Formation of memory assemblies through the DNA-sensing TLR9 pathway

Area of Science:

• Neuroscience
• Molecular Biology
• Genetics

Background:

• Hippocampal neurons form memory circuits through molecular adaptations.
• These adaptations can lead to transient DNA damage.

Purpose of the Study:

• Investigate molecular events in hippocampal neurons after learning.
• Determine the role of Toll-like receptor 9 (TLR9) in memory and DNA repair.

Main Methods:

• Observed DNA damage and cellular responses in hippocampal CA1 neurons post-learning.
• Utilized neuron-specific knockdown of Tlr9 in a fear conditioning model.
• Assessed gene expression changes and centrosome function.

Main Results:

• Identified persistent double-stranded DNA (dsDNA) breaks and nuclear envelope ruptures in specific neuronal clusters after learning.
• Observed an inflammatory phenotype with TLR9 activation and DNA damage repair complexes.
• Tlr9 knockdown impaired memory and blunted learning-induced gene expression changes.
• TLR9 is crucial for centrosome function, DNA repair, and perineuronal net formation.

Conclusions:

• A novel cascade links learning-induced DNA damage to TLR9-mediated repair and memory circuit recruitment.
• Compromised TLR9 function creates a pathway to genomic instability and cognitive impairments.
• Maintaining TLR9 signaling integrity is a potential strategy for preventing neurocognitive deficits.