Triptolide inhibits PDGF-induced proliferation of ASMCs through G0/G1 cell cycle arrest and suppression of the AKT/NF-κB/cyclinDl signaling pathway

Abnormal proliferation of airway smooth muscle cells (ASMCs) is a hallmark of airway remodeling. Platelet-derived growth factor (PDGF) is known to be a major stimulus inducing the proliferation of ASMCs. It has been reported that triptolide demonstrates protective effects against airway remodeling. In this study, we investigated the antiproliferative effects of triptolide on PDGF-induced ASMCs and its underlying mechanisms. Cell proliferation was determined using the Cell Counting Kit-8 (CCK-8) assay. Flow cytometry was used to study the influence of triptolide on cell cycle and apoptosis. Quantitative real-time PCR and Western blot analysis were employed to detect the expression of proliferating cell nuclear antigen (PCNA), cyclinD1 and cyclin dependent kinase 4 (CDK4). Proteins involved in the protein kinase B (AKT) and nuclear factor kappa B (NF-kappa B) signaling pathways were evaluated using Western blot analysis. Triptolide could significantly inhibit cell proliferation, induce cell cycle arrest in the G0/G1 phase, and reduce the expression of PCNA, cyclinD1, and CDK4 in PDGF-treated ASMCs. Levels of phosphorylated AKT, p65 and NF-kappa B inhibitor a (I kappa B alpha) stimulated by the presence of PDGF were markedly suppressed after triptolide treatment. Moreover, triptolide cotreatment with the phosphatidylinositol 3 kinase (PI3k) inhibitor, 2-(4-morpholinyl)-8-phenylchromone (LY294002), could further suppress the proliferation, NF-kappa B activation and cyclinD1 expression. Similar results were observed after triptolide cotreatment with the NF-kappa B inhibitor, ammonium pyrrolidinedithiocarbamate (PDTC). Our results suggest that triptolide could inhibit the PDGF-induced proliferation of ASMCs through G0/G1 cell cycle arrest and suppression of the AKT/NF-kappa B/cyclinD1 signaling pathway.