Hypothesis: Endothelial autophagy gates Weibel‑Palade body turnover and limits VWF/FVIII hypersecretion

Aging endothelial cells show declining autophagy and rising circulating VWF and Factor VIII. We propose that autophagy does not merely recycle bulk cytosol but selectively degrades damaged Weibel‑Palade bodies (WPBs), the secretory granules that store VWF and Factor VIII. When autophagic flux falls, defective WPBs accumulate, become enlarged, and are prone to agonist‑stimulated exocytosis, driving the hypercoagulable state seen in older individuals.

Mechanistic rationale

• Autophagy recognizes cargo via adaptor proteins such as p62/SQSTM1 and NBR1, which can bind ubiquitinated WPB membranes.
• In young endothelium, basal autophagy continuously turns over WPBs, limiting their size and cargo load (autophagy acts as a quality‑control gate).
• With age, reduced LC3‑II conversion and increased p62 accumulation signal autophagic stall, leading to WPB buildup.
• Enlarged WPBs contain more VWF/FVIII per granule and exhibit altered calcium sensitivity, resulting in greater secretion upon thrombin or histamine challenge.
• This model explains why autophagy enhancers (e.g., trehalose) lower VWF release in aged mice without directly affecting inflammatory pathways.

Testable predictions

1. Correlation: In human umbilical vein endothelial cells (HUVECs) from donors across ages, autophagic flux (LC3‑II/I ratio, p62 levels) will inversely correlate with WPB size (measured by EM or CD63‑VWF immunofluorescence) and basal VWF secretion【VWF antigen rises】.
2. Causality: Pharmacological inhibition of autophagy (e.g., chloroquine, bafilomycin A1) in young endothelial cells will recapitulate the aged phenotype: increased WPB volume, heightened VWF/FVIII release after low‑dose thrombin stimulation【Autophagy markers drop】.
3. Rescue: Activating autophagy with spermidine or trehalose in aged endothelial cells will shrink WPBs, normalize VWF/FVIII secretion, and reduce thrombus formation in a microfluidic flow assay【Trehalose rescues endothelial function】.
4. Specificity: Silencing WPB‑specific autophagy receptors (e.g., knocking down NBR1) will mimic autophagy inhibition effects on secretion, whereas knockdown of generic autophagy proteins (ATG5, ATG7) will affect both WPB turnover and general cytosolic clearance, allowing dissection of WPB‑specific contribution.

Experimental approach

• WPB quantification: Transfect endothelial cells with VWF‑mCherry and use live‑cell confocal imaging to track granule size and number; validate with transmission electron microscopy.
• Autophagy flux: Treat with lysosomal inhibitor (bafilomycin A1) and measure LC3‑II accumulation by western blot.
• Secretion assay: Stimulate with low concentrations of thrombin (0.1 U/mL) or histamine (10 µM) and quantify VWF antigen and Factor VIII activity in supernatant by ELISA.
• Functional thrombosis: Perfuse cell‑cultured monolayers under shear stress and monitor platelet adhesion using fluorescently labeled platelets.
• Statistical analysis: Linear regression to assess inverse correlation; ANOVA with post‑hoc tests for intervention groups.

If autophagy directly gates WPB turnover, then enhancing autophagic clearance should normalize VWF/FVIII levels independent of inflammation or oxidative stress markers. Conversely, if autophagy manipulation fails to alter WPB size or secretion, the hypothesis would be falsified, directing attention to alternative mechanisms (e.g., transcriptional upregulation of VWF, altered granule calcium handling).