Hongmei Liu1, Yu Zheng2, Yingxian Zhang3, Jin Li1, Steve M Fernandes4, Dongfeng Zeng5, Xiaohui Li1, Ronald L Schnaar6, Yi Jia7. 1. Institute of Materia Medica and Department of Pharmaceutics, College of Pharmacy, Third Military Medical University, ChongQing 400038, China. 2. Department of Pharmacy, Hainan Western Central Hospital, Danzhou, Hainan 571799, China. 3. Department of Pharmacy, Third Affiliated Hospital, ChongQing Medical University, Chongqing 401120, China. 4. Department of Pharmacology and Molecular Sciences, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA. 5. Department of Haematology, Daping Hospital, Army Medical University, ChongQing, 400042, China. 6. Department of Pharmacology and Molecular Sciences, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA. Electronic address: Schnaar@jhu.edu. 7. Institute of Materia Medica and Department of Pharmaceutics, College of Pharmacy, Third Military Medical University, ChongQing 400038, China. Electronic address: jy@tmmu.edu.cn.
Abstract
AIMS: Siglec-E, the mouse ortholog of human Siglec-9, is an immunosuppressive cell surface receptor. Both Siglec-E and Siglec-9 are primarily found on neutrophils, macrophages, and monocytes. When Siglec-E binds to sialoglycan ligands in its extracellular environment, it halts the immune cells' inflammatory responses. In the present study, we aimed to investigate expression, mechanisms of action and regulation of Siglec-E ligands during vascular inflammation induced by E. coli lipopolysaccharides (LPS) in mouse aorta. METHODS: The distribution, molecular size and glycoprotein class of Siglec-E ligands on mouse aorta were determined, and the protein carrier of the ligands was identified. In vivo, the expression of Siglec-E ligands was detected after LPS treatment, with or without NF-κB inhibitor administration. In vitro, cultured primary mouse aortic endothelial cells (MAECs) were used to study changes in expression of Siglec-E ligands induced by LPS with or without NF-κB inhibitors. MAECs induced by LPS were co-cultured with macrophages and the effect of increased expression of Siglec-E ligands analyzed. RESULTS: Siglec-E ligands are O-linked sialoglycoproteins with molecular weights of 70-300 kDa and are distributed broadly on mouse aorta as well as on MAECs in vitro. In vivo, the expression of Siglec-E ligands was increased in mice aortas in response to LPS treatment in an NF-κB signaling pathway dependent manner. In MAECs, the expression of Siglec-E ligands was also increased by LPS via an NF-κB signaling pathway. Deleted in malignant brain tumors-1 was identified to be one of multiple protein carriers of Siglec-E ligands, and glycans of ligands involved in MAECs induced by LPS. Notably, co-incubation of macrophages with LPS-treated MAECs induced macrophage apoptosis and decreased macrophage phagocytosis, effects that were completely reversed by blocking Siglec-E binding to Siglec-E ligands. CONCLUSIONS: These data demonstrated that Siglec-E ligands were highly expressed in response to LPS-induced vascular inflammation and inhibited the immune response of macrophages, which may be a therapeutic strategy to interfere with vascular inflammation.
AIMS: Siglec-E, the mouse ortholog of humanSiglec-9, is an immunosuppressive cell surface receptor. Both Siglec-E and Siglec-9 are primarily found on neutrophils, macrophages, and monocytes. When Siglec-E binds to sialoglycan ligands in its extracellular environment, it halts the immune cells' inflammatory responses. In the present study, we aimed to investigate expression, mechanisms of action and regulation of Siglec-E ligands during vascular inflammation induced by E. coli lipopolysaccharides (LPS) in mouse aorta. METHODS: The distribution, molecular size and glycoprotein class of Siglec-E ligands on mouse aorta were determined, and the protein carrier of the ligands was identified. In vivo, the expression of Siglec-E ligands was detected after LPS treatment, with or without NF-κB inhibitor administration. In vitro, cultured primary mouse aortic endothelial cells (MAECs) were used to study changes in expression of Siglec-E ligands induced by LPS with or without NF-κB inhibitors. MAECs induced by LPS were co-cultured with macrophages and the effect of increased expression of Siglec-E ligands analyzed. RESULTS:Siglec-E ligands are O-linked sialoglycoproteins with molecular weights of 70-300 kDa and are distributed broadly on mouse aorta as well as on MAECs in vitro. In vivo, the expression of Siglec-E ligands was increased in mice aortas in response to LPS treatment in an NF-κB signaling pathway dependent manner. In MAECs, the expression of Siglec-E ligands was also increased by LPS via an NF-κB signaling pathway. Deleted in malignant brain tumors-1 was identified to be one of multiple protein carriers of Siglec-E ligands, and glycans of ligands involved in MAECs induced by LPS. Notably, co-incubation of macrophages with LPS-treated MAECs induced macrophage apoptosis and decreased macrophage phagocytosis, effects that were completely reversed by blocking Siglec-E binding to Siglec-E ligands. CONCLUSIONS: These data demonstrated that Siglec-E ligands were highly expressed in response to LPS-induced vascular inflammation and inhibited the immune response of macrophages, which may be a therapeutic strategy to interfere with vascular inflammation.