title: Phosphate-induced apoptosis in human peritoneal mesothelial cells in vitro.
abstract: BACKGROUND
  It has been demonstrated that phosphate uptake through the type III sodium-dependent phosphate co-transporter, Pit-1, induced apoptosis of aortic vascular smooth muscle cells and endothelial cells in vitro. However, the apoptotic effects of high phosphate (HP) level in human peritoneal mesothelial cells (HPMCs) are not known.
  
  
  METHODS
  To examine whether Pit-1 is expressed in HPMCs, we checked the Western blot assay of immunoreactive Pit-1 and the transcription of Pit-1 by reverse transcriptase PCR. We treated several different phosphate concentrations (1-4 mM) and calcium concentrations (1.8 and 2.8 mM) on HPMCs to assess the effects of concentration. MTT, TUNEL assays, and flow cytometry analysis using Annexin V and propidium iodide were performed to identify cell death and apoptosis. Bax and Bcl-2 by Western blot and caspase-3 activity were evaluated by colorimetric assay. In addition, phosphonoformic acid (PFA) and pan-caspase inhibitor, Z-VAD-FMK, were given to prevent phosphate-induced apoptosis.
  
  
  RESULTS
  Pit-1 expression on HPMCs was demonstrated. Apoptosis in HPMCs significantly increased with a high concentration of phosphate in a dose- and time-dependent manner, and was enhanced in the presence of 2.8 mM calcium. HP concentrations significantly decreased the anti-apoptotic Bcl-2/Bax ratio and increased caspase-3 activity. The treatment with PFA and Z-VAD-FMK prevented cell death by HP.
  
  
  CONCLUSIONS
  Phosphate uptake through Pit-1 induces apoptosis in HPMCs by a caspase-related mechanism.
authors.affiliation: Department of Internal Medicine, Yeungnam University College of Medicine, Daegu, Korea.
authors.forename: Jong-Won
authors.initials: JW
authors.lastname: Park
authors.forename: Ju-Min
authors.initials: JM
authors.lastname: Yook
authors.forename: Hye-Myung
authors.initials: HM
authors.lastname: Ryu
authors.forename: Soon-Youn
authors.initials: SY
authors.lastname: Choi
authors.forename: Masayo
authors.initials: M
authors.lastname: Morishita
authors.forename: Jun-Young
authors.initials: JY
authors.lastname: Do
authors.forename: Sun-Hee
authors.initials: SH
authors.lastname: Park
authors.forename: Chan-Duck
authors.initials: CD
authors.lastname: Kim
authors.forename: Ji-Young
authors.initials: JY
authors.lastname: Choi
authors.forename: Ho-Young
authors.initials: HY
authors.lastname: Chung
authors.forename: Yong-Lim
authors.initials: YL
authors.lastname: Kim
mesh_terms: D017304:Annexin A5 / Q000378:metabolism; D017209:Apoptosis / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D053148:Caspase 3 / Q000378:metabolism*; D002470:Cell Survival; D002478:Cells, Cultured; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism; D006801:Humans; D010537:Peritoneum / Q000166:cytology / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism*; D011419:Propidium / Q000378:metabolism; D015398:Signal Transduction; D050611:Sodium-Phosphate Cotransporter Proteins, Type III / Q000378:metabolism*; D051028:bcl-2-Associated X Protein / Q000378:metabolism
chemical_list: D017304:Annexin A5; D010710:Phosphates; D050611:Sodium-Phosphate Cotransporter Proteins, Type III; D051028:bcl-2-Associated X Protein; D011419:Propidium; D053148:Caspase 3; D002118:Calcium