Abstract 093: Salt Resistance and Renal Gpr83 Function

Abstract

The G protein coupled receptor 83 (Gpr83) is an orphan receptor that has been associated with essential hypertension. Gpr83 is expressed in the kidney but its function is unknown. We found that Gpr83 is expressed in mouse renal proximal and distal convoluted tubules, as well as in human renal proximal tubule cells (hRPTCs). In C57Bl/6J mice on normal salt diet, the lack of one (Gpr83+/-) or both Gpr83 (Gpr83-/-) alleles resulted in an increase in systolic blood pressure (SBP, ~20 mm Hg (P<0.05; n=4/group, measured under anesthesia) compared with Gpr83+/+ littermates, suggesting that Gpr83 is needed to keep a normal BP. Renal specific Gpr83 silencing by the renal subcapsular infusion of Gpr83 siRNA (3 μg/day; 7 days) increased SBP in C57Bl/6J mice on a normal salt diet, relative to mice treated with nonsilencing siRNA (120±5 vs 98±6 mmHg; P<0.05; n=4/group). A high salt (4% NaCl) diet increased renal Gpr83 transcription by 2 fold (P<0.05; n=4/group) in SJL/J and BALB/c salt resistant mice, relative to C57Bl/6J salt sensitive mice. Gpr83 gene down-regulation in mouse and human renal proximal tubule cells decreased about 50% the expression of nuclear factor of activated T cells 5 (NFAT5). The renal expressions of NFAT5 and the NFAT5 targets UT-A3, Tau T and BGT1 were increased by a high salt diet in salt resistant mice. The neuropeptide PEN (PEN), a ligand of Gpr83, is also expressed in hRPTCs (0.43±0.03 mRNA PEN/mRNA GAPDH). We found that Gpr83 stimulation with PEN (1 μM, 3 hr) decreased the transcription of NFAT5 (0.59±0.05 vs 1.0±0.2fold, P<0.05; n=3-4/group), which was abolished by Gpr83 silencing. Our results suggest that Gpr83 may protect against the development of salt sensitivity. Gpr83 mediated regulation of NFAT5 may play a role in salt-sensitive hypertension.