Laboratory of Translational Endocrinology, Carlos Chagas Filho Institute of Biophysics, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
Laboratory of Metabolic Adaptations, Institute of Medical Biochemistry Leopoldo de Meis, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
Thyroid. 2020 Jul;30(7):1079-1090. doi: 10.1089/thy.2019.0124. Epub 2020 Apr 24.
Sepsis can cause the nonthyroidal illness syndrome (NTIS), resulting in perturbed thyroid hormone (TH) signaling and reduced thyroxine (T4) levels. TH is a major regulator of muscle function, via its influence on mitochondria. This study aimed at evaluating the relationship between TH signaling, mitochondrial function, and the antioxidant defense system in the diaphragms of septic mice. Male C57Bl/6 mice were divided into two groups: cecal ligation and puncture (CLP) and sham. Twenty-four hours after surgery, plasma, diaphragms, and livers were collected. TH metabolism and responses were analyzed by measuring messenger RNA (mRNA) expression of in the liver, and , , 2, , and (encodes MCT 10 and 8), in the diaphragm. T4 plasma levels were measured by radioimmunoassay. Damage to diaphragm mitochondria was assessed by electron microscopy and real-time polymerase chain reaction (qPCR), and function with oxygraphy. The diaphragm antioxidative defense system was examined by qPCR, analyzing superoxide dismutase (SOD) 1 (), mitochondrial superoxide dismutase (SOD 2; ), extracellular superoxide dismutase (SOD 3; ), glutathione peroxidase 1 (), and catalase () expression. The effect of TH replacement was tested by treating the mice with T4 and triiodothyronine (T3) (CLP+TH) after surgery. CLP mice presented reduced total plasma T4 concentrations, downregulated , and upregulated mRNA expression in the liver. CLP mice also displayed downregulated , and expression in the diaphragm, suggesting that TH signaling was compromised. The expression of (encoding PGC1a) was downregulated, which correlated with the decrease in the number of total mitochondria, increase in the percentage of injured mitochondria, downregulation of respiratory chain complex 2 and 3 mRNA expression, and reduced maximal respiration. In addition, septic animals presented a three-fold increase in and expression; downregulated , , and expression; and upregulated expression, potentially due to elevated reactive oxygen species levels. The mitochondrial number and the percentage of injured mitochondrial were similar between sham and CLP+TH mice. Sepsis induced responses consistent with NTIS, resulted in mitochondrial damage and functional impairment, and modulated the expression of key antioxidant enzymes in the diaphragm. Thus, impaired diaphragm function during sepsis seems to involve altered local TH signaling, mitochondrial dysfunction, and oxidative stress defense.
脓毒症可引起非甲状腺疾病综合征（NTIS），导致甲状腺激素（TH）信号转导紊乱和甲状腺素（T4）水平降低。TH 通过对线粒体的影响，是肌肉功能的主要调节因子。本研究旨在评估脓毒症小鼠膈肌中 TH 信号转导、线粒体功能和抗氧化防御系统之间的关系。雄性 C57Bl/6 小鼠分为结扎和穿刺盲肠（CLP）组和假手术组。术后 24 小时，收集血浆、膈肌和肝脏。通过测量肝脏中 、 、 2 、 、 和 （编码 MCT10 和 8）的信使 RNA（mRNA）表达，分析 TH 代谢和反应。通过放射免疫分析测量 T4 血浆水平。通过电子显微镜和实时聚合酶链反应（qPCR）评估膈肌线粒体损伤，并通过氧合图评估功能。通过 qPCR 分析超氧化物歧化酶 1（SOD1）（）、线粒体超氧化物歧化酶（SOD2；）、细胞外超氧化物歧化酶（SOD3；）、谷胱甘肽过氧化物酶 1（）和过氧化氢酶（）的表达，检查膈肌抗氧化防御系统。术后用 T4 和三碘甲状腺原氨酸（T3）（CLP+TH）治疗小鼠，测试 TH 替代的效果。CLP 小鼠的总血浆 T4 浓度降低，肝中 下调， 上调。CLP 小鼠膈肌中 、 表达也下调，提示 TH 信号转导受损。 （编码 PGC1a）的表达下调，与总线粒体数量减少、损伤线粒体比例增加、呼吸链复合物 2 和 3 mRNA 表达降低以及最大呼吸减少相关。此外，脓毒症动物的 、 表达增加三倍；下调 、 、 和 表达；上调 表达，可能是由于活性氧水平升高。 sham 组和 CLP+TH 组的膈肌线粒体数量和损伤线粒体比例相似。脓毒症引起的反应与 NTIS 一致，导致线粒体损伤和功能障碍，并调节膈肌中关键抗氧化酶的表达。因此，脓毒症期间膈肌功能障碍似乎涉及局部 TH 信号转导改变、线粒体功能障碍和氧化应激防御。
