Our brain is well protected by a barrier termed the “blood-brain
barrier (BBB).” The blood–brain barrier is a highly selective permeability
barrier that separates the circulating blood from the brain extracellular fluid
(BECF) in the central nervous system (CNS).
The stuffs that can pass through the blood-brain barrier are highly
selective including water, some gases, and lipid soluble molecules by passive
diffusion, as well as the selective transport of molecules such as glucose and
amino acids that are crucial to neural function. The
barrier exists to protect our brain from potential neurotoxins in the
environment.
A recent study published in the journal Science Translational Medicine suggests that the gut microbes living
in our guts can influence the integrity of the blood-brain barrier, meaning
that the transport of molecules across the blood-brain barrier can be modulated
by our gut microbes -- which therefore play an important role in the protection
of the brain.
In this study, the investigators compared the integrity and
development of the blood-brain barrier between two groups of mice: the first
group was raised in an environment where they were exposed to normal bacteria,
and the second (called germ-free mice) was kept in a sterile environment without
any bacteria. It was observed that the presence of the maternal gut microbiota blocked
the passage of labeled antibodies from the circulation into the brain of the
growing fetus; In contrast, in age-matched fetuses from germ-free mothers,
these labeled antibodies easily crossed the blood-brain barrier and was detected
within the brain.
The research also showed that the increased “leakiness” of
the blood-brain barrier, observed in germ-free mice from early life, was
maintained into adulthood. However, this “leakiness” was repaired when the mice
received fecal transplantation from normal gut microbes. The precise molecular
mechanisms remain to be identified. However, the researchers was able to show
that the tight junction proteins, which are known to be important for the
blood-brain barrier permeability, did undergo structural changes and had
altered levels of expression in the absence of gut bacteria.
The results support previous observations that gut
microbiota can impact brain development and function and further underscore the
importance of the maternal microbes during early life. Given that the microbiome composition and
diversity change over time, it is likely that the blood-brain barrier integrity
also may fluctuate depending on the microbiome, which has the implication on
the therapeutic or toxic effect of drugs or environmental pollutants.
Journal
Reference: V. Braniste, M. Al-Asmakh, C. Kowal, F. Anuar, A. Abbaspour, M.
Toth, A. Korecka, N. Bakocevic, N. L. Guan, P. Kundu, B. Gulyas, C. Halldin, K.
Hultenby, H. Nilsson, H. Hebert, B. T. Volpe, B. Diamond, S. Pettersson. The
gut microbiota influences blood-brain barrier permeability in mice. Science
Translational Medicine, 2014; 6 (263): 263ra158 DOI:
10.1126/scitranslmed.3009759
Thanks for reading.
Connie
Connie@cherruby.com
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