Targeting hypoxia-inducible factor-1 in a hypoxidative stress model protects retinal pigment epithelium cells from cell death and metabolic dysregulation

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.