A New Concept of Amelogenin-guided Mineralization in Enamel

牙釉质引导矿化的新概念

• 批准号: 8730112
• 负责人: Stefan Friedrich Habelitz
• 金额: $ 19.76万
• 依托单位: UNIVERSITY OF CALIFORNIA, SAN FRANCISCO
• 依托单位国家: 美国
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-09-04 至 2016-05-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8730112
• 关键词: Animals; Apatites; Appearance; Area; Atomic Force Microscopy; Caliber; Crystallization; Dental Enamel; Development; Electrons; Emulsions; Environment; Growth; Human; Human body; Hydrolysis; In Vitro; Ions; Knock-out; Lead; Length; MMP-20; Microscopy; Minerals; Modeling; Morphology; Mus; Nanosphere; Oils; Peptide Hydrolases; Phase; Process; Proteins; Recombinants; Research Design; Resolution; Role; Solutions; Spectrum Analysis; Staging; Structure; System; Testing; Tissues; Tooth structure; Water; Width; amelogenin; aqueous; base; calcium phosphate; enamel matrix proteins; in vivo; millimeter; mineralization; nanofiber; public health relevance; retinal rods; self assembly

DESCRIPTION (provided by applicant): Enamel, the hardest and most mineralized tissue in the human body, is comprised of a unique organization of apatite nanofibers of only 50 nm width but several micrometers to millimeters in length. Its structure is the result of a protein-guided uniaxial growth process of apatite crystals along their c-axes in a three-dimensional organic framework that hydrolyzes in coordination with advancing mineralization to transform into a tissue almost entirely comprised of mineral. While the role of self-asembly of enamel matrix proteins, in particular amelogenin, has widely been recognized as a crucial factor in controlling structure development of enamel, the current model based on the formation of amelogenin nanospheres has significant limitations with regards to the ability of a spherical structure guidin the anisotropic growth of initially ribbon-like apatite crystals and their transformation into a compact mineralized structure. Amelogenin is a hydrophobic protein which comprises about 90% of the enamel matrix proteins. Recently we discovered that the recombinant human full-length amelogenin protein (rH174) forms ribbons of 17 nm width, which grow over a period of days to several micrometer in length. Such ribbons have the ability to self-align and to form bundles which resemble the appearance of aligned apatite crystallites in an enamel rod. Ribbon formation requires the presence of both calcium and phosphate ions suggesting that ion bridges develop and drive the self-assembly process. Synthesis of such ribbons was kinetically enhanced in a water-oil emuslion system but ribbons were also generated in an oil-free environment and commonly formed within 3 to 5 days of incubation in calcium phosphate solutions. While nanoribbons of rH174 contain calcium and phosphate, they do not directly promote apatite crystllization, but instead appear to stabilize an amorphous mineral. Oriented apatite formed however on nanoribbons made from an amelogenin cleavage product, rH146, indicating that the processing of the full- length protein might induce a transformation from amorphous to crystalline apatite. This proposal is based on the hypothesis that amelogenin nanoribbons are the biologically relevant supramolecular structures in developing enamel and hydrolysis of nanoribbons is required to enable oriented calcium phosphate mineralization. This hypothesis will be tested through the following two specific aims: 1. To induce oriented calcium phosphate crystal growth on amelogenin nanoribbons in-vitro; 2. To demonstrate that amelogenin nanoribbons, as observed in-vitro, are the predominant supramolecular structure of developing enamel in-vivo.

描述（由申请人提供）：牙釉质是人体中最硬和矿化最多的组织，由宽度仅为50 nm但长度为几微米至几毫米的磷灰石纳米纤维的独特组织组成。它的结构是磷灰石晶体在三维有机框架中沿着其c轴的蛋白质引导的单轴生长过程的结果，该过程与促进的矿化协同水解以转化成几乎完全由矿物质组成的组织。虽然釉质基质蛋白，特别是釉原蛋白的自吸收作用被广泛认为是控制釉质结构发育的关键因素，目前基于釉原蛋白纳米球形成的模型在球形结构引导初始带状磷灰石晶体的各向异性生长及其转化为致密矿化结构的能力方面具有显著的局限性。釉原蛋白是一种疏水性蛋白质，占釉基质蛋白的90%左右。最近，我们发现重组人全长釉原蛋白（rH 174）形成17 nm宽的条带，其在几天内生长到几微米长。这样的带状物具有自对准的能力，并且形成类似于釉质棒中对准的磷灰石微晶的外观的束。带状物的形成需要钙离子和磷酸根离子的存在，这表明离子桥的发展和驱动的自组装过程。在水-油乳状液体系中，这种带状物的合成在动力学上得到增强，但带状物也在无油环境中产生，并且通常在磷酸钙溶液中孵育3至5天内形成。然而，在由釉原蛋白裂解产物rH 146制成的纳米带上形成了定向磷灰石，这表明全长蛋白质的加工可能诱导从无定形磷灰石到结晶磷灰石的转化。该建议是基于这样的假设，即釉原蛋白纳米带是发育釉质中的生物学相关的超分子结构，并且需要纳米带的水解来实现定向磷酸钙矿化。这一假设将通过以下两个具体目标进行检验：1。体外诱导磷酸钙晶体在釉原蛋白纳米带上定向生长; 2.证明体外观察到的釉原蛋白纳米带是体内发育釉质的主要超分子结构。