| Background | 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 (reviewed in 1). One highly conserved family of adipokines is adiponectin/ACRP30 and its structural and functional paralogs, the C1q/tumor necrosis factor-?-related proteins (CTRPs) 1-7 (2). Unlike adiponectin, which is expressed exclusively by differentiated adipocytes, the CTRPs are expressed in a wide variety of tissues (3). 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 (4). Of the CTRPs, CTRP2 is most similar structurally and functionally to adiponectin. Recombinant CTRP2 rapidly activated AMPK and MAPK in cultured C2C12 cells, leading to increased glycogen accumulation and fatty acid oxidation (3). |