Fibrous cap SMCs protect atherosclerotic lesions from rupturing and causing thrombosis, while other plaque SMCs may have detrimental roles in plaque development. To gain insight into recruitment of different plaque SMCs, we mapped their clonal architecture using aggregation chimeras of eGFP+Apoe-/- and Apoe-/- mouse embryos, and random recombination of an SMCrestricted multi-color Confetti fluorescent transgene combined with PCSK9-induced hypercholesterolemia. Fibrous caps in aggregation chimeras were found constructed from large, endothelial-aligned layers of either eGFP or non-fluorescent SMCs indicating substantial clonal
expansion of few cells. Similarly, plaques in mice with SMC-restricted Confetti expression showed oligoclonal SMC populations with little intermixing between the progeny of different medial SMCs. Phenotypes comprised both ACTA2+ SMCs in the cap and heterogeneous ACTA2- SMC in the plaque interior, including chondroid-like cells and cells with intracellular lipid and crystalline
material. Fibrous cap SMCs were invariably arranged in endothelium-aligned clonal sheets confirming results in the aggregation chimeras. Analysis of the clonal structure showed that a low number of local medial SMCs partake in atherosclerosis and that single medial SMCs can produce several different SMC phenotypes in plaque. The combined results show that few medial SMCs proliferate to form the entire, phenotypically heterogeneous, plaque SMC population in murine atherosclerosis.