Our objective was to estimate the strength of the effect of the I148M (rs738409 C/G) patatin-like phospholipase domain containing 3 (PNPLA3) variant on nonalcoholic fatty liver (NAFLD) and disease severity across different populations. We performed a systematic review by a meta-analysis; literature searches identified 16 studies. Our results showed that rs738409 exerted a strong influence not only on liver fat accumulation (GG homozygous showed 73% higher lipid fat content when compared with CC ones, data from 2,937 subjects; P < 1 3 10 29 ), but also on the susceptibility of a more aggressive disease (GG homozygous had 3.24-fold greater risk of higher necroinflammatory scores and 3.2-fold greater risk of developing fibrosis when compared with CC homozygous; P < 1 3 10 29 ; data from 1,739 and 2,251 individuals, respectively). Nonalcoholic steatohepatitis (NASH) was more frequently observed in GG than CC homozygous (odds ratio [OR] 3.488, 95% confidence interval [CI] 1.859-6.545, random model; P < 2 3 10 24 ; data from 2,124 patients). Evaluation of the risk associated with heterozygosity for the variant suggests that the additive genetic model best explains the effect of rs738409 on the susceptibility to develop NAFLD. Nevertheless, carrying two G alleles does not seem to increase the risk of severe histological features. Meta-regression showed a negative correlation between male sex and the effect of rs738409 on liver fat content (slope: 22.45 6 1.04; P < 0.02). The rs738409 GG genotype versus the CC genotype was associated with a 28% increase in serum alanine aminotransferase levels. Conclusion: By summarizing the amount of evidence, this study provided unequivocal evidence of rs738409 as a strong modifier of the natural history of NAFLD in different populations around the world.

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Objectives We used a screening strategy of global serum microRNA (miRNA) profiling, followed by a second stage of independent replication and exploration of liver expression of selected miRNAs to study: (1) the circulating miRNA signature associated with non-alcoholic fatty liver disease (NAFLD) progression and predictive power, (2) the role of miRNAs in disease biology and (3) the association between circulating miRNAs and features of the metabolic syndrome. Methods The study used a case-control design and included patients with NAFLD proven through biopsy and healthy controls. Results Among 84 circulating miRNAs analysed, miR-122, miR-192, miR-19a and miR-19b, miR-125b, and miR-375 were upregulated >2-fold (p<0.05) either in simple steatosis (SS) or non-alcoholic steatohepatitis (NASH). The most dramatic and significant fold changes were observed in the serum levels of miR-122 (7.2-fold change in NASH vs controls and 3.1-fold change in NASH vs SS) and miR-192 (4.4-fold change in NASH vs controls); these results were replicated in the validation set. The majority of serum miR-122 circulate in argonaute2-free forms. Circulating miR-19a/b and miR-125b were correlated with biomarkers of atherosclerosis. Liver miR-122 expression was 10-fold (p<0.03) downregulated in NASH compared with SS and was preferentially expressed at the edge of lipid-laden hepatocytes. In vitro exploration showed that overexpression of miR-122 enhances alanine aminotransferase activity. Conclusions miR-122 plays a role of physiological significance in the biology of NAFLD; circulating miRNAs mirror the histological and molecular events occurring in the liver. NAFLD has a distinguishing circulating miRNA profile associated with a global dysmetabolic disease state and cardiovascular risk.

Nonalcoholic fatty liver disease (NAFLD) affects 25% of the global adult population and is the most common chronic liver disease worldwide. Nonalcoholic steatohepatitis (NASH) is the active form of NAFLD, with hepatic necroinflammation and faster fibrosis progression. With an increasing number of patients developing NASH-related end-stage liver disease and pharmacological treatments on the horizon, there is a pressing need to develop NAFLD and NASH biomarkers for prognostication, selection of patients for treatment and monitoring. This requirement is particularly true as liver biopsy utility is limited by its invasive nature, poor patient acceptability and sampling variability. This article reviews current and potential biomarkers for different features of NAFLD, namely, steatosis, necroinflammation and fibrosis. For each biomarker, we evaluate its accuracy, reproducibility, responsiveness, feasibility and limitations. We cover biochemical, imaging and genetic biomarkers and discuss biomarker discovery in the omics era.

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Hepatic methylation and transcriptional activity of the MT-ND6 are associated with the histological severity of NAFLD. Epigenetic changes of mtDNA are potentially reversible by interventional programs, as physical activity could modulate the methylation status of MT-ND6.

Insulin resistance (IR) and mitochondrial dysfunction play a central role in the pathophysiology of nonalcoholic fatty liver disease (NAFLD). We hypothesized that genetic factors and epigenetic modifications occurring in the liver contribute to the IR phenotype. We specifically examined whether fatty liver and IR are modified by hepatic DNA methylation of the peroxisome proliferator-activated receptor c coactivator 1a (PPARGC1A) and mitochondrial transcription factor A (TFAM) promoters, and also evaluated whether liver mitochondrial DNA (mtDNA) content is associated with NAFLD and IR. We studied liver biopsies obtained from NAFLD patients in a case-control design. After bisulfite treatment of DNA, we used methylation-specific polymerase chain reaction (PCR) to assess the putative methylation of three CpG in the PPARGC1A and TFAM promoters. Liver mtDNA quantification using nuclear DNA (nDNA) as a reference was evaluated by way of realtime PCR. Liver PPARGC1A methylated DNA/unmethylated DNA ratio correlated with plasma fasting insulin levels and homeostasis model assessment of insulin resistance (HOMA-IR); TFAM methylated DNA/unmethylated DNA ratio was inversely correlated with insulin levels. PPARGC1A promoter methylation was inversely correlated with the abundance of liver PPARGC1A messenger RNA. The liver mtDNA/nDNA ratio was significantly higher in control livers compared with NAFLD livers. mtDNA/nDNA ratio was inversely correlated with HOMA-IR, fasting glucose, and insulin and was inversely correlated with PPARGC1A promoter methylation. Conclusion: Our data suggest that the IR phenotype and the liver transcriptional activity of PPARGC1A show a tight interaction, probably through epigenetic modifications. Decreased liver mtDNA content concomitantly contributes to peripheral IR.

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