Gut Microbes Shore Up Blood-Brain Barrier

IPA AdminFrom The Gut

“The brain is wider than the sky.”-Emily Dickinson

Protecting such a wonder is no easy task but the blood-brain barrier (BBB) does a good job of it, most days. Both the endothelial and epithelial barriers close ranks around the brain and are reinforced by complex junctions.

The blood-brain barrier:

  • Acts as a gatekeeper between the circulatory system and brain parenchyma
  • Keeps the central nervous system (CNS) stable
  • Controls what gets in or out

A high-functioning blood brain barrier is obviously crucial to a high-functioning mind. Yet defense of the brain from inflammation and peripheral mayhem is not always effective. Molecules like alcohol easily pay off the guards and make the brain a pickled mess; it is no surprise when toxic substances such as ethanol and drugs cause problems in thinking and memory.

Yet domestic disturbances can also impact blood brain barrier function and thus brain function. For instance metabolic imbalances in glucose—both hyper- and hypoglycemia—are risk factors. Metabolic stress leads to immune dysfunction which may be one mechanism of action. (read Metabolic Syndrome and the Immunological Affair with the Blood–Brain Barrier in Frontiers in Immunology for an excellent instruction on the complex structure and function of blood-brain barrier systems).

Researchers are beginning to explore the effect of microbes.

They recently discovered that germ-free mice were different than control mice in this regard:

  • Germ-free mice showed increased permeability of the blood-brain barrier in the womb
  • Germ-free mice showed increased permeability after birth and into adulthood.

How was this happening?

Proteins are the soldiers at the barrier gates. These “tight junction proteins” weren’t showing up for work when microbes weren’t present. Indeed, the study found that there was reduced expression of tight juncture proteins occludin and claudin-5.

In their report,  The gut microbiota influences blood-brain barrier permeability in mice, the authors led by Viorica Braniste of Karolinska Institute in Stockholm, Sweden  concluded:

“Exposure of germ-free adult mice to a pathogen-free gut microbiota decreased BBB permeability and up-regulated the expression of tight junction proteins. Our results suggest that gut microbiota–BBB communication is initiated during gestation and propagated throughout life.”

Maintaining healthy gatekeepers is vital. Researchers are also linking blood-brain barrier integrity to dementia in an article titled Blood-brain barrier breakdown in the aging human hippocampus which appeared in Neuron in January 2015.