Disrupted cross-laminar cortical processing in β amyloid pathology precedes cell death

Area of Science:

• Neuroscience
• Alzheimer's Disease Research
• Synaptic Plasticity

Background:

• Alzheimer's disease (AD) is characterized by cognitive and memory decline.
• Neuronal network disruption is a key correlate of cognitive impairment in AD patients.
• The role of synaptic disconnections versus cell death in early AD pathogenesis is debated.

Purpose of the Study:

• To investigate if functional synaptic disconnections, caused by beta-amyloid (Aβ) accumulation, precede cell death in causing cognitive impairments in AD.
• To identify the specific circuit-level changes underlying early cognitive deficits in AD.

Main Methods:

• Utilized the transgenic 5xFAD mouse model of Alzheimer's disease.
• Employed single-cell resolution mapping of neuronal thallium uptake to assess electrical activity.
• Conducted laminar analysis of cortical circuit function using current source density analysis.
• Administered the glutaminyl cyclase inhibitor PQ 529 to assess its therapeutic potential.

Main Results:

• Pyramidal cell electrical activity breakdown was observed in cortical layer V before significant cell death in 5xFAD mice.
• Treatment with PQ 529 partially preserved pyramidal cell activity, suggesting a role for pyroglutamate-modified Aβ species.
• Early loss of excitatory synaptic input in infragranular layers and pathological recurrent activations in supragranular layers were identified.
• These circuit disruptions correlated with a decline in contextual fear learning.

Conclusions:

• Functional synaptic disconnections within cortical microcircuits, rather than initial cell death, are likely drivers of early cognitive decline in Alzheimer's disease.
• Pathological beta-amyloid accumulation, potentially including pyroglutamate-modified forms, impairs neuronal activity and synaptic function.
• Targeting specific molecular pathways may offer therapeutic benefits for preserving cognitive function in early AD.