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Consumption of low dietary potassium, common with ultraprocessed foods, activates the thiazide-sensitive sodium chloride cotransporter (NCC) via the with no (K) lysine kinase/STE20/SPS1-related proline-alanine-rich protein kinase (WNK/SPAK) pathway to induce salt retention and elevate blood pressure (BP). However, it remains unclear how high-potassium 'DASH-like' diets (dietary approaches to stop hypertension) inactivate the cotransporter and whether this decreases BP. A transcriptomics screen identified Ppp1Ca, encoding PP1A, as a potassium- upregulated gene, and its negative regulator Ppp1r1a, as a potassium-suppressed gene in the kidney. PP1A directly binds to and dephosphorylates NCC when extracellular potassium is elevated. Using mice genetically engineered to constitutively activate the NCC-regulatory kinase SPAK and thereby eliminate the effects of the WNK/SPAK kinase cascade, we confirmed that PP1A dephosphorylated NCC directly in a potassium-regulated manner. Prior adaptation to a high-potassium diet was required to maximally dephosphorylate NCC and lower BP in constitutively active SPAK mice, and this was associated with potassium-dependent suppression of Ppp1r1a and dephosphorylation of its cognate protein, inhibitory subunit 1 (I1). In conclusion, potassium-dependent activation of PP1A and inhibition of I1 drove NCC dephosphorylation, providing a mechanism to explain how high dietary 1C lowers BP. Shifting signaling of PP1A in favor of activation of WNK/SPAK may provide an improved therapeutic approach for treating salt-sensitive hypertension., Introduction According to the WHO, hypertension is the single greatest contributor to premature death and disability in the world (1). High salt (NaCl) consumption has long been a major culprit, [...]

Dietary potassium deficiency causes stimulation of sodium reabsorption leading to an increased risk in blood pressure elevation. The distal convoluted tubule (DCT) is the main rheostat linking plasma K+ levels to the activity of the Na-Cl cotransporter (NCC). This occurs through basolateral membrane potential sensing by inwardly rectifying K+ channels (Kir4.1/5.1); decrease in intracellular Cl−; activation of WNK4 and interaction and phosphorylation of STE20/SPS1-related proline/alanine-rich kinase (SPAK); binding of calcium-binding protein 39 (cab39) adaptor protein to SPAK, leading to its trafficking to the apical membrane; and SPAK binding, phosphorylation, and activation of NCC. As kidney-specific with-no-lysine kinase 1 (WNK1) isoform (KS-WNK1) is another participant in this pathway, we examined its function in NCC regulation. We eliminated KS-WNK1 specifically in the DCT and demonstrated increased expression of WNK4 and long WNK1 (L-WNK1) and increased phosphorylation of NCC. As in other KS-WNK1 models, the mice were not hyperkalemic. Although wild-type mice under low-dietary K+ conditions demonstrated increased NCC phosphorylation, the phosphorylation levels of the transporter, already high in KS-WNK1, did not change under the low-K+ diet. Thus, in the absence of KS-WNK1, the transporter lost its sensitivity to low plasma K+. We also show that under low K+ conditions, in the absence of KS-WNK1, there was no formation of WNK bodies. These bodies were observed in adjacent segments, not affected by the targeting of KS-WNK1. As our data are overall consistent with those of the global KS-WNK1 knockout, they indicate that the DCT is the predominant segment affecting the salt transport regulated by KS-WNK1. NEW & NOTEWORTHY: In this paper, we show that KS-WNK1 is a critical component of the distal convoluted tubule (DCT) K+ switch pathway. Its deletion results in an inability of the DCT to sense changes in plasma potassium. Absence of KS-WNK1 leads to abnormally high levels of WNK4 and L-WNK1 in the DCT, resulting in increased Na-Cl phosphorylation and function. Our data are consistent with KS-WNK1 targeting WNK4 and L-WNK1 to degradation. [ABSTRACT FROM AUTHOR]

Gain-of-function mutations in with no lysine (K)1 (WNK1) and WNK4genes are responsible for familial hyperkalemic hypertension (FHHt), a rare, inherited disorder characterized by arterial hypertension and hyperkalemia with metabolic acidosis. More recently, FHHt-causing mutations in the Kelch-like 3-Cullin 3 (KLHL3-CUL3) E3 ubiquitin ligase complex have shed light on the importance of WNK's cellular degradation on renal ion transport. Using full exome sequencing for a 4-generation family and then targeted sequencing in other suspected cases, we have identified new missense variants in the WNK1 gene clustering in the short conserved acidic motif known to interact with the KLHL3-CUL3 ubiquitin complex. Affected subjects had an early onset of a hyperkalemic hyperchloremic phenotype, but normal blood pressure values' Functional experiments in Xenopus laevis oocytes and HEK293T cells demonstrated that these mutations strongly decrease the ubiquitination of the kidney-specific isoform KS-WNK1 by the KLHL3-CUL3 complex rather than the long ubiquitous catalytically active L-WNK1 isoform. A corresponding CRISPR/Cas9 engineered mouse model recapitulated both the clinical and biological phenotypes. Renal investigations showed increased activation of the Ste20 proline alanine-rich kinase-[Na.sup.+]-[Cl.sup.-] cotransporter (SPAK-NCC) phosphorylation cascade, associated with impaired ROMK apical expression in the distal part of the renal tubule. Together, these new WNK1 genetic variants highlight the importance of the KS-WNK1 isoform abundance on potassium homeostasis., Introduction Familial hyperkalemic hypertension (FHHt), also known as Gordon syndrome and pseudohypoaldosteronism type 2, is a rare disease associated with net positive [Na.sup.+] balance and renal [K.sup.+] retention resulting in [...]

Kidney development and physiology require polarization of epithelia that line renal tubules. Genetic studies show that polarization of invertebrate epithelia requires the crumbs, partition-defective-3, and discs large complexes. These evolutionarily conserved protein complexes occur in mammalian kidney; however, their role in renal development remains poorly defined. Here, we find that mice lacking the small PDZ protein mammalian LIN-7c (MALS-3) have hypomorphic, cystic, and fibrotic kidneys. Proteomic analysis defines MALS-3 as the only known core component of both the crumbs and discs large cell polarity complexes. MALS-3 mediates stable assembly of the crumbs tight junction complex and the discs large basolateral complex, and these complexes are disrupted in renal epithelia from MALS-3 knockout mice. Interestingly, MALS-3 controls apico-basal polarity preferentially in epithelia derived from metanephric mesenchyme, and defects in kidney architecture owe solely to MALS expression in these epithelia. These studies demonstrate that defects in epithelial cell polarization can cause cystic and fibrotic renal disease.

The urinary potassium (K+) excretion machinery is upregulated with increasing dietary K+, but the role of accompanying dietary anions remains inadequately characterized. Poorly absorbable anions, including HCO−3 , are thought to increase K+ secretion through a transepithelial voltage effect. Here, we tested if they also influence the K+ secretion machinery. Wild-type mice, aldosterone synthase (AS) knockout (KO) mice, or pendrin KO mice were randomized to control, high-KCl, or high-KHCO3 diets. The K+ secretory capacity was assessed in balance experiments. Protein abundance, modification, and localization of K+-secretory transporters were evaluated by Western blot analysis and confocal microscopy. Feeding the high-KHCO3 diet increased urinary K+ excretion and the transtubular K+ gradient significantly more than the high-KCl diet, coincident with more pronounced upregulation of epithelial Na+ channels (ENaC) and renal outer medullary K+ (ROMK) channels and apical localization in the distal nephron. Experiments in AS KO mice revealed that the enhanced effects of HCO−3 were aldosterone independent. The high-KHCO3 diet also uniquely increased the large-conductance Ca2+-activated K+ (BK) channel β4-subunit, stabilizing BKα on the apical membrane, the Cl−/HCO−3 exchanger, pendrin, and the apical KCl cotransporter (KCC3a), all of which are expressed specifically in pendrin-positive intercalated cells. Experiments in pendrin KO mice revealed that pendrin was required to increase K+ excretion with the high-KHCO3 diet. In summary, HCO−3 stimulates K+ excretion beyond a poorly absorbable anion effect, upregulating ENaC and ROMK in principal cells and BK, pendrin, and KCC3a in pendrin-positive intercalated cells. The adaptive mechanism prevents hyperkalemia and alkalosis with the consumption of alkaline ash-rich diets but may drive K+ wasting and hypokalemia in alkalosis. NEW & NOTEWORTHY Dietary anions profoundly impact K+ homeostasis. Here, we found that a K+-rich diet, containing HCO−3 as the counteranion, enhances the electrogenic K+ excretory machinery, epithelial Na+ channels, and renal outer medullary K+ channels, much more than a high-KCl diet. It also uniquely induces KCC3a and pendrin, in B-intercalated cells, providing an electroneutral KHCO3 secretion pathway. These findings reveal new K+ balance mechanisms that drive adaption to alkaline and K+-rich foods, which should guide new treatment strategies for K+ disorders. [ABSTRACT FROM AUTHOR]

Thiazide diuretics are used to treat hypertension; however, compensatory processes in the kidney can limit antihypertensive responses to this class of drugs. Here, we evaluated compensatory pathways in SPAK kinase-deficient mice, which are unable to activate the thiazide-sensitive sodium chloride cotransporter NCC (encoded by Slc12a3). Global transcriptional profiling, combined with biochemical, cell biological, and physiological phenotyping, identified the gene expression signature of the response and revealed how it establishes an adaptive physiology. Salt reabsorption pathways were created by the coordinate induction of a multigene transport system, involving solute carriers (encoded by Slc26a4, Slc4a8, and Slc4a9), carbonic anhydrase isoforms, and V-type [H.sup.+]-ATPase subunits in pendrin-positive intercalated cells (PP-ICs) and ENaC subunits in principal cells (PCs). A distal nephron remodeling process and induction of jagged 1/ NOTCH signaling, which expands the cortical connecting tubule with PCs and replaces acid-secreting [alpha]-ICs with PP- ICs, were partly responsible for the compensation. Salt reabsorption was also activated by induction of an [alpha]- ketoglutarate ([alpha]-KG) paracrine signaling system. Coordinate regulation of a multigene [alpha]-KG synthesis and transport pathway resulted in [alpha]-KG secretion into pro-urine, as the [alpha]-KG-activated GPCR (Oxgrl) increased on the PP-IC apical surface, allowing paracrine delivery of [alpha]-KG to stimulate salt transport. Identification of the integrated compensatory NaCl reabsorption mechanisms provides insight into thiazide diuretic efficacy., Introduction The sodium chloride cotransporter (NCC) of the SLC12A3 gene (1, 2) is the principal determinant of NaCl reabsorption in the distal convoluted tubule (DCT) (3) and the key target [...]

Urinary NH+4 excretion is decreased in chronic kidney disease (CKD), but very little is known about fecal NH+4 excretion. Sodium zirconium cyclosilicate (SZC) is a cation exchanger that selectively captures Kþ in the gastrointestinal tract. We investigated if SZC can sequester NH+4 in vivo and evaluated the effect of SZC on fecal NH+4 in a mouse model of CKD. Mice with CKD induced by 5/6 kidney ablation were fed either a regular diet or a diet containing SZC (4 g/kg) and followed for 7 days. Fecal NH+4 was measured before and after the addition of 50 meq KCl/L to release NH+4 from SZC. NH+4 sequestered in SZC in the gastrointestinal (GI) tract was estimated from the change in fecal NH+4 observed when KCl was added to liberate the sequestered NH+4 . In mice with CKD, fecal NH+4 excretion was higher than in normal mice and also higher than urine NH+4 excretion measured concurrently. Using data pooled from the SZC diet, the change in NH+4 was 6.5 ± 0.6 compared with 0.6 ± 0.6 lmol/g on the normal diet (P < 0.0001). In conclusion, fecal NH+4 excretion in CKD is increased and about sixfold higher than urine NH+4 excretion, revealing an important route of elimination of NH+4 present in the GI tract. SZC administration sequesters a substantial portion of NH+4 in the GI tract, suggesting that the binding of NH+4 offers therapeutic potential beyond its known primary action as a specific Kþ binder. [ABSTRACT FROM AUTHOR]

The Cl-/HCO3- exchanger pendrin in the kidney maintains acid-base balance and intravascular volume. Pendrin is upregulated in models associated with high circulating aldosterone concentration, such as dietary NaCl restriction or an aldosterone infusion. However, it has not been established if pendrin is similarly regulated by aldosterone with a high-K+ diet because the effects of accompanying anions have not been considered. Here, we explored how pendrin is modulated by different dietary potassium salts. Wild-type (WT) and aldosterone synthase (AS) knockout (KO) mice were randomized to control, high-KHCO3, or high-KCl diets. Dietary KCl and KHCO3 loading increased aldosterone in WT mice to the same extent but had opposite effects on pendrin abundance. KHCO3 loading increased pendrin protein and transcript abundance. Conversely, high-KCl diet feeding caused pendrin to decrease within 8 h of switching from the high-KHCO3 diet, coincident with an increase in plasma Cl- and a decrease in HCO3-. In contrast, switching the high-KCl diet to the high-KHCO3 diet caused pendrin to increase in WT mice. Experiments in AS KO mice revealed that aldosterone is necessary to optimally upregulate pendrin protein in response to the high-KHCO3 diet but not to increase pendrin mRNA. We conclude that pendrin is differentially regulated by different dietary potassium salts and that its regulation is prioritized by the dietary anion, providing a mechanism to prevent metabolic alkalosis with high-K+ base diets and safeguard against hyperchloremic acidosis with consumption of high-KCl diets. NEW & NOTEWORTHY Regulation of the Cl-/HCO3- exchanger pendrin has been suggested to explain the aldosterone paradox. A high-K+ diet has been proposed to downregulate a pendrin-mediated K+-sparing NaCl reabsorption pathway to maximize urinary K+ excretion. Here, we challenged the hypothesis, revealing that the accompanying anion, not K+, drives pendrin expression. Pendrin is downregulated with a high-KCl diet, preventing acidosis, and upregulated with an alkaline-rich high-K+ diet, preventing metabolic alkalosis. Pendrin regulation is prioritized for acid-base balance. [ABSTRACT FROM AUTHOR]