Vascular endothelial growth factor (VEGF) can induce matrix metalloproteinase (MMP)-9 activities and focal angiogenesis. We hypothesized that VEGF activation of cerebral MMP-9 would require nitric oxide (NO) participation.
We compared the in vivo effects of: (1) NG-monomethyl-L-arginine (L-NMMA), a non-specific NO synthase (NOS) inhibitor; (2) L-N6-(1-iminoethyl)lysine (L-NIL), an inducible NOS (iNOS) selective inhibitor; and (3) doxycycline, a known non-specific inhibitor of MMP in the mouse brain, using in situ zymography and endothelial marker CD31. 3-nitrotyrosine (3-NT) was used as a surrogate for NO activity. Inflammatory cell markers CD68 and MPO were used to confirm leukocyte infiltration.
VEGF-stimulated MMP-9 activity expressed primarily around cerebral microvessels. L-NMMA suppressed cerebral angiogenesis (p<0.05), especially those microvessels associated with MMP-9 activation (p<0.02) induced by VEGF, comparable to the effect of doxycycline. L-NIL showed similar inhibitory effects. 3-NT confirmed NO levels in the brain. Compared to the lacZ control, VEGF increased inflammatory cell infiltration, especially macrophages, in the induced brain angiogenic focuses.
Inhibition of NO production decreased MMP-9 activity and focal angiogenesis in the VEGF-stimulated brain. Both specific and non-specific inhibition of NOS resulted in similar reductions, suggesting that VEGF-stimulated cerebral MMP activity and angiogenesis are predominantly mediated through iNOS, a specific NOS isoform mediating inflammatory responses.
Keywords: nitric oxide, vascular endothelial growth factor, matrix metalloproteinase