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Tumor necrosis factor- reduces argininosuccinate synthase expression and nitric oxide production in aortic endothelial cells

¹Department of Molecular Medicine and ²Johnnie B. Byrd, Sr. Alzheimer's Center and Research Institute, University of South Florida, College of Medicine, Tampa, Florida

Submitted 9 October 2006 ; accepted in final form 9 May 2007

Endothelial dysfunction associated with elevated serum levels of TNF- observed in diabetes, obesity, and congenital heart disease results, in part, from the impaired production of endothelial nitric oxide (NO). Cellular NO production depends absolutely on the availability of arginine, substrate of endothelial nitric oxide synthase (eNOS). In this report, evidence is provided demonstrating that treatment with TNF- (10 ng/ml) suppresses not only eNOS expression but also the availability of arginine via the coordinate suppression of argininosuccinate synthase (AS) expression in aortic endothelial cells. Western blot and real-time RT-PCR demonstrated a significant and dose-dependent reduction of AS protein and mRNA when treated with TNF- with a corresponding decrease in NO production. Reporter gene analysis demonstrated that TNF- suppresses the AS proximal promoter, and EMSA analysis showed reduced binding to three essential Sp1 elements. Inhibitor studies suggested that the repression of AS expression by TNF- may be mediated, in part, via the NF-B signaling pathway. These findings demonstrate that TNF- coordinately downregulates eNOS and AS expression, resulting in a severely impaired citrulline-NO cycle. The downregulation of AS by TNF- is an added insult to endothelial function because of its important role in NO production and in endothelial viability.

nitric oxide synthase; NF-B; endothelial dysfunction; arginine