To measure mitochondrial superoxide and the mitochondrial membrane potential state, cells were labelled with 5 μM MitoSOX Red mitochondrial superoxide indicator reagent (ThermoFisher) or with 100 nM TMRM (ThermoFisher) and were incubated for 30 min at 37 ºC. Cells then were washed with PBS prior to cell surface staining as described above and analyzed by for flow cytometry.