Background: Premature exfoliation of deciduous teeth is a common manifestation in childhood patients with Hypophosphatasia (HPP), which is an autosomal inherited disease caused by ALPL mutations. Dysplasia of cementum, dentin and alveolar bone have been proposed to be the main reasons for the exfoliation of teeth, while the extraordinarily complex intracellular mechanisms remain elusive. Dental pulp stem cells (DPSCs) have been demonstrated to successfully regenerate functional pulp-dentin like tissue. Dental pulp cells derived from HPP patients impaired mineralization, however insight into the deeper mechanism is still unclear.
Methods: The effects of ALPL on odontoblastic differentiation of DPSCs from HPP patient were assessed by Alizarin Red staining, immunofluorescent staining, Western blot and RT-PCR, and micro-CT assays.
Results: Here, we found DPSCs from HPP patient exhibited low ALP activity and impaired odontoblastic differentiation. Meanwhile, we found that loss of function of ALPL reduced phosphorylation of GSK3β in DPSCs. While GSK3β rephosphorylation improved odontoblastic differentiation of HPP DPSCs with LiCl treatment. Finally, we demonstrated systemic LiCl injection ameliorated tooth associated defects in ALPL+/- mice by enhanced phosphorylation of GSK3β in teeth.
Conclusions: Our study indicates that ALPL regulates odontoblastic differentiation of DPSCs, and provides useful information for understanding how ALPL deficiency leaded to tooth dysplasia and, ultimately, may inform efforts at improvement tooth defects in HPP patients.