Functional Phenotype and Ontogeny of Olfr2 Expressing Vascular Macrophages in Atherosclerotic Plaques

Abstract Olfactory receptor 2 (Olfr2) and its human ortholog OR6A2 have emerged as a critical modulator of inflammation, with its presence detected in approximately 30% of vascular macrophages and its depletion shown to reduce atherosclerosis in mice. Single-cell RNA sequencing identified several distinct subsets of macrophages in the atherosclerotic plaque. This study investigates the functional phenotype and ontogeny of Olfr2-expressing vascular macrophages. Olfr2+ macrophage number increased in response to a western diet (WD) in the aorta and they expressed a variety of pro-inflammatory cytokines, including Il1b, and Il6, as well as Ccl5, Cx3cl1, and Ccl22. By extracting differentially expressed genes from bulk RNA-seq data of Olfr2+ vs. Olfr2- vascular macrophages, we defined a signature that mapped with mouse plaque single-cell data of monocytes, aortic intima resident macrophages (MacAir) and Trem2-Gpnmb foamy macrophages. Similar results were found in human plaque, with monocytes and foamy macrophages being significantly enriched. Olfr2 expression also increased in oxLDL-mediated foamy macrophages in vitro. Adoptive transfer experiments confirmed that Olfr2+ macrophages are monocyte-derived, accumulate in the aortic plaque within 72 hours, and display enhanced proliferative potential. Collectively, our findings indicate that Olfr2 expression is boosted by diet in monocytes-derived foamy macrophage subsets that by sensing octanal promote inflammation and atherosclerosis.