Renal‐selective Snx5 gene silencing increases blood pressure and renal sodium transporters in mice

Abstract

We have reported that sorting nexin 5 (SNX5) plays an important role in the positive regulation of the renal dopamine receptor subtype 1 (D1R). siRNA‐mediated gene silencing of renal Snx5 results in anti‐natriuresis and increases further the elevated blood pressure (BP) of spontaneously hypertensive rats. We tested the hypothesis that the increased renal sodium transport and increased BP following Snx5 gene silencing is accompanied by changes in the expression of renal transporters in C57BL6/J mice. We infused subcapsularly the Snx5‐specific siRNA (3 μg/kg/day), or non‐silencing “mock” siRNA as control, for 7 days in 8 1‐year old, previously uninephrectomized male C57BL6 mice. A 24‐hour urine was collected from the mice housed in metabolic cages a day prior to the end of the siRNA infusion. Renal SNX5 protein expression was decreased by 60% with Snx5‐siRNA relative to control group. Renal SNX5‐depleted mice had elevated systolic (119±5.2 mm Hg, measured under anesthesia) and diastolic BPs (91.8±7.3 mm Hg) relative to control mice (systolic BP=101.5±0.5 mm Hg, diastolic BP=72±2.3 mm Hg). Urine sodium excretion tended to decrease in SNX5‐depleted mice (0.68±0.22 mmol/Cr mg) relative to controls (1.08±0.30 mmol/ Cr mg). Moreover, renal SNX5 depletion shifted the pressure natriuresis curve to the right. Food and water intake, body weight, urine volume, and heart rate were similar in the two groups. SNX5 is mainly located at the apical membrane of proximal tubules (PT), thick ascending limbs of loop of Henle (TAL) and distal convoluted tubules (DCT). SNX5 was observed via confocal microscopy to colocalize with NHE3, NKCC2 and NCC in C57Bl/6J mice under basal conditions. However, the co‐staining is strongest with NHE3 in the PT, relative to NKCC 2 and NCC which are expressed in TAL and DCT, respectively. The expression of renal NHE3 (172±29 % of control), NaPi2 (223±12%), NKCC2 (440±12%) and NCC (177±23%) were greater in SNX5‐depleted mice than in control mice. Renal protein expressions of α,β,γ‐ENaCs, Na+K+ATPase and actin were similar in the 2 groups. These findings suggest that inhibition of SNX5 expression with siRNA increases sodium transporters in proximal and distal nephron segments. This may lead to the inability of renal D1R to inhibit renal sodium transport and may be responsible for the increased BP in Snx5‐siRNA‐ treated mice.Support or Funding InformationThis work was supported in part by grants from the National Institutes of Health, R37HL023081, R01DK039308, P01HL068686, P01HL074940, and R01HL092196. Dr. Xiaoyan Wang was supported, in part, by National Kidney Foundation of Maryland (Professional Development Award, 2014).