RETINAL GANGLION-CELL SURVIVAL IS PROMOTED BY GENETICALLY-MODIFIED ASTROCYTES DESIGNED TO SECRETE BRAIN-DERIVED NEUROTROPHIC FACTOR (BDNF)

Genetically engineered cells carrying genes for neurotrophic factors have potential application for treatment of neurodegenerative diseases and injuries to the nervous system. Brain-derived neurotrophic factor (BDNF) promotes the survival of specific neurons, including retinal ganglion cells (RGC). To determine whether genetically engineered astrocytes might be used for delivering bioactive BDNF, we infected primary type 1 rat astrocytes with a retrovirus harboring a human prepro-BDNF cDNA and assayed the medium conditioned by these astrocytes for effects on survival of rat RGCs in vitro. High levels of BDNF mRNA were expressed by infected astrocytes, but not by control astrocytes as determined by RNase protection assay using a BDNF specific probe. To test for secretion of bioactive BDNF from the transgenic astrocytes, embryonic day 17 rat retinas were dissociated and grown in medium conditioned (CM) for 24 h by astrocytes infected with a replication deficient retrovirus carrying BDNF, NGF, or alkaline phosphatase (AP) cDNA. After 3 days, the number of Thy-1 immunoreactive RGCs was counted. BDNF astrocyte CM significantly enhanced RGC survival by 15-fold compared to the AP control. NGF astrocyte CM had no significant effect. The rate of BDNF secretion was estimated at 83-166 pg/10(5) cells/h. This study demonstrates that astrocytes can be genetically engineered to synthesize and secrete bioactive BDNF. These techniques may be applicable to rescuing neurons from degenerative processes and also for enhancing their survival following transplantation.