title: Protective role of retinoid X receptor in H9c2 cardiomyocytes from hypoxia/reoxygenation injury in rats.
abstract: BACKGROUND
  Retinoid X receptor (RXR) plays a central role in the regulation of intracellular receptor signaling pathways. The activation of RXR has protective effect on H2O2-induced apoptosis of H9c2 ventricular cells in rats. But the protective effect and mechanism of activating RXR in cardiomyocytes against hypoxia/reoxygenation (H/R)-induced oxidative iniury are still unclear.
  
  
  METHODS
  The model of H/R injury was established through hypoxia for 2 hours and reoxygenation for 4 hours in H9c2 cardiomyocytes of rats. 9-cis-retinoic acid (9-cis RA) was obtained as an RXR agonist, and HX531 as an RXR antagonist. Cultured cardiomyocytes were randomly divided into four groups: sham group, H/R group, H/R+9-cis RA -pretreated group (100 nmol/L 9-cis RA), and H/R+9-cis RA+HX531-pretreated group (2.5 μmol/L HX531). The cell viability was measured by MTT, apoptosis rate of cardiomyocytes by flow cytometry analysis, and mitochondrial membrane potential (ΔΨm) by JC-1 fluorescent probe, and protein expressions of Bcl-2, Bax and cleaved caspase-9 with Western blotting. All measurement data were expressed as mean±standard deviation, and analyzed using one-way ANOVA and the Dunnett test. Differences were considered significant when P was <0.05.
  
  
  RESULTS
  Pretreatment with RXR agonist enhanced cell viability, reduced apoptosis ratio, and stabled ΔΨm. Dot blotting experiments showed that under H/R stress conditions, Bcl-2 protein level decreased, while Bax and cleaved caspase-9 were increased. 9-cis RA administration before H/R stress prevented these effects, but the protective effects of activating RXR on cardiomyocytes against H/R induced oxidative injury were abolished when pretreated with RXR pan-antagonist HX531.
  
  
  CONCLUSIONS
  The activation of RXR has protective effects against H/R injury in H9c2 cardiomyocytes of rats through attenuating signaling pathway of mitochondria apoptosis.
authors.affiliation: Department of Cardiology, First AffiliatedHospital of Wenzhou Medical University, Wenzhou 325100, China.
authors.forename: Pei-Ren
authors.initials: PR
authors.lastname: Shan
authors.affiliation: Department of Cardiology, First AffiliatedHospital of Wenzhou Medical University, Wenzhou 325100, China.
authors.forename: Wei-Wei
authors.initials: WW
authors.lastname: Xu
authors.affiliation: Department of Cardiology, First AffiliatedHospital of Wenzhou Medical University, Wenzhou 325100, China.
authors.forename: Zhou-Qing
authors.initials: ZQ
authors.lastname: Huang
authors.affiliation: Department of Cardiology, First AffiliatedHospital of Wenzhou Medical University, Wenzhou 325100, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Pu
authors.affiliation: Department of Cardiology, First AffiliatedHospital of Wenzhou Medical University, Wenzhou 325100, China.
authors.forename: Wei-Jian
authors.initials: WJ
authors.lastname: Huang
keywords: Apoptosis; Cardiomyocytes; Hypoxia reoxygenation; Mitochondria; Retinoid X receptor