α-Synuclein aggregations in Parkinson’s disease (PD) and multiple system atrophy (MSA) patients. Credit: Virginia Lee, PhD, Perelman School of Medicine, University of Pennsylvania; Nature
PHILADELPHIA – Different Parkinson’s-related brain disorders, called synucleionpathies, are characterized by misfolded proteins embedded in cells. Researchers in the Perelman School of Medicine at the University of Pennsylvania found that the type of brain cell afflicted dictates which pathological form of α-synuclein (α-syn) protein becomes the disease culprit. The team’s results were published this week in Nature.
“These unexpected findings of the effect of cell type on the generation of different α-syn strains addresses one of the most important mysteries in neurodegenerative disease research,” said first author Chao Peng, PhD, a research associate in the Center for Neurodegenerative Disease Research (CNDR).
The relationship between cell type and variety of disease protein has not been described for any other neurodegenerative brain disorder. For now, the hope is that one strain associated with multiple system atrophy (MSA) might point the way to new therapies.
What had been known before this Nature study is that in cases of Parkinson’s disease without and with dementia, dementia with Lewy bodies, and in about 50 percent of Alzheimer’s disease patients, α-syn aggregates in neurons as Lewy bodies (LBs) and Lewy neurites in axons and dendrites. However, in MSA, a rare neurodegenerative disease with widespread effects on the brain and body, α-syn behaves differently. It mainly accumulates as glial cytoplasmic inclusions (GCIs) outside the nucleus in the cytoplasm of oligodendrocytes, a brain structural cell important for myelin production (the insulation material of nerve cell fibers).
The Penn team found that pathological α-syn in GCIs versus LBs are distinct in shape and biology. The α-syn in GCIs forms more compact structures and is about 1,000-fold more potent in seeding and spreading α-syn aggregation in animal models, which is consistent with the highly aggressive nature of MSA.
“Years ago we found that α-syn fibrils act as ‘seeds’ that induce normal α-syn protein to aggregate into clumps,” said senior author Virginia M.-Y. Lee, PhD, CNDR director and a professor of Pathology and Laboratory Medicine. “We showed that α-syn fibrils were taken up by healthy neurons, which leads to the formation of Lewy bodies and neurites that impair neuron function, leading to nerve cell death.”
GCI-α-Syn and LB-α-Syn strains do not have cell-type preferences and they can both be initiated by the same misfolded α-Syn seeds (grey spheres), but different intracellular environments of neurons and oligodendrocytes convert these α-Syn seeds to different strains. Credit: Virginia Lee, PhD, Perelman School of Medicine, University of Pennsylvania; Nature
Surprisingly, say the researchers, pathological α-syn in GCIs and LBs did not show a preference for a specific cell type in starting pathology when human brain-derived α-syn of each type was used to induce aggregates in cell culture and mouse models.
“This raises the question of why α-syn pathology in Parkinson’s disease versus multiple system atrophy shows different potencies, properties, and distributions in neurons versus glial cells,” Lee said.
The researchers also found that oligodendrocytes, but not neurons, transform misfolded α-syn into the cytoplasmic strain, which explains the distribution of the two forms by cell type. On the other hand, cytoplasmic α-syn maintains its active seeding function when propagated from neuron to neuron. From this, the researchers concluded that α-syn strains are determined by both misfolded α-syn seeds and cell type.
The team’s next steps will be to uncover the underlying molecular mechanism for the differences between the strains. The molecules in oligodendrocytes responsible for the highly potent cytoplasmic strain might suggest viable drug targets for MSA and explain why therapies used to treat other synucleinopathies may not work for MSA patients.
Other coauthors, all from the department of Pathology and Laboratory Medicine, are Ronald J. Gathagan, Dustin J. Covell, Coraima Medellin, Anna Stieber, John L. Robinson, Bin Zhang, Rose M. Pitkin, Modupe F. Olufemi, Kelvin C. Luk, and John Q. Trojanowski.
This work was funded by the National Institute of Neurological Disorders and Stroke Udall Center (NS53488), the Ofer Nimerovsky Family Fund, the Jeff and Anne Keefer Fund, and the MSA Coalition Global Seed Grant.
Penn Medicine is one of the world’s leading academic medical centers, dedicated to the related missions of medical education, biomedical research, and excellence in patient care. Penn Medicine consists of the Raymond and Ruth Perelman School of Medicine at the University of Pennsylvania (founded in 1765 as the nation’s first medical school) and the University of Pennsylvania Health System, which together form a $8.6 billion enterprise.
The Perelman School of Medicine has been ranked among the top medical schools in the United States for more than 20 years, according to U.S. News & World Report's survey of research-oriented medical schools. The School is consistently among the nation's top recipients of funding from the National Institutes of Health, with $494 million awarded in the 2019 fiscal year.
The University of Pennsylvania Health System’s patient care facilities include: the Hospital of the University of Pennsylvania and Penn Presbyterian Medical Center—which are recognized as one of the nation’s top “Honor Roll” hospitals by U.S. News & World Report—Chester County Hospital; Lancaster General Health; Penn Medicine Princeton Health; and Pennsylvania Hospital, the nation’s first hospital, founded in 1751. Additional facilities and enterprises include Good Shepherd Penn Partners, Penn Medicine at Home, Lancaster Behavioral Health Hospital, and Princeton House Behavioral Health, among others.
Penn Medicine is powered by a talented and dedicated workforce of more than 43,900 people. The organization also has alliances with top community health systems across both Southeastern Pennsylvania and Southern New Jersey, creating more options for patients no matter where they live.
Penn Medicine is committed to improving lives and health through a variety of community-based programs and activities. In fiscal year 2019, Penn Medicine provided more than $583 million to benefit our community.