Objective: Several matrix metalloproteinases (MMPs) have been implicated in extracellular matrix destruction and other actions that lead to plaque rupture and myocardial infarction. Conversely, other MMPs have been shown to promote vascular smooth muscle cell (VSMC)-driven neointima formation, which contributes to restenosis, fibrous cap formation, and plaque stability. MMP-3 knockout reduced VSMC accumulation in mouse atherosclerotic plaques, implicating MMP-3 in neointima formation. We therefore investigated the effect of MMP-3 knockout on neointima formation after carotid ligation in vivo and VSMC migration in vitro.
Methods and results: Twenty-eight days after left carotid ligation, MMP-3 knockout significantly reduced neointima formation (75%, P<0.01) compared with wild-type (WT) littermates, and also reduced remodeling of ligated and contralateral carotid arteries. Gelatin zymography illustrated that MMP-3 knockout abolished MMP-9 activation in ligated carotids and scratch-wounded VSMC cultures. MMP-3 knockout also attenuated VSMC migration into a scratch wound by 59% compared with WT cells. Addition of exogenous MMP-3 or activated MMP-9 restored migration of MMP-3 knockouts to that of WT VSMCs, but exogenous MMP-3 had no effect on migration in MMP-9 knockout VSMCs. MMP-9 knockout or knockdown with small interfering RNA significantly retarded VSMC migration to the same extent as MMP-3 knockout.
Conclusions: These results indicate for the first time that MMP-3 mediated activation of MMP-9 is required for efficient neointima formation after carotid ligation in vivo and for VSMC migration in vitro, whereas MMP-12 plays a redundant role. These findings add to the understanding of MMP action in plaque stability and restenosis.