SURGICAL PREPARATIVE INJURY AND NEOINTIMA FORMATION INCREASE MMP-9 EXPRESSION AND MMP-2 ACTIVATION IN HUMAN SAPHENOUS-VEIN

Objectives: Injury stimulates smooth muscle cell (SMC) migration and p roliferation by mechanisms that are incompletely understood. Surgical preparative injury is an important determinant of neointimal thickenin g in human saphenous vein bypass grafts. We investigate here whether b asement-membrane-degrading metalloproteinases (MMPs) are stimulated by surgical preparation and culturing of human saphenous veins in organ culture. Methods: Secretion of MMP-2 and MMP-9 was measured by zymogra phy and Western blotting. Sites of MMP secretion were localised by imm unocytochemistry and in situ hybridisation. Results: Freshly isolated veins secreted pro-MMP-2 and much lower amounts of active MMP-2 and pr o-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 89 +/- 5% of m edial SMC (P < 0.05 vs. freshly isolated, n = 6). Culturing in serum f or 12 days increased pro-MMP-2, active MMP-2 and pro-MMP-9 secretion t o equal levels in freshly isolated and surgically prepared veins. MMP- 9 expression was greatest in the highly proliferative neointimal SMC a nd was more widespread in medial SMC of surgically prepared than fresh ly isolated veins (89 +/- 3 vs. 67 +/- 11%, n = 6, P < 0.05), parallel ing the differences in proliferative index (18 +/- 3 vs. 8 +/- 4 cell/ mm(2), P < 0.05). Conclusions: The data provide new insights into the mechanisms underlying human SMC proliferation. Activation of MMP-1 and increased MMP-9 expression are shown to be important components of th e response to injury in this model. Furthermore, MMP-9 expression is c losely associated with medial and neointimal SMC proliferation.