Attenuated muscle regeneration is a key factor in dysferlin-deficient muscular dystrophy

Abstract

Skeletal muscle requires an efficient and active membrane repair system to overcome the rigours of frequent contraction. Dysferlin is a component of that system and absence of dysferlin causes muscular dystrophy (dysferlinopathy) characterized by adult onset muscle weakness, high serum creatine kinase levels and a prominent inflammatory infiltrate. We have observed that dysferlinopathy patient biopsies show an excess of immature fibres and therefore investigated the role of dysferlin in muscle regeneration. Using notexin-induced muscle damage, we have shown that regeneration is attenuated in a mouse model of dysferlinopathy, with delayed removal of necrotic fibres, an extended inflammatory phase and delayed functional recovery. Satellite cell activation and myoblast fusion appear normal, but there is a reduction in early neutrophil recruitment in regenerating and also needle wounded muscle in dysferlin-deficient mice. Primary mouse dysferlinopathy myoblast cultures show reduced cytokine release upon stimulation, indicating that the secretion of chemotactic molecules is impaired. We suggest an extension to the muscle membrane repair model, where in addition to fusing patch repair vesicles with the sarcolemma dysferlin is also involved in the release of chemotactic agents. Reduced neutrophil recruitment results in incomplete cycles of regeneration in dysferlinopathy which combines with the membrane repair deficit to ultimately trigger dystrophic pathology. This study reveals a novel pathomechanism affecting muscle regeneration and maintenance in dysferlinopathy and highlights enhancement of the neutrophil response as a potential therapeutic avenue in these disorders.

Genetic ablation of complement C3 attenuates muscle pathology in dysferlin-deficient mice

“…Second, increased susceptibility to contraction-induced injury of the muscle membrane is usually caused by the loss of the dystrophin-glycoprotein complex (DGC); however, dysferlin-deficient skeletal muscle possesses a structurally intact and stable DGC (11). Indeed, recent data showed that dysferlin-deficient skeletal muscles are equal to normal skeletal muscles in resistance to contraction-induced injury (18). However, following either 15 repetitive large-strain LCs or 150 small-strain LCs, dysferlin-null muscles were observed to experience a strong inflammatory response that delayed their recovery from injury caused by LCs (19,20).…”

“…Dysferlindeficient monocytes from SJL/J mice were reported to have increased phagocytic activity (26), and dysferlin deficiency induces an upregulation of inflammasome (27). However, a more recent study (18) did not find a difference in phagocytic activity of dysferlindeficient monocytes using C57BL/10-SJL.Dysf mice, which have a more controlled genetic background. Instead, the authors reported an impaired secretion of chemotactic molecules in dysferlindeficient myocytes, thus reducing neutrophil recruitment at an early stage of regeneration with subsequent incomplete muscle remodeling and ultimate inflammatory responses and develop-ment of muscular dystrophy (18).…”

Membrane wounding triggers ATP release and dysferlin-mediated intercellular calcium signaling

“…It has been proposed that Ca 2+ influx through a plasma membrane breach triggers dysferlin-mediated membrane fusion to seal the lesion (Bansal et al, 2003;Glover and Brown, 2007;Lennon et al, 2003;McNeil and Kirchhausen, 2005). Alternatively, an indirect role for dysferlin in wound repair may involve intercellular signaling (Chiu et al, 2009). For example, upon plasma membrane wounding a cell might release factors that signal other cells to compensate for the impairment or loss of the wounded cell.…”

Dysferlin mediates membrane tubulation and links T-tubule biogenesis to muscular dystrophy

“…Dysferlin localizes to the plasma membrane and to the T-tubule membrane in striated muscle (Ampong et al, 2005;Anderson et al, 1999;Klinge et al, 2008), and transits to late endosomes, similar to myoferlin (Redpath et al, 2016). Dysferlin acts at intracellular membranes (Bansal et al, 2003;Marty et al, 2013), and the alteration of this process is held responsible for a defect in membrane repair (Bansal et al, 2003;Cooper and Head, 2014) during muscle regeneration (Chiu et al, 2009), and for changes in T-tubule morphology and the function of dysferlin-deficient muscle (Klinge et al, 2010b;Roostalu and Strähle, 2012). However, it is unknown how the dysferlin protein is mechanistically engaged in these functions (Al-Qusairi and Laporte, 2011; Kerr et al, 2014).…”