Men are more susceptible to Parkinson's disease than women. Alpha-synuclein aggregates are a hallmark of the disease and it is increasingly believed that alpha-synuclein oligomeric forms are the toxic species responsible for the neuropathological changes observed in Parkinson's disease and the related Disease Dementia with Lewy Bodies. This proposal is analyzing the equilibrium of the different alpha-synuclein oligomeric forms in the male and female human brain affected by Parkinson's disease and Dementia with Lewy Bodies.
We hypothesize that gender specific stabilization of alpha-synuclein oligomers may be mediated by modifications of the protein after its synthesis. To analyze gender differences in alpha-synuclein aggregate stability we will use human post-mortem temporal cortex of normal and diseased subjects. We will use mass spectrometry to investigate the composition of the detergent-insoluble protein fraction associated with the gender-specific detergent-insoluble alpha-synuclein oligomers. The latter are observed more often in female patients affected by alpha-synuclein-related pathology. We will also use immunoprecipitation in combination with mass spectrometry to analyze alpha-synuclein enriched protein fractions for modifications and truncations.
Relevance to Diagnosis/Treatment of Parkinson’s Disease:
Understanding the differences in the equilibrium of alpha-synuclein soluble and aggregated species will help us understand the biological basis for the gender differences observed in the incidence of the disease. As we move toward more personalized care for diseases, one factor that is often overlooked is the patient’s gender. We have the unique opportunity to analyze the impact of gender on Parkinson's disease and bring our results into the clinical world to better tailor neuroprotective strategies.
We expect to find gender-based differences in the composition of the detergent insoluble protein fraction. The differential protein composition of this fraction will provide insight into the type of proteins that associate with alpha-synuclein and their differences between the two genders.
We also expect to find differences in the frequencies of occurrence and/or in the magnitude of the presence of alpha-synuclein modifications between males and females affected by DLB.
This will help us understand the biological mechanisms of the gender differences observed in Parkinson's disease.
Our preliminary data showed increased levels of detergent insoluble alpha-synuclein in temporal cortex of women affected by Parkinson’s disease and in women affected by dementia with Lewy bodies compared to their male counterparts and to healthy men and women. We explored the modifications of alpha-synuclein that might underlie the increased levels of insoluble protein observed in women with Parkinson’s disease and dementia with Lewy bodies. To do so we analyzed 102 human post-mortem brains for post-translational modifications such as truncations or oxidative-stress induced modifications of alpha-synuclein. The analyses of soluble and insoluble alpha-synuclein fractions from temporal cortex of patients affected by Parkinson’s disease and by dementia with Lewy bodies showed that 90% of the women affected by dementia with Lewy bodies also showed the presence of alpha-synuclein missing the C-terminus, compared to healthy women or women with Parkinson’s disease. Men with Parkinson’s disease or dementia with Lewy bodies showed the presence of alpha-synuclein truncated at the c-terminus only in 20 and 30% of the cases respectively. This finding is particularly interesting because two of the enzymes known to cleave alpha-synuclein preferentially at the c-terminus (Cathepsin D and Kallikrein 6), are regulated by sex-related hormones. As of today we could not find other modifications of alpha-synuclein that associated preferentially with women affected by alpha-synuclein pathology.
Publication Based on MJFF Funding:
We have one paper in preparation with some of the data presented in this progress report and we are collecting additional data for an additional publication. Manuscript in preparation: Cantuti-Castelvetri I, Greenstein MR, Kett LR, Hollingsworth ZR, Danzer KM, McLean PJ, Hyman BT, Frosch MP, Young AB, Gender-specific Equilibrium of Oligomeric Alpha-Synuclein in Lewy Bodies Pathology
Grants Made Possible with MJFF Funding:
We do have a pending application with NINDS to continue this research. The application is requesting $250,000/year for 5 years and it is titled “Alpha-synuclein and gender in Lewy body pathology”. The grant if funded would start no earlier than April 2011, Interim funds from the MJFF would help us continue this research uninterruptedly.
Our group has been studying possible gender specific mechanisms of alpha-synuclein aggregation and processing that could underlie the higher incidence of PD and DLB in men compared to women. Our research has highlighted possible mechanisms that would increase the amount of truncated alpha-synuclein in women. In fact, using a multidisciplinary approach we could show that in women affected by DLP and PD there is a differential accumulation and sequestration of N-terminal alpha-synuclein fragments in the soluble non aggregated part of proteins, and of alpha-synuclein fragments missing the c-terminal tail in the aggregated part of brain proteins. We have also found in men affected by DLB there is a decreased activity of enzymes that can cut alpha-synuclein. This can explain why women seem to have a higher amount of aggregated protein as truncated alpha-synuclein is more likely to aggregate. We have also analyzed the clinical charts of the patients studied and we could not identify any one factor in their clinical history that could explain or contribute to the gender specific patterns we observe, leaving gender-specific mechanisms as the main explanation for our observations. Increased (stable) aggregation of alphasynuclein may sequester more rapidly potential toxic oligomeric species that might contribute to the higher incidence of the disease in males.