title: Glucose degradation products downregulate ZO-1 expression in human peritoneal mesothelial cells: the role of VEGF.
abstract: BACKGROUND
  Glucose degradation products (GDPs) are formed during heat sterilization of peritoneal dialysis fluid and, to a lesser extent, during their prolonged storage. In vitro studies have demonstrated that GDPs impair functions of peritoneal mesothelial cells, including proliferation, viability and cytokine release. In the present study, we studied the acute effect of GDPs on the expression of tight junction-associated protein, zonula occludens protein 1 (ZO-1), in human peritoneal mesothelial cells (HPMC). The role of the vascular endothelial growth factor (VEGF) induced by GDPs in the expression of ZO-1 was also examined.
  
  
  METHODS
  HPMC were cultured with GDPs, including 2-furaldehyde (FurA), methylglyoxal (M-Glx) and 3,4-dideoxyglucosone-3-ene (3,4-DGE). The expression of ZO-1 and the synthesis of VEGF were examined. To define the role of VEGF on the regulation of ZO-1 expression, HPMC were cultured with GDPs in the presence or absence of neutralizing antibody to VEGF. The signal pathways involved in VEGF synthesis induced by GDPs were also characterized.
  
  
  RESULTS
  ZO-1 expression in HPMC was downregulated in a time- and dose-dependent manner following culture with subtoxic concentrations of GDPs (FurA, M-Glx and 3,4-DGE). All three GDPs increased VEGF synthesis in HPMC. Exogenous VEGF downregulated the expression of ZO-1 and neutralizing anti-VEGF antibody reversed the effect of GDPs on ZO-1 expression in HPMC, suggesting the action of GDPs on ZO-1 expression was mediated by VEGF. All three GDPs activated the p42/p44 mitogen-activated protein kinase (MAPK) and protein kinase C (PKC) signal transduction pathways. The GDP-induced VEGF and transforming growth factor (TGF)-beta synthesis in HPMC was partially reduced by either the p42/p44 MAPK inhibitor (PD98059) or the PKC inhibitor (staurosporine). More importantly, the VEGF and TGF-beta synthesis induced by GDPs in HPMC was completely blocked by synergistic action of both inhibitors.
  
  
  CONCLUSIONS
  We have demonstrated that short-term exposure to GDPs downregulates ZO-1 expression in HPMC through the generation of VEGF. Our study provides evidence that GDPs can directly induce VEGF and TGF-beta production in HPMC through the activation of p42/44 MAPK and PKC signal transduction pathways.
authors.affiliation: Department of Medicine, University of Hong Kong, Room 409, Queen Mary Hospital, Pokfulam Road, Hong Kong.
authors.forename: Joseph C K
authors.initials: JC
authors.lastname: Leung
authors.forename: Loretta Y Y
authors.initials: LY
authors.lastname: Chan
authors.forename: Felix F K
authors.initials: FF
authors.lastname: Li
authors.forename: Sydney C W
authors.initials: SC
authors.lastname: Tang
authors.forename: Kwok Wa
authors.initials: KW
authors.lastname: Chan
authors.forename: Tak Mao
authors.initials: TM
authors.lastname: Chan
authors.forename: Man Fai
authors.initials: MF
authors.lastname: Lam
authors.forename: Anders
authors.initials: A
authors.lastname: Wieslander
authors.forename: Kar Neng
authors.initials: KN
authors.lastname: Lai
mesh_terms: D000447:Aldehydes / Q000494:pharmacology*; D018929:Cell Culture Techniques; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D005947:Glucose / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism*; D009852:Omentum / Q000166:cytology / Q000187:drug effects*; D010750:Phosphoproteins / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D042461:Vascular Endothelial Growth Factor A / Q000502:physiology*; D062826:Zonula Occludens-1 Protein
chemical_list: D000447:Aldehydes; D008565:Membrane Proteins; D010750:Phosphoproteins; D012333:RNA, Messenger; C569042:TJP1 protein, human; C467484:VEGFA protein, human; D042461:Vascular Endothelial Growth Factor A; D062826:Zonula Occludens-1 Protein; D005947:Glucose