Reduced light exposure mitigates streptozotocin-induced vascular changes and gliosis in diabetic retina by an anti-inflammatory effect and increased retinal cholesterol turnover

Diabetic retinopathy is not cured efficiently and changes of lifestyle measures may delay early retinal injury in diabetes. The aim of our study was to investigate the effects of reduced daily light exposure on retinal vascular changes in streptozotocin (STZ)-induced model of DM with emphasis on inflammation, Aqp4 expression, visual cycle and cholesterol metabolism-related gene expression in rat retina and RPE. Male Wistar rats were divided into the following groups: 1. control; 2. diabetic group (DM) treated with streptozotocin (100 mg/kg); 3. group exposed to light/dark cycle 6/18 h (6/18); 4. diabetic group exposed to light/dark cycle 6/18 h (DM+6/18). Retinal vascular abnormalities were estimated based on lectin staining, while the expression of genes involved in the visual cycle, cholesterol metabolism, and inflammation was determined by qRT-PCR. Reduced light exposure alleviated vasculopathy, gliosis and the expression of IL-1 and TNF-α in the retina with increased perivascular Aqp4 expression. The expression of genes involved in visual cycle and cholesterol metabolism was significantly up-regulated in RPE in DM+6/18 vs. DM group. In the retina only the expression of APOE was significantly higher in DM+6/18 vs. DM group. Reduced light exposure mitigates vascular changes and gliosis in DM via its anti-inflammatory effect, increased retinal cholesterol turnover and perivascular Aqp4 expression.

Regulation of renal aquaporin water channels in acute pyelonephritis

Acute pyelonephritis (APN) is most frequently caused by uropathogenic Escherichia coli (UPEC), which ascends from the bladder to the kidneys during a urinary tract infection. Patients with APN have been reported to have reduced renal concentration capacity under challenged conditions, polyuria, and increased aquaporin-2 (AQP2) excretion in the urine. We have recently shown increased AQP2 accumulation in the plasma membrane in cell cultures exposed to E. coli lysates and in the apical plasma membrane of inner medullary collecting ducts in a 5-day APN mouse model. This study aimed to investigate if AQP2 expression in host cells increases UPEC infection efficiency and to identify specific bacterial components that mediate AQP2 plasma membrane insertion. As the transepithelial water permeability in the collecting duct is codetermined by AQP3 and AQP4, we also investigated whether AQP3 and AQP4 localization is altered in the APN mouse model. We show that AQP2 expression does not increase UPEC infection efficiency and that AQP2 was targeted to the plasma membrane in AQP2-expressing cells in response to the two pathogen-associated molecular patterns (PAMPs), lipopolysaccharide and peptidoglycan. In contrast to AQP2, the subcellular localizations of AQP1, AQP3, and AQP4 were unaffected both in lysate-incubated cell cultures and in the APN mouse model. Our finding demonstrated that cellular exposure to lipopolysaccharide and peptidoglycan can trigger the insertion of AQP2 in the plasma membrane revealing a new regulatory pathway for AQP2 plasma membrane translocation, which may potentially be exploited in intervention strategies.NEW & NOTEWORTHY Acute pyelonephritis (APN) is associated with reduced renal concentration capacity and increased aquaporin-2 (AQP2) excretion. Uropathogenic Escherichia coli (UPEC) mediates changes in the subcellular localization of AQP2 and we show that in vitro, these changes could be elicited by two pathogen-associated molecular patterns (PAMPs), namely, lipopolysaccharide and peptidoglycan. UPEC infection was unaltered by AQP2 expression and the other renal AQPs (AQP1, AQP3, and AQP4) were unaltered in APN.

Glymphatic fluid transport is suppressed by the aquaporin-4 inhibitor AER-271

The glymphatic system transports cerebrospinal fluid (CSF) into the brain via arterial perivascular spaces and removes interstitial fluid from the brain along perivenous spaces and white matter tracts. This directional fluid flow supports the clearance of metabolic wastes produced by the brain. Glymphatic fluid transport is facilitated by aquaporin-4 (AQP4) water channels, which are enriched in the astrocytic vascular endfeet comprising the outer boundary of the perivascular space. Yet, prior studies of AQP4 function have relied on genetic models, or correlated altered AQP4 expression with glymphatic flow in disease states. Herein, we sought to pharmacologically manipulate AQP4 function with the inhibitor AER-271 to assess the contribution of AQP4 to glymphatic fluid transport in mouse brain. Administration of AER-271 inhibited glymphatic influx as measured by CSF tracer infused into the cisterna magna and inhibited increases in the interstitial fluid volume as measured by diffusion-weighted MRI. Furthermore, AER-271 inhibited glymphatic efflux as assessed by an in vivo clearance assay. Importantly, AER-271 did not affect AQP4 localization to the astrocytic endfeet, nor have any effect in AQP4 deficient mice. Since acute pharmacological inhibition of AQP4 directly decreased glymphatic flow in wild-type but not in AQP4 deficient mice, we foresee AER-271 as a new tool for manipulation of the glymphatic system in rodent brain.

The Role of Aquaporin 4 in Lacrimal Gland Ductal Fluid Secretion in Mice

Purpose

Earlier reports highlighted the predominant presence of aquaporin 4 (AQP4) in the duct cells of rabbit lacrimal glands (LGs). Whereas significant alterations in AQP4 mRNA levels have been observed in experimental dry eye and during pregnancy, the impact of AQP4 in LG ductal fluid production remains unclear. In our recent work, the role of AQP4 in LG ductal fluid secretion was investigated utilizing wild type (WT) and AQP4 knock out (KO) mice.

Methods

Tear production was assessed in both WT and KO animals. Immunostaining was used to identify AQP4 protein. Duct segments were harvested from LGs of WT and KO mice. Fluid secretion and filtration permeability (Pf) were quantified using video-microscopy. Ductal tear production, elicited by a cell-permeable cAMP analogue (8-bromo cAMP), carbachol, vasoactive intestinal peptide (VIP), and phenylephrine (PHE), were assessed in both WT and KO ducts.

Results

A higher expression of AQP4 protein was noted in the duct cells from WT mice when compared to acinar cells. Pf did not show notable alterations between WT and AQP4 KO ducts. Carbachol elicited comparable secretory responses in ducts from both WT and KO animals. However, 8-bromo cAMP, VIP, and PHE stimulation resulted in decreased secretion in ducts from AQP4 KO LGs.

Conclusions

Our findings underscore the functional relevance of AQP4 in the fluid production of mouse LG ducts. AQP4 seems to play different roles in fluid secretions elicited by different secretagogues. Specifically, cAMP-mediated, and adrenergic agonist-related secretions were reduced in AQP4 KO ducts.

AAV-Mediated Restoration of Dystrophin-Dp71 in the Brain of Dp71-Null Mice: Molecular, Cellular and Behavioral Outcomes

A deficiency in the shortest dystrophin-gene product, Dp71, is a pivotal aggravating factor for intellectual disabilities in Duchenne muscular dystrophy (DMD). Recent advances in preclinical research have achieved some success in compensating both muscle and brain dysfunctions associated with DMD, notably using exon skipping strategies. However, this has not been studied for distal mutations in the DMD gene leading to Dp71 loss. In this study, we aimed to restore brain Dp71 expression in the Dp71-null transgenic mouse using an adeno-associated virus (AAV) administrated either by intracardiac injections at P4 (ICP4) or by bilateral intracerebroventricular (ICV) injections in adults. ICP4 delivery of the AAV9-Dp71 vector enabled the expression of 2 to 14% of brain Dp71, while ICV delivery enabled the overexpression of Dp71 in the hippocampus and cortex of adult mice, with anecdotal expression in the cerebellum. The restoration of Dp71 was mostly located in the glial endfeet that surround capillaries, and it was associated with partial localization of Dp71-associated proteins, α1-syntrophin and AQP4 water channels, suggesting proper restoration of a scaffold of proteins involved in blood-brain barrier function and water homeostasis. However, this did not result in significant improvements in behavioral disturbances displayed by Dp71-null mice. The potential and limitations of this AAV-mediated strategy are discussed. This proof-of-concept study identifies key molecular markers to estimate the efficiencies of Dp71 rescue strategies and opens new avenues for enhancing gene therapy targeting cognitive disorders associated with a subgroup of severely affected DMD patients.

AQP4-DARPin1: A Chimeric Antigen Based on Scaffold Protein DARPin for Efficient Detection of AQP4-IgG in NMOSD

AQP4-IgG is an autoantibody associated with neuromyelitis optica spectroscopic disorder (NMOSD), a central nervous system inflammatory disease that requires early diagnosis and treatment. We designed two fusion proteins, AQP4-DARPin1 and AQP4-DARPin2, comprising the complete antigenic epitopes of aquaporin-4 (AQP4) and the constant region of the scaffold protein DARPin. These fusion proteins were expressed and purified from Escherichia coli and coated on microplates to develop an efficient method for detecting AQP4-IgG. Molecular dynamics simulation revealed that the fusion of AQP4 extracellular epitopes with DARPin did not alter the main structure of DARPin. The purified AQP4-DARPins bound recombinant antibody rAb-53 (AQP4-IgG) with affinities of 135 and 285 nM, respectively. Enzyme-linked immunosorbent assay (ELISA) and immunoprecipitation demonstrated that AQP4-DARPin1 specifically recognized AQP4-IgG in the NMOSD patient serum. AQP4-DARPin1 as a coated antigen showed higher ELISA signal and end point dilution ratio than full-length AQP4. Our AQP4-DARPin1-coated AQP4-IgG ELISA had 100% specificity and 90% sensitivity. These results indicate that AQP4-DARPin1, compared to existing detection strategies that use full-length or extracellular loop peptides of AQP4, provides a new and more effective approach to the ELISA detection of NMOSD.

Impacts of Age and Gender on Brain Edema in a Mouse Water Intoxication Model

Brain edema causes abnormal fluid retention and can be fatal in severe cases. Although it develops in various diseases, most treatments for brain edema are classical. We analyzed the impacts of age and gender on the characteristics of a water intoxication model that induces pure brain edema in mice and examined the model's usefulness for research regarding new treatments for brain edema. C57BL/6J mice received an intraperitoneal administration of 10% body weight distilled water, and we calculated the brain water content by measuring the brain-tissue weight immediately after dissection and after drying. We analyzed 8-OHdG and caspase-3 values to investigate the brain damage. We also applied this model in aquaporin 4 knockout (AQP4-) mice and compared these mice with wild-type mice. The changes in water content differed by age and gender, and the 8-OHdG and caspase-3 values differed by age. Suppression of brain edema by AQP4- was also confirmed. These results clarified the differences in the onset of brain edema by age and gender, highlighting the importance of considering the age and gender of model animals. Similar studies using genetically modified mice are also possible. Our findings indicate that this water intoxication model is effective for explorations of new brain edema treatments.

Non-coding RNAs and Aquaporin 4: Their Role in the Pathogenesis of Neurological Disorders

Neurological disorders are a major group of non-communicable diseases affecting quality of life. Non-Coding RNAs (ncRNAs) have an important role in the etiology of neurological disorders. In studies on the genesis of neurological diseases, aquaporin 4 (AQP4) expression and activity have both been linked to ncRNAs. The upregulation or downregulation of several ncRNAs leads to neurological disorder progression by targeting AQP4. The role of ncRNAs and AQP4 in neurological disorders is discussed in this review.

B cells orchestrate tolerance to the neuromyelitis optica autoantigen AQP4

Neuromyelitis optica is a paradigmatic autoimmune disease of the central nervous system, in which the water-channel protein AQP4 is the target antigen1. The immunopathology in neuromyelitis optica is largely driven by autoantibodies to AQP42. However, the T cell response that is required for the generation of these anti-AQP4 antibodies is not well understood. Here we show that B cells endogenously express AQP4 in response to activation with anti-CD40 and IL-21 and are able to present their endogenous AQP4 to T cells with an AQP4-specific T cell receptor (TCR). A population of thymic B cells emulates a CD40-stimulated B cell transcriptome, including AQP4 (in mice and humans), and efficiently purges the thymic TCR repertoire of AQP4-reactive clones. Genetic ablation of Aqp4 in B cells rescues AQP4-specific TCRs despite sufficient expression of AQP4 in medullary thymic epithelial cells, and B-cell-conditional AQP4-deficient mice are fully competent to raise AQP4-specific antibodies in productive germinal-centre responses. Thus, the negative selection of AQP4-specific thymocytes is dependent on the expression and presentation of AQP4 by thymic B cells. As AQP4 is expressed in B cells in a CD40-dependent (but not AIRE-dependent) manner, we propose that thymic B cells might tolerize against a group of germinal-centre-associated antigens, including disease-relevant autoantigens such as AQP4.

Chimeric AQP4-based immunosorbent for highly-specific removal of AQP4-IgG from blood

Anti-aquaporin-4 autoantibodies (AQP4-IgG) are implicated in the pathogenesis of neuromyelitis optica spectrum disorders (NMOSD), and their removal from the blood circulation is considered to be an effective method for acute treatment. An ideal extracorporeal AQP4-IgG removal system should have high specificity, which means that it can selectively remove AQP4-IgG without affecting normal immunoglobulins. However, the conventional tryptophan immobilized column lacks sufficient specificity and cannot achieve this goal. In this study, we successfully prepared a fusion protein chimeric AQP4, which consists of the complete antigenic epitopes of human AQP4 and the constant region of scaffold protein DARPin. Chimeric AQP4 was expressed and purified from Escherichia coli, and then immobilized on agarose gel as a ligand for selective capture of AQP4-IgG immunosorbent. The prepared immunosorbent had a theoretical maximum adsorption capacity of 20.48 mg/g gel estimated by Langmuir isotherm. In vitro plasma perfusion tests demonstrated that the chimeric AQP4 coupled adsorbent had remarkable adsorption performance, and could eliminate more than 85 % of AQP4-IgG under the gel-to-plasma ratio of 1:50. Moreover, it exhibited high specificity because other human plasma proteins were not adsorbed in the dynamic adsorption experiment. These results suggest that the chimeric AQP4 coupled immunosorbent can provide a new approach for specific immunoadsorption (IA) treatment of NMOSD.

Mechanisms of aquaporin-4 vesicular trafficking in mammalian cells

The aquaporin-4 (AQP4) water channel is abundantly expressed in the glial cells of the central nervous system and facilitates brain swelling following diverse insults, such as traumatic injury or stroke. Lack of specific and therapeutic AQP4 inhibitors highlights the need to explore alternative routes to control the water permeability of glial cell membranes. The cell surface abundance of AQP4 in mammalian cells fluctuates rapidly in response to changes in oxygen levels and tonicity, suggesting a role for vesicular trafficking in its translocation to and from the cell surface. However, the molecular mechanisms of AQP4 trafficking are not fully elucidated. In this work, early and recycling endosomes were investigated as likely candidates of rapid AQP4 translocation together with changes in cytoskeletal dynamics. In transiently transfected HEK293 cells a significant amount of AQP-eGFP colocalised with mCherry-Rab5-positive early endosomes and mCherry-Rab11-positive recycling endosomes. When exposed to hypotonic conditions, AQP4-eGFP rapidly translocated from intracellular vesicles to the cell surface. Co-expression of dominant negative forms of the mCherry-Rab5 and -Rab11 with AQP4-eGFP prevented hypotonicity-induced AQP4-eGFP trafficking and led to concentration at the cell surface or intracellular vesicles respectively. Use of endocytosis inhibiting drugs indicated that AQP4 internalisation was dynamin-dependent. Cytoskeleton dynamics-modifying drugs also affected AQP4 translocation to and from the cell surface. AQP4 trafficking mechanisms were validated in primary human astrocytes, which express high levels of endogenous AQP4. The results highlight the role of early and recycling endosomes and cytoskeletal dynamics in AQP4 translocation in response to hypotonic and hypoxic stress and suggest continuous cycling of AQP4 between intracellular vesicles and the cell surface under physiological conditions.

The Expression and Role of Aquaporin 4 in Colon Cancer

BACKGROUND/AIM

Aquaporins (AQPs) were initially discovered as water channel proteins that facilitate transcellular water movements. Recent studies have shown that AQPs are expressed and play an oncogenic role in various cancers. However, the expression and role of Aquaporin 4 (AQP4) in colon cancer have not been investigated. This study aimed to examine the clinical and pathophysiologic significance of AQP4 in colon cancer.

PATIENTS AND METHODS

Immunohistochemistry (IHC) of AQP4 for 145 primary tumor samples obtained from patients with stage II or III colon cancer was performed, and the relationship between AQP4 expression and patients' prognoses was analyzed. Knockdown experiments with AQP4 small interfering RNA using human colon cancer cells were conducted to analyze the effects on cell invasiveness.

RESULTS

IHC revealed that AQP4 was scarcely expressed in the noncancerous colonic mucosa. Of the 145 patients who enrolled in this study, 109 (75.2%) and 36 (24.8%) patients were classified as negative and positive for AQP4 expression, respectively. A high level of AQP4 expression is significantly associated with deeper tumors with lymph node metastasis and venous invasion. A 5-year progression-free survival rate of AQP4-positive patients was significantly worse than that of AQP-4 negative patients (70.7% vs. 87.0%, p=0.049). Furthermore, AQP4 knockdown significantly inhibited cell migration and invasion in HCT116 cells.

CONCLUSION

AQP4 may be a novel biomarker and therapeutic target for colon cancer.

Aquaporin-4 and Parkinson's Disease

The water-selective channel aquaporin-4 (AQP4) is implicated in water homeostasis and the functioning of the glymphatic system, which eliminates various metabolites from the brain tissue, including amyloidogenic proteins. Misfolding of the α-synuclein protein and its post-translational modifications play a crucial role in the development of Parkinson's disease (PD) and other synucleopathies, leading to the formation of cytotoxic oligomers and aggregates that cause neurodegeneration. Human and animal studies have shown an interconnection between AQP4 dysfunction and α-synuclein accumulation; however, the specific role of AQP4 in these mechanisms remains unclear. This review summarizes the current knowledge on the role of AQP4 dysfunction in the progression of α-synuclein pathology, considering the possible effects of AQP4 dysregulation on brain molecular mechanisms that can impact α-synuclein modification, accumulation and aggregation. It also highlights future directions that can help study the role of AQP4 in the functioning of the protective mechanisms of the brain during the development of PD and other neurodegenerative diseases.

Angelicin Alleviates Maternal Isoflurane Exposure-Induced Offspring Cognitive Defects Through the Carbonic Anhydrase 4/Aquaporin-4 Pathway

An increasing number of studies reveal the deleterious effects of isoflurane (Iso) exposure during pregnancy on offspring cognition. However, no effective therapeutic strategy for Iso-induced deleterious effects has been well developed. Angelicin exerts an anti-inflammatory effect on neurons and glial cells. This study investigated the roles and mechanism of action of angelicin in Iso-induced neurotoxicity in vitro and in vivo. After exposing C57BL/6 J mice on embryonic day 15 (E15) to Iso for 3 and 6 h, respectively, neonatal mice on embryonic day 18 (E18) displayed obvious anesthetic neurotoxicity, which was revealed by the elevation of cerebral inflammatory factors and blood-brain barrier (BBB) permeability and cognitive dysfunction in mice. Angelicin treatment could not only significantly reduce the Iso-induced embryonic inflammation and BBB disruption but also improve the cognitive dysfunction of offspring mice. Iso exposure resulted in an increase of carbonic anhydrase (CA) 4 and aquaporin-4 (AQP4) expression at both mRNA and protein levels in vascular endothelial cells and mouse brain tissue collected from neonatal mice on E18. Remarkably, the Iso-induced upregulation of CA4 and AQP4 expression could be partially reversed by angelicin treatment. Moreover, GSK1016790A, an AQP4 agonist, was used to confirm the role of AQP4 in the protective effect of angelicin. Results showed that GSK1016790A abolished the therapeutic effect of angelicin on Iso-induced inflammation and BBB disruption in the embryonic brain and on the cognitive function of offspring mice. In conclusion, angelicin may serve as a potential therapeutic for Iso-induced neurotoxicity in neonatal mice by regulating the CA4/AQP4 pathway.

Glymphatic system and aquaporin‑4 in epilepsy

Over the past decade glymphatic concept has gained more and more interest. Despite some lacking data regarding structural and functional aspects, glymphatic system is widely considered the main mechanism of water and solutes transport in brain parenchyma, as well as waste clearance from the brain. Glymphatic system modulates the extracellular space volume and is involved in spatial K+ buffering (via influencing Kir4.1 channel functioning), two factors crucial for neuronal excitability and seizure susceptibility, and is itself strongly stimulated during sleep. This review summarizes information regarding the potential role of the glymphatic system in the development and progression of epilepsy, especially the role of the glial water channel aquaporin‑4 in modulation of brain excitability and in epilepsy. Data from animal models and human studies are presented.

Epstein-Barr Virus and Human Endogenous Retrovirus in Japanese Patients with Autoimmune Demyelinating Disorders

Multiple sclerosis (MS), neuromyelitis optica spectrum disorder (NMOSD), and myelin oligodendrocytes glycoprotein-antibody disease (MOGAD) are distinct autoimmune demyelinating disorders characterized by varying clinical and pathological characteristics. While the precise origins of these diseases remain elusive, a combination of genetic and environmental factors, including viral elements, have been suggested as potential contributors to their development. Our goal was to assess the occurrence of antibodies against pathogenic peptides associated with Epstein-Barr virus (EBV) and the human endogenous retrovirus-W (HERV-W) in serum samples obtained from Japanese individuals diagnosed with MS, NMOSD, and MOGAD and to make comparisons with a group of healthy controls (HCs). We conducted a retrospective analysis involving 114 Japanese participants, comprising individuals with MS (34), NMOSD (20), MOGAD (20), and HCs (40). These individuals were tested using a peptide-based enzyme-linked immunosorbent assay. A marked increase in antibody response against EBV nuclear antigen 1 (EBNA1)386-405 was observed in the serum of MS and MOGAD patients, as compared to HCs. Notably, we observed a correlation between antibodies against EBNA1386-405 and HERV-W486-504 peptides in a subset of the antibody-positive MS patients. These findings emphasize the involvement of EBV in the pathogenesis of MS and potentially MOGAD, suggesting its role in the reactivation of HERV-W.

Inebilizumab reduces neuromyelitis optica spectrum disorder risk independent of FCGR3A polymorphism

Inebilizumab, a humanized, glycoengineered, IgG1 monoclonal antibody that depletes CD19+ B-cells, is approved to treat aquaporin 4 (AQP4) IgG-seropositive neuromyelitis optica spectrum disorder (NMOSD). Inebilizumab is afucosylated and engineered for enhanced affinity to Fc receptor III-A (FCGR3A) receptors on natural killer cells to maximize antibody-dependent cellular cytotoxicity. Previously, the F allele polymorphism at amino acid 158 of the FCGR3A gene (F158) was shown to decrease IgG-binding affinity and reduce rituximab (anti-CD20) efficacy for NMOSD attack prevention. In contrast, our current findings from inebilizumab-treated NMOSD patients indicate similar clinical outcomes between those with F158 and V158 allele genotypes.

Causal associations between prodromal infection and neuromyelitis optica spectrum disorder: A Mendelian randomization study

BACKGROUND AND PURPOSE

Prodromal infections are associated with neuromyelitis optica spectrum disorder (NMOSD), but it remains unclear which type of infection has a causal association with NMOSD. We aimed to explore the causal associations between four herpesvirus infections (chickenpox, cold sores, mononucleosis and shingles) and NMOSD, as well as between other types of infections and NMOSD.

METHODS

For data on infections, we used the genome-wide association study (GWAS) summary statistics from the 23andMe cohort. For outcomes, we used the GWAS data of participants of European ancestry, including 215 NMOSD patients (132 anti-aquaporin-4 antibody [AQP4-ab]-positive patients and 83 AQP4-ab-negative patients) and 1244 normal controls. Single-nucleotide polymorphism (SNP) identification and two-sample Mendelian randomization (MR) analyses were then performed.

RESULTS

In the 23andMe cohort, we identified one SNP for chickenpox (rs9266089 in HLA-B gene), one SNP for cold scores (rs885950 in the POU5F1 gene), one SNP for mononucleosis (rs2596465 in the HCP5 gene), and three SNPs for shingles (rs2523591 in the HLA-B gene; rs7047299 in the IFNA21 gene; rs9260809 in the MICD gene). The association between cold sores and AQP4-ab-positive NMOSD reached statistical significance (odds ratio [OR] 745.318; 95% confidence interval [CI] 22.176, 25,049.53 [p < 0.001, Q < 0.001]). The association between shingles and AQP4-ab-positive NMOSD was also statistically significant (OR 21.073; 95% CI 4.271, 103.974 [p < 0.001, Q < 0.001]). No significant association was observed between other infections and AQP4-ab-positive or AQP4-ab-negative NMOSD.

CONCLUSION

These findings suggest there are positive associations between cold sores and shingles and AQP4-ab-positive NMOSD, indicating there may be causal links between herpes simplex virus and varicella-zoster virus infection and AQP4-ab-positive NMOSD.

Aquaporin-4 Deficiency is Associated with Cognitive Impairment and Alterations in astrocyte-neuron Lactate Shuttle

Cognitive impairment refers to notable declines in cognitive abilities including memory, language, and emotional stability leading to the inability to accomplish essential activities of daily living. Astrocytes play an important role in cognitive function, and homeostasis of the astrocyte-neuron lactate shuttle (ANLS) system is essential for maintaining cognitive functions. Aquaporin-4 (AQP-4) is a water channel expressed in astrocytes and has been shown to be associated with various brain disorders, but the direct relationship between learning, memory, and AQP-4 is unclear. We examined the relationship between AQP-4 and cognitive functions related to learning and memory. Mice with genetic deletion of AQP-4 showed significant behavioral and emotional changes including hyperactivity and instability, and impaired cognitive functions such as spatial learning and memory retention. 18 F-FDG PET imaging showed significant metabolic changes in the brains of AQP-4 knockout mice such as reductions in glucose absorption. Such metabolic changes in the brain seemed to be the direct results of changes in the expression of metabolite transporters, as the mRNA levels of multiple glucose and lactate transporters in astrocytes and neurons were significantly decreased in the cortex and hippocampus of AQP-4 knockout mice. Indeed, AQP-4 knockout mice showed significantly higher accumulation of both glucose and lactate in their brains compared with wild-type mice. Our results show that the deficiency of AQP-4 can cause problems in the metabolic function of astrocytes and lead to cognitive impairment, and that the deficiency of AQP4 in astrocyte endfeet can cause abnormalities in the ANLS system.

Altered Clock Gene Expression in Female APP/PS1 Mice and Aquaporin-Dependent Amyloid Accumulation in the Retina

Alzheimer's disease (AD), the most prevalent form of dementia, is a neurodegenerative disorder characterized by different pathological symptomatology, including disrupted circadian rhythm. The regulation of circadian rhythm depends on the light information that is projected from the retina to the suprachiasmatic nucleus in the hypothalamus. Studies of AD patients and AD transgenic mice have revealed AD retinal pathology, including amyloid-β (Aβ) accumulation that can directly interfere with the regulation of the circadian cycle. Although the cause of AD pathology is poorly understood, one of the main risk factors for AD is female gender. Here, we found that female APP/PS1 mice at 6- and 12-months old display severe circadian rhythm disturbances and retinal pathological hallmarks, including Aβ deposits in retinal layers. Since brain Aβ transport is facilitated by aquaporin (AQP)4, the expression of AQPs were also explored in APP/PS1 retina to investigate a potential correlation between retinal Aβ deposits and AQPs expression. Important reductions in AQP1, AQP4, and AQP5 were detected in the retinal tissue of these transgenic mice, mainly at 6-months of age. Taken together, our findings suggest that abnormal transport of Aβ, mediated by impaired AQPs expression, contributes to the retinal degeneration in the early stages of AD.

Short-term topiramate treatment prevents radiation-induced cytotoxic edema in preclinical models of breast-cancer brain metastasis

BACKGROUND

Brain edema is a common complication of brain metastases (BM) and associated treatment. The extent to which cytotoxic edema, the first step in the sequence that leads to ionic edema, vasogenic edema, and brain swelling, contributes to radiation-induced brain edema during BM remains unknown. This study aimed to determine whether radiation-associated treatment of BM induces cytotoxic edema and the consequences of blocking the edema in preclinical models of breast-cancer brain metastases (BCBM).

METHODS

Using in vitro and in vivo models, we measured astrocytic swelling, trans-electric resistance (TEER), and aquaporin 4 (AQP4) expression following radiation. Genetic and pharmacological inhibition of AQP4 in astrocytes and cancer cells was used to assess the role of AQP4 in astrocytic swelling and brain water intake. An anti-epileptic drug that blocks AQP4 function (topiramate) was used to prevent cytotoxic edema in models of BM.

RESULTS

Radiation-induced astrocytic swelling and transient upregulation of AQP4 occurred within the first 24 hours following radiation. Topiramate decreased radiation-induced astrocytic swelling and loss of TEER in astrocytes in vitro, and acute short-term treatment (but not continuous administration), prevented radiation-induced increase in brain water content without pro-tumorigenic effects in multiple preclinical models of BCBM. AQP4 was expressed in clinical BM and breast-cancer cell lines, but AQP4 targeting had limited direct pro-tumorigenic or radioprotective effects in cancer cells that could impact its clinical translation.

CONCLUSIONS

Patients with BM could find additional benefits from acute and temporary preventive treatment of radiation-induced cytotoxic edema using anti-epileptic drugs able to block AQP4 function.

Connexin 43 Promotes Neurogenesis via Regulating Aquaporin-4 after Cerebral Ischemia

We aimed to test the effects of connexin43 (Cx43) on ischemic neurogenesis and examined whether it was dependent on aquaporin-4 (AQP4). We detected the expression of Cx43 and AQP4 in the ipsilateral subventricular zone (SVZ) and peri-infarct cortex after middle cerebral artery occlusion (MCAO). Also, we examined neurogenesis in the above regions via co-labeling of 5-bromo-2-deoxyuridine (BrdU)/neuronal nuclear antigen (NeuN) and BrdU/doublecortin (DCX). The effects of Cx43 and AQP4 were investigated by using two transgenic animals: heterozygous Cx43 (Cx43±) mice and AQP4 knockout (AQP4-/-) mice, and connexin mimetic peptide (CMP), a selective Cx43 blocker. We demonstrated AQP4 and Cx43 were co-expressed in the astrocytes after MCAO and the expression was highly increased in ipsilateral SVZ and peri-infarct cortex. Cx43± mice had larger infarction volumes and worse neurological function. Both BrdU/NeuN and BrdU/DCX co-labeled cells in the two regions were reduced in Cx43± and AQP4-/- mice compared to wild-type (WT) mice, suggesting Cx43 and AQP4 participated in neurogenesis of neural stem cells. Moreover, CMP decreased AQP4 expression and inhibited neurogenesis in WT mice, while the latter failed to be observed in AQP4-/- mice. Besides, higher levels of IL-1β and TNF-α were detected in the SVZ and peri-infarct cortex of AQP4-/- and Cx43± mice than those in WT mice. In conclusion, our data suggest that Cx43 elicits neuroprotective effects after cerebral ischemia through promoting neurogenesis in the SVZ to regenerate the injured neurons, which is AQP4 dependent and associated with down-regulation of inflammatory cytokines IL-1β and TNF-α.

Aquaporin-4 expression and modulation in a rat model of post-traumatic syringomyelia

Aquaporin-4 (AQP4) has been implicated in post-traumatic syringomyelia (PTS), a disease characterised by the formation of fluid-filled cysts in the spinal cord. This study investigated the expression of AQP4 around a mature cyst (syrinx) and the effect of pharmacomodulation of AQP4 on syrinx size. PTS was induced in male Sprague-Dawley rats by computerized spinal cord impact and subarachnoid kaolin injection. Immunofluorescence of AQP4 was carried out on mature syrinx tissue 12 weeks post-surgery. Increased AQP4 expression corresponded to larger, multiloculated cysts (R2 = 0.94), yet no localized changes to AQP4 expression in perivascular regions or the glia limitans were present. In a separate cohort of animals, at 6 weeks post-surgery, an AQP4 agonist (AqF026), antagonist (AqB050), or vehicle was administered daily over 4 days, with MRIs performed before and after the completion of treatment. Histological analysis was performed at 12 weeks post-surgery. Syrinx volume and length were not altered with AQP4 modulation. The correlation between increased AQP4 expression with syrinx area suggests that AQP4 or the glia expressing AQP4 are recruited to regulate water movement. Given this, further investigation should examine AQP4 modulation with dose regimens at earlier time-points after PTS induction, as these may alter the course of syrinx development.

Oily fish and raw vegetable consumption can decrease the risk of AQP4-positive neuromyelitis optica spectrum disorders: a Mendelian-randomization study

Neuromyelitis optica spectrum disorders (NMOSD) are severe inflammatory disorders of the central nervous system targeting aquaporin-4 (AQP4). The risk factors for NMOSD remain to be determined, though they may be related to diet and nutrition. This study aimed to explore the possibility of a causal relationship between specific food intake and AQP4-positive NMOSD risk. The study followed a two-sample Mendelian randomization (MR) design. Genetic instruments and self-reported information on the intake of 29 types of food were obtained from a genome-wide association study (GWAS) on 445,779 UK Biobank participants. A total of 132 individuals with AQP4-positive NMOSD and 784 controls from this GWAS were included in our study. The associations were evaluated using inverse-variance-weighted meta-analysis, weighted-median analysis, and MR-Egger regression. A high consumption of oily fish and raw vegetables was associated with a decreased risk of AQP4-positive NMOSD (odds ratio [OR] = 1.78 × 10-16, 95% confidence interval [CI] = 2.60 × 10-25-1.22 × 10-7, p = 0.001; OR = 5.28 × 10-6, 95% CI = 4.67 × 10-11-0.598, p = 0.041, respectively). The results were consistent in the sensitivity analyses, and no evidence of directional pleiotropy was observed. Our study provides useful implications for the development of AQP4-positive NMOSD prevention strategies. Further research is needed to determine the exact causal relationship and mechanisms underlying the association between specific food intake and AQP4-positive NMOSD.

Single nucleotide polymorphisms in aquaporin-4 associate with cognitive impairment status in people with HIV

Neurocognitive impairments are more frequent in people with HIV (PWH) compared to their uninfected counterparts. HIV-associated neurocognitive disorder (HAND) is a spectrum disorder and up to 50% of PWH are reported to suffer from HAND. Altered waste clearance from the brain, chronic neuroinflammation and impaired metabolic processes may contribute to abnormal aging in PWH and are more common among those who suffer from HAND. Thus, it is important to identify earlier predictors for development of HAND. A key contributor to cognitive impairment in HIV and in Alzheimer's disease (AD) is formation and accumulation of aberrant proteins including hyperphosphorylated Tau (pTau). Previous data from AD and traumatic brain injury studies report that impaired waste clearance from the brain contributes in part to cognitive impairments. Evidence suggests that the aquaporin 4 (aqp4) gene may have an important role in waste clearance from the brain as single nucleotide polymorphisms (SNPs) in aqp4 have been reported to associate with changes in cognitive decline in AD patients. Given some similarities between HAND and AD, we assessed potential associations of several aqp4 SNPS with cognitive impairment in PWH. Our data show that homozygous carriers of the minor allele in SNPs rs3875089 and rs3763040 had significantly lower neuropsychological test Z-scores in multiple domains compared to the other genotypes. Interestingly, this decrease in Z-scores was only observed in PWH and not in HIV-control participants. Conversely, homozygosity of the minor allele of rs335929 associated with better executive function in PWH. Based on these data, tracking large cohorts of PWH to determine if the presence of these SNPs associate with cognitive changes during disease progression is of interest. Furthermore, screening PWH for SNPs that may be associated with cognitive impairment risk after diagnosis could be considered in alignment with traditional treatment plans to potentially work on skills in areas shown to have cognitive decline with these SNPs present.