The discovery reveals the prolific ability of Schwann cells to generate myelin

Scientists have discovered that a particular type of cell produces a protective sheath covering nerve fibers much more prolific than previously thought.

The revelation on Schwann cells suggests new ways to treat nerve damage and various forms of neuropathy. Other research may prove useful for promoting myelin repair in central nervous system disorders such as multiple sclerosis, where myelin lesions slow down or block electrical signals from the brain.

"This completely disrupts the definition of the Schwann cell workbooks," said Kelly Monk, senior author, Ph.D., professor and co-director of the Vollum Institute at Oregon Health & Science University.

The research published today in the journal Nature Communications.

Myelin is produced by two types of cells: oligodendrocytes in the brain and spinal cord, and Schwann cells in the rest of the body. Until now, scientists thought that only oligodendrocytes generated several myelin sheaths around the axons, the thin projection of a nerve cell that carried electrical signals between cells.

The new research reveals that Schwann cells are also able to diffuse myelin on several axons.

The researchers made this discovery after performing a genetic screening in zebrafish in Monk's lab. They found that some fish contained more myelin than expected and that these fish carried a mutation of the fbxw7 gene. When they neutralized the gene in genetically modified mice, they discovered an unexpected feature: Individual Schwann cells began to spread myelin in many axons.

"This highlights a very plastic potential for these cells," said Monk.

By discovering how Schwann cells generate myelin at the molecular level, this discovery could lead to new gene therapy techniques to repair damaged myelin in disorders of the peripheral nervous system such as Charcot-Marie-Tooth disease, a form of painful hereditary neuropathy 2500 people in the United States.

Schwann cells and oligodendrocytes appeared at the same time in evolutionary history, with the appearance of jaws in the vertebrate lineage. Invertebrates lack myelin and some, such as modern squid, use thick axons to rapidly transmit signals between neurons.

"We could have evolved this way, but our spine would have the diameter of a giant sequoia," Monk said.

Instead, vertebrate axons developed myelin to protect axons and accelerate signal transmission. To create myelin, Schwann cells evolved to produce it around a single axon in the peripheral nervous system. Oligodendrocytes, in turn, generated myelin along several axons in the more confined environment of the brain and spine, the central nervous system.

"Real estate is fundamentally different in the central nervous system than in the peripheral nervous system," Monk said.

Monk believes that Schwann cells have developed a mechanism to repair damaged myelin cell by cell, as it would have been common for injuries to occur without necessarily killing the entire body. These traits have been transmitted and reinforced over generations.

In contrast, remyelinization in the central nervous system tended to be an evolutionary impasse since few would have survived violent shock to the brain or spine.

"There is no selective pressure in repairing myelin damage in the central nervous system because you will probably die," Monk said.

However, the discovery released today suggests a new opportunity to heal the brain and spine.

"Targeting the fbxw7 gene – or molecules in the downstream pathway – could be a powerful way to promote myelin repair in the central nervous system," said Monk.