Glucose/Fructose Delivery to the Distal Nephron Activates the Sodium-Chloride Cotransporter Via the Calcium-Sensing Receptor

Significance Statement The calcium-sensing receptor (CaSR) activates salt reabsorption through the sodium-chloride cotransporter (NCC) via the WNK4-SPAK pathway. Glucose and other sugars are positive allosteric modulators of the CaSR. This would be irrelevant for most cells that come into contact with glucose, except for the nephron segments beyond the proximal tubule. Using in vitro and in vivo models, this work shows that the arrival of glucose or fructose to the distal nephron modulates the CaSR due to a positive allosteric type II effect associated with activation of the WNK4-SPAK-NCC pathway. This study proposes a mechanism by which glucose or fructose delivered to the distal nephron contributes to renal salt retention by their allosteric effect on the CaSR. Background The calcium-sensing receptor (CaSR) in the distal convoluted tubule (DCT) activates the NaCl cotransporter (NCC). Glucose acts as a positive allosteric modulator of the CaSR. Under physiologic conditions, no glucose is delivered to the DCT, and fructose delivery depends on consumption. We hypothesized that glucose/fructose delivery to the DCT modulates the CaSR in a positive allosteric way, activating the WNK4-SPAK-NCC pathway and thus increasing salt retention. Methods We evaluated the effect of glucose/fructose arrival to the distal nephron on the CaSR-WNK4-SPAK-NCC pathway using HEK-293 cells, C57BL/6 and WNK4-knockout mice, ex vivo perfused kidneys, and healthy humans. Results HEK-293 cells exposed to glucose/fructose increased SPAK phosphorylation in a WNK4- and CaSR-dependent manner. C57BL/6 mice exposed to fructose or a single dose of dapagliflozin to induce transient glycosuria showed increased activity of the WNK4-SPAK-NCC pathway. The calcilytic NPS2143 ameliorated this effect, which was not observed in WNK4-KO mice. C57BL/6 mice treated with fructose or dapagliflozin showed markedly increased natriuresis after thiazide challenge. Ex vivo rat kidney perfused with glucose above the physiologic threshold levels for proximal reabsorption showed increased NCC and SPAK phosphorylation. NPS2143 prevented this effect. In healthy volunteers, cinacalcet administration, fructose intake, or a single dose of dapagliflozin increased SPAK and NCC phosphorylation in urinary extracellular vesicles. Conclusions Glycosuria or fructosuria was associated with increased NCC, SPAK, and WNK4 phosphorylation in a CaSR-dependent manner.