Revealing Snapshots: Advanced Imaging Uncovers How The Brain Responds to Vascular Injury

Source: Medical University of South Carolina

Summary: Researchers reported that pericytes, a type of cell on the brain’s blood vessels, grow into the empty space left when neighboring pericytes die. Such growth is a kind of brain plasticity.

Pericytes are contractile cells that wrap around the blood vessels. They help blood vessels mature as the brain grows; however, very little is known about how they function in the adult brain. They are thought to maintain the blood-brain barrier (BBB), a highly selective permeable membrane that helps to prevent unwanted substances from entering the brain through the bloodstream. Pericytes die in large numbers during a stroke, Alzheimer’s disease and other brain disorders that tend to afflict aging adults. Researchers from the Medical University of South Carolina reported that pericytes grow into the empty space left when neighboring pericytes die. Such growth is a kind of brain plasticity that might be harnessed to fight age-related vascular disorders. The study findings were published in the journal Cell Reports.

Pericytes help in blood vessel dysfunction

The long arms of pericytes (shown in red) appear draped over capillaries in the brain (shown in blue). Credit: Dr. Andy Shih, Medical University of South Carolina.

Pericytes are probably the least understood of the cells that comprise the neurovascular unit, which forms the blood vessel walls in the brain. To study, adult mice were genetically modified so that their brain pericytes glowed brightly under a powerful two-photon microscope. With this technique, researchers were able to take detailed pictures over several weeks to see what happened to the brain when pericytes were lost. In live mice, the pericytes were seen as oval cell bodies often located near junctions where two capillaries intersected. To observe what happens when a pericyte is lost, the team used a precision beam of laser light to burn off a single pericyte at a time a process called ablation. Intriguingly, when a pericyte was ablated, the capillary to which it had been clinging appeared to dilate.

As the researchers ablated more pericytes, they observed a curious pattern over a period of days to weeks, the processes of neighboring pericytes grew to cover the capillaries where pericytes had been ablated. When their neighbors were lost, the surviving pericytes seemed to compensate for the job of keeping capillaries toned, a feature that is essential to maintain healthy blood flow in the brain. The team is also studying the plasticity of pericytes which could reveal ways to facilitate new pericyte growth, which in turn could combat the type of blood vessel dysfunction observed in Alzheimer’s disease and stroke.

Asst. Prof. Andy Y. Shih said, “Most methods to study pericytes give you a snapshot in time. To be able to do this dynamically in a live animal’s brain is an important step forward,” and further added, “Are there ways to augment this plasticity, to protect it and stabilize it if we need to? There are mechanisms driving this that we need to understand.”

More Information: Andrée-Anne Berthiaume et al, “Dynamic Remodeling of Pericytes In Vivo Maintains Capillary Coverage in the Adult Mouse Brain”, Cell Reports (2018). DOI: 10.1016/j.celrep.2017.12.016

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