451
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Sørbø JG, Moe SE, Holen T. Early upregulation in nasal epithelium and strong expression in olfactory bulb glomeruli suggest a role for Aquaporin-4 in olfaction. FEBS Lett 2007; 581:4884-90. [PMID: 17897643 DOI: 10.1016/j.febslet.2007.09.018] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2007] [Revised: 09/05/2007] [Accepted: 09/10/2007] [Indexed: 11/18/2022]
Abstract
Aquaporin-4 (AQP4) has been reported to be upregulated post-partum in pregnancy and in early lung development. Several technical challenges exist in measuring AQP4 protein levels, among them sensitivity to detergent solubilization, sample heating and gel composition. Here we have optimized quantification of AQP4 using immuno-blots. Using improved methodology we find no evidence for AQP4 upregulation post-partum or in the early lung development. However, in the nasal epithelium AQP4 is upregulated as early as in the brain. Furthermore, AQP4 is strongly expressed in the glomerulus, the synaptic unit of the olfactory bulb, suggesting a role for AQP4 in olfactory function.
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Affiliation(s)
- Jan Gunnar Sørbø
- Center for Molecular Biology and Neuroscience (CMBN), University of Oslo, Norway
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452
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Romeiro RR, Romano-Silva MA, De Marco L, Teixeira AL, Correa H. Can variation in aquaporin 4 gene be associated with different outcomes in traumatic brain edema? Neurosci Lett 2007; 426:133-4. [PMID: 17890008 DOI: 10.1016/j.neulet.2007.09.004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2007] [Accepted: 09/05/2007] [Indexed: 11/18/2022]
Abstract
In traumatic brain injury (TBI), cerebral edema and hemorrhage are factors involved in the determination of the clinical presentation and outcome. The aquaporin 4 (AQP4) water channel is abundant in mammalian brain and there is a growing body of evidence suggesting that this protein plays a major role in the control of water flow within the central nervous system. Previous studies examined the influence of genetic variants in cerebral edema of TBI. However, to our knowledge, there are no previous studies of molecular variations of the AQP4 gene and its association with TBI. Thus, we sought to investigate if the clinical presentation and outcome of TBI could be influenced by the presence of mutations on exon 4 of the AQP4 gene. One hundred and two patients were enrolled in this study. A neurologist assessed the clinical severity at admission according to the GCS followed by a brain computer tomography (CT) scan. Then, DNA was extracted from blood cells and exon 4 of the AQP4 gene amplified by the polymerase chain reaction and directly sequenced. On discharge, GOS was assigned by a neurologist blind to the CGS on admission. We did not find any variation in exon 4 of the AQP4 gene in our considerable large sample. Despite this negative result, there is a strong biological rationale for the involvement of AQP4 gene in brain edema regulation and, as consequence, in TBI. Therefore, further studies should be performed, including the assessment of the other three exons of the AQP4 gene.
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Affiliation(s)
- Ricardo R Romeiro
- Emergency Unit, Hospital João XXIII, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil
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453
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Kimelberg HK. Supportive or information-processing functions of the mature protoplasmic astrocyte in the mammalian CNS? A critical appraisal. NEURON GLIA BIOLOGY 2007; 3:181-9. [PMID: 18545675 PMCID: PMC2423726 DOI: 10.1017/s1740925x08000094] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
It has been proposed that astrocytes should no longer be viewed purely as support cells for neurons, such as providing a constant environment and metabolic substrates, but that they should also be viewed as being involved in affecting synaptic activity in an active way and, therefore, an integral part of the information-processing properties of the brain. This essay discusses the possible differences between a support and an instructive role, and concludes that any distinction has to be blurred. In view of this, and a brief overview of the nature of the data, the new evidence seems insufficient to conclude that the physiological roles of mature astrocytes go beyond a general support role. I propose a model of mature protoplasmic astrocyte function that is drawn from the most recent data on their structure, the domain concept and their syncytial characteristics, of an independent rather than integrative functioning of the ends of each process where the activities that affect synaptic activity and blood vessel diameter will be concentrated.
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Affiliation(s)
- Harold K Kimelberg
- Neural and Vascular Biology, Ordway Research Institute, Inc., 150 New Scotland Ave, Albany, NY 12208, USA.
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454
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Harsan LA, Poulet P, Guignard B, Parizel N, Skoff RP, Ghandour MS. Astrocytic hypertrophy in dysmyelination influences the diffusion anisotropy of white matter. J Neurosci Res 2007; 85:935-44. [PMID: 17278151 DOI: 10.1002/jnr.21201] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The effect of a proteolipid protein (PLP) mutation on the developing white matter anisotropy was examined by diffusion tensor magnetic resonance imaging (DT-MRI) in a noninvasive study of a mouse model of Pelizaeus-Merzbacher disease (PMD). The jimpy PLP mutation in mice produces an irreversible dysmyelination in jimpy males, whereas heterozygous females exhibit a transient hypomyelination, as assessed by a longitudinal study of the same mice during development. Modifications of the different individual DT-MRI parameters were highlighted by specific changes in tissue structures caused by the mutation that includes the hypomyelination, axonal abnormalities, and recovery. Astrocytic hypertrophy is a striking cellular event in dysmyelinated jimpy brain, where most axons or bundles of fibers are entirely wrapped by astrocyte cytoplasmic processes, so its influences on DT-MRI parameters in dysmyelination were examined for the first time. DT-MRI data of the jimpy brain were compared with those obtained from dysmyelination of (oligo-TTK) transgenic mice, induced by oligodendrocyte killing, which have a mild astrocyte hypertrophy (Jalabi et al., 2005), and from recovering jimpy females, which have reduced astrocyte hypertrophy. The unique morphological feature of astrocytes in jimpy males coupled with an increase in the water channel protein aquaporin 4 (AQP4) was found to facilitate the directional water diffusion in the white matter. In addition to the major changes of DT-MRI parameters in the two dysmyelinated mice caused by the myelin loss and axonal modifications, the amplified magnitude of radial and axial diffusions in jimpy males was attributed principally to the strongly pronounced astrocyte hypertrophy.
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Affiliation(s)
- Laura A Harsan
- UMR 7004 CNRS/ULP, Institut de Physique Biologique, Strasbourg, France
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455
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Benfenati V, Amiry-Moghaddam M, Caprini M, Mylonakou MN, Rapisarda C, Ottersen OP, Ferroni S. Expression and functional characterization of transient receptor potential vanilloid-related channel 4 (TRPV4) in rat cortical astrocytes. Neuroscience 2007; 148:876-92. [PMID: 17719182 DOI: 10.1016/j.neuroscience.2007.06.039] [Citation(s) in RCA: 142] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2007] [Revised: 06/20/2007] [Accepted: 07/19/2007] [Indexed: 11/18/2022]
Abstract
Cell-cell communication in astroglial syncytia is mediated by intracellular Ca(2+) ([Ca(2+)](i)) responses elicited by extracellular signaling molecules as well as by diverse physical and chemical stimuli. Despite the evidence that astrocytic swelling promotes [Ca(2+)](i) elevation through Ca(2+) influx, the molecular identity of the channel protein underlying this response is still elusive. Here we report that primary cultured cortical astrocytes express the transient receptor potential vanilloid-related channel 4 (TRPV 4), a Ca(2+)-permeable cation channel gated by a variety of stimuli, including cell swelling. Immunoblot and confocal microscopy analyses confirmed the presence of the channel protein and its localization in the plasma membrane. TRPV4 was functional because the selective TRPV4 agonist 4-alpha-phorbol 12,13-didecanoate (4alphaPDD) activated an outwardly rectifying cation current with biophysical and pharmacological properties that overlapped those of recombinant human TRPV4 expressed in COS cells. Moreover, 4alphaPDD and hypotonic challenge promoted [Ca(2+)](i) elevation mediated by influx of extracellular Ca(2+). This effect was abolished by low micromolar concentration of the TRPV4 inhibitor Ruthenium Red. Immunofluorescence and immunogold electron microscopy of rat brain revealed that TRPV4 was enriched in astrocytic processes of the superficial layers of the neocortex and in astrocyte end feet facing pia and blood vessels. Collectively, these data indicate that cultured cortical astroglia express functional TRPV4 channels. They also demonstrate that TRPV4 is particularly abundant in astrocytic membranes at the interface between brain and extracerebral liquid spaces. Consistent with its roles in other tissues, these results support the view that TRPV4 might participate in astroglial osmosensation and thus play a key role in brain volume homeostasis.
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Affiliation(s)
- V Benfenati
- Department of Human and General Physiology, University of Bologna, Via S. Donato 19/2, 40127 Bologna, Italy
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456
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Affiliation(s)
- Marilyn J Cipolla
- Department of Neurology, University of Vermont College of Medicine, Burlington, VT 05405, USA.
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457
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Jacob A, Matiello M, Wingerchuk DM, Lucchinetti CF, Pittock SJ, Weinshenker BG. Neuromyelitis optica: Changing concepts. J Neuroimmunol 2007; 187:126-38. [PMID: 17512987 DOI: 10.1016/j.jneuroim.2007.04.009] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2007] [Revised: 03/29/2007] [Accepted: 04/03/2007] [Indexed: 11/15/2022]
Abstract
Neuromyelitis optica (NMO; Devic's disease) and the NMO spectrum disorders are idiopathic inflammatory demyelinating disorders that affect the central nervous system and have a predilection for optic nerves and spinal cord. The identification of NMO-IgG as a disease-specific marker and aquaporin 4 as the target antigen has renewed interest in NMO. Based on current data, we suspect that autoantibodies arising from peripheral B cells bind to aquaporin 4 expressed on astrocyte foot processes on the abluminal surface of microvessels, activate complement and initiate inflammatory demyelination and necrosis. The development of animal models and further analysis of the association of NMO-IgG with disease severity and treatment response will elucidate the pathobiology of NMO.
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Affiliation(s)
- Anu Jacob
- Department of Neurology, Mayo Clinic College of Medicine, Rochester, MN 55905, USA
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458
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Zhang S, Zhou F, Ding JH, Zhou XQ, Sun XL, Hu G. ATP-sensitive potassium channel opener iptakalim protects against MPP+-induced astrocytic apoptosis via mitochondria and mitogen-activated protein kinase signal pathways. J Neurochem 2007; 103:569-79. [PMID: 17635669 DOI: 10.1111/j.1471-4159.2007.04775.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Inhibition of astrocytic apoptosis has been regarded as a novel prospective strategy for treating neurodegenerative disorders such as Parkinson's disease. In the present study, we demonstrated that iptakalim (IPT), an ATP-sensitive potassium channel (K(ATP) channel) opener, exerted protective effect on MPP(+)-induced astrocytic apoptosis, which was reversed by selective mitochondrial K(ATP) channel blocker 5-hydroxydecanoate. Further study revealed that IPT inhibited glutathione (GSH) depletion, mitochondrial membrane potential loss and subsequent release of pro-apoptotic factors (cytochrome c and apoptosis-inducing factor (AIF), and c-Jun NH(2)-terminal kinase/mitogen-activated protein kinases (MAPK) phosphorylation induced by MPP(+). Meanwhile, extracellular signal-regulated kinase (ERK) 1/2 inhibitor PD98059 inhibited the protective effect of IPT on MPP(+)-induced astrocytic apoptosis. Furthermore, IPT could also activate ERK/MAPK and maintain increased phospho-ERK1/2 level after MPP(+) exposure. Taken together, these findings reveal for the first time that IPT protects against MPP(+)-induced astrocytic apoptosis via inhibition of mitochondria apoptotic pathway and regulating the MAPK signal transduction pathways by opening mitochondrial ATP-sensitive potassium (mitoK(ATP)) channels in astrocytes. And targeting K(ATP) channels expressed in astrocytes may provide a novel therapeutic strategy for neurodegenerative disorders.
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Affiliation(s)
- Shu Zhang
- Laboratory of Neuropharmacology, Institute of Neurosciences, Nanjing Medical University, Nanjing, Jiangsu, P. R. China
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459
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Wingerchuk DM, Lucchinetti CF. Comparative immunopathogenesis of acute disseminated encephalomyelitis, neuromyelitis optica, and multiple sclerosis. Curr Opin Neurol 2007; 20:343-50. [PMID: 17495631 DOI: 10.1097/wco.0b013e3280be58d8] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
PURPOSE OF REVIEW Advanced immunopathological techniques hold promise for more precise diagnosis of idiopathic demyelinating diseases of the central nervous system. We review recent progress in differentiating and understanding the disease mechanisms of acute disseminated encephalomyelitis, neuromyelitis optica, and classical multiple sclerosis. RECENT FINDINGS Four distinct immunopathological patterns have been described in multiple sclerosis patients, potentially implicating different inflammatory, demyelinating, and apoptotic mechanisms. A specific serum biomarker, neuromyelitis optica immunoglobulin G, is strongly associated with neuromyelitis optica and identifies patients with severe optic nerve and spinal cord lesions with specific pathological features such as eosinophilic and neutrophilic inflammatory infiltrates, necrosis, vascular hyalinization, and extensive vasculocentric immunoglobulin and complement deposition. This biomarker targets the water channel aquaporin-4, which is lost in neuromyelitis optica lesions. Acute disseminated encephalomyelitis still has no validated clinical diagnostic criteria but its perivenous pathological findings distinguish it from multiple sclerosis and neuromyelitis optica. SUMMARY The clinically heterogeneous group of idiopathic inflammatory demyelinating diseases of the central nervous system is characterized by several immunopathological patterns that suggest the involvement of diverse pathogenic effector mechanisms. Future advances in experimental pathology, immunology, molecular genetics, and neuroimaging, as well as the discovery of specific biomarkers, will more precisely define these disorders and lead to better targeted therapies.
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460
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Abstract
✓Cerebral edema is caused by a variety of pathological conditions that affect the brain. It is associated with two separate pathophysiological processes with distinct molecular and physiological antecedents: those related to cytotoxic (cellular) edema of neurons and astrocytes, and those related to transcapillary flux of Na+and other ions, water, and serum macromolecules. In this review, the authors focus exclusively on the first of these two processes. Cytotoxic edema results from unchecked or uncompensated influx of cations, mainly Na+, through cation channels. The authors review the different cation channels that have been implicated in the formation of cytotoxic edema of astrocytes and neurons in different pathological states. A better understanding of these molecular mechanisms holds the promise of improved treatments of cerebral edema and of the secondary injury produced by this pathological process.
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Affiliation(s)
- Danny Liang
- Department of Neurosurgery, University of Maryland School of Medicine, Baltimore, Maryland 21201-1595, USA
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461
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Davidsen T, Koomey M, Tønjum T. Microbial genome dynamics in CNS pathogenesis. Neuroscience 2007; 145:1375-87. [PMID: 17367950 DOI: 10.1016/j.neuroscience.2007.01.059] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2006] [Revised: 01/19/2007] [Accepted: 01/19/2007] [Indexed: 10/23/2022]
Abstract
The balancing act between microbes and their host in commensal and disease states needs to be deciphered in order to fully treat and combat infectious diseases. The elucidation of microbial genome dynamics in each instance is therefore required. In this context, the major bacterial meningitis pathogens are Neisseria meningitidis, Haemophilus influenzae and Streptococcus pneumoniae. In prokaryotic CNS pathogenesis both the intact organism as well as its released components can elicit disease, often resulting in neurological sequelae, neurodegeneration or fatal outcome. The study of microbial virulence in CNS disease is expected to generate findings that yield new information on the general mechanisms of brain edema and excitatory neuronal disturbances due to meningitis, with significant potential for discoveries that can directly influence and inspire new strategies for prevention and treatment of this serious disease.
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Affiliation(s)
- T Davidsen
- Centre for Molecular Biology and Neuroscience, Institute of Microbiology, Rikshospitalet-Radiumhospitalet Medical Centre, Sognsvannsveien 20, NO-0027 Oslo, Norway
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462
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Simard JM, Kent TA, Chen M, Tarasov KV, Gerzanich V. Brain oedema in focal ischaemia: molecular pathophysiology and theoretical implications. Lancet Neurol 2007; 6:258-68. [PMID: 17303532 PMCID: PMC2725365 DOI: 10.1016/s1474-4422(07)70055-8] [Citation(s) in RCA: 567] [Impact Index Per Article: 33.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Focal cerebral ischaemia and post-ischaemic reperfusion cause cerebral capillary dysfunction, resulting in oedema formation and haemorrhagic conversion. There are substantial gaps in understanding the pathophysiology, especially regarding early molecular participants. Here, we review physiological and molecular mechanisms involved. We reaffirm the central role of Starling's principle, which states that oedema formation is determined by the driving force and the capillary "permeability pore". We emphasise that the movement of fluids is largely driven without new expenditure of energy by the ischaemic brain. We organise the progressive changes in osmotic and hydrostatic conductivity of abnormal capillaries into three phases: formation of ionic oedema, formation of vasogenic oedema, and catastrophic failure with haemorrhagic conversion. We suggest a new theory suggesting that ischaemia-induced capillary dysfunction can be attributed to de novo synthesis of a specific ensemble of proteins that determine osmotic and hydraulic conductivity in Starling's equation, and whose expression is driven by a distinct transcriptional program.
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Affiliation(s)
- J Marc Simard
- Department of Neurosurgery, University of Maryland School of Medicine, Baltimore, MD, USA.
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463
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Abstract
Functional neuroimaging has emerged as an important approach to study the brain and the mind. Surprisingly, although they are based on radically different physical approaches both positron emission tomography (PET) and magnetic resonance imaging (MRI) make brain activation imaging possible through measurements involving water molecules. So far, PET and MRI functional imaging have relied on the principle that neuronal activation and blood flow are coupled through metabolism. However, a new paradigm has emerged to look at brain activity through the observation with MRI of the molecular diffusion of water. In contrast with the former approaches diffusion MRI has the potential to reveal changes in the intrinsic water physical properties during brain activation, which could be more intimately linked to the neuronal activation mechanisms and lead to an improved spatial and temporal resolution. However, this link has yet to be fully confirmed and understood. To shed light on the possible relationship between water and brain activation, this introductory paper reviews the most recent data on the physical properties of water and on the status of water in biological tissues, and evaluates their relevance to brain diffusion MRI. The biophysical mechanisms of brain activation are then reassessed to reveal their intimacy with the physical properties of water, which may come to be regarded as the 'molecule of the mind'.
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Affiliation(s)
- Denis Le Bihan
- NeuroSpin, Bâtiment 145, CEA Saclay, 91191 Gif-sur-Yvette, France.
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464
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Lopez IA, Ishiyama G, Lee M, Baloh RW, Ishiyama A. Immunohistochemical localization of aquaporins in the human inner ear. Cell Tissue Res 2007; 328:453-60. [PMID: 17318586 DOI: 10.1007/s00441-007-0380-z] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2006] [Accepted: 01/10/2007] [Indexed: 10/23/2022]
Abstract
We report the immunolocalization of aquaporins (AQPs) 1, 4, and 6 in the human auditory and vestibular endorgans. A rapid protocol was applied to audiovestibular endorgans microdissected from postmortem human temporal bones from six subjects (ages ranging from 75 to 97 years) with no history of audiovestibular disease. Temporal bones were fixed in formalin, and the endorgans were immediately microdissected. Cryostat sections were obtained from audiovestibular endorgans and were subjected to double-immunohistochemical staining with antibodies against AQPs and several cellular markers. In the human cochlea, AQP1 immunoreactivity was localized to the fibrocytes of the spiral ligament and the sub-basilar tympanic cells; AQP4 immunoreactivity was localized to the outer sulcus cells, Hensen's cells, and Claudius' cells; AQP6 immunoreactivity was localized to the apical portion of interdental cells in the spiral limbus. In the vestibular endorgans (macula utriculi and cristae), AQP1 was localized to fibrocytes and blood vessels of the underlying stroma and trabecular perilymphatic tissue; AQP4 immunoreactivity was localized to the basal pole of vestibular supporting cells; AQP6 was localized to the apical portion of vestibular supporting cells. Cochlear and vestibular hair cells and nerve fibers were not immunoreactive for any AQP. Supporting cells were identified with antibodies against glial fibrilar acidic protein. Nerve fibers and terminals were identified with antibodies against neurofilaments and Na(+)K(+)ATPase. The high degree of conservation of AQP expression in the human inner ear suggests that AQPs play a critical role in inner ear water homeostasis.
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Affiliation(s)
- Ivan A Lopez
- Division of Head and Neck Surgery CHS 62-132, UCLA School of Medicine, Los Angeles, CA 90095, USA
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465
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Jespersen SN, Kroenke CD, Østergaard L, Ackerman JJH, Yablonskiy DA. Modeling dendrite density from magnetic resonance diffusion measurements. Neuroimage 2007; 34:1473-86. [PMID: 17188901 DOI: 10.1016/j.neuroimage.2006.10.037] [Citation(s) in RCA: 243] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2006] [Accepted: 10/29/2006] [Indexed: 01/24/2023] Open
Abstract
Diffusion-weighted imaging (DWI) provides a noninvasive tool to probe tissue microstructure. We propose a simplified model of neural cytoarchitecture intended to capture the essential features important for water diffusion as measured by NMR. Two components contribute to the NMR signal in this model: (i) the dendrites and axons, which are modeled as long cylinders with two diffusion coefficients, parallel (D(L)) and perpendicular (D(T)) to the cylindrical axis, and (ii) an isotropic monoexponential diffusion component describing water diffusion within and across all other structures, i.e., in extracellular space and glia cells. The model parameters are estimated from 153 diffusion-weighted images acquired from a formalin-fixed baboon brain. A close correspondence between the data and the signal model is found, with the model parameters consistent with literature values. The model provides an estimate of dendrite density from noninvasive MR diffusion measurements, a parameter likely to be of value for understanding normal as well as abnormal brain development and function.
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Affiliation(s)
- Sune N Jespersen
- Center of Functionally Integrative Neuroscience, Aarhus University Hospital-Arhus Sygehus, Nørrebrogade 44, Building 30, 8000 Arhus C, Denmark.
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466
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Wingerchuk DM. Neuromyelitis Optica: New Findings on Pathogenesis. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2007; 79:665-88. [PMID: 17531863 DOI: 10.1016/s0074-7742(07)79029-3] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Neuromyelitis optica (NMO) is an idiopathic CNS demyelinating disorder that preferentially involves the optic nerve and spinal cord. Diverse sources of evidence support the hypothesis that NMO is distinct from classical multiple sclerosis (MS) and that the pathogenesis of NMO is dominated by humoral mechanisms. Such evidence includes clinical observations that systemic autoimmune diseases often coexist with NMO and that therapeutic plasmapheresis may provide meaningful rescue therapy for severe clinical attacks, immunopathologic studies that demonstrate prominent complement activation and immunoglobulin deposition, and the discovery of the serum autoantibody NMO-IgG, a potential NMO biomarker that targets aquaporin-4 (AQP4). The NMO-IgG marker is present in a majority of patients with "NMO-spectrum disorders," including isolated or recurrent longitudinally extensive transverse myelitis, recurrent optic neuritis with negative brain imaging, and the Asian optic-spinal form of MS. Preliminary experiments demonstrate that NMO-IgG can modulate AQP4 function and fix complement, characteristics that suggest it has the potential to be pathogenic in NMO. Other immunologic differences among NMO, NMO-spectrum disorders, and classical MS are reviewed.
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467
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Kobayashi H, Yokoo H, Yanagita T, Satoh S, Kis B, Deli M, Niwa M, Wada A. Induction of aquaporin 1 by dexamethasone in lipid rafts in immortalized brain microvascular endothelial cells. Brain Res 2006; 1123:12-9. [PMID: 17074307 DOI: 10.1016/j.brainres.2006.09.066] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2005] [Revised: 07/25/2006] [Accepted: 09/10/2006] [Indexed: 01/22/2023]
Abstract
Water homeostasis in the brain is essential for brain function. We have studied how aquaporin (AQP) 1 expression in GP8 immortalized rat brain microvascular endothelial cells is regulated by glucocorticoid. AQP1 protein level was raised by dexamethasone treatment in a time- and concentration-dependent manner. The up-regulation of AQP1 protein by dexamethasone was associated with an increase of AQP1 mRNA level, with no change in the degradation rate of AQP1 mRNA. AQP1 was concentrated in detergent-insoluble fractions in the cells treated with or without dexamethasone, suggesting that function/trafficking of AQP1 may be regulated via the interaction with lipid rafts. Since glucocorticoid therapy has well known beneficial effects in the treatment of brain edema, the induction of AQP1 by dexamethasone raises a possibility that AQP1 plays a role in ameliorating brain edema.
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Affiliation(s)
- Hideyuki Kobayashi
- Department of Pharmacology, Miyazaki Medical College, University of Miyazaki, 5200 Kihara, Kiyotake, Miyazaki 889-1692, Japan.
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468
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469
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Pérez E, Barrachina M, Rodríguez A, Torrejón-Escribano B, Boada M, Hernández I, Sánchez M, Ferrer I. Aquaporin expression in the cerebral cortex is increased at early stages of Alzheimer disease. Brain Res 2006; 1128:164-74. [PMID: 17123487 DOI: 10.1016/j.brainres.2006.09.109] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2006] [Revised: 09/23/2006] [Accepted: 09/26/2006] [Indexed: 12/21/2022]
Abstract
Abnormalities in the cerebral microvasculature are common in Alzheimer disease (AD). Expression levels of the water channels aquaporin 1 and aquaporin 4 (AQP1, AQP4) were examined in AD cases by gel electrophoresis and Western blotting, and densitometric values normalized with beta-actin were compared with corresponding values in age-matched controls processed in parallel. In addition, samples of cases with Pick disease (PiD) were examined for comparative purposes. A significant increase in the expression levels of AQP1 was observed in AD stage II (following Braak and Braak classification). Individual variations were seen in advanced stages which resulted in non-significant differences between AD stages V-VI and age-matched controls. No differences in AQP1 levels were observed between familial AD cases (FAD, all of them at advanced stages) and corresponding age-matched controls. Immunohistochemistry showed increased AQP1 in astrocytes at early stages of AD. Double-labelling immunofluorescence and confocal microscopy disclosed AQP1 immunoreactivity at the cell surface of astrocytes which were recognized with anti-glial fibrillary acidic protein antibodies. No differences in the levels of AQP4 were observed in AD, FAD and PiD when compared with corresponding controls. These results indicate abnormal expression of AQP1 in astrocytes in AD, and they add support to the idea that abnormal regulation of mechanisms involved in the control of water fluxes occurs at early stages in AD.
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Affiliation(s)
- Esther Pérez
- Institut de Neuropatologia, Servei Anatomia Patològica, Hospital Universitari de Bellvitge, carrer Feixa Llarga sn, 08907 Hospitalet de Llobregat, Spain
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470
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Rodríguez A, Pérez-Gracia E, Espinosa JC, Pumarola M, Torres JM, Ferrer I. Increased expression of water channel aquaporin 1 and aquaporin 4 in Creutzfeldt-Jakob disease and in bovine spongiform encephalopathy-infected bovine-PrP transgenic mice. Acta Neuropathol 2006; 112:573-85. [PMID: 16871401 DOI: 10.1007/s00401-006-0117-1] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2006] [Revised: 07/01/2006] [Accepted: 07/01/2006] [Indexed: 10/24/2022]
Abstract
Spongiform change is a cardinal feature in transmissible spongiform encephalopathies, including Creutzfeldt-Jakob disease (CJD) and bovine spongiform encephalopathy (BSE). It is characterized by swelling of the neuronal processes and vacuolization of the neuropil, leading to increased intraneuronal water content. The present study examines, by gel electrophoresis and Western blotting, the expression levels of the water channels aquaporin 1 (AQP1) and aquaporin 4 (AQP4) in the frontal cortex (area 8) homogenates of sporadic CJD cases (six men, four women; seven cases with methionine/methionine at codon 129 and PrP type 1; two cases with valine/valine at codon 129 and PrP type 2, and one case methionine/valine at codon 129 and PrP type 1) compared with age-matched controls, and cases with Alzheimer's disease (AD, stage VI of Braak and Braak) and diffuse Lewy body disease (DLB). AQP1 and AQP4 protein levels were also studied in the cerebral cortex of BSE-infected bovine-PrP transgenic mice (BoPrP-Tg110 mice) examined at 60, 150, 210 and 270 days post-inoculation (dpi) compared with healthy brain-inoculated control mice. Quantitative densitometry of AQP bands normalized for beta-actin was analyzed using Statgraphics plus 5.0 software from ANOVA and LSD statistical tests. Significant increased expression levels of AQP1 (as revealed with two different antibodies) and AQP4 were seen in CJD, but not in advanced AD and DLB cases when compared with controls. Immunohistochemistry revealed that AQP1 and AQP4 were expressed in astrocytes in diseased cases. No modifications in the expression levels of AQP1 and AQP4 were observed in BSE-infected bovine-PrP transgenic mice at 60, 150 and 210 dpi. However, a significant increase in the expression levels of AQP1 and AQP4 was found in mice at 270 dpi, the time corresponding with the appearance of PrP(res) immunoreactivity in Western blots and typical spongiform lesions in the brain. Together, these findings show increased expression of water channels in the brain in human and animal prion diseases. These modifications may have implications in the regulation of water transport in astrocytes and may account for an imbalance in water and ion homeostasis in prion diseases.
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Affiliation(s)
- Agustín Rodríguez
- Institut de Neuropatologia, Servei Anatomia Patològica, IDIBELL-Hospital Universitari de Bellvitge, Universitat de Barcelona, Hospitalet de Llobregat, Barcelona, Spain
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471
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Abstract
Epilepsy comprises a group of disorders characterized by the periodic occurrence of seizures, and pathologic specimens from patients with temporal lobe epilepsy demonstrate marked reactive gliosis. Since recent studies have implicated glial cells in novel physiological roles in the CNS, such as modulation of synaptic transmission, it is plausible that glial cells may have a functional role in the hyperexcitability characteristic of epilepsy. Indeed, alterations in distinct astrocyte membrane channels, receptors and transporters have all been associated with the epileptic state. This review integrates the current evidence regarding astroglial dysfunction in epilepsy and the potential underlying mechanisms of hyperexcitability. Functional understanding of the cellular and molecular alterations of astroglia-dependent hyperexcitability will help to clarify the physiological role of astrocytes in neural function as well as lead to the identification of novel therapeutic targets.
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Affiliation(s)
- Devin K Binder
- Department of Neurological Surgery, University of California, Irvine, Irvine, California, USA
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472
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Nesic O, Lee J, Ye Z, Unabia GC, Rafati D, Hulsebosch CE, Perez-Polo JR. Acute and chronic changes in aquaporin 4 expression after spinal cord injury. Neuroscience 2006; 143:779-92. [PMID: 17074445 PMCID: PMC1894918 DOI: 10.1016/j.neuroscience.2006.08.079] [Citation(s) in RCA: 119] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2006] [Revised: 08/17/2006] [Accepted: 08/30/2006] [Indexed: 01/03/2023]
Abstract
The effect of spinal cord injury (SCI) on the expression levels and distribution of water channel aquaporin 4 (AQP4) has not been studied. We have found AQP4 in gray and white matter astrocytes in both uninjured and injured rat spinal cords. AQP4 was detected in astrocytic processes that were tightly surrounding neurons and blood vessels, but more robustly in glia limitans externa and interna, which were forming an interface between spinal cord parenchyma and cerebrospinal fluid (CSF). Such spatial distribution of AQP4 suggests a critical role that astrocytes expressing AQP4 play in the transport of water from blood/CSF to spinal cord parenchyma and vice versa. SCI induced biphasic changes in astrocytic AQP4 levels, including its early down-regulation and subsequent persistent up-regulation. However, changes in AQP4 expression did not correlate well with the onset and magnitude of astrocytic activation, when measured as changes in GFAP expression levels. It appears that reactive astrocytes began expressing increased levels of AQP4 after migrating to the wound area (thoracic region) two weeks after SCI, and AQP4 remained significantly elevated for months after SCI. We also showed that increased levels of AQP4 spread away from the lesion site to cervical and lumbar segments, but only in chronically injured spinal cords. Although overall AQP4 expression levels increased in chronically-injured spinal cords, AQP4 immunolabeling in astrocytic processes forming glia limitans externa was decreased, which may indicate impaired water transport through glia limitans externa. Finally, we also showed that SCI-induced changes in AQP4 protein levels correlate, both temporally and spatially, with persistent increases in water content in acutely and chronically injured spinal cords. Although correlative, this finding suggests a possible link between AQP4 and impaired water transport/edema/syringomyelia in contused spinal cords.
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Affiliation(s)
- O Nesic
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, TX 77555-1072, USA.
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473
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Benfenati V, Nicchia GP, Svelto M, Rapisarda C, Frigeri A, Ferroni S. Functional down-regulation of volume-regulated anion channels in AQP4 knockdown cultured rat cortical astrocytes. J Neurochem 2006; 100:87-104. [PMID: 17064359 DOI: 10.1111/j.1471-4159.2006.04164.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In the brain, the astroglial syncytium is crucially involved in the regulation of water homeostasis. Accumulating evidence indicates that a dysregulation of the astrocytic processes controlling water homeostasis has a pathogenetic role in several brain injuries. Here, we have analysed by RNA interference technology the functional interactions occurring between the most abundant water channel in the brain, aquaporin-4 (AQP4), and the swelling-activated Cl(-) current expressed by cultured rat cortical astrocytes. We show that in primary cultured rat cortical astrocytes transfected with control small interfering RNA (siRNA), hypotonic shock promotes an increase in cellular volume accompanied by augmented membrane conductance mediated by volume-regulated anion channels (VRAC). Conversely, astroglia in which AQP4 was knocked down (AQP4 KD) by transfection with AQP4 siRNA changed their morphology from polygonal to process-bearing, and displayed normal cell swelling but reduced VRAC activity. Pharmacological manipulations of actin cytoskeleton in rat astrocytes, and functional analysis in mouse astroglial cells, which retain their morphology upon knockdown of AQP4, suggest that stellation of AQP4 KD rat cortical astrocytes was not causally linked to reduction of VRAC current. Molecular analysis of possible candidates of swelling-activated Cl(-) current provided evidence that in AQP4 KD astrocytes, there was a down-regulation of chloride channel-2 (CIC-2), which, however, was not involved in VRAC conductance. Inclusion of ATP in the intracellular saline restored VRAC activity upon hypotonicity. Collectively, these results support the view that in cultured astroglial cells, plasma membrane proteins involved in cell volume homeostasis are assembled in a functional platform.
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Affiliation(s)
- Valentina Benfenati
- Department of Human and General Physiology, University of Bologna, Bologna, Italy
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474
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Vitellaro-Zuccarello L, Bosisio P, Mazzetti S, Monti C, De Biasi S. Differential expression of several molecules of the extracellular matrix in functionally and developmentally distinct regions of rat spinal cord. Cell Tissue Res 2006; 327:433-47. [PMID: 17036229 DOI: 10.1007/s00441-006-0289-y] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2006] [Accepted: 06/16/2006] [Indexed: 12/22/2022]
Abstract
We have examined the regional distribution of several chondroitin sulfate proteoglycans (neurocan, brevican, versican, aggrecan, phosphacan), of their glycosaminoglycan moieties, and of tenascin-R in the spinal cord of adult rat. The relationships of these molecules with glial and neuronal populations, identified with appropriate markers, were investigated by using multiple fluorescence labeling combined with confocal microscopy. The results showed that the distribution of the examined molecules was similar at all spinal cord levels but displayed area-specific differences along the dorso-ventral axis, delimiting functionally and developmentally distinct areas. In the gray matter, laminae I and II lacked perineuronal nets (PNNs) of extracellular matrix and contained low levels of chondroitin sulfate glycosaminoglycans (CS-GAGs), brevican, and tenascin-R, possibly favoring the maintenance of local neuroplastic properties. Conversely, CS-GAGs, brevican, and phosphacan were abundant, with numerous thick PNNs, in laminae III-VIII and X. Motor neurons (lamina IX) were surrounded by PNNs that contained all molecules investigated but displayed various amounts of CS-GAGs. Double-labeling experiments showed that the presence of PNNs could not be unequivocally related to specific classes of neurons, such as motor neurons or interneurons identified by their expression of calcium-binding proteins (parvalbumin, calbindin, calretinin). However, a good correlation was found between PNNs rich in CS-GAGs and the neuronal expression of the Kv3.1b subunit of the potassium channel, a marker of fast-firing neurons. This observation confirms the correlation between the electrophysiological properties of these neurons and the specific composition of their microenvironment.
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Affiliation(s)
- Laura Vitellaro-Zuccarello
- Dip. Scienze Biomolecolari e Biotecnologie, Università degli Studi di Milano, Via Celoria 26, 20133 Milan, Italy.
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475
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Crewther SG, Liang H, Junghans BM, Crewther DP. Ionic control of ocular growth and refractive change. Proc Natl Acad Sci U S A 2006; 103:15663-8. [PMID: 17023537 PMCID: PMC1622878 DOI: 10.1073/pnas.0607241103] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The physiological mechanisms underlying the abnormal vitreal and ocular growth and myopic refractive errors induced under conditions of visual form deprivation in many animal species, including humans, are unknown. This study demonstrates, using energy dispersive x-ray microanalysis, a systematic pattern of changes in the elemental distribution of K, Na, and Cl across the entire retina in experimental form deprivation myopia and in the 5 days required for refractive normalization after occluder removal. In our report we link the ionic environment associated with physiological activity of the retina under a translucent occluder to refractive change and describe large but reversible environmentally driven increases in potassium, sodium, and chloride abundances in the neural retina. Our results are consistent with the notion of ionically driven fluid movements as the vector underlying the myopic increase in ocular size. New treatments for myopia, which currently affects nearly half of the human population, may result.
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Affiliation(s)
- Sheila G Crewther
- School of Psychological Science, La Trobe University, Melbourne VIC 3000, Australia.
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476
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Abstract
PURPOSE OF REVIEW Acute transverse myelitis is a pathogenetically heterogeneous inflammatory disorder of the spinal cord. Here we describe recent advances in inflammatory non-infectious transverse myelitis. Particular attention will be paid to the serum autoantibody marker NMO-IgG and its application to acute transverse myelitis. RECENT FINDINGS The recent identification of neuromyelitis optica-IgG, a novel marker of neuromyelitis optica spectrum disorders (including longitudinally extensive transverse myelitis), contributes to an evolving understanding of acute transverse myelitis. Other serological markers, such as collapsin response-mediator protein-5 -IgG and amphiphysin-IgG, predict specific cancers in the setting of a paraneoplastic acute transverse myelitis. Furthermore, novel inflammatory markers such as interleukin-6 or other proteins in their signaling pathways may represent markers of disease severity and potential therapeutic targets. Additional cerebrospinal fluid biomarkers, such as protein 14-3-3 and neuron-specific enolase, may be useful prognostic indicators in transverse myelitis. Acute transverse myelitis in children, in contrast to adults, is more likely to be longitudinally extensive, and has a better prognosis and lower likelihood of recurrence. Prognostic factors in pediatric transverse myelitis are reviewed. SUMMARY The recent identification of novel biomarkers associated with acute transverse myelitis has led to a better understanding of the spectrum of disorders associated with inflammatory transverse myelitis, as well as a greater appreciation of its diverse and complex pathogenetic basis.
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Affiliation(s)
- Sean J Pittock
- Department of Neurology, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA.
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477
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Hedfalk K, Törnroth-Horsefield S, Nyblom M, Johanson U, Kjellbom P, Neutze R. Aquaporin gating. Curr Opin Struct Biol 2006; 16:447-56. [PMID: 16837191 DOI: 10.1016/j.sbi.2006.06.009] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2006] [Revised: 06/02/2006] [Accepted: 06/27/2006] [Indexed: 10/24/2022]
Abstract
An acceleration in the rate at which new aquaporin structures are determined means that structural models are now available for mammalian AQP0, AQP1, AQP2 and AQP4, bacterial GlpF, AqpM and AQPZ, and the plant SoPIP2;1. With an apparent consensus emerging concerning the mechanism of selective water transport and proton extrusion, emphasis has shifted towards the issues of substrate selectivity and the mechanisms of aquaporin regulation. In particular, recently determined structures of plant SoPIP2;1, sheep and bovine AQP0, and Escherichia coli AQPZ provide new insights into the underlying structural mechanisms by which water transport rates are regulated in diverse organisms. From these results, two distinct pictures of 'capping' and 'pinching' have emerged to describe aquaporin gating.
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Affiliation(s)
- Kristina Hedfalk
- Chalmers University of Technology, Department of Chemistry and Bioscience, SE-405 30 Göteborg, Sweden
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478
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Egan JR, Butler TL, Au CG, Tan YM, North KN, Winlaw DS. Myocardial water handling and the role of aquaporins. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2006; 1758:1043-52. [PMID: 16876107 DOI: 10.1016/j.bbamem.2006.05.021] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2005] [Revised: 03/08/2006] [Accepted: 05/16/2006] [Indexed: 01/19/2023]
Abstract
Cardiac surgery is performed in approximately 770,000 adults and 30,000 children in the United States of America annually. In this review we outline the mechanistic links between post-operative myocardial stunning and the development of myocardial edema. These interrelated processes cause a decline in myocardial performance that account for significant morbidity and mortality after cardiac surgery. Factors leading to myocardial edema include hemodilution, ischemia and reperfusion as well as osmotic gradients arising from pathological change. Several members of the aquaporin family of water transport proteins have been described in the myocardium although their role in the pathogenesis and resolution of cardiac edema is not established. This review examines evidence for the involvement of aquaporins in myocardial water handling during normal and pathological conditions.
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Affiliation(s)
- Jonathan R Egan
- Kid's Heart Research, The Children's Hospital at Westmead, Sydney, Australia
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479
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Mack AF, Wolburg H. Growing axons in fish optic nerve are accompanied by astrocytes interconnected by tight junctions. Brain Res 2006; 1103:25-31. [PMID: 16814265 DOI: 10.1016/j.brainres.2006.04.135] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2005] [Revised: 03/23/2006] [Accepted: 04/30/2006] [Indexed: 11/19/2022]
Abstract
Mammalian astrocytes are in general interconnected by gap but not by tight junctions and play an ambiguous and controversially discussed role in central nervous system regeneration. At different neuroanatomical sites, fish astrocytes are interconnected by tight junctions and desmosomes and are involved in the successful regeneration of lesioned fiber tracts. In fish, newly generated retinal ganglion cells continuously grow new axons to the optic tectum but the interrelationship between glial tight junctions and axonal growth is undefined so far. We therefore investigated the occurrence of tight junctional structures and molecules within the ribbon-shaped optic nerve of a teleost fish (Astatotilapia burtoni) and found a predominant expression of zonula occludens protein-1 and claudin-1 in astrocytes where axons of new ganglion cells are assembled retinotopically within the optic nerve. This may support a previously formulated hypothesis according to that different properties of astrocytic membranes could be responsible for different glio-neuronal interactions which in turn may determine the micro-environmental conditions of growing axons.
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Affiliation(s)
- Andreas F Mack
- Institute of Anatomy, University of Tübingen, Osterbergstr. 3 72074 Tübingen, Germany.
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480
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Ribeiro MDC, Hirt L, Bogousslavsky J, Regli L, Badaut J. Time course of aquaporin expression after transient focal cerebral ischemia in mice. J Neurosci Res 2006; 83:1231-40. [PMID: 16511868 DOI: 10.1002/jnr.20819] [Citation(s) in RCA: 181] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Cerebral edema contributes to morbidity and mortality in stroke. Aquaporins (AQPs)-1, -4, and -9 have been identified as the three main water channels in the brain. To clarify their role in water movement, we have compared their expression patterns with brain swelling after transient focal brain ischemia. There were two peaks of maximal hemispheric swelling at 1 hr and at 48 hr after ischemia, coinciding with two peaks of AQP4 expression. At 1 hr after occlusion, AQP4 expression was significantly increased on astrocyte endfeet in the core and in the border of the lesion. At 48 hr, AQP4 expression was increased in astrocytes in the border of the lesion over the whole cell. AQP9 showed a significant induction at 24 hr that increased gradually with time, without correlation with the swelling. The expression of AQP1 remained unchanged. These results suggest that AQP4, but not AQP1 or AQP9, may play an important role in water movement associated with the pathophysiology of edema after transient cerebral ischemia in the mouse.
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481
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Hallene KL, Oby E, Lee BJ, Santaguida S, Bassanini S, Cipolla M, Marchi N, Hossain M, Battaglia G, Janigro D. Prenatal exposure to thalidomide, altered vasculogenesis, and CNS malformations. Neuroscience 2006; 142:267-83. [PMID: 16859833 PMCID: PMC3900293 DOI: 10.1016/j.neuroscience.2006.06.017] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2006] [Revised: 06/02/2006] [Accepted: 06/06/2006] [Indexed: 11/27/2022]
Abstract
Malformations of cortical development (MCD) result from abnormal neuronal positioning during corticogenesis. MCD are believed to be the morphological and perhaps physiological bases of several neurological diseases, spanning from mental retardation to autism and epilepsy. In view of the fact that during development, an appropriate blood supply is necessary to drive organogenesis in other organs, we hypothesized that vasculogenesis plays an important role in brain development and that E15 exposure in rats to the angiogenesis inhibitor thalidomide would cause postnatal MCD. Our results demonstrate that thalidomide inhibits angiogenesis in vitro at concentrations that result in significant morphological alterations in cortical and hippocampal regions of rats prenatally exposed to this vasculotoxin. Abnormal neuronal development was associated with vascular malformations and a leaky blood-brain barrier. Protein extravasation and uptake of fluorescent albumin by neurons, but not glia, was commonly associated with abnormal cortical development. Neuronal hyperexcitability was also a hallmark of these abnormal cortical regions. Our results suggest that prenatal vasculogenesis is required to support normal neuronal migration and maturation. Altering this process leads to failure of normal cerebrovascular development and may have a profound implication for CNS maturation.
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Affiliation(s)
- K. L. Hallene
- Department of Cerebrovascular Research, The Cleveland Clinic Foundation, Cleveland, OH, USA
- Department of Neurosurgery, The Cleveland Clinic Foundation, Cleveland, OH, USA
| | - E. Oby
- Department of Cerebrovascular Research, The Cleveland Clinic Foundation, Cleveland, OH, USA
- Department of Neurosurgery, The Cleveland Clinic Foundation, Cleveland, OH, USA
| | - B. J. Lee
- Department of Cerebrovascular Research, The Cleveland Clinic Foundation, Cleveland, OH, USA
| | - S. Santaguida
- Department of Cerebrovascular Research, The Cleveland Clinic Foundation, Cleveland, OH, USA
- Department of Neurosurgery, The Cleveland Clinic Foundation, Cleveland, OH, USA
| | - S. Bassanini
- Department of Cerebrovascular Research, The Cleveland Clinic Foundation, Cleveland, OH, USA
- Department of Experimental Neurophysiology, Neurological Institute “C. Besta,” Milano, Italy
| | - M. Cipolla
- Department of Neurology, The University of Vermont College of Medicine, Burlington, VT, USA
| | - N. Marchi
- Department of Cerebrovascular Research, The Cleveland Clinic Foundation, Cleveland, OH, USA
- Department of Neurosurgery, The Cleveland Clinic Foundation, Cleveland, OH, USA
| | - M. Hossain
- Department of Cerebrovascular Research, The Cleveland Clinic Foundation, Cleveland, OH, USA
- Department of Neurosurgery, The Cleveland Clinic Foundation, Cleveland, OH, USA
| | - G. Battaglia
- Department of Experimental Neurophysiology, Neurological Institute “C. Besta,” Milano, Italy
| | - D. Janigro
- Department of Cerebrovascular Research, The Cleveland Clinic Foundation, Cleveland, OH, USA
- Department of Molecular Medicine, The Cleveland Clinic Foundation, Cleveland, OH, USA
- Department of Neurosurgery, The Cleveland Clinic Foundation, Cleveland, OH, USA
- Correspondence to: D. Janigro, Cleveland Clinic Foundation, NB-20 LRI, 9500 Euclid Avenue, Cleveland, OH 44195, USA. Tel: +1-216-445-0561; fax: +1-216-445-1466. (D. Janigro)
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482
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Maier CM, Hsieh L, Crandall T, Narasimhan P, Chan PH. Evaluating therapeutic targets for reperfusion-related brain hemorrhage. Ann Neurol 2006; 59:929-38. [PMID: 16673393 DOI: 10.1002/ana.20850] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
OBJECTIVE Early reperfusion after an ischemic stroke can cause blood-brain barrier injury with subsequent cerebral edema and devastating brain hemorrhage. These complications of early reperfusion, which result from excess production of reactive oxygen species, significantly limit the benefits of stroke therapies. In this article, we use a novel animal model that facilitates identification of specific components of the reperfusion injury process, including vascular injury and secondary brain damage, and allows assessment of therapeutic interventions. METHODS Knock-out (KO) mice containing 50% manganese-superoxide dismutase activity (SOD2-KO) and transgenic mice overexpressing SOD2 undergo transient focal ischemia and reperfusion followed by assessment of infarct, edema, hemorrhage rates, metalloproteinase activation, and microvascular injury. RESULTS SOD2-KO mice demonstrate delayed (>24h) blood-brain barrier breakdown associated with activation of matrix metalloproteinases, inflammation, and high brain hemorrhage rates. These adverse consequences are absent in wild-type littermates and minocycline-treated SOD2-KO animals. Increased hemorrhage rates also are absent in SOD2 overexpressors, which have reduced vascular endothelial cell death. Finally, we show that the tight junction membrane protein, occludin, is an early and specific target in oxidative stress-induced microvascular injury. INTERPRETATION This model is ideal for studying ischemia/reperfusion-induced vascular injury and secondary brain hemorrhage and offers a unique opportunity to evaluate antioxidant-based neurovascular protective strategies as potential adjunct treatments to currently approved stroke therapies such as thrombolysis and endovascular clot retrieval.
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Affiliation(s)
- Carolina M Maier
- Department of Neurosurgery, Stanford University School of Medicine, Stanford, CA 94305-5487, USA
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483
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Abstract
Hydrocephalus is characterized by impaired cerebrospinal fluid (CSF) flow with enlargement of the ventricular cavities of the brain and progressive damage to surrounding tissue. Bulk water movement is altered in these brains. We hypothesized that increased expression of aquaporins, which are water-permeable channel proteins, would occur in these brains to facilitate water shifts. We used quantitative (real-time) RT-PCR, Western blotting and immunohistochemistry to evaluate the brain expression of aquaporins (AQP) 1, 4, and 9 mRNA and protein in Sprague-Dawley rats rendered hydrocephalic by injection of kaolin into cistern magna. AQP4 mRNA was significantly up-regulated in parietal cerebrum and hippocampus 4 weeks and 9 months after induction of hydrocephalus (P < 0.05). Although Western blot analysis showed no significant change, there was more intense perivascular AQP4 immunoreactivity in cerebrum of hydrocephalic brains at 3-4 weeks after induction. We did not detect mRNA or protein changes in AQP1 (located in choroid plexus) or AQP9 (located in select neuron populations). Kir4.1, a potassium channel protein linked to water flux, exhibited enhanced immunoreactivity in the cerebral cortex of hydrocephalic rats; the perineuronal distribution was entirely different from that of AQP4. These results suggest that brain AQP4 up-regulation might be a compensatory response to maintain water homeostasis in hydrocephalus.
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Affiliation(s)
- Xiaoyan Mao
- Department of Pathology, University of Manitoba, 715 McDermot Ave, Winnipeg MB, R3E 3P5 Canada
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484
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Binder DK, Yao X, Zador Z, Sick TJ, Verkman AS, Manley GT. Increased seizure duration and slowed potassium kinetics in mice lacking aquaporin-4 water channels. Glia 2006; 53:631-6. [PMID: 16470808 DOI: 10.1002/glia.20318] [Citation(s) in RCA: 268] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The glial water channel aquaporin-4 (AQP4) has been hypothesized to modulate water and potassium fluxes associated with neuronal activity. In this study, we examined the seizure phenotype of AQP4 -/- mice using in vivo electrical stimulation and electroencephalographic (EEG) recording. AQP4 -/- mice were found to have dramatically prolonged stimulation-evoked seizures after hippocampal stimulation compared to wild-type controls (33 +/- 2 s vs. 13 +/- 2 s). In addition, AQP4 -/- mice were found to have a higher seizure threshold (167 +/- 17 microA vs. 114 +/- 10 microA). To assess a potential effect of AQP4 on potassium kinetics, we used in vivo recording with potassium-sensitive microelectrodes after direct cortical stimulation. Although there was no significant difference in baseline or peak [K(+)](o), the rise time to peak [K(+)](o) (t(1/2), 2.3 +/- 0.5 s) as well as the recovery to baseline [K(+)](o) (t(1/2), 15.6 +/- 1.5 s) were slowed in AQP4 -/- mice compared to WT mice (t(1/2), 0.5 +/- 0.1 and 6.6 +/- 0.7 s, respectively). These results implicate AQP4 in the expression and termination of seizure activity and support the hypothesis that AQP4 is coupled to potassium homeostasis in vivo.
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Affiliation(s)
- Devin K Binder
- Department of Neurological Surgery, University of California, San Francisco, 94110, USA
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485
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Hansson E. Could chronic pain and spread of pain sensation be induced and maintained by glial activation? Acta Physiol (Oxf) 2006; 187:321-7. [PMID: 16734769 DOI: 10.1111/j.1748-1716.2006.01568.x] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
An injury often starts with acute physiological pain, which becomes inflammatory or neuropathic, and may sometimes become chronic. It has been proposed recently that activated glial cells, astrocytes and microglia within the central nervous system could maintain the pain sensation even after the original injury or inflammation has healed, and convert it into chronic by altering neuronal excitability. Glial cell activation has also been proposed to be involved in the phenomenon of spread of pain sensation ipsilaterally or to the contralateral side (i.e. mirror image pain). Substance P and calcitonin gene-related peptide, released due to an inflammatory process, interact with the endothelial cells of the blood-spinal cord and blood-brain barriers. The barriers open partially and substances may influence adjacent glial cells. Such substances are also released from neurones carrying the 'pain message' all the way from the injury to the cerebral cortex. Pro-inflammatory cytokines may be released from the microglial cells, and astroglial Ca2+-transients or oscillations may spread within the astroglial networks. One theory is that Ca2+-oscillations could facilitate the formation of new synapses. These new synapses could establish neuronal contacts for maintaining and spreading the pain sensation. If this theory holds true, it is possible that Ca2+ waves, production of cytokines and growth factors could be modified by selective anti-inflammatory drugs to achieve a balance in the activities of the different intercellular and intracellular processes. This paper reviews current knowledge about glial mechanisms underlying the phenomena of chronic pain and spread of the pain sensation.
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Affiliation(s)
- E Hansson
- Institute of Neuroscience and Physiology, Department of Clinical Neuroscience and Rehabilitation, The Sahlgrenska Academy at Göteborg University, Göteborg, Sweden.
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486
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Ben-Ari S, Toiber D, Sas AS, Soreq H, Ben-Shaul Y. Modulated splicing-associated gene expression in P19 cells expressing distinct acetylcholinesterase splice variants. J Neurochem 2006; 97 Suppl 1:24-34. [PMID: 16635247 DOI: 10.1111/j.1471-4159.2006.03725.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Alternative splicing configurations and acetylcholinesterase (AChE) gene expression are both modified in neurons under stress. However, it is unclear if these phenomena are functionally interrelated. Using a home-made spotted microarray focused on splicing-associated transcripts, we tested the effects of excess 3' splice variants of human AChE on splicing-related gene expression in semi-differentiated neuronal P19 cells. Of the tested transcripts, 17.3% and 20.2% showed modified expression levels (log2 of the ratio<-0.3 or>0.3) in transfected P19 cells overexpressing the stress-inducible AChE-R variant or the synaptic AChE-S protein, respectively. Multiple transcripts encoding serine-arginine rich (SR) and SR-related splicing regulators were suppressed in cells expressing either of these variants, whereas the gene groups including splicing-related helicases and transcripts involved in apoptosis displayed variant-specific changes. Our findings are compatible with the assumption that both neuronal overexpression and alternative splicing of pre-AChE mRNA may be causally involved in initiating global changes in neuronal alternative splicing, causing subsequent modifications in the expression patterns of numerous target genes.
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Affiliation(s)
- Shani Ben-Ari
- Department of Biological Chemistry and Israel Center for Neuronal Computation, The Hebrew University of Jerusalem, Jerusalem, Israel
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487
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Guo Q, Sayeed I, Baronne LM, Hoffman SW, Guennoun R, Stein DG. Progesterone administration modulates AQP4 expression and edema after traumatic brain injury in male rats. Exp Neurol 2006; 198:469-78. [PMID: 16445913 DOI: 10.1016/j.expneurol.2005.12.013] [Citation(s) in RCA: 154] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2005] [Revised: 10/28/2005] [Accepted: 12/14/2005] [Indexed: 10/25/2022]
Abstract
This study investigates whether progesterone administration regulates AQP4 and GFAP expression in rats with bilateral contusion injuries of the medial frontal cortex. Male rats were given 0 or 16 mg/kg injections of progesterone at 1, 6, 24, and 48 h post-injury. Brains were extracted at 24 h or 72 h post-injury and assayed for cerebral edema and AQP4 and GFAP expression using Western blot analysis. Progesterone treatments reduced brain water content significantly in the brain-injured groups. There was no significant change in AQP4 expression 24 h after progesterone treatment compared to lesion + vehicle animals. However, progesterone significantly reduced AQP4 expression at 72 h post-injury in the tissue bounded by the lateral ventricles and the peri-contusion areas compared to lesion+ vehicle rats, but increased AQP4 expression in the tissue surrounding the third ventricle. Also progesterone effects on GFAP expression varied according to brain region. Our results can be taken to show that the expression of AQP4 protein after TBI is time-dependent, region-specific, and possibly implicated in the formation and resolution of TBI-induced cerebral edema.
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Affiliation(s)
- Qingmin Guo
- Department of Emergency Medicine, Emory University, Atlanta, GA 30322, USA
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488
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Abbott NJ, Rönnbäck L, Hansson E. Astrocyte-endothelial interactions at the blood-brain barrier. Nat Rev Neurosci 2006; 7:41-53. [PMID: 16371949 DOI: 10.1038/nrn1824] [Citation(s) in RCA: 3646] [Impact Index Per Article: 202.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The blood-brain barrier, which is formed by the endothelial cells that line cerebral microvessels, has an important role in maintaining a precisely regulated microenvironment for reliable neuronal signalling. At present, there is great interest in the association of brain microvessels, astrocytes and neurons to form functional 'neurovascular units', and recent studies have highlighted the importance of brain endothelial cells in this modular organization. Here, we explore specific interactions between the brain endothelium, astrocytes and neurons that may regulate blood-brain barrier function. An understanding of how these interactions are disturbed in pathological conditions could lead to the development of new protective and restorative therapies.
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Affiliation(s)
- N Joan Abbott
- Wolfson Centre for Age-Related Diseases, King's College London, UK.
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489
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Aquaporins. Br J Pharmacol 2006. [DOI: 10.1038/sj.bjp.0706591] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
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490
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Goren O, Adorján I, Kálmán M. Heterogeneous occurrence of aquaporin-4 in the ependyma and in the circumventricular organs in rat and chicken. ACTA ACUST UNITED AC 2006; 211:155-72. [PMID: 16416308 DOI: 10.1007/s00429-005-0067-8] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/21/2005] [Indexed: 11/30/2022]
Abstract
Aquaporins are selective water channel proteins critical in volume homeostasis. In the CNS AQP4 predominates, localized mainly in the glia limitans, the perivascular endfeet and ependyma. The present immunofluorescent study reveals the distribution of aquaporin-4 in the circumventricular organs in rat and chicken brains. The ventricular ependyma (especially in the third one), the subfornical organ, the area postrema, the rat pineal body (in part), and the vascular organ of lamina terminalis were marked by intense immunopositivity. Several areas, however, proved to be immunonegative: the central canal, the subcommissural organ, the ependymal zone of the median eminence in rat but its whole thickness in chicken, the subtrochlear organ, and the paraventricular organ. The immunostaining of the lateral septal and subseptal organs were similar to their environment. Results on developing rats suggested that the aquaporin-4 immunonegativity is a secondary phenomenon. Surveying other structural and functional features, no clear explanation of the heterogeneous occurrence of aquaporin-4 was found. The absence of aquaporin-4 seems to correlate with some features of the "ependymal organs" (thickened, pseudostratified ependyma, presence of blood-brain barrier) and with the avoidance of GFAP. On the other hand, the organs rich in aquaporin-4 have features of the "hypendymal organs" (glial and vascular plexus but no blood-brain barrier). There are organs, however, which do not fit into either group completely, i.e. the lateral septal and subseptal organs. Presence of tight junctions coincides with the absence of aquaporin-4 in the ependyma of spinal cord, the subcommissural organ and the ependyma of median eminence.
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Affiliation(s)
- Oded Goren
- Department of Anatomy, Histology and Embryology, Semmelweis University of Medicine, Tuzoltó 58, 1094 Budapest, Hungary
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491
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Bragg AD, Amiry-Moghaddam M, Ottersen OP, Adams ME, Froehner SC. Assembly of a perivascular astrocyte protein scaffold at the mammalian blood–brain barrier is dependent on α-syntrophin. Glia 2006; 53:879-90. [PMID: 16609960 DOI: 10.1002/glia.20347] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
alpha-Syntrophin, a member of the dystrophin-associated protein complex, is required for proper localization of the water channel aquaporin-4 at the blood-brain barrier. Mice lacking alpha-syntrophin have reduced levels of aquaporin-4 in perivascular astroglial endfeet. Consequently, they exhibit reduced edema and infarct volume in brain trauma models and reduced K+ clearance from the neuropil, leading to increased seizure susceptibility. We have used the alpha-syntrophin null mice to investigate whether alpha-syntrophin is required for proper localization of other components of the dystrophin complex at the blood-brain barrier. We find that alpha-syntrophin is required for the full recruitment of gamma2-syntrophin and alpha-dystrobrevin-2 to glial endfeet in adult cerebellum. In contrast, the localization of beta1- and beta2-syntrophin and alpha-dystrobrevin-1 at the blood-brain barrier is not dependent on the presence of alpha-syntrophin. The localization patterns of alpha-dystrobrevin-1 and -2 in wild type cerebellum are strikingly different; while alpha-dystrobrevin-1 is present in glial endfeet throughout the cerebellum, alpha-dystrobrevin-2 is restricted to glial endfeet in the granular layer alone. Finally, we show that the enrichment of dystrophin in glial endfeet depends on the presence of alpha-syntrophin. This finding is the first demonstration that dystrophin localization is dependent on syntrophin. Since the localization of gamma2-syntrophin, alpha-dystrobrevin-2, and dystrophin is contingent on alpha-syntrophin, we conclude that alpha-syntrophin is a central organizer of the astrocyte dystrophin complex, an important molecular scaffold for localization of aquaporin-4 at the blood-brain barrier.
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Affiliation(s)
- April D Bragg
- Department of Physiology and Biophysics, Health Sciences Building, Rm G424, 1959 NE Pacific St, University of Washington, Seattle, 98195, USA.
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492
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Huynh GH, Deen DF, Szoka FC. Barriers to carrier mediated drug and gene delivery to brain tumors. J Control Release 2006; 110:236-259. [PMID: 16318895 DOI: 10.1016/j.jconrel.2005.09.053] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2005] [Accepted: 09/29/2005] [Indexed: 01/18/2023]
Abstract
Brain tumor patients face a poor prognosis despite significant advances in tumor imaging, neurosurgery and radiation therapy. Potent chemotherapeutic drugs fail when used to treat brain tumors because biochemical and physiological barriers limit drug delivery into the brain. In the past decade a number of strategies have been introduced to increase drug delivery into the brain parenchyma. In particular, direct drug administration into the brain tumor has shown promising results in both animal models and clinical trials. This technique is well suited for the delivery of liposome and polymer drug carriers, which have the potential to provide a sustained level of drug and to reach cellular targets with improved specificity. We will discuss the current approaches that have been used to increase drug delivery into the brain parenchyma in the context of fluid and solute transport into, through and from the brain, with a focus on liposome and polymer drug carriers.
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Affiliation(s)
- Grace H Huynh
- Joint Graduate Group in Bioengineering, University of California at San Francisco and Berkeley San Francisco, CA 94143-0446, United States
| | - Dennis F Deen
- Brain Tumor Research Center of the Department of Neurological Surgery, University of California at San Francisco, San Francisco, CA 94143-0520, United States
| | - Francis C Szoka
- Joint Graduate Group in Bioengineering, University of California at San Francisco and Berkeley San Francisco, CA 94143-0446, United States; Departments of Pharmaceutical Chemistry and Biopharmaceutical Sciences, University of California at San Francisco, San Francisco, CA 94143-0446, United States.
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493
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Binder DK, Yao X, Verkman AS, Manley GT. Increased seizure duration in mice lacking aquaporin-4 water channels. ACTA NEUROCHIRURGICA. SUPPLEMENT 2006; 96:389-92. [PMID: 16671491 DOI: 10.1007/3-211-30714-1_80] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Aquaporins are intrinsic membrane proteins involved in water transport in fluid-transporting tissues. In the brain, aquaporin-4 (AQP4) is expressed widely by glial cells, but its function is unclear. Extensive basic and clinical studies indicate that osmolarity affects seizure susceptibility, and in our previous studies we found that AQP4 -/- mice have an elevated seizure threshold in response to the chemoconvulsant pentylenetetrazol. In this study, we examined the seizure phenotype of AQP4 -/- mice in greater detail using in vivo electroencephalographic recording. AQP4 -/- mice were found to have dramatically longer stimulation-evoked seizures following hippocampal stimulation as well as a higher seizure threshold. These results implicate AQP4 in water and potassium regulation associated with neuronal activity and seizures.
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Affiliation(s)
- D K Binder
- Department of Neurological Surgery, University of California, San Francisco, CA 94110, USA
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494
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Hiroaki Y, Tani K, Kamegawa A, Gyobu N, Nishikawa K, Suzuki H, Walz T, Sasaki S, Mitsuoka K, Kimura K, Mizoguchi A, Fujiyoshi Y. Implications of the Aquaporin-4 Structure on Array Formation and Cell Adhesion. J Mol Biol 2006; 355:628-39. [PMID: 16325200 DOI: 10.1016/j.jmb.2005.10.081] [Citation(s) in RCA: 307] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2005] [Revised: 10/26/2005] [Accepted: 10/28/2005] [Indexed: 10/25/2022]
Abstract
Aquaporin-4 (AQP4) is the predominant water channel in the mammalian brain and an important drug target for treatment of cerebral edema, bipolar disorder and mesial temporal lobe epilepsy. We determined the AQP4 structure by electron crystallography of double-layered, two-dimensional (2D) crystals. The structure allows us to discuss how the expression ratio between the long and short AQP4 splicing variant can determine the size of in vivo orthogonal arrays. Furthermore, AQP4 contains a short 3(10) helix in an extracellular loop, which mediates weak but specific interactions between AQP4 molecules in adjoining membranes. This finding suggests a previously unexpected role for AQP4 in cell adhesion. This notion was corroborated by expression of AQP4 in L-cells, which resulted in clustering of the cells. Our AQP4 structure thus enables us to propose models for the size regulation of orthogonal arrays and channel-mediated cell adhesion.
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Affiliation(s)
- Yoko Hiroaki
- Department of Biophysics, Faculty of Science, Kyoto University, Kitashirakawa, Kyoto 606-8502, Japan
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495
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Abstract
It is now over 10 years ago that aquaporin 1 (AQP1) was discovered and cloned from the red blood cells, and in 2003 the Nobel price in Chemistry was awarded to Pr. Peter Agre for his work on AQPs, highlighting the importance of these proteins in life sciences. AQPs are water channels. To date this protein family is composed of 11 sub-types in mammalians. Three main AQPs described in the mammalian brain are AQP1, AQP4 and AQP9. Several recent studies have shown that these channels are implicated in numerous physiological functions. AQP1 has a role in cerebrospinal fluid formation, whereas AQP4 is involved in water homeostasis and extracellular osmotic pressure in brain parenchyma. AQP4 seems also to have an important function in oedema formation after brain trauma or brain ischemia. AQP9 is implicated in brain energy metabolism. The level of expression of each AQP is highly regulated. After a trauma or an ischemia perturbation of the central nervous system, the level of expression of each AQP is differentially modified, resulting in facilitating oedema formation. At present, the exact role of each AQP is not yet determined. A better understanding of the mechanisms of AQP regulation should permit the development of new pharmacological strategies to prevent oedema formation. AQP9 has been recently specifically detected in the catecholaminergic neurons of the brain. This new result strengthens the hypothesis that the AQPs are not only water channels, but that some AQPs may play a role in energy metabolism as metabolite channels.
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Affiliation(s)
- Céline F Guérin
- Groupe de recherche neurochirurgicale, Centre Hospitalier Universitaire Vaudois, Pavillon 3, Beaumont, 1011 Lausanne, Switzerland
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496
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Puwarawuttipanit W, Bragg AD, Frydenlund DS, Mylonakou MN, Nagelhus EA, Peters MF, Kotchabhakdi N, Adams ME, Froehner SC, Haug FM, Ottersen OP, Amiry-Moghaddam M. Differential effect of alpha-syntrophin knockout on aquaporin-4 and Kir4.1 expression in retinal macroglial cells in mice. Neuroscience 2005; 137:165-75. [PMID: 16257493 DOI: 10.1016/j.neuroscience.2005.08.051] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2005] [Revised: 07/04/2005] [Accepted: 08/07/2005] [Indexed: 11/20/2022]
Abstract
Aquaporin-4 water channels and the inwardly rectifying potassium channels Kir4.1 are coexpressed in a highly polarized manner at the perivascular and subvitreal endfeet of retinal Müller cells and astrocytes. The present study was aimed at resolving the anchoring mechanisms responsible for the coexpression of these molecules. Both aquaporin-4 and Kir4.1 contain PDZ-domain binding motifs at their C-termini and it was recently shown that mice with targeted disruption of the dystrophin gene display altered distribution of aquaporin-4 and Kir4.1 in the retina. To test our hypothesis that alpha-syntrophin (a PDZ-domain containing protein of the dystrophin associated protein complex) is involved in aquaporin-4 and Kir4.1 anchoring in retinal cells, we studied the expression pattern of these molecules in alpha-syntrophin null mice. Judged by quantitative immunogold cytochemistry, deletion of the alpha-syntrophin gene causes a partial loss (by 70%) of aquaporin-4 labeling at astrocyte and Müller cell endfeet but no decrease in Kir4.1 labeling at these sites. These findings suggest that alpha-syntrophin is not involved in the anchoring of Kir4.1 and only partly responsible for the anchoring of aquaporin-4 in retinal endfeet membranes. Furthermore we show that wild type and alpha-syntrophin null mice exhibit strong beta1 syntrophin labeling at perivascular and subvitreal Müller cell endfeet, raising the possibility that beta1 syntrophin might be involved in the anchoring of Kir4.1 and the alpha-syntrophin independent pool of aquaporin-4.
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Affiliation(s)
- W Puwarawuttipanit
- Centre for Molecular Biology and Neuroscience, and Nordic Centre for Water Imbalance Related Disorders, University of Oslo, P.O. Box 1105 Blindern, N-0317 Oslo, Norway
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497
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Benarroch EE. Neuron-astrocyte interactions: partnership for normal function and disease in the central nervous system. Mayo Clin Proc 2005; 80:1326-38. [PMID: 16212146 DOI: 10.4065/80.10.1326] [Citation(s) in RCA: 212] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Interactions between neurons and astrocytes are critical for signaling, energy metabolism, extracellular ion homeostasis, volume regulation, and neuroprotection in the central nervous system. Astrocytes face the synapses, send end-foot processes that enwrap the brain capillaries, and form an extensive network interconnected by gap junctions. Astrocytes express several membrane proteins and enzymes that are critical for uptake of glutamate at the synapses, ammonia detoxification, buffering of extracellular K+, and volume regulation. They also participate in detection, propagation, and modulation of excitatory synaptic signals, provide metabolic support to the active neurons, and contribute to functional hyperemia in the active brain tissue. Disturbances of these neuron-astrocyte interactions are likely to play an important role in neurologic disorders including cerebral ischemia, neurodegeneration, migraine, cerebral edema, and hepatic encephalopathy.
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Affiliation(s)
- Eduardo E Benarroch
- Department of Neurology, Mayo Clinic College of Medicine, 200 First St SW, Rochester, MN 55905, USA.
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498
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Stroman PW, Kornelsen J, Lawrence J, Malisza KL. Functional magnetic resonance imaging based on SEEP contrast: response function and anatomical specificity. Magn Reson Imaging 2005; 23:843-50. [PMID: 16275422 DOI: 10.1016/j.mri.2005.07.009] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2005] [Accepted: 07/07/2005] [Indexed: 12/01/2022]
Abstract
Functional magnetic resonance imaging based on a non-BOLD-contrast mechanism, which we have termed "SEEP" (Signal Enhancement by Extravascular water Protons), has previously been demonstrated. Here the reproducibility of areas of activity identified with both SEEP and BOLD contrast is assessed in duplicate experiments in healthy volunteers, with relatively high resolution (1.6 mm) image data at 1.5 T. These areas of activity are equally well localized to voxels containing primarily gray matter with the two contrast mechanisms. As in previous studies, areas of SEEP activity are observed to be immediately adjacent to areas of BOLD activity, with very little overlap. The response functions were estimated for both SEEP and BOLD contrast, and are observed to be distinct. The peak SEEP response is observed to lag the BOLD response by approximately 1 s and to decay more slowly with no poststimulus undershoot. Average BOLD signal changes (GE-EPI, TE=50 ms) were observed to be 3.4+/-1.2% (mean+/-S.D.), whereas SEEP signal changes (SE-EPI, TE=23 ms) were 1.9+/-0.5%, consistent with previous studies carried out at 0.2 and 3 T. These observations provide further support for the existence of a non-BOLD-contrast mechanism for fMRI, based on changes in extravascular spin density.
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Affiliation(s)
- Patrick W Stroman
- Department of Diagnostic Radiology, Queen's University, Kingston, Ontario, Canada K7L 2V7.
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499
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Quick AM, Cipolla MJ. Pregnancy-induced up-regulation of aquaporin-4 protein in brain and its role in eclampsia. FASEB J 2005; 19:170-5. [PMID: 15677340 DOI: 10.1096/fj.04-1901hyp] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Neurologic complications of eclampsia are thought to be similar to hypertensive encephalopathy in which an acute, excessive elevation in blood pressure causes blood-brain barrier (BBB) disruption and edema formation. Because women who develop eclampsia are in general normotensive and asymptomatic prior to pregnancy, we hypothesized that pregnancy alone predisposes the brain to edema formation by up-regulation of aquaporin 4 (AQP4), a water channel in the brain that has been shown to positively correlate with edema formation. To test this hypothesis, we compared localization (immunohistochemistry), mRNA (RT-PCR), and protein levels (Western analysis) of AQP4 in brains from Sprague Dawley rats that were nonpregnant (NP, proestrous), mid-pregnant (MP, days 9-10), late-pregnant (LP, days 19-20), and postpartum (PP, days 3-4). AQP4 mRNA was detected in the brains of all the animals and was localized primarily around the brain parenchymal blood vessels, strongly implicating its role in BBB function. Western analysis revealed that the major AQP4 band at approximately 32 kDa was significantly elevated in MP, LP, and PP animals compared with NP by 9-, 22-, and 17-fold, respectively. These results suggest that pregnancy and the postpartum state up-regulate AQP4 protein located around the intraparenchymal blood vessels, a consequence that could promote edema formation when blood pressure is acutely and excessively elevated, as during eclampsia.-Quick, A. M., Cipolla, M. J. Pregnancy-induced up-regulation of aquaporin-4 protein in brain and its role in eclampsia.
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Affiliation(s)
- Allison M Quick
- Department of Neurology, University of Vermont College of Medicine, Burlington, Vermont 05405, USA
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500
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Amiry-Moghaddam M, Lindland H, Zelenin S, Roberg BA, Gundersen BB, Petersen P, Rinvik E, Torgner IA, Ottersen OP. Brain mitochondria contain aquaporin water channels: evidence for the expression of a short AQP9 isoform in the inner mitochondrial membrane. FASEB J 2005; 19:1459-67. [PMID: 16126913 DOI: 10.1096/fj.04-3515com] [Citation(s) in RCA: 106] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Aquaporins are a family of water channels found in animals, plants, and microorganisms. A subfamily of aquaporins, the aquaglyceroporins, are permeable for water as well as certain solutes such as glycerol, lactate, and urea. Here we show that the brain contains two isoforms of AQP9--an aquaglyceroporin with a particularly broad substrate specificity--and that the more prevalent of these isoforms is expressed in brain mitochondria. The mitochondrial AQP9 isoform is detected as an approximately 25 kDa band in immunoblots. This isoform is likely to correspond to a new AQP9 mRNA that is obtained by alternative splicing and has a shorter ORF than the liver isoform. Subfractionation experiments and high-resolution immunogold analyses revealed that this novel AQP9 isoform is enriched in mitochondrial inner membranes. AQP9 immunopositive mitochondria occurred in astrocytes throughout the brain and in a subpopulation of neurons in the substantia nigra, ventral tegmental area, and arcuate nucleus. In the latter structures, the AQP9 immunopositive mitochondria were located in neurons that were also immunopositive for tyrosine hydroxylase, as demonstrated by double labeling immunogold electron microscopy. Our findings suggest that mitochondrial AQP9 is a hallmark of astrocytes and midbrain dopaminergic neurons. In physiological conditions, the flux of lactate and other metabolites through AQP9 may confer an advantage by allowing the mitochondria to adjust to the metabolic status of the extramitochondrial cytoplasm. We hypothesize that the complement of mitochondrial AQP9 in dopaminergic neurons may relate to the vulnerability of these neurons in Parkinson's disease.
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Affiliation(s)
- Mahmood Amiry-Moghaddam
- Centre for Molecular Biology and Neuroscience, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway.
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