Monocyte Chemoattractant Protein-1 Production by Intestinal Epithelial CellsIn Vitro:A Role for p38 in Epithelial Chemokine Expression

Epithelial RABGEF1 deficiency promotes intestinal inflammation by dysregulating intrinsic MYD88-dependent innate signaling

Intestinal epithelial cells (IECs) contribute to the regulation of intestinal homeostasis and inflammation through their interactions with the environment and host immune responses. Yet our understanding of IEC-intrinsic regulatory pathways remains incomplete. Here, we identify the guanine nucleotide exchange factor RABGEF1 as a regulator of intestinal homeostasis and innate pathways dependent on IECs. Mice with IEC-specific Rabgef1 deletion (called Rabgef1^IEC-KO mice) developed a delayed spontaneous colitis associated with the local upregulation of IEC chemokine expression. In mouse models of colitis based on Interleukin-10 deficiency or dextran sodium sulfate (DSS) exposure, we found that IEC-intrinsic RABGEF1 deficiency exacerbated development of intestinal pathology and dysregulated IEC innate pathways and chemokine expression. Mechanistically, we showed that RABGEF1 deficiency in mouse IECs in vitro was associated with an impairment of early endocytic events, an increased activation of the p38 mitogen-activated protein kinase (MAPK)-dependent pathway, and increased chemokine secretion. Moreover, we provided evidence that the development of spontaneous colitis was dependent on microbiota-derived signals and intrinsic MYD88-dependent pathways in vivo. Our study identifies mouse RABGEF1 as an important regulator of intestinal inflammation, MYD88-dependent IEC-intrinsic signaling, and chemokine production. This suggests that RABGEF1-dependent pathways represent interesting therapeutic targets for inflammatory conditions in the gut.

Skim milk powder with high content of Maillard reaction products affect weight gain, organ development and intestinal inflammation in early life in rats

BACKGROUND

The intestinal tract is important for development of immune tolerance and disturbances are suggested to trigger autoimmune disorders. The aim of this study was to explore the effect of Maillard products in skim milk powder obtained after long storage, compared to fresh skim milk powder.

METHODS

Young rats were weaned onto a diet based on skim milk powder with high concentration of Maillard products (HM-SM, n = 18) or low (C-SM, n = 18) for one week or four weeks. Weekly body weight and feed consumption were noted. At the end, organ weights, intestinal histology, permeability and inflammatory cytokines were evaluated.

RESULTS

Rats fed with HM-SM had after one week, 15% less weight gain than controls, despite equal feed intake. After one week thymus and spleen were smaller, intestinal mucosa thickness was increased and acute inflammatory cytokines (IL-17, IL-1β, MCP-1) were elevated. After four weeks, cytokines associated with chronic intestinal inflammation (fractalkine, IP-10, leptin, LIX, MIP-2, RANTES and VEGF) were increased in rats fed with HM-SM compared to C-SM.

CONCLUSION

High content of Maillard products in stored milk powder caused an intestinal inflammation. Whether this is relevant for tolerance development and future autoimmune diseases remains to be explored.

Deficiency of MAPK-activated protein kinase 2 (MK2) prevents adverse remodelling and promotes endothelial healing after arterial injury

Maladaptive remodelling of the arterial wall after mechanical injury (e. g. angioplasty) is characterised by inflammation, neointima formation and media hypertrophy, resulting in narrowing of the affected artery. Moreover, mechanical injury of the arterial wall causes loss of the vessel protecting endothelial cell monolayer. Mitogen-activated protein kinase (MAPK)-activated protein kinase 2 (MK2), a major downstream target of p38 MAPK, regulates inflammation, cell migration and proliferation, essential processes for vascular remodelling and reendothelialisation. Therefore, we investigated the role of MK2 in remodelling and reendothelialisation after arterial injury in genetically modified mice in vivo. Hypercholesterolaemic low-densitylipoprotein- receptor-deficient mice (ldlr-/- ) were subjected to wire injury of the common carotid artery. MK2-deficiency (ldlr-/-/mk2-/- ) nearly completely prevented neointima formation, media hypertrophy, and lumen loss after injury. This was accompanied by reduced proliferation and migration of MK2-deficient smooth muscle cells. In addition, MK2-deficiency severely reduced monocyte adhesion to the arterial wall (day 3 after injury, intravital microscopy), which may be attributed to reduced expression of the chemokine ligands CCL2 and CCL5. In line, MK2-deficiency significantly reduced the content of monocytes, neutrophiles and lymphocytes of the arterial wall (day 7 after injury, flow cytometry). In conclusion, in a model of endothelial injury (electric injury), MK2-deficiency strongly increased proliferation of endothelial cells and improved reendothelialisation of the arterial wall after injury. Deficiency of MK2 prevents adverse remodelling and promotes endothelial healing of the arterial wall after injury, suggesting that MK2-inhibition is a very attractive intervention to prevent restenosis after percutaneous therapeutic angioplasty.

Serratia marcescens is injurious to intestinal epithelial cells

Diarrhea causes substantial morbidity and mortality in children in low-income countries. Although numerous pathogens cause diarrhea, the etiology of many episodes remains unknown. Serratia marcescens is incriminated in hospital-associated infections, and HIV/AIDS associated diarrhea. We have recently found that Serratia spp. may be found more commonly in the stools of patients with diarrhea than in asymptomatic control children. We therefore investigated the possible enteric pathogenicity of S. marcescens in vitro employing a polarized human colonic epithelial cell (T84) monolayer. Infected monolayers were assayed for bacterial invasion, transepithelial electrical resistance (TEER), cytotoxicity, interleukin-8 (IL-8) release and morphological changes by scanning electron microscopy. We observed significantly greater epithelial cell invasion by S. marcescens compared to Escherichia coli strain HS (p = 0.0038 respectively). Cell invasion was accompanied by reduction in TEER and secretion of IL-8. Lactate dehydrogenase (LDH) extracellular concentration rapidly increased within a few hours of exposure of the monolayer to S. marcescens. Scanning electron microscopy of S. marcescens-infected monolayers demonstrated destruction of microvilli and vacuolization. Our results suggest that S. marcescens interacts with intestinal epithelial cells in culture and induces dramatic alterations similar to those produced by known enteric pathogens.

Evidence for widespread epithelial damage and coincident production of monocyte chemotactic protein 1 in a murine model of intestinal ricin intoxication

The development of small-animal models is necessary to understand host responses and immunity to emerging infectious diseases and potential bioterrorism agents. In this report we have characterized a murine model of intestinal ricin intoxication. Ricin administered intragastrically (i.g.) to BALB/c mice at doses ranging from 1 to 10 mg/kg of body weight induced dose-dependent morphological changes in the proximal small intestine (i.e., duodenum), including widespread villus atrophy and epithelial damage. Coincident with epithelial damage was a localized increase in monocyte chemotactic protein 1, a chemokine known to be associated with inflammation of the intestinal mucosa. Immunity to intestinal ricin intoxication was achieved by immunizing mice i.g. with ricin toxoid and correlated with elevated levels of antitoxin mucosal immunoglobulin A (IgA) and serum IgG antibodies. We expect that this model will serve as a valuable tool in identifying the inflammatory pathways and protective immune responses that are elicited in the intestinal mucosa following ricin exposure and will prove useful in the evaluation of antitoxin vaccines and therapeutics.

Effector ExoU from the type III secretion system is an important modulator of gene expression in lung epithelial cells in response to Pseudomonas aeruginosa infection

Pseudomonas aeruginosa is an important pathogen in immunocompromised patients and secretes a diverse set of virulence factors that aid colonization and influence host cell defenses. An important early step in the establishment of infection is the production of type III-secreted effectors translocated into host cells by the bacteria. We used cDNA microarrays to compare the transcriptomic response of lung epithelial cells to P. aeruginosa mutants defective in type IV pili, the type III secretion apparatus, or in the production of specific type III-secreted effectors. Of the 18,000 cDNA clones analyzed, 55 were induced or repressed after 4 h of infection and could be classified into four different expression patterns. These include (i) host genes that are induced or repressed in a type III secretion-independent manner (32 clones), (ii) host genes induced specifically by ExoU (20 clones), and (iii) host genes induced in an ExoU-independent but type III secretion dependent manner (3 clones). In particular, ExoU was essential for the expression of immediate-early response genes, including the transcription factor c-Fos. ExoU-dependent gene expression was mediated in part by early and transient activation of the AP1 transcription factor complex. In conclusion, the present study provides a detailed insight into the response of epithelial cells to infection and indicates the significant role played by the type III virulence mechanism in the initial host response.

Post-transcriptional regulation of gene expression by mitogen-activated protein kinase p38

The mitogen-activated protein kinase p38 pathway was originally identified as a signalling cascade activated by pro-inflammatory stimuli and cellular stresses, and playing a critical role in the translational regulation of pro-inflammatory cytokine synthesis. In almost a decade since this discovery, a great deal has been learned about the role of the p38 pathway in the post-transcriptional regulation of pro-inflammatory gene expression. However, important questions remain to be answered concerning the specificity and mechanism or mechanisms of action of p38. This review describes recent progress and remaining puzzles in the field of post-transcriptional regulation by p38.

Role of mitogen-activated protein kinase pathways in the production of tumor necrosis factor-alpha, interleukin-10, and monocyte chemotactic protein-1 by Mycobacterium tuberculosis H37Rv-infected human monocytes

The role of mitogen-activated protein kinase (MAPK) pathways in the secretion of tumor necrosis factor (TNF)-alpha, interleukin (IL)-10, IL-8, and monocyte chemotactic protein-1 (MCP-1) was investigated in human monocytes that were infected with Mycobacterium tuberculosis H37Rv. Analysis of extracellular signal-regulated kinases 1 and 2 (ERK1/2) and p38 kinase showed rapid phosphorylation of both subfamilies in response to M. tuberculosis H37Rv. Using highly specific inhibitors of p38 (SB203580) and of MAPK kinase-1 (U0126 and PD98059), we found that both p38 and ERK were essential for M. tuberculosis H37Rv-induced TNF-alpha production, whereas activation of the p38 pathway, but not that of ERK, was essential for M. tuberculosis H37Rv-induced IL-10 production. Interestingly, the ERK pathway, but not that of p38, was critical for MCP-1 secretion from human monocytes that were infected with M. tuberculosis H37Rv. However, IL-8 secretion was not regulated by ERK1/2 or p38 MAPK. Collectively, these results suggest that induction of the MAPK pathway is required for the expression of TNF-alpha, IL-10, and MCP-1 by human monocytes during M. tuberculosis H37Rv infection.

Transforming growth factor-β1 enhances the secretion of monocyte chemoattractant protein-1 by the IEC-18 intestinal epithelial cell line

Intestinal epithelial cells (IEC) are known to produce monocyte chemoattractant protein-1 (MCP-1). However, MCP-1 production, as with many other cytokines, can be regulated by a network of cytokines present in the environment of the IEC. Both IEC and inflammatory cells have been shown to produce transforming growth factor-beta (TGF-beta), and the regulatory effect of this cytokine on MCP-1 secretion by IEC has not been determined. Using the IEC-18 cell line, we have found that TGF-beta1 alone induced the secretion of high levels of MCP-1. Treatment with TGF-beta1 also enhanced the levels of MCP-1 messenger ribonucleic acid. However, costimulation of the cells with TGF-beta1 and interleukin-1beta (IL-1beta) resulted in significant, but less than additive, increases in MCP-1 secretion. Finally, the enhancing effect of TGF-beta1 on MCP-1 secretion was not due to IL-6. These results suggest that TGF-beta1 from IEC or inflammatory cells may significantly enhance the secretion of MCP-1 by IEC and play an important role in inflamed mucosal tissues.