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Leon M Tai,
Tina Bilousova,
Lisa Jungbauer,
Stephen K Roeske,
Katherine L Youmans,
Chunjiang Yu,
Wayne W Poon,
Lindsey B Cornwell,
Carol A Miller,
Harry V Vinters,
Linda J Van Eldik,
Dave W Fardo,
Steve Estus,
Guojun Bu,
Karen Hoppens Gylys, Mary Jo Ladu
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ABSTRACT: Human apolipoprotein E (apoE) isoforms may differentially modulate amyloid-beta (Aβ) levels. Evidence suggests physical interactions between apoE and Aβ are partially responsible for these functional effects. However, apoE/Aβ complex is not a single, static structure; rather, it is defined by detection methods. Thus, literature results are inconsistent and difficult to interpret. An ELISA was developed to measure soluble apoE/Aβ complex in a single, quantitative method, and used to address the hypothesis that reduced levels of soluble apoE/Aβ complex and an increase in soluble Aβ, specifically oligomeric Aβ (oAβ) are associated with APOE4 and AD. In a previous study, soluble Aβ42 and oAβ levels were greater with APOE4 compared with APOE2/APOE3 in hippocampal homogenates from EFAD transgenic mice (expressing 5 familial AD mutations and human apoE isoforms). In the current study, soluble apoE/Aβ levels were lower in E4FAD mice compared with E2FAD and E3FAD, evidence that apoE/Aβ levels isoform-specifically modulate soluble oAβ clearance. Similar results were observed in soluble preparations of human cortical synaptosomes; apoE/Aβ levels were lower in AD patients compared to controls, and lower with APOE4 in the AD cohort. In human CSF, apoE/Aβ levels were also lower in AD patients and with APOE4 in the AD cohort. Importantly, although total Aβ42 levels decreased in AD patients compared to controls, oAβ increased and were greater with APOE4 in the AD cohort. Overall, apoE isoform-specific formation of soluble apoE/Aβ complex modulates oAβ levels, suggesting a basis for APOE4-induced AD risk and a mechanistic approach to AD biomarkers.
Journal of Biological Chemistry 01/2013; · 4.77 Impact Factor
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ABSTRACT: Aggregation of amyloid-β (Aβ) peptides leads to synaptic disruption and neurodegeneration in Alzheimer's disease (AD). A major Aβ clearance pathway in the brain is cellular uptake and degradation. However, how Aβ traffics through the endocytic pathway and how AD risk factors regulate this event is unclear. Here we show that the majority of endocytosed Aβ in neurons traffics through early and late endosomes to the lysosomes for degradation. Overexpression of Rab5 or Rab7, small GTPases that function in vesicle fusion for early and late endosomes, respectively, significantly accelerates Aβ endocytic trafficking to the lysosomes. We also found that a portion of endocytosed Aβ traffics through Rab11-positive recycling vesicles. A blockage of this Aβ recycling pathway with a constitutively active Rab11 mutant significantly accelerates cellular Aβ accumulation. Inhibition of lysosomal enzymes results in Aβ accumulation and aggregation. Importantly, apolipoprotein E (apoE) accelerates neuronal Aβ uptake, lysosomal trafficking and degradation in an isoform-dependent manner with apoE3 more efficiently facilitates Aβ trafficking and degradation than apoE4, a risk factor for AD. Taken together, our results demonstrate that Aβ endocytic trafficking to lysosomes for degradation is a major Aβ clearance pathway that is differentially regulated by apoE isoforms. A disturbance of this pathway can lead to accumulation and aggregation of cellular Aβ capable of causing neurotoxicity and seeding amyloid.
Journal of Biological Chemistry 11/2012; · 4.77 Impact Factor
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Katherine L Youmans,
Leon M Tai,
Evelyn Nwabuisi-Heath,
Lisa Jungbauer,
Takahisa Kanekiyo,
Ming Gan,
Jungsu Kim,
William A Eimer,
Steve Estus,
G William Rebeck,
Edwin J Weeber,
Goujun Bu,
Chunjiang Yu, Mary Jo Ladu
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ABSTRACT: APOE4 is the greatest risk factor for Alzheimers disease (AD) and synergistic effects with amyloid-β peptide (Aβ) suggest interactions among apoE isoforms and different forms of Aβ accumulation. However, it remains unclear how APOE genotype affects plaque morphology, intraneuronal Aβ, soluble Aβ42, and oligomeric Aβ (oAβ), particularly in vivo. As introduction of human APOE significantly delays amyloid deposition in transgenic mice expressing familial-AD (FAD) mutations (FAD-Tg), 5xFAD-Tg mice, which exhibit amyloid deposition by 2-months, were crossed with apoE targeted-replacement mice to produce the new EFAD-Tg mice. Compared to 5xFAD mice, Aβ deposition was delayed ~4 months in the EFAD mice, allowing detection of early changes in Aβ accumulation from 2-6 months. While plaque deposition is generally greater in E4FAD mice, E2/E3FAD have significantly more diffuse and E4FAD more compact plaques. As a first report in FAD-Tg mice, APOE genotype had no effect on intraneuronal Aβ accumulation in EFAD mice. In E4FAD mice, total apoE levels were lower and total Aβ levels higher than E2FAD and E3FAD mice. Profiles from sequential three-step extractions (TBS, detergent and formic acid) demonstrate that the lower level of total apoE4 is reflected only in the detergent-soluble fraction, indicating that less apoE4 is lipoprotein-associated, and perhaps less lipidated, compared with apoE2 and apoE3. Soluble Aβ42 and oAβ levels were highest in E4FAD mice, although soluble apoE2, apoE3 and apoE4 levels were comparable, suggesting that the differences in soluble Aβ42 and oAβ result from functional differences among the apoE isoforms. Thus, APOE differentially regulates multiple aspects of Aβ accumulation.
Journal of Biological Chemistry 10/2012; · 4.77 Impact Factor
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ABSTRACT: Chronically activated glia associated with amyloid plaques might contribute to neuronal dysfunction in Alzheimer’s disease
(AD) through generation of neuroinflammatory molecules. Apolipoprotein E (apoE), also found associated with amyloid plaques,
has been hypothesized to serve an anti-inflammatory role in the CNS through its ability to modulate β-amyloid (Aβ)-induced
glial activation. To further characterize the effect of apoE on inflammation, we examined the ability of exogenously added
human apoE3 and apoE4 to modulate neuroinflammatory responses of cultured rat glia. Apolipoprotein E3 (apoE3) and apoE4 suppressed
oligomeric Aβ-induced production of inducible nitric oxide synthase and cyclo-oxygenase-2, supporting an anti-inflammatory
role for apoE. Exogenous apoE also inhibited Aβ-induced production of endogenous apoE. However, exogenous apoE in the absence
of Aβ stimulated production of the pro-inflammatory cytokine interleukin-1β in an isoform-dependent manner, with apoE4 inducing
a significantly greater response than apoE3. These data support the idea that Aβ stimulation of glial apoE limits neuroinflammation
but that overproduction of apoE by activated glia might exacerbate inflammation. In addition, the observation that apoE4 has
more robust pro-inflammatory activity than apoE3 provides a mechanistic link between the APOE4 allele and AD, and suggests potential apoE-based therapeutic strategies.
Journal of Molecular Neuroscience 04/2012; 23(3):205-212. · 2.50 Impact Factor
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ABSTRACT: Alterations in the density and morphology of dendritic spines are characteristic of multiple cognitive disorders. Elucidating the molecular mechanisms underlying spine alterations are facilitated by the use of experimental and analytical methods that permit concurrent evaluation of changes in spine density, morphology and composition. Here, an automated and quantitative immunocytochemical method for the simultaneous analysis of changes in the density and morphology of spines and excitatory glutamate receptors was established to analyze neuron maturation, in vitro. In neurons of long-term neuron-glia co-cultures, spine density as measured by drebrin cluster fluorescence, increased from DIV (days in vitro)10 to DIV18 (formation phase), remained stable from DIV18 to DIV21 (maintenance phase), and decreased from DIV21 to DIV26 (loss phase). The densities of spine-localized NMDAR and AMPAR clusters followed a similar trend. Spine head sizes as measured by the fluorescence intensities of drebrin clusters increased from DIV10 to DIV21 and decreased from DIV21 to DIV26. Changes in the densities of NR1-only, GluR2-only, and NR1+GluR2 spines were measured by the colocalizations of NR1 and GluR2 clusters with drebrin clusters. The densities of NR1-only spines remained stable from the maintenance to the loss phases, while GluR2-only and NR1+GluR2 spines decreased during the loss phase, thus suggesting GluR2 loss as a proximal molecular event that may underlie spine alterations during neuron maturation. This study demonstrates a sensitive and quantitative immunocytochemical method for the concurrent analysis of changes in spine density, morphology and composition, a valuable tool for determining molecular events involved in dendritic spine alterations.
Journal of neuroscience methods 04/2012; 207(2):137-47. · 2.30 Impact Factor
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ABSTRACT: The ε4 allele of the Apolipoprotein E (APOE) gene is the strongest genetic risk factor for late-onset Alzheimer's disease (AD), and affects clinical outcomes of chronic and acute brain damages. The mechanisms by which apoE affect diverse diseases and disorders may involve modulation of the glial response to various types of brain damage. We examined glial activation in a mouse model where each of the human APOE alleles are expressed under the endogenous mouse APOE promoter, as well as in APOE knock-out mice. APOE4 mice displayed increased glial activation in response to intracerebroventricular lipopolysaccharide (LPS) compared to APOE2 and APOE3 mice by several measures. There were higher levels of microglia/macrophage, astrocytes, and invading T-cells after LPS injection in APOE4 mice. APOE4 mice also displayed greater and more prolonged increases of cytokines (IL-1β, IL-6, TNF-α) than APOE2 and APOE3 mice. We found that APOE4 mice had greater synaptic protein loss after LPS injection, as measured by three markers: PSD-95, drebin, and synaptophysin. In all assays, APOE knock-out mice responded similar to APOE4 mice, suggesting that the apoE4 protein may lack anti-inflammatory characteristics of apoE2 and apoE3. Together, these findings demonstrate that APOE4 predisposes to inflammation, which could contribute to its association with Alzheimer's disease and other disorders.
Glia 04/2012; 60(4):559-69. · 4.82 Impact Factor
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Katherine L Youmans,
Leon M Tai,
Takahisa Kanekiyo,
W Blaine Stine,
Sara-Claude Michon,
Evelyn Nwabuisi-Heath,
Arlene M Manelli,
Yifan Fu,
Sean Riordan,
William A Eimer,
Lester Binder,
Guojun Bu,
Chunjiang Yu,
Dean M Hartley, Mary Jo LaDu
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ABSTRACT: The form(s) of amyloid-β peptide (Aβ) associated with the pathology characteristic of Alzheimer's disease (AD) remains unclear. In particular, the neurotoxicity of intraneuronal Aβ accumulation is an issue of considerable controversy; even the existence of Aβ deposits within neurons has recently been challenged by Winton and co-workers. These authors purport that it is actually intraneuronal APP that is being detected by antibodies thought to be specific for Aβ. To further address this issue, an anti-Aβ antibody was developed (MOAB-2) that specifically detects Aβ, but not APP. This antibody allows for the further evaluation of the early accumulation of intraneuronal Aβ in transgenic mice with increased levels of human Aβ in 5xFAD and 3xTg mice.
MOAB-2 (mouse IgG2b) is a pan-specific, high-titer antibody to Aβ residues 1-4 as demonstrated by biochemical and immunohistochemical analyses (IHC), particularly compared to 6E10 (a commonly used commercial antibody to Aβ residues 3-8). MOAB-2 did not detect APP or APP-CTFs in cell culture media/lysates (HEK-APPSwe or HEK-APPSwe/BACE1) or in brain homogenates from transgenic mice expressing 5 familial AD (FAD) mutation (5xFAD mice). Using IHC on 5xFAD brain tissue, MOAB-2 immunoreactivity co-localized with C-terminal antibodies specific for Aβ40 and Aβ42. MOAB-2 did not co-localize with either N- or C-terminal antibodies to APP. In addition, no MOAB-2-immunoreactivity was observed in the brains of 5xFAD/BACE-/- mice, although significant amounts of APP were detected by N- and C-terminal antibodies to APP, as well as by 6E10. In both 5xFAD and 3xTg mouse brain tissue, MOAB-2 co-localized with cathepsin-D, a marker for acidic organelles, further evidence for intraneuronal Aβ, distinct from Aβ associated with the cell membrane. MOAB-2 demonstrated strong intraneuronal and extra-cellular immunoreactivity in 5xFAD and 3xTg mouse brain tissues.
Both intraneuronal Aβ accumulation and extracellular Aβ deposition was demonstrated in 5xFAD mice and 3xTg mice with MOAB-2, an antibody that will help differentiate intracellular Aβ from APP. However, further investigation is required to determine whether a molecular mechanism links the presence of intraneuronal Aβ with neurotoxicity. As well, understanding the relevance of these observations to human AD patients is critical.
Molecular Neurodegeneration 03/2012; 7:8. · 4.28 Impact Factor
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ABSTRACT: The association between apolipoprotein E (apoE) and amyloid-β peptide (Aβ) may significantly impact the function of both proteins, thus affecting the etiology of Alzheimer's disease (AD). However, apoE/Aβ interactions remain fundamentally defined by the stringency of the detection method. Here we use size exclusion chromatography (SEC) as a non-stringent approach to the detection of apoE/Aβ interactions in solution, specifically apoE and both endogenous and exogenous Aβ from plasma, CSF and astrocyte conditioned media. By SEC analysis, Aβ association with plasma and CNS lipoproteins is apoE-dependent. While endogenous Aβ elutes to specific human plasma lipoproteins distinct from those containing apoE, it is the apoE-containing lipoproteins that absorb excess amounts of exogenous Aβ40. In human CSF, apoE, endogenous Aβ and phospholipid elute in an almost identical profile, as do apoE, exogenous Aβ and phospholipid from astrocyte conditioned media. Combining SEC fractionation with subsequent analysis for SDS-stable apoE/Aβ complex reveals that apoE-containing astrocyte lipoproteins exhibit the most robust interactions with Aβ. Thus, standardization of the methods for detecting apoE/Aβ complex is necessary to determine its functional significance in the neuropathology characteristic of AD. Importantly, a systematic understanding of the role of apoE-containing plasma and CNS lipoproteins in Aβ homeostasis could potentially contribute to identifying a plasma biomarker currently over-looked because it has multiple components.
Biochimica et Biophysica Acta 11/2011; 1821(2):295-302. · 4.66 Impact Factor
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Miranda N Reed,
Jacki J Hofmeister,
Lisa Jungbauer,
Alfred T Welzel,
Chunjiang Yu,
Mathew A Sherman,
Sylvain Lesné, Mary Jo LaDu,
Dominic M Walsh,
Karen H Ashe,
James P Cleary
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ABSTRACT: Soluble forms of amyloid-β peptide (Aβ) are a molecular focus in Alzheimer's disease research. Soluble Aβ dimers (≈8 kDa), trimers (≈12 kDa), tetramers (≈16 kDa) and Aβ*56 (≈56 kDa) have shown biological activity. These Aβ molecules have been derived from diverse sources, including chemical synthesis, transfected cells, and mouse and human brain, leading to uncertainty about toxicity and potency. Herein, synthetic Aβ peptide-derived oligomers, cell- and brain-derived low-n oligomers, and Aβ*56, were injected intracerebroventricularly (icv) into rats assayed under the Alternating Lever Cyclic Ratio (ALCR) cognitive assay. Cognitive deficits were detected at 1.3 μM of synthetic Aβ oligomers and at low nanomolar concentrations of cell-secreted Aβ oligomers. Trimers, from transgenic mouse brain (Tg2576), did not cause cognitive impairment at any dose tested, whereas Aβ*56 induced concentration-dependent cognitive impairment at 0.9 and 1.3μM. Thus, while multiple forms of Aβ have cognition impairing activity, there are significant differences in effective concentration and potency.
Neurobiology of aging 10/2011; 32(10):1784-94. · 5.94 Impact Factor
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ABSTRACT: Recent reports point to small soluble oligomers, rather than insoluble fibrils, of amyloid β (Aβ), as the primary toxic species in Alzheimer's disease. Previously, we developed a low-throughput assay in yeast that is capable of detecting small Aβ(42) oligomer formation. Specifically, Aβ(42) fused to the functional release factor domain of yeast translational termination factor, Sup35p, formed sodium dodecyl sulfate (SDS)-stable low-n oligomers in living yeast, which impaired release factor activity. As a result, the assay for oligomer formation uses yeast growth to indicate restored release factor activity and presumably reduced oligomer formation. We now describe our translation of this assay into a high-throughput screen (HTS) for anti-oligomeric compounds. By doing so, we also identified two presumptive anti-oligomeric compounds from a sub-library of 12,800 drug-like small molecules. Subsequent biochemical analysis confirmed their anti-oligomeric activity, suggesting that this form of HTS is an efficient, sensitive and cost-effective approach to identify new inhibitors of Aβ(42) oligomerization.
Disease Models and Mechanisms 08/2011; 4(6):822-31. · 4.94 Impact Factor
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ABSTRACT: Amyloid plaques composed of the 42 amino acid form of amyloid-β peptide (Aβ42) are a pathological hallmark of Alzheimer's disease (AD), but soluble and intraneuronal Aβ42 are the more proximal causes of synaptic dysfunction and neurotoxicity. Apolipoprotein E (apoE) modulates this disease process, as inheritance of the ɛ4 allele of the apoE gene is the primary genetic risk factor for AD. To address the solubility of Aβ42 and apoE, the 5xFAD-specific extraction profile for Aβ42 was optimized, a protein extraction protocol was optimized in the presence of minimal to extensive Aβ42 pathology. Sequential extractions with TBS, TBS+Triton X-100 (TBSX), and guanidine-HCl (GuHCl) or formic acid (FA) were used with tissue from young and old wild type or mice expressing 5 familial AD mutations (5xFAD), in disease-susceptible or -resistant brain regions. In older 5xFAD mice, the extraction of insoluble Aβ42 and m-apoE protein was increased with FA compared to GuHCl. The 5 FAD mutations significantly increase production of Aβ42, recapitulating AD-like pathology at a greatly accelerated rate. Consistent protein extraction and the specificity of extractions for soluble or membrane-associated proteins were demonstrated. Age-dependent increases in Aβ42 were observed in all extraction fractions, particularly in the cortex and hippocampus. In both young and old 5xFAD mice, Aβ42 is TBS- or GuHCl-soluble. While in WT mice m-apoE is TBSX-soluble, in 5xFAD mice m-apoE is TBS- or GuHCl-soluble. Thus, the 5xFAD-specific extraction profile of Aβ42 paralleled that of m-apoE. As now characterized, this method identifies the extraction profile for disease relevant apoE and Aβ in the brain, both normal or modified due to neuropathological processes.
Journal of neuroscience methods 03/2011; 196(1):51-9. · 2.30 Impact Factor
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ABSTRACT: This chapter outlines protocols that produce homogenous preparations of oligomeric and fibrillar amyloid-β peptide (Aβ). While there are several isoforms of this peptide, the 42 amino acid form is the focus because of its genetic and pathological link to Alzheimer's disease (AD). Past decades of AD research highlight the dependence of Aβ42 function on its structural assembly state. Biochemical, cellular and in vivo studies of Aβ42 usually begin with purified peptide obtained by chemical synthesis or recombinant expression. The initial steps to solubilize and prepare these purified dry peptide stocks are critical to controlling the structural assembly of Aβ. To develop homogenous Aβ42 assemblies, we initially monomerize the peptide, erasing any "structural history" that could seed aggregation, by using a strong solvent. It is this starting material that has allowed us to define and optimize conditions that consistently produce homogenous solutions of soluble oligomeric and fibrillar Aβ42 assemblies. These preparations have been developed and characterized by using atomic force microscopy (AFM) to identify the structurally discrete species formed by Aβ42 under specific solution conditions. These preparations have been used extensively to demonstrate a variety of functional differences between oligomeric and fibrillar Aβ42. We also present a protocol for fluorescently labeling oligomeric Aβ42 that does not affect structure, as measured by AFM, or function, as measured by a cellular uptake assay. These reagents are critical experimental tools that allow for defining specific structure/function connections.
Methods in molecular biology (Clifton, N.J.) 01/2011; 670:13-32.
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ABSTRACT: Apolipoprotein E (apoE) and apoE/amyloid-β (Aβ) transgenic (Tg) mouse models are critical to understanding apoE-isoform effects on Alzheimer's disease risk. Compared to wild type, apoE(-/-) mice exhibit neuronal deficits, similar to apoE4-Tg compared to apoE3-Tg mice, providing a model for Aβ-independent apoE effects on neurodegeneration. To determine the effects of apoE on Aβ-induced neuropathology, apoE(-/-) mice were crossed with Aβ-Tg mice, resulting in a significant delay in plaque deposition. Surprisingly, crossing human-apoE-Tg mice with apoE(-/-)/Aβ-Tg mice further delayed plaque deposition, which eventually developed in apoE4/Aβ-Tg mice prior to apoE3/Aβ-Tg. One approach to address hAPOE-induced temporal delay in Aβ pathology is an additional insult, like head injury. Another is crossing human-apoE-Tg mice with Aβ-Tg mice that have rapid-onset Aβ pathology. For example, because 5xFAD mice develop plaques by 2 months, the prediction is that human-apoE/5xFAD-Tg mice develop plaques around 6 months and 12 months before other human-apoE/Aβ-Tg mice. Thus, tractable models for human-apoE/Aβ-Tg mice continue to evolve.
International journal of Alzheimer's disease. 01/2011; 2011:810981.
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ABSTRACT: To date there is no effective therapy for Alzheimer disease (AD). High levels of circulating high density lipoprotein (HDL) and its main protein, apolipoprotein A-I (apoA-I), reduce the risk of cardiovascular disease. Clinical studies show that plasma HDL cholesterol and apoA-I levels are low in patients with AD. To investigate if increasing plasma apoA-I/HDL levels ameliorates AD-like memory deficits and amyloid-β (Aβ) deposition, we generated a line of triple transgenic (Tg) mice overexpressing mutant forms of amyloid-β precursor protein (APP) and presenilin 1 (PS1) as well as human apoA-I (AI). Here we show that APP/PS1/AI triple Tg mice have a 2-fold increase of plasma HDL cholesterol levels. When tested in the Morris water maze for spatial orientation abilities, whereas APP/PS1 mice develop age-related learning and memory deficits, APP/PS1/AI mice continue to perform normally during aging. Interestingly, no significant differences were found in the total level and deposition of Aβ in the brains of APP/PS1 and APP/PS1/AI mice, but cerebral amyloid angiopathy was reduced in APP/PS1/AI mice. Also, consistent with the anti-inflammatory properties of apoA-I/HDL, glial activation was reduced in the brain of APP/PS1/AI mice. In addition, Aβ-induced production of proinflammatory chemokines/cytokines was decreased in mouse organotypic hippocampal slice cultures expressing human apoA-I. Therefore, we conclude that overexpression of human apoA-I in the circulation prevents learning and memory deficits in APP/PS1 mice, partly by attenuating neuroinflammation and cerebral amyloid angiopathy. These findings suggest that elevating plasma apoA-I/HDL levels may be an effective approach to preserve cognitive function in patients with AD.
Journal of Biological Chemistry 11/2010; 285(47):36958-68. · 4.77 Impact Factor
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ABSTRACT: One pathological hallmark of Alzheimer's disease (AD) is amyloid plaques, composed primarily of amyloid-beta peptide (Abeta). Over-production or diminished clearance of the 42 amino acid form of Abeta (Abeta42) in the brain leads to accumulation of soluble Abeta and plaque formation. Soluble oligomeric Abeta (oAbeta) has recently emerged to be as a likely proximal cause of AD.
Here we demonstrate that endocytosis is critical in mediating oAbeta42-induced neurotoxicity and intraneuronal accumulation of Abeta. Inhibition of clathrin function either with a pharmacological inhibitor, knock-down of clathrin heavy chain expression, or expression of the dominant-negative mutant of clathrin-assembly protein AP180 did not block oAbeta42-induced neurotoxicity or intraneuronal accumulation of Abeta. However, inhibition of dynamin and RhoA by expression of dominant negative mutants reduced neurotoxicity and intraneuronal Abeta accumulation. Pharmacologic inhibition of the dynamin-mediated endocytic pathway by genistein also reduced neurotoxicity.
These data suggest that dynamin-mediated and RhoA-regulated endocytosis are integral steps for oligomeric Abeta42-induced neurotoxicity and intraneuronal Abeta accumulation.
Molecular Neurodegeneration 01/2010; 5:19. · 4.28 Impact Factor
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ABSTRACT: Alzheimer's disease (AD) is characterized by the presence of early intraneuronal deposits of amyloid-beta 42 (Abeta42) that precede extracellular amyloid deposition in vulnerable brain regions. It has been hypothesized that endosomal/lysosomal dysfunction might be associated with the pathological accumulation of intracellular Abeta42 in the brain. Our previous findings suggest that the LDL receptor-related protein 1 (LRP1), a major receptor for apolipoprotein E, facilitates intraneuronal Abeta42 accumulation in mouse brain. However, direct evidence of neuronal endocytosis of Abeta42 through LRP1 is lacking.
Here we show that LRP1 endocytic function is required for neuronal Abeta42 uptake. Overexpression of a functional LRP1 minireceptor, mLRP4, increases Abeta42 uptake and accumulation in neuronal lysosomes. Conversely, knockdown of LRP1 expression significantly decreases neuronal Abeta42 uptake. Disruptions of LRP1 endocytic function by either clathrin knockdown or by removal of its cytoplasmic tail decreased both uptake and accumulation of Abeta42 in neurons. Finally, we show that LRP1-mediated neuronal accumulation of Abeta42 is associated with increased cellular toxicity.
These results demonstrate that LRP1 endocytic function plays an important role in the uptake and accumulation of Abeta42 in neuronal lysosomes. These findings emphasize the central function of LRP1 in neuronal Abeta metabolism.
PLoS ONE 01/2010; 5(7):e11884. · 4.09 Impact Factor
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Sonya B Dumanis,
Joseph A Tesoriero,
Lenard W Babus,
Madeline T Nguyen,
Justin H Trotter, Mary Jo Ladu,
Edwin J Weeber,
R Scott Turner,
Baoji Xu,
G William Rebeck,
Hyang-Sook Hoe
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ABSTRACT: The three human alleles of apolipoprotein E (APOE) differentially influence outcome after CNS injury and affect one's risk of developing Alzheimer's disease (AD). It remains unclear how ApoE isoforms contribute to various AD-related pathological changes (e.g., amyloid plaques and synaptic and neuron loss). Here, we systematically examined whether apoE isoforms (E2, E3, E4) exhibit differential effects on dendritic spine density and morphology in APOE targeted replacement (TR) mice, which lack AD pathological changes. Using Golgi staining, we found age-dependent effects of APOE4 on spine density in the cortex. The APOE4 TR mice had significantly reduced spine density at three independent time points (4 weeks, 3 months, and 1 year, 27.7% +/- 7.4%, 24.4% +/- 8.6%, and 55.6% +/- 10.5%, respectively) compared with APOE3 TR mice and APOE2 TR mice. Additionally, in APOE4 TR mice, shorter spines were evident compared with other APOE TR mice at 1 year. APOE2 TR mice exhibited longer spines as well as significantly increased apical dendritic arborization in the cortex compared with APOE4 and APOE3 TR mice at 4 weeks. However, there were no differences in spine density across APOE genotypes in hippocampus. These findings demonstrate that apoE isoforms differentially affect dendritic complexity and spine formation, suggesting a role for APOE genotypes not only in acute and chronic brain injuries including AD, but also in normal brain functions.
Journal of Neuroscience 12/2009; 29(48):15317-22. · 7.11 Impact Factor
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ABSTRACT: The lipoprotein receptor system in the hippocampus is intimately involved in the modulation of synaptic transmission and plasticity. The association of specific apoE isoform expression with human neurodegenerative disorders has focused attention on the role of these apoE isoforms in lipoprotein receptor-dependent synaptic modulation. In the present study, we used the apoE2, apoE3 and apoE4 targeted replacement (TR) mice along with recombinant human apoE isoforms to determine the role of apoE isoforms in hippocampus area CA1 synaptic function. While synaptic transmission is unaffected by apoE isoform, long-term potentiation (LTP) is significantly enhanced in apoE4 TR mice versus apoE2 TR mice. ApoE isoform-dependent differences in LTP induction require NMDA-receptor function, and apoE isoform expression alters activation of both ERK and JNK signal transduction. Acute application of specific apoE isoforms also alters LTP induction while decreasing NMDA-receptor mediated field potentials. Furthermore, acute apoE isoform application does not have the same effects on ERK and JNK activation. These findings demonstrate specific, isoform-dependent effects of human apoE isoforms on adult hippocampus synaptic plasticity and highlight mechanistic differences between chronic apoE isoform expression and acute apoE isoform exposure.
Molecular Neurodegeneration 02/2009; 4:21. · 4.28 Impact Factor
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01/2008: pages 211 - 243; , ISBN: 9783527619344
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ABSTRACT: Autosomal dominant mutations that increase amyloid-beta(1-42) (Abeta42) cause familial Alzheimer's disease (AD), and the most common genetic risk factor for AD is the presence of the epsilon4 allele of apolipoprotein E (apoE). Previously, we characterized stable preparations of Abeta42 oligomers and fibrils and reported that oligomers induced a 10-fold greater increase in neurotoxicity than fibrils in Neuro-2A cells. To determine the effects of apoE genotype on Abeta42 oligomer- and fibril-induced neurotoxicity in vitro, we co-cultured wild type (WT) neurons with glia from WT, apoE-knockout (apoE-KO), and human apoE2-, E3-, and E4-targeted replacement (TR) mice. Dose-dependent neurotoxicity was induced by oligomeric Abeta42 with a ranking order of apoE4-TR>KO=apoE2-TR=apoE3-TR>WT. Neurotoxicity induced by staurosporine or glutamate were not affected by apoE genotype, indicating specificity for oligomeric Abeta42-induced neurotoxicity. These in vitro data demonstrate a gain of negative function for apoE4, synergistic with oligomeric Abeta42, in mediating neurotoxicity.
Neurobiology of aging 08/2007; 28(8):1139-47. · 5.94 Impact Factor
