Colonic cell proliferation and growth fraction in young, adult and old rats

Patterns of DNA methylation in individual colonic crypts reveal aging and cancer-related field defects in the morphologically normal mucosa

Methylation of CpG islands (CGIs) in the promoter regions of tumour suppressor genes is common in colorectal cancer and occurs also in an age-dependent manner in the morphologically normal colorectal mucosa. In this study, we quantified the level of methylation of six genes associated with the Wnt signalling pathway (adenomatous polyposis coli, DKK1, WIF1, SFRP1, SFRP2 and SFRP5) together with long-interspersed nuclear element-1 as a surrogate for global methylation. DNA methylation was analysed in 260 individual colorectal crypts obtained from eight female patients with no evidence of colorectal disease and five with colorectal cancer. Significant variation in methylation levels for each of the six genes existed between crypts from the same biopsy. The variation in both global and gene-specific CGI methylation between crypts from the same individual was significantly less than that between individuals. Bisulphite sequencing provided insight into the mechanism of aberrant methylation showing that CGI methylation occurs in an 'all-or-none' manner by the directional spreading of methylation from further upstream. Univariate statistical analyses revealed that there were significant differences in crypt-specific methylation associated with both aging and disease status. A multivariate statistical modelling approach was able to distinguish both subject age and health status based on crypt-specific methylation profiles. Our results indicate that the differential methylation of genes associated with the Wnt signalling pathway affecting individual morphologically normal crypts may contribute to the age-dependent generation of the colonic field defect and, in combination with mutations, to the stepwise development of colorectal neoplasia.

Differences in the effects of age on intestinal proliferation, crypt fission and apoptosis on the small intestine and the colon of the rat

The increase in gastrointestinal epithelial tissue mass and the development of the gut can occur through three main mechanisms, namely elevated cell production from the intestinal crypts, by raised crypt number, which occurs through the process of crypt fission or by altered apoptosis. The small bowel and the colon have various rates of these, which were studied in rats of various ages. Wistar rats were fed ad libitum, and were killed at 3, 4, 6, 9, 12, 18, 26 and 48 weeks of age. Tissue was later stained and microdissected and the number of native mitoses and apoptotic figures per crypt and the percentage of crypts in fission were determined. There was an almost linear increase in body weight from 3 to 9 weeks, followed by a more gradual rise until 18 weeks. The weight of the stomach and the small intestine reached maximum values at 9 weeks, whereas the caecum and the colon approached this at 12 weeks. Mitotic activity per crypt in the small intestine increased from 3.8 +/- 0.1 at 3 weeks to 7.8 +/- 0.4 mitoses per crypt (P < 0.001) at 9 weeks and then decreased slightly; crypt fission increased from 4.6% +/- 0.8 at 3 weeks to 8.4 +/- 0.9% at 6 weeks and then decreased gradually reaching a value of 1.5 +/- 0.4% at 48 weeks. Apoptosis also peaked at 6 weeks and was then very low. In the colon, the proliferation decreased from 4.2 +/- 0.2 mitoses per crypt in the young (3 weeks) rat and reached a plateau by 9 weeks (2.5 +/- 0.1 mitoses per crypt, P < 0.001). Crypt fission also declined rapidly in the first 9 weeks (from 67.6 +/- 4.2 to 23.1 +/- 4.6%, P < 0.01) and then continued to decline, although at a lower rate. The crypt fission index at 48 weeks was 9.8 +/- 1.0. Apoptosis in the colon persisted throughout the duration of the study, 0.19 +/- 0.06 apoptotic bodies per crypt were seen at week 48. The development of the small intestine is more dependent on cell proliferation, whereas in the colon crypt fission is far more predominant, with the colon having fission indices approximately six times greater than those of the small intestine. Proliferative activity in the colon was approximately half that of the small intestine.

Chemopreventive effect of dietary d-alpha-tocopheryl succinate supplementation on precancer colon aberrant crypt formation and vitamin E analogue levels in young and old rats

This study examined the effects of dietary d-alpha-tocopheryl succinate (TS) in female rats, 20 mo (OLD) or 2 mo (YNG) of age, on azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) and tissue distribution of d-alpha-tocopherol (alphaT), d-gamma-tocopherol (gammaT), and alphaTS. Rats were fed a commercial rodent chow supplemented with or without 1 (YNG) or 2 (OLD) g alphaTS/kg diet for 1 week prior to ip administration of AOM to induce colon ACF. The animals were sacrificed after 49 days of exposure. The results showed that OLD rats had significantly fewer ACF than YNG animals, and the percent body fat and serum triglycerides were significantly higher in the OLD group compared with the YNG. However, only OLD animals receiving alphaTS had significantly reduced numbers of larger ACF and significantly higher levels of colonic alphaT, gammaT, and alphaTS. These data support previous studies demonstrating that dietary alphaTS administration is protective against intestinal cancer. Also, this is the first study to show that alphaTS accumulates in most tissues following dietary exposure. We hypothesize that increased colon accumulation of fat-soluble vitamin E compounds and subsequent chemoprevention may be related to greater percent body fat and serum triglycerides in OLD animals receiving dietary TS.

Diverse developing mouse lineages exhibit high-level c-Myb expression in immature cells and loss of expression upon differentiation

The c-myb gene encodes a sequence specific transactivator that is required for fetal hematopoiesis, but its potential role in other tissues is less clear because of the early fetal demise of mice with targeted deletions of the c-myb gene and incomplete of knowledge about c-myb's expression pattern. In the hematopoietic system, c-Myb protein acts on target genes whose expression is restricted to individual lineages, despite Myb's presence and role in multiple immature lineages. This suggests that c-Myb actions within different cell type-specific contexts are strongly affected by combinatorial interactions. To consider the possibility of similar c-Myb actions could extend into non-hematopoietic systems in other cell and tissue compartments, we characterized c-myb expression in developing and adult mice using in situ hybridization and correlated this with stage-specific differentiation and mitotic activity. Diverse tissues exhibited strong c-myb expression during development, notably tooth buds, the thyroid primordium, developing trachea and proximal branching airway epithelium, hair follicles, hematopoietic cells, and gastrointestinal crypt epithelial cells. The latter three of these all maintained high expression into adulthood, but with characteristic restriction to immature cell lineages prior to their terminal differentiation. In all sites, during fetal and adult stages, loss of c-Myb expression correlated strikingly with the initiation of terminal differentiation, but not the loss of mitotic activity. Based on these data, we hypothesize that c-Myb's function during cellular differentiation is both an activator of immature gene expression and a suppressor of terminal differentiation in diverse lineages.

Differing proliferative responses in proximal and distal colons of growing rats fed food eaten by adenoma patients

Animal dietary studies related to human colorectal carcinogenesis are usually based on AIN-76A diet, which is dissimilar to human food in source, preparation, and content. Our aim was to examine colonic epithelial proliferation in rats fed a diet based on the mean daily food intake of adenoma patients. Foods were prepared as reported by the adenoma patients and dehydrated; 64 Sprague-Dawley rats were fed either "human adenoma" or AIN-76A diet and every eight weeks, eight from each group were sacrificed. Both groups gained weight equally, had no colonic histological changes, but during the study showed progressive lengthening of colonic crypts (P < 0.01) and decreased proliferation (P < 0.05) in distal colons. Compared to controls, rats fed human adenoma diet had significantly longer crypts (P < 0.01) and more labeled cells (P < 0.05) at 32 weeks; overall they had increased proliferation (P < 0.01), most significantly in the distal colon. Thus, food eaten by adenoma patients induced hyperproliferative changes in the rat colon during growth and maturity, especially the distal colon, as found in humans at risk for neoplasia.

Concentration polarization of fluorescent dyes in rat descending colonic crypts: evidence of crypt fluid absorption

1. Using confocal microscopy, the rate of fluid absorption into isolated perifused descending rat colonic crypt lumens is estimated from the concentration polarization and distribution of fluorescein sulphonate (FS) and fluorescein isothiocyanate-dextran (FITC-dextran; molecular weight, 10,000) within the crypt lumens and pericryptal fluid. 2. The probe dyes enter the crypt via the luminal opening, are concentrated in the lumen, then escape into the pericryptal space via the paracellular spaces spanning the crypt wall. 3. FITC-dextran is maximally accumulated at a luminal depth of 60 microns to 5 times the concentration at the crypt opening (p < 0.001) and penetrates 150-200 microns along the lumen. FS is maximally accumulated within crypt lumen close to the opening. At crypt luminal depths 10-60 microns from the opening FS is accumulated by a factor of 1.5-2.0 above that found in HgCl2-treated tissue (p < 0.001). 4. Dye enters the crypt lumen slowly from the basal side, but from this side does not accumulate above the bathing solution concentration. 5. HgCl2 (20 microM) or theophylline (10 mM) completely inhibit concentrative accumulation of FITC-dextran and FS within the crypts and pericryptal space (p < 0.001). 6. Computer simulation of the dye uptake indicates that the rate of water flow into the crypt luminal opening is 1 x 10(-3) cm s-1 which is equivalent to 15 microliters (cm mucosa)-2 h-1. Approximately 75% of the fluid entering the crypt is abosrbed across the proximal 50 microns of crypt wall as a consequence of the large osmotic pressure gradient between the pericryptal and crypt luminal solutions. A pericryptal diffusion barrier with lower permeability than that across the crypt wall is required to simulate dye accumulation in the pericryptal space. Differences between FITC-dextran and FS accumulation are explained by the lower diffusion coefficient within the crypt lumen, and lower crypt wall permeability of FITC-dextran.