Total RNA was harvested from heart tissue and H9c2 cells using Qiazol reagent (Qiagen, Valencia, CA, USA), according to the manufacturer's instructions [26 (link)]. The concentration of each sample was measured using a Nanodrop ND-2000 spectrophotometer (Thermo Fisher Scientific Inc., Wilmington, DE, USA). For real-time PCR analysis, total RNA was reverse transcribed with stem-loop primers and the TaqMan MicroRNA Reverse Transcription kit (Applied BioSystems, Foster City, CA, USA), according to the manufacturer's instructions [24 (link)]. Real-time PCR was performed in duplicate using the TaqMan MicroRNA assay kit and TaqMan Universal PCR MasterMix (Applied Biosystems) for miR-34a, miR-92a, miR-21, miR-320, miR-23a, and miR-15b, according to the manufacturer's instructions. Real-time PCR was performed using the LightCycler480 program (Roche) for 40 cycles, (10 seconds each, at 95℃, 60℃, 72℃). Relative miRNA expression levels were normalized using the RNU6B (U6) small non-coding RNA as an endogenous control.