FIGURE 3.

Tau RD aggregates transfer between cells and induce further aggregation. A, HEK293 cells transfected with RD(ΔK)-YFP were co-cultured for 48 h with an equivalent number of cells expressing RD(LM)-HA. Cells were fixed with 4% paraformaldehyde, and immunofluorescence/X-34 staining was performed. Multiple cells showed colocalization of RD(LM)-HA and RD(ΔK)-YFP within inclusions. These inclusions also stained positive for X-34, indicating β-sheet structure (solid arrows). In addition, some RD(LM)-HA inclusions stained positive for X-34 but did not colocalize with RD(ΔK)-YFP inclusions (open arrow). B, two populations of cells, one expressing RD(ΔK)-CFP/YFP, and the other expressing RD(LM)-HA, were co-cultured for 48 h. RD(PP)-HA or non-transfected cells (NT) were used as controls. FRET was increased by co-culture with RD(LM)-HA-transfected but not with RD(PP)-HA- or mock-transfected cells (n = 3). C, to test for cell death induced by Tau aggregates as a mechanism of Tau release, HEK293 cells were transfected for 48 h with RD-HA (PP, ΔK, or LM) or were mock-transfected. Mock-transfected cells were treated with varying concentrations of staurosporine (1, 2, 4, and 20 μm) for 30 min at 37 °C to induce cell death. Cells were then exposed to 5 μg/ml propidium iodide, and fluorescence was determined via a plate reader. No evidence for cell death in the various transfected populations was observed. **, p < 0.001; error bars, S.E.