Memories are made by breaking DNA — and fixing it (in mice)

From the article:

When a long-term memory forms, some brain cells experience a rush of electrical activity so strong that it snaps their DNA. Then, an inflammatory response kicks in, repairing this damage and helping to cement the memory, a study in mice shows.

The findings, published on 27 March in Nature, are “extremely exciting”, says Li-Huei Tsai, a neurobiologist at the Massachusetts Institute of Technology in Cambridge who was not involved in the work. They contribute to the picture that forming memories is a “risky business”, she says. Normally, breaks in both strands of the double helix DNA molecule are associated with diseases including cancer. But in this case, the DNA damage-and-repair cycle offers one explanation for how memories might form and last.

It also suggests a tantalizing possibility: this cycle might be faulty in people with neurodegenerative diseases such as Alzheimer’s, causing a build-up of errors in a neuron’s DNA, says study co-author Jelena Radulovic, a neuroscientist at the Albert Einstein College of Medicine in New York City.

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TLR9 was most active in a subset of hippocampal neurons in which DNA breaks resisted repair. In these cells, DNA repair machinery accumulated in an organelle called the centrosome, which is often associated with cell division and differentiation. However, mature neurons don’t divide, Radulovic says, so it is surprising to see centrosomes participating in DNA repair. She wonders whether memories form through a mechanism that is similar to how immune cells become attuned to foreign substances that they encounter. In other words, during damage-and-repair cycles, neurons might encode information about the memory-formation event that triggered the DNA breaks, she says.

There are some more details in this article:

DNA Damage and Inflammation Key to Memory Formation (Neuroscience News)

Contrary to previous beliefs associating inflammation with neurological diseases, this study highlights inflammation’s critical role in memory formation through the activation of the Toll-Like Receptor 9 (TLR9) pathway following DNA damage in hippocampal neurons.

These findings not only challenge conventional views on brain inflammation but also caution against indiscriminate inhibition of the TLR9 pathway, given its importance in memory encoding and the potential risks of genomic instability.

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During the week required to complete the inflammatory process, the mouse memory-encoding neurons were found to have changed in various ways, including becoming more resistant to new or similar environmental stimuli.

“This is noteworthy,” said Dr. Radulovic, “because we’re constantly flooded by information, and the neurons that encode memories need to preserve the information they’ve already acquired and not be ‘distracted’ by new inputs.”

Importantly, the researchers found that blocking the TLR9 inflammatory pathway in hippocampal neurons not only prevented mice from forming long-term memories but also caused profound genomic instability, i.e, a high frequency of DNA damage in these neurons.