ASTROCYTES RETROVIRALLY TRANSDUCED WITH BDNF ELICIT BEHAVIORAL IMPROVEMENT IN A RAT MODEL OF PARKINSONS-DISEASE

Neurotrophic factors that improve the survival of specific neuronal ty pes during development and after exposure to various neuronal insults hold potential for treatment of neurodegenerative diseases. In particu lar, brain-derived neurotrophic factor (BDNF) has been shown to exert trophic and protective effects on dopaminergic neurons, the cell type known to degenerate in Parkinson's disease. To determine whether incre ased levels of biologically produced BDNF affect the function or regen eration of damaged dopaminergic neurons, the effects of grafting astro cytes transduced with the human BDNF gene into the striatum of the par tially lesioned hemiparkinsonian rat were examined. Replication defici ent retroviruses carrying either human prepro-BDNF or human alkaline p hosphatase (AP) cDNA were used to transduce primary type 1 astrocytes purified from neonatal rat cortex. In vitro, BDNF mRNA was expressed b y BDNF transduced astrocytes (BDNF astrocytes), but not control Af tra nsduced astrocytes (AP astrocytes), as determined by reverse transcrip tion polymerase chain reaction (RT-PCR). The modified astrocytes were injected into the right striatum 15 days after partial lesioning of th e right substantia nigra with 6-hydroxydopamine. Transplantation of BD NF astrocytes, but not AP astrocytes, significantly attenuated ampheta mine-induced rotation by 45% 32 days after grafting. Apomorphine-induc ed rotation increased over time in both groups, but was not significan tly 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 ret roviral construct continued to be expressed at 42 days. Analysis of th e density of tyrosine hydroxylase (TH)-IR seers showed no effect of BD NF on TH-IR fiber density in the striatum on the lesioned side. These findings suggest that ex vivo gene therapy with BDNF ameliorates parki nsonian symptoms through a mechanism(s) other than one involving an ef fect of BDNF on regeneration or sprouting from dopaminergic neurons.