Induction of Cardiac Fibrosis by Transforming Growth Factor-β1

The role of transforming growth factor-β1 (TGF-β1) in the production and deposition of collagens and in the induction of gene expression in the myocardium in relation to the development of myocardial fibrosis will be discussed. Very low expression of TGF-β1 and collagen type I and III mRNA is seen in the normal rat heart. Both expressions are markedly increased in the infarcted heart and the levels of TGF-β1 mRNA precedes increases in mRNA levels for extracellular matrix (ECM) proteins, suggesting a possible role of TGF-β1 in remodeling processes in the myocardium. The TGF-β1 expression is normally only transient since continuous TGF-β1 overexpression seems to promote nonadaptive cardiac hypertrophy and myocardial fibrosis. In vitro, TGF-β1 induces an increase in collagen production and secretion and enhances the abundance of mRNA levels for collagen type I and III in rat cardiac fibroblasts in culture. TGF-β1 also stimulates in vivo the expression of ECM proteins and in vivo gene transfer of TGF-β1 can induce myocardial fibrosis. Increased myocardial TGF-β1 and ECM protein mRNA are found in myocardial fibrosis induced by angiotensin II infusion, by noradrenaline treatment, by isoprenaline infusion, and by long-term blockade of NO synthesis. In vivo antagonism of TGF-β1 by neutralizing anti-TGF-β1 antibodies or by proteoglycans prevents the increase in gene expression of ECM proteins and inhibits myocardial fibrosis, suggesting that the increases in matrix protein production and fibrosis are mediated by TGF-β1.