Astrocytes Infected with Replication-Defective Adenovirus Containing a Secreted Form of CNTF or NT3 Show Enhanced Support of Neuronal Populationsin Vitro

Abstract

Neurotrophic factors have been shown to ameliorate neuronal death in severalin vitroandin vivomodels of neurodegenerative disease. However, delivery of polypeptide growth factors to compromised neurons in the CNS is problematic as the blood–brain barrier prevents systemic delivery, and chronic in-dwelling cannulae are required for intraparenchymal delivery. To circumvent these problems and specifically target neurotrophic factors to the environment surrounding degenerating neurons in the CNS, we have generated replication-defective adenovirus (Ad) vectors that contain a secretable form of ciliary neurotrophic factor (sCNTF) or neurotrophin-3 (NT-3). In this study, we demonstrate that sCNTF/Ad and NT-3/Ad can efficiently infect primary astrocytes, resulting in gene transcription and the production of functional protein. Using Northern blot analysis, dose-dependent expression of sCNTF or NT-3 mRNA was detected 7 days after infection. The levels of mRNA expressed in transgenic astrocytes was dependent on virus titer and increased with increasing virus concentration. sCNTF or NT-3 protein was also detected in astrocyte supernatants by immunoblot analysis and 2-site ELISA. ELISA indicated that astrocytes infected with sCNTF/Ad or NT-3/Ad secreted neurotrophic factors at a rate of approximately 120 pg/106cells/h and 350 pg/106cells/h, respectively. To test for secretion of bioactive sCNTF or NT-3 protein, E8 chick ciliary ganglion or nodose ganglion neurons were grown in medium conditioned by control astrocytes or astrocytes treated with sCNTF/Ad or NT-3/Ad, showing a robust and dose-dependent increase in neuronal survival when compared to control supernatant. In addition, motor neurons plated onto astrocyte monolayers pretreated with sCNTF/Ad showed a two- to fourfold increase in ChAT activity when compared to those grown on astrocytes pretreated with Lac-Z/Ad. This study demonstrates that, using replication-defective adenovirus, primary astrocytes can be efficiently engineered to secrete bioactive sCNTF or NT-3, resulting in enhanced survival of responsive peripheral and central neuronal populations.