Modeling Amyloid-Beta Transport in hiPSC-Derived Models of the Blood-Brain Barrier

One of the earliest detectable changes in sporadic Alzheimer’s disease (AD) is dysfunction of the blood-brain barrier (BBB). A decrease in the ability of the BBB to transport amyloid-beta largely contributes to the accumulation of this peptide in the brain, a hallmark feature of AD. The causes of disrupted amyloid-beta transport across the BBB in AD are not fully understood. Here we used an in vitro model of the BBB composed of brain microvascular endothelial-like cells (iBMECs) differentiated from human induced pluripotent stem cells (hiPSCs) to model amyloid-beta transport. iBMEC expression of key receptors involved in amyloid-beta transcytosis, including the low-density lipoprotein receptor-related protein 1 (LRP1) and the receptor for advanced glycation endproducts (RAGE), was confirmed via immunocytochemistry and western blotting. Experimentation with iBMECs is commonly conducted 2-3 days after initial barrier formation. However, confocal microscopy revealed that proper polarization of the aforementioned receptors required iBMEC barriers to maintain a high transendothelial electrical resistance (TEER) (>1000 Ω·cm²) for at least eight days after barrier formation. Polarized barriers exhibited greater rates of amyloid-beta transport and lower sodium fluorescein permeability compared to non-polarized barriers. To probe the changes observed in polarized versus non-polarized barriers, proteomic profiling was performed using 16-plex TMT-LC/LC-MS/MS. Principal component analysis and hierarchical clustering of these data revealed that polarized and non-polarized barriers have distinct proteomes. This collective work demonstrates the suitability of iBMECs for examining amyloid-beta transport and suggests that length of time in culture is a parameter that should be taken into account when working with iBMECs.