Sucrase-isomaltase mRNA Research Articles

Dietary adaptation to high starch involves increased relative abundance of sucrase-isomaltase and its mRNA in nestling house sparrows.

Dietary flexibility in digestive enzyme activity is widespread in vertebrates but mechanisms are poorly understood. When laboratory rats are switched to a higher carbohydrate diet, the activities of the apical intestinal α-glucosidases (AGs) increase within 6-12 h, mainly by rapid increase in enzyme transcription, followed by rapid translation and translocation to the intestine's apical, brush-border membrane (BBM). We performed the first unified study of the overall process in birds, relying on activity, proteomic, and transcriptomic data from the same animals. Our avian model was nestling house sparrows (Passer domesticus), which switch naturally from a low-starch insect diet to a higher starch seed diet and in whom the protein sucrase-isomaltase (SI) is responsible for all maltase and sucrase intestinal activities. Twenty-four hours after the switch to a high-starch diet, SI activity was increased but not at 12 h post diet switch. SI was the only hydrolase increased in the BBM, and its relative abundance and activity were positively correlated. Twenty-four hours after a reverse switch back to the lower starch diet, SI activity was decreased but not at 12 h post diet switch. Parallel changes in SI mRNA relative abundance were associated with the changes in SI activity in both diet-switch experiments, but our data also revealed an apparent diurnal rhythm in SI mRNA. This is the first demonstration that birds may rely on rapid increase in abundance of SI and its mRNA when adjusting to high-starch diet. Although the mechanisms underlying dietary induction of intestinal enzymes seem similar in nestling house sparrows and laboratory rodents, the time course for modulation in nestlings seemed half as fast compared with laboratory rodents. Before undertaking modulation, an opportunistic forager facing limited resources might rely on more extensive or prolonged environmental sampling, because the redesign of the intestine's hydrolytic capacity shortly after just one or a few meals of a new substrate might be a costly mistake.

Influence of dietary fructose supplementation on visceral organ mass, carbohydrase activity, and mRNA expression of genes involved in small intestinal carbohydrate assimilation in neonatal calves

The hypothesis of this experiment was that dietary fructose would influence visceral organ mass, carbohydrase activity, and mRNA expression of carbohydrases and nutrient transporters in the small intestine in neonatal calves. Therefore, our objective was to use the neonatal calf as a model to evaluate the effects of postruminal fructose supply on small intestinal carbohydrate assimilation. Ten calves (<7 d of age; 41.2 ± 1.46 kg of body weight) were fed milk replacer at 2.0% of body weight daily (816 ± 90.5 g/d; 272 ± 30.1 g/L; dry-matter basis) in 2 equal portions and assigned to the following dietary treatment groups: (1) milk replacer (control; n = 6) or (2) milk replacer + 2.2 g of fructose/kg of body weight (fructose; n = 4). Calves were fed dietary treatments for 28 d, with jugular blood sampled every 7 d before and after the morning feeding. Calves were slaughtered, and visceral weights were recorded. Postruminal carbohydrase activities were assayed. Quantitative real-time PCR was conducted for small intestinal mRNA expression of nutrient transporters [solute carrier family 2 member 5 (GLUT5), solute carrier family 2 member 2 (GLUT2), and solute carrier family 5 member 1 (SGLT1)], carbohydrases (lactase, maltase-glucoamylase, and sucrase-isomaltase), and ketohexokinase (KHK). Data were analyzed using MIXED procedures in SAS version 9.4 (SAS Institute Inc, Cary, NC). Dietary fructose supplementation decreased serum glucose concentration. Small intestinal mass was greater in calves supplemented with fructose. Dietary fructose supplementation did not influence pancreatic α-amylase, small intestinal isomaltase, or maltase activities. Sucrase activity was undetected in the small intestine. Dietary fructose supplementation increased small intestinal glucoamylase activity per gram of tissue by 30% and increased maltase-glucoamylase mRNA expression by 6.8-fold. Dietary fructose supplementation did not influence mRNA expression of GLUT5, SGLT1, GLUT2, or KHK. Dietary fructose supplementation increased small intestinal lactase mRNA expression by 3.1-fold. Sucrase-isomaltase mRNA expression in the small intestine decreased 5.1-fold with dietary fructose supplementation. Dietary fructose supplementation does not induce sucrase activity in neonatal calves; however, sucrase-isomaltase may be transcriptionally regulated by dietary fructose in neonatal calves. More research is needed to compare glucose and fructose at isocaloric intakes to examine effects of dietary fructose at equal metabolizable energy intake.

MiR-26a and miR-26b downregulate the expression of sucrase-isomaltase enzyme: A new chapter in diabetes treatment

Type II diabetes is a metabolic disease that has affected 460 million people around the globe and become a heavy burden on health care system. Diabetic patients suffer from hyperglycemia and hyperinsulinemia which can damage vital organs in body like heart, kidneys, eyes and nervous system. Different strategies have been introduced to control or lessen these diabetic complications in which one of the most promising approaches is the inhibition of intestinal sucrase-isomaltase (SI). Inhibition of this enzyme will block the release of glucose into bloodstream and lead to reduced postprandial hyperglycemia. MicroRNAs are small regulatory molecules that play critical roles in different cellular pathways and molecular mechanisms. It is proved that microRNAs have significant effects on cellular mechanisms involved in diabetes and can be used as biomarkers for diagnosis of this metabolic disease. Based on bioinformatics analysis miR-26a and miR-26b can interact with a conserved 3′-UTR region of SI mRNA which lead to a hypothesis that these miRs may have negative regulatory effect on this enzyme. In this study, we investigated the impact of high glucose conditions on expression of sucrase-isomaltase, miR-26a and miR-26b in caco-2 cell line. It is proved that in a simulated diabetic condition there is a reverse correlation between the expression pattern of these miRs and SI. QRT-PCR method was used to evaluate the expression of our target molecules. Interestingly, transfection of miR-26a and miR-26b in caco-2 cell line reduced the transcription of SI mRNA and decreased the sucrase and maltase activity of its active sites. To sum up, our results demonstrate the first evidence of the significant effect of miR-26a and miR-26b on SI expression and activity. We proved that these microRNAs may directly inhibit this enzyme and can be used as a new scaffold in search of finding novel treatments for type II diabetes.

Indirect Chronic Effects of an Oleuropein-Rich Olive Leaf Extract on Sucrase-Isomaltase In Vitro and In Vivo.

Consumption of dietary bioactives is an avenue to enhancing the effective healthiness of diets by attenuating the glycaemic response. The intestinal brush border enzyme sucrase-isomaltase (SI) is the sole enzyme hydrolysing consumed sucrose, and we previously showed the acute effects of olive leaf extract (OLE) on sucrase activity when given together with sugars both in vitro and in vivo. Here we tested whether OLE could affect sucrase expression when pre-incubated chronically, a “priming” effect not dependent on competitive interaction with SI, in both a cell model and a human intervention. Using differentiated Caco-2/TC7 cells, long-term pre-treatment with oleuropein-rich olive leaf extract (OLE) lowered SI mRNA, surface protein and activity, and attenuated subsequent sucrose hydrolysis. Based on these results, a randomised, double-blinded, placebo-controlled, crossover pilot study was conducted. OLE (50 mg oleuropein) was consumed in capsule form 3 times a day for 1 week by 11 healthy young women followed by an oral sucrose tolerance test in the absence of OLE. However this treatment, compared to placebo, did not induce a change in post-prandial blood glucose maximum concentration (Glcmax), time to reach Glcmax and incremental area under the curve. These results indicate that changes in SI mRNA, protein and activity in an intestinal cell model by OLE are not sufficient under these conditions to induce a functional effect in vivo in healthy volunteers.

The Induction of Histone H3K4 Methylation on the SI Gene Correlates with SI mRNA Levels in Enterocyte-Like Caco-2 Cells

Background: Chromodomain-helicase-DNA-binding protein (CHD) 1 is Histone H3 lysine 4 (K4) methylation is thought to be important for the transcriptional activation of genes during differentiation. Methods: mRNA and histone modification around SI gene in a small intestinal cell line Caco-2 during the differentiation were determined by qRT-PCR and Chromatin immunoprecipitation assay, respectively. Results: Mono-, di- and tri-methylation of histone H3 K4 on the sucrase-isomaltase (SI) gene was associated with the induction of SI gene expression, RNA polymerase II binding and histones H3 and H4 acetylation close to the transcription initiation site during enterocyte-like differentiation in Caco-2 cells. Mono-methylation was prominent in the promoter/enhancer region, di-methylation was observed from the promoter/enhancer throughout the transcribed portion of the gene and tri-methylation was identified from the transcription initiation site throughout the transcribed region. Conclusions: Histone H3 K4 methylation is involved in SI gene induction during differentiation in Caco-2 cells, and that the induced mono-, di- and tri-methylation of histone H3 K4 in different regions of the SI gene may play different roles in SI gene induction.

Phenolic compounds increase the transcription of mouse intestinal maltase-glucoamylase and sucrase-isomaltase.

Diverse natural phenolic compounds show inhibition activity of intestinal α-glucosidases, which may constitute the molecular basis for their ability to control systemic glycemia. Additionally, phenolics can modify mRNA expression for proteins involved in nutritional, metabolic or immune processes. To explore the possibility that phenolics can regulate the mRNA expression, enzymatic activity, and protein synthesis/processing of intestinal Maltase-Glucoamylase (MGAM) and Sucrase-Isomaltase (SI), small intestinal explants from Balb/c mice were cultured for 24 h in the presence or absence of gallic acid, caffeic acid, and (+)-catechin at 0.1, 0.5, and 1 mM. We measured the levels of MGAM and SI mRNA expression by qRT-PCR, maltase and sucrase activities by a standard colorimetric method and the molecular size distribution of MGAM and SI proteins by western blotting. mRNA expression for MGAM was induced by the three phenolic compounds at 0.1 mM. mRNA expression for SI was induced by caffeic and gallic acids, but not by (+)-catechin. Caffeic acid was the most effective inducer of mRNA expression of these enzymes. Total maltase and sucrase activities were not affected by treatment with phenolics. The proportion of high molecular size forms of MGAM was significantly increased by two of the three phenolic compounds, but little effect was observed on SI proteins. Thus, changes in the protein synthesis/processing, affecting the proportions of the different molecular forms of MGAM, may account for the lack of correlation between mRNA expression and enzymatic activity.

Differential transcriptional responses underlie dietary induction of intestinal carbohydrase activities in house sparrow nestlings.

Many species show diet-induced flexibility of activity of intestinal enzymes; however, molecular and genetic mechanisms responsible for such modulation are less known, particularly in altricial birds. The goal of our study was to test whether a diet-induced increase in activity of intestinal maltase and sucrase in house sparrow nestlings is matched with an increase in maltase-glucoamylase (MG) and sucrase-isomaltase (SI) complex mRNAs respectively. Both enzyme activities were significantly higher in mid-intestine of nestlings fed a medium-starch (MS) diet compared to those fed a starch-free (SF) diet. In contrast to the similar pattern of dietary induction for both enzyme activities, diet MS elevated significantly only the level of MG mRNA, but not SI mRNA. The coordinated increase in activity of maltase and in MG mRNA is consistent with the hypothesis that dietary induction of this enzyme is under transcriptional control. In contrast, the lack of such coordination for changes in activity of sucrase and SI mRNA suggests that upregulation of this enzyme may be achieved by post-translational factor(s). We conclude that genetic mechanisms responsible for diet-induced flexibility of digestive enzymes in birds may differ from that observed in mammals.

Protein Synthesis Controls the Activity of Maltase‐Glucoamylase and Sucrase‐Isomaltase in non‐intestinal Tissues

Maltase‐Glucoamylase (MGAM) and Sucrase‐Isomaltase (SI) are α‐glucosidases of the membrane of small intestinal enterocytes responsible for the digestion of dietary carbohydrates into glucose and other monosaccharides. MGAM and SI mRNA expression, protein synthesis and catalytic activity of MGAM and SI are found predominantly in enterocytes; however, they are also found in lower amounts in other non‐intestinal tissues, notably blood leukocytes and kidney cells. Little information exists on the functions, the mRNA expression, the nature of the respective proteins and catalytic properties of MGAM and SI in non‐intestinal tissues. To correlate the transcription, synthesis and activity of these enzymes, we measured the mRNA expression of MGAM and SI; the catalytic activities of maltase, sucrase, and isomaltase; and the presence of the respective proteins in small intestine and other tissues such as spleen, kidney and pancreas of 8 weeks old mice. Small intestine showed the highest level of mRNA expression of MGAM and SI, as well as their typical WB pattern and catalytic activity. Blood, kidney, and spleen displayed substantial amount of mRNA expression particularly for MGAM, but lower than small intestine. The variable proportions of maltase/sucrase and sucrase/isomaltase enzyme activities and the WB protein bands, indicated differences in the protein synthesis and processing among different tissues. We conclude that mRNA expression and the corresponding protein translation control the activities of MGAM and SI among tissues.

Fibroblast Growth Factor Receptor-3 (FGFR-3) Regulates Expression of Paneth Cell Lineage-specific Genes in Intestinal Epithelial Cells through both TCF4/β-Catenin-dependent and -independent Signaling Pathways

Fibroblast growth factor receptor-3 (FGFR-3) expression in the developing intestine is restricted to the undifferentiated epithelial cells within the lower portion of the crypt. We previously showed that mice lacking functional FGFR-3 have a significant decrease in the number of Paneth cells in the small intestine. Here, we used Caco2 cells to investigate whether FGFR-3 signaling can directly modulate expression of Paneth cell differentiation markers through its effects on TCF4/β-catenin or through other signaling pathways downstream of this receptor. Caco2 cells treated with FGFR-3 ligands or expressing FGFR-3(K650E), a constitutively active mutant, resulted in a significantly increased expression of genes characteristic of mature Paneth cells, including human α-defensins 5 and 6 (HD5 and HD6) and Paneth cell lysozyme, whereas enterocytic differentiation markers were reduced. Activation of FGFR-3 signaling sustained high levels of β-catenin mRNA expression, leading to increased TCF4/β-catenin-regulated transcriptional activity in Caco2 cells. Sustained activity of the TCF4/β-catenin pathway was required for the induction of Paneth cell markers. Activation of the MAPK pathway by FGFR-3 is also required for the induction of Paneth cell markers in addition to and independent of the effect of FGFR-3 on TCF4/β-catenin activity. These studies suggest that coordinate activation of multiple independent signaling pathways downstream of FGFR-3 is involved in regulation of Paneth cell differentiation.

Acute induction of histone acetylation on the jejunal sucrase–isomaltase gene by dietary fructose

We have previously reported that dietary fructose rapidly induces jejunal sucrase–isomaltase (SI) gene expression in rats. In this study, we confirmed in mice that SI mRNA was induced 6 h after force-feeding fructose, but not glucose. Using the chromatin immunoprecipitation assay, we revealed that histones H3 and H4 on the promoter/enhancer regions of the SI gene in mice given fructose were highly acetylated, compared with those given glucose or water. These results suggest that acute induction of SI gene expression by dietary fructose is associated with acetylation of histones H3 and H4 on the SI gene.

Dietary Sucrose Enhances Intestinal Lactase Gene Expression in Euthyroid Rats

It is postulated that dietary carbohydrates and thyroid hormones are major regulators for expression of the lactase/phlorizin hydrolase (LPH) gene in rat jejunum. In this study, we investigated the effects of thyroid hormones and dietary sucrose on LPH gene expression and lactase activity in starved rats. Firstly, animals at 8 wk of age were fed a low-starch diet (5.5% energy as cornstarch) or high-starch diet (71% energy as cornstarch) for 7 d (experiment 1). The mRNA level of LPH as well as lactase activity significantly decreased in rats fed the low-starch diet as compared to those fed the high-starch diet. To investigate the effects of thyroid hormone status, the animals previously fed the low-starch diet were starved for 3 d, and half of the animals were given intraperitoneal (i.p.) injections of 20 microg/ 100 g body weight triiodothyronine (T3) twice daily (experiment 2). The LPH mRNA level and lactase activity were elevated by starvation for 3 d, but they were repressed by the injection of T3 during starvation. To investigate the effects of dietary sucrose in starved rats, they were force-fed a sucrose diet for 6 h (experiment 3). The LPH gene expression and lactase activity were up-regulated by force-feeding a sucrose diet, only when the animals were kept in euthyroid status by daily T3 administrations. In contrast, the sucrase-isomaltase mRNA levels and sucrase activity were unaffected by force-feeding the sucrose diet for both T3-treated and untreated starved rats. Our work suggests that dietary sucrose is capable of enhancing lactase gene expression in starved rats when they have a sustainable thyroid hormone level.

Hepatocyte nuclear factor-1α is required for expression but dispensable for histone acetylation of the lactase-phlorizin hydrolase gene in vivo

Hepatocyte nuclear factor-1alpha (HNF-1alpha) is a modified homeodomain-containing transcription factor that has been implicated in the regulation of intestinal genes. To define the importance and underlying mechanism of HNF-1alpha for the regulation of intestinal gene expression in vivo, we analyzed the expression of the intestinal differentiation markers and putative HNF-1alpha targets lactase-phlorizin hydrolase (LPH) and sucrase-isomaltase (SI) in hnf1alpha null mice. We found that in adult jejunum, LPH mRNA in hnf1alpha(-/-) mice was reduced 95% compared with wild-type controls (P < 0.01, n = 4), whereas SI mRNA was virtually identical to that in wild-type mice. Furthermore, SI mRNA abundance was unchanged in the absence of HNF-1alpha along the length of the adult mouse small intestine as well as in newborn jejunum. We found that HNF-1alpha occupies the promoters of both the LPH and SI genes in vivo. However, in contrast to liver and pancreas, where HNF-1alpha regulates target genes by recruitment of histone acetyl transferase activity to the promoter, the histone acetylation state of the LPH and SI promoters was not affected by the presence or absence of HNF-1alpha. Finally, we showed that a subset of hypothesized intestinal target genes is regulated by HNF-1alpha in vivo and that this regulation occurs in a defined tissue-specific and developmental context. These data indicate that HNF-1alpha is an activator of a subset of intestinal genes and induces these genes through an alternative mechanism in which it is dispensable for chromatin remodeling.

Ontogeny of brush border carbohydrate digestion and uptake in the chick.

Ingestion of carbohydrates from the small intestine is the major route of energy supply in animals. In mammals these functions develop both pre- and postnatally and are coordinated for the sucking period. In birds, the physiological requirements are different and hatchlings ingest diets rich in complex carbohydrates soon after hatching. The present study examined the ontogeny of intestinal carbohydrate uptake in the chicken. The expression of mRNA for a brush border enzyme, sucrase-isomaltase (SI), which is critical in disaccharide digestion, was determined, together with that of the Na-glucose transporter (SGLT)-1, which is the major apical glucose transporter, In addition, the homeobox gene cdx, which is involved in inducing SI expression in mammals was examined. It was found that the expression of cdxA mRNA and cdxA protein increased from day 15 of incubation until hatch, after which further changes were small. CdxA protein was shown to bind to the promoter region of SI in the chick indicating that cdxA is similar to the mammalian cdx2. The mRNA of SI was observed at 15 d incubation, increased from 17 d of incubation to a peak on day 19, decreased at hatch and had a further peak of expression 2 d post-hatch. In contrast, the mRNA of SGLT-1 was not detected until 19 d of incubation when a major peak of expression was observed followed by a decrease to low levels at hatch and small increases post-hatch. It appears that both SI and SGLT-1 mRNA are expressed before hatch in the chick, but the ontogeny of expression is controlled by different mechanisms.

MRNA localization in polarized intestinal epithelial cells.

An important feature of enterocyte maturation is the asymmetrical distribution of cellular functions including protein localization. mRNA sorting is one mechanism for establishment and maintenance of this process in other systems, and we have previously demonstrated differential localization of mRNAs in human enterocytes. To study regulation of mRNA sorting, we established a model in polarized Caco-2 cells. Proxy cDNA constructs containing beta-galactosidase (beta-gal)/green fluorescence protein (GFP) and the 3'-untranslated region (3'-UTR) of either human sucrase-isomaltase or villin were transfected transiently or stably. A control construct contained poly-A sequence in place of 3'-UTR. Expression of GFP was observed by confocal microscopy; intracellular location of the construct mRNA was imaged by in situ hybridization. The sucrase-isomaltase mRNA proxy localized to an apical position in Caco-2 cells as in native enterocytes; the villin mRNA proxy did not show significant localization. The control construct was not localized and was found diffusely throughout the cell. Proxy GFP proteins tended to localize with their mRNA proxies, but with less precision. This study establishes a valuable model for the investigation of mRNA localization in intestinal epithelial cells. Mechanisms controlling asymmetrical distribution of intestinal mRNAs can be now be elucidated.

Glucagon-like peptide 2 enhances maltase-glucoamylase and sucrase-isomaltase gene expression and activity in parenterally fed premature neonatal piglets.

Exogenous glucagon-like peptide 2 (GLP-2) mimics the stimulatory effect of enteral nutrition on intestinal mucosal growth in preterm neonatal pigs. Little is known about its effects on small intestinal function. In this study, we investigated whether the trophic actions of GLP-2 and enteral nutrition are paralleled by effects on small intestinal function. Cesarean-delivered piglets (92% of gestation) were given either a parenteral nutrient infusion [total parenteral nutrition (TPN), n = 7], TPN + human GLP-2 (25 nmol/kg/d, n = 8), or enteral nutrition (ENT, n = 6) for 6 d. Gene expression (mRNA) and activities of lactase phlorizin hydrolase (LPH), maltase-glucoamylase (MGA), sucrase-isomaltase (SI), aminopeptidase N (ApN), and A (ApA) and dipeptidyl peptidase IV (DPP IV) were measured. Both GLP-2 and enteral nutrition increased mucosal weight (+30-40%, p < 0.05) relative to TPN. GLP-2 stimulated jejunal MGA and SI mRNA abundance and activity levels but did not change LPH in parenterally fed pigs (p < 0.05). Enteral nutrition decreased jejunal LPH and MGA mRNA abundance and activity and increased ileal ApN, ApA, and DPP IV activities relative to TPN (p < 0.05). We conclude that GLP-2 and enteral nutrition exert different effects on intestinal enzyme function despite similar effects on intestinal growth. In addition, the effects of GLP-2 on intestinal function in these parenterally fed, premature neonatal pigs differed from those previously reported for similarly fed term neonates.

Glucagon-Like Peptide 2 Enhances Maltase-Glucoamylase and Sucrase-Isomaltase Gene Expression and Activity in Parenterally Fed Premature Neonatal Piglets

Exogenous glucagon-like peptide 2 (GLP-2) mimics the stimulatory effect of enteral nutrition on intestinal mucosal growth in preterm neonatal pigs. Little is known about its effects on small intestinal function. In this study, we investigated whether the trophic actions of GLP-2 and enteral nutrition are paralleled by effects on small intestinal function. Cesarean-delivered piglets (92% of gestation) were given either a parenteral nutrient infusion [total parenteral nutrition (TPN), n = 7], TPN + human GLP-2 (25 nmol/kg/d, n = 8), or enteral nutrition (ENT, n = 6) for 6 d. Gene expression (mRNA) and activities of lactase phlorizin hydrolase (LPH), maltase-glucoamylase (MGA), sucrase-isomaltase (SI), aminopeptidase N (ApN), and A (ApA) and dipeptidyl peptidase IV (DPP IV) were measured. Both GLP-2 and enteral nutrition increased mucosal weight (+30–40%, p < 0.05) relative to TPN. GLP-2 stimulated jejunal MGA and SI mRNA abundance and activity levels but did not change LPH in parenterally fed pigs (p < 0.05). Enteral nutrition decreased jejunal LPH and MGA mRNA abundance and activity and increased ileal ApN, ApA, and DPP IV activities relative to TPN (p < 0.05). We conclude that GLP-2 and enteral nutrition exert different effects on intestinal enzyme function despite similar effects on intestinal growth. In addition, the effects of GLP-2 on intestinal function in these parenterally fed, premature neonatal pigs differed from those previously reported for similarly fed term neonates.

A novel colonic repressor element regulates intestinal gene expression by interacting with Cux/CDP.

Intestinal gene regulation involves mechanisms that direct temporal expression along the vertical and horizontal axes of the alimentary tract. Sucrase-isomaltase (SI), the product of an enterocyte-specific gene, exhibits a complex pattern of expression. Generation of transgenic mice with a mutated SI transgene showed involvement of an overlapping CDP (CCAAT displacement protein)-GATA element in colonic repression of SI throughout postnatal intestinal development. We define this element as CRESIP (colon-repressive element of the SI promoter). Cux/CDP interacts with SI and represses SI promoter activity in a CRESIP-dependent manner. Cux/CDP homozygous mutant mice displayed increased expression of SI mRNA during early postnatal development. Our results demonstrate that an intestinal gene can be repressed in the distal gut and identify Cux/CDP as a regulator of this repression during development.

Development of glucocorticoid-responsiveness in mouse intestine.

There are conflicting data from human studies regarding the ability of exogenous glucocorticoids to stimulate maturation of the small intestine. The discrepancies may relate to differences in hormone doses and age administered. To explore this general concept, we have used a mouse model to determine intestinal responsiveness to dexamethasone (DEX) at various times during development. We first showed that trehalase mRNA is a sensitive marker of intestinal maturation in the mouse; being undetectable (by Northern blotting) in the prenatal period, expressed at low levels during the first 2 postnatal weeks and then displaying a marked increase in the 3rd postnatal week. DEX was unable to elicit detectable trehalase mRNA in fetal mice, but caused significant increases in the postnatal period. The use of a range of DEX doses (0.0125-2.5 nmol/g BW per day) established that there is no change in sensitivity between the 1st and 2nd postnatal weeks, but there is a significant increase in maximal responsiveness of trehalase mRNA to the hormone. Similar results were obtained when sucrase-isomaltase mRNA was assayed in the same animals. Thus, in this rodent model, there appears to be at least three phases in the DEX responsiveness of the developing intestine: an early phase (prenatal) when DEX is unable to elicit intestinal maturation; then a phase (first postnatal week) of modest responsiveness; then a transition to increased responsiveness. These findings point to the need for careful attention to dose and age in analyses of glucocorticoid effects in human infants.

Regulation of the expression of carbohydrate digestion/absorption-related genes.

To explore the underlying molecular mechanism whereby nutrients modulate the expression of intestinal digestion/absorption-related genes, we have cloned the 5' flanking regions of two representing disaccharidase genes, i.e. sucrase-isomaltase (SI) and lactase-phlorizin hydrolase (LPH), and investigated whether the binding activity of putative common nuclear factor(s) binding to the cis-elements located in these regions is altered by dietary manipulations. Oro-gastric feeding of a sucrose-containing diet to rats caused parallel increases in SI mRNA and LPH mRNA levels within 3 h. Among the monosaccharides tested, fructose gave rise to the most prominent increase in the mRNA levels of SI and LPH genes, which were accompanied by a coordinate rise in the mRNA levels of two microvillar hexose transporters, i.e. SGLT1 and GLUT5. Nuclear run-on assays revealed that fructose, but not glucose, increased the transcription of SI, LPH and GLUT5. DNase I footprinting analysis of the rat LPH gene showed that the protected region conserved the same sequence as the cis-element (CE-LPH1) reported in the pig LPH gene. Electrophoretic mobility shift assay using CE-LPH1 and the related cis-element of SI gene (SIF1) revealed that nuclear extracts from the jejunum of rats fed the high-starch diet gave greater density of retarded bands than those of rats fed the low-starch diet. Force feeding a fructose diet gave rise to an increase in the binding of the dimeric nuclear protein (Cdx-2) to the SIF1 element. These results suggest that the cis-elements of CE-LPH1 and SIF1 might be involved in the carbohydrate-induced increases of the transcription of LPH and SI, presumably through a change in the expression and/or binding activity of Cdx-2.

Cytokine gene expression during postnatal small intestinal development: regulation by glucocorticoids

BACKGROUNDIn the intestinal mucosa, numerous cytokines produced by the epithelium, fibroblasts, and immune cells were shown to affect epithelial differentiation and proliferation through epithelial-mesenchymal and epithelial-immune cell interactions. To date,...