Researchers report that they have identified a protein-protein interaction that contributes to Parkinson’s disease.

In Parkinson’s, the α-synuclein (a-syn) protein accumulates in the brain and leads to cell death. Much research is currently focused on clearing a-syn with antibodies or using small molecules to prevent a-syn from aggregating. In their study, “Disrupting the α-synuclein-ESCRT interaction with a peptide inhibitor mitigates neurodegeneration in preclinical models of Parkinson’s disease,” published in Nature Communications, the researchers took an alternate approach by looking for protein-protein interactions that may be promoting the accumulation of a-syn in Parkinson’s disease.

“Accumulation of α-synuclein into toxic oligomers or fibrils is implicated in dopaminergic neurodegeneration in Parkinson’s disease. Here we performed a high-throughput, proteome-wide peptide screen to identify protein-protein interaction inhibitors that reduce α-synuclein oligomer levels and their associated cytotoxicity,” the investigators wrote.

“We find that the most potent peptide inhibitor disrupts the direct interaction between the C-terminal region of α-synuclein and CHarged Multivesicular body Protein 2B (CHMP2B), a component of the Endosomal Sorting Complex Required for Transport-III (ESCRT-III). We show that α-synuclein impedes endolysosomal activity via this interaction, thereby inhibiting its own degradation.

“Conversely, the peptide inhibitor restores endolysosomal function and thereby decreases α-synuclein levels in multiple models, including female and male human cells harboring disease-causing α-synuclein mutations. Furthermore, the peptide inhibitor protects dopaminergic neurons from α-synuclein-mediated degeneration in hermaphroditic C. elegans and preclinical Parkinson’s disease models using female rats.

“Thus, the α-synuclein-CHMP2B interaction is a potential therapeutic target for neurodegenerative disorders.”

A slow and painstaking process

“Identifying a particular interaction that contributes to a disease and then finding ways to disrupt it, can be a painstaking and incredibly slow process,” explained Lorraine Kalia, MD, PhD, who is a staff neurologist at University Health Network and a scientist, Temerty Faculty of Medicine, at the University of Toronto’s Tanz Centre for Research in Neurodegenerative Diseases.

“We all started out a bit skeptical that we would have something useful at the end, and so the fact that we do have something that warrants further work is much more than we anticipated.”

According to Philip M. Kim, PhD, professor of molecular genetics, University of Toronto, the team took the reverse approach to expedite the discovery of potential therapies. “We developed a platform to screen molecules called peptide motifs—short strings of amino acids that can disrupt protein-protein interactions—for their ability to protect cells from a-syn. Once we identified candidate peptides, we determined which protein-protein interactions they target.”

Drs. Suneil and Lorraine Kalia are senior scientists at the Krembil Brain Institute at the University Health Network in Toronto.

Through this approach, the team identified a peptide that reduced a-syn levels in cells by disrupting the interaction between a-syn and a protein subunit of the cellular machinery called “endosomal sorting complex required for transport III” (ESCRT-III).

“ESCRT-III is a component of a pathway that cells use to break down proteins, called the endolysosomal pathway,” added Lorraine Kalia. “We discovered that a-syn interacts with a protein within ESCRT-III—CHMP2B—to inhibit this pathway, thereby preventing its own destruction.

“We were impressed that the platform worked. But what was more interesting is that, by doing this kind of screening, we were able to find an interaction that was really not previously characterized, and we also found a pathway that’s not yet been targeted for therapeutics.”

According to Suneil Kalia, MD, PhD, senior scientist, Krembil Research Institute, once the group identified this interaction, they confirmed that they could use their peptide to disrupt it, preventing a-syn from evading the cell’s natural clearance pathways.

“We tested the peptide in multiple experimental models of Parkinson’s disease, and we consistently found that it restored endolysosomal function, promoted a-syn clearance, and prevented cell death,” he said.

These findings indicate that the a-syn-CHMP2B interaction is a potential therapeutic target for the disease, as well as other conditions that involve a buildup of a-syn, such as dementia with Lewy bodies.

The next steps for this research are to clarify exactly how a-syn and CHMP2B interact to disrupt endolysosomal activity. Ongoing studies are also determining the best approach for delivering potential therapeutics to the brain.

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