William G. Coleman

Olfactomedin 4 down-regulates innate immunity against Helicobacter pylori infection.

Olfactomedin 4 (OLFM4) is a glycoprotein that has been found to be up-regulated in inflammatory bowel diseases and Helicobacter pylori infected patients. However, its role in biological processes such as inflammation or other immune response is not known. In this study, we generated OLFM4 KO mice to investigate potential role(s) of OLFM4 in gastric mucosal responses to H. pylori infection. H. pylori colonization in the gastric mucosa of OLFM4 KO mice was significantly lower compared with WT littermates. The reduced bacterial load was associated with enhanced infiltration of inflammatory cells in gastric mucosa. Production and expression of proinflammatory cytokines/chemokines such as IL-1β, IL-5, IL-12 p70, and MIP-1α was increased in OLFM4 KO mice compared with infected controls. Furthermore, we found that OLFM4 is a target gene of NF--κB pathway and has a negative feedback effect on NF-κB activation induced by H. pylori infection through a direct association with nucleotide oligomerization domain-1 (NOD1) and -2 (NOD2). Together these observations indicate that OLFM4 exerts considerable influence on the host defense against H. pylori infection acting through NOD1 and NOD2 mediated NF-κB activation and subsequent cytokines and chemokines production, which in turn inhibit host immune response and contribute to persistence of H. pylori colonization.

The crystal structure of ADP-L-glycero-D-mannoheptose 6-epimerase: catalysis with a twist.

BACKGROUND ADP-L-glycero--mannoheptose 6-epimerase (AGME) is required for lipopolysaccharide (LPS) biosynthesis in most genera of pathogenic and non-pathogenic Gram-negative bacteria. It catalyzes the interconversion of ADP-D-glycero-D-mannoheptose and ADP-L-glycero-D-mannoheptose, a precursor of the seven-carbon sugar L-glycero-mannoheptose (heptose). Heptose is an obligatory component of the LPS core domain; its absence results in a truncated LPS structure resulting in susceptibility to hydrophobic antibiotics. Heptose is not found in mammalian cells, thus its biosynthetic pathway in bacteria presents a unique target for the design of novel antimicrobial agents. RESULTS The structure of AGME, in complex with NADP and the catalytic inhibitor ADP-glucose, has been determined at 2.0 A resolution by multiwavelength anomalous diffraction (MAD) phasing methods. AGME is a homopentameric enzyme, which crystallizes with two pentamers in the asymmetric unit. The location of 70 crystallographically independent selenium sites was a key step in the structure determination process. Each monomer comprises two domains: a large N-terminal domain, consisting of a modified seven-stranded Rossmann fold that is associated with NADP binding; and a smaller alpha/beta C-terminal domain involved in substrate binding. CONCLUSIONS The first structure of an LPS core biosynthetic enzyme leads to an understanding of the mechanism of the conversion between ADP-D-glycero--mannoheptose and ADP-L-glycero-D-mannoheptose. On the basis of its high structural similarity to UDP-galactose epimerase and the three-dimensional positions of the conserved residues Ser116, Tyr140 and Lys144, AGME was classified as a member of the short-chain dehydrogenase/reductase (SDR) superfamily. This study should prove useful in the design of mechanistic and structure-based inhibitors of the AGME catalyzed reaction.

Olfactomedin 4 Inhibits Cathepsin C-Mediated Protease Activities, Thereby Modulating Neutrophil Killing of Staphylococcus aureus and Escherichia coli in Mice

Neutrophils kill bacteria generally through oxidative and nonoxidative mechanisms. Whereas much research has focused on the enzymes essential for neutrophil killing, little is known about the regulatory molecules responsible for such killing. In this study, we investigated the role of olfactomedin 4 (OLFM4), an olfactomedin-related glycoprotein, in neutrophil bactericidal capability and host innate immunity. Neutrophils from OLFM4−/− mice have increased intracellular killing of Staphylococcus aureus and Escherichia coli in vitro. The OLFM4−/− mice have enhanced in vivo bacterial clearance and are more resistant to sepsis when challenged with S. aureus or E. coli by i.p. injection. OLFM4 was found to interact with cathepsin C, a cysteine protease that plays an important role in bacterial killing and immune regulation. We demonstrated that OLFM4 inhibited cathepsin C activity in vitro and in vivo. The cathepsin C activity in neutrophils from OLFM4−/− mice was significantly higher than that in neutrophils from wild-type littermate mice. The activities of three serine proteases (neutrophil elastase, cathepsin G, and proteinase 3), which require cathepsin C activity for processing and maturity, were also significantly higher in OLFM4−/− neutrophils. The bacterial killing and clearance capabilities observed in OLFM4−/− mice that were enhanced relative to wild-type mice were significantly compromised by the additional loss of cathepsin C in mice with OLFM4 and cathepsin C double deficiency. These results indicate that OLFM4 is an important negative regulator of neutrophil bactericidal activity by restricting cathepsin C activity and its downstream granule-associated serine proteases.

A Reporter Mouse Reveals Lineage-Specific and Heterogeneous Expression of IRF8 during Lymphoid and Myeloid Cell Differentiation

The IFN regulatory factor family member 8 (IRF8) regulates differentiation of lymphoid and myeloid lineage cells by promoting or suppressing lineage-specific genes. How IRF8 promotes hematopoietic progenitors to commit to one lineage while preventing the development of alternative lineages is not known. In this study, we report an IRF8–EGFP fusion protein reporter mouse that revealed previously unrecognized patterns of IRF8 expression. Differentiation of hematopoietic stem cells into oligopotent progenitors is associated with progressive increases in IRF8-EGFP expression. However, significant induction of IRF8-EGFP is found in granulocyte–myeloid progenitors and the common lymphoid progenitors but not the megakaryocytic–erythroid progenitors. Surprisingly, IRF8-EGFP identifies three subsets of the seemingly homogeneous granulocyte–myeloid progenitors with an intermediate level of expression of EGFP defining bipotent progenitors that differentiation into either EGFPhi monocytic progenitors or EGFPlo granulocytic progenitors. Also surprisingly, IRF8-EGFP revealed a highly heterogeneous pre–pro-B population with a fluorescence intensity ranging from background to 4 orders above background. Interestingly, IRF8–EGFP readily distinguishes true B cell committed (EGFPint) from those that are noncommitted. Moreover, dendritic cell progenitors expressed extremely high levels of IRF8-EGFP. Taken together, the IRF8-EGFP reporter revealed previously unrecognized subsets with distinct developmental potentials in phenotypically well-defined oligopotent progenitors, providing new insights into the dynamic heterogeneity of developing hematopoietic progenitors.

Olfm4 deletion enhances defense against Staphylococcus aureus in chronic granulomatous disease

Chronic granulomatous disease (CGD) patients have recurrent life-threatening bacterial and fungal infections. Olfactomedin 4 (OLFM4) is a neutrophil granule protein that negatively regulates host defense against bacterial infection. The goal of this study was to evaluate the impact of Olfm4 deletion on host defense against Staphylococcus aureus and Aspergillus fumigatus in a murine X-linked gp91phox-deficiency CGD model. We found that intracellular killing and in vivo clearance of S. aureus, as well as resistance to S. aureus sepsis, were significantly increased in gp91phox and Olfm4 double-deficient mice compared with CGD mice. The activities of cathepsin C and its downstream proteases (neutrophil elastase and cathepsin G) and serum levels of IL-1β, IL-6, IL-12p40, CXCL2, G-CSF, and GM-CSF in Olfm4-deficient as well as gp91phox and Olfm4 double-deficient mice were significantly higher than those in WT and CGD mice after challenge with S. aureus. We did not observe enhanced defense against A. fumigatus in Olfm4-deficient mice using a lung infection model. These results show that Olfm4 deletion can successfully enhance immune defense against S. aureus, but not A. fumigatus, in CGD mice. These data suggest that OLFM4 may be an important target in CGD patients for the augmentation of host defense against bacterial infection.

Prevalence of Helicobacter pylori Infection and its Relation with Body Mass Index in a Chinese Population

Helicobacter pylori infection is highly prevalent worldwide. The association between obesity and H. pylori infection is controversial in the literature. This study aims to investigate the prevalence of H. pylori infection and its relation with body mass index (BMI) in a Chinese population.

Stimulation of Toll-Like Receptors profoundly influences the titer of polyreactive antibodies in the circulation.

Polyreactive antibodies are a major component of the natural antibody repertoire and bind to a variety of structurally unrelated molecules. These antibodies are thought to provide a first line of defense against bacterial infections and play a major role in the clearance of apoptotic cells. What triggers the secretion of these antibodies has remained an enigma. Using a surrogate assay for measuring polyreactive antibodies, we found that about 50% of serum IgM is polyreactive and that stimulation of TLR4+/+, but not TLR4−/−, mice resulted in a 40 fold increase in polyreactive antibodies. Stimulation of TLRs 3, 7, 9 also increased the secretion of polyreactive antibodies. Infection with a virus or tissue damage induced by a toxin similarly led to an increase in polyreactive antibodies in MyD88+/+, but not MyD88−/− mice. We conclude that stimulation of TLRs is a key link in the mechanism of polyreactive antibody secretion into the circulation.

Screening Helicobacter pylori genes induced during infection of mouse stomachs

AIM To investigate the effect of in vivo environment on gene expression in Helicobacter pylori (H. pylori) as it relates to its survival in the host. METHODS In vivo expression technology (IVET) systems are used to identify microbial virulence genes. We modified the IVET-transcriptional fusion vector, pIVET8, which uses antibiotic resistance as the basis for selection of candidate genes in host tissues to develop two unique IVET-promoter-screening vectors, pIVET11 and pIVET12. Our novel IVET systems were developed by the fusion of random Sau3A DNA fragments of H. pylori and a tandem-reporter system of chloramphenicol acetyltransferase and beta-galactosidase. Additionally, each vector contains a kanamycin resistance gene. We used a mouse macrophage cell line, RAW 264.7 and mice, as selective media to identify specific genes that H. pylori expresses in vivo. Gene expression studies were conducted by infecting RAW 264.7 cells with H. pylori. This was followed by real time polymerase chain reaction (PCR) analysis to determine the relative expression levels of in vivo induced genes. RESULTS In this study, we have identified 31 in vivo induced (ivi) genes in the initial screens. These 31 genes belong to several functional gene families, including several well-known virulence factors that are expressed by the bacterium in infected mouse stomachs. Virulence factors, vacA and cagA, were found in this screen and are known to play important roles in H. pylori infection, colonization and pathogenesis. Their detection validates the efficacy of these screening systems. Some of the identified ivi genes have already been implicated to play an important role in the pathogenesis of H. pylori and other bacterial pathogens such as Escherichia coli and Vibrio cholerae. Transcription profiles of all ivi genes were confirmed by real time PCR analysis of H. pylori RNA isolated from H. pylori infected RAW 264.7 macrophages. We compared the expression profile of H. pylori and RAW 264.7 coculture with that of H. pylori only. Some genes such as cagA, vacA, lpxC, murI, tlpC, trxB, sodB, tnpB, pgi, rbfA and infB showed a 2-20 fold upregulation. Statistically significant upregulation was obtained for all the above mentioned genes (P < 0.05). tlpC, cagA, vacA, sodB, rbfA, infB, tnpB, lpxC and murI were also significantly upregulated (P < 0.01). These data suggest a strong correlation between results obtained in vitro in the macrophage cell line and in the intact animal. CONCLUSION The positive identification of these genes demonstrates that our IVET systems are powerful tools for studying H. pylori gene expression in the host environment.

Investigating the Role of Helicobacter pylori PriA Protein

In bacteria, PriA protein, a conserved DEXH‐type DNA helicase, plays a central role in replication restart at stalled replication forks. Its unique DNA binding property allows it to recognize and stabilize stalled forks and the structures derived from them. PriA plays a very critical role in replication fork stabilization and DNA repair in E. coli and N. gonorrhoeae. In our in vivo expression technology screen, priA gene was induced in vivo when Helicobacter pylori infects mouse stomach.

Mo1791 MyD88 Has a Key Role for OLFM4, a Novel Anti-Inflammatory Mediator in H. pylori Infection

G A A b st ra ct s an important role in the homeostasis of PP in response to the microbiota. However, we do not know the respective roles of Nod2 in the epithelial and immune compartments of PP. Methods: To investigate the part of Nod2 in epithelial and immune compartments within PP, chimeric mice were developed by reconstituting sublethally irradiated wild-type (WT) mice with bone marrow (BM) stem cells from Nod2 Knockout mice (KO) and vice versa. Three months following BM transplantation, paracellular permeability (FITC 4kD dextran flux) and E. coli translocation were assessed in Ussing chamber. The number of immune cells and cellular composition from PP of chimeric mice were determined by flow cytometry. Results: An excess of permeability and E. coli translocation was observed in PP of KO mice reconstituted by BM of KO mice (KO→KO) compared to WT mice reconstituted by BM WT mice (WT→WT). Permeability and E. coli translocation were also higher in PP from chimeric mice that did not express Nod2 in the immune compartment but expressed it in epithelial cells (KO→WT). These excesses of permeability and translocation in PP were comparable to Nod2 Knockout mice (KO→KO). Conversely, permeability and E. coli translocation from chimeric mice expressing Nod2 in immune cells but not in epithelial cells (WT→KO) were similar to controls. An excess of CD3+ T-cells but a decreased number of dendritic cells were observed in the PP from chimeric mice that did not express Nod2 in immune cells (KO→KO and KO→WT). Conclusion: Nod2 deficiency in the immune compartment is sufficient to alter the cellular composition of PP and the functionality of the follicle associated epithelium. These results highlight the importance of Nod2 in the dialogue between the immune and epithelial cells and may contribute to understand CD mechanisms.