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Back to Journal »Journal of Inflammation Research» Volume 14

Circular RNA Foxo3 reduces myocardial ischemia/reperfusion injury by inhibiting KAT7 in myocardial infarction, inhibiting HMGB1 and inhibiting autophagy

Authors: Sun Geng, Shen Jinfeng, Wei Xinfeng, Qi GX

Published on December 1, 2021, the 2021 volume: 14 pages 6397-6407

DOI https://doi.org/10.2147/JIR.S339133

Single anonymous peer review

Reviewing editor: Professor Quan Ning

Sun Guang,1 Shen Jianfen,2 Wei Xiufang,1 Qi Guoxian1 1 Department of Geriatric Cardiology, First Affiliated Hospital of China Medical University, Shenyang, Liaoning, 110001; 2Department of Cardiology, First Affiliated Hospital of China Medical University, Shenyang, Liaoning, 110001 Corresponding Authors: Guo-Xian Qi Email [email protected] Introduction: Myocardial infarction is a coronary artery-related heart disease and the leading cause of global mortality. Circular RNA (circRNA) is a new type of regulatory RNA involved in a variety of pathological cardiac progression. Methods: However, the function of circFoxo3 in MI-induced myocardial injury remains unclear. Results: It is worth noting that we found that circFoxo3 was down-regulated in the MI rat model. Overexpression of circFoxo3 improved MI-induced cardiac dysfunction and attenuated MI-induced autophagy in the rat model. At the same time, the overexpression of circFoxo3 inhibited oxygen-glucose deprivation (OGD)-induced autophagy, apoptosis, inflammation and injury of cardiomyocytes in vitro. Mechanically, we found that overexpression of circFoxo3 in cardiomyocytes reduced the expression of KAT7. At the same time, the consumption of KAT7 in cardiomyocytes inhibited the expression of HMGB1. KAT7 knockdown suppressed histone H3 lysine 14 acetylation (H3K14ac) and RNA polymerase II (RNA pol II) enrichment on the HMGB1 promoter. In addition, overexpression of circFoxo3 inhibited the expression of HMGB1, while overexpression of KAT7 rescued the expression of HMGB1 in cardiomyocytes. Overexpression of circFoxo3 reduces the enrichment of KAT7, H3K14ac and RNA poly II on the HMGB1 promoter, while overexpression of KAT7 can reverse this effect. Overexpression of KAT7 or HMGB1 can reverse the cardiomyocyte damage and autophagy reduced by circFoxo3 in vitro. Therefore, we conclude that the circular RNA circFoxo3 inhibits autophagy by inhibiting KAT7 in MI and inhibiting HMGB1, thereby alleviating myocardial ischemia/reperfusion injury. Discussion: Our findings provide new insights into the mechanism by which circFoxo3 regulates MI-related cardiac dysfunction by targeting the KAT7/HMGB1 axis. Keywords: myocardial infarction, autophagy, circFoxo3, KAT7, HMGB1

Myocardial infarction1 is a coronary artery-related heart disease, which ranks first in death worldwide2. It is usually caused by insufficient blood supply to the heart to cause myocardial tissue ischemia and hypoxia, inflammation, and myocardial cell death, which ultimately leads to myocardial infarction. 3,4 In MI-induced cardiomyocyte response, cell death plays a central role in the pathogenesis of MI, which can be achieved through three main mechanisms: apoptosis, necrosis, and autophagy. 5 Although more and more evidence has clarified the pathogenesis of MI, MI, the incidence of MI continues to rise, and it is urgent to explore effective treatments. 6

circRNAs are covalently closed non-coding RNA loops, which are highly conserved and abundant. Compared with linear RNAs, they have higher stability under physical conditions. 7 More and more studies have shown that circRNAs are involved in the pathogenesis of various diseases including MI.8,9. 8,9 CircFoxo3 is a newly discovered circRNA derived from FoxO3 gene, which acts as a tumor activator in cancers including gastric cancer and glioblastoma. 10,11 Recent studies have also revealed that circFoxo3 is involved in the progression of coronary artery disease. 12,13 There are also reports that CircFoxo3 protects cardiomyocytes from radiation-induced cardiotoxicity. 14 However, the function of circFoxo3 in MI remains unclear. It is worth noting that circRNA mainly acts through sponge microRNA (miRNA) or directly binds to the target protein. 7 For example, circRHOT1 epigenetically regulates lung cancer progression by recruiting KAT5. 15 Importantly, previous studies have identified the key functions of circRNA in regulating the progression of MI, including circTtc3, circCDYL, and circFndc3b. 8,16,17 In addition, the high mobility group box 1 (HMGB1) is a non-histone DNA binding protein that is involved in the regulation of gene expression, including DNA replication, gene transcription, and assembly as a nucleosome. 18 Studies have shown the function of KAT7 in various diseases, such as cancer, sepsis, atherosclerosis, collagen disease, acute lung injury arthritis, epilepsy, and myocardial infarction. 19-21

In this work, we evaluated the role of circFoxo3 in the progression of MI. We discovered the cardioprotective function of circFoxo3 in MI models in vitro and in vivo, and deciphered that circFoxo3 inhibits HMGB1 expression and cardiomyocyte autophagy through the KAT7/HMGB1 axis. Molecular mechanism. Our findings may provide a new treatment for MI.

Rat cardiomyocytes H9c2 were purchased from the American Type Culture Collection (ATCC, United States) and were prepared at 37°C in DMEM (Thermo, United States) supplemented with 10% FBS (Gibco, United States) and 1% penicillin/streptomycin. C Culture in a humidified incubator filled with 5% CO2. Overexpression vectors of circFOXO3, KAT7 and HMGB1, small interfering RNA targeting KAT7 and HMGB1, and control oligonucleotides were purchased from Gene Pharma (Shanghai, China). The oligonucleotide (50 nM) was mixed with Lipofectamine 2000 (Invitrogen, USA) and incubated with the cells for 48 hours according to the manufacturer's protocol.

All animal experiments were authorized by the Animal Ethics Committee of the First Affiliated Hospital of China Medical University and carried out in accordance with the recommendations in the National Institutes of Health Laboratory Animal Care and Use Guidelines. 8-week-old SD rats (n=6 per group) were purchased from Charles River Laboratories (USA). In order to establish the MI model in vivo, we performed left anterior descending (LAD) ligation with 6-0 silk thread according to the previously reported protocol. 22 rats in the treatment group were injected with the designated oligonucleotides (80 mg/kg, 100 μL PBS). Rats in the sham operation group did not undergo ligation. One week after surgery, a transthoracic two-dimensional (2D) echocardiography (Vevo 2100) ultrasound system was used to detect heart function. Monitor left ventricular ejection fraction (LVEF), left ventricular fraction shortening (LVFS), left ventricular anterior diastolic wall thickness (LVAWd) and left ventricular posterior end diastolic (LVPWd). The rats were then sacrificed, and heart tissues were collected for follow-up studies.

The levels of inflammatory factors (IL-6 and IL-10) in rat serum, heart and H9c2 cell culture medium were determined by ELISA (Invitrogen, USA) according to the manufacturer's protocol.

The collected heart tissue was fixed with 4% paraformaldehyde (PFA) and made into 5 μm paraffin-embedded sections. To observe tissue damage, the samples were stained with hematoxylin and eosin (H&E) and photographed under a microscope (Leica, Germany). For triphenyltetrazolium chloride (TTC) staining, the aorta was separated from the rat and perfused with saline, and then stained with Evans blue solution (0.3%) (Sigma). Subsequently, the ventricles were sectioned and stained with TCC (1%).

H9c2 cells were seeded on a coverslip overnight, then fixed and permeabilized with ice-cold 100% methanol at room temperature for 5 minutes. After that, the cells were washed with PBS and blocked with 2% BSA in TBS buffer for 1 hour. Then use the LC3 specific primary antibody (Cell Signaling technology, USA) (1:100) in the blocking solution to incubate with the sample overnight at 4°C. The next day, the cells were incubated with Alexa fluor 633 secondary antibody for 1 hour at room temperature, then stained with DAPI for 10 minutes and fixed on a glass slide. The cells were then imaged on an SP8 confocal microscope (Leica, Germany).

Cardiac tissue cell apoptosis was detected using One Step TUNEL Apoptosis Assay Kit (Beyotime, China) according to the manufacturer's instructions. In short, the paraffin-embedded heart tissue is deparaffinized and reacted with the detection reagent at 37°C for 60 minutes. Then stain the nucleus with DAPI for 10 minutes. Observe the fluorescence under a microscope (Leica).

Statistical analysis is realized by SPSS software (USA). The statistical significance of the difference is determined by using Student's t-test or one-way analysis of variance. A P value less than 0.05 is defined as statistically significant.

In order to determine the role of circFoxo3 in MI-induced abnormal cardiac function, we established a MI rat model and performed circFoxo3 treatment on the MI infarct area. We found that circFoxo3 was reduced in MI rats, and the effectiveness of circFoxo3 overexpression was verified in the model (Figure 1A). Compared with the sham operation group, we observed inflammatory cell infiltration in MI heart tissue, which was hindered by overexpression of circFoxo3 (Figure 1B) and reduced infarct size (Figure 1C). Echocardiographic analysis showed that MI reduced LVEF and LVFS, and up-regulated LVAWd and LVPWd, while overexpression of circFoxo3 could significantly offset the changes in the levels of LVEF, LVFS, LVAWd and LVPWd in MI rats (Figure 1D-G). At the same time, overexpression of circFoxo3 in rats attenuated MI-induced apoptosis (Figure 1H). These results prove the successful establishment of the MI rat model and the protective effect of circFoxo3 in MI (Supplementary material). Figure 1 Overexpression of circFoxo3 attenuates MI-induced cardiac insufficiency in the rat model. (AH) Establish a MI rat model and inject circFoxo3 vector or control vector around the infarct area for treatment. (A) Detect the relative level of circFoxo3 RNA in heart tissue by qRT-PCR. (B) HE staining of inflammatory cell infiltration in hot tissue three days after surgery. (CG) Infarct size, 25 left ventricular fractional shortening (LVFS) (D), left ventricular ejection fraction (LVEF) (E), diastolic left ventricular anterior wall thickness (LVAWd) (F) and left ventricular posterior wall measurement diastolic Terminal stage (LVPWd) (G). (H) Apoptosis was detected by TUNEL staining. ** p <0.01.

Figure 1 Overexpression of circFoxo3 attenuates MI-induced cardiac insufficiency in the rat model. (AH) Establish a MI rat model and inject circFoxo3 vector or control vector around the infarct area for treatment. (A) Detect the relative level of circFoxo3 RNA in heart tissue by qRT-PCR. (B) HE staining of inflammatory cell infiltration in hot tissue three days after surgery. (CG) Infarct size, 25 left ventricular fractional shortening (LVFS) (D), left ventricular ejection fraction (LVEF) (E), diastolic left ventricular anterior wall thickness (LVAWd) (F) and left ventricular posterior wall measurement diastolic Terminal stage (LVPWd) (G). (H) Apoptosis was detected by TUNEL staining. ** p <0.01.

Then, we were interested in the function of circFoxo3 in autophagy and inflammation in the MI rat model. We found that the expression of LC3 and Beclin-1 was induced in MI rats and the expression of p62 was reduced, and the overexpression of circFoxo3 reversed the phenotype (Figure 2A-D). The levels of IL-6 and IL-10 in MI rats increased, and overexpression of circFoxo3 blocked the levels in rats (Figure 2E-H). Figure 2 Overexpression of circFoxo3 inhibited MI-induced autophagy and inflammation in the rat model. (AH) Establish a MI rat model and inject circFoxo3 vector or control vector around the infarct area for treatment. (A) The level of LC3 is measured by immunofluorescence. (BD) The expression of Beclin-1, p62 and LC3 was detected by Western blot analysis. (EH) Analyze the levels of IL-6 and IL-10 in heart tissue and serum by ELISA. ** p <0.01.

Figure 2 Overexpression of circFoxo3 inhibited MI-induced autophagy and inflammation in the rat model. (AH) Establish a MI rat model and inject circFoxo3 vector or control vector around the infarct area for treatment. (A) The level of LC3 is measured by immunofluorescence. (BD) The expression of Beclin-1, p62 and LC3 was detected by Western blot analysis. (EH) Analyze the levels of IL-6 and IL-10 in heart tissue and serum by ELISA. ** p <0.01.

We evaluated the expression of canonical and reverse spliced ​​forms of Foxo3 in H9c2 cells by agarose gel electrophoresis analysis and PCR in the presence or absence of RNase R supplements. After treatment with different primers and RNase R, circFoxo3 can be detected in cDNA, but not gDNA (Figure 3A). We next explored the protective effect of circFoxo3 in vitro. The expression of circFoxo3 was suppressed in OGD-treated H9c2 cells, and the effectiveness of circFoxo3 overexpression was verified in the cells (Figure 3B). Under OGD stimulation, overexpression of CircFoxo3 promoted cell viability (Figure 3C) and inhibited cell apoptosis (Figure 3D). In addition, OGD treatment resulted in down-regulation of the secretion of inflammatory cytokines IL-6 and IL-10, and overexpression of circFoxo3 reversed the phenotype (Figure 3E and F). These findings prove the in vitro protective effect of circFoxo3 in ischemic cardiomyocytes. Figure 3 Overexpression of circFoxo3 attenuated the cardiomyocyte damage induced by OGD in vitro. (A) In the presence or absence of RNase R supplements, the reverse spliced ​​and canonical form of Foxo3 expression was detected by agarose gel electrophoresis analysis and PCR in H9c2 cells. (BF) H9c2 cells were treated with OGD and simultaneously transfected with circFoxo3 overexpression vector (OE circ) or empty vector (NC) for 48 hours. (B) The relative level of circFoxo3 RNA was detected by qRT-PCR. 25 Determine cell viability by CCK-8 assay. (D) Apoptosis was measured by flow cytometry. (E) Check the levels of IL-6 and IL-10 in the culture medium by ELISA. ** p <0.01.

Figure 3 Overexpression of circFoxo3 attenuated the cardiomyocyte damage induced by OGD in vitro. (A) In the presence or absence of RNase R supplements, the reverse spliced ​​and canonical form of Foxo3 expression was detected by agarose gel electrophoresis analysis and PCR in H9c2 cells. (BF) H9c2 cells were treated with OGD and simultaneously transfected with circFoxo3 overexpression vector (OE circ) or empty vector (NC) for 48 hours. (B) The relative level of circFoxo3 RNA was detected by qRT-PCR. 25 Determine cell viability by CCK-8 assay. (D) Apoptosis was measured by flow cytometry. (E) Check the levels of IL-6 and IL-10 in the culture medium by ELISA. ** p <0.01.

Next, we explored the effect of circFoxo3 on autophagy in H9c2 cells treated with OGD. Our data showed that in OGD-treated H9c2 cells, the expression of LC3 and Beclin-1 was induced, and the expression of p62 was reduced, and the overexpression of circFoxo3 reversed the phenotype (Figure 4A-D). Figure 4 Overexpression of circFoxo3 reduces OGD-induced autophagy in vitro. (AD) H9c2 cells were treated with OGD and simultaneously transfected with circFoxo3 overexpression vector (OE circ) or empty vector (NC) for 48 hours. (A) The level of LC3 is measured by immunofluorescence. (BD) The expression of Beclin-1, p62 and LC3 was detected by Western blot analysis. ** p <0.01.

Figure 4 Overexpression of circFoxo3 reduces OGD-induced autophagy in vitro. (AD) H9c2 cells were treated with OGD and simultaneously transfected with circFoxo3 overexpression vector (OE circ) or empty vector (NC) for 48 hours. (A) The level of LC3 is measured by immunofluorescence. (BD) The expression of Beclin-1, p62 and LC3 was detected by Western blot analysis. ** p <0.01.

Next, we explored the effect of circFoxo3 on autophagy in H9c2 cells treated with OGD. Our data showed that in OGD-treated H9c2 cells, the expression of LC3 and Beclin-1 was induced, and the expression of p62 was reduced, and the overexpression of circFoxo3 reversed the phenotype (Figure 4A-D).

Then, we explored the underlying mechanism of circFoxo3-mediated cardiomyocyte damage. We observed that overexpression of circFoxo3 in H9c2 cells reduced the expression of KAT7 (Figure 5A). At the same time, the expression of HMGB1 was inhibited by the consumption of KAT7 in H9c2 cells (Figure 5B). KAT7 knockdown suppressed histone H3 lysine 14 acetylation (H3K14ac) and RNA polymerase II (RNA pol II) enrichment on the HMGB1 promoter (Figure 5C and D). In addition, overexpression of circFoxo3 suppressed the expression of HMGB1, while overexpression of KAT7 rescued the expression of HMGB1 in H9c2 cells (Figure 5E). Overexpression of circFoxo3 reduced the enrichment of KAT7, H3K14ac and RNA poly II on the HMGB1 promoter, while overexpression of KAT7 could reverse this effect (Figure 5F-H). Figure 5 CircFoxo3 reduces the expression of HMGB1 by inhibiting KAT7. (A) In H9c2 cells treated with circFoxo3 overexpression vector, the expression of KAT7 was measured by qPCR. (BD) H9c2 cells are treated with KAT7 shRNA. (B) Measure the expression of HMGB1 by qPCR. 25 The enrichment of H3K14ac on the HMGB1 promoter was detected by ChIP analysis. (D) The enrichment of RNA poly II on the HMGB1 promoter was analyzed by ChIP analysis. (EH) H9c2 cells are treated with circFoxo3 overexpression vector, or circFoxo3 overexpression vector and KAT7 overexpression vector are used together. (E) Measure the expression of HMGB1 by qPCR. (FH) The enrichment of KAT7, H3K14ac and RNA poly II is measured by ChIP analysis. ** p <0.01.

Figure 5 CircFoxo3 reduces the expression of HMGB1 by inhibiting KAT7. (A) In H9c2 cells treated with circFoxo3 overexpression vector, the expression of KAT7 was measured by qPCR. (BD) H9c2 cells are treated with KAT7 shRNA. (B) Measure the expression of HMGB1 by qPCR. 25 The enrichment of H3K14ac on the HMGB1 promoter was detected by ChIP analysis. (D) The enrichment of RNA poly II on the HMGB1 promoter was analyzed by ChIP analysis. (EH) H9c2 cells are treated with circFoxo3 overexpression vector, or circFoxo3 overexpression vector and KAT7 overexpression vector are used together. (E) Measure the expression of HMGB1 by qPCR. (FH) The enrichment of KAT7, H3K14ac and RNA poly II is measured by ChIP analysis. ** p <0.01.

Next, we analyzed the role of KAT7 in vitro. The expression of KAT7 was increased in H9c2 cells treated with OGD, and the effectiveness of KAT7 depletion was verified in the cells (Figure 6A). Under OGD stimulation, KAT7 depletion promotes cell viability (Figure 6B) and inhibits cell apoptosis (Figure 6C). In addition, OGD treatment resulted in a decrease in the secretion of the inflammatory cytokines IL-6 and IL-10 (Figure 6D and E). Figure 6 The consumption of KAT7 attenuates the cardiomyocyte damage induced by OGD in vitro. (AE) H9c2 cells were treated with OGD and simultaneously transfected with KAT7 shRNA for 48 hours. (A) Detect the relative level of KAT7 RNA in heart tissue by qRT-PCR. (B) Determine cell viability by CCK-8 assay. 25 Determine cell apoptosis by flow cytometry. (D and E) The levels of IL-6 and IL-10 in the culture medium were checked by ELISA assay. ** p <0.01.

Figure 6 The consumption of KAT7 attenuates the cardiomyocyte damage induced by OGD in vitro. (AE) H9c2 cells were treated with OGD and simultaneously transfected with KAT7 shRNA for 48 hours. (A) Detect the relative level of KAT7 RNA in heart tissue by qRT-PCR. (B) Determine cell viability by CCK-8 assay. 25 Determine cell apoptosis by flow cytometry. (D and E) The levels of IL-6 and IL-10 in the culture medium were checked by ELISA assay. ** p <0.01.

Next, we explored the effect of KAT7 on autophagy in OGD-treated H9c2 cells. Our data showed that in OGD-treated H9c2 cells, the expression of LC3 and Beclin-1 was induced, and the expression of p62 was reduced, and knockdown of KAT7 reversed the phenotype (Figure 7A-D). Figure 7 The consumption of KAT7 attenuates OGD-induced autophagy in vitro. (AD) H9c2 cells were treated with OGD and simultaneously transfected with KAT7 shRNA for 48 hours. (A) The level of LC3 is measured by immunofluorescence. (BD) The expression of Beclin-1, p62 and LC3 was detected by Western blot analysis. ** p <0.01.

Figure 7 The consumption of KAT7 attenuates OGD-induced autophagy in vitro. (AD) H9c2 cells were treated with OGD and simultaneously transfected with KAT7 shRNA for 48 hours. (A) The level of LC3 is measured by immunofluorescence. (BD) The expression of Beclin-1, p62 and LC3 was detected by Western blot analysis. ** p <0.01.

We next tried to verify the role of the circFoxo3/KAT7/HMGB1 axis in regulating cardiomyocyte damage and autophagy. Overexpression of circFoxo3 enhanced cell viability under OGD stimulation (Figure 8A) and inhibited cell apoptosis (Figure 8B), while overexpression of KAT7 or HMGB1 could reverse this effect. The secretion of IL-6 and IL-10 was inhibited by the overexpression of circFoxo3 in H9c2 cells treated with OGD, and the overexpression of KAT7 or HMGB1 rescued the levels of IL-6 and IL-10 (Figure 8C and D). In OGD-treated H9c2 cells, overexpression of circFoxo3 reduced the expression of LC3 and Beclin-1, and increased the expression of p62. The overexpression of KAT7 or HMGB1 reversed the phenotype (Figure 8E-G). Figure 8 CircFoxo3 reduces OGD-induced cardiomyocyte damage and autophagy by targeting the KAT7/HMGB1 axis in vitro. (AG) H9c2 cells were treated with OGD and simultaneously transfected with circFoxo3 overexpression vector, or treated with circFoxo3 overexpression vector and KAT7 or HMGB1 overexpression vector together. (A) Determine cell viability by CCK-8 assay. (B) Apoptosis was measured by flow cytometry. (C and D) The levels of IL-6 and IL-10 in the culture medium were checked by ELISA assay. (EG) The expression of Beclin-1, p62 and LC3 was detected by Western blot analysis. (H) shows the graph model of this study. ** p <0.01.

Figure 8 CircFoxo3 reduces OGD-induced cardiomyocyte damage and autophagy by targeting the KAT7/HMGB1 axis in vitro. (AG) H9c2 cells were treated with OGD and simultaneously transfected with circFoxo3 overexpression vector, or treated with circFoxo3 overexpression vector and KAT7 or HMGB1 overexpression vector together. (A) Determine cell viability by CCK-8 assay. (B) Apoptosis was measured by flow cytometry. (C and D) The levels of IL-6 and IL-10 in the culture medium were checked by ELISA assay. (EG) The expression of Beclin-1, p62 and LC3 was detected by Western blot analysis. (H) shows the graph model of this study. ** p <0.01.

MI is a coronary artery-related heart disease and the leading cause of death worldwide. 1 CircRNA is a new type of regulatory RNA, involved in a variety of pathological cardiac progression. However, the role of circFoxo3 in MI-induced myocardial injury remains unclear. In the current study, we have discovered a new function of circFoxo3 in regulating myocardial ischemia/reperfusion injury.

As an important pathological regulator, circRNA has been found to be involved in the regulation of MI-related myocardial injury. According to reports, Circular RNA CircFndc3b regulates cardiac repair in MI models through FUS/VEGF-A signaling. 8 Circular RNA Ttc3 regulates MI-induced cardiac dysfunction by targeting miR-15b. 16 Circular RNA ACR relieves myocardial ischemia/reperfusion injury by inhibiting myocardial ischemia/reperfusion injury. Autophagy regulates Pink1/FAM65B signal. 23 These reports prove the key role of circRNA in regulating cardiac ischemia/reperfusion injury. However, the understanding of the function of circRNAs in MI-induced cardiac ischemia/reperfusion injury is still elusive. In this work, we found that circFoxo3 was down-regulated in the MI rat model, and the overexpression of circFoxo3 improved MI-induced cardiac dysfunction and attenuated MI-induced autophagy in the rat model. At the same time, overexpression of circFoxo3 inhibits oxygen-glucose deprivation (OGD)-induced autophagy, apoptosis, inflammation and injury of cardiomyocytes in vitro. These data demonstrate the innovative role of circFoxo3 in inhibiting MI-induced cardiac dysfunction, and provide important evidence for the important function of circRNA in MI. At the same time, our research is consistent with previous studies that circRNA plays an important role in the progression of MI-induced cardiac ischemia/reperfusion injury.

Previous studies have identified the key function of HMGB1 in regulating the progression of MI. It has been determined that inhibition of lncRNA TUG1 enhances miR-142-3p by targeting Rac1 and HMGB1-induced autophagy to reduce myocardial damage during ischemia/reperfusion. 24 Resolvin D1 inhibits MI by targeting the HMGB1 pathway in rodent models. 25 TLR9 is HMGB1 required for HMGB1 to regulate tissue repair after MI by regulating angiogenesis, heart healing and apoptosis. 20 These reports reveal the important role of HMGB1 in MI. In this study, we found that overexpression of circFoxo3 in cardiomyocytes reduced the expression of KAT7. At the same time, the consumption of KAT7 in cardiomyocytes inhibited the expression of HMGB1. KAT7 knockdown suppressed histone H3 lysine 14 acetylation (H3K14ac) and RNA polymerase II (RNA pol II) enrichment on the HMGB1 promoter. In addition, overexpression of circFoxo3 inhibited the expression of HMGB1, while overexpression of KAT7 rescued the expression of HMGB1 in cardiomyocytes. Overexpression of circFoxo3 reduces the enrichment of KAT7, H3K14ac and RNA poly II on the HMGB1 promoter, while overexpression of KAT7 can reverse this effect. We verified in vitro that the consumption of KAT7 attenuated OGD-induced cardiomyocyte damage and autophagy. Overexpression of KAT7 or HMGB1 can reverse the cardiomyocyte damage and autophagy reduced by circFoxo3 in vitro. Our mechanism study reveals the unreported role of KAT7 in the progression of MI, and provides a new mechanism for circFoxo3-mediated cardiomyocyte damage and autophagy involving the KAT7/HMGB1 axis. The current research has some limitations. We evaluated the effect of circFoxo3 on myocardial ischemia/reperfusion injury in vitro and in vivo, but the clinical significance of circFoxo3 in myocardial ischemia/reperfusion injury should be confirmed in future studies. At the same time, the KAT7/HMGB1 axis may only be one of the downstream mechanisms of circFoxo3-mediated myocardial ischemia/reperfusion injury, and other potential mechanisms need to be explored in the future.

In conclusion, we concluded that circular RNA circFoxo3 inhibits autophagy by inhibiting KAT7 in MI and inhibiting HMGB1, thereby alleviating myocardial ischemia/reperfusion injury (Figure 8H). Our findings provide new insights into the mechanism by which circFoxo3 regulates MI-related cardiac dysfunction by targeting the KAT7/HMGB1 axis.

The authors report no conflicts of interest in this work.

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