Calsarcin-1 deficient mice develop dilated cardiomyopathy (DCM) phenotype in pure C57BL/6 genetic background (Cs1-ko) despite severe contractile dysfunction and robust activation of fetal gene program. Here we performed a microRNA microarray to identify the molecular causes of this cardiac phenotype that revealed the dysregulation of several microRNAs including miR-301a, which was highly downregulated in Cs1-ko mice compared to the wild-type littermates. Cofilin-2 (Cfl2) was identified as one of the potential targets of miR-301a using prediction databases, which we validated by luciferase assay and mutation of predicted binding sites. Furthermore, expression of miR-301a contrastingly regulated Cfl2 expression levels in neonatal rat ventricular cardiomyocytes (NRVCM). Along these lines, Cfl2 was significantly upregulated in Cs1-ko mice, indicating the physiological association between miR-301a and Cfl2 in vivo. Mechanistically, we found that Cfl2 activated serum response factor response element (SRF-RE) driven luciferase activity in neonatal rat cardiomyocytes and in C2C12 cells. Similarly, knockdown of miR301a activated, whereas, its overexpression inhibited the SRF-RE driven luciferase activity, further strengthening physiological interaction between miR-301a and Cfl2. Interestingly, the expression of SRF and its target genes was strikingly increased in Cs1-ko suggesting a possible in vivo correlation between expression levels of Cfl2/miR-301a and SRF activation, which needs to be independently validated. In summary, our data demonstrates that miR-301a regulates Cofilin-2 in vitro in NRVCM, and in vivo in Cs1-ko mice. Our findings provide an additional and important layer of Cfl2 regulation, which we believe has an extended role in cardiac signal transduction and dilated cardiomyopathy presumably due to the reported involvement of Cfl2 in these mechanisms.

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.