Identification of a gene-pathway associated with non-alcoholic steatohepatitis

A Gallbladder-Specific Hydrophobic Bile Acid-FXR-MUC1 Signaling Axis Mediates Cholesterol Gallstone Formation

Differences in the distribution of hydrophilic and hydrophobic bile acids (BA) are observed in mouse models of non-alcoholic fatty liver disease (NAFLD) induced by a high-fat-cholesterol "Western-style" diet (WD), and cholesterol gallstone disease (CGD) induced by a lithogenic diet. Despite sharing common pathological processes, these models exhibit distinct characteristics in their BA pools. The study investigates the impact of hydrophobic BA (HphoBA) and hydrophilic BA (HphilBA) on CGD development using cytochrome-P450-2c70 knockout (C70-KO) mice (miceC70-KO), genetically modified to resemble humans with a hydrophobic BA pool. All miceC70-KO fed the WD develop CGD, resembling human cholelithiasis patients, while WD-fed wild-type (WT) mice (miceWT) show cholesterol-saturated bile but rarely form gallstones. Compared to miceWT, WD-fed miceC70-KO display caveolae microdomain redistribution in the gallbladder mediated by the HphoBA, FXR, and miR30c/e axis, which enhances the Sp1 transcriptional activity of mucin-1 (MUC1) genes through nuclear translocation of protein kinase Cζ (PKCζ). These changes contribute to increased production of pronucleating agents (MUC1 and MUC5ac) and accelerate crystallization of gallbladder cholesterol. The data also suggest that WD-fed miceC70-KO appropriately model human CGD since lithogenic diet-fed miceWT have a larger BA pool that masks the negative effects of gallbladder FXR on CGD development.

Increased expression of sodium-glucose cotransporter 2 and O-GlcNAcylation in hepatocytes drives non-alcoholic steatohepatitis

AIMS

Steatosis reducing effects of sodium-glucose cotransporter 2 (SGLT2) inhibitors in non-alcoholic steatohepatitis (NASH) has been consistently reported in humans, but their mechanism remains uncertain. In this study, we examined the expression of SGLT2 in human livers and investigated the crosstalk between SGLT2 inhibition and hepatic glucose uptake, intracellular O-GlcNAcylation, and autophagic regulation in NASH.

MATERIALS AND METHODS

Human liver samples obtained from subjects with/without NASH were analyzed. For in vitro studies, human normal hepatocytes and hepatoma cells were treated with SGLT2 inhibitor under high-glucose and high-lipid conditions. NASH in vivo was induced by a high-fat, -fructose, and -cholesterol Amylin liver NASH (AMLN) diet for 10 weeks followed by an additional 10 weeks with/without SGLT2 inhibitor (empagliflozin 10 mg/kg/day).

RESULTS

Liver samples from subjects with NASH were associated with increased SGLT2 and O-GlcNAcylation expression compared with controls. Under NASH condition (in vitro condition with high glucose and lipid), intracellular O-GlcNAcylation and inflammatory markers were increased in hepatocytes and SGLT2 expression was upregulated; SGLT2 inhibitor treatment blocked these changes by directly reducing hepatocellular glucose uptake. In addition, decreased intracellular O-GlcNAcylation by SGLT2 inhibitor promoted autophagic flux through AMPK-TFEB activation. In the AMLN diet-induced NASH mice model, SGLT2 inhibitor alleviated lipid accumulation, inflammation, and fibrosis through autophagy activation related to decreased SGLT2 expression and O-GlcNAcylation in the liver.

CONCLUSIONS

This study firstly demonstrates increased SGLT2 expression in NASH and secondly reveals the novel effect of SGLT2 inhibition on NASH by activating autophagy mediated by inhibition of hepatocellular glucose uptake and consequently decreasing intracellular O-GlcNAcylation.

Clinically important alterations in pharmacogene expression in histologically severe nonalcoholic fatty liver disease

Polypharmacy is common in patients with nonalcoholic fatty liver disease (NAFLD) and previous reports suggest that NAFLD is associated with altered drug disposition. This study aims to determine if patients with NAFLD are at risk for altered drug response by characterizing changes in hepatic mRNA expression of genes mediating drug disposition (pharmacogenes) across the histological NAFLD severity spectrum. We utilize RNA-seq for 93 liver biopsies with histologically staged NAFLD Activity Score (NAS), fibrosis stage, and steatohepatitis (NASH). We identify 37 significant pharmacogene-NAFLD severity associations including CYP2C19 downregulation. We chose to validate CYP2C19 due to its actionability in drug prescribing. Meta-analysis of 16 independent studies demonstrate that CYP2C19 is significantly downregulated to 46% in NASH, to 58% in high NAS, and to 43% in severe fibrosis. Our data demonstrate the downregulation of CYP2C19 in NAFLD which supports developing personalized medicine approaches for drugs sensitive to metabolism by the CYP2C19 enzyme.

A robust gene expression signature for NASH in liver expression data

Non-Alcoholic Fatty Liver Disease (NAFLD) is a progressive liver disease that affects up to 30% of worldwide population, of which up to 25% progress to Non-Alcoholic SteatoHepatitis (NASH), a severe form of the disease that involves inflammation and predisposes the patient to liver cirrhosis. Despite its epidemic proportions, there is no reliable diagnostics that generalizes to global patient population for distinguishing NASH from NAFLD. We performed a comprehensive multicohort analysis of publicly available transcriptome data of liver biopsies from Healthy Controls (HC), NAFLD and NASH patients. Altogether we analyzed 812 samples from 12 different datasets across 7 countries, encompassing real world patient heterogeneity. We used 7 datasets for discovery and 5 datasets were held-out for independent validation. Altogether we identified 130 genes significantly differentially expressed in NASH versus a mixed group of NAFLD and HC. We show that our signature is not driven by one particular group (NAFLD or HC) and reflects true biological signal. Using a forward search we were able to downselect to a parsimonious set of 19 mRNA signature with mean AUROC of 0.98 in discovery and 0.79 in independent validation. Methods for consistent diagnosis of NASH relative to NAFLD are urgently needed. We showed that gene expression data combined with advanced statistical methodology holds the potential to serve basis for development of such diagnostic tests for the unmet clinical need.

Nonalcoholic Fatty Liver Disease (NAFLD) and Hepatic Cytochrome P450 (CYP) Enzymes

Nonalcoholic fatty liver disease (NAFLD) is characterized by excessive fat in the liver. An international consensus panel has recently proposed to rename the disease to metabolic dysfunction associated with fatty liver disease (MAFLD). The disease can range from simple steatosis (fat accumulation) to nonalcoholic steatohepatitis (NASH) which represents a severe form of NAFLD and is accompanied by inflammation, fibrosis, and hepatocyte damage in addition to significant steatosis. This review collates current knowledge of changes in human hepatic cytochrome P450 enzymes in NAFLD. While the expression of these enzymes is well studied in healthy volunteers, our understanding of the alterations of these proteins in NAFLD is limited. Much of the existing knowledge on the subject is derived from preclinical studies, and clinical translation of these findings is poor. Wherever available, the effect of NAFLD on these proteins in humans is debatable and currently lacks a consensus among different reports. Protein expression is an important in vitro physiological parameter controlling the pharmacokinetics of drugs and the last decade has seen a rise in the accurate estimation of these proteins for use with physiologically based pharmacokinetic (PBPK) modeling to predict drug pharmacokinetics in special populations. The application of label-free, mass spectrometry-based quantitative proteomics as a promising tool to study NAFLD-associated changes has also been discussed.

Multi-omics Analysis of Liver Infiltrating Macrophages Following Ethanol Consumption

Alcoholic liver disease (ALD) is a significant health hazard and economic burden affecting approximately 10 million people in the United States. ALD stems from the production of toxic-reactive metabolites, oxidative stress and fat accumulation in hepatocytes which ultimately results in hepatocyte death promoting hepatitis and fibrosis deposition. Monocyte-derived infiltrating Ly6C^hi and Ly6C^low macrophages are instrumental in perpetuating and resolving the hepatitis and fibrosis associated with ALD pathogenesis. In the present study we isolated liver infiltrating macrophages from mice on an ethanol diet and subjected them to metabolomic and proteomic analysis to provide a broad assessment of the cellular metabolite and protein differences between infiltrating macrophage phenotypes. We identified numerous differentially regulated metabolites and proteins between Ly6C^hi and Ly6C^low macrophages. Bioinformatic analysis for pathway enrichment of the differentially regulated metabolites showed a significant number of metabolites involved in the processes of glycerophospholipid metabolism, arachidonic acid metabolism and phospholipid biosynthesis. From analysis of the infiltrating macrophage proteome, we observed a significant enrichment in the biological processes of antigen presentation, actin polymerization and organization, phagocytosis and apoptotic regulation. The data presented herein could yield exciting new research avenues for the analysis of signaling pathways regulating macrophage polarization in ALD.

Influence of total polar compounds on lipid metabolism, oxidative stress and cytotoxicity in HepG2 cells

BACKGROUND

Recently, the harmful effects of frying oil on health have been gradually realized. However, as main components of frying oils, biochemical effects of total polar compounds (TPC) on a cellular level were underestimated.

METHODS

The effects of total polar compounds (TPC) in the frying oil on the lipid metabolism, oxidative stress and cytotoxicity of HepG2 cells were investigated through a series of biochemical methods, such as oil red staining, real-time polymerase chain reaction (RT-PCR), cell apoptosis and cell arrest.

RESULTS

Herein, we found that the survival rate of HepG2 cells treated with TPC decreased in a time and dose dependent manner, and thereby presented significant lipid deposition over the concentration of 0.5 mg/mL. TPC were also found to suppress the expression levels of PPARα, CPT1 and ACOX, elevate the expression level of MTP and cause the disorder of lipid metabolism. TPC ranged from 0 to 2 mg/mL could significantly elevate the amounts of reactive oxygen species (ROS) in HepG2 cells, and simultaneously increase the malondialdehyde (MDA) content from 21.21 ± 2.62 to 65.71 ± 4.20 μmol/mg of protein (p < 0.05) at 24 h. On the contrary, antioxidant enzymes superoxide dismutase (SOD), glutathione (GSH), and catalase (CAT) respectively decreased by 0.52-, 0.56- and 0.28-fold, when HepG2 cells were exposed to 2 mg/mL TPC for 24 h. In addition, TPC could at least partially induce the apoptosis of HepG2 cells, and the transition from G0/G1 to G2 phase in HepG2 cells was impeded.

CONCLUSIONS

TPC could progressively cause lipid deposition, oxidative stress and cytotoxicity, providing the theoretical support for the detrimental health effects of TPC.

Review article: drug-induced liver injury in the context of nonalcoholic fatty liver disease - a physiopathological and clinical integrated view

BACKGROUND

Nonalcoholic fatty disease (NAFLD) is the most common liver disease, since it is strongly associated with obesity and metabolic syndrome pandemics. NAFLD may affect drug disposal and has common pathophysiological mechanisms with drug-induced liver injury (DILI); this may predispose to hepatoxicity induced by certain drugs that share these pathophysiological mechanisms. In addition, drugs may trigger fatty liver and inflammation per se by mimicking NAFLD pathophysiological mechanisms.

AIMS

To provide a comprehensive update on (a) potential mechanisms whereby certain drugs can be more hepatotoxic in NAFLD patients, (b) the steatogenic effects of drugs, and (c) the mechanism involved in drug-induced steatohepatitis (DISH).

METHODS

A language- and date-unrestricted Medline literature search was conducted to identify pertinent basic and clinical studies on the topic.

RESULTS

Drugs can induce macrovesicular steatosis by mimicking NAFLD pathogenic factors, including insulin resistance and imbalance between fat gain and loss. Other forms of hepatic fat accumulation exist, such as microvesicular steatosis and phospholipidosis, and are mostly associated with acute mitochondrial dysfunction and defective lipophagy, respectively. Drug-induced mitochondrial dysfunction is also commonly involved in DISH. Patients with pre-existing NAFLD may be at higher risk of DILI induced by certain drugs, and polypharmacy in obese individuals to treat their comorbidities may be a contributing factor.

CONCLUSIONS

The relationship between DILI and NAFLD may be reciprocal: drugs can cause NAFLD by acting as steatogenic factors, and pre-existing NAFLD could be a predisposing condition for certain drugs to cause DILI. Polypharmacy associated with obesity might potentiate the association between this condition and DILI.

Methyl donor deficient diets cause distinct alterations in lipid metabolism but are poorly representative of human NAFLD

Background: Non-alcoholic fatty liver disease (NAFLD) is a global health issue. Dietary methyl donor restriction is used to induce a NAFLD/non-alcoholic steatohepatitis (NASH) phenotype in rodents, however the extent to which this model reflects human NAFLD remains incompletely understood. To address this, we undertook hepatic transcriptional profiling of methyl donor restricted rodents and compared these to published human NAFLD datasets.             

Methods: Adult C57BL/6J mice were maintained on control, choline deficient (CDD) or methionine/choline deficient (MCDD) diets for four weeks; the effects on methyl donor and lipid biology were investigated by bioinformatic analysis of hepatic gene expression profiles followed by a cross-species comparison with human expression data of all stages of NAFLD.

Results: Compared to controls, expression of the very low density lipoprotein (VLDL) packaging carboxylesterases ( Ces1d, Ces1f, Ces3b) and the NAFLD risk allele Pnpla3 were suppressed in MCDD; with Pnpla3 and the liver predominant Ces isoform, Ces3b, also suppressed in CDD. With respect to 1-carbon metabolism, down-regulation of Chka, Chkb, Pcty1a, Gnmt and Ahcy with concurrent upregulation of Mat2a suggests a drive to maintain S-adenosylmethionine levels. There was minimal similarity between global gene expression patterns in either dietary intervention and any stage of human NAFLD, however some common transcriptomic changes in inflammatory, fibrotic and proliferative mediators were identified in MCDD, NASH and HCC.

Conclusions: This study suggests suppression of VLDL assembly machinery may contribute to hepatic lipid accumulation in these models, but that CDD and MCDD rodent diets are minimally representative of human NAFLD at the transcriptional level.

Proteome Characteristics of Non-Alcoholic Steatohepatitis Liver Tissue and Associated Hepatocellular Carcinomas

To uncover mechanisms of nonalcoholic steatohepatitis (NASH) associated hepatocarcinogenesis, we compared the proteomes of human NASH-associated liver biopsies, resected hepatocellular carcinomas (HCCs) and HCCs of HCV⁺ patients with normal liver tissue of patients with gastrointestinal tumor metastasis, in formalin-fixed paraffin-embedded samples obtained after surgery in our hospital during the period from 2006 to 2011. In addition, proteome analysis of liver tumors in male STAM NASH-model mice was performed. Similar changes in the proteome spectrum such as overexpression of enzymes involved in lipid, cholesterol and bile acid biosynthesis and examples associated with suppression of fatty acid oxidation and catabolism, alcohol metabolism, mitochondrial function as well as low expression levels of cytokeratins 8 and 18 were observed in both human NASH biopsies and NASH HCCs, but not HCV⁺ HCCs. Alterations in downstream protein expression pointed to significant activation of transforming growth factor β, SMAD family member 3, β-catenin, Nrf2, SREBP-LXRα and nuclear receptor-interacting protein 1 (NRIP1), and inhibition of PPARs and p53 in human NASH biopsies and/or HCCs, suggesting their involvement in accumulation of lipids, development of fibrosis, oxidative stress, cell proliferation and suppression of apoptosis in NASH hepatocarcinogenesis. In STAM mice, PPARs inhibition was not obvious, while expression of cytokeratins 8 and 18 was elevated, indicative of essential differences between human and mouse NASH pathogenesis.

BAR502, a dual FXR and GPBAR1 agonist, promotes browning of white adipose tissue and reverses liver steatosis and fibrosis

Non-alcoholic steatohepatitis (NASH) is a highly prevalent chronic liver disease. Here, we have investigated whether BAR502, a non-bile acid, steroidal dual ligand for FXR and GPBAR1, reverses steato-hepatitis in mice fed a high fat diet (HFD) and fructose. After 9 week, mice on HFD gained ≈30% of b.w (P < 0.01 versus naïve) and were insulin resistant. These overweighting and insulin resistant mice were randomized to receive HFD or HFD in combination with BAR502. After 18 weeks, HFD mice developed NASH like features with severe steato-hepatitis and fibrosis, increased hepatic content of triacylglycerol and cholesterol and expression of SREPB1c, FAS, ApoC2, PPARα and γ, α-SMA, α1 collagen and MCP1 mRNAs. Treatment with BAR502 caused a ≈10% reduction of b.w., increased insulin sensitivity and circulating levels of HDL, while reduced steatosis, inflammatory and fibrosis scores and liver expression of SREPB1c, FAS, PPARγ, CD36 and CYP7A1 mRNA. BAR502 increased the expression of SHP and ABCG5 in the liver and SHP, FGF15 and GLP1 in intestine. BAR502 promoted the browning of epWAT and reduced liver fibrosis induced by CCl₄. In summary, BAR502, a dual FXR and GPBAR1 agonist, protects against liver damage caused by HFD by promoting the browning of adipose tissue.

Comparison of Gene Expression Patterns Between Mouse Models of Nonalcoholic Fatty Liver Disease and Liver Tissues From Patients

BACKGROUND & AIMS

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disorder in industrialized countries. Mouse models of NAFLD have been used in studies of pathogenesis and treatment, and have certain features of the human disease. We performed a systematic transcriptome-wide analysis of liver tissues from patients at different stages of NAFLD progression (ranging from healthy obese individuals to those with steatosis), as well as rodent models of NAFLD, to identify those that most closely resemble human disease progression in terms of gene expression patterns.

METHODS

We performed a systematic evaluation of genome-wide messenger RNA expression using liver tissues collected from mice fed a standard chow diet (controls) and 9 mouse models of NAFLD: mice on a high-fat diet (with or without fructose), mice on a Western-type diet, mice on a methionine- and choline-deficient diet, mice on a high-fat diet given streptozotocin, and mice with disruption of Pten in hepatocytes. We compared gene expression patterns with those of liver tissues from 25 patients with nonalcoholic steatohepatitis (NASH), 27 patients with NAFLD, 15 healthy obese individuals, and 39 healthy nonobese individuals (controls). Liver samples were obtained from patients undergoing liver biopsy for suspected NAFLD or NASH, or during liver or bariatric surgeries. Data sets were analyzed using the limma R-package. Overlap of functional profiles was analyzed by gene set enrichment analysis profiles.

RESULTS

We found differences between human and mouse transcriptomes to be significantly larger than differences between disease stages or models. Of the 65 genes with significantly altered expression in patients with NASH and 177 genes with significantly altered expression in patients with NAFLD, compared with controls, only 1-18 of these genes also differed significantly in expression between mouse models of NAFLD and control mice. However, expression of genes that regulate pathways associated with the development of NAFLD were altered in some mouse models (such as pathways associated with lipid metabolism). On a pathway level, gene expression patterns in livers of mice on the high-fat diet were associated more closely with human fatty liver disease than other models.

CONCLUSIONS

In comparing gene expression profiles between liver tissues from different mouse models of NAFLD and patients with different stages of NAFLD, we found very little overlap. Our data set is available for studies of pathways that contribute to the development of NASH and NAFLD and selection of the most applicable mouse models (http://www.nash-profiler.com).

Integrative genomic signatures of hepatocellular carcinoma derived from nonalcoholic Fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a risk factor for Hepatocellular carcinoma (HCC), but he transition from NAFLD to HCC is poorly understood. Feature selection algorithms in human and genetically modified mice NAFLD and HCC microarray data were applied to generate signatures of NAFLD progression and HCC differential survival. These signatures were used to study the pathogenesis of NAFLD derived HCC and explore which subtypes of cancers that can be investigated using mouse models. Our findings show that: (I) HNF4 is a common potential transcription factor mediating the transcription of NAFLD progression genes (II) mice HCC derived from NAFLD co-cluster with a less aggressive human HCC subtype of differential prognosis and mixed etiology (III) the HCC survival signature is able to correctly classify 95% of the samples and gives Fgf20 and Tgfb1i1 as the most robust genes for prediction (IV) the expression values of genes composing the signature in an independent human HCC dataset revealed different HCC subtypes showing differences in survival time by a Logrank test. In summary, we present marker signatures for NAFLD derived HCC molecular pathogenesis both at the gene and pathway level.

Nonalcoholic steatohepatitis in precision medicine: Unraveling the factors that contribute to individual variability

There are numerous factors in individual variability that make the development and implementation of precision medicine a challenge in the clinic. One of the main goals of precision medicine is to identify the correct dose for each individual in order to maximize therapeutic effect and minimize the occurrence of adverse drug reactions. Many promising advances have been made in identifying and understanding how factors such as genetic polymorphisms can influence drug pharmacokinetics (PK) and contribute to variable drug response (VDR), but it is clear that there remain many unidentified variables. Underlying liver diseases such as nonalcoholic steatohepatitis (NASH) alter absorption, distribution, metabolism, and excretion (ADME) processes and must be considered in the implementation of precision medicine. There is still a profound need for clinical investigation into how NASH-associated changes in ADME mediators, such as metabolism enzymes and transporters, affect the pharmacokinetics of individual drugs known to rely on these pathways for elimination. This review summarizes the key PK factors in individual variability and VDR and highlights NASH as an essential underlying factor that must be considered as the development of precision medicine advances. A multifactorial approach to precision medicine that considers the combination of two or more risk factors (e.g. genetics and NASH) will be required in our effort to provide a new era of benefit for patients.

Activation of farnesoid X receptor induces RECK expression in mouse liver

Farnesoid X receptor (FXR) belongs to the ligand-activated nuclear receptor superfamily, and functions as a transcription factor regulating the transcription of numerous genes involved in bile acid homeostasis, lipoprotein and glucose metabolism. In the present study, we identified RECK, a membrane-anchored inhibitor of matrix metalloproteinases, as a novel target gene of FXR in mouse liver. We found that FXR agonist substantially augmented hepatic RECK mRNA and protein expression in vivo and in vitro. FXR regulated the transcription of RECK through directly binding to FXR response element located within intron 1 of the mouse RECK gene. Moreover, FXR agonist reversed the down-regulation of RECK in the livers from mice fed a methionine and choline deficient diet. In summary, our data suggest that RECK is a novel transcriptional target of FXR in mouse liver, and provide clues to better understanding the function of FXR in liver.

Specific inhibition of the redox activity of ape1/ref-1 by e3330 blocks tnf-α-induced activation of IL-8 production in liver cancer cell lines

APE1/Ref-1 is a main regulator of cellular response to oxidative stress via DNA-repair function and co-activating activity on the NF-κB transcription factor. APE1 is central in controlling the oxidative stress-based inflammatory processes through modulation of cytokines expression and its overexpression is responsible for the onset of chemoresistance in different tumors including hepatic cancer. We examined the functional role of APE1 overexpression during hepatic cell damage related to fatty acid accumulation and the role of the redox function of APE1 in the inflammatory process. HepG2 cells were stably transfected with functional and non-functional APE1 encoding plasmids and the protective effect of APE1 overexpression toward genotoxic compounds or FAs accumulation, was tested. JHH6 cells were stimulated with TNF-α in the presence or absence of E3330, an APE1 redox inhibitor. IL-8 promoter activity was assessed by a luciferase reporter assay, gene expression by Real-Time PCR and cytokines (IL-6, IL-8, IL-12) levels measured by ELISA. APE1 over-expression did not prevent cytotoxicity induced by lipid accumulation. E3330 treatment prevented the functional activation of NF-κB via the alteration of APE1 subcellular trafficking and reduced IL-6 and IL-8 expression induced by TNF-α and FAs accumulation through blockage of the redox-mediated activation of NF-κB. APE1 overexpression observed in hepatic cancer cells may reflect an adaptive response to cell damage and may be responsible for further cell resistance to chemotherapy and for the onset of inflammatory response. The efficacy of the inhibition of APE1 redox activity in blocking TNF-α and FAs induced inflammatory response opens new perspectives for treatment of inflammatory-based liver diseases.

Solute carrier family 2 member 1 is involved in the development of nonalcoholic fatty liver disease

Susceptibility to develop nonalcoholic fatty liver disease (NAFLD) has genetic bases, but the associated variants are uncertain. The aim of the present study was to identify genetic variants that could help to prognose and further understand the genetics and development of NAFLD. Allele frequencies of 3,072 single-nucleotide polymorphisms (SNPs) in 92 genes were characterized in 69 NAFLD patients and 217 healthy individuals. The markers that showed significant allele-frequency differences in the pilot groups were subsequently studied in 451 NAFLD patients and 304 healthy controls. Besides this, 4,414 type 2 diabetes mellitus (T2DM) cases and 4,567 controls were genotyped. Liver expression of the associated gene was measured and the effect of its potential role was studied by silencing the gene in vitro. Whole genome expression, oxidative stress (OS), and the consequences of oleic acid (OA)-enriched medium on lipid accumulation in siSLC2A1-THLE2 cells were studied by gene-expression analysis, dihydroethidium staining, BODIPY, and quantification of intracellular triglyceride content, respectively. Several SNPs of SLC2A1 (solute carrier family 2 [facilitated glucose transporter] member 1) showed association with NAFLD, but not with T2DM, being the haplotype containing the minor allele of SLC2A1 sequence related to the susceptibility to develop NAFLD. Gene-expression analysis demonstrated a significant down-regulation of SLC2A1 in NAFLD livers. Enrichment functional analyses of transcriptome profiles drove us to demonstrate that in vitro silencing of SLC2A1 induces an increased OS activity and a higher lipid accumulation under OA treatment.

CONCLUSIONS

Genetic variants of SLC2A1 are associated with NAFLD, and in vitro down-regulation of this gene promotes lipid accumulation. Moreover, the oxidative response detected in siSLC2A1-THLE2 cells corroborated the antioxidant properties previously related to this gene and linked the most representative clinical characteristics of NAFLD patients: oxidative injury and increased lipid storage.

Reduced heme oxygenase-1 expression in steatotic livers infected with hepatitis C virus

Hepatic nonalcoholic fatty liver disease (NAFLD) is known to exacerbate liver injury due to chronic hepatitis C infection. Heme oxygenase-1 (HO-1) is an important protective antioxidative defense enzyme that is known to be induced in response to NAFLD and other liver injuries. The aim of this study was to evaluate HO-1 expression in HCV infected human livers with concomitant NAFLD.

METHODS

We compared levels of HO-1 in NAFLD liver biopsies from patients with or without chronic HCV infection using immunohistochemistry, immunoblots and real time RT-PCR. We also evaluated frozen sections of liver with dihydroethidium (DHE) or dichlorofluorescein (DCF) fluorescence staining to evaluate O(2)(-) and peroxide production respectively.

RESULTS

HO-1 expression was only increased in NAFLD livers without HCV infection, while HCV infected livers showed reduced HO-1 levels, regardless whether NAFLD was present. In uninfected livers with NAFLD, HO-1 expression was primarily localized in hepatocytes containing fat and areas of injury around the central vein. However, both NAFLD with and without concomitant HCV infection showed high levels of O(2)(-) or peroxide production compared to normal human liver control samples.

CONCLUSIONS

These findings support the hypothesis that NAFLD is an important process for hepatocyte oxidative stress and injury in liver diseases. They also suggest that HCV can repress HO-1 induction in vivo even when other inducers of HO-1 are present.

Deficiency in galectin-3 promotes hepatic injury in CDAA diet-induced nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is increasingly recognized as a condition in which excess fat accumulates in hepatocytes. Nonalcoholic steatohepatitis (NASH), a severe form of NAFLD in which inflammation and fibrosis in the liver are noted, may eventually progress to end-stage liver disease. Galectin-3, a β-galactoside-binding animal lectin, is a multifunctional protein. This protein is involved in inflammatory responses and carcinogenesis. We investigated whether galectin-3 is involved in the development of NASH by comparing galectin-3 knockout (gal3(-/-)) mice and wild-type (gal3(+/+)) mice with choline-deficient L-amino-acid-defined (CDAA) diet-induced NAFLD/NASH. Hepatic injury was significantly more severe in the gal3(-/-) male mice, as compared to the gal3(+/+) mice. Data generated by microarray analysis of gene expression suggested that galectin-3 deficiency causes alterations in the expression of various genes associated with carcinogenesis and lipid metabolism. Through canonical pathway analysis, involvement of PDGF and IL-6 signaling pathways was suggested in galectin-3 deficiency. Significant increase of CD14, Fos, and Jun, those that were related to lipopolysaccharide-mediated signaling, was candidate to promote hepatocellular damages in galectin-3 deficiency. In conclusion, galectin-3 deficiency in CDAA diet promotes NAFLD features. It may be caused by alterations in the expression profiles of various hepatic genes including lipopolysaccharide-mediated inflammation.

Proteomics analysis of human nonalcoholic fatty liver

Nonalcoholic fatty liver disease (NAFLD) is being increasingly recognized as a major cause of liver-related morbidity and mortality. Given the increasing prevalence of obesity in western countries, NAFLD has become an important public health problem. The principal aim of this study was to find differences in protein expression between patients with NAFLD and healthy controls. Changes in protein expression of liver samples from controls, nonalcoholic steatosis, and nonalcoholic steatohepatitis (NASH) subjects were analyzed by two-dimensional differential in-gel electrophoresis (DIGE). With this proteomic technique, hundreds of proteins can be analyzed simultaneously and their relative abundance can be calculated. Proteins showing significant changes (ratio ≥ 1.5, p < 0.05) were identified by MALDI TOF/TOF mass spectrometry. Western blot of tissue homogenates was then used as a complementary method to validate protein expression changes observed by DIGE. With the aim to have a noninvasive approach to detect changes produced in NAFLD-affected liver, validated proteins were further tested in serum samples of different cohorts of patients. Following this approach, we identified two candidate markers CPS1 and GRP78 that were differentially expressed between control, steatosis, and NASH. This proteomics approach demonstrates that DIGE combined with MALDI TOF/TOF and Western blot analysis of tissue and serum samples is a useful approach to identify candidate markers associated with NAFLD.

Analysis of global and absorption, distribution, metabolism, and elimination gene expression in the progressive stages of human nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is characterized by a series of pathological changes that range from simple fatty liver to nonalcoholic steatohepatitis (NASH). The objective of this study is to describe changes in global gene expression associated with the progression of human NAFLD. This study is focused on the expression levels of genes responsible for the absorption, distribution, metabolism, and elimination (ADME) of drugs. Differential gene expression between three clinically defined pathological groups-normal, steatosis, and NASH-was analyzed. Genome-wide mRNA levels in samples of human liver tissue were assayed with Affymetrix GeneChip Human 1.0ST arrays. A total of 11,633 genes exhibited altered expression out of 33,252 genes at a 5% false discovery rate. Most gene expression changes occurred in the progression from steatosis to NASH. Principal component analysis revealed that hepatic disease status was the major determinant of differential ADME gene expression rather than age or sex of sample donors. Among the 515 drug transporters and 258 drug-metabolizing enzymes (DMEs) examined, uptake transporters but not efflux transporters or DMEs were significantly over-represented in the number of genes down-regulated. These results suggest that uptake transporter genes are coordinately targeted for down-regulation at the global level during the pathological development of NASH and that these patients may have decreased drug uptake capacity. This coordinated regulation of uptake transporter genes is indicative of a hepatoprotective mechanism acting to prevent accumulation of toxic intermediates in disease-compromised hepatocytes.

A signature of six genes highlights defects on cell growth and specific metabolic pathways in murine and human hepatocellular carcinoma

Hepatocellular carcinoma (HCC) represents a major health problem as it afflicts an increasing number of patients worldwide. Albeit most of the risk factors for HCC are known, this is a deadly syndrome with a life expectancy at the time of diagnosis of less than 1 year. Definition of the molecular principles governing the neoplastic transformation of the liver is an urgent need to facilitate the clinical management of patients, based on innovative methods to detect the disease in its early stages and on more efficient therapies. In the present study, we have combined the analysis of a murine model and human samples of HCC to identify genes differentially expressed early in the process of hepatocarcinogenesis, using a microarray-based approach. Expression of 190 genes was impaired in murine HCC from which 65 were further validated by low-density array real-time polymerase chain reaction (RT-PCR). The expression of the best 45 genes was then investigated in human samples resulting in 18 genes in which expression was significantly modified in HCC. Among them, JUN, methionine adenosyltransferase 1A and 2A, phosphoglucomutase 1, and acyl CoA dehydrogenase short/branched chain indicate defective cell proliferation as well as one carbon pathway, glucose and fatty acid metabolism, both in HCC and cirrhotic liver, a well-known preneoplastic condition. These alterations were further confirmed in public transcriptomic datasets from other authors. In addition, vasodilator-stimulated phosphoprotein, an actin-associated protein involved in cytoskeleton remodeling, was also found to be increased in the liver and serum of cirrhotic and HCC patients. In addition to revealing the impairment of central metabolic pathways for liver homeostasis, further studies may probe the potential value of the reported genes for the early detection of HCC.

Risk of nonalcoholic steatohepatitis and fibrosis in patients with nonalcoholic fatty liver disease and low visceral adiposity

BACKGROUND & AIMS

Increased visceral adiposity is considered the hallmark of the metabolic syndrome, whose hepatic manifestation is nonalcoholic fatty liver disease (NAFLD), although a subset of patients does not have visceral obesity. Our study aimed to compare metabolic alterations and liver damage in patients with NAFLD with and without visceral obesity.

METHODS

Four hundred and thirty one consecutive patients with liver biopsy-confirmed NAFLD were divided in three groups according to waist circumference, the simplest surrogate marker of visceral obesity. One hundred and thirty three patients (31%) had a waist circumference ≤94 (males) and ≤80 cm (females) (group A), 157 (36%) between 94 and 102, and 80 and 88 (B), and the remaining 141 (33%) had values higher than 102 and 88 cm (C).

RESULTS

Significant trends for older age, higher prevalence of female gender, lower HDL, higher triglycerides, altered glucose metabolism, hypertension, and metabolic syndrome were observed with increasing visceral adiposity. In contrast, non-alcoholic steatohepatitis (NASH) detected in 55% and 72% of patients with normal and increased waist circumference, respectively, and the presence of fibrosis ≥2 were not associated with visceral adiposity. Alanine aminotransferase (ALT), ferritin, HOMA-IR >4, and severe steatosis were independently associated with NASH, whereas ferritin and impaired glucose tolerance were associated with fibrosis ≥2.

CONCLUSIONS

Patients with normal waist circumference, despite milder metabolic alterations, may have NASH and are at risk of developing fibrosis, suggesting that once NAFLD is present, visceral obesity is not a major determinant of liver damage severity.

Drug metabolism alterations in nonalcoholic fatty liver disease

Drug-metabolizing enzymes play a vital role in the elimination of the majority of therapeutic drugs. The major organ involved in drug metabolism is the liver. Chronic liver diseases have been identified as a potential source of significant interindividual variation in metabolism. Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in the United States, affecting between 60 and 90 million Americans, yet the vast majority of NAFLD patients are undiagnosed. NAFLD encompasses a spectrum of pathologies, ranging from steatosis to nonalcoholic steatohepatitis and fibrosis. Numerous animal studies have investigated the effects of NAFLD on hepatic gene expression, observing significant alterations in mRNA, protein, and activity levels. Information on the effects of NAFLD in human patients is limited, though several significant investigations have recently been published. Significant alterations in the activity of drug-metabolizing enzymes may affect the clearance of therapeutic drugs, with the potential to result in adverse drug reactions. With the enormous prevalence of NAFLD, it is conceivable that every drug currently on the market is being given to patients with NAFLD. The current review is intended to present the results from both animal models and human patients, summarizing the observed alterations in the expression and activity of the phase I and II drug-metabolizing enzymes.

Decreased immunoexpression of survivin could be a potential marker in human non-alcoholic fatty liver disease progression?

BACKGROUND/AIM

Regulation of apoptosis in non-alcoholic fatty liver disease (NAFLD) has been a theme of growing debate. Although no other study assessed the role of survivin in NAFLD, its expression has been reported in hepatic carcinogenesis because of other aetiological factors with relevant discrepancies. The aim of this study was to assess the pattern of survivin immunoexpression by tissue microarray along the whole spectrum of NAFLD, including non-alcoholic steatohepatitis (NASH)-related hepatocellular carcinoma (HCC).

METHODS

Liver biopsies from 56 patients with NAFLD were evaluated: 18 with steatosis, 21 non-cirrhotic NASH, 10 NASH-related cirrhosis, seven NASH-related HCC, as compared with 71 HCC related to other causes and with 12 normal livers.

RESULTS

Survivin immunoexpression in NAFLD was restricted to cytoplasm and was found to be progressively lower in advanced stages, including cirrhosis and HCC: steatosis vs NASH-related cirrhosis (P=0.0243); steatosis vs NASH-related HCC (P=0.0010); NASH vs NASH-related cirrhosis (P=0.0318); and NASH vs NASH-related HCC (P=0.0007), thus suggesting a deregulation of apoptosis from NAFLD towards HCC. Interestingly, survivin immunoreactivity in NASH-related HCC was also found to be significantly lower than in HCC related to other causes (P<0.05). Remarkably, nuclear staining for survivin was not detected in any case of NAFLD, contrasting to its presence in all other cases of HCC.

CONCLUSIONS

Survivin immunoexpression in NASH-related HCC is herein originally found substantially different than in HCC related to other causes, thus requiring further studies to elucidate the role of survivin in human NAFLD progression.

Difference in expression of hepatic microRNAs miR-29c, miR-34a, miR-155, and miR-200b is associated with strain-specific susceptibility to dietary nonalcoholic steatohepatitis in mice

The importance of dysregulation of microRNA (miRNA) expression in nonalcoholic steatohepatitis (NASH) has been increasingly recognized; however, the association between altered expression of miRNAs and pathophysiological features of NASH and whether there is a connection between susceptibility to NASH and altered expression of miRNAs are largely unknown. In this study, male inbred C57BL/6J and DBA/2J mice were fed a lipogenic methyl-deficient diet that causes liver injury similar to human NASH, and the expression of miRNAs and the level of proteins targeted by these miRNAs in the livers were determined. Administration of the methyl-deficient diet triggered NASH-specific changes in the livers of C57BL/6J and DBA/2J mice, with the magnitude being more severe in DBA/2J mice. This was evidenced by a greater extent of expression of fibrosis-related genes in the livers of methyl-deficient DBA/2J mice. The development of NASH was accompanied by prominent changes in the expression of miRNAs, including miR-29c, miR-34a, miR-155, and miR-200b. Interestingly, changes in the expression of these miRNAs and protein levels of their targets, including Cebp-β, Socs 1, Zeb-1, and E-cadherin, in the livers of DBA/2J mice fed a methyl-deficient diet were more pronounced as compared with those in C57BL/6J mice. These results show that alterations in the expression of miRNAs are a prominent event during development of NASH induced by methyl deficiency and strongly suggest that severity of NASH and susceptibility to NASH may be determined by variations in miRNA expression response. More important, our data provide a mechanistic link between alterations in miRNA expression and pathophysiological and pathomorphological features of NASH.

Non-alcoholic fatty liver disease proteomics

PURPOSE

Non-alcoholic fatty liver disease (NAFLD) is an important cause of chronic liver injury that has gained concern in clinical hepatology. The principal aim of this study was to find differences in protein expression between patients with NAFLD and healthy controls.

EXPERIMENTAL DESIGN

Changes in protein expression of liver samples from each of the three groups of subjects, controls, non-alcoholic steatosis, and non-alcoholic steatohepatitis (NASH), were analyzed by DIGE combined with MALDI TOF/TOF analysis, a proteomic approach that allows to compare hundreds of proteins simultaneously.

RESULTS

Forty-three proteins exhibiting significant changes (ratio ≥1.5, p<0.05) were characterized, 22 comparing steatosis samples versus control samples and 21 comparing NASH versus control samples. Ten of these proteins were further analyzed by Western blot in tissue samples to confirm the observed changes of protein expression using DIGE. The proteins validated were further tested in serum samples of different cohorts of patients.

CONCLUSIONS AND CLINICAL RELEVANCE

Following this approach we identified two candidate markers, carbamoyl phosphate synthase 1 and 78  kDa glucose-regulated protein, differentially expressed between control and NASH. This proteomics approach demonstrates that DIGE combined with MALDI TOF/TOF and Western blot analysis of tissue and serum samples is a useful approach to identify candidate markers associated with NAFLD, resulting in proteins whose level of expression can be correlated to a disease state.

Integrated hepatic transcriptome and proteome analysis of mice with high-fat diet-induced nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is the most common form of liver disease in the US and refers to a wide spectrum of liver damage, including simple steatosis, steatohepatitis, fibrosis and cirrhosis. The goal of the present study was to achieve a more detailed understanding of the molecular changes in response to high fat-induced liver steatosis through the identification of a differentially expressed liver transcriptome and proteome. Male C57/BL6 mice fed a high-fat lard diet for 8 weeks developed visceral obesity and hepatic steatosis characterized by significantly increased liver and plasma free fatty acid and triglyceride levels and plasma alanine aminotransferase activities. Transcriptome analysis demonstrated that, compared to the control diet (CD), high-fat diet changed the expression of 309 genes (132 up- and 177 down-regulated; by a twofold change and more, P<.05). Multiple genes encoding proteins involved in lipogenesis were down-regulated, whereas genes involved in fatty acid oxidation were up-regulated. Proteomic analysis revealed 12 proteins which were differentially expressed. Of these, glutathione S-transferases mu1 and pi1 and selenium-binding protein 2 were decreased at both the gene and protein levels. This is the first study to perform a parallel transcriptomic and proteomic analysis of diet-induced hepatic steatosis. Several key pathways involving xenobiotic and lipid metabolism, the inflammatory response and cell-cycle control were identified. These pathways provide targets for future mechanistic and therapeutic studies as related to the development and prevention of NAFLD.

Nonalcoholic steatohepatitis, animal models, and biomarkers: what is new?

Nonalcoholic fatty liver disease (NAFLD) is a clinicopathological term that encompasses a spectrum of abnormalities ranging from simple triglyceride accumulation in the hepatocytes (hepatic steatosis) to hepatic steatosis with inflammation (steatohepatitis, also known as nonalcoholic steatohepatitis or NASH). NASH can also progress to cirrhosis and hepatocellular carcinoma (HCC). Steatohepatitis has been estimated to affect around 5% of the total population and 20% of those who are overweight. The mechanisms leading to NASH and its progression to cirrhosis and HCC remain unclear, but it is a condition typically associated with obesity, insulin resistance, diabetes, and hypertriglyceridemia. This point corroborates the need for animal models and molecular markers that allow us to understand the mechanisms underlying this disease. Nowadays, there are numerous mice models to study abnormal liver function such as steatosis, NASH, and hepatocellular carcinoma. The study of the established animal models has provided many clues in the pathogenesis of steatosis and steatohepatitis, although these remain incompletely understood and no mice model completely fulfills the clinical features observed in humans. In addition, there is a lack of accurate sensitive diagnostic tests that do not involve invasive procedures. Current laboratory tests include some biochemical analysis, but their utility for diagnosing NASH is still poor. For that reason, a great effort is being made toward the identification and validation of novel biomarkers to assess NASH using high-throughput analysis based on genomics, proteomics, and metabolomics. The most recent discoveries and their validation will be discussed.

A subset of dysregulated metabolic and survival genes is associated with severity of hepatic steatosis in obese Zucker rats

We aimed to characterize the primary abnormalities associated with fat accumulation and vulnerability to hepatocellular injury of obesity-related fatty liver. We performed functional analyses and comparative transcriptomics of isolated primary hepatocytes from livers of obese insulin-resistant Zucker rats (comprising mild to severe hepatic steatosis) and age-matched lean littermates, searching for novel genes linked to chronic hepatic steatosis. Of the tested genome, 1.6% was identified as steatosis linked. Overexpressed genes were mainly dedicated to primary metabolism (100%), signaling, and defense/acute phase (approximately 70%); detoxification, steroid, and sulfur metabolism (approximately 65%) as well as cell growth/proliferation and protein synthesis/transformation (approximately 70%) genes were downregulated. The overexpression of key genes involved in de novo lipogenesis, fatty acid and glycerolipid import and synthesis, as well as acetyl-CoA and cofactor provision was paralleled by enhanced hepatic lipogenesis and production of large triacylglycerol-rich VLDL. Greatest changes in gene expression were seen in those encoding the lipogenic malic enzyme (up to 7-fold increased) and cell-to-cell interacting cadherin 17 (up to 8-fold decreased). Among validated genes, fatty acid synthase, stearoyl-CoA desaturase 1, fatty acid translocase/Cd36, malic enzyme, cholesterol-7 alpha hydroxylase, cadherin 17, and peroxisome proliferator-activated receptor alpha significantly correlated with severity of hepatic steatosis. In conclusion, dysregulated expression of metabolic and survival genes accompany hepatic steatosis in obese insulin-resistant rats and may render steatotic hepatocytes more vulnerable to cell injury in progressive nonalcoholic fatty liver disease.

Mechanisms of non-alcoholic steatohepatitis: pathophysiology and molecular biology

Non-alcoholic steatohepatitis (NASH), characterized by liver fatty infiltration, inflammation, hepatocellular injury and fibrosis, may easily develop into liver cirrhosis and hepatocellular carcinoma. The increased flow of FFAs (free fatty acids) to the liver and the de novo lipogenesis in the liver lead to fat overload. Lipotoxicity can induce oxidative stress, inflammatory reaction and apoptosis. Subsequently chronic liver injury activates a fibrogenic response that accelerates the evolution of NASH towards end-stage liver disease. Further research on pathophysiology and molecular biology is beneficial to clinical diagnosis and management of NASH.

Characterization and comprehensive proteome profiling of exosomes secreted by hepatocytes

Exosomes represent a discrete population of vesicles that are secreted from various cell types to the extracellular media. Their protein and lipid composition are a consequence of sorting events at the level of the multivesicular body, a central organelle which integrates endocytic and secretory pathways. Characterization of exosomes from different biological samples has shown the presence of common as well as cell-type specific proteins. Remarkably, the protein content of the exosomes is modified upon pathological or stress conditions. Hepatocytes play a central role in the body response to stress metabolizing potentially harmful endogenous substances as well as xenobiotics. In the present study, we described and characterized for the first time exosome secretion in nontumoral hepatocytes, and with the use of a systematic proteomic approach, we establish the first extensive proteome of a hepatocyte-derived exosome population which should be useful in furthering our understanding of the hepatic function and in the identification of components that may serve as biomarkers for hepatic alterations. Our analysis identifies a significant number of proteins previously described among exosomes derived from others cell types as well as proteins involved in metabolizing lipoproteins, endogenous compounds and xenobiotics, not previously described in exosomes. Furthermore, we demonstrated that exosomal membrane proteins can constitute an interesting tool to express nonexosomal proteins into exosomes with therapeutic purposes.

Causes and metabolic consequences of Fatty liver

Type 2 diabetes and cardiovascular disease represent a serious threat to the health of the population worldwide. Although overall adiposity and particularly visceral adiposity are established risk factors for these diseases, in the recent years fatty liver emerged as an additional and independent factor. However, the pathophysiology of fat accumulation in the liver and the cross-talk of fatty liver with other tissues involved in metabolism in humans are not fully understood. Here we discuss the mechanisms involved in the pathogenesis of hepatic fat accumulation, particularly the roles of body fat distribution, nutrition, exercise, genetics, and gene-environment interaction. Furthermore, the effects of fatty liver on glucose and lipid metabolism, specifically via induction of subclinical inflammation and secretion of humoral factors, are highlighted. Finally, new aspects regarding the dissociation of fatty liver and insulin resistance are addressed.

S-adenosylmethionine and proliferation: new pathways, new targets

SAMe (S-adenosylmethionine) is the main methyl donor group in the cell. MAT (methionine adenosyltransferase) is the unique enzyme responsible for the synthesis of SAMe from methionine and ATP, and SAMe is the common point between the three principal metabolic pathways: polyamines, transmethylation and transsulfuration that converge into the methionine cycle. SAMe is now also considered a key regulator of metabolism, proliferation, differentiation, apoptosis and cell death. Recent results show a new signalling pathway implicated in the proliferation of the hepatocyte, where AMPK (AMP-activated protein kinase) and HuR, modulated by SAMe, take place in HGF (hepatocyte growth factor)-mediated cell growth. Abnormalities in methionine metabolism occur in several animal models of alcoholic liver injury, and it is also altered in patients with liver disease. Both high and low levels of SAMe predispose to liver injury. In this regard, knockout mouse models have been developed for the enzymes responsible for SAMe synthesis and catabolism, MAT1A and GNMT (glycine N-methyltransferase) respectively. These knockout mice develop steatosis and HCC (hepatocellular carcinoma), and both models closely replicate the pathologies of human disease, which makes them extremely useful to elucidate the mechanism underlying liver disease. These new findings open a wide range of possibilities to discover novel targets for clinical applications.

Increased hepatic UCP2 expression in rats with nonalcoholic steatohepatitis is associated with upregulation of Sp1 binding to its motif within the proximal promoter region

Uncoupling protein-2 (UCP2) is a mitochondrial inner-membrane carrier protein that is involved in the control of fatty acid metabolism. To understand the mechanism of the transcriptional regulation of ucp2 in the pathogenesis of nonalcoholic steatohepatitis (NASH), we cloned 500 bp upstream of the ucp2 exon 1 from a rat liver cDNA library and identified cis-acting regulatory elements. The transcriptional start site was identified as "C," -359 bp from the ATG codon. A reporter gene assay showed that deletion of the nucleotide sequence between -264 and -60 bp resulted in a significant decrease in promoter activity in HepG2 and H4IIE cells. Electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) revealed that the increase in promoter activity is related to an enhanced ability of Sp1 to bind to its motifs at -84 to -61 bp within the ucp2 proximal promoter. Overexpression of exogenous Sp1 in H4IIE cells also increased the promoter activity. We demonstrated that the expression of UCP2 mRNA and protein is markedly increased in rats with nonalcoholic steatohepatitis (NASH). Coincidently, levels of Sp1 binding to -84/-61 bp were also increased. Overall, our data indicate that the Sp1-binding site located at the proximal promoter is involved in the regulation of rat UCP2 expression.

Much to know about proteolysis: intricate proteolytic machineries compromise essential cellular functions

Proteolysis has traditionally been considered as a radical way to terminate the function of a protein. However, protein destruction also is the starting point for many processes as they can only occur when the way has been cleared for the action of other proteins. Protein destruction can occur virtually in all compartments and organelles of the cell, associated with cell membranes or large protein complexes, it determines subcellular partitioning, association with positive or negative regulators which conditions the action of many critical cellular factors. The third intracellular proteolysis meeting held by the University La Laguna, Canary Islands, Spain, included speakers working with some of the most important proteolytic systems present in higher eukaryotes, such as the UPS (ubiquitin–proteasome system) and autophagy. Owing to the fact that these pathways directly or indirectly regulate many cell functions, this meeting brought together an audience with a wide range of research interests, including genetic, cell biological, biochemical and structural aspects of protein degradation. Some of these topics inspired interesting discussions and a significant number of these are developed in the issues reviewed herein.

Gene expression in human NAFLD

Despite the high prevalence of nonalcoholic fatty liver disease (NAFLD), little is known of its pathogenesis based on study of human liver samples. By the use of Affymetrix GeneChips (17,601 genes), we investigated gene expression in the human liver of subjects with extreme steatosis due to NAFLD without histological signs of inflammation (liver fat 66.0 +/- 6.8%) and in subjects with low liver fat content (6.4 +/- 2.7%). The data were analyzed by using sequence-based reannotation of Affymetrix probes and a robust model-based normalization method. We identified genes involved in hepatic glucose and lipid metabolism, insulin signaling, inflammation, coagulation, and cell adhesion to be significantly associated with liver fat content. In addition, genes involved in ceramide signaling (MAP2K4) and metabolism (UGCG) were found to be positively associated with liver fat content. Genes involved in lipid metabolism (PLIN, ACADM), fatty acid transport (FABP4, CD36), amino acid catabolism (BCAT1), and inflammation (CCL2) were validated by real-time PCR and were found to be upregulated in subjects with high liver fat content. The data show that multiple changes in gene expression characterize simple steatosis.

Genes and nonalcoholic fatty liver disease

Whereas most individuals with nonalcoholic fatty liver disease (NAFLD) will have steatosis, only a minority will ever develop progressive disease. Family studies and interethnic variations in susceptibility suggest that genetic factors may be important in determining disease risk. Although no genetic associations with advanced NAFLD have been replicated in large studies, preliminary data suggest that polymorphisms in the genes encoding microsomal triglyceride transfer protein, superoxide dismutase 2, the CD14 endotoxin receptor, tumor necrosis factor-alpha, transforming growth factor-beta, and angiotensinogen may be associated with steatohepatitis and/or fibrosis. With the advent of high-throughput gene analyses and the reduced cost of whole genome-wide scans, it seems likely that genes contributing to inherited susceptibility to this common disease will be identified in the near future.

Molecular basis and mechanisms of progression of non-alcoholic steatohepatitis

Non-alcoholic steatohepatitis (NASH), a cause of cirrhosis and hepatocellular carcinoma, is characterized by fatty infiltration of the liver, inflammation, hepatocellular damage and fibrosis. Progress has been made in understanding the molecular and cellular mechanisms implicated in the pathogenesis of this condition, therefore, we here review recent developments regarding the basic mechanisms of NASH development. Accumulation of triglycerides in the hepatocytes is the result of increased inflow of free fatty acids and de novo lipogenesis. Steatosis leads to lipotoxicity, which causes apoptosis, necrosis, generation of oxidative stress and inflammation. The resulting chronic injury activates a fibrogenic response that leads eventually to end-stage liver disease. A better understanding of these mechanisms is crucial for the design of novel diagnostic and therapeutic strategies.

Fatty Liver

Although the epidemic of obesity has been accompanied by an increase in the prevalence of the metabolic syndrome, not all obese develop the syndrome and even lean individuals can be insulin resistant. Both lean and obese insulin resistant individuals have an excess of fat in the liver which is not attributable to alcohol or other known causes of liver disease, a condition defined as nonalcoholic fatty liver disease (NAFLD) by gastroenterologists. The fatty liver is insulin resistant. Liver fat is highly significantly and linearly correlated with all components of the metabolic syndrome independent of obesity. Overproduction of glucose, VLDL, CRP, and coagulation factors by the fatty liver could contribute to the excess risk of cardiovascular disease associated with the metabolic syndrome and NAFLD. Both of the latter conditions also increase the risk of type 2 diabetes and advanced liver disease. The reason why some deposit fat in the liver whereas others do not is poorly understood. Individuals with a fatty liver are more likely to have excess intraabdominal fat and inflammatory changes in adipose tissue. Intervention studies have shown that liver fat can be decreased by weight loss, PPARγ agonists, and insulin therapy.