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Functional linkage between TRPV4 and calcium-activated chloride channels in choroid plexus epithelial cells
https://ir.soken.ac.jp/records/4093
https://ir.soken.ac.jp/records/40931a17ddc1-6be1-4852-aa4b-8980f5c01de6
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要旨・審査要旨 (358.8 kB)
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本文 (9.3 MB)
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| Item type | 学位論文 / Thesis or Dissertation(1) | |||||
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| 公開日 | 2013-11-26 | |||||
| タイトル | ||||||
| タイトル | Functional linkage between TRPV4 and calcium-activated chloride channels in choroid plexus epithelial cells | |||||
| タイトル | ||||||
| タイトル | Functional linkage between TRPV4 and calcium-activated chloride channels in choroid plexus epithelial cells | |||||
| 言語 | en | |||||
| 言語 | ||||||
| 言語 | eng | |||||
| 資源タイプ | ||||||
| 資源タイプ識別子 | http://purl.org/coar/resource_type/c_46ec | |||||
| 資源タイプ | thesis | |||||
| 著者名 |
高山, 靖規
× 高山, 靖規 |
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| フリガナ |
タカヤマ, ヤスノリ
× タカヤマ, ヤスノリ |
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| 著者 |
TAKAYAMA, Yasunori
× TAKAYAMA, Yasunori |
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| 学位授与機関 | ||||||
| 学位授与機関名 | 総合研究大学院大学 | |||||
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| 学位名 | 博士（理学） | |||||
| 学位記番号 | ||||||
| 内容記述タイプ | Other | |||||
| 内容記述 | 総研大甲第1613号 | |||||
| 研究科 | ||||||
| 値 | 生命科学研究科 | |||||
| 専攻 | ||||||
| 値 | 20 生理科学専攻 | |||||
| 学位授与年月日 | ||||||
| 学位授与年月日 | 2013-03-22 | |||||
| 学位授与年度 | ||||||
| 値 | 2012 | |||||
| 要旨 | ||||||
| 内容記述タイプ | Other | |||||
| 内容記述 | Transient receptor potential vanilloid 4 (TRPV4) is a non-selective cation channel known to be a sensor for hypo-osmolality, cell swelling, warm temperatures and some chemical compounds. Furthermore, the physiological significance of TRPV4 has attracted a great deal of attention, particularly its heat-sensitive properties. Previous reports showed the physiological functions of TRPV4 in several cell types, including skin, esophageal keratinocytes and hippocampal neurons. For instance, TRPV4 expressed in skin keratinocytes contributes to the enhancement of the skin barrier function at body temperature. Moreover, the release of ATP from esophageal keratinocytes or bladder epithelium is enhanced by extension-mediated TRPV4 activation. Additionally, neural activity increases with a rise in temperature in hippocampal neurons. However, the precise function of TRPV4 in the brain is still unknown except for regulation of neural activity in the hippocampus. In this study, the highest expression of TRPV4 in choroid plexus epithelial cells (CPECs) was found using in situ hybridization, immunohistochemistry and EGFP expression in transgenic mice in which EGFP was expressed in TRPV4-positive cells. In addition, calcium-activated chloride currents were observed for the first time in CPECs. Moreover, expression of anoctamin 1 (Ano1), Ano4, Ano6 and Ano10 genes in the choroid plexus was found by RT-PCR. These data suggest that upon TRPV4 activation, calcium entering CPECs enhances production of cerebrospinal fluid (CSF), a process dependent upon ion transports. To investigate this hypothesis, whole-cell patch-clamp recordings in HEK293T cells were performed. ANO1-mediated chloride currents were dramatically increased in HEK293T cells expressing mouse TRPV4 and mouse ANO1 when TRPV4 was activated by a low concentration of GSK1016790A (GSK). In contrast, the GSK-induced chloride currents were not significantly affected in the cells expressing ANO4, ANO6 or ANO10 with TRPV4. Additionally, the GSK-induced chloride currents in the cells expressing ANO1 and TRPV4 were not observed in the absence of extracellular calcium. These results indicated that chloride efflux through ANO1 depended on TRPV4 activity. Similar GSK-induced chloride currents were observed in CPECs isolated from the lateral and the fourth ventricle choroid plexus. Interestingly, the GSK-induced chloride currents were strongly inhibited by an ANO1/ANO2 blocker, T16Ainh-A01 (A01), and ANO2 expression was not suggested in choroid plexus. These results indicated a functional linkage between TRPV4 and ANO1 in CPECs. This is the first reported case of the linkage of these two proteins in native cells. It was recently reported that ANO1 is activated by noxious heat. In the author’s study, ANO1 was activated by heat in the range of body temperature. Heat-evoked chloride currents were also observed in CPECs isolated from wild-type (WT) and TRPV4-deficient (TRPV4KO) mice. Furthermore, heat-evoked currents were drastically enhanced after GSK application in WT, but not in TRPV4KO CPECs. These results indicated the possibility that heat-sensitivity of ANO1 is enhanced by TRPV4 activation in CPECs. However, the enhanced currents were not completely blocked by A01. Thus, the possibility of another heat-activated chloride channels also was suggested in CPECs. Accordingly, the author proposes a concept that functional linkage between TRPV4 and ANO1 enhances CSF production. First, the apical membrane of CPECs is extended by water influx from the basolateral side. Second, phospholipase A2 (PLA2) activity is increased by the extension of the plasma membrane and arachidonic acid is produced from phospholipids by the activated PLA2. Then, arachidonic acid is metabolized to epoxyeicosatrienoic acid (EET) by cytochrome P450 epoxygenase activity, and TRPV4 is activated by EET at body temperature. The TRPV4 activation leads to calcium influx, which in turn leads to ANO1 activation at body temperature. Finally, water efflux from CPECs is driven by efflux of chloride and some cations through a Donnan equilibrium. Production, transport and reabsorption of CSF are important for the maintenance of the brain environment in fetuses and adults. Among the three CSF-related events, the principle role of CPECs is CSF production. CSF transport is controlled by ependymal cells and the reabsorption is done by arachnoid granulation to the dural venous sinuses. Dysfunction of ciliary motility and the failure of cilia development of ependymal cells induce severe hydrocephalus. This indicates that CSF is continuously secreted from CPECs and the production is independent of the changes in brain pressure. There are currently only palliative therapies for hydrocephalus including external ventricular drainage or placement of a surgical shunt. Control of CSF production through regulation of TRPV4 activity could allow a safer way to treat those diseases. Thus, these studies suggest a fundamental new therapy for hydrocephalus caused by choroid plexus cysts and choroid plexus papillomas. |
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| 値 | 有 | |||||
