National & Local Joint Engineering Research Center of Biodiagnosis and Biotherapy, Precision Medicine Institute, The Second Affiliated Hospital of Xi'an Jiaotong University, No.157 Xiwu Road, Xi'an, 710004, China.
Xi'an Institute of Tissue Engineering and Regenerative Medicine, Xi'an, 710032, Shaanxi, China.
Stem Cell Res Ther. 2021 Apr 6;12(1):225. doi: 10.1186/s13287-021-02235-7.
Premature exfoliation of the deciduous teeth is a common manifestation in childhood patients with hypophosphatasia (HPP), which is an autosomal inherited disease caused by ALPL mutations. Dysplasia of the cementum, dentin, and alveolar bone has 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.
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.
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 the teeth.
Our study indicates that ALPL regulates odontoblastic differentiation of DPSCs and provides useful information for understanding how ALPL deficiency led to tooth dysplasia and, ultimately, may inform efforts at improvement tooth defects in HPP patients.
早失乳牙是成骨不全症（HPP）患儿的常见表现，该病为常染色体显性遗传性疾病，由 ALPL 基因突变引起。牙骨质、牙本质和牙槽骨的发育不良被认为是牙齿脱落的主要原因，而其异常复杂的细胞内机制仍难以捉摸。牙髓干细胞（DPSCs）已被证明可成功再生功能性牙髓-牙本质样组织。来源于 HPP 患者的牙髓细胞矿化受损，但对更深层次的机制仍不清楚。
通过茜素红染色、免疫荧光染色、Western blot 和 RT-PCR 以及 micro-CT 检测，评估 ALPL 对 HPP 患者 DPSCs 成牙本质分化的影响。
我们发现 HPP 患者的 DPSCs 碱性磷酸酶活性较低，成牙本质分化受损。同时，我们发现 ALPL 功能丧失会降低 DPSCs 中 GSK3β 的磷酸化。而 GSK3β 再磷酸化可通过 LiCl 处理改善 HPP DPSCs 的成牙本质分化。最后，我们通过体内 LiCl 注射证明，通过增强牙齿中 GSK3β 的磷酸化，改善了 ALPL 小鼠的牙齿相关缺陷。
我们的研究表明，ALPL 调节 DPSCs 的成牙本质分化，为理解 ALPL 缺乏如何导致牙齿发育不良提供了有用的信息，并可能为改善 HPP 患者的牙齿缺陷提供信息。
