We’ve known for a while that ETC subunits like NDUFS1 and SDHA are uniquely prone to modification by HNE and MDA [https://pmc.ncbi.nlm.nih.gov/articles/PMC2080815/]. Yet, researchers usually treat these adducts merely as static evidence that damage occurred. I’m proposing the "Proteostatic Sink" Hypothesis: these adducts aren't just markers; their accumulation triggers a pathological translocation of 26S proteasome complexes from the cytosol to the mitochondrial outer membrane (MOM) and intermembrane space.

The Mechanism

Lipid peroxidation products—especially HNE—function as electrophilic decoys. When matrix proteins like NDUFS1 are adducted, they shift shape, exposing hydrophobic patches and cryptic epitopes that the mitochondrial import machinery or stress chaperones (like mtHSP70) can't ignore. I suspect this leads to a "Proteostatic Sink" effect:

1. Sequestration: Chronic buildup of these adducted ETC subunits draws cytosolic 26S proteasomes to the MOM. This is likely an attempt to clear the damage, but it backfires. The high concentration of electrophilic lipids at the IMM/MOM interface "chokes" the proteasomes; the 19S regulators get adducted themselves, stalling the machinery exactly where it’s trying to import proteins.

2. Competitive Sourcing: As the mitochondria pull in these proteasomes, the cytosolic pool shrinks. This could explain why we see systemic protein aggregation in aging; it may not be a primary failure of the cytosol, but a secondary side effect of mitochondrial hijacking [https://pmc.ncbi.nlm.nih.gov/articles/PMC12121948/].

3. Membrane Remodeling: Stalled proteasomes likely encourage the formation of "lipid whiskers" by locally concentrating polyunsaturated fatty acid peroxidation byproducts [https://pmc.ncbi.nlm.nih.gov/articles/PMC12121948/]. This sets up a vicious cycle: more peroxidation brings in more proteasomes, which in turn fuels membrane instability.

Testable Predictions

• Spatial Proteomics: Using APEX2-labeling of the 26S proteasome, we should see a spike in subunits like PSMD1 and PSMC1 within the mitochondrial fractions of aged mouse kidney and cardiac tissue, but not in young tissue.
• Catalytic Stalling: If we expose purified 26S proteasomes to HNE levels seen in aged mitochondria, we should see the 19S regulatory particle’s ATPase activity drop in a dose-dependent way.
• Intervention Falsification: If this sink really drives senescence, then mitochondria-targeted scavenging (e.g., SkQ1) should do more than just lower HNE [https://www.aging-us.com/article/101174/text]. It should restore the mobility of cytosolic proteasomes and clear aggregates faster, which we could track using Dendra2-ubiquitin flux assays.

This shifts the focus from "damage-by-accumulation" to "damage-by-sequestration." It offers a cleaner explanation for why mitochondrial dysfunction seems to consistently trigger broader proteostatic collapse in aging and neurodegeneration.