Nerve growth factor released by transgenic astrocytes enhances the function of adrenal chromaffin cell grafts in a rat model of Parkinson's disease

Previous studies have demonstrated that astrocytes genetically modified to express recombinant nerve growth factor (NGF) support the survival and neuronal transdifferentiation of intrastriatal adrenal chromaffin cell grafts at 2 weeks post-transplantation [15]. The present study was performed to determine whether these effects would be maintained at longer times post-transplantation and, if so, whether the co-grafts would reduce rotational behavior in the unilateral 6-hydroxydopamine-le-sioned rat. In the present study, we have demonstrated that primary type I rat astrocytes infected with a replication-defective retrovirus conferring expression of a mouse β-NGF cDNA sequence secrete NGF at a rate that is approximately 40-fold higher than that of controls (i.e., 8.0 vs. 0.2 pg NGF/h/10⁵ cells, respectively). The genetically modified astrocytes were also found to express recombinant NGF following intrastriatal transplantation, as indicated by a 23% increase in striatal NGF content compared with controls, measured at 4 weeks post-transplantation. When NGF-producing astrocytes and adrenal chromaffin cells were co-grafted into the dopamine-denervated striatum of the unilateral 6-hydroxydopamine-lesioned rat, the chromaffin cells displayed extensive neurite outgrowth and a 5–12-fold increase in survival compared to controls at 10 weeks post-grafting. These effects were paralleled by a 60% reduction of apomorphine-induced rotational behavior, suggesting a partial normalization of striatal function. These results suggest that genetically modified astrocytes promote the prolonged survival and function of adrenal chromaffin cell grafts in a rat model of Parkinson's disease.