Modeling of neuronal hyperexcitability modulated by Aβ-mediated astrocyte dysfunction

Area of Science:

• Neuroscience
• Computational Biology
• Pathophysiology of Alzheimer's Disease

Background:

• Neuronal hyperexcitability is an early hallmark of Alzheimer's disease (AD).
• The precise mechanisms linking amyloid-beta peptide (Aβ)-induced astrocyte dysfunction to neuronal hyperexcitability remain incompletely understood.
• Astrocytes play a critical role in regulating synaptic transmission via glutamate handling.

Purpose of the Study:

• To develop a neurocomputational model of the astrocyte-neuron tripartite synapse to investigate Aβ-mediated astrocyte dysfunction.
• To elucidate the impact of altered astrocytic glutamate pathways on neuronal excitability in the context of AD.
• To explore the relationship between astrocyte calcium oscillations and neuronal hyperexcitability.

Main Methods:

• Developed a computational model simulating presynaptic neuron, postsynaptic neuron, and astrocyte interactions.
• Incorporated astrocytic glutamate transporters (GLT-syn, GLT-ess), metabotropic glutamate receptors (mGluR), and gliotransmitter release (Glio-Rel).
• Performed numerical simulations to analyze the effects of Aβ-induced changes in astrocytic function on neuronal activity.

Main Results:

• Simulations demonstrated that Aβ-induced down-regulation of glutamate transporters and increased gliotransmitter release lead to neuronal hyperexcitability.
• Observed increased neuronal firing rates, enhanced presynaptic glutamate release, and elevated postsynaptic calcium levels, consistent with experimental findings.
• Identified specific pathways (Glio-Rel, GLT-ess, GLT-syn) through which Aβ affects presynaptic and postsynaptic neuronal hyperexcitation.
• Revealed a strong positive correlation between neuronal firing rates and astrocyte calcium oscillation amplitude/frequency.

Conclusions:

• The computational model supports experimental findings on Aβ-mediated astrocyte dysfunction causing neuronal hyperexcitability in AD.
• Aβ primarily induces presynaptic hyperexcitation via Glio-Rel and GLT-ess pathways, and postsynaptic hyperexcitation via GLT-syn, Glio-Rel, and GLT-ess pathways.
• Highlights a significant link between astrocyte calcium dysregulation and neuronal hyperexcitability in Alzheimer's disease pathogenesis.