Fibronectin is an extracellular matrix glycoprotein with a regulatory role in fundamental cellular processes. Recent reports on the cardioprotective effect of fibronectin inhibition in a setting of myocardial injury suggest a role for fibronectin in cardiac fibroblast function, which remains largely unexplored. This study probed the molecular basis and functional implications of fibronectin gene expression in cardiac fibroblasts exposed to Angiotensin II, a potent pro-fibrotic factor in the myocardium. Using gene knockdown and over-expression approaches, western blotting and promoter pull-down assay, we show that collagen type I-activated Discoidin Domain Receptor 2 (DDR2) mediates Angiotensin II-stimulated transcriptional up-regulation of fibronectin expression by Yes-activated Protein in cardiac fibroblasts. Further, siRNA-mediated fibronectin knockdown attenuated Angiotensin II-dependent expression of anti-apoptotic cIAP2 and promoted cell death under oxidative stress. Fibronectin was also found to mediate Angiotensin II-stimulated collagen type I expression. Importantly, an obligate role for fibronectin was observed in Angiotensin II-stimulated expression of its receptor, AT1R, which would link ECM signalling and Angiotensin II signalling in cardiac fibroblasts. Moreover, the regulatory role of DDR2-dependent fibronectin expression in Ang II-stimulated cIAP2, collagen type I and AT1R expression was mediated by Integrin-β1-integrin-linked kinase signalling. The pro-survival role of fibronectin in cardiac fibroblasts and its regulatory role in collagen and AT1R expression, downstream of DDR2, could be critical determinants of cardiac fibroblast-mediated wound healing following myocardial injury. Our findings point to a complex mechanism of regulation of cardiac fibroblast function involving two major extracellular matrix proteins, collagen type I and fibronectin, and their receptors, DDR2 and Integrin-β1.
Effect of angiotensin II receptor blocker on TGF-β1, MMP-1, and collagen type I and type III concentration in New Zealand rabbit urethral stricture model