Does the Brain Heal After Head Trauma?
According to a new study from the National Institutes of Health, the protective lining surrounding the brain might get help from immune cells that develop following a mild traumatic brain injury (mTBI). Researchers studied mice in real-time and found that different immune cells took on carefully timed jobs to fix the damaged lining of the brain. Scientists say the results from the study might point them where to look for clues to whether the meninges in humans heal similarly following a mTBI, as well as why additional head trauma can be so devastating.
Dorian McGavern, Ph.D., senior author of the study, said “the lining of the brain, with help from the immune system, has a remarkable ability to put itself back together again after injury…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.”
Researchers observed MRI scans of adult patients who sustained a concussion or mTBI. Close to 50% of MRI scans of patients with mTBI revealed evidence of injury to blood vessels in the meninges. The meninges are a lining of membranes surrounding the central nervous system that help protect the brain and spinal cord tissue from injury. Damage to the meninges can cause cell death in underlying brain tissue.
According to Dr. McGavern’s research, most patients had repaired their leaky blood vessels within 20 days. However, 17% of patients still showed leakage on their MRI scans three months after injury, which suggests ongoing meningeal damage and incomplete recovery.
State-of-the-art imaging tools were used by the research team to watch in real-time what happened in the mouse meninges one week following injury. The team also created a method of analyzing where immune cells gathered in the damaged meninges during the repair process.
Within the first day of sustaining injury, researchers observed immune cells from the blood known as inflammatory monocytes enter the core of the injured meningeal tissue to begin clearing away dead cells. These cells received help a few days later from a different type of blood monocyte that worked around the lesion edge to help rebuild damaged blood vessels, which were completely restored and fully functional within a week.
Researchers also found that the timing of a second head injury severely impacts the repair process in mice. A second injury experienced within one day of the first TBI caused additional inflammation and the wound healing phase of repair, during which blood vessels are fixed, did not happen. However, if the second injury occurred after a few days after the healing phase had already begun, there was no effect on the meningeal repair process and blood vessels were rebuilt normally.
The research also found that when the molecule matrix metalloproteinase 2 (Mmp2) is blocked, there was a significant decrease in the number of vessels that were repaired. Additional research is necessary to uncover additional molecules and genes involved in the repair processes and identify ways to speed up the course of recovery following head injury.
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