Synergistic Control of KNDy Neuronal Influence on Energy Balance by Ghrelin and Estradiol

Abstract

The gut peptide, ghrelin, mediates negative energy homeostasis and the neuroendocrine control of energy homeostasis by acting through its receptor, growth hormone secretagogue receptor (GHSR). GHSR, expressed in hypothalamic Kisspeptin/Neurokinin B/Dynorphin (KNDy) neurons in the arcuate (ARC), is well known to regulate energy balance. We have previously shown 17-beta-estradiol (E2) robustly increases Ghsr expression in KNDy neurons, enhancing their sensitivity to ghrelin. We hypothesize that E2-induced increase in GHSR expression augments KNDy sensitivity in a fasting state by elevating ghrelin to reduce energy expenditure in females. We developed a Kiss1-specific GHSR knockout to determine the role of GHSR in ARC KNDy neurons and fed them either a low-fat diet (LFD) or a high-fat diet (HFD). Knockout (experimental) females were resistant to HFD in terms of body weight gain, adiposity, and food intake compared to HFD-fed controls. HFD-fed experimental females also exhibited slower glucose clearance compared to HFD-fed controls. Experimental females, regardless of diet, exhibited elevated fasting (5h) glucose. Metabolic rates (V.O2, V.CO2) and energy expenditure (heat) were not different. Respiratory Exchange Ratio (RER) was elevated in LFD-fed females, indicating the utilization of carbohydrates over fat for energy. Further meal pattern analysis revealed a reduction in meal duration in HFD-fed females, but elevated meal frequency, while HFD-fed experimental females exhibited a reduced meal size. In two separate meal pattern experiments, experimental and control females were fasted for 24h and refed or injected with ghrelin (I.P. 1mg/kg) or saline. We observed a striking delay in refeeding behavior in experimental females compared to controls during the refeeding period after fasting. After injection, control females responded to ghrelin with a rapid and sustained increase in food intake which was blunted in experimentals. Collectively, these data suggest that GHSR activation in KNDy neurons modulates metabolism, glucose homeostasis, and feeding behavior, illustrating a novel mechanism for E2 and ghrelin to synergistically control KNDy neuronal output and their subsequent behavioral and physiological outcomes.