Chronic hypoxia induces exaggerated growth responses in pulmonary artery adventitial fibroblasts - Potential contribution of specific protein kinase C isozymes

Enhanced proliferation of adventitial fibroblasts is a major contributor to the structural remodeling of the pulmonary artery (PA) that occurs during hypoxia-induced pulmonary hypertension. The mechanisms responsible for the exuberant growth of fibroblasts are unknown; however, protein kinase C (PKC ) isozymes have previously been shown to be important in the enhanced growt h properties of immature PA fibroblasts. We tested the hypotheses that PA a dventitial fibroblasts from neonatal calves exposed chronically to hypoxia after birth would express augmented growth responses compared with fibrobla sts from the control adventitia and that these properties would be associat ed with selective changes in expression of PKC isozymes. We studied the eff ects of serum, purified mitogens, and hypoxia on the,growth of aggregate po pulations of fibroblasts isolated from the PA of neonatal control calves (N eo-C) and calves chronically exposed to hypoxia for 2 wk beginning on Day 1 of life (Neo-Hyp). Neo-Hyp fibroblasts demonstrated higher proliferative c apabilities than did Neo-C cells in response to all the stimuli tested. Imp ortantly, hypoxia was found to act synergistically with peptide mitogens (p latelet-derived growth factor, basic fibroblast growth factor, insulin-like growth factor-I) to stimulate growth in Neo-Hyp but not in Neo-C cells. Us ing PKC-isozyme nonselective and selective inhibitors and immunoblot analys is, we found differences in utilization of PKC isozymes in Neo-Hyp and Neo- C fibroblasts and have identified PKC-beta I and -zeta as key contributors to the augmented growth of Neo-Hyp fibroblasts. Although the activity of PK C-beta I and -zeta isozymes was increased by hypoxia in serum-deprived Neo- C and Neo-Hyp fibroblasts, under normoxia, quiescent Neo-Hyp fibroblasts ha d higher PKC-zeta-specific activity than did Neo-C cells. These results sug gest that neonatal PA adventitial fibroblasts acquire new growth properties in the setting of hypoxia-induced pulmonary hypertension and that the augm ented proliferative characteristics of the Neo-Hyp fibroblasts might be ass ociated with changes in specifc PKC isozyme expression and activation patte rns.