particles in the fAD organoids (Fig 1H). To functionally assess endosome trafficking in the control and fAD organoids, we employed the transferrin endocytosis assay, in which labeled transferrin is taken up by live cells via clathrin-mediated endocytosis [73]. Following incubation with Alexa 488-conjugated transferrin, we observed a significant increase in the size of transferrin-containing endosomes in the fAD line, compared to controls (Fig 1I). Together, these results demonstrate that AD patient-derived organoids display a third hallmark AD: abnormal endosome morphology and recycling.
