Adipose tissue of an organism plays a major role in regulating physiologic and pathologic processes such as metabolism and immunity by producing and secreting a variety of bioactive molecules termed adipokines. One highly conserved family of adipokines is adiponectin/ACRP30 and its structural and functional paralogs, the C1q/tumor necrosis factor-alpha-related proteins (CTRPs) 1-7. Unlike the CTRPs, which are expressed in a wide variety of tissues, adiponectin is reported to be expressed exclusively by differentiated adipocytes. These proteins are thought to act mainly on liver and muscle tissue to control glucose and lipid metabolism. An analysis of the crystal structure of adiponectin revealed a structural and evolutionary link between TNF and C1q-containing proteins, suggesting that these proteins arose from a common ancestral innate immunity gene. It is present in high levels in normal human plasma, but is reduced in obese subjects and often in those with increased insulin resistance and type 2 diabetes, suggesting that adiponectin may be a useful pharmacological target in various metabolic diseases.
