title: Endoplasmic reticulum stress is involved in podocyte apoptosis induced by saturated fatty acid palmitate.
abstract: BACKGROUND
  Podocyte apoptosis is recently indicated as an early phenomenon of diabetic nephropathy. Pancreatic β-cells exposed to saturated free fatty acid palmitate undergo irreversible endoplasmic reticulum (ER) stress and consequent apoptosis, contributing to the onset of diabetes. We hypothesized that palmitate could induce podocyte apoptosis via ER stress, which initiates or aggravates proteinuria in diabetic nephropathy.
  
  
  METHODS
  Podocyte apoptosis was detected by 4',6-diamidio-2-phenylindole (DAPI) stained apoptotic cell count and Annexin V-PI stain. The expressions of ER molecule chaperone glucose-regulated protein 78 (GRP78), indicators of ER-associated apoptosis C/EBP homologous protein (CHOP), and Bcl-2 were assayed by Western blotting and real-time PCR. GRP78 and synaptopodin were co-localized by immunofluorescence stain.
  
  
  RESULTS
  Palmitate significantly increased the percentage of cultured apoptotic murine podocytes time-dependently when loading 0.75 mmol/L (10 hours, 13 hours, and 15 hours compared with 0 hour, P < 0.001) and dose-dependently when loading palmitate ranging from 0.25 to 1.00 mmol/L for 15 hours (compared to control, P < 0.001). Palmitate time-dependently and dose-dependently increased the protein expression of GRP78 and CHOP, and decreased that of Bcl-2. Palmitate loading ranging from 0.5 to 1.0 mmol/L for 12 hours significantly increased mRNA of GRP78 and CHOP, and decreased that of Bcl-2 compared to control (P < 0.001), with the maximum concentration being 0.75 mmol/L. Palmitate 0.5 mmol/L loading for 3 hours, 8 hours, and 12 hours significantly increased mRNA of GRP78 and CHOP, and decreased that of Bcl-2 compared to 0 hour (P < 0.001), with the maximum effect at 3 hours. Confocal microscopy demonstrated that GRP78 expression was significantly increased when exposed to 0.5 mmol/L of palmitate for 8 hours compared to control.
  
  
  CONCLUSIONS
  Palmitate could induce podocyte apoptosis via ER stress, suggesting podocyte apoptosis and consequent proteinuria caused by lipotoxic free fatty acid could be ameliorated by relief of ER stress.
authors.affiliation: Division of Nephrology, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences, Beijing 100730, China.
authors.forename: Jian-Ling
authors.initials: JL
authors.lastname: Tao
authors.forename: Yu-Bing
authors.initials: YB
authors.lastname: Wen
authors.forename: Bing-Yang
authors.initials: BY
authors.lastname: Shi
authors.forename: Hong
authors.initials: H
authors.lastname: Zhang
authors.forename: Xiong-Zhong
authors.initials: XZ
authors.lastname: Ruan
authors.forename: Hang
authors.initials: H
authors.lastname: Li
authors.forename: Xue-Mei
authors.initials: XM
authors.lastname: Li
authors.forename: Wen-Ji
authors.initials: WJ
authors.lastname: Dong
authors.forename: Xue-Wang
authors.initials: XW
authors.lastname: Li
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D002478:Cells, Cultured; D000091342:Endoplasmic Reticulum Chaperone BiP; D059865:Endoplasmic Reticulum Stress / Q000502:physiology*; D006360:Heat-Shock Proteins / Q000032:analysis / Q000502:physiology; D006801:Humans; D007333:Insulin Resistance; D019308:Palmitic Acid / Q000494:pharmacology*; D050199:Podocytes / Q000187:drug effects* / Q000473:pathology
chemical_list: D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; D019308:Palmitic Acid