Conference Coverage
WASHINGTON, DC—Investigators are examining alpha-synuclein as a target for Parkinson’s disease therapy in various ways, according to a presentation at the at the 67th Annual Meeting of the American Academy of Neurology. “You can block release of alpha-synuclein from bad cells or block uptake of misfolded seeds by healthy cells. You can prevent seeding of the pathology or you can promote degradation of misfolded alpha-synuclein,” said Virginia Man-Yee Lee, PhD, John H. Ware Third Endowed Professor in Alzheimer’s Disease Research at the University of Pennsylvania School of Medicine in Philadelphia.
Virginia Man-Yee Lee, PhD
Alpha-Synuclein Transmission
Parkinson’s disease pathology starts in the medulla or olfactory bulb and moves to other parts of the brain, including the substantial nigra, locus coeruleus, midbrain, basal forebrain, and cerebral cortex, Dr. Lee explained. Lewy body formation correlates with the development of movement disorders, as well as with cognitive impairment in late stages of the disease. “When you have this kind of spread, it is suggestive of a transmissible agent, and we wondered if alpha-synuclein could be that agent,” she said.
In a series of preclinical laboratory experiments and animal studies, Dr. Lee contributed to the field of Parkinson’s disease research that targets alpha-synuclein. Overexpression of alpha-synuclein does not lead to obvious pathology in mutant or wild-type mice, but Dr. Lee found that the purified protein form of alpha-synuclein could be manipulated in a test tube so that it would readily form fibrils similar to those found in Lewy bodies.
By seeding the primary neurons of wild-type mice with this form of alpha-synuclein, Dr. Lee induced Parkinson’s disease pathology that resembled human Lewy body disease. “Tremendous pathology developed in these neurons over time that were insoluble and phosphorylated, which are markers for pathological alpha synuclein,” she said. The seeded pathology was highly active, disrupting intracellular communication and compromising the viability of the cells. Fourteen days after treatment, Dr. Lee and her colleagues observed a 50% loss of neuronal cells in the mice.
Cell-to-cell transmission was demonstrated in an experiment in which neurons were placed in three discrete chambers that only allow axons to travel between them. When fibrils generated from purified protein forms of alpha synuclein were introduced into the first chamber, Lewy body pathology formed in all three chambers. In subsequent animal studies, synthetic alpha-synuclein fibrils were injected into the dorsal striatum of wild-type mice. Pathology emerged after 30 days at the injection site and the nearby cortex. At 180 days, pathology had spread across many regions of the brain.
More importantly, depletion of neurons over time became evident on the side of the substantial nigra where alpha-synuclein fibrils were injected, Dr. Lee reported. “Lewy body pathology forms first, and the neurons die later, clearly suggesting a causal relationship,” she said. Dopaminergic loss correlated directly with the onset of movement disorders in the mice, as measured by rotorod and wire hanger tests.
Blocking Transmission
The next experiments focused on the potential to block uptake of alpha synuclein seeds by treating wild-type mice with Syn 303, a conformational specific monoclonal antibody that binds to misfolded alpha-synuclein. Fibrils were injected into the dorsal striatum of mice, and within seven days, pathology appeared in the ipsilateral cortex and the nigra. The mice were then treated weekly for as long as 180 days with Syn 303 or IgG. “At 180 days, there were fewer Lewy body inclusions in the treated mice than in the IgG controls and more dopamine surviving in treated cells,” Dr. Lee reported. Syn 303 treatment also significantly reduced motor deficits, compared with IgG.
Dr. Lee returned to cell culture studies to look for further opportunities to block the transmission of alpha synuclein using Syn 303 as well as Syn 211, a human-specific monoclonal antibody. “Both 211 and 303, when added to pathology in culture, were able to reduce synaptic motor neuron death,” she said, and both were efficacious in blocking the entry of the fibrils into the cells, as demonstrated by a significant reduction of cells in pathology. “Immunotherapy may provide a therapeutic approach for the treatment of Parkinson’s disease and other synucleinopathies,” Dr. Lee concluded.
—Linda Peckel
