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Overabundance of a protein one of the causes of Parkinson’s disease: study (downtoearth)

Overabundance of a protein called alpha-synuclein has a key role in Parkinson’s disease, which affects more than 10 million people worldwide, says a study.

The study done by researchers at the Okinawa Institute of Science and Technology Graduate School (OIST) and is supposed to be published in Journal of Neuroscience says that overabundance of the protein in neuron play crucial role in development of the disease—the second most common neurodegenerative disorder after Alzheimer’s disease.

Parkinson’s disease results in declining physical functions, most noticeable of them being uncontrollable tremors. It involves malfunction and eventual death of the nerve cells in our brain. People with Parkinson’s disease also experience stiffness and cannot carry out movement as rapidly as before.

There is no cure for this disease and researchers have struggled for years to fully understand its cause.

Since 1990s, there has been an understanding that this particular protein causes the disease, but attempts at precisely finding its role in Parkinson’s have been unsuccessful until now.

Researchers have finally come with possible reason and role of this protein in the disease. They found that the protein hinders a key step involved in the transmission of neuronal signals essential for higher brain functions.

How does the protein affect?

Neurotransmission is a process that allows neurons to pass signals from one another, which is important for motor, sensory and cognitive functioning. When an electrical signal arrives at the nerve terminal and needs to be passed on to the next neuron, neurotransmitters (or chemical messengers) packed in a container made of lipid membrane called vesicle, mediate this process.

The neurotransmitter molecules are then released into the synaptic cleft—a small space between the neurons.

After being released, the neurotransmitter is received by the receptors in the adjacent neuron and the signal is passed along for further transmission and the vesicle is recycled back into the nerve terminal to be used again.

This retrieval of the empty vesicle membrane is called “endocytosis”, and it is this process that an overabundance of alpha-synuclein disrupts.

The process of endocytosis is critical for proper neurotransmission and when it is inhibited, the rest of the steps involved in transmission are affected as well.

Explainer: The white circles are empty vesicle and the blue ones contain a neurotransmitter. “Full” vesicles move toward the membrane of the nerve terminal, represented by the overall outline of the figure, where they attach and fuse into the terminal membrane, thereby releasing the transmitter into the space between neurons, the synaptic cleft. This release is illustrated by a blue omega-shaped structure at the bottom of the terminal membrane. When a vesicle becomes “empty,” the vesicle membrane is retrieved into the terminal—white circles on the right—and then recycled back to the release sites, which are illustrated as red bars.

“If you are using the vesicles mildly, this is okay, but if you start to use them heavily, then it becomes a problem,” explains OIST professor Tomoyuki Takahashi from the Cellular and Molecular Synaptic Function Unit.

Researchers believe that this inhibitory process caused by the overabundance of alpha-synuclein is what occurs in the early stages of Parkinson’s disease, before morphological changes such as loss of function and death of neurons take place.

When asked whether these results can help aid in developing treatment for Parkinson’s disease, Professor Takahashi replies: “I think we are getting close. We know the initial target and the mechanism but in order to step into the treatment stage, we should probably work a little bit more to know by what mechanism the microtubules interfere with endocytosis.”


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