Modulation of osteoblasts and periodontal ligament cells by IL-17 and IL-6

Background: Orthodontic tooth movement (OTM) requires mechanical stimuli to remodel the periodontal ligament and alveolar bone. During OTM, an inflammatory-like response is mediated by various signalling molecules. Two important cytokines involved in this response are interleukin-17 (IL-17) and interleukin-6 (IL-6). Aim: To determine whether the addition of IL-17 and/or IL-6 affects the expression of genes associated with osteogenesis. Methods: Cultures of human calvarial osteoblasts (hCO) (N=1) and human periodontal ligament cells (hPDLCs) (N=4) were grown alone or together (co-culture) in the presence of 0–75 ng/mL IL-17 and/or IL-6 for 72 hrs. The effect of osteogenic triple supplement (TS) was also investigated. Cell viability was monitored with PrestoBlueTM. Levels of osteogenic gene expression were determined by qPCR assays. ANOVA and Tukey’s post-hoc tests were employed for statistical analysis. Results: The addition of IL-17 and/or IL-6 had no significant effect on cell viability over 72 hrs. The addition of TS to hCO baseline cultures resulted in significantly increased OPG and ALP mRNA expression compared to negative control (3.8-fold; p=0.020 and 25-fold; p=0.034, respectively). RANK expression increased in response to IL-17 in a dose dependent manner (p=0.003). hPDLCs gene expression were unaffected by the addition of IL-6, but showed increased ALP mRNA expression in response to IL-17 (4-fold; p=0.042). In co-culture with TS, the addition of IL-17 and IL-6 increased hCO RANK expression (5.8-fold; p= 0.004). hCO ALP expression decreased in the presence of IL-17, IL-6, and IL-17 with IL-6 (148-fold; p=0.001, 2-fold; p=0.002 and 413-fold; p=0.001 respectively). When compared to monocultures, hPDLC RANK mRNA expression was greater for untreated cells (390-fold), and in the presence of IL-17 (33-fold) and IL-6 (9888-fold) in co-culture at 48 hrs. Conclusion: The addition of IL-6 and IL-17 decreases OPG and ALP expression and increases RANK in hCOs. This effect is amplified in the presence of hPDLCs, and may play a role in stimulation of bone remodelling associated with OTM