Adduct-Induced Conformational Switching of Mitochondrial Mitophagy Receptors as a Strain-Specific Determinant of Aging

Hypothesis

Lipid peroxidation adducts on mitochondrial proteins do more than indiscriminately damage function; they act as redox‑sensitive switches that alter the conformation of mitophagy receptors (BNIP3, FUNDC1, PGAM5) and thereby modulate their ability to recruit the autophagy machinery. In strains that accumulate adducts (e.g., C57BL/6), modification of specific lysine residues on these receptors promotes exposure of LC3‑interacting region (LIR) motifs, paradoxically enhancing mitophagy early but leading to receptor saturation and impaired clearance with age. In resistant strains (e.g., DBA/2), lower adduct burden or higher activity of aldehyde‑dehydratase enzymes (ALDH2, SIRT3) prevents this conformational shift, preserving receptor flexibility and sustaining mitophagic flux. Thus, the strain‑dependent trajectory of mitochondrial aging hinges on whether adduct accumulation drives a productive‑to‑non‑productive switch in mitophagy signaling.

Mechanistic Reasoning

1. Adduct‑induced conformational change – HNE/MDA form Michael‑addition adducts on lysine side chains, adding bulk and altering local charge. Structural modeling of BNIP3’s transmembrane domain predicts that modification of Lys‑27 and Lys‑31 destabilizes the α‑helix, exposing a buried LIR motif (WxxL). Similar sites exist in FUNDC1 (Lys‑49) and PGAM5 (Lys‑112).
2. Strain‑specific detoxification – C57BL/6 mice show lower basal ALDH2 activity and reduced SIRT3 deacetylase levels compared with DBA/2, as reported in proteomic surveys of liver mitochondria[2]. Consequently, adducts persist longer, increasing the probability of receptor modification.
3. Functional outcome – Early‑life adduct‑driven LIR exposure boosts mitophagy, clearing mildly damaged mitochondria. With chronic accumulation, receptors become constitutively modified, leading to either excessive autophagy (mitochondrial loss) or, paradoxically, receptor sequestration in aggregates that block LC3 binding, explaining the observed decline in mitophagy flux[3].
4. Testable prediction – Manipulating adduct levels or receptor modification status will invert the age‑related mitophagy phenotype in a strain‑dependent manner.

Experimental Plan

• Adduct mapping – Use immunoprecipitation of BNIP3, FUNDC1, PGAM5 from mitochondria of young and old C57BL/6 and DBA/2 mice, followed by LC‑MS/MS to quantify HNE/MDA adducts on predicted lysine residues[1][6].
• Conformational assay – Limited proteolysis coupled with western blot to detect increased LIR exposure in adduct‑enriched samples; synthesize peptide ligands bearing adduct‑modified lysines to measure LC3 binding affinity by surface plasmon resonance.
• Genetic manipulation – Overexpress mitochondrial ALDH2 or SIRT3 specifically in C57BL/6 muscle (AAV9‑MTC) and assess whether adduct burden on mitophagy receptors declines and mitophagy flux (mt‑Keima assay) improves with age[4][5]. Conversely, knock down ALDH2 in DBA/2 to see if adduct accumulation and premature mitophagy defects emerge.
• Pharmacological rescue – Treat aged C57BL/6 mice with the aldehyde‑scavenging compound hydralazine or a mito‑targeted GSH ester and monitor receptor modification, LC3 binding, and mitochondrial respiration.
• Readouts – Measure mitochondrial ROS (MitoSOX), ATP production, and mitophagy flux; correlate with tissue‑specific phenotypes (grip strength, fatigue).

Expected Outcomes & Falsifiability

If the hypothesis is correct, (1) adducts will be enriched on specific lysines of BNIP3/FUNDC1/PGAM5 in aged C57BL/6 but not DBA/2; (2) adduct‑modified receptors will show heightened LIR exposure and altered LC3 binding in vitro; (3) boosting ALDH2/SIRT3 will reduce receptor adducts, restore normal mitophagy flux, and alleviate age‑related decline in C57BL/6; (4) reducing ALDH2/SIRT3 in DBA/2 will reproduce the adduct‑dependent mitophagy defect seen in C57BL/6. Failure to observe adduct‑dependent conformational changes or lack of phenotypic rescue upon modulating detoxification pathways would falsify the model.