Key points:
- A new study shows gut microbes travel to other parts of the body to repair muscle and damaged organs.
- The findings could help design microbe-based treatments to promote healing of fatty livers and injured skeletal muscle.
- Overall, the study shows the important connection between gut microbes and the immune system.
Harvard Medical School researchers have found that a class of regulatory T cells (Tregs) made in the gut play a role in repairing injured muscles and mending damaged livers. The new study adds to a growing body of evidence showing how important the gut microbiota is in regulating various physiologic functions beyond the gut.
The research started when scientists observed, during routine cataloging, gut Tregs intermingled with muscle cells—a very rare occurrence. Once the team confirmed the Tregs origin as colonic, they tagged the cells with light and followed them as they made their way around the bodies of mice. According to the study results, published in Immunity, the light-tagged cells left the guts of the mice and migrated to other parts of the animals’ bodies. Then, the team completed a series of experiments to get a better understanding of what the migrated Tregs were doing.
In one experiment, mice genetically modified to lack this class of colonic Tregs showed markedly slower rates of muscle recovery. The animals had higher levels of inflammation in injured muscle tissue, and when they did eventually heal, the mice developed muscle scarring. In another experiment, researchers noted that colonic Tregs helped the muscle-healing process by suppressing an inflammatory signal called IL-17. Lowering levels of this signal during a precise time window moderated the inflammatory response and helped stop inflammation when it was no longer needed for the healing process.
In a third experiment, mice with fatty livers had notably higher levels of colonic Tregs than mice with healthy livers—an observation that affirmed the role of gut Tregs in controlling inflammation outside the intestines.
Moreover, mice that had fatty livers and were also genetically engineered to lack gut Tregs had markedly worse outcomes from their disease, showing worse liver scarring. This finding affirmed the protective role of gut Treg cells in reducing inflammation and scarring in fatty liver disease, the team concluded.
The new findings could help design new treatments using beneficial microbes to promote healing of fatty livers and injured skeletal muscle. More broadly, the authors say, the findings raise the possibility that gut immune cells may be involved in healing damage in various other organs throughout the body—a question they plan to explore in their subsequent research.
Information provided by Harvard Medical School.