Abstract

The hormone leptin is secreted from white adipocytes, and serum levels of leptin correlate with adipose tissue mass. Leptin was first described to act on the satiety center in the hypothalamus through specific receptors (leptin receptor [ObR]) to restrict food intake and enhance energy expenditure. Important peripheral actions of leptin involve inhibition of insulin biosynthesis and secretion in pancreatic β-cells. In turn, insulin stimulates leptin secretion from adipose tissue, establishing a hormonal regulatory feedback loop—the so-called “adipo-insular axis.” Multiple signal transduction pathways are involved in leptin signaling in pancreatic β-cells. We have identified the proinsulin gene and protein phosphatase 1 gene as leptin repressed genes and the gene for the suppressor of cytokine signaling 3 protein as a leptin-induced gene in pancreatic β-cells. The molecular effects of leptin culminate to restrict insulin secretion and biosynthesis to adapt glucose homeostasis to the amount of body fat. In most overweight individuals, however, physiological regulation of body weight by leptin seems to be disturbed, representing “leptin resistance.” This leptin resistance at the level of the pancreatic β-cell may contribute to dysregulation of the adipo-insular axis and promote the development of hyperinsulinemia and manifest type 2 diabetes in overweight patients.