Commensal bacterial endocytosis in epithelial cells is dependent on myosin light chain kinase-activated brush border fanning by interferon-γ.

Abnormal bacterial adherence and internalization in enterocytes have been documented in Crohn disease, celiac disease, surgical stress, and intestinal obstruction and are associated with low-level interferon (IFN)-γ production. How commensals gain access to epithelial soma through densely packed microvilli rooted on the terminal web (TW) remains unclear. We investigated molecular and ultrastructural mechanisms of bacterial endocytosis, focusing on regulatory roles of IFN-γ and myosin light chain kinase (MLCK) in TW myosin phosphorylation and brush border fanning. Mouse intestines were sham operated on or obstructed for 6 hours by loop ligation with intraluminally administered ML-7 (a MLCK inhibitor) or Y27632 (a Rho-associated kinase inhibitor). After intestinal obstruction, epithelial endocytosis and extraintestinal translocation of bacteria were observed in the absence of tight junctional damage. Enhanced TW myosin light chain phosphorylation, arc formation, and brush border fanning coincided with intermicrovillous bacterial penetration, which were inhibited by ML-7 and neutralizing anti-IFN-γ but not Y27632. The phenomena were not seen in mice genetically deficient for long MLCK-210 or IFN-γ. Stimulation of human Caco-2BBe cells with IFN-γ caused MLCK-dependent TW arc formation and brush border fanning, which preceded caveolin-mediated bacterial internalization through cholesterol-rich lipid rafts. In conclusion, epithelial MLCK-activated brush border fanning by IFN-γ promotes adherence and internalization of normally noninvasive enteric bacteria. Transcytotic commensal penetration may contribute to initiation or relapse of chronic inflammation.

Anti-apoptotic PI3K/Akt signaling by sodium/glucose transporter 1 reduces epithelial barrier damage and bacterial translocation in intestinal ischemia.

Intestinal ischemia/reperfusion (I/R) causes mucosal barrier damage and bacterial translocation (BT), leading to septic complications. Previous in vitro studies showed that activation of sodium/glucose transporter 1 (SGLT1) prevented the epithelial apoptosis and permeability rise induced by microbial products. Our aim was to investigate whether luminal glucose uptake by SGLT1 protects against ischemia-induced epithelial cell death and barrier dysfunction, and to explore the glucose-mediated cellular survival pathways in vivo. Rat jejunum was luminally instilled with either vehicle, a pancaspase inhibitor ZVAD, or glucose prior to I/R challenge (occlusion of the superior mesenteric artery for 20 min and reperfusion for 60 min). Histopathology and apoptosis in the jejunum were examined by TUNEL staining and caspase-3 cleavage. Intestinal permeability was evaluated using in vivo assays measuring luminal-to-blood passage of fluorescein-dextran and portal drainage of enterally administered gadodiamide by magnetic resonance imaging. BT was determined by culturing liver and spleen homogenates. Immunofluorescent analysis and kinase assay were used to study PI3K/Akt signaling pathways. Intestinal I/R caused enterocyte apoptosis and villous destruction. Intestinal infusion with ZVAD decreased the I/R-triggered gut permeability rise and BT, suggesting that the barrier damage was partly dependent on cell apoptosis. Enteral instillation of glucose attenuated the epithelial apoptosis, barrier damage, and mucosal inflammation caused by I/R. Phloridzin (a SGLT1 inhibitor) reduced the protective effect of glucose in a dose-dependent manner. Enteral glucose increased the mucosal Akt kinase activity as evidenced by the augmented phosphorylation of exogenous GSK3. Enhanced membrane translocation and phosphorylation of Akt in epithelial cells were associated with elevated phosphorylation of mTOR, Bad, and FoxO1/3a following glucose uptake. Inhibition of PI3K/Akt signaling by LY294002 and wortmannin partially blocked the glucose-mediated rescue of cell apoptosis and barrier damage. In conclusion, SGLT1 glucose uptake alleviated I/R-induced barrier dysfunction and BT, partly by inhibiting epithelial apoptosis via activation of PI3K/Akt signaling.

Prevention of dextran sulfate sodium-induced mouse colitis by the fungal protein Ling Zhi-8 via promoting the barrier function of intestinal epithelial cells.

The fungal immunomodulatory protein Ling Zhi-8 (LZ-8) isolated from Ganoderma lucidum (GL) regulates immune cells and inhibits tumor growth; however, the role of LZ-8 in protecting intestinal epithelial cells (IECs) is unknown. In this study, we aim to investigate the functional effect of LZ-8 on IECs. LZ-8 effectively rescued the pro-inflammatory cytokine-induced loss of tight junctions (TJs) by enhancing transepithelial electrical resistance (TEER), reducing permeability, and maintaining the distribution of TJ proteins, in Caco-2 cells. Mechanistically, LZ-8 blocked the upregulation of myosin light chain kinase (MLCK) and NF-kB activation by TLR2-mediated suppression of cytokine signaling (SOCS)-1 expression. Furthermore, LZ-8 pre-treatment reduced the pathological scores of dextran sulfate sodium (DSS)-induced colitis in mice. These results indicated that LZ-8 protected the barrier function of IECs against inflammation. Thus, LZ-8 may potentially be a novel candidate for treating inflammatory bowel disease (IBD).

Male gender and renal dysfunction are predictors of adverse outcome in nonpostoperative ischemic colitis patients.

OBJECTIVE: Ischemic colitis (IC) spans a broad spectrum from self-limiting illness to intestinal gangrene and mortality. Prognostic factors specifically for nonpostoperative IC were not fully characterized. We aim to focus on nonpostoperative IC in patients with renal dysfunction and try to identify prognostic factors for adverse outcomes. METHODS: We conducted a retrospective analysis at a university-affiliated tertiary medical center in Taiwan. From January 2003 to August 2008, 25 men and 52 women (mean age: 66 y) had colonoscopic biopsy-proven IC without prior culprit surgery. We estimated glomerular filtration rate with simplified Modification of Diet in Renal Disease equation. Nine patients with glomerular filtration rate below 30 mL per minute per 1.73 m were classified as renal dysfunction group (including 7 dialysis patients). Adverse outcomes were defined as need for surgery and mortality. Predictors for adverse outcomes were captured by univariate and multivariate analysis. Research ethical committee approved the study protocol. RESULTS: Patients with renal dysfunction more often had: diabetes mellitus (56% vs. 16%, P=0.02), prolonged symptoms (6.8 d vs. 3.5 d, P=0.01), lower hemoglobin (11.1 g/dL vs. 13.4 g/dL, P=0.01), and more often right colonic involvement (56% vs. 19%, P=0.03). Renal dysfunction patients also had longer hospitalization days (median 15 d vs. 4 d, P=0.045). However, there was no statistical significance in the rate of either surgery or mortality between these 2 groups (P>0.05). Univariate analysis showed that renal dysfunction, sex, emergency department referral, presentation with abdominal pain were significant for adverse outcome (P<0.1). Multivariate analysis revealed that male sex conveyed 9.5-fold risk (P=0.01) and renal dysfunction conveyed 8.5-fold risk (P=0.03) for adverse outcomes. CONCLUSIONS: Nonpostoperative IC patients with concurrent renal dysfunction had distinct clinical profiles. Multivariate analysis showed that male patients had 9.5-fold and renal dysfunction patients had 8.5-fold increased risk for adverse outcomes. Although IC is often self-limited, our data warrants special attention and aggressive therapy in treating these patients.

SGLT-1-mediated glucose uptake protects human intestinal epithelial cells against Giardia duodenalis-induced apoptosis.

Infection with Giardia duodenalis is one of the most common causes of waterborne diarrheal disease worldwide. Mechanisms of pathogenesis and host response in giardiasis remain incompletely understood. Previous studies have shown that exposure to G. duodenalis products induce apoptosis in enterocytes. We recently discovered that sodium-dependent glucose cotransporter (SGLT)-1-mediated glucose uptake modulates enterocytic cell death induced by bacterial lipopolysaccharide. The aim of this study was to examine whether enhanced epithelial SGLT-1 activity may constitute a novel mechanism of host defense against G. duodenalis-induced apoptosis. SGLT-1-transfected Caco-2 cells were exposed to G. duodenalis products in low (5mM) or high (25mM) glucose media. In low glucose environments, G. duodenalis-induced caspase-3 activation and DNA fragmentation in these cells. These apoptotic phenomena were abolished in the presence of high glucose. A soluble proteolytic fraction of G. duodenalis was found to upregulate SGLT-1-mediated glucose uptake in a dose- and time-dependent manner, in association with increased apical SGLT-1 expression on epithelial cells. Kinetic analysis showed that this phenomenon resulted from an increase in the maximal rate of sugar transport (V(max)) by SGLT-1, with no change in the affinity constant (K(m)). The addition of phloridzin (a competitive inhibitor for glucose binding to SGLT-1) abolished the anti-apoptotic effects exerted by high glucose. Together, the findings indicate that SGLT-1-dependent glucose uptake may represent a novel epithelial cell rescue mechanism against G. duodenalis-induced apoptosis.

SHANK3 Regulates Intestinal Barrier Function Through Modulating ZO-1 Expression Through the PKCε-dependent Pathway.

BACKGROUND: The integrity of the gut barrier in patients with inflammatory bowel disease is known to be impaired but the exact mechanisms remain mostly unknown. SHANK3 mutations are associated with autism, and patients with autism are known to have higher proportions of inflammatory bowel disease. Here, we explore the role of SHANK3 in inflammatory bowel disease, both in vivo and in vitro. METHODS: Dextran sulfate sodium colitis was induced in SHANK3 knockout mice. Transepithelial electrical resistance, paracellular permeability, and Salmonella invasion assays were used to evaluate epithelial barrier function, in vitro and in vivo. Expression of tight junction proteins, protein kinases, and MAP kinase phosphorylation changes were analyzed by immunoblotting after overexpression or knockdown of SHANK3 expression. SHANK3 expression in intestinal tissue from patients with Crohn's disease was analyzed by quantitative polymerase chain reaction and immunohistochemistry. RESULTS: SHANK3 knockout mice were more susceptible to dextran sulfate sodium. SHANK3 knockout resulted in a leaky epithelial barrier phenotype, as demonstrated by decreased transepithelial electrical resistance, increased paracellular permeability, and increased Salmonella invasion. Overexpression of SHANK3 enhanced ZO-1 expression, and knockdown of SHANK3 resulted in decreased expression of ZO-1. Regulation of ZO-1 expression by SHANK3 seems to be mediated through a PKCε-dependent pathway. SHANK3 expression correlated with ZO-1 and PKCε in colonic tissue of patients with Crohn's disease. CONCLUSIONS: The expression level of SHANK3 affects ZO-1 expression and the barrier function in intestinal epithelial cells. This may provide novel insights in Crohn's disease pathogenesis and treatment.

SGLT-1-mediated glucose uptake protects intestinal epithelial cells against LPS-induced apoptosis and barrier defects: a novel cellular rescue mechanism?

Excessive apoptosis induced by enteric microbes leads to epithelial barrier defects. This mechanism has been implicated in the pathogenesis of inflammatory bowel diseases (IBD) and bacterial enteritis. The sodium-dependent glucose cotransporter (SGLT-1) is responsible for active glucose uptake in enterocytes. The aim was to investigate the effects of SGLT-1 glucose uptake on enterocyte apoptosis and barrier defects induced by bacterial lipopolysaccharide (LPS). SGLT-1-transfected Caco-2 cells were treated with LPS (50 mug/mL) in low (5 mM) or high (25 mM) glucose media. LPS in low glucose induced caspase-3 cleavage, DNA fragmentation, and increased paracellular permeability to dextran in epithelial cells. These phenomena were significantly attenuated in high glucose. LPS increased SGLT-1 activity in high, but not low glucose media. Addition of phloridzin, which competitively binds to SGLT-1, inhibited the cytoprotection mediated by high glucose. Western blot showed that LPS in high glucose increased the levels of anti-apoptotic Bcl-2 and Bcl-X(L,) and did not change proapoptotic Bax. Differential extraction of membranous vs. cytosolic cell components demonstrated that high glucose inhibits mitochondrial cytochrome c translocation to cytosol. Collectively, SGLT-1-mediated glucose uptake increases anti-apoptotic proteins, and protects enterocytes from LPS-induced apoptosis and barrier defects. The understanding of this novel glucose-mediated rescue mechanism may lead to therapeutic interventions for various enteric diseases.

LPS/CD14 activation triggers SGLT-1-mediated glucose uptake and cell rescue in intestinal epithelial cells via early apoptotic signals upstream of caspase-3.

Recent findings indicate that enhanced glucose uptake protects enterocytes from excessive apoptosis and barrier defects induced by LPS exposure. The aim of this study was to characterize the mechanisms responsible for increased sodium-dependent glucose cotransporter (SGLT)-1 activity in enterocytes challenged with LPS. SGLT-1-transfected Caco-2 cells were incubated with LPS in high glucose media. LPS increased SGLT-1 activity in dose- and time-dependent fashion, and is due to increased V(max) of the cotransporter. Elevated apical expression of SGLT-1 was also demonstrated. This LPS-induced effect was colchicine-inhibitable, suggesting microtubule-dependent translocation of SGLT-1 onto apical surface. Immunofluorescence staining showed expression of CD14 on the apical surface, but no TLR-4, on these cells. Neutralizing anti-CD14 decreased the LPS-induced upregulation of SGLT-1 activity, whereas anti-TLR-4 had no effect. Pharmacological studies indicated that signaling for LPS-mediated SGLT-1 glucose uptake depends on caspase-8 and -9 activation, but occurs independently of caspase-3. The findings describe a novel feedback mechanism within the apoptotic signaling pathway for SGLT-1-dependent cytoprotection. The observation suggests a new function for CD14 on enterocytes, involving the induction of the caspase-dependent SGLT-1 activity, which ultimately leads to cell rescue. The understanding of these signaling events may shed light on enterocytic cytoprotection and homeostasis mechanism upon pro-apoptotic challenges.

Intracellular trafficking of CD23: differential regulation in humans and mice by both extracellular and intracellular exons.

In mouse models of food allergy, we recently characterized a new CD23b-derived splice form lacking extracellular exon 5, bDelta5, which undergoes constitutive internalization and mediates the transepithelial transport of free IgE, whereas classical CD23b is more efficient in transporting IgE/allergen complexes. These data suggested that regulation of endocytosis plays a central role in CD23 functions and drove us to systematically compare the intracellular trafficking properties of human and murine CD23 splice forms. We found that CD23 species show similar endocytic behaviors in both species; CD23a undergoes constitutive clathrin-dependent internalization, whereas CD23b is stable at the plasma membrane. However, the mechanisms controlling these similar behaviors appeared to be different. In mice, a positive internalization signal was localized in the cytoplasmic region shared by all CD23 splice forms. This positive signal was negatively regulated by the intracellular CD23b-specific exon. In addition, the fact that alternative splice forms lacking exons of the extracellular region (5, 6, 7, and/or 8) were all constitutively internalized suggested that endocytosis of murine CD23 is regulated by a process similar to the outside-in signaling of integrins. In humans, the internalization signal was mapped in the CD23a-specific intracellular exon. Interestingly, this signal also behaved as a basolateral targeting signal in polarized Madin-Darby canine kidney cells. The latter result and the fact that human intestinal cell lines were found to coexpress both CD23a and CD23b provide a molecular explanation for the initial observations that CD23 was found at the basolateral membrane of intestinal epithelial cells from allergic patients.

Differential role for CD23 splice forms in apical to basolateral transcytosis of IgE/allergen complexes.

The low affinity receptor for IgE (CD23) was recently implicated in the trans-epithelial transport of IgE-allergen complexes from the luminal side of enterocytes in animal models for intestinal allergy. Here, the respective functions of CD23 splice forms, b and bDelta5, in this apical to basolateral transport event have been investigated. First, the new bDelta5 splice form was further characterized, providing evidence that it binds IgE with high affinity, that its expression is induced by sensitization, and that bDelta5, unlike the classical b, undergoes constitutive internalization through clathrin-coated pits. These results suggested that the two CD23 splice forms were likely involved in different transcytotic events. MDCK cell lines expressing either b or bDelta5 were generated to directly test this hypothesis. In both cell lines, CD23 splice forms were localized at the apical membrane as in enterocytes from sensitized mice. Using mouse monoclonal IgE, we obtained evidence showing that bDelta5 mediates the apical to basolateral transport of free IgE, whereas classical b is much more efficient in mediating the transcytosis of IgE/allergen complexes. The present results shed new light on the role of CD23 species in IgE/allergen transepithelial transport and provide a new powerful physiological tool to study apical to basolateral transcytosis, a process which remains poorly characterized.

Role of CD8+ and CD4+ T lymphocytes in jejunal mucosal injury during murine giardiasis.

T-cell-mediated pathogenesis has been documented in various idiopathic and microbially induced intestinal disorders. Diffuse microvillous shortening seen in giardiasis is responsible for disaccharidase insufficiencies and malabsorption of electrolytes, nutrients, and water. Other mucosal changes include crypt hyperplasia and increased numbers of intraepithelial lymphocytes (IEL). A recent report using an athymic mouse model of infection showed that these epithelial injuries were dependent on T cells. The aim of the present study was to identify which subset of superior mesenteric lymph node (SMLN) T cells were responsible for mucosal alterations in giardiasis. CD4+ and CD8+ T cells, as well as whole lymphocyte populations, were isolated from SMLN of Giardia muris-infected mice for adoptive transfer. Jejunal segments of recipient mice were assessed for brush border ultrastructure, sucrase activity, crypt/villus ratio, and IEL numbers. Mice that received enriched CD8+ and whole SMLN lymphocytes, but not CD4+ T cells, from infected donors showed diffuse shortening of microvilli, loss of brush border surface area, impaired sucrase activity, and increased crypt/villus ratios compared to respective controls. Transfer of whole SMLN lymphocytes, as well as enriched CD4+ or CD8+ T cells, from infected donors led to increased IEL numbers in the recipient jejunum. The findings indicate that loss of intestinal brush border surface area, reduced disaccharidase activities, and increased crypt/villus ratios in giardiasis are mediated by CD8+ T cells, whereas both CD8+ and CD4+ SMLN T cells regulate the influx of IEL.

Intestinal epithelial CD23 mediates enhanced antigen transport in allergy: evidence for novel splice forms.

We previously demonstrated enhanced transepithelial antigen transport in the intestine of allergic rodents associated with elevated expression of the low-affinity IgE receptor CD23 on enterocytes. Here, we examined the role of CD23 in the transport phenomenon using CD23-/- mice and characterized the isoform of intestinal epithelial CD23. Jejunal segments of sensitized mice were challenged with antigen. Enhanced transepithelial antigen transport and transmucosal antigen flux were found in the intestine of sensitized CD23+/+ but not CD23-/- mice. RT-PCR showed that enterocytes expressed only the isoform b of CD23. Sequencing revealed classic and alternative CD23b transcripts lacking exon 5 (bDelta5) or 6, all of which were translated into functional IgE receptors. The protein encoded by bDelta5 but not the classic b transcript was able to mediate the uptake of anti-CD23 or IgE, whereas both CD23 proteins were internalized after binding to IgE/antigen complexes. Our results suggest that the classic and alternative forms of CD23b display distinct endocytic properties, suggesting that they are likely to play different roles in transepithelial transport of IgE and allergens.