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In vivo induction of membrane damage by β-amyloid peptide oligomers
Carl Julien1,2, Colson Tomberlin1, Christine M Roberts1
1Department of Integrative Physiology, University of Colorado at Boulder, Boulder, CO, USA.
Abstract:
Exposure to the β-amyloid peptide (Aβ) is toxic to neurons and other cell types, but the mechanism(s) involved are still unresolved. Synthetic Aβ oligomers can induce ion-permeable pores in synthetic membranes, but whether this ability to damage membranes plays a role in the ability of Aβ oligomers to induce tau hyperphosphorylation, or other disease-relevant pathological changes, is unclear. To examine the cellular responses to Aβ exposure independent of possible receptor interactions, we have developed an in vivo C. elegans model that allows us to visualize these cellular responses in living animals. We find that feeding C. elegans E. coli expressing human Aβ induces a membrane repair response similar to that induced by exposure to the CRY5B, a known pore-forming toxin produced by B. thuringensis. This repair response does not occur when C. elegans is exposed to an Aβ Gly37Leu variant, which we have previously shown to be incapable of inducing tau phosphorylation in hippocampal neurons. The repair response is also blocked by loss of calpain function, and is altered by loss-of-function mutations in the C. elegans orthologs of BIN1 and PICALM, well-established risk genes for late onset Alzheimer's disease. To investigate the role of membrane repair on tau phosphorylation directly, we exposed hippocampal neurons to streptolysin O (SLO), a pore-forming toxin that induces a well-characterized membrane repair response. We find that SLO induces tau hyperphosphorylation, which is blocked by calpain inhibition. Finally, we use a novel biarsenical dye-tagging approach to show that the Gly37Leu substitution interferes with Aβ multimerization and thus the formation of potentially pore-forming oligomers. We propose that Aβ-induced tau hyperphosphorylation may be a downstream consequence of induction of a membrane repair process.
Insights
Beta-amyloid (Aβ) peptide exposure triggers a cellular membrane repair response, similar to pore-forming toxins. This response, linked to Alzheimer's disease risk genes, may drive tau hyperphosphorylation.
Area of Science:
- Neuroscience
- Cell Biology
- Toxicology
Background:
- The precise mechanisms by which beta-amyloid (Aβ) peptide exerts its neurotoxicity remain incompletely understood.
- While synthetic Aβ oligomers can form pores in membranes, their role in Aβ-induced pathological changes like tau hyperphosphorylation is unclear.
- Investigating cellular responses to Aβ independent of receptor interactions is crucial.
Purpose of the Study:
- To develop and utilize an in vivo model to study cellular responses to Aβ exposure.
- To determine if Aβ-induced membrane damage and subsequent repair pathways contribute to tau hyperphosphorylation.
- To explore the involvement of Alzheimer's disease risk genes in Aβ-mediated cellular responses.
Main Methods:
- Development of an in vivo C. elegans model for visualizing cellular responses to Aβ.
- Exposure of C. elegans to wild-type and mutant Aβ, and pore-forming toxins (CRY5B, streptolysin O).
- Genetic analysis using loss-of-function mutations in C. elegans orthologs of BIN1 and PICALM, and calpain inhibition.
- Biarsenical dye-tagging to assess Aβ multimerization.
Main Results:
- Aβ feeding in C. elegans induced a membrane repair response, mimicking that caused by the pore-forming toxin CRY5B.
- This Aβ-induced repair response was absent with a Gly37Leu Aβ variant and blocked by calpain inhibition.
- Mutations in C. elegans BIN1 and PICALM orthologs altered the Aβ-induced repair response.
- Streptolysin O (SLO) induced tau hyperphosphorylation in hippocampal neurons, inhibited by calpain inhibitors.
- The Gly37Leu substitution impaired Aβ multimerization, suggesting reduced pore-forming potential.
Conclusions:
- Aβ-induced tau hyperphosphorylation may result from the activation of a cellular membrane repair process.
- The findings implicate membrane damage and repair mechanisms in Aβ toxicity and Alzheimer's disease pathogenesis.
- Genetic factors associated with Alzheimer's disease risk, such as BIN1 and PICALM, are involved in the cellular response to Aβ-induced membrane stress.
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