circRNA Mediates Silica-Induced Macrophage Activation Via HECTD1/ZC3H12A-Dependent Ubiquitination

Glutaminolysis regulates endometrial fibrosis in intrauterine adhesion via modulating mitochondrial function

BACKGROUND

Endometrial fibrosis, a significant characteristic of intrauterine adhesion (IUA), is caused by the excessive differentiation and activation of endometrial stromal cells (ESCs). Glutaminolysis is the metabolic process of glutamine (Gln), which has been implicated in multiple types of organ fibrosis. So far, little is known about whether glutaminolysis plays a role in endometrial fibrosis.

METHODS

The activation model of ESCs was constructed by TGF-β1, followed by RNA-sequencing analysis. Changes in glutaminase1 (GLS1) expression at RNA and protein levels in activated ESCs were verified experimentally. Human IUA samples were collected to verify GLS1 expression in endometrial fibrosis. GLS1 inhibitor and glutamine deprivation were applied to ESCs models to investigate the biological functions and mechanisms of glutaminolysis in ESCs activation. The IUA mice model was established to explore the effect of glutaminolysis inhibition on endometrial fibrosis.

RESULTS

We found that GLS1 expression was significantly increased in activated ESCs models and fibrotic endometrium. Glutaminolysis inhibition by GLS1 inhibitor bis-2-(5-phenylacetamido-1,2,4-thiadiazol-2-yl) ethyl sulfide (BPTES or glutamine deprivation treatment suppressed the expression of two fibrotic markers, α-SMA and collagen I, as well as the mitochondrial function and mTORC1 signaling in ESCs. Furthermore, inhibition of the mTORC1 signaling pathway by rapamycin suppressed ESCs activation. In IUA mice models, BPTES treatment significantly ameliorated endometrial fibrosis and improved pregnancy outcomes.

CONCLUSION

Glutaminolysis and glutaminolysis-associated mTOR signaling play a role in the activation of ESCs and the pathogenesis of endometrial fibrosis through regulating mitochondrial function. Glutaminolysis inhibition suppresses the activation of ESCs, which might be a novel therapeutic strategy for IUA.

Functional roles of circular RNAs in lung injury

Lung injury leads to respiratory dysfunction, low quality of life, and even life-threatening conditions. Circular RNAs (circRNAs) are endogenous RNAs produced by selective RNA splicing. Studies have reported their involvement in the progression of lung injury. Understanding the roles of circRNAs in lung injury may aid in elucidating the underlying mechanisms and provide new therapeutic targets. Thus, in this review, we aimed to summarize and discuss the characteristics and biological functions of circRNAs, and their roles in lung injury from existing research, to provide a theoretical basis for the use of circRNAs as a diagnostic and therapeutic target for lung injury.

Circ_0008657 regulates lung DNA damage induced by hexavalent chromium through the miR-203a-3p/ATM axis

Hexavalent chromium [Cr (VI)] is an important environmental pollutant and may cause lung injury when inhaled into the human body. Cr (VI) is genotoxic and can cause DNA damage, although the underlying epigenetic mechanisms remain unclear. To simulate the real-life workplace exposure to Cr (VI), we used a novel exposure dose calculation method. We evaluated the effect of Cr (VI) on DNA damage in human bronchial epithelial cells (16HBE and BEAS-2B) by calculating the equivalent real-time exposure dose of Cr (VI) (0 to 10 μM) in an environmental population. Comet experiments and olive tail moment measurements revealed increased DNA damage in cells exposed to Cr (VI). Cr (VI) treatment increased nuclear γ-H2AX foci and γ-H2AX protein expression, and caused DNA damage in the lung tissues of mice. An effective Cr (VI) dose (6 μM) was determined and used for cell treatment. Cr (VI) exposure upregulated circ_0008657, and knockdown of circ_0008657 decreased Cr (VI)-induced DNA damage, whereas circ_0008657 overexpression had the opposite effect. Mechanistically, we found that circ_0008657 binds to microRNA (miR)-203a-3p and subsequently regulates ATM serine/threonine kinase (ATM), a key protein involved in homologous recombination repair downstream of miR-203a-3p, thereby regulating DNA damage induced by Cr (VI). The present findings suggest that circ_0008657 competitively binds to miR-203a-3p to activate the ATM pathway and regulate the DNA damage response after environmental chemical exposure in vivo and in vitro.

Circular RNAs and their roles in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal lung disease with limited treatment options. Circular RNAs (circRNAs) have emerged as a novel class of non-coding RNAs with diverse functions in cellular processes. This review paper aims to explore the potential involvement of circRNAs in the pathogenesis of IPF and their diagnostic and therapeutic implications. We begin by providing an overview of the epidemiology and risk factors associated with IPF, followed by a discussion of the pathophysiology underlying this complex disease. Subsequently, we delve into the history, types, biogenesis, and functions of circRNAs and then emphasize their regulatory roles in the pathogenesis of IPF. Furthermore, we examine the current methodologies for detecting circRNAs and explore their diagnostic applications in IPF. Finally, we discuss the potential utility of circRNAs in the treatment of IPF. In conclusion, circRNAs hold great promise as novel biomarkers and therapeutic targets in the management of IPF.

circELP2 reverse-splicing biogenesis and function as a pro-fibrogenic factor by targeting mitochondrial quality control pathway

Idiopathic pulmonary fibrosis (IPF) is considered as a chronic, fibrosing interstitial pneumonia with unknown mechanism. The present work aimed to explore the function, biogenesis and regulatory mechanism of circELP2 in pulmonary fibrosis and evaluate the value of blocking circELP2-medicated signal pathway for IPF treatment. The results showed that heterogeneous nuclear ribonucleoprotein L initiated reverse splicing of circELP2 resulting in the increase of circELP2 generation. The biogenetic circELP2 activated the abnormal proliferation and migration of fibroblast and extracellular matrix deposition to promote pulmonary fibrogenesis. Mechanistic studies demonstrated that cytoplasmic circELP2 sponged miR-630 to increase transcriptional co-activators Yes-associated protein 1 (YAP1) and transcriptional co-activator with PDZ-binding motif (TAZ). Then, YAP1/TAZ bound to the promoter regions of their target genes, such as mTOR, Raptor and mLST8, which in turn activated or inhibited the genes expression in mitochondrial quality control pathway. Finally, the overexpressed circELP2 and miR-630 mimic were packaged into adenovirus vector for spraying into the mice lung to evaluate therapeutic effect of blocking circELP2-miR-630-YAP1/TAZ-mitochondrial quality control pathway in vivo. In conclusion, blocking circELP2-medicated pathway can alleviate pulmonary fibrosis, and circELP2 may be a potential target to treat lung fibrosis.

Alleviation of PM2.5-induced alveolar macrophage inflammation using extract of fermented Chenopodium formosanum Koidz sprouts via regulation of NF-κB pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Particulate matter 2.5 (PM2.5) is a dangerous airborne pollutant that has become a global issue due to its detrimental effect on macrophages. Chenopodium formosanum Koidz (Djulis), a native plant from Taiwan well known for its high antioxidant content and is frequently used in ethnomedicine, shows promise as a novel phytomedicine to combat against oxidative stress caused by PM2.5. However, the protective mechanism of Djulis against PM2.5 still remains unclear.

AIM OF THE STUDY

This study aimed to characterize the deleterious effect of emerging PM2.5 contaminants on the alveolar macrophage cell of the respiratory system and explore the underlying mechanisms in the suppression of PM2.5-induced inflammation using the extract of fermented Djulis.

METHODS AND MATERIALS

RNA sequencing, immunoblot, and ChIP assay approaches were used to gain insight into the deleterious effect of PM2.5 on the macrophage cell at the transcriptional and translational level; and to elucidate the contribution of fermented Djulis extract (FCS) as the remedy of PM-induced MH-S cell inflammation. UHPLC-ESI-MS/MS and LC-QQQ/MS were used to identify the bioactive compounds potentially contributing to phytomedicinal properties in the water fraction of FCS. Multiple ligands docking analysis was conducted to predict the in-silico interaction of Djulis metabolites and NF-κB.

RESULTS

Here, we showed that PM2.5 exposure at 200 ppm accelerated the production of intracellular ROS and phosphorylated NF-κB (p-NFκB), and negatively affecting the alveolar macrophage cell viability. Treating the cells with water-extracted FCS can restore their viability to 76% while simultaneously suppressing the generation of ROS and p-NFκB up to 38%. These ameliorative effects can be attributed to the occurrence of bioactive compounds such as gluconic acid, uridine, pantothenic acid, L-pyroglutamic acid, L-(-)-malic acid, and acetyl-L-carnitine in the water-extracted FCS which potentially dock to the RELA subunit site and consequently inhibit NF-κB activity along with its downstream inflammation signaling cascade.

CONCLUSION

This work demonstrated the hazardous effect of PM2.5 on alveolar macrophage and unveiled the potential of FCS as a therapeutic phytomedicine to alleviate PM-induced inflammation.

Macrophage-derived MMP12 promotes fibrosis through sustained damage to endothelial cells

Macrophages are essential for the maintenance of endothelial cell function. However, the potential impact and mechanisms of crosstalk between macrophages and endothelial cells during silicosis progression remain unexplored. To fill this knowledge gap, a mouse model of silicosis was established. Single cell sequencing, spatial transcriptome sequencing, western blotting, immunofluorescence staining, tube-forming and wound healing assays were used to explore the effects of silicon dioxide on macrophage-endothelial interactions. To investigate the mechanism of macrophage-mediated fibrosis, MMP12 was specifically inactivated using siRNA and pharmacological approaches, and macrophages were depleted using disodium chlorophosphite liposomes. Compared to the normal saline group, the silica dust group showed altered macrophage-endothelial interactions. Matrix metalloproteinase family member MMP12 was identified as a key mediator of the altered function of macrophage-endothelial interactions after silica exposure, which was accompanied by pro-inflammatory macrophage activation and fibrotic progression. By using ablation strategies, macrophage-derived MMP12 was shown to mediate endothelial cell dysfunction by accumulating on the extracellular matrix. During the inflammatory phase of silicosis, MMP12 secreted by pro-inflammatory macrophages caused decreased endothelial cell viability, reduced migration, decreased trans-endothelial resistance and increased permeability; while during the fibrotic phase, macrophage-derived MMP12 sustained endothelial cell injury through accumulation on the extracellular matrix.

CircZNF609 regulates pulmonary fibrosis via miR-145-5p/KLF4 axis and its translation function

BACKGROUND

Pulmonary fibrosis is a growing clinical problem that develops as a result of abnormal wound healing, leading to breathlessness, pulmonary dysfunction and ultimately death. However, therapeutic options for pulmonary fibrosis are limited because the underlying pathogenesis remains incompletely understood. Circular RNAs, as key regulators in various diseases, remain poorly understood in pulmonary fibrosis induced by silica.

METHODS

We performed studies with fibroblast cell lines and silica-induced mouse pulmonary fibrosis models. The expression of circZNF609, miR-145-5p, and KLF4 was determined by quantitative real-time polymerase chain reaction (qRT-PCR) analysis. RNA immunoprecipitation (RIP) assays and m6A RNA immunoprecipitation assays (MeRIP), Western blotting, immunofluorescence assays, and CCK8 were performed to investigate the role of the circZNF609/miR-145-5p/KLF4 axis and circZNF609-encoded peptides in fibroblast activation.

RESULTS

Our data showed that circZNF609 was downregulated in activated fibroblasts and silica-induced fibrotic mouse lung tissues. Overexpression of circZNF609 could inhibit fibroblast activation induced by transforming growth factor-β1 (TGF-β1). Mechanically, we revealed that circZNF609 regulates pulmonary fibrosis via miR-145-5p/KLF4 axis and circZNF609-encoded peptides. Furthermore, circZNF609 was highly methylated and its expression was controlled by N6-methyladenosine (m6A) modification. Lastly, in vivo studies revealed that overexpression of circZNF609 attenuates silica-induced lung fibrosis in mice.

CONCLUSIONS

Our data indicate that circZNF609 is a critical regulator of fibroblast activation and silica-induced lung fibrosis. The circZNF609 and its derived peptides may represent novel promising targets for the treatment of pulmonary fibrosis.

Macrophages enhance cisplatin resistance in gastric cancer through the transfer of circTEX2

Cisplatin-based chemotherapy is often used in advanced gastric cancer (GC) treatment, yet resistance to cisplatin may lead to treatment failure. Mechanisms underlying cisplatin resistance remain unclear. Recent evidence highlighted the role of macrophages in cancer chemoresistance. Macrophage-derived exosomes were shown to facilitate intercellular communication. Here, we investigated the cisplatin resistance mechanism based on macrophage-derived exosomes in gastric cancer. Cell growth and apoptosis detection experiments revealed that M2-polarized macrophages increased the resistance of GC cells to cisplatin. qRT-PCR, RNAase R assay, actinomycin D assay and cell nucleo-cytoplasmic separation experiments confirmed the existence of circTEX2 in macrophage cytoplasm, with a higher expression level in M2 macrophages than that in M1 macrophages. Further experiments showed that circTEX2 acted as microRNA sponges for miR-145 and regulated the expression of ATP Binding Cassette Subfamily C Member 1 (ABCC1). Inhibition of the circTEX2/miR-145/ABCC1 axis blocked the cisplatin resistance of gastric cancer induced by M2 macrophages, as evidenced by in vitro and in vivo experiments. In conclusion, our research suggests that the exosomal transfer of M2 macrophage-derived circTEX2 enhances cisplatin resistance in gastric cancer through miR-145/ABCC1. Additionally, communication between macrophages and cancer cells via exosomes may be a promising therapeutic target for the treatment of cisplatin-resistant gastric cancer.

ZC3H4 governs epithelial cell migration through ROCK/p-PYK2/p-MLC2 pathway in silica-induced pulmonary fibrosis

BACKGROUND

Increased epithelial migration capacity is a key step accompanying epithelial-mesenchymal transition (EMT). Our lab has described that ZC3H4 mediated EMT in silicosis. Here, we aimed to explore the mechanisms of ZC3H4 by which to stimulate epithelial cell migration.

METHODS

Silicon dioxide (SiO2)-induced pulmonary fibrosis (PF) animal models were administered by intratracheal instillation in C57BL/6 J mice. Pathological analysis and 2D migration assay were established to uncover the pulmonary fibrotic lesions and epithelial cell migration, respectively. Inhibitors targeting ROCK/p-PYK2/p-MLC2 and CRISPR/Cas9 plasmids targeting ZC3H4 were administrated to explore the signaling pathways.

RESULTS

1) SiO2 upregulated epithelial migration in pulmonary fibrotic lesions. 2) ZC3H4 modulated SiO2-induced epithelial migration. 3) ZC3H4 governed epithelial migration through ROCK/p-PYK2/p-MLC2 signaling pathway.

CONCLUSIONS

ZC3H4 regulates epithelial migration through the ROCK/p-PYK2/p-MLC2 signaling pathway, providing the possibility that molecular drugs targeting ZC3H4-overexpression may exert effects on pulmonary fibrosis induced by silica.

Crystalline Silica-Induced Proinflammatory Interstitial Macrophage Recruitment through Notch3 Signaling Promotes the Pathogenesis of Silicosis

Crystalline silica (CS) particles are ubiquitous in the environment, especially in occupational conditions, and exposure to respirable CS causes silicosis. The initial response to CS is mediated by innate immunity, where pulmonary macrophages act as central orchestrators. However, the repercussions of CS on functionally distinct macrophage subsets remain to be inconclusive. Herein, to study the effects of inhaled CS, we divided macrophages into three subsets: circulating monocytes, interstitial macrophages (IMs), and alveolar macrophages (AMs). CS-induced massive IMs increase in the lung, the phenotype and function of which differed from those of tissue-resident AMs and circulating monocytes. The augmented IMs were driven by recruitment of circulating macrophages rather than cell proliferation in situ. Moreover, the IMs predominantly exerted a classic activated (M1) phenotype and expressed proinflammatory cytokines, contributing to CS-induced lung injury. Notably, we demonstrated that IMs augmented Notch3 expression. Mechanistically, using myeloid-specific Notch3-knockout mice, we demonstrated that Notch3 signaling not only promoted IMs recruitment by regulating CCR2 expression but also manipulated the proinflammatory phenotype. Mice with conditional Notch3-knockout exhibited alleviation of CS-induced inflammation and fibrosis in lung. Overall, our study identifies IMs as critical mediators in response to CS and highlights the role of Notch3 in IMs recruitment and activation, providing new insights into CS toxicological effects in the lung.

Yangqing Chenfei formula alleviates crystalline silica induced pulmonary inflammation and fibrosis by suppressing macrophage polarization

OBJECTIVE

To explore the underlying mechanisms of the effects of Yangqing Chenfei formula (, YCF) on inflammation and fibrosis in silicosis via inhibition of macrophage polarization.

METHODS

A silicotic rat model was established via a single intratracheal instillation of silica particles on the first day of week 0. Subsequently, YCF was administered intragastrically to silicotic rats during weeks 0-2 and 5-8 twice daily. The mouse-derived alveolar macrophage cell line was used to investigate the mechanisms of YCF in M1/M2 polarization.

RESULTS

YCF treatment effectively inhibited lung pathological changes, including inflammatory cell infiltration and tissue damage, and increased the forced expiratory volume in the first 0.3 s, functional residual capacity, and maximal mid-expiratory flow in weeks 2 and 8. Furthermore, the treatment improved lung functions by upregulating tidal volume, pause increase, and expiratory flow at 50% tidal volume from weeks 5 to 8. Moreover, YCF could significantly suppressed the progression of inflammation and fibrosis, by reducing the levels of inflammatory cytokines, as well as collagen- I and III. YCF treatment also decreased the numbers of macrophages and M1/M2 macrophages and the level of transforming growth factor-β (TGF-β). Additionally, YCF5, the effective substance in YCF, decreased lipopolysaccharide and interferon-γ-induced M1 macrophage polarization in a concentration-dependent manner. The mechanism of anti-M1 polarization might be related to a decrease in extracellular signal-regulated kinase, c-JUN N-terminal kinase, P38, and P65 phosphorylation. Furthermore, YCF5 inhibited interleukin-4-induced M2 macrophages by decreasing the protein and mRNA expressions of arginase-1 and CD206 as well as the levels of profibrotic factors, such as TGF-β and connective tissue growth factor. The mechanisms underlying the anti-M2 polarization of YCF5 were primarily associated with the inhibition of the nuclear translocation of phosphorylated signal transducer and activator of transcription 6 (p-STAT6).

CONCLUSION

YCF significantly inhibits inflammation and fibrosis in silicotic rats probably via the suppression of M1/M2 macrophage polarization mediated by the inhibition of mitogen-activated protein kinase and nuclear factor kappa B signaling pathways and Janus kinase/STAT6 pathways.

Tumor-derived CircRNA_102191 promotes gastric cancer and facilitates M2 macrophage polarization

BACKGROUND

Gastric cancer is a common malignant tumor of the digestive tract and the fourth leading cause of death from cancer-related diseases. In recent years, many studies have found that circular RNAs play an important role in cancer. Tumor-associated macrophages (TAMs) are also critical for tumor progression.

OBJECTIVE

This study examined the role of circRNA_102191 in gastric cancer progression.

METHODS

The relative mRNA levels were determined by qRT-PCR. Western blotting and ELISA were used to detect the protein levels. In vitro proliferation was assessed using CCK8 and clonogenic assays. The migration and invasion of cell lines were assessed by transwell-based assays. The interactions between molecules were detected using a luciferase reporter assay. M0 macrophages were induced with PMA. M1 macrophages were induced with LPS and IFN-γ, and M2 macrophages were induced with IL-4.

RESULTS

The expression of circRNA_102191 was enhanced significantly in gastric cancer cell lines and clinical tumor tissues. CircRNA_102191 promotes gastric cancer cell progression by regulating miR-493-3p and its downstream target gene XPR1. CircRNA_102191 can enhance the EMT process of gastric cancer cells by promoting the M2 polarization of macrophages.

CONCLUSION

CircRNA_102191 promotes the biological function of gastric cancer cells by regulating the miR-493-3p/XPR1 axis and M2 macrophage polarization.

AT2 cell-derived IgA trapped by the extracellular matrix in silica-induced pulmonary fibrosis

Pulmonary fibrosis is an interstitial lung disease caused by various factors such as exposure to workplace environmental contaminants, drugs, or X-rays. Epithelial cells are among the driving factors of pulmonary fibrosis. Immunoglobulin A (IgA), traditionally thought to be secreted by B cells, is an important immune factor involved in respiratory mucosal immunity. In the current study, we found that lung epithelial cells are involved in IgA secretion, which, in turn, promotes pulmonary fibrosis. Spatial transcriptomics and single-cell sequencing suggest that Igha transcripts were highly expressed in the fibrotic lesion areas of lungs from silica-treated mice. Reconstruction of B-cell receptor (BCR) sequences revealed a new cluster of AT2-like epithelial cells with a shared BCR and high expression of genes related to IgA production. Furthermore, the secretion of IgA by AT2-like cells was trapped by the extracellular matrix and aggravated pulmonary fibrosis by activating fibroblasts. Targeted blockade of IgA secretion by pulmonary epithelial cells may be a potential strategy for treating pulmonary fibrosis.

Targeted miR-34a delivery with PD1 displayed bacterial outer membrane vesicles-coated zeolitic imidazolate framework nanoparticles for enhanced tumor therapy

MicroRNA (miRNA) has been widely used as an effective gene drug for tumor therapy, but its chemical instability limited its therapeutic application in vivo. In this research, we fabricate an efficient miRNA nano-delivery system using zeolitic imidazolate framework-8 (ZIF-8) coated with bacterial outer membrane vesicles (OMVs), aimed for cancer treatment. The acid-sensitive ZIF-8 core enables this system to encapsulate miRNA and release them from lysosome quickly and efficiently in the target cells. The OMVs engineered to display programmed death receptor 1 (PD1) on the surface provides a specific tumor-targeting capability. Using a murine breast cancer model, we show that this system has high miRNA delivery efficiency and accurate tumor targeting. Moreover, the miR-34a payloads in carriers can further synergize with immune activation and checkpoint inhibition triggered by OMV-PD1 to enhance tumor therapeutic efficacy. Overall, this biomimetic nano-delivery platform provides a powerful tool for the intracellular delivery of miRNA and has great potential in RNA-based cancer therapeutic applications.

Functions of Circular RNA in Human Diseases and Illnesses

Circular RNAs (circRNAs) represent single-stranded RNA species that contain covalently closed 3' and 5' ends that provide them more stability than linear RNA, which has free ends. Emerging evidence indicates that circRNAs perform essential functions in many DNA viruses, including coronaviruses, Epstein-Barr viruses, cytomegalovirus, and Kaposi sarcoma viruses. Recent studies have confirmed that circRNAs are present in viruses, including DNA and RNA viruses, and play various important functions such as evading host immune response, disease pathogenesis, protein translation, miRNA sponges, regulating cell proliferation, and virus replication. Studies have confirmed that circRNAs can be biological signatures or pathological markers for autoimmune diseases, neurological diseases, and cancers. However, our understanding of circRNAs in DNA and RNA viruses is still limited, and functional evaluation of viral and host circRNAs is essential to completely understand their biological functions. In the present review, we describe the metabolism and cellular roles of circRNA, including its roles in various diseases and viral and cellular circRNA functions. Circular RNAs are found to interact with RNA, proteins, and DNA, and thus can modulate cellular processes, including translation, transcription, splicing, and other functions. Circular RNAs interfere with various signaling pathways and take part in vital functions in various biological, physiological, cellular, and pathophysiological processes. We also summarize recent evidence demonstrating cellular and viral circRNA's roles in DNA and RNA viruses in this growing field of research.

Circ_0067934 as a novel therapeutic target in cancer: From mechanistic to clinical perspectives

Circular RNAs, as a type of non-coding RNAs, are identified in a various cell. Circular RNAs have stable structures, conserved sequence, and tissue and cell-specific level. High throughput technologies have proposed that circular RNAs act via various mechanisms like sponging microRNAs and proteins, regulating transcription factors, and scaffolding mediators. Cancer is one of the major threat for human health. Emerging data have proposed that circular RNAs are dysregulated in cancers as well as are associated with aggressive behaviors of cancer -related behaviors like cell cycle, proliferation, apoptosis, invasion, migration, and epithelial-mesenchymal transition (EMT). Among them, circ_0067934 was shown to act as an oncogene in cancers to enhance migration, invasion, proliferation, cell cycle, EMT, and inhibit cell apoptosis. In addition, these studies have proposed that it could be a promising diagnostic and prognostic biomarker in cancer. This study aimed to review the expression and molecular mechanism of circ_0067934 in modulating the malignant behaviors of cancers as well as to explore its potential as a target in cancer chemotherapy, diagnosis, prognosis and treatment.

circRNA_17725 Promotes Macrophage Polarization towards M2 by Targeting FAM46C to Alleviate Arthritis

Accumulating studies have implicated that circular RNAs (circRNAs) play vital roles in the pathogenesis of rheumatoid arthritis (RA). Dysregulation of macrophage polarization leads to immune homeostatic imbalance in RA. However, the altering effects and mechanisms of circRNAs on macrophages polarization and immune homeostatic balance remain largely unclear. We aimed to investigate the potential role of circRNA_17725 in RA. The high-throughput sequence was performed to identify the dysregulated circRNAs in RA. We confirmed the data by CCK-8, EdU, and Annexin V/PI staining to elucidate the proliferation and apoptosis. The expressions of M1/M2-associated markers were confirmed using real-time PCR and flow cytometry analysis. Luciferase reporter assay and RNA Binding Protein Immunoprecipitation (RIP) were used to demonstrate the underlying mechanism of circRNA_17725. The altering effect of circRNA_17725 on macrophages in vivo was evaluated using collagen-induced arthritis (CIA) mouse model. circRNA_17725 was demonstrated to be downregulated in peripheral blood mononuclear cells and CD14+ monocytes from RA cases in contrast to healthy controls. The negative association between circRNA_17725 and the disease activity indexes (CRP, ESR, and DAS28) was observed, suggesting a vital role of circRNA_17725 in RA disease activity. Besides, after a coexpression analysis based on high-input sequencing and the bioinformatics analysis in MiRanda and TargetScan databases, a circRNA_17725-miR-4668-5p-FAM46C competing endogenous RNA (ceRNA) network was hypothesized. A series of cytology experiments in vitro have implicated that circRNA_17725 could inhibit the proliferation but enhance the apoptosis of macrophages. Decreased expression of TNF-α, IL-1β, and MMP-9 were observed in the supernatant of circRNA_17725-overexpressed Raw264.7 macrophages, implicating the inhibitory effect of circRNA_17725 on macrophage inflammatory mediators. Furthermore, circRNA_17725 could promote macrophage polarization towards M2 by targeting miR-4668-5p/FAM46C as a miRNA sponge. Additionally, circRNA_17725-overexpressed macrophages alleviated arthritis and protected against joint injuries and bone destruction by inducing macrophage polarization towards M2 in collagen-induced arthritis (CIA) mice. This study has suggested that circRNA_17725 regulated macrophage proliferation, apoptosis, inflammation, and polarization by sponging miR-4668-5p and upregulating FAM46C in RA.

CircRNA-104718 promotes glioma malignancy through regulation of miR-218-5p/HMGB1 signalling pathway

Increasing number of studies have proven that circular RNAs (circRNAs) play a major role in the biological processes of many different cancers, including glioma, especially as competitive molecular sponges of microRNAs (miRNAs). However, the clear molecular mechanism of the circRNA network in glioma is still not well understood. The expression level of circRNA-104718 and microRNA (miR)-218-5p in glioma tissues and cells were detected by quantitative real-time polymerase chain reaction (qRT-PCR). The target protein's expression level was assessed by western blotting. Bioinformatics systems were used to predict the possible microRNAs and target genes of circRNA-104718, after which dual-luciferase reporter assays were used to confirm the predicted interactions. The proliferation, invasion, migration and apoptosis of glioma cells were detected by CCK, EdU, transwell, wound-healing and flow cytometry assays. CircRNA-104718 was upregulated in human glioma tissues, and a higher level of circRNA-104718 indicated poorer outcomes in glioma patients. In contrast, in glioma tissues, miR-218-5p was downregulated. Knockdown of circRNA-104718 suppressed migration and invasion while boosting the apoptosis rate of glioma cells. In addition, the upregulation of miR-218-5p in glioma cells caused the same suppression. Mechanistically, circRNA-104718 inhibited the protein expression level of high mobility group box-1 (HMGB1) by acting as a molecular sponge for miR-218-5p. CircRNA-104718 is a suppressive factor in glioma cells and might represent a new target for the treatment of glioma patients. CircRNA-104718 modulates glioma cell proliferation through the miR-218-5p/HMGB1 signalling axis. CircRNA-104718 provides a possible mechanism for understanding the pathogenesis of glioma.

Epigenetics as a versatile regulator of fibrosis

Fibrosis, a process caused by excessive deposition of extracellular matrix (ECM), is a common cause and outcome of organ failure and even death. Researchers have made many efforts to understand the mechanism of fibrogenesis and to develop therapeutic strategies; yet, the outcome remains unsatisfactory. In recent years, advances in epigenetics, including chromatin remodeling, histone modification, DNA methylation, and noncoding RNA (ncRNA), have provided more insights into the fibrotic process and have suggested the possibility of novel therapy for organ fibrosis. In this review, we summarize the current research on the epigenetic mechanisms involved in organ fibrosis and their possible clinical applications.

A novel circular RNA circNLRP3 alleviated ricin toxin-induced TNF-α production through sponging miR-221-5p

Acting as microRNA (miRNA) sponges, circular RNAs (circRNAs) have been discovered to be critical modulators of inflammatory processes. Ricin Toxin (RT) is highly toxic to mammalian cells and low doses of RT can induce acute inflammation. However, current researches on the underlying mechanism and function of circRNA/miRNA network in RT-induced inflammation are limited. Previously, we found miR-221-5p was aberrant and associated with the inflammation of RT induction. In this study, based on the circRNA high-throughput sequencing (circRNA-seq), we obtained a novel circRNA termed circNLRP3 and revealed that circNLRP3 can sponge miR-221-5p, release its target mRNA A20, and further suppress NF-κB signaling pathway to alleviated RT-induced TNF-α production. Our findings elucidated a possible mechanistic link between the circNLRP3/miR-221-5p/A20 axis and RT-induced inflammatory response, which may broaden our understanding of RT poisoning.

Human umbilical cord mesenchymal stem cell-derived extracellular vesicles alleviated silica induced lung inflammation and fibrosis in mice via circPWWP2A/miR-223-3p/NLRP3 axis

Silicosis is a progressive inflammatory disease with poorly defined mechanisms and limited therapeutic options. Recent studies found that microRNAs (miRNAs) and circular RNAs (circRNAs) were involved in the development of respiratory diseases; however, the function of non-coding RNAs in silicosis was still needed to be further explored. We found that miR-223-3p was significantly decreased in macrophages and lung tissues of mice after silica treatment, which were consistent with the results of GEO database microarray analysis. Notably, NLRP3 is a target gene downstream of miR-223-3p. And circular RNA PWWP2A (circPWWP2A) was significantly elevated after silica stimulation. To elucidate the role of these RNAs in silica-induced inflammation in macrophages and lung tissues, we investigated the upstream molecular mechanisms of circPWWP2A on the inflammatory response. The inhibitory effect of miR-223-3p on its target NLRP3 was suppressed by circPWWP2A, which led to lung fibrosis. Our study found that circPWWP2A could adsorb miR-223-3p to regulate NLRP3 after silica stimulation in pulmonary fibrosis. And our results revealed that the circPWWP2A-miR-223-3p-NLRP3 axis was potentially instrumental in managing silica-induced inflammation and fibrosis. Previous studies have demonstrated that human umbilical cord mesenchymal stem cell-derived extracellular vesicles (hucMSC-EVs) exhibit anti-inflammatory and anti-fibrotic effects in multiple organs. However, the potential effectiveness of hucMSC-EVs against silicosis or the underlying mechanisms of their biological outcomes remains unclear. Therefore, we used 3D culture technology to extract hucMSC-EVs and observed their effects in macrophages and lung tissues, respectively. According to the EVmiRNA database, miR-223-3p was abundant in MSC-EVs. In addition, hucMSC-EVs may modulate lung function, reduce the secretion of inflammatory factors (NLRP3, IL-1β, IL-18 and cleaved Caspase-1) and attenuate the deposition of fibrosis-related factors (Collagen Ⅰ, Collagen Ⅲ, fibronectin and α-SMA). In vitro results evinced that hucMSC-EVs reduced the inflammatory response of macrophages and restricted the activation and proliferation of fibroblasts. Moreover, our study showed that hucMSCs-EVs acted as a mediator to transfer miR-223-3p to suppress circPWWP2A, thereby alleviating pulmonary fibrosis through the NLRP3 signaling pathway. These data may provide potentially novel strategies for investigating the pathogenesis of silicosis and developing novel treatments for this disease.

The aggravate role of exosomal circRNA11:120406118|12040782 on macrophage pyroptosis through miR-30b-5p/NLRP3 axis in silica-induced lung fibrosis

Silica dust inhalation could lead to silicosis, and there is no specific biomarker for its early diagnosis and no effective treatment due to the lack of research on its pathogenesis. The homeostasis of macrophages was considered to be crucial during the development of silicosis from persistent chronic inflammation to irreversible fibrosis. However, its regulatory mechanism and the communication between macrophages and others are still not clear. Exosomal circRNAs emerge as favorable candidates for cellular communication. Therefore, our study aimed to illustrate the regulatory mechanism of silicosis from the view of exosomal circRNAs. Our study identified a novel exosomal circRNA, circRNA11:120406118|12040782, in the peripheral serum of silicosis patients. Furthermore, the detailed role of circRNA11:120406118|12040782 was investigated both in silicosis mouse model and in silica-stimulated macrophages and fibroblasts. On the one hand, circRNA11:120406118|12040782 was shown to regulate silica-stimulated macrophage pyroptosis through circRNA11:120406118|12040782/miR-30b-5p/NLRP3 network. And this macrophage-derived cirRNA could promote the activation of fibroblasts. On the other hand, overexpressing miR-30b-5p, the crucial component of circRNA11:120406118|12040782/miR-30b-5p/NLRP3 regulatory network, could inhibit pyroptosis and attenuate silica-induced lung inflammation and fibrosis in mice. Our findings suggested that exosomal circRNA11:120406118|12040782 could aggravate NLRP3-mediated macrophages pyroptosis through sponging miR-30b-5p in silicosis development, which provide an experimental basis and shed light on the early diagnosis and treatment of silicosis.

CircRNAs regulate the crosstalk between inflammation and tumorigenesis: The bilateral association and molecular mechanisms

Inflammation, a hallmark of cancer, has been associated with tumor progression, transition into malignant phenotype and efficacy of the chemotherapeutic agents in cancer. Chronic inflammation provides a favorable environment for tumorigenesis by inducing immunosuppression, whereas acute inflammation prompts tumor suppression by generating anti-tumor immune responses. Inflammatory factors derived from interstitial cells or tumor cells can stimulate cell proliferation and survival by modulating oncogenes and/or tumor suppressors. Recently, a new class of RNAs, i.e., circular RNAs (circRNAs), has been implicated in inflammatory diseases. Although there are reports on circRNAs imparting functions in inflammatory insults, whether these circularized transcripts hold the potential to regulate inflammation-induced cancer or tumor-related inflammation, and modulate the interactions between tumor microenvironment (TME) and the inflammatory stromal/immune cells, awaits further elucidation. Contextually, the current review describes the molecular association between inflammation and cancer, and spotlights the regulatory mechanisms by which circRNAs can moderate TME in response to inflammatory signals/triggers. We also present comprehensive information about the immune cell(s)-specific expression and functions of the circRNAs in TME, modulation of inflammatory signaling pathways to drive tumorigenesis, and their plausible roles in inflammasomes and tumor development. Moreover, the therapeutic potential of these circRNAs in harnessing inflammatory responses in cancer is also discussed.

The emerging role of epigenetic regulation in the progression of silicosis

Silicosis is one of the most severe occupational diseases worldwide and is characterized by silicon nodules and diffuse pulmonary fibrosis. However, specific treatments for silicosis are still lacking at present. Therefore, elucidating the pathogenesis of silicosis plays a significant guiding role for its treatment and prevention. The occurrence and development of silicosis are accompanied by many regulatory mechanisms, including epigenetic regulation. The main epigenetic regulatory mechanisms of silicosis include DNA methylation, non-coding RNA (ncRNA), and histone modifications. In recent years, the expression and regulation of genes related to silicosis have been explored at epigenetic level to reveal its pathogenesis further, and the identification of aberrant epigenetic markers provides new biomarkers for prediction and diagnosis of silicosis. Here, we summarize the studies on the role of epigenetic changes in the pathogenesis of silicosis to give some clues for finding specific therapeutic targets for silicosis.

Emerging Effects of IL-33 on COVID-19

Since the start of COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), more than 6 million people have lost their lives worldwide directly or indirectly. Despite intensified efforts to clarify the immunopathology of COVID-19, the key factors and processes that trigger an inflammatory storm and lead to severe clinical outcomes in patients remain unclear. As an inflammatory storm factor, IL-33 is an alarmin cytokine, which plays an important role in cell damage or infection. Recent studies have shown that serum IL-33 is upregulated in COVID-19 patients and is strongly associated with poor outcomes. Increased IL-33 levels in severe infections may result from an inflammatory storm caused by strong interactions between activated immune cells. However, the effects of IL-33 in COVID-19 and the underlying mechanisms remain to be fully elucidated. In this review, we systematically discuss the biological properties of IL-33 under pathophysiological conditions and its regulation of immune cells, including neutrophils, innate lymphocytes (ILCs), dendritic cells, macrophages, CD4⁺ T cells, Th17/Treg cells, and CD8⁺ T cells, in COVID-19 phagocytosis. The aim of this review is to explore the potential value of the IL-33/immune cell pathway as a new target for early diagnosis, monitoring of severe cases, and clinical treatment of COVID-19.

Biological functions and potential implications of circular RNAs

Circular RNAs (circRNAs) are characterized by a covalent closed-loop structure with an absence of both 5' cap structure and 3' polyadenylated tail. Numerous studies have found that circRNAs play an important role in various diseases and have a variety of biological regulatory mechanisms, including acting as microRNA sponges, interacting with proteins, modulating the expression of related genes and translating into peptides or proteins. CircRNAs have also been used as biomarkers for a number of diseases, which could improve clinical practice. This review summarizes the most recent advances in biogenesis and knowledge of the biological functions of circRNAs as well as the related bioinformatics databases. We specifically describe developments in understanding of circRNA functions in the field of environmental exposure-induced diseases. Finally, we focus on potential clinical implications of circRNAs to facilitate their clinical transformation into disease treatment.

The function and clinical implication of circular RNAs in lung cancer

Lung cancer is the leading cause of cancer-related deaths worldwide. Despite the recent advent of promising new targeted therapies, lung cancer diagnostic strategies still have difficulty in identifying the disease at an early stage. Therefore, the characterizations of more sensible and specific cancer biomarkers have become an important goal for clinicians. Circular RNAs are covalently close, endogenous RNAs without 5' end caps or 3'poly (A) tails and have been characterized by high stability, abundance, and conservation as well as display cell/tissue/developmental stage-specific expressions. Numerous studies have confirmed that circRNAs act as microRNA (miRNA) sponges, RNA-binding protein, and transcriptional regulators; some circRNAs even act as translation templates that participate in multiple pathophysiological processes. Growing evidence have confirmed that circRNAs are involved in the pathogenesis of lung cancers through the regulation of proliferation and invasion, cell cycle, autophagy, apoptosis, stemness, tumor microenvironment, and chemotherapy resistance. Moreover, circRNAs have emerged as potential biomarkers for lung cancer diagnosis and prognosis and targets for developing new treatments. In this review, we will summarize recent progresses in identifying the biogenesis, biological functions, potential mechanisms, and clinical applications of these molecules for lung cancer diagnosis, prognosis, and targeted therapy.

Mechanism underlying circRNA dysregulation in the TME of digestive system cancer

Circular RNAs (circRNAs) are a new series of noncoding RNAs (ncRNAs) that have been reported to be expressed in eukaryotic cells and have a variety of biological functions in the regulation of cancer pathogenesis and progression. The TME, as a microscopic ecological environment, consists of a variety of cells, including tumor cells, immune cells and other normal cells, ECM and a large number of signaling molecules. The crosstalk between circRNAs and the TME plays a complicated role in affecting the malignant behaviors of digestive system cancers. Herein, we summarize the mechanisms underlying aberrant circRNA expression in the TME of the digestive system cancers, including immune surveillance, angiogenesis, EMT, and ECM remodelling. The regulation of the TME by circRNA is expected to be a new therapeutic method.

Role of circRNA in E3 Modification under Human Disease

Circular RNA (circRNA) is often regarded as a special kind of non-coding RNA, involved in the regulation mechanism of various diseases, such as tumors, neurological diseases, and inflammation. In a broad spectrum of biological processes, the modification of the 76-amino acid ubiquitin protein generates a large number of signals with different cellular results. Each modification may change the result of signal transduction and participate in the occurrence and development of diseases. Studies have found that circRNA-mediated ubiquitination plays an important role in a variety of diseases. This review first introduces the characteristics of circRNA and ubiquitination and summarizes the mechanism of circRNA in the regulation of ubiquitination in various diseases. It is hoped that the emergence of circRNA-mediated ubiquitination can broaden the diagnosis and prognosis of the disease.

Non-coding RNA in idiopathic interstitial pneumonia and Covid-19 pulmonary fibrosis

Pulmonary fibrosis is the key feature of majority of idiopathic interstitial pneumonias (IIPs) as well as many patients with post-COVID-19. The pathogenesis of pulmonary fibrosis is a complex molecular process that involves myriad of cells, proteins, genes, and regulatory elements. The non-coding RNA mainly miRNA, circRNA, and lncRNA are among the key regulators of many protein coding genes and pathways that are involved in pulmonary fibrosis. Identification and molecular mechanisms, by which these non-coding RNA molecules work, are crucial to understand the molecular basis of the disease. Additionally, elucidation of molecular mechanism could also help in deciphering a potential diagnostic/prognostic marker as well as therapeutic targets for IIPs and post-COVID-19 pulmonary fibrosis. In this review, we have provided the latest findings and discussed the role of these regulatory elements in the pathogenesis of pulmonary fibrosis associated with Idiopathic Interstitial Pneumonia and Covid-19.

Role of Circular RNAs in Pulmonary Fibrosis

Pulmonary fibrosis is a chronic progressive form of interstitial lung disease, characterized by the histopathological pattern of usual interstitial pneumonia. Apart from aberrant alterations of protein-coding genes, dysregulation of non-coding RNAs, including microRNAs, long non-coding RNAs, and circular RNAs (circRNAs), is crucial to the initiation and progression of pulmonary fibrosis. CircRNAs are single-stranded RNAs that form covalently closed loops without 5′ caps and 3′ tails. Different from canonical splicing of mRNA, they are produced from the back-splicing of precursor mRNAs and have unique biological functions, as well as potential biomedical implications. They function as important gene regulators through multiple actions, including sponging microRNAs and proteins, regulating transcription, and splicing, as well as protein-coding and translation in a cap-independent manner. This review comprehensively summarizes the alteration and functional role of circRNAs in pulmonary fibrosis, with a focus on the involvement of the circRNA in the context of cell-specific pathophysiology. In addition, we discuss the diagnostic and therapeutic potential of targeting circRNA and their regulatory pathway mediators, which may facilitate the translation of recent advances from bench to bedside in the future.

circHECTD1 attenuates apoptosis of alveolar epithelial cells in acute lung injury

Circular RNAs (circRNAs) play important roles in many lung diseases. This study aimed to investigate the role of circHECTD1 in acute lung injury (ALI). The mouse and cell models of ALI were induced by lipopolysaccharide (LPS). The apoptosis of alveolar epithelial cells (AECs) was detected by flow cytometry. The relationships between circHECTD1, miRNAs, and target genes were assessed by RNA pull-down, luciferase reporter gene, and RNA-FISH assays. circHECTD1 was downregulated in LPS-induced human and mouse AECs (HBE and MLE-12). The knockdown of circHECTD1 increased the apoptotic rates and the expressions of miR-136 and miR-320a, while its overexpression caused opposite effects in LPS-induced HBE and MLE-12 cells. Mechanistically, circHECTD1 bound to miR-320a and miR-136. miR-320a targeted PIK3CA and mediated the effect of circHECTD1 on PIK3CA expression. miR-136 targeted Sirt1 and mediated the effect of circHECTD1 on Sirt1 expression. Silencing PIK3CA and/or Sirt1 reversed the effect of circHECTD1 overexpression on the apoptosis of LPS-induced HBE and MLE-12 cells. In vivo, overexpression of circHECTD1 alleviated the LPS-induced ALI of mice. Our findings suggested that circHECTD1 inhibits the apoptosis of AECs through miR-320a/PIK3CA and miR-136/Sirt1 pathways in LPS-induced ALI.

ZC3H4 regulates infiltrating monocytes, attenuating pulmonary fibrosis through IL-10

Silicosis is a pulmonary fibrosis-associated disease caused by the inhalation of large amounts of free silicon dioxide (SiO₂) that mainly manifests as early inflammation and late pulmonary fibrosis. As macrophage precursors, monocytes accumulate in the lung during early inflammation, but their role in the development of silicosis is unclear. Single-cell sequencing (cell numbers = 25,002), Western blotting, quantitative real-time PCR, ELISA and cell functional experiments were used to explore the specific effects of monocytes on fibroblasts. The CRISPR/Cas9 system was used to specifically knock down ZC3H4, a novel member of the CCCH zinc finger protein family, and was combined with pharmacological methods to explore the mechanism by which ZC3H4 affects chemokine and cytokine secretion. The results indicated that (1) SiO₂ induced an infiltrating phenotype in monocytes; (2) infiltrating monocytes inhibited the activation, viability and migration of fibroblasts by regulating IL-10 but not IL-8; and (3) SiO₂ downregulated IL-10 via ZC3H4-induced autophagy. This study revealed that ZC3H4 regulated the secretion function of monocytes, which, in turn, inhibited fibroblast function in early inflammation through autophagy signaling, thereby reducing pulmonary fibrosis. These findings provide a new idea for the clinical treatment of silicosis.

Circ_TLK1 knockdown alleviates oxygen-glucose deprivation/reoxygenation-induced PC12 cell injury by regulating microRNA-136-5p/follistatin like-1 axis

BACKGROUND

Circular RNAs (circRNAs) are aberrantly expressed in the central nervous system (CNS) and are involved in diverse CNS diseases. However, the functions of circRNAs in ischemic stroke (IS) are largely unknown. In this study, we aimed to explore the effect of circ_TLK1 in oxygen-glucose deprivation/reoxygenation (OGD/R)-induced PC12 cell injury.

METHODS

Quantitative real-time polymerase chain reaction (qRT-PCR) was performed for the levels of circ_TLK1, TLK1, microRNA-136-5p (miR-136-5p), and follistatin like-1 (FSTL1). RNase R and Actinomycin D assays were conducted to analyze the features of circ_TLK1. 3-(4, 5-ethynyl-2'-deoxyuridine [EdU] assay and 5-dimethyl-2-thiazolyl)-2, 5-diphenyl-2-H-tetrazolium bromide (MTT) assay were adopted to analyze cell proliferation capacity. Flow cytometry analysis was applied to determine cell death. Western blot assay was employed to measure protein levels. The release of lactate dehydrogenase (LDH) was measured with specific kits. The interaction between circ_TLK1 and miR-136-5p, as well as miR-136-5p and FSTL1, was verified by Dual-luciferase reporter assay.

RESULTS

Circ_TLK1 was upregulated in OGD/R-injured PC12 cells. OGD/R treatment inhibited cell proliferation, promoted cell death, and increased LDH release in PC12 cells, while circ_TLK1 knockdown partially alleviated OGD/R-induced PC12 cell injury. Circ_TLK1 directly bound to miR-136-5p and miR-136-5p inhibition reversed the effect of circ_TLK1 knockdown on OGD/R-induced PC12 cell damage. Moreover, FSTL1 was targeted by miR-136-5p. MiR-136-5p upregulation inhibited PC12 cell injury induced by OGD/R, while FSTL1 overexpression partially reversed the effect.

CONCLUSION

Circ_TLK1 knockdown ameliorated OGD/R-induced PC12 cell injury by modulating miR-136-5p and FSTL1, which might provide a new understanding of IS treatment.

Past, Present and Future: The Relationship Between Circular RNA and Immunity

The immune system has evolved since the birth of humans. However, immune-related diseases have not yet been overcome due to the lack of expected indicators and targeting specificity of current medical technology, subjecting patients to very uncomfortable physical and mental experiences and high medical costs. Therefore, the requirements for treatments with higher specificity and indicative ability are raised. Fortunately, the discovery of and continuous research investigating circular RNAs (circRNAs) represent a promising method among numerous methods. Although circRNAs wear regarded as metabolic wastes when discovered, as a type of noncoding RNA (ncRNA) with a ring structure and wide distribution range in the human body, circRNAs shine brilliantly in medical research by virtue of their special nature and structure-determined functions, such as high stability, wide distribution, high detection sensitivity, acceptable reproducibility and individual differences. Based on research investigating the role of circRNAs in immunity, we systematically discuss the hotspots of the roles of circRNAs in immune-related diseases, including expression profile analyses, potential biomarker research, ncRNA axis/network construction, impacts on phenotypes, therapeutic target seeking, maintenance of nucleic acid stability and protein binding research. In addition, we summarize the current situation of and problems associated with circRNAs in immune research, highlight the applications and prospects of circRNAs in the treatment of immune-related diseases, and provide new insight into future directions and new strategies for laboratory research and clinical applications.

M2 macrophage facilitated angiogenesis in cutaneous squamous cell carcinoma via circ_TNFRSF21/miR-3619-5p/ROCK axis

In recent years, the role of circular RNA in cancer cells has been studied broadly; however, the functional significance of circular RNA in the regulation of the tumor microenvironment (TME) is not fully understood. In this study, we aimed to reveal the role of circ_TNFRSF21 in M2 macrophage-induced cutaneous squamous cell carcinoma (cSCC) angiogenesis. Quantitative polymerase chain reaction and Western blotting were performed to determine the levels of the indicated genes. Direct binding between circ_TNFRSF21 and miR-3619-5p, miR-3619-5p, and ROCK2 was verified by dual-luciferase activity. The migration and invasion of human umbilical vein endothelial cells were evaluated by wound healing and transwell assays. Tube formation was performed to detect in vitro angiogenesis. Circ_TNFRSF21 and ROCK2 were upregulated in cSCC tissue, while miR-3619-5p was downregulated. Circ_TNFRSF21 negatively regulated the expression of miR-3619-5p, while miR-3619-5p negatively regulated the expression of ROCK2. miR-3619-5p suppressed tube formation by inhibiting ROCK signaling. M2 macrophages facilitated tube formation via the circ_TNFRSF21/miR-3619-5p/ROCK2 axis. Our present study revealed that circ_TNFRSF21 was elevated in M2 macrophages and mediated M2 macrophage-induced tube formation in vitro.

Peripheral blood circular RNA hsa_circ_0058493 as a potential novel biomarker for silicosis and idiopathic pulmonary fibrosis

Existing studies reported that some circular RNAs (circRNAs) play vital roles in the development of pulmonary fibrosis. However, few studies explored the biomarker potential of circRNAs for pulmonary fibrosis based on population data. Therefore, we aimed to identify peripheral blood circRNAs as potential biomarkers for diagnosing silicosis and idiopathic pulmonary fibrosis (IPF). In brief, an RNA-seq screening based on 4 silicosis cases and 4 controls was initially performed. Differentially expressed circRNAs were combined with the human serum circRNA dataset to identify overlapping serum-detectable circRNAs, followed by validation using the GEO dataset (3 IPF cases and 3 controls) and subsequent qRT-PCR, including 84 additional individuals. Following the above steps, 243 differentially expressed circRNAs were identified during the screening stage, with fold changes ≥ 1.5 and P < 0.05. Of note, the human serum circRNA dataset encompassed 28 of 243 circRNAs. GEO (GSE102660) validation revealed two highly expressed circRNAs (P < 0.05) in the IPF case group. Furthermore, at the enlarged sample validation stage, hsa_circ_0058493 was highly expressed in both silicosis and IPF cases (silicosis: P = 1.16 × 10^-6; IPF: P = 7.46 × 10^-5). Additionally, hsa_circ_0058493 expression was significantly increased in MRC-5 cells upon TGF-β1 treatment, while hsa_circ_0058493 knockdown inhibited the expression of fibrotic molecules by affecting the epithelial-mesenchymal transition process. These shreds of evidence indicated that hsa_circ_0058493 might serve as a novel biomarker for diagnosing silicosis and IPF.

Circular RNA circ_0000423 regulates cartilage ECM synthesis via circ_0000423/miRNA-27b-3p/MMP-13 axis in osteoarthritis

Circular RNA (circRNA) is related to many human diseases including osteoarthritis (OA). Our research purpose was to show that functional circRNAs have a role in the pathogenesis of OA, while also identifying potential circRNA that bind to miRNA-27b-3p. Microarray analysis was used to evaluate the expression of CircRNA in OA and normal cartilage. The role and functional mechanism of Circ_0000423 up-regulation were detected in OA and verified in vitro and in vivo. RNA transfection, qRT-PCR, Western blot analysis, immunofluorescence, and dual-luciferase assays were used to investigate the interaction between Circ_0000423 and miRNA-27b-3p in vitro. The roles of Circ_0000423 were discussed in vivo. Our results discovered 11 down-regulated circRNAs and 101 up-regulated circRNAs between control and OA tissues, and confirmed that Circ_0000423 an increase significantly in OA tissues by evaluating the different circRNAs expressions. Meanwhile, luciferase analysis confirmed Circ_0000423 can be directly targeted by miRNA-27b-3p and act as a miRNA-27b-3p sponge. Circ_0000423 can influence MMP-13 and collagen II expression by targeting miRNA-27b-3p expression as ceRNA in OA. Furthermore, AAV-shRNA-Circ 0000423 intra-articular injection slows the progression of OA by decreasing articular cartilage destruction and erosion, joint surface fibrosis, osteophyte formation, MMP-13 expression, and increasing collagen II expression in the articular cartilage of ACLT-induced OA mice model. These findings confirmed that the Circ_0000423-miRNA-27b-3p-MMP-13 axis could affect the pathogenesis of OA which might lead to a novel target for diagnostic molecular biological indicators and potential OA treatments.

Construction of a ceRNA Network Related to Rheumatoid Arthritis

(1) Background: Rheumatoid arthritis (RA) is a common systemic autoimmune disease affecting many people and has an unclear and complicated physiological mechanism. The competing endogenous RNA (ceRNA) network plays an essential role in the development and occurrence of various human physiological processes. This study aimed to construct a ceRNA network related to RA. (2) Methods: We explored the GEO database for peripheral blood mononuclear cell (PBMC) samples and then analyzed the RNA of 52 samples (without treatment) to obtain lncRNAs (DELs), miRNAs (DEMs), and mRNAs (DEGs), which can be differentially expressed with statistical significance in the progression of RA. Next, a ceRNA network was constructed, based on the DELs, DEMs, and DEGs. At the same time, the Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) analysis were used to validate the possible function of the ceRNA network. (3) Results: Through our analysis, 389 DELs, 247 DEMs, and 1081 DEGs were screened. After this, a ceRNA network was constructed for further statistical comparisons, including 16 lncRNAs, 1 miRNA, and 15 mRNAs. According to the GO and KEGG analysis, the ceRNA network was mainly enriched in the mTOR pathway, the dopaminergic system, and the Wnt signaling pathway. (4) Conclusions: The novel ceRNA network related to RA that we constructed offers novel insights into and targets for the underlying molecular mechanisms of the mTOR pathway, the dopaminergic system, and the Wnt signaling pathway (both classic and nonclassic pathways) that affect the level of the genetic regulator, which might offer novel ways to treat RA.

Circular RNA in Acute Central Nervous System Injuries: A New Target for Therapeutic Intervention

Acute central nervous system (CNS) injuries, including ischemic stroke, traumatic brain injury (TBI), spinal cord injury (SCI) and subarachnoid hemorrhage (SAH), are the most common cause of death and disability around the world. As a kind of non-coding ribonucleic acids (RNAs) with endogenous and conserve, circular RNAs (circRNAs) have recently attracted great attentions due to their functions in diagnosis and treatment of many diseases. A large number of studies have suggested that circRNAs played an important role in brain development and involved in many neurological disorders, particularly in acute CNS injuries. It has been proposed that regulation of circRNAs could improve cognition function, promote angiogenesis, inhibit apoptosis, suppress inflammation, regulate autophagy and protect blood brain barrier (BBB) in acute CNS injuries via different molecules and pathways including microRNA (miRNA), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), ph1osphatidylinositol-4,5-bisphosphate 3-kinase/protein kinase B (PI3K/AKT), Notch1 and ten-eleven translocation (TET). Therefore, circRNAs showed great promise as potential targets in acute CNS injuries. In this article, we present a review highlighting the roles of circRNAs in acute CNS injuries. Hence, on the basis of these properties and effects, circRNAs may be developed as therapeutic agents for acute CNS injury patients.

hnRNP L-activated circANKRD42 Reverse Splicing and the circANKRD42-mediated Crosstalk between Mechanical Stiffness and Biochemical Signals to Drive Pulmonary Fibrogenesis

Increasing circular RNAs (circRNAs) are involved in the progression of idiopathic pulmonary fibrosis (IPF). However, circRNA biogenesis and circRNA-mediated crosstalk between mechanical stiffness and biochemical signals in IPF remain obscure. In this study, a novel circRNA-ANKRD42 from peripheral blood of patients with IPF, which participated in pulmonary fibrosis through the close communication of mechanical stiffness and biochemical signals, was identified. Mechanistic studies revealed that the heterogeneous nuclear ribonucleoprotein L (hnRNP L) activated the circANKRD42 reverse splicing biogenesis. The biogenetic circANKRD42 sponged miR-324-5p to promote the AJUBA expression, which blocked the binding between phosphorylated yes-associated protein 1 (YAP1) and large tumor suppressor kinase 1/2 (LATS1/2), leading to increased YAP1 entering the nucleus. circANKRD42 also sponged miR-136-5p to promote the YAP1 translation. Accumulating YAP1 in nucleus bound to TEAD, which initiated the transcription of genes related to mechanical stiffness. Finally, the therapeutic effect of circANKRD42 was evaluated in mice and the association between circANKRD42 and clinicopathological features was analyzed in IPF patients. Our findings supported that circANKRD42 is a promising biomarker and a potential therapeutic target related to cytoskeleton tension for IPF treatment.

The Combined Effects of circRNA Methylation Promote Pulmonary Fibrosis

N6-methyladenosine (m6A) is the most common type of RNA methylation modification, mainly occurring on mRNA. Whether m6A-modified circRNAs are involved in pulmonary fibrosis in different settings remains unclear. Using an m6A-circRNA epitranscriptomic chip, candidate circRNAs were selected, among which hsa_circ_0000672 and hsa_circ_0005654 were specifically involved in SiO2-induced pulmonary fibrosis by targeting the same protein, eIF4A3, indicating that the m6A modification of these two circRNAs has a synergistic effect on fibroblast dysfunction induced by SiO2. A mechanistic study revealed that the m6A modification of circRNAs was mainly mediated by the methyltransferase METTL3. Furthermore, METTL3 promoted the activation, migration and activity of pulmonary fibroblasts and participated in SiO2-induced pulmonary fibrosis via the circRNA m6A modification. m6A methylation of circRNAs mediates silica-induced fibrosis, enriching the understanding of circRNAs and uncovering a potential new target for treating fibrosis-related diseases.

CircOGDH Is a Penumbra Biomarker and Therapeutic Target in Acute Ischemic Stroke

BACKGROUND

Acute ischemic stroke (AIS) is a leading cause of disability and mortality worldwide. Prediction of penumbra existence after AIS is crucial for making decision on reperfusion therapy. Yet a fast, inexpensive, simple, and noninvasive predictive biomarker for the poststroke penumbra with clinical translational potential is still lacking. We aim to investigate whether the CircOGDH (circular RNA derived from oxoglutarate dehydrogenase) is a potential biomarker for penumbra in patients with AIS and its role in ischemic neuronal damage.

METHODS

CircOGDH was screened from penumbra of middle cerebral artery occlusion mice and was assessed in plasma of patients with AIS by quantitative polymerase chain reaction. Magnetic resonance imaging was used to examine the penumbra volumes. CircOGDH interacted with miR-5112 in primary cortical neurons was detected by fluorescence in situ hybridization, RNA immunoprecipitation, and luciferase reporter assay. ADV-mediated CircOGDH knockdown ameliorated neuronal apoptosis induced by COL4A4 (Gallus collagen, type VI, alpha VI) overexpression. Transmission electron microscope, nanoparticle tracking analysis, and Western blot were performed to confirm exosomes.

RESULTS

CircOGDH expression was dramatically and selectively upregulated in the penumbra tissue of middle cerebral artery occlusion mice and in the plasma of 45 patients with AIS showing a 54-fold enhancement versus noncerebrovascular disease controls. Partial regression analysis revealed that CircOGDH expression was positively correlated with the size of penumbra in patients with AIS. Sequestering of miR-5112 by CircOGDH enhanced COL4A4 expression to elevate neuron damage. Additionally, knockdown of CircOGDH significantly enhanced neuronal cell viability under ischemic conditions. Furthermore, the expression of CircOGDH in brain tissue was closely related to that in the serum of middle cerebral artery occlusion mice. Finally, we found that CircOGDH was highly expressed in plasma exosomes of patients with AIS compared with those in noncerebrovascular disease individuals.

CONCLUSIONS

These results demonstrate that CircOGDH is a potential therapeutic target for regulating ischemia neuronal viability, and is enriched in neuron-derived exosomes in the peripheral blood, exhibiting a predictive biomarker of penumbra in patients with AIS.

ZC3H4 promotes pulmonary fibrosis via an ER stress-related positive feedback loop

BACKGROUND

Pulmonary fibrosis is a sequela of many pulmonary diseases, such as pneumoconiosis and idiopathic pulmonary fibrosis. The principal characteristics of pulmonary fibrosis comprise myofibroblast proliferation, alveolar damage and deposition of extracellular matrix components, which cause abnormal lung structure remodeling and an irreversible decline in lung function; however, the detailed mechanisms remain unclear. The current study focused on the role of ZC3H4, a new member of the zinc finger protein family, in SiO₂-induced pulmonary fibrosis.

METHODS

The expression of ZC3H4 and fibroblast activation markers (COL1A1, COL3A1 and ACTA1) was measured by western blotting and immunofluorescence staining after SiO₂ exposure (50 μg/cm²). The functional change in fibroblasts was studied with a scratch assay and a 3D migration assay. The CRISPR/Cas9 system was used to explore the regulatory mechanisms of ZC3H4 in pulmonary fibroblast cells.

RESULTS

The expression levels of ZC3H4 and sigmar1 (a key regulator of ER stress) were increased in pulmonary fibroblast cells and were associated with fibroblast activation, as indicated by the increase in COL1A1, COL3A1 and ACTA1, as well as the migration ability. SiO₂-enhanced fibroblast activation was attenuated by specific knockdown of ZC3H4 and inhibition of ER stress, demonstrating that ZC3H4 activated fibroblasts via the sigmar1/ER stress pathway. Interestingly, ER stress blockade also inhibited ZC3H4 expression, indicating the positive feedback regulatory mechanism of ER stress on ZC3H4.

CONCLUSIONS

Our results demonstrate that ZC3H4 and sigmar1 might act as novel therapeutic targets for silicosis, providing a reference for further pulmonary fibrosis research.

Role of circRNA-miRNA-mRNA interaction network in diabetes and its associated complications

The majority of the non-protein-coding RNAs are being identified with diversified functions that participate in cellular homeostasis. The circular RNAs (circRNAs) are emerging as noncoding transcripts with a key role in the initiation and development of many physiological and pathological conditions. The advancements in high-throughput RNA sequencing and bioinformatics tools help us to identify several circRNA regulatory pathways, one of which is microRNA (miRNA)-mediated regulation. Besides the direct influence over mRNA transcription, the circRNA can also control the target's expression via sponging miRNAs or the RNA-binding proteins. Studies have demonstrated the dysregulation of the circRNA-miRNA-mRNA interaction network in the pathogenesis of many diseases, including diabetes. This intricate mechanism is associated with the pathogenesis of diabetes and its complications. This review will focus on the circRNA-miRNA-mRNA interaction network that influences the gene expression in the progression of diabetes and its associated complications.

CircRNAs: Decrypting the novel targets of fibrosis and aging

Fibrosis is a typical aging-related pathological process involving almost all organs. It is usually initiated by organic injury and leads to the gradual decline of organ function or even loss. Circular RNAs (circRNAs) are being hailed as a newly rediscovered class of covalently closed transcripts without a 5' cap or 3' tail which draw increasing attention. In particular, circRNAs have been identified to be involved in the multifaceted processes of fibrosis in various organs, including the heart, liver, lung, and kidney. As more and more circRNAs are functionally characterized, they have become novel therapies for fibrosis. In this review, we systematically summarized current studies regarding the roles of circRNAs in fibrosis and shed light on the basis of circRNAs as a potential treatment for fibrosis.

Microglial lnc-U90926 facilitates neutrophil infiltration in ischemic stroke via MDH2/CXCL2 axis

Dysregulated long non-coding RNAs (lncRNAs) have been shown to contribute to the pathogenesis of ischemic stroke. However, the potential role of lncRNAs in post-stroke microglial activation remains largely unknown. Here, we uncovered that lncRNA-U90926 was significantly increased in microglia exposed to ischemia/reperfusion both in vivo and in vitro. In addition, adenovirus-associated virus (AAV)-mediated microglial U90926 silencing alleviated neurological deficits and reduced infarct volume in experimental stroke mice. Microglial U90926 knockdown could reduce the infiltration of neutrophils into ischemic lesion site, which might be attributed to the downregulation of C-X-C motif ligand 2 (CXCL2). Mechanistically, U90926 directly bound to malate dehydrogenase 2 (MDH2) and competitively inhibited the binding of MDH2 to the CXCL2 3' untranslated region (UTR), thus protecting against MDH2-mediated decay of CXCL2 mRNA. Taken together, our study demonstrated that microglial U90926 aggravated ischemic brain injury via facilitating neutrophil infiltration, suggesting that U90926 might be a potential biomarker and therapeutic target for ischemic stroke.

Emerging Role of Circular RNA-Protein Interactions

Circular RNAs (circRNAs) are emerging as novel regulators of gene expression in various biological processes. CircRNAs regulate gene expression by interacting with cellular regulators such as microRNAs and RNA binding proteins (RBPs) to regulate downstream gene expression. The accumulation of high-throughput RNA-protein interaction data revealed the interaction of RBPs with the coding and noncoding RNAs, including recently discovered circRNAs. RBPs are a large family of proteins known to play a critical role in gene expression by modulating RNA splicing, nuclear export, mRNA stability, localization, and translation. However, the interaction of RBPs with circRNAs and their implications on circRNA biogenesis and function has been emerging in the last few years. Recent studies suggest that circRNA interaction with target proteins modulates the interaction of the protein with downstream target mRNAs or proteins. This review outlines the emerging mechanisms of circRNA-protein interactions and their functional role in cell physiology.

Circular RNA circβ-catenin aggravates the malignant phenotype of non-small-cell lung cancer via encoding a peptide

Background

More and more evidences demonstrate that circular RNAs (circNRAs) can encode protein. As a circRNA with translation capabilities, outcomes of circβ‐catenin in non‐small cell lung cancer (NSCLC) still need to be explored.

Method

The research methods of circβ‐catenin in the article include qRT‐PCR, wound healing assay, CCK‐8, colony formation, and Transwell assay. Western blotting and immunofluorescence were provided to detect protein expression levels and peptide encoded by circβ‐catenin, respectively.

Results

A prominently higher circβ‐catenin expression was found in NSCLC tissues. Silencing of circβ‐catenin was able to inhibit NSCLC cell migrating, invasive, and proliferative phenotypes. Overexpression of circβ‐catenin could enhance the migrating, invasive, and proliferative phenotypes of NSCLC cells. Importantly, circβ‐catenin was found to encode a peptide in NSCLC cells. Silencing or overexpression of circβ‐catenin could reduce or increase β‐catenin protein expression via suppressing the degradation of β‐catenin.

Conclusion

Circβ‐catenin could promote NSCLC cell malignant phenotypes via peptide‐regulated β‐catenin pathway. Our study provided a new understanding for the mechanisms of NSCLC.