Rationale

Hypercholesterolemia-driven atherosclerosis is a systemic and chronic inflammatory disease propagated in part by monocytes and macrophages. Yet, our knowledge on how transcriptional profiles of these cells change over time and in different tissues is limited. Spatio-temporal characterization of tissue macrophages during atherosclerosis disease progression will aid in screening for novel aortic macrophage- and disease stage-specific therapeutic targets.

Methods and Results

Apolipoprotein E knock-out (APOE-/-) mice were studied at baseline (without atherosclerosis), after 1 and 6 months of high-cholesterol diet feeding, representing early and advanced stages of atherosclerosis development, respectively.  For these disease stages, peripheral blood monocytes, aortic macrophages and peritoneal macrophages were retrieved from the same animals. Comparing three cell types at three time points, we were able to identify nearly 400 genes differentially (DEG) and mostly selectively regulated in aortic tissue macrophages as opposed to circulating monocytes and peritoneal macrophages. More than 60% of DEG were upregulated in aortic macrophages at disease initiation and remained significantly overexpressed at 6 months of high-cholesterol diet feeding compared to baseline. Gpnmb was the only gene in aortic macrophages, which expression levels continuously increased from baseline to early and from early to advanced disease stages, specifically enriched within foam cell macrophages according to single cell RNA sequencing analysis of murine and human data sets. 

Conclusions

Using our novel gene expression matrix, we identified uniquely regulated genes in atheromatous aortic macrophages, associated biological processes linked to atheroma formation and progression and their regulation patterns. Our results may support the identification of promising macrophage-directed therapeutic targets at specific disease stages.