Gene knockout of amyloid precursor protein and amyloid precursor‐like protein‐2 increases cellular copper levels in primary mouse cortical neurons and embryonic fibroblasts

Abstract

Alzheimer's disease is characterised by the accumulation of amyloid-b peptide, which is cleaved from the copper-binding amyloid-b precursor protein. Recent in vivo and in vitro studies have illustrated the importance of copper in Alzheimer's disease neuropathogenesis and suggested a role for amyloid-b precursor protein and amyloid-b in copper homeostasis. Amyloid-b precursor protein is a member of a multigene family, including amyloid precursor-like proteins-1 and -2. The copper-binding domain is similar among amyloid-b precursor protein family members, suggesting an overall conservation in its function or activity. Here, we demonstrate that double knockout of amyloid-b precursor protein and amyloid precursor-like protein-2 expression results in significant increases in copper accumulation in mouse primary cortical neurons and embryonic fibroblasts. In contrast, over-expression of amyloid-b precursor protein in transgenic mice results in significantly reduced copper levels in primary cortical neurons. These findings provide cellular neuronal evidence for the role of amyloid-b precursor protein in copper homeostasis and support the existing hypothesis that amyloid-b precursor protein and amyloid precursor-like protein-2 are copper-binding proteins with functionally interchangeable roles in copper homeostasis. Keywords: Alzheimer's disease, amyloid precursor-like protein 2, amyloid precursor protein, cortical neurons, gene knockout-out mice, neuronal copper homeostasis. The amyloid-b precursor protein (APP) of Alzheimer's disease is a type 1 transmembrane cuproprotein. The proteolytic processing of APP by secretases yields the amyloid-b peptide (Ab), the primary constituent of the amyloid plaque (Haass and Selkoe 1993). APP is a member of a multigene family that contains the paralogues amyloid precursor-like protein 1 and 2 (APLP1 and APLP2) (Wasco et al. 1992(Wasco et al. , 1993. Orthologues have been identified in a diverse range of species including Drosophila melanogaster, Xenopus laevis and Caenorhabditis elegans (Rosen et al. 1989;Okado and Okamoto 1992;Daigle and Li 1993). APP has a primary copper-binding domain, located in the N-terminal cysteinerich region next to the growth factor-like domain, and a secondary copper-binding domain, which is generated in Ab after proteolytic processing of APP (Hesse et al. 1994;Atwood et al. 2000). Both APP and Ab can strongly bind copper, as Cu(II), and reduce it to Cu(I) in vitro (Multhaup et al. 1996;Huang et al. 1999). Elevated copper concentrations reduce Ab production and increase secretion of APP in a cell line transfected with human APP cDNA (Borchardt et al. 1999). More recently, reports show that increased brain copper levels cause a decrease in Ab production in APP transgenic mouse models in vivo (Bayer et al. 2003;Phinney et al. 2003), while severely depleted cellular copper decreases APP gene expression (Bellingham et al. 2004).The copper-binding region is well conserved amongst the different APP-gene family members (Simons et al. 2002; Received Jun...

Alzheimer disease β-amyloid activity mimics cholesterol oxidase

“…Increasing evidence indicates that Aβ and APP may constitutively handle copper and export it from the cell (55)(56)(57)(58)(59). Aβ is redox silent when bound to Cu 2+ as a lipid-embedded complex, and oxidation of this complex may lead to abnormal lipid integration and the release of redox activity (12,60).…”

High‐resolution NMR studies of the zinc‐binding site of the Alzheimer's amyloid β‐peptide

“…The N-terminal fragment Ab(1-28) has, however, been shown to undergo increased fibril formation upon interaction with zinc [25]. Another N-terminal fragment of Ab, Ab (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16), forms stable oligomers in the presence of both copper and zinc [26].…”

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

“…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). Because APP is a copper-binding protein, these effects are likely to be related to the ability of APP to bind copper; however, this link has not yet been elucidated.…”