Deiodinases in Thyroid Hormone Homeostasis

描述(由申请人提供)： 1和2型碘甲状腺脱碘酶(D1和D2)是将前激素T4转化为活性激素T3的酶。人和小鼠的Dio1基因被T3高度激活，不适当地增加了甲亢患者的甲亢严重程度。在转基因动物模型中，D1活性也被用作外周甲状腺状态的指标，但对于它对T3如此敏感的原因尚不清楚。有几种遗传模型中，D_1或D_2活性降低或缺失。C3H小鼠通过增加T4以维持正常的T3和TSH来适应D1基因的减少。D2“基因敲除”小鼠(D2KO)也有升高的血清T4，正常的T3，但TSH升高。令人惊讶的是，这些小鼠也增加了d1，这表明已经发生了外周代偿。在D2KO和C3H品系杂交产生的嵌合小鼠中也出现了类似的变化。因此，尽管T3水平看似正常，但至少有一个甲状腺状态的外周标志物，即D1活性，表明后两种小鼠模型中存在甲亢。我们推测，增加D1的表达是允许这些动物补偿它们对T4的抵抗力的适应机制之一，但目前还不清楚这是如何发展的。在目标I中，我们将定义T4活性受损小鼠的外周甲状腺状态，并确定D1是否是可靠的外周甲状腺状态标记物。生理参数(O2消耗量、骨密度、生长)和生物学参数(不同组织中T3响应性mRNAs的水平)将定义甲状腺状态。T4输注研究将揭示如何适应受损的T4到T3的转换。第二个目的是确定Diol基因对T3高度敏感的分子机制。各种分子技术将阐明我们在Diol基因中确定的甲状腺反应元件的作用，并确定它是如何赋予如此高的T3反应的。这些研究将确定增加T4向T3转化的因素，并阐明即使在甲亢状态下，T3如何继续刺激基因表达。使用这些生理学方法来评估这些小鼠的甲状腺状况，将有助于应试者追求她的短期目标，即获得坚实的背景，与体内模型一起工作，以补充她的分子生物学技能。这段经历将帮助她实现成为一名独立生物医学科学家的长期目标。

DESCRIPTION (provided by applicant): The types 1 and 2 iodothyroinine deiodinases (D1 and D2) are the enzymes which convert the prohormone T4 to the active hormone, T3. The Dio1 gene of humans and mice is highly stimulated by T3, inappropriately enhancing the severity of thyrotoxicosis of the hyperthyroid patient. D1 activity is also used as an index of peripheral thyroid status in transgenic animal models, but nothing is known as to why it is so T3 responsive. There are several genetic models in which the activities of D1 or D2 are reduced or absent. The C3H mouse adapts to a genetic decrease in D1 by increasing T4 to maintain a normal T3 and TSH. The D2 "knockout" mouse (D2KO) also has an elevated serum T4, and a normal T3, but an increased TSH. Surprisingly, these mice also have increased D1 suggesting peripheral compensation has occurred. Similar changes occur in chimeric mice produced by crossing the D2KO and C3H strains. Thus, despite seemingly normal T3 levels, at least one peripheral marker of thyroid status, D1 activity, suggests hyperthyroidism in the latter two mouse models. We hypothesize that increased D1 expression is one of the adaptive mechanisms allowing these animals to compensate for their resistance to T4, but it is not clear how this develops. In Aim I we will define the peripheral thyroid status of mice with impaired T4 activation and determine whether D1 is a reliable peripheral thyroid status marker. Physiological (02 consumption, bone density, growth) and biological ( the levels of T3 responsive mRNAs in various tissues) parameters will define the thyroid status. T4 infusion studies will reveal how the adaptation to the impaired T4 to T3 conversion occurs. The second Aim is to determine the molecular mechanism of the exquisite sensitivity of the Diol gene to T3. Various molecular techniques will elucidate the role of the thyroid response element we have identified in the Diol gene, and determine how it confers such a high T3 response. These studies will define factors increasing T4 to T3 conversion and elucidate how T3 continues to stimulate gene expression even in the hyperthyroid state. Employing these physiological approaches to assess the thyroid status of these mice will aid the candidate in pursing her short-term goal of gaining a solid background working with in vivo models to complement her molecular biological skills. This experience will help her achieve her long-term goal of becoming an independent biomedical scientist.