Astrocytes retrovirally transduced with BDNF elicit behavioral improvement in a rat model of Parkinson's disease

Neurotrophic factors that improve the survival of specific neuronal types during development and after exposure to various neuronal insults hold potential for treatment of neurodegenerative diseases. In particular, brain-derived neurotrophic factor (BDNF) has been shown to exert trophic and protective effects of dopaminergic neurons, the cell type known to degenerate in Parkinson's disease. To determine whether increased levels of biologically produced BDNF affect the function or regeneration of damaged dopaminergic neurons, the effects of grafting astrocytes transduced with the human BDNF gene into the striatum of the partially lesioned hemiparkinsonian rat were examined. Replication deficient retroviruses carrying either human prepro-BDNF or human alkaline phosphatase (AP) cDNA were used to transduce primary type 1 astrocytes purified from neonatal rat cortex. In vitro, BDNF mRNA was expressed by BDNF transduced astrocytes (BDNF astrocytes), but not control AP transduced astrocytes (AP astrocytes), as determined by reverse transcription polymerase chain reaction (RT-PCR). The modified astrocytes were injected into the right striatum 15 days after partial lesioning of the right substantia nigra with 6-hydroxydopamine. Transplantation of BDNF astrocytes, but not AP astrocytes, significantly attenuated amphetamine-induced rotation by 45% 32 days after grafting. Apomorphine-induced rotation increased over time in both groups, but was not significantly different in the BDNF-treated group. The modified BDNF astrocytes survived well with non-invasive growth in the brain for up to 42 days. Although BDNF mRNA positive cells were not detected within the graft site using in situ hybridization, alkaline phosphatase immunoreactive (IR) cells were present in control graft sites suggesting that the retroviral construct continued to be expressed at 42 days. Analysis of the density of tyrosine hydroxylase (TH)-IR fibers showed no effect of BDNF on TH-IR fiber density in the striatum on the lesioned side. These findings suggest that ex vivo gene therapy with BDNF ameliorates parkinsonian symptoms through a mechanism(s) other than one involving an effect of BDNF on regeneration or sprouting from dopaminergic neurons.