TNF-α/TNF-R System May Represent a Crucial Mediator of Proliferative Synovitis in Hemophilia A

Abstract: Hemophilic arthropathy (HA) typically begins with proliferative synovitis that sharessome similarities with inflammatory arthritides, in which the proinflammatory cytokine tumornecrosis factor (TNF)-α has a crucial pathogenetic role. Inappropriate release of TNF-α was shownto contribute to arthropathy development following intra-articular bleeding in hemophilic mice.Here, we were interested in determining whether systemic levels of TNF-α and synovial tissueexpression of the TNF-α/TNF receptor (TNF-R) system could be increased and related to jointdamage in hemophilia A patients with severe HA. Serum levels of TNF-α measured by quantitativeenzyme-linked immunosorbent assay (ELISA) were significantly increased in HA patients (n = 67)compared to healthy controls (n = 20). In HA patients, elevated TNF-α levels were significantlyassociated with the number of hemarthroses, the grade of synovial hypertrophy, and both theclinical World Federation of Hemophilia score and ultrasound score. The expression of TNF-α, TNFR1,and TNF-R2 was strongly increased in HA synovium (n = 10) compared to the non-inflamedosteoarthritis control synovium (n = 8), as assessed by both immunohistochemistry and Westernblotting. Increased protein levels of TNF-α, TNF-R1, and TNF-R2 were retained in vitro by HAfibroblast-like synoviocytes (n = 6) with respect to osteoarthritis control fibroblast-like synoviocytes(n = 6). Stimulation with TNF-α resulted in a significant increase in HA fibroblast-like synoviocyteproliferation quantified by the water-soluble tetrazolium (WST)-1 assay, while it had no relevanteffect on osteoarthritis fibroblast-like synoviocytes. Quantification of active/cleaved caspase-3 byELISA demonstrated that TNF-α did not induce apoptosis either in HA or in osteoarthritisfibroblast-like synoviocytes. The TNF-α/TNF-R system may represent a crucial mediator ofproliferative synovitis and, therefore, a new attractive target for the prevention and treatment ofjoint damage in HA patients. Our findings provide the groundwork for further clinical investigationof anti-TNF-α therapeutic feasibility in hemophiliacs.