Characterization of the Expression of CTRP9, a Paralog of Adiponectin

Adiponectin is one of the hormones secreted exclusively by the adipose tissue with anti-diabetic, anti-inflammatory, anti-atherogenic, anti-atherosclerotic, and insulin-sensitizing effects. Adiponectin has structural features including a signal peptide at the N terminus, a short variable region, a collagenous domain, and a C-terminal globular domain homologous to C1q. The family of proteins containing this globular domain is called the C1q/tumor necrosis factor-α-related proteins (CTRP). Among all the CTRPs characterized so far, the CTRP9 protein has the highest homology to adiponectin. However, little is known about the functions of CTRP9. This study examines the tissue expression of CTRP9 as well as the expression of CTRP9 during mouse development and 3T3-L1 preadipocyte differentiation. The effects of LPS, TNFα, and starvation on the expression of CTRP9 were also investigated. CTRP9 mRNA is shown to be expressed in a variety of tissues including the adipose tissues. The expression profile of CTRP9 differs from that of adiponectin, implying that they are functionally diverse although structurally homologous.