Haploinsufficient Rock1(+/−) and Rock2(+/−) Mice Are Not Protected from Cardiac Inflammation and Postinflammatory Fibrosis in Experimental Autoimmune Myocarditis

Progressive cardiac fibrosis is a common cause of heart failure. Rho-associated, coiled-coil-containing protein kinases (ROCKs) have been shown to enhance fibrotic processes in the heart and in other organs. In this study, using wild-type, Rock1(+/−) and Rock2(+/−) haploinsufficient mice and mouse model of experimental autoimmune myocarditis (EAM) we addressed the role of ROCK1 and ROCK2 in development of myocarditis and postinflammatory fibrosis. We found that myocarditis severity was comparable in wild-type, Rock1(+/−) and Rock2(+/−) mice at day 21 of EAM. During the acute stage of the disease, hearts of Rock1(+/−) mice showed unaffected numbers of CD11b(+)CD36(+) macrophages, CD11b(+)CD36(–)Ly6G(hi)Ly6c(hi) neutrophils, CD11b(+)CD36(–)Ly6G(–)Ly6c(hi) inflammatory monocytes, CD11b(+)CD36(–)Ly6G(–)Ly6c(–) monocytes, CD11b(+)SiglecF(+) eosinophils, CD11b(+)CD11c(+) inflammatory dendritic cells and type I collagen-producing fibroblasts. Isolated Rock1(+/−) cardiac fibroblasts treated with transforming growth factor-beta (TGF-β) showed attenuated Smad2 and extracellular signal-regulated kinase (Erk) phosphorylations that were associated with impaired upregulation of smooth muscle actin alpha (αSMA) protein. In contrast to cardiac fibroblasts, expanded Rock1(+/−) heart inflammatory myeloid cells showed unaffected Smad2 activation but enhanced Erk phosphorylation following TGF-β treatment. Rock1(+/−) inflammatory cells responded to TGF-β by a reduced transcriptional profibrotic response and failed to upregulate αSMA and fibronectin at the protein levels. Unexpectedly, in the EAM model wild-type, Rock1(+/−) and Rock2(+/−) mice developed a similar extent of cardiac fibrosis at day 40. In addition, hearts of the wild-type and Rock1(+/−) mice showed comparable levels of cardiac vimentin, periostin and αSMA. In conclusion, despite the fact that ROCK1 regulates TGF-β-dependent profibrotic response, neither ROCK1 nor ROCK2 is critically involved in the development of postinflammatory fibrosis in the EAM model.