TREM2 in neurodegenerative diseases and acute neurological injuries: mechanisms to targeted therapies.
Triggering receptor expressed on myeloid cells 2 (TREM2) is a critical myeloid receptor expressed on the surface of central nervous system microglia, capable of integrating signals from lipids, damage-associated molecular patterns, and abnormal protein aggregates to regulate phagocytosis, metabolic adaptation, inflammatory remodeling, and pathology-associated responses. Accumulating evidence indicates that TREM2 is neither uniformly protective nor uniformly pathogenic; rather, its biological effects are highly context-dependent, governed collectively by disease stage, pathological substrates, cellular compartments, and the local microenvironment. By coupling with TYROBP/DAP12 or DAP10, TREM2 actively drives the state remodeling of pathology-associated microglia. It profoundly influences the onset and progression of neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS), and amyotrophic lateral sclerosis (ALS), as well as acute central nervous system injuries, including ischemic stroke, spinal cord injury (SCI), and traumatic brain injury (TBI). Concurrently, soluble TREM2 (sTREM2) holds significant potential not only as a biomarker but also as a context-dependent effector molecule actively participating in pathological regulation. This review synthesizes current advancements by focusing on four core themes: the structural and signaling logic of the TREM2 axis; its regulation of disease-associated microglia (DAM) remodeling; the cross-disease significance of sTREM2; and the mechanistic basis for the divergent outcomes observed with TREM2-targeted therapies across different experimental models and disease stages. The objective is to elucidate the context-dependent roles of TREM2 by analyzing consensus mechanisms, sources of discrepancy, and translational implications, thereby providing a theoretical framework and strategic direction for more precise TREM2-targeted interventions.