Dietary methyl deficiency, microRNA expression and susceptibility to liver carcinogenesis

Deciphering the role of aberrant DNA methylation in NAFLD and NASH

The global incidence of nonalcoholic fatty liver disease (NAFLD) is mounting incessantly, and it is emerging as the most frequent cause of chronic and end stage liver disorders. It is the starting point for a range of conditions from simple steatosis to more progressive nonalcoholic steatohepatitis (NASH) and associated hepatocellular carcinoma (HCC). Dysregulation of insulin secretion and dyslipidemia due to obesity and other lifestyle variables are the primary contributors to establishment of NAFLD. Onset and progression of NAFLD is orchestrated by an interplay of metabolic environment with genetic and epigenetic factors. An incompletely understood mechanism of NAFLD progression has greatly hampered the progress in identification of novel prognostic and therapeutic strategies. Emerging evidence suggests altered DNA methylation pattern as a key determinant of NAFLD pathogenesis. Environmental and lifestyle factors can manipulate DNA methylation patterns in a reversible manner, which manifests as changes in gene expression. In this review we attempt to highlight the importance of DNA methylation in establishment and progression of NAFLD. Development of novel diagnostic, prognostic and therapeutic strategies centered around DNA methylation signatures and modifiers has also been explored.

One Carbon Metabolism and Mammalian Pregnancy Outcomes

One-carbon metabolism is involved in varieties of physiological processes in mammals, including nucleic acid synthesis, amino acid homeostasis, epigenetic regulation, redox balance and neurodevelopment. The current evidence linking levels of one-carbon nutrients during pregnancy to the development of oocytes, embryos, and placentas, as well as maternal and offspring health, is reviewed. The sources of mammalian one-carbon units, the pathways active in mammalian one-carbon metabolism, the maternal and fetal needs for one-carbon units and their functions during pregnancy are described. The demand for one-carbon metabolism is highest during pregnancy compared to the entire lifetime of a mammal. The primary types of one-carbon metabolism in mammals are the folate cycle, methionine cycle and transsulfuration pathway, which varies at different pregnancy stages (e.g., methylation programming of embryo, neural development of fetus, fetal growth and placenta development). Therefore, an overall consideration of one-carbon metabolism requirements for different pregnancy stages, is called for, specifically, the balance of all nutrients involved, not just one single nutrient in one-carbon metabolism. Moreover, the establishment of an ideal one-carbon metabolism requirement model is suggested according to the requirements for different pregnancy stages to support optimal pregnancy outcomes and maternal and offspring health.

Metabolic Inputs into the Epigenome

A number of molecular pathways play key roles in transmitting information in addition to the genomic sequence-epigenetic information-from one generation to the next. However, so-called epigenetic marks also impact an enormous variety of physiological processes, even under circumstances that do not result in heritable consequences. Perhaps inevitably, the epigenetic regulatory machinery is highly responsive to metabolic cues, as, for example, central metabolites are the substrates for the enzymes that catalyze the deposition of covalent modifications on histones, DNA, and RNA. Interestingly, in addition to the effects that metabolites exert over biological regulation in somatic cells, over the past decade multiple studies have shown that ancestral nutrition can alter the metabolic phenotype of offspring, raising the question of how metabolism regulates the epigenome of germ cells. Here, we review the widespread links between metabolism and epigenetic modifications, both in somatic cells and in the germline.

Supplementation with methyl donors during lactation to high-fat-sucrose-fed dams protects offspring against liver fat accumulation when consuming an obesogenic diet

Methyl donor supplementation has been reported to prevent obesity-induced liver fat accumulation in adult rats. We hypothesized that this protection could be mediated by perinatal nutrition. For this purpose, we assessed the response to an obesogenic diet (high-fat-sucrose, HFS) during adulthood depending on maternal diet during lactation. Female Wistar rats fed control diet during pregnancy were assigned to four postpartum dietary groups: control, control supplemented with methyl donors (choline, betaine, folic acid, vitamin B12), HFS and HFS supplemented with methyl donors. At weaning, the male offspring was transferred to a chow diet and at week 12th assigned to a control or a HFS diet during 8 weeks. The offspring whose mothers were fed HFS during lactation showed increased adiposity (19%, P<0.001). When fed the HFS diet as adults, offspring whose mothers were HFS supplemented had more body fat (23%, P<0.001) than those from HFS non-supplemented. However, they showed lower liver fat accumulation (-18%, P<0.001). Srebf1, Dnmt1 and Lepr liver mRNA levels increased after adulthood HFS feeding. In those animals HFS fed during adulthood, previous maternal HFS decreased Lepr and Dnmt1 expression levels when compared with c-HFS offspring, while the supplementation of control and HFS-fed dams, respectively, induced higher hepatic Mme and Lepr mRNA levels after adult HFS intake compared with hfs-HFS offspring. In conclusion, maternal HFS diet during lactation influenced the response to an obesogenic diet in the adult progeny. Interestingly, dietary methyl donor supplementation in lactating mothers fed an obesogenic diet reduced liver fat accumulation, but increased adipose tissue storage in adult HFS-fed offspring.

Maternal methyl donors supplementation during lactation prevents the hyperhomocysteinemia induced by a high-fat-sucrose intake by dams

Maternal perinatal nutrition may program offspring metabolic features. Epigenetic regulation is one of the candidate mechanisms that may be affected by maternal dietary methyl donors intake as potential controllers of plasma homocysteine levels. Thirty-two Wistar pregnant rats were randomly assigned into four dietary groups during lactation: control, control supplemented with methyl donors, high-fat-sucrose and high-fat-sucrose supplemented with methyl donors. Physiological outcomes in the offspring were measured, including hepatic mRNA expression and global DNA methylation after weaning. The newborns whose mothers were fed the obesogenic diet were heavier longer and with a higher adiposity and intrahepatic fat content. Interestingly, increased levels of plasma homocysteine induced by the maternal high-fat-sucrose dietary intake were prevented in both sexes by maternal methyl donors supplementation. Total hepatic DNA methylation decreased in females due to maternal methyl donors administration, while Dnmt3a hepatic mRNA levels decreased accompanying the high-fat-sucrose consumption. Furthermore, a negative association between Dnmt3a liver mRNA levels and plasma homocysteine concentrations was found. Maternal high-fat-sucrose diet during lactation could program offspring obesity features, while methyl donors supplementation prevented the onset of high hyperhomocysteinemia. Maternal dietary intake also affected hepatic DNA methylation metabolism, which could be linked with the regulation of the methionine-homocysteine cycle.

Epigenetic events in liver cancer resulting from alcoholic liver disease

Epigenetic mechanisms play an extensive role in the development of liver cancer (i.e., hepatocellular carcinoma [HCC]) associated with alcoholic liver disease (ALD) as well as in liver disease associated with other conditions. For example, epigenetic mechanisms, such as changes in the methylation and/or acetylation pattern of certain DNA regions or of the histone proteins around which the DNA is wrapped, contribute to the reversion of normal liver cells into progenitor and stem cells that can develop into HCC. Chronic exposure to beverage alcohol (i.e., ethanol) can induce all of these epigenetic changes. Thus, ethanol metabolism results in the formation of compounds that can cause changes in DNA methylation and interfere with other components of the normal processes regulating DNA methylation. Alcohol exposure also can alter histone acetylation/deacetylation and methylation patterns through a variety of mechanisms and signaling pathways. Alcohol also acts indirectly on another molecule called toll-like receptor 4 (TLR4) that is a key component in a crucial regulatory pathway in the cells and whose dysregulation is involved in the development of HCC. Finally, alcohol use regulates an epigenetic mechanism involving small molecules called miRNAs that control transcriptional events and the expression of genes important to ALD.

Dietary supplementation with methyl donors reduces fatty liver and modifies the fatty acid synthase DNA methylation profile in rats fed an obesogenic diet

Non-alcoholic fatty liver disease (NAFLD) is one of the first hepatic manifestations of metabolic syndrome, whose progression can lead to cirrhosis and hepatic carcinoma. Interestingly, methyl donor supplementation could improve obesogenic diet-induced hepatic triglyceride accumulation. The aim of this research is to describe methyl donor effects on a high-fat-sucrose (HFS) diet in both sexes and epigenetic changes induced on fatty acid synthase (FASN) promoter methylation pattern as well as gene expression of NAFLD key metabolic genes. Twenty-four male and 28 female Wistar rats were assigned to three dietary groups: control, HFS, and HFS supplemented with methyl donors (choline, betaine, vitamin B12, and folic acid). After 8 weeks of treatment, somatic, biochemical, mRNA, and epigenetic measurements were performed. Rats fed the HFS diet presented an overweight phenotype and alterations in plasma biochemical measurements. Methyl donor supplementation reverted the HFS-diet-induced hepatic triglyceride accumulation. Analysis of FASN promoter cytosine methylation showed changes in both sexes due to the obesogenic diet at -1,096, -780, -778, and -774 CpG sites with respect to the transcriptional start site. Methyl donor supplementation modified DNA methylation at -852, -833, -829, -743, and -733 CpGs depending on the sex. RT-PCR analysis confirmed that FASN expression tended to be altered in males. Our findings reinforce the hypothesis that methyl donor supplementation can prevent hepatic triglyceride accumulation induced by obesogenic diets in both sexes. Changes in liver gene expression profile and epigenetic-mediated mechanisms related to FASN DNA hypermethylation could be involved in methyl donor-induced NAFLD improvement.