Plasminogen activator inhibitor-1 promotes the proliferation and inhibits the apoptosis of pulmonary fibroblasts by Ca2+ signaling

Aim: Our previous investigation demonstrated that plasminogen activator inhibitor-1 (PAI-1) siRNA ameliorated bleomycin (BLM)-induced rat lung fibrosis. The present study was undertaken to explore the effect and the mechanism of PAI-1 siRNA and plasmid pcDNA on the proliferation and apoptosis of cultured fibroblasts from BLM-induced fibrotic lung tissues. Materials and Methods: The fibroblasts from BLM-induced fibrotic lung tissue were isolated and transfected using PAI-1 siRNA and plasmid pcDNA-PAI-1. The techniques of real time RT-PCR and/or western blot were used to determine the expression of PAI-1, alpha-smooth muscle actin (alpha-SMA) (real time RT-PCR only), collagen type-1 and type-3 (real time RT-PCR only), and the levels of caspase-3, ERK and AKT signal molecules. The proliferation of fibroblasts was measured by cell cycle with flow cytometry. The intracellular concentration of Ca2+ was examined by confocal laser microscopy. Results: PAI-1 siRNA downregulated the PAI-1 mRNA expression by 70%+/- 7% at 24 h and protein expression by 73.5%+/- 10% and 42%+/- 3% at 48 h and 72 h compared to Non-specific siRNA group. Flow cytometry showed that the fibroblasts at the G(2)M + S phase were significantly reduced by 20.56 +/- 1.03% after transfecting PAI-1 siRNA and were significantly increased by 43.8 +/- 1.21% after transfecting plasmid pcDNA-PAI-1. The mRNA expressions of alpha-SMA, collagen type-1and type-3 were downregulated after transfecting the PAI-1 siRNA, while upregulated after the transfection of pcDNA-PAI-1. PAI-1 siRNA increased the level of caspase-3, inhibited the expressions of p-ERK and p-AKT protein molecules, while the pcDNA-PAI-1 transfection showed a reversal effect on these expressions. Intracellular Ca2+ concentration was decreased after transfecting PAI-1 siRNA, whereas increased after transfecting pcDNA-PAI-1. Conclusion: PAI-1 promotes the proliferation, transforming into myofibroblasts, collagen synthesis, and inhibits apoptosis of pulmonary fibroblasts by activating Ca2+, ERK and AKT signaling pathway. Decreasing PAI-1 expression is an available strategy in inhibiting the progression of pulmonary fibrosis. (C) 2012 Elsevier Ltd. All rights reserved.