Decreased FSP1 expression under chronic hypoxia sensitizes human macrophages towards ferroptosis

Ferroptosis, an iron-dependent cell death, emerged as a new therapeutic approach to treat diseases such as cancer or diabetes. Several pathological conditions are characterized by the appearance of chronic hypoxia, which is known to attract immune cells, especially monocytes and macrophages. Therefore, we investigated how chronic hypoxia affects ferroptosis in primary human macrophages and THP-1 cells. Chronic but not acute hypoxia sensitized cells towards ferroptosis, in line with elevated cellular as well as mitochondrial lipid peroxides, and mitochondrial ROS. Time kinetics revealed an earlier increase in lipid peroxidation under chronic hypoxia compared to normoxia, which was followed by mitochondrial lipid peroxidation and mitochondrial ROS. Mechanistically, and in contrast to normoxia and/or acute hypoxia, chronic hypoxia diminished nuclear abundance and activity of the antioxidant transcription factor NRF2. Consequently, NRF2 target gene expression, including ferroptosis suppressor protein 1 (FSP1), decreased. Inhibition or knockdown of FSP1 mimicked the ferroptosis-sensitizing effect of chronic hypoxia. To causatively link decreased NRF2 activity to increased ferroptosis under hypoxia, we inhibited KEAP1, which preserved NRF2 activity, increased FSP1 expression, and decreased ferroptosis. Our data provides novel insights into NRF2 regulation under chronic hypoxia linked to FSP1 expression and ferroptosis sensitivity of primary human macrophages.