epididymis tail of adult male rats was excised, and sperm cells were fixated in slides. For each animal, a total of 300, 500, 1000, and 2000 cells were sequentially counted, and head abnormalities were registered. Counting 300 sperm cells failed to detect significant differences between groups and 500 counts resulted in marginally significant differences. Only when 1000 or 2000 sperm cells were counted, significant differences emerged between groups. We propose that studies addressing sperm shape abnormalities should standardize counts to an optimal value of 1000 cells per animal, warranting robust statistical results while providing the best compromise concerning labor time.

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.

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.

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.

An Imbalance in the Pro/mature BDNF Ratio Occurs in Multiple Brain Regions During Normal Ageing in Wild-Type Mice

The early transition to Alzheimer's disease is characterized by a period of accelerated brain atrophy that exceeds normal ageing. Identifying the molecular basis of this atrophy could facilitate the discovery of novel drug targets. The precursor of brain-derived neurotrophic factor, a well characterized neurotrophin, is increased in the hippocampus of aged rodents, while its mature isoform is relatively stable. This imbalance could increase the risk of Alzheimer's disease by precipitating its pathological hallmarks. However, less is known about how relative levels of these isoforms change in middle-aged mice. In addition, the underlying mechanisms that might cause an imbalance are unknown. The main aim of this study was to determine how precursor brain-derived neurotrophic factor changes relative to its mature isoform with normal brain ageing in wild type mice. A secondary aim was to determine if signaling through the neurotrophin receptor, p75 influences this ratio. An increasing ratio was identified in several brain regions, except the hippocampus, suggesting a neurotrophic imbalance occurs as early as middle age. Some changes in receptors that mediate the isoforms effects were also identified, but these did not correspond with trends in the isoforms. Relative amounts of precursor brain-derived neurotrophic factor were mostly unchanged in mutant p75 mice. The lack of changes suggested that signaling through the receptor had no influence on the ratio.

Effect of peripheral cellular senescence on brain aging and cognitive decline

We examine similar and differential effects of two senolytic treatments, ABT-263 and dasatinib + quercetin (D + Q), in preserving cognition, markers of peripheral senescence, and markers of brain aging thought to underlie cognitive decline. Male F344 rats were treated from 12 to 18 months of age with D + Q, ABT-263, or vehicle, and were compared to young (6 months). Both senolytic treatments rescued memory, preserved the blood-brain barrier (BBB) integrity, and prevented the age-related decline in hippocampal N-methyl-D-aspartate receptor (NMDAR) function associated with impaired cognition. Senolytic treatments decreased senescence-associated secretory phenotype (SASP) and inflammatory cytokines/chemokines in the plasma (IL-1β, IP-10, and RANTES), with some markers more responsive to D + Q (TNFα) or ABT-263 (IFNγ, leptin, EGF). ABT-263 was more effective in decreasing senescence genes in the spleen. Both senolytic treatments decreased the expression of immune response and oxidative stress genes and increased the expression of synaptic genes in the dentate gyrus (DG). However, D + Q influenced twice as many genes as ABT-263. Relative to D + Q, the ABT-263 group exhibited increased expression of DG genes linked to cell death and negative regulation of apoptosis and microglial cell activation. Furthermore, D + Q was more effective at decreasing morphological markers of microglial activation. The results indicate that preserved cognition was associated with the removal of peripheral senescent cells, decreasing systemic inflammation that normally drives neuroinflammation, BBB breakdown, and impaired synaptic function. Dissimilarities associated with brain transcription indicate divergence in central mechanisms, possibly due to differential access.

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.

Coenzyme Q10 supplementation improves the motor function of middle-aged mice by restoring the neuronal activity of the motor cortex

Physiological aging causes motor function decline and anatomical and biochemical changes in the motor cortex. We confirmed that middle-aged mice at 15-18 months old show motor function decline, which can be restored to the young adult level by supplementing with mitochondrial electron transporter coenzyme Q₁₀ (CoQ₁₀) as a water-soluble nanoformula by drinking water for 1 week. CoQ₁₀ supplementation concurrently improved brain mitochondrial respiration but not muscle strength. Notably, we identified an age-related decline in field excitatory postsynaptic potential (fEPSP) amplitude in the pathway from layers II/III to V of the primary motor area of middle-aged mice, which was restored to the young adult level by supplementing with CoQ₁₀ for 1 week but not by administering CoQ₁₀ acutely to brain slices. Interestingly, CoQ₁₀ with high-frequency stimulation induced NMDA receptor-dependent long-term potentiation (LTP) in layer V of the primary motor cortex of middle-aged mice. Importantly, the fEPSP amplitude showed a larger input‒output relationship after CoQ₁₀-dependent LTP expression. These data suggest that CoQ₁₀ restores the motor function of middle-aged mice by improving brain mitochondrial function and the basal fEPSP level of the motor cortex, potentially by enhancing synaptic plasticity efficacy. Thus, CoQ₁₀ supplementation may ameliorate the age-related decline in motor function in humans.

The Development of Synapses in Mouse and Macaque Primary Sensory Cortices

We report that the rate of synapse development in primary sensory cortices of mice and macaques is unrelated to lifespan, as was previously thought. We analyzed 28,084 synapses over multiple developmental time points in both species and find, instead, that net excitatory synapse development of mouse and macaque neurons primarily increased at similar rates in the first few postnatal months, and then decreased over a span of 1-1.5 years of age. The development of inhibitory synapses differed qualitatively across species. In macaques, net inhibitory synapses first increase and then decrease on excitatory soma at similar ages as excitatory synapses. In mice, however, such synapses are added throughout life. These findings contradict the long-held belief that the cycle of synapse formation and pruning occurs earlier in shorter-lived animals. Instead, our results suggest more nuanced rules, with the development of different types of synapses following different timing rules or different trajectories across species.

Age- and time-dependent mitochondrial genotoxic and myopathic effects of beta-guanidinopropionic acid, a creatine analog, on rodent skeletal muscles

Beta-guanidinopropionic acid (GPA) is a creatine analog suggested as a treatment for hypertension, diabetes, and obesity, which manifest primarily in older adults. A notable side effect of GPA is the induction of mitochondrial DNA deletion mutations. We hypothesized that mtDNA deletions contribute to muscle aging and used the mutation promoting effect of GPA to examine the impact of mtDNA deletions on muscles with differential vulnerability to aging. Rats were treated with GPA for up to 4 months starting at 14 or 30 months of age. We examined quadriceps and adductor longus muscles as the quadriceps exhibits profound age-induced deterioration, while adductor longus is maintained. GPA decreased body and muscle mass and mtDNA copy number while increasing mtDNA deletion frequency. The interactions between age and GPA treatment observed in the quadriceps were not observed in the adductor longus. GPA had negative mitochondrial effects in as little as 4 weeks. GPA treatment exacerbated mtDNA deletions and muscle aging phenotypes in the quadriceps, an age-sensitive muscle, while the adductor longus was spared. GPA has been proposed for use in age-associated diseases, yet the pharmacodynamics of GPA differ with age and include the detrimental induction of mtDNA deletions, a mitochondrial genotoxic stress that is pronounced in muscles that are most vulnerable to aging. Further research is needed to determine if the proposed benefits of GPA on hypertension, diabetes, and obesity outweigh the detrimental mitochondrial and myopathic side effects.

An automated feeding system for the African killifish reveals the impact of diet on lifespan and allows scalable assessment of associative learning

The African turquoise killifish is an exciting new vertebrate model for aging studies. A significant challenge for any model organism is the control over its diet in space and time. To address this challenge, we created an automated and networked fish feeding system. Our automated feeder is designed to be open-source, easily transferable, and built from widely available components. Compared to manual feeding, our automated system is highly precise and flexible. As a proof of concept for the feeding flexibility of these automated feeders, we define a favorable regimen for growth and fertility for the African killifish and a dietary restriction regimen where both feeding time and quantity are reduced. We show that this dietary restriction regimen extends lifespan in males (but not in females) and impacts the transcriptomes of killifish livers in a sex-specific manner. Moreover, combining our automated feeding system with a video camera, we establish a quantitative associative learning assay to provide an integrative measure of cognitive performance for the killifish. The ability to precisely control food delivery in the killifish opens new areas to assess lifespan and cognitive behavior dynamics and to screen for dietary interventions and drugs in a scalable manner previously impossible with traditional vertebrate model organisms.

Animal Care in Radiation Medical Countermeasures Studies

Animal models are necessary to demonstrate the efficacy of medical countermeasures (MCM) to mitigate/treat acute radiation syndrome and the delayed effects of acute radiation exposure and develop biodosimetry signatures for use in triage and to guide medical management. The use of animal models in radiation research allows for the simulation of the biological effects of exposure in humans. Robust and well-controlled animal studies provide a platform to address basic mechanistic and safety questions that cannot be conducted in humans. The U.S. Department of Health and Human Services has tasked the National Institute of Allergy and Infectious Diseases (NIAID) with identifying and funding early- through advanced-stage MCM development for radiation-induced injuries; and advancement of biodosimetry platforms and exploration of biomarkers for triage, definitive dose, and predictive purposes. Some of these NIAID-funded projects may transition to the Biomedical Advanced Research and Development Authority (BARDA), a component of the Office of the Assistant Secretary for Preparedness and Response in the U.S. Department of Health and Human Services, which is tasked with the advanced development of MCMs to include pharmacokinetic, exposure, and safety assessments in humans. Guided by the U.S. Food and Drug Administration's (FDA) Animal Rule, both NIAID and BARDA work closely with researchers to advance product and device development, setting them on a course for eventual licensure/approval/clearance of their approaches by the FDA. In August 2020, NIAID partnered with BARDA to conduct a workshop to discuss currently accepted animal care protocols and examine aspects of animal models that can influence outcomes of studies to explore MCM efficacy for potential harmonization. This report provides an overview of the two-day workshop, which includes a series of special topic presentations followed by panel discussions with subject-matter experts from academia, industry partners, and select governmental agencies.

Remdesivir does not affect mitochondrial DNA copy number or deletion mutation frequency in aged male rats: A short report

Remdesivir is a leading therapy in patients with moderate to severe coronavirus 2 (SARS-CoV-2) infection; the majority of whom are older individuals. Remdesivir is a nucleoside analog that incorporates into nascent viral RNA, inhibiting RNA-directed RNA polymerases, including that of SARS-CoV-2. Less is known about remdesivir's effects on mitochondria, particularly in older adults where mitochondria are known to be dysfunctional. Furthermore, its effect on age-induced mitochondrial mutations and copy number has not been previously studied. We hypothesized that remdesivir adversely affects mtDNA copy number and deletion mutation frequency in aged rodents. To test this hypothesis, 30-month-old male F333BNF1 rats were treated with remdesivir for three months. To determine if remdesivir adversely affects mtDNA, we measured copy number and mtDNA deletion frequency in rat hearts, kidneys, and skeletal muscles using digital PCR. We found no effects from three months of remdesivir treatment on mtDNA copy number or deletion mutation frequency in 33-month-old rats. These data support the notion that remdesivir does not compromise mtDNA quality or quantity at old age in mammals. Future work should focus on examining additional tissues such as brain and liver, and extend testing to human clinical samples.

Animal Models of Exercise From Rodents to Pythons

Acute and chronic animal models of exercise are commonly used in research. Acute exercise testing is used, often in combination with genetic, pharmacological, or other manipulations, to study the impact of these manipulations on the cardiovascular response to exercise and to detect impairments or improvements in cardiovascular function that may not be evident at rest. Chronic exercise conditioning models are used to study the cardiac phenotypic response to regular exercise training and as a platform for discovery of novel pathways mediating cardiovascular benefits conferred by exercise conditioning that could be exploited therapeutically. The cardiovascular benefits of exercise are well established, and, frequently, molecular manipulations that mimic the pathway changes induced by exercise recapitulate at least some of its benefits. This review discusses approaches for assessing cardiovascular function during an acute exercise challenge in rodents, as well as practical and conceptual considerations in the use of common rodent exercise conditioning models. The case for studying feeding in the Burmese python as a model for exercise-like physiological adaptation is also explored.

Male rat leukocyte population dynamics predict a window for intervention in aging

Many age-associated changes in the human hematopoietic system have been reproduced in murine models; however, such changes have not been as robustly explored in rats despite the fact these larger rodents are more physiologically similar to humans. We examined peripheral blood of male F344 rats ranging from 3 to 27 months of age and found significant age-associated changes with distinct leukocyte population shifts. We report CD25⁺ CD4⁺ population frequency is a strong predictor of healthy aging, generate a model using blood parameters, and find rats with blood profiles that diverge from chronologic age indicate debility; thus, assessments of blood composition may be useful for non-lethal disease profiling or as a surrogate measure for efficacy of aging interventions. Importantly, blood parameters and DNA methylation alterations, defined distinct juncture points during aging, supporting a non-linear aging process. Our results suggest these inflection points are important considerations for aging interventions. Overall, we present rat blood aging metrics that can serve as a resource to evaluate health and the effects of interventions in a model system physiologically more reflective of humans.

Our blood contains many types of white blood cells, which play important roles in defending the body against infections and other threats to our health. The number of these cells changes with age, and this in turn contributes to many other alterations that happen in the body as we get older. For example, the immune system generally gets weaker at fighting infections and preventing other cells from developing into cancer. On top of that, the white blood cells themselves can become cancerous, resulting in several types of blood cancer that are more likely to happen in older people.

Many previous studies have examined how the number of white blood cells changes with age in humans and mice. However, our understanding of this process in rats is still poor, despite the fact that the way the human body works has more in common with the rat body than the mouse body.

Here, Yanai, Dunn et al. have studied samples of blood from rats between three to 27 months old. The experiments found that it is possible to accurately predict the age of healthy rats by measuring the frequency of populations of white blood cells, especially a certain type known as CD25+ CD4+ cells. If the animals had any form of illness, their predicted age deviated from their actual age. Furthermore, while some changes in the blood were gradual and continuous, others displayed distinct shifts when the rats reached specific ages.

In the future, these findings may be used as a tool to help researchers diagnose illnesses in rats before the animals develop symptoms, or to more easily establish if a treatment is having a positive effect on the rats’ health. The work of Yanai, Dunn et al. also provides new insights into aging that could potentially aid the design of new screening methods to predict cancer and intervene using a model system that is more similar to humans.

Aging and matrix viscoelasticity affect multiscale tendon properties and tendon derived cell behavior

Aging is the largest risk factor for Achilles tendon associated disorders and rupture. Although Achilles tendon macroscale elastic properties are suggested to decline with aging, less is known about the effect of maturity and aging on multiscale viscoelastic properties and their effect on tendon cell behavior. Here, we show dose dependent changes in native multiscale tendon mechanical and structural properties and uncover several nanoindentation properties predicted by tensile mechanics and echogenicity. Alginate hydrogel systems designed to mimic juvenile tendon microscale mechanics revealed that stiffness and viscoelasticity affected Achilles tendon cell aspect ratio and proliferation during aging. This knowledge provides further evidence for the negative impact of maturity and aging on tendon and begins to elucidate how viscoelasticity can control tendon derived cell morphology and expansion. STATEMENT OF SIGNIFICANCE: Aging is the largest risk factor for Achilles tendon associated disorders and rupture. Although Achilles tendon macroscale elastic properties are suggested to decline with aging, less is known about the effect of maturity and aging on multiscale viscoelastic properties and their effect on tendon cell behavior. Here, we show dose dependent changes in native multiscale tendon mechanical and structural properties and uncover several nanoindentation properties predicted by tensile mechanics and echogenicity. Alginate hydrogel systems designed to mimic juvenile tendon microscale mechanics revealed that stiffness and viscoelasticity affected Achilles tendon cell spreading and proliferation during aging. This knowledge provides further evidence for the negative impact of maturity and aging on tendon and begins to elucidate how viscoelasticity can control tendon derived cell morphology and expansion.

Chronic aryl hydrocarbon receptor activity phenocopies smoking-induced skeletal muscle impairment

BACKGROUND

Chronic obstructive pulmonary disease (COPD) patients exhibit skeletal muscle atrophy, denervation, and reduced mitochondrial oxidative capacity. Whilst chronic tobacco smoke exposure is implicated in COPD muscle impairment, the mechanisms involved are ambiguous. The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that activates detoxifying pathways with numerous exogenous ligands, including tobacco smoke. Whereas transient AHR activation is adaptive, chronic activation can be toxic. On this basis, we tested the hypothesis that chronic smoke-induced AHR activation causes adverse muscle impact.

METHODS

We used clinical patient muscle samples, and in vitro (C2C12 myotubes) and in vivo models (mouse), to perform gene expression, mitochondrial function, muscle and neuromuscular junction morphology, and genetic manipulations (adeno-associated virus-mediated gene transfer).

RESULTS

Sixteen weeks of tobacco smoke exposure in mice caused muscle atrophy, neuromuscular junction degeneration, and reduced oxidative capacity. Similarly, smoke exposure reprogrammed the muscle transcriptome, with down-regulation of mitochondrial and neuromuscular junction genes. In mouse and human patient specimens, smoke exposure increased muscle AHR signalling. Mechanistically, experiments in cultured myotubes demonstrated that smoke condensate activated the AHR, caused mitochondrial impairments, and induced an AHR-dependent myotube atrophy. Finally, to isolate the role of AHR activity, expression of a constitutively active AHR mutant without smoke exposure caused atrophy and mitochondrial impairments in cultured myotubes, and muscle atrophy and neuromuscular junction degeneration in mice.

CONCLUSIONS

These results establish that chronic AHR activity, as occurs in smokers, phenocopies the atrophy, mitochondrial impairment, and neuromuscular junction degeneration caused by chronic tobacco smoke exposure.