Ligand-independent signaling of estrogen receptor beta and the aging brain

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DESCRIPTION (provided by applicant): Menopause is characterized as a state of reproductive senescence coincident with sharply decreased circulating estrogen levels. Recently, the women's health initiative (WHI) conducted a large-scale clinical study designed to evaluate the neurological benefits of estrogen replacement therapy for post-menopausal women. The results of that study, combined with other studies using animal models, have sparked a fervent debate about whether estrogen is beneficial or detrimental to normal brain function. Estrogen signaling in the brain is conveyed by two high specificity receptors, estrogen receptors alpha and beta (ER1, ER2). Data from our laboratory have focused on the biological function of ER2 for two neuronal-specific genes that are estrogen-responsive and dramatically altered as a direct result of the aging process: gonadotropin-releasing hormone (GnRH) and arginine vasopressin (AVP). GnRH is the primary central regulator of reproduction and AVP is a critical regulator of several processes including mood, circadian rhythms, and the stress response. Our data demonstrate that ER2 differentially regulates these genes in the presence and absence of estrogen, leading to our central hypothesis that the basic function of ER2 in the brain changes during the aging process. Understanding the molecular basis and the associated underlying consequences of changes in ER2 signaling is critical for evaluating the efficacy and necessity of exogenous hormone therapies. The activity of estrogen-bound ER2 can be modulated by different mechanisms, including posttranslational modifications of the receptor, recruitment of coregulatory proteins into the transcription complex, or binding to unique cis-acting promoter elements on the target genes. Whether the estrogen-independent activation of AVP and GnRH by ER2 is mediated by one or all of these mechanisms is unknown. The specific aims outlined in this proposal will investigate each of these possibilities using a variety of molecular biology techniques in neuronal cells. The expected results will further our understanding of ER2 signaling in the post-menopausal brain by elucidating the precise molecular mechanisms that drive estrogen-independent regulation of ER2 target genes. PUBLIC HEALTH RELEVANCE: During normal aging, there is a sharp decline in circulating estrogen levels. The positive health benefits of estrogen replacement therapy in the aged brain have gained considerable interest in recent years; however, our understanding of the molecular mechanisms regulating estrogen signaling in neurons is limited. This proposal will investigate the consequences of estrogen-independent gene regulation in neurons, which is imperative to understand in order to critically evaluate the efficacy and necessity of exogenous hormone therapies.