Glycosylation of the Sodium Channel β4 Subunit is Developmentally Regulated and Involves in Neuritic Degeneration

Aberrant protein glycosylation plays major roles in neurodegenerative diseases, including Parkinson's disease (PD). Glycoproteomics showed that the glycosylation of sodium channel β4 was significantly increased in human brain tissue. β4-specific antibodies reacted in immunoblot assays with the 35- and 38-kDa bands from the membrane fractions isolated from neonatal PD transgenic mice but only with the 35-kDa band of the neonatal wild-type mice. The size of the 38-kDa immunoreactive protein is in close agreement with previously reported, suggesting heavy glycosylation of this protein in adult wild-type and neonatal PD transgenic brain tissues. However, the neonatal wild-type mice membrane fractions only contained the 35-kDa immunoreactive protein, and the additional 38-kDa band was not shown until postnatal day 7. Enzymatic deglycosylation of the membrane preparations only converted the 38-kDa band into a faster migrating protein, which was consistent with heavy glycosylation of this protein. The glycosylated state of β4 was developmentally regulated and was altered in disease state. Neurite outgrowth assay demonstrated that overexpression of deglycosylated mutant β4-MUT accelerated neurite extension and increased the number of filopodia-like protrusions, when compared with β4-WT and the vector. These results suggest that extensive glycosylation of β4 subunit play roles in morphological changes, and the altered glycosylation may be involved in the pathogenesis of PD.