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Enterococcus species like the one pictured here became much more abundant in older mice as a result of faecal transplants of young people.
Eye of Science / Scientific Source
By Rachel Fritts
As you age, your brain slows down. You may forget where you left your glasses or have a hard time learning a new skill. Now, the rodent experiments give hope that some of these declines could be reversed, but it takes guts. New research shows that a transplant of gut microbes, in the form of feces, from young mice to older mice can set back the aging brain.
The study is “a tour de force” for the breadth of data it has collected, says Sean Gibbons, a gut microbe researcher at the Institute for Systems Biology. Still, he says, more work needs to be done before anyone plans to do something similar with humans.
Bacteria in our intestines influence everything from our daily mood to our overall health. This “gut microbiome” also changes over the course of our lives. But while some studies have shown that young blood can have rejuvenating effects in older mice, the microbiome’s impact on age-related declines is unclear.
To test whether a young microbiome could reverse the signs of aging, the researchers took stool samples from mice 3 to 4 months old, the equivalent of young adults, and transplanted them into animals 20 months old, according to mouse standards. The scientists gave the old mice a feces porridge through a feeding tube twice a week for 8 weeks. As controls, the old mice were transplanted from other old mice and the young from young.
The first thing the team noticed was that the gut microbiomes of the old mice that received young mouse microbes started to resemble those of the younger ones. The common gut microbe Enterococcus has become much more abundant in older mice, just like in young mice, for example.
There were also changes in the brain. The hippocampus of older mice, a region of the brain associated with learning and memory, has become more physically and chemically similar to the hippocampus of younger mice. Old mice who were given young mouse droppings also learned to solve mazes faster and remembered the maze layout better on subsequent attempts, the team reports today in Natural aging. None of these effects were observed in old mice given the droppings of old mice.
“It’s almost like… we can hit the rewind button on the aging process,” says John Cryan, a neuroscientist at University College Cork who led the new study.
However, some things did not change significantly for the older mice given young droppings. Many types of gut bacteria have stayed the same, for example, and old mice haven’t gotten more social, which Cryan found surprising as he saw the microbiome impact social interactions in other studies. .
Arya Biragyn, a molecular biologist at the National Institute on Aging, said he wished the team had done more to show that microbiomes had actually changed in older mice. Because the researchers checked for differences in the gut microbiome soon after the transplants, there is no way of knowing whether the new microbes had really taken hold or were just passing through, he argues.
Gibbons also notes that the field of fecal transplants in mice remains a mixed bag. While some studies have shown that such procedures appear to be beneficial, he says, at least one has found that they can lead to cognitive declines.
Cryan himself warns against passing the gun on to humans, given that the study was based entirely on rodents. Yet, he argues, the work offers hope. “The good thing about your microbiome, as opposed to your genome, is that you can change it. “
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