Aggregate Sequestration Hypothesis: Amyloid-like assemblies as inducible sinks that restrain SASP propagation in aging
Aggregate Sequestration Hypothesis
Core proposition: In aging cells, amyloid‑like protein aggregates function not as inert waste but as inducible, phase-separated sinks that capture misfolded clients and senescent‑associated secretory phenotype (SASP) factors, thereby limiting paracrine spread of senescence. Dissolving these sinks releases sequestered SASP, provoking a burst of inflammatory signaling that can be experimentally measurable.
Mechanistic rationale
- Phase-separated aggregates as SASP reservoirs – Liquid-liquid phase separation (LLPS) driven by oxidative thiol modification creates a dense, amyloid-prone core that can bind secretory proteins (IL-6, IL-8, MMPs) via hydrophobic patches and electrostatic interactions, similar to how stress granules sequester mRNAs 1.
- Thermodynamic sink capacity declines with age – The free-energy difference between soluble and aggregated states narrows as chaperone activity wanes, shifting the equilibrium toward larger, more stable fibrils that are less dynamic 2. When the sink saturates, excess SASP leaks out, fueling the paracrine senescence loop described in 's framework 3.
- Senolytic interruption – Removing SASP-secreting cells reduces extracellular oxidative pressure, allowing remaining cells to reset thiol redox balance, disassemble pathological aggregates via HSP70-mediated refolding, and restore LLPS dynamics 4.
Testable predictions
- Prediction 1: Pharmacological promotion of reversible LLPS (e.g., low-dose 1,6-hexanediol washout or small-molecule chaperone enhancers) will increase aggregate formation in senescent fibroblasts and decrease extracellular SASP levels measured by ELISA, whereas aggregate dissolution with HSP70 inhibitors will raise SASP.
- Prediction 2: CRISPR-mediated knock-down of key aggregate-nucleating proteins (e.g., TIA1, FUS) will reduce the capacity of cells to sequester SASP reporters (IL-6-GFP fusions) and accelerate senescence spread in co-culture assays.
- Prediction 3: In aged mouse tissues, imaging mass spectrometry will reveal a spatial inverse correlation between intra-cellular amyloid-signal intensity (Thioflavin-T) and nearby SASP cytokine concentration; senolytic treatment should flatten this gradient.
Falsifiability
If enhancing aggregate formation does not lower SASP, or if disrupting aggregates fails to increase SASP despite verified changes in aggregate load (confirmed by filter-trap assay and microscopy), the hypothesis is refuted. Likewise, a lack of inverse correlation between aggregate burden and SASP in vivo after senolytic clearance would falsify the proposed sink mechanism.
Broader implication
Should aggregates serve as inducible SASP sinks, therapeutic strategies that modulate rather than eliminate these structures—tuning their material state—could preserve proteostatic containment while preventing the inflammatory burst that drives age-related tissue decline.