Neuronal loss of Galnt2 in Mice Impairs O-glycosylation and Recapitulates Neurological Features of GALNT2-CDG

Abstract

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. However, the role of O-glycosylation in brain development and function remains poorly understood. To address this question, we selectively ablated Galnt2 from 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 spontaneous seizures, recapitulating characteristic neurological manifestations of GALNT2-CDG. Given the catalytic activity of GALNT2 in initiating mucin-type O-glycosylation, we used glycoproteomics to identify alterations in O-glycosylation in synaptosomes purified from cortical tissues. We ascertained a non-redundant, isoenzyme-specific contribution of GALNT2 to the cortical synaptosomal O-glycoproteome, revealing candidate glycoproteins and disrupted O-glycosites associated with behavioral abnormalities in knockout mice. Together, these findings demonstrate a functional role of O-glycosylation in neurons, implicating O-glycosylation in diverse molecular and cellular pathways important for neuronal function and provide new insights into the neurological pathophysiology of GALNT2-CDG.