Gene therapy with brain-derived neurotrophic factor as a protection: Retinal ganglion cells in a rat glaucoma model

PURPOSE. To develop a modified adenoassociated viral (AAV) vector capable of efficient transfection of retinal ganglion cells (RGCs) and to test the hypothesis that use of this vector to express brain-derived neurotrophic factor (BDNF) could be protective in experimental glaucoma. METHODS. Ninety-three rats received one unilateral, intravitreal injection of either normal saline (n = 30), AAV-BDNF-wood-chuck hepatitis posttranscriptional regulatory element (WPRE; n = 30), or AAV-green fluorescent protein (GFP)-WPRE (n = 33). Two weeks later, experimental glaucoma was induced in the injected eye by laser application to the trabecular mesh-work. Survival of RGCs was estimated by counting axons in optic nerve cross sections after 4 weeks of glaucoma. Transgene expression was assessed by immunohistochemistry, Western blot analysis, and direct visualization of GFP. RESULTS. The density of GFP-positive cells in retinal whole-mounts was 1,828 ± 299 cells/mm² (72,273 ± 11,814 cells/retina). Exposure to elevated intraocular pressure was similar in all groups. Four weeks after initial laser treatment, axon loss was 52.3% ± 27.1% in the saline-treated group (n = 25) and 52.3% ± 24.2% in the AAV-GFP-WPRE group (n = 30), but only 32.3% ± 23.0% in the AAV-BDNF-WPRE group (n = 27). Survival in AAV-BDNF-WPRE animals increased markedly and the difference was significant compared with those receiving either AAV-GFP-WPRE (P = 0.002, t-test) or saline (P = 0.006, t-test). CONCLUSIONS. Overexpression of the BDNF gene protects RGC as estimated by axon counts in a rat glaucoma model, further supporting the potential feasibility of neurotrophic therapy as a complement to the lowering of IOP in the treatment of glaucoma.