Connexin-43 reduction prevents muscle defects in a mouse model of manifesting Duchenne muscular dystrophy female carriers

Abstract

Duchenne muscular dystrophy (DMD) is a severe X-linked neuromuscular disorder that affects males. However, 8% of female carriers are symptomatic and underrepresented in research due to the lack of animal models. We generated a symptomatic mouse model of DMD carriers via injection of mdx (murine DMD) embryonic stem cells (ESCs) into wild-type (WT) blastocysts (mdx/WT chimera). mdx/WT chimeras developed cardiomyopathic features and dystrophic skeletal muscle phenotypes including elevated mononuclear invasion, central nucleation, fibrosis and declined forelimb grip strength. The disease was accompanied by connexin-43 (Cx43) aberrantly enhanced in both cardiac and skeletal muscles and remodeled in the heart. Genetic reduction of Cx43-copy number in mdx/WT-Cx43(+/−) chimeras protected them from both cardiac and skeletal muscle fiber damage. In dystrophic skeletal muscle, Cx43 expression was not seen in the fibers but in adjacent F4/80+ mononuclear cells. Ethidium Bromide uptake in purified F4/80+/CD11b+ mdx macrophages revealed functional activity of Cx43, which was inhibited by administration of Gap19 peptide mimetic, a Cx43 hemichannel-specific inhibitor. Thus, we suggest that Cx43 reduction in symptomatic DMD carrier mice leads to prevention of Cx43 remodeling in the heart and prevention of aberrant Cx43 hemichannel activity in the skeletal muscle macrophages neighboring Cx43 non-expressing fibers. Duchenne muscular dystrophy (DMD) is an incurable X-linked recessive disorder characterized by mutations in the dystrophin gene. The dystrophin protein is an essential part of the dystrophin-glycoprotein complex (DGC), which provides structure and mechanically-induced signal propagation between intracellular and extracellular environments 1. X-linked disorders only affect male patients; however, a percentage of female DMD heterozygotes are symptomatic. Symptomatic female carriers consist of about 8-40% of definite DMD carriers and begin to present symptoms between the ages of 2-47 years old 2,3. Patients display a range of severe to less severe phenotypes. It is generally accepted to affect 8% of female carriers, yet this statistic aligns with those affected by dilated cardiomyopathy. A higher percentage (17%) suffer from muscle weakness 3-10. Heart complications can be further expanded to include left-ventricle dilation (40%) 10. Research on symptomatic carriers has been confined to clinical observations largely due to the absence of a representative animal model 2,3,9,11,12. These epidemiological studies are subject to a larger margin of error from confounding variables, necessitating a DMD animal model that successfully recapitulates the symptomatic carrier phenotypes and mosaicism. X-linked muscular dystrophy mice (mdx) 13 heterozygotes, mdx(+/−), show normal muscle histology and do not develop cardiomyopathy 11,12. Recently, we described the generation of a model to study symptomatic DMD carriers that faithfully recapitulates the pathology and symptoms (mdx/WT mouse chimeras) 14. Symptomatic mdx mouse chimeras were ...

Knockout of MYOM1 in human cardiomyocytes leads to myocardial atrophy via impairing calcium homeostasis

“…After detecting Cx43, which affects myocardial electrical conduction and contraction, we only found a decrease in its abundance, but no apparent abnormal subcellular localization. As previously reported, the reduction of Cx43 in muscles could prevent and protect myocardial and skeletal muscle damage during muscular dystrophy 48,49 . We believe that the decrease of Cx43 in myomesin‐1‐deficient cardiomyocytes is a protective mechanism to prevent the damage of myocardial atrophy caused by myomesin‐1 deficiency.…”

“…were increased in KO CMs relative to WT CMs, their absolute expression was still at a low level and there was still no M-line in As previously reported, the reduction of Cx43 in muscles could prevent and protect myocardial and skeletal muscle damage during muscular dystrophy. 48,49 We believe that the decrease of reported that intact myomesin-1 and its specific Fn-like or Iglike domains can stimulate human myoblast proliferation. 37 To investigate the effect of MYOM1 knockout on the number of cardiomyocytes, we next tested the proliferation and apoptosis of cardiomyocytes.…”

GCN5 Maintains Muscle Integrity by Acetylating YY1 to Promote Dystrophin Expression

“…The links between Gcn5 Skm-/and muscular disease were further emphasized by observed negative correlations between the Gcn5 Skm-/bioset and that of KO mice for Mstn, Cx43 and Mir-21, genes that have been linked to playing a negative role on mdx mouse phenotypes (Fig. 3c) (Nouet et al, 2020;Zanotti et al, 2015;Ardite et al, 2012;Dumonceaux et al, 2010). The finding that the Gcn5 Skm-/bioset is negatively correlated with several Mstn KO biosets compliments findings that suggest myostatin pathway inhibition as a potential DMD therapeutic strategy (Campbell et al, 2017).…”

eATP/P2X7R Axis: An Orchestrated Pathway Triggering Inflammasome Activation in Muscle Diseases

“…The role of connexins (Cxs), particularly of Cx43, in different cardiomyopathies, including DMD-associated cardiomyopathies, is well established. Less is known regarding the role of Cx43 and other connexins in skeletal muscle [ 106 ].…”

“…Interestingly, in their study, they unveil that Cx43 is not expressed by wt or dystrophinopathic muscle fibers but rather by infiltrating F4/80 + mononuclear cells. Cx43 gene inactivation improved histological features of muscular dystrophy in mdx /chimera mice suggesting that the development of anti-Cx43 therapies could be beneficial to ameliorate inflammation in DMD [ 106 ].…”