CircRERE promotes myocardial ischemia/reperfusion injury by increasing UHRF1 mRNA decay through targeting PUM2 to reduce Drp1 promoter methylation

Abstract Background: Myocardial ischemia/reperfusion (I/R) injury contributes significantly to cardiac dysfunction following myocardial infarction, mainly due to excessive oxidative stress and mitochondrial injury. Despite advances in reperfusion therapies, secondary injuries remain a challenge, necessitating deeper insight into the molecular mechanisms underlying I/R injury. In the present study, we aim to investigate the roles of circular ribonucleic acid (circRNA) RERE (circRERE) in myocardial I/R injury. Methods: Hypoxia/reperfusion (H/R) cells and an I/R mouse model were used. Cell apoptosis was assessed using flow cytometry and terminal deoxynucleotidyl transferase dUTP nick-end labeling staining. The cell reactive oxygen species (ROS) and secreted lactate dehydrogenase (LDH) levels were measured. Quantitative reverse transcription polymerase chain reaction, western blot, immunofluorescence staining, and immunohistochemistry were used to assess mRNA and protein expression. MitoTracker and electron microscopy were used to examine mitochondrial morphology. The interactions between circRERE, Pumilio 2 (PUM2), ubiquitin-like with plant homeodomain and ring finger domain 1 (UHRF1), and dynamin-related protein 1 (Drp1) were validated by RNA immunoprecipitation, RNA pull-down, and/or chromatin immunoprecipitation assays. I/R-induced pathological changes in cardiac tissues were evaluated by Hematoxylin and Eosin (H&E) and 2,3,5-triphenyltetrazolium chloride (TTC) staining. Statistical analyses were performed using one-way analysis of variance and Student’s t-test, with P <0.05 considered statistically significant difference. Results: CircRERE expression was significantly elevated during I/R injury (about a 3.1-fold increase, P <0.001). CircRERE knockdown reduced ROS levels by 39.5% (P <0.01), improved mitochondrial membrane potential (P <0.01), and decreased apoptotic rates (P <0.001). Mechanistically, circRERE promoted UHRF1 mRNA decay by interacting with PUM2, leading to reduced Drp1 promoter methylation, increased Drp1 expression, and subsequent mitochondrial fission and dysfunction. In vivo, circRERE knockdown significantly reduced infarct size by 24.27% (P <0.001), improved cardiac tissue morphology, and restored mitochondrial homeostasis. Conclusions: CircRERE exacerbated myocardial I/R injury by promoting UHRF1 mRNA degradation and mitochondrial dysfunction. Targeting the circRERE/UHRF1/Drp1 axis may represent a novel therapeutic strategy against myocardial I/R injury.