Semaphorin 4D Promotes Osteoclast Formation but Inhibits Osteoblast Formation: Implication in Bisphosphonate-Related Osteonecrosis of the Jaw.

Introduction: Bisphosphonates are widely used for the treatment of osteoporosis, which could cause osteonecrosis of the jaw (also known as bisphosphonate-related osteonecrosis of the jaw [BRONJ]). Currently, there is no effective treatment for BRONJ. Here, we investigated the role of human recombinant semaphorin 4D (Sema4D) in BRONJ in vitro.

Methods: MG-63 and RAW264.7 cells were used to determine the effects of Sema4D on BRONJ. Osteoclast and osteoblast were differentiated by treatment with 50 ng/mL RANKL for 7 days. In vitro BRONJ model was induced by treatment with ZOL (2.5 μm). The development of osteoclasts and osteoblasts was evaluated using ALP activity and ARS staining. qRT-PCR was used to measure the genes relative expression involved in the development of osteoclasts and osteoblasts. In addition, ZOL decreased TRAP-positive area; TRAP protein and mRNA expression were determined using Western blot and qTR-PCR.

Results: ZOL treatment remarkedly suppressed Sema4D expression in RAW264.7 cells. Moreover, ZOL reduced TRAP-positive area and TRAP protein and mRNA expression. In parallel, genes involved in osteoclast formation were reduced by ZOL treatment. In contrast, osteoclast apoptosis was increased by ZOL treatment. Recombinant human Sema4D significantly abolished these effects of ZOL. In addition, ALP activity was reduced by recombinant human Sema4D.

Discussions: Genes involved in osteoblast formation were decreased by recombinant human Sema4D in a dose-dependent manner. We demonstrated that ZOL treatment inhibited Sema4D expression in RAW264.7 cells.

Conclusion: Recombinant human Sema4D treatment can effectively alleviate ZOL-induced inhibition of osteoclast formation and apoptosis and promote osteoblast formation.