Fraidenraich, D. | bioRxiv Science

bioRxiv2022

Microtubule-Connexin-43 regulation suppresses arrhythmias and fibrosis in Duchenne muscular dystrophy mice.

Dilated cardiomyopathy is the leading cause of death in Duchenne muscular dystrophy (DMD) patients due to advancements in skeletal muscle therapies yet limited presence of cardiac treatments. The phosphorylation status of gap junction protein Connexin-43 (Cx43) drives Cx43 remodeling and the development of arrhythmias and fibrosis. Based on evidence that Colchicine drug treatment improves Cx43 phosphorylation and remodeling, we compared the microtubule cytoskeleton in DMD mice (mdx) versus mdx mice genetically altered to be Cx43-phosphorylation-deficient (mdxS3A). Reciprocally, we analyzed the microtubule cytoskeleton in mdx mice genetically altered to be Cx43-phospho-mimicking (mdxS3E). We found a link between the phospho-status of Connexin-43 and regulation of microtubule organization, in which phospho-dead Cx43 (S3A) inhibits improvements seen with Colchicine treatment in mdx mice, and phospho-mimic S3E promotes microtubule reorganization in mdx mice. A reduction in arrhythmias and fibrosis suggests an unsuspecting Cx43-microtubule link for translational corrective activities for DMD cardiomyopathy.

cell biology↗

bioRxiv2022

Remodeled Connexin 43 hemichannels alter cardiac excitability and promote arrhythmias

Connexin-43 (Cx43) is the most abundant protein forming gap junction channels (GJCs) in cardiac ventricles. In multiple cardiac pathologies, including hypertrophy and heart failure, Cx43 is found remodeled at the lateral side of the intercalated discs of ventricular cardiomyocytes. Remodeling of Cx43 has been long linked to spontaneous ventricular arrhythmia, yet the mechanisms by which arrhythmias develop are still debated. Using a model of a dystrophic cardiomyopathy, we previously showed that remodeled Cx43 function as aberrant hemichannels (non-forming GJCs) that alter cardiomyocyte excitability and, consequently, promote arrhythmias. Here, we aim to evaluate if opening of remodeled Cx43 can serve as a general mechanism to alter cardiac excitability independent of cellular dysfunction associated with a particular cardiomyopathy. To address this issue, we used a genetically modified Cx43 knock-in mouse (S3A) that promotes cardiac remodeling of Cx43 protein without apparent cardiac dysfunction. Importantly, when S3A mice were subjected to cardiac stress using the {beta}-adrenergic agonist isoproterenol (Iso), they displayed acute and severe arrhythmias, which were not observed in WT mice. Pre-treatment of S3A mice with the Cx43 hemichannel blocker, Gap19, prevented Iso-induced abnormal electrocardiographic behavior. At the cellular level, when compared with WT, Iso-treated S3A cardiomyocytes showed increased membrane permeability and greater plasma membrane depolarization, which subsequently leads to triggered activity. These cellular dysfunctions were also prevented by Cx43 hemichannel blockers. Our results support the notion that opening of remodeled Cx43 hemichannels, regardless of the type of cardiomyopathy, is sufficient to mediate cardiac stress-induced arrhythmogenicity.

physiology↗