Your brain slows down as you age. You may misplace your glasses or have difficulty picking up a new skill. Now, rodent experiments offer hope that some of these declines may be reversible—but it will take courage.
A new study demonstrates that transplanting gut microbes in the form of faeces from young to old mice can rewind the clock on the aging brain.
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Our intestines’ bacteria have an effect on everything from our daily moods to our overall health. Additionally, our “gut microbiome” changes over the course of our lives. However, while some studies have demonstrated that young blood can rejuvenate elderly mice, the microbiome’s effect on age-related declines has been unclear.
To determine whether a young microbiome could reverse signs of aging, researchers transplanted faeces from 3- to 4-month-old mice, which are the equivalent of young adults, into 20-month-old mice, which are considered elderly by mouse standards. The scientists used a feeding tube to administer a faeces slurry to the elderly mice twice a week for eight weeks. As controls, old mice received transplants from other old mice and young mice received transplants from young mice.
The team noticed that when older mice were given young mouse microbes, their gut microbiomes began to resemble those of the younger mice. Enterococcus, a common gut microbe, became significantly more abundant in old mice, just as it is in young mice.
Additionally, there were changes in the brain. The hippocampus—a region of the brain associated with learning and memory—became more physically and chemically similar to the hippocampus of young mice as the mice aged. The elderly mice that received young mouse poop also improved their ability to solve mazes faster and retained the maze layout better on subsequent attempts, the team reports today in Nature Aging. None of these effects were observed in mice that had been fed old mouse faeces.
“It’s almost like … we could press the rewind button on the aging process,” says John Cryan, a neuroscientist at University College Cork who led the new study.
However, when older mice were given young faeces, certain things did not change significantly. Numerous types of gut bacteria remained unchanged, for example, and the old mice did not become more social, which Cryan found surprising given his prior experience with the microbiome influencing social interactions.
Arya Biragyn, a molecular biologist at the National Institute on Aging, wishes the team had done more to demonstrate that the microbiomes of older mice had changed. Because the researchers examined the gut microbiome shortly after the transplants, there is no way to determine whether the new microbes had established a permanent home or were simply passing through, he argues.
Additionally, Gibbons notes that the field of faecal transplantation in mice is still a mixed bag. While some studies have concluded that such procedures are beneficial, he notes that at least one has concluded that they can result in cognitive decline.
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Cryan cautions against applying the findings to humans prematurely, given that the study was entirely based on rodents. Nonetheless, he argues, the work provides hope.
“The good thing about your microbiome—as opposed to your genome—is that you can change it.”
Image Credit: Getty