Cited by 103Alzheimer's disease research and treatmentsNeuroinflammation and Neurodegeneration MechanismsNeuroscience and Neuropharmacology Research

The DOI matches its Crossref record; 62 of the 62 references it cites were found in a registry or an index; 24 of the 67 sources its claims cite were checked for support.

Apolipoprotein E Receptors Mediate the Effects of β-Amyloid on Astrocyte Cultures

Open access
LaDu, Mary Jo, Shah, Javeed Ali, Reardon, Catherine A., Getz, Godfrey S., Bu, Guojun, Hu, Jingru, Guo, Ling, Van Eldik, Linda J.·2000·Journal of Biological Chemistry

Abstract

We have previously shown that beta-amyloid (Abeta) induces astrocyte activation in vitro and that this reaction is attenuated by the addition of exogenous apolipoprotein E (apoE)-containing particles. However, the effects of Abeta on endogenous apoE and apoJ levels and the potential role of apoE receptors in astrocyte activation have not been addressed. Three activating stimuli (lipopolysaccharide, dibutyryl cAMP, and aged Abeta 1-42) were used to induce activation of rat astrocyte cultures, as assessed by changes in morphology and an increase in interleukin-1beta. However, only Abeta also induced approximately 50% reduction in the amount of released apoE and apoJ and an 8-fold increase in the levels of cell-associated apoE and apoJ. Experiments using two concentrations of receptor-associated protein, an inhibitor of apoE receptors with a differential affinity for the low density lipoprotein receptor (LDLR) and the LDLR-related protein (LRP), suggest that LRP mediates Abeta-induced astrocyte activation, whereas LDLR mediates the Abeta-induced changes in apoE levels. Receptor-associated protein had no effect on apoJ levels or on activation by either dibutyryl cAMP or lipopolysaccharide. These data suggest that apoE receptors translate the presence of extracellular Abeta into cellular responses, both initiating and modulating the inflammatory response induced by Abeta.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

Aged β-amyloid (Aβ 1-42) activates cultured rat astrocytes and, uniquely among the tested activators, alters endogenous apoE and apoJ levels. Receptor-associated protein (RAP) experiments suggest LRP mediates Aβ-induced astrocyte activation, whereas LDLR mediates Aβ-induced changes in apoE, with apoJ changes independent of RAP-inhibitable apoE receptors.

Key findings

  • Aβ 1-42 (10 µM), dibutyryl cAMP (1 mM), and LPS (10 µg/ml) all induced morphological activation and increased proIL-1β in rat astrocyte cultures; GFAP levels did not change.
  • Only Aβ altered endogenous apolipoproteins: cell-associated apoE and apoJ increased approximately 8-fold, while conditioned-medium apoE decreased by a mean of 35% and apoJ by 60% relative to control. The abstract describes an approximately 50% reduction in released apoE and apoJ.
  • RAP at 70 nM, which inhibits LRP but not LDLR, blocked Aβ-induced morphological activation and attenuated the Aβ-induced increase in proIL-1β, suggesting LRP mediates activation.
  • RAP at 1 µM, which inhibits both LRP and LDLR, blocked the Aβ-induced increase in cell-associated apoE and the decrease in released apoE, but 70 nM RAP did not; this suggests LDLR mediates the apoE changes. RAP did not block Aβ-induced apoJ changes, and heparin or heparan sulfate did not block the Aβ-induced increase in cell-associated apoE.

Methods

  • Primary astrocyte cultures were prepared from cerebral cortex of 1–2-day-old neonatal Harlan Sprague-Dawley rats; tertiary cultures were approximately 95–98% astrocytes with 2–5% microglial cells.
  • Cells were treated with aged Aβ 1-42 (10 µM), dbcAMP (1 mM), LPS (10 µg/ml), or control buffer. RAP (1 µM or 70 nM) was added 1 h before Aβ; heparin (100 µg/ml) and heparan sulfate (1 µM) were also tested.
  • Activation was assessed by morphology and Western blot for proIL-1β and GFAP. ApoE and apoJ protein levels in cell lysates and conditioned medium were measured by Western blot; apoE, apoJ, and IL-1β mRNA were measured by slot blot normalized to glyceraldehyde-3-phosphate dehydrogenase. Statistical significance was assessed by variance F tests and Student’s t test at p < 0.05.

Limitations

  • The paper states that the data do not address whether the Aβ/LRP pathway uses the same downstream activation signaling events as LPS and dbcAMP.
  • The paper states that the mechanism and function of Aβ-induced cell-associated apoJ accumulation are unclear, and that an unidentified apoJ receptor or other apoE receptors may be involved.
  • The paper notes that microglia may play a similar role but focuses on astrocytes; the findings are from in vitro rat astrocyte cultures, so in vivo relevance is not established in this study.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1074/jbc.m000602200

Cites

62 of 62 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Figures

Image 1
CC-BY · From the PDF
Image 2
CC-BY · From the PDF
FIG. 3 A b does not induce changes in apoE or apoJ mRNA levels. Cells were treated as described in the legend to Fig. 1, and the mRNA levels for apoE ( A ), apoJ ( B ), IL-1 b ( C ), and glyceraldehyde-3phosphate dehydrogenase ( D ) were determined using slot blots. The levels of apoE, apoJ, and IL-1 b mRNA were normalized to glyceraldehyde-3-phosphate dehydrogenase mRNA levels and expressed relative to control levels. The data shown are representative of two independent experiments.
FIG. 3 A b does not induce changes in apoE or apoJ mRNA levels. Cells were treated as described in the legend to Fig. 1, and the mRNA levels for apoE ( A ), apoJ ( B ), IL-1 b ( C ), and glyceraldehyde-3phosphate dehydrogenase ( D ) were determined using slot blots. The levels of apoE, apoJ, and IL-1 b mRNA were normalized to glyceraldehyde-3-phosphate dehydrogenase mRNA levels and expressed relative to control levels. The data shown are representative of two independent experiments.CC-BY · From the PDF
FIG. 4 RAP blocks A b -induced astrocyte activation. Astrocytes were treated with control buffer ( C ), 10 m M A b 1-42 ( A b ), A b 1 RAP, or RAP alone for 12 h. RAP was used at either 1 m M ( A and C ) or 70 nM ( B and D ) and was added to the cultures 1 h before treatment with A b . A and B , cell morphology was assessed as described under 'Experimental Procedures.' Data shown are the means 6 S.E. from three independent experiments. *, significantly different from control ( p , 0.05). C and D , pro-IL-1 b and GFAP levels in the cell lysates were examined by Western blotting. Data shown are representative of three independent experiments.
FIG. 4 RAP blocks A b -induced astrocyte activation. Astrocytes were treated with control buffer ( C ), 10 m M A b 1-42 ( A b ), A b 1 RAP, or RAP alone for 12 h. RAP was used at either 1 m M ( A and C ) or 70 nM ( B and D ) and was added to the cultures 1 h before treatment with A b . A and B , cell morphology was assessed as described under 'Experimental Procedures.' Data shown are the means 6 S.E. from three independent experiments. *, significantly different from control ( p , 0.05). C and D , pro-IL-1 b and GFAP levels in the cell lysates were examined by Western blotting. Data shown are representative of three independent experiments.CC-BY · From the PDF
FIG. 5 Differential effect of RAP on apoE and apoJ levels. Astrocytes were treated as described in the legend to Fig. 4, and apoE and apoJ levels in the cell lysates and conditioned media were quantitated from Western blots. Data are expressed relative to control levels and are the means 6 S.E. from 3-5 independent experiments. *, significantly different from control ( p , 0.05).
FIG. 5 Differential effect of RAP on apoE and apoJ levels. Astrocytes were treated as described in the legend to Fig. 4, and apoE and apoJ levels in the cell lysates and conditioned media were quantitated from Western blots. Data are expressed relative to control levels and are the means 6 S.E. from 3-5 independent experiments. *, significantly different from control ( p , 0.05).CC-BY · From the PDF
FIG. 6 Heparin and heparan sulfate do not block A b -induced increases in cell-associated apoE levels. Astrocytes were treated as described in the legend to Fig. 4 with control buffer ( C ), 10 m M A b 1-42 ( A b ), A b 1 70 nM RAP, A b 1 1 m M RAP, A b 1 100 m g/ml heparin ( H ), or A b 1 1 m M heparan sulfate ( HS ). RAP, heparin, and heparan sulfate were added to the cultures 1 h before treatment with A b . ApoE levels in the cell lysates were quantitated from Western blots. Data are expressed relative to the control levels and are shown as the means 6 S.E. from three independent experiments. The inset shows Western blot data from a representative experiment.
FIG. 6 Heparin and heparan sulfate do not block A b -induced increases in cell-associated apoE levels. Astrocytes were treated as described in the legend to Fig. 4 with control buffer ( C ), 10 m M A b 1-42 ( A b ), A b 1 70 nM RAP, A b 1 1 m M RAP, A b 1 100 m g/ml heparin ( H ), or A b 1 1 m M heparan sulfate ( HS ). RAP, heparin, and heparan sulfate were added to the cultures 1 h before treatment with A b . ApoE levels in the cell lysates were quantitated from Western blots. Data are expressed relative to the control levels and are shown as the means 6 S.E. from three independent experiments. The inset shows Western blot data from a representative experiment.CC-BY · From the PDF
FIG. 7 Model for the proposed role of apoE receptors in A b -induced astrocyte activation. LRP mediates A b -induced changes in astrocyte morphology and increased expression of IL-1 b . LPS and dbcAMPproduce similar effects independent of apoE receptors. The LDLR mediates the A b -induced increase in cell-associated apoE and the decrease in apoE in the conditioned medium. Although a portion of these changes may be the result of increased reuptake of apoE by the LDLR, the total amount of apoE also increases. This suggests that the LDLR may be linked to an intracellular pathway that signals an increase in apoE translation and/or a decrease in degradation (steady-state apoE mRNA levels do not change). To effect these changes in astrocyte activation and apoE levels, A b may be interacting directly with apoE receptors or via an interaction with an apoE receptor ligand. A b -induced changes in apoJ appear to be independent of apoE receptors.
FIG. 7 Model for the proposed role of apoE receptors in A b -induced astrocyte activation. LRP mediates A b -induced changes in astrocyte morphology and increased expression of IL-1 b . LPS and dbcAMPproduce similar effects independent of apoE receptors. The LDLR mediates the A b -induced increase in cell-associated apoE and the decrease in apoE in the conditioned medium. Although a portion of these changes may be the result of increased reuptake of apoE by the LDLR, the total amount of apoE also increases. This suggests that the LDLR may be linked to an intracellular pathway that signals an increase in apoE translation and/or a decrease in degradation (steady-state apoE mRNA levels do not change). To effect these changes in astrocyte activation and apoE levels, A b may be interacting directly with apoE receptors or via an interaction with an apoE receptor ligand. A b -induced changes in apoJ appear to be independent of apoE receptors.CC-BY · From the PDF

Verification

Claims the paper makes

33 Own result · 22 Own interpretation · 10 Partly supported · 10 No full text of the sources · 4 Supported · 3 Supported so far · 1 Couldn’t confirm · 1 Not checked yet · 1 Own method · 1 No basis given · accuracy not yet measured

Show all 53 claims

  • It may state two separate claims as one. 19
  • Probably not a substantial claim. 14
  • The quote only partly states this claim. 3
33 of 33
  • The paper relies on this without support.

    The effects of the aged Aβ1-42 preparation on astrocytes are attributable to Aβ and not to other components or contaminants in the preparation.

    “A␤ 1-42 aged according to this protocol is a mixture of fibrils and soluble globular aggregates, and is active to astrocytes (37,38) and toxic to neurons (26,27).”
  • The paper relies on this without support.

    RAP specifically inhibits apoE receptors (LRP/LDLR) without affecting other pathways, so RAP-sensitive effects can be attributed to apoE receptors.

    “RAP blocks A␤-induced astrocyte activation.”
    “The A␤-stimulated changes in apoJ persist in the presence of 1 M RAP and the changes in apoE persist in the presence of 70 nM RAP, both treatments that block morphological activation.”
  • The paper relies on this without support.

    Cultured rat cortical astrocytes respond to Aβ in a way that models relevant astrocyte responses in vivo.

    “A␤-induced changes in cultured astrocytes appear to involve both a novel mechanism of action and a unique set of responses.”
3 of 3

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Citations

Cites

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Research works printed but not linked: 1

  1. Kounnas, 1994, In Vivo, 8, 343

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Metadata

Authors
LaDu, M. J., Shah, J. A., Reardon, C. A., Getz, G. S., Bu, G., Hu, J., Guo, L., & Van Eldik, L. J.
Affiliations
  • Northwestern University (US)
  • University of Chicago (US)
  • Washington University in St. Louis (US)
Venue
Journal of Biological Chemistry
Publisher
Elsevier BV
Published
2000-10
Volume
275
Issue
43
Pages
33974-33980
ISSN
0021-9258 (ISSN-L)
OpenAlex
W1967940232
Cited by
103
References
61
Citations by year
2025: 1 · 2024: 6 · 2023: 2 · 2021: 3 · 2018: 1 · 2017: 4 · 2016: 5 · 2014: 4 · 2013: 2 · 2012: 9
FWCI
1.75
Type
journal article
Language
en
Open access
Locations
  • Journal of Biological Chemistry (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • Rare & Special e-Zone (The Hong Kong University of Science and Technology) (submittedVersion)
Funders
  • Brain Research Foundation
  • American Health Assistance Foundation
  • National Institutes of Health (AG13939)
  • National Institute on Aging (P01AG015501, AG13939, AG16776)
  • National Eye Institute (F31EY021714)
Topics
  • Life Sciences › Neuroscience › Cellular and Molecular Neuroscience › Alzheimer's disease research and treatments
  • Life Sciences › Neuroscience › Neurology › Neuroinflammation and Neurodegeneration Mechanisms
  • Life Sciences › Neuroscience › Cellular and Molecular Neuroscience › Neuroscience and Neuropharmacology Research
Keywords
apolipoprotein E receptor, amyloid-beta, astrocyte activation, clusterin, LDL receptor, receptor-associated protein, IL-1β, lipopolysaccharide, dibutyryl cyclic AMP, neuroinflammation, Alzheimer's disease
MeSH terms
Animals, Apolipoproteins E, Astrocytes, Cells, Cultured, Glycoproteins, Interleukin-1, Receptors, Immunologic, Receptors, LDL, Amyloid beta-Peptides, Rats, Sprague-Dawley, Receptors, Lipoprotein, Molecular Chaperones, Low Density Lipoprotein Receptor-Related Protein-1, Clusterin, Rats

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