MicroRNA (miRNA) are small non-coding RNA molecules that posttranscriptionally effect mRNA stability and translation by targeting the 3′-untranslated region (3′-UTR) of various transcripts. Thus, dysregulation of miRNA affects a wide range of cellular processes such as cell proliferation and differentiation involved in organ remodeling processes. Divergent miRNA patterns were observed during chronic liver diseases of various etiologies. Chronic liver diseases result in uncontrolled scar formation ending up in liver fibrosis or even cirrhosis. Since it has been shown that miR-29 dysregulation is involved in synthesis of extracellular matrix proteins, miR-29 is of special interest. The importance of miR-29 in hepatic collagen homeostasis is underlined by in vivo data showing that experimental severe fibrosis is associated with a prominent miR-29 decrease. The loss of miR-29 is due to the response of hepatic stellate cells to exposure to the profibrogenic mediators TGF-β and PDGF-BB. Several putative binding sites for the Smad proteins and the Ap1 complex are located in the miR-29 promoter, which are suggested to mediate miR-29 decrease in fibrosis. Other miRNA are highly increased after profibrogenic stimulation, such as miR-21. miR-21 is transcriptionally upregulated in response to Smad-3 rather than Smad-2 activation after TGF-β stimulation. In addition, TGF-β promotes miR-21 expression by formation of a microprocessor complex containing Smad proteins. Elevated miR-21 may then act as a profibrogenic miRNA by its repression of the TGF-β inhibitory Smad-7 protein.

BackgroundIn chronic liver disease, hepatic stellate cells (HSC) transdifferentiate into myofibroblasts, promoting extracellular matrix (ECM) synthesis and deposition. Stimulation of HSC by transforming growth factor-β (TGF-β) is a crucial event in liver fibrogenesis due to its impact on myofibroblastic transition and ECM induction. In contrast, hepatocyte growth factor (HGF), exerts antifibrotic activities. Recently, miR-29 has been reported to be involved in ECM synthesis. We therefore studied the influence of HGF and TGF-β on the miR-29 collagen axis in HSC.MethodologyHSC, isolated from rats, were characterized for HGF and Met receptor expression by Real-Time PCR and Western blotting during culture induced myofibroblastic transition. Then, the levels of TGF-β, HGF, collagen-I and -IV mRNA, in addition to miR-29a and miR-29b were determined after HGF and TGF-β stimulation of HSC or after experimental fibrosis induced by bile-duct obstruction in rats. The interaction of miR-29 with 3′-untranslated mRNA regions (UTR) was analyzed by reporter assays. The repressive effect of miR-29 on collagen synthesis was studied in HSC treated with miR-29-mimicks by Real-Time PCR and immunoblotting.Principal FindingsThe 3′-UTR of the collagen-1 and −4 subtypes were identified to bind miR-29. Hence, miR-29a/b overexpression in HSC resulted in a marked reduction of collagen-I and -IV synthesis. Conversely, a decrease in miR-29 levels is observed during collagen accumulation upon experimental fibrosis, in vivo, and after TGF-β stimulation of HSC, in vitro. Finally, we show that during myofibroblastic transition and TGF-β exposure the HGF-receptor, Met, is upregulated in HSC. Thus, whereas TGF-β stimulation leads to a reduction in miR-29 expression and de-repression of collagen synthesis, stimulation with HGF was definitely associated with highly elevated miR-29 levels and markedly repressed collagen-I and -IV synthesis.ConclusionsUpregulation of miRNA-29 by HGF and downregulation by TGF-β take part in the anti- or profibrogenic response of HSC, respectively.

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Human immunodeficiency virus (HIV) and hepatitis virus coinfection amplify and accelerate hepatic injury. MicroRNAs (miRNAs) are small regulatory RNAs suggested as biomarkers for liver injury. We analyzed the circulating levels of miRNAs in HIV patients with regard to the extent and etiology of liver injury. Total RNA was extracted from 335 serum samples of HIV patients and 22 healthy control participants using Qiazol. Comprehensive polymerase chain reaction (PCR) array analyses (768 miRNA) were performed in serum samples of eight HIV, eight HIV/HCV (hepatitis C virus), six HCV patients, and three healthy controls. Reverse transcription (RT)‐PCR measured levels of miRNA‐122, miRNA‐22, and miRNA‐34a in serum samples of 335 patients and 19 healthy control participants. Liver injury and fibrosis in these patients were defined using aspartate aminotransferase (AST) levels, fibrosis‐4 (FIB‐4) index and AST‐to‐platelet ratio index (APRI) score. The miRNA pattern of HIV/HCV samples showed altered expression of 57 and 33 miRNA compared to HCV and HIV infection, respectively. miRNA‐122, miRNA‐22, and miRNA‐34a were highly up‐regulated in HIV/HCV patients. Analyzing the entire cohort, these miRNAs were correlated with liver function tests and were independent predictors of liver injury (AST >2 × ULN). miRNA‐122 and miRNA‐22 were associated with relevant fibrosis (FIB‐4 >1.45; APRI >1). Circulating levels of miRNA‐122 were independent predictors for relevant fibrosis in HIV patients. Interestingly, miRNA‐122 and miRNA‐34a levels were higher in HIV/HCV patients, miRNA‐22 levels were highest in HIV/HBV patients, and circulating levels of miRNA‐34a correlated positively with illicit drug use and ethanol consumption. Conclusion: Circulating miRNA‐122, miRNA‐22, and miRNA‐34a correlates with the etiology of liver injury in HIV patients. These biomarkers not only mirror different mechanisms of hepatic injury, but also are independent predictors of liver injury in HIV patients. (Hepatology 2015;61:46–55)

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer deaths, worldwide. MicroRNAs, inhibiting gene expression by targeting various transcripts, are involved in genomic dysregulation during hepatocellular tumorigenesis. In previous studies, microRNA-198 (miR-198) was shown to be significantly downregulated in HCV-positive hepatocellular carcinoma (HCC). Herein, the function of miR-198 in hepatocellular carcinoma cell growth and gene expression was studied. In hepatoma cell-types with low levels of liver-specific transcription factor HNF1α indicating a low differentiation grade, miR-198 expression was most downregulated. However, miR-198 treatment did not restore the expression of the liver-specific transcription factors HNF1α or HNF4α. Importantly, overexpression of miR-198 in Pop10 hepatoma cells markedly reduced cell growth. In agreement, comprehensive gene expression profiling by microarray hybridisation and real-time quantification revealed that central signal transducers of proliferation pathways were downregulated by miR-198. In contrast, genes mediating cellular adherence were highly upregulated by miR-198. Thus, the low expression of E-cadherin and claudin-1, involved in cell adhesion and cell-cell contacts, was abolished in hepatoma cells after miR-198 overexpression. This definite induction of both proteins by miR-198 was shown to be accompanied by a significantly impaired migration activity of hepatoma Pop10 cells. In conclusion, miR-198 acts as a tumor suppressor by repression of mitogenic and motogenic pathways diminishing cell growth and migration.