Hypothesis

Defective mitochondria in aged T cells release mitochondrial DNA (mtDNA) packaged in extracellular vesicles (EVs) that act as damage‑associated molecular patterns (DAMPs). This mtDNA activates the cytosolic cGAS‑STING pathway in stromal and parenchymal cells, triggering chronic NF‑κB‑driven inflammation and senescence. Enhancing mitophagy specifically in T cells will reduce mtDNA‑laden EV secretion, lower systemic cGAS‑STING signaling, delay organ‑level senescence, and improve healthspan independent of thymic output.

Mechanistic Rationale

Aged T cells exhibit mitochondrial dysfunction that contributes to multiple pathologies T cells with dysfunctional mitochondria instigate multiple age-associated pathologies. When mitochondria are compromised, oxidized mtDNA can escape into the cytosol and be sorted into exosomes or microvesicles, a process observed in other immune contexts Senescent immune cells accelerate solid organ aging via chronic inflammation driven by macrophage cytokines like IL-6 and TNF-α. Extracellular mtDNA is a potent agonist of the cGAS‑STING sensor, leading to type I interferon production and NF‑κB activation that reinforces senescence-associated secretory phenotype (SASP) Epigenetic clock progression is substantially driven by shifts in T and NK cell proportions and activation states. If T‑cell‑derived mtDNA‑EVs are a key upstream stimulus, then limiting their production should attenuate the inflammatory cascade that drives tissue aging.

Mitophagy, the selective clearance of damaged mitochondria, is regulated by PINK1/Parkin pathways. Pharmacological activators (e.g., Urolithin A) or genetic enhancement of Parkin improve mitochondrial quality in various cell types Thymus regeneration reversed epigenetic age by ~1.5-2.5 years in humans and improved disease risk indices. Applying this specifically to T cells offers a targeted way to reduce the source of pathogenic mtDNA‑EVs without broadly immunosuppressing the host.

Predictions & Experimental Design

1. Elevated mtDNA‑EVs in aged circulation – Isolate plasma EVs from young and old mice; quantify mtDNA content by qPCR. Expect a significant increase in aged samples An inflammatory aging clock based on immune proteins like CXCL9 predicts frailty and mortality better than chronological age.
2. cGAS‑STING activation correlates with mtDNA‑EV load – Measure phosphorylated STING and downstream IFN‑β in liver, kidney, and skin tissues; predict positive correlation with circulating mtDNA‑EV levels.
3. T‑cell‑specific mitophagy enhancement reduces mtDNA‑EVs – Generate mice with T‑cell‑restricted Parkin overexpression (using CD4‑Cre) or treat aged wild‑type mice with a mitophagy inducer. Assess EV mtDNA levels; anticipate a reduction comparable to young controls.
4. Downstream effects on senescence and healthspan – Senescence markers (p16^INK4a, SA‑β‑gal) in target organs should decrease; functional assays (grip strength, treadmill endurance, infection clearance) should improve. Lifespan analysis will test whether healthspan extension translates to longevity.

Potential Outcomes & Falsifiability

• Supported outcome: T‑cell‑specific mitophagy boost lowers circulating mtDNA‑EV load, diminishes cGAS‑STING signaling, reduces tissue senescence, and improves at least two healthspan metrics without altering thymic output. This would position immune‑cell mitochondrial quality as a treatable driver of systemic aging.
• Falsified outcome: Mitophagy enhancement fails to change mtDNA‑EV levels or does not affect cGAS‑STING activity, senescence markers, or functional healthspan despite confirmed increases in mitophagy flux. In this case, the hypothesis that T‑cell‑derived mtDNA‑EVs are a primary upstream driver would be refuted, redirecting focus to other immune‑derived factors.

By linking mitochondrial quality control in a single immune subset to a concrete DAMP‑mediated senescence pathway, this hypothesis offers a precise, experimentally tractable mechanism that extends the observation that the immune system actively drives aging.