DT‐01‐01: Plasma Membrane Monoamine Transporter Modulates Bace1 Activity

Elevation and accumulation of amyloid b-peptide (Ab) are hallmark pathological characteristics of Alzheimer’s disease (AD) in animal models and patients. The production of Ab is mediated by cleavage of amyloid precursor protein (APP) by two proteolytic enzymes, b-site cleaving enzyme (BACE1) and γ-secretase. Recent work has identified a mutation in close proximity to the BACE1 cleavage site of APP rendering those who bear the mutation resistant to AD and age-associated cognitive decline. This indicates BACE1 mediated cleavage of APP is seminal for AD risk and disease progression, and validates the promise of mediating BACE1 activity for intervention. To find cellular regulators of BACE1, we employed a chemical genetics approach to identify chemical probes that that can target novel pathways which effect BACE1 cleavage of APP. An assay for detecting the specific BACE1 mediated APP cleavage product, secreted APPβ (sAPPb), was used to screen for chemical probes in a cell-based platform. A hit compound was identified which was structurally similar to a well characterized drug class active in the central nervous system (CNS). To improve the efficacy and explore the structure activity relationship, chemical analogs were subsequently synthesized (CNS-series) which were able to reduce sAPPb and Ab. However, the specific cellular target of the CNS-series remained unknown. Based on the drug class of the parent compound, expression of putative targets in brain and extensive pharmacological testing, we identified a candidate target, the plasma membrane monoamine transporter (PMAT). PMAT is an atypical monoamine transporter belonging to a highly druggable class of monoaomine transporters. Our preliminary studies indicated that pharmacologically inhibiting PMAT and genetically reducing PMAT expression in neurons resulted in decreased sAPPb and Ab levels. Based on preliminary studies with mutants affecting PMAT transport activity and PMAT subcellular localization, reduction of Ab apparently depends on transporter activity and plasma membrane localization. Furthermore, treatment of cells with pharmacological inhibitors of PMAT alters BACE1 subcellular localization. A novel mechanism for BACE1 regulation has been proposed and future studies may be able to elucidate therapeutic potential of PMAT inhibitors for amelioration of AD associated pathology.