A new method of communication between neurons and microglia in the brain has been discovered and may help to better understand multiple sclerosis.
According to the Brain Research Federation, the mammalian brain contains between 100 million and 100 billion neurons, depending on the species. In humans, the number is estimated to be between 86 and 100 billion. Neurons are specialized cells responsible for transmitting information to other cells. But there are other types of cells in our brain, such as glial cells, which play an important role in cleaning cellular waste and transporting nutrients to neurons, and microglia, cells of the immune system. Researchers have now just discovered for the first time the interaction between neurons and microglia. Their work was published in the journal Nature Communications.
Five essential elements for nerve message transmission
To understand this discovery, we first need to understand how a nerve message is transmitted. It is sent by neurons. The message first passes through axons (extensions of neurons), which are surrounded by myelin, a kind of protective membrane. Myelin insulates and protects nerve fibers in the brain and is important in the central and peripheral nervous system, especially for the transmission of nerve messages. Then there are the nodes of Ranvier, which are located between the myelin segments. They play a key role in the rapid transmission of information.
In a nutshell, there are four elements that are crucial for the transmission of nerve messages: the neuron, the axon, the myelin, and the nodes of Ranvier. The Institut national de la santé et de la recherche médicale (Inserm), the Centre national de la recherche scientifique (CNRS), the Assistance Publique – Hôpitaux de Paris (AP-HP) and researchers at the Sorbonne University have just discovered a fifth cell involved in this process: the microglia. These are immune cells that protect the brain and participate in regenerative processes such as remyelination, the production of myelin, which is reduced in diseases such as multiple sclerosis. According to the researchers, contact between neurons and microglia occurs at the junction of Ranvier.
A big step for a better understanding of multiple sclerosis
To reach this result, work was done on mice and human tissue. They observed interactions between neurons and microglia. These were particularly important during myelin regeneration. According to them, it is “neuronal activity that mediates and amplifies the interaction”. Microglia are able to ‘read’ information arriving at Ranvier’s nodes in the form of an ion signal (K+ flux). Alteration of this ionic signal can keep microglia in a pro-inflammatory state, preventing them from fulfilling their regenerative and myelin regeneration-promoting role.
In other words, when microglia no longer fulfill their regenerative role, this may be due to this interaction with neurons. This discovery is of particular relevance for future multiple sclerosis research. It may lead to a better understanding of this disease and, perhaps in the longer term, to the development of new therapies that can manipulate microglia to enhance their pro-regenerative role.