APOE and atherosclerosis: Meanwhile, macrophage lineage overexpressing MMP‐9 in apoE KO mice showed no effects on lesion size.41 It has been reported that MMP‐9 deficiency appears to enhance plaque growth in apoE/MMP‐9 double KO mice30 although MMP‐9 deficiency protected against cholesterol diet‐induced atherosclerosis in the same double KO mice.29