Topography of Vulnerability to Alpha-synuclein Fibrils in the Cerebral Cortex
Rapid Response Innovation Awards, 2013
Objective/Rationale: † † † † † ††
In Parkinsonís disease, the neocortex (outer layer of the brainís cerebral hemispheres, made of six layers) is less vulnerable than the allocortex (fewer than six layers) to alpha-synuclein pathology. No one knows the reason for this striking difference. However, we have found that the neocortex is more resistant to protein-misfolding stress (proteotoxicity) than allocortex in vitro, that it expresses higher levels of the protein ferroxidase ceruloplasmin in vivo, and that the stress of aging increases ceruloplasmin in vivo in neocortex but not in allocortex. The goal of this study is to examine whether the neocortex is more resistant to alpha-synuclein fibril toxicity in a ceruloplasmin-dependent manner.
Project Description: † † † † † ††
The primary motor neocortex and entorhinal allocortex will be infused with alpha-synuclein fibrils to examine whether the neocortex is less vulnerable to this form of proteotoxicity. Ceruloplasmin levels will be measured after synuclein infusions to assess whether neocortex responds by raising ceruloplasmin, similar to its response to the stress of aging. Ceruloplasmin levels will be knocked down to test the hypothesis that neocortex becomes more vulnerable to alpha-synuclein toxicity when ceruloplasmin is low. Ceruloplasmin levels will be raised with virally-mediated overexpression to test the hypothesis that allocortex becomes more resistant to alpha-synuclein toxicity when ceruloplasmin levels are high.
Relevance to Diagnosis/Treatment of Parkinsonís Disease: † † † † † † † † † ††
Ceruloplasmin has not been extensively explored in experimental models of Parkinsonís disease. However, ceruloplasmin levels are low in the serum and CSF of Parkinsonís patients and low levels are correlated with an earlier age of disease onset. This grant will therefore examine whether this protein is a rational target for drug development. If proteotoxicity in allocortex can be improved through gene- or pharmacotherapies that target ceruloplasmin, this may prevent the spread of pathology and ease non-motor symptoms such as cognitive dysfunction.
Anticipated Outcome: † † † † †
We anticipate that the neocortex will be more resistant to alpha-synuclein toxicity than the allocortex because of higher expression of ceruloplasmin. If ceruloplasmin mediates protection against alpha-synuclein toxicity in our model, this would suggest that this protein may keep inclusions at bay in the neocortices of Parkinsonís patients. Future studies targeting the ceruloplasmin protein with drugs would then be warranted.
Based on previous work that ceruloplasmin (a protein involved in iron metabolism) can confer neuroprotection to dopaminergic neurons, we added the human ceruloplasmin protein to primary neuron cultures harvested from four brain regions: the sensorimotor neocortex in the frontal and parietal lobes, the entorhinal/piriform allocortex in the temporal lobe, the hippocampus, and the olfactory bulb. We expanded our study to these four brain regions because all of them are known to develop Lewy pathology in Parkinsonís disease, albeit at different stages of the disorder.
We discovered that ceruloplasmin protected hippocampal and neocortical neurons against the formation of Lewy-like alpha-synuclein pathology after treatment with alpha-synuclein fibrils, a Parkinsonís disease model established by Dr. Virginia Lee at the University of Pennsylvania. However, ceruloplasmin was unable to protect temporal lobe or olfactory bulb neurons from Lewy-like pathology, suggesting that the effect depends entirely on the type of neuron. We also discovered that neocortical neurons were more resistant than neurons from the entorhinal/piriform allocortex to Lewy-like formations, consistent with our original hypothesis.
Since alpha-synuclein fibrils did not elicit significant cell loss in our models, even after several weeks of treatment, we used proteasome inhibitors in order to elicit cell death and test the neuroprotective effects of ceruloplasmin. Ceruloplasmin significantly protected neocortical neurons from cell death. In contrast, ceruloplasmin-treated cells from the olfactory bulb, entorhinal/piriform allocortex, and hippocampus revealed no such protection from proteasome inhibitors. These findings suggest that the protective effects of ceruloplasmin depend upon the type of injury as well as the type of neuron, which will have to be taken into consideration for future ceruloplasmin-based therapies.
Assistant Professor at Duquesne University
Location: Pittsburgh, Pennsylvania, United States