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A7160 - Protective Functions of Siglec-E and Siglec-9 and Expression of Their Ligands in Mouse Airway Inflammation and Lung Emphysema
Author Block: Z. Chen1, F. Zhang1, H. Tang1, R. Porell2, R. L. Schnaar2, T. Kumagai3, M. Tiemeyer3, B. S. Bochner4, L. Zhou5, C. Fang1, T. Zheng1, Z. Zhu1; 1Yale University School of Medicine, New Haven, CT, United States, 2Johns Hopkins Sch of Med, Baltimore, MD, United States, 3CCRC, University of Georgia, Athens, GA, United States, 4Northwestern University, Chicago, IL, United States, 5Nanjing Medical University, Nanjing, China.
Sialic acid-binding Ig-like lectins E and 9 (Siglec-E in mice, Siglec-9 in humans) are expressed on neutrophils and monocytes and are implicated in regulation of inflammation and infection. However, the roles of Siglec-E and Siglec-9 and the expression of their specific glycan ligands in non-infectious inflammatory lung diseases, such as emphysema and COPD, are not known. We generated transgenic mice expressing human Siglec-9 and investigated its potential roles, compared to Siglec-E and determined the alterations in lung tissue ligands in lung inflammation and emphysema models. Siglec-9 transgenic (Tg) mice were generated using a BAC construct containing the human Siglec-9 promoter and genomic DNA. Western blot and flow cytometry confirmed that Siglec-9 expressing cells were predominantly Gr-1+ cells and some CD11b+ cells, as seen in humans. After back-crossing to the Siglec-EKO mice, Siglec-9Tg/Siglec-EKO mice (or Siglec-9Tg) were obtained and tested in LPS (5µg/mouse, i.t. 24hr) induced airway inflammation and neutrophil elastase (0.8U/mouse, i.t., 28d) induced emphysema models and compared with wild type (WT) and Siglec-EKO mice. Siglec-E and Siglec-9 specific glycan ligands in lung tissues were detected using Siglec-E-Fc and Siglec-9-Fc as overlay probes. Bronchoalveolar lavage and lung histology revealed that WT mice had a neutrophilic inflammatory response and emphysematous changes in the lung tissue. Siglec-EKO mice had significantly enhanced inflammation and emphysema with increased chord length. Citrullinated Histone H3, a neutrophil extracellular traps marker, was markedly increased in the lung tissue of Siglec-EKO mice by Western blot and immunofluorescence. In contrast, Siglec-9Tg mice showed inflammation and emphysema responses similar to those in WT mice, suggesting a restoration of Siglec-E function by Siglec-9 in the mouse lung. Analyses of ligand expression by overlaying Siglec-E-Fc and Siglec-9-Fc on lung tissue sections showed that in WT mouse lung, Siglec-E ligands and Siglec-9 ligands were expressed in airway and lung epithelial cells at baseline (PBS control) but were significantly increased in response to elastase. In Siglec-EKO lung, Siglec-E ligands and Siglec-9 ligands were strikingly increased at baseline but without further increase upon elastase stimulation. In Siglec-9Tg lung, the patterns of ligand expression were more similar to those in the Siglec-EKO lung. Thus, Siglec-E is protective in lung inflammation and emphysema; Siglec-9 substitutes for Siglec-E and restores anti-inflammatory functions in vivo; and Siglec-E and Siglec-9 ligands are altered in lung inflammation and emphysema. The interactions between Siglec-E and Siglec-9 and their ligands in inflammatory lung diseases provide opportunities to understand and modulate these diseases.