Prostaglandin I₂ induces apoptosis via upregulation of Fas ligand in pulmonary artery smooth muscle cells from patients with idiopathic pulmonary arterial hypertension

Background: Pulmonary vascular remodeling with idiopathic pulmonary arterial hypertension (IPAH) is associated with impaired apoptosis of pulmonary artery smooth muscle cells (PASMCs). We have reported that high-dose prostaglandin I₂ (PGI₂) therapy markedly improved hemodynamics in IPAH patients. The therapy is thought to reverse vascular remodeling, though the mechanism is unclear. The aim of this study is to assess proapoptotic effects of PGI₂ on PASMCs obtained from IPAH patients. Methods: We investigated proapoptotic effects of PGI₂ in PAH-PASMCs by TUNEL assays, caspase-3,-7 assays and transmission electron microscopy. We examined the expression of Fas ligand (FasL), an apoptosis-inducing member of the TNF cytokine family, in PAH-PASMCs. We measured the serum FasL levels in IPAH patients treated with PGI₂. Results: TUNEL-positive, caspase-3, 7-active cells and fragmentation of the nucleus were detected in PAH-PASMCs treated with PGI₂. The percentage of apoptotic cells induced by PGI₂ at a high concentration was higher than that induced by PGI ₂ at a low concentration. PCR-array analysis revealed that PGI ₂ upregulated the FasL gene in PAH-PASMCs, and we measured the FasL expression by quantitative RT-PCR and Western blotting. PGI₂ significantly increased the mRNA level of FasL by 3.98 fold and the protein level of FasL by 1.70 fold. An IP receptor antagonist inhibited the induction of apoptosis, elevation of cyclic AMP and upregulation of FasL by PGI₂. Serum FasL level had a significant positive correlation with PGI₂ dose in IPAH patients treated with PGI₂. Conclusions: PGI₂ has proapoptotic effects on PAH-PASMCs via the IP receptor and upregulation of FasL.