Hyperoxia exposure arrests alveolarization in neonatal rats via PTEN-induced putative kinase 1-Parkin and Nip3-like protein X-mediated mitophagy disorders

Abstract

Bronchopulmonary dysplasia (BPD), also known as chronic lung disease, is one of the most common respiratory diseases in premature new-born humans. Mitochondria are not only the main source of reactive oxygen species but are also critical for the maintenance of homeostasis and a wide range of biological activities, such as producing energy, buffering cytosolic calcium and regulating signal transduction. However, as a critical quality control method for mitochondria, little is known about the role of mitophagy in BPD. The present study assessed mitochondrial function in hyperoxia-exposed alveolar type II (AT-II) cells of rats during lung development. New-born Sprague-Dawley rats were divided into hyperoxia (85% oxygen) and control (21% oxygen) groups. Histopathological and morphological properties of the lung tissues were assessed at postnatal days 1, 3, 7 and 14. Ultrastructural mitochondrial alteration was observed using transmission electron microscopy and the expression of the mitophagy proteins putative kinase (PINK)1, Parkin and Nip3-like protein X (NIX) in the lung tissues was evaluated using western blotting. Immunofluorescence staining was used to determine the co-localisation of PINK1 and Parkin. Real-time analyses of extracellular acidification rate and oxygen consumption rate were performed using primary AT-II cells to evaluate metabolic changes. Mitochondria in hyperoxia-exposed rat AT-II cells began to show abnormal morphological and physiological features. These changes were accompanied by decreased mitochondrial membrane potential and increased expression levels of PINK1-Parkin and NIX. Increased binding between a mitochondria marker (cytochrome C oxidase subunit IV isoform I) and an autophagy marker (microtubule-associated protein-1 light chain-3B) was observed in primary AT-II cells and was accompanied by decreased mitochondrial metabolic capacity in model rats. Thus, mitophagy mediated by PINK1, Parkin and NIX in AT-II cells occurred in hyperoxia-exposed new-born rats. These findings suggested that the accumulation of dysfunctional mitochondria may be a key factor in the pathogenesis of BPD and result in attenuated alveolar development.