376. Overexpression of Pitx3 in the SNpc and Protection from MPTP Toxicity

Abstract

In the brain, expression of the transcription factor Pituitary Homeobox 3 or Paired-Like Homeodomain Transcription Factor 3 (PITX3) is crucial to the development and maintenance of dopaminergic neurons. During brain development, PITX3 functions in concert with the transcription factors NURR1 and LMX1b to facilitate dopaminergic neuron maturation. In the mature brain, PITX3 promotes the dopaminergic phenotype by positively regulating tyrosine hydroxylase (TH), dopamine transporter (DAT), and vesicular monoamine transporter 2 (VMAT2), either singly or in concert with NURR1. PITX3 also positively regulates expression of the pro-survival factors brain-derived neurotrophic factor (BDNF) and glial-derived neurotropic factor (GDNF). PITX3 is endogenously expressed in the dopaminergic neurons of the substantia nigra pars compacta (SNpc) and ventral tegmental area (VTA). However, in Pitx3 null mouse models, perturbations of cell number are observed only in the SNpc, a situation that resembles the relative sparing of the VTA in early-stage Parkinson's disease (PD). Systemic administration of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) results in the degeneration of SN dopaminergic neurons via a mechanism thought to involve the inhibition of mitochondrial respiration and the generation of reactive oxygen species, both of which are implicated in the pathogenesis of PD. Recent work in muscle demonstrates that PITX3 regulates expression of antioxidant enzymes and genes involved in mitochondrial biogenesis via the transcription factor NRF1. We have overexpressed murine Pitx3 (or mCherry control) from the CMV promoter in the SN of C57BL/6J mice using an AAV2/10 viral vector, and tested for neuroprotection in a sub-chronic MPTP model of PD (5 × 20 mg/kg MPTP over 9 days) by assaying for striatal dopamine, stratial TH and DAT immunoreactivity, and SN neuronal number. We will present results from these assays and changes in expression of Pitx3 target genes (TH, DAT, VMAT2, BDNF and GDNF) after Pitx3 overexpression in the SN.