Involvement of the renin-angiotensin system in the development of left ventricular hypertrophy and dysfunction

Abstract

Objectives: To elucidate the regulation of cardiac gene expression by mechanical stress and to analyse molecular mechanisms associated with the involvement of angiotensin II (Ang II) in the development of cardiac hypertrophy and dysfunction.

Methods: Neonatal rat cardiocytes were cultured in deformable silicone dishes, and mechanical stress was imposed on the cardiocytes by stretching them. In in vivo studies, spontaneously hypertensive rats (SHR) were treated with a non-peptide, specific Ang II type 1 receptor antagonist, TCV 116.

Results: Expression of the c-fos gene was rapidly induced, and fetal type genes such as skeletal alpha actin and beta myosin heavy chain genes were re-expressed by stretching. The mechanical stress decreased the expression of Ca(2+)-ATPase in the sarcoplasmic reticulum. With regard to signals for the development of cardiac hypertrophy, mechanical stress evoked c-fos expression via the activation of protein kinase C. The phosphorylation cascade (sequential activation of protein kinase C, Raf-1 kinase, mitogen-activated protein kinase kinase, mitogen-activated protein kinase and S6 kinase), which may be involved in protein synthesis and gene expression, was activated by mechanical stress in cardiocytes. Stretch-induced cardiac cellular hypertrophy was partially inhibited by TCV 116. TCV 116 treatment of SHR reduced left ventricular weight, left ventricular wall thickness, myocyte transverse diameter, V3 myosin heavy chain levels and the interstitial collagen volume fraction.

Conclusions: These results indicate that AngII may, in part, mediate the stretch-induced hypertrophic growth of cardiomyocytes via the type 1 Ang II receptor.