Regulation of mucociliary differentiation of rat tracheal epithelial cells by type I collagen gel substratum

Adult rat tracheal epithelial cells plated at low density on type I collagen gel-coated permeable membranes in air-liquid interface cultures rapidly proliferate to reach high cell densities and display a pseudostratified mucociliary epithelium after 2 wk in culture. To determine the importance of exogenous extracellular matrix for RTE cell growth and differentiation, RTE cells were seeded on uncoated or type I collagen gel-coated membranes, Growth rate and plateau cell densities were similar under these two conditions; however, RTE cell attachment was twofold higher on type I collagen gel-coated membranes. Cell distribution during log growth was significantly different, with numerous small colonies observed on Giemsa-stained uncoated membranes and fewer, larger colonies observed on type I collagen gel-coated membranes. Under both conditions, the epithelial morphology was predominantly pseudostratified in plateau-phase cultures. Based on experiments measuring the percentage of secretory cells and the amount of mucous secretion, development of the secretory cell phenotype was delayed in the absence of exogenous matrix but reached similar levels of secretory differentiation by day 13 of culture. In contrast, the development of ciliated cells was markedly reduced on uncoated membranes, These data suggest that although plating cells on type I collagen gel enhances cell attachment and accelerates the onset of secretory differentiation, type I collagen gel seems to be more critical for ciliated cell differentiation than for secretory cell differentiation.