Uncovering the Molecular Mechanisms Underlying the Hypertension in Snx1 Knockout Mice

We have reported that sorting nexin 1 (SNX1) is crucial for renal dopamine D 5 receptor (D 5 R) trafficking, signal transduction, and function in human renal epithelial cells and in C57Bl/6J and BALB/cJ mice, as shown by the development of hypertension and impaired natriuretic response to agonist stimulation after an acute SNX1 depletion in the kidney. Thus, we elucidated the renal molecular mechanisms for these phenotypes in Snx1 -/- mice, which have congenital absence of SNX1. These mice have increased expression of glycosylated AT 1 R (123.8±2.1 vs . 100±2.0% in wild-type littermates, P<0.05, Student’s t -test, n=5/group), a receptor with pro-oxidant and hypertensinogenic effects. We next determined the expression profiles of the components of the NADPH oxidase (NOX), an enzyme complex that is a major source of reactive oxygen species (ROS). We found an increased expression of renal NOX1 (153.4±12.2% vs . 100±4.1%, P<0.05), NOX2 or gp91 phox (129.9±5.5% vs . 100±7.7%, P<0.05), and p47 phox (118.2±2.7% vs . 100±5.0%, P<0.05), suggesting increased oxidative stress in these mice. Interestingly, the Snx1 null mice have elevated renal D 5 R (142.9±4.7% vs . 100±6.8%, P<0.05) and D 3 R (134.3±5.3% vs . 100 ± 1.6%, P<0.05), receptors with anti-oxidant activity, as well as the antioxidant paraoxonase 2, perhaps as compensatory mechanisms; the loss of SNX1 impairs the function of D 5 R. To corroborate our findings, we treated the Snx1 -/- mice and controls with a 10-day renal infusion of apocynin, a drug that blocks NOX assembly by preventing p47 phox translocation to NOX2. Apocynin treatment resulted in the amelioration of systolic blood pressure (SBP) in Snx1 -/- mice (131.3±4.8 mm Hg to 105.7±1 mm Hg, P<0.05). There was no difference in the SBP with vehicle treatment in both strains, or with apocynin in control mice. Basal NOX activity was higher in Snx1 -/- mice (169±12.8 units/mg protein/min vs . 100±13.3 in controls, P<0.05), which was normalized by apocynin (99.4±16.5), while basal ROS levels were 2-fold higher in the Snx1 -/- mice (218.6±7.7 units/mg protein vs . 100±17.9, P<0.05), which was also normalized by apocynin (125.8±20.4). Our data indicate that the hypertension in Snx1 -/- mice is due to impaired D 5 R activity, higher NOX expression and activity, and increased AT 1 R.