Remyelination

Remyelination is the process of propagating oligodendrocyte precursor cells to form oligodendrocytes to create new myelin sheaths on demyelinated axons in the CNS. This is a process naturally regulated in the body and tends to be very efficient in a healthy CNS.The process creates a thinner myelin sheath than normal, but it helps to protect the axon from further damage, from overall degeneration, and proves to increase conductance once again. The processes underlying remyelination are under investigation in the hope of finding treatments for Demyelinating diseases, such as multiple sclerosis. Remyelination is the process of propagating oligodendrocyte precursor cells to form oligodendrocytes to create new myelin sheaths on demyelinated axons in the CNS. This is a process naturally regulated in the body and tends to be very efficient in a healthy CNS.The process creates a thinner myelin sheath than normal, but it helps to protect the axon from further damage, from overall degeneration, and proves to increase conductance once again. The processes underlying remyelination are under investigation in the hope of finding treatments for Demyelinating diseases, such as multiple sclerosis. Remyelination is activated and regulated by a variety of factors surrounding lesion sites that control the migration and differentiation of Oligodendrocyte Precursor Cells. Remyelination looks different from developmental myelination in the structure of the myelin formed. Reasons for this are unclear, but proper function of the axon is restored regardless. Perhaps of most interest are the inhibition and promotion factors of this physiological process. One way this process can be traced is by following different protein activation sequences which have shown just how quickly remyelination begins after injury (within a few of days). The most notable evidence that remyelination has taken place on an axon is its thin myelin sheath created by an oligodendrocyte, though the reason why the new myelin sheath is thinner remains unclear. This can be quantified in the g-ratio, the ratio between the diameter of the axon itself to the outer diameter of the myelinated fiber. Remyelinated axons tend to have values closer to 1, indicating a thinner myelin sheath than those myelinated naturally. The g-ratio differences are less apparent on smaller axons. The thinner myelin not only restores protection of the axon from degradation, but also restores a faster conduction velocity. The conduction velocity, however, is not as strong as naturally myelinated axons and the Nodes of Ranvier are inclined to be wider which results in less coverage in the axon by myelin than what is natural. Oligodendrocyte Precursor Cells, or OPC's, are the main cells responsible for the remyelination of demyelinated axons. There are two physiological changes that must occur to OPC's for remyelination to occur. Once a signal is sent that remyelination is needed, OPC's will first migrate to damaged axon. This process may be signaled or enhanced by microglia or astrocytes at the injured axon site that stimulate migratory OPC pathways From there the cells must differentiate from being progenitors to being pre-oligodendrocytes, then premyelinating oligodendrocytes, and finally mature oligodendrocytes. These oligodendrocytes can then wrap damaged axons with new myelin sheaths. This process of differentiation through several phases has many involved and direct pathways and factors necessary for the completion of this process. It is easy to completely stop remyelination with the failure of a number of pathways.