Abstract 19449: Upregulation of Cofilin-2 in Mouse Models Of DCM - Implications for SRF Signaling

Abstract

The dilated cardiomyopathy (DCM) is a major cause for heart failure. A causative genetic background is suspected in up to 50% of all DCM cases. However, the underlying molecular pathways remain incompletely understood. Here we analyze a calsarcin-1 deficient (CS1ko) mouse line as a model for DCM. These mice showed strong upregulation of fetal genes (e.g., Nppa, Nppb ) and the calcineurin-dependent gene Rcan1.4. Interestingly, we could not detect any signes of hypertrophy. In addition, there was no increase of fibrosis in CS1ko mice compared to wildtype controls. A screening experiment revealed upregulation of Cofilin2 (Cfl2), an actin depolymerisation factor and member of the ADF/Cofilin family, in Cs1ko mice (2.6-fold, p<0.002), whereas its inactive, phosphorylated form (Ser3) remained unchanged. We also found increased amounts of Cfl2 in MLP-/- (1,8-fold p<0.05) and Calcineurin TG mice (2.7-fold p<0.01) suggesting a general role for Cfl2 in DCM. As Cfl2 is a known regulator of actin dynamics we investigated the role of Cfl2 in SRF signaling. Using an SRF-responsive luciferase reporter, overexpression of Cfl2 together with RhoA as activator of SRF signaling lead to an increase of SRF activity in C2C12 myoblasts (14-fold vs. 5.8-fold with RhoA alone, p<0.001). SiRNA-mediated knockdown of Cfl2 yielded opposite effects (0.96-fold vs. 4.6-fold, p<0.001). In the heart Cfl2 is predominantly expressed in cardiac myocytes as compared to fibroblasts. Overexpression of Cfl2 in cardiomyocytes (NRVCM) revealed an increase of Nppa and Nppb , which could be further increased by co-stimulation with phenylephrine (PE). In contrast to these findings, cell size analysis revealed a Cfl2-mediated decrease in cell size with and without PE, while knockdown of Cfl2 did not influence cellular hypertrophy. Taken together, our data imply a role for Cfl2 in the pathogenesis of DCM. Cs-1ko mice show a dilated phenotype, strong upregulation of the fetal gene program without a change in cell size. This correlates with the findings of overexpression of Cfl2 in NRVCM. Furthermore, increased Cfl2 levels induce SRF activity with potential influence on cardiomyocyte function. Further analyses are required to delineate the involved molecular pathways.