The Retrograde Delivery of Adenovi rus Vector Carrying the Gene for Brain-Derived Neurotrophic Factor Protects Neurons and Oligodendrocytes From Apoptosis in the Chronically Compressed Spinal Cord of twy/twy Mice

Study Design. The twy/twy mouse undergoes spontaneous chronic mechanical compression of the spinal cord; this in vivo model system was used to examine the effects of retrograde adenovirus (adenoviral vector [AdV])-mediated brain-derived neurotrophic factor (BDNF) gene delivery to spinal neural cells. Objective. To investigate the targeting and potential neuroprotective effect of retrograde AdV-mediated BDNF gene transfection in the chronically compressed spinal cord in terms of prevention of apoptosis of neurons and oligodendrocytes. Summary of Background Data. Several studies have investigated the neuroprotective effects of neurotrophins, including BDNF, in spinal cord injury. However, no report has described the effects of retrograde neurotrophic factor gene delivery in compressed spinal cords, including gene targeting and the potential to prevent neural cell apoptosis. Methods. AdV-BDNF or AdV-LacZ (as a control gene) was injected into the bilateral sternomastoid muscles of 18-week old twy/twy mice for retrograde gene delivery via the spinal accessory motor neurons. Heterozygous Institute of Cancer Research mice (+/twy), which do not undergo spontaneous spinal compression, were used as a control for the effects of such compression on gene delivery. The localization and cell specificity of β-galactosidase expression (produced by LacZ gene transfection) and BDNF expression in the spinal cord were examined by coimmunofluorescence staining for neural cell markers (NeuN, neurons; reactive immunology protein, oligodendrocytes; glial fibrillary acidic protein, astrocytes; OX-42, microglia) 4 weeks after gene injection. The possible neuroprotection afforded by retrograde AdV-BDNF gene delivery versus AdV-LacZ― transfected control mice was assessed by scoring the prevalence of apoptotic cells (terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling-positive cells) and immunoreactivity to active caspases -3, -8, and -9, p75NTR, neurofilament 200 kD (NF), and for the oligodendroglial progenitor marker, NG2. Results. Four weeks after injection, the retrograde delivery of the LacZ marker gene was identified in cervical spinal neurons and some glial cells, including oligodendrocytes in the white matter of the spinal cord, in both the twy/twy mouse and the heterozygous Institute of Cancer Research mouse (+/twy). In the compressed spinal cord of twy/twy mouse, AdV-BDNF gene transfection resulted in a significant decrease in the number of terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling-positive cells present in the spinal cord and a downregulation in the caspase apoptotic pathway compared with AdV-LacZ (control) gene transfection. There was a marked and significant increase in the areas of the spinal cord of AdV-BDNF―injected mice that were NF-and NG2-immunopositive compared with AdV-LacZ―injected mice, indicating the increased presence of neurons and oligodendrocytes in response to BDNF transfection. Conclusion. Our results demonstrate that targeted retrograde BDNF gene delivery suppresses apoptosis in neurons and oligodendrocytes in the chronically compressed spinal cord of twy/twy mouse. Further work is required to establish whether this method of gene delivery may provide neuroprotective effects in other situations of compressive spinal cord injury.