Regulation of NADPH Oxidase in Vascular Endothelium: The Role of Phospholipases, Protein Kinases, and Cytoskeletal Proteins

Abstract

The generation of reactive oxygen species (ROS) in the vasculature plays a major role in the genesis of endothelial cell (EC) activation and barrier function. Of the several potential sources of ROS in the vasculature, the endothelial NADPH oxidase family of proteins is a major contributor of ROS associated with lung inflammation, ischemia=reperfusion injury, sepsis, hyperoxia, and ventilator-associated lung injury. The NADPH oxidase in lung ECs has most of the components found in phagocytic oxidase, and recent studies show the expression of several homologues of Nox proteins in vascular cells. Activation of NADPH oxidase of nonphagocytic vascular cells is complex and involves assembly of the cytosolic (p47 phox , p67 phox , and Rac1) and membrane-associated components (Noxes and p22 phox ). Signaling pathways leading to NADPH oxidase activation are not completely defined; however, they do appear to involve the cytoskeleton and posttranslation modification of the components regulated by protein kinases, protein phosphatases, and phospholipases. Furthermore, several key components regulating NADPH oxidase recruitment, assembly, and activation are enriched in lipid microdomains to form a functional signaling platform. Future studies on temporal and spatial localization of Nox isoforms will provide new insights into the role of NADPH oxidase-derived ROS in the pathobiology of lung diseases. Antioxid. Redox Signal. 11, 841-860.

Peroxiredoxin 6 Phosphorylation and Subsequent Phospholipase A2 Activity Are Required for Agonist-mediated Activation of NADPH Oxidase in Mouse Pulmonary Microvascular Endothelium and Alveolar Macrophages

“…However, the exact mechanisms that drive this assembly are not known. What is clear is that NOX2 assembly can be initiated by pathways involving either a receptor-or non-receptor-mediated process (1,4). An example of the former is Ang II that works through its receptor subtypes AT 1 and AT 2 to activate downstream signaling pathways, whereas non-receptor-mediated agonists include the phorbol esters (e.g.…”

“…NOX2 is also found in other cell types and is a major source of ROS in endothelial cells (1,2). In the unstimulated state, NOX2 is quiescent, with the intrinsic membrane subunits (cytochrome b 558 comprising gp91 phox and p22 phox ) and cytosolic subunits (Rac1, p47 phox , p67 phox , and p40 phox ) confined to their respective compartments (4). Activation of the enzyme complex by stimuli such as angiotensin II (Ang II), phorbol esters, or thrombin leads to translocation of the cytosolic components to the plasma membrane, resulting in assembly of the oxidase complex.…”

Reactive Oxygen Species in Inflammation and Tissue Injury

“…2) (233). NOX1, NOX2, and NOX4 are the major isoforms of NADPH oxidase that are expressed in the vascular system, and each is strongly implicated in inflammation-induced vascular injury (340). O 2 2 production by gp91 phox (current designation NOX2) in leukocytes is essential for killing engulfed microbes within phagolysosomes, the amalgam of phagosomes and lysosomes (155).…”

NOX Enzymes and Pulmonary Disease

“…A role for NOX4 in LPS-induced proinflammatory responses by human aortic ECs has been reported (92); in this study, downregulation of NOX4 by transfection of NOX4 small interfering RNA (siRNA) resulted in a failure to induce ROS generation and intercellular adhesion molecule (ICAM)-1, monocyte chemoattractant protein (MCP)-1, and interleukin (IL)-8 production in response to LPS. Pulmonary ECs have been shown to generate ROS via both NOX2 and NOX4 (94,95). Circulating blood cells from septic patients generate higher levels of phorbol ester-stimulated O 2 À production compared with those in control subjects, and this activation is inhibited by simvastatin, a widely used cholesterolreducing drug (28).…”

“…Exposure of human pulmonary artery ECs to hyperoxia (95% O 2 ) increases ROS production that is dependent on NOX activation and independent of the mitochondrial electron transport or xanthine=xanthine oxidase systems (91,95). NOX4, which is expressed at relatively higher levels compared with other NOX homologues, is a major source of ROS production in vascular ECs.…”