A new study in the Journal of Neuroscience shows that traumatic brain injury can disrupt the function of the brain’s “waste removal system,” according to a press release from the University of Rochester Medical Center. When this occurs, toxic proteins may accumulate in the brain, setting the stage for the onset of neurodegenerative diseases such as Alzheimer’s and chronic traumatic encephalopathy.
“We know that traumatic brain injury early in life is a risk factor for the early development of dementia in the decades that follow,” said Maiken Nedergaard, MD, DMSc, co-director of the University of Rochester Center for Translational Neuromedicine and senior author of the article. “This study shows that these injuries set into motion a cascading series of events that impair the brain’s ability to clear waste, allowing proteins like tau to spread throughout the brain and eventually reach toxic levels.”
These findings follow up on a 2012 study in which Nedergaard and her colleagues described a previously unknown system of waste removal that is unique to the brain. Researchers have dubbed it the glymphatic system.
Brain waste removal
Because of the blood-brain barrier, the body’s normal waste removal system does not extend to the brain. Nedergaard and her colleagues showed that mice possess what amounts to a plumbing system that piggybacks on blood vessels to pump cerebral spinal fluid (CSF) through brain tissue, flushing away the waste from the spaces between the brain’s cells.
The new research focuses on the impact that traumatic brain injury has on the glymphatic system. It has been long observed that the protein tau plays an important role in the long-term damage sustained by the brain after a trauma. Tau helps stabilize the axons that nerve cells send out to communicate with their neighbors.
However, during trauma, large numbers of these proteins are shaken free from the axons to drift in the space between the brain’s cells. Once unmoored from nerve cells, these sticky proteins are attracted to each other and, over time, form increasingly larger “tangles” that can become toxic to brain function.
Under normal circumstances, the glymphatic system is able to clear stray tau from the brain. However, when the researchers studied the brains of mice with traumatic brain injury, they found that the trauma damaged the glymphatic system, specifically the ability of astrocytes to regulate the cleaning process.
Neurodegeneration link
“The failure of the glymphatic system may be one of the reasons that the aging brain is so vulnerable to diseases like Alzheimer’s,” said Jeffrey Iliff, PhD, co-author of study and an assistant professor at Oregon Health and Science University. “It’s striking that the same changes that we see in the aging brain are mirrored in the young brain after traumatic brain injury. It suggests that these events may be the common link to neurodegeneration, between what happens in the elderly and what happens after brain trauma.” Read the Full Press Release