BACKGROUND & AIMS
Lipocalin 2 (Lcn2) is a multifunctional innate immune protein whose expression closely correlates with extent of intestinal inflammation. However, whether Lcn2 plays a role in the pathogenesis of gut inflammation is unknown. Herein, we investigated the extent to which Lcn2 regulates inflammation and gut bacterial dysbiosis in mouse models of IBD.
METHODS
Lcn2 expression was monitored in murine colitis models and upon microbiota ablation/restoration. WT and Lcn2 knockout (Lcn2KO) mice were analyzed for gut bacterial load, composition by 16S rRNA gene pyrosequencing and, their colitogenic potential by co-housing with Il-10KO mice. Acute (dextran sodium sulfate) and chronic (IL-10R neutralization and T-cell adoptive transfer) colitis was induced in WT and Lcn2KO mice with or without antibiotics.
RESULTS
Lcn2 expression was dramatically induced upon inflammation and was dependent upon presence of a gut microbiota and MyD88 signaling. Use of bone-marrow chimeric mice revealed non-immune cells are the major contributors of circulating Lcn2. Lcn2KO mice exhibited elevated levels of entA-expressing gut bacteria burden and, moreover, a broadly distinct bacterial community relative to WT littermates. Lcn2KO mice developed highly colitogenic T-cells and exhibited exacerbated colitis upon exposure to DSS or neutralization of IL-10. Such exacerbated colitis could be prevented by antibiotic treatment. Moreover, exposure to the microbiota of Lcn2KO mice, via cohousing, resulted in severe colitis in Il-10KO mice.
CONCLUSION
Lcn2 is a bacterially-induced, MyD88-dependent, protein that play an important role in gut homeostasis and a pivotal role upon challenge. Hence, therapeutic manipulation of Lcn2 levels may provide a strategy to help manage diseases driven by alteration of the gut microbiota.
Neutrophils are the primary immune cells that respond to inflammation and combat microbial transgression. In order to thrive, the bacteria residing in their mammalian host have to withstand the anti-bactericidal responses of neutrophils. We report that enterobactin (Ent), a catecholate siderophore expressed by E. coli, inhibited PMA-induced generation of reactive oxygen species (ROS) and neutrophil extracellular traps (NETs) in both mouse and human neutrophils. Ent also impaired the degranulation of primary granules, inhibited phagocytosis and bactericidal activity of neutrophils, but without affecting their migration and chemotaxis. Molecular analysis revealed that Ent can chelate intracellular labile iron that is required for neutrophil oxidative responses. Other siderophores (pyoverdine, ferrichrome, deferoxamine) likewise inhibited ROS and NETs in neutrophils, thus indicating that the chelation of iron may largely explain their inhibitory effects. To counter iron theft by Ent, neutrophils rely on the siderophore-binding protein lipocalin 2 (Lcn2) in a ‘tug-of-war’ for iron. The inhibition of neutrophil ROS and NETs by Ent was augmented in Lcn2-deficient neutrophils when compared to WT neutrophils, but rescued by the exogenous addition of recombinant Lcn2. Taken together, our findings illustrate the novel concept that microbial siderophore’s iron scavenging property may serve as an anti-radical defense system, that neutralizes immune functions of neutrophils.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.