By Joan Magruder

Jacob Israelachvilli   Joe Zasadzinski

UCSB scientists have made an important discovery that will increase the understanding of multiple sclerosis, a debilitating disease of the central nervous system. In MS, the myelin sheath, an insulating membrane surrounding the nerve cells in the brain and spinal cord, starts to unravel for reasons as yet unknown.

In a paper, which appeared last month in the Proceedings of the National Academy of Science, the researchers described results that show how the unraveling occurs.

The myelin sheath is made of a lipid bilayer (similar to those in the cell membrane) wrapped many times around the nerve axon—the part of a nerve cell through which electrical impulses travel away from the cell body.

One specific protein, called myelin basic protein, acts to hold the myelin sheath tightly together around the axon. Axons serve as the electrical wires that connect the nerve cells, and the myelin is t he insulation that keeps the impulses flowing quickly and reliably.

“If the myelin breaks down, the nerve’s electrical impulses leak out, slow down, and generally don’t work very well,” says Joe Zasadzinski, professor of chemical engineering at UCSB.

	Cynthia Husted

Zasadzinski, with co-authors Jacob Israelachvili, professor of chemical engineering, graduate student Yufang Hu, and postdoctoral fellow Ivo Doudevski, and Cynthia Husted, director of the Center for the Study of Neurodegenerative Disorders, write: “We have discovered that in the progression of MS, there are small changes in the lipid composition of myelin.

“There is less negatively charged lipid in the membrane and more neutral, or uncharged, lipids. Myelin basic protein is positively charged and gets in between the bilayers to link up the negatively-charged lipids and glue the myelin sheath together.”

The scientists explain that the tightest seal occurs when the amount of negative charge from the lipids match the amount of positive charge from the protein. If there is too much of either one, the bilayers start to repel each other.

“Although we can’t say why the lipid composition changes, with this new knowledge, perhaps we can suggest methods of trying to treat the unraveling before it gets too far along,” Zasadzinski says.

Zasadzinski, Husted, and Israelachvili discovered that the myelin basic protein acts as a patch to fill in holes in the myelin bilayers.

“It is similar to the stuff you put in your tires to fix punctures,” Zasadzinski explains. “The myelin basic protein floats around until it finds a hole, binds to the edge of the hole and then pushes the lipids to fill in the hole, insuring good insulation from the myelin sheath.”