Perforin Promotes Amyloid Beta Internalisation in Neurons. 
Studies on the mechanisms of neuronal amyloid-β (Aβ) internalisation are crucial for understanding the neuropathological progression of Alzheimer's disease (AD).  We here investigated how extracellular Aβ peptides are internalised and focused on three different pathways: (i) via endocytic mechanisms, (ii) via the receptor for advanced glycation end products (RAGE) and (iii) via the pore-forming protein perforin.  Both Aβ40 and Aβ42 were internalised in retinoic acid differentiated neuroblastoma (RA-SH-SY5Y) cells.  A higher concentration was required for Aβ40 (250 nM) compared with Aβ42 (100 nM).  The internalised Aβ40 showed a dot-like pattern of distribution whereas Aβ42 accumulated in larger and distinct formations.  By confocal microscopy, we showed that Aβ40 and Aβ42 co-localised with mitochondria, endoplasmic reticulum (ER) and lysosomes.  Aβ treatment of human primary cortical neurons (hPCN) confirmed our findings in RA-SH-SY5Y cells, but hPCN were less sensitive to Aβ; therefore, a 20 (Aβ40) and 50 (Aβ42) times higher concentration was needed for inducing uptake.  The blocking of endocytosis completely inhibited the internalisation of Aβ peptides in RA-SH-SY5Y cells and hPCN, indicating that this is a major pathway by which Aβ enters the cells.  In addition, the internalisation of Aβ42, but not Aβ40, was reduced by 55 % by blocking RAGE.  Finally, for the first time we showed that pore formation in cell membranes by perforin led to Aβ internalisation in hPCN.  Understanding how Aβ is internalised sheds light on the pathological role of Aβ and provides further ideas of inhibitory strategies for preventing Aβ internalisation and the spreading of neurodegeneration in AD.