Abstract 236: Rho Kinase-1 Mediates Cardiac Fibrosis by Regulating Fibroblast Precursor Cell Differentiation
We recently described a critical role for highly proliferative, CD34+, CD45+ fibroblasts derived from monocytic, blood-borne fibroblast precursors in the development of fibrosis in a murine ischemic/reperfusion cardiomyopathy model (I/RC). In addition, in vitro experiments with human monocytes (PBMC) demonstrated that monocyte differentiation into fibroblasts required MCP-1-induced transendothelial migration (TEM). Since Rho kinase-1 (ROCK-1) has been implicated in another model of cardiac fibrosis, we investigated the involvement of ROCK-1 in I/RC. We demonstrate that mice that lack expression of ROCK-1 (ROCK-1−/− mice) did not develop the fibrosis and cardiac dysfunction typical of I/RC. Compared to wild-type, ROCK-1−/− hearts showed markedly lower numbers of I/RC-induced α-smooth muscle actin+ fibroblasts and CD34+, CD45+ fibroblast precursors. Isolated cardiac fibroblasts were large and slowly proliferating, similar to fibroblasts isolated from sham treated hearts. To further examine the role of ROCK-1, we performed in vitro assays in which human PBMC migrated through HUVEC in response to MCP-1. Prior to migration, PBMC were incubated with siRNA to knock down ROCK-1 protein expression. We found that a 80% reduction of ROCK-1 protein in PBMC did not inhibit TEM, but markedly reduced the amount of mononuclear cells that differentiated into fibroblasts (by 95%), indicating that ROCK-1 was necessary for fibroblast formation but not for TEM. Together, our data implicate an important role for ROCK-1 in the differentiation of a blood-borne, myeloid cell population into cardiac fibroblasts and demonstrate that its deletion inhibits cardiac fibrosis.