Nutritional Regulation of Luteinizing Hormone Secretion

Project Summary
The long-term goal of the proposed research is to determine the central mechanisms by which
undernutrition and realimentation impact reproduction through regulation of gonadotropin-releasing
hormone (GnRH) and luteinizing hormone (LH) secretion, using male and female sheep as an animal
model. Puberty onset integrates various internal and external cues resulting in an increased release of
GnRH from the hypothalamus that imparts the capacity for sexual maturation and reproductive success.
Inadequate energy intake (undernutrition) has a significant negative impact on GnRH, and subsequently
LH secretion, thereby delaying puberty onset. However, the central mechanisms responsible for the
suppression of GnRH/LH secretion during undernutrition or the increase of GnRH/LH secretion following
re-feeding (realimentation) remain largely unknown. Thus, the objectives of this proposal are 1) to
determine the role that AgRP signaling plays in regulating GnRH and kisspeptin neurons during
undernutrition and realimentation, and 2) to determine the role that microglia play in regulating GnRH and
kisspeptin neurons during undernutrition and realimentation. In Aim 1, we will characterize changes in
AgRP signaling in GnRH and kisspeptin neurons in feed-restricted (FR) sheep, examine the in vivo effect
of AgRP immunoneutralization in the arcuate nucleus (ARC) of the hypothalamus on LH secretion in FR
sheep, and characterize changes in AgRP signaling in GnRH and kisspeptin neurons in refed sheep. In
Aim 2, we will characterize changes central immune signaling in GnRH and kisspeptin neurons in FR
sheep, examine the in vivo effect of central infusion of an interleukin-1 receptor antagonist on LH secretion
in FR sheep, characterize changes in central immune signaling in GnRH and kisspeptin neurons in refed
sheep, and examine the in vitro effect of low glucose and insulin on microglia phenotype and function.
Herein, with our expertise in whole-animal physiology, in vivo drug delivery, immunohistochemistry, and in
vitro cell culture we have designed experiments to apply the highly innovative technique of a fluorescent
in situ hybridization assay, RNAscope, for detection of signaling components for AgRP (Aim 1) and
interleukin-1β (Aim 2). The proposed experiments will not only address the neuronal networks by which
changes in metabolic state impact reproduction, but also provide important insight into the role the immune
system likely plays. Thus, this work will provide a greater understanding of how undernutrition impacts
central networks that regulate GnRH/LH secretion and yield novel and critical insight that may allow for
better control of the timing of puberty, and ultimately lead to improved human health through prevention of
disorders (e.g. cardiovascular disease and depression) associated with delayed puberty.