Dietary sodium modulates nephropathy in Nedd4-2-deficient mice

Salt homeostasis is maintained by tight control of Na⁺ filtration and reabsorption. In the distal part of the nephron the ubiquitin protein ligase Nedd4-2 regulates membrane abundance and thus activity of the epithelial Na⁺ channel (ENaC), which is rate-limiting for Na⁺ reabsorption. Nedd4-2 deficiency in mouse results in elevated ENaC and nephropathy, however the contribution of dietary salt to this has not been characterized. In this study we show that high dietary Na⁺ exacerbated kidney injury in Nedd4-2-deficient mice, significantly perturbing normal postnatal nephrogenesis and resulting in multifocal areas of renal dysplasia, increased markers of kidney injury and a decline in renal function. In control mice, high dietary Na⁺ resulted in reduced levels of ENaC. However, Nedd4-2-deficient kidneys maintained elevated ENaC even after high dietary Na⁺, suggesting that the inability to efficiently downregulate ENaC is responsible for the salt-sensitivity of disease. Importantly, low dietary Na⁺ significantly ameliorated nephropathy in Nedd4-2-deficient mice. Our results demonstrate that due to dysregulation of ENaC, kidney injury in Nedd4-2-deficient mice is sensitive to dietary Na⁺, which may have implications in the management of disease in patients with kidney disease.