Change in claudin expression during CACO-2 cells differentiation

Abstract

Epithelia create barriers and regulate solute and water transport through transcellular and paracellular pathways. The paracellular pathways of different tissues vary remarkably in size selectivity, ionic charge selectivity and electrical resistance. The claudin family of tight junction proteins includes twenty four members which are responsible for providing these variable properties. Claudin proteins interact with each others and with other proteins, and based on these interactions epithelial monolayers can range from leaky to tight. In order to better understand the contribution of claudins to the regulation of paracellular permeability, claudin expression in epithelial monolayers should be understood. We are studying the claudin expression profile in Caco-2 cells. These cells were grown on permeable and plastic supports for twenty days, which stimulated them to differentiate into enterocyte-like cells. Under these conditions, Caco-2 cells formed an epithelial monolayer where the cells gradually exhibited tight junctions. The permeability of the monolayer was monitored by measuring transepithelial electrical resistance (TER), which reflected the tightness of the claudin-based junctions. Measurements revealed a sharp increase in TER during the first five days followed by a slower increase till day sixteen where a plateau value was reached. Throughout the differentiation process, the relative expression of all twenty two human claudins (claudins 1- 12, 14-20, 22-24) was monitored by quantitative real-time PCR. Our results demonstrate that the expression of claudins (1, 2, 14, 15, 16 and 18) change during the differentiation of Caco2 cells, while the expression of all other human claudins did not show a significant change. These results suggest that Caco-2 cells modulate the properties of their tight junctions as they differentiate. Interestingly, these changes in claudin expression are not always consistent between cells grown on plastic and cells grown on filters supports highlighting the importance of the extracellular matrix in tight junction formation.