Comparison of AAV-Mediated Optogenetic Vision Restoration between Retinal Ganglion Cell Expression and ON Bipolar Cell Targeting

Abstract

The loss of photoreceptors in individuals with retinal degenerative diseases leads to partial or complete blindness. Optogenetic therapy is a promising approach for restoring vision to the blind. Multiple strategies have been employed by targeting genetically encoded light sensors, particularly channelrhodopsins, to surviving retinal neurons in animal models. In particular, the strategy of targeting retinal bipolar cells has commonly been expected to result in better vision than ubiquitous expression in retinal ganglion cells. However, a direct comparison of the channelrhodopsin-restored vision between these two strategies has not been performed. Here, we compared the restored visual functions achieved by adenoassociated virus (AAV)-mediated expression of a channelrhodopsin in ON-type bipolar cells and retinal ganglion cells driven by an improved mGluR6 promoter and a CAG promoter, respectively, in a blind mouse model by performing electrophysiological recordings and behavioral assessments. Unexpectedly, the efficacy of the restored vision based on light sensitivity and visual acuity was much higher following ubiquitous retinal ganglion cell expression than that of the strategy targeting ON-type bipolar cells. Our study suggests that, at least based on currently available gene delivery techniques, the expression of genetically encoded light sensors in retinal ganglion cells is likely a practical and advantageous strategy for optogenetic vision restoration.

Expression of Channelrhodopsin‐2 in Rod Bipolar Cells Restores ON and OFF Responses at High Spatial Resolution in Blind Mouse Retina

“…Previous studies reported the occurrence of ON and OFF RGC responses. [9][10][11][12]44] However, in the cited studies, no detailed spike sorting or quantification was performed. Here, we conclusively demonstrate the occurrence of pure opto ON and of pure opto OFF activity in RGCs (see Table 1).…”

“…However, we also identified additional response types, which are partially explained by the activation of remnant photoreceptors but also indicate non-classical signal processing in photoreceptor-degenerated retinas. Batabyal [14] Mouse (rd10) √ ON-BCs vMCO1-mgluR6 OMR ≥ 0.1 < 10 μW mm −2 @continuum Hulliger [13] Mouse (rd1) √ ON-BCs Opn1mw OMR 0.28 ± 0.02 10 11 @screen van Wyk [10] Mouse (rd1) √ /X ON-BCs Opto-mGluR6 OMR, patchclamp 0.17 ± 0.04 ON+OFF 25-50 100 2 ⋅ 10 11 @473nm Lu [12] Mouse (TKO)…”

“…[7] Depending on the state of retinal degeneration, different cell types are preferable as cellular targets for optogenetic vision restoration. Previous studies investigated optogenetic transduction in remnant photoreceptor somata, [8] bipolar cells (BCs), [9][10][11][12][13][14] amacrine cells, [15] or retinal ganglion cells (RGCs). [16][17][18][19][20] Among all the retinal cell types, bipolar cells appear to be particularly interesting targets for two reasons: First, they represent the cell layer adjacent to the lost photoreceptors in RP, and their synaptic connections to the inner plexiform layer (IPL) stay preserved in the advanced degenerative stage.…”

Sight of Action: the Rationale and Evolution of Gene Therapy Approaches to the Treatment of Retinal Diseases

“…More than 70 genes are involved in RP, with one of the most prevalent forms accounting for~1-2% of all human RP involving a mutation in the gene encoding the β subunit of rod cGMP-phosphodiesterase 6 (PDE6β). Subretinal administration of AAV2/5-hPDE6b preserved photoreceptor function and vision in a naturally occurring PDE6β deficiency dog model, [30] making way for the evaluation of its potential to arrest photoreceptor degradation in a phase1/2 clinical trial [31].…”

A systematic comparison of optogenetic approaches to visual restoration

“…To date, only a very small number of studies have directly compared candidate optogenetic tools, and none have systematically addressed the role of the different classes of optogenetic tools and target cell populations in the same model system. 3 , 5 , 6 , 7 , 8 , 20 , 21 , 22 , 23 In addition, none have compared responses in a degenerate model devoid of both rod, cone, and melanopsin responses 7 , 23 , 24 to remove the confounder of residual native light responses.…”