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.

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Human genomic DNA fragments containing catechol 0-methyltransferase (COMT) sequences were isolated and the exon-intron structure analysed by sequencing, PCR and comparing to the human COMT cDNA sequences. The gene contains six exons, of which exons 1 and 2 are noncoding. MB-ATG and S-ATG codons, responsible for the initiation of translation of the membranebound (MB) and soluble (S) forms of the enzyme, are located in exon 3. Two distinct COMTspecific transcripts, 1.3 kb and 1.5 kb, were detected in various human tissues and cell lines. Different quantities of the shorter COMT-specific mRNA in the tissues studied suggest a tissue-specific regulation of the COMT gene at transcriptional level. Mapping of the 5' ends of the COMT mRNAs showed that transcription initiates at multiple sites in two separate DNA regions, which are preceded by functional promoter sequences. The proximal promoter (Pl), located between the two translation initiation codons and extending approximately 200 bp upstream of the MB-ATG initiation codon, apparently gives rise to the 1.3-kb S-COMT mRNA (S-mRNA). The distal promoter (P2) is located in a DNA fragment in front of and partly overlapping the transcription-start region of the 1.5-kb transcript, suggesting that it controls the expression of this MB-mRNA. Similarities between the rat and human COMT gene promoters are analyzed.

OBJECTIVE-The objective of this study is to quantitate expression of genes possibly contributing to insulin resistance and fat deposition in the human liver.RESEARCH DESIGN AND METHODS-A total of 24 subjects who had varying amounts of histologically determined fat in the liver ranging from normal (n ϭ 8) to steatosis due to a nonalcoholic fatty liver (NAFL) (n ϭ 16) were studied. The mRNA concentrations of 21 candidate genes associated with fatty acid metabolism, inflammation, and insulin sensitivity were quantitated in liver biopsies using real-time PCR. In addition, the subjects were characterized with respect to body composition and circulating markers of insulin sensitivity. . PPAR␥ coactivator 1 (PGC1) was significantly lower in subjects with NAFL than in those without. Genes significantly associated with obesity included nine genes: plasminogen activator inhibitor 1, PPAR␥, PPAR␦, MCP-1, CCL3 (macrophage inflammatory protein [MIP]-1␣), PPAR␥2, carnitine palmitoyltransferase (CPT1A), FABP4, and FABP5. The following parameters were associated with liver fat independent of obesity: serum adiponectin, insulin, C-peptide, and HDL cholesterol concentrations and the mRNA concentrations of MCP-1, MIP-1␣, ACSL4, FABP4, FABP5, and LPL. RESULTS-TheCONCLUSIONS-Genes involved in fatty acid partitioning and binding, lipolysis, and monocyte/macrophage recruitment and inflammation are overexpressed in the human fatty liver.

Aims/hypothesis It has recently been suggested that the rs738409 G allele in PNPLA3, which encodes adiponutrin, is strongly associated with increased liver fat content in three different ethnic groups. The aims of the present study were as follows: (1) to try to replicate these findings in European individuals with quantitative measures of hepatic fat content; (2) to study whether the polymorphism influences hepatic and adipose tissue insulin sensitivity; and (3) to investigate whether PNPLA3 expression is altered in the human fatty liver. Methods We genotyped 291 Finnish individuals in whom liver fat had been measured using proton magnetic resonance spectroscopy. Hepatic PNPLA3 expression was measured in 32 participants. Hepatic and adipose tissue insulin sensitivities were measured using a euglycaemic-hyperinsulinaemic (insulin infusion 0.3 mU kg −1 min Results The rs738409 G allele in PNPLA3 was associated with increased quantitative measures of liver fat content (p=0.011) and serum aspartate aminotransferase concentrations (p=0.002) independently of age, sex and BMI. Fasting serum insulin and hepatic and adipose tissue insulin sensitivity were related to liver fat content independently of genotype status. PNPLA3 mRNA expression in the liver was positively related to obesity (r=0.62, p<0.0001) and to liver fat content (r=0.58, p=0.025) in participants who were not morbidly obese (BMI <40 kg/m 2 ). Conclusions/interpretation A common variant in PNPLA3 increases the risk of hepatic steatosis in humans.