Dysferlin, Annexin A1, and Mitsugumin 53 Are Upregulated in Muscular Dystrophy and Localize to Longitudinal Tubules of the T-System With Stretch

Abstract

Mutations in dysferlin cause an inherited muscular dystrophy because of defective membrane repair. Three interacting partners of dysferlin are also implicated in membrane resealing: caveolin-3 (in limb girdle muscular dystrophy type 1C), annexin A1, and the newly identified protein mitsugumin 53 (MG53). Mitsugumin 53 accumulates at sites of membrane damage, and MG53-knockout mice display a progressive muscular dystrophy. This study explored the expression and localization of MG53 in human skeletal muscle, how membrane repair proteins are modulated in various forms of muscular dystrophy, and whether MG53 is a primary cause of human muscle disease. Mitsugumin 53 showed variable sarcolemmal and/or cytoplasmic immunolabeling in control human muscle and elevated levels in dystrophic patients. No pathogenic MG53 mutations were identified in 50 muscular dystrophy patients, suggesting that MG53 is unlikely to be a common cause of muscular dystrophy in Australia. Western blot analysis confirmed upregulation of MG53, as well as of dysferlin, annexin A1, and caveolin-3 to different degrees, in different muscular dystrophies. Importantly, MG53, annexin A1, and dysferlin localize to the t-tubule network and show enriched labeling at longitudinal tubules of the t-system in overstretch. Our results suggest that longitudinal tubules of the t-system may represent sites of physiological membrane damage targeted by this membrane repair complex.

Dysferlin stabilizes stress-induced Ca 2+ signaling in the transverse tubule membrane

“…These results agree with earlier reports associating dysferlin with the dihydropyridine receptor (DHPR, L-type Ca 2+ channel), Ahnak, caveolin 3, and several other proteins involved in Ca 2+ -based signaling and the function of transverse (t-) tubules (11)(12)(13)(14). Consistent with this localization and the potential for a functional role in this specialized compartment, dysferlin-deficient murine muscle demonstrates altered transverse tubule (t-tubule) structure (15) as well as increased oxidative stress (16,17), inflammation, and necrosis (18)(19)(20) after injury.…”

“…Dysferlin was also found to coimmunoprecipitate with DHPR from developing myotubes and was hypothesized to be important for the development of the t-tubule (11,15). Other studies found dysferlin at the level of the A-I junction of stretched muscle (14), and we previously localized dysferlin to that region in mature muscle (10). Our current data (cf.…”

Intermittent glucocorticoid steroid dosing enhances muscle repair without eliciting muscle atrophy

“…Notably, GC steroid treatment in dystrophic muscle upregulated many genes encoding proteins implicated in muscle repair (16); thus, the effect of GC steroids on recovery from injury is not just limited to annexin gene expression. Transcriptome analysis showed that genes including caveolin 3 (Cav3), myoferlin (Myof), dysferlin (Dysf), and Trim72 (encoding MG53) were all increased (19,44,45). More refined studies are needed to shed light on whether transcriptional regulation of those genes is directly stimulated by GCs or is an indirect effect of enhanced muscle repair.…”

Unmasking Potential Intracellular Roles For Dysferlin through Improved Immunolabeling Methods

“…Recent reports suggest that cytoplasmic dysferlin may be present, at least in part, in the transverse tubules (t-tubules) of skeletal muscle (Ampong et al 2005;Lostal et al 2010;Waddell et al 2011). This location suggests that dysferlin is required for maintaining the integrity of the t-tubules or perhaps for their coupling with the junctional sarcoplasmic reticulum (SR).…”