Microglial GM3 accumulation impairs Aβ phagocytic activity and promotes neuroinflammation in Alzheimer's disease

Growing evidence underscores the critical role of lipid metabolism in the pathogenesis of Alzheimer's disease (AD). We previously demonstrated that 5xFAD mice exhibit a marked accumulation of ganglioside GM3 in the cerebral cortex and hippocampus as the disease progresses, with this increase being more pronounced in females than in males. However, the specific brain cell types exhibiting elevated GM3 accumulation, along with GM3's underlying molecular mechanisms and functional significance in AD pathogenesis, remain to be fully elucidated. Here, we report that elevated GM3 levels in 5xFAD are associated with increased expression of Hexa and Hexb-which encode the α- and β-subunits, respectively, of lysosomal β-hexosaminidase A (HexA), the enzyme that catalyzes the conversion of GM2 to GM3 within lysosomes-but not with St3gal5. Analysis of a publicly available single-nucleus RNA sequencing dataset from 5xFAD mice revealed that Hexa and Hexb are highly expressed in microglial cells, with their expression considerably upregulated in these cells compared to other brain cell types. Functional studies demonstrated that overexpression of Hexa and Hexb in microglial cells results in lysosomal GM3 accumulation, impaired Aβ phagocytosis, and increased production of proinflammatory cytokines. Conversely, microglia-specific knockdown of Hexa and Hexb using AA5-microRNA30-based shRNAs not only enhances cognitive function but also alleviates Aβ pathology and neuroinflammation in 5xFAD mice. Collectively, these findings implicate HexA-driven GM3 accumulation in microglia as a key contributor to impaired Aβ clearance and heightened neuroinflammation in AD, highlighting HexA as a potential therapeutic target for restoring microglial function and mitigating disease progression.