Division of Inflammation Biology, La Jolla Institute for Immunology, 9420 Athena Cir, La Jolla, CA 92037, USA.
Immunology Center of Georgia, Augusta University, 1410 Laney Walker Blvd, Augusta, GA 30912, USA.
Cardiovasc Res. 2024 Nov 5;120(13):1577-1589. doi: 10.1093/cvr/cvae153.
Olfactory receptor 2 (Olfr2) has been identified in a minimum of 30% of vascular macrophages, and its depletion was shown to reduce atherosclerosis progression. Mononuclear phagocytes, including monocytes and macrophages within the vessel wall, are major players in atherosclerosis. Single-cell RNA sequencing studies revealed that atherosclerotic artery walls encompass several monocytes and vascular macrophages, defining at least nine distinct subsets potentially serving diverse functions in disease progression. This study investigates the functional phenotype and ontogeny of Olfr2-expressing vascular macrophages in atherosclerosis.
Olfr2+ macrophages rapidly increase in Apoe-/- mice's aorta when fed a Western diet (WD). Mass cytometry showed that Olfr2+ cells are clustered within the CD64 high population and enriched for CD11c and Ccr2 markers. Olfr2+ macrophages express many pro-inflammatory cytokines, including Il1b, Il6, Il12, and Il23, and chemokines, including Ccl5, Cx3cl1, Cxcl9, and Ccl22. By extracting differentially expressed genes from bulk RNA sequencing (RNA-seq) of Olfr2+ vs. Olfr2- macrophages, we defined a signature that significantly mapped to single-cell data of plaque myeloid cells, including monocytes, subendothelial MacAir, and Trem2Gpnmb foamy macrophages. By adoptive transfer experiments, we identified that Olfr2 competent monocytes from CD45.1Apoe-/-Olfr2+/+ mice transferred into CD45.2Apoe-/-Olfr2-/- recipient mice fed WD for 12 weeks, accumulate in the atherosclerotic aorta wall already at 72 h, and differentiate in macrophages. Olfr2+ macrophages showed significantly increased BrdU incorporation compared to Olfr2- macrophages. Flow cytometry confirmed that at least 50% of aortic Olfr2+ macrophages are positive for BODIPY staining and have increased expression of both tumour necrosis factor and interleukin 6 compared to Olfr2- macrophages. Gene set enrichment analysis of the Olfr2+ macrophage signature revealed a similar enrichment pattern in human atherosclerotic plaques, particularly within foamy/TREM2hi-Mφ and monocytes.
In summary, we conclude that Olfr2+ macrophages in the aorta originate from monocytes and can accumulate at the early stages of disease progression. These cells can undergo differentiation into MacAir and Trem2Gpnmb foamy macrophages, exhibiting proliferative and pro-inflammatory potentials. This dynamic behaviour positions them as key influencers in shaping the myeloid landscape within the atherosclerotic plaque.
嗅觉受体 2（Olfr2）已在至少 30%的血管巨噬细胞中被鉴定出来，其耗竭被证明可以减少动脉粥样硬化的进展。单核吞噬细胞，包括血管壁内的单核细胞和巨噬细胞，是动脉粥样硬化的主要参与者。单细胞 RNA 测序研究表明，动脉粥样硬化的动脉壁包含多个单核细胞和血管巨噬细胞，定义了至少九个不同的亚群，这些亚群可能在疾病进展中具有不同的功能。本研究调查了动脉粥样硬化中表达 Olfr2 的血管巨噬细胞的功能表型和发生。
当 Apoe-/- 小鼠喂食西方饮食（WD）时，主动脉中的 Olfr2+巨噬细胞迅速增加。质谱流式细胞术显示，Olfr2+细胞在 CD64 高群体内聚集，并富集 CD11c 和 Ccr2 标志物。Olfr2+巨噬细胞表达许多促炎细胞因子，包括 Il1b、Il6、Il12 和 Il23，以及趋化因子，包括 Ccl5、Cx3cl1、Cxcl9 和 Ccl22。通过从 Olfr2+与 Olfr2-巨噬细胞的批量 RNA 测序（RNA-seq）中提取差异表达的基因，我们定义了一个显著映射到斑块髓样细胞单细胞数据的特征，包括单核细胞、亚内皮 MacAir 和 Trem2Gpnmb 泡沫巨噬细胞。通过过继转移实验，我们发现来自 CD45.1Apoe-/-Olfr2+/+ 小鼠的 Olfr2 功能齐全的单核细胞转移到 CD45.2Apoe-/-Olfr2-/- 受体小鼠中，在喂食 WD 的 12 周时已在动脉粥样硬化的主动脉壁中积累，并分化为巨噬细胞。与 Olfr2-巨噬细胞相比，Olfr2+巨噬细胞的 BrdU 掺入明显增加。流式细胞术证实，至少 50%的主动脉 Olfr2+巨噬细胞对 BODIPY 染色呈阳性，并且与 Olfr2-巨噬细胞相比，肿瘤坏死因子和白细胞介素 6 的表达均增加。Olfr2+巨噬细胞特征的基因集富集分析显示，人类动脉粥样硬化斑块中存在类似的富集模式，特别是在泡沫/TREM2hi-Mφ 和单核细胞中。
总之，我们的结论是，主动脉中的 Olfr2+巨噬细胞来源于单核细胞，并可以在疾病进展的早期阶段积累。这些细胞可以分化为 MacAir 和 Trem2Gpnmb 泡沫巨噬细胞，表现出增殖和促炎潜力。这种动态行为使它们成为塑造动脉粥样硬化斑块内髓样细胞景观的关键因素。
