CTHRC1 Expression Results in Secretion-Mediated, SOX9-Dependent Suppression of Adipogenesis: Implications for the Regulatory Role of Newly Identified CTHRC1+/PDGFR-Alpha+ Stromal Cells of Adipose

Adipogenesis is regulated by the coordinated activity of adipogenic transcription factors including PPAR-gamma and C/EBP alpha, while dysregulated adipogenesis can predispose adipose tissues to adipocyte hypertrophy and hyperplasia. We have previously reported that <i>Cthrc1</i>-null mice have increased adiposity compared to wildtype mice, supporting the notion that CTHRC1 regulates body composition. Herein, we derived conditioned medium from 3T3-L1 cells expressing human <i>CTHRC1</i> and investigated its anti-adipogenic activity. This constituent significantly reduced 3T3-L1 cell adipogenic differentiation commensurate to the marked suppression of <i>Cebpa</i> and <i>Pparg</i> gene expression. It also increased the expression of the anti-adipogenic transcription factor SOX9 and promoted its nuclear translocation. Importantly, <i>Sox9</i> gene knockdown demonstrated that the anti-adipogenic effect produced by this conditioned medium is dependent on SOX9 expression, while its ability to positively regulate SOX9 was attenuated by the application of Rho and Rac1 signaling pathway inhibitors. We also identified the selective expression of <i>CTHRC1</i> in <i>PDGFRA</i>-expressing cell populations in human white adipose tissue, but not brown or perivascular adipose tissues. Congruently, flow cytometry revealed CTHRC1 expression in PDGFR-alpha⁺ stromal cells of mouse white adipose tissue, thus defining a novel stromal cell population that could underpin the ability of CTHRC1 to regulate adiposity.