Cited by 657Alzheimer's disease research and treatmentsNeuroscience and Neuropharmacology ResearchNeuroinflammation and Neurodegeneration Mechanisms

Protection of synapses against Alzheimer's-linked toxins: Insulin signaling prevents the pathogenic binding of Aβ oligomers

Open access
De Felice, Fernanda G., Vieira, Marcelo N. N., Bomfim, Theresa R., Decker, Helena, Velasco, Pauline T., Lambert, Mary P., Viola, Kirsten L., Zhao, Wei-Qin +2 more·2009·Proceedings of the National Academy of Sciences

Abstract

Synapse deterioration underlying severe memory loss in early Alzheimer's disease (AD) is thought to be caused by soluble amyloid beta (Aβ) oligomers. Mechanistically, soluble Aβ oligomers, also referred to as Aβ-derived diffusible ligands (ADDLs), act as highly specific pathogenic ligands, binding to sites localized at particular synapses. This binding triggers oxidative stress, loss of synaptic spines, and ectopic redistribution of receptors critical to plasticity and memory. We report here the existence of a protective mechanism that naturally shields synapses against ADDL-induced deterioration. Synapse pathology was investigated in mature cultures of hippocampal neurons. Before spine loss, ADDLs caused major downregulation of plasma membrane insulin receptors (IRs), via a mechanism sensitive to calcium calmodulin-dependent kinase II (CaMKII) and casein kinase II (CK2) inhibition. Most significantly, this loss of surface IRs, and ADDL-induced oxidative stress and synaptic spine deterioration, could be completely prevented by insulin. At submaximal insulin doses, protection was potentiated by rosiglitazone, an insulin-sensitizing drug used to treat type 2 diabetes. The mechanism of insulin protection entailed a marked reduction in pathogenic ADDL binding. Surprisingly, insulin failed to block ADDL binding when IR tyrosine kinase activity was inhibited; in fact, a significant increase in binding was caused by IR inhibition. The protective role of insulin thus derives from IR signaling-dependent downregulation of ADDL binding sites rather than ligand competition. The finding that synapse vulnerability to ADDLs can be mitigated by insulin suggests that bolstering brain insulin signaling, which can decline with aging and diabetes, could have significant potential to slow or deter AD pathogenesis.

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Written from the paper’s full text.

TL;DR

In mature hippocampal cultures, insulin signaling prevented Aβ oligomer (ADDL) binding, oxidative stress, insulin receptor loss, and spine degeneration, with protection requiring insulin receptor tyrosine kinase activity rather than simple ligand competition. Rosiglitazone potentiated submaximal insulin’s protection, suggesting that enhancing CNS insulin signaling may defend synapses against Alzheimer’s-linked toxins.

Key findings

  • ADDLs caused loss of surface insulin receptors (IRs): surface-exposed IR levels decreased by 22% after 30 min and 68% after 3 h of exposure to 100 nM ADDLs.
  • The CK2 inhibitor DMAT completely blocked ADDL-induced loss of both IRs and NMDA receptors; the CaMKII inhibitor KN93 afforded partial protection.
  • Insulin at 100 nM partially prevented and 1 μM completely blocked ADDL-induced dendritic IR loss; 1 μM insulin caused a major (≈70%) blockade of ADDL binding, and 100 nM insulin + 10 μM rosiglitazone produced IR levels similar to control or 1 μM insulin.
  • Insulin prevented ADDL-induced oxidative stress and 24-h spine degeneration; protection required IR activity, because AG1024 (5 μM) abolished insulin’s ability to block ADDL binding and increased binding when added alone or with insulin.

Methods

  • Primary mature hippocampal neuronal cultures were used after 21 DIV and treated at 37 °C for 3 h with 100 nM ADDLs or vehicle; insulin (100 nM or 1 μM) or rosiglitazone (10 μM) was added 30 min before ADDLs, and AG1024 (5 μM) was added 30 min before insulin.
  • ADDLs were prepared from Aβ1–42; outcomes were assessed by surface biotinylation/Western blot, immunocytochemistry with IRα and NU4 anti-ADDL antibodies, phalloidin labeling of spines, and dihydroethidium (DHE) for reactive oxygen species.
  • Immunofluorescence intensities were analyzed with NIH ImageJ.

Limitations

  • The paper states that the nature of the ADDL binding sites “has yet to be determined” and that future identification of proteins lost from the membrane in response to insulin could provide insight into them.
  • Evident from the text: all experiments were performed in mature hippocampal neuronal cultures; no in vivo or human data are reported in this study.

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

Integrity signals

Registry

Crossref · 10.1073/pnas.0809158106

Cites

51 of 51 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

0 of 1 cited sources checked · 0 supported · 0 flagged

  • Findingown data

    DMAT, a CK2 inhibitor, completely blocked ADDL-induced loss of both IRs and NMDARs from dendrites of hippocampal neurons.

    “we found that DMAT, a CK2 inhibitor, completely blocked ADDL-induced loss of both IRs and NMDARs from the dendrites of hippocampal neurons”
    Quote in the paperSubstantial claim
  • Interpretationown data

    ADDLs have a selective impact in accelerating the endocytosis of particular surface proteins, such as IRs.

    “These results are consistent with the notion that ADDLs have a selective impact in accelerating the endocytosis of particular surface proteins, such as IRs.”
    Quote in the paperSubstantial claim
  • Interpretationown data

    Decreased binding is the result of downregulation of ADDL binding sites through a mechanism requiring IR tyrosine kinase activity.

    “Decreased binding is the result of downregulation of ADDL binding sites through a mechanism requiring insulin receptor (IR) tyrosine kinase activity.”
    Quote in the paperSubstantial claim
  • Interpretationown data

    The beneficial effect of insulin in AD derives at least in part from an acute decrease in ADDL synaptotoxicity.

    “Results here support the hypothesis that the beneficial effect of insulin in AD derives at least in part from an acute decrease in ADDL synaptotoxicity.”
    Quote in the paperSubstantial claim
  • Interpretationown data

    The current finding that rosiglitazone potentiates the ability of insulin to protect synapses against ADDLs provides a plausible mechanism of protection.

    “A plausible mechanism of protection is provided by the current finding that rosiglitazone potentiates the ability of insulin to protect synapses against ADDLs.”
    Quote in the paperSubstantial claim
  • May combine two claims. 7
  • Classified as probably not a substantial claim. 1
  • May combine two claims.

    Findingown data

    AG1024 caused significant increases in neuronal ADDL binding both when added alone and in the presence of exogenous insulin.

    “In fact, AG1024 caused significant increases in neuronal ADDL binding both when AG1024 was added alone and in the presence of exogenous insulin.”
    Quote in the paperSubstantial claim
  • Classified as probably not a substantial claim.

    Premisenone given

    ADDLs are soluble neurotoxins putatively responsible for the synaptic deterioration underlying Alzheimer's memory failure.

    “We have identified a unique molecular mechanism that protects CNS neurons against ADDLs, soluble neurotoxins putatively responsible for the synaptic deterioration underlying Alzheimer's memory failure.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Interpretationreasoning

    Physiological insulin and pathological ADDLs negatively regulate the abundance of each other's binding sites, creating a competitive balance between synapse survival and degeneration.

    “Thus, physiological insulin and pathological ADDLs negatively regulate the abundance of each other's binding sites, creating a competitive balance between synapse survival and degeneration.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Interpretationown data

    The mechanism of protection does not involve simple competition between ADDLs and insulin for a common binding site on the neuronal surface, but rather is a signaling-dependent downregulation of ADDL binding sites.

    “Thus the mechanism of protection does not involve simple competition between ADDLs and insulin for a common binding site on the neuronal surface, but rather is a signaling-dependent downregulation of ADDL binding sites.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Interpretationown data

    Insulin blocks ADDL binding to synapses, thereby preventing the ensuing neurotoxicity.

    “Results show that insulin blocks ADDL binding to synapses, thereby preventing the ensuing neurotoxicity.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Interpretationown data

    Loss of insulin receptors precedes and is not a consequence of overall collapse and retraction of synaptic spines.

    “This indicates that loss of insulin receptors precedes and is not a consequence of overall collapse and retraction of synaptic spines.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Premisecitation

    An elevated risk for AD exists in type 2 diabetes patients, who manifest deficient CNS insulin signaling.

    “An elevated risk for AD also exists in type 2 diabetes patients, who manifest deficient CNS insulin signaling.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [31] Craft S. Insulin resistance and Alzheimer's disease pathogenesis: potential mechanisms and implications for treatment. Curr Alzheimer Res. 2007;4:147–152. doi: 10.2174/156720507780362137. [[DOI](https://doi.org/10.2174/156720507780362137)] [[PubMed](https://pubmed.ncbi.nlm.nih.gov/17430239/)] [[Google Scholar](https://scholar.google.com/scholar_lookup?journal=Curr%20Alzheimer%20Res&title=Insulin%20resistance%20and%20Alzheimer's%20disease%20pathogenesis:%20potential%20mechanisms%20and%20implications%20for%20treatment&author=S%20Craft&volume=4&publication_year=2007&pages=147-152&pmid=17430239&do source

      Not checked in the free run.

  • May combine two claims.

    Interpretationown data

    Insulin signaling downregulates ADDL binding, while ADDLs downregulate IRs.

    “Insulin signaling downregulates ADDL binding, while ADDLs downregulate IRs.”
    Quote in the paperSubstantial claim
8 of 8

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

  • Insulin receptor internalization occurs by a mechanism mediated by casein kinase 2 and Ca2+/calmodulin-dependent kinase 2, which also are involved in ADDL-induced internalization of NMDA receptors.

    “Internalization occurs by a mechanism mediated by casein kinase 2 (CK2) and Ca2+/calmodulin-dependent kinase 2 (CaMK II), which also are involved in ADDL-induced internalization of NMDA receptors (De Felice et al., 2009).”
  • Aβ oligomers induce a striking redistribution of insulin receptors, causing their internalization from dendritic membranes and accumulation in the cell body, which renders neurons insulin resistant.

    “Aβ oligomers induce a striking redistribution of IRs, causing their internalization from dendritic membranes and accumulation in the cell body. This renders neurons insulin resistant (De Felice et al., 2009; De Felice et al., 2008; Zhao et al., 2008).”
  • Insulin itself blocks the pathological binding of Aβ oligomers and the resulting redistribution of insulin receptors and synapse loss.

    “insulin itself blocks the pathological binding of Aβ oligomers and the resulting redistribution of IRs and synapse loss (De Felice et al., 2009).”
  • Clustering of oligomers at synapses shows a cause-and-effect relationship with characteristic Alzheimer neuropathologies: AD-type tau hyperphosphorylation, redistribution of insulin receptors, spine loss and oxidative stress are manifest exclusively in neurons showing synapses targeted by oligomers.

    “Clustering of oligomers at synapses, moreover, shows a cause-and-effect relationship with characteristic Alzheimer neuropathologies. AD type tau hyperphosphorylation (De Felice et al., 2008), redistribution of insulin receptors (De Felice et al., 2009; Zhao et al., 2008), spine loss (Lacor et al., 2007) and oxidative stress (De Felice et al., 2007; Decker et al., 2010a) are manifest exclusively in”
  • Pharmacological experiments indicate involvement of CaMKII and casein kinase II in the receptor trafficking dysfunction.

    “pharmacological experiments indicate involvement of CaMKII and casein kinase II (De Felice et al., 2009).”

Cites

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Authors
De Felice, F. G., Vieira, M. N. N., Bomfim, T. R., Decker, H., Velasco, P. T., Lambert, M. P., Viola, K. L., Zhao, W.-Q., Ferreira, S. T., & Klein, W. L.
Affiliations
  • Department of Neurobiology and Physiology, Northwestern University, Evanston, IL 60208; and
  • Universidade Federal do Rio de Janeiro (BR)
  • Instituto de Bioquímica Médica and
  • Northwestern University (US)
Venue
Proceedings of the National Academy of Sciences
Published
2009-02-10
Volume
106
Issue
6
Pages
1971-1976
ISSN
  • 0027-8424 (ISSN-L)
  • 1091-6490
OpenAlex
W2097335530
Cited by
657
References
51
Citations by year
2026: 11 · 2025: 27 · 2024: 17 · 2023: 20 · 2022: 30 · 2021: 41 · 2020: 41 · 2019: 42 · 2018: 44 · 2017: 42 · 2016: 44 · 2015: 53 · 2014: 44 · 2013: 57 · 2012: 46
FWCI
31.69
Type
journal article
Language
en
Open access
Locations
  • Proceedings of the National Academy of Sciences (publishedVersion)
  • PubMed Central (publishedVersion)
  • PubMed (publishedVersion)
Funders
  • Foundation for the National Institutes of Health
  • Howard Hughes Medical Institute
  • Alzheimer's Association
  • American Health Assistance Foundation
  • National Institute on Aging (R01AG022547, R01-AG22547, R01-AG18877, R01AG018877)
Topics
  • Health Sciences › Medicine › Physiology › Alzheimer's disease research and treatments
  • Life Sciences › Neuroscience › Cellular and Molecular Neuroscience › Neuroscience and Neuropharmacology Research
  • Life Sciences › Neuroscience › Neurology › Neuroinflammation and Neurodegeneration Mechanisms
Keywords
Alzheimer's disease, amyloid-beta oligomers, insulin signaling, insulin receptor, synaptic plasticity, oxidative stress, CaMKII, casein kinase 2, rosiglitazone, insulin receptor tyrosine kinase, hippocampal neurons, memory loss
MeSH terms
Rosiglitazone, Alzheimer Disease, Animals, Cattle, Cells, Cultured, Hippocampus, Humans, Insulin, Neurons, Protein Binding, Receptor, Insulin, Synapses, Signal Transduction, Amyloid beta-Peptides, Oxidative Stress, Dimerization, Protective Agents, Thiazolidinediones

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