Phosphatidylinositol-3-Kinase/Akt Regulates Bleomycin-Induced Fibroblast Proliferation and Collagen Production

Abstract

Abnormal repair and dysregulated angiogenesis have been implicated in the pathogenesis of pulmonary fibrosis, but the underlying mechanisms of regulation are not well understood. The present study investigated the role of phosphatidylinositol-3-kinase (PI3K)/ Akt in fibrogenesis of human lung fibroblasts and its regulation by reactive oxygen species (ROS). Exposure of lung fibroblasts to bleomycin, a known inducer of fibrosis, resulted in rapid activation of PI3K/Akt and a parallel increase in fibroblast proliferation and collagen production, characteristics of lung fibrosis. Bleomycin had no significant effect on total Akt protein expression but induced phosphorylation of the protein at threonine 308 and serine 473 positions. Inhibition of this phosphorylation by PI3K inhibitors or by dominant-negative Akt (T308A/S473A) expression abrogated the effects of bleomycin on fibroblast proliferation and collagen production, suggesting the role of PI3K/Akt in the fibrogenic process. Activation of PI3K/Akt by bleomycin also led to transcriptional activation and protein expression of hypoxia-inducible factor-1a (HIF-1a) and vascular endothelial growth factor, which contributed to the fibroproliferative and collagen-inducing effects of bleomycin. The fibrogenic effects of bleomycin were dependent on ROS generation, particularly superoxide anion and hydrogen peroxide, which were induced by bleomycin. Inhibition of ROS generation by antioxidant enzymes, catalase and superoxide dismutase mimetic MnTBAP, abrogated the fibrogenic effects of bleomycin as well as its induction of PI3K/Akt and HIF-1a activation. Together, our results indicate a novel role of PI3K/Akt in fibrogenesis of human lung fibroblasts and its regulation by ROS, which could be exploited for the treatment of pulmonary fibrosis and related disorders.

Mesenchymal stem cell-conditioned media recovers lung fibroblasts from cigarette smoke-induced damage

“…Recently, the PI3K/Akt pathway was reported to regulate proliferation and collagen production in lung fibroblasts exposed to bleomycin (27). On the basis of the findings that bleomycin induced VEGF release from lung fibroblasts, and that VEGF caused proliferation and collagen production, this report suggested that VEGF was in part responsible for fibroblast activation.…”

“…In human lung fibroblasts, Col1A1 mRNA is stabilized in a PI3K-dependent manner (40), and bleomycin-induced collagen production is regulated by PI3K/Akt (27). LY294002 was found to completely abolish collagen production and to induce a significant decrease in secretion of laminin ␤2 and fibronectin from keloid fibroblasts (26).…”

“…Both VEGF (27) and FGF (28) have been shown to induce proliferation of lung fibroblasts. In addition, TGF-␤ 1 is also produced by MSCs (12) and enhances proliferation of fibroblasts (47), collagen production, and collagen gel contraction (33).…”

“…To identify growth factors in 10ϫ hMSC-CM, we measured concentrations of 40 growth factors by using an antibody array chip (Table 1). Among them, we assessed involvement of FGF2, TGF-␤ 1 , and VEGF, which are known to enhance fibroblast proliferation (27,28,47), with each blocking antibody. Antibodies against FGF2, TGF-␤ 1 , and VEGF significantly suppressed hMSC-CM-induced proliferation of NHLFs that were not exposed to CSE (Fig.…”

Role of transforming growth factor and vascular endothelial growth factor and their receptors in the pathogenesis of bleomycin induced lung fibrosis

“…It is characterized by prominent fibroblast proliferation and amplified deposition of extracellular matrix (ECM) (Lu et al, 2010). The pathogenesis of pulmonary fibrosis is not clearly defined, with the evidence of abnormal parenchymal repair, aberrant vascular remodeling and neoangiogenesis, which are seen in both animal models and patient samples (Nobel and Norman, 2003;Steurer et al, 2007).…”