Regional variability of colonocyte growth and differentiation in the rat

Ultrastructural and histochemical study on the Paneth cells in the rat ascending colon

Paneth cells (PCs) contribute to the host defense against indigenous bacteria in the small intestine. We found Paneth cell-like cells (PLCs) in the rat ascending colon, but the nature of PLCs is never clarified. Therefore, the present study aimed to clarify the cytological characteristics of PLCs and discuss their cellular differentiation. PLCs were localized in the bases of intestinal crypts, especially follicle-associated intestinal crypts in proximal colonic lymphoid tissue, but were very seldom found in the ordinary intestinal crypts of the ascending colon. PLCs possessed specific granules with highly electron-dense cores and haloes, as well as PCs in the small intestine. The secretory granules of PLCs were positive for PAS reaction, lysozyme and soluble phospholipase A2, but negative for Alcian blue staining, β-defensin-1 and -2, as well as the ones of PCs. Furthermore, intermediate cells possessing both the PLC-specific granules and the mucus granules similar to those of goblet cells (GCs) were occasionally found in the vicinity of PLCs. Intermediate cells ranged from goblet cell-like cells rich in mucus granules to PLC-like cells with few mucus granules. The cellular condensation and fragmentation were exclusively found in PLCs but never seen in intermediate cells or GCs. The PLCs, which were identified as PC, were suggested to be transformed from GCs through intermediate cells and finally to die by apoptosis in intestinal crypts of proximal colonic lymphoid tissue in the rat ascending colon.

Genomic homeostasis is dysregulated in favour of apoptosis in the colonic epithelium of the azoxymethane treated rat

Background

The acute response to genotoxic carcinogens in rats is an important model for researching cancer initiation events. In this report we define the normal rat colonic epithelium by describing transcriptional events along the anterior-posterior axis and then investigate the acute effects of azoxymethane (AOM) on gene expression, with a particular emphasis on pathways associated with the maintenance of genomic integrity in the proximal and distal compartments using whole genome expression microarrays.

Results

There are large transcriptional changes that occur in epithelial gene expression along the anterior-posterior axis of the normal healthy rat colon. AOM administration superimposes substantial changes on these basal gene expression patterns in both the distal and proximal rat colonic epithelium. In particular, the pathways associated with cell cycle and DNA damage and repair processes appear to be disrupted in favour of apoptosis.

Conclusions

The healthy rats’ colon exhibits extensive gene expression changes between its proximal and distal ends. The most common changes are associated with metabolism, but more subtle expression changes in genes involved in genomic homeostasis are also evident. These latter changes presumably protect and maintain a healthy colonic epithelium against incidental dietary and environmental insults. AOM induces substantial changes in gene expression, resulting in an early switch in the cell cycle process, involving p53 signalling, towards cell cycle arrest leading to the more effective process of apoptosis to counteract this genotoxic insult.

CD24 can be used to isolate Lgr5+ putative colonic epithelial stem cells in mice

A growing body of evidence has implicated CD24, a cell-surface protein, as a marker of colorectal cancer stem cells and target for antitumor therapy, although its presence in normal colonic epithelium has not been fully characterized. Previously, our group showed that CD24-based cell sorting can be used to isolate a fraction of murine small intestinal epithelial cells enriched in actively cycling stem cells. Similarly, we hypothesized that CD24-based isolation of colonic epithelial cells would generate a fraction enriched in actively cycling colonic epithelial stem cells (CESCs). Immunohistochemistry performed on mouse colonic tissue showed CD24 expression in the bottom half of proximal colon crypts and the crypt base in the distal colon. This pattern of distribution was similar to enhanced green fluorescent protein (EGFP) expression in Lgr5-EGFP mice. Areas expressing CD24 contained actively proliferating cells as determined by ethynyl deoxyuridine (EdU) incorporation, with a distinct difference between the proximal colon, where EdU-labeled cells were most frequent in the midcrypt, and the distal colon, where they were primarily at the crypt base. Flow cytometric analyses of single epithelial cells, identified by epithelial cell adhesion molecule (EpCAM) positivity, from mouse colon revealed an actively cycling CD24(+) fraction that contained the majority of Lgr5-EGFP(+) putative CESCs. Transcript analysis by quantitative RT-PCR confirmed enrichment of active CESC markers [leucine-rich-repeat-containing G protein-coupled receptor 5 (Lgr5), ephrin type B receptor 2 (EphB2), and CD166] in the CD24(+)EpCAM(+) fraction but also showed enrichment of quiescent CESC markers [leucine-rich repeats and immunoglobin domains (Lrig), doublecortin and calmodulin kinase-like 1 (DCAMKL-1), and murine telomerase reverse transcriptase (mTert)]. We conclude that CD24-based sorting in wild-type mice isolates a colonic epithelial fraction highly enriched in actively cycling and quiescent putative CESCs. Furthermore, the presence of CD24 expression in normal colonic epithelium may have important implications for the use of anti-CD24-based colorectal cancer therapies.

Activation of NF-kappaB is required for mediating proliferative and antiapoptotic effects of progastrin on proximal colonic crypts of mice, in vivo

Mice overexpressing progastrin (PG) in intestinal mucosa (fatty acid-binding protein (Fabp)-PG mice) are at an increased risk of proximal colon carcinogenesis in response to azoxymethane. Here, we report a significant increase in the length of proximal colonic crypts in Fabp-PG mice, associated with potent antiapoptotic effects of PG, which likely contributed to the previously reported increase in colon carcinogenesis in Fabp-PG mice. Phosphorylation of kinase of IkappaBalpha (IKKalpha/beta), inhibitor of kappaB (IkappaB)alpha and p65NF-kappaB was significantly elevated in proximal colonic crypts of Fabp-PG versus wild-type mice, which was associated with degradation of IkappaBalpha and nuclear translocation/activation of p65. Surprisingly, distal colonic crypt cells were not as responsive to elevated levels of PG in Fabp-PG mice. Annexin II, recently described as a high-affinity receptor for PG, strongly co-localized with PG intracellularly and on basolateral membranes of proximal crypt cells, providing evidence that annexin-II binds PG in situ in colonic crypt cells. Proliferative and antiapoptotic effects of PG on proximal crypts of Fabp-PG mice were attenuated to wild-type levels, on treatment with NEMO peptide (an inhibitor of nuclear factor-kappaB (NF-kappaB) activation), demonstrating for the first time a critical role of NF-kappaB in mediating hyperproliferative affects of PG on colonic crypts of Fabp-PG mice, in vivo. Thus, downregulation of NF-kappaB may significantly reduce the increased risk of colon carcinogenesis in response to PG.

Smad3 deficiency promotes tumorigenesis in the distal colon of ApcMin/+ mice

Colorectal cancer, one of the most common human malignancies in the Western world, is often subdivided based on tumor location in either the distal or proximal colon. Several mouse models have been developed to study human colorectal cancer, but few display this clear distinction between the two colonic locations. By crossing Apc(Min/+) and Smad3 mutant mice, we showed that combined activation of the Wnt pathway and attenuation of the transforming growth factor-beta (TGF-beta) pathway causes high multiplicity and rapid onset of invasive tumorigenesis almost exclusively in the distal colon, closely mimicking the familial adenomatous polyposis (FAP) disease and consisting with distinct colorectal cancer etiologies based on tumor location. Transcriptional profiling revealed higher expression of several TGF-beta activators in the normal distal mucosa than in proximal mucosa, suggesting a stronger reliance on TGF-beta-mediated growth control in the distal than in the proximal colon. Apc(Min/+)Smad3(-/-) mice provide an alternative model to Apc(Min/+) mice to study FAP and distal sporadic colorectal cancer. This model will be useful in dissecting mechanistic and etiologic differences between proximal and distal colonic cancer, whereas the confinement of tumorigenesis to the distal colon offers unique advantages in monitoring tumor progression by in vivo imaging.

Insights into c-Myb functions through investigating colonic crypts

c-Myb has been investigated in the context of the hematopoietic system where it has been shown to regulate progenitor cell expansion and differentiation of a number of lineages. The capacity to grow and expand specific blood cell lineages in vitro using well defined growth factors plus the vast range of cell surface lineage markers that identify different cell types has driven our understanding of the spectrum of roles that c-Myb plays in this tissue compartment. In addition, c-Myb is also an important transcription factor in non-hematopoietic tissues but the restricted spectrum of cell phenotyping reagents has hampered in-depth investigation. In the case of the colonic crypt the absence of phenotyping reagents of the quality employed in identifying blood cell lineages is partly compensated for by the spatial and temporal information that is inherent in the crypt structure. Using different tools to those used in the blood system we have gained insights in the multiple roles played by c-Myb in colon epithelial cells. These observations, when combined with the understanding of c-Myb action in blood cells, is providing a clearer view as to how c-Myb operates in normal cells and how this is subverted in diseases like cancer.

An enteroendocrine cell-based model for a quiescent intestinal stem cell niche

We have shown that the kinetics of conversion of intestinal crypt cell populations to a partially or wholly mutant phenotype are consistent with a model in which each crypt contains an infrequently dividing 'deep' stem cell that is the progenitor of several more frequently dividing 'proximate' stem cells. An assumption of our model is that each deep stem cell exists in a growth inhibitory niche. We have used information from the literature to develop a model for a quiescent intestinal stem cell niche. This niche is postulated to be primarily defined by an enteroendocrine cell type that maintains stem cell quiescence by secretion of growth inhibitory peptides such as somatostatin and guanylin/uroguanylin. Consistent with this model, there is evidence that the proteins postulated as defining a growth-inhibitory stem cell niche can act as intestinal tumour suppressors. Confirmation that a growth-inhibitory niche does exist would have important implications for our understanding of intestinal homeostasis and tumorigenesis.

Epithelial cell proliferation is promoted by the histamine H3 receptor agonist (R)-α-methylhistamine throughout the rat gastrointestinal tract

The temporal effect of (R)-alpha-methylhistamine on epithelial cell proliferation throughout the rat gastrointestinal tract was investigated. (R)-alpha-methylhistamine was administered at 100 mg/kg orally and the rats were sacrificed 1, 24, 48, 72 and 144 h later. All the animals received 5-bromo-2'-deoxyuridine, (BrdU), 200 mg/kg i.p., 2 h before sacrifice. Gastrointestinal tissue was processed for histology and immunohistochemistry. (R)-alpha-methylhistamine caused a progressive increase in mucosal thickness of gastric fundus, distal small intestine and distal colon. Statistically significant differences from control values were found between 48 and 72 h after (R)-alpha-methylhistamine. (R)-alpha-methylhistamine significantly increased the number of BrdU-positive cells in the gastric fundus and antrum, intermediate and distal small intestine and distal colon. Peak effects were observed between 1 and 24 h after (R)-alpha-methylhistamine administration. Proliferating cell number and mucosal thickness were comparable to those of control rats at 144 h. (R)-alpha-methylhistamine exerts a long lasting growth-promoting effect on the stomach, distal small intestine and distal colon. Present data support a role of histamine H(3) receptors in the normal regulation of cell cycle in epithelial tissue.

Dietary intakes of fruit, vegetables, and fiber, and risk of colorectal cancer in a prospective cohort of women (United States)

OBJECTIVE

Although animal studies suggest an inverse association between consumption of plant foods and risk of colorectal cancer, many observational data have failed to support such an association. We prospectively examined the association between dietary intakes of fruit, vegetables, and fiber and colorectal cancer risk in a large female cohort from the Women's Health Study.

METHODS

Among 39,876 healthy women aged >/=45 years at baseline, 36,976 with baseline self-reported information on dietary intakes and other risk factors for colorectal cancer were included in the analyses. During an average follow-up of 10 years, 223 women were diagnosed with colorectal cancer. Intakes of fruit, vegetables, and fiber were assessed by a baseline food-frequency questionnaire. The analyses were carried out using the Cox proportional hazards regression and all tests were two-sided.

RESULTS

Intakes of fruit, vegetables, and the specific subgroups were not found to be associated with colorectal cancer risk. Multivariate relative risks (RRs) comparing the highest with lowest quintile were 0.79 (95% CI=0.49-1.27,p for trend =0.30) for fruit intake, and 0.88 (95% CI=0.56-1.38,p for trend=0.30) for vegetables intake. Similarly, intake of total fiber was not associated with colorectal cancer risk; the RR for the highest relative to lowest quintile was 0.75 (95% CI=0.48-1.17,p for trend=0.12). However, higher intake of legume fiber was associated with a lower risk of colorectal cancer; the RR for the highest versus slowest quintile was 0.60 (95% CI=0.40-0.91,p for trend=0.02).

CONCLUSIONS

Our data offer little support for associations between intakes of fruit, vegetables, and fiber, and colorectal cancer risk. However, our data suggest that legume fiber and/or other related sources may reduce risk of colorectal cancer.

Modulation of aberrant crypt foci and apoptosis by dietary herbal supplements (quercetin, curcumin, silymarin, ginseng and rutin)

It is estimated that one-third of Americans use dietary herbal supplements on a regular basis. Diets rich in bioactive phytochemicals are associated with reduced risk of certain cancers, notably, colon cancer. Herbal supplements have not been directly tested as sources of bioactive cancer preventives. Hence, this study compares the ability of four herbal flavonoids (quercetin, curcumin, rutin and silymarin) and one whole herb mixture (ginseng powder) to suppress aberrant crypt foci (ACF) in an azoxymethane (AOM)-induced rat colon cancer model. Second, this study examines the effect of these herbal compounds on apoptosis and the mechanisms by which these compounds evoke apoptosis. The results of this study show that diets containing quercetin, curcumin, silymarin, ginseng and rutin decreased the number of ACFs by 4-, 2-, 1.8-, 1.5- and 1.2-fold, respectively compared with control. Histological analysis of the colon mucosa revealed that all the herbal supplements, except silymarin, induced apoptosis, with quercetin being the most potent (3x increase compared with control). Furthermore, ginseng and curcumin were region-specific in inducing apoptosis. The ability of quercetin and curcumin to modulate ACFs correlates well with their ability to induce apoptosis. Western blot analysis of caspase 9, Bax (proapoptotic) and Bcl-2 (antiapoptotic) proteins from the colon scraping suggests that quercetin and curcumin induce apoptosis via the mitochondrial pathway. Taken together, the results of this study suggest that these herbal supplements may exert significant and potentially beneficial effects on decreasing the amount of precancerous lesions and inducing apoptosis in the large intestine.

Real-time PCR of host DNA in feces to study differential exfoliation of colonocytes between rats and humans

BACKGROUND

Colonic mucosa has a high turnover rate. At the end of their lifespan, colonocytes become senescent and die. Histological studies indicate that senescent colonocytes are shed (exfoliated) into the fecal stream in rats, but phagocytosed by mucosal macrophages in humans. We study whether quantification of host DNA in feces can be used as a non-invasive marker for this differential disposal of colonocytes.

METHODS

Selective primers and probes for the rat and human beta-globin genes were designed and used in real-time PCR reactions.

RESULTS

Host DNA was quantitatively extracted and detected in fecal samples of both species. Feces of rats fed a humanized diet contained approximately 100 microg rat DNA per g freeze-dried feces. In human feces, however, only 5 out of 12 samples contained detectable, though very low (less than 0.35 microg/g), levels of host DNA. This about 300-fold difference could not be attributed to differences in DNase activities in the fecal stream.

CONCLUSION

Our results indicate that there is considerable luminal shedding of senescent colonocytes in rats, whereas mucosal phagocytosis is the main route of colonocyte disposal in humans. Thus, real-time PCR of host DNA in feces can be applied as a non-invasive method for studying the differential exfoliation of colonocytes.

Fish oil enhances targeted apoptosis during colon tumor initiation in part by downregulating Bcl-2

We have shown that fish oil is protective against colon tumorigenesis, primarily by upregulating apoptosis. Production of prostaglandin E2 (PGE2) in colon cancer cells by cyclooxygenase (COX)-I and -II is known to inhibit apoptosis by induction of bcl-2. Because we have shown that fish oil downregulates PGE2 and COX-II, we hypothesized that this upregulation of apoptosis would be coincident with a downregulation of bcl-2. Bcl-2 was localized within the colonic crypt by quantitative immunohistochemistry (IHC), and scraped colonic mucosa was used for immunoblot analysis of bcl-2. The tissue used for bcl-2 analysis was from the rats used to determine apoptosis. Briefly, tissues were collected from rats consuming diets containing either corn oil or fish oil at 3, 6, 9, and 12 h after carcinogen injection. The correlation between bcl-2 and apoptosis was also determined. Bcl-2 expression decreased until 9 h (P < 0.05), whereas apoptosis increased until 9 h (P < 0.01). Bcl-2 expression and apoptosis were negatively correlated in both the proximal (P < 0.05) and distal colon (P < 0.005). Fish oil decreased bcl-2 expression (P < 0.05) and increased apoptosis (P < 0.05) in the top third of the crypt in the distal colon. In conclusion, one pathway by which fish oil may mediate apoptosis and thus protect against colon tumorigenesis is by downregulation of anti-apoptotic bcl-2.

Leptin reduces the development of the initial precancerous lesions induced by azoxymethane in the rat colonic mucosa

BACKGROUND & AIMS

Recent studies suggest that leptin, a hormone involved in food intake regulation, released into the circulation and gastrointestinal juice, may be a growth factor for intestine and may be involved in carcinogenesis; however, data are contradictory. This study investigates in rat colonic mucosa (1) the effects of hyperleptinemia on epithelial cell proliferation and development of aberrant crypts, earliest preneoplastic lesions, and (2) whether luminal leptin affects cell proliferation.

METHODS

Leptin (1 mg/kg/d) or vehicle was administered systemically by miniosmotic pump in Fischer 344 rats either for 7 days (BrdU-labeling indices study) or 23 days (azoxymethane-induced colonic lesions study). The effects of injections or continuous infusion of leptin into the colon were also studied.

RESULTS

In systemic leptin-treated rats, plasma leptin levels were 4- to 5-fold increased (P < 0.008 to P < 0.001); labeling indices were higher in proximal colon than in pair-fed control rats (P = 0.006) but unaffected in distal colon. Unexpectedly, in azoxymethane-treated rats, leptin significantly inhibited aberrant crypt foci formation in the middle and distal colon compared with controls (P = 0.006). Under these conditions, plasma insulin levels were reduced by 41%-58%, but gastrin levels were unchanged. In controls, luminal immunoreactive leptin reached the colon. A 3.6-fold increase in intraluminal leptin had no effect on epithelial cell proliferation.

CONCLUSIONS

This study provides the first evidence that leptin reduces the development of chemically induced precancerous lesions in colon, perhaps through decreased insulinemia, and thus does not support an important role for leptin in carcinogenesis promotion. Moreover, the study indicates that leptin is not a potent growth factor for normal intestine.

Ethylene diamine tetraacetic acid induced colonic crypt cell hyperproliferation in rats

AIM: To investigate the effect of ethylene diamine tetraacetic acid (EDTA) on proliferation of rat colonic cells.

METHODS: EDTA was administered into Wistar rats, carcinogenesis induced by 1,2-dimethylhydrazine (DMH) in rats was studied with immunohistochemistry.

RESULTS: Marked regional differences in cell proliferation were found in all groups. In EDTA-treated animals, total labelling indexes in both proximal (10.00 ± 0.44 vs 7.20 ± 0.45) and distal (11.05 ± 0.45 vs 8.65 ± 0.34) colon and proliferative zone size (21.67 ± 1.13 vs 16.75 ± 1.45, 27.73 ± 1.46 vs 21.74 ± 1.07) were significantly higher than that in normal controls (P < 0.05) and lower than that in DMH group (10.00 ± 0.44 vs 11.54 ± 0.45, 11.05 ± 0.45 vs 13.13 ± 0.46, 21.67 ± 1.13 vs 35.52 ± 1.58, 27.73 ± 1.46 vs 39.61 ± 1.32, P < 0.05). Cumulative frequency distributions showed a shift of the EDTA distal curve to the right (P < 0.05) while the EDTA proximal curve did not change compared to normal controls. Despite the changes of proliferative parameters, tumours did not develop in EDTA treated animals.

CONCLUSION: Hyperproliferation appears to be more easily induced by EDTA in distal colon than in proximal colon. Hyperproliferation may need to exceed a threshold to develop colonic tumours. EDTA may work as a co-factor in colonic tumorigenesis.

Differences in plasma gastrin, CEA, and CA 19-9 concentration in patients with proximal and distal colorectal cancer

AIM

We investigated whether there are differences in plasma gastrin, as compared with carcinoembryonic antigen (CEA) and cancer antigen (CA) 19-9 between patients with proximal and distal colorectal cancer. Gastrin concentration has also been analyzed, dependent on the tumor stage, in order to evaluate the possible prognostic role of this measurement.

METHODS

In 50 patients with colon cancer-fasting gastrin, CA 19-9 and CEA levels were evaluated.

RESULTS

Mean plasma-gastrin level in patients with distal tumor yielded 105.31 +/- 12.5 microU/L and was significantly higher than in patients with the proximal tumor site (42.2 +/- 3.1 microU/L) as well as in controls (p < 0.001). No significant difference was observed between mean plasma gastrin in patients with proximal tumors and the control group. The mean CEA plasma level was significantly higher (p < 0.01) in patients with distal tumors (9.1 +/- 1.1 ng/mL) than in those with proximal tumors (1.48 +/- 0.1 ng/mL). Similarly, the mean CA 19-9 plasma level was significantly higher (p < 0.01) in patients with distal tumor (19.9 +/- 2.1 U/mL) than in those with proximal tumor: 1.8 +/- 0.2 U/mL. The mean gastrin plasma, CA 19-9, and CEA level was significantly higher in group of Duke's stage C and D as compared to A and B.

CONCLUSION

We speculate that observed differences in gastrin concentration in patients with distal and proximal tumors may contribute to the distinct pathogenesis and biological properties of those cancers. The significance of gastrin as a marker for diagnostic or prognostic purposes in colorectal cancer requires further study.

Identification and isolation of candidate human colonic clonogenic cells based on cell surface integrin expression

BACKGROUND & AIMS

The surface epithelium of the colon is being replaced constantly with cells derived from the stem cells of the crypt. Although the location of the stem cells is known, there are no markers for these cells. This study tested the hypothesis that colonic stem cells might be isolated and cultured on the basis of specific integrin expression patterns in normal human colonic epithelium.

METHODS

Integrin expression in normal human colonic mucosa was determined by using indirect immunofluorescence. Crypt cells were then isolated as single cells from normal colon tissues and the expression pattern of integrins was analyzed by flow cytometry. Based on the specific expression of integrin beta1 in colonic crypts, the cells were sorted by using a flow cytometer, and colony assays in soft agar were performed to evaluate the clonogenicity of the sorted cells.

RESULTS

By immunofluorescence, the cells located in the lower one third of crypts expressed higher levels of beta1-integrin than the cells in the remainder of the crypt. When isolated crypt cells were stained with the beta1-integrin antibody and examined in a flow cytometer, there were 2 peaks of fluorescence. Sorting of crypt cells based on staining with anti-beta1 integrin antibody produced a cell population with a significantly enhanced ability to form colonies.

CONCLUSIONS

beta1-integrin is a candidate surface marker for the proliferative zone of the human colonic crypt. Our in vitro culture system for the clonal growth of a single colonic crypt cell suspension could facilitate the identification of other candidate stem cell markers.

Variability of cell proliferation in the proximal and distal colon of normal rats and rats with dimethylhydrazine induced carcinogenesis

AIM: To investigate the patterns of cell proliferation in proximal and distal colons in normal rats and rats with 1,2-dimethylhydrazine (DMH) induced carcinogenesis using the thymidine analogue bromodeoxyuridine.

METHODS: Colonic crypt cell proliferation was immunohistochemically detected using the anti-bromodeoxyuridine Bu20a monoclonal antibody.

RESULTS: Marked regional differences were found in both groups. Total labelling index (LI) and proliferative zone size in both normal (8.65 ± 0.34 vs 7.2 ± 0.45, 27.74 ± 1.07 vs 16.75 ± 1.45) and DMH groups (13.13 ± 0.46 vs 11.55 ± 0.45, 39.60 ± 1.32 vs 35.52 ± 1.58) were significantly higher in distal than in proximal colon (P < 0.05), although the number of cells per proximal crypt was greater (31.45 ± 0.20 vs 34.45 ± 0.39, 42.68 ± 0.53 vs 49.09 ± 0.65, P < 0.0001). Crypt length, total LI and proliferative zone size all increased in both proximal and distal regions of DMH rats compared to normal controls (P < 0.0001). In DMH-treated rat colon a shift of labelled cells to higher crypt cell positions was demonstrated distally whilst a bi-directional shift was evident proximally (P < 0.05).

CONCLUSION: Our results show that changes in cell proliferation patterns, as assessed by bromodeoxyuridine uptake, can act as a reliable intermediate marker of colonic cancer formation. Observed differences between proliferation patterns in distal and proximal colon may be associated with the higher incidence of tumors in the distal colon.

Epithelial cell dynamics in rabbit cecum and proximal colon P1

The large intestine of mammals has long been viewed as an osmoregulatory organ, and evidence suggests that fluid and solute transport mechanisms within the intestine are heterogeneous, varying depending on the particular segment involved. Variations in function are often matched by morphological correlates, but despite the widespread use of rabbit large intestine as an experimental model, there is a lack of knowledge about the cellular makeup and dynamics in the colonic mucosal epithelium. The presence of mitotic figures and immunohistochemical localization of proliferating cell nuclear antigen (PCNA) were used to identify the proliferative zone(s). Cellular migration patterns were determined through the use of the thymidine analog 5-bromo-2-deoxyuridine (BrdU) over a 24-, 48-, and 72-hr period. Apoptotic nuclei were identified utilizing terminal deoxynucleotidyl transferase d-UTP nick-end labeling (TUNEL). Both cecum and the initial portion of the proximal colon (P1) exhibited a proliferative zone at or near the crypt base, and migration proceeded upwards toward the surface epithelium lining the intestinal lumen, where apoptosis occurred Turnover time of crypt columnar cells was determined to be about 3 days; that of mucous cells was estimated to be about 5 weeks. Rabbit cecum and proximal colon P1 are similar in their cellular morphology and epithelial cell kinetics. In both, the major proliferative zone is located at or near the crypt base, from which crypt columnar cells migrate toward the lumenal surface epithelium over a period of 3 days. Goblet cell turnover rate is much slower than that of columnar cells.

Aging is associated with increased proliferation and decreased apoptosis in the colonic mucosa

Although the incidence of colon cancer increases with advancing age, reasons for this increase are not fully understood. Earlier studies have demonstrated that in Fischer-344 rats, aging is associated with increased crypt cell production in the colon, an event considered to be central to the initiation of carcinogenesis. Apoptosis also plays a critical role in the development and progression of colon cancer. Therefore, we have examined the age-related changes in proliferation and apoptosis in the colonic mucosa of 4-5, 12-14, and 22-24 month-old Fischer-344 rats. We have observed that proliferative activity in the colon, as assessed by proliferating cell nuclear antigen immunoreactivity, is higher (50-80%) in 12-14 and 22-24 month-old rats than in their 4-6 month-old counterparts. In contrast, the number of apoptotic cells, (as determined by TdT-mediated dUTP nick-end labeling assay) in the colonic mucosa of 12-14 and 22-24 month-old rats are considerably lower (50-60%) than in 4-6 month-old animals. These changes are accompanied by a concomitant reduction (75%) in pro-apoptotic Bak and stimulation (200%) of anti-apoptotic Bcl-xL levels. Since activation of caspases is associated with initiation and maintenance of apoptosis, we also analyzed the levels of pro and active forms of caspase-3, 8 and 9. The levels of active forms of caspase-3, 8 and 9 are found to be considerably (60-80%) lower in the colonic mucosa of 22-24 month-old rats, compared to their younger counterparts. This is accompanied by decreased cleavage of poly(ADP-ribose) polymerase, a substrate for caspases. In conclusion, our data show that aging enhances proliferation, but attenuates apoptosis in the colonic mucosa. These changes may partly be responsible for the age-related rise in colorectal cancer.

Morphodensitometric analysis of protein kinase C beta(II) expression in rat colon: modulation by diet and relation to in situ cell proliferation and apoptosis

We have recently demonstrated that overexpression of PKC beta(II) renders transgenic mice more susceptible to carcinogen-induced colonic hyperproliferation and aberrant crypt foci formation. In order to further investigate the ability of PKC beta(II) to modulate colonocyte cytokinetics, we determined the localization of PKC beta(II) with respect to cell proliferation and apoptosis along the entire colonic crypt axis following carcinogen and diet manipulation. Rats were provided diets containing either corn oil [containing n-6 polyunsaturated fatty acids (PUFA)] or fish oil (containing n-3 PUFA), cellulose (non-fermentable fiber) or pectin (fermentable fiber) and injected with azoxymethane (AOM) or saline. After 16 weeks, an intermediate time point when no macroscopic tumors are detected, colonic sections were utilized for immunohistochemical image analysis and immunoblotting. Cell proliferation was measured by incorporation of bromodeoxyuridine into DNA and apoptosis by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling. In the distal colon, PKC beta(II) staining was localized to the upper portion of the crypt. In comparison, proximal crypts had more (P < 0.05) staining in the lower tertile. AOM enhanced (P < 0.05) PKC beta(II) expression in all regions of the distal colonic crypt (upper, middle and lower tertiles). There was also an interaction (P < 0.05) between dietary fat and fiber on PKC beta(II) expression (corn/pectin > fish/cellulose, fish/pectin > corn/cellulose) in all regions of the distal colonic crypt. With respect to colonic cell kinetics, proliferation paralleled the increase in PKC beta(II) expression in carcinogen-treated animals. In contrast, apoptosis at the lumenal surface was inversely proportional to PKC beta(II) expression in the upper tertile. These results suggest that an elevation in PKC beta(II) expression along the crypt axis in the distal colon is linked to enhancement of cell proliferation and suppression of apoptosis, predictive intermediate biomarkers of tumor development. Therefore, select dietary factors may confer protection against colon carcinogenesis in part by blocking carcinogen-induced PKC beta(II) expression.

Intestinal mucosal secretion of basic fibroblast growth factor in patients with ulcerative colitis

BACKGROUND

Basic fibroblast growth factor (bFGF) promotes angiogenesis and several other biologic processes, including proliferation of mesenchymal cells and tumor progression. We investigated whether bFGF could be detected in the intraluminal secretion of the small intestine, sigmoid colon, and rectum in healthy individuals and in patients with ulcerative colitis.

METHODS

We used endoscopic perfusion techniques to obtain samples from well-defined intestinal segments. The perfusion fluid concentrations of bFGF, biochemical markers of inflammation, myeloperoxidase (MPO), interleukin-6 (IL-6), and permeability (albumin) were determined with immunochemical methods.

RESULTS

In the perfusion fluids the albumin concentration, which reflects passive diffusion, was less than 1% of the plasma concentration, whereas the intestinal concentration of bFGF was similar to that in plasma. Among healthy subjects the concentration of bFGF was eightfold higher in the jejunum and twofold higher in the rectum than in the sigmoid colon. The perfusion fluid from colorectal segments in patients with ulcerative colitis had a significantly higher mean concentration of bFGF than that from healthy individuals; an almost 10-fold difference was found in rectal segments. There were strong correlations between the concentration of bFGF and the concentrations of MPO and IL-6.

CONCLUSIONS

The high concentrations of bFGF in the intestinal perfusion fluid reflect either a local synthesis or an active secretion of bFGF within the mucosa. The bFGF concentration differs in intestinal anatomic location and increases significantly in patients with ulcerative colitis in close relationship with biochemical markers of inflammation and permeability.

Dietary calcium supplementation increases apoptosis in the distal murine colonic epithelium

BACKGROUND

Increased dietary calcium might reduce colorectal cancer risk, possibly by reduction of colonic epithelial hyperproliferation, but not all studies have demonstrated this. Little is known about the effects of calcium on colonic apoptosis.

AIM

To quantify the effects of increasing calcium on apoptosis and cell proliferation in normal murine colonic crypt epithelium.

METHODS

Twenty one day old male C57B1/6 mice were fed either control AIN-76 diet (0.5% calcium wt/wt; n = 10) or the same supplemented with calcium carbonate (1.0% calcium; n = 10) for 12 weeks. Apoptotic cells in proximal and distal segments were counted and expressed as an apoptotic index (AI: frequency of apoptosis/100 longitudinal crypts). The bromodeoxyuridine (BrdU) labelling index was also determined. Differences were analysed by the student's t test.

RESULTS

In control animals, the AI was significantly higher in the caecum/proximal colon (mean, 28.6; SEM, 2.0) compared with the distal colon (mean, 19.9; SEM, 1.8; p = 0.004). In the calcium treated group, the AI in the caecum/proximal colon (mean, 30.6; SEM, 1.7) was similar to controls (p = 0.71) but the AI in the distal colon was significantly greater (mean, 32.6; SEM, 1.8; p = 0.001) than in control mice and was raised to values similar to those in the proximal colon. Calcium was also associated with reduced crypt cellularity and, in the proximal colon, a downward shift in the crypt position at which apoptosis occurred. There were no significant differences in the BrdU labelling index between groups or between proximal and distal colonic segments in each group.

CONCLUSIONS

Increased dietary calcium is associated with the induction of apoptosis in normal mouse distal colonic epithelium without affecting cell proliferation. This might contribute to its putative chemopreventive role in colorectal carcinogenesis. Whether this effect is direct or indirect requires further study.

Transcriptional regulation in intestinal development. Implications for colorectal cancer

Deciphering the complex mechanisms of intestinal epithelial development will require multiple cell and molecular approaches in both in vitro and whole animal systems. Additionally, the use of model organisms such as D. melanogaster, C. elegans, and zebrafish will help describe paradigms that may be investigated in mammals as well as serve as test systems for findings from mammals. This manuscript reviewed only one approach to understanding intestinal development. However, the Cdx story and the information to be mined from an understanding of SI gene transcription is not at an end. As the other pieces of the transcriptional puzzle of the SI gene are assembled there will be new information to generate hypotheses on the relationship of transcriptional mechanisms to cancer pathogenesis.

Overexpression of protein kinase C betaII induces colonic hyperproliferation and increased sensitivity to colon carcinogenesis

Protein kinase C betaII (PKC betaII) has been implicated in proliferation of the intestinal epithelium. To investigate PKC betaII function in vivo, we generated transgenic mice that overexpress PKC betaII in the intestinal epithelium. Transgenic PKC betaII mice exhibit hyperproliferation of the colonic epithelium and an increased susceptibility to azoxymethane-induced aberrant crypt foci, preneoplastic lesions in the colon. Furthermore, transgenic PKC betaII mice exhibit elevated colonic beta-catenin levels and decreased glycogen synthase kinase 3beta activity, indicating that PKC betaII stimulates the Wnt/adenomatous polyposis coli (APC)/beta-catenin proliferative signaling pathway in vivo. These data demonstrate a direct role for PKC betaII in colonic epithelial cell proliferation and colon carcinogenesis, possibly through activation of the APC/beta-catenin signaling pathway.

The relationship between ionizing radiation-induced apoptosis and stem cells in the small and large intestine

Apoptosis is observed in the crypts of the small intestine of healthy animals and man (spontaneous apoptosis). The levels can be dramatically elevated 3-6 h following ionizing radiation exposure. Both the spontaneous and radiation-induced apoptosis in the small intestine crypts are most frequently observed at the positions in the crypt associated with stem cells (about four cell positions from the base of the crypt). The number of apoptotic deaths can be counted in routine histological preparations, but interpretation of the counts is complicated by numerous factors. However, recording the number of cells containing one or more apoptotic fragments in crypt sections provides a good estimate for the absolute number of cell deaths in crypts. Similarities are noted in the frequency and cell positional relationship of radiation-induced apoptosis in the small intestine of various strains of mice and one strain of rat. Apoptosis in the large intestine is generally lower in frequency than in the small intestine and, for the mid-colonic and rectal regions, has a different cell positional frequency distribution, with the highest apoptotic yield at the crypt base. The caecal colon has a pattern of apoptotic distribution more similar to that in the small intestine. After exposure to 1 Gy ionizing radiation, the maximum apoptotic yield occurs over a period of 3-6 h in the small intestine. There is some unexplained variability in the values between groups of mice and between different mouse strains. After 8 Gy, the yield remains elevated for several days, however a similar maximum yield is still observed at the early times. In mouse large intestine and rat small intestine, the yield continues to rise until about 6 Gy in mouse large intestine and until at least 10 Gy in rat small intestine. Spontaneous apoptosis is interpreted as part of the homeostatic mechanism regulating stem cell numbers. About 1.6 cells per crypt are dying at any one time. Following irradiation, there is an apparent relationship between mitotic and apoptotic levels, suggesting that these processes are linked. The dose-response relationship suggests that there are about six apoptosis-susceptible cells in crypts of the small intestine, with about 2-4 of these occurring at cell positions in which there are other more resistant clonogenic cells. In the large intestine, the position of these apoptosis-susceptible cells varies with region, but the numbers are similar.

Proliferation of goblet cells and vacuolated cells in the rabbit distal colon

Previous studies of colonic epithelial cell kinetics in mice and rats revealed a pattern similar to small intestine, where basally located stem cells proliferate, differentiating as they migrate towards the surface epithelium. Vacuolated and goblet cells are assumed to co-migrate at the same rate. The present study indicates that rabbit distal colon has more complicated epithelial cell kinetics. The zone of proliferation was detected immunohistochemically using proliferating cell nuclear antigen (PCNA) and confirmed with the use of colchicine to arrest dividing cells in metaphase. Migrating cells were tracked from the zero-hour position (PCNA labeling, mitosis) to positions 24, 48, 72 hrs by monitoring cell migration with the thymidine analog 5-Bromo-2-Deoxyuridine (BrdU). PCNA revealed a major proliferative zone in the upper third of the crypt column and the presence of mitotic figures after colchicine corroborated these results. Differentiated vacuolated cell proliferation was detected at three crypt sites: base, middle, and top of the crypt, while columnar cells arose from a population of dividing cells at the top of the crypt. Turnover of columnar and vacuolated cells occurred within 72 hrs. Goblet cells exhibited maximal proliferation at the crypt base and migrated at a much slower rate than the other cell types. In rabbit distal colon, populations of proliferating cells exist at multiple levels of the crypt column. Vacuolated and goblet cells differ in their labeling indices and migration rates, suggesting that the two cell types arise and migrate independently.

Differential responsiveness of proximal and distal colonic mucosa to gastrin

In vivo and in vitro experiments were performed to examine the responsiveness of the proximal and distal colonic mucosa to the growth-promoting action of gastrin. Infusion (osmotic minipump) of gastrin G-17-I (250 ng/kg/h) for 5 days to 4-month-old male Fischer-344 rats resulted in a significant (90-150%) increase in proliferative activity (as assessed by BrdU or PCNA immunoreactivity) in the distal colonic mucosa. In contrast, gastrin caused no apparent change in proliferative activity in the proximal colon. Because tyrosine kinases (Tyr-ks) are thought to be critically involved in regulating the trophic action of gastrin, responsiveness of isolated colonocytes from both segments of the colon to gastrin (1 x 10(-9) M) was also examined. Exposure of isolated colonocytes from the distal, but not from the proximal, colon to gastrin for 2 min resulted in a significant (73%) stimulation in Tyr-k activity. This was also accompanied by a marked rise in phosphorylation of at least six membrane proteins with M, of 55, 60, 70, 94, and 170 kDa. Tyr-k activity induced by gastrin in colonocytes from the distal colon was inhibited by tyrphostin (3.2 microM) but not by staurosporine (20 nM). In colonocytes from the distal colon, gastrin also stimulated phospholipase C (PLC) activity, which could also be inhibited by tyrphostin, but not by staurosporine. We conclude that mucosa of the distal, but not the proximal, colon responds to the trophic action of gastrin. Tyr-ks are thought to be involved in the regulation of this process.

Relationship among colonocyte proliferation, differentiation, and apoptosis as a function of diet and carcinogen

To determine the relationship among colonocyte proliferation, differentiation, and apoptosis as a function of fiber and carcinogen, we conducted a 2 x 2 factorial design study with two fibers (pectin or cellulose) and two injection protocols (azoxymethane or saline) in male Sprague-Dawley rats. Rats were killed six weeks after the injections, and in vivo cell proliferation was measured by incorporation of bromodeoxyuridine into DNA, differentiation by binding of the lectin Dolichos biflorus agglutinin, and apoptosis by immunoperoxidase detection of digoxigenin-labeled genomic DNA. In the proximal colon, pectin decreased differentiation and apoptosis, resulting in a greater number of cells per crypt column. In the distal colon, pectin increased cell proliferation, resulting in more crypts per millimeter of colon and a greater number of surface cells. Azoxymethane increased cell proliferation and decreased differentiation and apoptosis in the proximal and the distal colon. This resulted in a greater number of surface cells proximally and more crypts per millimeter of colon distally. These results illustrate the importance of considering all three parameters (proliferation, differentiation, and apoptosis) when evaluating neoplastic growth.

Bromodeoxyuridine: a diagnostic tool in biology and medicine, Part III. Proliferation in normal, injured and diseased tissue, growth factors, differentiation, DNA replication sites and in situ hybridization

This paper is a continuation of parts I (history, methods and cell kinetics) and II (clinical applications and carcinogenesis) published previously (Dolbeare, 1995 Histochem. J. 27, 339, 923). Incorporation of bromodeoxyuridine (BrdUrd) into DNA is used to measure proliferation in normal, diseased and injured tissue and to follow the effect of growth factors. Immunochemical detection of BrdUrd can be used to determine proliferative characteristics of differentiating tissues and to obtain birth dates for actual differentiation events. Studies are also described in which BrdUrd is used to follow the order of DNA replication in specific chromosomes, DNA replication sites in the nucleus and to monitor DNA repair. BrdUrd incorporation has been used as a tool for in situ hybridization experiments.

Regulation of cell number in the mammalian gastrointestinal tract: the importance of apoptosis

The regulation of cell number in adult tissues is determined by the balance of cell production and cell loss. In the gastrointestinal tract, where there are well defined zones of proliferation and migration of both epithelial cells and associated fibroblasts, it is widely held that cell loss occurs by shedding into the gut lumen. Since the evidence for this is not compelling, we investigated the distribution and amount of apoptosis in the normal mammalian gut. In the stomach, small intestine and colon of rodents and man, there is a small number of apoptotic bodies in the epithelium and in the immediate sub-epithelial connective tissue. Engulfment by adjacent epithelial cells and sub-epithelial macrophages accounts for the removal of apoptotic bodies. Apoptotic bodies are not randomly distributed but are found towards the distal end of the known cellular migration routes of both epithelial and mesenchymal cells. Furthermore, consideration of the absolute numbers of apoptotic bodies, their rapid clearance and the dimensions of the small intestinal villi and colonic crypts indicates that the cell loss in the normal murine intestine can largely be explained on the basis of the observed apoptosis. Despite being inconspicuous in histological material, apoptosis probably accounts for the bulk of cell loss in the gut and is a central feature of the regulation of cell number in adult tissues.

Keratinocyte growth factor induces proliferation of hepatocytes and epithelial cells throughout the rat gastrointestinal tract

Keratinocyte growth factor (KGF), a member of the fibroblast growth factor (FGF) family, was identified as a specific keratinocyte mitogen after isolation from a lung fibroblast line. Recently, recombinant (r)KGF was found to influence proliferation and differentiation patterns of multiple epithelial cell lineages within skin, lung, and the reproductive tract. In the present study, we designed experiments to identify additional target tissues, and focused on the rat gastrointestinal (GI) system, since a putative receptor, K-sam, was originally identified in a gastric carcinoma. Expression of KGF receptor and KGF mRNA was detected within the entire GI tract, suggesting the gut both synthesized and responded to KGF. Therefore, rKGF was administered to adult rats and was found to induce markedly increased proliferation of epithelial cells from the foregut to the colon, and of hepatocytes, one day after systemic treatment. Daily treatment resulted in the marked selective induction of mucin-producing cell lineages throughout the GI tract in a dose-dependent fashion. Other cell lineages were either unaffected (e.g., Paneth cells), or relatively decreased (e.g., parietal cells, enterocytes) in rKGF-treated rats. The direct effect of rKGF was confirmed by demonstrating markedly increased carcinoembryonic antigen production in a human colon carcinoma cell line, LIM1899. Serum levels of albumin were specifically and significantly elevated after daily treatment. These results demonstrate rKGF can induce epithelial cell activation throughout the GI tract and liver. Further, endogenous KGF may be a normal paracrine mediator of growth within the gut.

Morphological changes and cellular proliferation in mouse colon during fetal and postnatal development

To document regional structural and cellular proliferation changes in the developing mouse colon, tissues from fetal, suckling, and weanling mice were analyzed by light microscopy (LM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), [3H]-thymidine incorporation studies, and radioautography. The proximal and distal colon were studied independently at all ages. At 17-18 days of gestation, the mouse proximal colonic mucosa was projected into high and low longitudinal folds disposed in a V-shaped pattern. From birth up to 9 days, the mucosal folds observed by SEM can easily be misinterpreted as being a succession of high and low villus-like structures at LM level. TEM study confirmed the presence of highly specialized absorptive cells in the upper halves of the mucosal folds during this period. No recognizable crypts were noted at birth. Instead, LM and radioautography showed the presence of cell aggregates developing at the base of the epithelium at all levels of the mucosal folds. These cell aggregates evolved into rudimentary crypts giving fully differentiated crypts by day 16 with radiolabeled cells located in the midcrypt portion. As opposed to the proximal segment, a flat mucosa interspersed with well defined short crypts at birth was observed in the distal colon. During the following days, crypts further developed and by 16 days, the radiolabeled epithelial cells were still exclusively located at the base of the crypt. TEM observations illustrated that specialized cells as those found in the proximal segment did not differentiate in this segment.(ABSTRACT TRUNCATED AT 250 WORDS)

A putative H(+)-K(+)-ATPase is selectively expressed in surface epithelial cells of rat distal colon

Recently, a putative distal colon H(+)-K(+)-ATPase alpha-subunit has been identified and characterized (M. S. Crowson and G. E. Shull. J. Biol. Chem. 267:13740-13748, 1992). In the present study, we report the tissue and cell expression of this putative H(+)-K(+)-ATPase. The results indicate that, first, in the gut, the putative H(+)-K(+)-ATPase alpha-subunit is restricted to the distal part of the colon and is predominantly expressed in surface epithelial cells, in marked contrast to the alpha 1-subunit of Na(+)-K(+)-ATPase that is also expressed in glands. These data suggest that the H(+)-K(+)-ATPase alpha-subunit is a potential marker for terminal differentiation of distal colon. Second, in the uterus, the putative H(+)-K(+)-ATPase is restricted to the region of the myometrium between the inner and midmuscular zone that is very rich in vascular supply and nerve cells. This striking expression suggests that the H(+)-K(+)-ATPase may not be involved in the control of pH and potassium concentration of the uterine fluid but rather in distinct functions of vascular and/or nerve cells. Third, with the use of three independent and different approaches (Northern blot analysis, ribonuclease protection assay, and in situ hybridization), we were unable to detect any significant amount of H(+)-K(+)-ATPase transcripts in kidney tissue. Our data suggest that the putative distal colon H(+)-K(+)-ATPase is probably distinct from the kidney isoform. Finally, we report the sequence of a set of degenerate oligonucleotides that are useful to clone alpha-subunits of the Na(+)-K(+)-/H(+)-K(+)-ATPase gene family in different tissues and different species.