Molecular Mediators Associated With Myelination, Demyelination, and Remyelination in the Peripheral Nervous System

The peripheral nervous system (PNS) is responsible for innervating all regions of the body outside of the central nervous system (CNS), the latter consisting of the brain, spinal cord, and optic nerves. While myelin is an essential component for the efficient functioning of both CNS and peripheral nerve cells, it is particularly important for PNS neurons since their cell bodies lie at considerable distances from their innervated targets. As such, regulation of myelin content and formation in the PNS is a carefully controlled process that involves many cellular and molecular players. The peripheral nerve is a multicellular environment containing several non-neuronal cell types such as fibroblasts, endothelial cells, pericytes, resident macrophages, and nonmyelinating and myelinating Schwann cells, all of which contribute to PNS homeostasis. This review focuses on the contributions of Schwann cells and macrophages and their molecular mediators in the formation, maintenance, degradation, and reformation of peripheral myelin during homeostasis of, and after damage to the PNS.