Emerging role of WNK1 in pathologic central nervous system signaling

Analysis of CNS autoimmunity in genetically diverse mice reveals unique phenotypes and mechanisms

Multiple sclerosis (MS) is a complex disease with significant heterogeneity in disease course and progression. Genetic studies have identified numerous loci associated with MS risk, but the genetic basis of disease progression remains elusive. To address this, we leveraged the Collaborative Cross (CC), a genetically diverse mouse strain panel, and experimental autoimmune encephalomyelitis (EAE). The 32 CC strains studied captured a wide spectrum of EAE severity, trajectory, and presentation, including severe-progressive, monophasic, relapsing remitting, and axial rotary-EAE (AR-EAE), accompanied by distinct immunopathology. Sex differences in EAE severity were observed in 6 strains. Quantitative trait locus analysis revealed distinct genetic linkage patterns for different EAE phenotypes, including EAE severity and incidence of AR-EAE. Machine learning-based approaches prioritized candidate genes for loci underlying EAE severity (Abcc4 and Gpc6) and AR-EAE (Yap1 and Dync2h1). This work expands the EAE phenotypic repertoire and identifies potentially novel loci controlling unique EAE phenotypes, supporting the hypothesis that heterogeneity in MS disease course is driven by genetic variation.

Probing the basis of disease heterogeneity in multiple sclerosis using genetically diverse mice

Multiple sclerosis (MS) is a complex disease with significant heterogeneity in disease course and progression. Genetic studies have identified numerous loci associated with MS risk, but the genetic basis of disease progression remains elusive. To address this, we leveraged the Collaborative Cross (CC), a genetically diverse mouse strain panel, and experimental autoimmune encephalomyelitis (EAE). The thirty-two CC strains studied captured a wide spectrum of EAE severity, trajectory, and presentation, including severe-progressive, monophasic, relapsing remitting, and axial rotary (AR)-EAE, accompanied by distinct immunopathology. Sex differences in EAE severity were observed in six strains. Quantitative trait locus analysis revealed distinct genetic linkage patterns for different EAE phenotypes, including EAE severity and incidence of AR-EAE. Machine learning-based approaches prioritized candidate genes for loci underlying EAE severity ( Abcc4 and Gpc6 ) and AR-EAE ( Yap1 and Dync2h1 ). This work expands the EAE phenotypic repertoire and identifies novel loci controlling unique EAE phenotypes, supporting the hypothesis that heterogeneity in MS disease course is driven by genetic variation.

Summary

The genetic basis of disease heterogeneity in multiple sclerosis (MS) remains elusive. We leveraged the Collaborative Cross to expand the phenotypic repertoire of the experimental autoimmune encephalomyelitis (EAE) model of MS and identify loci controlling EAE severity, trajectory, and presentation.

Focal adhesion kinase confers lenvatinib resistance in hepatocellular carcinoma via the regulation of lysine-deficient kinase 1

Lenvatinib is a clinically effective multikinase inhibitor approved for first-line therapy of advanced hepatocellular carcinoma (HCC). Although resistance against lenvatinib often emerges and limits its antitumor activity, the underlying molecular mechanisms involved in endogenous and acquired resistance remain elusive. In this study, we identified focal adhesion kinase (FAK) as a critical contributor to lenvatinib resistance in HCC. The elevated expression and phosphorylation of FAK were observed in both acquired and endogenous lenvatinib-resistant (LR) HCC cells. Furthermore, inhibition of FAK reversed lenvatinib resistance in vitro and in vivo. Mechanistically, FAK promoted lenvatinib resistance through regulating lysine-deficient kinase 1 (WNK1). Phosphorylation of WNK1 was significantly increased in LR-HCC cells. Further, WNK1 inhibitor WNK463 resensitized either established or endogenous LR-HCC cells to lenvatinib treatment. In addition, overexpression of WNK1 desensitized parental HCC cells to lenvatinib treatment. Conclusively, our results establish a crucial role and novel mechanism of FAK in lenvatinib resistance and suggest that targeting the FAK/WNK1 axis is a promising therapeutic strategy in HCC patients showing lenvatinib resistance.

Expression pattern analysis and characterization of the hereditary sensory and autonomic neuropathy 2 A (HSAN2A) gene with no lysine kinase (WNK1) in human dorsal root ganglion

Inherited painless neuropathies arise due to genetic insults that either block the normal signaling of or destroy the sensory afferent neurons in the dorsal root ganglion (DRG) responsible for transducing noxious stimuli. Complete loss of these neurons leads to profound insensitivity to all sensory modalities including pain. Hereditary sensory and autonomic neuropathy type 2 (HSNAII) is a rare genetic neuropathy characterized by a progressive distal early onset sensory loss. This syndrome is caused by autosomal recessive mutations in the with-no-lysine protein kinase 1 (WNK1) serine-threonine kinase gene. Of interest, disease-associated mutations are found in the large exon, termed "HSN2," which encodes a 498 amino acid domain C-terminal to the kinase domain. These mutations lead to truncation of the HSN2-containing proteins through the addition of an early stop codon (nonsense mutation) leading to loss of the C-terminal domains of this large protein. The present study evaluates the transcripts, gene structure, and protein structure of HSN2-containing WNK1 splice variants in DRG and spinal cord in order to establish the basal expression patterns of WNK1 and HSN2-containing WNK1 splice variants using multiplex fluorescent situ hybridization. We hypothesized that these transcripts would be enriched in pain-sensing DRG neurons, and, potentially, that enrichment in nociceptive neurons was responsible for the painless phenotypes observed. However, our in-depth analyses revealed that the HSN2-WNK1 splice variants were ubiquitously expressed but were not enriched in tachykinin 1-expressing C-fiber neurons, a class of neurons with a highly nociceptive character. We subsequently identified other subpopulations of DRG neurons with higher levels of HSN2-WNK1 expression, including mechanosensory large fibers. These data are inconsistent with the hypothesis that this transcript is enriched in nociceptive fibers, and instead suggest it may be related to general axon maintenance, or that nociceptive fibers are more sensitive to the genetic insult. These findings clarify the molecular and cellular expression pattern of this painless neuropathy gene in human tissue.

Chloride transporters controlling neuronal excitability

Synaptic inhibition plays a crucial role in regulating neuronal excitability, which is the foundation of nervous system function. This inhibition is largely mediated by the neurotransmitters GABA and glycine that activate Cl^--permeable ion channels, which means that the strength of inhibition depends on the Cl^- gradient across the membrane. In neurons, the Cl^- gradient is primarily mediated by two secondarily active cation-chloride cotransporters (CCCs), NKCC1 and KCC2. CCC-mediated regulation of the neuronal Cl^- gradient is critical for healthy brain function, as dysregulation of CCCs has emerged as a key mechanism underlying neurological disorders including epilepsy, neuropathic pain, and autism spectrum disorder. This review begins with an overview of neuronal chloride transporters before explaining the dependent relationship between these CCCs, Cl^- regulation, and inhibitory synaptic transmission. We then discuss the evidence for how CCCs can be regulated, including by activity and their protein interactions, which underlie inhibitory synaptic plasticity. For readers who may be interested in conducting experiments on CCCs and neuronal excitability, we have included a section on techniques for estimating and recording intracellular Cl^-, including their advantages and limitations. Although the focus of this review is on neurons, we also examine how Cl^- is regulated in glial cells, which in turn regulate neuronal excitability through the tight relationship between this nonneuronal cell type and synapses. Finally, we discuss the relatively extensive and growing literature on how CCC-mediated neuronal excitability contributes to neurological disorders.

Pharmacological tools to target NKCC1 in brain disorders

The chloride importer NKCC1 and the chloride exporter KCC2 are key regulators of neuronal chloride concentration. A defective NKCC1/KCC2 expression ratio is associated with several brain disorders. Preclinical/clinical studies have shown that NKCC1 inhibition by the United States FDA-approved diuretic bumetanide is a potential therapeutic strategy in preclinical/clinical studies of multiple neurological conditions. However, bumetanide has poor brain penetration and causes unwanted diuresis by inhibiting NKCC2 in the kidney. To overcome these issues, a growing number of studies have reported more brain-penetrating and/or selective bumetanide prodrugs, analogs, and new molecular entities. Here, we review the evidence for NKCC1 pharmacological inhibition as an effective strategy to manage neurological disorders. We also discuss the advantages and limitations of bumetanide repurposing and the benefits and risks of new NKCC1 inhibitors as therapeutic agents for brain disorders.

Prognostic and Clinical Implications of WNK Lysine Deficient Protein Kinase 1 Expression in Patients With Hepatocellular Carcinoma

BACKGROUND/AIM

Hepatocellular carcinoma (HCC) is a particularly malignant form of cancer prevalent throughout the world; however, there is a pressing need for HCC biomarkers to facilitate prognosis and risk assessment.

PATIENTS AND METHODS

This paper reports on the potential prognostic value of WNK lysine deficient protein kinase 1 (WNK1) in cases of HCC. We analyzed the expression of WNK1 at the mRNA level using omics data from the UALCAN database. We then verified our findings through the immunohistochemical (IHC) staining of various human cancer tissue as well as 59 HCC samples paired with corresponding normal tissues. The prognostic value of mRNA or protein expression by WNK1 was evaluated using the Kaplan-Meier method.

RESULTS

Initial screening results revealed significantly higher WNK1 expression levels in HCC tissue compared to normal tissue. Verification using the paired HCC samples confirmed that the expression of WNK1 was indeed significantly higher in HCC tissue samples than in adjacent normal tissues. High WNK1 expression levels were significantly correlated with clinicopathological variables, including gender and histologic grade. Kaplan-Meier survival analysis revealed that high WNK1 expression levels were associated with poor HCC prognosis. Finally, univariate and multivariate analysis identified WNK1 as a prognostic factor for TNM stage in cases of HCC.

CONCLUSION

In summary, WNK1 is overexpressed at the mRNA and protein levels, and correlated with poor prognosis. Thus, WNK1 expression could potentially be used as a biomarker in HCC prognosis.

Human adenylate kinase 6 regulates WNK1 (with no lysine kinase-1) phosphorylation states and affects ion homeostasis in NT2 cells

Adenylate kinase 6 (AK6), a nucleus localized phosphotransferase in mammalians, shows ubiquitously expression and broad substrate activity in different tissues and cell types. Although the function of AK6 has been extensively studied in different cancer cell lines, its role in mammalian germline is still unknown. Here we showed that knockdown of AK6 inhibits cell proliferation and promotes cell apoptosis in human testicular carcinoma (NT2 cells). Co-immunoprecipitation experiment and in vitro pull down assay identified WNK1 (with no lysine kinase-1) as one of the AK6 interacting proteins in NT2 cells. Moreover, we found that AK6 regulates the phosphorylation states of WNK1 (Thr60) and affects phosphorylation level of Akt (Ser473) upon hypotonic condition, probably affecting chloride channel and regulating ion transport and homeostasis in NT2 cells and consequently contributing to the decreased cell proliferation rate. In conclusion, AK6 regulates WNK1 phosphorylation states and affects ion homeostasis in NT2 cells. These findings provide new insights into the function of AK6 and WNK1 in human testicular carcinoma. This work also provides foundation for further mechanism study of AK6 in spermatogenesis.

OSR1 phosphorylates the Smad2/3 linker region and induces TGF-β1 autocrine to promote EMT and metastasis in breast cancer

Oxidative stress-responsive kinase 1 (OSR1) plays a critical role in multiple carcinogenic signal pathways, and its overexpression has been found in various types of cancer; however, the pathophysiological role of OSR1 in breast cancer has not been evaluated. This study aims to elaborate on the role of OSR1 in breast cancer metastasis and the specific regulatory mechanism. Our results showed that OSR1 mRNA and protein were upregulated in both human breast cancer samples and cell lines. Moreover, phosphorylated OSR1 (p-OSR1) was an independent poor prognostic indicator in patients with breast cancer. OSR1 upregulation induced epithelial-to-mesenchymal transition (EMT) in normal and malignant mammary epithelial cells with the increasing metastatic capacity. In contrast, deleting OSR1 in aggressive breast cancer cells inhibited these phenotypes. OSR1 is the critical activator for transcription factors of EMT. Mechanistically, we found that OSR1 can directly interact and phosphorylate the linker region of Smad2 at Thr220 and Smad3 at Thr179. Phosphorylated Smad2/3 translocated into the nucleus to enhance transforming growth factor-β1 (TGF-β1) autocrine signalling and increase the transcription of EMT regulators. Importantly, interruption of the OSR1-Smad2/3-TGF-β1 signalling axis elicited a robust anti-EMT and anti-metastatic effect in vitro and in vivo. Taken together, we conclude that OSR1-mediated Smad2/3-TGF-β1 signalling promotes EMT and metastasis representing a promising therapeutic target in breast cancer treatment.

Suppression of WNK1-SPAK/OSR1 Attenuates Bone Cancer Pain by Regulating NKCC1 and KCC2

Our preliminary experiment indicated the activation of with-nolysine kinases 1 (WNK1) in bone cancer pain (BCP) rats. This study aimed to investigate the underlying mechanisms via which WNK1 contributed to BCP. A rat model of BCP was induced by Walker-256 tumor cell implantation. WNK1 expression and distribution in the lumbar spinal cord dorsal horn and dorsal root ganglion were examined. SPS1-related proline/alanine-rich kinase (SPAK), oxidative stress-responsive kinase 1 (OSR1), sodium-potassium-chloride cotransporter 1 (NKCC1), and potassium-chloride cotransporter 2 (KCC2) expression were assessed. Pain behaviors including mechanical allodynia and movement-evoked pain were measured. BCP rats exhibited significant mechanical allodynia, with increased WNK1 expression in the dorsal horn and dorsal root ganglion neurons, elevated SPAK/OSR1 and NKCC1 expression in the dorsal root ganglion, and decreased KCC2 expression in the dorsal horn. WNK1 knock-down by small interfering alleviated mechanical allodynia and movement-evoked pain, inhibited WNK1-SPAK/OSR1-NKCC1 activities, and restored KCC2 expression. In addition, closantel (a WNK1-SPAK/OSR1 inhibitor) improved pain behaviors, downregulated SPAK/OSR1 and NKCC1 expression, and upregulated KCC2 expression in BCP rats. Activation of WNK1-SPAK/OSR1 signaling contributed to BCP in rats by modulating NKCC1 and KCC2 expression. Therefore, suppression of WNK1-SPAK/OSR1 may serve as a potential target for BCP therapy. PERSPECTIVE: Our findings demonstrated that the WNK1-SPAK/OSR1 signaling contributed to BCP in rats via regulating NKCC1 and KCC2. Suppressing this pathway reduced pain behaviors. Based on these findings, the WNK1-SPAK/OSR1 signaling may be a potential target for BCP therapy.

Yoga: Can it be integrated with treatment of neuropathic pain?

Background

Neuropathic pain (NP) is a debilitating condition that may result from spinal cord injury (SCI). Nearly 75% of all SCI results in NP affecting 17,000 new individuals in the United States every year, and an estimated 7–10% of people worldwide. It is caused by damaged or dysfunctional nerve fibers sending aberrant signals to pain centers in the central nervous system causing severe pain that affects daily life and routine. The mechanisms underlying NP are not fully understood, making treatment difficult. Identification of specific molecular pathways that are involved in pain syndromes and finding effective treatments has become a major priority in current SCI research. Yoga has therapeutic applications may prove beneficial in treating subjects suffering chronically with SCI induced NP, chronic back and associated pains if necessary experimental data is generated

Summary

This review aims to discuss the implications of various mechanistic approaches of yoga which can be tested by new study designs around various nociceptive molecules including matrix metalloproteinases (MMPs), cation-dependent chloride transporter (NKCC1) etc in SCI induced NP patients.

Key messages

Thus, yogic practices could be used in managing SCI induced NP pain by regulating the action of various mechanisms and its associated molecules. Modern prescriptive treatment strategies combined with alternative approaches like yoga should be used in rehabilitation centers and clinics in order to ameliorate chronic NP. We recommend practical considerations of careful yoga practice as part of an integrative medicine approach for NP associated with SCI.

A novel nonsense mutation in WNK1/HSN2 associated with sensory neuropathy and limb destruction in four siblings of a large Iranian pedigree

Background

Hereditary sensory and autonomic neuropathy type 2 (HSAN2) is an autosomal recessive disorder with predominant sensory dysfunction and severe complications such as limb destruction. There are different subtypes of HSAN2, including HSAN2A, which is caused by mutations in WNK1/HSN2 gene.

Methods

An Iranian family with four siblings and autosomal recessive inheritance pattern whom initially diagnosed with HSAN2 underwent whole exome sequencing (WES) followed by segregation analysis.

Results

According to the filtering criteria of the WES data, a novel candidate variation, c.3718C > A in WNK1/HSN2 gene that causes p.Tyr1025* was identified. This variation results in a truncated protein with 1025 amino acids instead of the wild-type product with 2645 amino acids. Sanger sequencing revealed that the mutation segregates with disease status in the pedigree.

Conclusions

The identified novel nonsense mutation in WNK1/HSN2 in an Iranian HSAN2 pedigree presents allelic heterogeneity of this gene in different populations. The result of current study expands the spectrum of mutations of the HSN2 gene as the genetic background of HSAN2A as well as further supports the hypothesis that HSN2 is a causative gene for HSAN2A. However, it seems that more research is required to determine the exact effects of this product in the nervous system.

Role of nitric oxide and WNK-SPAK/OSR1-KCC2 signaling in daily changes in GABAergic inhibition in the rat dorsal raphe neurons

Serotonergic neurons in the dorsal raphe nucleus (DRN) act as wake-inducing neurons in the sleep-wake cycle and are controlled by gamma-aminobutyric acid (GABA) synaptic inputs. We investigated daily changes in GABAergic inhibition of the rat DRN neurons and the role of nitric oxide (NO) and cation-chloride co-transporters in the GABAergic action. Neuronal NO synthase (nNOS) was co-expressed in 74% of serotonergic DRN neurons and nNOS expression was higher during daytime (the sleep cycle) than that during nighttime (the wake cycle). GABAergic hyperpolarization of DRN neurons produced by GABAA receptor agonist muscimol was greater and the equilibrium potential of muscimol showed a hyperpolarizing shift during daytime compared to that during nighttime. Expression levels of potassium-chloride co-transporter 2 (KCC2) were higher during daytime than that during nighttime, whereas there were no changes in sodium-potassium-chloride co-transporter 1 (NKCC1) expression. With-no-lysine kinase (WNK) isoform 1 was more highly expressed during daytime than that during nighttime. Total Ste20-related proline alanine rich kinase (SPAK) and oxidative stress response kinase 1 (OSR1) were also higher during daytime than during nighttime, while there were no changes in phosphorylated SPAK and OSR1. Consistent with the findings during the sleep-wake cycle, ex vivo treatment of DRN slices with a NO donor sodium nitroprusside (SNP) increased the expression of KCC2, WNK1, WNK2, WNK3, SPAK, and OSR1, whilst decreasing phosphorylated SPAK. These results suggest that GABAergic synaptic inhibition of DRN serotonergic neurons shows daily changes during the sleep-wake cycle, which might be regulated by daily changes in nNOS-derived NO and WNK-SPAK/OSR1-KCC2 signaling.

Pathogenesis of spinal cord injury induced edema and neuropathic pain: expression of multiple isoforms of wnk1

Background

Neuropathic pain (NP) is a common occurrence following spinal cord injury (SCI). Identification of specific molecular pathways that are involved in pain syndromes has become a major priority in current SCI research. We have investigated the role of a cation-dependent chloride transporter, Cl-regulatory protein Na⁺-K⁺-Cl^- 1 (NKCC1), phosphorylation profile of NKCC1 and its specific involvement in neuropathic pain following contusion SCI (cSCI) using a rat model. Administration of the NKCC1 inhibitor bumetanide (BU) increases the mean hindpaw withdrawal latency time (WLT), thermal hyperalgesia (TH) following cSCI. These results demonstrate implication of NKCC1 co-transporter and BUin SCI-induced neuropathic pain. The with-no-lysine (K)–1 (WNK1) kinase has been shown to be an important regulator of NKCC1 phosphorylation in many systems, including nocioception. Mutations in a neuronal-specific exon of WNK1 (HSN2) was identified in patients that have hereditary sensory neuropathy type II (HSANII) also implicates WNK1 in nocioception, such that these patients have loss of perception to pain, touch and heat. In our ongoing research we proposed two studies utilizing our contusion SCI (cSCI) NP model of rat.

Purpose

Study 1 aimed at NKCC1 expression and activity is up-regulated following cSCI in the early edema and chronic neuropathic pain phases. Study 2 aimed at identifying the expression profile of alternatively spliced WNK1 isoforms in animals exhibiting thermal hyperalgesia (TH) following cSCI.

Methods

Adult male Sprague Dawley rats (275–300 g) following laminectomy received cSCI at T9 with the NYU impactor-device II by dropping 10 g weight from the height of 12.5 mm. Control rats obtained laminectomy but no impaction. Following injury, functional recovery was assessed by BBB locomotor scores on day 1, 7, 14, 21, 35, and 42 and development of thermal hyperalgesia on day 21, 28, 35, and 42 day of injury by monitoring hind paw withdraw latency time (WLT) in seconds compared with the baseline data before injury.

Results

Increased NKCC1 may explain observed increase in magnetic resonance imaging (MRI) T2, exhibiting NKCC1 localization in neurons. This data supports NKCC1’s role in the pathogenesis of acute and chronic phases of injury, namely spinal cord edema and chronic phase neuropathic pain. NKCC1 dependent chloride influx requires the phosphorylation at specific residues. Probing for the HSN2 exon of WNK1 reveals two key findings: i) the HSN2 exon is found in alternatively spliced neuronal isoforms found at 250 kDa and 230 kDa; ii) the 250 kDa isoform is found only in tissue that is injured.

Conclusions

This data implicates the NKCC1/WNK1/WNK1HSN2 involvement in post-injury response that contributes to the development of neuropathic pain. Targeting this system may have therapeutic benefit.