ABSTRACT
AIM:To investigate the effect of activation of retinoid X receptor (RXR) on transforming growth factor β1 (TGF-β1) induced collagen synthesis under hypoxic environment in rat cardiac fibroblasts (CFs) and underlying molecular mechanisms .METHODS: CFs were cultured using myocardial tissue with dry method .Hypoxic environment was established for CFs by continuous nitrogen supplement .Type I and type III collagens in supernatants were detected by ELISA.Nuclear and cytoplasmic extractions were prepared using NE-PER nuclear and cytoplasmic extraction reagents .The protein levels of Smad2 and p-Smad2 were determined by Western blot and immunocytochemical staining .RESULTS:Un-der hypoxic condition , TGF-β1 (0.01~10 μg/L) increased the synthesis of type I and type III collagens in a dose-de-pendent manner in the CFs .At the concentration of 5μg/L, the synthesis of collagen I and III was significantly increased as compared with control group (P<0.01).RXR agonist 9-cis-retinoic acid (9-cis-RA;10 -9 ~10 -6 mol/L) decreased TGF-β1 (5μg/L)-induced synthesis of type I and III collagens in a dose-dependent manner in the CFs under hypoxic con-dition.The synthesis of type I and type III collagens was significantly inhibited by 9-cis-RA (P<0.01).Smad2 inhibitor ( 20 nmol/L) showed similar inhibitory effect on the synthesis of type I and III collagens induced by TGF -β1 under hypoxic condition.Compared with TGF-β1 intervention group, the cytoplasmic level of p-Smad2 in the CFs was significantly in-creased in TGF-β1+9-cis-RA group, but the nuclear p-Smad2 level was significantly decreased (P<0.05).CONCLU-SION:Retinoid X receptor agonist 9-cis-RA inhibits TGF-β1-induced synthesis of type I and type III collagens in the CFs by repressing p-Smad2 nuclear translocation under hypoxic condition .