Abstract 1043: Single-cell Characterization Of Mouse Aorta During Atherosclerosis Regression

Atherosclerosis is a cardiovascular disease characterized by the accumulation of fibro-fatty plaque in the arteries. Over half the cells in a mature atherosclerotic lesion are smooth muscle cells (SMCs) or SMC-derived cells (SDCs). SMCs can undergo a process called phenotypic switching, which involves dedifferentiation to an intermediate multipotent cell state, migration, and transdifferentiation into alternative cell types (SDCs). Increased SMC phenotypic switching is associated with worse atherosclerosis progression. However, little is known of the roles of SMCs and SDCs in atherosclerosis regression. We hypothesize that SDCs may promote plaque stability during atherosclerosis regression. In this study, we used an SMC lineage tracing mouse model (Ldlr–/–; LoxP-stop-LoxP-ZsGreen1+/-; Myh11-CreERT2+/-) that is limited to male mice. At 6 weeks of age, the mice were administered a tamoxifen diet for 1 week, followed by a week of chow diet. Mice were then fed a 16-week Western diet to induce atherosclerosis. We modeled lipid-lowering induced regression by switching to chow diet and administering HDAd-hLDLR. Mice were harvested at timepoints 0, 2, 5, 10, and 20 weeks. Arterial tissues, such as the aorta, brachiocephalic artery, and aortic root were used for histological characterization of disease and for single cell RNA-sequencing (scRNA-seq). The scRNA-seq data showed no major changes in SMC and SDC cell clusters, showing that our hypothesis was likely null. We noted an overall decrease in macrophages, and an increase in both of the two fibroblast clusters, which also had transcriptional signatures of increased proliferation and reduced apoptosis and senescence. Our histology data showed thicker fibrous caps and increased collagen, as expected in a regression model. Going forward, we will assess whether one or both fibroblast clusters are necessary for the stabilization of plaques during atherosclerosis regression.