IL-17 inhibits osteoblast differentiation and bone regeneration in rat

Objective The interleukin-17 (IL-17) family is a group of pro-inflammatory cytokines that are produced by a subset of helper T cells. IL-17 family members are not only involved in the immune response of tissues but also play a role in bone metabolism. Although the role of IL-17 in osteoclast-mediated bone resorption has been extensively studied, its role during osteoblast-mediated bone formation has rarely been investigated. In this study, we examined the effect of IL-17 on osteogenesis in rats both in vitro and in vivo. Design To evaluate osteogenesis in vitro, rat calvarial osteoblast precursor cells were cultured for 14 days in osteogenic medium with or without 50 ng/mL IL-17. Osteogenic activity was evaluated by alkaline phosphatase and alizarin red staining. The mRNA expression of alkaline phosphatase, osteocalcin, and osterix was also measured by using real-time PCR. To test whether IL-17 affects bone formation in vivo, bone filling was examined by micro-computed tomography and histological observations at 8 weeks after critical-sized defects were made in rat calvaria. Results The presence of IL-17 significantly reduced alkaline phosphatase and alizarin red staining and the expression of alkaline phosphatase, osteocalcin, and osterix in vitro. IL-17 also significantly inhibited the filling of calvarial defects in vivo. Conclusion IL-17 exerted a negative effect on osteogenesis in a rat model. In contrast to the previously reported beneficial effect on osteogenic differentiation of human mesenchymal stem cells, our results suggest a species or cell type-specific role for IL-17 in bone formation.