Neuronal loss of Galnt2 Impairs O-glycosylation and Leads to Neurobehavioral Deficits Mimicking GALNT2-CDG

GALNT2-CDG is a multi-system genetic disorder due to biallelic pathogenic mutations in GALNT2, which encodes a ubiquitously expressed Golgi-localized glycosyltransferase that initiates mucin-type O-glycosylation. Affected individuals exhibit dysmorphic facial features, short stature, decreased HDL-C, and notable impairments in brain function. GALNT2-CDG patients show global developmental delay without speech development, childhood epilepsy, autistic-like features, and white-matter brain abnormalities. The extent of O-glycosylation in brain development and function remains poorly understood. To address this question, we selectively ablated Galnt2 from pan-neuronal cells in the brain and found that conditional knockout mice exhibit deficits across numerous behavioral domains, including locomotion, motor coordination, sociability, learning, and memory, as well as experience spontaneous seizures, recapitulating characteristic neurological manifestations of GALNT2-CDG. Given the catalytic activity of GALNT2 to initiate mucin-type O-glycosylation, we used glycoproteomics to identify disrupted O-glycosylation in synaptosomes purified from cortical tissues. We ascertained a non-redundant, isoform-specific contribution of GALNT2 to the cortical synaptosomal O-glycoproteome, identifying candidate glycoproteins and disrupted O-glycosites that accompany behavioral abnormalities in knockout mice. These findings demonstrate functional impact of O-glycosylation in neurons, implicating roles of O-glycosylation in diverse molecular and cellular pathways related to neuronal function and provide new opportunities to gain insights into the neurological pathophysiology of GALNT2-CDG.