Neuroprotection of Retinal Ganglion Cells with AAV2-BDNF Pretreatment Restoring Normal TrkB Receptor Protein Levels in Glaucoma.

Anna Wójcik-Gryciuk,Olga Gajewska-Woźniak,Wioletta Waleszczyk,Małgorzata Skup,Katarzyna Kordecka,Paweł M Boguszewski

doi:10.3390/ijms21176262

Abstract

Intravitreal delivery of brain-derived neurotrophic factor (BDNF) by injection of recombinant protein or by gene therapy can alleviate retinal ganglion cell (RGC) loss after optic nerve injury (ONI) or laser-induced ocular hypertension (OHT). In models of glaucoma, BDNF therapy can delay or halt RGCs loss, but this protection is time-limited. The decreased efficacy of BDNF supplementation has been in part attributed to BDNF TrkB receptor downregulation. However, whether BDNF overexpression causes TrkB downregulation, impairing long-term BDNF signaling in the retina, has not been conclusively proven. After ONI or OHT, when increased retinal BDNF was detected, a concomitant increase, no change or a decrease in TrkB was reported. We examined quantitatively the retinal concentrations of the TrkB protein in relation to BDNF, in a course of adeno-associated viral vector gene therapy (AAV2-BDNF), using a microbead trabecular occlusion model of glaucoma. We show that unilateral glaucoma, with intraocular pressure ( IOP) increased for five weeks, leads to a bilateral decrease of BDNF in the retina at six weeks, accompanied by up to four-fold TrkB upregulation, while a moderate BDNF overexpression in a glaucomatous eye triggers changes that restore normal TrkB concentrations, driving signaling towards long-term RGCs neuroprotection. We conclude that for glaucoma therapy, the careful selection of the appropriate BDNF concentration is the main factor securing the long-term responsiveness of RGCs and the maintenance of normal TrkB levels.

Highlights

Increased intraocular pressure (IOP) remains a major, though not the only, risk factor for developing glaucoma
We have shown for the first time that in the microbead trabecular occlusion model of glaucoma characterized by an initial severe glaucoma attack [30], a single AAV2-brain-derived neurotrophic factor (BDNF) intraocular injection, when given 3 weeks prior to glaucoma induction, significantly protects retinal ganglion cell (RGC) from degeneration
We decided to inject AAV-BDNF three weeks prior to glaucoma induction to ensure stable BDNF overexpression in the retina prior to glaucomatous changes development. This was based on the data of others [32] and on our own experience [33], showing that in different models the stable expression is achieved around 2 weeks after injection. This management strategy was due to the lack of detailed data on the dynamics of retinal ganglion cell mortality as a result of a sudden, radical increase in IOP

Summary

Introduction

Increased intraocular pressure (IOP) remains a major, though not the only, risk factor for developing glaucoma. Intraocular injections of adeno-associated viral vectors carrying BDNF gene construct (AAV-BDNF) are an attractive alternative for eliciting a long-term increase in BDNF concentration in the retina and supporting the survival of RGCs [11,12,13,14,15]. This approach has been shown to be superior to BDNF treatment directed to the neurotrophin-releasing superior colliculus, which is targeted by the RGCs. Viral vector-induced BDNF overexpression in the superior colliculus, thought to boost the retrograde neurotrophin delivery, did not increase BDNF in the retina and failed to protect RGCs in the glaucoma models used [16]

Methods

Results

Conclusion