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Background: Sepsis-induced cardiomyopathy contributes to the high mortality of septic shock in critically ill patients. Since the underlying mechanisms are incompletely understood, we hypothesized that sepsis-induced impairment of sirtuin 3 (SIRT3) activity contributes to the development of septic cardiomyopathy., Methods and Results: Treatment of mice with lipopolysaccharide (LPS) for 6 h resulted in myocardial NAD + depletion and increased mitochondrial protein acetylation, indicating impaired myocardial SIRT3 activity due to NAD + depletion. LPS treatment also resulted in impaired cardiac output in isolated working hearts, indicating endotoxemia-induced cardiomyopathy. Maintaining normal myocardial NAD + levels in LPS-treated mice by Poly(ADP-ribose)polymerase 1 (PARP1) deletion prevented cardiac dysfunction, whereas additional SIRT3 deficiency blunted this beneficial effect, indicating that impaired SIRT3 activity contributes to cardiac dysfunction in endotoxemia. Measurements of mitochondrial ATP synthesis suggest that LPS-induced contractile dysfunction may result from cardiac energy depletion due to impaired SIRT3 activity. Pharmacological inhibition of mitochondrial calpains using MDL28170 normalized LPS-induced cleavage of the ATP5A1 subunit of ATP synthase and normalized contractile dysfunction, suggesting that cardiac energy depletion may result from calpain-mediated cleavage of ATP5A1. These beneficial effects were completely blunted by SIRT3 deficiency. Finally, a gene set enrichment analysis of hearts of patients with septic, ischemic or dilated cardiomyopathy revealed a sepsis-specific suppression of SIRT3 deacetylation targets, including ATP5A1, indicating a functional relevance of SIRT3-dependent pathways in human sepsis., Conclusions: Impaired SIRT3 activity may mediate cardiac dysfunction in endotoxemia by facilitating calpain-mediated disruption of ATP synthesis, suggesting SIRT3 activation as a potential therapeutic strategy to treat septic cardiomyopathy., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Lack of the mitochondrial deacetylase sirtuin 3 (SIRT3) impairs mitochondrial function and increases the susceptibility to induction of the mitochondrial permeability transition pore. Because these alterations contribute to myocardial ischemia-reperfusion (IR) injury, we hypothesized that SIRT3 deficiency may increase cardiac injury following myocardial IR. Hearts of 10-week-old mice were perfused in the isolated working mode and subjected to 17.5 min of global no-flow ischemia, followed by 30 min of reperfusion. Measurements before ischemia revealed a decrease in cardiac power (-20%) and rate pressure product (-15%) in SIRT3(-/-) mice. Mitochondrial state 3 respiration (-15%), ATP synthesis (-39%), and ATP/O ratios (-29%) were decreased in hearts of SIRT3(-/-) mice. However, percent recovery of cardiac power (WT 94% ± 9%; SIRT3(-/-) 89% ± 9%) and rate pressure product (WT 89% ± 16%; SIRT3(-/-) 96% ± 3%) following IR was similar in both groups. Myocardial infarct size was not increased in SIRT3(-/-) mice following permanent ligation of the left anterior descending coronary artery (LAD). Left ventricular pressure and dP/dtmax, and mitochondrial respiration and ATP synthesis were not different between groups following LAD ligation. Thus, despite pre-existing defects in cardiac function and mitochondrial respiratory capacity in SIRT3(-/-) mice, SIRT3 deficiency does not additionally impair cardiac function following IR or following myocardial infarction.

Sirtuin 3 (SIRT3) is a mitochondrial NAD(+)-dependent deacetylase that regulates energy metabolic enzymes by reversible protein lysine acetylation in various extracardiac tissues. The role of SIRT3 in myocardial energetics and in the development of mitochondrial dysfunction in cardiac pathologies, such as the failing heart, remains to be elucidated. To investigate the role of SIRT3 in the regulation of myocardial energetics and function SIRT3(-/-) mice developed progressive age-related deterioration of cardiac function, as evidenced by a decrease in ejection fraction and an increase in enddiastolic volume at 24 but not 8 weeks of age using echocardiography. Four weeks following transverse aortic constriction, ejection fraction was further decreased in SIRT3(-/-) mice compared to WT mice, accompanied by a greater degree of cardiac hypertrophy and fibrosis. In isolated working hearts, a decrease in cardiac function in SIRT3(-/-) mice was accompanied by a decrease in palmitate oxidation, glucose oxidation, and oxygen consumption, whereas rates of glycolysis were increased. Respiratory capacity and ATP synthesis were decreased in cardiac mitochondria of SIRT3(-/-) mice. HPLC measurements revealed a decrease of the myocardial ATP/AMP ratio and of myocardial energy charge. Using LC-MS/MS, we identified increased acetylation of 84 mitochondrial proteins, including 6 enzymes of fatty acid import and oxidation, 50 subunits of the electron transport chain, and 3 enzymes of the tricarboxylic acid cycle. Lack of SIRT3 impairs mitochondrial and contractile function in the heart, likely due to increased acetylation of various energy metabolic proteins and subsequent myocardial energy depletion.