However, in response to injury, the number of Sca-1+ cells in the endothelial layer of the aorta increases.119 In addition, apolipoprotein E–deficient (ApoE−/−) mice, which model atherosclerosis, have elevated numbers of Sca-1+ cells in the aortic endothelium.120 Hu et al26 demonstrated that adventitia-resident vascular progenitor cells express Sca-1 and that these cells contributed to atherosclerosis via migration and differentiation into SMCs. Here, APOE is linked to atherosclerosis.