Silencing of Hsa_circ_0055440 Alleviates Hypoxia-Induced Cardiomyocyte Injury by Regulating the MiR-499b-5p/ACSL1 Axis.

Circular RNAs (circRNAs) are a new type of regulatory RNAs, which are involved in various cardiac processes. However, the role of circRNA hsa_circ_0055440 (circ-USP39) in acute myocardial infarction regulation has not been studied yet.This study aims to explore the effect of circ-USP39 on hypoxia-induced cardiomyocyte injury.The head-to-tail splicing of circ-USP39 was verified by agarose gel electrophoresis. AC16 cell viability was detected using 3- (4,5-dimethylthiazol-2-yl) -2,5-diphenyltetrazolium bromide assays. The apoptosis of the AC16 cell was determined by flow cytometry and detection of caspase-3 activity. The levels of creatine kinase-muscle/brain and cTnl were evaluated by specific detection kits. The interactions between miR-499b-5p and circ-USP39 (or acyl-CoA synthetase long-chain family member-1 (ACSL1) ) were verified by luciferase reporter assays.After confirming the circular characteristics of circ-USP39, we further found that the circ-USP39 expression was upregulated in hypoxia-induced cardiomyocytes and the circ-USP39 knockdown facilitated the viability of hypoxia-induced AC16, while suppressing cardiomyocyte apoptosis and injury. Importantly, circ-USP39 negatively regulated miR-499b-5p expression. As a downstream target of miR-499b-5p, ACSL1 partially counteracted the protective effect of circ-USP39 depletion on cardiomyocyte injury.Silencing of circ-USP39 alleviates hypoxia-induced cardiomyocyte injury via the miR-499b-5p/ACSL1 axis.