title: Panax quinquefolium saponin attenuates cardiomyocyte apoptosis induced by thapsigargin through inhibition of endoplasmic reticulum stress.
abstract: BACKGROUND
  Endoplasmic reticulum (ER) stress-related apoptosis is involved in the pathophysiology of many cardiovascular diseases, and Panax quinquefolium saponin (PQS) is able to inhibit excessive ER stress-related apoptosis of cardiomyocytes following hypoxia/reoxygenation and myocardial infarction. However, the pathway by which PQS inhibits the ER stress-related apoptosis is not well understood. To further investigate the protective effect of PQS against ER stress-related apoptosis, primary cultured cardiomyocytes were stimulated with thapsigargin (TG), which is widely used to model cellular ER stress, and it could induce apoptotic cell death in sufficient concentration.
  
  
  METHODS
  Primary cultured cardiomyocytes from neonatal rats were exposed to TG (1 µmol/L) treatment for 24 h, following PQS pre-treatment (160 µg/mL) for 24 h or pre-treatment with small interfering RNA directed against protein kinase-like endoplasmic reticulum kinase (Si-PERK) for 6 h. The viability and apoptosis rate of cardiomyocytes were detected by cell counting kit-8 and flow cytometry respectively. ER stress-related protein expression, such as glucose-regulated protein 78 (GRP78), calreticulin, PERK, eukaryotic translation initiation factor 2α (eIF2α), activating transcription factor 4 (ATF4), and C/EBP homologous protein (CHOP) were assayed by western blotting.
  
  
  RESULTS
  Both PQS pre-treatment and PERK knockdown remarkably inhibited the cardiomyocyte apoptosis induced by TG, increased cell viability, decreased phosphorylation of both PERK and eIF2α, and decreased protein levels of both ATF4 and CHOP. There was no statistically significant difference between PQS pre-treatment and PERK knockdown in the cardioprotective effect.
  
  
  CONCLUSIONS
  Our data indicate that the PERK-eIF2α-ATF4-CHOP pathway of ER stress is involved in the apoptosis induced by TG, and PQS might prevent TG-induced cardiomyocyte apoptosis through a mechanism involving the suppression of this pathway. These findings provide novel data regarding the molecular mechanisms by which PQS inhibits cardiomyocyte apoptosis.
authors.affiliation: Department of Pathophysiology, Chinese PLA General Hospital, Beijing, China ; Xiyuan Hospital, China Academy of Chinese Medical Sciences, Beijing, China.
authors.forename: Mi
authors.initials: M
authors.lastname: Liu
authors.affiliation: Xiyuan Hospital, China Academy of Chinese Medical Sciences, Beijing, China.
authors.forename: Mei
authors.initials: M
authors.lastname: Xue
authors.affiliation: Department of Pathophysiology, Chinese PLA General Hospital, Beijing, China.
authors.forename: Xiao-Reng
authors.initials: XR
authors.lastname: Wang
authors.affiliation: Department of Pathophysiology, Chinese PLA General Hospital, Beijing, China.
authors.forename: Tian-Qi
authors.initials: TQ
authors.lastname: Tao
authors.affiliation: Department of Pathophysiology, Chinese PLA General Hospital, Beijing, China.
authors.forename: Fei-Fei
authors.initials: FF
authors.lastname: Xu
authors.affiliation: Department of Pathophysiology, Chinese PLA General Hospital, Beijing, China.
authors.forename: Xiu-Hua
authors.initials: XH
authors.lastname: Liu
authors.affiliation: Xiyuan Hospital, China Academy of Chinese Medical Sciences, Beijing, China.
authors.forename: Da-Zhuo
authors.initials: DZ
authors.lastname: Shi
keywords: Cardiomyocyte apoptosis; Endoplasmic reticulum stress; Panax quinquefolium saponin; Thapsigargin