Mechanisms of vascular permeability and remodeling associated with hemarthrosis in factor VIII-deficient mice

Background Vascular remodeling associated with hemophilic arthropathy (HA) may contribute to bleed propagation, but the mechanisms remain poorly understood. Objectives To explore molecular mechanisms of HA and the effects of hemostasis correction on synovial vascular remodeling after joint injury in hypocoagulable mice. Methods Factor VIII (FVIII)-deficient mice +/- FVIII treatment and hypocoagulable wild-type mice ((Hypo)BALB/c) were subjected to subpatellar puncture. (Hypo)BALB/c mice were treated with warfarin and anti-FVIII before injury, after which warfarin was continued for 2 weeks or reversed +/- continuous anti-FVIII until harvest. Synovial vascularity was analyzed at baseline and 2 to 4 weeks post injury by histology, musculoskeletal ultrasound with power Doppler (microvascular flow), and Evans blue extravasation (vascular permeability). Synovial gene expression and systemic markers of vascular collagen turnover were studied in FVIII-deficient mice by RNA sequencing and enzyme-linked immunosorbent assay. Results Vascular changes occurred in FVIII-deficient and (Hypo)BALB/c mice after injury with minimal effect of hemostasis correction. Increased vascular permeability was only significant in FVIII-deficient mice, who exhibited more pronounced vascular remodeling than (Hypo)BALB/c mice despite similar bleed volumes. FVIII-deficient mice exhibited a strong transcriptional response in synovium that was only partially affected by FVIII treatment and involved genes relating to angiogenesis and extracellular matrix remodeling, with vascular collagen turnover markers detected systemically. Conclusions Intact hemostasis at the time of hemarthrosis and during healing are both critical to prevent vascular remodeling, which appears worse with severe and prolonged FVIII deficiency. Unbiased RNA sequencing revealed potential targets for intervention and biomarker development to improve management of HA.