Abstract 3462: GM-CSF Mediated Proinflammatory State in Pulmonary Vascular Cells Enhanced by Reduced BMPR-II and Its Association With Vascular Lesions in Idiopathic Pulmonary Arterial Hypertension
Background: Accumulating evidence indicates that inflammation is a necessary component of PAH in human as well as in animal models with haploinsufficinecy of BMPR-II. However, the mechanisms linking loss of BMPR-II with vascular inflammation and pulmonary vascular disease (PVD) are not well defined. TNF-α, a major pro-inflammatory cytokine, is known to increase GM-CSF, a chemokine important in the mobilization of endothelial progenitor and other stem cells to sites of injury. GM-CSF also induces vascular smooth muscle cell (SMC) proliferation. We hypothesized that that loss of BMPR-II signaling enhances cytokine mediated GM-CSF production that is linked to the pathogenesis of PVD.
Methods: we investigated TNF-α mediated GM-CSF production in pulmonary artery (PA) endothelial cell (EC) and PA SMC transfected with BMPR2 siRNA or control siRNA by ELISA and qRT-PCR. Translation efficiency of GM-CSF mRNA was determined by polysome analysis. We also assessed TNF-α and GM-CSF expression in lung tissues removed from patients with Idiopathic PAH(IPAH)(n=11) who had undergone lung transplantation and in unused donor control lungs (n=7) by immunohistochemistry.
Results:. In both PA ECs and PA SMC, TNF-α significantly increased GM-CSF mRNA and secreted protein. When we pre-treated PA ECs with BMP-2 (10 and 100ng/ml) we documented a reduction in TNF-α stimulated GM-CSF expression (p <0.05) indicating that BMP-2 has anti-inflammatory properties. Conversely, in PAECs transfected with BMPR2 siRNA compared with control siRNA, TNF-α mediated GM-CSF secretion was significantly increased (p <0.05) but not GM-CSF mRNA levels. Consistent with enhanced mRNA translation, reducing BMPR2 increased GM-CSF mRNA transcripts in polysome fractions. A marked increase in GM-CSF immunoreactivity was observed in IPAH vs. control patient lungs (p<0.05) particularly in PAs showing intimal thickening and plexiform lesions where heightened TNF-α expression was also apparent.
Conclusions: Loss of BMPR-II appears to exaggerate the response to proinflammatory cytokines by enhancing translation of GM-CSF mRNA and we speculate that GM-CSF contributes to the pathogenesis of IPAH, by its ability to recruit progenitor cells and to induce SMC proliferation.