Differential upregulation of Nox homologues of NADPH oxidase by tumor necrosis factor‐α in human aortic smooth muscle and embryonic kidney cells

Abstract

Oxidative stress induced by superoxide (O 2¯⋅ ) and other reactive oxygen species (ROS) has critical roles in the pathogenesis of cardiovascular disease [1]. Potential enzymatic sources of ROS in vasculature include the mitochondrial respiration chain, lipoxygenase and cyclooxygenase, xanthine oxidase, NADPH oxidase, nitric oxide (NO) synthase and cytochrome P450 enzymes. Although our understanding of the mechanisms for superoxide production in vascular cells is incomplete, increasing evidence suggests that NADPH oxidase is a AbstractNADPH oxidases are important sources of vascular superoxide, which has been linked to the pathogenesis of atherosclerosis. Previously we demonstrated that the Nox4 subunit of NADPH oxidase is a critical catalytic component for superoxide production in quiescent vascular smooth muscle cells. In this study we sought to determine the role of Nox4 in superoxide production in human aortic smooth muscle cells (AoSMC) and embryonic kidney (HEK293) cells under proinflammatory conditions. Incubation with tumor necrosis factor-α (TNF-α, 10 ng/ml) for 12h increased superoxide production in both cell types, whereas angiotensin II, platelet-derived growth factor or interleukin-1β had little effects. Superoxide production was completely abolished by the NADPH oxidase inhibitors diphenyline iodonium and apocynin, but not by inhibitors of xanthine oxidase, nitric oxide synthase or mitochondrial electron transport. TNF-α upregulated the expression of Nox4 in AoSMC at both message and protein levels, while Nox1 and Nox2 were unchanged. In contrast, upregulation of Nox2 appeared to mediate the enhanced superoxide production by TNF-α in HEK293 cells. We suggest that Nox4 may be involved in increased superoxide generation in vascular smooth muscle cells under proinflammatory conditions.

NADPH oxidase has a directional response to shear stress

“…(8,39,45). Those signal pathways may be involved in a myogenic response of the blood vessel (38,49).…”

Nox enzymes, ROS, and chronic disease: An example of antagonistic pleiotropy

“…Hypertension of vascular origin is associated with increased vascular contractility and with hypertrophy and proliferation of vascular smooth muscle and other cells. Nox enzymes (particularly Nox1) and ROS are induced in vascular cells by growth stimuli [Angiotensin II, PDGF, lyso-phosphatidylcholine, thrombin [42,44,64], urokinase plasminogen activator [65], by PGF2α and ATF-1 [66]] and by inflammatory stimuli [e.g., TNFα and IL1β [67]]. Nox1 was also markedly overexpressed in transgenic hypertensive rats overexpressing the Ren2 gene [64] and in stroke-prone spontaneously hypertensive rats [68].…”

Quinone compounds regulate the level of ROS production by the NADPH oxidase Nox4

“…Nox4 is unique among other Nox isoenzymes in that its activity is constitutive and may depend on a specific conformation of the dehydrogenase DH domain that should allow a spontaneous transfer of electrons from NADPH to FAD and to the hemes [24,25]. Data from various studies indicated clearly that Nox4 activity is regulated at the mRNA level, implying that an increase or decrease of ROS production by Nox4 is correlated to an up regulation [9,16,[26][27][28][29][30][31][32][33] or to a decline [34] of Nox4 transcripts. Although it has not been reported yet, post-translational regulation of Nox4 oxidase activity cannot be excluded.…”