Osteopontin regulates adhesion of calcium oxalate crystals to renal epithelial cells.
BACKGROUND
The association of calcium crystals with renal tubular cells is an important factor during the formation of urinary stones. We previously reported the strong expression of osteopontin (OPN) on renal tubular cells in the stone-forming kidney, suggesting that OPN plays a role in the crystal-cell interaction. In the present study, we examined the biological consequences of inhibiting OPN expression at the translational level on the formation and adhesion of crystals.


METHODS
We synthesized antisense OPN expression vector (pTet-OPNas) using the tetracycline-regulated expression system. The pTet-OPNas was constructed using a mouse OPN cDNA sequence in an inverted (antisense) orientation. Two clones (NRK-52E/ASs) were identified by transfection of pTet-OPNas into NRK-52E cells and they showed a marked reduction of OPN synthesis in the absence of tetracycline. Calcium oxalate (CaOx) crystal suspension was spread homogeneously on top of the NRK-52E cells. After incubation, the association of CaOx crystals and cells was visualized by scanning electron microscopy.


RESULTS
Intact NRK-52E cells, NRK-52E cells transfected with empty vector and tetracycline-treated antisense clones (NRK-52E/ASs), under identical conditions, were associated with CaOx crystals. In contrast, the expression of antisense OPN prevented the association of CaOx crystals with NRK-52E cells.


CONCLUSIONS
Osteopontin plays a crucial role in the adhesion process of CaOx crystals to renal tubular cells in stone formation.
Yasui
Takahiro
T
Department of Urology, Nagoya City University Medical School, Mizuho-cho, Mizuho-ku, Japan. yasui@med.nagoya-cu.ac.jp
Fujita
Keiji
K
Asai
Kiyofumi
K
Kohri
Kenjiro
K
D000818:Animals; D002129:Calcium Oxalate; D002448:Cell Adhesion / Q000502:physiology; D002478:Cells, Cultured; D003460:Crystallization; D004847:Epithelial Cells / Q000502:physiology*; D005822:Genetic Vectors; D007684:Kidney Tubules / Q000502:physiology*; D053495:Osteopontin; D016372:RNA, Antisense; D051381:Rats; D012795:Sialoglycoproteins / Q000235:genetics / Q000502:physiology*; D014162:Transfection; D014545:Urinary Calculi / Q000209:etiology
D016372:RNA, Antisense; D012795:Sialoglycoproteins; C506896:Spp1 protein, mouse; C506897:Spp1 protein, rat; D053495:Osteopontin; D002129:Calcium Oxalate