RhoA-Rho kinase and platelet-activating factor stimulation of ovine foetal pulmonary vascular smooth muscle cell proliferation

Objectives Platelet‐activating factor (PAF) is produced by pulmonary vascular smooth muscle cells (PVSMC). We studied effects of Rho kinase on PAF stimulation of PVSMC proliferation in an attempt to understand the role of RhoA/Rho kinase on PAF‐induced ovine foetal pulmonary vascular remodelling. Our hypothesis is that PAF acts through Rho kinase, as one of its downstream signals, to induce arterial (SMC‐PA) and venous (SMC‐PV) cell proliferation in the hypoxic lung environment of the foetus, in utero. Materials and methods Rho kinase and MAPK effects on PAF receptor (PAFR)‐mediated cell population expansion, and PAFR expression, were studied by DNA synthesis, western blot analysis and immunocytochemistry. Effects of constructs T19N and G14V on PAF‐induced cell proliferation were also investigated. Results Hypoxia increased PVSMC proliferation and Rho kinase inhibitors, Y‐27632 and Fasudil (HA‐1077) as well as MAPK inhibitors PD 98059 and SB 203580 attenuated PAF stimulation of cell proliferation. RhoA T19N and G14V stimulated cell proliferation, but co‐incubation with PAF did not affect proliferative effects of the constructs. PAFR protein expression was significantly downregulated in both cell types by both Y‐27632 and HA‐1077, with comparable profiles. Also, cells treated with Y‐27632 had less PAF receptor fluorescence with significant disruption of cell morphology. Conclusions Our results show that Rho kinase non‐specifically modulated PAFR‐mediated responses by a translational modification of PAFR protein, and suggest that, in vivo, activation of Rho kinase by PAF may be a further pathway to sustain PAFR‐mediated PVSMC proliferation.