Increased MMP-9 expression and activity by aortic smooth muscle cells after nitric oxide synthase inhibition is associated with increased nuclear factor-kappaB and activator protein-1 activity.

Objective: To determine the mechanism underlying increased expression and activity of matrix metalloproteinase 9 (MMP-9) by rat aortic smooth muscle cells (RA-SMC) after inhibition of inducible nitric oxide synthase (iNOS).

Methods And Results: Treatment of interleukin-1beta-stimulated RA-SMC with aminoguanidine led to an increase of 96% in MMP-9 activity (P = 0.003) by gelatin zymography, a 40% increase in pro-MMP-9 protein (P = 0.018) by Western blot, and a 155% increase in MMP-9 mRNA (P = 0.06) by reverse transcription polymerase chain reaction. Aminoguanidine also caused a 26% decrease in cytosolic IkappaB levels (P = 0.014) by Western blot, as well as a 97% increase in nuclear factor-kappaB binding and a 216% increase in activator protein-1 binding as measured by electrophoretic mobility shift assay. No significant changes were noted in MMP-2 or TIMP-1 expression, protein levels, or activity after aminoguanidine administration.

Conclusions: MMP-9 expression and activity is increased in cytokine stimulated RA-SMCs after iNOS inhibition, coincident with activation of the nuclear factor-kappaB and activator protein-1 pathways. We speculate that local derangements in iNOS may favor MMP-9-dependent vessel wall damage in vivo via an inflammatory cascade mechanism.