GD3 SYNTHASE DEFICIENCY PROMPTS ALTERED ACTIVITY OF NA<SUP >+</SUP>/K<SUP>+</SUP>-ATPASE (NKA) AND PLASMA MEMBRANE CA<SUP>2+</SUP>-ATPASE (PMCA) IN GD3S-DEFICIENT MICE (GD3S<SUP>-/-</SUP>) AND CRISPR/CAS9 KNOCKOUT <EM>ST8SIA1</EM> SH-SY5Y CELLS

GD3 synthase (GD3S), encoded by the St8Sia1 (ST8SIA1) gene, is a key enzyme in the biosynthesis of complex glycosphingolipids - gangliosides. The aim of this study was to investigate the physiological implications of GD3S deficiency on Na⁺/K⁺-ATPase (NKA) and plasma membrane Ca²⁺-ATPase (PMCA), within the context of altered membrane ganglioside composition. We utilized both mice and human cell models: GD3S-deficient mice (GD3S^-/-) and CRISPR/Cas9 knockout ST8SIA1 SH-SY5Y human neuroblastoma cells respectively, and explored changes in gene expression, protein levels, submembrane localization and enzyme activity of the abovementioned membrane proteins essential for maintaining ion homeostasis and cellular excitability. Microarray analysis in mouse model revealed significant alterations in gene expression for NKA in GD3S^-/- mice, which was confirmed by qRT-PCR. The results also showed increased expression of NKA catalytic subunits but decreased enzyme activity, suggesting a compensatory mechanism due to altered membrane environment where the change in specific ganglioside pattern was confirmed by dot-blot. This study also highlights the redistribution of NKA and PMCA isoforms within lipid rafts, influenced by ganglioside composition and cholesterol levels. Altogether, these findings indicate that the absence of b- and c-series gangliosides leads to decreased NKA and PMCA activity which could have important implications in studying the pathophysiology of neurodegenerative disorders, while simultaneously underscoring the intricate relationship between ganglioside composition, ion transporter function, and potential therapeutic approaches targeting ganglioside biosynthesis pathways.