Abstract
Abstract: :
Purpose: We previously demonstrated that in vivo upregulation of the neurotrophin receptor TrkB in combination with its ligand, brain-derived neurotrophic factor (BDNF), promote extensive survival of axotomized adult RGCs. The goal of this study was to establish if TrkB/BDNF-induced neuronal survival was also accompanied by RGC axonal regeneration after acute optic nerve lesion. Methods: Recombinant adeno-associated virus (AAV) containing the TrkB gene was injected into the vitreous chamber of adult rats. Micro-crush lesion of the optic nerve and simultaneous intravitreal injection of BDNF were performed 3 weeks after administration of AAV. Regenerating RGC axons were visualized with the anterograde tracer cholera toxin ß-subunit. The extent of axonal regeneration was quantified at 14 days post-injury. Control animal groups received intraocular injection of: i) a reporter gene virus (AAV.GFP), or ii) BDNF protein or saline at the time of lesion, without AAV treatment. In addition, BDNF or saline were injected in the superior colliculus to determine the effect of retrograde delivery of this neurotrophin on axon growth. Lens injury, which has been shown to promote RGC regeneration, was used as positive control for axon growth. Results: TrkB upregulation alone or in combination with BDNF did not stimulate an increase in RGC regeneration with respect to control optic nerves. Of interest, optic nerves from eyes that received a single intravitreal injection of BDNF showed a marked decrease in the number of RGC axons that were able to grow over the glial scar when compared to saline-treated nerves. Retrograde delivery of BDNF did not enhance RGC axon regeneration. In contrast, extensive axonal growth was visualized in the nerves of lens-injured animals, thus validating our surgical and imaging techniques. Conclusions: Although treatment with AAV.TrkB in combination with BDNF has been shown to promote robust RGC survival, our data demonstrate that activation of the TrkB/BDNF signaling pathway does not stimulate adult RGC regeneration in vivo. Importantly, our results suggest that BDNF has an inhibitory effect on RGC axon growth within the optic nerve environment.
Keywords: gene transfer/gene therapy • regeneration • ganglion cells