Dopaminergic regulation of a transfected preproenkephalin promoter in primary rat astrocytes in vitro and in vivo.

The clinical benefit of transplantation therapies utilizing genetically modified cells could be enhanced if expression of engineered genes was regulated by clinically useful pharmacological agents. Toward this end, we examined pharmacologic effects on the expression of hybrid gene constructs transfected into primary rat striatal astrocytes. These astrocytes are known to express receptors for the neurotransmitter dopamine (DA). In vitro, we found that expression of a transiently transfected human ppEnk promoter-driven chloramphenicol acetyltransferase (CAT) reporter construct was induced by DAergic agonists, as much as 20-fold. This induction was blocked by a DA receptor antagonist. The same concentration of DA also increased the endogenous rat ppEnk mRNA, by > 2-fold. In vivo, regulation of CAT expression by DA was tested by implanting the genetically modified astrocytes into the normal striatum and the contralateral striatum which had > 95% DA depletion induced by a previous 6-hydroxy-DA lesion of the substantia nigra. As hypothesized on the basis of the in vitro data, CAT activity on the lesioned side, where the stimulating effect of endogenous DA was lacking, was 30% lower than on the control side where the normal DA content was present. The data suggest that control of the enkephalin gene in astrocytes may involve second messenger pathways activated by DA receptors. Moreover, the evidence that clinically applicable drugs can regulate inducible genes introduced into the brain by astrocyte implantation is of potential importance in development of therapeutic strategies.