Effects of intermittent compressive force on extracellular matrix homeostasis of human periodontal ligament stem cells

Background: Mechanical force, caused by orthodontic tooth movement, affects periodontal tissue homeostasis including destruction and formation. For instance, the compression side causes bone resorption while bone formation lines in the tension side. Periodontal ligament cells play roles in modulating periodontal tissue homeostasis as well as regeneration via immunomodulation, proliferation, and migration. Extracellular matrix (ECM) is a cellular microenvironment that aids in cell migration, cell growth, and differentiation and serves as a physical barrier against microorganisms. Matrix metalloproteinase (MMP) plays a key role in the degradation of ECM, including collagen, gelatines, and casein. The MMP functions can be inhibited by tissue inhibitor of matrix metalloproteinase (TIMP) which has 4 subtypes, and each subtype acts specifically in controlling different types of MMP. The balance between MMP and TIMP is involved in both normal and pathological conditions. Previous reports showed that mechanical loading affects the expression and activities of MMP and TIMP; however, the study of intermittent compressive force (ICF) on MMP and TIMP expression of human periodontal ligament cells (hPDLCs) is still unclear. TGF-β1 is involved in the modulation of ECM homeostasis as it is a potent stimulator of ECM formation, which enhances the expression of several matrix genes, including type I, III, and, IV collagens, and fibronectin. In addition, previous studies showed that TGF-β1 affects the expression of some MMP members and their inhibitors or TIMP. However, whether TGF-β1 is involved in the expression of MMP and TIMP in hPDLCs under ICF has not been clearly understood. Aim: This study aims to investigate the roles of ICF on the expression of MMPs and TIMPs in hPDLCs and clarify the underlying mechanisms. Methods: The cells are subjected to ICF with a magnitude of 1.5 g/cm2 for 24 hours. The ICF was set to press for 1 second and un-press for 2 seconds to produce a cycle of around 14 rounds per minute. The control of the various functions of the apparatus is carried out through a computerized program. The mRNA and protein expression of MMPs, TIMPs, and TGF-β1 are assessed using RT-PCR and ELISA, respectively. The enzyme activity of MMPs was performed using an MMP activity assay. The treatment of TGF-β inhibitor (SB431542) was used to assess the role of TGF-β in this study. Statistical analysis used in this study is one-way ANOVA for comparison of more than two groups and the Mann-Whitney U Test for comparison between two groups. Results: mRNA and protein analyses showed that ICF significantly induced expression of TIMP1 and TIMP3, but decreased expression of MMP1. Incubation with the TGF-β inhibitor and subjected to ICF showed a downregulation of TIMP3, but expression of MMP1 was not affected. Conclusion: ICF is likely to affect ECM homeostasis by hPDLCs by regulating the expression of MMP1 and TIMPs. Expression of TIMP3 was regulated by TGF-β1. These findings suggest ICF may decrease MMP1-mediated digestion of ECM and may thus be beneficial for periodontal regenerative therapy.