Microbiota-inducible Innate Immune, Siderophore Binding Protein Lipocalin 2 is Critical for Intestinal Homeostasis

CD4+ T Cell-Derived NGAL Modifies the Outcome of Ischemic Acute Kidney Injury

CD4⁺ T cells mediate the pathogenesis of ischemic and nephrotoxic acute kidney injury (AKI). However, the underlying mechanisms of CD4⁺ T cell-mediated pathogenesis are largely unknown. We therefore conducted unbiased RNA-sequencing to discover novel mechanistic pathways of kidney CD4⁺ T cells after ischemia compared with normal mouse kidney. Unexpectedly, the lipocalin-2 (Lcn2) gene, which encodes neutrophil gelatinase-associated lipocalin (NGAL) had the highest fold increase (∼60). The NGAL increase in CD4⁺ T cells during AKI was confirmed at the mRNA level with quantitative real-time PCR and at the protein level with ELISA. NGAL is a potential biomarker for the early detection of AKI and has multiple potential biological functions. However, the role of NGAL produced by CD4⁺ T cells is not known. We found that ischemic AKI in NGAL knockout (KO) mice had worse renal outcomes compared with wild-type (WT) mice. Adoptive transfer of NGAL-deficient CD4⁺ T cells from NGAL KO mice into CD4 KO or WT mice led to worse renal function than transfer of WT CD4⁺ T cells. In vitro-simulated ischemia/reperfusion showed that NGAL-deficient CD4⁺ T cells express higher levels of IFN-γ mRNA compared with WT CD4⁺ T cells. In vitro differentiation of naive CD4⁺ T cells to Th17, Th1, and Th2 cells led to significant increase in Lcn2 expression. Human kidney CD4⁺ T cell NGAL also increased significantly after ischemia. These results demonstrate an important role for CD4⁺ T cell NGAL as a mechanism by which CD4⁺ T cells mediate AKI and extend the importance of NGAL in AKI beyond diagnostics.

Lipocalin 2 Protects Against Escherichia coli Infection by Modulating Neutrophil and Macrophage Function

Lipocalin 2 (Lcn2) is an essential component of the antimicrobial innate immune system. It attenuates bacterial growth by binding and sequestering the iron-scavenging siderophores to prevent bacterial iron acquisition. Whereas, the ability of Lcn2 to sequester iron is well-described, the role of Lcn2 in regulating immune cells during bacterial infection remains unclear. In this study, we showed that upon infection with Escherichia coli (O157:H7), Lcn2-deficient (Lcn2 ^-/-) mice carried more bacteria in blood and liver, and the acute-phase sera lost their antibacterial activity in vitro. Neutrophils from Lcn2 ^-/- mice were defective in homeostasis and morphological development. E. coli O157:H7 infection of Lcn2 ^-/- mice resulted in a reduced neutrophil migration capacity, with 30% reduction of extravasated neutrophils, and impaired chemotaxis, as shown by a reduction in the secretion of chemoattractants, such as tumor necrosis factor (TNF)-α, monocyte chemoattractant protein (MCP)-1, and macrophage inflammatory protein (MIP)-2, which are instrumental in eliciting a neutrophil response. We also found that some secreted cytokines [interleukin (IL)-6, IL-1β, and TNF-α] were decreased. Transcripts of inflammatory cytokines (IL-6, IL-1β, TNF-α, and IL-10), chemokines (MIP-2 and MCP-1), and iNOS production were all strongly repressed in Lcn2 ^-/- macrophages. Furthermore, Lcn2 could induce the production of chemokines and promote the migration and phagocytosis of macrophages. Thus, Lcn2 deficiency could impair the migration and chemotaxis ability of neutrophils and disturb the normal secretion of inflammatory cytokines of macrophages. Therefore, the heightened sensitivity of Lcn2 ^-/- mice to E. coli O157:H7 is not only due to the antibacterial function of Lcn2 but also a consequence of impaired functions of immune cells, including neutrophils and macrophages.

Intestinal SIRT1 Deficiency Protects Mice from Ethanol-Induced Liver Injury by Mitigating Ferroptosis

Aberrant liver sirtuin 1 (SIRT1), a mammalian NAD⁺-dependent protein deacetylase, is implicated in the pathogenesis of alcoholic liver disease (ALD). However, the role of intestinal SIRT1 in ALD is presently unknown. This study investigated the involvement of intestine-specific SIRT1 in ethanol-induced liver dysfunction in mice. Ethanol feeding studies were performed on knockout mice with intestinal-specific SIRT1 deletion [SIRT1i knockout (KO)] and flox control [wild-type (WT)] mice with a chronic-plus-binge ethanol feeding protocol. After ethanol administration, hepatic inflammation and liver injury were substantially attenuated in the SIRT1iKO mice compared with the WT mice, suggesting that intestinal SIRT1 played a detrimental role in the ethanol-induced liver injury. Mechanistically, the hepatic protective effect of intestinal SIRT1 deficiency was attributable to ameliorated dysfunctional iron metabolism, increased hepatic glutathione contents, and attenuated lipid peroxidation, along with inhibition of a panel of genes implicated in the ferroptosis process in the livers of ethanol-fed mice. This study demonstrates that ablation of intestinal SIRT1 protected mice from the ethanol-induced inflammation and liver damage. The protective effects of intestinal SIRT1 deficiency are mediated, at least partially, by mitigating hepatic ferroptosis. Targeting intestinal SIRT1 or dampening hepatic ferroptosis signaling may have therapeutic potential for ALD in humans.

Microbiota fermentation-NLRP3 axis shapes the impact of dietary fibres on intestinal inflammation

OBJECTIVE

Diets rich in fermentable fibres provide an array of health benefits; however, many patients with IBD report poor tolerance to fermentable fibre-rich foods. Intervention studies with dietary fibres in murine models of colonic inflammation have yielded conflicting results on whether fibres ameliorate or exacerbate IBD. Herein, we examined how replacing the insoluble fibre, cellulose, with the fermentable fibres, inulin or pectin, impacted murine colitis resulting from immune dysregulation via inhibition of interleukin (IL)-10 signalling and/or innate immune deficiency (Tlr5KO).

DESIGN

Mice were fed with diet containing either cellulose, inulin or pectin and subjected to weekly injections of an IL-10 receptor (αIL-10R) neutralising antibody. Colitis development was examined by serological, biochemical, histological and immunological parameters.

RESULTS

Inulin potentiated the severity of αIL10R-induced colitis, while pectin ameliorated the disease. Such exacerbation of colitis following inulin feeding was associated with enrichment of butyrate-producing bacteria and elevated levels of caecal butyrate. Blockade of butyrate production by either metronidazole or hops β-acids ameliorated colitis severity in inulin-fed mice, whereas augmenting caecal butyrate via tributyrin increased colitis severity in cellulose containing diet-fed mice. Elevated butyrate levels were associated with increased IL-1β activity, while inhibition of the NOD-like receptor protein 3 by genetic, pharmacologic or dietary means markedly reduced colitis.

CONCLUSION

These results not only support the notion that fermentable fibres have the potential to ameliorate colitis but also caution that, in some contexts, prebiotic fibres can lead to gut dysbiosis and surfeit colonic butyrate that might exacerbate IBD.

Functions and regulation of lipocalin-2 in gut-origin sepsis: a narrative review

Lipocalin-2 (Lcn2), an innate immune protein, has come to be recognized for its roles in iron homeostasis, infection, and inflammation. In this narrative review, we provide a comprehensive description based on currently available evidence of the clinical implications of Lcn2 and its therapeutic potency in gut-origin sepsis. Lcn2 appears to mitigate gut barrier injury via maintaining homeostasis of the microbiota and exerting antioxidant strategy, as well as by deactivating macrophages and inducing immune cell apoptosis to terminate systemic hyper-inflammation. We propose that development of a therapeutic strategy targeting lipocalin-2 could be highly promising in the management of gut-origin sepsis.

Interleukin (IL)-22 from IL-20 Subfamily of Cytokines Induces Colonic Epithelial Cell Proliferation Predominantly through ERK1/2 Pathway

The interleukin (IL)-20 subfamily of cytokines consists of IL-19, IL-20, IL-22, IL-24, and IL-26, and the expression of IL-20, IL-22, and IL-24 is reported to be higher in the colon of patients with ulcerative colitis. Although the receptors for these cytokines are highly expressed in the colon epithelium, their effects on epithelial renewal are not clearly understood. This study evaluated the effects of IL-20, IL-22, and IL-24 in epithelial renewal using the LS174T human colon cancer epithelial cell line. LS174T cells were treated with IL-20, IL-22, and IL-24 (25, 50, and 100 ng/mL) and a live-cell imaging system was used to evaluate the effects on cell proliferation. Following treatment, the signaling pathways contributing to cell proliferation were investigated through Western blotting in LS174T cells and downstream transcriptional changes through qRT-PCR in LS174T cells, and RNA-Seq in primary murine intestinal epithelial cells. Our results demonstrated that only IL-22 promoted LS174T cell proliferation, mediated via extracellular-signal-regulated kinase (ERK)1/2-mediated downstream regulation of p90RSK, c-Jun, and transcriptional changes of TRIM15 and STOM. IL-22 also promoted expression of ERK1/2-independent genes such as DDR2, LCN2, and LRG1, which are known to be involved in cell proliferation and migration. This study suggests that IL-22 induces cell proliferation in highly proliferative cells such as intestinal epithelial cells.

Lipocalin-2 levels in acute and chronic graft-versus-host disease following allogeneic hematopoietic stem cell transplantation

Lipocalin-2 (LCN2) is an immunomodulatory protein holding major metabolic and immune functions. It is involved in several inflammatory processes and induced by cytokines of the interleukin-1 family known as contributors to the morbidity in graft-versus-host disease (GVHD) following hematopoietic stem cell transplantation (HSCT). The possible role of LCN2 in predicting outcome and course of illness has never been elucidated in patients undergoing HSCT for hematologic malignancies. We conducted a prospective cohort study including 40 patients following autologous or allogeneic HSCT by collecting plasma samples at seven time points with respect to GVHD, relapse, and outcome. LCN2 levels were significantly increased in acute patients with GVHD compared with autologous and healthy controls (125.7 ng/mL vs. 65.9 and 71.4 ng/mL) and correlated with its severity. Similarly, LCN2 levels were significantly elevated in chronic GHVD compared with autologous and healthy controls (295.0 ng/mL vs. 54.9 and 76.5 ng/mL). Moreover, LCN2 correlated with mortality. The suspected role of LCN2 as a predictive parameter for outcome and prognosis needs to be further investigated.

Lipocalin 24p3 Induction in Colitis Adversely Affects Inflammation and Contributes to Mortality

Recognition of microorganism associated molecular patterns by epithelial cells elicits signaling cascades resulting in the production of host defense proteins. Lipocalin 24p3 is purported to be one such protein. 24p3 binds prokaryotic and eukaryotic siderophores and by sequestering iron laden bacterial siderophores it was believed to restrict bacterial replication. As such mice deficient for 24p3 are susceptible to systemic infections. However, it is not clear whether deficiency of 24p3 on the gut mucosa contributes to inflammation. In line with 24p3's function as a bacteriostat, it would be reasonable to assume that deficiencies in the control of intestinal flora from 24p3 absence play a role in inflammatory intestinal diseases. Surprisingly, we show 24p3 is a contributor of inflammation and 24p3 deficiency protects mice from dextran sodium sulfate (DSS)-induced colitis. 24p3 was found to be a negative regulator of platelet-derived growth factor (PDGF), which helps maintain the integrity of the gut mucosa. Neutralization of PDGF-BB abrogated resistance of 24p3 null mice to DSS confirming the direct link between 24p3 and PDGF-BB. Finally, iron handling in wild-type and 24p3-null mice upon DSS treatment also differed. In summary, differential iron levels and enhanced expression of PDGF-BB in 24p3 null mice confers resistance to DSS.

Innate lymphoid cell type 3-derived interleukin-22 boosts lipocalin-2 production in intestinal epithelial cells via synergy between STAT3 and NF-κB

Escherichia coli and Klebsiella pneumoniae are opportunistic pathogens that are commonly associated with infections at mucosal surfaces, such as the lung or the gut. The host response against these types of infections includes the release of epithelial-derived antimicrobial factors such as lipocalin-2 (LCN-2), a protein that specifically inhibits the iron acquisition of Enterobacteriaceae by binding and neutralizing the bacterial iron-scavenging molecule enterobactin. Regulation of epithelial antimicrobial responses, including the release of LCN-2, has previously been shown to depend on IL-22, a cytokine produced by innate lymphoid cells type 3 (ILC3) during Enterobacteriaceae infections. However, much remains unknown about the extent to which antimicrobial responses are regulated by IL-22 and how IL-22 regulates the expression and production of LCN-2 in intestinal epithelial cells (IECs). Our study demonstrates how IL-22-induced activation of STAT3 synergizes with NF-κB-activating cytokines to enhance LCN-2 expression in human IECs and elucidates how ILC3 are involved in LCN-2-mediated host defense against Enterobacteriaceae. Together, these results provide new insight into the role of ILC3 in regulating LCN-2 expression in human IECs and could prove useful in future studies aimed at understanding the host response against Enterobacteriaceae as well as for the development of antimicrobial therapies against Enterobacteriaceae-related infections.

G.I. pros: Antimicrobial defense in the gastrointestinal tract

The gastrointestinal tract is a complex environment in which the host immune system interacts with a diverse array of microorganisms, both symbiotic and pathogenic. As such, mobilizing a rapid and appropriate antimicrobial response depending on the nature of each stimulus is crucial for maintaining the balance between homeostasis and inflammation in the gut. Here we focus on the mechanisms by which intestinal antimicrobial peptides regulate microbial communities during dysbiosis and infection. We also discuss classes of bacterial peptides that contribute to reducing enteric pathogen outgrowth. This review aims to provide a comprehensive overview on the interplay of diverse antimicrobial responses with enteric pathogens and the gut microbiota.

Pathobiont release from dysbiotic gut microbiota biofilms in intestinal inflammatory diseases: a role for iron?

Gut microbiota interacting with an intact mucosal surface are key to the maintenance of homeostasis and health. This review discusses the current state of knowledge of the biofilm mode of growth of these microbiota communities, and how in turn their disruptions may cause disease. Beyond alterations of relative microbial abundance and diversity, the aim of the review is to focus on the disruptions of the microbiota biofilm structure and function, the dispersion of commensal bacteria, and the mechanisms whereby these dispersed commensals may become pathobionts. Recent findings have linked iron acquisition to the expression of virulence factors in gut commensals that have become pathobionts. Causal studies are emerging, and mechanisms common to enteropathogen-induced disruptions, as well as those reported for Inflammatory Bowel Disease and colo-rectal cancer are used as examples to illustrate the great translational potential of such research. These new observations shed new light on our attempts to develop new therapies that are able to protect and restore gut microbiota homeostasis in the many disease conditions that have been linked to microbiota dysbiosis.

NOX1-derived ROS drive the expression of Lipocalin-2 in colonic epithelial cells in inflammatory conditions

Inflammatory bowel disease (IBD) is characterized by severe and recurrent inflammation of the gastrointestinal tract, associated with altered patterns of cytokine synthesis, excessive reactive oxygen species (ROS) production, and high levels of the innate immune protein, lipocalin-2 (LCN-2), in the mucosa. The major source of ROS in intestinal epithelial cells is the NADPH oxidase NOX1, which consists of the transmembrane proteins, NOX1 and p22^PHOX, and the cytosolic proteins, NOXO1, NOXA1, and Rac1. Here, we investigated whether NOX1 activation and ROS production induced by key inflammatory cytokines in IBD causally affects LCN-2 production in colonic epithelial cells. We found that the combination of TNFα and IL-17 induced a dramatic upregulation of NOXO1 expression that was dependent on the activation of p38MAPK and JNK1/2, and resulted into an increase of NOX1 activity and ROS production. NOX1-derived ROS drive the expression of LCN-2 by controlling the expression of IκBζ, a master inducer of LCN-2. Furthermore, LCN-2 production and colon damage were decreased in NOX1-deficient mice during TNBS-induced colitis. Finally, analyses of biopsies from patients with Crohn's disease showed increased JNK1/2 activation, and NOXO1 and LCN-2 expression. Therefore, NOX1 might play a key role in mucosal immunity and inflammation by controlling LCN-2 expression.

Lipocalin-2 Functions as Inhibitor of Innate Resistance to Mycobacterium tuberculosis

Lipocalin-2 is a constituent of the neutrophil secondary granules and is expressed de novo by macrophages and epithelium in response to inflammation. Lipocalin-2 acts in a bacteriostatic fashion by binding iron-loaded siderophores required for bacterial growth. Mycobacterium tuberculosis (M.tb) produces siderophores that can be bound by lipocalin-2. The impact of lipocalin-2 in the innate immune response toward extracellular bacteria has been established whereas the effect on intracellular bacteria, such as M.tb, is less well-described. Here we show that lipocalin-2 surprisingly confers a growth advantage on M.tb in the early stages of infection (3 weeks post-challenge). Using mixed bone marrow chimeras, we demonstrate that lipocalin-2 derived from granulocytes, but not from epithelia and macrophages, leads to increased susceptibility to M.tb infection. In contrast, lipocalin-2 is not observed to promote mycobacterial growth at later stages of M.tb infection. We demonstrate co-localization of granulocytes and mycobacteria within the nascent granulomas at week 3 post-challenge, but not in the consolidated granulomas at week 5. We hypothesize that neutrophil-derived lipocalin-2 acts to supply a source of iron to M.tb in infected macrophages within the immature granuloma, thereby facilitating mycobacterial growth.

A bacterial immunomodulatory protein with lipocalin-like domains facilitates host-bacteria mutualism in larval zebrafish

Stable mutualism between a host and its resident bacteria requires a moderated immune response to control bacterial population size without eliciting excessive inflammation that could harm both partners. Little is known about the specific molecular mechanisms utilized by bacterial mutualists to temper their hosts' responses and protect themselves from aggressive immune attack. Using a gnotobiotic larval zebrafish model, we identified an Aeromonas secreted immunomodulatory protein, AimA. AimA is required during colonization to prevent intestinal inflammation that simultaneously compromises both bacterial and host survival. Administration of exogenous AimA prevents excessive intestinal neutrophil accumulation and protects against septic shock in models of both bacterially and chemically induced intestinal inflammation. We determined the molecular structure of AimA, which revealed two related calycin-like domains with structural similarity to the mammalian immune modulatory protein, lipocalin-2. As a secreted bacterial protein required by both partners for optimal fitness, AimA is an exemplar bacterial mutualism factor.

Expression of neutrophil gelatinase-associated lipocalin (NGAL) in the gut in Crohn's disease

The antimicrobial glycoprotein neutrophil gelatinase-associated lipocalin (NGAL) is strongly expressed in several infectious, inflammatory and malignant disorders, among these inflammatory bowel disease (IBD). Fecal and serum NGAL is elevated during active IBD and we have recently shown that fecal NGAL is a novel biomarker for IBD with a test performance comparable to the established fecal biomarker calprotectin. This study examines expression of NGAL in the healthy gut and in Crohn’s disease (CD), with emphasis on the previously unexplored small intestine. Pinch biopsies were taken from active and inactive CD in jejunum, ileum and colon and from the same sites in healthy controls. Microarray gene expression showed that the NGAL gene, LCN2, was the second most upregulated among 1820 differentially expressed genes in terminal ileum comparing active CD and controls (FC 5.86, p = 0.027). Based on immunohistochemistry and in situ hybridization findings, this upregulation most likely represented increased expression in epithelial cells. Double immunofluorescence showed NGAL expression in 49% (range 19–70) of Paneth cells (PCs) in control ileum with no change during inflammation. In healthy jejunum, the NGAL expression in PCs was weak to none but markedly increased during active CD. We further found NGAL also in metaplastic PCs in colon. Finally, we show for the first time that NGAL is expressed in enteroendocrine cells in small intestine as well as in colon.

Interleukin 1α-Deficient Mice Have an Altered Gut Microbiota Leading to Protection from Dextran Sodium Sulfate-Induced Colitis

Here, we show a connection between IL-1α expression, microbiota composition, and clinical outcomes of DSS-induced colitis. Specifically, we show that the mild colitis symptoms seen in IL-1α-deficient mice following administration of DSS are correlated with the unique gut microbiota compositions of the mice. However, when these mice are exposed to WT microbiota by cohousing, their gut microbiota composition returns to resemble that of WT mice, and their disease severity increases significantly. As inflammatory bowel diseases are such common diseases, with limited effective treatments to date, there is a great need to better understand the interactions between microbiota composition, the immune system, and colitis. This study shows correlation between microbiota composition and DSS resistance; it may potentially lead to the development of improved probiotics for IBD treatment.

Inflammatory bowel diseases (IBD) are a group of chronic inflammatory disorders of the intestine, with as-yet-unclear etiologies, affecting over a million people in the United States alone. With the emergence of microbiome research, numerous studies have shown a connection between shifts in the gut microbiota composition (dysbiosis) and patterns of IBD development. In a previous study, we showed that interleukin 1α (IL-1α) deficiency in IL-1α knockout (KO) mice results in moderate dextran sodium sulfate (DSS)-induced colitis compared to that of wild-type (WT) mice, characterized by reduced inflammation and complete healing, as shown by parameters of weight loss, disease activity index (DAI) score, histology, and cytokine expression. In this study, we tested whether the protective effects of IL-1α deficiency on DSS-induced colitis correlate with changes in the gut microbiota and whether manipulation of the microbiota by cohousing can alter patterns of colon inflammation. We analyzed the gut microbiota composition in both control (WT) and IL-1α KO mice under steady-state homeostasis, during acute DSS-induced colitis, and after recovery using 16S rRNA next-generation sequencing. Additionally, we performed cohousing of both mouse groups and tested the effects on the microbiota and clinical outcomes. We demonstrate that host-derived IL-1α has a clear influence on gut microbiota composition, as well as on severity of DSS-induced acute colon inflammation. Cohousing both successfully changed the gut microbiota composition and increased the disease severity of IL-1α-deficient mice to levels similar to those of WT mice. This study shows a strong and novel correlation between IL-1α expression, microbiota composition, and clinical outcomes of DSS-induced colitis.

IMPORTANCE Here, we show a connection between IL-1α expression, microbiota composition, and clinical outcomes of DSS-induced colitis. Specifically, we show that the mild colitis symptoms seen in IL-1α-deficient mice following administration of DSS are correlated with the unique gut microbiota compositions of the mice. However, when these mice are exposed to WT microbiota by cohousing, their gut microbiota composition returns to resemble that of WT mice, and their disease severity increases significantly. As inflammatory bowel diseases are such common diseases, with limited effective treatments to date, there is a great need to better understand the interactions between microbiota composition, the immune system, and colitis. This study shows correlation between microbiota composition and DSS resistance; it may potentially lead to the development of improved probiotics for IBD treatment.

Transcriptomic and Proteomic Profiling Revealed High Proportions of Odorant Binding and Antimicrobial Defense Proteins in Olfactory Tissues of the House Mouse

Mammalian olfaction depends on chemosensory neurons of the main olfactory epithelia (MOE), and/or of the accessory olfactory epithelia in the vomeronasal organ (VNO). Thus, we have generated the VNO and MOE transcriptomes and the nasal cavity proteome of the house mouse, Mus musculus musculus. Both transcriptomes had low levels of sexual dimorphisms, while the soluble proteome of the nasal cavity revealed high levels of sexual dimorphism similar to that previously reported in tears and saliva. Due to low levels of sexual dimorphism in the olfactory receptors in MOE and VNO, the sex-specific sensing seems less likely to be dependent on receptor repertoires. However, olfaction may also depend on a continuous removal of background compounds from the sites of detection. Odorant binding proteins (OBPs) are thought to be involved in this process and in our study Obp transcripts were most expressed along other lipocalins (e.g., Lcn13, Lcn14) and antimicrobial proteins. At the level of proteome, OBPs were highly abundant with only few being sexually dimorphic. We have, however, detected the major urinary proteins MUP4 and MUP5 in males and females and the male-biased central/group-B MUPs that were thought to be abundant mainly in the urine. The exocrine gland-secreted peptides ESP1 and ESP22 were male-biased but not male-specific in the nose. For the first time, we demonstrate that the expression of nasal lipocalins correlates with antimicrobial proteins thus suggesting that their individual variation may be linked to evolvable mechanisms that regulate natural microbiota and pathogens that regularly enter the body along the ‘eyes-nose-oral cavity’ axis.

Novel insights into microbiome in colitis and colorectal cancer

PURPOSE OF REVIEW

Microbiota is a major player in the pathogenesis of inflammatory bowel diseases (IBD) and colorectal cancer (CRC). Here, we summarize the key advances achieved in the past 18 months (ending June 2017) toward a better understanding of the role of microbiota in colitis and CRC development.

RECENT FINDINGS

Accumulating evidence shows the essential role of intestinal barrier function (e.g. mucus, IgA, LCN2, LYPD8) in protecting against bacteria-induced inflammation and tumor development. Numerous signaling pathways (e.g. TLRs and NLRs), metabolites (e.g. indole, bile acids, retinoic acid) and small noncoding RNAs (e.g. miRNA) have been identified as key mediators regulating host-microbe interactions in the intestine. Novel microbial drivers of colitis and tumorigenesis (e.g. Alistipes finegoldii, Atopobium parvalum, Peptostreptococcus anaerobius) have been identified and their disease-promoting activities have been described.

SUMMARY

IBD-associated colorectal cancer results from a complex breakdown of communication between the host and its microbiota, involving barrier function, immune signaling and metabolites.

Supplementation of Low- and High-fat Diets with Fermentable Fiber Exacerbates Severity of DSS-induced Acute Colitis

BACKGROUND

Lack of dietary fiber has been suggested to increase the risk of developing various chronic inflammatory diseases, whereas supplementation of diets with fiber might offer an array of health-promoting benefits. Consistent with this theme, we recently reported that in mice, compositionally defined diets that are made with purified ingredients and lack fermentable fiber promote low-grade inflammation and metabolic syndrome, both of which could be ameliorated by supplementation of such diets with the fermentable fiber inulin.

METHODS

Herein, we examined if, relative to a grain-based mouse diet (chow), compositionally defined diet consumption would impact development of intestinal inflammation induced by dextran sulfate sodium (DSS) and moreover, whether DSS-induced colitis might also be attenuated by diets supplemented with inulin.

RESULTS

Analogous to their promotion of low-grade inflammation, compositionally defined diet of high- and low-fat content with cellulose increased the severity of DSS-induced colitis relative to chow. However, in contrast to the case of low-grade inflammation, addition of inulin, but not the insoluble fiber cellulose, further exacerbated the severity of colitis and its associated clinical manifestations (weight loss and bleeding) in both low- and high-fat diets.

CONCLUSIONS

While inulin, and perhaps other fermentable fibers, can ameliorate low-grade inflammation and associated metabolic disease, it also has the potential to exacerbate disease severity in response to inducers of acute colitis.

Ectopic Expression of Innate Immune Protein, Lipocalin-2, in Lactococcus lactis Protects Against Gut and Environmental Stressors

BACKGROUND

Lipocalin-2 (Lcn2) is a multifunctional innate immune protein that exhibits antimicrobial activity by the sequestration of bacterial siderophores, regulates iron homeostasis, and augments cellular tolerance to oxidative stress. Studies in the murine model of colitis have demonstrated that Lcn2 deficiency exacerbates colitogenesis; however, the therapeutic potential of Lcn2 supplementation has yet to be elucidated. In light of its potential mucoprotective functions, we, herein, investigated whether expression of Lcn2 in the probiotic bacterium can be exploited to alleviate experimental colitis.

METHODS

Murine Lcn2 was cloned into the pT1NX plasmid and transformed into Lactococcus lactis to generate L. lactis-expressing Lcn2 (Lactis-Lcn2) or the empty plasmid (Lactis-Con). Lactis-Lcn2 was characterized by immunoblot and enzyme-linked immunosorbent assay and tested for its antimicrobial efficacy on Escherichia coli. The capacity of Lactis-Lcn2 and Lactis-Con to withstand adverse conditions was tested using in vitro viability assays. Dextran sodium sulfate colitis model was used to investigate the colonization ability and therapeutic potential of Lactis-Lcn2 and Lactis-Con.

RESULTS

Lcn2 derived from Lactis-Lcn2 inhibited the growth of E. coli and reduced the bioactivity of enterobactin (E. coli-derived siderophore) in vitro. Lactis-Lcn2 displayed enhanced tolerance to adverse pH, high concentration of bile acids, and oxidative stress in vitro and survived better in the inflamed gut than Lactis-Con. Consistent with these features, Lactis-Lcn2 displayed better mucoprotection against intestinal inflammation than Lactis-Con when administered into mice with dextran sulfate sodium-induced acute colitis.

CONCLUSIONS

Our findings suggest that Lcn2 expression can be exploited to enhance the survivability of probiotic bacteria during inflammation, which could further improve its efficacy to treat experimental colitis.

Lipocalin 2: An Emerging Player in Iron Homeostasis and Inflammation

Lipocalin 2 (Lcn2), an innate immune protein, has emerged as a critical iron regulatory protein during physiological and inflammatory conditions. As a bacteriostatic factor, Lcn2 obstructs the siderophore iron-acquiring strategy of bacteria and thus inhibits bacterial growth. As part of host nutritional immunity, Lcn2 facilitates systemic, cellular, and mucosal hypoferremia during inflammation, in addition to stabilizing the siderophore-bound labile iron pool. In this review, we summarize recent advances in understanding the interaction between Lcn2 and iron, and its effects in various inflammatory diseases. Lcn2 exerts mostly a protective role in infectious and inflammatory bowel diseases, whereas both beneficial and detrimental functions have been documented in neurodegenerative diseases, metabolic syndrome, renal disorders, skin disorders, and cancer. Further animal and clinical studies are necessary to unveil the multifaceted roles of Lcn2 in iron dysregulation during inflammation and to explore its therapeutic potential for treating inflammatory diseases.

Lipocalin-2: A Master Mediator of Intestinal and Metabolic Inflammation

Lipocalin-2 (LCN2), also known as neutrophil gelatinase-associated lipocalin (NGAL), is released by various cell types and is an attractive biomarker of inflammation, ischemia, infection, and kidney damage. Both intestinal and metabolic inflammation, as observed in obesity and related disorders, are associated with increased LCN2 synthesis. While LCN2 in the intestinal tract regulates the composition of the gut microbiota and shows anti-inflammatory activities, it also exhibits proinflammatory activities in other experimental settings. In animal models of metabolic inflammation, type 2 diabetes mellitus (T2DM), or nonalcoholic steatohepatitis (NASH), increased LCN2 expression favors inflammation via the recruitment of inflammatory cells, such as neutrophils, and the induction of proinflammatory cytokines. A better understanding of this crucial marker of innate immunity might pave the way for targeting this pathway in future therapies.

Data on IL-10R neutralization-induced chronic colitis in Lipocalin 2 deficient mice on BALB/c background

The data herein is related to the research article entitled “Microbiota-inducible Innate Immune, Siderophore Binding Protein Lipocalin 2 is Critical for Intestinal Homeostasis” (Singh et al., 2016) [1] where we have demonstrated that C57BL/6 Lipocalin 2 deficient mice (Lcn2KO) developed chronic colitis upon anti-interleukin-10 receptor (αIL-10R) monoclonal antibody administration. In the present article, we evaluated the susceptibility of BALB/c Lcn2KO mice and their WT littermates to the αIL-10R neutralization-induced chronic colitis. Our data showed that αIL-10R mAb-treated BALB/c Lcn2KO mice exhibited severe chronic colitis (i.e., splenomegaly, colomegaly, colonic pathology, and incidence of rectal prolapse) when compared to WT mice.

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

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.

Interferon-Alpha Promotes Th1 Response and Epithelial Apoptosis via Inflammasome Activation in Human Intestinal Mucosa

BACKGOUND & AIMS

Several lines of investigation suggest that interferon (IFN) alpha can alter human intestinal mucosa homeostasis. These include the endogenous production of IFN alpha in celiac disease or inflammatory bowel diseases, as well as the occurrence of intestinal side effects of exogenous IFN alpha used as a therapeutic tool. Here, we present an ex vivo translational approach to investigate the effects of IFN alpha on the human normal intestinal mucosa, as well as its underlying mechanisms.

METHODS

Human normal colonic mucosa explants were cultured in the presence or absence of IFN alpha 2a. Epithelial homeostasis was assessed using the immunohistochemical marker of apoptosis M30. The Wnt inhibitor Dickkopf-Homolog-1 (DKK1) was assayed in the supernatants by enzyme-linked immunosorbent assay. Activation of the inflammasome (caspase-1/interleukin [IL]18) and of a Th1 response was determined by in situ detection of active caspase-1, as well as by measurement of mature IL18 production and the prototype Th1 cytokine IFN gamma by enzyme-linked immunosorbent assay. In addition, mechanistic studies were performed using the specific caspase-1 inhibitor Tyr-Val-Ala-Asp(OMe)-fluoromethylketone (YVAD-FMK), IL18-binding protein, neutralizing anti-IFN gamma, and anti-DKK1 antibodies.

RESULTS

IFN alpha 2a elicited a rapid (24 hours) disruption of surface and crypt colonic epithelial cells via apoptosis that was variable in intensity among the 20 individuals studied. This apoptotic effect was dependent on the initiation of an IFN gamma response elicited by resident T box expressed in T cells-positive lamina propria cells. Both apoptosis and Th1 response were subordinated to active caspase-1 and IL18 production. Finally, neutralization of IFN gamma-induced DKK1 partially protected against IFN alpha-induced epithelial apoptosis.

CONCLUSIONS

By using an ex vivo model, we show an interindividual heterogeneity of IFN alpha effects. We show that IFN alpha is able to disrupt both epithelial and immune homeostasis in the human intestine, by activation of an innate immunity platform, the inflammasome, which drives a Th1 response and leads to epithelial barrier disruption.

Feed your gut with caution!

The intestinal epithelium, a single layer of cells organized into crypts and villi, is an important component of host defense against microbial community and its noxious metabolites. To preserve the epithelium integrity under constant exposure of intense physiological and environmental stressors, this surface is continuously and rapidly renewed by pluripotent intestinal epithelial stem cells that reside in the base of crypts. A recent study by Kaiko et al. shows that structural design of intestinal crypts protects the colonic epithelial stem/progenitor cells from proliferation-suppressing metabolites derived from the gut microbiota. Among these metabolites, butyrate is identified as the most potent inhibitor of colonic epithelial stem/progenitor cells proliferation. By rapidly metabolizing the butyrate, the colonocytes at the crypt further institute a metabolic barrier to protect the crypt-resident stem cells that fuel its renewal and repair.

Data on importance of hematopoietic cell derived Lipocalin 2 against gut inflammation

The data herein is related to the research article entitled “Microbiota-inducible innate immune siderophore binding protein Lipocalin 2 is critical for intestinal homeostasis” (Singh et al., 2016) [1]. In the present article, we monitored dextran sodium sulfate (DSS)-induced colitis development upon Lipocalin 2 (Lcn2) neutralization, and examined the survival of Lcn2 deficient (Lcn2KO) mice and their WT littermates upon DSS challenge. To dissect the relative contribution of immune and non-immune cells-derived Lcn2 in mediating protection against gut inflammation, we generated respective bone marrow chimera and evaluated their susceptibility to IL-10 receptor neutralization-induced chronic colitis.

Neutralization of Lcn2 in WT mice resulted in exacerbated DSS-induced colitis. Notably, mice lacking Lcn2 exhibited 100% mortality whereas only 20% mortality was observed in WT mice upon DSS challenge. Further, data from bone marrow chimera showed that immune cell-derived Lcn2 is the major contributor in conferring protection against colitis.