ENHANCED GROWTH OF FETAL AND NEONATAL PULMONARY-ARTERY ADVENTITIAL FIBROBLASTS IS DEPENDENT ON PROTEIN-KINASE-C

The earliest and most striking proliferative changes in the neonatal p ulmonary arterial wall occur in the adventitia where the fibroblast re sides. The protein kinase C (PKC) pathway is developmentally regulated and important in vascular cell growth. We tested the hypothesis that developmental differences in growth of pulmonary artery adventitial fi broblasts would be detectable in vitro and dependent on PKC. Fibroblas ts were isolated from bovine fetal, neonatal, and adult pulmonary arte ries. Growth was measured by [H-3]thymidine incorporation and cell cou nts. Under serum-stimulated conditions, fetal and neonatal pulmonary a rtery fibroblasts grew faster and reached higher plateau densities tha n adult cells. Increased growth of fetal cells in vitro was dependent on time of harvest during fetal life (early > late). Under quiescent c onditions, fetal and neonatal fibroblasts had increased DNA synthesis compared with adult cells in response to the PKC agonist phorbol 12-my ristate 13-acetate. To test whether the developmental differences in f ibroblast growth were dependent on PKC, three different inhibitor stra tegies were used (dihydrosphingosine, phorbol-ester-induced downregula tion, and heparin). Fetal and neonatal fibroblasts were more susceptib le than adult cells to each antagonist strategy. Finally, we measured whole cellular PKC catalytic activity and found it correlated with gro wth,and susceptibility to PKC inhibition (i.e., fetal PRC activity > n eonatal > adult). We conclude that PKC-dependent developmental differe nces in growth of pulmonary artery fibroblasts are detectable in vitro and that the enhanced growth capacity of fetal and neonatal cells may contribute to the dramatic adventitial thickening seen in vivo after hypoxic exposure in the neonatal calf.