Structural Characterization of Glycoprotein Glycans and Glycosaminoglycans of Brain Tissues in Slc35a3-Knockout Mice

Glycosylation depends on luminal nucleotide sugars delivered by solute carrier 35 (SLC35) transporters. SLC35A3 is a uridine diphosphate N-acetylglucosamine (UDP-GlcNAc) transporter. In humans, biallelic mutations in SLC35A3 cause arthrogryposis, mental retardation, and seizures (AMRS). To define how loss of SLC35A3 function reshapes the neural glycome, we profiled N-, O-, and glycosaminoglycans (GAGs) in Slc35a3 knockout mouse brains. N- and O-glycans were analyzed by MALDI-TOF MS, and GAG disaccharides were quantified by anion-exchange HPLC. Knockout mouse brains exhibited attenuation of complex-type N-glycans with a reciprocal rise in high-mannose species, as revealed by MALDI-TOF MS profiling. In contrast, ConA lectin blotting showed no significant change, consistent with its preferential detection of mannose-rich glycans. Branching analysis revealed loss of tri- and tetra-antennary structures compared with biantennary species. O-glycan profiling showed core-2-type species (Hex2HexNAc2 backbone) decreased. The dominant disialyl core-1 remained stable. Total GAG output (chondroitin/dermatan sulfate, heparan sulfate, and hyaluronan) was preserved. These findings support a microdomain model in which SLC35A3 acts as a locally effective supplier of UDP-GlcNAc to MGAT4 (branching N-acetylglucosaminyltransferase that installs the β1,4-GlcNAc arm) in the brain, while alternative routes buffer UDP-GlcNAc delivery for GAG and mucin-type O-glycan biosynthesis. Accordingly, AMRS may be attributed to impaired higher-order N-glycan branching in the brain.