Mitochondrial reactive oxygen species are required for hypoxia‐induced degradation of keratin intermediate filaments

Abstract

Hypoxia can cause stress and structural changes to the epithelial cytoskeleton. The intermediate filament network is known to reorganization in response to stress. We examined whether rats exposed to hypoxia (8% O2; 24 h) had altered keratin IF expression in their alveolar epithelial cells (AEC). There was a significant decrease in keratin protein abundance in hypoxic AEC as compared to AEC isolated from normoxic, control rats. To define the potential mechanisms regulating this process we studied changes to the keratin IF network in human A549 cells exposed to 1.5% oxygen; 24 h. We observed a time dependent disassembly/degradation of keratin 8 and 18 proteins which was associated with an increase in reactive oxygen species (ROS). Hypoxia‐treated A549 cells deficient in mitochondrial DNA or A549 cells treated with a small interfering RNA against the Rieske iron‐sulfur protein of mitochondrial complex III did not have increased levels of ROS, nor was the keratin IF network disassembled/degraded. The catalase/superoxide dismutase (SOD) mimetic (EUK‐134) prevented the hypoxia‐mediated keratin IF degradation as did the overexpression of SOD1, but not SOD2. Accordingly, we provide evidence that hypoxia promotes the disassembly/degradation of the keratin IF network via mitochondrial complex III‐generated reactive oxygen species.