The Role of Epiregulin in Idiopathic Pulmonary Fibrosis

Abstract

Idiopathic pulmonary fibrosis (IPF) remains a progressive and fatal disease despite current antifibrotic therapies, highlighting the need for the identification of novel targetable pathways. This thesis investigated the role of the ErbB ligand epiregulin (EREG) in IPF pathogenesis, focusing on its effects on airway epithelial cell morphology, proliferation and senescence.<br>In vitro, EREG promoted proliferation and differentiation of human airway epithelial cells, causing replication stress and DNA damage in basal cells, as shown by increased numbers of p63+/PCNA+ and p63+/γH2Ax+ cells, finally leading to senescence indicated by p21+ co-staining. In vivo, intratracheal administration of EREG in bleomycin-treated mice had little effect on pulmonary fibrosis, as lung function, histology and senescence-associated secretory phenotype (SASP) mediators in bronchoalveolar lavage fluid (BALF) remained largely unchanged. Immunohistochemistry (IHC) revealed increased numbers of ΔNp63+, PCNA+ and p21+ cells after bleomycin instillation, further augmented by EREG treatment. Notably, clusters of Δp63+ cells were detected in lung parenchyma in dense fibrotic regions, suggesting expansion of specific basal cell subsets, including abnormal basal or aberrant basaloid cells (ABCs) following injury. Fluorescence-activated cell sorting (FACS) analysis revealed no additional effect of EREG beyond those induced by bleomycin. However, distinct responses emerged between MHCII-proximal airway and MHCII+ alveolar epithelial cells. In the latter, SOX2 and p21 signal increased following bleomycin exposure, suggesting the induction of senescence and a partial reversion toward a progenitor-like state. These observations underscore the cellular plasticity and complexity of basal cell dynamics in lung injury and repair.<br>Future studies using additional epithelial and mesenchymal markers will be essential to define these cell populations more precisely and clarify their roles in fibrotic remodeling. Overall, these findings indicate that EREG promotes hyperproliferation, DNA damage and senescence in vitro, whereas its direct impact in vivo appears limited, highlighting the need for more refined animal models. Nevertheless, the in vivo results offer new insights into epithelial cell dynamics during injury response and their contribution to bronchiolization, maladaptive remodeling and senescence, processes also observed in IPF. Future studies should investigate species-specific differences, employ transgenic models with EREG overexpression and further characterize basal cell subpopulations to entangle the complex interplay between EREG signaling, epithelial remodeling and fibrogenesis.