Fructose consumption induces hypomethylation of hepatic mitochondrial DNA in rats

GPX4 Promoter Hypermethylation Induced by Ischemia/Reperfusion Injury Regulates Hepatocytic Ferroptosis

Background and Aims

Glutathione peroxidase 4 (GPX4) is a key factor in ferroptosis, which is involved in ischemia-reperfusion injury. However, little is known about its role in hepatic ischemia-reperfusion injury (HIRI). This study aimed to investigate the role of GPX4 methylation in ferroptosis during HIRI.

Methods

For the in vitro experiments, an oxygen and glucose deprivation cell model was established. For the in vivo experiments, an ischemia-reperfusion model was created by subjecting mice to simulated HIRI. Ferroptosis occurrence, GPX4 promoter methylation, and global methylation levels were then assessed.

Results

Ferroptosis was observed in oxygen and glucose deprivation, characterized by a significant decrease in cellular viability (P < 0.05), an increase in lipid peroxidation (P < 0.01), iron overload (P < 0.05), and down-regulation of GPX4 (P < 0.05). This ferroptosis was exacerbated by GPX4 knockdown (P < 0.01) and mitigated by exogenous glutathione (P < 0.01). Similarly, ferroptosis was evident in mice subjected to HIRI, with a down-regulation of GPX4 mRNA and protein expression (all P < 0.01), and an upregulation of acyl-CoA synthetase long-chain family member 4 mRNA and protein (all P < 0.01), as well as prostaglandin-endoperoxide synthase 2 mRNA and protein expression (all P < 0.05). Methylation levels increased, evidenced by upregulation of DNA methylation transferase expression (P < 0.05) and down-regulation of Ten-eleven translocation family demethylases (P < 0.01), along with an upregulation of GPX4 promoter methylation.

Conclusions

Ferroptosis may be the primary mode of cell death in hepatocytes following ischemia-reperfusion injury. The methylation of the GPX4 promoter and elevated levels of global hepatic methylation are involved in the regulation of ferroptosis.

Therapeutic potential of tLyp-1-EV-shCTCF in inhibiting liver cancer stem cell self-renewal and immune escape via SALL3 modulation in hepatocellular carcinoma

The progression of hepatocellular carcinoma (HCC) is influenced by disrupted metabolic processes, presenting challenges in prognostic outcomes. Hepatocellular carcinoma (HCC), a leading cause of cancer-related mortality, is closely associated with metabolic reprogramming and stem cell-like properties in liver cancer stem cells (LCSCs). This study explored the potential molecular mechanisms by which tLyP-1-modified extracellular vesicles (EVs) delivering CTCF shRNA (tLyp-1-EV-shCTCF) regulate mitochondrial DNA methylation-induced glycolytic metabolic reprogramming and LCSC self-renewal. Through a series of methods, including Western blot, nanoparticle tracking analysis, and immunofluorescence, we demonstrated the successful delivery and internalization of tLyp-1-EV in HCC cells. Our results identified SALL3 as a critical factor underexpressed in HCC and LCSCs, while CTCF was overexpressed. Overexpression of SALL3 inhibited LCSC self-renewal and immune evasion by blocking the CTCF-DNMT3A interaction, thus repressing DNMT3A methyltransferase activity and subsequent mitochondrial DNA methylation-mediated glycolytic metabolic reprogramming. In vivo experiments further supported these findings, showing that tLyp-1-EV-shCTCF treatment significantly reduced tumor growth by upregulating SALL3 expression, thereby inhibiting glycolytic metabolic reprogramming and enhancing the immune response against HCC cells. This study provides novel insights into the role of SALL3 and mitochondrial DNA methylation in HCC progression, offering potential therapeutic targets for combating HCC and its stem cell-like properties.

Mitochondrial DNA content and methylation in sperm of patients with asthenozoospermia

PURPOSE

The aim of the current study was to investigate the mtDNA methylation levels and mtDNA copy numbers in the sperm of patients with asthenozoospermia and compare them to those observed in controls with normozoospermia.

METHODS

Pyrosequencing analysis of the methylation levels of the mitochondrial D-loop and MT-CO1/chr1:631,907-632083/chrX:26,471,887-126,472,063 (hereinafter referred to as "MT-CO1-AVG") region and quantitative PCR analysis of the mtDNA copy number were performed on sperm from 30 patients with asthenozoospermia and 30 controls with normozoospermia.

RESULTS

Compared with those of controls with normozoospermia, the methylation levels of D-loop and MT-CO1-AVG regions and mtDNA copy number were significantly higher in patients with asthenozoospermia. The methylation level of the D-loop region in patients with asthenozoospermia and controls with normozoospermia and that of MT-CO1-AVG region in patients with asthenozoospermia showed a decreasing tendency with increasing total sperm motility. A significant inverse correlation between the mtDNA copy number and total sperm motility was observed in patients with asthenozoospermia but not in controls with normozoospermia. In patients with asthenozoospermia, but not in controls with normozoospermia, we observed a significant inverse correlation between D-loop methylation levels and mtDNA copy number, while no significant correlation was observed between MT-CO1-AVG methylation levels and mtDNA copy number.

CONCLUSION

These results reveal the occurrence of mtDNA methylation in human sperm and altered D-loop and MT-CO1-AVG methylation levels in patients with asthenozoospermia. Additional research is needed to determine the function of these features in the etiology and course of asthenozoospermia.

Approaches to nutritional research using organoids; fructose treatment induces epigenetic changes in liver organoids

Nutritional researches have successfully used animal models to gain new insights into nutrient action. However, comprehensive descriptions of their molecular mechanisms of action remain elusive as appropriate in vitro evaluation systems are lacking. Organoid models can mimic physiological structures and reproduce in vivo functions, making them increasingly utilized in biomedical research for a better understand physiological and pathological phenomena. Therefore, organoid modeling can be a powerful approach for to understand the molecular mechanisms of nutrient action. The present study aims to demonstrate the utility of organoids in nutritional research by further investigating the molecular mechanisms responsible for the negative effects of fructose intake using liver organoids. Here, we treated liver organoids with fructose and analyzed their gene expression profiles and DNA methylation levels. Microarray analysis demonstrated that fructose-treated organoids exhibited increased selenoprotein p (Sepp1) gene expression, whereas pyrosequencing assays revealed reduced DNA methylation levels in the Sepp1 region. These results were consistent with observations using hepatic tissues from fructose-fed rats. Conversely, no differences in Sepp1 mRNA and DNA methylation levels were observed in two-dimensional cells. These results suggest that organoids serve as an ideal in vitro model to recapitulate in vivo tissue responses and help to validate the molecular mechanisms of nutrient action compared to conventional cellular models.

Low mitochondrial DNA copy number in peripheral blood mononuclear cells is associated with future mortality risk: a long-term follow-up study from Japan

OBJECTIVES

The mitochondrial DNA (mtDNA) is unique and circular with multiple copies of the genome. The lower mtDNA copy number (mtDNA-CN) in leukocytes is associated with the risk of all-cause mortality. However, its long-term association is unknown. Thus, the study examined the association between mtDNA-CN and the risk of all-cause mortality in a long-term follow-up study in the Japanese population.

DESIGN

This longitudinal study included the study cohort from an annual, population-based health checkup in the town of Yakumo, Hokkaido, Japan.

SETTING AND PARTICIPANTS

814 participants (baseline age range: 38-80 years, mean: 56.3 years) were included in this study in 1990. They were followed-up regarding mortality for about 30 years (median: 28.1 years) till 2019.

MEASURES

The genomic DNA was extracted from peripheral blood mononuclear cells and the mtDNA-CN was measured using real-time polymerase chain reaction. The level of the mtDNA-CN was divided into tertiles (low, middle, and high). The participants were categorized based on their age into middle-aged (<60 years old) or old-aged (≥60 years old). Survival analysis was performed for tertile of mtDNA-CN and compared using the log-rank test. Univariate and multivariable Cox proportional hazard regression analyses were performed to assess the association between mtDNA-CN and all-cause mortality. The model adjusted with age, sex, body mass index, systolic blood pressure, smoking habit, alcohol consumption, exercise habit, and education level.

RESULTS

The low levels of mtDNA-CN resulted in a significant decrease in cumulative survival rate (P <  0.05). The risk of mortality was significantly higher in the middle-aged cohort when mtDNA-CN levels were low (hazard ratios [95% confidence intervals]: 1.98 [1.10-3.56]).

CONCLUSION

This study demonstrated that leukocyte mtDNA-CN is associated with future mortality risk. Our study findings may lead to further research on the early prediction of mortality and its underlying mechanisms.

The Role of Epigenetic Control of Mitochondrial (Dys)Function in MASLD Onset and Progression

Metabolic dysfunction-associated steatotic fatty liver disease (MASLD), a novel definition for NAFLD, represents one of the most common causes of liver disease, and its incidence is increasing worldwide. It is characterized by a complex etiopathogenesis in which mitochondrial dysfunction exerts a pivotal role together with alteration of lipid metabolism, inflammation, and oxidative stress. Nutrients and bioactive compounds can influence such mechanisms so that changes in diet and lifestyle are regarded as important treatment strategies. Notably, natural compounds can exert their influence through changes of the epigenetic landscape, overall resulting in rewiring of molecular networks involved in cell and tissue homeostasis. Considering such information, the present review aims at providing evidence of epigenetic modifications occurring at mitochondria in response to natural and bioactive compounds in the context of liver (dys)function. For this purpose, recent studies reporting effects of compounds on mitochondria in the context of NAFLD/MASLD, as well as research showing alteration of DNA methylation and non-coding RNAs-related circuits occurring at liver mitochondria, will be illustrated. Overall, the present review will highlight the importance of understanding the bioactive compounds-dependent epigenetic modulation of mitochondria for improving the knowledge of MASLD and identifying biomarkers to be employed for effective preventative strategies or treatment protocols.

Maternal High-Fructose Corn Syrup Intake Impairs Corticosterone Clearance by Reducing Renal 11β-Hsd2 Activity via miR-27a-Mediated Mechanism in Rat Offspring

We previously reported that maternal fructose consumption increases blood corticosterone levels in rat offspring. However, the underlying mechanism of action remains unclear. In the present study, we aimed to elucidate the molecular mechanism by which maternal high-fructose corn syrup (HFCS) intake increases circulating GC levels in rat offspring (GC; corticosterone in rodents and cortisol in humans). Female Sprague Dawley rats received HFCS solution during gestation and lactation. The male offspring were fed distilled water from weaning to 60 days of age. We investigated the activities of GC-metabolizing enzymes (11β-Hsd1 and 11β-Hsd2) in various tissues (i.e., liver, kidney, adrenal glands, muscle, and white adipose tissue) and epigenetic modification. 11β-Hsd2 activity decreased in the kidney of the HFCS-fed dams. Moreover, the epigenetic analysis suggested that miR-27a reduced Hsd11b2 mRNA expression in the kidney of offspring. Maternal HFCS-induced elevation of circulating GC levels in offspring may be explained by a decrease in 11β-Hsd2 activity via renal miR-27a expression. The present study may allow us to determine one of the mechanisms of GC elevation in rat offspring that is often observed in the developmental origins of the health and disease (DOHaD) phenomenon.

Nutrients, Physical Activity, and Mitochondrial Dysfunction in the Setting of Metabolic Syndrome

Metabolic syndrome (MetS) is a cluster of metabolic risk factors for diabetes, coronary heart disease, non-alcoholic fatty liver disease, and some tumors. It includes insulin resistance, visceral adiposity, hypertension, and dyslipidemia. MetS is primarily linked to lipotoxicity, with ectopic fat deposition from fat storage exhaustion, more than obesity per se. Excessive intake of long-chain saturated fatty acid and sugar closely relates to lipotoxicity and MetS through several pathways, including toll-like receptor 4 activation, peroxisome proliferator-activated receptor-gamma regulation (PPARγ), sphingolipids remodeling, and protein kinase C activation. These mechanisms prompt mitochondrial dysfunction, which plays a key role in disrupting the metabolism of fatty acids and proteins and in developing insulin resistance. By contrast, the intake of monounsaturated, polyunsaturated, and medium-chain saturated (low-dose) fatty acids, as well as plant-based proteins and whey protein, favors an improvement in sphingolipid composition and metabolic profile. Along with dietary modification, regular exercises including aerobic, resistance, or combined training can target sphingolipid metabolism and improve mitochondrial function and MetS components. This review aimed to summarize the main dietary and biochemical aspects related to the physiopathology of MetS and its implications for mitochondrial machinery while discussing the potential role of diet and exercise in counteracting this complex clustering of metabolic dysfunctions.

d-Allulose Supplementation Prevents Diet-Induced Hepatic Lipid Accumulation via miR-130-Mediated Regulation in C57BL/6 Mice

SCOPE

d-allulose is a low-calorie rare sugar. It has been reported that d-allulose supplementation significantly inhibits diet-induced hepatic fat accumulation. However, the underlying molecular mechanisms remain unclear. This study elucidates the mechanism underlying the suppressive effect of d-allulose on hepatic fat accumulation in terms of miRNA regulation.

METHODS AND RESULTS

Male C57BL/6 mice are divided into three experimental groups-normal diet and distilled water (CC group), high-fat diet (HFD) and distilled water (HC group), and HFD and 5% d-allulose solution (HA group)-and fed the respective diets for 8 weeks. Weight gain is significantly lower in the HA group than that in the HC group, although the caloric intake is the same in both. Histological analysis of liver tissues reveals excessive lipid accumulation in the HC group; this is greatly attenuated in the HA group. Real-time PCR and western blot analyses demonstrate that, compared to the HC group, the HA group exhibits decreased hepatic PPARγ and CD36 expression. Hepatic miR-130 expression levels are higher in the HA group than those in the CC and HC groups.

CONCLUSIONS

These results indicate that miRNA changes associated with PPARγ may underlie the suppression of hepatic lipid accumulation induced by d-allulose intake.

High-fructose corn syrup intake increases hepatic mitochondrial DNA copy number and methylation in adolescent rats

High-fructose corn syrup (HFCS) is consumed worldwide. However, it has been demonstrated that an increased intake of sweetened beverages, including those sweetened using fructose, is associated with the development of childhood obesity. It is unknown why the negative effects of fructose are stronger in young persons than in elderly individuals. In recent years, mitochondria have been identified as 1 of the targets of the negative effects of fructose; they possess their own genome called mitochondrial DNA (mtDNA), which encodes genes involved in metabolic functions. We hypothesized that HFCS intake affects mtDNA in the livers of rats, and that the intensity of these effects is age-dependent. The experimental period was divided into 3 parts: childhood and adolescence (postnatal day [PD] 21-60), young adulthood (PD61-100), and adulthood (PD101-140). Rats in the different age groups were assigned to receive either water (control group [CONT]) or a 20% HFCS solution (HFCS). The hepatic mtDNA copy number of the HFCS group was higher than that of the CONT group in childhood and adolescence. In addition, the mtDNA methylation level was increased in the HFCS group in the same experimental period. No significant differences were observed between the CONT and HFCS groups during the other experimental periods. We demonstrated that HFCS has the strongest effect on mtDNA during childhood and adolescence, suggesting a need to analyze the HFCS intake of young people.

Effects of High-Fructose Corn Syrup Intake on Glucocorticoid Metabolism in Rats During Childhood, Adolescence and Adulthood

The consumption of high-fructose corn syrup (HFCS) has been increasing in recent decades, especially among children. Some reports suggest that children and adolescents are more sensitive to the adverse effects of fructose intake than adults. However, the underlying mechanism of the difference in vulnerability between adolescence and adulthood have not yet been elucidated. In this study, we attempted to elucidate the different effects of HFCS intake at different growth stages in rats: childhood and adolescence (postnatal day (PD) 21–60), young adulthood (PD60–100), and adulthood (PD100–140). Since alterations in hepatic glucocorticoid (GC) metabolism can cause diseases including insulin resistance, we focused on GC metabolizing enzymes such as 11 beta-hydroxysteroid dehydrogenase 1 and 2 (Hsd11b1 and Hsd11b2) and steroid 5 alpha-reductase 1 (Srd5a1). Western blotting showed an increase in Hsd11b1 expression and a decrease in Hsd11b2 expression in childhood and adolescence but not in adulthood. We also observed changes in Hsd11b1 and Hsd11b2 activities only in childhood and adolescence, consistent with the results of mRNA and protein expression analysis. The effect of high-fructose intake with regards to GC metabolism may therefore vary with developmental stage. This study provides insight into the adverse effects of fructose on GC metabolism in children in the context of increasing rates of HFCS consumption.

Association between the Extent of Peripheral Blood DNA Methylation of HIF3A and Accumulation of Adiposity in community-dwelling Women: The Yakumo Study

INTRODUCTION

DNA methylation in the CpG sites of intron 1 of HIF3A is associated with body mass index (BMI). This cross-sectional study investigated correlations between DNA methylation of HIF3A and BMI or adiposity parameters in the Japanese population.

METHOD

DNA methylation of HIF3A was quantified via pyrosequencing.

RESULT

DNA methylation of HIF3A differed only in women; DNA methylation level at cg27146050 was associated with visceral adipose tissue thickness and correlated with BMI and percent (%) body fat after excluding smokers.

CONCLUSION

Peripheral blood DNA methylation at the CpG site (cg27146050) of HIF3A correlated with VAT thickness in Japanese women.

Differential effects of excess high-fructose corn syrup on the DNA methylation of hippocampal neurotrophic factor in childhood and adolescence

Consumption of fructose-containing beverages such as high-fructose corn syrup (HFCS) is increasing, raising concerns about the negative effects of excessive fructose intake. A recent report indicated that excess HFCS intake impairs hippocampal function. In this study, we focused on neurotrophic factors (NFs) in the hippocampus from the viewpoint of epigenetics to clarify the adverse effects of fructose. We analyzed the effects of HFCS intake on hippocampal function in three age categories: childhood and adolescence (postnatal day (PD) 21–60), young adulthood (PD60-100), and late adulthood (PD100-140). For the experiments, male Sprague-Dawley rats were divided into three age categories, the control group was received distilled water and the HFCS group was received 20% HFCS solution for 40 days in each period. We analyzed mRNA and protein levels for qPCR and western blotting, respectively, of a hippocampal NF, brain-derived neurotrophic factor (Bdnf). HFCS consumption reduced hippocampal Bdnf mRNA and protein expressions in childhood and adolescence. Moreover, pyrosequencing assays revealed increased DNA methylation at the Bdnf promoter in childhood and adolescence. This Bdnf levels reduction may be due to hypermethylation of the promoter regions. It should be noted that this phenomenon was observed only in childhood and adolescence fructose consumption. Our results indicate that the sensitivity of the hippocampus to fructose may vary with age. This study provides insight into the adverse effects of excessive HFCS consumption on the hippocampus in children.

High-fructose corn syrup intake has stronger effects on the transcription level of hepatic lipid metabolism-related genes, via DNA methylation modification, in childhood and adolescence than in other generations

AIMS

This study aimed to analyze differences in sensitivity to hepatic lipid metabolism at different ages, through DNA methylation, using an experimental rat model of high-fructose corn syrup (HFCS) intake.

MAIN METHODS

The experimental was divided into three periods: childhood and adolescence (postnatal day (PD) 21-60), young adulthood (PD61-100), and adulthood (PD101-140). Rats in the different age groups were assigned to receive either water (C: control group) or 20% HFCS solution (H: HFCS-fed group). We measured hepatic mRNA levels of peroxisome proliferator-activated receptor alpha (Ppara), carnitine palmitoyltransferase 1A (Cpt1a), fatty acid synthase (Fasn), and peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (Pgc1a) using real-time PCR. Additionally, we examined the DNA methylation levels of Ppara, Cpt1a, Fasn, and Pgc1a using pyrosequencing.

KEY FINDINGS

Gene expressions of Cpt1a and Ppara in childhood and adolescence were significantly lower in the H group than in the C group. Conversely, Fasn and Pgc1a expressions were significantly higher in the H group than in the C group. Additionally, there was hypermethylation of Cpt1a and Ppara and hypomethylation of Fasn and Pgc1a in the H groups of childhood and adolescence. However, only one gene expression and methylation change was observed in young adulthood and adulthood groups. We found that HFCS intake in rats had stronger lipid metabolic effects in childhood and adolescence than in other generations, and that its mechanism involved epigenetic regulation.

SIGNIFICANCE

We anticipate that these research findings will be a breakthrough for elucidating the varying effects of growth stage in the future.

DNA methylation level of the gene encoding thioredoxin-interacting protein in peripheral blood cells is associated with metabolic syndrome in the Japanese general population

Metabolic syndrome (MetS) is cluster of metabolic diseases, including abdominal obesity, hyperglycemia, high blood pressure, and dyslipidemia, that directly escalate the risk of type 2 diabetes, heart disease, and stroke. Thioredoxin-interacting protein (TXNIP) is a binding protein for thioredoxin, a molecule that is a key inhibitor of cellular oxidation, and thus regulates the cellular redox state. Epigenetic alteration of the TXNIP-encoding locus has been associated with components of MetS. In the present study, we sought to determine whether the level of TXNIP methylation in blood is associated with MetS in the general Japanese population. DNA was extracted from the peripheral blood cells of 37 subjects with and 392 subjects without MetS. The level of TXNIP methylation at cg19693031 was assessed by the bisulfite-pyrosequencing method. We observed that TXNIP methylation levels were lower in MetS subjects (median 74.9%, range 71.7-78.4%) than in non-MetS subjects (median 77.7%, range 74.4-80.5%; p = 0.0024). Calculation of the confounding factor-adjusted odds ratios (ORs) and 95% confidence intervals (CIs) for hypomethylation revealed that subjects with MetS exhibited significantly higher ORs for hypomethylation than did those without MetS (OR, 2.92; 95% CI, 1.33-6.62; p = 0.009). Our findings indicated that lower levels of TXNIP methylation are associated with MetS in the general Japanese population. Altered levels of DNA methylation in TXNIP at cg19693031 might play an important role in the pathogenesis of MetS.

An Update in Epigenetics in Metabolic-Associated Fatty Liver Disease

Metabolic-associated fatty liver disease (MAFLD) is characterized by hepatic steatosis accompanied by one of three features: overweight or obesity, T2DM, or lean or normal weight with evidence of metabolic dysregulation. It is distinguished by excessive fat accumulation in hepatocytes, and a decrease in the liver's ability to oxidize fats, the accumulation of ectopic fat, and the activation of proinflammatory pathways. Chronic damage will keep this pathophysiologic cycle active causing progression from hepatic steatosis to cirrhosis and eventually, hepatocarcinoma. Epigenetics affecting gene expression without altering DNA sequence allows us to study MAFLD pathophysiology from a different perspective, in which DNA methylation processes, histone modifications, and miRNAs expression have been closely associated with MAFLD progression. However, these considerations also faced us with the circumstance that modifying those epigenetics patterns might lead to MAFLD regression. Currently, epigenetics is an area of great interest because it could provide new insights in therapeutic targets and non-invasive biomarkers. This review comprises an update on the role of epigenetic patterns, as well as innovative therapeutic targets and biomarkers in MAFLD.

Hepatic Global DNA Hypomethylation Phenotype in Rainbow Trout Fed Diets Varying in Carbohydrate to Protein Ratio

BACKGROUND

A high carbohydrate-low protein diet can induce hepatic global DNA hypomethylation in trout. The mechanisms remain unclear.

OBJECTIVES

We aimed to investigate whether an increase in dietary carbohydrates (dHCs) or a decrease in dietary proteins (dLPs) can cause hepatic global DNA hypomethylation, as well as explore the underlying mechanisms in trout.

METHODS

Two feeding trials were conducted on juvenile males, both of which involved a 4-d fasting and 4-d refeeding protocol. In trial 1, trout were fed either a high protein-no carbohydrate [HP-NC, protein 60% dry matter (DM), carbohydrates 0% DM] or a moderate protein-high carbohydrate (MP-HC, protein 40% DM, carbohydrates 30% DM) diet. In trial 2, fish were fed either a moderate protein-no carbohydrate (MP-NC, protein 40% DM, carbohydrates 0% DM), an MP-HC (protein 40% DM, carbohydrates 30% DM), or a low protein-no carbohydrate (LP-NC, protein 20% DM, carbohydrates 0% DM) diet to separate the effects of dHCs and dLPs on the hepatic methylome. Global CmCGG methylation, DNA demethylation derivative concentrations, and mRNA expression of DNA (de)methylation-related genes were measured. Differences were tested by 1-factor ANOVA when data were normally distributed or by Kruskal-Wallis nonparametric test if not.

RESULTS

In both trials, global CmCGG methylation concentrations remained unaffected, but the hepatic 5-mdC content decreased after refeeding (1-3%). The MP-HC group had 3.4-fold higher hepatic 5-hmdC and a similar 5-mdC concentration compared with the HP-NC group in trial 1. Both MP-HC and LP-NC diets lowered the hepatic 5-mdC content (1-2%), but only the LP-NC group had a significantly lower 5-hmdC concentration (P < 0.01) compared with MP-NC group in trial 2.

CONCLUSIONS

dHC and dLP independently induced hepatic global DNA demethylation in trout. The alterations in other methylation derivative concentrations indicated the demethylation process was achieved through an active demethylation pathway and probably occurred at non-CmCGG sites.

Reproductive disorders in male rats induced by high-fructose consumption from juvenile age to puberty

There is compelling evidence that a hypercaloric, high-fructose diet can cause metabolic syndrome (MetS) and a whole range of other metabolic changes. In the context of androgen deficiency, MetS in boys merits special attention, but the effects of fructose-rich diet in youth on future male reproductive function are still poorly evidenced. The aim of this study was to address this issue and analyse the effects of high-fructose intake starting from weaning to puberty (postnatal day 23 up to 83) on the reproductive function of male rats. For this purpose juvenile male Wistar rats were divided in two groups: control and the group receiving 10 % fructose solution instead of drinking water. Reproductive function was evaluated in terms of fertility, sperm count, testes/epididymis morphology, and serum sex hormones. The fructose-treated group showed a decrease in testosterone and twofold increase in luteinising and follicle-stimulating hormone levels in the serum. This was accompanied with lower testis/epididymis weights, sperm count, and changed testis/epididymis morphology. Their fertility remained unchanged, but the fertility of females mating with these males diminished. In addition, pre-implantation and post-implantation embryonic death rate rose in these females. Our results have confirmed that high fructose consumption from early age until puberty can impair the reproductive function of male rats, and call for further animal and epidemiological investigation.

Mitochondrial DNA Methylation and Human Diseases

Epigenetic modifications of the nuclear genome, including DNA methylation, histone modifications and non-coding RNA post-transcriptional regulation, are increasingly being involved in the pathogenesis of several human diseases. Recent evidence suggests that also epigenetic modifications of the mitochondrial genome could contribute to the etiology of human diseases. In particular, altered methylation and hydroxymethylation levels of mitochondrial DNA (mtDNA) have been found in animal models and in human tissues from patients affected by cancer, obesity, diabetes and cardiovascular and neurodegenerative diseases. Moreover, environmental factors, as well as nuclear DNA genetic variants, have been found to impair mtDNA methylation patterns. Some authors failed to find DNA methylation marks in the mitochondrial genome, suggesting that it is unlikely that this epigenetic modification plays any role in the control of the mitochondrial function. On the other hand, several other studies successfully identified the presence of mtDNA methylation, particularly in the mitochondrial displacement loop (D-loop) region, relating it to changes in both mtDNA gene transcription and mitochondrial replication. Overall, investigations performed until now suggest that methylation and hydroxymethylation marks are present in the mtDNA genome, albeit at lower levels compared to those detectable in nuclear DNA, potentially contributing to the mitochondria impairment underlying several human diseases.

Prolonged Changes in Hepatic Mitochondrial Activity and Insulin Sensitivity by High Fructose Intake in Adolescent Rats

Persistence of damage induced by unhealthy diets during youth has been little addressed. Therefore, we investigated the impact of a short-term fructose-rich diet on liver metabolic activity in adolescent rats and the putative persistence of alterations after removing fructose from the diet. Adolescent rats were fed a fructose-rich diet for three weeks and then switched to a control diet for further three weeks. Body composition and energy balance were not affected by fructose-rich diet, while increased body lipids and lipid gain were found after the rescue period. Switching to a control diet reversed the upregulation of plasma fructose, uric acid, lipocalin, and haptoglobin, while plasma triglycerides, alanine aminotransferase, lipopolysaccharide, and tumor necrosis factor alpha remained higher. Hepatic steatosis and ceramide were increased by fructose-rich diet, but reversed by returning to a control diet, while altered hepatic response to insulin persisted. Liver fatty acid synthase and stearoyl-CoA desaturase (SCD) activities were upregulated by fructose-rich diet, and SCD activity remained higher after returning to the control diet. Fructose-induced upregulation of complex II-driven mitochondrial respiration, peroxisome proliferator-activated receptor-gamma coactivator 1 alpha, and peroxisome proliferator activated receptor α also persisted after switching to control diet. In conclusion, our results show prolonged fructose-induced dysregulation of liver metabolic activity.

Fructose-mediated effects on gene expression and epigenetic mechanisms associated with NAFLD pathogenesis

Nonalcoholic fatty liver disease (NAFLD) is a chronic, frequently progressive condition that develops in response to excessive hepatocyte fat accumulation (i.e., steatosis) in the absence of significant alcohol consumption. Liver steatosis develops as a result of imbalanced lipid metabolism, driven largely by increased rates of de novo lipogenesis and hepatic fatty acid uptake and reduced fatty acid oxidation and/or disposal to the circulation. Fructose is a naturally occurring simple sugar, which is most commonly consumed in modern diets in the form of sucrose, a disaccharide comprised of one molecule of fructose covalently bonded with one molecule of glucose. A number of observational and experimental studies have demonstrated detrimental effects of dietary fructose consumption not only on diverse metabolic outcomes such as insulin resistance and obesity, but also on hepatic steatosis and NAFLD-related fibrosis. Despite the compelling evidence that excessive fructose consumption is associated with the presence of NAFLD and may even promote the development and progression of NAFLD to more clinically severe phenotypes, the molecular mechanisms by which fructose elicits effects on dysregulated liver metabolism remain unclear. Emerging data suggest that dietary fructose may directly alter the expression of genes involved in lipid metabolism, including those that increase hepatic fat accumulation or reduce hepatic fat removal. The aim of this review is to summarize the current research supporting a role for dietary fructose intake in the modulation of transcriptomic and epigenetic mechanisms underlying the pathogenesis of NAFLD.

Maternal fructose consumption down-regulates Lxra expression via miR-206-mediated regulation

Maternal fructose consumption affects the metabolic functions of offspring later in life. However, the molecular mechanism remains poorly understood. Differences of microRNA expression profile and DNA methylation status are a candidate mechanism to explain the developmental programming that contributes to the development of a metabolic disorder. This study examined the transgenerational effect of maternal fructose consumption from the perspective of epigenetic modification. To do this, we collected serum and liver tissues from male offspring rats that were exposed to maternal distilled water or 20% fructose water during gestation and lactation. A decreased serum high-density lipoprotein cholesterol (HDL-C) level was observed in the offspring of fructose-fed dams at postnatal day (PD) 160. Given research indicating a role of liver X receptor alpha (LXRA) in cholesterol metabolism, we analyzed Lxra expression. Real-time polymerase chain reaction analysis demonstrated that offspring that were delivered from fructose-fed dams exhibited decreased Lxra gene expression in their liver tissue. There is a well-established association between Lxra expression and the level of DNA methylation and miR-206 expression. Pyrosequencing assays revealed no differences in the level of DNA methylation in the Lxra promoter region, whereas miR-206 expression was increased in the liver at PD 60 and 160. Our data indicate that early-life exposure to maternal fructose results in changing of miR-206 expression level in the liver that suppresses the expression of Lxra. This phenomenon may be associated with the decreased serum HDL-C level in offspring.

Association of Hepatic Global DNA Methylation and Serum One-Carbon Metabolites with Histological Severity in Patients with NAFLD

OBJECTIVE

Clinical relevance of global DNA methylation and one-carbon metabolite levels with histological severity remains uncertain in patients with nonalcoholic fatty liver disease (NAFLD). This study aimed to evaluate hepatic global DNA methylation and serum one-carbon metabolite concentrations in patients with NAFLD and the possible associations of these parameters with liver histology.

METHODS

Liver biopsies from 18 control participants and 47 patients with NAFLD were evaluated.

RESULTS

The hepatic global DNA methylation level was significantly lower in the NAFLD group than in the control group among participants with overweight. Participants with moderate inflammation and mild fibrosis had significantly lower levels of global DNA methylation than those without these characteristics. Participants with borderline nonalcoholic steatohepatitis had significantly lower global DNA methylation levels than controls. The hepatic global DNA methylation level tended to decrease with the increasing hepatic inflammation grade and disease progression. The NAFLD group had a significantly higher serum homocysteine concentration than the control group among participants with overweight. This level tended to increase with increasing hepatic steatosis grade and disease progression.

CONCLUSIONS

Patients with NAFLD exhibited lower hepatic levels of global DNA methylation and elevated serum homocysteine concentrations, which are associated with the histological severity of NAFLD.

Association of circulating miR-20a, miR-27a, and miR-126 with non-alcoholic fatty liver disease in general population

Non-alcoholic fatty liver disease (NAFLD) is closely associated with obesity, metabolic syndrome, and type II diabetes mellitus. Recently, circulating microRNAs (miRNAs) have been proposed as useful disease biomarkers. We examined whether circulating miRNAs, such as miR-20a, miR-27a, and miR-126, were useful biomarkers for NAFLD. We conducted a cross-sectional analysis of 527 subjects aged 39 years or older who had undergone a health examination in the Yakumo Study. Of the residents, 92 were diagnosed with NAFLD using a registered medical sonographer. Serum miR-20a, miR-27a and miR-126 levels were measured by quantitative real-time PCR. We then calculated the odds ratios for serum miRNA level changes according to the severity of NAFLD using normal liver status as the reference group. Serum levels of miR-20a and 27a, but not miR-126, were significantly lower in NAFLD subjects than normal subjects. Serum miR-20a and miR-27a levels were significantly lower in both male and female severe NAFLD subjects. Logistic regression analysis showed a significant relationship between low circulating miR-20a and 27a levels and severe NAFLD. Down-regulated circulating miR-20a and 27a levels were significantly associated with severe NAFLD in the general population. Circulating miR-20a and miR-27a may be useful biomarkers for severe NAFLD.

Cytosine methylation of mitochondrial DNA at CpG sequences impacts transcription factor A DNA binding and transcription

In eukaryotes, cytosine methylation of nuclear DNA at CpG sequences (5mCpG) regulates epigenetic inheritance through alterations in chromatin structure. However, mitochondria lack nucleosomal chromatin, therefore the molecular mechanisms by which 5mCpG influences mitochondria must be different and are as yet unknown. Mitochondrial Transcription Factor A (TFAM) is both the primary DNA-compacting protein in the mitochondrial DNA (mtDNA) nucleoid and a transcription-initiation factor. TFAM must encounter hundreds of CpGs in mtDNA, so the occurrence of 5mCpG has the potential to impact TFAM-DNA recognition. We used biophysical approaches to determine whether 5mCpG alters any TFAM-dependent activities. 5mCpG in the heavy strand promoter (HSP1) increased the binding affinity of TFAM and induced TFAM multimerization with increased cooperativity compared to nonmethylated DNA. However, 5mCpG had no apparent effect on TFAM-dependent DNA compaction. Additionally, 5mCpG had a clear and context-dependent effect on transcription initiating from the three mitochondrial promoters. Taken together, our findings demonstrate that 5mCpG in the mitochondrial promoter region does impact TFAM-dependent activities in vitro.

Single nanomolar doxorubicin exposure triggers compensatory mitochondrial responses in H9c2 cardiomyoblasts

Dose-dependent and cumulative cardiotoxicity associated with doxorubicin (DOX) is the main limitation of anticancer therapy. Pediatric cancer survivors are particularly vulnerable, and no effective prevention measures are available. The aim of the present study was to investigate the persistent effects of nanomolar DOX concentrations and determine whether a pretreatment would induce mitochondrial adaptations in H9c2 cardiomyoblasts. H9c2 cells were incubated with DOX (10 and 25 nM) for 24 h, followed by 9 days of recovery in drug-free medium. We found that the sub-therapeutic DOX treatment induced persistent hypertrophy and dose-dependent cell cycle arrest in G2/M. Glycolytic activity, indirectly based on extracellular acidification rate, and basal respiration were significantly decreased in DOX-treated cells compared to controls, although both groups showed similar maximal respiration. Additionally, nanomolar DOX pretreatment resulted in upregulation of mitochondrial DNA transcripts accompanied by a decrease in DNA methyltransferase 1 (DNMT1) and global methylation levels. Finally, the pretreatment with DOX ameliorated H9c2 cells resistance against a subsequent exposure to DOX. These results suggest that nanomolar DOX pretreatment induced a beneficial and possibly epigenetic-based mitochondrial adaptation, raising the possibility that an early sub-therapeutic DOX treatment can be used as a preconditioning and protective approach during anticancer therapies.

Mitochondrial role in the neonatal predisposition to developing nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a global epidemic in obese children and adults, and the onset might have fetal origins. A growing body of evidence supports the role of developmental programming, whereby the maternal environment affects fetal and infant development, altering the risk profile for disease later in life. Human and nonhuman primate studies of maternal obesity demonstrate that risk factors for pediatric obesity and NAFLD begin in utero. The pathologic mechanisms for NAFLD are multifactorial but have centered on altered mitochondrial function/dysfunction that might precede insulin resistance. Compared with the adult liver, the fetal liver has fewer mitochondria, low activity of the fatty acid metabolic enzyme carnitine palmitoyl-CoA transferase-1, and little or no gluconeogenesis. Exposure to excess maternal fuels during fetal life uniquely alters hepatic fatty acid oxidation, tricarboxylic acid cycle activity, de novo lipogenesis, and mitochondrial health. These events promote increased oxidative stress and excess triglyceride storage, and, together with altered immune function and epigenetic changes, they prime the fetal liver for NAFLD and might drive the risk for nonalcoholic steatohepatitis in the next generation.

High fructose diet-induced metabolic syndrome: Pathophysiological mechanism and treatment by traditional Chinese medicine

Fructose is a natural monosaccharide broadly used in modern society. Over the past few decades, epidemiological studies have demonstrated that high fructose intake is an etiological factor of metabolic syndrome (MetS). This review highlights research advances on fructose-induced MetS, especially the underlying pathophysiological mechanism as well as pharmacotherapy by traditional Chinese medicine (TCM), using the PubMed, Web of science, China National Knowledge Infrastructure, China Science and Technology Journal and Wanfang Data. This review focuses on de novo lipogenesis (DNL) and uric acid (UA) production, two unique features of fructolysis different from glucose glycolysis. High level of DNL and UA production can result in insulin resistance, the key pathological event in developing MetS, mostly through oxidative stress and inflammation. Some other pathologies like the disturbance in brain and gut microbiota in the development of fructose-induced MetS in the past years, are also discussed. In management of MetS, TCM is an excellent representative in alternative and complementary medicine with a complete theory system and substantial herbal remedies. TCMs against MetS or MetS components, including Chinese patent medicines, TCM compound formulas, single TCM herbs and active compounds of TCM herbs, are reviewed on their effects and molecular mechanisms. TCMs with hypouricemic activity, which specially target fructose-induced MetS, are highlighted. And new technologies and strategies (such as high-throughput assay and systems biology) in this field are further discussed. In summary, fructose-induced MetS is a multifactorial disorder with the underlying complex mechanisms. Current clinical and pre-clinical evidence supports the potential of TCMs in management of MetS. Additionally, TCMs may show some advantages against complex MetS as their holistic feature through multiple target actions. However, further work is needed to confirm the effectivity and safety of TCMs by high-standard clinical trials, clarify the molecular mechanisms, and develop new anti-MetS drugs by development and application of optimized and feasible strategies and methods.

Maternal trans-general analysis of the human mitochondrial DNA pattern

There is an intimate connection between mitochondrial DNA (mtDNA) methylation and some diseases, such as cancer. MtDNA is almost strictly maternally inherited. However, whether the aberrant mtDNA methylation involved in breast cancer progression and whether mtDNA methylation can be transmitted through maternal line are poorly understood. Here we applied bisulfite sequencing to global mitochondrial DNA and whole genomic DNA methylation array from fifteen members of five three-female-generation families with one breast cancer patient in each family. We found that mtDNA methylation was maternally inherited in D-loop region and eight aberrant mtDNA methylation sites were correlated with breast cancer. Furthermore, conjoint analysis showed that mtDNA methylation sites could be potential biomarkers combined with nuclear DNA methylation sites for breast cancer risk prediction.

Wilson disease: At the crossroads between genetics and epigenetics-A review of the evidence

Environmental factors, including diet, exercise, stress, and toxins, profoundly impact disease phenotypes. This review examines how Wilson disease (WD), an autosomal recessive genetic disorder, is influenced by genetic and environmental inputs. WD is caused by mutations in the copper-transporter gene ATP7B, leading to the accumulation of copper in the liver and brain, resulting in hepatic, neurological, and psychiatric symptoms. These symptoms range in severity and can first appear anytime between early childhood and old age. Over 300 disease-causing mutations in ATP7B have been identified, but attempts to link genotype to the phenotypic presentation have yielded little insight, prompting investigators to identify alternative mechanisms, such as epigenetics, to explain the highly varied clinical presentation. Further, WD is accompanied by structural and functional abnormalities in mitochondria, potentially altering the production of metabolites that are required for epigenetic regulation of gene expression. Notably, environmental exposure affects the regulation of gene expression and mitochondrial function. We present the "multi-hit" hypothesis of WD progression, which posits that the initial hit is an environmental factor that affects fetal gene expression and epigenetic mechanisms and subsequent "hits" are environmental exposures that occur in the offspring after birth. These environmental hits and subsequent changes in epigenetic regulation may impact copper accumulation and ultimately WD phenotype. Lifestyle changes, including diet, increased physical activity, stress reduction, and toxin avoidance, might influence the presentation and course of WD, and therefore may serve as potential adjunctive or replacement therapies.

Fructose-Rich Diet Affects Mitochondrial DNA Damage and Repair in Rats

Evidence indicates that many forms of fructose-induced metabolic disturbance are associated with oxidative stress and mitochondrial dysfunction. Mitochondria are prominent targets of oxidative damage; however, it is not clear whether mitochondrial DNA (mtDNA) damage and/or its lack of repair are events involved in metabolic disease resulting from a fructose-rich diet. In the present study, we evaluated the degree of oxidative damage to liver mtDNA and its repair, in addition to the state of oxidative stress and antioxidant defense in the liver of rats fed a high-fructose diet. We used male rats feeding on a high-fructose or control diet for eight weeks. Our results showed an increase in mtDNA damage in the liver of rats fed a high-fructose diet and this damage, as evaluated by the expression of DNA polymerase γ, was not repaired; in addition, the mtDNA copy number was found to be significantly reduced. A reduction in the mtDNA copy number is indicative of impaired mitochondrial biogenesis, as is the finding of a reduction in the expression of genes involved in mitochondrial biogenesis. In conclusion, a fructose-rich diet leads to mitochondrial and mtDNA damage, which consequently may have a role in liver dysfunction and metabolic diseases.

Epigenetic modification by dietary factors: Implications in metabolic syndrome

Dietary factors play a role in normal biological processes and are involved in the regulation of pathological progression over a lifetime. Evidence has emerged indicating that dietary factor-dependent epigenetic modifications can significantly affect genome stability and the expression of mRNA and proteins, which are involved in metabolic dysfunction. Since metabolic syndrome is a progressive phenotype characterized by insulin resistance, obesity, hypertension, dyslipidemia, or type 2 diabetes, gene-diet interactions are important processes involved in the initiation of particular symptoms of metabolic syndrome and their progression. Some epigenetic risk markers can be initiated or reversed by diet and environmental factors. In this review, we discuss recent advances in our understanding of the interactions between dietary factors and epigenetic changes in metabolic syndrome. We discuss the contribution of nutritional factors in transgenerational inheritance of epigenetic markers and summarize the current knowledge of epigenetic modifications by dietary bioactive components in metabolic diseases. The intake of dietary components that regulate epigenetic modifications can provide significant health effects and, as an epigenetic diet, may prevent various pathological processes in the development of metabolic disease.

Sustained kidney biochemical derangement in treated experimental diabetes: a clue to metabolic memory

The occurrence of biochemical alterations that last for a long period of time in diabetic individuals even after adequate handling of glycemia is an intriguing phenomenon named metabolic memory. In this study, we show that a kidney pathway is gradually altered during the course of diabetes and remains persistently changed after late glycemic control in streptozotocin-induced diabetic rats. This pathway comprises an early decline of uric acid clearance and pAMPK expression followed by fumarate accumulation, increased TGF-β expression, reduced PGC-1α expression, and downregulation of methylation and hydroxymethylation of mitochondrial DNA. The sustained decrease of uric acid clearance in treated diabetes may support the prolonged kidney biochemical alterations observed after tight glycemic control, and this regulation is likely mediated by the sustained decrease of AMPK activity and the induction of inflammation. This manuscript proposes the first consideration of the possible role of hyperuricemia and the underlying biochemical changes as part of metabolic memory in diabetic nephropathy development after glycemic control.

Molecular Pathogenesis of NASH

Nonalcoholic steatohepatitis (NASH) is the main cause of chronic liver disease in the Western world and a major health problem, owing to its close association with obesity, diabetes, and the metabolic syndrome. NASH progression results from numerous events originating within the liver, as well as from signals derived from the adipose tissue and the gastrointestinal tract. In a fraction of NASH patients, disease may progress, eventually leading to advanced fibrosis, cirrhosis and hepatocellular carcinoma. Understanding the mechanisms leading to NASH and its evolution to cirrhosis is critical to identifying effective approaches for the treatment of this condition. In this review, we focus on some of the most recent data reported on the pathogenesis of NASH and its fibrogenic progression, highlighting potential targets for treatment or identification of biomarkers of disease progression.