Transferrin receptor is a specific ferroptosis marker

Ferroptosis is a form of regulated cell death driven by the iron-dependent accumulation of oxidized polyunsaturated-fatty-acid-containing phospholipids (PUFA-PLs). Three key molecular features of ferroptosis are peroxidation of PUFA-PLs, accumulation of redox-active ferrous iron, and defective lipid peroxide repair (Dixon and Stockwell, 2019). However, there is currently no reliable way to selectively stain ferroptotic cells in tissue sections to characterize the extent of ferroptosis in animal models of disease and in patient tissue samples. We sought to address this gap by immunizing mice with membranes from lymphoma cells treated with the ferroptosis inducer piperazine erastin (PE), and screening ~4,750 of the resulting monoclonal antibodies generated for their ability to selectively detect cells undergoing ferroptosis. We found that one antibody, termed 3F3 Ferroptotic Membrane Antibody (3F3-FMA), was effective as a selective ferroptosis-staining reagent using immunofluorescence (IF). The antigen of 3F3-FMA was identified by immunoprecipitation and mass spectrometry as the human transferrin receptor 1 protein (TfR1), which imports iron from the extracellular environment into cells. We validated this finding with several additional anti-TfR1 antibodies, and compared them to other potential ferroptosis-detecting reagents via immunofluorescence staining, using fluorescence microscopy and flow cytometry. We found that anti-TfR1 and anti-malondialdehyde (MDA) adduct antibodies were effective at reliably staining ferroptotic tumor cells in numerous cell culture and tissue contexts. In summary, these findings suggest that anti-TfR1 antibodies can be used to selectively label cells undergoing ferroptosis.