Pericytes, a cell type in blood vessel walls, were found to regulate the BBB.

The key to the blood-brain barrier (BBB) is a cell type in blood vessel walls called pericytes, according to researchers at Karolinska Institutet. Reporting in Nature, Christer Betsholtz, Ph.D., professor of vascular biology at the department of medical biochemistry, who led the study, says, “It can be opened in a way that allows the passage of molecules of different sizes while keeping the brain’s basic functions operating properly.”

The study is detailed in a paper titled “Pericytes regulate the blood-brain barrier.” The Karolinska team discovered that pericytes normally maintain the barrier function, though they haven’t yet figured out how. In their absence, a special transport process called transcytosis opens a path through the capillary walls so that molecules of different sizes including large plasma proteins can pass from the blood into the brain.

The pericytes also regulate another type of brain cell known as an astrocyte, which contribute to the BBB through special extensions called end-feet. These extensions envelop the capillaries and regulate water and ion flows.

“Another interesting find is that the cancer drug Imatinib, which inhibits certain signal proteins for cell growth, has a similar effect in the presence of pericytes in that they also close the capillary wall transport paths,” says Dr. Betsholtz.

“Our new knowledge of how the BBB is regulated could be used in two ways,” Dr. Betsholtz concludes. “To protect the brain under conditions such as stroke and inflammation that lead to the opening of the BBB and the release of neurodamaging substances and to open the barrier temporarily to allow the transport of drugs against neurodegenerative and other diseases of the brain.”

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