Amyolid precursor protein mediates presynaptic localization and activity of the high-affinity choline transporter

Abstract

The key pathological features of Alzheimer's disease include synaptic dysfunction, profound changes in the cholinergic system, and deposition of ␤-amyloid peptides generated by proteolytic processing of the amyloid-␤ precursor protein (APP). However, the pathways linking APP with synaptic activity and cholinergic neuronal function are poorly understood. We report here that APP is essential in regulating the presynaptic expression and activity of the high-affinity choline transporter (CHT), a molecule that mediates the rate-limiting step of cholinergic synaptic transmission in both the neuromuscular junction and central cholinergic neurons. Loss of APP leads to aberrant localization of CHT at the neuromuscular synapses and reduced CHT activity at cholinergic projections. At the cellular level, we show that APP and CHT can be found in Rab5-positive endosomal compartments and that APP affects CHT endocytosis. Furthermore, we demonstrate that APP interacts with CHT through the C-terminal domain, providing support for a specific and direct regulation of CHT by APP through proteinprotein interactions. These results identify a physiological activity of APP in cholinergic neurons, and our data indicate that deregulation of APP function may contribute to cholinergic impairment and AD pathogenesis. neuromuscular synapse ͉ Alzheimer's disease ͉ cholinergic neurons ͉ knockout mice ͉ endocytosis G enetic and biochemical evidence establishes a pivotal role of the amyloid-␤ precursor protein (APP) in Alzheimer's disease (AD) pathogenesis. APP processing generates ␤-amyloid (A␤) peptides, which are deposited as amyloid plaques in the brains of affected individuals; point mutations or gene duplications of APP are causal for a subset of early onset familial AD (1, 2). APP is a member of a family of conserved type I membrane proteins with three mammalian homologs: APP, APP-like protein 1 (APLP1), and APLP2 (3). APP is highly expressed in neurons, where it has been shown to localize to postsynaptic densities, axons, and dendrites (4, 5). APP undergoes rapid anterograde transport (6-9) and is targeted to the synaptic sites of both the CNS and the peripheral nervous system. Despite the extensive studies on APP expression and processing, the physiological function of APP remains speculative and controversial (3).Besides the amyloid pathology, AD is correlated with synaptic dysfunction and is recognized by profound changes in the cholinergic system. These changes include the loss of basal forebrain cholinergic neurons and impaired cholinergic innervation to the cortex and hippocampus, areas that have been implicated in memory, learning, and attention (10-12). Acetylcholine (ACh) is the neurotransmitter for central and peripheral cholinergic synapses, and the latter includes the mammalian neuromuscular junction (NMJ). ACh is synthesized by choline acetyltransferase (Chat) and packaged to synaptic vesicles by vesicular acetylcholine transporter (VaChT). ACh released from presynaptic terminals binds to acetylcholine receptors (AChRs) to e...

Substrate-Induced Internalization of the High-Affinity Choline Transporter

“…This has recently been explained by activity-dependent vesicular trafficking of the intracellular pool of CHT1 to the plasma membrane Ribeiro et al, 2003Ribeiro et al, , 2007Ivy et al, 2010). Cellular trafficking of CHT1 may also be regulated by its phosphorylation (Gates et al, 2004) or its interaction with other proteins, such as the amyloid-␤ precursor protein (Wang et al, 2007). However, the endogenous physiological factors regulating the expression level of CHT1 at the plasma membrane remain to be elucidated.…”

Impact of Oxidative - Nitrosative Stress on Cholinergic Presynaptic Function

“…Notably, it has been determined that CHT interacts with the carboxyl-terminus of amyloid precursor protein (APP) family members (B. Wang et al, 2007) and with A peptide (Bales et al, 2006). Mice lacking both APP and APP-like protein 2 have reduced levels of CHT protein at nerve terminals and this is seen as decreased highaffinity choline uptake activity; APP appears to be a modulator of both presynaptic localization and endocytosis of CHT proteins (B.…”

“…Mice lacking both APP and APP-like protein 2 have reduced levels of CHT protein at nerve terminals and this is seen as decreased highaffinity choline uptake activity; APP appears to be a modulator of both presynaptic localization and endocytosis of CHT proteins (B. Wang et al, 2007). Recent data indicate that modulation of APP metabolism or processing is an early cellular response to oxidative stress (Recuero et al, 2010).…”

“…Since PKC plays an important role in regulation of both ChAT and CHT function, it will be interesting to determine how oxidative stress alters phosphorylation-dependent regulation of ChAT, CHT and ACh synthesis, and the role that this plays in the failure of cholinergic neurotransmission in Alzheimer's disease and related disorders. Protein-protein interactions are another molecular mode of regulation of protein function and/or subcellular localization, and some protein binding partners for ChAT and CHT have now been identified (Bales et al, 2006;Dobransky et al 2003;Ribeiro et al, 2007a;B. Wang et al, 2007;Xie & Guo, 2004).…”

Peroxynitrite Donor SIN-1 Alters High-Affinity Choline Transporter Activity by Modifying Its Intracellular Trafficking

“…Multiple kinases are altered by ONOO Ϫ , including activation of p38 kinase and Src kinase (Li et al, 1998;Di Stasi et al, 1999;OhHashi et al, 2001), but there are no data on the effects of kinases that are modulated by ONOO Ϫ on CHT disposition. CHT interacts with amyloid precursor protein (APP) through its C-terminal tail, and APP has a role in regulating CHT subcellular trafficking in cholinergic neurons (Wang et al, 2007); APP serves as substrate for generation of ␤-amyloid, a critical feature in Alzheimer's disease pathogenesis, which is involved in production of oxidative stress in brain. APP is internalized from plasma membrane by endocytosis and moves through the endosomal pathway to lysosomes where it is cleaved by secretases.…”