Accelerated neointima formation after vascular injury in mice with stromelysin-3 (MMP-11) gene inactivation

The hypothesis that stromelysin-3 (MMP-11), a unique member of the matrix m etalloproteinase (MMP) family, plays a role in neointima formation was test ed with the use of a vascular injury model in wild-type (MMP-11(+/+)) and M MP-11-deficient (MMP-11(-/-)) mice. Neointima formation 2 to 3 weeks after electric injury of the femoral artery was significantly enhanced in MMP-11- /- as compared with MMP-11(+/+) mice, in both mice of a pure 129SV genetic background (0.014 versus 0.0010 mm(2) at 2 weeks, P<0.001) and those of a 5 0/50 mixed 129SV/BL6 background (0.030 versus 0.013 mm(2) at 3 weeks, P<0.0 5). The medial areas were comparable, resulting in intima/media ratios that were significantly increased in MMP-11(-/-) as compared with MMP-11(+/+) a rteries, in mice of both the 129SV (1.0 versus 0.18, P<0.001) and mixed (1. 5 versus 0.70, P<0.05) backgrounds. Nuclear cell counts in cross-sectional areas of the intima of the injured region were higher in arteries from MMP- 11(-/-) mice than in those from MMP-11(+/+) mice (210 versus 48, P<0.001, i n pure 129SV mice and 290 versus 150, P<0.01, in mice of the mixed genetic background). Immunocytochemical analysis revealed that alpha-actin-positive and CD45-positive cells were more abundant in intimal sections of MMP-11-/ - mice. Degradation of the internal elastic lamina was more extensive in ar teries of MMP-11(-/-) mice than in those of MMP-11(+/+) mice (39% versus 6. 8% at 3 weeks, P<0.005). The mechanisms by which MMP-11 could impair elasti n degradation and cellular migration in this model remain, however, unknown .