Loss of sirtuin 4 confers cardioprotection by lowering succinate oxidation during ischemia-reperfusion

N. Byrne (Graz)¹, C. Koentges (Freiburg im Breisgau)², K. Pfeil (Graz)³, S. Sohn (Freiburg im Breisgau)⁴, A. Tarkhnishvili (Freiburg im Breisgau)⁴, L. Birkle (Freiburg im Breisgau)⁵, S. P. Birkle (Freiburg im Breisgau)⁶, I. Vosko (Graz)³, T. Rathner (Graz)⁷, J. Gollmer (Graz)³, S. Barnes (Birmingham)⁸, L. Wilson (Birmingham)⁹, M. M. Hoffmann (Freiburg)¹⁰, M. Wallner (Graz)¹¹, S. Ljubojevic-Holzer (Graz)¹¹, D. von Lewinski (Graz)¹², S. Sedej (Graz)¹³, A. Wende (Birmingham)¹⁴, A. Zirlik (Graz)¹¹, H. Bugger (Graz)^11
1Medical University of Graz Cardiology Graz, Österreich; ²Universitäts-Herzzentrum Freiburg - Bad Krozingen Institut für Humangenetik - Abteilung Kardiologie Freiburg im Breisgau, Deutschland; ³Medical University of Graz Kardiologie Graz, Österreich; ⁴Universitäts-Herzzentrum Freiburg - Bad Krozingen Klinik für Kardiologie und Angiologie Freiburg im Breisgau, Deutschland; ⁵Freiburg im Breisgau, Deutschland; ⁶Universitäts-Herzzentrum Freiburg - Bad Krozingen Institut für Humangenetik Freiburg im Breisgau, Deutschland; ⁷Graz, Österreich; ⁸Birmingham, Deutschland; ⁹Birmingham, USA; ¹⁰Universitätsklinikum Freiburg Institut für Klinische Chemie und Laboratoriumsmedizin Freiburg, Deutschland; ¹¹LKH-Univ. Klinikum Graz - Universitätsklinik für Innere Medizin Klinische Abteilung für Kardiologie Graz, Österreich; ¹²Medizinische Universität Graz Graz, Österreich; ¹³LKH-Univ. Klinikum Graz - Universitätsklinik für Innere Medizin Experimentelle Kardiologie Graz, Österreich; ¹⁴University of Alabama at Birmingham Department of Pathology Birmingham, USA

Myocardial ischemia-reperfusion (I/R) injury is determined by various detrimental mechanisms, including increased reactive oxygen species (ROS) generation, mitochondrial dysfunction and altered energy metabolism. The mitochondrial NAD⁺-dependent deacylase, sirtuin 4 (SIRT4), controls cellular energy substrate utilization and ROS homeostasis. Thus, we hypothesized that targeting SIRT4 may modulate the extent of I/R injury. Subjecting mice with cardiomyocyte-specific overexpression of Sirt4 (cSirt4-Tg) to transient ligation of the left anterior descending (LAD) coronary artery in vivo, or to I/R in the Langendorff model ex vivo did not differentially affect cardiac infarct size or recovery of contractile function following ischemia, respectively. In contrast, mice with global deletion of Sirt4 (Sirt4^-/-) displayed markedly reduced cardiac infarct size or improved recovery of contractile function following LAD ligation or ex vivo I/R, respectively. Cardioprotection in Sirt4^-/- mice was accompanied by higher gene expression of several antioxidant enzymes and the transcription factor Forkhead Box O1, indicating increased antioxidant capacity. In addition, metabolomics revealed less succinate accumulation in Sirt4^-/- mice during ischemia as the most significant contributor to cardioprotection. Importantly, inhibition of succinate dehydrogenase during I/R using dimethylmethoxymalonate blunted cardioprotection in Sirt4^-/- mice, suggesting that SIRT4 deficiency provides cardioprotection by limiting succinate accumulation and SDH-driven ROS production. Metabolite analysis demonstrated depletion of tricarboxylic acid cycle intermediates, accompanied by decreased levels of pyruvate and lactate, decreased glucose transporter 1 expression and increased pyruvate dehydrogenase kinase 4 expression. Thus, SIRT4 deficiency attenuates myocardial I/R injury by lowering succinate oxidation, likely by mitigating glucose utilization and subsequent succinate accumulation during ischemia.