Another Piece of the Alzheimer’s Puzzle?
A breakdown of memory processes in humans can lead to conditions such as Alzheimer’s disease and dementia. By looking at the simpler brain of a honeybee, per a study recently published in Frontiers in Molecular Neuroscience, researchers move a step closer to understanding the different processes behind long-term memory formation.
The honeybee can form complex memories through processes much like those occurring in human brains. The new study shows that DNA methylation is a molecular mechanism that regulates memory specificity and relearning, and therefore, could control how experiences are integrated over a lifetime.
“We show that DNA methylation is one molecular mechanism that regulates memory specificity and relearning and through which experiences of the organism could be accumulated and integrated over their lifetime,” says Stephanie Biergans, PhD, first author of the study and a researcher at the University of Queensland in Australia.
“Honeybees have an amazing capacity to learn and remember,” she says. “They can count up to four and orient themselves by learning patterns and landmarks. They are also social insects that interact, teach, and learn, making them successful foragers. Bees remember how to find a food source, how good the source was, and how to return to the hive.”
The honeybee can form complex memories through processes much like those happening in human brains. But the honeybee brain is simpler and they have a smaller genome. This makes them an ideal model for investigating how the different processes needed for long-term memories occur.
Scientists know that when a memory is formed, molecular changes can trigger physical changes to the brain, including new or altered neural connections and activity. These build up over a lifetime to create our long-term memory.
One series of molecular changes that can occur due to experience or environmental changes and that affect memory formation is the differential expression of certain genes, mediated, among others, through processes collectively called epigenetic mechanisms. They regulate gene expression through modifications of the DNA or its associated proteins, without changing the genes themselves.
“We knew that DNA methylation is an epigenetic process that occurs in the brain and is related to memory formation,” Biergans explains. “When we block this process in honeybees, it affects how they remember.”
Biergans taught two groups of honeybees to expect sugar in the presence of a particular smell. One group learned over an extended period, being exposed to the sugar and smell together many times. The other group was given the combination only once. Using an inhibitor compound, Biergans halted DNA methylation in some bees in each group. The bees’ memory formation in the two groups was tested and compared with and without DNA methylation occurring. By changing the smell that accompanied the food, Biergans and colleagues found that DNA methylation affects how a bee can relearn.
“When the bees were presented with sugar and a smell many times together, the presence of DNA methylation increased memory specificity and they were less responsive to a novel odor. On the other hand, when introduced to the combination only once, DNA methylation decreased specificity,” she says.
For a foraging honeybee this makes total sense. When a bee gets food from a single flower, it’s not worthwhile remembering how it smells. That bee will have a general memory of the site, but will shop around and try other flowers; there is no specificity to its foraging. But when each flower with that smell proves over and over to be a good source of nourishment, the bee will stick to those flowers and seek them out.
DNA methylation also occurs in the human brain, and the team’s findings are key to understanding how we remember—and how we forget.
“By understanding how changes to the epigenome accumulate, manifest, and influence brain function, we may in the future be able to develop treatments for brain diseases that develop over a lifetime. There is thought to be a genetic predisposition for some conditions, such as Alzheimer’s and dementia, but in many cases environmental factors determine whether the disease will manifest,” Biergans says.
— Source: Frontiers in Molecular Neuroscience