RESUMEN
CTHRC1 is transiently expressed by activated fibroblasts during tissue repair and in certain cancers, and CTHRC1 derived from osteocytes is detectable in circulation. Because its biological activity is poorly understood, we investigated whether the N terminus of CTHRC1 encodes a propeptide requiring cleavage to become activated. The effects of full-length versus cleaved recombinant CTHRC1 on endothelial cell metabolism and gene expression were examined in vitro. Respirometry was performed on Cthrc1 null and wildtype mice to obtain evidence for biological activity of CTHRC1 in vivo. Cleavage of the propeptide observed in vitro was attenuated in the presence of protease inhibitors, and cleaved CTHRC1 significantly promoted glycolysis whereas full-length CTHRC1 was less effective. The respiratory exchange ratio was significantly higher in wildtype mice compared to Cthrc1 null mice, supporting the findings of CTHRC1 promoting glycolysis in vivo. Key enzymes involved in glycolysis were significantly upregulated in endothelial cells in response to treatment with CTHRC1. In healthy human subjects, 58% of the cohort had detectable levels of circulating full-length CTHRC1, whereas all subjects with undetectable levels of full-length CTHRC1 (with one exception) had measurable levels of truncated CTHRC1 (88 pg/ml to >400 ng/ml). Our findings support a concept where CTHRC1 induction in activated fibroblasts at sites of ischemia such as tissue injury or cancer functions to increase glycolysis for ATP production under hypoxic conditions, thereby promoting cell survival and tissue repair. By promoting glycolysis under normoxic conditions, CTHRC1 may also be a contributor to the Warburg effect characteristically observed in many cancers.