Role of microRNA-582 in cardiac signal transduction, hypertrophy and heart failure

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Heart failure still a leading cause of death worldwide. Cardiac muscle diseases (cardiomyopathies) are a major underlying cause for the development of heart failure and a substantial fraction is due to genetic causes. Mutations in human Muscle LIM protein (MLP) can lead to cardiomyopathy. Likewise, in mice, loss of MLP also results in dilated cardiomyopathy and progressive heart failure. However, despite of multiple efforts so far, the exact molecular mechanism of MLP function is still elusive.In a microRNA microarray screen performed with MLP knockout mice versus wildtype mice we identified miR-582 to be highly upregulated in MLP knockout mice. For this microRNA no cardiac function is known so far. We also observed differential regulation of miR-582 in several mouse models of cardiac hypertrophy as well as in vitro in stretched cardiomyocytes. These findings lead to the hypothesis that this microRNA might play an important role during the development or progression of cardiac muscle diseases. Interestingly, microRNA-582 is localized in an intron of the cAMP-specific 3',5'-cyclic phosphodiesterase 4D (PDE4D) gene. PDE’s control cAMP-signaling in various types of cells, including cardiomyocytes, and ablation of PDE4D leads to the development of cardiac hypertrophy in mice. We could show that the PDE4D-isoform PDE4D7 is upregulated along with microRNA-582 in MLP knockout mice.To further elucidate the function of miR-582 in the heart, we generated both transgenic mice that overexpress microRNA-582 specifically in the heart as well as a miR-582 knockout mouse line. As no cardiac phenotype for any of these mouse lines was observed at baseline, we now plan to subject MiR-582-KO mice to biomechanical stress with TAC (transverse aortic constriction) surgery, a widely used model to induce cardiac hypertrophy that eventually progresses to heart failure. Additionally we aim to crossbreed these lines to the MLP KO mice to assess if overexpression or knockout of miR-582 modulates the MLP knockout phenotype. Another important goal will be to identify relevant cardiac target genes for miR-582, which we plan to achieve by applying several methods, including Ago2-HITS-CLIP. Finally, we plan to further analyze the host gene of miR-582, PDE4D, and especially the isoform PDE4D7, which we found to be coregulated with miR-582. It is known that PDE4D plays an important role in the regulation of cardiac calcium homeostasis which is also dysregulated in MLP knockout mice. Therefore we plan to perform calcium transient measurements, to analyze the expression of calcium cycling genes and to identify the subcellular localization of PDE4D7. Taken together, we hope that our proposal will assist in the identification of new molecular mechanisms in MLP-mediated cardiomyopathy as well as general heart failure pathogenesis.