TRPV4 activation affects transepithelial ion transport in the choroid plexus epithelium
Authors: Preston Daniel , Simpson Stefanie , Schwerk Christian , Schroten Horst , Blazer‐Yost Bonnie 
Published: June 2021

Cerebrospinal fluid (CSF) is thought to be produced primarily by the Choroid Plexus (CP), which is found in the lateral, third and fourth ventricles of the brain. The CP is composed of a high resistance monolayer of ciliated cuboidal epithelial cells surrounding an underlying capillary network. The epithelium acts as a barrier, regulating the trafficking of small molecules, ions and water between the CSF and blood. Transient Receptor Potential Vanilloid‐4 (TRPV4) is a membrane‐bound cation channel expressed in a wide variety of tissues including the CP. TRPV4 is activated by various mechanisms including fluid sheer stress, temperature, hypotonicity, among others. When activated TRPV4 allows the influx of Ca2+, which can secondarily stimulate Ca2+‐activated ion channels. We utilized the high‐resistance porcine choroid plexus cell line (PCP‐R) for Ussing chamber electrophysiology studies of TRPV4 activation and its role in transepithelial ion transport. Treatment with GSK1016790A, a TRPV4 agonist, stimulated a change in short circuit current (SCC), consistent with either cation secretion or anion absorption. The two most likely families of channels responsible for this transepithelial ion movement are the Ca2+‐activated K+ channels, including the large, intermediate, and small conductance potassium channels (BK, IK, and SK1, SK2 and SK3, respectively) as well as Ca2+‐activated Cl− channels such as TMEM16A. Iberiotoxin, a specific inhibitor of the BK channel, did not have an effect on TRPV4‐mediated ion flux. We previously demonstrated that fluoxetine, a non‐specific inhibitor of all three SK channels, blocked the SCC produced in response to GSK1016790A. However, this effect was not replicated when Apamin was utilized at a concentration high enough to inhibit all three SK channels. High dose TRAM34, a specific inhibitor of IK also prevented GSK1016790A‐stimulated transepithelial ion transport. Treatment with T16Ainh‐a01, a TMEM16A‐specific inhibitor also prevented the short circuit current change observed with TRPV4 activation. RT‐PCR was used to determine the presence of channels in the PCP‐R cell line. Present were TRPV4, SK2, IK, and TMEM16A, while SK1, SK3, and BK were shown to be absent and verified using additional primers. Using a WPK rat model of hydrocephalus, we have also previously demonstrated that treatment with the TRPV4 antagonist RN‐1734 was capable of diminishing the ventriculomegaly associated with acute hydrocephalus. These data suggest that the TRPV4‐induced transepithelial ion flux is mediated by both Ca2+‐activated K+ channels as well as Ca2+‐activated Cl− channels. This further implies that TRPV4 may be involved in the control of CSF production. These data, provide intriguing new targets to explore in the treatment of hydrocephalus.Support or Funding InformationFunding: Hydrocephalus Association Innovator Award; Indiana University Collaborative Research Grant and Indiana Clinical and Translational Sciences Institute CTR Award.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.