Glucose sensing neurons (GSN) of the ventromedial hypothalamus (VMH) are believed to play a role in the regulation of energy and glucose homeostasis. However, the underlying mechanisms by which GSNs fulfill this role remain elusive. The current obesity epidemic and the rise in the prevalence of Type II Diabetes Mellitus (TIIDM) underscore the necessity to clarify these mechanisms and potentially illuminate novel therapeutic targets for these diseases. This is especially important for females since there is a greater incidence of obesity and TIIDM in females yet virtually all studies of GSNs have been performed in males. We have previously shown, in male mice, that VMH GSNs are dysfunctional during TIIDM. The strong correlation between estrogen receptor (ER) expression, in both sexes, and the location of VMH GSNs within the ventrolateral VMH suggests that estrogen regulates GSNs. This project hypothesizes that ER activation attenuates VMH GSN sensitivity to decreased glucose. Thus diminished estrogen levels following menopause may enhance responsiveness of GSNs to glucose decreases. This could lead to inappropriate signals of energy deficit and initiation of inappropriate compensatory mechanisms during energy sufficiency. Such a response may explain the increased susceptibility to TIIDM in post-menopausal females. To test this hypothesis, the pre-doctoral fellow will first determine whether glucose-excited or glucose-inhibited neurons are ER positive (either alpha or beta) using immunohistochemical and single-cell PCR methodologies. The neurotransmitter phenotype of these neurons will also be determined in order to better understand their role in energy homeostasis. Secondly, electrophysiological patch-clamp techniques will be used to determine how estrogen and the membrane impermeable BSA-conjugated estrogen regulate the acute activity as well as the glucose sensitivity of GSNs. The fellow will also utilize inhibitors of potential ER signaling molecules and western blot analysis to understand the mechanism of estrogenic regulation of VMH GSNs sensitivity. Using these same techniques, the fellow will investigate the effects of ER1 or ER2 ablation on the glucose sensitivity of VMH GSNs via the use of steroidogenic factor-1 driven ER1- or ER2-knockout mice (VMH exclusive knockout) and selective ER1 or ER2 antagonist application. Finally, using a fluorescent retrograde tracer, the fellow will determine whether estrogen-sensitive GSNs project directly to the anterior pituitary or to the preoptic area where they could potentially relay nutrient status information influencing the reproductive state of the individual.
Females, and especially post-menopausal women, are more prone than males to develop two of the most serious diseases of the modern world: obesity and Type II Diabetes Mellitus (TIIDM). Glucose sensing neurons (GSNs) in the ventromedial hypothalamus, which express the estrogen receptor, may play a key role in regulating glucose and energy homeostasis. This proposal will investigate whether estrogen regulates GSNs and thus, whether diminished estrogen could contribute to the increased susceptibility of post-menopausal women to obesity and TIIDM.
|Santiago, Ammy M; Clegg, Deborah J; Routh, Vanessa H (2016) Ventromedial hypothalamic glucose sensing and glucose homeostasis vary throughout the estrous cycle. Physiol Behav 167:248-254|
|Santiago, Ammy M; Clegg, Deborah J; Routh, Vanessa H (2016) Estrogens modulate ventrolateral ventromedial hypothalamic glucose-inhibited neurons. Mol Metab 5:823-33|