Hypothesis

When the cellular capacity to form organized aggresomes is exceeded, hyper‑acetylation of vimentin within the cage impairs HDAC6‑dynein recruitment, stalling aggregate transport and converting protective deposits into static, oligomer‑seeding inclusions.

Mechanistic Basis

• Aggresomes rely on a vimentin cage that is dynamically remodeled by acetylation/deacetylation cycles 2.
• HDAC6 binds acetylated vimentin, linking cargo to dynein for microtubule‑minus‑end transport.
• Chronic stress in aging raises cytosolic acetyl‑CoA and reduces SIRT2 activity, leading to vimentin hyper‑acetylation.
• Hyper‑acetylated vimentin has lower affinity for HDAC6, weakening the dynein bridge and causing aggregates to stall at the perinuclear region.
• Stalled aggregates lose the protective chaperone exchange and begin to expose β‑sheet rich surfaces that seed toxic oligomers.

Testable Predictions

1. In aged cells, vimentin acetylation levels will correlate positively with the size of stationary aggresome‑like inclusions and negatively with HDAC6 colocalization.
2. Pharmacological increase of SIRT2 activity or genetic HDAC6 overexpression will reduce vimentin acetylation, restore dynein‑driven transport, and lower soluble oligomer concentrations despite unchanged total aggregate load.
3. Conversely, mimicking vimentin acetylation (e.g., K→Q mutants) in young cells will reproduce the aged phenotype: increased stationary aggregates, higher oligomer toxicity, and reduced cell viability.

Experimental Approach

• Model: Human iPSC‑derived neurons or fibroblasts treated with low‑dose proteasome inhibitor (MG‑132) to induce misfolded protein load, compared between young (<30 passages) and aged (>60 passages) cultures.
• Readouts:
  • Immunofluorescence for vimentin acetylation (acetyl‑lysine), HDAC6, dynein, and ubiquitin.
  • Live‑cell imaging of aggregate movement along microtubules (kymograph analysis).
  • Filter‑trap assay and conformation‑specific oligomer antibodies (A11) to quantify toxic oligomers.
  • Cell viability (MTT) and apoptosis (caspase‑3).
• Interventions:
  • SIRT2 activator (AGK2) or HDAC6 overexpression via lentivirus.
  • Vimentin WT vs. acetylation‑mimic (K49Q/K52Q) mutants via CRISPR knock‑in.
• Analysis: Correlation of acetylation status with transport velocity (µm/s) and oligomer levels; statistical comparison using ANOVA with post‑hoc Tukey.

Potential Implications

If validated, the hypothesis reframes therapeutic strategies: enhancing vimentin deacetylation (via SIRT2 activators or HDAC6 upregulation) could re‑engage the protective aggresome machinery even when aggregate burden is high, shifting the equilibrium from toxic oligomers back to inert deposits. This approach complements, rather than contradicts, efforts to boost autophagy or proteasome activity, offering a node where the proteostasis network can be tuned to preserve the ‘last attempt at order’ without triggering pathological sequestration.

References

[1] Aggresomes as organized defense – https://pmc.ncbi.nlm.nih.gov/articles/PMC4451085/ [2] Microtubule transport of aggregates – https://pmc.ncbi.nlm.nih.gov/articles/PMC4204729/ [3] Age‑related increase in aggregation – https://www.aging-us.com/article/101141/text [4] Rapid amyloid‑like aggregates from nascent proteins – https://elifesciences.org/articles/43059