The expression and implication of TRPV5, calbindin-D28k and NCX1 in idiopathic hypercalciuria

Abstract

The expression of calcium epithelium TRPV5, alcium binding protein Calbindin-D28k and Na⁺/Ca²⁺ exchanger NCX1 was detected in renal distal convoluted tubule, and their effects on urine calcium reabsorption and the possible pathogenic mechanism in idiopathic hypercalciuria (IH) were investigated. Genetic hypercalciuric stone-forming (GHS) rats were chosen as animal models to study urine calcium reabsorption and IH. The cognate female and male rats that had maximal urine calcium were matched to breed next generation. Twelve GHS rats and 12 normal control (NC) SD rats were selected. Western blot and real time quantitative PCR were used to detect the protein and gene expression of TRPV5, Calbindin-D28k and NCX1 respectively. The expression levels of TRPV5 protein and mRNA in GHS rats were significantly lower than in NC rats (P<0.05). Western blot revealed that the expression levels of Calbindin-D28k in GHS rats and NC rats were 0.49±0.02 and 0.20±0.01 respectively, with the difference being significant between them (P<0.05). By using real time quantitative PCR, it was found that there was no significant difference in Calbindin-28k mRNA expression levels between GHS rats and NC rats (P>0.05). There was no significant difference in the NCX1 expression between GHS rats and NC rats (P>0.05). It was suggested that TRPV5 and Calbindin-D28k might play an important role in urine calcium reabsorption and IH, but they differently contributed to the pathogenesis: The down-regulation of TRPV5 decreases urine calcium reabsorption, directly leading to loss of the urine calcium and resulting in hypercalciuria, and the increased Calbindin-D28k expression could relieve, neutralize and decrease intracellular Ca²⁺ concentration to maintain calcium balance. NCX1 is not the key protein in urine calcium reabsorption.

Keywords

TRPV5 / Calbindin-D28k / NCX1 / idiopathic hypercalciuria / reabsorption / VDR

References

[1] DominikM., HoenderopJ. G., CarelH., et al.. The epithelial calcium channel, ECaC1: molecular details of a novel player in renal calcium handling. Nephrol Dial Transplant, 2001, 16: 1329-1335

[2] MariaR., GiovambattistaC., MarkusB., et al.. Effect of chronic metabolic acidosis on Calbindin expression along the rat distal tubule. J Am Soc Nephrol, 2000, 11: 203-210

[3] WangS. G., LuoD. X., LiuJ. H., et al.. Establishment of genetic hypercalciuric stone-forming rats model. Chin J Urol (Chinese), 2006, 27(Suppl2): 63-65

[4] TascaA., CacciolaA., FerrareseP., et al.. Bone alterations in patients with idiopathic hypercalciuria and calcium nephrolithiasis. Urology, 2002, 59(6): 865-869

[5] HoenderopJ. G., VanA. W., HartogA., et al.. Molecular identification of the apical Ca²⁺ channel in 1,25-dihydroxyvitamin D3-responsive epithelia. J Biol Chem, 1999, 274: 8375-8378

[6] LeeC. T., LienY. H., LaiL. W., et al.. Increased renal calcium and magnesium transporter abundance in streptozotocin-induced diabetes mellitus. Kidney Int, 2006, 69: 1786-1791

[7] HoenderopJ. G., NiliusB., BindelsR. J.. Molecular mechanisms of active Ca²⁺ reabsorption in the distal nephron. Ann Rev Physiol, 2002, 64: 529-549

[8] LuoD. X., WangS. G., LiuJ. H., et al.. Construction of rat VDR protein expression plasmid and analysis of GHS rats duodenumm VDR cDNA. Chin J Exp Sur (Chinese), 2006, 23(11): 1358-1360

[9] YaoJ., KathpaliaP., BushinskyD. A., et al.. Hyperresponsiveness of vitamin D receptor gene expression to 1,25-dihydroxyvitamin D₃. A new characteristic of genetic hypercalciuric stone-forming rats. J Clin Invest, 1998, 101: 2223-2232

[10] RizzoM., MetaforaS., MorelliF., et al.. Chronic administration of bumetanide upregulates calbindin D28k mRNA and protein abundance in rat distal convoluted tubules. Nephron Physiol, 2004, 97: 16-22