Aging Female Brain Research Articles

Exercise rejuvenates microglia and reverses T cell accumulation in the aged female mouse brain.

Slowing and/or reversing brain ageing may alleviate cognitive impairments. Previous studies have found that exercise may mitigate cognitive decline, but the mechanisms underlying this remain largely unclear. Here we provide unbiased analyses of single-cell RNA sequencing data, showing the impacts of exercise and ageing on specific cell types in the mouse hippocampus. We demonstrate that exercise has a profound and selective effect on aged microglia, reverting their gene expression signature to that of young microglia. Pharmacologic depletion of microglia further demonstrated that these cells are required for the stimulatory effects of exercise on hippocampal neurogenesis but not cognition. Strikingly, allowing 18-month-old mice access to a running wheel did by and large also prevent and/or revert T cell presence in the ageing hippocampus. Taken together, our data highlight the profound impact of exercise in rejuvenating aged microglia, associated pro-neurogenic effects and on peripheral immune cell presence in the ageing female mouse brain.

Age and 17β-Estradiol (E2) Facilitate Nuclear Export and Argonaute Loading of microRNAs in the Female Brain.

Aging in women is accompanied by a dramatic change in circulating sex steroid hormones. Specifically, the primary circulating estrogen, 17β-estradiol (E2), is nearly undetectable in post-menopausal women. This decline is associated with a variety of cognitive and mood disorders, yet hormone replacement therapy is only effective within a narrow window of time surrounding the menopausal transition. Our previous work identified microRNAs as a potential molecular substrate underlying the change in E2 efficacy associated with menopause in advanced age. Specifically, we showed that E2 regulated a small subset of mature miRNAs in the aging female brain. In this study, we hypothesized that E2 regulates the stability of mature miRNAs by altering their subcellular localization and their association with argonaute proteins. We also tested the hypothesis that the RNA binding protein, hnRNP A1, was an important regulator of mature miR-9-5p expression in neuronal cells. Our results demonstrated that E2 treatment affected miRNA subcellular localization and its association with argonaute proteins differently, depending on the length of time following E2 deprivation (i.e., ovariectomy). We also provide strong evidence that hnRNP A1 regulates the transcription of pri-miR-9 and likely plays a posttranscriptional role in mature miR-9-5p turnover. Taken together, these data have important implications for considering the optimal timing for hormone replacement therapy, which might be less dependent on age and more related to how long treatment is delayed following menopause.

Cell Senescence as a Mediator of Age-Dependent Brain Inflammation

Cellular senescence and inflammation are interconnected causes and consequences of tissue aging. Here, we implemented orthogonal approaches to study their interaction in steady-state mature and aged mouse brain. Using single cell sequencing, we identified a putative senescent microglial population, which increased in abundance with age and was characterized by increased expression of p16 and chemotactic senescence associated secretory phenotype (SASP) factors. Using p16-INK-ATTAC transgenic mice to eliminate p16ink4a-positive senescent cells and mass cytometry, we show that p16ink4a-positive cell targeting reduced the abundance of activated inflammatory cells in the aged female brain. Age-dependent declines in executive cognitive function were improved following transgenic p16ink4a-positive cell targeting, and executive function robustly correlated with inflammatory brain cell composition in females. Collectively, our findings demonstrate fundamental differences in the age- and sex-dependent brain inflammatory landscape and implicate p16ink4a-positive senescent cell targeting as a therapeutic strategy to attenuate age-related inflammation and cognitive decline.

Midlife Chronological and Endocrinological Transitions in Brain Metabolism: System Biology Basis for Increased Alzheimer\u2019s Risk in Female Brain

Decline in brain glucose metabolism is a hallmark of late-onset Alzheimer’s disease (LOAD). Comprehensive understanding of the dynamic metabolic aging process in brain can provide insights into windows of opportunities to promote healthy brain aging. Chronological and endocrinological aging are associated with brain glucose hypometabolism and mitochondrial adaptations in female brain. Using a rat model recapitulating fundamental features of the human menopausal transition, results of transcriptomic analysis revealed stage-specific shifts in bioenergetic systems of biology that were paralleled by bioenergetic dysregulation in midlife aging female brain. Transcriptomic profiles were predictive of outcomes from unbiased, discovery-based metabolomic and lipidomic analyses, which revealed a dynamic adaptation of the aging female brain from glucose centric to utilization of auxiliary fuel sources that included amino acids, fatty acids, lipids, and ketone bodies. Coupling between brain and peripheral metabolic systems was dynamic and shifted from uncoupled to coupled under metabolic stress. Collectively, these data provide a detailed profile across transcriptomic and metabolomic systems underlying bioenergetic function in brain and its relationship to peripheral metabolic responses. Mechanistically, these data provide insights into the complex dynamics of chronological and endocrinological bioenergetic aging in female brain. Translationally, these findings are predictive of initiation of the prodromal / preclinical phase of LOAD for women in midlife and highlight therapeutic windows of opportunity to reduce the risk of late-onset Alzheimer’s disease.

Age and Sex Influence the Neuro-inflammatory Response to a Peripheral Acute LPS Challenge.

Aging is associated with an exaggerated response to peripheral inflammatory challenges together with behavioral and cognitive deficits. Studies considering both age and sex remain limited, despite sex dimorphism of astrocytes and microglial cells is largely recognized. To fill this knowledge gap, we investigated the effect of a single intraperitoneal lipopolysaccharide (LPS) administration in adult and aged mice. We assessed the expression of different inflammatory mediators, and the microglial response through binding of [18F]-VC701 tracer to translocator protein (TSPO) receptors in the male and female brain. Aged female brain showed a higher pro-inflammatory response to LPS compared to adult female and to aged male, as revealed by ex vivo binding to TSPO receptors and pro-inflammatory mediator transcript levels. The highest astroglial reaction was observed in the brain of aged females. Differently to the other groups of animals, in aged males LPS challenge did not affect transcription of triggering receptor expressed on myeloid cells 2 (TREM2). In conclusion, our study shows that in the mouse’s brain the neuro-inflammatory response to an acute peripheral insult is sex- and age-dependent. Moreover, our results might set the basis for further studies aimed at identifying sex-related targets involved in the modulation of the aberrant neuro-inflammatory response that characterizes aging. This knowledge could be relevant for the treatment of conditions such as delirium and dementia.

The diabetes drug metformin reverses cognitive impairment and membrane functions in diabetic aging female rat brain: A link with diabetes and Alzheimer’s disease

The objective of this study was to investigate effects of metformin on body weight, blood glucose levels, glucose transporter (GLUT1), interleukin 1 β (IL-1β) and protein kinase B expression, antioxidant enzymes, expression of synaptic molecules, biomarkers of oxidative stress, lipid peroxidation, membrane fluidity and acetylcholinesterase (AChE) in diabetic aging brain of female rats. Male Wistar rats, young (3 months) adult (12 months) and aged (24 months) were diabetic by using alloxan monohydrate. Metformin was administered i.p. at a dose of 200mg/kg/day for 30 days to both control and diabetic aging rats. A detailed study was carried on expression of inflammatory cytokines, insulin receptor pathology and synapse, GLUT 1, biomarkers of oxidative stress and AChE activity. Present study shows that there was a similar pattern of increased expression of interleukin, protein kinase B, lipid peroxidation, blood glucose, insulin receptor expression and RNS levels with AChE activity, and a decrease in membrane fluidity, antioxidant enzymes activity and (GLUT1) expression in brain of both aging and diabetes. On the other hand, metformin treated groups exhibited significant reduction in helped to reverse the age related changes studied, to normal levels. Metformin treatments improved attention and memory functions with enhanced the levels of synaptic molecules synaptophysin and synapsin I. Our data showed that exogenous administration of metformin brought these changes to near normalcy in diabetic aging female rats. The results illuminate mechanisms of neuroprotection by metformin, and applying new strategies for control of neurodegenerative diseases including metabolic syndrome and Alzheimer’s disease.

8-Oxoguanine accumulation in aged female brain impairs neurogenesis in the dentate gyrus and major island of Calleja, causing sexually dimorphic phenotypes

In mammals, including humans, MTH1 with 8-oxo-dGTPase and OGG1 with 8-oxoguanine DNA glycosylase minimize 8-oxoguanine accumulation in genomic DNA. We investigated age-related alterations in behavior, 8-oxoguanine levels, and neurogenesis in the brains of Mth1/Ogg1-double knockout (TO-DKO), Ogg1-knockout, and human MTH1-transgenic (hMTH1-Tg) mice. Spontaneous locomotor activity was significantly decreased in wild-type mice with age, and females consistently exhibited higher locomotor activity than males. This decrease was significantly suppressed in female but not male TO-DKO mice and markedly enhanced in female hMTH1-Tg mice. Long-term memory retrieval was impaired in middle-aged female TO-DKO mice. 8-Oxoguanine accumulation significantly increased in nuclear DNA, particularly in the dentate gyrus (DG), subventricular zone (SVZ) and major island of Calleja (ICjM) in middle-aged female TO-DKO mice. In middle-aged female TO-DKO mice, neurogenesis was severely impaired in SVZ and DG, accompanied by ICjM and DG atrophy. Conversely, expression of hMTH1 efficiently suppressed 8-oxoguanine accumulation in both SVZ and DG with hypertrophy of ICjM. These findings indicate that newborn neurons from SVZ maintain ICjM in the adult brain, and increased accumulation of 8-oxoguanine in nuclear DNA of neural progenitors in females is caused by 8-oxo-dGTP incorporation during proliferation, causing depletion of neural progenitors, altered behavior, and cognitive function changes with age.

Persistent metabolic youth in the aging female brain.

Sex differences influence brain morphology and physiology during both development and aging. Here we apply a machine learning algorithm to a multiparametric brain PET imaging dataset acquired in a cohort of 20- to 82-year-old, cognitively normal adults (n = 205) to define their metabolic brain age. We find that throughout the adult life span the female brain has a persistently lower metabolic brain age-relative to their chronological age-compared with the male brain. The persistence of relatively younger metabolic brain age in females throughout adulthood suggests that development might in part influence sex differences in brain aging. Our results also demonstrate that trajectories of natural brain aging vary significantly among individuals and provide a method to measure this.

Alterations of metabolic parameters and antioxidant enzymes in diabetic aging female rat brain: Neuroprotective role of metformin

Background: The objective of this study was to investigate beneficial effects of metformin on membrane bound enzymes (monoamine oxidase, Na+ K+ ATPse,) and antioxidant enzymes (sueroxidase dismutase, glutathione S-transferases), lipid peroxidation, neurolipofuscin, DNA degradation in diabetic aging brain of female rats.

17β-estradiol regulates the RNA-binding protein Nova1, which then regulates the alternative splicing of estrogen receptor β in the aging female rat brain

Alternative RNA splicing results in the translation of diverse protein products arising from a common nucleotide sequence. These alternative protein products are often functional and can have widely divergent actions from the canonical protein. Studies in humans and other vertebrate animals have demonstrated that alternative splicing events increase with advanced age, sometimes resulting in pathological consequences. Menopause represents a critical transition for women, where the beneficial effects of estrogens are no longer evident; therefore, factors underlying increased pathological conditions in women are confounded by the dual factors of aging and declining estrogens. Estrogen receptors (ERs) are subject to alternative splicing, the spliced variants increase following menopause, and they fail to efficiently activate estrogen-dependent signaling pathways. However, the factors that regulate the alternative splicing of ERs remain unknown. We demonstrate novel evidence supporting a potential biological feedback loop where 17β-estradiol regulates the RNA-binding protein Nova1, which, in turn, regulates the alternative splicing of ERβ. These data increase our understanding of ER alternative splicing and could have potential implications for women taking hormone replacement therapy after menopause.

FUELING THE GLUCOSE-STARVED ALZHEIMER’S BRAIN: CATABOLISM OF WHITE MATTER IN THE BRAIN TO GENERATE KETONE BODIES

The brain is the most energetically demanding organ of the body, and is thus vulnerable to even a modest decline in glucose availability and metabolism required to generate ATP. Glucose hypometabolism is an early endophenotype of risk for Alzheimer's disease (AD) which progressively worsens with disease. Analyses were conducted in the aging female mouse followed by analyses in brain of gene expression, biochemical analyses and electron microscopy of myelin with AD relevant brain regions. Early during female brain aging the decline in estrogenic control of the bioenergetic system is associated with decline in glucose metabolism and activation of a systems biology adaptive response which involves activation of a starvation response pathway and reliance on ketone bodies as an alternative fuel to generate ATP. Activation of the myelin catabolism pathway was initiated by decline in mitochondrial respiration, increased mitochondrial hydrogen peroxide production and induction of the cytosolic-phospholipase-A2 sphingomyelinase pathway. Electron microscopic and lipidomic analyses confirmed myelin degeneration. An increase in fatty acids and mitochondrial fatty acid metabolism machinery was coincident with a rise in brain ketone bodies and decline in plasma ketone bodies. This mechanistic pathway and its sequentially phased activation, links glucose hypometabolism and mitochondrial dysfunction associated with endocrine aging with later age development of white matter degeneration. The catabolism of myelin lipids to generate ketone bodies can be viewed as a systems level adaptive response to address brain fuel and energy demand. The mechanistic pathway leading to white matter catabolism in the aging female brain provides multiple therapeutic targets to prevent and treat white matter degeneration in AD. Further, the pathways leading to catabolism of white matter in the female brain is likely to be relevant to the aging male brain at risk for AD. Therapeutically targeting stages of disease and associated mechanisms will be critical. Research was supported by NIH National Institute on Aging P01AG026572 and R01AG032236 to RDB.

Alterations of metabolic parameters and antioxidant enzymes in diabetic aging female rat brain: Neuroprotective role of metformin

Alterations of metabolic parameters and antioxidant enzymes in diabetic aging female rat brain: Neuroprotective role of metformin

Abstract #216: Modulation of Metabolic Parameters and Antioxidant Enzymes in Diabetic Aging Female Rat Brain: Beneficial Role of Metformin

Abstract #216: Modulation of Metabolic Parameters and Antioxidant Enzymes in Diabetic Aging Female Rat Brain: Beneficial Role of Metformin

White Matter Lipids as a Ketogenic Fuel Supply in Aging Female Brain: Implications for Alzheimer's Disease

White matter degeneration is a pathological hallmark of neurodegenerative diseases including Alzheimer's. Age remains the greatest risk factor for Alzheimer's and the prevalence of age-related late onset Alzheimer's is greatest in females. We investigated mechanisms underlying white matter degeneration in an animal model consistent with the sex at greatest Alzheimer's risk. Results of these analyses demonstrated decline in mitochondrial respiration, increased mitochondrial hydrogen peroxide production and cytosolic-phospholipase-A2 sphingomyelinase pathway activation during female brain aging. Electron microscopic and lipidomic analyses confirmed myelin degeneration. An increase in fatty acids and mitochondrial fatty acid metabolism machinery was coincident with a rise in brain ketone bodies and decline in plasma ketone bodies. This mechanistic pathway and its chronologically phased activation, links mitochondrial dysfunction early in aging with later age development of white matter degeneration. The catabolism of myelin lipids to generate ketone bodies can be viewed as a systems level adaptive response to address brain fuel and energy demand. Elucidation of the initiating factors and the mechanistic pathway leading to white matter catabolism in the aging female brain provides potential therapeutic targets to prevent and treat demyelinating diseases such as Alzheimer's and multiple sclerosis. Targeting stages of disease and associated mechanisms will be critical.

Therapeutic Potential of 17<i>β</i> Estradiol with Tachykinin Neuropeptide NKB and A<i>β</i>(25 - 35) on Na<sup>+</sup> - K<sup>+</sup> ATPase Activity in Aging Female Rat Brain

The Na+ - K+ ATPase is an enzyme responsible for the active transport of Na+ and K+ in most eukaryotic cells. The aim of the present study was to determine the effect of Tachykinin neuropeptide, Neurokinin B (NKB) and Amyloid beta fragment Aβ (25 - 35) on 17β estradiol (E2) treated aging female rat brain synaptosomes of different age groups, by assaying Na+ - K+ ATPase enzyme activity. An in vitro incubation of isolated synaptosomes with Aβ (25 - 35) showed toxic effects while NKB showed stimulating effect on the Na+ - K+ ATPase activity, and the combined NKB + Aβ (25 - 35) incubations showed a partial effect as compared to the Aβ (25 - 35) alone. To understand whether E2 affects the expression of Na+ - K+ ATPase molecules, we examined the expression of Na+ - K+ ATPase subunit α1 and β2 in E2 treated aging female rat brain synaptosomes. The enzyme was quantified by SDS PAGE in control and E2 treated rat brain. We observed that the expression of α1 and β2 Na+ - K+ ATPase molecules increased and reversed to a normal level in E2 treated synaptosomes. These results confirmed that E2 increased turnover of Na+ - K+ ATPase molecules in aging rat brain. The present findings also suggest a possible role of NKB with E2 in the age related changes in the brain.

Abstract W P90: Insulin-like Growth Factor-1-mediated Reduction of Stroke-induced Brain Infarction is Preceded by Improvement of Blood Brain Barrier Integrity and Inflammatory Cytokines

Background and Purpose: Although insulin-like growth factor (IGF)-1 treatment has been shown to reduce stroke-induced infarct volume, the mechanisms underlying its neuroprotective actions are not fully understood. The present study tested the hypothesis that IGF-1 may regulate the neuroinflammatory cascade initiated by ischemic stroke, specifically, by promoting the integrity of the blood brain barrier. Methods: Middle-aged (10-12 month old) female rats were implanted with a cannula directed toward the lateral ventricle. One week later, animals were anesthetized using isoflurane and the middle-cerebral artery was occluded using an intraluminal suture maintained in place for 90 mins. IGF-1 or vehicle was delivered icv, via a mini-pump, following reperfusion. All animals were terminated at 4h or 24h post MCAo. Blood brain barrier permeability was determined using Evan’s blue extravasation and infarct volumes were determined from TTC-stained brain sections. Inflammatory cytokines were analyzed from brain lysates by ELISA. Results: IGF-1 treatment to middle-aged females resulted in a 39% reduction in infarct volume when measured 24h post MCAo, confirming the neuroprotective action of this peptide hormone. In order to assess the effects of IGF-1 on early stroke induced effects, we next determined blood brain permeability 4h post stroke as well as the expression of cytokines in the ischemic hemisphere. IGF-1 treatment resulted in a significant reduction of blood brain barrier permeability at 4h post-stroke compared to vehicle treated animals. Moreover, multiplex cytokine analysis showed that IGF-1 significantly reduced inflammatory markers such as IL-6, IFN-gamma, TNF-alpha, eotaxin, GM-CSF. Brain infarct volume at 4h was similar in both IGF-1 and vehicle groups, indicating that the effects of IGF-1 on inflammatory markers precede its effects on infarct volume. IGF-1 also suppressed IL-6, MIP-2, GRO-KC, MCP-1, EGF and MIP-1-alpha expression at 24h post stroke, indicating a persistent anti-inflammatory effect for this growth factor. Conclusions: The above findings support the hypothesis that IGF-1 has unique anti-inflammatory action in the aging female brain, and suggest that brain endothelial cells may be a primary target of IGF-1.

Early Decline in Glucose Transport and Metabolism Precedes Shift to Ketogenic System in Female Aging and Alzheimer's Mouse Brain: Implication for Bioenergetic Intervention

We previously demonstrated that mitochondrial bioenergetic deficits in the female brain accompanied reproductive senescence and was accompanied by a shift from an aerobic glycolytic to a ketogenic phenotype. Herein, we investigated the relationship between systems of fuel supply, transport and mitochondrial metabolic enzyme expression/activity during aging (3–15 months) in the hippocampus of nontransgenic (nonTg) background and 3xTgAD female mice. Results indicate that during female brain aging, both nonTg and 3xTgAD brains undergo significant decline in glucose transport, as detected by FDG-microPET, between 6–9 months of age just prior to the transition into reproductive senescence. The deficit in brain metabolism was sustained thereafter. Decline in glucose transport coincided with significant decline in neuronal glucose transporter expression and hexokinase activity with a concomitant rise in phosphorylated/inactivated pyruvate dehydrogenase. Lactate utilization declined in parallel to the decline in glucose transport suggesting lactate did not serve as an alternative fuel. An adaptive response in the nonTg hippocampus was a shift to transport and utilization of ketone bodies as an alternative fuel. In the 3xTgAD brain, utilization of ketone bodies as an alternative fuel was evident at the earliest age investigated and declined thereafter. The 3xTgAD adaptive response was to substantially increase monocarboxylate transporters in neurons while decreasing their expression at the BBB and in astrocytes. Collectively, these data indicate that the earliest change in the metabolic system of the aging female brain is the decline in neuronal glucose transport and metabolism followed by decline in mitochondrial function. The adaptive shift to the ketogenic system as an alternative fuel coincided with decline in mitochondrial function. Translationally, these data provide insights into the earliest events in bioenergetic aging of the female brain and provide potential targets for preventing shifts to less efficient bioenergetic fuels and transition to the ketogenic phenotype of the Alzheimer's brain.

A bioenergetic trajectory of female brain aging and Alzheimer's disease 2: Mechanistic link between mitochondrial dysfunction and white matter degeneration in the normal mammalian aging female brain

A bioenergetic trajectory of female brain aging and Alzheimer's disease 2: Mechanistic link between mitochondrial dysfunction and white matter degeneration in the normal mammalian aging female brain

MicroRNAs in the aging female brain: a putative mechanism for age-specific estrogen effects.

Menopause is characterized by the rapid age-related decline of circulating 17β-estradiol (E(2)) levels in women, which can sometimes result in cognitive disorders such as impaired memory and increased anxiety. Hormone therapy (HT) is a widely used treatment for the adverse effects associated with menopause; however, evidence suggests that HT administered to postmenopausal women age 65 years and over can lead to increased risks for cognitive disorders. We hypothesized that these age-related changes in E(2) action are due to posttranscriptional gene regulation by microRNAs (miRNAs). miRNAs are a class of small noncoding RNAs that regulate gene expression by binding to the 3'-untranslated region of target mRNAs and subsequently target these transcripts for degradation. In the present study, 3- and 18-month-old female rats were oophorectomized (OVX) and treated 1 week after surgery with 2.5 μg E(2) once per day for 3 days. Total RNA was isolated from the ventral and dorsal hippocampus, central amygdala, and paraventricular nucleus. Our results showed that E(2) differentially altered miRNA levels in an age- and brain region-dependent manner. Multiple miRNA target prediction algorithms revealed putative target genes that are important for memory and stress regulation, such as BDNF, glucocorticoid receptor, and SIRT-1. Indeed, quantitative RT-PCR analyses of some of the predicted targets, such as SIRT1, showed that the mRNA expression levels were the inverse of the targeting miRNA, thereby confirming the prediction algorithms. Taken together, these data show that E(2) regulates miRNA expression in an age- and E(2)-dependent manner, which we hypothesize results in differential gene expression and consequently altered neuronal function.

The Effects of Long-Term Treatment with Estradiol and Medroxyprogesterone Acetate on Tyrosine Hydroxylase Fibers and Neuron Number in the Medial Prefrontal Cortex of Aged Female Rats

Menopausal women often initiate hormone treatment to alleviate the symptoms of menopause. Research suggests that these treatments also affect cognition, and studies in young animals indicate that hormone treatment can alter several neuroanatomical measures. However, very little is known about the effects of long-term hormone treatment on the aging female brain. This study investigated the effects of hormone treatment on neuron number and tyrosine hydroxylase (TH) in the rat medial prefrontal cortex (mPFC). Female Long Evans rats were ovariectomized at middle age (12-13 months) and placed in one of four groups: no replacement (NR) (n = 12), 17β-estradiol (E(2)) (n = 12), E(2) and progesterone (n = 7), or E(2) and medroxyprogesterone acetate (MPA) (n = 10). Animals were euthanized at 20 months, and the brains were Nissl stained; a subset was immunostained for TH [NR (n = 5); E(2) (n = 6); E(2) + MPA (n = 4); E(2) + progesterone (n = 6)]. E(2) was administered through the drinking water, and progestagens were administered via pellets inserted at the nape of the neck. Neuron number and TH fiber density were quantified in the mPFC. Hormone treatment did not alter neuron number. Treatment with E(2) and MPA resulted in greater TH densities than NR in layer 1 (P < 0.05). In layers 2/3, animals receiving E(2) had greater TH densities than NR animals (P < 0.01). These results indicate that long-term hormone treatments alter dopaminergic fibers and potentially the functioning of the aging mPFC.