The gut microbiome consists of trillions of microorganisms that live in our bowels. We’re finding out that this microbiome as profound effects on health and the functions of the human body. Now, a new study at the Washington University School of Medicine in St. Louis demonstrates that the state of the gut microbiome has profound effects on the functions of the brain.
Using a mice model, the researchers found that gut bacteria affect immune cells in the brain, not only damaging brain tissue but also contributing to the development of neurodegenerative conditions such as Alzheimer’s disease. It suggests the possibility that altering the microbiome may be a means of preventing or treating neurodegenerative disorders.
“We gave young mice antibiotics for just a week, and we saw a permanent change in their gut microbiomes, their immune responses, and how much neurodegeneration related to a protein called tau they experienced with age,” says Dr. David M. Holtzman, a neurology professor at the university, in a statement. “What’s exciting is that manipulating the gut microbiome could be a way to have an effect on the brain without putting anything directly into the brain,”
There is considerable research showing that the gut microbiomes in people with Alzheimer’s disease is unlike those of healthy people. It is not known, however, if the differences cause the disease or are a result of the disease, or how altering the microbiome might affect it.
To test if the gut microbiome is a contributing cause to Alzheimer’s disease, the researchers altered the microbiomes of mice genetically altered to develop brain damage and cognitive deterioration like that of Alzheimer’s disease.
The genetically engineered mice were raised in a sterile environment, so they did not acquire gut microorganisms. Their brains were much less damaged at 40 weeks of age than the brains of mice raised in a normal, nonsterile environment, with normal microbiomes.
“We already know, from studies of brain tumors, normal brain development and related topics, that immune cells in male and female brains respond very differently to stimuli,” Holtzman says. “So, it’s not terribly surprising that when we manipulated the microbiome we saw a sex difference in response, although it is hard to say what exactly this means for men and women living with Alzheimer’s disease and related disorders.”
“This study may offer important insights into how the microbiome influences tau-mediated neurodegeneration, and suggests therapies that alter gut microbes may affect the onset or progression of neurodegenerative disorders,” adds Linda McGavern, PhD, program director at the National Institute of Neurological Disorders and Stroke (NINDS), which provided some of the funding for the study.
“What I want to know is, if you took mice genetically destined to develop neurodegenerative disease, and you manipulated the microbiome just before the animals start showing signs of damage, could you slow or prevent neurodegeneration?” Holtzman asks. “That would be the equivalent of starting treatment in a person in late middle age who is still cognitively normal but on the verge of developing impairments. If we could start a treatment in these types of genetically sensitized adult animal models before neurodegeneration first becomes apparent, and show that it worked, that could be the kind of thing we could test in people.”
This study is published in Science.