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Abstract: FR-PO588

Fructose Increases the NCC Activity Through the Calcium-Sensing Receptor-WNK4-SPAK Pathway

Session Information

Category: Fluid and Electrolytes

  • 901 Fluid and Electrolytes: Basic

Authors

  • Bahena-López, Jessica Paola, Instituto Nacional de Ciencias Medicas y Nutricion Salvador Zubiran, Tlalpan, Mexico City, Mexico
  • Rojas, Lorena Leonor, Instituto Nacional de Ciencias Medicas y Nutricion Salvador Zubiran, Tlalpan, Mexico City, Mexico
  • Bazua-Valenti, Silvana, Instituto Nacional de Ciencias Medicas y Nutricion Salvador Zubiran, Tlalpan, Mexico City, Mexico
  • Barrera-Chimal, Jonatan, Instituto de Investigaciones Biomedicas, UNAM, Mexico City, Mexico
  • Vázquez, Norma Hilda, Instituto de Investigaciones Biomedicas, UNAM, Mexico City, Mexico
  • Gamba, Gerardo, Instituto Nacional de Ciencias Medicas y Nutricion Salvador Zubiran, Tlalpan, Mexico City, Mexico
Background

We have recently shown that the Calcium Sensing Receptor (CaSR) activates NCC via the WNK4-SPAK pathway (JASN 2018). It is known that glucose and other sugars behave as positive allosteric modulators of CaSR. The effect of glucose on CaSR is particularly relevant in the apical membrane of distal convoluted tubule (DCT), which is not exposed to glucose, except during diabetic glycosuria. The exposure of DCT to fructose varies from low to high because it occurs in an intake-dependent manner. Thus, we hypothesize that sugar delivery to the DCT, by their allosteric effect on the CaSR, might activate NCC via the CaSR-WNK4-SPAK pathway.

Methods

To test if glucose or fructose induce SPAK phosphorylation, we used HEK-293 cells cotransfected with CaSR + SPAK +/- WNK4 cDNA. Expression and phosphorylation of SPAK were assessed using a constant low-calcium medium (0.5mM), but varying the glucose or fructose concentration from 0, to 5.5 or 25mM. The calcimimetic R568 was used as a positive control. To corroborate NCC activation in vivo, we analyzed WNK4-SPAK-NCC pathway in kidneys of mice subjected to a 3h treatment with vehicle, oral calcilytic NPS2143, 20% fructose (in drinking water) ad libitum, or 20% fructose ad libitum + NPS2143.

Results

Exposure of HEK-293 cells to glucose or fructose increased SPAK and ERK phosphorylation (p<0.001). In contrast, when WNK4 cDNA was not transfected, ERK phosphorylation (as a surrogate of CaSR activation) increased, but there was no effect on SPAK phosphorylation (p<0.01). In mice, 20% fructose intake resulted in increased NCC phosphorylation (p<0.01). Moreover, fructose intake activated WNK4 and SPAK (p<0.05). The effect of fructose was abrogated by coadministration of the calcilytic NPS2143 (p<0.01).

Conclusion

Our results show that glucose and fructose induce SPAK phosphorylation in cells in a WNK4-dependent manner. In vivo, fructose intake increased NCC phosphorylation via WNK4 and SPAK, which were in turn activated by CaSR, since the calcylitic compound NPS2143 prevented the effect. Our observations suggest that activation of NCC by glucose or fructose via CaSR could be one of the mechanisms involved in the development of increased salt reabsorption and hence hypertension in diabetes mellitus or during high fructose consumption.

Funding

  • Government Support - Non-U.S.