TrkB Overexpression via Gene Therapy: Enhanced Optic Nerve Uptake With Associated Increases in Mitochondria and Axoplasmic Transport.

INTRODUCTION: Glaucoma is a progressive neurodegenerative disease that affects retinal ganglion cells (RGCs), ultimately leading to vision loss. In this study, we investigated gene therapy-mediated transduction of RGCs and examined axonal transport changes in the optic nerve using a viral vector designed to upregulate tropomyosin receptor kinase B (TrkB) expression. METHOD: TrkB expression was evaluated in retinae and optic nerves of rats following genetic intravitreal delivery of AAV2-TrkB. Axonal transport and preliminary mitochondrial changes were assessed in optic nerves by immunohistochemical staining for kinesin and voltage-dependent anion channel (VDAC), a mitochondrial component. RESULTS: The results revealed an approximately 30% increase in TrkB expression in the retina, which was confirmed to be vector-driven by a P2A tag attached to the TrkB protein. This increased protein expression could be seen independent of injury and in eyes with elevated intraocular pressure. Observations along the optic nerve of rats treated with AAV2-TrkB revealed elevated transport of TrkB along axons (50% in TrkB, 120% in P2A tag) and significant increases in kinesin (12%) and VDAC (16%) immunoreactivity. CONCLUSION: This study provides early indications that improving TrkB expression in the eye may increase anterograde transport of motor proteins, which in turn could improve mitochondrial transport within the optic nerve.