Korin Albert, PhD student in the Sela Lab (UMass Amherst)
September 1, 2015
Many studies are showing that an individual’s microbiome influences gastrointestinal health. The impact, however, of commensal microbes on most other body systems is still emerging. Recently, there have been several discoveries linking the microbiome and the nervous system.
In a paper recently by Erny et al. investigated modulation of microglia by the microbiome. Microglia are the immune cells of the central nervous system, protecting the brain and maintaining healthy neural circuitry. People with microglial deficiencies are susceptible to neurological and neuropsychiatric diseases.
To understand the influence of the microbiome on microglia, the researchers compared mice that had a normal microbiome to special germ-free (GF) mice that are raised without any microbes. Interestingly, several genes important for cell growth and proliferation were turned on in the microglia of GF mice. Examination of the brains of the GF mice showed an increase in a specific type of microglia cell that could lead to inflammation. However, GF mice had normal brain tissue when fed short chain fatty acids normally produced by gut microbes. When the scientists examined the microglia structure they observed anatomical differences between microglia from GF mice versus those from normal mice. Finally, microglia from GF mice are incapable of mounting the appropriate attack against a virus that typically infects neural tissue.
This paper is interesting as it describes a previously unknown interaction of the human microbiome with the both the immune and nervous systems.
Erny, Daniel, et al. “Host microbiota constantly control maturation and function of microglia in the CNS.” Nature neuroscience (2015).
Recently, my niece Nora and I did a science experiment about mold growing on bread that is exposed to various germs from hands that had touched various dirty surfaces. To our surprise, none of our samples grew any mold! See bread. Why was this? What is going on with food additives and what effect do they have on the microbiome and our health? As I browsed through Google, I found a recent article (and lots of press about the research described) linking emulsifiers to inflammatory bowel diseases. The studies were done in mice and the specific emulsifiers used were carboxymethylcellulose and polysorbate-80. Both are commonly used to smooth the texture of foods such as ice cream, mayonnaise, and to keep foods that tend to separate homogenous. Yum!
Benoit Chassaing at Georgia State University fed mice the emulsifiers in large doses (note, the amounts are equal to how much a person would eat if the only thing they ate was ice cream). Mice fed emulsifiers had less diversity in their microbiome and the microbes had moved closer to the cells lining the gut. These mice also showed more signs of intestinal inflammation. In certain mice that were bred to be more susceptible to gut diseases, the mice developed inflammatory bowel disease (IBD) at a rate more frequent and more severe than typical.
In heathy guts, there is a layer of mucus that lines the gut and prevents bacteria from coming into contact with the gut cells. They believe that the heavy mucus is broken down by emulsifiers, allowing the bacteria to get closer to the gut cells and cause inflammation.
In addition to inflammation, feeding healthy mice lots of the emulsifiers lead to increased weight gain and adiposity (more body fat) and decreased ability to regulate blood sugar levels. These kinds of symptoms are similar to what is observed in obesity-associated diseases.
The authors of the study suggest that the use of emulsifying agents in food may contribute to obesity and chronic inflammatory diseases in people. We have a program here at UMass Med that is looking at the relationship between diet and various gastrointestinal disorders. Our dieticians specialize in creating palatable recipes (without additives!) that facilitate gut healing while maintaining nutritional balance for patients with IBD, Crohn’s and Colitis. Watch here as we share with you more of their recipes over time.