A Comparison of the Gene Expression Profiles of Non-Alcoholic Fatty Liver Disease between Animal Models of a High-Fat Diet and Methionine-Choline-Deficient Diet

Non-alcoholic fatty liver disease (NAFLD) embraces several forms of liver disorders involving fat disposition in hepatocytes ranging from simple steatosis to the severe stage, namely, non-alcoholic steatohepatitis (NASH). Recently, several experimental in vivo animal models for NAFLD/NASH have been established. However, no reproducible experimental animal model displays the full spectrum of pathophysiological, histological, molecular, and clinical features associated with human NAFLD/NASH progression. Although methionine-choline-deficient (MCD) diet and high-fat diet (HFD) models can mimic histological and metabolic abnormalities of human disease, respectively, the molecular signaling pathways are extremely important for understanding the pathogenesis of the disease. This review aimed to assess the differences in gene expression patterns and NAFLD/NASH progression pathways among the most common dietary animal models, i.e., HFD- and MCD diet-fed animals. Studies showed that the HFD and MCD diet could induce either up- or downregulation of the expression of genes and proteins that are involved in lipid metabolism, inflammation, oxidative stress, and fibrogenesis pathways. Interestingly, the MCD diet model could spontaneously develop liver fibrosis within two to four weeks and has significant effects on the expression of genes that encode proteins and enzymes involved in the liver fibrogenesis pathway. However, such effects in the HFD model were found to occur after 24 weeks with insulin resistance but appear to cause less severe fibrosis. In conclusion, assessing the abnormal gene expression patterns caused by different diet types provides valuable information regarding the molecular mechanisms of NAFLD/NASH and predicts the clinical progression of the disease. However, expression profiling studies concerning genetic variants involved in the development and progression of NAFLD/NASH should be conducted.

TGF-β/YB-1/Atg7 axis promotes the proliferation of hepatic progenitor cells and liver fibrogenesis

Hepatic fibrosis is characterized by excessive extracellular matrix deposition and ductular reactions, manifested as the expansion of hepatic progenitor cells (HPCs). We previously reported that the Y-box binding protein 1 (YB-1) in HPCs is involved in chronic liver injury. In this study, we constructed YB-1f/f Foxl1-Cre mice and investigated the role of YB-1 in HPC expansion in murine choline-deficient, ethionine-supplemented (CDE), and 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) models. Liver injury and fibrosis were measured using hematoxylin and eosin (HE), Masson, and Sirius Red staining. HPC proliferation was detected using EdU and immunofluorescence (IF). Autophagic flow was measured by mCherry-GFP-LC3B staining and transmission electron microscopy (TEM). YB-1 expression was measured by immunofluorescence and western blotting. CUT & Tag analysis, chromatin immunoprecipitation, and RT-PCR were performed to explore the regulation of autophagy-related protein 7 (Atg7) transcription by YB-1. Our results indicated that liver injury was accompanied by high expression of YB-1, proliferative HPCs, and activated autophagy in the CDE and DDC models. YB-1f/f Cre+/- mice displayed less liver injury and fibrosis than YB-1f/f Cre-/- mice in the CDE and DDC models. YB-1 promoted proliferation and autophagy of HPCs in vitro and in vivo. Transforming growth factor-β (TGF-β) induced YB-1 nuclear translocation and facilitated the proliferation and autophagy of HPCs. YB-1 nuclear translocation promoted the transcription of Atg7, which is essential for TGF-β/YB-1 mediated HPCs expansion in vitro and in vivo. In summary, YB-1 nuclear translocation induced by TGF-β in HPCs promotes the proliferation and autophagy of HPCs and Atg7 participates in YB-1-mediated HPC-expansion and liver fibrosis.

Salvia-Nelumbinis naturalis extract protects mice against MCD diet-induced steatohepatitis via activation of colonic FXR-FGF15 pathway

Salvia-Nelumbinis naturalis (SNN) formula is a traditional Chinese medicine prescription, and has been confirmed to be effective in treating non-alcoholic steatohepatitis (NASH), but the underlying mechanisms are still unknown. Here we showed that 4-week SNN administration alleviated methionine-choline-deficiency (MCD) diet-induced hepatic steatosis and inflammation as well as serum levels of alanine transaminase (ALT) increase in C57BL/6 mice. Fecal 16S rDNA sequencing indicated that SNN altered the structure of gut microbiota and partially reversed the gut dysbiosis. Simultaneously, we analyzed the fecal BA profile using liquid chromatography coupled with triple quadrupole mass spectrometry (UPLC-TQMS) -based metabolomics, and found that SNN modulated fecal BA profile, predominantly increased the microbiomes related BA species (e.g. nordeoxycholic acid) which in turn, activated farnesoid X receptor (FXR)-fibroblast growth factor 15 (FGF15) signaling pathway in the colon but not the ileum. The activation of intestinal FXR-FGF15 signaling was accompanied by increase of liver protein kinase B (PKB/Akt) phosphorylation, and decrease of p-65 subunit of NF-κB phosphorylation, resulting in less liver CD68 positive macrophages, and inflammatory cytokine IL-1β and TNF-α expression. Our results established the link between SNN treatment, gut microbiota, BA profile and NASH, which might shed light into the mechanisms behind the beneficial effects of SNN on NASH, thus provide evidence for the clinical application of SNN.

Deletion of TRPC3 or TRPC6 Fails to Attenuate the Formation of Inflammation and Fibrosis in Non-alcoholic Steatohepatitis

Non-alcoholic steatohepatitis (NASH) is a disease that has progressed from non-alcoholic fatty liver disease (NAFLD) and is characterized by inflammation and fibrosis. Two transient receptor potential canonical (TRPC) subfamily members, TRPC3 and TRPC6 (TRPC3/6), reportedly participate in the development of fibrosis in cardiovascular and renal systems. We hypothesized that TRPC3/6 may also participate in NASH fibrosis. We evaluated the effects of TRPC3 or TRPC6 functional deficiency in a NASH mouse model using choline-deficient, L-amino acid-defined, high-fat diet (CDAHFD). Wild-type (WT) and TRPC3 or TRPC6 gene-deficient (KO) mice were fed with CDAHFD or standard diet for 6 weeks. The CDAHFD-induced body weight loss in TRPC6 KO mice was significantly lower compared with WT mice with CDAHFD. CDAHFD treatment significantly increased TRPC3 mRNA expression level and tissue weight in WT liver, which were suppressed in TRPC3 KO mice. However, either systemic deletion of TRPC3 or TRPC6 failed to attenuate liver steatosis, inflammation and fibrosis. These results imply that TRPC3 and TRPC6 are unlikely to be involved in liver dysfunction and fibrosis of NASH model mice.

Low Maternal Dietary Intake of Choline Regulates Toll-Like Receptor 4 Expression Via Histone H3K27me3 in Fetal Mouse Neural Progenitor Cells

SCOPE

Choline is an essential nutrient and a primary dietary source of methyl groups that are vital for brain development. Low choline (LC) in the maternal diet during pregnancy alters neurogenesis in the fetal brain and leads to low cognitive performance. However, the key signaling pathways that are sensitive to maternal choline supply during neural progenitor cell (NPC) development and the epigenetic mechanisms by which choline availability regulates gene expression are unclear.

METHODS AND RESULTS

Timed-pregnant Nestin-CFPnuc transgenic mice are fed either a control diet or LC diet during E11-17. Gene expression changes in sorted E17 NPCs are identified by RNA sequencing. A maternal LC diet significantly increases Tlr4 transcription, causing premature neuronal differentiation and enhanced ethanol-induced NLRP3 inflammasome activation. No changes in DNA methylation at the Tlr4 gene promoter region are detected; however, a 70% decrease in H3K27me3 is observed in the LC-treated NPCs. Inhibition of EZH2 decreases H3K27me3 levels and increases Tlr4 expression. Conversely, the application of catalytically inactive Cas9 with EZH2 to increase H3K27me3 at the Tlr4 promoter causes reduced Tlr4 expression.

CONCLUSION

These data reveal an epigenetic mechanism for the effect of maternal choline availability on brain development, suggesting a likely intervention for neurodevelopmental diseases.

Fatty acids in non-alcoholic steatohepatitis: Focus on pentadecanoic acid

Non-alcoholic fatty liver disease (NAFLD) is the most common form of liver disease and ranges from isolated steatosis to NASH. To determine whether circulating fatty acids could serve as diagnostic markers of NAFLD severity and whether specific fatty acids could contribute to the pathogenesis of NASH, we analyzed two independent NAFLD patient cohorts and used the methionine- and choline-deficient diet (MCD) NASH mouse model. We identified six fatty acids that could serve as non-invasive markers of NASH in patients with NAFLD. Serum levels of 15:0, 17:0 and 16:1n7t negatively correlated with NAFLD activity scores and hepatocyte ballooning scores, while 18:1n7c serum levels strongly correlated with fibrosis stage and liver inflammation. Serum levels of 15:0 and 17:0 also negatively correlated with fasting glucose and AST, while 16:1n7c and 18:1n7c levels positively correlated with AST and ferritin, respectively. Inclusion of demographic and clinical parameters improved the performance of the fatty acid panels in detecting NASH in NAFLD patients. The panel [15:0, 16:1n7t, 18:1n7c, 22:5n3, age, ferritin and APRI] predicted intermediate or advanced fibrosis in NAFLD patients, with 82% sensitivity at 90% specificity [AUROC = 0.92]. 15:0 and 18:1n7c were further selected for functional studies in vivo. Mice treated with 15:0-supplemented MCD diet showed reduced AST levels and hepatic infiltration of ceroid-laden macrophages compared to MCD-treated mice, suggesting that 15:0 deficiency contributes to liver injury in NASH. In contrast, 18:1n7c-supplemented MCD diet didn’t affect liver pathology. In conclusion, 15:0 may serve as a promising biomarker or therapeutic target in NASH, opening avenues for the integration of diagnosis and treatment.

Supplementary choline attenuates olive oil lipid emulsion-induced enterocyte apoptosis through suppression of CELF1/AIF pathway

Enterocyte apoptosis induced by lipid emulsions is a key cause of intestinal atrophy under total parenteral nutrition (TPN) support, and our previous work demonstrated that olive oil lipid emulsion (OOLE) could induce enterocyte apoptosis via CUGBP, Elav‐like family member 1 (CELF1)/ apoptosis‐inducing factor (AIF) pathway. As TPN‐associated complications are partially related to choline deficiency, we aimed to address whether choline supplementation could attenuate OOLE‐induced enterocyte apoptosis. Herein we present evidence that supplementary choline exhibits protective effect against OOLE‐induced enterocyte apoptosis both in vivo and in vitro. In a rat model of TPN, substantial reduction in apoptotic rate along with decreased expression of CELF1 was observed when supplementary choline was added to OOLE. In cultured Caco‐2 cells, supplementary choline attenuated OOLE‐induced apoptosis and mitochondria dysfunction by suppressing CELF1/AIF pathway. Compared to OOLE alone, the expression of CELF1 and AIF was significantly decreased by supplementary choline, whereas the expression of Bcl‐2 was evidently increased. No obvious alterations were observed in Bax expression and caspase‐3 activation. Mechanistically, supplementary choline repressed the expression of CELF1 by increasing the recruitment of CELF1 mRNA to processing bodies, thus resulting in suppression of its protein translation. Taken together, our data suggest that supplementary choline exhibits effective protection against OOLE‐induced enterocyte apoptosis, and thus, it has the potential to be used for the prevention and treatment of TPN‐induced intestinal atrophy.

Carbon monoxide protects against hepatic steatosis in mice by inducing sestrin-2 via the PERK-eIF2α-ATF4 pathway

Nonalcoholic fatty liver disease (NAFLD), the hepatic manifestation of the metabolic syndrome, has emerged as one of the most common causes of chronic liver disease in developed countries over the last decade. NAFLD comprises a spectrum of pathological hepatic changes, including steatosis, steatohepatitis, advanced fibrosis, and cirrhosis. Autophagy, a homeostatic process for protein and organelle turnover, is decreased in the liver during the development of NAFLD. Previously, we have shown that carbon monoxide (CO), a reaction product of heme oxygenase (HO) activity, can confer protection in NAFLD, though the molecular mechanisms remain unclear. We therefore investigated the mechanisms underlying the protective effect of CO on methionine/choline-deficient (MCD) diet-induced hepatic steatosis. We found that CO induced sestrin-2 (SESN2) expression through enhanced mitochondrial ROS production and protected against MCD-induced NAFLD progression through activation of autophagy. SESN2 expression was increased by CO or CO-releasing molecule (CORM2), in a manner dependent on signaling through the protein kinase R-like endoplasmic reticulum kinase (PERK), eukaryotic initiation factor-2 alpha (eIF2α)/ activating transcription factor-4 (ATF4)-dependent pathway. CO-induced SESN2 upregulation in hepatocytes contributed to autophagy induction through activation of 5'-AMP-activated protein kinase (AMPK) and inhibition of mechanistic target of rapamycin (mTOR) complex I (mTORC1). Furthermore, we demonstrate that CO significantly induced the expression of SESN2 and enhanced autophagy in the livers of MCD-fed mice or in MCD-media treated hepatocytes. Conversely, knockdown of SESN2 abrogated autophagy activation and mTOR inhibition in response to CO. We conclude that CO ameliorates hepatic steatosis through the autophagy pathway induced by SESN2 upregulation.

Common Genetic Variants Alter Metabolism and Influence Dietary Choline Requirements

Nutrient needs, including those of the essential nutrient choline, are a population wide distribution. Adequate Intake (AI) recommendations for dietary choline (put forth by the National Academies of Medicine to aid individuals and groups in dietary assessment and planning) are grouped to account for the recognized unique needs associated with age, biological sex, and reproductive status (i.e., pregnancy or lactation). Established and emerging evidence supports the notion that common genetic variants are additional factors that substantially influence nutrient requirements. This review summarizes the genetic factors that influence choline requirements and metabolism in conditions of nutrient deprivation, as well as conditions of nutrient adequacy, across biological sexes and reproductive states. Overall, consistent and strong associative evidence demonstrates that common genetic variants in choline and folate pathway enzymes impact the metabolic handling of choline and the risk of nutrient inadequacy across varied dietary contexts. The studies characterized in this review also highlight the substantial promise of incorporating common genetic variants into choline intake recommendations to more precisely target the unique nutrient needs of these subgroups within the broader population. Additional studies are warranted to facilitate the translation of this evidence to nutrigenetics-based dietary approaches.

Effects of Nonalcoholic Fatty Liver Disease on Hepatic CYP2B1 and in Vivo Bupropion Disposition in Rats Fed a High-Fat or Methionine/Choline-Deficient Diet

Nonalcoholic fatty liver disease (NAFLD) refers to hepatic pathologies, including simple fatty liver (SFL), nonalcoholic steatohepatitis (NASH), fibrosis, and cirrhosis, that may progress to hepatocellular carcinoma. These liver disease states may affect the activity and expression levels of drug-metabolizing enzymes, potentially resulting in an alteration in the pharmacokinetics, therapeutic efficacy, and safety of drugs. This study investigated the hepatic cytochrome P450 (CYP) 2B1-modulating effect of a specific NAFLD state in dietary rat models. Sprague-Dawley rats were given a methionine/choline-deficient (MCD) or high-fat (HF) diet to induce NASH and SFL, respectively. The induction of these disease states was confirmed by plasma chemistry and liver histological analysis. Both the protein and mRNA levels of hepatic CYP2B1 were considerably reduced in MCD diet-fed rats; however, they were similar between the HF diet-fed and control rats. Consistently, the enzyme-kinetic and pharmacokinetic parameters for CYP2B1-mediated bupropion metabolism were considerably reduced in MCD diet-fed rats; however, they were also similar between the HF diet-fed and control rats. These results may promote a better understanding of the influence of NAFLD on CYP2B1-mediated metabolism, which could have important implications for the safety and pharmacokinetics of drug substrates for the CYP2B subfamily in patients with NAFLD.

Purified anthocyanins from bilberry and black currant attenuate hepatic mitochondrial dysfunction and steatohepatitis in mice with methionine and choline deficiency

The berries of bilberry and black currant are a rich source of anthocyanins, which are thought to have favorable effects on nonalcoholic steatohepatitis (NASH). This study was designed to examine whether purified anthocyanins from bilberry and black currant are able to limit the disorders related to NASH induced by a methionine-choline-deficient (MCD) diet in mice. The results showed that treatment with anthocyanins not only alleviated inflammation, oxidative stress, steatosis, and even fibrosis but also improved depletion of mitochondrial content and damage of mitochondrial biogenesis and electron transfer chain developed concomitantly in the liver of mice fed the MCD diet. Furthermore, anthocyanins treatment promoted activation of AMP-activated protein kinase (AMPK) and expression of peroxisome proliferator-activated receptor-gamma coactivator-1α (PGC-1α). These data provide evidence that anthocyanins possess significant protective effects against NASH and mitochondrial defects in response to a MCD diet, with a mechanism maybe through affecting the AMPK/PGC-1α signaling pathways.

Clonal tracing of Sox9+ liver progenitors in mouse oval cell injury

Proliferating ducts, termed "oval cells," have long been thought to be bipotential, that is, produce both biliary ducts and hepatocytes during chronic liver injury. The precursor to oval cells is considered to be a facultative liver stem cell (LSC). Recent lineage tracing experiments indicated that the LSC is SRY-related HMG box transcription factor 9 positive (Sox9(+) ) and can replace the bulk of hepatocyte mass in several settings. However, no clonal relationship between Sox9(+) cells and the two epithelial liver lineages was established. We labeled Sox9(+) mouse liver cells at low density with a multicolor fluorescent confetti reporter. Organoid formation validated the progenitor activity of the labeled population. Sox9(+) cells were traced in multiple oval cell injury models using both histology and fluorescence-activated cell sorting. Surprisingly, only rare clones containing both hepatocytes and oval cells were found in any experiment. Quantitative analysis showed that Sox9(+) cells contributed only minimally (<1%) to the hepatocyte pool, even in classic oval cell injury models. In contrast, clonally marked mature hepatocytes demonstrated the ability to self-renew in all classic mouse oval cell activation injuries. A hepatocyte chimera model to trace hepatocytes and nonparenchymal cells also demonstrated the prevalence of hepatocyte-driven regeneration in mouse oval cell injury models.

CONCLUSION

Sox9(+) ductal progenitor cells give rise to clonal oval cell proliferation and bipotential organoids, but rarely produce hepatocytes in vivo. Hepatocytes themselves are the predominant source of new parenchyma cells in prototypical mouse models of oval cell activation.

Dietary choline deficiency causes DNA strand breaks and alters epigenetic marks on DNA and histones

Dietary choline is an important modulator of gene expression (via epigenetic marks) and of DNA integrity. Choline was discovered to be an essential nutrient for some humans approximately one decade ago. This requirement is diminished in young women because estrogen drives endogenous synthesis of phosphatidylcholine, from which choline can be derived. Almost half of women have a single nucleotide polymorphism that abrogates estrogen-induction of endogenous synthesis, and these women require dietary choline just as do men. In the US, dietary intake of choline is marginal. Choline deficiency in people is associated with liver and muscle dysfunction and damage, with apoptosis, and with increased DNA strand breaks. Several mechanisms explain these modifications to DNA. Choline deficiency increases leakage of reactive oxygen species from mitochondria consequent to altered mitochondrial membrane composition and enhanced fatty acid oxidation. Choline deficiency impairs folate metabolism, resulting in decreased thymidylate synthesis and increased uracil misincorporation into DNA, with strand breaks resulting during error-prone repair attempts. Choline deficiency alters DNA methylation, which alters gene expression for critical genes involved in DNA mismatch repair, resulting in increased mutation rates. Any dietary deficiency which increases mutation rates should be associated with increased risk of cancers, and this is the case for choline deficiency. In rodent models, diets low in choline and methyl-groups result in spontaneous hepatocarcinomas. In human epidemiological studies, there are interesting data that suggest that this also may be the case for humans, especially those with SNPs that increase the dietary requirement for choline.

The supply of choline is important for fetal progenitor cells

Fetal progenitor cells proliferate, migrate, differentiate and undergo apoptosis at specific times during fetal development. Choline is needed by these cells for membrane synthesis and for methylation. There is growing evidence that this nutrient also modulates epigenetic regulation of gene expression in both neuronal and endothelial progenitor cells, thereby modifying brain development. It is likely that these mechanisms explain why, in rodent models, maternal dietary intake of choline influences both angiogenesis and neurogenesis in fetal hippocampus, and results in life-long changes in memory function. This also may explain why women eating diets low in choline have a greater risk of having a baby with a birth defect. Choline is mainly found in foods that contain fat and cholesterol, and intake of such foods has diminished in response dietary advice from nutritionists and physicians. Forty years ago, diets commonly contained choline-rich foods but now women in the USA tend to eat diets low in choline content. Premenopausal women normally may require less choline in their diet than do men and postmenopausal women, because estrogen induces the gene for the enzyme catalyzing endogenous biosynthesis of the choline-containing phospholipid phosphatidylcholine. However, many women have a single nucleotide polymorphism (SNP) that blocks the induction of endogenous biosynthesis, thereby making them require more dietary choline. When these women eat diets low in choline, the supply of this nutrient to the fetus is likely to be inadequate, and may perturb progenitor cell proliferation, migration, differentiation and apoptosis.

Mutations and aberrant transcriptions of Stk11 (Lkb1) gene in rat liver tumors

To clarify the involvement of the Stk11/Lkb1 gene in the development of hepatocellular carcinomas (HCCs), its alteration in rat HCCs induced by exogenous and endogenous liver carcinogenesis models was investigated.

MATERIALS AND METHODS

Fifteen HCCs induced by N-nitrosodiethylamine (DEN) and 12 HCCs induced by a choline-deficient L-amino acid-defined (CDAA) diet were obtained. To assess mutations and aberrant transcriptions of the Stk11 gene, polymerase chain reaction (PCR)-single strand conformation polymorphism (SSCP) and reverse transcription (RT)-PCR analyses were performed, respectively.

RESULTS

A mutation was detected in only 1 out of 15 HCCs by DEN, but no mutations in 12 HCCs by the CDAA diet. Aberrant transcripts were found in 4 out of 15 HCCs by DEN and in 3 out of 12 HCCs by the CDAA diet.

CONCLUSION

These results suggest that alterations of the Stk11 gene may play a limited role in both exogenous and endogenous rat liver carcinogenesis.

Variable number tandem repeats in the promoter region of prostacyclin synthase gene in choline deficient rats

Weanling Sprague-Dawley rats were fed on a choline-deficient diet with hydrogenated vegetable oil and corn oil as lipids develop acute renal failure. Pathogenesis of the latter is controversial and an ischemic mechanism has been proposed. Arachidonic acid derivatives are involved in the regulation of vascular tonus. Vasospasm could be due to an increase in tromboxane A2-mediated vasoconstriction or to a decrease in prostacyclin-induced vasodilatation. Enzymes involved in the synthesis of both compounds are tromboxane A2- and prostacyclin-synthase respectively. The aim of this study was to identify the variable number tandem repeats (VNTR) in the promoter region of prostacyclin synthase gene and verify if there exists a relationship between the occurrence of VNTR in those choline-deficient rats which die because of acute renal failure and those which do not. We verified the presence of the VNTR in the prostacyclin synthase rat gene, but we did not find any difference in the molecular weight of the alleles between experimental and control rats. Renal reparation of the acute kidney injury due to choline deficiency in some rats is not related with differences in VNTR in the promoter region of the prostacyclin synthase gene.

A methyl-deficient diet modifies histone methylation and alters Igf2 and H19 repression in the prostate

BACKGROUND

Folate and methyl-group deficiency has been linked to prostate cancer susceptibility, yet the mechanisms underlying these observations are incompletely understood. The region of the genome containing the imprinted genes insulin-like growth factor 2 (Igf2) and H19, both of which display oncogenic functions, may be particularly sensitive to environmental influences.

METHODS

To determine whether a methyl-deficient diet impacts epigenetic controls at the Igf2-H19 locus, we placed C57BL/6 mice containing a polymorphism at the imprinted Igf2-H19 locus on a choline and methionine deficient (CMD) diet. We interrogated this locus for expression and epigenetic changes in prostate tissues.

RESULTS

A significant increase in both Igf2 and H19 expression was found in CMD prostate tissues compared to controls. These expression changes were reversible with shorter exposure to the CMD diet. Chromatin immunoprecipitation (ChIP) revealed significant decreases in repressive histone modifications (dimethyl-H3K9) within the H19 promoter, as well as Igf2 P2 and P3 promoters. DNA methylation within these promoters was not altered. No significant change in Igf2 or H19 imprinting was observed.

CONCLUSIONS

These findings highlight the plasticity of the epigenome in an epithelial organ vulnerable to neoplastic change. They further suggest that chromatin modifications are more susceptible to methyl-deficient diets than DNA methylation at this locus.

Disturbance of DNA methylation patterns in the early phase of hepatocarcinogenesis induced by a choline-deficient L-amino acid-defined diet in rats

The authors investigated the DNA methylation patterns of the E-cadherin, Connexin 26 (Cx26), Rassf1a and c-fos genes in the early phase of rat hepatocarcinogenesis induced by a choline-deficient L-amino acid-defined (CDAA) diet. Six-week-old F344 male rats were continuously fed with the CDAA diet, and three animals were then killed at each of 4 and 8 days and 3 weeks. Genomic DNA was extracted from livers for assessment of methylation status in the 5' upstream regions of E-cadherin, Cx26, Rassf1a and c-fos genes by bisulfite sequencing, compared with normal livers. The livers of rats fed the CDAA diet for 4 and 8 days and 3 weeks were methylated in E-cadherin, Cx26 and Rassf1a genes, while normal livers were all unmethylated. In contrast, normal livers were highly methylated in c-fos gene. Although the livers at 4 days were weakly methylated, those at 8 days and 3 weeks were markedly unmethylated. Methylation patterns of CpG sites in E-cadherin, Cx26 and Rassf1a were sparse and the methylation was not associated with gene repression. These results indicate that gene-specific DNA methylation patterns were found in livers of rats after short-term feeding of the CDAA diet, suggesting gene-specific hypermethylation might be involved in the early phase of rat hepatocarcinogenesis induced by the CDAA diet.

Lymphocyte gene expression in subjects fed a low-choline diet differs between those who develop organ dysfunction and those who do not

BACKGROUND

Some humans fed a low-choline diet develop hepatosteatosis, liver and muscle damage, and lymphocyte apoptosis. The risk of developing such organ dysfunction is increased by the presence of single-nucleotide polymorphisms (SNPs) in genes involved in folate and choline metabolism.

OBJECTIVE

We investigated whether these changes that occur in the expression of many genes when humans are fed a low-choline diet differ between subjects who develop organ dysfunction and those who do not. We also investigated whether expression changes were dependent on the presence of the SNPs of interest.

DESIGN

Thirty-three subjects aged 20-67 y were fed for 10 d a baseline diet containing the recommended adequate intake of choline. They then were fed a low-choline diet for up to 42 d or until they developed organ dysfunction. Blood was collected at the end of each phase, and peripheral lymphocytes were isolated and used for genotyping and for gene expression profiling with the use of microarray hybridization.

RESULTS

Feeding a low-choline diet changed the expression of 259 genes, and the profiles of subjects who developed and those who did not develop signs of organ dysfunction differed. Group clustering and gene ontology analyses found that the diet-induced changes in gene expression profiles were significantly influenced by the SNPs of interest and that the gene expression phenotype of the variant gene carriers differed significantly even with the baseline diet.

CONCLUSION

These findings support our hypothesis that a person's susceptibility to organ dysfunction when fed a low-choline diet is modulated by specific SNPs in genes involved in folate and choline metabolism.

Prenatal choline availability modulates hippocampal and cerebral cortical gene expression

An increased supply of the essential nutrient choline during fetal development [embryonic day (E) 11-17] in rats causes life-long improvements in memory performance, whereas choline deficiency during this time impairs certain aspects of memory. We analyzed mRNA expression in brains of prenatally choline-deficient, choline-supplemented, or control rats of various ages [postnatal days (P) 1 to 34 for hippocampus and E16 to P34 for cortex] using oligonucleotide microarrays and found alterations in gene expression levels evoked by prenatal choline intake that were, in most cases, transient occurring during the P15-P34 period. We selected a subset of genes, encoding signaling proteins, and verified the microarray data by reverse transcriptase-polymerase chain reaction analyses. Prenatally choline-supplemented rats had the highest expression of calcium/calmodulin (CaM)-dependent protein kinase (CaMK) I and insulin-like growth factor (IGF) II (Igf2) in the cortex and of the transcription factor Zif268/EGR1 in the cortex and hippocampus. Prenatally choline deficient rats had the highest expression of CaMKIIbeta, protein kinase Cbeta2, and GABA(B) receptor 1 isoforms c and d in the hippocampus. Similar changes in the expression of the proteins encoded by these genes were observed using immunoblot analyses. These data show that the prenatal supply of choline causes multiple modifications in the developmental patterns of expression of genes known to influence learning and memory and provide molecular correlates for the cognitive changes evoked by altered availability of choline in utero.

Choline: critical role during fetal development and dietary requirements in adults

Choline is an essential nutrient needed for the structural integrity and signaling functions of cell membranes; for normal cholinergic neurotransmission; for normal muscle function; for lipid transport from liver; and it is the major source of methyl groups in the diet. Choline is critical during fetal development, when it influences stem cell proliferation and apoptosis, thereby altering brain and spinal cord structure and function and influencing risk for neural tube defects and lifelong memory function. Choline is derived not only from the diet, but from de novo synthesis as well. Though many foods contain choline, there is at least a twofold variation in dietary intake in humans. When deprived of dietary choline, most men and postmenopausal women developed signs of organ dysfunction (fatty liver or muscle damage), while less than half of premenopausal women developed such signs. Aside from gender differences, there is significant variation in the dietary requirement for choline that can be explained by very common genetic polymorphisms.

Quantitative trait loci analysis of mice administered the methionine-choline deficient dietary model of experimental steatohepatitis

BACKGROUND

Nonalcoholic steatohepatitis (NASH) is a common disease with a poorly understood etiology, and the methionine-choline-deficient (MCD) diet is a nutritional model of NASH. Quantitative trait loci (QTL) analysis is a standard method for chromosomal mapping of polygenic disease traits. The purpose of this study is to administer mice an MCD diet in order to determine the strain-specific susceptibility for developing steatohepatitis, and to apply a computational methodology of QTL analysis to identify associated chromosomal susceptibility loci.

METHODS

Inbred mice were fed an MCD diet and alanine aminotransferase (ALT), hepatic triglycerides, liver weight, and weight loss were measured as phenotypic markers of steatohepatitis.

RESULTS

A/J mice developed the highest ALT and hepatic triglyceride levels. Using linear regression analysis, gene loci affecting serum ALT levels were identified on four chromosomes, and four loci that affect liver weight were also identified. In contrast, no QTLs for hepatic triglycerides or body weight were identified. Of note, loci for ALT and liver weight co-localized to proximal segments of chromosomes 2 and 15, in regions previously identified as QTLs for liver fibrosis.

CONCLUSIONS

These data indicate that experimental steatohepatitis is a polygenic disease with genes determining ALT, liver weight, and liver fibrosis.

Common genetic polymorphisms affect the human requirement for the nutrient choline

Humans eating diets deficient in the essential nutrient choline can develop organ dysfunction. We hypothesized that common single nucleotide polymorphisms (SNPs) in genes involved in choline metabolism influence the dietary requirement of this nutrient. Fifty-seven humans were fed a low choline diet until they developed organ dysfunction or for up to 42 days. We tested DNA SNPs for allelic association with susceptibility to developing organ dysfunction associated with choline deficiency. We identified an SNP in the promoter region of the phosphatidylethanolamine N-methyltransferase gene (PEMT; -744 G-->C; rs12325817) for which 18 of 23 carriers of the C allele (78%) developed organ dysfunction when fed a low choline diet (odds ratio 25, P=0.002). The first of two SNPs in the coding region of the choline dehydrogenase gene (CHDH; +318 A-->C; rs9001) had a protective effect on susceptibility to choline deficiency, while a second CHDH variant (+432 G-->T; rs12676) was associated with increased susceptibility to choline deficiency. A SNP in the PEMT coding region (+5465 G-->A; rs7946) and a betaine:homocysteine methyltransferase (BHMT) SNP (+742 G-->A; rs3733890) were not associated with susceptibility to choline deficiency. Identification of common polymorphisms that affect dietary requirements for choline could enable us to identify individuals for whom we need to assure adequate dietary choline intake.

Genetic variation of folate-mediated one-carbon transfer pathway predicts susceptibility to choline deficiency in humans

Choline is a required nutrient, and some humans deplete quickly when fed a low-choline diet, whereas others do not. Endogenous choline synthesis can spare some of the dietary requirement and requires one-carbon groups derived from folate metabolism. We examined whether major genetic variants of folate metabolism modify susceptibility of humans to choline deficiency. Fifty-four adult men and women were fed diets containing adequate choline and folate, followed by a diet containing almost no choline, with or without added folate, until they were clinically judged to be choline-deficient, or for up to 42 days. Criteria for clinical choline deficiency were a more than five times increase in serum creatine kinase activity or a >28% increase of liver fat after consuming the low-choline diet that resolved when choline was returned to the diet. Choline deficiency was observed in more than half of the participants, usually within less than a month. Individuals who were carriers of the very common 5,10-methylenetetrahydrofolate dehydrogenase-1958A gene allele were more likely than noncarriers to develop signs of choline deficiency (odds ratio, 7.0; 95% confidence interval, 2.0-25; P < 0.01) on the low-choline diet unless they were also treated with a folic acid supplement. The effects of the C677T and A1298C polymorphisms of the 5,10-methylene tetrahydrofolate reductase gene and the A80C polymorphism of the reduced folate carrier 1 gene were not statistically significant. The most remarkable finding was the strong association in premenopausal women of the 5,10-methylenetetrahydrofolate dehydrogenase-1958A gene allele polymorphism with 15 times increased susceptibility to developing organ dysfunction on a low-choline diet.

Gene expression profiling of choline-deprived neural precursor cells isolated from mouse brain

Choline is an essential nutrient and an important methyl donor. Choline deficiency alters fetal development of the hippocampus in rodents and these changes are associated with decreased memory function lasting throughout life. Also, choline deficiency alters global and gene-specific DNA methylation in several models. This gene expression profiling study describes changes in cortical neural precursor cells from embryonic day 14 mice, after 48 h of exposure to a choline-deficient medium. Using Significance Analysis of Microarrays, we found the expression of 1003 genes to be significantly changed (from a total of 16,000 total genes spotted on the array), with a false discovery rate below 5%. A total of 846 genes were overexpressed while 157 were underexpressed. Classification by gene ontology revealed that 331 of these genes modulate cell proliferation, apoptosis, neuronal and glial differentiation, methyl metabolism, and calcium-binding protein classes. Twenty-seven genes that had changed expression have previously been reported to be regulated by promoter or intron methylation. These findings support our previous work suggesting that choline deficiency decreases the proliferation of neural precursors and possibly increases premature neuronal differentiation and apoptosis.

SOCS1 is a suppressor of liver fibrosis and hepatitis-induced carcinogenesis

Hepatocellular carcinomas (HCCs) mainly develop from liver cirrhosis and severe liver fibrosis that are established with long-lasting inflammation of the liver. Silencing of the suppressor of the cytokine signaling-1 (SOCS1) gene, a negative regulator of cytokine signaling, by DNA methylation has been implicated in development or progress of HCC. However, how SOCS1 contributes to HCC is unknown. We examined SOCS1 gene methylation in >200 patients with chronic liver disease and found that the severity of liver fibrosis is strongly correlated with SOCS1 gene methylation. In murine liver fibrosis models using dimethylnitrosamine, mice with haploinsufficiency of the SOCS1 gene (SOCS1^−/+ mice) developed more severe liver fibrosis than did wild-type littermates (SOCS1^+/+ mice). Moreover, carcinogen-induced HCC development was also enhanced by heterozygous deletion of the SOCS1 gene. These findings suggest that SOCS1 contributes to protection against hepatic injury and fibrosis, and may also protect against hepatocarcinogenesis.

Alterations of the M6p/Igf2 receptor gene in hepatocellular carcinomas induced byN-nitrosodiethylamine and a choline-deficientL-amino acid-defined diet in rats

To elucidate whether the M6p/Igf2 receptor (M6p/Igf2r) gene might be involved in exogenous and endogenous liver carcinogenesis, we investigated its alteration in hepatocellular carcinomas (HCCs) induced by N-nitrosodiethylamine (DEN) and by a choline-deficient L-amino acid-defined (CDAA) diet in rats. Male F344 rats, 6 wk old, received a single intraperitoneal (i.p.) injection of DEN at a dose of 10 mg/kg body weight, followed by combined treatment with partial hepatectomy and colchicine to induce cell cycle disturbance, and a selection procedure regimen, HCCs being obtained after 42 wk. With continuous CDAA diet feeding, tumors were sampled after 75 wk. Total RNA was extracted from individual HCCs for assessment of mutations within exons 27, 28, 31, 33, and 34, and aberrant transcript of the M6p/Igf2r gene by reverse transcription (RT)-polymerase chain reaction (PCR)-single strand conformation polymorphism (SSCP) and RT-PCR analyses, respectively. Mutations were detected in three of 15 HCCs (20%) induced by the CDAA diet, a TTT to TTG (Phe to Leu) transversion at codon 1516 and two AAG to AGG (Lys to Arg) transitions at codon 1620, but in none of those caused by DEN. Aberrant transcripts were found in seven of 15 HCCs after DEN treatment (46.7%) and in two of 15 HCCs induced by the CDAA diet (13.3%). These results suggest that alterations of the M6p/Igf2r gene may be involved in both exogenous and endogenous liver carcinogenesis with the different patterns and frequencies.

Adenoviral delivery of human and viral IL-10 in murine sepsis

Adenovirus (Ad) gene therapy has been proposed as a drug-delivery system for the targeted administration of protein-based therapies, including growth factors and biological response modifiers. However, inflammation associated with Ad transduction has raised concern about its safety and efficacy in acute inflammatory diseases. In the present report, intratracheal and i.v. administration of a first-generation adenoviral recombinant (E1,E3 deleted) either containing an empty cassette or expressing the anti-inflammatory cytokines viral or human IL-10 (IL-10) was administered to mice subjected to zymosan-induced multisystem organ failure or to acute necrotizing pancreatitis. Pretreatment of mice with the intratracheal instillation of Ad expressing human IL-10 or viral IL-10 reduced weight loss, attenuated the proinflammatory cytokine response, and reduced mortality in the zymosan-induced model, whereas pretreatment with a control adenoviral recombinant did not significantly exacerbate the response. Pretreatment of mice with pancreatitis using adenoviral vectors expressing IL-10 significantly reduced the degree of pancreatic and liver injury and liver inflammation when administered systemically, but not intratracheally. We conclude that adenoviral vectors can be administered prophylactically in acute inflammatory syndromes, and expression of the anti-inflammatory protein IL-10 can be used to suppress the underlying inflammatory process.

DNA stability and genomic methylation status in colonocytes isolated from methyl-donor-deficient rats

BACKGROUND

Epidemiological studies report an inverse relationship between intake of the B vitamin folic acid and colon cancer. Folate is important for DNA synthesis and repair. Moreover, the production of S-adenosylmethionine (SAM), essential for normal DNA methylation and gene expression, is dependent on folic acid. Folate deficiency may increase the risk of malignant transformation by perturbing these pathways.

AIMS OF THE STUDY

The principal aim of this study was to determine the effects of folate deficiency on DNA stability and DNA methylation in rat colonocytes in vivo. As the metabolic pathways of folate and other dietary methyl donors are closely linked, the effects of methionine and choline deficiency were also evaluated.

METHODS

Male Hooded-Lister rats were fed a diet deficient in folic acid, or in methionine and choline, or in folate, methionine and choline for 10 weeks. DNA strand breakage and misincorporated uracil were determined in isolated colonocytes using alkaline single cell gel electrophoresis. Global DNA methylation was measured in colonic scrapings. Folate was measured in plasma, erythrocyte and liver samples.

RESULTS

Methyl donor deficiency induced DNA strand breakage in colonocytes isolated from all experimental groups. Uracil levels in colonocyte DNA remained unchanged compared with controls. DNA methylation was unaffected either by folate and/or methionine and choline depletion. Rats fed a folate-deficient diet had less folate in plasma, red blood cells and liver than controls.

CONCLUSIONS

Folate and methyl deficiency in vivo primarily affects DNA stability in isolated colonocytes of rats, without affecting overall DNA methylation.

Choline deficiency selects for resistance to p53-independent apoptosis and causes tumorigenic transformation of rat hepatocytes

The mechanisms which drive initiated cells to progress to form carcinomas are poorly understood. CWSV-1 rat hepatocytes, in which p53 protein is inactivated by SV40 large T antigen, respond by inducing p53-independent apoptosis when acutely switched to medium containing low choline (16% apoptotic at 48 h in 5 microM choline) as compared with controls (1% apoptotic at 48 h in 70 microM choline). The rate of apoptosis was inversely correlated with cellular phosphatidylcholine content. Choline deficiency (CD)-induced apoptosis is probably mediated by TGFbeta1 and reactive oxygen species, since immunoneutralization of TGFbeta1 in the medium or treatment with N-acetylcysteine (an antioxidant) or addition of neocuproine (a transition metal chelator) prevented CD-induced apoptosis. CWSV-1 hepatocytes could be gradually adapted to survive in 5 microM choline. CD-adapted cells had increased membrane phosphatidylcholine concentrations (compared with acute CD cells). Adapted cells acquired relative resistance to CD-induced apoptosis (7% of adapted cells compared with 19% of non-adapted cells were apoptotic at 48 h in 5 microM choline). They also became relatively resistant to another p53-independent form of apoptosis (TGFbeta1-induced). CD-adapted hepatocytes developed increased capability for anchorage-independent growth and formed tumors when transplanted into nude mice; passage-matched control hepatocytes did not possess these properties. Cell transformation was dependent on exposure to the selective pressure of CD apoptosis, as we observed that when CD apoptosis was inhibited with an antioxidant during adaptation, cells did not become anchorage independent. Acquisition by p53-deficient cells of resistance to p53-independent inducers of apoptosis (CD, TGFbeta1 and reactive oxygen species) may leave cells without another important apoptotic defensive barrier and may be responsible for the progression of initiated cells to frank carcinomas.

Expression of alpha, mu and pi class glutathione S-transferases in oval and ductal cells in liver of rats placed on a choline-deficient, ethionine-supplemented diet

Expression of the alpha, mu and pi class glutathione S-transferases (GSTs) in hepatocytes, oval cells and ductal cells derived from the livers of rats placed on a choline-deficient, ethionine-supplemented (CDE) diet for 5 weeks was investigated. An overall decrease in the expression of alpha and mu class GSTs and an over-expression of pi class GST was observed in the liver after CDE treatment as indicated by Northern blotting analysis. Massive disruption of the liver with oval cell infiltration in the sinusoids throughout the lobule occurred after 5 weeks CDE treatment. 'Duct-like' structures consisting of oval-like cells (ductal cells) with rounder nuclei and more cytoplasm than oval cells within the sinusoids were also apparent. Immunocytochemical analysis revealed that the altered expression of GST in the whole liver is attributed to a differential expression of alpha, mu and pi class GSTs in the different cell types in the liver, including hepatocytes, oval cells around the portal region and among the sinusoids, and oval-like cells (ductal cells) in the 'duct-like' structures. In vitro studies using purified oval-ductal cells and hepatocyte populations confirmed the differential expression of GSTs in the varying cell populations in situ. The expression of the alpha and mu class GSTs in hepatocytes does not appear to be altered by the CDE diet. Heterogeneity in distribution of pi class GST was observed in the hepatocyte population, some hepatocytes were stained strongly while no staining was observed in others. Oval and ductal cells represent two distinct populations displaying different expression of GSTs. Pi class GST was detected in the majority of oval and ductal cells. Alpha class GST was detected in < 5% of the oval cell population and was found in > 50% of the ductal cell population. In contrast, mu class GST was absent in ductal cells and was present in 24% of oval cells around the portal region. This supports the view that ductal cells are not of bile ductal origin since mu GST is present in normal bile duct epithelial cells. Furthermore the change in expression of GSTs in the liver after CDE treatment is attributed to the large increase in oval and ductal cell populations.

Altered expression of retrovirus-like sequences and cellular oncogenes in mice fed methyl-deficient diets

Methyl-deficient (lipotrope-deficient) diets enhance liver carcinogenesis in rodents. Although the mechanisms responsible for the cancer-promoting activity of such diets have not been identified, they have been observed to cause impaired immune response, alterations in methylation of liver RNA and DNA, and enhanced susceptibility to oxidative damage. Since alterations in gene expression may also play a critical role, the present studies examined the expression of the c-myc, c-H-ras, epidermal growth factor receptor, and ornithine decarboxylase genes, as well as endogenous retrovirus-like sequences, in C57BL/6J x C3H/HeJ F1 mouse liver during the first 2 weeks of feeding of a methyl-deficient diet. The kinetics of liver cell proliferation was investigated in parallel. Increased [3H]thymidine incorporation into liver DNA was found at day 4 and reached a maximum at days 7-11 after commencement of the methyl-deficient diet, when compared to age-matched mice fed a complete diet. Northern blot analysis of polyadenylated liver RNA samples indicated an increase in the levels of RNA homologous to Moloney murine leukemia virus and intracisternal A particle sequences but no significant change in the level of VL30 retrovirus-related RNA in the samples from mice fed methyl-deficient diets. A marked increase in the levels of c-myc and a slight increase in the levels of ornithine decarboxylase and c-H-ras transcripts were seen in the liver RNA samples from the treated mice. Of particular interest was a decrease in the abundance of epidermal growth factor receptor transcripts in the liver RNA samples from the treated mice. These changes in cellular levels of specific RNA resemble, in several respects, those we have previously described in rodent liver during regeneration and tumor promotion and also those seen in rodent hepatomas. They may reflect, therefore, a common profile of gene expression relevant to cell proliferation.

c-myc gene amplification during hepatocarcinogenesis by a choline-devoid diet

Liver tumors arise in rats fed a choline-devoid diet without added carcinogens. We found amplification of the c-myc gene in 13/13 of these tumors. The amplification ranged from 2- to 70-fold and was accompanied by an increase in c-myc gene expression. Amplification of c-myc was larger in tumors of rats fed a choline-devoid diet followed by a choline-supplemented diet than in tumors from animals fed a choline-devoid diet exclusively. In the former animals, low levels of c-myc gene amplification were also detected in nontumorous regions of tumor-bearing livers. The choline-devoid diet provides an in vivo experimental model for the induction of gene amplification in the rat liver. In this setting, amplification of the c-myc gene may be an early and critical event in carcinogenesis.

32P-postlabeling analysis of liver DNA adducts in rats chronically fed a choline-devoid diet

Liver DNA, obtained at various time intervals from rats chronically fed a choline-devoid diet, was analysed for the presence of aromatic or alkyl adducts by the 32P-postlabeling assay. Alkyl adducts were not detected. Aromatic DNA adduct lesions were revealed, but only at levels (1 adduct per 0.5-3 X 10(9) nucleotides) which are at the limits of the extremely high sensitivity of the method used, levels which remained constant throughout the period of feeding. Thus, contamination of the total environment of the animals with chemical carcinogens does not appear to be responsible for the genesis of the hepatocellular carcinomas that develop in rats chronically fed a choline-devoid diet. The diet, therefore, either acts as a complete carcinogen, or promotes the evolution to cancer of endogenous, 'spontaneously' initiated liver cells.