The small leucine-rich proteoglycan fibromodulin exerts anti-fibrotic effects in cultured human cardiac fibroblasts
Cardiac fibrosis is common and detrimental in numerous heart diseases, affecting millions of patients worldwide. Cardiac fibrosis is characterized by excessive production of extracellular matrix (ECM) constituents such as fibrillar collagens, produced by activated cardiac fibroblasts, i.e.: myofibroblasts. Therapeutic targeting of cardiac fibrosis is highly attractive; however, it remains a major medical challenge. Fibromodulin is a small leucine-rich proteoglycan localized in the ECM. Fibromodulin binds to collagen fibrils, and plays a critical role in collagen fibrillogenesis, ECM organization, wound healing and regulation of the pro-fibrotic cytokine transforming growth factor beta (TGFβ) in several organs. Fibromodulin is highly upregulated in mice and patients with heart failure, but little is known about its role in cardiac fibrosis. Our recent findings from primary cultures of cardiac fibroblasts from neonatal rat hearts suggest that fibromodulin has anti-fibrotic effects. Here we investigated the translational value of these findings by overexpressing fibromodulin in cultured human fetal and adult cardiac fibroblasts. The effects of fibromodulin overexpression on gene expression were measured by qPCR and gene arrays, whereas protein levels were measured by Western blotting, and collagen synthesis by radioactive proline incorporation. The results support our previous findings and indicate relevance for human disease. We found that fibromodulin reduced the expression levels of the collagen cross-linking enzymes lysyl oxidase (LOX) and transglutaminase 2 (TGM2). Fibromodulin also reduced the levels of connective tissue growth factor (CTGF) and periostin (POSTN), indicating reduced TGFβ activity. Reduced levels of intercellular adhesion molecule 1 (ICAM1) and vascular cell adhesion molecule 1 (VCAM1) suggested reduced potential for immune cell adhesion, and gene arrays indicated altered integrin expression, suggesting altered ECM-cell adhesion. Expression of fibrillar collagens was unaffected. In conclusion, fibromodulin reduced TGFβ activity and down-regulated central collagen-crosslinking enzymes, in line with an anti-fibrotic effect of fibromodulin in human cardiac fibroblasts.