1,25-Dihydroxyvitamin D3-Independent Stimulatory Effect of Estrogen on the Expression of ECaC1 in the Kidney

Abstract

Abstract. Estrogen deficiency results in a negative Ca 2ϩ balance and bone loss in postmenopausal women. In addition to bone, the intestine and kidney are potential sites for estrogen action and are involved in Ca 2ϩ handling and regulation. The epithelial Ca 2ϩ channel ECaC1 (or TRPV5) is the entry channel involved in active Ca 2ϩ transport. Ca 2ϩ entry is followed by cytosolic diffusion, facilitated by calbindin-D 28K and/or calbindin-D 9k , and active extrusion across the basolateral membrane by the Na ϩ /Ca 2ϩ -exchanger (NCX1) and plasma membrane Ca 2ϩ -ATPase (PMCA1b). In this transcellular Ca 2ϩ transport, ECaC1 probably represents the final regulatory target for hormonal control. The aim of this study was to determine whether 17␤-estradiol (17␤-E 2 ) is involved in Ca 2ϩ reabsorption via regulation of the expression of ECaC1. The ovariectomized rat model was used to investigate the regulation of ECaC1, at the mRNA and protein levels, by 17␤-E 2 replacement therapy. Using real-time quantitative PCR and immunohistochemical analyses, this study demonstrated that 17␤-E 2 treatment at pharmacologic doses increased renal mRNA levels of ECaC1, calbindin-D 28K , NCX1, and PMCA1b and increased the protein abundance of ECaC1. Furthermore, the involvement of 1,25-dihydroxyvitamin D 3 in the effects of 17␤-E 2 was examined in 25-hydroxyvitamin D 3 -1␣-hydroxylase-knockout mice. Renal mRNA expression of calbindin-D 9K , calbindin-D 28K , NCX1, and PMCA1b was not significantly altered after 17␤-E 2 treatment. In contrast, ECaC1 mRNA and protein levels were both significantly upregulated. Moreover, 17␤-E 2 treatment partially restored serum Ca 2ϩ levels, from 1.63 Ϯ 0.06 to 2.03 Ϯ 0.12 mM. In conclusion, this study suggests that 17␤-E 2 is positively involved in renal Ca 2ϩ reabsorption via the upregulation of ECaC1, an effect independent of 1,25-dihydroxyvitamin D 3 .

The epithelial calcium channels TRPV5 and TRPV6: regulation and implications for disease

“…In ovariectomized 1α-OHase knockout mice 17β-estradiol replacement therapy resulted in upregulation of renal TRPV5 mRNA and protein levels, which was accompanied by a normalization of serum Ca 2+ levels. In addition, in duodenum both TRPV5 and TRPV6 mRNA levels were upregulated in these supplemented mice (van Abel et al 2002(van Abel et al , 2003. Thus, TRPV5 and TRPV6 expression is transcriptionally controlled by estrogen in a vitamin D-independent manner.…”

“…In premenopausal women kidney stone formation is less commonly than in age-matched men, which is associated with a lower urinary Ca 2+ excretion (Heller et al 2002;Soucie et al 1994). As shown by van Abel et al estrogen has a stimulatory effect on the expression of active Ca 2+ transport proteins in both kidney and duodenum, including TRPV5 and TRPV6 (van Abel et al 2002(van Abel et al , 2003. Thus, the presence of estrogen may protect premenopausal women against Ca 2+ nephrolithiasis by increasing TRPV5 expression and stimulating Ca 2+ reabsorption.…”

The Epithelial Mg2+ Channel Transient Receptor Potential Melastatin 6 Is Regulated by Dietary Mg2+ Content and Estrogens

“…The effect of 17␤-E 2 on the renal TRPM6 mRNA expression level was evaluated by sham-operated, bilateral ovariectomized (OVX), and OVX rats that received 2 ϫ 500 g 17␤-E 2 /d as described previously (18). The effect of PTH was studied by sham-operated, parathyroidectomized (PTX), and PTX rats that received 6 units/d bovine PTH as described previously (19).…”

Downregulation of Ca2+ and Mg2+ Transport Proteins in the Kidney Explains Tacrolimus (FK506)-Induced Hypercalciuria and Hypomagnesemia

“…The obtained RNA was subjected to DNAse treatment to prevent genomic DNA contamination. Thereafter, 2 g of RNA was reverse transcribed by Moloney-murine leukemia virusreverse transcriptase (Life Technologies BRL) as described previously (19). The obtained cDNA was used to determine TRPV5, calbindin-D 28K , and TRPM6 mRNA levels in kidney cortex as well as TRPV6, calbindin-D 9K , and TRPM6 mRNA expression in duodenum.…”