Thyrocyte Protein Transport to the Cell Surface

描述（由申请人提供）：甲状腺是影响人类发育和氧化代谢的关键内分泌回路的一部分，在脊椎动物中大部分是保守的。作为腺体的基本激素形成单位，每个甲状腺滤泡由一层上皮细胞组成，这些上皮细胞分泌甲状腺球蛋白（Tg）进入中央顶腔（滤泡腔）。甲状腺细胞利用基底外侧膜上的电化学梯度获取碘化物，驱动细胞内碘化物的积累，并最终在细胞顶端运输，在H2O2生成和过氧化物酶活性的作用下，Tg被碘化，形成碘酪氨酸和碘甲状腺原氨酸。最终，内吞作用和蛋白水解消化允许活性甲状腺激素释放到血液中，而碘酪氨酸的脱碘回收碘化物用于未来的Tg碘化。这个新的给予周期侧重于Tg通过分泌途径的运输。在Tg中，激素生成的简单结构要求被保存碘化物的进化压力所抵消，这导致了复杂的分泌糖蛋白。这种复杂性产生了关于细胞内蛋白质转运和内质网（ER）质量控制功能的几个基本问题，这些问题与临床疾病直接相关。在概述中，我们的目标是继续进行基础科学分析，以解释最具临床相关性的表型。我们在这项更新应用中的主要重点是围绕Tg蛋白及其细胞内运输困难与甲状腺疾病（包括伴有或不伴有甲状腺肿的先天性甲状腺功能减退）患者和动物模型的关系。我们未来5年的具体目标是阐明Tg的胆碱酯酶样（ChEL）结构域在甲状腺激素生物合成中的作用，并建立一种体内模式来研究与先天性Tg缺乏相关的细胞生物学缺陷。这些研究对甲状腺学具有特殊的临床意义，同时对内质网蓄积病的基础和临床问题提供了更全面的认识。公共卫生相关性：甲状腺是影响人类发育和代谢的关键内分泌回路的一部分。为了制造甲状腺激素，甲状腺滤泡细胞将甲状腺球蛋白（Tg）分泌到一个中央腔中，这个腔的功能是碘化物和甲状腺激素的储存库，因为碘酪氨酸和甲状腺激素都是在Tg蛋白中形成和储存的。因此，碘化Tg对人体具有甲状腺激素储存库和碘化物储存库的双重功能。甲状腺激素的碘化和储存需要Tg通过分泌途径进行转运。一组报告说，编码Tg的基因突变是先天性甲状腺功能减退症最常见的原因（碘缺乏症除外，碘缺乏症威胁着全世界2亿人）。在迄今为止鉴定的Tg突变体中，所有突变体在通过分泌途径运输时都存在缺陷，被保留在称为内质网（ER）的隔室中。我们的主要研究重点是Tg蛋白及其与甲状腺疾病（包括但不限于先天性甲状腺肿）患者和动物模型的关系。

DESCRIPTION (provided by applicant): The thyroid gland is part of a critical endocrine circuit that influences development and oxidative metabolism in humans, which is largely conserved amongst the vertebrates. As the basic hormone-forming unit of the gland, each thyroid follicle is comprised of a monolayer of epithelial cells secreting thyroglobulin (Tg) into a central apical cavity (the follicle lumen). Thyrocytes access iodide using an electrochemical gradient at the basolateral membrane to drive intracellular accumulation of iodide with eventual transport apically where, in conjunction with H2O2 generation and peroxidase activity, Tg becomes iodinated to form both iodotyrosines and iodothyronines. Ultimately, endocytosis and proteolytic digestion allows for release of active thyroid hormones to the bloodstream while deiodination of iodotyrosines reclaims iodide for future Tg iodination. This new grant cycle focuses on Tg transport through the secretory pathway. In Tg, simple structural requirements for hormonogenesis are counterbalanced by evolutionary pressures to conserve iodide, which has resulted in a complex secretory glycoprotein. This complexity generates several fundamental questions concerning intracellular protein transport and endoplasmic reticulum (ER) quality control function that link directly to clinical disease. In the overview, our objective in this grant remains to pursue a basic science analysis in order to explain the most clinically relevant phenotypes. Our primary focus in this renewal application centers around the Tg protein and how difficulties in its intracellular transport relate to patients and animal models with thyroid disease including congenital hypothyroidism with and without goiter. Our Specific Aims for the next 5 years are to elucidate the role of the cholinesterase-like (ChEL) domain of Tg in thyroid hormone biosynthesis, and to develop an in vivo paradigm in which to study cell biological defects associated with congenital Tg deficiency. These studies have clinical significance specific to thyroidology while providing more general insight into the basic and clinical problems found in endoplasmic reticulum storage diseases. PUBLIC HEALTH RELEVANCE: The thyroid gland is part of a critical endocrine circuit that influences development and metabolism in humans. To make thyroid hormone, thyroid follicle cells secrete thyroglobulin (Tg) into a central cavity that functions as a storage depot for iodide and for thyroid hormones, because both iodotyrosines and and thyroid hormones are formed and stored within the Tg protein. Iodinated Tg thus serves the dual function of both thyroid hormone reservoir and iodide reservoir for the body. Tg transport through the secretory pathway is required for its iodination and storage of thyroid hormones. One group reports that mutations in the gene encoding Tg are the most common cause of congenital hypothyroidism (other than iodide deficiency which threatens 200 million peple worldwide). Of the Tg mutants characterized to date, all are defective for transport through the secretory pathway, being retained in a compartment known as the endoplasmic reticulum (ER). Our primary focus centers on the Tg protein and its relationship to patients and animal models with thyroid disease including, but not limited to, congenital goiter.