Proliferation, differentiation and morphogenesis of fetal rat glandular stomach transplanted under the kidney capsule of syngeneic hosts

Endogenous glucocorticoids prevent gastric metaplasia by suppressing spontaneous inflammation

In the stomach, chronic inflammation causes metaplasia and creates a favorable environment for the evolution of gastric cancer. Glucocorticoids are steroid hormones that repress proinflammatory stimuli, but their role in the stomach is unknown. In this study, we show that endogenous glucocorticoids are required to maintain gastric homeostasis. Removal of circulating glucocorticoids in mice by adrenalectomy resulted in the rapid onset of spontaneous gastric inflammation, oxyntic atrophy, and spasmolytic polypeptide-expressing metaplasia (SPEM), a putative precursor of gastric cancer. SPEM and oxyntic atrophy occurred independently of lymphocytes. However, depletion of monocytes and macrophages by clodronate treatment or inhibition of gastric monocyte infiltration using the Cx3cr1 knockout mouse model prevented SPEM development. Our results highlight the requirement for endogenous glucocorticoid signaling within the stomach to prevent spontaneous gastric inflammation and metaplasia, and suggest that glucocorticoid deficiency may lead to gastric cancer development.

Runx3 controls growth and differentiation of gastric epithelial cells in mammals

Runx3 is a transcription factor expressed by gastric epithelial cells. In the Runx3(-/-) mouse, gastric epithelia exhibited hyperplasia, and epithelial apoptosis was suppressed. By analyzing growth of the epithelial cells in primary culture, we found that Runx3(-/-) gastric epithelial cells are less sensitive to the growth-inhibitory and apoptosis-inducing activities of TGF-beta, suggesting that Runx3 is a major growth regulator of gastric epithelial cells by regulating their response to TGF-beta. We also found that Runx3 plays an important role in the control of gastric epithelial differentiation. When subcutaneously implanted into nude mice, Runx3(-/-) gastric epithelial cells formed tumors in which some cells differentiated into intestinal-type cells. Clonal analysis showed that gastric epithelial cells transdifferentiate into intestinal-type cells in the tumor. Considering that gastric epithelial differentiation is very stable, and that intestinal-type cells never differentiate in the mouse stomach, it is remarkable that gastric epithelial cells transdifferentiate into intestinal-type cells. We conclude that Runx3 is deeply involved in the control of both growth and differentiation of gastric epithelial cells. The role of Runx3 in the specification of gastric epithelial cells is discussed.

Runx3-/- gastric epithelial cells differentiate into intestinal type cells

We have previously reported that Runx3, a runt domain transcription factor, is a major growth regulator of gastric epithelial cells, that a lack of RUNX3 function is causally related to the genesis and progression of human gastric cancer, and that expression of RUNX3 is greatly reduced in intestinal metaplasias in human stomachs. Here we examined the differentiation of Runx3-/- mouse gastric epithelial cells and found that some cells differentiated into intestinal type cells, which expressed Cdx2, a transcription factor that has been shown to induce intestinal metaplasia in transgenic mice. Differentiation of intestinal type cells was not found in culture of Runx3+/+ gastric epithelial cells. These results suggest that gastric epithelial cells can differentiate into intestinal type cells, probably due to expression of Cdx2 in them when the function of Runx3 is impaired. The relationship between loss of function of Runx3, formation of intestinal metaplasia, and gastric cancer was discussed.

Stem cells and gastric cancer: role of gastric and intestinal mixed intestinal metaplasia

All of the different types of stomach epithelial cells are known to be derived from a single progenitor cell in each gland. Similarly, cancers develop from single cells, based on data from clonality analysis in C3H/HeN<-->BALB/c chimeric mice. Using gastric and intestinal epithelial cell markers, intestinal metaplasia (IM) can be divided into two major types: a gastric and intestinal (GI) mixed type, and a solely intestinal (I) type. Ectopic expression of Cdx genes and down-regulation of Sox2 in isolated single GI mixed IM glands suggests abnormal differentiation of stem cells that can produce both gastric (G) and I type cells. Similarly, phenotypic expression of gastric cancer cells of each histological type can be clearly classified into G and I type epithelial cells. The heterogeneity of phenotypic expression of gastric cancer cells in individual cancers is assumed to reflect this intrinsic potential for differentiation in two directions. Gastric cancers at early stages, independent of the histological type, mainly consist of G type cells, and phenotypic shift from G to I type expression is clearly observed with progression. The data thus suggest IM may not be a preneoplastic change in gastric carcinoma, but rather that cells of the I type may appear independently in the gastric mucosa in IM and in gastric cancers. Intestinalization of gastric mucosa and cancer cells may represent a kind of homeotic transformation. Whether disturbance of the regulation of Sox2 and Cdx genes may be of importance to the biological behavior of gastric cancers should therefore be clarified in future studies.

Xenografted human whole embryonic and fetal entoblastic organs develop and become functional adult-like micro-organs

BACKGROUND AND AIMS

The aim of this study was to study the morphological and functional development in vivo of whole human embryonic and fetal stomachs, intestines, tracheas, and lungs, which would otherwise be ethically and technically impossible to perform in utero, by microsurgically grafting these organs into nude mice.

MATERIALS AND METHODS

Five hundred fifty-seven human organs obtained from legally aborted embryos and fetuses of 6-10 weeks were microsurgically grafted into nude mice for 1 to 273 days. Following different grafting times, biopsies were taken for optical and electron microscopy, in situ hybridization, and cellular kinetics studies. A catheter was introduced into the human organs in order to collect and analyze secretions.

RESULTS

All of the grafts took successfully. Macroscopic growth was fast during the first 6 to 10 weeks, following which organ size was stable. In situ hybridization studies detected only a minute level of mouse mesenchymal chimerism in the grafts. The different epithelial cells differentiated, became of adult type, and remained normal during the remainder of the grafting periods. The pH of gastric juice from stomachs grafted for 10 to over 90 days dropped from 8.0 +/- 0.1 to 1.58 +/- 0.29 over this time period (P < 0.001), intrinsic factor levels were stable, and pepsin ranged from 6.8 +/- 7.8 to 134 +/- 51 units (P < 0.001).

CONCLUSIONS

These results demonstrate that the development of entoblastic organs from human embryos and fetuses microsurgically grafted into nude mice is similar to that occurring in utero. As such, this method provides a model for the analysis of whole human organs in development and later normal adult-like micro-organs for physiological, therapeutic, and pathological studies.

Morphologic and functional development of whole human fetal stomachs grafted into nude mice

To study in vivo the cellular differentiation and secretion of human developing fetal stomach, ethically and technically impossible to perform in utero, 256 fetal stomachs were xenografted. Human stomachs from 6- to 10-week-old fetuses were grafted for 1-273 days into nude mice. Biopsies for immunohistochemistry, hybridization and electron microscopy were taken and a catheter introduced into the human stomach. Macroscopic growth was fast and cells in S phase were numerous during the first 9 weeks, then the stomach size was stable and the gastric mucosa, of adult type, remained normal. In situ hybridization detected only a minute mouse mesenchymal chimerism in the graft. Chromogranin A, intrinsic factor and H+/K+ adenosine triphosphatase were immunohistolocally detected in epithelial cells 20 days after grafting, gastrin was detected after 30 days and pepsinogen after 60 days. The pH in gastric juice, which was at 8.0 +/- 0.1 from days 10-25, dropped from 4.39 +/- 1.80 at 30 days to 1.58 +/- 0.29 at 90 days. Intrinsic factor was stable and pepsin ranged from 6.8 +/- 7.8 to 134 +/- 51 units at 90 days. The differentiation of the epithelial cells in xenografts was very accelerated in comparison to that in utero.

Metamorphosis of summer flounder, Paralichthys dentatus: cell proliferation and differentiation of the gastric mucosa and developmental effects of altered thyroidal status

Summer flounder, like most marine fishes studied to date, are stomachless at first feeding, and subsequently acquire gastric function during the process of metamorphosis. Stomach formation is controlled largely by thyroxine (T4). In the present work we sought to understand gastric organogenesis in terms of cell proliferation and its relationship to histological differentiation. The objectives of the study were (1) to obtain a developmental pattern of cell proliferation in the gastric mucosa and to relate that pattern to the progress of gastric differentiation; and (2) to understand the regulatory role of T4 on cell proliferation and histological differentiation by altering the thyroidal status of the developing larvae. We observed that (1) in normally developing larvae, cell proliferation increased by early metamorphic climax (MC), remained high until mid-MC, and decreased to basal levels by late MC; concomitantly, the gastric glands appeared and differentiated in the fundic mucosa, and were complete by late MC; (2) T4 accelerated the differentiation of gastric glands and mucus neck cells, while inhibiting the concomitant increase in cell proliferation observed in controls; and (3) the goitrogen thiourea inhibited both cell proliferation and gastric differentiation compared to controls. These results indicate that T(4) is necessary for the three-fold increase in cell proliferation that occurs in early metamorphic climax, but that high T4 levels promote differentiation at the expense of proliferation. The observed effects would be consistent with the normal, metamorphosis-related increase in whole body T4.

Induction of precocious pepsinogen synthesis by glucocorticoids in fetal rat gastric epithelium in organ culture: importance of mesenchyme for epithelial differentiation

Glucocorticoids significantly affect both proliferation and differentiation of gastric epithelial cells in vivo. Here we examined the mechanism of action of glucocorticoids on the cells in vitro, with special reference to the epithelial-mesenchymal interaction. When 16.5-day fetal rat gastric explants were maintained in organ culture, the epithelial cells began to invaginate into mesenchyme on days 3 to 4, and formed glandular structures on days 5 to 6 in culture. Immunohistochemical analysis with specific antibodies revealed that pepsinogen-synthesizing cells first appeared on day 2, and they increased in number with epithelial morphogenesis to about 20%-30% of total epithelial cells on days 4 to 6, and that these cells were localized at the base of glandular structures in control media. When the explants were treated with hydrocortisone (1 microgram/ml), epithelial morphogenesis was mostly suppressed, but epithelial cytodifferentiation was significantly stimulated, indicating that epithelial morphogenesis is not necessary for their cytodifferentiation. In glucocorticoid-treated explants, pepsinogen-synthesizing cells first appeared on day 1, and more than 90% of the cells were positively stained with the antibodies from days 3 to 5 in culture. Biochemical analysis showed that much higher acid protease activity could be detected in glucocorticoid-treated explants than in controls from days 2 to 6 in culture, and analysis by zymography indicated that the synthesis of pepsinogen 1 but not cathepsin E was stimulated by the hormone. Northern blotting analysis showed that the level of pepsinogen 1 mRNA was greatly increased by glucocorticoids. Examination of the effect of the hormone on the epithelial proliferation showed that hydrocortisone (1 microgram/ml) significantly inhibited the epithelial growth from days 1 to 3 in culture. To investigate the role of epithelial-mesenchymal interaction in the glucocorticoid-induced differentiation of the gastric epithelial cells, effects of the hormone on the proliferation and differentiation of the cells in the absence of mesenchyme were examined, using a recently established primary culture system. The epithelial cells synthesized cathepsin E but not pepsinogen in cell culture, irrespective of glucocorticoid treatment, and the level of acid protease activity was not affected by the hormone, indicating that mesenchyme is necessary for the hormone to induce pepsinogen gene expression in the epithelial cells. In the cell culture system, glucocorticoids did not inhibit but significantly stimulated epithelial proliferation. This suggests that the hormone indirectly inhibited epithelial proliferation in organ culture, probably via mesenchyme. The mechanism of action of glucocorticoids on the epithelial-mesenchymal interaction in the fetal glandular stomach is discussed.