miRNAs and NAFLD: from pathophysiology to therapy

Chrysophanol Alleviates Metabolic Syndrome by Activating the SIRT6/AMPK Signaling Pathway in Brown Adipocytes

Chrysophanol, a primary active ingredient of Cassia mimosoides Linn or Rhei radix et rhizoma, has various pharmacological properties, including anticancer, antidiabetic, and anti-inflammatory, as well as blood lipid regulation. However, whether chrysophanol can mitigate obesity, and its underlying mechanisms remains unclear. This study investigated whether chrysophanol effects energy metabolism in high-fat diet- (HFD-) induced obese mice and fat-specific Sirtuin 6- (SIRT6-) knockout (FKO) mice, targeting the SIRT6/AMPK signaling pathway in brown and white fat tissue. Our results showed that chrysophanol can effectively inhibit lipid accumulation in vitro and reduce mice's body weight, improve insulin sensitivity and reduced fat content of mice, and induce energy consumption in HFD-induced obese mice by activating the SIRT6/AMPK pathway. However, a treatment with OSS-128167, an SIRT6 inhibitor, or si-SIRT6, SIRT6 target specific small interfering RNA, in vitro blocked chrysophanol inhibition of lipid accumulation. Similar results were obtained when blocking the AMPK pathway. Moreover, in the HFD-induced obese model with SIRT6 FKO mice, histological analysis and genetic test results showed that chrysophanol treatment did not reduce lipid droplets and upregulated the uncoupling protein 1 (UCP1) expression. Rather, it upregulated the expression of thermogenic genes and activated white fat breakdown by inducing phosphorylation of adenosine 5′-monophosphate- (AMP-) activated protein kinase (AMPK), both in vitro and in vivo. OSS-128167 or si-SIRT6 blocked chrysophanol's upregulation of peroxisome proliferator-activated receptor-γ coactivator-1α (Pgc-1α) and Ucp1 expression. In conclusion, this study demonstrated that chrysophanol can activate brown fat through the SIRT6/AMPK pathway and increase energy consumption, insulin sensitivity, and heat production, thereby alleviating obesity and metabolic disorders.

Impact of Long-Term Supplementation with Fish Oil in Individuals with Non-Alcoholic Fatty Liver Disease: A Double Blind Randomized Placebo Controlled Clinical Trial

Non-alcoholic fatty liver disease (NAFLD) is a chronic disease affecting up to 25% of the population worldwide. n-3 long-chain polyunsaturated fatty acids (n-3 PUFA) have been associated with improved clinical parameters of NAFLD. Our purpose was to conduct a pilot study to evaluate the effects of n-3 PUFA supplementation in a randomized, double-blind, placebo-controlled clinical study performed on NAFLD individuals diagnosed by ultrasound. Patients received n-3 PUFA (n = 13) or placebo (n = 11) supplementation for six months. Circulating miR-122 expression (determined by quantitative real time-polymerase chain reaction (qRT-PCR), liver fibrosis (FibroScan^®), red blood cells (RBC) fatty acids (gas chromatography), and biochemical tests were performed at baseline and after intervention. After the intervention, in the n-3 PUFA group, docosahexaenoic acid (DHA) and omega index increased significantly in RBC (p = 0.022 and p = 0.012, respectively), in addition to a significant reduction in alkaline phosphatase (ALP) (p = 0.002) and liver fibrosis (p = 0.039). However, there was no change in the expression of circulating miR-122 in both groups. Our results showed that omega-3 PUFA were incorporated in erythrocytes after six months of fish oil supplementary intake, and that n-3 PUFA were effective in reducing ALP and liver fibrosis without altering the expression of circulating miR-122 in individuals with NAFLD.

Genetic Ablation of MiR-22 Fosters Diet-Induced Obesity and NAFLD Development

miR-22 is one of the most abundant miRNAs in the liver and alterations of its hepatic expression have been associated with the development of hepatic steatosis and insulin resistance, as well as cancer. However, the pathophysiological roles of miR-22-3p in the deregulated hepatic metabolism with obesity and cancer remains poorly characterized. Herein, we observed that alterations of hepatic miR-22-3p expression with non-alcoholic fatty liver disease (NAFLD) in the context of obesity are not consistent in various human cohorts and animal models in contrast to the well-characterized miR-22-3p downregulation observed in hepatic cancers. To unravel the role of miR-22 in obesity-associated NAFLD, we generated constitutive Mir22 knockout (miR-22KO) mice, which were subsequently rendered obese by feeding with fat-enriched diet. Functional NAFLD- and obesity-associated metabolic parameters were then analyzed. Insights about the role of miR-22 in NAFLD associated with obesity were further obtained through an unbiased proteomic analysis of miR-22KO livers from obese mice. Metabolic processes governed by miR-22 were finally investigated in hepatic transformed cancer cells. Deletion of Mir22 was asymptomatic when mice were bred under standard conditions, except for an onset of glucose intolerance. However, when challenged with a high fat-containing diet, Mir22 deficiency dramatically exacerbated fat mass gain, hepatomegaly, and liver steatosis in mice. Analyses of explanted white adipose tissue revealed increased lipid synthesis, whereas mass spectrometry analysis of the liver proteome indicated that Mir22 deletion promotes hepatic upregulation of key enzymes in glycolysis and lipid uptake. Surprisingly, expression of miR-22-3p in Huh7 hepatic cancer cells triggers, in contrast to our in vivo observations, a clear induction of a Warburg effect with an increased glycolysis and an inhibited mitochondrial respiration. Together, our study indicates that miR-22-3p is a master regulator of the lipid and glucose metabolism with differential effects in specific organs and in transformed hepatic cancer cells, as compared to non-tumoral tissue.

Reversal of diet-induced hepatic steatosis by peripheral CB1 receptor blockade in mice is p53/miRNA-22/SIRT1/PPARα dependent

OBJECTIVE

The endocannabinoid (eCB) system is increasingly recognized as being crucially important in obesity-related hepatic steatosis. By activating the hepatic cannabinoid-1 receptor (CB₁R), eCBs modulate lipogenesis and fatty acid oxidation. However, the underlying molecular mechanisms are largely unknown.

METHODS

We combined unbiased bioinformatics techniques, mouse genetic manipulations, multiple pharmacological, molecular, and cellular biology approaches, and genomic sequencing to systematically decipher the role of the hepatic CB₁R in modulating fat utilization in the liver and explored the downstream molecular mechanisms.

RESULTS

Using an unbiased normalized phylogenetic profiling analysis, we found that the CB₁R evolutionarily coevolves with peroxisome proliferator-activated receptor-alpha (PPARα), a key regulator of hepatic lipid metabolism. In diet-induced obese (DIO) mice, peripheral CB₁R blockade (using AM6545) induced the reversal of hepatic steatosis and improved liver injury in WT, but not in PPARα^-/- mice. The antisteatotic effect mediated by AM6545 in WT DIO mice was accompanied by increased hepatic expression and activity of PPARα as well as elevated hepatic levels of the PPARα-activating eCB-like molecules oleoylethanolamide and palmitoylethanolamide. Moreover, AM6545 was unable to rescue hepatic steatosis in DIO mice lacking liver sirtuin 1 (SIRT1), an upstream regulator of PPARα. Both of these signaling molecules were modulated by the CB₁R as measured in hepatocytes exposed to lipotoxic conditions or treated with CB₁R agonists in the absence/presence of AM6545. Furthermore, using microRNA transcriptomic profiling, we found that the CB₁R regulated the hepatic expression, acetylation, and transcriptional activity of p53, resulting in the enhanced expression of miR-22, which was found to specifically target SIRT1 and PPARα.

CONCLUSIONS

We provide strong evidence for a functional role of the p53/miR-22/SIRT1/PPARα signaling pathway in potentially mediating the antisteatotic effect of peripherally restricted CB₁R blockade.

miR-29a Modulates GSK3β/SIRT1-Linked Mitochondrial Proteostatic Stress to Ameliorate Mouse Non-Alcoholic Steatohepatitis

MicroRNA-29a (miR-29a) has been shown to ameliorate hepatocellular damage, such as in the context of non-alcoholic fatty liver disease (NAFLD), steatohepatitis (NASH), and cholestatic injury. However, the mechanism mediating the hepatoprotective effect of miR-29a in diet-induced NASH remains elusive. In the present study, C57BL/6 mice of wild-type (WT) or miR-29a overexpression were fed with methionine–choline sufficient (MCS) or methionine–choline-deficient (MCD) diet for four weeks. The C57BL/6 mice harboring miR-29a overexpression presented reduced plasma AST, hepatic CD36, steatosis, and fibrosis induced by MCD. The TargetScan Release7.2-based bioinformatic analysis, KEGG pathway analysis, and luciferase reporter assay confirmed that miR-29a targets 3′UTR of glycogen synthase kinase 3 beta (Gsk3b) mRNA in the HepG2 hepatocyte cell line. Furthermore, miR-29a overexpression in the MCD-fed group resulted in inhibition of Gsk3b mRNA and GSK3β protein levels in the liver. GSK3β was notably expressed jointly with the extent of aggregated protein, which was then identified to be associated with mitochondrial unfolded protein response (UPR^mt), but not with endoplasmic reticulum UPR (UPR^ER). Additionally, in silico analysis of protein–protein interaction, in vivo, and in vitro correlation analyses of protein expression demonstrated that GSK3β closely associated with sirtuin 1(SIRT1). Finally, the implication of SIRT1-mediated mitochondrial biogenesis in the perturbation of proteostasis was observed. We herein provide novel insight into a hepatoprotective pathway, whereby miR-29a inhibits GSK3β to repress SIRT1-mediated mitochondrial biogenesis, leading to alleviation of mitochondrial proteostatic stress and UPR^mt in the context of NASH. miR-29a, GSK3β, and SIRT1 could thus serve as possible therapeutic targets to improve the treatment of NAFLD/NASH.

mRNA Post-Transcriptional Regulation by AU-Rich Element-Binding Proteins in Liver Inflammation and Cancer

AU-rich element-binding proteins (AUBPs) represent important post-transcriptional regulators of gene expression. AUBPs can bind to the AU-rich elements present in the 3'-UTR of more than 8% of all mRNAs and are thereby able to control the stability and/or translation of numerous target mRNAs. The regulation of the stability and the translation of mRNA transcripts by AUBPs are highly complex processes that occur through multiple mechanisms depending on the cell type and the cellular context. While AUBPs have been shown to be involved in inflammatory processes and the development of various cancers, their important role and function in the development of chronic metabolic and inflammatory fatty liver diseases (FLDs), as well as in the progression of these disorders toward cancers such as hepatocellular carcinoma (HCC), has recently started to emerge. Alterations of either the expression or activity of AUBPs are indeed significantly associated with FLDs and HCC, and accumulating evidence indicates that several AUBPs are deeply involved in a significant number of cellular processes governing hepatic metabolic disorders, inflammation, fibrosis, and carcinogenesis. Herein, we discuss our current knowledge of the roles and functions of AUBPs in liver diseases and cancer. The relevance of AUBPs as potential biomarkers for different stages of FLD and HCC, or as therapeutic targets for these diseases, are also highlighted.

Current Trends of Essential Trace Elements in Patients with Chronic Liver Diseases

Essential trace elements play crucial roles in the maintenance of health, since they are involved in many metabolic pathways. A deficiency or an excess of some trace elements, including zinc, selenium, iron, and copper, frequently causes these metabolic disorders such as impaired glucose tolerance and dyslipidemia. The liver largely regulates most of the metabolism of trace elements, and accordingly, an impairment of liver functions can result in numerous metabolic disorders. The administration or depletion of these trace elements can improve such metabolic disorders and liver dysfunction. Recent advances in molecular biological techniques have helped to elucidate the putative mechanisms by which liver disorders evoke metabolic abnormalities that are due to deficiencies or excesses of these trace elements. A genome-wide association study revealed that a genetic polymorphism affected the metabolism of a specific trace element. Gut dysbiosis was also responsible for impairment of the metabolism of a trace element. This review focuses on the current trends of four trace elements in chronic liver diseases, including chronic hepatitis, liver cirrhosis, nonalcoholic fatty liver disease, and autoimmune liver diseases. The novel mechanisms by which the trace elements participated in the pathogenesis of the chronic liver diseases are also mentioned.

Efficacy of serum miRNA test as a non-invasive method to diagnose nonalcoholic steatohepatitis: a systematic review and meta-analysis

Background

Nonalcoholic steatohepatitis (NASH) is a key turning point during the progression of nonalcoholic fatty liver disease (NAFLD). Recent studies have shown that serum miRNA tests may be effective in the diagnosis of NAFLD. We conducted a meta-analysis to assess the evidence for the diagnostic efficacy of serum miRNAs in patients with NAFLD and its subtype, NASH, in particular.

Methods

After a systematic review, sensitivity, specificity, and area under the receiver operating characteristics curve (AUROC) were pooled to determine the efficacy of serum miRNA test for the diagnosis of NAFLD and NASH. Clinical utility was evaluated by Fagan’s nomogram and likelihood ratio scattergram. Heterogeneity was evaluated by subgroup analysis and meta-regression. Publication bias was detected by Deeks’ funnel plot.

Results

We included 27 trials containing 1775 NAFLD patients (including simple steatosis and NASH) and 586 NASH patients. For NAFLD vs NASH, the pooled sensitivity, specificity, and AUROC were (0.71 vs. 0.74), (0.76 vs. 0.85) and (0.80 vs. 0.86), respectively. Serum miRNA had high accuracy for distinguishing NASH from simple steatosis, with an AUROC of 0.91. Among the most commonly studied serum miRNAs, miRNA-34a showed moderate diagnostic accuracy for NAFLD and the lowest heterogeneity (sensitivity I² = 5.73%, specificity I² = 33.16%, AUROC = 0.85). According to subgroup analysis and meta-regression, a lower BMI (< 30 kg/m²) might be a crucial source of heterogeneity.

Conclusions

As a novel non-invasive method, serum miRNA test exhibited robust diagnostic efficacy for NASH. Among these well-studied miRNAs, miRNA-34a was more available for diagnosis. Diagnosis of NAFLD by serum miRNA is more likely to be accurate in patients with BMI ≥ 30 kg/m².

Overexpression of miR-142-5p inhibits the progression of nonalcoholic steatohepatitis by targeting TSLP and inhibiting JAK-STAT signaling pathway

This study aimed to figure out the underlying mechanism of miR-142-5p in the non-alcoholic steatohepatitis (NASH). Bioinformatics, luciferase assay and Western blot were performed. The NASH mouse model was established through feeding a high fat diet (HFD). Relative expressions of miR-142-5p, thymic stromal lymphopoietin (TSLP), inflammatory factors were detected by qRT-PCR. The injury level of liver was assessed via measurement of serum alanine aminotransferase (ALT) and serum aspartate aminotransferase (AST). H&E staining and Masson's trichrome staining examine the liver fatty degeneration and fibrosis. MiR-142-5p and TSLP were differentially expressed and JAK-STAT signaling pathway was activated in the NASH group. Luciferase assay identified that TSLP was the downstream target of miR-142-5p. Through overexpression of miR-142-5p, ALT and AST in serum were inhibited, pro-inflammatory factors, liver fatty degeneration and fibrosis in liver tissues were decreased, while anti-inflammatory factors were increased. Overexpression of TSLP and JAK-STAT signaling pathway activation could reverse the effects of miR-142-5p on NASH. Taken together, overexpression of miR-142-5p could attenuate NASH progression via inhibiting TSLP and JAK-STAT pathway. MiR-142-5p might be a novel latent target for NASH therapy.

The Emerging Role of MicroRNAs in NAFLD: Highlight of MicroRNA-29a in Modulating Oxidative Stress, Inflammation, and Beyond

Non-alcoholic fatty liver disease (NAFLD) is a common cause of chronic liver disease and ranges from steatosis to steatohepatitis and to liver fibrosis. Lipotoxicity in hepatocytes, elevated oxidative stress and the activation of proinflammatory mediators of Kupffer cells, and fibrogenic pathways of activated hepatic stellate cells can contribute to the development of NAFLD. MicroRNAs (miRs) play a crucial role in the dysregulated metabolism and inflammatory signaling connected with NAFLD and its progression towards more severe stages. Of note, the protective effect of non-coding miR-29a on liver damage and its versatile action on epigenetic activity, mitochondrial homeostasis and immunomodulation may improve our perception of the pathogenesis of NAFLD. Herein, we review the biological functions of critical miRs in NAFLD, as well as highlight the emerging role of miR-29a in therapeutic application and the recent advances in molecular mechanisms underlying its liver protective effect.

MiR-30b-5p regulates the lipid metabolism by targeting PPARGC1A in Huh-7 cell line

BACKGROUND

MiRNAs are a group of multifunctional non-coding RNAs which play an important role in the various physiological processes including the development of NAFLD. Recent studies have shown that miR-30b-5p tightly associated with the abnormal lipid metabolism in patients with NAFLD, but the detailed mechanism of miR-30b-5p in the lipid metabolism was remain unclear. The aim of this study was to investigate the effect of miR-30b-5p on the lipid metabolism in hepatocellular carcinoma Huh-7 cells.

MATERIAL AND METHODS

The correlation of intracellular fat content with the expression of miR-30b-5p in Huh-7 cells and HepG2 cells was investigated by treated cells with different concentrations of FFAs. The effect of miR-30b-5p on the lipid deposition in Huh-7 cells was tested by oil red O staining and TG concentrations measurement. qRT-PCR and western blot were used to investigate the lipid metabolism-related genes PPAR-α, SREBP-1, and GULT1 in miR-30b-5p overexpressed or inhibited Huh-7 cells. Target genes of miR-30b-5p were predicted using starBase, miRDB, and TargetScan databases and verified by qRT-PCR and western blot.

RESULTS

The expression of miR-30b-5p was significant decreased in the FFAs treated Huh-7 cells and HepG2 cells. Overexpressing miR-30b-5p in Huh-7 cells decreased the number and size of lipid droplets and intracellular TG concentrations in Huh-7 cells. Expression of fatty acid oxidation related gene PPAR-α was increased and expression of lipid synthesis related gene SREBP-1 was decreased in the miR-30b-5p overexpressed Huh-7 cells. In addition, miR-30b-5p regulates the intracellular lipid metabolism by targeting PPARGC1A.

CONCLUSIONS

Overexpression of miR-30b-5p could reduce the intracellular fat deposition in Huh-7 cells, and miR-30b-5p might regulate the intracellular lipid metabolism by targeting the PPARGC1A in Huh-7 cells.

Dysregulated CD4+ T Cells and microRNAs in Myocarditis

Myocarditis is a polymorphic disease complicated with indeterminate etiology and pathogenesis, and represents one of the most challenging clinical problems lacking specific diagnosis and effective therapy. It is caused by a complex interplay of environmental and genetic factors, and causal links between dysregulated microribonucleic acids (miRNAs) and myocarditis have also been supported by recent epigenetic researches. Both dysregulated CD4+ T cells and miRNAs play critical roles in the pathogenesis of myocarditis, and the classic triphasic model of its pathogenesis consists of the acute infectious, subacute immune, and recovery/chronic myopathic phase. CD4+ T cells are key pathogenic factors underlying the development and progression of myocarditis, and the effector and regulatory subsets, respectively, promote and inhibit autoimmune responses. Furthermore, the reciprocal interplay of these subsets influences the pathogenesis as well. Dysregulated miRNAs along with their mRNA and protein targets have been identified in heart biopsies (intracellular miRNAs) and body fluids (circulating miRNAs) during myocarditis. These miRNAs show phase-dependent changes, and correlate with viral infection, immune status, fibrosis, destruction of cardiomyocytes, arrhythmias, cardiac functions, and outcomes. Thus, miRNAs are promising diagnostic markers and therapeutic targets in myocarditis. In this review, we review myocarditis with an emphasis on its pathogenesis, and present a summary of current knowledge of dysregulated CD4+ T cells and miRNAs in myocarditis.

Epigenetic silencing of microRNA-125b-5p promotes liver fibrosis in nonalcoholic fatty liver disease via integrin α8-mediated activation of RhoA signaling pathway

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is one of the most common chronic liver diseases that may progress to liver fibrosis or cancer. The present study aimed to investigate the role of microRNA-125b-5p (miR-125b-5p) in NAFLD and to further explore underlying molecular mechanisms.

METHODS

A mouse model of NAFLD was constructed by high cholesterol diet feeding and a cell-model was developed by treating the mouse liver cell line NCTC1469 with palmitic acid. Gain- and loss-of-function experiments were performed to determine the effects of miR-125b-5p, integrin α8 (ITGA8), and the RhoA signaling pathway on liver fibrosis in NAFLD. After the expression levels of miR-125b-5p, ITGA8, and RhoA were determined, liver fibrosis was evaluated in vivo and in vitro. The binding relationship of miR-125b-5p and ITGA8 was then validated. Finally, miR-125b-5p promoter methylation in NAFLD liver tissues and cells was determined.

RESULTS

In NAFLD clinical samples, mouse model, and cell-model, miR-125b-5p expression was reduced, while ITGA8 expression was increased. Moreover, miR-125b-5p targeted and downregulated ITGA8, leading to inhibition of the RhoA signaling pathway. In NAFLD liver tissues and cells, the CpG island in the miR-125b-5p promoter was methylated, causing epigenetic silencing of miR-125b-5p. Both miR-125b-5p silencing and ITGA8 overexpression promoted in vitro and in vivo liver fibrosis in NAFLD via activation of the RhoA signaling pathway.

CONCLUSIONS

Collectively, epigenetic silencing of miR-125b-5p upregulates ITGA8 expression to activate the RhoA signaling pathway, leading to liver fibrosis in NAFLD.

MicroRNA-103 represses hepatic de novo lipogenesis and alleviates NAFLD via targeting FASN and SCD1

MicroRNAs are well acknowledged as key mediators in the development of chronic metabolic diseases, including NAFLD. However, their roles in hepatic lipid metabolism and fatty liver still remain well elucidated. Here, we found that miR-103 represses de novo lipogenesis (DNL) and dampens the development of obesity/diet-induced fatty liver through targeting at Fasn and Scd1 in mouse liver. miR-103, robustly amplified in obese livers, inhibits the expression of Fasn and Scd1 via directly interacting with their mRNA 3' untranslated regions. Upregulated miR-103 sufficiently reduces the expression of Fasn and Scd1 and blocks the lipid accumulation in oleate-incubated hepatocytes. Furthermore, specifically overexpressing miR-103 in mouse liver by adenovirus significantly inhibits hepatic DNL to repress HCD-promoted hepatic lipid contents as well as NAFLD development. Meanwhile, enforced expression of hepatic miR-103 also alleviates obesity-associated fatty liver via reducing Fasn and Scd1 in db/db mice. Together, our study reveals a critical role of miR-103 in lipid homeostasis of liver and pathogenesis of NAFLD.

Gene-Hydrogel Microenvironment Regulates Extracellular Matrix Metabolism Balance in Nucleus Pulposus

Gene therapy provides an ideal potential treatment for intervertebral disk degeneration by delivering synthetic microRNAs (miRNAs) to regulate the gene expression levels. However, it is very challenging to deliver miRNAs directly, which leads to inactivation, low transfection efficiency, and short half-life. Here, Agomir is loaded in hydrogel to construct a gene-hydrogel microenvironment for regulating the synthesis/catabolism balance of the tissue extracellular matrix (ECM) to treat degenerative diseases. Agomir is a cholesterol-, methylation-, and phosphorothioate-modified miRNA, which can mimic the function of miRNA to regulate the expression of the target gene. Agomir874 that mimics miRNA874 is synthesized to down regulate the expression of matrix metalloproteinases (MMPs) in nucleus pulposus (NP). At the same time, a polyethylene glycol (PEG) hydrogel is synthesized through Ag-S coordination of 4-arm PEG-SH and silver ion solution, which has injectable, self-healing, antimicrobial, degradable, and superabsorbent properties and matches perfectly with the mechanism of intervertebral disk. By delivering Agomir-loaded PEG-hydrogel to a degenerative intervertebral disk, a gene-hydrogel microenvironment is constructed in situ, which reduces the expression of MMPs, regulates the synthesis/catabolism balance of ECM in the NP of the intervertebral disk, and improves the tissue microenvironment regeneration.

miRNA Dysregulation in the Development of Non-Alcoholic Fatty Liver Disease and the Related Disorders Type 2 Diabetes Mellitus and Cardiovascular Disease

According to the World Health Organization, the continuing surge in obesity pandemic creates a substantial increase in incidences of metabolic disorders, such as non-alcoholic fatty liver disease (NAFLD), type 2 diabetes mellitus, and cardiovascular disease. MicroRNAs (miRNAs) belong to an evolutionarily conserved class of short (20-22 nucleotides in length) and single-stranded non-coding RNAs. In mammals, miRNAs function as critical post-transcriptional negative regulators involved not only in many biological processes but also in the development of many diseases such as NAFLD and comorbidities. More recently, it has been described that cells can secrete miRNAs in extracellular vesicles, transported by body fluids, and uptaken by other tissues regulating gene expression. Therefore, this could be a mechanism of signaling involved not only in physiological pathways but also in the development of diseases. The association of some miRNA expression profiles with certain disorders has made them very interesting molecules for diagnosis, prognosis, and disease management. The finding of specific miRNA signatures to diagnose NAFLD and related diseases could anticipate the risk of development of related complications and, actually, it is the driving force of present health strategies worldwide. In this review, we have included latest advances in knowledge about the miRNAs involved in the development of NAFLD and related diseases and examined how this knowledge could be used to identify new non-invasive biomarkers and new pharmacological interventions.

Deciphering miRNAs' Action through miRNA Editing

MicroRNAs (miRNAs) are small non-coding RNAs with the capability of modulating gene expression at the post-transcriptional level either by inhibiting messenger RNA (mRNA) translation or by promoting mRNA degradation. The outcome of a myriad of physiological processes and pathologies, including cancer, cardiovascular and metabolic diseases, relies highly on miRNAs. However, deciphering the precise roles of specific miRNAs in these pathophysiological contexts is challenging due to the high levels of complexity of their actions. Indeed, regulation of mRNA expression by miRNAs is frequently cell/organ specific; highly dependent on the stress and metabolic status of the organism; and often poorly correlated with miRNA expression levels. Such biological features of miRNAs suggest that various regulatory mechanisms control not only their expression, but also their activity and/or bioavailability. Several mechanisms have been described to modulate miRNA action, including genetic polymorphisms, methylation of miRNA promoters, asymmetric miRNA strand selection, interactions with RNA-binding proteins (RBPs) or other coding/non-coding RNAs. Moreover, nucleotide modifications (A-to-I or C-to-U) within the miRNA sequences at different stages of their maturation are also critical for their functionality. This regulatory mechanism called "RNA editing" involves specific enzymes of the adenosine/cytidine deaminase family, which trigger single nucleotide changes in primary miRNAs. These nucleotide modifications greatly influence a miRNA's stability, maturation and activity by changing its specificity towards target mRNAs. Understanding how editing events impact miRNA's ability to regulate stress responses in cells and organs, or the development of specific pathologies, e.g., metabolic diseases or cancer, should not only deepen our knowledge of molecular mechanisms underlying complex diseases, but can also facilitate the design of new therapeutic approaches based on miRNA targeting. Herein, we will discuss the current knowledge on miRNA editing and how this mechanism regulates miRNA biogenesis and activity.

The Crosstalk of miRNA and Oxidative Stress in the Liver: From Physiology to Pathology and Clinical Implications

The liver is the central metabolic organ of mammals. In humans, most diseases of the liver are primarily caused by an unhealthy lifestyle-high fat diet, drug and alcohol consumption- or due to infections and exposure to toxic substances like aflatoxin or other environmental factors. All these noxae cause changes in the metabolism of functional cells in the liver. In this literature review we focus on the changes at the miRNA level, the formation and impact of reactive oxygen species and the crosstalk between those factors. Both, miRNAs and oxidative stress are involved in the multifactorial development and progression of acute and chronic liver diseases, as well as in viral hepatitis and carcinogenesis, by influencing numerous signaling and metabolic pathways. Furthermore, expression patterns of miRNAs and antioxidants can be used for biomonitoring the course of disease and show potential to serve as possible therapeutic targets.