Nitric oxide and cyclic GMP increase the expression of matrix metalloproteinase-9 in vascular smooth muscle

Interactions and possible cross talk between inducible nitric-oxide synthase (iNOS), cyclooxygenase-2 (COX-2) and matrix metalloproteinase-9 (MMP-9), were studied in rat aortic vascular smooth muscle cells stimulated with bacterial lipopolysaccharide (LPS), interferon-gamma (IFN-gamma), and phorbol 12-myristate-13-acetate (PMA). The expression and activity of iNOS, COX-2, and MMP-9 were characterized at the transcriptional, protein, and enzyme activity levels. The NOS inhibitor N-omega-nitro-L- arginine methyl ester (L-NAME) was used to investigate the effects of NO on COX-2 and MMP-9 at the transcriptional level. The measurements of mRNAs for these enzymes using real-time polymerase chain reaction (PCR) showed that COX-2 mRNA was up-regulated 2.3-fold, whereas MMP-9 mRNA upregulation was 11.7-fold in the presence of LPS, IFN-gamma, and PMA. Real-time PCR results indicated that L-NAME exerted an inhibitory effect on COX-2 and MMP-9 mRNA synthesis. Both superoxide dismutase (SOD) and the SOD mimetic Mn(III) tetrakis( 1-methyl-4-pyridyl) porphyrin pentachloride (MnTMPyP) did not modify significantly the up-regulation of these enzymes, indicating that neither superoxide nor peroxynitrite are involved in this mechanism. Furthermore, NO-mediated up-regulation of MMP-9 was cGMP-dependent since 1H-[1,2,4] oxadiazolo[4,3a] quinoxalin-1-one (ODQ), an inhibitor of soluble guanylate cyclase, blocked, in a concentration-dependent manner, the increased expression of MMP-9, an effect reversed by 8-bromo-cGMP, a soluble analog of cGMP. Our findings suggest that NO and cGMP are necessary to up-regulate the expression of MMP-9.