Stress in the ER (endoplasmic reticulum): a matter of life and death for epithelial cells

Interstitial lung disease: physiopathology in the context of lung growth

Interstitial lung diseases (ILDs) in children represent a heterogeneous group of respiratory disorders characterized by derangements of the alveolar walls. The key pathologic feature of ILDs is the altered repair of the alveolar surface after injury with a marked disruption in the integrity of the epithelium and, consequently, a dysregulated communication between epithelial and mesenchymal pulmonary components. Concomitant to the loss of cell-cell contact, epithelial cells undergo a process called epithelial to mesenchymal transition and acquire a mesenchymal identity. Among the factors involved in disease progression, transforming growth factor-β has been identified as a master switch in the induction of fibrosis. This article reviews recent advances in the understanding of the mechanisms involved in the pathogenesis of ILDs, and provides information on their adaptation in the context of lung growth.

Lung alveolar epithelium and interstitial lung disease

Interstitial lung diseases (ILDs) comprise a group of lung disorders characterized by various levels of inflammation and fibrosis. The current understanding of the mechanisms underlying the development and progression of ILD strongly suggests a central role of the alveolar epithelium. Following injury, alveolar epithelial cells (AECs) may actively participate in the restoration of a normal alveolar architecture through a coordinated process of re-epithelialization, or in the development of fibrosis through a process known as epithelial-mesenchymal transition (EMT). Complex networks orchestrate EMT leading to changes in cell architecture and behaviour, loss of epithelial characteristics and gain of mesenchymal properties. In the lung, AECs themselves may serve as a source of fibroblasts and myofibroblasts by acquiring a mesenchymal phenotype. This review covers recent knowledge on the role of alveolar epithelium in the pathogenesis of ILD. The mechanisms underlying disease progression are discussed, with a main focus on the apoptotic pathway, the endoplasmic reticulum stress response and the developmental pathway.