Correction of a Rat Model of Parkinson's Disease by Coexpression of Tyrosine Hydroxylase and Aromatic Amino Acid Decarboxylase from a Helper Virus-Free Herpes Simplex Virus Type 1 Vector

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Abstract
We previously reported long-term biochemical and behavioral correction of the 6-hydroxydopamine (6-OHDA) rat model of Parkinson's disease (PD) by expression of tyrosine hydroxylase (TH) in the partially denervated striatum, using a herpes simplex virus type 1 (HSV-1) vector. This study had a number of limitations, including the use of a helper virus packaging system, limited long-term expression, and expression of only TH. To address these issues, we developed a helper virus-free packaging system, a modified neurofilament gene promoter that supports long-term expression in forebrain neurons, and a vector that coexpresses TH and aromatic amino acid decarboxylase (AADC). Coexpression of TH and AADC supported high-level (80%), behavioral correction of the 6-OHDA rat model of PD for 5 weeks. Biochemical correction included increases in extracellular dopamine and DOPAC concentrations between 2 and 4 months after gene transfer. Histologic analyses demonstrated neuronal-specific coexpression of TH and AADC at 4 days to 7 months after gene transfer, and cell counts revealed 1000 to 10,000 TH positive cells per rat at 2 months after gene transfer. This improved system efficiently corrects the rat model of PD.