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Abstract: PO0515

High Sodium Reduced the Expression of PTH1R and Klotho by Inhibiting 1,25 (OH)2D3 Synthesis

Session Information

Category: Bone and Mineral Metabolism

  • 401 Bone and Mineral Metabolism: Basic

Authors

  • You, Huaizhou, Division of Nephrology, Huashan Hospital, Fudan University, Shanghai, Shanghai, China
  • Gu, Jie, Division of Nephrology, Huashan Hospital, Fudan University, Shanghai, Shanghai, China
  • Shi, Jialin, Division of Nephrology, Huashan Hospital, Fudan University, Shanghai, Shanghai, China
  • Chen, Jing, Division of Nephrology, Huashan Hospital, Fudan University, Shanghai, Shanghai, China
Background

The proximal tubule is not only the sensing site of sodium and phosphorus, but also the main place for the synthesis and metabolism of 1,25 (OH)2D3. Sodium may share the sensing mechanism with phosphate in proximal tubule epithelial cells, whether sodium cooperates with phosphate, or it plays an independent role in the regulation of phosphorus homeostasis remains unknown. In this in vitro study, we were to investigate the effects of high sodium on the synthesis and function of active vitamin D and local phosphorus regulation in proximal tubular epithelial cells.

Methods

Human proximal tubule epithelial (HK-2) cells were treatment with different concentrations of sodium/phosphorus. The expressions of 1α-OHase (Cyp27b1) and 24-OHase (Cyp24a1) were determined by RT-PCR and Western Blot respectively. LC/MS and ELISA were used to detect the levels of 1,25 (OH)2D3. Intracellular Ca2+ ([Ca2+]i) was detected with the Ca2+ indicator dye Fura-4. Chromatin samples were immunoprecipitated with antibodies against PTH1R and klotho.

Results

High sodium decreased the expression of 1,25 (OH)2D3 through reducing 1α-OHase and 24-OHase in HK-2 cells. Sodium phosphorus transporter inhibitor (PFA) and sodium hydrogen transporter inhibitor (Caliporide) increased the expression of 1α-OHase and 24-OHase, while ouabain decreased their expressions. High sodium intervention increased intracellular calcium concentration, and chelating extracellular calcium reversed high sodium induced 1α-OHase and 24-OHase expression. High sodium reduced the expression of PTH1R and klotho, combined use of PFA and Caliporide significantly increased the gene and protein expressions of PTH1R and klotho, while ouabain intervention further decreased their levels. Vitamin D receptor agonists significantly increased the recruitment of VDR to the VDRE of PTH1R and klotho promoter, thus increased the expression of PTH1R and klotho.

Conclusion

High extracellular sodium can not only lead to a decrease in the synthesis of active vitamin D in the proximal tubules, but also affect the gene regulation of 1,25 (OH)2D3/VDR, and significantly reduce the expression of PTH1R and Klotho. It suggests the influence of high sodium diet on mineral metabolism and the core role of vitamin D in kidney mineral metabolism.