Several animal studies have emphasized the role of gut microbiota in nonalcoholic fatty liver disease (NAFLD). However, data about gut dysbiosis in human NAFLD remain scarce in the literature, especially studies including the whole spectrum of NAFLD lesions. We aimed to evaluate the association between gut dysbiosis and severe NAFLD lesions, that is, nonalcoholic steatohepatitis (NASH) and fibrosis, in a well‐characterized population of adult NAFLD. Fifty‐seven patients with biopsy‐proven NAFLD were enrolled. Taxonomic composition of gut microbiota was determined using 16S ribosomal RNA gene sequencing of stool samples. Thirty patients had F0/F1 fibrosis stage at liver biopsy (10 with NASH), and 27 patients had significant F≥2 fibrosis (25 with NASH). Bacteroides abundance was significantly increased in NASH and F≥2 patients, whereas Prevotella abundance was decreased. Ruminococcus abundance was significantly higher in F≥2 patients. By multivariate analysis, Bacteroides abundance was independently associated with NASH and Ruminococcus with F≥2 fibrosis. Stratification according to the abundance of these two bacteria generated three patient subgroups with increasing severity of NAFLD lesions. Based on imputed metagenomic profiles, Kyoto Encyclopedia of Genes and Genomes pathways significantly related to NASH and fibrosis F≥2 were mostly related to carbohydrate, lipid, and amino acid metabolism. Conclusion: NAFLD severity associates with gut dysbiosis and a shift in metabolic function of the gut microbiota. We identified Bacteroides as independently associated with NASH and Ruminococcus with significant fibrosis. Thus, gut microbiota analysis adds information to classical predictors of NAFLD severity and suggests novel metabolic targets for pre‐/probiotics therapies. (Hepatology 2016;63:764–775)

Nonalcoholic steatohepatitis is a major cause of cirrhosis and liver cancer. It is associated with visceral adiposity and the metabolic syndrome and is nearly as common as type 2 diabetes. Metabolic stress, inflammation, and fibrosis are the primary pathogenic mechanisms.

Background & Aims Cirrhosis and liver cancer are potential outcomes of advanced nonalcoholic fatty liver disease (NAFLD). It is not clear what factors determine whether patients will develop advanced or mild NAFLD, limiting noninvasive diagnosis and treatment before clinical sequelae emerge. We investigated whether DNA methylation profiles can distinguish patients with mild disease from those with advanced NAFLD, and how these patterns are functionally related to hepatic gene expression. Methods We collected frozen liver biopsies and clinical data from patients with biopsy-proven NAFLD (56 in the discovery cohort and 34 in the replication cohort). Samples were divided into groups based on histologic severity of fibrosis: F0−1 (mild) and F3−4 (advanced). DNA methylation profiles were determined and coupled with gene expression data from the same biopsies; differential methylation was validated in subsets of the discovery and replication cohorts. We then analyzed interactions between the methylome and transcriptome. Results Clinical features did not differ between patients known to have mild or advanced fibrosis based on biopsy analysis. There were 69,247 differentially methylated CpG sites (76% hypomethylated, 24% hypermethylated) in patients with advanced vs mild NAFLD (P < .05). Methylation at fibroblast growth factor receptor 2, methionine adenosyl methyltransferase 1A, and caspase 1 was validated by bisulfite pyrosequencing and the findings were reproduced in the replication cohort. Methylation correlated with gene transcript levels for 7% of differentially methylated CpG sites, indicating that differential methylation contributes to differences in expression. In samples with advanced NAFLD, many tissue repair genes were hypomethylated and overexpressed, and genes in certain metabolic pathways, including 1-carbon metabolism, were hypermethylated and underexpressed. Conclusions Functionally relevant differences in methylation can distinguish patients with advanced vs mild NAFLD. Altered methylation of genes that regulate processes such as steatohepatitis, fibrosis, and carcinogenesis indicate the role of DNA methylation in progression of NAFLD.

Clinicians rely upon the severity of liver fibrosis to segregate patients with well-compensated nonalcoholic fatty liver disease (NAFLD) into subpopulations at high- versus low-risk for eventual liver-related morbidity and mortality. We compared hepatic gene expression profiles in high- and low-risk NAFLD patients to identify processes that distinguish the two groups and hence might be novel biomarkers or treatment targets. Microarray analysis was used to characterize gene expression in percutaneous liver biopsies from low-risk, “mild” NAFLD patients (fibrosis stage 0–1; n = 40) and high-risk, “severe” NAFLD patients (fibrosis stage 3–4; n = 32). Findings were validated in a second, independent cohort and confirmed by real-time polymerase chain reaction and immunohistochemistry (IHC). As a group, patients at risk for bad NAFLD outcomes had significantly worse liver injury and more advanced fibrosis (severe NAFLD) than clinically indistinguishable NAFLD patients with a good prognosis (mild NAFLD). A 64-gene profile reproducibly differentiated severe NAFLD from mild NAFLD, and a 20-gene subset within this profile correlated with NAFLD severity, independent of other factors known to influence NAFLD progression. Multiple genes involved with tissue repair/regeneration and certain metabolism-related genes were induced in severe NAFLD. Ingenuity Pathway Analysis and IHC confirmed deregulation of metabolic and regenerative pathways in severe NAFLD and revealed overlap among the gene expression patterns of severe NAFLD, cardiovascular disease, and cancer. Conclusion : By demonstrating specific metabolic and repair pathways that are differentially activated in livers with severe NAFLD, gene profiling identified novel targets that can be exploited to improve diagnosis and treatment of patients who are at greatest risk for NAFLD-related morbidity and mortality. (Hepatology 2014;59:471–482)

The outcome of liver injury is dictated by the effectiveness of repair. Successful repair (i.e., regeneration) results in replacement of dead epithelial cells with healthy epithelial cells, and reconstructs normal hepatic structure and function. Liver regeneration is known to involve replication of surviving mature hepatocytes and bile duct cells. This review discusses recent evidence for other mechanisms that might also replace dead hepatic epithelial cells and repair liver damage, particularly during chronic injury. According to this theory, certain epithelial cells in developing livers and/or injured adult livers undergo epithelial‐to‐mesenchymal transition (EMT) and move into the hepatic mesenchyme where they exhibit fibroblastic features. Some of these epithelia‐derived mesenchymal cells, however, may be capable of undergoing subsequent mesenchymal‐to‐epithelial transition (MET), reverting to epithelial cells that ultimately become hepatocytes or cholangiocytes. Although these concepts remain to be proven, the theory predicts that the balance between EMT and MET modulates the outcome of chronic liver injury. When EMT activity outstrips MET, repair is mainly fibrogenic, causing liver fibrosis. Conversely, predominance of MET favors more normal liver regeneration. In this review, we summarize evidence that certain resident liver cells are capable of EMTs in vitro and during chronic liver injury. (HEPATOLOGY 2009.)