Role of glucocorticoids on the maturation of brush border enzymes in fetal rat gut endoderm

Igf-I accelerates ileal epithelial cell migration in culture and newborn mice and may be a mediator of steroid-induced maturation

We have previously hypothesized that IGF-I is a mediator of dexamethasone (DEX) effect in the newborn mouse ileum-a model designed to mimic the precocious mucosal maturation associated with spontaneous ileal perforations in extremely premature neonates. We have further investigated this hypothesis using in vivo and in vitro models of accelerated epithelial migration (a transient property, temporally associated with mucosal maturation). These experiments include a steroid-treatment model comparing IGF-I immunolocalization with bromo-deoxyuridine (BrdU)-pulse-labeling, as a means of assessing epithelial cell migration, within the ileum of newborn mice that received either daily intraperitoneal injections of DEX (1 microg/gm) or vehicle. Likewise, a transgenic newborn mouse model was used to compare the effect of IGF-I overexpression upon the clearance of BrdU-pulse-labeled epithelial cells traveling up the villus during the same time period. For our in vitro model, rat ileal epithelial cells (IEC-18) were cultured to confluence in serum-free media then treated with DEX, a stable IGF-I agonist, or nothing before being subjected to linear scarification. Serial photomicrographs of migrating cells were taken over time and the average speed was determined for each treatment condition. Our data demonstrate that IGF-I accelerates ileal epithelial cell migration in every model. However, DEX was only associated with accelerated epithelial cell migration in models where IGF-I (or a synthetic agonist) was highly abundant. In contrast, DEX by itself slowed migration speed in cell culture. These findings suggest that IGF-I may be a mediator of steroid effect during precocious maturation of the ileal mucosa.

Indomethacin, dexamethasone, and intestinal damage in infant rats

BACKGROUND

Indomethacin is commonly used in the Neonatal Intensive Care Unit to induce closure of the patent ductus arteriosus and to prevent intraventricular hemorrhage. It is known that indomethacin causes intestinal ulceration in adults, but its effect in infants is less clear. In a preliminary experiment, it was found that the administration of 10 mg/kg/d of indomethacin, a dose that damages the adult rat intestine, had no detrimental effects on newborn suckling rats whereas dexamethasone at 0.25 mg/kg/d caused significant growth failure and villous blunting. It was then hypothesized that the lack of intestinal damage with indomethacin in infants was related to protection given by mother's milk.

METHODS

Subsequent experiments were performed wherein 10 mg/kg/d of indomethacin was provided to infant mother-reared, infant artificially fed, and adult rats. The expression of intestinal cyclooxygenases in the prostaglandin synthetic pathway of control rats was examined to initiate an exploration into a mechanism for the developmental response to indomethacin.

RESULTS

Mother-reared and artificially fed infant rats demonstrated resistance to the ulcerogenic effects of indomethacin, in contrast to the adults. A differential presence of cyclooxygenase-1 and cyclooxygenase-2 was not distinctly seen between infancy and adulthood.

CONCLUSIONS

The results indicate that a varying response to the damaging effects of indomethacin on the intestine occurs during development with the infant being less susceptible than the adult. This differed from the effects of dexamethasone administration, which caused significant intestinal atrophy in the infant rats. The intestinal protection to the effects of indomethacin in infants is not dependent on mother's milk or a developmental difference in the prostaglandin biosynthetic pathway.

The clinical, morphologic, and molecular changes in the ileum associated with early postnatal dexamethasone administration: from the baby's bowel to the researcher's bench

Focal small bowel perforation (FSBP) is a life-threatening event that predominantly affects extremely low birth weight (ELBW) infants. Histopathology from surgical specimens of ileum with FSBP shows a healthy mucosa overlying a thinned muscularis with segmental degeneration. Clinical data strongly support an association between early postnatal administration of dexamethasone (EPD) and FSBP. Additional risk factors, including gestational age, administration of prophylactic indomethacin, and severity of illness, may be synergistic with EPD for the pathogenesis of perforations. Animal models of dexamethasone administration show morphologic changes in the ileum, similar to those seen in ELBW infants, including increased mucosal maturation and thinning of the muscularis. These tissue-specific differences may be mediated by a perturbation in growth factor expression or accumulation. In support of this hypothesis, dexamethasone has been associated with increased IGF-I immunolocalization in the mucosa and decreased immunolocalization in the muscularis. The known growth-promoting functions of IGF-I are consistent with the observed dexamethasone-associated changes within both the mucosa and the muscularis. Ongoing studies in this animal model are exploring the potential mechanisms by which dexamethasone might affect IGF-I availability.

Tissue architecture: the ultimate regulator of epithelial function?

The architecture of a tissue is defined by the nature and the integrity of its cellular and extracellular compartments, and is based on proper adhesive cell-cell and cell-extracellular matrix interactions. Cadherins and integrins are major adhesion-mediators that assemble epithelial cells together laterally and attach them basally to a subepithelial basement membrane, respectively. Because cell adhesion complexes are linked to the cytoskeleton and to the cellular signalling pathways, they represent checkpoints for regulation of cell shape and gene expression and thus are instructive for cell behaviour and function. This organization allows a reciprocal flow of mechanical and biochemical information between the cell and its microenvironment, and necessitates that cells actively maintain a state of homeostasis within a given tissue context. The loss of the ability of tumour cells to establish correct adhesive interactions with their microenvironment results in disruption of tissue architecture with often fatal consequences for the host organism. This review discusses the role of cell adhesion in the maintenance of tissue structure and analyses how tissue structure regulates epithelial function.

Delay in natural decline of lactase activity in the small intestine of prematurely weaned rats as related to changes in their thyroid status

Premature weaning of suckling rats on the 15th day of life delayed the natural reduction of lactase activity in the small intestine and reduced the level of T4 in serum. Preliminary treatments (from day 12 to 14 of life) with exogenous T4 (1 mg/kg BW) or exposure to cold (10 degrees C) significantly increased the level of T4 in serum on the 15th day of life, and sharply accelerated the reduction of lactase activity. It is concluded that the delay in lactase reduction in prematurely weaned rats may be related to a decrease in serum thyroxine level. Cold as well as exogenous thyroxine may be considered as a means for regulation of the functional maturation of the small intestine.

Fetal endoderm primarily holds the temporal and positional information required for mammalian intestinal development

In rodents, the intestinal tract progressively acquires a functional regionalization during postnatal development. Using lactase-phlorizin hydrolase as a marker, we have analyzed in a xenograft model the ontogenic potencies of fetal rat intestinal segments taken prior to endoderm cytodifferentiation. Segments from the presumptive proximal jejunum and distal ileum grafted in nude mice developed correct spatial and temporal patterns of lactase protein and mRNA expression, which reproduced the normal pre- and post-weaning conditions. Segments from the fetal colon showed a faint lactase immunostaining 8-10 d after transplantation in chick embryos but not in mice; it is consistent with the transient expression of this enzyme in the colon of rat neonates. Heterotopic cross-associations comprising endoderm and mesenchyme from the presumptive proximal jejunum and distal ileum developed as xenografts in nude mice, and they exhibited lactase mRNA and protein expression patterns that were typical of the origin of the endodermal moiety. Endoderm from the distal ileum also expressed a normal lactase pattern when it was associated to fetal skin fibroblasts, while the fibroblasts differentiated into muscle layers containing alpha-smooth-muscle actin. Noteworthy, associations comprising colon endoderm and small intestinal mesenchyme showed a typical small intestinal morphology and expressed the digestive enzyme sucrase-isomaltase normally absent in the colon. However, in heterologous associations comprising lung or stomach endoderm and small intestinal mesenchyme, the epithelial compartment expressed markers in accordance to their tissue of origin but neither intestinal lactase nor sucrase-isomaltase. A thick intestinal muscle coat in which cells expressed alpha-smooth-muscle actin surrounded the grafts. The results demonstrate that: (a) the temporal and positional information needed for intestinal ontogeny up to the post-weaning stage results from an intrinsic program that is fixed in mammalian fetuses prior to endoderm cytodifferentiation; (b) this temporal and positional information is primarily carried by the endodermal moiety which is also able to change the fate of heterologous mesodermal cells to form intestinal mesenchyme; and (c) the small intestinal mesenchyme in turn may deliver instructive information as shown in association with colonic endoderm; yet this effect is not obvious with nonintestinal endoderms.

In vitro study of the intestinal brush border enzyme activities in developing anuran amphibian: effects of thyroxine, cortisol, and insulin

The effects of several hormones on intestinal brush border membrane enzymatic activities have been investigated in intestinal explants taken from the amphibian midwife toad at different developmental stages. Explants were treated for at least 2 days with thyroxine (0.1 microgram/ml of culture medium) or for 2 days with cortisol (25 micrograms/ml) or insulin (6 mU/ml). The hydrolases examined were maltase, trehalase, glucoamylase, and alkaline phosphatase. In the explants from tadpoles in prometamorphosis, thyroxine had no effect on hydrolase activities; cortisol increased the activity of only glucoamylase, and insulin increased activity of maltase, glucoamylase, and alkaline phosphatase. When the explants were taken from tadpoles at the beginning of climax, cortisol and insulin generally stimulated the enzyme activities studied. When taken from tadpoles at the end of climax, at the moment when the embryonic cells under the degenerating epithelium divide, cortisol and insulin had little effect on these activities. When the animals terminate their metamorphosis, the intestinal epithelium of the explants is totally newly formed (secondary epithelium). At this time, cortisol stimulated the activities of maltase, glucoamylase, and alkaline phosphatase, while insulin decreased the activities of maltase and glucoamylase.

Epithelial-mesenchymal interactions in intestinal epithelial differentiation

The complex morphogenetic events and the concomitant structural and functional differentiation of intestinal progenitor cells are dependent on tissue interactions. Several experimental models of hetero-species or -topic recombinants between epithelial and mesenchymal anlagen are described. They enabled us to elucidate the respective roles of these tissue components in morphogenesis, epithelial differentiation, and hormone-elicited responses. Among the mechanisms of tissue interactions, the possible mediation of permissive and instructive information via the extracellular matrix is postulated. Arguments in favor of this are provided by the observation of compositional changes in matrix molecules during intestinal development and differentiation. On the other hand, in vitro experimental data emphasize the role of actual contacts between epithelial and mesenchymal cell populations and the importance of the mesenchyme for basement membrane formation.

Importance of a fibroblastic support for in vitro differentiation of intestinal endodermal cells and for their response to glucocorticoids

Microexplants of 14- or 15-day-old fetal rat intestinal endoderm, separated from mesenchyme by collagenase, were placed on culture dishes coated with different extracellular matrix components or on confluent monolayers of intestinal mesenchymal cells or of fetal skin fibroblasts. Only small variations in the attachment or spreading of the endodermal cells could be observed when they were cultured on the different acellular substrata, and their survival never exceeded one week. When cocultured with intestinal or skin fibroblasts, endodermal cells proliferated and the survival time was prolonged to 2 or 3 weeks. Furthermore, differentiation, as assessed by the polarization of the cells, occurred and was characterized by the maturation of apical brush borders and by the synthesis of microvillar digestive enzymes visualized immunocytochemically with monoclonal antibodies. Glucocorticoids accelerated structural differentiation and stimulated or induced brush border enzymes only in the coculture conditions. These experiments emphasize the role of a fibroblastic support without tissue specificity on the cytodifferentiation of intestinal endodermal cells. They also suggest a mesenchymal dependence on the hormonal response.

Fetal gut mesenchyme induces differentiation of cultured intestinal endodermal and crypt cells

An experimental model was designed to analyze the effect of fetal gut mesenchyme on the cytodifferentiation of crypt cells and of embryonic progenitor cells. The cells used were the rat intestinal crypt cell line, IEC-17, and primary cell cultures prepared form isolated 14-day-old fetal intestinal endoderm (EC). Both cultures prepared from isolated 14-day-old fetal rat intestinal endoderm (EC). Both types of cells were associated with 14-day-old fetal rat gut mesenchyme (Rm) and grafted under the kidney capsule of adult rats. Seventy percent of the Rm/EC and ten percent of the Rm/IEC recombinants, recovered after 9 days, exhibited well-vascularized structures in which the mesenchyme had induced morphogenesis of the cells into a villus epithelium. The four main intestinal epithelial cell types, absorptive, goblet, endocrine, and Paneth cells, were identified using electron microscopy. Biochemical determinations of enzyme activities associated with brush border membranes revealed that alkaline phosphatase, lactase, sucrase, and maltase were expressed in both types of associations. These results were confirmed by immunofluorescence staining using monoclonal antibodies to brush border enzymes. Both enzyme assays and immunocytochemistry showed that the amount of enzymes present in the brush border membrane of Rm/IEC grafts was in general lower than that of the Rm/EC recombinants. The results indicate that fetal rat gut mesenchyme enables morphogenesis and cytodifferentiation of both crypt and embryonic progenitor cells.

Hormonal control of the intestinal brush border enzyme activities in developing anuran amphibians. I. Effects of hydrocortisone and insulin during and after spontaneous metamorphosis

The effects of hydrocortisone and insulin on the intestinal brush border membrane enzymatic activities in an anuran amphibian, Alytes obstetricans, were investigated at the end of spontaneous metamorphosis and 2 weeks after its completion. At the end of metamorphosis, the brush border is differentiating in the apical region of a developing neoformed epithelium. Two weeks after the completion of metamorphosis, this epithelium is entirely formed. The animals received one hormone injection per day for 2 or 3 days running (hydrocortisone: 1, 5, or 25 micrograms/g body wt/day; insulin: 0.5, 1, or 5 mU/g body wt/day). The hydrolases studied were three glucosidases (maltase, glucoamylase, trehalase), gamma-glutamyl-transferase and alkaline phosphatase. In animals reaching the end of metamorphosis, hormonal treatments rarely modify the three glucosidase activities. Two weeks after metamorphosis, a 5 microgram/g body wt/day hydrocortisone injection usually results in a significant increase of the three glucosidase activities. Conversely, a 0.5 mU/g body wt/day insulin injection induced a marked decrease in these activities. At the end of metamorphosis, hydrocortisone has variable effects on gamma-glutamyl-transferase activity; insulin, however, does not significantly modify this activity. Two weeks later, insulin and sometimes hydrocortisone inhibit gamma-glutamyl-transferase activity. Whatever the developmental stage is, hydrocortisone is able to stimulate alkaline phosphatase activity. At the end of metamorphosis, insulin has no influence on this activity, but 2 weeks after metamorphosis, low doses of the hormone (0.5 mU/g body wt/day) significantly reduce it. These results emphasize the possibility that after spontaneous metamorphosis the enzymatic activities of the new intestinal brush border are hormone controlled. This control could be related to the development of the interrenal and pancreatic islet functions.

Effects of human fetal gastroenteric mesenchymal cells on some developmental aspects of animal gut endoderm

Human intestinal and gastric mesenchymal cells were associated with chick and rat intestinal endoderm in order to test their species-specific capacity on epithelial differentiation. Primary cell cultures were established from human intestinal and gastric mesenchyme. Animal intestinal endoderms were associated with both cell types, grafted in ovo and allowed to develop for 12 days. The morphologic and enzymatic differentiation of the recombinants demonstrated two types of inductive properties exerted by human fetal intestinal and gastric mesenchymal cells, respectively. Firstly, human intestinal mesenchymal cells triggered intrinsic developmental capacities in chick and rat endoderm, i.e. enhanced structural brush-border maturation in both species and precocious sucrase induction in rat endoderm. Secondly, human gastric mesenchymal cells provoked the partial conversion of chick intestinal endoderm into gastric structures. Such properties were not found in homologous animal mesenchymes.