Insulin signaling in LepR cells modulates fat and glucose homeostasis independent of leptin.

Hypothalamic neurons detect changes in circulating hormones such as leptin and insulin and put forward outputs to sustain energy and glucose homeostasis. Because leptin and insulin receptors colocalize in about 40-60% of neurons in the hypothalamus, we characterized the metabolic phenotype of mice with selective deletion of the InsR in LepR cells. LRΔInsR mice presented no difference in body weight and insulin levels, but increased fat mass. In the light phase, LRΔInsR mice exhibited increased food intake, locomotor activity, VCO2 and RER. These mice showed reduced fat oxidation and reduced expression of Cd36 and Prkaa1 in the liver, increased glucose oxidation in the light phase and overall reduced basal glucose levels. To verify the impact of InsR deletion in LepR cells in obesity, we generated ob/ob InsRfl , ob/ob LRcre and ob/ob LRΔInsR mice. The ob/ob LRΔInsR mice had higher body weight, fat mass and expression of genes related to fat metabolism in the liver. No difference in food intake despite increased Npy and Agrp expression, and no difference in energy expenditure, fat or glucose oxidation were found in ob/ob LRΔInsR compared to LRcre or LRΔInsR controls. Remarkably, basal glucose levels were reduced and the expression of genes associated with glucose metabolism in the liver was higher. Insulin signaling in LepR cells is required for the proper fat and glucose oxidation. These effects are independent of leptin given that the leptin-deficient ob/ob LRΔInsR mice also presented reduced glycemia and higher adiposity. The mechanisms underlying these responses remain to be unveiled.