In the current discussion about the origin of Multiple Sclerosis and the development of new drugs based on this, the term “glial cell” often comes up. But what are glial cells? What does this term mean?
In the following, I will compile some facts about these cells, because I believe it can help to better follow the current discussion about disease mechanisms, disease progression and drug development.
In the central nervous system (CNS, i.e., brain and spinal cord), a traditional distinction is made between nerve cells (neurons), which are responsible for signal transmission (and thus for our thinking and acting), and the glial cells, whose task is to support the neurons in their function – glial cells are thus helper cells, which are essential for a smooth function of nerve cells (and thus our central nervous system).
Glial is thus the generic term for a group of cells that play an important role in maintaining the health and function of nerve cells. This group includes
- the astrocytes,
- the oligodendrocytes, and
- the microglial cells.
Astrocytes: Let in nutrients, keep out pollutants
Astrocytes are supportive cells that help regulate the chemical and physical environment of the CNS. They help maintain the blood-brain barrier, which protects the brain from harmful substances in the blood, and also help supply nerve cells with nutrients.
Oligodendrocytes: Promote Myelin Production
Oligodendrocytes are cells that form the myelin sheath. A single oligodendrocyte ensures that about 10 nerve cells are enveloped in myelin. They are thus very metabolically active cells, which on the one hand ensure a smooth and rapid conduction of nerve fibers, but on the other hand also protect the extensions of nerve fibers from external influences. The proteins of the myelin sheath, i.e., a product of the oligodendrocytes, are the primary target of the harmful immune reaction in patients with relapsing multiple sclerosis. Restoring this myelin sheath (remyelination) is considered a promising therapeutic concept, for which satisfactory strategies have not yet been found.
Microglia: Immune Police and Waste Disposal
Microglia are finally referred to as immune cells that migrated into the central nervous system (CNS) during embryonic development and became resident here. They also play an important role in maintaining the health of the CNS. Thus, microglia constantly monitor the brain and spinal cord for signs of injury or infection. When a problem is detected, microglial cells are activated and release cytokines and other signaling molecules that attract immune cells from the periphery. In addition, microglial cells are responsible for removing damaged cells and cell debris (through phagocytosis = eating) – they thus take on the important role of “garbage disposal” in the CNS.
In the development of Multiple Sclerosis (MS), microglia cells, as resident immune cells, naturally play an important role. Especially the overactivation of microglia cells, especially in the late, progressive phases of Multiple Sclerosis, has recently put this cell type at the center of scientific interest. Modulating microglia cells is now seen as a promising approach to positively influence progressive MS courses. The drug group of Bruton tyrosine kinase inhibitors (BTKi) is able to slow down microglia activation and is therefore seen as a promising approach to achieve an effect even in progressive MS (see corresponding contributions to BTKi at MS DocBlog). – Whether this approach is effective and how great the extent of its effectiveness is, however, must first be demonstrated by clinical studies currently being conducted.
