β-Catenin in the Fibroproliferative Response to Acute Lung Injury

Abstract

Resolution of alveolar epithelial/capillary membrane damage after acute lung injury requires coordinated and effective tissue repair to reestablish a functional alveolar epithelial/capillary membrane barrier. We hypothesized that signaling pathways important in lung alveolar bud ontogeny are activated in the recovery and remodeling phases after profound oxidant stress lung injury in a murine model. To test this, we characterized the expression of noncanonical ␤-catenin pathway proteins E-cadherin, integrin-linked kinase-1, and ␤-catenin in mice undergoing normoxic recovery after exposure to butylated hydroxytoluene (BHT, ionol) and concomitant sublethal (75% O 2 ) hyperoxia. Mice developed early acute lung injury with subsequent inflammation, collagen deposition, interstitial cellular proliferation, and lung architectural distortion. Reduced E-cadherin expression after 6 d of BHT and hyperoxia was accompanied by enhanced expression and nuclear localization of ␤-catenin and increased integrin-linked kinase-1 expression during subsequent normoxic recovery. This resulted in increased expression of the cotranscriptional regulators TCF-1 and -3 and cyclin D1. Proliferation of murine lung epithelial-12 cells in vitro after 8 h of treatment with BHT quinone-methide and hyperoxia and 48 h of normoxic recovery was enhanced 2.7-fold compared with vehicle-treated control mice at the same time point. BHT/hyperoxia-exposed mice treated with the pan-caspase inhibitor z-ASP had increased acute lung injury and reduced survival despite the presence of TUNEL-positive cells, suggesting enhanced lung cell necrosis. ␤-Catenin expression was reduced in z-ASP-co-treated lungs after BHT/hyperoxia. The noncanonical cadherin-␤-catenin axis is associated with fibroproliferative repair after BHT/hyperoxia exposure and may regulate epithelial proliferation and lung matrix remodeling and repair in response to lung injury. Keywords: ␤-catenin; E-cadherin; lung injury repair; cell junctions; caspase Resolution of alveolar epithelial/capillary membrane damage after acute lung injury (ALI) requires coordinated and effective tissue reconstruction to reestablish a functional barrier. In particular, restoration of the normal air space architecture requires reconstitution of denuded type I alveolar epithelial cells that undergo apoptotic and necrotic death during the exudative phase of ALI. Coordination of extracellular matrix turnover and regeneration of type II epithelial cells is important in reestablishing surfactant production and ion transport (1). Orderly re-epithelialization suppresses fibroblast proliferation and matrix deposition after ALI (1, 2). However, resolution of ALI can result in disordered repair of the alveolus, characterized by impaired fibrinolysis of the in-

Inhibition of β-catenin signaling protects against CTGF-induced alveolar and vascular pathology in neonatal mouse lung

“…Cyclin D1 is a cell cycle regulatory molecule that is active in G1 phase transition and functions as an important mitogenic regulator (26). Increased cyclin D1 expression is linked to acute and chronic lung injuries induced by inflammatory agents, and it is postulated to contribute to interstitial cell proliferation and fibrosis formation (27,28). Collagen 1a1 and fibronectin are the main components of ECM that participate in tissue and vascular remodeling.…”

Matrix Metalloproteinase 3 Is a Mediator of Pulmonary Fibrosis

“…17 Cyclin D1 immunohistochemistry and ␤-catenin immunofluorescence staining (both from Cell Signaling Technology, Danvers, MA) were performed on paraffin-embedded lung tissue. 18,19 Briefly, lung tissue sections were deparaffinized and rehydrated. Antigen retrieval was performed by boiling slides in sodium citrate buffer (pH 6.0) for 10 minutes.…”

Loss of myeloid cell-derived vascular endothelial growth factor accelerates fibrosis

“…Pulmonary fibrotic lesions frequently exhibit a heterogeneous increase in vessel density, and an extant and important question is whether the release of angiogenic factors enables the development of fibrosis or, conversely, if it is a compensatory mechanism to prevent more severe fibrotic changes (3,5,6). Detection of VEGF protein by Western Blot analysis in whole-lung lysates revealed markedly elevated VEGF levels after intraperitoneal bleomycin treatment (i.p.)…”

“…Among myeloid cells that infiltrate the lung during the inflammatory phase of pulmonary fibrosis, macrophages represent a major population that is also known for its ability to release large amounts of VEGF (2). The significance of angiogenesis, particularly expression of the angiogenic factor VEGF, in pulmonary fibrosis is a matter of controversy (3)(4)(5), however. In lung tissue, recent work has shown that delivery of VEGF can aggravate pulmonary fibrosis but alleviate pulmonary hypertension, highlighting the complexity of its role (6).…”

“…It has been shown in vitro that chronic hypoxia is a strong stimulus for collagen synthesis (8,9), and many genes involved in the remodeling of extracellular matrix and epithelial-to-mesenchymal transition are known HIF target genes (10); in turn, HIFs have been suggested to be involved in the development of tissue fibrosis (11). Besides the regulation of genes involved in angiogenesis, oxygen transport, and glucose metabolism (12), hypoxia and HIFs have been shown to affect Wnt/ β-catenin signaling (13,14), and the canonical Wnt/β-catenin pathway regulates crucial processes like fibroblast proliferation, myofibroblast differentiation, and epithelial-to-mesenchymal transformation, and is therefore a major pathway in the development of tissue fibrosis (5,(15)(16)(17)(18).…”