BS31 VSMC contribution to neointimal lesions arises from the clonal expansion of few primed cells

In healthy blood vessels, vascular smooth muscle cells (VSMCs) exist in a contractile, quiescent state but can switch phenotype to activate proliferation, migration and remodelling of the extracellular matrix. Phenotypically switched VSMCs contribute most cells within neointimal lesions, characteristic of atherosclerosis and in-stent restenosis, diseases that underlie heart attack and stroke. Using multicolour ‘Confetti’ VSMC-specific lineage tracing in animal models of vascular disease, we showed that the extensive VSMC contribution to these lesions results from the clonal expansion of few cells. To understand how oligoclonal VSMC lesion contribution arises and to identify the signals activating VSMC proliferation in vivo, we used confocal microscopy to quantify VSMC clonal development over time in two models of vascular disease. We observed that the number and sizes of patches of clonally expanded VSMCs steadily increased, then plateaued post-injury. This suggests VSMC investment results from activation of a small number of VSMCs, rather than clonal competition following general VSMC activation. Selective VSMC activation in plaques was evidenced by the absence of plaques with high numbers of colours at any stage of plaque development. In both models, VSMC activation was associated with vascular regions displaying elastic lamina alterations, medial acellularity and immune cell recruitment, implicating these as proliferation-triggering cues. However, not all VSMCs in these regions formed patches, suggesting that VSMCs must be primed to respond. In culture, few VSMCs gave rise to patches, suggesting cell-autonomous activation. This work supports the targeting of primed VSMCs in the healthy vessel as a therapeutic strategy against vascular lesion development. Conflict of Interest None