Abstract 418: Genetic Rescue of Connexin 43 Remodeling in Muscular Dystrophy Cardiomyopathy

Abstract

Dilated cardiomyopathy has emerged as a major cause of lethality in Duchenne Muscular Dystrophy (DMD). Despite the growing influence on mortality, studies of dystrophic cardiomyopathy remain limited. We have found key evidence suggesting that aberrant expression of Connexin 43 (Cx43), a critical component of cardiomyocyte gap junctions, plays a detrimental role in DMD-cardiomyopathy. We showed Cx43 protein upregulation and lateralization away from the intercalated discs (IDs) to the lateral sarcolemma borders in both mouse (mdx) and human DMD cardiac tissues. Selective inhibition of the function of lateralized Cx43 protected Isoproterenol (Iso) challenged mdx mice from severe arrhythmias. We determined that Cx43 in mdx hearts is hypo-phosphorylated in a specific triplet of serine residues (S325/S328/S330). Reduction of phosphorylation in this same triplet promotes Cx43 lateralization and has been directly linked to cardiac ischemia, hypertrophy and arrhythmias. To investigate the role of the serine-triplet toward Cx43 remodeling and DMD cardiac pathology, we generated knock-in mutant mdx mice where the serine-triplet was modified to either non-phosphorylatable alanine (mdx:S3A) or phospho-mimetic glutamic acid residues (mdx:S3E). The changes in Cx43 phosphorylation status were confirmed by immunoblotting wherein mdx:S3E cardiac extracts prominently display slowly-migrating phosphorylated Cx43 bands while mdx:S3A extracts display a faster migrating isoform. We observed that 4 month-old mdx:S3E mice are protected from arrhythmias upon Iso challenge. Unlike mdx and mdx:S3A, mdx:S3E cardiomyocytes displayed strong Cx43 co-localization with N-Cadherin at the IDs, demonstrating improved Cx43 gap junction targeting. Together, these results suggest that the Cx43-serine triplet contributes toward Cx43 localization and cardiac dysfunction in mdx mice. This project will help identify possible molecular targets for pharmaceutical treatments to protect against cardiac failure and extend the lives of DMD patients.