Regulation of gene expression of inducible nitric oxide synthase (iNOS) in cardiovascular system and its molecular mechanism of action

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Excessive production of NO by iNOS is implicated in the development of endotoxic shock and atherosclerotic lesion. To elucidate the role of iNOS-derived NO, we have studied the molecular mechanisms of iNOS gene expression and its actions in cultured rat vascular smooth muscle cells (VSMC). Transfection of iNOS cDNA construct into VSMC by lipofection caused a massive generation of NO accompanied by apoptosis and inhibition of DNA synthesis, suggesting the role of NO as proapoptotic factor to prevent intimal thickening in atherosclerosis. Addition of NO donors caused massive apoptosis of cultured rat endothelial cells (EC), whose effect was blocked by endothelin-1 (ET-1), suggesting that NO functions as a proapoptotic factor, whereas ET-1 function as an anti-apoptotic factor, thereby conteracting with each other to maintain endothelial integrity.Inflammatory cytokines, such as interleukin (IL)-1 and tumor necrosis factor (TNF)-α, activate nuclear factor (NF)-kB by phosphorylation and degradation of IkBα, thereby leading to transactivation of iNOS gene promoter. However, NO donors inhibited cytokines-induced iNOS gene expression by blocking phosphorylation and subsequent degradation of IkBα, suggesting that endogenous NO generated from iNOS inhibits overexpression of iNOS in an autofeedback fashion. Glucocorticoid also inhibited cytokines-induced iNOS gene expression by blockade of IkBα phosphorylation and degradation. In contrast, nonsteroidal anti-inlflammatory drugs (NSAID), such as aspirin and sodium salicylate, inhibited cytokines-stimulated NO production by blocking (post) translational level without affecting NF-kB activation or iNOS gene transcription. These data suggest that glucocorticoid and NSAID exert their anti-inflammatory effects by blocking NO production via different sites of action.