Summary
Recurrent joint bleeding is the most common manifestation of haemophilia resulting
in haemophilic arthropathy (HA). The exact pathophysiology is unknown, but it is suggested
that arthropathy is stimulated by liberation of fibrinolytic activators from the synovium
during haemarthrosis. The aim of this study was to test the hypothesis that haemarthrosis
activates the local synovial fibrinolytic system in a murine haemophilia model. The
right knees of haemophilic and control mice were punctured to induce haemarthrosis.
The left knees served as internal control joints. Synovial levels of urokinase-type
plasminogen activator (uPA), plasminogen activator inhibitor 1 (PAI-1), plasmin, and
alpha-2-antiplasmin (A2AP) were compared between the punctured and control knees.
In haemophilic mice, an increase in synovial cells expressing urokinase-type plasminogen
activator (uPA) in the right punctured knee versus the left unaffected knee was observed:
(47% vs 43%) (p=0.03). Additionally, in haemophilic mice, haemar-throsis induced an
increase in uPA (0.016 ng/ml vs 0.01 ng/ml) (p=0.03) and plasmin (0.53 μg/ml vs 0.46
μg/ml) (p=0.01) as promoters of fibrinolysis. Synovial levels of PAI-1 (0.32 ng/ml
vs 0.17 ng/ ml) (p<0.01) was also increased, whereas synovial levels of A2AP were
unchanged: (0.021 μg/ml vs 0.021 μg/ml) (p=0.15). Enhanced uPA production was confirmed
in human stimulated synovial fibroblast cultures and elevated levels of plasmin were
confirmed harmful to human cartilage tissue explants. In this study we demonstrate
that haemarthrosis in haemophilic mice induces synovial uPA expression and results
in an increase in synovial plasmin levels, making the joint more vulnerable to prolonged
and subsequent bleedings, and adding directly to cartilage damage.
Keywords
Fibrinolysis - haemophilia - haemarthrosis - synovium - haemophilic arthropathy