Modeling Alzheimer's disease using iPS cells reveals stress phenotypes associated with intracellular beta-amyloid oligomer and differential drug responsiveness

Abstract

Background:Aberrant metabolism of amyloid b peptide (A b) results in the formation of amyloid plaques (APs), which are pathological hallmarks of Alzheimer’s disease (AD). Most cases of AD are also associated with cerebral amyloid angiopathy (CAA) which is characterized by A b deposition around brain blood microvessels. The molecular and cellular mechanism underlying the formation of APs and CAA remain unclear. In particular, the neural cell(s) responsible for the formation of these amyloid deposits has not yet been identified, although neurons are currently believed to be the major source of A b. However, this view lacks concrete evidence. In fact, reactive astrocytes have been shown to be very active for the production of A b, and brain vascular microvessel endothelial cells (ECs) and brain vascular smooth muscle cells (BVSMCs) can produce A b. In this study, we further characterized the A b production in ECs in terms of the pathogenesis of CAA. Methods: Human umbilical vein endothelial cells were used as a model of ECs. A b is adhesive and can bind to the extracellular matrix (EM). As the EM is more abundant at a high cell density, the level of free A b released from ECs may be affected by the cell density.To test this hypothesis, ECs were cultured at different cell densities, and the level of A b in the culture medium was analyzed by ELISA. Results: The Ab production in ECs was 2-4-fold higher at a low cell density than at a high cell density, where A b degrading activity was detected in the culture medium. Conclusions: The A b production in ECs was dependent on the cell density and it was suppressed at a high cell density, where physiologically-relevant cell-cell interactions in bloodmicrovessels may occur. Even under such conditions, the A b production of ECs was more than 100-fold higher than that of human BVSMCs cultured under similar conditions. These findings suggest that ECs, rather than the BVSMCs, play a major causative role in CAA, although the contribution of pericytes and astroglial cells, which are other components of the brain microvessels, remains unclear.