Summary Alzheimer’s Disease (AD) is complicated by pro-oxidant intraneuronal Fe2+ elevation as well as extracellular Zn2+ accumulation within amyloid plaque. We found that the AD β-amyloid protein precursor (APP) possesses ferroxidase activity mediated by a conserved H-ferritin-like active site, which is inhibited specifically by Zn2+. Like ceruloplasmin, APP catalytically oxidizes Fe2+, loads Fe3+ into transferrin, and has a major interaction with ferroportin in HEK293T cells (that lack ceruloplasmin) and in human cortical tissue. Ablation of APP in HEK293T cells and primary neurons induces marked iron retention, whereas increasing APP695 promotes iron export. Unlike normal mice, APP−/− mice are vulnerable to dietary iron exposure, which causes Fe2+ accumulation and oxidative stress in cortical neurons. Paralleling iron accumulation, APP ferroxidase activity in AD post-mortem neocortex is inhibited by endogenous Zn2+, which we demonstrate can originate from Zn2+-laden amyloid aggregates and correlates with Aβ burden. Abnormal exchange of cortical zinc may link amyloid pathology with neuronal iron accumulation in AD.

The microtubule-associated protein tau has risk alleles for both Alzheimer's disease and Parkinson's disease and mutations that cause brain degenerative diseases termed tauopathies. Aggregated tau forms neurofibrillary tangles in these pathologies, but little is certain about the function of tau or its mode of involvement in pathogenesis. Neuronal iron accumulation has been observed pathologically in the cortex in Alzheimer's disease, the substantia nigra (SN) in Parkinson's disease and various brain regions in the tauopathies. Here we report that tau-knockout mice develop age-dependent brain atrophy, iron accumulation and SN neuronal loss, with concomitant cognitive deficits and parkinsonism. These changes are prevented by oral treatment with a moderate iron chelator, clioquinol. Amyloid precursor protein (APP) ferroxidase activity couples with surface ferroportin to export iron, but its activity is inhibited in Alzheimer's disease, thereby causing neuronal iron accumulation. In primary neuronal culture, we found loss of tau also causes iron retention, by decreasing surface trafficking of APP. Soluble tau levels fall in affected brain regions in Alzheimer's disease and tauopathies, and we found a similar decrease of soluble tau in the SN in both Parkinson's disease and the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model. These data suggest that the loss of soluble tau could contribute to toxic neuronal iron accumulation in Alzheimer's disease, Parkinson's disease and tauopathies, and that it can be rescued pharmacologically.

Accumulation of cerebral amyloid-beta peptide (Abeta) is essential for developing synaptic and cognitive deficits in Alzheimer's disease. However, the physiological functions of Abeta, as well as the primary mechanisms that initiate early Abeta-mediated synaptic dysfunctions, remain largely unknown. Here we examine the acute effects of endogenously released Abeta peptides on synaptic transfer at single presynaptic terminals and synaptic connections in rodent hippocampal cultures and slices. Increasing extracellular Abeta by inhibiting its degradation enhanced release probability, boosting ongoing activity in the hippocampal network. Presynaptic enhancement mediated by Abeta was found to depend on the history of synaptic activation, with lower impact at higher firing rates. Notably, both elevation and reduction in Abeta levels attenuated short-term synaptic facilitation during bursts in excitatory synaptic connections. These observations suggest that endogenous Abeta peptides have a crucial role in activity-dependent regulation of synaptic vesicle release and might point to the primary pathological events that lead to compensatory synapse loss in Alzheimer's disease.

Alzheimer's disease (AD) is characterized by the presence of neurofibrillary tangles and amyloid plaques, which are abnormal protein deposits. The major constituent of the plaques is the neurotoxic beta-amyloid peptide (Abeta); the genetics of familial AD support a direct role for this peptide in AD. Abeta neurotoxicity is linked to hydrogen peroxide formation. Abeta coordinates the redox active transition metals, copper and iron, to catalytically generate reactive oxygen species. The chemical mechanism underlying this process is not well defined. With the use of density functional theory calculations to delineate the chemical mechanisms that drive the catalytic production of H2O2 by Abeta/Cu, tyrosine10 (Y10) was identified as a pivotal residue for this reaction to proceed. The relative stability of tyrosyl radicals facilitates the electron transfers that are required to drive the reaction. Confirming the theoretical results, mutation of the tyrosine residue to alanine inhibited H2O2 production, Cu-induced radicalization, dityrosine cross-linking, and neurotoxicity.

In studies of Alzheimer's disease pathogenesis there is an increasing focus on mechanisms of intracellular amyloid-␤ (A␤) generation and toxicity. Here we investigated the inhibitory potential of the 42 amino acid A␤ peptide (A␤ 1-42 ) on activity of electron transport chain enzyme complexes in human mitochondria. We found that synthetic A␤ 1-42 specifically inhibited the terminal complex cytochrome c oxidase (COX) in a dose-dependent manner that was dependent on the presence of Cu 2ϩ and specific "aging" of the A␤ 1-42 solution. Maximal COX inhibition occurred when using A␤ 1-42 solutions aged for 3-6 h at 30°C. The level of A␤ 1-42 -mediated COX inhibition increased with aging time up to ϳ6 h and then declined progressively with continued aging to 48 h. Photo-induced cross-linking of unmodified proteins followed by SDS-PAGE analysis revealed dimeric A␤ as the only A␤ species to provide significant temporal correlation with the observed COX inhibition. Analysis of brain and liver from an Alzheimer's model mouse (Tg2576) revealed abundant A␤ immunoreactivity within the brain mitochondria fraction. Our data indicate that endogenous A␤ is associated with brain mitochondria and that A␤ 1-42 , possibly in its dimeric conformation, is a potent inhibitor of COX, but only when in the presence of Cu 2ϩ . We conclude that Cu 2ϩ -dependent A␤-mediated inhibition of COX may be an important contributor to the neurodegeneration process in Alzheimer's disease.

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Amelyoid-␤ peptide (A␤) is a major causative agent responsible for Alzheimer's disease (AD). A␤ contains a high affinity metal binding site that modulates peptide aggregation and toxicity. Therefore, identifying molecules targeting this site represents a valid therapeutic strategy. To test this hypothesis, a range of L-PtCl2 (L ‫؍‬ 1,10-phenanthroline derivatives) complexes were examined and shown to bind to A␤, inhibit neurotoxicity and rescue A␤-induced synaptotoxicity in mouse hippocampal slices. Coordination of the complexes to A␤ altered the chemical properties of the peptide inhibiting amyloid formation and the generation of reactive oxygen species. In comparison, the classic anticancer drug cisplatin did not affect any of the biochemical and cellular effects of A␤. This implies that the planar aromatic 1,10-phenanthroline ligands L confer some specificity for A␤ onto the platinum complexes. The potent effect of the L-PtCl 2 complexes identifies this class of compounds as therapeutic agents for AD.

Amyloid-␤ peptide (A␤) is pivotal to the pathogenesis of Alzheimer disease. Here we report the formation of a toxic A␤-Cu 2؉ complex formed via a histidine-bridged dimer, as observed at Cu 2؉ / peptide ratios of >0.6:1 by EPR spectroscopy. The toxicity of the A␤-Cu 2؉ complex to cultured primary cortical neurons was attenuated when either the -or -nitrogen of the imidazole side chains of His were methylated, thereby inhibiting formation of the His bridge. Toxicity did not correlate with the ability to form amyloid or perturb the acyl-chain region of a lipid membrane as measured by diphenyl-1,3,5-hexatriene anisotropy, but did correlate with lipid peroxidation and dityrosine formation. 31 P magic angle spinning solid-state NMR showed that A␤ and A␤-Cu 2؉ complexes interacted at the surface of a lipid membrane. These findings indicate that the generation of the A␤ toxic species is modulated by the Cu 2؉ concentration and the ability to form an intermolecular His bridge.