Astrocytes can phagocytose and degrade β-amyloid in AD (Chung et al., 2013, Wyss-Coray et al., 2003). We used flow cytometry to examine the ability of control hiPSC-astrocytes to phagocytose pHrodo red conjugated myelin or zymosan bioparticles (pHrodo red dye fluoresces red in the acidic environment of phagosomes; zymosan is an agonist of Toll-like receptor 2 [TLR2] [Marinelli et al., 2015, Richard et al., 2008]). hiPSC-astrocytes, primary human fetal astrocytes, and BV2 microglia showed a similar capacity to internalize myelin purified from brain homogenates, while zymosan bioparticle uptake was much greater in microglia (consistent with higher levels of TLR2 reported in microglia) (Jana et al., 2008) (Figures 4A, 4B, and S4A–S4C; Movie S1. Phagocytosis of Myelin in BV2 Microglia, Movie S2. Phagocytosis of Myelin in hiPSC-Astrocytes, Movie S3. Phagocytosis of Myelin in Primary Astrocytes). The specificity of bioparticle uptake was confirmed by treating cells with cytochalasin D, an inhibitor of β-actin polymerization that reduces phagocytosis (Figures 4A and 4B).
