Degradation of the Alzheimer Disease Amyloid β-Peptide by Metal-dependent Up-regulation of Metalloprotease Activity

Department of Pathology, University of Melbourne, Cnr. Grattan Street and Royal Parade, Victoria 3010, Australia.
Journal of Biological Chemistry (Impact Factor: 4.57). 07/2006; 281(26):17670-80. DOI: 10.1074/jbc.M602487200
Source: PubMed


Biometals play an important role in Alzheimer disease, and recent reports have described the development of potential therapeutic agents based on modulation of metal bioavailability. The metal ligand clioquinol (CQ) has shown promising results in animal models and small phase clinical trials; however, the actual mode of action in vivo has not been determined. We now report a novel effect of CQ on amyloid beta-peptide (Abeta) metabolism in cell culture. Treatment of Chinese hamster ovary cells overexpressing amyloid precursor protein with CQ and Cu(2+) or Zn(2+) resulted in an approximately 85-90% reduction of secreted Abeta-(1-40) and Abeta-(1-42) compared with untreated controls. Analogous effects were seen in amyloid precursor protein-overexpressing neuroblastoma cells. The secreted Abeta was rapidly degraded through up-regulation of matrix metalloprotease (MMP)-2 and MMP-3 after addition of CQ and Cu(2+). MMP activity was increased through activation of phosphoinositol 3-kinase and JNK. CQ and Cu(2+) also promoted phosphorylation of glycogen synthase kinase-3, and this potentiated activation of JNK and loss of Abeta-(1-40). Our findings identify an alternative mechanism of action for CQ in the reduction of Abeta deposition in the brains of CQ-treated animals and potentially in Alzheimer disease patients.

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    • "Cohen , 2001 ) , cell survival ( Takashima et al . , 1993 ) , cell motility ( Lucas et al . , 1998 ) , and memory formation ( Bradley et al . , 2012 ) . Hyperphosphorylation of tau and Ab production in AD have been linked to GSK - 3 dysfunction ( DaRocha - Souto et al . , 2012 ; Noble et al . , 2005 ; Phiel et al . , 2003 ; Pooler et al . , 2012 ; White et al . , 2006 ; Kimura et al . , 2013 ) . In double transgenic APP / tau mice , GSK - 3 inhibition ameliorates plaque - related neuritic changes , suggesting a role of this kinase in Ab - induced pathology ( DaRocha - Souto et al . , 2012 ) . However , the molecular mechanisms linking Ab oligomers toxicity to GSK - 3 are still poorly understood . Our "
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    ABSTRACT: Amyloid β-protein (Aβ) pathologies have been linked to dysfunction of excitability in neurons of the hippocampal circuit, but the molecular mechanisms underlying this process are still poorly understood. Here we applied whole-cell patch-clamp electrophysiology to primary hippocampal neurons and show that intracellular Aβ42 delivery leads to increased spike discharge and action potential broadening through down-regulation of A-type K+ currents. Pharmacological studies showed that caspases and GSK-3 activation are required for these Aβ42-induced effects. Extracellular perfusion and subsequent internalization of Aβ42 increase spike discharge and promote GSK-3-dependent phosphorylation of the Kv4.2 α-subunit, a molecular determinant of A-type K+ currents, at Ser-616. In acute hippocampal slices derived from an adult triple-transgenic Alzheimer’s mouse model (3xTg-AD), characterized by endogenous intracellular accumulation of Aβ42, CA1 pyramidal neurons exhibit hyperexcitability accompanied by increased phosphorylation of Kv4.2 at Ser-616. Collectively, these data suggest that intraneuronal Aβ42 accumulation leads to an intracellular cascade culminating into caspases activation and GSK-3-dependent phosphorylation of Kv4.2 channels. These findings provide new insights into the toxic mechanisms triggered by intracellular Aβ42 and offer potentially new therapeutic targets for Alzheimer’s disease (AD) treatment.
    Neurobiology of aging 11/2014; DOI:10.1016/j.neurobiolaging.2014.10.034 · 5.01 Impact Factor
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    • "The signal intensity was quantified using NIH ImageJ software. Western blotting of secreted A␤ in culture media was carried out as previously described [14]. In the case of SK-N-SH neurons, the culture media volume was reduced by ∼5 fold using Speed-vac (Savant) prior to analysis. "
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    ABSTRACT: Brain cholesterol homeostasis is regulated by a group of proteins called ATP-binding cassette subfamily A (ABCA) transporters. Certain ABCA transporters regulate amyloid-β protein precursor (AβPP) processing to generate amyloid-β peptides (Aβ) and are associated with an increased risk for late-onset Alzheimer's disease (AD). ABCA5 is a little-known member of the ABCA subfamily with no known function. In this study we undertook a comprehensive analysis of ABCA5 expression in the human and mouse brains. We explored the potential role of ABCA5 in AβPP processing associated with AD pathology. ABCA5 was differentially expressed in multiple regions of both human and mouse brains. It was strongly expressed in neurons with only weak expression in microglia, astrocytes, and oligodendrocytes. ABCA5 was able to stimulate cholesterol efflux in neurons. ABCA5 expression was specifically elevated in the hippocampus of AD brains. Using two in vitro cell systems we demonstrated that ABCA5 reduces Aβ production, both Aβ40 and Aβ42, without altering AβPP mRNA and protein levels, indicating that the decrease in the Aβ levels was due to changes in AβPP processing and not AβPP expression. This report represents the first extensive expression and functional study of ABCA5 in the human brain and our data suggest a plausible function of ABCA5 in the brain as a cholesterol transporter associated with Aβ generation, information that may offer a potential new target for controlling Aβ levels in the brain.
    Journal of Alzheimer's disease: JAD 08/2014; 43(3). DOI:10.3233/JAD-141320 · 4.15 Impact Factor
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    • "Rather than acting as metal chelators to remove metal ions, the 8-hydroxyquinoline bidentate ligands, CQ and PBT2 can exert their effects in cell culture and animal models of AD by redistributing metal ions. CQ delivered Cu and Zn into cultured cells and stimulated Aβ degrading metallo-enzymes including matrix metalloprotease 2 (MMP2) [8]. PBT2 removed Zn from aggregated Aβ, redistributed the Zn into neuronal-like SH-SY5Y cells, inhibited glycogen synthase kinase 3 beta (GSK3β) and decreased calcineurin activity [9]. "
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    ABSTRACT: Abnormal biometal homeostasis is a central feature of many neurodegenerative disorders including Alzheimer's disease (AD), Parkinson's disease (PD), and motor neuron disease. Recent studies have shown that metal complexing compounds behaving as ionophores such as clioquinol and PBT2 have robust therapeutic activity in animal models of neurodegenerative disease; however, the mechanism of neuroprotective action remains unclear. These neuroprotective or neurogenerative processes may be related to the delivery or redistribution of biometals, such as copper and zinc, by metal ionophores. To investigate this further, we examined the effect of the bis(thiosemicarbazonato)-copper complex, Cu(II)(gtsm) on neuritogenesis and neurite elongation (neurogenerative outcomes) in PC12 neuronal-related cultures. We found that Cu(II)(gtsm) induced robust neurite elongation in PC12 cells when delivered at concentrations of 25 or 50 nM overnight. Analogous effects were observed with an alternative copper bis(thiosemicarbazonato) complex, Cu(II)(atsm), but at a higher concentration. Induction of neurite elongation by Cu(II)(gtsm) was restricted to neurites within the length range of 75-99 µm with a 2.3-fold increase in numbers of neurites in this length range with 50 nM Cu(II)(gtsm) treatment. The mechanism of neurogenerative action was investigated and revealed that Cu(II)(gtsm) inhibited cellular phosphatase activity. Treatment of cultures with 5 nM FK506 (calcineurin phosphatase inhibitor) resulted in analogous elongation of neurites compared to 50 nM Cu(II)(gtsm), suggesting a potential link between Cu(II)(gtsm)-mediated phosphatase inhibition and neurogenerative outcomes.
    PLoS ONE 02/2014; 9(2):e90070. DOI:10.1371/journal.pone.0090070 · 3.23 Impact Factor
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