Abstract 108: C1q-TNF Related Protein-9, a Novel Cardioprotective Cardiokine, Requires Proteolytic Cleavage to Generate a Biologically Active Globular Domain Isoform
The discovery of the cardiac secretomes, known as “cardiokines”, significantly enhanced appreciation of the local microenvironment’s influence upon disease development. We previously reported cardiomyocytes produce cardioprotective adiponectin (APN). However, cardiac APN levels are several orders of magnitude below adipocytes, thereby making APN an unlikely physiologically relevant cardiokine. C1qTNF-related proteins (CTRP1-15) is a newly descovered family of APN paralogs. However, whether any of the CTRP members may function as a “true” cardiokine remains unknown. Here we demonstrated that several CTRPs (CTRP1,4,7,9,13) were expressed in the heart at levels significantly greater than APN. Most notably, the mRNA level of CTRP9 exceeded APN by >100-fold in cardiac tissue. Adult cardiac cells were isolated and cultured in vitro. Conditioned medium was collected 1-8 hours after culture and CTRP9 protein levels were determined by ELISA. A significant increase of CTRP9 in conditioned medium was detected as early as 1 hour in culture, steadily accumulating thereafter. These results indicate CTRP9 is secreted by cardiac cell at levels that may function as a cardiokine. Addional experiemnt unexpectedly demonstarted that CTRP9 circulates in the plasma primarily in the globular domain isoform (gCTRP9), opposing from APN which circulates as full length multimers. Recombinant full length CTRP9 (fCTRP9) was cleaved when incubated with cardiac tissue extracts, generating gCTRP9, a process inhibited by protease inhibitor cocktail. To gain more insight into the biological significance of gCTRP9 production, isolated adult cardiomyocytes were treated with gCTRP9 or fCTRP9. gCTRP9 rapidly activates cardiac survival kinases, including AMPK, Akt, and eNOS. However, fCTRP9-mediated kinase activation is much less potent, and significantly delayed. Kinase activation by fCTRP9, but not gCTRP9, is inhibited by protease inhibitor cocktail. These results demonstrate for the first time CTRP9 is a novel cardiokine undergoing proteolytic cleavage to generate cardioprotective isoform, gCTRP9. Enhancing cardiac CTRP9 production and/or its proteolytic post-translational modification are of therapeutic potential, attenuating cardiac injury.
Author Disclosures: Y. Du: None. Y. Yuan: None. W. Lau: None. T. Christopher: None. B. Lopez: None. Y. Wang: None. X. Ma: None.
- © 2015 by American Heart Association, Inc.