NF-kappaB p50 and p65 subunits control intestinal homeostasis

IL-1β and the Intestinal Epithelial Tight Junction Barrier

The intestinal epithelial tight junction (TJ) barrier controls the paracellular permeation of contents from the intestinal lumen into the intestinal tissue and systemic circulation. A defective intestinal TJ barrier has been implicated as an important pathogenic factor in inflammatory diseases of the gut including Crohn's disease, ulcerative colitis, necrotizing enterocolitis, and celiac disease. Previous studies have shown that pro-inflammatory cytokines, which are produced during intestinal inflammation, including interleukin-1β (IL-1β), tumor necrosis factor-α, and interferon-γ, have important intestinal TJ barrier-modulating actions. Recent studies have shown that the IL-1β-induced increase in intestinal TJ permeability is an important contributing factor of intestinal inflammation. The IL-1β-induced increase in intestinal TJ permeability is mediated by regulatory signaling pathways and activation of nuclear transcription factor nuclear factor-κB, myosin light chain kinase gene activation, and post-transcriptional occludin gene modulation by microRNA and contributes to the intestinal inflammatory process. In this review, the regulatory role of IL-1β on intestinal TJ barrier, the intracellular mechanisms that mediate the IL-1β modulation of intestinal TJ permeability, and the potential therapeutic targeting of the TJ barrier are discussed.

Neutrophil L-Plastin Controls Ocular Paucibacteriality and Susceptibility to Keratitis

Why ocular mucosa is paucibacterial is unknown. Many different mechanisms have been suggested but the comprehensive experimental studies are sparse. We found that a deficiency in L-plastin (LCP1), an actin bundling protein, resulted in an ocular commensal overgrowth, characterized with increased presence of conjunctival Streptococcal spp. The commensal overgrowth correlated with susceptibility to P. aeruginosa-induced keratitis. L-plastin knock-out (KO) mice displayed elevated bacterial burden in the P. aeruginosa-infected corneas, altered inflammatory responses, and compromised bactericidal activity. Mice with ablation of LPL under the LysM Cre (LysM. CreposLPLfl/fl ) and S100A8 Cre (S100A8.CreposLPLfl/fl ) promoters had a similar phenotype to the LPL KOs mice. In contrast, infected CD11c.CreposLPLfl/fl mice did not display elevated susceptibility to infection, implicating the myeloid L-plastin-sufficient cells (e.g., macrophages and neutrophils) in maintaining ocular homeostasis. Mechanistically, the elevated commensal burden and the susceptibility to infection were linked to defects in neutrophil frequencies at steady state and during infection and compromised bactericidal activities upon priming. Macrophage exposure to commensal organisms primed neutrophil responses to P. aeruginosa, augmenting PMN bactericidal capacity in an L-plastin dependent manner. Cumulatively, our data highlight the importance of neutrophils in controlling ocular paucibacteriality, reveal molecular and cellular events involved in the process, and suggest a link between commensal exposure and resistance to infection.

Damaging heterozygous mutations in NFKB1 lead to diverse immunologic phenotypes

BACKGROUND

The nuclear factor κ light-chain enhancer of activated B cells (NF-κB) signaling pathway is a key regulator of immune responses. Accordingly, mutations in several NF-κB pathway genes cause immunodeficiency.

OBJECTIVE

We sought to identify the cause of disease in 3 unrelated Finnish kindreds with variable symptoms of immunodeficiency and autoinflammation.

METHODS

We applied genetic linkage analysis and next-generation sequencing and functional analyses of NFKB1 and its mutated alleles.

RESULTS

In all affected subjects we detected novel heterozygous variants in NFKB1, encoding for p50/p105. Symptoms in variant carriers differed depending on the mutation. Patients harboring a p.I553M variant presented with antibody deficiency, infection susceptibility, and multiorgan autoimmunity. Patients with a p.H67R substitution had antibody deficiency and experienced autoinflammatory episodes, including aphthae, gastrointestinal disease, febrile attacks, and small-vessel vasculitis characteristic of Behçet disease. Patients with a p.R157X stop-gain experienced hyperinflammatory responses to surgery and showed enhanced inflammasome activation. In functional analyses the p.R157X variant caused proteasome-dependent degradation of both the truncated and wild-type proteins, leading to a dramatic loss of p50/p105. The p.H67R variant reduced nuclear entry of p50 and showed decreased transcriptional activity in luciferase reporter assays. The p.I553M mutation in turn showed no change in p50 function but exhibited reduced p105 phosphorylation and stability. Affinity purification mass spectrometry also demonstrated that both missense variants led to altered protein-protein interactions.

CONCLUSION

Our findings broaden the scope of phenotypes caused by mutations in NFKB1 and suggest that a subset of autoinflammatory diseases, such as Behçet disease, can be caused by rare monogenic variants in genes of the NF-κB pathway.

Impact of Microbiota on Resistance to Ocular Pseudomonas aeruginosa-Induced Keratitis

The existence of the ocular microbiota has been reported but functional analyses to evaluate its significance in regulating ocular immunity are currently lacking. We compared the relative contribution of eye and gut commensals in regulating the ocular susceptibility to Pseudomonas aeruginosa–induced keratitis. We find that in health, the presence of microbiota strengthened the ocular innate immune barrier by significantly increasing the concentrations of immune effectors in the tear film, including secretory IgA and complement proteins. Consistent with this view, Swiss Webster (SW) mice that are typically resistant to P. aeruginosa–induced keratitis become susceptible due to the lack of microbiota. This was exemplified by increased corneal bacterial burden and elevated pathology of the germ free (GF) mice when compared to the conventionally maintained SW mice. The protective immunity was found to be dependent on both eye and gut microbiota with the eye microbiota having a moderate, but significant impact on the resistance to infection. These events were IL-1ß–dependent as corneal IL-1ß levels were decreased in the infected GF and antibiotic-treated mice when compared to the SPF controls, and neutralization of IL-1ß increased the ocular bacterial burden in the SPF mice. Monocolonizing GF mice with Coagulase Negative Staphylococcus sp. isolated from the conjunctival swabs was sufficient to restore resistance to infection. Cumulatively, these data underline a previously unappreciated role for microbiota in regulating susceptibility to ocular keratitis. We predict that these results will have significant implications for contact lens wearers, where alterations in the ocular commensal communities may render the ocular surface vulnerable to infections.

Contact lens wear is associated with frequent Pseudomonas aeruginosa–induced keratitis, however the reasons for this association remain unclear. Recent genomics–based approaches revealed that contact lens wearers harbor altered ocular commensal communities when compared to non-lens wearers raising important questions, namely, does wearing of contact lenses increase the frequency of keratitis in patients due to contamination of the contact lenses with species derived from the skin or does ocular microbiota exert immune functions that are required for the maintenance of ocular health? We demonstrate a clear role for ocular microbiota in regulating protection against Pseudomonas aeruginosa–induced infections. At the ocular surface, commensal bacteria provide signals that regulate the magnitude of neutrophil recruitment during infection. These events may be driven by a frequent gram-positive commensal–Coagulase Negative Staphylococcus (CNS) sp. In addition to the impact of ocular microbiota, there is an important contribution of gut microbiota that stimulate neutrophil development in the bone marrow, thereby regulating the pool of mature neutrophils and their activation state. Cumulatively, these data show for the first time a role for microbiota in regulating the susceptibility to P. aeruginosa–keratitis.

Epithelial cell shedding and barrier function: a matter of life and death at the small intestinal villus tip

The intestinal epithelium is a critical component of the gut barrier. Composed of a single layer of intestinal epithelial cells (IECs) held together by tight junctions, this delicate structure prevents the transfer of harmful microorganisms, antigens, and toxins from the gut lumen into the circulation. The equilibrium between the rate of apoptosis and shedding of senescent epithelial cells at the villus tip, and the generation of new cells in the crypt, is key to maintaining tissue homeostasis. However, in both localized and systemic inflammation, this balance may be disturbed as a result of pathological IEC shedding. Shedding of IECs from the epithelial monolayer may cause transient gaps or microerosions in the epithelial barrier, resulting in increased intestinal permeability. Although pathological IEC shedding has been observed in mouse models of inflammation and human intestinal conditions such as inflammatory bowel disease, understanding of the underlying mechanisms remains limited. This process may also be an important contributor to systemic and intestinal inflammatory diseases and gut barrier dysfunction in domestic animal species. This review aims to summarize current knowledge about intestinal epithelial cell shedding, its significance in gut barrier dysfunction and host-microbial interactions, and where research in this field is directed.

A mouse model of pathological small intestinal epithelial cell apoptosis and shedding induced by systemic administration of lipopolysaccharide

The gut barrier, composed of a single layer of intestinal epithelial cells (IECs) held together by tight junctions, prevents the entrance of harmful microorganisms, antigens and toxins from the gut lumen into the blood. Small intestinal homeostasis is normally maintained by the rate of shedding of senescent enterocytes from the villus tip exactly matching the rate of generation of new cells in the crypt. However, in various localized and systemic inflammatory conditions, intestinal homeostasis can be disturbed as a result of increased IEC shedding. Such pathological IEC shedding can cause transient gaps to develop in the epithelial barrier and result in increased intestinal permeability. Although pathological IEC shedding has been implicated in the pathogenesis of conditions such as inflammatory bowel disease, our understanding of the underlying mechanisms remains limited. We have therefore developed a murine model to study this phenomenon, because IEC shedding in this species is morphologically analogous to humans. IEC shedding was induced by systemic lipopolysaccharide (LPS) administration in wild-type C57BL/6 mice, and in mice deficient in TNF-receptor 1 (Tnfr1^−/−), Tnfr2 (Tnfr2^−/−), nuclear factor kappa B1 (Nfκb1^−/−) or Nfĸb2 (Nfĸb2^−/−). Apoptosis and cell shedding was quantified using immunohistochemistry for active caspase-3, and gut-to-circulation permeability was assessed by measuring plasma fluorescence following fluorescein-isothiocyanate–dextran gavage. LPS, at doses ≥0.125 mg/kg body weight, induced rapid villus IEC apoptosis, with peak cell shedding occurring at 1.5 hours after treatment. This coincided with significant villus shortening, fluid exudation into the gut lumen and diarrhea. A significant increase in gut-to-circulation permeability was observed at 5 hours. TNFR1 was essential for LPS-induced IEC apoptosis and shedding, and the fate of the IECs was also dependent on NFκB, with signaling via NFκB1 favoring cell survival and via NFκB2 favoring apoptosis. This model will enable investigation of the importance and regulation of pathological IEC apoptosis and cell shedding in various diseases.

Active modification of host inflammation by Salmonella

The dampening of host immune responses is a critical aspect of pathogenesis for the enteropathogen Salmonella enterica. Our laboratory has recently described a role for the secreted effector GogB in disruption of NFκB activation and limitation of the host inflammatory response to infection. GogB alters the NFκB pathway by preventing IκB degradation by the host SCF E3 ubiquitin ligase, through an interaction with Skp1 and FBXO22. The prevention of NFκB activation through this interaction dampens the host inflammatory response in the gut, which in turn limits the damage to host tissues during chronic infection. In this addendum, we summarize these recent findings and discuss their implications and impact in the area of host-pathogen interactions.

The role of FoxO4 in the relationship between alcohol-induced intestinal barrier dysfunction and liver injury

Forkhead box 'Other' (FoxO) proteins, a subgroup of the Forkhead transcription factor family, play an important role in mediating the effects of insulin and growth factors on diverse physiological functions. In this study, we investigated the role of FoxO4 in the relationship between alcohol liver disease and intestinal barrier dysfunction using an animal model. Six to eight-week-old male WT rats were divided into eight groups. They were separately administered corn starch dissolved in PBS; 40% alcohol (5 g/kg body weight) through stomach feeding every 12 h/time, three times in total; tumor necrosis factor α (TNFα) (10 µg/kg) injected intraperitoneally 30 min before alcohol administration; wortmannin (1.4 mg/kg) 30 min before alcohol administration; IGF-1 (0.2 mg/kg) 30 min before alcohol administration; anti-TNFα (5 mg/kg) injected intravenously 30 min before alcohol administration. In addition, two placebo groups were treated with PBS either intraperitoneally or intravenously prior to alcohol administration. TNFα and endotoxin in plasma were measured by ELISA and Tachypleus Amebocye Lysate assays. Immunohistochemistry and western blotting were used to identify the mechanisms of FoxO4 action in regulating epithelial permeability. Furthermore, electron microscopy, reverse transcription-polymerase chain reaction and western blotting were used to examine the expression of tight junction proteins and nuclear factor-κB (NF-κB). Compared with the control group, TNFα in the alcohol group was significantly higher. TNFα could induce FoxO4 phosphorylation; p-FoxO4 was limited into the cytoplasm and inactivated; inactive FoxO4 which was in high levels lost the ability to suppress NF-κB. Therefore, the expression of NF-κB was increased and it downregulated tight junction protein (including ZO-1 and occludin) expression, and increased epithelial permeability. As a result, intestinal bacteria grew excessively, endotoxin was released into the portal circulation and liver injury deteriorated. These results indicate that a complex network of mechanisms is involved in the beneficial effects of FoxO4 in epithelial barrier dysfunction. TNFα can upregulate phosphorylation of FoxO4. FoxO4 which is located in the nucleus is limited into the cytoplasm and inactivated; it loses the ability to suppress NF-κB activity, it downregulates the expression of tight junction proteins and increases epithelial permeability. Disruption of the intestinal barrier allows endotoxin and other bacterial products in the gut lumen to pass into the portal circulation and cause hepatic inflammation. At the same time, the changes of liver injury deteriorate.

Treatment with intestinal trefoil factor regulates TLR2/4 and NF-κB expression and protects against LPS-induced intestinal injury in rats

AIM: To investigate whether intestinal trefoil factor (ITF) regulates the expression of Toll-like receptor (TLR) 2/4 and nuclear factor-κB (NF-κB) and exerts a protective effect against lipopolysaccharide (LPS)-induced intestinal injury in rats.

METHODS: Twenty-four 10-day-old Wistar rats were randomly and equally divided into three groups: control group (intraperitoneally injected with normal saline 1 mL/kg ), endotoxemia group (intraperitoneally injected with LPS 5 mg/kg), and LPS + ITF group (intraperitoneally injected with LPS 5 mg/kg and recombinant ITF 0.1 mL/per rat). Rats were sacrificed 3 h after injection. A segment of the distal ileum was dissected for hematoxylin-eosin staining. Pathological changes in the small intestine were observed under an optical microscope. The mRNA and protein expression of TLR2/4 and NF-κB was detected by RT-PCR and immunohistochemistry, respectively.

RESULTS: The structure of the small intestine of rats in the control group was normal. Inflammatory cell infiltration and interstitial/epithelial edema were observed in rats in the LPS group and LPS + ITF group, and the pathological changes were significantly milder in the LPS + ITF group than in the LPS group. The expression of TLR2 mRNA and protein in the LPS + ITF group was significantly higher than that in the LPS group (7.453 ± 1.90 vs 3.069 ± 0.08, 52.125 ± 4.1 vs 20.688 ± 2.4, both P < 0.01). The expression of TLR4 and NF-κB mRNAs and proteins in the LPS + ITF group was significantly lower than that in the LPS group (TLR4 mRNA: 5.373 ± 1.18 vs 16.711 ± 1.28, P< 0.01; TLR4 protein: 16.338 ± 4.98 vs 22.760 ± 3.68, P< 0.01; NF-κB mRNA: 0.533 ± 0.05 vs 2.228 ± 0.72, P< 0.01; NF-κB protein: 36.526 ± 9.18 vs 50.433 ± 3.37, P< 0.05).

CONCLUSION: Treatment with ITF protects against LPS-induced intestinal injury in rats possibly via mechanisms associated with down-regulation of TLR4 and NF-κB expression.

CD74 deficiency ameliorates Pseudomonas aeruginosa-induced ocular infection

Eye trauma and contact lens wear are the main factors that predispose to the development of infectious keratitis. The existing therapies fail to control the inflammation-driven tissue damage that occurs during Pseudomonas aeruginosa infection. Antibiotic treatment reduces bacterial burdens, but better interventions are needed to alleviate tissue damage resulting from local inflammation. We have previously documented that inhibition of macrophage migration inhibitory factor (MIF) reduces the bacterial levels and the inflammatory damage during keratitis. Here, we report that mice deficient for CD74, the putative MIF receptor, developed milder Pseudomonas aeruginosa-induced disease, characterized by decreased proinflammatory mediators and reduced bacterial presence in the cornea. However, topical inhibition of MIF using antibodies applied to the cornea further promoted recovery from disease, suggesting that in addition to MIF-dependent signaling events, MIF-triggered CD74-independent signaling pathways regulate sensitization to P. aeruginosa-induced infection.

Glutamine protects against endotoxin-induced intestinal injury by down-regulating TLR4 and NF-κB expression in rats

AIM: To investigate whether glutamine (Gln) exerts protective effects against endotoxin-induced intestinal injury in rats and to explore possible mechanisms involved.

METHODS: Twenty-four 10-day-old Wistar rats were equally and randomly divided into three groups: control group (intraperitoneally injected with normal saline 1 mL/kg), lipopolysaccharide (LPS) group (intraperitoneally injected with LPS 5 g/L), and Gln group (intraperitoneally injected with Gln 10 mL/kg and LPS 5 mg/kg). Rats were sacrificed 3 h after injection. A segment of distal ileum was dissected. The pathologic changes in the small intestine were observed under an optical microscope after hematoxylin-eosin staining. The mRNA and protein expression of TLR2/4 and NF-κB was detected by RT-PCR and immunohistochemistry, respectively.

RESULTS: The structure of the small intestine of rats in the control group was normal. Although inflammatory cell infiltration and interstitial and epithelial edema were observed in both the LPS group and Gln group, the pathological changes were significantly milder in the Gln group than in the LPS group. Compared to the LPS group, the mRNA and protein expression of TLR4 and NF-κB was significantly lower in the Gln group (TLR4: 3.92 ± 0.50 vs 16.71 ± 1.28, 38.80 ± 2.42 vs 20.69 ± 2.42; NF-κB: 0.37 ± 0.14 vs 2.23 ± 0.72, 17.21 ± 5.07 vs 22.76 ± 3.68, P < 0.01, P < 0.05).

CONCLUSION: Gln exerts protective effects against intestinal injury in rats possibly by down-regulating TLR4 and NF-κB mRNA and protein expression.

Human serum-derived hydroxy long-chain fatty acids exhibit anti-inflammatory and anti-proliferative activity

Background

Circulating levels of novel long-chain hydroxy fatty acids (called GTAs) were recently discovered in the serum of healthy subjects which were shown to be reduced in subjects with colorectal cancer (CRC), independent of tumor burden or disease stage. The levels of GTAs were subsequently observed to exhibit an inverse association with age in the general population. The current work investigates the biological activity of these fatty acids by evaluating the effects of enriched human serum extracts on cell growth and inflammation.

Methods

GTAs were extracted from commercially available bulk human serum and then chromatographically separated into enriched (GTA-positive) and depleted (GTA-negative) fractions. SW620, MCF7 and LPS stimulated RAW264.7 cells were treated with various concentrations of the GTA-positive and GTA-negative extracts, and the effects on cell growth and inflammation determined.

Results

Enriched fractions resulted in poly-ADP ribose polymerase (PARP) cleavage, suppression of NFκB, induction of IκBα, and reduction in NOS2 mRNA transcript levels. In RAW264.7 mouse macrophage cells, incubation with enriched fractions prior to treatment with LPS blocked the induction of several pro-inflammatory markers including nitric oxide, TNFα, IL-1β, NOS2 and COX2.

Conclusions

Our results show that human serum extracts enriched with endogenous long-chain hydroxy fatty acids possess anti-inflammatory and anti-proliferative activity. These findings support a hypothesis that the reduction of these metabolites with age may result in a compromised ability to defend against uncontrolled cell growth and inflammation, and could therefore represent a significant risk for the development of CRC.

Z-FA.FMK activates duodenal epithelial cell proliferation through oxidative stress, NF-kappaB and IL-1beta in D-GalN/TNF-alpha-administered mice

This study was designed to evaluate the effect of Z-FA.FMK (benzyloxycarbonyl-l-phenylalanyl-alanine-fluoromethylketone), a pharmacological inhibitor of cathepsin B, on the proliferation of duodenal mucosal epithelial cells and the cellular system that controls this mechanism in these cells in vivo. For this investigation, BALB/c male mice were divided into four groups. The first group received physiological saline, the second group was administered Z-FA.FMK, the third group received D-GalN (D-galactosamine) and TNF-alpha (tumour necrosis factor-alpha) and the fourth group was given both D-GalN/TNF-alpha and Z-FA.FMK. When D-GalN/TNF-alpha was administered alone, we observed an increase in IL-1beta-positive and active NF-kappaB-positive duodenal epithelial cells, a decrease in PCNA (proliferative cell nuclear antigen)-positive duodenal epithelial cells and an increase in degenerative changes in duodenum. On the other hand, Z-FA.FMK pretreatment inhibited all of these changes. Furthermore, lipid peroxidation, protein carbonyl and collagen levels were increased, glutathione level and superoxide dismutase activity were decreased, while there was no change in catalase activity by D-GalN/TNF-alpha injection. On the contrary, the Z-FA.FMK pretreatment before D-GalN/TNF-alpha blocked these effects. Based on these findings, we suggest that Z-FA.FMK might act as a proliferative mediator which is controlled by IL-1beta through NF-kappaB and oxidative stress in duodenal epithelial cells of D-GalN/TNF-alpha-administered mice.

Inhibition of macrophage migration inhibitory factor ameliorates ocular Pseudomonas aeruginosa-induced keratitis

Pseudomonas aeruginosa causes severe sight-threatening corneal infections, with the inflammatory response to the pathogen being the major factor resulting in damage to the cornea that leads to loss of visual acuity. We found that mice deficient for macrophage migration inhibitory factor (MIF), a key regulator of inflammation, had significantly reduced consequences from acute P. aeruginosa keratitis. This improvement in the outcome was manifested as improved bacterial clearance, decreased neutrophil infiltration, and decreased inflammatory responses when P. aeruginosa-infected MIF knock out (KO) mice were compared to infected wild-type mice. Recombinant MIF applied to infected corneas restored the susceptibility of MIF deficient mice to P. aeruginosa-induced disease, demonstrating that MIF is necessary and sufficient to cause significant pathology at this immune privileged site. A MIF inhibitor administered during P. aeruginosa-induced infection ameliorated the disease-associated pathology. MIF regulated epithelial cell responses to infection by enhancing synthesis of proinflammatory mediators in response to P. aeruginosa infection and by promoting bacterial invasion of corneal epithelial cells, a correlate of virulence in the keratitis model. Our results uncover a host factor that elevates inflammation and propagates bacterial cellular invasion, and further suggest that inhibition of MIF during infection may have a beneficial therapeutic effect.

FoxO4 inhibits NF-kappaB and protects mice against colonic injury and inflammation

BACKGROUND & AIMS

FoxO4 is a member of the forkhead box transcription factor O (FoxO) subfamily. FoxO proteins are involved in diverse biological processes. In this study, we examine the role of FoxO4 in intestinal mucosal immunity and inflammatory bowel disease (IBD).

METHODS

Foxo4-null mice were subjected to trinitrobenzene sulfonic acid (TNBS) treatment. Microarray analysis and quantitative reverse transcription polymerase chain reaction were used to identify the cytokine transcripts that were altered by Foxo4 deletion. The effects of Foxo4 deficiency on the intestinal epithelial permeability and levels of tight junction proteins were examined by permeable fluorescent dye and Western blot. The molecular and cellular mechanisms by which FoxO4 regulates the mucosal immunity were explored through immunologic and biochemical analyses. The expression level of FoxO4 in intestinal epithelial cells of patients with IBD was examined with immunohistochemistry.

RESULTS

Foxo4-null mice were more susceptible to TNBS injury-induced colitis. The chemokine CCL5 is significantly up-regulated in the colonic epithelial cells of Foxo4-null mice, with increased recruitment of CD4(+) intraepithelial T cells and up-regulation of cytokines interferon-gamma and tumor necrosis factor-alpha in the colon. Foxo4 deficiency also resulted in an increase in intestinal epithelial permeability and down-regulation of the tight junction proteins ZO-1 and claudin-1. Mechanistically, FoxO4 inhibited the transcriptional activity of nuclear factor-kappaB (NF-kappaB), and Foxo4 deficiency is associated with increased NF-kappaB activity in vivo. FoxO4 transcription is transiently repressed in response to TNBS treatment and in patients with IBD.

CONCLUSION

These results indicate that FoxO4 is an endogenous inhibitor of NF-kappaB and identify a novel function of FoxO4 in the regulation of NF-kappaB-mediated mucosal immunity.

Nuclear factor-kappa B in intestinal protection and destruction

PURPOSE OF REVIEW

Nuclear factor-kappa B (NF-kappaB) is a key transcriptional regulator of innate and adaptive immunity. This review highlights new insights into the functions of NF-kappaB in normal homeostasis and specific disease processes in the intestinal tract.

RECENT FINDINGS

Inflammatory bowel disease and experimental intestinal inflammation are characterized by NF-kappaB activation and increased expression of proinflammatory NF-kappaB target genes. Accordingly, NF-kappaB inhibition protects against chronic intestinal inflammation and necrotizing enterocolitis in animal models. However, recent findings suggest that NF-kappaB has not only proinflammatory but also tissue-protective functions. Thus, genetic ablation of the regulatory subunit, IkappaB kinase (IKK)gamma, of the central kinase complex required for NF-kappaB activation, IKK, or of both kinase subunits, IKKalpha and IKKbeta, in intestinal epithelial cells causes spontaneous murine colitis. Pharmacological inhibition of IKKbeta, and loss of IKKbeta or NF-kappaB p65 in the epithelium, sensitizes mice to acute inflammatory and injurious challenges. Deficiency in Toll-like receptor 5, a strong activator of NF-kappaB, results in spontaneous colitis and exacerbates mucosal inflammatory responses to Salmonella infection. Conversely, Toll-like receptor 5 stimulation confers radioprotection in the intestine.

SUMMARY

NF-kappaB has multiple, often opposing functions in the intestine. Antiapoptotic actions of NF-kappaB in intestinal epithelial cells dominate tissue responses to many acute inflammatory and injurious challenges, whereas proinflammatory and cell survival functions of NF-kappaB in macrophages and T cells govern chronic intestinal inflammation.

Effects of simulated gravity loss on nuclear factor kappa-B expression in rat intestinal tissues

AIM: To investigate the effects of simulated gravity loss on NF-κB expression in rat intestinal tissues, and its significance.

METHODS: Tail-suspension (TS) was used to simulate the physiological effects of gravity loss. Eighty male Wistar rats were randomly assigned to 10 experimental groups suspended for 0.5, 1, 2, 7, 21 d respectively and their corresponding control groups. The dynamic expressions of NF-κB in intestinal tissues were seperately measured using the immunohistochemistry.

RESULTS: Compared with control groups, the expression levels of NF-κB in the intestinal tissue of tail-suspension 0.5, 1, 2, 7, 21 d groups were elevated significantly (10.11% ± 3.29% vs 5.50% ± 1.92%, 22.00% ± 5.31% vs 6.50% ± 2.32%, 25.50% ± 4.11% vs 8.75% ± 6.36%, 21.50% ± 3.02% vs 6.75% ± 2.12%, 10.87% ± 2.64% vs 5.62% ± 2.13%, all P < 0.01). NF-κB expression level began to rise in 0.5 tail-suspension group, and reached the maxium level in in 2 d group, then went down gradually.

CONCLUSION: The results suggest that simulated gravity loss acts as a kind of stress to elevate NF-κB expression and indicate a close link between altered intestinal NF-κB expression and tolerance of gravity loss.