Obstructive uropathy in the mouse: role of osteopontin in interstitial fibrosis and apoptosis.
BACKGROUND
Osteopontin is a macrophage adhesive protein that is expressed by renal tubules in tubulointerstitial disease.


METHODS
To investigate the function of OPN, we induced tubulointerstitial disease in OPN null mutant (OPN-/-) and wild-type (OPN+/+) mice by unilateral ureteral ligation. Tissue was analyzed for macrophages (ED-1), types I and IV collagen deposition, TGF-beta expression, and for tubular and interstitial cell apoptosis.


RESULTS
Obstructed kidneys from both OPN-/- and OPN+/+ mice developed hydronephrosis, tubular atrophy, interstitial inflammation and fibrosis. OPN was absent in OPN-/- kidneys but was increased in obstructed OPN+/+ kidneys. Macrophage influx, measured by computer-assisted quantitative immunostaining, was less in OPN-/- mice compared to OPN+/+ mice at day 4 (threefold, P < 0.02), day 7 (fivefold, P < 0.02), but not at day 14. Interstitial deposition of types I and IV collagen were also two- to fourfold less in obstructed OPN-/- kidneys (P < 0.02). There was also a reduction of TGF-beta mRNA expression in the interstitium at day 7 (by in situ hybridization) and a near significant 34% reduction in cortical TGF-beta activity (P = 0.06) compared to obstructed OPN+/+ kidneys at day 14. Obstructed kidneys from OPN-/- mice also had more interstitial and tubular apoptotic cells (TUNEL assay) compared to obstructed OPN+/+ mice at all time points. The ability of OPN to act as a cell survival factor was also documented by showing that the apoptosis of serum-starved NRK52E renal epithelial cells was markedly enhanced in the presence of neutralizing anti-OPN antibody.


CONCLUSIONS
OPN mediates early interstitial macrophage influx and interstitial fibrosis in unilateral ureteral obstruction. OPN may also function as a survival factor for renal tubulointerstitial cells.
Ophascharoensuk
V
V
Division of Nephrology, Department of Medicine, University of Washington, Seattle 98195, USA.
Giachelli
C M
CM
Gordon
K
K
Hughes
J
J
Pichler
R
R
Brown
P
P
Liaw
L
L
Schmidt
R
R
Shankland
S J
SJ
Alpers
C E
CE
Couser
W G
WG
Johnson
R J
RJ
D000818:Animals; D017209:Apoptosis / Q000276:immunology*; D002470:Cell Survival / Q000502:physiology; D003094:Collagen / Q000032:analysis / Q000378:metabolism; D004195:Disease Models, Animal; D004847:Epithelial Cells / Q000737:chemistry / Q000166:cytology / Q000378:metabolism; D005260:Female; D005355:Fibrosis; D017403:In Situ Hybridization; D020287:In Situ Nick-End Labeling; D007684:Kidney Tubules / Q000737:chemistry / Q000378:metabolism / Q000502:physiology; D008264:Macrophages / Q000276:immunology; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D053495:Osteopontin; D010641:Phenotype; D012333:RNA, Messenger / Q000032:analysis; D012795:Sialoglycoproteins / Q000235:genetics* / Q000276:immunology; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D014517:Ureteral Obstruction / Q000235:genetics* / Q000276:immunology / Q000473:pathology*
D012333:RNA, Messenger; D012795:Sialoglycoproteins; C506896:Spp1 protein, mouse; D016212:Transforming Growth Factor beta; D053495:Osteopontin; D003094:Collagen