The leptin-dependent and -independent melanocortin signaling system: regulation of feeding and energy expenditure.

The brain hypothalamus coordinates extra-hypothalamic regions to maintain energy homeostasis through the regulation of food intake and energy expenditure. A number of anorexigenic and orexigenic molecules in the hypothalamic nuclei participate in the control of energy homeostasis. Leptin and pro-opiomelanocortin (POMC)-derived alpha-melanocyte-stimulating hormone are key anorectic molecules, and the leptin receptor and POMC gene are both expressed in the hypothalamic arcuate nucleus. Although it has been considered that melanocortin signaling is localized downstream to leptin signaling, data have accumulated to support the concept of a leptin-independent melanocortin signaling system. We focus on and review the melanocortin signaling system that functions dependently or independently of leptin signaling in the regulation of energy homeostasis.