Hypothesis

Aged hematopoietic stem cells (HSCs) accumulate mitochondrial DNA (mtDNA) leaks that activate the cytosolic DNA sensor cGAS-STING pathway in myeloid descendants, turning them into a chronic source of SASP and inflammaging. Inhibiting cGAS-STING in these cells will reset immune senescence, enhance senescent‑cell clearance, and delay multi‑organ aging.

Mechanistic Basis

1. mtDNA release from aged HSCs – Age-related decline in mitophagy and increased ROS cause mtDNA to escape into the cytosol of HSCs and their progeny (1).
2. cGAS-STING activation – Cytosolic mtDNA binds cGAS, producing cGAMP, which stimulates STING-dependent TBK1-IRF3 signaling, driving NF‑κB and interferon‑stimulated gene expression that fuels SASP secretion (2).
3. Paracrine senescence – SASP cytokines (IL-6, IL-1β, MMPs) from myeloid cells induce secondary senescence in parenchymal cells of liver, kidney, muscle, creating a feed‑forward loop of tissue damage and further immune dysfunction.

Novel insight: The cGAS-STING axis acts as a molecular "alarmlight" that converts intrinsic HSC aging into extrinsic inflammatory signaling. Unlike broad anti‑inflammatory approaches, targeting this node preserves pathogen‑sensing capacity while silencing the maladaptive SASP program.

Predictions

• Pharmacological inhibition of STING (e.g., with C-176) in aged mice will reduce SASP cytokine levels in plasma and immune cell supernatants without compromising acute infection responses.
• Adoptive transfer of STING‑deficient aged HSCs into young recipients will prevent the induction of systemic senescence seen with wild‑type aged HSCs.
• Long‑term STING inhibition will lower senescent‑cell burden (p16^INK4a^+, SA‑β‑gal^+) in non‑lymphoid tissues and improve functional readouts (grip strength, treadmill endurance, glomerular filtration rate).
• These benefits will be attenuated if senescent‑cell clearance is blocked (e.g., via anti-NK1.1 antibody), confirming that improved surveillance mediates the effect.

Experimental Approach

1. In vitro: Isolate HSCs from 20‑month‑old mice, culture with STING inhibitor or DMSO, measure mtDNA efflux (qPCR for cytosolic mtDNA), cGAMP levels (ELISA), and SASP secretion (IL-6, IL-1β) by Luminex.
2. In vivo: Treat aged mice (20‑mo) with C-176 or vehicle for 8 weeks. Collect blood and tissues for cytokine profiling, flow‑cytometric analysis of myeloid activation markers (CD86, MHC‑II), and senescent‑cell staining.
3. Transplantation: Transplant HSCs from treated or untreated aged donors into lethally irradiated young recipients (3 mo). Monitor chimerism, SASP in serum, and tissue senescence at 4 and 8 weeks post‑transplant.
4. Functional assays: Grip strength, rotarod, indirect calorimetry, and renal clearance tests.
5. Controls: Include young mice, STING‑KO aged mice, and a group receiving senolytic (dasatinib + quercetin) to compare magnitude of effect.

If STING inhibition reverses the immune‑driven aging circuit, it would position the cGAS-STING pathway as a leverage point where rejuvenating the immune system precedes and potentially drives broader systemic rejuvenation.