IL-17 regulates expression of cytokines in human osteoblasts rather than bone-specific genes

Abstract

Abstract Objective The cytokine IL-17 plays a crucial role in the development and promoting of inflammatory rheumatic diseases, such as psoriasis arthritis and ankylosing spondylitis. The influence of IL-17 on the osteoblast differentiation from mesenchymal stem cells has already been well studied. However, the effect of IL-17 on mature osteoblasts is not yet fully understood. Methods In this study, the influence of IL-17 on the expression of osteogenic markers and pro-inflammatory cytokines was analyzed on mRNA and protein level in an osteoblast cell culture model. Results Our data indicate that IL-17 alone has no significant influence on the expression of osteoblast-specific genes. However, a significant upregulation of pro-inflammatory cytokines at the transcriptional level by IL-17 was observed in primary osteoblasts. This effect on the regulation of pro-inflammatory cytokines was abolished completely by administration of a therapeutic anti-IL-17 antibody. Co-stimulation with TNF-α and IL-17 led to an upregulation of pro-inflammatory cytokines, which significantly exceeded the additive effect of both cytokines. In this co-stimulation, the anti-IL-17 antibody could not completely reverse the IL-17 effect. The same IL-17 and TNF-α effect was observed in osteoblast-like cells (MG63), whereas IL-17 alone did not induce the expression of pro-inflammatory cytokines. Conclusion The upregulation of the pro-inflammatory cytokines IL-1, IL-6, and IL-8 in primary osteoblasts by IL-17 indicates an indirect regulatory effect on osteoclastogenesis and activation of bone resorption. The therapeutic IL-17 antibody reduced the IL-17 induced release of pro-inflammatory cytokines by osteoblasts and this, in turn, could also reduce the effect on osteoclast differentiation and bone resorption. Our study underlines the important role of osteoblasts as major players in the osteoimmunologic network.