The Na+Cl- cotransporter (NCC) is expressed in the apical plasma membrane (APM) of the distal convoluted tubule (DCT). NCC inhibition provokes salt wasting and can lower BP, while NCC stimulation can raise BP: WNK kinases mutations increase APM NCC and activity, inactivating the WNK substrate SPAK kinase reduces NCC phosphorylation (NCCp) and BP. The renin angiotensin system (RAS) stimulates NCC activity via an AngII-WNK4-SPAK dependent pathway. We provided in vivo evidence that NCC redistributes out of the APM into subapical cytoplasmic vesicles (SCV) during high NaCl diet and ACE inhibition and redistributes into the APM from SCV during low NaCl diet and AngII infusion. We now show that NCCp increases with AngII treatment and decreases with high salt diet. AngII via AT1R stimulates NADPH oxidase (Nox), generating reactive oxygen species (ROS). We now show that ROS scavenging during AngII treatment blocks NCC trafficking and NCCp. Renal sympathetic nerve activity (RSNA) also plays a primary role in hypertension pathogenesis. We show that both RSNA and adrenergic agonists stimulate NCC trafficking to APM and increase NCCp. The overall aim of this proposal is to determine the molecular mechanisms responsible for integrated regulation of NCC in response to AngII and/or RSNA and the influence of dietary NaCl on these pathways. Our hypothesis is that AngII (via AT1R) and adrenergic agonists (via a1bAR) stimulate Nox generation of ROS and activates SPAK kinase which stimulates NCC accumulation in APM and NCCp. We postulate that dietary salt independently stimulates ROS generation via Nox.
Aim 1. What is the role of NADPH oxidase and SPAK in AngII stimulated NCC phosphorylation and/or redistribution to APM? Are these effects influenced by dietary salt? Aim 2. Do RSNA or adrenergic agonists stimulate DCT NCC activity? Are NADPH oxidase stimulation and/or SPAK phosphorylation requisite? How is this regulation affected by dietary salt? By AngII? Methods.
The aims will be examined in rats treated acutely or chronically with agonists and inhibitors of RAS, NADPH oxidase, RSNA and altered salt diets. Mouse knockout models of SPAK, p47phox, and alpha1b adrenoreceptors will be examined in parallel to define the roles of these regulatory pathways or intermediates in NCC regulation. Distribution of NCC, NCCp, SPAK and SPAKp will be examined by both subcellular fractionation and immunoblots and immunofluorescence and immuno-EM. Renal function, oxidative stress and BP will be measured routinely and NCC activity measured using a thiazide diuretic test. Accomplishing the aims will establish integrated effects of major BP regulating signals on DCT NCC cellular distribution, NCCp and activity, providing novel insights into homeostatic set point regulation of ECFV and BP by the DCT and, ideally, indicating strategies for the development of therapies to treat resistant hypertension and/or edema based on inhibiting multiple pathways that regulate DCT NCC activity.
A short region of the kidney nephron known as the distal convoluted tubule reabsorbs only 5-10% of the salt delivered to the kidney, via the sodium-chloride cotransporter (NCC), yet this region appears to be a key determinant of blood pressure (BP), and also a key region to target therapies to lower BP. More than 25% of the population has high BP and a significant fraction of this population is resistant to current therapies. We aim to define how the major BP regulating signals, namely, hormones, nervous system and dietary salt, affect the NCC activity in the distal tubule, and determine how these signals are simultaneously integrated. The results will provide insight into how BP is set by the kidney and, ideally, indicate strategies for the development of combination therapies to treat resistant hypertension and/or edema based on inhibiting multiple pathways that regulate NCC activity.
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