Galectin-3 deletion modulates microglial phenotype and Aβ response via TREM2 activation while attenuating neuroinflammation
Neuroinflammation is a hallmark of Alzheimers disease (AD), yet the molecular mediators driving microglial dysfunction and neurotoxicity remain poorly understood. Here, we identify Galectin-3 (Gal3) as a central regulator of plaque-associated microglial responses, linking amyloid-beta (A{beta}) aggregation, lysosomal function and plaque-associated neuritic damage. Using postmortem brain tissue from AD patients, we demonstrated that Gal3 microglia are selectively enriched around highly immunogenic dense-core plaques, and correlate with increased LAMP1+ dystrophic neurites. Notably, Gal3 was also detected in extra-microglial dystrophic structures and in close association with extracellular amyloid fibrils, suggesting a role in both intracellular and extracellular A{beta} dynamics. In APP mice, Gal3 deficiency resulted in more compact plaques, reduced neuronal dystrophies and increased TREM2 expression around amyloid plaques, suggesting altered plaque-associated microglial responses. Mechanistically, in vitro studies revealed that Gal3 modulates A{beta} uptake and its intracellular processing while lysosomal stress conditions showed increased A{beta} fibrillation from monomeric species in Gal3-deficient microglia. In parallel, cell-free assays demonstrated that Gal3 directly interacts with A{beta} and selectively inhibits secondary nucleation, thereby stabilizing intermediate assemblies associated with increased neurotoxic potential. Finally, in silico and transcriptomic analysis revealed that Gal3 interacts with key immune receptor patterns, having leucine-rich repeats as well as immunoglobulin-like domains. Moreover, Gal3 favors pro-inflammatory microglial programs, while its deletion suppresses type I interferon and microglial neurodegenerative (MGnD) signatures. Together, these findings position Gal3 as a central regulator of amyloid aggregation, lysosomal dysfunction, and microglial activation, driving a neurotoxic phase of AD and highlighting a potential therapeutic window for intervention. Significance StatementNeuroinflammation and amyloid-beta (A{beta}) plaques drive Alzheimers disease progression, but the molecular bridges between plaque formation, microglial dysfunction, and neurodegeneration remain unclear. This study identifies Galectin-3 (Gal3) as a pivotal regulator at this interface. We demonstrate that Gal3 is enriched around amyloid dense-core plaques in human brains and directly shapes A{beta} aggregation into highly neurotoxic intermediate structures. Genetic deletion of Gal3 in Alzheimers mouse models reduces nerve cell damage and change microglial cells toward a protective, less inflammatory state. By linking extracellular protein aggregation with intracellular lysosomal stress and inflammatory gene expression, these findings establish Gal3 as a major driver of Alzheimers neurotoxicity and highlight it as a promising therapeutic target