Inflammatory bowel disease (IBD) is a term that describes chronic gut inflammation and includes ulcerative colitis and Crohn's disease (though the disorders present similarly, IBD is not irritable bowel syndrome or Celiac disease, and the causes and effective treatments surrounding these diseases are thought to be different). Symptom of IBD can include persistent diarrhea, fatigue, and abdominal pain.
The causes of IBD are still unclear, although research has suggested that it's due to immune system dysfunction, and that diet probably can exacerbate the symptoms of IBD, but does not cause it. The causes may also be slightly different in different people.
IBD can also lead to problems in other organ systems. For example, there seems to be a strong connection between IBD and mental disorders; about 40 percent of IBD patients report such symptoms, including anxiety and depression. The gut-brain axis could be a factor here, with bacterial molecules, inflammation or other factors playing a role. The gut microbiome, a huge group of microbes that perform important functions in the human gut, has been shown to be tightly linked to the brain through the gut-brain axis.
New research reported in Science by investigators at Humanitas University has used a mouse model to find an intriguing reason why psychiatric symptoms may be connected to IBD.
When the gut is inflamed, the host, in this case mice but maybe also in humans, the barrier that lines the gut and holds bacteria inside and away from the rest of the body begins to become permeable. This is the leaky gut hypothesis, in which the substances that are produced by the gut microbiome move out of the gastrointestinal tract and cause inflammation in other areas. In that case, the body seems to move to isolate and contain that inflammation.
One thing that happens during that containment is the closure of a vascular barrier that sits in a part of the brain called the choroid plexus. Once it's closed, large molecules can't move through it anymore. In this study, the researchers suggested that when this barrier is closed, some brain functions become impaired and signaling between organs is impaired. The study authors found that the closure of the barrier may be due to disruptions in a signaling pathway known as Wnt/β-catenin.
The researchers created a genetically engineered mouse model in which the endothelial cells in the choroid plexus were closed. They found that these mice exhibited behaviors that are associated with anxiety and short-term memory deficits, supporting the hypothesis that the closure of this barrier is what connects psychiatric disorders and IBD. If this is confirmed with additonal studies, it will pave the way to new treatments.