DKK1 and atherosclerosis: While many different cells participate in ACS,48 apoptosis of ECs is a key event in the initiation of atherosclerotic plaque formation47 and the progression to advanced atherosclerosis, which is vulnerable to rupture.3, 6, 7, 49, 50, 51 We found that both SMCs and macrophages take up the GFP-labeled DKK1 from co-cultured ECs (Supplementary Figure 6a).