Mild depletion of dietary folate combined with other B vitamins alters multiple components of the Wnt pathway in mouse colon

Whole-Genome Resequencing of Ujimqin Sheep Identifies Genes Associated with Vertebral Number

The number of vertebrae is a crucial economic trait that can significantly impact the carcass length and meat production in animals. However, our understanding of the quantitative trait loci (QTLs) and candidate genes associated with the vertebral number in sheep (Ovis aries) remains limited. To identify these candidate genes and QTLs, we collected 73 Ujimqin sheep with increased numbers of vertebrae (T13L7, T14L6, and T14L7) and 23 sheep with normal numbers of vertebrae (T13L6). Through high-throughput genome resequencing, we obtained a total of 24,130,801 effective single-nucleotide polymorphisms (SNPs). By conducting a selective-sweep analysis, we discovered that the most significantly selective region was located on chromosome 7. Within this region, we identified several genes, including VRTN, SYNDIG1L, LTBP2, and ABCD4, known to regulate the spinal development and morphology. Further, a genome-wide association study (GWAS) performed on sheep with increased and normal vertebral numbers confirmed that ABCD4 is a candidate gene for determining the number of vertebrae in sheep. Additionally, the most significant SNP on chromosome 7 was identified as a candidate QTL. Moreover, we detected two missense mutations in the ABCD4 gene; one of these mutations (Chr7: 89393414, C > T) at position 22 leads to the conversion of arginine (Arg) to glutamine (Gln), which is expected to negatively affect the protein's function. Notably, a transcriptome expression profile in mouse embryonic development revealed that ABCD4 is highly expressed during the critical period of vertebral formation (4.5-7.5 days). Our study highlights ABCD4 as a potential major gene influencing the number of vertebrae in Ujimqin sheep, with promising prospects for future genome-assisted breeding improvements in sheep.

Folate deficiency promotes cervical squamous carcinoma SiHa cells progression by targeting miR-375/FZD4/β-catenin signaling

Epidemiological studies suggest an association between folate deficiency (FD) and cervical squamous cell carcinoma (SCC) progression. However, the underlying mechanism is unclear. Our study showed that FD-driven downregulation of miR-375 promoted proliferation of SCC SiHa cells and progression of xenograft tumors developed from SiHa; however, the exact mechanism of this process remained unclear. The current study aimed to elucidate the underlying mechanisms by which FD promotes the progression of SiHa cells by downregulating miR-375 expression. The results showed that miR-375 acted as a suppressor of SCC and inhibited the proliferation, migration, and invasion of SiHa cells. The FZD4 gene was identified as a target gene of miR-375, which can reverse the anti-onco effect of miR-375 and promote the proliferation and migration of SiHa cells. Furthermore, the regulatory effects of miR-375 and FZD4 on SiHa cells may be achieved by activating the β-catenin signaling pathway. Moreover, FD may regulate the expression of miR-375 by regulating its DNA methylation level in the promoter region. In conclusion, our study reveals that FD regulates the miR-375/FZD4 axis by increasing the methylation of the miR-375 promoter, thereby activating β-catenin signaling to promote SiHa cells progression. This study may provide new insights into the role of folic acid in the prevention and treatment of SCC.

Genome-wide association study revealed ABCD4 on SSC7 and GREB1L and MIB1 on SSC6 as crucial candidate genes for rib number in Beijing Black pigs

As one of the few animals with variation in the number of rib pairs (RIB), the pig is a good model to study the mechanism of RIB regulation. Quantitative trait loci (QTL) for porcine RIB are present on Sus scrofa chromosome 7 (SSC7). Although several candidate genes exist in this QTL region on SSC7, the causal gene has yet to be verified. Beijing Black pig with 14-17 RIB is a good population for candidate gene mining and 1104 individuals were genotyped using the Illumina Porcine 50K BeadChip. A total of 14 SNPs from 95.49 to 97.78 Mb on SSC7 showed genome-wide significant association with RIB. On SSC7, a locuszoom plot using pairwise linkage disequilibrium displayed the narrowest linkage region encompassing only two genes, ABCD4 and VRTN. In mice, a transcriptome expression profile was obtained using three embryos at E9.5 (the critical period for rib formation). ABCD4 was highly expressed, but no expression of VRTN was detected. On SSC6, there were four genome-wide significant SNPs from 106.42 to 106.92 Mb associated with RIB. GREB1L and MIB1, in this region, were regarded as novel candidate genes. These results revealed a crucial candidate causal gene on SSC7 and novel genes on SSC6 for rib number and provided interesting new insights into its genetic basis.

B Vitamins and Their Roles in Gut Health

B vitamins act as coenzymes in a myriad of cellular reactions. These include energy production, methyl donor generation, neurotransmitter synthesis, and immune functions. Due to the ubiquitous roles of these vitamins, their deficiencies significantly affect the host’s metabolism. Recently, novel roles of B vitamins in the homeostasis of gut microbial ecology and intestinal health continue to be unravelled. This review focuses on the functional roles and biosynthesis of B vitamins and how these vitamins influence the growth and proliferation of the gut microbiota. We have identified the gut bacteria that can produce vitamins, and their biosynthetic mechanisms are presented. The effects of B vitamin deficiencies on intestinal morphology, inflammation, and its effects on intestinal disorders are also discussed.

Ability of dietary factors to affect homocysteine levels in mice: a review

Homocysteine is associated with several diseases, and a series of dietary factors are known to modulate homocysteine levels. As mice are often used as model organisms to study the effects of dietary hyperhomocysteinemia, we collected data about concentrations of vitamin B₁₂, vitamin B₆, folate, methionine, cystine, and choline in mouse diets and the associated plasma/serum homocysteine levels. In addition, we more closely examined the composition of the control diet, the impact of the mouse strain, sex and age, and the duration of the dietary intervention on homocysteine levels. In total, 113 out of 1103 reviewed articles met the inclusion criteria. In the experimental and control diets, homocysteine levels varied from 0.1 to 280 µmol/l. We found negative correlations between dietary vitamin B₁₂ (rho = − 0.125; p < 0.05), vitamin B₆ (rho = − 0.191; p < 0.01) and folate (rho = − 0.395; p < 0.001) and circulating levels of homocysteine. In contrast, a positive correlation was observed between dietary methionine and homocysteine (methionine: rho = 0.146; p < 0.05). No significant correlations were found for cystine or choline and homocysteine levels. In addition, there was no correlation between the duration of the experimental diets and homocysteine levels. More importantly, the data showed that homocysteine levels varied widely in mice fed control diets as well. When comparing control diets with similar nutrient concentrations (AIN-based), there were significant differences in homocysteine levels caused by the strain (ANOVA, p < 0.05) and age of the mice at baseline (r = 0.47; p < 0.05). When comparing homocysteine levels and sex, female mice tended to have higher homocysteine levels than male mice (9.3 ± 5.9 µmol/l vs. 5.8 ± 4.5 µmol/l; p = 0.069). To conclude, diets low in vitamin B₁₂, vitamin B₆, or folate and rich in methionine are similarly effective in increasing homocysteine levels. AIN recommendations for control diets are adequate with respect to the amounts of homocysteine-modulating dietary parameters. In addition, the mouse strain and the age of mice can affect the homocysteine level.

Response of MiRNA-22-3p and MiRNA-149-5p to Folate Deficiency and the Differential Regulation of MTHFR Expression in Normal and Cancerous Human Hepatocytes

Background/Aims

Folic acid (FA) is a core micronutrient involved in DNA synthesis/methylation, and the metabolism of FA is responsible for genomic stability. MicroRNAs may affect gene expression during folate metabolism when cellular homeostasis is changed. This study aimed to reveal the relationship between FA deficiency and the expression of miR-22-p/miR-149-5p and the targeted regulation of miR-22-3p/miR-149-5p on the key folate metabolic gene Methylenetetrahydrofolate reductase (MTHFR).

Methods

Normal (HL-7702 cells) and cancerous (QGY-7703 cells) human hepatocytes were intervened in modified RPMI 1640 with FA deficiency for 21 days. The interaction between MTHFR and the tested miRNAs was verified by Dual-Luciferase Reporter Assays. The changes in the expression of miR-22-3p/miR-149-5p in response to FA deficiency were detected by Poly (A) Tailing RT-qPCR, and the expression of MTHFR at both the transcriptional and translational levels was determined by RT-qPCR and Western blotting, respectively.

Result

MiR-22-3p/miR-149-5p directly targeted the 3’UTR sequence of the MTHFR gene. FA deficiency led to an upregulation of miR-22-3p/miR-149-5p expression in QGY-7703/HL-7702 cells, while the transcription of MTHFR was decreased in QGY-7703 cells but elevated in HL-7702 cells. Western blotting showed that FA deficiency resulted in a decline of the MTHFR protein in QGY-7703 cells, whereas in HL-7702 cells, the MTHFR protein level remained constant.

Conclusion

The results suggested that miR-22-3p/miR-149-5p exert different post-transcriptional effects on MTHFR under conditions of FA deficiency in normal and cancerous human hepatocytes. The results also implied that miR-22-3p/miR-149-5p might exert anticancer effects in cases of long-term FA deficiency.

Cellular and molecular effects of yeast probiotics on cancer

The cancer is one of the main causes of human deaths worldwide. The exact mechanisms of initiation and progression of malignancies are not clear yet, but there is a common agreement about the role of colonic microbiota in the etiology of different cancers. Probiotics have been examined for their anti-cancer effects, and different mechanisms have been suggested about their antitumor functions. Nonpathogenic yeasts, as members of probiotics family, can be effective on gut microbiota dysbiosis. Generally safe yeasts have shown so many beneficial effects on human health. Probiotic yeasts influence physiology, metabolism, and immune homeostasis in the colon and contribute to cancer treatment due to possessing anti-inflammatory, anti-proliferative and anti-cancer properties. This study reviews some of the health-beneficial effects of probiotic yeasts and their biological substances like folic acid and β-glucan on cancer and focuses on the possible cellular and molecular mechanisms of probiotic yeasts such as influencing pathogenic bacteria, inactivation of carcinogenic compounds, especially those derived from food, improvement of intestinal barrier function, modulation of immune responses, antitoxic function, apoptosis, and anti-proliferative effects.

Folate deficient tumor microenvironment promotes epithelial-to-mesenchymal transition and cancer stem-like phenotypes

Clinically, serum level of folate has been negatively correlated to the stage and progression of liver cancer. Nevertheless, the functional consequence of folate deficiency (FD) in malignancy has not been fully investigated. Human hepatocellular carcinoma (HCC) cells (as study model) and other cancer types such as lung and glioma were cultured under folate deficient (FD) and folate complete (FD) conditions. Molecular characterization including intracellular ROS/RNS (reactive oxygen/nitrogen species), viability, colony formation, cancer stem-like cell (CSC) phenotype analyses were performed. In vivo tumorigenesis under FD and FC conditions were also examined. FD induced a significant increase in ROS and RNS, suppressing proliferative ability but inducing metastatic potential. Mesenchymal markers such as Snail, ZEB2, and Vimentin were significantly up-regulated while E-cadherin down-regulated. Importantly, CSC markers such as Oct4, β-catenin, CD133 were induced while PRRX1 decreased under FD condition. Furthermore, FD-conditioned HCC cells showed a decreased miR-22 level, leading to the increased expression of its target genes including HDAC4, ZEB2 and Oct4. Finally, xenograft mouse model demonstrated that FD diet promoted tumorigenesis and metastasis as compared to their FC counterparts. Our data provides rationales for the consideration of folate supplement as a metastasis preventive measure.

Paternal B Vitamin Intake Is a Determinant of Growth, Hepatic Lipid Metabolism and Intestinal Tumor Volume in Female Apc1638N Mouse Offspring

Background

The importance of maternal nutrition to offspring health and risk of disease is well established. Emerging evidence suggests paternal diet may affect offspring health as well.

Objective

In the current study we sought to determine whether modulating pre-conception paternal B vitamin intake alters intestinal tumor formation in offspring. Additionally, we sought to identify potential mechanisms for the observed weight differential among offspring by profiling hepatic gene expression and lipid content.

Methods

Male Apc^1638N mice (prone to intestinal tumor formation) were fed diets containing replete (control, CTRL), mildly deficient (DEF), or supplemental (SUPP) quantities of vitamins B₂, B₆, B₁₂, and folate for 8 weeks before mating with control-fed wild type females. Wild type offspring were euthanized at weaning and hepatic gene expression profiled. Apc^1638N offspring were fed a replete diet and euthanized at 28 weeks of age to assess tumor burden.

Results

No differences in intestinal tumor incidence or burden were found between male Apc^1638N offspring of different paternal diet groups. Although in female Apc^1638N offspring there were no differences in tumor incidence or multiplicity, a stepwise increase in tumor volume with increasing paternal B vitamin intake was observed. Interestingly, female offspring of SUPP and DEF fathers had a significantly lower body weight than those of CTRL fed fathers. Moreover, hepatic trigylcerides and cholesterol were elevated 3-fold in adult female offspring of SUPP fathers. Weanling offspring of the same fathers displayed altered expression of several key lipid-metabolism genes. Hundreds of differentially methylated regions were identified in the paternal sperm in response to DEF and SUPP diets. Aside from a few genes including Igf2, there was a striking lack of overlap between these genes differentially methylated in sperm and differentially expressed in offspring.

Conclusions

In this animal model, modulation of paternal B vitamin intake prior to mating alters offspring weight gain, lipid metabolism and tumor growth in a sex-specific fashion. These results highlight the need to better define how paternal nutrition affects the health of offspring.

Mechanisms by Which Pleiotropic Amphiphilic n-3 PUFA Reduce Colon Cancer Risk

Colorectal cancer is one of the major causes of cancer-related mortality in both men and women worldwide. Genetic susceptibility and diet are primary determinants of cancer risk and tumor behavior. Experimental, epidemiological, and clinical data substantiate the beneficial role of n-3 polyunsaturated fatty acids (PUFA) in preventing chronic inflammation and colon cancer. From a mechanistic perspective, n-3 PUFA are pleiotropic and multifaceted with respect to their molecular mechanisms of action. For example, this class of dietary lipid uniquely alters membrane structure/ cytoskeletal function, impacting membrane receptor function and downstream signaling cascades, including gene expression profiles and cell phenotype. In addition, n-3 PUFA can synergize with other potential anti-tumor agents, such as fermentable fiber and curcumin. With the rising prevalence of diet-induced obesity, there is also an urgent need to elucidate the link between chronic inflammation in adipose tissue and colon cancer risk in obesity. In this review, we will summarize recent developments linking n-3 PUFA intake, membrane alterations, epigenetic modulation, and effects on obesity-associated colon cancer risk.

Azoxymethane-induced colon carcinogenesis in mice occurs independently of de novo thymidylate synthesis capacity

Folate metabolism affects DNA synthesis, methylation, mutation rates, genomic stability, and gene expression, which are altered in colon cancer. Serine hydroxymethyltransferase 1 (SHMT1) regulates thymidylate (dTMP) biosynthesis and uracil accumulation in DNA, and as such affects genome stability. Previously, we showed that decreased SHMT1 expression in Shmt1 knockout mice (Shmt1(-/+)) or its impaired nuclear localization, as occurs in mice over-expressing an Shmt1 transgene (Shmt1(tg+)), results in elevated uracil incorporation into DNA, which could affect colon cancer risk. We used these 2 models to determine the effect of altered SHMT1 expression and localization, and its interaction with folate insufficiency, on azoxymethane (AOM)-induced colon cancer in mice. Shmt1(-/+) and Shmt1(tg+) mice were weaned to a control or folate-and-choline-deficient (FCD) diet and fed the diet for 28 or 32 wk, respectively. At 6 wk of age, mice were injected weekly for 6 wk with 10 mg/kg AOM (w/v in saline). Colon uracil concentrations in nuclear DNA were elevated 2-7 fold in Shmt1(-/+) and Shmt1(tg+) mice. However, colon tumor incidence and numbers were not dependent on SHMT1 expression in Shmt1(-/+) or Shmt1(-/-) mice. The FCD diet reduced tumor load independent of Shmt1 genotype. In contrast, Shmt1(tg+) mice exhibited a 30% reduction in tumor incidence, a 50% reduction in tumor number, and a 60% reduction in tumor load compared with wild-type mice independent of dietary folate intake. Our data indicate that uracil accumulation in DNA does not predict tumor number in AOM-mediated carcinogenesis. Furthermore, enrichment of SHMT1 in the cytoplasm, as observed in Shmt1(tg+) mice, protects against AOM-mediated carcinogenesis independent of its role in nuclear de novo dTMP biosynthesis.

Effect of maternal and postweaning folic acid supplementation on global and gene-specific DNA methylation in the liver of the rat offspring

SCOPE

Intrauterine and early-life exposure to folic acid has significantly increased in North America owing to folic acid fortification, widespread supplemental use, and periconceptional supplementation. We investigated the effect of maternal and postweaning folic acid supplementation on DNA methylation in the rat offspring.

METHODS AND RESULTS

Female rats were placed on a control or folic acid-supplemented diet during pregnancy and lactation. At weaning, pups from each maternal diet group were randomized to the control or supplemented diet for 11 weeks. At weaning, maternal folic acid supplementation significantly decreased global (p < 0.001) and site-specific DNA methylation of the Ppar-γ, ER-α, p53, and Apc genes (p < 0.05) in the liver. At 14 weeks of age, postweaning, but not maternal, folic acid supplementation significantly decreased global DNA methylation (p < 0.05). At 14 weeks of age, both maternal and postweaning folic acid supplementation significantly increased DNA methylation of the Ppar-γ, p53, and p16 genes (p < 0.05) whereas only postweaning FA supplementation significantly increased DNA methylation of the ER-α and Apc genes (p < 0.05).

CONCLUSION

Our data suggest that maternal and postweaning folic acid supplementation can significantly modulate global and gene-specific DNA methylation in the rat offspring. The functional ramifications of the observed DNA methylation changes need to be determined in future studies.

Vitamin D intake is negatively associated with promoter methylation of the Wnt antagonist gene DKK1 in a large group of colorectal cancer patients

Diet and lifestyle influence colorectal cancer (CRC) risk but the molecular events that mediate these effects are poorly characterized. Several dietary and lifestyle factors can modulate DNA methylation suggesting that they may influence CRC risk through epigenetic regulation of cancer-related genes. The Wnt regulatory genes DKK1 and Wnt5a are important contributors to colonic carcinogenesis and are often silenced by promoter hypermethylation in CRC; however, the dietary contributions to these events have not been explored. To investigate the link between dietary/lifestyle factors and epigenetic regulation of these Wnt signaling genes, we assessed promoter methylation of these genes in a large cohort of Canadian CRC patients from Ontario (n = 549) and Newfoundland (n = 443) and examined associations to dietary/lifestyle factors implicated in CRC risk and/or DNA methylation including intake of vitamins, fats, cholesterol, fiber, and alcohol as well as body mass index (BMI), and smoking status. Several factors were associated with methylation status including alcohol intake, BMI, and cigarette smoking. Most significantly, however, dietary vitamin D intake was strongly negatively associated with DKK1 methylation in Newfoundland (P = 0.001) and a similar trend was observed in Ontario. These results suggest that vitamin D and other dietary/lifestyle factors may alter CRC risk by mediating extracellular Wnt inhibition.

A randomized clinical trial of the effects of supplemental calcium and vitamin D3 on the APC/β-catenin pathway in the normal mucosa of colorectal adenoma patients

APC/β-catenin pathway perturbation is a common early event in colorectal carcinogenesis and is affected by calcium and vitamin D in basic science studies. To assess the effects of calcium and vitamin D on adenomatous polyposis coli (APC), β-catenin, and E-cadherin expression in the normal appearing colorectal mucosa of sporadic colorectal adenoma patients, we conducted a randomized, double-blinded, placebo-controlled 2 × 2 factorial clinical trial. Pathology-confirmed colorectal adenoma cases were treated with 2 g/day elemental calcium and/or 800 IU/day vitamin D(3) versus placebo over 6 months (N = 92; 23/group). Overall APC, β-catenin, and E-cadherin expression and distributions in colon crypts in normal-appearing rectal mucosa biopsies were detected by standardized automated immunohistochemistry and quantified by image analysis. In the vitamin D(3)-supplemented group relative to placebo, the proportion of APC in the upper 40% of crypts (Φh APC) increased 21% (P = 0.01), β-catenin decreased 12% (P = 0.18), E-cadherin increased 72% (P = 0.03), and the Φh APC/β-catenin ratio (APC/β-catenin score) increased 31% (P = 0.02). In the calcium-supplemented group Φh APC increased 10% (P = 0.12), β-catenin decreased 15% (P = 0.08), and the APC/β-catenin score increased 41% (P = 0.01). In the calcium/vitamin D(3)-supplemented group, β-catenin decreased 11% (P = 0.20), E-cadherin increased 51% (P = 0.08), and the APC/β-catenin score increased 16% (P = 0.26). These results support (i) that calcium and vitamin D modify APC, β-catenin, and E-cadherin expression in humans in directions hypothesized to reduce risk for colorectal neoplasms, (ii) calcium and vitamin D as potential chemopreventive agents against colorectal neoplasms, and (iii) the potential of APC, β-catenin, and E-cadherin expression as modifiable, preneoplastic risk biomarkers for colorectal neoplasms.

Markers of the APC/β-catenin signaling pathway as potential treatable, preneoplastic biomarkers of risk for colorectal neoplasms

BACKGROUND

Malfunctioning of the adenomatous polyposis coli (APC)/β-catenin signaling pathway is both an early and common event in sporadic colorectal cancer. To assess the potential of APC/β-catenin signaling pathway markers as treatable, preneoplastic biomarkers of risk for colorectal neoplasms, we conducted a pilot colonoscopy-based case-control study (51 cases and 154 controls) of incident, sporadic colorectal adenoma.

METHODS

We evaluated APC, β-catenin, and E-cadherin expression in normal mucosa from the rectum and ascending and sigmoid colon using automated immunohistochemical and quantitative image analysis. Diet, lifestyle, and medical history were assessed with validated questionnaires.

RESULTS

In the normal rectal mucosa, the ratio of the proportion of APC expression in the upper 40% of crypts with total β-catenin expression (APC/β-catenin score) was 14.3% greater in controls than in cases [P = 0.02; OR, 0.40; 95% confidence interval (CI), 0.14-1.14]. Compared with controls, in cases, APC expression was 3.2% lower, β-catenin expression was 3.0% higher, and E-cadherin expression was 0.7% lower; however, none of these differences were statistically significant. The APC/β-catenin score statistically significantly differed according to categories of plausible risk factors for colorectal cancer [e.g., it was 17.7% higher among those with 25(OH) vitamin D(3) concentrations ≥ 27 ng/mL].

CONCLUSIONS

These preliminary data suggest that the combined expression of APC and β-catenin in the normal rectal mucosa may be associated with risk for incident, sporadic colorectal neoplasms, as well as with modifiable risk factors for colorectal neoplasms.

IMPACT

Our results may help advance the development of treatable, preneoplastic biomarkers of risk for colorectal neoplasms.

Maternal one-carbon nutrient intake and cancer risk in offspring

Dietary intake of one-carbon nutrients, particularly folate, vitamin B(2) (riboflavin), vitamin B(6) , vitamin B(12) , and choline have been linked to the risk of cancers of the colon and breast in both human and animal studies. More recently, experimental and epidemiological data have emerged to suggest that maternal intake of these nutrients during gestation may also have an impact on the risk of cancer in offspring later in life. Given the plasticity of DNA methylation in the developing embryo and the established role of one-carbon metabolism in supporting biological methylation reactions, it is plausible that alterations in maternal one-carbon nutrient availability might induce subtle epigenetic changes in the developing embryo and fetus that persist into later life, altering the risk of tumorigenesis throughout the lifespan. This review summarizes the current literature on maternal one-carbon nutrient intake and offspring cancer risk, with an emphasis on cancers of the colon and breast, and discusses specific epigenetic modifications that may play a role in their pathogenesis.

Nutritional influences on epigenetics and age-related disease

Nutritional epigenetics has emerged as a novel mechanism underlying gene-diet interactions, further elucidating the modulatory role of nutrition in aging and age-related disease development. Epigenetics is defined as a heritable modification to the DNA that regulates chromosome architecture and modulates gene expression without changes in the underlying bp sequence, ultimately determining phenotype from genotype. DNA methylation and post-translational histone modifications are classical levels of epigenetic regulation. Epigenetic phenomena are critical from embryonic development through the aging process, with aberrations in epigenetic patterns emerging as aetiological mechanisms in many age-related diseases such as cancer, CVD and neurodegenerative disorders. Nutrients can act as the source of epigenetic modifications and can regulate the placement of these modifications. Nutrients involved in one-carbon metabolism, namely folate, vitamin B12, vitamin B6, riboflavin, methionine, choline and betaine, are involved in DNA methylation by regulating levels of the universal methyl donor S-adenosylmethionine and methyltransferase inhibitor S-adenosylhomocysteine. Other nutrients and bioactive food components such as retinoic acid, resveratrol, curcumin, sulforaphane and tea polyphenols can modulate epigenetic patterns by altering the levels of S-adenosylmethionine and S-adenosylhomocysteine or directing the enzymes that catalyse DNA methylation and histone modifications. Aging and age-related diseases are associated with profound changes in epigenetic patterns, though it is not yet known whether these changes are programmatic or stochastic in nature. Future work in this field seeks to characterise the epigenetic pattern of healthy aging to ultimately identify nutritional measures to achieve this pattern.

Unraveling the complex relationship between folate and cancer risk

Epidemiologic evidence generally indicates that an abundant intake of foodstuffs rich in folate conveys protection against the development of colorectal cancer and perhaps some other common cancers as well. Preclinical models substantiate that the relationship is a genuinely causal one. However, the issue is rather complex because some observations in animal and human studies demonstrate that an overly abundant intake of folate among those who harbor existing foci of neoplasia might instead produce a paradoxical promotion of tumorigenesis. The pharmaceutical form of the vitamin, folic acid, might affect the process in a manner that is distinct from natural forms of the vitamin, although this remains a speculative concept. We should not allow the complex nature of this relationship to compel us to ignore it, as understanding its true nature will greatly facilitate our ability to construct intelligent, effective, and safe strategies for the prevention of birth defects and cancer.

Combined inadequacies of multiple B vitamins amplify colonic Wnt signaling and promote intestinal tumorigenesis in BAT-LacZxApc1638N mice

The Wnt pathway is a pivotal signaling cascade in colorectal carcinogenesis. The purpose of this work is to determine whether depletion of folate and other metabolically related B vitamins induces in vivo activation of intestinal Wnt signaling and whether this occurs in parallel with increased tumorigenesis. A hybrid mouse was created by crossing a Wnt-reporter animal (BAT-LacZ) with a model of colorectal cancer (Apc1638N). A mild depletion of folate and vitamins B₂, B₆, and B₁₂ was induced over 16 wk, and the control animals in each instance were pair fed a diet containing the basal requirement of these nutrients. The multiplicity of macroscopic tumors and aberrant crypt foci both increased by ~50% in the hybrid mice fed the depletion diet (P<0.05). A 4-fold elevation in Wnt signaling was produced by the depletion diet (P<0.05) and was accompanied by significant changes in the expression of a number of Wnt-related genes in a pattern consistent with its activation. Proliferation and apoptosis of the colonic mucosa both changed in a protransformational direction (P<0.05). In summary, mild depletion of multiple B vitamins produces in vivo activation of colonic Wnt signaling, implicating it as a key pathway by which B-vitamin inadequacies enhance intestinal tumorigenesis.

Altered folate availability modifies the molecular environment of the human colorectum: implications for colorectal carcinogenesis

Low folate status increases colorectal cancer risk. Paradoxically, overly abundant folate supplementation, which is not uncommon in the United States, may increase risk. The mechanisms of these effects are unknown. We conducted two translational studies to define molecular pathways in the human colon altered either by folate supplementation or by dietary folate depletion (followed by repletion). In the first study, 10 healthy, at-risk volunteers (with documented stable/normal folate intake) received supplemental folic acid (1 mg/d) for 8 weeks. In the second study, 10 similar subjects were admitted to a hospital as inpatients for 12 weeks to study folate depletion induced by a low folate diet. A repletion regimen of folic acid (1 mg/d) was provided for the last 4 of these weeks. Both studies included an 8-week run-in period to ensure stabilized folate levels prior to intervention. We obtained 12 rectosigmoid biopsies (from 4 quadrants of normal-appearing mucosa 10-15 cm from the anal verge) at baseline and at measured intervals in both studies for assessing the primary endpoints: genome-wide gene expression, genomic DNA methylation, promoter methylation (depletion/repletion study only), and p53 DNA strand breaks. Serum and rectosigmoid folate concentrations accurately tracked all changes in folate delivery (P < 0.05). In the first study, gene array analysis revealed that supplementation upregulated multiple inflammation- and immune-related pathways in addition to altering several 1-carbon-related enzymes (P < 0.001). In the second study, folate depletion downregulated genes involved in immune response, inflammation, the cell cycle, and mitochondrial/energy pathways; repletion reversed most of these changes. However, changes in gene expression after repletion in the second study (involving immune response and inflammation) did not reach the levels seen after supplementation in the first study. Neither genomic nor promoter-specific DNA methylation changed during the course of the depletion/repletion protocol, and genomic methylation did not change with supplementation in the first study. p53 DNA strand breaks increased with depletion after 12 weeks. In sum, depletion downregulates, whereas repletion or supplementation upregulates pathways related to inflammation and immune response. These findings provide novel support to the concept that excessive folate supplementation might promote colorectal carcinogenesis by enhancing proinflammatory and immune response pathways. These results indicate that modest changes in folate delivery create substantial changes in the molecular milieu of the human colon.

Shmt1 heterozygosity impairs folate-dependent thymidylate synthesis capacity and modifies risk of Apc(min)-mediated intestinal cancer risk

Folate-mediated one-carbon metabolism is required for the de novo synthesis of purines, thymidylate, and S-adenosylmethionine, the primary cellular methyl donor. Impairments in folate metabolism diminish cellular methylation potential and genome stability, which are risk factors for colorectal cancer (CRC). Cytoplasmic serine hydroxymethyltransferase (SHMT1) regulates the partitioning of folate-activated one-carbons between thymidylate and S-adenosylmethionine biosynthesis. Therefore, changes in SHMT1 expression enable the determination of the specific contributions made by thymidylate and S-adenosylmethionine biosynthesis to CRC risk. Shmt1 hemizygosity was associated with a decreased capacity for thymidylate synthesis due to downregulation of enzymes in its biosynthetic pathway, namely thymidylate synthase and cytoplasmic thymidine kinase. Significant Shmt1-dependent changes to methylation capacity, gene expression, and purine synthesis were not observed. Shmt1 hemizygosity was associated with increased risk for intestinal cancer in Apc(min)(/+) mice through a gene-by-diet interaction, indicating that the capacity for thymidylate synthesis modifies susceptibility to intestinal cancer in Apc(min)(/+) mice.

The Micronutrient Genomics Project: a community-driven knowledge base for micronutrient research

Micronutrients influence multiple metabolic pathways including oxidative and inflammatory processes. Optimum micronutrient supply is important for the maintenance of homeostasis in metabolism and, ultimately, for maintaining good health. With advances in systems biology and genomics technologies, it is becoming feasible to assess the activity of single and multiple micronutrients in their complete biological context. Existing research collects fragments of information, which are not stored systematically and are thus not optimally disseminated. The Micronutrient Genomics Project (MGP) was established as a community-driven project to facilitate the development of systematic capture, storage, management, analyses, and dissemination of data and knowledge generated by biological studies focused on micronutrient–genome interactions. Specifically, the MGP creates a public portal and open-source bioinformatics toolbox for all “omics” information and evaluation of micronutrient and health studies. The core of the project focuses on access to, and visualization of, genetic/genomic, transcriptomic, proteomic and metabolomic information related to micronutrients. For each micronutrient, an expert group is or will be established combining the various relevant areas (including genetics, nutrition, biochemistry, and epidemiology). Each expert group will (1) collect all available knowledge, (2) collaborate with bioinformatics teams towards constructing the pathways and biological networks, and (3) publish their findings on a regular basis. The project is coordinated in a transparent manner, regular meetings are organized and dissemination is arranged through tools, a toolbox web portal, a communications website and dedicated publications.

A lentivirus-mediated genetic screen identifies dihydrofolate reductase (DHFR) as a modulator of beta-catenin/GSK3 signaling

The multi-protein beta-catenin destruction complex tightly regulates beta-catenin protein levels by shuttling beta-catenin to the proteasome. Glycogen synthase kinase 3beta (GSK3beta), a key serine/threonine kinase in the destruction complex, is responsible for several phosphorylation events that mark beta-catenin for ubiquitination and subsequent degradation. Because modulation of both beta-catenin and GSK3beta activity may have important implications for treating disease, a complete understanding of the mechanisms that regulate the beta-catenin/GSK3beta interaction is warranted. We screened an arrayed lentivirus library expressing small hairpin RNAs (shRNAs) targeting 5,201 human druggable genes for silencing events that activate a beta-catenin pathway reporter (BAR) in synergy with 6-bromoindirubin-3'oxime (BIO), a specific inhibitor of GSK3beta. Top screen hits included shRNAs targeting dihydrofolate reductase (DHFR), the target of the anti-inflammatory compound methotrexate. Exposure of cells to BIO plus methotrexate resulted in potent synergistic activation of BAR activity, reduction of beta-catenin phosphorylation at GSK3-specific sites, and accumulation of nuclear beta-catenin. Furthermore, the observed synergy correlated with inhibitory phosphorylation of GSK3beta and was neutralized upon inhibition of phosphatidyl inositol 3-kinase (PI3K). Linking these observations to inflammation, we also observed synergistic inhibition of lipopolysaccharide (LPS)-induced production of pro-inflammatory cytokines (TNFalpha, IL-6, and IL-12), and increased production of the anti-inflammatory cytokine IL-10 in peripheral blood mononuclear cells exposed to GSK3 inhibitors and methotrexate. Our data establish DHFR as a novel modulator of beta-catenin and GSK3 signaling and raise several implications for clinical use of combined methotrexate and GSK3 inhibitors as treatment for inflammatory disease.

Folate rescues lithium-, homocysteine- and Wnt3A-induced vertebrate cardiac anomalies

Elevated plasma homocysteine (HCy), which results from folate (folic acid, FA) deficiency, and the mood-stabilizing drug lithium (Li) are both linked to the induction of human congenital heart and neural tube defects. We demonstrated previously that acute administration of Li to pregnant mice on embryonic day (E)6.75 induced cardiac valve defects by potentiating Wnt-beta-catenin signaling. We hypothesized that HCy may similarly induce cardiac defects during gastrulation by targeting the Wnt-beta-catenin pathway. Because dietary FA supplementation protects from neural tube defects, we sought to determine whether FA also protects the embryonic heart from Li- or HCy-induced birth defects and whether the protection occurs by impacting Wnt signaling. Maternal elevation of HCy or Li on E6.75 induced defective heart and placental function on E15.5, as identified non-invasively using echocardiography. This functional analysis of HCy-exposed mouse hearts revealed defects in tricuspid and semilunar valves, together with altered myocardial thickness. A smaller embryo and placental size was observed in the treated groups. FA supplementation ameliorates the observed developmental errors in the Li- or HCy-exposed mouse embryos and normalized heart function. Molecular analysis of gene expression within the avian cardiogenic crescent determined that Li, HCy or Wnt3A suppress Wnt-modulated Hex (also known as Hhex) and Islet-1 (also known as Isl1) expression, and that FA protects from the gene misexpression that is induced by all three factors. Furthermore, myoinositol with FA synergistically enhances the protective effect. Although the specific molecular epigenetic control mechanisms remain to be defined, it appears that Li or HCy induction and FA protection of cardiac defects involve intimate control of the canonical Wnt pathway at a crucial time preceding, and during, early heart organogenesis.

Polymorphisms in uracil-processing genes, but not one-carbon nutrients, are associated with altered DNA uracil concentrations in an urban Puerto Rican population

BACKGROUND

Five genes--UNG, SMUG1, MBD4, TDG, and DUT--are involved in the repair or prevention of uracil misincorporation into DNA, an anomaly that can cause mutagenic events that lead to cancer. Little is known about the determinants of uracil misincorporation, including the effects of single nucleotide polymorphisms (SNPs) in the abovementioned genes. Because of their metabolic function, folate and other one-carbon micronutrients may be important factors in the control of uracil misincorporation.

OBJECTIVES

We sought to identify polymorphisms in uracil-processing genes that are determinants of DNA uracil concentration and to establish whether one-carbon nutrient status can further modify their effects.

DESIGN

We examined the relations between 23 selected variants in the 5 uracil-processing genes, uracil concentrations in whole-blood DNA, and one-carbon nutrient (folate, vitamins B-6 and B-12, and riboflavin) status in 431 participants of the Boston Puerto Rican Health Study.

RESULTS

Four SNPs in DUT, UNG, and SMUG1 showed a significant association with DNA uracil concentration. The SNPs in SMUG1 (rs2029166 and rs7296239) and UNG (rs34259) were associated with increased uracil concentrations in the variant genotypes (P = 0.011, 0.022, and 0.045, respectively), whereas the DUT SNP (rs4775748) was associated with a decrease (P = 0.023). In this population, one-carbon nutrient status was not associated with DNA uracil concentration, and it did not modify the effect of these 4 identified SNPs.

CONCLUSION

Because elevated uracil misincorporation may induce mutagenic lesions, possibly leading to cancer, we propose that the 4 characterized SNPs in DUT, UNG, and SMUG1 may influence cancer risk and therefore deserve further investigation.

Folate, cancer risk, and the Greek god, Proteus: a tale of two chameleons

Evidence indicates that an abundant intake of foodstuffs rich in folate conveys protection against the development of colorectal cancer, and perhaps some other common cancers as well. The issue is complex, however, since some observations in animal and human studies demonstrate that an overly abundant intake of folate among those who harbor existing foci of neoplasia might instead produce a paradoxical promotion of tumorigenesis. The pharmaceutical form of the vitamin, folic acid, might affect the process in a manner that is distinct from natural forms of the vitamin, although this remains a speculative concept. Our limited understanding of this complex relationship is impeding efforts to move ahead with widespread folic acid fortification, but this delay may be necessary to ensure that such programs are instituted in a safe manner.

Intestinal neoplasia induced by low dietary folate is associated with altered tumor expression profiles and decreased apoptosis in mouse normal intestine

Epidemiological studies suggest that low dietary folate increases risk for intestinal neoplasia. We recently developed a unique tumor model in which mice fed low dietary folate developed DNA damage and intestinal tumors. To identify additional mechanisms by which reduced folate intake contributes to tumor formation in this model, we characterized gene expression signatures in tumors. A total of 175 probe sets had altered expression, with the majority (173) showing increased expression compared with normal intestine. Functional categorization revealed that most genes were involved in cancer (51 genes) or cell death (37 genes); 31 genes appeared in both categories. Because apoptosis resistance is a hallmark of neoplasia, we assessed apoptosis in normal intestine of mice fed control (CD) and low-folate diets (FD); apoptosis was reduced in FD normal intestine compared with CD intestine by active caspase-3 expression (P = 0.027) and caspase-3/7 activities (P = 0.059). We selected candidate genes with antiapoptotic properties that had increased expression in tumor microarrays, CD44, and gelsolin and confirmed these increases at the mRNA and protein levels. CD44 and gelsolin protein also increased in mice fed the FD compared with the CD, normal intestine. Bcl-2-like 1:Bcl-2-antagonist/killer 1 mRNA ratios tended to be greater in FD than in CD normal intestine (P = 0.056). In conclusion, tumors induced by low dietary folate exhibited gene expression profiles that are characteristic of disrupted apoptosis. Folate depletion in normal intestine may trigger neoplasia through increased DNA damage and defective apoptosis; upregulation of CD44 and gelsolin, and the mitochondrial apoptotic pathway are implicated.

Multiple B-vitamin inadequacy amplifies alterations induced by folate depletion in p53 expression and its downstream effector MDM2

Folate is required for biological methylation and nucleotide synthesis, aberrations of which are thought to be the mechanisms that enhance colorectal carcinogenesis produced by folate inadequacy. These functions of folate also depend on the availability of other B-vitamins that participate in "one-carbon metabolism," including B2, B6 and B12. Our study therefore investigated whether combined dietary restriction of these vitamins amplifies aberrations in the epigenetic and genetic integrity of the p53 gene that is induced by folate depletion alone. Ninety-six mice were group pair-fed diets with different combinations of B-vitamin depletion over 10 weeks. DNA and RNA were extracted from epithelial cells isolated from the colon. Within the hypermutable region of p53 (exons 5-8), DNA strand breaks were induced within exons 6 and 8 by folate combined with B2, B6 and B12 restriction (p < 0.05); such effects were not significantly induced by mild folate depletion alone. Similarly, a minor degree of hypomethylation of exon 6 produced by isolated folate depletion was significantly amplified (p < or = 0.05) by simultaneous depletion of all 4 B-vitamins. Furthermore, the expression of p53 and MDM2 were significantly decreased (p < or = 0.05) by the combined depletion state but not by folate depletion alone. These data indicate that inadequacies of other 1-carbon vitamins may amplify aberrations of the p53 gene induced by folate depletion alone, implying that concurrent inadequacies in several of these vitamins may have added tumorigenic potential beyond that observed with isolated folate depletion.