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      Lipocalin 2 prevents intestinal inflammation by enhancing phagocytic bacterial clearance in macrophages

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          Abstract

          Lipocalin 2 (Lcn2), also called neutrophil gelatinase B-associated lipocalin (NGAL), is an anti-microbial peptide originally identified in neutrophil granules. Although Lcn2/NGAL expression is increased in the inflamed intestinal tissues of patients with inflammatory bowel disease, the role of Lcn2/NGAL in the development of intestinal inflammation remains unclear. Here we investigated the role of Lcn2/NGAL in intestinal inflammation using a spontaneous mouse colitis model, interleukin-10 knock out (IL-10 KO) mice. Lcn2 expression in the colonic tissues of IL-10 KO mice increased with the development of colitis. Lcn2/IL-10 double-KO mice showed a more rapid onset and development of colitis compared to IL-10 KO mice. Lcn2 enhanced phagocytic bacterial clearance in macrophages in vitro after infection with Escherichia coli. Transfer of Lcn2-repleted macrophages prevented the development of colitis in Lcn2/IL-10 double-KO mice in vivo. Our findings revealed that Lcn2 prevents the development of intestinal inflammation. One crucial factor seems to be the enhancement of phagocytic bacterial clearance in macrophages by Lcn2.

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          Most cited references 33

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          Lipocalin 2 mediates an innate immune response to bacterial infection by sequestrating iron.

          Although iron is required to sustain life, its free concentration and metabolism have to be tightly regulated. This is achieved through a variety of iron-binding proteins including transferrin and ferritin. During infection, bacteria acquire much of their iron from the host by synthesizing siderophores that scavenge iron and transport it into the pathogen. We recently demonstrated that enterochelin, a bacterial catecholate siderophore, binds to the host protein lipocalin 2 (ref. 5). Here, we show that this event is pivotal in the innate immune response to bacterial infection. Upon encountering invading bacteria the Toll-like receptors on immune cells stimulate the transcription, translation and secretion of lipocalin 2; secreted lipocalin 2 then limits bacterial growth by sequestrating the iron-laden siderophore. Our finding represents a new component of the innate immune system and the acute phase response to infection.
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            The neutrophil lipocalin NGAL is a bacteriostatic agent that interferes with siderophore-mediated iron acquisition.

            First identified as a neutrophil granule component, neutrophil gelatinase-associated lipocalin (NGAL; also called human neutrophil lipocalin, 24p3, uterocalin, or neu-related lipocalin) is a member of the lipocalin family of binding proteins. Putative NGAL ligands, including neutrophil chemotactic agents such as N-formylated tripeptides, have all been refuted by recent biochemical and structural results. NGAL has subsequently been implicated in diverse cellular processes, but without a characterized ligand, the molecular basis of these functions remained mysterious. Here we report that NGAL tightly binds bacterial catecholate-type ferric siderophores through a cyclically permuted, hybrid electrostatic/cation-pi interaction and is a potent bacteriostatic agent in iron-limiting conditions. We therefore propose that NGAL participates in the antibacterial iron depletion strategy of the innate immune system.
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              Iron and microbial infection.

              The use of iron as a cofactor in basic metabolic pathways is essential to both pathogenic microorganisms and their hosts. It is also a pivotal component of the innate immune response through its role in the generation of toxic oxygen and nitrogen intermediates. During evolution, the shared requirement of micro- and macroorganisms for this important nutrient has shaped the pathogen-host relationship. Here, we discuss how pathogens compete with the host for iron, and also how the host uses iron to counteract this threat.
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                Author and article information

                Journal
                Sci Rep
                Sci Rep
                Scientific Reports
                Nature Publishing Group
                2045-2322
                13 October 2016
                2016
                : 6
                Affiliations
                [1 ]Center for Advanced IBD Research and Treatment, Kitasato University Kitasato Institute Hospital, 5-9-1, Shirokane, Minato-ku, Tokyo , 108-8642, Japan
                [2 ]Department of Gastroenterology & Hepatology, Graduate School of Medicine, Kyoto University, 54 shogoin, Kawahara-cho, Sakyo-ku, Kyoto , 606-8397, Japan
                [3 ]School of Pharmaceutical Sciences, University of Shizuoka, 52-1, Yada, Suruga-ku, Shizuoka , 422-8526, Japan
                [4 ]Department of Gastroenterology and Hepatology, Sapporo Medical University School of Medicine, S-1, W-16, Chuo-ku, Sapporo , 060-8543, Japan.
                Author notes
                Article
                srep35014
                10.1038/srep35014
                5062163
                27734904
                Copyright © 2016, The Author(s)

                This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

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