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Deciphering the molecular effects of alpha-synuclein in the nucleus: A new concept in synucleinopathies

Alpha-synuclein (aSyn), a common player in both sporadic and familiar forms of Parkinson’s Disease (PD), was first described as a pre-synaptic and nuclear protein. While the role of aSyn in the pre-synaptic compartment has been widely studied, both the nuclear localization and the role of the protein in the nucleus are still unclear. Recent efforts revealed that nuclear aSyn binds histones and modulates their acetylation, suggesting a putative effect of aSyn on transcription. Here, we investigated both transcriptional changes in rapid and slow progressive PD patients and the role of aSyn in the nucleus. We analyzed the gene expression profiles of a large cohort of two clinically-distinguishable groups of PD patients, based on the rate of disease progression. By analyzing the transcriptional profiles in blood samples from those patients, we identified a subset of >200 differentially expressed genes whose function is linked to DNA repair, purine/pyrimidine biosynthesis, transcription regulation, ubiquitin-proteasome system and membrane trafficking. Selected genes were further validated by real-time PCR, in a subset of patients’ blood cells. Importantly, some of the selected genes were also found to be significantly deregulated in differentiated Lund Human Mesencephalic cells that were either treated with MPP+, or over expressed aSyn. To investigate the presence of aSyn in the nucleus we used cell culture models, and transgenic mice expressing either wild type or A30P mutant aSyn. Our results demonstrated that aSyn is present in nuclear fractions of embryonic stage (E14) and in the midbrain region of adult A30P mice, as well as in human neuroblastoma cells. We also found that oxidative stress promoted the translocation of A30P and E46K aSyn mutants from the cytoplasm into the nucleus of cells 24h after H2O2 treatment. Next, to identify nuclear factors that interact with aSyn, we studied aSyn-DNA interactions by performing NMR experiments, genome-wide chromatin immunoprecipitation (ChIP)-sequencing and dual-luciferase assays. Our preliminary NMR results indicate that aSyn interacted with both DNA fragments and mononucleosomes. ChIP-sequencing experiments showed that aSyn can bind to the promoter regions of several genes, including NEDD4, CDC42 and SLC4A5. Furthermore, dual-luciferase assays confirmed that asyn overexpression increased SLC4A5 promoter activity. Altogether, our results suggest that transcriptional deregulation and nuclear aSyn might be important players in the pathophysiology of PD, and identify a panel of fingerprint genes that may serve as biomarkers in the prognosis of PD progression.

alpha-synuclein; nucleus; transcription

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