PICTURED: Soil microbes. PC: Pacific Northwest National Laboratory. CC 2.0.
Story at a glance..
When receiving a sample of a young mouse’s gut microbiome, age-related cognitive decline was reversed in older mice.
This included measures of anxiety, learning and memory, but also immune functions in the brain.
While more research is needed, the finding joins a generous body of evidence suggesting fecal microbiome transplants could be key to ensuring a healthy aging process in humans.
Organ transplants are an extremely important medical procedure, but growing literature could see regular “fecal microbe transplants” given to us as we age, as animal studies showing the effect this bizarre intervention has on attenuating the aging process, particularly in the brain and gut, are promising.
Now a new study published in Nature Aging, has found that transplanting a piece of the gut microbiome—the trillions of individual bacteria, viruses, and protozoa that live in our gastrointestinal system, from a younger mouse into an older one, reversed age-related changes in the immune function of the brain as well as returning the patterns of anxiety, learning, and memory, to those of a younger mouse.
Their study reported the fecal microbiome transplant (FMT) from a 3-4 month-old mouse into a 19-20 month-old mouse “reversed aging-associated differences in peripheral and brain immunity, as well as the hippocampal metabolome and transcriptome of aging recipient mice” as well as “attenuated selective age-associated impairments in cognitive behavior”.
The brains of old mice receiving young donor-derived fecal transplants were found after to contain metabolites and patterns of gene regulation that resembled the brains of the younger mice.
Aging is a complex process of systematic decline, and age-related changes in gut microbiota are linked with decline in cognitive abilities in young rats receiving an FMT from old rats. This same study also found the aged FMT increased expression of pro-inflammatory cytokines and oxidative stress, suggesting the mechanism for gut-related cognitive decline during aging is driven by inflammation.
The age-related decline in microbiome diversity and richness is also linked to a poorer diet which in turn worsens the condition of the microbiome, worsening cognitive decline. One study found that separating 178 elderly patients by microbiome richness simultaneously separated them by diversity of diet, as well as by measures of frailty.
The Gut-Brain Axis
FMTs have been utilized at least since the 4th century CE in China, and traditionally by the Bedouin to treat various stomach conditions (in their case the FMT was done by eating fresh camel dung). Hippocrates wrote more than 2,000 years ago that all disease begins in the gut.
While the therapeutic mechanism of FMT isn’t totally understood, one hypothesis is simply bacterial competition, with more easy-living cultures crowding out invasive and harmful ones.
But how, one might ask, do the bacteria in one’s stomach manage to actively affect one’s brain activity or immune-system responses? The subject is that of the gut-brain axis, a linking of the gut to many important parts of the brain such as the hippocampus, thalamus, amygdala, and hypothalamus. An information super highway connects these quite-distinct patterns of life called the “vagus nerve”.
An author of the new paper helped write a review of the gut-brain axis for the American Physiological Association in 2018, in which he wrote…
This axis is gaining ever more traction in fields investigating the biological and physiological basis of psychiatric, neurodevelopmental, age-related, and neurodegenerative disorders. The microbiota and the brain communicate with each other via various routes including the immune system, tryptophan metabolism, the vagus nerve and the enteric nervous system, involving microbial metabolites such as short-chain fatty acids, branched chain amino acids, and peptidoglycans.
Much recent work has implicated the gut microbiota in many conditions including autism, anxiety, obesity, schizophrenia, Parkinson’s disease, and Alzheimer’s disease.
Unlike organs, fecal microbiome matter from young people is easy to come across, and could be both a useful source of income for healthy young adults, and a robust therapeutic intervention for the elderly.
Slowing the decline in dietary composition, neurogenesis and cognition, as well as the increases in chronic inflammation associated with aging before such problems become too serious is key to healthy aging, a topic exploding in scientific popularity as the world population continues to live longer.