Hypothesis

Aging‑induced senescence in endothelial cells of brain, lung and liver secretes specific microRNAs that suppress ADAMTS13 activity, leading to accumulation of ultra‑large VWF multimers and a procoagulant phenotype.

Mechanistic rationale

• Senescent endothelial cells upregulate p53 and SASP factors, including miR-29b, which directly targets ADAMTS13 mRNA for degradation (SASP and miRNA regulation).
• Reduced ADAMTS13 fails to cleave newly secreted VWF, allowing high‑molecular‑weight multimers to persist in plasma.
• This effect is organ‑specific because senescent endothelial burden is highest in brain, lung and liver vasculature, matching the observed tissue‑selective VWF rise (Organ‑specific VWF elevation).
• Non‑O blood groups already have higher baseline VWF, so miR-29b‑mediated ADAMTS13 suppression amplifies the age‑related increase in these genotypes (Blood group modulation).

Testable predictions

1. Aged mice show elevated miR-29b levels in isolated brain, lung and liver endothelial cells compared with young controls.
2. Antagomir‑mediated inhibition of miR-29b in aged endothelial cultures restores ADAMTS13 activity and reduces ultra‑large VWF multimers.
3. Systemic delivery of a miR-29b antagomir in aged mice normalizes plasma VWF multimer distribution without affecting heart or kidney VWF levels.
4. Individuals with non‑O blood type exhibit a stronger correlation between plasma miR-29b and VWF levels than O‑type counterparts.

Experimental approach

• Isolate CD31+ endothelial cells from young (3 mo) and aged (24 mo) mice brains, lungs, livers, hearts and kidneys; quantify miR-29b by qPCR and ADAMTS13 activity by fluorometric assay.
• Transfect aged endothelial cells with miR-29b antagomir or scrambled control; measure ADAMTS13 cleavage of VWF-GFP substrate and VWF multimer profile by agarose gel electrophoresis.
• Treat aged mice with intravenous miR-29b antagomir (2 mg/kg) twice weekly for 4 weeks; collect plasma for VWF antigen, FVIII activity, and multimer analysis; assess organ‑specific VWF mRNA by RT‑qPCR.
• In a human cohort, stratify participants by blood group, measure circulating miR-29b (exosome‑associated) and VWF multimer ratio; test interaction via linear regression.

If miR-29b inhibition normalizes VWF multimer distribution in aged, organ‑specific fashion, the hypothesis is supported; lack of effect would falsify the proposed mechanism.