Induction of alveolar type II cell differentiation in embryonic tracheal epithelium in mesenchyme-free culture

We have previously shown that fetal lung mesenchyme can reprogram embryonic rat tracheal epithelium to express a distal lung phenotype, We have also d emonstrated that embryonic rat lung epithelium can be induced to proliferat e and differentiate in the absence of lung mesenchyme, In the present study we used a complex growth medium to induce proliferation and distal lung ep ithelial differentiation in embryonic tracheal epithelium. Day-13 embryonic rat tracheal epithelium was separated from its mesenchyme, enrobed in grow th factor-reduced Matrigel, and cultured for up to 7 days in medium contain ing charcoal-stripped serum, insulin, epidermal growth factor, hepatocyte g rowth factor, cholera toxin, fibroblast growth factor 1 (FGF1), and keratin ocyte growth factor (FGF7), The tracheal epithelial cells proliferated exte nsively in this medium, forming lobulated structures within the extracellul ar matrix. Many of the cells differentiated to express a type II epithelial cell phenotype, as evidenced by expression of SP-C and osmiophilic lamella r bodies. Deletion studies showed that serum, insulin, cholera toxin, and F GF7 were necessary for maximum growth. While no single deletion abrogated e xpression of SP-C, deleting both FGF7 and FGF1 inhibited growth and prevent ed SP-C expression. FGF7 or FGF1 as single additions to the medium, however , were unable to induce SP-C expression, which required the additional pres ence of serum or cholera toxin, FGF10, which binds the same receptor as FGF 7, did not support transdifferentiation when used in place of FGF7, These d ata indicate that FGF7 is necessary, but not sufficient by itself, to induc e the distal rat lung epithelial phenotype, and that FGF7 and FGF10 play di stinct roles in lung development.