Blood-brain barrier controlled by intestinal bacteria

Blood-brain barrier is affected by intestinal bacteria

24/11/2014

Scientists have discovered in animal studies that gut bacteria in the mother can affect the permeability of certain antibodies to the brain. The intestinal flora apparently has an influence on the development of the blood-brain barrier, because without the maternal intestinal bacteria, this protective barrier for pathogens and toxins becomes passable, according to an international research team headed by Viorica Braniste of the Stockholm Karolinska Institute in the journal "Science Translational Medicine" , Thus, this impairment will last a lifetime. However, they let the barrier subsequently seal by transplanting intestinal bacteria.

How important the importance of the intestinal flora to health, have been several studies in the recent past already shown. The new study by Braniste and her colleagues has now for the first time been able to demonstrate the influence of intestinal bacteria on the formation of the blood-brain barrier in unborn mammals.

Blood-brain barrier becomes more permeable
This barrier ensures that the brain is protected from pathogens and toxins. It consists of tightly arranged endothelial cells, which are connected by so-called tight junctions, tight seams of membrane proteins.

Specifically, researchers examined the barrier to two groups of mice, one consisting of animals kept in a sterile environment and the other of those living in a normal environment with the usual bacteria. With the help of labeled antibodies was tested whether they reached the brain of the offspring via the blood of the mother. "We showed that the presence of maternal intestinal microorganisms during late pregnancy blocked the passage of labeled antibodies from the circulation into the brain tissue of the growing fetus," Braniste is quoted in a statement from her institute. "In age-matched fetuses from aseptic mothers, these labeled antibodies readily cross the blood-brain barrier and were detected in brain tissue."

Further studies showed that "the offspring of these germ-free animals produced less of the membrane proteins important for the cohesion of the barrier and continued to increase permeability until adulthood."

Nutrition of pregnant women is related to child development
If the animals subsequently received normal intestinal bacteria, the barrier developed as in the non-germ-free animals and the permeability decreased. From this, in turn, the researchers conclude that the condition intestinal flora are closely related to the functional fluctuations of the blood-brain barrier. "Given that the composition and diversity of the microbiome changes over time, one could speculate that the integrity of the blood-brain barrier may vary depending on the microbiome," says study leader Sven Pettersson. This knowledge can be used to increase the effectiveness of brain cancer drugs and to develop treatments that enhance the integrity of the blood-brain barrier, "but further studies would be needed to confirm the results." Nonetheless, Nga Bien-Ly and Ryan Watts of Genentech, a biotechnology company in San Francisco, commented in a Science Translational Medicine comment that "the present study suggests the importance of gut flora for the development of the blood-brain barrier in mammals . "

"These findings underscore the importance of maternal microbes in early life and the gut bacteria are an integral part of our body physiology," says Professor Sven Pettersson, principal investigator at the Institute of Microbiology, Tumor and Cell Biology. Accordingly, it may be assumed that the diet of the mother during pregnancy not only affects the formation of intestinal bacteria, but also affect the formation of the blood-brain barrier, the researchers said.

In this context, it is also important to investigate how the use of broad spectrum antibacterial agents destroying intestinal bacteria during pregnancy affects the development of the blood-brain barrier in the offspring. (Sb)