Silencing hsa_circ_0049271 attenuates hypoxia-reoxygenation (H/R)-induced myocardial cell injury via the miR-17-3p/FZD4 signaling axis.

Background: This study sought to explore the role and molecular mechanism of circ_0049271 in hypoxia-reoxygenation (H/R)-induced cardiomyocyte injury. Methods: Significantly upregulated circular ribonucleic acids (circRNAs) in Gene Expression Omnibus (GEO) data sets were identified using a Venn diagram. A H9c2 (rat cardiomyocytes) cell model of acute myocardial infarction (AMI) was induced by 1% H/R. Quantitative reverse transcription-polymerase chain reaction was used to detect the expression levels of circ_0049271, miR-17-3p, and FZD4 in clinical blood samples and cells, and Cell Counting Kit-8 (CCK-8) was used to determine the proliferation rate of the cells in each group. Next, flow cytometry and Western blot were used to evaluate cell apoptosis. Biochemical tests and enzyme-linked immunosorbent assays (ELISAs) were then used to determine the activities/levels of the cell damage markers [i.e., creatine kinase (CK) and lactate dehydrogenase (LDH)], oxidative stress substances [i.e., malondialdehyde (MDA), reactive oxygen species (ROS), and superoxide dismutase (SOD)], and inflammatory factors [i.e., interleukin (IL)-1β, IL-6, and IL-8]. In addition, intermolecular interactions were verified using dual-luciferase reporter and RNA pull-down experiments. Results: Circ_0049271 was significantly upregulated in both the blood of the AMI patients and the H/R-induced H9c2 cells. The knockdown of circ_0049271 increased the cell proliferation rate, decreased the apoptosis rate, inhibited oxidative stress (ROS and MDA were upregulated, and SOD was downregulated) and inflammatory responses (IL-1, IL-6, and IL-8 were downregulated), and relieved cell damage. However, the overexpression of circ_0049271 promoted H/R-induced H9c2 cell damage. Further experiments showed that miR-17-3p was a target of circ_0049271, and miR-17-3p was negatively correlated with circ_0049271 in the AMI blood samples. Additionally, miR-17-3p was found to target FZD4. A further exploration also revealed that miR-17-3p knockdown or FZD4 overexpression reversed the effects of si-circ_0049271 on the H/R-induced H9c2 cells; that is, miR-17-3p knockdown or FZD4 overexpression promoted H/R-induced injury in the H9c2 cells. Conclusions: Circ_0049271 promoted cellular function damage (e.g., proliferation inhibition, apoptosis, oxidative stress, and inflammation) in H/R-induced H9c2 cardiomyocytes via the miR-17-3p/FZD4 signaling axis.