Hypothalamic leptin and insulin signals aligning metabolic state and fertility

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The dramatic increases in childhood and adolescent obesity in the U.S. have serious consequences for the health of the next generation. Along with its well-known health risks, childhood obesity impairs reproductive health and development. Indeed, early onset of obesity in girls, particularly during adolescence, favors the development of menses irregularities, chronic anovulation, infertility, and PCOS in adulthood. While the primary cause of this relationship is uncertain, central resistance to insulin and leptin, circulating markers of adiposity, appears to inhibit the reproductive axis. The key sites of communication between the metabolic and reproductive systems, however, remain unclear. This proposal is designed to advance our long-term goal of elucidating the molecular and genetic determinants of metabolic infertility. We hypothesize that leptin and insulin act directly on hypothalamic POMC and NPY/AgRP neurons that provide input to GnRH neurons. This hypothesis rests on findings that altered activity of POMC and NPY/AgRP neurons in response to leptin and insulin appear to depend on the phosphatidylinositol 3-kinase (PI3K) intracellular signaling pathway. In addition, previous studies have shown that brain-specific leptin receptor and insulin receptor knockouts have dramatic effects on the reproductive axis, but preventing leptin receptor signaling through non-PI3K pathways does not impair fertility. Thus, our studies will determine if insulin and leptin signaling through PI3K is required for normal (1) energy homeostasis and (2) reproductive functioning and in POMC neurons and/or in NPY/AgRP neurons. To accomplish these goals, we will genetically target the critical neurons using the cre/lox system. Specifically, we will examine the metabolic and reproductive phenotype of mice lacking insulin and leptin receptors or functional PI3K only in POMC neurons and only in NPY/AgRP neurons. We will then use electrophysiology and a novel method of visualizing Akt signaling in vitro to determine the impact of PI3K deletion on neuronal function. Collectively, these data may provide a new target for therapeutic advances in the treatment and prevention of obesity-related infertility. With a background in the diverse fields of reproduction and metabolism, Dr. Hill is uniquely qualified to undertake these studies. The novel genetic approaches assembled during her post-doctoral fellowship will be powerful tools for investigating the understudied area of interacting hypothalamic metabolic and reproductive pathways. By providing a vehicle for her transition to research independence, this proposal lays the groundwork for a research program focused on reproductive health and the discovery of new approaches for treating nutritional and obesity-related infertility.