NLRP3-driven mitochondrial DNA release epigenetically locks T‑cell exhaustion via cGAS‑STING–DNMT3a axis

Hypothesis: Chronic NLRP3 inflammasome activation in aging immune cells releases oxidized mitochondrial DNA (mtDNA) into the cytosol, where it engages the cGAS‑STING pathway. This signaling cascade upregulates DNMT3a activity and promotes promoter methylation of exhaustion‑associated genes (PD‑1, TIM‑3, TOX), thereby converting reversible T‑cell dysfunction into an epigenetically fixed exhausted state. Restoring autophagy or inhibiting NLRP3 prevents mtDNA efflux, blocks cGAS‑STING–DNMT3a signaling, and preserves T‑cell plasticity.

Mechanistic rationale:

1. Autophagy failure → accumulation of damaged mitochondria → mtDNA oxidation and release (linking autophagy decline to NLRP3 activation) {1}.
2. Cytosolic mtDNA activates cGAS → STING → TBK1/IKKε → IRF3 phosphorylation, which not only drives type‑I IFN production but also phosphorylates and stabilizes DNMT3a, enhancing its methyltransferase activity {2}.
3. Elevated DNMT3a methylates CpG islands in the promoters of PD‑1, TIM‑3, and TOX, locking their expression in a high‑exhaustion pattern that persists even after the inflammatory stimulus wanes.
4. NLRP3 inhibition (e.g., OLT1177) reduces inflammasome oligomerization and IL‑1β release, limiting mitochondrial damage and mtDNA release {3}. Rapamycin‑induced autophagy clears damaged mitochondria before mtDNA can escape, providing a synergistic blockade.

Testable predictions:

• In CD8⁺ T cells from elderly donors, cytosolic mtDNA levels will correlate positively with phospho‑STING, DNMT3a activity, and methylation of PD‑1/TIM‑3/TOX promoters, and inversely with autophagic flux (LC3‑II/I ratio).
• Treatment with OLT1177 will decrease cytosolic mtDNA and phospho‑STING, leading to reduced DNMT3a activity and lower promoter methylation within 48 h.
• Combined OLT1177 + rapamycin will restore autophagic flux, further diminish mtDNA release, and prevent the epigenetic fixation of exhaustion markers upon chronic antigenic stimulation, whereas either agent alone will show only partial effects.
• Epigenetic editing (CRISPR‑dCas9‑TET1) targeting the TOX promoter will rescue cytokine production even when NLRP3 remains active, demonstrating that methylation is downstream of inflammasome signaling.

Falsifiability: If NLRP3 inhibition fails to reduce cytosolic mtDNA or does not alter DNMT3a activity/T‑cell exhaustion marker methylation, or if autophagy enhancement does not lower mtDNA release, the proposed mechanistic link would be refuted. Conversely, observing the predicted biochemical and epigenetic changes would support the hypothesis.