iNOS activity is essential for endothelial stress gene expression protecting against oxidative damage

Abstract

In endothelial cells, the expression of the inducible nitric oxide synthase (iNOS) and the resulting high-output nitric oxide synthesis have often been assumed as detrimental to endothelial function, but recent publications have demonstrated a protective role resulting from iNOS espression and activity. To address this question, we used antisense-mediated iNOS knockdown during proinflammatory cytokine challenge in primary endothelial cell cultures and studied endothelial function by monitoring the expression of stress defense genes. Using antisense oligonucleotides, we achieved a block of iNOS protein formation, accompanied by a strong decrease in the expression of the protective stress response genes bcl-2, vascular endothelial growth factor, and heme oxygenase-1 (HO-1). Additionally, cells were also maintained in the presence of limited exogenous substrate concentrations during cytokine challenge, thereby mimicking a situation of low serum arginine level during inflammation. Under these conditions, cytokine addition results in full iNOS protein expression with minimal nitric oxide formation, concomitant with a significant reduction in stress response gene expression and susceptibility to cell death induced by reactive oxygen species. Taken together, our data suggest that cytokine-induced endogenous iNOS expression and activity have key functions in increasing endothelial survival and maintaining function. Thus suppression of iNOS expression or limited substrate supply, as has been reported to occur in atherosclerosis patients, appears to significantly contribute to endothelial dysfunction and death during oxidative stress.

Aging-related induction of inducible nitric oxide synthase is vasculo-protective to the arterial media

“…In addition, although endothelial damage was increased with aging as expected in the penile dorsal artery, L-NIL did not increase the apoptotic index, thus suggesting that agingrelated iNOS induction does not cause endothelial dysfunction. In fact, it has recently been claimed that iNOS may protect the endothelium in atherosclerosis [41]. This, together with the well known effects of NO in scavenging the profibrotic compound, ROS, thereby decreasing collagen synthesis and down-regulating its breakdown (see Refs.…”

NO Modulates NADPH Oxidase Function Via Heme Oxygenase-1 in Human Endothelial Cells

“…Studies in both ECs and macrophages have shown that proinflammatory cytokine-induced HO-1 expression is at least partly dependent on iNOS expression and subsequent NO generation. 27,28 In a rat model of adjuvant arthritis, blockade of NO production from iNOS suppressed HO-1 upregulation at the site of inflammation. 29 These findings suggest that NO-mediated HO-1 expression may have important roles in preventing tissue damage associated with inflammation.…”

Nitric oxide modulates vascular inflammation and intimal hyperplasia in insulin resistance and the metabolic syndrome

“…Systemically, NO can lead to vasodilation and refractory hypotension. Finally, it is still highly debated what the role of iNOS is in atherogenesis with data to support both pro-and anti-atherogenic effects (21,31). These aspects of NO biology underly the importance of localizing iNOS gene transfer and fully evaluating the consequences of this treatment before clinical application.…”