Gene transfer methods have created the opportunity for developing gene therapy for human neurological diseases such as Parkinson's Disease (PD). Since PD represents a group of clinically similar syndromes each triggered by a different mechanism we hypothesize the existence of a shared downstream pathophysiologic pathway. Our goal is to develop therapy for PD directed at a shared common node in the pathway. The elaboration of such neuroprotective gene therapy is contingent on the development of safe and efficacious gene transfer vectors that can express a therapeutic gene for a prolonged period in specific neuronal populations. Of the currently available vehicles for direct gene therapy only plasmid based herpes simplex virus (HSV) """"""""amplicon"""""""" vectors have been demonstrated to both accommodate a large (9 kb) tyrosine hydroxylase (TH) promoter fragment and to provide highly selective gene expression in dopamine (DA) neurons in the substantia nigra. However, HSV amplicon vectors exhibit transgene silencing that is an impediment to one-time dosing for a chronic disease such as PD. Our data indicate that transgene silencing results from heterochromatin formation. One of the goals of this project is to subvert transgene silencing by altering the propensity of vector to form heterochromatin.
In Specific Aim 1 we examine multiple different approaches to stimulate euchromatin formation, that chromatin state posited to support long term gene expression. A second issue pertinent to the development of PD gene therapy is to direct different therapeutic genes to each compartment of the diseased nigrostriatal pathway: dopamine neurons and target striatum.
In Specific Aim 2 we will develop separate vectors which will afford direct expression of different gene products to each anatomical compartment. A third issue for successful PD gene therapy is evaluation in appropriate animal models of the disease.
Specific Aim 3 will employ two animal models: Our novel a-synuclein mice which develop progressive nigrostriatal dysfunction, reduction of substantia nigra TH and hypokinetic activity; and our modified chronic MPTP model which produces striatal denervation, dopaminergic cell loss and a neurobehavorial syndrome. The proposed studies will yield optimized HSV vectors, provide a detailed understanding of their characteristics, and evaluate their effectiveness in mechanistically different models of PD.
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