Repopulating Microglia Promote Brain Repair

Repopulating Microglia Promote Brain Repair

Researchers have identified a major shift in how to treat brain injuries, after rejuvenating immune cells to support the repair process.

The study focused on the brain's learning and memory centre, the hippocampus, and its unique ability to produce new brain nerve cells during adult life, which is critical for learning.

The team used animal models to investigate how the immune system interacts with brain nerve cells after injury and how this influenced the ability to learn and remember.

The senior author said up until now, the brain's immune cells, known as microglia, were considered to drive inflammation, resulting in cognitive deficits after injury.

"However, when we removed microglia from mice we were surprised that there was absolutely no change in their behaviour or ability to repair brain tissue," the author said.

The team then depleted microglia and allowed them to repopulate the brain, finding this profoundly increased brain repair.

"The rejuvenated microglia improved the mice's learning and memory, preserved tissue loss and stimulated the birth of neurons," said the author.

The beneficial effects of these repopulating microglia are critically dependent on interleukin-6 (IL-6) trans-signaling via the soluble IL-6 receptor (IL-6R) and robustly support adult neurogenesis, specifically by augmenting the survival of newborn neurons that directly support cognitive function. 

"We have shown that microglia, in part, have been misunderstood and that we need to learn more about how they support and stimulate pathways to promote repair."
Brain injuries impact on a person's ability to concentrate, make decisions, learn and remember, and can range from mild to severe, and be short-term or permanent.

"It's no longer about inhibiting microglia's pro-inflammatory elements, it's about finding a way to shift them to a state that supports brain repair," the lead author said.