Version history

{
  "session_id": "sess_SDA-2026-04-04-gap-20260404-microglial-priming-early-ad_20260412-073015",
  "round_number": 1,
  "agent_persona": "persona-theorist",
  "agent_backend": "minimax/MiniMax-M2.7",
  "action": "propose",
  "content": "\n\n# Mechanistic Hypotheses: Microglial Priming in Preclinical AD\n\n---\n\n## Hypothesis 1: TREM2-ICD Nuclear Translocation as Priming Signal Generator\n\n**Title:** TREM2 Intracellular Domain Drives Proinflammatory Microglial Memory\n\n**Mechanism:** Proteolytic cleavage of TREM2 by ADAM10/ADAM17 releases the soluble ectodomain (sTREM2) while permitting the intracellular domain (TREM2-ICD) to translocate to the nucleus. TREM2-ICD binds to TYROBP promoter regions and cooperates with SPI1 to establish a self-sustaining transcriptional circuit that locks microglia in a primed, non-resolving state. This nuclear gain-of-function operates independently of TREM2's membrane-bound signaling via SYK/PI3K, creating a decoupled transcriptional program resistant to homeostatic resolution signals.\n\n**Key Evidence:**\n- TREM2 undergoes γ-secretase–dependent proteolysis generating a stable ICD fragment that localizes to nucleus and chromatin in macrophage cell lines (PMID: 30206223)\n- SPI1 (PU.1) cooperates with TYROBP to orchestrate disease-associated microglia (DAM) transcriptional identity, with SPI1 binding sites enriched in TREM2-ICD target genes (PMID: 30550849)\n\n**Testable Prediction:** CRISPRi-mediated nuclear export-deficient TREM2 mutation (ΔCTD) introduced into iPSC-derived microglia or Trem2^R47H mice crossed to 5xFAD will prevent nuclear accumulation of TREM2-ICD, attenuate TYROBP/SPI1 enhancer binding, and block primed microglial transcriptional signatures (Cxcl10, Il1b, Ccl2 upregulation) while preserving TREM2-dependent phagocytic functions—demonstrating separable nuclear vs. membrane signaling domains.\n\n**Primary Target:** TREM2-ICD / ADAM10/17 cleavage machinery\n\n---\n\n## Hypothesis 2: cGAS-STING-Driven Interferon Response Creates Self-Reinforcing Primed Niche\n\n**Title:** Mitochondrial DNA Leakage Activates cGAS-STING Type I IFN in Primed Microglia\n\n**Mechanism:** In early amyloid pathology, microglial mitochondrial dysfunction (driven by TREM2 loss-of-function or APOE ε4) causes permeability transition pore opening, releasing mtDNA into the cytosol. Cytosolic mtDNA activates cGAS, which synthesizes 2'3'-cGAMP that activates STING on the endoplasmic reticulum. STING signaling induces TBK1/IRF3-mediated type I interferon (IFN-β) production, creating an autocrine/paracrine feedback loop where IFNAR signaling primes neighboring microglia via STAT1/STAT2 phosphorylation, lowering the threshold for subsequent inflammatory triggers. This creates a \"primed niche\" where microglia exist in a hyper-sensitized state unable to resolve Aβ without IFN signature dampening.\n\n**Key Evidence:**\n- cGAS localizes to the nucleus and mitochondria; mtDNA release triggers cGAS-STING–dependent inflammation in macrophages and microglia (PMID: 29695804)\n- STING activation in microglia drives neurotoxic phenotype in 5xFAD mice; STING inhibition reduces microglial inflammatory gene expression and neuronal loss (PMID: 35177627)\n\n**Testable Prediction:** Conditional microglial knockout of cGAS (Cx3cr1-CreERT2; cGAS^fl/fl) in 5xFAD mice crossed to a mitochondrial-targeted catalase line (to reduce ROS-induced mPTP opening) will demonstrate that mtDNA release is the proximal signal for cGAS activation. If cGAS deletion blocks IFN signature without altering amyloid",
  "tokens_used": "820"
}