Sympathetic Stimulation of Thiazide-Sensitive Sodium Chloride Cotransport in the Generation of Salt-Sensitive Hypertension

Abstract

Excessive renal efferent sympathetic nerve activity contributes to hypertension in many circumstances. While both hemodynamic and tubular effects likely participate, most evidence supports a major role for α-adrenergic receptors in mediating the direct epithelial stimulation of sodium retention. Recently, it was reported, however, that norepinephrine activates the thiazide-sensitive transporter, NCC, by stimulating β-adrenergic receptors. Here, we confirmed this effect and developed an acute adrenergic stimulation model to study the signaling cascade. The results show that norepinephrine increases the abundance of phosphorylated NCC rapidly (161% increase), an effect largely dependent on β-adrenergic receptors. This effect is not mediated by activation of angiotensin II receptors. We used immunodissected mouse distal convoluted tubule (DCT) to show that DCT cells are especially enriched for β1-adrenergic receptors, and that the effects of adrenergic stimulation can occur ex vivo (79% increase), suggesting they are direct. As two protein kinases, Ste20p-related Proline Alanine-rich kinase (SPAK) and Oxidative stress responsive 1 (OxSR1), phosphorylate and activate NCC, we examined their roles in norepinephrine effects. Surprisingly, norepinephrine did not affect SPAK abundance or its localization in the DCT; instead, we observed a striking activation of OxSR1. We confirmed that SPAK is not required for NCC activation, using SPAK knockout mice. Together, the data provide strong support for a signaling system involving β1- receptors in the DCT that activates NCC, at least in part via OxSR1. The results have implications regarding device- and drug-based treatment of hypertension.

Integrated compensatory network is activated in the absence of NCC phosphorylation

“…To identify genes that are regulated to maintain salt balance when phosphorylation of NCC is compromised, genome-wide analysis of factors (25,26). Once stimulated, WNK kinases bind to and phosphorylate SPAK (27).…”

Caveolin-1 Deficiency Inhibits the Basolateral K+ Channels in the Distal Convoluted Tubule and Impairs Renal K+ and Mg2+ Transport

“…Because SPAK has been shown to stimulate NCC activity through phosphorylation, [28][29][30] it is conceivable that the disruption of cav-1-induced inhibition of SPAK should reduce the NCC phosphorylation. Figure 7D is a Western blot showing the expression of Thr 53 -phosphorylated NCC, which is an index of activated NCC, 31 and the total NCC in the kidney from the WT and cav-1 KO mice. In comparison with the control value, the disruption of cav-1 decreased the expression of phosphorylated NCC and total NCC by 80%610% and 45%610% (n=5), respectively.…”

“…At the end of the experiments, the blood samples were collected through cardiac puncture. 31 The data are presented as mean6SEM. We used the paired t test or one-way ANOVA to determine the statistical significance.…”

Short Forms of Ste20-related Proline/Alanine-rich Kinase (SPAK) in the Kidney Are Created by Aspartyl Aminopeptidase (Dnpep)-mediated Proteolytic Cleavage

“…For instance, the PAPA box could direct SPAK to apical actin bundles, and the action of Dnpep could release this interaction and allow SPAK to move away from the membrane. The PAPA box could account for the significant differences in cellular distribution of SPAK and OSR1 that have been observed in renal tubule cells (14,16,41).…”