Hypothesis

Proteostatic amyloid and tau aggregates act as controlled sinks for redox‑active iron, preventing the Fenton‑driven lipid peroxidation that triggers ferroptosis. When the cell’s disaggregation machinery (Hsp70‑Hsp110‑Bag3) extracts proteins from these deposits, the released iron must be immediately sequestered by cytosolic chelators (e.g., ferritin, NCOA4) or exported; otherwise, the surge of free Fe²⁺ overwhelms antioxidant defenses and drives lethal membrane damage. Thus, therapeutic strategies that dissolve aggregates without enhancing iron handling convert a protective depot into a source of oxidative catastrophe.

Mechanistic Rationale

1. Iron‑binding capacity of aggregates – In vitro, fibrillar Aβ and tau bind Fe²⁺/Fe³⁺ with high affinity, reducing catalytic iron pools ([1][2]).
2. Disaggregation releases cargo – The Hsp70–Bag3 axis actively extracts sequestered proteins during stress recovery, a process that also liberates bound metals ([3]).
3. Ferroptosis link – Labile iron catalyzes peroxidation of polyunsaturated fatty acids; inhibition of ferroptosis (e.g., with liproxstatin‑1) rescues cells from aggregate‑associated toxicity ([4]).
4. Cellular iron buffering – Ferritin heavy chain (FTH1) and NCOA4‑mediated ferritinophagy regulate cytosolic iron; their upregulation coincides with disaggregation during recovery ([5]).

Testable Predictions

• Prediction 1: Inducing disaggregation (via Hsp110 overexpression) in neurons expressing aggregation‑prone tau will increase labile iron (measured by Calcein‑AM quenching) and lipid peroxidation (C11‑BODIPY fluorescence) unless ferritin or the iron chelator deferoxamine is co‑expressed.
• Prediction 2: In vivo, mice with tau‑P301S aggregates treated with an aggregasome‑disaggregating peptide will show heightened hippocampal ferroptosis markers (ACSL4, PTGS2) and memory decline, effects mitigated by concurrent ferritin‑H overexpression.
• Prediction 3: Human iPSC‑derived astrocytes exposed to extracellular Aβ fibrils will exhibit reduced ferroptosis sensitivity; CRISPR‑mediated knockout of FTH1 abolishes this protection, rendering cells vulnerable to disaggregation‑triggered death.

Experimental Approach

1. Use lentiviral vectors to modulate Hsp110, FTH1, or NCOA4 in primary cortical neurons transfected with tau‑RD‑P301S.
2. Apply a disaggregation stimulus (e.g., transient heat shock or Hsp110‑inducing drug) and quantify:
   • Labile iron (RhoNox‑1 probe)
   • Lipid peroxidation (C11‑BODIPY 581/591)
   • Cell viability (propidium iodide exclusion)
   • Ferroptosis rescue (liproxstatin‑1, deferoxamine)
3. Parallel in vivo validation with AAV‑mediated gene delivery in tau‑transgenic mice, monitoring behavior and hippocampal histology.

Falsifiability

If disaggregation increases neuroprotection without altering labile iron or lipid peroxidation, or if iron chelation fails to rescue viability after disaggregation, the hypothesis is refuted. Conversely, consistent rescue by iron‑handling enhancements would support the model.

References

[1] https://pmc.ncbi.nlm.nih.gov/articles/PMC7538195/ [2] https://www.asbmb.org/asbmb-today/science/083121/protein-aggregation-defective-or-protective [3] https://doi.org/10.1073/pnas.1803130115 [4] https://pubmed.ncbi.nlm.nih.gov/37401177/ [5] https://pmc.ncbi.nlm.nih.gov/articles/PMC12059050/