709. rAAV-Mediated Regulation of Striatal Nurr1 Expression Alters Development and Severity of Levodopa-Induced Dyskinesias in the 6-OHDA Rat Model of Parkinson's Disease

Abstract

Primary motor symptoms in Parkinson's disease arise due to a loss of dopaminergic innervation in the striatum. Treatment with levodopa (L-DOPA) is the current gold standard treatment for the motor symptoms that arise in PD due to dopamine (DA) depletion. However, a large portion of patients receiving L-DOPA treatment develop a series of debilitating hyperkinetic and dystonic movements known as L-DOPA-induced dyskinesias (LIDs). The molecular mechanisms behind LID development are unclear, as well as why some patients are resistant to LIDs and never acquire these symptoms. In an attempt to identify transcriptional differences between LID responders and LID non-responders in the rat parkinsonian 6-hydroxydopamine (6-OHDA) model, we performed a full genome array to identify differential transcript expression between these two groups. The orphan nuclear receptor Nurr1 was one transcript that was expressed at significantly higher levels—greater than 30 fold—in LID+ animals when compared to LID- animals. In the current study we sought to determine whether Nurr1 expression both promotes, and is required for, LID formation. Adult male Sprague-Dawley rats were rendered parkinsonian using6-OHDA. Animals that did not show a difference in paw use compared to a pre-lesion state were removed from the study one month later. At this time, remaining animals received a striatal injection of recombinant adeno-associated virus (rAAV) type 2/5 overexpressing either: 1) Nurr1 (or GFP as a control)(5×1013 vector genomes (vg)/ml) in order to test whether Nurr1 overexpression causes LIDs or 2) A shRNA targeting Nurr1 (or a titer-matched scrambled shRNA control)(2×1013 vg/ml) in order to test whether Nurr1 is required for LIDs. Four weeks following the vector injection, animals received escalating doses (0mg/kg – 24mg.kg) of L-DOPA every other day (M-Fr), and were evaluated for LIDs at 25 min intervals for 2-4 hours using the abnormal involuntary movement (AIM) rating scale. At doses equal to or exceeding 12mg/kg, Nurr1 overexpressing animals exhibited both more severe and longer lasting LIDs than their rAAV-GFP control counterparts. Conversely, dyskinesias were attenuated in animals receiving Nurr1-shRNA up to 18mg/kg of L-DOPA. In addition, postmortem analysis of striatal tissue revealed that the overexpression of the Nurr1 shRNA effectively inhibited the induction of L-DOPA induced Nurr1. These results demonstrate that overexpression of Nurr1 in the DA-depleted striatum of parkinsonian rats has a causative role in the expression of LIDs. Further, our data show that Nurr1 silencing in the striatum effectively inhibits the LID development. These data suggest that the maladaptive upregulation of Nurr1 in striatal neurons is a core event in the formation of LIDs. Consequently, targeting striatal Nurr1 activity may represent a novel therapeutic modality in the treatment of LIDs.