TREM2 as a central hub of neuroimmune-metabolic crosstalk in central nervous system disorders: from microglial biology to therapeutic targeting.

Triggering receptor expressed on myeloid cells 2 (TREM2) is a microglia-enriched immunoreceptor that functions as a central regulator of microglial adaptation by integrating immune surveillance, lipid sensing, metabolic reprogramming, and phagocytic responses in the central nervous system (CNS). Through association with the adaptor protein DAP12, TREM2 activates interconnected signaling networks involving the SYK pathway, PLCγ2-mediated Ca2+ signaling, PI3K-AKT-mTOR signaling, NF-κB activation and inflammatory regulatory pathways, thereby shaping microglial survival, migration, clearance capacity, and interactions with surrounding neural and immune cells. Increasing evidence from genetic studies, single-cell transcriptomics, spatial analyses, and human-derived microglial models indicates that TREM2 dysfunction contributes to diverse CNS disorders; however, its biological consequences are highly dependent on disease stage, pathological substrate, cellular context, and microenvironmental cues. In Alzheimer's disease, TREM2 regulates amyloid-β-associated microglial responses, lipid metabolism, and synaptic remodeling, while its effects on tau-driven neurodegeneration remain controversial. In Parkinson's disease, stroke, epilepsy, and amyotrophic lateral sclerosis, TREM2 influences α-Syn clearance, inflammatory resolution, tissue repair, and microglial state transitions, but may exert beneficial or maladaptive effects depending on temporal dynamics and disease-specific stressors. Emerging clinical evidence, including TREM2 variants, soluble TREM2 (sTREM2) biomarkers, and human multi-omics studies, highlights both the translational potential and complexity of targeting this pathway. Herein, this review summarizes the molecular mechanisms, physiological functions, and disease-specific roles of TREM2 in CNS disorders, critically discusses unresolved controversies and species-specific challenges, and evaluates emerging therapeutic strategies toward biomarker-guided and stage-specific modulation of TREM2 signaling. Understanding how to restore appropriate microglial adaptability rather than simply enhance or suppress TREM2 activity may provide a foundation for precision therapies in CNS disorders.