Campus Only Senior Thesis
Bachelor of Arts
W.M. Keck Science Department
© 2013 Belen A. Cruz
Background: Platelet activating factor (PAF) is a phospholipid synthesized by the action of phospholipase A2 and acetyl transferase. PAF possesses a wide range of biological activities. In the lung of the fetus and newborn, PAF binds to its G protein couple receptor to evoke its biological activities via a well-defined signaling pathway. High levels of PAF receptor (PAFr) activity in fetal ovine lung vascular smooth muscle cells (PVSMC) at baseline has previously been demonstrated, a finding that is further perpetuated by conditions of hypoxia similar to fetal lung environment. Additionally in fetal ovine PVSMC, a cross-talk between PAFr-mediated cell signaling and activity of the vasodilator cyclic nucleotides cGMP and cAMP acting via their respective receptors protein kinase (PK) G and PKA has been shown. The interaction of PAF with its receptor has been implicated in the pathogenesis of persistent pulmonary hypertension in the newborn (PPHN) which has a high incidence of hospitalization and death of newborn infants. Successful transition of fetus to newborn life entails a mechanism whereby vasoconstrictors necessary for fetal existence are abrogated in the immediate newborn. Hypothesis: We hypothesize that PPHN results from the failure to down regulate PAFr- mediated activity and /or failure to up-regulate activity of the vasodilators cGMP and cAMP. PPHN is triggered by chronic intrauterine or postnatal hypoxia. Then newborn PVSMC undergo hyperplasia and hypertrophy, which over time, results in irreversible vascular remodeling. Methods: My study aims to employ in vitro models to delineate the consequences of PAF-PAFr mediated pathway in the pharmacological effects of the cAMP-PKA and cGMP-PKG signaling and the involvement of this cross-talk in the pathogenesis of PPHN. I modeled my cell culture studies to mimic the low oxygen environment of fetal lungs (hypoxia), the normal oxygen environment of newborn lungs (normoxia) and high oxygen environment (hyperoxia) to which the newborn lung may be exposed in incidental clinical condition of PPHN. I studied the effect of PAF, a vasoconstrictor, cAMP/cGMP, vasodilators, and other inhibitors of the PAFr pathway on growth of newborn PVSMC, by DNA synthesis, and measured their effects on expression of mitogenic and non-mitogenic proteins. Results: We found that both hypoxia and hyperoxia decreased cell growth even in the presence of PAF which up-regulates cell growth in fetal PVSMC. Also PAF treatment of cells resulted in down regulation of the vasodilator proteins, PKA and PKG. Conclusion: Our data suggests that in the lung of the newborn a high activity of PAF-PAFr mediated activities will worsen the condition of PPHN imposed on the newborn lung by environmental or therapeutic conditions. We can speculate that, in the long run, these findings may translate into the establishment of less toxic protein-based management of PPHN.
Cruz, Belen A., "Oxygen Tension Modulates Growth Of Ovine Newborn Pulmonary Vascular Smooth Muscle Cells" (2014). Scripps Senior Theses. 333.
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