Glucocorticoids, tumor necrosis factor-alpha, and epidermal growth factor regulation of pulmonary morphogenesis: a multivariate in vitro analysis of their related actions.

The mouse lung commences development on embryonic day 11 as an epithelial evagination from the posterior pharyngeal wall into undifferentiated mesenchyme, this epithelium bifurcating to form the lung primordium. Branching morphogenesis, as well as terminal differentiation, requires epithelial-mesenchymal interactions utilizing precise regulatory controls. Not surprisingly, specific hormones and growth factors appear to play a key role in this regulation. We report here a series of experiments designed to investigate morphodifferentiation (epithelial branching number, generation number, and fractal dimension) and histodifferentiation (cell morphology and SP-A immunolocalization), as they relate to glucocorticoid (CORT)-regulation of growth factor function and expression (Northern analysis). These experiments were conducted in embryonic lung primordia (E11.5-E12) cultured under defined conditions in the presence of single or combined CORT, TNF-alpha, and EGF supplementation. EGF supplementation enhances branching morphogenesis, but not immunodetectable SP-A expression, in embryonic lung primordia cultured for 4 or 7 days. TNF-alpha supplementation also enhances branching morphogenesis on days 4 or 7 in vitro; on day 7, SP-A expression is also enhanced. By contrast, the introduction of exogenous CORT to embryonic explants cultured 4 or 7 days markedly alters morphodifferentiation and histodifferentiation. Early on it would appear to enhance morphodifferentiation by changing the process of branching, while contemporaneously initiating precocious SP-A expression; later on, it alters morphogenesis by continued terminal differentiation of normal lung epithelium and a singular transdifferentiation of lung mesenchyme into an epithelioid morphotype expressing SP-A. This is correlated with a CORT-induced, highly significant, down-regulation of TGF-beta 2 and TGF-beta 3 transcripts. Explants supplemented with CORT + TNF-alpha or CORT + EGF.demonstrate a microanatomy and SP-A expression pattern identical to that seen with CORT supplementation alone. EGF inhibits the accelerated lung maturation normally seen in the presence of exogenous TNF-alpha alone, suggesting a relationship between these two seemingly disparate regulatory pathways.