Fukutin is prerequisite to ameliorate muscular dystrophic phenotype by myofiber-selective LARGE expression

alpha-Dystroglycanopathy (alpha-DGP) is a group of muscular dystrophy characterized by abnormal glycosylation of alpha-dystroglycan (alpha-DG), including Fukuyama congenital muscular dystrophy (FCMD), muscle-eye-brain disease, Walker-Warburg syndrome, and congenital muscular dystrophy type 1D (MDC1D), etc. LARGE, the causative gene for MDC1D, encodes a glycosyltransferase to form [-3Xyl-alpha 1,3GlcA beta 1-] polymer in the terminal end of the post-phosphoryl moiety, which is essential for alpha-DG function. It has been proposed that LARGE possesses the great potential to rescue glycosylation defects in alpha-DGPs regardless of causative genes. However, the in vivo therapeutic benefit of using LARGE activity is controversial. To explore the conditions needed for successful LARGE gene therapy, here we used Large-deficient and fukutin-deficient mouse models for MDC1D and FCMD, respectively. Myofibre-selective LARGE expression via systemic adeno-associated viral gene transfer ameliorated dystrophic pathology of Large-deficient mice even when intervention occurred after disease manifestation. However, the same strategy failed to ameliorate the dystrophic phenotype of fukutin-conditional knockout mice. Furthermore, forced expression of Large in fukutin-deficient embryonic stem cells also failed to recover alpha-DG glycosylation, however coexpression with fukutin strongly enhanced alpha-DG glycosylation. Together, our data demonstrated that fukutin is required for LARGE-dependent rescue of alpha-DG glycosylation, and thus suggesting new directions for LARGE-utilizing therapy targeted to myofibres.