Circular RNA: A novel potential biomarker for skin diseases

Non-coding RNA in infantile hemangioma

Infantile hemangioma (IH) is the most common benign vascular tumor of infancy, but its pathogenesis has not been fully discovered. From the cellular perspective, CD133+ stem cells orchestrate the proliferation and development of IH. Regarding molecular mechanisms, hypoxia inducible factor-1α, renin-angiotensin system, and vascular endothelial growth factor are current study hotspots, while non-coding RNAs (ncRNAs) might be essential factors participating in this network. Therefore, this article reviewed published studies concerning the roles of ncRNAs in IH and listed noted miRNAs, lncRNAs, and circRNAs. Other ncRNAs, such as snRNAs, snoRNAs, and tsRNAs, though have not been examined in IH, are mentioned as well to discuss their potential functions. Due to the continuous development of sequencing technologies and computational pipelines for ncRNAs annotation, relevant studies will provide evidence to gradually enhance acknowledgments of ncRNAs' role in IH. The pathogenesis of IH might be revealed and the treatment protocol would be optimized in the future. IMPACT: Non-coding RNAs (ncRNAs) play critical roles in infantile hemangioma. This article thoroughly reviewed all ncRNAs (miRNAs, lncRNAs, and circRNAs) mentioned in previous studies regarding the pathogenesis of infantile hemangioma. Other ncRNAs are promising subjects for further investigation. This review introduced the emerging ncRNAs that need to be explored in IH.

A novel UVA-associated circUBE2I mediates ferroptosis in HaCaT cells

Alternative splicing of precursor messenger RNA (pre-mRNA), including linear splicing and back splicing, produces multiple isoforms that lead to diverse cell fates in response to stimuli including ultraviolet radiation (UVR). Although UVR-induced linear gene splicing has been extensively studied in skin cells, the UVR-induced gene back-splicing events that lead to the production of circular RNAs (circRNAs) have not been thoroughly investigated. The present study used circRNA transcriptome sequencing to screen the differentially expressed circRNAs in human keratinocytes (HaCaT) after UVA irradiation. A total of 312 differentially expressed circRNAs were found in HaCaT cells post-UVR. Among the UVA-induced differentially expressed circRNAs, circUBE2I-a novel circRNA formed by exons 2-6 of the UBE2I gene-was the most significantly upregulated circRNA. RT-qPCR assay further confirmed the increase of circUBE2I level in HaCaT cells after UVA irradiation or H2O2 treatment. RNase R digestion experiment revealed the stability of circUBE2I. Overexpression of circUBE2I in keratinocytes induced ferroptosis after UVA or H2O2, preventable by the ferroptosis inhibitor ferrostatin-1. Our study provides new insights into the role of circular RNAs in UVA-induced skin cell damage and suggests that circUBE2I could be a therapeutic target in UVR-aroused ferroptosis in skin cells.

Unraveling the crosstalk: circRNAs and the wnt signaling pathway in cancers of the digestive system

Circular RNA (circRNA) is a unique type of noncoding RNA molecule characterized by its closed-loop structure. Functionally versatile, circRNAs play pivotal roles in gene expression regulation, protein activity modulation, and participation in cell signaling processes. In the context of cancers of the digestive system, the Wnt signaling pathway holds particular significance. Anomalous activation of the Wnt pathway serves as a primary catalyst for the development of colorectal cancer. Extensive research underscores the notable participation of circRNAs associated with the Wnt pathway in the progression of digestive system tumors. These circRNAs exhibit pronounced dysregulation across esophageal cancer, gastric cancer, liver cancer, colorectal cancer, pancreatic cancer, and cholangiocarcinoma. Furthermore, the altered expression of circRNAs linked to the Wnt pathway correlates with prognostic factors in digestive system tumors. Additionally, circRNAs related to the Wnt pathway showcase potential as diagnostic, therapeutic, and prognostic markers within the realm of digestive system tumors. This comprehensive review outlines the interplay between circRNAs and the Wnt signaling pathway in cancers of the digestive system. It seeks to provide a comprehensive perspective on their association while delving into ongoing research that explores the clinical applications of circRNAs associated with the Wnt pathway.

WTAP mediated m6A-modified circ_0056856 contributes to the proliferation, migration, and invasion of IL-22-stimulated human keratinocyte by miR-197-3p/CDK1 axis

BACKGROUND

Psoriasis is a chronic inflammation-associated skin disorder, and interleukin-22 (IL-22) is involved in psoriasis pathogenesis by boosting the proliferation and migration of keratinocytes. Mounting evidence has shown that circRNAs might play an important role in several aspects of psoriasis. This study is designed to explore the role and mechanism of circ_0056856 in regulating the phenotypes of IL-22-induced keratinocytes (HaCaT cells).

METHODS

Circ_0056856, microRNA-197-3p (miR-197-3p), Cyclin-dependent kinase 1 (CDK1), and Wilms tumor 1-associated protein (WTAP) levels were detected using real-time quantitative polymerase chain reaction (RT-qPCR). Cell viability, proliferation, migration, and invasion were analyzed using 3-(4, 5-dimethyl-2-thiazolyl)-2, 5-diphenyl-2-H-tetrazolium bromide (MTT), 5-ethynyl-2'-deoxyuridine (EdU), Wound scratch, and Transwell assays. After being predicted by Circinteractome or TargetScan, binding between miR-197-3p and circ_0056856 or CDK1 was verified by a dual-luciferase reporter assay. CDK1 and WTAP protein levels were determined using Western blot. Interaction between WTAP and circ_0056856 was assessed using methylated RNA immunoprecipitation (MeRIP) assay.

RESULTS

Increased circ_0056856, CDK1, and WTAP were observed in psoriasis patients and IL-22-treated HaCaT cells. Moreover, circ_0056856 knockdown might repress IL-22-induced HaCaT cell proliferation, migration, and invasion in vitro. In mechanism, circ_0056856 might function as a sponge of miR-197-3p to modulate CDK1 expression, and WTAP improved circ_0056856 expression via m6A methylation.

CONCLUSION

WTAP-guided m6A modified circ_0056856 facilitates IL-22-stimulated HaCaT cell damage through the miR-197-3p/CDK1 axis, which could provide novel insights into psoriasis treatment.

The Role of Epigenetic Factors in the Pathogenesis of Psoriasis

Psoriasis is a chronic inflammatory skin disease, the prevalence of which is increasing. Genetic, genomic, and epigenetic changes play a significant role in the pathogenesis of psoriasis. This review summarizes the impact of epigenetics on the development of psoriasis and highlights challenges for the future. The development of epigenetics provides a basis for the search for genetic markers associated with the major histocompatibility complex. Genome-wide association studies have made it possible to link psoriasis to genes and therefore to epigenetics. The acquired knowledge may in the future serve as a solid foundation for developing newer, increasingly effective methods of treating psoriasis. In this narrative review, we discuss the role of epigenetic factors in the pathogenesis of psoriasis.

Hydroxysafflor Yellow A Promotes HaCaT Cell Proliferation and Migration by Regulating HBEGF/EGFR and PI3K/AKT Pathways and Circ_0084443

OBJECTIVE

To investigate the effect and possible mechanism of hydroxysafflor yellow A (HSYA) on human immortalized keratinocyte cell proliferation and migration.

METHODS

HaCaT cells were treated with HSYA. Cell proliferation was detected by the cell counting kit-8 assay, and cell migration was measured using wound healing assay and Transwell migration assay. The mRNA and protein expression levels of heparin-binding epidermal growth factor (EGF)-like growth factor (HBEGF), EGF receptor (EGFR), phosphatidylinositol 3-kinase (PI3K), protein kinase B (AKT), mammalian target of rapamycin (mTOR), and hypoxia-inducible factor-1α (HIF-1α) were detected by quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot, respectively. Circ_0084443-overexpressing HaCaT cells and empty plasmid HaCaT cells were constructed using the lentiviral stable transfection and treated with HSYA. The expression of circ_0084443 was detected by qRT-PCR.

RESULTS

HSYA (800 µmol/L) significantly promoted HaCaT cell proliferation and migration (P<0.05 or P<0.01). It also increased the mRNA and protein expression levels of HBEGF, EGFR, PI3K, AKT, mTOR and HIF-1α, and increased the phosphorylation levels of PI3K and AKT (P<0.05 or P<0.01). Furthermore, HSYA promoted HaCaT cell proliferation and migration via the HBEGF/EGFR and PI3K/AKT/mTOR signaling pathways (P<0.01). Circ_0084443 attenuated the mRNA expression levels of HBEGF, EGFR, PI3K, AKT, mTOR and HIF-1α (P<0.05). HSYA inhibited the circ_0084443 expression, further antagonized the inhibition of circ_0084443 on HBEGF, EGFR, PI3K, AKT, mTOR and HIF-1α, and promoted the proliferation of circ_0084443-overexpressing HaCaT cells (P<0.05 or P<0.01). However, HSYA could not influence the inhibitory effect of circ_0084443 on HaCaT cell migration (P>0.05).

CONCLUSION

HSYA played an accelerative role in HaCaT cell proliferation and migration, which may be attributable to activating HBEGF/EGFR and PI3K/AKT signaling pathways, and had a particular inhibitory effect on the keratinocyte negative regulator circ_0084443.

Adipocyte-derived exosomes promote the progression of triple-negative breast cancer through circCRIM1-dependent OGA activation

Triple-negative breast cancer (TNBC) has an escalating morbidity and a dismal prognosis. Obesity has been reported to be strongly linked to adverse TNBC outcomes. Exosomes (Exos) transport RNA and proteins between cells and serve as intermediaries for cell-to-cell communication. Accumulated evidence suggests that adipose-secreted circular RNAs (circRNAs) can modulate protein glycosylation in TNBC to facilitate tumor cell outgrowth. Herein, exo-circCRIM1 expression was found to be elevated in TNBC patients with a high body fat percentage. Functional experiments demonstrated that by inhibiting miR-503-5p, exo-circCRIM1 enhanced TNBC evolution and metastasis while activating glycosylation hydrolase OGA. Furthermore, OGA negatively regulates FBP1 by decreasing its protein stability. Moreover, the levels of OGA and FBP1 were positively related to the infiltration level of some immune cells in TNBC. These findings indicate that exo-cirCRIM1 secreted by adipocytes contributes to TNBC progression by inhibiting miR-503-5p and activating the OGA/FBP1 signaling pathway. The findings reveal a novel intercellular signaling pathway mediated by adipose-derived exosomes and suggest that treatment targeting the secreted exosome-circCRIM1 may reverse TNBC progression.

Expression and Regulatory Mechanisms of MicroRNA in Cholesteatoma: A Systematic Review

Cholesteatoma is a temporal bone disease characterized by dysfunctions of keratinocytes. MicroRNAs (miRNAs) are evolutionary conserved noncoding RNAs that regulate mRNA expression. They can be packaged into exosomes and transported to target cells that can be used in the future therapy of cholesteatoma. This study aimed to collect knowledge on the role of miRNAs and exosomal miRNAs in cholesteatoma and was conducted according to the PRISMA guidelines for systematic reviews. Four databases were screened: Pubmed/MEDLINE, Web of Science, Scopus, and the Cochrane Library. The last search was run on the 6th of June 2023. We included full-text original studies written in English, which examined miRNAs in cholesteatoma. The risk of bias was assessed using the Office of Health Assessment and Translation (OHAT) Risk of Bias Rating Tool, modified for the needs of this review. We identified 118 records and included 18 articles. Analyses revealed the downregulation of exosomal miR-17 as well as miR-10a-5p, miR-125b, miR-142-5p, miR34a, miR-203a, and miR-152-5p and the overexpression of exosomal miR-106b-5p as well as miR-1297, miR-26a-5p, miR-199a, miR-508-3p, miR-21-3p, miR-584-5p, and miR-16-1-3p in cholesteatoma. The role of differentially expressed miRNAs in cholesteatoma, including cell proliferation, apoptosis, the cell cycle, differentiation, bone resorption, and the remodeling process, was confirmed, making them a potential therapeutic target in this disease.

A review on circular RNAs and bacterial infections

Bacterial infections and related diseases have been a major burden on social public health and economic stability around the world. However, the effective diagnostic methods and therapeutic approaches to treat bacterial infections are still limited. As a group of non-coding RNA, circular RNAs (circRNAs) that were expressed specifically in host cells and played a key regulatory role have the potential to be of diagnostic and therapeutic value. In this review, we systematically summarize the role of circRNAs in common bacterial infections and their potential roles as diagnostic markers and therapeutic targets.

Unique regulatory roles of ncRNAs changed by PM2.5 in human diseases

PM_2.5 is a type of particulate matter with an aerodynamic diameter smaller than 2.5 µm, and exposure to PM_2.5 can adversely damage human health. PM_2.5 may impair health through oxidative stress, inflammatory reactions, immune function alterations and chromosome or DNA damage. Through increasing in-depth studies, researchers have found that noncoding RNAs (ncRNAs), particularly microRNAs (miRNAs), circular RNAs (circRNAs) as well as long noncoding RNAs (lncRNAs), might play significant roles in PM_2.5-related human diseases via some of the abovementioned mechanisms. Therefore, in this review, we mainly discuss the regulatory function of ncRNAs altered by PM_2.5 in human diseases and summarize the potential molecular mechanisms. The findings reveal that these ncRNAs might induce or promote diseases via inflammation, the oxidative stress response, cell autophagy, apoptosis, cell junction damage, altered cell proliferation, malignant cell transformation, disruption of synaptic function and abnormalities in the differentiation and status of immune cells. Moreover, according to a bioinformatics analysis, the altered expression of potential genes caused by these ncRNAs might be related to the development of some human diseases. Furthermore, some ncRNAs, including lncRNAs, miRNAs and circRNAs, or processes in which they are involved may be used as biomarkers for relevant diseases and potential targets to prevent these diseases. Additionally, we performed a meta-analysis to identify more promising diagnostic ncRNAs as biomarkers for related diseases.

Circ_0082476 targets miR-138-5p to promote proliferation, invasion, migration and inflammation in IL-22-treated human keratinocytes by upregulating BRD4

BACKGROUND

Circular RNAs (circRNAs) are implicated in the disease progression via acting as sponges of microRNAs (miRNAs) to regulate gene expression. The purpose of this study was to analyze the involvement of circ_0082476 in Interleukin-22 (IL-22)-induced psoriasis.

METHODS

Expression detection for circ_0082476, microRNA-424-5p (miR-138-5p) or toll-like receptor (BRD4) was completed using reverse transcription-quantitative polymerase chain reaction assay. Cell Counting Kit-8 assay and EdU assay were used for analysis of cell viability and proliferation, respectively. Cell invasion and migration abilities were assessed through transwell assay and wound healing assay. The protein expression was examined via western blot. Inflammatory reaction was determined via Enzyme-linked immunosorbent assay. Dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay were conducted for target binding research.

RESULTS

Circ_0082476 was significantly elevated in psoriasis patients and IL-22-treated keratinocytes (HaCaT). Knockdown of circ_0082476 reduced cell proliferation, invasion and migration in IL-22-treated HaCaT cells. Circ_0082476 induced sponge effect on miR-138-5p. Circ_0082476 regulated IL-22-induced cell injury through targeting miR-138-5p. BRD4 was confirmed as a target of miR-138-5p, and miR-138-5p relieved IL-22-induced cell dysfunction by the direct downregulation of BRD4. BRD4 was positively regulated by circ_0082476 via sponging miR-138-5p.

CONCLUSION

These findings disclosed that circ_0082476 facilitated the IL22-induced epidermis cell injury in psoriasis through the upregulation of BRD4 via binding to miR-138-5p.

CIRC_0008882 STIMULATES PDE7A TO SUPPRESS SEPTIC ACUTE KIDNEY INJURY PROGRESSION BY SPONGING MIR-155-5P

ABSTRACT

Background: The importance of circular RNA (circRNA) in the progression of septic acute kidney injury (AKI) was gradually recognized. It has been confirmed that circ_0008882 expression was decreased in the blood of patients with AKI. However, the role of circ_0008882 in septic AKI progression remains unclear. Methods: Human kidney-2 (HK2) cells were stimulated with lipopolysaccharide (LPS) to establish a septic AKI cell model. The RNA and protein expression of circ_0008882, miR-155-5p, phosphodiesterase 7A (PDE7A), PCNA, Bax, and Bcl-2 were detected by quantitative real-time polymerase chain reaction and Western blot. Cell viability was investigated by cell counting kit-8 assay. Enzyme-linked immunosorbent assay (ELISA) was adopted to measure the levels of inflammatory factors (TNF-α, IL-1β, and IL-6). Flow cytometry was implemented to evaluate cell cycle and cell apoptosis. The Caspase3 activity was examined using Caspase3 Assay Kit. Dual-luciferase reporter assay and RNA immunoprecipitation assay were applied to verify the molecular target relations. Results: Septic AKI serum samples and LPS-induced HK2 cells displayed low expression of circ_0008882 and PDE7A, and high expression of miR-155-5p when compared with the controls. Overexpression of circ_0008882 relieved LPS-induced HK2 cell injury. MiR-155-5p was a target of circ_0008882, and miR-155-5p mimic restored circ_0008882 overexpression-mediated effects on LPS-treated HK2 cells. PDE7A was identified as a target gene of miR-155-5p, and PDE7A downregulation almost reverted the improvement impacts induced by the miR-155-5p inhibitor. Conclusions: Overexpression of circ_0008882 impeded LPS-induced HK2 cell injury by modulating miR-155-5p/PDE7A pathway, implying that circ_0008882 might be a possible circRNA-targeted therapy for septic AKI.

Overview of m6A and circRNAs in human cancers

N⁶-methyladenosine (m⁶A), the richest post-transcriptional modification of RNA in eukaryotic cells, is dynamically installed/uninstalled by the RNA methylase complex ("writer") and demethylase ("eraser") and recognized by the m⁶A-binding protein ("reader"). M⁶A modification on RNA metabolism involves maturation, nuclear export, translation and splicing, thereby playing a critical role in cellular pathophysiology and disease processes. Circular RNAs (circRNAs) are a class of non-coding RNAs with a covalently closed loop structure. Due to its conserved and stable properties, circRNAs could participate in physiological and pathological processes through unique pathways. Despite the recent discovery of m⁶A and circRNAs remains in the initial stage, research has shown that m⁶A modifications are widespread in circRNAs and regulates circRNA metabolism, including biogenesis, cell localization, translation, and degradation. In this review, we describe the functional crosstalk between m⁶A and circRNAs, and illustrate their roles in cancer development. Moreover, we discuss the potential mechanisms and future research directions of m⁶A modification and circRNAs.

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

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

Pathogenesis, multi-omics research, and clinical treatment of psoriasis

Psoriasis is a common inflammatory skin disease involving interactions between keratinocytes and immune cells that significantly affects the quality of life. It is characterized by hyperproliferation and abnormal differentiation of keratinocytes and excessive infiltration of immune cells in the dermis and epidermis. The immune mechanism underlying this disease has been elucidated in the past few years. Research shows that psoriasis is regulated by the complex interactions among immune cells, such as keratinocytes, dendritic cells, T lymphocytes, neutrophils, macrophages, natural killer cells, mast cells, and other immune cells. An increasing number of signaling pathways have been found to be involved in the pathogenesis of psoriasis, which has prompted the search for new treatment targets. In the past decades, studies on the pathogenesis of psoriasis have focused on the development of targeted and highly effective therapies. In this review, we have discussed the relationship between various types of immune cells and psoriasis and summarized the major signaling pathways involved in the pathogenesis of psoriasis, including the PI3K/AKT/mTOR, JAK-STAT, JNK, and WNT pathways. In addition, we have discussed the results of the latest omics research on psoriasis and the epigenetics of the disease, which provide insights regarding its pathogenesis and therapeutic prospects; we have also summarized its treatment strategies and observations of clinical trials. In this paper, the various aspects of psoriasis are described in detail, and the limitations of the current treatment methods are emphasized. It is necessary to improve and innovate treatment methods from the molecular level of pathogenesis, and further provide new ideas for the treatment and research of psoriasis.

Circ_0007534 as new emerging target in cancer: Biological functions and molecular interactions

Circular RNA (circRNAs), an important member of the non-coding RNA (ncRNA) family, are widely expressed in a variety of biological cells. Owing to their stable structures, sequence conservations, and cell- or tissue-specific expressions, these RNA have become a popular subject of scientific research. With the development of sequencing methods, it has been revealed that circRNAs exert their biological function by sponging microRNAs (miRNAs), regulating transcription, or binding to proteins. Humans have historically been significantly impacted by various types of cancer. Studies have shown that circRNAs are abnormally expressed in various cancers and are involved in the occurrence and development of malignant tumors, such as tumor cell proliferation, migration, and invasion. As one of its star molecules, circ_0007534 is upregulated in colorectal, cervical, and pancreatic cancers; is closely related to the occurrence, development, and prognosis of tumors; and is expected to become a novel tumor marker and therapeutic target. This article briefly reviews the expression and mechanism of circ_0007534 in malignant tumors based on the domestic and foreign literature.

Roles and mechanisms of CircRNAs in ovarian cancer

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

Circ_0077109 sponges miR-139-5p and upregulates HOXD10 in trophoblast cells as potential mechanism for preeclampsia progression

BACKGROUND

One of the important reasons for the development of preeclampsia (PE) is the abnormal function of trophoblast cells. Many circular RNAs (circRNAs) have been confirmed to participate in the regulation of trophoblast cell function to mediate PE progression. However, whether circ_0077109 is involved in PE progression through regulating trophoblast cell function remains unclear.

METHODS

Quantitative real-time PCR was utilized for measuring the expression of circ_0077109, microRNA (miR)-139-5p and homeobox D10 (HOXD10). Trophoblast cell proliferation, apoptosis, invasion, and angiogenesis was assessed cell counting kit 8 assay, EdU assay, flow cytometry, transwell assay and tube formation assay. In addition, western blot analysis was used to determine protein expression. The interaction between miR-139-5p and circ_0077109 or HOXD10 was verified by dual-luciferase reporter assay and RIP assay.

RESULTS

Our results pointed out that circ_0077109 was a circRNA with upregulated expression in PE patients. Overexpression of circ_0077109 suppressed trophoblast cell proliferation, invasion, and angiogenesis, while increased apoptosis. MiR-139-5p was found to be sponged by circ_0077109, and its mimic reversed the suppressive effect of circ_0077109 on trophoblast cell function. HOXD10 was a target of miR-139-5p, and its overexpression inhibited trophoblast cell proliferation, invasion, and angiogenesis. MiR-139-5p inhibitor could repress trophoblast cell function, while this effect could be reversed by HOXD10 knockdown.

CONCLUSION

In summary, we confirmed that circ_0077109 inhibited trophoblast cell function through the regulation of miR-139-5p/HOXD10 axis, which might be a potential target for PE treatment. This article is protected by copyright. All rights reserved.

CircRNA-Encoded Peptides or Proteins as New Players in Digestive System Neoplasms

Circular RNAs (circRNAs) were considered non-coding RNAs. Nowadays, a large number of studies have found that these RNAs contain open reading frames that can be translated in a cap-independent manner, such as internal ribosome entry site (IRES) and N6-methyladenosine (m6A). The encoded peptides or proteins affect the occurrence and development of tumors by regulating the Yap-hippo and the Wnt/β-catenin signaling pathways, as well as the malignant progression of tumors through phosphorylation and ubiquitination of specific molecules. This review will summarize the regulation of circRNA translation and the functional roles and underlying mechanisms of circRNA-derived peptides or proteins in digestive tract tumors. Some circRNA-encoded peptides or proteins may be used as tumor biomarkers and prognostic factors for early screening and treatment of clinical gastrointestinal tumors.

Identification of Novel Circular RNAs of the Human Protein Arginine Methyltransferase 1 (PRMT1) Gene, Expressed in Breast Cancer Cells

Circular RNAs (circRNAs) constitute a type of RNA formed through back-splicing. In breast cancer, circRNAs are implicated in tumor onset and progression. Although histone methylation by PRMT1 is largely involved in breast cancer development and metastasis, the effect of circular transcripts deriving from this gene has not been examined. In this study, total RNA was extracted from four breast cancer cell lines and reversely transcribed using random hexamer primers. Next, first- and second-round PCRs were performed using gene-specific divergent primers. Sanger sequencing followed for the determination of the sequence of each novel PRMT1 circRNA. Lastly, bioinformatics analysis was conducted to predict the functions of the novel circRNAs. In total, nine novel circRNAs were identified, comprising both complete and truncated exons of the PRMT1 gene. Interestingly, we demonstrated that the back-splice junctions consist of novel splice sites of the PRMT1 exons. Moreover, the circRNA expression pattern differed among these four breast cancer cell lines. All the novel circRNAs are predicted to act as miRNA and/or protein sponges, while five circRNAs also possess an open reading frame. In summary, we described the complete sequence of nine novel circRNAs of the PRMT1 gene, comprising distinct back-splice junctions and probably having different molecular properties.

Circ_0060531 knockdown ameliorates IL-22-induced keratinocyte damage by binding to miR-330-5p to decrease GAB1 expression

BACKGROUND

Psoriasis is a chronic immune-mediated skin disease. Recent studies showed its pathogenesis involved circular RNA (circRNA). However, the role of circ_0060531 in psoriasis development and the behind mechanism remain to be explored.

METHODS

Psoriasis cell model was constructed by treating keratinocytes (HaCaT cells) using interleukin 22 (IL-22). Expression of circ_0060531, microRNA-330-5p (miR-330-5p) and GRB2 associated binder 1 (GAB1) was determined by quantitative real-time polymerase chain reaction. The functional effects of circ_0060531 on IL-22-caused cell injury were investigated by 3-(4,5-Dimethylthazol-2-yl)-2,5-diphenyltetrazolium bromide, 5-Ethynyl-29-deoxyuridine, wound-healing and enzyme-linked immunosorbent assays. Protein expression was analysed by Western blot. The interactions among circ_0060531, miR-330-5p and GAB1 were identified by dual-luciferase reporter or RNA immunoprecipitation assay.

RESULTS

Circ_0060531 and GAB1 expression were significantly increased, while miR-330-5p was decreased in psoriatic skin biopsies and IL-22-stimulated HaCaT cells in comparison with controls. In function, circ_0060531 knockdown assuaged IL-22-induced cell proliferation, cell migration and inflammation. Besides, circ_0060531 acted as a miR-330-5p sponge, and regulated the processes of IL-22-treated HaCaT cells by binding to the miRNA. Under the treatment of IL-22, miR-330-5p mediated HaCaT cell damage by targeting GAB1. Importantly, circ_0060531 modulated GAB1 production by interacting with miR-330-5p.

CONCLUSION

Circ_0060531 knockdown assuaged IL-22-induced keratinocyte dysfunction through miR-330-5p/GAB1 pathway, proving a novel target for the therapy of psoriasis.

Non-coding RNAs in photoaging-related mechanisms: a new paradigm in skin health

The aging of skin is a biological process affected by environmental or genetic factors. Exposure to ultraviolet (UV) radiation is the main environmental factor causing skin aging. Cumulative UV-induced photodamage of the skin tissue is associated with premature cellular senescence, extracellular degradation, and inflammatory responses in photoaging processes. Non-coding RNAs (ncRNAs) are untranslated transcripts and master regulators of protein-coding genes. ncRNAs have a critical regulatory role in maintaining skin structure, skin barrier function, morphogenesis, and development. Altered ncRNA expression has been reported in various skin disorders such as photoaging and skin cancers. ncRNAs contribute to the suppression and promotion of photoaging by modulating signaling pathways such as mitogen-activated protein kinase (MAPK) pathway and regulating inflammatory cytokines, matrix metalloproteinases (MMPs), and senescence-associated genes. Elucidation of the functions of ncRNAs will improve the identification of molecular mechanisms underlying photoaging, and can be used in the development of therapeutic approaches in skin health and prevention of sun-induced aging. This review summarized the currently described ncRNAs and their functions in photoaging.

Hsa_circ_0062270 Promotes Tumorigenesis of Melanoma by Stabilizing the Linear Transcript Cell Division Cycle Protein 45

Background: To elucidate the potential biological function of hsa_circ_0062270 in the malignant process of melanoma and its potential target. Methods: Quantitative real-time polymerase chain reaction (qRT-PCR) was conducted to examine relative level of hsa_circ_0062270 in melanoma tissues and normal skin tissues. The diagnostic and prognostic potentials of hsa_circ_0062270 in melanoma were evaluated. The regulatory effect of hsa_circ_0062270 on the expression of linear transcript Cell division cycle protein 45 (CDC45) was also examined. Results: Hsa_circ_0062270 was up-regulated in melanoma samples and cell lines, which displayed certain diagnostic and prognostic potentials in melanoma. Inhibition of hsa_circ_0062270 attenuated the proliferative, migratory and invasive functions. Hsa_circ_0062270 could stabilize the expression of linear transcript CDC45, and thus participated in the malignant process of melanoma. Conclusion: Hsa_circ_0062270 promotes proliferative, migratory and invasive functions of melanoma cells via stabilizing the linear transcript CDC45. Hsa_circ_0062270 can be used to diagnosis and treatment of melanoma.

Beyond the Code: Noncoding RNAs in Skin Wound Healing

An increasing number of noncoding RNAs (ncRNAs) have been found to regulate gene expression and protein functions, playing important roles in diverse biological processes and diseases. Their crucial functions have been reported in almost every cell type and all stages of skin wound healing. Evidence of their pathogenetic roles in common wound complications, such as chronic nonhealing wounds and excessive scarring, is also accumulating. Given their unique expression and functional properties, ncRNAs are promising therapeutic and diagnostic entities. In this review, we discuss current knowledge about the functional roles of noncoding elements, such as microRNAs, long ncRNAs, and circular RNAs, in skin wound healing, focusing on in vivo evidence from studies of human wound samples and animal wound models. Finally, we provide a perspective on the outlook of ncRNA-based therapeutics in wound care.

Circular RNA VMA21 ameliorates lung injury in septic rat via targeting microRNA-497-5p/CD2-associated protein axis

Sepsis was characterized via an acute inflammatory response to infection, often accompanying by multiple organ failure, particularly lung damage. Circular RNA (circRNA) played an important role in the pathology of a variety of diseases. However, the role of circRNA in sepsis-induced lung injury (LI) remained unknown. This study was to explore the expression and role of circVMA21 in sepsis LI and the possible molecular mechanism. The results manifested circVMA21 and CD2-associated protein (CD2AP) were down-regulated in lung tissue and lipopolysaccharide (LPS)-treated BEAS-2B, while microRNA (miR)-497-5p was up-regulated. A large number of deaths in rats after surgery of 72 h were caused via cecal ligation-perforation surgery, W/D value and Bax positive cells were increased, LI was caused, cell apoptosis, tumor necrosis factor-α, Interleukin (IL)-1β and IL-6 expression were promoted and Bcl-2 positive cells were decreased. Overexpression of circVMA21 ameliorated these phenomena. In addition, LPS-induced apoptosis and inflammation of BEAS-2B cells was improved via overexpression of circVMA21, while overexpression of miR-497-5P was opposite. Apoptosis, inflammation, and oxidative damage of BEAS-2B cells were aggravated via knockdown of circVMA21, but it was reversed by knockdown of miR-497-5p or overexpression of CD2AP. Mechanistically, CircVMA21 mediated CD2AP expression through competitive adsorption of miR-497-5p. In conclusion, this work showed circVMA21 improved LI in sepsis rats by targeting miR-497-5p/CD2AP axis, suggesting that circVMA21 may be a novel therapeutic target for sepsis-induced LI.

Involvement of CircRNA Expression Profile in Diabetic Retinopathy and Its Potential Diagnostic Value

Background: Circular RNAs (circRNAs), a class of non-coding and undegradable RNAs, play many pathological functions by acting as miRNA sponges, interacting with RNA-binding proteins, and others. The recent literature indicates that circRNAs possess the advanced superiority for the early screening of diabetic retinopathy (DR).

Methods: CircRNA sources of peripheral blood mononuclear cells (PBMCs) from healthy controls (n = 4), diabetes mellitus patients (DM) (n = 4), and DR patients (n = 4) were extracted for circular RNA microarray analysis. Enriched biological modules and signaling pathways were analyzed by Gene Ontology Enrichment and Kyoto Encyclopedia of Genes and Genomes analysis, respectively. Real-time quantitative reverse transcription PCR (RT-qPCR) was performed to validate differentiated levels of several circRNAs (fold change ≥2, p < .05) in different groups of healthy control subjects (n = 20), DM patients (n = 60), and DR patients (n = 42). Based on our clinical data from DR, the diagnostic performance of candidate circRNAs was measured by operating characteristic curves (ROCs). Subsequently, their circRNA–miRNA networks were constructed by bioinformatics analysis.

Results: Circular RNA microarray analysis was performed, and 2,452 and 289 circRNAs were screened with differential expression in DR patients compared to healthy controls and DM patients, respectively. Enrichment analyses showed that circRNAs in DR patients were enriched in extracellular matrix (ECM)–receptor interaction and focal adhesion pathways. The top 5 differential circRNAs in circRNA microarray analysis were subsequently quantified and verified by RT-qPCR. Consistently, a significant 2.2-fold reduction of hsa_circ_0095008 and 1.7-fold increase in hsa_circ_0001883 were identified in DR patients compared to DM patients. Meanwhile, the area under curves of hsa_circ_0095008 and hsa_circ_0001883 were 0.6710 (95% CI, 0.5646–0.7775) (p = 0.003399) and 0.6071 (95% CI, 0.4953–0.7189) (p = 0.06644), respectively, indicating a good diagnostic value.

Conclusion: Our study provided a new sight for the pathological mechanism of DR and revealed the potential value of hsa_circ_0095008 and hsa_circ_0001883 as diagnostic biomarkers for the early diagnosis of DR patients.

The pleiotropic roles of circular and long noncoding RNAs in cutaneous melanoma

Cutaneous melanoma (CM) is a very aggressive disease, often characterized by unresponsiveness to conventional therapies and high mortality rates worldwide. The identification of the activating BRAFV600 mutations in approximately 50% of CM patients has recently fueled the development of novel small-molecule inhibitors that specifically target BRAFV600 -mutant CM. In addition, a major progress in CM treatment has been made by monoclonal antibodies that regulate the immune checkpoint inhibitors. However, although target-based therapies and immunotherapeutic strategies have yielded promising results, CM treatment remains a major challenge. In the last decade, accumulating evidence points to the aberrant expression of different types of noncoding RNAs (ncRNAs) in CM. While studies on microRNAs have grown exponentially leading to significant insights on CM biology, the role of circular RNAs (circRNAs) and long noncoding RNAs (lncRNAs) in this tumor is less understood, and much remains to be discovered. Here, we summarize and critically review the available evidence on the molecular functions of circRNAs and lncRNAs in BRAFV600 -mutant CM and CM immunogenicity, providing recent updates on their functional role in targeted therapy and immunotherapy resistance. In addition, we also include an evaluation of several algorithms and databases for prediction and validation of circRNA and lncRNA functional interactions.

Emerging Role and Mechanism of circRNAs in Pediatric Malignant Solid Tumors

Circular RNAs (circRNAs) are non-coding RNAs with covalent closed-loop structures and are widely distributed in eukaryotes, conserved and stable as well as tissue-specific. Malignant solid tumors pose a serious health risk to children and are one of the leading causes of pediatric mortality. Studies have shown that circRNAs play an important regulatory role in the development of childhood malignant solid tumors, hence are potential biomarkers and therapeutic targets for tumors. This paper reviews the biological characteristics and functions of circRNAs as well as the research progress related to childhood malignant solid tumors.

Role of circular RNAs in gastrointestinal tumors and drug resistance

The incidence of gastrointestinal cancers has increased significantly over the past decade and gastrointestinal malignancies now rank among the leading causes of mortality globally. Although newer therapeutic strategies such as targeted therapies have greatly improved patient outcomes, their clinical success is limited by drug resistance, treatment failure and recurrence of metastatic disease. Therefore, there is an urgent need for further research identifying accurate and reliable biomarkers for precise treatment strategies. Circular RNAs (circRNAs) exhibit a covalently closed structure, high stability and biological conservation, and their expression is associated with the occurrence and development of gastrointestinal tumors. Moreover, circRNAs may significantly influence drug resistance of gastrointestinal cancers. In this article, we review the role of circRNAs in the occurrence and development of gastrointestinal cancer, their association with drug resistance, and potential application for early diagnosis, treatment and prognosis in gastrointestinal malignancies. Furthermore, we summarize characteristics of circRNA, including mechanism of formation and biological effects via mRNA sponging, chromatin replication, gene regulation, translational modification, signal transduction, and damage repair. Finally, we discuss whether circRNA-related noninvasive testing may be clinically provided in the future. This review provides new insights for the future development of diagnostics and therapeutics based on circRNAs in gastrointestinal tumors.

Circ_0084443 Inhibits Wound Healing Via Repressing Keratinocyte Migration Through Targeting the miR-17-3p/FOXO4 Axis

Keratinocyte migration is a crucial process during skin wound healing, and circular RNAs are associated with keratinocyte migration. The purpose of our study was to clarify the role of circ_0084443 in wound healing. The levels of circ_0084443, microRNA (miR)-17-3p, and forkhead box protein O4 (FOXO4) were examined by quantitative reverse transcription-PCR. Cell migration was detected via wound scratch assay or transwell assay. The protein expression was measured using western blot. The binding analysis between miR-17-3p and circ_0084443 or FOXO4 was determined by dual-luciferase reporter assay and RNA Immunoprecipitation assay. TGF-β1 decreased the levels of circ_0084443 and FOXO4 while increased the miR-17-3p expression in keratinocytes by a concentration-dependent manner. Circ_0084443 acted as a miR-17-3p sponge and circ_0084443 overexpression alleviated TGF-β1-induced migration of keratinocytes by sponging miR-17-3p. FOXO4 was a target for miR-17-3p. The downregulation of miR-17-3p suppressed cell migration in TGF-β1-induced cells by increasing the FOXO4 level. Circ_0084443 positively regulated the FOXO4 expression by sponging miR-17-3p. Circ_0084443 suppressed the TGFβ signaling pathway by affecting the miR-17-3p/FOXO4 axis. These results exhibited that circ_0084443 suppressed the TGF-β1-induced keratinocyte migration by regulating the miR-17-3p/FOXO4 axis, suggesting the application potential of circ_0084443 in wound-healing-related diseases.

Dynamic m6A-ncRNAs association and their impact on cancer pathogenesis, immune regulation and therapeutic response

Several types of modifications have been proven to participate in the metabolism and processing of different RNA types, including non-coding RNAs (ncRNAs). N-6-methyladenosine (m6A) is a dynamic and reversible RNA modification that is closely involved in the ncRNA homeostasis, and serves as a crucial regulator for multiple cancer-associated signaling pathways. The ncRNAs usually regulate the epigenetic modification, mRNA transcription and other biological processes, displaying enormous roles in human cancers. In this review, we summarized the significant implications of m6A-ncRNA interaction in various types of cancers. In particular, the interplay between m6A and ncRNAs in cancer pathogenesis and therapeutic resistance are being widely recognized. We also discussed the relevance of m6A-ncRNA interaction in immune regulation, followed by the interference on cancer immunotherapeutic procedures. In addition, we briefly highlighted the computation tools that could identify the accurate features of m6A methylome among ncRNAs. In summary, this review would pave the way for a better understanding of the biological functions of m6A-ncRNA crosstalk in cancer research and treatment.

Effect, Mechanism, and Applications of Coding/Non-coding RNA m6A Modification in Tumor Microenvironment

The tumor microenvironment (TME), which includes immune cells, fibroblasts, and other components, is the site of tumor cell growth and metastasis and significantly impacts tumor development. Among them, N6-methyladenosine RNA modifications (m6A RNA modifications) are the most abundant internal modifications in coding and non-coding RNAs, which can significantly influence the cancer process and have potential as biomarkers and potential therapeutic targets for tumor therapy. This manuscript reviews the role of m6A RNA modifications in TME and their application in tumor therapy. To some extent, an in-depth understanding of the relationship between TME and m6A RNA modifications will provide new approaches and ideas for future cancer therapy.

Circular RNA ZNF609 drives tumor progression by regulating the miR-138-5p/SIRT7 axis in melanoma

Melanoma serves as a prevailing and lethal skin malignancy with high mortality and a growing number of patients globally. Circular RNAs (circRNAs), as a type of emerging cellular regulator, are involved in the modulation of melanoma. Nevertheless, the function of circZNF609 in melanoma development remains obscure. In this study, we were interested in the effect and the underlying mechanism of circZNF609 on DNA damage during melanoma progression. The circZNF609 depletion significantly suppressed melanoma cell invasion, migration, and proliferation, and stimulated apoptosis. Meanwhile, comet assays showed that the tail length and γH2AX levels were elevated by circZNF609 depletion. Mechanically, circZNF609 sponged miR-138-5p and miR-138-5p targeted SIRT7 in the melanoma cells. The SIRT7 overexpression and miR-138-5p inhibitor could reverse circZNF609 depletion-mediated DNA damage and malignant progression in melanoma cells. Functionally, CircZNF609 promoted cell growth of melanoma in the nude mice. Consequently, we conclude that circZNF609 suppresses DNA damage and potentially enhances melanoma progression at the experimental condition by modulating the miR-138-5p/SIRT7 axis. Our finding provides new insights into the mechanism by which circZNF609 modulates the development of melanoma. CircZNF609 and miR-138-5p may be utilized as therapeutic targets for melanoma.

N6-Methyladenosine Modification Opens a New Chapter in Circular RNA Biology

As the most abundant internal modification in eukaryotic cells, N6-methyladenosine (m6A) in mRNA has shown widespread regulatory roles in a variety of physiological processes and disease progressions. Circular RNAs (circRNAs) are a class of covalently closed circular RNA molecules and play an essential role in the pathogenesis of various diseases. Recently, accumulating evidence has shown that m6A modification is widely existed in circRNAs and found its key biological functions in regulating circRNA metabolism, including biogenesis, translation, degradation and cellular localization. Through regulating circRNAs, studies have shown the important roles of m6A modification in circRNAs during immunity and multiple diseases, which represents a new layer of control in physiological processes and disease progressions. In this review, we focused on the roles played by m6A in circRNA metabolism, summarized the regulatory mechanisms of m6A-modified circRNAs in immunity and diseases, and discussed the current challenges to study m6A modification in circRNAs and the possible future directions, providing a comprehensive insight into understanding m6A modification of circRNAs in RNA epigenetics.

Circ_PRKDC knockdown promotes skin wound healing by enhancing keratinocyte migration via miR-31/FBN1 axis

Circular RNA protein kinase, DNA-activated, catalytic subunit (circ_PRKDC) has been found to impede wound healing in diabetic foot ulcers via regulating keratinocyte proliferation and migration. However, the mechanisms underlying circ_PRKDC in skin wound healing remain unclear. The expression of circ_PRKDC, microRNA (miR)-31 and fibrillin 1 (FBN1) was detected using quantitative reverse transcription-polymerase chain reaction and Western blot assays. The migration ability and the changes of matrix metallopeptidase 9 (MMP-9) and MMP2 levels were determined using wound healing, transwell and Western blot assays. The interaction between miR-31 and circ_PRKDC or FBN1 was verified by dual-luciferase reporter assay. The expression of circ_PRKDC was gradually down-regulated in wound edge at 1 and 7 days after injury relative to the unwounded skin. In human epidermal keratinocytes (HEKa), knockdown of circ_PRKDC promoted cell migration partly through up-regulating MMP-2 and MMP9, while circ_PRKDC overexpression showed opposite effects. In a mechanical study, we confirmed that miR-31 was a target of circ_PRKDC, and inhibition of miR-31 reversed the promotive effect of circ_PRKDC knockdown on HEKa migration. Besides that, miR-31 was verified to target FBN1, and ectopic overexpression of miR-31 accelerated HEKa migration via FBN1. Importantly, we also demonstrated that FBN1 overexpression attenuated the effects of circ_PRKDC knockdown on HEKa migration. In all, circ_PRKDC knockdown promoted HEKa migration during wound healing through miR-31/FBN1 axis, suggesting the therapeutic potential for circ_PRKDC on skin wound healing.

Circ_0013359 facilitates the tumorigenicity of melanoma by regulating miR-136-5p/RAB9A axis

Background

Circular RNAs play crucial roles in tumor occurrence and progression. This research aimed to explore the role and potential mechanism of hsa_circ_0013359 (circ_0013359) in melanoma.

Methods

The levels of circ_0013359, microRNA-136-5p (miR-136-5p), and member RAS oncogene family (RAB9A) in melanoma tissues and cells were detected using quantitative reverse transcriptase-polymerase chain reaction or western blot. Cell proliferation, apoptosis, cell cycle, cell migration, and invasion were evaluated by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide assay, colony formation assay, flow cytometry, and transwell assay. Glycolysis was determined by detecting glucose consumption, lactate production, and extracellular acidification rate. The levels of hexokinase 2 and lactate dehydrogenase A were examined by western blot. The targeting relationship between miR-136-5p and circ_0013359 or RAB9A was confirmed by dual-luciferase reporter assay. Xenograft experiments were used to analyze tumor growth in vivo.

Results

Circ_0013359 and RAB9A levels were increased, while the miR-136-5p level was reduced in melanoma tissues and cells. Circ_0013359 knockdown inhibited proliferation, migration, invasion, and glycolysis and promoted apoptosis and cycle arrest in A875 and SK-MEL-1 cells. Circ_0013359 sponged miR-136-5p to regulate melanoma progression. In addition, miR-136-5p suppressed melanoma progression by targeting RAB9A. Besides, circ_0013359 silencing inhibited tumor growth in vivo.

Conclusion

Depletion of circ_0013359 hindered melanoma progression by regulating miR-136-5p/RAB9A axis.

Epigenetic regulation of cellular functions in wound healing

Stringent spatiotemporal regulation of the wound healing process involving multiple cell types is associated with epigenetic mechanisms of gene regulation, such as DNA methylation, histone modification and chromatin remodelling, as well as non-coding RNAs. Here, we discuss the epigenetic changes that occur during wound healing and the rapidly expanding understanding of how these mechanisms affect healing resolution in both acute and chronic wound milieu. We provide a focussed overview of current research into epigenetic regulators that contribute to wound healing by specific cell type. We highlight the role of epigenetic regulators in the molecular pathophysiology of chronic wound conditions. The understanding of how epigenetic regulators can affect cellular functions during normal and impaired wound healing could lead to novel therapeutic approaches, and we outline questions that can provide guidance for future research on epigenetic-based interventions to promote healing. Dissecting the dynamic interplay between cellular subtypes involved in wound healing and epigenetic parameters during barrier repair will deepen our understanding of how to improve healing outcomes in patients affected by chronic non-healing wounds.