The regulation of salt transport and blood pressure by the WNK-SPAK/OSR1 signalling pathway

WNK1 Alleviates Chloride Efflux-Induced NLRP3 Inflammasome Activation and Subsequent Neuroinflammation in Early Brain Injury Following Subarachnoid Hemorrhage

The nod-like receptor family pyrin domain containing 3 (NLRP3) inflammasome plays a crucial role in the prognosis of subarachnoid hemorrhage (SAH). WNK1 kinase negatively regulates NLRP3 in various inflammatory conditions, but its role in early brain injury (EBI) after SAH remains unclear. In this study, we used an in vivo SAH model in rats/mice and AAV-WNK1 intraventricular injection to investigate its neuroprotective mechanisms. WNK1 expression was significantly reduced in SAH patient blood and SAH model brain tissue, correlating negatively with microglial activation. AAV-WNK1 alleviated brain edema, neuronal necrosis, behavioral deficits, and inflammation by inhibiting NLRP3 inflammasome activation. In hemin-stimulated BV-2 cells, WNK1 overexpression reduced NLRP3 activation and inflammatory cytokines. Chloride counteracted WNK1's inhibitory effects, and WNK1 suppressed P2X7R-induced NLRP3 activation. Mechanistically, WNK1 functioned via the OXSR1/STK39 pathway. These findings highlight WNK1 as a key regulator of intracellular chloride balance and neuroinflammation, presenting a potential therapeutic target for SAH treatment.

TNF inhibits NKCC2 phosphorylation by a calcineurin-dependent pathway

We previously demonstrated that tumor necrosis factor-alpha (TNF) inhibits Na+-K+-2Cl- cotransporter (NKCC2) phosphorylation in the thick ascending limb (TAL); however, the underlying mechanism remains unclear. We tested the hypothesis that the induction of calcineurin (CN) activity and the expression of CN isoforms contribute to the mechanism by which TNF inhibits phospho-NKCC2 (pNKCC2) expression. CN activity increased by approximately twofold in primary cultures of medullary (m)TAL cells challenged with mouse recombinant TNF. In contrast, silencing TNF production in mTAL cells using lentivirus U6-TNF-ex4 reduced CN activity. pNKCC2 expression decreased in mTAL cells challenged with TNF, whereas inhibition of CN activity with cyclosporine A (CsA) increased pNKCC2 expression. Although mTAL cells express both the calcineurin A subunit (CNA) α and β isoforms, only CNA β isoform mRNA increased after mTAL cells were challenged with TNF. In vivo, both TNF and CNA β expression increased in outer medulla (OM) from mice given 1% NaCl in the drinking water for 7 days and intrarenal lentivirus silencing of TNF selectively reduced expression of CNA β. Intrarenal injection of a lentivirus that specifically silenced CNA β (U6-CNAβ-ex6) increased pNKCC2 expression and attenuated the inhibitory effects of TNF on pNKCC2 expression in freshly isolated TAL tubules. Collectively, the study is the first to demonstrate that TNF increases CN activity and specifically induces β-isoform expression in the kidney. Since NKCC2 is a known target of the CNA β isoform, these findings suggest that a CN-dependent signaling pathway involving this isoform contributes to the mechanism by which TNF inhibits pNKCC2 expression.NEW & NOTEWORTHY The beneficial immunosuppressive effects of CsA are tempered by renal side effects including reduction of GFR, proximal tubule damage, reduced urinary concentration, fibrosis and hypertension. As chronic administration of CN inhibitors frequently induce hypertension and renal nephropathy in humans, understanding the molecular mechanisms by which CN isoforms regulate the activity of renal transporters may provide the framework for developing new drugs that more selectively modulate the diverse functions of CN.

A "Knob Switch" Model for the Phosphoregulatory Mechanism of KCC3 at the Carboxy-Terminal Domain

Phosphorylation is a reversible post-translational modification that can modulate protein function. For example, phosphorylation modifications of solute carrier family 12 (SLC12) proteins function as molecular switches that precisely regulate cation-chloride ion transport. Elucidating the phosphoregulatory mechanism of SLC12 at the carboxy-terminal domain (CTD) through structural determination approaches remains challenging due to the domain's disordered and flexible nature. In this study, molecular dynamics (MD) simulations and enhanced sampling techniques were employed to investigate the CTD phosphoregulatory mechanism of SLC12A6 (also known as KCC3). Atomistic MD and metadynamics simulations revealed that the dephosphorylation of residues T940 and T997 stabilizes CTD to a favorable state that "switches on" the solvent accessibility of the inward-facing pocket. Meanwhile, phosphorylation induces distinct orientations of the CTD, transitioning the dimer into another favorable state that "switches off" the solvent accessibility. The alteration of solvent accessibility in the inward-facing pocket influences the water and ion dynamics. Based on these findings, we propose a "knob switch" model to illustrate how CTD phosphorylation regulates ion transport in KCC3.

Target inhibition of SPAK in choroid plexus attenuates T cell infiltration and demyelination in experimental autoimmune encephalomyelitis

BACKGROUND

Disease-modifying therapies (DMTs) that prevent immune cell infiltration into the brain have demonstrated efficacy in multiple sclerosis (MS) treatment. However, their unpredictable adverse effects necessitate the development of safer therapeutic alternatives. The choroid plexus (ChP) functions as a crucial barrier against immune cell invasion, and previous studies have shown that preventing immune cell infiltration across the ChP reduces brain lesion in MS animal models. Understanding ChP barrier regulation is therefore essential for identifying novel therapeutic targets for MS. Here, we explored the role of Ste20-related proline/alanine-rich kinase (SPAK) in experimental autoimmune encephalomyelitis (EAE).

METHODS

We examined the expression patterns of SPAK signaling in ChP using immunofluorescence in the EAE model. To investigate the roles of SPAK, matrix metalloproteinase (MMP) 2 and MMP9 in EAE pathology, we performed ChP-specific gene manipulation via intracerebroventricular (ICV) injection of recombinant adeno-associated virus 2/5 (rAAV2/5). T cell infiltration into the central nervous system (CNS) was analyzed using CD4 immunostaining and flow cytometry. We employed cell immunofluorescence, transwell assays, and rescue experiments in vitro to study SPAK's effects on ChP epithelial barrier integrity. We also evaluated the protective effects of SPAK-Na-K-2Cl cotransporter-1 (NKCC1) inhibitors (ZT-1a and bumetanide) on immune invasion and demyelination during EAE using pharmacological approaches.

RESULTS

Following EAE induction, we observed progressive increases in both total and phosphorylated SPAK levels in ChP epithelium. Notably, ChP-specific SPAK knockdown significantly reduced T cell invasion and ameliorated EAE pathology, while SPAK overexpression exacerbated these effects. Bulk RNA sequencing and subsequent qPCR validation revealed that SPAK knockdown decreased the expression of MMP2 and MMP9, MMPs that compromise barrier integrity by degrading tight junction proteins. In vitro studies demonstrated that SPAK overexpression impaired ChP barrier function through the activator protein-1 (AP-1)-MMP2/9-zonula occludens-1 (ZO-1) axis. Furthermore, ChP-specific knockdown of either MMP2 or MMP9 protected against EAE pathology. Additionally, we identified SPAK-NKCC1 antagonists (bumetanide and ZT-1a) as promising therapeutic candidates for MS/EAE treatment.

CONCLUSIONS

Our findings demonstrate that targeting ChP-SPAK signaling represents a novel therapeutic strategy for MS treatment.

Osmotic stress influences microtubule drug response via WNK1 kinase signaling

Ion homeostasis is critical for numerous cellular processes, and disturbances in ionic balance underlie diverse pathological conditions, including cancer progression. Targeting ion homeostasis is even considered as a strategy to treat cancer. However, very little is known about how ion homeostasis may influence anticancer drug response. In a genome-wide CRISPR-Cas9 resistance drug screen, we identified and validated the master osmostress regulator WNK1 kinase as a modulator of the response to the mitotic inhibitor rigosertib. Osmotic stress and WNK1 inactivation lead to an altered response not only to rigosertib treatment but also to other microtubule-related drugs, minimizing the prototypical mitotic arrest produced by these compounds. This effect is due to an alteration in microtubule stability and polymerization dynamics, likely maintained by fluctuations in intracellular molecular crowding upon WNK1 inactivation. This promotes resistance to microtubule depolymerizing compounds, and increased sensitivity to microtubule stabilizing drugs. In summary, our data proposes WNK1 osmoregulation activity as an important modulator for microtubule-associated chemotherapy response.

PTEN mutations impair CSF dynamics and cortical networks by dysregulating periventricular neural progenitors

Enlargement of the cerebrospinal fluid (CSF)-filled brain ventricles (ventriculomegaly) is a defining feature of congenital hydrocephalus (CH) and an under-recognized concomitant of autism. Here, we show that de novo mutations in the autism risk gene PTEN are among the most frequent monogenic causes of CH and primary ventriculomegaly. Mouse Pten-mutant ventriculomegaly results from aqueductal stenosis due to hyperproliferation of periventricular Nkx2.1+ neural progenitor cells (NPCs) and increased CSF production from hyperplastic choroid plexus. Pten-mutant ventriculomegalic cortices exhibit network dysfunction from increased activity of Nkx2.1+ NPC-derived inhibitory interneurons. Raptor deletion or postnatal everolimus treatment corrects ventriculomegaly, rescues cortical deficits and increases survival by antagonizing mTORC1-dependent Nkx2.1+ NPC pathology. Thus, PTEN mutations concurrently alter CSF dynamics and cortical networks by dysregulating Nkx2.1+ NPCs. These results implicate a nonsurgical treatment for CH, demonstrate a genetic association of ventriculomegaly and ASD, and help explain neurodevelopmental phenotypes refractory to CSF shunting in select individuals with CH.

The evolving concepts of KS-WNK1 effect on NCC activity

The field of the with-no-lysine kinases (WNKs) regulation of the thiazide-sensitive NaCl cotransporter (NCC) began at the start of the century with the discovery that mutations in two members of the family, WNK1 and WNK4, resulted in a condition known as familial hyperkalemic hypertension (FHHt). Since FHHt is the mirror image of Gitelman's syndrome that is caused by inactivating mutations of the SLC12A3 gene encoding NCC, it was expected that WNKs modulated NCC activity and that the increased function of the cotransporter is the pathophysiological mechanism of FFHt. This turned out to be the case. However, experiments over the first years generated unexpected observations that confused the field. Although most has been clarified, one issue still under a certain level of controversy is the role of an isoform of WNK1 that is only expressed in the kidney, almost entirely in the distal convoluted tubule, known as KS-WNK1. In this work, we present an overview of how the knowledge about the physiology of KS-WNK1 evolved over the years and propose explanations to understand its role in renal physiology.

Update on NKCC2 regulation in the thick ascending limb (TAL) by membrane trafficking, phosphorylation, and protein-protein interactions

Purpose of review

The thick ascending limb (TAL) of loop of Henle is essential for NaCl, calcium and magnesium homeostasis, pH balance and for urine concentration. NKCC2 is the main transporter for NaCl reabsorption in the TAL and its regulation is very complex. There have been recent advancements toward understanding how NKCC2 is regulated by protein trafficking, protein-protein interaction, and phosphorylation/dephosphorylation. Here, we update the latest molecular mechanisms and players that control NKCC2 function, which gives an increasingly complex picture of NKKC2 regulation in the apical membrane of the TAL.

Recent Findings

Protein-protein interactions are required as a regulatory mechanism in many cellular processes. A handful of proteins have been recently identified as an interacting partner of NKCC2, which play major roles in regulating NKCC2 trafficking and activity. New players in NKCC2 internalization and trafficking have been identified. NKCC2 activity is also regulated by kinases and phosphatases, and there have been developments in that area as well.

Summary

Here we review the current understanding of apical trafficking of NKCC2 in the thick ascending limb (TAL) which is tightly controlled by protein-protein interactions, protein turnover and by phosphorylation and dephosphorylation. We discuss new proteins and processes that regulate NKCC2 that have physiological and pathological significance.

Water and chloride as allosteric inhibitors in WNK kinase osmosensing

Osmotic stress and chloride regulate the autophosphorylation and activity of the WNK1 and WNK3 kinase domains. The kinase domain of unphosphorylated WNK1 (uWNK1) is an asymmetric dimer possessing water molecules conserved in multiple uWNK1 crystal structures. Conserved waters are present in two networks, referred to here as conserved water networks 1 and 2 (CWN1 and CWN2). Here, we show that PEG400 applied to crystals of dimeric uWNK1 induces de-dimerization. Both the WNK1 the water networks and the chloride-binding site are disrupted by PEG400. CWN1 is surrounded by a cluster of pan-WNK-conserved charged residues. Here, we mutagenized these charges in WNK3, a highly active WNK isoform kinase domain, and WNK1, the isoform best studied crystallographically. Mutation of E314 in the Activation Loop of WNK3 (WNK3/E314Q and WNK3/E314A, and the homologous WNK1/E388A) enhanced the rate of autophosphorylation, and reduced chloride sensitivity. Other WNK3 mutants reduced the rate of autophosphorylation activity coupled with greater chloride sensitivity than wild-type. The water and chloride regulation thus appear linked. The lower activity of some mutants may reflect effects on catalysis. Crystallography showed that activating mutants introduced conformational changes in similar parts of the structure to those induced by PEG400. WNK activating mutations and crystallography support a role for CWN1 in WNK inhibition consistent with water functioning as an allosteric ligand.

Actin cytoskeleton and associated myosin motors within the renal epithelium

This review highlights the complexity of renal epithelial cell membrane architectures and organelles through careful review of ultrastructural and physiological studies published over the past several decades. We also showcase the vital roles played by the actin cytoskeleton and actin-associated myosin motor proteins in regulating cell type-specific physiological functions within the cells of the renal epithelium. The purpose of this review is to provide a fresh conceptual framework to explain the structure-function relationships that exist between the actin cytoskeleton, organelle structure, and cargo transport within the mammalian kidney. With recent advances in technologies to visualize the actin cytoskeleton and associated proteins within intact kidneys, it has become increasingly imperative to reimagine the functional roles of these proteins in situ to provide a rationale for their unique, cell type-specific functions that are necessary to establish and maintain complex physiological processes.

Water and chloride as allosteric inhibitors in WNK kinase osmosensing

Osmotic stress and chloride regulate the autophosphorylation and activity of the WNK1 and WNK3 kinase domains. The kinase domain of unphosphorylated WNK1 (uWNK1) is an asymmetric dimer possessing water molecules conserved in multiple uWNK1 crystal structures. Conserved waters are present in two networks, referred to here as conserved water networks 1 and 2 (CWN1and CWN2). Here we show that PEG400 applied to crystals of dimeric uWNK1 induces de-dimerization. Both the WNK1 the water networks and the chloride binding site and are disrupted by PEG400. CWN1 is surrounded by a cluster of pan-WNK-conserved charged residues. Here we mutagenized these charges in WNK3, a highly active WNK isoform kinase domain, and WNK1, the isoform best studied crystallographically. Mutation of E314 in the Activation Loop of WNK3 (WNK3/E314Q and WNK3/E314A, and the homologous WNK1/E388A) enhanced the rate of autophosphorylation, and reduced chloride sensitivity. Other WNK3 Cluster mutants reduced the rate of autophosphorylation activity coupled with greater chloride sensitivity than wild-type. The water and chloride regulation thus appear linked. The lower activity of some mutants may reflect effects on catalysis. Crystallography showed that activating mutants introduced conformational changes in similar parts of the structure to those induced by PEG400. WNK activating mutations and crystallography support a role for CWN1 in WNK inhibition consistent with water functioning as an allosteric ligand.

Role of calcineurin in regulating renal potassium (K+) excretion: Mechanisms of calcineurin inhibitor-induced hyperkalemia

Calcineurin, protein phosphatase 2B (PP2B) or protein phosphatase 3 (PP3), is a calcium-dependent serine/threonine protein phosphatase. Calcineurin is widely expressed in the kidney and regulates renal Na+ and K+ transport. In the thick ascending limb, calcineurin plays a role in inhibiting NKCC2 function by promoting the dephosphorylation of the cotransporter and an intracellular sorting receptor, called sorting-related-receptor-with-A-type repeats (SORLA), is involved in modulating the effect of calcineurin on NKCC2. Calcineurin also participates in regulating thiazide-sensitive NaCl-cotransporter (NCC) in the distal convoluted tubule. The mechanisms by which calcineurin regulates NCC include directly dephosphorylation of NCC, regulating Kelch-like-3/CUL3 E3 ubiquitin-ligase complex, which is responsible for WNK (with-no-lysin-kinases) ubiquitination, and inhibiting Kir4.1/Kir5.1, which determines NCC expression/activity. Finally, calcineurin is also involved in regulating ROMK (Kir1.1) channels in the cortical collecting duct and Cyp11 2 expression in adrenal zona glomerulosa. In summary, calcineurin is involved in the regulation of NKCC2, NCC, and inwardly rectifying K+ channels in the kidney, and it also plays a role in modulating aldosterone synthesis in adrenal gland, which regulates epithelial-Na+-channel expression/activity. Thus, application of calcineurin inhibitors (CNIs) is expected to abrupt calcineurin-mediated regulation of transepithelial Na+ and K+ transport in the kidney. Consequently, CNIs cause hypertension, compromise renal K+ excretion, and induce hyperkalemia.

The biogenesis of potassium transporters: implications of disease-associated mutations

The concentration of intracellular and extracellular potassium is tightly regulated due to the action of various ion transporters, channels, and pumps, which reside primarily in the kidney. Yet, potassium transporters and cotransporters play vital roles in all organs and cell types. Perhaps not surprisingly, defects in the biogenesis, function, and/or regulation of these proteins are linked to range of catastrophic human diseases, but to date, few drugs have been approved to treat these maladies. In this review, we discuss the structure, function, and activity of a group of potassium-chloride cotransporters, the KCCs, as well as the related sodium-potassium-chloride cotransporters, the NKCCs. Diseases associated with each of the four KCCs and two NKCCs are also discussed. Particular emphasis is placed on how these complex membrane proteins fold and mature in the endoplasmic reticulum, how non-native forms of the cotransporters are destroyed in the cell, and which cellular factors oversee their maturation and transport to the cell surface. When known, we also outline how the levels and activities of each cotransporter are regulated. Open questions in the field and avenues for future investigations are further outlined.

Targeting kelch-like (KLHL) proteins: achievements, challenges and perspectives

Kelch-like proteins (KLHLs) are a large family of BTB-containing proteins. KLHLs function as the substrate adaptor of Cullin 3-RING ligases (CRL3) to recognize substrates. KLHLs play pivotal roles in regulating various physiological and pathological processes by modulating the ubiquitination of their respective substrates. Mounting evidence indicates that mutations or abnormal expression of KLHLs are associated with various human diseases. Targeting KLHLs is a viable strategy for deciphering the KLHLs-related pathways and devising therapies for associated diseases. Here, we comprehensively review the known KLHLs inhibitors to date and the brilliant ideas underlying their development.

Excess Salt Intake Activates IL-21-Dominant Autoimmune Diabetogenesis via a Salt-Regulated Ste20-Related Proline/Alanine-Rich Kinase in CD4 T Cells

The fundamental mechanisms by which a diet affects susceptibility to or modifies autoimmune diseases are poorly understood. Excess dietary salt intake acts as a risk factor for autoimmune diseases; however, little information exists on the impact of salt intake on type 1 diabetes. To elucidate the potential effect of high salt intake on autoimmune diabetes, nonobese diabetic (NOD) mice were fed a high-salt diet (HSD) or a normal-salt diet (NSD) from 6 to 12 weeks of age and monitored for diabetes development. Our results revealed that the HSD accelerated diabetes progression with more severe insulitis in NOD mice in a CD4+ T-cell-autonomous manner when compared with the NSD group. Moreover, expression of IL-21 and SPAK in splenic CD4+ T cells from HSD-fed mice was significantly upregulated. Accordingly, we generated T-cell-specific SPAK knockout (CKO) NOD mice and demonstrated that SPAK deficiency in T cells significantly attenuated diabetes development in NOD mice by downregulating IL-21 expression in CD4+ T cells. Furthermore, HSD-triggered diabetes acceleration was abolished in HSD-fed SPAK CKO mice when compared with HSD-fed NOD mice, suggesting an essential role of SPAK in salt-exacerbated T-cell pathogenicity. Finally, pharmacological inhibition of SPAK activity using a specific SPAK inhibitor (closantel) in NOD mice ameliorated diabetogenesis, further illuminating the potential of a SPAK-targeting immunotherapeutic approach for autoimmune diabetes. Here, we illustrate that a substantial association between salt sensitivity and the functional impact of SPAK on T-cell pathogenicity is a central player linking high-salt-intake influences to immunopathophysiology of diabetogenesis in NOD mice.

ARTICLE HIGHLIGHTS

Kinome and phosphoproteome reprogramming underlies the aberrant immune responses in critically ill COVID-19 patients

SARS-CoV-2 infection triggers extensive host immune reactions, leading to severe diseases in certain individuals. However, the molecular basis underlying the excessive yet non-productive immune responses in severe COVID-19 remains incompletely understood. In this study, we conducted a comprehensive analysis of the peripheral blood mononuclear cell (PBMC) proteome and phosphoproteome in sepsis patients positive or negative for SARS-CoV-2 infection, as well as healthy subjects, using quantitative mass spectrometry. Our findings demonstrate dynamic changes in the COVID-19 PBMC proteome and phosphoproteome during disease progression, with distinctive protein or phosphoprotein signatures capable of distinguishing longitudinal disease states. Furthermore, SARS-CoV-2 infection induces a global reprogramming of the kinome and phosphoproteome, resulting in defective adaptive immune response mediated by the B and T lymphocytes, compromised innate immune responses involving the SIGLEC and SLAM family of immunoreceptors, and excessive cytokine-JAK-STAT signaling. In addition to uncovering host proteome and phosphoproteome aberrations caused by SARS-CoV-2, our work recapitulates several reported therapeutic targets for COVID-19 and identified numerous new candidates, including the kinases PKG1, CK2, ROCK1/2, GRK2, SYK, JAK2/3, TYK2, DNA-PK, PKCδ, and the cytokine IL-12.

Genome-wide identification and expression analysis of the WNK kinase gene family in soybean

WNK kinases are a unique class of serine/threonine protein kinases that lack a conserved catalytic lysine residue in the kinase domain, hence the name WNK (with no K, i.e., lysine). WNK kinases are involved in various physiological processes in plants, such as circadian rhythm, flowering time, and stress responses. In this study, we identified 26 WNK genes in soybean and analyzed their phylogenetic relationships, gene structures, chromosomal distribution, cis-regulatory elements, expression patterns, and conserved protein motifs. The soybean WNK genes were unevenly distributed on 15 chromosomes and underwent 21 segmental duplication events during evolution. We detected 14 types of cis-regulatory elements in the promoters of the WNK genes, indicating their potential involvement in different signaling pathways. The transcriptome database revealed tissue-specific and salt stress-responsive expression of WNK genes in soybean, the second of which was confirmed by salt treatments and qRT-PCR analysis. We found that most WNK genes were significantly up-regulated by salt stress within 3 h in both roots and leaves, except for WNK5, which showed a distinct expression pattern. Our findings provide valuable insights into the molecular characteristics and evolutionary history of the soybean WNK gene family and lay a foundation for further analysis of WNK gene functions in soybean.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-024-01440-5.

Sex differences in renal transporters: assessment and functional consequences

Mammalian kidneys are specialized to maintain fluid and electrolyte homeostasis. The epithelial transport processes along the renal tubule that match output to input have long been the subject of experimental and theoretical study. However, emerging data have identified a new dimension of investigation: sex. Like most tissues, the structure and function of the kidney is regulated by sex hormones and chromosomes. Available data demonstrate sex differences in the abundance of kidney solute and electrolyte transporters, establishing that renal tubular organization and operation are distinctly different in females and males. Newer studies have provided insights into the physiological consequences of these sex differences. Computational simulations predict that sex differences in transporter abundance are likely driven to optimize reproduction, enabling adaptive responses to the nutritional requirements of serial pregnancies and lactation - normal life-cycle changes that challenge the ability of renal transporters to maintain fluid and electrolyte homeostasis. Later in life, females may also undergo menopause, which is associated with changes in disease risk. Although numerous knowledge gaps remain, ongoing studies will provide further insights into the sex-specific mechanisms of sodium, potassium, acid-base and volume physiology throughout the life cycle, which may lead to therapeutic opportunities.

Genome-Wide Identification and Expression Analysis of WNK Kinase Gene Family in Acorus

WNK (With No Lysine) kinases are members of serine/threonine protein kinase family, which lack conserved a catalytic lysine (K) residue in protein kinase subdomain II and this residue is replaced by either asparagine, serine, or glycine residues. They are involved in various physiological regulations of flowering time, circadian rhythms, and abiotic stresses in plants. In this study, we identified the WNK gene family in two species of Acorus, and analyzed their phylogenetic relationship, physiochemical properties, subcellular localization, collinearity, and cis-elements. The results showed twenty-two WNKs in two Acorus (seven in Ac. gramineus and fifteen in Ac. calamus) have been identified and clustered into five main clades phylogenetically. Gene structure analysis showed all WNKs possessed essential STKc_WNK or PKc_like superfamily domains, and the gene structures and conserved motifs of the same clade were similar. All the WNKs harbored a large number of light response elements, plant hormone signaling elements, and stress resistance elements. Through a collinearity analysis, two and fourteen segmental duplicated gene pairs were identified in the Ac. gramineus and Ac. calamus, respectively. Moreover, we observed tissue-specificity of WNKs in Acorus using transcriptomic data, and their expressions in response to salt stress and cold stress were analyzed by qRT-PCR. The results showed WNKs are involved in the regulation of abiotic stresses. There were significant differences in the expression levels of most of the WNKs in the leaves and roots of Acorus under salt stress and cold stress, among which two members in Ac. gramineus (AgWNK3 and AgWNK4) and two members in Ac. calamus (AcWNK8 and AcWNK12) were most sensitive to stress. In summary, this paper will significantly contribute to the understanding of WNKs in monocots and thus provide a set up for functional genomics studies of WNK protein kinases.

SLC12A cryo-EM: analysis of relevant ion binding sites, structural domains, and amino acids

The solute carrier family 12A (SLC12A) superfamily of membrane transporters modulates the movement of cations coupled with chloride across the membrane. In doing so, these cotransporters are involved in numerous aspects of human physiology: cell volume regulation, ion homeostasis, blood pressure regulation, and neurological action potential via intracellular chloride concentration modulation. Their physiological characterization has been largely studied; however, understanding the mechanics of their function and the relevance of structural domains or specific amino acids has been a pending task. In recent years, single-particle cryogenic electron microscopy (cryo-EM) has been successfully applied to members of the SLC12A family including all K+:Cl- cotransporters (KCCs), Na+:K+:2Cl- cotransporter NKCC1, and recently Na+:Cl- cotransporter (NCC); revealing structural elements that play key roles in their function. The present review analyzes the data provided by these cryo-EM reports focusing on structural domains and specific amino acids involved in ion binding, domain interactions, and other important SCL12A structural elements. A comparison of cryo-EM data from NKCC1 and KCCs is presented in the light of the two recent NCC cryo-EM studies, to propose insight into structural elements that might also be found in NCC and are necessary for its proper function. In the final sections, the importance of key coordination residues for substrate specificity and their implication on various pathophysiological conditions and genetic disorders is reviewed, as this could provide the basis to correlate structural elements with the development of novel and selective treatments, as well as mechanistic insight into the function and regulation of cation-coupled chloride cotransporters (CCCs).

Hydrostatic Pressure Sensing by WNK kinases

Previous study has demonstrated that the WNK kinases 1 and 3 are direct osmosensors consistent with their established role in cell-volume control. WNK kinases may also be regulated by hydrostatic pressure. Hydrostatic pressure applied to cells in culture with N2 gas or to Drosophila Malpighian tubules by centrifugation induces phosphorylation of downstream effectors of endogenous WNKs. In vitro, the autophosphorylation and activity of the unphosphorylated kinase domain of WNK3 (uWNK3) is enhanced to a lesser extent than in cells by 190 kPa applied with N2 gas. Hydrostatic pressure measurably alters the structure of uWNK3. Data from size exclusion chromatography in line with multi-angle light scattering (SEC-MALS), SEC alone at different back pressures, analytical ultracentrifugation (AUC), NMR, and chemical crosslinking indicate a change in oligomeric structure in the presence of hydrostatic pressure from a WNK3 dimer to a monomer. The effects on the structure are related to those seen with osmolytes. Potential mechanisms of hydrostatic pressure activation of uWNK3 and the relationships of pressure activation to WNK osmosensing are discussed.

Maternal taurine as a modulator of Cl- homeostasis as well as of glycine/GABAA receptors for neocortical development

During brain and spinal cord development, GABA and glycine, the inhibitory neurotransmitters, cause depolarization instead of hyperpolarization in adults. Since glycine and GABAA receptors (GABAARs) are chloride (Cl-) ion channel receptor, the conversion of GABA/glycine actions during development is influenced by changes in the transmembrane Cl- gradient, which is regulated by Cl- transporters, NKCC1 (absorption) and KCC2 (expulsion). In immature neurons, inhibitory neurotransmitters are released in a non-vesicular/non-synaptic manner, transitioning to vesicular/synaptic release as the neuron matures. In other word, in immature neurons, neurotransmitters generally act tonically. Thus, the glycine/GABA system is a developmentally multimodal system that is required for neurogenesis, differentiation, migration, and synaptogenesis. The endogenous agonists for these receptors are not fully understood, we address taurine. In this review, we will discuss about the properties and function of taurine during development of neocortex. Taurine cannot be synthesized by fetuses or neonates, and is transferred from maternal blood through the placenta or maternal milk ingestion. In developing neocortex, taurine level is higher than GABA level, and taurine tonically activates GABAARs to control radial migration as a stop signal. In the marginal zone (MZ) of the developing neocortex, endogenous taurine modulates the spread of excitatory synaptic transmission, activating glycine receptors (GlyRs) as an endogenous agonist. Thus, taurine affects information processing and crucial developmental processes such as axonal growth, cell migration, and lamination in the developing cerebral cortex. Additionally, we also refer to the possible mechanism of taurine-regulating Cl- homeostasis. External taurine is uptake by taurine transporter (TauT) and regulates NKCC1 and KCC2 mediated by intracellular signaling pathway, with-no-lysine kinase 1 (WNK1) and its subsequent kinases STE20/SPS1-related proline-alanine-rich protein kinase (SPAK) and oxidative stress response kinase-1 (OSR1). Through the regulation of NKCC1 and KCC2, mediated by the WNK-SPAK/OSR1 signaling pathway, taurine plays a role in maintaining Cl- homeostasis during normal brain development.

WNK1 promotes water homeostasis by acting as a central osmolality sensor for arginine vasopressin release

Maintaining internal osmolality constancy is essential for life. Release of arginine vasopressin (AVP) in response to hyperosmolality is critical. Current hypotheses for osmolality sensors in circumventricular organs (CVOs) of the brain focus on mechanosensitive membrane proteins. The present study demonstrated that intracellular protein kinase WNK1 was involved. Focusing on vascular-organ-of-lamina-terminalis (OVLT) nuclei, we showed that WNK1 kinase was activated by water restriction. Neuron-specific conditional KO (cKO) of Wnk1 caused polyuria with decreased urine osmolality that persisted in water restriction and blunted water restriction-induced AVP release. Wnk1 cKO also blunted mannitol-induced AVP release but had no effect on osmotic thirst response. The role of WNK1 in the osmosensory neurons in CVOs was supported by neuronal pathway tracing. Hyperosmolality-induced increases in action potential firing in OVLT neurons was blunted by Wnk1 deletion or pharmacological WNK inhibitors. Knockdown of Kv3.1 channel in OVLT by shRNA reproduced the phenotypes. Thus, WNK1 in osmosensory neurons in CVOs detects extracellular hypertonicity and mediates the increase in AVP release by activating Kv3.1 and increasing action potential firing from osmosensory neurons.

Dietary sodium enhances the expression of SLC4 family transporters, IRBIT, L-IRBIT, and PP1 in rat kidney: Insights into the molecular mechanism for renal sodium handling

The kidney plays a central role in maintaining the fluid and electrolyte homeostasis in the body. Bicarbonate transporters NBCn1, NBCn2, and AE2 are expressed at the basolateral membrane of the medullary thick ascending limb (mTAL). In a previous study, NBCn1, NBCn2, and AE2 are proposed to play as a regulatory pathway to decrease NaCl reabsorption in the mTAL under high salt condition. When heterologously expressed, the activity of these transporters could be stimulated by the InsP3R binding protein released with inositol 1,4,5-trisphosphate (IRBIT), L-IRBIT (collectively the IRBITs), or protein phosphatase PP1. In the present study, we characterized by immunofluorescence the expression and localization of the IRBITs, and PP1 in rat kidney. Our data showed that the IRBITs were predominantly expressed from the mTAL through the distal renal tubules. PP1 was predominantly expressed in the TAL, but is also present in high abundance from the distal convoluted tubule through the medullary collecting duct. Western blotting analyses showed that the abundances of NBCn1, NBCn2, and AE2 as well as the IRBITs and PP1 were greatly upregulated in rat kidney by dietary sodium. Co-immunoprecipitation study provided the evidence for protein interaction between NBCn1 and L-IRBIT in rat kidney. Taken together, our data suggest that the IRBITs and PP1 play an important role in sodium handling in the kidney. We propose that the IRBITs and PP1 stimulates NBCn1, NBCn2, and AE2 in the basolateral mTAL to inhibit sodium reabsorption under high sodium condition. Our study provides important insights into understanding the molecular mechanism for the regulation of sodium homeostasis in the body.

Consideration of Kinase Inhibitors for the Treatment of Hydrocephalus

Hydrocephalus is a devastating condition characterized by excess cerebrospinal fluid (CSF) in the brain. Currently, the only effective treatment is surgical intervention, usually involving shunt placement, a procedure prone to malfunction, blockage, and infection that requires additional, often repetitive, surgeries. There are no long-term pharmaceutical treatments for hydrocephalus. To initiate an intelligent drug design, it is necessary to understand the biochemical changes underlying the pathology of this chronic condition. One potential commonality in the various forms of hydrocephalus is an imbalance in fluid–electrolyte homeostasis. The choroid plexus, a complex tissue found in the brain ventricles, is one of the most secretory tissues in the body, producing approximately 500 mL of CSF per day in an adult human. In this manuscript, two key transport proteins of the choroid plexus epithelial cells, transient receptor potential vanilloid 4 and sodium, potassium, 2 chloride co-transporter 1, will be considered. Both appear to play key roles in CSF production, and their inhibition or genetic manipulation has been shown to affect CSF volume. As with most transporters, these proteins are regulated by kinases. Therefore, specific kinase inhibitors are also potential targets for the development of pharmaceuticals to treat hydrocephalus.

Renal CD81 interacts with sodium potassium 2 chloride cotransporter and sodium chloride cotransporter in rats with lipopolysaccharide-induced preeclampsia

The kidney regulates blood pressure through salt/water reabsorption affected by tubular sodium transporters. Expanding our prior research on placental cluster of differentiation 81 (CD81), this study explores the interaction of renal CD81 with sodium transporters in preeclampsia (PE). Effects of renal CD81 with sodium transporters were determined in lipopolysaccharide (LPS)-induced PE rats and immortalized mouse renal distal convoluted tubule cells. Urinary exosomal CD81, sodium potassium 2 chloride cotransporter (NKCC2), and sodium chloride cotransporter (NCC) were measured in PE patients. LPS-PE rats had hypertension from gestational days (GD) 6 to 18 and proteinuria from GD9 to GD18. Urinary CD81 in both groups tented to rise during pregnancy. Renal CD81, not sodium transporters, was higher in LPS-PE than controls on GD14. On GD18, LPS-PE rats exhibited higher CD81 in kidneys and urine exosomes, higher renal total and phosphorylated renal NKCC2 and NCC with elevated mRNAs, and lower ubiquitinated NCC than controls. CD81 was co-immunoprecipitated with NKCC2 or NCC in kidney homogenates and co-immunostained with NKCC2 or NCC in apical membranes of renal tubules. In plasma membrane fractions, LPS-PE rats had greater amounts of CD81, NKCC2, and NCC than controls with enhanced co-immunoprecipitations of CD81 with NKCC2 or NCC. In renal distal convoluted tubule cells, silencing CD81 with siRNA inhibited NCC and prevented LPS-induced NCC elevation. Further, PE patients had higher CD81 in original urines, urine exosomes and higher NKCC2 and NCC in urine exosomes than controls. Thus, the upregulation of renal CD81 on NKCC2 and NCC may contribute to the sustained hypertension observed in LPS-PE model. Urine CD81 with NKCC2 and NCC may be used as biomarkers for PE.

The choroid plexus links innate immunity to CSF dysregulation in hydrocephalus

The choroid plexus (ChP) is the blood-cerebrospinal fluid (CSF) barrier and the primary source of CSF. Acquired hydrocephalus, caused by brain infection or hemorrhage, lacks drug treatments due to obscure pathobiology. Our integrated, multi-omic investigation of post-infectious hydrocephalus (PIH) and post-hemorrhagic hydrocephalus (PHH) models revealed that lipopolysaccharide and blood breakdown products trigger highly similar TLR4-dependent immune responses at the ChP-CSF interface. The resulting CSF "cytokine storm", elicited from peripherally derived and border-associated ChP macrophages, causes increased CSF production from ChP epithelial cells via phospho-activation of the TNF-receptor-associated kinase SPAK, which serves as a regulatory scaffold of a multi-ion transporter protein complex. Genetic or pharmacological immunomodulation prevents PIH and PHH by antagonizing SPAK-dependent CSF hypersecretion. These results reveal the ChP as a dynamic, cellularly heterogeneous tissue with highly regulated immune-secretory capacity, expand our understanding of ChP immune-epithelial cell cross talk, and reframe PIH and PHH as related neuroimmune disorders vulnerable to small molecule pharmacotherapy.

Comprehensive analysis of MAPK gene family in Populus trichocarpa and physiological characterization of PtMAPK3-1 in response to MeJA induction

Mitogen-activated protein kinases (MAPKs) play important roles in plant growth and development, as well as hormone and stress responses by signaling to eukaryotic cells, through MAPK cascade, the presence of various cues; thereby, regulating various responses. The MAPK cascade consists mainly of three gene families, MAPK, MAPKK, and MAPKKK, which activate downstream signaling pathways through sequential phosphorylation. Although the MAPK cascade gene family has been reported in several species, there is a lack of comprehensive analysis in poplar. We identified 21 MAPK genes, 11 MAPKK genes, and 104 MAPKKK genes in Populus trichocarpa. The phylogenetic classification was supported by conservative motif, gene structure and motif analysis. Whole genome duplication has an important role in the expansion of MAPK cascade genes. Analysis of promoter cis-elements and expression profiles indicates that MAPK cascade genes have important roles in plant growth and development, abiotic and biotic stresses, and phytohormone response. Expression profiling revealed a significant upregulation of PtMAPK3-1 expression in response to drought, salt and disease stresses. Poplar transiently overexpressing PtMAPK3-1 and treated with methyl jasmonic acid (MeJA) had higher catalase and peroxidase levels than non-overexpressing poplar. This work represents the first complete inventory of the MAPK cascade in P. trichocarpa, which reveals that PtMAPK3-1 is induced by the MeJA hormone and participates in the MeJA-induced enhancement of the antioxidant enzyme system.

Physiological Responses of the Bivalves Mytilus galloprovincialis and Ruditapes decussatus Following Exposure to Phenanthrene: Toxicokinetics, Dynamics and Biomarkers Study

The aim of the current study was to assess the multifaceted effects of the polycylic aromatic hydrocarbon phenanthrene, mainly used in the colouring, explosive, and pharmaceutical industries, on the physiology of two bivalve species with economic value as seafood, namely, the Mediterranean mussel Mytilus galloprovincyalis and the European clam Ruditapes decussatus. The current study assessed how the phenanthrene affected several biomarkers and biometric endpoints in both bivalves, based on an in vivo experiment in silico approach. The bivalves were exposed during four time slots (i.e., 7, 15, 21, and 28 days) to two concentrations of phenanthrene in water (50 µg/L and 100 µg/L). For the clam R. decussatus, an additional contamination of sediment was applied due their typical benthic lifestyle (50 µg/kg and 100 µg/kg). The phenanthrene significantly reduced the ability of bivalves to tolerate desiccation and their Median Lethal Time, and also inhibited the activity of the enzyme acetylcholinesterase in a time-dependent manner. The activity of catalase indicated that bivalves also experienced oxidative stress during the first 21 days of the experiment. The significant decline in catalase activity observed during the last week of the experiment for the mussel M. galloprovincyalis supported a depletion of enzymes caused by the phenanthrene. The phenanthrene has also toxicokinetic and toxicodynamic properties, as assessed by the in silico approach. Overall, the results obtained suggest that the bivalves Ruditapes decussatus and M. galloprovincyalis can be used as a sentinel species in monitoring studies to assess the environmental impact of phenanthene in marine ecosystems. The significance of our findings is based on the fact that in ecotoxicology, little is known about the chronic effects, the simultaneous use of multiple species as bioindicators, and the interactions molecular modelling.

Relation of Low Chloride Concentration to Diuretic Efficiency and Transplant-Free Survival in Children Hospitalized With Heart Failure

Serum chloride plays an important role in fluid homeostasis and is associated with impaired diuretic responsiveness and mortality in adults with heart failure (HF). We sought to characterize the relationship of serum chloride and diuretic efficiency (DE) and to determine its prognostic importance in children hospitalized with acute decompensated HF (ADHF). We studied DE, defined as net fluid output/kg+constant per mg of loop diuretic/kg, in 200 children hospitalized with ADHF. Median serum chloride at admission was 102 mmol/L (interquartile range 99 to 105 mmol/L), and hypochloremia (chloride ≤96 mmol/L) was present in 16% of the population at admission. Serum chloride correlated with serum sodium (r = 0.66; p < 0.001) and bicarbonate (r = -0.39; p < 0.001). In the adjusted analysis, lower chloride was associated with reduced DE (p < 0.001). Serum sodium was associated with DE on the unadjusted analysis; however, the association was eliminated when added to the model with chloride (p = 0.442). Lower chloride was also associated with features of inadequate decongestion during hospitalization: a positive fluid balance (p = 0.003), greater cumulative loop diuretic dose per weight (p = 0.001), addition of a thiazide diuretic during hospitalization (p < 0.001), less weight loss (p = 0.025), and longer length of stay (p = 0.003). Chloride concentration was independently associated with death or transplant 1 year after admission (hazard ratio 0.94; p < 0.001). As a dichotomous variable, hypochloremia was independently associated with reduced DE (p < 0.001) and decreased 1-year transplant-free survival (hazard ratio 2.3, p < 0.001). Lower serum chloride at hospital admission is strongly and independently associated with impaired DE and reduced transplant-free survival in children hospitalized with ADHF.

Potassium homeostasis: sensors, mediators, and targets

Transmembrane potassium (K) gradients are key determinants of membrane potential that can modulate action potentials, control muscle contractility, and influence ion channel and transporter activity. Daily K intake is normally equal to the amount of K in the entire extracellular fluid (ECF) creating a critical challenge - how to maintain ECF [K] and membrane potential in a narrow range during feast and famine. Adaptations to maintain ECF [K] include sensing the K intake, sensing ECF [K] vs. desired set-point and activating mediators that regulate K distribution between ECF and ICF, and regulate renal K excretion. In this focused review, we discuss the basis of these adaptions, including (1) potential mechanisms for rapid feedforward signaling to kidney and muscle after a meal (before a rise in ECF [K]), (2) how skeletal muscles sense and respond to changes in ECF [K], (3) effects of K on aldosterone biosynthesis, and (4) how the kidney responds to changes in ECF [K] to modify K excretion. The concepts of sexual dimorphisms in renal K handling adaptation are introduced, and the molecular mechanisms that can account for the benefits of a K-rich diet to maintain cardiovascular health are discussed. Although the big picture of K homeostasis is becoming more clear, we also highlight significant pieces of the puzzle that remain to be solved, including knowledge gaps in our understanding of initiating signals, sensors and their connection to homeostatic adjustments of ECF [K].

NKCC1 and KCC2: Structural insights into phospho-regulation

Inhibitory neurotransmission plays a fundamental role in the central nervous system, with about 30–50% of synaptic connections being inhibitory. The action of both inhibitory neurotransmitter, gamma-aminobutyric-acid (GABA) and glycine, mainly relies on the intracellular Cl^– concentration in neurons. This is set by the interplay of the cation chloride cotransporters NKCC1 (Na⁺, K⁺, Cl^– cotransporter), a main Cl^– uptake transporter, and KCC2 (K⁺, Cl^– cotransporter), the principle Cl^– extruder in neurons. Accordingly, their dysfunction is associated with severe neurological, psychiatric, and neurodegenerative disorders. This has triggered great interest in understanding their regulation, with a strong focus on phosphorylation. Recent structural data by cryogenic electron microscopy provide the unique possibility to gain insight into the action of these phosphorylations. Interestingly, in KCC2, six out of ten (60%) known regulatory phospho-sites reside within a region of 134 amino acid residues (12% of the total residues) between helices α8 and α9 that lacks fixed or ordered three-dimensional structures. It thus represents a so-called intrinsically disordered region. Two further phospho-sites, Tyr⁹⁰³ and Thr⁹⁰⁶, are also located in a disordered region between the ß8 strand and the α8 helix. We make the case that especially the disordered region between helices α8 and α9 acts as a platform to integrate different signaling pathways and simultaneously constitute a flexible, highly dynamic linker that can survey a wide variety of distinct conformations. As each conformation can have distinct binding affinities and specificity properties, this enables regulation of [Cl^–]_i and thus the ionic driving force in a history-dependent way. This region might thus act as a molecular processor underlying the well described phenomenon of ionic plasticity that has been ascribed to inhibitory neurotransmission. Finally, it might explain the stunning long-range effects of mutations on phospho-sites in KCC2.

WNK1 in Malignant Behaviors: A Potential Target for Cancer?

Metastasis is the major cause of mortality in cancer patients. Analyses of mouse models and patient data have implicated the protein kinase WNK1 as one of a handful of genes uniquely linked to a subset of invasive cancers. WNK1 signaling pathways are widely implicated in the regulation of ion co-transporters and in controlling cell responses to osmotic stress. In this review we will discuss its actions in tumor malignancy in human cancers and present evidence for its function in invasion, migration, angiogenesis and mesenchymal transition.

NF-κB Signaling-Mediated Activation of WNK-SPAK-NKCC1 Cascade in Worsened Stroke Outcomes of Ang II-Hypertensive Mice

BACKGROUND

Worsened stroke outcomes with hypertension comorbidity are insensitive to blood pressure-lowering therapies. In an experimental stroke model with comorbid hypertension, we investigated causal roles of ang II (angiotensin II)-mediated stimulation of the brain WNK (with no lysine [K] kinases)-SPAK (STE20/SPS1-related proline/alanine-rich kinase)-NKCC1 (Na-K-Cl cotransporter) complex in worsened outcomes.

METHODS

Saline- or ang II-infused C57BL/6J male mice underwent stroke induced by permanent occlusion of the distal branches of the middle cerebral artery. Mice were randomly assigned to receive either vehicle dimethyl sulfoxide/PBS (2 mL/kg body weight/day, IP), a novel SPAK inhibitor, 5-chloro-N-(5-chloro-4-((4-chlorophenyl)(cyano)methyl)-2-methylphenyl)-2-hydroxybenzamide (ZT-1a' 5 mg/kg per day, IP) or a NF-κB (nuclear factor-κB) inhibitor TAT-NBD (transactivator of transcription-NEMO-binding domain' 20 mg/kg per day, IP). Activation of brain NF-κB and WNK-SPAK-NKCC1 cascade as well as ischemic stroke outcomes were examined.

RESULTS

Stroke triggered a 2- to 5-fold increase of WNK (isoforms 1, 2, 4), SPAK/OSR1 (oxidative stress-responsive kinase 1), and NKCC1 protein in the ang II-infused hypertensive mouse brains at 24 hours after stroke, which was associated with increased nuclear translocation of phospho-NF-κB protein in the cortical neurons (a Pearson correlation r of 0.77, P<0.005). The upregulation of WNK-SPAK-NKCC1 cascade proteins resulted from increased NF-κB recruitment on Wnk1, Wnk2, Wnk4, Spak, and Nkcc1 gene promoters and was attenuated by NF-κB inhibitor TAT-NBD. Poststroke administration of SPAK inhibitor ZT-1a significantly reduced WNK-SPAK-NKCC1 complex activation, brain lesion size, and neurological function deficits in the ang II-hypertensive mice without affecting blood pressure and cerebral blood flow.

CONCLUSIONS

The ang II-induced stimulation of NF-κB transcriptional activity upregulates brain WNK-SPAK-NKCC1 cascade and contributes to worsened ischemic stroke outcomes, illustrating the brain WNK-SPAK-NKCC1 complex as a therapeutic target for stroke with comorbid hypertension.

CCT and CCT-Like Modular Protein Interaction Domains in WNK Signaling

The WNK [with no lysine (K)] kinases and their downstream effector kinases, oxidative stress responsive 1 (OSR1) and SPS/STE20-related proline-alanine-rich kinase (SPAK), have well established functions in the maintenance of cell volume and ion homeostasis. Mutations in these kinases have been linked to an inherited form of hypertension, neurologic defects, and other pathologies. A rapidly expanding body of evidence points to the involvement of WNKs in regulating multiple diverse cellular processes as well as the progression of some forms of cancer. How OSR1 and SPAK contribute to these processes is well understood in some cases but completely unknown in others. OSR1 and SPAK are targeted to both WNKs and substrates via their conserved C-terminal (CCT) protein interaction domains. Considerable effort has been put forth to understand the structure, function, and interaction specificity of the CCT domains in relation to WNK signaling, and multiple inhibitors of WNK signaling target these domains. The domains bind RFxV and RxFxV protein sequence motifs with the consensus sequence R-F-x-V/I or R-x-F-x-V/I, but residues outside the core motif also contribute to specificity. CCT interactions are required for OSR1 and SPAK activation and deactivation as well as cation-chloride cotransporter substrate phosphorylation. All four WNKs also contain CCT-like domains that have similar structures and conserved binding residues when compared with CCT domains, but their functions and interaction specificities are mostly unknown. A better understanding of the varied actions of these domains and their interactions will better define the known signaling mechanisms of the WNK pathway as well as uncover new ones. SIGNIFICANCE STATEMENT: WNK [with no lysine (K)] kinases and their downstream effector kinases, oxidative stress responsive 1 (OSR1) and SPS/STE20-related proline-alanine-rich kinase (SPAK), have been shown to be involved in an array of diverse cellular processes. Here we review the function of modular protein interaction domains found in OSR1 and SPAK as well as related domains found in WNKs.

Sequence and structural variations determining the recruitment of WNK kinases to the KLHL3 E3 ligase

The BTB-Kelch protein KLHL3 is a Cullin3-dependent E3 ligase that mediates the ubiquitin-dependent degradation of kinases WNK1-4 to control blood pressure and cell volume. A crystal structure of KLHL3 has defined its binding to an acidic degron motif containing a PXXP sequence that is strictly conserved in WNK1, WNK2 and WNK4. Mutations in the second proline abrograte the interaction causing the hypertension syndrome pseudohypoaldosteronism type II. WNK3 shows a diverged degron motif containing four amino acid substitutions that remove the PXXP motif raising questions as to the mechanism of its binding. To understand this atypical interaction, we determined the crystal structure of the KLHL3 Kelch domain in complex with a WNK3 peptide. The electron density enabled the complete 11-mer WNK-family degron motif to be traced for the first time revealing several conserved features not captured in previous work, including additional salt bridge and hydrogen bond interactions. Overall, the WNK3 peptide adopted a conserved binding pose except for a subtle shift to accommodate bulkier amino acid substitutions at the binding interface. At the centre, the second proline was substituted by WNK3 Thr541, providing a unique phosphorylatable residue among the WNK-family degrons. Fluorescence polarisation and structural modelling experiments revealed that its phosphorylation would abrogate the KLHL3 interaction similarly to hypertension-causing mutations. Together, these data reveal how the KLHL3 Kelch domain can accommodate the binding of multiple WNK isoforms and highlight a potential regulatory mechanism for the recruitment of WNK3.

Activation of the Thiazide-Sensitive Sodium-Chloride Cotransporter by Beta3-Adrenoreceptor in the Distal Convoluted Tubule

We previously showed that the beta-3 adrenergic receptor (BAR3) is expressed in most segments of the nephron where its agonism promotes a potent antidiuretic effect. We localized BAR3 in distal convoluted tubule (DCT) cells expressing the thiazide-sensitive sodium-chloride cotransporter (NCC). Aim of this study is to investigate the possible functional role of BAR3 on NCC modulation in DCT cells. Here, we found that, in mice, the knockout of BAR3 was paralleled by a significant attenuation of NCC phosphorylation, paralleled by reduced expression and activation of STE-20/SPS1-related proline-alanine-rich kinase (SPAK) and WNKs the main kinases involved in NCC activation. Conversely, in BAR1/2 knockout mice, we found reduced NCC abundance with no changes in the phosphorylation state of NCC. Moreover, selective BAR3 agonism promotes both SPAK and NCC activation in wild-type mouse kidney slices. In conclusion, our findings suggest a novel role for BAR3 in the regulation of NCC in DCT.

Pharmacogenetic polymorphisms affecting bisoprolol response

β-blockers are commonly prescribed to treat multiple cardiovascular (CV) diseases, but, frequently, adverse drug reactions and intolerance limit their use in clinical practice. Interindividual variability in response to β-blockers may be explained by genetic differences. In fact, pharmacogenetic interactions for some of these drugs have been widely studied, such as metoprolol. But studies that explore genetic variants affecting bisoprolol response are inconclusive, limited or confusing because of mixed results with other β-Blockers, different genetic polymorphisms observed, endpoint studied etc. Because of this, we performed a systematic review in order to find relevant genetic variants affecting bisoprolol response. We have found genetic polymorphism in several genes, but most of the studies focused in ADRB variants. The ADRB1 Arg389Gly (rs1801253) was the most studied genetic polymorphism and it seems to influence the response to bisoprolol, although studies are inconclusive. Even, we performed a meta-analysis about its influence on systolic/diastolic blood pressure in patients treated with bisoprolol, but this did not show statistically significant results. In conclusion, many genetic polymorphisms have been assessed about their influence on patients´ response to bisoprolol and the ADRB1 Arg389Gly (rs1801253) seems the most relevant genetic polymorphism in this regard but results have not been confirmed with a meta-analysis. Our results support the need of further studies about the impact of genetic variants on bisoprolol response, considering different genetic polymorphisms and conducting single and multiple SNPs analysis, including other clinical parameters related to bisoprolol response in a multivariate study.

Obesity Attenuates Ventilator-Induced Lung Injury by Modulating the STAT3-SOCS3 Pathway

Background

Ventilator-induced lung injury (VILI) is characterized by vascular barrier dysfunction and suppression of alveolar fluid clearance (AFC). Obesity itself leads to chronic inflammation, which may initiate an injurious cascade to the lungs and simultaneously induce a protective feedback. In this study, we investigated the protective mechanism of obesity on VILI in a mouse model.

Methods

The VILI model was set up via 6-h mechanical ventilation with a high tidal volume. Parameters including lung injury score, STAT3/NFκB pathway, and AFC were assessed. Mice with diet-induced obesity were obtained by allowing free access to a high-fat diet since the age of 3 weeks. After a 9-week diet intervention, these mice were sacrificed at the age of 12 weeks. The manipulation of SOCS3 protein was achieved by siRNA knockdown and pharmaceutical stimulation using hesperetin. WNK4 knockin and knockout obese mice were used to clarify the pathway of AFC modulation.

Results

Obesity itself attenuated VILI. Knockdown of SOCS3 in obese mice offset the protection against VILI afforded by obesity. Hesperetin stimulated SOCS3 upregulation in nonobese mice and provided protection against VILI. In obese mice, the WNK4 axis was upregulated at the baseline, but was significantly attenuated after VILI compared with nonobese mice. At the baseline, the manipulation of SOCS3 by siRNA and hesperetin also led to the corresponding alteration of WNK4, albeit to a lesser extent. After VILI, WNK4 expression correlated with STAT3/NFκB activation, regardless of SOCS3 status. Obese mice carrying WNK4 knockout had VILI with a severity similar to that of wild-type obese mice. The severity of VILI in WNK4-knockin obese mice was counteracted by obesity, similar to that of wild-type nonobese mice only.

Conclusions

Obesity protects lungs from VILI by upregulating SOCS3, thus suppressing the STAT3/NFκB inflammatory pathway and enhancing WNK4-related AFC. However, WNK4 activation is mainly from direct NFκB downstreaming, and less from SOCS3 upregulation. Moreover, JAK2-STAT3/NFκB signaling predominates the pathogenesis of VILI. Nevertheless, the interaction between SOCS3 and WNK4 in modulating VILI in obesity warrants further investigation.

Molecular Mechanism of Inhibiting WNK Binding to OSR1 by Targeting the Allosteric Pocket of the OSR1-CCT Domain with Potential Antihypertensive Inhibitors: An In Silico Study

The oxidative-stress-responsive kinase 1 (OSR1) and the STE20/SPS1-related proline-alanine-rich kinase (SPAK) are physiological substrates of the with-no-lysine (WNK) kinase. They are the master regulators of cation Cl- cotransporters that could be targeted for discovering novel antihypertensive agents. Both kinases have a conserved carboxy-terminal (CCT) domain that recognizes a unique peptide motif (Arg-Phe-Xaa-Val) present in their upstream kinases and downstream substrates. Here, we have combined molecular docking with molecular dynamics simulations and free-energy calculations to identify potential inhibitors that can bind to the allosteric pocket of the OSR1-CCT domain and impede its interaction with the WNK peptide. Our study revealed that STOCK1S-14279 and Closantel bound strongly to the allosteric pocket of OSR1 and displaced the WNK peptide from the primary pocket of OSR1. We showed that primarily Arg1004 and Gln1006 of the WNK4-peptide motif were involved in strong H-bond interactions with Glu453 and Arg451 of OSR1. Besides, our study revealed that atoms of Arg1004 were solvent-exposed in cases of STOCK1S-14279 and Closantel, implying that the WNK4 peptide was moved out of the pocket. Overall, the predicted potential inhibitors altogether abolish the OSR1-WNK4-peptide interaction, suggesting their potency as a prospective allosteric inhibitor against OSR1.

Osmosensing by WNK Kinases

With No Lysine (K) WNK kinases regulate electro-neutral cotransporters that are controlled by osmotic stress and chloride. We showed previously that autophosphorylation of WNK1 is inhibited by chloride, raising the possibility that WNKs are activated by osmotic stress. Here we demonstrate that unphosphorylated WNK isoforms 3 and 1 autophosphorylate in response to osmotic pressure in vitro, applied with the crowding agent polyethylene glycol (PEG)400 or osmolyte ethylene glycol (EG), and that this activation is opposed by chloride. Small angle x-ray scattering of WNK3 in the presence and absence of PEG400, static light scattering in EG, and crystallography of WNK1 were used to understand the mechanism. Osmosensing in WNK3 and WNK1 appears to occur through a conformational equilibrium between an inactive, unphosphorylated, chloride-binding dimer and an autophosphorylation-competent monomer. An improved structure of the inactive kinase domain of WNK1, and a comparison with the structure of a monophosphorylated form of WNK1, suggests that large cavities, greater hydration, and specific bound water may participate in the osmosensing mechanism. Our prior work showed that osmolytes have effects on the structure of phosphorylated WNK1, suggestive of multiple stages of osmotic regulation in WNKs.

Axon morphogenesis and maintenance require an evolutionary conserved safeguard function of Wnk kinases antagonizing Sarm and Axed

The molecular and cellular mechanisms underlying complex axon morphogenesis are still poorly understood. We report a novel, evolutionary conserved function for the Drosophila Wnk kinase (dWnk) and its mammalian orthologs, WNK1 and 2, in axon branching. We uncover that dWnk, together with the neuroprotective factor Nmnat, antagonizes the axon-destabilizing factors D-Sarm and Axundead (Axed) during axon branch growth, revealing a developmental function for these proteins. Overexpression of D-Sarm or Axed results in axon branching defects, which can be blocked by overexpression of dWnk or Nmnat. Surprisingly, Wnk kinases are also required for axon maintenance of adult Drosophila and mouse cortical pyramidal neurons. Requirement of Wnk for axon maintenance is independent of its developmental function. Inactivation of dWnk or mouse Wnk1/2 in mature neurons leads to axon degeneration in the adult brain. Therefore, Wnk kinases are novel signaling components that provide a safeguard function in both developing and adult axons.

Mechanistic interactions of uromodulin with the thick ascending limb: perspectives in physiology and hypertension

Hypertension is a significant risk factor for cardiovascular disease and mortality worldwide. The kidney is a major regulator of blood pressure and electrolyte homeostasis, with monogenic disorders indicating a link between abnormal ion transport and salt-sensitive hypertension. However, the association between salt and hypertension remains controversial. Thus, there is continued interest in deciphering the molecular mechanisms behind these processes. Uromodulin (UMOD) is the most abundant protein in the normal urine and is primarily synthesized by the thick ascending limb epithelial cells of the kidney. Genome-wide association studies have linked common UMOD variants with kidney function, susceptibility to chronic kidney disease and hypertension independent of renal excretory function. This review will discuss and provide predictions on the role of the UMOD protein in renal ion transport and hypertension based on current observational, biochemical, genetic, pharmacological and clinical evidence.

Phosphorylated WNK kinase networks in recoded bacteria recapitulate physiological function

Advances in genetic code expansion have enabled the production of proteins containing site-specific, authentic post-translational modifications. Here, we use a recoded bacterial strain with an expanded genetic code to encode phosphoserine into a human kinase protein. We directly encode phosphoserine into WNK1 (with-no-lysine [K] 1) or WNK4 kinases at multiple, distinct sites, which produced activated, phosphorylated WNK that phosphorylated and activated SPAK/OSR kinases, thereby synthetically activating this human kinase network in recoded bacteria. We used this approach to identify biochemical properties of WNK kinases, a motif for SPAK substrates, and small-molecule kinase inhibitors for phosphorylated SPAK. We show that the kinase inhibitors modulate SPAK substrates in cells, alter cell volume, and reduce migration of glioblastoma cells. Our work establishes a protein-engineering platform technology that demonstrates that synthetically active WNK kinase networks can accurately model cellular systems and can be used more broadly to target networks of phosphorylated proteins for research and discovery.

WNK-SPAK/OSR1-NCC kinase signaling pathway as a novel target for the treatment of salt-sensitive hypertension

Hypertension is the most prevalent health condition worldwide, affecting ~1 billion people. Gordon's syndrome is a form of secondary hypertension that can arise due to a number of possible mutations in key genes that encode proteins in a pathway containing the With No Lysine [K] (WNK) and its downstream target kinases, SPS/Ste20-related proline-alanine-rich kinase (SPAK) and oxidative stress responsive kinase 1 (OSR1). This pathway regulates the activity of the thiazide-sensitive sodium chloride cotransporter (NCC), which is responsible for NaCl reabsorption in the distal nephron. Therefore, mutations in genes encoding proteins that regulate the NCC proteins disrupt ion homeostasis and cause hypertension by increasing NaCl reabsorption. Thiazide diuretics are currently the main treatment option for Gordon's syndrome. However, they have a number of side effects, and chronic usage can lead to compensatory adaptations in the nephron that counteract their action. Therefore, recent research has focused on developing novel inhibitory molecules that inhibit components of the WNK-SPAK/OSR1-NCC pathway, thereby reducing NaCl reabsorption and restoring normal blood pressure. In this review we provide an overview of the currently reported molecular inhibitors of the WNK-SPAK/OSR1-NCC pathway and discuss their potential as treatment options for Gordon's syndrome.

Molecular characteristics and physiological roles of Na+ -K+ -Cl- cotransporter 2

Na+ -K+ -Cl- cotransporter 2 (NKCC2; SLC12A1) is an integral membrane protein that comes as three splice variants and mediates the cotranslocation of Na+ , K+ , and Cl- ions through the apical membrane of the thick ascending loop of Henle (TALH). In doing so, and through the involvement of other ion transport systems, it allows this nephron segment to reclaim a large fraction of the ultrafiltered Na+ , Cl- , Ca2+ , Mg2+ , and HCO3- loads. The functional relevance of NKCC2 in human is illustrated by the many abnormalities that result from the inactivation of this transport system through the use of loop diuretics or in the setting of inherited disorders. The following presentation aims at discussing the physiological roles and molecular characteristics of Na+ -K+ -Cl- cotransport in the TALH and those of the individual NKCC2 splice variants more specifically. Many of the historical and recent data that have emerged from the experiments conducted will be outlined and their larger meaning will also be placed into perspective with the aid of various hypotheses.

Surfactant Attenuates Air Embolism-Induced Lung Injury by Suppressing NKCC1 Expression and NF-κB Activation

Excessive amounts of air can enter the lungs and cause air embolism (AE)-induced acute lung injury (ALI). Pulmonary AE can occur during diving, aviation, and iatrogenic invasive procedures. AE-induced lung injury presents with severe hypoxia, pulmonary hypertension, microvascular hyper-permeability, and severe inflammatory responses. Pulmonary AE-induced ALI is a serious complication resulting in significant morbidity and mortality. Surfactant is abundant in the lungs and its function is to lower surface tension. Earlier studies have explored the beneficial effects of surfactant in ALI; however, none have investigated the role of surfactant in pulmonary AE-induced ALI. Therefore, we conducted this study to determine the effects of surfactant in pulmonary AE-induced ALI. Isolated-perfused rat lungs were used as a model of pulmonary AE. The animals were divided into four groups (n = 6 per group): sham, air embolism (AE), AE + surfactant (0.5 mg/kg), and AE+ surfactant (1 mg/kg). Surfactant pretreatment was administered before the induction of pulmonary AE. Pulmonary AE was induced by the infusion of 0.7 cc air through a pulmonary artery catheter. After induction of air, pulmonary AE was presented with pulmonary edema, pulmonary microvascular hyper-permeability, and lung inflammation with neutrophilic sequestration. Activation of NF-κB was observed, along with increased expression of pro-inflammatory cytokines, and Na-K-Cl cotransporter isoform 1 (NKCC1). Surfactant suppressed the activation of NF-κB and decreased the expression of pro-inflammatory cytokines and NKCC1, thereby attenuating AE-induced lung injury. Therefore, AE-induced ALI presented with pulmonary edema, microvascular hyper-permeability, and lung inflammation. Surfactant suppressed the expressions of NF-κB, pro-inflammatory cytokines, and NKCC1, thereby attenuating AE-induced lung injury.

The Human Tissue-Engineered Cornea (hTEC): Recent Progress

Each day, about 2000 U.S. workers have a job-related eye injury requiring medical treatment. Corneal diseases are the fifth cause of blindness worldwide. Most of these diseases can be cured using one form or another of corneal transplantation, which is the most successful transplantation in humans. In 2012, it was estimated that 12.7 million people were waiting for a corneal transplantation worldwide. Unfortunately, only 1 in 70 patients received a corneal graft that same year. In order to provide alternatives to the shortage of graftable corneas, considerable progress has been achieved in the development of living corneal substitutes produced by tissue engineering and designed to mimic their in vivo counterpart in terms of cell phenotype and tissue architecture. Most of these substitutes use synthetic biomaterials combined with immortalized cells, which makes them dissimilar from the native cornea. However, studies have emerged that describe the production of tridimensional (3D) tissue-engineered corneas using untransformed human corneal epithelial cells grown on a totally natural stroma synthesized by living corneal fibroblasts, that also show appropriate histology and expression of both extracellular matrix (ECM) components and integrins. This review highlights contributions from laboratories working on the production of human tissue-engineered corneas (hTECs) as future substitutes for grafting purposes. It overviews alternative models to the grafting of cadaveric corneas where cell organization is provided by the substrate, and then focuses on their 3D counterparts that are closer to the native human corneal architecture because of their tissue development and cell arrangement properties. These completely biological hTECs are therefore very promising as models that may help understand many aspects of the molecular and cellular mechanistic response of the cornea toward different types of diseases or wounds, as well as assist in the development of novel drugs that might be promising for therapeutic purposes.

Targeting the WNK-SPAK/OSR1 Pathway and Cation-Chloride Cotransporters for the Therapy of Stroke

Stroke is one of the major culprits responsible for morbidity and mortality worldwide, and the currently available pharmacological strategies to combat this global disease are scanty. Cation-chloride cotransporters (CCCs) are expressed in several tissues (including neurons) and extensively contribute to the maintenance of numerous physiological functions including chloride homeostasis. Previous studies have implicated two CCCs, the Na+-K+-Cl- and K+-Cl- cotransporters (NKCCs and KCCs) in stroke episodes along with their upstream regulators, the with-no-lysine kinase (WNKs) family and STE20/SPS1-related proline/alanine rich kinase (SPAK) or oxidative stress response kinase (OSR1) via a signaling pathway. As the WNK-SPAK/OSR1 pathway reciprocally regulates NKCC and KCC, a growing body of evidence implicates over-activation and altered expression of NKCC1 in stroke pathology whilst stimulation of KCC3 during and even after a stroke event is neuroprotective. Both inhibition of NKCC1 and activation of KCC3 exert neuroprotection through reduction in intracellular chloride levels and thus could be a novel therapeutic strategy. Hence, this review summarizes the current understanding of functional regulations of the CCCs implicated in stroke with particular focus on NKCC1, KCC3, and WNK-SPAK/OSR1 signaling and discusses the current and potential pharmacological treatments for stroke.

Nonionic surfactant attenuates acute lung injury by restoring epithelial integrity and alveolar fluid clearance

Introduction: Acute lung injury (ALI) has a great impact and a high mortality rate in intensive care units (ICUs). Excessive air may enter the lungs, causing pulmonary air embolism (AE)-induced ALI. Some invasive iatrogenic procedures cause pulmonary AE-induced ALI, with the presentation of severe inflammatory reactions, hypoxia, and pulmonary hypertension. Pulmonary surfactants are vital in the lungs to reduce the surface tension and inflammation. Nonionic surfactants (NIS) are a kind of surfactants without electric charge on their hydrophilic parts. Studies on NIS in AE-induced ALI are limited. We aimed to study the protective effects and mechanisms of NIS in AE-induced ALI. Materials and methods: Five different groups (n = 6 in each group) were created: sham, AE, AE + NIS pretreatment (0.5 mg/kg), AE + NIS pretreatment (1 mg/kg), and AE + post-AE NIS (1 mg/kg). AE-induced ALI was introduced by the infusion of air via the pulmonary artery. Aerosolized NIS were administered via tracheostomy. Results: Pulmonary AE-induced ALI showed destruction of the alveolar cell integrity with increased pulmonary microvascular permeability, pulmonary vascular resistance, pulmonary edema, and lung inflammation. The activation of nuclear factor-κB (NF-κB) increased the expression of pro-inflammatory cytokines, and sodium-potassium-chloride co-transporter isoform 1 (NKCC1). The pretreatment with NIS (1 mg/kg) prominently maintained the integrity of the epithelial lining and suppressed the expression of NF-κB, pro-inflammatory cytokines, and NKCC1, subsequently reducing AE-induced ALI. Conclusions: NIS maintained the integrity of the epithelial lining and suppressed the expression of NF-κB, pro-inflammatory cytokines, and NKCC1, thereby reducing hyperpermeability, pulmonary edema, and inflammation in ALI.