TNF-α Increases Sclerostin Expression in Osteocyte during Orthodontic Tooth Movement

Objectives: TNF-α has an important role in osteoclastogenesis during orthodontic tooth movement (OTM). Several studies suggested that sclerostin (SCL) promotes bone remodeling via RANKL expression in osteocyte during OTM. However, there has been no report investigating the effect of TNF-α on osteocyte SCL expression. The objective of this study is to clarify SCL expression in osteocyte via TNF-α and SCL involvement in OTM.
Methods: In vitro analysis, osteocytes were isolated from DMP1-Topaz mice by sorting Topaz variant of GFP positive cells through cell sorter. Osteocytes were treated with TNF-α, and SOST mRNA expression was evaluated by real-time PCR. Moreover, osteocytes were cultured with SCL, and RANKL mRNA expression was analyzed with real-time PCR. In vivo analysis, TNF-α was injected into supracalvaria of C57BL/6J mice to investigate SCL expression by immunohistochemistry and SOST mRNA expression by real-time PCR. Finally, as OTM model, a Ni-Ti closed-coil spring was fixed between the upper incisors and the upper-left first molar to move first molar to the mesial direction in C57BL/6J mice and TNF receptors deficient mice. After OTM, SCL positive osteocytes on the mesial side of the maxillary left first molar were evaluated by immunohistochemistry.
Results: In vitro anlysis, SOST mRNA expression increased when osteocytes were treated with TNF-α. RANKL mRNA expression increased in osteocytes treated with SCL. SCL and SOST mRNA expression increased in the calvariae treated with TNF-α in vivo. Furthermore, SCL positive osteocytes in TNF receptor deficient mice were decreased as compared to C57BL/6J mice after OTM.
Conclusions: We found that TNF-α produced during OTM increases SCL expression of osteocytes, and SCL promotes RANKL expression of osteocytes. Our findings suggest that TNF-α plays an important role in increasing SCL expression and enhancing osteoclast formation during OTM.