Jiejing Xu

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Pulmonary surfactant replacement therapy and antenatal glucocorticoid administration are the two treatment strategies used for Respiratory Distress Syndrome. Because of the important roles surfactant-associated proteins play in surfactant function, understanding the mechanisms involved in regulation of the genes encoding for the proteins in fetal development or upon glucocorticoid treatment is therefore of paramount importance in the overall design of an effective treatment regimen. We attempted in this project to investigate the developmental and glucocorticoid regulation of three surfactant proteins, SP-A, SP-B and SP-C, using the rabbit as a model. The mRNA levels for these three proteins were examined in developing rabbit lung. By measuring both mRNA accumulation and synthesis, using Northern and slot blot analysis and nuclear transcription run-on assays, respectively, we were able to show that the genes encoding the three proteins were regulated independently with respect to the initiation of gene expression and changing patterns in either transcriptional or mRNA accumulation during perinatal period in rabbit lung. Effects of in vitro glucocorticoid treatment on mRNA levels and the relative transcriptional activities of the SP-A, SP-B and SP-C genes were also examined in an explant system using lung tissues from two different gestational age fetuses. It was observed that (1) glucocorticoids accelerated SP-B mRNA levels but not gene transcription, implying an apparent involvement of post-transcriptional mechanisms; (2) the hormone had a dose-dependent biphasic effect on both SP-A mRNA accumulation and synthesis, however, dexamethasone at 10{dollar}\sp{lcub}-8{rcub}{dollar}M showed no apparent influence on SP-A mRNA production as a function of incubation time, indicating also a dose-dependent (perhaps age-dependent too) responsiveness of the SP-A gene to glucocorticoid; and (3) there was a dose-dependent response to in vitro dexamethasone treatment of SP-C gene transcription but not mRNA levels. When examined as a function of incubation time, 10{dollar}\sp{lcub}-8{rcub}{dollar}M dexamethasone showed a more profound effect on the SP-C mRNA levels with 26-day lungs. These suggested the involvement of both transcriptional and post-transcriptional regulation of the SP-C gene by in vitro glucocorticoid treatment.



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