Cyclic tensile strain affects the response of human periodontal ligament stromal cells to tumor necrosis factor-α

Objectives Orthodontic treatment in adult patients predisposed to mild or severe periodontal disease is challenging for orthodontists. Orthodontic malpractice or hyper-occlusal forces may aggravate periodontitis-induced destruction of periodontal tissues, but the specific mechanism remains unknown. In the present study, the combined effect of mechanical stress and tumor necrosis factor (TNF)-alpha on the inflammatory response in human periodontal ligament stromal cells (hPDLSCs) was investigated. Materials and methods hPDLSCs from 5 healthy donors were treated with TNF-alpha and/or subjected to cyclic tensile strain (CTS) of 6% or 12% elongation with 0.1 Hz for 6- and 24 h. The gene expression of interleukin (IL)-6, IL-8 and cell adhesion molecules VCAM and ICAM was analyzed by qPCR. The protein levels of IL-6 and IL-8 in conditioned media was measured by ELISA. The surface expression of VCAM-1 and ICAM-1 was quantified by immunostaining followed by flow cytometry analysis. Results TNF-alpha-induced IL-6 gene and protein expression was inhibited by CTS, whereas TNF-alpha-induced IL-8 expression was decreased at mRNA expression level but enhanced at the protein level in a magnitude-dependent manner. CTS downregulated the gene expression of VCAM-1 and ICAM-1 under TNF-alpha stimulation, but the downregulation of the surface expression analyzed by flow cytometry was observed chiefly for VCAM-1. Conclusions Our findings show that mechanical force differentially regulates TNF-alpha-induced expression of inflammatory mediators and adhesion molecules at the early stage of force application. The effect of cyclic tensile strain is complex and could be either anti-inflammatory or pro-inflammatory depending on the type of pro-inflammatory mediators and force magnitude.

Automated summary

The study investigates the combined effect of mechanical stress and TNF-alpha on inflammatory response in human periodontal ligament stromal cells. It was found that mechanical force can differentially regulate the expression of inflammatory mediators and adhesion molecules induced by TNF-alpha, with potential anti-inflammatory or pro-inflammatory effects depending on the type of mediators and force magnitude.