Carotid plaque macrophage burden and inflammatory lipid-associated macrophage markers predict secondary major adverse cardiovascular events after endarterectomy

BACKGROUND AND AIMS: Atherosclerosis is a chronic lipid-driven inflammatory disease and one of the leading underlying causes of cardiovascular morbidity and mortality in Western society. Macrophages are key players in atherosclerotic development. Although the cellular composition of carotid atherosclerotic lesions has been determined, macrophage population definitions lack granularity and lineage data. Moreover, to date no direct link has been established between cellular content of atherosclerotic lesions and secondary clinical outcome. This study is aimed at characterization of atherosclerotic lesion macrophages and identification of plaque cell types and marker genes that predict the risk of secondary major adverse cardiovascular events in a clinical setting. METHODS: Single-cell RNA sequencing on blood and plaques from 46 carotid endarterectomy patients enrolled in the AtheroExpress cohort. Deconvolution was done on bulk transcriptome data from 656 AtheroExpress patients, and findings were validated in 82 patients enrolled in the Carotid Plaque Imaging Project. RESULTS: Four major archetypes of plaque macrophages were identified: inflammatory macrophages, lipid-associated macrophages (LAMs), tissue-resident-like LAMs, and inflammatory LAMs. Cellular trajectory and fate analyses revealed that these are derived from both classical and non-classical monocytes. Functionally, this study demonstrated the capacity of monocytes to differentiate into inflammatory LAMs via inflammatory- or resident-like LAM and LAM stages. Next, the AtheroExpress bulk RNA-seq cohort was deconvoluted. Macrophages were shown to be the only cell population significantly associated with both symptoms at time of surgery and increased risk of major adverse cardiovascular events during a 3-year follow-up period. Within the macrophage population, mostly LAM and inflammatory LAM foam cell markers such as PLIN2 and TREM1 were associated with an increased risk of major adverse cardiovascular events after 3-year follow-up. These associations were validated in the Carotid Plaque Imaging Project cohort. CONCLUSIONS: Together, these findings provide critical insights into the functional differences and origin of macrophage subpopulations in human atherosclerosis and show their clinical significance and risk prediction value in relation to future cardiovascular events.