Role of Circular RNA in Kidney-Related Diseases

Circular RNAs and the regulation of gene expression in diabetic nephropathy (Review)

Circular RNAs (circRNAs) are non‑coding single‑stranded covalently closed RNA molecules that are considered important as regulators of gene expression at the transcriptional and post‑transcriptional levels. These molecules have been implicated in the initiation and progression of multiple human diseases, ranging from cancer to inflammatory and metabolic diseases, including diabetes mellitus and its vascular complications. The present article aimed to review the current knowledge on the biogenesis and functions of circRNAs, as well as their role in cell processes associated with diabetic nephropathy. In addition, novel potential interactions between circRNAs expressed in renal cells exposed to high‑glucose concentrations and the transcription factors c‑Jun and c‑Fos are reported.

Functional roles of circular RNAs in lung injury

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

CircRNA_0017076 acts as a sponge for miR-185-5p in the control of epithelial-to-mesenchymal transition of tubular epithelial cells during renal interstitial fibrosis

Renal interstitial fibrosis (RIF) is a common pathological hallmark of progressive chronic kidney disease (CKD). Circular RNAs (circRNAs) are involved in certain renal diseases, but their role in RIF is largely unknown. The present study investigated the effects and potential mechanisms of circRNA_0017076 in RIF. CircRNA_0017076 expression was markedly upregulated in transforming growth factor-β1 (TGF-β1)-treated renal tubular epithelial cells (RTECs) and kidney biopsy samples from patients with RIF. Functional assays showed that circRNA_0017076 colocalized with microRNA-185-5p (miR-185-5p) and inhibited miR-185-5p function via direct binding to miR-185-5p. In vitro, the knockdown of circRNA_0017076 inhibited the calcium ion (Ca²⁺) influx-mediated epithelial-to-mesenchymal transition (EMT) of RTECs and downregulated the expression of stromal interaction molecule 1 (STIM1), which is a target protein of miR-185-5p. Silencing mmu_circ_0004488 reduced fibrotic lesions in the kidneys of unilateral ureteral obstruction (UUO) mice by targeting the miR-185-5p/Stim1 axis. For the first time, we identified circRNA_0017076 as a sponge for miR-185-5p, which regulates STIM1 gene expression and is involved in RIF. Our results support circRNA_0017076 as a potential therapeutic target for RIF disease.

The Intersection of Acute Kidney Injury and Non-Coding RNAs: Inflammation

Acute renal injury (AKI) is a complex clinical syndrome, involving a series of pathophysiological processes, in which inflammation plays a key role. Identification and verification of gene signatures associated with inflammatory onset and progression are imperative for understanding the molecular mechanisms involved in AKI pathogenesis. Non-coding RNAs (ncRNAs), involved in epigenetic modifications of inflammatory responses, are associated with the aberrant expression of inflammation-related genes in AKI. However, its regulatory role in gene expression involves precise transcriptional regulation mechanisms which have not been fully elucidated in the complex and volatile inflammatory response of AKI. In this study, we systematically review current research on the intrinsic molecular mechanisms of ncRNAs that regulate the inflammatory response in AKI. We aim to provide potential research directions and strategies for developing ncRNA-targeted gene therapies as an intervention for the inflammatory damage in AKI.

Circ_0037866 Contributes to the Tumorigenesis of Renal Cell Carcinoma by Sequestering miR-384 to Elevate Chromobox 5 Expression

BACKGROUND

Circular RNAs (circRNAs) were demonstrated to have roles in the carcinogenesis of renal cell carcinoma (RCC). Hence, this work aimed to determine the functions and molecular mechanism of circ_0037866 in regulating the progression of RCC.

METHODS

Quantitative real-time polymerase chain reaction and Western blotting were used to detect the levels of genes and proteins. In vitro assays, including colony formation, 5-ethynyl-2'-deoxyuridine, flow cytometry, transwell assays, and in vivo tumor formation, were conducted to investigate the effects of circ_0037866 on RCC tumorigenesis. Dual-luciferase reporter assay, RNA pull-down, and RNA immunoprecipitation assay were used to confirm the interaction between miR-384 and circ_0037866 or Chromobox 5 (CBX5).

RESULTS

Circ_0037866 is a stable circRNA and was found to be increased in RCC tissues and cells. Functionally, circ_0037866 silencing suppressed RCC cell survival, invasion, and migration in vitro, and impeded RCC cell tumorigenesis in the subcutaneous xenograft model. Mechanistically, circ_0037866 could function as a sponge for miR-384 to elevate the expression of its target CBX5. Furthermore, a series of rescue experiments showed that miR-384 inhibition reversed the anticancer effects of circ_0037866 knockdown on RCC cells; besides that, miR-384 restoration suppressed RCC cell growth and mobility, which were attenuated by CBX5 overexpression.

CONCLUSION

Circ_0037866 knockdown restrains the tumorigenesis of RCC by miR-384/CBX5, revealing a promising molecular target for RCC therapy.

Integrated Analysis of the CircRNA-Based ceRNA Network in Renal Fibrosis Induced by Ischemia Reperfusion Injury

Background: Circular RNAs (circRNAs), which have broad posttranscriptional regulatory potencies, are involved in the pathogenesis of fibrotic diseases and are promising diagnostic biomarkers and therapeutic targets. However, their specific roles in renal fibrosis remain elusive.

Methods: A robust unilateral renal ischemia reperfusion injury (UIRI) mouse model was established to recapitulate the pathophysiology of renal fibrosis. The expression of circRNAs, miRNAs, and mRNAs was profiled by high-throughput RNA sequencing technology.

Results: In total, 4983 circRNAs, 216 miRNAs, and 6371 mRNAs were differentially expressed in UIRI-induced fibrotic kidneys. Candidate circRNAs and miRNAs were validated by RT–qPCR in both UIRI and unilateral ureteral obstruction mouse models. Bioinformatic analysis indicated that the parental genes of the differentially expressed circRNAs were predominantly implicated in focal adhesion, adhesion junctions, and regulation of actin cytoskeleton pathways. Through circRNA-miRNA-mRNA construction, we identified two hub genes, circSlc8a1 and circApoe, that targeted a large number of differentially expressed miRNAs and mRNAs related to metabolism and cytokine–cytokine receptor pathways, respectively.

Conclusion: CircRNAs were dysregulated in the UIRI model and might be potentially involved in the pathogenesis of renal fibrosis. Research efforts should focus on unravelling the functions of aberrantly expressed circRNAs in renal fibrosis to uncover biomarkers that would enable early diagnosis and the design of prompt therapeutic interventions to prevent disease progression.

Circular RNA-Is the Circle Perfect?

Circular RNA (circRNA) is a distinct class of non-coding RNA produced, in principle, using a back-splicing mechanism, conserved during evolution, with increased stability and a tissue-dependent expression. Circular RNA represents a functional molecule with roles in the regulation of transcription and splicing, microRNA sponge, and the modulation of protein–protein interaction. CircRNAs are involved in essential processes of life such as apoptosis, cell cycle, and proliferation. Due to the regulatory role (upregulation/downregulation) in pathogenic mechanisms of some diseases (including cancer), its potential roles as a biomarker or therapeutic target in these diseases were studied. This review focuses on the importance of circular RNA in cancer.

The Role and Clinical Potentials of Circular RNAs in Prostate Cancer

Globally, prostate cancer (PCa) is the second most commonly diagnosed cancer in men globally. Early diagnosis may help in promoting survival in the affected patients. Circular RNAs (circRNAs) are a novel class of non-coding RNAs (ncRNAs) which have been found to show extensive dysregulation in a handful of human diseases including cancers. Progressions in RNA identification techniques have provided a vast number of circRNAs exhibiting either up-regulation or down-regulation in PCa tissues compared to normal adjacent tissues. The mechanism of action is not clear for most of dysregulated circRNAs. Among them, function of a number of newly identified dysregulated circRNAs have been assessed in PCa cells. Increase in cell proliferation, migration, invasion, and metastasis have been reported for up-regulated circRNAs which suggest their role as oncogenes. On the other hand, down-regulated circRNAs have shown tumor suppressing actions in experimental studies. Furthermore, in a majority of studies, circRNAs have been found to sponge microRNAs (miRNAs), negatively regulating expression or activity of the downstream miRNAs. Additionally, they have been identified in interaction with regulatory proteins. This axis consequently regulates a signaling pathway, a tumor suppressor, or an oncogene. Easy, quick, and reliable detection of circRNAs in human body fluids also suggests their potentials as biomarker candidates for diagnosis and prediction of prognosis in PCa patients. In this review, we have discussed the role and potentials of a number of dysregulated circRNAs in PCa.

Circular RNAs as Novel Diagnostic Biomarkers and Therapeutic Targets in Kidney Disease

Circular RNAs (circRNAs) are a novel type of non-coding RNAs that have aroused growing attention in this decade. They are widely expressed in eukaryotes and generally have high stability owing to their special closed-loop structure. Many circRNAs are abundant, evolutionarily conserved, and exhibit cell-type-specific and tissue-specific expression patterns. Mounting evidence suggests that circRNAs have regulatory potency for gene expression by acting as microRNA sponges, interacting with proteins, regulating transcription, or directly undergoing translation. Dysregulated expression of circRNAs were found in many pathological conditions and contribute to the pathogenesis and progression of various disorders, including renal diseases. Recent studies have revealed that circRNAs may serve as novel reliable biomarkers for the diagnosis and prognosis prediction of multiple kidney diseases, such as renal cell carcinoma (RCC), acute kidney injury (AKI), diabetic kidney disease (DKD), and other glomerular diseases. Furthermore, circRNAs expressed by intrinsic kidney cells are shown to play a substantial role in kidney injury, mostly reported in DKD and RCC. Herein, we review the biogenesis and biological functions of circRNAs, and summarize their roles as promising biomarkers and therapeutic targets in common kidney diseases.

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

Objective

Explore the possibility of circRNAs as markers of sepsis.

Background

Sepsis is an abnormal immune response of our body to infection that can lead to organ failure and death. Although the research on sepsis has been extensive in the past few years, sepsis-associated morbidity and mortality are still increasing. Early diagnosis and early treatment are important for patients with sepsis. Although many markers, including procalcitonin and C-reactive protein, have been proposed as diagnostic indicators of sepsis, there are still challenges in the early diagnosis and treatment of sepsis due to the lack of sensitivity and specificity of these substances. Recently, a large number of studies have found that circular RNAs (circRNAs) participate in a variety of biological functions, such as immune response, regulating the expression of miRNAs, and they are closely related to the occurrence and development of many diseases, including sepsis. However, the clear mechanism of the role of circRNAs has not been fully elucidated. An increasing number of studies have confirmed that circRNAs have potential in the diagnosis and treatment of sepsis. By studying the regulatory mechanism of circRNAs in sepsis, we can search for new molecular intervention targets for the treatment of sepsis, which is conducive to the development of new molecular therapeutic drugs for sepsis.

Methods

In the present study, we summarize and analyze the role of circRNAs in the pathogenesis of sepsis and discuss the possibility of circRNA as a biomarker for the diagnosis of sepsis.

Conclusions

The biological characteristics of circRNAs and their role in the occurrence and development of sepsis make them possible markers of sepsis.