In recent years, researchers have learned more about how important the gut is to human health. Trillions of microbes live in the gastrointestinal system, and they play essential roles in metabolism and are important to protective immunity. The gut is coated in a mesh network of nerves known as the enteric nervous system, and it has a direct link to the brain, a connection known as the gut-brain axis. The inside of the gut is coated with mucus, which has critical physiological functions. Researchers have now suggested in a review reported in Frontiers in Microbiology that changes in gut mucus are commonly found in a wide variety of brain disorders, and that the two are related.
"Mucus is a critical protective layer that helps balance good and bad bacteria in your gut but you need just the right amount -- not too little and not too much," said the senior author of the review, RMIT University Associate Professor Elisa Hill-Yardin. "Researchers have previously shown that changes to intestinal mucus affect the balance of bacteria in the gut but until now, no one has made the connection between gut mucus and the brain. Alterations in gut mucus may be causing an imbalance in the microbiome, and exacerbating symptoms of neurological diseases, Hill-Yardin suggested.
"Our review reveals that people with autism, Parkinson's disease, Alzheimer's and multiple sclerosis have different types of bacteria in their gut mucus compared with healthy people, and different amounts of good and bad bacteria. It's a new gut-brain connection that opens up fresh avenues for scientists to explore, as we search for ways to better treat disorders of the brain by targeting our 'second brain' -- the gut."
Different parts of the gastrointestinal tract have different kinds of mucus. In the small intestine, for example, it is porous enough to allow nutrients from digested food to pass through. The mucus in the colon is thicker, however, so that bacteria will not pass through. Peptides in the mucus can both kill bacteria and feed it.
Scientists know that brain disorders can have an effect on gut neurons. Patients with neurological diseases might be more prone to gastrointestinal dysfunction because of reductions in gut mucus, the researchers suggested. Severe gut problems might also make symptoms of brain disease worse.
"If we can understand the role that gut mucus plays in brain disease, we can try to develop treatments that harness this precise part of the gut-brain axis," said Hill-Yardin. "Our work shows that microbial engineering, and tweaking the gut mucus to boost good bacteria, have potential as therapeutic options for neurological disorders."