When you hit your head hard, such as during contact sports or in a car accident, it can cause what is known as traumatic brain injury. While in the long term, repeated injury can lead to an increased risk of developing Alzheimer’s disease, in the short term it causes damage to the lining of the brain.
Now for the first time ever, doctors have watched as the lining of the brain heals itself in real time, observing as different immune cells took different jobs to heal the lining. It is hoped that this will offer the potential to develop a way to speed this process up, and possibly reduce the risk of long-term damage in patients.
“The lining of the brain, with help from the immune system, has a remarkable ability to put itself back together again after injury,” explained Dr Dorian McGavern, senior author of the paper describing the process, published in Nature Immunology. “As we learn more about all the cells involved in the repair process, we may be able to identify potential targets for therapy that lead to better outcomes for patients.”
The team of researchers from the National Institute of Health wanted to investigate how mild traumatic brain injury impacted on the lining of the brain, known as the meninges, after observing that around 50 percent of patients who were being treated for head trauma showed evidence that it was leaking fluid following injury.
While in most people this healed within 20 days, in around 17 percent of patients it was still leaking after three months, increasing the risk that underlying brain cells will be damaged. The researchers were curious to find out why there was such disparity between patients.
They used precise imaging tools that allowed them to watch – in real time – the healing of the meninges of mice that had experienced traumatic brain injury, and could even track where in the lining the immune cells of the rodents were concentrating. Incredibly, they could watch as different cells from the immune system took on carefully timed jobs to fix the meninges.
Within a day inflammatory monocytes, immune cells that reside in the blood, had already entered the injured area of the meninges and began clearing away all the dead cells and preparing the area. A few days later, they were then joined by a second type of blood monocyte which, starting at the edges, began rebuilding the damaged blood vessels until within just a week the lining was completely repaired.
“Following a head injury, the meninges call in a clean-up crew, followed by a separate repair crew, to help fix damaged blood vessels,” said Dr McGavern.
Interestingly, they found that if the mice experienced a second head trauma within 24 hours of the first, this process is severely disrupted. They think that those patients who had trouble healing their meninges may have had multiple head injuries within a very short amount of time, as this is likely having a significant impact on how their brain lining heals.
The team now hope to study this process further and determine the different molecule and genes that control the healing process in a bid to develop ways to speed the process up.