Hippocampal DNA Methylation Promotes Contextual Fear Memory Persistence by Facilitating Systems Consolidation and...

Area of Science:

• Neuroscience
• Molecular Biology
• Epigenetics

Background:

• Long-term fear memory storage involves systems consolidation, a gradual reorganization of brain regions where memories shift from the hippocampus to the neocortex.
• While hippocampal activity drives this memory transfer, the underlying molecular mechanisms, particularly the role of DNA methylation, remain largely unknown.
• DNA methylation changes are observed in the hippocampus and cortex during fear memory formation, but their causal role in memory persistence and systems consolidation is unclear.

Purpose of the Study:

• To investigate the causal role of hippocampal DNA methylation in the persistence of fear memories.
• To determine if DNA methylation in the hippocampus influences the process of systems consolidation and long-term memory storage.
• To identify the molecular and transcriptional changes associated with DNA methylation in fear memory.

Main Methods:

• Investigated DNA methylation's role using recombinant adeno-associated virus (rAAV)-mediated gene transfer to overexpress or knockdown DNA methyltransferase DNMT3A2 in the mouse dorsal hippocampus.
• Employed engram tagging and manipulation tools to examine the stabilization of fear memory traces in the cortex.
• Conducted RNA sequencing to identify transcriptional alterations induced by DNMT3A2 overexpression.

Main Results:

• Overexpression of hippocampal DNMT3A2 resulted in persistent fear memory, while its knockdown impaired remote memory recall.
• RNA sequencing indicated that DNMT3A2 overexpression altered the expression of genes regulating synaptic transmission.
• Genetic manipulation confirmed that hippocampal DNA methylation promotes the transfer of fear memory traces to the cortex and enhances the stabilization of these cortical memory traces.

Conclusions:

• Hippocampal DNA methylation is a key regulator of long-term persistent fear memory storage.
• DNA methylation facilitates the crucial transfer of memory traces from the hippocampus to the neocortex and stabilizes these traces in the cortex.
• These findings establish DNA methylation as a critical molecular mechanism underlying systems consolidation and the enduring nature of fear memories.