P.8.7 Assessment of neuromuscular junction abnormalities induced by α-dystroglycan glycosylation defects

Abstract

The dystroglcanopathies are a group of diseases with a broad phenotype range that emerge as a consequence of defective glycosylation of α-dystroglycan. Mouse models for this group of diseases include the LARGEmyd and the FKRP knock down (FKRPKD), each of which are characterized by a progressive form of muscular dystrophy. Previous work suggests that impaired neuromuscular transmission contributes to muscle weakness in LARGEmyd mice and that this may be due to glycosylation defects impairing the stability of the endplate of the neuromuscular junction (NMJ). Here we characterize the defects induced by both hypo and hyperglycosylation of α-dystroglycan at the NMJs. We show that both types of altered glycosylation lead to fragmentation of the NMJ (labelled with α-bungarotoxin). The number of fragments corresponding to each NMJ on both LARGE overexpressing mice and FKRPKD were significantly higher than the controls, without changing the total volume or the surface area of the junction. Colocalization of the presynaptic marker synaptophysin and AChR clusters of the postsynaptic apparatus was generally maintained in all groups, and only lost in some NMJs of the FKRPKD mice. We studied potential denervation induced processes by NCAM staining and by labelling axons emerging from the endplates with neurofilament antibodies. Finally, we characterize the expression of agrin around the NMJs as one of the glycoproteins that has been shown to be a key player on the aggregation and clustering of the AChR receptors at the NMJs.