TREM2 agonism vs antagonism in DAM microglia

## Core Hypothesis and Rationale The central hypothesis posits that the therapeutic failure of single-target TREM2 interventions in Alzheimer's disease (AD) may be mechanistically explained by the epistatic relationship between TREM2 signaling and APOE4-mediated lipid dyshomeostasis in disease-associated microglia (DAM). Specifically, we hypothesize that APOE4 expression creates a cell-intrinsic lipid trafficking defect that renders DAM functionally refractory to TREM2 agonism, and that simulta...

## Stage-Selective TREM2 Agonism — Boosting DAM Phagocytosis in Early Amyloid Phase ### Background and Biological Rationale TREM2 (Triggering Receptor Expressed on Myeloid Cells 2) is a surface receptor expressed predominantly on microglia and macrophages throughout the central nervous system. It belongs to the immunoglobulin superfamily and signals through the adaptor protein DAP12 (DNAX Activation Protein of 12 kDa), which contains an immunoreceptor tyrosine-based activation motif (ITAM). Up...

## Core Hypothesis and Rationale This hypothesis proposes that the therapeutic polarity of TREM2 modulation in Alzheimer's disease must be dynamically inverted according to the dominant pathological phase: TREM2 agonism is beneficial during the amyloid-dominant early phase (Braak NFT stages I–II, amyloid PET-positive/tau PET-negative or low), whereas TREM2 antagonism becomes preferable during the tau-dominant late phase (Braak stages IV–VI, high tau PET burden with established neurodegeneration...

## TREM2 R47H Variant Correction — AAV-Mediated Rescue of Common Risk Allele ### TREM2 R47H as the Preeminent AD Risk Variant The R47H variant of TREM2 (rs75932628) represents one of the strongest known genetic risk factors for Alzheimer's disease, with an odds ratio of approximately 2.5-3.0 for heterozygous carriers — comparable to the risk conferred by the APOE ε4 allele, though with a different mechanistic basis and pattern of risk modification. This variant was originally identified throug...

## Soluble TREM2 (sTREM2) as Therapeutic Mimic — Decoupling Phagocytosis from Inflammation ### The Central Paradox of TREM2 Biology TREM2 signaling presents a fundamental therapeutic paradox: the receptor's beneficial phagocytic functions and its potentially harmful inflammatory amplification effects are mediated through the same DAP12-ITAM-SYK signaling axis. Classical receptor pharmacology suggests that a single downstream cascade cannot easily be selectively activated to produce one set of ...

## Core Hypothesis and Rationale The central hypothesis posits that selective enhancement of the TREM2-DAP12 signalosome—specifically by augmenting downstream PI3K-AKT-mTOR axis signaling—will restore and sustain the metabolic fitness required for disease-associated microglia (DAM) to execute their neuroprotective amyloid surveillance functions during the early-to-mid stages of Alzheimer's disease pathology. This hypothesis explicitly sides with the agonist camp of the TREM2 debate, but with a ...

## TREM2 Antagonism in Late-Stage Tauopathy — Reducing Neuroinflammatory Amplification ### Background: The Dual Role of TREM2 Across Disease Stages The hypothesis that TREM2 antagonism could be therapeutically beneficial in late-stage tauopathy represents a paradigm-shifting reframe of TREM2 as a context-dependent, stage-specific target rather than a uniformly beneficial immune modulator. This reframing emerges from a sophisticated understanding of microglial biology that has evolved substanti...