Studies on the function of Rho A protein in cardiac myofibrillogenesis

Abstract

The aim of this study was to provide morphological evidence for the presence of rho A protein in developing cardiomyocytes and to investigate its possible role in myofibrillogenesis. Immunostaining with a monoclonal anti-rho antibody gave a diffuse pattern in the cytosol of cultured cardiomyocytes. Introduction of C3 exoenzyme into the cells by electroporation was used to inactivate rho A protein by ADP-ribosylation. An immunostaining with anti-vinculin, anti-talin, and anti-integrin antibodies showed the focal adhesions in electroporation control cardiomyocytes to be evenly distributed in the ventral sarcolemma; the costameric structure was also detected using these antibodies. In contrast, in C3 exoenzyme treated cells, focal adhesions were disassembled and costamere were absent; in addition, beta-actin-positive, non-striated fibrils were lost and assembly of M-protein, titin, and alpha-actinin into myofibrils was poor, as shown by diffuse and filamentous staining pattern. C3 exoenzyme treatment had a less marked effect on mature cardiomyocytes than on immature cells; in this case, cells became distorted and few myofibrils were seen. The intensity of anti-phosphotyrosine antibody staining of the focal adhesion was also decreased or diffuse in C3 exoenzyme-treated cardiomyocytes, suggesting dephosphorylation of focal adhesion components. We therefore conclude that small G protein rho A plays an important role in myofibril assembly in cardiomyocytes.

Cardiac-specific overexpression of RhoA results in sinus and atrioventricular nodal dysfunction and contractile failure

“…Conversely, a constitutively activated mutant of RhoA induced ANF expression and the organization of actin myofilaments into sarcomeric units (11). These data, together with those of other laboratories (12)(13)(14)(15), suggested that RhoA was a mediator of hypertrophic responses in cardiomyocytes.…”

“…More recently, we and others have demonstrated that a Ras-related small G protein, RhoA, is also a key mediator of hypertrophic responses in ventricular myocytes (10)(11)(12)(13)(14)(15). RhoA belongs to the Rho subfamily of GTPbinding proteins best known for their involvement in the regulation of the actin cytoskeleton.…”

Hypertonicity triggers RhoA-dependent assembly of myosin-containing striated polygonal actin networks in endothelial cells

“…The morphological similarity between the BAEC transition from stress fiber to SPAN and actin remodeling in embryonic cardiomyofibrillogenesis suggests possible mechanistic similarity of filament reorganization. Indeed, the RhoA pathway participates in cardiac myofibrillogenesis (5,85).…”

Pleiotropic Effects of Statins

“…In the myocardium, the small GTP-binding proteins, Ras, Rho, and Rac, and oxidative stress are involved in the hypertrophic response (136,137). Indeed, recent animal studies suggest that a phagocyte-type NADPH oxidase may be a relevant source of ROSin the myocardium (138)(139)(140).…”