remyelination

Remyelination is the process by which the myelin sheath around demyelinated axons is restored after injury or disease. This restoration re-establishes saltatory conduction, increases nerve impulse speed, and helps protect axons from degeneration. Remyelination can occur in both the central nervous system (CNS) and the peripheral nervous system (PNS), though the cellular players and mechanisms differ between these compartments.

In the CNS, remyelination is mainly carried out by oligodendrocyte precursor cells (OPCs). OPCs proliferate, migrate to sites of demyelination, differentiate into mature oligodendrocytes, and form new myelin sheaths around exposed axons. Microglia and macrophages help by clearing myelin debris and releasing factors that support repair, while axonal signals influence the timing and extent of remyelination. The newly formed myelin is typically thinner than during development, resulting in a higher g-ratio, and the nodes of Ranvier are re-established to restore conduction.

In the PNS, remyelination is performed by Schwann cells. Following injury, Schwann cells dedifferentiate, proliferate, and remyelinate axons, often producing relatively robust myelin sheaths compared with CNS repair. The regulatory environment and cellular cues differ from the CNS, reflecting the distinct biology of Schwann cells.

Clinical relevance and limitations: Remyelination can occur in diseases such as multiple sclerosis but is often incomplete and patchy, and its efficiency declines with age and chronic inflammation. Successful remyelination can restore conduction and protect axons, whereas failure to remyelinate contributes to progressive neurological decline.

Assessment and research: Remyelination is evaluated with imaging techniques sensitive to myelin content, as well as histology and electron microscopy to measure myelin thickness and g-ratio. Therapeutic strategies aim to enhance OPC recruitment and differentiation, modulate inflammation, or replace cells, but no widely approved remyelination therapy exists yet.