Scientists discover brain's waste removal pathway via dura mater lymphatics

A groundbreaking study by South Korean researchers has pinpointed the precise route cerebrospinal fluid (CSF) and brain waste products take to exit the brain through lymphatic vessels located in the dura mater, the outermost of the three brain membranes. This discovery sheds new light on the brain's "cleaning" process.

The research, led by Dr. Ko Kyu-young at the Institute for Basic Science (IBS), identified that CSF and waste are expelled through specialized pores called "arachnoid fenestrations." These microscopic openings, measuring about 4.5 micrometers in diameter, are found in the arachnoid mater, specifically near the olfactory bulb and the cribriform plate, which separates the brain from the nasal cavity. These fenestrations allow CSF to pass from the subarachnoid space into the lymphatic vessels within the dura mater.

Crucially, the study revealed a significant age-related decline in this drainage system. Comparing aged mice with younger ones, the team observed that the size and number of arachnoid fenestrations decreased by 50-60% in older mice. Concurrently, the volume of the dura mater lymphatic vessels and the openings they pass through also reduced, leading to a 58% and 64% decrease in outflow, respectively. This diminished "brain cleaning" efficiency is thought to contribute to the accumulation of toxic proteins like amyloid-beta, a hallmark of neurodegenerative diseases such as Alzheimer's.

However, the research also offers a potential therapeutic avenue. By administering a gene therapy vector carrying VEGF-C, a gene that promotes lymphatic vessel growth, into the nasal cavity of aged mice, the researchers observed a significant recovery in CSF outflow. While the fenestrations themselves did not enlarge, the dura mater lymphatic vessels increased in size two to three times, restoring the outflow to levels seen in younger mice. This suggests that stimulating lymphatic vessel regeneration could be a viable strategy to combat age-related decline in brain waste clearance.

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We have secured key clues to elucidating the human brain cleaning mechanism by confirming the same arachnoid fenestration structure in primates. We plan to expand research using human tissues and develop new therapeutic strategies applicable to various neurodegenerative diseases.