Copper Promotes the Trafficking of the Amyloid Precursor Protein

Abstract

Accumulation of the amyloid ␤ peptide in the cortical and hippocampal regions of the brain is a major pathological feature of Alzheimer disease. Amyloid ␤ peptide is generated from the sequential protease cleavage of the amyloid precursor protein (APP). We reported previously that copper increases the level of APP at the cell surface. Here we report that copper, but not iron or zinc, promotes APP trafficking in cultured polarized epithelial cells and neuronal cells. In SH-SY5Y neuronal cells and primary cortical neurons, copper promoted a redistribution of APP from a perinuclear localization to a wider distribution, including neurites. Importantly, a change in APP localization was not attributed to an up-regulation of APP protein synthesis. Using live cell imaging and endocytosis assays, we found that copper promotes an increase in cell surface APP by increasing its exocytosis and reducing its endocytosis, respectively. This study identifies a novel mechanism by which copper regulates the localization and presumably the function of APP, which is of major significance for understanding the role of APP in copper homeostasis and the role of copper in Alzheimer disease. The neuropathology of Alzheimer disease (AD)3 includes the accumulation of extracellular plaques containing amyloid ␤ peptide (A␤) in the cortical and hippocampal regions of the brain, intracellular neurofibrillary tangles, and trace metal dyshomeostasis. The trace metals copper, zinc, and iron are significantly enriched in the amyloid plaques of AD patients compared with age-matched subjects (1, 2). Interaction between A␤ and copper or zinc promotes peptide oligomerization and aggregation, eventually leading to further amyloid deposition (3-7). In addition, A␤ is able to catalyze the reduction of Cu(II) and Fe(III), generating reactive oxygen species that contribute to the oxidative stress observed in the AD brain (8 -14). Paradoxically, there is evidence of copper deficiency in neighboring cells (15-18), compromising the activity of copper-dependent enzymes, such as cytochrome c-oxidase and copper/zinc-superoxide dismutase (SOD1), which are essential for cellular respiration and as antioxidant defense, respectively (19 -21). Restoration of copper balance using ionophores (22), such as clioquionol and PBT-2, has shown promising results in both animal and human trials (23)(24)(25)(26). A proposed mechanism of action of these drugs is to bind to extracellular copper and restore intracellular copper levels, hence correcting copper dyshomeostasis. Importantly, these ionophores are capable of reducing amyloid load and attenuate cognitive decline (23-26).Amyloid precursor protein (APP) is differentially processed by the ␣-, ␤-, and ␥-secretases in two alternative processing pathways, commonly referred to as the nonamyloidogenic and amyloidogenic pathways (supplemental Fig. S1). In the non-amyloidogenic pathway, APP is initially cleaved by an ␣-secretase that is predominantly localized to the plasma membrane (27, 28), generating an N-terminal ectodomain (s...

The Amyloid Precursor Protein Copper Binding Domain Histidine Residues 149 and 151 Mediate APP Stability and Metabolism

“…Previous findings showed that copper increases APP cell surface localization (58) and promotes APP trafficking from the Golgi to intracellular compartments and to the cell surface (32). This supports H147N-APP decreased post-Golgi trafficking because His 147 might be necessary for APP copper binding.…”

“…In cellular models, increased intracellular copper levels up-regulated APP expression (30) and promoted the non-amyloidogenic processing of APP (31). Moreover, APP trafficked from the Golgi to the plasma membrane exhibited a decreased endocytosis in response to copper (32). Conversely, a decrease in intracellular copper levels led to decreased APP expression (33) and increased amyloidogenic processing of APP (34).…”

“…Conversely, a decrease in intracellular copper levels led to decreased APP expression (33) and increased amyloidogenic processing of APP (34). In addition, APP is thought to modulate copper homeostasis by participating in copper efflux (32). Studies in both animal and cellular models demonstrated increased levels of copper when the APP gene was knocked out (35,36).…”

Copper signaling in the brain and beyond

“…PrP C and APP bind copper through their extracellular domains (43,44), and PrP C may serve as a buffer for copper binding in the extracellular space, perhaps at the synapse (45). Indeed, expression levels of PrP C (43) and APP (46,47) have been shown to influence neural copper levels, placing PrP C and APP in the network of proteins that regulate neural copper homeostasis.…”

Sub-Chronic Copper Pretreatment Reduces Oxidative Damage in an Experimental Huntington’s Disease Model

“…The same finding has been observed in HD experimental models involving excitotoxicity [14,23], suggesting that Cu could play a role at the onset of neuronal damage in HD. In contrast, other research groups have demonstrated that Cu exerts a neuroprotective effect in HD, Parkinson's disease (PD), and Alzheimer's disease (AD) experimental models regarding excitotoxicity and cell death [17,24,33,34]. In a previous work, our group showed that Cu administered i.p.…”