Sustained up-regulation of neuroprotective intracellular signalling pathways in retinal ganglion cells following intravitreal injection of QTA020V, a novel rAAV2 vector

Abstract

Purpose : Enhancement of BDNF signalling has previously been shown to protect retinal ganglion cells (RGCs) in experimental glaucoma models. However, elevating BDNF by intravitreal injection of protein or gene therapy vectors is associated with a loss of neuroprotective efficacy over time due to TrkB receptor down-regulation. This study examined whether QTA020V, a novel recombinant adeno-associated virus serotype-2 (AAV2) vector, could increase expression of mature BDNF (mBDNF), its cognate receptor (TrkB), and also up-regulate neuroprotective pathways in RGC for at least 6 months.

Methods : QTA020V (rAAV2 TrkB-2A-mBDNF) and control (rAAV2-GFP) vectors were injected intravitreally into groups of adult C57/BL6 mice (2microL, 1x10e10 viral particles/eye). At various time points (1, 3, 6, 12, 24 weeks) following vector administration, expression of mBDNF and TrkB were measured by Western blot of retinal homogenates and by immunocytochemistry. Levels of phosphorylated TrkB, AKT and ERK were also measured. Values shown are mean ± SEM (ANOVA followed by Bonferroni modified t-tests).

Results : Intravitreal QTA020V increased both BDNF and TrkB levels in retinal homogenates by 3-4-fold compared to control eyes or eyes injected with rAAV2-GFP vector (Western blots, n=3 mice/time point). Increased transgene expression was seen 1 week after vector injection and was maintained to week 24 without attenuation. Quantitative immunocytochemical analysis of pY⁵¹⁵-TrkB, p-AKT and p-ERK immunoreactivity showed a significant up-regulation at all time points (eg p-AKT at 3 weeks: QTA020V = 1751±72; rAAV2-eGFP = 375±76; naïve eyes = 538±69; P<0.001). Sustained pathway activation with QTA020V was observed in RGCs only. Maximal stimulation in p-AKT and p-ERK immunoreactivity was seen between 6 and 24 weeks (p<0.001 versus controls or rAAV2-GFP injected eyes).

Conclusions : QTA020V mediated increased expression of both mBDNF and TrkB in RGCs for at least 6 months. The demonstration of significant and sustained elevation of active pY⁵¹⁵-TrkB, p-AKT and p-ERK following QTA020V administration is further evidence that this vector can drive effective long-term activation of neuroprotective pathways in RGC. Additional studies are underway to assess further the potential of the TrkB-2A-mBDNF vector as a possible future treatment for glaucoma.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.