Hypothesis

Hierarchical autophagy selectively removes damaged centriolar satellites (e.g., PCM1‑containing complexes) before degrading core centriolar proteins such as Cep63. In aged stem cells, oxidative stress modifies PCM1, weakening its LIR‑GABARAP interaction and causing it to escape autophagy. The resulting accumulation of abnormal satellites nucleates ectopic microtubule‑organizing centers, driving centrosome amplification and chromosomal instability. Thus, aging‑related decline stems not from loss of autophagy capacity per se but from a breakdown in the substrate‑selection hierarchy.

Mechanistic Rationale

• The autophagy machinery recognizes short LIR motifs on PCM1 that bind GABARAP/LLC proteins with high affinity, earmarking satellites for 'doryphagy' [1]
• Oxidative modifications (e.g., cysteine sulfonation) of PCM1 alter its LIR motif conformation, reducing GABARAP binding without affecting its structural integrity.
• When PCM1 escapes autophagy, it continues to recruit pericentriolar material, forming aberrant satellites that act as seeding platforms for extra centrioles.
• Cep63, lacking redox‑sensitive residues, continues to be cleared via 'centrinophagy' [2], creating a mismatch where satellite load rises while core centriole turnover remains normal.
• This imbalance produces centrosome amplification, a known driver of anaphase lag and micronuclei formation in aged tissues [3,4].

Testable Predictions

1. In old mouse intestinal stem cells, PCM1‑LIR affinity for GABARAP will be significantly reduced compared with young cells, measurable by pull‑down assays.
2. Pharmacological stabilization of the PCM1‑GABARAP interaction (e.g., using a peptide mimetic) will restore selective satellite clearance, lower centrosome amplification, and decrease chromosomal instability scores.
3. Conversely, forced expression of a phospho‑mimetic PCM1 mutant that disrupts LIR binding will phenocopy aging‑associated centrosome excess even in young cells.
4. Proteomic analysis of autophagosome‑enriched fractions will show a shift: decreased PCM1 peptide abundance but unchanged Cep63 levels in aged samples.

Experimental Approach

• Isolate Lgr5+ stem cells from young (2 mo) and old (24 mo) mice.
• Perform GST‑LIR pull‑downs with recombinant GABARAPLC3, quantify bound PCM1 by Western blot and mass spec.
• Treat old cell cultures with a cell‑permeable PCM1‑LIR stabilizing peptide (derived from the PCM1 LIR flank) and assess centrosome number (γ‑tubulin immunostaining) and mitotic errors (live‑cell imaging of H2B‑mCherry).
• Generate a CRISPR knock‑in of PCM1‑S→D mutant mimicking oxidative sulfonation; evaluate centrosome amplification in young animals.
• Conduct autophagosome enrichment followed by LC3‑Western and targeted proteomics to compare PCM1 and Cep63 turnover.

Implications

If confirmed, this model reframes autophagy decline in aging as a qualitative defect in substrate triage rather than a quantitative loss of bulk degradation. It pinpoints PCM1‑LIR regulation as a nodal point where oxidative stress hijacks the centrosome quality‑control hierarchy, offering a therapeutic window to preserve genomic stability in stem cell niches without globally upregulating autophagy, which may have deleterious side‑effects.