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

Abstract

α-Dystroglycanopathy (α-DGP) is a group of muscular dystrophy characterized by abnormal glycosylation of α-dystroglycan (α-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-α1,3GlcAβ1-] polymer in the terminal end of the post-phosphoryl moiety, which is essential for α-DG function. It has been proposed that LARGE possesses the great potential to rescue glycosylation defects in α-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 α-DG glycosylation, however coexpression with fukutin strongly enhanced α-DG glycosylation. Together, our data demonstrated that fukutin is required for LARGE-dependent rescue of α-DG glycosylation, and thus suggesting new directions for LARGE-utilizing therapy targeted to myofibres.

Treating pediatric neuromuscular disorders: The future is now

“…However, it has also been shown that LARGE overexpression can aggravate the dystrophic phenotype, specifically in mouse models of MDC1A, FCMD, and Fkrp related CMD (Saito et al, ; Whitmore et al, ). Resolution of this discrepancy (which may relate to a requirement for Fukutin expression (Ohtsuka et al, )) is key to considering whether (or for which subtypes) such a therapy could be advanced to patients with dystroglycanopathies.…”

Glycan Engineering for Cell and Developmental Biology

“…Finally, patients with Fukuyama-type congenital muscular dystrophy, a frequent disorder in Japan that presents as brain micropolygria due to improper neuronal migration, contained mutations in a novel gene called fukutin ( FKTN ) (Kobayashi et al, 1998). Although its exact function remains unknown, FKTN was postulated to be a glycosyltransferase and was found to be required for LARGE activity (Ohtsuka et al, 2015). Thus, an examination of these and other α-dystroglycanopathies converged on genes involved in the synthesis of the α-dystroglycan O -mannosyl glycan, linking the biosynthetic pathway of a complex glycan to a suite of developmental disorders.…”

212th ENMC International Workshop:

“…Furthermore, forced expression of Large in fukutin-deficient embryonic stem cells also failed to recover α-DG glycosylation, however coexpression with fukutin strongly enhanced α-DG glycosylation. Together, these data demonstrated that fukutin is required for LARGE-dependent rescue of α-DG glycosylation, with important implications for LARGE-utilizing therapy targeted to myofibers [16,17]. …”