Salt Sensing and Salt Response of Renal Neuropeptide FF Receptor 2

Abstract

The causal role of dietary NaCl intake in the development of hypertension and salt sensitivity has long been recognized. The kidney sits at the fulcrum of maintaining an appropriate sodium balance and blood pressure homeostasis. As such, identifying new regulators of sodium balance in the kidney is crucial to understand the intricate mechanisms involved. Neuropeptide FF (NPFF) is a hormone expressed in the central nervous system that subserves nociception, hormonal modulation, and body temperature control. We now demonstrate for the first time that NPFF and its receptors, NPFF‐R1 and NPFF‐R2, are expressed in the kidney and endowed with pro‐hypertensive properties. The renal‐restricted bolus (1‐hr) or chronic infusion (7‐day) of NPFF increased blood pressure (*P<0.05, n=4/group) and decreased sodium excretion (UNaV; *P<0.05, N=4/group) in C57Bl/6 mice. This tubular effect was due solely to NPFF‐R2 since its silencing resulted in ~3‐fold increase in UNaV, unlike NPFF‐R1 silencing which did not affect UNaV. Therefore, we further explored the changes in NPFF‐R2 expression or activity in response to changes in salt. We now report that we have newly identified a “Sodium Response Element” (SRE), a homolog of “Dehydration‐Responsive Element” (“TACCGACAT”) in Arabidopsis thaliana genome, at the NPFF‐R2 promoter ~ 2.3 Kb upstream of the transcription start point. Exposing human renal proximal tubule cells (hRPTCs) from normal (145 μM NaCl) to low (90 μM NaCl) sodium concentration resulted in increased promoter activity (~2.5‐fold, *P<0.05, vs. DSRE, 3/group; via luciferase activity) and increased mRNA and protein expression of NPFFR2 (*P<0.05, 3–4/group; 0–8 hr). Exposure of hRPTCs from normal to high (175 μM NaCl) sodium concentration was accompanied by a reduction in promoter activity (−0.5‐fold, *P<0.05), and a decrease in mRNA and protein expression of NPFFR2 (*P<0.05, 0–8 hr). Moreover, there was a markedly increased co‐immunoprecipitation between pro‐hypertensive NPFF‐R2 and anti‐hypertensive dopamine D1 receptor, resulting in increased antagonism between the two receptors on cAMP response and sodium transport (*P<0.05, vs. fenoldopam or NPFF treatment [1 mM/30 min], 4/group). Lastly, exposure to high salt concentration resulted in greater co‐immunoprecipitation of NPFF‐R2 with Gαi3 and none with Gαs (“Gα switch”), which may explain its pro‐hypertensive activity. NPFF, via NPFF‐R2, may be a crucial determinant of sodium balance and blood pressure homeostasis and thus, may be an important target for new pharmacological and biological intervention.Support or Funding InformationR01DK039308, R01HL092196, and P01HL074940This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.