Endothelin-1 Induces Alveolar Epithelial–Mesenchymal Transition through Endothelin Type A Receptor–Mediated Production of TGF-β1

Abstract

Endothelin-1 (ET-1) is implicated in the pathogenesis of idiopathic pulmonary fibrosis (IPF), but the cellular mechanisms underlying the role it plays in this disease are not well characterized. Epithelialmesenchymal transition (EMT), which was recently demonstrated in alveolar epithelial cells (AEC), may play an important role in the pathogenesis of IPF and other forms of pulmonary fibrosis. Whether ET-1 contributes to the induction of EMT in AEC is unknown. The aims of this study were to evaluate AEC production of ET-1 and to determine if ET-1 induces EMT in AEC. We demonstrate that ET-1 is produced at physiologically relevant levels by primary AEC and is secreted preferentially toward the basolateral surface. We also demonstrate that AEC express high levels of endothelin type A receptors (ET-A) and, to a lesser extent, type B receptors (ET-B), suggesting autocrine or paracrine function for alveolar ET-1. In addition, ET-1 induces EMT through ET-A activation. Furthermore, TGF-␤1 synthesis is increased by ET-1, ET-1 induces Smad3 phosphorylation, and ET-1-induced EMT is attenuated by a TGF-␤1-neutralizing antibody. Thus, ET-1 is an important mediator of EMT in AEC, acting through ET-A-mediated TGF-␤1 production. These findings increase our basic understanding of the role of ET-1 in pulmonary fibrosis and suggest potential roles for AEC-derived ET-1 in the pathogenesis of other alveolar epithelial-mediated lung diseases.

Insights into cellular signalling by G protein coupled receptor transactivation of cell surface protein kinase receptors

“…The thrombin mediated increase of phospho-Smad2C is insensitive to cycloheximide, suggesting the transactivation pathway is independent of gene activation and de novo protein synthesis ) and therefore meets the earlier mentioned definition of GPCR transactivation signalling (Little 2013). Other GPCR agonists such as factor Xa, Ang II, endothelin-1 and LPA also lead to time-dependent generation of phosphorylated Smad2/3 via an interplay of the various mechanisms described below Scotton et al 2009;Jain et al 2007;Jenkins et al 2006;Tatler et al 2011). Our work in VSMCs shows thrombin transactivation of the TGFBR1 involves cytoskeletal rearrangement which activates ROCK signalling leading to the activation of integrin-dependent signalling and ultimately the activation of the large latent complex which holds TGF-β near the cell surface with the potential for rearrangement and activation of TGFBR1 .…”

Transforming Growth Factor β1 Function in Airway Remodeling and Hyperresponsiveness. The Missing Link?

“…In addition, collagen and cadherin, two profibrotic proteins induced by TGF-b1, have been shown to promote EMT (70,71). Furthermore, p38 MAPK activation, oxidative stress, endothelin-1, Wnt signaling, and cytokine signaling modulate TGF-b1-induced EMT (68,(72)(73)(74)(75)(76).…”

Transforming Growth Factor-β1 (TGF-β1) Driven Epithelial to Mesenchymal Transition (EMT) is Accentuated by Tumour Necrosis Factor α (TNFα) via Crosstalk Between the SMAD and NF-κB Pathways

“…This process involves the down regulation of epithelial markers such as cytokeratin and the adherens proteins E-cadherin and ZO-1 and the up regulation of mesenchymal markers including vimentin, fibronectin and α-smooth muscle actin (α-SMA). Additionally cells undergoing EMT gain functional characteristics of mesenchymal cells such as acquiring invasive potential and the ability to secrete matrix metalloprotinases (MMP's) and extra cellular matrix (ECM) proteins [2][3][4].…”