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Snuggs JW, Tessier S, Bunning RAB, Shapiro IM, Risbud MV, Le Maitre CL. TonEBP regulates the hyperosmotic expression of aquaporin 1 and 5 in the intervertebral disc. Sci Rep 2021; 11:3164. [PMID: 33542263 PMCID: PMC7862284 DOI: 10.1038/s41598-021-81838-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2020] [Accepted: 12/22/2020] [Indexed: 01/30/2023] Open
Abstract
The central region of the intervertebral disc (IVD) is rich in proteoglycans, leading to a hyperosmotic environment, which fluctuates with daily loading. The cells of the nucleus pulposus (NP cells) have adapted to this environment via the function of tonicity enhancer binding protein (TonEBP), and NP cells have been shown to express several water channels known as aquaporins (AQP). We have previously shown that AQP1 and 5 decrease during IVD degeneration. Here, the regulation of AQP1 and 5 by hyperosmotic conditions and the role of TonEBP in this regulation was investigated. AQP1 and 5 gene expression was upregulated by hyperosmotic conditions mimicking the osmolality of the healthy IVD, which was abrogated by TonEBP knockdown. Furthermore, AQP1 and 5 immunopositivity was significantly reduced in TonEBPΔ/Δ E17.5 mice when compared with wildtype controls, indicating in vivo expression of AQP1 and 5 is controlled at least in part by TonEBP. This hyperosmotic regulation of AQP1 and 5 could help to explain the decreased AQP1 and 5 expression during degeneration, when the osmolality of the NP decreases. Together this data suggests that TonEBP-regulated osmo-adaptation may be disrupted during IVD degeneration when the expression of both AQPs is reduced.
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Affiliation(s)
- J. W. Snuggs
- grid.5884.10000 0001 0303 540XBiomolecular Sciences Research Centre, Sheffield Hallam University, City Campus, Howard Street, Sheffield, S1 1WB UK
| | - S. Tessier
- grid.265008.90000 0001 2166 5843Department of Orthopaedic Surgery, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, PA USA
| | - R. A. B. Bunning
- grid.5884.10000 0001 0303 540XBiomolecular Sciences Research Centre, Sheffield Hallam University, City Campus, Howard Street, Sheffield, S1 1WB UK
| | - I. M. Shapiro
- grid.265008.90000 0001 2166 5843Department of Orthopaedic Surgery, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, PA USA ,grid.265008.90000 0001 2166 5843Graduate Program in Cell Biology and Regenerative Medicine, Thomas Jefferson University, Philadelphia, PA USA
| | - M. V. Risbud
- grid.265008.90000 0001 2166 5843Department of Orthopaedic Surgery, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, PA USA ,grid.265008.90000 0001 2166 5843Graduate Program in Cell Biology and Regenerative Medicine, Thomas Jefferson University, Philadelphia, PA USA
| | - C. L. Le Maitre
- grid.5884.10000 0001 0303 540XBiomolecular Sciences Research Centre, Sheffield Hallam University, City Campus, Howard Street, Sheffield, S1 1WB UK
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Huckhagel T, Flitsch J, Rotermund R, Knospe V. Prevalence of Signs and Symptoms of Pseudotumor Cerebri Syndrome Before and After Transsphenoidal Surgery for Cushing's Disease - A Prospective Consecutive Case Series. Exp Clin Endocrinol Diabetes 2020; 129:465-472. [PMID: 32722820 DOI: 10.1055/a-1200-1528] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
INTRODUCTION Pseudotumor cerebri syndrome (PTCS) has anecdotally been described after successful treatment of Cushing's disease (CD), but the prevalence following transsphenoidal surgery has not been determined so far in a prospective study. PATIENTS AND METHODS 41 consecutive adult CD patients were prospectively screened for signs and symptoms of PTCS, headache-related impairment, and ophthalmological features associated with intracranial pressure elevation before surgery and at follow-up (mean 4 months). RESULTS Biochemical remission was achieved in 36 of 41 (87.8%) patients after surgery. The most frequent preoperative complaints were visual acuity impairment (19 cases; 46.3%), headache (13 cases; 31.7%), and ear noise (9 cases; 22.0%). A significant reduction of visual disturbances was seen at follow-up. Overall, CD patients presented with fairly low headache-related emotional and functional restrictions before and after surgery. One of 34 (2.9%) patients with sufficient ophthalmological follow-up showed new-onset papilledema combined with temporary worsening of visual acuity and scotoma. CONCLUSION Our results suggest a very low frequency of signs and symptoms of PTCS after surgical treatment for CD in adults. This estimate is in line with previous outcomes from retrospective pediatric CD series. Further large-scale studies are needed to determine the actual prevalence of this condition following biochemical remission of CD.
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Affiliation(s)
- Torge Huckhagel
- Department of Neurosurgery, Division of Pituitary Surgery, University Medical Center, Hamburg-Eppendorf, Germany.,Department of Diagnostic and Interventional Neuroradiology, University Medical Center, Göttingen, Germany
| | - Jörg Flitsch
- Department of Neurosurgery, Division of Pituitary Surgery, University Medical Center, Hamburg-Eppendorf, Germany
| | - Roman Rotermund
- Department of Neurosurgery, Division of Pituitary Surgery, University Medical Center, Hamburg-Eppendorf, Germany
| | - Volker Knospe
- Department of Ophthalmology, University Medical Center, Hamburg-Eppendorf, Germany
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Brace RA, Cheung CY. Regulation of Amniotic Fluid Volume: Evolving Concepts. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2014; 814:49-68. [DOI: 10.1007/978-1-4939-1031-1_5] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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Nabiuni M, Nazari Z, Safaeinejad Z, Delfan B, Miyan JA. Curcumin downregulates aquaporin-1 expression in cultured rat choroid plexus cells. J Med Food 2013; 16:504-10. [PMID: 23735000 DOI: 10.1089/jmf.2012.0208] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Aquaporin-1 (AQP1) is a water channel that is highly expressed on the apical side of the choroid plexus epithelium (CP) and thought to be one of the major pathways for the high water permeability of this structure. Blockade of AQP1 in the CP reduce the production of cerebrospinal fluid (CSF). Downregulation of AQP1 might be protective against some neurological disorders correlated with increased intracranial pressure and/or poor drainage of CSF. Curcumin, the major constituent of the rhizome of Curcuma longa, has been shown to inhibit potassium channels, Na⁺-K⁺ ATPase, as well as AQP3 in some cells. We therefore speculated that curcumin might be a useful tool to inhibit and/or decrease AQP1, and thus might be useful in the regulation of CSF production in pathophysiological conditions, including traumatic brain injury, hydrocephalus, stroke, systemic hyponatremia, acute cerebral edema, and hypertension. Choroidal epithelial cells of the lateral ventricle of Wistar rats were isolated and grown in in-vitro cultures for 24 h. Curcumin was then added to the medium at different concentrations, and the cell viability tested by the (3,4,5-dimethylthiazol-2-yl)-2-5-diphenyltetrazolium bromide assay. Additional wells of cells were tested for AQP1 protein expression using immunocytochemistry, immunoblotting, and flow cytometry. Our results showed that curcumin treatment decreases AQP1 expression in rat choroid epithelium cells in a dose-dependent manner. We conclude that curcumin may be a useful tool to regulate CSF production in pathophysiological conditions such as hydrocephalus, systemic hyponatremia, hypertension, and other neurological conditions.
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Affiliation(s)
- Mohammad Nabiuni
- Department of Cell and Molecular Biology, Faculty of Biological Sciences, Kharazmi University-TMU, Tehran, Iran
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Johanson CE, Stopa EG, McMillan PN. The blood-cerebrospinal fluid barrier: structure and functional significance. Methods Mol Biol 2011; 686:101-131. [PMID: 21082368 DOI: 10.1007/978-1-60761-938-3_4] [Citation(s) in RCA: 136] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The choroid plexus (CP) of the blood-CSF barrier (BCSFB) displays fundamentally different properties than blood-brain barrier (BBB). With brisk blood flow (10 × brain) and highly permeable capillaries, the human CP provides the CNS with a high turnover rate of fluid (∼400,000 μL/day) containing micronutrients, peptides, and hormones for neuronal networks. Renal-like basement membranes in microvessel walls and underneath the epithelium filter large proteins such as ferritin and immunoglobulins. Type IV collagen (α3, α4, and α5) in the subepithelial basement membrane confers kidney-like permselectivity. As in the glomerulus, so also in CP, the basolateral membrane utrophin A and colocalized dystrophin impart structural stability, transmembrane signaling, and ion/water homeostasis. Extensive infoldings of the plasma-facing basal labyrinth together with lush microvilli at the CSF-facing membrane afford surface area, as great as that at BBB, for epithelial solute and water exchange. CSF formation occurs by basolateral carrier-mediated uptake of Na+, Cl-, and HCO3-, followed by apical release via ion channel conductance and osmotic flow of water through AQP1 channels. Transcellular epithelial active transport and secretion are energized and channeled via a highly dense organelle network of mitochondria, endoplasmic reticulum, and Golgi; bleb formation occurs at the CSF surface. Claudin-2 in tight junctions helps to modulate the lower electrical resistance and greater permeability in CP than at BBB. Still, ratio analyses of influx coefficients (Kin) for radiolabeled solutes indicate that paracellular diffusion of small nonelectrolytes (e.g., urea and mannitol) through tight junctions is restricted; molecular sieving is proportional to solute size. Protein/peptide movement across BCSFB is greatly limited, occurring by paracellular leaks through incomplete tight junctions and low-capacity transcellular pinocytosis/exocytosis. Steady-state concentration ratios, CSF/plasma, ranging from 0.003 for IgG to 0.80 for urea, provide insight on plasma solute penetrability, barrier permeability, and CSF sink action to clear substances from CNS.
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Affiliation(s)
- Conrad E Johanson
- Department of Clinical Neuroscience, Alpert Medical School at Brown University, Providence, RI, USA
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Kurita T, Nakamura K, Tabuchi M, Orita M, Ooshima K, Higashino H. Effects of Gorei-san: A Traditional Japanese Kampo Medicine, on Aquaporin 1, 2, 3, 4 and V2R mRNA Expression in Rat Kidney and Forebrain. JOURNAL OF MEDICAL SCIENCES 2010. [DOI: 10.3923/jms.2011.30.38] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Zelenina M. Regulation of brain aquaporins. Neurochem Int 2010; 57:468-88. [DOI: 10.1016/j.neuint.2010.03.022] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2009] [Revised: 03/21/2010] [Accepted: 03/31/2010] [Indexed: 01/27/2023]
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Qi H, Li L, Zong W, Hyer BJ, Huang J. Expression of aquaporin 8 is diversely regulated by osmotic stress in amnion epithelial cells. J Obstet Gynaecol Res 2009; 35:1019-25. [DOI: 10.1111/j.1447-0756.2009.01061.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Close association of water channel AQP1 with amyloid-beta deposition in Alzheimer disease brains. Acta Neuropathol 2008; 116:247-60. [PMID: 18509662 PMCID: PMC2516196 DOI: 10.1007/s00401-008-0387-x] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2008] [Revised: 05/05/2008] [Accepted: 05/05/2008] [Indexed: 11/25/2022]
Abstract
Aquaporin-1 (AQP1), a membrane water channel protein, is expressed exclusively in the choroid plexus epithelium in the central nervous system under physiological conditions. However, AQP1 expression is enhanced in reactive astrocytes, accumulating in brain lesions of Creutzfeldt-Jakob disease and multiple sclerosis, suggesting a role of AQP1-expressing astrocytes in brain water homeostasis under pathological conditions. To clarify a pathological implication of AQP1 in Alzheimer disease (AD), we investigated the possible relationship between amyloid-beta (Aβ) deposition and astrocytic AQP1 expression in the motor cortex and hippocampus of 11 AD patients and 16 age-matched other neurological disease cases. In all cases, AQP1 was expressed exclusively in a subpopulation of multipolar fibrillary astrocytes. The great majority of AQP1-expressing astrocytes were located either on the top of or in close proximity to Aβ plaques in AD brains but not in non-AD cases, whereas those independent of Aβ deposition were found predominantly in non-AD brains. By Western blot, cultured human astrocytes constitutively expressed AQP1, and the levels of AQP1 protein expression were not affected by exposure to Aβ1-42 peptide, but were elevated by hypertonic sodium chloride. By immunoprecipitation, the C-terminal fragment-beta (CTFβ) of amyloid precursor protein interacted with the N-terminal half of AQP1 spanning the transmembrane helices H1, H2 and H3. These observations suggest the possible association of astrocytic AQP1 with Aβ deposition in AD brains.
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Johanson CE, Duncan JA, Klinge PM, Brinker T, Stopa EG, Silverberg GD. Multiplicity of cerebrospinal fluid functions: New challenges in health and disease. Cerebrospinal Fluid Res 2008; 5:10. [PMID: 18479516 PMCID: PMC2412840 DOI: 10.1186/1743-8454-5-10] [Citation(s) in RCA: 515] [Impact Index Per Article: 32.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2007] [Accepted: 05/14/2008] [Indexed: 11/10/2022] Open
Abstract
UNLABELLED This review integrates eight aspects of cerebrospinal fluid (CSF) circulatory dynamics: formation rate, pressure, flow, volume, turnover rate, composition, recycling and reabsorption. Novel ways to modulate CSF formation emanate from recent analyses of choroid plexus transcription factors (E2F5), ion transporters (NaHCO3 cotransport), transport enzymes (isoforms of carbonic anhydrase), aquaporin 1 regulation, and plasticity of receptors for fluid-regulating neuropeptides. A greater appreciation of CSF pressure (CSFP) is being generated by fresh insights on peptidergic regulatory servomechanisms, the role of dysfunctional ependyma and circumventricular organs in causing congenital hydrocephalus, and the clinical use of algorithms to delineate CSFP waveforms for diagnostic and prognostic utility. Increasing attention focuses on CSF flow: how it impacts cerebral metabolism and hemodynamics, neural stem cell progression in the subventricular zone, and catabolite/peptide clearance from the CNS. The pathophysiological significance of changes in CSF volume is assessed from the respective viewpoints of hemodynamics (choroid plexus blood flow and pulsatility), hydrodynamics (choroidal hypo- and hypersecretion) and neuroendocrine factors (i.e., coordinated regulation by atrial natriuretic peptide, arginine vasopressin and basic fibroblast growth factor). In aging, normal pressure hydrocephalus and Alzheimer's disease, the expanding CSF space reduces the CSF turnover rate, thus compromising the CSF sink action to clear harmful metabolites (e.g., amyloid) from the CNS. Dwindling CSF dynamics greatly harms the interstitial environment of neurons. Accordingly the altered CSF composition in neurodegenerative diseases and senescence, because of adverse effects on neural processes and cognition, needs more effective clinical management. CSF recycling between subarachnoid space, brain and ventricles promotes interstitial fluid (ISF) convection with both trophic and excretory benefits. Finally, CSF reabsorption via multiple pathways (olfactory and spinal arachnoidal bulk flow) is likely complemented by fluid clearance across capillary walls (aquaporin 4) and arachnoid villi when CSFP and fluid retention are markedly elevated. A model is presented that links CSF and ISF homeostasis to coordinated fluxes of water and solutes at both the blood-CSF and blood-brain transport interfaces. OUTLINE 1 Overview2 CSF formation2.1 Transcription factors2.2 Ion transporters2.3 Enzymes that modulate transport2.4 Aquaporins or water channels2.5 Receptors for neuropeptides3 CSF pressure3.1 Servomechanism regulatory hypothesis3.2 Ontogeny of CSF pressure generation3.3 Congenital hydrocephalus and periventricular regions3.4 Brain response to elevated CSF pressure3.5 Advances in measuring CSF waveforms4 CSF flow4.1 CSF flow and brain metabolism4.2 Flow effects on fetal germinal matrix4.3 Decreasing CSF flow in aging CNS4.4 Refinement of non-invasive flow measurements5 CSF volume5.1 Hemodynamic factors5.2 Hydrodynamic factors5.3 Neuroendocrine factors6 CSF turnover rate6.1 Adverse effect of ventriculomegaly6.2 Attenuated CSF sink action7 CSF composition7.1 Kidney-like action of CP-CSF system7.2 Altered CSF biochemistry in aging and disease7.3 Importance of clearance transport7.4 Therapeutic manipulation of composition8 CSF recycling in relation to ISF dynamics8.1 CSF exchange with brain interstitium8.2 Components of ISF movement in brain8.3 Compromised ISF/CSF dynamics and amyloid retention9 CSF reabsorption9.1 Arachnoidal outflow resistance9.2 Arachnoid villi vs. olfactory drainage routes9.3 Fluid reabsorption along spinal nerves9.4 Reabsorption across capillary aquaporin channels10 Developing translationally effective models for restoring CSF balance11 Conclusion.
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Affiliation(s)
- Conrad E Johanson
- Department of Clinical Neurosciences, Warren Alpert Medical School at Brown University, Providence, RI 02903, USA
| | - John A Duncan
- Department of Clinical Neurosciences, Warren Alpert Medical School at Brown University, Providence, RI 02903, USA
| | - Petra M Klinge
- International Neuroscience Institute Hannover, Rudolph-Pichlmayr-Str. 4, 30625 Hannover, Germany
| | - Thomas Brinker
- International Neuroscience Institute Hannover, Rudolph-Pichlmayr-Str. 4, 30625 Hannover, Germany
| | - Edward G Stopa
- Department of Clinical Neurosciences, Warren Alpert Medical School at Brown University, Providence, RI 02903, USA
| | - Gerald D Silverberg
- Department of Clinical Neurosciences, Warren Alpert Medical School at Brown University, Providence, RI 02903, USA
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Carpenter J, Weinstein S, Myseros J, Vezina G, Bell MJ. Inadvertent hyponatremia leading to acute cerebral edema and early evidence of herniation. Neurocrit Care 2007; 6:195-9. [PMID: 17572863 DOI: 10.1007/s12028-007-0032-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
INTRODUCTION For years, the maintenance of normal or supranormal serum sodium (Na) concentrations has been believed to be beneficial in brain injuries. Recently published guidelines for cerebral trauma recommend the use of hypertonic saline to achieve hypernatremia for the management of increased intracranial pressure and these standards are generally practiced across most diseases in neurocritical care including stroke, hemorrhage and tumors. Severe hyponatremia has long been known to be detrimental, but objective evidence for the harm of mild hyponatremia as a secondary injury has been scarce. DESCRIPTION OF CASE In this case report, we describe a child with aneurysmal subarachnoid hemorrhage who had a sudden, inadvertent decrease in serum Na (128 meq/l) that was associated with a deterioration of her neurological examination and evidence of early transtentorial herniation on emergent brain CT scan. These findings were quickly reversed after the serum Na was corrected. DISCUSSION This report emphasizes that close monitoring of serum Na and osmolarity in acute head injured children is important, and provides evidence that alterations of these parameters is a substantial risk for cerebral edema in children with evolving brain injuries and briefly reviews the literature regarding the risks of hyponatremia in children.
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Affiliation(s)
- Jessica Carpenter
- Department of Neurology, Children's Research Institute, Children's National Medical Center, Washington, DC, USA.
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Satoh JI, Tabunoki H, Yamamura T, Arima K, Konno H. Human astrocytes express aquaporin-1 and aquaporin-4 in vitro and in vivo. Neuropathology 2007; 27:245-56. [PMID: 17645239 DOI: 10.1111/j.1440-1789.2007.00774.x] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Aquaporins (AQP) constitute an evolutionarily conserved family of integral membrane water transport channel proteins. Previous studies indicate that AQP1 is expressed exclusively in the choroid plexus epithelium, while AQP4 is localized on the vascular foot of astrocytes in the central nervous system (CNS) under physiological conditions. To investigate a role of AQP in the pathophysiology of neurological diseases involving astrogliosis we studied the expression of AQP1 and AQP4 in cultured human astrocytes and brain tissues of multiple sclerosis (MS), cerebral infarction and control cases. By reverse transcriptasepolymerase chain reaction and western blot analysis, cultured human astrocytes co-expressed both AQP1 and AQP4 mRNA and proteins, where AQP4 levels were elevated by exposure to interferon-gamma but neither by tumor necrosis factor-alpha nor interleukin-1beta, whereas AQP1 levels were unaffected by any of the cytokines examined. By western blot analysis, AQP1 and AQP4 proteins were detected in the brain homogenates of the MS and non-MS cases, where both levels were correlated with those of glial fibrillary acid protein. By immunohistochemistry, astrocytes with highly branched processes surrounding blood vessels, along with glial scar, expressed intensely AQP1 and AQP4 in MS and ischemic brain lesions, whereas neither macrophages, neurons nor oligodendrocyte cell bodies were immunopositive. These immunohistochemical results indicate that the expression not only of AQP4 but also of AQP1 was enhanced in MS and ischemic brain lesions located predominantly in astrocytes, suggesting a pivotal role of astrocytic AQP in the maintenance of water homeostasis in the CNS under pathological conditions.
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Affiliation(s)
- Jun-ichi Satoh
- Department of Bioinformatics, Meiji Pharmaceutical University, 2-522-1 Noshio, Kiyose, Tokyo 204-8588, Japan.
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Praetorius J. Water and solute secretion by the choroid plexus. Pflugers Arch 2006; 454:1-18. [PMID: 17120021 DOI: 10.1007/s00424-006-0170-6] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2006] [Accepted: 09/12/2006] [Indexed: 12/23/2022]
Abstract
The cerebrospinal fluid (CSF) provides mechanical and chemical protection of the brain and spinal cord. This review focusses on the contribution of the choroid plexus epithelium to the water and salt homeostasis of the CSF, i.e. the secretory processes involved in CSF formation. The choroid plexus epithelium is situated in the ventricular system and is believed to be the major site of CSF production. Numerous studies have identified transport processes involved in this secretion, and recently, the underlying molecular background for some of the mechanisms have emerged. The nascent CSF consists mainly of NaCl and NaHCO(3), and the production rate is strictly coupled to the rate of Na(+) secretion. In contrast to other secreting epithelia, Na(+) is actively pumped across the luminal surface by the Na(+),K(+)-ATPase with possible contributions by other Na(+) transporters, e.g. the luminal Na(+),K(+),2Cl(-) cotransporter. The Cl(-) and HCO(3) (-) ions are likely transported by a luminal cAMP activated inward rectified anion conductance, although the responsible proteins have not been identified. Whereas Cl(-) most likely enters the cells through anion exchange, the functional as well as the molecular basis for the basolateral Na(+) entry are not yet well-defined. Water molecules follow across the epithelium mainly through the water channel, AQP1, driven by the created ionic gradient. In this article, the implications of the recent findings for the current model of CSF secretion are discussed. Finally, the clinical implications and the prospects of future advances in understanding CSF production are briefly outlined.
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Affiliation(s)
- Jeppe Praetorius
- The Water and Salt Research Center & Institute of Anatomy, University of Aarhus, Wilhelm Meyers Allé, 8000 Aarhus, Denmark.
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