Fast skeletal myofibers of mdx mouse, model of Duchenne muscular dystrophy, express connexin hemichannels that lead to apoptosis

Abstract

Skeletal muscles of patients with Duchenne muscular dystrophy (DMD) show numerous alterations including inflammation, apoptosis, and necrosis of myofibers. However, the molecular mechanism that explains these changes remains largely unknown. Here, the involvement of hemichannels formed by connexins (Cx HCs) was evaluated in skeletal muscle of mdx mouse model of DMD. Fast myofibers of mdx mice were found to express three connexins (39, 43 and 45) and high sarcolemma permeability, which was absent in myofibers of mdx Cx43(fl/fl)Cx45(fl/fl):Myo-Cre mice (deficient in skeletal muscle Cx43/Cx45 expression). These myofibers did not show elevated basal intracellular free Ca(2+) levels, immunoreactivity to phosphorylated p65 (active NF-κB), eNOS and annexin V/active Caspase 3 (marker of apoptosis) but presented dystrophin immunoreactivity. Moreover, muscles of mdx Cx43(fl/fl)Cx45(fl/fl):Myo-Cre mice exhibited partial decrease of necrotic features (big cells and high creatine kinase levels). Accordingly, these muscles showed similar macrophage infiltration as control mdx muscles. Nonetheless, the hanging test performance of mdx Cx43(fl/fl)Cx45(fl/fl):Myo-Cre mice was significantly better than that of control mdx Cx43(fl/fl)Cx45(fl/fl) mice. All three Cxs found in skeletal muscles of mdx mice were also detected in fast myofibers of biopsy specimens from patients with muscular dystrophy. Thus, reduction of Cx expression and/or function of Cx HCs may be potential therapeutic approaches to abrogate myofiber apoptosis in DMD.

Prevention of connexin-43 remodeling protects against Duchenne muscular dystrophy cardiomyopathy

“…As opposed to cardiac muscle, adult skeletal muscle does not require gap junctions to coordinate muscle contraction (81). However, de novo expression of Cx43 hemichannels contributes toward muscle degeneration in denervated dystrophic fast skeletal muscle fibers, such as the diaphragm (82)(83)(84). Thus, Cx43 hemichannels were suggested to be a viable therapeutic target for dystrophic muscle.…”

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

“…S6. www.nature.com/scientificreports www.nature.com/scientificreports/ Despite the different roles of Cx43 in response to cardiac and skeletal muscle damage, higher expression is correlated to enhanced cell death 34,47,48 .…”

“…Aberrant hemichannel activity has also been observed in mdx mouse myofibers to cause apoptosis 22,33,48,52 . Based on localization of Cx43 to the mononuclear cells, we postulate that reduction of hemichannel activity in skeletal muscle macrophages is linked to decreased cell death, suppressed activation of pro-inflammatory factors, and therefore, slowed muscle deterioration 17,34,53 .…”

P2X7 purinoceptor as a therapeutic target in muscular dystrophies

“…Furthermore, alongside P2X7 expression and activation in inflammatory cells, studies showed a dramatic up-regulation of this purinoceptor in DMD patients' muscle biopsy samples [32] and also in muscle and isolated muscle cells from the mouse model of DMD [33][34][35]. P2X7 overexpression was particularly evident on mdx fast skeletal myofibres, where it was linked to enhanced sarcolemma permeability [35 • ].…”