2026 — Tian — gut dysbiosis → microglial TREM2/SYK/NF-κB → neuroinflammation chain (AD model with bidirectional FMT causal dissection)
One-paragraph summary
Primary mouse mechanism study in APP/PS1 Alzheimer's-disease model with bidirectional fecal microbiota transplantation (FMT) causal dissection (AD → wild-type and WT → AD), 16S rRNA sequencing, metabolomics, immunohistochemistry, and in vitro receptor-signaling experiments. Key empirical chain: AD mice show reduced microbial diversity (decreased Bacteroidetes and Lactobacillus) → decreased fecal butyrate + elevated circulating LPS → hippocampal microglial M1 polarization with elevated TNF-α, IL-1β, IL-6 → TREM2 downregulation + SYK phosphorylation + NF-κB activation → synaptic protein loss + cognitive decline. Bidirectional FMT proves causation: healthy-donor FMT into AD mice reverses the molecular and behavioral abnormalities; AD-microbiota FMT into wild-type mice induces mild pathology in previously-healthy recipients. In vitro: TREM2 activation OR SYK inhibition independently attenuate Aβ-induced M1 polarization and cytokine release in microglia. For the project, this paper supplies the microglial-receptor-signaling resolution layer the B2 bridge framework has been missing — Tian's TREM2/SYK/NF-κB pathway is the specific microglial-immune-receptor signaling axis that connects gut-derived inflammatory signals (butyrate↓, LPS↑) to the M1 microglial polarization the Coluzzi 2025 FM TSPO-PET work documents. The dysbiosis → butyrate↓ → LPS↑ → microglial M1 chain is the same biochemical signature as Dorta-Aguilar 2023 in FM (intestinal permeability + zonulin + LPS + sCD14 elevation). Adds fostamatinib (FDA-approved 2018 for chronic ITP) as a candidate clinical-stage SYK-inhibitor cross-condition repurposing-tier cure-path-arm candidate.
Claims as triples
gut_brain_axis_disruption — causes → microglial_M1_polarization[evidence: bidirectional FMT in APP/PS1 mice; causal direction confirmed; confidence: emerging (in AD)]LPS — activates → microglial_M1_polarization[evidence: butyrate↓ → LPS↑ → M1 chain demonstrated; confidence: emerging]microglial_M1_polarization — has_signaling_pathway → TREM2_SYK_NFkB[evidence: TREM2↓ + SYK phosphorylation↑ + NF-κB↑ co-occur; confidence: emerging]TREM2 — regulates → microglial_M1_polarization[evidence: TREM2 activation attenuates M1 polarization in vitro; confidence: emerging]SYK — required_for → microglial_M1_polarization[evidence: SYK inhibition attenuates M1 polarization + cytokine release in vitro; confidence: emerging]fostamatinib — has_mechanism → SYK_inhibitor[evidence: pharmacology established (FDA-approved 2018 for ITP); confidence: established]fmt — interrupts → gut_brain_axis_disruption_chain[evidence: healthy-donor FMT reverses AD-model abnormalities + improves cognition; confidence: emerging]gut_dysbiosis_signature — present_in → alzheimer_disease[evidence: reduced Bacteroidetes + Lactobacillus in AD mice vs WT; confidence: emerging (in AD)]
Triangulation notes
- Microglial-signaling-pathway resolution layer for B2 bridge. The project's B2 bridge (microbiome ↔ FM via SCFA / bile acids → glial → autoantibody production) has correlational + mechanistic + interventional evidence in place but lacks the specific microglial receptor signaling axis that translates gut-derived signals into central neuroinflammation. Tian 2026 provides exactly that: TREM2 / SYK / NF-κB. Adds a candidate downstream-of-LPS signaling layer below the gut→serum-LPS step Dorta-Aguilar 2023 documented in FM patients.
- Same biochemical signature as Dorta-Aguilar 2023 FM cohort. Dorta-Aguilar reported elevated zonulin, LPS, sCD14, anti-β-LGB in FM and ME/CFS patients vs HCs. Tian's APP/PS1 mice show the same butyrate↓ + LPS↑ pattern. The dysbiosis → LPS → microglial-M1 chain is convergent across AD (Tian), FM (Dorta-Aguilar inferred), and substance-misuse-neurotoxicity (Tian deferred 2026-05-13 batch on Bacillus aerolatus). Strengthens the chain-redundancy property at the dysbiosis-inflammatory-axis level.
- Cross-condition repurposing-tier cure-path-arm candidate: fostamatinib (SYK inhibitor). Fostamatinib was FDA-approved in 2018 for chronic immune thrombocytopenia (ITP); it has 8+ years of post-approval safety data, established chronic dosing protocols, and oral administration. Tian's in vitro data show SYK inhibition attenuates M1 polarization independently of TREM2 activation — making fostamatinib a candidate microglial-M1-deactivator that bypasses the upstream gut-dysbiosis driver. Investigator-initiated stratified pilot framework: FM patients with TSPO-PET-positive microglial activation (Coluzzi 2025) + serum LPS / sCD14 elevation (Dorta-Aguilar 2023) → fostamatinib vs placebo with TSPO-PET ΔBPND primary endpoint.
- TREM2 as candidate FM biomarker dimension. TREM2 is principally a microglial-expressed receptor; soluble TREM2 (sTREM2) is detectable in CSF and to a lesser extent serum, and has been used as a biomarker of microglial-activation state in Alzheimer's biomarker work. Candidate addition to biomarker-mapping cohort: serum sTREM2 as a microglial-activation surrogate that's cheaper and less invasive than TSPO-PET.
- Connects to existing project H1 framework. NF-κB activation is one branch of the type-I IFN amplifier's downstream output; the LPS → TLR4 → NF-κB pathway parallels the mtDNA → cGAS-STING → NF-κB pathway. Adds a candidate convergence-with-H1 framing: LPS-driven NF-κB activation (microbiome-axis upstream) and mtDNA-driven NF-κB activation (HERV-mito-loop upstream) may share downstream effector consequences, strengthening the chain-redundancy property at the inflammatory-effector level too.
Open questions raised
- Q73 candidate. Are TREM2 expression or SYK phosphorylation levels altered in FM patient PBMCs or post-mortem brain tissue? Tractable: serum sTREM2 by ELISA in stored Seefried 2025 or Krock 2023 cohort; PBMC monocyte SYK-phosphorylation by flow cytometry if fresh-blood collection.
- Q74 candidate. Does fostamatinib (or another SYK inhibitor) attenuate central-sensitization or microglial activation in FM animal models? Tractable in the Dahl SS rat FAM-index platform (Ferrari 2026) — already validated for predictive validity against FM analog model.
- Does the FMT-reverses-pathology finding in AD mice generalize to FM? Martín Pérez 2024 systematic review showed FMT reduces FM symptoms but didn't measure TREM2/SYK/NF-κB markers. Combined-design BASIS-FM Stage 2 candidate: FMT + serial cf-mtDNA + sTREM2 + LPS/sCD14 measurement.
- Is the TREM2-downregulation phenotype reversible by direct TREM2 agonists (clinical-stage in AD: AL002, AL003) — and would TREM2 agonism be additive vs SYK antagonism in microglial M1 modulation?
- Does the chronic-stress P2X7-cGAS-STING entry to H1's amplifier (He 2026) intersect with the SYK pathway, or do they converge independently on NF-κB?