Hemophilia is a genetic disease due to the deficiency of blood coagulation factor VIII or IX. Bleeding is common, especially into joints where a proliferative synovitis develops resulting in a debilitating arthritis, hemophilic arthropathy. The pathogenesis of blood-induced hemophilic synovitis (HS) is poorly understood. Repeated episodes of bleeding induce synoviocyte hypertrophy and hyperplasia, an intense neovascular response and inflammation of the synovial membrane. The component(s) in blood that initiates these changes is (are) not known, although iron is often proposed as one possibility. Previously, we reported that iron promotes the proliferation of human synovial fibroblasts and increases c-myc expression in vitro (

). Here, we describe the proliferative effects of joint bleeding following traumatic hemarthrosis in a murine model of severe, human hemophilia A. Controlled, blunt trauma to the right knee joint consistently resulted in joint swelling due to a combination of bleeding and inflammation. The left, control knee was sham injured and remained normal for the duration of the experiment. Hemarthrosis resulted in acute morbidity evidenced by inactivity, weight loss and immobility. Hemosiderin was found in the synovial membrane of the right knees only. The numbers of synovial cell layers present in the membrane of the right (injured) knee increased during the experiment (figure). Expression of Ki67 in the nucleus, a marker of cell proliferation, confirmed the increase in synovial cell proliferation in membranes from the right (injured) knees. Taken together these data support the notion that iron causes aberrant gene expression and is, at least in part, responsible for the pathological findings observed in the joints of patients following bleeding and contributes to the development of hemophilic synovits.

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