Impact of cofilin 1-associated alterations on right ventricular mouse cardiomyocytes and fibroblasts

Background

Cardiac hypertrophy is characterized by increased thickening of the ventricular wall in response to overload associated with hypertension, ischemic heart disease and other cardiovascular diseases. Actin filament dynamics and reorganization play an essential role in the formation of sarcomeres und contractile function in muscle and are therefore affected by pressure-overload induced cardiac hypertrophy or failure. Cofilin 1 and 2 are part of the ADF/cofilin-family, which act as actin binding proteins and are able to accelerate depolymerisation of actin filaments. Here, we investigated whether cofilin 1 is involved in hypertrophic remodeling in mouse cardiac cells.

Methods

Expression of Cofilin 1 (Cfl-1) mRNA and protein was analyzed in right ventricular (RV) mouse cardiomyocytes, fibroblasts and endothelial cells following pulmonary artery banding (PAB) or sham surgery. Mice with an inducible, cardiomyocyte-specific knockout of Cfl-1 (Cofilin 1^flox/flox Tg x Myh6-cre/Esr1*)1Jmk) were generated and tamoxifen was administered to induce the knockout in order to analyze the functional impact of Cfl-1 on cardiomyocytes and fibroblasts.

Results

Cfl-1 is the main isoform in cardiac fibroblasts, but not in cardiomyocytes, which largely express Cfl-2. In PAB mice, we could show that RV overload leads to increased expression and phosphorylation (Ser3) of Cfl-1, not only in cardiac fibroblasts, but also in right ventricular cardiomyocytes compared to cells from sham animals. Cfl-2 expression was not altered in any of the investigated RV cell types following PAB. Similar effects on Cfl-1 were observed under hypoxia, but not under conditions of diet-induced obesity. Neuroendocrine stimulation with angiotensin II and endothelin, representing a conceivable neuroendocrine situation in heart failure, had similar Cfl-1 inducing effects in fibroblasts and cardiomyocytes. Knockdown of Cfl-1 leads to increasing F-actin (microscopy, G-actin/F-actin in vivo assay) suggesting an actin depolymerizing function of Cfl-1 in fibroblasts. Cfl-1 knockdown in mouse cardiomyocytes also leads to an increase in F actin. These cardiomyocytes showed lower BNP and ß-MHC mRNA expression than wild-type cells under basal conditions (without overload). However, Cfl-1 downregulation did not change the protein expression of SERCA and NCX, other genes typically altered in cardiomyocytes in heart failure.

Conclusions

Cofilin 1 and 2 are relevant players in actin dynamics and alterations in cofilin function are associated with heart failure and idiopathic dilated cardiomyopathy. Hemodynamic stress and neuroendocrine activation in heart failure are able to induce changes in cofilin isoform expression towards Cfl-1. Cfl-1 downregulation alters actin polymerization but has no strong effect on the expression of typical load-induced cardiac genes under basal conditions (no in vivo pressure overload). Future studies will investigate the impact of Cfl-1 loss on RV hypertrophy and failure.