HERV-K Env-induced cell death was blocked by the endolysosome iron chelator deferoxamine in human cortical neurons (HCNs). Cell death was measured with propidium iodide (PI, red) 24 h posttreatment, and the plasma membrane was stained with MemBrite Fix 488 Cell Surface staining kit (green). A, Qualitatively, HERV-K Env (30 nM) increased PI fluorescence staining (red) and decreased and fragmented MemBrite Cell Surface fluorescence staining (green); the increases in PI staining were blocked by pretreatment (1 h) with DFO (50 µM). DFO alone (50 µM) increased neurite length in human cortical neurons. B, Quantitatively, HERV-K Env (30 nM) significantly (p < 0.0001) decreased the neurite length of HCNs; these decreases were blocked by pretreatment (1 h) with DFO (50 µM). DFO alone (50 µM) significantly (p < 0.0001) increased neurite length in HCNs. C, Quantitatively, HERV-K Env (30 nM) significantly (p < 0.0001) increased HCN cell death; this increase was blocked by pretreatment (1 h) with DFO (50 µM). An ANOVA with Tukey's post hoc multiple-comparisons test was used for analysis. Each data point represents the mean fluorescence of 10 cells performed independently three times for each group (n = 30). n = total number of cells for each group plotted. Cells were chosen randomly in the microscope's field of view and no cells were intentionally excluded. Scale bar = 20 µm. B, F_(3,16) = 48.98, p < 0.0001; (C) F_(3,16) = 379.4, p < 0.0001.