Gene expression changes during hyperoxaluria and calcium oxalate crystal deposition (Khan, Thamilselban, Peck)

We have been investigating the pathogenesis of calcium oxalate nephrolithiasis, a common urological disorder with lifetime prevalence rate at approximately 5% in females and 12% in men. Increased urinary excretion of oxalate is a major risk factor. Interaction between epithelial cells lining the renal tubules and high levels of oxalate and calcium oxalate crystals plays a significant role in the development of the disease. To induce hyperoxaluria in animals we give them 0.75% ethylene glycol solution to drink. After 3 days the animals become hyperoxaluric and have calcium oxalate crystals in their urine. After 2 weeks the animals become nephrolithic with crystals visibly deposited in the kidney tissue. In previous studies we have seen an increase in the expression of osteopontin (Opn) and bikunin (Bik) in the kidney tissue following exposure to oxalate and calcium oxalate crystals. Immunostaining of the kidney sections showed an increase in the staining for Opn and Bik. This confirmed the results witnessed when the urine from the treated animals was analyzed by SDS-polyacrylamide gels (SDS-Page) and Western blotting which showed an increase in both of these proteins. Quantitative RT-PCR also revealed an increase of Opn and Bik mRNA in the ethylene glycol treated animals over normal control animals, suggesting that the protein increases are attributable to direct increases in mRNA production in the kidney itself. In situ hybridization of the kidney sections also confirmed the PCR results and showed the specific sites of production of OPN and Bik in the kidney. These observations indicate that hyperoxaluria does induce increases in OPN and Bik mRNA expression, production of these proteins and their excretion in the kidney. Exposure of renal epithelial cells in culture to oxalate and calcium oxalate crystals also induces a production of these macromolecules. In addition, a variety of other genes such as c-myc are also turned on. Therefore we propose to further study the effects that oxalate and calcium oxalate crystals might have on other genes in the kidney. We will induce CaOx nephrolithiasis in mice and examine the kidneys for changes in gene expression during hyperoxaluria and calcium oxalate crystal deposition

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