Abstract Body: Rationale
The effects of a high salt (HS) diet on O₂ and substrate metabolism in the kidneys have attracted growing attention, however, significant gaps remain in our understanding of how oxidative stress influences the efficiency of energy production and substance metabolism. In this study, we compared Dahl salt-sensitive (SS) rats and SS rats lacking NADPH oxidase 4 (SS^NOX4-/-) to investigate the kidney’s metabolic and redox responses to HS intake
Methods
Male SS and SS^Nox4-/- rats were fed a 0.4% NaCl (LS) diet. At 7-8 weeks of age, the rats were implanted with a left renal artery ultrasonic flow probe (Transonic) together with a femoral arterial catheter and a renal venous catheter. Renal blood flow (RBF) and mean arterial pressure (MAP) were measured continuously (24/7) and arterial (A) and renal venous (Vr) blood was sampled intermittently when rats were fed the LS and on days 7, 14, and 21 after switching to the HS diet. GFR was measured in age-matched rats. Blood O₂ content was determined by radiometry. A global metabolomic analysis was performed on plasma, urine, and Cx and OM tissue samples at JAX laboratories (Thermo Q-Exactive Orbitrap coupled to Vanquich UPLC system) and together with an mRNAseq analysis for Cx and OM by Novogene Inc.
Results
The MAP of SS rats increased from 122 ± 2 to 164 ± 5 mmHg by HS21, whereas this rise was significantly attenuated in SS^Nox4-/- rats. In both strains, GFR initially rose and subsequently declined over time. In SS rats, the kidneys exhibited early upregulation of glutaminase and enhanced glutamate utilization, reflecting a glutamine-driven metabolic profile associated with increased energy demand, O₂ utilization, and reactive oxygen species (ROS) production. In contrast, SS^NOX4-/- rats demonstrated inherently higher NO production and a metabolic preference for fatty acid oxidation, resulting in more efficient O₂ usage for energy production. Notably, only SS^NOX4-/- rats released lactate from the kidneys following salt loading, despite no corresponding increase in the expression of glycolysis-related genes. Furthermore, unlike SS rats, SS^NOX4-/- rats did not exhibit increased amino acid metabolism, indicating a protein-sparing, protective metabolic phenotype.
Conclusion
These findings highlight a unique interplay between redox balance and metabolic reprogramming in SS^NOX4-/- rats during HS intake, promoting more efficient energy production and contributing to renal protection compared to SS rats.