title: Regulation of proximal tubular osteopontin in experimental hydronephrosis in the rat.
abstract: BACKGROUND
  Osteopontin is a tubular-derived glycoprotein with macrophage chemoattractant properties. Our previous observations demonstrate that osteopontin is involved in the accumulation of macrophages within the renal cortex of rats following unilateral ureteral obstruction (UUO).
  
  
  METHODS
  The present study performed Northern and Western blot analyses of isolated proximal tubular cells exposed to exogenous angiotensin II, and cultured rat proximal tubular cells subjected to one hour of cyclic mechanical stretch, which provided insight into mechanisms involving the proximal tubular renin-angiotensin system in the increased expression of cortical osteopontin following hydronephrosis.
  
  
  RESULTS
  In situ hybridization, using a 35S-labeled antisense riboprobe, showed osteopontin mRNA transcription localized to the cortical tubules of the obstructed kidney. Freshly isolated proximal tubules incubated with angiotensin II (10-5 M) for one hour had increased osteopontin mRNA and protein expression by Northern and Western blot analyses, respectively. Pre-treatment of proximal tubules with losartan (10-5 M) for one hour prior to the addition of exogenous angiotensin II (10-5 M) decreased osteopontin mRNA and protein expression. Rat proximal tubule cells subjected to cyclic mechanical stretch for one hour exhibited a 2.1-fold increment in osteopontin mRNA levels, which was normalized following pre-treatment with losartan.
  
  
  CONCLUSIONS
  This study provides evidence that angiotensin II, produced by the proximal tubule in the obstructed kidney as a result of mechanical injury, possibly mechanical stretch, may stimulate angiotensin II type I receptor activation, leading to up-regulated osteopontin expression and secretion by the proximal tubule, thereby facilitating macrophage recruitment into the renal interstitium.
authors.affiliation: Departments of Medicine and Cellular and Molecular Physiology and Department of Surgery, Milton S. Hershey Medical Center, Hershey, Pennsylvania, USA.
authors.forename: J R
authors.initials: JR
authors.lastname: Diamond
authors.forename: R
authors.initials: R
authors.lastname: Kreisberg
authors.forename: R
authors.initials: R
authors.lastname: Evans
authors.forename: T A
authors.initials: TA
authors.lastname: Nguyen
authors.forename: S D
authors.initials: SD
authors.lastname: Ricardo
mesh_terms: D000818:Animals; D015152:Blotting, Northern; D005786:Gene Expression Regulation; D006869:Hydronephrosis / Q000378:metabolism*; D007150:Immunohistochemistry; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008297:Male; D053495:Osteopontin; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D012084:Renin-Angiotensin System / Q000502:physiology; D012795:Sialoglycoproteins / Q000032:analysis / Q000235:genetics*; D014517:Ureteral Obstruction / Q000378:metabolism
chemical_list: D012333:RNA, Messenger; D012795:Sialoglycoproteins; C506897:Spp1 protein, rat; D053495:Osteopontin