Objective To observe the effects of tumor necrosis factor-or (TNF-α) and platelet derived growth factor (PDGF) on vascular neointimal hyperplasia on matrix metalloproteinase 9/2 gene knockout (MMP9/2-/-) mice and explore related mechanisms.Methods Mice of control group,MMP9-/-group,MMP2-/-group and MMP9/2-/-group were studied.Femoral artery was injured by transluminal wire,the mRNA expression levels of TNF-o and PDGF on femoral artery were detected by RT-PCR;the protein expression of MMP9 and MMP2 were assessed by Western blot on day 0,1,3,7,14and 28 post injury.Mice in control group received TNF-α(5 ng/ml,0.10 ml),TNF-α(0.05 ml) + MMP inhibitor SB-3CT (0.50 ng/ml,0.05 ml) injection,or PDGF-bb (10 ng/ml,0.10 ml) and PDGF-bb (0.05 ml) + SB-3CT(0.05 ml) injection around injured artery,intimal hyperplasia at 2 and 4 weeks after injury was observed.Intimal hyperplasia at 2 and 4 weeks after injury was also observed in MMP9/2-/-mice.TNF-α(5 ng/ml,0.10 ml) was injected to MMP2-/-mice,PDGF-bb (0.1 ml) was injected to MMP9-/-mice around injured artery,intimal hyperplasia at 2 and 4 weeks after injury was observed.The degree of neointimal hyperplasia were observed by the Elastica-van Gieson staining and the area of neointima and media of the arteries were measured by SigmaPlot and intima ratio was calculated.Vascular smooth muscle cell (VSMC) mediums of MMP9-/-and MMP2-/-mice were stimulated by TNF-α and PDGF-bb,respectively,and migration assay,and proliferation assay were performed,relative migration and proliferation cells numbers were counted.Results (1) mRNA expression of TNF-o (235.33 ± 23.68) and PDGF-bb (3.30 ±0.56) in femoral arteries peaked at 1 day after injury,while MMP9 or MMP2 protein expression peaked at 7 or 28 days after injury.(2) In control mice,TNF-α intervention significantly enhanced intimal hyperplasia at 2 weeks after injury (2.21 ±0.05 vs.1.55 ±0.03 in blank control group,P ＜ 0.05),while PDGF-bb intervention significantly enhanced intimal hyperplasia at 4 weeks after injury (2.60 ± 0.07 vs.1.89 ± 0.04,P =0.03).(3) Intima hyperplasia was significantly higher in control group than in MMP9/2-/-group at 2 weeks (1.63 ± 0.05 vs.0.46 ± 0.01,P =0.008) and 4 weeks (2.24 ±0.06 vs.0.51 ±0.01) after injury(P =0.005).(4) TNF-o intervention stimulated intimal hyperplasia in MMP2-/-mice (intimal ratio at 2 weeks after injury:1.73 ± 0.05 vs.1.23 ± 0.03,P =0.02) and PDGF-bb intervention stimulated intimal hyperplasia in MMP9-/-mice(intimal ratio at 4 weeks after injury:2.32 ± 0.06 vs.1.35 ± 0.03,P =0.03).(5) Reduced VSMC migration was evidenced in MMP9-/-mice post TNF-α stimulation (1.45 ±0.03 vs.2.16 ±0.04 in control group,P =0.03),while reduced VSMC proliferation post PDGF was seen in MMP2-/-group (1.15 ± 0.02 vs.1.82 ± 0.04 in control group,P =0.03).Conclusions TNF-o induced MMP9 activation plays a major role on promoting VSMC migration at the first 2 weeks after vascular injury,while PDGF induced MMP2 activation plays a crucial role on VSMC proliferation on the following 2 weeks after vascular injury in this mice model.Thus,the axis of TNF-α-MMP9-VSMC migration axis and PDGF-MMP2-VSMC proliferation axis are the two major working mechanisms responsible for intimal hyperplasia post vascular injury.