Gain-of-function Modulation of TREM2 and its Impact on Amyloid-β and Tau Pathologies in Alzheimer's Disease: A Systematic Review and Meta-analysis of Animal Studies.

Alzheimer's disease (AD) is characterized by amyloid-β (Aβ) deposition, hyperphosphorylated Tau accumulation, and chronic neuroinflammation, with microglial function playing a crucial role in modulating these pathological cascades. The microglial receptor TREM2 has emerged as a key regulator of microglial responses to AD-related pathology, and gain-of-function strategies targeting TREM2 have shown substantial therapeutic potential in preclinical models. However, outcomes of these strategies on Aβ and Tau pathologies have exhibited marked heterogeneity across studies, and no systematic integration of the relevant evidence so far. This deficiency has substantially hindered the rational development and clinical translation of TREM2-targeted therapeutic strategies. The objective of this study is to evaluate the effects of TREM2-targeted interventions on Aβ and Tau pathologies in AD animal models. A systematic search of PubMed, Embase, and Cochrane Library identified studies using AD animal models with TREM2-targeted interventions and reporting Aβ or Tau outcomes. This review was registered in PROSPERO (CRD420251131147). A total of 12 studies were included, with overall moderate risk of bias, mainly due to inadequate randomization and blinding. In APP/PS1 mice, TREM2 overexpression significantly reduced Aβ plaque number (SMD =  - 0.87; 95% CI, - 1.28 to - 0.47) and plaque area (SMD =  - 0.98; 95% CI, - 1.46 to - 0.50), with more pronounced effects observed in younger mice (≤ 7 months), where reductions in insoluble Aβ42 were also observed; phosphorylated Tau levels decreased as well. TREM2 agonist antibodies also reduced Aβ plaque number (SMD =  - 2.03; 95% CI, - 2.83 to - 1.24). However, effects on Aβ plaque area, insoluble and soluble Aβ isoforms levels were inconsistent. Antibody treatment also attenuated Tau pathology and Aβ pathology in certain models, including 5XFAD mice or Tau transgenic mice. In addition, both TREM2 overexpression and agonist antibodies could reverse the cognitive impairment of AD animal models. This systematic review and meta-analysis provides the first comprehensive synthesis of preclinical evidence supporting TREM2 gain-of-function modulation as an AD therapeutic strategy targeting both Aβ and Tau pathologies. Our findings reveal that therapeutic efficacy is governed by disease stage, model pathological complexity, and intervention mode. These insights highlight the need for developing stage-specific and pathology-stratified strategies in translational research, establishing TREM2 as a condition-dependent yet promising immunotherapeutic target for AD.