C-reactive protein decreases endothelial nitric oxide synthase activity via uncoupling.
C-reactive protein (CRP), a cardiovascular risk marker, induces endothelial dysfunction. We have previously shown that CRP decreases endothelial nitric oxide synthase (eNOS) expression and bioactivity in human aortic endothelial cells (HAECs). In this study, we examined the mechanisms by which CRP decreases eNOS activity in HAECs. To this end, we explored different strategies such as availability of tetrahydrobiopterin (BH4)-a critical cofactor for eNOS, superoxide (O(2)(-)) production resulting in uncoupling of eNOS and phosphorylation/dephosphorylation of eNOS. CRP treatment significantly decreased levels of BH4 thereby promoting eNOS uncoupling. Pretreatment with sepiapterin, a BH4 precursor, prevented CRP-mediated effects on BH(4) levels, superoxide production as well as eNOS activity. The gene expression and enzymatic activity of GTPCH1, the first enzyme in the de novo biosynthesis of BH(4), were significantly inhibited by CRP. Importantly, GTPCH1 is known to be regulated by cAMP-mediated pathway. In the present study, CRP-mediated inhibition of GTPCH1 activity was reversed by pretreatment with cAMP analogues. Furthermore, CRP-induced O(2)(-) production was reversed by pharmacologic inhibition and siRNAs to p47 phox and p22 phox. Additionally, CRP treatment significantly decreased the eNOS dimer: monomer ratio confirming CRP-mediated eNOS uncoupling. The pretreatment of cells with NO synthase inhibitor (N-nitro-l-arginine methyl ester [l-NAME]) also prevented CRP-mediated O(2)(-) production further strengthening CRP-mediated eNOS uncoupling. Additionally, CRP decreased eNOS phosphorylation at Ser1177 as well as increased phosphorylation at Thr495. CRP appears to mediate these effects through the Fcgamma receptors, CD32 and CD64. To conclude, CRP uncouples eNOS resulting in increased superoxide production, decreased NO production and altered eNOS phosphorylation.
Singh
Uma
U
Laboratory for Atherosclerosis and Metabolic Research, UC Davis Medical Center, University of California-Davis, 4635 2nd Avenue, Sacramento, CA 95817, USA.
Devaraj
Sridevi
S
Vasquez-Vivar
Jeannette
J
Jialal
Ishwarlal
I
D001708:Biopterins / Q000031:analogs & derivatives / Q000378:metabolism; D015153:Blotting, Western; D002097:C-Reactive Protein / Q000378:metabolism*; D002478:Cells, Cultured; D006152:Cyclic GMP / Q000378:metabolism; D019281:Dimerization; D004579:Electron Transport / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006136:GTP Cyclohydrolase / Q000235:genetics / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D006801:Humans; D008954:Models, Biological; D019255:NADPH Oxidases / Q000037:antagonists & inhibitors; D009500:Neutralization Tests; D052250:Nitric Oxide Synthase Type III / Q000235:genetics / Q000378:metabolism*; D011622:Pterins / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013997:Time Factors; D014475:Uncoupling Agents / Q000378:metabolism*; D042461:Vascular Endothelial Growth Factor A / Q000494:pharmacology
D004791:Enzyme Inhibitors; D011622:Pterins; D012333:RNA, Messenger; D014475:Uncoupling Agents; D042461:Vascular Endothelial Growth Factor A; D001708:Biopterins; D002097:C-Reactive Protein; C016727:sepiapterin; D052250:Nitric Oxide Synthase Type III; D019255:NADPH Oxidases; D006136:GTP Cyclohydrolase; C003402:sapropterin; D006152:Cyclic GMP