Continuous root formation in developing teeth by molecular cues

 描述(申请人提供)：龋齿和牙髓炎导致儿童和青少年恒牙牙根发育停滞。张开的根尖很容易受到创伤和感染，经常导致幼年(通常为18岁)的牙齿脱落。儿童和青少年患者的牙齿缺失是毁灭性的，因为钛种植体是不适用的，因为金属浸泡在牙槽骨中，经历活跃的垂直生长。目前，儿童青少年根尖开放感染恒牙尚无有效的临床治疗方法。促进牙本质形成和牙根持续发育的再生细胞或线索为解决这一未得到满足的临床需求提供了唯一的希望。发育中的颅面部间充质干细胞/前体细胞分化为成牙本质细胞，形成牙本质。我们的初步数据显示，当颅面间充质干细胞/祖细胞分化为成牙本质细胞时，一组948个基因和转录因子上调或下调。我们提出了两个经过理性选择的因素 在临床前的活体模型中，在根管治疗的根管中发现了强大的牙本质再生，如电子显微镜所证明的那样，牙本质以具有牙本质小管和成牙本质突起的管状牙本质的形式存在。再生牙本质的机械性能与天然牙本质相当，天然牙本质是新形成的再生牙本质的基质。值得注意的是，没有细胞被移植到经过根管治疗的根管中。因此，所有再生的牙本质都来自宿主内源性细胞，这些细胞是由这两个分子线索招募的。在这一应用中，我们将新获得的关于成熟牙齿内源性牙本质再生的知识转化为具有广泛根尖开放的未成熟牙齿，在临床前的大型动物模型中，这相当于儿童和青少年患者的恒牙发育。这种从成熟牙到未成熟牙的转换远非简单的时间转换，而是将解决两个科学上未知和临床上相关的问题：1)单分子信号不仅能诱导足够的内源性根尖乳头干/祖细胞的招募，而且能将它们转化为牙本质生成成牙本质细胞？2)分子信号的时空传递能否促进牙本质定向生长以完成牙根发育？因此，为响应PAR-13-137(生物工程研究资助，BRG)，这项建议的总体目标是在临床前的大型动物模型中开发新的策略，在具有广泛根尖开放的未成熟牙齿中再生牙本质。我们的主要假设是，在根尖完全开放的未成熟牙齿中，牙本质的再生是通过诱导内源性干细胞/祖细胞招募和分化的新分子线索的信号梯度来实现的。

 DESCRIPTION (provided by applicant): Dental caries and pulpitis cause developmental arrest of tooth roots of permanent teeth in children and adolescents. Wide-open root apex is susceptible to trauma and infections, frequently resulting in tooth loss at a young age (typically <18 years old). Tooth loss in children and adolescent patients is devastating because titanium dental implants are contra-indicated due to metal submerge in the alveolar bone that undergoes active vertical growth. Currently, there is no effective clinical treatment for infected permanent teeth with open root apex in children and adolescent patients. Regenerative cells or cues that promote dentin formation and continuous root development offer the only hope to address this unmet clinical need. Craniofacial mesenchymal stem/progenitor cells in development differentiate into odontoblasts that form dentin. Our preliminary data show that a panel of 948 genes and transcriptional factors are up- or down-regulated when craniofacial mesenchymal stem/progenitor cells differentiate into odontoblasts. We delivered two rationally selected factors in endodontically treated root canals in a preclinical model in vivo and found robust dentin regeneration in the form of tubular dentin with dentinal tubules and odontoblast processes as demonstrated by electron microscopy. Mechanical properties of the regenerated dentin were at par with native dentin that served as a substrate for the newly formed, regenerated dentin. Strikingly, no cells were transplanted in endodontically treated root canals. Thus, all of the regenerated dentin was derived from host endogenous cells that were recruited by these two molecular cues. In this application, we transform our newly gained knowledge on endogenous dentin regeneration in mature teeth into immature teeth with wide-open root apex in a preclinical, large animal model that is equivalent to developing permanent teeth in children and adolescent patients. This translation from mature teeth to immature teeth is far from a simple chronological switch, but will address two scientifically unknown and clinically relevant questions: 1) Can single molecular cues not only induce the recruitment of sufficient endogenous apical papilla stem/progenitor cells, but also transform them into dentin-generating odontoblasts? 2) Can spatiotemporal delivery of molecular cues promote directional dentin growth to complete root development? Accordingly, the overall objectives of this proposal, in response to PAR-13-137 (Bioengineering Research Grants, BRG), are to develop novel strategies for dentin regeneration in immature teeth with wide open root apex in a preclinical, large animal model. Our overarching hypothesis is that dentin regeneration in immature teeth with wide-open root apex is enabled by signal gradients of novel molecular cues that induce the recruitment and differentiation of endogenous stem/progenitor cells.