Role of ADP ribosylation factor6- Cytohesin1-PhospholipaseD signaling axis in U46619 induced activation of NADPH oxidase in pulmonary artery smooth muscle cell membrane

Does coupling to ADP ribosylation factor 6 explain differences between muscarinic and other receptors in interaction with β-adrenoceptor-mediated smooth muscle relaxation?

Numerous studies in airways, ileum, and urinary bladder have demonstrated that relaxation by β-adrenoceptor agonists has lower potency and/or efficacy when contraction was elicited by muscarinic receptor agonists as compared to other G-protein-coupled receptors, KCl, or basal tone, but the molecular mechanisms behind this relative resistance remain unclear. A paper by Huang et al. in this issue demonstrates that NAV2729, an inhibitor of ADP ribosylation factor 6, inhibits contraction of isolated blood vessels elicited by muscarinic receptor agonists, but not by α₁-adrenoceptor agonists or KCl. Against this background, we discuss the role of ADP ribosylation factor 6 in cellular responses to G-protein-coupled receptor stimulation. While ADP ribosylation factor 6 apparently is the only promising molecular explanation for the relative resistance of smooth muscle contraction elicited by muscarinic agonists, the existing data are insufficient for a robust conclusion.

Arf6 regulates energy metabolism in neutrophils

The small GTPase Arf6 regulates many cellular processes, including cytoskeletal remodeling, receptor endocytosis, and pathogen phagocytosis. Arf6 silencing in neutrophil (PMN)-like cells is well-known to inhibit chemotactic peptide-mediated activation of phospholipase D, the oxidative burst, and β2 integrin-dependent adhesion. In conditional knockout (cKO) mice, the migration to inflammatory sites of Arf6-deficient PMNs was diminished and associated with reduced cell surface expression of β2 integrins. In this study we assessed the impact of Arf6 depletion on the functions and gene expression profile of PMNs isolated from the mouse air pouch. Numerous genes involved in response to oxygen levels, erythrocyte and myeloid differentiation, macrophage chemotaxis, response to chemicals, apoptosis, RNA destabilization, endosome organization, and vesicle transport were differentially expressed in PMNs cKO for Arf6. Lpar6 and Lacc-1 were the most up-regulated and down-regulated genes, respectively. The deletion of Arf6 also decreased Lacc-1 protein level in PMNs, and silencing of Arf6 in THP-1 monocytic cells delayed LPS-mediated Lacc-1 expression. We report that fMLP or zymosan-induced glycolysis and oxygen consumption rate were both decreased in air pouch PMNs but not in bone marrow PMNs of Arf6 cKO mice. Reduced oxygen consumption correlated with a decrease in superoxide and ROS production. Deletion of Arf6 in PMNs also reduced phagocytosis and interfered with apoptosis. The data suggest that Arf6 regulates energy metabolism, which may contribute to impaired phagocytosis, ROS production, and apoptosis in PMN-Arf6 cKO. This study provides new information on the functions and the inflammatory pathways influenced by Arf6 in PMNs.

PKCζ-NADPH Oxidase-PKCα Dependent Kv1.5 Phosphorylation by Endothelin-1 Modulates Nav1.5-NCX1-Cav1.2 Axis in Stimulating Ca2+ Level in Caveolae of Pulmonary Artery Smooth Muscle Cells

Endothelin-1 (ET-1) is a potent endogenously derived vasoconstrictor, which increases pulmonary hypertension via stimulation of [Ca²⁺]_i level in pulmonary artery smooth muscle cells (PASMCs). In this communication, we sought to investigate the mechanism by which ET-1 causes stimulation of Ca²⁺ concentration in caveolae vesicles of bovine PASMCs (BPASMCs). ET-1 activates PKC-α in the caveolae vesicles by O₂^.- derived from PKCζ-NADPH oxidase dependent pathway. PKC-α phosphorylates Kv1.5 channels leading to a marked stimulation of Na⁺ and Ca²⁺ concentration in the caveolae vesicles. The stimulation of Ca²⁺ concentration in the caveolae vesicles by ET-1 occurs predominantly via Cav1.2 channels. Additionally, an increase in Na⁺ concentration by ET-1 due to stimulation of Nav1.5 channels marginally increases Ca²⁺ level in the caveolae vesicles via reverse-mode Na⁺/Ca²⁺ exchanger (NCX-1) and also through "slip-mode conductance" Nav1.5 channels. 4-AP, a well-known inhibitor of Kv channels, also increases Ca²⁺ concentration in the caveolae vesicles via Cav1.2 channels, reverse-mode NCX-1 and Nav1.5 channels by phosphorylation independent modulation of Kv1.5 channels without the involvement of PKCζ-NADPH oxidase-PKCα signaling axis. Overall, PKCζ-NADPH oxidase-PKCα dependent phosphorylation of Kv1.5 by ET-1 modulates Nav1.5-NCX1-Cav1.2 axis for stimulation of Ca²⁺ concentration in caveolae vesicles of BPASMCs, which provides a crucial mechanism for better understanding of ET-1-mediated modulation of pulmonary vascular tone.

Role of PKCζ-NADPH oxidase signaling axis in PKCα-mediated Giα2 phosphorylation for inhibition of adenylate cyclase activity by angiotensin II in pulmonary artery smooth muscle cells

We sought to determine the mechanism by which angiotensin II (AngII) inhibits isoproterenol induced increase in adenylate cyclase (AC) activity and cyclic adenosine monophosphate (cAMP) production in bovine pulmonary artery smooth muscle cells (BPASMCs). Treatment with AngII stimulates protein kinase C-ζ (PKC-ζ), nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, and PKC-α activities, and also inhibits isoproterenol induced increase in AC activity and cAMP production in the cells. Pertussis toxin pretreatment eliminates AngII caused inhibition of isoproterenol induced increase in AC activity without a discernible change in PKC-ζ, NADPH oxidase, and PKC-α activities. Treatment of the cells with AngII increases α2 isoform of Gi (Giα2) phosphorylation; while pretreatment with chemical and genetic inhibitors of PKC-ζ and NADPH oxidase attenuate AngII induced increase in PKC-α activity and Giα2 phosphorylation, and also reverse AngII caused inhibition of isoproterenol induced increase in AC activity. Pretreatment of the cells with chemical and genetic inhibitors of PKC-α attenuate AngII induced increase in Giα2 phosphorylation and inhibits isoproterenol induced increase in AC activity without a discernible change in PKC-ζ and NADPH oxidase activities. Overall, PKCζ-NADPH oxidase-PKCα signaling axis plays a crucial role in Giα2 phosphorylation resulting in AngII-mediated inhibition of isoproterenol induced increase in AC activity in BPASMCs.

NADPH oxidase in the vasculature: Expression, regulation and signalling pathways; role in normal cardiovascular physiology and its dysregulation in hypertension

The last 20-25 years have seen an explosion of interest in the role of NADPH oxidase (NOX) in cardiovascular function and disease. In vascular smooth muscle and endothelium, NOX generates reactive oxygen species (ROS) that act as second messengers, contributing to the control of normal vascular function. NOX activity is altered in response to a variety of stimuli, including G-protein coupled receptor agonists, growth-factors, perfusion pressure, flow and hypoxia. NOX-derived ROS are involved in smooth muscle constriction, endothelium-dependent relaxation and smooth muscle growth, proliferation and migration, thus contributing to the fine-tuning of blood flow, arterial wall thickness and vascular resistance. Through reversible oxidative modification of target proteins, ROS regulate the activity of protein tyrosine phosphatases, kinases, G proteins, ion channels, cytoskeletal proteins and transcription factors. There is now considerable, but somewhat contradictory evidence that NOX contributes to the pathogenesis of hypertension through oxidative stress. Specific NOX isoforms have been implicated in endothelial dysfunction, hyper-contractility and vascular remodelling in various animal models of hypertension, pulmonary hypertension and pulmonary arterial hypertension, but also have potential protective effects, particularly NOX4. This review explores the multiplicity of NOX function in the healthy vasculature and the evidence for and against targeting NOX for antihypertensive therapy.

Role of PLD-PKCζ signaling axis in p47phox phosphorylation for activation of NADPH oxidase by angiotensin II in pulmonary artery smooth muscle cells

We sought to determine the mechanism by which angiotensin II (ANGII) stimulates NADPH oxidase-mediated superoxide (O₂ ^.- ) production in bovine pulmonary artery smooth muscle cells (BPASMCs). ANGII-induced increase in phospholipase D (PLD) and NADPH oxidase activities were inhibited upon pretreatment of the cells with chemical and genetic inhibitors of PLD2, but not PLD1. Immunoblot study revealed that ANGII treatment of the cells markedly increases protein kinase C-α (PKC-α), -δ, -ε, and -ζ levels in the cell membrane. Pretreatment of the cells with chemical and genetic inhibitors of PKC-ζ, but not PKC-α, -δ, and -ε, attenuated ANGII-induced increase in NADPH oxidase activity without a discernible change in PLD activity. Transfection of the cells with p47phox small interfering RNA inhibited ANGII-induced increase in NADPH oxidase activity without a significant change in PLD activity. Pretreatment of the cells with the chemical and genetic inhibitors of PLD2 and PKC-ζ inhibited ANGII-induced p47phox phosphorylation and subsequently translocation from cytosol to the cell membrane, and also inhibited its association with p22phox (a component of membrane-associated NADPH oxidase). Overall, PLD-PKCζ-p47phox signaling axis plays a crucial role in ANGII-induced increase in NADPH oxidase-mediated O₂ ^.- production in the cells.

Protective role of epigallocatechin-3-gallate in NADPH oxidase-MMP2-Spm-Cer-S1P signalling axis mediated ET-1 induced pulmonary artery smooth muscle cell proliferation

The signalling pathway involving MMP-2 and sphingosine-1-phosphate (S1P) in endothelin-1 (ET-1) induced pulmonary artery smooth muscle cell (PASMC) proliferation is not clearly known. We, therefore, investigated the role of NADPH oxidase derived O₂^.--mediated modulation of MMP2-sphingomyeline-ceramide-S1P signalling axis in ET-1 induced increase in proliferation of PASMCs. Additionally, protective role of the tea cathechin, epigallocatechin-3-gallate (EGCG), if any, in this scenario has also been explored. ET-1 markedly increased NADPH oxidase and MMP-2 activities and proliferation of bovine pulmonary artery smooth muscle cells (BPASMCs). ET-1 also caused significant increase in sphingomyelinase (SMase) activity, ERK1/2 and sphingosine kinase (SPHK) phosphorylations, and S1P level in the cells. EGCG inhibited ET-1 induced increase in SMase activity, ERK1/2 and SPHK phosphorylations, S1P level and the SMC proliferation. EGCG also attenuated ET-1 induced activation of MMP-2 by inhibiting NADPH oxidase activity upon inhibiting the association of the NADPH oxidase components, p47phox and p67phox in the cell membrane. Molecular docking study revealed a marked binding affinity of p47phox with the galloyl group of EGCG. Overall, our study suggest that ET-1 induced proliferation of the PASMCs occurs via NADPH oxidase-MMP2- Spm- Cer-S1P signalling axis, and EGCG attenuates ET-1 induced increase in proliferation of the cells by inhibiting NADPH oxidase activity.