BINDING OF CALCIUM CRYSTALS WITH RENAL CELLS

University Of Chicago, Chicago IL

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Abstract

Although nephrolithiasis is a common condition, the sequence of events by which crystals are retained in the kidney and form stones is poorly understood. Therefore, additional knowledge is required to identify susceptible patients and formulate new therapeutic strategies to prevent kidney stones which cause pain, hematuria, urinary tract obstruction and infection, and to eliminate the need for expensive procedures such as extracorporeal shock wave lithotripsy or surgery. Our previous studies demonstrate that calcium oxalate monohydrate (COM) crystals bind within seconds to anionic, sialic acid-containing glycoproteins on the apical surface of kidney epithelial cells in culture (employed to model the tubule), suggesting one mechanism whereby crystals could be retained in the kidney. Identification of those molecules on the renal cell surface that mediate crystal binding, and how their expression is modulated, will greatly increase insight into the pathogenesis of nephrolithiasis. Our Preliminary Studies provide evidence that the capacity of renal cells to bind COM crystals is not static, but is regulated by exogenous prostaglandin E (PGE) and intracellular cyclic AMP. Additionally, our recent work utilizing a novel experimental protocol, crystal-affinity chromatography, provides new information about the nature of receptors on the surface of cultured renal cells that bind calcium oxalate crystals, including one apparently novel Cell Surface Protein (CSP) that has been isolated and partially sequenced. Our Specific Aims are to: 1) Define mechanisms by which PGE modulates renal cell crystal affinity by investigating its effect on adhesion of hydroxyapatite (HA) crystals to cells, and its role during crystal adhesion to wounded monolayers; study PGE release in response to renal cell-crystal interactions; study regulation of intracellular cAMP in response to PGE; define the effect of PGE on renal cell protein and glycoprotein synthesis; and define the expression of specific crystal receptor proteins after exposure to PGE. 2) Identify and characterize renal epithelial cell surface glycoprotein receptor(s) for COM and HA crystals; obtain a full-length cDNA clone encoding an apparently novel CSP COM crystal receptor; study regulation of CSP expression in renal cells; define CSP gene and protein distribution in renal and non-renal tissues; and characterize cell surface receptors for other urinary crystals, and in different types of cells. The results will provide new understanding of the mechanisms that control adhesion of urinary crystals to the surface of kidney epithelial cells.