Remyelination: Function, Role & Diseases

In medicine, remyelination describes a process in which the body partially restores the insulating myelin layer that normally surrounds nerve fibers (axons). Often, remyelination is not completely successful, so permanent damage is possible. Various diseases (for example, multiple sclerosis, funicular myelosis, or Miller-Fisher syndrome) can affect the myelin sheaths of nerve cells.

What is remyelination?

In medicine, remyelination describes a process in which the body partially restores the insulating myelin sheath (shown in light blue in the figure) that normally surrounds nerve fibers (axons). Remyelination is a process that aims to restore myelin sheaths after they have been lost or damaged. Myelin sheaths arise from Schwann’s cells or oligodendrocytes, which are found on the nerve fibers (axons) of neuronal cells, among others. Whether Schwann’s cells or oligodendrocytes serve as the origin for myelin formation depends on where the respective nerve cell is located. While Schwann’s cells primarily form the myelin layer of neurons in the peripheral nervous system, oligodendrocytes are primarily responsible for its formation on nerve fibers in the central nervous system (brain and spinal cord). Both Schwann’s cells and oligodendrocytes belong to the glial cells, which account for a significant proportion of the total mass in the brain. As they grow, the myelin sheath spirals around the filamentous axon, forming a multilayered sheet. A myelin sheath can comprise about 50 such wrappings. Without the myelin sheaths, neurons are not optimally able to communicate with each other. This results in numerous problems in information processing. For example, destruction of the myelin sheaths may be due to a disease such as multiple sclerosis or Miller-Fisher syndrome.

Function and task

Remyelination is an attempt by the human body to repair damage to the myelin sheaths and resolve associated functional limitations of the nervous system. However, the organism often cannot fully compensate for the loss of myelin. Myelin is a biological membrane formed by glial cells that serves as an insulating layer for the nerve fibers in the central and peripheral nervous system. The nerve fibers are thin extensions of the cells through which information is removed from the cell bodies by electrical impulses. When information is transmitted to other nerve cells, the electrical impulse travels along the axon to the thickened terminal nodules, which convert it into a chemical signal. The messenger substances formed reach the next cell through the synaptic cleft, where they again trigger an electrical signal. The insulating myelin sheath improves transmission: the impulse jumps from one cord ring to the next. Damage to the myelin sheath leads to poorer electrical insulation of the neurons and thus impairs the transmission and processing of information in the nervous system. Remyelination, which is initiated by the human body itself, is therefore extremely important. However, in severe neurological diseases, it is usually not sufficient to stop or reverse the course of the disease. Medical researchers, however, see hope in future therapeutic approaches. Drugs and other treatments could then potentially enhance natural remyelination.

Diseases and conditions

Remyelination becomes especially necessary when people suffer from certain diseases of the nervous system, such as demyelinating diseases or demyelinating neuropathies. One of the demyelinating diseases is multiple sclerosis, also known by the Latin name encephalomyelitis disseminata. This is a clinical picture characterized by multiple foci of inflammation in the brain. In areas of the brain affected by these foci of inflammation, damage occurs to the myelin sheaths that electrically insulate the axons of nerve cells. As a rule, multiple sclerosis occurs in relapses, during which patients are particularly severely affected. Less frequently, the disease progresses in a continuously worsening manner.Symptoms that may occur in the context of multiple sclerosis include pain, visual disturbances, numbness, and motor disturbances such as paresis. If the disease progresses far, subcortical dementia may develop. The various symptoms manifest due to impaired signal transmission in the brain and are therefore extraordinarily diverse. It depends on the location of the inflammatory foci which symptoms develop. Researchers assume that the immune system plays an important role in the development of multiple sclerosis. So far, however, there is still a great deal of uncertainty about the exact causes, so that general statements are difficult to make. The demyelinating diseases also include Miller-Fisher syndrome, which is also associated with demyelination of the nerve cells and is a rare form of Guillain-Barré syndrome. The disease can manifest as paralysis of the eye muscles, impaired coordination of movement, and complete absence of at least one reflex. As with multiple sclerosis, an inflammatory response is responsible for Miller-Fisher syndrome. Another example of a demyelinating disease is funicular myelosis. Possible symptoms include sensory disturbances (e.g., burning sensation in the hands and feet), impaired coordination of movement, paralysis in the legs, and psychological symptoms, including depressive or psychotic symptoms. In Funicular Myelosis, demyelination of nerve fibers occurs in the spinal cord, which is why there is a risk of paraplegia. The neurological disease is due to a deficiency of vitamin B12.