Pre-clinical animal studies have shown that triiodothyronine (T3) replacement therapy improves cardiac contractile function after myocardial infarction (MI). We hypothesized that T3 treatment could prevent adverse post-infarction cardiomyocyte remodeling by maintaining transverse-tubule (TT) structures, thus improving calcium dynamics and contractility.MethodsMyocardial infarction (MI) or sham surgeries were performed on female Sprague-Dawley rats (aged 12 wks), followed by treatment with T3 (5μg/kg/d) or vehicle in drinking water for 16 wks (n = 10–11/group). After in vivo echocardiographic and hemodynamic analyses, left ventricular myocytes were isolated by collagenase digestion and simultaneous calcium and contractile transients in single cardiomyocytes were recorded using IonOptix imaging. Live cardiomyocytes were stained with AlexaFluor-488 conjugated wheat germ agglutinin (WGA-488) or di-8-ANEPPS, and multiple z-stack images per cell were captured by confocal microscopy for analysis of TT organization. RTqPCR and immunoblot approaches determined expression of TT proteins.ResultsEchocardiography and in vivo hemodynamic measurements showed significant improvements in systolic and diastolic function in T3- vs vehicle-treated MI rats. Isolated cardiomyocyte analysis showed significant dysfunction in measurements of myocyte relengthening in MI hearts, and improvements with T3 treatment: max relengthening velocity (Vmax, um/s), 2.984 ± 1.410 vs 1.593 ± 0.325, p < 0.05 and time to Vmax (sec), 0.233 ± 0.037 vs 0.314 ± 0.019, p < 0.001; MI + T3 vs MI + Veh, respectively. Time to peak contraction was shortened by T3 treatment (0.161 ± 0.021 vs 0.197 ± 0.011 s., p < 0.01; MI + T3 vs MI + Veh, respectively). Analysis of TT periodicity of WGA- or ANEPPS-stained cardiomyocytes indicated significant TT disorganization in MI myocytes and improvement with T3 treatment (transverse-oriented tubules (TE%): 9.07 ± 0.39 sham, 6.94 ± 0.67 MI + Veh and 8.99 ± 0.38 MI + T3; sham vs MI + Veh, p < 0.001; MI + Veh vs MI + T3, p < 0.01). Quantitative RT-PCR showed that reduced expression of BIN1 (Bridging integrator-1), Jph2 (junctophilin-2), RyR2 (ryanodine receptor) and Cav1.2 (L-type calcium channel) in the failing myocardium were increased by T3 and immunoblot analysis further supporting a potential T3 effect on the TT-associated proteins, BIN1 and Jph2.In conclusion, low dose T3 treatment initiated immediately after myocardial infarction attenuated adverse TT remodeling, improved calcium dynamics and contractility, thus supporting the potential therapeutic utility of T3 treatment in heart failure.

中文翻译：

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低剂量三碘甲腺原氨酸治疗可减轻心力衰竭大鼠模型中的不良横小管重塑

临床前动物研究表明，三碘甲腺原氨酸 (T3) 替代疗法可改善心肌梗塞 (MI) 后的心脏收缩功能。我们假设 T3 治疗可以通过维持横小管 (TT) 结构来防止不良的梗塞后心肌细胞重塑，从而改善钙动力学和收缩力。方法对雌性 Sprague-Dawley 大鼠（12 周龄）进行心肌梗塞（MI）或假手术)，然后在饮用水中用 T3 (5μg/kg/d) 或载体治疗 16 周（n = 10-11/组）。在体内超声心动图和血流动力学分析后，通过胶原酶消化分离左心室肌细胞，并使用 IonOptix 成像记录单个心肌细胞中同时发生的钙和收缩瞬变。活心肌细胞用 AlexaFluor-488 共轭小麦胚芽凝集素 (WGA-488) 或 di-8-ANEPPS 染色，通过共聚焦显微镜捕获每个细胞的多个 z-stack 图像以分析 TT 组织。RTqPCR 和免疫印迹方法确定了 TT 蛋白的表达。结果超声心动图和体内血液动力学测量显示 T3 与媒介物处理的 MI 大鼠的收缩和舒张功能显着改善。孤立的心肌细胞分析显示 MI 心脏中心肌细胞再延长的测量显着功能障碍，以及 T3 治疗的改善：最大再延长速度（Vmax，um/s），2.984 ± 1.410 与 1.593 ± 0.325，p < 0.05 和到达 Vmax 的时间（秒） , 0.233 ± 0.037 vs 0.314 ± 0.019, p < 0.001; 分别为 MI + T3 与 MI + Veh。T3 治疗缩短了达到收缩峰值的时间 (0. 161 ± 0.021 vs 0.197 ± 0.011 秒，p < 0.01；分别为 MI + T3 与 MI + Veh）。WGA 或 ANEPPS 染色的心肌细胞的 TT 周期性分析表明 MI 心肌细胞中显着的 TT 解体和 T3 治疗的改善（横向小管 (TE%)：9.07 ± 0.39 假手术，6.94 ± 0.67 MI + Veh 和 8.99 ± 0.38 MI + T3；假手术 vs MI + Veh，p < 0.001；MI + Veh vs MI + T3，p < 0.01)。定量 RT-PCR 显示，T3 和免疫印迹增加了衰竭心肌中 BIN1（桥接积分器-1）、Jph2（junctophilin-2）、RyR2（兰尼碱受体）和 Cav1.2（L 型钙通道）的表达降低分析进一步支持 T3 对 TT 相关蛋白 BIN1 和 Jph2 的潜在影响。 总之，心肌梗塞后立即开始的低剂量 T3 治疗减弱了不利的 TT 重塑，