Multiple sclerosis (MS) is a brain disease caused by nerves losing their electrical insulation and the degeneration of nerve fibers called axons.
It was previously thought by most scientists that once axons lose their insulation they are unable to function. So it was a surprise for a team of researchers who found that axons in rats with MS could survive for long periods even after losing myelin (the electrical insulation).
This is a ground-breaking discovery that challenges the accepted view of MS. The study, led by graduate student Chelsey Smith and former undergraduate Elizabeth Cooksey, will be published in the Journal of Neuroscience.
The axons in the rats continued to survive for months after myelin deterioration.
Senior author, Ian Duncan, professor in the School of Veterinary Medicine at the University of Wisconsin-Madison, said:
"This was the first study to demonstrate long-term axon survival after myelin deterioration. Nine months is a relatively long period in a rat's lifetime, and there wasn't a loss of axons, so the assumption that axons must automatically die without myelin seems incorrect."
The insulating myelin is normally created by oligodendrocytes which are cells that are found near the axons. The researchers discovered that these cells produce growth factors essential for the survival of neurons.
"That is just speculation, but in our study, the oligodendrocytes were found in much greater numbers, probably in an attempt to produce more myelin, and we saw an overall increase in growth factor production."
The study is the first of its kind to reveal the true extent of oligodendrocytes expressing growth factors. It's known that these cells produce growth factors early on in life, however, they found three different neural growth factors that these cells produce in older animals.
Duncan said: "This paper was the first to show that oligodendrocytes continue to express growth factors in mature animals, and that could be important."
The absence of growth factors - proteins that are necessary for growth and development - is associated with a series of neurological diseases.
Duncan stresses the need to carry out further studies of growth factors, as it might be crucial in preventing myelin loss in MS.
Although scientists have known about the degeneration and gradual disappearance of axons in MS, until now it hasn't been certain whether degeneration occurs at the same time as demyelination.
"Much in vogue is the idea that you have to protect axons above and beyond everything else, that MS is not primarily a demyelinating disease, it's primarily an axonal disease. Our finding shows that it is not absolutely certain that axons will degenerate when they are demyelinated. If we are correct in our speculation, we could potentially protect the axon if we can increase the amount of growth factor being produced by the helper cells."
German scientists recently identified an inhibitor of myelin formation in the central nervous system. They say their finding may help provide a molecular explanation for myelination failures in MS, which may help eventually devise treatment to prevent this failure.
Written by Joseph Nordqvist