Four-week rapamycin treatment improves muscular dystrophy in a fukutin-deficient mouse model of dystroglycanopathy. Issue 1 (December 2016)

• Record Type: Journal Article
• Authors: Foltz, Steven; Luan, Junna; Call, Jarrod; Patel, Ankit; Peissig, Kristen; Fortunato, Marisa; Beedle, Aaron
• Is Part Of: Skeletal muscle. Volume 6:Issue 1(2016)
• Page Start: 1
• Page End: 18
• Publication Date: 2016-12
• Subjects: Dystroglycan -- Fukutin -- Mammalian target of rapamycin (mTOR) -- Muscular dystrophy -- Rapamycin -- Skeletal muscle; Musculoskeletal system -- Periodicals; 612.7
• DOI: 10.1186/s13395-016-0091-9
• Languages: English
• ISSNs: 2044-5040

Abstract

Abstract Background Secondary dystroglycanopathies are a subset of muscular dystrophy caused by abnormal glycosylation of α-dystroglycan (αDG). Loss of αDG functional glycosylation prevents it from binding to laminin and other extracellular matrix receptors, causing muscular dystrophy. Mutations in a number of genes, includingFKTN (fukutin), disrupt αDG glycosylation. Methods We analyzed conditionalFktn knockout (Fktn KO) muscle for levels of mTOR signaling pathway proteins by Western blot. Two cohorts of Myf5-cre/Fktn KO mice were treated with the mammalian target of rapamycin (mTOR) inhibitor rapamycin (RAPA) for 4 weeks and evaluated for changes in functional and histopathological features. Results Muscle from 17- to 25-week-old fukutin-deficient mice has activated mTOR signaling. However, in tamoxifen-inducibleFktn KO mice, factors related to Akt/mTOR signaling were unchanged before the onset of dystrophic pathology, suggesting that Akt/mTOR signaling pathway abnormalities occur after the onset of disease pathology and are not causative in early dystroglycanopathy development. To determine any pharmacological benefit of targeting mTOR signaling, we administered RAPA daily for 4 weeks to Myf5/Fktn KO mice to inhibit mTORC1. RAPA treatment reduced fibrosis, inflammation, activity-induced damage, and central nucleation, and increased muscle fiber size in Myf5/Fktn KO mice compared to controls. RAPA-treated KO mice also produced significantly higher torque at the conclusion of dosing. Conclusions These findings validate a misregulation of mTOR signaling in dystrophic dystroglycanopathy skeletal muscle and suggest that such signaling molecules may be relevant targets to delay and/or reduce disease burden in dystrophic patients.