CTGF Expression is Induced by TGF- β in Cardiac Fibroblasts and Cardiac Myocytes: a Potential Role in Heart Fibrosis

Connective tissue growth factor (CTGF) is a cysteine-rich protein induced by transforming growth factor beta (TGF- β) in connective tissue cells. CTGF can trigger many of the cellular processes underlying fibrosis, such as cell proliferation, adhesion, migration and the synthesis of extracellular matrix; however, its role in acute and chronic cardiac injury is not fully understood. Here, we show that TGF- β is a specific inducer of CTGF expression in both cardiac fibroblasts and cardiac myocytes. The activity of a CTGF promoter-based reporter construct correlated with endogenous CTGF expression, suggesting that TGF- β induces CTGF expression most likely by activating its promoter. Upregulation of CTGF coincided with an increase in fibronectin, collagen type I and plasminogen activator inhibitor-1 production. Forskolin, a stimulator of cyclic AMP, blocked TGF- β induced CTGF expression and reduced the basal level of CTGF, whereas an inhibitor that blocks the MAP kinase signaling pathway (PD 98059) significantly enhanced TGF- β induced CTGF expression. Furthermore, we found that both TGF- β and CTGF mRNAs were significantly elevated in the left ventricles and septa of rat hearts 2–16 weeks following myocardial infarction. This correlated well with concomitant increases in fibronectin, and type I and type III collagen mRNA levels in these animal hearts. Significant upregulation of CTGF was also detected in human heart samples derived from patients diagnosed with cardiac ischemia. Based on these findings, we propose that CTGF is an important mediator of TGF- β signaling in the heart and abnormal expression of this gene could be used as a diagnostic marker for cardiac fibrosis.