Special Issue "Aquaporins in Brain Disease".

Water is an abundant and important component of the human brain, the homeostasis of which is rigorously controlled [...].

Absence of Aquaporin-4 (AQP4) Prolongs the Presence of a CD11c+ Microglial Population during Postnatal Corpus Callosum Development.

Aquaporin-4 (AQP4) expression is associated with the development of congenital hydrocephalus due to its structural role in the ependymal membrane. Gene expression analysis of periaqueductal tissue in AQP4-knockout (KO) mice at 11 days of age (P11) showed a modification in ependymal cell adhesion and ciliary protein expression that could alter cerebrospinal fluid homeostasis. A microglial subpopulation of CD11c+ cells was overexpressed in the periaqueductal tissue of mice that did not develop hydrocephalus, suggesting a possible protective effect. Here, we verified the location of this CD11c+ expression in the corpus callosum (CC) and cerebellum of AQP4-KO mice and analysed its time course. Immunofluorescence labelling of the CD11c protein in the CC and cerebellum of WT and KO animals at P3, P5, P7 and P11 confirmed an expanded presence of these cells in both tissues of the KO animal; CD11c+ cells appeared at P3 and reached a peak at P11, whereas in the WT animal, they appeared at P5, reached their peak at P7 and were undetectable by P11. The gene expression analysis in the CC samples at P11 confirmed the presence of CD11c+ microglial cells in this tissue. Among the more than 4000 overexpressed genes, Spp1 stood out with the highest differential gene expression (≅600), with other genes, such as Gpnmb, Itgax, Cd68 and Atp6v0d2, also identified as overexpressed. Therefore, CD11c+ cells appear to be necessary for normal corpus callosum development during postnatal life, and the absence of AQP4 prolonged its expression in this tissue.

Aquaporin-4 Expression Switches from White to Gray Matter Regions during Postnatal Development of the Central Nervous System.

Aquaporin-4 (AQP4) is the most abundant water channel in the central nervous system and plays a fundamental role in maintaining water homeostasis there. In adult mice, AQP4 is located mainly in ependymal cells, in the endfeet of perivascular astrocytes, and in the glia limitans. Meanwhile, its expression, location, and function throughout postnatal development remain largely unknown. Here, the expression of AQP4 mRNA was studied by in situ hybridization and RT-qPCR, and the localization and amount of protein was studied by immunofluorescence and western blotting, both in the brain and spinal cord. For this, wild-type mice of the C57BL/6 line, aged 1, 3, 7, 11, 20, and 60 days, and 18 months were used. The results showed a change in both the expression and location of AQP4 in postnatal development compared to those during adult life. In the early stages of postnatal development it appears in highly myelinated areas, such as the corpus callosum or cerebellum, and as the animal grows, it disappears from these areas, passing through the cortical regions of the forebrain and concentrating around the blood vessels. These findings suggest an unprecedented possible role for AQP4 in the early cell differentiation process, during the first days of life in the newborn animal, which will lead to myelination.

Generation of Periventricular Reactive Astrocytes Overexpressing Aquaporin 4 Is Stimulated by Mesenchymal Stem Cell Therapy.

Aquaporin-4 (AQP4) plays a crucial role in brain water circulation and is considered a therapeutic target in hydrocephalus. Congenital hydrocephalus is associated with a reaction of astrocytes in the periventricular white matter both in experimental models and human cases. A previous report showed that bone marrow-derived mesenchymal stem cells (BM-MSCs) transplanted into the lateral ventricles of hyh mice exhibiting severe congenital hydrocephalus are attracted by the periventricular astrocyte reaction, and the cerebral tissue displays recovery. The present investigation aimed to test the effect of BM-MSC treatment on astrocyte reaction formation. BM-MSCs were injected into the lateral ventricles of four-day-old hyh mice, and the periventricular reaction was detected two weeks later. A protein expression analysis of the cerebral tissue differentiated the BM-MSC-treated mice from the controls and revealed effects on neural development. In in vivo and in vitro experiments, BM-MSCs stimulated the generation of periventricular reactive astrocytes overexpressing AQP4 and its regulatory protein kinase D-interacting substrate of 220 kDa (Kidins220). In the cerebral tissue, mRNA overexpression of nerve growth factor (NGF), vascular endothelial growth factor (VEGF), hypoxia-inducible factor-1 (HIF1α), and transforming growth factor beta 1 (TGFß1) could be related to the regulation of the astrocyte reaction and AQP4 expression. In conclusion, BM-MSC treatment in hydrocephalus can stimulate a key developmental process such as the periventricular astrocyte reaction, where AQP4 overexpression could be implicated in tissue recovery.

Aquaporin-4 Mediates Permanent Brain Alterations in a Mouse Model of Hypoxia-Aged Hydrocephalus.

Aquaporin-4 (AQP4) is the principal water channel in the brain being expressed in astrocytes and ependymal cells. AQP4 plays an important role in cerebrospinal fluid (CSF) homeostasis, and alterations in its expression have been associated with hydrocephalus. AQP4 contributes to the development of hydrocephalus by hypoxia in aged mice, reproducing such principal characteristics of the disease. Here, we explore whether these alterations associated with the hydrocephalic state are permanent or can be reverted by reexposure to normoxia. Alterations such as ventriculomegaly, elevated intracranial pressure, and cognitive deficits were reversed, whereas deficits in CSF outflow and ventricular distensibility were not recovered, remaining impaired even one month after reestablishment of normoxia. Interestingly, in AQP4-/- mice, the impairment in CSF drainage and ventricular distensibility was completely reverted by re-normoxia, indicating that AQP4 has a structural role in the chronification of those alterations. Finally, we show that aged mice subjected to two hypoxic episodes experience permanent ventriculomegaly. These data reveal that repetitive hypoxic events in aged cerebral tissue promote the permanent alterations involved in hydrocephalic pathophysiology, which are dependent on AQP4 expression.

Predictive Value of Serum Antibodies and Point Mutations of AQP4, AQP1 and MOG in A Cohort of Spanish Patients with Neuromyelitis Optica Spectrum Disorders.

The detection of IgG aquaporin-4 antibodies in the serum of patients with Neuromyelitis optica (NMO) has dramatically improved the diagnosis of this disease and its distinction from multiple sclerosis. Recently, a group of patients have been described who have an NMO spectrum disorder (NMOsd) and who are seronegative for AQP4 antibodies but positive for IgG aquaporin-1 (AQP1) or myelin oligodendrocyte glycoprotein (MOG) antibodies. The purpose of this study was to determine whether AQP1 and MOG could be considered new biomarkers of this disease; and if point mutations in the gDNA of AQP4, AQP1 and MOG genes could be associated with the etiology of NMOsd. We evaluated the diagnostic capability of ELISA and cell-based assays (CBA), and analyzed their reliability, specificity, and sensitivity in detecting antibodies against these three proteins. The results showed that both assays can recognize these antigen proteins under appropriate conditions, but only anti-AQP4 antibodies, and not AQP1 or MOG, appears to be a clear biomarker for NMOsd. CBA is the best method for detecting these antibodies; and serum levels of AQP4 antibodies do not correlate with the progression of this disease. So far, the sequencing analysis has not revealed a genetic basis for the etiology of NMOsd, but a more extensive analysis is required before definitive conclusions can be drawn.

Long-term immunosuppression for CNS mouse xenotransplantation: Effects on nigrostriatal neurodegeneration and neuroprotective carotid body cell therapy.

BACKGROUND: The use of long-term immunosuppressive treatments on neural transplantation has been controversial during the last decades. Although nowadays there is a consensus about the necessity of maintaining a permanent state of immunosuppression to preserve the survival of cerebral grafts, little is known about the effects that chronic immunosuppression produces both on the neurodegenerative process and on transplants function. METHODS: Here, we establish a new immunosuppressive protocol, based on the discontinuous administration of CsA (15 mg/kg; s.c.) and prednisone (20 mg/kg; s.c.), to produce long-term immunosuppression in mice. Using this treatment, we analyse the effects that long-term immunosuppression induces in a chronic 1-methyl-4-phenyl-1,2,3,6,-tetrahydropyridine (MPTP) model of parkinsonism and on the neuroprotective and neurorestorative anti-parkinsonian actions exerted by rat carotid body (CB) xenografts. RESULTS: This protocol preserves the survival of rat CB xenotransplants maintaining the general wellness of the grafted mice. Although permanent immunosuppression does not prevent the MPTP-induced cell death of nigral neurons and the consequent degeneration of dopaminergic striatal innervation, allowing for its use as Parkinson's disease (PD) model, it reduces the microglial activation and slightly declines the striatal damage. Moreover, we reported that chronic administration of immunosuppressant drugs does not alter the neuroprotective and restorative anti-parkinsonian actions of rat CB xenografts into parkinsonian mice. CONCLUSIONS: This new immunosuppressive protocol provides a new murine model to assay the long-term effects of cerebral xenografts and offer a pharmacological alternative to the commonly used genetic immunodeficient mice, allowing the use of genetically modified mice as hosts. In addition, it will permit the experimental analysis of the effects produced by human CB xenografts in the chronic PD murine model, with the final aim of using CB allografts as an option of cell therapy in PD patients.

Aquaporin-1 plays important role in proliferation by affecting cell cycle progression.

Aquaporin-1 (AQP1) has been associated with tumor development. Here, we investigated how AQP1 may affect cell proliferation. The proliferative rate of adult carotid body (CB) cells, known to proliferate under chronic hypoxia, was analyzed in wild-type (AQP1(+/+) ) and knock out (AQP1(-/-) ) mice, maintained in normoxia or exposed to hypoxia while BrdU was administered. Fewer numbers of total BrdU(+) and TH-BrdU(+) cells were observed in AQP1(-/-) mice, indicating a role for AQP1 in CB proliferation. Then, by flow cytometry, cell cycle state and proliferation of cells overexpressing AQP1 were compared to those of wild-type cells. In the AQP1-overexpressing cells, we observed higher cell proliferation and percentages of cells in phases S and G2/M and fewer apoptotic cells after nocodazole treatment were detected by annexin V staining. Also in these cells, proteomic assays showed higher expression of cyclin D1 and E1 and microarray analysis revealed changes in many cell proliferation-related molecules, including, Zeb 2, Jun, NF-kß, Cxcl9, Cxcl10, TNF, and the TNF receptor. Overall, our results indicate that the presence of AQP1 modifies the expression of key cell cycle proteins apparently related to increases in cell proliferation. This contributes to explaining the presence of AQP1 in many different tumors.

Chronic and progressive Parkinson's disease MPTP model in adult and aged mice.

Despite the different animal models of Parkinson's disease developed during the last years, they still present limitations modelling the slow and progressive process of neurodegeneration. Here, we undertook a histological, neurochemical and behavioural analysis of a new chronic parkinsonian mouse model generated by the subcutaneous administration of low doses of MPTP (20 mg/kg, 3 times per week) for 3 months, using both young adult and aged mice. The MPTP-induced nigrostriatal neurodegeneration was progressive and was accompanied by a decrease in striatal dopamine levels and motor impairment. We also demonstrated the characteristic neuroinflammatory changes (microglial activation and astrogliosis) associated with the neurodegenerative process. Aged animals showed both a faster time course of neurodegeneration and an altered neuroinflammatory response. The long-term systemic application of low MPTP doses did not induce any increase in mortality in either young adult or aged mice and better resembles the slow evolution of the neurodegenerative process. This treatment could be useful to model different stages of Parkinson's disease, providing a better understanding of the pathophysiology of the disease and facilitating the testing of both protective and restorative treatments. Here, we show a new chronic and progressive parkinsonian mouse model, in young and aged mice. This model produces a stable degeneration of the dopaminergic nigrostriatal pathway, continuous neuroinflammatory reaction and motor deficits. Aged animals showed a faster neurodegeneration and an altered neuroinflammatory response. This treatment could be useful to model different stages of PD and to test both protective and restorative therapeutic approaches.

Comparative Analysis for the Presence of IgG Anti-Aquaporin-1 in Patients with NMO-Spectrum Disorders.

Detection of IgG anti-Aquaporin-4 (AQP4) in serum of patients with Neuromyelitis optica syndrome disorders (NMOSD) has improved diagnosis of these processes and differentiation from Multiple sclerosis (MS). Recent findings also claim that a subgroup of patients with NMOSD, serum negative for IgG-anti-AQP4, present antibodies anti-AQP1 instead. Explore the presence of IgG-anti-AQP1 using a previously developed cell-based assay (CBA) highly sensitive to IgG-anti-AQP4. Serum of 205 patients diagnosed as NMOSD (8), multiple sclerosis (94), optic neuritis (39), idiopathic myelitis (29), other idiopathic demyelinating disorders of the central nervous system (9), other neurological diseases (18) and healthy controls (8), were used in a CBA over fixed HEK cells transfected with hAQP1-EGFP or hM23-AQP4-EGFP, treated with Triton X-100 and untreated. ELISA was also performed. Analysis of serum with our CBA indicated absence of anti-AQP1 antibodies, whereas in cells pretreated with detergent, noisy signal made reliable detection impossible. ELISA showed positive results in few serums. The low number of NMOSD serums included in our study reduces its power to conclude the specificity of AQP1 antibodies as new biomarkers of NMOSD. Our study does not sustain detection of anti-AQP1 in serum of NMOSD patients but further experiments are expected.

Functional inhibition of aquaporin-3 with a gold-based compound induces blockage of cell proliferation.

AQP3 has been correlated with higher transport of glycerol, increment of ATP content, and larger proliferation capacity. Recently, we described the gold(III) complex Auphen as a very selective and potent inhibitor of AQP3's glycerol permeability (Pgly ). Here we evaluated Auphen effect on the proliferation of various mammalian cell lines differing in AQP3 expression level: no expression (PC12), moderate (NIH/3T3) or high (A431) endogenous expression, cells stably expressing AQP3 (PC12-AQP3), and human HEK293T cells transiently transfected (HEK-AQP3) for AQP3 expression. Proliferation was evaluated in the absence or presence of Auphen (5 µM) by counting number of viable cells and analyzing 5-bromo-2'-deoxyuridine (BrdU) incorporation. Auphen reduced ≈50% the proliferation in A431 and PC12-AQP3, ≈15% in HEK-AQP3 and had no effect in PC12-wt and NIH/3T3. Strong arrest in the S-G2/M phases of the cell cycle, supported by analysis of cyclins (A, B1, D1, E) levels, was observed in AQP3-expressing cells treated with Auphen. Flow-cytometry of propidium iodide incorporation and measurements of mitochondrial dehydrogenases activity confirmed absence of cytotoxic effect of the drug. Functional studies evidenced ≈50% inhibition of A431 Pgly by Auphen, showing that the compound's antiproliferative effect correlates with its ability to inhibit AQP3 Pgly . Role of Cys-40 on AQP3 permeability blockage by Auphen was confirmed by analyzing the mutated protein (AQP3-Ser-40). Accordingly, cells transfected with mutated AQP3 gained resistance to the antiproliferative effect of Auphen. These results highlight an Auphen inhibitory effect on proliferation of cells expressing AQP3 and suggest a targeted therapeutic effect on carcinomas with large AQP3 expression.

An immunoassay that distinguishes real neuromyelitis optica signals from a labeling detected in patients receiving natalizumab.

BACKGROUND: Cell-based assays for neuromyelitis optica (NMO) diagnosis are the most sensitive and specific methods to detect anti-aquaporin 4 (AQP4) antibodies in serum, but some improvements in their quantitative and specificity capacities would be desirable. Thus the aim of the present work was to develop a sensitive quantitative method for detection of anti-AQP4 antibodies that allows clear diagnosis of NMO and distinction of false labeling produced by natalizumab treatment. METHODS: Sera from 167 individuals, patients diagnosed with NMO (16), multiple sclerosis (85), optic neuritis (24), idiopathic myelitis (21), or other neurological disorders (13) and healthy controls (8), were used as the primary antibody in an immunofluorescence assay on HEK cells transfected with the M23 isoform of human AQP4 fused with enhanced green fluorescent protein. Cells used were freshly transfected or stored frozen and then thawed just before adding the serum. RESULTS: Microscopic observation and fluorescence quantification produced similar results in fresh and frozen samples. Serum samples from patients diagnosed with NMO were 100% positive for anti-AQP4 antibodies, while all the other sera were negative. Using serum from patients treated with natalizumab, a small and unspecific fluorescent signal was produced from all HEK cells, regardless of AQP4 expression. CONCLUSIONS: Our cell-based double-label fluorescence immunoassay protocol significantly increases the signal specificity and reduces false diagnosis of NMO patients, especially in those receiving natalizumab treatment. Frozen pretreated cells allow faster detection of anti-AQP4 antibodies.

Impact of aquaporin-4 and CD11c + microglia in the development of ependymal cells in the aqueduct: inferences to hydrocephalus.

AQP4 is expressed in the endfeet membranes of subpial and perivascular astrocytes and in the ependymal cells that line the ventricular system. The sporadic appearance of obstructive congenital hydrocephalus (OCHC) has been observed in the offspring of AQP4-/- mice (KO) due to stenosis of Silvio's aqueduct. Here, we explore whether the lack of AQP4 expression leads to abnormal development of ependymal cells in the aqueduct of mice. We compared periaqueductal samples from wild-type and KO mice. The microarray-based transcriptome analysis reflected a large number of genes with differential expression (809). Gene sets (GS) associated with ependymal development, ciliary function and the immune system were specially modified qPCR confirmed reduced expression in the KO mice genes: (i) coding for transcription factors for ependymal differentiation (Rfx4 and FoxJ1), (ii) involved in the constitution of the central apparatus of the axoneme (Spag16 and Hydin), (iii) associated with ciliary assembly (Cfap43, Cfap69 and Ccdc170), and (iv) involved in intercellular junction complexes of the ependyma (Cdhr4). By contrast, genes such as Spp1, Gpnmb, Itgax, and Cd68, associated with a Cd11c-positive microglial population, were overexpressed in the KO mice. Electron microscopy and Immunofluorescence of vimentin and γ-tubulin revealed a disorganized ependyma in the KO mice, with changes in the intercellular complex union, unevenly orientated cilia, and variations in the planar cell polarity of the apical membrane. These structural alterations translate into reduced cilia beat frequency, which might alter cerebrospinal fluid movement. The presence of CD11c + microglia cells in the periaqueductal zone of mice during the first postnatal week is a novel finding. In AQP4-/- mice, these cells remain present around the aqueduct for an extended period, showing peak expression at P11. We propose that these cells play an important role in the normal development of the ependyma and that their overexpression in KO mice is crucial to reduce ependyma abnormalities that could otherwise contribute to the development of obstructive hydrocephalus.

Cellular Distribution of Brain Aquaporins and Their Contribution to Cerebrospinal Fluid Homeostasis and Hydrocephalus.

Brain aquaporins facilitate the movement of water between the four water compartments: blood, cerebrospinal fluid, interstitial fluid, and intracellular fluid. This work analyzes the expression of the four most abundant aquaporins (AQPs) (AQP1, AQP4, AQP9, and AQP11) in the brains of mice and discuss their contribution to hydrocephalus. We analyzed available data from single-cell RNA sequencing of the central nervous system of mice to describe the expression of aquaporins and compare their distribution with that based on qPCR, western blot, and immunohistochemistry assays. Expression of AQP1 in the apical cell membrane of choroid plexus epithelial cells and of AQP4 in ependymal cells, glia limitans, and astrocyte processes in the pericapillary end foot is consistent with the involvement of both proteins in cerebrospinal fluid homeostasis. The expression of both aquaporins compensates for experimentally induced hydrocephalus in the animals. Recent data demonstrate that hypoxia in aged animals alters AQP4 expression in the choroidal plexus and cortex, increasing the ventricle size and intraventricular pressure. Cerebral distensibility is reduced in parallel with a reduction in cerebrospinal fluid drainage and cognitive deterioration. We propose that aged mice chronically exposed to hypoxia represent an excellent experimental model for studying the pathophysiological characteristics of idiopathic normal pressure hydrocephalus and roles for AQPs in such disease.

Aquaporin-4 Removal from the Plasma Membrane of Human Müller Cells by AQP4-IgG from Patients with Neuromyelitis Optica Induces Changes in Cell Volume Homeostasis: the First Step of Retinal Injury?

Aquaporin-4 (AQP4) is the target of the specific immunoglobulin G autoantibody (AQP4-IgG) produced in patients with neuromyelitis optica spectrum disorders (NMOSD). Previous studies demonstrated that AQP4-IgG binding to astrocytic AQP4 leads to cell-destructive lesions. However, the early physiopathological events in Müller cells in the retina are poorly understood. Here, we investigated the consequences of AQP4-IgG binding to AQP4 of Müller cells, previous to the inflammatory response, on two of AQP4's key functions, cell volume regulation response (RVD) and cell proliferation, a process closely associated with changes in cell volume. Experiments were performed in a human retinal Müller cell line (MIO-M1) exposed to complement-inactivated sera from healthy volunteers or AQP4-IgG positive NMOSD patients. We evaluated AQP4 expression (immunofluorescence and western blot), water permeability coefficient, RVD, intracellular calcium levels and membrane potential changes during hypotonic shock (fluorescence videomicroscopy) and cell proliferation (cell count and BrdU incorporation). Our results showed that AQP4-IgG binding to AQP4 induces its partial internalization, leading to the decrease of the plasma membrane water permeability, a reduction of swelling-induced increase of intracellular calcium levels and the impairment of RVD in Müller cells. The loss of AQP4 from the plasma membrane induced by AQP4-IgG positive sera delayed Müller cells' proliferation rate. We propose that Müller cell dysfunction after AQP4 removal from the plasma membrane by AQP4-IgG binding could be a non-inflammatory mechanism of retinal injury in vivo, altering cell volume homeostasis and cell proliferation and consequently, contributing to the physiopathology of NMOSD.

Evaluation of aquaporins in the cerebrospinal fluid in patients with idiopathic normal pressure hydrocephalus.

Brain aquaporin 1 (AQP1) and AQP4 are involved in cerebrospinal fluid (CSF) homeostasis and might participate in the origin of hydrocephalus. Studies have shown alterations of perivascular AQP4 expression in idiopathic normal pressure hydrocephalus (iNPH) and Alzheimer's disease (AD). Due to the overlapping of clinical signs between iNPH and certain neurological conditions, mainly AD, specific biomarkers might improve the diagnostic accuracy for iNPH. The goal of the present study was to analyze and quantify the presence of AQP1 and AQP4 in the CSF of patients with iNPH and AD to determine whether these proteins can be used as biomarkers of iNPH. We examined AQP1 and AQP4 protein levels in the CSF of 179 participants (88 women) classified into 5 groups: possible iNPH (81 participants), hydrocephalus associated with other neurological disorders (13 participants), AD (41 participants), non-AD dementia (32 participants) and healthy controls (12 participants). We recorded each participant's demographic and clinical variables and indicated, when available in the clinical history, the record of cardiovascular and respiratory complications. An ELISA showed virtually no AQP content in the CSF. Information on the vascular risk factors (available for 61 patients) confirmed some type of vascular risk factor in 86% of the patients with possible iNPH and 58% of the patients with AD. In conclusion, the ELISA analysis showed insufficient sensitivity to detect the presence of AQP1 and AQP4 in CSF, ruling out the possible use of these proteins as biomarkers for diagnosing iNPH.

Non-productive angiogenesis disassembles Aß plaque-associated blood vessels.

The human Alzheimer's disease (AD) brain accumulates angiogenic markers but paradoxically, the cerebral microvasculature is reduced around Aß plaques. Here we demonstrate that angiogenesis is started near Aß plaques in both AD mouse models and human AD samples. However, endothelial cells express the molecular signature of non-productive angiogenesis (NPA) and accumulate, around Aß plaques, a tip cell marker and IB4 reactive vascular anomalies with reduced NOTCH activity. Notably, NPA induction by endothelial loss of presenilin, whose mutations cause familial AD and which activity has been shown to decrease with age, produced a similar vascular phenotype in the absence of Aß pathology. We also show that Aß plaque-associated NPA locally disassembles blood vessels, leaving behind vascular scars, and that microglial phagocytosis contributes to the local loss of endothelial cells. These results define the role of NPA and microglia in local blood vessel disassembly and highlight the vascular component of presenilin loss of function in AD.

AQP1 mediates water transport in the carotid body.

In this study, we explored the presence of aquaporins (AQPs), a family of membrane water channel proteins, in carotid body (CB) type I chemoreceptor cells. The CB is a polymodal chemoreceptor whose major function is to detect changes in arterial O2 tension to elicit hyperventilation during hypoxia. The CB has also been proposed to function as a systemic osmoreceptor, thus we hypothesized that the presence of AQPs in type I cell membrane may confer higher sensitivity to osmolarity changes and hence accelerate the activation of chemoreceptor cells. We detected the expression of AQP1, AQP7, and AQP8 in the CB and confirmed the location of AQP1 in type I cells. We have also shown that inhibition of AQP1 expression clearly reduced type I cell swelling after a hyposmotic shock, demonstrating that AQP1 has a major contribution in transmembrane water movement in these chemoreceptor cells. Interestingly, CB AQP1 expression levels change during postnatal development, increasing during the first postnatal weeks as the organ matures. In conclusion, in this study, we report the novel observation that AQPs are expressed in the CB. We also show that AQP1 mediates water transport across the cell membrane of type I cells, supporting the contribution of this protein to the osmoreception function of the CB.

AQP1 and AQP4 Contribution to Cerebrospinal Fluid Homeostasis.

Aquaporin 1 (AQP1), expressed in epithelial cells of the choroid plexus, and aquaporin 4 (AQP4) present in ependymal cells and glia limitants have been proposed to play a significant role in cerebrospinal fluid (CSF) production and homeostasis. However, the specific contribution of each water channel to these functions remains unknown, being a subject of debate during the last years. Here, we analyzed in detail how AQP1 and AQP4 participate in different aspects of the CSF homeostasis such as the load and drainage of ventricles, and further explored if these proteins play a role in the ventricular compliance. To do that, we carried out records of intraventricular pressure and CSF outflow, and evaluated ventricular volume by magnetic resonance imaging in AQP1-/-, AQP4-/-, double AQP1-/--AQP4-/- knock out and wild type mice controls. The analysis performed clearly showed that both AQPs have a significant participation in the CSF production, and additionally revealed that the double AQP1-AQP4 mutation alters the CSF drainage and the ventricular compliance. The data reported here indicate a significant extra-choroidal CSF formation mediated by AQP4, supporting the idea of an important and constant CSF production/absorption process, sustained by efflux/influx of water between brain capillaries and interstitial fluid. Moreover, our results suggest the participation of AQPs in structural functions also related with CSF homeostasis such as the distensibility capacity of the ventricular system.

Expression Pattern of Aquaporin 1 and Aquaporin 3 in Melanocytic and Nonmelanocytic Skin Tumors.

OBJECTIVES: Study of aquaporin 1 (AQP1) and aquaporin 3 (AQP3) expression to understand its potential role in the pathophysiology of skin cancer. METHODS: Analysis of AQP1 and AQP3 expression by immunohistochemistry of 72 skin biopsy specimens from melanocytic skin tumors, nonmelanocytic tumors, or healthy samples. RESULTS: AQP1 showed strong labeling in 100% of benign common melanocytic nevi. Small blood vessels, stroma, and melanophages surrounding different types of melanomas tumors also were positive. Tumoral melanocytes in atypical nevi and melanomas were negative for AQP1. AQP3 showed strong labeling in 100% of melanocytic nevi, 100% of atypical melanocytic nevi, and 100% of melanomas. In all basal cell carcinomas and squamous cell carcinomas, staining for AQP3 was positive. CONCLUSIONS: To our knowledge, this work represents the first demonstration of AQP1/AQP3 expression in human melanocytic skin tumors. More studies are needed to understand the underlying molecular mechanisms of expression of both AQPs in melanocytic tumors and their potential as molecular therapeutic targets.