SFRP5 acts as a mature adipocyte marker but not as a regulator in adipogenesis.

WNT/β-catenin signalling is involved in regulating adipogenesis, and its dysregulation occurs in obesity. Secreted frizzled-related protein 5 (SFRP5) is a WNT protein inhibitor; however, its role in adipogenesis and obesity is controversial. In this study, we observed that SFRP5 mRNA levels were increased in the fat tissues of obese humans and mice. Sfrp5 expression was gradually induced during differentiation of white and brown adipocytes and was highly increased in mature adipocytes rather than preadipocytes. However, the effects of the exogenous overexpression of Sfrp5 indicated that Sfrp5 may not directly regulate adipogenesis in vitro under the conditions studied. Moreover, SFRP5 did not inhibit the canonical WNT/β-catenin signalling pathway in preadipocytes. Subsequently, we measured the levels of circulating SFRP5 in obese patients and non-obese subjects using ELISA and did not find any significant difference. Collectively, these findings indicate that Sfrp5 represents a candidate for a mature adipocyte marker gene. Our data provide new evidence concerning the role of SFRP5 in adipogenesis of white and brown adipocytes and obesity.