Circular RNA Foxo3 in cardiac ischemia-reperfusion injury in heart transplantation: A new regulator and target

CircFOXO3 mediates hypoxia-induced autophagy of endometrial stromal cells in endometriosis

Endometriosis is a benign gynecological disease that shares some common features of malignancy. Autophagy plays vital roles in endometriosis and influences endometrial cell metastasis, and hypoxia was identified as the initiator of this pathological process through hypoxia inducible factor 1 alpha (HIF-1α). A newly discovered circular RNA FOXO3 (circFOXO3) is critical in cell autophagy, migration, and invasion of various diseases and is reported to be related to hypoxia, although its role in endometriosis remains to be elucidated up to now. In this study, a lower circFOXO3 expression in ectopic endometrium was investigated. Furthermore, we verified that circFOXO3 could regulate autophagy by downregulating the level of p53 protein to mediate the migration and invasion of human endometrial stromal cells (T HESCs). Additionally, the effects of HIF-1α on circFOXO3 and autophagy were examined in T HESCs. Notably, overexpression of HIF-1α could induce autophagy and inhibit circFOXO3 expression, whereas overexpressing of circFOXO3 under hypoxia significantly inhibited hypoxia-induced autophagy. Mechanistically, the direct combination between HIF-1α and HIF-1α-binding site on adenosine deaminase 1 acting on RNA (ADAR1) promoter increased the level of ADAR1 protein, which bind directly with circFOXO3 pre-mRNA to block the cyclization of circFOXO3. All these results support that hypoxia-mediated ADAR1 elevation inhibited the expression of circFOXO3, and then autophagy was induced upon loss of circFOXO3 via inhibition of p53 degradation, participating in the development of endometriosis.

Circular RNA MAP2K2-modified immunosuppressive dendritic cells for preventing alloimmune rejection in organ transplantation

Long-term patient and graft survival has been achieved in organ transplantation but at the expense of toxic side effects that are associated with long-term use of nonspecific immunosuppressive drugs. Discovering new regulators of dendritic cells is the key for development of an ideal treatment to prevent immune rejection. We hypothesized that knockdown of circMAP2K2 induces immunosuppressive DCs and that treatment with circMAP2K2 silenced-DCs can prevent alloimmune rejection. DCs were cultured and transfected with siRNA for circMAP2K2. circMAP2K2 levels were measured by qRT-PCR. DC's maturation and immune function were assessed by flow cytometry and mixed lymphocyte reactions. The function of circMAP2K2 was illustrated by a series of RIP and IP. The therapeutics of engineered DCs was tested in a mouse heart transplantation model. We found that circMAP2K2 was highly expressed in mature DCs. Knockdown of circMAP2K2 reduced expression of MHCII, CD40 and CD80, attenuated the ability of DCs to activate allogeneic naïve T cells, and enhanced CD4+CD25+FOXP3+ regulatory T cells (Treg). circMAP2K2-induced immunosuppressive DCs by interacting with SENP3. Treatment with circMAP2K2-knockdown DCs attenuated alloimmune rejection and prolonged allograft survival in a murine heart transplantation model. The immune suppression induced in vivo was donor-antigen specific. In conclusion, knockdown of circMAP2K2 can induce immunosuppressive DCs which are able to inhibit overactive immune response, highlighting a new promising therapeutic approach for immune disorder diseases.

Exploring the Multifaceted Biologically Relevant Roles of circRNAs: From Regulation, Translation to Biomarkers

CircRNAs are a category of regulatory RNAs that have garnered significant attention in the field of regulatory RNA research due to their structural stability and tissue-specific expression. Their circular configuration, formed via back-splicing, results in a covalently closed structure that exhibits greater resistance to exonucleases compared to linear RNAs. The distinctive regulation of circRNAs is closely associated with several physiological processes, as well as the advancement of pathophysiological processes in several human diseases. Despite a good understanding of the biogenesis of circular RNA, details of their biological roles are still being explored. With the steady rise in the number of investigations being carried out regarding the involvement of circRNAs in various regulatory pathways, understanding the biological and clinical relevance of circRNA-mediated regulation has become challenging. Given the vast landscape of circRNA research in the development of the heart and vasculature, we evaluated cardiovascular system research as a model to critically review the state-of-the-art understanding of the biologically relevant functions of circRNAs. We conclude the review with a discussion of the limitations of current functional studies and provide potential solutions by which these limitations can be addressed to identify and validate the meaningful and impactful functions of circRNAs in different physiological processes and diseases.

Circular RNA FEACR inhibits ferroptosis and alleviates myocardial ischemia/reperfusion injury by interacting with NAMPT

BACKGROUND

Emerging research has reported that circular RNAs (circRNAs) play important roles in cardiac cell death after myocardial ischemia and reperfusion (I/R). Ferroptosis, a new form of cell death discovered in recent years, has been proven to participate in the regulation of myocardial I/R. This study used circRNA sequencing to explore the key circRNA in the regulation of cardiac ferroptosis after I/R and study the mechanisms of potential circRNA function.

METHODS

We performed circRNA sequencing to explore circRNAs differentially expressed after myocardial I/R. We used quantitative polymerase chain reactions to determine the circRNA expression in different tissues and detect the circRNA subcellular localization in the cardiomyocyte. Gain- and loss-of-function experiments were aimed to examine the function of circRNAs in cardiomyocyte ferroptosis and cardiac tissue damage after myocardial I/R. RNA pull-down was applied to explore proteins interacting with circRNA.

RESULTS

Here, we identified a ferroptosis-associated circRNA (FEACR) that has an underlying regulatory role in cardiomyocyte ferroptosis. FEACR overexpression suppressed I/R-induced myocardial infarction and ameliorated cardiac function. FEACR inhibition induces ferroptosis in cardiomyocytes and FEACR overexpression inhibits hypoxia and reoxygenation-induced ferroptosis. Mechanistically, FEACR directly bound to nicotinamide phosphoribosyltransferase (NAMPT) and enhanced the protein stability of NAMPT, which increased NAMPT-dependent Sirtuin1 (Sirt1) expression, which promoted the transcriptional activity of forkhead box protein O1 (FOXO1) by reducing FOXO1 acetylation levels. FOXO1 further upregulated the transcription of ferritin heavy chain 1 (Fth1), a ferroptosis suppressor, which resulted in the inhibition of cardiomyocyte ferroptosis.

CONCLUSIONS

Our finding reveals that the circRNA FEACR-mediated NAMPT-Sirt1-FOXO1-FTH1 signaling axis participates in the regulation of cardiomyocyte ferroptosis and protects the heart function against I/R injury. Thus, FEACR and its downstream factors could be novel targets for alleviating ferroptosis-related myocardial injury in ischemic heart diseases.

Pro-fibrotic and apoptotic activities of circARAP1 in myocardial ischemia-reperfusion injury

Reperfusion modality can cause damage to cardiomyocytes, known as myocardial ischemia-reperfusion injury (MI/RI). Circular RNAs (circRNAs) are fundamental regulators associated with many cardiac diseases, including MI/RI. However, their functional impact on cardiomyocyte fibrosis and apoptosis remains elusive. Therefore, this study aimed to explore possible molecular mechanisms of circARPA1 in animal models and in hypoxia/reoxygenation (H/R)-treated cardiomyocytes. GEO dataset analysis showed that has_circ_0023461 (circARPA1) was differentially expressed in myocardial infarction samples. Real-time quantitative PCR further supported that circARPA1 was expressed at high levels in animal models and in H/R-triggered cardiomyocytes. Then, loss-of-function assays were performed to show that circARAP1 suppression effectively ameliorated cardiomyocyte fibrosis and apoptosis in MI/RI mice. Mechanistic experiments showed that miR-379-5p, KLF9 and Wnt signaling pathways were associated with circARPA1. circARPA1 can sponge miR-379-5p to regulate KLF9 expression, thereby activating the wnt/β-catenin pathway. Finally, gain-of-function assays revealed that circARAP1 aggravated MI/RI in mice and H/R-induced cardiomyocyte injury by regulating the miR-379-5p/KLF9 axis to activate Wnt/β-catenin signaling.

Oxidant stress-sensitive circRNA Mdc1 controls cardiomyocyte chromosome stability and cell cycle re-entry during heart regeneration

Targeting cardiomyocyte plasticity has emerged as a new strategy for promoting heart repair after myocardial infarction. However, the precise mechanistic network underlying heart regeneration is not completely understood. As noncoding RNAs, circular RNAs (circRNAs) play essential roles in regulating cardiac physiology and pathology. The present study aimed to investigate the potential roles of circMdc1 in cardiac repair after injury and elucidate its underlying mechanisms. Here, we identified that circMdc1 levels were upregulated in postnatal mouse hearts but downregulated in the regenerative myocardium. The expression of circMdc1 in cardiomyocytes is sensitive to oxidative stress, which was attenuated by N-acetyl-cysteine. Enforced circMdc1 expression inhibited cardiomyocyte proliferation, while circMdc1 silencing led to cardiomyocyte cell cycle re-entry. In vivo, the cardiac-specific adeno-associated virus-mediated knockdown of circMdc1 promoted cardiac regeneration and heart repair accompanied by improved heart function. Conversely, circMdc1 overexpression blunted the regenerative capacity of neonatal hearts after apex resection. Moreover, circMdc1 was able to block the translation of its host gene Mdc1 specifically by binding to PABP, affecting DNA damage and the chromosome stability of cardiomyocytes. Furthermore, overexpression of Mdc1 caused damaged mouse hearts to regenerate and repair after myocardial infarction in vivo. Oxidative stress-sensitive circMdc1 plays an important role in cardiac regeneration and heart repair after injury by regulating DNA damage and chromosome stability in cardiomyocytes by blocking the translation of the host gene Mdc1.

Circular RNAs and Drug Resistance in Genitourinary Cancers: A Literature Review

Simple Summary

Drug resistance to systematic treatment in genitourinary tumors severely aggravated the burden on patients and society. Multiple mechanisms were involved in drug resistance. As typical non-coding RNAs, circRNAs play a critical role in the onset and development of cancers and several studies implied their function in the regulation of drug resistance. Here, we reviewed the investigations of circRNAs’ behavior in drug resistance of genitourinary cancers and summarized the underlying mechanisms. This review emphasized the essential role of circRNAs in drug resistance development and also pointed out the potential topics that need further investigations in the future.

Abstract

In recent years, systematic treatment has made great progress in genitourinary tumors. However, some patients develop resistance to the treatments, resulting in an increase in mortality. Circular RNAs (circRNAs) form a class of non-coding RNAs with high stability and significant clinical relevance. Accumulating evidence indicates that circRNAs play a vital role in cancer development and tumor chemotherapy resistance. This review summarizes the molecular and cellular mechanisms of drug resistance mediated by circRNAs to common drugs used in the treatment of genitourinary tumors. Several circRNAs were identified to regulate the responsiveness to systemic treatments in genitourinary tumors, including chemotherapies such as cisplatin and targeted therapies such as enzalutamide. Canonically, cicrRNAs participate in the competing endogenous RNA (ceRNA) network, or in some cases directly interact with proteins, regulate downstream pathways, and even some circRNAs have the potential to produce proteins or polypeptides. Several cellular mechanisms were involved in circRNA-dependent drug resistance, including autophagy, cancer stem cells, epithelial-mesenchymal transition, and exosomes. The potential clinical prospect of circRNAs in regulating tumor drug resistance was also discussed.

MicroRNA-136-5p protects cardiomyocytes from coronary microembolization through the inhibition of pyroptosis

This study investigated how miR-136-5p partially affected cardiomyocyte pyroptosis in rats with coronary microembolization (CME). The cardiac function and structure of rats with CME were evaluated using echocardiography, hematoxylin and eosin staining, Masson staining, and troponin I level. Pyroptosis was induced by lipopolysaccharide (LPS) in isolated rat cardiomyocytes and evaluated by the expression of caspase-1, NOD-like receptor family pyrin domain-containing 3, interleukin-1β, and gasdermin D-N. After cell transfection, the expression of Ataxin-1 like (ATXN1L), pyrin domain-containing 1 (PYDC1), and pyroptosis-related proteins was assessed. Dual-luciferase reporter and immunoprecipitation assays were used to verify the relationships among miR-136-5p, ATXN1L, and capicua (CIC). MiR-136-5p was under-expressed, whereas ATXN1L was overexpressed in rats with CME and in LPS-treated primary cardiomyocytes. MiR-136-5p targeted ATXN1L, and ATXN1L bound to CIC to suppress PYDC1 expression. MiR-136-5p overexpression suppressed pyroptosis by inhibiting the binding of ATXN1L with CIC and promoting PYDC1 expression, which was reversed by simultaneous elevation of ATXN1L. In conclusion, miR-136-5p suppressed pyroptosis by upregulating PYDC1 via ATXN1L/CIC axis, thereby attenuating cardiac damage caused by CME.

Expression Profiles of Circular RNA in Aortic Vascular Tissues of Spontaneously Hypertensive Rats

Background: Circular RNAs (circRNAs), as a kind of endogenous non-coding RNA, have been implicated in ischemic heart diseases and vascular diseases. Based on theirs high stability with a closed loop structure, circRNAs function as a sponge and bind specific miRNAs to exert inhibitory effects in heart and vasculature, thereby regulating their target gene and protein expression, via competitive endogenous RNA (ceRNA) mechanism. However, the exact roles and underlying mechanisms of circRNAs in hypertension and related cardiovascular diseases remain largely unknown. Methods and Results: High-throughput RNA sequencing (RNA-seq) was used to analyze the differentially expressed (DE) circRNAs in aortic vascular tissues of spontaneously hypertensive rats (SHR). Compared with the Wistar-Kyoto (WKY) rats, there were marked increases in the levels of systolic blood pressure, diastolic blood pressure and mean blood pressure in SHR under awake conditions via the tail-cuff methodology. Totally, compared with WKY rats, 485 DE circRNAs were found in aortic vascular tissues of SHR with 279 up-regulated circRNAs and 206 down-regulated circRNAs. Furthermore, circRNA-target microRNAs (miRNAs) and the target messenger RNAs (mRNAs) of miRNAs were predicted by the miRanda and Targetscan softwares, respectively. Additionally, real-time RT-PCR analysis verified that downregulation of rno_circRNA_0009197, and upregulation of rno_circRNA_0005818, rno_circRNA_0005304, rno_circRNA_0005506, and rno_circRNA_0009301 were observed in aorta of SHR when compared with that of WKY rats. Then, the potential ceRNA regulatory mechanism was constructed via integrating 5 validated circRNAs, 31 predicted miRNAs, and 266 target mRNAs. More importantly, three hub genes (NOTCH1, FOXO3, and STAT3) were recognized according to PPI network and three promising circRNA-miRNA-mRNA regulatory axes were found in hypertensive rat aorta, including rno_circRNA_0005818/miR-615/NOTCH1, rno_circRNA_0009197/ miR-509-5p/FOXO3, and rno_circRNA_0005818/miR-10b-5p/STAT3, respectively. Conclusions: Our results demonstrated for the first time that circRNAs are expressed aberrantly in aortic vascular tissues of hypertensive rats and may serve as a sponge linking with relevant miRNAs participating in pathogenesis of hypertension and related ischemic heart diseases via the circRNA-miRNA-mRNA ceRNAnetwork mechanism.

Knockdown of circFOXO3 ameliorates cigarette smoke-induced lung injury in mice

Background

Chronic obstructive pulmonary disease (COPD) remains a prevalent chronic airway inflammatory disease. Circular RNAs (circRNAs) are associated with inflammation regulation; therefore, we examined distinct effects of circRNA FOXO3 (circFOXO3) against pneumonic inflammatory processes in COPD.

Methods

We first quantified and localized circFOXO3 in mouse lung epithelial cell line MLE12 by quantitative reverse-transcription PCR and in situ hybridization. Next, circFOXO3 was suppressed by therapeutic administration of circFOXO3 knockdown lentivirus in mice exposed to air or cigarette smoke (CS) for 12 weeks, and several hallmarks of COPD were evaluated.

Results

We noticed that circFOXO3 is upregulated in CS-exposed lungs and cigarette smoke extract (CSE)-treated murine alveolar epithelial cells. Knockdown of circFOXO3 attenuated the release of CXCL1 and IL-6 as well as inflammatory processes in the lungs of CS-exposed mice. In addition, we identified miR-214-3p as a circFOXO3-targeted microRNA. MiR-214-3p overexpression exerted protective effects against pneumonic inflammation after CS exposure. Silencing of circFOXO3 downregulated IKK-β mRNA (miR-214-3p’s target), resulting in the dysfunction of the NF-κB signaling pathway and attenuation of CSE-induced inflammatory-cytokine expression.

Conclusions

Collectively, these findings reveal a crucial function of circFOXO3 in the pathological remodeling related to CS-induced inflammatory processes. Hence, circFOXO3 might be a good target for the treatment of inflammatory disorders similar to CS-induced lung inflammation.

Hypoxia Tolerant Species: The Wisdom of Nature Translated into Targets for Stroke Therapy

Human neurons rapidly die after ischemia and current therapies for stroke management are limited to restoration of blood flow to prevent further brain damage. Thrombolytics and mechanical thrombectomy are the available reperfusion treatments, but most of the patients remain untreated. Neuroprotective therapies focused on treating the pathogenic cascade of the disease have widely failed. However, many animal species demonstrate that neurons can survive the lack of oxygen for extended periods of time. Here, we reviewed the physiological and molecular pathways inherent to tolerant species that have been described to contribute to hypoxia tolerance. Among them, Foxo3 and Eif5A were reported to mediate anoxic survival in Drosophila and Caenorhabditis elegans, respectively, and those results were confirmed in experimental models of stroke. In humans however, the multiple mechanisms involved in brain cell death after a stroke causes translation difficulties to arise making necessary a timely and coordinated control of the pathological changes. We propose here that, if we were able to plagiarize such natural hypoxia tolerance through drugs combined in a pharmacological cocktail it would open new therapeutic opportunities for stroke and likely, for other hypoxic conditions.

Circle the Cardiac Remodeling With circRNAs

Cardiac remodeling occurs after the heart is exposed to stress, which is manifested by pathological processes such as cardiomyocyte hypertrophy and apoptosis, dendritic cells activation and cytokine secretion, proliferation and activation of fibroblasts, and finally leads to heart failure. Circular RNAs (circRNAs) are recently recognized as a specific type of non-coding RNAs that are expressed in different species, in different stages of development, and in different pathological conditions. Growing evidences have implicated that circRNAs play important regulatory roles in the pathogenesis of a variety of cardiovascular diseases. In this review, we summarize the biological origin, characteristics, functional classification of circRNAs and their regulatory functions in cardiomyocytes, endothelial cells, fibroblasts, immune cells, and exosomes in the pathogenesis of cardiac remodeling.