2026 — Xu — Tempol interrupts oxidative-stress → mtDNA → cGAS-STING in autoimmune uveitis

One-paragraph summary

Mechanistic primary study in an experimental autoimmune uveitis (EAU) rat model with parallel patient-sample comparison. Six experimental arms: normal control, EAU vehicle, EAU + cGAS shRNA knockdown, EAU + empty vector, EAU + STING inhibitor H-151, and EAU + Tempol (4-hydroxy-TEMPO, a nitroxide free-radical scavenger). Measurements: ROS, mitochondrial membrane potential, mitochondrial respiration (Seahorse XF), cytosolic mtDNA, cGAS-STING pathway activation (cGAS, STING, p-TBK1, p-p65, IFN-β by Western), downstream inflammatory output (TNF-α, iNOS), macrophage polarization (M1/M2), mitophagy markers (PINK1/Parkin, p62), antioxidant pathway (Nrf2/Keap1/HO-1). Key empirical chain: EAU induces elevated ROS → loss of mitochondrial membrane potential → impaired mitochondrial respiration → elevated cytosolic mtDNA → cGAS-STING-NF-κB activation → IFN-β + TNF-α + iNOS upregulation → M1 macrophage polarization → ocular tissue injury. Tempol, sh-cGAS, and H-151 each independently interrupt this chain, each restoring mitochondrial homeostasis, reducing cytosolic mtDNA, decreasing cGAS-STING-NF-κB activation, improving mitophagy quality control, and reducing M1 polarization. For the project, this paper establishes Tempol as a candidate fourth OTC-tier loop-interrupter in §12.6 alongside resveratrol (Duan 2026), with a distinct upstream mechanism (ROS scavenging rather than STING-translocation inhibition). Tempol acts at the upstream end of the H1 HERV-mitochondrial-inflammation loop (oxidative stress → mtDNA release), while resveratrol acts at the downstream end (STING ER-Golgi translocation + TBK1 phosphorylation). Combined-arm logic candidate.

Claims as triples

• oxidative_stress — causes → mitochondrial_dysfunction [evidence: EAU model ROS elevation precedes loss of mitochondrial membrane potential; confidence: established (in EAU)]
• mitochondrial_dysfunction — causes → mtDNA cytosol_release [evidence: cytosolic mtDNA quantitatively elevated in EAU; confidence: established (in EAU)]
• mtDNA — activates → cGAS_STING_pathway [evidence: pathway activation tracks with cytosolic mtDNA; sh-cGAS confirms necessity; confidence: established]
• tempol — interrupts → herv_mito_inflammation_loop [evidence: Tempol reduces oxidative stress, mtDNA, cGAS-STING activation, M1 polarization in EAU; confidence: emerging]
• tempol — has_mechanism → ros_scavenger [evidence: nitroxide free-radical scavenger pharmacology; confidence: established]
• H-151 — has_mechanism → sting_inhibitor [evidence: small-molecule clinical-stage STING inhibitor used as pathway-causal probe; confidence: established]

Triangulation notes

• Adds Tempol as a candidate §12.6 OTC-tier intervention. The white paper §12.6 currently names resveratrol (Duan 2026) as the OTC-tier loop-interrupter; Tempol adds a second compound with an upstream-of-mtDNA mechanism (ROS scavenging) that is mechanistically complementary to resveratrol's downstream-of-STING mechanism (translocation + TBK1 inhibition).
• Provides a third pathway-causal confirmation of the cGAS-STING amplifier of the HERV-mitochondrial-inflammation loop, with sh-cGAS (genetic) and H-151 (pharmacological) each reproducing the protective effect.
• H-151 is the same clinical-stage STING inhibitor under watchlist WL-6 (clinical-stage STING inhibitors in autoinflammatory disease). This paper provides preclinical autoimmune-disease evidence supporting WL-6's monitoring rationale.
• Cross-condition generalizability of the cGAS-STING amplifier. This is the third condition (alongside He et al 2026 chronic-stress depression and Duan et al 2026 cognitive decline) demonstrating the mtDNA→cGAS-STING→type-I-IFN amplifier as a chain-redundant convergent mechanism — strengthening the project's framing of this amplifier as condition-agnostic.

Open questions raised

• Has Tempol been tested in FM, ME/CFS, post-COVID, or HERV+ cohorts? (Tempol has been used in oncology and radioprotection trials — pharmacokinetics in chronic-pain populations need review.)
• Would combined-arm Tempol + resveratrol produce additive loop-interrupter effects, given the upstream + downstream mechanistic separation?
• What is the maximum-tolerated-dose ceiling for Tempol in chronic dosing (the EAU model used short-term high-dose; chronic FM dosing would require different pharmacokinetic profile)?