title: Calcium Overload Accelerates Phosphate-Induced Vascular Calcification Via Pit-1, but not the Calcium-Sensing Receptor.
abstract: OBJECTIVE
  Vascular calcification (VC) is a risk factor of cardiovascular and all-cause mortality in patients with chronic kidney disease (CKD). CKD-mineral and bone metabolism disorder is an important problem in patients with renal failure. Abnormal levels of serum phosphate and calcium affect CKD-mineral and bone metabolism disorder and contribute to bone disease, VC, and cardiovascular disease. Hypercalcemia is a contributing factor in progression of VC in patients with CKD. However, the mechanisms of how calcium promotes intracellular calcification are still unclear. This study aimed to examine the mechanisms underlying calcium-induced calcification in a rat aortic tissue culture model.
  
  
  METHODS
  Aortic segments from 7-week-old male Sprague-Dawley rats were cultured in serum-supplemented medium for 10 days. We added high calcium (HiCa; calcium 3.0 mM) to high phosphate (HPi; phosphate 3.8 mM) medium to accelerate phosphate and calcium-induced VC. We used phosphonoformic acid and the calcimimetic R-568 to determine whether the mechanism of calcification involves Pit-1 or the calcium-sensing receptor.
  
  
  RESULTS
  Medial VC was significantly augmented by HPi+HiCa medium compared with HPi alone (300%, p＜0.05), and was associated with upregulation of Pit-1 protein. Pit-1 protein concentrations in HPi+HiCa medium were greater than those in HPi medium. Phosphonoformic acid completely negated the augmentation of medial VC induced by HPi+HiCa. R-568 had no additive direct effect on medial VC.
  
  
  CONCLUSIONS
  These results indicated that exposure to HPi+HiCa accelerates medial VC, and this is mediated through Pit-1, not the calcium-sensing receptor.
authors.affiliation: Division of Nephrology, Department of Internal Medicine, Wakayama Medical University.
authors.forename: Asuka
authors.initials: A
authors.lastname: Masumoto
authors.affiliation: Division of Nephrology, Department of Internal Medicine, Wakayama Medical University.
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Sonou
authors.affiliation: Division of Nephrology, Department of Internal Medicine, Wakayama Medical University.
authors.forename: Masaki
authors.initials: M
authors.lastname: Ohya
authors.affiliation: Division of Nephrology, Department of Internal Medicine, Wakayama Medical University.
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Yashiro
authors.affiliation: Division of Nephrology, Department of Internal Medicine, Wakayama Medical University.
authors.forename: Yuri
authors.initials: Y
authors.lastname: Nakashima
authors.affiliation: Division of Nephrology, Department of Internal Medicine, Wakayama Medical University.
authors.forename: Kouji
authors.initials: K
authors.lastname: Okuda
authors.affiliation: Division of Nephrology, Department of Internal Medicine, Wakayama Medical University.
authors.forename: Yuko
authors.initials: Y
authors.lastname: Iwashita
authors.affiliation: Division of Nephrology, Department of Internal Medicine, Wakayama Medical University.
authors.forename: Toru
authors.initials: T
authors.lastname: Mima
authors.affiliation: Division of Nephrology, Department of Internal Medicine, Wakayama Medical University.
authors.forename: Shigeo
authors.initials: S
authors.lastname: Negi
authors.affiliation: Division of Nephrology, Department of Internal Medicine, Wakayama Medical University.
authors.forename: Takashi
authors.initials: T
authors.lastname: Shigematsu
mesh_terms: D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000473:pathology*; D002118:Calcium / Q000009:adverse effects*; D018450:Disease Progression; D008297:Male; D010710:Phosphates / Q000009:adverse effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D044169:Receptors, Calcium-Sensing / Q000378:metabolism*; D051436:Renal Insufficiency, Chronic / Q000503:physiopathology*; D050817:Transcription Factor Pit-1 / Q000378:metabolism*; D061205:Vascular Calcification / Q000139:chemically induced / Q000378:metabolism / Q000473:pathology*
chemical_list: D010710:Phosphates; D044169:Receptors, Calcium-Sensing; D050817:Transcription Factor Pit-1; D002118:Calcium
keywords: Calcium; Calcium-sensing receptor; Mönckeberg's arteriosclerosis; Phosphate; Pit-1