This article is mentioned in:

Introduction

Acute myocardial infarction (AMI) is characterized by myocardial necrosis caused by acute and persistent ischemia and hypoxia of cardiac cells (1). Clinically, AMI presents as sharp and persistent substernal pain that cannot be fully relieved by resting or nitrate medications, and is accompanied by elevated levels of serum myocardial enzymes, including creatine kinase and lactate dehydrogenase (LDH), as well as abnormal progression on an electrocardiogram (2-4). AMI can occur at the same time as arrhythmias, shock or heart failure, and is often life threatening. This disease is most common in North American and European countries, where ~1.5 million new cases of AMI are reported in the United States annually (5,6). In China, the incidence of AMI has continued to increase in the last decade, with ≥500,000 new cases annually and ~2 million patients currently diagnosed (7). Myocardial ischemia/reperfusion (I/R) injury is often the result of different types of coronary artery disease, including myocardial infarction, ischemic cardiomyopathy and sudden coronary death (8). Reperfusion is a standard therapy for acute cases of coronary artery diseases, including MI, and is also an inevitable inducer of I/R injury of coronary microvessels and myocardium (9-11).

Phosphodiesterase 4B (PDE4B) is one of the 11 members of the PDE enzyme family that are known for their exclusive ability to decompose cyclic nucleotides, and it can regulate several biological processes (12). A recent microarray study identified PDE4B as a metabolism-related gene that was strongly associated with the onset and recurrence of AMI (13). Previous studies have reported that activation of PDE4B induced cognitive impairment and neuronal apoptosis, and aggravated neuroinflammation and oxidative stress in the central nervous system (14,15).

Jun dimerization protein 2 (JDP2) is a bZip-type transcription factor that belongs to the activator protein-1 (AP-1) family (16). JDP2 upregulation in mice has been reported to have a direct association with impaired cardiac function manifested as cardiomyocyte apoptosis, cardiac hypertrophy, fibrosis and inflammation (17).

Therefore, the present study aimed to investigate how PDE4B expression affected myocardial hypoxia/reoxygenation (H/R) injury, and to determine the function of JDP2 in the process.

Materials and methods

Bioinformatics tools

JASPAR database (jaspar.genereg.net) which is a regularly maintained open-access database storing manually curated transcription factors (TF) binding profiles as position frequency matrices (PFMs) was applied to predict the interaction between the transcription factor JDP2 and PDE4B promoter.

Cell culture and treatment

H9c2 rat embryo heart-derived cardiomyocytes (American Type Culture Collection) were cultured in low-glucose DMEM supplemented with 10% FBS (Gibco, Thermo Fisher Scientific, Inc.) in a 5% CO2 incubator at 37˚C. To create a hypoxic condition, H9c2 cells were cultured at 37˚C for 6 h in serum-free and glucose-free DMEM in a tri-gas incubator with 94% N2, 5% CO2 and 1% O2. Subsequently, cells were re-oxygenated for 2 h in DMEM supplemented with 10% FBS in 95% air and 5% CO2 at 37˚C, as previously described (18). Cells incubated in a humidified atmosphere of 5% CO2 incubator at 37˚C for 20 h were used as a control throughout the experiments.

Cell transfection

Short hairpin (sh)RNA plasmids specific for PDE4B which were ligated into the plasmid of U6/GFP/Neo [sh-PDE4B-1 forward, 5'-CCGGTACTCCTTCTCTGTGAAATTTCTCGAGAAATTTCACAGAGAAGGAGTATTTTTG-3' and reverse, 5'-AATTCAAAAATACTCCTTCTCTGTGAAATTTCTCGAGAAATTTCACAGAGAAGGAGTA-3'; sh-PDE4B-2 forward, 5'-CCGGTCCATCTACAGTCTGAGATTACTCGAGTAATCTCAGACTGTAGATGGATTTTTG-3' and reverse, 5'-AATTCAAAAATCCATCTACAGTCTGAGATTACTCGAGTAATCTCAGACTGTAGATGGA-3', shRNA with empty vectors which was regarded as negative control (NC), pcDNA3.1(+) JDP2 overexpression vector (Oe-JDP2) and Oe-NC were purchased from Shanghai GenePharma Co., Ltd. H9c2 cells (4x105 cells/well) were transfected with 50 nM sh-PDE4B-1/2, sh-NC, Oe-JDP2 or Oe-NC using Lipofectamine® 2000 (Invitrogen; Thermo Fisher Scientific, Inc.) according to the manufacturer's protocol. After incubation at 37˚C for 48 h, cells were harvested for subsequent experiments.

Reverse transcription-quantitative PCR (RT-qPCR)

Total RNA was extracted from H9c2 cells using the RNAeasy™ Viral RNA Isolation kit with Spin Column (Beyotime Institute of Biotechnology). Total RNA was reverse transcribed into cDNA using the Revert Aid™ cDNA Synthesis kit (Takara Biotechnology co., Ltd.) according to the manufacturer's protocol. Subsequently, qPCR was performed using BeyoFast™ Probe qPCR mix (Beyotime Institute of Biotechnology). The thermocycling conditions were as follows: Pre-denaturation at 95˚C for 30 sec, followed by denaturation at 95˚C for 10 sec and annealing at 55˚C for 30 sec for 40 cycles. The following primers were used for qPCR: PDE4B forward, 5'-ACGGTGGCTCATACATGCT-3' and reverse, 5'-GTACCAGTCCCGACGAAGAG-3'; JDP2 forward, 5'-CCCAGGGACCTCGAGCTTT-3' and reverse, 5'-GGTCTTCAGCTCTGCGTTCA-3'; and GADPH forward, 5'-GAATGGGCAGCCGTTAGGAA-3' and reverse, 5'-AAAAGCATCACCCGGAGGAG-3'. Relative expression levels were calculated using the 2-ΔΔCq method (19) and normalized to the internal reference gene GAPDH.

Western blotting

Total protein was extracted from H9c2 cells using RIPA lysis buffer (Shanghai Yeasen Biotechnology Co., Ltd.) and quantified using a BCA kit (Shanghai Enzyme-linked Biotechnology Co., Ltd.). Proteins (20 µg per lane) were separated via 10% SDS-PAGE (Beyotime Institute of Biotechnology) and transferred onto PVDF membranes. The membranes were incubated at 4˚C overnight with primary antibodies targeted against: PDE4B (1:1,000; cat. no. ab14628; Abcam), Bcl-2 (1:1,000; cat. no. ab196495; Abcam), Bax (1:1,000; cat. no. ab32503; Abcam), cleaved-caspase3 (1:1,000; cat. no. 9661; Cell Signaling Technology, Inc.), cleaved-caspase9 (1:1,000; cat. no. 10380-1-AP; ProteinTech Group, Inc.), JDP2 (1:1,000; cat. no. orb336272; Biorbyt Ltd.) and GAPDH (1:10,000; cat. no. ab181602; Abcam). Following the primary incubation, membranes were incubated with a HRP-labeled Goat Anti-Rabbit IgG (H+L) secondary antibody (1:1,000; cat. no. A0208; Beyotime Institute of Biotechnology) at 37˚C for 2 h. Protein bands were visualized using ECL reagents (PerkinElmer, Inc.) and analyzed by Image J software (version 1.48v; National Institutes of Health). GAPDH was used as the loading control.

Cell viability and cytotoxicity

The Cell Counting Kit-8 (CCK-8; Beijing Solarbio Science & Technology Co., Ltd.) assay was performed was to assess cell viability. Briefly, H9c2 cells (2x103 cells/100 µl/well) were incubated with 10 µl/well CCK-8 solution in a 96-well plate for 2 h. Subsequently, optical density was measured at a wavelength of 450 nm using a microplate reader (Bio-Rad Laboratories, Inc.).

The LDH Cytotoxicity Assay Kit (Beyotime Institute of Biotechnology) was used to detect H/R-induced cytotoxicity according to the manufacturer's instructions. LDH activity was measured at a wavelength of 490 nm using a microplate reader (Bio-Rad Laboratories, Inc.).

Detection of oxidative stress levels

The levels of malondialdehyde (MDA) and superoxide dismutase (SOD) in H9c2 cells were detected using MDA (A003-1-2) and SOD (A001-3-2) assay kits (both Nanjing Jiancheng Bioengineering Institute), respectively. The glutathione (GSH) to glutathione oxidized (GSSG) ratio was measured using the GSH/GSSG Ratio Assay kit (cat. no. KA6046; Abnova). Briefly, the cell precipitate was collected via centrifugation at 1,600 x g for 10 min at 4˚C and freeze-thawed twice with liquid nitrogen and 37˚C water baths prior to centrifugation at 1,000 x g for 10 min at room temperature. Subsequently, working solution and NADPH solution from the kits were prepared and added successively into the supernatant. Following incubation, the absorbance at 412 nm was determined using a microplate reader (BioTek instruments, inc.).

Measurement of apoptotic rate and apoptosis-related proteins

H9c2 cell apoptosis was detected using the TUNEL Apoptosis Assay kit (Beyotime Institute of Biotechnology). After washing with PBS, cells were fixed with 4% paraformaldehyde at 4˚C for 10 min, permeabilized with 0.3% PBS in Triton X-100 at room temperature for 30 min and then incubated with 0.3% H2O2 in PBS on ice for 2 min prior to biotin labeling. Cells were incubated with TUNEL detection solution at 37˚C for 60 min in the dark and stained with 10 µg/ml DAPI (Shanghai Haoyang Bio Technology Co., Ltd.) at 37˚C for 2-3 min. In total, three fields of view were selected at random and the images were captured using a fluorescence microscope (magnification, x200; Olympus Corporation). Apoptosis-related protein expression levels were detected via western blotting according to the aforementioned protocol.

Verification of interaction between JDP2 and PDE4B

For the dual luciferase reporter assay, H9c2 cells (5x105 cells/well) were seeded (1x104 cells/well) into 96-well plates. Subsequently, H9c2 cells were co-transfected with PDE4B-WT and PDE4B-MUT, Oe-JDP2 or Oe-NC (0.5 µg) and Renilla luciferase reporter vector (Promega Corporation) using Lipofectamine® 2000 (Invitrogen; Thermo Fisher Scientific, Inc.) for 48 h at 37˚C. At 48 h post-transfection, firefly luciferase activities was measured using a Dual Luciferase Reporter Assay system (Promega Corporation) and normalized to Renilla luciferase activities.

For the chromatin immunoprecipitation (ChIP) assay, ultrasound-treated samples were centrifuged at 12,000-14,000 x g for 5 min at 4˚C. A total of 300 µl SDS lysis buffer (Active Motif, Inc.) was then used to lyse the cells, which were subsequently sonicated at 150 Hz and sheared with four sets of 10 sec pulses on wet ice using a high intensity ultrasonic processor. ChIP Dilution Buffer containing 1 mM PMSF was prepared using the ChIP Assay kit (Beyotime Institute of Biotechnology) and added to part of the samples to serve as the input. A total of 40 µl protein A/G agarose beads (Santa Cruz Biotechnology, Inc.) was added to the rest of the samples. Following centrifugation at 16,000 x g for 10 min at 4˚C, supernatant (100 µl) was incubated with 5 µg anti-IgG (cat. no. sc-2025; Santa Cruz Biotechnology, Inc.) or anti-JDP2 (cat. no. sc-517133; Santa Cruz Biotechnology, Inc.) primary antibodies and protein A/G agarose at 4˚C overnight. The precipitated chromatin was purified by phenol/chloroform/isoamyl extraction and analyzed via RT-qPCR according to the aforementioned protocol.

Statistical analysis

Statistical analyses were performed using GraphPad Prism (version 8; GraphPad Software, Inc.). All experiments were performed in triplicate. Data are presented as the mean ± SD from at least three independent experiments. Comparisons between two groups were analyzed using an unpaired Student's t-test, whereas comparisons among multiple groups were analyzed using one-way ANOVA followed by Tukey's post hoc test. P<0.05 was considered to indicate a statistically significant difference.

Results

Effect of PDE4B knockdown on H9c2 cell viability and cytotoxicity following H/R

Firstly, H9c2 cells were transfected with sh-PDE4B-1/2 or sh-NC, and then PDE4B expression was detected via RT-qPCR and western blotting (Fig. 1A and B). sh-PDE4B-1 and sh-PDE4B-2 significantly decreased PDE4B expression levels compared with sh-NC. Moreover, PDE4B was expressed at significantly higher levels in H9c2 cells exposed to H/R compared with the control group (Fig. 1C and D). In addition, transfection with sh-PDE4B-1/2 significantly decreased the expression of PDE4B under H/R conditions, with sh-PDE4B-1 displaying a higher knockdown effect compared with sh-PDE4B-2 (Fig. 1C and D). Thus, sh-PDE4B-1 was selected for use in subsequent experiments. Compared with the control group, cells exposed to H/R displayed a significant decline in viability, whereas PDE4B interference significantly increased cell viability under H/R conditions (Fig. 1E). Cytotoxicity detection in H9c2 cells demonstrated that PDE4B knockdown significantly decreased H/R-induced upregulated LDH levels (Fig. 1F). Taken together, these results suggested that PDE4B knockdown prevented decreases in cell viability and alleviated the cytotoxicity of H/R-stimulated H9c2 cells.

Figure 1 PDE4B knockdown increases H9c2 cell viability and decreases cytotoxicity following H/R injury. (A) Western blotting and (B) RT-qPCR were performed to detect the transfection efficiency of PDE4B knockdown. (C) Western blotting and (D) RT-qPCR were performed to detect PDE4B expression in H/R-stimulated H9c2 cells following PDE4B knockdown. (E) Cell viability and (F) cytotoxicity in H/R-stimulated H9c2 cells following PDE4B knockdown were assessed using Cell Counting Kit-8 and lactate dehydrogenase assays, respectively. **P<0.01 and ***P<0.001. PDE4B, phosphodiesterase 4B; H/R, hypoxia/reoxygenation; sh, short hairpin RNA; NC, negative control; LDH, lactate dehydrogenase; RT-qPCR, reverse transcription-quantitative PCR.

Effect of PDE4B knockdown on H/R-induced oxidative stress and apoptosis in H9c2 cells

The present study assessed the degrees of oxidative stress and apoptosis of H9c2 cells following H/R, before and after transfection with sh-PDE4B. The results demonstrated that the concentration of MDA was significantly higher (Fig. 2A), whereas the concentration of SOD and the GSH/GSSG ratio were significantly lower (Fig. 2B and C) in cells exposed to H/R compared with those in the control group. However, PDE4B knockdown significantly decreased the concentration of MDA, and significantly elevated the concentration of SOD and the ratio of GSH to GSSG under H/R conditions. In addition, the number of TUNEL+ cells was significantly increased in the H/R group compared with the control group, which was significantly reversed following PDE4B knockdown (Fig. 3A). Consistently, in H/R-stimulated H9c2 cells, anti-apoptotic Bcl-2 expression was significantly decreased, whereas proapoptotic Bax expression was significantly increased, and the expression levels of cleaved-caspase3 and cleaved-caspase9 were significantly increased compared with those in the control group. Notably, these effects were significantly reversed following PDE4B knockdown (Fig. 3B). Collectively, these results suggested that PDE4B knockdown ameliorated H/R-induced oxidative stress and apoptosis in H9c2 cells.

Figure 2 PDE4B knockdown ameliorates H/R-induced oxidative stress in H9c2 cells. Commercial kits were used to detect (A) MDA concentration, (B) SOD concentration and (C) the ratio of GSH to GSSG in H/R-stimulated H9c2 cells following PDE4B knockdown. ***P<0.001. PDE4B, phosphodiesterase 4B; H/R, hypoxia/reoxygenation; MDA, malondialdehyde; SOD, superoxide dismutase; GSH, glutathione; GSSG, glutathione oxidized; sh, short hairpin RNA; NC, negative control.

Figure 3 PDE4B knockdown suppresses H/R-induced H9c2 cell apoptosis. (A) Cell apoptosis was determined by assessing the number of TUNEL+ cells (green fluorescence). (B) Western blotting was performed to detect the expression levels of apoptosis-related proteins. **P<0.01 and ***P<0.001. PDE4B, phosphodiesterase 4B; H/R, hypoxia/reoxygenation; sh, short hairpin RNA; NC, negative control.

Binding interaction between PDE4B and transcription factor JDP2

RT-qPCR and western blotting confirmed that JDP2 expression was upregulated in H9c2 cells following H/R (Fig. 4A and B). JASPAR was used to predict the binding sites between JDP2 and PDE4B (Fig. 4C). This interaction was confirmed by performing dual luciferase reporter and ChIP assays, which demonstrated significantly upregulated luciferase activities in cells co-transfected with PDE4B-wild-type (WT) and Oe-JDP2 compared with those co-transfected with PDE4B-WT and Oe-NC. No apparent changes were observed in the luciferase activity of PDE4B-MUT after co-transfection of Oe-NC or Oe-JDP2 (Fig. 4D). Compared with cells treated with IgG, significantly increased PDE4B expression was observed in cells treated with anti-JDP2 (Fig. 4E). The RT-qPCR results confirmed the successful transfection of Oe-JDP2 in H9c2 cells (Fig. 4F). mRNA level of PDE4B was also enhanced after transfection of Oe-JDP2 (Fig. 4G). Additionally, the results demonstrated that JDP2 overexpression significantly increased PDE4B expression in H9c2 cells exposed to H/R (Fig. 4H). Taken together, these results suggested that the transcription factor JDP2 activated PDE4B in H9c2 cells exposed to H/R.

Figure 4 JDP2 expression is upregulated in H/R-stimulated H9c2 cells, which activates PDE4B expression. (A) Western blotting and (B) RT-qPCR were performed to detect JDP2 expression in H/R-stimulated H9c2 cells. (C) JASPAR database was used to predict the binding sites between JDP2 and PDE4B promoter regions. (D) Dual luciferase reporter assays were performed to detect relative luciferase activities in cells co-transfected with PDE4B-WT or MUT and Oe-NC or Oe-JDP2. (E) Chromatin immunoprecipitation assays were performed to detect PDE4B enrichment in IgG and anti-JDP2 groups. (F) RT-qPCR was performed to assess the transfection efficiency of Oe-JDP2 in H9c2 cells. (G) RT-qPCR was performed to detect PDE4B mRNA expression levels after JDP2 overexpression in H9c2 cells. (H) RT-qPCR was performed to detect PDE4B mRNA expression in H/R-stimulated H9c2 cells following transfection with sh-PDE4B or co-transfection with Oe-JDP2. ***P<0.001. JDP2, c-Jun dimerization protein 2; H/R, hypoxia/reoxygenation; PDE4B, phosphodiesterase 4B; RT-qPCR, reverse transcription-quantitative PCR; WT, wild-type; MUT, mutant; Oe, overexpression; NC, negative control; sh, short hairpin RNA.

Role of JDP2 in PDE4B knockdown-mediated alleviation of H9c2 cell injury following H/R

The present study investigated how the interaction between JDP2 and PDE4B affected H/R-induced H9c2 cell injury. Analysis of cell viability and cytotoxicity under H/R conditions demonstrated a significant decrease in H9c2 cell viability (Fig. 5A) and a significant increase in the level of LDH (Fig. 5B) following co-transfection with sh-PDE4B and Oe-JDP2 compared with that observed in sh-PDE4B + Oe-NC group. Therefore, the results indicated that JDP2 overexpression reversed the effect of PDE4B knockdown on H/R-induced H9c2 cell injury.

Figure 5 JDP2 overexpression partly reverses the effects of PDE4B knockdown on cell viability, cytotoxicity and oxidative stress in H/R-stimulated H9c2 cells. Analysis of (A) cell viability, (B) cytotoxicity, (C) MDA concentration, (D) SOD concentration and (E) GSH/GSSG ratio in H/R-stimulated H9c2 cells following transfection with sh-PDE4B or co-transfection with Oe-JDP2. *P<0.05, **P<0.01 and ***P<0.001. JDP2, c-Jun dimerization protein 2; PDE4B, phosphodiesterase 4B; H/R, hypoxia/reoxygenation; MDA, malondialdehyde; SOD, superoxide dismutase; GSH, glutathione; GSSG, glutathione oxidized; sh, short hairpin RNA; Oe, overexpression; NC, negative control; LDH, lactate dehydrogenase.

Role of JDP2 in PDE4B interference-alleviated oxidative stress and apoptosis of H9c2 cells following H/R

The results demonstrated significantly increased MDA concentration (Fig. 5C), and significantly decreased SOD concentration (Fig. 5D) and GSH/GSSG ratio (Fig. 5E) in H/R-stimulated H9c2 cells co-transfected with sh-PDE4B and Oe-JDP2 compared with those co-transfected with sh-PDE4B and Oe-NC. Notably, JDP overexpression significantly increased the number of TUNEL+ cells (Fig. 6A), decreased Bcl-2 expression, increased Bax expression, and increased the expression levels of cleaved-caspase3 and cleaved-caspase9 following H/R in PDE4B-knockdown H9c2 cells (Fig. 6B). Collectively, these results suggested that JDP2 overexpression reversed the ameliorative effect of PDE4B knockdown on H/R-induced oxidative stress and apoptosis in H9c2 cells.

Figure 6 JDP2 overexpression partly reverses effect of PDE4B knockdown on H/R-induced cell apoptosis. (A) Apoptotic H9c2 cells and (B) the expression of apoptosis-related proteins in H/R-stimulated H9c2 cells following transfection with sh-PDE4B or co-transfection with Oe-JDP2. *P<0.05, **P<0.01 and ***P<0.001. JDP2, c-Jun dimerization protein 2; PDE4B, phosphodiesterase 4B; H/R, hypoxia/reoxygenation; sh, short hairpin RNA; Oe, overexpression; NC, negative control.

Discussion

AMI is a serious consequence of atherosclerotic cardiovascular disease and coronary artery disease. Rapid development of cardiac interventional therapy and bypass surgery has improved the treatment of coronary heart disease (20). However, several issues associated with AMI treatment remain, particularly cardiomyocyte necrosis or apoptosis from prolonged myocardial ischemia (21,22). Myocardial I/R injury is the primary pathological manifestation of coronary artery disease, which continues to increase the global morbidity and mortality of AMI despite therapeutic intervention (23). Cytotoxic oxygen species production, inflammatory response, oxidative stress, and interplay between apoptosis and autophagy are critical participants in I/R-induced cardiomyocyte injury (24-26).

Previous studies have reported the roles of certain genes in the process of AMI (27-29). In the present study, a high expression level of PDE4B expression was observed in H9c2 cardiomyocytes exposed to H/R, indicating the involvement of PDE4B in H/R-induced AMI. Aberrantly high PDE4B expression has been identified as a contributing factor in the pathogenesis of several diseases, including colorectal cancer, neurological conditions and injury, allergy and heart failure (30-33). In the setting of oxygen-glucose deprivation-induced HT22 mouse hippocampal neuronal cell injury, PDE4B overexpression promotes endoplasmic reticulum stress and the release of reactive oxygen species (34). Furthermore, PDE4B knockdown in primary microglia increases LC-3II expression and decreases inflammasome activity (35). The results of the present study demonstrated that PDE4B knockdown increased H9c2 viability and decreased cytotoxicity under H/R conditions. According to a study on acute lung injury, PDE4B knockout could effectively inhibit lipopolysaccharide (LPS)-induced activation of the NF-κB-related inflammatory response and generation of reactive oxygen species in multiple pulmonary cell lines, including epithelial cells (A549), microvascular endothelial cells (pulmonary microvascular endothelial cells) and vascular smooth muscle cells (36). PDE4B has also been reported to be upregulated in patients with acute kidney injury, whereas treatment with rutaecarpine derivative compound-6c exerts an anti-oxidative effect by downregulating PDE4B to protect kidney tubular epithelial cells against oxidative stress and programmed cell death (37). The results of the present study demonstrated that PDE4B knockdown alleviated H/R-induced oxidative stress and apoptosis in H9c2 cardiomyocytes, which was consistent with previous findings.

In the present study, the JASPAR database was used to predict the binding sites between PDE4B promoter and JDP2, a transcription factor that is differentially expressed in patients with MI (38). In view of the critical regulatory role of JDP2 in impaired cardiac function (17), the present study also confirmed that JDP2 was upregulated in H9c2 cells exposed to H/R, and verified the interaction between JDP2 and the PDE4B promoter region. In addition, JDP2 expression is activated by hypoxia in a murine model of MI and is regulated by testis-specific transcript, Y-linked 15-targeted microRNA-455-5p to prevent cardiomyocyte apoptosis and rescue cell migration and invasion (39). In mice with traumatic brain injury, LPS stimulates the expression of JDP2, and JDP2 overexpression aggravates LPS-induced inflammation and apoptosis of mouse astrocytes (40). Consistent with these findings, the results of the present study demonstrated that JDP2 overexpression attenuated the ameliorative effect of PDE4B knockdown on cell viability, cytotoxicity, oxidative stress and apoptosis in H/R-stimulated H9c2 cardiomyocytes.

In conclusion, the results of the present study demonstrated that the transcription factor JDP2 activated PDE4B expression to participate in H/R-induced oxidative and apoptotic injuries of H9c2 cardiomyocytes, partially explaining the pathogenic mechanism underlying myocardial I/R injury. Taken together, the results of the present study suggested that PDE4B and JDP2 may serve as promising biomarkers and therapeutic targets in AMI diagnosis and treatment. However, further in vivo studies are required to confirm the results of the present study.

Acknowledgements

Not applicable.

Funding

Funding: No funding was received.

Availability of data and materials

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Authors' contributions

SL and ZZ were responsible for the conception of the study and the drafting of the manuscript. SL, YC, YJ, TX and XH assisted in obtaining experimental data and analyzed the data. ZZ revised the manuscript. SL and ZZ confirm the authenticity of all the raw data. All authors have read and approved the final manuscript.

Ethics approval and consent to participate

Not applicable.

Patient consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

References