Mitochondrial production of reactive oxygen species contributes to the β‐adrenergic stimulation of mouse cardiomycytes

Abstract

Non-technical summary When under stress, the heart beat becomes stronger, in part due to enhanced fluxes of Ca 2+ at the level of the cardiac cell. It is known that this effect is mediated by activation of β-receptors on the cardiac cell surface. This leads to modifications of intracellular proteins that in turn increase the flux of Ca 2+ within the cell. In this study we show that activation of β-receptors increases the production of reactive oxygen species (ROS) in the heart cell. These ROS generate enhanced Ca 2+ fluxes and more vigorous contraction. This finding shows a new cellular signalling route for regulating the power of the heart beat and might contribute to our understanding of diseases with defective cardiac contraction, such as heart failure.Abstract The sympathetic adrenergic system plays a central role in stress signalling and stress is often associated with increased production of reactive oxygen species (ROS). Furthermore, the sympathetic adrenergic system is intimately involved in the regulation of cardiomyocyte Ca 2+ handling and contractility. In this study we hypothesize that endogenously produced ROS contribute to the inotropic mechanism of β-adrenergic stimulation in mouse cardiomyocytes. Cytoplasmic Ca 2+ transients, cell shortening and ROS production were measured in freshly isolated cardiomyocytes using confocal microscopy and fluorescent indicators. As a marker of oxidative stress, malondialdehyde (MDA) modification of proteins was detected with Western blotting. Isoproterenol (ISO), a β-adrenergic agonist, increased mitochondrial ROS production in cardiomyocytes in a concentration-and cAMP-protein kinase A-dependent but Ca 2+ -independent manner. Hearts perfused with ISO showed a twofold increase in MDA protein adducts relative to control. ISO increased Ca 2+ transient amplitude, contraction and L-type Ca 2+ current densities (measured with whole-cell patch-clamp) in cardiomyocytes and these increases were diminished by application of the general antioxidant N -acetylcysteine (NAC) or the mitochondria-targeted antioxidant SS31. In conclusion, increased mitochondrial ROS production plays an integral role in the acute inotropic response of cardiomyocytes to β-adrenergic stimulation. On the other hand, chronically sustained adrenergic stress is associated with the development of heart failure and cardiac arrhythmias and prolonged increases in ROS may contribute to these defects.

Mitochondrial Redox Signaling: Interaction of Mitochondrial Reactive Oxygen Species with Other Sources of Oxidative Stress

“…In this respect, a recently published study showed that mtROS are necessary for the inotropic response in cardiomyocytes (10). Since catecholaminergic stimulation is mediated by sympathetic neurons and contributes to the progression of heart failure, an interesting study by Yin and coworkers identified mtROS as a key signaling event leading to AT-IIinduced neuronal activation (139).…”

Inhibition of NADPH oxidase 2 (NOX2) prevents sepsis-induced cardiomyopathy by improving calcium handling and mitochondrial function

“…One hospital-based study found that 43% of patients with bacteremia had positive serum troponin, indicating myocardial damage (2). Clinical studies have shown that if sepsis causes cardiac systolic dysfunction (also called sepsis-induced cardiomyopathy) the mortality rate increases up to 80%, compared with a 20% mortality rate for sepsis with normal systolic function (3,4). Sepsis can also cause abnormal cardiac electrophysiology, as indicated by the fact that patients with sepsis often have abnormal electrocardiograms and/or arrhythmias (5,6).…”

Reaktívoxigén-származékok szerepe a szívműködés szabályozásában

“…Mindez arra utal, hogy a ROS bazális szintje nem módosítja a myocardialis kontraktilitást, ugyanakkor a β 1 -AR-stimuláció során a megnövekedett endogén ROS-termelődés ellensúlyozni ké-pes az agonisták pozitív inotrop hatását. Azonban az in vivo [13] és az ex vivo adatokkal ellentétben [14], az N-acetil-cisztein gyengítette az izoproterenolra adott pozitív inotrop választ, illetve az intracelluláris Ca 2+ -tranziensek növekedését izolált szívizomsejteken [15].…”

“…A közelmúltban direkt módon igazolták a β-AR-stimuláció és a ROS-produkció közötti kapcsolatot: a β-AR-agonista izoproterenol dó-zisfüggő módon fokozta a mitokondriumok ROS-termelését izolált szívizomsejteken, amelynek célzott gátlá-sával csökkenthető volt a β-AR inotrop hatás [15]. A mitokondriumok mellett a O 2 −• fontos forrásai a NADPH-oxidázok [2].…”

“…Az endogén ROS-produkció mérsékelt, átmene-ti fokozódása befolyásolja az ET-1- [14,18,19] és a β-AR-stimuláció pozitív inotrop effektusát [13,14,15], az angiotenzin-II [29], a leptin [30] és a TGF-β 1 negatív inotrop hatását [31]. Az antioxidáns vegyületekkel folytatott klinikai tanulmányok ez idáig csalódást okoztak, a ROS-termelődés csökkentése nem javította a szív pumpafunkcióját a szívelégtelen betegekben általánosan [32].…”