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Thursday, 17 October, 2002, 23:01 GMT 00:01 UK
Scientists reveal how CJD kills cells
Brain scans
CJD progressively kills brain cells
Researchers may have uncovered why the "rogue" prion protein which causes BSE and vCJD is such an efficient destroyer of brain cells.

Scientists at two US research centres have discovered that the presence of the protein in one particular part of the brain cell is enough to poison it.


If we know how they kill cells we might be able to come up with a means of stopping cell death

Dr Sean Heaphy, University of Leicester
CJD is the best-known type of disease thought to be caused by "rogue" prions.

These are "misshapen" versions of a normal cell protein, which stop behaving in the normal way and cannot be disposed of by the cell.

However, it is their ability to convert normal prion proteins into further rogue versions that allows them to propagate and spread.

It is thought that eating beef infected with prions from a similar bovine disease, BSE, could have contributed to the illness.

However, there is little available evidence as to why and how the rogue prion kills the cell.

Clumpy clues

The only clue to date are large clumps of the misshapen protein gathered in the cells of humans and animals which have developed either vCJD or BSE.

However, the US research suggests that relatively small amounts of the "misfolded" prion can accumulate in part of the cell called the cytosol and somehow poison it.

The experiments found this was the case in both laboratory cells and genetically-altered mice.

The finding could help doctors devise ways of heading off the process - and assist the cell in its bid to clear itself of the misfolded protein.

Death toll

The research, published in the top US journal Science, sheds new light on a type of "infectious" agent which only came to light a couple of decades ago.

Brain lobe
CJD is thought to be caused by prions
More than 100 people in the UK have so far died from the variant form of CJD, and "worst-case" estimates still suggests that many thousands could fall ill over the course of an epidemic.

In the US, there is some concern over similar "spongiform" diseases in elk and deer, and the possibility that infective prions might have entered the food chain through hunted meat.

There is still no recognised way to treat patients who have already developed the signs of CJD.

Learning more about how the cell tries and fails to deal with rogue prions could help scientists find ways to block them.

Proteins, including the healthy version of the prion protein, carry out a variety of vital chemical roles inside and outside the cells.

Although the precise role of the prion protein is unclear, it is possible that plays a part in grabbing much needed copper ions floating past its surface and dragging them inside.

Recycling

Every brain cell has methods to deal with proteins that have become faulty or simply too old to be trusted to do their job safely.

One way is to "recycle them", by moving them to a part of the cell within the cytosol where they can be "degraded" and their parts used to make new proteins.

This, it appears is what happens with the rogue prion protein, called PrPSc.

However, while the misfolded prion is efficiently dragged back into the cytosol, its particular shape makes it insoluble - extremely difficult for the cell to break down.

Instead, increasing amounts of PrPSc start to build up.

Cell suicide

Scientists are divided over how this harms the cell, with some suggesting that the sheer volume of PrPSc in this cell space eventually overwhelms the cell - producing the "clumps" seen in the brains of CJD patients.

However the latest research suggests that, as relatively little PrPSc in the cytosol is enough to kill a cell, its presence must trigger a reaction which leads to the cell committing suicide.

Professor Ian Jones, a virologist from the University of Reading, said: "If we can identify the key changes - exactly what happens when a misfolded prion forms, we may be able to interfere with that process."

Dr Sean Heaphy, an expert in microbiology from the University of Leicester, told BBC News Online that while much research was focused on ways of preventing the prion getting out of shape in the first place - preventing illness from developing - it was "far more difficult" to help the body either convert it back or dispose of it once the change had taken place.

"Stopping it starting is definitely the best option at the moment.

"But if we know how they kill cells we might be able to come up with a means of stopping cell death."

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