Abstract MP35: Single-cell Analysis Uncovers Multiple Adventitial Fibroblast Populations With Expression Of CAD GWAS Genes In Murine Atherosclerosis

Abstract

The arterial adventitia is a layer of cells outside the external lamina of blood vessels that contribute to the progression of coronary artery disease (CAD) like atherosclerosis. Adventitial fibroblasts are known regulators of vascular remodeling through their deposition of collagen fibrils around vessels during atherosclerotic lesion development. However, the molecular identity and function of the participating fibroblasts have not been well studied. We used single cell RNA sequencing (scRNA-seq) to characterize the transcriptome of adventitial fibroblasts and other cell types at multiple timepoints during atherogenesis in hyperlipidemic Ldlr knockout mice. Specifically, scRNA-seq was applied to Ldlr KO aortic adventitia after 0, 9, and 16 weeks of western diet (WD) feeding. Unbiased clustering analysis uncovered 9 different cell clusters, including 5 different fibroblast populations (Fibro1-5), and a single cluster each of macrophages, T cells, SMCs, and ECs. We observed that, as atherosclerosis progressed from 9 to 16 weeks of feedings, the proportion of total cells that were Fibro1, 3, and 4 decreased (33, 40, and 13%), while populations of Fibro2 and 5 slightly increased (13 and 18%). All of non-fibroblast populations (Macrophage, T cells, SMCs and ECs) increased from 9-16wks of diet. Next, we asked whether genes associated with coronary artery disease by human genome-wide association studies (GWAS) are expressed in different adventitial fibroblast clusters. We determined the expression of 266 genes implicated in CAD by GWAS and found 201 genes (76%) were expressed in adventitial cells at either/both 9 or 16wks. 34 genes displayed large changes in expression from 9 to 16wks. We identified five genes that were highly expressed in the adventitial Fibro5 cluster specifically, and additional other CAD GWAS genes specifically expressed in adventitial macrophages, SMCs, and ECs. In summary, we present here a cell atlas defined by scRNA-seq that reveals the heterogeneity amongst the fibroblasts in adventitial cells during atherogenesis. Additionally, we find that many CAD GWAS genes are expressed in adventitial cell populations, raising the intriguing possibility that CAD GWAS are identifying adventitial mechanisms that contribute to CAD.