Leptin is the protein product encoded by the obese （ob） gene. It is a circulating hormone produced primarily by the adipose tissue, Which is an adipocyte-derived hormone that acts as a major regulator for food intake and energy homeostasis. Leptin deficiency or resistance can result in profound obesity, diabetes, and infertility in humans. Leptin serves as an adiposity signal to inform the brain the adipose tissue mass in a negative feedback loop regulating food intake and energy expenditure. It also plays important roles in angiogenesis, immune function, fertility, and bone formation.