Insulin-like growth factor-I attenuates the inhibitory effect of type I collagen through β1 integrin receptor

Mechanical stress induces osteopontin expression in human periodontal ligament cells through rho kinase

BACKGROUND

Mechanical stress such as orthodontic forces can produce mechanical damage and inflammatory reaction in the periodontium. Osteopontin (OPN) is a multifunctional cytokine that has been correlated with periodontal disease progression. Because the periodontal ligament (PDL) can be affected by stress and PDL cells are involved in periodontal destruction and remodeling, we aimed to study the influence of mechanical stress on the expression and regulation of OPN in human PDL (HPDL) cells.

METHODS

The mechanical stress was generated by continuous compressive force, and the expression of OPN was examined by reverse transcription-polymerase chain reaction and Western analysis. The application of inhibitors was used to examine the mechanism involved.

RESULTS

Both mRNA and protein expression of OPN significantly increased in a force-dependent manner. Increase of receptor activator of nuclear factor-kappa B ligand (RANKL) was also observed. Interestingly, application of indomethacin could abolish the induction of RANKL but not that of OPN, suggesting the cyclooxygenase-independent mechanism for stress-induced OPN expression. In addition, the upregulation of OPN was diminished by Rho kinase inhibitor but not by cytochalasin B.

CONCLUSIONS

Mechanical stress affects OPN expression in HPDL cells through the Rho kinase pathway. Because OPN participates in bone resorption and remodeling induced by mechanical and biologic signals, these results suggest the significance of stress-induced OPN in HPDL cells in alveolar bone resorption and remodeling.

Extracellular Signal-Regulated Kinase 1/2 Is Involved in Ascorbic Acid–Induced Osteoblastic Differentiation in Periodontal Ligament Cells

BACKGROUND

Periodontal ligament (PDL) cells possess osteoblast-like properties and play key roles in periodontal regeneration. Previously, we have reported that ascorbic acid promotes the osteoblastic differentiation of PDL cells by modulating the type I collagen-integrin interaction. However, the signaling pathway activated following collagen-integrin interaction is still unclear. In this study, we examined the involvement of extracellular signal-regulated kinase (ERK)1/2 in the expression of osteoblastic marker genes such as the osteoblast-specific transcriptional factor runt-related transcription factor 2 (Runx2), alkaline phosphatase (ALP), and osteocalcin (OCN) in PDL cells.

METHODS

PDL cells were cultured on a conventional or type I collagen-coated dish in the presence or absence of ascorbic acid and examined for ALP activity and osteoblastic marker genes. For detection of ERK1/2, cells were plated on a petri (non-adhesive) dish or type I collagen-coated dish, and Western blot analysis was performed. The effect of the ERK1/2 inhibitor on osteoblastic marker gene expression was examined.

RESULTS

Ascorbic acid increased gene expression of Runx2, ALP, and OCN. A combination of ascorbic acid and type I collagen remarkably upregulated Runx2, ALP, and OCN gene expression and ALP activity. Western blot analysis revealed an increased level of ERK1/2 phosphorylation in cells plated on type I collagen. An ERK1/2 inhibitor suppressed ascorbic acid-induced ALP and OCN gene expression, whereas Runx2 was not affected in PDL cells.

CONCLUSION

These results indicate that ERK1/2 is involved in ascorbic acid-induced osteoblastic differentiation during PDL cell attachment to type I collagen.