The effect of type I collagen and insulin-like growth factor-I on osteopontin expression in human periodontal ligament cells

Abstract

Extracellular matrix and growth factors might be the crucial factors that regulate healing and regenerating process in human periodontal ligament (HPDL) cells. The purpose of this study was to examine the effects of type I collagen and IGF-I on OPN expression in HPDL cells. Cells were cultured on plastic or type I collagen-coated plates for 48 hours, then cell extracts were collected. RT-PCR and Western blot analysis were used to analyze OPN expression at transcriptional and translational level, respectively. It was found that OPN expression was significantly decreased when cells were cultured on collagen-coated plates and this effect could be diminished by blocking with an inhibitory antibody to [beta]1 integrin. This result indicates that the inhibitory effect on the OPN expression exerted by type I collagen is signaled through [beta]1 integrin receptor. We also found that after HPDL cells were treated with 5 ng/ml of IGF-I, OPN expression was increased in cells grown on collagen-coated plates but not in uncoated condition. This result implies that IGF-I can attenuate the inhibitory effect of type I collagen on OPN expression in HPDL cells. In the last experiment, the cells were treated with the combination of inhibitory antibody to [beta]1 integrin and IGF-I. The result showed that OPN expression was increased to the same level as in the group treated with the inhibitory antibody to [beta]1 integrin or IGF-I alone. This result suggests that the effect of IGF-I associated in counteracting the inhibitory signal from type I collagen mediated by [beta]1 integrin. In conclusion, type I collagen inhibited OPN expression in HPDL cells via [beta]1 integrin and IGF-I can attenuate this inhibitory effect. It is possible that type I collagen and IGF-I play a role in periodontal regeneration by regulating the expression of the OPN in HPDL cells.