The signal transducer and activator of transcription (Stat)-1 mediates growth arrest and apoptosis. We postulated that lung fibrosis characterized by excessive proliferation of lung fibroblasts would be enhanced in Stat1-deficient (Stat1 ؊/؊ ) mice. Two weeks after bleomycin aspiration (3 U/kg), Stat1 Pulmonary fibrosis is characterized by the excessive deposition of collagen in alveolar regions resulting in thickened alveolar septae and subsequent impairment of gas exchange. Lung fibroblasts are the central cell type that secrete collagen and other extracellular matrix proteins to define the fibrotic lesion.1 Proliferation of the fibroblasts within the lung is therefore a key feature in the development of fibrosis. Fibroblast proliferation is driven by several polypeptide growth factors that are up-regulated after lung injury, including platelet-derived growth factor (PDGF) and epidermal growth factor (EGF) receptor ligands.2,3 The action of these growth factors in promoting cell division is mediated by the phosphorylation of their specific receptor tyrosine kinases and the subsequent downstream activation of mitogen-activated protein (MAP) kinase cascades and transcription factors.

Background: Nanotechnology is a rapidly advancing industry with many new products already available to the public. Therefore, it is essential to gain an understanding of the possible health risks associated with exposure to nanomaterials and to identify biomarkers of exposure. In this study, we investigated the fibrogenic potential of SWCNT synthesized by chemical vapor deposition using cobalt (Co) and molybdenum (Mo) as catalysts. Following a single oropharyngeal aspiration of SWCNT in rats, we evaluated lung histopathology, cell proliferation, and growth factor mRNAs at 1 and 21 days post-exposure. Comparisons were made to vehicle alone (saline containing a biocompatible nonionic surfactant), inert carbon black (CB) nanoparticles, or vanadium pentoxide (V 2 O 5 ) as a known inducer of fibrosis.

IL-13 is a key cytokine involved in airway remodeling in asthma. We previously reported that IL-13 stimulated the mitogenesis of lung fibroblasts via platelet-derived growth factor (PDGF)-AA. In this report, we show that IL-13 increases PDGF-A and PDGF-C mRNA levels through a dual intracellular cascade that requires coactivation of Stat6 and Stat1 to impact transcriptional regulation of the early growth response (Egr)-1 gene, which then drives PDGF expression. Increased levels of PDGF-AA and PDGF-CC protein were observed in vivo in the airways of IL-13 transgenic mice. IL-13 up-regulated PDGF-A and PDGF-C mRNA levels in lung fibroblasts isolated from three different background strains of mice. However, IL-13-induced PDGF-A and PDGF-C mRNA levels were significantly reduced in Stat6-deficient (Stat6−/−) fibroblasts as compared with wild-type Stat6+/+ fibroblasts. In contrast, IL-13-induced PDGF-A and PDGF-C mRNAs were enhanced in Stat1−/− fibroblasts as compared with Stat1+/+ fibroblasts. IL-13 did not up-regulate PDGF-A or PDGF-C mRNA levels in Egr-1−/− fibroblasts. Moreover, IL-13 did not increase Egr-1 mRNA and protein levels in Stat6−/− fibroblasts and yet enhanced Egr-1 mRNA and protein levels in Stat1−/− fibroblasts. Our findings support the hypothesis that Stat6 and Stat1 exert stimulatory and inhibitory effects on Egr-1 and PDGF ligand mRNA transcription, respectively. This novel mechanism could aid in identifying molecular targets for the treatment of chronic airway remodeling and fibrosis in asthma.

The inhalation of vanadium pentoxide (V2O5) results in bronchitis and airway fibrosis. The lung fibrotic response to V2O5 partially resolves where fibroblasts first proliferate and deposit collagen, but then undergo growth arrest and apoptosis. STAT-1 mediates fibroblast growth arrest and apoptosis. We previously reported that STAT-1 is a protective factor and mice lacking STAT-1 are more susceptible to lung fibrosis. We also reported that V2O5-induced STAT-1 phosphorylation in lung fibroblasts requires H2O2 and de novo protein synthesis. In this study, we identified IFN-β as the protein that mediates STAT-1 activation by V2O5 in normal human lung fibroblasts and identified NADPH and xanthine oxidase systems as sources of H2O2 that drive IFN-β gene expression. STAT-1 phosphorylation was decreased with neutralizing Abs to IFN-β as well as an inhibitor of JAK. V2O5 also increased transcription of an IFN-inducible and STAT-1-dependent chemokine, CXCL10. Inhibition of H2O2-generating enzyme systems NADPH oxidase by apocynin and xanthine oxidase by allopurinol individually reduced STAT-1 phosphorylation. Apocynin and allopurinol also decreased V2O5-induced IFN-β mRNA levels and CXCL10 expression. IFN-α transcription was inhibited only by allopurinol. Taken together, these data indicate that fibroblasts play a role in the innate immune response to vanadium-induced oxidative stress by synthesizing IFN-β and activating STAT-1 to cause growth arrest and increase levels of CXCL10, a potent antifibrotic factor. This mechanism is postulated to counterbalance profibrogenic mechanisms that follow V2O5 injury.

Background: Exposure to vanadium pentoxide (V 2 O 5 ) is a cause of occupational bronchitis. We evaluated gene expression profiles in cultured human lung fibroblasts exposed to V 2 O 5 in vitro in order to identify candidate genes that could play a role in inflammation, fibrosis, and repair during the pathogenesis of V 2 O 5 -induced bronchitis.