Huntington’s disease (HD) is a progressive neurodegenerative disorder caused by a polyglutamine-encoding CAG expansion in the huntingtin gene. Iron accumulates in the brains of HD patients and mouse disease models. However, the cellular and subcellular sites of iron accumulation, as well as significance to disease progression are not well understood. We used independent approaches to investigate the location of brain iron accumulation. In R6/2 HD mouse brain, synchotron x-ray fluorescence analysis revealed iron accumulation as discrete puncta in the perinuclear cytoplasm of striatal neurons. Further, perfusion Turnbull’s staining for ferrous iron (II) combined with transmission electron microscope ultra-structural analysis revealed increased staining in membrane bound peri-nuclear vesicles in R6/2 HD striatal neurons. Analysis of iron homeostatic proteins in R6/2 HD mice revealed decreased levels of the iron response proteins (IRPs 1 and 2) and accordingly decreased expression of iron uptake transferrin receptor (TfR) and increased levels of neuronal iron export protein ferroportin (FPN). Finally, we show that intra-ventricular delivery of the iron chelator deferoxamine results in an improvement of the motor phenotype in R6/2 HD mice. Our data supports accumulation of redox-active ferrous iron in the endocytic / lysosomal compartment in mouse HD neurons. Expression changes of IRPs, TfR and FPN are consistent with a compensatory response to an increased intra-neuronal labile iron pool leading to increased susceptibility to iron-associated oxidative stress. These findings, together with protection by deferoxamine, support a potentiating role of neuronal iron accumulation in HD.
Cross-sectional genetic association studies have reported equivocal results on the relationship between the brain-derived neurotrophic factor (BDNF) Val66Met and risk of Alzheimer’s disease (AD). As AD is a neurodegenerative disease, genetic influences may become clearer from prospective study. We aimed to determine whether BDNF Val66Met polymorphism influences changes in memory performance, hippocampal volume, and Aβ accumulation in adults with amnestic mild cognitive impairment (aMCI) and high Aβ.
Thirty-four adults with aMCI were recruited from the Australian, Imaging, Biomarkers and Lifestyle (AIBL) Study. Participants underwent PiB-PET and structural MRI neuroimaging, neuropsychological assessments and BDNF genotyping at baseline, 18 month, and 36 month assessments.
In individuals with aMCI and high Aβ, Met carriers showed significant and large decline in episodic memory (d = 0.90, p = .020) and hippocampal volume (d = 0.98, p = .035). BDNF Val66Met was unrelated to the rate of Aβ accumulation (d = −0.35, p = .401).
Although preliminary due to the small sample size, results of this study suggest that high Aβ levels and Met carriage may be useful prognostic markers of accelerated decline in episodic memory, and reductions in hippocampal volume in individuals in the prodromal or MCI stage of AD.
Alzheimer’s disease (AD) is a multifactorial neurodegenerative disease. It begins years prior to the onset of clinical symptoms, such as memory loss and cognitive decline. Pathological hallmarks of AD include the accumulation of β-amyloid in plaques and hyperphosphorylated tau in neurofibrillary tangles. Copper, iron, and zinc are abnormally accumulated and distributed in the aging brain. These metal ions can adversely contribute to the progression of AD. Dysregulation of cholesterol metabolism has also been implicated in the development of AD pathology. To date, large bodies of research have been carried out independently to elucidate the role of metals or cholesterol on AD pathology. Interestingly, metals and cholesterol affect parallel molecular and biochemical pathways involved in AD pathology. The possible links between metal dyshomeostasis and altered brain cholesterol metabolism in AD are reviewed.
Alzheimer’s disease; amyloid precursor protein; Aβ; cholesterol; metals; iron; copper; zinc
Alzheimer's disease (AD) is the leading cause of dementia and represents a significant burden on the global economy and society. The role of transition metals, in particular copper (Cu), in AD has become of significant interest due to the dyshomeostasis of these essential elements, which can impart profound effects on cell viability and neuronal function. We tested the hypothesis that there is a systemic perturbation in Cu compartmentalization in AD, within the brain as well as in the periphery, specifically within erythrocytes. Our results showed that the previously reported decrease in Cu within the human frontal cortex was confined to the soluble (P < 0.05) and total homogenate (P < 0.05) fractions. No differences were observed in Cu concentration in erythrocytes. Our data indicate that there is a brain specific alteration in Cu levels in AD localized to the soluble extracted material, which is not reflected in erythrocytes. Further studies using metalloproteomics approaches will be able to elucidate the metabolic mechanism(s) that results in the decreased brain Cu levels during the progression of AD.
Zinc deficiency due to poor nutrition or genetic mutations in zinc transporters is a global health problem and approaches to providing effective dietary zinc supplementation while avoiding potential toxic side effects are needed.
Conditional knockout of the intestinal zinc transporter Zip4 (Slc39a4) in mice creates a model of the lethal human genetic disease acrodermatitis enteropathica (AE). This knockout leads to acute zinc deficiency resulting in rapid weight loss, disrupted intestine integrity and eventually lethality, and therefore provides a model system in which to examine novel approaches to zinc supplementation. We examined the efficacy of dietary clioquinol (CQ), a well characterized zinc chelator/ionophore, in rescuing the Zip4intest KO phenotype. By 8 days after initiation of the knockout neither dietary CQ nor zinc supplementation in the drinking water was found to be effective at improving this phenotype. In contrast, dietary CQ in conjunction with zinc supplementation was highly effective. Dietary CQ with zinc supplementation rapidly restored intestine stem cell division and differentiation of secretory and the absorptive cells. These changes were accompanied by rapid growth and dramatically increased longevity in the majority of mice, as well as the apparent restoration of the homeostasis of several essential metals in the liver.
These studies suggest that oral CQ (or other 8-hydroxyquinolines) coupled with zinc supplementation could provide a facile approach toward treating zinc deficiency in humans by stimulating stem cell proliferation and differentiation of intestinal epithelial cells.
Abnormal interaction of β-amyloid 42 (Aβ42) with copper, zinc and iron induce peptide aggregation and oxidation in Alzheimer's disease (AD). However, in health, Aβ degradation is mediated by extracellular metalloproteinases, neprilysin, insulin degrading enzyme (IDE) and matrix metalloproteinases. We investigated the relationship between levels of Aβ and biological metals in CSF. We assayed CSF copper, zinc, other metals and Aβ42 in ventricular autopsy samples of Japanese American men (N= 131) from the population-based Honolulu–Asia Aging Study. There was a significant inverse correlation of CSF Aβ42 with copper, zinc, iron, manganese and chromium. The association was particularly strong in the subgroup with high levels of both zinc and copper. Selenium and aluminum levels were not associated to CSF Aβ42. In vitro, the degradation of synthetic Aβ substrate added to CSF was markedly accelerated by low levels (2 μM) of exogenous zinc and copper. While excessive interaction with copper and zinc may induce neocortical Aβ precipitation in AD, soluble Aβ degradation is normally promoted by physiological copper and zinc concentrations.
amyloid; Alzheimer's disease; metalloproteinase; cerebrospinal fluid; zinc; copper; iron; manganese; chromium
Alzheimer’s disease (AD), the most common form of dementia in the elderly, is characterized by elevated brain iron levels and accumulation of copper and zinc in cerebral β-amyloid deposits; e.g., senile plaques. Both ionic zinc and copper are able to accelerate the aggregation of Aβ, the principle component of β-amyloid deposits. Copper (and iron) can also promote the neurotoxic redox activity of Aβ and induce oxidative cross-linking of the peptide into stable oligomers. Recent reports have documented the release of Aβ together with ionic zinc and copper in cortical glutamatergic synapses following excitation. This, in turn, leads to the formation of Aβ oligomers, which, in turn, modulate long-term potentiation (by controlling synaptic levels of the NMDA receptor). The excessive accumulation of Aβ oligomers in the synaptic cleft would then be predicted to adversely affect synaptic neurotransmisson. Based on these findings, we have proposed the “Metal Hypothesis of Alzheimer’s Disease” which stipulates that the neuropathogenic effects of Aβ in AD are promoted by, and possibly even dependent upon Aβ-metal interactions. Increasingly sophisticated pharmaceutical approaches are now being implemented to attenuate abnormal Aβ-metal interactions without causing systemic disturbance of essential metals. Small molecules targeting Aβ–metal interactions, e.g. PBT2, are currently advancing through clinical trials and show increasing promise as disease-modifying agents for AD based on the “metal hypothesis”.
copper; zinc; amyloid; free radical; oxidation; PBT2
Altered copper homeostasis and hypercholesterolemia have been identified independently as risk factors for Alzheimer's disease (AD). Abnormal copper and cholesterol metabolism are implicated in the genesis of amyloid plaques and neurofibrillary tangles (NFT), which are two key pathological signatures of AD. Amyloidogenic processing of a sub-population of amyloid precursor protein (APP) that produces Aβ occurs in cholesterol-rich lipid rafts in copper deficient AD brains. Co-localization of Aβ and a paradoxical high concentration of copper in lipid rafts fosters the formation of neurotoxic Aβ:copper complexes. These complexes can catalytically oxidize cholesterol to generate H2O2, oxysterols and other lipid peroxidation products that accumulate in brains of AD cases and transgenic mouse models. Tau, the core protein component of NFTs, is sensitive to interactions with copper and cholesterol, which trigger a cascade of hyperphosphorylation and aggregation preceding the generation of NFTs. Here we present an overview of copper and cholesterol metabolism in the brain, and how their integrated failure contributes to development of AD.
copper; cholesterol; Alzheimer's disease; ApoE; amyloid precursor protein; Aβ; tau; lipid rafts
Dietary copper is essential for multicellular organisms. Copper is redox active and required as a cofactor for enzymes such as the antioxidant Superoxide Dismutase 1 (SOD1). Copper dyshomeostasis has been implicated in Alzheimer’s disease. Mutations in the presenilin genes encoding PS1 and PS2 are major causes of early-onset familial Alzheimer’s disease. PS1 and PS2 are required for efficient copper uptake in mammalian systems. Here we demonstrate a conserved role for presenilin in dietary copper uptake in the fly Drosophila melanogaster. Ubiquitous RNA interference-mediated knockdown of the single Drosophila presenilin (PSN) gene is lethal. However, PSN knockdown in the midgut produces viable flies. These flies have reduced copper levels and are more tolerant to excess dietary copper. Expression of a copper-responsive EYFP construct was also lower in the midgut of these larvae, indicative of reduced dietary copper uptake. SOD activity was reduced by midgut PSN knockdown, and these flies were sensitive to the superoxide-inducing chemical paraquat. These data support presenilin being needed for dietary copper uptake in the gut and so impacting on SOD activity and tolerance to oxidative stress. These results are consistent with previous studies of mammalian presenilins, supporting a conserved role for these proteins in mediating copper uptake.
The abnormal accumulation of amyloid β-peptide (Aβ) in the form of senile (or amyloid) plaques is one of the main characteristics of Alzheimer disease (AD). Both cholesterol and Cu2+ have been implicated in AD pathogenesis and plaque formation. Aβ binds Cu2+ with very high affinity, forming a redox-active complex that catalyzes H2O2 production from O2 and cholesterol. Here we show that Aβ:Cu2+ complexes oxidize cholesterol selectively at the C-3 hydroxyl group, catalytically producing 4-cholesten-3-one and therefore mimicking the activity of cholesterol oxidase, which is implicated in cardiovascular disease. Aβ toxicity in neuronal cultures correlated with this activity, which was inhibited by Cu2+ chelators including clioquinol. Cell death induced by staurosporine or H2O2 did not elevate 4-cholesten-3-one levels. Brain tissue from AD subjects had 98% more 4-cholesten-3-one than tissue from age-matched control subjects. We observed a similar increase in the brains of Tg2576 transgenic mice compared with nontransgenic littermates; the increase was inhibited by in vivo treatment with clioquinol, which suggests that brain Aβ accumulation elevates 4-cholesten-3-one levels in AD. Cu2+-mediated oxidation of cholesterol may be a pathogenic mechanism common to atherosclerosis and AD.
The definitive indicator of Alzheimer’s disease (AD) pathology is the profuse accumulation of amyloid-ß (Aß) within the brain. Various in vitro and cell-based models have been proposed for high throughput drug screening for potential therapeutic benefit in diseases of protein misfolding. Caenorhabditis elegans offers a convenient in vivo system for examination of Aß accumulation and toxicity in a complex multicellular organism. Ease of culturing and a short life cycle make this animal model well suited to rapid screening of candidate compounds.
We have generated a new transgenic strain of C. elegans that expresses full length Aß1-42. This strain differs from existing Aß models that predominantly express amino-truncated Aß3-42. The Aß1-42 is expressed in body wall muscle cells, where it oligomerizes, aggregates and results in severe, and fully penetrant, age progressive-paralysis. The in vivo accumulation of Aß1-42 also stains positive for amyloid dyes, consistent with in vivo fibril formation. The utility of this model for identification of potential protective compounds was examined using the investigational Alzheimer’s therapeutic PBT2, shown to be neuroprotective in mouse models of AD and significantly improve cognition in AD patients. We observed that treatment with PBT2 provided rapid and significant protection against the Aß-induced toxicity in C. elegans.
This C. elegans model of full length Aß1-42 expression can now be adopted for use in screens to rapidly identify and assist in development of potential therapeutics and to study underlying toxic mechanism(s) of Aß.
Amyloid beta peptide; Alzheimer’s disease; Caenorhabditis elegans; 8-hydroxyquinoline; PBT2 and drug screen
Our understanding of the roles played by zinc in the physiological and pathological functioning of the brain is rapidly expanding. The increased availability of genetically modified animal models, selective zinc-sensitive fluorescent probes, and novel chelators is producing a remarkable body of exciting new data that clearly establishes this metal ion as a key modulator of intracellular and intercellular neuronal signaling. In this Mini-Symposium, we will review and discuss the most recent findings that link zinc to synaptic function as well as the injurious effects of zinc dyshomeostasis within the context of neuronal death associated with major human neurological disorders, including stroke, epilepsy, and Alzheimer’s disease.
The PET imaging agent CuII(atsm) improves motor and cognitive function in Parkinson’s disease.
Parkinson’s disease (PD) is a progressive, chronic disease characterized by dyskinesia, rigidity, instability, and tremors. The disease is defined by the presence of Lewy bodies, which primarily consist of aggregated α-synuclein protein, and is accompanied by the loss of monoaminergic neurons. Current therapeutic strategies only give symptomatic relief of motor impairment and do not address the underlying neurodegeneration. Hence, we have identified CuII(atsm) as a potential therapeutic for PD. Drug administration to four different animal models of PD resulted in improved motor and cognition function, rescued nigral cell loss, and improved dopamine metabolism. In vitro, this compound is able to inhibit the effects of peroxynitrite-driven toxicity, including the formation of nitrated α-synuclein oligomers. Our results show that CuII(atsm) is effective in reversing parkinsonian defects in animal models and has the potential to be a successful treatment of PD.
N-acetyl cysteine (NAC) is a glutathione precursor that has been shown to have antidepressant efficacy in a placebo-controlled trial. The current study aimed to investigate the maintenance effects of NAC following eight weeks of open-label treatment for bipolar disorder.
The efficacy of a double blind randomized placebo controlled trial of 2 g/day NAC as adjunct maintenance treatment for bipolar disorder was examined. Participants (n = 149) had a Montgomery Asberg Depression Rating Score of ≥12 at trial entry and, after eight weeks of open-label NAC treatment, were randomized to adjunctive NAC or placebo, in addition to treatment as usual. Participants (primarily outpatients) were recruited through public and private services and through newspaper advertisements. Time to intervention for a mood episode was the primary endpoint of the study, and changes in mood symptoms, functionality and quality of life measures were secondary outcomes.
There was a substantial decrease in symptoms during the eight-week open-label NAC treatment phase. During the subsequent double-blind phase, there was minimal further change in outcome measures with scores remaining low. Consequently, from this low plateau, between-group differences did not emerge on recurrence, clinical functioning or quality of life measures.
There were no significant between-group differences in recurrence or symptomatic outcomes during the maintenance phase of the trial; however, these findings may be confounded by limitations.
The trial was registered with the Australian New Zealand Clinical Trials Registry (ACTRN12607000074493).
N-acetyl cysteine; depression; bipolar disorder; maintenance; mania; oxidative
Bioinorganic chemistry is critical to cellular function. Homeostasis of manganese (Mn), for example, is essential for life. A lack of methods for direct in situ visualization of Mn and other biological metals within intact multicellular eukaryotes limits our understanding of management of these metals. We provide the first quantitative subcellular visualization of endogenous Mn concentrations (spanning two orders of magnitude) associated with individual cells of the nematode, Caenorhabditis elegans.
Inhibition of GSL (glycosphingolipid) synthesis reduces Aβ (amyloid β-peptide) production in vitro. Previous studies indicate that GCS (glucosylceramide synthase) inhibitors modulate phosphorylation of ERK1/2 (extracellular-signal-regulated kinase 1/2) and that the ERK pathway may regulate some aspects of Aβ production. It is not clear whether there is a causative relationship linking GSL synthesis inhibition, ERK phosphorylation and Aβ production. In the present study, we treated CHO cells (Chinese-hamster ovary cells) and SH-SY5Y neuroblastoma cells, that both constitutively express human wild-type APP (amyloid precursor protein) and process this to produce Aβ, with GSL-modulating agents to explore this relationship. We found that three related ceramide analogue GSL inhibitors, based on the PDMP (D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol) structure, reduced cellular Aβ production and in all cases this was correlated with inhibition of pERK (phosphorylated ERK) formation. Importantly, the L-threo enantiomers of these compounds (that are inferior GSL synthesis inhibitors compared with the D-threo-enantiomers) also reduced ERK phosphorylation to a similar extent without altering Aβ production. Inhibition of ERK activation using either PD98059 [2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one] or U0126 (1,4-diamino-2,3-dicyano-1,4-bis[2-aminophenylthio] butadiene) had no impact on Aβ production, and knockdown of endogenous GCS using small interfering RNA reduced cellular GSL levels without suppressing Aβ production or pERK formation. Our data suggest that the alteration in pERK levels following treatment with these ceramide analogues is not the principal mechanism involved in the inhibition of Aβ generation and that the ERK signalling pathway does not play a crucial role in processing APP through the amyloidogenic pathway.
Alzheimer's disease; amyloid β-peptide; amyloid precursor protein; extracellular-signal-regulated kinase (ERK); glycosphingolipid; 2AA, 2-anthranilic acid; Aβ, amyloid β-peptide; Aβ40, Aβ-(1–40); Aβ42, Aβ-(1–42); AD, Alzheimer's disease; APP, amyloid precursor protein; BACE-1, β-site APP-cleaving enzyme; CHO cell, Chinese-hamster ovary cell; DAPT, N-[N-(3,5-difluorophenacetyl)-L-alanyl]-(S)-phenylglycine t-butyl ester; ERK, extracellular-signal-regulated kinase; EtDO-P4, D-threo-ethylenedioxy-1-phenyl-2-palmitoylamino-3-pyrrolidino-1-propanol; FBS, fetal bovine serum; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; GCS, glucosylceramide synthase; GlcCer, glucosylceramide; GSL, glycosphingolipid; LacCer, lactosylceramide; MAPK, mitogen-activated protein kinase; MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-2H-tetrazolium bromide; PDMP, D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol; pERK, phosphorylated ERK; PPMP, D-threo-1-phenyl-2-hexadecanoylamino-3-morpholino-1-propanol; PS, presenilin; sAPPα, soluble APPα fragment; siRNA, small interfering RNA
Recent data from in vitro, animal, and human studies have shed new light on the positive roles of copper in many aspects of AD. Copper promotes the non-amyloidogenic processing of APP and thereby lowers the Aβ production in cell culture systems, and it increases lifetime and decreases soluble amyloid production in APP transgenic mice. In a clinical trial with Alzheimer patients, the decline of Aβ levels in CSF, which is a diagnostic marker, is diminished in the verum group (8 mg copper/day), indicating a beneficial effect of the copper treatment. These observations are in line with the benefit of treatment with compounds aimed at normalizing metal levels in the brain, such as PBT2. The data reviewed here demonstrate that there is an apparent disturbance in metal homeostasis in AD. More research is urgently needed to understand how this disturbance can be addressed therapeutically.
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 insulin-like signaling (ILS) pathway regulates metabolism and is known to modulate adult lifespan in C. elegans. Altered stress responses and resistance to a wide range of stressors are also associated with changes in ILS and contribute to enhanced longevity. The transcription factors DAF-16 and HSF-1 are key effectors of the longevity phenotype. We demonstrate that increased intrinsic thermotolerance, due to lower ILS, is not dependent on stress induced transcriptional responses but instead requires active protein translation. Translation profiling experiments reveal genes that are post-transcriptionally regulated in response to altered ILS during heat shock in a DAF-16-dependent manner. Furthermore, several novel proteins are specifically required for ILS effects on thermotolerance. We propose that lowered-ILS results in metabolic and physiological changes. These DAF-16-induced changes precondition a translational response under acute stress to modulate survival.
Alzheimer’s disease (AD) is characterized by progressive neurodegeneration associated with the aggregation and deposition of β-amyloid (Aβ40 and Aβ42) peptide in senile plaques. Recent studies suggest that copper may play an important role in AD pathology. Copper concentrations are elevated in amyloid plaques and copper binds with high affinity to the Aβ peptide and promotes Aβ oligomerization and neurotoxicity. Despite this connection between copper and AD, it is unknown whether the expression of proteins involved in regulating copper homeostasis is altered in this disorder. In this study we demonstrate that the copper transporting P-type ATPase, ATP7A, is highly expressed in activated microglial cells that are specifically clustered around amyloid plaques in the TgCRND8 mouse model of AD. Using a cultured microglial cell line, ATP7A expression was found to be increased by the pro-inflammatory cytokine IFN-γ, but not by TNFα or IL-1β. IFN-γ also elicited marked changes in copper homeostasis, including copper-dependent trafficking of ATP7A from the Golgi to cytoplasmic vesicles, increased copper uptake and elevated expression of the CTR1 copper importer. These findings suggest that pro-inflammatory conditions associated with AD cause marked changes in microglial copper trafficking, which may underlie the changes in copper homeostasis in AD. It is concluded that copper sequestration by microglia may provide a neuroprotective mechanism in AD.
Alzheimer’s disease; copper homeostasis; ATP7A; microglia; inflammation
The role of metals in the pathophysiology of Alzheimer's disease (AD) has gained considerable support in recent years, with both in vitro and in vivo data demonstrating that a mis-metabolism of metal ions, such as copper and zinc, may affect various cellular cascades that ultimately leads to the development and/or potentiation of AD. In this paper, we will provide an overview of the preclinical and clinical literature that specifically relates to attempts to affect the AD cascade by the modulation of brain copper levels. We will also detail our own novel animal data, where we treated APP/PS1 (7-8 months old) mice with either high copper (20 ppm in the drinking water), high cholesterol (2% supplement in the food) or a combination of both and then assessed β-amyloid (Aβ) burden (soluble and insoluble Aβ), APP levels and behavioural performance in the Morris water maze. These data support an interaction between copper/cholesterol and both Aβ and APP and further highlight the potential role of metal ion dyshomeostasis in AD.
Glycogen synthase kinase-3 (GSK-3) regulates multiple cellular processes, and its dysregulation is implicated in the pathogenesis of diverse diseases. In this paper we will focus on the dysfunction of GSK-3 in Alzheimer's disease and Parkinson's disease. Specifically, GSK-3 is known to interact with tau, β-amyloid (Aβ), and α-synuclein, and as such may be crucially involved in both diseases. Aβ production, for example, is regulated by GSK-3, and its toxicity is mediated by GSK-induced tau phosphorylation and degeneration. α-synuclein is a substrate for GSK-3 and GSK-3 inhibition protects against Parkinsonian toxins. Lithium, a GSK-3 inhibitor, has also been shown to affect tau, Aβ, and α-synuclein in cell culture, and transgenic animal models. Thus, understanding the role of GSK-3 in neurodegenerative diseases will enhance our understanding of the basic mechanisms underlying the pathogenesis of these disorders and also facilitate the identification of new therapeutic avenues.
We have previously demonstrated that brief treatment of APP transgenic mice with metal ionophores (PBT2, Prana Biotechnology) rapidly and markedly improves learning and memory. To understand the potential mechanisms of action underlying this phenomenon we examined hippocampal dendritic spine density, and the levels of key proteins involved in learning and memory, in young (4 months) and old (14 months) female Tg2576 mice following brief (11 days) oral treatment with PBT2 (30 mg/kg/d). Transgenic mice exhibited deficits in spine density compared to littermate controls that were significantly rescued by PBT2 treatment in both the young (+17%, p<0.001) and old (+32%, p<0.001) animals. There was no effect of PBT2 on spine density in the control animals. In the transgenic animals, PBT2 treatment also resulted in significant increases in brain levels of CamKII (+57%, p = 0.005), spinophilin (+37%, p = 0.04), NMDAR1A (+126%, p = 0.02), NMDAR2A (+70%, p = 0.05), pro-BDNF (+19%, p = 0.02) and BDNF (+19%, p = 0.04). While PBT2-treatment did not significantly alter neurite-length in vivo, it did increase neurite outgrowth (+200%, p = 0.006) in cultured cells, and this was abolished by co-incubation with the transition metal chelator, diamsar. These data suggest that PBT2 may affect multiple aspects of snaptic health/efficacy. In Alzheimer's disease therefore, PBT2 may restore the uptake of physiological metal ions trapped within extracellular β-amyloid aggregates that then induce biochemical and anatomical changes to improve cognitive function.