Stem cell and niche regulation in human short bowel syndrome.

Loss of functional small bowel surface area following surgical resection for disorders such as Crohn's disease, intestinal ischemic injury, radiation enteritis, and in children, necrotizing enterocolitis, atresia, and gastroschisis, may result in short bowel syndrome, with attendant high morbidity, mortality, and health care costs in the United States. Following resection, the remaining small bowel epithelium mounts an adaptive response, resulting in increased crypt cell proliferation, increased villus height, increased crypt depth, and enhanced nutrient and electrolyte absorption. Although these morphologic and functional changes are well described in animal models, the adaptive response in humans is less well understood. Clinically the response is unpredictable and often inadequate. Here we address the hypotheses that human intestinal stem cell populations are expanded and that the stem cell niche is regulated following massive gut resection in short bowel syndrome (SBS). We use intestinal enteroid cultures from patients with SBS to show that the magnitude and phenotype of the adaptive stem cell response are both regulated by stromal niche cells, including intestinal subepithelial myofibroblasts, which are activated by intestinal resection to enhance epithelial stem and proliferative cell responses. Our data suggest that myofibroblast regulation of bone morphogenetic protein signaling pathways plays a role in the gut adaptive response after resection.

Patient-derived small intestinal myofibroblasts direct perfused, physiologically responsive capillary development in a microfluidic Gut-on-a-Chip Model.

The development and physiologic role of small intestine (SI) vasculature is poorly studied. This is partly due to a lack of targetable, organ-specific markers for in vivo studies of two critical tissue components: endothelium and stroma. This challenge is exacerbated by limitations of traditional cell culture techniques, which fail to recapitulate mechanobiologic stimuli known to affect vessel development. Here, we construct and characterize a 3D in vitro microfluidic model that supports the growth of patient-derived intestinal subepithelial myofibroblasts (ISEMFs) and endothelial cells (ECs) into perfused capillary networks. We report how ISEMF and EC-derived vasculature responds to physiologic parameters such as oxygen tension, cell density, growth factors, and pharmacotherapy with an antineoplastic agent (Erlotinib). Finally, we demonstrate effects of ISEMF and EC co-culture on patient-derived human intestinal epithelial cells (HIECs), and incorporate perfused vasculature into a gut-on-a-chip (GOC) model that includes HIECs. Overall, we demonstrate that ISEMFs possess angiogenic properties as evidenced by their ability to reliably, reproducibly, and quantifiably facilitate development of perfused vasculature in a microfluidic system. We furthermore demonstrate the feasibility of including perfused vasculature, including ISEMFs, as critical components of a novel, patient-derived, GOC system with translational relevance as a platform for precision and personalized medicine research.

Epimorphin regulates the intestinal stem cell niche via effects on the stromal microenvironment.

Stem cell therapy is a potential therapeutic approach for disorders characterized by intestinal injury or loss of functional surface area. Stem cell function and proliferation are mediated by the stem cell niche. Stromal cells such as intestinal subepithelial myofibroblasts (ISEMFs) are important but poorly studied components of the stem cell niche. To examine the role of ISEMFs, we have previously generated mice with deletion of epimorphin ( Epim), an ISEMF protein and member of the syntaxin family of intracellular vesicle docking proteins that regulate cell secretion. Herein we explore the mechanisms for previous observations that Epim deletion increases gut crypt cell proliferation, crypt fission, and small bowel length in vivo. Stem cell-derived crypt culture techniques were used to explore the interaction between enteroids and myofibroblasts from Epim-/- and WT mice. Enteroids cocultured with ISEMFS had increased growth and crypt-like budding compared with enteroids cultured without stromal support. Epim deletion in ISEMFs resulted in increased enteroid budding and surface area compared with cocultures with wild-type (WT) ISEMFs. In primary crypt cultures, Epim-/- enteroids had significantly increased surface area and budding compared with WTs. However, stem cell assays comparing the number of Epim-/- vs. WT colony-forming units after first passage showed no differences in the absence of ISEMF support. Epim-/- vs. WT ISEMFs had increased Wnt4 expression, and addition of Wnt4 to WT cocultures enhanced budding. We conclude that ISEMFs play an important role in the stem cell niche. Epim regulates stem cell proliferation and differentiation via stromal contributions to the niche microenvironment. NEW & NOTEWORTHY The role of subepithelial intestinal myofibroblasts (ISEMFs) in the gut stem cell niche is controversial. We provide novel evidence supporting ISEMFs as important niche contributors. We show that the in vivo intestinal effects of deletion of myofibroblast Epim can be recapitulated in crypt stem cell cultures in vitro. ISEMFs support cocultured stem cell proliferation and enteroid growth, and these effects are augmented by deletion of Epim, a syntaxin that regulates myofibroblast cell secretion.

Proline Absorption and SGK1 Expression are Inhibited in Intestinal Tis7 Transgenic Mice.

BACKGROUND/AIMS: Expression of the transcriptional co-regulator tis7 is markedly increased in the adaptive small intestine in a mouse model of short bowel syndrome. Transgenic mice with enterocytic overexpression of tis7 (tis7tg) have accelerated triglyceride absorption, with increased adiposity yet reduced skeletal muscle mass. To further explore this phenotype, we examined whether tis7 also regulates amino acid and carbohydrate absorption. METHODS: Small intestinal glucose and amino acid uptake were quantified in wild type (WT) and tis7tg mice. Amino acid transporter expression was assessed by qRT-PCR and immunoblot. Apical cell surface transporter expression was quantified by cell surface biotinylation. RESULTS: Active glucose uptake rates were unchanged. Uptake of proline but not leucine was significantly reduced in tis7tg vs. WT jejunum. Expression of serum and glucocorticoid-induced kinase 1 (SGK1), a solute carrier activator, was inhibited in tis7tg jejunum. Apical membrane expression of the proline transporter SLC6A20 was reduced in tis7tg jejunum. CONCLUSIONS: Tis7 overexpression in enterocytes inhibits proline uptake, associated with decreased expression of activated SGK1 and reduced cell surface expression of SLC6A20. Consistent with the observed tis7tg phenotype, tis7 overexpression increases triglyceride absorption but has adverse effects on the uptake of selected amino acids. Tis7 has pleiotropic effects on nutrient absorption.

Tis7 deletion reduces survival and induces intestinal anastomotic inflammation and obstruction in high-fat diet-fed mice with short bowel syndrome.

Effective therapies are limited for patients with parenteral nutrition-dependent short bowel syndrome. We previously showed that intestinal expression of the transcriptional coregulator tetradecanoyl phorbol acetate-induced sequence 7 (tis7) is markedly increased during the adaptive response following massive small bowel resection and tis7 plays a role in normal gut lipid metabolism. Here, we further explore the functional implications of tis7 deletion in intestinal lipid metabolism and the adaptive response following small bowel resection. Intestinal tis7 transgenic (tis7(tg)), tis7(-/-), and wild-type (WT) littermates were subjected to 50% small bowel resection. Mice were fed a control or a high-saturated-fat (42% energy) diet for 21 days. Survival, body weight recovery, lipid absorption, mucosal lipid analysis, and the morphometric adaptive response were analyzed. Quantitative real-time PCR was performed to identify tis7 downstream gene targets. Postresection survival was markedly reduced in high-fat, but not control, diet-fed tis7(-/-) mice. Decreased survival was associated with anastomotic inflammation and intestinal obstruction postresection. High-fat, but not control, diet-fed tis7(-/-) mice had increased intestinal IL-6 expression. Intestinal lipid trafficking was altered in tis7(-/-) compared with WT mice postresection. In contrast, high-fat diet-fed tis7(tg) mice had improved survival postresection compared with WT littermates. High-fat diet feeding in the setting of tis7 deletion resulted in postresection anastomotic inflammation and small bowel obstruction. Tolerance of a calorie-rich, high-fat diet postresection may require tis7 and its target genes. The presence of luminal fat in the setting of tis7 deletion promotes an intestinal inflammatory response postresection.

Epimorphin(-/-) mice are protected, in part, from acute colitis via decreased interleukin 6 signaling.

Epimorphin (Epim), a member of the syntaxin family of membrane-bound, intracellular vesicle-docking proteins, is expressed in intestinal myofibroblasts and macrophages. We demonstrated previously that Epimorphin(-/-)(Epim(-/-)) mice are protected, in part, from dextran sodium sulfate (DSS)-induced colitis. Although interleukin (IL)-6/p-Stat3 signaling has been implicated in the pathogenesis of colitis, the myofibroblast contribution to IL-6 signaling in colitis remains unexplored. Our aim was to investigate the IL-6 pathway in Epim(-/-) mice in the DSS colitis model. Whole colonic tissue, epithelium, and stroma of WT and congenic Epim(-/-) mice treated with 5% DSS for 7 days were analyzed for IL-6 and a downstream effector, p-Stat3, by immunostaining and immunoblot. Colonic myofibroblast and peritoneal macrophage IL-6 secretion were evaluated by enzyme-linked immunosorbent assay. IL-6 and p-Stat3 expression were decreased in Epim(-/-) vs WT colon. A relative increase in stromal vs epithelial p-Stat3 expression was observed in WT mice but not in Epim(-/-) mice. Epim deletion abrogates IL-6 secretion from colonic myofibroblasts treated with IL-1ß and decreases IL-6 secretion from peritoneal macrophages in a subset of DSS-treated mice. Epim deletion inhibits IL-6 secretion most profoundly from colonic myofibroblasts. Distribution of Stat3 activation is altered in DSS-treated Epim(-/-) mice. Our findings support the notion that myofibroblasts modulate IL-6/p-Stat3 signaling in DSS-treated Epim(-/-) mice.

Epimorphin deletion inhibits polyposis in the Apcmin/+ mouse model of colon carcinogenesis via decreased myofibroblast HGF secretion.

Interactions between the epithelium and surrounding mesenchyme/stroma play an important role in normal gut morphogenesis, the epithelial response to injury, and epithelial carcinogenesis. The tumor microenvironment, composed of stromal cells including myofibroblasts and immune cells, regulates tumor growth and the cancer stem cell niche. Deletion of epimorphin (Epim), a syntaxin family member expressed in myofibroblasts and macrophages, results in partial protection from colitis and from inflammation-induced colon cancer in mice. We sought to determine whether epimorphin deletion protects from polyposis in the Apcmin/+ mouse model of intestinal carcinogenesis. Epim-/- mice were crossed to Apcmin/+ mice; Apcmin/+ and Apcmin/+/Epim-/- mice were killed at 3 mo of age. Polyp numbers and sizes were quantified in small intestine and colon, and gene expression analyses for pathways relevant to epithelial carcinogenesis were performed. Primary myofibroblast cultures were isolated, and expression and secretion of selected growth factors from Apcmin/+ and Apcmin/+/Epim-/- myofibroblasts were examined by ELISA. Small bowel polyposis was significantly inhibited in Apcmin/+/Epim-/- compared with Apcmin/+ mice. Apcmin/+/Epim-/- compared with Apcmin/+ polyps and adjacent uninvolved intestinal mucosa had increased transforming growth factor-ß (TGF-ß) expression and signaling with increased P-Smad2/3 expression. Myofibroblasts isolated from Apcmin/+/Epim-/- vs. Apcmin/+ mice had markedly decreased hepatocyte growth factor (HGF) expression and secretion. We concluded that Epim deletion inhibits polyposis in Apcmin/+ mice, associated with increased mucosal TGF-ß signaling and decreased myofibroblast HGF expression and secretion. Our data suggest that Epim deletion reduces tumorigenicity of the stromal microenvironment.

Stromal cells participate in the murine esophageal mucosal injury response.

We identified α-smooth muscle actin (α-SMA)- and vimentin-expressing spindle-shaped esophageal mesenchymal cells in the adult and neonate murine esophageal lamina propria. We hypothesized that these esophageal mesenchymal cells express and secrete signaling and inflammatory mediators in response to injury. We established primary cultures of esophageal mesenchymal cells using mechanical and enzymatic digestion. We demonstrate that these primary cultures are nonhematopoietic, nonendothelial, stromal cells with myofibroblast-like features. These cells increase secretion of IL-6 in response to treatment with acidified media and IL-1ß. They also increase bone morphogenetic protein (Bmp)-4 secretion in response to sonic hedgehog. The location of these cells and their biological functions demonstrate their potential role in regulating esophageal epithelial responses to injury and repair.

Deletion of Tis7 protects mice from high-fat diet-induced weight gain and blunts the intestinal adaptive response postresection.

After loss of intestinal surface area, the remaining bowel undergoes a morphometric and functional adaptive response. Enterocytic expression of the transcriptional coregulator tetradecanoyl phorbol acetate induced sequence 7 (Tis7) is markedly increased in a murine model of intestinal adaptation. Mice overexpressing Tis7 in intestine have greater triglyceride absorption and weight gain when fed a high-fat diet (42% energy) than their wild-type (WT) littermates fed the same diet. These and other data suggest that Tis7 has a unique role in nutrient absorptive and metabolic adaptation. Herein, male Tis7(-/-) and WT mice were fed a high-fat diet (42% energy) for 8 wk. Weight was monitored and metabolic analyses and hepatic and intestinal lipid concentrations were compared after 8 wk. Intestinal lipid absorption and metabolism studies and intestinal resection surgeries were performed in separate groups of Tis7(-/-) and WT mice. At 8 wk, weight gain was less and jejunal mucosal and hepatic triglyceride and cholesterol concentrations were lower in Tis7(-/-) mice than in the WT controls. Following corn oil gavage, serum cholesterol, triglyceride, and FFA concentrations were lower in the Tis7(-/-) mice than in the WT mice. Incorporation of oral (3)[H] triolein into intestinal mucosal cholesterol ester and FFA was less in Tis7(-/-) compared with WT mice. Following resection, crypt cell proliferation rates and villus heights were lower in Tis7(-/-) than in WT mice, indicating a blunted adaptive response. Our results suggest a novel physiologic function for Tis7 in the gut as a global regulator of lipid absorption and metabolism and epithelial cell proliferation.

Epimorphin deletion protects mice from inflammation-induced colon carcinogenesis and alters stem cell niche myofibroblast secretion.

Epithelial-mesenchymal interactions regulate normal gut epithelial homeostasis and have a putative role in inflammatory bowel disease and colon cancer pathogenesis. Epimorphin is a mesenchymal and myofibroblast protein with antiproliferative, promorphogenic effects in intestinal epithelium. We previously showed that deletion of epimorphin partially protects mice from acute colitis, associated with an increase in crypt cell proliferation. Here we explored the potential therapeutic utility of modulating epimorphin expression by examining the effects of epimorphin deletion on chronic inflammation-associated colon carcinogenesis using the azoxymethane/dextran sodium sulfate (AOM/DSS) model. We found that mice in which epimorphin expression was absent had a marked reduction in incidence and extent of colonic dysplasia. Furthermore, epimorphin deletion in myofibroblasts altered the morphology and growth of cocultured epithelial cells. Loss of epimorphin affected secretion of soluble mesenchymal regulators of the stem cell niche such as Chordin. Importantly, IL-6 secretion from LPS-treated epimorphin-deficient myofibroblasts was completely inhibited, and stromal IL-6 expression was reduced in vivo. Taken together, these data show that epimorphin deletion inhibits chronic inflammation-associated colon carcinogenesis in mice, likely as a result of increased epithelial repair, decreased myofibroblast IL-6 secretion, and diminished IL-6-induced inflammation. Furthermore, we believe that modulation of epimorphin expression may have therapeutic benefits in appropriate clinical settings.

Epimorphin(-/-) mice have increased intestinal growth, decreased susceptibility to dextran sodium sulfate colitis, and impaired spermatogenesis.

Dynamic and reciprocal epithelial-mesenchymal interactions are critical for the normal morphogenesis and maintenance of epithelia. Epimorphin has been identified as a unique molecule expressed by mesenchymal cells and myofibroblasts and has putative morphogenetic effects in multiple epithelial tissues, including intestine, skin, mammary gland, lung, gallbladder, and liver. To define the in vivo role of epimorphin, we created epimorphin-null mice by targeted inactivation of the epimorphin gene. Male epimorphin-/- mice are sterile due to abnormal testicular development and impaired spermatogenesis. Intestinal growth is increased in epimorphin-/- mice due to augmented crypt cell proliferation and crypt fission during the neonatal (suckling) period, mediated at least in part by changes in bone morphogenetic protein (Bmp) and Wnt/beta-catenin signaling pathways. Colonic mucosal injury and colitis induced by dextran sodium sulfate (DSS) are ameliorated in epimorphin-/- mice, probably due to the increased proliferative capacity of the epimorphin-/- colon. These in vivo findings support the notion that epimorphin is a key stromal regulator of epithelial cell proliferation and growth in the intestine. In addition, our studies demonstrate a novel and critical role for epimorphin in regulating testicular development and growth as well as spermatogenesis.

Increased apoptosis and accelerated epithelial migration following inhibition of hedgehog signaling in adaptive small bowel postresection.

The intestinal epithelium undergoes a marked adaptive response following loss of functional small bowel surface area characterized by increased crypt cell proliferation and increased enterocyte migration from crypt to villus tip, resulting in villus hyperplasia and enhanced nutrient absorption. Hedgehog (Hh) signaling plays a critical role in regulating epithelial-mesenchymal interactions during morphogenesis of the embryonic intestine. Our previous studies showed that blocking Hh signaling in neonatal mice results in increased small intestinal epithelial crypt cell proliferation and altered enterocyte fat absorption and morphology. Hh family members are also expressed in the adult intestine, but their role in the mature small bowel is unclear. With the use of a model of intestinal adaptation following partial small bowel resection, the role of Hh signaling in the adult gut was examined by determining the effects of blocking Hh signaling on the regenerative response following loss of functional surface area. Hh-inactivating monoclonal antibodies or control antibodies were administered to mice that sustained a 50% intestinal resection. mRNA analyses of the preoperative ileum by quantitative real-time PCR revealed that Indian hedgehog was the most abundant Hh family member. The Hh receptor Patched was more abundant than Patched 2. Analyses of downstream targets of Hh signaling demonstrated that Gli3 was twofold more abundant than Gli1 and Gli2 and that bone morphogenetic protein (BMP)2 was most highly expressed compared with BMP1, -4, and -7. Following intestinal resection, the expression of Hh, Patched, Gli, and most BMP genes was markedly downregulated in the remnant ileum, and, in anti-Hh antibody-treated mice, expression of Patched 2 and Gli 1 was further suppressed. In Hh antibody-treated mice following resection, the enterocyte migration rate from crypt to villus tip was increased, and by 2 wk postoperation, apoptosis was increased in the adaptive gut. However, crypt cell proliferation, villus height, and crypt depth were not augmented. These data indicate that Hh signaling plays a role in adult gut epithelial homeostasis by regulating epithelial cell migration from crypt to villus tip and by enhancing apoptosis.

Targeted intestinal overexpression of the immediate early gene tis7 in transgenic mice increases triglyceride absorption and adiposity.

Following loss of functional small bowel surface area due to surgical resection, the remnant gut undergoes an adaptive response characterized by increased crypt cell proliferation and enhanced villus height and crypt depth, resulting in augmented intestinal nutrient absorptive capacity. Previous studies showed that expression of the immediate early gene tis7 is markedly up-regulated in intestinal enterocytes during the adaptive response. To study its role in the enterocyte, transgenic mice were generated that specifically overexpress TIS7 in the gut. Nucleotides -596 to +21 of the rat liver fatty acid-binding protein promoter were used to direct abundant overexpression of TIS7 into small intestinal upper crypt and villus enterocytes. TIS7 transgenic mice had increased total body adiposity and decreased lean muscle mass compared with normal littermates. Oxygen consumption levels, body weight, surface area, and small bowel weight were decreased. On a high fat diet, transgenic mice exhibited a more rapid and proportionately greater gain in body weight with persistently elevated total body adiposity and increased hepatic fat accumulation. Bolus fat feeding resulted in a greater increase in serum triglyceride levels and an accelerated appearance of enterocytic, lamina propria, and hepatic fat. Changes in fat homeostasis were linked to increased expression of genes involved in enterocytic triglyceride metabolism and changes in growth with decreased insulin-like growth factor-1 expression. Thus, TIS7 overexpression in the intestine altered growth, metabolic rate, adiposity, and intestinal triglyceride absorption. These results suggest that TIS7 is a unique mediator of nutrient absorptive and metabolic adaptation following gut resection.

Inhibition of Hedgehog signaling protects adult mice from diet-induced weight gain.

Hedgehog (Hh) signaling plays an important role in embryonic development of many tissues, including the gastrointestinal tract. Sonic Hh-and Indian Hh-deficient mice die before or soon after birth, precluding further study of this signaling pathway in the mature intestine. Maternal transfer of inactivating monoclonal antibodies to Hh proteins (anti-Hh moAb) during late stages of embryogenesis or to early postnatal mice produced intestinal villous abnormalities, progressive runting, and severe malabsorption of dietary fat. In the present study, we sought to determine the effect of inhibiting Hh signaling on weight gain and lipid absorption in adult mice. Anti-Hh moAb was administered to adult Balb/c mice fed either a low-fat, nonpurified diet or a high-fat, semipurified diet, and to adult ob/ob mice fed the low-fat, nonpurified diet. Weight gain was significantly inhibited by anti-Hh moAb treatment in Balb/C mice fed the high-fat, but not the low-fat diet and in ob/ob mice. Further analysis of adult Balb/c mice fed the high-fat diet demonstrated that although total lipid absorption was normal, the rate of triglyceride absorption was significantly delayed in mice treated with anti-Hh moAb and they had significantly increased fecal FFA excretion. Hepatic steatosis, found in high-fat fed Balb/c mice treated with the control moAb, was abrogated by anti-Hh moAb administration. These findings point to a potential role for Hh signaling pathways in diet-induced abnormalities of lipid metabolism.

Bax is required for resection-induced changes in apoptosis, proliferation, and members of the extrinsic cell death pathways.

BACKGROUND AND AIMS: To define better the homeostatic mechanisms contributing to small intestinal adaptation following partial resection, the relative contributions of apoptosis, cell proliferation, and enterocyte migration and the comparative roles of the intrinsic (mitochondrial) and extrinsic (death receptor-mediated) apoptotic pathways were assessed. METHODS: After 50% jejunoileal resections or transections, adaptation was analyzed in duodenal-jejunal and ileal segments from C57BL/6 Bax(+/+) (16, 48, and 168 hours postoperative) and Bax(-/-) mice (168 hours). RESULTS: Basal apoptotic rates were equivalent in all mice. By 1-week postresection, villus heights and crypt depths were increased in the duodenal-jejunal and ileal remnants of both genotypes. In Bax(+/+) mice, adaptation occurred in concert with increased crypt proliferative and apoptotic indices. Bax(-/-) mice did not show increases in proliferation or apoptosis, yet adaptive increases in villus height were enhanced relative to Bax(+/+) mice. Enterocyte migration increased in both genotypes. Postresection, the expression of caspases and genes involved in death receptor-mediated apoptosis was decreased in Bax(-/-) compared with Bax(+/+) mice. CONCLUSIONS: Postresection adaptation involves parallel changes in crypt proliferation and apoptosis, but, as observed in Bax(-/-) mice, it can occur without increased proliferation. These studies demonstrate that spontaneous gut apoptosis is Bax independent, whereas adaptation-related apoptosis is Bax-dependent. Differences between resected Bax(+/+) and Bax(-/-) mice suggest that apoptosis in the adapting gut utilizes the extrinsic pathway, but this requires linkage to the mitochondrial pathway via Bax. The increased adaptive response in Bax(-/-) mice indicates that modulation of apoptosis may be useful for enhancing adaptation.

Growth factor regulation of PC4/TIS7, an immediate early gene expressed during gut adaptation after resection.

BACKGROUND: To define the molecular mechanisms underlying the intestinal adaptive response after partial small bowel resection, we previously identified a cohort of genes regulated in the remnant adaptive ileum. One is PC4/TIS7, an immediate early gene preferentially up-regulated during the first 48 hours after resection. To further the mechanisms that regulate gut adaptation, we sought to identify upstream regulators of PC4/TIS7 expression. METHODS: PC4/TIS7 expression in adaptive versus transection control mouse gut was examined at 48 hours after 50% intestinal resection, and its cellular localization was determined by immunohistochemistry. The effects of intestinotrophic peptides and growth factors on PC4/TIS7 expression were examined in vitro in the crypt epithelial cell line IEC 18 and in vivo in the mouse. RESULTS: PC4/TIS7 was expressed in the cytoplasm of IEC 18 cells and in adaptive mouse ileal crypt and villus enterocytes. Epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) increased PC4/TIS7 mRNA levels in postconfluent, quiescent IEC 18 cells, but insulin-like growth factor 1 (IGF-1) and nerve growth factor (NGF) had no effect. A stable derivative of glucagon-like peptide 2 (GLP-2), r(gly2)GLP-2, was most potent in increasing PC4/TIS7 expression; however, stimulation of proliferation and differentiation were not observed. To determine the effect of GLP-2 on PC4/TIS7 expression in vivo, r(gly2)GLP-2 was administered intraperitoneally to mice. PC4/TIS7 mRNA expression was increased in small bowel in response to GLP-2 compared with vehicle control. CONCLUSIONS: These results suggest that PC4/TIS7 plays a role in intracellular signaling in the intestinal epithelium during the adaptive response, possibly as a common downstream effector for several intestinotrophic growth factors.

Epimorphin expression in intestinal myofibroblasts induces epithelial morphogenesis.

The formation of the crypt-villus axis during gut ontogeny requires continued reciprocal interactions between the endoderm and mesenchyme. Epimorphin/syntaxin 2 (epimorphin) is a mesenchymal protein expressed in the fetal gastrointestinal tract during villus morphogenesis. To elucidate its role in gut ontogeny, the epimorphin cDNA was transfected, in sense and antisense orientations, into a rat intestinal myofibroblast cell line, MIC 216. To determine the effects of epimorphin on the epithelium, myofibroblasts were cocultured with the Caco2 cell line. Caco2 cells spread in a simple monolayer over antisense-transfected cells lacking epimorphin. In contrast, sense-transfected myofibroblasts induced Caco2 cells to form compact, round clusters with small lumens. These morphologic differences were preserved in Transwell cocultures in which cell-cell contact was prevented, suggesting that epimorphin's effects were mediated by secreted factor(s). To determine the effects of epimorphin on crypt-villus axis formation in an in vivo model, rat gut endoderm was combined with epimorphin-transfected myofibroblasts and implanted into the chick intracoelomic cavity. The grafts in which epimorphin was overexpressed revealed multiple well-formed villi with crypt-like units, whereas those in which epimorphin expression was inhibited developed into round cystic structures without crypts or villi. Of several potential secreted morphogens, only the expression of bone morphogenetic protein 4 (Bmp4) was increased in the epimorphin-transfected cells. Incubation with noggin partially blocked the transfected myofibroblasts' effects on Caco2 colony morphology. These results indicate that mesenchymal epimorphin has profound effects on crypt-villus morphogenesis, mediated in part by secreted factor(s) including the Bmp's.