P-glycoprotein: a role in the export of amyloid-β in Alzheimer's disease?

The accumulation of amyloid-beta (A beta) peptides is a key histopathological feature of the Alzheimer's brain. Defective clearance mechanisms result in toxic levels of soluble A beta(40) and A beta(42) oligomers, leading to impaired synaptic function, neurodegeneration and cognitive decline. Growing evidence points to the involvement of P-glycoprotein (P-gp or ABCB1), an ATP-binding cassette transporter highly expressed on the luminal side of the blood-brain barrier, in facilitating the clearance of A beta from the brain. In this review, we summarise evidence from human, animal and in vitro studies examining the contribution of P-gp to A beta clearance, and discuss the potential for P-gp as a novel pharmacological target in Alzheimer's disease (AD). P-gp expression and activity in the brain are inversely correlated with ageing, A beta deposition and AD. Moreover, A beta itself has been found to compromise the expression of P-gp, thereby exacerbating A beta deposition and disease. Despite decades of research, the pathophysiology of AD remains elusive. Understanding the normal versus impaired processing and clearance mechanisms affecting A beta peptides will assist the development of more effective therapeutic agents to combat this progressive neurodegenerative condition that continues to devastate millions of patients globally.