Hypothesis

Core idea: In aging endothelium, elevated von Willebrand factor (VWF) and Factor VIII are not merely by‑products of inflammation but represent a chaperone‑driven liquid‑liquid phase separation (LLPS) that matures into ordered, amyloid‑like multimers. This process sequesters pro‑inflammatory cytokines and damaged proteins, acting as a proteostatic safety net. When the LLPS‑to‑fibril transition exceeds a threshold set by declining autophagy and ubiquitin‑proteasome activity, the aggregates become pathogenic, driving thrombosis.

Mechanistic rationale

1. Chaperone scaffolding – HSP70/HSP90 bind nascent VWF dimers, promoting transient multivalent interactions that nucleate LLPS droplets, similar to stress granule formation (PMC3501694).
2. Post‑translational tuning – Age‑associated increase in p53‑dependent transcription raises VWF synthesis, while oxidative stress promotes disulfide‑bond formation that stabilizes the droplet interior (33221577).
3. Maturation to HMWM‑VWF – Within droplets, HSP90 facilitates conformational conversion of VWF A2 domain into β‑sheet‑rich structures, generating high‑molecular‑weight multimers (HMWM‑VWF) that are resistant to proteolysis (AHJ).
4. Sequestration function – The resulting fibrillar network captures soluble TNF‑α, IL‑6, and misfolded plasma proteins, lowering their bioactive concentration (PMC5270681).
5. Pathological tipping point – Autophagic decline in aged endothelium reduces clearance of LLPS droplets; persistent droplets over‑mature into stable fibrils that promote platelet adhesion and thrombin generation (25099191).

Testable predictions

• Prediction 1: In endothelial cells from old vs. young donors, VWF will colocalize with HSP70/HSP90 and markers of LLPS (e.g., FUS, DDX4) in cytosolic droplets detectable by super‑resolution microscopy (PMC6907691).
• Prediction 2: Pharmacological inhibition of HSP90 (e.g., geldanamycin) will reduce HMWM‑VWF formation without affecting total VWF secretion, measurable by ELISA and multimera agarose gel electrophoresis.
• Prediction 3: Inducing autophagy (e.g., spermidine) in aged endothelial cultures will shift VWF from insoluble HMWM‑VWF to soluble monomers, decreasing platelet‑aggregation assays.
• Prediction 4: Plasma from elderly individuals will show a positive correlation between HMWM‑VWF levels and sequestered cytokine complexes (TNF‑α·VWF) detectable by co‑immunoprecipitation, inversely correlated with autophagic flux markers (LC3‑II/I) in circulating endothelial‑derived vesicles.

Falsifiability

If HSP90 inhibition does not alter HMWM‑VWF multimer distribution, or if autophagy induction fails to reduce insoluble VWF despite increasing LC3‑II, the hypothesis that chaperone‑mediated LLPS underlies protective VWF aggregation would be refuted. Likewise, absence of VWF‑cytokine co‑precipitates in aged plasma would weaken the sequestration argument.

Broader implication

Reframing age‑related hemostatic shifts as a chaperone‑guided phase‑separation response unifies proteostasis and coagulation biology, suggesting that therapeutic strategies should modulate droplet dynamics rather than bluntly lower VWF levels.