Abstract
Oxidative stress and hypoxia lead to dysfunction of retinal pigment epithelium (RPE) cells and are hallmarks of diseases such as age-related macular degeneration (AMD), the most common blinding disease in the elderly population. We have previously shown that a combination of these two risk factors, i.e. hypoxidative stress, exacerbates RPE cell death by ferroptosis. Hypoxia leads to stabilization of hypoxia-inducible factors (HIFs), key regulators of cellular adaptation to hypoxic conditions. In the present study, we have therefore investigated the roles of HIF-1 and HIF-2 in RPE cell death in a human RPE cell line under hypoxidative stress. For this purpose, we conducted siRNA-mediated knockdowns of the α-subunits of HIF-1 and HIF-2. We found that especially iron metabolism, in particular the expression of transferrin receptor 1 (TFR1) was affected by HIF-1α silencing, resulting in decreased intracellular iron levels and ferroptosis susceptibility. We also found that heme oxygenase 1 (HO-1) contributed to cell death by hypoxidative stress. In addition, we also observed that cell metabolism was improved by HIF-1α silencing under hypoxia, most likely contributing to the protective effect. Furthermore, we identified an FDA-approved small molecule inhibitor, Vorinostat, to downregulate HIF-1α, TFR1, and HO-1 and improve cell metabolism, which eventually resulted in a full rescue of RPE cells from hypoxidative stress-induced cell death. In conclusion, this study highlights the importance of considering targeted HIF inhibition as a promising approach to protect RPE cells from degeneration.