Abstract
Increases in cardiovascular load (pressure overload) are known to elicit ventricular remodeling including cardiomyocyte hypertrophy and interstitial fibrosis. While numerous studies have focused on the mechanisms of myocyte hypertrophy, comparatively little is known regarding the response of the interstitial fibroblasts to increased cardiovascular load. Fibroblasts are the most numerous cell type in the mammalian myocardium and have long been recognized as producing the majority of the myocardial extracellular matrix. It is only now becoming appreciated that other aspects of fibroblast behavior are important to overall cardiac function. The present studies were performed to examine the temporal alterations in fibroblast activity in response to increased cardiovascular load. Rat myocardial fibroblasts were isolated at specific time-points (3, 7, 14, and 28 days) after induction of pressure overload by abdominal aortic constriction. Bioassays were performed to measure specific parameters of fibroblast function including remodeling and contraction of 3-dimensional collagen gels, migration, and proliferation. In addition, the expression of extracellular matrix receptors of the integrin family was examined. Myocardial hypertrophy and fibrosis were evident within 7 days after constriction of the abdominal aorta. Collagen gel contraction, migration, and proliferation were enhanced in fibroblasts from pressure-overloaded animals compared to fibroblasts from sham animals. Differences in fibroblast function and protein expression were evident within 7 days of aortic constriction, concurrent with the onset of hypertrophy and fibrosis of the intact myocardium. These data provide further support for the idea that rapid and dynamic changes in fibroblast phenotype accompany and contribute to the progression of cardiovascular disease.