Disturbed Flow Induces Reprogramming of Endothelial Cells to Immune-like and Foam Cells under Hypercholesterolemia during Atherogenesis

Atherosclerosis occurs preferentially in the arteries exposed to disturbed flow (d-flow), while the stable flow (s-flow) regions are protected even under hypercholesterolemic conditions. We previously showed that d-flow alone triggers flow-induced reprogramming of endothelial cells (FIRE), including inflammation and endothelial-to-mesenchymal transition (EndMT), while initiating a partial endothelial-to-immune-cell-like transition (EndIT). Now, to compare the effects of d-flow alone, hypercholesterolemia alone, and d-flow under hypercholesterolemia, we performed an extensive single-cell RNA sequencing study, which consisted of 98,553 single cells from 95 mice with 25 unique cell clusters: 5 EC, 3 vascular smooth muscle cell, 5 macrophage, and additional fibroblast, T cell, natural killer cell, dendritic cell, neutrophil, and B cell clusters. We found that healthy ECs transitioned to proinflammatory/angiogenic and EndMT by d-flow. Our scRNA-seq analyses showed that d-flow under hypercholesterolemia transitioned healthy ECs to full EndIT and, more surprisingly, foam cells (EndFT). Further, EC-derived foam cells shared remarkably similar transcriptomic profiles with foam cells derived from smooth muscle cells and macrophages.