Collagens facilitate epithelial migration in restitution of native guinea pig intestinal epithelium

Human Colonoid Monolayers to Study Interactions Between Pathogens, Commensals, and Host Intestinal Epithelium

Human 3-dimensional (3D) enteroid or colonoid cultures derived from crypt base stem cells are currently the most advanced ex vivo model of the intestinal epithelium. Due to their closed structures and significant supporting extracellular matrix, 3D cultures are not ideal for host-pathogen studies. Enteroids or colonoids can be grown as epithelial monolayers on permeable tissue culture membranes to allow manipulation of both luminal and basolateral cell surfaces and accompanying fluids. This enhanced luminal surface accessibility facilitates modeling bacterial-host epithelial interactions such as the mucus-degrading ability of enterohemorrhagic E. coli (EHEC) on colonic epithelium. A method for 3D culture fragmentation, monolayer seeding, and transepithelial electrical resistance (TER) measurements to monitor the progress towards confluency and differentiation are described. Colonoid monolayer differentiation yields secreted mucus that can be studied by the immunofluorescence or immunoblotting techniques. More generally, enteroid or colonoid monolayers enable a physiologically-relevant platform to evaluate specific cell populations that may be targeted by pathogenic or commensal microbiota.

Equine Intestinal Mucosal Pathobiology

The equine intestinal mucosa is intimately involved in maintaining homeostasis both on a systemic level by controlling extracellular fluid movement and at the local level to maintain barrier function. Horses are particularly susceptible to the clinical syndrome of colic, with the most severe cases involving strangulating obstruction that induces ischemia. Because of the mucosal vascular architecture, the mucosal epithelium is particularly susceptible to ischemic injury. The potential for reperfusion injury has been investigated and found to play a minimal role. However, inflammation does affect mucosal repair. Mechanisms of repair, including villus contraction, epithelial restitution, and tight junction closure, are critical to reforming the mucosal barrier. Nonsteroidal anti-inflammatory drugs have an impact on this repair, particularly at the level of the tight junctions. Completion of mucosal regeneration requires proliferation, which is now being actively studied in equine enteroids. All of these aspects of equine mucosal pathobiology are reviewed in depth.

Prostaglandin E2 promotes intestinal repair through an adaptive cellular response of the epithelium

Adaptive cellular responses are often required during wound repair. Following disruption of the intestinal epithelium, wound-associated epithelial (WAE) cells form the initial barrier over the wound. Our goal was to determine the critical factor that promotes WAE cell differentiation. Using an adaptation of our in vitro primary epithelial cell culture system, we found that prostaglandin E2 (PGE₂) signaling through one of its receptors, Ptger4, was sufficient to drive a differentiation state morphologically and transcriptionally similar to in vivo WAE cells. WAE cell differentiation was a permanent state and dominant over enterocyte differentiation in plasticity experiments. WAE cell differentiation was triggered by nuclear β-catenin signaling independent of canonical Wnt signaling. Creation of WAE cells via the PGE₂-Ptger4 pathway was required in vivo, as mice with loss of Ptger4 in the intestinal epithelium did not produce WAE cells and exhibited impaired wound repair. Our results demonstrate a mechanism by which WAE cells are formed by PGE₂ and suggest a process of adaptive cellular reprogramming of the intestinal epithelium that occurs to ensure proper repair to injury.

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.

Down-regulation of collagen I biosynthesis in intestinal epithelial cells exposed to indomethacin: a comparative proteome analysis

In contrast to accumulated knowledge about gastroduodenal injury associated with nonsteroidal antiinflammatory drugs (NSAIDs) such as indomethacin, small intestinal mucosal injuries have been noticed only recently, and the precise mechanism remains to be elucidated. To clarify the mechanism, we performed 2-DE on IEC-6 rat normal intestinal cells that were treated with indomethacin (200μΜ, 24h) or a vehicle control and identified 18 up-regulated and 8 down-regulated proteins through MALDI-TOF/TOF mass spectrometry. Among these proteins, collagen I and proteins involved in collagen I biosynthesis and maturation, including prolyl 4-hydroxylase subunit α1, protein disulfide isomerase A3 (PDIA3), calreticulin, and endoplasmin, were all down-regulated by indomethacin. Immunohistochemical staining of the intestinal mucosa of indomethacin-administered rats showed a decrease of collagen I on the apical surface of intestinal cells. Cell death induced by indomethacin was prominently suppressed when IEC-6 cells were grown on collagen I-coated plates. cis-4-Hydroxy-l-proline, a proline analog that inhibits collagen synthesis, depressed IEC-6 cell viability in a concentration-dependent manner. Cell death was also induced by short interfering RNA knockdown of endogenous collagen I in IEC-6 cells. In conclusion, by comparative proteome analysis, we identified down-regulation of collagen I as an important mechanism in NSAID-induced intestinal injury.

BIOLOGICAL SIGNIFICANCE

Small intestinal lesions induced by NSAIDs are of great concern in clinical settings. Various hypotheses have been proposed for the origin of these inflammatory responses, such as reduction in the blood flow, intestinal hypermotility, abnormal intestinal mucosal permeability, mitochondrial dysfunction, and reactive oxygen species, many of which are related to the inhibition of prostaglandin synthesis. However, the precise mechanism is yet to be known. The cellular process of the lesions must involve up- and down-regulations of a large number of proteins and complex interactions between them. To elucidate it, global and systematic identification of the proteins in intestinal cells affected by NSAIDs is essential. We found that the proteins exhibiting reduced expression by indomethacin treatment are collagen I and the proteins involved in collagen I synthesis and maturation. Consistent with this, immunohistochemical analysis showed that the indomethacin-treated rat intestinal mucosal cells exhibits decreased collagen I expression on its apical surface. Furthermore, the cell-protective effect of collagen on intestinal mucosal cells was demonstrated by the use of a collagen-synthesis inhibitor, short interfering RNA (siRNA) knockdown of endogenous collagen I, and cell cultivation on collagen I-coated plates versus uncoated plates. These results give important information on the role of the collagen synthesis in intestinal mucosa in the mechanism of NSAID-induced small intestinal lesions.

Heparin-binding EGF-like growth factor (HB-EGF) promotes cell migration and adhesion via focal adhesion kinase

BACKGROUND

Cell migration and adhesion are essential in intestinal epithelial wound healing and recovery from injury. Focal adhesion kinase (FAK) plays an important role in cell-extracellular matrix signal transduction. We have previously shown that heparin-binding EGF-like growth factor (HB-EGF) promotes intestinal epithelial cell (IEC) migration and adhesion in vitro. The present study was designed to determine whether FAK is involved in HB-EGF-induced IEC migration and adhesion.

MATERIALS AND METHODS

A scrape wound healing model of rat IECs was used to examine the effect of HB-EGF on FAK-dependent cell migration in vitro. Immunofluorescence and Western blot analyses were performed to evaluate the effect of HB-EGF on the expression of phosphorylated FAK (p-FAK). Cell adhesion assays were performed to determine the role of FAK in HB-EGF-induced cell adhesion on fibronectin (FN).

RESULTS

HB-EGF significantly increased healing after scrape wounding, an effect that was reversed in the presence of an FAK inhibitor 14 (both with P < 0.05). HB-EGF increased p-FAK expression and induced p-FAK redistribution and actin reorganization in migrating rat IECs. Cell adhesion and spreading on FN were significantly increased by HB-EGF (P < 0.05). FAK inhibitor 14 significantly inhibited both intrinsic and HB-EGF-induced cell adhesion and spreading on FN (both with P < 0.05).

CONCLUSIONS

FAK phosphorylation and FAK-mediated signal transduction play essential roles in HB-EGF-mediated IEC migration and adhesion.

Rapid reversal of human intestinal ischemia-reperfusion induced damage by shedding of injured enterocytes and reepithelialisation

Background

Intestinal ischemia-reperfusion (IR) is a phenomenon related to physiological conditions (e.g. exercise, stress) and to pathophysiological events (e.g. acute mesenteric ischemia, aortic surgery). Although intestinal IR has been studied extensively in animals, results remain inconclusive and data on human intestinal IR are scarce. Therefore, an experimental harmless model for human intestinal IR was developed, enabling us to clarify the sequelae of human intestinal IR for the first time.

Methods and Findings

In 30 patients undergoing pancreatico-duodenectomy we took advantage of the fact that in this procedure a variable length of jejunum is removed. Isolated jejunum (5 cm) was subjected to 30 minutes ischemia followed by reperfusion. Intestinal Fatty Acid Binding Protein (I-FABP) arteriovenous concentration differences across the bowel segment were measured before and after ischemia to assess epithelial cell damage. Tissue sections were collected after ischemia and at 25, 60 and 120 minutes reperfusion and stained with H&E, and for I-FABP and the apoptosis marker M30. Bonferroni's test was used to compare I-FABP differences. Mean (SEM) arteriovenous concentration gradients of I-FABP across the jejunum revealed rapidly developing epithelial cell damage. I-FABP release significantly increased from 290 (46) pg/ml before ischemia towards 3,997 (554) pg/ml immediately after ischemia (p<0.001) and declined gradually to 1,143 (237) pg/ml within 1 hour reperfusion (p<0.001). Directly after ischemia the intestinal epithelial lining was microscopically normal, while subepithelial spaces appeared at the villus tip. However, after 25 minutes reperfusion, enterocyte M30 immunostaining was observed at the villus tip accompanied by shedding of mature enterocytes into the lumen and loss of I-FABP staining. Interestingly, within 60 minutes reperfusion the epithelial barrier resealed, while debris of apoptotic, shedded epithelial cells was observed in the lumen. At the same time, M30 immunoreactivity was absent in intact epithelial lining.

Conclusions

This is the first human study to clarify intestinal IR induced cell damage and repair and its direct consequences. It reveals a unique, endogenous clearing mechanism for injured enterocytes: rapid detachment of damaged apoptotic enterocytes into the lumen. This process is followed by repair of the epithelial continuity within an hour, resulting in a normal epithelial lining.

Restitution of single-cell defects in the mouse colon epithelium differs from that of cultured cells

Integrity of colon epithelium is of crucial importance and, as small defects occur constantly, rapid repair (restitution) is essential. To investigate the mechanism of restitution, single-cell lesions were induced in mouse colonic surface epithelia by iontophoretic injection of Ca2+. Closure of the resulting defects was monitored using confocal laser scanning microscopy (CLSM), and functional sealing by electrophysiological techniques. Restitution was evaluated as the time constant tau of the exponential decrease in conductance of an induced leak and amounted to 0.28 min under control conditions. After 4 min, the leak was completely sealed. Repair was thus considerably faster than in previously investigated HT-29/B6 cells (tau=5.73 min). As in cultured cells, cytochalasin D delayed restitution in native colon epithelia (tau=0.69 min), indicating the involvement of actin in the healing process; however, no accumulation of actin surrounding the lesion was detected. Long-term incubation of epithelia with IFN-gamma alone or in combination with TNF-alpha increased tau to 0.49 and 0.59 min, respectively. In contrast to cultured cells, TNF-alpha alone did not affect restitution. A brief (<10 min) exposure to the sterile filtered supernatant of hemolytic E. coli O4 cultures did not affect the morphology of the epithelium, but delayed restitution. In CLSM studies, defects were still clearly visible 4 min after the onset of lesion induction. The supernatant of a nonhemolytic E. coli O4 mutant did not exhibit this effect. In conclusion, single-cell defects in native colon cause functional leaks that seal faster than in cell cultures. Proinflammatory cytokines and pathogenic bacteria delay restitution. This suggests a key role of very small lesions at the onset of pathogenic processes in the intestine.

Variability of bacterial translocation in the absence of intestinal mucosal damage following injury and the influence of interleukin-6

Bacterial translocation and intestinal mucosal damage have been reported as potentially clinically important sequelae of injury. Evidence that endogenous interleukin-6 (IL-6) is able to protect against infection, and that orally administered IL-6 could prevent bacterial translocation and mucosal damage following haemorrhage, led us to evaluate the impact of injury on the intestinal mucosa and the role of endogenous IL-6. Normal and IL-6-deficient (IL-6-/-) mice were subjected to haemorrhage of increasing severity, hind limb ischaemia, or both. Mucosal integrity and bacterial translocation to the liver, spleen and mesenteric lymph nodes (MLN) were examined after 16 h. Bacterial translocation to each of these tissues was observed in unoperated animals. The more severe haemorrhage procedures, and hind limb ischaemia, increased bacterial translocation to the liver significantly in most experiments with normal mice. The IL-6-/- mice survived the most severe haemorrhage procedure less well (p = 0.0015), although increased bacterial translocation was not seen. There was no clear evidence of mucosal damage, or bacterial translocation to spleen and mesenteric lymph nodes, in either normal or IL-6-/- mice. Intestinal IgA concentrations were the same in IL-6-/- mice and controls. These data demonstrate that increased bacterial translocation can be observed following severe injury, but that neither bacterial translocation nor severe injury are inevitably associated with morphological damage to the intestinal mucosa, and endogenous IL-6 is more likely to promote bacterial translocation than protect the gut.

Intestinal injury after thoracic aortic cross-clamping in the pig

BACKGROUND

The mucosal surface epithelium is an essential part of the functional intestinal barrier, but its structural response to ischemia/reperfusion is only partly characterized. The purpose of this study was to provide a detailed morphological evaluation of intestinal surface epithelium after aortic cross-clamping.

MATERIAL AND METHODS

Pigs were subjected to thoracic aortic cross-clamping for 60 min and subsequent reperfusion for 120 min. Tissue blood flow and high-energy phosphates were measured with microspheres and HPLC, respectively. Urinary excretion of (14)C polyethylene glycol (MW 4000 Da) (PEG-4000), loaded into an intestinal loop, provided an index of intestinal permeability.

RESULTS

Jejunal blood flow was restored at 10 min after aortic declamping. Denudation of the basement membrane of the intestinal villi tips, as a consequence of epithelial shedding, increased markedly during the initial 60 min of reperfusion (P = 0.002). During the following 45 min, the denuded basement membrane was partly covered with low cuboidal and squamous-shaped cells extending lamellipodia over a wavy basement membrane. Restoration of ATP at 60 min after aortic declamping correlated inversely to the extent of denuded basement membrane (r = 0.75, P = 0.032). Permeability of PEG-4000 increased markedly after aortic declamping and was linearly correlated to the area of denuded basement membrane (r = 0.87, P = 0.01).

CONCLUSIONS

Reperfusion for 2 h after aortic cross-clamping is associated with initial aggravation of ischemia-induced injury in the porcine jejunum, but thereafter with restitution of the surface epithelium. Restoration of ATP may be important to avoid intestinal injury after ischemia. Increased permeability of a macromolecule in response to reperfusion is closely correlated to injury of the surface epithelium.

Treatment of gastrointestinal ischemic injury

Ischemic injury is one of the most important causes of mortality in equine veterinary medicine. Although treatment of reperfusion injury has been attempted in a number of experimental trials to reduce the level of injury subsequent to an ischemic episode, this research has not resulted in the development of useful clinical treatments. Nevertheless, recent studies assessing intraluminal application of solutions containing antioxidants, nutrients, and vasodilators are promising. Furthermore, focusing on improving mucosal recovery after an ischemic event may provide an alternative method of reducing mortality. Potential treatments include administration of basement membrane components like hyaluronic acid, gut-specific nutrients like glutamine, and early return to feeding to stimulate endogenous repair mechanisms. Finally, recent studies evaluating NSAIDs have revealed the potential of flunixin meglumine to retard the mucosal repair process, indicating the need for judicious use of this drug.

Heparin-binding epidermal growth factor-like growth factor and intestinal ischemia-reperfusion injury

Intestinal ischemia/reperfusion (I/R) injury affects patients of different ages, especially premature babies and the elderly. The outcome after intestinal I/R is often dismal, which may be attributed to loss of the barrier and immune functions of the intestines, as well as development of secondary injury in remote organs. The available treatment for advanced gut ischemia mandates extensive resection, which may cause growth retardation in infants and nutritional problems in the elderly. Throughout the past decade we have been investigating the potential therapeutic role of heparin-binding epidermal growth factor-like factor (HB-EGF) in intestinal I/R. The mitogenic and chemoattractant functions of HB-EGF formed the initial rationale for our investigations. In addition, HB-EGF is a potent antiapoptotic protein that enables cells and tissues exposed to different apoptotic stimuli to survive hypoxic, oxidative, and nutritional stresses. HB-EGF is known to have a vital role in wound healing and postischemic regeneration in different organs. In the current review, we summarize the results of our findings of the beneficial effects of HB-EGF in intestinal I/R, supported by additional evidence from the literature and an explanation of different possible mechanisms of its actions. Collectively, the data strongly suggest a potential therapeutic role for the use of HB-EGF to treat intestinal ischemic diseases such as I/R and necrotizing enterocolitis.

Mucosal repair in the gastrointestinal tract

OBJECTIVE

The epithelial response to injury in the intestinal mucosa will be described.

DESIGN

A comprehensive evaluation of the literature was performed to provide a thorough review of mucosal injury and repair.

RESULTS

The intestinal mucosa is a rapidly proliferating sheet of epithelial cells that sustains injury in response to stresses ranging from physiologic daily digestive trauma to severe insults associated with ischemia, chemicals, and infection. Breaks in epithelial continuity impair mucosal barrier function, perturb normal absorptive and secretory transport properties, and render the host susceptible to local infection and distant organ pathology. Minor breaches are rapidly repaired by epithelial restitution, a process independent of cell proliferation. Restitution is regulated by a variety of cytokines and growth factors and is modulated by integrin-dependent interactions with the extracellular matrix. The intracellular mechanisms that control restitution are complex and involve signaling pathways that control dynamic remodeling of the actin cytoskeleton. Emerging understanding of reparative processes suggest several possible therapeutic strategies to enhance gastrointestinal wound healing.

CONCLUSION

Minor epithelial injuries are repaired with the complex process of epithelial restitution independent of cell proliferation.

Role of stem cell factor and c-kit signaling in regulation of fetal intestinal epithelial cell adhesion to fibronectin

The interaction of stem cell factor (SCF) and c-kit is considered to be an important signaling event for the homeostasis of the epithelial barrier function in the intestinal tract. This study was designed to investigate the role of the SCF and c-kit signaling pathway in adhesion of intestinal epithelial cells (IECs) to fibronectin (FN) using primary cells. Fetal murine IECs were prepared from the small intestine of mouse fetus. The mRNAs coding for SCF in mesenchymes and c-kit in IECs were detected by reverse transcription-PCR. The expression of FN receptor VLA-5 on IECs was examined by flow cytometry. A cell adhesion assay showed that the stimulation of IECs with SCF increased the number of cells adhering to FN. Experiments using specific antibody against SCF indicated that this increase in cell adhesion was SCF-dependent. On the other hand, SCF did not influence the expression of VLA-5 on IECs. The IEC adhesion to FN was inhibited by specific antibody against the FN receptor (VLA-5), as well as competitive Arg-Gly-Asp (RGD) peptide. When alteration of intracellular signal transduction induced by SCF was examined, it was found that SCF stimulated a tyrosine-specific c-kit autophosphorylation cascade of IECs. Further, preincubation of IECs with an optimal concentration of genistein resulted in the inhibition of SCF-induced c-kit phosphorylation and adhesion of IECs to FN. These results suggested that adhesion of immature IECs to FN is regulated by activation of RGD-dependent VLA-5 through the SCF and c-kit signal transduction pathway. SCF, which may be produced by mesenchymes locally, is an important regulatory factor for the adhesion of immature IECs to basement membrane matrix via VLA-5 and FN interaction. This cytokine-regulated interaction between VLA-5 and FN may play an important role in the development and wound repair of the intestinal tract.

Collagen IV synthesis is restricted to the enteroendocrine pathway during multilineage differentiation of human colorectal epithelial stem cells

The human large intestine is lined by a rapidly renewing epithelial monolayer where cell loss is precisely balanced with cell production. The continuous supply of new cells is produced by undifferentiated multipotent stem cells via a coordinated program of proliferation and differentiation yielding three epithelial lineages: absorptive, goblet and enteroendocrine. Cell-matrix interactions have been suggested to be regulators of the multilineage differentiation program of the colorectal crypt but the expression of matrix proteins or their receptors does not appear to have the subtlety expected for this task.

We have developed an in vitro model system of intestinal epithelial stem cells to facilitate the direct analysis of stem cells undergoing lineage commitment and differentiation. Using this culture system, we can now directly investigate the role of cell-matrix signalling in stem-cell decisions. In this study, collagen-IV synthesis has been followed in monolayers of multipotent cells that have been induced to differentiate into absorptive, goblet and enteroendocrine cells. Our experiments demonstrate that commitment to the enteroendocrine lineage is specifically accompanied by the expression of type-IV collagen that remains enteroendocrine-cell associated. Undifferentiated cells, absorptive cells and goblet cells do not express collagen IV. To confirm that the differential lineage-specific expression of collagen IV observed in the model system was representative of the in vivo situation, collagen-IV synthesis was analysed in isolated human colorectal crypts and tissue sections using immunocytochemistry and in situ hybridisation. These studies confirmed the in vitro findings, in that implementation of the enteroendocrine differentiation program involves synthesis and accumulation of a collagen-IV matrix. Thus, human colorectal enteroendocrine cells are unique in the colorectal crypt in that they assemble a cell-associated collagen-IV-rich matrix not observed on other colorectal epithelial cells.

This study provides the first evidence for differential matrix synthesis between colorectal epithelial lineages in human colorectal epithelium. The specialised pericellular environment of the enteroendocrine cells might explain some of the unique phenotypic characteristics of this cell lineage. Furthermore, these findings suggest a potential mechanism whereby individual epithelial cells could modulate their cell-matrix signalling even while rapidly migrating in heterogeneous sheets over a shared basement membrane.

Modulation of barrier function during Fas-mediated apoptosis in human intestinal epithelial cells

BACKGROUND & AIMS

Intestinal epithelial cell apoptosis occurs continually without apparent permeability defects and is increased in response to intestinal inflammation. We hypothesized that increased, immune-mediated apoptosis during inflammation might result in barrier dysfunction of the epithelium.

METHODS

T84 cells were cultured as a polarized monolayer and exposed to agonist antibody to Fas. Barrier function was assessed by transepithelial resistance and permeability measurements. Immunofluorescent staining was used to examine junctional protein expression.

RESULTS

Fas expression is predominantly basolateral in polarized T84 monolayers. Basolateral cross-linking of the Fas receptor resulted in T84 cell apoptosis and a loss of 50% of the cells within 24 hours. Apoptosis was coincident with a decrease in transepithelial electrical resistance and increased flux of small but not large molecules. Preservation of barrier function was associated with dramatic rearrangement of tight junctions and desmosomal junctions in apoptotic monolayers. E-cadherin-mediated cell contact was maintained between intact cells in the monolayer, thus sealing gaps created by apoptotic cells. Apoptosis and barrier dysfunction could be prevented by caspase inhibition.

CONCLUSIONS

Immune-mediated apoptosis of intestinal epithelial cells may contribute to the permeability defects associated with inflammatory conditions of the bowel, but the intestinal epithelium is remarkably resilient in the face of apoptosis.

Review article: healing after inflammatory injury--coordination of a regulatory peptide network

Intestinal epithelial cells are capable of producing a variety of cytokines and other regulatory factors that can affect functional regulation of the epithelium itself, through autocrine and paracrine mechanisms, as well as functional integration with lamina propria populations. The bi-directional nature of this cytokine network is now apparent, with the demonstration that both rat and human intestinal epithelium-derived cell lines possess a much greater array of cytokine receptors than previously anticipated.

Epidermal and hepatocyte growth factors stimulate chemotaxis in an intestinal epithelial cell line

The migration of intestinal cells is important in the development and maintenance of normal epithelium, in a process that may be regulated by growth factors and cytokines. Although a number of growth factor receptors are expressed by intestinal cells, little progress has been made toward assignment of functional roles for these ligand-receptor systems. This study compares several growth factors and cytokines for their chemoattraction of the mouse small intestinal epithelial cell line. Epidermal and hepatocyte growth factors stimulated a rapid 30-fold chemotaxis of cells with delayed threefold migration toward transforming growth factor-beta1. Despite stimulating proliferation, keratinocyte, fibroblast, or insulin-like growth factors did not stimulate directed migration. Chemotaxis required tyrosine kinase and phosphatidylinositol phospholipase C activities but not protein kinase C or mitogen-activated protein kinase activity. These findings suggest that the repertoire of growth factors capable of regulating directed intestinal epithelial cell migration is limited and that a divergence exists in the signal transduction pathways for directed vs. nondirected migration.

Mucosal immunity and inflammation. V. Innate mechanisms of mucosal defense and repair: the best offense is a good defense

Well-coordinated mechanisms have evolved that provide both innate protection against gastrointestinal mucosal injury and facilitation of rapid mucosal repair following mucosal damage. Generic protection from injury is provided by intrinsic structural features of the epithelium that form a highly competent barrier and a complex formed at the apical surface by trefoil peptides that comprise the interface between mucosa and lumen. When the epithelial barrier has been broken, regardless of the nature of the injury, epithelial surface continuity is rapidly reestablished through restitution as cells migrate and elongate. This process is promoted by trefoil peptides at the apical surface and a large array of cytokines and growth factors acting at the basolateral pole. Many of these regulatory peptides are products of the immune and other lamina propria cell populations, which are activated following disruption of the mucosal barrier. Thus efforts to repair the epithelium follow inherently from inflammatory effects after initial damage; the repair process in turn may allow abrogation of further inflammation. Ultimate repair of injury requires both proliferative replacement of damaged epithelial cells and remodeling of extracellular matrix and deeper cell populations to restore normal architecture and a fully functional mucosa.

Ultrastructural effects of intravascularly injected polyethylene glycol-hemoglobin in intestinal mucosa

Polyethylene glycol (PEG)-conjugated Hb (PEG-Hb) is being considered as a blood substitute. Previously, we showed that PEG-Hb extravasates rapidly from the intestinal mucosa and causes transient epithelial sloughing, resulting in temporary unimpeded passage of material between the intestinal lumen and the microcirculation. The present study quantifies the time course of factors related to this disturbance. Anesthetized Sprague-Dawley rats (350-450 g) were injected with a bolus of PEG-Hb (10 mg/ml) in saline. Control animals received saline, alone or with Dextran 70 (5 mg/ml). After 2, 8, 15, 60, or 90 min, the small intestine was perfusion fixed for microscopy (4 animals for each time point). Epithelial cell detachment and mucosal mast cell degranulation peaked at 2 and 8-15 min, respectively, but by 90 min were back to normal. Goblet cell secretion increased with time up to 8-15 min, after which it leveled off. Mean interstitial width was significantly greater 8 min after injection than for controls and continued to increase with time. In capillaries, endothelial fenestral diaphragms were replaced by thick, amorphous structures. Mesenteric mast cell degranulation was significantly greater 60-90 min after injection compared with controls. We propose that these results are consistent with intravascular injection of PEG-Hb invoking a transient inflammatory response in the intestine.

Role of integrins in enterocyte migration

1. Enterocyte motility depends critically on cell-matrix interactions. Although still incompletely understood, these appear critically dependent upon integrin-mediated cell adhesion. 2. In addition to providing a mechanism for cell adhesion and traction, the integrins are likely to serve as true receptors for the matrix across which cell motility occurs, initiating signals by both mechanical and chemical means that alter cell phenotype and proliferation as well as cell motility. 3. Sound rationale now exists to postulate that soluble growth factors within the extracellular milieu regulate intestinal mucosal healing not only directly but also indirectly by modulating integrin expression and organization.

Laminin stimulates rapid epithelial restitution of rabbit duodenal mucosa in vitro

BACKGROUND

This study investigated the effect of the basal lamina constituents fibronectin, collagen IV, and laminin on epithelial restitution of rabbit duodenum in vitro.

METHODS

Rabbit duodenal mucosal sheets were mounted in Ussing chambers, luminally exposed to 10 mM HCI for 10 min, and incubated with buffer or luminal buffer containing 25-100 micrograms/ml of collagen IV, fibronectin, laminin, or polyclonal antisera directed against these proteins (diluted 1:50-1:20) for 3 h. Resistance was calculated from potential difference and short-circuit current. Mucosal damage was assessed by morphometry on hematoxylin- and eosin-stained sections.

RESULTS

Acid exposure caused a 40% drop in resistance (119 +/- 5 versus 71 +/- 5 Ohm.cm2 before versus after injury; P < 0.05, n = 6) and mucosal damage of 58 +/- 4% (n = 6). Three hours after injury resistance was 102 +/- 6, 117 +/- 4, and 48 +/- 5 Ohm.cm2 in the control, laminin, and anti-laminin groups, respectively. Furthermore, 36 +/- 2%, 16 +/- 2%, and 64 +/- 5% of the mucosa was damaged in the control, laminin, and anti-laminin groups, respectively, 3 h after injury (P < 0.05 versus controls). Laminin promoted epithelial wound closure by stimulation of enterocyte migration, which was inhibited by anti-laminin. Fibronectin, collagen IV, anti-fibronectin, and anti-collagen IV did not impair restitution.

CONCLUSION

Our results show that laminin promotes electrophysiologic restoration and epithelial restitution of rabbit duodenum in vitro. We therefore suggest that laminin plays an important part in the orchestration of epithelial integrity and barrier function.

Regulation of the mucosal epithelial barrier

Rapid re-sealing of the intestinal epithelial barrier is initially accomplished by migration of viable epithelial cells from the wound edge into the denuded area ('restitution') and only later by cell proliferation. Whereas proliferation of intestinal epithelial cells has been studied intensively, much less is known about the pivotal initial phase of cell migration. Restitution appears to be modulated by peptide growth factors/cytokines, extracellular matrix molecules, and luminally secreted products of mucus-producing cells (schematically summarized in Figure 1). Recent work has demonstrated that various cytokines (TGF-beta 1, TGF-alpha, EGF, IL-1 beta, IFN-gamma, basic FGF, KGF and HGF) present in the intestinal mucosa enhance intestinal epithelial restitution, presumably by mediating its effects through the basolateral pole of the epithelial monolayer. In addition to their effects on cell adhesion, differentiation, and spatial organization, the extracellular matrix molecules on which intestinal epithelial cells reside also have the potential to stimulate intestinal epithelial cell migration. The basement membrane components fibronectin and collagen type IV may be especially important. Finally, trefoil factors, a recently identified family of peptides which are secreted onto the luminal surface where they form the visco-elastic mucus layer through interaction with mucin glycoproteins, also promote the important process of restitution through a pathway distinct from that used by factors acting at the basolateral cell surface.

Effect of L-glutamine and n-butyrate on the restitution of rat colonic mucosa after acid induced injury

BACKGROUND

L-glutamine and n-butyrate are important nutrients for colonocytes affecting both their structure and function. The effect of these epithelial substrates on resealing of rat distal colon after acid induced injury was studied.

METHODS

Isolated colonic mucosa of 32 rats was mounted in Ussing chambers and exposed to Krebs-Ringer solution for four hours. Epithelial injury was induced by short-term exposure to luminal hydrochloric acid and resealing was studied with or without added glutamine or butyrate.

RESULTS

Glutamine (luminal and serosal) reduced tissue conductance, mannitol and lactulose permeability, and permeation of enteropathogenic Escherichia coli. Glutamine (serosal) diminished conductance and mannitol permeability. Both interventions stimulated bromodeoxyuridine incorporation in nuclei of colonocytes. Luminal butyrate had no measurable effect on these parameters.

CONCLUSIONS

These data suggest that L-glutamine stimulates repair mechanisms of rat colonic mucosa after acid injury. This effect on the gut barrier is associated with a stimulation of crypt cell proliferation. The addition of glutamine to parenteral solutions may be beneficial for patients under intensive care whose intestinal barrier is weakened in the course of sepsis and trauma.

Mixed reflux of gastric and duodenal juices is more harmful to the esophagus than gastric juice alone. The need for surgical therapy re-emphasized

OBJECTIVE

The author's goal was to determine the role of duodenal components in the development of complications of gastroesophageal reflux disease.

SUMMARY AND BACKGROUND DATA

There is a disturbing increase in the prevalence of complications, specifically the development of Barrett's esophagus among patients with gastroesophageal reflux disease. Earlier studies using pH monitoring and aspiration techniques have shown that increased esophageal exposure to fluid with a pH above 7, that is, of potential duodenal origin, may be an important factor in this phenomenon.

METHODS

The presence of duodenal content in the esophagus was studied in 53 patients with gastroesophageal reflux disease confirmed by 24-hour pH monitoring. A portable spectrophotometer (Bilitec 2000, Synectics, Inc.) with a fiberoptic probe was used to measure intraluminal bilirubin as a marker for duodenal juice in the esophagus. Normal values for bilirubin monitoring were established for 25 healthy subjects. In a subgroup of 22 patients, a custom-made program was used to correlate simultaneous pH and bilirubin absorbance readings.

RESULTS

Fifty-eight percent of patients were found to have increased esophageal exposure to gastric and duodenal juices. The degree of mucosal damage increased when duodenal juice was refluxed into the esophagus, in that patients with Barrett's metaplasia (n = 27) had a significantly higher prevalence of abnormal esophageal bilirubin exposure than did those with erosive esophagitis (n = 10) or with no injury (n = 16). They also had a greater esophageal bilirubin exposure compared with patients without Barrett's changes, with or without esophagitis. The correlation of pH and bilirubin monitoring showed that the majority (87%) of esophageal bilirubin exposure occurred when the pH of the esophagus was between 4 and 7.

CONCLUSIONS

Reflux of duodenal juice in gastroesophageal reflux disease is more common than pH studies alone would suggest. The combined reflux of gastric and duodenal juices causes severe esophageal mucosal damage. The vast majority of duodenal reflux occurs at a pH range of 4 to 7, at which bile acids, the major component of duodenal juice, are capable of damaging the esophageal mucosa.

Mixed reflux of gastric and duodenal juices is more harmful to the esophagus than gastric juice alone. The need for surgical therapy re-emphasized

OBJECTIVE

The author's goal was to determine the role of duodenal components in the development of complications of gastroesophageal reflux disease.

SUMMARY AND BACKGROUND DATA

There is a disturbing increase in the prevalence of complications, specifically the development of Barrett's esophagus among patients with gastroesophageal reflux disease. Earlier studies using pH monitoring and aspiration techniques have shown that increased esophageal exposure to fluid with a pH above 7, that is, of potential duodenal origin, may be an important factor in this phenomenon.

METHODS

The presence of duodenal content in the esophagus was studied in 53 patients with gastroesophageal reflux disease confirmed by 24-hour pH monitoring. A portable spectrophotometer (Bilitec 2000, Synectics, Inc.) with a fiberoptic probe was used to measure intraluminal bilirubin as a marker for duodenal juice in the esophagus. Normal values for bilirubin monitoring were established for 25 healthy subjects. In a subgroup of 22 patients, a custom-made program was used to correlate simultaneous pH and bilirubin absorbance readings.

RESULTS

Fifty-eight percent of patients were found to have increased esophageal exposure to gastric and duodenal juices. The degree of mucosal damage increased when duodenal juice was refluxed into the esophagus, in that patients with Barrett's metaplasia (n = 27) had a significantly higher prevalence of abnormal esophageal bilirubin exposure than did those with erosive esophagitis (n = 10) or with no injury (n = 16). They also had a greater esophageal bilirubin exposure compared with patients without Barrett's changes, with or without esophagitis. The correlation of pH and bilirubin monitoring showed that the majority (87%) of esophageal bilirubin exposure occurred when the pH of the esophagus was between 4 and 7.

CONCLUSIONS

Reflux of duodenal juice in gastroesophageal reflux disease is more common than pH studies alone would suggest. The combined reflux of gastric and duodenal juices causes severe esophageal mucosal damage. The vast majority of duodenal reflux occurs at a pH range of 4 to 7, at which bile acids, the major component of duodenal juice, are capable of damaging the esophageal mucosa.

An alternative method of skin grafting: the scalp microdermis graft

Although microskin grafting has been used successfully to treat major burns, when the donor skin areas are inadequate, it is still not in popular use because of the difficulties of mincing and floating procedures. Floating is expected to produce more microskin patches with the dermal side upwards than with the epidermal side upwards. Another problem is that many microskin patches will be lost in the container during floating. This problem may be solved by preparing the microskin from the second layer scalp skin. This will be a graft of hair follicle cells, which can be sowed on the wound no matter which side is upwards. Grafting was carried out on well-prepared granulation beds, or on the fat surface after tangential excision, or on the bed after fascial excision of the burn. Allograft and Biobrane were used as cover dressings. The combination of fascial excision and allograft overlay gave an acceptable result. This can be an alternative method of skin grafting for burns with very limited donor skin areas when the scalp skin is not burned.

An in vitro model of urothelial regeneration: effects of growth factors and extracellular matrix proteins

Although the cellular turnover of resting urothelium is very low, its regenerative capacity is known to be outstanding. In organotypic mouse urothelial cultures closely mimicking the differentiation and multilayering of normal urothelium, we examined the cell biological mechanisms underlying urothelial regeneration and the specific role of growth factors and several extracellular matrix (ECM) components. Exposure to epidermal growth factor (EGF) and acidic fibroblast growth factor (aFGF) and culture on laminin resulted in enhanced expansion of the urothelium. Microscopy and assessment of proliferative activity revealed that enhanced urothelial expansion due to EGF could be attributed to increased proliferative activity and an increase in cell numbers, whereas aFGF-stimulated expansion must be considered the consequence of increased cellularity and migration. Laminin-enhanced urothelial expansion was shown to be the result of spreading of the entire urothelial organotypic culture. This was associated with a considerable decrease in the number of cell layers. A synergistic effect of growth factors and laminin was not found. This organotypic urothelial cell culture model seems to be very useful in studying strategies to improve urothelial regeneration.

Localization of brush border cytoskeletal proteins in gastric oxynticopeptic cells from the bullfrog Rana catesbeiana

The contribution of brush border cytoskeletal proteins (actin, villin, fimbrin, and brush border myosin-1) to organization of the cytoskeletal network underlying apical plications of oxynticopeptic cells was examined by immunohistochemical techniques in frozen sections of gastric mucosa from the bullfrog, Rana catesbeiana. Apical localization of F-actin with phalloidin in oxynticopeptic cells inhibited with cimetidine revealed small, punctate domains within the apical cytoplasm that were consistent with the presence of short microvilli revealed by electron microscopy. Localization of F-actin in cells stimulated with forskolin was limited to a wide continuous band of cytoplasm corresponding to the location of numerous long surface folds. Inhibition of protein synthesis with cycloheximide did not prevent acid secretion or formation of actin filaments within surface folds in stimulated oxynticopeptic cells, suggesting that the formation of filaments does not require actin synthesis. Staining of gastric mucosae with fluorescent DNase-1 demonstrated that oxynticopeptic cells possess an unusually large pool of non-filamentous actin. Taken together, these results suggest that actin-filament formation in stimulated cells occurs by polymerization of an existing pool of non-filamentous actin. Localization of antibodies specific for villin and fimbrin revealed that these proteins were present within intestinal absorptive cells and gastric surface and neck cells but were not present within inhibited or stimulated oxynticopeptic cells. Brush border myosin-1, present in intestinal absorptive cells, was not present in gastric epithelium. Thus, we propose that actin-containing projections in oxynticopeptic cells are not organized like intestinal microvilli and that filament formation occurs after stimulation by modulating intracellular pools of filamentous and non-filamentous actin.

Transglutaminase in response to hypertonic NaCl-induced gastric mucosal injury in rats

BACKGROUND

Polyamines serve as substitutes for transglutaminase-catalyzed protein cross-linking and are essential to the healing of gastric mucosal lesions. This study determines whether transglutaminase and protein cross-linking have a role in the healing of hypertonic NaCl-induced gastric lesions.

METHODS

Rats were fasted 22 hours before given 1 mL 3.4 Mol/L NaCl intragastrically. Gastric mucosa was examined histologically and grossly, and transglutaminase activity was measured as the Ca(2+)-dependent covalent incorporation of [3H]putrescine into acid-precipitable protein.

RESULTS

Transglutaminase activity increased significantly from 2 to 8 hours, peaking between 4 and 6 hours after NaCl administration. Lesions were significantly produced after 2 hours, and damage paralleled transglutaminase activity. Dansylcadaverine (200 mg/kg orally), a specific inhibitor of protein cross-linking, prevented the increases in transglutaminase activity and significantly delayed healing but had no effect on lesion formation.

CONCLUSIONS

These results indicate that (1) hypertonic NaCl-induced gastric mucosal damage is associated with a significant increase in transglutaminase activity and (2) increased transglutaminase activity is involved in the mechanism of normal mucosal healing.