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Making Personalized Blood-Brain Barriers in a Dish

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Credit: Vatine et al, Cell Stem Cell, 2019

The blood-brain barrier, or BBB, is a dense sheet of cells that surrounds most of the brain’s blood vessels. The BBB’s tiny gaps let vital small molecules, such as oxygen and water, diffuse from the bloodstream into the brain while helping to keep out larger, impermeable foreign substances that don’t belong there.

But in people with certain neurological disorders—such as amyotrophic lateral sclerosis (ALS) and Huntington’s disease—abnormalities in this barrier may block the entry of biomolecules essential to healthy brain activity. The BBB also makes it difficult for needed therapies to reach their target in the brain.

To help look for solutions to these and other problems, researchers can now grow human blood-brain barriers on a chip like the one pictured above. The high-magnification image reveals some of the BBB’s cellular parts. There are endothelial-like cells (magenta), which are similar to those that line the small vessels surrounding the brain. In close association are supportive brain cells known as astrocytes (green), which help to regulate blood flow.

While similar organ chips have been created before, what sets apart this new BBB chip is its use of induced pluripotent stem cell (iPSC) technology combined with advanced chip engineering. The iPSCs, derived in this case from blood samples, make it possible to produce a living model of anyone’s unique BBB on demand.

The researchers, led by Clive Svendsen, Cedars-Sinai, Los Angeles, first use a biochemical recipe to coax a person’s white blood cells to become iPSCs. At this point, the iPSCs are capable of producing any other cell type. But the Svendsen team follows two different recipes to direct those iPSCs to differentiate into endothelial and neural cells needed to model the BBB.

Also making this BBB platform unique is its use of a sophisticated microfluidic chip, produced by Boston-based Emulate, Inc. The chip mimics conditions inside the human body, allowing the blood-brain barrier to function much as it would in a person.

The channels enable researchers to flow cerebral spinal fluid (CSF) through one side and blood through the other to create the fully functional model tissue. The BBB chips also show electrical resistance and permeability just as would be expected in a person. The model BBBs are even able to block the entry of certain drugs!

As described in Cell Stem Cell, the researchers have already created BBB chips using iPSCs from a person with Huntington’s disease and another from an individual with a rare congenital disorder called Allan-Herndon-Dudley syndrome, an inherited disorder of brain development.

In the near term, his team has plans to model ALS and Parkinson’s disease on the BBB chips. Because these chips hold the promise of modeling the human BBB more precisely than animal models, they may accelerate studies of potentially promising new drugs. Svendsen suggests that individuals with neurological conditions might one day have their own BBB chips made on demand to help in selecting the best-available therapeutic options for them. Now that’s a future we’d all like to see.

Reference:

[1] Human iPSC-Derived Blood-Brain Barrier Chips Enable Disease Modeling and Personalized Medicine Applications. Vatine GD, Barrile R, Workman MJ, Sances S, Barriga BK, Rahnama M, Barthakur S, Kasendra M, Lucchesi C, Kerns J, Wen N, Spivia WR, Chen Z, Van Eyk J, Svendsen CN. Cell Stem Cell. 2019 Jun 6;24(6):995-1005.e6.

Links:

Tissue Chip for Drug Screening (National Center for Advancing Translational Sciences/NIH)

Stem Cell Information (NIH)

Svendsen Lab (Cedars-Sinai, Los Angeles)

NIH Support: National Institute of Neurological Disorders and Stroke; National Center for Advancing Translational Sciences


Scoliosis Traced to Problems in Spinal Fluid Flow

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Zebra fish model for scoliosis study

Caption: Normal zebrafish (top left) and a normal skeleton (bottom left); zebrafish with scoliosis (top right) and an abnormal scoliotic skeleton (bottom right).
Credit: Grimes DT, Boswell CW, Morante NF, Henkelman RM.

Many of us may remember undergoing a simple screening test in school to look for abnormal curvatures of the spine. The condition known as adolescent idiopathic scoliosis (IS) affects 3 percent of children, typically showing up in the tween or early teen years when kids are growing rapidly. While scoliosis can occur due to physical defects in bones or muscles, more often the C- or S-shaped spinal curves develop for unknown reasons. Because the basic biological mechanisms of IS have been poorly understood, treatment to prevent further progression and potentially painful disfigurement has been limited to restrictive braces or corrective surgery.

Now, in work involving zebrafish models of IS, a team of NIH-funded researchers and their colleagues report a surprising discovery that suggests it may be possible to develop more precisely targeted therapeutics to reduce or even prevent scoliosis. The team’s experiments have, for the first time, shown that mutation of a gene associated with spinal curvature in both zebrafish and humans has its effect by altering the function of the tiny hair-like projections, known as cilia, that line the spinal cord. Without the cilia’s normal, beating movements, the fluid that bathes the brain and spinal cord doesn’t flow properly, and zebrafish develop abnormal spinal curves that look much like those seen in kids with scoliosis. However, when the researchers used genetic engineering to correct such mutations and thereby restore normal cilia function and flow of cerebral spinal fluid (CSF), the zebrafish did not develop spinal curvature.