Post-ischemic myocardial fibrosis occurs independent of hemodynamic changes

Objectives: Myocardial fibrosis is a major component of ventricular remodeling after large myocardial infarction (MI). The present study tests the hypothesis that post-ischemic myocardial fibrosis can occur independent of hemodynamic changes. Methods: A mouse model of distal left coronary artery ligation was established to induce a small infarct (less than 15% of the left ventricle) in order to avoid significant mechanical overload after permanent myocardial ischemia. Left heart catheterization was performed to evaluate the post-infarct hemodynamics. Tissues from both ischemic and non-ischemic myocardium were examined for mRNA and protein expression at 24, 72 h and 7 days after ligation. Results: Heart/body weight ratio after ligation was increased by approximately 10% over sham control although there is no statistically significant difference in hemodynamic parameters between the two groups. Non-ischemic myocardium distant from the infarct site showed molecular evidence of myocardial fibrosis 72 h and 7 days after ligation. There was marked up-regulation of mRNAs for extracellular matrix (ECM) proteins and their cross-linking enzyme, such as collagens type I, III and VI, and lysyl oxidase. Immunohistochemical study confirmed that the expression of these ECM proteins was significantly increased in the non-ischemic myocardium after 7 days. TGF-β1 was up-regulated after 72 h in both ischemic and non-ischemic myocardium. Conclusions: Molecular and histopathological findings demonstrate that abnormal myocardial fibrosis can be induced by a small infarct independent of secondary hemodynamic changes.