Novel Grm6 Variant in a no b-wave (nob) Mouse Model: Phenotype Characterization and Gene Therapy.
Lin Pei-Hsuan, Kang Eugene Yu-Chuan, Makrides Neoklis, Lee Winston, Tseng Yun-Ju, Wu Pei-Liang, Peregrin John, Sherman Emmet, Wang Jason Hunghsuan, Swayne Theresa C
AI Summary
This study characterized a new Grm6-variant mouse model of night blindness. Gene therapy restored protein expression but offered limited functional improvement, highlighting the need for early, efficient treatment strategies.
Abstract
Purpose
To characterize a no b-wave (nob) mouse model of congenital stationary night blindness (CSNB) caused by a Grm6 variant that disrupts photoreceptor-to-bipolar cell signaling. Additionally, we aim to evaluate the efficacy of gene therapy in restoring visual function.
Methods
The nob mouse was generated through selective breeding to regenerate the nob phenotype. Adeno-associated viruses encoding Grm6 and GFP, driven by two promoters (hGRM6 and CMV), were administered to nob mice at postnatal days 5 (P5) and 30 (P30), respectively. Electroretinography and spectral domain optical coherence tomography (SD-OCT) were conducted three months after gene therapy.
Results
The nob phenotype was successfully regenerated, and a homozygous missense variant c.1037G>A (p.Arg346His) in Grm6 was identified as the causal variant. Scotopic b waves were absent, whereas a waves remained normal, indicating intact rod function but impaired bipolar cell function. SD-OCT revealed thinning of the retinal nerve fiber layer and outer plexiform layer (OPL) in affected mice. Immunofluorescence and immunoblotting revealed decreased mGluR6 levels and associated signaling proteins. Gene therapy restored mGluR6 expression and reestablished synaptic protein localization in the OPL, although improvements in b/a ratios and OPL thickness were modest. Notably, the hGRM6 promoter at P5 was more effective at restoring OPL.
Conclusions
We identified a new nob mouse model that mimics the CSNB phenotype in human patients. Whereas gene therapy successfully restored mGluR6 expression, functional improvements were limited. Early treatment using a specific promoter is critical, and increasing transduction efficiency may improve gene therapy strategies.
MeSH Terms
Shields Classification
Key Concepts6
A homozygous missense variant c.1037G>A (p.Arg346His) in Grm6 was identified as the causal variant for the nob phenotype in the regenerated nob mouse model.
Electroretinography in the nob mouse model showed absent scotopic b waves and normal a waves, indicating intact rod function but impaired bipolar cell function.
Gene therapy using adeno-associated viruses encoding Grm6 and GFP, driven by two promoters (hGRM6 and CMV), restored mGluR6 expression and reestablished synaptic protein localization in the outer plexiform layer (OPL) of nob mice.
Improvements in b/a ratios and outer plexiform layer (OPL) thickness were modest in nob mice treated with gene therapy using adeno-associated viruses encoding Grm6 and GFP.
Early treatment at postnatal day 5 (P5) using the hGRM6 promoter was more effective at restoring the outer plexiform layer (OPL) in nob mice treated with gene therapy.
A no b-wave (nob) mouse model of congenital stationary night blindness (CSNB) was generated through selective breeding.
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