Circular RNA as An Epigenetic Regulator in Chronic Liver Diseases

Revisiting Epigenetics Fundamentals and Its Biomedical Implications

In light of the post-genomic era, epigenetics brings about an opportunity to better understand how the molecular machinery works and is led by a complex dynamic set of mechanisms, often intricate and complementary in many aspects. In particular, epigenetics links developmental biology and genetics, as well as many other areas of knowledge. The present work highlights substantial scopes and relevant discoveries related to the development of the term from its first notions. To our understanding, the concept of epigenetics needs to be revisited, as it is one of the most relevant and multifaceted terms in human knowledge. To redirect future novel experimental or theoretical efforts, it is crucial to compile all significant issues that could impact human and ecological benefit in the most precise and accurate manner. In this paper, the reader can find one of the widest compilations of the landmarks and epistemic considerations of the knowledge of epigenetics across the history of biology from the earliest epigenetic formulation to genetic determinism until the present. In the present work, we link the current body of knowledge and earlier pre-genomic concepts in order to propose a new definition of epigenetics that is faithful to its regulatory nature.

Knockdown of circ_0044226 promotes endoplasmic reticulum stress-mediated autophagy and apoptosis in hepatic stellate cells via miR-4677-3p/SEC61G axis

Downregulation of circ_0044226 has been demonstrated to reduce pulmonary fibrosis, but the role of circ_0044226 in liver fibrosis remains to be explored. In this work, we found that circ_0044226 expression was upregulated during liver fibrosis. Knockdown of circ_0044226 inhibited proliferation, promoted autophagy and apoptosis of hepatic stellate cell LX-2. Bioinformatic analysis and dual luciferase reporter assays confirmed the interaction between circ_0044226, miR-4677-3p and SEC61G. Mechanistically, knockdown of circ_0044226 suppressed SEC61G expression by releasing miR-4677-3p, thereby enhancing endoplasmic reticulum stress. Overexpression of SEC61G or endoplasmic reticulum stress inhibitor 4-phenylbutiric acid partially reversed the effect of knockdown circ_0044226 on LX-2 cell function. In vivo experiments showed that inhibition of circ_0044226 attenuated CCL4-induced liver fibrosis in mice. These imply that circ_0044226 may be a potential target for the treatment of liver fibrosis.

The hsa_circ_0082152 maintains NF-κB mRNA stability by binding to MTDH to promote anti-tuberculosis drug-induced liver injury

Anti-tuberculosis drug-induced liver injury (ADLI) is a common adverse reaction during anti-tuberculosis treatment and often leads to treatment interruptions. Circular RNAs (circRNAs) have been identified as key modulators in liver diseases. CircRNAs is a special class of noncoding RNAs that have been found to have significant impacts on the progression of inflammation via various mechanisms. In the serum of ADLI patients, upregulation of the circular RNA hsa_circ_0082152 (derived from the host gene snd1) was observed, along with increased ALT and AST levels, as well as alterations in the levels of inflammation-related factors such as NF-κB, IL-1β and TNF-α. To elucidate the underlying mechanisms, we established an HL-7702-ADLI cell model and confirmed similar upregulation of hsa_circ_0082152. Downregulation of hsa_circ_0082152 significantly inhibited inflammatory injury in ADLI cells, while upregulation had the opposite effect. RNA immunoprecipitation showed that hsa_circ_0082152 functions by interacting with metadherin (MTDH). Our study further verified that the interaction of hsa_circ_0082152 with the MTDH protein binding to NF-κB mRNA to maintain NF-κB mRNA stability, which increases the expression of NF-κB and its targets IL-1β and TNF-α. Conversely, depletion of MTDH rescued the promotive effect of hsa_circ_0082152 overexpression on ADLI inflammation. Therefore, hsa_circ_0082152 overexpression promotes ADLI progression via the MTDH/NF-κB axis.

Epigenetic modification in liver fibrosis: Promising therapeutic direction with significant challenges ahead

Liver fibrosis, characterized by scar tissue formation, can ultimately result in liver failure. It's a major cause of morbidity and mortality globally, often associated with chronic liver diseases like hepatitis or alcoholic and non-alcoholic fatty liver diseases. However, current treatment options are limited, highlighting the urgent need for the development of new therapies. As a reversible regulatory mechanism, epigenetic modification is implicated in many biological processes, including liver fibrosis. Exploring the epigenetic mechanisms involved in liver fibrosis could provide valuable insights into developing new treatments for chronic liver diseases, although the current evidence is still controversial. This review provides a comprehensive summary of the regulatory mechanisms and critical targets of epigenetic modifications, including DNA methylation, histone modification, and RNA modification, in liver fibrotic diseases. The potential cooperation of different epigenetic modifications in promoting fibrogenesis was also highlighted. Finally, available agonists or inhibitors regulating these epigenetic mechanisms and their potential application in preventing liver fibrosis were discussed. In summary, elucidating specific druggable epigenetic targets and developing more selective and specific candidate medicines may represent a promising approach with bright prospects for the treatment of chronic liver diseases.

Bulbils of Aerial Yam Attenuate Ethanol-Induced Hepatotoxicity in HepG2 Cells through Inhibition of Oxidative Stress by Activation of the Nuclear Factor Erythroid-2-Related Factor 2 Signaling Pathway

Bulbil of yam (BY) extract contains various active compounds possessing many pharmacological properties. However, little is known about the effect and underlying mechanism of BY extract on ethanol-induced liver damage. The present study explored the beneficial potential of BY extract on ethanol-induced hepatotoxicity. To evaluate its effectiveness, ethanol-induced HepG2 liver cells were pretreated with BY extract. BY extract effectively rescued cells from ethanol treatment through inhibition of apoptotic cell death as well as inhibiting expression of mitogen-activated protein kinase (MAPK) proteins as stress inducers. BY extract increased the expression of typical antioxidants. Furthermore, BY extract significantly inhibited mitochondrial dysfunction and endoplasmic reticulum (ER) stress, which are major ROS-inducing factors. Finally, as an underlying mechanism of the protective effects of BY extract on ethanol-induced liver damage, it activated Nrf2 protein through translocation from the cytosol to the nucleus, which in turn activated its target oxidative stress suppressor genes. Collectively, our findings demonstrate that BY extract has potential antioxidative effects in ethanol-induced liver cells and contributes to the establishment of a treatment strategy for alcohol-derived liver injuries.

Circular RNA expression profile identifies potential circulating biomarkers for keratoconus

Early diagnosis is important for improving the outcomes of keratoconus (KC). Stable expression and a closed-loop structure of circular RNAs (circRNAs) make them ideal for the diagnosis and treatment of diseases. However, the expression pattern and potential function of circRNAs in KC is not studied yet. Hence, this study explored the circRNA expression profile of KC corneas through transcriptome sequencing and circRNA expression profile analysis. The diagnostic potential of blood circRNAs for KC was explored by analysing the circRNAs' expression levels of fifty paired blood samples from patients with KC and normal controls. The results showed that 107 significantly upregulated and 145 significantly downregulated circRNAs (|fold change| ≥ 2.0, p-value <0.05) were identified in KC tissues. Eight top differently expressed circRNAs were further validated in more cornea samples. Among them, five circRNAs expressed in peripheral blood, and four circRNAs (circ_0006156, circ_0006117, circ_0000284 and circ_0001801) showed significant downregulation in KC patients' peripheral blood too. The blood circ_0000284 expression levels of early, moderate, and advanced KC patients both were significantly lower than the controls. The blood circ_0006117 expression levels present a positive correlation with corrected distance visual acuity values, and a negative correlation with back elevation values of KC eyes. Notably, the expression levels of these circRNAs distinguished KC patients from their healthy counterparts, with the area under the curve (AUC) of circ_0000284, circ_0001801, and circ_0006117 being 0.7306, 0.6871 and 0.6701, respectively. Further, the AUC value for five circRNAs under the logistic regression model was 0.8203, indicating that they can function as effective biomarkers for the KC diagnostics. In conclusion, the expression of circRNAs showed a relationship with KC, with four significantly differentially expressed circRNAs demonstrating potential as biomarkers for the disease.

Upregulation of ATG9b by propranolol promotes autophagic cell death of hepatic stellate cells to improve liver fibrosis

Proranolol has long been recommended to prevent variceal bleeding in patients with cirrhosis. However, the mechanisms of propranolol in liver fibrosis have not yet been thoroughly elucidated. Autophagic cell death (ACD) of activated hepatic stellate cells (HSCs) is important in the alleviation of liver fibrosis. Our study aims to assess the mechanisms of propranolol regulating HSC ACD and liver fibrosis. ACD of HSCs was investigated using lentivirus transfection. The molecular mechanism was determined using a PCR profiler array. The role of autophagy-related protein 9b (ATG9b) in HSC ACD was detected using co-immunoprecipitation and co-localization of immunofluorescence. Changes in the signalling pathway were detected by the Phospho Explorer antibody microarray. Propranolol induces ACD and apoptosis in HSCs. ATG9b upregulation was detected in propranolol-treated HSCs. ATG9b upregulation promoted ACD of HSCs and alleviated liver fibrosis in vivo. ATG9b enhanced the P62 recruitment to ATG5-ATG12-LC3 compartments and increased the co-localization of P62 with ubiquitinated proteins. The PI3K/AKT/mTOR pathway is responsible for ATG9b-induced ACD in activated HSCs, whereas the p38/JNK pathway is involved in apoptosis. This study provides evidence for ATG9b as a new target gene and propranolol as an agent to alleviate liver fibrosis by regulating ACD of activated HSCs.

Chuanxiong Rhizoma extracts prevent liver fibrosis via targeting CTCF-c-MYC-H19 pathway

Objective

Hepatic fibrosis has been widely considered as a conjoint consequence of almost all chronic liver diseases. Chuanxiong Rhizoma (Chuanxiong in Chinese, CX) is a traditional Chinese herbal product to prevent cerebrovascular, gynecologic and hepatic diseases. Our previous study found that CX extracts significantly reduced collagen contraction force of hepatic stellate cells (HSCs). Here, this study aimed to compare the protection of different CX extracts on bile duct ligation (BDL)-induced liver fibrosis and investigate plausible underlying mechanisms.

Methods

The active compounds of CX extracts were identified by high performance liquid chromatography (HPLC). Network pharmacology was used to determine potential targets of CX against hepatic fibrosis. Bile duct hyperplasia and liver fibrosis were evaluated by serologic testing and histopathological evaluation. The expression of targets of interest was determined by quantitative real-time PCR (qPCR) and Western blot.

Results

Different CX extracts were identified by tetramethylpyrazine, ferulic acid and senkyunolide A. Based on the network pharmacological analysis, 42 overlap targets were obtained via merging the candidates targets of CX and liver fibrosis. Different aqueous, alkaloid and phthalide extracts of CX (CXAE, CXAL and CXPHL) significantly inhibited diffuse severe bile duct hyperplasia and thus suppressed hepatic fibrosis by decreasing CCCTC binding factor (CTCF)-c-MYC-long non-coding RNA H19 (H19) pathway in the BDL-induced mouse model. Meanwhile, CX extracts, especially CXAL and CXPHL also suppressed CTCF-c-MYC-H19 pathway and inhibited ductular reaction in cholangiocytes stimulated with taurocholate acid (TCA), lithocholic acid (LCA) and transforming growth factor beta (TGF-β), as illustrated by decreased bile duct proliferation markers.

Conclusion

Our data supported that different CX extracts, especially CXAL and CXPHL significantly alleviated hepatic fibrosis and bile duct hyperplasia via inhibiting CTCF-c-MYC-H19 pathway, providing novel insights into the anti-fibrotic mechanism of CX.

CircMIRLET7BHG, upregulated in an m6A-dependent manner, induces the nasal epithelial barrier dysfunction in allergic rhinitis pathogenesis

OBJECTIVE

Allergic rhinitis (AR) remains a frequent aspiratory allergic inflammatory disorder with a high incidence. Circular RNAs (circRNAs) have been revealed to participate in the pathogenesis of AR. This study investigated the biological function of circMIRLET7BHG (hsa_circ_0008668) in AR progression.

METHODS

Ovalbumin (OVA)-exposed human nasal epithelial cell line (HNEpC) and mice were adopted as the in vitro and in vivo models of AR. Immunofluorescence staining was used to determine epithelial tight junction protein expression. Target molecule levels were assessed by RT-qPCR and Western blotting. Localization of circMIRLET7BHG and IGF2BP1 was observed by RNA-FISH and immunofluorescence. Epithelial barrier damage was determined by transepithelial electrical resistance and fluorescein isothiocyanate-dextran (FD4) permeability. Serum concentrations of IgE, sIgE, IFN-γ, IL-4, and IL-5 were detected by ELISA. Apoptosis, pathological changes, and eosinophil infiltration in nasal mucosa tissues were evaluated by TUNEL, H&E, and Sirius red staining, respectively. Molecular mechanism was analyzed by RNA pull-down, RIP, and MeRIP assays.

RESULTS

An increased expression of circMIRLET7BHG was found in AR patients and experimental models. Down-regulation of circMIRLET7BHG attenuated OVA-induced allergic symptoms via relieving epithelial thicknesses, eosinophil infiltration, apoptosis, and inflammatory response in mice. Subsequently, circMIRLET7BHG deficiency prevented OVA-induced epithelial barrier dysfunction by reducing epithelial permeability, and inhibiting tight junction proteins. Mechanistically, methyltransferase-like 3 (METTL3) enhanced circMIRLET7BHG expression via m6A methylation, which enhanced ADAM10 mRNA stability via interaction with IGF2BP1.

CONCLUSION

METTL3-mediated m6A modification increased circMIRLET7BHG expression that consequently raised ADAM10 mRNA stability via interplay with IGF2BP1, thereby promoting AR by inducing epithelial barrier dysfunction.

Exploring the interplay between PARP1 and circRNA biogenesis and function

PARP1 (poly-ADP-ribose polymerase 1) is a multidomain protein with a flexible and self-folding structure that allows it to interact with a wide range of biomolecules, including nucleic acids and target proteins. PARP1 interacts with its target molecules either covalently via PARylation or non-covalently through its PAR moieties induced by auto-PARylation. These diverse interactions allow PARP1 to participate in complex regulatory circuits and cellular functions. Although the most studied PARP1-mediated functions are associated with DNA repair and cellular stress response, subsequent discoveries have revealed additional biological functions. Based on these findings, PARP1 is now recognized as a major modulator of gene expression. Several discoveries show that this multifunctional protein has been intimately connected to several steps of mRNA biogenesis, from transcription initiation to mRNA splicing, polyadenylation, export, and translation of mRNA to proteins. Nevertheless, our understanding of PARP1's involvement in the biogenesis of both coding and noncoding RNA, notably circular RNA (circRNA), remains restricted. In this review, we outline the possible roles of PARP1 in circRNA biogenesis. A full examination of the regulatory roles of PARP1 in nuclear processes with an emphasis on circRNA may reveal new avenues to control dysregulation implicated in the pathogenesis of several diseases such as neurodegenerative disorders and cancers. This article is categorized under: RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications Regulatory RNAs/RNAi/Riboswitches > Regulatory RNAs RNA Processing > Splicing Regulation/Alternative Splicing.

Hsa_circ_0072765 knockdown inhibits proliferation, activation and migration in transforming growth factor-beta (TGF-β)-induced hepatic stellate cells (HSCs) by the miR-197-3p/TRPV3 axis

BACKGROUND

Circular RNAs (circRNAs) participate in the progression of diverse human diseases. However, the effects of circRNAs on liver fibrosis are limited. In this study, we aimed to investigate the functions of hsa_circ_0072765 in liver fibrosis.

METHODS

Transforming growth factor-beta (TGF-β)-treated hepatic stellate cells (HSCs) were used as the cell model of liver fibrosis. Quantitative real-time polymerase chain reaction (qRT-PCR) or western blot was performed to determine the expression of hsa_circ_0072765, microRNA-197-3p (miR-197-3p) and transient receptor potential cation channel subfamily V member 3 (TRPV3). 5'-ethynyl-2'-deoxyuridine (EdU) assay, flow cytometry analysis and wound-healing assay were conducted to evaluate cell proliferation, cell cycle and migration. HSC activation was assessed by determining the expression of alpha-smooth muscle actin (α-SMA) and type I collagen alpha 1 (Col1A1). Dual-luciferase reporter assay and RNA immunoprecipitation (RIP) were manipulated to analyze the relationship of hsa_circ_0072765, miR-197-3p and TRPV3. The exosome morphology was observed under transmission electron microscopy (TEM).

RESULTS

Hsa_circ_0072765 level was increased in TGF-β-induced HSCs. Hsa_circ_0072765 knockdown inhibited cell proliferation, cell cycle, activation and migration in TGF-β-induced HSCs. Hsa_circ_0072765 sponged miR-197-3p and negatively regulated miR-197-3p expression. MiR-197-3p inhibition reversed the effects of hsa_circ_0072765 knockdown on TGF-β-induced HSC proliferation, cell cycle, activation and migration. In addition, TRPV3 was the target gene of miR-197-3p and miR-197-3p overexpression inhibited TGF-β-treated HSC proliferation, cell cycle, activation and migration by targeting TRPV3. Besides, we found that exosomal hsa_circ_0072765 was increased in TGF-β-treated HSCs.

CONCLUSION

Hsa_circ_0072765 promoted the progression of TGF-β-treated HSCs by decoying miR-197-3p and upregulating TRPV3.

Dietary Morus alba L. leaf supplementation improves hepatic lipid accumulation of laying hens via downregulating CircACACA

Fatty liver hemorrhagic syndrome (FLHS) is the most common metabolic disease in laying hens. Morus alba L. (mulberry) leaf has the effect of regulating lipid metabolism. We evaluated the effects of dietary 3% mulberry leaf (MUL) supplementation in production performance, egg quality, and liver lipid deposition in laying hens. Differentially expressed genes and circRNAs in the liver were identified using whole-transcriptome sequencing. We also evaluated the effects of the MUL extract using an in vitro model of primary hepatocytes induced by free fatty acids and explored the role of key circRNAs in this process. Dietary supplementation with 3% MUL alleviated liver steatosis in laying hens, as shown by decreased fatty liver color score, relative liver weight (P < 0.01), and triglyceride levels (P < 0.05), and showed a tendency to reduce the mortality rate of laying hens (P = 0.09). In addition, mulberry leaf supplementation significantly reduced cholesterol content in egg yolk (P < 0.01). Dietary mulberry leaf supplementation downregulated the expression of genes involved in fatty acid and cholesterol biosynthesis, and upregulated the expression of fatty acid oxidation-related genes in the liver. CircACACA, which is derived from exons 2 and 3 of the acetyl-CoA carboxylase alpha (ACACA) pre-mRNA, was significantly reduced in the MUL group (P < 0.01). Upregulation of circACACA expression reversed the lipid-lowering effect of mulberry leaf extract by upregulating sterol regulatory element-binding proteins 1 c (SREBP-1c) and fatty acid synthase (FASN) (P < 0.05). Overall, mulberry leaf is an effective therapeutic strategy for FLHS in hens and can improve liver lipid metabolism by downregulating circACACA.

Targeting a novel circITCH/miR-421/BTG1 axis is effective to suppress the malignant phenotypes in hepatocellular carcinoma (HCC) cells

Circular RNA-based competing endogenous RNA (ceRNA) networks contribute to the initiation and development of various types of cancer, including hepatocellular carcinoma (HCC). Although a novel circular RNA itchy E3 ubiquitin protein ligase (circITCH) is identified as a tumor suppressor in HCC, its detailed molecular mechanisms have not been fully delineated. The present study was designed to resolve this issue, and we firstly verified that circITCH suppressed the malignant phenotypes in HCC cells by regulating a novel miR-421/B-cell translocation gene 1 (BTG1) axis. Specifically, through performing the Real-Time qPCR analysis, we noticed that circITCH expression in HCC tumor tissues or cell lines were significantly lower than that in adjacent normal tissues or normal hepatocytes, and the expression levels of circITCH were negatively correlated with tumor size and TNM stage in HCC patients. Next, our functional experiments confirmed that overexpression of circITCH induced cell cycle arrest and apoptosis, and reduced cell viability and colony forming ability in Hep3B and Huh7 cells. Mechanically, bioinformatics analysis, RNA immunoprecipitation and luciferase reporter assay demonstrated that circITCH served as RNA sponges for miR-421 to elevate BTG1 levels in HCC cells. The rescuing experiments verified that upregulation of miR-421 promoted cell viability and colony formation, and reduced apoptosis, which were abrogated by overexpression of circITCH or BTG1. In conclusion, this study identified a novel circITCH/miR-421/BTG1 axis that restrained the development of HCC, and our findings provided novel biomarkers for the treatment of this disease.

Regulatory Role of circRNA-0067835 in Behcet Disease through Targeting Micro RNA-155: Implication of ATG1, AKT and MTOR

Background

Autophagy has been proven to contribute to maintaining eukaryotic cells' normal intracellular homeostasis, whereas autophagy malfunction may predispose to Behcet Disease (BD). The accumulation of the products of autophagic degradation as well as impairment in autophagic flux in cases with BD, may be attributed to dysregulated miRNA-155 expression. This study attempts to determine the contribution of circRNA-0067835 in miRNA-155-mediated modulation of the autophagy axis as well as to investigate its impact on the production of pro-inflammatory cytokines in BD.

Methods

This study was carried out on 40 cases with BD and 40 healthy control subjects. The collection of serum samples was done before performing a real-time PCR to estimate the relative gene expression of ATG1, AKT, miRNA-155, mTOR, TAB2, and circRNA-0067835. Additionally, IL-1β, IL-17, and TNF-α serum levels were determined by ELISA.

Results

Behcet Disease (BD) patients had significantly upregulated circRNA-0067835, with subsequent downregulation of its target gene, miRNA-155 than controls (P<0.05). In addition, decreased miRNA-155 gene expression was correlated with significantly increased TAB2 gene expression levels in BD patients compared to the controls (P<0.05). Furthermore, enhanced production of pro-inflammatory cytokines was detected in cases with BD than in controls.

Conclusion

The correlation between circRNA-0067835 and miRNA-155 fairly contributes to the regulation of cytokine production in BD via the modulation of autophagy. The investigation of the circRNA-0067835 and the microRNA-155 and their downstream adaptor molecules could be a potential therapeutic agent for BD.

Proangiogenic role of circRNA-007371 in liver fibrosis

Circular RNAs (circRNAs) are crucially involved in cancers as competing endogenous RNA (ceRNA) or microRNA (miRNA) sponges. However, the function and mechanism of circRNAs in liver fibrosis remain unknown and are the focus of this study. Murine fibrotic models were induced by thioacetamide (TAA) or carbon tetrachloride (CCl₄ ). Increased angiogenesis is accompanied by liver fibrosis in TAA- and CCl₄ -induced murine fibrotic livers. circRNA microarray and argonaute 2 (AGO2)-RNA immunoprecipitation (RIP) sequencing (AGO2-RIP sequencing) were performed in murine livers to screen for functional circRNAs. Compared to control livers, 86 differentially expressed circRNAs were obtained in TAA-induced murine fibrotic livers using circRNA microarray. In addition, 551 circRNAs were explored by AGO2-RIP sequencing of murine fibrotic livers. The circRNA-007371 was then selected and verified for back-spliced junction, resistance to RNase R, and loop formation. In vitro, murine hemangioendothelioma endothelial (EOMA) cells were transfected with circRNA-007371 overexpressing plasmid or empty plasmid. circRNA-007371 overexpression promoted tube formation, migration, and cell proliferation of EOMA cells. RNA sequencing and miRNA sequencing were then performed to explore the mechanism of the proangiogenic effects of circRNA-007371. circRNA-007371 promotes liver fibrosis via miRNA sponges or ceRNA mechanisms. Stag1, the parent gene of circRNA-007371, may play a significant role in proangiogenic progression. In conclusion, circRNA-007371 enhances angiogenesis via a miRNA sponge mechanism in liver fibrosis. The antiangiogenic effect of circRNA-007371 inhibition may provide a new strategy for treating patients with liver cirrhosis.

Regulatory Functions and Mechanisms of Circular RNAs in Hepatic Stellate Cell Activation and Liver Fibrosis

Chronic liver injury induces the activation of hepatic stellate cells (HSCs) into myofibroblasts, which produce excessive amounts of extracellular matrix (ECM), resulting in tissue fibrosis. If the injury persists, these fibrous scars could be permanent and disrupt liver architecture and function. Currently, effective anti-fibrotic therapies are lacking; hence, understanding molecular mechanisms that control HSC activation could hold a key to the development of new treatments. Recently, emerging studies have revealed roles of circular RNAs (circRNAs), a class of non-coding RNAs that was initially assumed to be the result of splicing errors, as new regulators in HSC activation. These circRNAs can modulate the activity of microRNAs (miRNAs) and their interacting protein partners involved in regulating fibrogenic signaling cascades. In this review, we will summarize the current knowledge of this class of non-coding RNAs for their molecular function in HSC activation and liver fibrosis progression.

Exosomal circular RNAs: New player in breast cancer progression and therapeutic targets

Breast cancer is the most prevalent type of malignancy among women. Exosomes are extracellular vesicles of cell membrane origin that are released via exocytosis. Their cargo contains lipids, proteins, DNA, and different forms of RNA, including circular RNAs. Circular RNAs are new class of non-coding RNAs with a closed-loop shape involved in several types of cancer, including breast cancer. Exosomes contained a lot of circRNAs which are called exosomal circRNAs. By interfering with several biological pathways, exosomal circRNAs can have either a proliferative or suppressive role in cancer. The involvement of exosomal circRNAs in breast cancer has been studied with consideration to tumor development and progression as well as its effects on therapeutic resistance. However, its exact mechanism is still unclear, and there have not been available clinical implications of exo-circRNAs in breast cancer. Here, we highlight the role of exosomal circRNAs in breast cancer progression and to highlight the most recent development and potential of circRNAas therapeutic targets and diagnostics for breast cancer.

CircRNA expression profiles and functional analysis in a mouse model of chronic intermittent hypoxia-induced renal injury: new insight into pathogenesis

Increasing evidence has demonstrated that circular RNAs (circRNAs) play crucial roles in the pathogenesis of multiple diseases. However, the functions of circRNAs in renal injury induced by obstructive sleep apnea (OSA) are poorly understood. The aim of this current study is to identify the global changes of circRNAs expression in OSA-induced renal damage. The mouse model of OSA treated by chronic intermittent hypoxia (CIH) was established. We assessed the expression profiles of circRNAs in CIH caused renal injury by microarray analysis. Bioinformatic analyses were further performed by us to assess those differentially expressed circRNAs. Quantitative realtime PCR (qRT-PCR) were then conducted to assure the data of microarray. Finally, a circRNA-miRNA -mRNA competing endogenous RNA (ceRNA) regulatory network was constructed. We found 11 upregulated and 13 downregulated circRNAs in CIH-induced renal injury. The qRT-PCR validated that the six selected circRNAs were identical to the results of microarray. Both Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis were further employed to annotate the potential functions of dysregulated circRNAs. Finally, we established a ceRNA network to predict the target genes of circRNAs. In general, our results first illustrate that circRNAs are aberrantly expressed in OSA-induced renal injury, which might aid in offering novel genetic insights into this disease and potential therapeutic targets for OSA-associated chronic kidney disease.

Role of follistatin-like protein 1 in liver diseases

Liver diseases, including viral hepatitis, fatty liver, metabolic-associated fatty liver disease, liver cirrhosis, alcoholic liver disease, and liver neoplasms, are major global health challenges. Despite the continued development of new drugs and technologies, the prognosis of end-stage liver diseases, including advanced liver cirrhosis and liver neoplasms, remains poor. Follistatin-like protein 1 (FSTL1), an extracellular glycoprotein, is secreted by various cell types. It is a glycoprotein that belongs to the family of secreted proteins acidic and rich in cysteine (SPARC). It is also known as transforming growth factor-beta inducible TSC-36 and follistatin-related protein (FRP). FSTL1 plays a key role in cell survival, proliferation, differentiation, and migration, as well as the regulation of inflammation and immunity. Studies have demonstrated that FSTL1 significantly affects the occurrence and development of liver diseases. This article reviews the role and mechanism of FSLT1 in liver diseases.

Detangling the interrelations between MAFLD, insulin resistance, and key hormones

Metabolic dysfunction-associated fatty liver disease (MAFLD) has increasingly become a significant and highly prevalent cause of chronic liver disease, displaying a wide array of risk factors and pathophysiologic mechanisms of which only a few have so far been clearly elucidated. A bidirectional interaction between hormonal discrepancies and metabolic-related disorders, including obesity, type 2 diabetes mellitus (T2DM), and polycystic ovarian syndrome (PCOS) has been described. Since the change in nomenclature from non-alcoholic fatty liver disease (NAFLD) to MAFLD is based on the clear impact of metabolic elements on the disease, the reciprocal interactions of hormones such as insulin, adipokines (leptin and adiponectin), and estrogens have strongly pointed to the intrinsic links that lead to the heterogeneous epidemiology, clinical presentations, and risk factors involved in MAFLD in different populations. The objective of this work is twofold. Firstly, there is a brief discussion regarding the change in nomenclature as well as epidemiology, risk factors, and pathophysiologic mechanisms other than hormonal effects, which include nutrition and the gut microbiome, as well as genetic and epigenetic influences. Secondly, we review the basis of the most important hormonal factors involved in the development and progression of MAFLD that act both independently and in an interrelated manner.

Roles and mechanisms of CircRNAs in ovarian cancer

Ovarian cancer (OC) is one of the female malignancies with nearly 45% 5-year survival rate. Circular RNAs (circRNAs), a kind of single-stranded non-coding RNAs, are generated from the back-splicing of cellular housekeeping noncoding RNAs and precursor messenger RNAs. Recent studies revealed that circRNAs have different biological function, including sponging miRNAs, encoding micropeptides, regulating stability of cytoplasmic mRNAs, affecting transcription and splicing, via interacting with DNA, RNA and proteins. Due to their stability, circRNAs have the potential of acting as biomarkers and treatment targets. In this review, we briefly illustrate the biogenesis mechanism and biological function of circRNAs in OC, and make a perspective of circRNAs drug targeting immune responses and signaling pathways in OC. This article can provide a systematic view into the current situation and future of circRNAs in OC.

Suppressing circ_0008494 inhibits HSCs activation by regulating the miR-185-3p/Col1a1 axis

Background: Hepatic fibrosis (HF) is characterized by activation of hepatic stellate cells (HSCs) and extensive deposition of extracellular matrix components, especially collagens. However, effective antifibrotic therapies are still lacking. Recently, circular RNAs (circRNAs) have been identified as novel regulators of HF. Methods: circRNAs profile was screened by RNA sequencing and the location of circ_0008494 was confirmed by fluorescence in situ hybridization assay in human HF tissues. Bioinformatics analysis was used for result prediction and dual-luciferase reporter, together with AGO-RIP and biotin-coupled miRNA capture assays, were used to determine miR-185-3p/collagen type I alpha 1 chain (Col1a1) as the target of circ_0008494. A stable circ_0008494-interfering human HSCs cell line was constructed and used to determine the regulatory mechanism of circ_0008494/miR-185-3p/Col1a1 axis. Results: circ_0008494 was abundantly and significantly over-expressed in human HF tissues and located at the cytoplasm of HSCs. Together, dual-luciferase reporter, AGO-RIP and biotin-coupled miRNA capture assays confirmed that circ_0008494 acted as a sponge of miR-185-3p. Cell functional experiments and rescue assays demonstrated suppressing circ_0008494 could inhibit activation, proliferation, migration of HSCs and promote their apoptosis through miR-185-3p. In particular, the HF indicator, Col1a1, was validated as the direct target of miR-185-3p and the suppression of circ_0008494 inhibited the expression of Col1a1 by releasing miR-185-3p. Conclusion: Knocking down circ_0008494 inhibited HSCs activation through the miR-185-3p/Col1a1 axis. circ_0008494 could be a promising treatment target for HF.

The role of microRNAs on the pathogenesis, diagnosis and management of portal hypertension in patients with chronic liver disease

INTRODUCTION

Portal hypertension (PH) is the elevated pressure in the portal vein, which results in poor functioning of the liver and is influenced by various factors like liver cirrhosis, nonalcoholic fatty liver disease, schistosomiasis, thrombosis, and angiogenesis. Though the diagnosis and treatment have been advanced, early diagnosis of the disease remains a challenge, and the diagnosis methods are often invasive. Hence, the clear understanding of the molecular mechanisms of PH can give rise to the development of novel biomarkers which can pave way for early diagnosis in noninvasive methods, and also the identification of target genes can elucidate an efficient therapeutic target.

AREAS COVERED

PubMed and Embase database was used to search articles with search terms 'Portal Hypertension' or 'pathophysiology' and 'diagnosis' and 'treatment' or "role of miRNAs in portal hypertension.

EXPERT OPINION

Interestingly, biomarkers like microRNAs (miRNAs) have been studied for their potential role in various diseases including hypertension. In recent years, miRNAs have been proved to be an efficient biomarker and therapeutic target and few studies have assessed the roles of miRNAs in PH. The present paper highlights the potential roles of miRNAs in PH.

Non-coding RNAs in skin cancers:Biological roles and molecular mechanisms

Cutaneous malignancies, including basal cell carcinoma, cutaneous squamous cell carcinoma, and cutaneous melanoma, are common human tumors. The incidence of cutaneous malignancies is increasing worldwide, and the leading cause of death is malignant invasion and metastasis. The molecular biology of oncogenes has drawn researchers’ attention because of the potential for targeted therapies. Noncoding RNAs, including microRNAs, long noncoding RNAs, and circular RNAs, have been studied extensively in recent years. This review summarizes the aspects of noncoding RNAs related to the metastasis mechanism of skin malignancies. Continuous research may facilitate the identification of new therapeutic targets and help elucidate the mechanism of tumor metastasis, thus providing new opportunities to improve the survival rate of patients with skin malignancies.

Epigenetic Aspects and Prospects in Autoimmune Hepatitis

The observed risk of autoimmune hepatitis exceeds its genetic risk, and epigenetic factors that alter gene expression without changing nucleotide sequence may help explain the disparity. Key objectives of this review are to describe the epigenetic modifications that affect gene expression, discuss how they can affect autoimmune hepatitis, and indicate prospects for improved management. Multiple hypo-methylated genes have been described in the CD4⁺ and CD19⁺ T lymphocytes of patients with autoimmune hepatitis, and the circulating micro-ribonucleic acids, miR-21 and miR-122, have correlated with laboratory and histological features of liver inflammation. Both epigenetic agents have also correlated inversely with the stage of liver fibrosis. The reduced hepatic concentration of miR-122 in cirrhosis suggests that its deficiency may de-repress the pro-fibrotic prolyl-4-hydroxylase subunit alpha-1 gene. Conversely, miR-155 is over-expressed in the liver tissue of patients with autoimmune hepatitis, and it may signify active immune-mediated liver injury. Different epigenetic findings have been described in diverse autoimmune and non-autoimmune liver diseases, and these changes may have disease-specificity. They may also be responses to environmental cues or heritable adaptations that distinguish the diseases. Advances in epigenetic editing and methods for blocking micro-ribonucleic acids have improved opportunities to prove causality and develop site-specific, therapeutic interventions. In conclusion, the role of epigenetics in affecting the risk, clinical phenotype, and outcome of autoimmune hepatitis is under-evaluated. Full definition of the epigenome of autoimmune hepatitis promises to enhance understanding of pathogenic mechanisms and satisfy the unmet clinical need to improve therapy for refractory disease.

Inflammasomes and Pyroptosis of Liver Cells in Liver Fibrosis

Inflammasomes are multiprotein complexes that can sense danger signals and activate caspase-1 to mediate pro-inflammatory cytokines release and pyroptotic cell death. There are two main canonical and non-canonical signaling pathways that trigger inflammasome activation. Inflammasomes are expressed and assembled in parenchymal and nonparenchymal cells in response to liver injury in the liver. Additionally, the hepatocytes, biliary epithelial cells (cholangiocytes), hepatic stellate cells (HSCs), hepatic macrophages, and liver sinusoidal endothelial cells (LSECs) contribute to liver fibrosis via different mechanisms. However, the underlying mechanism of the inflammasome and pyroptosis in these liver cells in liver fibrosis remains elusive. This review summarizes the activation and function of inflammasome complexes and then discusses the association between inflammasomes, pyroptosis, and liver fibrosis. Unlike other similar reviewers, we will focus on the effect of inflammasome activation and pyroptosis in the various liver cells during the development of liver fibrosis. We will also highlight the latest progress of pharmacological intervention in inflammasome-mediated liver fibrosis.

Role of Immune Cells in Biliary Repair

The biliary system is comprised of cholangiocytes and plays an important role in maintaining liver function. Under normal conditions, cholangiocytes remain in the stationary phase and maintain a very low turnover rate. However, the robust biliary repair is initiated in disease conditions, and different repair mechanisms can be activated depending on the pathological changes. During biliary disease, immune cells including monocytes, lymphocytes, neutrophils, and mast cells are recruited to the liver. The cellular interactions between cholangiocytes and these recruited immune cells as well as hepatic resident immune cells, including Kupffer cells, determine disease outcomes. However, the role of immune cells in the initiation, regulation, and suspension of biliary repair remains elusive. The cellular processes of cholangiocyte proliferation, progenitor cell differentiation, and hepatocyte-cholangiocyte transdifferentiation during biliary diseases are reviewed to manifest the underlying mechanism of biliary repair. Furthermore, the potential role of immune cells in crucial biliary repair mechanisms is highlighted. The mechanisms of biliary repair in immune-mediated cholangiopathies, inherited cholangiopathies, obstructive cholangiopathies, and cholangiocarcinoma are also summarized. Additionally, novel techniques that could clarify the underlying mechanisms of biliary repair are displayed. Collectively, this review aims to deepen the understanding of the mechanisms of biliary repair and contributes potential novel therapeutic methods for treating biliary diseases.

Noncoding RNAs in the Glycolysis of Ovarian Cancer

Energy metabolism reprogramming is the characteristic feature of tumors. The tumorigenesis, metastasis, and drug resistance of ovarian cancer (OC) is dependent on energy metabolism. Even under adequate oxygen conditions, OC cells tend to convert glucose to lactate, and glycolysis can rapidly produce ATP to meet their metabolic energy needs. Non-coding RNAs (ncRNAs) interact directly with DNA, RNA, and proteins to function as an essential regulatory in gene expression and tumor pathology. Studies have shown that ncRNAs regulate the process of glycolysis by interacting with the predominant glycolysis enzyme and cellular signaling pathway, participating in tumorigenesis and progression. This review summarizes the mechanism of ncRNAs regulation in glycolysis in OC and investigates potential therapeutic targets.

The function and regulation network mechanism of circRNA in liver diseases

Circular RNA (circRNA), a new type of endogenous non-coding RNA, is abundantly present in eukaryotic cells, and characterized as stable high conservation and tissue specific expression. It has been generated increasing attention because of their close association with the progress of diseases. The liver is the vital organ of humans, while it is prone to acute and chronic diseases due to the influence of multiple pathogenic factors. Moreover, hepatocellular carcinoma (HCC) is the one of most common cancer and the leading cause of cancer death worldwide. Overwhelming evidences indicate that some circRNAs are differentially expressed in liver diseases, such as, HCC, chronic hepatitis B, hepatic steatosis and hepatoblastoma tissues, etc. Additionally, these circRNAs are related to proliferation, invasion, migration, angiogenesis, apoptosis, and metastasis of cell in liver diseases and act as oncogenic agents or suppressors, and linked to clinical manifestations. In this review, we briefly summarize the biogenesis, characterization and biological functions, recent detection and identification technologies of circRNA, and regulation network mechanism of circRNA in liver diseases, and discuss their potential values as biomarkers or therapeutic targets for liver diseases, especially on HCC.

The Emerging Roles of Circular RNAs in the Chemoresistance of Gastrointestinal Cancer

Gastrointestinal (GI) cancer represents a major global health problem due to its aggressive characteristics and poor prognosis. Despite the progress achieved in the development of treatment regimens, the clinical outcomes and therapeutic responses of patients with GI cancer remain unsatisfactory. Chemoresistance arising throughout the clinical intervention is undoubtedly a critical barrier for the successful treatment of GI cancer. However, the precise mechanisms associated with chemoresistance in GI cancer remain unclear. In the past decade, accumulating evidence has indicated that circular RNAs (circRNAs) play a key role in regulating cancer progression and chemoresistance. Notably, circRNAs function as molecular sponges that sequester microRNAs (miRNAs) and/or proteins, and thus indirectly control the expression of specific genes, which eventually promote or suppress drug resistance in GI cancer. Therefore, circRNAs may represent potential therapeutic targets for overcoming drug resistance in patients with GI cancer. This review comprehensively summarizes the regulatory roles of circRNAs in the development of chemoresistance in different GI cancers, including colorectal cancer, gastric cancer and esophageal cancer, as well as deciphers the underlying mechanisms and key molecules involved. Increasing knowledge of the important functions of circRNAs underlying drug resistance will provide new opportunities for developing efficacious therapeutic strategies against GI cancer.

Nonalcoholic Fatty Liver Disease (NAFLD): Pathogenesis and Noninvasive Diagnosis

The global prevalence of nonalcoholic fatty liver disease (NAFLD) or metabolic associated fatty liver disease (MAFLD), as it is now known, has gradually increased. NAFLD is a disease with a spectrum of stages ranging from simple fatty liver (steatosis) to a severe form of steatosis, nonalcoholic steatohepatitis (NASH), which could progress to irreversible liver injury (fibrosis) and organ failure, and in some cases hepatocellular carcinoma (HCC). Although a liver biopsy remains the gold standard for accurate detection of this condition, it is unsuitable for clinical screening due to a higher risk of death. There is thus an increased need to find alternative techniques or tools for accurate diagnosis. Early detection for NASH matters for patients because NASH is the marker for severe disease progression. This review summarizes the current noninvasive tools for NAFLD diagnosis and their performance. We also discussed potential and newer alternative tools for diagnosing NAFLD.

Noncoding RNAs Interactions in Hepatic Stellate Cells during Hepatic Fibrosis

Hepatic fibrosis is a reversible wound healing process following liver injury. Although this process is necessary for maintaining liver integrity, severe excessive extracellular matrix accumulation (ECM) could lead to permanent scar formation and destroy the liver structure. The activation of hepatic stellate cells (HSCs) is a key event in hepatic fibrosis. Previous studies show that most antifibrotic therapies focus on the apoptosis of HSCs and the prevention of HSC activation. Noncoding RNAs (ncRNAs) play a substantial role in HSC activation and are likely to be biomarkers or therapeutic targets for the treatment of hepatic fibrosis. This review summarizes and discusses the previously reported ncRNAs, including the microRNAs, long noncoding RNAs, and circular RNAs, highlighting their regulatory roles and interactions in the signaling pathways that regulate HSC activation in hepatic fibrosis.

Mechanism and Therapeutic Opportunities of Histone Modifications in Chronic Liver Disease

Chronic liver disease (CLD) represents a global health problem, accounting for the heavy burden of disability and increased health care utilization. Epigenome alterations play an important role in the occurrence and progression of CLD. Histone modifications, which include acetylation, methylation, and phosphorylation, represent an essential part of epigenetic modifications that affect the transcriptional activity of genes. Different from genetic mutations, histone modifications are plastic and reversible. They can be modulated pharmacologically without changing the DNA sequence. Thus, there might be chances to establish interventional solutions by targeting histone modifications to reverse CLD. Here we summarized the roles of histone modifications in the context of alcoholic liver disease (ALD), metabolic associated fatty liver disease (MAFLD), viral hepatitis, autoimmune liver disease, drug-induced liver injury (DILI), and liver fibrosis or cirrhosis. The potential targets of histone modifications for translation into therapeutics were also investigated. In prospect, high efficacy and low toxicity drugs that are selectively targeting histone modifications are required to completely reverse CLD and prevent the development of liver cirrhosis and malignancy.