| Summary: | During orthodontic tooth movement, transcription factor hypoxia-inducible factor 1α (HIF1α) is stabilised in the periodontal ligament. While HIF1α in periodontal ligament fibroblasts can be stabilised by mechanical compression, in macrophages pressure application alone is not sufficient to stabilise HIF1α. The present study was conducted to investigate the role of myeloid HIF1α during orthodontic tooth movement. Orthodontic tooth movement was performed in wildtype and <i>Hif1α</i><sup>Δmyel</sup> mice lacking HIF1α expression in myeloid cells. Subsequently, µCT images were obtained to determine periodontal bone loss, extent of orthodontic tooth movement and bone density. RNA was isolated from the periodontal ligament of the control side and the orthodontically treated side, and the expression of genes involved in bone remodelling was investigated. The extent of tooth movement was increased in <i>Hif1α</i><sup>Δmyel</sup> mice. This may be due to the lower bone density of the <i>Hif1α</i><sup>Δmyel</sup> mice. Deletion of myeloid Hif1α was associated with increased expression of <i>Ctsk</i> and <i>Acp5</i>, while both <i>Rankl</i> and its decoy receptor <i>Opg</i> were increased. HIF1α from myeloid cells thus appears to play a regulatory role in orthodontic tooth movement.
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