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ABSTRACT: Apolipoprotein (apo) E4 is the leading genetic risk factor for Alzheimer's disease (AD), and it has a gene dose-dependent effect on the risk and age of onset of AD. Although apoE4 is primarily produced by astrocytes in the brain, neurons can also produce apoE4 under stress conditions. ApoE4 is known to inhibit neurite outgrowth and spine development in vitro and in vivo, but the potential influence of apoE4's cellular source on dendritic arborization and spine development has not yet been investigated. In this study, we report impairments in dendritic arborization and a loss of spines, especially thin (learning) and mushroom (memory) spines, in the hippocampus and entorhinal cortex of 19-21-month-old female neuron-specific-enolase (NSE)-apoE4 and apoE4-knockin (KI) mice compared to their respective apoE3-expressing counterparts. In general, NSE-apoE4 mice had more severe and widespread deficits in dendritic arborization as well as spine density and morphology than apoE4-KI mice. The loss of dendritic spines, especially mushroom spines, occurred in NSE-apoE4 mice as early as 7-8 months of age. In contrast, glial fibrillary acidic protein (GFAP)-apoE4 mice, which express apoE4 solely in astrocytes, did not have impairments in their dendrite arborization or spine density and morphology compared to GFAP-apoE3 mice at both ages. These results indicate that the effects of apoE4 on dendrite arborization, spine density, and spine morphology depend critically on its cellular source, with neuronal apoE4 having more detrimental effects than astrocytic apoE4.
PLoS ONE 01/2013; 8(3):e59478. · 4.09 Impact Factor
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ABSTRACT: Apolipoprotein (apo) E4 is the major genetic risk factor for Alzheimer's disease and is associated with poor clinical outcome following traumatic brain injury and other neuropathological disorders. Protein instability and an isoform-specific apoE property called domain interaction are responsible for these neuropathological effects. ApoE4 is the most neurotoxic isoform and can induce neuropathology through various cellular pathways. Neuronal damage or stress induces apoE synthesis as part of the repair response; however, when apoE4 is expressed in neurons, its unique conformation makes it susceptible to proteolysis, resulting in the generation of neurotoxic fragments. These fragments cause pathological mitochondrial dysfunction and cytoskeletal alterations. Here, we review data supporting the hypothesis that apoE4 (> apoE3 > apoE2) has direct neurotoxic effects and highlight studies showing that blocking domain interaction reverses these detrimental effects.
Neuron 12/2012; 76(5):871-885. · 14.74 Impact Factor
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ABSTRACT: An attractive strategy to treat proteinopathies (diseases caused by malformed or misfolded proteins) is to restore protein function by inducing proper three-dimensional structure. We hypothesized that this approach would be effective in reversing the detrimental effects of apolipoprotein (apo) E4, the major allele that significantly increases the risk of developing Alzheimer's disease and other neurodegenerative disorders. ApoE4's detrimental effects result from its altered protein conformation ("domain interaction"), making it highly susceptible to proteolytic cleavage and the generation of neurotoxic fragments. Here, we review apoE structure and function and how apoE4 causes neurotoxicity, and describe the identification of potent small-molecule-based "structure correctors" that induce proper apoE4 folding. SAR studies identified a series of small molecules that significantly reduced apoE4's neurotoxic effects in cultured neurons and a series that reduced apoE4 fragment levels in vivo, providing proof-of-concept for our approach. Structure-corrector-based therapies could prove to be highly effective for the treatment of many protein-misfolding diseases.
Journal of Medicinal Chemistry 09/2012; · 4.80 Impact Factor
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ABSTRACT: The generation of induced pluripotent stem cells (iPSCs) and induced neuronal cells (iNCs) from somatic cells provides new avenues for basic research and potential transplantation therapies for neurological diseases. However, clinical applications must consider the risk of tumor formation by iPSCs and the inability of iNCs to self-renew in culture. Here we report the generation of induced neural stem cells (iNSCs) from mouse and human fibroblasts by direct reprogramming with a single factor, Sox2. iNSCs express NSC markers and resemble wild-type NSCs in their morphology, self-renewal, ability to form neurospheres, and gene expression profiles. Cloned iNSCs differentiate into several types of mature neurons, as well as astrocytes and oligodendrocytes, indicating multipotency. Implanted iNSCs can survive and integrate in mouse brains and, unlike iPSC-derived NSCs, do not generate tumors. Thus, self-renewable and multipotent iNSCs without tumorigenic potential can be generated directly from fibroblasts by reprogramming.
Cell stem cell 06/2012; 11(1):100-9. · 23.56 Impact Factor
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Keith A Vossel,
Nga Bien-Ly,
Aubrey Bernardo,
Katya Rascovsky,
Anna Karydas,
Gil D Rabinovici,
Manu Sidhu,
Eric J Huang,
Bruce L Miller, Yadong Huang,
William W Seeley
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ABSTRACT: Frontotemporal lobar degeneration with motor neuron disease (FTLD-MND) is characterized by neuronal cytoplasmic inclusions containing TDP-43. Apolipoprotein E4 (apoE4), derived from the apoE ε4 allele, enhances brain atrophy in FTLD through unknown mechanisms. Here, we studied two siblings with C9ORF72-linked familial FTLD-MND, an apoE ε4 homozygote and an apoE ε3 homozygote. The apoE ε4 homozygote had more cognitive-behavioral symptoms, fronto-insulo-temporal atrophy, and apoE fragments and aggregates in the anterior cingulate cortex. ApoE formed complexes with TDP-43 that were more abundant in the apoE ε4 homozygote. Although differences seen in a sibling pair could arise due to chance, these findings raise the possibility that apoE4 exacerbates brain pathology in FTLD through formation of neurotoxic apoE fragments and interactions with TDP-43.
Neurocase 04/2012; · 1.11 Impact Factor
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ABSTRACT: Apolipoprotein E4 (apoE4) plays a major role in the pathogenesis of Alzheimer's disease. Brain amyloid-β (Aβ) accumulation depends on age and apoE isoforms (apoE4 > apoE3) both in humans and in transgenic mouse models. Brain apoE levels are also isoform dependent, but in the opposite direction (apoE4 < apoE3). Thus, one prevailing hypothesis is to increase brain apoE expression to reduce Aβ levels. To test this hypothesis, we generated mutant human amyloid precursor protein transgenic mice expressing one or two copies of the human APOE3 or APOE4 gene that was knocked in and flanked by LoxP sites. We report that reducing apoE3 or apoE4 expression by 50% in 6-month-old mice results in efficient Aβ clearance and does not increase Aβ accumulation. However, 12-month-old mice with one copy of the human APOE gene had significantly reduced Aβ levels and plaque loads compared with mice with two copies, regardless of which human apoE isoform was expressed, suggesting a gene dose-dependent effect of apoE on Aβ accumulation in aged mice. Additionally, 12-month-old mice expressing one or two copies of the human APOE4 gene had significantly higher levels of Aβ accumulation and plaque loads than age-matched mice expressing one or two copies of the human APOE3 gene, suggesting an isoform-dependent effect of apoE on Aβ accumulation in aged mice. Moreover, Cre-mediated APOE4 gene excision in hippocampal astrocytes significantly reduced insoluble Aβ in adult mice. Thus, reducing, rather than increasing, apoE expression is an attractive approach to lowering brain Aβ levels.
Journal of Neuroscience 04/2012; 32(14):4803-11. · 7.11 Impact Factor
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ABSTRACT: There are still no effective treatments to prevent, halt, or reverse Alzheimer's disease, but research advances over the past three decades could change this gloomy picture. Genetic studies demonstrate that the disease has multiple causes. Interdisciplinary approaches combining biochemistry, molecular and cell biology, and transgenic modeling have revealed some of its molecular mechanisms. Progress in chemistry, radiology, and systems biology is beginning to provide useful biomarkers, and the emergence of personalized medicine is poised to transform pharmaceutical development and clinical trials. However, investigative and drug development efforts should be diversified to fully address the multifactoriality of the disease.
Cell 03/2012; 148(6):1204-22. · 32.40 Impact Factor
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ABSTRACT: The ability to distinguish between similar experiences is a critical feature of episodic memory and is primarily regulated by the dentate gyrus (DG) region of the hippocampus. However, the molecular mechanisms underlying such pattern separation tasks are poorly understood. We report a novel role for the small GTPase ADP ribosylation factor 4 (Arf4) in controlling pattern separation by regulating dendritic spine development. Arf4(+/-) mice at 4-5 months of age display severe impairments in a pattern separation task, as well as significant dendritic spine loss and smaller miniature excitatory post-synaptic currents (mEPSCs) in granule cells of the DG. Arf4 knockdown also decreases spine density in primary neurons, whereas Arf4 overexpression promotes spine development. A constitutively active form of Arf4, Arf4-Q71L, promotes spine density to an even greater extent than wildtype Arf4, whereas the inactive Arf4-T31N mutant does not increase spine density relative to controls. Arf4's effects on spine development are regulated by ASAP1, a GTPase-activating protein that modulates Arf4 GTPase activity. ASAP1 overexpression decreases spine density, and this effect is partially rescued by concomitant overexpression of wildtype Arf4 or Arf4-Q71L. In addition, Arf4 overexpression rescues spine loss in primary neurons from an Alzheimer's disease-related apolipoprotein (apo) E4 mouse model. Our findings suggest that Arf4 is a critical modulator of DG-mediated pattern separation by regulating dendritic spine development.
PLoS ONE 01/2012; 7(9):e46340. · 4.09 Impact Factor
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Yaisa Andrews-Zwilling,
Anna K Gillespie,
Alexxai V Kravitz,
Alexandra B Nelson,
Nino Devidze,
Iris Lo,
Seo Yeon Yoon,
Nga Bien-Ly,
Karen Ring,
Daniel Zwilling,
Gregory B Potter,
John L R Rubenstein,
Anatol C Kreitzer, Yadong Huang
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ABSTRACT: Although extensive research has demonstrated the importance of excitatory granule neurons in the dentate gyrus of the hippocampus in normal learning and memory and in the pathogenesis of amnesia in Alzheimer's disease (AD), the role of hilar GABAergic inhibitory interneurons, which control the granule neuron activity, remains unclear.
We explored the function of hilar GABAergic interneurons in spatial learning and memory by inhibiting their activity through Cre-dependent viral expression of enhanced halorhodopsin (eNpHR3.0)--a light-driven chloride pump. Hilar GABAergic interneuron-specific expression of eNpHR3.0 was achieved by bilaterally injecting adeno-associated virus containing a double-floxed inverted open-reading frame encoding eNpHR3.0 into the hilus of the dentate gyrus of mice expressing Cre recombinase under the control of an enhancer specific for GABAergic interneurons. In vitro and in vivo illumination with a yellow laser elicited inhibition of hilar GABAergic interneurons and consequent activation of dentate granule neurons, without affecting pyramidal neurons in the CA3 and CA1 regions of the hippocampus. We found that optogenetic inhibition of hilar GABAergic interneuron activity impaired spatial learning and memory retrieval, without affecting memory retention, as determined in the Morris water maze test. Importantly, optogenetic inhibition of hilar GABAergic interneuron activity did not alter short-term working memory, motor coordination, or exploratory activity.
Our findings establish a critical role for hilar GABAergic interneuron activity in controlling spatial learning and memory retrieval and provide evidence for the potential contribution of GABAergic interneuron impairment to the pathogenesis of amnesia in AD.
PLoS ONE 01/2012; 7(7):e40555. · 4.09 Impact Factor
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ABSTRACT: Apolipoprotein (apo) E4 is the major genetic risk factor for Alzheimer's disease (AD). ApoE4 has sex-dependent effects, whereby the risk of developing AD is higher in apoE4-expressing females than males. However, the mechanism underlying the sex difference, in relation to apoE4, is unknown. Previous findings indicate that apoE4 causes age-dependent impairments of hilar GABAergic interneurons in female mice, leading to learning and memory deficits. Here, we investigate whether the detrimental effects of apoE4 on hilar GABAergic interneurons are sex-dependent using apoE knock-in (KI) mice across different ages. We found that in female apoE-KI mice, there was an age-dependent depletion of hilar GABAergic interneurons, whereby GAD67- or somatostatin-positive-but not NPY- or parvalbumin-positive-interneuron loss was exacerbated by apoE4. Loss of these neuronal populations was correlated with the severity of spatial learning deficits at 16 months of age in female apoE4-KI mice; however, this effect was not observed in female apoE3-KI mice. In contrast, we found an increase in the numbers of hilar GABAergic interneurons with advancing age in male apoE-KI mice, regardless of apoE genotype. Moreover, male apoE-KI mice showed a consistent ratio of hilar inhibitory GABAergic interneurons to excitatory mossy cells approximating 1.5 that is independent of apoE genotype and age, whereas female apoE-KI mice exhibited an age-dependent decrease in this ratio, which was exacerbated by apoE4. Interestingly, there are no apoE genotype effects on GABAergic interneurons in the CA1 and CA3 subregions of the hippocampus as well as the entorhinal and auditory cortexes. These findings suggest that the sex-dependent effects of apoE4 on developing AD is in part attributable to inherent sex-based differences in the numbers of hilar GABAergic interneurons, which is further modulated by apoE genotype.
PLoS ONE 01/2012; 7(12):e53569. · 4.09 Impact Factor
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Hung-Kai Chen,
Zhaoping Liu,
Anke Meyer-Franke,
Jens Brodbeck,
Rene D Miranda,
James G McGuire,
Michael A Pleiss,
Zhong-Sheng Ji,
Maureen E Balestra,
David W Walker,
Qin Xu,
Dah-eun Jeong,
Madhu S Budamagunta,
John C Voss,
Stephen B Freedman,
Karl H Weisgraber, Yadong Huang,
Robert W Mahley
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ABSTRACT: Apolipoprotein E4 (apoE4), the major genetic risk factor for late onset Alzheimer disease, assumes a pathological conformation, intramolecular domain interaction. ApoE4 domain interaction mediates the detrimental effects of apoE4, including decreased mitochondrial cytochrome c oxidase subunit 1 levels, reduced mitochondrial motility, and reduced neurite outgrowth in vitro. Mutant apoE4 (apoE4-R61T) lacks domain interaction, behaves like apoE3, and does not cause detrimental effects. To identify small molecules that inhibit domain interaction (i.e. structure correctors) and reverse the apoE4 detrimental effects, we established a high throughput cell-based FRET primary assay that determines apoE4 domain interaction and secondary cell- and function-based assays. Screening a ChemBridge library with the FRET assay identified CB9032258 (a phthalazinone derivative), which inhibits domain interaction in neuronal cells. In secondary functional assays, CB9032258 restored mitochondrial cytochrome c oxidase subunit 1 levels and rescued impairments of mitochondrial motility and neurite outgrowth in apoE4-expressing neuronal cells. These benefits were apoE4-specific and dose-dependent. Modifying CB9032258 yielded well defined structure-activity relationships and more active compounds with enhanced potencies in the FRET assay (IC(50) of 23 and 116 nm, respectively). These compounds efficiently restored functional activities of apoE4-expressing cells in secondary assays. An EPR binding assay showed that the apoE4 structure correction resulted from direct interaction of a phthalazinone. With these data, a six-feature pharmacophore model was constructed for future drug design. Our results serve as a proof of concept that pharmacological intervention with apoE4 structure correctors negates apoE4 detrimental effects in neuronal cells and could be further developed as an Alzheimer disease therapeutic.
Journal of Biological Chemistry 12/2011; 287(8):5253-66. · 4.77 Impact Factor
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Yadong Huang
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ABSTRACT: ApoE4 (apolipoprotein E4) is the major known genetic risk factor for AD (Alzheimer's disease). In most clinical studies, apoE4 carriers account for 65-80% of all AD cases, highlighting the importance of apoE4 in AD pathogenesis. Emerging data suggest that apoE4, with its multiple cellular origins and multiple structural and biophysical properties, contributes to AD in multiple ways either independently or in combination with other factors, such as Aβ (amyloid β-peptide) and tau. Many apoE mouse models have been established to study the mechanisms underlying the pathogenic actions of apoE4. These include transgenic mice expressing different apoE isoforms in neurons or astrocytes, those expressing neurotoxic apoE4 fragments in neurons and human apoE isoform knock-in mice. Since apoE is expressed in different types of cells, including astrocytes and neurons, and in brains under diverse physiological and/or pathophysiological conditions, these apoE mouse models provide unique tools to study the cellular source-dependent roles of apoE isoforms in neurobiology and in the pathogenesis of AD. They also provide useful tools for discovery and development of drugs targeting apoE4's detrimental effects.
Biochemical Society Transactions 08/2011; 39(4):924-32. · 3.71 Impact Factor
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Daniel Zwilling,
Shao-Yi Huang,
Korrapati V Sathyasaikumar,
Francesca M Notarangelo,
Paolo Guidetti,
Hui-Qiu Wu,
Jason Lee,
Jennifer Truong,
Yaisa Andrews-Zwilling,
Eric W Hsieh, [......],
Flaviano Giorgini,
Saliha Moussaoui,
Grit Laue,
Arash Rassoulpour,
Gunnar Flik, Yadong Huang,
Joseph M Muchowski,
Eliezer Masliah,
Robert Schwarcz,
Paul J Muchowski
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ABSTRACT: Metabolites in the kynurenine pathway, generated by tryptophan degradation, are thought to play an important role in neurodegenerative disorders, including Alzheimer's and Huntington's diseases. In these disorders, glutamate receptor-mediated excitotoxicity and free radical formation have been correlated with decreased levels of the neuroprotective metabolite kynurenic acid. Here, we describe the synthesis and characterization of JM6, a small-molecule prodrug inhibitor of kynurenine 3-monooxygenase (KMO). Chronic oral administration of JM6 inhibits KMO in the blood, increasing kynurenic acid levels and reducing extracellular glutamate in the brain. In a transgenic mouse model of Alzheimer's disease, JM6 prevents spatial memory deficits, anxiety-related behavior, and synaptic loss. JM6 also extends life span, prevents synaptic loss, and decreases microglial activation in a mouse model of Huntington's disease. These findings support a critical link between tryptophan metabolism in the blood and neurodegeneration, and they provide a foundation for treatment of neurodegenerative diseases.
Cell 06/2011; 145(6):863-74. · 32.40 Impact Factor
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Jens Brodbeck,
Jim McGuire,
Zhaoping Liu,
Anke Meyer-Franke,
Maureen E. Balestra,
Dah-eun Jeong,
Mike Pleiss,
Casey McComas,
Fred Hess,
David Witter,
Scott Peterson,
Matthew Childers,
Mark Goulet,
Nigel Liverton,
Richard Hargreaves,
Stephen Freedman,
Karl H. Weisgraber,
Robert W. Mahley, Yadong Huang
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ABSTRACT: Apolipoprotein (apo) E4 is the major genetic risk factor for Alzheimer disease (AD) and likely contributes to neuropathology
through various pathways. Here we report that the intracellular trafficking of apoE4 is impaired in Neuro-2a cells and primary
neurons, as shown by measuring fluorescence recovery after photobleaching. In Neuro-2a cells, more apoE4 than apoE3 molecules
remained immobilized in the endoplasmic reticulum (ER) and the Golgi apparatus, and the lateral motility of apoE4 was significantly
lower in the Golgi apparatus (but not in the ER) than that of apoE3. Likewise, the immobile fraction was larger, and the lateral
motility was lower for apoE4 than apoE3 in mouse primary hippocampal neurons. ApoE4 with the R61T mutation, which abolishes
apoE4 domain interaction, was less immobilized, and its lateral motility was comparable with that of apoE3. The trafficking
impairment of apoE4 was also rescued by disrupting domain interaction with the small-molecule structure correctors GIND25
and PH002. PH002 also rescued apoE4-induced impairments of neurite outgrowth in Neuro-2a cells and dendritic spine development
in primary neurons. ApoE4 did not affect trafficking of amyloid precursor protein, another AD-related protein, through the
secretory pathway. Thus, domain interaction renders more newly synthesized apoE4 molecules immobile and slows their trafficking
along the secretory pathway. Correcting the pathological structure of apoE4 by disrupting domain interaction is a potential
therapeutic approach to treat or prevent AD related to apoE4.
Journal of Biological Chemistry 05/2011; 286(19):17217-17226. · 4.77 Impact Factor
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Jens Brodbeck,
Jim McGuire,
Zhaoping Liu,
Anke Meyer-Franke,
Maureen E Balestra,
Dah-eun Jeong,
Mike Pleiss,
Casey McComas,
Fred Hess,
David Witter,
Scott Peterson,
Matthew Childers,
Mark Goulet,
Nigel Liverton,
Richard Hargreaves,
Stephen Freedman,
Karl H Weisgraber,
Robert W Mahley, Yadong Huang
[show abstract]
[hide abstract]
ABSTRACT: Apolipoprotein (apo) E4 is the major genetic risk factor for Alzheimer disease (AD) and likely contributes to neuropathology through various pathways. Here we report that the intracellular trafficking of apoE4 is impaired in Neuro-2a cells and primary neurons, as shown by measuring fluorescence recovery after photobleaching. In Neuro-2a cells, more apoE4 than apoE3 molecules remained immobilized in the endoplasmic reticulum (ER) and the Golgi apparatus, and the lateral motility of apoE4 was significantly lower in the Golgi apparatus (but not in the ER) than that of apoE3. Likewise, the immobile fraction was larger, and the lateral motility was lower for apoE4 than apoE3 in mouse primary hippocampal neurons. ApoE4 with the R61T mutation, which abolishes apoE4 domain interaction, was less immobilized, and its lateral motility was comparable with that of apoE3. The trafficking impairment of apoE4 was also rescued by disrupting domain interaction with the small-molecule structure correctors GIND25 and PH002. PH002 also rescued apoE4-induced impairments of neurite outgrowth in Neuro-2a cells and dendritic spine development in primary neurons. ApoE4 did not affect trafficking of amyloid precursor protein, another AD-related protein, through the secretory pathway. Thus, domain interaction renders more newly synthesized apoE4 molecules immobile and slows their trafficking along the secretory pathway. Correcting the pathological structure of apoE4 by disrupting domain interaction is a potential therapeutic approach to treat or prevent AD related to apoE4.
Journal of Biological Chemistry 03/2011; 286(19):17217-26. · 4.77 Impact Factor
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[show abstract]
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ABSTRACT: Apolipoprotein (apo) E4 is the major genetic risk factor for late-onset Alzheimer disease (AD). ApoE4 assumes a pathological
conformation through an intramolecular interaction mediated by Arg-61 in the amino-terminal domain and Glu-255 in the carboxyl-terminal
domain, referred to as apoE4 domain interaction. Because AD is associated with mitochondrial dysfunction, we examined the
effect of apoE4 domain interaction on mitochondrial respiratory function. Steady-state amounts of mitochondrial respiratory
complexes were examined in neurons cultured from brain cortices of neuron-specific enolase promoter-driven apoE3 (NSE-apoE3)
or apoE4 (NSE-apoE4) transgenic mice. All subunits of mitochondrial respiratory complexes assessed were significantly lower
in NSE-apoE4 neurons compared with NSE-apoE3 neurons. However, no significant differences in levels of mitochondrial complexes
were detected between astrocytes expressing different apoE isoforms driven by the glial fibrillary acidic protein promoter,
leading to our conclusion that the effect of apoE4 is neuron specific. In neuroblastoma Neuro-2A (N2A) cells, apoE4 expression
reduced the levels of mitochondrial respiratory complexes I, IV, and V. Complex IV enzymatic activity was also decreased,
lowering mitochondrial respiratory capacity. Mutant apoE4 (apoE4-Thr-61) lacking domain interaction did not induce mitochondrial
dysfunction in N2A cells, indicating that the effect is specific to apoE4-expressing cells and dependent on domain interaction.
Consistent with this finding, treatment of apoE4-expressing N2A cells with a small molecule that disrupts apoE4 domain interaction
restored mitochondrial respiratory complex IV levels. These results suggest that pharmacological intervention with small molecules
that disrupt apoE4 domain interaction is a potential therapeutic approach for apoE4-carrying AD subjects.
Journal of Biological Chemistry 02/2011; 286(7):5215-5221. · 4.77 Impact Factor
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[show abstract]
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ABSTRACT: Apolipoprotein (apo) E4 is the major genetic risk factor for late-onset Alzheimer disease (AD). ApoE4 assumes a pathological conformation through an intramolecular interaction mediated by Arg-61 in the amino-terminal domain and Glu-255 in the carboxyl-terminal domain, referred to as apoE4 domain interaction. Because AD is associated with mitochondrial dysfunction, we examined the effect of apoE4 domain interaction on mitochondrial respiratory function. Steady-state amounts of mitochondrial respiratory complexes were examined in neurons cultured from brain cortices of neuron-specific enolase promoter-driven apoE3 (NSE-apoE3) or apoE4 (NSE-apoE4) transgenic mice. All subunits of mitochondrial respiratory complexes assessed were significantly lower in NSE-apoE4 neurons compared with NSE-apoE3 neurons. However, no significant differences in levels of mitochondrial complexes were detected between astrocytes expressing different apoE isoforms driven by the glial fibrillary acidic protein promoter, leading to our conclusion that the effect of apoE4 is neuron specific. In neuroblastoma Neuro-2A (N2A) cells, apoE4 expression reduced the levels of mitochondrial respiratory complexes I, IV, and V. Complex IV enzymatic activity was also decreased, lowering mitochondrial respiratory capacity. Mutant apoE4 (apoE4-Thr-61) lacking domain interaction did not induce mitochondrial dysfunction in N2A cells, indicating that the effect is specific to apoE4-expressing cells and dependent on domain interaction. Consistent with this finding, treatment of apoE4-expressing N2A cells with a small molecule that disrupts apoE4 domain interaction restored mitochondrial respiratory complex IV levels. These results suggest that pharmacological intervention with small molecules that disrupt apoE4 domain interaction is a potential therapeutic approach for apoE4-carrying AD subjects.
Journal of Biological Chemistry 02/2011; 286(7):5215-21. · 4.77 Impact Factor
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ABSTRACT: Apolipoprotein (apo) E4 is the major known genetic risk factor for Alzheimer's disease (AD). We have shown in vitro and in vivo that apoE4 preferentially undergoes aberrant cleavage in neurons, yielding neurotoxic C-terminal-truncated fragments. To study the effect of these fragments on amyloid-β (Aβ) clearance/deposition and their potential synergy with Aβ in eliciting neuronal and behavioral deficits, we cross-bred transgenic mice expressing apoE3, apoE4, or apoE4(Δ272-299) with mice expressing human amyloid protein precursor (APP) harboring familial AD mutations (hAPP(FAD)). At 6-8 mo of age, hAPP(FAD) mice expressing apoE3 or apoE4 had lower levels of hippocampal Aβ (94% and 89%, respectively) and less Aβ deposition (89% and 87%) than hAPP(FAD) mice without apoE, whereas hAPP(FAD) mice expressing mouse apoE had higher Aβ levels. Thus, human apoE stimulates Aβ clearance, but mouse apoE does not. Expression of apoE4(Δ272-299) reduced total Aβ levels by only 63% and Aβ deposition by 46% compared with hAPP(FAD) mice without apoE. Unlike apoE3 and apoE4, the C-terminal-truncated apoE4 bound poorly with Aβ peptides, leading to decreased Aβ clearance and increased Aβ deposition. Despite their lower levels of Aβ and Aβ deposition, hAPP(FAD)/apoE4(Δ272-299) mice accumulated pathogenic Aβ oligomers and displayed neuronal and behavioral deficits similar to or more severe than those in hAPP(FAD) mice. Thus, the C-terminal-truncated apoE4 fragment inefficiently clears Aβ peptides and acts in concert with low levels of Aβ to elicit neuronal and behavioral deficits in mice.
Proceedings of the National Academy of Sciences 02/2011; 108(10):4236-41. · 9.68 Impact Factor
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ABSTRACT: Apolipoprotein E4 (apoE4) is the major genetic risk factor for Alzheimer's disease. However, the underlying mechanisms are unclear. We found that female apoE4 knock-in (KI) mice had an age-dependent decrease in hilar GABAergic interneurons that correlated with the extent of learning and memory deficits, as determined in the Morris water maze, in aged mice. Treating apoE4-KI mice with daily peritoneal injections of the GABA(A) receptor potentiator pentobarbital at 20 mg/kg for 4 weeks rescued the learning and memory deficits. In neurotoxic apoE4 fragment transgenic mice, hilar GABAergic interneuron loss was even more pronounced and also correlated with the extent of learning and memory deficits. Neurodegeneration and tauopathy occurred earliest in hilar interneurons in apoE4 fragment transgenic mice; eliminating endogenous Tau prevented hilar GABAergic interneuron loss and the learning and memory deficits. The GABA(A) receptor antagonist picrotoxin abolished this rescue, while pentobarbital rescued learning deficits in the presence of endogenous Tau. Thus, apoE4 causes age- and Tau-dependent impairment of hilar GABAergic interneurons, leading to learning and memory deficits in mice. Consequently, reducing Tau and enhancing GABA signaling are potential strategies to treat or prevent apoE4-related Alzheimer's disease.
Journal of Neuroscience 10/2010; 30(41):13707-17. · 7.11 Impact Factor
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Yadong Huang
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ABSTRACT: The purpose of this review is to provide insights into recent advances in mechanisms linking apolipoprotein (apo) E isoforms to cardiovascular and neurological diseases.
Human apoE has three common isoforms (apoE2, apoE3, and apoE4) with different structural and biophysical properties and different effects on lipid and neuronal homeostasis. ApoE is a protein constituent of different plasma lipoproteins and serves as a high-affinity ligand for several receptors. By interacting with its receptors, apoE mediates the clearance of different lipoproteins from the circulation. Absence or structural mutations of apoE cause significant disorders in lipid metabolism and cardiovascular disease. ApoE also has significant roles in neurobiology. ApoE4 is the major known genetic risk factor for Alzheimer's disease. It increases the occurrence and lowers the age of onset of Alzheimer's disease. ApoE4 carriers account for 65-80% of all Alzheimer's disease cases, highlighting the importance of apoE4 in Alzheimer's disease pathogenesis. ApoE4 has both amyloid beta-dependent and amyloid beta-independent roles in Alzheimer's disease pathogenesis.
Emerging data suggest that apoE isoforms, with their multiple cellular origins and multiple structural and biophysical properties, contribute to cardiovascular and neurological diseases by interacting with different factors through various pathways.
Current opinion in lipidology 08/2010; 21(4):337-45. · 6.13 Impact Factor
