A Positive Feed Forward Loop between Wnt/β-Catenin and NOX4 Promotes Silicon Dioxide-Induced Epithelial-Mesenchymal Transition of Lung Epithelial Cells

Abstract

Silicosis is a chronic fibrotic lung disease caused by the accumulation of silica dust in the distal lung. Canonical Wnt signaling and NADPH oxidase 4 (NOX4) have been demonstrated to play a crucial role in the pathogenesis of pulmonary fibrosis including silicosis. However, the underlying mechanisms of crosstalk between these two signalings are not fully understood. In the present study, we aimed to explore the interaction of Wnt/β-catenin and NOX4 of human epithelial cells in response to an exposure of silica dust. Results demonstrated an elevated expression of key components of Wnt/β-catenin signaling and NOX4 in the lungs of silicon dioxide- (SiO2-) induced silicosis mice. Furthermore, the activated Wnt/β-catenin and NOX4 signaling are accompanied by an inhibition of cell proliferation, an increase of ROS production and cell apoptosis, and an upregulation of profibrogenic factors in BEAS-2B human lung epithelial cells exposed to SiO2. A mechanistic study further demonstrated that the Wnt3a-mediated activation of canonical Wnt signaling could augment the SiO2-induced NOX4 expression and reactive oxygen species (ROS) production but reduced glutathione (GSH), while Wnt inhibitor DKK1 exhibited an opposite effect to Wnt3a. Vice versa, an overexpression of NOX4 further activated SiO2-induced Wnt/β-catenin signaling and NFE2-related factor 2 (Nrf2) antioxidant response along with a reduction of GSH, whereas the shRNA-mediated knockdown of NOX4 showed an opposite effect to NOX4 overexpression. These results imply a positive feed forward loop between Wnt/β-catenin and NOX4 signaling that may promote epithelial-mesenchymal transition (EMT) of lung epithelial cells in response to an exposure of silica dust, which may thus provide an insight into the profibrogenic role of Wnt/β-catenin and NOX4 crosstalk in lung epithelial cell injury and pathogenesis of silicosis.

Metformin attenuates silica-induced pulmonary fibrosis via AMPK signaling

“…Increased apoptosis was accompanied by the induction of SiO 2 [ 35 ]. JC-1 staining showed that SiO 2 induced epithelium cell apoptosis by depolarizing the mitochondrial membrane potential.…”

“…The inhalation of respiratory silica dust can induce inflammatory responses, the secretion of inflammatory factors, and high ROS levels, which contribute to chronic lung injury [ 35 ]. It has been reported that metformin could inhibit the production of pro-inflammatory cytokines such as TNF-α from macrophages by inhibiting NF-κB [ 61 ].…”

Metformin Attenuates Silica-induced Pulmonary Fibrosis via AMPK Signaling

“…The inhalation of respiratory silica dust can induce in ammatory responses, the secretion of in ammatory factors, and high ROS levels, which contribute to chronic lung injury. [31] Importantly, the overproduction of intracellular ROS promotes the activation of alveolar macrophages and the secretion of pro-in ammatory cytokines, which aggravates lung dysfunction [49]. In this study, we found that SiO2 exposure signi cantly increased the level of intracellular ROS, which was effectively attenuated after the metformin treatment.…”

“…Increased apoptosis was accompanied by the induction of SiO2 [31]. JC-1 staining showed that SiO2 induced epithelium cell apoptosis by depolarizing the mitochondrial membrane potential.…”

Wnt/β-catenin signaling regulates lipopolysaccharide-altered polarizations of RAW264.7 cells and alveolar macrophages in mouse lungs

“…Adenoviral vectors expressing mouse Wnt3a (Ad.Wnt3a), Dkk1 (Ad.Dkk1), and adenoviral backbone vector control BglII (Ad.Bgl II) were kindly offered by Dr John F. Engelhardt at University of Iowa (Iowa City, Iowa, USA). 18 To investigate the role of Wnt signaling in regulation of inflammation-induced alveolar macrophages in vivo, LPS was used as the inducer of inflammation, mice were randomly divided into four groups with (3 males and three females, six mice per group): 1 Saline control, 2 Ad.BglII + LPS, 3 Ad.Wnt3a + LPS, 4 and Ad.Dkk1 + LPS. Each mouse was intratracheally instilled with saline, or 2.5 × 10 11 particles of adenoviral vector in a total volume of 25 μL PBS.…”