London, Jan 25 (ANI): A new study suggests that prion proteins that can cause Creutzfeldt-Jakob disease (CJD) play an important role in the nervous system.
According to an international team of neuroscientists, these proteins help maintain the myelin sheath, which plays a key role in the protection of the ody's nerves.
"This opens a new door to studying some of the many common neuropathy disorders - which lead to weakness or loss of sensitivity of limbs - where we don't know the cause," Nature quoted prion expert Simon Mead at University College London's Institute of Neurology, as saying.
The authors believe their conclusions can also be applied to brain neurons. If this is the case, the research would open new avenues for the treatment of CJD and other transmissible spongiform encephalopathies.
It could also give scientists a chance to look at multiple sclerosis - an incurable disease caused by demyelination of nerves in the brain and spinal cord - in a new way.
Prions have been ascribed with many functions in the last couple of decades but none could be established.
Adriano Aguzzi at the University Hospital of Zurich in Switzerland, who led the new work, said: "The first mouse with knocked-out prion genes was made back in 1991.
"We leapt on it, and studied it in every way we could think of - but never managed to find any obvious sign that lack of the prion was causing it harm."
In fact, initially, it seemed that the lack of prions was good since it made mice immune to prion infection.
But four years ago, Aguzzi began thinking about a generally overlooked 1999 paper by Japanese researchers, which suggested the lack of prion protein caused the degeneration and demyelination of nerves outside the brain. Now, he made up his mind to conduct a thorough and systematic analysis of prions' effects on such peripheral nerves.
Aguzzi and his team studied four different strains of mice lacking the gene for the prion PrPC. Every mouse tested showed early evidence of myelin damage just six weeks after birth. By two months of age, the nerves were extensively demyelinated, and the mice were more sensitive to pain.
Aguzzi explained: "Because there is no myelin damage at birth, we assumed prions are needed to maintain the quality of the myelin sheath, which diminishes throughout life."
When the scientists re-introduced prion proteins specifically into nerves, the demyelination did not occur. Interestingly, only variants of prion proteins prone to cleavage by enzymes were effective.
But no variant of prion protein was able to prevent demyelination when introduced specifically into the Schwann cells, which surround and support peripheral nerve cells.
Aguzzi said: "This surprised us...since Schwann cells actually do the job of manufacturing fresh myelin."
Aguzzi pointed out that when nerves' sheathes are going through wear and tear, the nerves enzymatically cleave their prion proteins, releasing fragments that travel to Schwann cells, where they signal activation of myelin repair.
He also thinks prion proteins may play the same part in supporting myelination in the brain.
He said: "So it is going to be interesting to see if prions play any role in demyelinating diseases that stem from the brain."
Mead added: "Treatment of CJD targets prion proteins, which are assumed to be doing the damage...But if CJD did indeed turn out to be caused by absence of prions, then we would have to rethink this therapeutic approach."
The study has appeared online in Nature Neuroscience. (ANI)
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