THYROID PHYSIOLOGY STUDIES OF INHERITED DISORDERS

描述（由申请人提供）：本研究计划的总体目标是通过研究关键调控过程中的遗传缺陷来促进对甲状腺生理学的理解。更具体地说，研究重点是通过研究MCT8（单羧酸转运体）、SBP2（硒代半胱氨酸插入序列结合蛋白）和TR（核TH受体）或辅助因子基因突变引起的细胞膜转运、代谢和作用缺陷导致对TH敏感性降低的综合征，从而介导甲状腺激素（TH）的作用。这些缺陷将通过临床（体内）、组织（体外）和动物（基因工程小鼠）三种方法进行研究，以补充和补偿每种方法固有的局限性。1）. 临床研究将把中枢和外周组织对活性TH、Ta及其前体甲状腺素（t1,4）的反应联系起来，以确定器官和细胞特异性TH转运和代谢。2）. 患者的成纤维细胞，在培养中繁殖，将用于碘甲状腺原氨酸跨细胞膜的特异性运输和细胞内代谢的直接检查。SBP2在硒蛋白合成层次中的作用也将被研究。微阵列分析促甲状腺激素在成纤维细胞中的作用将有助于识别有TRR基因突变和没有TRR基因突变的受试者之间的差异，从而揭示在没有TRB基因突变的情况下促甲状腺激素耐药的病因，并确定重要的辅助因子。3）. Mct8基因缺失的小鼠将有助于深入研究导致人类Mct8缺陷表现的甲状腺和大脑异常。行为和运动功能将被测试，中枢神经系统形态学将被原位杂交和免疫组织化学检查。将调查甲状腺和精神运动障碍之间的差异，以确定它们是否有因果关系。具有菌株依赖性TH敏感性差异的小鼠将用于鉴定假定的TH作用修饰因子。4）. 将测试各种方法来恢复或减少Mct8缺乏症的精神运动缺陷。在胎儿发育的关键阶段，将给Mct8缺陷小鼠注射促甲状腺激素。与肌酸结合的TH将通过肌酸转运蛋白将激素输送到大脑，从而绕过TH转运缺陷。硒补充将用于提高SBP2缺陷的硒蛋白水平。现实意义：临床研究将表征这些遗传缺陷引起的表型，建立基因检测标准。突变的早期识别将提供产前诊断和遗传咨询的基础，特别是在MCT8缺陷导致男性后代丧失能力的疾病时。产前治疗的成功发展将使受影响的雄性免于这种严重的残疾。产前检测携带TRS突变的妇女所携带的未受影响的胎儿将提供早期治疗的选择。

DESCRIPTION (provided by applicant): The broad objective of this research proposal is to advance understanding of thyroid physiology through study of genetic defects at key regulatory processes. More specifically, research is centered on the mediation of thyroid hormone (TH) effects by studying syndromes of reduced sensitivity to TH due to defects in cell membrane transport, metabolism and action caused by mutations in the MCT8 (monocarboxylate transporter), SBP2 (selenocysteine insertion sequence binding protein) and TR (nuclear TH receptor) or cofactors genes, respectively. These defects will be studied with a triple approach, clinical (in-vivo), tissue (in- vitro) and animal (genetically engineered mice) that complement and compensate for limitations inherent in each. 1). Clinical studies will correlate the central and peripheral tissue responses to the administration of the active TH, Ta and its precursor thyroxine (T,4) in order to determine organ and cell specific TH transport and metabolism. 2). Patient's fibroblasts, propagated in culture, will serve for the direct examination of iodothyronine specific transport across the cell membrane and their intracellular metabolism. The role of SBP2 in the hierarchy of selenoprotein synthesis will also be studied. Microarray analysis of TH action in fibroblasts will serve to identify differences in subjects with and without TRR gene mutations, in order to uncover the etiology of resistance to TH in the absence of TRB gene mutations and identify important cofactors. 3). Mice deficient in the Mct8 gene will serve to study in depth the thyroid and brain abnormalities responsible for the manifestations of MCT8 defects in man. Behavior and motor function will be tested, and central nervous system morphology will be examined by in-situ hybridization and immunohistochemistry. The discrepancy between the magnitude of thyroid and psychomotor disorders will be investigated to determine if they are causally linked. Mice with strain dependent differences in TH sensitivity will serve to identify putative modifiers of TH action. 4). Various means will be tested to revert or diminish the psychomotor defect of Mct8 deficiency. TH hormone will be given to Mct8 deficient mice at crucial stages of fetal development. TH conjugated to creatine will serve to deliver the hormone to brain through the creatine transporter, thus bypassing the TH transport defect. Selenium supplementation will be used in an attempt to increase the selenoprotein levels in SBP2 defects. Practical Significance: Clinical studies will characterize the phenotypes caused by these genetic defects, establishing criteria for genetic testing. Early identification of mutations will provide prenatal diagnosis and the basis for genetic counseling, particularly in MCT8 defects producing incapacitating illness in male offspring. Successful development of prenatal treatment would rescue affected males from this severe handicap. The prenatal detection of unaffected fetuses carried by women with TRS mutations will provide the option of early treatment.