Changes in Extracellular Matrix and in Transforming Growth Factor Beta Isoforms After Coronary Artery Ligation in Rats

Extensive myocardial remodeling occurs after transmural myocardial infarction (MI). The infarcted myocardium is being replaced by scar tissue after gradual resorption of the necrotic tissue. The remodeling process involves both synthesis and degradation of collagens as major components of the extracellular matrix (ECM). In the present study we have analyzed the time-dependent changes of the processes related to this fibrosis in the infarct area and in the non-infarcted left ventricle (LV) six hours to 82 days after occlusion of the left anterior descending coronary artery (LAD) in rats. We also examined whether changes occurred in the expression pattern of the transforming growth factor (TGF) β isoforms, since this cytokine is known as powerful inductor of fibrosis. Elevation in colligin expression preceded the pronounced increase in mRNA expression of both type I and type III collagen after MI from day three onwards. The maximal increase in colligin protein in the infarct area coincided with the most pronounced expression of collagen I and collagen III mRNA expression. Also, the expression and activity of matrix metalloproteinases (MMPs) and of tissue inhibitor of matrix metalloproteinase (TIMP)-2 mRNA were increased predominantly in the infarct area. TGF β1and TGF- β2expression increased within the first days after MI, whereas TGF- β3expression was elevated predominantly in the infarct area. This pronounced increase in TGF- β3persisted up to 82 days and correlated positively with the parameters of ECM metabolism. Thus, the scar formation is an ongoing dynamic process in which TGF- β3seems to play an active role in the complex ventricular remodeling.