OXYGEN MODULATES THE DIFFERENTIATION OF HUMAN FETAL LUNG INVITRO AND ITS RESPONSIVENESS TO CAMP

Previously, it was found that lung explants from mid-trimester human a bortuses differentiate spontaneously in organ culture in serum-free de fined medium in an atmosphere of 95% air-5% CO2. Dibutyryl adenosine 3 ',5'-cyclic monophosphate (DBcAMP) treatment of human fetal lung in cu lture increases the rate of morphological differentiation and enhances expression of the surfactant protein A (SP-A) gene. To begin to defin e the factors responsible for this accelerated in vitro differentiatio n, we analyzed the effects of atmospheric oxygen on the morphological and biochemical development of human fetal lung in culture and on resp onsiveness of the cultured tissue to DBcAMP. We found that when lung e xplants were maintained in an atmosphere containing 1% oxygen they fai led to differentiate spontaneously and no induction of SP-A gene expre ssion was apparent. Furthermore, at 1% oxygen, DBcAMP had no effect to stimulate morphological differentiation or SP-A gene expression. When lung tissues that had been maintained for 5 days in 1% oxygen were tr ansferred to an environment containing 20% oxygen, there was rapid mor phological development and induction of SP-A gene expression. The effe cts on morphological development were manifest within 24 h of transfer to the 20% oxygen environment; within 72 h, a marked stimulatory effe ct of DBcAMP on SP-A gene expression also was observed. Our findings f urther suggest that the effects of oxygen on the levels of SP-A and SP -A mRNA are concentration dependent. Interestingly, the inductive effe cts of DBcAMP on SP-A gene expression were apparent only at oxygen con centrations greater-than-or-equal-to 10%. Morphological differentiatio n of the cultured human fetal lung tissue also was influenced by oxyge n in a concentration-dependent manner. These findings suggest that oxy gen plays an important permissive role in the spontaneous differentiat ion of human fetal lung in vitro.