Failure to clear amyloid-β (Aβ) from the brain is in part responsible for Aβ brain accumulation in Alzheimer's disease (AD). A critical protein for clearing Aβ across the blood–brain barrier is the efflux transporter P-glycoprotein (P-gp) in the luminal plasma membrane of the brain capillary endothelium. P-gp is reduced at the blood–brain barrier in AD, which has been shown to be associated with Aβ brain accumulation. However, the mechanism responsible for P-gp reduction in AD is not well understood. Here we focused on identifying critical mechanistic steps involved in reducing P-gp in AD. We exposed isolated rat brain capillaries to 100 nm Aβ40, Aβ40, aggregated Aβ40, and Aβ42. We observed that only Aβ40 triggered reduction of P-gp protein expression and transport activity levels; this occurred in a dose- and time-dependent manner. To identify the steps involved in Aβ-mediated P-gp reduction, we inhibited protein ubiquitination, protein trafficking, and the ubiquitin–proteasome system, and monitored P-gp protein expression, transport activity, and P-gp-ubiquitin levels. Thus, exposing brain capillaries to Aβ40 triggers ubiquitination, internalization, and proteasomal degradation of P-gp. These findings may provide potential therapeutic targets within the blood–brain barrier to limit P-gp degradation in AD and improve Aβ brain clearance.
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This work was supported by National Institute on Aging Grant 1R01AG039621 to A.M.S.H., 3M Science and Technology Doctoral Fellowship to A.W., 3M Grant P01-AG005119-20 to H.L., and the Division of Intramural Research at National Institute of Environmental Health Sciences/National Institutes of Health to D.S.M.
Hartz, Anika M. S.; Zhong, Yu; Wolf, Andrea; LeVine, Harry III; Miller, David S.; and Bauer, Björn, "Aβ40 Reduces P-Glycoprotein at the Blood-Brain Barrier Through the Ubiquitin-Proteasome Pathway" (2016). Sanders-Brown Center on Aging Faculty Publications. 75.