Expression of a Mutant Lamin A That Causes Emery-Dreifuss Muscular Dystrophy Inhibits In Vitro Differentiation of C2C12 Myoblasts

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Abstract
Autosomal dominantly inherited missense mutations in lamins A and C cause several tissue-specific diseases, including Emery-Dreifuss muscular dystrophy (EDMD) and Dunnigan-type familial partial lipodystrophy (FPLD). Here we analyze myoblast-to-myotube differentiation in C2C12 clones overexpressing lamin A mutated at arginine 453 (R453W), one of the most frequent mutations in EDMD. In contrast with clones expressing wild-type lamin A, these clones differentiate poorly or not at all, do not exit the cell cycle properly, and are extensively committed to apoptosis. These disorders are correlated with low levels of expression of transcription factor myogenin and with the persistence of a large pool of hyperphosphorylated retinoblastoma protein. Since clones mutated at arginine 482 (a site responsible for FPLD) differentiate normally, we conclude that C2C12 clones expressing R453W-mutated lamin A represent a good cellular model to study the pathophysiology of EDMD. Our hypothesis is that lamin A mutated at arginine 453 fails to build a functional scaffold and/or to maintain the chromatin compartmentation required for differentiation of myoblasts into myocytes.