Silvestri Elena, Lombardi Assunta, Coppola Maria, Gentile Alessandra, Cioffi Federica, Senese Rosalba, Goglia Fernando, Lanni Antonia, Moreno Maria, de Lange Pieter
Department of Science and Technology, University of Sannio, Benevento, Italy.
Department of Biology, University of Naples "Federico II", Naples, Italy.
Cell Physiol Biochem. 2018;47(6):2471-2483. doi: 10.1159/000491620. Epub 2018 Jul 10.
BACKGROUND/AIMS: Both 3,5-diiodo-L-thyronine (3,5-T2) and 3,5,3'-triiodo-L-tyronine (T3) affect energy metabolism having mitochondria as a major target. However, the underlying mechanisms are poorly understood. Here, using a model of chemically induced hypothyroidism in male Wistar rats, we investigated the effect of administration of either 3,5-T2 or T3 on liver oxidative capacity through their influence on mitochondrial processes including: proton-leak across the mitochondrial inner membrane; complex I-, complex II- and glycerol-3-phosphate-linked respiratory pathways; respiratory complex abundance and activities as well as individual complex aggregation into supercomplexes.
Hypothyroidism was induced by propylthiouracil and iopanoic acid; 3,5-T2 and T3 were intraperitoneally administered at 25 and 15 µg/100 g BW for 1 week, respectively. Resulting alterations in mitochondrial function were studied by combining respirometry, Blue Native-PAGE followed by in-gel activity, and Western blot analyses.
Administration of 3,5-T2 and T3 to hypothyroid (hypo) rats enhanced mitochondrial respiration rate with only T3 effectively stimulating proton-leak (450% vs. Hypo). T3 significantly enhanced complex I (+145% vs. Hypo), complex II (+66% vs. Hypo), and glycerol-3 phosphate dehydrogenase (G3PDH)-linked oxygen consumptions (about 6- fold those obtained in Hypo), while 3,5-T2 administration selectively restored Euthyroid values of complex II- and increased G3PDH- linked respiratory pathways (+165% vs. Hypo). The mitochondrial abundance of all respiratory complexes and of G3PDH was increased by T3 administration whereas 3,5-T2 only increased complex V and G3PDH abundance. 3,5-T2 enhanced complex I and complex II in gel activities with less intensity than did T3, and T3 also enhanced the activity of all other respiratory complexes tested. In addition, only T3 enhanced individual respiratory component complex assembly into supercomplexes.
The reported data highlight novel molecular mechanisms underlying the effect elicited by iodothyronine administration to hypothyroid rats on mitochondrial processes related to alteration in oxidative capacity in the liver. The differential effects elicited by the two iodothyronines indicate that 3,5-T2, by influencing the kinetic properties of specific mitochondrial respiratory pathways, would promote a rapid response of the organelle, while T3, by enhancing the abundance of respiratory chain component and favoring the organization of respiratory chain complex in supercomplexes, would induce a slower and prolonged response of the organelle.
背景/目的：3,5-二碘-L-甲状腺原氨酸（3,5-T2）和3,5,3'-三碘-L-甲状腺原氨酸（T3）均影响能量代谢，且以线粒体作为主要靶点。然而，其潜在机制尚不清楚。在此，我们利用化学诱导的雄性Wistar大鼠甲状腺功能减退模型，研究了给予3,5-T2或T3对肝脏氧化能力的影响，及其对线粒体相关过程的影响，包括：线粒体内膜的质子泄漏；复合体I、复合体II以及甘油-3-磷酸连接的呼吸途径；呼吸复合体的丰度和活性，以及单个复合体聚集成超复合体。
通过丙硫氧嘧啶和碘番酸诱导甲状腺功能减退；分别以25和15μg/100g体重的剂量腹腔注射3,5-T2和T3，持续1周。通过结合呼吸测定法、蓝色非变性聚丙烯酰胺凝胶电泳（BN-PAGE）及凝胶内活性分析和蛋白质免疫印迹分析，研究由此导致的线粒体功能改变。
对甲状腺功能减退（甲减）大鼠给予3,5-T2和T3可提高线粒体呼吸速率，只有T3能有效刺激质子泄漏（与甲减组相比增加450%）。T3显著提高复合体I（与甲减组相比增加145%）、复合体II（与甲减组相比增加66%）以及甘油-3-磷酸脱氢酶（G3PDH）连接的氧消耗（约为甲减组的6倍），而给予3,5-T2可选择性恢复复合体II的甲状腺功能正常水平，并增加G3PDH连接的呼吸途径（与甲减组相比增加165%）。给予T3可增加所有呼吸复合体及G3PDH的线粒体丰度，而3,5-T2仅增加复合体V和G3PDH的丰度。3,5-T2增强了凝胶中复合体I和复合体II的活性，但强度低于T3，且T3还增强了所有其他测试呼吸复合体的活性。此外，只有T3增强了单个呼吸成分复合体组装成超复合体。
本研究数据揭示了甲状腺功能减退大鼠给予碘甲状腺原氨酸后，对肝脏氧化能力改变相关线粒体过程产生影响的新分子机制。两种碘甲状腺原氨酸产生的不同效应表明，3,5-T2通过影响特定线粒体呼吸途径的动力学特性，促进细胞器的快速反应，而T3通过增加呼吸链成分的丰度并促进呼吸链复合体在超复合体中的组织化，诱导细胞器产生较慢且持久的反应。
