Abstract Tu0032: Olfactory Receptor 2 Signaling in Monocytes and Macrophages Facilitates Chemotactic Migration in Atherosclerotic Aorta

Atherosclerosis is an inflammatory disease of the arterial wall initiated by monocyte recruitment and macrophage (Mφ) function. Human and mouse vascular macrophages, mouse bone marrow-derived macrophages (BMDMs), and monocytes express several Olfactory Receptors (ORs), including Olfr2 and its human orthologue OR6A2. Ligation of Olfr2 and OR6A2 with their ligand Octanal activates the NLRP3 inflammasome pathway while knocking out (KO) Olfr2 in mice reduces atherosclerosis progression in vivo. Octanal, a product of lipid peroxidation, is proposed to derive from endothelial dysfunction (ED), which leads to atherosclerosis initiation. Recently, we identified Olfr2/OR6A2 protein expression in about 20% of monocytes, with expression increasing in disease states in humans and mice. However, the role of Olfr2 in monocytes and what controls its expression in the diseased condition is unknown. Interestingly, competitive adoptive transfer experiments with labeled WT and Olfr2 KO bone marrow monocytes injected into CD45.1 Apoe KO mice, revealed that WT monocytes were significantly enriched in the aorta compared to Olfr2 KO monocytes and could differentiate into Olfr2+ macrophages. To address the pathway driving this phenotype, we performed Bulk RNA sequencing on WT and Olfr2 KO bone marrow monocytes treated or untreated with LPS, Octanal, or both to address the pathway driving this phenotype. Data analysis showed significant differences, especially in the LPS-Octanal group, with interleukin signaling response pathways significantly modulated in WT and not in the Olfr2 KO. In vitro, Bone Marrow Derived Macrophages (BMDMs) significantly migrate in response to octanal, a response completely ablated in Olfr2 KO BMDMs. We verified this further with Raw246 and THP1 cell lines. We also found that Pertussis Toxin, a multi-subunit protein toxin and an inhibitor of Gai protein, blocks octanal-induced BMDMs migration. This suggests that Olfr2 could bind to both GaS and GaI proteins after Octanal stimulation. Overall, these findings reveal Olfr2 as a previously unrecognized chemotactic receptor in monocytes and macrophages, highlighting its potential role in directing immune cell migration within the atherosclerotic aorta. This discovery opens promising new avenues for therapeutic strategies aimed at modulating monocyte trafficking and inflammation in atherosclerosis.