PULMONARY-ARTERY SMOOTH-MUSCLE CELLS FROM CHRONICALLY HYPOXIC NEONATAL CALVES RETAIN FETAL-LIKE AND ACQUIRE NEW GROWTH-PROPERTIES

Growth properties retained and acquired by immature pulmonary artery ( PA) smooth muscle cells (SMC) in vivo after chronic exposure to hypoxi a and the mechanisms that regulate hypoxia-induced change in prolifera tive phenotype are not known. We tested the hypothesis that PA SMC fro m neonatal calves exposed to hypoxia after birth would both retain fet al-like and acquire new growth characteristics and that these changes would be at least partially dependent on protein kinase C (PKC), a key pro-proliferative signal transduction pathway. Like fetal cells, PA S MC from hypoxic calves grew faster in the presence and absence of seru m and were more responsive to insulin-like growth factor I and platele t-derived growth factor-BB than control neonatal and adult cells. PA S MC from hypoxic calves also acquired other growth properties (i.e., in cluding increased hypoxic growth after PKC activation) that were new c ompared with those observed for fetal cells. The proliferative respons e to hypoxia was first detectable in the neonatal period and was furth er increased in cells from hypoxic calves. SMC from fetuses and hypoxi c calves were more susceptible to the growth-inhibiting effects of PKC antagonists (dihydrosphingosine and calphostin C) than control neonat al and adult cells. To test if the Ca2+-dependent isozymes of PKC were uniquely important in the developmental and acquired growth changes o bserved, the antagonistic effect of the specific, but isozyme nonselec tive, PKC inhibitor Ro-31-8220 was then compared with GF-109203X, a st ructural analog with relative specificity for the Ca2+-dependent isozy mes of PKC (alpha and beta in PA SMC). The faster growing PA SMC from bovine fetuses and hypoxia-exposed calves again demonstrated greater g rowth inhibition in response to both inhibitors. GF-109203X was equipo tent to Ro-31-8220, and its antiproliferative effects were shown to no t be due to an increase in apoptosis. Phorbol ester-induced PKC downre gulation, another inhibitor strategy that selectively depletes bovine PA SMC of PKC-alpha, but not -beta, mimicked the antiproliferative eff ects of GF-109203X. Whole cellular PKC catalytic activity paralleled t he pattern of peptide-induced growth and susceptibility to PKC inhibit ion. These results suggest that PA SMC from hypoxia-exposed neonatal c alves retain enhanced fetal-like proliferative capacity and acquire ne w growth properties that are at least partially dependent on the Ca2+- regulated isozymes of PKC and in particular PKC-alpha.