Circular RNA cMTO1 Promotes PTEN Expression Through Sponging miR-181b-5p in Liver Fibrosis

Systematic loss-of-function screens identify pathway-specific functional circular RNAs

Circular RNA (circRNA) is covalently closed, single-stranded RNA produced by back-splicing. A few circRNAs have been implicated as functional; however, we lack understanding of pathways that are regulated by circRNAs. Here we generated a pooled short-hairpin RNA library targeting the back-splice junction of 3,354 human circRNAs that are expressed at different levels (ranging from low to high) in humans. We used this library for loss-of-function proliferation screens in a panel of 18 cancer cell lines from four tissue types harbouring mutations leading to constitutive activity of defined pathways. Both context-specific and non-specific circRNAs were identified. Some circRNAs were found to directly regulate their precursor, whereas some have a function unrelated to their precursor. We validated these observations with a secondary screen and uncovered a role for circRERE(4-10) and circHUWE1(22,23), two cell-essential circRNAs, circSMAD2(2-6), a WNT pathway regulator, and circMTO1(2,RI,3), a regulator of MAPK signalling. Our work sheds light on pathways regulated by circRNAs and provides a catalogue of circRNAs with a measurable function.

The Role of the MiR-181 Family in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the fourth-leading cause of cancer-related death worldwide. Due to the high mortality rate in HCC patients, discovering and developing novel systemic treatment options for HCC is a vital unmet medical need. Among the numerous molecular alterations in HCCs, microRNAs (miRNAs) have been increasingly recognised to play critical roles in hepatocarcinogenesis. We and others have recently revealed that members of the microRNA-181 (miR-181) family were up-regulated in some, though not all, human cirrhotic and HCC tissues-this up-regulation induced epithelial-mesenchymal transition (EMT) in hepatocytes and tumour cells, promoting HCC progression. MiR-181s play crucial roles in governing the fate and function of various cells, such as endothelial cells, immune cells, and tumour cells. Previous reviews have extensively covered these aspects in detail. This review aims to give some insights into miR-181s, their targets and roles in modulating signal transduction pathways, factors regulating miR-181 expression and function, and their roles in HCC.

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.

Enhanced reparatory effect of EI1 on dental pulp via extracellular matrix remodeling by miR-181b-2-3p inhibitor

Background/purpose

Extracellular matrix (ECM) is crucial for dental pulp repair. The aim of this paper is to investigate the ECM remodeling effect of miR-181b-2-3p (a microRNA) and to verify the reparatory effect of EI1 (an epigenetic drug) and miR-181b-2-3p inhibitor on dental pulp.

Materials and methods

Levels of ECM-related factors in EI1-treated human dental pulp cells (hDPCs) were measured by qRT-PCR and Western blot. The anti-inflammation effect of EI1 was examined in Lipopolysaccharide-stimulated hDPCs. miR-181b-2-3p mimics or inhibitors were transfected into hDPCs and then the cells' functions were detected. A dual luciferase reporter assay was used to identify the targets of miR-181b-2-3p. Pulpotomy using miR-181b-2-3p antagomirs and EI1 as pulp capping materials was performed in male six-week-old Sprague-Dawley rats.

Results

EI1 upregulated ECM-related genes expression in hDPCs, but failed to upregulate the collagen1A1 (COL1A1) protein level. Pro-inflammatory factors were downregulated by EI1 in Lipopolysaccharide-stimulated hDPCs. Overexpression of miR-181b-2-3p downregulated the expression of transforming growth factor-β2 (TGF-β2) and fibronectin type III domain-containing protein 5 precursor (FNDC5), while the inhibition had the opposite effect. Dual luciferase reporter assays demonstrated that miR-181b-2-3p targets TGF-β2, FNDC5 and integrin alpha 4 protein (ITGA4). Compared to EI1 was used alone, EI1 combined with the inhibitor upregulated the protein levels of COL1A1, fibronectin (FN1) and TGF-β2 in hDPCs, promoted hDPCs migration, and exhibited reparatory effects on inflamed rat pulp tissue.

Conclusion

miR-181b-2-3p inhibitor could enhance the reparatory effect of EI1 via ECM remodeling in dental pulp both in vitro and in vivo.

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.

Integrated mRNA and microRNA profiling in lung tissue and blood from human silicosis

BACKGROUND

The overwhelming majority of subjects in the current silicosis mRNA and microRNA (miRNA) expression profile are of human blood, lung cells or a rat model, which puts limits on the understanding of silicosis pathogenesis and therapy. To address the limitations, our investigation was focused on differentially expressed mRNA and miRNA profiles in lung tissue from silicosis patients to explore potential biomarker for early detection of silicosis.

METHODS

A transcriptome study was conducted based on lung tissue from 15 silicosis patients and eight normal people, and blood samples from 404 silicosis patients and 177 normal people. Three early stage silicosis, five advanced silicosis and four normal lung tissues were randomly selected for microarray processing and analyze. The differentially expressed mRNAs were further used to conduct Gene Ontology and pathway analyses. Series test of cluster was performed to explore possible changes in differentially expressed mRNA and miRNA expression patterns during the process of silicosis. The blood samples and remaining lung tissues were used in a quantitative real-time PCR (RT-qPCR) (RT-qPCR).

RESULTS

In total, 1417 and 241 differentially expressed mRNAs and miRNAs were identified between lung tissue from silicosis patients and normal people (p < 0.05). However, there was no significant difference in most mRNA or miRNA expression between early stage and advanced stage silicosis lung tissues. RT-qPCR validation results in lung tissues showed expression of four mRNAs (HIF1A, SOCS3, GNAI3 and PTEN) and seven miRNAs was significantly down-regulated compared to those of control group. Nevertheless, PTEN and GNAI3 expression was significantly up-regulated (p < 0.001) in blood samples. The bisulfite sequencing PCR demonstrated that PTEN had significantly decreased the methylation rate in blood samples of silicosis patients.

CONCLUSIONS

PTEN might be a potential biomarker for silicosis as a result of low methylation in the blood.

Overview of CircRNAs Roles and Mechanisms in Liver Fibrosis

Liver fibrosis represents the reversible pathological process with the feature of the over-accumulation of extracellular matrix (ECM) proteins within the liver, which results in the deposition of fibrotic tissues and liver dysfunction. Circular noncoding RNAs (CircRNAs) have the characteristic closed loop structures, which show high resistance to exonuclease RNase, making them far more stable and recalcitrant against degradation. CircRNAs increase target gene levels by playing the role of a microRNA (miRNA) sponge. Further, they combine with proteins or play the role of RNA scaffolds or translate proteins to modulate different biological processes. Recent studies have indicated that CircRNAs play an important role in the occurrence and progression of liver fibrosis and may be the potential diagnostic and prognostic markers for liver fibrosis. This review summarizes the CircRNAs roles and explores their underlying mechanisms, with a special focus on some of the latest research into key CircRNAs related to regulating liver fibrosis. Results in this work may inspire fruitful research directions and applications of CircRNAs in the management of liver fibrosis. Additionally, our findings lay a critical theoretical foundation for applying CircRNAs in diagnosing and treating liver fibrosis.

CircRNAs: versatile players and new targets in organ fibrosis

Organ fibrosis can occur in virtually all major organs with relentlessly progressive and irreversible progress, ultimately resulting in organ dysfunction and potentially death. Unfortunately, current clinical treatments cannot halt or reverse the progression of fibrosis to end-stage organ failure, and thus, advanced antifibrotic therapeutics are urgently needed. In recent years, a growing body of research has revealed that circular RNAs (circRNAs) play pivotal roles in the development and progression of organ fibrosis through highly diverse mechanisms of action. Thus, manipulating circRNAs has emerged as a promising strategy to mitigate fibrosis across different organ types. In this review, we systemically summarize the current state of knowledge about circRNA biological properties and the regulatory mechanisms of circRNAs. A comprehensive overview of major fibrotic signaling pathways and representative circRNAs that are known to modulate fibrotic signals are outlined. Then, we focus on the research progress of the versatile functional roles and underlying molecular mechanisms of circRNAs in various fibrotic diseases in different organs, including the heart, liver, lung, kidney and skin. Finally, we offer a glimpse into the prospects of circRNA-based interference and therapy, as well as their utilization as biomarkers in the diagnosis and prognosis of fibrotic diseases. Video abstract.

Small-molecule natural plants for reversing liver fibrosis based on modulation of hepatic stellate cells activation: An update

BACKGROUND

Liver fibrosis (LF) is a trauma repair process carried out by the liver in response to various acute and chronic liver injuries. Its primary pathological characteristics are excessive proliferation and improper dismissal of the extracellular matrix, and if left untreated, it will progress into cirrhosis, liver cancer, and other diseases. Hepatic stellate cells (HSCs) activation is intimately associated to the onset of LF, and it is anticipated that addressing HSCs proliferation can reverse LF. Plant-based small-molecule medications have anti-LF properties, and their mechanisms of action involve suppression of extracellular matrix abnormally accumulating as well as anti-inflammation and anti-oxidative stress. New targeting HSC agents will therefore be needed to provide a potential curative response.

PURPOSE

The most recent HSC routes and small molecule natural plants that target HSC described domestically and internationally in recent years were examined in this review.

METHODS

The data was looked up using resources including ScienceDirect, CNKI, Web of Science, and PubMed. Keyword searches for information on hepatic stellate cells included "liver fibrosis", "natural plant", "hepatic stellate cells", "adverse reaction", "toxicity", etc. RESULTS: We discovered that plant monomers can target and control various pathways to prevent the activation and proliferation of HSC and promote the apoptosis of HSC in order to achieve the anti-LF effect in this work by compiling the plant monomers that influence many common pathways of HSC in recent years. It demonstrates the wide-ranging potential of plant monomers targeting different routes to combat LF, with a view to supplying new concepts and new strategies for natural plant therapy of LF as well as research and development of novel pharmaceuticals. The investigation of kaempferol, physalin B, and other plant monomers additionally motivated researchers to focus on the structure-activity link between the main chemicals and LF.

CONCLUSION

The creation of novel pharmaceuticals can benefit greatly from the use of natural components. They are often harmless for people, non-target creatures, and the environment because they are found in nature, and they can be employed as the starting chemicals for the creation of novel medications. Natural plants are valuable resources for creating new medications with fresh action targets because they feature original and distinctive action mechanisms.

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.

Mesenchymal stem cell-derived exosomes and non-coding RNAs: Regulatory and therapeutic role in liver diseases

Liver disease has become a major health problem worldwide due to its high morbidity and mortality. In recent years, a large body of literature has shown that mesenchymal stem cell-derived exosomes (MSC-Exo) are able to play similar physiological roles as mesenchymal stem cells (MSCs). More importantly, there is no immune rejection caused by transplanted cells and the risk of tumor formation, which has become a new strategy for the treatment of various liver diseases. Moreover, accumulating evidence suggests that non-coding RNAs (ncRNAs) are the main effectors by which they exert hepatoprotective effects. Therefore, by searching the databases of Web of Science, PubMed, ScienceDirect, Google Scholar and CNKI, this review comprehensively reviewed the therapeutic effects of MSC-Exo and ncRNAs in liver diseases, including liver injury, liver fibrosis, and hepatocellular carcinoma. According to the data, the therapeutic effects of MSC-Exo and ncRNAs on liver diseases are closely related to a variety of molecular mechanisms, including inhibition of inflammatory response, alleviation of liver oxidative stress, inhibition of apoptosis of hepatocytes and endothelial cells, promotion of angiogenesis, blocking the cell cycle of hepatocellular carcinoma, and inhibition of activation and proliferation of hepatic stellate cells. These important findings will provide a direction and basis for us to explore the potential of MSC-Exo and ncRNAs in the clinical treatment of liver diseases in the future.

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.

Circular RNA as a Novel Biomarker and Therapeutic Target for HCC

Circular RNA (circRNA) is a kind of endogenous non-coding RNA (ncRNA), which is produced by the reverse splicing of precursor mRNA (pre mRNA). It is widely expressed in a variety of biological cells. Due to the special formation mode, circRNA does not have a 5′ terminal cap and 3′ poly (A) tail structure. Compared with linear RNA, circRNA is more stable to exonuclease and ribonuclease. In addition, circRNA is structurally conserved, has a stable sequence and is tissue-specific. With the development of high-throughput sequencing and bioinformatics technology, more and more circRNAs have been found. CircRNA plays an important pathophysiological role in the occurrence and development of alcoholic liver injury (ALI), hepatic fibrosis (HF), hepatocellular carcinoma (HCC), and other liver diseases. Our group has been committed to the research of liver disease diagnosis and treatment targets. We review the function and mechanism of circRNA in ALI, HF and HCC, expecting to provide new ideas for the diagnosis, treatment, and prognosis of liver diseases.

Orientin Alleviates Liver Inflammation via Downregulation of ZEB-2/PTEN Markers—Hepatic Stellate Cells Approach

Liver inflammation is associated with an increased risk of liver fibrosis that substantially progresses to cirrhosis. Recently, usage of the herbal supplement has been increased because of its emerging role to dominate oxidative stress in hepatic injury. Orientin is one of the bioactive flavonoids that possesses a diversity of curative activities. Therefore, the present study was conducted to evaluate the anti-inflammatory role of orientin (1 mg/kg) in vitro in lipopolysaccharide (LPS)-induced inflammation in hepatic stellate cells (HSCs) and in vivo in carbon tetrachloride (CCl4)-induced liver fibrosis in mice. Moreover, the current study was supported by in silico investigation. Orientin demonstrated protection against LPS-induced HSC inflammation as evidenced by a decrease in iNOS, NO, and TNF-α and inhibition of the fibrotic markers ZEB-2 and PTEN. In addition, orientin afforded protection against CCl4-induced liver fibrosis in mice as shown from decreased AST/ALT ratio, inhibition of the pro-inflammatory mediators TNF-α, IL-6, IL-8, and IFN-γ, reduction of fibrotic markers ZEB-2 and PTEN, and improvement of the histopathological changes. Furthermore, the docking study demonstrated virtual interactions of orientin with ZEB-2 and PTEN. Taken together, the current study suggested that the protective effects of orientin against LPS- and CCl4-induced liver inflammation are via inhibition of fibrotic markers and reduction of pro-inflammatory mediators.

Diagnostic Accuracy of Circular RNAs in Different Types of Samples for Detecting Hepatocellular Carcinoma: A Meta-Analysis

The lack of accurate biomarkers impeded the screening, diagnosis and early treatment of hepatocellular carcinoma (HCC). As a result of the development of high-throughput transcriptome analysis techniques, circular RNAs, a newly discovered class of noncoding RNAs, were recognized as potential novel biomarkers. This meta-analysis was performed to update the diagnostic roles of circular RNAs for HCC. We acquired 23 articles from PubMed, Web of Science, EMBASE, and Cochrane Library databases up to September 2021. The overall sensitivity was 0.80 (95% CI: 0.77–0.84), and the specificity was 0.83 (95% CI: 0.79–0.85), with an AUC of 0.88 (0.85–0.91). Considering of the significant heterogeneity, studies were divided into four groups based on the control types. The circular RNAs in exosomes had a sensitivity of 0.69 (95% CI: 0.61–0.75), and a highest specificity of 0.91 (95% CI: 0.83–0.96). The pooled sensitivity of circular RNAs in serum/plasma was 0.84 (95% CI: 0.81–0.87), and the pooled specificity was 0.83 (95% CI: 0.79–0.86). The pooled sensitivity of circular RNAs distinguishing tumor tissue from chronic hepatitis/cirrhosis tissues was 0.56 (95% CI: 0.48–0.64), and specificity was 0.76 (95% CI: 0.67–0.82). When the controls were adjacent tissues, the sensitivity was 0.78 (95% CI: 0.70–0.84), and the specificity was 0.78 (95% CI: 0.71–0.85). Hsa_circ_0001445 with a pooled sensitivity of 0.81, a specificity of 0.76 and an AUC of 0.85 in two studies, might be a suitable diagnostic blood biomarker for HCC. Relying on function in HCC, the AUC of subgroups were 0.88 (95%CI: 0.84–0.90) (function group) and 0.87 (95%CI: 0.84–0.90) (unknown function group). As for only reported in HCC or not, these circular RNAs had an AUC of 0.89 (95%CI: 0.86–0.91) (only in HCC) and 0.85 (95%CI: 0.82–0.88) (not only in HCC). In conclusion, the results suggested that circular RNAs were acceptable biomarkers for detecting HCC, especially those circular RNAs existing in exosomes or serum/plasma.

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.

Down-Regulation of CXXC5 De-Represses MYCL1 to Promote Hepatic Stellate Cell Activation

Liver fibrosis is mediated by myofibroblasts, a specialized cell type involved in wound healing and extracellular matrix production. Hepatic stellate cells (HSC) are the major source of myofibroblasts in the fibrotic livers. In the present study we investigated the involvement of CXXC-type zinc-finger protein 5 (CXXC5) in HSC activation and the underlying mechanism. Down-regulation of CXXC5 was observed in activated HSCs compared to quiescent HSCs both in vivo and in vitro. In accordance, over-expression of CXXC5 suppressed HSC activation. RNA-seq analysis revealed that CXXC5 influenced multiple signaling pathways to regulate HSC activation. The proto-oncogene MYCL1 was identified as a novel target for CXXC5. CXXC5 bound to the proximal MYCL1 promoter to repress MYCL1 transcription in quiescent HSCs. Loss of CXXC5 expression during HSC activation led to the removal of CpG methylation and acquisition of acetylated histone H3K9/H3K27 on the MYCL1 promoter resulting in MYCL1 trans-activation. Finally, MYCL1 knockdown attenuated HSC activation whereas MYCL1 over-expression partially relieved the blockade of HSC activation by CXXC5. In conclusion, our data unveil a novel transcriptional mechanism contributing to HSC activation and liver fibrosis.

Circular RNA as An Epigenetic Regulator in Chronic Liver Diseases

Circular RNA (circRNA) is a type of non-coding RNA characterized by a covalently closed continuous loop. CircRNA is generated by pre-mRNA through back-splicing and is probably cleared up by extracellular vesicles. CircRNAs play a pivotal role in the epigenetic regulation of gene expression at transcriptional and post-transcriptional levels. Recently, circRNAs have been demonstrated to be involved in the regulation of liver homeostasis and diseases. However, the epigenetic role and underlying mechanisms of circRNAs in chronic liver diseases remain unclear. This review discussed the role of circRNAs in non-neoplastic chronic liver diseases, including alcoholic liver disease (ALD), metabolic-associated fatty liver disease (MAFLD), viral hepatitis, liver injury and regeneration, liver cirrhosis, and autoimmune liver disease. The review also highlighted that further efforts are urgently needed to develop circRNAs as novel diagnostics and therapeutics for chronic liver diseases.

Circular RNA circUbe2k promotes hepatic fibrosis via sponging miR-149-5p/TGF-β2 axis

Abundant regulatory genes and complex circuits involving non-coding RNAs (ncRNAs) monitor the formation and development of hepatic fibrosis (HF). Circular RNAs (circRNAs) are a class of RNAs generated from protein coding genes by back-splicing, playing crucial roles in various pathological processes, including HF. However, little is known about mechanisms of action of circRNAs, let alone in HF. In this study, we found circUbe2k enhanced in CCl₄ -induced HF mice and LX-2 cells stimulated with TGF-β1, regulating the development of HF. Restraining the expression of circUbe2k inhibited α-SMA and Col1α1 expression in CCl₄ -induced HF mice and in LX-2 cells stimulated with TGF-β1. Furthermore, inhibiting circUbe2k expression reduced hepatic stellate cells (HSCs) activation and proliferation in vivo and in vitro. Mechanistically, we demonstrated a direct interaction between circUbe2k and miR-149-5p, which results in the modulation of TGF-β2 expressions. Together, circUbe2k may act as a "catalyst" of HSCs activation and HF through the circUbe2k/miR-149-5p/TGF-β2 axis. Our results provide unprecedented evidence for a significant role for circUbe2k to serve as a potential biomarker for HF therapy.

Role of circular RNAs in visceral organ fibrosis

Circular RNAs (circRNAs) are a novel class of noncoding RNAs produced during pre-mRNA splicing and are emerging as new members of the gene regulatory network. Unlike linear RNAs, circRNAs have a unique structure with a covalently closed loop formed from the ligation of exons, introns, or both. CircRNAs are widely expressed in various organisms in a species-, tissue-, developmental stage- and disease-specific manner; circRNAs have been demonstrated to play a vital role in the pathogenesis and progression of human diseases. Fibrosis is characterized by an abnormal excessive deposition of extracellular matrix (ECM) in the extracellular space and plays important roles in many different pathologies of various organs. CircRNAs function as master regulators of gene expression to "sponge" or sequester other genes and target gene expression, transcription, splicing, etc. Increasing evidence has revealed that circRNAs are tightly associated with fibrotic diseases in various organs, including the lungs, liver, heart and kidneys. Herein, we provide the current understanding of the molecular characteristics of circRNAs and summarize the findings from circRNA studies in which the functions and mechanisms of action of circRNAs in organ fibrosis were proposed.

Recent Update on the Role of Circular RNAs in Hepatocellular Carcinoma

After being overlooked for decades, circular RNAs (circRNAs) have recently generated considerable interest. circRNAs play a role in a variety of normal and pathological biological processes, including hepatocarcinogenesis. Many circRNAs contribute to hepatocarcinogenesis through sponging of microRNAs (miRs) and disruption of cellular signaling pathways that play a part in control of cell proliferation, metastasis and apoptosis. In most cases, overexpressed circRNAs sequester miRs to cause de-repressed translation of mRNAs that encode oncogenic proteins. Conversely, low expression of circRNAs has also been described in hepatocellular carcinoma (HCC) and is associated with inhibited production of tumor suppressor proteins. Other functions of circRNAs that contribute to hepatocarcinogenesis include translation of truncated proteins and acting as adapters to regulate influence of transcription factors on target gene expression. circRNAs also affect hepatocyte transformation indirectly. For example, the molecules regulate immune surveillance of cancerous cells and influence the liver fibrosis that commonly precedes HCC. Marked over- or under-expression of circRNA expression in HCC, with correlating plasma concentrations, has diagnostic utility and assays of these RNAs are being developed as biomarkers of HCC. Although knowledge in the field has recently surged, the myriad of described effects suggests that not all may be vital to hepatocarcinogenesis. Nevertheless, investigation of the role of circRNAs is providing valuable insights that are likely to contribute to improved management of a serious and highly aggressive cancer.

Circular RNA CircCOL5A1 Sponges the MiR-7-5p/Epac1 Axis to Promote the Progression of Keloids Through Regulating PI3K/Akt Signaling Pathway

Keloids, as a result of abnormal wound healing in susceptible individuals, are characterized by the hyper-proliferation of fibroblasts and exaggerated deposition of extracellular matrix. Current surgical and therapeutic modalities provide limited satisfactory results. Growing evidence has highlighted the roles of circRNAs in acting as miRNA sponges. However, up to date, the regulatory mechanism of circRNAs in the pathological process of keloids has rarely been reported. In this study, cell proliferation, cell migration, flow cytometry, western blotting, fluorescence in situ hybridization, dual-luciferase activity, and immunohistochemistry assays were applied to explore the roles and mechanisms of the circCOL5A1/miR-7-5p/Epac1 axis in the keloid. The therapeutic potential of circCOL5A1 was investigated by establishing keloid implantation models. The RT-qPCR result revealed that circCOL5A1 expression was obviously higher in keloid tissues and keloid fibroblasts. Subsequent cellular experiments demonstrated that circCOL5A1 knockdown repressed the proliferation, migration, extracellular matrix (ECM) deposition, whereas promoted cell apoptosis, through the PI3K/Akt signaling pathway. Furthermore, RNA-fluorescence in situ hybridization (RNA-FISH) illustrated that both circCOL5A1 and miR-7-5p were located in the cytoplasm. The luciferase reporter gene assay confirmed that exact binding sites were present between circCOL5A1 and miR-7-5p, as well as between miR-7-5p and Epac1. Collectively, the present study revealed that circCOL5A1 functioned as competing endogenous RNA (ceRNA) by adsorbing miR-7-5p to release Epac1, which contributed to pathological hyperplasia of keloids through activating the PI3K/Akt signaling pathway. Our data indicated that circCOL5A1 might serve as a novel promising therapeutic target and represent a new avenue to understand underlying pathogenesis for keloids.

CircAMOTL1 Promotes Tumorigenesis Through miR-526b/SIK2 Axis in Cervical Cancer

Background

Cervical cancer is one of the most common malignancies in women, leading to major health problems for its high morbidity and mortality. Numerous studies have demonstrated that circular RNAs (circRNAs) could be participated in the progression of multifarious diseases, especially plentiful carcinomas. CircAMOTL1 (angiomotin-like1, ID: hsa_circ_0004214), which is located on human chromosome 11:9 4532555-94533477, is involved in the occurrence of breast cancer, etc. However, the intrinsic and concrete molecular mechanism of circAMOTL1 in cervical carcinomas remained thoroughly unclear, which was also the bottleneck of circRNAs studies in cancer.

Methods

The relative expression levels of circAMOTL1 and miR-526b in cervical carcinoma patients’ specimens and cervical carcinoma cell lines were detected by RT-qPCR. Through experiments including loss-function and overexpression, the biological effects of circAMOTL1 and miR-526b on the proliferation, migration, apoptosis, and tumorigenicity were explored in cervical carcinomas. Dual luciferase reporter gene analysis, western blot, and other methods were adopted to explore the circAMOTL1 potential mechanism in cervical carcinomas.

Results

In our experiments, our researches displayed that circAMOTL1 was significantly higher expression in cervical carcinomas specimens and cell lines. Further experiments illustrated that the knockdown of circAMOTL1 could restrain the malignant phenotype, AKT signaling, and epithelial–mesenchymal transition (EMT) of in cervical carcinomas cells. Meanwhile miR-526b was downregulated in cervical carcinomas and even miR-526b could partially reverse circAMOTL1 function in malignant cervical tumor cells. CircAMOTL1 acts as a microRNA (miRNA) sponge that actively regulates the expression of salt-inducible kinase 2 (SIK2) to sponge miR-526b and subsequently increases malignant phenotypes of cervical carcinomas cells. In a word, circAMOTL1 acts a carcinogenic role and miR-526b serves as the opposite function of antioncogene in the cervical carcinoma pathogenesis.

Conclusion

CircAMOTL1-miR-526b-SIK2 axis referred to the malignant progression and development of cervical carcinomas. CircAMOTL1 expression was inversely correlated with miR-526b and positively correlated with SIK2 mRNA in cervical cancer tissues. Thus, circAMOTL1 exerted an oncogenic role in cervical cancer progression through sponging miR-526b. Taken together, our study revealed that circAMOTL1 acted as an oncogene and probably was a potential therapeutic target for the cervical cancer.

Cyclic RNA Circ_0000735 sponges miR-502-5p to promote bladder cancer cell proliferation and invasion and inhibit apoptosis

OBJECTIVE

The objective of this study was to investigate the effect on the proliferation, invasion, and apoptosis of bladder cancer cells through miR-502-5p of the Circ_0000735 circular RNA.

METHODS

Circ_0000735 and miR-502-5p expression of bladder cancer patients in malignant and paracancerous tissues was identified using qRT-PCR. Nucleoplasm isolation assay and RNase R enzymatic assay were used to classify Circ_0000735 subcellular origin and stability. Dual luciferase reporter assay and RIP assay were used to confirm Circ_0000735 and miR-502-5p targeting relationships. Cell proliferation, apoptosis, and invasion capacity were identified using CCK8, flow cytometry, and transwell assays. To confirm the effect of Circ_0000735 on tumorigenesis in nude mice, in vivo experiments were conducted.

RESULTS

Circ_0000735 expression was increased in bladder cancer tissues and cells compared with paraneoplastic tissues and normal cells, and miR-502-5p expression was reduced (both P<0.05). In the cytoplasm, Circ_0000735 was largely clustered and could not be digested by the RNase R enzyme, and ceRNA may play a role in bladder cancer cells. Circ_0000735 silencing prevented cell proliferation and invasion and facilitated apoptosis (all P<0.05). The incorporation of miR-502-5p inhibitor rescued the effect on bladder cancer cells of Circ_0000735 silencing. In vitro experiments showed that inhibition of Circ_0000735 expression was beneficial in suppressing tumorigenic ability in nude mice.

CONCLUSION

Circ_0000735 can adsorb miR-502-5p to promote bladder cancer cell proliferation and invasion and inhibit apoptosis. Circ_0000735 may be an effective molecular target for bladder cancer therapy.

Regulatory role of microRNAs on PTEN signaling

Phosphatase and tensin homolog (PTEN) gene encodes a tumor suppressor protein which is altered in several malignancies. This protein is a negative regulator of the PI3K/AKT signaling. Several transcription factors regulate the expression of PTEN in positive or negative directions. Moreover, numerous microRNAs (miRNAs) have functional interactions with PTEN and inhibit its expression. Suppression of PTEN can attenuate the response of cancer cells to chemotherapeutic agents. Based on the critical role of this tumor suppressor gene, the identification of negative regulators of its expression has practical significance particularly in the prevention and management of cancer. Meanwhile, the interaction between miRNAs and PTEN has functional consequences in non-malignant disorders including myocardial infarction, osteoporosis, cerebral ischemic stroke, and recurrent abortion. In the present review, we describe the role of miRNAs in the regulation of expression and activity of PTEN.