Differential interleukin-8 response of intestinal epithelial cell line to reactogenic and nonreactogenic candidate vaccine strains of Vibrio cholerae

Elucidation of cellular signaling mechanism involved in Vibrio cholerae chitin-binding protein GbpA mediated IL-8 secretion in the intestinal cells

Background

Vibrio cholerae N-acetylglucosamine-binding protein (GbpA) is a four-domain, secretory colonization factor which is essential for chitin utilization in the environment, as well as in adherence to intestinal cells. GbpA is also involved in inducing intestinal inflammation by enhancing mucin and interleukin-8 secretion. The underlying cell signaling mechanism involved in the induction of the pro-inflammatory response and IL-8 secretion has yet to be deciphered in detail.

Methods

Herein, the process through which GbpA triggers the induction of IL-8 in intestinal cells was investigated by examining the role of GbpA in intestinal cell line HT 29.

Results

GbpA, specifically through the fourth domain, forms a binding connection with Toll-like receptor 2 (TLR2) and additionally, recruits TLR1 along with CD14 within a lipid raft micro-domain to initiate the signaling pathway. Notably, disruption of this micro-domain complex resulted in a reduction in IL-8 secretion. The lipid raft association served as the catalyst that invoked a downstream cellular inflammatory signaling pathway. This cascade involved the activation of various MAP kinases and NFκB and assembly of the AP-1 complex. This coordinated activation of signaling molecules eventually leads to enhanced IL-8 transcription via increased promoter activity. These findings suggested that GbpA is a crucial protein in V. cholerae, capable of inciting a pro-inflammatory response during infection by orchestrating the formation of the GbpA-TLR1/2-CD14 lipid raft complex. Activation of AP-1 and NFκB in the nucleus eventually enhanced IL-8 transcription through increased promoter activity.

Conclusion

Collectively, these findings indicated that GbpA plays a pivotal role within V. cholerae by triggering a pro-inflammatory response during infection. This response is instrumented by the formation of the GbpA-TLR1/2-CD14 lipid raft complex.

Vibrio cholerae, classification, pathogenesis, immune response, and trends in vaccine development

Vibrio cholerae is the causative agent of cholera, a highly contagious diarrheal disease affecting millions worldwide each year. Cholera is a major public health problem, primarily in countries with poor sanitary conditions and regions affected by natural disasters, where access to safe drinking water is limited. In this narrative review, we aim to summarize the current understanding of the evolution of virulence and pathogenesis of V. cholerae as well as provide an overview of the immune response against this pathogen. We highlight that V. cholerae has a remarkable ability to adapt and evolve, which is a global concern because it increases the risk of cholera outbreaks and the spread of the disease to new regions, making its control even more challenging. Furthermore, we show that this pathogen expresses several virulence factors enabling it to efficiently colonize the human intestine and cause cholera. A cumulative body of work also shows that V. cholerae infection triggers an inflammatory response that influences the development of immune memory against cholera. Lastly, we reviewed the status of licensed cholera vaccines, those undergoing clinical evaluation, and recent progress in developing next-generation vaccines. This review offers a comprehensive view of V. cholerae and identifies knowledge gaps that must be addressed to develop more effective cholera vaccines.

The Vibrio cholerae MARTX toxin silences the inflammatory response to cytoskeletal damage before inducing actin cytoskeleton collapse

Multifunctional autoprocessing repeats-in-toxin (MARTX) toxins are pore-forming bacterial toxins that translocate multiple functionally independent effector domains into a target eukaryotic cell. Vibrio cholerae colonizes intestinal epithelial cells (IECs) and uses a MARTX toxin with three effector domains-an actin cross-linking domain (ACD), a Rho inactivation domain (RID), and an α/β hydrolase domain (ABH)-to suppress innate immunity and enhance colonization. We investigated whether these multiple catalytic enzymes delivered from a single toxin functioned in a coordinated manner to suppress intestinal innate immunity. Using cultured human IECs, we demonstrated that ACD-induced cytoskeletal collapse activated extracellular signal-regulated kinase, p38, and c-Jun amino-terminal kinase mitogen-activated protein kinase (MAPK) signaling to elicit a robust proinflammatory response characterized by the secretion of interleukin-8 (IL-8; also called CXCL8) and the expression of CXCL8, tumor necrosis factor (TNF), and other proinflammatory genes. However, RID and ABH, which are naturally delivered together with ACD, blocked MAPK activation through Rac1 and thus prevented ACD-induced inflammation. RID also abolished IL-8 secretion induced by heat-killed bacteria, TNF, or latrunculin A. Thus, MARTX toxins use enzymatic multifunctionality to silence the host response to bacterial factors and to the damage caused by the toxins. Furthermore, these data show how V. cholerae MARTX toxin suppresses intestinal inflammation and contributes to cholera being classically defined as a noninflammatory diarrheal disease.

Killed Whole-Cell Oral Cholera Vaccine Induces CCL20 Secretion by Human Intestinal Epithelial Cells in the Presence of the Short-Chain Fatty Acid, Butyrate

Short-chain fatty acids (SCFAs), such as acetate, butyrate, and propionate, modulate immune responses in the gut. However, the effect of SCFAs on mucosal vaccine-induced immune cell migration is poorly understood. Here, we investigated whether SCFAs modulate chemokine expression induced by the killed whole-cell oral cholera vaccine, Shanchol™, in human intestinal epithelial cells. Shanchol™ induced expression of CCL2, CCL5, CCL20, and CXCL10 at the mRNA level, but not at the protein level. Interestingly, CCL20 secretion was substantially increased by co-stimulation with Shanchol™ and butyrate, while neither acetate nor propionate showed such effect. Enhanced CCL20 secretion was associated with GPR109A activation, and histone deacetylase (HDAC) inhibition. In addition, co-treatment with Shanchol™ and butyrate synergistically increased the secretion of adenosine triphosphate (ATP). Moreover, CCL20 secretion was decreased by inhibiting the extracellular ATP receptor P2X7. However, neither inflammasomes nor caspases were involved in CCL20 production. The culture supernatant of cells treated with Shanchol™ and butyrate augmented human immature dendritic cell migration. Collectively, these results suggest that butyrate enhances Shanchol™-induced CCL20 production in human intestinal epithelial cells via HDAC inhibition and ATP-P2X7 signaling by activating GPR109A. These effects potentially enhance the mucosal immune responses in the gut induced by this oral cholera vaccine.

6-Gingerol inhibits Vibrio cholerae-induced proinflammatory cytokines in intestinal epithelial cells via modulation of NF-κB

Context The effect of 6-gingerol (6G), the bioactive component of Zingiber officinale Roscoe (Zingiberaceae), in the reduction of Vibrio cholerae (Vibrionaceae)-induced inflammation has not yet been reported. Materials and methods Cell viability assay was performed to determine the working concentration of 6G. Elisa and RT-PCR were performed with Int 407 cells treated with 50 μM 6G and 100 multiplicity of infection (MOI) V. cholerae for 0, 2, 3, 3.5, 6 and 8 h to determine the concentration of IL-8, IL-6, IL-1α and IL-1β in both protein and RNA levels. Furthermore, the effect of 50 μM 6G on upstream MAP-kinases and NF-κB signalling pathways was evaluated at 0, 10, 15, 30, 60 and 90 min. Results The effective dose (ED50) value of 6G was found to be 50 μM as determined by cell viability assay. Pre-treatment with 50 μM 6G reduced V. cholerae infection-triggered levels of IL-8, IL-6, IL-1α and IL-1β by 3.2-fold in the protein level and two-fold in the RNA level at 3.5 h. The levels of MAP-kinases signalling molecules like p38 and ERK1/2 were also reduced by two- and three-fold, respectively, after 30 min of treatment. Additionally, there was an increase in phosphorylated IκBα and down-regulation of p65 resulting in down-regulation of NF-κB pathway. Conclusion Our results showed that 6G could modulate the anti-inflammatory responses triggered by V. cholerae-induced infection in intestinal epithelial cells by modulating NF-κB pathway.

Vibrio cholerae-induced inflammation in the neonatal mouse cholera model

Vibrio cholerae is the causative agent of the acute diarrheal disease of cholera. Innate immune responses to V. cholerae are not a major cause of cholera pathology, which is characterized by severe, watery diarrhea induced by the action of cholera toxin. Innate responses may, however, contribute to resolution of infection and must be required to initiate adaptive responses after natural infection and oral vaccination. Here we investigated whether a well-established infant mouse model of cholera can be used to observe an innate immune response. We also used a vaccination model in which immunized dams protect their pups from infection through breast milk antibodies to investigate innate immune responses after V. cholerae infection for pups suckled by an immune dam. At the peak of infection, we observed neutrophil recruitment accompanied by induction of KC, macrophage inflammatory protein 2 (MIP-2), NOS-2, interleukin-6 (IL-6), and IL-17a. Pups suckled by an immunized dam did not mount this response. Accessory toxins RtxA and HlyA played no discernible role in neutrophil recruitment in a wild-type background. The innate response to V. cholerae deleted for cholera toxin-encoding phage (CTX) and part of rtxA was significantly reduced, suggesting a role for CTX-carried genes or for RtxA in the absence of cholera toxin (CTX). Two extracellular V. cholerae DNases were not required for neutrophil recruitment, but DNase-deficient V. cholerae caused more clouds of DNA in the intestinal lumen, which appeared to be neutrophil extracellular traps (NETs), suggesting that V. cholerae DNases combat NETs. Thus, the infant mouse model has hitherto unrecognized utility for interrogating innate responses to V. cholerae infection.

Immunogenicity and protective efficacy of Vibrio cholerae outer membrane vesicles in rabbit model

We show here that oral immunization with purified outer membrane vesicles (OMVs) of Vibrio cholerae induces a prolonged high rise in the protective antibody titre. Rabbit immune sera were vibriocidal against the homologous and against several heterologous V. cholerae strains in vitro. In addition, OMV immunization conferred significant protective immunity against subsequent bacterial challenges. Thirty OMV-immunized rabbits were challenged with different V. cholerae strains; each challenged group contained five immunized and three unimmunized animals. All the immunized rabbits survived bacterial challenges and were healthy after 24 h, except the two from each group that received the SG24 and SG06 strains, respectively, which developed watery diarrhoea. In contrast, all the unimmunized animals developed cholera-like symptoms, with a death toll of eight within 24 h of challenge. This is the first report of the induction of protective immunity by V. cholerae OMVs in a rabbit model (removable intestinal tie-adult rabbit diarrhoea) that mimics the human disease. Finally, OMVs were found to be significantly less reactogenic than the live and the heat-killed bacteria. Our studies show that oral immunization with OMVs of V. cholerae may induce long-term immunity and may be useful as a 'nonliving' vaccine candidate for the future.

Studies on a novel serine protease of a ΔhapAΔprtV Vibrio cholerae O1 strain and its role in hemorrhagic response in the rabbit ileal loop model

Background

Two well-characterized proteases secreted by Vibrio cholerae O1 strains are hemagglutinin protease (HAP) and V. cholerae protease (PrtV). The hapA and prtV knock out mutant, V. cholerae O1 strain CHA6.8ΔprtV, still retains residual protease activity. We initiated this study to characterize the protease present in CHA6.8ΔprtV strain and study its role in pathogenesis in rabbit ileal loop model (RIL).

Methodology/Principal Findings

We partially purified the residual protease secreted by strain CHA6.8ΔprtV from culture supernatant by anion-exchange chromatography. The major protein band in native PAGE was identified by MS peptide mapping and sequence analysis showed homology with a 59-kDa trypsin-like serine protease encoded by VC1649. The protease activity was partially inhibited by 25 mM PMSF and 10 mM EDTA and completely inhibited by EDTA and PMSF together. RIL assay with culture supernatants of strains C6709 (FA ratio 1.1+/−0.3 n = 3), CHA6.8 (FA ratio 1.08+/−0.2 n = 3), CHA6.8ΔprtV (FA ratio 1.02+/−0.2 n = 3) and partially purified serine protease from CHA6.8ΔprtV (FA ratio 1.2+/−0.3 n = 3) induced fluid accumulation and histopathological studies on rabbit ileum showed destruction of the villus structure with hemorrhage in all layers of the mucosa. RIL assay with culture supernatant of CHA6.8ΔprtVΔVC1649 strain (FA ratio 0.11+/−0.005 n = 3) and with protease incubated with PMSF and EDTA (FA ratio 0.3+/−0.05 n = 3) induced a significantly reduced FA ratio with almost complete normal villus structure.

Conclusion

Our results show the presence of a novel 59-kDa serine protease in a ΔhapAΔprtV V. cholerae O1 strain and its role in hemorrhagic response in RIL model.

Activation of proinflammatory response in human intestinal epithelial cells following Vibrio cholerae infection through PI3K/Akt pathway

Vibrio cholerae activates proinflammatory response in cultured intestinal epithelial cells. In this study, we demonstrate that V. cholerae O395 infection of intestinal epithelial cells results in the activation of Akt. Inhibition of Akt significantly decreases IL-1alpha, IL-6, and TNF-alpha production in V. cholerae infected Int407 cells. Analysis of the mechanisms of Akt influences on cytokine response demonstrates that Akt promotes NF-kappaB activation. We have extended these findings to show that Akt activation may be regulated by bacterial genes associated with virulence, adherence, or motility. Insertion mutants in the virulence genes coding for CtxA, ToxT, and OmpU of V. cholerae modulate the activation of PI3K/Akt signaling pathway, whereas an aflagellate non-motile mutant (O395FLAN) and a adherent and less motile mutant (O395Y3N/O395Y4N) of V. cholerae both show very significant down-regulation of Akt activity in Int407 cells. Together, these observations indicate that Akt promotes proinflammatory cytokine production by V. cholerae infected human intestinal epithelial cells through its influences on NF-kappaB.

Involvement of intracellular signaling cascades in inflammatory responses in human intestinal epithelial cells following Vibrio cholerae infection

Vibrio cholerae, the etiological agent of cholera, leads to the induction of host cell nuclear responses and the activation of proinflammatory cytokines in the cultured intestinal epithelial cells. However, the host cell signaling pathway leading to proinflammatory response is not explored. In this study, we demonstrated that V. cholerae infection on intestinal epithelial cells results in the activation of extracellular signal-regulated kinases1/2(ERK1/2) and p38 of the mitogen activated protein kinase (MAPK) family. V. cholerae induced intracellular pathways in Int407 cells leading to the activation of protein kinase A (PKA) and protein tyrosine kinase (PTK) in upstream of MAPK and nuclear factor-kappaB (NF-kappaB) pathway. Inhibitor study of Ca(2+) and phospholipase-gamma (PLC-gamma) pathway suggested the possible involvement of Ca(2+) signaling in the V. cholerae pathogenesis. V. cholerae culture supernatants as also insertional mutants of ctxA, toxR and toxT genes modulate the activation of MAPK and NF-kappaB signaling pathways. MAPK and NF-kappaB signaling pathway activation were also modulated by adherence and motility of V. cholerae. Studies with inhibitor of NF-kappaB, MAPK, PTK, PKA, PKC, Ca(2+) and PLC pathways showed differential cytokine secretion in Int407 following V. cholerae infection. Therefore V. cholerae mediated induction of nuclear responses through signal transduction pathway and subsequent activation of proinflammatory cytokines in Int407 modulated by V. cholerae secretory factors, virulence, adhesion/motility which might explain some of its reactogenic mechanisms.

Vibrio cholerae flagellins induce Toll-like receptor 5-mediated interleukin-8 production through mitogen-activated protein kinase and NF-kappaB activation

Vaccine reactogenicity has complicated the development of safe and effective live, oral cholera vaccines. Delta ctx Vibrio cholerae mutants have been shown to induce inflammatory diarrhea in volunteers and interleukin-8 (IL-8) production in cultured intestinal epithelial cells. Bacterial flagellins are known to induce IL-8 production through Toll-like receptor 5 (TLR5). Since the V. cholerae genome encodes five distinct flagellin proteins, FlaA to FlaE, with homology to conserved TLR5 recognition regions of Salmonella FliC, we hypothesized that V. cholerae flagellins may contribute to IL-8 induction through TLR5 and mitogen-activated protein kinase (MAPK) signaling. Each purified recombinant V. cholerae flagellin induced IL-8 production in T84 intestinal epithelial cells and also induced nuclear factor kappa B (NF-kappaB) activation in HEK293T/TLR5 transfectants, which was blocked by cotransfection with a TLR5 dominant-negative construct, demonstrating TLR5 specificity. Supernatants derived from Delta flaAC and Delta flaEDB mutants induced IL-8 production in HT-29 intestinal epithelial cells and in HEK293T cells overexpressing TLR5, whereas Delta flaABCDE supernatants induced significantly less IL-8 production, demonstrating the contribution of multiple flagellins in IL-8 induction. NF-kappaB activation by Delta flaABCDE supernatants was partially restored by flaA or flaAC complementation. Western analysis confirmed the presence of V. cholerae flagellins in culture supernatants. Purified recombinant V. cholerae FlaA activated the MAPKs p38, c-jun N-terminal kinase (JNK), and extracellular regulated kinase (ERK) in T84 cells. FlaA-induced IL-8 production in T84 cells was inhibited by the p38 inhibitor in combination with either the JNK or ERK inhibitors. Collectively, these data suggest that V. cholerae flagellins are present in culture supernatants and can induce TLR5- and MAPK-dependent IL-8 secretion in host cells.

Blastocystis ratti contains cysteine proteases that mediate interleukin-8 response from human intestinal epithelial cells in an NF-kappaB-dependent manner

Blastocystis is a ubiquitous enteric protozoan found in the intestinal tracts of humans and a wide range of animals. Evidence accumulated over the last decade suggests association of Blastocystis with gastrointestinal disorders involving diarrhea, abdominal pain, constipation, nausea, and fatigue. Clinical and experimental studies have associated Blastocystis with intestinal inflammation, and it has been shown that Blastocystis has potential to modulate the host immune response. Blastocystis is also reported to be an opportunistic pathogen in immunosuppressed patients, especially those suffering from AIDS. However, nothing is known about the parasitic virulence factors and early events following host-parasite interactions. In the present study, we investigated the molecular mechanism by which Blastocystis activates interleukin-8 (IL-8) gene expression in human colonic epithelial T84 cells. We demonstrate for the first time that cysteine proteases of Blastocystis ratti WR1, a zoonotic isolate, can activate IL-8 gene expression in human colonic epithelial cells. Furthermore, we show that NF-kappaB activation is involved in the production of IL-8. In addition, our findings show that treatment with the antiprotozoal drug metronidazole can avert IL-8 production induced by B. ratti WR1. We also show for the first time that the central vacuole of Blastocystis may function as a reservoir for cysteine proteases. Our findings will contribute to an understanding of the pathobiology of a poorly studied parasite whose public health importance is increasingly recognized.

Transcriptional upregulation of inflammatory cytokines in human intestinal epithelial cells following Vibrio cholerae infection

Coordinated expression and upregulation of interleukin-1alpha, interleukin-1beta, tumor necrosis factor-alpha, interleukin-6, granulocyte-macrophage colony-stimulating factor, interleukin-8, monocyte chemotactic protein-1 (MCP-1) and epithelial cell derived neutrophil activator-78, with chemoattractant and proinflammatory properties of various cytokine families, were obtained in the intestinal epithelial cell line Int407 upon Vibrio cholerae infection. These proinflammatory cytokines also showed increased expression in T84 cells, except for interleukin-6, whereas a striking dissimilarity in cytokine expression was observed in Caco-2 cells. Gene expression studies of MCP-1, granulocyte-macrophage colony-stimulating factor, interleukin-1alpha, interleukin-6 and the anti-inflammatory cytokine transforming growth factor-beta in Int407 cells with V. cholerae culture supernatant, cholera toxin, lipopolysaccharide and ctxA mutant demonstrated that, apart from cholera toxin and lipopolysaccharide, V. cholerae culture supernatant harbors strong inducer(s) of interleukin-6 and MCP-1 and moderate inducer(s) of interleukin-1alpha and granulocyte-macrophage colony-stimulating factor. Cholera toxin- or lipopolysaccharide-induced cytokine expression is facilitated by activation of nuclear factor-kappaB (p65 and p50) and cAMP response element-binding protein in Int407 cells. Studies with ctxA mutants of V. cholerae revealed that the mutant activates the p65 subunit of nuclear factor-kappaB and cAMP response element-binding protein, and as such the activation is mediated by cholera toxin-independent factors as well. We conclude that V. cholerae elicits a proinflammatory response in Int407 cells that is mediated by activation of nuclear factor-kappaB and cAMP response element-binding protein by cholera toxin, lipopolysaccharide and/or other secreted products of V. cholerae.

Enterotoxigenicity of mature 45-kilodalton and processed 35-kilodalton forms of hemagglutinin protease purified from a cholera toxin gene-negative Vibrio cholerae non-O1, non-O139 strain

Cholera toxin gene-negative Vibrio cholerae non-O1, non-O139 strain PL-21 is the etiologic agent of cholera-like syndrome. Hemagglutinin protease (HAP) is one of the major secretory proteins of PL-21. The mature 45-kDa and processed 35-kDa forms of HAP were purified in the presence and absence of EDTA from culture supernatants of PL-21. Enterotoxigenicities of both forms of HAP were tested in rabbit ileal loop (RIL), Ussing chamber, and tissue culture assays. The 35-kDa HAP showed hemorrhagic fluid response in a dose-dependent manner in the RIL assay. Histopathological examination of 20 microg of purified protease-treated rabbit ileum showed the presence of erythrocytes and neutrophils in the upper part of the villous lamina propria. Treatment with 40 microg of protease resulted in gross damage of the villous epithelium with inflammation, hemorrhage, and necrosis. The 35-kDa form of HAP, when added to the lumenal surface of rat ileum loaded in an Ussing chamber, showed a decrease in the intestinal short-circuit current and a cell rounding effect on HeLa cells. The mature 45-kDa form of HAP showed an increase in intestinal short-circuit current in an Ussing chamber and a cell distending effect on HeLa cells. These results show that HAP may play a role in the pathogenesis of PL-21.

Induction of interleukin-8 production via nuclear factor-kappaB activation in human intestinal epithelial cells infected with Vibrio vulnificus

Vibrio vulnificus, a Gram-negative estuarine bacterium, is a causative agent of food-borne diseases, such as life-threatening septicaemia and wound infection disease. V. vulnificus penetrating into the epithelial barrier stimulates an inflammatory response in the adjacent mucosa. Therefore, interaction between V. vulnificus and epithelial cells is important for understanding of both the immunology of mucosal surfaces and V. vulnificus. In this study, we investigated the effect and action mechanism of V. vulnificus infection on production of interleukin (IL)-8, a proinflammatory cytokine, in human intestinal epithelial INT-407 cells. V. vulnificus infection significantly induced IL-8 production in a time- and multiplicity of infection (MOI)-dependent manner, as determined by human IL-8 enzyme-linked immunosorbent assay (ELISA). In addition, V. vulnificus infection significantly increased IL-8 mRNA levels in INT-407 cells, indicating that the increased IL-8 production by V. vulnificus occurred at the transcriptional level. V. vulnificus infection also enhanced IL-8 gene promoter activity in INT-407 cells transiently transfected with IL-8 promoter constructs, but this effect was impaired in INT-407 cells transfected with IL-8 promoter constructs deleted or mutated of a kappaB site. V. vulnificus infection increased the nuclear factor-kappaB (NF-kappaB) binding activity to a kappaB site and the degradation of IkappaB-alpha protein in a time- and a MOI-dependent manner. Furthermore, BAY11-7082, an inhibitor of NF-kappaB activation, significantly reduced the IL-8 production, NF-kappaB binding activity and IkappaB-alpha degradation induced by V. vulnificus infection. Taken together, these results indicate clearly that V. vulnificus infection significantly induces IL-8 production in human intestinal epithelial cells via NF-kappaB activation.

Cholera toxin induced novel genes in human lymphocytes and monocytes

Cholera toxin (CT) is well known as an inducer of the accumulation of cellular cAMP through the ADP-ribosylation of the Gs protein by CT. CT is also one of the most powerful mucosal adjuvants. However, the molecular mechanisms of the CT adjuvanticity are not well understood. Here, the transcriptional responses of cultured human lymphocytes and monocytes in response to CT were analyzed using differential display-PCR. The full complement of cellular mRNA was examined by high resolution polyarylamide gel electrophoresis and sequence analyses of the PCR products of 240 primer sets. Over 100 genes with altered expression were initially identified. The expressions of 65 of these genes were further analyzed and confirmed using custom glass cDNA arrays, RT-PCR and real-time PCR. Immunomodulatory genes such as CD2, HIF1, CXCL2, L-plastin, LILR and IFI30 were affected by CT. In addition, 14 novel genes with previously unknown functions were found to be CT induced. These CT induced gene expression alterations provide more insight in the mechanisms of CT actions. The CT induced gene expressions alterations could contribute to the CT adjuvanticity.

Upregulation of human mitochondrial NADH dehydrogenase subunit 5 in intestinal epithelial cells is modulated byVibrio choleraepathogenesis

Cholera still remains an important global predicament especially in India and other developing countries. Vibrio cholerae, the etiologic agent of cholera, colonizes the small intestine and produces an enterotoxin that is largely responsible for the watery diarrheal symptoms of the disease. Using RNA arbitrarily primed PCR, ND5 a mitochondria encoded subunit of complex I of the mitochondrial respiratory chain was found to be upregulated in the human intestinal epithelial cell line Int407 following exposure to V. cholerae. The upregulation of ND5 was not observed when Int407 was infected with Escherichia coli strains. Incubation with heat-killed V. cholerae or cholera toxin or culture supernatant also showed no such upregulation indicating the involvement of live bacteria in the process. Infection of the monolayer with aflagellate non-motile mutant of V. cholerae O395 showed a very significant (59-fold) downregulation of ND5. In contrast, a remarkable upregulation of ND5 expression (200-fold) was observed in a hyperadherent icmF insertion mutant with reduced motility. V. cholerae cheY4 null mutant defective in adherence and motility also resulted in significantly reduced levels of ND5 expression while mutant with the cheY4 gene duplicated showing increased adherence and motility resulted in increased expression of ND5. These results clearly indicate that both motility and adherence to intestinal epithelial cells are possible triggering factors contributing to ND5 mRNA expression by V. cholerae. Interestingly infection with insertion mutant in the gene coding for ToxR, the master regulator of virulence in V. cholerae resulted in significant downregulation of ND5 expression. However, infection with ctxA or toxT insertion mutants did not show any significant changes in ND5 expression compared to wild-type. Almost no expression of ND5 was observed in case of mutation in the gene coding for OmpU, a ToxR activated protein. Thus, infection of Int407 with virulence mutant strains of V. cholerae revealed that the ND5 expression is modulated by the virulence of V. cholerae in a ToxT independent manner. Although no difference in the mitochondrial copy number could be detected between infected and uninfected cells, the modulation of the expression of other mitochondrial genes were also observed. Incidentally, upon V. cholerae infection, complex I activity was found to increase about 3-folds after 6 h. This is the first report of alteration in mitochondrial gene expression upon infection of a non-invasive enteric bacterium like V. cholerae showing its modulation with adherence, motility and virulence of the organism.

Inhibitory effect of luteolin on TNF-α-induced IL-8 production in human colon epithelial cells

Interleukin (IL)-8 plays a central role in the initiation and maintenance of inflammatory responses in the inflammatory bowel disease. The proinflammatory cytokine-mediated production of IL-8 requires activation of various kinases, which leads to the IkappaB degradation and NF-kappaB activation. In this study, we investigated the role of luteolin, a major flavonoid of Lonicera japonica, on TNF-alpha-induced IL-8 production in human colonic epithelial cells. HT29 cells were stimulated with TNF-alpha in the presence or absence of luteolin. IL-8 production was measured by enzyme-linked immunosorbent assay (ELISA) and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis, and the mitogen-activated protein kinases (MAPKs) activation and IkappaB degradation were determined by Western blot analysis. NF-kappaB activation was assessed by the electrophoretic motility shift assay (EMSA). Luteolin suppressed TNF-alpha-induced IL-8 production in dose-dependent manner. In addition, luteolin inhibited TNF-alpha-induced phosphorylation of p38 MAPK and extracellular-regulated kinases (ERK), IkappaB degradation, and NF-kappaB activation. These results suggest that luteolin has the inhibitory effects on TNF-alpha-induced IL-8 production in the intestinal epithelial cells through blockade in the phosphorylation of MAPKs, following IkappaB degradation and NF-kappaB activation.

Transcriptional responses of intestinal epithelial cells to infection with Vibrio cholerae

Vibrio cholerae is a noninvasive enteric bacterium that causes the severe diarrheal disease cholera. Candidate cholera vaccines have been engineered by deleting genes encoding known virulence factors in V. cholerae; however, many of these attenuated strains were still reactogenic in human volunteers. In this study, DNA arrays were utilized to monitor the transcriptional responses of human intestinal epithelial cells (T84) to eight strains of V. cholerae, including attenuated, toxigenic, and environmental isolates. cDNA probes generated from host RNA samples were hybridized against low- and high-density gene arrays. V. cholerae induced the transcription of a variety of host genes and repressed the expression of a lower number of genes. Expression patterns were confirmed for certain genes by reverse transcriptase PCR and enzyme-linked immunosorbent assays. A core subset of genes was found to be differentially regulated in all experiments. These genes included genes involved in innate mucosal immunity, intracellular signaling, and cellular proliferation. Reactogenic vaccine strains induced greater expression of genes for certain proinflammatory cytokines than nonreactogenic strains. Wild-type and attenuated derivatives induced and repressed many genes in common, although there were differences in the transcription profiles. These results indicate that the types of host genes modulated by attenuated V. cholerae, and the extent of their induction, may mediate the symptoms seen with reactogenic cholera vaccine strains.

Modulation of human enteric epithelial barrier and ion transport function by Peyer’s patch lymphocytes

AIM: To investigate the role of Peyer’s patch lymphocytes in the regulation of enteric epithelial barrier and ion transport function in homeostasis and host defense.

METHODS: Mouse Peyer’s patch lymphocytes were co-cultured with human intestinal epithelial cell line Caco-2 either in the mixed or separated (isolated but permeable compartments) culture configuration. Barrier and transport functions of the Caco-2 epithelial monolayers were measured with short-circuit current (Isc) technique. Release of cytokines was measured by enzyme-linked immunosorbent assay (ELISA) and cytokine mRNA expression was analyzed by semi-quantitative RT-PCR. Barrier and iontransport functions of both culture conditions following exposure to Shigella lipopolysaccharide (LPS) were also examined.

RESULTS: The transepithelial resistance (TER) of the epithelial monolayers co-cultured with Peyer’s patch lymphocytes was maintained whereas that of the Caco-2 monolayers alone significantly decreased after eight days in culture. The forskolin-induced anion secretion, in either absence or presence of LPS, was significantly suppressed in the both co-cultures as compared with the Caco-2 cells alone. Furthermore, only the mixed co-culture condition induced the expression and release of mIL-6 from Peyer’s patch lymphocytes, which could be further enhanced by LPS. However, both co-culture conditions suppressed expression and release of epithelial hIL-8 under the unstimulated conditions, while the treatment with LPS stimulated their hIL-8 expression and release.

CONCLUSION: Peyer’s patch lymphocytes may modulate intestinal epithelial barrier and ion transport function in homeostasis and host defense via cell-cell contact and cytokine signaling.

Association of adherence and motility in interleukin 8 induction in human intestinal epithelial cells by Vibrio cholerae

Interleukin 8 (IL-8) mRNA expression in Vibrio cholerae-infected human intestinal epithelial cells Int407 was determined by quantitative real-time RT-PCR and secretion measured by ELISA. Incubation of Int407 with V. cholerae O395 resulted in increased IL-8 mRNA expression as early as within 2 h of infection. Kinetics of IL-8 secretion reached a peak at about 8 h (780 pg/ml) and decreased thereafter. Induction of IL-8 was significantly high among various toxin-producing strains of V. cholerae belonging to serovar O1, O139 and non-O1 compared to non-toxinogenic strains. Induction of IL-8 was maximum in V. cholerae O395, required live cells and was dependent on de novo protein synthesis. The bacterial culture supernatant and crude cell envelope showed IL-8 stimulating activity. Infection of the monolayer with V. cholerae O395 cheY4 null mutant (O395YN), defective in adherence and motility, resulted in highly reduced levels of IL-8 expression, while hyperadherent and hypermotile mutant (O395Y) with the cheY4 gene duplicated also showed very high IL-8 expression. Another hyperadherent icmF insertion mutant (O395F) with reduced motility showed almost half the amount of IL-8 expression compared to O395Y. These results clearly indicate that both motility and adherence to intestinal epithelial cells are possible triggering factors contributing to IL-8 mRNA expression by V. cholerae.

Acanthoic acid inhibits IL-8 production via MAPKs and NF-κB in a TNF-α-stimulated human intestinal epithelial cell line

BACKGROUND

Intestinal epithelial cells (IECs) can produce cytokines and chemokines that play an important role in the mucosal immune response. Regulation of this production is important to prevent inflammatory tissue damage. The root and stem barks of Acanthopanax species have been used as a tonic and sedative as well as in the treatment of rheumatism and diabetes. The aim of this study was to examine the inhibitory effect of acanthoic acid isolated from Acanthopanax koreanum (Araliaceae), on IL-8 production via mitogen-activated protein kinases (MAPKs) and nuclear factor-kappa B (NF-kappaB) in TNF-alpha-stimulated human colon epithelial cells.

METHODS

HT29 cells were stimulated with TNF-alpha in the presence or absence of acanthoic acid. IL-8 production was measured by enzyme-linked immunosorbent assay (ELISA) and reverse transcription-PCR (RT-PCR). MAPK activation and IkappaB/NF-kappaB expression were assessed by Western blot analysis. NF-kappaB activation was determined using immunofluorescence localization and electrophoretic mobility shift assay (EMSA).

RESULTS

Acanthoic acid suppressed TNF-alpha-induced IL-8 production in a dose-dependent manner. Furthermore, acanthoic acid inhibited TNF-alpha-induced MAPKs (p38, JNK1/2, and ERK1/2) activation, IkappaB degradation, NF-kappaB nuclear translocation, and NF-kappaB/DNA binding activity.

CONCLUSION

Acanthoic acid might inhibit TNF-alpha-mediated IL-8 production by blocking in both the MAPKs and NF-kappaB pathways in HT29 cells.

Induction of interleukin-8 in T84 cells by Vibrio cholerae

The induction of interleukin-8 (IL-8) in vitro has been suggested to correlate with the reactogenicity of Vibrio cholerae vaccine candidates. V. cholerae vaccine candidate 638, a hemagglutinin protease/hap-defective strain, was recently reported to be well tolerated in human volunteers, suggesting a role for Hap in reactogenicity. We examined the role of hap in the induction of IL-8 in intestinal epithelial T84 cells. Wild-type V. cholerae strains 3038 and C7258 and a vaccine candidate strain, JBK70, induced levels of IL-8 similar to those of their isogenic hap mutants. Supernatant containing Hap did not stimulate IL-8 production at a variety of concentrations tested, suggesting that Hap itself does not induce IL-8 production. Furthermore, supernatant from CVD115, which had deletions of hap and rtxA (encoding repeats in toxin) and was derived from a reactogenic strain, CVD110, induced IL-8 production in T84 cells in a dose-dependent manner. The IL-8-stimulating activity of CVD115 culture supernatants was growth phase dependent and was strongest in stationary phase cultures. This IL-8 stimulator(s) was resistant to heat treatment but sensitive to proteinase. Protease activity in vitro did not correlate with the reactogenicity of V. cholerae vaccine candidates. Our data suggest that Hap is not an IL-8 inducer in T84 cells and that the IL-8 stimulator in the supernatant of V. cholerae culture may play a role in reactogenicity.

Construction and characterisation of O139 cholera vaccine candidates

The hemagglutinin/protease (HA/P) seems to be an attractive locus for the insertion of heterologous tags in live cholera vaccine strains. A deltaCTXphi spontaneous mutant derived from a pathogenic strain of O139 Vibrio cholerae was sequentially manipulated to obtain hapA Colon, two colons celA derivatives which were later improved in their environmental safety by means of a thyA mutation. All the strains here obtained showed similar phenotypes in traits known to be remarkable for live cholera vaccines irrespective of their motility phenotypes, although the hapA mutants had a 10-fold decrease in their colonisation capacity compared with their parental strains in the infant mouse cholera model. However, the subsequent thyA mutation did not affect their colonisation properties in the same model. These preliminary results pave the way for further clinical assays to confirm the possibilities of these vaccine prototypes as safe and effective tools for the prevention of O139 cholera.