Osteoblast differentiation of Gli1⁺ cells via Wnt and BMP signaling pathways during orthodontic tooth movement.

OBJECTIVES

Factors that induce bone formation during orthodontic tooth movement (OTM) remain unclear. Gli1 was recently identified as a stem cell marker in the periodontal ligament (PDL). Therefore, we evaluated the mechanism of differentiation of Cre/LoxP-mediated Gli1/Tomato cells into osteoblasts during OTM.

METHODS

After the final administration of tamoxifen to 8-week-old Gli1-Cre/ROSA26-loxP-stop-loxP-tdTomato mice for 2 days, nickel-titanium closed coil springs were attached between the upper anterior alveolar bone and the first molar. Immunohistochemical localizations of β-catenin, Smad4, and Runx2 were observed in the PDL on 2, 5, and 10 days after OTM initiation.

RESULTS

In the untreated tooth, few Gli1/Tomato cells were detected in the PDL. Two days after OTM initiation, the number of Gli1/Tomato cells increased in the PDL on the tension side. On this side, 49.3 ± 7.0% of β-catenin and 48.7 ± 5.7% of Smad4 cells were found in the PDL, and Runx2 expression was detected in some Gli1/Tomato cells apart from the alveolar bone. The number of positive cells in the PDL reached a maximum on day 5. In contrast, on the compression side, β-catenin and Smad4 exhibited less immunoreactivity. On day 10, Gli1/Tomato cells were aligned on the alveolar bone on the tension side, with some expressing Runx2.

CONCLUSIONS

Gli1 cells in the PDL differentiated into osteoblasts during OTM. Wnt and bone morphogenetic proteins signaling pathways may be involved in this differentiation.