The Role Of IL-17 In The Pathogenesis Of Periodontal Bone Destruction: A Preliminary Study

OBJECTIVES:The immune pathogenesis of periodontitis is still unclear.Th17 cells and its representative cytokine,IL-17,have been reported to involve in periodontal diseases.The aim of this study is to investigate the effect of IL-17 on human periodontal ligament fibroblasts(HPDLFs)during the differentiation of osteoclasts,and thus explore the potential mechanism of Th17 cytokine in the development and progression of periodontal bone destruction.METHODS:HPDLFs were isolated and cultured.With different concentrations(0,1,10,25,50,100 ng/ml)of recombinant human IL-17 treatment on HPDLFs,the expression levles of receptor activator of nuclear factor-?B ligand(RANKL)and osteoprotegerin(OPG)mRNA were determined by real-time quantitative reverse transcriptase PCR(RT-PCR),while the expression of RANKL and OPG protein were analyzed by ELISA and Western blot.Besides,10 uM of PDTC,SB203580 and LY294002,specific signaling inhibitors of NF-?B,p38 MAPK and PI3K/Akt,respectively,were used to pretreat with HPDLFs for 1h,followed by an incubation with 25 ng/ml of IL-17 for 24h,and then the expression changing trends of RANKL after pretreatment with various signaling inhibitors were compared to explore possible signal transduction pathways of IL-17 in the induction of RANKL expression in human periodontal ligament fibroblasts.RESULTS:The mRNA expression of RANKL and OPG were up-regulated by different concentrations of IL-17(0,1,10,25,50,100 ng/ml)treatment in HPDLFs,nevertheless,the effect on RANKL was more significant,and the effect on RANKL and OPG was most significant at the concentration of 25 ng/ml(P<0.001 and P<0.01,respectively),and the corresponding ratio of RANKL and OPG was increased(P<0.001).As for protein expression levels,the concentration of sRANKL in the cell supernatant was lower than the minimum detection limit of ELISA kit,and the result of western blot of RANKL was basically in the same trend with its mRNA level;However,the secretion of OPG in the cell supernatant was all decreased after treatment with IL-17(P<0.001).Moreover,with pretreatment of various signaling inhibitors,the expression of RANKL in HPDLFs was down-regulated,among which the inhibitory effect of SB203580 was most significant(P<0.01).CONCLUSIONS:Th17 cytokine,IL-17,could induce the expression of RANKL on HPDLFs,disrupt the balance of RANKL/OPG ratio,and thus play a role in the pathogenesis of periodontal bone loss through influencing the cytokinemicroenvironment of osteoclast differentiation.The preliminary results of signaling pathways implied that the MAPK pathway might be the critical way of IL-17 participated in the pathogenesis of periodontal bone destruction.Overall,the results would contribute to comprehensive understanding of the immune pathogenesis of periodontitis and also provide evidence for screening potential targets of periodontitisimmune intervention therapy.