Tracheal ligation increases mitogen-activated protein kinase activity and attenuates surfactant protein B mRNA in fetal sheep lungs

Background. Tracheal ligation has been shown to accelerate fetal pulmonary growth in normal and hypoplastic lungs. Our aim was to study the effects of tracheal ligation on established molecular markers of growth and differentiation [mitogen-activated protein (MAP) kinase] and maturity [surfactant protein B (SPB) and fatty acid synthase (FAS)]. Materials and methods. Tracheal ligation was performed on four 100-day-gestation fetal sheep, with four age-matched fetuses undergoing maternal laparotomy and hysterotomy as control. Lungs from surviving fetuses (n = 2 in each group) were harvested after 4 days and frozen in liquid nitrogen. Protein lysates were prepared, and MAP kinase enzymatic assays [extracellular signal regulated protein kinase (ERK)-1 and -2] and Western blots were performed. Total RNA was isolated, and a fetal sheep lung cDNA library was created. The sheep SPB and FAS genes were cloned and sequenced. Northern blots were performed with the new clones, normalizing to β-actin. Results. Tracheal ligation lungs contained a larger volume of fluid (40 ml) compared with age- matched controls (8 ml). MAP kinase enzymatic ERK-1 activity was increased and SPB mRNA expression was reduced in fetal lungs after tracheal ligation. Neither ERK-2 enzymatic activities and FAS mRNA nor ERK protein levels were affected by tracheal ligation, by Western blot analysis. Conclusion. Tracheal ligation-induced fetal lung growth may be mediated in part via the MAP kinase pathway. Expression of SPB mRNA is attenuated by tracheal ligation, whereas FAS, one of the key enzymes that synthesizes the lipid portion of surfactant, is not affected.