Activation of TRPV4 Strengthens the Tight-Junction Barrier in Human Epidermal Keratinocytes

Abstract

The transient receptor potential cation channel, subfamily V (TRPV), is expressed in the epidermis and considered to be a sensor of extrinsic stimuli such as temperature and other physical or chemical factors. In this study, we examined whether or not the activation of TRPVs by their agonists alters the epidermal tight junction (TJ) function in cultured human epidermal keratinocytes. Reverse transcription-polymerase chain reaction (RT-PCR) analyses showed that mRNA for TRPV1, 3 and 4 were expressed in differentiated keratinocytes in which TJs had formed. Stimulation of the keratinocytes with a TRPV4 agonist (4α-phorbol 12, 13-didecanoate, 4α-PDD) strengthened the TJ-associated barrier, analyzed by means of transepithelial electric resistance measurements and flux measurements of the paracellular tracer. Stimulation with TRPV1 and TRPV3 agonists did not have the same result. Simultaneously, the 4α-PDD-stimulated keratinocytes showed an upregulation of TJ structural proteins, occludin and claudin-4, and TJ regulatory factors, phospho-atypical PKCζ/ι. It was also observed that the amounts of occludin and phospho-atypical PKCζ/ι complex were higher in 4α-PDD stimulated keratinocytes. In conclusion, we demonstrated that the activation of TRPV4 strengthened the TJ-associated barrier of epidermal cells. It was also suggested that the upregulation of TJ structural proteins and/or the posttranslational modification of TJ structural proteins by phospho-atypical PKCζ/ι are responsible for the enhancement of TJ function. Our study supports the hypothesis that TJs change their function in response to a change in the external environment sensed through TRPVs.

Claudin-4 is required for modulation of paracellular permeability by muscarinic acetylcholine receptor in epithelial cells

“…The extracellular loops of claudins interact with each other to seal the cellular sheet and regulate paracellular transport between luminal and basolateral spaces (Lal-Nag and Morin, 2009). Claudin-4 has been detected in diverse epithelia, such as salivary, renal, lung, intestinal and epidermal cells (Akazawa et al, 2013;Cong et al, 2013;Gong et al, 2014;Kage et al, 2014;Shrestha et al, 2014). In rat submandibular SMIE cells, overexpression of claudin-4 increases TER and decreases the epithelial permeability of 70 kDa dextran (Michikawa et al, 2008).…”

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

“…It is noteworthy that TRPV4 is highly expressed in chondrocytes (Muramatsu et al, 2007); indeed, it is important for the normal development of the bone growth plates. In the skin, TRPV4 activation strengthens the epidermal tight junction (which includes occludin, claudin-4, and tight junction regulatory proteins), and is thus important for the integrity of the skin barrier (Akazawa et al, 2013). Deduced from the Trpv4 knockout phenotype, TRPV4 might function as a mechanosensor and chemosensor, such as sensing for osmoreceptive neurons of the circumventricular organ and for sensing luminal tonicity in cholangiocyte cilia, which are required for bile formation.…”

TRP Channels in Skin Biology and Pathophysiology

“…A role for this channel in epidermal barrier homeostasis comes from the observations that activation of this channel increases intracellular calcium in human keratinocytes and promotes cell-cell junction formation between these cells, and that knockdown of TRPV4 expression impairs development of high transepithelial resistance in cultured human keratinocytes [128]. Furthermore, warm temperatures and chemical agonists of TRPV4 accelerate barrier recovery in explanted human skin tissues after stratum corneum removal [129]. …”