Several reviews have highlighted the different roles of specific MMPs that emerge from knockout studies in the same Apoe−/− background.17,45 For example, we previously demonstrated that MMP-3, MMP-7, MMP-9, and MMP-12 exert highly divergent effects on atherosclerotic plaque development, particularly cellular composition, in mice studied under very similar conditions.43 MMP-14, also known as MT1-MMP, has been linked to atherosclerosis progression and plaque vulnerability in mice15,16 owing to its ability to deplete collagen. Here, MMP9 is linked to atherosclerosis.