PHYSIOLOGICAL ROLE OF THYROXINE-BINDING PROTEINS

描述（由申请人提供）：本合作研究将在巴西南里奥格兰德联邦大学医学院内分泌科进行，作为NIH资助#RO 1 DK-36256的扩展，以扩展人体生理和病理生理条件下碘甲腺原氨酸脱碘酶功能的研究。1型、2型和3型脱碘酶（D1、D2和D3）组成氧化还原酶家族，催化甲状腺激素的外环（D1和D2，活化）或内环（D1和D3，失活）碘的去除。脱碘途径是甲状腺激素激活和失活的关键步骤，允许以组织特异性方式快速改变细胞内甲状腺状态，而不影响全身甲状腺激素水平。在这些研究中，我们将探索硒代脱碘酶家族的第三个成员D3在完整细胞中的催化机制。D3酶催化T4和T3的失活，其过度表达，如发生在大血管瘤中，导致婴儿和成人严重的甲状腺功能减退症。D3活性的增加，导致局部甲状腺功能减退，也可能是人类对疾病或禁食以保存能量的适应性反应的重要因素。此外，在衰竭的心脏中已证实D3活性增加，表明局部细胞内TS减少可能导致心肌中甲状腺功能减退。我们的共聚焦显微镜研究预测，D3的活性催化中心是细胞外的。我们将确定是否甲状腺激素失活D3发生在细胞外的空间和催化是否可以改变通过共价修饰的酶的不渗透探针或通过阻断正常的细胞内循环D3。这里提出的研究将阐明这种脱碘酶的功能，并将对我们理解健康和患病个体中控制甲状腺激素水平的因素产生重大影响。

DESCRIPTION (provided by applicant): This collaborative study will be performed in Brazil at the Endocrinology Division, Medical School of the Universidade Federal do Rio Grande do Sul, as an extension of NIH grant # RO1 DK-36256 to extend studies on the function of the iodothyronine deiodinases under physiological and pathophysiological circumstances in humans. The types 1, 2, and 3 deiodinases (D1, D2, and D3) constitute a family of oxidoreductases that catalyze the removal of iodine from the outer (D1 and D2, activation) or inner ring (D1 and D3, inactivation) of the thyroid hormones. The deiodination pathway is a critical step in thyroid hormone activation and inactivation, allowing for rapid changes in intracellular thyroid status in a tissue-specific manner, without affecting systemic thyroid hormone levels. In these studies, we will explore the mechanism of catalysis in intact cells by the third member of the selenodeiodinase family, D3. The D3 enzyme catalyzes the inactivation of T4 and T3 and its overexpression, as occurs in large hemangiomas, causes severe hypothyroidism in infants and adults. Increases in D3 activity, causing local hypothyroidism, may also be important in the adaptive response of humans to illness or fasting to conserve energy. Furthermore, increased D3 activity has been demonstrated in failing hearts, indicating that reduction of local intracellular TS may contribute to a hypothyroid condition in the myocardium. Our confocal microscopic studies predict that the active catalytic center of D3 is extracellular. We will determine if thyroid hormone inactivation by D3 occurs in the extracellular space and whether catalysis can be altered by either covalent modification of the enzyme by impermeant probes or by blocking the normal intracellular cycling of D3. The studies proposed here will shed light on the function of this deiodinase and will have major implications for our understanding of factors controlling thyroid hormone levels in healthy and sick individuals.