Microarray analysis of gene expression in the liver during the urinary ethanol cycle in rats fed ethanol intragastrically at a constant rate

Prenatal alcohol exposure is associated with changes in placental gene co-expression networks

Alcohol consumption during pregnancy can result in a range of adverse postnatal outcomes among exposed children. However, identifying at-risk children is challenging given the difficulty to confirm prenatal alcohol exposure and the lack of early diagnostic tools. Placental surveys present an important opportunity to uncover early biomarkers to identify those at risk. Here, we report the first transcriptome-wide evaluation to comprehensively evaluate human placental pathways altered by fetal alcohol exposure. In a prospective longitudinal birth cohort in Cape Town, South Africa, we performed bulk tissue RNAseq in placenta samples from 32 women reporting heavy drinking during pregnancy and 30 abstainers/light drinkers. Weighted gene co-expression network analysis (WGCNA) and differential gene expression analysis were performed to assess associations between fetal alcohol exposure and placental gene expression patterns at a network-wide and single gene level, respectively. The results revealed altered expression in genes related to erythropoiesis and angiogenesis, which are implicated in established postnatal phenotypes related to alcohol exposure, including disruptions in iron homeostasis, growth, and neurodevelopment. The reported findings provide insights into the molecular pathways affected by prenatal alcohol exposure and highlight the potential of placental biomarkers for detecting and understanding the effects of alcohol on fetal development.

Alterations in the Transcriptional Profile of the Liver Tissue and the Therapeutic Effects of Propolis Extracts in Alcohol-induced Steatosis in Rats

The hepatoprotective effects of the ethanolic extracts of propolis (EEP) on alcohol-induced liver steatosis were investigated in Wistar rats. Chronic alcoholic fatty liver was induced by administration of 52% alcohol to male Wistar rats at the dose of 1% body weight for 7 weeks. Then animals were simultaneously treated with 50% ethanol solutions of EEP or normal saline at the dose of 0.1% body weight for 4 further weeks. Serological analyses and liver histopathology studies were performed to investigate the development of steatosis. Microarray analysis was conducted to investigate the alterations of hepatic gene expression profiling. Our results showed that 4-week treatment of EEP helped to restore the levels of various blood indices, liver function enzymes and the histopathology of liver tissue to normal levels. Results from the microarray analysis revealed that the hepatic expressions of genes involved in lipogenesis were significantly down-regulated by EEP treatment, while the transcriptional expressions of functional genes participating in fatty acids oxidation were markedly increased. The ability of EEP to reduce the negative effects of alcohol on liver makes propolis a potential natural product for the alternative treatment of alcoholic fatty liver.

S-adenosylmethionine decreases the peak blood alcohol levels 3 h after an acute bolus of ethanol by inducing alcohol metabolizing enzymes in the liver

INTRODUCTION

An alcohol bolus causes the blood alcohol level (BAL) to peak at 1-2 h post ingestion. The ethanol elimination rate is regulated by alcohol metabolizing enzymes, primarily alcohol dehydrogenase (ADH1), acetaldehyde dehydrogenase (ALDH), and cytochrome P450 (CYP2E1). Recently, S-adenosylmethionine (SAMe) was found to reduce acute BALs 3 h after an alcohol bolus. The question, then, was: what is the mechanism involved in this reduction of BAL by feeding SAMe? To answer this question, we investigated the changes in ethanol metabolizing enzymes and the epigenetic changes that regulate the expression of these enzymes during acute binge drinking and chronic drinking.

METHODS

Rats were fed a bolus of ethanol with or without SAMe, and were sacrificed at 3 h or 12 h after the bolus.

RESULTS

RT-PCR and Western blot analyses showed that SAMe significantly induced ADH1 levels in the 3 h liver samples. However, SAMe did not affect the changes in ADH1 protein levels 12 h post bolus. Since SAMe is a methyl donor, it was postulated that the ADH1 gene expression up regulation at 3 h was due to a histone modification induced by methylation from methyl transferases. Dimethylated histone 3 lysine 4 (H3K4me2), a modification responsible for gene expression activation, was found to be significantly increased by SAMe at 3 h post bolus.

CONCLUSION

These results correlated with the low BAL found at 3 h post bolus, and support the concept that SAMe increased the gene expression to increase the elimination rate of ethanol in binge drinking by increasing H3K4me2.

The cyclic pattern of blood alcohol levels during continuous ethanol feeding in rats: the effect of feeding S-adenosylmethionine

S-adenosylmethionine (SAMe), the major methyl donor for DNA and histone methylation was fed with ethanol for 1month in order to modify the effects of ethanol on rat liver. The following parameters were studied to determine the effects of SAMe; liver histology, the blood alcohol cycle (BAL), changes in gene expression mined from microarray analysis, changes in histone methylation, changes in liver SAMe levels and its metabolites and ADH. SAMe changed the type of fatty liver, reduced liver ALT levels and prevented the BAL cycle caused by intragastric ethanol feeding. Microarray analysis showed that SAMe feeding prevented most of the changes in gene expression induced by ethanol feeding, presumably by inducing H3K27me3 and gene silencing. H3K27me3 was significantly increased by SAMe with or without ethanol feeding. It is concluded that SAMe feeding stabilized global gene expression so that the changes in gene expression involved in the blood alcohol cycle were prevented.

Alcohol-induced alterations of the hepatocyte cytoskeleton

The hepatocyte cytoskeleton consists of three filamentous networks: microtubules, actin microfilaments and keratin intermediate filaments. Because of the abundance of the proteins that comprise each system and the central role each network plays in a variety of cellular processes, the three filament systems have been the focus of a host of studies aimed at understanding the progression of alcohol-induced liver injury. In this review, we will briefly discuss the hepatic organization of each cytoskeletal network and highlight some components of each system. We will also describe what is known about ethanol-induced changes in the dynamics and distributions of each cytoskeletal system and discuss what is known about changes in protein expression levels and post-translational modifications. Finally, we will describe the possible consequences of these cytoskeletal alterations on hepatocyte function and how they might contribute to the progression of liver disease.

The effect of propranolol on gene expression during the blood alcohol cycle of rats fed ethanol intragastrically

Propranolol, a beta adrenergic blocker prevents the blood alcohol (BAL) cycle in rats fed ethanol intragastrically at a constant rate by preventing the cyclic changes in the metabolic rate caused by fluctuating levels of norepinephrine released into the blood. The change in the rate of metabolism changes the rate of alcohol elimination in the blood which causes the BAL to cycle. Microarray analysis of the livers from the rats fed ethanol and propranolol showed similar changes in clusters of functionally related gene expressions. The controls and the trough of the cycle differed dramatically from the cluster pattern seen in the rats at the peaks of the blood alcohol cycle. The changes in gene expression induced by ethanol were similar when propranolol was fed without ethanol especially with the changes in the kinases and phosphatases, Toll-like receptor signaling and cytokine-cytokine receptor interaction were also changed. The changes in gene expression caused by ethanol and propranolol feeding are alike probably because both drugs induce beta adrenergic receptor desensitization.

Chronic ethanol feeding alters hepatocyte memory which is not altered by acute feeding

BACKGROUND

Gene expression changes in the liver after acute binge drinking may differ from the changes seen in chronic ethanol feeding in the rat. The changes in gene expression after chronic ethanol feeding may sensitize the liver to alcohol-induced liver damage, which is not seen after acute binge drinking.

METHODS

To test this hypothesis, gene microarray analysis was performed on the livers of rats (n = 3) fed an acute binge dose of ethanol (6 g/kg body wt) and killed at 3 and 12 hours after ethanol by gavage. The gene microarrays were compared with those made on the liver of rats from a previous study, in which the rats were fed ethanol by intragastric tube for 1 month (36% of calories derived from ethanol).

RESULTS

Microarray analysis data varied between the acute and chronic models in several important respects. Growth factors increased mainly in the chronic alcohol fed rat. Changes in enzymes involved in oxidative stress were noted only with chronic ethanol feeding. Gene expression of fat metabolism was increased only with chronic ethanol feeding. Most importantly, epigenetic related enzymes and acetylation and methylation of histones changed only after chronic ethanol feeding.

CONCLUSIONS

The results support the concept that chronic ethanol ingestion induces altered gene expression as a result of changes in epigenetic mechanisms, where acetylation and methylation of histones were altered.

Epigenetics of proteasome inhibition in the liver of rats fed ethanol chronically

AIM: To examine the effects of ethanol-induced proteasome inhibition, and the effects of proteasome inhibition in the regulation of epigenetic mechanisms.

METHODS: Rats were fed ethanol for 1 mo using the Tsukamoto-French model and were compared to rats given the proteasome inhibitor PS-341 (Bortezomib, Velcade™) by intraperitoneal injection. Microarray analysis and real time PCR were performed and proteasome activity assays and Western blot analysis were performed using isolated nuclei.

RESULTS: Chronic ethanol feeding caused a significant inhibition of the ubiquitin proteasome pathway in the nucleus, which led to changes in the turnover of transcriptional factors, histone-modifying enzymes, and, therefore, affected epigenetic mechanisms. Chronic ethanol feeding was related to an increase in histone acetylation, and it is hypothesized that the proteasome proteolytic activity regulated histone modifications by controlling the stability of histone modifying enzymes, and, therefore, regulated the chromatin structure, allowing easy access to chromatin by RNA polymerase, and, thus, proper gene expression. Proteasome inhibition by PS-341 increased histone acetylation similar to chronic ethanol feeding. In addition, proteasome inhibition caused dramatic changes in hepatic remethylation reactions as there was a significant decrease in the enzymes responsible for the regeneration of S-adenosylmethionine, and, in particular, a significant decrease in the betaine-homocysteine methyltransferase enzyme. This suggested that hypomethylation was associated with proteasome inhibition, as indicated by the decrease in histone methylation.

CONCLUSION: The role of proteasome inhibition in regulating epigenetic mechanisms, and its link to liver injury in alcoholic liver disease, is thus a promising approach to study liver injury due to chronic ethanol consumption.

Sirt1 is involved in energy metabolism: the role of chronic ethanol feeding and resveratrol

Sirt1, a deacetylase involved in regulating energy metabolism in response to calorie restriction, is up regulated after chronic ethanol feeding using the intragastric feeding model of alcohol liver disease. PGC1 alpha is also up regulated in response to ethanol. These changes are consistent with activation of the Sirt1/PGC1 alpha pathway of metabolism and aging, involved in alcohol liver disease including steatosis, necrosis and fibrosis of the liver. To test this hypothesis, male rats fed ethanol intragastrically for 1 month were compared with rats fed ethanol plus resveratrol or naringin. Liver histology showed macrovesicular steatosis caused by ethanol and this change was unchanged by resveratrol or naringin treatment. Necrosis occurred with ethanol alone but was accentuated by resveratrol treatment, as was fibrosis. The expression of Sirt1 and PGC1 alpha was increased by ethanol but not when naringin or resveratrol was fed with ethanol. Sirt3 was also up regulated by ethanol but not when resveratrol was fed with ethanol. These results support the concept that ethanol induces the Sirt1/PGC1 alpha pathway of gene regulation and both naringin and resveratrol prevent the activation of this pathway by ethanol. However, resveratrol did not reduce the liver pathology caused by chronic ethanol feeding.

Distinct methylation patterns in histone H3 at Lys-4 and Lys-9 correlate with up- & down-regulation of genes by ethanol in hepatocytes

Ethanol induced liver injury is associated with a global change in gene expression but its mechanisms are not known. We studied whether alcohol-induced gene expression is associated with post-translational methylations of histone H3. Primary culture of rat hepatocytes was treated with ethanol (50 or 100 mM) for 24 h and the status of methylation of H3 at lys 4 (H3dimeK4) or lys 9 (H3dimeK9) was monitored by Western blotting using antibodies to dimethylated histone H3 at lys 4 or lys 9. The cells exposed to ethanol showed strikingly opposing behaviors in methylation patterns; H3dimeK9 methylation was decreased whereas H3dimeK4 increased. Similar results were obtained in the interphase nuclei. Their binding on the metaphase chromosomes exhibits distinct site specific pattern of accumulation. Next, chromatin immunoprecipitation of the ethanol treated samples with antibodies for methylated lys 4 or lys 9 histone H3 followed by amplification of the immunoprecipitated DNA, was used to determine their association with the promoters of genes up- or downregulated by ethanol. Lys4 methylation was associated with ethanol upregulated genes (Adh, GST-yc2) whereas lys 9 methylation with downregulated genes (Lsdh, cytP4502c11) demonstrating a difference between these two methylations. These results suggest that exposure of hepatocytes to ethanol changes the expression of several susceptible genes which are associated with site specific modification of dimethylated forms of histone H3 amino termini at their regulatory regions.

Dose-dependent effects of alcohol on insulin signaling: partial explanation for biphasic alcohol impact on human health

Routine consumption of alcohol at low doses is associated with decreased risk of acquiring type 2 diabetes, whereas chronic and excessive alcohol consumption increases the risk. Although there is good epidemiologic evidence for these biphasic effects, careful validation of these effects on insulin signaling has not been reported, nor have biological mechanisms underlying these biphasic effects been proposed. In this study, we provide evidence in rats that low-dose alcohol intake (4 g/kg x d) enhances hepatic insulin signaling by suppressing p55gamma (a phosphatidylinositol 3-kinase regulatory subunit isoform) at the posttranscriptional level, leading to the increased association of the phosphatidylinositol 3-kinase catalytic subunit (p110) with insulin receptor substrate-1 (P < 0.05) and subsequent activation of downstream effectors such as Akt, glycogen synthase kinase 3beta, and nuclear sterol regulatory element binding protein (SREBP)-1. These results, combined with our previous data (confirmed in the present study) demonstrating that ethanol intake at high doses (13 g/kg x d) disrupts hepatic insulin signaling by inducing TRB3, a mammalian homolog of Drosophila (tribbles-related protein 3) that prevented activation of downstream effectors (such as Akt, GSK3beta, and nSREBP-1), provide clear mechanistic validation of the biphasic effects of ethanol on insulin signaling. We also report that ethanol induction of TRB3 can be partially blocked (P < 0.01) by compounds (4-phenyl butyric acid and taurine-ursodeoxycholic acid) known to reduce endoplasmic reticulum stress. Thus, alcohol exerts biphasic actions on hepatic insulin signaling, such that low doses activate insulin signaling pathways associated with reduced p55gamma to increase nSREBP-1, whereas high doses of ethanol elevate TRB3 and suppress insulin signaling to decrease SREBP-1.

Hepatic gene expression and lipid parameters in complement C3(-/-) mice that do not develop ethanol-induced steatosis

BACKGROUND/AIMS

Fatty infiltration initiates alcohol-induced liver changes and complement component C3 affects lipid metabolism. We recently observed that ethanol-induced steatosis seen in normal (C3(+/+)) mice was absent in livers of C3-deficient (C3(-/-)) mice. To understand the underlying molecular mechanisms we analyzed lipid parameters and liver gene expression profiles in these mice.

METHODS

A Western-type high-fat diet with ethanol or carbohydrates (control) was fed for 6 weeks to C3(+/+) and C3(-/-) mice. Serum and liver lipid parameters were analyzed and liver mRNA expression patterns studied by micro-array analysis and RT-PCR.

RESULTS

In both genotypes ethanol markedly reduced serum cholesterol, apolipoprotein A-I, phospholipid transfer protein activity and hepatic mRNA levels of fatty acid-binding proteins and fatty acid beta-oxidation enzymes. In contrast, exclusively in C3(-/-) mice, ethanol treatment increased serum and liver adiponectin levels but down-regulated transcripts of lipogenic enzymes, adiponectin receptor 2 and adipose differentiation-related protein and up-regulated phospholipase D1.

CONCLUSIONS

We propose that these ethanol-induced alterations observed exclusively in C3(-/-) mice contribute to protection against fatty infiltration and subsequent inflammatory processes in the liver of these mice. The results suggest important cross-talk between complement factor C3 and lipid regulators in ethanol-induced steatosis.

Histone acetyltransferase p300 modulates gene expression in an epigenetic manner at high blood alcohol levels

When rats are fed ethanol intragastrically at a constant rate for 1 month, the urinary alcohol level (UAL) cycles over 7-9 day intervals. At the peak UAL, the liver is hypoxic shifting the redox state to a reduced rate. Microarray analysis done on livers at the UAL peaks shows changes in approximately 1300 gene expression compared to the pair-fed controls. To determine the mechanism of the gene expression changes, histone acetylation regulation was investigated in liver nuclear extracts at the peaks and troughs of the UAL and their pair-fed controls. No change occurred in SirT-1. P300, a histone acetyltransferase (HAT), which acetylates histone H3 on lysine 9, was increased at the peaks. Histone 3 acetylated at lysine 9 was also increased at the peaks. This indicates that the up regulated genes at the UAL peaks resulted from an increase in p300 transcription regulation, epigenetically. P300 activates transcription of numerous genes in response to signal transcription factors such as H1F 1alpha, increased in the nucleus at UAL peaks. Signal transduction pathways, such as NFkappaB, AP-1, ERK, JNK, and p38 were not increased at the peaks. beta-Catenin was increased in the nuclear extract at the UAL troughs, where increased gene expression was absent. The increase in gene expression at the peaks was due, in part, to increased acetylation of histone 3 at lysine 9.

Gene expression patterns of the liver in response to alcohol: in vivo and in vitro models compared

Two basic models of alcoholic liver disease pathogenesis exist, one in vivo and one in vitro. To justify the in vitro model, evidence is needed to show that it stimulates the in vivo model. Therefore, changes in gene expression caused by high ethanol level were compared using the two models. Many functional pathways were upregulated in both models. These included the insulin signaling pathway, TGFbeta signaling pathway, apoptosis, MAPK signaling pathway, wnt signaling pathway and apoptosis. Differences were found in the fatty acids synthesis pathway, which was upregulated in vivo; and glycosylation enzymes which were downregulated in vivo. Also, downregulated in vitro were beta oxidation by mitochondria and translation factors. Catalase and superoxide dismutase in mitochondria were upregulated in vitro. These two enzymes have antioxidant effects. In summary, remarkably similar responses to high alcohol levels in the form of changes in gene expression pathways were found in the in vivo and in vitro models tested.