Lgr5+ intestinal crypt base columnar cells function as stem cells whose progeny populate the villi, and Lgr5+ cells in which Apc is inactivated can give rise to tumors. Surprisingly, these Lgr5+ stem cell properties were abrogated by the lower dietary vitamin D and calcium in a semi-purified diet that promotes both genetically initiated and sporadic intestinal tumors. Inactivation of the vitamin D receptor in Lgr5+ cells established that compromise of Lgr5 stem cell function was a rapid, cell autonomous effect of signaling through the vitamin D receptor. The loss of Lgr5 stem cell function was associated with presence of Ki67 negative Lgr5+ cells at the crypt base. Therefore, vitamin D, a common nutrient and inducer of intestinal cell maturation, is an environmental factor that is a determinant of Lgr5+ stem cell functions in vivo. Since diets used in reports that establish and dissect mouse Lgr5+ stem cell activity likely provided vitamin D levels well above the range documented for human populations, the contribution of Lgr5+ cells to intestinal homeostasis and tumor formation in humans may be significantly more limited, and variable in the population, then suggested by published rodent studies.

Nutritional and genetic risk factors for intestinal tumors are additive on mouse tumor phenotype, establishing that diet and genetic factors impact risk by distinct combinatorial mechanisms. In a mouse model of dietary-induced sporadic small and large intestinal cancer in WT mice in which tumor etiology, lag, incidence, and frequency reflect >90% of intestinal cancer in Western societies, dietary-induced risk altered gene expression profiles predominantly in villus cells of the histologically normal mucosa, in contrast to targeting of crypt cells by inheritance of an Apc 1638N allele or homozygous inactivation of p21 Waf1/cip1 , and profiles induced by each risk factor were distinct at the gene or functional group level. The dietary-induced changes in villus cells encompassed ectopic expression of Paneth cell markers (a lineage normally confined to the bottom of small intestinal crypts), elevated expression of the Wnt receptor Fzd5 and of EphB2 (genes necessary for Paneth cell differentiation and localization to the crypt bottom), and increased Wnt signaling in villus cells. Ectopic elevation of these markers was also present in the colon crypts, which are also sites of sporadic tumors in the nutritional model. Elevating dietary vitamin D 3 and calcium, which prevents tumor development, abrogated these changes in the villus and colon cells. Thus, common intestinal cancer driven by diet involves mechanisms of tumor development distinct from those mechanisms that cause tumors induced by the rare inheritance of a mutant adenomatous polyposis coli (Apc) allele. This is fundamental for understanding how common sporadic tumors arise and in evaluating relative risk in the population.sporadic | colon cancer | Western diet | microarray

Male and female C57Bl6 mice were fed a control AIN76A diet, a new Western-style diet (NWD1) reflecting dietary patterns linked to elevated colon cancer incidence (higher fat, lower cholecalciferol, calcium, methyl donors, fiber), or NWD1 with elevated cholecalciferol and calcium (NWD2) from weaning. After 24 wk, serum 25-hydroxyvitamin D [25(OH)D] decreased by >80% in the NWD1 group compared with controls, but with no alteration in serum calcium or bone mineral density. The decreased serum 25(OH)D was prevented in the NWD2 group. After 32 wk, the NWD1 group compared with controls reduced overall energy expenditure by 15% without altering food consumption or physical activity and induced glucose intolerance, phenotypes associated with metabolic syndrome. These responses were unexpectedly exacerbated in the NWD2 group, further shifting mice toward greater fatty acid storage rather than oxidation compared with both control and NWD1 groups, but there was no change in physical activity, causing significant weight gain due to increased fat mass. The NWD1 group also exhibited inflammatory responses compared with controls, including macrophage-associated crown-like structures in epididymal adipose tissue and increased serum concentrations of the proinflammatory cytokine IL-1β, and of its targets, MCP-1 and Rantes, which were prevented or greatly mitigated in the NWD2 group. However, there was also elevated lipid storage in the liver and steatosis not seen in the control and NWD1 groups. Thus, elevating cholecalciferol and calcium in a Western-style diet can reduce inflammation associated with risk for colon tumor development, but interaction of nutrients in this diet can compromise liver function when fed long term.

The mucus layer in the intestine affects several aspects of intestinal biology, encompassing physical, chemical protection, immunomodulation and growth, thus contributing to homeostasis. Mice with genetic inactivation of the Muc2 gene, encoding the MUC2 mucin, the major protein component of mucus, exhibit altered intestinal homeostasis, which is strictly dependent on the habitat, likely due to differing complements of intestinal microbes. Our previous work established that Muc2 deficiency was linked to low chronic inflammation resulting in tumor development in the small, large intestine including the rectum. Here, we report that inactivation of Muc2 alters metabolic pathways in the normal appearing mucosa of Muc2−/− mice. Comparative analysis of gene expression profiling of isolated intestinal epithelial cells (IECs) and the entire intestinal mucosa, encompassing IECs, immune and stromal cells underscored that more than 50% of the changes were common to both sets of data, suggesting that most alterations were IEC-specific. IEC-specific expression data highlighted perturbation of lipid absorption, processing and catabolism linked to altered Pparα signaling in IECs. Concomitantly, alterations of glucose metabolism induced expression of genes linked to de novo lipogenesis, a characteristic of tumor cells. Importantly, gene expression alterations characterizing Muc2−/− IECs are similar to those observed when analyzing the gene expression signature of IECs along the crypt-villus axis in WT B6 mice, suggesting that Muc2−/− IECs display a crypt-like gene expression signature. Thus, our data strongly suggest that decreased lipid metabolism, and alterations in glucose utilization characterize the crypt proliferative compartment, and may represent a molecular signature of pre-neoplastic lesions.

Dietary factors are significant in determining probability for intestinal tumor development even in the presence of strong genetic initiation. For example, a rodent Western-style diet (WD1), modeled to reproduce intake of nutrient risk factors in the human diet associated with sporadic colon cancer, potentiates the formation of intestinal tumors in Apc1638N/+ mice, even when the genetic initiation by Apc is augmented by targeted inactivation of the p21Waf1/cip1 locus. To investigate mechanisms of this synergistic effect, we profiled gene expression along the mouse crypt-villus axis (CVA) using cells isolated as a function of their position along this axis from WT, Apc1638N/+ and p21−/− mice fed control AIN76A diet, and WT mice fed the WD1. Modulation of sequence expression by the WD1 was enriched in the villus compartment, while changes induced by targeting either genetic locus (Apc1638N/+ or p21−/−) were largely in the crypt, where the overlap in altered gene sets was greatest for the genetic models. There was greater overlap among expression changes between Apc1638N/+ and p21−/− mice, than between these genetic mice models and mice fed the WD1, in both the villus and crypt. Paneth cell markers, whose deregulation has been reported in intestinal tumors, were up-regulated in the p21−/− mouse crypt and in WD1 mouse villus. Moreover, there was attenuated expression of secretory cell lineage markers (ie goblet and enteroendocrine cells), but enhanced expression of enterocyte markers, for both the genetic and dietary models. Genes that encode tricarboxylic acid (TCA) cycle enzymes were uniformly decreased in the crypt of both genetic models, with fewer changes in this pathway altered in the WD1 mouse. Gene ontology and biological pathway analysis also showed that Wnt pathway and c-myc target genes were overrepresented in the villus of the WD1 mouse. Supplementation of WD1 with calcium and vitamin D (WD2) reversed aberrantly up-regulated cyclin D1, cyclin D2, defensins and lysozymes in the WD1 villus back to control levels. In summary, complementary changes in cell reprogramming contributed by a western style diet and targeted inactivation of the p21 gene are important in the synergy of these factors in elevating probability of intestinal tumorigenesis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4157.