Pictured: Pericytes (red) and blood vessels (green). Image source: Dr. Louis-Philippe Bernier, the MacVicar lab at the Djavad Mowafaghian Centre for Brain Health.

During an ischemic stroke, a blockage in an artery prevents blood flow through the affected area of the brain, resulting in oxygen deprivation and cell death. Ischemic stroke, caused by blood clots, is the most common type of stroke.

Dr. Brian MacVicar and Dr. Louis-Philippe Bernier recently uncovered how two types of cells, astrocytes and pericytes, work together to regenerate blood flow in the areas affected by ischemic stroke. These results were presented at the 2018 Canadian Neuroscience Meeting in Vancouver today.

Astrocytes are a class of brain cells that are known to proliferate and become active following brain injury. Pericytes (pictured above) are known to regulate blood flow in capillaries, the smallest blood vessels of the body. Until now, the role of pericytes in repairing the brain after injury was not well understood. Dr. MacVicar’s team has now demonstrated that following stroke, pericytes also proliferate and migrate to the damaged area of the brain, inside a region that is bordered by astrocytes.

His team also showed that new blood vessels were formed at the interface between astrocytes and pericytes, in a wave that goes from the edge of the injured region towards the centre, thereby re-establishing blood flow in the region.

“Our results show that these two types of cell cooperate to re-establish blood flow in the injured region, and that within a few weeks, the area is fully vascularized, meaning that normal blood flow is restored,” said Dr. MacVicar. “Additionally, we showed that the blood brain barrier is also re-established.”

The blood-brain barrier is a protective mechanism that makes capillaries in the brain less permeable than blood vessels in the rest of the body, preventing the passage of bacteria and certain toxins that could be present in the blood, while allowing oxygen and nutrients to reach brain cells.

“Our work shows that pericytes are a dynamic population of cells in the brain that become activated and proliferate in response to injury,” said Dr. Bernier, a research associate in Dr. MacVicar’s lab. “This occurs through cross-talk between astrocytes and pericytes.”

“These findings represent progress in our understanding of the ways the brain can repair itself following stroke,” said Dr. MacVicar. “This is a positive finding, one that has the potential to lead to the identification of new targets for treatments to prevent damage or repair the brain.”

According to The Heart and Stroke Foundation of Canada, there are 62,000 strokes in Canada each year, and through 80 per cent of people survive stroke, it remains one of three leading causes of death in Canada and leads to permanent disability in about half of survivors. The Public Health Agency of Canada estimates that close to 742 000 Canadians live with the effects of stroke.