Gene Therapy with Mutant TrkB Receptors Protects Retinal Neurons and Promotes Optic Nerve Regeneration without Ligands

Abstract

Purpose : TrkB is a receptor for the neurotrophin BDNF and activation of TrkB upon ligand binding exerts neuroprotective effects on retinal ganglion cells (RGCs). In this study, to strengthen the efficiency of gene therapy, we developed a membrane-targeted form of mutant TrkB that contains only the intracellular region of TrkB (iTrkB) as an AAV vector. We then examined the therapeutic effects of AAV-iTrkB on neuroprotection and optic nerve regeneration.

Methods : GLAST KO mice, a mouse model of normal tension glaucoma, and the optic nerve crush (ONC) model were used for examining the effects of AAV-iTrkB. AAV-iTrkB or AAV-control was injected intravitreally into GLAST KO mice (3 weeks old) and WT mice (6 weeks old) for ONC. The number of RGCs was determined by immunostaining of the wholemounted retina with an anti-RBPMS antibody and multifocal electroretinogram (mfERG) was measured for assessment of retinal function. ONC was performed 2 weeks after intravitreal administration of AAV-iTrkB or AAV-control. Regenerating axons were detected by injecting Cholera toxin B with alexa 647. Visual function was analyzed electrophysiologically by visual evoked potentials and behaviorally by the optokinetic response test and pupillary light reflex test.

Results : AAV-iTrkB treatment, without BDNF, increased the survival rate of RGCs in GLAST KO mice. Moreover, visual responses measured by mfERG were higher in AAV-iTrkB-treated mice than AAV-control-treated mice. In the ONC model, AAV-iTrkB treatment alone promoted RGC survival and induced robust axon regeneration compared with AAV-control. Regenerated axons reached their brain targets, resulting in partial recovery of visual function and behavior in some mice.

Conclusions : AAV-iTrkB is a potential candidate for treatment of glaucoma and other neurodegenerative diseases.

This is a 2021 ARVO Annual Meeting abstract.