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.