Insulin Signaling in the Anterior Pituitary

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DESCRIPTION (provided by applicant): Evidence from studies in humans, animal models, and in vitro cell model systems suggest the tight metabolic control of reproductive fitness. In particular, insulin receptor signaling has been shown to play an important role in fertility in systems ranging from C. elegans to mice. Clinical studies in humans and observations in knockout mouse models suggest a direct link between insulin action and the neuroendocrine control of reproduction. Studies in animal model systems ranging from Syrian hamsters, rats, ewes and some clinical observations indicate that insulin can suppress pituitary reproductive hormone synthesis. Studies in primary pituitary culture indicate that insulin is a positivie regulator of hormone synthesis. Thus the role of insulin as a positive or negative regulator of reproductive function is still controversial. We will utilize an in vitro cell model of the pituitary gonadotropes and mouse primary pituitary culture to investigate the role of insulin signaling in the modulation of gonadotropin output and to address the mechanistic basis for this action. We will identify the point in gonadotropin synthesis and release that is regulated by insulin. We will also identify the mechanism of convergent GnRH and insulin signaling. It is our overall goal to understand how insulin serves as a modulator of gonadotropin synthesis, and ultimately of reproductive function. Aim 1: Insulin regulation of gonadotropin production. Circulating insulin level inversely correlates with gonadotropin production. Using the gonadotrope cell line, LbetaT2, we will determine the point of insulin action by assessing the effects on hormone secretion, protein synthesis, and transcription of gonadotropins. Aim 2: Cross receptor signaling of GnRH and insulin in a gonadotrope cell model. Preliminary observations indicate that insulin attenuates the response to GnRH stimulation. We hypothesize that this is due .to modification of signaling components targeted by the GnRH receptor. We will determine the points of convergent intracellular signaling by GnRH and insulin. We will investigate PIS kinase, MAP kinase, and G protein signalling cascades and negative feedback regulators of receptor signaling to determine which cascades and intermediate proteins mediate insulin effects on GnRH signaling in gonadotropes.