Polyamines are required for phospholipase C-gamma1 expression promoting intestinal epithelial restitution after wounding

The Roles of Polyamines in Intestinal Development and Function in Piglets

The gastrointestinal tract plays crucial roles in the digestion and absorption of nutrients, as well as in maintenance of a functional barrier. The development and maturation of the intestine is important for piglets to maintain optimal growth and health. Polyamines are necessary for the proliferation and growth of enterocytes, which play a key role in differentiation, migration, remodeling and integrity of the intestinal mucosa after injury. This review elaborates the development of the structure and function of the intestine of piglets during embryonic, suckling and weaning periods, the utilization and metabolism of polyamines in the intestine, as well as the role of polyamines in intestinal development and mucosal repair. The nutritional intervention to improve intestinal development and functions by modulating polyamine metabolism in piglets is also put forward. These results may help to promote the adaption to weaning in pigs and provide useful information for the development and health of piglets.

Stabilization of Cx43 mRNA via RNA-binding protein HuR regulated by polyamines enhances intestinal epithelial barrier function

Gut barrier dysfunction occurs commonly in patients with critical disorders, leading to the translocation of luminal toxic substances and bacteria to the bloodstream. Connexin 43 (Cx43) acts as a gap junction protein and is crucial for intercellular communication and the diffusion of nutrients. The levels of cellular Cx43 are tightly regulated by multiple factors, including polyamines, but the exact mechanism underlying the control of Cx43 expression remains largely unknown. The RNA-binding protein HuR regulates the stability and translation of target mRNAs and is involved in many aspects of intestinal epithelial pathobiology. Here we show that HuR directly bound to Cx43 mRNA via its 3'-untranslated region in intestinal epithelial cells (IECs) and this interaction enhanced Cx43 expression by stabilizing Cx43 mRNA. Depletion of cellular polyamines inhibited the [HuR/Cx43 mRNA] complex and decreased the level of Cx43 protein by destabilizing its mRNA, but these changes were prevented by ectopic overexpression of HuR. Polyamine depletion caused intestinal epithelial barrier dysfunction, which was reversed by ectopic Cx43 overexpression. Moreover, overexpression of checkpoint kinase 2 in polyamine-deficient cells increased the [HuR/Cx43 mRNA] complex, elevated Cx43 levels, and promoted barrier function. These findings indicate that Cx43 mRNA is a novel target of HuR in IECs and that polyamines regulate Cx43 mRNA stability via HuR, thus playing a critical role in the maintenance of intestinal epithelial barrier function.NEW & NOTEWORTHY The current study shows that polyamines stabilize the Cx43 mRNA via HuR, thus enhancing the function of the Cx43-mediated gap junction. These findings suggest that induced Cx43 by HuR plays a critical role in the process by which polyamines regulate intestinal epithelial barrier.

Impact of Preoperative Immunonutrition on Oxidative Stress and Gut Barrier Function in Surgical Patients with Crohn's Disease

Several international guidelines recommend a peri-operative immunonutrition (IN) support for patients care in elective colorectal surgery, to reduce postoperative complications, particularly infections. In Crohn's patients, is also used to mitigate the severity of the disease. We performed a pilot study on 16 Crohn's patients undergoing intestinal surgery for active disease, not responsive to pharmacological treatment; half of them received an oral nutritional supplement enriched with immunonutrients (IN patients) for 7 days prior to surgery, in addition to normal food intake. Markers of oxidative stress (Advanced Glycated End-products (AGEs) and Advanced Oxidation Protein Products (AOPPs) were measured both in plasma and tissue samples wherein the Receptor for Advanced Glycation End products (RAGE) and Tight Junction Protein 1 (TJP1) gene expression were also determined. Plasma AGEs were significantly and positively correlated with tissue levels of AGEs (p = 0.0354) and AOPPs (p = 0.0043) while they were negatively correlated with TJP1 expression (p = 0.0159). The expression of RAGE was also negatively correlated with that of TJP1 gene (p = 0.0146). IN patients exhibited significantly lower AGEs plasma levels (p = 0.0321) and a higher mucosal TJP1 expression (p = 0.0182). No patient had postoperative complications and the length of hospital stay was similar in the two groups, but IN patients, showed a significantly shorter time to resume fluid and solid diet. These preliminary data suggest that IN might support patient's recovery by improving intestinal mucosa barrier function through the regulation of AGEs/RAGE signaling.

Polysaccharides from Panax ginseng promote intestinal epithelial cell migration through affecting the Ca2+ related regulators

Background and aim

Panax ginseng, a key herbal medicine of replenishing Qi and tonifying Spleen, is widely used in the treatment of gastrointestinal diseases in East Asia. In this study, we aim to investigate the potential effects and mechanisms of polysaccharides from P. ginseng (PGP) on intestinal mucosal restitution which is one of the crucial repair modalities during the recovery of mucosal injury controlled by the Ca²⁺ signaling.

Methods

Rat model of intestinal mucosal injury was induced by indomethacin. The fractional cell migration was carried out by immunohistochemistry staining with BrdU. The morphological observations on intestinal mucosal injury were also performed. Intestinal epithelial cell (IEC-6) migration in vitro was conducted by scratch method. Western-blot was adopted to determine the expressions of PLC-γ1, Rac1, TRPC1, RhoA and Cav-1. Immunoprecipitation was used to evaluate the levels of Rac1/PLC-γ1, RhoA/TRPC1 and Cav-1/TRPC1.

Results

The results showed that PGP effectively reduced the assessment of intestinal mucosal injury, reversed the inhibition of epithelial cell migration induced by Indomethacin, and increased the level of Ca²⁺ in intestinal mucosa in vivo. Moreover, PGP dramatically promoted IEC-6 cell migration, the expression of Ca²⁺ regulators (PLC-γ1, Rac1, TRPC1, Cav-1 and RhoA) as well as protein complexes (Rac1/PLC-γ1, Cav-1/TRPC1 and RhoA/TRPC1) in vitro.

Conclusion

PGP increases the Ca²⁺ content in intestinal mucosa partly through controlling the regulators of Ca²⁺ mobilization, subsequently promotes intestinal epithelial cell migration, and then prevents intestinal mucosal injury induced by indomethacin.

The role of Astragalus polysaccharides in promoting IEC-6 cell migration from polyamine-mediated Ca2+ regulation

Astragalus polysaccharide (APS) has a protective effect on injured intestinal mucosa by promoting intestinal cell migration, but the specific mechanism is unclear. The polyamine-mediated calcium signaling pathway is an important mechanism of cell migration, generally, and we tested the hypothesis that APS can protect damaged intestinal mucosa through the polyamine-mediated calcium signaling pathway. High-performance liquid chromatography (HPLC), infrared chromatography, cell scratch test, Western blot, co-immunoprecipitation, polyamine inhibitor (DFMO), si-Cav1, RhoA inhibitor (Rhosin) and Rac1 inhibitor (NSC23766) were used to detect the pharmacodynamic of APS. The results show that APS can promote cell migration. In addition, APS increased the formations of RhoA/TRPC1, Cav1/TRPC1, and Rac1/PLCγ-1 complexes as well as the expressions of TRPC1, PLCγ-1, RhoA, Cav1, and Rac1, and it reversed the inhibitory effect of DFMO on the above factors. APS also reversed the inhibitory effect of si-Cav1 on Cav1 expression, cytoplasmic Ca²⁺ concentrations ([Ca²⁺]cyt), and cell migration. Moreover, APS removed the inhibition of NSC23766 and Rhosin on [Ca²⁺]cyt and cell migration. In vivo study, the water extract of Astragalus membranaceus (WEA) (15 g/kg) reduced the indomethacin-induced injury of intestinal mucosa as well. These observations suggest that APS can treat gastrointestinal mucosal injury through the polyamine calcium signaling pathway.

The Promotive Effect of the Active Ingredients of Atractylodes macrocephala on Intestinal Epithelial Repair Through Activating Ca2+ Pathway

Atractylodes macrocephala ( AM) is a famous traditional Chinese medicine for intestinal epithelial restitution through activating Ca2+ channels. However, the roles of specific AM compositions in intestinal epithelial restitution are sparse. Therefore, this study aimed to compare the concrete effects of the 4 active ingredients (atractylon, β-eudesmol, atractylenolide II, atractylenolide III) of AM and their combination on intestinal epithelial repair and the Ca2+ pathway in intestinal epithelial cell (IEC-6) cells. First, the best combination of the 4 ingredients with an optimal mixing ratio of atractylon: β-eudesmol: atractylenolide II: atractylenolide III = 1:2:2:2 was demonstrated by a 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide orthogonal experiment. Subsequently, enzyme-linked immunosorbent assay was used to measure anti-inflammatory cytokine levels, the migratory ability was evaluated by cell scratch experiments, cell cycle analysis and [Ca2+]cyt concentration in cells were detected by flow cytometry, and the expression of the Ca2+ pathway-related genes was detected by immunofluorescence staining, quantitative polymerase chain reaction and whole blood assays. Our result showed that atractylon, β-Eudesmol, atractylenolide II, and atractylenolide III showed different abilities to promote the IEC-6 cells proliferation, migration, and the expression of anti-inflammatory cytokines interleukin (IL)-2, IL-10, and ornithine decarboxylase, as well as the intracellular [Ca2+]cyt concentration through stromal interaction molecule 1 transposition to activate Ca2+ pathway. Thereinto, atractylenolide III was the main active ingredient of AM for pro-proliferation and anti-inflammation, and the combination of 4 AM ingredients performed better beneficial effects on IEC-6 cells. Therefore, our study suggested that atractylenolide III was the active ingredient of AM for intestinal epithelial repair through activating the Ca2+ pathway, and the 4 ingredients of AM have a synergy in intestinal epithelial repair.

Effects of spermine on the proliferation and migration of porcine intestinal epithelial cells

Whether spermine promotes the repair of porcine intestinal epithelium damage through Ras-related C3 botulinum toxin substrate 1 (Rac1)/phospholipase C-γ1 (PLC-γ1) signaling remains unclear. The current study investigated the effects of spermine addition on the proliferation and migration of IPEC-J2 cells and the effects of Rac1/PLC-γ1 signaling on cell migration. We showed that the inhibitors of Rac1 (NSC-23766) and PLC-γ1 (U73122) reduced cell migration and decreased the protein levels of Rac1 and PLC-γ1 in the cells. Moreover, spermine promoted the proliferation and migration of the IPEC-J2 cells, that is, 1 µM spermine exhibited the best effect, and spermine treatment increased the protein levels of Rac1 and PLC-γ1. Further experiments showed that spermine treatment increased cell migration and enhanced Rac1 and PLC-γ1 protein levels, compared with NSC-23766 and U73122 treatments with spermine. In conclusion, spermine treatment promoted the repair of damaged porcine intestinal epithelium by accelerating cell proliferation and migration mediated by Rac1/PLC-γ1 signaling.

Regulatory role of l-proline in fetal pig growth and intestinal epithelial cell proliferation

l-proline (Pro) is a precursor of ornithine, which is converted into polyamines via ornithine decarboxylase (ODC). Polyamines plays a key role in the proliferation of intestinal epithelial cells. The study investigated the effect of Pro on polyamine metabolism and cell proliferation on porcine enterocytes in vivo and in vitro. Twenty-four Huanjiang mini-pigs were randomly assigned into 1 of 3 groups and fed a basal diet that contained 0.77% alanine (Ala, iso-nitrogenous control), 1% Pro or 1% Pro + 0.0167% α-difluoromethylornithine (DFMO) from d 15 to 70 of gestation. The fetal body weight and number of fetuses per litter were determined, and the small and large intestines were obtained on d 70 ± 1.78 of gestation. The in vitro study was performed in intestinal porcine epithelial (IPEC-J2) cells cultured in Dulbecco's modified Eagle medium-high glucose (DMEM-H) containing 0 μmol/L Pro, 400 μmol/L Pro, or 400 μmol/L Pro + 10 mmol/L DFMO for 4 d. The results showed that maternal dietary supplementation with 1% Pro increased fetal weight; the protein and DNA concentrations of the fetal small intestine; and mRNA levels for potassium voltage-gated channel, shaker-related subfamily, member 1 (Kv1.1) in the fetal small and large intestines (P < 0.05). Supplementing Pro to either gilts or IPEC-J2 cells increased ODC protein abundances and polyamine concentrations in the fetal intestines and IPEC-J2 cells (P < 0.05). In comparison with the Pro group, the combined administration of Pro and DFMO reduced the expression of ODC protein and spermine concentration in the fetal intestine, as well as the concentrations of putrescine, spermidine and spermine in IPEC-J2 cells (P < 0.05). Meanwhile, the percentage of cells in the S-phase and the mRNA levels of proto-oncogenes c-fos and c-myc were increased in response to Pro supplementation, whereas depletion of cellular polyamines with DFMO increased tumor protein p53 (p53) mRNA levels (P < 0.05). Taken together, dietary supplementation with Pro improved fetal pig growth and intestinal epithelial cell proliferation via enhancing polyamine synthesis.

Multiple calcium sources are required for intracellular calcium mobilization during gastric organoid epithelial repair

Calcium (Ca2+ ) is a known accelerator for gastric wound repair. We have demonstrated in vivo and in vitro that intracellular Ca2+ increases in the gastric epithelial cells directly adjacent to a damaged cell, and that this Ca2+ rise is essential for the cellular migration that rapidly repairs the epithelium (restitution). While intracellular Ca2+ has been shown to be an important signaling factor during epithelial restitution, the source from which this intracellular Ca2+ originates remains unclear. Using gastric organoids derived from mice transgenic for a genetically encoded Ca2+ indicator, we sought to investigate the potential sources of intracellular Ca2+ mobilization. During confocal imaging, photodamage (PD) was induced to 1-2 gastric organoid epithelial cells and epithelial restitution measured simultaneously with changes in intracellular Ca2+ (measured as FRET/CFP ratio in migrating cells adjacent to the damaged area). Inhibition of voltage-gated Ca2+ channels (verapamil, 10 µM) or store-operated calcium entry (YM58483, 20 µM) resulted in delayed repair and dampened intracellular Ca2+ response. Furthermore, inhibition of phospholipase C (U73122, 10 µM) or inositol trisphosphate receptor (2-APB, 50 µM) likewise resulted in delayed repair and dampened Ca2+ response. Results suggest both extracellular and intracellular Ca2+ sources are essential for supplying the Ca2+ mobilization that stimulates repair.

miR-222 represses expression of zipcode binding protein-1 and phospholipase C-γ1 in intestinal epithelial cells

Both zipcode binding protein-1 (ZBP1) and phospholipase C-γ1 (PLCγ1) are intimately involved in many aspects of early intestinal mucosal repair after acute injury, but the exact mechanisms that control their cellular abundances remain largely unknown. The present study shows that microRNA-222 (miR-222) interacts with the mRNAs encoding ZBP1 and PLCγ1 and regulates ZBP1 and PLCγ1 expression in intestinal epithelial cells (IECs). The biotinylated miR-222 bound specifically to the ZBP1 and PLCγ1 mRNAs in IECs. Ectopically expressed miR-222 precursor destabilized the ZBP1 and PLCγ1 mRNAs and consequently lowered the levels of cellular ZBP1 and PLCγ1 proteins. Conversely, decreasing the levels of cellular miR-222 by transfection with its antagonism increased the stability of the ZBP1 and PLCγ1 mRNAs and increased the levels of ZBP1 and PLCγ1 proteins. Overexpression of miR-222 also inhibited cell migration over the wounded area, which was partially abolished by overexpressing ZBP1 and PLCγ1. Furthermore, prevention of the increased levels of ZBP1 and PLCγ1 in the miR-222-silenced cells by transfection with specific small interfering RNAs targeting ZBP1 or PLCγ1 mRNA inhibited cell migration after wounding. These findings indicate that induced miR-222 represses expression of ZBP1 and PLCγ1 at the posttranscriptional level, thus inhibiting IEC migration during intestinal epithelial restitution after wounding.

β-PIX plays an important role in regulation of intestinal epithelial restitution by interacting with GIT1 and Rac1 after wounding

Early gut mucosal restitution is a process by which intestinal epithelial cells (IECs) migrate over the wounded area, and its defective regulation occurs commonly in various critical pathological conditions. This rapid reepithelialization is mediated by different activating small GTP-binding proteins, but the exact mechanism underlying this process remains largely unknown. Recently, it has been reported that interaction between p21-activated kinase-interacting exchange factor (β-PIX) and G protein-coupled receptor kinase-interacting protein 1 (GIT1) activates small GTPases and plays an important role in the regulation of cell motility. Here, we show that induced association of β-PIX with GIT1 is essential for the stimulation of IEC migration after wounding by activating Rac1. Levels of β-PIX and GIT1 proteins and their association in differentiated IECs (line of IEC-Cdx2L1) were much higher than those observed in undifferentiated IECs (line of IEC-6), which was associated with an increase in IEC migration after wounding. Decreased levels of endogenous β-PIX by its gene-silencing destabilized β-PIX/GIT1 complexes, repressed Rac1 activity and inhibited cell migration over the wounded area. In contrast, ectopic overexpression of β-PIX increased the levels of β-PIX/GIT1 complexes, stimulated Rac1 activity, and enhanced intestinal epithelial restitution. Increased levels of cellular polyamines also stimulated β-PIX/GIT1 association, increased Rac1 activity, and promoted the epithelial restitution. Moreover, polyamine depletion decreased cellular abundances of β-PIX/GIT1 complex and repressed IEC migration after wounding, which was rescued by ectopic overexpression of β-PIX or GIT1. These results indicate that β-PIX/GIT1/Rac1 association is necessary for stimulation of IEC migration after wounding and that this signaling pathway is tightly regulated by cellular polyamines. NEW & NOTEWORTHY Our current study demonstrates that induced association of β-PIX with GIT1 is essential for the stimulation of intestinal epithelial restitution by activating Rac1, and this signaling pathway is tightly regulated by cellular polyamines.

Protective effect of glutamine and arginine against soybean meal-induced enteritis in the juvenile turbot (Scophthalmus maximus)

Soybean meal can induce enteritis in the distal intestine (DI) and decrease the immunity of several cultured fish species, including turbot Scophthalmus maximus. Glutamine and arginine supplementation have been used to improve immunity and intestinal morphology in fish. This study was conducted to investigate the effects of these two amino acids on the immunity and intestinal health of turbot suffering from soybean meal-induced enteritis. Turbots (initial weight 7.6 g) were fed one of three isonitrogenous and isolipidic diets for 8 weeks: SBM (control diet), with 40% soybean meal; GLN, SBM diet plus 1.5% glutamine; ARG, the SBM diet plus 1.5% arginine. Symptoms that are typical of soybean meal-induced enteritis, including swelling of the lamina propria and subepithelial mucosa and a strong infiltration of various inflammatory cells was observed in fish that fed the SBM diet. Glutamine and arginine supplementation significantly increased (1) the weight gain and feed efficiency ratio; (2) the height and vacuolization of villi and the integrity of microvilli in DI; (3) serum lysozyme activity, and the concentrations of C3, C4, and IgM. These two amino acids also significantly decreased the infiltration of leucocytes in the lamina propria and submucosa and the expression of inflammatory cytokines including il-8, tnf-α, and tgf-β. For the mucosal microbiota, arginine supplementation significantly increased microbiota community richness and diversity, and glutamine supplementation significantly increased the relative abundance of Lactobacillus and Bacillus. These results indicate that dietary glutamine and arginine improved the growth performance, feed utilization, and distal intestinal morphology, activated the innate and adaptive immune systems, changed the intestinal mucosal microbiota community, and relieved SBMIE possibly by suppression of the inflammation response.

Atractylenolide I stimulates intestinal epithelial repair through polyamine-mediated Ca2+ signaling pathway

BACKGROUND

An impairment of the integrity of the mucosal epithelial barrier can be observed in the course of various gastrointestinal diseases. The migration and proliferation of the intestinal epithelial (IEC-6) cells are essential repair modalities to the healing of mucosal ulcers and wounds. Atractylenolide I (AT-I), one of the major bioactive components in the rhizome of Atractylodes macrocephala Koidz. (AMR), possesses multiple pharmacological activities. This study was designed to investigate the therapeutic effects and the underlying molecular mechanisms of AT-I on gastrointestinal mucosal injury.

METHODS

Scratch method with a gel-loading microtip was used to detect IEC-6 cell migration. The real-time cell analyzer (RTCA) system was adopted to evaluate IEC-6 cell proliferation. Intracellular polyamines content was determined using high performance liquid chromatography (HPLC). Flow cytometry was used to measure cytosolic free Ca²⁺ concentration ([Ca²⁺]_c). mRNA and protein expression of TRPC1 and PLC-γ₁ were determined by real-time PCR and Western blotting assay respectively.

RESULTS

Treatment of IEC-6 cells with AT-I promoted cell migration and proliferation, increased polyamines content, raised cytosolic free Ca²⁺ concentration ([Ca²⁺]_c), and enhanced TRPC1 and PLC-γ₁ mRNA and protein expression. Depletion of cellular polyamines by DL-a-difluoromethylornithine (DFMO, an inhibitor of polyamine synthesis) suppressed cell migration and proliferation, decreased polyamines content, and reduced [Ca²⁺]_c, which was paralleled by a decrease in TRPC1 and PLC-γ₁ mRNA and protein expression in IEC-6 cells. AT-I reversed the effects of DFMO on polyamines content, [Ca²⁺]_c, TRPC1 and PLC-γ₁ mRNA and protein expression, and restored IEC-6 cell migration and proliferation to near normal levels.

CONCLUSION

Our data demonstrate that AT-I stimulates intestinal epithelial cell migration and proliferation via the polyamine-mediated Ca²⁺ signaling pathway. Therefore, AT-I may have the potential to be further developed as a promising therapeutic agent to treat diseases associated with gastrointestinal mucosal injury, such as inflammatory bowel disease and peptic ulcer.

HuR Enhances Early Restitution of the Intestinal Epithelium by Increasing Cdc42 Translation

The mammalian intestinal mucosa exhibits a spectrum of responses after acute injury and repairs itself rapidly to restore the epithelial integrity. The RNA-binding protein HuR regulates the stability and translation of target mRNAs and is involved in many aspects of gut epithelium homeostasis, but its exact role in the regulation of mucosal repair after injury remains unknown. We show here that HuR is essential for early intestinal epithelial restitution by increasing the expression of cell division control protein 42 (Cdc42) at the posttranscriptional level. HuR bound to the Cdc42 mRNA via its 3' untranslated region, and this association specifically enhanced Cdc42 translation without an effect on the Cdc42 mRNA level. Intestinal epithelium-specific HuR knockout not only decreased Cdc42 levels in mucosal tissues, but it also inhibited repair of damaged mucosa induced by mesenteric ischemia/reperfusion in the small intestine and by dextran sulfate sodium in the colon. Furthermore, Cdc42 silencing prevented HuR-mediated stimulation of cell migration over the wounded area by altering the subcellular distribution of F-actin. These results indicate that HuR promotes early intestinal mucosal repair after injury by increasing Cdc42 translation and demonstrate the importance of HuR deficiency in the pathogenesis of delayed mucosal healing in certain pathological conditions.

c-Jun enhances intestinal epithelial restitution after wounding by increasing phospholipase C-γ1 transcription

c-Jun is an activating protein 1 (AP-1) transcription factor and implicated in many aspects of cellular functions, but its exact role in the regulation of early intestinal epithelial restitution after injury remains largely unknown. Phospholipase C-γ1 (PLCγ1) catalyzes hydrolysis of phosphatidylinositol 4,5 biphosphate into the second messenger diacylglycerol and inositol 1,4,5 triphosphate, coordinates Ca²⁺ store mobilization, and regulates cell migration and proliferation in response to stress. Here we reported that c-Jun upregulates PLCγ1 expression and enhances PLCγ1-induced Ca²⁺ signaling, thus promoting intestinal epithelial restitution after wounding. Ectopically expressed c-Jun increased PLCγ1 expression at the transcription level, and this stimulation is mediated by directly interacting with AP-1 and CCAAT-enhancer-binding protein (C/EBP) binding sites that are located at the proximal region of the rat PLCγ1 promoter. Increased levels of PLCγ1 by c-Jun elevated cytosolic free Ca²⁺ concentration and stimulated intestinal epithelial cell migration over the denuded area after wounding. The c-Jun-mediated PLCγ1/Ca²⁺ signal also plays an important role in polyamine-induced cell migration after wounding because increased c-Jun rescued Ca²⁺ influx and cell migration in polyamine-deficient cells. These findings indicate that c-Jun induces PLCγ1 expression transcriptionally and enhances rapid epithelial restitution after injury by activating Ca²⁺ signal.

RhoA enhances store-operated Ca2+ entry and intestinal epithelial restitution by interacting with TRPC1 after wounding

Early mucosal restitution occurs as a consequence of epithelial cell migration to resealing of superficial wounds after injury. Our previous studies show that canonical transient receptor potential-1 (TRPC1) functions as a store-operated Ca(2+) channel (SOC) in intestinal epithelial cells (IECs) and plays an important role in early epithelial restitution by increasing Ca(2+) influx. Here we further reported that RhoA, a small GTP-binding protein, interacts with and regulates TRPC1, thus enhancing SOC-mediated Ca(2+) entry (SOCE) and epithelial restitution after wounding. RhoA physically associated with TRPC1 and formed the RhoA/TRPC1 complexes, and this interaction increased in stable TRPC1-transfected IEC-6 cells (IEC-TRPC1). Inactivation of RhoA by treating IEC-TRPC1 cells with exoenzyme C3 transferase (C3) or ectopic expression of dominant negative RhoA (DNMRhoA) reduced RhoA/TRPC1 complexes and inhibited Ca(2+) influx after store depletion, which was paralleled by an inhibition of cell migration over the wounded area. In contrast, ectopic expression of wild-type (WT)-RhoA increased the levels of RhoA/TRPC1 complexes, induced Ca(2+) influx through activation of SOCE, and promoted cell migration after wounding. TRPC1 silencing by transfecting stable WT RhoA-transfected cells with siRNA targeting TRPC1 (siTRPC1) reduced SOCE and repressed epithelial restitution. Moreover, ectopic overexpression of WT-RhoA in polyamine-deficient cells rescued the inhibition of Ca(2+) influx and cell migration induced by polyamine depletion. These findings indicate that RhoA interacts with and activates TRPC1 and thus stimulates rapid epithelial restitution after injury by inducing Ca(2+) signaling.

L-arginine and aminoguanidine reduce colonic damage of acetic acid-induced colitis in rats: potential modulation of nuclear factor-κB/p65

The transcription factor, nuclear factor-κB (NF-κB) is a key inducer of inducible nitric oxide synthase (iNOS) gene expression. The aim of the present study was to investigate the potential protective effect of l-arginine (Arg; nitric oxide precursor) and aminoguanidine (inducible nitric oxide synthase inhibitor) against acetic acid (AA)-induced colitis in rats, and the potential role of NF-κB. Colitis was induced by intrarectal inoculation of rats with 4% acetic acid for three consecutive days. The effect of Arg and aminoguanidine on nitric oxide levels was assessed by Greiss assay and protein expression of NF-κB/p65, and inducible nitric oxide synthase was also investigated by immunohistochemistry. Slides were examined using ImageJ, and results reported as the percent area positive for each marker. Intrarectal AA caused a significant increase in bodyweight loss and colon weights. Arg at 100 mg/day for 7 days before induction of colitis diminished the changes in both bodyweight loss and colon weights. Furthermore, Arg attenuated the colonic tissues macroscopic and microscopic damage induced by acetic acid. In addition, i.p. AG 100 mg/kg given during and after induction of colitis recovered the colonic ulcerative lesion induced by AA. Arg can protect against colonic inflammation; an effect that probably be attributed to its nitric oxide-donating property, resulting in modulatory effects on the expression of NF-κB/p65 in the colon tissues. The results suggested that Arg might reduce the inflammation associated with colitis as confirmed by histopathological investigations. Arg might inhibit AA-induced colitis through the NF-κB/nitric oxide pathway.

Glucose-dependent insulinotropic polypeptide-mediated signaling pathways enhance apical PepT1 expression in intestinal epithelial cells

We have shown recently that glucose-dependent insulinotropic polypeptide (GIP), but not glucagon-like peptide 1 (GLP-1) augments H(+) peptide cotransporter (PepT1)-mediated peptide absorption in murine jejunum. While we observed that inhibiting cAMP production decreased this augmentation of PepT1 activity by GIP, it was unclear whether PKA and/or other regulators of cAMP signaling pathway(s) were involved. This study utilized tritiated glycyl-sarcosine [(3)H-glycyl-sarcosine (Gly-Sar), a relatively nonhydrolyzable dipeptide] uptake to measure PepT1 activity in CDX2-transfected IEC-6 (IEC-6/CDX2) cells, an absorptive intestinal epithelial cell model. Similar to our earlier observations with mouse jejunum, GIP but not GLP-1 augmented Gly-Sar uptake (control vs. +GIP: 154 ± 22 vs. 454 ± 39 pmol/mg protein; P < 0.001) in IEC-6/CDX2 cells. Rp-cAMP (a PKA inhibitor) and wortmannin [phosophoinositide-3-kinase (PI3K) inhibitor] pretreatment completely blocked, whereas neither calphostin C (a potent PKC inhibitor) nor BAPTA (an intracellular Ca(2+) chelator) pretreatment affected the GIP-augmented Gly-Sar uptake in IEC-6/CDX2 cells. The downstream metabolites Epac (control vs. Epac agonist: 287 ± 22 vs. 711 ± 80 pmol/mg protein) and AKT (control vs. AKT inhibitor: 720 ± 50 vs. 75 ± 19 pmol/mg protein) were shown to be involved in GIP-augmented PepT1 activity as well. Western blot analyses revealed that both GIP and Epac agonist pretreatment enhance the PepT1 expression on the apical membranes, which is completely blocked by wortmannin in IEC-6/CDX2 cells. These observations demonstrate that both cAMP and PI3K signaling pathways augment GIP-induced peptide uptake through Epac and AKT-mediated pathways in intestinal epithelial cells, respectively. In addition, these observations also indicate that both Epac and AKT-mediated signaling pathways increase apical membrane expression of PepT1 in intestinal absorptive epithelial cells.

Mucosal healing in inflammatory bowel diseases: is there a place for nutritional supplementation?

Advanced mucosal healing (MH) after intestinal mucosal inflammation coincides with sustained clinical remission and reduced rates of hospitalization and surgical resection, explaining why MH is increasingly considered as a full therapeutic goal and as an endpoint for clinical trials. Intestinal MH is a complex phenomenon viewed as a succession of steps necessary to restore tissue structure and function. These steps include epithelial cell migration and proliferation, cell differentiation, restoration of epithelial barrier functions, and modulation of cell apoptosis. Few clinical studies have evaluated the needs for specific macronutrients and micronutrients and their effects on intestinal MH, most data having been obtained from animal and cell studies. These data suggest that supplementation with specific amino acids including arginine, glutamine, glutamate, threonine, methionine, serine, proline, and the amino acid-derived compounds, polyamines can favorably influence MH. Short-chain fatty acids, which are produced by the microbiota from undigested polysaccharides and protein-derived amino acids, also exert beneficial effects on the process of intestinal MH in experimental models. Regarding supplementation with lipids, although the effects of ω-3 and ω-6 fatty acids remain controversial, endogenous prostaglandin synthesis seems to be necessary for MH. Finally, among micronutrients, several vitamin and mineral deficiencies with different frequencies have been observed in patients with inflammatory bowel diseases and supplementation with some of them (vitamin A, vitamin D3, vitamin C, and zinc) are presumed to favor MH. Future work, including clinical studies, should evaluate the efficiency of supplementation with combination of dietary compounds as adjuvant nutritional intervention for MH of the inflamed intestinal mucosa.

Caveolin-1 enhances rapid mucosal restitution by activating TRPC1-mediated Ca2+ signaling

Early rapid mucosal restitution occurs as a consequence of epithelial cell migration to reseal superficial wounds, a process independent of cell proliferation. Our previous studies revealed that the canonical transient receptor potential-1 (TRPC1) functions as a store-operated Ca(2+) channel (SOCs) in intestinal epithelial cells (IECs) and regulates epithelial restitution after wounding, but the exact mechanism underlying TRPC1 activation remains elusive. Caveolin-1 (Cav1) is a major component protein that is associated with caveolar lipid rafts in the plasma membrane and was recently identified as a regulator of store-operated Ca(2+) entry (SOCE). Here, we showed that Cav1 plays an important role in the regulation of mucosal restitution by activating TRPC1-mediated Ca(2+) signaling. Target deletion of Cav1 delayed gastric mucosal repair after exposure to hypertonic NaCl in mice, although it did not affect total levels of TRPC1 protein. In cultured IECs, Cav1 directly interacted with TRPC1 and formed Cav1/TRPC1 complex as measured by immunoprecipitation assays. Cav1 silencing in stable TRPC1-transfected cells by transfection with siCav1 reduced SOCE without effect on the level of resting [Ca(2+)]cyt. Inhibition of Cav1 expression by siCav1 and subsequent decrease in Ca(2+) influx repressed epithelial restitution, as indicated by a decrease in cell migration over the wounded area, whereas stable ectopic overexpression of Cav1 increased Cav1/TRPC1 complex, induced SOCE, and enhanced cell migration after wounding. These results indicate that Cav1 physically interacts with and activates TRPC1, thus stimulating TRPC1-mediated Ca(2+) signaling and rapid mucosal restitution after injury.

Src-mediated caveolin-1 phosphorylation regulates intestinal epithelial restitution by altering Ca(2+) influx after wounding

Early mucosal restitution occurs as a consequence of intestinal epithelial cell (IEC) migration to reseal superficial wounds, but its exact mechanism remains largely unknown. Caveolin-1 (Cav1), a major component associated with caveolar lipid rafts in the plasma membrane, is implicated in many aspects of cellular functions. This study determined if c-Src kinase (Src)-induced Cav1 phosphorylation promotes intestinal epithelial restitution after wounding by activating Cav1-mediated Ca(2+) signaling. Src directly interacted with Cav1, formed Cav1-Src complexes, and phosphorylated Cav1 in IECs. Inhibition of Src activity by its chemical inhibitor PP2 or suppression of the functional caveolin scaffolding domain by caveolin-scaffolding domain peptides prevented Cav1-Src interaction, reduced Cav1 phosphorylation, decreased Ca(2+) influx, and inhibited cell migration after wounding. Disruption of caveolar lipid raft microdomains by methyl-β-cyclodextrin reduced Cav1-mediated Ca(2+) influx and repressed epithelial restitution. Moreover, Src silencing prevented subcellular redistribution of phosphorylated Cav1 in migrating IECs. These results indicate that Src-induced Cav1 phosphorylation stimulates epithelial restitution by increasing Cav1-mediated Ca(2+) signaling after wounding, thus contributing to the maintenance of gut mucosal integrity under various pathological conditions.

Atractylodes macrocephala Koidz promotes intestinal epithelial restitution via the polyamine--voltage-gated K+ channel pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Atractylodes macrocephala Koidz (AMK) has been used widely as a digestive and tonic in traditional Chinese medicine. AMK has shown noteworthy promoting effect on intestinal epithelial cell migration, which might represent a promising candidate for the treatment of intestinal mucosa injury. The aim of this study was to investigate the efficacy of AMK on intestinal mucosal restitution and the underlying mechanisms via IEC-6 cell migration model.

MATERIALS AND METHODS

A wounding model of IEC-6 cells was induced by a single-edge razor blade along the diameter of six-well polystyrene plates. The cells were grown in control cultures and in cultures containing spermidine (5 μmol/L, SPD, reference drug), alpha-difluoromethylornithine (2.5 mmol/L, DFMO, polyamine inhibitor), AMK (50, 100, and 200 μg/mL), DFMO plus SPD and DFMO plus AMK for 24h. The membrane potential (MP) and cytosolic free Ca(2+) concentration ([Ca(2+)]cyt) were detected by flow cytometry, and polyamines content was determined via high-performance liquid chromatography (HPLC). The expression of Kv1.1 mRNA and protein levels were assessed by RT-qPCR and Western blot analysis, respectively. Cell migration assay was carried out using the Image-Pro Plus software. All of these indexes were used to evaluate the effectiveness of AMK.

RESULTS

(1) Treatment with AMK caused significant increases in cellular polyamines content, membrane hyperpolarization, an elevation of [Ca(2+)]cyt and an acceleration of cell migration in IEC-6 cells, as compared to control group. (2) AMK not only reversed the inhibitory effects of DFMO on the polyamines content, MP, and [Ca(2+)]cyt but also restored IEC-6 cell migration to control levels. (3) The Kv1.1 mRNA and protein expression were significantly increased by AMK treatment in control and polyamine-deficient IEC-6 cells.

CONCLUSIONS

The results of our current studies revealed that treatment with AMK significantly stimulates the migration of intestinal epithelial cells through polyamine-Kv1.1 channel signaling pathway, which could promote the healing of intestinal injury. These results suggest the potential usefulness of AMK to cure intestinal disorders characterized by injury and ineffective repair of the intestinal mucosa.

Elevated polyamines in urothelial cells from OAB subjects mediate oxotremorine-evoked rapid intracellular calcium rise and delayed acetylcholine release

Increased polyamine signaling in bladder urothelial cells (BUC) may play a role in the pathophysiology of overactive bladder (OAB). We quantitated intracellular polyamine levels in cultured BUC from OAB and asymptomatic (NB) subjects. We assessed whether polyamines modulated rapid intracellular calcium ([Ca(2+)]i) changes and delayed acetylcholine (ACh) release evoked by oxotremorine (OXO, a muscarinic agonist). BUC were cultured from cystoscopic biopsies. High-performance liquid chromatography (HPLC) quantitated intracellular putrescine, spermidine, and spermine levels. Five-millimeter difluoromethylornithine (DFMO), and one-millimeter methylglyoxalbisguanylhydrazone (MGBG) treatments were used to deplete intracellular polyamines. Ten micrometers of OXO were used to increase [Ca(2+)]i levels (measured by fura 2 microfluorimetry) and trigger extracellular ACh release (measured by ELISA). Polyamine levels were elevated in OAB compared with NB BUC (0.5 ± 0.15 vs. 0.16 ± 0.03 nmol/mg for putrescine, 2.4 ± 0.21 vs. 1.01 ± 0.13 nmol/mg for spermidine, and 1.90 ± 0.27 vs. 0.86 ± 0.26 nmol/mg for spermine; P < 0.05 for all comparisons). OXO evoked greater [Ca(2+)]i rise in OAB (205.10 ± 18.82% increase over baseline) compared with in NB BUC (119.54 ± 13.01%; P < 0.05). After polyamine depletion, OXO evoked [Ca(2+)]i rise decreased in OAB and NB BUC to 43.40 ± 6.45 and 38.82 ± 3.5%, respectively. OXO tended to increase ACh release by OAB vs. NB BUC (9.02 ± 0.1 vs. 7.04 ± 0.09 μM, respectively; P < 0.05). Polyamine depletion reduced ACh release by both OAB and NB BUC. In conclusion, polyamine levels were elevated twofold in OAB BUC. OXO evoked greater increase in [Ca(2+)]i and ACh release in OAB BUC, although these two events may be unrelated. Depletion of polyamines caused OAB BUC to behave similarly to NB BUC.

Polyamines regulate intestinal epithelial restitution through TRPC1-mediated Ca²+ signaling by differentially modulating STIM1 and STIM2

Early epithelial restitution occurs as a consequence of intestinal epithelial cell (IEC) migration after wounding, and its defective regulation is implicated in various critical pathological conditions. Polyamines stimulate intestinal epithelial restitution, but their exact mechanism remains unclear. Canonical transient receptor potential-1 (TRPC1)-mediated Ca(2+) signaling is crucial for stimulation of IEC migration after wounding, and induced translocation of stromal interaction molecule 1 (STIM1) to the plasma membrane activates TRPC1-mediated Ca(2+) influx and thus enhanced restitution. Here, we show that polyamines regulate intestinal epithelial restitution through TRPC1-mediated Ca(2+) signaling by altering the ratio of STIM1 to STIM2. Increasing cellular polyamines by ectopic overexpression of the ornithine decarboxylase (ODC) gene stimulated STIM1 but inhibited STIM2 expression, whereas depletion of cellular polyamines by inhibiting ODC activity decreased STIM1 but increased STIM2 levels. Induced STIM1/TRPC1 association by increasing polyamines enhanced Ca(2+) influx and stimulated epithelial restitution, while decreased formation of the STIM1/TRPC1 complex by polyamine depletion decreased Ca(2+) influx and repressed cell migration. Induced STIM1/STIM2 heteromers by polyamine depletion or STIM2 overexpression suppressed STIM1 membrane translocation and inhibited Ca(2+) influx and epithelial restitution. These results indicate that polyamines differentially modulate cellular STIM1 and STIM2 levels in IECs, in turn controlling TRPC1-mediated Ca(2+) signaling and influencing cell migration after wounding.

Recent advances in small bowel diseases: Part I

As is the case in all parts of gastroenterology and hepatology, there have been many advances in our knowledge and understanding of small intestinal diseases. Over 1000 publications were reviewed for 2008 and 2009, and the important advances in basic science as well as clinical applications were considered. In Part I of this Editorial Review, seven topics are considered: intestinal development; proliferation and repair; intestinal permeability; microbiotica, infectious diarrhea and probiotics; diarrhea; salt and water absorption; necrotizing enterocolitis; and immunology/allergy. These topics were chosen because of their importance to the practicing physician.

Effect of m-3m3FBS on Ca2+ handling and viability in OC2 human oral cancer cells

The effect of 2,4,6-trimethyl-N-(meta-3-trifluoromethyl-phenyl)-benzenesulfonamide (m-3M3FBS), a presumed phospholipase C activator, on cytosolic free Ca2+ concentrations ([Ca2+]i) in OC2 human oral cancer cells is unclear. This study explored whether m-3M3FBS changed basal [Ca2+]i levels in suspended OC2 cells by using fura-2 as a Ca2+-sensitive fluorescent dye. M-3M3FBS at concentrations between 10-60 μM increased [Ca2+]i in a concentration-dependent manner. The Ca2+ signal was reduced partly by removing extracellular Ca2+. M-3M3FBS-induced Ca2+ influx was inhibited by the store-operated Ca2+ channel blockers nifedipine, econazole and SK&F96365, and by the phospholipase A2 inhibitor aristolochic acid. In Ca2+-free medium, 30 μM m-3M3FBS pretreatment inhibited the [Ca2+]i rise induced by the endoplasmic reticulum Ca2+ pump inhibitors thapsigargin and 2,5-di-tert-butylhydroquinone (BHQ). Conversely, pretreatment with thapsigargin, BHQ or cyclopiazonic acid partly reduced m-3M3FBS-induced [Ca2+]i rise. Inhibition of inositol 1,4,5-trisphosphate formation with U73122 did not alter m-3M3FBS-induced [Ca2+]i rise. At concentrations between 5 and 100 μM m-3M3FBS killed cells in a concentration-dependent manner. The cytotoxic effect of m-3M3FBS was not reversed by prechelating cytosolic Ca2+ with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA). Propidium iodide staining data suggest that m-3M3FBS (20 or 50 μM) induced apoptosis in a Ca2+-independent manner. Collectively, in OC2 cells, m-3M3FBS induced [Ca2+]i rise by causing inositol 1,4,5-trisphosphate-independent Ca2+ release from the endoplasmic reticulum and Ca2+ influx via phospholipase A2-sensitive store-operated Ca2+ channels. M-3M3FBS also induced Ca2+-independent cell death and apoptosis.

Ornithine decarboxylase mRNA is stabilized in an mTORC1-dependent manner in Ras-transformed cells

Upon Ras activation, ODC (ornithine decarboxylase) is markedly induced, and numerous studies suggest that ODC expression is controlled by Ras effector pathways. ODC is therefore a potential target in the treatment and prevention of Ras-driven tumours. In the present study we compared ODC mRNA translation profiles and stability in normal and Ras12V-transformed RIE-1 (rat intestinal epithelial) cells. While translation initiation of ODC increased modestly in Ras12V cells, ODC mRNA was stabilized 8-fold. Treatment with the specific mTORC1 [mTOR (mammalian target of rapamycin) complex 1] inhibitor rapamycin or siRNA (small interfering RNA) knockdown of mTOR destabilized the ODC mRNA, but rapamycin had only a minor effect on ODC translation initiation. Inhibition of mTORC1 also reduced the association of the mRNA-binding protein HuR with the ODC transcript. We have shown previously that HuR binding to the ODC 3'UTR (untranslated region) results in significant stabilization of the ODC mRNA, which contains several AU-rich regions within its 3'UTR that may act as regulatory sequences. Analysis of ODC 3'UTR deletion constructs suggests that cis-acting elements between base 1969 and base 2141 of the ODC mRNA act to stabilize the ODC transcript. These experiments thus define a novel mechanism of ODC synthesis control. Regulation of ODC mRNA decay could be an important means of limiting polyamine accumulation and subsequent tumour development.

Radiation protection following nuclear power accidents: a survey of putative mechanisms involved in the radioprotective actions of taurine during and after radiation exposure

There are several animal experiments showing that high doses of ionizing radiation lead to strongly enhanced leakage of taurine from damaged cells into the extracellular fluid, followed by enhanced urinary excretion. This radiation-induced taurine depletion can itself have various harmful effects (as will also be the case when taurine depletion is due to other causes, such as alcohol abuse or cancer therapy with cytotoxic drugs), but taurine supplementation has been shown to have radioprotective effects apparently going beyond what might be expected just as a consequence of correcting the harmful consequences of taurine deficiency per se. The mechanisms accounting for the radioprotective effects of taurine are, however, very incompletely understood. In this article an attempt is made to survey various mechanisms that potentially might be involved as parts of the explanation for the overall beneficial effect of high levels of taurine that has been found in experiments with animals or isolated cells exposed to high doses of ionizing radiation. It is proposed that taurine may have radioprotective effects by a combination of several mechanisms: (1) during the exposure to ionizing radiation by functioning as an antioxidant, but perhaps more because it counteracts the prooxidant catalytic effect of iron rather than functioning as an important scavenger of harmful molecules itself, (2) after the ionizing radiation exposure by helping to reduce the intensity of the post-traumatic inflammatory response, and thus reducing the extent of tissue damage that develops because of severe inflammation rather than as a direct effect of the ionizing radiation per se, (3) by functioning as a growth factor helping to enhance the growth rate of leukocytes and leukocyte progenitor cells and perhaps also of other rapidly proliferating cell types, such as enterocyte progenitor cells, which may be important for immunological recovery and perhaps also for rapid repair of various damaged tissues, especially in the intestines, and (4) by functioning as an antifibrogenic agent. A detailed discussion is given of possible mechanisms involved both in the antioxidant effects of taurine, in its anti-inflammatory effects and in its role as a growth factor for leukocytes and nerve cells, which might be closely related to its role as an osmolyte important for cellular volume regulation because of the close connection between cell volume regulation and the regulation of protein synthesis as well as cellular protein degradation. While taurine supplementation alone would be expected to exert a therapeutic effect far better than negligible in patients that have been exposed to high doses of ionizing radiation, it may on theoretical grounds be expected that much better results may be obtained by using taurine as part of a multifactorial treatment strategy, where it may interact synergistically with several other nutrients, hormones or other drugs for optimizing antioxidant protection and minimizing harmful posttraumatic inflammatory reactions, while using other nutrients to optimize DNA and tissue repair processes, and using a combination of good diet, immunostimulatory hormones and perhaps other nontoxic immunostimulants (such as beta-glucans) for optimizing the recovery of antiviral and antibacterial immune functions. Similar multifactorial treatment strategies may presumably be helpful in several other disease situations (including severe infectious diseases and severe asthma) as well as for treatment of acute intoxications or acute injuries (both mechanical ones and severe burns) where severely enhanced oxidative and/or nitrative stress and/or too much secretion of vasodilatory neuropeptides from C-fibres are important parts of the pathogenetic mechanisms that may lead to the death of the patient. Some case histories (with discussion of some of those mechanisms that may have been responsible for the observed therapeutic outcome) are given for illustration of the likely validity of these concepts and their relevance both for treatment of severe infections and non-infectious inflammatory diseases such as asthma and rheumatoid arthritis.

Activation of Wnt3a signaling stimulates intestinal epithelial repair by promoting c-Myc-regulated gene expression

In response to mucosal injury, epithelial cells modify the patterns of expressed genes to repair damaged tissue rapidly. Our previous studies have demonstrated that the transcription factor c-Myc is necessary for stimulation of epithelial cell renewal during mucosal healing, but the up-stream signaling initiating c-Myc gene expression after injury remains unknown. Wnts are cysteine-rich glycoproteins that act as short-range ligands to locally activate receptor-mediated signaling pathways and correlate with the increased expression of the c-Myc gene. The current study tested the hypothesis that Wnt3a signaling is implicated in intestinal epithelial repair after wounding by stimulating c-Myc expression. Elevated Wnt3a signaling in intestinal epithelial cells (IEC-6 line) by coculturing with stable Wnt3a-transfected fibroblasts or ectopic overexpression of the Wnt3a gene enhanced intestinal epithelial repair after wounding. This stimulatory effect on epithelial repair was prevented by silencing the Wnt coreceptor LRP6 or by c-Myc silencing. Activation of the Wnt3a signaling pathway increased β-catenin nuclear translocation by decreasing its phosphorylation and stimulated c-Myc expression during epithelial repair after wounding. In stable Wnt3a-transfected IEC-6 cells, increased levels of c-Myc were associated with an increase in expression of c-Myc-regulated genes cyclcin D1 and cyclin E, whereas c-Myc silencing inhibited expression of cyclin D1 and cyclin E and delayed epithelial repair. These results indicate that elevated Wnt3a signaling in intestinal epithelial cells after wounding stimulates epithelial repair by promoting c-Myc-regulated gene expression.

STIM1 translocation to the plasma membrane enhances intestinal epithelial restitution by inducing TRPC1-mediated Ca2+ signaling after wounding

Early epithelial restitution is an important repair modality in the gut mucosa and occurs as a consequence of epithelial cell migration. Canonical transient receptor potential-1 (TRPC1) functions as a store-operated Ca2+ channel (SOCs) in intestinal epithelial cells (IECs) and regulates intestinal restitution, but the exact upstream signals initiating TRPC1 activation after mucosal injury remain elusive. Stromal interaction molecule 1 (STIM1) is a single membrane-spanning protein and is recently identified as essential components of SOC activation. The current study was performed to determine whether STIM1 plays a role in the regulation of intestinal epithelial restitution by activating TRPC1 channels. STIM1 translocation to the plasma membrane increased after wounding, which was followed by an increase in IEC migration to reseal wounds. Increased STIM1 levels at the plasma membrane by overexpressing EF-hand mutant STIM1 enhanced Ca2+ influx through SOCs and stimulated IEC migration after wounding. STIM1 interacted with TRPC1 and formed STIM1/TRPC1 complex, whereas inactivation of STIM1 by STIM1 silencing decreased SOC-mediated Ca2+ influx and inhibited epithelial restitution. In cells overexpressing EF-hand mutant STIM1, TRPC1 silencing also decreased STIM1/TRPC1 complex, reduced SOC-mediated Ca2+ influx, and repressed cell migration after wounding. Our findings demonstrate that induced STIM1 translocation to the plasma membrane promotes IEC migration after wounding by enhancing TRPC1-mediated Ca2+ signaling and provide new insight into the mechanism of intestinal epithelial restitution.

Transcriptional regulation of the rice arginine decarboxylase (Adc1) and S-adenosylmethionine decarboxylase (Samdc) genes by methyl jasmonate

We investigated the effect of methyl jasmonate (MeJa) treatment on the expression of two genes in the rice polyamine biosynthesis pathway and on the polyamine content in wild type plants and transgenic rice plants expressing a Datura stramonium (Ds) Adc cDNA, the latter accumulating up to three-fold the normal level of putrescine. Exogenous MeJa transiently inhibited the expression of OsAdc1, OsSamdc and Spermidine synthase (OsSpds) genes in the polyamine biosynthesis pathway, probably through transcriptional repression. There was also a similar negative impact on the DsAdc transgene in transgenic plants, even though a constitutive promoter was used to drive transgene expression. The free putrescine content was reduced significantly in the leaves of both wild type and transgenic plants in response to MeJa, although the magnitude of the effect was greater in wild type plants. We discuss our findings with respect to the previously proposed threshold model of polyamine metabolism in plants subjected to abiotic stress.

Stabilization of XIAP mRNA through the RNA binding protein HuR regulated by cellular polyamines

The X chromosome-linked inhibitor of apoptosis protein (XIAP) is the most potent intrinsic caspase inhibitor and plays an important role in the maintenance of intestinal epithelial integrity. The RNA binding protein, HuR, regulates the stability and translation of many target transcripts. Here, we report that HuR associated with both the 3'-untranslated region and coding sequence of the mRNA encoding XIAP, stabilized the XIAP transcript and elevated its expression in intestinal epithelial cells. Ectopic HuR overexpression or elevated cytoplasmic levels of endogenous HuR by decreasing cellular polyamines increased [HuR/XIAP mRNA] complexes, in turn promoting XIAP mRNA stability and increasing XIAP protein abundance. Conversely, HuR silencing in normal and polyamine-deficient cells rendered the XIAP mRNA unstable, thus reducing the steady state levels of XIAP. Inhibition of XIAP expression by XIAP silencing or by HuR silencing reversed the resistance of polyamine-deficient cells to apoptosis. Our findings demonstrate that HuR regulates XIAP expression by stabilizing its mRNA and implicates HuR-mediated XIAP in the control of intestinal epithelial apoptosis.

Augmented bladder urothelial polyamine signaling and block of BK channel in the pathophysiology of overactive bladder syndrome

Overactive bladder syndrome (OAB) is an idiopathic condition characterized by urinary urgency and urge incontinence. Detrusor overactivity has been traditionally described as the physiologic mechanism for OAB. However, the bladder urothelium (BU) may also be involved in the pathophysiology. This study measured polyamine signaling and its downstream effects on membrane conductivity in bladder urothelial cells (BUC) obtained from asymptomatic and OAB subjects. Immunohistofluorescence was used to measure ornithine decarboxylase (ODC) expression in BU. BUC, cultured from BU biopsies, were used for electrophysiologic studies. dl-alpha-Difluoromethylornithine (DFMO), spermine, or spermidine was used to modulate polyamine signaling in BUC. Results showed ODC overexpression in OAB BU. In OAB BUC, whole cell and cell-attached configuration showed significantly decreased currents. Using inside-out patches, outward currents increased significantly, suggesting a cytoplasmic source of the outward current block in OAB BUC. In control BUC, outward currents were mediated by the large-conductance calcium-activated potassium (BK) channel due to calcium dose-dependence and block by iberiotoxin. Spermidine and spermine blocked the outward current in normal BUC in dose-dependent fashion. Conversely, DFMO significantly increased (P < 0.01) outward currents in OAB BUC both in cell-attached and in whole cell configuration. The outward currents in DFMO-treated-OAB BUC could be significantly reduced (P < 0.05) by adding back spermidine and spermine. These data suggest that polyamine signaling is upregulated in OAB urothelium and OAB BUC. Furthermore, polyamines in BUC block the BK channel. Targeting of bladder urothelial polyamine signaling may represent a novel approach for OAB treatment based on pathophysiologic mechanisms.

Effect of m-3M3FBS on Ca(2+) movement in Madin-Darby canine renal tubular cells

The effect of 2,4,6-trimethyl-N-(meta-3-trifluoromethyl-phenyl)-benzenesulfonamide (m-3M3FBS), a presumed phospholipase C (PLC) activator, on cytosolic free Ca(2+) concentrations ([Ca( 2+)](i)) in Madin-Darby canine kidney (MDCK) cells is unclear. This study explored whether m-3M3FBS changed basal [Ca(2+)](i) levels in suspended MDCK cells using fura-2 as a Ca(2+)-sensitive fluorescent dye. M-3M3FBS at concentrations between 0.1 and 20 microM increased [Ca(2+)](i) in a concentration-dependent manner. The Ca(2+) signal was decreased by removing extracellular Ca(2+). M-3M3FBS-induced Ca(2+) influx was inhibited by the store-operated Ca(2+) channel blockers nifedipine, econazole, and SK&F96365, and by the phospholipase A2 inhibitor aristolochic acid. In Ca(2+)-free medium, 20-microM m-3M3FBS pretreatment abolished the [Ca(2+)](i) rise induced by the endoplasmic reticulum Ca(2+) pump inhibitors thapsigargin (TG) and cyclopiazonic acid (CPA). Conversely, pretreatment with TG or CPA partly reduced m-3M3FBS-induced [Ca(2+)](i) rise. The inhibition of PLC with U73122 did not alter m-3M3FBS-induced [Ca(2+)](i) rise. Collectively, in MDCK cells, m-3M3FBS induced [Ca(2+)](i) rises by causing PLC-independent Ca(2+) release from the endoplasmic reticulum and Ca(2+) influx via store-operated Ca(2+) channels and other unidentified Ca(2+) channels.

Polyamines regulate E-cadherin transcription through c-Myc modulating intestinal epithelial barrier function

The integrity of the intestinal epithelial barrier depends on intercellular junctions that are highly regulated by numerous extracellular and intracellular factors. E-cadherin is found primarily at the adherens junctions in the intestinal mucosa and mediates strong cell-cell contacts that have a functional role in forming and regulating the epithelial barrier. Polyamines are necessary for E-cadherin expression, but the exact mechanism underlying polyamines remains elusive. The current study was performed to determine whether polyamines induce E-cadherin expression through the transcription factor c-Myc and whether polyamine-regulated E-cadherin plays a role in maintenance of the epithelial barrier integrity. Decreasing cellular polyamines reduced c-Myc and repressed E-cadherin transcription as indicated by a decrease in levels of E-cadherin promoter activity and its mRNA. Forced expression of the c-myc gene by infection with adenoviral vector containing c-Myc cDNA stimulated E-cadherin promoter activity and increased E-cadherin mRNA and protein levels in polyamine-deficient cells. Experiments using different E-cadherin promoter mutants revealed that induction of E-cadherin transcription by c-Myc was mediated through the E-Pal box located at the proximal region of the E-cadherin promoter. Decreased levels of E-cadherin in polyamine-deficient cells marginally increased basal levels of paracellular permeability but, remarkably, potentiated H(2)O(2)-induced epithelial barrier dysfunction. E-cadherin silencing by transfection with its specific small interfering RNA also increased vulnerability of the epithelial barrier to H(2)O(2). These results indicate that polyamines enhance E-cadherin transcription by activating c-Myc, thus promoting function of the epithelial barrier.

Combined glutamine and arginine decrease proinflammatory cytokine production by biopsies from Crohn's patients in association with changes in nuclear factor-kappaB and p38 mitogen-activated protein kinase pathways

Glutamine (Gln) and arginine (Arg) are conditionally essential amino acids with immunomodulatory properties. The aim of the study was to assess the effects of Gln and Arg alone or in combination on cytokine release by cultured colonic biopsies from patients with active Crohn's disease (CD). Ten consecutive patients [mean (range) age 26 (18-39) y] with active colonic CD (mean CD activity index: 383.7 +/- 129.8) were prospectively included in the study. Eight colonic biopsies were obtained via a colonoscopy and incubated during 18 h with low (physiological) or high (pharmacological) doses of Arg (0.1 or 2 mmol/L designated as Arg(low) or Arg(high), respectively) and Gln (0.6 or 10 mmol/L designated as Gln(low) or Gln(high), respectively). The concentrations of cytokines [interleukin (IL)-4, IL-10, IL-8, IL-6, tumor necrosis factor-alpha (TNFalpha), IL-1beta, interferon-gamma) were assessed by ELISA, and nitric oxide (NO) production was evaluated by Griess assay. Nuclear factor (NF)-kappaB p65 subunit, inhibitor of NFkappaB-alpha, and p38 mitogen-activated protein kinase (MAPK) were assessed by immunoblotting. Arg(high)/Gln(high) decreased the production of TNFalpha, IL-1beta, IL-8, and IL-6 (each P < 0.01). Arg(low)/Gln(high) decreased IL-6 and IL-8 production (both P < 0.01), whereas Arg(high)/Gln(low) did not affect cytokine and NO production. Arg(low)/Gln(high) and Arg(high)/Gln(high) decreased NF-kappaB p65 subunit expression, whereas p38 MAPK was decreased only by Arg(high)/Gln(high). Combined pharmacological doses of Arg and Gln decreased TNFalpha and the main proinflammatory cytokines release in active colonic CD biopsies via NF-kappaB and p38 MAPK pathways. These results could be the basis of prospective studies evaluating the effects of enteral supply of combined Arg and Gln during active CD.

Rac1 promotes intestinal epithelial restitution by increasing Ca2+ influx through interaction with phospholipase C-(gamma)1 after wounding

Intestinal mucosal restitution occurs as a consequence of epithelial cell migration and reseals superficial wounds after injury. This rapid reepithelialization is mediated in part by a phospholipase C-gamma1 (PLC-gamma1)-induced Ca(2+) signaling, but the exact mechanism underlying such signaling and its regulation remains elusive. The small GTP-binding protein Rac1 functions as a pivotal regulator of several signaling networks and plays an important role in regulating cell motility. The current study tests the hypothesis that Rac1 modulates intestinal epithelial cell migration after wounding by altering PLC-gamma1-induced Ca(2+) signaling. Inhibition of Rac1 activity by treatment with its inhibitor NSC-23766 or Rac1 silencing with small interfering RNA decreased store depletion-induced Ca(2+) influx and suppressed cell migration during restitution, whereas ectopic overexpression of Rac1 increased Ca(2+) influx and promoted cell migration. Rac1 physically interacted with PLC-gamma1 and formed Rac1/PLC-gamma1 complex in intestinal epithelial cells. PLC-gamma1 silencing in cells overexpressing Rac1 prevented stimulation of store depletion-induced Ca(2+) influx and cell migration after wounding. Polyamine depletion inhibited expression of both Rac1 and PLC-gamma1, decreased Rac1/PLC-gamma1 complex levels, reduced Ca(2+) influx, and repressed cell migration. Overexpression of Rac1 alone failed to rescue Ca(2+) influx after store depletion and cell migration in polyamine-deficient cells, because it did not alter PLC-gamma1 levels. These results indicate that Rac1 promotes intestinal epithelial cell migration after wounding by increasing Ca(2+) influx as a result of its interaction with PLC-gamma1.

Transforming growth factor-beta stimulates intestinal epithelial focal adhesion kinase synthesis via Smad- and p38-dependent mechanisms

Focal adhesion kinase (FAK) regulates cell migration, proliferation, and apoptosis. FAK protein is reduced at the edge of migrating gut epithelial sheets in vitro, but it has not been characterized in restitutive gut mucosa in vivo. Here we show that FAK and activated phospho-FAK (FAK(397)) immunoreactivity was lower in epithelial cells immediately adjacent to human gastric and colonic ulcers in vivo, but dramatically increased in epithelia near the ulcers, possibly reflecting stimulation by growth factors absent in vitro. Transforming growth factor (TGF)-beta, but not fibroblast growth factor, platelet-derived growth factor, or vascular endothelial growth factor, increased FAK levels in Caco-2 and IEC-6 cells. Epithelial immunoreactivity to TGF-beta and phospho-Smad3 was also higher near the ulcers, varying in parallel with FAK. The TGF-beta receptor antagonist SB431542 completely blocked TGF-beta-induced Smad2/3 and p38 activation in IEC-6 cells. SB431542, the p38 antagonist SB203580, and siRNA-mediated reduction of Smad2 and p38alpha prevented TGF-beta stimulation of both FAK transcription and translation (as measured via a FAK promoter-luciferase construct). FAK(397) levels were directly related to total FAK protein expression. Although gut epithelial motility is associated with direct inhibition of FAK protein adjacent to mucosal wounds, TGF-beta may increase FAK protein near but not bordering mucosal ulcers via Smad2/3 and p38 signals. Our results show that regulation of FAK expression may be as important as FAK phosphorylation in critically influencing gut epithelial cell migration after mucosal injury.

Varied role of the gut epithelium in mucosal homeostasis

PURPOSE OF REVIEW

The epithelium makes numerous important contributions to intestinal function. It acts as a physical barrier to prevent pathogenic infection, but allows nutrient uptake and the bidirectional passage of ions and water to lubricate the intestinal lumen while restricting fluid loss. The epithelium mediates communication between the immune system and the commensal flora, and plays a major role in antigen sampling and development of tolerance. After mucosal injury, the epithelium must reestablish its barrier and transport functions for homeostasis to be restored. Here, we will discuss recent advances in our understanding of the roles of the epithelium in intestinal homeostasis.

RECENT FINDINGS

Mechanisms responsible for epithelial communication with enteric flora and pathogens include the regulation and function of Toll-like receptors and nucleotide-binding oligomerization domain-2, and maintenance and repair of epithelial barrier properties, including the role of growth factors and bacterial peptides in epithelial repair.

SUMMARY

Recent advances in our understanding of mechanisms by which the gut epithelium modulates, and is modified by, enteric flora and the mucosal immune system illuminate the importance of the epithelium in gut physiology. The work discussed may also identify novel targets that can potentially be modulated therapeutically, either with existing medications or newer agents in development.