Neuroscience could be in for a great upheaval. For a long time, it was understood that the functioning of nervous systems (including the brain) happened mostly due to neurons and “glial cells.” Now, scientists have discovered that there is a hidden “hybrid cell” that is somewhere in between these two categories. This could change the way scientists develop treatments for neurodegenerative diseases like Alzheimer’s disease.
For a long time, neuroscientists understood that the brain works mainly due to neurons and their ability to process and transfer information through networks. They are supported in this task by glial cells, which give structural, energetic, and immune functions.
Astrocytes, a particular kind of glial cells, surround synapses, or the points where neurons connect and communicate. Neuroscientists have long suggested that these astrocytes may play an important role in transmission in the synapses and, therefore, in information processing. But most studies conducted to date have delivered conflicting results.
But a new study published in the journal Nature could end years of doubt by confirming that astrocytes, like neurons, release neurotransmitters.
Experimental evidence
Researchers began by scrutinising the contents of astrocytes in mouse tissues using molecular biology technology. They found traces of the “machinery” that was required for the rapid secretion of glutamate, one of the main neurotransmitters used by neurons. But finding the machines was not enough; they also needed to find out if the machines worked effectively.
For that, the “hybrid” cell needed to release glutamate with a speed similar to that of synaptic transmission. They did this by using advanced imaging techniques that could visualise glutamate released by brain tissue in living mice. The hypothesis was confirmed.
Interestingly, when the researchers disrupted these glutamatergic astrocytes, the research team saw effects on memory consolidation. They also saw links to conditions like epilepsy with disruption and worsening seizures.
This study could have large-scale potential implications for the study of brain disorders. “Our discovery reveals an even larger complexity of brain cells than understood until today, a complexity extending also to non-neuronal cells like astrocytes, which enlarges the spectrum of players in brain computations, and at the same time defines more specialised roles for each subpopulation, and therefore increases the number of possible therapeutic targets and refines the therapeutic strategies,” said Ludovic Telley, co-director of the study. Telley is an assistant professor at the University of Lausanne.
Essentially, the discovery of new cells opens up new doors for neuroscience, increasing the complexity of the brain and the nervous system as scientists understand it. This could mean that future treatments for neurodegenerative diseases like Parkinson’s and Alzheimer’s potentially have more targets than before. The researchers first plan to explore potentially protective roles that this new kind of cell plays against diseases like Alzheimer’s.
“The first step will be to define if the population of glutamatergic astrocytes is altered in patients (for example, in Alzheimer’s disease patients): this is doable using bioinformatic analysis of existing transcriptomic databases of patients. Once established a role in specific pathologies, we can generate therapeutic strategies (mostly involving gene therapy) to selectively target this cell population and increase or decrease its function,” explained Telley.
But there are still many questions that the researchers need to answer, including where these cells are located in the brain and how they are conserved in humans. They will now work to map their distribution while studying their links to various diseases. They will also try to understand the evolutionary significance of these cells in human biology.
