Inhibition of histone deacetylase 3 in dental mesenchyme regulates the development of tooth root

Studies on human and animal models have demonstrated a complex molecular regulatory network between the dental mesenchyme and epithelium governing tooth development. However, epigenetic regulation of tooth development is largely unexplored. This study aimed to elucidate the relationship between epigenetic modifiers and dental root development using mice deficient in histone deacetylase 3 (Hdac3) under the control of the osterix promoter (Osx-Cre/Hdac3fl/fl or Hdac3-CKOosx). We observed tooth root size and histology in Hdac3-CKOosx mice. Dental pulp progenitor cells (DPCs) were isolated from lower incisors, and calcification and gene expression were assessed. Hdac3 depletion in osterix-expressing dental pulp stem cells, including odontoblasts, caused a progressive postnatal obstruction, resulting in relatively short roots and small root apices of the first molar. Mild degeneration was observed during the development of dentin and cementum structures. Dentin and cementum had uneven borders and showed disordered H&E staining in Hdac3-CKOosx mice that had a thin cementum compared to that of WT mice. Hdac3 inhibition/deletion in dental pulp stem cells probably influenced Msh homeobox 1 (Msx1) and Col1a1 expression in the early developmental stage, thereby driving differentiation in DPCs. Subsequently, Msx1, Col1a1, and osteocalcin expression were remarkably downregulated during calcification. Deletion or inhibition of Hdac3 in conditional KO dental pulp stem cells cultured in mineralization medium resulted in aberrant cell cycle control, and the early stages of maturation of DPCs and odontoblasts were inhibited. Inhibition of Hdac3 in cementocytes also restricted their proliferation and calcification. These results suggested that the deletion or inhibition of Hdac3 in the dental mesenchyme may cause development and maturation deficiency of tooth root.