Hypothesis

In older adults with non‑O blood groups, chronically elevated plasma FVIII and vWF drive endothelial autophagy defect‑mediated hypersecretion of ultra‑large vWF multimers. These multimers sequester ADAMTS13 and bind platelets, creating a prothrombotic surface that accelerates protein C activation via thrombomodulin. The resulting consumption of endogenous protein C produces a relative anticoagulant state that lowers measured thrombin generation (ETP and peak thrombin) in plasma‑based assays, paradoxically increasing ischemic stroke risk while protecting against venous thrombosis.

Rationale

• Aging raises FVIII (+12 IU/dL/decade) and vWF (+18 IU/dL/decade) more steeply in non‑O individuals [1].
• Endothelial autophagy impairment promotes vWF hypersecretion from Weibel‑Palade bodies and tissue factor expression [2].
• Ultra‑large vWF multimers are poorly cleaved by ADAMTS13, prolonging platelet adhesion [3].
• Platelet‑bound vWF enhances thrombin‑thrombomodulin complex formation, boosting protein C activation [4].
• Protein C consumption reduces anticoagulant capacity, which can manifest as low thrombin generation in calibrated automated thrombography yet still predispose to microthrombi that cause cerebral embolism [5].

Mechanistic Insight

We propose that the balance between procoagulant (FVIII/vWF, tissue factor) and anticoagulant (protein C pathway) arms determines the clinical phenotype. When autophagy‑deficient endothelium releases excess ultra‑large vWF, the system tilts toward rapid protein C consumption. In assays that start with platelet‑poor plasma, this consumption lowers thrombin potential, but in vivo the platelet‑vWF aggregates generate localized, thrombin‑rich microenvironments that escape bulk measurement and provoke stroke.

Testable Predictions

1. Biomarker stratification – In a cohort aged ≥65, individuals with non‑O blood group, high FVIII/vWF (>90th percentile), and low protein C activity (<40% of normal) will show reduced endogenous thrombin potential (ETP) yet have the highest incidence of ischemic stroke over 2 years.
2. Direction of risk – The same biomarker profile will be associated with lower rates of venous thromboembolism (VTE) compared with peers having high FVIII/vWF but normal/high protein C activity.
3. Intervention test – Short‑term administration of recombinant thrombomodulin (to boost protein C activation) will further decrease ETP in high‑risk subjects but increase microthrombi formation in a microfluidic model of cerebral capillaries, confirming the mechanistic link.
4. Genetic modifier – Presence of clonal hematopoiesis of indeterminate potential (CHIP) with DNMT3A or TET2 mutations will amplify the phenotype by increasing IL‑6‑driven endothelial senescence, worsening autophagy flux and vWF secretion.

Experimental Design

• Population: 1,200 community‑dwelling adults aged 65‑85, stratified by ABO blood group (O vs non‑O).
• Baseline assays: Plasma FVIII activity, vWF antigen, ADAMTS13 activity, protein C activity, thrombomodulin levels, inflammatory cytokines (IL‑6, TNF‑α), mitochondrial ROS in platelets, and CHIP sequencing.
• Thrombin generation: Calibrated automated thrombography (ETP, peak thrombin, time‑to‑peak) performed in platelet‑poor and platelet‑rich plasma.
• Follow‑up: Clinical adjudication of stroke, transient ischemic attack, VTE, and myocardial infarction over 24 months.
• Analysis: Multivariable Cox models testing interaction between FVIII/vWF quartiles, protein C activity tertiles, and blood group on stroke/VTE risk; mediation analysis to assess whether thrombin generation metrics mediate the biomarker‑outcome relationship.

Potential Implications

If validated, the hypothesis redefines "hypercoagulability" in aging as a dynamic coupling of pro‑ and anticoagulant forces, explaining contradictory thrombin generation data. It suggests that routine anticoagulation based solely on elevated FVIII/vWF may be harmful in the protein C‑deficient subgroup, while strategies enhancing endothelial autophagy (e.g., spermidine, rapamycin analogs) or modulating ADAMTS13 activity could personalize prophylaxis.

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