Effect of platelet-activating factor (PAF) receptor blockers on smooth muscle cell replication in vitro and allograft arteriosclerosis in vivo

Mechanism by which nuclear factor-kappa beta (NF-kB) regulates ovine fetal pulmonary vascular smooth muscle cell proliferation

Platelet activating factor (PAF) modulates ovine fetal pulmonary hemodynamic. PAF acts through its receptors (PAFR) in pulmonary vascular smooth muscle cells (PVSMC) to phosphorylate and induce nuclear translocation of NF-kB p65 leading to PVSMC proliferation. However, the interaction of NF-kB p65 and PAF in the nuclear domain to effect PVSMC cell growth is not clearly defined. We used siRNA-dependent translation initiation arrest to study a mechanism by which NF-kB p65 regulates PAF stimulation of PVSMC proliferation. Our hypotheses are: (a) PAF induces NF-kB p65 DNA binding and (b) NF-kB p65 siRNA attenuates PAF stimulation of PVSMC proliferation. For DNA binding, cells were fed 10 nM PAF with and without PAFR antagonists WEB 2170, CV 3988 or BN 52021 and incubated for 12 h. DNA binding was measured by specific ELISA. For NF-kB p65 siRNA effect, starved cells transfected with the siRNA were incubated for 24 h with and without 10 nM PAF. Cell proliferation was measured by DNA synthesis while expression of NF-kB p65 and PAFR protein was measured by Western blotting. In both studies, the effect of 10% FBS alone was used as the positive control. In general, PAF stimulated DNA binding which was inhibited by PAFR antagonists. siRNAs to NF-kB p65 and PAFR significantly attenuated cell proliferation compared to 10% FBS and PAF effect. Inclusion of PAF in siRNA-treated cells did not reverse inhibitory effect of NF-kB p65 siRNA on DNA synthesis. PAFR expression was inhibited in siRNA-treated cells. These data show that PAF-stimulation of PVSMC proliferation occurs via a PAFR-NF-kB p65 linked pathway.

Platelet-activating factor stimulates ovine foetal pulmonary vascular smooth muscle cell proliferation: role of nuclear factor-kappa B and cyclin-dependent kinases

OBJECTIVE

Platelet-activating factor (PAF) is implicated in pathogenesis of persistent pulmonary hypertension of the neonate (PPHN); PAF is a mitogen for lung fibroblasts. PAF's role in pulmonary vascular smooth muscle cell (PVSMC) proliferation and in hypoxia-induced pulmonary vein (PV) remodelling has not been established and mechanisms for PAF's cell-proliferative effects are not well understood. We investigated involvement of PAF and PAF receptors in PVSMC proliferation.

MATERIALS AND METHODS

Cells from pulmonary arteries (SMC-PA) and veins (SMC-PV) were serum starved for 72 h in 5% CO2 in air (normoxia). They were cultured for 24 h more in normoxia or 2% O(2) (hypoxia) in 0.1% or 10% foetal bovine serum with 5 microCi/well of [(3)H]-thymidine, with and without 10 nm PAF. Nuclear factor-kappa B (NF-kappaB), CDK2 and CDK4 protein expression, and their roles in cell proliferation control were studied.

RESULTS

PAF and hypoxia increased SMC-PA and SMC-PV proliferation. WEB2170 inhibited PAF-induced cell proliferation while lyso-PAF had no effect. SMC-PV proliferated more than SMC-PA and PAF plus hypoxia augmented NF-kappaB protein expression. NF-kappaB inhibitory peptide attenuated PAF-induced cell proliferation by 50% and PAF increased CDK2 and CDK4 protein expression. The data show that hypoxia and PAF up-regulate PVSMC proliferation via PAF receptor-specific pathway involving NF-kappaB, CDK2 and CDK4 activations.

CONCLUSION

They suggest that in vivo, in foetal lung low-oxygen environment, where PAF level is high, proliferation of PVSMC will occur readily to modulate PV development and that failure of down-regulation of PAF effects postnatally may result in PPHN.