Restoration of low light vision in a mouse model of complete congenital stationary night blindness by intravitreal delivery of rAAV vectors targeting ON bipolar cells

Abstract

Purpose : The human disease, complete congenital stationary night blindness (cCSNB) is a genetically heterogeneous disorder of the retina characterized by impairment of low light vision and loss of b-wave of electroretinogram (ERG). Synaptic signaling requires proper alignment of pre- and postsynaptic proteins, and the localization of these proteins is interdependent. Nyctalopin, a postsynaptic, leucine-rich repeat protein is essential for TRPM1 cation channel localization and critical for light-evoked ON BCs depolarization. Mutation in nyctalopin (NYX) is the main cause of disease in the majority of cCSNB patients. Here, we introduced Nyx gene in a mouse model of cCSNB using rAAVs to rescue the expression of Nyctalopin, and thus TRPM1, and to restore dim light vision.

Methods : To express nyctalopin in ON BCs we used a mouse Grm6 promoter to limit the expression of nyctalopin in ON BCs. The construct Grm6::Nyx was then packaged in rAAV2 and rAAV8, which were injected intravitreally into adult and P5 mice. We characterized the overall retinal function of rAAVs Grm6::Nyx treated Nyx^nob mice by recording ERG. Expression and localization of nyctalopin and TRPM1 were examined by immunohistochemistry.

Results : We show that expression of nyctalopin in ON BCs restores light-evoked retinal function. Scotopic and photopic ERGs b-waves from AAV2 Grm6::Nyx treated adult Nyx^nob mice (n=7) showed restoration of 14.3±1.1% and 20.5±1.3% of WT values, respectively. AAV8 Grm6::Nyx treated adult Nyx^nob (n=9) showed restoration of scotopic and photopic b-waves to 18.5±2.4% and 26.2±2.3%, respectively. When we injected AAV2 Grm6::Nyx at P5 (n=6), the scotopic and photopic b-wave restored to 35.6±10.2% and 39.6±8.8% of WT ERGs, respectively. Furthermore, AAV8 Grm6::Nyx treatment of P5 mice (n=5) restored scotopic and photopic b-wave to 30±10.3% and 24.2±4.9%, respectively. Immunohistochemistry showed that nyctalopin expression was restored to ON BCs dendritic tips, and it rescued TRPM1 localization.

Conclusions : Our data show that intravitreally injected rAAVs drive robust and targeted expression of nyctalopin at ON BCs dendrites, which partially restores both scotopic and photopic retinal function in both postnatal and adult Nyx^nob mice. Our data also show the potential for gene delivery to BCs and potentially of cCSNB patients with mutations in NYX.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.