Yale Researchers Identify Key Proteins Behind Parkinson's Disease Spread in the Brain

Researchers at Yale School of Medicine have identified two proteins on the surface of neurons that appear to play a crucial role in spreading the toxic protein responsible for Parkinson's disease throughout the brain. The findings, published in the journal Nature Communications, suggest a potential new avenue for therapies aimed at slowing or stopping the neurodegenerative disorder rather than merely managing its symptoms.

Parkinson's disease is a progressive neurological condition in which brain cells gradually become damaged and die. A hallmark of the disease is the accumulation of a misfolded protein known as alpha-synuclein. As this toxic protein moves from one neuron to another, it drives the worsening of symptoms over time, including tremors, impaired balance, and slowed movement.

Unraveling How Alpha-Synuclein Invades Healthy Neurons

Until now, scientists have not fully understood how alpha-synuclein enters healthy neurons after escaping from dying ones. The Yale research team, led by senior author Stephen Strittmatter, MD, PhD, set out to uncover the molecular mechanism behind this process. Strittmatter, who serves as the Vincent Coates Professor of Neurology and chair of the Department of Neuroscience at Yale School of Medicine, described misfolded alpha-synuclein as the pathologic hallmark of Parkinson's disease.

If researchers can understand how the protein gets into neurons, they could potentially block or slow down the progression of the disease, Strittmatter noted. However, he emphasized that achieving this goal requires understanding exactly how the protein spreads at the molecular level.

To investigate, the research team produced 4,400 groups of cells, each engineered to display a different surface protein. They then tested whether misfolded alpha-synuclein would bind to any of them. The vast majority showed no interaction, but 16 surface proteins did bind to the toxic protein. Among them were two proteins called mGluR4 and NPDC1, which are found on dopamine-producing neurons in the substantia nigra, the brain region most heavily affected by Parkinson's disease. The team discovered that these proteins actively transported misfolded alpha-synuclein into the cells.

Blocking the Proteins Halts Disease Progression in Mice

Having identified the two proteins, the researchers next examined whether they were responsible for helping alpha-synuclein move from neuron to neuron. They genetically engineered mice so that either mGluR4 or NPDC1 no longer functioned, then exposed the animals to misfolded alpha-synuclein.

Normal mice developed accumulations of the toxic protein in their brains and subsequently showed Parkinson's-like symptoms. In contrast, mice lacking functional mGluR4 or NPDC1 did not. In a separate mouse model of Parkinson's disease, removing the genes for either protein also reduced symptom progression and lowered the risk of death.

Together, the findings indicate that mGluR4 and NPDC1 work as partners to transport misfolded alpha-synuclein into neurons, at least in mice. Strittmatter said this mechanism represents a promising target for future therapies, noting that existing treatments mainly help manage symptoms and do not significantly slow the underlying disease process. Blocking the spread of alpha-synuclein between neurons could provide a way to slow or even halt Parkinson's progression.

A Growing Public Health Challenge

Neurodegenerative disorders such as Parkinson's and Alzheimer's disease pose an increasingly significant public health challenge in the United States. According to the Parkinson's Foundation, approximately 1.1 million Americans are currently living with Parkinson's disease, and nearly 90,000 new cases are diagnosed each year.

The need for disease-slowing therapies is expected to grow in the years ahead. Parkinson's disease and other neurodegenerative disorders primarily affect older adults, and the number of Americans over age 65 is projected to rise substantially over the coming decades, expanding the population at risk.

Strittmatter underscored the urgency of the situation, noting that the aging population makes the question of how to stop or slow neurons from dying an enormous problem. He described the current moment as the time to make real inroads into figuring out how to slow the disease down.

The discovery of mGluR4 and NPDC1 as key transporters of alpha-synuclein offers a concrete molecular target that researchers can build upon. If future studies confirm these findings in humans, blocking the spread of the toxic protein between neurons could transform how Parkinson's disease is treated, shifting the focus from symptom management to genuinely altering the course of the disease.

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Source: ScienceDaily