Reduced Na current in dystrophin-deficient ventricular cardiomyocytes is rescued by tenascin-C inhibition

Abstract Background Duchenne muscular dystrophy (DMD) is an X-linked hereditary disease triggered by the deficiency of the structural protein dystrophin, which leads to muscular degeneration mainly affecting young males. Major contributors to early death in DMD patients are cardiac arrhythmias and dystrophic cardiomyopathy. One cause for arrhythmias is impaired ventricular impulse conduction, which leads to ventricular asynchrony and reentrant mechanisms. We recently showed that the disruption of dystrophin results in a significant reduction of Na current in ventricular cardiomyocytes (vCMs) of the dystrophin-deficient mdx mouse model for human DMD. Na current reduction provides a mechanistic explanation for the impaired ventricular conduction and accompanying arrhythmias in the dystrophic heart. The extracellular matrix protein tenascin-C (TN-C) is a significant remodeling factor in the injured and diseased heart and is strongly upregulated in dystrophic cardiomyopathy. To this date, it is unknown how the upregulation of TN-C in DMD patients affects dystrophic cardiomyopathy. Purpose In this study, we examined the effect of TN-C inhibition on diminished Na currents in dystrophin-deficient vCMs. Methods We compared four different mouse genotypes with each other, namely wild-type, dystrophin-deficient mdx, TN-C-deficient and dystrophin- plus TN-C-deficient mice. Furthermore, a cohort of mdx mice was injected with TN-C siRNA twice a week for 9 weeks to investigate the effect of TN-C knockdown. Hearts from adult male mice were enzymatically digested using a Langendorff system to isolate single vCMs. Na currents were then measured with the whole cell patch clamp technique. Results Na current densities were increased in TN-C deficient vCMs compared to wild-type vCMs. Accordingly, 24-hour incubation of wild-type vCMs with human recombinant TN-C resulted in a significant decrease in Na current. Na currents of vCMs from mdx mice were reduced, but restored to the wild-type level in vCMs from TN-C-deficient mdx mice. Moreover, vCMs of TN-C siRNA-treated mdx mice had significantly increased Na currents compared to control mdx vCMs. Conclusion Upregulation of TN-C in dystrophin-deficient vCMs reduces Na currents, whereas inhibition of TN-C prevents this reduction. Therefore, inhibition of TN-C in DMD patients may be considered as a potential new therapeutic strategy to improve ventricular conduction and reduce arrhythmia vulnerability.