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Microbial Exposure During Early Life Has Persistent Effects on Natural Killer T Cell Function

Microbes: Early and Often Epidemiological studies have suggested that the increase in the incidence of asthma and other inflammatory diseases seen in many parts of the world may be due to a reduced exposure to microbes during early childhood. Olszak et al. (p. 489, published online 22 March) now show that commensal microflora help to regulate the numbers and functions of natural killer T (NKT) cells in the colon and lung in mice. Germ-free mice had elevated numbers of NKT cells in these tissues and were more susceptible to chemically induced colitis and allergic asthma. Neonatal recolonization of germ-free mice with microflora prevented enhanced colitis and asthma sensitivity; however, exposure of adult mice to these conditions was not effective. Thus, early exposure to microbes has important, lasting effects on the immune systems sensitivity to inflammation. Early exposure of germ-free mice to microbes keeps later inflammation in check by modulating immune cells. Exposure to microbes during early childhood is associated with protection from immune-mediated diseases such as inflammatory bowel disease (IBD) and asthma. Here, we show that in germ-free (GF) mice, invariant natural killer T (iNKT) cells accumulate in the colonic lamina propria and lung, resulting in increased morbidity in models of IBD and allergic asthma as compared with that of specific pathogen-free mice. This was associated with increased intestinal and pulmonary expression of the chemokine ligand CXCL16, which was associated with increased mucosal iNKT cells. Colonization of neonatal—but not adult—GF mice with a conventional microbiota protected the animals from mucosal iNKT accumulation and related pathology. These results indicate that age-sensitive contact with commensal microbes is critical for establishing mucosal iNKT cell tolerance to later environmental exposures.

Sphingolipids from a Symbiotic Microbe Regulate Homeostasis of Host Intestinal Natural Killer T Cells

Coevolution of beneficial microorganisms with the mammalian intestine fundamentally shapes mammalian physiology. Here, we report that the intestinal microbe Bacteroides fragilis modifies the homeostasis of host invariant natural killer T (iNKT) cells by supplementing the hosts endogenous lipid antigen milieu with unique inhibitory sphingolipids. The process occurs early in life and effectively impedes iNKT cell proliferation during neonatal development. Consequently, total colonic iNKT cell numbers are restricted into adulthood, and hosts are protected against experimental iNKT cell-mediated, oxazolone-induced colitis. In studies with neonatal mice lacking access to bacterial sphingolipids, we found that treatment with B. fragilis glycosphingolipids-exemplified by an isolated peak (MW = 717.6) called GSL-Bf717-reduces colonic iNKT cell numbers and confers protection against oxazolone-induced colitis in adulthood. Our results suggest that the distinctive inhibitory capacity of GSL-Bf717 and similar molecules may prove useful in the treatment of autoimmune and allergic disorders in which iNKT cell activation is destructive.

Mucin–Pseudomonas aeruginosa interactions promote biofilm formation and antibiotic resistance

Pseudomonas aeruginosa is an opportunistic pathogen that causes chronic lung infections in people suffering from cystic fibrosis (CF). In CF airways, P. aeruginosa forms surface‐associated communities called biofilms. Compared with free‐swimming cultures, biofilms resist clearance by the host immune system and display increased resistance to antimicrobial agents. In this study we developed a technique to coat surfaces with molecules that are abundant in CF airways in order to investigate their impact on P. aeruginosa biofilm development. We found that P. aeruginosa biofilm development proceeds differently on surfaces coated with the glycoprotein mucin compared with biofilm development on glass and surfaces coated with actin or DNA. Biofilms formed on mucin‐coated surfaces developed large cellular aggregates and had increased tolerance to the antibiotic tobramycin compared with biofilms grown on glass. Analysis of selected mutant backgrounds in conjunction with time‐lapse microscopy revealed that surface‐associated motility was blocked on the mucin surface. Furthermore, our data suggest that a specific adhesin–mucin interaction immobilizes the bacterium on the surface. Together, these experiments suggest that mucin, which may serve as an attachment surface in CF airways, impacts P. aeruginosa biofilm development and function.

Membrane sphingolipids as essential molecular signals for Bacteroides survival in the intestine

As predominant intestinal symbiotic bacteria, Bacteroides are essential in maintaining the health of the normal mammalian host; in return, the host provides a niche with plentiful nutrients for the symbionts. However, the intestinal environment is replete with chemical, physical, and biological challenges that require mechanisms for prompt and adept sensing of and responses to stress if the bacteria are to survive. Herein we propose that to persist in the intestine Bacteroides take advantage of their unusual bacterial sphingolipids to mediate signaling pathways previously known to be available only to higher organisms. Sphingolipids convey diverse signal transduction and stress response pathways and have profound physiological impacts demonstrated in a variety of eukaryotic cell types. We propose a mechanism by which the formation of specific sphingolipid membrane microdomains initiates signaling cascades that facilitate survival strategies within the bacteria. Our preliminary data suggest that sphingolipid signaling plays an important role in Bacteroides physiology, enabling these bacteria to persist in the intestine and to perform other functions related to symbiosis.

Multifunctional and Recollectable Carbon Nanotube Ponytails for Water Purification

Carbon nanotubes (CNTs) are promising nanomaterials that have the potential to revolutionize water treatment practices in the future. The direct use of unbounded CNTs, however, poses health risks to humans and ecosystems because they are difficult to separate from treated water. Here, we report the design and synthesis of carbon nanotube ponytails (CNPs) by integrating CNTs into micrometer-sized colloidal particles, which greatly improves the effectiveness of post-treatment separation using gravitational sedimentation, magnetic attraction, and membrane filtration. We further demonstrate that CNPs can effectively perform major treatment tasks including adsorption, disinfection, and catalysis. Using model pollutants such as methylene blue, Escherichia coli, and p-nitrophenol, we show that all the surfaces of individual CNTs in CNPs are accessible during water treatment. Our results suggest that the rational design of hierarchical structures represents a feasible approach to develop nanomaterials for engineering applications such as water and wastewater treatment.

The Pathogenic Properties of a Novel and Conserved Gene Product, KerV, in Proteobacteria

Identification of novel virulence factors is essential for understanding bacterial pathogenesis and designing antibacterial strategies. In this study, we uncover such a factor, termed KerV, in Proteobacteria. Experiments carried out in a variety of eukaryotic host infection models revealed that the virulence of a Pseudomonas aeruginosa kerV null mutant was compromised when it interacted with amoebae, plants, flies, and mice. Bioinformatics analyses indicated that KerV is a hypothetical methyltransferase and is well-conserved across numerous Proteobacteria, including both well-known and emerging pathogens (e.g., virulent Burkholderia, Escherichia, Shigella, Vibrio, Salmonella, Yersinia and Brucella species). Furthermore, among the 197 kerV orthologs analyzed in this study, about 89% reside in a defined genomic neighborhood, which also possesses essential DNA replication and repair genes and detoxification gene. Finally, infection of Drosophila melanogaster with null mutants demonstrated that KerV orthologs are also crucial in Vibrio cholerae and Yersinia pseudotuberculosis pathogenesis. Our findings suggested that KerV has a novel and broad significance as a virulence factor in pathogenic Proteobacteria and it might serve as a new target for antibiotic drug design.

Commensal Bacteria Play an Important Role in Ulcerative Colitis via Bacterial Sphingolipids-Mediated Regulation of Host Invariant Natural Killer T Cells: P-174 YI

insights in mammalian development and human disease. However, there are few reports of the molecular function of miRNA in IBD, particularly in children. METHODS: Large-scale analysis of miRNA expression was performed in rectal tissues obtained from children with Crohn disease (CD), ulcerative colitis (UC), and normal controls. The Nanostring platform was used to avoid artifacts due to nucleic acid amplification or affinity hybridization. Bioinformatic tools were used to identify candidate miRNA:mRNA target relationships, and these were tested by reporter assays in cultured intestinal epithelial cells. RESULTS: We have found a unique signature of tissueand disease-specific miRNA expression in children with IBD. Based on these results, we have identified several candidate miRNA:mRNA relationships of potential pathologic significance, including regulation of the CD-associated gene NOD2/CARD15. The results have been validated by reporter assays in cultured intestinal epithelial cells. CONCLUSION(S): IBD in children is associated with widespread changes in miRNA expression. Some of these changes are linked to altered expression of genes of known significance in IBD. Because miRNAs are particularly amenable to pharmacologic inhibition, these findings may lead to novel therapeutic strategies in IBD.