Defective membrane fusion and repair inAnoctamin5-deficient muscular dystrophy

Abstract

Limb-girdle muscular dystrophies are a genetically diverse group of diseases characterized by chronic muscle wasting and weakness. Recessive mutations in ANO5 (TMEM16E) have been directly linked to several clinical phenotypes including limb-girdle muscular dystrophy type 2L and Miyoshi myopathy type 3, although the pathogenic mechanism has remained elusive. ANO5 is a member of the Anoctamin/TMEM16 superfamily that encodes both ion channels and regulators of membrane phospholipid scrambling. The phenotypic overlap of ANO5 myopathies with dysferlin-associated muscular dystrophies has inspired the hypothesis that ANO5, like dysferlin, may be involved in the repair of muscle membranes following injury. Here we show that Ano5-deficient mice have reduced capacity to repair the sarcolemma following laser-induced damage, exhibit delayed regeneration after cardiotoxin injury and suffer from defective myoblast fusion necessary for the proper repair and regeneration of multinucleated myotubes. Together, these data suggest that ANO5 plays an important role in sarcolemmal membrane dynamics. Genbank Mouse Genome Informatics accession no. 3576659.

Anoctamins/TMEM16 Proteins: Chloride Channels Flirting with Lipids and Extracellular Vesicles

“…ANO5 is likely to be a phospholipid scramblase because it is 65% identical to ANO6 in the transmembrane domains and it contains a scramblase domain nearly identical to the one we described in ANO6 (22, 40). Knockout of ANO5 in mice phenocopies human limb girdle muscular dystrophy type 2L (LGMD2L) (102). Ano5 -deficient mice exhibit delayed regeneration of muscle after cardiotoxin injury.…”

“…In addition, the number of nuclei per myotube was greatly reduced in Ano5 −/− cells. (102). Because humans with ANO5 myopathies and Ano5 knockout mice have no obvious muscle phenotypes at birth, this suggests that ANO5 may not play a significant role in myoblast fusion during embryogenesis but may be more important in satellite cell fusion in the adult.…”

“…This may be related to genetic background or to the way in which the knockouts were constructed. The Xu et al (104) and Gyobu et al (22) mice may be true nulls, with knockout constructs inserted in exons 1 or 2, while the Griffin et al (102) mice may express residual truncated transcript, as stop codons are inserted after exon 8. This may mimic more closely the LGMD2L founder mutation (c.190dupA) in exon5 that is predicted to cause a frameshift and premature stop.…”

“…This idea is supported by observations that muscles from ANO5-myopathy patients have sarcolemmal lesions at the electron-microscope level (97) and that fibroblasts from MMD3 patients fail to repair wounded membranes (97, 125). Repair of muscle fibers damaged by a laser pulse is defective in ANO5 knockout mice, suggesting that ANO5 plays a role in membrane fusion (102). …”

Early‐onset limb‐girdle muscular dystrophy‐2L in a female athlete

“…ANO5 is primarily localized to skeletal muscle and thyroid and is localized intracellularly within the endoplasmic reticulum . The function of ANO5 is not well known, but high sequence similarity to ANO6 suggests that it may behave as a scramblase . A recent study by Griffin et al in which they investigated normal ANO5 function, revealed that the protein may be involved in repair of muscle membranes following injury, similar to dysferlin .…”