Current experimental models of esophageal epithelium in vitro suffer from either poor differentiation or complicated culture systems. We have established a model to study stratified squamous epithelium in vitro, which is very similar to esophageal epithelium in vivo. A stratified squamous multilayer epithelium was formed by seeding primary normal human bronchial epithelial (NHBE) cells onto collagen- and fibronectin-coated trans-well inserts and then cultivating the cells under air-liquid interface (ALI) conditions in the presence of growth factors and low levels of all-trans-retinoic acid. Trans-epithelial electrical resistance (TEER) measurements revealed the presence of a tight barrier, previously only achievable with esophageal biopsies mounted in Ussing chambers. Molecular markers for desmosomes, cornified envelope, tight junctions, and mature esophageal epithelium were upregulated in the differentiating culture in parallel with functional properties, such as decreased permeability and acid resistance and restoration. Acid exposure resulted in a decrease in TEER, but following 1-h recovery the TEER values were fully restored. Treatment with all-trans-retinoic acid decreased TEER and inhibited the recovery after acid challenge. PPAR-delta agonist treatment increased TEER, and this temporary increase in TEER was consistent with an increase in involucrin mRNA. Global gene expression analysis showed that ALI-differentiated NHBE cells had expression profiles more similar to epithelial biopsies from the esophageal tissue of healthy volunteers than to any other cell line. With respect to morphology, molecular markers, barrier properties, and acid resistance, this model presents a new way to investigate barrier properties and the possible effects of different agents on human esophagus-like epithelium.
All-trans retinoic acid converts E2F into a transcriptional suppressor and inhibits the growth of normal human bronchial epithelial cells through a retinoic acid receptor- dependent signaling pathway.
