Insights into the deregulations of Rbm20 in Lamin A-C and emerin related cardiomyopathies -

Abstract

Cardiomyopathies are among the leading causes of premature sudden death. Their etiology is genetically heterogeneous with more than 50 genes linked to them. The most substantial mutations involved in the cardiac phenotypes are those affecting the integrity and structure of the nuclear lamina; LMNA gene coding for Lamin A-C, and EMD gene coding for the inner nuclear membrane (INM) protein emerin. Additionally, recent studies identified mutations in the RBM20 gene coding for the intracellular RNA-binding protein as highly implicated in familial cardiomyopathies. We sought to get a better understanding of how Emery-Dreifuss Muscular Dystrophy (EDMD) and Dilated Cardiomyopathy (DCM) originate from deficiency and-or mutations in the LMNA and EMD genes. Accordingly, we aimed to investigate potential deregulations in Rbm20 transcript and protein expression in addition to intracellular localization in the context of Lmna and Emd deficiency. For the purpose of this pilot study, we used mouse embryo fibroblast (MEF) lines that were derived from mice lacking the expression of either Lamin A-C (Lmna---) or emerin (Emd--Y) which have an EDMD phenotype, or mice expressing the Lmna N195K homozygote mutation (LmnaN195K-N195K) which have the DCM phenotype versus wild-type (WT) controls, under baseline conditions. We have also used Lmna null MEFs that were transduced by retroviral infection to re-express the Lmna WT or different mutant forms that result in EDMD (E358K, L530P). Real Time PCR quantification, Western Blot analysis, and immunofluorescence staining were performed on these cell lines to test for alterations in Rbm20 transcript or protein expression and intracellular localization. Rbm20 showed a significant reduction in the transcript levels in all the three mutant MEFs which was reversed upon re-expression of Lmna confirming the direct effect of lamina disruption on the expression of Rbm20. Likewise, the protein expression of Rbm20 was significantly reduced in the mutant cell lines compared to the wildtype, while there