Scientists: the brain expels waste through the nose

Scientists from the Gladstone Institutes in the United States have made a discovery that overturns previous understanding of how the brain works: it turns out that a significant portion of protein waste is expelled through the nasal passages, brain membranes, and skull tissues, and not through the cervical lymph nodes, as had been believed for decades. The researchers are convinced that malfunctions in this clearance system may be directly linked to the development of Alzheimer's disease. The results of the study have been published in the journal Cell.

The brain continuously produces proteins that, once they have served their purpose, must be removed from the tissues. For a long time, the scientific community held an established view: the main channel for removing such waste was the lymph nodes of the neck. However, new research fundamentally changes this picture.

To trace the path of the proteins, the scientists employed an elegant technique: they genetically modified mouse neurons, causing them to produce a glowing green protein. Thanks to this, it became possible for the first time to observe in real time the entire route of the waste — from the moment of its formation to its complete removal from the body.

The results proved unexpected: only a small fraction of proteins reaches the cervical lymph nodes. The main flow of waste leaves the brain through entirely different pathways — through its membranes, skull tissues, and nasal passages.

Another surprise was that different brain regions use their own independent clearance routes. Proteins from the upper regions were expelled through the nearest pathways, while waste from deep structures exited through channels at the base of the brain. The researchers called this principle the "nearest exit model."

When Alzheimer's disease was modeled, the picture changed dramatically: the clearance system malfunctioned, protein waste struggled to leave the brain and began accumulating in the tissues. The authors of the study believe that precisely such disruptions may trigger the accumulation of toxic proteins characteristic of neurodegenerative diseases.

The researchers are confident that their discovery will help to more deeply understand the mechanisms behind the development of Alzheimer's disease and, in the future, could lead to the creation of fundamentally new treatment methods aimed at restoring the brain's natural clearance system.