CAG-GFP Adeno-associated virus(AAV Serotype 2)

Previous studies have shown that intravitreal delivery of brain-derived neurotrophic factor (BDNF) via injection of recombinant protein or gene therapy can alleviate retinal ganglion cell (RGC) loss following optic nerve injury. Here, researchers describe a novel adeno-associated virus (AAV) gene therapy (AAV2 TrkB-2A-mBDNF) that not only increases BDNF production but also improves long-term neuroprotective signaling by increasing expression of the BDNF receptor (TrkB) in the inner retina. This approach resulted in significant and sustained elevations of the survival signaling pathways ERK and AKT within RGCs over 6 months and avoided the receptor downregulation observed with AAV2 BDNF treatment alone. The researchers validated the neuroprotective efficacy of AAV2 TrkB-2A-mBDNF in a mouse optic nerve injury model, outperforming traditional AAV2 BDNF or AAV2 TrkB therapy, before showing powerful proof of concept neuroprotection of RGCs and axons in a rat model of chronic intraocular pressure (IOP) elevation.

The researchers tested the neuroprotective capacity of AAV2 TrkB-2A-mBDNF in the mouse optic nerve crush (ONC) model to investigate whether increased TrkB and BDNF expression and signaling could protect RGCs from injury (Figure 1). AAV2 TrkB-2A-mBDNF vectors controlled by either the CAG or Synapsin-1 (SYN1) promoter were examined, with the latter tested to see if more specific neuronal targeting would be beneficial. AAV2 CAG GFP was used as a control vector and AAV2 CAG BDNF was used as a benchmark for the new constructs, expressing only unmodified BDNF. Seven days after ONC, eyes injected with AAV2 CAG GFP had lost a significant portion of their RGCs compared to non-crushed controls (Figure 1b-ei). Pretreatment of mice with AAV2 CAG TrkB-2A-mBDNF or AAV2 SYN1 TrkB-2A-mBDNF resulted in significantly increased RGC survival after ONC compared to eyes that received AAV2 CAG GFP (Figure 1b-hi). The higher RGC survival after treatment with AAV2 CAG TrkB-2A-mBDNF suggests that the CAG promoter is more efficient than synapsin-1 in driving transgene expression in RGCs. The number of surviving RGCs was also significantly increased in ONC eyes treated with AAV2 CAG BDNF compared to AAV2 CAG GFP, but the effect of the vector was significantly less than that of AAV2 CAG TrkB-2A-mBDNF (Figure 1b-hi).

Figure 1. Neuroprotection using AAV2 TrkB-2A-mBDNF vs AAV2 BDNF in a mouse optic nerve crush (ONC) injury model. (Osborne A, et al., 2018)