Page last updated at 00:02 GMT, Monday, 25 January 2010

Prions 'may keep nerves healthy'

Removing prion proteins led to a breakdown of the myelin sheath surrounding the nerve

Experiments on mice may help scientists understand the workings of the prion protein linked to brain disease vCJD.

Swiss researchers say there is evidence that prions play a vital role in the maintenance of the sheath surrounding our nerves.

They say it is possible that an absence of prions causes diseases of the peripheral nervous system.

One expert said there was growing evidence that the prion had a number of important roles in the body.

As well as the latest research in the journal Nature Neuroscience, other studies have indicated prions may protect us from Alzheimer's disease or even play a role in our sense of smell.

Most people started by focusing on prions in relation to a human disease, and have only recently started to examine what it normally does
Professor Nigel Hooper, Leeds University

The prion protein only came to the attention of scientists in recent years as they searched for the cause of vCJD - the human variant of BSE, or Mad Cow Disease.

This degenerative and incurable brain condition is now thought to be caused by a "mis-folded" version of the prion.

However, there is still little understanding of what the protein is supposed to do in its normal, healthy, form.

Healthy prions

The study, by scientists at the University Hospital in Zurich, looked at mice bred with fewer prion proteins.

While these mice are known to be resistant to prion diseases equivalent to vCJD in humans, they showed a number of abnormalities, including a degeneration, later in life, of the peripheral nerve cells, and the protective myelin sheath which surrounds them.

Peripheral nerves are those which link the limbs and organs to the central nervous system - the spinal cord and brain.

Looking more closely, researchers examined the effects of removing the prion protein in both the nerve cells themselves, and the Schwann cells surrounding them, which are responsible for making the myelin sheath.

While removing protein from the Schwann cells had no effect, taking it from the neurons led to a breakdown of the myelin and degeneration of the nerve cells.

They said that the knowledge that prion protein played some role in the healthy upkeep of nerve cells could offer a new avenue of research into diseases affecting humans.

However, scientists caution that it is too early to pick out a particular peripheral nerve condition which might correspond to the mouse experiments.

Recent work

Professor Nigel Hooper, from the University of Leeds, agreed that the role of the protein was not well understood.

His own work, published in 2007, suggested that it might offer some protection from the development of Alzheimer's disease.

But he said this was unlikely to be the complete answer.

He said: "Most people started by focusing on prions in relation to a human disease, and have only recently started to examine what it normally does.

"There is some evidence that it could have a number of different roles, depending on its whereabouts in the body - a recent paper linked it to olfaction or the sense of smell."

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