Effects of Tension Force on Proliferation and Differentiation of Human Periodontal Ligament Cells Induced by Lipopolysaccharides

Human periodontal ligament cells (hPDLCs), with the potential for multi-directional differentiation and reproduction, are the target cells of orthodontic tooth movement. The aim of this study was to examine the effect of mechanical tension force and lipopolysaccharides (LPS) on hPDLCs and whether they induce proliferative and differentiated characters in vitro. Tension force was applied to hPDLCs stimulated with and without LPS for 24 hrs. Real-time polymerase chain reaction (qPCR) was carried out to analyze the mRNA expression of Cyclin 2 (CCND2), WNT1 inducible signaling pathway protein 1 (WISP1), runt-related transcription factor 2 (RUNX2) and alkaline phosphatase (ALP). Analysis of variance (ANOVA) was used for statistical analysis. Significant differences were indicated by P < 0.05. The results showed that tension force promoted the mRNA expression of both the proliferation-related genes (CCND2 and WISP1) and differentiation-related genes (RUNX2 and ALP), and that both were enhanced by the simulation of LPS. In addition, the relative expression ratios CCND2/RUNX2 and CCND2/ALP both increased significantly after the application of tension, and this effect was further enhanced by LPS. All results indicated that with the assessed level of mechanical force loading, tension could promote both the proliferation and differentiation of hPDLCs, which could be enhanced by LPS, and that proliferation is promoted to a greater extent than differentiation. These findings may be valuable for understanding the importance of the application of suitable mechanical force in periodontal remodeling, especially in the process of orthodontic tooth movement with inflammation.