Irazoqui JE (2011) Virulence "Transparent worms help survey the fortress of innate immunity."

Irazoqui JE

[Virulence, 2011]

Irazoqui JE (2015) Immunity "Why worms watch their hemidesmosomes and why you should, too."

Irazoqui JE

[Immunity, 2015]

Hemidesmosomes are cellular attachment structures of great importance to the epidermis. In this issue of Immunity, Zhang et al. (2015) have discovered that in addition to having structural functions, invertebrate and human hemidesmosomes are actively monitored by the cell as a novel mechanism for detecting pathogenic infection.

Irazoqui JE (2014) Cell Host Microbe "DAF-tly depart stinky situations with elegans."

Irazoqui JE

[Cell Host Microbe, 2014]

During acute infection our behavior tends to change. Despite how common sickness behavior is, its molecular basis is not well understood. In a study published in Cell, Kim and colleagues (Meisel etal., 2014) implicate bacterial secondary metabolites as triggers of neural TGF-? signaling, which results in behavioral change during infection.

Irazoqui JE et al. (2010) Nat Rev Immunol "Evolution of host innate defence: insights from Caenorhabditis elegans and primitive invertebrates."

Ausubel FM, Irazoqui JE, Urbach JM

[Nat Rev Immunol, 2010]

The genetically tractable model organism Caenorhabditis elegans was first used to model bacterial virulence in vivo a decade ago. Since then, great strides have been made in identifying the host response pathways that are involved in its defence against infection. Strikingly, C. elegans seems to detect, and respond to, infection without the involvement of its homologue of Toll-like receptors, in contrast to the well-established role for these proteins in innate immunity in mammals. What, therefore, do we know about host defence mechanisms in C. elegans and what can they tell us about innate immunity in higher organisms?

Irazoqui JE et al. (2010) PLoS Pathog "Distinct pathogenesis and host responses during infection of C. elegans by P. aeruginosa and S. aureus."

Ausubel FM, Troemel ER, Irazoqui JE, Luhachack LG, Feinbaum RL, Cezairliyan BO

[PLoS Pathog, 2010]

The genetically tractable model host Caenorhabditis elegans provides a valuable tool to dissect host-microbe interactions in vivo. Pseudomonas aeruginosa and Staphylococcus aureus utilize virulence factors involved in human disease to infect and kill C. elegans. Despite much progress, virtually nothing is known regarding the cytopathology of infection and the proximate causes of nematode death. Using light and electron microscopy, we found that P. aeruginosa infection entails intestinal distention, accumulation of an unidentified extracellular matrix and P. aeruginosa-synthesized outer membrane vesicles in the gut lumen and on the apical surface of intestinal cells, the appearance of abnormal autophagosomes inside intestinal cells, and P. aeruginosa intracellular invasion of C. elegans. Importantly, heat-killed P. aeruginosa fails to elicit a significant host response, suggesting that the C. elegans response to P. aeruginosa is activated either by heat-labile signals or pathogen-induced damage. In contrast, S. aureus infection causes enterocyte effacement, intestinal epithelium destruction, and complete degradation of internal organs. S. aureus activates a strong transcriptional response in C. elegans intestinal epithelial cells, which aids host survival during infection and shares elements with human innate responses. The C. elegans genes induced in response to S. aureus are mostly distinct from those induced by P. aeruginosa. In contrast to P. aeruginosa, heat-killed S. aureus activates a similar response as live S. aureus, which appears to be independent of the single C. elegans Toll-Like Receptor (TLR) protein. These data suggest that the host response to S. aureus is possibly mediated by pathogen-associated molecular patterns (PAMPs). Because our data suggest that neither the P. aeruginosa nor the S. aureus-triggered response requires canonical TLR signaling, they imply the existence of unidentified mechanisms for pathogen detection in C. elegans, with potentially conserved roles also in mammals.

Irazoqui JE et al. (2008) Proc Natl Acad Sci U S A "Role for beta-catenin and HOX transcription factors in Caenorhabditis elegans and mammalian host epithelial-pathogen interactions."

Ng A, Xavier RJ, Irazoqui JE, Ausubel FM

[Proc Natl Acad Sci U S A, 2008]

We used the model nematode Caenorhabditis elegans infected with the human pathogen Staphylococcus aureus to identify components of epithelial immunity. Transcriptional profiling and reverse genetic analysis revealed that mutation of the C. elegans beta-catenin homolog bar-1 or the downstream homeobox gene egl-5 results in a defective response and hypersensitivity to S. aureus infection. Epistasis analysis showed that bar-1 and egl-5 function in parallel to previously described C. elegans immune-response pathways. Overexpression of human homologs of egl-5 modulated NF-kappaB-dependent TLR2 signaling in epithelial cells. These data suggest that beta-catenin and homeobox genes play an important and conserved role in innate immune defense.

Irazoqui JE et al. (2010) Clin Exp Immunol "99th Dahlem conference on infection, inflammation and chronic inflammatory disorders: Caenorhabditis elegans as a model to study tissues involved in host immunity and microbial pathogenesis."

Irazoqui JE, Ausubel FM

[Clin Exp Immunol, 2010]

The molecular mechanisms involved in host-microbe interactions during the initial stages of infection are poorly understood. The bacteria-eating nematode Caenorhabditis elegans provides an opportunity to dissect host-microbe interactions in the context of the whole organism, using powerful genomic, genetic and cell-biological tools. Because of the evolutionary conservation of ancient innate host defences and bacterial virulence mechanisms, studies in C. elegans hold great promise to shed light on defences in higher organisms, including mammals. Additionally, C. elegans pathogenesis models provide a platform for the identification of novel classes of anti-infective compounds with therapeutic value.

Lhuegbu, N. et al. (2011) International Worm Meeting "HLH-30 is a novel transcription factor important for the C. elegans host response to S. aureus."

Luhachack, L.G., Stormo, G.D., Lhuegbu, N., Irazoqui, J.E., Visvikis, O.

[International Worm Meeting, 2011]

The human pathogen Staphylococcus aureus can infect and kill Caenorhabditis elegans. Previous microarray analysis showed that S. aureus triggers a pathogen-specific transcriptional host response, which appears to be regulated by Toll-like receptor-independent sensing of pathogen-associated molecular patterns (PAMPs). BAR-1/b-catenin and EGL-5/HOX were shown to be important for triggering part of this response. However, because many host defense genes are triggered independently of BAR-1 and EGL-5, it is likely that additional signaling pathways are important for the C. elegans response to S. aureus. To identify new components that orchestrate the host response, we performed bioinformatic analysis and identified evolutionarily conserved DNA motifs that are over-represented in the promoters of S. aureus induced transcripts (SAITs). One such motif, the M-box/E-box, is known in mammals to be bound by the Microphthalmia-TFE (MiT) transcription factor family. Phylogenetic analysis revealed that hlh-30 is the unique MiT homologous gene in C. elegans. Therefore, we hypothesized that hlh-30 is important for the expression of host defense genes during S. aureus infection. To test this hypothesis, we first analyzed the expression of hlh-30 by RT-qPCR and found that it was up-regulated by 2-fold upon infection. We then monitored the expression of a subset of SAITs in hlh-30(-) strain relative to wild type. We found that HLH-30 is required for the expression of 15 out of 17 SAITs tested in infected animals, 7 out of these 15 SAITs being regulated by hlh-30 in uninfected animals as well. Thus HLH-30 controls expression of a large number of genes implicated in the host response. To understand the role of HLH-30 at the global level, we performed RNA-Seq to determine the downstream target genes of HLH-30. Of 989 SAITs identified in wild-type animals, 619 SAITs were not induced in hlh-30(-) animals, confirming that HLH-30 plays a key role in the C. elegans host response to S. aureus. Consistently, we found that hlh-30(-) mutants exhibited enhanced susceptibility to S. aureus-mediated killing. Therefore, we suspect that the transcriptional defect observed in hlh-30(-) animals is biologically significant for host defense. We are currently investigating potential mechanisms of regulation of HLH-30 during infection. Altogether, these data indicate that HLH-30 is a major transcription factor controlling a biologically significant transcriptional host response to infection.

Xu X et al. (2005) FEBS Lett "Linking integrin to IP(3) signaling is important for ovulation in Caenorhabditis elegans."

Lee M, Shih HY, Seo S, Xu X, Ahn J, Lee D

[FEBS Lett, 2005]

Signals from germ and myoepithelial sheath cells initiate ovulation in Caenorhabditis elegans. The coordinated dilation and contraction of spermatheca lead to subsequent fertilization of oocyte. Either the dominant negative mutant pat-3 beta integrin or disruption of talin expression block ovulation [Cram, E.J., Clark, S.G. and Schwarzbauer, J.E. (2003) Talin loss-of-function uncovers roles in cell contractility and migration in C. elegans. J. Cell. Sci. 116, 3871-3878; Lee, M., Cram, E.J., Shen, B. and Schwarzbauer, J.E. (2001) Role of beta pat-3 integrins in development and function of Caenorhabditis elegans muscles and gonads. J. Biol. Chem. 276, 36404-36410], suggesting that the interaction between the cell and the extracellular matrix (ECM) is also important for ovulation. Here, we report that integrin plays an essential role in fertility via IP(3) signaling. Sterility caused by RNAi of pat-3 and ECM molecules was suppressed by increased IP(3) signaling. Our data suggest that the cell-ECM interaction controls ovulation via IP(3) signaling.

Wani, K.A. et al. (2019) International Worm Meeting "NHR-49 regulates HLH-30-mediated innate immune response via a flavin-containing monooxygenase in C. elegans."

Irazoqui, J.E., Wani, K.A., Goswamy, D., Ghazi, A., Ratnappan, R., Taubert, S.

[International Worm Meeting, 2019]

C. elegans mounts an innate immune response against Gram-positive bacteria S. aureus by the transcriptional induction of various host defense genes. The expression of a majority of these genes is under the control of HLH-30, the C. elegans homolog of TFEB (transcription factor EB) that also functions in the innate immune response in mammals. In addition to its role in host defense against S. aureus, HLH-30 acts as a nutritionally-controlled stress response factor. We wanted to deconvolve C. elegans response to the nutritional challenge from the antibacterial response against S. aureus. To this end, we performed RNAseq profiling in wildtype and hlh-30 mutant animals that were either infected with S. aureus or were starved. Our RNAseq analysis showed that multiple HLH-30-dependent or-independent genes are specifically induced by S. aureus infection, and not under starvation. One of the genes that are strongly induced by infection and not starvation is fmo-2, which encodes a member of the flavin-containing monooxygenase (FMO) family in C. elegans. We decided to characterize the role of FMO-2 in host defense in C. elegans by employing genetic, transgenic and molecular approaches. We found that FMO-2 functions in host defense against S. aureus and its induction during infection is controlled by two transcription factors, HLH-30 and NHR-49. Our results propose a model in which NHR-49 functions upstream of HLH-30 to bind to the fmo-2 promoter and to induce its upregulation by functioning specifically in C. elegans intestine (the site of innate immune response), thereby providing host defense against S. aureus infection.