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Liu Z, Li H, Li Y, Wang Y, Zong Y, Feng Y, Feng Z, Deng Y, Qu S. Up-regulation of VLDL receptor expression and its signaling pathway induced by VLDL and beta-VLDL. ACTA ACUST UNITED AC 2009; 29:1-7. [PMID: 19224153 DOI: 10.1007/s11596-009-0101-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2008] [Indexed: 11/26/2022]
Abstract
Very low density lipoprotein receptor (VLDLR) is thought to participate in the pathogenesis of atherosclerosis induced by VLDL and beta-VLDL. The present study was undertaken to elucidate the effects of VLDL and beta-VLDL on VLDLR expression and its signaling pathway. RAW264.7 cells were incubated with VLDL and beta-VLDL. The expression of VLDLR mRNA was detected by RT-PCR. The transcriptional activity of VLDLR gene was detected in recombinant plasmid pGL4.2VR-luciferase transfected RAW264.7. Western blot assay was used to detect the changes of phosphorylated ERK1/2 protein. Inhibitors or activators were used to observe the signal pathway involving VLDLR expression regulation. The results showed that VLDL and beta-VLDL stimulated ERK1/2 activity in a PKC-dependent manner. VLDL or beta-VLDL-induced VLDLR expression on macrophages was extremely abolished by inhibitors ERK1/2 or PKC. Our findings revealed that VLDL or beta-VLDL-induced VLDLR expression via PKC/ERK cascades and the effect was linked to the transcriptional activation of VLDLR gene promoter.
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Affiliation(s)
- Zhiguo Liu
- Department of Biochemistry and Molecular Biology, School of Basic Medical Sciences, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China.
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Wang L, Chopp M, Zhang RL, Zhang L, LeTourneau Y, Feng YF, Jiang A, Morris DC, Zhang ZG. The Notch pathway mediates expansion of a progenitor pool and neuronal differentiation in adult neural progenitor cells after stroke. Neuroscience 2009; 158:1356-63. [PMID: 19059466 PMCID: PMC2757073 DOI: 10.1016/j.neuroscience.2008.10.064] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2008] [Revised: 10/13/2008] [Accepted: 10/29/2008] [Indexed: 12/13/2022]
Abstract
Molecular mechanisms by which stroke increases neurogenesis have not been fully investigated. Using neural progenitor cells isolated from the subventricular zone (SVZ) of the adult rat subjected to focal cerebral ischemia, we investigated the Notch pathway in regulating proliferation and differentiation of adult neural progenitor cells after stroke. During proliferation of neural progenitor cells, ischemic neural progenitor cells exhibited substantially increased levels of Notch, Notch intracellular domain (NICD), and hairy enhancer of split (Hes) 1, which was associated with a significant increase of proliferating cells. Blockage of the Notch pathway by short interfering ribonucleic acid (siRNA) against Notch or a gamma secretase inhibitor significantly reduced Notch, NICD and Hes1 expression and cell proliferation induced by stroke. During differentiation of neural progenitor cells, Notch and Hes1 expression was downregulated in ischemic neural progenitor cells, which was coincident with a significant increase of neuronal population. Inhibition of the Notch pathway with a gamma secretase inhibitor further substantially increased neurons, but did not alter astrocyte population in ischemic neural progenitor cells. These data suggest that the Notch signaling pathway mediates adult SVZ neural progenitor cell proliferation and differentiation after stroke.
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Affiliation(s)
- Lei Wang
- Department of Neurology, Henry Ford Health Sciences Center, 2799 W. Grand Boulevard, Detroit, Michigan 48202
| | - Michael Chopp
- Department of Neurology, Henry Ford Health Sciences Center, 2799 W. Grand Boulevard, Detroit, Michigan 48202
- Department of Physics, Oakland University, Rochester, Michigan 48309
| | - Rui Lan Zhang
- Department of Neurology, Henry Ford Health Sciences Center, 2799 W. Grand Boulevard, Detroit, Michigan 48202
| | - Li Zhang
- Department of Neurology, Henry Ford Health Sciences Center, 2799 W. Grand Boulevard, Detroit, Michigan 48202
| | - Yvonne LeTourneau
- Department of Neurology, Henry Ford Health Sciences Center, 2799 W. Grand Boulevard, Detroit, Michigan 48202
| | - Yi fan Feng
- Department of Neurology, Henry Ford Health Sciences Center, 2799 W. Grand Boulevard, Detroit, Michigan 48202
| | - Angela Jiang
- Department of Neurology, Henry Ford Health Sciences Center, 2799 W. Grand Boulevard, Detroit, Michigan 48202
| | | | - Zheng Gang Zhang
- Department of Neurology, Henry Ford Health Sciences Center, 2799 W. Grand Boulevard, Detroit, Michigan 48202
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De Gasperi R, Gama Sosa MA, Wen PH, Li J, Perez GM, Curran T, Elder GA. Cortical development in the presenilin-1 null mutant mouse fails after splitting of the preplate and is not due to a failure of reelin-dependent signaling. Dev Dyn 2008; 237:2405-14. [PMID: 18729224 PMCID: PMC2566957 DOI: 10.1002/dvdy.21661] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Cortical development is disrupted in presenilin-1 null mutant (Psen1-/-) mice. Prior studies have commented on similarities between Psen1-/- and reeler mice. Reelin induces phosphorylation of Dab1 and activates the phosphatidylinositol 3-kinase (PI3K)/Akt pathway. Psen1 is known to modulate PI3K/Akt signaling and both known reelin receptors (apoER2 and VLDLR) are substrates for Psen1 associated gamma-secretase activity. The purpose of this study was to determine whether reelin signaling is disrupted in Psen1-/- mice. We show that, while Dab1 is hypophosphorylated late in cortical development in Psen1-/- mice, it is normally phosphorylated at earlier ages and reelin signaling is intact in Psen1-/- primary neuronal cultures. gamma-secretase activity was also not required for reelin-induced phosphorylation of Dab1. Unlike reeler mice the preplate splits in Psen1-/- brain. Thus cortical development in Psen1-/- mice fails only after splitting of the preplate and is not due to an intrinsic failure of reelin signaling.
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Affiliation(s)
- Rita De Gasperi
- Research and Development, James J. Peters Department of Veterans Affairs Medical Center, Bronx, NY 10468
- Department of Psychiatry, Mount Sinai School of Medicine, New York, NY 10029
| | - Miguel A. Gama Sosa
- Research and Development, James J. Peters Department of Veterans Affairs Medical Center, Bronx, NY 10468
- Department of Psychiatry, Mount Sinai School of Medicine, New York, NY 10029
| | - Paul H. Wen
- Research and Development, James J. Peters Department of Veterans Affairs Medical Center, Bronx, NY 10468
- Department of Psychiatry, Mount Sinai School of Medicine, New York, NY 10029
| | - Jingjun Li
- Department of Psychiatry, Mount Sinai School of Medicine, New York, NY 10029
| | - Gissel M. Perez
- Research and Development, James J. Peters Department of Veterans Affairs Medical Center, Bronx, NY 10468
- Department of Psychiatry, Mount Sinai School of Medicine, New York, NY 10029
| | - Tom Curran
- Abramson Research Center, Children’s Hospital of Philadelphia, Philadelphia, PA 19104
| | - Gregory A. Elder
- Research and Development, James J. Peters Department of Veterans Affairs Medical Center, Bronx, NY 10468
- Rehabilitation Medicine Services, James J. Peters Department of Veterans Affairs Medical Center, Bronx, NY 10468
- Department of Psychiatry, Mount Sinai School of Medicine, New York, NY 10029
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Abstract
The beta-amyloid precursor protein (APP) is central to the pathogenesis of Alzheimer's disease, but its normal functions in the brain are poorly understood. A number of APP-interacting proteins have been identified: intracellularly, APP interacts with adaptor proteins through its conserved NPXY domain; extracellularly, APP interacts with a component of the extracellular matrix, F-spondin. Interestingly, many of these APP-interacting proteins also interact with the family of receptors for apolipoprotein E (apoE), the Alzheimer's disease risk factor. apoE receptors also share with APP the fact that they are cleaved by the same secretase activities. apoE receptors are shed from the cell surface, a cleavage that is regulated by receptor-ligand interactions, and C-terminal fragments of apoE receptors are cleaved by gamma-secretase. Functionally, both APP and apoE receptors affect neuronal migration and synapse formation in the brain. This review summarizes these numerous interactions between APP and apoE receptors, which provide clues about the normal functions of APP.
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Affiliation(s)
- Hyang-Sook Hoe
- Department of Neuroscience, Georgetown University, Washington, District of Columbia 20007, USA
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Abstract
Gamma-Secretase is a promiscuous protease that cleaves bitopic membrane proteins within the lipid bilayer. Elucidating both the mechanistic basis of gamma-secretase proteolysis and the precise factors regulating substrate identification is important because modulation of this biochemical degradative process can have important consequences in a physiological and pathophysiological context. Here, we briefly review such information for all major classes of intramembranously cleaving proteases (I-CLiPs), with an emphasis on gamma-secretase, an I-CLiP closely linked to the etiology of Alzheimer's disease. A large body of emerging data allows us to survey the substrates of gamma-secretase to ascertain the conformational features that predispose a peptide to cleavage by this enigmatic protease. Because substrate specificity in vivo is closely linked to the relative subcellular compartmentalization of gamma-secretase and its substrates, we also survey the voluminous body of literature concerning the traffic of gamma-secretase and its most prominent substrate, the amyloid precursor protein.
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Affiliation(s)
- A. J. Beel
- Department of Biochemistry and Center for Structural Biology, Vanderbilt University School of Medicine, Rm. 5142 MRBIII, 21st Ave. S., Nashville, Tennessee 37232-8725 USA
| | - C. R. Sanders
- Department of Biochemistry and Center for Structural Biology, Vanderbilt University School of Medicine, Rm. 5142 MRBIII, 21st Ave. S., Nashville, Tennessee 37232-8725 USA
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Regulated proteolysis of APP and ApoE receptors. Mol Neurobiol 2008; 37:64-72. [PMID: 18415033 DOI: 10.1007/s12035-008-8017-0] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2008] [Accepted: 03/24/2008] [Indexed: 10/22/2022]
Abstract
The beta-amyloid precursor protein (APP) shares intracellular and extracellular-binding partners with the family of receptors for apolipoprotein E (apoE). Binding of APP and apoE receptors to specific extracellular matrix proteins (F-spondin and Reelin) promotes their presence on the cell surface and influences whether they will interact with specific cytoplasmic adaptor proteins. Cleavage of APP and apoE receptors at the cell surface occurs by alpha-secretase activities; thus, the processing of these proteins can be regulated by their trafficking either to or from the cell surface. Their cleavages can also be regulated by tissue inhibitor of metalloproteinase-3 (TIMP-3), a metalloprotease inhibitor in the extracellular matrix. ApoE receptors have functions in neuronal migration during development and in proper synaptic function in the adult. Thus, the functions of apoE receptors and by analogy of APP will be modified by the various extracellular and intracellular interactions reviewed in this paper.
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Hoe HS, Minami SS, Makarova A, Lee J, Hyman BT, Matsuoka Y, Rebeck GW. Fyn modulation of Dab1 effects on amyloid precursor protein and ApoE receptor 2 processing. J Biol Chem 2007; 283:6288-99. [PMID: 18089558 DOI: 10.1074/jbc.m704140200] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Dab1 is an intracellular adaptor protein that interacts with amyloid precursor protein (APP) and apoE receptor 2 (apoEr2), increases their levels on the cell surface, and increases their cleavage by alpha-secretases. To investigate the mechanism underlying these alterations in processing and trafficking of APP and apoEr2, we examined the effect of Fyn, an Src family-tyrosine kinase known to interact with and phosphorylate Dab1. Co-immunoprecipitation, co-immunostaining, and fluorescence lifetime imaging demonstrated an association between Fyn and APP. Fyn induced phosphorylation of APP at Tyr-757 of the (757)YENPTY(762) motif and increased cell surface expression of APP. Overexpression of Fyn alone did not alter levels of sAPPalpha or cytoplasmic C-terminal fragments, although it significantly decreased production of Abeta. However, in the presence of Dab1, Fyn significantly increased sAPPalpha and C-terminal fragments. Fyn-induced APP phosphorylation and cell surface levels of APP were potentiated in the presence of Dab1. Fyn also induced phosphorylation of apoEr2 and increased its cell surface levels and, in the presence of Dab1, affected processing of its C-terminal fragment. In vivo studies showed that sAPPalpha was decreased in the Fyn knock-out, supporting a role for Fyn in APP processing. These data demonstrate that Fyn, due in part to its effects on Dab1, regulates the phosphorylation, trafficking, and processing of APP and apoEr2.
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Affiliation(s)
- Hyang-Sook Hoe
- Department of Neuroscience, Georgetown University Medical Center, 3970 Reservoir Road NW, Washington, DC 20057, USA
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Crawford DC, Nord AS, Badzioch MD, Ranchalis J, McKinstry LA, Ahearn M, Bertucci C, Shephard C, Wong M, Rieder MJ, Schellenberg GD, Nickerson DA, Heagerty PJ, Wijsman EM, Jarvik GP. A common VLDLR polymorphism interacts with APOE genotype in the prediction of carotid artery disease risk. J Lipid Res 2007; 49:588-96. [PMID: 18056683 DOI: 10.1194/jlr.m700409-jlr200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The genetic factors associated with carotid artery disease (CAAD) are not fully known. Because of its role in lipid metabolism, we hypothesized that common genetic variation in the very low density lipoprotein receptor (VLDLR) gene is associated with severe CAAD (>80% stenosis), body mass index (BMI), and lipid traits in humans. VLDLR was resequenced for variation discovery in 92 subjects, and single nucleotide polymorphisms (tagSNPs) were chosen for genotyping in a larger cohort (n = 1,027). Of the 17 tagSNPs genotyped, one tagSNP (SNP 1226; rs1454626) located in the 5' flanking region of VLDLR was associated with CAAD, BMI, and LDL-associated apolipoprotein B (apoB). We also identified receptor-ligand genetic interactions between VLDLR 1226 and APOE genotype for predicting CAAD case status. These findings may further our understanding of VLDLR function, its ligand APOE, and ultimately the pathogenesis of CAAD in the general population.
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Affiliation(s)
- Dana C Crawford
- Department of Molecular Physiology and Biophysics, Center for Human Genetics Research, Vanderbilt University, Nashville, TN, USA
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Hoe HS, Cooper MJ, Burns MP, Lewis PA, van der Brug M, Chakraborty G, Cartagena CM, Pak DTS, Cookson MR, Rebeck GW. The metalloprotease inhibitor TIMP-3 regulates amyloid precursor protein and apolipoprotein E receptor proteolysis. J Neurosci 2007; 27:10895-905. [PMID: 17913923 PMCID: PMC6672812 DOI: 10.1523/jneurosci.3135-07.2007] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2007] [Revised: 08/08/2007] [Accepted: 08/20/2007] [Indexed: 01/08/2023] Open
Abstract
Cellular cholesterol levels alter the processing of the amyloid precursor protein (APP) to produce Abeta. Activation of liver X receptors (LXRs), one cellular mechanism to regulate cholesterol homeostasis, has been found to alter Abeta levels in vitro and in vivo. To identify genes regulated by LXR, we treated human neuroblastoma cells with an LXR agonist (TO-901317) and examined gene expression by microarray. As expected, TO-901317 upregulated several cholesterol metabolism genes, but it also decreased expression of a metalloprotease inhibitor, TIMP-3. We confirmed this finding using real-time PCR and by measuring TIMP-3 protein in glia, SY5Y cells, and COS7 cells. TIMP-3 is a member of a family of metalloproteinase inhibitors and blocks A disintegrin and metalloproteinase-10 (ADAM-10) and ADAM-17, two APP alpha-secretases. We found that TIMP-3 inhibited alpha-secretase cleavage of APP and an apolipoprotein E (apoE) receptor, ApoER2. TIMP-3 decreased surface levels of ADAM-10, APP, and ApoER2. These changes were accompanied by increased APP beta-C-terminal fragment and Abeta production. These data suggest that TIMP-3 preferentially routes APP and ApoER2 away from the cell surface and alpha-secretase cleavage and encourages endocytosis and beta-secretase cleavage. In vivo, TO-901317 decreased brain TIMP-3 levels. TIMP-3 protein levels were increased in human Alzheimer's disease (AD) brain and in APP transgenic mice, suggesting that increased levels of TIMP-3 in AD may contribute to higher levels of Abeta.
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Affiliation(s)
| | | | | | - Patrick A. Lewis
- Laboratory of Neurogenetics, National Institute on Aging, Bethesda, Maryland 20892-3707
| | - Marcel van der Brug
- Laboratory of Neurogenetics, National Institute on Aging, Bethesda, Maryland 20892-3707
| | | | | | - Daniel T. S. Pak
- Pharmacology, Georgetown University Medical Center, Washington, DC 20057-1464, and
| | - Mark R. Cookson
- Laboratory of Neurogenetics, National Institute on Aging, Bethesda, Maryland 20892-3707
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Fuentealba RA, Barría MI, Lee J, Cam J, Araya C, Escudero CA, Inestrosa NC, Bronfman FC, Bu G, Marzolo MP. ApoER2 expression increases Abeta production while decreasing Amyloid Precursor Protein (APP) endocytosis: Possible role in the partitioning of APP into lipid rafts and in the regulation of gamma-secretase activity. Mol Neurodegener 2007; 2:14. [PMID: 17620134 PMCID: PMC1939850 DOI: 10.1186/1750-1326-2-14] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2007] [Accepted: 07/09/2007] [Indexed: 11/10/2022] Open
Abstract
Background The generation of the amyloid-β peptide (Aβ) through the proteolytic processing of the amyloid precursor protein (APP) is a central event in the pathogenesis of Alzheimer's disease (AD). Recent studies highlight APP endocytosis and localization to lipid rafts as important events favoring amyloidogenic processing. However, the precise mechanisms underlying these events are poorly understood. ApoER2 is a member of the low density lipoprotein receptor (LDL-R) family exhibiting slow endocytosis rate and a significant association with lipid rafts. Despite the important neurophysiological roles described for ApoER2, little is known regarding how ApoER2 regulates APP trafficking and processing. Results Here, we demonstrate that ApoER2 physically interacts and co-localizes with APP. Remarkably, we found that ApoER2 increases cell surface APP levels and APP association with lipid rafts. The increase of cell surface APP requires the presence of ApoER2 cytoplasmic domain and is a result of decreased APP internalization rate. Unexpectedly, ApoER2 expression correlated with a significant increase in Aβ production and reduced levels of APP-CTFs. The increased Aβ production was dependent on the integrity of the NPxY endocytosis motif of ApoER2. We also found that expression of ApoER2 increased APP association with lipid rafts and increased γ-secretase activity, both of which might contribute to increased Aβ production. Conclusion These findings show that ApoER2 negatively affects APP internalization. However, ApoER2 expression stimulates Aβ production by shifting the proportion of APP from the non-rafts to the raft membrane domains, thereby promoting β-secretase and γ-secretase mediated amyloidogenic processing and also by incrementing the activity of γ-secretase.
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Affiliation(s)
- Rodrigo A Fuentealba
- FONDAP Center for Cell Regulation and Pathology (CRCP), Departamento de Biología Celular y Molecular, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Maria Ines Barría
- FONDAP Center for Cell Regulation and Pathology (CRCP), Departamento de Biología Celular y Molecular, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Jiyeon Lee
- Departments of Pediatrics and Cell Biology & Physiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
| | - Judy Cam
- Departments of Pediatrics and Cell Biology & Physiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
| | - Claudia Araya
- FONDAP Center for Cell Regulation and Pathology (CRCP), Departamento de Biología Celular y Molecular, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Claudia A Escudero
- FONDAP Center for Cell Regulation and Pathology (CRCP), Departamento de Ciencias Fisiológicas, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Nibaldo C Inestrosa
- FONDAP Center for Cell Regulation and Pathology (CRCP), Departamento de Biología Celular y Molecular, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Francisca C Bronfman
- FONDAP Center for Cell Regulation and Pathology (CRCP), Departamento de Ciencias Fisiológicas, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Guojun Bu
- Departments of Pediatrics and Cell Biology & Physiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
| | - Maria-Paz Marzolo
- FONDAP Center for Cell Regulation and Pathology (CRCP), Departamento de Biología Celular y Molecular, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile
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Pennings MTT, Derksen RHWM, Urbanus RT, Tekelenburg WL, Hemrika W, de Groot PG. Platelets express three different splice variants of ApoER2 that are all involved in signaling. J Thromb Haemost 2007; 5:1538-44. [PMID: 17470198 DOI: 10.1111/j.1538-7836.2007.02605.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
BACKGROUND beta2-Glycoprotein I is the most relevant antigen in antiphospholipid syndrome. We have shown that binding of dimerized beta2-GPI to platelets via ApoER2' sensitizes platelets for second activating stimuli. OBJECTIVE Determine the region of ApoER2 involved in the binding of dimeric beta2-GPI. METHODS Cultured human megakaryocytes (MK) and three different human megakaryocytic cell lines were used for mRNA isolation to clone and express recombinant soluble platelet ApoER2. Domain deletion mutants of ApoER2 were constructed to identify the binding site for dimeric beta2-GPI. The presence of ApoER2 splice variants in platelets was demonstrated by immuno-blotting. RESULTS Three different mRNA splice variants were isolated from all four types of megakaryocytic cells used. Sequence analysis identified the splice variants: (i) shApoER2Delta5 lacking low-density lipoprotein (LDL) binding domains 4, 5 and 6; (ii) shApoER2Delta4-5 lacking LDL binding domains 3, 4, 5, 6 and (iii) shApoER2Delta3-4-5 lacking LDL binding domains 3, 4, 5, 6 and 7. The presence of three splice variants of ApoER2 on platelets was confirmed by immuno-blotting, with ApoER2Delta4-5 being the most abundantly expressed splice variant. Upon stimulation with dimeric beta2-GPI, all three splice variants were translocated to the cytosol; however, ApoER2Delta4-5 translocation was most prominent. Dimeric beta2-GPI binds platelet ApoER2 variants via LDL-binding domain 1. CONCLUSIONS Three different ApoER2 mRNA splice variants were isolated from MK and platelets express all three splice variants. All splice variants were shown to be functional by translocation upon stimulation with dimeric beta2-GPI. All three splice variants express LDL-binding domain 1.
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Affiliation(s)
- M T T Pennings
- Laboratory of Thrombosis and Haemostasis, Department of Clinical Chemistry and Hematology, UMCU Utrecht, Utrecht, The Netherlands
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Abstract
Low-density lipoprotein receptor-related protein 6 (LRP6) is a member of low-density lipoprotein receptor (LDLR) family which cooperates with Frizzled receptors to transduce the canonical Wnt signal. As a critical component of the canonical Wnt pathway, LRP6 is essential for appropriate brain development, however, the mechanism by which LRP6 facilitates Wnt canonical signaling has not been fully elucidated. Interestingly, LRP6 which lacks its extracellular domain can constitutively activate TCF/LEF and potentiate the Wnt signal. Further, the free cytosolic tail of LRP6 interacts directly with glycogen synthase kinase (GSK3) and inhibits GSK3's activity in the Wnt canonical pathway which results in increased TCF/LEF activation. However, whether these truncated forms of LRP6 are physiologically relevant is unclear. Recent studies have shown that other members of the LDLR family undergo gamma-secretase dependent regulated intramembrane proteolysis (RIP). Using independent experimental approaches, we show that LRP6 also undergoes RIP. The extracellular domain of LRP6 is shed and released into the surrounding milieu and the cytoplasmic tail is cleaved by gamma-secretase-like activity to release the intracellular domain. Furthermore, protein kinase C, Wnt 3a and Dickkopf-1 modulate this process. These findings suggest a novel mechanism for LRP6 in Wnt signaling: induction of ectodomain shedding of LRP6, followed by the gamma-secretase involved proteolytic releasing its intracellular domain (ICD) which then binds to GSK3 inhibiting its activity and thus activates the canonical Wnt signaling pathway.
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Affiliation(s)
- Kaihong Mi
- Department of Psychiatry, University of Alabama at Birmingham, Birmingham, Alabama 35294-0017, USA
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63
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Hoe HS, Freeman J, Rebeck GW. Apolipoprotein E decreases tau kinases and phospho-tau levels in primary neurons. Mol Neurodegener 2006; 1:18. [PMID: 17166269 PMCID: PMC1713232 DOI: 10.1186/1750-1326-1-18] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2006] [Accepted: 12/13/2006] [Indexed: 11/25/2022] Open
Abstract
Apolipoprotein E (apoE) receptors act as signaling molecules in neurons, altering phosphorylation of numerous proteins after extracellular ligand binding and affecting neurite outgrowth, synapse formation, and neuronal migration. Since apoE is important in the pathogenesis of Alzheimer's disease (AD), we tested whether apoE treatment of neurons affected molecules important to phosphorylation of tau, such as GSK 3β, P35, and CDK5, and the phosphorylation of tau itself. Treatment of primary neurons with 2 uM apoE (or an apoE-derived peptide) decreased levels of phospho-GSK 3β, P35 and CDK5, and decreased levels of phosphorylated forms of tau. A lower concentration of apoE (100 nM) had no effect on these molecules. The alteration of tau phosphorylation by apoE was blocked by an inhibitor of the low-density lipoprotein receptor family, demonstrating the effects were due to receptor interactions. These results demonstrate that apoE affects several downstream signaling cascades in neurons: decreased tau kinases phosphorylation and inhibition of tau phosphorylation at Thr171 and Ser202/Thr205 epitopes. We conclude that apoE can alter levels of tau kinases and phospho-tau epitopes, potentially affecting tau neuropathological changes seen in AD brains.
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Affiliation(s)
- Hyang-Sook Hoe
- Department of Neuroscience, Georgetown University, 3970 Reservoir Road NW, Washington, DC 20057-1464, USA
| | - Jacob Freeman
- Department of Neuroscience, Georgetown University, 3970 Reservoir Road NW, Washington, DC 20057-1464, USA
| | - G William Rebeck
- Department of Neuroscience, Georgetown University, 3970 Reservoir Road NW, Washington, DC 20057-1464, USA
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Rebeck GW, LaDu MJ, Estus S, Bu G, Weeber EJ. The generation and function of soluble apoE receptors in the CNS. Mol Neurodegener 2006; 1:15. [PMID: 17062143 PMCID: PMC1635701 DOI: 10.1186/1750-1326-1-15] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2006] [Accepted: 10/24/2006] [Indexed: 01/11/2023] Open
Abstract
More than a decade has passed since apolipoprotein E4 (APOE-epsilon4) was identified as a primary risk factor for Alzheimer 's disease (AD), yet researchers are even now struggling to understand how the apolipoprotein system integrates into the puzzle of AD etiology. The specific pathological actions of apoE4, methods of modulating apolipoprotein E4-associated risk, and possible roles of apoE in normal synaptic function are still being debated. These critical questions will never be fully answered without a complete understanding of the life cycle of the apolipoprotein receptors that mediate the uptake, signaling, and degradation of apoE. The present review will focus on apoE receptors as modulators of apoE actions and, in particular, explore the functions of soluble apoE receptors, a field almost entirely overlooked until now.
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Affiliation(s)
- G William Rebeck
- Department of Neuroscience, Georgetown University, Washington DC, USA
| | - Mary Jo LaDu
- Department of Anatomy and Cell Biology, University of Illinois at Chicago, Chicago, USA
| | - Steven Estus
- Department of Physiology, University of Kentucky, Lexington, USA
- Sanders-Brown Center on Aging, University of Kentucky, Lexington, USA
| | - Guojun Bu
- Department of Pediatrics, Washington University, St. Louis, USA
- Department of Cell Biology and Physiology, Washington University, St. Louis, USA
- Hope Center for Neurological Disorders, Washington University, St. Louis, USA
| | - Edwin J Weeber
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, USA
- Department of Pharmacology, Vanderbilt University, Nashville, USA
- Vanderbilt Kennedy Center for Research on Human Development, Vanderbilt University, Nashville, USA
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65
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Belinson H, Dolev I, Michaelson DM. Neuron-specific susceptibility to apolipoprotein E4. Neurobiol Aging 2006; 28:689-92; discussion 704-6. [PMID: 17023093 DOI: 10.1016/j.neurobiolaging.2006.06.027] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2006] [Accepted: 06/19/2006] [Indexed: 10/24/2022]
Affiliation(s)
- Haim Belinson
- Department of Neurobiochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, 69978 Tel Aviv, Israel
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66
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Stolt PC, Bock HH. Modulation of lipoprotein receptor functions by intracellular adaptor proteins. Cell Signal 2006; 18:1560-71. [PMID: 16725309 DOI: 10.1016/j.cellsig.2006.03.008] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2006] [Accepted: 03/21/2006] [Indexed: 10/24/2022]
Abstract
Members of the low density lipoprotein (LDL) receptor gene family are critically involved in a wide range of physiological processes including lipid and vitamin homeostasis, cellular migration, neurodevelopment, and synaptic plasticity, to name a few. Lipoprotein receptors exert these diverse biological functions by acting as cellular uptake receptors or by inducing intracellular signaling cascades. It was discovered that a short sequence in the intracellular region of all lipoprotein receptors, Asn-Pro-X-Tyr (NPXY) is important for mediating either endocytosis or signal transduction events, and that this motif serves as a binding site for phosphotyrosine-binding (PTB) domain containing scaffold proteins. These molecular adaptors connect the transmembrane receptors with the endocytosis machinery and regulate cellular trafficking, or function as assembly sites for dynamic multi-protein signaling complexes. Whereas the LDL receptor represents the archetype of an endocytic lipoprotein receptor, the structurally closely related apolipoprotein E receptor 2 (apoER2) and very low density lipoprotein (VLDL) receptor activate a kinase-dependent intracellular signaling cascade after binding to the neuronal signaling molecule Reelin. This review focuses on two related PTB domain containing adaptor proteins that mediate these divergent lipoprotein receptor responses, ARH (autosomal recessive hypercholesterolemia protein) and Dab1 (disabled-1), and discusses the structural and molecular basis of this different behaviour.
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Affiliation(s)
- Peggy C Stolt
- Max Planck Institute for Biophysics, Max-von-Laue Str. 3, D-60438 Frankfurt/Main, Germany
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67
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Hoe HS, Pocivavsek A, Dai H, Chakraborty G, Harris DC, Rebeck GW. Effects of apoE on neuronal signaling and APP processing in rodent brain. Brain Res 2006; 1112:70-9. [PMID: 16905123 DOI: 10.1016/j.brainres.2006.07.035] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2006] [Revised: 06/14/2006] [Accepted: 07/04/2006] [Indexed: 11/26/2022]
Abstract
We previously reported that primary neuronal cells treated with apolipoprotein E (apoE) or an apoE-derived peptide (EP) increased ERK activation and decreased JNK activation via apoE receptors. Here, we examined if the effects observed in vitro were observed in vivo. Similar to our observations in primary neurons, in vivo we found that injections of 2muM EP into the rat hippocampus increased the levels of ERK activation and decreased JNK activation. However, the time course of these effects was slower in vivo. Immunohistochemical analysis of the tissue showed prominently increased ERK phosphorylation and decreased JNK phosphorylation in neuronal cells throughout the hippocampus, particularly in the CA3 regions. To determine if apoE was endocytosed by neurons, we conjugated fluorescent microspheres with the EP and injected them into the rat hippocampus. After 7 days, the microspheres were present in neurons. We also examined the in vivo effects of apoE on ApoEr2 and APP processing. EP and full-length apoE3 and apoE4 increased C-terminal fragments of ApoEr2 and APP after a single injection, multiple injections, and chronic infusion paradigms. ApoE3 produced higher levels of ApoEr2 and APP C-terminal fragments than apoE4. These results demonstrate that apoE alters ApoEr2 and APP processing in vivo. The increase in ERK activation is consistent with a role for apoE in a neuronal response to stress, and the decrease in JNK activation suggests that apoE may have anti-apoptotic effects, over several days.
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Affiliation(s)
- Hyang-Sook Hoe
- Department of Neuroscience, Georgetown University, 3970 Reservoir Road NW, Washington, DC 20057-1464, USA
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68
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Hoe HS, Tran TS, Matsuoka Y, Howell BW, Rebeck GW. DAB1 and Reelin effects on amyloid precursor protein and ApoE receptor 2 trafficking and processing. J Biol Chem 2006; 281:35176-85. [PMID: 16951405 DOI: 10.1074/jbc.m602162200] [Citation(s) in RCA: 137] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Numerous cytoplasmic adaptor proteins, including JIP1, FE65, and X11alpha, affect amyloid precursor protein (APP) processing and Abeta production. Dab1 is another adaptor protein that interacts with APP as well as with members of the apoE receptor family. We examined the effect of Dab1 on APP and apoEr2 processing in transfected cells and primary neurons. Dab1 interacted with APP and apoEr2 and increased levels of their secreted extracellular domains and their cytoplasmic C-terminal fragments. These effects depended on the NPXY domains of APP and apoEr2 and on the phosphotyrosine binding domain of Dab1 but did not depend on phosphorylation of Dab1. Dab1 decreased the levels of APP beta-C-terminal fragment and secreted Abeta. Full-length Dab1 or its phosphotyrosine binding domain alone increased surface levels of APP, as determined by surface protein biotinylation and live cell staining. A ligand for apoEr2, the extracellular matrix protein Reelin, significantly increased the interaction of apoEr2 with Dab1. Surprisingly, we also found that Reelin treatment significantly increased the interaction of APP and Dab1. Moreover, Reelin treatment increased cleavage of APP and apoEr2 and decreased production of the beta-C-terminal fragment of APP and Abeta. Together, these data suggest that Dab1 alters trafficking and processing of APP and apoEr2, and this effect is influenced by extracellular ligands.
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Affiliation(s)
- Hyang-Sook Hoe
- Department of Neuroscience, Georgetown University Medical Center, Washington, DC 20057-1464, USA
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69
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Cam JA, Bu G. Modulation of beta-amyloid precursor protein trafficking and processing by the low density lipoprotein receptor family. Mol Neurodegener 2006; 1:8. [PMID: 16930455 PMCID: PMC1563464 DOI: 10.1186/1750-1326-1-8] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2006] [Accepted: 08/18/2006] [Indexed: 01/28/2023] Open
Abstract
Amyloid-β peptide (Aβ) accumulation in the brain is an early, toxic event in the pathogenesis of Alzheimer's disease (AD). Aβ is produced by proteolytic processing of a transmembrane protein, β-amyloid precursor protein (APP), by β- and γ-secretases. Mounting evidence has demonstrated that alterations in APP cellular trafficking and localization directly impact its processing to Aβ. Recent studies have shown that members of the low-density lipoprotein receptor family, including LRP, LRP1B, SorLA/LR11, and apolipoprotein E (apoE) receptor 2, interact with APP and regulate its endocytic trafficking. Another common feature of these receptors is their ability to bind apoE, which exists in three isoforms in humans and the presence of the ε4 allele represents a genetic risk factor for AD. In this review, we summarize the current understanding of the function of these apoE receptors with a focus on their role in APP trafficking and processing. Knowledge of the interactions between these distinct low-density lipoprotein receptor family members and APP may ultimately influence future therapies for AD.
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Affiliation(s)
- Judy A Cam
- Departments of Pediatrics, and Cell Biology & Physiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
- Department of Pathology, New York University, 550 1Avenue, New York, New York 10016, USA
| | - Guojun Bu
- Departments of Pediatrics, and Cell Biology & Physiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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70
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Hoe HS, Magill LA, Guenette S, Fu Z, Vicini S, Rebeck GW. FE65 Interaction with the ApoE Receptor ApoEr2. J Biol Chem 2006; 281:24521-30. [PMID: 16638748 DOI: 10.1074/jbc.m600728200] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The adaptor protein FE65 interacts with the beta-amyloid precursor protein (APP) via its C-terminal phosphotyrosine binding (PTB) domain and affects APP processing and Abeta production. Our previous data demonstrate that the apoE receptor ApoEr2 co-precipitated with APP and suggest that there are extracellular and intracellular interactions between these two transmembrane proteins. We hypothesized that FE65 acts as an intracellular link between ApoEr2 and APP. Co-immunoprecipitation experiments in COS7 cells demonstrated an interaction between ApoEr2 and FE65 that depended on the N-terminal PTB domain of FE65. Full-length FE65 increased co-immunoprecipitation of ApoEr2 and APP. Full-length FE65 also increased surface expression of ApoEr2, as determined by surface protein biotinylation and live cell surface staining. Constructs containing both the C- and N-terminal PTB domains of FE65 increased secreted APP, secreted ApoEr2, APP C-terminal fragment, and ApoEr2 C-terminal fragment, but constructs containing only single PTB domains did not affect APP or ApoEr2 processing. In addition, full-length FE65 decreased Abeta to a significantly greater extent than individual FE65 domains. These data suggest that FE65 can bind APP and ApoEr2 at the same time and affect the processing of each.
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Affiliation(s)
- Hyang-Sook Hoe
- Department of Neuroscience, Georgetown University Medical Center, Washington, D. C. 20057-1464, USA
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71
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Nyborg AC, Ladd TB, Zwizinski CW, Lah JJ, Golde TE. Sortilin, SorCS1b, and SorLA Vps10p sorting receptors, are novel gamma-secretase substrates. Mol Neurodegener 2006; 1:3. [PMID: 16930450 PMCID: PMC1513133 DOI: 10.1186/1750-1326-1-3] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2006] [Accepted: 06/12/2006] [Indexed: 11/30/2022] Open
Abstract
Background The mammalian Vps10p sorting receptor family is a group of 5 type I membrane homologs (Sortilin, SorLA, and SorCS1-3). These receptors bind various cargo proteins via their luminal Vps10p domains and have been shown to mediate a variety of intracellular sorting and trafficking functions. These proteins are highly expressed in the brain. SorLA has been shown to be down regulated in Alzheimer's disease brains, interact with ApoE, and modulate Aβ production. Sortilin has been shown to be part of proNGF mediated death signaling that results from a complex of Sortilin, p75NTR and proNGF. We have investigated and provide evidence for γ-secretase cleavage of this family of proteins. Results We provide evidence that these receptors are substrates for presenilin dependent γ-secretase cleavage. γ-Secretase cleavage of these sorting receptors is inhibited by γ-secretase inhibitors and does not occur in PS1/PS2 knockout cells. Like most γ-secretase substrates, we find that ectodomain shedding precedes γ-secretase cleavage. The ectodomain cleavage is inhibited by a metalloprotease inhibitor and activated by PMA suggesting that it is mediated by an α-secretase like cleavage. Conclusion These data indicate that the α- and γ-secretase cleavages of the mammalian Vps10p sorting receptors occur in a fashion analogous to other known γ-secretase substrates, and could possibly regulate the biological functions of these proteins.
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Affiliation(s)
- Andrew C Nyborg
- Department of Neuroscience, Mayo Clinic Jacksonville, Mayo Clinic College of Medicine, 4500 San Pablo Road, Jacksonville, Florida 32224, USA
| | - Thomas B Ladd
- Department of Neuroscience, Mayo Clinic Jacksonville, Mayo Clinic College of Medicine, 4500 San Pablo Road, Jacksonville, Florida 32224, USA
| | - Craig W Zwizinski
- Department of Neuroscience, Mayo Clinic Jacksonville, Mayo Clinic College of Medicine, 4500 San Pablo Road, Jacksonville, Florida 32224, USA
| | - James J Lah
- Department of Neurology, Center for Neurodegenerative Disease, Emory University, Whitehead Biomedical Research Building, 615 Michael Street, Suite 505, Atlanta, GA 30322, USA
| | - Todd E Golde
- Department of Neuroscience, Mayo Clinic Jacksonville, Mayo Clinic College of Medicine, 4500 San Pablo Road, Jacksonville, Florida 32224, USA
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72
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Wicher G, Larsson M, Fex Svenningsen A, Gyllencreutz E, Rask L, Aldskogius H. Low density lipoprotein receptor-related protein-2/megalin is expressed in oligodendrocytes in the mouse spinal cord white matter. J Neurosci Res 2006; 83:864-73. [PMID: 16463279 DOI: 10.1002/jnr.20774] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Lipoprotein receptor-related protein-2 (LRP2)/megalin is a member of the low density lipoprotein receptor (LDLR) family, and is essential in absorptive epithelia for endocytosis of lipoproteins, low molecular weight proteins, cholesterol and vitamins, as well as in cellular signaling. Previous studies have shown megalin expression in ependymal cells and choroid plexus. We have investigated megalin expression in the spinal cord of postnatal mice with immunohistochemistry and immunoblot. Antibodies recognizing either the cytoplasmic tail (MM6) or the extracellular domain (E11) of megalin labeled oligodendrocytes in the spinal cord white matter, in parallel with myelination. MM6 antibodies, predominantly labeled the nuclei, whereas E11 antibodies labeled the cytoplasm of these cells. MM6 antibodies labeled also nuclei of oligodendrocytes cultured from embryonic mouse spinal cord. Immunoblots of spinal cord showed intact megalin, as well as its carboxyterminal fragment, the part remaining after shedding of the extracellular domain of megalin. Megalin-immunoreactive oligodendrocytes also expressed presenilin 1, an enzyme responsible for gamma-secretase mediated endodomain cleavage. These findings show that spinal cord oligodendrocytes are phenotypically different from those in the brain, and indicate that megalin translocates signals from the cell membrane to the nucleus of oligodendrocytes during the formation and maintenance of myelin of long spinal cord pathways.
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Affiliation(s)
- Grzegorz Wicher
- Department of Neuroscience, Biomedical Center, Uppsala University, Uppsala, Sweden.
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73
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Hoe HS, Pocivavsek A, Chakraborty G, Fu Z, Vicini S, Ehlers MD, Rebeck GW. Apolipoprotein E Receptor 2 Interactions with the N-Methyl-D-aspartate Receptor. J Biol Chem 2006; 281:3425-31. [PMID: 16332682 DOI: 10.1074/jbc.m509380200] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In our previous studies we showed that apoE treatment of neurons activated ERK 1/2 signaling, and activation was blocked by treatment with inhibitors of the low density lipoprotein receptor family, the N-methyl-d-aspartate (NMDA) receptor antagonist MK 801, and calcium channel blockers. We hypothesized an interaction between the low density lipoprotein receptor family members and the NMDA receptor. In the present study, we confirmed through co-immunoprecipitation experiments an interaction between the apoE receptor, ApoEr2, and NMDAR1 through their extracellular domains. We also found that the PDZ1 domain of PSD95, a postsynaptic scaffolding protein, interacted with the C terminus of ApoEr2 via an alternatively spliced, intracellular exon. This interaction between ApoEr2 and PSD95 in neurons was modulated by NMDA receptor activation and an ApoEr2 ligand. We also found that the PDZ2 domain of PSD95 interacted with the NR2A and NR2B subunits of NMDA receptors. Full-length PSD95 increased cell surface levels of ApoEr2 and its cleavage, resulting in increases in secreted ApoEr2 and C-terminal fragments of ApoEr2. These studies suggest that ApoEr2 can form a multiprotein complex with NMDA receptor subunits and PSD95.
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Affiliation(s)
- Hyang-Sook Hoe
- Department of Neuroscience and Physiology, Georgetown University Medical Center, Washington, DC 20057-1464, USA
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Hoe HS, Wessner D, Beffert U, Becker AG, Matsuoka Y, Rebeck GW. F-spondin interaction with the apolipoprotein E receptor ApoEr2 affects processing of amyloid precursor protein. Mol Cell Biol 2005; 25:9259-68. [PMID: 16227578 PMCID: PMC1265841 DOI: 10.1128/mcb.25.21.9259-9268.2005] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
A recent study showed that F-spondin, a protein associated with the extracellular matrix, interacted with amyloid precursor protein (APP) and inhibited beta-secretase cleavage. F-spondin contains a thrombospondin domain that we hypothesized could interact with the family of receptors for apolipoprotein E (apoE). Through coimmunoprecipitation experiments, we demonstrated that F-spondin interacts with an apoE receptor (apoE receptor 2 [ApoEr2]) through the thrombospondin domain of F-spondin and the ligand binding domain of ApoEr2. Full-length F-spondin increased coimmunoprecipitation of ApoEr2 and APP in transfected cells and primary neurons and increased surface expression of APP and ApoEr2. Full-length F-spondin, but none of the individual F-spondin domains, increased cleavage of APP and ApoEr2, resulting in more secreted forms of APP and ApoEr2 and more C-terminal fragments (CTF) of these proteins. In addition, full-length F-spondin, but not the individual domains, decreased production of the beta-CTF of APP and Abeta in transfected cells and primary neurons. The reduction in APP beta-CTF was blocked by receptor-associated protein (RAP), an inhibitor of lipoprotein receptors, implicating ApoEr2 in the altered proteolysis of APP. ApoEr2 coprecipitated with APP alpha- and beta-CTF, and F-spondin reduced the levels of APP intracellular domain signaling, suggesting that there are also intracellular interactions between APP and ApoEr2, perhaps involving adaptor proteins. These studies suggest that the extracellular matrix molecule F-spondin can cluster APP and ApoEr2 together on the cell surface and affect the processing of each, resulting in decreased production of Abeta.
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Affiliation(s)
- Hyang-Sook Hoe
- Department of Neuroscience, Georgetown University Medical Center, 3970 Reservoir Road NW, Washington, DC 20057-1464, USA
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75
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Qiu S, Korwek KM, Weeber EJ. A fresh look at an ancient receptor family: emerging roles for low density lipoprotein receptors in synaptic plasticity and memory formation. Neurobiol Learn Mem 2005; 85:16-29. [PMID: 16198608 DOI: 10.1016/j.nlm.2005.08.009] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2005] [Revised: 07/30/2005] [Accepted: 08/11/2005] [Indexed: 01/11/2023]
Abstract
The well-known family of low-density lipoprotein receptors represents a collection of ancient membrane receptors that have been remarkably conserved throughout evolution. These multifunctional receptors, known to regulate cholesterol transport, are becoming increasingly interesting to the neuroscience community due to their ability to transduce a diversity of extracellular signals across the membrane in the adult CNS. Their roles in modulating synaptic plasticity and necessity in hippocampus-specific learning and memory have recently come to light. In addition, genetic, biochemical and behavioral studies have implicated these signaling systems in a number of human neurodegenerative and neuropsychiatric disorders involving loss of cognitive ability, such as Alzheimer's disease, schizophrenia and autism. This review describes the known functions of these receptors and discusses their potential role in processes of synaptic regulation and memory formation.
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Affiliation(s)
- Shenfeng Qiu
- Department of Molecular Physiology and Biophysics, Vanderbilt University Medical Center, Nashville, TN 37232-0615, USA
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