The circular RNA ACR attenuates myocardial ischemia/reperfusion injury by suppressing autophagy via modulation of the Pink1/ FAM65B pathway

Research Progress on the Interaction Between Autophagy and Energy Homeostasis in Cardiac Remodeling

Cardiac remodeling is a common pathological process in various heart diseases, such as cardiac hypertrophy, diabetes-associated cardiomyopathy and ischemic heart diseases. The inhibition of cardiac remodeling has been suggested to be a potential strategy for preventing heart failure. However, the mechanisms involved in cardiac remodeling are quite complicated. Recent studies have reported a close correlation between autophagy and energy homeostasis in cardiac remodeling associated with various heart diseases. In this review, we summarize the roles of autophagy and energy homeostasis in cardiac remodeling and discuss the relationship between these two processes in different conditions to identify potential targets and strategies for treating cardiac remodeling by regulating autophagy.

Autophagy in cardiovascular diseases: role of noncoding RNAs

Cardiovascular diseases (CVDs) remain the world's leading cause of death. Cardiomyocyte autophagy helps maintain normal metabolism and functioning of the heart. Importantly, mounting evidence has revealed that autophagy plays a dual role in CVD pathology. Under physiological conditions, moderate autophagy maintains cell metabolic balance by degrading and recycling damaged organelles and proteins, and it promotes myocardial survival, but excessive or insufficient autophagy is equally deleterious and contributes to disease progression. Noncoding RNAs (ncRNAs) are a class of RNAs transcribed from the genome, but most ncRNAs do not code for functional proteins. In recent years, increasingly, various ncRNAs have been identified, and they play important regulatory roles in the physiological and pathological processes of organisms, as well as in autophagy. Thus, determining whether ncRNA-regulated autophagy plays a protective role in CVDs or promotes their progression can help us to develop ncRNAs as therapeutic targets in autophagy-related CVDs. In this review, we briefly summarize the regulatory roles of several important ncRNAs, including microRNAs (miRNAs), long ncRNAs (lncRNAs), and circular RNAs (circRNAs), in the autophagy of various CVDs to provide a theoretical basis for the etiology and pathogenesis of CVDs and develop novel therapies to treat CVDs.

Dexmedetomidine inhibits inflammatory response and autophagy through the circLrp1b/miR-27a-3p/Dram2 pathway in a rat model of traumatic brain injury

Circular RNAs (circRNAs) have a regulatory function on inflammation and autophagy, of which rno-circRNA_010705 (circLrp1b) appears to be significantly up-regulated following traumatic brain injury (TBI). Dexmedetomidine (DEX) shows improvement effects in TBI by inhibiting NLRP3/caspase-1. However, whether circLrp1b plays critical roles in DEX-mediated TBI attenuation and the underlying mechanisms remain unclear. After TBI was established in rats by controlled cortical impact (CCI) to cause brain trauma, they received an intracerebroventricular injection of lentiviral vector, followed by intraperitoneal injection of DEX. Administration of DEX ameliorated autophagy in rats following TBI, accompanied by up-regulated circLrp1b and Dram2 and down-regulated miR-27a-3p. DEX promoted the effects of circLrp1b in attenuating TBI-induced neurologic impairment, autophagy, and inflammation, which was significantly reversed by inhibition of miR-27a-3p or Dram2 overexpression. Mechanistically, northern blot and luciferase reporter assays indicated that circLrp1b up-regulated Dram2 expression by functioning as a sponge for miR-27a-3p to promote autophagy involved in TBI, which was reversed by DEX treatment. Collectively, this study demonstrated that DEX inhibits inflammatory response and autophagy involved in TBI in vivo through inactivation of the circLrp1b/miR-27a-3p/Dram2 signaling pathway.

CircPDZD8 promotes gastric cancer progression by regulating CHD9 via sponging miR-197-5p

CircRNAs have been shown to be associated with gastric cancer tumorigenesis. But little was known about the role of circPDZD8 in gastric cancer. CircPDZD8 was up-regulated in gastric cancer tissues and cells, Kaplan-Meier survival analysis indicated that gastric patients had a poor overall survival when circPDZD8 levels were high. CircPDZD8 knockdown could hinder proliferation and migration of gastric cancer cells. MiR-197-5p, which was down-regulated in gastric cancer, was shown to be a target of circPDZD8 and was inversely correlated with circPDZD8 expression. CHD9, as a target gene of miR-197-5p, was negatively regulated by miR-197-5p and positively correlated with circPDZD8 expression. Importantly, circPDZD8 could up-regulate CHD9 expression by sponging miR-197-5p, and modulate cell progression by regulation of the miR-197-5p/CHD9 axis in gastric cancer. CircPDZD8 knockdown repressed the progression of gastric cancer cells by sponging miR-197-5p and down-regulating CHD9.

Circ_0010729 regulates hypoxia-induced cardiomyocyte injuries by activating TRAF5 via sponging miR-27a-3p

Ischemic cardiomyopathy is a severe cardiovascular disease with high mortality. Circular RNAs (circRNAs) are widely regulated in diverse human diseases, including Ischemic cardiomyopathy. This study aimed to investigate a novel functional mechanism of circRNA circ_0010729 in hypoxia-induced cardiomyocyte injuries. Human cardiomyocytes (AC16) were exposed to hypoxia to mimic ischemic cardiomyopathy in vitro. Cell viability, apoptosis/necrosis and glycolysis progress, were determined using 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay, flow cytometry assay and glycolysis stress test, respectively. Cell apoptosis was also assessed by the activity of cleaved caspase-3/7. The levels of glycolysis-related proteins and tumor necrosis factor receptor-associated factor 5 (TRAF5) were examined by western blot. The expression of circ_0010729 and miR-27a-3p was measured by real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR). The prediction about the targeted relationship was verified by dual-luciferase reporter assay, RNA immunoprecipitation (RIP) assay and RNA pull-down assay. As a result, hypoxia treatment inhibited cell viability, induced cell apoptosis and blocked glycolysis, however, these injuries were alleviated by circ_0010729 knockdown. MiR-27a-3p was targeted by circ_0010729, and miR-27a-3p inhibition reversed the role of circ_0010729 knockdown, leading to the deterioration of cell injuries. Further, TRAF5 was a target of miR-27a-3p, and circ_0010729 upregulated the expression of TRAF5 by sponging miR-27a-3p. MiR-27a-3p restoration enhanced cell viability, depleted cell apoptosis and promoted glycolysis of hypoxia-induced AC16 cells, while these effects were abolished by TRAF5 overexpression. In conclusion, circ_0010729 knockdown alleviated hypoxia-induced AC16 cell injuries by mediating the miR-27a-3p/TRAF5 axis.

A novel epigenetic regulation of circFoxp1 on Foxp1 in colon cancer cells

Foxp1 is a tumor suppressor in colon cancer. However, circFoxp1 derived from Foxp1 is an oncogene. In this study, we aim to investigate the role of circFoxp1 in colon cancer and the regulatory mechanism between circFoxp1 and Foxp1. 78 human colon tumor tissues and the matched paracancerous tissues were collected. Quantitative polymerase chain reaction, immunohistochemistry, quantitative methylation-specific PCR, chromatin immunoprecipitation assay, CCK-8 assay, and Tumor xenograft in nude mice were performed. The expression of circFoxp1 was increased and Foxp1 was reduced in colon cancer tissues, which were associated with a poor overall survival rate of the patients with colon cancer. CircFoxp1 recruited DNMT1 to the promoter of Foxp1, leading to promotor hypermethylation, thereby inhibiting Foxp1 transcription. Interfering circFoxp1 by siRNA in SW620 cells significantly inhibited cell viability, while knockdown Foxp1 expression partially restored SW620 cell viability. In addition, knockdown of circFoxp1 significantly sensitized colon cancer cells to Capecitabine in vitro and vivo through regulating Foxp1. We discovered a novel epigenetic pathway that circFoxp1 regulated Foxp1 in colon cancer cells. CircFoxp1 may regulate DNA methylation and demethylation to coordinate colon cancer cell proliferation and participate in chemotherapy drug responses. Therefore, circFoxp1 may be a potential therapeutic target for colon cancer.

UBAC2 promotes bladder cancer proliferation through BCRC-3/miRNA-182-5p/p27 axis

Emerging evidences have demonstrated that ubiquitin-associated domain-containing protein 2 (UBAC2) is closely related to the occurrence and development of malignant tumors. However, the functions and underlying molecular mechanisms of UBAC2 in bladder cancer (BC) development have not been defined. In this study, we found that both UBAC2 mRNA and protein levels were upregulated in BC tissues and cell lines, and knockdown of UBAC2 inhibited BC cells proliferation both in vitro and in vivo. Meanwhile, Kaplan-Meier survival plots of 406 BC cases from TCGA database showed that higher expression of UBAC2 in BC patients was associated with lower survival rate. Mechanistic studies revealed that knockdown of UBAC2 increased the expression of p27 by posttranscriptional regulation. Our previous study indicated that circular RNA BCRC-3 (BCRC-3) promoted the expression of p27 through interacting with miR-182-5p, and reversed miR-182-5p-induced inhibition of p27 3'UTR activity. In the present study, we found that UBAC2 could bind to BCRC-3, and subsequently affected the interaction of BCRC-3 with miR-182-5p to inhibit the expression of p27. Furthermore, knockdown of BCRC-3 partly reversed the upregulation of p27 expression induced by knockdown of UBAC2. Our findings highlight a novel mechanism of UBAC2 in regulating p27 through affecting the function of BCRC-3, and provide a research basis for the diagnostic and therapeutic application of BC.

Salidroside inhibits apoptosis and autophagy of cardiomyocyte by regulation of circular RNA hsa_circ_0000064 in cardiac ischemia-reperfusion injury

Salidroside (Sal), a natural extract of Rhodiola rosea, shows a latent effect on protecting cardiovascular system. Our study explored the effect of salidroside on ischemia-reperfusion (I/R) injury in rat heart. I/R was performed on Wistar rat hearts, and Sal pretreatment was performed in I/R rats. Cardiac marker enzyme, myocardial infarct size, malondialdehyde (MDA) and superoxide dismutase (SOD) content were then measured. Compared with the untreated group, Sal pretreatment observably ameliorated the cardiac function, decreased the myocardial infarct size, reduced the levels of cardiac lactate creatine kinase-MB (CK-MB) and dehydrogenase (LDH), and inhibited the anti-oxidative stress. In addition, Sal treatment also significantly inhibited autophagy and apoptosis, which could be partially reversed by Rapamycin (RAPA), an autophagic agonist. Furthermore, Sal treatment attenuated autophagy by up-regulating the expression of hsa_circ_0000064 (circ-0000064) and Rapamycin (RAPA) treatment abolished it. Our study showed that Sal protected the heart from I/R injury, which might berelated to the upregulation of circ-0000064 and the inhibition of autophagy.

Role of Circular RNAs in the Pathogenesis of Cardiovascular Disease

Circular RNAs (circRNAs) are single-strand covalently closed circular noncoding RNAs that are endogenous transcripts generated from linear precursor mRNA through a backsplicing mechanism. With the development of high-throughput sequencing technology, a number of circRNAs have been identified and proved to play key roles in various pathophysiological processes, such as metabolic diseases, cancers, and cardiovascular diseases. An increasing number of studies have shown that circRNAs are widely expressed in cardiac tissues and play important roles in the development of multiple cardiovascular diseases. Here, we review the current understanding of circRNA biogenesis and functions and the roles of circRNAs in cardiovascular diseases. We also highlight the molecular mechanisms underlying the role of circRNAs in the pathogenesis of cardiovascular diseases. A better understanding of the biological function of circRNAs in cardiovascular diseases will be helpful for the development of effective biomarkers for the diagnosis and treatment of these diseases.

Circular RNAs: New Epigenetic Signatures in Viral Infections

Covalent closed circular RNAs (circRNAs) can act as a bridge between non-coding RNAs and coding messenger RNAs. CircRNAs are generated by a back-splicing mechanism during post-transcriptional processing and are abundantly expressed in eukaryotic cells. CircRNAs can act via the modulation of RNA transcription and protein production, and by the sponging of microRNAs (miRNAs). CircRNAs are now thought to be involved in many different biological and pathological processes. Some studies have suggested that the expression of host circRNAs is dysregulated in several types of virus-infected cells, compared to control cells. It is highly likely that viruses can use these molecules for their own purposes. In addition, some viral genes are able to produce viral circRNAs (VcircRNA) by a back-splicing mechanism. However, the viral genes that encode VcircRNAs, and their functions, are poorly studied. In this review, we highlight some new findings about the interaction of host circRNAs and viral infection. Moreover, the potential of VcircRNAs derived from the virus itself, to act as biomarkers and therapeutic targets is summarized.

TFPIα alleviated vascular endothelial cell injury by inhibiting autophagy and the class III PI3K/Beclin-1 pathway

Endothelium (EC) dysfunction plays an important role in vascular diseases, such as arteriosclerosis and hypoxia/reoxygenation (H/R) injury. Tissue factor pathway inhibitor (TFPI) is the only physiological inhibitor of the TF/FVIIa complex in vivo. This experiment aimed to determine the effect of TFPIα on H/R-induced EC injury and the possible mechanisms. The MIC101 hypoxia system was used to establish an EC H/R injury model in vitro. Our results showed that 6 h after reoxygenation, the EC injury in H/R group was higher than that in the control group, whereas after adding TFPIα, the EC injury was alleviate than that in H/R group. The level of ROS was higher in the H/R group than in the control group, while it was apparently lower in the H/R+TFPIα group than in the H/R group. After H/R, the number of autophagosomes and the autophagic flux were significantly increased, whereas TFPIα could decrease the autophagy level after H/R. The expressions of LC3-II/LC3-I, Beclin-1 and PI3K were obviously higher after H/R and lower after adding TFPIα. In conclusion, autophagy contributes to EC injury during the H/R period. TFPIα could decrease autophagy in ECs, and the mechanism might be class III PI3K/Beclin-1 pathway regulation.

Circular RNA circMAGI3 accelerates the glycolysis of non-small cell lung cancer through miR-515-5p/HDGF

The emerging roles of circular RNAs (circRNAs) in non-small cell lung cancer (NSCLC) have been convincingly proved. However, there are still numerous unknown circRNAs needing exploration. Here, present research performed a circRNA microarray analysis for the expression profile and identified a novel circRNA (circMAGI3, hsa_circ_0110498). Clinically, circMAGI3 was significantly up-regulated in NSCLC tissue and cells, which was closely correlated with unfavorable outcome for NSCLC patients. Functionally, circMAGI3 promoted the glycolysis and proliferation of NSCLC cells. Mechanistically, circMAGI3 functioned as a sponge for miR-515-5p to relieve its target gene HDGF expression, thereby accelerating the glycolysis of NSCLC. Collectively, this research identified the oncogenic role of circMAGI3 in the tumorigenesis through miR-515-5p/HDGF axis, providing a vital theoretical basis for treatment of NSCLC.

The emerging landscape of circular RNAs in immunity: breakthroughs and challenges

Circular RNAs (circRNAs) are covalently linked RNAs that exhibit individual strand with a closed-loop framework compared with a conserving, steady and abundant linear counterpart. In recent years, as high-throughput sequencing advancement has been developing, functional circRNAs have been increasingly recognized, and more extensive analyses expounded their effect on different diseases. However, the study on the function of circRNAs in the immune system remains insufficient. This study discusses the basic principles of circRNAs regulation and the systems involved in physiology-related and pathology-related processes. The effect of circRNAs on immune regulation is elucidated. The ongoing development of circRNAs and basic immunology has multiplied their potential in treating diseases. Such perspective will summarize the status and effect of circRNAs on various immune cells in cancer, autoimmune diseases and infections. Moreover, this study will primarily expound the system of circRNAs in T lymphocytes, macrophages and other immune cells, which creates a novel perspective and lay a theoretical basis for treating diseases.

Epigenetic Clock: DNA Methylation in Aging

Aging, which is accompanied by decreased organ function and increased disease incidence, limits human lifespan and has attracted investigators for thousands of years. In recent decades, with the rapid development of biology, scientists have shown that epigenetic modifications, especially DNA methylation, are key regulators involved in this process. Regular fluctuations in global DNA methylation levels have been shown to accurately estimate biological age and disease prognosis. In this review, we discuss recent findings regarding the relationship between variations in DNA methylation level patterns and aging. In addition, we introduce the known mechanisms by which DNA methylation regulators affect aging and related diseases. As more studies uncover the mechanisms by which DNA methylation regulates aging, antiaging interventions and treatments for related diseases may be developed that enable human life extension.

Competing Endogenous RNAs, Non-Coding RNAs and Diseases: An Intertwined Story

MicroRNAs (miRNAs), a class of small non-coding RNA molecules, are responsible for RNA silencing and post-transcriptional regulation of gene expression. They can mediate a fine-tuned crosstalk among coding and non-coding RNA molecules sharing miRNA response elements (MREs). In a suitable environment, both coding and non-coding RNA molecules can be targeted by the same miRNAs and can indirectly regulate each other by competing for them. These RNAs, otherwise known as competing endogenous RNAs (ceRNAs), lead to an additional post-transcriptional regulatory layer, where non-coding RNAs can find new significance. The miRNA-mediated interplay among different types of RNA molecules has been observed in many different contexts. The analyses of ceRNA networks in cancer and other pathologies, as well as in other physiological conditions, provide new opportunities for interpreting omics data for the field of personalized medicine. The development of novel computational tools, providing putative predictions of ceRNA interactions, is a rapidly growing field of interest. In this review, I discuss and present the current knowledge of the ceRNA mechanism and its implications in a broad spectrum of different pathologies, such as cardiovascular or autoimmune diseases, cancers and neurodegenerative disorders.

Circular RNA (circRNA) CDYL Induces Myocardial Regeneration by ceRNA After Myocardial Infarction

Background

The aim of the study was to assess the effect of circRNA CDYL on myocardial angiogenesis after acute myocardial infarction (AMI).

Material/Methods

We compared changes in circRNA CDYL and myocardial angiogenesis in myocardial infarction tissue and normal heart tissue by establishing a myocardial infarction mouse model to clarify the relationship between circRNA CDYL and changes in myocardial infarction and myocardial angiogenesis. Secondly, we used the RegRNA website to predict downstream miRNA, and we performed gain-of-function and loss-of-function experiments.

Results

CircCDYL was downregulated in myocardial tissues and hypoxia myocardial cells, and overexpression and downregulation of circCDYL improved and aggravated, respectively, heart function after AMI. CircCDYL overexpression and downregulation can promote and inhibit, respectively, proliferation of cardiomyocytes in vitro. Finally, we found that circCDYL can sponge miR-4793-5p and regulate its expression, and then miR-4793-5p regulates APP expression.

Conclusions

CircCDYL can promote the proliferation of cardiomyocytes through the miR-4793-5p/APP pathway.

miRNA-182/Deptor/mTOR axis regulates autophagy to reduce intestinal ischaemia/reperfusion injury

It had been reported miR‐182 was down‐regulated after intestinal ischaemia/reperfusion (I/R) damage. However, its role and potential mechanisms are still unknown. This study was aimed to elucidate the function of miR‐182 in intestinal I/R injury and the underlying mechanisms. The model of intestinal injury was constructed in wild‐type and Deptor knockout (KO) mice. Haematoxylin‐eosin staining, Chiu's score and diamine oxidase were utilized to detect intestinal damage. RT‐qPCR assay was used to detected miR‐182 expression. Electronic microscopy was used to detect autophagosome. Western blot was applied to detect the expression of Deptor, S6/pS6, LC3‐II/LC3‐I and p62. Dual‐luciferase reporter assay was used to verify the relationship between miR‐182 and Deptor. The results showed miR‐182 was down‐regulated following intestinal I/R. Up‐regulation of miR‐182 reduced intestinal damage, autophagy, Deptor expression and enhanced mTOR activity following intestinal I/R. Moreover, suppression of autophagy reduced intestinal damage and inhibition of mTOR by rapamycin aggravated intestinal damage following intestinal I/R. Besides, damage of intestine was reduced and mTOR activity was enhanced in Deptor KO mice. In addition, Deptor was the target gene of miR‐182 and was indispensable for the protection of miR‐182 on intestine under I/R condition. Together, our research implicated up‐regulation of miR‐182 inhibited autophagy to alleviate intestinal I/R injury via mTOR by targeting Deptor.

Regulatory Roles of Circular RNAs in Coronary Artery Disease

Coronary artery disease (CAD) is a cardiac disorder caused by abnormal structure or function of the coronary artery, which leads to myocardial ischemia and hypoxia. CAD is a major cause of morbidity and mortality worldwide. Although there are currently effective drug therapies, there is a pressing need to find novel molecular therapeutic targets for CAD. The development of molecular biology technology has allowed the recognition of circular RNAs (circRNAs) as a novel class of noncoding RNAs that regulate gene function. The pathological roles of circRNAs in CAD have not, however, been comprehensively summarized. In this article, we review published research linking circRNAs to CAD and summarize the regulatory roles of circRNAs in the pathogenesis of coronary atherosclerosis, myocardial infarction, ischemia/reperfusion injury, and ischemic heart failure.

The Role of Non-coding RNAs in Ischemic Myocardial Reperfusion Injury

MicroRNAs (miRNA) are non-coding RNAs that regulate gene expression in up to 90% of the human genome through interactions with messenger RNA (mRNA). The expression of miRNAs varies and changes in diseased and healthy states, including all stages of myocardial ischemia-reperfusion and subsequent ischemia-reperfusion injury (IRI). These changes in expression make miRNAs an attractive potential therapeutic target. Herein, we review the differences in miRNA expression prior to ischemia (including remote ischemic conditioning and ischemic pre-conditioning), the changes during ischemia-reperfusion, and the changes in miRNA expression after IRI, with an emphasis on inflammatory and fibrotic pathways. Additionally, we review the effects of manipulating the levels of certain miRNAs on changes in infarct size, inflammation, remodeling, angiogenesis, and cardiac function after either ischemia-reperfusion or permanent coronary ligation. Levels of target miRNA can be increased using molecular mimics ("agomirs"), or can be decreased by using "antagomirs" which are antisense molecules that act to bind and thus inactivate the target miRNA sequence. Other non-coding RNAs, including long non-coding RNAs and circular RNAs, also regulate gene expression and have a role in the regulation of IRI pathways. We review the mechanisms and downstream effects of the miRNAs that have been studied as therapy in both permanent coronary ligation and ischemia-reperfusion models.

The Circular RNA circSKA3 Binds Integrin β1 to Induce Invadopodium Formation Enhancing Breast Cancer Invasion

Metastatic cancer cells invade surrounding tissues by forming dynamic actin-based invadopodia, which degrade the surrounding extracellular matrix and allow cancer cell invasion. Regulatory RNAs, including circular RNA, have been implicated in this process. By microarray, we found that the circular RNA circSKA3 was highly expressed in breast cancer cells and human breast cancer tissues. We further found that the invasive capacity of breast cancer cells was positively correlated with circSKA3 expression, through the formation of invadopodia. Mechanistically, we identified Tks5 and integrin β1 as circSKA3 binding partners in these tumor-derived invadopodia. Ectopic circSKA3 expression conferred increased tumor invasiveness in vitro and in vivo. We further identified the RNA-protein binding sites between circSKA3, Tks5 and integrin β1. In tumor formation assays, we found that circSKA3 expression promoted tumor progression and invadopodium formation. Mutation of the circSKA3 binding sites or transfection with blocking oligos abrogated the observed effects. Thus, we provide evidence that the circular RNA circSKA3 promotes tumor progression by complexing with Tks5 and integrin β1, inducing invadopodium formation.

A Roadmap for Fixing the Heart: RNA Regulatory Networks in Cardiac Disease

With the continuous development of RNA biology and massive genome-wide transcriptome analysis, more and more RNA molecules and their functions have been explored in the last decade. Increasing evidence has demonstrated that RNA-related regulatory networks play an important role in a variety of human diseases, including cardiovascular diseases. In this review, we focus on RNA regulatory networks in heart disease, most of which are devastating conditions with no known cure. We systemically summarize recent discoveries of important new components of RNA regulatory networks, including microRNAs, long non-coding RNAs, and circular RNAs, as well as multiple regulators that affect the activity of these networks in cardiac physiology and pathology. In addition, this review covers emerging micropeptides, which represent short open reading frames (sORFs) in long non-coding RNA transcripts that may modulate cardiac physiology. Based on the current knowledge of RNA regulatory networks, we think that ongoing discoveries will not only provide us a better understanding of the molecular mechanisms that underlie heart disease, but will also identify novel biomarkers and therapeutic targets for the diagnosis and treatment of cardiac disease.

Insights into the role of circular RNA in macrophage activation and fibrosis disease

Circular RNAs (circRNAs) are single-stranded RNAs which form a covalent bond structure without a 5' cap or a 3' polyadenylated tail, which is deleted through back-splicing. The expression of circRNAs in highly divergent eukaryotes is abundant. With the development of high-throughput sequencing, the mysteries of circRNAs have gradually been revealed. Increased attention has been paid to determining their biological functions and whether their changed expression profiles are linked to disease progression. Functionally, circRNAs have been shown to act as miRNA sponges or nuclear transcription factor regulators, and to play a part in RNA splicing. Various types of circRNAs have been discovered to be differentially expressed under steady physiological and pathological conditions. Recently, several studies have focused on the roles of circRNAs in macrophages on inflammatory stimulation. In this study, we review the current advances in the understanding of circRNAs in macrophages under various pathological conditions, in particular during organ fibrosis, and summarize possible directions for future circRNA applications.

Autophagy-associated circRNA circCDYL augments autophagy and promotes breast cancer progression

BACKGROUND

Although both circular RNAs (circRNAs) and autophagy are associated with the function of breast cancer (BC), whether circRNAs regulate BC progression via autophagy remains unknown. In this study, we aim to explore the regulatory mechanisms and the clinical significance of autophagy-associated circRNAs in BC.

METHODS

Autophagy associated circRNAs were screened by circRNAs deep sequencing and validated by qRT-PCR in BC tissues with high- and low- autophagic level. The biological function of autophagy associated circRNAs were assessed by plate colony formation, cell viability, transwells, flow cytometry and orthotopic animal models. For mechanistic study, RNA immunoprecipitation, circRNAs pull-down, Dual luciferase report assay, Western Blot, Immunofluorescence and Immunohistochemical staining were performed.

RESULTS

An autophagy associated circRNA circCDYL was elevated by 3.2 folds in BC tissues as compared with the adjacent non-cancerous tissues, and circCDYL promoted autophagic level in BC cells via the miR-1275-ATG7/ULK1 axis; Moreover, circCDYL enhanced the malignant progression of BC cells in vitro and in vivo. Clinically, increased circCDYL in the tumor tissues and serum of BC patients was associated with higher tumor burden, shorter survival and poorer clinical response to therapy.

CONCLUSIONS

circCDYL promotes BC progression via the miR-1275-ATG7/ULK1-autophagic axis and circCDYL could act as a potential prognostic and predictive molecule for breast cancer patients.

Potential diagnostic and therapeutic value of circular RNAs in cardiovascular diseases

Cardiovascular diseases (CVDs) have imposed a massive health and financial burden worldwide with high mortality and morbidity. However, the diagnostic value of current biomarkers might be impaired by a wide variety of noncardiac causes. Moreover, cardiovascular outcomes, survival, and prognosis of patients with CVDs remain poor despite advances in treatment. Therefore, novel diagnostic and therapeutic strategies are urgently required for timely identification of possible heart diseases in the early stage, which might effectively contribute to reducing the CVDs-caused morbidity and mortality. Circular RNA (circRNA) was initially identified as aberrant byproducts or abnormally spliced transcripts. However, with advances in bioinformatics and high-throughput sequencing technology, circRNAs has become an essential topic on a wide range of biological functions and emerged as novel players in diagnostic and therapeutic strategies for CVDs. In this article, we briefly introduce the biogenesis and functions of circRNAs. Moreover, we describe the roles of circRNAs in multiple CVDs, including atherosclerosis, coronary artery disease, myocardial infarction, as well as cardiomyopathy. In addition, we provide an overview on the current challenges and directions for further application.

The Long Noncoding RNA Hotair Regulates Oxidative Stress and Cardiac Myocyte Apoptosis during Ischemia-Reperfusion Injury

Oxidative stress and subsequent cardiac myocyte apoptosis play central roles in the initiation and progression of myocardial ischemia-reperfusion (I/R) injury. Homeobox transcript antisense intergenic RNA (Hotair) was previously implicated in various heart diseases, yet its role in myocardial I/R injury has not been clearly demonstrated. Mice with cardiac-restricted knockdown or overexpression of Hotair were exposed to I/R surgery. H9c2 cells were cultured and subjected to hypoxia/reoxygenation (H/R) stimulation to further verify the role and underlying mechanisms of Hotair in vitro. Histological examination, molecular detection, and functional parameters were determined in vivo and in vitro. In response to I/R or H/R treatment, Hotair expression was increased in a bromodomain-containing protein 4-dependent manner. Cardiac-restricted knockdown of Hotair exacerbated, whereas Hotair overexpression prevented I/R-induced oxidative stress, cardiac myocyte apoptosis, and cardiac dysfunction. Mechanistically, we observed that Hotair exerted its beneficial effects via activating AMP-activated protein kinase alpha (AMPKα). Further detection revealed that Hotair activated AMPKα through regulating the enhancer of zeste homolog 2/microRNA-451/calcium-binding protein 39 (EZH2/miR-451/Cab39) axis. We provide the evidence that endogenous lncRNA Hotair is an essential negative regulator for oxidative stress and cardiac myocyte apoptosis in myocardial I/R injury, which is dependent on AMPKα activation via the EZH2/miR-451/Cab39 axis.

Revealing new landscape of cardiovascular disease through circular RNA-miRNA-mRNA axis

Non-coding RNA (ncRNA) is a kind of RNA, produced by genomic transcription and does not encode protein, but can regulate the function of genes, thus widely regulating pathological and physiological processes. The dynamic balance of the reticular structure between them is needed to regulate the homeostasis, the abnormal regulation of one of them may lead to the occurrence of the disease. CircRNA is mainly involved in the evolution of CVD through sponge-like regulation of miRNAs, subsequently regulating miRNAs and their targets, mRNA functions. The role of circRNA-miRNA-mRNA axis in pathogenesis of cardiovascular diseases has been recently reported and highlighted. In this review, the emerging roles of circRNA-miRNA-mRNA axis in cardiovascular pathophysiology and regulation were discussed, with a novel focus on cardioprotective network activities of the circRNA.

Urolithin B, a gut microbiota metabolite, protects against myocardial ischemia/reperfusion injury via p62/Keap1/Nrf2 signaling pathway

Ischemia/reperfusion (IR) induces additional damage during the restoration of blood flow to ischemic myocardium. Urolithin B (UB) is one of the gut metabolites of ellagitannins, a class of antioxidant polyphenols, which was found to be protective against oxidative stress in multiple organs. However, the role of UB in cardiovascular disease remains elusive. Adult Sprague Dawley rats were subjected to left anterior descending artery ligation for 30 min followed by 120 min of reperfusion, with or without UB treatment. In vitro, the H9c2 cardiomyocytes were subjected to hypoxia (94 %N₂/5 %CO₂/1 %O₂) for 3 h, followed by reoxygenation (74 %N₂/5 %CO₂/21 %O₂) for 3 h (HR). UB was found to decrease myocardial infarct size and attenuate the cardiac dysfunction in the rats after IR, and protect against HR injury in H9c2 cardiomyocytes. Mechanistically, UB inhibited autophagy by activating Akt/mTOR/ULK1 pathway and protected against oxidative stress and caspase 3-dependent cell apoptosis. In particular, UB induced accumulation of p62 and its interaction with Keap1, which promoted Nrf2 nuclear translocation during HR insult. Of note, the protection of UB against superoxide production and apoptotic cell death was compromised with Nrf2 gene silencing. Taken together, our findings suggested that UB protected against myocardial IR injury at least partially via the p62/Keap1/Nrf2 signaling pathway, which highlights the potential of UB as a novel therapy for ischemic heart disease.

Identification and characterization of circular RNAs in atrial appendage of patients with atrial fibrillation

Circular RNAs (circRNAs) have emerged as a novel type of non-coding RNA (ncRNA) of interest in gene regulation, especially for its vital function underlying many diseases. Atrial fibrillation is the most common sustained arrythmia. However, the expression spectrum and function of circRNAs in atrial appendage of patients with atrial fibrillation (AF) has seldomly been investigated. Human atrial appendage tissues were acquired during cardiac surgery, which were divided into the AF group and the Sinus rhythm (SR) group. The expression characterization of circRNAs of two groups was revealed by high-throughput sequencing. The dysregulated circRNAs were identified and analyzed by bioinformatics methods, and further validated by realtime PCR. A total 18109 circRNAs in human atrial appendage tissues were targeted. Among them, 147 differentially expressed circRNAs (102 up-regulated and 45 down-regulated) were found between AF group and SR group. Gene ontology (GO) and KEGG pathway analysis indicated that many mRNAs transcribed from the host genes of altered circRNAs were implicated in regulation of sequence-specific DNA binding transcription factor activity, as well as nicotinate and nicotinamide metabolism pathways. Analysis of the association between differently expressed circRNA and miRNA were explored, which revealed an ample interaction. Our study firstly revealed the expression spectrum of circRNAs in both left and right atrial appendage of patients with or without AF. Differentially expressed circRNAs in the atrial appendage were also identified, analyzed and validated. The results of this study may provide novel biomarkers and potential therapeutic targets for AF.

Circular RNA circDENND2A protects H9c2 cells from oxygen glucose deprivation-induced apoptosis through sponging microRNA-34a

Background/Aims: Myocardial ischemia (MI) is a serious threat to human health. Circular RNAs (circRNAs) play an important role in many diseases including MI. The effect and mechanism of circDENND2A in MI have not been studied.Methods: We used oxygen glucose deprivation (OGD) treatment to simulate MI in vitro. We detected circDENND2A and microRNA (miR)-34a levels by RT-qPCR. The transfection process used INTERFER and jetPRIME. Cell growth indexes including viability, apoptosis, and migration were detected by CCK8, flow cytometry, and transwell assays, respectively. In addition, the Bax, Cleaved-Caspase-3, matrix metalloproteinase (MMP)-2, MMP-9 and pathway-related protein levels were tested by Western blot.Results: OGD upregulated circDENND2A expression in H9c2 cells. Overexpression of circDENND2A enhanced cell viability and migration but declined apoptosis under OGD. Silenced circDENND 2A played the opposite effects. circDENND2A negatively regulated miR-34a. miR-34a overexpression weakened the protective effects of circDENND2A in OGD-injury. Moreover, we considered circDENND2A and miR-34a may work via β-catenin and Ras/Raf/MEK/ERK pathways.Conclusion: circDENND2A overexpression enhanced OGD-inhibited cell viability and migration but declined OGD-promoted apoptosis by downregulating miR-34a and via β-catenin and Ras/Raf/MEK/ERK pathways.

Non-coding RNAs regulate autophagy process via influencing the expression of associated protein

Autophagy is a tightly-regulated multi-step process involving the lysosomal degradation of proteins and cytoplasmic organelles. Central to this process is the formation of the autophagosome, a double membrane-bound vesicle, which is fuse with lysosomes or endosomes, and then deliver its cytoplasmic cargo to the lysosomes. Here, we summarize the recent process of autophagy, focusing on protein molecules, their complexes, and its essential roles of autophagy in various phases. Emerging evidence has revealed that miRNAs, lncRNAs, and circRNAs play an indispensable role in autophagy regulation by modulating targeting gene expression. This review we will summarize the main features of ncRNAs and point to gaps in our current knowledge of the connection between ncRNAs and autophagy, as well as their potential utilization in various disease phenotypes. Also, we highlight recent advances in ncRNAs and autophagy-associated protein interaction and how they regulate the autophagy process.

EIF4A3-Induced circ-BNIP3 Aggravated Hypoxia-Induced Injury of H9c2 Cells by Targeting miR-27a-3p/BNIP3

Acute myocardial infarction (AMI) results from long-term diminished blood supply diminishment (ischemia) to the heart, and the main reason for ischemia is hypoxia. BCL2 interaction protein 3 (BNIP3) can be upregulated by hypoxia and participates in the mediation of hypoxia-activated apoptosis in cardiac myocyte death. The purpose of this study was to interrogate the mechanism of BNIP3 in hypoxia-activated cardiac myocyte injury. Cell viability and apoptosis were evaluated by Cell counting kit 8 (CCK-8), 5-ethynyl-2’-deoxyuridine (EdU), TdT-mediated dUTP Nick-End Labeling (TUNEL), and caspase-3 activity assays. Molecular interactions were assessed by RNA immunoprecipitation (RIP) and pull-down assays. Gene levels were assessed via quantitative real-time PCR and western blot. BNIP3 expression was upregulated by hypoxia in H9c2 cells. We found that circ-BNIP3 (hsa_circ_0005972), whose annotated gene was BNIP3, was induced by hypoxia and positively regulated BNIP3 expression. Knockdown of BNIP3 or circ-BNIP3 reversed the effect of hypoxia in attenuating H9c2 cell viability and inducing apoptosis. circ-BNIP3 sponged miRNA-27a-3p (miR-27a-3p) to upregulate BNIP3 expression. Moreover, eukaryotic translation initiation factor 4A3 (EIF4A3) bound with the upstream region of the circ-BNIP3 mRNA transcript and induced circ-BNIP3 expression in H9c2 cells. EIF4A3-induced circ-BNIP3 aggravated hypoxia-caused injury of H9c2 cells through targeting miR-27a-3p/BNIP3 pathway, indicating circ-BNIP3 as a new target for relieving hypoxia-induced injury of cardiac myocytes.

Guidance of circular RNAs to proteins' behavior as binding partners

Circular RNAs (circRNAs) are single-stranded and covalently closed back-splicing products of pre-mRNAs. They can be derived from exons, introns, or exons with intron retained between exons of transcripts, as well as antisense transcripts. CircRNAs have been reported to function as microRNA sponges, regulate gene transcription mediated by RNA polymerase II, and modulate the splicing or stability of mRNA. However, emerging studies demonstrate that they affect the behavior of proteins via direct interactions with them. Here, we summarize that by binding directly with proteins; circRNAs can facilitate their nuclear or cytoplasmic localizations, regulate their functions or stability, promote or inhibit the interactions between them, or influence the interactions between them and DNA. Furthermore, these circRNA-binding proteins contain transcription factors, RNA processing proteins, proteases, and some other RNA-binding proteins. As a consequence, circRNAs are involved in the regulation of multiple physiological or pathological processes, including tumorigenesis, atherosclerosis, wound repair, cardiac senescence, myocardial ischemia/reperfusion injury, and so forth. Nonetheless, it is worthwhile to further explore more types of proteins that interact with circRNAs, which would be helpful in revealing other unknown biological functions of circRNAs that guide the variation in behavior of cellular proteins.

Genome-wide differential expression profiling of lncRNAs and mRNAs associated with early diabetic cardiomyopathy

Diabetic cardiomyopathy is one of the main causes of heart failure and death in patients with diabetes. There are no effective approaches to preventing its development in the clinic. Long noncoding RNAs (lncRNA) are increasingly recognized as important molecular players in cardiovascular disease. Herein we investigated the profiling of cardiac lncRNA and mRNA expression in type 2 diabetic db/db mice with and without early diabetic cardiomyopathy. We found that db/db mice developed cardiac hypertrophy with normal cardiac function at 6 weeks of age but with a decreased diastolic function at 20 weeks of age. LncRNA and mRNA transcripts were remarkably different in 20-week-old db/db mouse hearts compared with both nondiabetic and diabetic controls. Overall 1479 lncRNA transcripts and 1109 mRNA transcripts were aberrantly expressed in 6- and 20-week-old db/db hearts compared with nondiabetic controls. The lncRNA-mRNA co-expression network analysis revealed that 5 deregulated lncRNAs having maximum connections with differentially expressed mRNAs were BC038927, G730013B05Rik, 2700054A10Rik, AK089884, and Daw1. Bioinformatics analysis revealed that these 5 lncRNAs are closely associated with membrane depolarization, action potential conduction, contraction of cardiac myocytes, and actin filament-based movement of cardiac cells. This study profiles differently expressed lncRNAs in type 2 mice with and without early diabetic cardiomyopathy and identifies BC038927, G730013B05Rik, 2700054A10Rik, AK089884, and Daw1 as the core lncRNA with high significance in diabetic cardiomyopathy.

Interaction among inflammasome, autophagy and non-coding RNAs: new horizons for drug

Autophagy and inflammasomes are shown to interact in various situations including infectious disease, cancer, diabetes and neurodegeneration. Since multiple layers of molecular regulators contribute to the interplay between autophagy and inflammasome activation, the detail of such interplay remains largely unknown. Non-coding RNAs (ncRNAs), which have been implicated in regulating an expanding list of cellular processes including immune defense against pathogens and inflammatory response in cancer and metabolic diseases, may join in the crosstalk between inflammasomes and autophagy in physiological or disease conditions. In this review, we summarize the latest research on the interlink among ncRNAs, inflammasomes and autophagy and discuss the emerging role of these three in multiple signaling transduction pathways involved in clinical conditions. By analyzing these intriguing interconnections, we hope to unveil the mechanism inter-regulating these multiple processes and ultimately discover potential drug targets for some refractory diseases.

Circular RNAs as potential biomarkers and therapeutics for cardiovascular disease

Circular RNAs (circRNAs) are genetic regulators that were earlier considered as "junk". In contrast to linear RNAs, they have covalently linked ends with no polyadenylated tails. CircRNAs can act as RNA-binding proteins, sequestering agents, transcriptional regulators, as well as microRNA sponges. In addition, it is reported that some selected circRNAs are transformed into functional proteins. These RNA molecules always circularize through covalent bonds, and their presence has been demonstrated across species. They are usually abundant and stable as well as evolutionarily conserved in tissues (liver, lung, stomach), saliva, exosomes, and blood. Therefore, they have been proposed as the "next big thing" in molecular biomarkers for several diseases, particularly in cancer. Recently, circRNAs have been investigated in cardiovascular diseases (CVD) and reported to play important roles in heart failure, coronary artery disease, and myocardial infarction. Here, we review the recent literature and discuss the impact and the diagnostic and prognostic values of circRNAs in CVD.

Biogenesis and Function of Circular RNAs in Health and in Disease

Circular RNAs (circRNAs) are a class of non-coding RNA that were previously thought to be insignificant byproducts of splicing errors. However, recent advances in RNA sequencing confirmed the presence of circRNAs in multiple cell lines and across different species suggesting a functional role of this RNA species. CircRNAs arise from back-splicing events resulting in a circular RNA that is stable, specific and conserved. They can be generated from exons, exon-introns, or introns. CircRNAs have multifaceted functions. They are likely part of the competing endogenous RNA class. They can regulate gene expression by sponging microRNAs, binding proteins or they can be translated into a protein themselves. CircRNAs have been associated with health and disease, some with disease protective effects, some with disease promoting functions. The widespread expression and disease regulatory mechanisms endow circRNAs to be used as functional biomarkers and therapeutic targets for a variety of different disorders. In this concise article we provide an overview of the association of circRNAs with various diseases including cancer, cardiovascular and kidney disease as well as cellular senescence. We conclude with an assessment of the current status and future outlook of this new field of research that carries immense potential with respect to diagnostic and therapeutic approaches of a variety of diseases.

Follistatin-Like 1 Attenuates Ischemia/Reperfusion Injury in Cardiomyocytes via Regulation of Autophagy

Background

The cardioprotective effect of FSTL1 has been extensively studied in recent years, but its role in myocardial ischemia/reperfusion injury (IRI) is unclear. In this study, we investigated the effect of FSTL1 pretreatment on myocardial IRI as well as the possible involvement of autophagic pathways in its effects.

Methods

The effects of FSTL1 on the viability and apoptosis of rat cardiomyocytes were investigated after exposure of cardiomyocytes to hypoxia/ischemia by using the CCK-8 assay and Annexin V/PI staining. Further, western blot analysis was used to detect the effects of FSTL1 pretreatment on autophagy-associated proteins, and confocal microscopy was used to observe autophagic flux. To confirm the role of autophagy, the cells were treated with the autophagy promoter rapamycin or the autophagy inhibitor 3-methyladenine, and cell viability and apoptosis during IRI were observed. These effects were also observed after treatment with rapamycin or 3-methyladenine followed by FSTL1 administration and IRI.

Results

FSTL1 pretreatment significantly increased viability and reduced apoptosis in cardiomyocytes exposed to hypoxia/ischemia conditions. Further, FSTL1 pretreatment affected the levels of the autophagy-related proteins and enhanced autophagic flux during IRI. In addition, cell viability was enhanced and apoptosis was decreased by rapamycin treatment, while these effects were reversed by 3-MA treatment. However, when the myocardial cells were pretreated with rapamycin or 3-methyladenine, there was no significant change in their viability or apoptosis with FSTL1 treatment during IRI.

Conclusions

FSTL1 plays a protective role in myocardial IRI by regulating autophagy.

Comprehensive analysis of circular RNAs in pathological states: biogenesis, cellular regulation, and therapeutic relevance

Circular RNAs (circRNAs) are members of the non-coding transcriptome; however, some of them are translated into proteins. These transcripts have important roles in both physiological and pathological mechanisms due to their ability to directly influence cellular signaling pathways. Specifically, circRNAs are regulators of transcription, translation, protein interaction, and signal transduction. An increased knowledge within their area is observed over the last few years, concomitant with the development of next-generation sequencing techniques. circRNAs are mostly tissue and disease specific with the ability of specifically changing the biological behavior of cells. The altered expression profile is currently investigated as novel minimally invasive diagnosis/prognosis tool and also therapeutic target in human disease. The diagnosis approach is based on their level modification within pathological states, especially cancer, where circRNAs' therapies are intensively explored in anti-aging strategies, diabetes, cardiovascular diseases, and malignant pathologies, and are relying on the restoration of homeostatic profiles.

Circular RNA PVT1 promotes metastasis via miR-145 sponging in CRC

Circular RNAs (circRNAs) are a class of covalently closed non-coding RNAs and are widely involved in various cancers including colorectal cancer (CRC). Circular RNA PVT1 (circPVT1) was reported in several malignancies but the role it plays in CRC remains unclear. In our current research, we focused on the expression and function of circPVT1) works in CRC. We found that circPVT1 was upregulated in CRC. Also, we illustrated that the upregulated circPVT1 was closely correlated with poor prognosis and bad clinicopathological features of patients with CRC. Through a loss of function experiment, we showed that a downregulation of circPVT1 suppressed CRC cells metastasis. Through online prediction, we found that circPVT1 had a microRNA response element (MRE) for miR-145. Additionally, we demonstrated that miR-145 was downregulated in CRC. Even further, we showed that miR-145 was involved in circPVT1 mediated facilitation of CRC metastasis. In a further mechanical study, we demonstrated that circPVT1 could target miR-145. Lastly, we revealed that the metastasis-promoting role of circPVT1 in CRC was partially achieved via miR-145 sponging. In brief, the findings of the present study illustrated that circPVT1, working as an oncogene, promotes metastasis via miR-145 sponging in CRC. CircPVT1/miR-145 axial might be a novel point in targeting treatment of CRC.

Novel Aspects of Cardiac Ischemia and Reperfusion Injury Mechanisms

Introduction.The present article, in which a contemporary analysis of the literature on the pathophysiology of ischemic and reperfusion injury (IRI) of the myocardium is presented, focuses on the possible role played by of the calpain system and oxidative stress. Several process development options were proposed, including cytosolic and mitochondrial Ca2+ overload, reactive oxygen stress release, acute inflammatory response and metabolic degradation. The combined effect of all of the above factors produces irreversible ischemic and reperfused damage of cardiomyocytes.Materials and methods.The role of the calpain system in the creation of myocardial IRI was experimentally investigated. It was found that active calpain substrates play a significant role in the processes of cell cycle, apoptosis and differentiation, adversely affecting cardiomyocyte functionality. The calpain system is part of an integrated proteolytic system that is critical to the relationship between the structure and function of the cardiac sarcomere. Uncontrolled activation of calpain is indicated in the pathophysiology of many cardiovascular disorders. As shown by research, inhibitor calpain reduces the size of the zone of infarction following ischemia reperfusion and thus lessens the risk of “stunning” the myocardium. As is known, a consequence of IRI is acute myocardial infarction (AMI), which is a central factor in cardiovascular disease (CVD) and is one of the primary causes of mortality. Understanding the exact pathophysiological mechanisms remains an urgent problem for clinical physicians. To date, the mechanisms of IRI are not fully known, which creates certain difficulties in further treatment and prevention tactics. In addition, myocardial IRI is also an important issue for pathoanatomical service, since sudden coronary death can occur despite timely reperfusion therapy following AMI.Conclusion.The development of strategies for creating conditions that limit the degree of damage to myocardial tissues significantly increases the ability of the heart to withstand ischemic damage.