Affiliations: [a] Department of Radiation Oncology, Houston Methodist Research Institute, Houston, TX, USA
| [b] Centre for Neuroscience, Instituto de Investigaciones Científicas y Servicios de Alta Tecnología, City of Knowledge, Republic of Panama | [c] Department of Biotechnology, Acharya Nagarjuna University, Guntur, India
| [d]
Houston Methodist Neurological Institute, Institute of Academic Medicine, Houston Methodist Hospital, Houston, TX, USA
| [e]
Weill Cornell Medical College of Cornell University, NY, USA
Correspondence:
[*]
Correspondence to: Muralidhar L. Hegde, PhD, Department of Radiation Oncology, Houston Methodist Research Institute, Fannin St., Smith 8-05, Houston, Texas 77030, USA. Tel.: +1 713 441 7456; Fax: +1 713 790 3755; E-mail: mlhegde@houstonmethodist.org. and K.S. Rao, Centre for Neuroscience, Instituto de Investigaciones Científicas y Servicios de Alta Tecnología (INDICASAT AIP), City of Knowledge, Republic of Panama. E-mail: kjr5n2009@gmail.com.
Abstract: Alpha-synuclein (α-Syn) overexpression and misfolding/aggregation in degenerating dopaminergic neurons have long been implicated in Parkinson’s disease (PD). The neurotoxicity of α-Syn is enhanced by iron (Fe) and other pro-oxidant metals, leading to generation of reactive oxygen species in PD brain. Although α-Syn is predominantly localized in presynaptic nerve terminals, a small fraction exists in neuronal nuclei. However, the functional and/or pathological role of nuclear α-Syn is unclear. Following up on our earlier report that α-Syn directly binds DNA in vitro, here we confirm the nuclear localization and chromatin association of α-Syn in neurons using proximity ligation and chromatin immunoprecipitation analysis. Moderate (∼2-fold) increase in α-Syn expression in neural lineage progenitor cells (NPC) derived from induced pluripotent human stem cells (iPSCs) or differentiated SHSY-5Y cells caused DNA strand breaks in the nuclear genome, which was further enhanced synergistically by Fe salts. Furthermore, α-Syn required nuclear localization for inducing genome damage as revealed by the effect of nucleus versus cytosol-specific mutants. Enhanced DNA damage by oxidized and misfolded/oligomeric α-Syn suggests that DNA nicking activity is mediated by the chemical nuclease activity of an oxidized peptide segment in the misfolded α-Syn. Consistent with this finding, a marked increase in Fe-dependent DNA breaks was observed in NPCs from a PD patient-derived iPSC line harboring triplication of the SNCA gene. Finally, α-Syn combined with Fe significantly promoted neuronal cell death. Together, these findings provide a novel molecular insight into the direct role of α-Syn in inducing neuronal genome damage, which could possibly contribute to neurodegeneration in PD.
