Regulation of renal Naϩ transport is essential for controlling blood pressure, as well as Na ϩ and K ϩ homeostasis. Aldosterone stimulates Na ϩ reabsorption by the Na ϩ -Cl Ϫ cotransporter (NCC) in the distal convoluted tubule (DCT) and by the epithelial Na ϩ channel (ENaC) in the late DCT, connecting tubule, and collecting duct. Aldosterone increases ENaC expression by inhibiting the channel's ubiquitylation and degradation; aldosterone promotes serum-glucocorticoid-regulated kinase SGK1-mediated phosphorylation of the ubiquitin-protein ligase Nedd4-2 on serine 328, which prevents the Nedd4-2/ENaC interaction. It is important to note that aldosterone increases NCC protein expression by an unknown post-translational mechanism. Here, we present evidence that Nedd4-2 coimmunoprecipitated with NCC and stimulated NCC ubiquitylation at the surface of transfected HEK293 cells. In Xenopus laevis oocytes, coexpression of NCC with wild-type Nedd4-2, but not its catalytically inactive mutant, strongly decreased NCC activity and surface expression. SGK1 prevented this inhibition in a kinase-dependent manner. Furthermore, deficiency of Nedd4-2 in the renal tubules of mice and in cultured mDCT 15 cells upregulated NCC. In contrast to ENaC, Nedd4-2-mediated inhibition of NCC did not require the PY-like motif of NCC. Moreover, the mutation of Nedd4-2 at either serine 328 or 222 did not affect SGK1 action, and mutation at both sites enhanced Nedd4-2 activity and abolished SGK1-dependent inhibition. Taken together, these results suggest that aldosterone modulates NCC protein expression via a pathway involving SGK1 and Nedd4-2 and provides an explanation for the well-known aldosterone-induced increase in NCC protein expression.

Angiotensin II (Ang II)-induced hypertension is associated with an increase in T cell production of interleukin 17A (IL-17A). Recently, we reported that IL-17A−/− mice exhibit blunted hypertension, preserved natriuresis in response to a saline challenge, and decreased renal sodium hydrogen exchanger 3 (NHE3) expression after 2 weeks of Ang II infusion compared to wild type (WT) mice. In the current study, we performed renal transporter profiling in mice deficient in IL-17A or the related isoform, IL-17F, after 4 weeks of Ang II infusion, a time when the blood pressure reduction in IL-17A−/− mice is most prominent. Deficiency of IL-17A abolished the activation of distal tubule transporters, specifically the sodium-chloride cotransporter (NCC) and the epithelial sodium channel (ENaC) and protected mice from glomerular and tubular injury. In human proximal tubule (HK-2) cells, IL-17A increased NHE3 expression through a serum and glucocorticoid regulated kinase 1 (SGK1) dependent pathway. In mouse distal convoluted tubule (mDCT15) cells, IL-17A increased NCC activity in an SGK1/Nedd4-2 dependent pathway. In both cell types, acute treatment with IL-17A induced phosphorylation of SGK1 at serine 78, and treatment with an SGK1 inhibitor blocked the effects of IL-17A on NHE3 and NCC. Interestingly, both HK-2 and mDCT15 cells produce endogenous IL-17A. IL17F had little or no effect on blood pressure or renal sodium transporter abundance. These studies provide a mechanistic link by which IL-17A modulates renal sodium transport and suggest that IL-17A inhibition may improve renal function in hypertension and other autoimmune disorders.

Recent studies suggest a role for T lymphocytes in hypertension. However, whether T cells contribute to renal sodium retention and salt-sensitive hypertension is unknown. Here we demonstrate that T cells infiltrate into the kidney of salt-sensitive hypertensive animals. In particular, CD8+ T cells directly contact the distal convoluted tubule (DCT) in the kidneys of DOCA-salt mice and CD8+ T cell-injected mice, leading to up-regulation of the Na-Cl co-transporter NCC, p-NCC and the development of salt-sensitive hypertension. Co-culture with CD8+ T cells upregulates NCC in mouse DCT cells via ROS-induced activation of Src kinase, up-regulation of the K+ channel Kir4.1, and stimulation of the Cl− channel ClC-K. The last event increases chloride efflux, leading to compensatory chloride influx via NCC activation at the cost of increasing sodium retention. Collectively, these findings provide a mechanism for adaptive immunity involvement in the kidney defect in sodium handling and the pathogenesis of salt-sensitive hypertension.

Background:The role of the circadian protein Per1 in the regulation of sodium reabsorption in the distal convoluted tubule (DCT) is unknown. Results: Per1 transcriptionally regulates the sodium transporter NCC and the WNK kinase cascade. Conclusion: Per1 regulates sodium reabsorption in the DCT through NCC and the WNK cascade.Significance: These data demonstrate a role for Per1 in the regulation of renal sodium transporters.