Temporal Dynamics of APOE and TREM2 Expression in Microglial Activation of NMOSD Mouse Models

Neuromyelitis optica spectrum disorder (NMOSD) is a severe autoimmune demyelinating disease characterized by recurrent neuroinflammation and disability. Microglial activation plays a critical role in NMOSD pathogenesis, yet the mechanisms regulating its temporal dynamics remain poorly understood. The interplay between apolipoprotein E (APOE) and triggering receptor expressed on myeloid cells 2 (TREM2), key regulators of microglial function in neurodegenerative diseases, has not yet been explored in NMOSD. We conducted bulk RNA-seq in NMOSD mouse models and integrated transcriptomic sequencing, bioinformatics, and machine learning (LASSO, SVM-RFE, random forest) to identify microglia-associated hub genes in an NMOSD mouse model. Immune cell infiltration was analyzed via ImmuCC. Candidate genes were validated using Western blotting and immunofluorescence. Temporal microglial activation and APOE/TREM2 expression were assessed at 3, 7, and 10 days postmodeling. Transcriptomic analysis identified 94 microglia-associated differentially expressed genes (MDEGs), with APOE and TREM2 emerging as central hubs through machine learning. ImmuCC revealed significant infiltration of macrophages, likely indicating microglial polarization. APOE and TREM2 expression peaked on day 3 postinduction, which was correlated with maximal microglial activation (IBA1 +), followed by a gradual decrease. Experimental validation confirmed elevated APOE and TREM2 protein levels in NMOSD mice, with immunofluorescence showing colocalization in activated microglia. This study establishes the APOE-TREM2 axis as a critical regulator of microglial activation in NMOSD, exhibiting early proinflammatory and later reparative roles. The biphasic expression pattern aligns with microglial phenotypic switching, suggesting therapeutic potential for stage-specific interventions. Our findings bridge computational predictions with experimental validation, offering novel insights into NMOSD mechanisms and actionable targets for therapy.