Nuclear Localization of α-Synuclein and its Interaction with Histones

Abstract

Pathological accumulation of alpha-synuclein (&alpha;Syn) is a hallmark of Parkinson's disease (PD). While &alpha;Syn primarily localizes at synaptic terminals under physiological conditions, emerging evidence suggests translocation to the nucleus may contribute to PD pathophysiology. Despite growing interest in nuclear &alpha;Syn, previous detection methods have lacked reliability, and critical questions regarding the mechanisms of nuclear translocation, intranuclear &alpha;Syn behavior, and potential reversibility of nuclear accumulation remain unanswered. This study aimed to establish robust methodologies for detecting nuclear &alpha;Syn, to elucidate conditions prompting nuclear &alpha;Syn translocation, and to assess intranuclear consequences and clearance dynamics following &alpha;Syn nuclear accumulation. <br/> We utilized three complementary <em>in-vivo</em> models: constitutive &alpha;Syn overexpression via intraparenchymal injections of adeno-associated viral vectors in the rat substantia nigra; a doxycycline-inducible system allowing for controlled initiation and cessation of &alpha;Syn overexpression; and nigrostriatal pathology triggered by systemic paraquat injections. Comprehensive analyses included immunohistochemistry, multiple proximity ligation assays (PLAs), co-immunoprecipitation (Co-IP), and proteasome activity assays. <br/> Across all models, increased neuronal &alpha;Syn expression promoted its nuclear translocation. Once it gained access into the nuclei, &alpha;Syn directly interacted with histones, as demonstrated by our novel PLA approach and confirmed by Co-IP. &alpha;Syn overexpression altered epigenetic modifications, indicating a potential mechanistic link to transcriptional dysregulation. Moreover, our data revealed that nuclear &alpha;Syn formed aggregates that also interact with histones. Finally, using the doxycycline-regulated model, we demonstrated for the first time that nuclear &alpha;Syn accumulation, aggregation, and &alpha;Syn-histone interactions were reversible upon cessation of &alpha;Syn overexpression. This reversibility was due, at least in part, to &alpha;Syn clearance facilitated by the nuclear ubiquitin-proteasome system. <br/> In summary, using multiple <em>in-vivo</em> approaches and analytical techniques, we provide compelling new evidence for conditions and mechanisms associated with &alpha;Syn nuclear translocation and accumulation that may play a role in pathogenic processes in PD and other synucleinopathies. Our findings support the conclusion that nuclear &alpha;Syn and &alpha;Syn- 82 histone interactions should be considered important therapeutic targets. One strategy for therapeutic intervention could be to reverse the deleterious effects of nuclear &alpha;Syn accumulation by promoting specific mechanisms involved in nuclear &alpha;Syn clearance.