CD33 Isoform Splicing Dysregulation: A Molecular Determinant of Microglial Dysfunction in Alzheimer's Disease Pathology.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by amyloid-β (Aβ) plaques, neurofibrillary tangles, and chronic neuroinflammation. Genome-wide association studies (GWAS) have identified microglial dysfunction as central to AD pathogenesis, with CD33 emerging as a critical genetic risk factor. This review explores the dual roles of CD33 isoforms, CD33M (pro-pathogenic) and CD33m (protective), in modulating microglial activity, Aβ clearance, and neuroinflammatory responses. We dissect the molecular mechanisms underlying isoform formation, including genetic polymorphisms (e.g., rs3865444, rs12459419) and splicing regulation by hnRNPA/B, PTBP1, and SRSF1. Additionally, we highlight the antagonistic interplay between CD33 and TREM2, emphasizing their convergence on DAP12 signaling and downstream pathways. Emerging therapeutic strategies targeting CD33, such as isoform-specific immunotherapies, small-molecule splicing modulators, and Siglec-glycan interactions, are critically evaluated for their potential to mitigate AD pathology. By integrating recent preclinical and clinical advancements, this review underscores the necessity of precision approaches to harness CD33's therapeutic potential while addressing challenges like blood-brain barrier penetration and species-specific discrepancies.