Adipokine Signaling: Implications for Obesity

Adipose tissue has gained recognition not only as the main energy storage organ, but also as a source of secreted peptides. This review highlights the roles of leptin, adiponectin, and proinflammatory cytokines in obesity, diabetes, and related disorders. The current epidemic of obesity and related diseases is attributed mainly to increased intake of energy-dense foods rich in fat and sugar, and sedentary lifestyle. The roles of leptin signaling molecules are studied in mice. Although leptin deficiency offers important lessons on LRb signaling, obesity is often associated with elevated levels of leptin. Reduced adiponectin levels in obesity and insulin resistant states contribute to the excess cardiovascular risk observed in these conditions. The knowledge of adipokine signaling has benefited immensely from animal models, but there are potential pitfalls, e.g., differences in the sources of adipokines and target tissues. Moreover, important differences exist between rodent and human circadian rhythms, thermoregulation, immune function, and glucose and lipid metabolism. Current research areas include the origin of adipose tissue, and specific functions of subcutaneous and visceral adipose tissue, and how they relate to normal physiology and disease.