Transport of the Alzheimer's Disease Associated Amyloid‐Beta Peptide by P‐Glycoprotein

Abstract

The broad range of substrates that can be transported by the transmembrane protein, P‐glycoprotein (P‐gp), has been well established. While best known for the ability to confer general multidrug resistance to a population of cancer cells and for its pharmacokinetic implications in being a critical transporter in the blood brain barrier (BBB), P‐gp action has also been implicated in Alzheimer's disease (AD). One clearance pathway across the BBB for amyloid‐β, which is thought to be a causative agent in neurodegeneration and symptom onset in AD, was hypothesized to be catalyzed by P‐gp. A dynamic P‐gp model similar to that used in McCormick et al. (Biochemistry 2015) was used here to allow docking of amyloid‐β and an unrelated peptide of the same size to P‐gp. Simulations of the catalytic cycles through four different crystallographic conformations of P‐gp‐related proteins using targeted molecular dynamics (TMD) were performed. Even though movement of amyloid‐β was not targeted by the method, transport of amyloid‐β through the membrane was observed during the putative catalytic cycles. These simulations started with amyloid‐β bound to P‐gp in conformations that were open to the cytoplasm and ended with amyloid‐β bound to P‐gp in conformations that would allow amyloid‐β access to the extracellular space. In simulations using a control peptide of the same length, no transport was observed. In experiments to physically evaluate the computational results, synthetic amyloid‐β 42 was fluorescently labeled with carboxyfluorescein and incubated with cells having P‐gp overexpressed. The experiments showed that cell lines with high levels of P‐gp had measurably less accumulation of the fluorescent amyloid‐β 42 than cells with low expression levels of P‐gp. Amyloid‐β accumulation was inhibited in the presence of P‐gp specific inhibitors, supporting the hypothesis that P‐gp plays a role in the clearance of amyloid‐β 42 from the brain.Support or Funding InformationThis work is supported by NIH NIGMS [R15GM09477102] to JGW/PDV, SMU University Research Council, SMU Engaged Learning program, the SMU Center for Drug Discovery, Design and Delivery, the Communities Foundation of Texas, and a private gift from Ms. Suzy Ruff of Dallas, Texas.