The secrets of brain structure are far from being solved (pixabay)
This latest research was co-led by Professor Kjeld Møllgård from the University of Copenhagen in Denmark and Professor Maiken Nedergaard from the University of Rochester in the United States. Ten years ago, Professor Nedergaard led another major breakthrough in the field of brain structure: her team discovered the glymphatic system, which is composed of glial cells and plays a role in clearing waste from the brain. The breakthrough also points to the complex role of cerebrospinal fluid in transporting and clearing waste from the brain. However, how cerebrospinal fluid is transported under the arachnoid membrane has always been an unsolved mystery, and this has become the starting point for the latest research and exploration.
The latest research focuses on the meninges that surround brain tissue. It is the meninges that form a barrier from the rest of the brain, and the brain is bathed in cerebrospinal fluid within the barrier. According to previous observations, the meninges are composed of three membranes: dura mater, arachnoid mater, and pia mater.
Now, with the development of neuroimaging technology, the scientific community can study living brains at higher resolutions. The study’s authors used two-photon microscopy, a technique capable of probing the internal structure deep within tissue.
The research team used green fluorescent protein to label the Prox1 protein (a transcription factor required for lymph to function), and also labeled blood vessels, astrocytes, etc. respectively. In this way, they can capture the structural distribution of these molecules or cells under two-photon microscopy. The high resolution of this technology also allows them to see structures that have never been seen before. In the space under the arachnoid membrane, a layer of cells containing Prox1 protein is neatly arranged and intertwined with loose collagen fibers. This membrane divides the space under the arachnoid membrane into two areas: inner and outer areas. The research team named this newly discovered structure Subarachnoidal LYmphatic-like Membrane (SLYM).
Of course, the empty membrane structure is not enough. Subsequent research confirmed that this membrane also plays a functional role in separation. Although SLYM is very thin, with a thickness of only one or a few cells, it forms a tight barrier that small molecular substances in cerebrospinal fluid such as cytokines and growth factors cannot pass through. Thus, SLYM separates “clean” and “dirty” cerebrospinal fluid.
The authors note that the newly discovered SLYM is similar to mesothelium found elsewhere in the body. For example, the membranes surrounding our lungs and heart contain mesothelium, which not only protects the organs but also serves as a shelter for immune cells. Likewise, recent studies in mice have revealed SLYM’s dual functions.
In the glymphoid system, the presence of SLYM directs the controlled flow of cerebrospinal fluid and the exchange of substances with venous blood: fresh cerebrospinal fluid can flow in while flushing away toxic proteins associated with Alzheimer’s disease or other neurological diseases. On the other hand, SLYM also plays an important role in the immune defense mechanism of the brain. SLYM contains a large number of central nervous system immune cells. These cells monitor the surface of the brain through SLYM, thereby scanning the flowing cerebrospinal fluid to monitor for signs of infection.
The research team noticed that in brains with inflammation and aging, the number and types of immune cells gathered on SLYM were larger and more diverse. When the brain encounters trauma and SLYM is damaged, it will affect the flow of cerebrospinal fluid, cause damage to the lymphatic system, and cause external immune cells to pass through SLYM and reach the brain. This may explain why brains that have experienced trauma will have long-term neurological problems. inflammation.
SLYM (public domain)
The discovery of SLYM not only deepened our understanding of the brain structure, rewriting the 3-layer structure of the meninges into 4 layers, but also gave us a deeper understanding of the working mechanism of the lymphoid system, and began to realize the role of SLYM in brain diseases. . According to this study, diseases such as multiple sclerosis, central nervous system infections, and Alzheimer’s disease may be caused or exacerbated by SLYM dysfunction. It seems that there are still many unknown functions waiting to be discovered on this extremely thin film.
References:
[1] Kjeld Møllgård et al., A mesothelium divides the subarachnoid space into functional compartments. Nature (2023). DOI: 10.1126/science.adc8810
[2] Newly discovered anatomy shields and monitors brain. Retrieved Jan. 5th, 2023 from https://www.eurekalert.org/news-releases/975546
2023-09-16 08:46:27
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