Cardiac dysfunction in heart failure (HF) and diabetic cardiomyopathy (DCM) is associated with aberrant intracellular Ca²⁺ handling and impaired mitochondrial function accompanied with reduced mito-[Ca²⁺]. Pharmacological or genetic facilitation of mito-Ca²⁺ uptake was shown to restore Ca²⁺ transient amplitude in DCM and HF, improving contractility. However, recent reports suggest that pharmacological enhancement of mito-Ca²⁺ uptake can exacerbate ryanodine receptor-mediated spontaneous sarcoplasmic reticulum (SR) Ca²⁺ release in ventricular myocytes (VMs) from diseased animals, increasing propensity to stress-induced ventricular tachyarrhythmia. To test whether chronic recovery of mito-[Ca²⁺] restores systolic Ca²⁺ release without adverse effects in diastole, we overexpressed mitochondrial Ca²⁺ uniporter (MCU) in VMs from male rat hearts with hypertrophy induced by thoracic aortic banding (TAB). Measurement of mito-[Ca²⁺] using genetic probe mtRCamp1h revealed that mito-[Ca²⁺] in TAB VMs paced at 2 Hz under β-adrenergic stimulation is lower compared to Shams. Adenoviral 2.5-fold MCU overexpression in TAB VMs fully restored mito-[Ca²⁺]. However, it failed to improve cytosolic Ca²⁺ handling and reduce pro-arrhythmic spontaneous Ca²⁺ waves. Furthermore, mitochondrial-targeted genetic probes MLS-HyPer7 and OMM-HyPer revealed a significant increase in emission of reactive oxygen species (ROS) in TAB VMs with 2.5-fold MCU overexpression. Conversely, 1.5-fold MCU overexpression in TABs, that led to partial restoration of mito-[Ca²⁺], reduced mito-ROS and spontaneous Ca²⁺ waves. Our findings emphasize the key role of elevated mito-ROS in disease-related pro-arrhythmic Ca²⁺ mishandling. These data establish non-linear mito-[Ca²⁺]/mito-ROS relationship, whereby partial restoration of mito-[Ca²⁺] in diseased VMs is protective, while further enhancement of MCU-mediated Ca²⁺-uptake exacerbates damaging mito-ROS emission.

中文翻译：

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MCU 过表达对肥大大鼠心肌细胞的 mito-ROS 和自发 Ca2+ 释放引起不同的剂量依赖性影响

心力衰竭 (HF) 和糖尿病性心肌病 (DCM) 中的心脏功能障碍与细胞内 Ca ²⁺处理异常和线粒体功能受损以及 mito-[Ca ²⁺ ]减少有关。药理学或遗传促进 mito-Ca ²⁺摄取显示恢复DCM 和 HF 中的Ca ²⁺瞬时振幅，改善收缩性。然而，最近的报告表明，mito-Ca ²⁺摄取的药理学增强会加剧兰尼碱受体介导的自发性肌浆网 (SR) Ca ²⁺从患病动物的心室肌细胞 (VMs) 中释放，增加应激引起的室性快速性心律失常的倾向。为了测试 mito-[Ca ²⁺ ] 的慢性恢复是否能恢复收缩期 Ca ²⁺释放而不会对舒张期产生不利影响，我们在来自胸主动脉束带 (TAB) 诱导肥大的雄性大鼠心脏 VM 中过表达线粒体 Ca ²⁺单向转运蛋白）。mito-的测量的[Ca ²⁺ ]使用基因探针mtRCamp1h揭示mito-的[Ca ²⁺ ]在TAB的VM在下β肾上腺素能刺激2赫兹节奏被下相比姆斯。TAB VM 中腺病毒 2.5 倍 MCU 过表达完全恢复了 mito-[Ca ²⁺ ]。然而，它未能提高细胞溶质 Ca ²⁺处理和减少促心律失常的自发 Ca ²⁺波。此外，线粒体靶向遗传探针 MLS-HyPer7 和 OMM-HyPer 显示 TAB VM 中活性氧 (ROS) 的排放显着增加，MCU 过表达为 2.5 倍。相反，TAB 中 1.5 倍的 MCU 过度表达导致 mito-[Ca ²⁺ ] 的部分恢复，减少了 mito-ROS 和自发的 Ca ²⁺波。我们的研究结果强调了升高的 mito-ROS 在与疾病相关的促心律失常 Ca ²⁺错误处理中的关键作用。这些数据建立了非线性 mito-[Ca ²⁺ ]/mito-ROS 关系，从而部分恢复 mito-[Ca ²⁺] 在患病 VM 中是保护性的，而 MCU 介导的 Ca ²⁺摄取的进一步增强会加剧破坏性的 mito-ROS 排放。