Adipose tissue-derived adipokines influence a number of organs critical for energy homeostasis and metabolism. One of the most extensively studied adipokines is adiponectin, which exerts anti-diabetic, anti-inflammatory, and anti-atherogenic functions on various cell types. CTRP3, a paralog of adiponectin, is a member of the C1q and tumor necrosis factor-related protein (CTRP) superfamily. CTRP3 reduces hepatic triglyceride levels in diet-induced obese (DIO) mice. However, the physiological role of CTRP3 in adipocytes is largely unknown. In the course of our investigation of expression profiles of CTRPs during adipocyte differentiation, we found that CTRP3 expression pattern is different from that previously reported. Therefore, we examined the effect of CTRP3 on adipogenesis using 3T3-L1 cells. The expression level of CTRP3 was markedly decreased during the differentiation of 3T3-L1 cells. Recombinant CTRP3 (rCTRP3) treatment significantly reduced intracellular lipid content and decreased expression of adipogenic marker genes such as peroxisome proliferator-activated receptor gamma (PPARγ), CCAAT/enhancer binding protein alpha (C/EBPα), adiponectin, and fatty acid binding protein 4 (FABP4) in 3T3-L1 cells. Furthermore, rCTRP3 induced the phosphorylation of extracellular signal-regulated protein kinase 1/2 (ERK1/2) and Akt in differentiated 3T3-L1 adipocytes. These results suggest that CTRP3 may negatively regulate lipid metabolism during adipocyte differentiation.

We made a mistake in the unit of the left-vertical axis in Fig. 3(b). It is not "10 4 dB/cm", but "10 4 cm ¹1 ". The corrected figure is shown below. This correction, however, never affects discussions and conclusions in this paper.