The Inflammatory Transcription Factor C/EBPβ Plays a Critical Role in Cardiac Fibroblast Differentiation and a Rat Model of Cardiac Fibrosis Induced by Autoimmune Myocarditis

The aim of the present study was to investigate the mechanisms of CCAAT/enhancer-binding protein β (C/EBPβ) in cardiac myofibroblast (CMF) differentiation and in a rat model of cardiac fibrosis induced by experimental autoimmune myocarditis (EAM).In vitro studies performed in primary neonatal rat CMF revealed that silencing of C/EBPβ expression (via lentiviral mediated shRNA strategies) was sufficient to reduce C/EBPβ mRNA and protein levels as well as to decrease the expressions of actin cytoskeletal proteins, cofilin, and filamin A (FLNA). TGFβ increased IL-1β, IL-6 and TNF-a production in cardiac fibroblasts (CF), while C/EBPβ knockdown reduced the secretion of these inflammatory mediators. In vivo studies performed in rats exhibiting EAM revealed that lentiviral-mediated silencing of C/EBPβ was sufficient to reduce the expression of C/EBPβ as well as inflammation and fibrosis in the hearts of EAM rats, when compared to controls. Echocardiography further revealed that C/EBPβ knockdown was sufficient to significantly improve cardiac dimensions and function in EAM rats. Immunohistochemical results showed that C/EBPβ knockdown attenuated the expression of C/EBPβ protein as well as the expressions of collagen I, collagen III, MMP-2, MMP-9, and α-SMA in heart tissue sections from rats in the EAM + Lenti-shC/EBPβ group.Strategies targeted at inhibiting C/EBPβ expression can be potentially exploited to regulate cofilin and FLNA expression, thereby regulating actin polymerization/depolymerization, cytoskeleton rearrangement, and CF differentiation into CMF and the production of inflammatory cytokines. C/EBPβ knock down reduces the degree of inflammation-mediated myocardial fibrosis in a rat model of EAM.