Summary: P-glycoprotein (P-gp), a key cellular toxin pump, can remove amyloid plaques from the brain. Researchers report that boosting P-gp activity at the blood–brain barrier in people at risk for Alzheimer’s disease might delay or prevent the condition’s onset.
Source: Southern Methodist University
Researchers in the SMU Department of Biological Sciences have confirmed that P-glycoprotein (P-gp) can transport a toxin linked to Alzheimer’s disease out of brain cells.
This discovery could inform new approaches to treating or preventing Alzheimer’s, a disorder that affects millions. The study was motivated in part by personal experience: lead researchers James W. McCormick and Lauren Ammerman pursued the work after each lost a grandmother to the disease while they were graduate students at SMU.
In people with Alzheimer’s, amyloid-β proteins can accumulate and clump into plaques between neurons, disrupting cell communication and contributing to memory loss and cognitive decline. Understanding how those proteins are cleared from the brain is critical to developing therapies that slow or stop disease progression.
“Using computational models and laboratory experiments, we showed that P-gp — a crucial cellular pump — can transport amyloid-β,” said John Wise, associate professor in the SMU Department of Biological Sciences and co-author of the study published in PLOS ONE.
Wise added that if scientists can safely increase P-gp expression or activity at the blood–brain barrier for people at risk of Alzheimer’s, such interventions might postpone or prevent development of the disease. He emphasized that this idea requires further research and careful testing.
The SMU study also provides strong evidence that P-gp can handle much larger molecular cargo than previously thought, expanding our understanding of what this transporter can do.
P-glycoprotein acts like a cellular pump that removes harmful substances from cells. Much like a sump pump removes unwanted water from a basement, P-gp binds potentially toxic molecules inside the cell and expels them back into the surrounding tissue.
“P-gp is found wherever the body needs to protect an organ from toxins, and the brain is no exception,” explained co-author Pia Vogel, SMU professor and director of SMU’s Center for Drug Discovery, Design and Delivery.
Because amyloid-β molecules are relatively large compared with typical drug-like compounds, there was reason to doubt whether P-gp could capture and transport them. “Amyloid-β is roughly five times larger than the small molecules P-gp usually handles,” Wise said. “It’s like trying to fit a large pizza slice into your mouth all at once.”
The finding that P-gp can transport amyloid-β suggests a wider substrate range for the transporter and raises the possibility that it interacts with other large molecules previously considered beyond its capability, said McCormick, a former SMU graduate student.
The research was personal
This line of inquiry began because McCormick wanted to probe a tentative link between P-gp and amyloid-β. While his advisors Vogel and Wise initially focused on P-gp’s role in chemotherapy resistance, McCormick persisted in exploring whether the pump could protect against Alzheimer’s. He and his colleagues used computational modeling to test the idea.
Working with a computer-generated model of P-gp created by Wise and McCormick, the team examined how different molecules might interact with the pump. McCormick carried out extensive simulations on SMU’s high-performance computer, ManeFrame II, with support from his then-fiancé Lauren Ammerman, who also completed a Ph.D. in biology at SMU.
Their molecular dynamics simulations repeatedly showed that P-gp could bind and move amyloid-β monomers through a putative transport cycle, indicating the pump’s capacity to handle larger peptide substrates.
“For the scientist in me, it was remarkable to see a pump consume something that size,” Vogel said. “John and I did not expect this outcome.”
Two in vitro experiments confirmed the computational predictions
The team validated their simulations with two laboratory experiments.
In the first experiment, Ammerman used fluorescently labeled amyloid-β proteins to visualize their movement under a microscope. She exposed two types of human cells to the labeled amyloid-β: one cell line that highly expressed P-gp and another with little or no P-gp expression. The cells overexpressing P-gp showed clear evidence that the labeled amyloid-β was being expelled, supporting the idea that P-gp can remove these proteins from cells.
A separate biochemical experiment, conducted by former graduate student Gang (Mike) Chen in SMU’s Center for Drug Discovery, Design and Delivery, measured how amyloid-β affects P-gp’s ATPase activity. ATP hydrolysis powers P-gp transport; when P-gp engages cargo, its ATPase activity increases. Chen found that exposure to amyloid-β altered P-gp’s ATP usage, indicating a direct physical interaction and active transport of the peptide.
“Although this work cannot help our own grandparents, we hope it will aid others in the future,” Ammerman said. “The more we understand these mechanisms, the better positioned future researchers will be to develop therapies targeting devastating diseases like Alzheimer’s.”
About this Alzheimer’s disease research news
Source: Southern Methodist University
Contact: Monifa Thomas-Nguyen – Southern Methodist University
Image: The image is in the public domain
Original Research: Open access. “Transport of Alzheimer’s associated amyloid-β catalyzed by P-glycoprotein” by James W. McCormick et al., PLOS One
Abstract
Transport of Alzheimer’s associated amyloid-β catalyzed by P-glycoprotein
P-glycoprotein (P-gp) is an important membrane transporter at the blood–brain barrier and has been implicated in Alzheimer’s disease (AD). Prior studies gave conflicting results about whether P-gp can directly transport Alzheimer’s-associated amyloid-β (Aβ).
In this study, researchers combined molecular dynamics simulations, substrate accumulation assays in cell culture, and biochemical activity measurements to demonstrate that P-gp actively transports Aβ.
The team observed transport of Aβ40 and Aβ42 monomers in detailed molecular dynamics simulations of a catalytic-like cycle. In vitro, cells overexpressing P-gp accumulated more fluorescent Aβ42 when treated with Tariquidar, a potent P-gp inhibitor, indicating that blocking P-gp increases intracellular Aβ. Isolated P-gp in membrane nanodiscs also showed stimulated ATP hydrolysis in the presence of Aβ42, consistent with active transport.
These results broaden the known substrate profile of P-gp and suggest it may play a role in the onset and progression of Alzheimer’s disease by participating in Aβ clearance at the blood–brain barrier.