The circular RNA circTXNRD1 promoted ambient particulate matter-induced inflammation in human bronchial epithelial cells by regulating miR-892a/COX-2 axis

CircRNA: a rising therapeutic strategy for lung injury induced by pulmonary toxicants

Lung injury has been a serious medical problem that requires new therapeutic approaches and biomarkers. Circular RNAs (circRNAs) are non-coding RNAs (ncRNAs) that exist widely in eukaryotes. CircRNAs are single-stranded RNAs that form covalently closed loops. CircRNAs are significant gene regulators that have a role in the development, progression, and therapy of lung injury by controlling transcription, translating into protein, and sponging microRNAs (miRNAs) and proteins. Although the study of circRNAs in lung injury caused by pulmonary toxicants is just beginning, several studies have revealed their expression patterns. The function that circRNAs perform in relation to pulmonary toxicants (severe acute respiratory distress syndrome coronavirus-2 (SARS-CoV-2), drug abuse, PM2.5, and cigarette smoke) is the main topic of this review. A variety of circRNAs can serve as potential biomarkers of lung injury. In this review, the biogenesis, properties, and biological functions of circRNAs were concluded, and the relationship between circRNAs and pulmonary toxicants was discussed. It is expected that the new ideas and potential treatment targets that circRNAs provide would be beneficial to research into the molecular mechanisms behind lung injury.

MicroRNA miR-212-5p Regulates the MEK/ERK Signaling Pathway by Targeting A-Raf proto-oncogene serine/threonine-protein kinase (ARAF) to Regulate Cowshed PM2.5-Induced NR8383 Apoptosis

Objective: To investigate the role of miR-212-5p-targeted ARAF during the apoptosis of rat alveolar macrophages induced by cowshed PM2.5. Methods: miRNA and related target genes and pathways were predicted using the KEGG, TargetScan, and other prediction websites. NR8383 macrophages were treated with cowshed PM2.5 to establish an in vitro lung injury model in rats; meanwhile, for the assessment of cell viability, apoptosis, intracellular calcium ions, and mitochondrial membrane potential in NR8383 cells, RT-qPCR was used to detect the expression of miR-212-5p and the target gene ARAF. Results: The bioinformatic analyses showed that miR-212-5p and ARAF were involved in PM2.5-associated cellular damage. Exposure to different concentrations (0 μg/mL, 60 μg/mL, 180 μg/mL, 300 μg/mL) with different durations (0 h, 12 h, 24 h, 48 h) of cowshed PM2.5 resulted in apoptosis, increased intracellular calcium ions, and decreased mitochondrial membrane potential. The miR-212-5p mimic group showed an up-regulation of Bax and cleaved Caspase 3 expression but decreased Bcl2 expression compared to the NC group, and overexpression of ARAF up-regulated the expression of p-MEK1/2 and p-ERK1/2 and simultaneously reversed the above phenomena. Conclusions: miR-212-5p targets ARAF to affect the cowshed PM2.5-induced apoptosis through the MEK/ERK signaling pathway, providing a potential target for relevant farming industry and pathology studies.

Circular RNAs and inflammation: Epigenetic regulators with diagnostic role

Circular RNAs (circRNAs) are a group of transcripts generally known to be non-coding transcripts, but occasionally producing short peptides. Circ_Ttc3/miR-148a, circ_TLK1/miR-106a-5p, circ_VMA21/miR-9-3p, circ_0068,888/miR-21-5p, circ_VMA21/miR-199a-5p, circ_AFF2/miR-375, circ_0008360/miR-135b-5p and circ-FBXW7/miR-216a-3p are examples of circRNA/miRNA pairs that contribute in the pathogenesis of immune-related conditions. CircRNAs have been found to regulate function of immune system and participate in the pathophysiology of immune-related disorders. In the current study, we searched PubMed and Google Scholar databases until July 2022 with the key words "circRNA" OR "circular RNA" AND "inflammation". Then, we assessed the abstract of retrieved articles to include original articles that assessed contribution of circRNAs in the pathoetiology of inflammation and related disorders. Finally, we went through the main texts of the articles and tabulated the available information. Therefore, the current study summarizes the role of circRNAs in the pathoetiology of sepsis, atherosclerosis, rheumatoid arthritis and osteoarthritis, immune-related cardiovascular, pulmonary, gastrointestinal and nervous system disorders.

The potential role of plasma miR-4301 in PM2.5 exposure-associated lung function reduction

The effect of PM_2.5 exposure on lung function reduction has been well-documented, but the underlying mechanism remains unclear. MiR-4301 may be involved in regulating pathways related to lung injury/repairment, and this study aimed to explore the potential role of miR-4301 in PM_2.5 exposure-associated lung function reduction. A total of 167 Wuhan community nonsmokers were included in this study. Lung function was measured and personal PM_2.5 exposure moving averages were evaluated for each participant. Plasma miRNA was determined by real-time polymerase chain reaction. A generalized linear model was conducted to assess the relationships among personal PM_2.5 moving average concentrations, lung function, and plasma miRNA. The mediation effect of miRNA on the association of personal PM_2.5 exposure with lung function reduction was estimated. Finally, we performed pathway enrichment analysis to predict the underlying pathways of miRNA in lung function reduction from PM_2.5 exposure. We found that each 10 μg/m³ increase in the 7-day personal PM_2.5 moving average concentration (Lag0-7) was related to a 46.71 mL, 1.15%, 157.06 mL/s, and 188.13 mL/s reductions in FEV₁, FEV₁/FVC, PEF, and MMF, respectively. PM_2.5 exposure was negatively associated with plasma miR-4301 expression levels in a dose‒response manner. Additionally, each 1% increase in miR-4301 expression level was significantly associated with a 0.36 mL, 0.01%, 1.14 mL/s, and 1.28 mL/s increases in FEV₁, FEV₁/FVC, MMF, and PEF, respectively. Mediation analysis further revealed that decreased miR-4301 mediated 15.6% and 16.8% of PM_2.5 exposure-associated reductions in FEV₁/FVC and MMF, respectively. Pathway enrichment analyses suggested that the wingless related-integration site (Wnt) signaling pathway might be one of the pathways regulated by miR-4301 in the reduction of lung function from PM_2.5 exposure. In brief, personal PM_2.5 exposure was negatively associated with plasma miR-4301 or lung function in a dose‒response manner. Moreover, miR-4301 partially mediated the lung function reduction associated with PM_2.5 exposure.

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.

Perturbation of arachidonic acid and glycerolipid metabolism promoted particulate matter-induced inflammatory responses in human bronchial epithelial cells

Particulate matter (PM) has become the main risk factor for public health, being linked with an increased risk of respiratory diseases. However, the potential mechanisms underlying PM-induced lung injury have not been well elucidated. In this study, we systematically integrated the metabolomics, lipidomics, and transcriptomics data obtained from the human bronchial epithelial cells (HBECs) exposed to PM to reveal metabolic disorders in PM-induced lung injury. We identified 170 differentially expressed metabolites (82 upregulated and 88 downregulated metabolites), 218 differentially expressed lipid metabolites (125 upregulated and 93 downregulated lipid metabolites), and 1417 differentially expressed genes (643 upregulated and 774 downregulated genes). Seven key metabolites (prostaglandin E2, inosinic acid, L-arginine, L-citrulline, L-leucine, adenosine, and adenosine monophosphate), and two main lipid subclasses (triglyceride and phosphatidylcholine) were identified in PM-exposed HBECs. The amino acid metabolism, lipid metabolism, and carbohydrate metabolism were the significantly enriched pathways of identified differentially expressed genes. Then, conjoint analysis of these three omics data and further qRT-PCR validation showed that arachidonic acid metabolism, glycerolipid metabolism, and glutathione metabolism were the key metabolic pathways in PM-exposed HBECs. The knockout of AKR1C3 in arachidonic acid metabolism or GPAT3 in glycerolipid metabolism could significantly inhibit PM-induced inflammatory responses in HBECs. These results revealed the potential metabolic pathways in PM-exposed HBECs and provided a new target to protect from PM-induced airway damage.

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.

Edaravone Attenuated Particulate Matter-Induced Lung Inflammation by Inhibiting ROS-NF-κB Signaling Pathway

Background

Particulate matter (PM) exposure is related to mitochondria dysfunction and airway inflammation. Antioxidant drug edaravone (EDA) is reported to improve the occurrence and development of oxidative stress-related diseases. At present, there is no data on whether EDA can alleviate lung inflammation caused by PM.

Methods

The anti-inflammatory effects of EDA were investigated in urban PM-induced human bronchial epithelial cells (HBECs) and C57/BL6J mouse models. In vitro, its effects on the production of intracellular reactive oxygen species (ROS), mitochondrial membrane potential (MMP), and inflammatory cytokines were assessed by DCFH-DA staining, JC-1 assay, and real-time PCR, respectively. In vivo, the oxidant stress in lung tissues was assessed by dihydroethidium (DHE) staining and malondialdehyde (MDA) activity, and inflammatory cytokines in bronchoalveolar lavage fluid (BALF) were assessed by ELISA, respectively. Furthermore, the potential signaling pathways were studied by siRNA transfection and western blot.

Results

PM increased the expression of inflammatory cytokines and protein, including IL-6, IL-1α, IL-1β, and COX-2, while these alternations were significantly alleviated following EDA treatment in a dose-dependent manner. EDA treatment also alleviated the inflammatory responses in lung tissues of PM-exposed mice. We further showed mitochondrial dysfunction in PM-exposed HBECs and mice, which were reversed by EDA treatment. Moreover, the phosphorylation of NF-κB p65 in PM-exposed HBECs and mice was weakened by EDA. Transfection with NF-κB p65 siRNA further inhibited PM-induced inflammation in HBECs.

Conclusion

We demonstrated that EDA treatment had a protective role in PM-induced lung inflammation through maintaining mitochondrial balance and regulating the ROS-NF-κB p65 signaling pathway. This provided a new therapeutic method for PM-induced lung inflammation in the future.