Transforming growth factor beta 1 binding and receptor kinetics in fetal mouse lung fibroblasts

TGFbeta1 inhibits fetal lung maturation in vitro. As TGFbeta1 is present in fetal lung, mechanisms must exist to overcome this inhibition and allow late gestation maturation to progress. We studied the ontogeny of TGFbeta1 binding, and TGFbeta receptor kinetics and subtypes in primary cultures of fetal mouse lung fibroblasts from Day 16 to Day 18 of gestation. TGFbeta1 specific binding in fetal lung fibroblasts declined with advancing gestation. The decrease occurred earlier, and was more pronounced in female fibroblasts (50% decrease) than in the male fibroblasts (29% decrease). Dihydrotestosterone treatment of Day 18 female fibroblasts resulted in a dose-dependent increase in TGFbeta1 binding. Scatchard analysis revealed a decline in receptor number with advancing gestation (Day 16 female Bmax: 7.3 x 10(-16); Day 18 female Bmax: 5.5 x 10[-16]) whereas binding affinities remained constant. Affinity labeling followed by chemical cross-linking and autoradiography showed the three known TGFbeta receptor subtypes at both Days 16 and 18 of gestation. The relative abundance of nonsignaling Type III receptors in comparison to signaling Type II and Type I receptors was increased at Day 18 versus Day 16. Incorporation of [3H]thymidine into DNA after treatment with TGFbeta1 changed from Day 16 to Day 18, consistent with changes previously reported between fetal and adult lung fibroblasts. We conclude that as fetal mouse lung maturation progresses, TGFbeta receptor number decreases in fibroblasts, the relative proportion of nonsignaling versus signaling receptor types increases, and the response to TGFbeta1 stimulation changes. These changes may contribute to overcoming TGFbeta1 inhibition of lung maturation.