RESUMO
Alzheimer's Disease (AD) is complicated by pro-oxidant intraneuronal Fe(2+) elevation as well as extracellular Zn(2+) accumulation within amyloid plaque. We found that the AD ß-amyloid protein precursor (APP) possesses ferroxidase activity mediated by a conserved H-ferritin-like active site, which is inhibited specifically by Zn(2+). Like ceruloplasmin, APP catalytically oxidizes Fe(2+), loads Fe(3+) 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 Fe(2+) accumulation and oxidative stress in cortical neurons. Paralleling iron accumulation, APP ferroxidase activity in AD postmortem neocortex is inhibited by endogenous Zn(2+), which we demonstrate can originate from Zn(2+)-laden amyloid aggregates and correlates with Aß burden. Abnormal exchange of cortical zinc may link amyloid pathology with neuronal iron accumulation in AD.
Assuntos
Doença de Alzheimer/patologia , Precursor de Proteína beta-Amiloide/antagonistas & inibidores , Precursor de Proteína beta-Amiloide/metabolismo , Ceruloplasmina/antagonistas & inibidores , Zinco/metabolismo , Doença de Alzheimer/metabolismo , Sequência de Aminoácidos , Precursor de Proteína beta-Amiloide/química , Animais , Linhagem Celular , Ceruloplasmina/química , Ceruloplasmina/metabolismo , Humanos , Ferro/metabolismo , Camundongos , Alinhamento de SequênciaRESUMO
Amyloidogenic processing of the amyloid precursor protein (APP) forms the amyloid-ß peptide (Aß) component of pathognomonic extracellular plaques of AD. Additional early cortical changes in AD include neuroinflammation and elevated iron levels. Activation of the innate immune system in the brain is a neuroprotective response to infection; however, persistent neuroinflammation is linked to AD neuropathology by uncertain mechanisms. Non-parametric machine learning analysis on transcriptomic data from a large neuropathologically characterised patient cohort revealed the acute phase protein lactoferrin (Lf) as the key predictor of amyloid pathology. In vitro studies showed that an interaction between APP and the iron-bound form of Lf secreted from activated microglia diverted neuronal APP endocytosis from the canonical clathrin-dependent pathway to one requiring ADP ribosylation factor 6 trafficking. By rerouting APP recycling to the Rab11-positive compartment for amyloidogenic processing, Lf dramatically increased neuronal Aß production. Lf emerges as a novel pharmacological target for AD that not only modulates APP processing but provides a link between Aß production, neuroinflammation and iron dysregulation.
Assuntos
Doença de Alzheimer , Lactoferrina , Proteínas de Fase Aguda , Doença de Alzheimer/genética , Secretases da Proteína Precursora do Amiloide/metabolismo , Peptídeos beta-Amiloides/metabolismo , Precursor de Proteína beta-Amiloide/genética , Precursor de Proteína beta-Amiloide/metabolismo , HumanosRESUMO
The proteolytic cleavage of ß-amyloid precursor protein (APP) to form the amyloid beta (Aß) peptide is related to the pathogenesis of Alzheimer's disease (AD) because APP mutations that influence this processing either induce familial AD or mitigate the risk of AD. Yet Aß formation itself may not be pathogenic. APP promotes neuronal iron efflux by stabilizing the cell-surface presentation of ferroportin, the only iron export channel of cells. Mislocalization of APP can promote iron retention, thus we hypothesized that changes in endocytotic trafficking associated with altered APP processing could contribute to the neuronal iron elevation and oxidative burden that feature in AD pathology. Here, we demonstrate, using genetic and pharmacological approaches, that endocytotic amyloidogenic processing of APP impairs iron export by destabilizing ferroportin on the cell surface. Conversely, preferential non-amyloidogenic processing of APP at the cell surface promotes ferroportin stabilization to decrease intraneuronal iron. A new Aß-independent hypothesis emerges where the amyloidogenic processing of APP, combined with age-dependent iron elevation in the tissue, increases pro-oxidant iron burden in AD.
Assuntos
Doença de Alzheimer , Precursor de Proteína beta-Amiloide , Doença de Alzheimer/genética , Secretases da Proteína Precursora do Amiloide , Peptídeos beta-Amiloides , Precursor de Proteína beta-Amiloide/genética , Humanos , Ferro , NeurôniosRESUMO
Cell surface ß-Amyloid precursor protein (APP) is known to have a functional role in iron homeostasis through stabilising the iron export protein ferroportin (FPN). Mechanistic evidence of this role has previously only been provided through transcriptional or translational depletion of total APP levels. However, numerous post-translational modifications of APP are reported to regulate the location and trafficking of this protein to the cell surface. Stable overexpressing cell lines were generated that overexpressed APP with disrupted N-glycosylation (APPN467K and APPN496K) or ectodomain phosphorylation (APPS206A); sites selected for their proximity to the FPN binding site on the E2 domain of APP. We hypothesise that impaired N-glycosylation or phosphorylation of APP disrupts the functional location on the cell surface or binding to FPN to consequentially alter intracellular iron levels through impaired cell surface FPN stability. Outcomes confirm that these post-translational modifications are essential for the correct location of APP on the cell surface and highlight a novel mechanism by which the cell can modulate iron homeostasis. Further interrogation of other post-translational processes to APP is warranted in order to fully understand how each modification plays a role on regulating intracellular iron levels in health and disease.
Assuntos
Precursor de Proteína beta-Amiloide/metabolismo , Homeostase/fisiologia , Ferro/metabolismo , Neurônios/metabolismo , Precursor de Proteína beta-Amiloide/genética , Animais , Linhagem Celular Tumoral , Glicosilação , Camundongos , Fosforilação/genética , Mutação Puntual , Processamento de Proteína Pós-Traducional/genética , Transporte Proteico/genéticaRESUMO
Iron dysregulation, dopamine depletion, cellular oxidative stress and α-synuclein protein mis-folding are key neuronal pathological features seen in the progression of Parkinson's disease. Iron chelators endowed with one or more therapeutic modes of action have long been suggested as disease modifying therapies for its treatment. In this study, novel 1-hydroxypyrazin-2(1H)-one iron chelators were synthesized and their physicochemical properties, iron chelation abilities, antioxidant capacities and neuroprotective effects in a cell culture model of Parkinson's disease were evaluated. Physicochemical properties (log ß, log D7.4, pL0.5) suggest that these ligands have a poorer ability to penetrate cell membranes and form weaker iron complexes than the closely related 1-hydroxypyridin-2(1H)-ones. Despite this, we show that levels of neuroprotection provided by these ligands against the catecholaminergic neurotoxin 6-hydroxydopamine in vitro were comparable to those seen previously with the 1-hydroxypyridin-2(1H)-ones and the clinically used iron chelator Deferiprone, with two of the ligands restoring cell viability to ≥89% compared to controls. Two of the ligands were endowed with additional phenol moieties in an attempt to derive multifunctional chelators with dual iron chelation/antioxidant activity. However, levels of neuroprotection with these ligands were no greater than ligands lacking this moiety, suggesting the neuroprotective properties of these ligands are due primarily to chelation and passivation of intracellular labile iron, preventing the generation of free radicals and reactive oxygen species that otherwise lead to the neuronal cell death seen in Parkinson's disease.
Assuntos
Doença de ParkinsonRESUMO
Objectives: The objective of this study was to determine whether a breakdown in proteins regulating cortical iron homeostasis could be involved in the pathophysiology of mood disorders.Methods: Levels of select proteins responsible for cortical iron transport were quantitated by Western blotting of Brodmann's (BA) areas 6 and 10 from patients with major depressive disorder (n = 13), bipolar disorder (n = 12) and age/sex matched controls (n = 13).Results: We found the inactive form of ceruloplasmin was lower in BA 6 from males compared to females. Levels of copper containing ceruloplasmin was lower in BA 6 from suicide completers whilst levels of amyloid precursor protein, TAU and transferrin were higher in BA 10 from those individuals. The level of prion protein was lower in BA 6 from subjects with major depressive disorder.Conclusions: Our data suggests that perturbation in cortical iron transport proteins is not prevalent in mood disorders. By contrast, our data suggests changes in iron transport proteins in BA 6 and BA 10 are present after suicide completion. If these changes were present before death, they could have had a role in the genesis of the contemplation and completion of suicide.
Assuntos
Transtorno Bipolar , Transtorno Depressivo Maior , Suicídio , Proteínas de Transporte , Córtex Cerebral , Feminino , Humanos , Ferro/metabolismo , MasculinoRESUMO
Amyloid precursor protein (APP) and its extracellular domain, soluble APP alpha (sAPPα) play important physiological and neuroprotective roles. However, rare forms of familial Alzheimer's disease are associated with mutations in APP that increase toxic amyloidogenic cleavage of APP and produce amyloid beta (Aß) at the expense of sAPPα and other non-amyloidogenic fragments. Although mitochondrial dysfunction has become an established hallmark of neurotoxicity, the link between Aß and mitochondrial function is unclear. In this study we investigated the effects of increased levels of neuronal APP or Aß on mitochondrial metabolism and gene expression, in human SH-SY5Y neuroblastoma cells. Increased non-amyloidogenic processing of APP, but not Aß, profoundly decreased respiration and enhanced glycolysis, while mitochondrial DNA (mtDNA) transcripts were decreased, without detrimental effects to cell growth. These effects cannot be ascribed to Aß toxicity, since higher levels of endogenous Aß in our models do not cause oxidative phosphorylation (OXPHOS) perturbations. Similarly, chemical inhibition of ß-secretase decreased mitochondrial respiration, suggesting that non-amyloidogenic processing of APP may be responsible for mitochondrial changes. Our results have two important implications, the need for caution in the interpretation of mitochondrial perturbations in models where APP is overexpressed, and a potential role of sAPPα or other non-amyloid APP fragments as acute modulators of mitochondrial metabolism.
Assuntos
Peptídeos beta-Amiloides/metabolismo , Precursor de Proteína beta-Amiloide/metabolismo , Mitocôndrias/metabolismo , Fosforilação Oxidativa , Doença de Alzheimer/metabolismo , Secretases da Proteína Precursora do Amiloide/metabolismo , Precursor de Proteína beta-Amiloide/genética , Linhagem Celular , Respiração Celular/genética , Complexo IV da Cadeia de Transporte de Elétrons/genética , Complexo IV da Cadeia de Transporte de Elétrons/metabolismo , Ativação Enzimática , Dosagem de Genes , Genes Mitocondriais , Glicólise , Humanos , Mitocôndrias/genética , Mutação , Neurônios/metabolismo , Transcrição GênicaRESUMO
Brain iron accumulation has been associated with inciting the generation of oxidative stress in a host of chronic neurological diseases, including Parkinson's disease. Using the catecholaminergic neurotoxin 6-hydroxydopamine to lesion cellular dopaminergic pathways as a model of Parkinson's disease in culture, a selection of 1-hydroxypyridin-2-one (1,2-HOPO) metal chelators were synthesized and their neuroprotective properties were compared to the 3-hydroxypyridin-4-one; deferiprone (3,4-HOPO; DFP). Protection against 6-OHDA and iron insult by the novel compounds 6 and 9 was comparable to DFP. Iron associated changes by 6-OHDA imply that the neuroprotective capacity of these compounds are due to chelation of the neuronal labile iron pool and the requirement of the iron binding moiety of compound 6 for efficacy supported this hypothesis. In conclusion, two novel 1,2-HOPO's and DFP have comparable neuroprotection against Parkinsonian-associated neurotoxins and supports the continued development of hydroxypyridinone compounds as a non-toxic therapeutic agent in the treatment of neurodegenerative disease.
Assuntos
Quelantes de Ferro/química , Quelantes de Ferro/farmacologia , Fármacos Neuroprotetores/química , Fármacos Neuroprotetores/farmacologia , Doença de Parkinson Secundária/prevenção & controle , Piridonas/química , Piridonas/farmacologia , Linhagem Celular , Cristalografia por Raios X , Deferiprona , Humanos , Modelos Moleculares , Neurônios/efeitos dos fármacos , Neurônios/patologia , OxidopaminaRESUMO
Ceruloplasmin is a ferroxidase that interacts with ferroportin to export cellular iron, but is not expressed in neurons. We recently reported that the amyloid precursor protein (APP) is the analogous iron-exporting chaperone for neurons and other cells. The ferroxidase activity of APP has since been called into question. Using a triplex Fe2+ oxidation assay, we analyzed the activity of a soluble form of APP (sAPPα) within a buffer of physiological pH and anionic charge, and determined that iron oxidation originated from phosphate. Using various techniques such as flow-cytometry to measure surface presented proteins, we confirmed that endogenous APP is essential for ferroportin persistence on the neuronal surface. Therefore, despite lacking ferroxidase activity, APP still supports iron export from neurons.
Assuntos
Precursor de Proteína beta-Amiloide/metabolismo , Proteínas de Transporte de Cátions/metabolismo , Ceruloplasmina/metabolismo , Animais , Células HEK293 , Humanos , Camundongos , OxirreduçãoRESUMO
There is increasing evidence that some cancers are hierarchically organized, sustained by a relatively rare population of cancer-initiating cells (C-ICs). Although the capacity to initiate tumors upon serial transplantation is a hallmark of all C-ICs, little is known about the genes that control this process. Here, we establish that ID1 and ID3 function together to govern colon cancer-initiating cell (CC-IC) self-renewal through cell-cycle restriction driven by the cell-cycle inhibitor p21. Regulation of p21 by ID1 and ID3 is a central mechanism preventing the accumulation of excess DNA damage and subsequent functional exhaustion of CC-ICs. Additionally, silencing of ID1 and ID3 increases sensitivity of CC-ICs to the chemotherapeutic agent oxaliplatin, linking tumor initiation function with chemotherapy resistance.
Assuntos
Neoplasias do Colo/genética , Inibidor de Quinase Dependente de Ciclina p21/genética , Proteína 1 Inibidora de Diferenciação/genética , Proteínas Inibidoras de Diferenciação/genética , Proteínas de Neoplasias/genética , Células-Tronco Neoplásicas/metabolismo , Animais , Antineoplásicos/farmacologia , Western Blotting , Ciclo Celular/efeitos dos fármacos , Ciclo Celular/genética , Proliferação de Células/efeitos dos fármacos , Neoplasias do Colo/tratamento farmacológico , Neoplasias do Colo/patologia , Inibidor de Quinase Dependente de Ciclina p21/metabolismo , Regulação Neoplásica da Expressão Gênica , Humanos , Proteína 1 Inibidora de Diferenciação/metabolismo , Proteínas Inibidoras de Diferenciação/metabolismo , Camundongos , Camundongos Endogâmicos NOD , Camundongos SCID , Microscopia Confocal , Proteínas de Neoplasias/metabolismo , Células-Tronco Neoplásicas/efeitos dos fármacos , Células-Tronco Neoplásicas/patologia , Compostos Organoplatínicos/farmacologia , Oxaliplatina , Interferência de RNA , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Esferoides Celulares/efeitos dos fármacos , Esferoides Celulares/metabolismo , Esferoides Celulares/patologia , Células Tumorais Cultivadas , Ensaios Antitumorais Modelo de XenoenxertoRESUMO
PBT2 is a copper/zinc ionophore that rapidly restores cognition in mouse models of Alzheimer's disease (AD). A recent Phase IIa double-blind, randomized, placebo-controlled trial found that the 250 mg dose of PBT2 was well-tolerated, significantly lowered cerebrospinal fluid (CSF) levels of amyloid-beta42, and significantly improved executive function on a Neuro-psychological Test Battery (NTB) within 12 weeks of treatment in patients with AD. In the post-hoc analysis reported here, the cognitive, blood marker, and CSF neurochemistry outcomes from the trial were subjected to further analysis. Ranking the responses to treatment after 12 weeks with placebo, PBT2 50 mg, and PBT2 250 mg revealed that the proportions of patients showing improvement on NTB Composite or Executive Factor z-scores were significantly greater in the PBT2 250 mg group than in the placebo group. Receiver-operator characteristic analyses revealed that the probability of an improver at any level coming from the PBT2 250 mg group was significantly greater, compared to placebo, for Composite z-scores (Area Under the Curve [AUC] =0.76, p=0.0007), Executive Factor z-scores (AUC =0.93, p=1.3 x 10(-9)), and near-significant for the ADAS-cog (AUC =0.72, p=0.056). There were no correlations between changes in CSF amyloid-beta or tau species and cognitive changes. These findings further encourage larger-scale testing of PBT2 for AD.
Assuntos
Doença de Alzheimer/complicações , Clioquinol/análogos & derivados , Transtornos Cognitivos/tratamento farmacológico , Transtornos Cognitivos/etiologia , Ionóforos/uso terapêutico , Doença de Alzheimer/sangue , Doença de Alzheimer/líquido cefalorraquidiano , Peptídeos beta-Amiloides/líquido cefalorraquidiano , Área Sob a Curva , Austrália , Clioquinol/farmacologia , Clioquinol/uso terapêutico , Transtornos Cognitivos/sangue , Transtornos Cognitivos/líquido cefalorraquidiano , Cobre/sangue , Relação Dose-Resposta a Droga , Método Duplo-Cego , Função Executiva/efeitos dos fármacos , Humanos , Cooperação Internacional , Ionóforos/farmacologia , Testes Neuropsicológicos , Fragmentos de Peptídeos/líquido cefalorraquidiano , Curva ROC , Superóxido Dismutase/sangue , Superóxido Dismutase-1 , Suécia , Proteínas tau/líquido cefalorraquidianoRESUMO
Abnormal interaction of beta-amyloid 42 (Abeta42) with copper, zinc and iron induce peptide aggregation and oxidation in Alzheimer's disease (AD). However, in health, Abeta degradation is mediated by extracellular metalloproteinases, neprilysin, insulin degrading enzyme (IDE) and matrix metalloproteinases. We investigated the relationship between levels of Abeta and biological metals in CSF. We assayed CSF copper, zinc, other metals and Abeta42 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 Abeta42 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 Abeta42. In vitro, the degradation of synthetic Abeta substrate added to CSF was markedly accelerated by low levels (2microM) of exogenous zinc and copper. While excessive interaction with copper and zinc may induce neocortical Abeta precipitation in AD, soluble Abeta degradation is normally promoted by physiological copper and zinc concentrations.
Assuntos
Doença de Alzheimer/líquido cefalorraquidiano , Peptídeos beta-Amiloides/líquido cefalorraquidiano , Encéfalo/metabolismo , Líquido Cefalorraquidiano/metabolismo , Cobre/líquido cefalorraquidiano , Zinco/líquido cefalorraquidiano , Idoso , Idoso de 80 Anos ou mais , Doença de Alzheimer/fisiopatologia , Peptídeos beta-Amiloides/análise , Asiático , Encéfalo/fisiopatologia , Química Encefálica/fisiologia , Cromo/análise , Cromo/líquido cefalorraquidiano , Estudos de Coortes , Cobre/análise , Humanos , Ferro/análise , Ferro/líquido cefalorraquidiano , Masculino , Manganês/análise , Manganês/líquido cefalorraquidiano , Fragmentos de Peptídeos/análise , Fragmentos de Peptídeos/líquido cefalorraquidiano , Zinco/análiseRESUMO
BACKGROUND: Ion transporters of the Slc30A- (ZnT-) family regulate zinc fluxes into sub-cellular compartments. beta-cells depend on zinc for both insulin crystallization and regulation of cell mass. METHODOLOGY/PRINCIPAL FINDINGS: This study examined: the effect of glucose and zinc chelation on ZnT gene and protein levels and apoptosis in beta-cells and pancreatic islets, the effects of ZnT-3 knock-down on insulin secretion in a beta-cell line and ZnT-3 knock-out on glucose metabolism in mice during streptozotocin-induced beta-cell stress. In INS-1E cells 2 mM glucose down-regulated ZnT-3 and up-regulated ZnT-5 expression relative to 5 mM. 16 mM glucose increased ZnT-3 and decreased ZnT-8 expression. Zinc chelation by DEDTC lowered INS-1E insulin content and insulin expression. Furthermore, zinc depletion increased ZnT-3- and decreased ZnT-8 gene expression whereas the amount of ZnT-3 protein in the cells was decreased. Zinc depletion and high glucose induced apoptosis and necrosis in INS-1E cells. The most responsive zinc transporter, ZnT-3, was investigated further; by immunohistochemistry and western blotting ZnT-3 was demonstrated in INS-1E cells. 44% knock-down of ZnT-3 by siRNA transfection in INS-1E cells decreased insulin expression and secretion. Streptozotocin-treated mice had higher glucose levels after ZnT-3 knock-out, particularly in overt diabetic animals. CONCLUSION/SIGNIFICANCE: Zinc transporting proteins in beta-cells respond to variations in glucose and zinc levels. ZnT-3, which is pivotal in the development of cellular changes as also seen in type 2 diabetes (e.g. amyloidosis in Alzheimer's disease) but not previously described in beta-cells, is present in this cell type, up-regulated by glucose in a concentration dependent manner and up-regulated by zinc depletion which by contrast decreased ZnT-3 protein levels. Knock-down of the ZnT-3 gene lowers insulin secretion in vitro and affects in vivo glucose metabolism after streptozotocin treatment.