Involvement of TRPV4-mediated intracellular Ca²⁺ increase in cell-cell junction formation of keratinocytes and barrier function of skin

Abstract

Barrier function of the skin is essential to protect against infection and dehydration. In addition to a hydrophobic cornified cell layer, formation of adherence- and tight-junctions among the keratinocytes also form a significant barrier. Differentiation and formation of these junctions need an increase in intracellular Ca²⁺, however, the molecular mechanism remains poorly understood. TRPV4 is a Ca²⁺-permeable ion channel, which is known to be expressed in keratinocytes, and activated by warm temperatures (–33°C). Therefore, we examined the role of TRPV4 in the differentiation process of keratinocytes and epidermis using TRPV4-KO mice. Yeast two-hybrid screening identified an interaction between TRPV4 and β-catenin, both of which were observed at cell-cell junction areas in keratinocytes. Reorganization of actin cytoskeleton in TRPV4-KO keratinocytes was delayed and immature. An in vitro barrier function assay of a keratinocyte sheet revealed higher permeability of dextran across the sheet in TRPV4-KO keratinocytes. Barrier function in vivo was also impaired. Change in basal Ca²⁺ level after addition of extracellular high Ca²⁺ under 33°C was significantly lower in TRPV4-KO keratinocytes. Therefore, we hypothesize that TRPV4 is an important player for Ca²⁺ entry in keratinocytes that is necessary for differentiation and formation of cell-cell junctions. [J Physiol Sci. 2007;57 Suppl:S126]