Epithelial Cell Mitochondrial Dysfunction and PINK1 Are Induced by Transforming Growth Factor- Beta1 in Pulmonary Fibrosis

Abstract

BackgroundEpithelial cell death is a major contributor to fibrogenesis in the lung. In this study, we sought to determine the function of mitochondria and their clearance (mitophagy) in alveolar epithelial cell death and fibrosis.MethodsWe studied markers of mitochondrial injury and the mitophagy marker, PTEN-induced putative kinase 1 (PINK1), in IPF lung tissues by Western blotting, transmission electron microscopy (TEM), and immunofluorescence. In vitro experiments were carried out in lung epithelial cells stimulated with transforming growth factor-β1 (TGF-β1). Changes in cell function were measured by Western blotting, flow cytometry and immunofluorescence. In vivo experiments were performed using the murine bleomycin model of lung fibrosis.ResultsEvaluation of IPF lung tissue demonstrated increased PINK1 expression by Western blotting and immunofluorescence and increased numbers of damaged mitochondria by TEM. In lung epithelial cells, TGF-β1 induced mitochondrial depolarization, mitochondrial ROS, and PINK1 expression; all were abrogated by mitochondrial ROS scavenging. Finally, Pink1 -/- mice were more susceptible than control mice to bleomycin induced lung fibrosis.ConclusionTGF-β1 induces lung epithelial cell mitochondrial ROS and depolarization and stabilizes the key mitophagy initiating protein, PINK1. PINK1 ameliorates epithelial cell death and may be necessary to limit fibrogenesis.

Mitochondria in the spotlight of aging and idiopathic pulmonary fibrosis

“…Hawkins and collaborators recently demonstrated that mutations within a surfactant protein that is linked to familial pulmonary fibrosis cause defective clearance of mitochondria (84). Studies by Patel and collaborators confirmed that PINK1-deficient mice have higher susceptibility to lung fibrosis associated with increased apoptosis (85). In addition, studies focused on lung fibroblasts demonstrated that TGF-β induces amelioration of PINK1 expression and low expression of PINK1 resulted in promotion of myofibroblast transformation (19).…”

“…Controversially, TGF-β also plays a role in the regulation of damaged mitochondria-specific autophagy or mitophagy. In lung fibroblasts, TGF-β has been shown to reduce the expression of PINK1, an important modulator of mitophagy (19), yet it has the opposite effect on PINK1 expression within the lung's epithelial cells (85).…”

“…Fibrosis results from abnormal tissue repair, and exaggerated remodeling is frequently associated with persistent and/or severe injury and cell apoptosis. Current evidence suggests that mitochondrial dysfunction plays a critical role in the vulnerability to fibrotic conditions (17,19,84,85,87,122,123). Tissue-and cell-specific pathways regulate or respond to mitochondrial function to meet ever-changing physiological needs.…”

Mitochondria in lung disease

“…In contrast, loss of mitochondrial biogenesis is associated with COPD, which may be associated with a significantly lower body mass index and lower muscle mass (ref. 48 and (44) PGC1-α and TFAM increased after S. aureus sepsis in the distal lung (44) Increased in ALI, pneumonia, hyperoxia (43) Increased upon S. aureus-associated sepsis (44), may be associated with resolution of lung injury (42) Increased in bronchial smooth muscle remodeling in asthma (46) Increased in lung cancer (47) Reduced in COPD, which may be associated with a significantly lower body mass index and less muscle mass (48) (53), and loss of PINK1 and defective mitophagy promote pulmonary fibrosis (PF) in animal models and in human idiopathic pulmonary fibrosis (IPF) (54,55). PF is characterized by irreversible destruction of lung architecture, abnormal wound healing, and deposition of extracellular matrix (ECM) proteins, leading to disruption of gas exchange and death from respiratory failure.…”

“…Mitochondria consistently play a vital role in stress responses and programmed cell death pathways. (40) Increased mROS in the PF (54) Increased in COPD (20) Increased in asthma (104) Increased in PH (108) Increased in lung cancer (106 (12) In extracellular space directly, activates inflammasome (100) Externalization during mitophagy (49) Elevated in BALF of individuals with pneumonia (12) Intratracheal injection of cardiolipin results in lower lung compliance with higher elastance and resistance (12) LYCAT altered in IPF (102).…”