P.1.19 Impaired viability of muscle precursor cells in muscular dystrophy with glycosylation defects and amelioration of its severe phenotype by limited gene expression

Abstract

A group of muscular dystrophies, dystroglycanopathy, is caused by abnormalities in post-translational modifications of dystroglycan (DG). To better understand the pathophysiological roles of DG modification and to establish effective treatment for dystroglycanopathy, we generated 2 distinct conditional knock-out (cKO) mice for fukutin, the first dystroglycanopathy gene identified for Fukuyama congenital muscular dystrophy. The first dystroglycanopathy model – myofiber-selective fukutin-cKO (MCK-fukutin-cKO) mice – showed mild muscular dystrophy. Forced exercise experiments in presymptomatic MCK-fukutin-cKO mice revealed that myofiber membrane fragility triggered disease manifestation. The second dystroglycanopathy model – muscle precursor cell (MPC)-selective cKO (Myf5-fukutin-cKO) mice – exhibited more severe phenotypes of muscular dystrophy. Using an isolated MPC culture system, we demonstrated that defects in the fukutin-dependent modification of DG lead to impairment of MPC proliferation, differentiation, and muscle regeneration. These results suggest that impaired MPC viability contributes to the pathology of dystroglycanopathy. Since our data suggested that frequent cycles of myofiber degeneration/regeneration accelerate substantial and/or functional loss of MPC, we expected that protection from disease-triggering myofiber degeneration provides therapeutic effects even in mouse models with MPC defects; therefore, we restored fukutin expression in myofibers. Adeno-associated virus (AAV)-mediated rescue of fukutin expression that was limited in myofibers successfully ameliorated the severe pathology even after disease progression. In addition, compared to other gene therapy studies, considerably low AAV titers were associated with therapeutic effects. Our findings indicated that fukutin-deficient dystroglycanopathy is a regeneration-defective disorder, and gene therapy is a feasible treatment for the wide range of dystroglycanopathy even after disease progression.