Previously unknown anatomical structure found in the brain that may protect against Alzheimer's
A team of scientists has discovered a previously unknown component of the brain's anatomy. It serves both as a protective barrier and as a basis from which immune cells can monitor any signs of infection or inflammation in the brain. It is possible that malfunctions in this component may trigger the development of Alzheimer's disease.
The study is reported in the journal Science. The scientists were able to make the discovery thanks to the latest advances in neuroimaging and molecular biology, which allowed them to study the living brain in unprecedented detail.
The authors of the study are neuroscientist Maiken Nedergaard, who is co-director of the Centre for Translational Neuroscience at the University of Rochester and the University of Copenhagen, and professor of neuroanatomy Kjeld Melgaard from the University of Copenhagen.
"The discovery of a new anatomical structure that separates and helps control the flow of cerebrospinal fluid (CSF) in and around the brain now gives us a much greater understanding of the complex role that CSF plays not only in transporting and removing waste from the brain, but also in maintaining its immune defences," Nedergaard was quoted as saying by SciTechDaily.
The research focused on the membranes surrounding the brain that create a barrier from the rest of the body, keeping it in the cerebrospinal fluid environment. It is a barrier consisting of separate layers known as the dura, arachnoid and meninges.
The new layer, discovered by a research team from the United States and Denmark, divides the space beneath the spider's web into two compartments separated by a newly discovered layer that the researchers named SLYM, an acronym for Subarachnoid LYmphatic-like Membrane. Although most of the studies in the article describe the function of the SLYM in mice, they also report its actual presence in the adult brain.
SLYM belongs to a type of membrane called mesothelium, which is known to form a protective layer around other organs in the body, including the lungs and heart. Mesothelium normally surrounds and protects organs and also contains immune cells.
The idea that such a membrane could also be found in the central nervous system (CNS) was first proposed by Melgord, whose research focuses on the neurobiology of development and the barrier systems that protect the brain.
The new membrane is very thin and delicate. It is as thick as one or more cells. However, the SLYM is a tight barrier and allows only very small molecules to pass through, separating "clean" and "dirty" cerebrospinal fluid.
Scientists suspect that the SLYM plays an important role in the circulation of cerebrospinal fluid, ensuring the flow of fresh CSF and flushing out toxic proteins associated with Alzheimer's disease and other neurological diseases from the central nervous system.
SLYM is also important for brain protection. The membrane prevents immune cells from entering from the outside and also contains its own population of CNS immune cells, which use the SLYM to monitor the surface of the brain. This allows them to scan the cerebrospinal fluid for signs of infection.
The researchers found that during inflammation and aging, large and diverse concentrations of immune cells accumulate on the membrane. They also learned that when the membrane was ruptured during a traumatic brain injury, it allowed immune cells that do not belong to the CNS to enter the brain.
Thus, scientists suggest that SLYM may play a significant role in the development of diseases such as multiple sclerosis, central nervous system infections and Alzheimer's disease. They can be triggered or worsened by malfunction of the membrane.
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