Gut Microbes Affect Extent of Brain Injury After Stroke
Altering the intestinal microbiota of mice can reduce the extent of brain damage after a stroke, researchers found. These findings provide a previously unrecognized link between the intestine and the brain.
The composition of the intestinal microbiome affects development of the immune system and metabolic processes, and is altered in patients with disorders including inflammatory bowel disease, obesity, and asthma.
Corinne Benakis et al report in the March 28 issue of Nature Medicine that in mice, microbes in the gut regulate populations of inflammatory cells that migrate from the intestine to the brain after ischemic stroke.
Science Daily reported that mice received a combination of antibiotics. Two weeks later the researchers induced ischemic stroke, in which an obstructed blood vessel prevents blood from reaching the brain.
Mice given the antibiotics had a stroke that was produced about 60% less damage than in mice that did not receive the antibiotics. Science Daily said that microbial environment in the gut regulated immune cells there that protect the brain, shielding it from the stroke’s full force.
Benakis et al reported that mice given antibiotics had increased numbers of anti-inflammatory, regulatory T (Treg) cells and reduced numbers of interleukin-17 (IL17)–positive γδ T cells, via altered dendritic cell activity. This ultimately reduced the number of inflammatory cells that traveled to the brain after the stroke, reducing the level of brain damage.
Transfer of microbes from mice given antibiotics to mice that were not given antibiotics provided similar protection from brain damage after stroke.
Benakis et al found that IL10 and IL17 were required for the neuroprotection afforded by intestinal dysbiosis. They state that their findings reveal previously unrecognized interactions among the intestinal flora, T-cell populations, and ischemic brain injury.
Immune cell migration to the brain might be altered to affect stroke outcomes in patients, if this specific link between the intestine and the brain is also found in humans.
Science Daily wrote that the bacteria did not interact with the brain directly, but instead affected neural survival by modifying the behavior of immune cells. Immune cells from the gut made their way to the meninges, where they organized and directed a response to the stroke.
Statnews wrote that the authors still don’t know whether the antibiotics eliminated bad bacteria that stimulate inflammatory immune cells, or their replacement with good bacteria helped reduce the immune reaction.
The authors propose that diets of individuals at risk for stroke might be altered to reduce risk of or damage from stroke.
The study’s senior author, Josef Anrather, told Science Daily that the “diet has the biggest effect of composition of microbiota, and once beneficial and deleterious species are identified, we can address them with dietary intervention.”