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Abstract: TH-OR24

Positive Allosteric Modulation of the Calcium-Sensing Receptor (CaSR) by Glucose or Fructose Induces Activation of the Sodium-Chloride Cotransporter (NCC)

Session Information

Category: Fluid, Electrolyte, and Acid-Base Disorders

  • 901 Fluid, Electrolyte, and Acid-Base Disorders: Basic

Authors

  • Bahena-López, Jessica Paola, Molecular Physiology Unit, INCMNSZ and IIB, UNAM, Mexico City, D.F., Mexico
  • Rojas, Lorena Leonor, Molecular Physiology Unit, INCMNSZ and IIB, UNAM, Mexico City, D.F., Mexico
  • Bazua-Valenti, Silvana, Molecular Physiology Unit, INCMNSZ and IIB, UNAM, Mexico City, D.F., Mexico
  • Vázquez, Norma Hilda, Molecular Physiology Unit, INCMNSZ and IIB, UNAM, Mexico City, D.F., Mexico
  • Chavez-Canales, Maria, Traslational Medicine Unit, INCICH and IIB, UNAM, Mexico City, D.F., Mexico
  • Castañeda-Bueno, Maria, Molecular Physiology Unit, INCMNSZ and IIB, UNAM, Mexico City, D.F., Mexico
  • Madero, Magdalena, Instituto Nacional de Cardiologia Ignacio Chavez, Mexico City, D.F., Mexico
  • Gamba, Gerardo, Molecular Physiology Unit, INCMNSZ and IIB, UNAM, Mexico City, D.F., Mexico
Background

NCC is activated via the CaSR-WNK4-SPAK pathway. Glucose and other sugars act as positive allosteric modulators of the CaSR. This might be relevant in the distal convoluted tubule (DCT), since most glucose is reabsorbed proximally and fructose delivery to the DCT depends largely on dietary intake. Here we studied if positive allosteric modulation of the CaSR by glucose/fructose induces NCC activation via CaSR-WNK4-SPAK.

Methods

We used 1) HEK-293 cells cotransfected with SPAK, WNK4 and/or CaSR and exposed to 0.5 mM extracellular Ca2+ with 0, 5.5 or 25mM of glucose/fructose. 2) C57BL/6 wild-type mice treated with vehicle, 20% fructose or dapagliflozin (3 mg/kg ip), +/- calcilytic NPS2143 (30 mg/kg oral gavage). Renal proteins for western blot were extracted 3 h latter. 3) Urinary exosomes from male healthy volunteers to assess NCC activity after exposure to placebo, cinacalcet 30mg at time 0 (n=4) or 5% fructose with water intake (n=3).

Results

Stimulation of HEK293 cells with glucose or fructose increased SPAK phosphorylation, but only if both WNK4 and CaSR were present (p<0.01). In mice, we observed increased pNCC in kidneys, together with increased activation of WNK4-SPAK (p<0.01), after exposure to 20% fructose. Dapagliflozin also induced activation of SPAK and NCC. These effects of fructose and dapagliflozin were abrogated by co-administration of NPS2143 (p<0.01). Preliminary data on human subjects show that when compared to baseline (urinary exoxome pNCC/NCC ratio = 1.0), cinacalcet induced a 77% increase in pNCC/NCC ratio (1.77, p=0.018) and fructose induced a a near two-fold increase in pNCC/NCC ratio (2.69, p=0.006).

Conclusion

In vitro glucose or fructose increases SPAK phosphorylation in a CaSR-WNK4-dependent manner. In vivo glucose (dapagliflozin) or fructose increases NCC activity via WNK4-SPAK and data suggest a calcimimetic-like behavior for glucose or fructose in the DCT; this effect appears to be reproduced in humans and represents the first evidence of NCC activation via CaSR with cinacalcet in humans. Our results suggest that the presence of glucose or fructose in DCT could increase the activity of NCC via CaSR-WNK4-SPAK pathway.

Funding

  • NIDDK Support