Abstract 054: High Protein Diet-Induced Glomerular Hyperfiltration is Dependent on NOS1β

Abstract

High protein diet is associated with glomerular hyperfiltration, but the mechanism has not been fully elucidated. In the present study, we tested a hypothesis that an increased intake of protein enhances the generation of neuronal nitric oxide synthase β (NOS1β)–dependent nitric oxide (NO) in the macula densa, which inhibits the tubuloglomerular feedback (TGF) response and promotes the rise in glomerular filtration rate (GFR). We used microperfusion, micropuncture, and renal clearance of FITC–sinistrin to examine the effects of high protein intake on NO generation at the macula densa, TGF, and GFR in C57BL/6, NOS1 flox/flox and macula densa–specific NOS1 knockout (KO) mice. In C57BL/6 mice, a 4-weeks high protein diet increased kidney weight by 25.7±2.4 %, GFR by 33.6±3.7 % and renal blood flow (RBF) by 38.0±2.9 %, while reduced renal vascular resistance (RVR) by 25.8±3.1 % compared with a low protein diet. TGF response in vivo and in vitro were inhibited by 32.1±2.5 % and 31.7±4.2 % and NO generation by the macula densa was increased by 104.2±11.6 % following the high protein diet, associated with a 1.9±0.1-fold upregulation in NOS1β expression and a 2.4±0.1-fold upregulation in NOS1β phosphorylation at Ser1417 in renal cortex. The phenotype of the NOS1 flox/flox mice in response to the high protein diet was similar to the C57BL/6 mice. In the KO mice, the high protein diet had no effect on the TGF-induced NO generation at the macula densa. The TGF response in vivo or in vitro was not significantly changed in the KO mice on the high protein diet. Furthermore, the increases of GFR and RBF, as well as kidney weight in response to the high protein diet were largely attenuated to 14.2±2.2 %, 16.1±2.4 %, and 10.9±1.9 % in the KO mice compared with the NOS1 flox/flox mice.In conclusion, we identified a novel mechanism of high protein diet–induced hyperfiltration wherein an increase in protein intake upregulates the macula densa NOS1 β expression and activity via phosphorylation at Ser1417, which enhances the NO generation by the macula densa and blunts the TGF response, thereby promoting glomerular hyperfiltration.