@misc{oai:ir.soken.ac.jp:00004093,
 author = {高山, 靖規 and タカヤマ, ヤスノリ and TAKAYAMA, Yasunori},
 month = {2016-02-26, 2016-02-17},
 note = {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., 総研大甲第1613号},
 title = {Functional linkage between TRPV4 and calcium-activated chloride channels in choroid plexus epithelial cells},
 year = {}
}