Mitochondrial heteroplasmy drives intercellular inflammaging via exosomal mtDNA‑DAMP signaling

Hypothesis: Heteroplasmic mutant mtDNA released in mitochondrial‑derived vesicles (MDVs) or exosomes acts as a damage‑associated molecular pattern (DAMP) that triggers cGAS‑STING activation in recipient cells, propagating a sterile inflammatory response that accelerates nuclear epigenetic aging and tissue dysfunction.

Rationale: mtDNA lacks histones and repair machinery, leading to higher mutation rates and oxidative damage that accumulate with age [mtDNA mutations accumulate with age]. These mutant genomes are packaged into MDVs and exosomes under stress, a process observed in cultured neurons and macrophages. Once extracellular, mtDNA can engage cytosolic DNA sensors; oxidized mtDNA is a potent agonist of the cGAS‑STING pathway, driving type‑I interferon production and NF‑κB‑mediated inflammasome activation [oxidized mtDNA activates cGAS‑STING] (citation added for context). Chronic cGAS‑STING signaling sustains low‑grade inflammation, alters NAD⁺ metabolism, and shifts the nuclear epigenome toward age‑associated methylation patterns, thereby linking mitochondrial genotype to systemic aging.

Novel mechanistic insight: We propose that the inflammaging signal is not merely a by‑product of ROS leakage but a specific nucleic‑acid‑based communication channel. Heteroplasmy level determines the potency of the DAMP: higher mutant load increases immunostimulatory CpG motifs and 8‑oxoguanine residues, strengthening cGAS binding. Consequently, tissues with high energy demand (brain, muscle) exhibit a threshold where exosomal mtDNA transfer propagates a wave of inflammation that outpaces cell‑autonomous damage.

Testable predictions:

1. Isolating exosomes from aged mice with high mtDNA heteroplasmy will induce cGAS‑STING phosphorylation and interferon‑β secretion in naïve young fibroblasts; exosomes from heteroplasmy‑reduced mice (via MitoTALEN treatment) will fail to do so [MitoTALENs eliminate mutant mtDNA].
2. Pharmacological inhibition of STING (e.g., H‑151) in aged animals will attenuate the spread of inflammation markers (IL‑6, CCL2) and delay epigenetic clock advancement measured by murine blood methylation arrays.
3. Engineered exosomes carrying wild‑type mtDNA will competitively inhibit mutant mtDNA‑induced STING activation, rescuing respiratory capacity in recipient myotubes—a rescue observable with Seahorse assays.
4. Single‑cell multi‑omics of human donors will reveal a correlation between circulating exosomal mtDNA mutant load, cGAS‑STING pathway activation signatures in monocytes, and accelerated GrimAge acceleration.

Falsifiability: If exosomal mtDNA from heteroplasmic cells does not activate cGAS‑STING in vitro, or if STING blockade does not modify aging biomarkers in vivo despite successful mtDNA editing, the hypothesis is refuted. Conversely, positive results would elevate mtDNA‑derived nucleic acid signaling to a central mechanistic axis of aging, redirecting therapeutic focus toward intercellular nucleic acid trafficking alongside organelle‑targeted genome editing.