Amphiregulin-Dependent Mucous Cell Metaplasia in a Model of Nonallergic Lung Injury

Abstract

Proliferation and differentiation of the pulmonary epithelium after injury is a critical process in the defense against the external environment. Defects in this response can result in airway remodeling, such as mucus cell metaplasia (MCM), commonly seen in patients with chronic lung disease. We have previously shown that amphiregulin (AREG), a ligand to the epidermal growth factor receptor (EGFR), is induced during the repair/differentiation process elicited by naphthaleneinduced lung injury. Thus, we hypothesized that AREG signaling plays an important role in epithelial proliferation and differentiation of the repairing airway. Mice deficient in AREG and lung epithelial EGFR were used to define roles for AREG-dependent EGFR signaling in airway repair and remodeling. We show that AREG and epithelial EGFR expression is dispensable to pulmonary epithelial repair after naphthalene-induced lung injury, but regulates secretory cell differentiation to a mucusproducing phenotype. We show that the pulmonary epithelium is the source of AREG, suggesting that naphthalene-induced MCM is mediated through an autocrine signaling mechanism. However, induction of MCM resulting from allergen exposure was independent of AREG. Our data demonstrate that AREG-dependent EGFR signaling in airway epithelial cells contributes to MCM in naphthaleneinduced lung injury. We conclude that AREG may represent a determinant of nonallergic chronic lung diseases complicated by MCM.Keywords: Clara cells; epidermal growth factor receptor; amphiregulin; mucus cell metaplasiaThe epithelium lining the lungs plays a critical role in defense against inhaled particles, viruses, and xenobiotics. In health, the pulmonary epithelium can adapt to these insults by the induction of defensive mechanisms, which include increased secretory cells and the secretions they produce, such as mucins (1). Even though these changes typically resolve after acute airway injury, in humans with chronic lung diseases, such as asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis, these mechanisms may be compromised, resulting in pathologic remodeling of airways, including mucus cell metaplasia (MCM) and mucus hypersecretion (2-4). Much attention has been placed on understanding roles for T helper cell type 2 cytokines and inflammatory mediators in regulating epithelial remodeling and mucus production. Growth factors, such as epidermal growth factor (EGF) and related ligands for the EGF receptor (EGFR), have been shown to contribute to cellular proliferation and MCM that accompanies exposure to allergens and pneumotropic viruses (5). However, it is not clear what mechanisms drive epithelial remodeling and MCM in nonallergic lung diseases.We previously demonstrated that amphiregulin (AREG), a ligand that binds to EGFR, was significantly up-regulated during repair from naphthalene-induced lung injury (6). Parenterally delivered naphthalene is bioactivated to a toxic naphthalene dihydrodiol by cytochrome P450 mono-oxygenases, which results in depletion of airwa...

Alveolar Epithelial A2B Adenosine Receptors in Pulmonary Protection during Acute Lung Injury

“…Alveolar-epithelial-cell-specific Adora2b deletion was achieved by crossing transgenic mice with a floxed Adora2b gene with mice that constitutively express Cre recombinase in alveolar epithelial cells ( Adora2b loxP/loxP SPC Cre+). Indeed, Adora2b loxP/loxP SPC Cre+ mice had normal expression levels of the Adora2b transcript in isolated pulmonary endothelial cells and alveolar macrophages, whereas A2B adenosine receptor transcript levels in isolated murine alveolar epithelial cells were essentially undetectable (42) (Fig. 4A).…”

DUOX1 mediates persistent epithelial EGFR activation, mucous cell metaplasia, and airway remodeling during allergic asthma

“…These observations suggest that AREG is primarily responsible for the observed sustained EGFR activation in asthmatic airways. Moreover, AREG may also contribute to mucous cell metaplasia in some conditions, although its contribution to mucous cell metaplasia in the context of allergic asthma is less clear (50). Although the EGF ligands responsible for the various asthma phenotypes need to be further unraveled, DUOX1 is clearly involved in EGFR activation irrespective of the activating ligand.…”

Human neutrophil elastase-mediated goblet cell metaplasia is attenuated in TACE-deficient mice

“…Our results are consistent with conditional deletion of Tace attenuating GCM through inhibition of EGFR activation, which builds on evidence that EGFR is a prominent mediator in airway remodeling events, including GCM (3). TACE proteolytically sheds a variety of EGFR ligands, such as amphiregulin (18), TGF-␣ (14,29), and heparin-binding epidermal growth factor-like growth factor (30), which together contribute to the activation of EGFR and the development of GCM in different model systems. We previously showed that TACE deletion attenuated EGFR-mediated responses in cultured mouse tracheal epithelial cells in vitro (30), demonstrating that TACE acts as a common upstream mediator of EGFR ligand shedding in these cells.…”

“…TACE, also known as a disintegrin and metalloproteinase 17 (ADAM17), is a membrane-anchored enzyme that cleaves cell-surface proteins including epidermal growth factor receptor (EGFR) ligands, cytokines and their receptors, and adhesion molecules (2,27). Among EGFR ligands, amphiregulin has been shown to contribute to GCM that occurs during naphthalene-induced lung injury in mice (18).…”