Inhibition of MCU forces extramitochondrial adaptations governing physiological and pathological stress responses in heart

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 112; no. 29; pp. 9129 - 9134
• Main Authors: Rasmussen, Tyler P, Yuejin Wu, Mei-ling A. Joiner, Olha M. Koval, Nicholas R. Wilson, Elizabeth D. Luczak, Qinchuan Wang, Biyi Chen, Zhan Gao, Zhiyong Zhu, Brett A. Wagner, Jamie Soto, Michael L. McCormick, William Kutschke, Robert M. Weiss, Liping Yu, Ryan L. Boudreau, E. Dale Abel, Fenghuang Zhan, Douglas R. Spitz, Garry R. Buettner, Long-Sheng Song, Leonid V. Zingman, Mark E. Anderson
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 21.07.2015; National Acad Sciences
• Subjects: Adaptation, Physiological; adenosine triphosphate; animal models; Animals; Biological Sciences; Blood Pressure; Calcium; Calcium - metabolism; Calcium Channels - metabolism; Cardiac Pacing, Artificial; Cellular Reprogramming; Cytoplasm; Cytosol - drug effects; Cytosol - metabolism; Dialysis; Diastole; Electrocardiography; energy; Genes, Dominant; genetically modified organisms; Glucose - metabolism; Heart - physiopathology; Heart Ventricles - pathology; Heart Ventricles - physiopathology; Homeostasis; Ischemia; ischemia-reperfusion injury; Mice; Mitochondria; Mitochondria, Heart - drug effects; Mitochondria, Heart - metabolism; mitochondrial calcium uniporter; Myocardial Reperfusion; myocardium; Myocardium - metabolism; Myocardium - pathology; oxidative phosphorylation; oxygen; Oxygen Consumption; Physiology; Prostaglandin-Endoperoxide Synthases - metabolism; Rodents; Sarcoplasmic Reticulum - metabolism; stress response; Stress, Physiological; supply balance; Transcription, Genetic; ischemia-reperfusion injury; mitochondrial calcium uniporter; myocardium
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1504705112

Myocardial mitochondrial Ca ²⁺ entry enables physiological stress responses but in excess promotes injury and death. However, tissue-specific in vivo systems for testing the role of mitochondrial Ca ²⁺ are lacking. We developed a mouse model with myocardial delimited transgenic expression of a dominant negative (DN) form of the mitochondrial Ca ²⁺ uniporter (MCU). DN-MCU mice lack MCU-mediated mitochondrial Ca ²⁺ entry in myocardium, but, surprisingly, isolated perfused hearts exhibited higher O ₂ consumption rates (OCR) and impaired pacing induced mechanical performance compared with wild-type (WT) littermate controls. In contrast, OCR in DN-MCU–permeabilized myocardial fibers or isolated mitochondria in low Ca ²⁺ were not increased compared with WT, suggesting that DN-MCU expression increased OCR by enhanced energetic demands related to extramitochondrial Ca ²⁺ homeostasis. Consistent with this, we found that DN-MCU ventricular cardiomyocytes exhibited elevated cytoplasmic [Ca ²⁺] that was partially reversed by ATP dialysis, suggesting that metabolic defects arising from loss of MCU function impaired physiological intracellular Ca ²⁺ homeostasis. Mitochondrial Ca ²⁺ overload is thought to dissipate the inner mitochondrial membrane potential (ΔΨm) and enhance formation of reactive oxygen species (ROS) as a consequence of ischemia-reperfusion injury. Our data show that DN-MCU hearts had preserved ΔΨm and reduced ROS during ischemia reperfusion but were not protected from myocardial death compared with WT. Taken together, our findings show that chronic myocardial MCU inhibition leads to previously unanticipated compensatory changes that affect cytoplasmic Ca ²⁺ homeostasis, reprogram transcription, increase OCR, reduce performance, and prevent anticipated therapeutic responses to ischemia-reperfusion injury. Mitochondrial Ca ²⁺ is a fundamental signal that allows for adaptation to physiological stress but a liability during ischemia-reperfusion injury in heart. On one hand, mitochondrial Ca ²⁺ entry coordinates energy supply and demand in myocardium by increasing the activity of matrix dehydrogenases to augment ATP production by oxidative phosphorylation. On the other hand, inhibiting mitochondrial Ca ²⁺ overload is promulgated as a therapeutic approach to preserve myocardial tissue following ischemia-reperfusion injury. We developed a new mouse model of myocardial-targeted transgenic dominant-negative mitochondrial Ca ²⁺ uniporter (MCU) expression to test consequences of chronic loss of MCU-mediated Ca ²⁺ entry in heart. Here we show that MCU inhibition has unanticipated consequences on extramitochondrial pathways affecting oxygen utilization, cytoplasmic Ca ²⁺ homeostasis, physiologic responses to stress, and pathologic responses to ischemia-reperfusion injury.