Intestinal mucosal atrophy and adaptation

Nutritional Control of Stem Cell Division through S-Adenosylmethionine in Drosophila Intestine

The intestine has direct contact with nutritional information. The mechanisms by which particular dietary molecules affect intestinal homeostasis are not fully understood. In this study, we identified S-adenosylmethionine (SAM), a universal methyl donor synthesized from dietary methionine, as a critical molecule that regulates stem cell division in Drosophila midgut. Depletion of either dietary methionine or SAM synthesis reduces division rate of intestinal stem cells. Genetic screening for putative SAM-dependent methyltransferases has identified protein synthesis as a regulator of the stem cells, partially through a unique diphthamide modification on eukaryotic elongation factor 2. In contrast, SAM in nutrient-absorptive enterocytes controls the interleukin-6-like protein Unpaired 3, which is required for rapid division of the stem cells after refeeding. Our study sheds light upon a link between diet and intestinal homeostasis and highlights the key metabolite SAM as a mediator of cell-type-specific starvation response.

EB 2017 Article: Interpretation of the lactulose:mannitol test in rural Malawian children at risk for perturbations in intestinal permeability

The dual sugar absorption test, specifically the lactulose:mannitol test, is used to assess gut health. Lactulose absorption is said to represent gut damage and mannitol absorption is used as a measure of normal small bowel function and serves as normalizing factor for lactulose. A underappreciated limitation of this common understanding of the lactulose:mannitol test is that mannitol is not absorbed to any substantial extent by a transcellular process. Additionally, this interpretation of lactulose:mannitol is not consistent with current understanding of paracellular pathways, where three pathway types exist: pore, leak, and unrestricted. Pore and leak pathways are regulated biological constructions of the small bowel barrier, and unrestricted pathways represent micropathological damage. We analyzed 2334 lactulose:mannitol measurements rigorously collected from 622 young rural Malawian children at high risk for poor gut health in light of the pathway model. An alternative method of normalizing for gut length utilizing autopsy data is described. In our population, absorbed lactulose and mannitol are strongly correlated, r = 0.68 P <0.0001, suggesting lactulose and mannitol are traversing the gut barrier via the same pathways. Considering measurements where pore pathways predominate, mannitol flux is about 14 times that of lactulose. As more leak pathways are present, this differential flux mannitol:lactulose falls to 8:1 and when increased numbers of unrestricted pathways are present, the differential flux of mannitol:lactulose is 6:1. There was no substantial correlation between the lactulose:mannitol and linear growth. Given that mannitol will always pass through a given pathway at a rate at least equal to that of lactulose, and lactulose absorption is a composite measure of flux through both physiologic and pathologic pathways, we question the utility of the lactulose:mannitol test. We suggest using lactulose alone is as informative as lactulose:mannitol in a sugar absorption testing in subclinical gut inflammation. Impact statement Our work integrates the standard interpretation of the lactulose:mannitol test (L:M), with mechanistic insight of intestinal permeability. There are three paracellular pathways in the gut epithelium; pore, leak, and unrestricted. Using thousands of L:M measurements from rural Malawian children at risk for increased intestinal permeability, we predict the differential flux of L and M through the pathways. Our findings challenge the traditional notions that little L is absorbed through a normal epithelial barrier and that M is a normalizing factor for L. Our observations are consistent with pore pathways allowing only M to pass. And that substantial amounts of L and M pass through leak pathways which are normal, regulated, cell-junctional adaptations. So M is a composite measure of all pathways, and L is not a measure solely of pathologic gut damage. Using L alone as a probe will yield more information about gut health than L:M.

Protective effects of oral glutathione on fasting-induced intestinal atrophy through oxidative stress

AIM

To determine whether oral glutathione (GSH) administration can alleviate the effects of fasting-induced intestinal atrophy in the small intestinal mucosa.

METHODS

Rats were divided into eight groups. One group was fed ad libitum, another was fed ad libitum and received oral GSH, and six groups were administrated saline (SA) or GSH orally during fasting. Mucosal height, apoptosis, and cell proliferation in the jejunum were histologically evaluated. iNOS protein expression (by immunohistochemistry), nitrite levels (by high performance liquid chromatography, as a measure of NO production), 8-hydroxydeoxyguanosine formation (by ELISA, indicating ROS levels), glutathione/oxidized glutathione (GSH/GSSG) ratio (by enzymatic colorimetric detection), and γ-glutamyl transpeptidase (Ggt1) mRNA levels in the jejunum (by semi-quantitative RT-PCR) were also estimated.

RESULTS

Oral GSH administration was demonstrated to drastically reduce fasting-induced intestinal atrophy in the jejunum. In particular, jejunal mucosal height was enhanced in GSH-treated animals compared to SA-treated animals [527.2 ± 6.9 for 50 mg/kg GSH, 567.6 ± 5.4 for 500 mg/kg GSH vs 483.1 ± 4.9 (μm), P < 0.01 at 72 h]. This effect was consistent with decreasing changes in GSH-treated animals compared to SA-treated animals for iNOS protein staining [0.337 ± 0.016 for 50 mg/kg GSH, 0.317 ± 0.017 for 500 mg/kg GSH vs 0.430 ± 0.023 (area of staining part/area of tissue), P < 0.01 at 72 h] and NO [2.99 ± 0.29 for 50 mg/kg GSH, 2.88 ± 0.19 for 500 mg/kg GSH vs 5.34 ± 0.35 (nmol/g tissue), P < 0.01 at 72 h] and ROS [3.92 ± 0.46 for 50 mg/kg GSH, 4.58 ± 0.29 for 500 mg/kg GSH vs 6.42 ± 0.52 (8-OHdG pg/μg DNA), P < 0.01, P < 0.05 at 72 h, respectively] levels as apoptosis mediators in the jejunum. Furthermore, oral GSH administration attenuated cell proliferation decreases in the fasting jejunum [182.5 ± 1.9 for 500 mg/kg GSH vs 155.8 ± 3.4 (5-BrdU positive cells/10 crypts), P < 0.01 at 72 h]. Notably, both GSH concentration and Ggt1 mRNA expression in the jejunum were also attenuated in rats following oral administration of GSH during fasting as compared with fasting alone [0.45 ± 0.12 vs 0.97 ± 0.06 (nmol/mg tissue), P < 0.01; 1.01 ± 0.11 vs 2.79 ± 0.39 (Ggt1 mRNA/Gapdh mRNA), P < 0.01 for 500 mg/kg GSH at 48 h, respectively].

CONCLUSION

Oral GSH administration during fasting enhances jejunal regenerative potential to minimize intestinal mucosal atrophy by diminishing fasting-mediated ROS generation and enterocyte apoptosis and enhancing cell proliferation.

Effects of herbal medicine Sijunzi decoction on rabbits after relieving intestinal obstruction

Intestinal obstruction leads to blockage of the movement of intestinal contents. After relieving the obstruction, patients might still suffer with compromised immune function and nutritional deficiency. This study aimed to evaluate the effects of Sijunzi decoction on restoring the immune function and nutritional status after relieving the obstruction. Experimental rabbits (2.5±0.2 kg) were randomly divided into normal control group, 2-day intestinal obstruction group, 2-day natural recovery group, 4-day natural recovery group, 2-day treated group, and 4-day treated group. Sijunzi decoction was given twice a day to the treated groups. The concentration of markers was analyzed to evaluate the immune function and nutritional status. The concentration of interleukin-2, immunoglobulins and complement components of the treated groups were significantly higher than the natural recovery group (P<0.05). The levels of CD4⁺ and CD4⁺/CD8⁺ increased then decreased in the treated groups. The levels of tumor necrosis factor-α and CD8⁺ were significantly lower than the natural recovery group. The level of total protein in the treated groups also increased then decreased after relieving the obstruction. The levels of albumin, prealbumin and insulin-like growth factor-1 were significantly higher in the treated groups than in the natural recovery group (P<0.05). Transferrin level in the treated groups was significantly higher than the obstruction group (P<0.05). Sijunzi decoction can lessen the inflammatory response and improve the nutrition absorption after relieving the obstruction.

Cooperative Repression of Insulin-Like Growth Factor Type 2 Receptor Translation by MicroRNA 195 and RNA-Binding Protein CUGBP1

Insulin-like growth factor type 2 (IGF2) receptor (IGF2R) recognizes mannose 6-phosphate-containing molecules and IGF2 and plays an important role in many pathophysiological processes, including gut mucosal adaptation. However, the mechanisms that control cellular IGF2R abundance are poorly known. MicroRNAs (miRNAs) and RNA-binding proteins (RBPs) critically regulate gene expression programs in mammalian cells by modulating the stability and translation of target mRNAs. Here we report that miRNA 195 (miR-195) and RBP CUG-binding protein 1 (CUGBP1) jointly regulate IGF2R expression at the posttranscriptional level in intestinal epithelial cells. Both miR-195 and CUGBP1 interacted with the 3' untranslated region (3'-UTR) of Igf2r mRNA, and the association of CUGBP1 with Igf2r mRNA enhanced miR-195 binding to Igf2r mRNA. Ectopically expressed CUGBP1 and miR-195 repressed IGF2R translation cooperatively without altering the stability of Igf2r mRNA. Importantly, the miR-195- and CUGBP1-repressed levels of cellular IGF2R led to a disruption in the structure of the trans-Golgi network. These findings indicate that IGF2R expression is controlled posttranscriptionally by two factors that associate with Igf2r mRNA and suggest that miR-195 and CUGBP1 dampen IGF signaling by inhibiting IGF2R translation.

Long-term effect of parasympathetic or sympathetic denervation on intestinal epithelial cell proliferation and apoptosis

Intestinal epithelial tissue is constantly regenerated as a means to maintain proper tissue function. Previous studies have demonstrated that denervation of the parasympathetic or sympathetic nervous system to the intestine alters this process. However, results are inconsistent between studies, showing both increases and decreases in proliferation after denervation of the parasympathetic or sympathetic. The effect appears to correlate with (1) the timing post-denervation, (2) denervation-induced changes in food intake, (3) the denervation technique used, and (4) which intestinal segment is investigated. Thus, we proposed that parasympathetic or sympathetic denervation does not have an effect on intestinal epithelial regeneration when you (1) evaluate denervation after long-term denervation, (2) control for post-surgical changes in food intake, (3) use minimally invasive surgical techniques and (4) include a segmental analysis. To test this, adult male Sprague Dawley rats underwent parasympathetic denervation via subdiaphragmatic vagotomy, sympathetic denervation via celiacomesenteric ganglionectomy, a parasympathetic denervation sham surgery, or a sympathetic denervation sham surgery. Sham surgery ad libitum-fed groups and sham surgery pair-fed groups were used to control for surgically induced changes in food intake. Three weeks post-surgery, animals were sacrificed and tissue from the duodenum, jejunum, and ileum was excised and immunohistochemically processed to visualize indicators of proliferation (bromodeoxyuridine-positive cells) and apoptosis (caspase-3-positive cells). Results showed no differences between groups in proliferation, apoptosis, or total cell number in any intestinal segment. These results suggest that parasympathetic or sympathetic denervation does not have a significant long-term effect on intestinal epithelial turnover. Thus, intestinal epithelial regeneration is able to recover after autonomic nervous system injury. Impact statement This study investigates the long-term effect of autonomic denervation on intestinal epithelial cell turnover, as measured by proliferation, apoptosis, and total cell number. Although previous research has established that autonomic denervation can alter intestinal epithelial turnover under short-term conditions, here we establish for the first time that these changes do not persist long-term when you control for surgical-induced changes in food intake and use targeted denervation procedures. These findings add to the base of knowledge on autonomic control of tissue turnover, highlight the ability of the intestinal epithelium to recover after autonomic injury and reveal possible implications of the use of ANS denervation for disease treatment in humans.

Effect of Splenectomy to Short Bowel Syndrome in Rats

The aim of this study was to determine the effect of splenectomy in the short bowel syndrome. Twenty-four Wistar-albino rats weighing between 210 and 375 g were used. They were divided into three groups. In group A, short bowel syndrome (SBS) was created by 75 % bowel resection. In group B, SBS and splenectomy was performed. In group C, after transecting the bowel, it was anastomosed. Before and 45 days after the procedures, all rats were weighed. In all three groups, the first and final weight of the rats, the final bowel weight and length, the ileal and jejunal crypt depths, the villus height, the luminal diameter, the bowel wall thickness, and the number of apoptotic cells and mitosis per 100 crypt cell were compared. Periportal fibrosis, infiltration, bile stasis, and bile duct proliferation were detected in liver samples. The rat intestinal length and weight was the least in group B while the jejunal crypt depth was higher in group B than in group A and it was exactly the opposite for the jejunal and ileal villus heights. The ileal and jejunal luminal diameter, the ileal bowel wall thickness, the jejunal and ileal apoptotic cell number, the jejunal mitosis, and the periportal fibrosis were highest in group B. Adding splenectomy to an SBS model has a negative impact on bowel adaptation.

Inducible and neuronal nitric oxide synthases exert contrasting effects during rat intestinal recovery following fasting

We investigated the effects of endogenous inducible (iNOS) and neuronal nitric oxide synthase on recovery from intestinal mucosal atrophy caused by fasting-induced apoptosis and decreased cell proliferation during refeeding in rats. Rats were divided into five groups, one of which was fed ad libitum, and four of which underwent 72 h of fasting, followed by refeeding for 0, 6, 24, and 48 h, respectively. iNOS and neuronal nitric oxide synthase mRNA and protein levels in jejunal tissues were measured, and mucosal height was histologically evaluated. Apoptotic indices, interferon-γ (IFN-γ) transcription levels, nitrite levels (as a measure of nitric oxide [NO] production),8-hydroxydeoxyguanosine formation (indicating reactive oxygen species [ROS] levels), crypt cell proliferation, and the motility indices (MI) were also estimated. Associations between mucosal height and NOS protein levels were determined using Spearman's rank correlation test. Notably, we observed significant increases in mucosal height and in neuronal nitric oxide synthase mRNA and protein expression as refeeding time increased. Indeed, there was a significant positive correlation between neuronal nitric oxide synthase protein level and mucosal height during the 48-h refeeding period ( r = 0.725, P < 0.01). Conversely, iNOS mRNA and protein expression decreased according to refeeding time, with a significant negative correlation between iNOS protein level and mucosal height being recorded during the 48-h refeeding period ( r = -0.898, P < 0.01). We also noted a significant negative correlation between jejunal neuronal nitric oxide synthase and iNOS protein concentrations over this same period ( r = -0.734, P < 0.01). Refeeding also restored the decreased jejunal MI caused by fasting. Our finding suggests that refeeding likely repairs fasting-induced jejunal atrophy by suppressing iNOS expression and subsequently inhibiting NO, ROS, and IFN-γ as apoptosis mediators, and by promoting neuronal nitric oxide synthase production and inducing crypt cell proliferation via mechanical stimulation. Impact statement Besides providing new data confirming the involvement of iNOS and nNOS in intestinal mucosal atrophy caused by fasting, this study details their expression and function during recovery from this condition following refeeding. We demonstrate a significant negative correlation between iNOS and nNOS levels during refeeding, and associate this with cell proliferation and apoptosis in crypts and villi. These novel findings elucidate the relationship between these NOS isoforms and its impact on recovery from intestinal injury. A mechanism is proposed comprising the up-regulation of nNOS activity by mechanical stimulation due to the presence of food in the intestine, restricting iNOS-associated apoptosis and promoting cell proliferation and gut motility. Our investigation sheds light on the molecular basis behind the repercussions of total parenteral nutrition on intestinal mucosal integrity, and more importantly, the beneficial effects of early enteral feeding.

Intestinal Epithelial-Specific mTORC1 Activation Enhances Intestinal Adaptation After Small Bowel Resection

BACKGROUND & AIMS

Intestinal adaptation is a compensatory response to the massive loss of small intestine after surgical resection. We investigated the role of intestinal epithelial cell-specific mammalian target of rapamycin complex 1 (i-mTORC1) in intestinal adaptation after massive small bowel resection (SBR).

METHODS

We performed 50% proximal SBR on mice to study adaptation. To manipulate i-mTORC1 activity, Villin-Cre^ER transgenic mice were crossed with tuberous sclerosis complex (TSC)1^flox/flox or Raptor^flox/flox mice to inducibly activate or inactivate i-mTORC1 activity with tamoxifen. Western blot was used to confirm the activity of mTORC1. Crypt depth and villus height were measured to score adaptation. Immunohistochemistry was used to investigate differentiation and rates of crypt proliferation.

RESULTS

After SBR, mice treated with systemic rapamycin showed diminished structural adaptation, blunted crypt cell proliferation, and significant body weight loss. Activating i-mTORC1 via TSC1 deletion induced larger hyperproliferative crypts and disorganized Paneth cells without a significant change in villus height. After SBR, ablating TSC1 in intestinal epithelium induced a robust villus growth with much stronger crypt cell proliferation, but similar body weight recovery. Acute inactivation of i-mTORC1 through deletion of Raptor did not change crypt cell proliferation or mucosa structure, but significantly reduced lysozyme/matrix metalloproteinase-7-positive Paneth cell and goblet cell numbers, with increased enteroendocrine cells. Surprisingly, ablation of intestinal epithelial cell-specific Raptor after SBR did not affect adaptation or crypt proliferation, but dramatically reduced body weight recovery after surgery.

CONCLUSIONS

Systemic, but not intestinal-specific, mTORC1 is important for normal adaptation responses to SBR. Although not required, forced enterocyte mTORC1 signaling after resection causes an enhanced adaptive response.

Di- and tripeptide transport in vertebrates: the contribution of teleost fish models

Solute Carrier 15 (SLC15) family, alias H⁺-coupled oligopeptide cotransporter family, is a group of membrane transporters known for their role in the cellular uptake of di- and tripeptides (di/tripeptides) and peptide-like molecules. Of its members, SLC15A1 (PEPT1) chiefly mediates intestinal absorption of luminal di/tripeptides from dietary protein digestion, while SLC15A2 (PEPT2) mainly allows renal tubular reabsorption of di/tripeptides from ultrafiltration, SLC15A3 (PHT2) and SLC15A4 (PHT1) possibly interact with di/tripeptides and histidine in certain immune cells, and SLC15A5 has unknown function. Our understanding of this family in vertebrates has steadily increased, also due to the surge of genomic-to-functional information from 'non-conventional' animal models, livestock, poultry, and aquaculture fish species. Here, we review the literature on the SLC15 transporters in teleost fish with emphasis on SLC15A1 (PEPT1), one of the solute carriers better studied amongst teleost fish because of its relevance in animal nutrition. We report on the operativity of the transporter, the molecular diversity, and multiplicity of structural-functional solutions of the teleost fish orthologs with respect to higher vertebrates, its relevance at the intersection of the alimentary and osmoregulative functions of the gut, its response under various physiological states and dietary solicitations, and its possible involvement in examples of total body plasticity, such as growth and compensatory growth. By a comparative approach, we also review the few studies in teleost fish on SLC15A2 (PEPT2), SLC15A4 (PHT1), and SLC15A3 (PHT2). By representing the contribution of teleost fish to the knowledge of the physiology of di/tripeptide transport and transporters, we aim to fill the gap between higher and lower vertebrates.

Oral drug therapy following bariatric surgery: an overview of fundamentals, literature and clinical recommendations

Bariatric surgery is the most effective solution for severe obesity and obesity with comorbidities, and the number of patients going through bariatric surgery is rapidly and constantly growing. The modified gastrointestinal anatomy of the patient may lead to significant pharmacokinetic alterations in the oral absorption of drugs after the surgery; however, because of insufficient available literature and inadequate awareness of the medical team, bariatric surgery patients may be discharged from the hospital with insufficient instructions regarding their medication therapy. In this article, we aim to present the various mechanisms by which bariatric surgery may influence oral drug absorption, to provide an overview of the currently available literature on the subject, and to draw guidelines for the recommendations bariatric surgery patients should be instructed before leaving the hospital. To date, and until more robust data are published, it is essential to follow and monitor patients closely for safety and efficacy of their medication therapies, both in the immediate and distant time post-surgery.

Human splanchnic amino-acid metabolism

Plasma levels of several amino acids are correlated with metabolic dysregulation in obesity and type 2 diabetes. To increase our understanding of human amino-acid metabolism, we aimed to determine splanchnic interorgan amino-acid handling. Twenty patients planned to undergo a pylorus preserving pancreatico-duodenectomy were included in this study. Blood was sampled from the portal vein, hepatic vein, superior mesenteric vein, inferior mesenteric vein, splenic vein, renal vein, and the radial artery during surgery. The difference between arterial and venous concentrations of 21 amino acids was determined using liquid chromatography as a measure of amino-acid metabolism across a given organ. Whereas glutamine was significantly taken up by the small intestine (121.0 ± 23.8 µmol/L; P < 0.0001), citrulline was released (−36.1 ± 4.6 µmol/L; P < 0.0001). This, however, was not seen for the colon. Interestingly, the liver showed a small, but a significant uptake of citrulline from the circulation (4.8 ± 1.6 µmol/L; P = 0.0138) next to many other amino acids. The kidneys showed a marked release of serine and alanine into the circulation (−58.0 ± 4.4 µmol/L and −61.8 ± 5.2 µmol/L, P < 0.0001), and a smaller, but statistically significant release of tyrosine (−12.0 ± 1.3 µmol/L, P < 0.0001). The spleen only released taurine (−9.6 ± 3.3 µmol/L; P = 0.0078). Simultaneous blood sampling in different veins provides unique qualitative and quantitative information on integrative amino-acid physiology, and reveals that the well-known intestinal glutamine–citrulline pathway appears to be functional in the small intestine but not in the colon.

Apo AIV and Citrulline Plasma Concentrations in Short Bowel Syndrome Patients: The Influence of Short Bowel Anatomy

INTRODUCTION

Parenteral nutrition (PN) dependence in short bowel syndrome (SBS) patients is linked to the functionality of the remnant small bowel (RSB). Patients may wean off PN following a period of intestinal adaptation that restores this functionality. Currently, plasma citrulline is the standard biomarker for monitoring intestinal functionality and adaptation. However, available studies reveal that the relationship the biomarker with the length and function of the RSB is arguable. Thus, having additional biomarkers would improve pointing out PN weaning.

AIM

By measuring concomitant changes in citrulline and the novel biomarker apolipoprotein AIV (Apo AIV), as well as taking into account the anatomy of the RSB, this exploratory study aims to a better understanding of the intestinal adaptation process and characterization of the SBS patients under PN.

METHODS

Thirty four adult SBS patients were selected and assigned to adapted (aSBS) and non-adapted (nSBS) groups after reconstructive surgeries. Remaining jejunum and ileum lengths were recorded. The aSBS patients were either on an oral diet (ORAL group), those with intestinal insufficiency, or on oral and home parenteral nutrition (HPN group), those with chronic intestinal failure. Apo AIV and citrulline were analyzed in plasma samples after overnight fasting. An exploratory ROC analysis using citrulline as gold standard was performed.

RESULTS

Biomarkers, Apo AIV and citrulline showed a significant correlation with RSBL in aSBS patients. In jejuno-ileocolic patients, only Apo AIV correlated with RSBL (rb = 0.54) and with ileum length (rb = 0.84). In patients without ileum neither biomarker showed any correlation with RSBL. ROC analysis indicated the Apo AIV cut-off value to be 4.6 mg /100 mL for differentiating between the aSBS HPN and ORAL groups.

CONCLUSIONS

Therefore, in addition to citrulline, Apo AIV can be set as a biomarker to monitor intestinal adaptation in SBS patients. As short bowel anatomy is shown to influence citrulline and Apo AIV plasma values, both biomarkers complement each other furnishing a new insight to manage PN dependence.

Higher plasma motilin levels in obese patients decrease after Roux-en-Y gastric bypass surgery and regulate hunger

OBJECTIVE

Motilin-induced phase III contractions of the migrating motor complex (MMC) signal hunger in healthy volunteers. The current aim was to study the role of motilin as a hunger-inducing factor in obese patients and to evaluate the effect of Roux-en-Y gastric bypass (RYGB) surgery on plasma motilin levels and hunger scores.

DESIGN

Motilin and ghrelin plasma levels were determined during a complete MMC cycle in controls and obese patients selected for RYGB before, 6 months and 1 year after surgery. 20 min after the end of the second phase III, obese patients received an intravenous infusion of 40 mg erythromycin. Hunger was scored every 5 min. Hedonic hunger was assessed in obese patients with the Power of Food Scale questionnaire.

RESULTS

Obesity caused a switch in the origin of phase III from antrum to duodenum. Obese patients had significantly higher motilin levels compared with controls during the MMC but tended to lack the motilin peak prior to phase III necessary to trigger hunger. Hunger scores during phase III were significantly lower in obese patients, but could be restored to control levels through the administration of a low dose of the motilin agonist, erythromycin. After RYGB surgery motilin, but not ghrelin, levels decreased in parallel with hedonic hunger scores.

CONCLUSIONS

Motilin may be an important regulator involved in the pathogenesis of obesity.

Schlafen 3 Mediates the Differentiating Effects of Cdx2 in Rat IEC-Cdx2L1 Enterocytes

AIM

Mature, differentiated enterocytes are essential for normal gut function and critical to recovery from pathological conditions. Little is known about the factors that regulate intestinal epithelial cell differentiation in the adult intestine. The transcription factor, Cdx2, involved in enterocytic differentiation, remains expressed in the adult. Since we have implicated Slfn3 in differentiation in vivo and in vitro, we examined whether it also mediated differentiation in the IEC-Cdx2-L1 cell model of differentiation.

MATERIALS AND METHODS

IEC-Cdx2-L1 cells, permanently transfected with Cdx2 under the control of isopropyl-β-D-thiogalactoside (IPTG), were stimulated to differentiate by 16-day exposure to IPTG. Transcript levels of Cdx2, Slfn 3, and villin were determined by quantitative reverse transcriptase-polymerase chain reaction of mRNA isolated from IPTG-treated and control cells. Slfn3 expression was lowered with specific siRNA to investigate the role of Slfn3 in Cdx2-driven villin expression in IPTG-differentiated cells.

RESULTS

Slfn3 and villin expression were significantly greater in IPTG-treated cells. Slfn3 siRNA lowered Slfn3 expression and abolished the IPTG-induced rise in villin expression (p < .05 by ANOVA); Cdx2 expression was unaffected by Slfn3 siRNA.

DISCUSSION

The data indicate that the presence of Slfn3 is required for Cdx2 to induce villin expression, and thus differentiation. However, Slfn3 must also promote differentiation of Cdx2 independently since IEC-6 cells that do not normally express Cdx2 can be differentiated by a variety of Slfn3-dependent mechanisms.

Iron depletion suppresses mTORC1-directed signalling in intestinal Caco-2 cells via induction of REDD1

Iron is an indispensable micronutrient that regulates many aspects of cell function, including growth and proliferation. These processes are critically dependent upon signalling via the mammalian or mechanistic target of rapamycin complex 1 (mTORC1). Herein, we test whether iron depletion induced by cell incubation with the iron chelator, deferoxamine (DFO), mediates its effects on cell growth through mTORC1-directed signalling and protein synthesis. We have used Caco-2 cells, a well-established in vitro model of human intestinal epithelia. Iron depletion increased expression of iron-regulated proteins (TfR, transferrin receptor and DMT1, divalent metal transporter, as predicted, but it also promoted a marked reduction in growth and proliferation of Caco-2 cells. This was strongly associated with suppressed mTORC1 signalling, as judged by reduced phosphorylation of mTOR substrates, S6K1 and 4E-BP1, and diminished protein synthesis. The reduction in mTORC1 signalling was tightly coupled with increased expression and accumulation of REDD1 (regulated in DNA damage and development 1) and reduced phosphorylation of Akt and TSC2. The increase in REDD1 abundance was rapidly reversed upon iron repletion of cells but was also attenuated by inhibitors of gene transcription, protein phosphatase 2A (PP2A) and by REDD1 siRNA — strategies that also antagonised the loss in mTORC1 signalling associated with iron depletion. Our findings implicate REDD1 and PP2A as crucial regulators of mTORC1 activity in iron-depleted cells and indicate that their modulation may help mitigate atrophy of the intestinal mucosa that may occur in response to iron deficiency.

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Cellular iron (Fe) depletion dramatically reduces growth of intestinal Caco-2 cells.

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mTORC1-directed signalling and protein synthesis are reduced in Fe-depleted cells.

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Fe deficiency induces expression and gain of REDD1 in a PP2A-dependent manner.

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PP2A inhibition blocks REDD1 gain and restores mTORC1 activity in Fe-depleted cells.

Effect of Roux-en-Y gastric bypass and laparoscopic adjustable gastric banding on gastrointestinal metabolism of ingested glucose

BACKGROUND

Data from studies conducted in animal models suggest that intestinal glucose uptake and metabolism are upregulated after Roux-en-Y gastric bypass (RYGB) surgery, which contributes to a weight-loss-independent improvement in glycemic control.

OBJECTIVE

We conducted a cohort study to evaluate whether an increase in gastrointestinal metabolism of ingested glucose occurs in obese people who underwent RYGB compared with those who underwent laparoscopic adjustable gastric banding (LAGB).

DESIGN

A mixed meal containing stable isotope-labeled glucose was used to determine the gastrointestinal (small intestine and liver) retention, and presumably metabolism, of ingested glucose in obese subjects before and after matched weight loss (∼21%) induced by RYGB (n = 16) or LAGB (n = 9).

RESULTS

The total percentage of ingested glucose that appeared in the systemic circulation was slightly lower after than before RYGB (85% ± 9% and 90% ± 8%, respectively) but was slightly higher after than before LAGB (89% ± 3% and 85% ± 4%, respectively) (P-interaction < 0.05). Accordingly, gastrointestinal clearance of ingested glucose (cumulative percentage cleared over 6 h postprandially) increased after RYGB (from 10% ± 8% before to 15% ± 9% after surgery) but decreased after LAGB (from 15% ± 4% before to 11% ± 3% after surgery) (P < 0.05). Surgery-induced weight loss caused a similar decrease in the 6-h postprandial plasma glucose area under the curve in both RYGB and LAGB groups (-4% ± 9% and -6% ± 5%, respectively; P = 0.475).

CONCLUSIONS

These data support the notion that intestinal glucose disposal increases after RYGB surgery. However, the magnitude of the effect was small and did not result in weight-loss-independent therapeutic effects on postprandial glycemic control. This trial was registered at clinicaltrials.gov as NCT00981500.

Myo5b knockout mice as a model of microvillus inclusion disease

Inherited MYO5B mutations have recently been associated with microvillus inclusion disease (MVID), an autosomal recessive syndrome characterized by intractable, life-threatening, watery diarrhea appearing shortly after birth. Characterization of the molecular mechanisms underlying this disease and development of novel therapeutic approaches is hampered by the lack of animal models. In this study we describe the phenotype of a novel mouse model with targeted inactivation of Myo5b. Myo5b knockout mice show perinatal mortality, diarrhea and the characteristic mislocalization of apical and basolateral plasma membrane markers in enterocytes. Moreover, in transmission electron preparations, we observed microvillus atrophy and the presence of microvillus inclusion bodies. Importantly, Myo5b knockout embryos at day 20 of gestation already display all these structural defects, indicating that they are tissue autonomous rather than secondary to environmental cues, such as the long-term absence of nutrients in the intestine. Myo5b knockout mice closely resemble the phenotype of MVID patients and constitute a useful model to further investigate the underlying molecular mechanism of this disease and to preclinically assess the efficacy of novel therapeutic approaches.

Glutamine and alanyl-glutamine promote crypt expansion and mTOR signaling in murine enteroids

L-glutamine (Gln) is a key metabolic fuel for intestinal epithelial cell proliferation and survival and may be conditionally essential for gut homeostasis during catabolic states. We show that L-alanyl-L-glutamine (Ala-Gln), a stable Gln dipeptide, protects mice against jejunal crypt depletion in the setting of dietary protein and fat deficiency. Separately, we show that murine crypt cultures (enteroids) derived from the jejunum require Gln or Ala-Gln for maximal expansion. Once expanded, enteroids deprived of Gln display a gradual atrophy of cryptlike domains, with decreased epithelial proliferation, but stable proportions of Paneth and goblet cell differentiation, at 24 h. Replenishment of enteroid medium with Gln selectively activates mammalian target of rapamycin (mTOR) signaling pathways, rescues proliferation, and promotes crypt regeneration. Gln deprivation beyond 48 h leads to destabilization of enteroids but persistence of EGFP-Lgr5-positive intestinal stem cells with the capacity to regenerate enteroids upon Gln rescue. Collectively, these findings indicate that Gln deprivation induces a reversible quiescence of intestinal stem cells and provides new insights into nutritional regulation of intestinal epithelial homeostasis.

The role of gut adaptation in the potent effects of multiple bariatric surgeries on obesity and diabetes

Bariatric surgical procedures such as vertical sleeve gastrectomy (VSG) and Roux-en-Y gastric bypass (RYGB) are the most potent treatments available to produce sustained reductions in body weight and improvements in glucose regulation. While traditionally these effects are attributed to mechanical aspects of these procedures, such as restriction and malabsorption, a growing body of evidence from mouse models of these procedures points to physiological changes that mediate the potent effects of these surgeries. In particular, there are similar changes in gut hormone secretion, bile acid levels, and composition after both of these procedures. Moreover, loss of function of the nuclear bile acid receptor (FXR) greatly diminishes the effects of VSG. Both VSG and RYGB are linked to profound changes in the gut microbiome that also mediate at least some of these surgical effects. We hypothesize that surgical rearrangement of the gastrointestinal tract results in enteroplasticity caused by the high rate of nutrient presentation and altered pH in the small intestine that contribute to these physiological effects. Identifying the molecular underpinnings of these procedures provides new opportunities to understand the relationship of the gastrointestinal tract to obesity and diabetes as well as new therapeutic strategies to harness the effectiveness of surgery with less-invasive approaches.

Massive bowel resection upregulates the intestinal mRNA expression levels of cellular retinol-binding protein II and apolipoprotein A-IV and alters the intestinal vitamin A status in rats

Short bowel (SB) syndrome causes the malabsorption of various nutrients. Among these, vitamin A is important for a number of physiological activities. Vitamin A is absorbed by epithelial cells of the small intestine and is discharged into the lymphatic vessels as a component of chylomicrons and is delivered to the liver. In the present study, we used a rat model of SB syndrome in order to assess its effects on the expression of genes associated with the absorption, transport and metabolism of vitamin A. In the rats with SB, the intestinal mRNA expression levels of cellular retinol-binding protein II (CRBP II, gene symbol Rbp2) and apolipoprotein A-IV (gene symbol Apoa4) were higher than those in the sham-operated rats, as shown by RT-qPCR. Immunohistochemical analysis revealed that absorptive epithelial cells stained positive for both CRBP II and lecithin retinol acyltransferase, which are both required for the effective esterification of vitamin A. In the rats with SB, the retinol content in the ileum and the retinyl ester content in the jejunum were lower than those in the sham-operated rats, as shown by quantitative analysis of retinol and retinyl esters by high performance liquid chromatography. These results suggest that the elevated mRNA expression levels of Rbp2 and Apoa4 in the rats with SB contribute to the effective esterification and transport of vitamin A.

Nutrient-induced intestinal adaption and its effect in obesity

Obese and lean individuals respond differently to nutrients with changes in digestion, absorption and hormone release. This may be a result of differences in intestinal epithelial morphology and function driven by the hyperphagia or the type of diet associated with obesity. It is well known that the maintenance and growth of the intestine is driven by the amount of luminal nutrients, with high nutrient content resulting in increases in cell number, villi length and crypt depth. In addition, the type of nutrient appears to contribute to alterations in the morphology and function of the epithelial cells. This intestinal adaptation may be what is driving the differences in nutrient processing in lean versus obese individuals. This review describes how nutrients may be able to induce changes in intestinal epithelial cell proliferation, differentiation and function and the link between intestinal adaptation and obesity.

Jnk2 deletion disrupts intestinal mucosal homeostasis and maturation by differentially modulating RNA-binding proteins HuR and CUGBP1

Homeostasis and maturation of the mammalian intestinal epithelium are preserved through strict regulation of cell proliferation, apoptosis, and differentiation, but the exact mechanism underlying this process remains largely unknown. c-Jun NH2-terminal kinase 2 (JNK2) is highly expressed in the intestinal mucosa, and its activation plays an important role in proliferation and also mediates apoptosis in cultured intestinal epithelial cells (IECs). Here, we investigated the in vivo function of JNK2 in the regulation of intestinal epithelial homeostasis and maturation by using a targeted gene deletion approach. Targeted deletion of the jnk2 gene increased cell proliferation within the crypts in the small intestine and disrupted mucosal maturation as indicated by decreases in the height of villi and the villus-to-crypt ratio. JNK2 deletion also decreased susceptibility of the intestinal epithelium to apoptosis. JNK2-deficient intestinal epithelium was associated with an increase in the level of the RNA-binding protein HuR and with a decrease in the abundance of CUG-binding protein 1 (CUGBP1). In studies in vitro, JNK2 silencing protected intestinal epithelial cell-6 (IEC-6) cells against apoptosis and this protection was prevented by inhibiting HuR. Ectopic overexpression of CUGBP1 repressed IEC-6 cell proliferation, whereas CUGBP1 silencing enhanced cell growth. These results indicate that JNK2 is essential for maintenance of normal intestinal epithelial homeostasis and maturation under biological conditions by differentially modulating HuR and CUGBP1.

The LEAF questionnaire: a screening tool for the identification of female athletes at risk for the female athlete triad

BACKGROUND

Low energy availability (EA) in female athletes with or without an eating disorder (ED) increases the risk of oligomenorrhoea/functional hypothalamic amenorrhoea and impaired bone health, a syndrome called the female athlete triad (Triad). There are validated psychometric instruments developed to detect disordered eating behaviour (DE), but no validated screening tool to detect persistent low EA and Triad conditions, with or without DE/ED, is available.

AIM

The aim of this observational study was to develop and test a screening tool designed to identify female athletes at risk for the Triad.

METHODS

Female athletes (n=84) with 18-39 years of age and training ≥5 times/week filled out the Low Energy Availability in Females Questionnaire (LEAF-Q), which comprised questions regarding injuries and gastrointestinal and reproductive function. Reliability and internal consistency were evaluated in a subsample of female dancers and endurance athletes (n=37). Discriminant as well as concurrent validity was evaluated by testing self-reported data against measured current EA, menstrual function and bone health in endurance athletes from sports such as long distance running and triathlon (n=45).

RESULTS

The 25-item LEAF-Q produced an acceptable sensitivity (78%) and specificity (90%) in order to correctly classify current EA and/or reproductive function and/or bone health.

CONCLUSIONS

The LEAF-Q is brief and easy to administer, and relevant as a complement to existing validated DE screening instruments, when screening female athletes at risk for the Triad, in order to enable early detection and intervention.

Glucagonlike peptide 2 analogue teduglutide: stimulation of proliferation but reduction of differentiation in human Caco-2 intestinal epithelial cells

IMPORTANCE

Short bowel syndrome occurs when a shortened intestine cannot absorb sufficient nutrients or fluids. Teduglutide is a recombinant analogue of human glucagonlike peptide 2 that reduces dependence on parenteral nutrition in patients with short bowel syndrome by promoting enterocytic proliferation, increasing the absorptive surface area. However, enterocyte function depends not only on the number of cells that are present but also on differentiated features that facilitate nutrient absorption and digestion.

OBJECTIVE

To test the hypothesis that teduglutide impairs human intestinal epithelial differentiation.

DESIGN AND SETTING

We investigated the effects of teduglutide in the modulation of proliferation and differentiation in human Caco-2 intestinal epithelial cells at a basic science laboratory. This was an in vitro study using Caco-2 cells, a human-derived intestinal epithelial cell line commonly used to model enterocytic biology.

EXPOSURE

Cells were exposed to teduglutide or vehicle control.

MAIN OUTCOMES AND MEASURES

We analyzed the cell cycle by bromodeoxyuridine incorporation or propidium iodide staining and flow cytometry and measured cell proliferation by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay. We used quantitative reverse transcription-polymerase chain reaction to assay the expression of the enterocytic differentiation markers villin, sucrase-isomaltase, glucose transporter 2 (GLUT2), and dipeptidyl peptidase 4 (DPP-4), as well as that of the putative differentiation signals schlafen 12 (SLFN12) and caudal-related homeobox intestine-specific transcription factor (Cdx2). Villin promoter activity was measured by a luciferase-based assay.

RESULTS

The MTS assay demonstrated that teduglutide increased cell numbers by a mean (SD) of 10% (2%) over untreated controls at a maximal 500 nM (n = 6, P < .05). Teduglutide increased bromodeoxyuridine-positive cells vs untreated controls by a mean (SD) of 19.4% (2.3%) vs 12.0% (0.8%) (n = 6, P < .05) and increased the S-phase fraction by flow cytometric analysis. Teduglutide reduced the mean (SD) expression of villin by 29% (6%), Cdx2 by 31% (10%), DPP-4 by 15% (6%), GLUT2 by 40% (11%), SLFN12 by 61% (14%), and sucrase-isomaltase by 28% (8%) (n = 6, P < .05 for all).

CONCLUSIONS AND RELEVANCE

Teduglutide increased Caco-2 proliferation but tended to inhibit intestinal epithelial differentiation. The effects of mitogenic stimulation with teduglutide in patients with short bowel syndrome might be greater if the more numerous teduglutide-treated cells could be stimulated toward a more fully differentiated phenotype.

The effect of ileal interposition surgery on enteroendocrine cell numbers in the UC Davis type 2 diabetes mellitus rat

AIM

To investigate the short-term effect of ileal interposition (IT) surgery on gut morphology and enteroendocrine cell numbers in the pre-diabetic UC Davis type 2 diabetes mellitus (UCD-T2DM) rat.

STUDY DESIGN

Two-month old male UCD-T2DM rats underwent either sham (n=5) or IT (n=5) surgery. Intestines were collected 1.5months after surgery. The jejunum, ileum and colon regions were processed for histochemical and immunohistochemical labeling and stereological analyses of changes in gut morphometry and number of enteroendocrine cells.

RESULTS

Stereological analysis showed that intestinal volume, luminal surface area and the number of all chromogranin A-positive enteroendocrine cells were markedly increased in the IT rats compared with sham-operated animals. Subanalyses of the glucagon-like peptide 2, cholecystokinin, serotonin cells and the neurotensin immunoreactive sub-pool of enteroendocrine cells in the IT region revealed an increase in numbers across phenotypes. However, the density of the different cell types varied.

CONCLUSION

IT surgery in the UCD-T2DM rat leads to rapid alterations in gut morphometry and an increase in the number of enteroendocrine cells. This effect may potentially explain why IT surgery delays the onset of type 2 diabetes in the UCD-T2DM rat.

The correlation between the expression of differentiation markers in rat small intestinal mucosa and the transcript levels of schlafen 3

IMPORTANCE

The normal absorptive function and structural maintenance of the intestinal mucosa depend on a constant process of proliferation of enterocytic stem cells followed by progressive differentiation toward a mature phenotype. The mechanisms that govern enterocytic differentiation in the mucosa of the small intestine are poorly understood.

OBJECTIVE

To determine whether schlafen 3 (but not other schlafen proteins) act in vivo and whether its effects are limited to the small intestine. We have previously demonstrated in nonmalignant rat intestinal IEC-6 cells that schlafen 3 levels correlate with the expression of various differentiation markers in vitro in response to differentiation stimuli.

DESIGN

Randomized controlled experiment.

SETTING

Animal science laboratory.

PARTICIPANTS

Male Sprague-Dawley rats 8 to 13 weeks old.

MAIN OUTCOMES AND MEASURES

Messenger RNA (mRNA) from jejunal and colonic mucosa was isolated, and transcript levels of schlafen proteins 1, 2, 3, 4, 5, 13, and 14; sucrase isomaltase (SI); dipeptidyl peptidase 4 (Dpp4); glucose transporter type 2 (Glut2); and villin were measured by quantitative reverse transcriptase-polymerase chain reaction. We tested parallel variations in protein levels by Western blotting and Dpp4 enzyme activity.

RESULTS

The transcript level of schlafen 3 (Slfn3) correlated with the levels of the differentiation markers SI, Dpp4, Glut2, and villin. However, the expression of schlafen proteins 1, 2, 4, 5, 13, and 14 did not correlate with the expression of the differentiation markers. The mucosal mRNA levels of Slfn3, SI, Glut2, and Dpp4 were all substantially higher in the rat jejunum than in colonic mucosa by a mean (SE) factor of 51.0 (13.2) for 6 rats (P < .05), 599 (99) for 8 rats (P < .01), 12.5 (5.5) for 8 rats (P < .01), and 14.0 (3.9) for 8 rats (P < .01), respectively. In IEC-6 cells, infection with adenovirus-expressing GFP-tagged Slfn3 significantly increased Slfn3 expression and Dpp4-specific activity compared with GFP-expressing virus (in 6 rats; P < .05).

CONCLUSIONS AND RELEVANCE

Taken together with our previous in vitro observations, the results suggest that small intestinal enterocytic epithelial differentiation in rats may be regulated by Slfn3 in vivo, as in vitro, and that these effects may be specific to the small intestinal enterocytic phenotype as opposed to that of the mature colonocyte. Slfn3 human orthologs may be targeted to stimulate intestinal differentiation in patients with short bowel syndrome.

Laminin receptor 37/67LR regulates adhesion and proliferation of normal human intestinal epithelial cells

Interactions between the cell basal membrane domain and the basement membrane are involved in several cell functions including proliferation, migration and differentiation. Intestinal epithelial cells can interact with laminin, a major intestinal basement membrane glycoprotein, via several cell-surface laminin-binding proteins including integrin and non-integrin receptors. The 37/67kDa laminin receptor (37/67LR) is one of these but its role in normal epithelial cells is still unknown. The aim of this study was to characterise the expression pattern and determine the main function of 37/67LR in the normal human small intestinal epithelium. Immunolocalization studies revealed that 37/67LR was predominantly present in the undifferentiated/proliferative region of the human intestinal crypt in both the immature and adult intestine. Using a human intestinal epithelial crypt (HIEC) cell line as experimental model, we determined that 37/67LR was expressed in proliferative cells in both the cytoplasmic and membrane compartments. Small-interfering RNA-mediated reduction of 37/67LR expression led to HIEC cell-cycle reduction and loss of the ability to adhere to laminin-related peptides under conditions not altering ribosomal function. Taken together, these findings indicate that 37/67LR regulates proliferation and adhesion in normal intestinal epithelial cells independently of its known association with ribosomal function.

Internal frontier: The pathophysiology of the small intestine

Even though the small intestine occupies a major portion of the abdominal space and is essential for life, in most pathology textbooks any chapter on small intestinal diseases, especially in human beings, is typically shorter than those for other gastrointestinal organs. Clinical and experimental investigations of the small intestine in various clinical situations, such as nutrition management, obesity interventions, and emergency care, have elucidated several important biological problems associated with the small intestine, the last frontier of gastroenterology. In this issue, a review by Professor Basson and his team at Michigan State University sheds light on the changes in the human small intestine under various conditions based on their clinical and surgical experience. With the advent of recent innovations in enteroscopy, a form of endoscopy used to examine deep within the small intestine, the issue that they highlighted, i.e., mucosal adaptation and atrophy of the human small intestine, has emerged as a major and manageable challenge for gastroenterologists in general, including the readers of the World Journal of Gastroenterology.