Newborn Ovine Pulmonary Vascular Smooth Muscle Cell (PVSMC) Proliferation Occurs Independent of Platelet Activating Factor Receptor (PAFr) Activation

Abstract

PAF is an endogenous lipid mediator involved in perinatal pulmonary adaptation. In ovine fetal PVSMC, PAFr binding stimulates cell proliferation via a distinct intracellular signaling pathway. Role of PAF in proliferation of newborn lamb PVSMC is unknown. We compared PAFr-mediated cell proliferation of ovine fetal and newborn PVSMC in culture so as to understand a postnatal role of PAF in PPHN. PVSMC from the two groups were cultured in normoxia (nmx) and hypoxia (hpx) without stimulation. We measured proliferation by DNA synthesis and expression of PAFr, TLR4, and MAPK by Western blotting. Our hypothesis is that PAF stimulates fetal and newborn lamb PVSMC proliferation via PAFr activation and induction of TLR4 and MAPK expression. In fetal PVSMC, PAFr binding and PAFr expression were detected in nmx and hpx, but not in newborn PVSMC. Fetal PVSMC proliferation was inhibited by PAF receptor antagonists, but proliferation of newborn PVSMC was up-regulated by PAFr antagonist or had no effect. Newborn PVSMC expressed TLR4 and MAPK in nmx and hpx. Proliferation was inhibited by MAPK inhibitors. These data suggest that proliferation of newborn PVSMC occurs via a mechanism independent of direct PAFr activation as occurs in fetal PVSMC