Cytokine and inflammatory mediator effects on TRPV4 function in choroid plexus epithelial cells

Abstract

The choroid plexus (CP), composed of capillaries surrounded by a barrier epithelium, is the main producer of cerebrospinal fluid (CSF). The CP epithelium regulates the transport of ions and water between the blood and the ventricles, contributing to CSF production and composition. Several studies suggest a connection between the cation channel transient receptor potential vanilloid-4 (TRPV4) and transepithelial ion movement. TRPV4 is a nonselective, calcium-permeable cation channel present in CP epithelia reported to be activated by cytokines and inflammatory mediators. Utilizing the PCP-R (porcine choroid plexus-Riems) cell line, we investigated the effects of various cytokines and inflammatory mediators on TRPV4-mediated activity. Select proinflammatory cytokines (TNF-α, IL-1β, TGF-β1) had inhibitory effects on TRPV4-stimulated transepithelial ion flux and permeability changes, whereas anti-inflammatory cytokines (IL-10, IL-4, and IL-6) had none. Quantitative mRNA analysis showed that these cytokines had no effect on TRPV4 transcription levels. Inhibition of the transcription factor NF-κB, involved in the production and regulation of several inflammatory cytokines, inhibited TRPV4-mediated activity, suggesting a link between TRPV4 and cytokine production. Contrary to published studies, the proinflammatory mediator arachidonic acid (AA) had inhibitory rather than stimulatory effects on TRPV4-mediated responses. However, inhibition of AA metabolism also caused inhibitory effects on TRPV4, suggesting a complex interaction of AA and its metabolites in the regulation of TRPV4 activity. Together these data imply that TRPV4 activity is involved in the inflammatory response; it is negatively affected by proinflammatory mediators. Furthermore, arachidonic acid metabolites, but not arachidonic acid itself, are positive regulators of TRPV4.

TRPV4 antagonists ameliorate ventriculomegaly in a rat model of hydrocephalus

“…In the Tmem67 -/genetic model of communicating hydrocephalus, we have shown that 2 different TRPV4 antagonists inhibit the development of ventriculomegaly. These data are in agreement with in vitro studies in cultured CP epithelia demonstrating that TRPV4 agonists stimulate a multiphasic transepithelial ion flux that can be inhibited by either of the 2 antagonists used in the current study (10)(11)(12). The mechanism of action and the role of TRPV4 in the development of hydrocephalus do not appear to be dependent on increased expression of the channel protein, suggesting that the mechanism is, rather, a change in cell surface expression and/or activation.…”

“…However, the nonselective nature of the channel allows for the transport of other cations, notably Na + (22). The changes in intracellular ion concentrations secondarily alter other channels and transporters leading to the transepithelial flux of both electrolytes and water (10,11,23). Figure 8A shows the effect of TRPV4 activation on the influx of Ca 2+ in freshly isolated CP from the rat model.…”

“…We are studying a potential hub protein, the transient receptor potential vanilloid 4 (TRPV4) channel, which is expressed in both native CP (9) and in a CP-derived cell line (10,11). Importantly, when TRPV4 is activated, it allows Ca 2+ and Na + to enter the cell, resulting in compensatory changes in both electrolyte and fluid movement across the epithelial monolayer.…”

TRPV4-Mediated Regulation of the Blood Brain Barrier Is Abolished During Inflammation

“…Of note, inflammatory cytokines abolished this effect and led to a downregulation of Trpv4 in MbMECs. Consistently, previous data showed that proinflammatory cytokines (e.g., TNF-α and IL-1β) had inhibitory effects on TRPV4-stimulated transepithelial ion flux and permeability changes in the choroid plexus, whereas antiinflammatory cytokines (e.g., IL-10 and IL-4) showed no effect (Simpson et al, 2019). However, in this study the cytokines reduced only the functional but not the transcriptional regulation of TRPV4.…”

This was the year that was: brain barriers and brain fluid research in 2019

“…Evidence suggests that inflammatory pathways at the choroid plexus regulate CSF secretion. Interestingly, Simpson et al [73] showed that cytokines and other inflammatory mediators regulate a non-selective cation channel, transient receptor potential vanilloid-4 (TRPV4), at the epithelium. There is some controversy about the role of the apically located Na + /K + /Cl −cotransporter (NKCC1) at the choroid plexus epithelium.…”