Dynamic regulation of aquaporin-4 water channels in neurological disorders

Revolutionizing Stroke Care: Nanotechnology-Based Brain Delivery as a Novel Paradigm for Treatment and Diagnosis

Stroke, a severe medical condition arising from abnormalities in the coagulation-fibrinolysis cycle and metabolic processes, results in brain cell impairment and injury due to blood flow obstruction within the brain. Prompt and efficient therapeutic approaches are imperative to control and preserve brain functions. Conventional stroke medications, including fibrinolytic agents, play a crucial role in facilitating reperfusion to the ischemic brain. However, their clinical efficacy is hampered by short plasma half-lives, limited brain tissue distribution attributed to the blood-brain barrier (BBB), and lack of targeted drug delivery to the ischemic region. To address these challenges, diverse nanomedicine strategies, such as vesicular systems, polymeric nanoparticles, dendrimers, exosomes, inorganic nanoparticles, and biomimetic nanoparticles, have emerged. These platforms enhance drug pharmacokinetics by facilitating targeted drug accumulation at the ischemic site. By leveraging nanocarriers, engineered drug delivery systems hold the potential to overcome challenges associated with conventional stroke medications. This comprehensive review explores the pathophysiological mechanism underlying stroke and BBB disruption in stroke. Additionally, this review investigates the utilization of nanocarriers for current therapeutic and diagnostic interventions in stroke management. By addressing these aspects, the review aims to provide insight into potential strategies for improving stroke treatment and diagnosis through a nanomedicine approach.

Astrocytic Slc4a4 regulates blood-brain barrier integrity in healthy and stroke brains via a CCL2-CCR2 pathway and NO dysregulation

Astrocytes play vital roles in blood-brain barrier (BBB) maintenance, yet how they support BBB integrity under normal or pathological conditions remains poorly defined. Recent evidence suggests that ion homeostasis is a cellular mechanism important for BBB integrity. In the current study, we investigated the function of an astrocyte-specific pH regulator, Slc4a4, in BBB maintenance and repair. We show that astrocytic Slc4a4 is required for normal astrocyte morphological complexity and BBB function. Multi-omics analyses identified increased astrocytic secretion of CCL2 coupled with dysregulated arginine-NO metabolism after Slc4a4 deletion. Using a model of ischemic stroke, we found that loss of Slc4a4 exacerbates BBB disruption, which was rescued by pharmacological or genetic inhibition of the CCL2-CCR2 pathway in vivo. Together, our study identifies the astrocytic Slc4a4-CCL2 and endothelial CCR2 axis as a mechanism controlling BBB integrity and repair, while providing insights for a therapeutic approach against BBB-related CNS disorders.

Astrocytic Slc4a4 regulates blood-brain barrier integrity in healthy and stroke brains via a NO-CCL2-CCR2 pathway

Astrocytes play vital roles in blood-brain barrier (BBB) maintenance, yet how they support BBB integrity under normal or pathological conditions remains poorly defined. Recent evidence suggests pH homeostasis is a new cellular mechanism important for BBB integrity. In the current study, we investigated the function of an astrocyte-specific pH regulator, Slc4a4, in BBB maintenance and repair. We show that astrocytic Slc4a4 is required for normal astrocyte morphological complexity and BBB function. Multi-omics analyses identified increased astrocytic secretion of CCL2 coupled with dysregulated arginine-NO metabolism after Slc4a4 deletion. Using a model of ischemic stroke, we found that loss of Slc4a4 exacerbates BBB disruption and reactive gliosis, which were both rescued by pharmacological or genetic inhibition of the NO-CCL2 pathway in vivo. Together, our study identifies the astrocytic Slc4a4-NO-CCL2 axis as a pivotal mechanism controlling BBB integrity and repair, while providing insights for a novel therapeutic approach against BBB-related CNS disorders.

Cell Therapy of Stroke: Do the Intra-Arterially Transplanted Mesenchymal Stem Cells Cross the Blood-Brain Barrier?

Animal model studies and first clinical trials have demonstrated the safety and efficacy of the mesenchymal stem cells' (MSCs) transplantation in stroke. Intra-arterial (IA) administration looks especially promising, since it provides targeted cell delivery to the ischemic brain, is highly effective, and can be safe as long as the infusion is conducted appropriately. However, wider clinical application of the IA MSCs transplantation will only be possible after a better understanding of the mechanism of their therapeutic action is achieved. On the way to achieve this goal, the study of transplanted cells' fate and their interactions with the blood-brain barrier (BBB) structures could be one of the key factors. In this review, we analyze the available data concerning one of the most important aspects of the transplanted MSCs' action-the ability of cells to cross the blood-brain barrier (BBB) in vitro and in vivo after IA administration into animals with experimental stroke. The collected data show that some of the transplanted MSCs temporarily attach to the walls of the cerebral vessels and then return to the bloodstream or penetrate the BBB and either undergo homing in the perivascular space or penetrate deeper into the parenchyma. Transmigration across the BBB is not necessary for the induction of therapeutic effects, which can be incited through a paracrine mechanism even by cells located inside the blood vessels.

Acetazolamide Alleviate Cerebral Edema Induced by Ischemic Stroke Through Inhibiting the Expression of AQP4 mRNA

OBJECTIVE

We want to investigate the effect of aquaporin-4 (AQP4) on cerebral edema induced by ischemic stroke in rats and explore whether inhibiting the expression of AQP4 through acetazolamide (AZA) could attenuate brain edema and protect cerebral function.

METHODS

The Sprague Dawley (SD) rats were randomly divided into four groups: sham + saline group, sham + AZA group, AZA intervention group, and nonintervention group. Each group was divided into five subgroups according to the time of cerebral ischemia (6 h, 1 day, 3 days, 5 days, and 7 days). The model of cerebral infarction in rats was adopted by means of the bilateral carotid arteries ligation (2-VO) method. The rats in intervention group were given intraperitoneal injection of AZA (35 mg/kg/day). Hematoxylin-eosin staining was performed for pathological analysis of the infarcted area. The brain water content was calculated to evaluate the degree of brain edema. The messenger RNA (mRNA) and protein expressions of AQP4 in the brain were measured by quantitative real-time polymerase chain reaction and immunohistochemistry, respectively.

RESULTS

Significant cerebral pathological damages were found in ischemic stroke rats. The brain water content, protein, and mRNA expression of AQP4 of the intervention and nonintervention groups were markedly higher than those of the sham groups. By contrast, AZA administration reduced the brain water content, whereas improved cerebral dysfunction was induced by ischemic stroke. Moreover, AZA obviously reduced the protein and mRNA expression of AQP4 after ischemic stroke in rats' brains.

CONCLUSIONS

The expression of AQP4 was closely related to cerebral edema induced by ischemic stroke. Decreasing the expression of AQP4 mRNA by AZA administration can effectively relieve cerebral edema and decrease cerebral pathological damage.

BMP signaling alters aquaporin-4 expression in the mouse cerebral cortex

Aquaporin-4 (AQP4) is a predominant water channel expressed in astrocytes in the mammalian brain. AQP4 is crucial for the regulation of homeostatic water movement across the blood–brain barrier (BBB). Although the molecular mechanisms regulating AQP4 levels in the cerebral cortex under pathological conditions have been intensively investigated, those under normal physiological conditions are not fully understood. Here we demonstrate that AQP4 is selectively expressed in astrocytes in the mouse cerebral cortex during development. BMP signaling was preferentially activated in AQP4-positive astrocytes. Furthermore, activation of BMP signaling by in utero electroporation markedly increased AQP4 levels in the cerebral cortex, and inhibition of BMP signaling strongly suppressed them. These results indicate that BMP signaling alters AQP4 levels in the mouse cerebral cortex during development.

High-altitude cerebral edema: its own entity or end-stage acute mountain sickness?

High-altitude cerebral edema (HACE) and acute mountain sickness (AMS) are neuropathologies associated with rapid exposure to hypoxia. However, speculation remains regarding the exact etiology of both HACE and AMS and whether they share a common mechanistic pathology. This review outlines the basic principles of HACE development, highlighting how edema could develop from 1) a progression from cytotoxic swelling to ionic edema or 2) permeation of the blood brain barrier (BBB) with or without ionic edema. Thereafter, discussion turns to the available neuroimaging literature in the context of cytotoxic, ionic, or vasogenic edema in both HACE and AMS. Although HACE is clearly caused by an increase in brain water of ionic and/or vasogenic origin, there is very little evidence that this type of edema is present when AMS develops. However, cerebral vasodilation, increased intracranial blood volume, and concomitant intracranial fluid shifts from the extracellular to the intracellular space, as interpreted from changes in diffusion indices within white matter, are observed consistently in persons acutely exposed to hypoxia and with AMS. Therefore, herein we explore the idea that intracellular swelling occurs alongside AMS, and is a critical precursor to extracellular ionic edema formation. We propose that this process produces a subtle modulation of the BBB, which either together with or independent of vasogenic edema provides a transvascular segue from the end-stage of AMS to HACE. Ultimately, this review seeks to shed light on the possible processes underlying HACE pathophysiology, and thus highlights potential avenues for future prevention and treatment.

Tight junctions in the blood-brain barrier promote edema formation and infarct size in stroke - Ambivalent effects of sealing proteins

The outcome of stroke is greatly influenced by the state of the blood-brain barrier (BBB). The BBB endothelium is sealed paracellularly by tight junction (TJ) proteins, i.e., claudins (Cldns) and the redox regulator occludin. Functions of Cldn3 and occludin at the BBB are largely unknown, particularly after stroke. We address the effects of Cldn3 deficiency and stress factors on the BBB and its TJs. Cldn3 tightened the BBB for small molecules and ions, limited endothelial endocytosis, strengthened the TJ structure and controlled Cldn1 expression. After middle cerebral artery occlusion (MCAO) and 3-h reperfusion or hypoxia of isolated brain capillaries, Cldn1, Cldn3 and occludin were downregulated. In Cldn3 knockout mice (C3KO), the reduction in Cldn1 was even greater and TJ ultrastructure was impaired; 48 h after MCAO of wt mice, infarct volumes were enlarged and edema developed, but endothelial TJs were preserved. In contrast, junctional localization of Cldn5 and occludin, TJ density, swelling and infarction size were reduced in affected brain areas of C3KO. Taken together, Cldn3 and occludin protect TJs in stroke, and this keeps the BBB intact. However, functional Cldn3, Cldn3-regulated TJ proteins and occludin promote edema and infarction, which suggests that TJ modulation could improve the outcome of stroke.

Pathophysiology of Cerebral Edema—A Comprehensive Review

Cerebral edema is a condition where an excess of cerebral water accumulates due to primary neurological or non-neurological causes. Cerebral edema complicates many brain pathologies causing additional injury often in excess of the original neurological insult. Classic descriptions divide cerebral edema into cytotoxic, vasogenic, interstitial, and osmotic subtypes. The interplay of different mechanisms is important in the clinical manifestations. Recent research has advanced our understanding of the molecular pathophysiology of cerebral edema, exposing the central role of aquaporins and specific ion channels. The aim of this review is to provide a comprehensive overview of the molecular pathophysiology of cerebral edema including unique disease specific mechanisms.

Abnormalities of aquaporin-4 in the cerebellum in bipolar II disorder: An ultra-high b-values diffusion weighted imaging study

BACKGROUND

Cumulative evidence indicated the cerebellum is involved in the pathophysiology of bipolar disorder (BD). It was reported that the apparent diffusion coefficient from ultra-high b-values (ADC_uh) could reflect the function of aquaporin-4 (AQP4) which was involved in neurological disorders. However, no studies have reported the AQP4 alteration in the cerebellum in BD. Therefore, this study aimed to investigate the ADC_uh and AQP4 in the cerebellum in BD-II.

METHODS

Fifty patients with BD-II as well as 43 healthy controls underwent enhance diffusion weighted imaging (eDWI) with ultra-high b-values. The eDWI parameters including ADC_uh , pure water diffusion (D) and pseudodiffusion (D*) was measured using regions-of-interest analysis in the superior cerebellar peduncles (SCP), middle cerebellar peduncles (MCP) , cerebellar hemisphere, dentate nuclei, tonsil and vermis of the cerebellum.

RESULTS

BD-II exhibited increased ADC_uh values in the bilateral SCP, cerebellar hemisphere, tonsil and right dentate nuclei, and increased D* and D in the bilateral SCP, and decreased D* in the tonsil. Additionally, there were positive correlations between Hamilton Rating Scale for Depression-24 scores and bilateral ADC_uh values in the SCP and cerebellar hemisphere.

CONCLUSIONS

The alteration of the ADC_uh values in the cerebellum may reflect the changes of the AQP4, especially the abnormality of eDWI parameters in the SCP may be a key neurobiological feature of BD-II. The current results provide a novel insight to look into the pathophysiology mechanisms underlying BD-II.

Neurovascular Unit as a Source of Ischemic Stroke Biomarkers-Limitations of Experimental Studies and Perspectives for Clinical Application

Cerebral stroke, which is one of the most frequent causes of mortality and leading cause of disability in developed countries, often leads to devastating and irreversible brain damage. Neurological and neuroradiological diagnosis of stroke, especially in its acute phase, is frequently uncertain or inconclusive. This results in difficulties in identification of patients with poor prognosis or being at high risk for complications. It also makes difficult identification of these stroke patients who could benefit from more aggressive therapies. In contrary to the cardiovascular disease, no single biomarker is available for the ischemic stroke, addressing the abovementioned issues. This justifies the need for identifying of effective diagnostic measures characterized by high specificity and sensitivity. One of the promising avenues in this area is studies on the panels of biomarkers characteristic for processes which occur in different types and phases of ischemic stroke and represent all morphological constituents of the brains' neurovascular unit (NVU). In this review, we present the current state of knowledge concerning already-used or potentially applicable biomarkers of the ischemic stroke. We also discuss the perspectives for identification of biomarkers representative for different types and phases of the ischemic stroke, as well as for different constituents of NVU, which concentration levels correlate with extent of brain damage and patients' neurological status. Finally, a critical analysis of perspectives on further improvement of the ischemic stroke diagnosis is presented.

Methods to measure, model and manipulate fluid flow in brain

The brain consists of a complex network of cells and matrix that is cushioned and nourished by multiple types of fluids: cerebrospinal fluid, blood, and interstitial fluid. The movement of these fluids through the tissues has recently gained more attention due to implications in Alzheimer's Disease and glioblastoma. Therefore, methods to study these fluid flows are necessary and timely for the current study of neuroscience. Imaging modalities such as magnetic resonance imaging have been used clinically and pre-clinically to image flows in healthy and diseased brains. These measurements have been used to both parameterize and validate models of fluid flow both computational and in vitro. Both of these models can elucidate the changes to fluid flow that occur during disease and can assist in linking the compartments of fluid flow with one another, a difficult challenge experimentally. In vitro models, though in limited use with fluid flow, allow the examination of cellular responses to physiological flow. To determine causation, in vivo methods have been developed to manipulate flow, including both physical and pharmacological manipulations, at each point of fluid movement of origination resulting in exciting findings in the preclinical setting. With new targets, such as the brain-draining lymphatics and glymphatic system, fluid flow and tissue drainage within the brain is an exciting and growing research area. In this review, we discuss the methods that currently exist to examine and test hypotheses related to fluid flow in the brain as we attempt to determine its impact on neural function.

Polymorphisms in the Human Aquaporin 4 Gene Are Associated With Schizophrenia in the Southern Chinese Han Population: A Case-Control Study

BACKGROUND

In psychiatric illness, pathogenic role of neuroinflammation has been supported by multiple lines of evidence. Astrocytes contribute to the blood-brain barrier (BBB) with formation of the "glymphatic" drainage system of the central nervous system (CNS) through perivascular processes. Found primarily at the end-feet of astrocytes, the aquaporin 4 (AQP4) gene has been suspected to play putative roles in the development of psychiatric disorders as well as the clearance of the glymphatic system. However, there remain many uncertainties because of the limited research on AQP4. The present study is focused on the association between AQP4 gene polymorphisms and schizophrenia (SCZ) in the Southern Chinese Han population.

METHODS

Two hundred ninety-two patients and 100 healthy controls were enrolled in this study. To study the relationship of AQP4 gene polymorphisms and SCZ, genetic information was drawn from a cohort of 100 healthy controls and 100 matched patients with SCZ of Southern Han Chinese descent. Comparisons of the allele and genotype distributions between control and case groups were made using the χ2 test. Two-group comparisons were made to assess the linkage equilibrium and haplotype.

RESULTS

Three SNPs were found. In comparison to healthy controls, patients had higher T-allele frequencies at rs1058424 and G-allele frequencies at rs3763043 (p = 0.043 and p = 0.045, respectively). Furthermore, there is an association between the decreased risk of SCZ and the AA genotype at both rs1058424 (p = 0.021, OR = 2.04) and rs3763043 (p = 0.018, OR = 2.25) The TCG haplotype (p = 0.036) was associated with a potential risk of SCZ, while the ACA haplotype (p = 0.0007) was associated with a decreased risk of SCZ and retained statistical significance after Bonferroni correction (p = 0.006).

CONCLUSIONS

An etiological reference for SCZ is provided by the association between AQP4 gene polymorphisms and SCZ in Southern Han Chinese population.

Mesenchymal stem cells alleviate AQP-4-dependent glymphatic dysfunction and improve brain distribution of antisense oligonucleotides in BACHD mice

Huntington's disease (HD) is a neurodegenerative disorder caused by a mutation in the huntingtin (HTT) gene that results in the production of neurotoxic mutant HTT (mHTT) protein. Suppressing HTT production with antisense oligonucleotides (ASOs) is a promising treatment strategy for HD; however, the difficulty of delivering ASOs to deep brain structures is a major barrier for its clinical application. The glymphatic system of astrocytes involving aquaporin 4 (AQP-4) controls the entry of macromolecules from the cerebrospinal fluid into the brain. Mesenchymal stem cells (MSCs) target astrocytes to inhibit neuroinflammation. Here we examined the glymphatic distribution of ASO in the brain and the therapeutic potential of combining intravenously injection of mesenchymal stem cells (IV-MSC) and ASOs for the treatment of HD. Our results show that Cy3-labeled ASOs entered the brain parenchyma via the perivascular space following cisternal injection, but the brain distribution was significantly lower in AQP-4^-/- as compared with wild-type mice. Downregulation of the AQP-4 M23 isoform was accompanied by decreased brain levels of ASOs in BACHD mice as well as an increase in astrogliosis and phosphorylation of nuclear factor κB (NF-κB) p65. IV-MSC treatment restored AQP-4 M23 expression, attenuated astrogliosis, and decreased NF-κB p65 phosphorylation; it also increased the brain distribution of ASOs and enhanced the suppression of mHTT in BACHD mice. These results suggest that modulating glymphatic activity using IV-MSC is a novel strategy for improving the potency of ASO in the treatment of HD.

The Dual Role of AQP4 in Cytotoxic and Vasogenic Edema Following Spinal Cord Contusion and Its Possible Association With Energy Metabolism via COX5A

Spinal cord edema, mainly including vasogenic and cytotoxic edema, influences neurological outcome after spinal cord contusion (SCC). Aquaporin 4 (AQP4) is the most ubiquitous water channel in the central nervous system (CNS), which is a rate-limiting factor in vasogenic edema expressing in brain injury, and it contributes to the formation of cytotoxic edema locating in astrocytes. However, little is known about the regulatory mechanism of AQP4 within vasogenic and cytotoxic edema in SCC, and whether the regulation mechanism of AQP4 is related to Cytochrome coxidase (COX5A) affecting energy metabolism. Therefore, the SCC model is established by Allen’s method, and the degree of edema and neuronal area is measured. The motor function of rats is evaluated by the Basso, Beattie, and Bresnahan (BBB) scoring system. Meanwhile, AQP4 and COX5A are detected by real-time quantitative PCR (qRT-PCR) and western blot (WB). The localization of targeted protein is exhibited by immunohistochemical staining (IHC) and immunofluorescence (IF). Additionally, the methodology of AQP4 lentivirus-mediated RNA interference (AQP4-RNAi) is used to reveal the effect on edema of SCC and the regulating molecular mechanism. Firstly, we observe that the tissue water content increases after SCC and decreases after the peak value of tissue water content at 3 days (P < 0.05) with abundant expression of AQP4 protein locating around vascular endothelial cells (VECs), which suggests that the increasing AQP4 promotes water reabsorption and improves vasogenic edema in the early stage of SCC. However, the neuronal area is larger than in the sham group in the 7 days (P < 0.05) with the total water content of spinal cord decrease. Meanwhile, AQP4 migrates from VECs to neuronal cytomembrane, which indicates that AQP4 plays a crucial role in aggravating the formation and development of cytotoxic edema in the middle stages of SCC. Secondly, AQP4-RNAi is used to elucidate the mechanism of AQP4 to edema of SCC. The neuronal area shrinks and the area of cytotoxic edema reduces after AQP4 downregulation. The BBB scores are significantly higher than in the vector group after AQP4-RNAi at 5, 7, and 14 (P < 0.05). There is a relationship between AQP4 and COX5A shown by bioinformatics analysis. After AQP4 inhibition, the expression of COX5A is significantly upregulated in the swelling astrocytes. Therefore, the inhibition of AQP4 expression reduces cytotoxic edema in SCC and improves motor function, which may be associated with upregulation of COX5A via affecting energy metabolism. Moreover, it is not clear how the inhibition of AQP4 directly causes the upregulation of COX5A.

Controversies and Misconceptions Related to Cerebrospinal Fluid Circulation: A Review of the Literature from the Historical Pioneers' Theories to Current Models

Models of cerebrospinal fluid (CSF) circulation have been mainly proposed in the last century: CSF goes from the ventricles to the subarachnoidal space (SAS), passing through the aqueduct and the foramen of Luschka and Magendie. Indeed, new models, involving the Virchow-Robin space (VRS) and the perivascular space (PVS), have been proposed. We critically reviewed the literature, in order to clarify the “classical” errors and to discuss the “new” models that are evolving currently. Conclusions of past experiments are often not justified, due to lack of reproducibility and methodological issues. On the other hand, investigation on the microanatomy of Virchow-Robin spaces (VRS) and several new experiments showed a potential pathway for a more complex CSF “circulation,” with chaotic and unpredictable flows. It seems reasonable to elaborate a new model of CSF physiology, including new findings and questioning old certainties. However, proved data are still missing and it is hazardous to come to final conclusions. More studies are needed.

The role of brain barriers in fluid movement in the CNS: is there a 'glymphatic' system?

Brain fluids are rigidly regulated to provide stable environments for neuronal function, e.g., low K⁺, Ca²⁺, and protein to optimise signalling and minimise neurotoxicity. At the same time, neuronal and astroglial waste must be promptly removed. The interstitial fluid (ISF) of the brain tissue and the cerebrospinal fluid (CSF) bathing the CNS are integral to this homeostasis and the idea of a glia-lymph or 'glymphatic' system for waste clearance from brain has developed over the last 5 years. This links bulk (convective) flow of CSF into brain along the outside of penetrating arteries, glia-mediated convective transport of fluid and solutes through the brain extracellular space (ECS) involving the aquaporin-4 (AQP4) water channel, and finally delivery of fluid to venules for clearance along peri-venous spaces. However, recent evidence favours important amendments to the 'glymphatic' hypothesis, particularly concerning the role of glia and transfer of solutes within the ECS. This review discusses studies which question the role of AQP4 in ISF flow and the lack of evidence for its ability to transport solutes; summarizes attributes of brain ECS that strongly favour the diffusion of small and large molecules without ISF flow; discusses work on hydraulic conductivity and the nature of the extracellular matrix which may impede fluid movement; and reconsiders the roles of the perivascular space (PVS) in CSF-ISF exchange and drainage. We also consider the extent to which CSF-ISF exchange is possible and desirable, the impact of neuropathology on fluid drainage, and why using CSF as a proxy measure of brain components or drug delivery is problematic. We propose that new work and key historical studies both support the concept of a perivascular fluid system, whereby CSF enters the brain via PVS convective flow or dispersion along larger caliber arteries/arterioles, diffusion predominantly regulates CSF/ISF exchange at the level of the neurovascular unit associated with CNS microvessels, and, finally, a mixture of CSF/ISF/waste products is normally cleared along the PVS of venules/veins as well as other pathways; such a system may or may not constitute a true 'circulation', but, at the least, suggests a comprehensive re-evaluation of the previously proposed 'glymphatic' concepts in favour of a new system better taking into account basic cerebrovascular physiology and fluid transport considerations.

Methylprednisolone Administration Following Spinal Cord Injury Reduces Aquaporin 4 Expression and Exacerbates Edema

Spinal cord injury (SCI) is an incapacitating condition that affects motor, sensory, and autonomic functions. Since 1990, the only treatment administered in the acute phase of SCI has been methylprednisolone (MP), a synthetic corticosteroid that has anti-inflammatory effects; however, its efficacy remains controversial. Although MP has been thought to help in the resolution of edema, there are no scientific grounds to support this assertion. Aquaporin 4 (AQP4), the most abundant component of water channels in the CNS, participates in the formation and elimination of edema, but it is not clear whether the modulation of AQP4 expression by MP plays any role in the physiopathology of SCI. We studied the functional expression of AQP4 modulated by MP following SCI in an experimental model in rats along with the associated changes in the permeability of the blood-spinal cord barrier. We analyzed these effects in male and female rats and found that SCI increased AQP4 expression in the spinal cord white matter and that MP diminished such increase to baseline levels. Moreover, MP increased the extravasation of plasma components after SCI and enhanced tissue swelling and edema. Our results lend scientific support to the increasing motion to avoid MP treatment after SCI.

Aquaporin 4 Forms a Macromolecular Complex with Glutamate Transporter 1 and Mu Opioid Receptor in Astrocytes and Participates in Morphine Dependence

The water channel aquaporin 4 (AQP4) is abundantly expressed in astrocytes and provides a mechanism by which water permeability of the plasma membrane can be regulated. Evidence suggests that AQP4 is associated with glutamate transporter-1 (GLT-1) for glutamate clearance and contributes to morphine dependence. Previous studies show that AQP4 deficiency changed the mu opioid receptor expression and opioid receptors' characteristics as well. In this study, we focused on whether AQP4 could form macromolecular complex with GLT-1 and mu opioid receptor (MOR) and participates in morphine dependence. By using immunofluorescence staining, fluorescence resonance energy transfer, and co-immunoprecipitation, we demonstrated that AQP4 forms protein complexes with GLT-1 and MOR in both brain tissue and primary cultured astrocytes. We then showed that the C-terminus of AQP4 containing the amino acid residues 252 to 323 is the site of interaction with GLT-1. Protein kinase C, activated by morphine, played an important role in regulating the expression of these proteins. These findings may help to reveal the mechanism that AQP4, GLT-1, and MOR form protein complex and participate in morphine dependence, and deeply understand the reason that AQP4 deficiency maintains extracellular glutamate homeostasis and attenuates morphine dependence, moreover emphasizes the function of astrocyte in morphine dependence.

Hydrocephalus: the role of cerebral aquaporin-4 channels and computational modeling considerations of cerebrospinal fluid

Aquaporin-4 (AQP4) channels play an important role in brain water homeostasis. Water transport across plasma membranes has a critical role in brain water exchange of the normal and the diseased brain. AQP4 channels are implicated in the pathophysiology of hydrocephalus, a disease of water imbalance that leads to CSF accumulation in the ventricular system. Many molecular aspects of fluid exchange during hydrocephalus have yet to be firmly elucidated, but review of the literature suggests that modulation of AQP4 channel activity is a potentially attractive future pharmaceutical therapy. Drug therapy targeting AQP channels may enable control over water exchange to remove excess CSF through a molecular intervention instead of by mechanical shunting. This article is a review of a vast body of literature on the current understanding of AQP4 channels in relation to hydrocephalus, details regarding molecular aspects of AQP4 channels, possible drug development strategies, and limitations. Advances in medical imaging and computational modeling of CSF dynamics in the setting of hydrocephalus are summarized. Algorithmic developments in computational modeling continue to deepen the understanding of the hydrocephalus disease process and display promising potential benefit as a tool for physicians to evaluate patients with hydrocephalus.