Blood-Brain Barrier P-Glycoprotein a New Target for Alzheimers Disease

There is a fundamental lack in understanding the mechanism that reduces P-glycoprotein (P-gp) expression and transport activity at the blood-brain barrier in Alzheimer’s disease (AD). Lack of this knowledge is a signifi-cant clinical problem since it prevents development of an effective therapy to enhance Aâ clearance from the brain and lower Aâ brain levels in AD. The long-term goal of the investigator is to better understand the molec-ular mechanisms that regulate blood-brain barrier function in neurodegenerative disorders, a goal which may lead to new therapeutic strategies to treat AD. The objectives of this particular application are to identify the mechanism responsible for reducing P-gp in AD, to validate this mechanism as a target to protect P-gp, and to test a novel therapeutic strategy for restoring P-gp levels. Accomplishing these objectives is expected to re-duce Aâ brain levels and improve cognition in AD. Based on preliminary data, the central hypothesis is that Aâ mediates proteasomal degradation of P-gp, that blocking such degradation protects P-gp, and that restoring P-gp levels through PXR activation reduces Aâ brain burden and improves cognition in mice with AD. The ra-tionale for the proposed research is that identifying the mechanism that reduces brain capillary P-gp and pro-tecting and/or restoring P-gp to improve Aâ brain clearance will potentially provide novel therapeutic targets to lower Aâ brain levels in AD. To accomplish the objectives of this application, we will test our central hypothesis by pursuing the following three specific aims: 1) Identify the mechanism of Aâ-mediated P-gp reduction at the blood-brain barrier. 2) Validate the ubiquitin-proteasome system as a target to protect P-gp in an AD mouse model. 3) Develop a therapeutic strategy to restore P-gp and reduce Aâ brain levels in an AD mouse model. In Aim 1, we will inhibit ubiquitination, protein trafficking, and the proteasome to identify the steps involved in Aâ-mediated P-gp reduction, and we will determine expression, transport activity, and ubiquitination of P-gp. In Aim 2, we will treat hAPP mice with inhibitors of the ubiquitin-proteasome system, monitor P-gp expression, transport activity, and ubiquitination, and measure Aâ brain levels. We will conduct brain perfusion to assess P-gp activity in vivo and perform tail-flick experiments to determine the pharmacological consequence of changes in P-gp. In Aim 3, we will conduct a 2-year PCN-feeding study with hAPP mice to assess the long-term therapeutic effect of restoring P-gp through PXR activation on Aâ brain levels. P-gp expression and transport activity, Aâ brain load, learning, and memory will be periodically determined. The proposed research is innovative because it focuses on two independent strategies designed specifically to enhance Aâ clearance from the brain in AD. The proposed research is significant because it holds the promise of two new therapeutic strategies to lower Aâ brain burden and slow progression of AD. The proposed research is translational be-cause drugs for either strategy, proteasome inhibition and PXR activation, are currently on the market, and both therapeutic strategies could potentially be translated into the clinic for the treatment of AD patients.