Résumé :
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RATIONALE: Alterations in the balance between sarcomeric and extra-sarcomeric cytoskeleton as well as energetic proteins are involved in the remodelling of cardiomyocytes cytoarchitecture in dilated cardiomyopathy (DCM). OBJECTIVE: Inactivation in the adult mouse heart of the Serum Response transcription Factor (SRF) that regulates muscle genes, provides a time-course model of DCM. We used 2D-DIGE proteomics as a discovery approach to identify key molecular changes taking place during cardiac dilation. RESULTS: Sarcomeric proteins and M-creatine kinase, encoded by direct SRF target genes were the primary down-regulated proteins in the mutant heart. On the contrary, _B-crystallin (CryAB), a chaperone of the cytoskeleton, and desmin, the muscle intermediate filament (IF), were up-regulated and phosphorylated. In vivo, phospho-CryAB was specifically recruited at the deficient F-actin while desmin network was progressively disorganized in the dilated heart. We found that desmin is a preferential target of advanced glycation end-products (AGE) in dilated hearts of SRF-KO and human patients. To decipher the molecular cascade leading to these phenotypes, we performed a series of experiments in cultured neonatal cardiomyocytes. We show that inhibition of creatine phosphorylation with bGPA is sufficient to trigger actin depolymerization and AGE modification of desmin. Short-term 30 min treatment of cells with glyoxal, an AGE product, or cytochalasin-D (Cyto-D), which disrupts F-actin, severely disorganize desmin network. Both treatments activate CryAB phosphorylation. We show that if we pre-activate phospho-CryAB by heat-shock before treatment with glyoxal or cytochalasin, desmin network is protected. However, longer treatment with cyto-D (6h) leads to preferential recruitment of phospho-CryAB at the collapsing actin filaments and desmin is not protected anymore. CONCLUSION: Remodelling of cardiomyocyte cytoskeleton networks is a typical feature of dilated cardiomyopathy and all types of cardiac remodelling in general. Our study recapitulates the cascade of events that take place when proteins of the sarcomere are affected and the subsequent impact on the extrasarcomeric desmin network. In addition, we show that desmin is sensitive to AGE modification, which could play an important role in cardiac dilation because it alters the organization of the main cardiac IF network that normally supports stress response and mitochondrial functions in cardiomyocytes.
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