Aquaporin Water Channels Research Articles

Melatonin alleviates depression-like behaviors and cognitive dysfunction in mice by regulating the circadian rhythm of AQP4 polarization

Depression is a common chronic psychiatric illness, which is resistant to medical treatments. While melatonin may alleviate certain depression symptoms, evidence for its efficacy against core symptoms is lacking. Here, we tested a mechanism whereby melatonin rescues the behavioral outcomes of the chronic unpredictable mild stress (CUMS) mouse model of depression. CUMS mice showed depressive behaviors to tail suspension, open field behavior, and sucrose preference test, and cognitive dysfunction in the Morris water maze. Impairments in these measures were relieved by melatonin treatment. Moreover, CUMS mice had impaired glymphatic function across the sleep-wake cycle due to the astrocytic loss and disturbance of circadian regulation of the polarized expression of aquaporin-4 (AQP4) water channels in perivascular astrocytes. EEG results in CUMS mice showed a reduced total sleep time and non-rapid eye movement (NREM) sleep, due to sleep fragmentation in the light phase. CUMS mice lost the normal rhythmic expressions of circadian proteins Per2, Cry2, Bmal1, Clock, and Per1. However, the melatonin treatment restored glymphatic system function and the polarization of AQP4, while improving sleep structure, and rectifying the abnormal expression of Per2, Bmal1, Clock, and Per1 in CUMS mice. Interestingly, Per2 expression correlated negatively with the polarization of AQP4. Further studies demonstrated that Per2 directed the location of AQP4 expression via interactions with the α-dystrobrevin (Dtna) subunit of AQP4 in primary cultured astrocytes. In conclusion, we report a new mechanism whereby melatonin improves depression outcomes by regulating the expression of the circadian protein Per2, maintaining the circadian rhythm of astrocytic AQP4 polarization, and restoring glymphatic function.

Association between RS3763040 polymorphism of the AQP4 and idiopathic intracranial hypertension in a Spanish Caucasian population.

Idiopathic intracranial hypertension (IIH) is a condition of increased intracranial pressure of unknown aetiology. Principal symptoms are headache, visual disturbances, and obesity, together with elevated intracranial pressure. Unspecified MRI, despite normal ventricle size, suggests alterations in the water flux cellular mediated by the brain water channel aquaporin-4 (AQP4). The association among IIH, cerebral spinal fluid malfunction, reabsorption, and functional or regulatory modifications of AQP4 is a hypothesis not confirmed. Blood samples were collected from 72 Spanish Caucasian patients with IIH. A genetic association study was performed with bi-allelic SNPs rs1049305 and rs10244884 in AQ1 and rs2075575, rs3763043, and rs3763040 in AQ4. Genetic data were compared with 94 healthy Caucasian control. Statistics studies were assessed by Pearson's χ 2 tests for 2 × 2 (alleles) or 3 × 2 (genotypes) contingency tables. A P value < 0.05 was considered to be statistically significant. Statistically significant differences were found when comparing the results of the rs3763040 polymorphism of the AQ4 locus of IIH patients with controls, in genotypic frequencies (P = 0.0442) and allele frequencies (P = 0.0171). Furthermore, a statistically significant difference (P = 0.0207) was found in individuals carrying and not carrying the minor allele (GG + GA individuals vs GG homozygotes). No statistically significant differences were found when comparing allele and genotypic frequencies for SNPs rs1049305 and rs10244884 of AQ1 and rs2075575 and rs3763043 of AQ4. The association of AQP4 and specifically of its polymorphic variant rs3763040 with IIH should be validated in other ethnic groups in order to assess more precisely the role of AQP4 in the etiopathogenesis of IIH.

The Coexisting Neuromyelitis Optica Spectrum Disorder and Systemic Lupus Erythematosus: A Therapeutic Challenge.

Neuromyelitis Optica (NMO), or Devic's disease, is an immune-mediated, usually relapsing, central nervous system (CNS) demyelination disorder associated with optic neuritis and transverse myelitis. It is characterised by the presence of longitudinally extensive transverse myelitis (LETM) and antibodies against water channel aquaporin-4 (AQP4-immunoglobulin G [IgG]). The term NMO spectrum disorder (NMOSD) includes patients with limited forms of NMO who are at risk of recurrence. Often patients with NMO or NMOSD have an associated systemic autoimmune disease, most commonly systemic lupus erythematosus (SLE) or Sjogren syndrome (SS) or a related profile of non-organ-specific autoantibodies. The intriguing aspect of coexisting NMOSD and SLE is whether they are independent diseases that can coexist with each other or the serological findings specific to both diseases in a patient is a non-specific finding of no prognostic or therapeutic concern. We have presented two cases of NMOSD coexisting with SLE and based upon the existing evidence in the literature we present that the two conditions are independent of each other, and, at times, it can throw a therapeutic challenge to any clinician.

AQP4-independent TRPV4 modulation of plasma membrane water permeability.

Despite of the major role of aquaporin (AQP) water channels in controlling transmembrane water fluxes, alternative ways for modulating water permeation have been proposed. In the Central Nervous System (CNS), Aquaporin-4 (AQP4) is reported to be functionally coupled with the calcium-channel Transient-Receptor Potential Vanilloid member-4 (TRPV4), which is controversially involved in cell volume regulation mechanisms and water transport dynamics. The present work aims to investigate the selective role of TRPV4 in regulating plasma membrane water permeability in an AQP4-independent way. Fluorescence-quenching water transport experiments in Aqp4-/- astrocytes revealed that cell swelling rate is significantly increased upon TRPV4 activation and in the absence of AQP4. The biophysical properties of TRPV4-dependent water transport were therefore assessed using the HEK-293 cell model. Calcein quenching experiments showed that chemical and thermal activation of TRPV4 overexpressed in HEK-293 cells leads to faster swelling kinetics. Stopped-flow light scattering water transport assay was used to measure the osmotic permeability coefficient (Pf, cm/s) and activation energy (Ea, kcal/mol) conferred by TRPV4. Results provided evidence that although the Pf measured upon TRPV4 activation is lower than the one obtained in AQP4-overexpressing cells (Pf of AQP4 = 0.01667 ± 0.0007; Pf of TRPV4 = 0.002261 ± 0.0004; Pf of TRPV4 + 4αPDD = 0.007985 ± 0.0006; Pf of WT = 0.002249 ± 0.0002), along with activation energy values (Ea of AQP4 = 0.86 ± 0.0006; Ea of TRPV4 + 4αPDD = 2.73 ± 1.9; Ea of WT = 8.532 ± 0.4), these parameters were compatible with a facilitated pathway for water movement rather than simple diffusion. The possibility to tune plasma membrane water permeability more finely through TRPV4 might represent a protective mechanism in cells constantly facing severe osmotic challenges to avoid the potential deleterious effects of the rapid cell swelling occurring via AQP channels.

The Peritoneal Membrane and Its Role in Peritoneal Dialysis.

A healthy and functional peritoneal membrane is key to achieving sufficient ultrafiltration and restoring fluid balance, a major component of high-quality prescription in patients treated with peritoneal dialysis (PD). Variability in membrane function at the start of PD or changes over time on treatment influence dialysis prescription and outcomes, and dysfunction of the peritoneal membrane contributes to fluid overload and associated complications. In this review, we summarize the current knowledge about the structure, function, and pathophysiology of the peritoneal membrane with a focus on clinical implications for patient-centered care. We also discuss the molecular and genetic mechanisms of solute and water transport across the peritoneal membrane, including the role of aquaporin water channels in crystalloid versus colloid osmosis; why and how to assess membrane function using peritoneal equilibration tests; the etiologies of membrane dysfunction and their specific management; and the effect of genetic variation on membrane function and outcomes in patients treated with PD. This review also identifies the gaps in current knowledge and perspectives for future research to improve our understanding of the peritoneal membrane and, ultimately, the care of patients treated with PD.

Aquaporin 3 inhibition suppresses the mitochondrial respiration rate and viability of multiple myeloma cells

Aquaporin 3 (AQP3) is a member of the aquaporin water channel family expressed by numerous cell types, including some cancer cells. Accumulating evidence suggests that AQP3 inhibition may impede cancer progression, but drugs targeting AQP3 are still in the early pre-clinical stage of development. Here, we examined the effect of AQP3 inhibition on multiple myeloma (MM), an incurable plasma cell malignancy. Four MM cell lines were cultured in the presence of an anti-AQP3 monoclonal antibody (mAb), the AQP3 inhibitor DFP00173, or corresponding controls, and the effects on cell viability, proliferation, apoptosis, and mitochondrial respiration capacity were compared. Both anti-AQP3 mAb and DFP00173 reduced cell growth, mitochondrial respiration rate, and electron transport chain complex I activity. Both agents also potentiated the antiproliferative efficacy of the anticancer drug venetoclax. Administration of the anti-AQP3 mAb to immunodeficient mice inoculated with RPMI8226 or KMS-11 MM cells significantly suppressed tumor growth. These data provide evidence that AQP3 blockade can suppress MM cell growth in vitro and tumor growth in mice. Thus, AQP3 inhibition may be an effective therapeutic strategy for MM.

Aquaporin water channels: roles beyond renal water handling.

Aquaporin (AQP) water channels are pivotal to renal water handling and therefore in the regulation of body water homeostasis. However, beyond the kidney, AQPs facilitate water reabsorption and secretion in other cells and tissues, including sweat and salivary glands and the gastrointestinal tract. A growing body of evidence has also revealed that AQPs not only facilitate the transport of water but also the transport of several small molecules and gases such as glycerol, H2O2, ions and CO2. Moreover, AQPs are increasingly understood to contribute to various cellular processes, including cellular migration, adhesion and polarity, and to act upstream of several intracellular and intercellular signalling pathways to regulate processes such as cell proliferation, apoptosis and cell invasiveness. Of note, several AQPs are highly expressed in multiple cancers, where their expression can correlate with the spread of cancerous cells to lymph nodes and alter the response of cancers to conventional chemotherapeutics. These data suggest that AQPs have diverse roles in various homeostatic and physiological systems and may be exploited for prognostics and therapeutic interventions.

Many kinases for controlling the water channel aquaporin-2.

Aquaporin-2 (AQP2) is a member of the aquaporin water channel family. In the kidney, AQP2 is expressed in collecting duct principal cells where it facilitates water reabsorption in response to antidiuretic hormone (arginine vasopressin, AVP). AVP induces the redistribution of AQP2 from intracellular vesicles and its incorporation into the plasma membrane. The plasma membrane insertion of AQP2 represents the crucial step in AVP-mediated water reabsorption. Dysregulation of the system preventing the AQP2 plasma membrane insertion causes diabetes insipidus (DI), a disease characterised by an impaired urine concentrating ability and polydipsia. There is no satisfactory treatment of DI available. This review discusses kinases that control the localisation of AQP2 and points out potential kinase-directed targets for the treatment of DI.

A Young Lady with Quadriparesis

Neuromyelitis optica spectrum disorder (NMOSD) is a rare autoimmune disease, causing multifocal CNS inflammation affecting the optic nerves &amp; spinal cord. In the 20th century, ‘Devics disease’ was considered as a variant of Multiple sclerosis(MS) that spared the brain. However, the discovery of IgG-class antibodies that bind to the water channel aquaporin-4 (AQP4-IgG) in serum from patients with Devic’s disease, but not from those with typical MS, established NMO as a distinct entity with a chronic, relapsing course. Our patient, a 42-year-old woman has been suffering from vomiting for 2 months followed by inability to move all extremities for last 7 days. It was the very 1st episode of such type of illness. We are reporting this case to highlight the presentation of NMOSD, which is itself a rare disease, outcropped as ‘Area postrema syndrome’, an inaugural manifestation in this patient. J MEDICINE 2023; 24(2): 158-161

Monoclonal Antibody Therapies for Neuromyelitis Optica Spectrum Disorder

Neuromyelitis optica spectrum disorder (NMOSD) is caused by antibodies that target the aquaporin-4 (AQP4) water channel expressed on astrocytes. Specific antibody binding to AQP4 produces complement-dependent cytotoxicity, resulting in inflammation and demyelination. New biologic treatments demonstrate high efficacy and good safety for patients with AQP4-immunoglobulin G-positive NMOSD. They were eculizumab, an anti-complement C5 antibody, satralizumab, an anti-interleukin-6 receptor antibody, and inebilizumab and rituximab, which targets CD19 and CD20, respectively, causing depletion of B-cells. In this review, the pathophysiology of NMOSD, the methodology and results of the recent studies examining monoclonal antibody therapies, and the optimal therapeutic strategy for NMOSD were covered.

Aldosterone Contributes to Vasopressin Escape through Changes in Water and Urea Transport.

Hyponatremia (hypo-osmolality) is a disorder of water homeostasis due to abnormal renal diluting capacity. The body limits the degree to which serum sodium concentration falls through a mechanism called "vasopressin escape". Vasopressin escape is a process that prevents the continuous decrease in serum sodium concentration even under conditions of sustained high plasma vasopressin levels. Previous reports suggest that aldosterone may be involved in the vasopressin escape mechanism. The abilities of aldosterone synthase (Cyp11b2) knockout and wild-type mice to escape from vasopressin were compared. Wild-type mice escaped while the aldosterone synthase knockout mice did not. Both the water channel aquaporin 2 (AQP2) and the urea transporter UT-A1 protein abundances were higher in aldosterone synthase knockout than in wild-type mice at the end of the escape period. Vasopressin escape was also blunted in rats given spironolactone, a mineralocorticoid receptor blocker. Next, the role of the phosphatase, calcineurin (protein phosphatase 2B, PP2B), in vasopressin escape was studied since aldosterone activates calcineurin in rat cortical collecting ducts. Tacrolimus, a calcineurin inhibitor, blunted vasopressin escape in rats compared with the control rats, increased UT-A1, AQP2, and pS256-AQP2, and decreased pS261-AQP2 protein abundances. Our results indicate that aldosterone regulates vasopressin escape through calcineurin-mediated protein changes in UT-A1 and AQP2.

The Role of Aquaporins in Spinal Cord Injury.

Edema formation following traumatic spinal cord injury (SCI) exacerbates secondary injury, and the severity of edema correlates with worse neurological outcome in human patients. To date, there are no effective treatments to directly resolve edema within the spinal cord. The aquaporin-4 (AQP4) water channel is found on plasma membranes of astrocytic endfeet in direct contact with blood vessels, the glia limitans in contact with the cerebrospinal fluid, and ependyma around the central canal. Local expression at these tissue-fluid interfaces allows AQP4 channels to play an important role in the bidirectional regulation of water homeostasis under normal conditions and following trauma. In this review, we consider the available evidence regarding the potential role of AQP4 in edema after SCI. Although more work remains to be carried out, the overall evidence indicates a critical role for AQP4 channels in edema formation and resolution following SCI and the therapeutic potential of AQP4 modulation in edema resolution and functional recovery. Further work to elucidate the expression and subcellular localization of AQP4 during specific phases after SCI will inform the therapeutic modulation of AQP4 for the optimization of histological and neurological outcomes.

Engineering Ultra-Permeable and Antifouling Water Channel-based Biomimetic Membranes toward Sustainable Water Purification

Water channel-based biomimetic membranes (WBMs) are gaining increasing attention due to the effectiveness of water channels in enhancing water permeability and breaking the permselectivity trade-off. However, the ultra-permeable WBMs may suffer from severe membrane fouling issue because a high-water flux tends to result in an accelerated fouling and thus compromises the benefits gained from the usage of water channels. Herein, a novel in-situ modification protocol was proposed to enhance the antifouling performance of ultra-permeable WBMs. The nanovesicles incorporated with aquaporin (AQP) water channels were functionalized with polyethylene glycol brushes (i.e., PEGylation) via a facile self-assembly approach and subsequently encapsulated in the selective layer of thin-film composite membranes through interfacial polymerization. The modification had minimal impact on the function of AQPs, resulting in WBMs with a high water permeance (∼8.2 LMH/bar) and good NaCl rejection (96.4%) comparable to the unmodified WBMs. Moreover, the in-situ modification drastically enhanced the surface hydrophilicity, which endowed the membrane with a superior fouling resistance to organic foulants. The improved fouling resistance ensured a more sustainable operation of ultra-permeable WBMs, particularly in scenarios that favor high water fluxes. This facile modification strategy provides an efficient way to fabricate ultra-permeable and antifouling WBMs for sustainable water purification.

Structural analysis of the water channel AQP2 by single-particle cryo-EM

Water channels, which are small membrane proteins almost entirely buried in lipid membranes, are challenging research targets for single-particle cryo-electron microscopy (cryo-EM), a powerful technique routinely used to determine the structures of membrane proteins. Because the single-particle method enables structural analysis of a whole protein with flexible parts that interfere with crystallization, we have focused our efforts on analyzing water channel structures. Here, utilizing this system, we analyzed the structure of full-length aquaporin-2 (AQP2), a primary regulator of vasopressin-dependent reabsorption of water at the renal collecting ducts. The 2.9 Å resolution map revealed a cytoplasmic extension of the cryo-EM density that was presumed to be the highly flexible C-terminus at which the localization of AQP2 is regulated in the renal collecting duct cells. We also observed a continuous density along the common water pathway inside the channel pore and lipid-like molecules at the membrane interface. Observations of these constructions in the AQP2 structure analyzed without any fiducial markers (e.g., a rigidly bound antibody) indicate that single-particle cryo-EM will be useful for investigating water channels in native states as well as in complexes with chemical compounds.

GABA promotes interstitial fluid clearance in an AQP4-dependent manner by activating the GABAA R.

The glymphatic system is a newly discovered perivascular network where cerebrospinal fluid mixes with interstitial fluid, facilitating clearance of protein solutes and metabolic waste from the parenchyma. The process is strictly dependent on water channel aquaporin-4 (AQP4) expressed on the perivascular astrocytic end-feet. Various factors, such as noradrenaline levels related to the arousal state, influence clearance efficiency, highlighting the possibility that other neurotransmitters additionally modulate this process. To date, the specific role of γ-aminobutyric acid (GABA) in the glymphatic system remains unknown. We used C57BL/6J mice to observe the regulatory effect of GABA on glymphatic pathway by administering a cerebrospinal fluid tracer containing GABA or its GABAA receptor (GABAA R) antagonist through cisterna magna injection. Then, we employed an AQP4 knockout mouse model to explore the regulatory effects of GABA on glymphatic drainage and further study whether transcranial magnetic stimulation-continuous theta burst stimulation (cTBS) could regulate the glymphatic pathway through the GABA system. Our data showed that GABA promotes glymphatic clearance in an AQP4-dependent manner by activating the GABAA R. Furthermore, cTBS was found to modulate the glymphatic pathway by activating the GABA system. Accordingly, we propose that regulating the GABA system by cTBS could modulate glymphatic clearance and provide new insight for clinical prevention and treatment of abnormal protein deposition-related diseases.

New advancements in the management of Neuromyelitis Optica spectrum disease: literature review.

Neuromyelitis Optica spectrum disorder (NMOSD) is a relapsing autoimmune disease of the central nervous system (CNS) where aquaporin-4 water channels are the antigenic target of the disease. The spectrum of the disease involves regions of the CNS where the water channel is widely expressed including the spinal cord, the optic nerve, dorsal medulla, brainstem, and thalamus/hypothalamus. Management of NMOSD includes acute as well as long term treatment. Acute symptoms are typically treated with intravenous corticosteroids and/or plasma exchange while long-term treatment involves the use of immunosuppression/immune modulation. The year 2019 is thought to be the "year of the NMOSD" as three new medications became available for this devastating disease. In this review, FDA approved NMOSD medications are discussed.

Aquaporin-4 and GPRC5B: old and new players in controlling brain oedema.

Brain oedema is a life-threatening complication of various neurological conditions. Understanding molecular mechanisms of brain volume regulation is critical for therapy development. Unique insight comes from monogenic diseases characterized by chronic brain oedema, of which megalencephalic leukoencephalopathy with subcortical cysts (MLC) is the prototype. Variants in MLC1 or GLIALCAM, encoding proteins involved in astrocyte volume regulation, are the main causes of MLC. In some patients, the genetic cause remains unknown. We performed genetic studies to identify novel gene variants in MLC patients, diagnosed by clinical and MRI features, without MLC1 or GLIALCAM variants. We determined subcellular localization of the related novel proteins in cells and in human brain tissue. We investigated functional consequences of the newly identified variants on volume regulation pathways using cell volume measurements, biochemical analysis and electrophysiology. We identified a novel homozygous variant in AQP4, encoding the water channel aquaporin-4, in two siblings, and two de novo heterozygous variants in GPRC5B, encoding the orphan G protein-coupled receptor GPRC5B, in three unrelated patients. The AQP4 variant disrupts membrane localization and thereby channel function. GPRC5B, like MLC1, GlialCAM and aquaporin-4, is expressed in astrocyte endfeet in human brain. Cell volume regulation is disrupted in GPRC5B patient-derived lymphoblasts. GPRC5B functionally interacts with ion channels involved in astrocyte volume regulation. In conclusion, we identify aquaporin-4 and GPRC5B as old and new players in genetic brain oedema. Our findings shed light on the protein complex involved in astrocyte volume regulation and identify GPRC5B as novel potentially druggable target for treating brain oedema.

Water channel Aquaporin 4 is required for T cell activation.

Abstract Aquaporins are a family of ubiquitously expressed transmembrane water channels. We have previously reported that Aquaporin 4 (AQP4) is expressed on T cells and that treatment with a small molecule AQP4 inhibitor significantly delays T cell mediated heart allograft rejection. The goal of this study was to identify mechanisms of prolonged graft survival following AQP4 blockade. Stimulation of murine WT T cells + AER-270 or AQP4 −/−T cells resulted in decreased expression of T cell activation markers CD25 and CD44, and reduced cell volume when compared to control WT T cells. In addition, the absence or inhibition of AQP4 also limited IL-2 production by T cells following stimulation. Intact AQP4 was also required for optimal IFNg production by T cells. Analogously, AQP4 inhibition significantly limited the ability of human T cells to proliferate following TCR stimulation. We then examined the role of AQP4 in TCR signal transduction and found that AQP4 was required for nuclear translocation of NF-KB and NFAT and for optimal calcium flux following TCR stimulation. Either the absence or inhibition of AQP4 impaired TCR signal transduction as early as phosphorylation of Lck (pY394), ZAP70 (pY319) and LAT (p171). AQP4 was previously shown to associate with the actin cytoskeleton in other cell types, we next tested its involvement in TCR polarization/capping. We found that loss of AQP4 resulted in significantly impaired TCR capping and dysfunctional post-TCR stimulation actin remodeling kinetics. Our findings reveal novel mechanisms underlying the importance of AQP4 in optimal T lymphocyte activation and identify AQP4 as a potential therapeutic target for preventing TCR-mediated T cell activation in solid organ transplantation and other diseases.

Pediatric Neuromyelitis Optica Spectrum Disorder

Neuromyelitis Optica Spectrum Disorder (NMOSD) is a demyelinating disease with a high relapse rate and risk of disability accrual. The condition is an astrocytopathy, with antibodies to the aquaporin-4 (AQP4) water channel being detected in AQP4-IgG seropositive disease. Presentation is uncommon in the pediatric age range, accounting for about 3%-5% of cases. NMOSD is more prevalent in populations of Black or East Asian ancestry. Core clinical syndromes include optic neuritis, acute myelitis, area postrema syndrome, acute brainstem syndrome, acute diencephalic syndrome, and symptomatic cerebral syndrome. First-line treatment options in pediatrics include rituximab, azathioprine, and mycophenolate mofetil. Over half of children with AQP4-IgG seropositive NMOSD develop permanent disability, particularly in visual and motor domains. Novel therapeutic targets in the adult population have been developed and are changing the treatment landscape for this disorder.

Epithelial sodium channel (ENaC) in GtoPdb v.2023.1

Epithelial sodium channel (ENaC) in GtoPdb v.2023.1