Expression of genes for microRNA-processing enzymes is altered in advanced non-alcoholic fatty liver disease

Exploration of the Key Genes Involved in Non-alcoholic Fatty Liver Disease and Possible MicroRNA Therapeutic Targets

Background

MicroRNAs (miRNAs) are promising therapeutic agents for non-alcoholic fatty liver disease (NAFLD). This study aimed to identify key genes/proteins involved in NAFLD pathogenesis and progression and to evaluate miRNAs influencing their expression.

Methods

Gene expression profiles from datasets GSE151158, GSE163211, GSE135251, GSE167523, GSE46300, and online databases were analyzed to identify significant NAFLD-related genes. Then, protein-protein interaction networks and module analysis identified hub genes/proteins, which were validated using real-time PCR in oleic acid-treated HepG2 cells. Functional enrichment analysis evaluated signaling pathways and biological processes. Gene-miRNA interaction networks identified miRNAs targeting critical NAFLD genes.

Results

The most critical overexpressed hub genes/proteins included: TNF, VEGFA, TLR4, CYP2E1, ACE, SCD, FASN, SREBF2, and TGFB1 based on PPI network analysis, of which TNF, TLR4, SCD, FASN, SREBF2, and TGFB1 were up-regulated in oleic acid-treated HepG2 cells. Functional enrichment analysis for biological processes highlighted programmed necrotic cell death, lipid metabolic process response to reactive oxygen species, and inflammation. In the Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, the highest adjusted P-value signaling pathways encompassed AGE-RAGE in diabetic complications, TNF, and HIF-1 signaling pathways. In gene-miRNA network analysis, miR-16 and miR-124 were highlighted as the miRNAs exerting the most influence on important NAFLD-related genes.

Conclusion

In silico analyses identified NAFLD therapeutic targets and miRNA candidates to guide further experimental investigation.

Significance of MiRNA-34a and MiRNA-192 as a risk factor for nonalcoholic fatty liver disease

BACKGROUND AND AIMS

NAFLD is one of the fast-growing health problems that affects up to 25% of people worldwide. Numerous miRNAs have been clarified as important regulators of liver pathophysiology, including NAFLD. Thus, we investigated the expression of the MiRNA-34a and MiRNA-192 as diagnostic markers for NAFLD.

PATIENTS AND METHODS

Blood samples were collected from NAFLD cases and healthy controls. The expression profile of both studied miRNAs was detected via real-time PCR analysis.

RESULTS

The present study showed that both studied miRNAs were upregulated in NAFLD patients compared to controls. Interestingly, miRNA-34a and MiRNA-192 are upregulated in NAFLD patients with early fibrosis compared to controls [with a fold change of 4.02 ± 11.49 (P = 0.05) and 18.43 ± 47.8 (P = 0.017), respectively]. However, miRNA-34a is downregulated in NAFLD patients with advanced fibrosis compared to controls, with fold expression of 0.65 ± 1.17 (P = 0.831). The area under the receiver operating characteristics (AUROC) for miRNA-34a and miRNA-192 were 0.790 and 0.643, respectively; furthermore, the sensitivities and specificities were 76.7%, 100% for miRNA-34a and 63.3%, and 93.3% for miRNA-192 (P < 0.05). Additionally, MiRNA34a was positively correlated with hypertension and fasting blood sugar, and it also was negatively correlated with hemoglobin level and total leucocyte count (P < 0.05).

CONCLUSION

The results obtained indicated that both studied miRNAs could potentially be used as diagnostic biomarkers for the early stage of liver fibrosis in NAFLD cases. Also, miRNA-34a was positively correlated with metabolic disorders associated with NAFLD such as hypertension and diabetes. However, their expression showed no association with advanced fibrosis. Thus, larger cohorts are necessitated to certify the utility of serum MiRNA-34a and MiRNA-192 in monitoring the deterioration of NAFLD.

Deciphering the role of epigenetic modifications in fatty liver disease: A systematic review

BACKGROUND

Fatty liver disease (FLD), primarily nonalcoholic fatty liver disease (NAFLD), is the most common liver disorder that affects a quarter of the global population. NAFLD is a spectrum of disease ranging from simple steatosis to nonalcoholic steatohepatitis, which is associated with increased risk of developing liver cancer. Given that the pathogenic mechanisms of fatty liver remain largely elusive, it is important to further investigate potential underlying mechanisms including epigenetic modifications. Here, we performed a systematic review of human epigenetic studies on FLD presence.

METHODS

Five bibliographic databases were screened until 28 August 2020. We included cross-sectional, case-control and cohort studies in humans that examined the association of epigenetic modifications including global, candidate or epigenome-wide methylation of DNA, noncoding RNAs and histone modifications with FLD.

RESULTS

In total 36 articles, based on 33 unique studies, consisting of 12 112 participants met the inclusion criteria. Among these, two recent epigenome-wide association studies conducted among large population-based cohorts have reported the association between cg06690548 (SLC7A11) and FLD. Moreover, several studies have demonstrated the association between microRNAs (miRNAs) and FLD, in which miR-122, miR-34a and miR-192 were recognized as the most relevant miRNAs as biomarkers for FLD. We did not find any studies examining histone modifications in relation to FLD.

CONCLUSIONS

Cumulative evidence suggests a link between epigenetic mechanisms, specifically DNA methylation and miRNAs, and FLD. Further efforts should investigate the molecular pathways by which these epigenetic markers may regulate FLD and also the potential role of histone modifications in FLD.

The Connection between MicroRNAs from Visceral Adipose Tissue and Non-Alcoholic Fatty Liver Disease

Non-Alcoholic Fatty Liver Disease (NAFLD) is one of the most important causes of liver disease worldwide leading the foreground cause of liver transplantation. Recently miRNAs, small non-coding molecules were identified as an important player in the negative translational regulation of many protein-coding genes involved in hepatic metabolism. Visceral adipose tissue was found to take part in lipid and glucose metabolism and to release many inflammatory mediators that may contribute to progression of NAFLD from simple steatosis to Non-Alcoholic SteatoHepatitis. Since visceral adipose tissue enlargement and dysregulated levels of miRNAs were observed in patients with NAFLD, the aim of this paper is to reflect the current knowledge of the role of miRNAs released from visceral adipose tissue and NAFLD.

miRNA Signature in NAFLD: A Turning Point for a Non-Invasive Diagnosis

Nonalcoholic fatty liver disease (NAFLD) defines a wide pathological spectrum ranging from simple steatosis to nonalcoholic steatohepatitis (NASH) which may predispose to liver cirrhosis and hepatocellular carcinoma. It represents the leading cause of hepatic damage worldwide. Diagnosis of NASH still requires liver biopsy but due to the high prevalence of NAFLD, this procedure, which is invasive, is not practicable for mass screening. Thus, it is crucial to non-invasively identify NAFLD patients at higher risk of progression to NASH and fibrosis. It has been demonstrated that hepatic fat content and progressive liver damage have a strong heritable component. Therefore, genetic variants associated with NAFLD have been proposed as non-invasive markers to be used in clinical practice. However, genetic variability is not completely explained by these common variants and it is possible that many of the phenotypic differences result from gene-environment interactions. Indeed, NAFLD development and progression is also modulated by epigenetic factors, in particular microRNAs (miRNAs), which control at post-transcriptional level many complementary target mRNAs and whose dysregulation has been shown to have high prognostic and predictive value in NAFLD. The premise of the current review is to discuss the role of miRNAs as pathogenic factors, risk predictors and therapeutic targets in NAFLD.

miR-26a Potentially Contributes to the Regulation of Fatty Acid and Sterol Metabolism In Vitro Human HepG2 Cell Model of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a metabolic-related disorder ranging from steatosis to steatohepatitis, which may progress to cirrhosis and hepatocellular carcinoma (HCC). This study aimed at assessing the regulatory and protective role of miR-26a on lipid metabolism and progression of NAFLD in human HepG2 cells loaded with free fatty acids (FFA). Lentivirus expressing miR-26a or negative control miR was used to transduce HepG2 cells and to establish stable cell lines. Gain or loss of function using an miR-26a inhibitor was used to compare triglyceride content (TG), total cholesterol level (CL), total antioxidant capacity (TAC), malondialdehyde (MDA) and the level of apoptosis. In addition, quantitative reverse transcription polymerase chain reaction (qPCR) was used to assess the mRNA levels of lipogenesis, TG synthesis, storage genes, inflammatory and fibrogenic markers, and autophagic besides endoplasmic reticulum (ER) stress markers after gaining or losing the function of miR-26a. miR-26a levels decreased in response to FFA in human HepG2 cells. After the establishment of a stable cell line, the upregulation of miR-26a resulted in the downregulation of TG, CL, and MDA levels, through regulating mRNA levels of genes involved in lipid homeostasis, ER stress marker, inflammatory and fibrogenic markers. Nevertheless, there was a marked increment in the mRNA expression of autophagic marker genes. Moreover, miR-26a overexpression protects the cells from apoptosis, whereas inhibition of miR-26a, using an anti-miR-26a oligonucleotide, decreased the expression of miR-26a which potentially contributes to altered lipid metabolism in HepG2 cells loaded with FFA. In conclusion, these findings suggested that miR-26a has a crucial role in regulating fatty acid and cholesterol homeostasis in HepG2 cells, along with the offered protection against the progression of NAFLD in vitro. Hence, miRNAs could receive growing attention as useful noninvasive diagnostic markers to follow the progression of NAFLD and to identify novel therapeutic targets.

Rifaximin for the prevention of spontaneous bacterial peritonitis and hepatorenal syndrome in cirrhosis: a systematic review and meta-analysis

Prophylactic antibiotics have been recommended in patients with a previous history of spontaneous bacterial peritonitis (SBP). Recently, there has been interest in the use of rifaximin for the prevention of SBP and hepatorenal syndrome (HRS). We conducted a meta-analysis to evaluate this association of rifaximin. We searched several databases from inception through 24 January 2017, to identify comparative studies evaluating the effect of rifaximin on the occurrence of SBP and HRS. We performed predetermined subgroup analyses based on the type of control group, design of the study, and type of prophylaxis. Pooled odds ratios (ORs) were calculated using a random effects model. We included 13 studies with 1703 patients in the meta-analysis of SBP prevention. Pooled OR [95% confidence interval (CI)] was 0.40 (95% CI: 0.22-0.73) (I=58%). On sensitivity analysis, adjusted OR was 0.29 (95% CI: 0.20-0.44) (I=0%). The results of the subgroup analysis based on type of control was as follows: in the quinolone group, pooled OR was 0.42 (95% CI: 0.14-1.25) (I=55%), and in the no antibiotic group, pooled OR was 0.40 (95% CI: 0.18-0.86) (I=64%). However, with sensitivity analysis, benefit of rifaximin was demonstrable; pooled ORs were 0.32 (95% CI: 0.17-0.63) (I=0%) and 0.28 (95% CI: 0.17-0.45) (I=0%) for the comparison with quinolones and no antibiotics, respectively. Pooled OR based on randomized controlled trials was 0.41 (95% CI: 0.22-0.75) (I=13%). For the prevention of HRS, the pooled OR was 0.25 (95% CI: 0.13-0.50) (I=0%). Rifaximin has a protective effect against the development of SBP in cirrhosis. However, the quality of the evidence as per the GRADE framework was very low. Rifaximin appeared effective for the prevention of HRS.

Extracellular RNAs Are Associated With Insulin Resistance and Metabolic Phenotypes

OBJECTIVE

Insulin resistance (IR) is a hallmark of obesity and metabolic disease. Circulating extracellular RNAs (ex-RNAs), stable RNA molecules in plasma, may play a role in IR, though most studies on ex-RNAs in IR are small. We sought to characterize the relationship between ex-RNAs and metabolic phenotypes in a large community-based human cohort.

RESEARCH DESIGN AND METHODS

We measured circulating plasma ex-RNAs in 2,317 participants without diabetes in the Framingham Heart Study (FHS) Offspring Cohort at cycle 8 and defined associations between ex-RNAs and IR (measured by circulating insulin level). We measured association between candidate ex-RNAs and markers of adiposity. Sensitivity analyses included individuals with diabetes. In a separate cohort of 90 overweight/obese youth, we measured selected ex-RNAs and metabolites. Biology of candidate microRNAs was investigated in silico.

RESULTS

The mean age of FHS participants was 65.8 years (56% female), with average BMI 27.7 kg/m²; participants in the youth cohort had a mean age of 15.5 years (60% female), with mean BMI 33.8 kg/m². In age-, sex-, and BMI-adjusted models across 391 ex-RNAs in FHS, 18 ex-RNAs were associated with IR (of which 16 were microRNAs). miR-122 was associated with IR and regional adiposity in adults and IR in children (independent of metabolites). Pathway analysis revealed metabolic regulatory roles for miR-122, including regulation of IR pathways (AMPK, target of rapamycin signaling, and mitogen-activated protein kinase).

CONCLUSIONS

These results provide translational evidence in support of an important role of ex-RNAs as novel circulating factors implicated in IR.

Disease-specific miR-34a as diagnostic marker of non-alcoholic steatohepatitis in a Chinese population

AIM

To assess disease-specific circulating microRNAs (miRNAs) in non-alcoholic steatohepatitis (NASH) patients.

METHODS

A total of 111 biopsy-proven non-alcoholic fatty liver disease (NAFLD) or chronic hepatitis B (CHB) patients and healthy controls from mainland China were enrolled to measure their serum levels of miR-122, -125b, -146b, -16, -21, -192, -27b and -34a. The correlations between serum miRNAs and histological features of NAFLD were determined. The diagnostic value of miRNA in NASH and significant fibrosis was analyzed and compared with that of cytokeratin-18 (CK-18), fibrosis-4 (FIB-4), and aspartate aminotransferase to platelet ratio index (APRI), respectively.

RESULTS

Circulating miR-122, -16, -192 and -34a showed differential expression levels between NAFLD and CHB patients, and miR-34a had an approximately 2-fold increase in NAFLD samples compared with that of CHB samples (P < 0.01). Serum miR-122, -192 and -34a levels were correlated with steatosis (R = 0.302, 0.323 and 0.470, respectively, P < 0.05) and inflammatory activity (R = 0.445, 0.447 and 0.517, respectively, P < 0.01); only serum miR-16 levels were associated with fibrosis (R = 0.350, P < 0.05) in patients with NAFLD. The diagnostic value of miR-34a for NASH (area under the receiver operating characteristic, 0.811, 95%CI: 0.670-0.953) was superior to that of alanine aminotransferase, CK-18, FIB-4 and APRI in NAFLD, but miR-16 showed a limited performance in the diagnosis of significant fibrosis in NASH.

CONCLUSION

Circulating miR-34a may serve as a disease-specific noninvasive biomarker for the diagnosis of NASH.

Epigenetics in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD), a common hepatic disorder ranging from simple steatosis through steatohepatitis to fibrosis and cirrhosis, is an emerging health concern. NAFLD is a pathologic condition characterized by the buildup of extra fat in liver cells that is not caused by alcohol consumption. Excess hepatic fat accumulation results from increased delivery of triglycerides (TG) to the liver or conversion of surplus carbohydrates to TG. Importantly, a subgroup of NAFLD results in hepatocellular injury and inflammation, which is referred to as non-alcoholic steatohepatitis (NASH), and may progress to irreversible cirrhosis and hepatocellular carcinoma (HCC). NAFLD shares, in part, the common pathogenesis of metabolic syndrome including obesity, hyperlipidemia, insulin resistance, mitochondrial damage, oxidative stress response, and the release of inflammatory cytokines. Epigenetics, an inheritable phenomenon that affects gene expression without altering the DNA sequence, provides a new perspective on the pathogenesis of NAFLD. Reversible epigenetic changes take place at the transcriptional level and provide a phenotypic connection between the host and environment. An accumulating body of evidence suggests the importance of epigenetic roles in NAFLD, which in turn can be identified as potential therapeutic targets and non-invasive biomarkers of NAFLD. It is anticipated that the epigenetic modifiers in NAFLD may provide novel molecular indicators that can determine not only the initial risk but also the disease progression and prognosis. In the present review, we update the roles of epigenetics as pathologic mechanisms, therapeutic targets and biomarkers in NAFLD.

MicroRNAs as biomarkers and regulators of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a complicated disease affected by the interaction of environmental and genetic factors; however, the precise pathogenesis of the disease has not been fully determined. There is a need to better understand the pathogenesis of NAFLD and to identify non-invasive diagnostic modalities. Recent advances in systematic biology and epigenetics have improved our understanding of the genotype-phenotype relationships in NAFLD. MicroRNAs (miRNAs) are important regulators of a wide range of biological processes. MiRNAs are extremely stable and protect from RNAase-mediated degradation in body fluids, making them attractive candidate biomarkers for the early detection of the disease and the monitoring of disease progression. In this review, we summarized the current knowledge on miRNAs as potential biomarkers of NAFLD at different stages and for the prognosis of advanced diseases. Furthermore, we discussed the implications of miRNAs that functioning in lipid metabolism and hepatic steatosis as well as in hepatic inflammation and fibrosis with regard to the pathogenesis of NAFLD.

A micro-RNA expression signature for human NAFLD progression

BACKGROUND

The spectrum of nonalcoholic fatty liver disease (NAFLD) describes disease conditions deteriorating from nonalcoholic fatty liver (NAFL) to nonalcoholic steatohepatitis (NASH) to cirrhosis (CIR) to hepatocellular carcinoma (HCC). From a molecular and biochemical perspective, our understanding of the etiology of this disease is limited by the broad spectrum of disease presentations, the lack of a thorough understanding of the factors contributing to disease susceptibility, and ethical concerns related to repeat sampling of the liver. To better understand the factors associated with disease progression, we investigated by next-generation RNA sequencing the altered expression of microRNAs (miRNAs) in liver biopsies of class III obese subjects (body mass index ≥40 kg/m(2)) biopsied at the time of elective bariatric surgery.

METHODS

Clinical characteristics and unbiased RNA expression profiles for 233 miRs, 313 transfer RNAs (tRNAs), and 392 miscellaneous small RNAs (snoRNAs, snRNAs, rRNAs) were compared among 36 liver biopsy specimens stratified by disease severity.

RESULTS

The abundances of 3 miRNAs that were found to be differentially regulated (miR-301a-3p and miR-34a-5p increased and miR-375 decreased) with disease progression were validated by RT-PCR. No tRNAs or miscellaneous RNAs were found to be associated with disease severity. Similar patterns of increased miR-301a and decreased miR-375 expression were observed in 134 hepatocellular carcinoma (HCC) samples deposited in The Cancer Genome Atlas (TCGA).

CONCLUSIONS

Our analytical results suggest that NAFLD severity is associated with a specific pattern of altered hepatic microRNA expression that may drive the hallmark of this disorder: altered lipid and carbohydrate metabolism. The three identified miRNAs can potentially be used as biomarkers to access the severity of NAFLD. The persistence of this miRNA expression pattern in an external validation cohort of HCC samples suggests that specific microRNA expression patterns may permit and/or sustain NAFLD development to HCC.

Role of MicroRNAs in NAFLD/NASH

MicroRNAs (miRNAs) are highly conserved, small, 18-25 nucleotide, non-coding RNAs that regulate gene expression at the post-transcriptional level. Each miRNA can regulate hundreds of target genes, and vice versa each target gene can be regulated by numerous miRNAs, suggesting a very complex network and explaining how miRNAs play pivotal roles in fine-tuning essentially all biological processes in all cell types in the liver. Here, we summarize the current knowledge on the role of miRNAs in the pathogenesis and diagnosis of nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) with an outlook to the broader aspects of metabolic syndrome. Furthermore, we discuss the role of miRNAs as potential biomarkers and therapeutic targets in NAFLD/NASH.

Mechanistically linked serum miRNAs distinguish between drug induced and fatty liver disease of different grades

Hepatic steatosis is characterised by excessive triglyceride accumulation in the form of lipid droplets (LD); however, mechanisms differ in drug induced (DIS) and/or non-alcoholic fatty liver disease (NAFLD). Here we hypothesized distinct molecular circuits of microRNA/LD-associated target genes and searched for mechanistically linked serum and tissue biomarkers that would distinguish between DIS and human NAFLD of different grades. We analysed >800 rat hepatic whole genome data for 17 steatotic drugs and identified 157 distinct miRNAs targeting 77 DIS regulated genes. Subsequently, genomic data of N = 105 cases of human NAFLD and N = 32 healthy controls were compared to serum miRNA profiles of N = 167 NAFLD patients. This revealed N = 195 tissue-specific miRNAs being mechanistically linked to LD-coding genes and 24 and 9 miRNAs were commonly regulated in serum and tissue of advanced and mild NAFLD, respectively. The NASH serum regulated miRNAs informed on hepatic inflammation, adipocytokine and insulin signalling, ER-and caveolae associated activities and altered glycerolipid metabolism. Conversely, serum miRNAs associated with blunt steatosis specifically highlighted activity of FOXO1&HNF4α on CPT2, the lipid droplet and ER-lipid-raft associated PLIN3 and Erlin1. Altogether, serum miRNAs informed on the molecular pathophysiology of NAFLD and permitted differentiation between DIS and NAFLD of different grades.

Dicer and microRNA expression in multiple sclerosis and response to interferon therapy

Dysregulation of microRNA expression has been shown in multiple sclerosis (MS); however, the mechanisms underlying these changes, their response to therapy and the impact of microRNA changes in MS are not completely understood. Dicer mediates the cleavage of precursor microRNAs to mature microRNAs and is dysregulated in multiple pathologies. Having shown that interferons regulate Dicer in vitro, we hypothesized that MS patient IFNβ1a treatment could potentially alter Dicer expression. Dicer mRNA and protein levels, as well as microRNA expression, were determined in MS patient and healthy control PBL. Acute responses to IFNβ1a were assessed in 50 patients. We found that Dicer protein but not mRNA levels decreases in MS patients while both are selectively induced in patients responding well to IFNβ1a. Potential microRNA biomarkers for relapsing remitting multiple sclerosis (RRMS), secondary progressive multiple sclerosis (SPMS) and IFNβ1a response are described. Contrasts in Dicer and microRNA expression levels between patient populations may offer insight into mechanisms underlying disease courses and responses to IFNβ1a therapy. This work identifies Dicer regulation as both a potential mediator of MS pathology and a therapeutic target.

Circulating microRNAs as Potential Biomarkers in Non-Alcoholic Fatty Liver Disease and Hepatocellular Carcinoma

Obesity and metabolic syndrome are growing epidemics worldwide and greatly responsible for many liver diseases, including nonalcoholic fatty liver disease (NAFLD). NAFLD often progresses to cirrhosis, end-stage liver failure and hepatocellular carcinoma (HCC), the most common primary liver cancer and one of the leading causes for cancer-related deaths globally. Currently available tools for the diagnosis of NAFLD staging and progression towards HCC are largely invasive and of limited accuracy. In light of the need for more specific and sensitive noninvasive molecular markers, several studies have assessed the potential of circulating microRNAs (miRNAs) as biomarkers of liver injury and hepatocarcinogenesis. Indeed, extracellular miRNAs are very stable in the blood, can be easily quantitated and are differentially expressed in response to different pathophysiological conditions. Although standardization procedures and larger, independent studies are still necessary, miRNAs constitute promising, clinically-useful biomarkers for the NAFLD-HCC spectrum.

MicroRNAs in Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) has become the most common liver disorder. Strongly linked to obesity and diabetes, NAFLD has the characteristics of complex diseases with substantial heterogeneity. Accordingly, our ability to predict the risk of advanced NAFLD and provide efficient treatment may improve by a better understanding of the relationship between genotype and phenotype. MicroRNAs (miRNAs) play a major role in the fine-tuning of gene expression and they have recently emerged as novel biomarkers and therapeutic tools in the management of NAFLD. These short non-coding RNA sequences act by partial repression or degradation of targeted mRNAs. Deregulation of miRNAs has been associated with different stages of NAFLD, while their biological role in the pathogenesis remains to be fully understood. Systems biology analyses based on predicted target genes have associated hepatic miRNAs with molecular pathways involved in NAFLD progression such as cholesterol and lipid metabolism, insulin signaling, oxidative stress, inflammation, and pathways of cell survival and proliferation. Moreover, circulating miRNAs have been identified as promising noninvasive biomarkers of NAFLD and linked to disease severity. This rapidly growing field is likely to result in major advances in the pathomechanism, prognostication, and treatment of NAFLD.

SUMOylation at K707 of DGCR8 controls direct function of primary microRNA

DGCR8 (DiGeorge syndrome critical region gene 8) is essential for primary microRNA (pri-miRNA) processing in the cell nucleus. It specifically combines with Drosha, a nuclear RNase III enzyme, to form the Microprocessor complex (MC) that cleaves pri-miRNA to precursor miRNA (pre-miRNA), which is further processed to mature miRNA by Dicer, a cytoplasmic RNase III enzyme. Increasing evidences suggest that pri-/pre-miRNAs have direct functions in regulation of gene expression, however the underlying mechanism how it is fine-tuned remains unclear. Here we find that DGCR8 is modified by SUMO1 at the major site K⁷⁰⁷, which can be promoted by its ERK-activated phosphorylation. SUMOylation of DGCR8 enhances the protein stability by preventing the degradation via the ubiquitin proteasome pathway. More importantly, SUMOylation of DGCR8 does not alter its association with Drosha, the MC activity and miRNA biogenesis, but rather influences its affinity with pri-miRNAs. This altered affinity of DGCR8 with pri-miRNAs seems to control the direct functions of pri-miRNAs in recognition and repression of the target mRNAs, which is evidently linked to the DGCR8 function in regulation of tumorigenesis and cell migration. Collectively, our data suggest a novel mechanism that SUMOylation of DGCR8 controls direct functions of pri-miRNAs in gene silencing.

MicroRNA responses to environmental liver carcinogens: Biological and clinical significance

A large number of biological, chemical, and dietary factors have been implicated in the development of liver cancer. These involve complex and protracted interactions between genetic, epigenetic, and environmental factors. The survival rate for patients diagnosed with late-stage liver cancer is currently low due to the aggressive nature of the disease and resistance to therapy. An increasing body of evidence has offered support for the crucial role of non-coding microRNA (miRNA) in directing hepatic responses to environmental risk factors for liver cancer. In this review we focus on miRNA responses to environmental liver cancer risk factors and their potential biological and clinical significance.

Micro RNAs in the development of non-alcoholic fatty liver disease

Nonalcoholic fatty liver disease or nonalcoholic fatty liver disease (NAFLD) refers to a group of disorders that arise from the accrual of fat in hepatocytes. Although various factors have been associated with the development of NAFLD, including genetic predisposition and environmental exposures, little is known about the underlying pathogenesis of the disease. Research efforts are ongoing to identify biological targets and signaling pathways that mediate NAFLD. Emerging evidence has implicated a role for micro RNAs (miRNAs), short single-stranded molecules that regulate gene expression either transcriptionally, through targeting of promoter regions, or post-transcriptionally, by blocking translation or promoting cleavage of specific target mRNAs. Several miRNAs have been associated with NAFLD, although our understanding of the biology underlying their role is still emerging. The goal of this review is to present an overview of the current state of knowledge of miRNAs involved in the development of NAFLD across a range of in vitro and in vivo models, including miRNAs that contribute to pathological mechanisms related to fatty liver in humans. Much less is known about the specific targets of miRNAs in cells, nor the molecular mechanisms involved in the development and progression NAFLD and related outcomes. More recently, the identification and validation of miRNA signatures in serum may facilitate the development of improved methods for diagnosis and clinical monitoring of disease progression.

Possible role of tocopherols in the modulation of host microRNA with potential antiviral activity in patients with hepatitis B virus-related persistent infection: a systematic review

Hepatitis B virus (HBV) infection represents a serious global health problem and persistent HBV infection is associated with an increased risk of cirrhosis, hepatocellular carcinoma and liver failure. Recently, the study of the role of microRNA (miRNA) in the pathogenesis of HBV has gained considerable interest as well as new treatments against this pathogen have been approved. A few studies have investigated the antiviral activity of vitamin E (VE) in chronic HBV carriers. Herein, we review the possible role of tocopherols in the modulation of host miRNA with potential anti-HBV activity. A systematic research of the scientific literature was performed by searching the MEDLINE, Cochrane Library and EMBASE databases. The keywords used were 'HBV therapy', 'HBV treatment', 'VE antiviral effects', 'tocopherol antiviral activity', 'miRNA antiviral activity' and 'VE microRNA'. Reports describing the role of miRNA in the regulation of HBV life cycle, in vitro and in vivo available studies reporting the effects of VE on miRNA expression profiles and epigenetic networks, and clinical trials reporting the use of VE in patients with HBV-related chronic hepatitis were identified and examined. Based on the clinical results obtained in VE-treated chronic HBV carriers, we provide a reliable hypothesis for the possible role of this vitamin in the modulation of host miRNA profiles perturbed by this viral pathogen and in the regulation of some cellular miRNA with a suggested potential anti-HBV activity. This approach may contribute to the improvement of our understanding of pathogenetic mechanisms involved in HBV infection and increase the possibility of its management and treatment.

Surgical treatment of nonalcoholic fatty liver disease in severely obese patients

Obesity is a multi-organ system disease with underlying metabolic abnormalities and chronic systemic inflammation. Nonalcoholic fatty liver disease (NAFLD) is a hepatic manifestation of obesity metabolic dysfunction and its associated cardiovascular- and liver-related morbidities and mortality. Our current understanding of NAFLD pathogenesis, disease characteristics, the role of insulin resistance, chronic inflammation, gut–liver and gut–brain crosstalk and the effectiveness of pharmacotherapy is still evolving. Bariatric surgery significantly improves metabolic and NAFLD histology in severely obese patients, although its positive effects on fibrosis are not universal. Bariatric surgery benefits NAFLD through its metabolic effect on insulin resistance, inflammation, and insulinotropic and anorexinogenic gastrointestinal hormones. Further studies are needed to understand the natural course of NAFLD in severely obese patients and the role of weight loss surgery as a primary treatment for NAFLD.

Revisiting the metabolic syndrome and paving the way for microRNAs in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) comprises a spectrum of stages from simple steatosis to non-alcoholic steatohepatitis, which can progress to fibrosis, cirrhosis and, ultimately, hepatocellular carcinoma. Despite being one of the most common chronic liver diseases, NAFLD pathogenesis remains largely unknown. In this review, we discuss the key molecular mechanisms involved in NAFLD development and progression, focusing on the emerging role of microRNAs. NAFLD is intrinsically related to obesity and the metabolic syndrome. Changes in lipid metabolism increase free fatty acids in blood, which in turn induces peripheral insulin resistance and increases oxidative and endoplasmic reticulum stress. Although not yet considered in the diagnosis of NAFLD, recent reports also reinforce the crucial role of apoptosis in disease progression via activation of either death receptor or mitochondrial pathways and p53. In addition, the role of gut microbiota and the gut-liver axis has been recently associated with NAFLD. Finally, there is an accumulating and growing body of evidence supporting the role of microRNAs in NAFLD pathogenesis and progression, as well as hinting at their use as biomarkers or therapeutic tools. The ultimate goal is to review different molecular pathways that may underlie NAFLD pathogenesis in the hope of finding targets for new and efficient therapeutic interventions.

Regulation of microRNAs and their role in liver development, regeneration and disease

Since their discovery more than a decade ago microRNAs have been demonstrated to have profound effects on almost every aspect of biology. Numerous studies in recent years have shown that microRNAs have important roles in development and in the etiology and progression of disease. This review is focused on microRNAs and the roles they play in liver development, regeneration and liver disease; particularly chronic liver diseases such as alcoholic liver disease, non-alcoholic fatty liver disease, non-alcoholic steatohepatitis, viral hepatitis and primary liver cancer. The key microRNAs identified in liver development and chronic liver disease will be discussed together with, where possible, the target messenger RNAs that these microRNAs regulate to profoundly alter these processes. This article is part of a Directed Issue entitled: The Non-coding RNA Revolution.

MicroRNAs in nonalcoholic fatty liver disease: novel biomarkers and prognostic tools during the transition from steatosis to hepatocarcinoma

Nonalcoholic fatty liver disease (NAFLD) is a metabolic-related disorder ranging from steatosis to steatohepatitis, which may progress to cirrhosis and hepatocellular carcinoma (HCC). The influence of NAFLD on HCC development has drawn attention in recent years. HCC is one of the most common malignant tumors and the third highest cause of cancer-related death. HCC is frequently diagnosed late in the disease course, and patient's prognosis is usually poor. Early diagnosis and identification of the correct stage of liver damage during NAFLD progression can contribute to more effective therapeutic interventions, improving patient outcomes. Therefore, scientists are always searching for new sensitive and reliable markers that could be analysed through minimally invasive tests. MicroRNAs are short noncoding RNAs that act as posttranscriptional regulators of gene expression. Several studies identified specific miRNA expression profiles associated to different histological features of NAFLD. Thus, miRNAs are receiving growing attention as useful noninvasive diagnostic markers to follow the progression of NAFLD and to identify novel therapeutic targets. This review focuses on the current knowledge of the miRNAs involved in NAFLD and related HCC development, highlighting their diagnostic and prognostic value for the screening of NAFLD patients.

Molecular mechanisms of hepatic apoptosis

Apoptosis is a prominent feature of liver diseases. Causative factors such as alcohol, viruses, toxic bile acids, fatty acids, drugs, and immune response, can induce apoptotic cell death via membrane receptors and intracellular stress. Apoptotic signaling network, including membrane death receptor-mediated cascade, reactive oxygen species (ROS) generation, endoplasmic reticulum (ER) stress, lysosomal permeabilization, and mitochondrial dysfunction, is intermixed each other, but one mechanism may dominate at a particular stage. Mechanisms of hepatic apoptosis are complicated by multiple signaling pathways. The progression of liver disease is affected by the balance between apoptotic and antiapoptotic capabilities. Therapeutic options of liver injury are impacted by the clear understanding toward mechanisms of hepatic apoptosis.

Molecular mechanisms of hepatic apoptosis

Apoptosis is a prominent feature of liver diseases. Causative factors such as alcohol, viruses, toxic bile acids, fatty acids, drugs, and immune response, can induce apoptotic cell death via membrane receptors and intracellular stress. Apoptotic signaling network, including membrane death receptor-mediated cascade, reactive oxygen species (ROS) generation, endoplasmic reticulum (ER) stress, lysosomal permeabilization, and mitochondrial dysfunction, is intermixed each other, but one mechanism may dominate at a particular stage. Mechanisms of hepatic apoptosis are complicated by multiple signaling pathways. The progression of liver disease is affected by the balance between apoptotic and antiapoptotic capabilities. Therapeutic options of liver injury are impacted by the clear understanding toward mechanisms of hepatic apoptosis.