Impaired vitamin D signaling reveals novel targets in tooth and alveolar bone.

Abstract

Teeth are established as targets for vitamin D metabolites but have retained less attention than the well-defined bone cell metabolism. Here we report that VDRgem mice, which bear a point-mutated vitamin D receptor (VDR) unresponsive to the endogenous bioactive vitamin D, are more severely affected and have a greater severity of tooth and alveolar bone defects than VDR-null mice. Transcriptional profiling of postnatal day 5 VDRgem and VDR-null mutant incisors revealed vitamin D ligand signaling targets that promote mineralization, induce alveolar bone growth, and assure dentin integrity. RNA-sequencing analysis of VDRgem mutants uniquely showed defects in developmental targets- notably Hedgehog and Wnt signaling reductions. Micro computed tomography (μCT) and microscopy analysis of adult VDRgem mice unravels severely reduced alveolar bone density, with abnormal root and pulp morphology. VDRgem mutants have severely hypocalcified alveolar bone and dentin- comparatively worse than VDR-null mice- as confirmed by scanning electron microscopy and mineral analysis. This genetically confirmed that vitamin D, acting through its receptor, enables bone and tooth to accumulate enough calcium and phosphorous for structural integrity. In addition, enamel structure is defective in VDRgem mice, displaying hypomineralized areas. Collectively, the severe defects in VDRgem tooth and alveolar bone demonstrate the importance of vitamin D actions at early stages of tooth development.