Project description:Traditional treatments for bacterial infection have focused upon directly inhibiting growth of the pathogen. However, an equally important determinant of infection outcome is the host defense response. We previously performed a high-throughput chemical screen to identify small molecules that rescued the nematode Caenorhabditis elegans from infection by Pseudomonas aeruginosa. Over 20 of the hits stimulated host defense gene expression. During in-depth studies of five such molecules using microarray analysis, bioinformatic clustering, and RNAi knockdown of candidate gene targets, we identified PMK-1/p38 MAPK and SKN-1/Nrf2 as two key pathways modulated by these hits. Interestingly, the molecules studied did not depend on a single pathway for ameliorating P. aeruginosa pathogenesis in liquid-based assay, but did rely on the PMK-1/p38 MAPK pathway during a colonization-based infection assay on agar. A subset of these molecules was also protective against Enterococcus faecalis and Staphylococcus aureus. In general, the compounds showed little toxicity against mammalian cells or worms, consistent with their identification in a phenotypic, high-content screen. These molecules possess significant potential for use as tools to study innate immune processes
Project description:C-type lectin-like domain (CTLD) encoding genes are highly diverse in C. elegans, comprising a clec gene family of 283 members. Since vertebrate CTLD proteins have characterized functions in defense responses against pathogens and since expression of C. elegans clec genes is pathogen-dependent, it is generally assumed that clec genes function in C. elegans immune defenses. In this study we challenged this assumption and focused on the C. elegans clec gene clec-4, whose expression is highly upregulated upon infection with various pathogens. We tested the involvement of clec-4 in the defense response to infection with Pseudomonas aeruginosa PA14, Bacillus thuringiensis BT18247, and the natural pathogen Serratia rubidaea MYb237. Contrary to our expectation clec-4(ok2050) mutant worms were not more susceptible to pathogen infection than wildtype worms. To explore potential redundant function between different C. elegans clec genes, we investigated expression of several clec-4 paralogs, finding that clec-4, clec-41, and clec-42 expression shows similar infection-dependent changes and co-localizes to the intestine. We found that only clec-42 is required for the C. elegans defense response to BT18247 infection and that clec-4 genetically interacts with clec-41 and clec-42. The exact role of clec-4 in pathogen defense responses however remains enigmatic. Our results further indicate that a complex interplay between different clec genes regulates C. elegans defense responses.
Project description:Discriminating pathogenic bacteria from energy-harvesting commensals is key to host immunity. Using mutants defective in the enzymes of O-linked N-acetylglucosamine (O-GlcNAc) cycling, we examined the role of this nutrient-sensing pathway in the Caenorhabidits elegans innate immune response. Using whole genome transcriptional profiling, O-GlcNAc cycling mutants exhibited deregulation of unique stress- and immune-responsive genes as well as genes shared with the p38 MAPK/PMK-1 pathway. Moreover, genetic analysis showed that deletion of O-GlcNAc transferase (ogt-1) yielded animals hypersensitive to the human pathogen S. aureus but not to P. aeruginosa. Genetic interaction studies further revealed that nutrient-responsive OGT-1 acts through the conserved ß-catenin (BAR-1) pathway and in concert with p38 MAPK/PMK-1 to modulate the immune response to S. aureus. The participation of the nutrient sensor O-GlcNAc transferase in an immunity module conserved from C. elegans to humans reveals an unexplored nexus between nutrient availability and a pathogen-specific immune response. In C. elegans, three mutant strains(genotypes used: N2 (wild-type), ogt-1 (ok1474), oga-1 (ok1207), and pmk-1 (km25)) were treated with the human pathogen S. aureus (SA) or P. aeruginosa(PA) and OP50 (E. coli control) with three biological replications.
Project description:The Caenorhabditis elegans bus (bacterial unswollen) mutants were isolated by their altered response to the nematode pathogen Microbacterium nematophilum. The bus-2, bus-4 and bus-17 mutants are resistant to infection by this bacterium and to infection by human pathogens Yersinia pestis and Yersinia pseudotuberculosis. Here we extend that list to Staphylococcus aureus. The bus-2, bus-4 and bus-17 mutants each harbors a defect in a different glycosyltransferase involved in O-glycosylation. Glycomics analysis of these strains reveals significant O-glycosylation defects. We further investigated the nature of bus mutant phenotypes in bus-2, bus-4 and bus-17 by gene expression analysis. Three distinct areas of altered expression were identified: 1) N- and O-glycosylation; 2) innate immune response; 3) protein folding and editing control. As expected N- and O-glycosylation gene expression was altered at key enzymatic steps. Innate immune system expression patterns were altered in a way that significantly overlapped with expression patterns seen in wild-type upon exposure to Staphylococuss aureus. Upon infection with S. aureus markers of innate immune activity increased significantly compared to wild-type. The abu/pqn genes, active in the non-canonical unfolded protein response (UPR) pathway were dramatically upregulated in bus when these mutants were exposed to the pathogen. This work demonstrates a genetic link between O-glycosylation and expression of key components of the innate immune response.
Project description:Insulin/IGF-1 signaling (IIS) mediates metabolic and developmental acclimation to stressful conditions including starvation. The transcription factor DAF-16/FoxO actuates many of the physiological effects of reduced IIS, yet the specific contributions of DAF-16 target genes to stress resistance remain poorly understood. We explore the function of C. elegans H1 linker histone variant hil-1/H1.0, a DAF-16 target that is upregulated during starvation. The HIL-1 sequence is divergent from the other eight annotated C. elegans H1 variants, and the others are not so highly responsive to nutrient availability and DAF-16 activity, suggesting distinct function. Using knock-in reporters, we find that HIL-1 is expressed ubiquitously in nuclei of L1 and dauer larvae during starvation, but that expression is largely undetectable in fed larvae. Disrupting hil-1 activity through mutation or auxin-inducible degradation led to reduced growth after extended L1 starvation, revealing reduced starvation resistance. RNA-seq of hil-1 mutants showed that hil-1 affects expression of relatively few genes. However, hil-1 activates genes involved in the innate immune response, Pseudomonas aeruginosa infection, and components of the nipi-3/TRIB1 immunity pathway. hil-1 mutants display compromised survival upon exposure to P. aeruginosa under reduced IIS, and genes activated by hil-1 promote resistance to P. aeruginosa. Together these results suggest that DAF-16/FoxO activates transcription of hil-1 during starvation to promote resistance to starvation and pathogens. We demonstrate conditional regulation of an H1 histone, and we reveal a novel mechanism for how IIS promotes stress resistance by identifying a histone variant that connects nutrient sensing to immunity.
Project description:The neuronal G protein-coupled receptor NMUR-1, a homolog to the mammalian neuromedin U receptor, has been implicated in the specificity of Caenorhabditis elegans innate immune response against pathogen infections. NMUR-1 controls C. elegans transcription activity by regulating transcription factors, which, in turn control the expression of distinct defense genes. This study further investigates the role of NMUR-1 at the protein level in regulating innate immune responses against pathogens Salmonella enterica and Enterococcus faecalis by utilizing mass spectrometry-based quantitative proteomics. We found that NMUR-1 regulates a class of proteins responsible for transmembrane transport during infection. Specifically, a group of proteins forming F1FO ATP synthase responsible for ATP biosynthesis is downregulated in NMUR-1 loss of function mutants during both S. enterica and E. faecalis infections. ATP measurements further revealed that nmur-1 mutants have reduced ATP production in response to both S. enterica and E. faecalis infections. Functional assays demonstrated that inhibiting F1FO ATP synthase using RNA interference or chemical modification mimicked the survival phenotypes of the untreated nmur-1 knockout mutants on S. enterica and E. faecalis. These findings provide valuable insights into the mechanism by which NMUR-1 regulates energy homeostasis at the protein level as part of an innate immune response against specific pathogens.
Project description:Discriminating pathogenic bacteria from energy-harvesting commensals is key to host immunity. Using mutants defective in the enzymes of O-linked N-acetylglucosamine (O-GlcNAc) cycling, we examined the role of this nutrient-sensing pathway in the Caenorhabidits elegans innate immune response. Using whole genome transcriptional profiling, O-GlcNAc cycling mutants exhibited deregulation of unique stress- and immune-responsive genes as well as genes shared with the p38 MAPK/PMK-1 pathway. Moreover, genetic analysis showed that deletion of O-GlcNAc transferase (ogt-1) yielded animals hypersensitive to the human pathogen S. aureus but not to P. aeruginosa. Genetic interaction studies further revealed that nutrient-responsive OGT-1 acts through the conserved ß-catenin (BAR-1) pathway and in concert with p38 MAPK/PMK-1 to modulate the immune response to S. aureus. The participation of the nutrient sensor O-GlcNAc transferase in an immunity module conserved from C. elegans to humans reveals an unexplored nexus between nutrient availability and a pathogen-specific immune response.