P97Cyclic stretch induces connective tissue growth factor expression in isolated adult rabbit cardiomyocytes

Abstract

Introduction: A chronic increase in cardiac workload leads to hypertrophic growth of cardiomyocytes, often accompanied by accumulation of extracellular matrix (fibrosis). This structural remodeling of the myocardial wall impairs cardiac function and may eventually lead to heart failure. Connective Tissue Growth Factor (CTGF, CCN2) is considered to play an important role in cardiac structural remodeling. We studied whether stretch is a primary stimulus to induce CTGF expression in vivo in rabbit heart, and in vitro in isolated adult rabbit cardiomyocytes and fibroblasts. Methods: Cardiac function, structural remodeling and CTGF expression were studied in a rabbit model of combined pressure and volume overload. Furthermore, CTGF expression was investigated in cardiomyocytes and fibroblasts isolated from adult rabbit hearts, cultured and subjected to 10% cyclic equibiaxial stretch (1Hz) using the Flexcell FX4000 strain unit for up to 48 h. Results: Twenty weeks of combined volume and pressure overload resulted in eccentric left ventricular (LV) hypertrophy, with increased LV internal diameter (+36%) and LV weight (+53%). In the overloaded animals, myocardial CTGF mRNA levels were increased 5-fold and Western blot analyses showed a substantial increase in myocardial CTGF protein levels. In isolated adult rabbit cardiomyocytes, cyclic stretch strongly induced CTGF mRNA expression (2.9-fold at 48h), whereas CTGF-induction in cardiac fibroblasts was transient and modest (1.4-fold after 4h). Conditioned medium from stretched fibroblasts induced CTGF mRNA expression in non-stretched cardiomyocytes (2.3-fold at 48h). Conclusion: Our results show that cyclic stretch is a primary and strong stimulus to increase CTGF expression in isolated cardiomyocytes, and indicate that the elevated expression of CTGF in the overloaded heart is derived from mechanically stimulated cardiomyocytes.