Restoration of Functional Glycosylation of α-Dystroglycan in FKRP Mutant Mice Is Associated with Muscle Regeneration

Abstract

Mutations in fukutin-related protein (FKRP) gene are characterized with lack of functionally glycosylated α-dystroglycan (F-α-DG). Surprisingly, a few muscle fibers express strong F-α-DG. Herein, we investigated the restoration of F-α-DG in the FKRP mutant muscles and showed that the restoration of glycosylation is associated with muscle regeneration and dependent on the expression of both like-glycosyltransferase (LARGE) and partially functional FKRP. F-α-DG in the regenerating fibers reaches up to normal levels and lasts for >4 weeks, but no up-regulation of the LARGE and FKRP is detected during the regeneration process. The FKRP protein with P448L mutation is sufficient for functional glycosylation of α-DG in regenerating fibers, but not in mature fibers. Thus, factors other than FKRP enable regenerating fibers to produce functional α-DG, compensating for the defect in FKRP function. Identification of factors other than LARGE and FKRP could generate new approaches for restoration of F-α-DG in mature muscle fibers with defects in FKRP functions.

B4GALNT2 (GALGT2) Gene Therapy Reduces Skeletal Muscle Pathology in the FKRP P448L Mouse Model of Limb Girdle Muscular Dystrophy 2I

“…59 IIH6 also can block laminin binding to the O-mannosephosphateelinked glycans present on the a dystroglycan protein. 7 Consistent with the findings reported by Lu and colleagues, 60 we observed IIH6 expression predominantly Figure 5 Quantification of immunoglobulin G (IgG) uptake after overexpression of GALGT2 in FKRP P448Lneo À mice. The gastroc, quad, and TA muscles of FKRP P448Lneo À mutant mice were injected with rAAVrh74.MCK.GALGT2 (treated) or PBS (untreated) and compared at 1, 3, and 6 months after injection.…”

A limb-girdle muscular dystrophy 2I model of muscular dystrophy identifies corrective drug compounds for dystroglycanopathies

“…We also noticed strongly reduced expression levels of glycosylated α-dystroglycan protein using monoclonal antibody IIH6C4 ( Figure 1E). These results are consistent with previous findings in our FKRP-morphant zebrafish and in the Fkrp (P448L) severe mouse model (23,24). Likewise, we observed significant decreases in overall laminin expression ( Figure 1E), a hallmark of FKRP-dependent dystroglycanopathies, as also observed in whole-brain protein lysates of Fkrp Y307N-mutant mice (15).…”

“…Recent work in gene therapy has shown that overexpression of full-length FKRP protein using systemic AAV delivery can block muscle wasting and cardiac symptoms associated with LGMD2I (33,46). Additionally, AAV-mediated FKRP overexpression is capable of restoring the expression levels and complexity of α-dystroglycan glycosylation in FKRP-mutant mice (24). Nevertheless, a comprehensive functional role of FKRP in skeletal muscle along with other tissues remains to be elucidated.…”

Adeno-Associated Virus–Mediated Mini-Agrin Delivery Is Unable to Rescue Disease Phenotype in a Mouse Model of Limb Girdle Muscular Dystrophy Type 2I

“…In previous studies, genetic and biochemical analyses of FKRP-related dystroglycanopathies indicated that residual glycosylation is present in patients as well as in the muscles of our FKRP P448L mutant model. 6,26 Therefore, we investigated whether purified recombinant chick mAgrin could enhance the binding of the residual glycosylated a-DG or the hypoglycosylated a-DG to laminin(s) or other extracellular matrix proteins. We examined such potential effects in vitro using cultured myoblasts and fibroblasts from both the FKRP P448L mutant and normal C57BL/6 mice ( Figure 1).…”