The aim of this study was to demonstrate the biological function of Semaphorin 4D (Sema4D)/Plexin-B1 in the bone formation features of osteoblasts in early-stage temporomandibular joint (TMJ) osteoarthritis.
Sema4D/Plexin-B1, expressed by osteoclasts/osteoblasts, plays a balancing role in bone formation and resorption. However, previous studies have mainly focused on bone resorption by osteoclasts in early-stage osteoarthritis. This study used our reported experimental unilateral anterior crossbite (UAC) mouse model to explore subchondral bone changes, which were assessed by micro-CT analysis. The changes in osteoblasts were investigated after the inhibition of Sema4D by BMA-12 injection with the detection of bone formation-related markers. A Transwell migration assay was performed to reveal the specific impact of Sema4D on osteoblasts in vitro.
The data demonstrated that subchondral bone loss in early-stage TMJ osteoarthritis was accompanied by the upregulated expression of Sema4D in cartilage and subchondral bone and Plexin-B1 in subchondral bone. Reducing Sema4D levels could inhibit subchondral bone loss and cartilage degeneration in early-stage TMJ osteoarthritis. In vitro, the results revealed that Sema4D could reduce the expression of osteocalcin and alkaline phosphatase and increase the migrating capability of Plexin-B1-positive osteoblasts.
Our results revealed that elevated Sema4D expression in early-stage TMJ osteoarthritis might decrease the bone formation activity of osteoblasts in the subchondral bone by binding to Plexin-B1 expressed by osteoblasts. Inhibiting Sema4D/Plexin-B1 signaling in early-stage osteoarthritis represents a promising strategy for new therapeutic approaches to osteoarthritis.

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