TRPV4-Mediated Calcium Influx and Ciliary Activity in Human Native Airway Epithelial Cells

Abstract

The transient receptor potential vanilloid 4 (TRPV4) is a calcium permeable ion channel expressed in airway epithelial cells. Based on studies of cell lines and animals, TRPV4 has been suggested to play a role in the regulation of ciliary beat frequency (CBF). Whether the same is true for human ciliated epithelial cells is not known. Therefore, the aim was to examine the expression and function of TRPV4 in human native nasal epithelial cells. Expression of TRPV4 mRNA in nasal epithelial cells and in the cell lines BEAS2B and 16HBE was confirmed by quantitative real-time PCR. A marked apical TRPV4 immunoreactivity was observed in nasal epithelial cells using immunocytochemistry. Responses to pharmacological modulation of TRPV4 were assessed with calcium imaging and CBF measurements. The TRPV4 agonist GSK1016790A produced concentration-dependent calcium responses in TRPV4-expressing HEK293, BEAS2B and 16HBE cells, and the TRPV4 antagonist HC067047 caused a rightward shift of the GSK1016790A concentration-response curves. Nasal epithelial cells responded to the TRPV4 agonist GSK1016790A with increased intracellular calcium signals and increased CBF, followed by cessation of ciliary beating and cell death. These effects were prevented or inhibited by the TRPV4 antagonist HC067047, the TRP channel blocker ruthenium red or removal of extracellular calcium. We conclude that TRPV4 is expressed in human primary nasal epithelial cells and modulates epithelial calcium levels and CBF. Thus, TRPV4 may participate in mucociliary clearance and airway protection. However, exaggerated activation of TRPV4 may result in epithelial cell death.TRPV4 is a widely expressed TRP ion channel that functions as a calcium entry channel upon activation by diverse stimuli, including hypotonicity, innocuous heat, the synthetic ligand 4alpha-phorbol 12,13-didecanoate (4a-PDD), and endogenous metabolites of arachidonic acid [1][2][3][4]. In the human airways, TRPV4 expression has been shown in the epithelium of trachea and lung, including serous cells of submucosal glands [5]. TRPV4 expression has also been demonstrated in human sinus mucosa with increased levels in chronic rhinosinusitis [6].The airway epithelium is constantly exposed to fluctuations in extracellular osmolarity and mechanical respiratory efforts, and needs to be equipped with compensatory mechanisms. In line with this, expression of TRPV4 in a human bronchial epithelial cell line was suggested to detect hypotonic conditions and play a role in cellular volume regulation through potassium efflux due to activation of calcium-activated potassium channels [7,8]. TRPV4 activation has also been shown to decrease activity of aquaporin-5, a water channel located in the apical cell membrane, under hypotonic conditions in mouse lung epithelial cells and when expressed in human embryonal kidney (HEK) 293 cells [9]. Decreased aquaporin-5 activity in response to TRPV4-mediated calcium influx was proposed to enhance epithelial barrier function in response to hypotonic conditions or ...

Recent Advances in Lipopolysaccharide Recognition Systems

“…This suggests involvement of TRPV1 in sensing LPS and neurogenic inflammation [85]. Moreover, using recombinant TRP expression in HEK293T cells, Alenmyr and colleagues demonstrated that, in addition to TRPA1 and TRPV1, LPS weakly activated TRPM3 and TRPM8 to promote calcium influx [86]. It should be noted that other studies have demonstrated expression of TLR4 in a subclass of TRPV1 containing trigeminal nociceptors and that LPS sensitized TRPV1 via TLR4-mediated signaling [87,88].…”

“…In addition to sensory neuronal TRP, a recent study has shown the presence of a non-neuronal TRP channel that can detect LPS; specifically, the TRPV4 channel in airway epithelium in mice can detect LPS [89]. TRPV4 is expressed in both murine and human airway epithelial cells [86,90]. Alipzar et al demonstrated that murine airway tracheobronchial epithelial cells (mTECs), when stimulated with LPS, induced calcium influx that was dependent on TRPV4 and independent of TLR4 [89].…”

Functional coupling of GABA A/B receptors and the channel TRPV4 mediates rapid progesterone signaling in the oviduct

“…Considering that intracellular Ca 2+ is a key regulator of the CBF (8,29), we sought to identify whether P4 regulated CBF through the modulation of Ca 2+ signaling in oviductal ciliated cells. We found that P4 increased the intracellular concentration of Ca 2+ through a mechanism that required both the TRPV4 channel, which produces Ca 2+ signals linked to CBF modulation (30)(31)(32)(33), and GABA receptors, which are the main inhibitory receptors in the mammalian central nervous system (34). GABAergic signaling involving the ligand-gated GABA A chloride channel and the metabotropic G i/o protein-coupled GABA B receptor has been found in epithelial tissues (35)(36)(37).…”

Transient Receptor Potential Channels as Drug Targets: From the Science of Basic Research to the Art of Medicine

“…If this model holds true, inhaled TRPV4 blockers may represent a new class of bronchodilator drugs. The possible link between TRPV4 and COPD is also gaining strength: TRPV4 is expressed in murine and human airway epithelial cells, where it is believed to play a key role in mucociliary clearance by regulating ciliary beats (Lorenzo et al, 2008;Alenmyr et al, 2014). Impairment of this airway protective function by toxic inhalants (Li et al, 2011b) and/or carrying a gain-of-function TRPV4 variant ) is thought to increase the risk for developing COPD.…”