Abstract P336: Constitutive Activation of ROCK1 in Mouse Heart Leads to Fibrotic Cardiomyopathy

Background: Our previous study demonstrated that genetic deletion of ROCK1 inhibited stress-induced cardiac fibrosis and ROCK1 was cleaved by caspase 3 into a constitutively active Rho kinase isoform, ROCKΔ1 that led to increase in Rho kinase activity in human failing hearts. However, the function of truncated ROCK1 accumulated in human failing myocardium and the molecular signaling linked between ROCKΔ1 and cardiac remodeling remain obscure. Methods and Results: To recapitulate this human pathophysiological situation and define the pathogenic role of ROCKΔ1 in heart, we generated transgenic mice expressing ROCKΔ1 in heart. Significant increase in Rho kinase activity was achieved. The mice developed fibrotic cardiomyopathy along with upregulation of TGFβ1 and NF-κB signaling. Significant increases in fibrotic factors were observed. Echocardiography revealed diastolic dysfunction in the transgenic heart. The transgenic mice were predisposed to angiotensin II treatment that led to massive fibrotic cardiomyopathy. Rho kinase inhibitor Fasudil treatment attenuated the fibrotic maladaption. To elucidate the molecular mechanism underlying ROCKΔ1-mediated fibrotic cardiomyopathy, wild-type cardiac fibroblasts were co-cultured with transgenic cardiomyocytes. Large amount of fibroblasts were activated and induced to express α-SMA by the transgenic cardiomyocytes but not by the wild-type control cardiomyocytes. Addition of Rho kinase, TGFβR1 and NF-κB inhibitors to the culture media attenuated the fibroblast activation. The results suggested that the pro-fibrotic TGFβ and NF-κB signaling are responsible for ROCKΔ1-mediated fibrotic cardiomyopathy. Finally, we demonstrated TGFβ1 was a SRF (serum response factor) new target gene. EMSA, luciferase and CHIP assay revealed SRF binding to TGFβ1 promoter. Genetic deletion of SRF in mouse heart resulted in marked decrease in TGFβ1 expression. Conclusions: Our studies demonstrated the pro-fibrotic role of truncated ROCK1 in vivo and provided an animal model that recapitulated human heart failure. The results elucidated that activation of NF-κB and TGFβ1 signaling contributed to Rho kinase-mediated fibrotic cardiomyopathy, the later was regulated by SRF.