Collagen VI and endotrophin: potential extracellular matrix targets to attenuate adverse cardiac remodeling post-infarction

Abstract Background The extracellular matrix (ECM) is a key component of cardiac repair after myocardial infarction (post-MI). After tissue damage following myocardial ischaemia, the ECM becomes enriched in proteases that are known to induce partial enzymatic cleavage and fragmentation of native structural and fibrillar macromolecules such as collagens. While some of the resulting protein fragments (matrikines) may have beneficial effects by mediating an active scar formation, other such as the collagen VI (COL6) proteolytic component "endothrophin" has been related to deleterious evolution and fibrosis, particularly in the presence of cardiovascular risk factors. Purpose We aimed to investigate the collagen profile in the structural fraction of ECM (enriched in fibrillar and structural proteins) of post-MI hearts at late evolution stages after MI. Methods The ECM protein profile was investigated in the ischemic (ISCH) and non-ischemic (NISCH) zones of the post-MI myocardium in pigs. MI was induced by closed-chest balloon occlusion of the LAD for 90 minutes. Studies were performed in normo- and hypercholesterolemic (diet induced) animals. Myocardial tissue was obtained 30d after MI. ECM proteins were selectively extracted, identified by LC/MS-MS and validated by Western Blot. Plasma levels of endothrophin were quantified by ELISA. Myocardial tissue from the same areas was characterized by immunohistochemistry. Results The ECM in the ISCH zone showed a differential signature of 39 proteins (14 upregulated / 25 downregulated) 30 days after MI compared to the NISCH area of the same animals. In the ISCH region, significant changes in collagen referring to COL6A3 and COL6A1 (increase) and COL6A2 and COL6A6 (decrease) were detected. COL6A3 protein content was 1.8fold higher (p=0.01) in the ISCH-ECM. A similar increase was found in normo- and hypercholesterolemic animals. A higher trend in COL6A3 levels was found in the ISCH- vs, the NISCH-zone in the myocardial cellular fraction suggesting that the COL6 ECM-related increase in ISCH is produced at a transcript level. Importantly, the COL6A3 found in the ECM did not contain the protein peptide (C5 domain) corresponding to endotrophin matrikine, suggesting its cleavage and release. Using a specific ELISA, hypercholesterolemic animals showed significantly higher endothrophin plasma levels than normolipemic controls (p=0.003) even in the absence of MI. Conclusion Our results evidence an increase in COL6A3 content in the ECM of the ischemic myocardium at 30 days post-MI. COL6A3 is depleted in a peptide of the C5 domain corresponding to endotrophin, found to be enhanced in hypercholesterolemia. These findings support a role for collagen type VI in adverse cardiac remodeling post-MI.