The Interaction of Neuroendocrine Repro. Function and Metabolic Signaling

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There are a number of physiologic situations in which metabolic signals, particularly those related to glucoregulatory and lipid metabolism, impinge on reproductive function. The networks that control metabolic homeostasis and the hypothalamic (H)/pituitary (P)/gonadal (G) axis are highly complex, reflecting a large set of intersecting feedback regulatory circuits. In this proposal, we will undertake a molecular and biochemical dissection of selected elements of the metabolic signaling system to determine their impact on HP function. Thus, insulin, adiponectin, and PPARgamma signaling are all key elements in major metabolic regulatory networks, and we will test a number of hypotheses related to how these pathways affect HP function. The program proposed is a broad-based approach involving genetic, in vivo physiology, and in vitro studies. In specific, based on genetic deletion of insulin receptors (IR), it is clear that absence of IRs in the brain leads to infertility. Our own in vitro data show substantial effects of insulin on HP function in cultured cells. We will use a variety of genetic approaches, including knockout and transgenic methodology as well as stereotaxic gene manipulation to create novel animal models for investigation. In vitro studies in immortalized GnRH neuronal cells (GT1-7) and pituitary cells (LbetaT2) are also proposed. Adiponectin is an adipose-derived factor that has major effects on glucose and lipid metabolism. Transgenic hyperadiponectinemic mice are infertile and hyperadiponectinemic rats display decreased LH secretion. These findings will be pursued at genetic, physiologic, and in vitro levels to understand the effects of this adipocytokine on reproduction. Lastly, stimulation of the PPARgamma receptor can restore fertility in PCOS women, and we have now found that PPARgamma modulates GnRH signaling and LH release in LbetaT2 cells. In addition, we have initial evidence showing that TZD treatment of PCOS women lowers the elevated LH levels. Taken together, this approach should allow us to parse out specific metabolic signaling pathways to deduce their individual and combined effects on HP function. These studies should provide new insights into the interactions between metabolic homeostasis and reproductive function allowing us to begin unraveling these multi-faceted interacting pathways. The results will also improve our understanding of reproductive function in metabolic disorders such as PCOS, Type 2 diabetes, and obesity, in which abnormalities of HP function have been well described.