A highly conserved family of adiponectin paralogs designated as C1q Tumor Necrosis Factor-α-related Proteins (CTRP; C1QTNF) 1-7 (see below) has been described recently. While the seven members exhibit similar structural properties as adiponectin their expression is not restricted to adipose tissue. Among this family, CTRP1 has been reported to be a vascular wall protein that inhibits collagen-induced platelet aggregation by blocking the binding of the Willebrand factor to collagen.CTRP1 expression is increased in adipose tissues of db/db mice and Zucker diabetic fatty (fa/fa) rats and the protein has been shown to stimulate aldosterone production. CTRP2, the mouse paralog with the highest similarity to adiponectin, enhances glycogen accumulation and fatty acid oxidation and has been shown to induce AMPK phosphorylation. CTRP3 (cartducin; CORS-26; cartonectin) has been identified as a novel growth factor important in regulating both chondrogenesis and cartilage development. The protein has been shown to exert anti-inflammatory properties, to be expressed in murine and human adipocytes and to stimulate secretion of other adipokines such as adiponectin and resistin from murine but not human adipocytes. CTRP5 has been associated with retinal degeneration.
