Surgical preparative injury and neointima formation increase MMP-9 expression and MMP-2 activation in human saphenous...

Injury stimulates smooth muscle cell (SMC) migration and proliferation by mechanisms that are incompletely understood. Surgical preparative injury is an important determinant of neointimal thickening in human saphenous vein bypass grafts. We investigate here whether basement-membrane-degrading metalloproteinases (MMPs) are stimulated by surgical preparation and culturing of human saphenous veins in organ culture.

Secretion of MMP-2 and MMP-9 was measured by zymography and Western blotting. Sites of MMP secretion were localised by immunocytochemistry and in situ hybridisation.

Freshly isolated veins secreted pro-MMP-2 and much lower amounts of active MMP-2 and pro-MMP-9. MMP-2 was expressed in all cells whereas MMP-9 expression was confined to endothelial cells and at low levels to 55 +/- 10% (mean +/- s.e.m., n = 6) of medial SMC. Surgical preparative injury increased pro-MMP-2, active MMP-2 and pro-MMP-9 secretion. MMP-9 expression 3 h after surgical preparation occurred at high levels in 59 +/- 5% of medial SMC (P < 0.05 vs. freshly isolated, n = 6). Culturing in serum for 12 days increased pro-MMP-2, active MMP-2 and pro-MMP-9 secretion to equal levels in freshly isolated and surgically prepared veins. MMP-9 expression was greatest in the highly proliferative neointimal SMC and was more widespread in medial SMC of surgically prepared than freshly isolated veins (89 +/- 3 vs. 67 +/- 11%, n = 6, P < 0.05), paralleling the differences in proliferative index (18 +/- 3 vs. 8 +/- 4 cell/mm2, P < 0.05).

The data provide new insights into the mechanisms underlying human SMC proliferation. Activation of MMP-2 and increased MMP-9 expression are shown to be important components of the response to injury in this model. Furthermore, MMP-9 expression is closely associated with medial and neointimal SMC proliferation.