Regulatory effects of biomechanical strain on the insulin-like growth factor system in human periodontal cells

During mastication, dental trauma and functional dental habits the tissues that surround and support the teeth, i.e. the periodontium, are subject to complex biomechanical forces. The exact mechanisms mediating the anabolic and catabolic biomechanical effects on the periodontium are yet poorly understood. Therefore, the objective of this in-vitro study was to determine if continuous tensile strain (CTS) regulates the synthesis of components of the insulin-like growth factor (IGF) system in human periodontal ligament (PDL) cells. PDL cells from six donors were phenotyped, seeded on collagen type-I coated silicone membranes, and subjected to CTS of low (3%) or high (20%) magnitudes for 4 and 24 h. The gene expression of IGF1, IGF2, IGF1 receptor (IGF1R), insulin receptor substrate (IRS)1, and IGF-binding proteins (IGFBPs) was detected by real-time PCR. The protein synthesis was determined by immunoblotting. For statistical analysis, ANOVA and the Tukey test (p<0.05) were applied. When cells were subjected to low CTS for 4 h, the IGF1 expression was significantly increased, whereas high CTS or CTS applied for 24 h reduced the constitutive IGF1 synthesis. Although PDL cells also expressed IGF2, IGF1R, and IRS1, no significant differences for these molecules were found between stretched cells and controls. High CTS caused a significant upregulation of IGFBP1 and significant downregulation of IGFBP3 and IGFBP5 at 24 h. In conclusion, this in-vitro study suggests that biomechanical forces may regulate several components of the local IGF system in the human periodontium.