Mitofusin 2 is essential for IP3-mediated SR/Mitochondria metabolic feedback in ventricular myocytes

Aim: Endothelin-1 (ET-1) and angiotensin II (Ang II) are multifunctional peptide hormones that regulate the function of the cardiovascular and renal systems. Both hormones increase the intracellular production of inositol-1,4,5-trisphosphate (IP$_3$) by activating their membrane-bound receptors. We have previously demonstrated that IP$_3$-mediated sarcoplasmic reticulum (SR) Ca$^{2+}$ release results in mitochondrial Ca$^{2+}$ uptake and activation of ATP production. In this study, we tested the hypothesis that intact SR/mitochondria microdomains are required for metabolic IP$_3$-mediated SR/mitochondrial feedback in ventricular myocytes. Methods: As a model for disrupted mitochondrial/SR microdomains, cardio-specific tamoxifen-inducible mitofusin 2 (Mfn2) knock out (KO) mice were used. Mitochondrial Ca$^{2+}$ uptake, membrane potential, redox state, and ATP generation were monitored in freshly isolated ventricular myocytes from Mfn2 KO mice and their control wild-type (WT) littermates. Results: Stimulation of ET-1 receptors in healthy control myocytes increases mitochondrial Ca$^{2+}$ uptake, maintains mitochondrial membrane potential and redox balance leading to the enhanced ATP generation. Mitochondrial Ca$^{2+}$ uptake upon ET-1 stimulation was significantly higher in interfibrillar (IFM) and perinuclear (PNM) mitochondria compared to subsarcolemmal mitochondria (SSM) in WT myocytes. Mfn2 KO completely abolished mitochondrial Ca$^{2+}$ uptake in IFM and PNM mitochondria but not in SSM. However, mitochondrial Ca2+ uptake induced by beta-adrenergic receptors activation with isoproterenol (ISO) was highest in SSM, intermediate in IFM, and smallest in PNM regions. Furthermore, Mfn2 KO did not affect ISO-induced mitochondrial Ca$^{2+}$ uptake in SSM and IFM mitochondria; however, enhanced mitochondrial Ca$^{2+}$ uptake in PNM. In contrast to ET-1, ISO induced a decrease in ATP levels in WT myocytes. Mfn2 KO abolished ATP generation upon ET-1 stimulation but increased ATP levels upon ISO application with highest levels observed in PNM regions. Conclusion: When the physical link between SR and mitochondria by Mfn2 was disrupted, the SR/mitochondrial metabolic feedback mechanism was impaired resulting in the inability of the IP$_3$-mediated SR Ca$^{2+}$ release to induce ATP production in ventricular myocytes from Mfn2 KO mice. Furthermore, we revealed the difference in Mfn2-mediated SR-mitochondrial communication depending on mitochondrial location and type of communication (IP$_3$R-mRyR1 vs. ryanodine receptor type 2-mitochondrial calcium uniporter)

Mitofusin 2 is essential for IP3-mediated SR/mitochondria metabolic feedback in ventricular myocytes

Aim: Endothelin-1 (ET-1) and angiotensin II (Ang II) are multifunctional peptide hormones that regulate the function of the cardiovascular and renal systems. Both hormones increase the intracellular production of inositol-1,4,5-trisphosphate (IP$_3$) by activating their membrane-bound receptors. We have previously demonstrated that IP$_3$-mediated sarcoplasmic reticulum (SR) Ca$^{2+}$ release results in mitochondrial Ca$^{2+}$ uptake and activation of ATP production. In this study, we tested the hypothesis that intact SR/mitochondria microdomains are required for metabolic IP$_3$-mediated SR/mitochondrial feedback in ventricular myocytes. Methods: As a model for disrupted mitochondrial/SR microdomains, cardio-specific tamoxifen-inducible mitofusin 2 (Mfn2) knock out (KO) mice were used. Mitochondrial Ca$^{2+}$ uptake, membrane potential, redox state, and ATP generation were monitored in freshly isolated ventricular myocytes from Mfn2 KO mice and their control wild-type (WT) littermates. Results: Stimulation of ET-1 receptors in healthy control myocytes increases mitochondrial Ca$^{2+}$ uptake, maintains mitochondrial membrane potential and redox balance leading to the enhanced ATP generation. Mitochondrial Ca$^{2+}$ uptake upon ET-1 stimulation was significantly higher in interfibrillar (IFM) and perinuclear (PNM) mitochondria compared to subsarcolemmal mitochondria (SSM) in WT myocytes. Mfn2 KO completely abolished mitochondrial Ca$^{2+}$ uptake in IFM and PNM mitochondria but not in SSM. However, mitochondrial Ca2+ uptake induced by beta-adrenergic receptors activation with isoproterenol (ISO) was highest in SSM, intermediate in IFM, and smallest in PNM regions. Furthermore, Mfn2 KO did not affect ISO-induced mitochondrial Ca$^{2+}$ uptake in SSM and IFM mitochondria; however, enhanced mitochondrial Ca$^{2+}$ uptake in PNM. In contrast to ET-1, ISO induced a decrease in ATP levels in WT myocytes. Mfn2 KO abolished ATP generation upon ET-1 stimulation but increased ATP levels upon ISO application with highest levels observed in PNM regions. Conclusion: When the physical link between SR and mitochondria by Mfn2 was disrupted, the SR/mitochondrial metabolic feedback mechanism was impaired resulting in the inability of the IP$_3$-mediated SR Ca$^{2+}$ release to induce ATP production in ventricular myocytes from Mfn2 KO mice. Furthermore, we revealed the difference in Mfn2-mediated SR-mitochondrial communication depending on mitochondrial location and type of communication (IP$_3$R-mRyR1 vs. ryanodine receptor type 2-mitochondrial calcium uniporter)

Effect of mitofusin 2 deficiency on the IP3_3-induced mitochondrial calcium regulation in cardiomyocytes

Das Herz ist physiologisch auf einen fein regulierten und ausgeglichenen bioenergetischen Energiehaushalt angewiesen, um auf akute Belastungssituationen adäquat reagieren zu können und oxidativen Stress zu vermeiden. Ca2+ reguliert zentral sowohl die zyklischen Kontraktions-/Relaxationsprozesse (ECC) als auch unmittelbar den mitochondrialen Metabolismus. Der ECC liegt in den Kardiomyozyten die Ca2+- Freisetzung durch die RyR2 zu Grunde; die IP3 Rezeptoren des sarkoplasmatischen Retikulums (SR) führen davon unabhängig zu einer Ca2+ Freisetzung aus dem SR. Diese IP3R vermittelten Signale werden in den räumlich nahe gelegenen Mitochondrien zum Teil über den mRyR1 in die mitochondriale Matrix aufgenommen und stimulieren dort langfristig die oxidative Phosphorylierung und den Erhalt der antioxidativen Kapazität. Die enge räumliche Nähe zwischen SR und Mitochondrien wird durch Strukturproteine wie Mitofusin 2 (Mfn2) ergänzt, die das SR mit der äußeren Mitochondrienmembran koppeln und so die Ca2+-Interaktion beeinflussen. Ziel der Arbeit war, den Effekt von Mfn2 Defizienz auf die IP3 induzierte mitochondriale Ca2+-Regulation in Kardiomyozyten zu evaluieren. Dazu erfolgten Fluoreszenzfärbungen an adulten isolierten Ventrikelkardiomyozyten kardiospezifischer Mfn2 Knock-Out (KO) Mäusen bzw. deren wildtypischen Geschwistertieren (WT). Erhobene Parameter umfassten das mitochondriale Ca2+, das mitochondriale Membranpotenzial, die mitochondriale Superoxidbildung und mitochondriale ATP-Gehalt. Die Ergebnisse bestätigten eine Signalachse, bei der die Stimulation von isolierten murinen Kardiomyozyten mit dem IP3 Agonisten ET-1 zu einer mitochondrialen Ca2+ Aufnahme führte, dem Erhalt des mitochondrialen Membranpotenzials diente und der ATP Gehalt stiegt. Bei induzierter kardiospezifischer Ablation von Mfn2 geht diese SR-mitochondriale Interaktion verloren, und es entstand ein energetisches Defizit sowie eine verminderte Superoxidbildung. Bei beta-adrenerger Stimulation mit Isoproterenol (ISO) resultierte in WT zwar eine mitochondriale Ca2+-Aufnahme, allerdings ein Abfall des ATP-Gehaltes. In den Mfn2 defizienten Kardiomyozyten zeigte sich eine Steigerung des ATP-Gehaltes auch auf beta-adrenerge Stimulation, die einen energetischen Kompensationsmechanismus in den Mfn2 KO Tieren vermuten lässt. Dies identifiziert Mfn2 als kritische Strukturkomponente für die basale bioenergetische Adaptation der durch IP3R-mRyR1 vermittelten Signalachse unter physiologischen Bedingungen.Under physiological conditions the heart needs a finely tuned bioenergetic adaptation system to adequately match sudden changes in the workload and to avoid oxidative stress. Ca2+ regulates the excitation-contraction-coupling (ECC) as well as the mitochondrial metabolism. The ECC is based on the release of Ca2+ via the RyR2 while the IP3 receptor (IP3R) releases Ca2+ independently from the sarcoplasmatic reticulum (SR). The signals from the latter are taken up by the surrounding mitochondria via the mRyR1 channel to stimulate both the basal oxidative phosphorylation and the antioxidative capacity. The close functional relationship between mitochondria and SR is affected by membrane-coupling proteins like mitofusin 2 (Mfn2) that may influence the Ca2+ transmission. This work aimed at evaluating the effect of Mfn2 deficiency on the IP3-induced mitochondrial calcium regulation in cardiomyocytes. Mitochondrial Ca2+ uptake, membrane potential, redox state and ATP generation were monitored in isolated ventricular cardiomyocytes of cardio-specific mitofusin 2 Knock-out (KO) mice and their wildtype littermates (WT) via fluorescent staining using laser scanning confocal microscopy. The results show that stimulation with the IP3 agonist ET-1 led to mitochondrial calcium uptake, ATP generation and maintained mitochondrial membrane potential. The cardio-specific loss of the tethering protein Mfn2 resulted in an energetic deficit and decreased levels of superoxide. Beta adrenergic receptor activation with isoproterenol (ISO) in WT resulted in a mitochondrial calcium uptake but decreased ATP content, while leading in Mfn2 KO cardiomyocyte to increased levels of ATP, pointing probably towards an energetic compensatory mechanism. Taken together these results propose Mfn2 as a critical structural component that affects under physiological conditions the privileged SR-mitochondrial metabolic feedback mechanism via IP3R and mRYR1 to maintain normal cardiac function and bioenergetics

Psychiatric symptoms and mortality in older adults with major psychiatric disorders: results from a multicenter study

International audienc

Effects of depression and cognitive impairment on quality of life in older adults with schizophrenia spectrum disorder: Results from a multicenter study

International audienc

Association between antithrombotic treatment and outcomes at 1-year follow-up in patients with atrial fibrillation: the EORP-AF General Long-Term Registry

International audienceAims In recent years, stroke prevention in patients with atrial fibrillation (AF) has radically changed, with increasing use of non-vitamin K antagonist oral anticoagulants (NOACs). Contemporary European data on AF thromboprophylaxis are needed. Methods and results We report 1-year follow-up data from the EURObservational Research Programme in Atrial Fibrillation (EORP-AF) General Long-Term Registry. Outcomes were assessed according to antithrombotic therapy. At 1-year follow-up, 9663 (88.0%) patients had available data for analysis: 586 (6.1%) were not treated with any antithrombotic; 681 (7.0%) with antiplatelets only; 4066 (42.1%) with vitamin K antagonist (VKA) only; 3167 (32.8%) with NOACs only; and 1163 (12.0%) with antiplatelet and oral anticoagulant. At 1-year follow-up, there was a low rate of stroke (0.7%) and any thromboembolic event (TE) (1.2%), while haemorrhagic events occurred in 222 patients (2.3%). Cardiovascular (CV) death and all-cause death occurred in 3.9% and 5.2% of patients, respectively. Cumulative survival for all the three main outcomes considered was highest amongst patients treated only with NOACs (P < 0.0001). Multivariable-adjusted Cox regression analysis found that VKA or NOACs use was independently associated with a lower risk for any TE/acute coronary syndrome/CV death, while all treatments were independently associated with a lower risk for CV death and all-cause death. Conclusion The 1-year follow-up of EORP-AF General Long-Term Registry reported a low occurrence of thromboembolic and haemorrhagic events, although mortality was high. Both VKA and NOACs were associated with a lower risk of all main adverse outcomes. All treatments were associated with a lower risk for CV death and all-cause death