A role for sweet taste receptors (T1R2/T1R3) in fructose-induced increase in nkcc2 phosphorylation in thick ascending limbs (TALs)
Kassem KM, Ares G, and Ortiz P. A role for sweet taste receptors (T1R2/T1R3) in fructose-induced increase in nkcc2 phosphorylation in thick ascending limbs (TALs). FASEB Journal 2017; 31(1 Suppl):853.2.
High fructose consumption has been implicated in hypertension, renal damage and metabolic syndrome in humans. We previously showed that a fructose-enriched diet does not increase blood pressure in rats unless it is combined with high salt intake. This effect was accompanied by a large increase in phosphorylation of the renal Na/K/2Cl cotransporter NKCC2 at threonine 96/101. The mechanisms by which fructose induces salt-sensitive hypertension are not clear. In a proteomics screen, we found that the sweet taste receptor T1R2 was present in TALs. Others reported mRNA expression of T1R2 and T1R3 in whole kidney homogenates. Both T1R2 and T1R3 are required to initiate signaling by sweet agonists such as fructose. Unlike glucose, fructose is not fully reabsorbed in the proximal tubule, thus it is possible that activation of sweet taste receptors induce signaling leading to NKCC2 phosphorylation. We hypothesize that a fructose-enriched diet (20% fructose in drinking water) stimulates NKCC2 phosphorylation in part by acting on sweet taste receptors (T1R2/T1R3). To test this, we used C57 wild-type mice (WT) and mice on the C57 background with dual deletion of T1R2 and T1R3 (T1R2/T1R3 KO). Mice were given tap water or 20% fructose in drinking water for 7-8 days. TAL suspensions from WT and T1R2/T1R3 KO mice were obtained to measure total NKCC2 expression, GAPDH (loading control) and NKCC2 phosphorylation at Thre96/101 by Western blot. In WT mice, fructose in drinking water increased phosphorylated NKCC2 by 248 ± 82% (n=5, p<0.01), whereas it decreased total NKCC2 expression by 38 ± 18% (p<0.05). In contrast, in TALs from T1R2/T1R3 KO mice, fructose in drinking water did not affect phosphorylated NKCC2 (PNKCC2/total NKCC2: - 16 ± 28%, p=0.88). We conclude that 1-week of a fructose-enriched diet enhances NKCC2 phosphorylation in the mouse TAL, and this effect is in part due to sweet taste receptors T1R2/T1R3. Hence, our data shows for the first time that sweet taste receptors T1R2 and T1R3 play a role in regulating renal transporters. These receptors could play a role in the deleterious effects of fructose intake in the kidney.