Hypothesis

HNE adduct formation on the mitochondrial Complex I subunit NDUFS1 functions as a redox‑sensitive retrograde signal that couples mitochondrial ROS output to nuclear epigenetic remodeling, thereby acting as an upstream coordinator of multiple aging hallmarks.

Mechanistic Rationale

1. Lipid peroxidation generates HNE, which covalently modifies NDUFS1 at Cys‑39 (shown to increase ~8‑fold with age)【2】.
2. This modification destabilizes Complex I, increasing electron leak and ROS, while also altering NDUFS1’s affinity for mitochondrial ribosomal proteins, leading to a selective defect in translation of mitochondrially encoded oxidative phosphorylation subunits.
3. The resulting imbalance triggers release of mitochondrial double‑stranded RNA (mt‑dsRNA) into the cytosol, activating the MDA5‑MAVS interferon pathway and low‑grade NF‑κB signaling.
4. Concurrently, HNE‑NDUFS1 promotes export of acetyl‑CoA from the matrix via altered citrate shuttle activity, decreasing nuclear acetyl‑CoA levels and reducing histone acetylation at promoters of proteostasis and DNA‑repair genes.
5. The combined signaling—innate immune activation plus epigenetic hypoacetylation—replicates several hallmarks: inflammation, genomic instability, loss of proteostasis, and cellular senescence.

Thus, HNE‑NDUFS1 sits at the nexus where a mitochondrial lesion propagates both ROS‑driven damage and nuclear reprogramming, providing a plausible upstream controller.

Testable Predictions

• Preventing HNE adduction on NDUFS1 (e.g., knock‑in of Cys39Ser) will blunt age‑dependent ROS increase without affecting basal mitochondrial content.
• Mice with the Cys39Ser substitution will show attenuated mt‑dsRNA release, lower cytosolic MDA5 activation, and preserved nuclear histone acetylation levels during aging.
• Consequently, these mice will exhibit delayed onset of multiple hallmarks: reduced protein carbonylation, lower γH2AX foci, decreased SASP expression, and extended median lifespan compared with wild‑type controls.
• Conversely, mimicking the HNE adduct by targeted crosslinking of NDUFS1 (using a photo‑activatable HNE analog) in young mice should precipitate premature hallmarks.

Experimental Approach

1. Generate CRISPR‑edited C57BL/6 mice carrying NDUFS1‑C39S.
2. Cohorts aged to 24 months; assess:
   • Mitochondrial ROS (MitoSOX) and respiration (Seahorse)【1】.
   • HNE adduct levels via dot‑blot with anti‑HNE【2】.
   • Cytosolic mt‑dsRNA (immunofluorescence for MDA5) and phospho‑IRF3.
   • Nuclear acetyl‑CoA (LC‑MS) and histone H3K27ac (ChIP‑seq).
   • Hallmark readouts: protein carbonylation (OxyBlot), DNA damage (γH2AX IHC), senescence (p16^INK4a^ qPCR), plasma cytokines.
3. Parallel pharmacologic arm: treat young wild‑type mice with a mitochondria‑targeted HNE scavenger (e.g., Mito‑PPG) and compare outcomes.
4. Gain‑of‑function: deliver AAV9‑mito‑targeted HNE‑NDUFS1 crosslinker to young mice; monitor early hallmark emergence.

Expected Outcomes and Falsifiability

If HNE‑NDUFS1 is a upstream coordinator, the C39S mice will dissociate mitochondrial ROS from downstream hallmarks: ROS may remain elevated due to other sources, yet inflammatory, epigenetic, and proteostatic markers will stay youthful. Lack of such dissociation would falsify the hypothesis. Similarly, inducing the adduct in young animals must recapitulate the multi‑hallmark phenotype; failure to do so would indicate that HNE‑NDUFS1 is correlative rather than causative.