Enhanced Muscular Dystrophy from Loss of Dysferlin Is Accompanied by Impaired Annexin A6 Translocation after Sarcolemmal Disruption

Abstract

Dysferlin is a membrane-associated protein implicated in membrane resealing; loss of dysferlin leads to muscular dystrophy. We examined the same loss-of-function Dysf mutation in two different mouse strains, 129T2/SvEmsJ (Dysf 129 ) and C57BL/6J (Dysf B6 ). Although there are many genetic differences between these two strains, we focused on polymorphisms in Anxa6 because these variants were previously associated with modifying a pathologically distinct form of muscular dystrophy and increased the production of a truncated annexin A6 protein. Dysferlin deficiency in the C57BL/6J background was associated with increased Evan's Blue dye uptake into muscle and increased serum creatine kinase compared to the 129T2/SvEmsJ background. In the C57BL/6J background, dysferlin loss was associated with enhanced pathologic severity, characterized by decreased mean fiber cross-sectional area, increased internalized nuclei, and increased fibrosis, compared to that in Dysf 129 mice. Macrophage infiltrate was also increased in Dysf B6 muscle. High-resolution imaging of live myofibers demonstrated that fibers from Dysf B6 mice displayed reduced translocation of full-length annexin A6 to the site of laser-induced sarcolemmal disruption compared to Dysf 129 myofibers, and impaired translocation of annexin A6 associated with impaired resealing of the sarcolemma. These results provide one mechanism by which the C57BL/6J background intensifies dysferlinopathy, giving rise to a more severe form of muscular dystrophy in the Dysf B6 mouse model through increased membrane leak and inflammation. (Am J Pathol 2016 http://dx

Intermittent Glucocorticoid Dosing Improves Muscle Repair and Function in Mice with Limb-Girdle Muscular Dystrophy

“…5e7 Dysferlin is a membrane-associated protein, composed of multiple C2 domains, some of which bind phospholipids in the presence of Ca 2þ . 8 LGMD 2C arises from disruption of g-sarcoglycan, a dystrophin-associated protein, and is accompanied by a similar sarcolemmal fragility, as seen in dystrophin-deficient muscle. 9,10 LGMD 2B and 2C are effectively modeled in Dysferlin-null (Dysf-null ) and Sgcgnull mice, respectively, recapitulating many of the same histopathological features seen in human LGMD 2B and 2C.…”

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.…”

“…We visualized muscle membrane repair in real time using high-resolution microscopy (16,19). In this assay, a laser was used to disrupt the myofiber sarcolemma.…”

“…After completion of the physiologic analyses, serum was acquired and processed as previously described (19). Serum CK was analyzed in triplicate for each mouse using the EnzyChrom Creatine Kinase Assay (catalog ECPK-100, BioAssay Systems) following the manufacturer's instructions.…”

Muscle cell communication in development and repair

“…Dysferlin's role in muscle membrane repair was first observed utilizing laser-ablation to induce membrane injury [16]. Dysferlin-null myofibers reseal membrane disruptions much more slowly than normal myofibers, illustrated by an increase in fluorescent FM 1-43 dye uptake after sarcolemmal disruption [16,31]. Immunofluorescence microscopy was used to demonstrate dysferlin's recruitment to the site of membrane insult [16].…”