Interleukin-6 induces keratin expression in intestinal epithelial cells: potential role of keratin-8 in interleukin-6-induced barrier function alterations

Proteomic analysis of rainbow trout (Oncorhynchus mykiss) intestinal epithelia: physiological acclimation to short-term starvation

The intestinal epithelia form the first line of defense against harmful agents in the gut lumen of most monogastric vertebrates, including teleost fishes. Previous investigations into the effect of starvation on the intestinal epithelia of teleost fishes have focused primarily on changes in morphological characteristics and targeted molecular analysis of specific enzymes. The goal of this study was to use a comprehensive approach to help reveal how the intestinal epithelia of carnivorous teleost fishes acclimate to short-term nutrient deprivation. We utilized two-dimensional gel electrophoresis (2-DE) to conduct the proteomic analysis of the mucosal and epithelial layer of the anterior gut intestinal tract (GIT) from satiation fed vs. 4 week starved rainbow trout (Oncorhynchus mykiss). A total of 40 proteins were determined to be differentially expressed and were subsequently picked for in-gel trypsin digestion. Peptide mass fingerprint analysis was conducted using matrix assisted laser desorption time-of-flight/time-of-flight. Nine of the 11 positively identified proteins were directly related to innate immunity. The expression of α-1 proteinase inhibitor decreased in starved vs. fed fish. Also, the concentration of one leukocyte elastase inhibitor (LEI) isomer decreased in starved fish, though the concentration of another LEI isomer increased in due to starvation. In addition, starvation promoted an increased concentration of the important xenobiotic-transporter p-glycoprotein. Finally, starvation resulted in a significant increase in type II keratin E2. Overall, our results indicate that starvation promoted a reduced capacity to inhibit enzymatic stress but increased xenobiotic resistance and paracellular permeability of epithelial cells in the anterior intestine of rainbow trout.

Interleukin-6 modulates colonic transepithelial ion transport in the stress-sensitive wistar kyoto rat

Immunological challenge stimulates secretion of the pro-inflammatory cytokine interleukin (IL)-6, resulting in variety of biological responses. In the gastrointestinal tract, IL-6 modulates the excitability of submucosal neurons and stimulates secretion into the colonic lumen. When considered in the context of the functional bowel disorder, irritable bowel syndrome (IBS), where plasma levels of IL-6 are elevated, this may reflect an important molecular mechanism contributing to symptom flares, particularly in the diarrhea-predominant phenotype. In these studies, colonic ion transport, an indicator of absorption and secretion, was assessed in the stress-sensitive Wistar Kyoto (WKY) rat model of IBS. Mucosa-submucosal colonic preparations from WKY and control Sprague Dawley (SD) rats were mounted in Ussing chambers and the basal short circuit current (I_SC) was electrophysiologically recorded and compared between the strains. Exposure to IL-6 (1 nM) stimulated a secretory current of greater amplitude in WKY as compared to SD samples. Furthermore, the observed IL-6-mediated potentiation of secretory currents evoked by veratridine and capsaicin in SD rats was blunted in WKY rats. Exposure to IL-6 also stimulated an increase in transepithelial resistance in both SD and WKY colonic tissue. These studies demonstrate that the neuroexcitatory effects of IL-6 on submucosal plexi have functional consequences with alterations in both colonic secretory activity and permeability. The IL-6-induced increase in colonic secretory activity appears to neurally mediated. Thus, local increases in IL-6 levels and subsequent activation of enteric neurons may underlie alterations in absorpto-secretory function in the WKY model of IBS.

Keratins in oral cancer: necessity of mass spectrometry for validation of antibody based identifications

Keratins are intermediate filament family proteins which are predominantly expressed in the epithelial cells. Most of the studies which evaluate the status of keratins in clinical samples of the oral cavity are based on the identification of their presence and localization by immunohistochemistry using monoclonal antibodies. It is very well known that many monoclonal/polyclonal antibodies show cross-reactivity with the other closely related or non-related proteins. This cross-reactivity might be the result of epitope similarity, but it is not always necessary. Therefore studies done with only antibody based techniques can mislead interpretation unless they are validated with additional techniques like mass-spectrometry. In this investigation we have evaluated the status of keratin 18 in cancer of buccal mucosa using 1DE, 2DE and western blotting with monoclonal antibody to keratin 18. The patterns emerging showed aberrant as well as differential expression of K18 in adjacent normal versus tumor tissue samples of buccal mucosa. Mass spectrometry analysis of the immunodetected spots however revealed that it is keratin 13. Thus this study emphasizes the necessity of validation of antibody based findings when dealing with proteins of a large family having similarity/homology in amino acid sequence.

Chloride channel ClC-2 modulates tight junction barrier function via intracellular trafficking of occludin

Previously, we have demonstrated that the chloride channel ClC-2 modulates intestinal mucosal barrier function. In the present study, we investigated the role of ClC-2 in epithelial barrier development and maintenance in Caco-2 cells. During early monolayer formation, silencing of ClC-2 with small interfering (si)RNA led to a significant delay in the development of transepithelial resistance (TER) and disruption of occludin localization. Proteomic analysis employing liquid chromatography-mass spectrometry /mass spectrometry revealed association of ClC-2 with key proteins involved in intracellular trafficking, including caveolin-1 and Rab5. In ClC-2 siRNA-treated cells, occludin colocalization with caveolin-1 was diffuse and in the subapical region. Subapically distributed occludin in ClC-2 siRNA-treated cells showed marked colocalization with Rab5. To study the link between ClC-2 and trafficking of occludin in confluent epithelial monolayers, a Caco-2 cell clone expressing ClC-2 short hairpin (sh)RNA was established. Disruption of caveolae with methyl-β-cyclodextrin (MβCD) caused a marked drop in TER and profound redistribution of caveolin-1-occludin coimmunofluorescence in ClC-2 shRNA cells. In ClC-2 shRNA cells, focal aggregations of Rab5-occludin coimmunofluorescence were present within the cytoplasm. Wortmannin caused an acute fall in TER in ClC-2 shRNA cells and subapical, diffuse redistribution of Rab5-occludin coimmunofluorescence in ClC-2 shRNA cells. An endocytosis and recycling assay for occludin revealed higher basal rate of endocytosis of occludin in ClC-2 shRNA cells. Wortmannin significantly reduced the rate of recycling of occludin in ClC-2 shRNA cells. These data clearly indicate that ClC-2 plays an important role in the modulation of tight junctions by influencing caveolar trafficking of the tight junction protein occludin.

Cytotoxicity of single-walled carbon nanotubes on human hepatoma HepG2 cells: an iTRAQ-coupled 2D LC-MS/MS proteome analysis

Single-walled carbon nanotubes (SWCNTs) and its derivatives are promising candidates for applications in electronics, energy, materials and biomedical areas. However, with the growing potential biomedical applications and the rising societal concerns on nanosafety, mechanistic understanding of the interactions between nanomaterials and living systems has become imperative. In the present study, our group applied the iTRAQ-coupled 2D LC-MS/MS approach to analyze the protein profile change of mammalian cells in response to SWCNTs. Specifically, the human hepatoma HepG2 cells were chosen as the in vitro model to study the potential cytotoxicity of SWCNTs on the vital organ of liver. Overall 51 differentially expressed proteins that involved in metabolic pathway, redox regulation, signaling pathway, cytoskeleton formation and cell growth were identified. We found SWCNTs triggered the up-regulation of metabolic enzymes, heat shock proteins and proteins involved in redox regulation, which indicated SWCNTs could induce oxidative stress, perturb protein synthesis and interfere cellular metabolism. Our data also suggested that SWCNTs might induce the activation of apoptosis signal-regulating kinase 1, and finally lead to stress-induced apoptosis. The comparative protein profile obtained here provided molecular evidence on the cellular functions in response to SWCNTs, which should very useful to elucidate the cytotoxicity caused by those nanomaterials.

Interleukin-6 (IL-6) regulates claudin-2 expression and tight junction permeability in intestinal epithelium

In inflammatory bowel diseases (IBD), intestinal barrier function is impaired as a result of deteriorations in epithelial tight junction (TJ) structure. IL-6, a pleiotropic cytokine, is elevated in IBD patients, although the role of IL-6 in barrier function remains unknown. We present evidence that IL-6 increases TJ permeability by stimulating the expression of channel-forming claudin-2, which is required for increased caudal-related homeobox (Cdx) 2 through the MEK/ERK and PI3K pathways in intestinal epithelial cells. IL-6 increases the cation-selective TJ permeability without any changes to uncharged dextran flux or cell viability in Caco-2 cells. IL-6 markedly induces claudin-2 expression, which is associated with increased TJ permeability. The colonic mucosa of mice injected with IL-6 also exhibits an increase in claudin-2 expression. The claudin-2 expression and TJ permeability induced by IL-6 are sensitive to the inhibition of gp130, MEK, and PI3K. Furthermore, expression of WT-MEK1 induces claudin-2 expression in Caco-2 cells. Claudin-2 promoter activity is increased by IL-6 in a MEK/ERK and PI3K-dependent manner, and deletion of Cdx binding sites in the promoter sequence results in a loss of IL-6-induced promoter activity. IL-6 increases Cdx2 protein expression, which is suppressed by the inhibition of MEK and PI3K. These observations may reveal an important mechanism by which IL-6 can undermine the integrity of the intestinal barrier.

Involvement of afadin in barrier function and homeostasis of mouse intestinal epithelia

Afadin interacts with the cytoplasmic region of nectins, which are immunoglobulin-like cell adhesion molecules at adherens junctions, and links them to the actin cytoskeleton. Afadin regulates activities of cells in culture such as directional motility, proliferation and survival. We used Cre-loxP technology to generate mice conditionally lacking afadin specifically in the intestinal epithelia after birth. The loss of afadin caused increased paracellular permeability in the intestinal mucosa and enhanced susceptibility to the tissue destruction induced by dextran sulfate sodium. The junctional architecture of the intestinal epithelia appeared to be preserved, whereas the deficiency of afadin caused the mislocalization of nectin-2 and nectin-3 from adherens junctions to basolateral membrane domains but not that of other components of apical junctions. By contrast, such phenotypic changes were undetected in mice lacking nectin-2, nectin-3 or both. These findings suggest that afadin plays crucial roles, independently of the role as the nectin-afadin module, in barrier function and homeostasis of the intestinal epithelia once the epithelial structure has been established.

Impact of obesity and leptin on protein expression profiles in mouse colon

BACKGROUND

Elevated leptin levels in obesity are associated with increased risk of colon pathology, implicating leptin signaling in colon disease. However, leptin-regulated processes in the colon are currently uncharacterized. Previously, we demonstrated that leptin receptors are expressed on colon epithelium and that increased adiposity and elevated plasma leptin in rats are associated with perturbed metabolism in colon tissue. Thus, we hypothesize that obesity disrupts expression of proteins regulated by leptin in the colon.

METHODS

A proteomic analysis was conducted to investigate firstly, differences in the colon of mice lacking leptin and leptin signaling (ob/ob and db/db, respectively) by comparing protein expression profiles with wild-type mice. Secondly, responses to leptin challenge in wild-type mice and ob/ob mice were compared to identify leptin-regulated proteins and associated cellular processes.

RESULTS

Forty proteins were identified with significantly altered expression patterns associated with differences in leptin status in comparisons between all groups of mice. These proteins are associated with calcium binding, cell cycle, cell proliferation, electron transport chain, energy metabolism, protein folding and transport, redox regulation, structural proteins, and proteins involved in transport and regulation of mucus production.

CONCLUSIONS

This study provides evidence that obesity and leptin significantly alter protein profiles of a number of proteins linked to cellular processes in colon tissues that may be linked to the increased risk of colon pathology associated with obesity.

Colonic soluble mediators from the maternal separation model of irritable bowel syndrome activate submucosal neurons via an interleukin-6-dependent mechanism

Irritable bowel syndrome (IBS) is characterized by episodic bouts of abdominal pain, bloating, and altered bowel habit. Accumulating evidence has linked immune activation with IBS, including reports of increases in circulating levels of the proinflammatory cytokine interleukin (IL)-6. However, it is unknown whether IL-6 contributes directly to disease manifestation. As enteric nervous activity mediates motility and secretory function, the aims of this study were to determine the effects of IL-6 on submucosal neurons and related gastrointestinal (GI) function. In these studies, we examined the colons of maternally separated (MS) rats, which exhibit elevated circulating levels of IL-6 in addition to GI dysfunction. To our knowledge, these studies are the first to provide evidence of the sensitivity of submucosal neurons to colonic secretions from MS rats (n = 50, P < 0.05), thus recapitulating clinical biopsy data. Moreover, we demonstrated that the excitatory action is IL-6 dependent. Thereafter, the impact of IL-6 on neuronal and glial activation and absorpto/secretory function was pharmacologically characterized. Other proinflammatory cytokines including IL-8 (n = 30, P > 0.05), IL-1β (n = 56, P > 0.05), and TNF-α (n = 56, P > 0.05) excited fewer neurons. Both muscarinic and nicotinic cholinergic receptors participate in the effect and cause downstream activation of ERK, JAK-STAT, and NF-κB signaling cascades. Functionally, IL-6 increases transepithelial resistance and enhances neurally and cholinergically mediated ion transport. These data provide a role for IL-6 in colonic secretory functions and relate these effects to GI dysfunction in an animal model of IBS, thereby elucidating a potential relationship between circulating levels of IL-6 and aberrant GI function.

Protective effects of Lactobacillus paracasei F19 in a rat model of oxidative and metabolic hepatic injury

The liver is susceptible to such oxidative and metabolic stresses as ischemia-reperfusion (I/R) and fatty acid accumulation. Probiotics are viable microorganisms that restore the gut microbiota and exert a beneficial effect on the liver by inhibiting bacterial enzymes, stimulating immunity, and protecting intestinal permeability. We evaluated Lactobacillus paracasei F19 (LP-F19), for its potential protective effect, in an experimental model of I/R (30 min ischemia and 60 min reperfusion) in rats fed a standard diet or a steatogen [methionine/choline-deficient (MCD)] diet. Both groups consisted of 7 sham-operated rats, 10 rats that underwent I/R, and 10 that underwent I/R plus 8 wk of probiotic dietary supplementation. In rats fed a standard diet, I/R induced a decrease in sinusoid perfusion (P < 0.001), severe liver inflammation, and necrosis besides an increase of tissue levels of malondialdehyde (P < 0.001), tumor necrosis factor-alpha (P < 0.001), interleukin (IL)-1beta (P < 0.001), and IL-6 (P < 0.001) and of serum levels of transaminase (P < 0.001) and lipopolysaccharides (P < 0.001) vs. sham-operated rats. I/R also induced a decrease in Bacterioides, Bifidobacterium, and Lactobacillus spps (P < 0.01, P < 0.001, and P < 0.001, respectively) and an increase in Enterococcus and Enterobacteriaceae (P < 0.01 and P < 0.001, respectively) on intestinal mucosa. The severity of liver and gut microbiota alterations induced by I/R was even greater in rats with liver inflammation and steatosis, i.e., MCD-fed animals. LP-F19 supplementation significantly reduced the harmful effects of I/R on the liver and on gut microbiota in both groups of rats, although the effect was slightly less in MCD-fed animals. In conclusion, LP-F19 supplementation, by restoring gut microbiota, attenuated I/R-related liver injury, particularly in the absence of steatosis.

Upregulation of Salmonella-induced IL-6 production in Caco-2 cells by PJ-34, PARP-1 inhibitor: involvement of PI3K, p38 MAPK, ERK, JNK, and NF-kappaB

Following Salmonella invasion, intestinal epithelial cells release a distinct array of proinflammatory cytokines. Interleukin (IL)-6 produced by enterocytes may have anti-inflammatory and cell-protective effects, and may counteract some of the injurious effects of sepsis and endotoxemia. Recent studies in a variety of rodent models of experimental colitis by using PJ-34, a potent poly (ADP-ribose) polymerase-1 (PARP-1) inhibitor, support the concept that the marked beneficial effect of PJ-34 can be exploited to treat human inflammatory diseases. The present study was to investigate the effect of PJ-34 on Salmonella-induced enterocyte IL-6 production and its mechanisms. We found that PJ-34 enhanced Salmonella-induced IL-6 production in Caco-2 cells, either secreted protein or mRNA expression. PJ-34 treatment enhanced the activity of NF-κB in Salmonella-infected Caco-2 cells. Besides, the involvement of PJ-34 in up-regulating IL-6 production in S. typhimurium-infected Caco-2 cells might be also through the ERK but not p38 MAPK, JNK or PI3K/Akt pathways, as demonstrated by Western blot of phosphorylated ERK, p38, JNK and Akt proteins. It suggests that PJ-34 may exert its protective effect on intestinal epithelial cells against invasive Salmonella infection by up-regulating IL-6 production through ERK and NF-κB but not P38 MAPK, JNK or PI3K/Akt signal pathways.

Intermediate filaments take the heat as stress proteins

Intermediate filament (IF) proteins and heat shock proteins (HSPs) are large multimember families that share several features, including protein abundance, significant upregulation in response to a variety of stresses, cytoprotective functions, and the phenocopying of several human diseases after IF protein or HSP mutation. We are now coming to understand that these common elements point to IFs as important cellular stress proteins with some roles akin to those already well-characterized for HSPs. Unique functional roles for IFs include protection from mechanical stress, whereas HSPs are characteristically involved in protein folding and as chaperones. Shared IF and HSP cytoprotective roles include inhibition of apoptosis, organelle homeostasis, and scaffolding. In this report, we review data that corroborate the view that IFs function as highly specialized cytoskeletal stress proteins that promote cellular organization and homeostasis.

Regulation of intestinal epithelial cells transcriptome by enteric glial cells: impact on intestinal epithelial barrier functions

BACKGROUND

Emerging evidences suggest that enteric glial cells (EGC), a major constituent of the enteric nervous system (ENS), are key regulators of intestinal epithelial barrier (IEB) functions. Indeed EGC inhibit intestinal epithelial cells (IEC) proliferation and increase IEB paracellular permeability. However, the role of EGC on other important barrier functions and the signalling pathways involved in their effects are currently unknown. To achieve this goal, we aimed at identifying the impact of EGC upon IEC transcriptome by performing microarray studies.

RESULTS

EGC induced significant changes in gene expression profiling of proliferating IEC after 24 hours of co-culture. 116 genes were identified as differentially expressed (70 up-regulated and 46 down-regulated) in IEC cultured with EGC compared to IEC cultured alone. By performing functional analysis of the 116 identified genes using Ingenuity Pathway Analysis, we showed that EGC induced a significant regulation of genes favoring both cell-to-cell and cell-to-matrix adhesion as well as cell differentiation. Consistently, functional studies showed that EGC induced a significant increase in cell adhesion. EGC also regulated genes involved in cell motility towards an enhancement of cell motility. In addition, EGC profoundly modulated expression of genes involved in cell proliferation and cell survival, although no clear functional trend could be identified. Finally, important genes involved in lipid and protein metabolism of epithelial cells were shown to be differentially regulated by EGC.

CONCLUSION

This study reinforces the emerging concept that EGC have major protective effects upon the IEB. EGC have a profound impact upon IEC transcriptome and induce a shift in IEC phenotype towards increased cell adhesion and cell differentiation. This concept needs to be further validated under both physiological and pathophysiological conditions.

Enterocyte-specific epidermal growth factor prevents barrier dysfunction and improves mortality in murine peritonitis

Systemic administration of epidermal growth factor (EGF) decreases mortality in a murine model of septic peritonitis. Although EGF can have direct healing effects on the intestinal mucosa, it is unknown whether the benefits of systemic EGF in peritonitis are mediated through the intestine. Here, we demonstrate that enterocyte-specific overexpression of EGF is sufficient to prevent intestinal barrier dysfunction and improve survival in peritonitis. Transgenic FVB/N mice that overexpress EGF exclusively in enterocytes (IFABP-EGF) and wild-type (WT) mice were subjected to either sham laparotomy or cecal ligation and puncture (CLP). Intestinal permeability, expression of the tight junction proteins claudins-1, -2, -3, -4, -5, -7, and -8, occludin, and zonula occludens-1; villus length; intestinal epithelial proliferation; and epithelial apoptosis were evaluated. A separate cohort of mice was followed for survival. Peritonitis induced a threefold increase in intestinal permeability in WT mice. This was associated with increased claudin-2 expression and a change in subcellular localization. Permeability decreased to basal levels in IFABP-EGF septic mice, and claudin-2 expression and localization were similar to those of sham animals. Claudin-4 expression was decreased following CLP but was not different between WT septic mice and IFABP-EGF septic mice. Peritonitis-induced decreases in villus length and proliferation and increases in apoptosis seen in WT septic mice did not occur in IFABP-EGF septic mice. IFABP-EGF mice had improved 7-day mortality compared with WT septic mice (6% vs. 64%). Since enterocyte-specific overexpression of EGF is sufficient to prevent peritonitis-induced intestinal barrier dysfunction and confers a survival advantage, the protective effects of systemic EGF in septic peritonitis appear to be mediated in an intestine-specific fashion.

Cytokeratin 8/18 overexpression and complex formation as an indicator of GST-P positive foci transformation into hepatocellular carcinomas

Screening of the proteome of microdissected glutathione S-transferase placental form (GST-P) positive foci and normal-appearing liver on anionic (Q10), and cationic (CM10) surface-enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF-MS) ProteinChip arrays demonstrated significant overexpression of cytokeratin 8 (CK8; m/z 54,020), cytokeratin 18 (CK18; m/z 47,760), microsomal cytochrome 5A (m/z 15,224) and histone type 2 H2aa3 (m/z 15,964) in the livers of rats initiated with diethylnitrosamine (DEN) followed by 10 weeks on phenobarbital (PB) at a dose of 500 ppm. Furthermore, formation of CK8 and CK18 complexes due to CK8 phosphorylation at Ser73 and Ser431 was found to be strongly associated with promotion of hepatocarcinogenesis by PB and the development of hepatocellular carcinomas. The data were confirmed by immunohistochemistry and real-time Q-PCR and profound overexpression of CK8 and CK18 (CK8/18) proteins and mRNAs were detected in several large size GST-P positive foci and liver tumors. A strong correlation between CK8/18 positive foci development and multiplicity of hepatocellular carcinomas was further observed. Moreover, elevation of CK8/18 was strongly associated with induction of cell proliferation in GST-P positive foci and tumors. In conclusion, our data imply that CK8/18 overexpression, those two cytokeratins complex formation associated with histone type 2 H2aa3 up-regulation and intermediate filament reorganization may drive neoplastic transformation of GST-P positive foci during rat hepatocarcinogenesis leading to the formation of hepatocellular carcinomas.

Campylobacter jejuni drives MyD88-independent interleukin-6 secretion via Toll-like receptor 2

Gastrointestinal disease caused by Campylobacter jejuni is characterized by localized inflammation and the destruction of the epithelial cell barrier that forms host innate protection against pathogens. This can lead to an imbalance in fluid transport across the gastrointestinal tract, resulting in severe diarrhea. The mechanisms of host cell receptor recognition of C. jejuni and downstream immune signaling pathways leading to this inflammatory disease, however, remain unclear. The aim of this study was to analyze the mechanisms involved in C. jejuni induction of the acute-phase inflammatory response regulator interleukin-6 (IL-6). Polarized intestinal epithelial Caco-2 monolayers responded to infections with Salmonella enterica serovar Typhimurium and eight isolates of C. jejuni by an increase in levels of expression and secretion of IL-6. No such IL-6 response, however, was produced upon infection with the human commensal organism Lactobacillus rhamnosus GG. The IL-6 signaling pathway was further characterized using short interfering RNA complexes to block gene expression. The inhibition of myeloid differentiation primary response protein 88 (MyD88) expression in this manner did not affect C. jejuni-induced IL-6 secretion, suggesting a MyD88-independent route to IL-6 signal transduction in C. jejuni-infected human epithelial cells. However, a significant reduction in levels of IL-6 was evident in the absence of Toll-like receptor 2 (TLR-2) expression, implying a requirement for TLR-2 in C. jejuni recognition. Caco-2 cells were also treated with heat-inactivated and purified membrane components of C. jejuni to isolate the factor responsible for triggering IL-6 signaling. The results demonstrate that C. jejuni surface polysaccharides induce IL-6 secretion from intestinal epithelial cells via TLR-2 in a MyD88-independent manner.

The drug monosodium luminol (GVT) preserves crypt-villus epithelial organization and allows survival of intestinal T cells in mice infected with the ts1 retrovirus

Of the cytopathic retroviruses that affect mammals, including HIV-1, many selectively infect CD4+ T cells and cause immunosuppressive syndromes. These diseases destroy both the thymus and the small and large intestines, after infecting and killing T-lineage cells in both tissues. A mutant of the murine leukemia retrovirus MoMuLV-TB, called ts1, causes this syndrome in susceptible strains of mice. In FVB/N strain mice that are infected at birth, thymic atrophy, CD4+ T cell loss, intestinal collapse, body wasting, and death occur by approximately 30-40 days postinfection (dpi). Apoptosis of ts1-infected T-lineage cells, in the thymus, peripheral lymphoid system and intestines is caused by accumulation of the ts1 mutant viral envelope preprotein gPr80(env), which is inefficiently cleaved into the mature viral proteins gp70 and PrP15E. We show here that ts1 infection in the small intestine is followed by loss of intestinal epithelial cell (IEC) thyroid-stimulating hormone (TSH) and cell cycling gradients (along the crypt-villus axes), accumulation of gPr80(env) in intestinal cells, apoptosis of developing T cells in the lamina propria (LP), and intestinal collapse by approximately 30 dpi. In infected mice treated with the antioxidant drug monosodium luminol (GVT), however, normal intestinal epithelial cell gradients are still in place at 30 dpi, and IECs covering both the crypts and villi contain large amounts of the antioxidant transcription factor Nrf2. In addition, no apoptotic cells are present, and accumulated gpr80(env) is absent from the tissue at this time. We conclude that GVT treatment can make ts1 a noncytopathic virus for intestinal lymphoid cells, as it does for thymocytes [25]. As in the thymus, GVT may protect the intestine by reducing oxidant stress in infected intestinal T cells, perhaps by prevention of gPr80(env) accumulation via Nrf2 upregulation in the IECs. These results identify GVT as a potential therapy for intestinal diseases or inflammatory conditions, including HIV-AIDS, in which oxidative stress is a triggering or exacerbating factor.

Mechanism of cytokine modulation of epithelial tight junction barrier

Cytokines play a crucial role in the modulation of inflammatory response in the gastrointestinal tract. Pro-inflammatory cytokines including tumor necrosis factor-alpha, interferon-gamma, interleukin-1beta?IL-1beta?, and interleukin-12 are essential in mediating the inflammatory response, while anti-inflammatory cytokines including interleukin-10 and transforming growth factor-beta are important in the attenuation or containment of inflammatory process. It is increasingly recognized that cytokines have an important physiological and pathological effect on intestinal tight junction (TJ) barrier. Consistent with their known pro-inflammatory activities, pro-inflammatory cytokines cause a disturbance in intestinal TJ barrier, allowing increased tissue penetration of luminal antigens. Recent studies indicate that the inhibition of cytokine induced increase in intestinal TJ permeability has an important protective effect against intestinal mucosal damage and development of intestinal inflammation. In this review, the effects of various pro-inflammatory and anti-inflammatory cytokines on intestinal TJ barrier and the progress into the mechanisms that mediate the cytokine modulation of intestinal TJ barrier are reviewed.

IL-6-dependent mucosal protection prevents establishment of a microbial niche for attaching/effacing lesion-forming enteric bacterial pathogens

Enteric infections with attaching/effacing lesion-inducing bacterial pathogens are a worldwide health problem. A murine infection model with one such pathogen, Citrobacter rodentium, was used to elucidate the importance of the pleiotropic immune regulator, IL-6, in the pathogenesis of infection. IL-6 was strongly induced in colonic epithelial cells and macrophages upon C. rodentium infection and was required for effective host defense, because mice lacking IL-6 failed to control bacterial numbers 2-3 wk after infection and exhibited increased mortality. IL-6 was not needed for mounting effective T and B cell responses to the pathogens, nor was it important for induction of IFN-gamma or TNF-alpha, cytokines involved in host defense against the bacteria, or the antibacterial effector, NO. Instead, IL-6 played a key role in mucosal protection, since its absence was associated with marked infection-induced apoptosis in the colonic epithelium and subsequent ulcerations. Cell culture studies confirmed that IL-6 protected colon epithelial cells directly against inducible apoptosis, which was accompanied by increased expression of an array of genes encoding antiapoptotic proteins, including Bcl-x(L), Mcl-1, cIAP-2, and Bcl-3. Ulcerations appeared to be pathogenetically important, because bacteria localized preferentially to those regions, and chemically induced colonic ulcerations promoted bacterial colonization. Furthermore, blood components likely present in ulcer exudates, particularly alanine, asparagine, and glycine, promoted bacterial growth. Thus, IL-6 is an important regulator of host defense against C. rodentium by protecting the mucosa against ulcerations which can act as a microbial niche for the bacteria.

Keratins let liver live: Mutations predispose to liver disease and crosslinking generates Mallory-Denk bodies

Keratin polypeptides 8 and 18 (K8/K18) are the cytoskeletal intermediate filament proteins of hepatocytes while K8/K18/K19 are the keratins of hepatobiliary ductal cells. Hepatocyte K8/K18 are highly abundant and behave as stress proteins with injury-inducible expression. Human association studies show that K8/K18 germline heterozygous mutations predispose to end-stage liver disease of multiple etiologies ( approximately 3 fold increased risk), and to liver disease progression in patients with chronic hepatitis C infection. These findings are supported by extensive transgenic mouse and ex vivo primary hepatocyte culture studies showing that K8 or K18 mutations predispose the liver to acute or subacute injury and promote apoptosis and fibrosis. Mutation-associated predisposition to liver injury is likely related to mechanical and nonmechanical keratin functions including maintenance of cell integrity, protection from apoptosis and oxidative injury, serving as a phosphate sponge, regulation of mitochondrial organization/function and protein targeting. These functions are altered by mutation-induced changes in keratin phosphorylation, solubility and filament organization/reorganization. Keratins are also the major constituents of Mallory-Denk bodies (MDBs). A toxin-induced K8>K18 ratio, and keratin crosslinking by transglutaminase-2 play essential roles in MDB formation. Furthermore, intracellular or cell-released K18 fragments, generated by caspase-mediated proteolysis during apoptosis serve as markers of liver injury. Therefore, K8 and K18 are cytoprotective stress proteins that play a central role in guarding hepatocytes from apoptosis. Keratin involvement in liver disease is multi-faceted and includes modulating disease progression upon mutation, formation of MDBs in response to unique forms of injury, and serving as markers of epithelial cell death.

Reg-II is an exocrine pancreas injury-response product that is up-regulated by keratin absence or mutation

The major keratins in the pancreas and liver are keratins 8 and 18 (K8/K18), but their function seemingly differs in that liver K8/K18 are essential cytoprotective proteins, whereas pancreatic K8/K18 are dispensable. This functional dichotomy raises the hypothesis that K8-null pancreata may undergo compensatory cytoprotective gene expression. We tested this hypothesis by comparing the gene expression profile in pancreata of wild-type and K8-null mice. Most prominent among the up-regulated genes in K8-null pancreas was mRNA for regenerating islet-derived (Reg)-II, which was confirmed by quantitative reverse transcription-polymerase chain reaction and by an anti-Reg-II peptide antibody we generated. Both K8-null and wild-type mice express Reg-II predominantly in acinar cells as determined by in situ hybridization and immunostaining. Analysis of Reg-II expression in various keratin-related transgenic mouse models showed that its induction also occurs in response to keratin cytoplasmic filament collapse, absence, or ablation of K18 Ser52 but not Ser33 phosphorylation via Ser-to-Ala mutation, which represent situations associated with predisposition to liver but not pancreatic injury. In wild-type mice, Reg-II is markedly up-regulated in two established pancreatitis models in response to injury and during the recovery phase. Thus, Reg-II is a likely mouse exocrine pancreas cytoprotective candidate protein whose expression is regulated by keratin filament organization and phosphorylation.