Table 4.

circRNAs associated with myocardial infarction or ischaemia reperfusion injury

CircRNA/miRNA interaction
CircRNA	miRNA target	Protein target	Findings of the study	Methods	Reference
CDR1as	miR-7a	Poly (ADP-ribose) polymerase (PRP) and SP/KLF family of transcription factors (SP1)	Overexpression of CDR1 in vivo promoted apoptosis and increased cardiac infarct size; overexpression of miR-7a had the opposite effect	RT-qPCR from mouse cardiomyocytes. No direct evidence of circRNA/miRNA interaction. CDR1as induced apoptosis could be reverse by miR-7 overexpression	Geng et al 2016 [61]
Mitchondrial fission and apoptosis-related circRNA (MFACR)	miR-652-3p	MTP18	Regulated mitochondrial fission and apoptosis in the heart	Mouse cardiomyocytes. AGO2 immunoprecipitation	Wang et al 2017 [122]
Ncx1	miR-133a-3p	Pro-apoptotic gene cell death-inducing protein (CDIP1)	Increased in response to reactive oxygen species (ROS) and promotes cardiomyocyte apoptosis	H9c2 cells and neonatal rat cardiomyocytes. Biotinylated pulldown of miRNA-133 and circMFACR. AGO2 immunoprecipitation	Li et al 2018 [123]
CircHIPK3	circHIPK3 by binding to miRNA-124-3p	Overexpression upregulated pro-apoptotic Bax, and downregulated anti-apoptotic Bcl-2	Inhibited proliferative ability and induced apoptosis of cardiomyocytes after myocardial IR injury	Mouse cardiomyocytes. Dual-luciferase reporter gene assay	Bai et al 2019 [134]
Ttc3	miR-15b	ADP ribosylation factor like 2 (Arl2)	Played a cardioprotective role after myocardial infarction. Overexpression counteracted hypoxia-induced ATP depletion and apoptotic death.	Rat cardiomyocytes and cardiac fibroblasts. Dual-luciferase reporter assay	Cai et al 2019 [126]
Circ_0010729	miR-145-5p	mTOR and MEK/ERK pathways	Silencing circular RNA circ_0010729 protected human cardiomyocytes from oxygen-glucose deprivation-induced injury	4 h oxygen-glucose-deprivation (OGD) human cardiomyocytes. No direct evidence for circRNA/miRNA interaction. Expression studies after overexpression of one against the other.	Jin et al 2019 [117]
Circ_0010729	miR-27a-3p	Tumour necrosis factor receptor-associated factor 5 (TRAF5)	Circ_0010729 knockdown alleviated cell viability inhibition and cell apoptosis under hypoxic conditions. MiR-27a-3p was targeted by circ_0010729. MiR-27a-3p restoration enhanced cell viability, depleted cell apoptosis and promoted glycolysis of hypoxia-induced cells, while these effects were abolished by TRAF5 overexpression	miR-27a-3p/TRAF5 relationship was verified by dual-luciferase reporter assay, RNA immunoprecipitation (RIP) assay and RNA pull-down assay	Lei et al 2020 [120]
Circ_0010729	miR-370-3p	Tumour necrosis factor receptor-associated factor 5 (TRAF5)	Circ_0010729 knockdown protected cardiomyocytes against hypoxic dysfunction. MiR-370-3p inhibition attenuated the protective effects of circ_0010729 knockdown on hypoxia-modulated cardiomyocyte dysfunction.	miR-370-3p/TRAF6 relationship was verified by dual-luciferase reporter assay, RNA immunoprecipitation (RIP) assay and RNA pull-down assay	Zhang et al 2020 [121]
CircMACF1	miR-500b-5p	Epithelial membrane protein 1 (EMP1)	Attenuated Acute Myocardial Infarction	Mouse cardiomyocytes. Dual-luciferase reporter gene assay	Zhao et al 2020 [127]
Circular RNA_101237	let‑7a‑5p	Insulin-like-growth factor 2 mRNA-binding protein 3 (IGF2BP3)	Mediated anoxia/reoxygenation injury	Mouse cardiomyocytes biotinylated miRNA pull-down. AGO2 immunoprecipitation	Gan et al 2020 [124]
Circ_LAS1L	miR-125b	Secreted frizzled-related protein 5 (SFRP5)	Down-regulated in acute myocardial infarction (AMI). Regulates cardiac fibroblast activation, growth, and migration and apoptosis	Mouse cardiomyocytes. Luciferase reporter gene assay. Biotinylated RNA pull down. AGO2 immunoprecipitation	Sun et al 2020 [125]
CircDLPAG4/HECTD1	miR-143	HECT Domain E3 Ubiquitin Protein Ligase 1 (HECTD1)	CircDLPAG4/HECTD1 played a vital role in apoptosis and cell migration in endothelial cells through ER stress in response to ischaemia/reperfusion injury	Primary Human Umbilical Vein Endothelial Cells (HUVEC)/mice. No direct evidence for circRNA/miRNA interaction. Expression studies after overexpression of one against the other.	Chen et al 2020 [118]
Circ_ Pan3	miR-31-5p	Quaking (QKI)	Silencing of miR-31-5p significantly alleviated the myocardial apoptosis induced by Doxorubicin (DOX) treatment. MiR-31-5p acts as a negative regulator of circPan3 by directly suppressing QKI both in vivo and in vitro	Mouse cardiomyocytes. No direct evidence for circRNA/miRNA interaction. Dual-luciferase reporter gene assay of QKI/miR-31-5p interaction. RNA immunoprecipitation of QKI/circPan3 interaction. Expression levels of circPan3 when miR-31-5p was inhibited	Ji et al 2020 [119]
Circ_0007623	miR-297	Vascular Endothelial Growth Factor A (VEGFA)	Hsa_circ_0007623 promoted cardiac repair after acute myocardial ischaemia, and protect cardiac function	Hypoxia-induced human umbilical vein endothelial cells (HUVECs). Dual luciferase reporter gene assay of circ_0007623/miR-297	Zhang et al 2020 [128]
CircDENND2A	miR-34a	May work via β-catenin and Ras/Raf/MEK/ERK pathways	Overexpression of circDENND2A enhanced cell viability and migration but declined apoptosis under oxygen glucose deprivation (OGD)	Rat H9c2 cells. Luciferase activity assay For interaction of circDENND2A/miR-34a	Shao et al 2020 [129]
CircRNA/Protein interaction
CircRNA	Protein target		Findings of the study	Methods	Reference
Autophagy-related circRNA (ACR)	DNA (cytosine-5-)-methyltransferase 3 beta (Dnmt3B)		Inhibition of autophagy – a type of cell death protects cardiomyocytes during ischaemia/reperfusion. CircRNA ACR was able to inhibit autophagy and cell death in cardiomyocytes to protect the heart from reducing I/R induced infarct sizes. ARC activated PTEN-induced kinase 1 (PINK1) expression (an autophagy associated gene) by directly binding to and blocking Dnmt3B-mediated methylation of the Pink1 promoter.	Microarray on mouse cardiomyocytes to look at differential expression in autophagy induced mouse hearts by I/R injury. Transcriptome microarray after ACR knockdown. RNA-binding protein immunoprecipitation (RIP) of ACR/Dnmt3B association. Chromatin immunoprecipitation (ChIP) assay showing Dnmt3B/Pink1 association	Zhou et al 2019 [131]
CircNfix	Y-Box Binding Protein 1 (Ybx1)		Ybx1 is a transcription factor that is involved with cardiomyocyte differentiation. Interaction between circNfix and Ybx1 prevented nuclear translocation of Ybx1, causing cytoplasmic retention and degradation. Nfix also bound to miR-214, which has been demonstrated to be essential for cardiomyocyte proliferation. Loss of circNfix induced cardiac regeneration and angiogenesis and inhibited cardiomyocyte apoptosis after MI, which significantly restored cardiac function and improved the prognosis	Used RNA Sequencing data from another study [138] to filter for circRNAs differentially expressed in human, mouse and rat MI vs control/sham. RT-qPCR of circNfix. RNA pulldown assays and mass spectrometry analysis for Nfix/Ybx1 association. Luciferase, RNA pulldown for Nfix/mIR-214 association	Huang et al 2019 [132]
CircFndc3b	Fused in Sarcoma (FUS)		CircFndc3b significantly downregulated in post MI mouse hearts and in human cardiac tissues of ischaemic cardiomyopathy patients. Overexpression in cardiac endothelial cells increases vascular endothelial growth factor-A (VEGF-A) expression which enhances angiogenic activity and reduces cardiomyocytes and endothelial cell apoptosis. CircFndc3b interacts with the RNA binding protein Fused in Sarcoma to regulate VEGF expression and signalling	Microarrays on sham or MI mouse hearts (n = 2) and ischaemic cardiomyopathy human heart tissue (n = 7), normal heart tissue (n = 4). RNA Immunoprecipitation (RIP)	Garikipati et al 2019 [133]
CircFoxo3	p21-CDK2		Circ-Foxo3 highly expressed in the tissues of aged mice and patients. Ectopic expression of circFoxo3 induced cellular senescence of mouse embryonic fibroblasts (MEFs), where it interacted with the anti-senescence proteins ID1 and E2F1, and anti-stress proteins FAK and HIF1α. These interactions prevented nuclear translocation of these transcription factors, causing cytoplasmic retention and reduced function	Primary cardiomyocytes isolated from neonatal and 12-week heart mouse tissues (n = 20) RT-PCR for expression levels. Antibody pulldown for protein/circRNA association	Du et al 2017 [130]
Mechanism unknown
CircRNA	Protein target		Findings of the study	Methods	Reference
CircRNA 010567	May be related to the inhibition on the TGF-β1 signalling pathway		Cardiac function and myocardial infarction (MI)-induced myocardial fibrosis (MF) improved, myocardial apoptosis was ameliorated in circRNA 010567 siRNA group compared with that in Model group. Regulatory mechanism may be related to the inhibition on the TGF-β1 signalling pathway	Rat MI model by ligation of the left anterior descending coronary artery. Model rats were randomly divided into circRNA 010567 siRNA group and Model group, with sham operation group as Control group (n = 30). The effects of circRNA 010567 on myocardial infarction (MI)-induced myocardial fibrosis (MF), myocardial apoptosis, mRNA, and protein expression levels of TGF-β1 and Smad3 in heart tissues of MI rats were detected using the small animal ultrasound system, Masson staining, terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling (TUNEL) staining, reverse transcription-polymerase chain reaction (RT-qPCR), and Western blotting	Bai et al 2020 [135]