Thyrocyte Protein Transport to the Cell Surface

描述(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循环的一部分，这在脊椎动物中很大程度上是保守的。作为腺体的基本激素形成单位，每个甲状腺滤泡由单层上皮细胞组成，分泌甲状腺球蛋白(TG)进入中央顶腔(滤泡腔)。甲状腺细胞在基底膜上使用电化学梯度获得碘，以驱动细胞内碘的积累，最终在顶端运输，结合过氧化氢的产生和过氧化物酶活性，甘油三酯被碘化，形成碘酪氨酸和碘甲状腺原氨酸。最终，内吞作用和蛋白分解消化允许活性甲状腺激素释放到血液中，而脱碘酪氨酸为未来的甘油三酯碘化回收碘。这一新的授权周期侧重于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的进化压力所抵消，这导致了一种复杂的分泌型糖蛋白。这种复杂性产生了几个与细胞内蛋白运输和内质网(ER)质量控制功能有关的基本问题，这些功能直接与临床疾病有关。综上所述，我们在这笔赠款中的目标仍然是进行基础科学分析，以解释最具临床相关性的表型。我们在这一更新应用中的主要焦点集中在TG蛋白及其细胞内转运的困难与甲状腺疾病患者和动物模型之间的关系，包括先天性甲状腺功能减退症伴或不伴甲状腺肿。我们未来5年的具体目标是阐明甘油三酯的胆碱酯酶(CHEL)结构域在甲状腺激素生物合成中的作用，并开发一种体内范例来研究与先天性甘油三酯缺乏症相关的细胞生物学缺陷。这些研究具有特定于甲状腺学的临床意义，同时为内质网储存性疾病中发现的基本和临床问题提供了更全面的见解。与公共健康相关：甲状腺是影响人类发育和新陈代谢的关键内分泌循环的一部分。为了制造甲状腺激素，甲状腺滤泡细胞将甲状腺球蛋白(TG)分泌到中央腔中，作为碘和甲状腺激素的储存库，因为碘酪氨酸和甲状腺激素都形成并存储在TG蛋白中。因此，碘化甘油三酯对人体具有甲状腺荷尔蒙储存库和碘储存库的双重功能。甘油三酯通过分泌途径转运是其碘化和甲状腺激素储存所必需的。一个小组报告说，编码甘油三酯的基因突变是先天性甲状腺功能减退症最常见的原因(除了碘缺乏，它威胁着全球2亿人)。到目前为止，所有的TG突变体都有缺陷，不能通过分泌途径运输，被保留在一个被称为内质网(ER)的隔室中。我们主要关注TG蛋白及其与甲状腺疾病患者和动物模型的关系，包括但不限于先天性甲状腺肿。

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.