Research progress of circRNA as a biomarker of sepsis: a narrative review

Circular RNAs as potential biomarkers for male severe sepsis

Circular RNAs (circRNAs) play important roles in many human diseases. However, their role in the development of severe sepsis, a condition that remains one of the main causes of death in intensive care units, has not yet been defined. In this study, we interrogated the molecular mechanisms of circRNAs in severe sepsis. We profiled the expression levels of 5,680 circRNAs in plasma extracted from blood samples of 9 severe sepsis cases or 9 controls (male, age 78 ± 7) using the Human circRNA Array. To enrich protein-coding genes hosting severe sepsis-related circRNAs, we conducted gene ontology and pathways analyses. Out of the identified 760 differentially expressed circRNAs, 404 were upregulated while 356 were downregulated (fold change [FC] ≥2 or ≤-2, and false discovery ratio <0.05). Circ-0008285 (located in exons of CDYL), showed significant upregulation in severe sepsis with an FC of 13.7, and Bonferroni-corrected P < 0.05/5. In silico analysis identified Circ-0008285 interacting microRNAs as well as protein-coding genes. We systematically investigated the differential expression pattern of circRNAs in severe sepsis. The circRNAs we identified might serve as potential biomarkers for diagnosis and prognosis of sepsis.

Circular RNA Circ_0122396 Regulates Human Lens Epithelial Cell Progression by Regulating miR-23a-3p and MMP16 in Age-Related Cataract

BACKGROUND

CircRNA plays a regulatory role in multiple life processes. Circ_0122396 could participate in the regulation of age-related cataract (ARC) progression. However, the precise molecular mechanisms of circ_0122396 In ARC remain enigmatic.

METHODS

Circ_0122396, microRNA (miR)-23a-3p, and matrix metalloprotease (MMP)-16 (MMP16) expression levels were detected via quantitative real-time polymerase chain reaction. Western blot was used to detect the levels of MMP16 and apoptosis-related proteins. Cell counting kit-8 analysis and 5-ethynyl-2'-deoxyuridine assay were used to assess human lens epithelial cells (HLECs) proliferation. Flow cytometry was performed to determine cell apoptosis. Levels of malondialdehyde (MDA) and glutathione peroxidase (GSH-PX) were measured using commercial kits. Luciferase reporter assay, RNA immunoprecipitation (RIP) assay, and RNA pull-down assay were used to examine the interaction among circ_0122396, miR-23a-3p, and MMP16.

RESULTS

Circ_0122396 and MMP16 were down-regulated while miR-23a-3p was up-regulated in ARC. H2O2 constrained proliferation and GSH-PX level, promotes apoptosis and MDA level in HLECs, and overexpression of circ_0122396 attenuated these effects. miR-23a-3p was a direct target of circ_0122396, and MMP16 was a direct target of miR-23a-3p. The effect of circ_0122396 overexpression on H2O2-induced HLECs was reversed by miR-23a-3p, and MMP16 elevation overturned the impacts of miR-23a-3p in H2O2-induced HLECs.

CONCLUSIONS

Circ_0122396 may regulate the progression of ARC via the miR-23a-3p/MMP16 pathway in H2O2-stimulated HLECs, which may serve as a potentially valuable biomarker and novel therapeutic target for ARC.

Long noncoding RNAs and circular RNAs as potential diagnostic biomarkers of inflammatory bowel diseases: a systematic review and meta-analysis

Introduction

Inflammatory bowel disease (IBD) poses a growing global burden, necessitating the discovery of reliable biomarkers for early diagnosis. The clinical significance of dysregulated expression of long noncoding RNAs (lncRNAs) and circular RNAs (circRNAs) in diagnosing IBD has not been well established. Thus, our study aimed to investigate the diagnostic value of lncRNAs and circRNAs for IBD based on currently available studies.

Methods

A comprehensive search was carried out in diverse electronic databases, such as PubMed, Embase, Scopus, Science Direct and Wiley Online Library to retrieve articles published until October 30, 2023. Stata 17.0 software was employed to determine pooled sensitivity, specificity, positive likelihood ratio (PLR), negative likelihood ratio (NLR), diagnostic ratio (DOR), and area under the curve (AUC). Heterogeneity, subgroup analysis, and meta-regression were explored, and publication bias was assessed using Deeks' funnel plot. Fagan's nomogram and likelihood ratio scattergram were employed to evaluate the clinical validity.

Result

A total of 11 articles encompassing 21 studies which involved 1239 IBD patients and 985 healthy controls were investigated. The findings revealed lncRNAs exhibit high level of pooled sensitivity 0.94 (95% CI: 0.87-0.97) and specificity 0.99 (95% CI: 0.89-1.00), along with PLR, NLR, DOR, and AUC values of 64.25 (95% CI: 7.39-558.66), 0.06 (95% CI: 0.03-0.13), 1055.25 (95% CI: 70.61-15770.77), and 0.99 (95% CI: 0.97-0.99), respectively. Conversely, CircRNAs showed moderate accuracy in IBD diagnosis, with sensitivity of 0.68 (95% CI: 0.61-0.73), specificity of 0.73 (95% CI: 0.65-0.79), PLR of 2.47 (95% CI: 1.94-3.16), NLR of 0.45 (95% CI: 0.38-0.53), DOR of 5.54 (95% CI: 3.88-7.93), and AUC value of 0.75 (95% CI: 0.71-0.79). Moreover, findings from subgroup analysis depicted heightened diagnostic efficacy when employing lncRNA H19 and a large sample size (≥100), with notable efficacy in diagnosing both ulcerative colitis (UC) and Crohn's disease (CD).

Conclusion

LncRNAs exhibit high diagnostic accuracy in distinguishing patients with IBD from healthy controls signifying their possible use as potential biomarkers, while circRNAs showed moderate diagnostic accuracy. Nevertheless, to validate our findings and confirm the clinical utility of lncRNAs and circRNAs in IBD diagnosis, a large pool of prospective and multi-center studies should be undertaken.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO, identifier CRD42023491840.

CIRC_0033530 KNOCKDOWN ALLEVIATES LIPOPOLYSACCHARIDE-INDUCED ACUTE LUNG INJURY MODEL OF HUMAN LUNG FIBROBLASTS BY MIR-1184/TLR4 AXIS

ABSTRACT

Background: Circular RNAs have been reported to be involved in regulating the progression of sepsis and sepsis-associated damage. Herein, this work investigated whether circ_0033530 had roles in the process of septic acute lung injury (sepsis-ALI) and its associated mechanism. Methods: Lipopolysaccharide (LPS)-stimulated human lung fibroblasts MRC-5 were used to mimic the cell model of sepsis-ALI in vitro . Levels of genes and proteins were detected by quantitative real-time polymerase chain reaction and Western blotting. Functional experiments were conducted using 5-ethynyl-2'-deoxyuridine assay, Cell Counting Kit-8 assay, flow cytometry, and enzyme-linked immunosorbent assay. The interaction between miR-1184 and circ_0033530 or toll-like receptor 4 (TLR4) was confirmed by dual-luciferase reporter and RNA immunoprecipitation assays. Results: Circ_0033530 expression was lower in sepsis patients and LPS-induced fibroblasts than those in healthy control and untreated cells. Functionally, knockdown of circ_0033530 protected fibroblasts against LPS-induced proliferation arrest, apoptosis, and inflammatory response. Mechanistically, circ_0033530 acted as a sponge for miR-1184, and TLR4 RNA was targeted by miR-1184, indicating the circ_0033530/miR-1184/TLR4 axis. Further rescue experiments showed that circ_0033530 silencing-mediated growth inhibition and inflammation on fibroblasts were attenuated by miR-1184 downregulation or TLR4 upregulation. Conclusion: Circ_0033530 knockdown alleviated LPS-induced proliferation arrest, apoptosis, and inflammation in lung fibroblasts by miR-1184/TLR4 axis, and provided molecular theoretical basis for circ_0033530 on the pathogenesis of sepsis-ALI.

INTERFERING HSA_CIRC_0001226 MITIGATES LPS-INDUCED BEAS-2B CELL INJURY BY REGULATING MIR-940/TGFBR2 PATHWAY

ABSTRACT

Background: Sepsis-associated acute lung injury (SA-ALI) is a serious threat to human health. A growing body of evidence suggested that circular RNAs may be involved in ALI progression. The aim of this study was to investigate the effect and mechanism of circ_0001226 on lipopolysaccharide (LPS)-induced BEAS-2B cells. Methods: BEAS-2B cells were stimulated with LPS to establish a SA-ALI cell model. The expression of circ_0001226, miR-940, and transforming growth factor beta receptor II (TGFBR2) were monitored by quantitative real-time polymerase chain reaction. Cell proliferation and apoptosis were evaluated by the Cell Counting Kit-8, 5-ethynyl-2'-deoxyuridine assay, and flow cytometry. The levels of interleukin-6 (IL-6), IL-1β, and tumor necrosis factor-α were calculated by enzyme-linked immunosorbent assay. Western blot was implemented to test the protein levels of PCNA, Bax, and TGFBR2. Dual-luciferase reporter assay and RNA pull-down assay were adopted to investigate the interaction between circ_0001226 and miR-940, as well as TGFBR2 and miR-940. Results: The levels of circ_0001226 and TGFBR2 were elevated, and miR-940 was decreased in SA-ALI serum specimens and LPS-evoked BEAS-2B cells. Besides that, circ_0001226 interference contributed to cell proliferation and restrained apoptosis and inflammation in LPS-induced BEAS-2B cells. Mechanically, circ_0001226 worked as a molecular sponge of miR-940 to regulate TGFBR2 expression. Conclusion: Circ_0001226 deficiency weakened LPS-mediated proliferation inhibition and inflammatory processes in BEAS-2B cells by binding miR-940 and regulating TGFBR2.

circFLNA promotes intestinal injury during abdominal sepsis through Fas-mediated apoptosis pathway by sponging miR-766-3p

BACKGROUND

Intra-abdominal infections are the second most common cause of sepsis in the intensive care unit. Intestinal epithelial injury due to abdominal sepsis results in a variety of pathological changes, such as intestinal bacteria and toxins entering the blood, leading to persistent systemic inflammation and multiple organ dysfunction. The increased apoptosis of intestinal epithelial cells induced by sepsis further exacerbates the progression of sepsis. Although several studies have revealed that circRNAs are involved in intestinal epithelial injury in sepsis, few studies have identified the roles of circRNAs in intestinal epithelial apoptosis.

METHODS

We used laser capture microdissection to obtain purified epithelial cells located in intestinal crypts from four patients with abdominal sepsis induced by intestinal perforation and four samples from age and sex-matched non-septic patients. Microarray analysis of circRNAs was conducted to assess differentially expressed circRNAs between patients with and without sepsis. Lastly, in vitro and in vivo assays were performed to study the mechanism of circFLNA in intestinal epithelial apoptosis during sepsis.

RESULTS

circFLNA was upregulated in the intestinal epithelium after abdominal sepsis induced by intestinal perforation. Inhibition of miR-766-3p impaired si-circFLNA-mediated inhibition of apoptosis and inflammation factor levels in lipopolysaccharide (LPS)-treated HIEC-6 cells. circFLNA aggravated apoptosis and inflammation through the Fas-mediated apoptosis pathway in both LPS-treated HIEC-6 cells and a mouse cecal ligation and puncture model.

CONCLUSION

Our findings showed that circFLNA promotes intestinal injury in abdominal sepsis through the Fas-mediated apoptosis pathway by sponging miR-766-3p. The circFLNA/miR-766-3p/Fas axis has potential as a novel therapeutic target for treating intestinal injury in sepsis.

Systemic inflammation as a biomarker of seizure propensity and a target for treatment to reduce seizure propensity

People with diabetes can wear a device that measures blood glucose and delivers just the amount of insulin needed to return the glucose level to within bounds. Currently, people with epilepsy do not have access to an equivalent wearable device that measures a systemic indicator of an impending seizure and delivers a rapidly acting medication or other intervention (e.g., an electrical stimulus) to terminate or prevent a seizure. Given that seizure susceptibility is reliably increased in systemic inflammatory states, we propose a novel closed-loop device where release of a fast-acting therapy is governed by sensors that quantify the magnitude of systemic inflammation. Here, we review the evidence that patients with epilepsy have raised levels of systemic indicators of inflammation than controls, and that some anti-inflammatory drugs have reduced seizure occurrence in animals and humans. We then consider the options of what might be incorporated into a responsive anti-seizure system.

SCREENING OF POTENTIAL CORE GENES IN PERIPHERAL BLOOD OF ADULT PATIENTS WITH SEPSIS BASED ON TRANSCRIPTION REGULATION FUNCTION

ABSTRACT

Objective: The aim of the study is to screen transcription factor genes related to the prognosis of adult patients with sepsis. Methods: Twenty-three patients with sepsis and 10 healthy individuals admitted for RNA-seq. Differential factors were enriched by four transcription factor databases, and survival analysis was adopted for core factors. Then, target genes were submitted to STRING to constitute the protein-protein interaction network. Single-cell technology was used to localize cell lines. Finally, a transcription-target gene regulation network was constituted. Results: A total of 4,224 differentially expressed genes were obtained between sepsis and normal control groups. Protein-protein interaction results showed that FOXO3, NFKB1, SPI1, STAT5A, and PPARA were located in the center of the network. Target genes were related to cytokine-mediated signaling pathway and transcription regulator activity, etc. SPI1 was mainly located in monocyte cell lines, while FOXO3, PPARA, SP1, STAT3, and USF1 were expressed in monocyte cell lines, NK-T cell lines, and B cell lines. Compared with those in the control group, FOXO3, SP1, SPI1, STAT3, and USF1 were highly expressed in the sepsis group, while PPARA had low expression. Conclusions: Transcription factors, such as FOXO3, PPARA, SP1, SPI1, STAT3, and USF1, are correlated with the prognosis of sepsis patients and thus may have a potential research value. Clinical Trial Registration: The clinical trial registration number is ChiCTR1900021261.

Circular RNA protein tyrosine kinase 2 aggravates pyroptosis and inflammation in septic lung tissue by promoting microRNA-766/eukaryotic initiation factor 5A axis-mediated ATP efflux

PURPOSE

Sepsis is characterized by an acute inflammatory response to infection, often with multiple organ failures, especially severe lung injury. This study was implemented to probe circular RNA (circRNA) protein tyrosine kinase 2 (circPTK2)-associated regulatory mechanisms in septic acute lung injury (ALI).

METHODS

A cecal ligation and puncture-based mouse model and an lipopolysaccharides (LPS)-based alveolar type II cell (RLE-6TN) model were generated to mimic sepsis. In the two models, inflammation- and pyroptosis-related genes were measured.

RESULTS

The degree of lung injury in mice was analyzed by hematoxylin and eosin (H&E) staining and the apoptosis was by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling staining. In addition, pyroptosis and toxicity were detected in cells. Finally, the binding relationship between circPTK2, miR-766, and eukaryotic initiation factor 5A (eIF5A) was detected. Data indicated that circPTK2 and eIF5A were up-regulated and miR-766 was down-regulated in LPS-treated RLE-6TN cells and lung tissue of septic mice. Lung injury in septic mice was ameliorated after inhibition of circPTK2.

CONCLUSIONS

It was confirmed in the cell model that knockdown of circPTK2 effectively ameliorated LPS-induced ATP efflux, pyroptosis, and inflammation. Mechanistically, circPTK2 mediated eIF5A expression by competitively adsorbing miR-766. Taken together, circPTK2/miR-766/eIF5A axis ameliorates septic ALI, developing a novel therapeutic target for the disease.

Screening of Sepsis Biomarkers Based on Bioinformatics Data Analysis

Methods

Gene expression profiles of GSE13904, GSE26378, GSE26440, GSE65682, and GSE69528 were obtained from the National Center for Biotechnology Information (NCBI). The differentially expressed genes (DEGs) were searched using limma software package. Gene Ontology (GO) functional analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis, and protein-protein interaction (PPI) network analysis were performed to elucidate molecular mechanisms of DEGs and screen hub genes.

Results

A total of 108 DEGs were identified in the study, of which 67 were upregulated and 41 were downregulated. 15 superlative diagnostic biomarkers (CCL5, CCR7, CD2, CD27, CD274, CD3D, GNLY, GZMA, GZMH, GZMK, IL2RB, IL7R, ITK, KLRB1, and PRF1) for sepsis were identified by bioinformatics analysis.

Conclusion

15 hub genes (CCL5, CCR7, CD2, CD27, CD274, CD3D, GNLY, GZMA, GZMH, GZMK, IL2RB, IL7R, ITK, KLRB1, and PRF1) have been elucidated in this study, and these biomarkers may be helpful in the diagnosis and therapy of patients with sepsis.

Circ_UBE2D2 Attenuates the Progression of Septic Acute Kidney Injury in Rats by Targeting miR-370-3p/NR4A3 Axis

As circ_UBE2D2 has been confirmed to have targeted binding sites with multiple miRNAs involved in septic acute kidney injury (SAKI), efforts in this study are directed to unveiling the specific role and relevant mechanism of circ_UBE2D2 in SAKI. HK-2 cells were treated with lipopolysaccharide (LPS) to construct SAKI model in vitro. After sh-circ_UBE2D2 was transfected into cells, the transfection efficiency was detected by qRT-PCR, cell viability and apoptosis were determined by MTT assay and flow cytometry, and expressions of Bcl-2, Bax and Cleaved-caspase 3 were quantified by western blot. Target genes associated with circ_UBE2D2 were predicted using bioinformatics analysis. After the establishment of SAKI rat model, HE staining and TUNEL staining were exploited to observe the effect of circ_UBE2D2 on tissue damage and cell apoptosis. The expression of circ_UBE2D2 was overtly elevated in LPS-induced HK-2 cells. Sh-circ_UBE2D2 can offset the inhibition of cell viability and the promotion of cell apoptosis induced by LPS. Circ_UBE2D2 and miR-370-3p as well as miR-370-3p and NR4A3 have targeted binding sites. MiR-370-3p inhibitor reversed the promoting effect of circ_UB2D2 silencing on viability of LPS-treated cells, but shNR4A3 neutralized the above inhibitory effect of miR-370-3p inhibitor. MiR-370-3p inhibitor weakened the down-regulation of NR4A3, Bax and Cleaved caspase-3 and the up-regulation of Bcl-2 induced by circ_UB2D2 silencing, but these trends were reversed by shNR4A3. In addition, sh-circ_UBE2D2 could alleviate the damage of rat kidney tissue. Circ_UBE2D2 mitigates the progression of SAKI in rats by targeting miR-370-3p/NR4A3 axis.

Serum and Serum Exosomal CircRNAs hsa_circ_0001492, hsa_circ_0001439, and hsa_circ_0000896 as Diagnostic Biomarkers for Lung Adenocarcinoma

Background

Circular RNAs (circRNAs) play an important role in tumorigenesis and several circulating circRNA signatures are closely associated with tumor diagnosis. However, the expression and clinical significance of the two forms of circulating circRNAs, serum and serum exosomal, in patients with lung adenocarcinoma (LUAD), have not been characterized.

Methods

Three differentially expressed exosomal circRNAs, hsa_circ_0001492, hsa_circ_0001439, and hsa_circ_0000896, were selected based on previous exosomal circRNA sequencing data analyses of LUAD patients. The expression of these circRNAs in serum and serum-derived exosomes of LUAD patients was assessed using quantitative real-time PCR (qRT-PCR), and correlations between circRNA expression and clinicopathological characteristics were analyzed. The reliability of serum and serum exosomal hsa_circ_0001492, hsa_circ_0001439, and hsa_circ_0000896 to diagnose LUAD was evaluated using receiver operating characteristic (ROC) analysis.

Results

Expression of serum and serum exosomal hsa_circ_0001492, hsa_circ_0001439, and hsa_circ_0000896 were significantly higher in LUAD patients than in healthy donors, and significantly lower after surgery. These three serum exosomal circRNAs were also associated with a higher cancer stage. Exosomal hsa_circ_0001492 expression was positively correlated with carcinoembryonic antigen (CEA) and neuron-specific enolase (NSE) levels. An association between the expression of the three serum circRNAs and clinical characteristics was not observed. In addition, the three serum exosomal circRNAs had higher diagnostic sensitivity and specificity than the serum circRNAs, and the area under the curve (AUC) of all three serum exosomal circRNAs was &gt;0.75. The combination of exosomal hsa_circ_0001492, hsa_circ_0001439, and hsa_circ_0000896 had better diagnostic sensitivity and specificity than that of a single marker, with an AUC value of 0.805.

Conclusions

The serum and serum exosomal circRNAs, hsa_circ_0001492, hsa_circ_0001439, and hsa_circ_0000896, were upregulated in LUAD patients. Serum exosomal circRNAs may serve as more effective biomarkers than serum circRNAs for LUAD diagnosis and may further aid the detection of this disease.

Circular RNAs in the pathogenesis of sepsis and their clinical implications: A narrative review

Introduction: Sepsis is defined as a life-threatening complication that occurs when the body responds to an infection attacking the host. Sepsis rapidly progresses and patients deteriorate and develop septic shock, with multiple organ failure, if not promptly treated. Currently no effective therapy is available for sepsis; therefore, early diagnosis is crucial to decrease the high mortality rate. Genome-wide expression analyses of patients in critical conditions have confirmed that the expression levels of the majority of genes are changed, suggesting that the molecular basis of sepsis is at the gene level. This review aims to elucidate the role of circular (circ) RNAs in the pathogenesis of sepsis and sepsis-induced organ damage. In addition, the feasibility of using circRNAs as novel diagnostic biomarkers for sepsis is also discussed, as well as circRNA-based therapy. Method: This narrative review is based on a literature search using Medline database. Search terms used were “circular RNAs and sepsis”, “circRNAs and sepsis”, “non-coding RNAs and sepsis”, “ncRNAs and sepsis”, “circRNAs and septic pathogenesis”, “circRNAs and septic model”, “circRNAs and septic shock” and “circRNAs, biomarker, and sepsis”. Results: Numerous studies indicate that circRNAs might exert pivotal roles in regulating the immune system of the host against various pathogens, such as bacteria and viruses. Dysregulation of circRNA expression levels has been confirmed as an early event in sepsis and associated with the inflammatory response, immunosuppression and coagulation dysfunction. This impairment in regulation eventually leads to multiple organ dysfunctions, including of the kidneys, lungs and heart. Conclusion: By investigating the regulation of circRNAs in sepsis, new molecular targets for the diagnosis and intervention of sepsis can be identified. Such an understanding will be important for the development of therapeutic drugs. Keywords: Acute kidney injury, biomarker, circRNAs, inflammation, sepsis

CircRNAs in Malignant Tumor Radiation: The New Frontier as Radiotherapy Biomarkers

World Health Organization (WHO) data show that of the top 20 factors that threaten human life and health, cancer is at the forefront, and the therapeutic approaches for cancer consist of surgery, radiotherapy, chemotherapy and immunotherapy. For most highly metastatic and recurrent cancer, radiation therapy is an essential modality to mitigate tumor burden and improve patient survival. Despite the great accomplishments that have been made in clinical therapy, an inevitable challenge in effective treatment is radioresistance, the mechanisms of which have not yet been completely elucidated. In addition, radiosensitization methods based on molecular mechanisms and targets, and clinical applications are still inadequate. Evidence indicates that circular RNAs (circRNAs) are important components in altering tumor progression, and in influencing resistance and susceptibility to radiotherapy. This review summarizes the reasons for tumor radiotherapy resistance induced by circRNAs, and clarifies the molecular mechanisms and targets of action. Moreover, we determine the potential value of circRNAs as clinical indicators in radiotherapy, providing a theoretical basis for circRNAs-based strategies for cancer radiotherapy.

CircN4bp1 Facilitates Sepsis-Induced Acute Respiratory Distress Syndrome through Mediating Macrophage Polarization via the miR-138-5p/EZH2 Axis

We recently reported the differential circRNA expression patterns of the pulmonary macrophages in sepsis-induced acute respiratory distress syndrome (ARDS) mice model by microarray analysis. However, their function and hidden molecular mechanism in regulation of macrophage activation and inflammation remain poorly understood. In this study, we found that circN4bp1was overexpressed in PBMC and monocytes, and its expression levels were correlated with a poor prognosis in sepsis induced ARDS patients induced by sepsis. Knockdown of circN4bp1 inhibited the lung injury and improved the long-time survival through blunting the M1 macrophage activation in cecal ligation and puncture- (CLP-) induced ARDS mice. Moreover, bioinformatics analysis predicated a circN4bp1/miR-138-5p ceRNA network, which was confirmed by luciferase reporter assay and RNA binding protein immunoprecipitation (RIP). CircN4bp1 affected macrophage differentiation by binding to miR-138-5p, thus regulating the expression of EZH2 in vivo and ex vivo. Lastly, the m6A level of circN4bp1was found to be elevated in ARDS mice; inhibition of m6A methyltransferase METTL3 blocked this response in vitro. Therefore, circN4bp1 can function as a miR-138-5p sponge for the modulation of macrophage polarization through regulation the expression of EZH2 and may serve as a potential target and/or prognostic marker for ARDS patients following sepsis.

A Novel Age-Related Circular RNA Circ-ATXN2 Inhibits Proliferation, Promotes Cell Death and Adipogenesis in Rat Adipose Tissue-Derived Stromal Cells

Adipose tissue-derived stromal cells are promising candidates investigating the stem cell-related treatment. However, their proportion and utility in the human body decline with time, rendering stem cells incompetent to complete repair processes in vivo. The involvement of circRNAs in the aging process is poorly understood. Rat subcutaneous adipose tissue from 10-week-old and 27-month-old rats were used for hematoxylin and eosin (H and E) staining, TUNEL staining, and circRNA sequencing. Rat adipose tissue-derived stromal cells were cultured and overexpressed with circ-ATXN2. Proliferation was examined using xCELLigence real-time cell analysis, EdU staining, and cell cycle assay. Apoptosis was induced by CoCl2 and examined using flow cytometry. RT-PCR assay and Oil Red O staining were used to measure adipogenesis at 48 h and 14 days, respectively. H and E staining showed that the diameter of adipocytes increased; however, the number of cells decreased in old rats. TUNEL staining showed that the proportion of apoptotic cells was increased in old rats. A total of 4,860 and 4,952 circRNAs was detected in young and old rats, respectively. Among them, 67 circRNAs exhibited divergent expression between the two groups (fold change ≥2, p ≤ 0.05), of which 33 were upregulated (49.3%) and 34 were downregulated (50.7%). The proliferation of circ-ATXN2-overexpressing cells decreased significantly in vitro, which was further validated by xCELLigence real-time cell analysis, EdU staining, and cell cycle assay. Overexpression of circ-ATXN2 significantly increased the total apoptotic rate from 5.78 ± 0.46% to 11.97 ± 1.61%, early apoptotic rate from 1.76 ± 0.22% to 5.50 ± 0.66%, and late apoptosis rate from 4.02 ± 0.25% to 6.47 ± 1.06% in adipose tissue-derived stromal cells. Furthermore, in circ-ATXN2-overexpressing cells, RT-PCR assay revealed that the expression levels of adipose differentiation-related genes PPARγ and CEBP/α were increased and the Oil Red O staining assay showed more lipid droplets. Our study revealed the expression profile of circRNAs in the adipose tissue of old rats. We found a novel age-related circular RNA—circ-ATXN2—that inhibits proliferation and promotes cell death and adipogenesis in rat adipose tissue-derived stromal cells.