Characterization of stratification and tight junction formation in cultured human urothelial cells

Abstract

The urothelium is composed of stratified transitional epithelium of 3 cell types: basal, intermediate, and superficial. It has been proposed that urothelial cells acquire their mature characteristics through differentiation. The most differentiated, superficial cells develop tight junctions (TJs) that restrict urine movement and abnormalities in barrier function may be involved in syndromes such as interstitial cystitis. To further our understanding of urothelial differentiation, we used cells from normal human ureter and examined the zonula occludens (ZOs), “undercoat” scaffolding proteins in the cytosol that interact with claudins and actin filaments. Cell monolayers were stratified and differentiated using Ca and fetal bovine serum (FBS) and the process was studied using impedance, videomicroscopy, and confocal immunohistochemistry. With addition of Ca and FBS, impedance quickly increased by 2.5 fold. Withdrawal of the supplements returned impedance to baseline, suggesting the formation of tight junctions, rather than increased cell proliferation and immunohistochemistry demonstrated the appearance of ZO‐1 at cell junctions minutes after supplement addition. Observation by videomicroscopy suggested that cell division continued to occur after the cells had differentiated. Taken together, these studies increase our understanding of urothelial development.Supported by DK66119 (JM)