Amyloid ß aggregation induces human brain microvascular endothelial cell death with abnormal actin organization.

Cerebral amyloid angiopathy (CAA) is a disease in which amyloid ß (Aß) is deposited on the walls of blood vessels in the brain, making those walls brittle and causing cerebral hemorrhage. However, the mechanism underlying its onset is not well understood. The aggregation and accumulation of Aß cause the occlusion and fragility of blood vessels due to endothelial cell damage, breakdown of the blood-brain barrier, and replacement with elements constituting the blood vessel wall. In this study, we observed the effect of Aß on human primary brain microvascular endothelial cells (hBMECs) in real-time using quantum dot nanoprobes to elucidate the mechanism of vascular weakening by Aß. It was observed that Aß began to aggregate around hBMECs after the start of incubation and that the cells were covered with aggregates. Aß aggregates firmly anchored the cells on the plate surface, and eventually suppressed cell motility and caused cell death. Furthermore, Aß aggregation induced the organization of abnormal actin, resulting in a significant increase in intracellular actin dots over 10 µm2. These results suggest that the mechanism by which Aß forms a fragile vessel wall is as follows: Aß aggregation around vascular endothelial cells anchors them to the substrate, induces abnormal actin organization, and leads to cell death.

Three-dimensional real time imaging of amyloid ß aggregation on living cells.

Alzheimer's disease (AD) is a progressive disorder of the brain that gradually decreases thinking, memory, and language abilities. The aggregation process of amyloid ß (Aß) is a key step in the expression of its neurocytotoxicity and development of AD because Aß aggregation and accumulation around neuronal cells induces cell death. However, the molecular mechanism underlying the neurocytotoxicity and cell death by Aß aggregation has not been clearly elucidated. In this study, we successfully visualized real-time process of Aß42 aggregation around living cells by applying our established QD imaging method. 3D observations using confocal laser microscopy revealed that Aß42 preferentially started to aggregate at the region where membrane protrusions frequently formed. Furthermore, we found that inhibition of actin polymerization using cytochalasin D reduced aggregation of Aß42 on the cell surface. These results indicate that actin polymerization-dependent cell motility is responsible for the promotion of Aß42 aggregation at the cell periphery. 3D observation also revealed that the aggregates around the cell remained in that location even if cell death occurred, implying that amyloid plaques found in the AD brain grew from the debris of dead cells that accumulated Aß42 aggregates.