Decoding TREM2: A microglial receptor governing the fate of myelin

Impaired myelin integrity and defective myelin regeneration represent core pathological features shared by central nervous system (CNS) diseases, such as multiple sclerosis (MS), Alzheimer's disease (AD), ischemic cerebral white matter lesions and spinal cord injury (SCI). Triggering Receptor Expressed on Myeloid Cells 2 (TREM2) is highly enriched in central resident microglia; it is also expressed by border-associated macrophages and lesion-infiltrating monocyte-derived macrophages, rather than being restricted to parenchymal microglia, acting as a key membrane receptor regulating microglial immune balance, lipid transport, lysosomal degradation and cell polarization. Existing studies demonstrate that TREM2 binds various ligands including myelin lipid debris, apolipoprotein E (APOE) and apoptotic cell components, then activates multiple DNAX-activating protein of 12 kDa (DAP12)-dependent signaling cascades: spleen tyrosine kinase (SYK)-phosphatidylinositol 3-kinase (PI3K), phospholipase C gamma 2 (PLCγ2), beta-catenin and transcription factor EB (TFEB). These pathways jointly clear myelin debris, remodel cholesterol circulation, restrain pro-inflammatory microenvironment and promote oligodendrocyte precursor cell (OPCs) differentiation, exerting bidirectional functions in physiological myelin homeostasis, acute injury response and chronic repair. This narrative review summarizes TREM2's gene and protein structure, ligand recognition modes and full signal transduction network. It illustrates the molecular mechanisms of TREM2 in myelin maintenance, debris clearance and regeneration, compares its distinct pathological roles in various demyelinating diseases, and concludes translational strategies including TREM2 agonism, downstream pathway intervention and biomarker exploitation. Furthermore, this narrative review analyzes unsolved core scientific issues and puts forward research routes for mechanistic research and clinical transformation, offering systematic theoretical basis for targeted drug development against demyelinating encephalopathies.