DR3 Regulates Intestinal Epithelial Homeostasis and Regeneration After Intestinal Barrier Injury.

BACKGROUND & AIMS: Tumor necrosis factor (TNF) superfamily member tumor necrosis factor-like protein 1A (TL1A) has been associated with the susceptibility and severity of inflammatory bowel diseases. However, the function of the tumor necrosis factor-like protein 1A and its receptor death receptor 3 (DR3) in the development of intestinal inflammation is incompletely understood. We investigated the role of DR3 expressed by intestinal epithelial cells (IECs) during intestinal homeostasis, tissue injury, and regeneration. METHODS: Clinical phenotype and histologic inflammation were assessed in C57BL/6 (wild-type), Tl1a-/- and Dr3-/- mice in dextran sulfate sodium (DSS)-induced colitis. We generated mice with an IEC-specific deletion of DR3 (Dr3ΔIEC) and assessed intestinal inflammation and epithelial barrier repair. In vivo intestinal permeability was assessed by fluorescein isothiocyanate dextran uptake. Proliferation of IECs was analyzed by bromodeoxyuridine incorporation. Expression of DR3 messenger RNA was assessed by fluorescent in situ hybridization. Small intestinal organoids were used to determine ex vivo regenerative potential. RESULTS: Dr3-/- mice developed more severe colonic inflammation than wild-type mice in DSS-induced colitis with significantly impaired IEC regeneration. Homeostatic proliferation of IECs was increased in Dr3-/- mice, but blunted during regeneration. Cellular localization and expression of the tight junction proteins Claudin-1 and zonula occludens-1 were altered, leading to increased homeostatic intestinal permeability. Dr3ΔIEC mice recapitulated the phenotype observed in Dr3-/- mice with increased intestinal permeability and IEC proliferation under homeostatic conditions and impaired tissue repair and increased bacterial translocation during DSS-induced colitis. Impaired regenerative potential and altered zonula occludens-1 localization also were observed in Dr3ΔIEC enteroids. CONCLUSIONS: Our findings establish a novel function of DR3 in IEC homeostasis and postinjury regeneration independent of its established role in innate lymphoid cells and T-helper cells.

Genetic coding variant in complement factor B (CFB) is associated with increased risk for perianal Crohn's disease and leads to impaired CFB cleavage and phagocytosis.

OBJECTIVE: Perianal Crohn's disease (pCD) occurs in up to 40% of patients with CD and is associated with poor quality of life, limited treatment responses and poorly understood aetiology. We performed a genetic association study comparing CD subjects with and without perianal disease and subsequently performed functional follow-up studies for a pCD associated SNP in Complement Factor B (CFB). DESIGN: Immunochip-based meta-analysis on 4056 pCD and 11 088 patients with CD from three independent cohorts was performed. Serological and clinical variables were analysed by regression analyses. Risk allele of rs4151651 was introduced into human CFB plasmid by site-directed mutagenesis. Binding of recombinant G252 or S252 CFB to C3b and its cleavage was determined in cell-free assays. Macrophage phagocytosis in presence of recombinant CFB or serum from CFB risk, or protective CD or healthy subjects was assessed by flow cytometry. RESULTS: Perianal complications were associated with colonic involvement, OmpC and ASCA serology, and serology quartile sum score. We identified a genetic association for pCD (rs4151651), a non-synonymous SNP (G252S) in CFB, in all three cohorts. Recombinant S252 CFB had reduced binding to C3b, its cleavage was impaired, and complement-driven phagocytosis and cytokine secretion were reduced compared with G252 CFB. Serine 252 generates a de novo glycosylation site in CFB. Serum from homozygous risk patients displayed significantly decreased macrophage phagocytosis compared with non-risk serum. CONCLUSION: pCD-associated rs4151651 in CFB is a loss-of-function mutation that impairs its cleavage, activation of alternative complement pathway, and pathogen phagocytosis thus implicating the alternative complement pathway and CFB in pCD aetiology.

BATF3 Protects Against Metabolic Syndrome and Maintains Intestinal Epithelial Homeostasis.

The intestinal immune system and microbiota are emerging as important contributors to the development of metabolic syndrome, but the role of intestinal dendritic cells (DCs) in this context is incompletely understood. BATF3 is a transcription factor essential in the development of mucosal conventional DCs type 1 (cDC1). We show that Batf3-/- mice developed metabolic syndrome and have altered localization of tight junction proteins in intestinal epithelial cells leading to increased intestinal permeability. Treatment with the glycolysis inhibitor 2-deoxy-D-glucose reduced intestinal inflammation and restored barrier function in obese Batf3-/- mice. High-fat diet further enhanced the metabolic phenotype and susceptibility to dextran sulfate sodium colitis in Batf3-/- mice. Antibiotic treatment of Batf3-/- mice prevented metabolic syndrome and impaired intestinal barrier function. Batf3-/- mice have altered IgA-coating of fecal bacteria and displayed microbial dysbiosis marked by decreased obesity protective Akkermansia muciniphila, and Bifidobacterium. Thus, BATF3 protects against metabolic syndrome and preserves intestinal epithelial barrier by maintaining beneficial microbiota.

Pathogen size alters C-type lectin receptor signaling in dendritic cells to influence CD4 Th9 cell differentiation.

Dectin-1 recognizes ß-glucan in fungal cell walls, and activation of Dectin-1 in dendritic cells (DCs) influences immune responses against fungi. Although many studies have shown that DCs activated via Dectin-1 induce different subsets of T helper cells according to different cytokine milieus, the mechanisms underlying such differences remain unknown. By harnessing polymorphic Candida albicans and polystyrene beads of different sizes, we find that target size influences production of cytokines that control differentiation of T helper cell subsets. Hyphal C. albicans and large beads activate DCs but cannot be phagocytosed due to their sizes, which prolongs the duration of Dectin-1 signaling. Transcriptomic analysis reveals that expression of Il33 is significantly increased by larger targets, and increased IL-33 expression promotes TH9 responses. Expression of IL-33 is regulated by the Dectin-1-SYK-PLCγ-CARD9-ERK pathway. Altogether, our study demonstrates that size of fungi can be a determining factor in how DCs induce context-appropriate adaptive immune responses.

Direct signaling of TL1A-DR3 on fibroblasts induces intestinal fibrosis in vivo.

Tumor necrosis factor-like cytokine 1A (TL1A, TNFSF15) is implicated in inflammatory bowel disease, modulating the location and severity of inflammation and fibrosis. TL1A expression is increased in inflamed mucosa and associated with fibrostenosing Crohn's disease. Tl1a-overexpression in mice causes spontaneous ileitis, and exacerbates induced proximal colitis and fibrosis. Intestinal fibroblasts express Death-receptor 3 (DR3; the only know receptor for TL1A) and stimulation with TL1A induces activation in vitro. However, the contribution of direct TL1A-DR3 activation on fibroblasts to fibrosis in vivo remains unknown. TL1A overexpressing naïve T cells were transferred into Rag-/- , Rag-/- mice lacking DR3 in all cell types (Rag-/-Dr3-/-), or Rag-/- mice lacking DR3 only on fibroblasts (Rag-/-Dr3∆Col1a2) to induce colitis and fibrosis, assessed by clinical disease activity index, intestinal inflammation, and collagen deposition. Rag-/- mice developed overt colitis with intestinal fibrostenosis. In contrast, Rag-/-Dr3-/- demonstrated decreased inflammation and fibrosis. Despite similar clinical disease and inflammation as Rag-/-, Rag-/-Dr3∆Col1a2 exhibited reduced intestinal fibrosis and attenuated fibroblast activation and migration. RNA-Sequencing of TL1A-stimulated fibroblasts identified Rho signal transduction as a major pathway activated by TL1A and inhibition of this pathway modulated TL1A-mediated fibroblast functions. Thus, direct TL1A signaling on fibroblasts promotes intestinal fibrosis in vivo. These results provide novel insight into profibrotic pathways mediated by TL1A paralleling its pro-inflammatory effects.

Malassezia Is Associated with Crohn's Disease and Exacerbates Colitis in Mouse Models.

Inflammatory bowel disease (IBD) is characterized by alterations in the intestinal microbiota and altered immune responses to gut microbiota. Evidence is accumulating that IBD is influenced by not only commensal bacteria but also commensal fungi. We characterized fungi directly associated with the intestinal mucosa in healthy people and Crohn's disease patients and identified fungi specifically abundant in patients. One of these, the common skin resident fungus Malassezia restricta, is also linked to the presence of an IBD-associated polymorphism in the gene for CARD9, a signaling adaptor important for anti-fungal defense. M. restricta elicits innate inflammatory responses largely through CARD9 and is recognized by Crohn's disease patient anti-fungal antibodies. This yeast elicits strong inflammatory cytokine production from innate cells harboring the IBD-linked polymorphism in CARD9 and exacerbates colitis via CARD9 in mouse models of disease. Collectively, these results suggest that targeting specific commensal fungi may be a therapeutic strategy for IBD.

A role for BATF3 in TH9 differentiation and T-cell-driven mucosal pathologies.

T helper 9 (TH9) cells are important for the development of inflammatory and allergic diseases. The TH9 transcriptional network converges signals from cytokines and antigen presentation but is incompletely understood. Here, we identified TL1A, a member of the TNF superfamily, as a strong inducer of mouse and human TH9 differentiation. Mechanistically, TL1A induced the expression of the transcription factors BATF and BATF3 and facilitated their binding to the Il9 promoter leading to enhanced secretion of IL-9. BATF- and BATF3-deficiencies impaired IL-9 secretion under TH9 and TH9-TL1A-polarizing conditions. In vivo, using a T-cell transfer model, we demonstrated that TL1A promoted IL-9-dependent, TH9 cell-induced intestinal and lung inflammation. Neutralizing IL-9 antibodies attenuated TL1A-driven mucosal inflammation. Batf3-/- TH9-TL1A cells induced reduced inflammation and cytokine expression in vivo compared to WT cells. Our results demonstrate that TL1A promotes TH9 cell differentiation and function and define a role for BATF3 in T-cell-driven mucosal inflammation.

Failure of the Anti-Inflammatory Parasitic Worm Product ES-62 to Provide Protection in Mouse Models of Type I Diabetes, Multiple Sclerosis, and Inflammatory Bowel Disease.

Parasitic helminths and their isolated secreted products show promise as novel treatments for allergic and autoimmune conditions in humans. Foremost amongst the secreted products is ES-62, a glycoprotein derived from Acanthocheilonema viteae, a filarial nematode parasite of gerbils, which is anti-inflammatory by virtue of covalently-attached phosphorylcholine (PC) moieties. ES-62 has been found to protect against disease in mouse models of rheumatoid arthritis, systemic lupus erythematosus, and airway hyper-responsiveness. Furthermore, novel PC-based synthetic small molecule analogues (SMAs) of ES-62 have recently been demonstrated to show similar anti-inflammatory properties to the parent molecule. In spite of these successes, we now show that ES-62 and its SMAs are unable to provide protection in mouse models of certain autoimmune conditions where other helminth species or their secreted products can prevent disease development, namely type I diabetes, multiple sclerosis and inflammatory bowel disease. We speculate on the reasons underlying ES-62's failures in these conditions and how the negative data generated may help us to further understand ES-62's mechanism of action.

Inflammation-independent TL1A-mediated intestinal fibrosis is dependent on the gut microbiome.

Tumor necrosis factor-like cytokine 1A (TL1A, TNFSF15) is implicated in inflammatory bowel disease (IBD), modulating the location and severity of intestinal inflammation and fibrosis. TL1A expression is increased in inflamed gut mucosa and associated with fibrostenosing Crohn's disease. Tl1a-overexpression in mice lead to spontaneous ileitis, and exacerbated induced proximal colitis and fibrosis. IBD is associated with shifts in the gut microbiome, but the effect of differing microbial populations and their interaction with TL1A on fibrosis has not been investigated. We demonstrate that the pro-fibrotic and inflammatory phenotype resulting from Tl1a-overexpression is abrogated in the absence of resident microbiota. To evaluate if this is due to the absence of a unique bacterial population, as opposed to any bacteria per se, we gavaged germ-free (GF) wild-type and Tl1a-transgenic (Tl1a-Tg) mice with stool from specific pathogen free (SPF) mice and a healthy human donor (Hu). Reconstitution with SPF, but not Hu microbiota, resulted in increased intestinal collagen deposition and fibroblast activation in Tl1a-Tg mice. Notably, there was reduced fibroblast migration and activation under GF conditions compared to native conditions. We then identified several candidate organisms that correlated directly with increased fibrosis in reconstituted mice and showed that these organisms directly impact fibroblast function in vitro. Thus, Tl1a-mediated intestinal fibrosis and fibroblast activation are dependent on specific microbial populations.

The TNF family member TL1A induces IL-22 secretion in committed human Th17 cells via IL-9 induction.

TL1A contributes to the pathogenesis of several chronic inflammatory diseases, including those of the bowel by enhancing TH1, TH17, and TH2 responses. TL1A mediates a strong costimulation of these TH subsets, particularly of mucosal CCR9+ T cells. However, the signaling pathways that TL1A induces in different TH subsets are incompletely understood. We investigated the function of TL1A on human TH17 cells. TL1A, together with TGF-ß, IL-6, and IL-23, enhanced the secretion of IL-17 and IFN-γ from human CD4+ memory T cells. TL1A induced expression of the transcription factors BATF and T-bet that correlated with the secretion of IL-17 and IFN-γ. In contrast, TL1A alone induced high levels of IL-22 in memory CD4+ T cells and committed TH17 cells. However, TL1A did not enhance expression of IL-17A in TH17 cells. Expression of the transcription factor aryl hydrocarbon receptor, which regulates the expression of IL-22 was not affected by TL1A. Transcriptome analysis of TH17 cells revealed increased expression of IL-9 in response to TL1A. Blocking IL-9 receptor antibodies abrogated TL1A-induced IL-22 secretion. Furthermore, TL1A increased IL-9 production by peripheral TH17 cells isolated from patients with Crohn's disease. These data suggest that TL1A differentially induces expression of TH17 effector cytokines IL-17, -9, and -22 and provides a potential target for therapeutic intervention in TH17-driven chronic inflammatory diseases.

Chronic intestinal inflammation alters hippocampal neurogenesis.

BACKGROUND: Adult neurogenesis in the subgranular zone of the hippocampus is involved in learning, memory, and mood control. Decreased hippocampal neurogenesis elicits significant behavioral changes, including cognitive impairment and depression. Inflammatory bowel disease (IBD) is a group of chronic inflammatory conditions of the intestinal tract, and cognitive dysfunction and depression frequently occur in patients suffering from this disorder. We therefore tested the effects of chronic intestinal inflammation on hippocampal neurogenesis. METHODS: The dextran sodium sulfate (DSS) mouse model of IBD was used. Mice were treated with multiple-cycle administration of 3% wt/vol DSS in drinking water on days 1 to 5, 8 to 12, 15 to 19, and 22 to 26. Mice were sacrificed on day 7 (acute phase of inflammation) or day 29 (chronic phase of inflammation) after the beginning of the treatment. RESULTS: During the acute phase of inflammation, we found increased plasma levels of IL-6 and TNF-α and increased expression of Iba1, a marker of activated microglia, accompanied by induced IL-6 and IL-1ß, and the cyclin-dependent kinase inhibitor p21(Cip1) (p21) in hippocampus. During the chronic phase of inflammation, plasma levels of IL-6 were elevated. In the hippocampus, p21 protein levels were continued to be induced. Furthermore, markers of stem/early progenitor cells, including nestin and brain lipid binding protein (BLBP), and neuronal marker doublecortin (DCX) were all down-regulated, whereas glial fibrillary acidic protein (GFAP), a marker for astroglia, was induced. In addition, the number of proliferating precursors of neuronal lineage assessed by double Ki67 and DCX staining was significantly diminished in the hippocampus of DSS-treated animals, indicating decreased production of new neurons. CONCLUSIONS: We show for the first time that chronic intestinal inflammation alters hippocampal neurogenesis. As p21 arrests early neuronal progenitor proliferation, it is likely that p21 induction during acute phase of inflammation resulted in the reduction of hippocampal neurogenesis observed later, on day 29, after the beginning of DSS treatment. The reduction in hippocampal neurogenesis might underlie the behavioral manifestations that occur in patients with IBD.

HMPL-004 (Andrographis paniculata extract) prevents development of murine colitis by inhibiting T-cell proliferation and TH1/TH17 responses.

BACKGROUND: Extracts of the plant Andrographis paniculata have been used to treat inflammatory diseases in Asian countries. A recent double-blind, placebo-controlled trial of HMPL-004 (A. paniculata extract) has demonstrated its safety and effectiveness for induction of clinical response, remission, and mucosal healing in patients with mild to moderate ulcerative colitis (UC). We aimed to determine if HMPL-004 could prevent the development of T-cell-dependent murine colitis and to define its in vivo mechanism(s) of action. METHODS: CD(+)4CD45RB(high) T cells were transferred into Rag1(-/-) mice and gavaged daily with HMPL-004 or methyl cellulose (MC). Severity of colitis was evaluated by weight loss, histology, and cytokine expression. RESULTS: Mice treated with MC developed colitis within 4-7 weeks, as evaluated by weight loss, and severe intestinal inflammation. HMPL-004-treated mice did not lose weight and displayed only very mild intestinal inflammation. Tumor necrosis factor alpha (TNF-α), interleukin (IL)-1ß, interferon-gamma (IFN-γ), and IL-22 expression were significantly decreased in HMPL-004-treated mice. We observed higher percentages of naïve CD4(+) T cells in the lamina propria of HMPL-004-treated mice. At early timepoints HMPL-004-treated mice have significantly reduced splenic cell counts, reduced CD4(+), and IL-17(+), and IFN-γ T(+) cells. Furthermore, HMPL-004 inhibited the proliferation of CD4 T cells and differentiation into TH1/TH17 cells in vitro. CONCLUSIONS: HMPL-004 inhibits the development of chronic colitis by affecting early T-cell proliferation, differentiation, and TH(1)/TH(17) responses in a T-cell-driven model of colitis, presenting a unique mechanism of action. Our data suggest that HMPL-004 could be an attractive herbal therapeutic for inflammatory bowel disease.

Constitutive TL1A expression under colitogenic conditions modulates the severity and location of gut mucosal inflammation and induces fibrostenosis.

Intestinal fibrostenosis is a hallmark of severe Crohn's disease and can lead to multiple surgeries. Patients with certain TNFSF15 variants overexpress TL1A. The aim of this study was to determine the effect of TL1A overexpression on intestinal inflammation and the development of fibrostenosis. We assessed the in vivo consequences of constitutive TL1A expression on gut mucosal inflammation and fibrostenosis using two murine models of chronic colitis. In the dextran sodium sulfate (DSS) and adoptive T-cell transfer models, there was proximal migration of colonic inflammation, worsened patchy intestinal inflammation, and long gross intestinal strictures in Tl1a transgenic compared to wild-type littermates. In the DSS model, myeloid- and T-cell-expressing Tl1a transgenic mice had increased T-cell activation markers and interleukin-17 expression compared to wild-type mice. In the T-cell transfer model, Rag1(-/-) mice receiving Tl1a transgenic T cells had increased interferon-γ expression but reduced T-helper 17 cells and IL-17 production. Narrowed ureters with hydronephrosis were found only in the Tl1a transgenic mice in all chronic colitis models. In human translational studies, Crohn's disease patients with higher peripheral TL1A expression also exhibited intestinal fibrostenosis and worsened ileocecal inflammation with relative sparing of rectosigmoid inflammation. These data show that TL1A is an important cytokine that not only modulates the location and severity of mucosal inflammation, but also induces fibrostenosis.

Myeloid differentiation factor-2 interacts with Lyn kinase and is tyrosine phosphorylated following lipopolysaccharide-induced activation of the TLR4 signaling pathway.

Stimulation with LPS induces tyrosine phosphorylation of numerous proteins involved in the TLR signaling pathway. In this study, we demonstrated that myeloid differentiation factor-2 (MD-2) is also tyrosine phosphorylated following LPS stimulation. LPS-induced tyrosine phosphorylation of MD-2 is specific; it is blocked by the tyrosine kinase inhibitor, herbimycin A, as well as by an inhibitor of endocytosis, cytochalasin D, suggesting that MD-2 phosphorylation occurs during trafficking of MD-2 and not on the cell surface. Furthermore, we identified two possible phospho-accepting tyrosine residues at positions 22 and 131. Mutant proteins in which these tyrosines were changed to phenylalanine had reduced phosphorylation and significantly diminished ability to activate NF-κB in response to LPS. In addition, MD-2 coprecipitated and colocalized with Lyn kinase, most likely in the endoplasmic reticulum. A Lyn-binding peptide inhibitor abolished MD-2 tyrosine phosphorylation, suggesting that Lyn is a likely candidate to be the kinase required for MD-2 tyrosine phosphorylation. Our study demonstrated that tyrosine phosphorylation of MD-2 is important for signaling following exposure to LPS and underscores the importance of this event in mediating an efficient and prompt immune response.

Constitutive TL1A (TNFSF15) expression on lymphoid or myeloid cells leads to mild intestinal inflammation and fibrosis.

TL1A is a member of the TNF superfamily and its expression is increased in the mucosa of inflammatory bowel disease patients. Moreover, a subset of Crohn's disease (CD) patients with the risk TL1A haplotype is associated with elevated TL1A expression and a more severe disease course. To investigate the in vivo role of elevated TL1A expression, we generated two transgenic (Tg) murine models with constitutive Tl1a expression in either lymphoid or myeloid cells. Compared to wildtype (WT) mice, constitutive expression of Tl1a in either lymphoid or myeloid cells showed mild patchy inflammation in the small intestine, which was more prominent in the ileum. In addition, mice with constitutive Tl1a expression exhibited enhanced intestinal and colonic fibrosis compared to WT littermates. The percentage of T cells expressing the gut homing chemokine receptors CCR9 and CCR10 was higher in the Tl1a Tg mice compared to WT littermates. Sustained expression of Tl1A in T cells also lead to increased Foxp3+ Treg cells. T cells or antigen presenting cells (APC) with constitutive expression of Tl1a were found to have a more activated phenotype and mucosal mononuclear cells exhibit enhanced Th1 cytokine activity. These results indicated an important role of TL1A in mucosal T cells and APC function and showed that up-regulation of TL1A expression can promote mucosal inflammation and gut fibrosis.

Toll-like receptor 2 signaling protects mice from tumor development in a mouse model of colitis-induced cancer.

Inflammatory bowel disease (IBD) is a disorder of chronic inflammation with increased susceptibility to colorectal cancer. The etiology of IBD is unclear but thought to result from a dysregulated adaptive and innate immune response to microbial products in a genetically susceptible host. Toll-like receptor (TLR) signaling induced by intestinal commensal bacteria plays a crucial role in maintaining intestinal homeostasis, innate immunity and the enhancement of intestinal epithelial cell (IEC) integrity. However, the role of TLR2 in the development of colorectal cancer has not been studied. We utilized the AOM-DSS model for colitis-associated colorectal cancer (CAC) in wild type (WT) and TLR2(-/-) mice. Colons harvested from WT and TLR2(-/-) mice were used for histopathology, immunohistochemistry, immunofluorescence and cytokine analysis. Mice deficient in TLR2 developed significantly more and larger colorectal tumors than their WT controls. We provide evidence that colonic epithelium of TLR2(-/-) mice have altered immune responses and dysregulated proliferation under steady-state conditions and during colitis, which lead to inflammatory growth signals and predisposition to accelerated neoplastic growth. At the earliest time-points assessed, TLR2(-/-) colons exhibited a significant increase in aberrant crypt foci (ACF), resulting in tumors that developed earlier and grew larger. In addition, the intestinal microenvironment revealed significantly higher levels of IL-6 and IL-17A concomitant with increased phospho-STAT3 within ACF. These observations indicate that in colitis, TLR2 plays a protective role against the development of CAC.

Platelet-activating factor induces TLR4 expression in intestinal epithelial cells: implication for the pathogenesis of necrotizing enterocolitis.

Necrotizing enterocolitis (NEC) is a leading cause of morbidity and mortality in neonatal intensive care units, however its pathogenesis is not completely understood. We have previously shown that platelet activating factor (PAF), bacteria and TLR4 are all important factors in the development of NEC. Given that Toll-like receptors (TLRs) are expressed at low levels in enterocytes of the mature gastrointestinal tract, but were shown to be aberrantly over-expressed in enterocytes in experimental NEC, we examined the regulation of TLR4 expression and signaling by PAF in intestinal epithelial cells using human and mouse in vitro cell lines, and the ex vivo rat intestinal loop model. In intestinal epithelial cell (IEC) lines, PAF stimulation yielded upregulation of both TLR4 mRNA and protein expression and led to increased IL-8 secretion following stimulation with LPS (in an otherwise LPS minimally responsive cell line). PAF stimulation resulted in increased human TLR4 promoter activation in a dose dependent manner. Western blotting and immunohistochemical analysis showed PAF induced STAT3 phosphorylation and nuclear translocation in IEC, and PAF-induced TLR4 expression was inhibited by STAT3 and NFκB Inhibitors. Our findings provide evidence for a mechanism by which PAF augments inflammation in the intestinal epithelium through abnormal TLR4 upregulation, thereby contributing to the intestinal injury of NEC.

Identification of a novel human MD-2 splice variant that negatively regulates Lipopolysaccharide-induced TLR4 signaling.

Myeloid differentiation factor 2 (MD-2) is a secreted gp that assembles with TLR4 to form a functional signaling receptor for bacterial LPS. In this study, we have identified a novel alternatively spliced isoform of human MD-2, termed MD-2 short (MD-2s), which lacks the region encoded by exon 2 of the MD-2 gene. Similar to MD-2, MD-2s is glycosylated and secreted. MD-2s also interacted with LPS and TLR4, but failed to mediate LPS-induced NF-kappaB activation and IL-8 production. We show that MD-2s is upregulated upon IFN-gamma, IL-6, and TLR4 stimulation and negatively regulates LPS-mediated TLR4 signaling. Furthermore, MD-2s competitively inhibited binding of MD-2 to TLR4. Our study pinpoints a mechanism that may be used to regulate TLR4 activation at the onset of signaling and identifies MD-2s as a potential therapeutic candidate to treat human diseases characterized by an overly exuberant or chronic immune response to LPS.

TLR8-mediated activation of human monocytes inhibits TL1A expression.

TLR play important roles in inflammation and innate immune response to pathogens. TLR8 recognizes ssRNA and induces NF-kappaB via MyD88 signaling. TL1A is a member of the TNF superfamily that markedly enhances IFN-gamma production by IL-12/IL-18-stimulated peripheral and mucosal CD4(+) T cells. TL1A expression is increased in the mucosa of patients with inflammatory bowel disease and is considered a key mediator of Crohn's disease (CD). We have previously shown that TL1A is strongly induced by immune complexes (IC) but not TLR ligands in antigen-presenting cells. However, a potential interaction between these pro-inflammatory signaling pathways has not been investigated. IC-induced TL1A expression of monocytes was potently inhibited by a TLR8 or TLR7/8 ligand (R848) in a dose-dependent manner. Furthermore, when co-cultured with CD4(+) T cells, TLR8 ligands inhibited TL1A production, resulting in almost complete inhibition of IFN-gamma production by the CD4(+) T cells. Furthermore, we demonstrate that IFN-alpha is not required for this suppressive effect by TLR8 signaling. Our data demonstrate for the first time a direct interaction between TLR and TL1A signaling pathways. TLR8 activation may be an important, novel pathway for targeted treatment of Th1-mediated diseases, such as CD.