Matrix metalloproteinase-9 modulation by resident arterial cells is responsible for injury-induced accelerated atherosclerotic plaque development in apolipoprotein E-deficient mice.

OBJECTIVE Although matrix metalloproteinase-9 (MMP-9) has been implicated in atherosclerotic plaque instability, the exact role it plays in the plaque development and progression remains largely unknown. We generated apolipoprotein E (apoE)-deficient (apoE-/-) MMP-9-deficient (MMP-9-/-) mice to determine the mechanisms and the main cell source of MMP-9 responsible for the plaque composition during accelerated atherosclerotic plaque formation. METHODS AND RESULTS Three weeks after temporary carotid artery ligation revealed that while on a Western-type diet, apoE-/- MMP-9-/- mice had a significant reduction in intimal plaque length and volume compared with apoE-/- MMP-9+/+ mice. The reduction in plaque volume correlated with a significantly lower number of intraplaque cells of resident cells and bone marrow-derived cells. To determine the cellular origin of MMP-9 in plaque development, bone marrow transplantation after total-body irradiation was performed with apoE-/- MMP-9+/+ and apoE-/- MMP-9-/- mice, which showed that only MMP-9 derived from resident arterial cells is required for plaque development. CONCLUSIONS MMP-9 is derived from resident arterial cells and is required for early atherosclerotic plaque development and cellular accumulation in apoE-/- mice.