Osteoarthritis (OA) is characterized by progressive joint destruction, including synovial membrane alteration. EphB4 and its ligand ephrin-B2 were found in vitro to positively affect OA subchondral bone and cartilage. In vivo in an experimental mouse model overexpressing bone-specific Ephb4 (TgEphB4), a protective effect was found on both the subchondral bone and cartilage during OA. We investigated in the TgEphB4 mouse model the in vivo effect on synovial membrane during OA. Knee OA was surgically induced by destabilization of the medial meniscus (DMM). Synovial membrane was evaluated using histology, histomorphometry, IHC, and real-time PCR. Compared to DMM-wild-type (WT) mice, DMMTgEphB4 mice had a significant decrease in synovial membrane thickness, vascular endothelial growth factor, and the profibrotic markers fibrin, type 1 procollagen, type 3 collagen, connective tissue growth factor, smooth muscle actin-α, cartilage oligomeric matrix protein, and procollagen-lysine, and 2-oxoglutarate 5-dioxygenase 2. Moreover, factors known to modulate transforming growth factor-β signaling, transforming growth factor receptor 1/ALK1, phosphorylated Smad-1, and heat shock protein 90β were significantly decreased in DMM-TgEphB4 compared with DMM-WT mice. Ephb4 overexpression also exhibited a protective effect on synovial membrane thickness of aged (24-month-old) mice. Overexpression of bone-specific Ephb4 clearly demonstrated prevention of the development and/or progression of fibrosis in OA synovial membrane, reinforcing the hypothesis that protecting the subchondral bone prophylactically and during OA reduces the pathologic changes in other articular tissues.
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