In the intestine, a protective layer of mucus envelops the intestinal walls and the feces. How exactly this protective layer is built up and regulated was previously unknown. A study with mice now shows that the mucus is produced in two different regions of the colon and that this production is regulated by the bacteria living in the intestine. Conversely, the mucus affects the intestinal flora. The findings shed new light on the symbiosis between the body and the microbiome and could open up new approaches for the diagnosis and treatment of bowel diseases.
Several billion bacteria live in the human intestine. They help to utilize food, synthesize vital vitamins and stimulate the immune system. If the intestinal microbiome is disturbed, this can lead to diseases such as intestinal inflammation, obesity and intestinal tumors. It is important to have a protective barrier made of sugary mucus that prevents the bacteria from coming into direct contact with the body’s cells. Until now, it was assumed that this mucus is mainly produced in the last section of the colon and lines the inner wall of the intestine. However, the exact processes were unknown.
Mucus from different sections of the intestine
A team led by Kirk Bergstrom from the Oklahoma Medical Research Foundation has now gained extensive knowledge on mice. Contrary to what was previously thought, the anterior sections of the large intestine make an extremely important contribution to the protective barrier of mucus. Specialized cells in the front sections of the large intestine form a mucus that surrounds the stool and the bacteria in it and moves with them through the intestine. The production of the mucus is regulated by the microbiome. The mucus itself, in turn, affects the microbiome.
The feces are already surrounded by a mobile layer of mucus when they reach the last section of the large intestine. Another layer is added there. This double mucus barrier is important for the healthy functioning of the intestines, as the researchers explain. However, it can be disturbed, for example by antibiotics, but also if parts of the intestine have to be removed due to illnesses. “That can lead to painful inflammation,” says Bergstrom’s colleague Lijun Xia.
Antibiotics disrupt the microbiome
As the researchers found, however, healthy intestinal bacteria can help to stimulate mucus production again. To do this, Bergstrom and colleagues first treated mice with a broad spectrum antibiotic that disrupted their intestinal flora. The feces pellets of the animals were then no longer enclosed by a layer of mucus. With the help of a stool transplant, the researchers returned a healthy intestinal microbiome to their test animals. And indeed: the mucus production soon started again.
This finding can have a significant impact on the treatment of patients whose microbiome is out of whack, explains Xia: “Now that we better understand the role and origin of this mucus, we shall investigate how we can supplement it or restore its production . “The new findings could also be helpful for the medical monitoring of patients with chronic inflammatory bowel diseases such as ulcerative colitis and Crohn’s disease. “Instead of repeatedly doing invasive procedures like colonoscopies to track the progression of bowel disease, we may be able to measure the presence of the mucus in a fecal sample to assess a patient’s bowel health,” said Xia.
Implications for bowel disease in humans
Bergstrom and colleagues have already been able to prove that such a layer of mucus also exists on human feces. Before the findings can actually have an impact on the treatment of humans, further research must clarify how the mucous system in the human intestine works. Biomedical scientists George Birchenough and Malin Johansson from the University of Gothenburg, who were not involved in the study, point out in an accompanying comment that it takes significantly longer for food to pass through the intestines in humans compared to mice, and stool also contains more water. “That probably places different demands on the surface of the mucous membranes,” they comment.
However, the current study provides important foundations, as Stephen Prescott, President of the Oklahoma Medical Research Foundation emphasizes: “Our researchers had to understand the origin and function of this mucus and how it relates to the microbiome in order to find out what compounds it is to diseases there. We now understand that the long-term health effects can be devastating if this symbiosis gets out of whack. “
Source: Kirk Bergstrom (Oklahoma Medical Research Foundation) et al., Science, doi: 10.1126 / science.aay7367