Dysferlin maintains the integrity of transverse tubules and the junctional sarcoplasmic reticulum following contraction‐induced injury

Abstract

BackgroundMutations in the DYSF gene that encodes the protein, dysferlin, lead to human muscular dystrophies known as dysferlinopathies.HypothesisWe tested the hypothesis that dysferlin is present at transverse tubules (TT) and that it helps stabilize TT and their interaction with the junctional sarcoplasmic reticulum (j‐SR) following contraction‐induced injury in vivo.Methods and ResultsThrough improved tissue fixation and antigen unmasking, we found that most of the dysferlin in skeletal muscle is present in a myoplasmic reticulum that flanks Z‐disks in a pattern similar to markers of TT in healthy rat, mouse, and human skeletal muscle. Dysferlin is enriched in TT and SR fractions in sucrose gradients of rat muscle. Injury by large‐strain lengthening contractions increased the labeling intensity of myoplasmic dysferlin in wild type A/WySnJ mouse muscle. At 3hr post‐injury, dysferlin‐null A/J mouse muscle showed disrupted labeling for TT and j‐SR markers in ~75% fibers, whereas only ~20% showed disruption in wild type muscle. By 72hr post‐injury, ~20% and ~2% fibers were necrotic in A/J and A/WySnJ muscle, respectively, and the number of necrotic fibers was reduced 5‐fold in A/J mice treated with the L‐type calcium channel blocker, diltiazem.ConclusionDysferlin plays an important role in protecting TT and the j‐SR from damage following contraction‐induced injury.