Introduction to Schwann Cell Dedifferentiation and Plasticity

The peripheral nerves consist of sensory nerves that transmit somatic and visceral afferent information to the brain via the spinal cord and motor nerves that convey efferent outputs of the brain to effector organs such as skeletal muscles and glands. The nerve conduction velocities (NCV) of mammalian peripheral nerves range from 10 m/s to 150 m/s, depending on the type of information being transmitted. Mechanistically, two important factors determine the velocity of nerve conduction, axonal diameter and the presence of myelin sheath [1]. For example, the NCV of large myelinated nerves controlling skeletal muscle contraction or transmitting proprioceptive sensory information is far faster than that of unmyelinated or small myelinated nerves that transmit pain signals [1]. Peripheral nerve myelination is achieved by the plasma membrane of Schwann cells (SCs), the sole glial cells of peripheral nerves, wrapping around axons during perinatal and early postnatal development. In fact, the myelin sheath is a notable outcome of the differentiation of SCs [2-4]. Once the myelin sheath is formed and matured postnatally, the integrity of the myelin sheath is maintained throughout life unless the nerve is physically or chemically damaged. For sustaining the structure and function of the myelin sheath during adulthood, SCs need to express continuously high levels of myelin proteins such as myelin protein zero (MPZ) and myelin basic protein (MBP) in Mitogen Activated Protein Kinase Family Proteins and c-jun Signaling in Injury-induced Schwann Cell Plasticity