This study reports the consequences of knocking out NADPH oxidase 4 (Nox4) upon the development of hypertension and kidney injury in the Dahl salt-sensitive (SS) rat. Zinc finger nuclease injection of single cell SS embryos was used to create an 8 base-pair frame-shift deletion of Nox4 resulting in a loss of the ~68 kD band in Western blot analysis of renal cortical tissue of the SSNox4−/− rats. SSNox4−/− rats exhibited a significant reduction of salt-induced hypertension compared to SS rats after 21 days of 4.0% NaCl diet (134±5 vs 151±3 mmHg in SS) and a significant reduction of albuminuria, tubular casts, and glomerular injury. Optical fluorescence 3D cryoimaging revealed significantly higher redox ratios (NADH/FAD) in the kidneys of SSNox4−/− rats even when fed the 0.4% NaCl diet indicating greater levels of mitochondrial electron transport chain metabolic activity and reduced oxidative stress compared to SS rats. Prior to the development of hypertension, RNA expression levels of NADPH oxidase subunits Nox2, p67phox, and p22phox were found to be significantly lower (p<0.05) in SSNox4−/− compared to SS rats in the renal cortex. Thus the mutation of Nox4 appears to modify transcription of a number of genes in ways that contribute to the protective effects observed in the SSNox4−/− rats. We conclude that the reduced renal injury and attenuated blood pressure response to high salt in the SSNox4−/− rat could be the result of multiple pathways including gene transcription, mitochondrial energetics, oxidative stress, and protein matrix production impacted by the knock out of Nox4.

Renal T-cell infiltration is a key component of salt-sensitive hypertension in Dahl salt-sensitive rats. Here we use an electronic servo-control technique to determine the contribution of renal perfusion pressure to T-cell infiltration in the Dahl salt-sensitive rat kidney. An aortic balloon occluder placed around the aorta between the renal arteries was used to maintain perfusion pressure to the left kidney at control levels, approximately 128 mmHg, during 7-days of salt-induced hypertension while the right kidney was exposed to increased renal perfusion pressure which averaged 157 ± 4 mmHg by high salt day-7. The number of infiltrating T-cells was compared between the two kidneys. Renal T-cell infiltration was significantly blunted in the left servo-controlled kidney compared to the right uncontrolled kidney. The number of CD3+, CD3+CD4+ and CD3+CD8+ T-cells were all significantly lower in the left servo-controlled kidney. This effect was not specific to T-cells since CD45R+ (B-cells) and CD11b/c+ (monocytes and macrophages) cell infiltrations were all exacerbated in the hypertensive kidneys. Increased renal perfusion pressure was also associated with augmented renal injury, with increased protein casts and glomerular damage in the hypertensive kidney. Levels of norepinephrine were comparable between the two kidneys, suggestive of equivalent sympathetic innervation. Renal infiltration of T-cells was not reversed by the return of renal perfusion pressure to control levels after 7-days of salt-sensitive hypertension. We conclude that increased pressure contributes to the initiation of renal T-cell infiltration during the progression of salt-sensitive hypertension in Dahl salt-sensitive rats.

Environmental exposure of parents or early in life may affect disease development in adults. We found that hypertension and renal injury induced by a high-salt diet were substantially attenuated in Dahl SS/JrHsdMcwiCrl (SS/Crl) rats that had been maintained for many generations on the grain-based 5L2F diet compared to SS/JrHsdMcwi rats (SS/Mcw) maintained on the casein-based AIN-76A diet (mean arterial pressure 116±9 vs. 154±25 mmHg; urinary albumin excretion 23±12 vs. 170±80 mg/day). RNA-seq analysis of the renal outer medulla identified 129 and 82 genes responding to a high-salt diet uniquely in SS/Mcw and SS/Crl rats, respectively, along with minor genetic differences between the SS substrains. The 129 genes responding to salt in the SS/Mcw strain included numerous genes with homologs associated with hypertension, cardiovascular disease, or renal disease in human. To narrow the critical window of exposure, we performed embryo transfer experiments in which single-cell embryos from one colony (SS/Mcw or SS/Crl) were transferred to surrogate mothers from the other colony, with parents and surrogate mothers maintained on their respective original diet. All offspring were fed the AIN-76A diet after weaning. Salt-induced hypertension and renal injury were substantially exacerbated in rats developed from SS/Crl embryos transferred to SS/Mcw surrogate mothers. Conversely, salt-induced hypertension and renal injury were significantly attenuated in rats developed from SS/Mcw embryos transferred to SS/Crl surrogate mothers. Together, the data suggests that maternal diet during the gestational-lactational period has substantial effects on the development of salt-induced hypertension and renal injury in adult SS rats.

Implanted optical fibers and laser-Doppler flow measurement techniques were used for the sequential measurement of regional renal blood flow in conscious rats to determine the effects of an increase of daily NaCl intake on the renal cortical blood flow and blood flow to the outer and inner medulla. Cortical blood flow was increased significantly (32%) by the second day when NaCl intake was increased from 1 to 7 meq/day and was increased further (50%) on the second day after a further elevation of NaCl intake to 13 meq/day. Blood flow to the outer and inner medulla was not changed as NaCl intake was elevated. The increase in renal cortical flow was closely associated with significant reductions in circulating concentrations of ANG II from 31 to 16 pg/ml. Rats given a continuous infusion of nonpressor doses of ANG II (5.0 ng ⋅ kg−1 ⋅ min−1) to maintain constant plasma concentrations of ANG II as sodium intake was increased exhibited no increase of cortical flow. We conclude that reductions of plasma ANG II associated with incremental increases of daily sodium intake result in a rise of renal cortical flow. The elevated blood flow to the renal cortex may enhance sodium excretion and contribute to long-term sodium homeostasis.