Kidney Stones and the Zip10 Transporter: An Analysis of Calcium Oxalate Stone Formation Using Frog and Fruit Fly Models

Abstract

Kidney stones are a health ailment (~1% population occurrence), yet the mechanism and initiation of stone formation remains incompletely explained. Calcium oxalate (CaOx) stones seem to initially form on sites called Randall’s Plaques that are high in zinc content. A suggested correlation between stone disease and the Zip10 transporter in a GWAS (genome wide association study) on Miniature Schnauzers allowed me to investigate the role of zinc and Zip10 on CaOx stone formation. Our results from radioactive 63Zn uptakes in injected frog (Xenopus laevis) oocytes indicate that (human, canine and Drosophila) Zip10 transport Zn2+. The Zip10 clones had highest function at pH 7.5, with lower uptakes at both acidic pH and alkaline pH. The effects of Zn2+ and Zip10 on CaOx stone formation in a fruit fly (Drosophila) model are also presented in this paper. Drosophila Zip10 knockdown (KD) flies were created and compared to wild type (WT) flies in tubule experiments using in vitro Malphigian Tubule (MT) experiments. MTs taken from WT and KD flies and immersed in sodium oxalate (NaOx) solutions develop CaOx crystals (the fly form of stones) within 45 minutes. When Zn2+ was added to immersion solutions, crystal volume in both WT and KD flies increased. Cd2+ (cadmium, another group IIB transition metal) addition to immersion solutions also increased crystal volume. KD flies formed larger crystals than WT flies among all solutions in tubule immersion experiments. WT flies formed more crystals than KD flies among all solutions besides the Cd2+ + Zn2+ + oxalate solution during tubule immersion experiments. In feeding experiments, KD flies formed smaller crystals with Zn2+ present than without Zn2+. The difference in results between feeding and tubule immersion experiments is likely attributed to gut absorption of solutes. Our results indicate that WT flies formed larger crystals when zinc was present in an oxalate rich diet, and KD flies formed larger crystals when an oxalate rich diet lacked Zn2+. Both a knockdown of Zip10 and the addition of Zn2+ to immersion solutions and diet altered crystal formation. The present study suggests that Zip10 and Zn2+ play a role in CaOx crystal formation. Our results support previous studies on the correlation between kidney stones and Zn2+ intake. Further studies should determine the exact mechanism of Zn2+/Cd2+ transport by Zip10, as well as the relationship between the Zn2+/Cd2+ transporter and CaOx stones.