Gene Transfer in Astrogial Cells in a Rat Model of Parkinson' Disease

Abstract

Intracerebral transplantation of embryonic dopaminergic cells have shown, in particular, that local striatal restoration of dopaminergic neurotransmission may compensate for sensori-motor impairment associated with the nigro-striatal degeneration in animal models of Parkinson' disease. We are studying gene transfer as a tool to express the neurotransmitter synthesizing enzyme tyrosine hydroxylase (TH) locally in the striatum. We are exploring both the retroviral system and the adenoviral one, with the aim of comparing their efficiency and safety. Initially, we have constructed two human TH recombinant retroviruses using either the Long Terminal Repeat (LTR) from the Moloney murine leukemia virus or the immediate early promoter from the cytomegalovirus to drive the expression of TH into primary cultures of embryonic striatal cells. Retroviruses only permit the genetic modification through incorporation into chromosomal DNA of dividing cells. We therefore made use of the ability of glial cells to divide in the presence of foetal calf serum or growth factors to allow their infection in vitro by the recombinant retroviruses. We could thereby modify up to 100% of glial cells as characterized by their endogenous GFAP, an astroglial marker, as well as the exogenous TH protein expression. The genetically modified astroglial cells were found to release DOPA in a constitutive manner in vitro. The functional capacity of the TH-expressing astroglial cells as well as their survival properties were studied after grafting to striatum of rats with 6-hydroxydopamine lesions. Two weeks after transplantation, apomorphine-induced turning was reduced by mean of 60%. TH immunoreactive cells were observed in the denervated striatum three weeks postgrafting. The adenovirus allows the infection of dividing as well as of non-dividing cells such as neurons, resulting in the introduction of recombinant genes in an episomal form. The relative efficiency of this system with that of the retrovirus system will be discussed.