Aging and the coincident loss of circulating estrogens at menopause lead to increased risks for neurological and cardiovascular pathologies. Clinical studies show that estrogen therapy (ET) can be ...beneficial in mitigating these negative effects, in both the brain and heart, when it is initiated shortly after the perimenopausal transition. However, this same therapy is detrimental when initiated >10 years postmenopause. Importantly, the molecular mechanisms underlying this age-related switch in ET efficacy are unknown. Estrogen receptors (ERs) mediate the neuroprotective and cardioprotective functions of estrogens by modulating gene transcription or, non-genomically, by activating second messenger signaling pathways, such as mitogen activated protein kinases (MAPK). These kinases are critical regulators of cell signaling pathways and have widespread downstream effects. Our hypothesis is that age and estrogen deprivation following menopause alters the expression and activation of the MAPK family members p38 and ERK in the brain and heart. To test this hypothesis, we used a surgically induced model of menopause in 18 month old rats through bilateral ovariectomy (OVX) followed by an acute dose of 17β-estradiol (E2) administered at varying time points post-OVX (1 week, 4 weeks, 8 weeks, or 12 weeks). Age and E2 treatment differentially regulated kinase activity in both the brain and heart, and the effects were also brain region specific. MAPK signaling plays an integral role in aging, and the aberrant regulation of those signaling pathways might be involved in age-related disorders. Clinical studies show benefits of ET during early menopause but detrimental effects later, which might be reflective of changes in kinase expression and activation status.
•This review gives a brief summary of miRNA biogenesis and function in the brain.•The impact of hormones on miRNA function are discussed.•MiRNA function during puberty could be distinct from other ...developmental stages.
Over two decades ago the discovery of microRNAs (miRNA) broadened our understanding of the diverse molecular pathways mediating post-transcriptional control over gene expression. These small non-coding RNAs dynamically fluctuate, temporally and spatially, throughout the lifespan of all organisms. The fundamental role that miRNAs have in shaping embryonic neurodevelopment provides strong evidence that adolescent brain remodeling could be rooted in the changing miRNA landscape of the cell. Few studies have directly measured miRNA gene expression changes in the brain across pubertal development, and even less is known about the functional impact of those miRNAs on the maturational processes that occur in the developing adolescent brain. This review summarizes miRNA biogenesis and function in the brain in the context of normal (i.e. not diseased) physiology. These landmark studies can guide predictions about the role of miRNAs in facilitating maturation of the adolescent brain. However, there are clear indicators that adolescence/puberty is a unique life stage, suggesting miRNA function during adolescence is distinct from those in any other previously described system.
Adolescent binge alcohol abuse induces long-term changes in gene expression, which impacts the physiological stress response and memory formation, two functions mediated in part by the ventral (VH) ...and dorsal (DH) hippocampus. microRNAs (miRs) are small RNAs that play an important role in gene regulation and are potential mediators of long-term changes in gene expression. Two genes important for regulating hippocampal functions include brain-derived neurotrophic factor (BDNF) and sirtuin-1 (SIRT1), which we identified as putative gene targets of miR-10a-5p, miR-26a, miR-103, miR-495. The purpose of this study was to quantify miR-10a-5p, miR-26a, miR-103, miR-495 expression levels in the dorsal and ventral hippocampus of male Wistar rats during normal pubertal development and then assess the effects of repeated binge-EtOH exposure. In addition, we measured the effects of binge EtOH-exposure on hippocampal Drosha and Dicer mRNA levels, as well as the putative miR target genes, BDNF and SIRT1. Overall, mid/peri-pubertal binge EtOH exposure altered the normal expression patterns of all miRs tested in an age- and brain region-dependent manner and this effect persisted for up to 30 days post-EtOH exposure. Moreover, our data revealed that mid/peri-pubertal binge EtOH exposure significantly affected miR biosynthetic processing enzymes, Drosha and Dicer. Finally, EtOH-induced significant changes in the expression of a subset of miRs, which correlated with changes in the expression of their predicted target genes. Taken together, these data demonstrate that EtOH exposure during pubertal development has long-term effects on miRNA expression in the rat hippocampus.
Loss of circulating 17β-estradiol (E2) that occurs during menopause can have detrimental effects on cognitive function. The efficacy of hormone replacement therapy declines as women become farther ...removed from the menopausal transition, yet the molecular mechanisms underlying this age-related switch in E2 efficacy are unknown. We hypothesized that aging and varying lengths of E2 deprivation alters the ratio of alternatively spliced estrogen receptor (ER)β isoforms in the brain of female rats. Further, we tested whether changes in global transcriptional activity and splicing kinetics regulate the alternative splicing of ERβ. Our results revealed brain region-specific changes in ERβ alternative splicing in both aging and E2-deprivation paradigms and showed that ERβ could mediate E2-induced alternative splicing. Global transcriptional activity, as measured by phosphorylated RNA polymerase II, was also regulated by age and E2 in specific brain regions. Finally, we show that inhibition of topoisomerase I resulted in increased ERβ2 splice variant expression.
Adolescent binge alcohol exposure has long-lasting effects on the expression of hypothalamic genes that regulate the stress response, even in the absence of subsequent adult alcohol exposure. This ...suggests that alcohol can induce permanent gene expression changes, potentially through epigenetic modifications to specific genes. Epigenetic modifications can be transmitted to future generations therefore, and in these studies we investigated the effects of adolescent binge alcohol exposure on hypothalamic gene expression patterns in the F1 generation offspring. It has been well documented that maternal alcohol exposure during fetal development can have devastating neurological consequences. However, less is known about the consequences of maternal and/or paternal alcohol exposure outside of the gestational time frame. Here, we exposed adolescent male and female rats to a repeated binge EtOH exposure paradigm and then mated them in adulthood. Hypothalamic samples were taken from the offspring of these animals at postnatal day (PND) 7 and subjected to a genome-wide microarray analysis followed by qRT-PCR for selected genes. Importantly, the parents were not intoxicated at the time of mating and were not exposed to EtOH at any time during gestation therefore the offspring were never directly exposed to EtOH. Our results showed that the offspring of alcohol-exposed parents had significant differences compared to offspring from alcohol-naïve parents. Specifically, major differences were observed in the expression of genes that mediate neurogenesis and synaptic plasticity during neurodevelopment, genes important for directing chromatin remodeling, posttranslational modifications or transcription regulation, as well as genes involved in regulation of obesity and reproductive function. These data demonstrate that repeated binge alcohol exposure during pubertal development can potentially have detrimental effects on future offspring even in the absence of direct fetal alcohol exposure.
Menopause is characterized by the rapid age-related decline of circulating 17β-estradiol (E2) 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 E2 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 E2 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 E2 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 E2 regulates miRNA expression in an age- and E2-dependent manner, which we hypothesize results in differential gene expression and consequently altered neuronal function.
Administration of 17β-estradiol (E2) has beneficial effects on cognitive function in peri- but not post-menopausal women, yet the molecular mechanisms underlying age-related changes in E2 action ...remain unclear. We propose that there is a biological switch in E2 action that occurs coincident with age and length of time after ovarian hormone depletion, and we hypothesized that age-dependent regulation of microRNAs (miRNAs) could be the molecular basis for that switch. Previously we showed that miRNAs are regulated by E2 in young compared to aged female rats. Here we tested whether increasing lengths of ovarian hormone deprivation in aged females altered E2 regulation of these mature miRNAs. In addition, we determined where along the miRNA biogenesis pathway E2 exerted its effects. Our results showed that age and increased lengths of ovarian hormone deprivation abolished the ability of E2 to regulate mature miRNA expression in the brain. Further, we show that E2 acted at specific points along the miRNA biogenesis pathway.
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.
The hypothalamo–pituitary–adrenal (HPA) and hypothalamo–pituitary–gonadal (HPG) axes have an intricate cross talk that results in the inhibition of reproductive functions during periods of chronic ...physiological or psychological stress. Recent studies have shown that kisspeptin neurons have projections to many non-reproductive areas of the brain including the paraventricular nucleus (PVN) of the hypothalamus, thereby providing evidence of an anatomical framework for kisspeptin to regulate the HPA axis. In this study, we tested as to whether kisspeptin modulates the HPA axis at three potential levels of regulation: (1) transcription of stress-related genes CRH, AVP, and oxytocin (OXY); (2) release of neuropeptides from PVN-derived neuronal cells via mobilization of intracellular calcium stores; and (3) in vivo regulation of the HPA axis under basal and stress-induced conditions in adult male rats. Overall, our data showed that kisspeptin did not alter basal, or stress-induced HPA axis activity (plasma corticosterone (CORT) and adrenocorticotropin hormone (ACTH)) in adult male rats and had modest, yet significant effects on CRH, AVP, and OXY gene expressions.
Adolescence is hallmarked by two parallel processes of sexual maturation and adult patterning of the brain. Therefore, adolescence represents a vulnerable postnatal period for neurodevelopment where ...exogenous factors can negatively impact adult brain function. For example, alcohol exposure during pubertal development can lead to long-term and widespread neurobiological dysfunction and these effects have been shown to persist even in the absence of future alcohol exposure. However, the molecular mechanisms mediating the persistent effects of alcohol are unclear. We propose that dysregulation of microRNAs (miR) could be a unifying epigenetic mechanism underlying these widespread long-term changes. We tested the hypothesis that repeated alcohol exposure during pubertal development would cause disruption of normal miR expression profiles during puberty and, subsequently, their downstream mRNA target genes in the ventral hippocampus using an established rat model of adolescent binge drinking. We found 6 alcohol-sensitive miRs that were all downregulated following alcohol exposure and we also investigated the normal age-dependent changes in those miRs throughout the pubertal period. Interestingly, these miRs were normally decreased throughout the process of puberty, but alcohol prematurely exacerbated the normal decline in miR expression levels. The work presented herein provides foundational knowledge about the expression patterns of miRs during this critical period of neurodevelopment. Further, this regulation of miR and mRNA expression by alcohol exposure presents a complex regulatory mechanism by which perturbation in this time-sensitive period could lead to long-term neurological consequences.
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