Osteopontin mRNA in the kidney on an experimental rat model of renal stone formation without renal failure.

We had sequenced a cDNA of calcium oxalate urinary stone protein extracted with 0.1 M EDTA. cDNA sequences showed complete homology between urinary stone protein and human osteopontin (OPN, bone sialoprotein I). In the present study, we investigated the expression of OPN mRNA in the rat kidney in an experimental model of renal stone formation using glyoxylic acid and 1,25-dihydroxyvitamin D3 (D3). In the renal stone formation model with and without renal failure, OPN mRNA was shown to be localized by in situ hybridization using an OPN cRNA probe mainly in the distal convoluted tubule of the kidney, and was enhanced compared with the normal control which was sporadically positive. By Northern blot analysis, the expression of OPN mRNA was shown to be increased by about 5.2-fold in the renal stone formation model and 2.3-fold in D3-administered rats compared with controls. However, no change in the expression of OPN mRNA was observed in an acute renal failure model induced by gentamicin or in rats administered glycoxylic acid alone. Therefore, the promotion of OPN mRNA expression was intrinsic to this stone formation model, and not secondary to acute renal failure because of obstruction by microcrystals in the renal tubules or gentamicin.