Swelling-activated Ca2+ Entry via TRPV4 Channel Is Defective in Cystic Fibrosis Airway Epithelia

Abstract

The vertebrate transient receptor potential cationic channel TRPV4 has been proposed as an osmo-and mechanosensor channel. Studies using knock-out animal models have further emphasized the relevance of the TRPV4 channel in the maintenance of the internal osmotic equilibrium and mechanosensation. However, at the cellular level, there is still one important question to answer: does the TRPV4 channel generate the Ca 2؉ signal in those cells undergoing a Ca 2؉ -dependent regulatory volume decrease (RVD) response? RVD in human airway epithelia requires the generation of a Ca 2؉ signal to activate Ca 2؉ -dependent K ؉ channels. The RVD response is lost in airway epithelia affected with cystic fibrosis (CF), a disease caused by mutations in the cystic fibrosis transmembrane conductance regulator channel. We have previously shown that the defective RVD in CF epithelia is linked to the lack of swelling-dependent activation of Ca 2؉ -dependent K ؉ channels. In the present study, we show the expression of TRPV4 in normal human airway epithelia, where it functions as the Ca 2؉ entry pathway that triggers the RVD response after hypotonic stress, as demonstrated by TRPV4 antisense experiments. However, cell swelling failed to trigger Ca 2؉ entry via TRPV4 channels in CF airway epithelia, although the channel's response to a specific synthetic activator, 4␣-phorbol 12,13-didecanoate, was maintained. Furthermore, RVD was recovered in CF airway epithelia treated with 4␣-phorbol 12,13-didecanoate. Together, these results suggest that defective RVD in CF airway epithelia might be caused by the absence of a TRPV4-mediated Ca 2؉ signal and the subsequent activation of Ca 2؉ -dependent K ؉ channels.

TRPV4 channel participates in receptor-operated calcium entry and ciliary beat frequency regulation in mouse airway epithelial cells

“…We have shown that TRPV4 Ϫ/Ϫ cells, unlike TRPV4 ϩ/ϩ cells and cultured human airway epithelial cells (20,24,27), are unresponsive to 4␣PDD when measuring intracellular [Ca 2ϩ ]. The CBF response to 4␣PDD was also abrogated in TRPV4 Ϫ/Ϫ ciliated cells, providing evidence for the coupling of TRPV4 activity to the regulation of CBF.…”

“…TRPV4 can be also sensitized by coapplication of different stimuli (18)(19)(20) or participation of different cell signaling pathways (21). TRPV4 messenger and protein have been identified in both native ciliated epithelial cells of oviducts (21)(22)(23) and cell lines derived from human ciliated airway cells (24). In these epithelial cells, the TRPV4 channel plays a key role in cell volume homeostasis, by activating Ca 2ϩ -dependent K ϩ channels (25,26) and in the regulation of CBF, by providing a Ca 2ϩ entry pathway in response to changes in fluid viscosity or tonicity (21,22).…”

Phosphatidylinositol-4,5-biphosphate-dependent rearrangement of TRPV4 cytosolic tails enables channel activation by physiological stimuli

“…structure | regulation | thermosensitivity T he transient receptor potential vanilloid 4 (TRPV4) is a nonselective cation channel that responds to osmotic (1)(2)(3)(4), mechanical (5-7), and temperature stimulation (8), thereby contributing to many different physiological functions, including cellular (4,9) and systemic volume homeostasis (10), vasodilation (11,12), nociception (13), epithelial hydroelectrolyte transport (14), bladder voiding (15), ciliary beat frequency regulation (7,16,17), chondroprotection (18), and skeletal regulation (19). The osmotic (20) and mechanical (7,16) sensitivity of TRPV4 depends on the activation of phospholipase A 2 and subsequent production of the arachidonic acid metabolite 5′-6′-epoxyeicosatrienoic acid (EET), whereas the mechanism leading to temperature-mediated activation (observed only in intact cells) is not known at present (21).…”

Stimulus-specific Modulation of the Cation Channel TRPV4 by PACSIN 3

“…However, little is known about the mechanisms that regulate TRPV4 function in these different physiological settings, and it is unclear whether all known activation mechanisms are operating in every TRPV4-expressing cell. Heterologously expressed TRPV4 can be activated by a broad range of physical and chemical stimuli, including osmotic cell swelling (1,2,4,20,21), moderate heat (12,22), synthetic ligands stimuli as 4␣-phorbol 12,13-didecanoate (4␣-PDD) (13,23), mechanical force (14, 19, 24 -26), fluid viscosity (27), and endogenous ligands such as anandamide and arachidonic acid (AA)-derived epoxyeicosatrienoic acids (28 -30).…”