Detecting physiological concentrations of Alzheimer's associated amyloid-β oligomers with a cell-based response.

Abstract

Alzheimer's disease (AD) is characterized by blood-brain barrier (BBB) breakdown and neuronal cell death, associated with aggregated amyloid-β (Aβ) plaques deposited around brain vasculature and within the brain. Changes in the brain occur up to 20 years before symptoms arise; however, there is currently no pre-symptomatic detection method available for AD. An intact BBB requires tight junctions (TJ) that render relatively high transendothelial electrical resistance (TEER). AD-associated breakdown of the BBB correlates with vascular Aβ deposition, suggesting that aggregated, pathological Aβ can modulate TEER. We explore leveraging this cellular response for early disease diagnosis via detection of early Aβ aggregates. Primary human brain microvascular endothelial cells (HBMVECs) were cultured on a suspended membrane and supplemented to mimic the BBB. Once TEER values reflected TJ formation, HBMVEC monolayers were treated with oligomeric Ab at picomolar to nanomolar concentrations, and TEER was monitored. Oligomeric Aβ at picomolar and nanomolar concentrations, but not monomer, induced a reduction of TEER and disruption of TJs. These results demonstrate that pathogenic Aβ aggregates are uniquely responsible for inducing endothelial monolayer permeability and reducing monolayer electrical resistance, and this response can be detected at physiological concentrations. This work also validates that introduction of physiologically active Aβ oligomers can increase permeability of an endothelial monolayer, while non-pathogenetic monomer is inert. These results provide evidence that oligomers, the pathogenic form of Aβ, selectively break down the BBB. Future work will include establishing a threshold of Aβ oligomer concentrations that reduce TEER to establish cellular sensitivity, and sensitizing cells to obtain a more pronounced response. Translation of this experimental system to a cell-based biosensor platform will lay the groundwork for the development of cost-effective, early AD detection.