Breakthrough Method How the Blood-Brain Barrier Opens and Closes: Researchers Uncover New Pathways

A new proteomics method is shedding light on how the blood-brain barrier opens and closes. By identifying two proteins that help preserve barrier integrity, researchers have uncovered molecular pathways that could inform future therapies for neurological diseases and improve drug delivery to the brain.

Understanding what controls the permeability of the blood-brain barrier could potentially help researchers better understand diseases like multiple sclerosis and neurodegeneration and develop better ways to deliver medicines to treat neurological conditions, including Alzheimer’s disease and Parkinson’s disease.

Think it was hard to get into Studio 54? Try getting through the blood-brain barrier.

Like a bouncer at a nightclub, the cells that line the blood vessels in our brains are highly selective. By deciding which molecules are allowed in and out of our most important organ, the barrier these cells form is critical for keeping us alive. But how our brain’s bouncer chooses who passes beyond this velvet rope has been difficult to decipher.

Now, a team led by Janelia Research Campus Group Leader Jiefu Li has developed a new method to examine the proteins lining the inside surface of blood vessels. The technique enabled them to uncover two proteins and pathways that play a role in opening and closing the blood-brain barrier — a first step in starting to understand how this important interface works.

Uncovering how the blood-brain barrier functions could help scientists figure out what happens when it goes awry, contributing to conditions like multiple sclerosis, encephalitis, and dementia. It could also help researchers develop better ways to deliver medicines that treat neurodegenerative diseases like Alzheimer's and Parkinson’s, which are often blocked from entering the brain.

“Understanding how the blood-brain barrier works, particularly figuring out the molecular targets that you can play with to open and close the barrier, will provide new possibilities for drug delivery,” Li says.

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Probing Proteins Inside Blood Vessels

The blood-brain barrier is a specialized part of the vascular system: the network of blood vessels that transport oxygen, carbon dioxide, nutrients, waste, hormones, cytokines, and immune cells throughout our body to our organs.

The luminal, or inside, surface of these vessels forms the interface between our circulating blood and our tissues — like the inside of a pipe. Proteins on the luminal surface selectively transport structures like nutrients and immune cells from the blood vessels to different tissues.

“So basically, everything in the circulating blood, if they want to have an exchange with the organ, they need to pass through this interface,” Li says.

To understand how this interface works, Li and his team developed a new, easy-to-use method to label and examine all the proteins on the luminal surface of the vasculature system.

Because of the key role luminal surface proteins play in catalyzing processes, figuring out which ones are present and how they change over time could help scientists better understand how the interface functions.

“This will allow us to say: we know that the vasculature system is doing different things in different organs and it relies on this luminal surface, but how does that happen? What are the molecular players there?” Li says.

Examining the Blood-Brain Barrier

In collaboration with the Proteomics Platform at the Broad Institute, the team used their new method to examine all the proteins that make up the brain vasculature luminal surface, which is part of the blood-brain barrier, during development, adulthood, and aging.

They found that as the brain matures from development to adulthood, proteins involved in making new blood vessels and transporting molecules decrease. As the brain aged, the team saw changes in proteins that caused the vasculature to become stiff and less adaptable.

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The team then used virus tools developed by HHMI Investigator Viviana Gradinaru to test how these changes affect the function of the brain vasculature system in laboratory models.

Together, the researchers identified two proteins (SLC7A1 and HYAL2) that control the integrity of the blood-brain barrier that, when lost, cause the barrier to break down and become leaky. They linked these proteins — one that’s present during development and one that’s present throughout an organism’s lifetime — to two different cellular processes that are required for the integrity of the blood-brain barrier.

“What we know now is that we have two new pathways, potentially, to open the blood-brain barrier and to inform some therapeutic developments,” says Li.

The study also provides a comprehensive dataset of all the proteins in the brain vasculature system from development to aging and details a new method for studying the luminal surface of the entire vascular system — resources that can be used by other scientists in the field.

“This method solves an important need but it’s also a very easy-to-use method so everyone can use it,” Li says.

Original Article: Luminal surface proteome of the brain vasculature uncovers blood-brain barrier regulators; Science; DOI:10.1126/science.aea2100

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