A blow to the head may actually disrupt the function of the brain’s waste removal system. The new findings reveal that head injuries may be far more dangerous than first thought, and could cause toxic proteins to accumulate in the brain and set the stage for neurodegenerative diseases, such as Alzheimer’s
The brain is essentially closed off from the rest of the body by a complex system of molecular gateways, called the blood-brain barrier. This barrier tightly controls what enters and exits the brain. Consequently, the body’s normal waste removal system doesn’t extend to the brain.
In this case, the scientists found that mice, whose brains are similar to humans’, possess what amounts to a plumbing system that can pump cerebral spinal fluid (CSF), the fluid surrounding the brain, through brain tissue. This flushes away waste from the spaces between the brain’s cells. In fact, recent studies have shown that the glymphatic system is more active during sleep, which may explain the necessity for sleep.
Now, researchers have found that traumatic brain injury may impact the glymphatic system. During trauma, large numbers of tau proteins are shaken free from the axons and drift in the space between the brain’s cells. Once unmoored, these proteins stick together and, over time, form increasingly larger “tangles” that can become toxic.
“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, senior author of the new article, in a news release. “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.”
Under normal circumstances, the glymphatic system can clear stray tau away from the brain. Yet it turns out that trauma can affect the glymphatic system and cause it to be unable to perform its function.
“For a long time, we have viewed neurodegenerative diseases like Alzheimer’s as a supply problem, meaning that we believed the brain was producing too much tau or amyloid beta,” said Benjamin Plog, co-author of the new study. “It now appears that these conditions may ultimately be linked to a clearance problem, where something is preventing the glymphatic system from removing waste from the brain fast enough.”