New Brain Anatomy Component Discovered: Acts as Protective Barrier and Immune Monitoring Platform

The breakthrough discovery of previously unknown brain structure could provide insights into brain health and disease.

In a major advancement, scientists have identified a new component of brain anatomy that serves as both a protective barrier and a platform for immune cells to monitor the brain for infection and inflammation.

This discovery, published in the journal Science, represents a significant step forward in our understanding of the human brain, which has long guarded its secrets.

Using advanced neuro-imaging and molecular biology techniques, researchers at the University of Rochester and the University of Copenhagen have been able to study the living brain at a level of detail previously unattainable.

The findings, from the labs of Maiken Nedergaard and Kjeld Møllgård, could have important implications for our understanding of diseases such as Alzheimer’s, multiple sclerosis, and CNS infections, as well as the delivery of drugs and gene therapies to the brain.

Nedergaard and her colleagues have made significant contributions to the field of neuroscience and transformed our understanding of the basic workings of the human brain. They have revealed the numerous vital roles played by glia, previously overlooked brain cells, as well as the unique way the brain eliminates waste, which they have dubbed the glymphatic system.

“The discovery of a new anatomic structure that segregates and helps control the flow of cerebrospinal fluid (CSF) in and around the brain,” says Nedergaard, “now provides us much greater appreciation of the sophisticated role that CSF plays not only in transporting and removing waste from the brain, but also in supporting its immune defenses.”

The team focused on the membranes that surround the brain, known as the meningeal layer, which have long been understood to create a barrier between the brain and the rest of the body, keeping it bathed in cerebrospinal fluid (CSF). This layer is made up of three individual membranes known as the dura, arachnoid, and pia matter.

The subarachnoid area, which lies below the arachnoid layer, is further divided into two compartments by the newly found layer, which the U.S. and Danish-based research team refers to as the SLYM, or Subarachnoidal LYmphatic-like Membrane.

While a large portion of the study discusses SLYM’s role in mice, they also note that it is present in the adult human brain.

The SLYM is a mesothelium-type membrane, which is also known to border the lungs and heart among other human organs.

Immune cells are often housed in and around mesothelium, which also protects organs. Mllgrd, the study’s lead author, raised the possibility that a similar membrane may exist in the central nervous system.

His work focuses on the systems of barriers that protect the brain as well as developmental neurobiology.

Only one or a few cells make up the new membrane, which is very thin and sensitive. However, the SLYM is a strict barrier that only lets extremely tiny molecules get through; it seems to separate “clean” and “dirty” CSF.

This final discovery suggests that SLYM may have a function in the glymphatic system, which needs a regulated flow and exchange of CSF, enabling new CSF to enter while flushing toxic proteins linked with Alzheimer’s and other neurological illnesses from the central nervous system.

Additionally, it seems that the SLYM is home to a unique population of immune cells from the central nervous system that utilize it as a surveillance platform at the brain’s surface to look for infections.

Finding the SLYM makes it possible to learn more about its role in brain diseases. For example, the researchers note that when the body is inflamed or getting older, more and different kinds of immune cells gather on the membrane.

When the membrane was torn following a traumatic brain injury, the disturbance in CSF flow hampered the glymphatic system and enabled non-central nervous system immune cells to reach the brain.

These and other findings suggest that problems with SLYM function could cause or make diseases like multiple sclerosis, infections of the central nervous system, and Alzheimer’s worse.

They also imply that SLYM function may have an influence on the brain’s ability to receive drugs and gene treatments, which will need to be taken into account when new biologic therapy generations are created.

Source: 10.1126/science.adc8810

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