Ahmed A Mohsin1, Jeremy Thompson2, Ying Hu2, John Hollander3, Edward J Lesnefsky4, Qun Chen5. 1. Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, VA, 23298, USA; Radiological Techniques Department, Health and Medical Technology College-Baghdad, Middle Technical University (MTU), Iraq. 2. Pauley Heart Center, Division of Cardiology, Department of Medicine, Virginia Commonwealth University, Richmond, VA, 23298, USA. 3. Division of Exercise Physiology, West Virginia University School of Medicine, Morgantown, WV, 25606, USA; Mitochondria, Metabolism & Bioenergetics Working Group, West Virginia University School of Medicine, Morgantown, WV, 25606, USA. 4. Pauley Heart Center, Division of Cardiology, Department of Medicine, Virginia Commonwealth University, Richmond, VA, 23298, USA; Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, VA, 23298, USA; Medical Service, McGuire Department of Veterans Affairs Medical Center, Richmond, VA, 23249, USA. 5. Pauley Heart Center, Division of Cardiology, Department of Medicine, Virginia Commonwealth University, Richmond, VA, 23298, USA. Electronic address: qun.chen@vcuhealth.org.
Abstract
BACKGROUND: ER (endoplasmic reticulum) stress leads to decreased complex I activity in cardiac mitochondria. The aim of the current study is to explore the potential mechanisms by which ER stress leads to the complex I defect. ER stress contributes to intracellular calcium overload and oxidative stress that are two key factors to induce mitochondrial dysfunction. Since oxidative stress is often accompanied by intracellular calcium overload during ER stress in vivo, the role of oxidative stress and calcium overload in mitochondrial dysfunction was studied using in vitro models. ER stress results in intracellular calcium overload that favors activation of calcium-dependent calpains. The contribution of mitochondrial calpain activation in ER stress-mediated complex I damage was studied. METHODS: Thapsigargin (THAP) was used to induce acute ER stress in H9c2 cells and C57BL/6 mice. Exogenous calcium (25 μM) and H2O2 (100 μM) were used to induce modest calcium overload and oxidative stress in isolated mitochondria. Calpain small subunit 1 (CAPNS1) is essential to maintain calpain 1 and calpain 2 (CPN1/2) activities. Deletion of CAPNS1 eliminates the activities of CPN1/2. Wild type and cardiac-specific CAPNS1 deletion mice were used to explore the role of CPN1/2 activation in calcium-induced mitochondrial damage. RESULTS: In isolated mitochondria, exogenous calcium but not H2O2 treatment led to decreased oxidative phosphorylation, supporting that calcium overload contributes a key role in the mitochondrial damage. THAP treatment of H9c2 cells decreased respiration selectively with complex I substrates. THAP treatment activated cytosolic and mitochondrial CPN1/2 in C57BL/6 mice and led to degradation of complex I subunits including NDUFS7. Calcium treatment decreased NDUFS7 content in wild type but not in CAPNS1 knockout mice. CONCLUSION: ER stress-mediated activation of mitochondria-localized CPN1/2 contributes to complex I damage by cleaving component subunits.
BACKGROUND: ER (endoplasmic reticulum) stress leads to decreased complex I activity in cardiac mitochondria. The aim of the current study is to explore the potential mechanisms by which ER stress leads to the complex I defect. ER stress contributes to intracellular calcium overload and oxidative stress that are two key factors to induce mitochondrial dysfunction. Since oxidative stress is often accompanied by intracellular calcium overload during ER stress in vivo, the role of oxidative stress and calcium overload in mitochondrial dysfunction was studied using in vitro models. ER stress results in intracellular calcium overload that favors activation of calcium-dependent calpains. The contribution of mitochondrial calpain activation in ER stress-mediated complex I damage was studied. METHODS: Thapsigargin (THAP) was used to induce acute ER stress in H9c2 cells and C57BL/6 mice. Exogenous calcium (25 μM) and H2O2 (100 μM) were used to induce modest calcium overload and oxidative stress in isolated mitochondria. Calpain small subunit 1 (CAPNS1) is essential to maintain calpain 1 and calpain 2 (CPN1/2) activities. Deletion of CAPNS1 eliminates the activities of CPN1/2. Wild type and cardiac-specific CAPNS1 deletion mice were used to explore the role of CPN1/2 activation in calcium-induced mitochondrial damage. RESULTS: In isolated mitochondria, exogenous calcium but not H2O2 treatment led to decreased oxidative phosphorylation, supporting that calcium overload contributes a key role in the mitochondrial damage. THAP treatment of H9c2 cells decreased respiration selectively with complex I substrates. THAP treatment activated cytosolic and mitochondrial CPN1/2 in C57BL/6 mice and led to degradation of complex I subunits including NDUFS7. Calcium treatment decreased NDUFS7 content in wild type but not in CAPNS1 knockout mice. CONCLUSION: ER stress-mediated activation of mitochondria-localized CPN1/2 contributes to complex I damage by cleaving component subunits.
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