Nonalcoholic steatohepatitis is associated with altered hepatic MicroRNA expression

Abstract

The expression of microRNA in nonalcoholic steatohepatitis (NASH) and their role in the genesis of NASH are not known. The aims of this study were to: (1) identify differentially expressed microRNAs in human NASH, (2) tabulate their potential targets, and (3) define the effect of a specific differentially expressed microRNA, miR-122, on its targets and compare these effects with the pattern of expression of these targets in human NASH. The expression of 474 human microRNAs was compared in subjects with the metabolic syndrome and NASH versus controls with normal liver histology. Differentially expressed microRNAs were identified by the Paraflo microRNA microarray assay and validated using quantitative real-time polymerase chain reaction (PCR). The effects of a specific differentially expressed miRNA (miR-122) on its predicted targets were assessed by silencing and overexpressing miR-122 in vitro. A total of 23 microRNAs were underexpressed or overexpressed. The predicted targets of these microRNAs are known to affect cell proliferation, protein translation, apoptosis, inflammation, oxidative stress, and metabolism. The miR-122 level was significantly decreased in subjects with NASH (63% by real-time PCR, P < 0.00001). Silencing miR-122 led to an initial increase in mRNA levels of these targets (P < 0.05 for all) followed by a decrease by 48 hours. This was accompanied by an increase in protein levels of these targets (P < 0.05 for all). Overexpression of miR-122 led to a significant decrease in protein levels of these targets. Conclusions: NASH is associated with altered hepatic microRNA expression. Underexpression of miR-122 potentially contributes to altered lipid metabolism implicated in the pathogenesis of NASH. (HEPATOLOGY 2008;48: 1810-1820.)

MicroRNAs in Liver Disease: Bench to Bedside

“…40,44,45 Serum/plasma levels of miR-122 correlate with hepatic necro-inflammation, liver damage, cell death and increased aminotransferase levels in acute and chronic liver diseases. 44,[46][47][48][49] Interestingly, hepatic and circulating miR-122 levels do not correlate in NAFLD 14,39,[50][51][52][53][54][55] or viral hepatitis 41,47,49,56 although both have been statistically associated with various measures of disease severity in these studies. Together these studies show that miR-122 may play a role in most liver diseases.…”

“…14 Together these studies suggest that differentially expressed miRs in humans and animal models of NASH regulate genes with diverse functions involved in the pathogenesis of NAFLD, including metabolism of lipid and glucose, regulation of the unfolded protein response, endoplasmic reticulum stress, oxidative stress, cellular differentiation, inflammation and apoptosis. 14,36 Notably, miR-34a has been shown to be up-regulated in both human serum 50,51 and liver in humans and animal models of NAFLD.…”

“…14 Together these studies suggest that differentially expressed miRs in humans and animal models of NASH regulate genes with diverse functions involved in the pathogenesis of NAFLD, including metabolism of lipid and glucose, regulation of the unfolded protein response, endoplasmic reticulum stress, oxidative stress, cellular differentiation, inflammation and apoptosis. 14,36 Notably, miR-34a has been shown to be up-regulated in both human serum 50,51 and liver in humans and animal models of NAFLD. 14,55,121,122 Two recent studies suggest two differing mechanisms for the involvement of miR-34a in NASH pathogenesis through down-regulation of SIRT-1; a) leading to AMP kinase dephosphorylation and subsequent decreased phosphorylation of HMGCoA, ultimately leading to cholesterol accumulation 121 ; b) increased acetylation of p53 causing activation of apoptosis.…”

“…[37][38][39] It is highly expressed in hepatocytes due to its liver specific transcriptional regulation by hepatic nuclear transcription factors 34,40 and is elevated in most hepatic diseases including hepatitis C virus (HCV) and hepatitis B virus (HBV) infections as well as alcohol and drug-induced liver injury, HCC and NAFLD. 13,14,[37][38][39][40][41][42][43][44][45] There are four miR-122 binding sites in the HCV genome 42 and miR-122 may promote viral replication by direct interaction with seed-sequencebinding to two target sites, S1 and S2, in the 5 0 -UTR of the HCV genome resulting in HCV-RNA genome stabilization and enhanced viral RNA abundance. 42,43 Dedifferentiation of hepatocytes during hepatocellular carcinogenesis is associated with the loss of miR-122.…”

“…8,9 MiRs are abundant in the liver and modulate a diverse spectrum of cellular processes associated with liver injury such as inflammation, apoptosis, and hepatocyte regeneration and deregulation of miR expression may be a key pathogenic factor in many liver diseases including viral hepatitis, hepatocellular carcinoma (HCC), metabolic and acute liver diseases; miR expression profiles are altered in many hepatic diseases compared to healthy subjects. [10][11][12][13][14] Many miRs are abundantly expressed in the liver; however miR-122 is liver specific, and is estimated to make up 70% of the total hepatic miR complement and is expressed at high levels (around 66,000 copies per cell). [10][11][12] Studies suggest that miRs are not only localized within the cell but are also present in circulation.…”