Hypothesis: Stress granule metastability determines the switch from protective aggregation to pathogenic seeding

The proteostasis network responds to chronic misfolding stress by sequestering risky proteins into stress granules (SGs) that act as metastable sinks, steering clients away from irreversible fibrils2. When SG material properties shift toward increased stability—due to mutations, post‑translational modifications, or age‑related decline in chaperone activity—the same condensates begin to nucleate rather than inhibit amyloid formation. This predicts that manipulating SG material state will toggle aggregation outcomes without altering overall protein load.

Testable prediction: In a cellular model expressing an aggregation‑prone reporter (e.g., 'PolyQ‑GFP'), pharmacological or genetic stiffening of SGs will increase the rate of fibrillar seed formation measured by fluorescence recovery after photobleaching (FRAP) and Thioflavin‑T uptake, whereas SG fluidization will reduce seed burden despite unchanged total aggregate mass.

Experimental design: 1) Use CRISPR to introduce point mutations in SG nucleators (G3BP1) known to alter material properties2. 2) Treat parallel cultures with low doses of 1,6‑hexanediol or with overexpress HSP70 to promote fluidity. 3) Quantify SG dynamics via FRAP, seed competence via seeding assay in naïve cells, and cell viability over time. 4) Correlate SG half‑time of recovery with seeding efficiency.

Falsifiable outcome: If SG stiffening does not change seeding propensity, or fluidizing SGs fails to lower seed load, the hypothesis that SG metastability gates the protective‑to‑pathogenic transition is refuted. Conversely, a consistent inverse relationship between SG fluidity and seed activity across multiple stressors (heat shock, oxidative stress, proteasome inhibition) would support the model.

Mechanistic insight: SGs may not merely hold misfolded proteins; their internal microenvironment—regulated by RNA‑protein interactions, electrostatic screening, and post‑translational modifications—can either sterically block β‑sheet stacking or locally concentrate nucleation‑competent conformers. Age‑dependent decline in ATP‑dependent chaperones reduces the energy barrier for SG solidification, tipping the balance toward seed generation. This reframes therapeutic strategies: rather than dissolving aggregates globally, interventions should tune SG material state to preserve their sink function while preventing premature solidification.