Edoardo Bertero1,2, Alexander Nickel1, Michael Kohlhaas1, Mathias Hohl3, Vasco Sequeira1, Carolin Brune3, Julia Schwemmlein1, Marco Abeßer4, Kai Schuh4, Ilona Kutschka1, Christopher Carlein5, Kai Münker1,3, Sarah Atighetchi1,3, Andreas Müller6, Andrey Kazakov3, Reinhard Kappl5, Karina von der Malsburg7, Martin van der Laan7, Anna-Florentine Schiuma1, Michael Böhm3, Ulrich Laufs8, Markus Hoth5, Peter Rehling9,10,11, Michaela Kuhn4, Jan Dudek1,9, Alexander von der Malsburg7, Leticia Prates Roma5, Christoph Maack1,3,12. 1. Department of Translational Research, Comprehensive Heart Failure Center, University Clinic, Würzburg, Germany (E.B., A.N., M. Kohlhaas, V.S., J.S., I.K., K.M., S.A., A.-F.S., J.D., C.M.). 2. Now with Department of Internal Medicine and Specialties (Di.M.I.), University of Genoa, Italy (E.B.). 3. Clinic for Internal Medicine III (M. Hohl, C.B., K.M., S.A., A.K., M.B., C.M.), Saarland University Clinic, Homburg/Saar, Germany. 4. Institute of Physiology, University of Würzburg, Germany (M.A., K.S., M. Kuhn). 5. Department for Biophysics, ZHMB, CIPMM (C.C., R.K., M. Hoth, L.P.R.), Saarland University, Homburg/Saar, Germany. 6. Clinic for Radiology (A.M.), Saarland University Clinic, Homburg/Saar, Germany. 7. Medical Biochemistry and Molecular Biology, Center for Molecular Signaling, PZMS, Faculty of Medicine (K.v.d.M., M.v.d.L., A.v.d.M.), Saarland University, Homburg/Saar, Germany. 8. Now with Klinik und Poliklinik für Kardiologie, Universitätsklinikum Leipzig, Germany (U.L.). 9. Department of Cellular Biochemistry, Georg-August University, Göttingen, Germany (P.R., J.D.). 10. Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC), University of Göttingen, Germany (P.R.). 11. Max-Planck Institute for Biophysical Chemistry, Göttingen, Germany (P.R.). 12. Department for Internal Medicine 1, University Clinic Würzburg, Germany (C.M.).
Abstract
BACKGROUND: Barth syndrome (BTHS) is caused by mutations of the gene encoding tafazzin, which catalyzes maturation of mitochondrial cardiolipin and often manifests with systolic dysfunction during early infancy. Beyond the first months of life, BTHS cardiomyopathy typically transitions to a phenotype of diastolic dysfunction with preserved ejection fraction, blunted contractile reserve during exercise, and arrhythmic vulnerability. Previous studies traced BTHS cardiomyopathy to mitochondrial formation of reactive oxygen species (ROS). Because mitochondrial function and ROS formation are regulated by excitation-contraction coupling, integrated analysis of mechano-energetic coupling is required to delineate the pathomechanisms of BTHS cardiomyopathy. METHODS: We analyzed cardiac function and structure in a mouse model with global knockdown of tafazzin (Taz-KD) compared with wild-type littermates. Respiratory chain assembly and function, ROS emission, and Ca2+ uptake were determined in isolated mitochondria. Excitation-contraction coupling was integrated with mitochondrial redox state, ROS, and Ca2+ uptake in isolated, unloaded or preloaded cardiac myocytes, and cardiac hemodynamics analyzed in vivo. RESULTS: Taz-KD mice develop heart failure with preserved ejection fraction (>50%) and age-dependent progression of diastolic dysfunction in the absence of fibrosis. Increased myofilament Ca2+ affinity and slowed cross-bridge cycling caused diastolic dysfunction, in part, compensated by accelerated diastolic Ca2+ decay through preactivated sarcoplasmic reticulum Ca2+-ATPase. Taz deficiency provoked heart-specific loss of mitochondrial Ca2+ uniporter protein that prevented Ca2+-induced activation of the Krebs cycle during β-adrenergic stimulation, oxidizing pyridine nucleotides and triggering arrhythmias in cardiac myocytes. In vivo, Taz-KD mice displayed prolonged QRS duration as a substrate for arrhythmias, and a lack of inotropic response to β-adrenergic stimulation. Cellular arrhythmias and QRS prolongation, but not the defective inotropic reserve, were restored by inhibiting Ca2+ export through the mitochondrial Na+/Ca2+ exchanger. All alterations occurred in the absence of excess mitochondrial ROS in vitro or in vivo. CONCLUSIONS: Downregulation of mitochondrial Ca2+ uniporter, increased myofilament Ca2+ affinity, and preactivated sarcoplasmic reticulum Ca2+-ATPase provoke mechano-energetic uncoupling that explains diastolic dysfunction and the lack of inotropic reserve in BTHS cardiomyopathy. Furthermore, defective mitochondrial Ca2+ uptake provides a trigger and a substrate for ventricular arrhythmias. These insights can guide the ongoing search for a cure of this orphaned disease.
BACKGROUND: Barth syndrome (BTHS) is caused by mutations of the gene encoding tafazzin, which catalyzes maturation of mitochondrial cardiolipin and often manifests with systolic dysfunction during early infancy. Beyond the first months of life, BTHS cardiomyopathy typically transitions to a phenotype of diastolic dysfunction with preserved ejection fraction, blunted contractile reserve during exercise, and arrhythmic vulnerability. Previous studies traced BTHS cardiomyopathy to mitochondrial formation of reactive oxygen species (ROS). Because mitochondrial function and ROS formation are regulated by excitation-contraction coupling, integrated analysis of mechano-energetic coupling is required to delineate the pathomechanisms of BTHS cardiomyopathy. METHODS: We analyzed cardiac function and structure in a mouse model with global knockdown of tafazzin (Taz-KD) compared with wild-type littermates. Respiratory chain assembly and function, ROS emission, and Ca2+ uptake were determined in isolated mitochondria. Excitation-contraction coupling was integrated with mitochondrial redox state, ROS, and Ca2+ uptake in isolated, unloaded or preloaded cardiac myocytes, and cardiac hemodynamics analyzed in vivo. RESULTS: Taz-KD mice develop heart failure with preserved ejection fraction (>50%) and age-dependent progression of diastolic dysfunction in the absence of fibrosis. Increased myofilament Ca2+ affinity and slowed cross-bridge cycling caused diastolic dysfunction, in part, compensated by accelerated diastolic Ca2+ decay through preactivated sarcoplasmic reticulum Ca2+-ATPase. Taz deficiency provoked heart-specific loss of mitochondrial Ca2+ uniporter protein that prevented Ca2+-induced activation of the Krebs cycle during β-adrenergic stimulation, oxidizing pyridine nucleotides and triggering arrhythmias in cardiac myocytes. In vivo, Taz-KD mice displayed prolonged QRS duration as a substrate for arrhythmias, and a lack of inotropic response to β-adrenergic stimulation. Cellular arrhythmias and QRS prolongation, but not the defective inotropic reserve, were restored by inhibiting Ca2+ export through the mitochondrial Na+/Ca2+ exchanger. All alterations occurred in the absence of excess mitochondrial ROS in vitro or in vivo. CONCLUSIONS: Downregulation of mitochondrial Ca2+ uniporter, increased myofilament Ca2+ affinity, and preactivated sarcoplasmic reticulum Ca2+-ATPase provoke mechano-energetic uncoupling that explains diastolic dysfunction and the lack of inotropic reserve in BTHS cardiomyopathy. Furthermore, defective mitochondrial Ca2+ uptake provides a trigger and a substrate for ventricular arrhythmias. These insights can guide the ongoing search for a cure of this orphaned disease.
Authors: Mohit M Hulsurkar; Satadru K Lahiri; Jason Karch; Meng C Wang; Xander H T Wehrens Journal: Expert Opin Ther Targets Date: 2022-04-25 Impact factor: 6.797
Authors: Kathrin Renner; Alexander G Nickel; Michael G Paulus; Christoph Brochhausen; Katharina Limm; Elmar Zügner; Maria J Baier; Steffen Pabel; Stefan Wallner; Christoph Birner; Andreas Luchner; Christoph Magnes; Peter J Oefner; Klaus J Stark; Stefan Wagner; Christoph Maack; Lars S Maier; Katrin Streckfuss-Bömeke; Samuel Sossalla; Alexander Dietl Journal: Basic Res Cardiol Date: 2022-09-06 Impact factor: 12.416