The effect of ethanol on paracellular permeability and claudin expression in CaCo-2 cells during the course of differentiation

Abstract

In multicellular organisms, compartmentalization and isolation between external and internal environments is established by a cellular sheet of epithelial cells. To accomplish their function as a barrier, epithelial cells are held together with different forms of junctions known as the junctional complex. Tight junctions or Zonula Occludens are described as being the most apical structure of the junctional complex. Tight junctions are composed of three different types of integral membrane proteins connected to the cytoskeleton via a complex cytosolic plaque of scaffolding proteins. Integral membrane proteins include occludins, claudins, and JAM. Claudins are the major components of the tight junction strands that determine the permeability and the integrity of the paracellular pathway. Previous studies have shown that acute ethanol treatment increased the permeability of caco-2 monolayer, and decreased transepithelial resistance via the activation of MLCK and RhoA. Hence, the aim of this study is to assess the effect of ethanol on intestinal epithelial tight junctions by studying its effect on transepithelial resistance and claudins expression and localization in caco-2 cells throughout the course of differentiation. This aim was studied by culturing caco-2 cells on filter membranes to assess the transepithelial resistance during the course of 20 days. This was followed by Western blot analysis to determine the level of expression of different claudins; immunofluorescence was used to study the localization of claudins. We observed an increase in electrical resistance in the monolayers treated with ethanol as compared to the control. These results correlate with Western Blot analysis which shows a decrease in claudin-2 expression without affecting the expression of claudin-1. Furthermore chronic exposure to ethanol did not inhibited cellular differentiation since no alteration in the expression of the differentiation marker PLAP between the cells treated with ethanol and the control cells. No misslocalization of both claudin-1 and -2 is seen on both days as compared to control. Our results contradict earlier reports since we observed that ethanol causes an increase in transepithelial resistance, and propose a mechanism of this increase via the modulation of claudin-2 expression.