Mitochondrial ROS-induced ROS release: an update and review.

Environmental stresses converge on the mitochondria that can trigger or inhibit cell death. Excitable, postmitotic cells, in response to sublethal noxious stress, engage mechanisms that afford protection from subsequent insults. We show that reoxygenation after prolonged hypoxia reduces the reactive oxygen species (ROS) threshold for the mitochondrial permeability transition (MPT) in cardiomyocytes and that cell survival is steeply negatively correlated with the fraction of depolarized mitochondria. Cell protection that exhibits a memory (preconditioning) results from triggered mitochondrial swelling that causes enhanced substrate oxidation and ROS production, leading to redox activation of PKC, which inhibits glycogen synthase kinase-3beta (GSK-3beta). Alternatively, receptor tyrosine kinase or certain G protein-coupled receptor activation elicits cell protection (without mitochondrial swelling or durable memory) by inhibiting GSK-3beta, via protein kinase B/Akt and mTOR/p70(s6k) pathways, PKC pathways, or protein kinase A pathways. The convergence of these pathways via inhibition of GSK-3beta on the end effector, the permeability transition pore complex, to limit MPT induction is the general mechanism of cardiomyocyte protection.

/pdf/glycogen-synthase-kinase-3b-mediates-convergence-of-1mx20t6q4w.pdf

Glycogen synthase kinase-3β mediates convergence of protection signaling to inhibit the mitochondrial permeability transition pore

Subcellular localization of nitric oxide (NO) synthases with effector molecules is an important regulatory mechanism for NO signalling. In the heart, NO inhibits L-type Ca2+ channels but stimulates sarcoplasmic reticulum (SR) Ca2+ release, leading to variable effects on myocardial contractility. Here we show that spatial confinement of specific NO synthase isoforms regulates this process. Endothelial NO synthase (NOS3) localizes to caveolae, where compartmentalization with beta-adrenergic receptors and L-type Ca2+ channels allows NO to inhibit beta-adrenergic-induced inotropy. Neuronal NO synthase (NOS1), however, is targeted to cardiac SR. NO stimulation of SR Ca2+ release via the ryanodine receptor (RyR) in vitro, suggests that NOS1 has an opposite, facilitative effect on contractility. We demonstrate that NOS1-deficient mice have suppressed inotropic response, whereas NOS3-deficient mice have enhanced contractility, owing to corresponding changes in SR Ca2+ release. Both NOS1-/- and NOS3-/- mice develop age-related hypertrophy, although only NOS3-/- mice are hypertensive. NOS1/3-/- double knockout mice have suppressed beta-adrenergic responses and an additive phenotype of marked ventricular remodelling. Thus, NOS1 and NOS3 mediate independent, and in some cases opposite, effects on cardiac structure and function.

Nitric oxide regulates the heart by spatial confinement of nitric oxide synthase isoforms.

Experimental work during the past 15 years has demonstrated that endothelial cells in the heart play an obligatory role in regulating and maintaining cardiac function, in particular, at the endocardium and in the myocardial capillaries where endothelial cells directly interact with adjacent cardiomyocytes. The emerging field of targeted gene manipulation has led to the contention that cardiac endothelial-cardiomyocytal interaction is a prerequisite for normal cardiac development and growth. Some of the molecular mechanisms and cellular signals governing this interaction, such as neuregulin, vascular endothelial growth factor, and angiopoietin, continue to maintain phenotype and survival of cardiomyocytes in the adult heart. Cardiac endothelial cells, like vascular endothelial cells, also express and release a variety of auto- and paracrine agents, such as nitric oxide, endothelin, prostaglandin I(2), and angiotensin II, which directly influence cardiac metabolism, growth, contractile performance, and rhythmicity of the adult heart. The synthesis, secretion, and, most importantly, the activities of these endothelium-derived substances in the heart are closely linked, interrelated, and interactive. It may therefore be simplistic to try and define their properties independently from one another. Moreover, in relation specifically to the endocardial endothelium, an active transendothelial physicochemical gradient for various ions, or blood-heart barrier, has been demonstrated. Linkage of this blood-heart barrier to the various other endothelium-mediated signaling pathways or to the putative vascular endothelium-derived hyperpolarizing factors remains to be determined. At the early stages of cardiac failure, all major cardiovascular risk factors may cause cardiac endothelial activation as an adaptive response often followed by cardiac endothelial dysfunction. Because of the interdependency of all endothelial signaling pathways, activation or disturbance of any will necessarily affect the others leading to a disturbance of their normal balance, leading to further progression of cardiac failure.

/pdf/cardiac-endothelial-myocardial-signaling-its-role-in-cardiac-2fjkofy30k.pdf

Cardiac Endothelial-Myocardial Signaling: Its Role in Cardiac Growth, Contractile Performance, and Rhythmicity

Arrhythmogenic right ventricular cardiomyopathy (ARVD/C) is a genetically heterogeneous disease characterized by progressive degeneration of the right ventricular myocardium and increased risk of sudden death. Here, we report on a genome scan in one Italian family in which the disease appeared unlinked to any of the six different ARVD loci reported so far; we identify a mutation (S299R) in exon 7 of desmoplakin (DSP), which modifies a putative phosphorylation site in the N-terminal domain binding plakoglobin. It is interesting that a nonsense DSP mutation was reported elsewhere in the literature, inherited as a recessive trait and causing a biventricular dilative cardiomyopathy associated with palmoplantar keratoderma and woolly hairs. Therefore, different DSP mutations might produce different clinical phenotypes, with different modes of inheritance.

https://www.cell.com/ajhg/pdf/S0002-9297(07)60414-5.pdf

Mutation in human desmoplakin domain binding to plakoglobin causes a dominant form of arrhythmogenic right ventricular cardiomyopathy

Stretching of cardiac muscle modulates contraction through the enhancement of the Ca2+ transient, but how this occurs is still not known. We found that stretching of myocytes modulates the elementary Ca2+ release process from ryanodine-receptor Ca2+-release channels (RyRCs), Ca2+ sparks and the electrically stimulated Ca2+ transient. Stretching induces PtdIns-3-OH kinase (PI(3)K)-dependent phosphorylation of both Akt and the endothelial isoform of nitric oxide synthase (NOS), nitric oxide (NO) production, and a proportionate increase in Ca2+-spark frequency that is abolished by inhibiting NOS and PI(3)K. Exogenously generated NO reversibly increases Ca2+-spark frequency without cell stretching. We propose that myocyte NO produced by activation of the PI(3)K-Akt-endothelial NOS axis acts as a second messenger of stretch by enhancing RyRC activity, contributing to myocardial contractile activation.

Suhn Hee Kim

Papers

Endogenous nitric oxide mechanisms mediate the stretch dependence of Ca2+ release in cardiomyocytes