Developmental expression of trehalase: role of transcriptional activation

Mouse fetal intestinal organoids: new model to study epithelial maturation from suckling to weaning

During the suckling-to-weaning transition, the intestinal epithelium matures, allowing digestion of solid food. Transplantation experiments with rodent fetal epithelium into subcutaneous tissue of adult animals suggest that this transition is intrinsically programmed and occurs in the absence of dietary or hormonal signals. Here, we show that organoids derived from mouse primary fetal intestinal epithelial cells express markers of late fetal and neonatal development. In a stable culture medium, these fetal epithelium-derived organoids lose all markers of neonatal epithelium and start expressing hallmarks of adult epithelium in a time frame that mirrors epithelial maturation in vivo In vitro postnatal development of the fetal-derived organoids accelerates by dexamethasone, a drug used to accelerate intestinal maturation in vivo Together, our data show that organoids derived from fetal epithelium undergo suckling-to-weaning transition, that the speed of maturation can be modulated, and that fetal organoids can be used to model the molecular mechanisms of postnatal epithelial maturation.

Glucocorticoids alleviate intestinal ER stress by enhancing protein folding and degradation of misfolded proteins

Dexamethasone suppresses ER stress in inflammatory bowel disease by promoting correct protein folding and ER-associated degradation.

Endoplasmic reticulum (ER) stress in intestinal secretory cells has been linked with colitis in mice and inflammatory bowel disease (IBD). Endogenous intestinal glucocorticoids are important for homeostasis and glucocorticoid drugs are efficacious in IBD. In Winnie mice with intestinal ER stress caused by misfolding of the Muc2 mucin, the glucocorticoid dexamethasone (DEX) suppressed ER stress and activation of the unfolded protein response (UPR), substantially restoring goblet cell Muc2 production. In mice lacking inflammation, a glucocorticoid receptor antagonist increased ER stress, and DEX suppressed ER stress induced by the N-glycosylation inhibitor, tunicamycin (Tm). In cultured human intestinal secretory cells, in a glucocorticoid receptor-dependent manner, DEX suppressed ER stress and UPR activation induced by blocking N-glycosylation, reducing ER Ca²⁺ or depleting glucose. DEX up-regulated genes encoding chaperones and elements of ER-associated degradation (ERAD), including EDEM1. Silencing EDEM1 partially inhibited DEX’s suppression of misfolding-induced ER stress, showing that DEX enhances ERAD. DEX inhibited Tm-induced MUC2 precursor accumulation, promoted production of mature mucin, and restored ER exit and secretion of Winnie mutant recombinant Muc2 domains, consistent with enhanced protein folding. In IBD, glucocorticoids are likely to ameliorate ER stress by promoting correct folding of secreted proteins and enhancing removal of misfolded proteins from the ER.

Blimp1 regulates the transition of neonatal to adult intestinal epithelium

In many mammalian species, the intestinal epithelium undergoes major changes that allow a dietary transition from mother's milk to the adult diet at the end of the suckling period. These complex developmental changes are the result of a genetic programme intrinsic to the gut tube, but its regulators have not been identified. Here we show that transcriptional repressor B lymphocyte-induced maturation protein 1 (Blimp1) is highly expressed in the developing and postnatal intestinal epithelium until the suckling to weaning transition. Intestine-specific deletion of Blimp1 results in growth retardation and excessive neonatal mortality. Mutant mice lack all of the typical epithelial features of the suckling period and are born with features of an adult-like intestine. We conclude that the suckling to weaning transition is regulated by a single transcriptional repressor that delays epithelial maturation.

Nutritional programming of gastrointestinal tract development. Is the pig a good model for man?

The consequences of early-life nutritional programming in man and other mammalian species have been studied chiefly at the metabolic level. Very few studies, if any, have been performed in the gastrointestinal tract (GIT) as the target organ, but extensive GIT studies are needed since the GIT plays a key role in nutrient supply and has an impact on functions of the entire organism. The possible deleterious effects of nutritional programming at the metabolic level were discovered following epidemiological studies in human subjects, and confirmed in animal models. Investigating the impact of programming on GIT structure and function would need appropriate animal models due to ethical restrictions in the use of human subjects. The aim of the present review is to discuss the use of pigs as an animal model as a compromise between ethically acceptable animal studies and the requirement of data which can be interpolated to the human situation. In nutritional programming studies, rodents are the most frequently used model for man, but GIT development and digestive function in rodents are considerably different from those in man. In that aspect, the pig GIT is much closer to the human than that of rodents. The swine species is closely comparable with man in many nutritional and digestive aspects, and thus provides ample opportunity to be used in investigations on the consequences of nutritional programming for the GIT. In particular, the 'sow-piglets' dyad could be a useful tool to simulate the 'human mother-infant' dyad in studies which examine short-, middle- and long-term effects and is suggested as the reference model.

Regulation of Bcl-2 expression by HuR in HL60 leukemia cells and A431 carcinoma cells

Overexpression of the proto-oncogene bcl-2 promotes abnormal cell survival by inhibiting apoptosis. Expression of bcl-2 is determined, in part, by regulatory mechanisms that control the stability of bcl-2 mRNA. Elements in the 3'-untranslated region of bcl-2 mRNA have been shown to play a role in regulating the stability of the message. Previously, it was found that the RNA binding proteins nucleolin and Ebp1 have a role in stabilizing bcl-2 mRNA in HL60 cells. Here, we have identified HuR as a component of bcl-2 messenger ribonucleoprotein (mRNP) complexes. RNA coimmunoprecipitation assays showed that HuR binds to bcl-2 mRNA in vivo. We also observed an RNA-dependent coprecipitation of HuR and nucleolin, suggesting that the two proteins are present in common mRNP complexes. Moreover, nucleolin and HuR bind concurrently to bcl-2 AU-rich element (ARE) RNA in vitro, suggesting separate binding sites for these proteins on bcl-2 mRNA. Knockdown of HuR in A431 cells leads to down-regulation of bcl-2 mRNA and protein levels. Observation of a decreased ratio of bcl-2 mRNA to heterogeneous nuclear RNA in HuR knockdown cells confirmed a positive role for HuR in regulating bcl-2 stability. Recombinant HuR retards exosome-mediated decay of bcl-2 ARE RNA in extracts of HL60 cells. This supports a role for HuR in the regulation of bcl-2 mRNA stability in HL60 cells, as well as in A431 cells. Addition of nucleolin and HuR to HL60 cell extracts produced a synergistic protective effect on decay of bcl-2 ARE RNA. HuR knockdown also leads to redistribution of bcl-2 mRNA from polysomes to monosomes. Thus, HuR seems to play a positive role in both regulation of bcl-2 mRNA translation and mRNA stability.

Overexpression of nucleolin in chronic lymphocytic leukemia cells induces stabilization of bcl2 mRNA

B-cell chronic lymphocytic leukemia (CLL) is characterized by the accumulation of clonal B cells that are resistant to apoptosis as a result of bcl2 oncogene overexpression. Studies were done to determine the mechanism for the up-regulation of bcl-2 protein observed in CD19+ CLL cells compared with CD19+ B cells from healthy volunteers. The 11-fold higher level of bcl-2 protein in CLL cells was positively correlated with a 26-fold elevation in the cytosolic level of nucleolin, a bcl2 mRNA-stabilizing protein. Measurements of the bcl2 heterogeneous nuclear/bcl2 mRNA (hnRNA)/mRNA ratios and the rates of bcl2 mRNA decay in cell extracts indicated that the 3-fold higher steady-state level of bcl2 mRNA in CLL cells was the result of increased bcl2 mRNA stability. Nucleolin was present throughout the nucleus and cytoplasm of CLL cells, whereas in normal B cells nucleolin was only detected in the nucleus. The addition of recombinant human nucleolin to extracts of normal B cells markedly slowed the rate of bcl2 mRNA decay. SiRNA knockdown of nucleolin in MCF-7 cells resulted in decreased levels of bcl2mRNA and protein but no change in beta-actin. These results indicate that bcl-2 overexpression in CLL cells is related to stabilization of bcl2 mRNA by nucleolin.

Diverse patterns of cell-specific gene expression in response to glucocorticoid in the developing small intestine

Although glucocorticoids are known to elicit functional maturation of the gastrointestinal tract, the molecular mechanisms of glucocorticoid action on the developing intestine have not been fully elucidated. Our previous microarray studies identified 66 transcripts as being rapidly induced in the jejunum following dexamethasone (Dex) administration to suckling mice. Now we report the specific cellular location of a subset of these transcripts. Mouse pups at P8 received Dex or vehicle and intestinal segments were collected 3-4 h later. Robotic-based in situ hybridization (ISH) was performed with digoxygenin-labeled riboprobes. Transcripts studied included Ndrg1, Sgk1, Fos, and two unknown genes (Gene 9 and Gene 36). As predicted, ISH revealed marked diversity of cellular expression. In small intestinal segments, Sgk1 mRNA was in all epithelial cells; Fos mRNA was confined to epithelial cells at the villus tip; and Ndrg1 and Gene 36 mRNAs were localized to epithelial cells of the upper crypt and villus base. The remaining transcript (Gene 9) was induced modestly in villus stroma and strongly in the muscle layers. In the colon, Ndrg1, Sgk1, and Gene 36 were induced in all epithelial cells; Gene 9 was in muscle layers only; and Fos was not detectable. For jejunal segments, quantitation of ISH signals in tissue from Dex-treated and vehicle-treated mice demonstrated mRNA increases very similar to those measured by Northern blotting. We conclude that glucocorticoid action in the intestine reflects diverse molecular mechanisms operating in different cell types and that quantitative ISH is a valuable tool for studying hormone action in this tissue.

Epigenetic mechanisms and gastrointestinal development

This review considers the hypothesis that nutrition during infancy affects developmental epigenetics in the gut, causing metabolic imprinting of gastrointestinal (GI) structure and function. Fundamentals of epigenetic gene regulation are reviewed, with an emphasis on the epigenetic mechanism of DNA methylation. Recent data indicate that transient nutritional and other stimuli during critical periods of prenatal and early postnatal development can affect the establishment or developmental maturation of gene-specific DNA methylation, thereby inducing permanent changes in gene expression. Although epigenetic processes are clearly involved in postnatal mammalian GI development, we currently know very little about these mechanisms. Data indicating that epigenetic gene regulation plays an important role in GI development and pathology are reviewed, and suggestions for future research in this area are offered.

Immediate early genes of glucocorticoid action on the developing intestine

Prior studies have demonstrated that glucocorticoid hormones elicit functional maturation of the small intestine as evidenced by their ability to induce increases in the expression of various digestive hydrolases, such as sucrase-isomaltase and trehalase. However, these increases have a lag time of approximately 24 h, suggesting that they are secondary effects of hormone action. To identify candidate primary response genes, we performed microarray analysis on pooled RNA from jejunums of untreated postnatal day 8 mouse pups and from littermates who earlier received dexamethasone 2 h. Fluorescent dye-labeled samples were hybridized in quadruplicate to glass-spotted cDNA microarrays containing 15,000 cDNA clones from the National Institute of Aging cDNA clone set. Analysis of the resulting signals using relatively stringent criteria identified 66 transcripts upregulated and 36 downregulated by 2 h of glucocorticoid treatment. Among the upregulated transcripts, the magnitude of the increase detected by microarray ranged from 1.4- to 16-fold. Selected mRNAs from throughout the range were subsequently analyzed by Northern blot analysis. Of 11 mRNAs chosen all were confirmed, and there was a strong correlation between the magnitude of the increase observed from the microarray analysis and from Northern blot analysis. Additional time points showed that these transcripts peaked between 2 and 6 h and had returned to baseline by 24 h. Gene ontology analysis showed pleiotropic effects of dexamethasone on the developing intestine and pointed to genes in the development category as being likely candidates for mediation of glucocorticoid-induced maturation of intestinal function.

Rapid induction of GATA transcription factors in developing mouse intestine following glucocorticoid administration

In the developing intestine, transcription of alpha-glucosidase genes such as sucrase-isomaltase and trehalase is stimulated by glucocorticoid administration. The consequent increase of their respective mRNAs is characterized by a 12-h lag, suggesting that the response to glucocorticoids represents a secondary effect. We hypothesized that the primary response of the tissue to glucocorticoids includes induction of one or more intestinal transcription factors. To investigate this hypothesis, we identified a region in the mouse trehalase promoter (located at nucleotides -406 to -377 from the transcription start site) with potential binding sites for three transcription factors: Cdx-2, GATA, and C/EBP. Gel shifts were performed using labeled oligonucleotides from this region with nuclear extracts from jejunums of either control 8-day-old mouse pups or littermates treated with dexamethasone (DEX) 4 h before death. A specific shifted band was observed with DEX extracts but not with control extracts. Supershift assays indicated the presence of GATA-4 and GATA-6 but not GATA-5 nor Cdx-2, C/EBP alpha, C/EBP beta, or C/EBP delta. GATA binding was further implicated by competition studies with mutated oligonucleotides. Finally, Western blot analysis showed GATA-4 and GATA-6 proteins in DEX but not control nuclear extracts. For GATA-4, the same pattern was demonstrated with whole cell extracts and with the cytosol fraction. We conclude that expression of GATA-4 and GATA-6 proteins in the suckling mouse jejunum is stimulated by DEX. This novel finding constitutes an important first step in understanding the molecular mechanism of glucocorticoid action on the developing intestine.

Carbohydrate intolerance

PURPOSE OF REVIEW

The small intestinal mucosa is highly specialized for terminal digestion of nutrient polysaccharides and disaccharides and absorption of monosaccharides. However, in the case of digestive or absorptive deficiency, symptoms of carbohydrate intolerance result. Significant progress has been made toward defining the molecular genetic mechanisms responsible for several carbohydrate intolerances.

RECENT FINDINGS

This review summarizes monosaccharide and disaccharide intolerance conditions and recent clinical and basic science reports related to carbohydrate digestion and membrane transport. Genetic polymorphisms closely associated with lactase persistence/nonpersistence have been identified. Lactose intolerance is capable of preventing the achievement of adequate peak bone mass in susceptible young adults and may predispose to osteoporosis. Recent studies support previous reports that fructose malabsorption is associated with unexplained gastrointestinal symptoms. GLUT2 may be recruited from the basolateral to the apical membrane of enterocytes to facilitate small intestinal fructose absorption.

SUMMARY

Knowledge regarding the clinical aspects of and the physiologic mechanisms responsible for specific carbohydrate intolerances has allowed for improved diagnostic and treatment options and has contributed to continuing investigation of intestinal gene expression.

Development of the fetal intestine in mice lacking the glucocorticoid receptor (GR)

During rodent development there are two surges of circulating corticosterone: one just prior to birth and then one in the third postnatal week. Prior studies have shown that the latter controls the rate of intestinal development in the postnatal period. To date, a role for the earlier surge in the prenatal phase of intestinal development has not been investigated. We hypothesized that the late fetal surge of circulating corticosterone is involved in both morphologic and functional maturation of the intestinal epithelium, and thus that such maturation would be delayed if glucocorticoid action was abrogated. The hypothesis was tested by studying intestinal development in mice lacking a functional glucocorticoid receptor (GR). After GR+/- mice were bred onto a C57Bl/6 background, heterozygote matings yielded the expected ratios of -/-, +/-, and +/+ offspring. Analysis of GR mRNA in intestines of +/+ and -/- fetuses confirmed expression in wild-type mice but not in the GR-null mice. Intestinal histology of GR+/+ and -/- littermates at E13.5, E15.5, and E18.5 showed no effect of GR genotype on morphologic development. Further studies at E18.5 showed that GR-/- mice have normal functional maturation of the intestinal epithelium as assessed by: lactase activity in the enterocyte lineage, normal numbers of goblet and enteroendocrine cells, and normal numbers of proliferating cells in the intestinal crypts. Neither the minerolocorticoid receptor (MR) nor the pregnane X receptor (PXR) showed compensatory up-regulation in GR-/- mice. We conclude that, in contrast to our original hypothesis, the rodent intestine passes through a phase of glucocorticoid independence (late fetal) prior to becoming responsive to glucocorticoids in the postnatal period. These findings have implications for the clinical use of corticosteroids to enhance intestinal maturation in preterm infants.