Abstract 529: Asporin - Extracellular Matrix Protein Mitigates Pathological Remodeling

Abstract

The cardiac extracellular matrix is a complex network of proteins and plays a key role in cardiac remodeling after myocardial infarction. One of the extracellular matrix proteins, asporin, is a member of the SLRP family and inhibits TGFβ signaling. However, very little is known about the function and regulation of asporin in cardiac remodeling. Using bioinformatics approach, microarray data analysis from publicly available datasets identified asporin as a top candidate showing an increase in left ventricle tissue with ischemic cardiomyopathy as compared to control donor hearts. To confirm, we detected an increase in asporin expression in paired heart biopsies taken before and after cardiopulmonary bypass surgery by western blot analysis. Our group showed that glucagon like receptor 1 agonist (GLP-1Ra) is beneficial for cardiac remodeling and prevents fibrosis. In a permanent coronary artery ligation model, we found increased extracellular asporin expression after 30 days in border zone and scar area with GLP-1Ra treatment compared to vehicle-treatment. To further elucidate the mechanism of asporin secretion, we used H9c2 cells as well as left ventricle tissue from mice and found that asporin was predominantly present in the heavy membrane enriched fraction (8,000xg pellet from postnuclear supernatant). Sequence analysis of asporin protein using SecretomeP 2.0 server predicted asporin might use the non-conventional form of secretion (secretory autophagy). Differentiation of H9c2 cells is accompanied by autophagy and mitochondrial biogenesis, and we found that the abundance of asporin in total lysate and heavy membrane fraction decreased suggesting it could be released via secretory autophagy. Using recombinant human asporin, we demonstrated that asporin stimulates an increase in LC3 and p62 in parallel to a decrease in COX IV and SMAD2 phosphorylation, indicating mitophagy induction and a decrease in TGFβ signaling. Based on our preliminary data and sequence comparison to a previously reported human peptide, we developed a rodent asporin peptide which is predicted to induce mitophagy while decreasing TGFβ signaling to prevent fibrosis. Studies are ongoing to establish the clinical relevance of asporin in animal models of ischemic injury.