POWRE: Leptin Action on Gonadotropin-releasing Hormone Neurons Suzanne M. Moenter The goal of the research to be performed with this NSF POWRE funding is to explore the link between energy balance and reproduction. This project is particularly suited for a POWRE award because it will allow exploratory work to determine the feasibility of a new line of inquiry. Negative energy balance inhibits reproduction but the mechanisms involved are only partially understood. The central nervous system controls reproduction through the episodic secretion of gonadotropin-releasing hormone (GnRH). Negative energy balance is known to slow the frequency of or completely stop GnRH release; this leads to infertility. The mediator conveying metabolic information to the GnRH neurosecretory system is unknown. This research will test the possibility that leptin serves as a messenger to convey information regarding energy balance to the neuroendocrine system regulating reproduction. Leptin is a hormone produced by fat tissue and leptin levels in the circulation are highly correlated with the percentage of body fat. Leptin is thus a logical candidate for conveying information on energy stores to the rest of the body. Our specific hypothesis is that leptin acts directly on GnRH neurons to alter the pattern of episodic GnRH release. We established the receptor required for leptin action is expressed in an immortalized GnRH neuronal cell line (GT1-7 cells-a source of pure GnRH neurons in the absence of other cell types), as well as in the anterior hypothalamus and preoptic area, regions of the brain that contain the majority of GnRH cell bodies in the mouse. This provides a basis for the direct regulation of GnRH release by leptin. Subsequent studies of GT1-7 cells have demonstrated that although the gene for the leptin receptor is expressed, the resulting protein is altered, preventing leptin action. The proposed research will thus pursue the feasibility of studying leptin ac tion on the GnRH neurosecretory system in both animal models and in GT1-7 cells transfected with the cDNA for the leptin receptor. The PI has four specific aims. In Specific Aim 1, we will determine if GnRH neurons in vivo express the leptin receptor by using in situ hybridization to localize the expression of that gene specifically to GnRH neurons (our preliminary studies placed it only in the general vicinity). In Specific Aim 2, we will generate GT1-7 cells stably expressing the cDNA for the unaltered leptin receptor enabling us to study leptin action on isolated GnRH-like neurons. In Specific Aim 3, the effects of leptin on GnRH release from the transfected GT1-7 cells will be studied. The long and short term effects of leptin treatment on the pattern of GnRH release will be determined. In Specific Aim 4, we will begin to examine the signaling pathways of leptin in stably transfected GT1-7 cells and GnRH neurons and changes in gene expression induced by leptin. These experiments should provide important insights into communication of energy balance to the neural systems involved in regulating reproduction, the underlying cellular mechanisms, and overall rhythmic hormone release.
