Mkx regulates the orthodontic tooth movement via osteoclast induction

J Bone Miner Metab. 2021 Sep;39(5):780-786. doi: 10.1007/s00774-021-01233-2. Epub 2021 May 14.

Abstract

Introduction: The periodontal ligament (PDL) plays an important role in orthodontic tooth movement; however, the underlying molecular mechanism remains unclear. We have previously reported that the Mohawk homeobox (Mkx), a tendon-specific transcription factor, is expressed in the PDL and regulates its homeostasis.

Materials and methods: In the present study, we examined the role of Mkx in orthodontic tooth movement via bone remodeling induced by mechanical stimulation in Mkx-deficient rats, which are widely used as experimental animals for orthodontic force application. Orthodontic tooth movement of the maxillary first molar was performed in 7-week-old male Mkx-deficient rats (n = 4) and wild-type Wistar rats (n = 4) using coil springs for 14 days. Hematoxylin and eosin (H&E) staining and tartrate-resistant acid phosphatase (TRAP) staining were performed to evaluate morphological changes and osteoclasts. Furthermore, changes in the expression of receptor activator nuclear factor-kappa B ligand (RANKL) were demonstrated using immunostaining.

Results: The amount of tooth movement was significantly lower in Mkx-deficient rats than in wild-type rats. The number of TRAP-positive cells was suppressed in Mkx-deficient rats on the compression side.

Conclusion: Orthodontic tooth movement experiments in Mkx-deficient rats suggested that Mkx is involved in osteoclast induction at the alveolar bone surface on the compression side. This study reveals the possibility that Mkx plays a mechanosensory role in orthodontic tooth movement by inducing RANKL expression and osteoclastogenesis.

Keywords: Mohawk; Orthodontic tooth movement; Osteoclast; PDL; Rat.