Tissue samples
Peripheral blood samples of 50 patients with chronic heart failure and normal volunteers were collected from the Department of Cardiology, HeXian Memorial Hospital in Guangzhou (Guangzhou, China). All participants have been informed of the details and signed informed consent and all assays have been supported by the Medical Ethics Committee of HeXian Memorial Hospital in Guangzhou.
Cell culture and transfection
Human cardiomyocytes AC16 and HCM were cultured in DMEM/F12 basic medium, supplemented with 10% fetal bovine serum (FBS; Gibco, Gaithersburg, MD, USA) and 100 U/mL penicillin and 100 µg/mL streptomycin. Both were cultured in a 37°C 5% CO2 environment. For the transfection of plasmid, RNA interference (RNAi), miRNA and their controls, lipofectamine 2000 (Invitrogen, California, USA) was taken to carry out, and then the old cell culture medium was replaced with fresh culture medium 6 hours after transfection.
Quantitative PCR analysis
The total RNA of cells and whole blood was extracted using the trizol (Thermo Fisher Scientific, Gaithersburg, MD, USA) method according to the instructions. The concentration and purity of the extracted RNA were tested by NanoDorp. Then 5ug of RNA was reverse transcribed into cDNA and the cDNA was finally diluted to 40ng/µl. SYBR premix EX TAQ II kit (Takara, Dalian, China) was used to perform amplification in the 7500 Real Time PCR Systerm (Applied Biosystems/Life Technologies, Carlsbad, CA, USA) , and the results were calculated when the assay was over. GAPDH serves as an internal reference. All primer sequences were from Shanghai Sangon Biotechnology Co., Ltd. (Shanghai, China).
CCK8
The AC16 and HCM cells that overexpress or interfere with circ_00404141 were seeded into 96-well plates. The cells were cultured for 0h, 24h, 48h and 72h in a cell incubator, and then 10ul of CCK8 reaction solution was added to the cell culture medium at the indicated time and incubated with the cells for 4 hours. Subsequently, the light absorption values (OD value) of cells cultured for different time was measured at a wavelength of 450 nm using a microplate reader (Thermo Fisher Scientific).
Flow cytometry
Apoptosis detection was performed using the Apoptosis Detection Kit (PharMingen, San Jose, CA, USA), AC16 and HCM cells with indicated treatment were trypsinized, washed twice with PBS, and then resuspended in staining solution. Subsequently, Annexin V-FITC and PI were added to the cell resuspension, incubated with the cells in the dark for half an hour, then the cell suspension was centrifuged, the cells were washed twice with PBS, and BD FACSCantoTM II Flow Cytometer (BD Biosciences) was used for apoptosis detection.
Western blot
The cells were lysed by RIPA Lysis Buffer on ice, and the protein concentration was determined by the BCA kit (Thermo Fisher Scientific). Proteins was separated by polyacrylamide gel and transferred to PVDF membrane. The PVDF membrane loaded with protein was blocked by 5% skimmed milk for 1 hour, and then incubated with primary antibody anti-Bax (CST, #5023), anti-Cleaved Caspase-3 (CST, #9661), anti-Bcl-2 (CST, #15071), anti-PTEN (CST, #9188), anti-p-AKT (CST, #4060), anti- AKT (CST, #4685), anti-GAPDH (CST, #5174) at 4°C overnight. Subsequently, the PVDF membrane was washed 3 times with TBST for 5min each time. The washed membrane was incubated with the HRP-conjugated secondary antibody (sigma) for 1 hour, and washed 5 times with TBST for 10 minutes each time. Finally, the PVDF membrane was incubated with the enhanced chemiluminescence reagent (Thermo Fisher Scientific) in a dark room, and then the results were analyzed. ImageJ software was used to perform grayscale analysis.
ELISA
the supernatant of AC16 and HCM cells with indicated treatment was collected, and then the concentrations of IL-6, TNF-α and IL-β in the supernatants were detected using a sandwich ELISA kit (eBioscience, San Diego, California, USA) according to the manufacturer's instructions.
RNA Subcellular Isolation
The RNA Subcellular Isolation Kit (Active Motif, California, USA) was used to separate nuclear and cytoplasmic RNA according to the manufacturer's instructions. The concentration of RNA was measured by NanoDorp, and reverse transcription was performed using the SYBR premix EX TAQ II kit (Takara). The expression level of circ_00404141 was determined by RT-qPCR.
Luciferase reporter assay
AC16 and HCM cells were co-transfected with miR-NC/miR-186 and WT-circ_00404141/mut-circ_00404141 dual luciferase reporter plasmid using Lipofectamine 2000 reagent (Invitrogen). The dual luciferase reporter plasmid was constructed with the pmirGLO vector (Promega, Madison, WI, USA). The cells were incubated at 37°C with 5% CO2 for 48 hours, and then taken out and washed twice with PBS. Subsequently, the luciferase activity was detected by the dual luciferase reporter system (Promega). The binding of miR-186 to PTEN mRNA was also detected by the above method.
Statistical analysis
SPSS 13 software (SPSS Inc., Chicago, IL, USA) was used for statistical analysis of data. The data was presented as mean ± standard deviation (SD). Student’s t-test was implemented to compare the difference between the experimental group and the control group. Two-way ANOVA was performed to compare the differences between different treatment groups at different time points. P<0.05 was considered statistically significant.