Intestinal Epithelial Cell Turnover Research Articles

Acute epithelial injury in the rat small intestine in vivo is associated with expanded expression of transforming growth factor alpha and beta.

Previous studies have shown the importance of transforming growth factors alpha and beta (TGF alpha and TGF beta) in modulating epithelial cell restitution after injury in vitro. To investigate the role of the growth factors TGF alpha and TGF beta after acute epithelial injury in vivo. An in vivo model of phytohaemagglutinin (PHA) induced acute epithelial injury in rat small intestine was used. Epithelial cell turnover was assessed by autoradiography and liquid scintillation counting of thymidine uptake. Expression of TGF alpha and TGF beta was assessed by immunohistochemistry. An expansion of the proliferative compartment and increased turnover of intestinal epithelial cells was seen in rats with PHA induced intestinal epithelial injury. Expression of TGF alpha and TGF beta peptides was shown in both the epithelial cell and lamina propria compartment. Different patterns of TGF alpha and TGF beta expression were seen, however, within the epithelium of rats with acute intestinal injury compared with untreated controls, while the expression of these peptides within the lamina propria was not changed. These findings suggest that acute intestinal epithelial cell injury in vivo is associated with compensatory changes in expression of TGF alpha and TGF beta in the epithelial cell compartment, while the lamina propria does not seem to be significantly affected.

Exogenous Nucleotides Alter the Proliferation, Differentiation and Apoptosis of Human Small Intestinal Epithelium

The turnover of intestinal epithelial cells is a finely regulated process extending from undifferentiated crypt stem cells to terminally differentiated villus cells. The final phase of this maturation process is apoptosis and extrusion. Recent studies have shown that programmed cell death (PCD) occurs not only in senescent cells and in rapidly developing tissues but also in response to cellular stress preventing damaged cells from entering uncontrolled proliferation without repair. This study examined the role of exogenous nucleotides on cell proliferation, differentiation and apoptosis in organ cultures of human fetal small intestine. The addition of adenosine monophosphate (AMP), a putative stress reactant, to the culture media resulted in the suppression of crypt cell proliferation followed by the restoration of differentiation and the induction of apoptosis across a broad range of villus epithelium when compared with controls without added nucleotide. In contrast, the addition to cytidine monophosphate (CMP) to the culture media did not increase apoptosis, despite the nucleotide being taken up by the fetal small intestine in a similar dose- and time-dependent manner to AMP. Furthermore, Bax mRNA, an apoptosis-inducer gene, was increased with addition of AMP, suggesting that the induction of apoptosis may be channeled through the p53 pathway. These results suggest that a specific exogenous nucleotide, AMP, may have an important role in controlling the dynamic balance of cellular turnover in the developing human small intestine.

Regulation of intestinal epithelial proliferation: a few answers, many questions

The epithelium of the gastrointestinal tract mucosa is a highly dynamic and diverse mixture of cell populations requiring exquisite integration of the processes of cellular proliferation, differentiation, and senescence. It is likely that the proliferative compartment of the intestinal epithelium encompasses a hierarchy of totipotent and pluripotent stem cells in a manner similar to that which generates diversity in hematopoietic cell populations. Identification and characterization of the stem cell and progenitor populations in the intestine has been limited by the absence of markers or culture systems to identify these cells. Regulation of the proliferative compartment may be accomplished through the combined integration of key peptide growth factors and constituents of the extracellular matrix. The relative contribution of the epithelial populations themselves and the contributions made by associated cell populations such as pericryptal fibroblasts remain unclear. Recent studies have suggested that the transforming growth factors-alpha and -beta, two structurally unrelated peptide growth factors, might serve to regulate the balanced proliferation and turnover of intestinal epithelial cells. The proproliferative effects of TGF-alpha may be counterbalanced by the proliferation-inhibiting TGF-beta. Recent studies have demonstrated close interregulation of these peptides, which act through autocrine and paracrine mechanisms in model intestinal epithelial cell lines.

Effects of epidermal growth factor on diamine oxidase expression and cell growth in Caco-2 cells

To investigate the role of diamine oxidase (DAO) in the intestinal mucosa, we compared its expression with cell proliferation and differentiation in the human colon carcinoma cell line Caco-2. DAO synthesis was evaluated in subconfluent and confluent cultures and in the presence of epidermal growth factor (EGF), a polypeptide hormone known to have specific trophic effects on the small intestinal mucosa. EGF stimulated DNA synthesis, significantly increased cellular DAO activity and the amount of enzyme secreted into the culture medium, but decreased expression of dipeptidyl peptidase IV, a marker of cell differentiation in confluent Caco-2 cells. Immunoprecipitation of DAO from cells labeled metabolically with [35S]methionine failed to demonstrate an increased enzyme synthesis in EGF-treated cells, suggesting that this hormone acted primarily at a posttranslational level by reducing DAO degradation before intracellular storage or secretion. A possible relationship between changes in cellular DAO activity and cell proliferation was also investigated by using aminoguanidine, a specific and potent DAO inhibitor. Although DAO activity was markedly suppressed, aminoguanidine had no significant effects on the rate of DNA synthesis. These results demonstrated that in Caco-2 cells EGF stimulated DNA synthesis and DAO expression; however, cell proliferation and differentiation were not correlated with the levels of cellular DAO, suggesting that this enzyme does not play a major role in the regulation of intestinal epithelial cell turnover.

Quantitative study of apoptosis in normal rat gastroduodenal mucosa

The occurrence of apoptosis in the normal gastrointestinal mucosa has been given little consideration until now, although the phenomenon may be of interest in the light of recent hypotheses about its role in physiological cell renewal. In the present study, a quantitative evaluation conducted on normal gastric and duodenal mucosa of young rats has shown that apoptosis is a rare but constant phenomenon: 1.4 +/- 1.1 (mean +/- 1 s.d.) apoptotic bodies were observed within the surface epithelium of single gastric pits and 3 +/- 1 in duodenal villi. In both situations, the apoptosis showed a preferential localization in the juxtaluminal segments of the epithelium. This phenomenon appears distinct from passive exfoliation of mucosal cells and, as an expression of 'programmed cell death', it is likely to contribute to the normal intestinal epithelial cell turnover.

A villous cell-derived inhibitor of intestinal cell proliferation.

To test the hypothesis that the intestinal villous cell synthesizes a mitotic inhibitor that is specific for crypt cells, we have partially purified an extract from rat intestinal villous cells (VCE) and have demonstrated that it strongly and reversibly inhibits cell division and DNA synthesis in an intestinal epithelial cell line (IEC-6 cells). VCE produced a 60--70% inhibition of [3H]thymidine incorporation into DNA and a similar magnitude of inhibition of labeling of nuclei in autoradiographic studies. This inhibition was not associated with cytotoxicity as assessed by the effect of VCE on 51Cr release, hexose or amino acid uptake, and protein synthesis. VCE appears specific for IEC-6 cells because it did not affect DNA synthesis in 10 other cell lines, and extracts derived from other cell lines and from colonic mucosa did not affect DNA synthesis in IEC-6 cells. VCE may represent a villous cell factor involved in the control of intestinal epithelial cell turnover in vivo.

Effects of hypoxia and fasting on the cytochrome concentration in intestinal epithelial villous cell mitochondria. Role of changes in the life-span of the cells.

The effects of hypoxia in vivo (40.8 kPa barometric pressure up to 120 h) and fasting on the characteristics of intestinal epithelial villous cell mitochondria and the turnover of epithelial villous cells and mitochondria were studied in rats. Using cells and mitochondria isolated in the isotonic mannitol medium, it was found that 24-h hypoxia or fasting did not alter the mitochondrial cytochrome content, but 48-h hypoxia or fasting led to increases of 70% and 37% in the cytochrome aa3 concentration in the hypoxic and fasting animals respectively. The turnover of intestinal epithelial cells was studied by observing the labelling kinetics of the cells with 3H-thymidine and the turnover of the cell and mitochondrial proteins with (guanido-14C)-arginine or 3H-leucine. The decay in thymidine radioactivity obeyed exponential kinetics from which half-lives of 1.15, 1.31 and 1.53 days were calculated in the control, fasting and hypoxic animals respectively. The half-lives for total cellular protein were 1.31, 1.54 and 1.54 days respectively when calculated from the (guanido-14C)-arginine experiments, or 0.69, 0.75 and 0.99 days when calculated from the leucine experiments. The labelling experiments with (guanido-14C)-arginine indicated that the turnover of mitochondrial proteins in intestinal epithelial cells is the same as that of the cells themselves. Since the turnover of mitochondrial proteins in other tissues is shown to be a relatively slow process, the increase in the cytochrome concentration in the intestinal cells of the hypoxic rats must be due to the longer life of the cells, which allows for the synthesis of larger amounts of the mitochondrial components.

Studies on the mechanism of action of calciferol: V. Turnover time of chick intestinal epithelial cells in relation to the intestinal action of vitamin D

Autoradiography following administration of 3H-thymidine, has been employed to study the total transit time of intestinal epithelial cells from (1) vitamin D deficient; (2) vitamin D replete; (3) normal chicks. The turnover time of ileal epithelial cells is 90–98 h for the three groups. Treatment with vitamin D for more than 110 h results in an increase in villus length so that the villus of normal chicks is 30% longer than that of vitamin D deficient chicks. Since the total transit times were only slightly different in these groups, the rates of migration are 7.0 × 10 −3 cm/h for the normal as compared with 5.9 × 10 −3 cm/h for vitamin D replete and 4.3 × 10 −3 in the vitamin D deficient groups. A comparison between the intestinal epithelial cell turnover time found in the present study and previous data concerning the time course of vitamin D mediated intestinal responses is compatible with the induction hypothesis for vitamin D action and implies that the active metabolite of vitamin D, 1,25-dihydroxyvitamin D, can exert its action only on cells well advanced in their migration up the villus.

Independence of intestinal epithelial cell turnover from cessation of absorption of macromolecules (closure) in the neonatal mouse, rabbit, hamster and guinea pig.

Independence of intestinal epithelial cell turnover from cessation of absorption of macromolecules (closure) in the neonatal mouse, rabbit, hamster and guinea pig.

Cell loss from small intestinal mucosa: a morphological study.

Large numbers of cells are shed from small intestinal mucosa but they are so rapidly destroyed that there is little direct information about their morphological types. Material obtained by washing the human and rat small intestine was immediately processed and examined by light and electron microscopy. Small intestinal epithelial cells could not be identified by light microscopy but were readily recognized-by the presence of brush borders-using the electron microscope. Eighty to 85% of the cells from both rats and patients with normal small intestinal mucosa were intestinal absorptive cells. This was also the case in four patients with the coeliac syndrome and flat intestinal mucosa. These findings provide further support for the view that measurements of cell loss using intestinal washing techniques and the DNA-loss method, reflect predominantly small intestinal epithelial cell loss and turnover.

Time Response of Jejunal Sucrose and Maltase Activity to a High Sucrose Diet in Normal Man

This study determined the time required for the adaptive changes in human jejunal sucrase and maltase activities when dietary carbohydrate was changed from glucose to sucrose, sucrose to carbohydrate-free, and glucose to fructose. Four volunteer subjects were studied. The time for the increases and decreases in activity was 2 to 5 days and there was no further change for 9 weeks thereafter. This time response is similar to the estimated time for intestinal epithelial cell turnover in the small intestine of man. It is proposed that the changes in disaccharidase activity produced by changes in dietary sugar content are due primarily to an effect on the crypt cell. The effect becomes increasingly manifest as these crypt cells divide and migrate up the villus.

Eimeria: Effect of meticlorpindol and methyl benzoquate on endogenous stages in the chicken

Meticlorpindol and methyl benzoquate had no action on the sporozoites of Eimeria brunetti in vitro. The drugs exert an inhibitory action on the sporozoites after invasion of the intestinal mucosa when the sporozoites have completed their migration. Some drug must be absorbed from the intestine since chicks treated with meticlorpindol in the food were protected from an infection induced via the blood-stream. The drugs may have an effect on later stages of the life cycle of some species of Eimeria, but not with others. Sporozoites of E. tenella, E. mivati and E. acervulina could develop even after treatment for 60 days with meticlorpindol, whereas other species ( E. maxima) did not develop after 21 days of exposure to the drug. Possible reasons for the differences in survival of sporozoites of different species are discussed in relation to the turnover of intestinal epithelial cells and to the role of macrophages in the transport of sporozoites within the intestinal tissues. Chickens treated with meticlorpindol for 70 days did not exhibit latent infection after drug withdrawal, but were susceptible to infection with species of Eimeria used initially. This indicates that the presence of inhibited sporozoites did not stimulate resistance to reinfection.