What gives the dentin-enamel junction strength? Structural and mechanical function of collagen and amelogenin.

牙齿中的牙本质-牙釉质连接部（DEJ）提供了坚固和坚韧的界面，其可以承受长的工作寿命， 几乎没有重塑。然而，分子组成和结构，导致这些显着的机械 属性仍然知之甚少。具体来说，牙釉质基质中的蛋白质如何与牙本质胶原蛋白相互作用 纤维形成连续矿化的组织，需要解决。该项目的目标是推进我们的 理解DEJ的强度和韧性的纳米级起源。我们建议定义胶原蛋白的作用 和釉原蛋白，分别来自牙本质和釉质的主要蛋白质，通过两个特异性的DEJ的强度， 目标。在第一个目标中，我们将测试釉原蛋白不是从牙本质的矿物晶体的延伸所必需的。 胶原蛋白，同时阻止全长蛋白质的切割改变了DEJ的结构。在第二个目标中， 证明牙本质胶原的突变可以影响DEJ的形成和机械性能。我们的第一 釉原蛋白基因敲除小鼠的DEJ似乎完好无损，而小鼠模型缺乏DEJ，这一事实支持了这一假设 基质金属蛋白酶-20（MMP-20），在釉质形成过程中负责釉质蛋白裂解的主要酶 分泌物，具有受损的DEJ和釉质从牙本质分层。在我们的第二个目标中，我们将探索如何 在牙本质形成的小鼠模型中I型胶原的突变改变DEJ。我们将测试这些假设， 使用高分辨率电子显微镜和免疫组织化学技术来表征原位形态 的DEJ以及有机基质组成的野生型和突变小鼠。同样，我们将探索有机基质 纳米结构与矿物组织和结晶度有关。我们还将评估胶原蛋白突变对 其对体外釉质蛋白的亲和力。最后，我们将量化突变对强度和韧性的影响， DEJ使用创新的原子力显微镜表征。总的来说，该项目的结果将 显著提高了我们对DEJ的理解，以及导致其令人难以置信的机械行为的机制。

The dentin-enamel junction (DEJ) in teeth provide a strong and tough interface that can withstand a long working life with little to no remodeling. However, the molecular composition and structure that leads to these remarkable mechanical properties are still poorly understood. Specifically, how proteins from the enamel matrix interact with dentin collagen fibrils to form a continuously mineralized tissue, needs to be addressed. The goal of this project is to advance our understanding of the nanoscale origin of the strength and toughness of the DEJ. We propose to define the role of collagen and amelogenin, the major proteins from dentin and enamel respectively, on the strength of DEJ through two specific aims. In the first aim we will test that amelogenin is not required for the extension of mineral crystals from dentin’s collagen, while preventing the cleavage of the full-length protein alters the structure of the DEJ. In the second aim we will demonstrate that mutations in dentin collagen can affect the formation and mechanical properties of the DEJ. Our first hypothesis is supported by the fact that the DEJ of amelogenin knock-out mice appears intact while mouse models lacking matrix metalloproteinase-20 (MMP-20), the main enzyme responsible for the cleavage of enamel proteins during enamel secretion, have a compromised DEJ and enamel delaminates from the dentin. In our second aim, we will explore how mutation of type I collagen in mouse models of dentinogenesis imperfecta alter the DEJ. We will test these hypotheses by using high-resolution electron microscopy and immunohistochemistry techniques to characterize in situ the morphology of DEJ as well as the organic matrix composition in wild type and mutant mice. Similarly, we will explore the organic matrix nanostructure in relation to mineral organization and crystallinity. We will also assess the impact of collagen mutation on its affinity to enamel proteins in vitro. Finally, we will quantify the impact of mutations on the strength and toughness of the DEJ using innovative atomic force microscopy characterization. Taken together, the results of this project will significantly improve our understanding of the DEJ and on the mechanisms leading to its incredible mechanical behavior.