The Circular RNA ciRs-126 Predicts Survival in Critically Ill Patients With Acute Kidney Injury

RfxCas13d-mediated inhibition of Circ1647 alleviates renal fibrosis via PI3K/AKT signaling pathway

BACKGROUND

Circular RNAs (CircRNAs) have been shown to be involved in the development of chronic kidney disease (CKD). This study aimed to investigate the role of Circ1647 in renal fibrosis, which is a hallmark of CKD.

METHODS

In this study, we established a unilateral ureteral obstruction (UUO) model and delivered Circ1647 RfxCas13d knockdown plasmid into renal parenchymal cells via retrograde injection through the ureter followed by electroporation. After that, the pathological changes were determined by Hematoxylin and Eosin. Meanwhile, Immunohistochemistry, qRT-PCR and Western blot were conducted to assess the degree of fibrosis. In addition, overexpressing of Circ1647 in renal tubular epithelial cells (TCMK1) was performed to investigate the underlying mechanisms of Circ1647.

RESULTS

Our results displayed that electroporation-mediated knockdown of Circ1647 by RfxCas13d knockdown plasmid significantly inhibited renal fibrosis in UUO mice as evidenced by reduced expression of fibronectin and α-SMA (alpha-smooth muscle actin). Conversely, overexpression of Circ1647 in TCMK1 cells promoted the fibrosis. In terms of mechanism, Circ1647 may mediate the PI3K/AKT Signaling Pathway as demonstrated by the balance of the phosphorylation of PI3K and AKT in vivo and the aggravated phosphorylation of PI3K and AKT in vitro. These observations were corroborated by the effects of the PI3K inhibitor LY294002, which mitigated fibrosis post Circ1647 overexpression.

CONCLUSION

Our study suggests that Circ1647 plays a significant role in renal fibrosis by mediating the PI3K/AKT signaling pathway. RfxCas13d-mediated inhibition of Circ1647 may serve as a therapeutic target for renal fibrosis in CKD.

Circ-0000953 deficiency exacerbates podocyte injury and autophagy disorder by targeting Mir665-3p-Atg4b in diabetic nephropathy

Circular RNAs (circRNAs) are special non-coding RNA (ncRNA) molecules that play a significant role in many diseases. However, the biogenesis and regulation of circRNAs in diabetic nephropathy (DN) are largely unknown. Here, we investigated the expression profile of circRNAs in kidney of DN mice through circular RNA sequencing (circRNA-seq). The renal biopsy samples of patients with DN had low circ -0,000,953 expression, which was significantly associated with renal function. Furthermore, loss-of-function and gain-of-function experiments were carried out to prove the role of circ -0,000,953 in DN. Podocyte conditional knockin (cKI) or systemic overexpression of circ -0,000,953 alleviated albuminuria and restored macroautophagy/autophagy in kidney of diabetic mice. However, circ -0,000,953 knockdown exacerbated albuminuria and podocyte injury. Mechanistically, we found circ -0,000,953 directly binds to Mir665-3p-Atg4b to perform its function. Silencing of Mir665-3p or overexpression of Atg4b recovered podocyte autophagy both in vitro and in vivo. To examine the cause of circ -0,000,953 downregulation in DN, bioinformatics prediction found that circ -0,000,953 sequence has a high possibility of containing an m6A methylation site. Additionally, METTL3 was proved to regulate the expression and methylation level of circ -0,000,953 through YTHDF2 (YTH N6-methyladenosine RNA binding protein 2). In conclusion, this study revealed that circ -0,000,953 regulates podocyte autophagy by targeting Mir665-3p-Atg4b in DN. Therefore, circ -0,000,953 is a potential biomarker for prevention and cure of DN.Abbreviation: CCL2/MCP-1: C-C motif chemokine ligand 2; ceRNA: competing endogenous RNA; circRNA: circular RNA; cKI: conditional knockin; cKO: conditional knockout; CRE: creatinine; DM: diabetes mellitus; DN: diabetic nephropathy; ESRD: end-stage renal disease; HG: high glucose; IF: immunofluorescence; MAP1LC3/LC3B: microtubule-associated protein 1 light chain 3 beta; MPC5: mouse podocyte clone 5; MTECs: mouse tubular epithelial cells; MTOR: mechanistic target of rapamycin kinase; NC: normal control; ncRNA: non-coding RNA; NPHS1: nephrosis 1, nephrin; NPHS2: nephrosis 2, podocin; PAS: periodic acid-Schiff; RELA/p65: v-rel reticuloendotheliosis viral oncogene homolog A (avian); SDs: slit diaphragm proteins; Seq: sequencing; STZ: streptozotocin; SV40: SV40-MES13-cells, mouse mesangial cell line; T1D: type 1 diabetes mellitus; T2D: type 2 diabetes mellitus; TEM: transmission electron microscopy; TNF/TNF-α: tumor necrosis factor; VECs: vascular endothelial cells; WT1: WT1 transcription factor; YTHDF2: YTH N6-methyladenosine RNA binding protein 2.

Potential therapeutic applications of circular RNA in acute kidney injury

Acute kidney injury (AKI) is a common clinical syndrome characterized by a rapid deterioration in renal function, manifested by a significant increase in creatinine and a sharp decrease in urine output. The incidence of morbidity and mortality associated with AKI is on the rise, with most patients progressing to chronic kidney disease or end-stage renal disease. Treatment options for patients with AKI remain limited. Circular RNA (circRNA) is a wide and diverse class of non-coding RNAs that are present in a variety of organisms and are involved in gene expression regulation. Studies have shown that circRNA acts as a competing RNA, is involved in disease occurrence and development, and has potential as a disease diagnostic and prognostic marker. CircRNA is involved in the regulation of important biological processes, including apoptosis, oxidative stress, and inflammation. This study reviews the current status and progress of circRNA research in the context of AKI.

Circular RNA hsa_circ_0005519 contributes to acute kidney injury via sponging microRNA-98-5p

BACKGROUND

This study intends to explore the role and molecular mechanism of hsa_circ_0005519 in acute kidney injury (AKI).

METHODS

We conducted reverse transcription-qPCR for human serum to determine levels of hsa_circ_0005519 in AKI patients and healthy controls. Hsa_circ_0005519 was inhibited for expression in HK-2 cells using specific siRNAs. A number of techniques, MTT and ELISA assays, were used to analyze the potential role of hsa_circ_0005519 in cell viability, oxidative stress, and inflammation of LPS-induced HK-2 cells.

RESULTS

The serum of patients with AKI exhibited a significant increase in hsa_circ_0005519 expression, compared with healthy controls. Hsa_circ_0005519 was knockdown by siRNA, and its knockdown led to cell viability increase in LPS-induced HK-2 cells. Inhibition of hsa_circ_0005519 can reverse the TNF-α, IL-6 and IL-1β increase in LPS-induced HK-2 cells. Inhibiting hsa_circ_0005519 led to downregulation of MPO and MDA levels. MiR-98-5p was a downstream miRNA for hsa_circ_0005519. MiR-98-5p can offset the effects of hsa_circ_0005519 on LPS-induced HK-2 cells. IFG1R was a target gene for miR-98-5p.

CONCLUSIONS

These findings indicate that the highly expressed hsa_circ_0005519 plays a promoting role in AKI.

The role of non-protein-coding RNAs in ischemic acute kidney injury

Acute kidney injury (AKI) is a condition characterized by a rapid decline in kidney function within a span of 48 hours. It is influenced by various factors including inflammation, oxidative stress, excessive calcium levels within cells, activation of the renin-angiotensin system, and dysfunction in microcirculation. Ischemia-reperfusion injury (IRI) is recognized as a major cause of AKI; however, the precise mechanisms behind this process are not yet fully understood and effective treatments are still needed. To enhance the accuracy of diagnosing AKI during its early stages, the utilization of innovative markers is crucial. Numerous studies suggest that certain noncoding RNAs (ncRNAs), such as long noncoding RNAs (lncRNAs), microRNAs (miRNAs), and circular RNAs (circRNAs), play a central role in regulating gene expression and protein synthesis. These ncRNAs are closely associated with the development and recovery of AKI and have been detected in both kidney tissue and bodily fluids. Furthermore, specific ncRNAs may serve as diagnostic markers and potential targets for therapeutic interventions in AKI. This review aims to summarize the functional roles and changes observed in noncoding RNAs during ischemic AKI, as well as explore their therapeutic potential.

CIRCUSP42 AMELIORATES LPS-INDUCED HUMAN RENAL EPITHELIAL CELLS IN VITRO BY REGULATING THE MIR-182-5P/DUSP1 AXIS

ABSTRACT

Background: Sepsis is a life-threatening systemic inflammatory disease that can cause many diseases, including acute kidney injury (AKI). Increasing evidence showed that a variety of circular RNAs were considered to be involved in the development of the disease. In this study, we aimed to elucidate the role and potential mechanism of circUSP42 in sepsis-induced AKI. Methods: HK2 cells were treated with lipopolysaccharide (LPS) to establish septic AKI cell model. The expression levels of circUSP42, microRNA-182-5p (miR-182-5p), and DUSP1 in LPS-treated HK2 cells were measured by quantitative real-time polymerase chain reaction or Western blot. Functional experiments were performed by using Cell Counting Kit-8, 5-ethynyl-2'-deoxyuridine staining, flow cytometry, oxidative stress assay, and enzyme-linked immunosorbent assay. The potential target binding site between miR-182-5p and CircUSP42 or DUSP1 was verified by dual-luciferase reporter and RNA immunoprecipitation assays. Results: CircUSP42 and DUSP1 were downregulated in serum samples from patients with AKI and LPS-treated HK2 cells, while miR-182-5p was upregulated. Functionally, overexpression of CircUSP42 promoted cell proliferation and inhibited apoptosis, inflammation, and oxidative stress in LPS-triggered HK2 cells. Further mechanism analysis showed that miR-182-5p had potential binding sites with circUSP42 and DUSP1, and circUSP42 regulated LPS-induced cell damage by targeting miR-182-5p. At the same time, miR-182-5p knockdown inhibited LPS-treated HK2 cell damage by regulating DUSP1. In addition, circUSP42 induced DUSP1 expression via sponging miR-182-5p to ameliorate LPS-induced HK2 cell damage. Conclusion : Our results showed that circUSP42 overexpression might attenuate LPS-induced HK2 cell injury by regulating miR-182-5p/DUSP1 axis. This might provide therapeutic strategy for the treatment of sepsis.

Multiple novel functions of circular RNAs in diabetes mellitus

Circular RNAs (circRNAs), as an emerging group of non-coding RNAs (ncRNAs), have received the attention given evidence indicating that these novel ncRNAs are implicated in various biological processes. Due to the absence of 5' and 3' ends in circ-RNAs, their two ends are covalently bonded together, and they are synthesised from pre-mRNAs in a process called back-splicing, which makes them more stable than linear RNAs. There is accumulating evidence showing that circRNAs play a critical role in the pathogenesis of diabetes mellitus (DM). Moreover, it has been indicated that dysregulation of circRNAs has made them promising diagnostic biomarkers for the detection of DM. Recently, increasing attention has been paid to investigate the mechanisms underlying the DM process. It has been demonstrated that there is a strong correlation between the expression of circRNAs and DM. Hence, our aim is to discuss the crosstalk between circRNAs and DM and its complications.

The AKI-to-CKD Transition: The Role of Uremic Toxins

After acute kidney injury (AKI), renal function continues to deteriorate in some patients. In a pro-inflammatory and profibrotic environment, the proximal tubules are subject to maladaptive repair. In the AKI-to-CKD transition, impaired recovery from AKI reduces tubular and glomerular filtration and leads to chronic kidney disease (CKD). Reduced kidney secretion capacity is characterized by the plasma accumulation of biologically active molecules, referred to as uremic toxins (UTs). These toxins have a role in the development of neurological, cardiovascular, bone, and renal complications of CKD. However, UTs might also cause CKD as well as be the consequence. Recent studies have shown that these molecules accumulate early in AKI and contribute to the establishment of this pro-inflammatory and profibrotic environment in the kidney. The objective of the present work was to review the mechanisms of UT toxicity that potentially contribute to the AKI-to-CKD transition in each renal compartment.

Circulating non-coding RNAs in chronic kidney disease and its complications

Post-transcriptional regulation by non-coding RNAs (ncRNAs) can modulate the expression of genes involved in kidney physiology and disease. A large variety of ncRNA species exist, including microRNAs, long non-coding RNAs, piwi-interacting RNAs, small nucleolar RNAs, circular RNAs and yRNAs. Despite early assumptions that some of these species may exist as by-products of cell or tissue injury, a growing body of literature suggests that these ncRNAs are functional and participate in a variety of processes. Although they function intracellularly, ncRNAs are also present in the circulation, where they are carried by extracellular vesicles, ribonucleoprotein complexes or lipoprotein complexes such as HDL. These systemic, circulating ncRNAs are derived from specific cell types and can be directly transferred to a variety of cells, including endothelial cells of the vasculature and virtually any cell type in the kidney, thereby affecting the function of the host cell and/or its response to injury. Moreover, chronic kidney disease itself, as well as injury states associated with transplantation and allograft dysfunction, is associated with a shift in the distribution of circulating ncRNAs. These findings may provide opportunities for the identification of biomarkers with which to monitor disease progression and/or the development of therapeutic interventions.

Circ_0001806 relieves LPS-induced HK2 cell injury by regulating the expression of miR-942-5p and TXNIP

Sepsis is a systemic inflammatory disease that can cause a variety of diseases, including septic acute kidney injury (AKI). Circular RNAs (circRNAs) are believed to be involved in the development of this disease. This study aims to clarify the function of circ_0001806 in lipopolysaccharide (LPS)-induced HK2 cell model and its related mechanisms. Circ_0001806 was up-regulated in septic AKI serum specimens and LPS-induced HK2 cells. Circ_0001806 knockdown promoted cell proliferation and restrained apoptosis, inflammation and oxidative stress in LPS-induced HK2 cells. In mechanism, circ_0001806 can be used as a sponge for miR-942-5p, and miR-942-5p can directly target TXNIP. Functional experiments revealed that the miR-942-5p inhibitor could reverse the alleviating effect of circ_0001806 knockdown on LPS-induced HK2 cell injury, and TXNIP addition can also reverse the inhibitory effect of miR-942-5p overexpression on LPS-induced HK2 cell injury. In addition, circ_0001806 regulated TXNIP expression through sponging miR-942-5p. Besides, exosome-derived circ_0001806 was upregulated in LPS-induced HK2 cells, while was downregulated by GW4869. The results showed that circ_0001806 knockdown could reduce LPS-induced HK2 cell injury by regulating TXNIP expression via targeting miR-942-5p, indicating that circ_0001806 might be an important biomarker for alleviating sepsis-related AKI. This might provide therapeutic strategy for the treatment of sepsis.

Mitochondrial dysfunction and oxidative stress: Role in chronic kidney disease

Chronic kidney disease (CKD) is associated with a variety of distinct disease processes that permanently change the function and structure of the kidney across months or years. CKD is characterized as a glomerular filtration defect or proteinuria that lasts longer than three months. In most instances, CKD leads to end-stage kidney disease (ESKD), necessitating kidney transplantation. Mitochondrial dysfunction is a typical response to damage in CKD patients. Despite the abundance of mitochondria in the kidneys, variations in mitochondrial morphological and functional characteristics have been associated with kidney inflammatory responses and injury during CKD. Despite these variations, CKD is frequently used to define some classic signs of mitochondrial dysfunction, including altered mitochondrial shape and remodeling, increased mitochondrial oxidative stress, and a marked decline in mitochondrial biogenesis and ATP generation. With a focus on the most significant developments and novel understandings of the involvement of mitochondrial remodeling in the course of CKD, this article offers a summary of the most recent advances in the sources of procured mitochondrial dysfunction in the advancement of CKD. Understanding mitochondrial biology and function is crucial for developing viable treatment options for CKD.

CircNRIP1 KNOCKDOWN ALLEVIATES LIPOPOLYSACCHARIDE-INDUCED HUMAN KIDNEY 2 CELL APOPTOSIS AND INFLAMMATION THROUGH miR-339-5p/OXSR1 PATHWAY

ABSTRACT

Background: CircRNA regulates sepsis-induced acute kidney injury (AKI). CircNRIP1 is overexpressed in the blood of AKI patients, but its role in septic AKI occurrence remains unknown. Methods: Human kidney 2 (HK2) cells were stimulated using lipopolysaccharide (LPS) to generate a septic AKI cell model. The expression levels of circNRIP1, miR-339-5p, oxidative stress-responsive kinase 1 (OXSR1), B-cell lymphoma-2 (Bcl2), BCL2-associated x protein (Bax), and cleaved-caspase 3 were detected by quantitative real-time polymerase chain reaction or Western blotting analysis. Cell viability and apoptosis were investigated by cell counting kit-8 and flow cytometry analysis. The release of proinflammatory cytokines was monitored using commercial kits. The associations among circNRIP1, miR-339-5p, and OXSR1 were identified by mechanism assays. Results: CircNRIP1 was dramatically upregulated in the blood of septic AKI patients and LPS-induced HK2 cells. CircNRIP1 depletion protected HK2 cells from LPS-induced apoptosis and inflammation. MiR-339-5p expression was downregulated in the blood of septic AKI patients, and miR-339-5p combined with circNRIP1. Moreover, circNRIP1 knockdown-induced effects involved the upregulation of miR-339-5p in LPS-treated HK2 cells. Comparatively, OXSR1 expression was increased in the blood of septic AKI patients. MiR-339-5p bound to OXSR1, and circNRIP1 modulated OXSR1 expression by interacting with miR-339-5p. Further, ectopic expression of OXSR1 relieved circNRIP1 knockdown-mediated effects in LPS-induced HK2 cells. Conclusion: CircNRIP1 depletion ameliorated LPS-induced HK2 cell damage by regulating the miR-339-5p/OXSR1 pathway.

CIRC_0114428 INFLUENCES THE PROGRESSION OF SEPTIC ACUTE KIDNEY INJURY VIA REGULATING MIR-370-3P/TIMP2 AXIS

ABSTRACT

Background: Septic acute kidney injury (AKI) is a serious complication of sepsis, which greatly threatened the life safety of critically ill patients. Recently, circular RNA is considered to be implicated in sepsis-induced renal cell damage. However, the role of circ_0114428 in sepsis AKI is still unclear. Methods: LPS was used to establish a sepsis-related AKI cell model. The expression of circ_0114428, microRNA (miR)-370-3p, tissue inhibitor of metalloproteinase-2 (TIMP2), Proliferating cell nuclear antigen, Bax, and Bcl-2 were detected by quantitative real-time polymerase chain reaction and Western blot. Cell counting kit 8 and enzyme-linked immunosorbent assay were used to measure cell proliferation ability and the secretion of inflammatory factors (tumor necrosis factor α, interleukin 1β, and interleukin 6), respectively. Cell cycle and apoptosis rate were analyzed by flow cytometry. Caspase-3 assay kits were used to detect Caspase-3 activity. Interaction between miR-370-3p and circ_0114428 or TIMP2 was analyzed by bioinformatics analysis, a dual-luciferase reporter assay, and RNA immunoprecipitation assay. Results: Circ_0114428 was upregulated in septic AKI serum samples and LPS-induced HK2 cells. The knockdown of circ_0114428 notably promoted cell proliferation and cycle, whereas it restrained cell inflammation and apoptosis in LPS-stimulated HK2 cells. Subsequent mechanism analysis revealed that miR-370-3p was a target of circ_0114428, and miR-370-3p inhibition could rescue the effects of circ_0114428 downregulation on LPS-induced cell injury. Meanwhile, TIMP2 was a target gene of miR-370-3p. miR-370-3p mimic could attenuate LPS-induced cell injury, whereas these impacts were overturned by overexpressed TIMP2. Furthermore, circ_0114428 enhanced TIMP2 protein expression by sponging miR-370-3p. Conclusion: Our data demonstrated that circ_0114428 contributed to septic AKI progression by regulating miR-370-3p-mediated TIMP2 expression, which provided a promising target for septic AKI treatment.

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.

Urinary exosomes derived circRNAs as biomarkers for chronic renal fibrosis

BACKGROUND

Chronic renal disease (CKD) is a common and irreversible loss of renal function. Renal fibrosis reflected the degree of renal dysfunction. However, the current biomarkers only characterize the renal function instead of indicating the fibrosis degree. The potential diagnostic value of urinary exosomes derived circRNAs for renal fibrosis needs to be further studied.

METHODS

Urine exosomes from 3 chronic kidney disease (CKD) patients without renal fibrosis and 3 renal fibrotic patients were collected and human circRNAs microarray analysis were performed to detect the circRNAs expression profile. 110 biopsy-proven CKD patients and 54 healthy controls were enrolled and urine exosomes derived RNA was isolated. The expression of hsa_circ_0036649 was measured and the correlation with renal function parameter and pathological indicators was performed. The receiver operating characteristic (ROC) curve for the diagnosis of renal fibrosis was calculated.

RESULTS

Human circRNAs microarray showed 365 circRNAs up expressed and 195 circRNAs down expressed in renal fibrotic patients compared to none fibrosis CKD patients. The expression of hsa_circ_0036649 was decreased in renal fibrotic patients according to RT-PCR and correlated with serum creatinine, blood urea nitrogen (BUN), estimated glomerular filtration rate and cystatin c. Further, the expression of hsa_circ_0036649 was correlated with the score of tubulointerstitial fibrosis (TIF) and the score of glomerular sclerosis. The ROC curve showed that hsa_circ_0036649 may predict renal fibrosis at a cut-off value of 0.597 with a sensitivity of 45.5% and specificity of 87.9%.

CONCLUSION

Expression of urinary exosomes derived hsa_circ_0036649 associated with the degree of renal fibrosis. Its potential role as a biomarker in CKD remained to be supported by further follow-up studies.Key MessagescircRNAs profile in urine exosomes in renal fibrosis patients was revealed.The expression of urine exosomes derived hsa_circ_0036649 was correlated to renal function and fibrosis degree.circRNAs derived from urinary exosomes may become a new research direction for biomarkers of renal fibrosis.

A circular RNA, circPTPN14, increases MYC transcription by interacting with FUBP1 and exacerbates renal fibrosis

Fibrosis is a relentlessly progressive and irreversible cause of organ damage, as in chronic kidney disease (CKD), but its underlying mechanisms remain elusive. We found that a circular RNA, circPTPN14, is highly expressed in human kidneys with biopsy-proved chronic interstitial fibrosis, mouse kidneys subjected to ischemia/reperfusion (IR) or unilateral ureteral obstruction (UUO), and TGFβ1-stimulated renal tubule epithelial cells (TECs). The intrarenal injection of circPTPN14 shRNA alleviated the progression of fibrosis in kidneys subjected to IR or UUO. Knockdown of circPTPN14 in TECs inhibited TGFβ1-induced expression of profibrotic genes, whereas overexpressing circPTPN14 increased the profibrotic effect of TGFβ1. The profibrotic action of circPTPN14 was ascribed to an increase in MYC transcription. The binding of circPTPN14 to the KH3 and KH4 domains of far upstream element (FUSE) binding protein 1 (FUBP1) enhanced the interaction between FUBP1 and FUSE domain, which was required for the initiation of MYC transcription. In human kidneys (n = 30) with biopsy-proved chronic interstitial fibrosis, the expression of circPTPN14 positively correlated with MYC expression. Taken together these studies show a novel mechanism in the pathogenesis of renal fibrosis, mediated by circPTPN14, which can be a target in the diagnosis and treatment of CKD.

circMTND5 Participates in Renal Mitochondrial Injury and Fibrosis by Sponging MIR6812 in Lupus Nephritis

Recent studies have focused on nuclear-encoded circular RNAs (circRNAs) in kidney diseases, but little is known about mitochondrial circRNAs. Differentially expressed circRNAs were analyzed by RNA deep sequencing from lupus nephritis (LN) biopsies and normal human kidneys. In LN renal biopsies, the most downregulated circRNA was circMTND5, which is encoded in the mitochondrial genome. We quantitated circMTND5 by qPCR and localized by fluorescence in situ hybridization (FISH). Mitochondrial abnormalities were identified by electron microscopy. The expression of mitochondrial genes was decreased, and the expression of profibrotic genes was increased on qPCR and immunostaining. RNA binding sites for MIR6812 and circMTND5 were predicted. MIR6812 expression was increased by FISH and qPCR. In HK-2 cells and its mitochondrial fraction, the role of circMTND5 sponging MIR6812 was assessed by their colocalization in mitochondria on FISH, RNA immunoprecipitation, and RNA pulldown coupled with luciferase reporter assay. circMTND5 knockdown upregulated MIR6812, decreased mitochondrial functional gene expression, and increased profibrotic gene expression. Overexpression of circMTND5 reversed these effects in hTGF-β stimulated HK-2 cells. Similar effects were observed in HK-2 cells with overexpression and with knockdown of MIR6812. We conclude that circMTND5 alleviates renal mitochondrial injury and kidney fibrosis by sponging MIR6812 in LN.

The role of small extracellular vesicle non-coding RNAs in kidney diseases

Kidney diseases have become an increasingly common public health concern worldwide. The discovery of specific biomarkers is of substantial clinical significance in kidney disease diagnosis, therapy and prognosis. The small extracellular vesicle (sEV) can be secreted by several cell types, like renal tubular epithelial cells, podocytes, collecting duct cells and leap cells, and functions as a communication medium between cells by delivering signaling molecules, including proteins, lipids and nucleic acids. There has been growing evidence that kidney diseases are associated with aberrant expression of sEV-derived non-coding RNAs (sEV-ncRNAs). As a result, sEV-ncRNAs may provide valuable information about kidney diseases. In this paper, a systematic review is presented of what has been done in recent years regarding sEV-ncRNAs in kidney disease diagnosis, treatment and prognosis.

Silencing circ_0074371 inhibits the progression of sepsis-induced acute kidney injury by regulating miR-330-5p/ELK1 axis

BACKGROUND

Sepsis-induced acute kidney injury (AKI) is a common in clinic. Circular RNAs (circRNAs) play significant roles in ameliorating AKI. The purpose of this study was aimed to identify the role of circ_0074371 and the potential action mechanism in sepsis-induced AKI.

METHODS

AKI patients and healthy individual serum samples were collected and the relative expression of circ_0074371 was measured by real-time polymerase chain reaction (RT-PCR). HK2 cells were treated with different dose (0, 2.5, 5 and 10 μg/ml) lipopolysaccharide (LPS) to establish the AKI cell model. The cell viability and apoptosis of HK2 cells were detected using cell counting kit-8 (CCK-8) and flow cytometry, respectively. The contents of malondialdehyde (MDA), and superoxide dismutase (SOD) were evaluated using the relative commercial kits. The IL-1β and TNF-α levels in cell culture supernatants were measured by ELISA. The interaction relationship between miR-330-5p and circ_0074371 or ELK1 was predicted by Targetscan database and further confirmed by the dual-luciferase reporter assay system.

RESULTS

The circ_0074371 expression was up-regulated in sepsis patients and LPS-induced HK2 cells. Silencing circ_0074371 promoted HK2 cells viability and inhibited the HK2 cells apoptosis. miR-330-5p inhibitor weakened circ_0074371 inhibitor-induced cell viability, apoptosis and oxidative stress. Further mechanism analysis showed that circ_0074371 acted as a sponge for miR-330-5p to increase ELK1 expression level. Importantly, miR-330-5p downregulation or ELK1 upregulation reversed the action of circ_0074371 knockdown on LPS-induced HK2 cells.

CONCLUSION

Knockdown of circ_0074371 ameliorated LPS-induced HK2 cells apoptosis, inflammation and oxidative stress via regulating miR-330-5p/ELK1, opening a new window into the pathogenesis AKI.

Circular RNAs in Acute Kidney Injury: Roles in Pathophysiology and Implications for Clinical Management

Acute kidney injury (AKI) is a common clinical condition, results in patient morbidity and mortality, and incurs considerable health care costs. Sepsis, ischaemia-reperfusion injury (IRI) and drug nephrotoxicity are the leading causes. Mounting evidence suggests that perturbations in circular RNAs (circRNAs) are observed in AKI of various aetiologies, and have pathogenic significance. Aberrant circRNA expressions can cause altered intracellular signalling, exaggerated oxidative stress, increased cellular apoptosis, excess inflammation, and tissue injury in AKI due to sepsis or IRI. While circRNAs are dysregulated in drug-induced AKI, their roles in pathogenesis are less well-characterised. CircRNAs also show potential for clinical application in diagnosis, prognostication, monitoring, and treatment. Prospective observational studies are needed to investigate the role of circRNAs in the clinical management of AKI, with special focus on the safety of therapeutic interventions targeting circRNAs and the avoidance of untoward off-target effects.

Icariin and Competing Endogenous RNA Network: A Potential Protective Strategy Against Contrast-Induced Acute Kidney Injury

Background

Icariin presents protective effect in several kidney diseases. However, the role of icariin in contrast-induced acute kidney injury (CIAKI) is still unclear. This study aimed to investigate the effect of icariin in CIAKI, as well as exploring the underlying mechanism from the aspect of interaction between protein-coding genes and non-coding RNAs.

Methods

The effect of icariin was evaluated in both in vivo and in vitro CIAKI models. Rat kidneys were collected for genome-wide sequencing. The differentially expressed genes (DEGs) were screened and visualized by R software. The function annotation of DEGs was analyzed by Metascape. By Cytoscape software, the competing endogenous RNA (ceRNA) network was constructed, and hub genes were selected. Expressions of hub genes were validated by PCR. Association of hub genes in the ceRNA network and renal function was also examined.

Results

Icariin protected against CIAKI in both in vivo and in vitro models. Based on DEGs in icariin pretreated CIAKI rats, lncRNA- and circRNA-associated ceRNA networks were constructed, respectively. Function annotation showed the ceRNA networks were enriched in ERK1 and ERK2 cascade, MAPK signaling and NF-κB signaling. Further, two circRNAs, six lncRNAs, four miRNAs and nine mRNAs were selected as hub genes of the ceRNA network. Among them, eight mRNAs (Acot1, Cbwd1, Ly6i, Map3k14, Mettl2b, Nyap1, Set and Utp20) were negatively correlated with renal function, while one mRNA (Tmem44) was positively correlated with renal function.

Conclusion

Icariin presented a protective effect against CIAKI. The ceRNA network, involving Acot1, Cbwd1, Ly6i, Map3k14, Mettl2, Nyap1, Set, Tmem44 and Utp20, might partially contribute to the underlying mechanism of icariin protection by regulation of ERK1 and ERK2 cascade, MAPK signaling and NF-κB signaling.

GATA1 regulates the microRNA‑328‑3p/PIM1 axis via circular RNA ITGB1 to promote renal ischemia/reperfusion injury in HK‑2 cells

Acute kidney injury (AKI) is caused by renal ischemia/reperfusion injury (IRI) during kidney transplantation. The levels of both circular RNAs (circRNAs) and microRNAs (miRNAs/miR) appear to be critical for AKI detection. While several RNA interactions in AKI have been found, the regulatory mechanisms between the molecules remain to be fully elucidated. In the present study, miRNA expression profiling analysis was conducted using an online dataset to identify the differentially expressed miRNAs in rats with IRI. miR-328-3p was also found to be downregulated in human kidney-2 (HK-2) cells subjected to hypoxia/reperfusion (H/R), and its overexpression targeting pim-1 proto-oncogene (PIM1) resulted in an increased viability and a reduced apoptosis, as well as in the decreased expression of inflammatory factors upon H/R exposure. Putative targets and circRNAs of miR-328-3p were identified using publically available databases. The inhibition of circRNA integrin beta 1 (ITGB1; circITGB1) suppressed the inflammatory response induced by H/R by sponging miR-328-3p in HK-2 cells. Furthermore, a sequence of the functional ITGB1 promoter was studied for transcription factor GATA binding protein 1 (GATA1) binding sites. GATA1 binds to the ITGB1 promoter, leading to the expression of circITGB1. On the whole, the findings of the present study revealed a regulatory pathway modulating miR-328-3p in IRI, demonstrating that the GATA1-mediated regulation of circITGB1 enhanced the H/R-induced inflammatory response via the miR-328-3p/PIM1 axis.

Inhibition of Circ-Snrk ameliorates apoptosis and inflammation in acute kidney injury by regulating the MAPK pathway

Background

Circular RNA (circRNA) is involved in the process of acute kidney injury (AKI), but only a few circRNAs have been reported. In the study, we investigated a new circRNA and its association with AKI.

Methods

An AKI model was established in Sprague-Dawley rats, followed by serum creatinine and urea nitrogen tests measured by a biochemical analyzer. The pathological changes and apoptosis in the renal tissue were detected by Hematoxylin and Eosin, and TUNEL staining. Then, circRNA expression in AKI was determined by quantitative real-time-PCR (qRT-PCR). NRK-52E cells were induced with hypoxia/reoxygenation (H/R) as in vitro models and the circ-Snrk level was tested by qRT-PCR. The effects of circ-Snrk in H/R-induced NRK-52E cells were assessed by flow cytometry, western blot, and enzyme-linked immunosorbent assay. Finally, RNA sequencing and western blot analysis were used to validate the mRNA profile and pathways involved in circ-Snrk knockdown in H/R-induced NRK-52E.

Results

A reliable AKI rat model and H/R cell model were established. qRT-PCR demonstrated that circ-Snrk level was upregulated in AKI left kidney tissue and NRK-52E cells with H/R treatment. Circ-Snrk knockdown inhibited apoptosis of NRK-52E cells and secretion of inflammatory factors (IL-6 and TNF-α). RNA sequencing showed that the mRNA profile changed after inhibition of circ-Snrk and differential expression of mRNA mainly enriched various signaling pathways, including MAPK signaling pathway. Furthermore, western blot indicated that circ-Snrk knockdown could inhibit the activation of p-JNK and p-38 transcription factors.

Conclusions

Circ-Snrk is involved in AKI development and associated with the MAPK signaling pathway in AKI.

Exosomal hsa_circ_0008925 from Urine Is Related to Chronic Renal Fibrosis

At present, there is no noninvasive biomarker of renal fibrosis. The potential diagnostic value of urinary exosome-derived circRNAs from glomerular disease patients for renal fibrosis is still uncertain. Here, we first detected the expression of hsa_circ_0008925 in TGF-β1-cultured HK-2 cell-derived exosomes. Secondly, we collected urine samples from 95 biopsy-proven glomerular disease patients and 34 healthy controls. The expression of hsa_circ_0008925 was analyzed, and the correlation with renal function and pathological changes was calculated. The receiver operating characteristic (ROC) curve for the diagnosis of renal fibrosis was performed. The results showed that in exosomes derived from TGF-β1-cultured HK-2 cells, the expression of hsa_circ_0008925 was increased compared with normal cultured. Further, the expression level of hsa_circ_0008925 was increased in urinary exosomes from renal fibrosis patients and correlated with serum creatinine, blood urea nitrogen (BUN), estimated glomerular filtration rate, and cystatin C. The level of hsa_circ_0008925 was furthermore correlated with the score of tubulointerstitial fibrosis (TIF) and the score of glomerular sclerosis. The ROC curve showed that hsa_circ_0008925 can diagnose renal fibrosis at a cut-off value of 0.093 with a sensitivity of 52.2% and specificity of 96.4%. In summary, we indicated that urinary exosomal hsa_circ_0008925 could be acted as a noninvasive biomarker for renal fibrosis in glomerular diseases patients.

Circular RNA ciRs-126 promotes hypoxia/reoxygenation cardiac injury possibly through miR-21

Background

This study aimed to analyze the role of circular RNA ciRs-126 in hypoxia/reoxygenation cardiac injury (H/R).

Methods

Expression of ciRs-126 and miR-21 in plasma samples from patients with H/R and healthy controls was determined by RT-qPCR. Correlations were analyzed by linear regression. Overexpression of ciRs-126 and miR-21 was achieved in cardiomyocytes to explore their crosstalk. The roles of ciRs-126 and miR-21 in H/R-induced apoptosis of cardiomyocytes were analyzed using cell apoptosis assay.

Results

CiRs-126 was upregulated and miR-21 was downregulated in H/R patients. They were inversely correlated across plasma samples from H/R patients. In H/R cardiomyocytes, ciRs-126 was upregulated and miR-21 was downregulated. In cardiomyocytes, ciRs-126 overexpression decreased miR-21 level and reduced the inhibitory effects of miR-21 overexpression on H/R-induced cell apoptosis.

Conclusions

Circular RNA ciRs-126 may suppress miR-21 expression to promote H/R cardiac injury.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12959-021-00355-x.

Circular RNAs in kidney disease and cancer

Circular RNAs (circRNAs) are a class of endogenously expressed regulatory RNAs with a single-stranded circular structure. They are generated by back splicing and their expression can be tightly regulated by RNA binding proteins. Cytoplasmic circRNAs can function as molecular sponges that inhibit microRNA-target interactions and protein function or as templates for the efficient generation of peptides via rolling circle amplification. They can also act as molecular scaffolds that enhance the reaction kinetics of enzyme-substrate interactions. In the nucleus, circRNAs might facilitate chromatin modifications and promote gene expression. CircRNAs are resistant to degradation and can be packaged in extracellular vesicles and transported in the circulation. Initial studies suggest that circRNAs have roles in kidney disease and associated cardiovascular complications. They have been implicated in hypertensive nephropathy, diabetic kidney disease, glomerular disease, acute kidney injury and kidney allograft rejection, as well as in microvascular and macrovascular complications of chronic kidney disease, including atherosclerotic vascular disease. In addition, several circRNAs have been reported to have oncogenic or tumour suppressor roles or to regulate drug resistance in kidney cancer. The available data suggest that circRNAs could be promising diagnostic and/or prognostic biomarkers and potential therapeutic targets for kidney disease, cardiovascular disease and kidney cancer.

Circ-BNIP3L knockdown alleviates LPS-induced renal tubular epithelial cell injury during sepsis-associated acute kidney injury by miR-370-3p/MYD88 axis

Sepsis-associated acute kidney injury (SA-AKI) is a frequent complication of the critically ill patient with high morbidity and mortality. Thus, the goal of this study was to investigate the role of circular RNA BCL2 Interacting Protein 3 Like (circ-BNIP3L) in the pathophysiological mechanism of SA-AKI. The SA-AKI cell model was established by using lipopolysaccharide (LPS)-induced HK-2 cells in vitro. Cell survival was analyzed using cell counting kit-8 (CCK-8) assay, EdU (5-ethynyl-2'-deoxyuridine) assay, flow cytometry and Western blot, respectively. Levels of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) were detected using ELISA analysis. The superoxide dismutase (SOD) activity and malondialdehyde (MDA) level were examined using commercial kits. Levels of genes and proteins were detected by qRT-PCR and Western blot. Dual-luciferase reporter and RNA immunoprecipitation (RIP) assays were used to identify the target relationship between miR-370-3p and circ-BNIP3L or MYD88 (myeloid differentiation primary response 88). Circ-BNIP3L was highly expressed in SA-AKI patients and LPS-induced HK-2 cells. Silencing of circ-BNIP3L attenuated LPS-induced growth inhibition, inflammation, and oxidative stress in HK-2 cells. Mechanistically, circ-BNIP3L competitively bound to miR-370-3p to up-regulate the expression of its target MYD88. Moreover, miR-370-3p inhibition reversed the beneficial effects of circ-BNIP3L knockdown on LPS-stimulated HK-2 cells. Meanwhile, miR-370-3p overexpression abolished LPS-induced injury in HK-2 cells, which was counteracted by MYD88 up-regulation. Circ-BNIP3L knockdown alleviated LPS-induced renal tubular epithelial cell injury by miR-370-3p/MYD88 axis, opening up a completely new avenue for the treatment of sepsis-associated AKI.

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.

The role of physical activity and miRNAs in the vascular aging and cardiac health of dialysis patients

Cardiovascular comorbidities are independent risk factors for mortality in dialysis patients. MicroRNA signaling has an important role in vascular aging and cardiac health, while physical activity is a primary nonpharmacologic treatment for cardiovascular comorbidities in dialysis patients. To identify the relationships between muscle function, miRNA signaling pathways, the presence of vascular calcifications and the severity of cardiovascular comorbidities, we initially enrolled 90 subjects on hemodialysis therapy and collected complete data from 46 subjects. A group of 26 subjects inactiv group (INC) was monitored during 12 weeks of physical inactivity and another group of 20 patients exercise group (EXC) was followed during 12 weeks of intradialytic, moderate intensity, resistance training intervention applied three times per week. In both groups, we assessed the expression levels of myo‐miRNAs, proteins, and muscle function (MF) before and after the 12‐week period. Data on the presence of vascular calcifications and the severity of cardiac comorbidities were collected from the patients’ EuCliD^® records. Using a full structural equitation modelling of the total study sample, we found that the higher the increase in MF was observed in patients, the higher the probability of a decrease in the expression of miR‐206 and TRIM63 and the lower severity of cardiac comorbidities. A reduced structural model in INC patients showed that the higher the decrease in MF, the higher the probability of the presence of calcifications and the higher severity of cardiac comorbidities. In EXC patients, we found that the higher the increase in MF, the lower the probability of higher severity of cardiovascular comorbidities.

Circ_0023404 sponges miR-136 to induce HK-2 cells injury triggered by hypoxia/reoxygenation via up-regulating IL-6R

The significance of circular RNAs (circRNAs) is reported in various kidney diseases including acute kidney injury (AKI). Specific circRNAs have the capacity to function as novel indicators of AKI. Circ_0023404 exhibits an important role in several diseases. Nevertheless, the detailed biological role of circ_0023404 in AKI remains poorly known. The present study aimed to investigate the effect of circ_0023404 on renal ischaemia/reperfusion (I/R) injury in vitro. Here, we evaluated the function of circ_0023404 in HK-2 cells in response to hypoxia/reoxygenation (H/R). We established a cell AKI model induced by H/R in HK-2 cells. We found circ_0023404 was significantly increased in AKI. Then, we found loss of circ_0023404 increased cell growth, repressed apoptosis, reduced inflammatory factors secretion and oxidative stress generation in vitro. Besides, circ_0023404 sponged miR-136. miR-136 overturned the effects of circ_0023404 on HK-2 cell injury. We assumed IL-6 receptor (IL-6R) as a target of miR-136 and IL-6R was activated by circ_0023404 via sponging miR-136. In conclusion, we revealed circ_0023404 contributed to HK-2 cells injury stimulated by H/R via sponging miR-136 and activating IL-6R.

Circular RNAs: Novel potential regulators in embryogenesis, female infertility, and pregnancy-related diseases

Circular RNAs (circRNAs) are endogenous noncoding RNAs with unique cyclic structures. Although they were previously considered as nonfunctional transcription byproducts, numerous studies have demonstrated that circRNAs regulate gene transcription and expression via different mechanisms. Reproductive health influences the quality of life and affects offspring propagation in women. CircRNAs have been found to modify pregnancy-related diseases, gynecologic cancers, polycystic ovary syndrome, aging, gamete, and embryo development. It's promising for circRNAs to be the novel diagnostic and therapeutic targets for multiple reproductive diseases. With the widespread application of assisted reproduction technology (ART), it has been revealed that circRNA identification contributes to estimating the quality of gametes and embryos, reflecting the success rate of ART. CRISPR-Cas9 gene editing technology has enabled the discovery of new roles of circRNAs. So far, the roles of circRNAs in the reproductive system remain poorly defined. In this review, we describe the classification and functions of circRNAs in embryogenesis and the female reproductive system diseases, revealing potential roles of circRNAs physiologically and pathologically. In so-doing, we provide ideas for developing circRNA-based therapeutic treatment and clinical application of various female reproductive system diseases.

Non-Coding RNA and Diabetic Kidney Disease

Diabetic kidney disease (DKD) is one of the most common chronic microvascular complications of diabetes. In addition to the characteristic clinical manifestations of proteinuria, it also has a complex pathological process that results from the combined effects of multiple factors involving the whole renal structure such as glomeruli, renal tubules, and blood vessels. Non-coding RNAs (ncRNA) are transcripts with no or low coding potential, among which micro RNA (miRNA) has been widely studied as a functional miRNA involved in regulation and a potential biomarker for disease prediction. The abundance of long coding RNA (lncRNA) in vivo is highly expressed with a certain degree of research progress, but the structural similarity makes the research still challenging. The research of circular RNA (circRNA) is still in its early stages. It is more relevant to the study to provide a more relevant link between diseases in the kidney and other tissues or organs. This classification review mainly summarized the biogenesis characteristics, the pathological mechanism of ncRNA-regulating diseases, the ways of ncRNA in the clinical prediction as a potential biomarker, and the interaction networks of ncRNA.

Role of Circular RNA in Kidney-Related Diseases

The kidney is vital in maintaining fluid, electrolyte, and acid–base balance. Kidney-related diseases, which are an increasing public health issue, can happen to people of any age and at any time. Circular RNAs (circRNAs) are endogenous RNA that are produced by selective RNA splicing and are involved in progression of various diseases. Studies have shown that various kidney diseases, including renal cell carcinoma, acute kidney injury, and chronic kidney disease, are linked to circRNAs. This review outlines the characteristics and biological functions of circRNAs and discusses specific studies that provide insights into the function and potential of circRNAs for application in the diagnosis and treatment of kidney-related diseases.

Circular RNA-based biomarkers in blood of patients with Fabry disease and related phenotypes

BACKGROUND

Fabry disease is a rare X-linked lysosomal storage disease caused by mutations in the galactosidase α gene. Deficient activity of α-galactosidase A leads to glycosphingolipid accumulations in multiple organs. Circular RNAs represent strong regulators of gene expression. Their circular structure ensures high stability in blood. We hypothesised that blood-based circular RNA profiles improve phenotypic assignment and therapeutic monitoring of Fabry disease.

METHODS

A genome-wide circular RNA expression analysis was performed in blood of genetically diagnosed patients with Fabry disease (n=58), age-matched and sex-matched healthy volunteers (n=14) and disease control patients with acute kidney injury (n=109). Most highly dysregulated circular RNAs were validated by quantitative real-time PCR. Circular RNA biomarker sensitivity, specificity, predictive values and area under the curve (AUC) were determined. Linear regression analyses were conducted for validated circular RNA biomarkers and clinical patient characteristics.

RESULTS

A distinct circular RNA transcriptome signature identified patients with Fabry disease. Level of circular RNAs hsa_circ_0006853 (AUC=0.73), hsa_circ_0083766 (AUC=0.8) and hsa_circ_0002397 (AUC=0.8) distinguished patients with Fabry disease from both healthy controls and patients with acute kidney injury. Hsa_circ_0002397 was, furthermore, female-specifically expressed. Circular RNA level were significantly related to galactosidase α gene mutations, early symptoms, phenotypes, disease severities, specific therapies and long-term complications of Fabry disease.

CONCLUSION

The discovery of circular RNA-based and Fabry disease-specific biomarkers may advance future diagnosis of Fabry disease and help to distinguish related phenotypes.

Knockdown of circ-FANCA alleviates LPS-induced HK2 cell injury via targeting miR-93-5p/OXSR1 axis in septic acute kidney injury

BACKGROUND

Sepsis is life-threatening disease with systemic inflammation and can lead to various diseases, including septic acute kidney injury (AKI). Recently, diverse circular RNAs (circRNAs) are considered to be involved in the development of this disease. In this study, we aimed to elucidate the role of circ-FANCA and the potential action mechanism in sepsis-induced AKI.

METHODS

HK2 cells were treated with lipopolysaccharide (LPS) to establish septic AKI cell model. The expression of circ-FANCA, microRNA-93-5p (miR-93-5p) and oxidative stress responsive 1 (OXSR1) mRNA was determined by quantitative real-time polymerase chain reaction (qRT-PCR). Cell viability was assessed using cell counting kit-8 (CCK-8) assay. Cell apoptosis and cell cycle distribution were measured by flow cytometry. The inflammatory response was monitored according to the release of pro-inflammatory cytokines via enzyme-linked immunosorbent assay (ELISA). The activities of oxidative indicators were examined using the corresponding kits. Dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay were applied to validate the interaction between miR-93-5p and circ-FANCA or OXSR1. Protein analysis was conducted through western blot.

RESULTS

Circ-FANCA was upregulated in septic AKI serum specimens and LPS-treated HK2 cells. Functionally, circ-FANCA knockdown facilitated cell proliferation and restrained apoptosis, inflammation and oxidative stress in LPS-triggered HK2 cells. Further mechanism analysis revealed that miR-93-5p was a target of circ-FANCA and circ-FANCA modulated LPS-induced cell damage by targeting miR-93-5p. Meanwhile, miR-93-5p overexpression repressed LPS-treated HK2 cell injury by sponging OXSR1. Furthermore, circ-FANCA regulated OXSR1 expression by sponging miR-93-5p. Besides, exosome-derived circ-FANCA was upregulated in LPS-induced HK2 cells, which was downregulated by GW4869.

CONCLUSION

Circ-FANCA knockdown attenuated LPS-induced HK2 cell injury by regulating OXSR1 expression via targeting miR-93-5p.

Hsa_circ_0123190 acts as a competitive endogenous RNA to regulate APLNR expression by sponging hsa-miR-483-3p in lupus nephritis

Background

Lupus nephritis (LN) is one of the most severe complications of systemic lupus erythematosus (SLE). Circular RNAs (circRNAs) can act as competitive endogenous RNAs (ceRNAs) to regulate gene transcription, which is involved in mechanism of many diseases. However, the role of circRNA in lupus nephritis has been rarely reported. In this study, we aim to investigate the clinical value of circRNAs and explore the mechanism of circRNA involvement in the pathogenesis of LN.

Methods

Renal tissues from three untreated LN patients and three normal controls (NCs) were used to identify differently expressed circRNAs by next-generation sequencing (NGS). Validated assays were used by quantitative reverse transcription polymerase chain reaction (qRT-PCR). The interactions between circRNA and miRNA, or miRNA and mRNA were further determined by luciferase reporter assay. The extent of renal fibrosis between the two groups was assessed by Masson-trichome staining and immunohistochemistry (IHC) staining.

Results

159 circRNAs were significantly dysregulated in LN patients compared with NCs. The expression of hsa_circ_0123190 was significantly decreased in the renal tissues of patients with LN (P = 0.014). Bio-informatics analysis and luciferase reporter assay illustrated that hsa_circ_0123190 can act as a sponge for hsa-miR-483-3p, which was also validated to interact with APLNR. APLNR mRNA expression was related with chronicity index (CI) of LN (P = 0.033, R² = 0.452). Moreover, the fibrotic-related protein, transforming growth factor-β1 (TGF-β1), which was regulated by APLNR, was more pronounced in the LN group (P = 0.018).

Conclusion

Hsa_circ_0123190 may function as a ceRNA to regulate APLNR expression by sponging hsa-miR-483-3p in LN.

Circular RNA circ_0068,888 protects against lipopolysaccharide-induced HK-2 cell injury via sponging microRNA-21-5p

Our previous findings revealed that hsa_circ_0068,888 was markedly down-regulated in the plasma of patients with sepsis-associated acute kidney injury (AKI). However, its molecular mechanism in AKI remains unclear. Herein, we explored the role of hsa_circ_0068,888 in AKI. Human renal proximal tubular cell line HK-2 was stimulated with lipopolysaccharide (LPS) to mimic AKI in vitro. Decreased hsa_circ_0068,888 expression was observed in AKI cell model. The overexpression of hsa_circ_0068,888 significantly increased the viability of LPS-stimulated HK-2 cells, whereas hsa_circ_0068,888 downregulation showed the opposite effect. Furthermore, LPS triggered inflammatory response and oxidative stress, which was inhibited by hsa_circ_0068,888 overexpression and enhanced by hsa_circ_0068,888 down-regulation. Hsa_circ_0068,888 overexpression suppressed the activation of nuclear factor-κB (NF-κB) pathway triggered by LPS as evidenced by decreased p-p65 protein level and nuclear translocation of p65 in hsa_circ_0068,888 overexpressed cells. Additionally, we proved that hsa_circ_0068,888 targeted microRNA-21-5p (miR-21-5p). The expression of miR-21-5p was markedly increased and was negatively regulated by hsa_circ_0068,888 in LPS-stimulated HK-2 cells. Furthermore, we demonstrated that miR-21-5p overexpression reversed the effects on cell viability, inflammatory response, oxidative stress, and NF-κB pathway induced by hsa_circ_0068,888 overexpression in LPS-stimulated HK-2 cells. Overall, these results implied that hsa_circ_0068,888 shows a protective effect on AKI by sponging miR-21-5p. Hence, up-regulation of hsa_circ_0068,888 might be a potential strategy in treatment for AKI.

Hsa_Circ_0007841 Enhances Multiple Myeloma Chemotherapy Resistance Through Upregulating ABCG2

The current researches have reported that circular RNA is an important regulatory factor in the progression of various human disease. However, the function and mechanism of most circular RNAs remain unknown in cancers including multiple myeloma. Our study has confirmed that hsa_circ_0007841 is up regulated in U266 doxorubicin resistant cells (U266R) and 8226 doxorubicin resistant cells (8226R) compared to U266 parent cells (U266P) and 8226 parent cells (8226P). Silence of hsa_circ_0007841 in U266R and 8226R could reduce the half-maximal inhibitory concentration which indicated reduction in chemoresistance. In doxorubicin resistant cells, the messenger RNA and protein level of ATP-binding cassette transporters G2 increased. Silence of hsa_circ_0007841 in drug resistant cells could decrease both the messenger RNA and protein levels of ATP-binding cassette transporters G2; reexpression of hsa_circ_0007841 could block the reduction. However, overexpression of hsa_circ_0007841 could effectively upregulate the ATP-binding cassette transporters G2 messenger RNA and protein level. Inhibition of ATP-binding cassette transporters G2 could block hsa_circ_0007841 overexpression induced chemoresistance in U266P and 8226P cells. What’s more, inhibition of ATP-binding cassette transporters G2 could reduce differences of half-maximal inhibitory concentration between parent cell lines and drug-resistant cell lines. Our data collectively suggest a new model in which hsa_circ_0007841 promotes acquired chemotherapy resistance by upregulating ATP-binding cassette transporters G2 providing a novel molecular basis of chemotherapy in multiple myeloma cancer.

CircPAN3 ameliorates myocardial ischaemia/reperfusion injury by targeting miR-421/Pink1 axis-mediated autophagy suppression

Cardiovascular diseases are considered the leading cause of death worldwide. Myocardial ischaemia/reperfusion (I/R) injury is recognized as a critical risk factor for cardiovascular diseases. Although increasing advances have been made recently in understanding the mechanisms of I/R injury, they remain largely unknown. In this study, we found that the expression of circPAN3 (circular RNA PAN3) was decreased in a mouse model of myocardial I/R. Overexpression of circPAN3 significantly inhibited autophagy and alleviated cell apoptosis of cardiomyocytes, which was further verified in vivo by decreased autophagic vacuoles and reduced myocardial infarct sizes. Moreover, miR-421 (microRNA-421) was identified as a downstream target involved in circPAN3-mediated myocardial I/R injury. Additionally, miR-421 could negatively regulate Pink1 (phosphatase and tensin homologue-induced putative kinase 1) via a direct binding relationship. Furthermore, the mitigating effects of circPAN3 overexpression on myocardial I/R injury by suppressing autophagy and apoptosis were abolished by knockdown of Pink1. Our findings reveal a novel role for circPAN3 in modulating autophagy and apoptosis in myocardial I/R injury and the circPAN3-miR-421-Pink1 axis as a regulatory network, which might provide potential therapeutic targets for cardiovascular diseases.

The circular RNA TLK1 exacerbates myocardial ischemia/reperfusion injury via targeting miR-214/RIPK1 through TNF signaling pathway

PURPOSE

Myocardial ischemia/reperfusion injury (IRI) induces cardiomyocytes death and leads to loss of cardiac function. Circular RNAs (circRNA) have gain increasing interests in modulating myocardial IRI. In this study, we aim to investigate the role and exact mechanism of circTLK1 in the pathogenesis of myocardial IRI.

METHODS

Myocardial IRI was developed in mice with measuring hemodynamic parameters and the activity of serum myocardial enzymes to evaluate cardiac function. HE and TTC staining were performed to assess infarct area. Expression patterns of circTLK1 and miR-214 were investigated using qRT-PCR assay. Gene expression of circTLK1, miR-214 or RIPK was altered by transfecting with their overexpression or knockdown vectors. The apoptosis of cardimyocytes was assessed by TUNEL staining and Caspase-3 activity analysis. Apoptosis-related markers Bcl-2, Bax, and caspase3, as well as TNF-α signals were determined by western blotting. The interactions of circTLK1/miR-214 and miR-214/RIPK1 were verified using luciferase reporter assay. RNA immunoprecipitation (RIP) was subjected to further definite the direct binding of circTLK1/miR-214. The regulatory network of circTLK1/miR-214/RIPK1 was further validated in vivo.

RESULTS

circTLK1 was an up-regulated circRNA found in a myocardial IRI mouse model. Mice with silencing circTLK1 significantly alleviated the impaired cardiac function indexes and decreased infarct area, thus attenuating the pathogenesis of myocardial IRI. Knockdown of circTLK1 dramatically decreased cardiomyocytes apoptosis, which was determined by apoptosis-related proteins. miR-214 was identified as a downstream effector to reverse circTLK1-mediated damage effects in myocardial IRI. miR-214 could directly target RIPK1 via binding to its' 3'-UTR. Overexpression of RIPK1 led to impaired cardiac function indexes, increased infarct area, and cell apoptosis, which abolished the protective effects of miR-214. The TNF signaling pathway was demonstrated to be involved in the circTLK1/miR-214/RIPK1 regulatory network in myocardial IRI.

CONCLUSION

Taken together, our study revealed an up-regulated circRNA, circTLK1, could exacerbate myocardial IRI via targeting miR-214/RIPK1-mediated TNF signaling pathway, which may provide therapeutic targets for treatment.

Transcriptome sequencing of circular RNA reveals a novel circular RNA-has_circ_0114427 in the regulation of inflammation in acute kidney injury

Acute kidney injury (AKI) is a common serious syndrome characterized by rapid decrease of glomerular filtration rate and the progressive increase of serum creatinine. Circular RNAs (circRNAs) are regulatory RNAs that recently became popular among various diseases. However, the expression profile and function of circRNAs in AKI remain largely unknown. The main function of circRNAs is acting as competing endogenous RNAs (ceRNAs) by binding with microRNAs (miRNAs), as indicated by recent research. In the present study, we established cisplatin-induced AKI model in mice and isolated renal tubular tissues to extract circRNAs for next-generation sequencing (NGS) and bioinformatics analysis. We analyzed the composition, distribution and Gene Ontology terms of circRNAs in cisplatin-induced AKI and revealed differentially expressed circRNAs related to AKI. By finding homologous genes between mouse and human, we identified circRNA- circ-0114427 in humans. We further investigated its function in AKI cell model. Circ-0114427 expression was significantly up-regulated in different AKI cell models. Knockdown of circ-0114427 indicated that circ-0114427 bound to miR-494 as a miRNA sponge to regulate ATF3 expression and further affected the expression of downstream cytokine IL-6. Circ-0114427 regulates inflammatory progression in AKI's early stage via circ-0114427/miR-494/ATF3 pathway. Our findings reveal the expression profile of circRNAs in cisplatin-induced AKI and provide a novel insight into the regulatory mechanism of circRNAs, which may become a new molecular target resource for early diagnosis and treatment strategies.

Circular RNA in renal diseases

Circular RNA (circRNA) is a newly described type of non-coding RNA. Active research is greatly enriching the current understanding of the expression and role of circRNA, and a large amount of evidence has implicated circRNA in the pathogenesis of certain renal diseases, such as renal cell carcinoma, acute kidney injury, diabetic nephropathy and lupus nephritis. Studies have found evidence that circRNAs regulate programmed cell death, invasion, and metastasis and serve as biomarkers in renal diseases. Recently, circRNAs were identified in exosomes secreted by the kidneys. Nevertheless, the function of circRNA in renal diseases remains ambiguous. Given that circRNAs are regulators of gene expression, they may be involved in the pathology of multiple renal diseases. Additionally, emerging evidence is showing that circulating circRNAs may serve as novel biomarkers for renal disease. In this review, we have summarized the identification, biogenesis, degradation, and functions of circRNA and have evaluated the roles of circRNA in renal diseases.

Circular RNA YAP1 acts as the sponge of microRNA-21-5p to secure HK-2 cells from ischaemia/reperfusion-induced injury

Circular RNA YAP1 (circYAP1) was reported to participate in progression of gastric cancer. However, the role of circYAP1 in acute kidney injury (AKI) remains obscure. We attempted to examine the effects of circYAP1 on ischaemia/reperfusion-stimulated renal injury. AKI model was established by treating HK-2 cells in ischaemia/reperfusion (I/R) environment. CircYAP1 expression in blood of AKI patients and I/R-treated HK-2 cells was evaluated via RT-qPCR. CCK-8, flow cytometry, ELISA and ROS assay were executed to test the impact of circYAP1 on cell viability, apoptosis, inflammatory cytokines and ROS generation. Bioinformatic analysis was executed to explore miRNA targets. The relativity between circYAP1 and miR-21-5p was verified by RT-qPCR and luciferase assay. The functions of miR-21-5p in I/R-triggered injury were reassessed. PI3K/AKT/mTOR pathway was detected by Western blot. Down-regulated circYAP1 was observed in AKI blood samples and I/R-treated HK-2 cells. CircYAP1 overexpression expedited cell growth and weakened secretion of inflammatory factors and ROS generation in I/R-disposed cells. Besides, we found circYAP1 could sponge to miR-21-5p. Interestingly, miR-21-5p overexpression overturned the repressive effects of circYAP1 on cell injury. Moreover, PI3K/AKT/mTOR pathway was activated by circYAP1 via inhibiting miR-21-5p. We demonstrated that circYAP1 activated PI3K/AKT/mTOR pathway and secured HK-2 cells from I/R injury via sponging miR-21-5p.

Diagnostic, Prognostic, and Therapeutic Value of Non-Coding RNA Expression Profiles in Renal Transplantation

End-stage renal disease is a public health problem responsible for millions of deaths worldwide each year. Although transplantation is the preferred treatment for patients in need of renal replacement therapy, long-term allograft survival remains challenging. Advances in high-throughput methods for large-scale molecular data generation and computational analysis are promising to overcome the current limitations posed by conventional diagnostic and disease classifications post-transplantation. Non-coding RNAs (ncRNAs) are RNA molecules that, despite lacking protein-coding potential, are essential in the regulation of epigenetic, transcriptional, and post-translational mechanisms involved in both health and disease. A large body of evidence suggests that ncRNAs can act as biomarkers of renal injury and graft loss after transplantation. Hence, the focus of this review is to discuss the existing molecular signatures of non-coding transcripts and their value to improve diagnosis, predict the risk of rejection, and guide therapeutic choices post-transplantation.

Circular RNA circC3P1 restrains kidney cancer cell activity by regulating miR-21/PTEN axis and inactivating PI3K/AKT and NF- kB pathways

Kidney cancer (KC) seriously impacts public health. We detected the function and mechanism of circular RNA C3P1 (circC3P1) in KC cells. CCK-8, flow cytometry, migration, and invasion assay were respectively used to investigate the efficacies of circC3P1 and microRNA (miR)-21 on cell viability, apoptosis, migration, and invasion. Phosphatase and tensin homologue deleted on chromosome 10 (PTEN), circC3P1, and miR-21 expression were changed by cell transfection and detected by quantitative reverse-transcription polymerase chain reaction. Moreover, the apoptosis/pathways-related proteins and proteins were detected by western blot analysis. Besides, the relation between PTEN and miR-21 was detected by luciferase assay. circC3P1 and PTEN were downregulated while miR-21 was upregulated in KC tissues. circC3P1 declined cell viability, migration, and invasion and caused apoptosis. Furthermore, circC3P1 negatively regulated miR-21; miR-21 mimic could reverse the efficacies of circC3P1. Besides, circC3P1 restrained the PI3K/AKT and NF-κB pathways by downregulating miR-21. Finally, PTEN was authenticated as a target of miR-21. circC3P1 restrained KC cell growth, migration, and invasion by regulating miR-21/PTEN axis and inactivating PI3K/AKT and NF-κB signaling pathways.

Circular RNA circFNDC3B protects renal carcinoma by miR-99a downregulation

Various circular RNAs (circRNAs) have been reported to involve in carcinoma. This study explored the role and mechanism of circRNA circFNDC3B (circFNDC3B) in renal carcinoma (RC). The detection indicators in this paper were viability, colony, and migration, which respectively investigated by Cell Counting Kit-8, colony formation, and migration assay. Reverse transcriptase quantitative polymerase chain reaction tested and cell transfection changed circFNDC3B and miR-99a expression. Moreover, western blot tested relate-proteins of proliferation, migration, and cell pathways were examined by western blot. circFNDC3B was upregulated at RC tissues. circFNDC3B enhanced cell viability, colony and migration, and miR-99a mimic played reverse impacts. Furthermore, circFNDC3B negatively regulated miR-99aand circFNDC3B restrained the janus kinase 1/signal transducer and activator of transcription 3 (JAK1/STAT3) and extracellular signal-regulated kinase (ERK) kinase (MEK)/ERK pathways by miR-99a downregulation. Overexpression of circFNDC3B enhanced cell viability, colony formation and migration by miR-99a downregulation via JAK1/STAT3 and MEK/ERK pathways.

Circular RNAs in Urine of Kidney Transplant Patients with Acute T Cell-Mediated Allograft Rejection

BACKGROUND

Circular RNAs (circRNAs) have recently been described as novel noncoding regulators of gene expression. They are detectable in the blood of patients with acute kidney injury. We tested whether circRNAs were present in urine and could serve as new predictors of outcome in renal transplant patients with acute rejection.

METHODS

A global circRNA expression analysis using RNA from urine of patients with acute T cell-mediated renal allograft rejection and control transplant patients was performed. Dysregulated circRNAs were confirmed in a cohort of 62 patients with acute rejection, 10 patients after successful antirejection therapy, 18 control transplant patients without rejection, and 13 stable transplant patients with urinary tract infection.

RESULTS

A global screen revealed several circRNAs to be altered in urine of patients with acute rejection. Concentrations of 2 circRNAs including hsa_circ_0001334 and hsa_circ_0071475 were significantly increased. These were validated in the whole cohort of patients. hsa_circ_0001334 was upregulated in patients with acute rejection compared with controls. Concentrations of hsa_circ_0001334 normalized in patients with acute rejection following successful antirejection therapy. hsa_circ_0001334 was associated with higher decline in glomerular filtration rate 1 year after transplantation.

CONCLUSIONS

CircRNA concentrations are significantly dysregulated in patients with acute rejection at subclinical time points. Urinary hsa_circ_0001334 is a novel biomarker of acute kidney rejection, identifying patients with acute rejection and predicting loss of kidney function.