The Structure and Function of the Na,K-ATPase Isoforms in Health and Disease

Sodium triple quantum MR signal extraction using a single-pulse sequence with single quantum time efficiency

PURPOSE

Sodium triple quantum (TQ) signal has been shown to be a valuable biomarker for cell viability. Despite its clinical potential, application of Sodium TQ signal is hindered by complex pulse sequences with long scan times. This study proposes a method to approximate the TQ signal using a single excitation pulse without phase cycling.

METHODS

The proposed method is based on a single excitation pulse and a comparison of the free induction decay (FID) with the integral of the FID combined with a shifting reconstruction window. The TQ signal is calculated from this FID only. As a proof of concept, the method was also combined with a multi-echo UTE imaging sequence on a 9.4 T preclinical MRI scanner for the possibility of fast TQ MRI.

RESULTS

The extracted Sodium TQ signals of single-pulse and spin echo FIDs were in close agreement with theory and TQ measurement by traditional three-pulse sequence (TQ time proportional phase increment [TQTPPI)]. For 2%, 4%, and 6% agar samples, the absolute deviations of the maximum TQ signals between SE and theoretical (time proportional phase increment TQTPPI) TQ signals were less than 1.2% (2.4%), and relative deviations were less than 4.6% (6.8%). The impact of multi-compartment systems and noise on the accuracy of the TQ signal was small for simulated data. The systematic error was <3.4% for a single quantum (SQ) SNR of 5 and at maximum <2.5% for a multi-compartment system. The method also showed the potential of fast in vivo SQ and TQ imaging.

CONCLUSION

Simultaneous SQ and TQ MRI using only a single-pulse sequence and SQ time efficiency has been demonstrated. This may leverage the full potential of the Sodium TQ signal in clinical applications.

(Na+, K+)- ATPase kinetics in Macrobrachium pantanalense: highlighting intra- and interspecific variation within the Macrobrachium amazonicum complex

The Macrobrachium amazonicum complex is composed of at least the Macrobrachium amazonicum and Macrobrachium pantanalense species, with the latter described from specimens originally identified as part of an endemic M. amazonicum population in the Brazilian Pantanal region. While there may be a reproductive barrier between these two Macrobrachium species, both are phylogenetically close, with small genetic distance. However, there is currently no available biochemical information of Macrobrachium pantanalense (Na+, K+)-ATPase. Here, we report the kinetic characteristics of the gill (Na+, K+)-ATPase in two populations of M. pantanalense from Baiazinha Lagoon (Miranda, MS, Brazil) and Araguari River (Uberlândia, MG, Brazil), and compare them with Macrobrachium amazonicum populations from the Paraná-Paraguay River Basin. (Na+, K+)-ATPase activities were 67.9 ± 3.4 and 93.3 ± 4.1 nmol Pi min-1 mg-1 protein for the Baiazinha Lagoon and Araguari River populations, respectively. Two ATP hydrolyzing sites were observed for the Araguari River population while a single ATP site was observed for the Baiazinha Lagoon shrimps. Compared to the Araguari River population, a 3-fold greater apparent affinity for Mg2+ and Na+ was estimated for the Baiazinha Lagoon population, but no difference in K+ affinity and ouabain inhibition was seen. The kinetic differences observed in the gill (Na+, K+)-ATPase between the two populations of M. pantanalense, compared with those of various M. amazonicum populations, highlight interspecific divergence within the Macrobrachium genus, now examined from a biochemical perspective.

Navigating the multifaceted intricacies of the Na+-Cl- cotransporter, a highly regulated key effector in the control of hydromineral homeostasis

The Na+-Cl- cotransporter (NCC; SLC12A3) is a highly regulated integral membrane protein that is known to exist as three splice variants in primates. Its primary role in the kidney is to mediate the cosymport of Na+ and Cl- across the apical membrane of the distal convoluted tubule. Through this role and the involvement of other ion transport systems, NCC allows the systemic circulation to reclaim a fraction of the ultrafiltered Na+, K+, Cl-, and Mg+ loads in exchange for Ca2+ and [Formula: see text]. The physiological relevance of the Na+-Cl- cotransport mechanism in humans is illustrated by several abnormalities that result from NCC inactivation through the administration of thiazides or in the setting of hereditary disorders. The purpose of the present review is to discuss the molecular mechanisms and overall roles of Na+-Cl- cotransport as the main topics of interest. On reading the narrative proposed, one will realize that the knowledge gained in regard to these themes will continue to progress unrelentingly no matter how refined it has now become.

Photobiomodulation of Na,K-ATPase in native membrane fraction and reconstituted in DPPC:DPPE-liposome

Studies focusing on how photobiomodulation (PBM) can affect the structure and function of proteins are scarce in the literature. Few previous studies have shown that the enzymatic activity of Na,K-ATPAse (NKA) can be photo-modulated. However, the variability of sample preparation and light irradiation wavelengths have not allowed for an unequivocal conclusion about the PBM of NKA. Here, we investigate minimal membrane models containing NKA, namely, native membrane fraction and DPPC:DPPE proteoliposome upon laser irradiation at wavelengths 532, 650, and 780 nm. Interestingly, we show that the PBM on the NKA enzymatic activity has a bell-shaped profile with a stimulation peak (~15% increase) at around 20 J.cm-2 and 6 J.cm-2 for the membrane-bound and the proteoliposome samples, respectively, and are practically wavelength independent. Further, by normalizing the enzymatic activity by the NKA enzyme concentration, we show that the PBM response is related to the protein amount with small influence due to protein's environment. The stimulation decays over time reaching the basal level around 6 h after the irradiation for the three lasers and both NKA samples. Our results demonstrate the potential of using low-level laser therapy to modulate NKA activity, which may have therapeutic implications and benefits.

Protein interactome analysis of ATP1B1 in alveolar epithelial cells using Co-Immunoprecipitation mass spectrometry and parallel reaction monitoring assay

Aims

Alveolar epithelial barrier integrity is essential for lung homeostasis. Na, K-ATPase β1 subunit (ATP1B1) involves alveolar edema fluid clearance and alveolar epithelial barrier stability. However, the underlying molecular mechanism of ATP1B1 in alveolar epithelial cells still needs to be understood.

Main methods

We utilized Co-Immunoprecipitation mass spectrometry proteomic analysis, protein-protein interaction (PPI) analysis, enrichment analysis, and parallel reaction monitoring (PRM) analysis to investigate proteins interacting with ATP1B1 in A549 cells.

Key findings

A total of 159 proteins were identified as significant proteins interacting with ATP1B1 in A549 cells. Ribosomal and heat shock proteins were major constituents of the two main functional modules based on the PPI network. Enrichment analysis showed that significant proteins were involved in protein translation, posttranslational processing, and function regulation. Moreover, 10 proteins of interest were verified by PRM, and fold changes in 6 proteins were consistent with proteomics results. Finally, HSP90AB1, EIF4A1, TUBB4B, HSPA8, STAT1, and PLEC were considered candidates for binding to ATP1B1 to function in alveolar epithelial cells.

Significance

Our study provides new insights into the role of ATP1B1 in alveolar epithelial cells and indicates that six proteins, in particular HSP90AB1, may be key proteins interacting with and regulating ATP1B1, which might be potential targets for the treatment of acute respiratory distress syndrome.

ATP1A3 Disease Spectrum Includes Paroxysmal Weakness and Encephalopathy Not Triggered by Fever

Background and Objectives

Heterozygous pathogenic variants in ATP1A3, which encodes the catalytic alpha subunit of neuronal Na+/K+-ATPase, cause primarily neurologic disorders with widely variable features that can include episodic movement deficits. One distinctive presentation of ATP1A3-related disease is recurrent fever-triggered encephalopathy. This can occur with generalized weakness and/or ataxia and is described in the literature as relapsing encephalopathy with cerebellar ataxia. This syndrome displays genotype-phenotype correlation with variants at p.R756 causing temperature sensitivity of ATP1A3. We report clinical and in vitro functional evidence for a similar phenotype not triggered by fever but associated with protein loss-of-function.

Methods

We describe the phenotype of an individual with de novo occurrence of a novel heterozygous ATP1A3 variant, NM_152296.5:c.388_390delGTG; p.(V130del). We confirmed the pathogenicity of p.V130del by cell survival complementation assay in HEK293 cells and then characterized its functional impact on enzymatic ion transport and extracellular sodium binding by two-electrode voltage clamp electrophysiology in Xenopus oocytes. To determine whether variant enzymes reach the cell surface, we surface-biotinylated oocytes expressing N-tagged ATP1A3.

Results

The proband is a 7-year-old boy who has had 2 lifetime episodes of paroxysmal weakness, encephalopathy, and ataxia not triggered by fever. He had speech regression and intermittent hand tremors after the second episode but otherwise spontaneously recovered after episodes and is at present developmentally appropriate. The p.V130del variant was identified on clinical trio exome sequencing, which did not reveal any other variants possibly associated with the phenotype. p.V130del eliminated ATP1A3 function in cell survival complementation assay. In Xenopus oocytes, p.V130del variant Na+/K+-ATPases showed complete loss of ion transport activity and marked abnormalities of extracellular Na+ binding at room temperature. Despite this clear loss-of-function effect, surface biotinylation under the same conditions revealed that p.V130del variant enzymes were still present at the oocyte's cell membrane.

Discussion

This individual's phenotype expands the clinical spectrum of ATP1A3-related recurrent encephalopathy to include presentations without fever-triggered events. The total loss of ion transport function with p.V130del, despite enzyme presence at the cell membrane, indicates that haploinsufficiency can cause relatively mild phenotypes in ATP1A3-related disease.

Targeting NKAα1 to treat Parkinson's disease through inhibition of mitophagy-dependent ferroptosis

Dysfunction of the Na+/K+-ATPase (NKA) has been documented in various neurodegenerative diseases, yet the specific role of NKAα1 in Parkinson's disease (PD) remains incompletely understood. In this investigation, we utilized NKAα1 haploinsufficiency (NKAα1+/-) mice to probe the influence of NKAα1 on dopaminergic (DA) neurodegeneration induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Our findings reveal that NKAα1+/- mice displayed a heightened loss of DA neurons and more pronounced motor dysfunction compared to the control group when exposed to MPTP. Intriguingly, this phenomenon coincided with the activation of ferroptosis and impaired mitophagy both in vivo and in vitro. To scrutinize the role and underlying mechanism of NKAα1 in PD, we employed DR-Ab, an antibody targeting the DR-region of the NKA α subunit. Our study demonstrates that the administration of DR-Ab effectively reinstated the membrane abundance of NKAα1, thereby mitigating MPTP-induced DA neuron loss and subsequent improvement in behavioral deficit. Mechanistically, DR-Ab heightened the formation of the surface NKAα1/SLC7A11 complex, inhibiting SLC7A11-dependent ferroptosis. Moreover, DR-Ab disrupted the cytosolic interaction between NKAα1 and Parkin, facilitating the translocation of Parkin to mitochondria and enhancing the process of mitophagy. In conclusion, this study establishes NKAα1 as a key regulator of ferroptosis and mitophagy, identifying its DR-region as a promising therapeutic target for PD.

Na+/K+-ATPase: More than an Electrogenic Pump

The sodium pump, or Na+/K+-ATPase (NKA), is an essential enzyme found in the plasma membrane of all animal cells. Its primary role is to transport sodium (Na+) and potassium (K+) ions across the cell membrane, using energy from ATP hydrolysis. This transport creates and maintains an electrochemical gradient, which is crucial for various cellular processes, including cell volume regulation, electrical excitability, and secondary active transport. Although the role of NKA as a pump was discovered and demonstrated several decades ago, it remains the subject of intense research. Current studies aim to delve deeper into several aspects of this molecular entity, such as describing its structure and mode of operation in atomic detail, understanding its molecular and functional diversity, and examining the consequences of its malfunction due to structural alterations. Additionally, researchers are investigating the effects of various substances that amplify or decrease its pumping activity. Beyond its role as a pump, growing evidence indicates that in various cell types, NKA also functions as a receptor for cardiac glycosides like ouabain. This receptor activity triggers the activation of various signaling pathways, producing significant morphological and physiological effects. In this report, we present the results of a comprehensive review of the most outstanding studies of the past five years. We highlight the progress made regarding this new concept of NKA and the various cardiac glycosides that influence it. Furthermore, we emphasize NKA's role in epithelial physiology, particularly its function as a receptor for cardiac glycosides that trigger intracellular signals regulating cell-cell contacts, proliferation, differentiation, and adhesion. We also analyze the role of NKA β-subunits as cell adhesion molecules in glia and epithelial cells.

Comparison of triple quantum (TQ) TPPI and inversion recovery TQ TPPI pulse sequences at 9.4 and 21.1 T

PURPOSE

Both sodium T1 triple quantum (TQ) signal and T1 relaxation pathways have a unique sensitivity to the sodium molecular environment. In this study an inversion recovery time proportional phase increment (IRTQTPPI) pulse sequence was investigated for simultaneous and reliable quantification of sodium TQ signal and bi-exponential T1 relaxation times.

METHODS

The IRTQTPPI sequence combines inversion recovery TQ filtering and time proportional phase increment. The reliable and reproducible results were achieved by the pulse sequence optimized in three ways: (1) optimization of the nonlinear fit for the determination of both T1-TQ signal and T1 relaxation times; (2) suppression of unwanted signals by assessment of four different phase cycles; (3) nonlinear sampling during evolution time for optimal scan time without any compromises in fit accuracy. The relaxation times T1 and T2 and the TQ signals from IRTQTPPI and TQTPPI were compared between 9.4 and 21.1 T. The motional environment of the sodium nuclei was evaluated by calculation of correlation times and nuclear quadrupole interaction strengths.

RESULTS

Reliable measurements of the T1-TQ signals and T1 bi-exponential relaxation times were demonstrated. The fit parameters for all four phase cycles were in good agreement with one another, with a negligible influence of unwanted signals. The agar samples yielded normalized T1-TQ signals from 3% to 16% relative to single quantum (SQ) signals at magnetic fields of both 9.4 and 21.1 T. In comparison, the normalized T2-TQ signal was in the range 15%-35%. The TQ/SQ signal ratio was decreased at 21.1 T as compared with 9.4 T for both T1 and T2 relaxation pathways. The bi-exponential T1 relaxation time separation ranged from 15 to 18 ms at 9.4 T and 15 to 21 ms at 21.1 T. The T2 relaxation time separation was larger, ranging from 28 to 35 ms at 9.4 T and 37 to 40 ms at 21.1 T.

CONCLUSION

The IRTQTPPI sequence, while providing a less intensive TQ signal than TQTPPI, allows a simultaneous and reliable quantification of both the T1-TQ signal and T1 relaxation times. The unique sensitivities of the T1 and T2 relaxation pathways to different types of molecular motion provide a deeper understanding of the sodium MR environment.

Differentially Altered Metabolic Pathways in the Amygdala of Subjects with Schizophrenia, Bipolar Disorder and Major Depressive Disorder

Background and hypothesis

A growing number of studies implicate a key role for metabolic processes in psychiatric disorders. Recent studies suggest that ketogenic diet may be therapeutically effective for subgroups of people with schizophrenia (SCZ), bipolar disorder (BPD) and possibly major depressive disorder (MDD). Despite this promise, there is currently limited information regarding brain energy metabolism pathways across these disorders, limiting our understanding of how brain metabolic pathways are altered and who may benefit from ketogenic diets. We conducted gene expression profiling on the amygdala, a key region involved in in the regulation of mood and appetitive behaviors, to test the hypothesis that amygdala metabolic pathways are differentially altered between these disorders.

Study Design

We used a cohort of subjects diagnosed with SCZ, BPD or MDD, and non-psychiatrically ill control subjects (n=15/group), together with our bioinformatic 3-pod analysis consisting of full transcriptome pathway analysis, targeted pathway analysis, leading-edge gene analysis and iLINCS perturbagen analysis.

Study Results

We identified differential expression of metabolic pathways in each disorder. Subjects with SCZ displayed downregulation of mitochondrial respiration and nucleotide metabolism pathways. In comparison, we observed upregulation of mitochondrial respiration pathways in subjects with MDD, while subjects with BPD displayed enrichment of pathways involved in carbohydrate metabolism. Several pathways associated with brain metabolism including immune system processes and calcium ion transport were also differentially altered between diagnosis groups.

Conclusion

Our findings suggest metabolic pathways are differentially altered in the amygdala in these disorders, which may impact approaches for therapeutic strategies.

Periparturient Mineral Metabolism: Implications to Health and Productivity

Mineral metabolism, in particular Ca, and to a lesser extent phosphorus (P) and magnesium (Mg), is altered with the onset of lactation because of extensive irreversible loss to synthesize colostrum and milk. The transient reduction in the concentration of Ca in blood, particularly when it lasts days, increases the risk of mineral-related disorders such as hypocalcemia and, to a lesser extent, hypophosphatemia. Although the incidence of clinical hypocalcemia can be reduced by prepartum dietary interventions, subclinical hypocalcemia remains prevalent, affecting up to 60% of the dairy cows in the first 3 d postpartum. More importantly, strong associations exist between hypocalcemia and increased susceptibility to other peripartum diseases and impaired reproductive performance. Mechanistic experiments have demonstrated the role of Ca on innate immune response in dairy cows, which presumably predisposes them to other diseases. Hypocalcemia is not related to inadequate Ca intake as prepartum diets marginal to deficient in Ca reduce the risk of the disease. Therefore, the understanding of how Ca homeostasis is regulated, in particular how calciotropic hormones such as parathyroid hormone and 1,25-dihydroxyvitamin D3, affect blood Ca concentrations, gastrointestinal Ca absorption, bone remodeling, and renal excretion of Ca become critical to develop novel strategies to prevent mineral imbalances either by nutritional or pharmacological interventions. A common method to reduce the risk of hypocalcemia is the manipulation of the prepartum dietary cation-anion difference. Feeding acidogenic diets not only improves Ca homeostasis and reduces hypocalcemia, but also reduces the risk of uterine diseases and improves productive performance. Feeding diets that induce a negative Ca balance in the last weeks of gestation also reduce the risk of clinical hypocalcemia, and recent work shows that the incorporation of mineral sequestering agents, presumably by reducing the absorption of P and Ca prepartum, increases blood Ca at calving, although benefits to production and health remain to be shown. Alternative strategies to minimize subclinical hypocalcemia with the use of vitamin D metabolites either fed prepartum or as a pharmacological agent administered immediately after calving have shown promising results in reducing hypocalcemia and altering immune cell function, which might prove efficacious to prevent diseases in early lactation. This review summarizes the current understanding of Ca homeostasis around parturition, the limited knowledge of the exact mechanisms for gastrointestinal Ca absorption in bovine, the implications of hypocalcemia on the health of dairy cows, and discusses the methods to minimize the risk of hypocalcemia and their impacts on productive performance and health in dairy cows.

The involvement of Akt, mTOR, and S6K in the in vivo effect of IGF-1 on the regulation of rat cardiac Na+/K+-ATPase

BACKGROUND

We previously demonstrated that insulin-like growth factor-1 (IGF-1) regulates sodium/potassium adenosine triphosphatase (Na+/K+-ATPase) in vascular smooth muscle cells (VSMC) via phosphatidylinositol-3 kinase (PI3K). Taking into account that others' work show that IGF-1 activates the PI3K/protein kinase B (Akt) signaling pathway in many different cells, we here further questioned if the Akt/mammalian target of rapamycin (mTOR)/ribosomal protein p70 S6 kinase (S6K) pathway stimulates Na+/K+-ATPase, an essential protein for maintaining normal heart function.

METHODS AND RESULTS

There were 14 adult male Wistar rats, half of whom received bolus injections of IGF-1 (50 μg/kg) for 24 h. We evaluated cardiac Na+/K+-ATPase expression, activity, and serum IGF-1 levels. Additionally, we examined the phosphorylated forms of the following proteins: insulin receptor substrate (IRS), phosphoinositide-dependent kinase-1 (PDK-1), Akt, mTOR, S6K, and α subunit of Na+/K+-ATPase. Additionally, the mRNA expression of the Na+/K+-ATPase α1 subunit was evaluated. Treatment with IGF-1 increases levels of serum IGF-1 and stimulates Na+/K+-ATPase activity, phosphorylation of α subunit of Na+/K+-ATPase on Ser23, and protein expression of α2 subunit. Furthermore, IGF-1 treatment increased phosphorylation of IRS-1 on Tyr1222, Akt on Ser473, PDK-1 on Ser241, mTOR on Ser2481 and Ser2448, and S6K on Thr421/Ser424. The concentration of IGF-1 in serum positively correlates with Na+/K+-ATPase activity and the phosphorylated form of mTOR (Ser2448), while Na+/K+-ATPase activity positively correlates with the phosphorylated form of IRS-1 (Tyr1222) and mTOR (Ser2448).

CONCLUSION

These results indicate that the Akt/mTOR/S6K signalling pathway may be involved in the IGF-1 regulating cardiac Na+/K+-ATPase expression and activity.

Autosis: a new form of cell death in myocardial ischemia-reperfusion injury

Cardiomyocytes undergo a variety of cell death events during myocardial ischemia‒reperfusion injury (MIRI). Understanding the causes of cardiomyocyte mortality is critical for the prevention and treatment of MIRI. Among the various types of cell death, autosis is a recently identified type of autophagic cell death with distinct morphological and chemical characteristics. Autosis can be attenuated by autophagy inhibitors but not reversed by apoptosis or necrosis inhibitors. In recent years, it has been shown that during the late phase of reperfusion, autosis is activated, which exacerbates myocardial injury. This article describes the characteristics of autosis, autophagic cell death, and the relationship between autophagic cell death and autosis; reviews the mechanism of autosis in MIRI; and discusses its clinical significance.

Sensational site: the sodium pump ouabain-binding site and its ligands

Cardiotonic steroids (CTS), used by certain insects, toads, and rats for protection from predators, became, thanks to Withering's trailblazing 1785 monograph, the mainstay of heart failure (HF) therapy. In the 1950s and 1960s, we learned that the CTS receptor was part of the sodium pump (NKA) and that the Na+/Ca2+ exchanger was critical for the acute cardiotonic effect of digoxin- and ouabain-related CTS. This "settled" view was upended by seven revolutionary observations. First, subnanomolar ouabain sometimes stimulates NKA while higher concentrations are invariably inhibitory. Second, endogenous ouabain (EO) was discovered in the human circulation. Third, in the DIG clinical trial, digoxin only marginally improved outcomes in patients with HF. Fourth, cloning of NKA in 1985 revealed multiple NKA α and β subunit isoforms that, in the rodent, differ in their sensitivities to CTS. Fifth, the NKA is a cation pump and a hormone receptor/signal transducer. EO binding to NKA activates, in a ligand- and cell-specific manner, several protein kinase and Ca2+-dependent signaling cascades that have widespread physiological effects and can contribute to hypertension and HF pathogenesis. Sixth, all CTS are not equivalent, e.g., ouabain induces hypertension in rodents while digoxin is antihypertensinogenic ("biased signaling"). Seventh, most common rodent hypertension models require a highly ouabain-sensitive α2 NKA and the elevated blood pressure is alleviated by EO immunoneutralization. These numerous phenomena are enabled by NKA's intricate structure. We have just begun to understand the endocrine role of the endogenous ligands and the broad impact of the ouabain-binding site on physiology and pathophysiology.

Loss of the Na + /K + cation pump CATP-1 suppresses nekl -associated molting defects

The conserved C. elegans protein kinases NEKL-2 and NEKL-3 regulate multiple steps of membrane trafficking and are required for larval molting. Through a forward genetic screen we identified a loss-of-function mutation in catp-1 as a suppressor of molting defects in synthetically lethal nekl-2; nekl-3 double mutants. catp-1 is predicted to encode a membrane- associated P4-type ATPase involved in Na + -K + exchange. Moreover, a mutation predicted to abolish CATP-1 ion-pump activity also suppressed nekl-2; nekl-3 mutants. Endogenously tagged CATP-1 was primarily expressed in epidermal (hypodermal) cells within punctate structures located at or near the apical plasma membrane. Through whole genome sequencing, we identified two additional nekl-2; nekl-3 suppressor strains containing coding-altering mutations in catp-1 but found that neither mutation, when introduced into nekl-2; nekl-3 mutants using CRISPR methods, was sufficient to elicit robust suppression of molting defects. Our data also suggested that the two catp-1 isoforms, catp-1a and catp-1b , may in some contexts be functionally redundant. On the basis of previously published studies, we tested the hypothesis that loss of catp-1 may suppress nekl -associated defects by inducing partial entry into the dauer pathway. Contrary to expectations, however, we failed to obtain evidence that loss of catp-1 suppresses nekl-2; nekl-3 defects through a dauer-associated mechanism or that loss of catp-1 leads to entry into the pre-dauer L2d stage. As such, loss of catp-1 may suppress nekl- associated molting and membrane trafficking defects by altering electrochemical gradients within membrane-bound compartments.

Astrocytic Na+, K+ ATPases in physiology and pathophysiology

The Na+, K+ ATPases play a fundamental role in the homeostatic functions of astrocytes. After a brief historic prologue and discussion of the subunit composition and localization of the astrocytic Na+, K+ ATPases, the review focuses on the role of the astrocytic Na+, K+ pumps in extracellular K+ and glutamate homeostasis, intracellular Na+ and Ca2+ homeostasis and signaling, regulation of synaptic transmission and neurometabolic coupling between astrocytes and neurons. Loss-of-function mutations in the gene encoding the astrocytic α2 Na+, K+ ATPase cause a rare monogenic form of migraine with aura (familial hemiplegic migraine type 2). On the other hand, the α2 Na+, K+ ATPase is upregulated in spinal cord and brain samples from amyotrophic lateral sclerosis and Alzheimer disease patients, respectively. In the last part, the review focuses on i) the migraine relevant phenotypes shown by familial hemiplegic migraine type 2 knock-in mice with 50 % reduced expression of the astrocytic α2 Na+, K+ ATPase and the insights into the pathophysiology of migraine obtained from these genetic mouse models, and ii) the evidence that upregulation of the astrocytic α2 Na+, K+ ATPase in mouse models of amyotrophic lateral sclerosis and Alzheimer disease promotes neuroinflammation and contributes to progressive neurodegeneration.

A century of exercise physiology: effects of muscle contraction and exercise on skeletal muscle Na+,K+-ATPase, Na+ and K+ ions, and on plasma K+ concentration-historical developments

This historical review traces key discoveries regarding K+ and Na+ ions in skeletal muscle at rest and with exercise, including contents and concentrations, Na+,K+-ATPase (NKA) and exercise effects on plasma [K+] in humans. Following initial measures in 1896 of muscle contents in various species, including humans, electrical stimulation of animal muscle showed K+ loss and gains in Na+, Cl- and H20, then subsequently bidirectional muscle K+ and Na+ fluxes. After NKA discovery in 1957, methods were developed to quantify muscle NKA activity via rates of ATP hydrolysis, Na+/K+ radioisotope fluxes, [3H]-ouabain binding and phosphatase activity. Since then, it became clear that NKA plays a central role in Na+/K+ homeostasis and that NKA content and activity are regulated by muscle contractions and numerous hormones. During intense exercise in humans, muscle intracellular [K+] falls by 21 mM (range - 13 to - 39 mM), interstitial [K+] increases to 12-13 mM, and plasma [K+] rises to 6-8 mM, whilst post-exercise plasma [K+] falls rapidly, reflecting increased muscle NKA activity. Contractions were shown to increase NKA activity in proportion to activation frequency in animal intact muscle preparations. In human muscle, [3H]-ouabain-binding content fully quantifies NKA content, whilst the method mainly detects α2 isoforms in rats. Acute or chronic exercise affects human muscle K+, NKA content, activity, isoforms and phospholemman (FXYD1). Numerous hormones, pharmacological and dietary interventions, altered acid-base or redox states, exercise training and physical inactivity modulate plasma [K+] during exercise. Finally, historical research approaches largely excluded female participants and typically used very small sample sizes.

Mechanisms of PVP-functionalized silver nanoparticle toxicity in fish: Intravascular exposure disrupts cardiac pacemaker function and inhibits Na+/K+-ATPase activity in heart, but not gill

Polyvinylpyrrolidone-functionalized silver nanoparticles (nAgPVP) are popular in consumer products for their colloidal stability and antimicrobial activity. Whole lake additions of nAgPVP cause long term, ecosystem-scale changes in fish populations but the mechanisms underlying this effect are unclear. We have previously shown that in fish, nAgPVP impairs cardiac contractility and Na+/K+-ATPase (NKA) activity in vitro, raising the possibility that heart dysfunction could underlie population-level exposure effects. The goal of this study was to determine if nAgPVP influences the control of heart rate (fh), blood pressure, or cardiac NKA activity in vivo. First, a dose-response curve for the effects of 5 nm nAgPVP on contractility was completed on isometrically contracting ventricular muscle preparations from Arctic char (Salvelinus alpinus) and showed that force production was lowest at 500 μg L-1 and maximum pacing frequency increased with nAgPVP concentration. Stroke volume, cardiac output, and power output were maintained in isolated working heart preparations from brook char (Salvelinus fontinalis) exposed to 700 μg L-1 nAgPVP. Both fh and blood pressure were elevated after 24 h in brook char injected with 700 μg kg body mass-1 nAgPVP and fh was insensitive to modulation with blockers of β-adrenergic and muscarinic cholinergic receptors. Na+/K+-ATPase activity was significantly lower in heart, but not gill of nAgPVP injected fish. The results indicate that nAgPVP influences cardiac function in vivo by disrupting regulation of the pacemaker and cardiomyocyte ionoregulation. Impaired fh regulation may prevent fish from appropriately responding to environmental or social stressors and affect their ability to survive.

Involvement of the Na+, K+-ATPase α1 Isoform and Endogenous Cardiac Steroids in Depression- and Manic-like Behaviors

Bipolar disorder (BD) is a severe and common chronic mental illness characterized by recurrent mood swings between depression and mania. The biological basis of the disease is poorly understood, and its treatment is unsatisfactory. Na+, K+-ATPase is a major plasma membrane transporter and signal transducer. The catalytic α subunit of this enzyme is the binding site for cardiac steroids. Three α isoforms of the Na+, K+-ATPase are present in the brain. Previous studies have supported the involvement of the Na+, K+-ATPase and endogenous cardiac steroids (ECS) in the etiology of BD. Decreased brain ECS has been found to elicit anti-manic and anti-depressive-like behaviors in mice and rats. However, the identity of the specific α isoform involved in these behavioral effects is unknown. Here, we demonstrated that decreasing ECS through intracerebroventricular (i.c.v.) administration of anti-ouabain antibodies (anti-Ou-Ab) decreased the activity of α1+/- mice in forced swimming tests but did not change the activity in wild type (wt) mice. This treatment also affected exploratory and anxiety behaviors in α1+/- but not wt mice, as measured in open field tests. The i.c.v. administration of anti-Ou-Ab decreased brain ECS and increased brain Na+, K+-ATPase activity in wt and α1+/- mice. The serum ECS was lower in α1+/- than wt mice. In addition, a study in human participants demonstrated that serum ECS significantly decreased after treatment. These results suggest that the Na+, K+-ATPase α1 isoform is involved in depressive- and manic-like behaviors and support that the Na+, K+-ATPase/ECS system participates in the etiology of BD.

The Na/K-ATPase role as a signal transducer in lung inflammation

Acute respiratory distress syndrome (ARDS) is marked by damage to the capillary endothelium and alveolar epithelium following edema formation and cell infiltration. Currently, there are no effective treatments for severe ARDS. Pathologies such as sepsis, pneumonia, fat embolism, and severe trauma may cause ARDS with respiratory failure. The primary mechanism of edema clearance is the epithelial cells' Na/K-ATPase (NKA) activity. NKA is an enzyme that maintains the electrochemical gradient and cell homeostasis by transporting Na+ and K+ ions across the cell membrane. Direct injury on alveolar cells or changes in ion transport caused by infections decreases the NKA activity, loosening tight junctions in epithelial cells and causing edema formation. In addition, NKA acts as a receptor triggering signal transduction in response to the binding of cardiac glycosides. The ouabain (a cardiac glycoside) and oleic acid induce lung injury by targeting NKA. Besides enzymatic inhibition, the NKA triggers intracellular signal transduction, fostering proinflammatory cytokines production and contributing to lung injury. Herein, we reviewed and discussed the crucial role of NKA in edema clearance, lung injury, and intracellular signaling pathway activation leading to lung inflammation, thus putting the NKA as a protagonist in lung injury pathology.

Regulation of Na+-K+-ATPase leads to disturbances of isoproterenol-induced cardiac dysfunction via interference of Ca2+-dependent cardiac metabolism

Reductions in Na+-K+-ATPase (NKA) activity and expression are often observed in the progress of various reason-induced heart failure (HF). However, NKA α1 mutation or knockdown cannot cause spontaneous heart disease. Whether the abnormal NKA α1 directly contributes to HF pathogenesis remains unknown. Here, we challenge NKA α1+/- mice with isoproterenol to evaluate the role of NKA α1 haploinsufficiency in isoproterenol (ISO)-induced cardiac dysfunction. Genetic knockdown of NKA α1 accelerated ISO-induced cardiac cell hypertrophy, heart fibrosis, and dysfunction. Further studies revealed decreased Krebs cycle, fatty acid oxidation, and mitochondrial OXPHOS in the hearts of NKA α1+/- mice challenged with ISO. In ISO-treated conditions, inhibition of NKA elevated cytosolic Na+, further reduced mitochondrial Ca2+ via mNCE, and then finally down-regulated cardiac cell energy metabolism. In addition, a supplement of DRm217 alleviated ISO-induced heart dysfunction, mitigated cardiac remodeling, and improved cytosolic Na+ and Ca2+ elevation and mitochondrial Ca2+ depression in the NKA α1+/- mouse model. The findings suggest that targeting NKA and mitochondria Ca2+ could be a promising strategy in the treatment of heart disease.

ATP1A1 is a promising new target for melanoma treatment and can be inhibited by its physiological ligand bufalin to restore targeted therapy efficacy

Despite advancements in treating metastatic melanoma, many patients exhibit resistance to targeted therapies. Our study focuses on ATP1A1, a sodium pump subunit associated with cancer development. We aimed to assess ATP1A1 prognostic value in melanoma patients and examine the impact of its ligand, bufalin, on melanoma cell lines in vitro and in vivo. High ATP1A1 expression (IHC) correlated with reduced overall survival in melanoma patients. Resistance to BRAF inhibitor was linked to elevated ATP1A1 levels in patient biopsies (IHC, qPCR) and cell lines (Western blot, qPCR). Additionally, high ATP1A1 mRNA expression positively correlated with differentiation/pigmentation markers based on data from The Cancer Genome Atlas (TCGA) databases and Verfaillie proliferative gene signature analysis. Bufalin specifically targeted ATP1A1 in caveolae, (proximity ligation assay) and influenced Src phosphorylation (Western blot), thereby disrupting multiple signaling pathways (phosphokinase array). In vitro, bufalin induced apoptosis in melanoma cell lines by acting on ATP1A1 (siRNA experiments) and, in vivo, significantly impeded melanoma growth using a nude mouse xenograft model with continuous bufalin delivery via an osmotic pump. In conclusion, our study demonstrates that ATP1A1 could serve as a prognostic marker for patient survival and a predictive marker for response to BRAF inhibitor therapy. By targeting ATP1A1, bufalin inhibited cell proliferation, induced apoptosis in vitro, and effectively suppressed tumor development in mice. Thus, our findings strongly support ATP1A1 as a promising therapeutic target, with bufalin as a potential agent to disrupt its tumor-promoting activity.

Intracellular K+ Limits T-cell Exhaustion and Preserves Antitumor Function

T cells are often compromised within cancers, allowing disease progression. We previously found that intratumoral elevations in extracellular K+, related to ongoing cell death, constrained CD8+ T-cell Akt-mTOR signaling and effector function. To alleviate K+-mediated T-cell dysfunction, we pursued genetic means to lower intracellular K+. CD8+ T cells robustly and dynamically express the Na+/K+ ATPase, among other K+ transporters. CRISPR-Cas9-mediated disruption of the Atp1a1 locus lowered intracellular K+ and elevated the resting membrane potential (i.e., Vm, Ψ). Despite compromised Ca2+ influx, Atp1a1-deficient T cells harbored tonic hyperactivity in multiple signal transduction cascades, along with a phenotype of exhaustion in mouse and human CD8+ T cells. Provision of exogenous K+ restored intracellular levels in Atp1a1-deficient T cells and prevented damaging levels of reactive oxygen species (ROS), and both antioxidant treatment and exogenous K+ prevented Atp1a1-deficient T-cell exhaustion in vitro. T cells lacking Atp1a1 had compromised persistence and antitumor activity in a syngeneic model of orthotopic murine melanoma. Translational application of these findings will require balancing the beneficial aspects of intracellular K+ with the ROS-dependent nature of T-cell effector function. See related Spotlight by Banuelos and Borges da Silva, p. 6.

Sex differences in blood pressure regulation and hypertension: renal, hemodynamic, and hormonal mechanisms

The teleology of sex differences has been argued since at least as early as Aristotle's controversial Generation of Animals more than 300 years BC, which reflects the sex bias of the time to contemporary readers. Although the question "why are the sexes different" remains a topic of debate in the present day in metaphysics, the recent emphasis on sex comparison in research studies has led to the question "how are the sexes different" being addressed in health science through numerous observational studies in both health and disease susceptibility, including blood pressure regulation and hypertension. These efforts have resulted in better understanding of differences in males and females at the molecular level that partially explain their differences in vascular function and renal sodium handling and hence blood pressure and the consequential cardiovascular and kidney disease risks in hypertension. This review focuses on clinical studies comparing differences between men and women in blood pressure over the life span and response to dietary sodium and highlights experimental models investigating sexual dimorphism in the renin-angiotensin-aldosterone, vascular, sympathetic nervous, and immune systems, endothelin, the major renal sodium transporters/exchangers/channels, and the impact of sex hormones on these systems in blood pressure homeostasis. Understanding the mechanisms governing sex differences in blood pressure regulation could guide novel therapeutic approaches in a sex-specific manner to lower cardiovascular risks in hypertension and advance personalized medicine.

Sodium homeostasis and signalling: The core and the hub of astrocyte function

Neuronal activity and neurochemical stimulation trigger spatio-temporal changes in the cytoplasmic concentration of Na+ ions in astrocytes. These changes constitute the substrate for Na+ signalling and are fundamental for astrocytic excitability. Astrocytic Na+ signals are generated by Na+ influx through neurotransmitter transporters, with primary contribution of glutamate transporters, and through cationic channels; whereas recovery from Na+ transients is mediated mainly by the plasmalemmal Na+/K+ ATPase. Astrocytic Na+ signals regulate the activity of plasmalemmal transporters critical for homeostatic function of astrocytes, thus providing real-time coordination between neuronal activity and astrocytic support.

Chronic Ouabain Targets Pore-Forming Claudin-2 and Ameliorates Radiation-Induced Damage to the Rat Intestinal Tissue Barrier

Ionizing radiation (IR) causes disturbances in the functions of the gastrointestinal tract. Given the therapeutic potential of ouabain, a specific ligand of the Na,K-ATPase, we tested its ability to protect against IR-induced disturbances in the barrier and transport properties of the jejunum and colon of rats. Male Wistar rats were subjected to 6-day intraperitoneal injections of vehicle or ouabain (1 µg/kg/day). On the fourth day of injections, rats were exposed to total-body X-ray irradiation (10 Gy) or a sham irradiation. Isolated tissues were examined 72 h post-irradiation. Electrophysiological characteristics and paracellular permeability for sodium fluorescein were measured in an Ussing chamber. Histological analysis and Western blotting were also performed. In the jejunum tissue, ouabain exposure did not prevent disturbances in transepithelial resistance, paracellular permeability, histological characteristics, as well as changes in the expression of claudin-1, -3, -4, tricellulin, and caspase-3 induced by IR. However, ouabain prevented overexpression of occludin and the pore-forming claudin-2. In the colon tissue, ouabain prevented electrophysiological disturbances and claudin-2 overexpression. These observations may reveal a mechanism by which circulating ouabain maintains tight junction integrity under IR-induced intestinal dysfunction.

In vitro and in vivo accumulation of the anticancer Ru complexes [RuII(cym)(HQ)Cl] and [RuII(cym)(PCA)Cl]Cl

The cellular accumulation and the underlying mechanisms for the two ruthenium-based anticancer complexes [RuII(cym)(HQ)Cl] 1 (cym = η6-p-cymene, HQ = 8-hydroxyquinoline) and [RuII(cym)(PCA)Cl]Cl 2 (PCA = N-fluorophenyl-2-pyridinecarbothioamide) were investigated in HCT116 human colorectal carcinoma cells. The results showed that the cellular accumulation of both complexes increased over time and with higher concentrations, and that 2 accumulates in greater quantities in cells than 1. Inhibition studies of selected cellular accumulation mechanisms indicated that both 1 and 2 may be transported into the cells by both passive diffusion and active transporters, similar to cisplatin. Efflux experiments indicated that 1 and 2 are subjected to efflux through a mechanism that does not involve p-glycoprotein, as addition of verapamil did not make any difference. Exploring the influence of the Cu transporter by addition of CuCl2 resulted in a higher accumulation of 1 and 2 whilst the amount of Pt detected was slightly reduced when cells were treated with cisplatin. Complexes 1 and 2 were further explored in zebrafish where accumulation and distribution were determined with ICP-MS and LA-ICP-MS. The results correlated with the in vitro observations and zebrafish treated with 2 showed higher Ru contents than those treated with 1. The distribution studies suggested that both complexes mainly accumulated in the intestines of the zebrafish.

Electrostatic switch mechanisms of membrane protein trafficking and regulation

Lipid-protein interactions are normally classified as either specific or general. Specific interactions refer to lipid binding to specific binding sites within a membrane protein, thereby modulating the protein's thermal stability or kinetics. General interactions refer to indirect effects whereby lipids affect membrane proteins by modulating the membrane's physical properties, e.g., its fluidity, thickness, or dipole potential. It is not widely recognized that there is a third distinct type of lipid-protein interaction. Intrinsically disordered N- or C-termini of membrane proteins can interact directly but nonspecifically with the surrounding membrane. Many peripheral membrane proteins are held to the cytoplasmic surface of the plasma membrane via a cooperative combination of two forces: hydrophobic anchoring and electrostatic attraction. An acyl chain, e.g., myristoyl, added post-translationally to one of the protein's termini inserts itself into the lipid matrix and helps hold peripheral membrane proteins onto the membrane. Electrostatic attraction occurs between positively charged basic amino acid residues (lysine and arginine) on one of the protein's terminal tails and negatively charged phospholipid head groups, such as phosphatidylserine. Phosphorylation of either serine or tyrosine residues on the terminal tails via regulatory protein kinases allows for an electrostatic switch mechanism to control trafficking of the protein. Kinase action reduces the positive charge on the protein's tail, weakening the electrostatic attraction and releasing the protein from the membrane. A similar mechanism regulates many integral membrane proteins, but here only electrostatic interactions are involved, and the electrostatic switch modulates protein activity by altering the stabilities of different protein conformational states.

Screening of Peptides that Specifically Binds to M3-M4 Extracellular Domain of Sodium Pump α1 Subunit and Analysis of Their Bioactivity In Vitro and In Vivo

Interaction between ouabain (OUA) and Na+/K+-pump remains in the current focus of hypertension research. This study aimed to find an oligopeptide that would antagonize the inhibitory effect of endogenous OUA on Na+/K+-pump and examine its activity at the cellular and organism levels. To this end, Phage Random 12 Peptide Library was employed to screen for specific polypeptide ligands that interact with M3-M4 extracellular domain of Na+/K+-pump α1 subunit known as OUA-binding site. Synthetic sequence ILEYTWLEAGGGS of extracellular domain M3-M4 of Na+/K+-pump α1 subunit was used as the target. The phage positive clones were screened and identified using the phage library and double sandwich ELISA. DNA was extracted and sequenced to synthesize 3 peptide ligands to Na+/K+-pump: P-A, P-B, and P-C. We also studied the effects of the short peptide with the highest potency for countering OUA on proliferation and apoptosis of EA.hy926 vascular endothelial cells and on systolic BP in spontaneously hypertensive rats (SHR). The effect of peptide P-A on proliferation (stimulation with physiological concentrations of OUA) and on apoptosis (stimulation with OUA in high concentrations) of EA.hy926 vascular endothelial cells was assessed by the MTT test and flow cytometry, respectively. In SHR rats, intravenous injection of P-A decreased systolic BP. Oligopeptide P-A competitively antagonized the inhibitory action of OUA on Na+/K+-pump, OUA-induced proliferation, and OUA-provoked apoptosis of cultured EA.hy926 cells. Our findings open vista for the emergence of novel hypertensive drugs.

FXYD3 functionally demarcates an ancestral breast cancer stem cell subpopulation with features of drug-tolerant persisters

The heterogeneity of cancer stem cells (CSCs) within tumors presents a challenge in therapeutic targeting. To decipher the cellular plasticity that fuels phenotypic heterogeneity, we undertook single-cell transcriptomics analysis in triple-negative breast cancer (TNBC) to identify subpopulations in CSCs. We found a subpopulation of CSCs with ancestral features that is marked by FXYD domain-containing ion transport regulator 3 (FXYD3), a component of the Na+/K+ pump. Accordingly, FXYD3+ CSCs evolve and proliferate, while displaying traits of alveolar progenitors that are normally induced during pregnancy. Clinically, FXYD3+ CSCs were persistent during neoadjuvant chemotherapy, hence linking them to drug-tolerant persisters (DTPs) and identifying them as crucial therapeutic targets. Importantly, FXYD3+ CSCs were sensitive to senolytic Na+/K+ pump inhibitors, such as cardiac glycosides. Together, our data indicate that FXYD3+ CSCs with ancestral features are drivers of plasticity and chemoresistance in TNBC. Targeting the Na+/K+ pump could be an effective strategy to eliminate CSCs with ancestral and DTP features that could improve TNBC prognosis.

Diet, cellular, and systemic homeostasis control the cycling of potassium stable isotopes in endothermic vertebrates

The naturally occurring stable isotopes of potassium (41K/39K, expressed as δ41K) have the potential to make significant contributions to vertebrate and human biology. The utility of K stable isotopes is, however, conditioned by the understanding of the dietary and biological factors controlling natural variability of δ41K. This paper reports a systematic study of K isotopes in extant terrestrial endothermic vertebrates. δ41K has been measured in 158 samples of tissues, biofluids, and excreta from 40 individuals of four vertebrate species (rat, guinea pig, pig and quail) reared in two controlled feeding experiments. We show that biological processing of K by endothermic vertebrates produces remarkable intra-organism δ41K variations of ca. 1.6‰. Dietary δ41K is the primary control of interindividual variability and δ41K of bodily K is +0.5-0.6‰ higher than diet. Such a trophic isotope effect is expected to propagate throughout trophic chains, opening promising use for reconstructing dietary behaviors in vertebrate ecosystems. In individuals, cellular δ41K is related to the intensity of K cycling and effectors of K homeostasis, including plasma membrane permeability and electrical potential. Renal and intestinal transepithelial transports also control fractionation of K isotopes. Using a box-modeling approach, we establish a first model of K isotope homeostasis. We predict a strong sensitivity of δ41K to variations of intracellular and renal K cycling in normal and pathological contexts. Thus, K isotopes constitute a promising tool for the study of K dyshomeostasis.

Biological rhythms are correlated with Na+, K+-ATPase and oxidative stress biomarkers: A translational study on bipolar disorder

BACKGROUND

Bipolar disorder (BD) is a chronic, severe, and multifactorial psychiatric disorder. Although biological rhythms alterations, sodium potassium pump (Na+, K+-ATPase) changes, and oxidative stress appear to play a critical role in the etiology and pathophysiology of BD, the inter-connection between them has not been described. Therefore this study evaluated the association between biological rhythms, Na+, K+-ATPase, and oxidative stress parameters in BD patients and the preclinical paradoxical sleep deprivation model (PSD).

METHODS

A translational study was conducted, including a case-control protocol with 36 BD and 46 healthy controls (HC). Subjects completed the Biological Rhythm Interview of Assessment in Neuropsychiatry (BRIAN). In addition, Erythrocyte Na+, K+-ATPase activity, and oxidative and nitrosative stress markers were assessed (4-hydroxynonenal [4-HNE], 8-isoprostane [8-ISO], thiobarbituric acid reactive substances [TBARS], carbonyl, 3-nitrotyrosine [3-nitro]). In the preclinical protocol, the same biomarkers were evaluated in the frontal cortex, hippocampus, and striatum from mice submitted to the PSD.

RESULTS

BD patients had a significantly higher total score of BRIAN versus HCs. Additionally, individuals with BD showed decreased Na+, K+-ATPase activity and increased oxidative stress parameters compared to HC without psychiatric disorders. This difference was driven by actively depressed BD subjects. The mice submitted to the PSD also demonstrated decreased Na+, K+-ATPase activity and increased oxidative stress parameters.

LIMITATIONS

BRIAN biological underpinning is less well characterized; We did not control for medication status; Sample size is limited; PSD it is not a true model of BD.

CONCLUSIONS

The present study found a significant correlation between Na+, K+-ATPase and oxidative stress with changes in biological rhythms, reinforcing the importance of these parameters to BD.

The vascular Na,K-ATPase: clinical implications in stroke, migraine, and hypertension

In the vascular wall, the Na,K-ATPase plays an important role in the control of arterial tone. Through cSrc signaling, it contributes to the modulation of Ca2+ sensitivity in vascular smooth muscle cells. This review focuses on the potential implication of Na,K-ATPase-dependent intracellular signaling pathways in severe vascular disorders; ischemic stroke, familial migraine, and arterial hypertension. We propose similarity in the detrimental Na,K-ATPase-dependent signaling seen in these pathological conditions. The review includes a retrospective proteomics analysis investigating temporal changes after ischemic stroke. The analysis revealed that the expression of Na,K-ATPase α isoforms is down-regulated in the days and weeks following reperfusion, while downstream Na,K-ATPase-dependent cSrc kinase is up-regulated. These results are important since previous studies have linked the Na,K-ATPase-dependent cSrc signaling to futile recanalization and vasospasm after stroke. The review also explores a link between the Na,K-ATPase and migraine with aura, as reduced expression or pharmacological inhibition of the Na,K-ATPase leads to cSrc kinase signaling up-regulation and cerebral hypoperfusion. The review discusses the role of an endogenous cardiotonic steroid-like compound, ouabain, which binds to the Na,K-ATPase and initiates the intracellular cSrc signaling, in the pathophysiology of arterial hypertension. Currently, our understanding of the precise control mechanisms governing the Na,K-ATPase/cSrc kinase regulation in the vascular wall is limited. Understanding the role of vascular Na,K-ATPase signaling is essential for developing targeted treatments for cerebrovascular disorders and hypertension, as the Na,K-ATPase is implicated in the pathogenesis of these conditions and may contribute to their comorbidity.

PrP meets alpha-synuclein: Molecular mechanisms and implications for disease

The discovery of prions has challenged dogmas and has revolutionized our understanding of protein-misfolding diseases. The concept of self-propagation via protein conformational changes, originally discovered for the prion protein (PrP), also applies to other proteins that exhibit similar behavior, such as alpha-synuclein (aSyn), a central player in Parkinson's disease and in other synucleinopathies. aSyn pathology appears to spread from one cell to another during disease progression, and involves the misfolding and aggregation of aSyn. How the transfer of aSyn between cells occurs is still being studied, but one important hypothesis involves receptor-mediated transport. Interestingly, recent studies indicate that the cellular prion protein (PrPC ) may play a crucial role in this process. PrPC has been shown to act as a receptor/sensor for protein aggregates in different neurodegenerative disorders, including Alzheimer's disease and amyotrophic lateral sclerosis. Here, we provide a comprehensive overview of the current state of knowledge regarding the interaction between aSyn and PrPC and discuss its role in synucleinopathies. We examine the properties of PrP and aSyn, including their structure, function, and aggregation. Additionally, we discuss the current understanding of PrPC 's role as a receptor/sensor for aSyn aggregates and identify remaining unanswered questions in this area of research. Ultimately, we posit that exploring the interaction between aSyn and PrPC may offer potential treatment options for synucleinopathies.

Silencing of ATP1A1 attenuates cell membrane disruption by nanosecond electric pulses

This study explored the role of the Na/K-ATPase (NKA) in membrane permeabilization induced by nanosecond electric pulses. Using CRISPR/Cas9 and shRNA, we silenced the ATP1A1 gene, which encodes α1 NKA subunit in U937 human monocytes. Silencing reduced the rate and the cumulative uptake of YoPro-1 dye after electroporation by 300-ns, 7-10 kV/cm pulses, while ouabain, a specific NKA inhibitor, enhanced YoPro-1 entry. We conclude that the α1 subunit supports the electropermeabilized membrane state, by forming or stabilizing electropores or by hindering repair mechanisms, and this role is independent of NKA's ion pump function.

Dynamic lipid interactions in the plasma membrane Na+,K+-ATPase

The function of ion-transporting Na+,K+-ATPases depends on the surrounding lipid environment in biological membranes. Two established lipid-interaction sites A and B within the transmembrane domain have been observed to induce protein activation and stabilization, respectively. In addition, lipid-mediated inhibition has been assigned to a site C, but with the exact location not experimentally confirmed. Also, possible effects on lipid interactions by disease mutants dwelling in the membrane-protein interface remain relatively uncharacterized. We simulated human Na+,K+-ATPase α1β1FXYD homology models in E1 and E2 states in an asymmetric, multicomponent plasma membrane to determine both wild-type and disease mutant lipid-protein interactions. The simulated wild-type lipid interactions at the established sites A and B were in agreement with experimental results thereby confirming the membrane-protein model system. The less well-characterized, proposed inhibitory site C was dominated by lipids lacking inhibitory properties. Instead, two sites hosting inhibitory lipids were identified at the extracellular side and also a cytoplasmic CHL-binding site that provide putative alternative locations of Na+,K+-ATPase inhibition. Three disease mutations, Leu302Arg, Glu840Arg and Met859Arg resided in the lipid-protein interface and caused drastic changes in the lipid interactions. The simulation results show that lipid interactions to the human Na+,K+-ATPase α1β1FXYD protein in the plasma membrane are highly state-dependent and can be disturbed by disease mutations located in the lipid interface, which can open up for new venues to understand genetic disorders.

Intracellular K + limits T cell exhaustion and preserves antitumor function

The cancer-killing activity of T cells is often compromised within tumors, allowing disease progression. We previously found that intratumoral elevations in extracellular K + related to ongoing cell death constrained CD8 + T cell Akt-mTOR signaling and effector function (1,2). To alleviate K + mediated T cell suppression, we pursued genetic means to lower intracellular K + . Transcriptomic analysis of CD8 + T cells demonstrated the Na + /K + ATPase to be robustly and dynamically expressed. CRISPR-Cas9 mediated deletion of the catalytic alpha subunit of the Na + /K + ATPase lowered intracellular K + but produced tonic hyperactivity in multiple signal transduction cascades along with the acquisition of co-inhibitory receptors and terminal differentiation in mouse and human CD8 + T cells. Mechanistically, Na + /K + ATPase disruption led to ROS accumulation due to depletion of intracellular K + in T cells. Antioxidant treatment or high K + media prevented Atp1a1 deficient T cells from exhausted T (T Ex ) cell formation. Consistent with transcriptional and proteomic data suggesting a T Ex cell phenotype, T cells lacking Atp1a1 had compromised persistence and antitumor activity in a syngeneic model of orthotopic murine melanoma. Translational application of these findings will include efforts to lower intracellular K + while limiting ROS accumulation within tumor specific T cells.

Synopsis

High extracellular K + (↑[K + ] e ) is found within tumors and suppresses T cell effector function. Collier et al. find that deletion of the Na + /K + ATPase in T cells lowers intracellular K + and promotes ROS accumulation, tonic signal transduction and T cell exhaustion owing to ROS accumulation. Engineering T cell ion transport is an important consideration for cancer immunotherapy.

Identified and potential internalization signals involved in trafficking and regulation of Na+/K+ ATPase activity

The sodium-potassium pump (NKA) or Na+/K+ ATPase consumes around 30-40% of the total energy expenditure of the animal cell on the generation of the sodium and potassium electrochemical gradients that regulate various electrolyte and nutrient transport processes. The vital role of this protein entails proper spatial and temporal regulation of its activity through modulatory mechanisms involving its expression, localization, enzymatic activity, and protein-protein interactions. The residence of the NKA at the plasma membrane is compulsory for its action as an antiporter. Despite the huge body of literature reporting on its trafficking between the cell membrane and intracellular compartments, the mechanisms controlling the trafficking process are by far the least understood. Among the molecular determinants of the plasma membrane proteins trafficking are intrinsic sequence-based endocytic motifs. In this review, we (i) summarize previous reports linking the regulation of Na+/K+ ATPase trafficking and/or plasma membrane residence to its activity, with particular emphasis on the endocytic signals in the Na+/K+ ATPase alpha-subunit, (ii) map additional potential internalization signals within Na+/K+ ATPase catalytic alpha-subunit, based on canonical and noncanonical endocytic motifs reported in the literature, (iii) pinpoint known and potential phosphorylation sites associated with NKA trafficking, (iv) highlight our recent studies on Na+/K+ ATPase trafficking and PGE2-mediated Na+/K+ ATPase modulation in intestine, liver, and kidney cells.

Insulin reverses impaired alveolar fluid clearance in ARDS by inhibiting LPS-induced autophagy and inflammatory

Until now, acute respiratory distress syndrome (ARDS) has been a difficult clinical condition with a high mortality and morbidity rate, and is characterized by a build-up of alveolar fluid and impaired clearance. The underlying mechanism is not yet fully understood and no effective medications available. Autophagy activation is associated with ARDS caused by different pathogenic factors. It represents a new direction of prevention and treatment of ARDS to restrain autophagy to a reasonable level through pharmacological and molecular genetic methods. Na, K-ATPase is the main gradient driver of pulmonary water clearance in ARDS and could be degraded by the autophagy-lysosome pathway to affect its abundance and enzyme activity. As a normal growth hormone in human body, insulin has been widely used in clinical for a long time. To investigate the association of insulin with Na, K-ATPase, autophagy and inflammatory markers in LPS-treated C57BL/6 mice by survival assessment, proteomic analysis, histologic examination, inflammatory cell counting, myeloperoxidase, TNF-α and IL-1β activity analysis etc. This was also verified on mouse alveolar epithelial type II (AT II) and A549 cells by transmission electron microscopy. We found that insulin restored the expression of Na, K-ATPase, inhibited the activation of autophagy and reduced the release of inflammatory factors caused by alveolar epithelial damage. The regulation mechanism of insulin on Na, K-ATPase by inhibiting autophagy function may provide new drug targets for the treatment of ARDS.

Endogenous Digitalis-like Factors as a Key Molecule in the Pathophysiology of Pregnancy-Induced Hypertension and a Potential Therapeutic Target in Preeclampsia

Preeclampsia (PE), the most severe presentation of hypertensive disorders of pregnancy, is the major cause of morbidity and mortality linked to pregnancy, affecting both mother and fetus. Despite advances in prophylaxis and managing PE, delivery of the fetus remains the only causative treatment available. Focus on complex pathophysiology brought the potential for new treatment options, and more conservative options allowing reduction of feto-maternal complications and sequelae are being investigated. Endogenous digitalis-like factors, which have been linked to the pathogenesis of preeclampsia since the mid-1980s, have been shown to play a role in the pathogenesis of various cardiovascular diseases, including congestive heart failure and chronic renal disease. Elevated levels of EDLF have been described in pregnancy complicated by hypertensive disorders and are currently being investigated as a therapeutic target in the context of a possible breakthrough in managing preeclampsia. This review summarizes mechanisms implicating EDLFs in the pathogenesis of preeclampsia and evidence for their potential role in treating this doubly life-threatening disease.

The zebrafish mutant dreammist implicates sodium homeostasis in sleep regulation

Sleep is a nearly universal feature of animal behaviour, yet many of the molecular, genetic, and neuronal substrates that orchestrate sleep/wake transitions lie undiscovered. Employing a viral insertion sleep screen in larval zebrafish, we identified a novel gene, dreammist (dmist), whose loss results in behavioural hyperactivity and reduced sleep at night. The neuronally expressed dmist gene is conserved across vertebrates and encodes a small single-pass transmembrane protein that is structurally similar to the Na+,K+-ATPase regulator, FXYD1/Phospholemman. Disruption of either fxyd1 or atp1a3a, a Na+,K+-ATPase alpha-3 subunit associated with several heritable movement disorders in humans, led to decreased night-time sleep. Since atpa1a3a and dmist mutants have elevated intracellular Na+ levels and non-additive effects on sleep amount at night, we propose that Dmist-dependent enhancement of Na+ pump function modulates neuronal excitability to maintain normal sleep behaviour.

In Vitro Study of the Multimodal Effect of Na+/K+ ATPase Blocker Ouabain on the Tumor Microenvironment and Malignant Cells

Na+/K+ ATPase is a protein involved in the active transport of ions across the cellular membrane. Ouabain is a cardiotonic glycoside that, by inhibiting the Na+/K+ pump, interferes with cell processes mediated directly by the pump, but also indirectly influences other cellular processes such as cell cycle and proliferation, growth, cell differentiation, angiogenesis, migration, adhesion, and invasion. We used the SK-BR-3 breast cancer cell line, mesenchymal stem cells (MSCs), and tumor-associated fibroblasts (TAFs) in vitro to determine the effects of ouabain exposure on these cellular types. The results showed a multi-level effect of ouabain mainly on tumor cells, in a dose-dependent manner, while the TAFs and their normal counterparts were not significantly influenced. Following exposure to ouabain, the SK-BR-3 cells changed their morphologic appearance, decreased the expression of immunophenotypic markers (CD29, Her2, VEGF), the proliferation rate was significantly decreased (Ki67 index), the cells were blocked in the G0 phase of the cell cycle and suffered necrosis. These data were correlated with the variable expression of α and β Na+/K+ pump subunits in tumor cells, resulting in decreased ability to adhere to the VCAM-1 substrate in functional flow chamber studies. Being indicative of the pro-apoptotic and inhibitory effect of ouabain on tumor invasion and metastasis, the results support the addition of ouabain to the oncological therapeutic arsenal, trailing the "repurposing drugs" approach.

The Na+,K+-ATPase and its stoichiometric ratio: some thermodynamic speculations

 Almost seventy years after its discovery, the sodium-potassium adenosine triphosphatase (the sodium pump) located in the cell plasma membrane remains a source of novel mechanistic and physiologic findings. A noteworthy feature of this enzyme/transporter is its robust stoichiometric ratio under physiological conditions: it sequentially counter-transports three sodium ions and two potassium ions against their electrochemical potential gradients per each hydrolyzed ATP molecule. Here we summarize some present knowledge about the sodium pump and its physiological roles, and speculate whether energetic constraints may have played a role in the evolutionary selection of its characteristic stoichiometric ratio.

Cation leak through the ATP1A3 pump causes spasticity and intellectual disability

ATP1A3 encodes the α3 subunit of the sodium-potassium ATPase, one of two isoforms responsible for powering electrochemical gradients in neurons. Heterozygous pathogenic ATP1A3 variants produce several distinct neurological syndromes, yet the molecular basis for phenotypic variability is unclear. We report a novel recurrent variant, ATP1A3(NM_152296.5):c.2324C>T; p.(Pro775Leu), in nine individuals associated with the primary clinical features of progressive or non-progressive spasticity and developmental delay/intellectual disability. No patients fulfil diagnostic criteria for ATP1A3-associated syndromes, including alternating hemiplegia of childhood, rapid-onset dystonia-parkinsonism or cerebellar ataxia-areflexia-pes cavus-optic atrophy-sensorineural hearing loss (CAPOS), and none were suspected of having an ATP1A3-related disorder. Uniquely among known ATP1A3 variants, P775L causes leakage of sodium ions and protons into the cell, associated with impaired sodium binding/occlusion kinetics favouring states with fewer bound ions. These phenotypic and electrophysiologic studies demonstrate that ATP1A3:c.2324C>T; p.(Pro775Leu) results in mild ATP1A3-related phenotypes resembling complex hereditary spastic paraplegia or idiopathic spastic cerebral palsy. Cation leak provides a molecular explanation for this genotype-phenotype correlation, adding another mechanism to further explain phenotypic variability and highlighting the importance of biophysical properties beyond ion transport rate in ion transport diseases.

Wfs1E864K knock-in mice illuminate the fundamental role of Wfs1 in endocochlear potential production

Wolfram syndrome (WS) is a rare neurodegenerative disorder encompassing diabetes mellitus, diabetes insipidus, optic atrophy, hearing loss (HL) as well as neurological disorders. None of the animal models of the pathology are presenting with an early onset HL, impeding the understanding of the role of Wolframin (WFS1), the protein responsible for WS, in the auditory pathway. We generated a knock-in mouse, the Wfs1E864K line, presenting a human mutation leading to severe deafness in affected individuals. The homozygous mice showed a profound post-natal HL and vestibular syndrome, a collapse of the endocochlear potential (EP) and a devastating alteration of the stria vascularis and neurosensory epithelium. The mutant protein prevented the localization to the cell surface of the Na+/K+ATPase β1 subunit, a key protein for the maintenance of the EP. Overall, our data support a key role of WFS1 in the maintenance of the EP and the stria vascularis, via its binding partner, the Na+/K+ATPase β1 subunit.

α-synuclein promotes neuronal dysfunction and death by disrupting the binding of ankyrin to ß-spectrin

α-synuclein plays a key role in the pathogenesis of Parkinson's disease and related disorders, but critical interacting partners and molecular mechanisms mediating neurotoxicity are incompletely understood. We show that α-synuclein binds directly to ß-spectrin. Using males and females in a Drosophila model of α-synuclein-related disorders we demonstrate that ß-spectrin is critical for α-synuclein neurotoxicity. Further, the ankyrin binding domain of ß-spectrin is required for α-synuclein binding and neurotoxicity. A key plasma membrane target of ankyrin, Na+/K+ ATPase, is mislocalized when human α-synuclein is expressed in Drosophila. Accordingly, membrane potential is depolarized in α-synuclein transgenic fly brains. We examine the same pathway in human neurons and find that Parkinson's disease patient-derived neurons with a triplication of the α-synuclein locus show disruption of the spectrin cytoskeleton, mislocalization of ankyrin and Na+/K+ ATPase, and membrane potential depolarization. Our findings define a specific molecular mechanism by which elevated levels of α-synuclein in Parkinson's disease and related α-synucleinopathies leads to neuronal dysfunction and death.

Cardamom oil ameliorates behavioral and neuropathological disorders in a rat model of depression induced by reserpine

ETHNOPHARMACOLOGICAL RELEVANCE

Depression is a public health problem. Despite the availability of treatment options, its prevalence is increasing. A high rate of treatment failure is often reported, along with considerable side effects associated with synthetic antidepressants. Therefore, developing effective and safe antidepressants from traditional herbs or natural products as an alternative strategy is warranted to avoid side effects and increase drug efficacy. In traditional medicine, cardamom has traditionally been used to treat conditions like asthma, tooth and gum infections, cataracts, nausea, diarrhea, and even depression and anxiety as well as some problems with the heart, kidneys, and digestive system.

AIM OF THE STUDY

The current study aimed to evaluate the antidepressant activity of cardamom oil in a rat model of depression induced by reserpine and compare it with the activity of the antidepressant drug fluoxetine.

MATERIALS AND METHODS

Depression-like symptoms were induced in male rats by daily i. p. injection of reserpine (0.2 mg/kg/d for 15 d followed by 0.1 mg/kg/d for 21 d to maintain the depressive state), and the rats were treated with cardamom oil (oral dose = 200 mg/kg/d) for 21 d along with the maintenance dose of reserpine. We performed behavioral tests (forced swimming test and open-field test) and evaluated biochemical markers of depression.

RESULTS

Our findings revealed that cardamom oil attenuated depression-like symptoms in reserpine-injected rats by improving the behavioral changes measured by the forced swimming test and the locomotor activities measured by the open-field test. In reserpine-injected rats, cardamom oil exerted antidepressant-like effects by modulating lower levels of brain monoamine neurotransmitters (serotonin, norepinephrine, and dopamine), GSH, and higher oxido-nitrosative stress parameters (malondialdehyde and nitric oxide). Moreover, cardamom oil alleviated depression-like behaviors by lowering monoamine oxidase activity and raising the activities of Na⁺/K⁺-ATPase and acetylcholinesterase and levels of a brain-derived neurotrophic factor in the cortex and hippocampus.

CONCLUSION

We recommend the use of cardamom oil as a safe and reliable treatment or an adjuvant for preventing depression-like symptoms in patients suffering from depression.

Polyploidy in Xenopus lowers metabolic rate by decreasing total cell surface area

Although polyploidization is frequent in development, cancer, and evolution, impacts on animal metabolism are poorly understood. In Xenopus frogs, the number of genome copies (ploidy) varies across species and can be manipulated within a species. Here, we show that triploid tadpoles contain fewer, larger cells than diploids and consume oxygen at a lower rate. Drug treatments revealed that the major processes accounting for tadpole energy expenditure include cell proliferation, biosynthesis, and maintenance of plasma membrane potential. While inhibiting cell proliferation did not abolish the oxygen consumption difference between diploids and triploids, treatments that altered cellular biosynthesis or electrical potential did. Combining these results with a simple mathematical framework, we propose that the decrease in total cell surface area lowered production and activity of plasma membrane components including the Na+/K+ ATPase, reducing energy consumption in triploids. Comparison of Xenopus species that evolved through polyploidization revealed that metabolic differences emerged during development when cell size scaled with genome size. Thus, ploidy affects metabolism by altering the cell surface area to volume ratio in a multicellular organism.

Hypoxic Stress-Dependent Regulation of Na,K-ATPase in Ischemic Heart Disease

In cardiomyocytes, regular activity of the Na,K-ATPase (NKA) and its Na/K pump activity is essential for maintaining ion gradients, excitability, propagation of action potentials, electro-mechanical coupling, trans-membrane Na⁺ and Ca²⁺ gradients and, thus, contractility. The activity of NKA is impaired in ischemic heart disease and heart failure, which has been attributed to decreased expression of the NKA subunits. Decreased NKA activity leads to intracellular Na⁺ and Ca²⁺ overload, diastolic dysfunction and arrhythmias. One signal likely related to these events is hypoxia, where hypoxia-inducible factors (HIF) play a critical role in the adaptation of cells to low oxygen tension. HIF activity increases in ischemic heart, hypertension, heart failure and cardiac fibrosis; thus, it might contribute to the impaired function of NKA. This review will mainly focus on the regulation of NKA in ischemic heart disease in the context of stressed myocardium and the hypoxia-HIF axis and argue on possible consequences of treatment.

Targeting the Na+/K+ ATPase DR-region with DR-Ab improves doxorubicin-induced cardiotoxicity

Doxorubicin (DOX) is a potent chemotherapeutic drug for various cancers. Yet, the cardiotoxic side effects limit its application in clinical uses, in which ferroptosis serves as a crucial pathological mechanism in DOX-induced cardiotoxicity (DIC). A reduction of Na+/K + ATPase (NKA) activity is closely associated with DIC progression. However, whether abnormal NKA function was involved in DOX-induced cardiotoxicity and ferroptosis remains unknown. Here, we aim to decipher the cellular and molecular mechanisms of dysfunctional NKA in DOX-induced ferroptosis and investigate NKA as a potential therapeutic target for DIC. A decrease activity of NKA further aggravated DOX-triggered cardiac dysfunction and ferroptosis in NKAα1 haploinsufficiency mice. In contrast, antibodies against the DR-region of NKAα-subunit (DR-Ab) attenuated the cardiac dysfunction and ferroptosis induced by DOX. Mechanistically, NKAα1 interacted with SLC7A11 to form a novel protein complex, which was directly implicated in the disease progression of DIC. Furthermore, the therapeutic effect of DR-Ab on DIC was mediated by reducing ferroptosis by promoting the association of NKAα1/SLC7A11 complex and maintaining the stability of SLC7A11 on the cell surface. These results indicate that antibodies targeting the DR-region of NKA may serve as a novel therapeutic strategy to alleviate DOX-induced cardiotoxicity.