Long-term retinal cone rescue using a capsid mutant AAV8 vector in a mouse model of CNGA3-achromatopsia
November
Long-term retinal cone rescue using a capsid mutant AAV8 vector in a mouse model of CNGA3-achromatopsia
Xufeng Dai 0 1
Ying He¤ 0 1
Hua Zhang 0 1
Yangyang Zhang 0 1
Yan Liu 0 1
Muran Wang 0 1
Hao Chen 0 1
Ji- jing Pang 0 1
0 School of Ophthalmology and Optometry, The Eye Hospital, Wenzhou Medical University , Wenzhou, Zhejiang , P.R. China
1 Editor: Anand Swaroop, National Eye Institute , UNITED STATES
Adeno-associated virus (AAV) vectors are important gene delivery tools for the treatment of many recessively inherited retinal diseases. For example, a wild-type (WT) AAV5 vector can deliver a full-length Cnga3 (cyclic nucleotide-gated channel alpha-3) cDNA to target cells of the cone photoreceptor function loss 5 (cpfl5) mouse, a spontaneous animal model of achromatopsia with a Cnga3 mutation. Gene therapy restores cone-mediated function and blocks cone degeneration in the mice. However, since transgene expression delivered by an AAV vector shows relatively short-term effectiveness, this cannot be regarded as a very successful therapy. AAV2 and AAV8 vectors with capsid mutations have significantly enhanced transduction efficiency in retinas compared to WT AAV controls. In this study, AAV8 (Y447, 733F+T494V)-treated cpfl5 retinas showed greater preservation of short-term cone electroretinogram (ERG) responses than AAV8 (Y447, 733F)- or AAV2 (Y272, 444, 500, 730F+T491V)-mediated treatments. To explore the long-term rescue effect, AAV8 (Y447, 733F+T494V)-treated cpfl5 retinas were evaluated at 9 months following postnatal day 14 (P14) treatment. Rescued ERG responses in the cones of treated cpfl5 eyes decreased with increasing age, but still maintained more than 60% of the WT mouse responses at the oldest time point examined. Expression of CNGA3 and M/S-opsins was maintained in cone outer segments of the treated cpfl5 eyes and was equal to expression in age-matched WT retinas. Near-normal cone-mediated water maze behavior was observed in the treated cpfl5 mice. As these are the longest follow-up data reported thus far, AAV8 with capsid Y-F and T-V mutations may be one of the most effective AAV vectors for long-term treatment in a naturally occurring mouse model of CNGA3 achromatopsia.
Data Availability Statement; All relevant data are within the paper
Introduction
Achromatopsia, also known as rod monochromatism, is a relatively rare autosomal recessive
retinal disorder characterized by cone photoreceptor dysfunction. Clinically, the disease is generally
classified into complete (typical) and incomplete (atypical) forms [
1
]. Typical symptoms of
collection and analysis, decision to publish, or
preparation of the manuscript.
complete achromatopsia are more severe than the incomplete form. They include seriously
reduced visual acuity, nystagmus, photophobia, and color blindness [
1
]. With only rod-mediated
vision, patients are extremely sensitive to light and have daylight blindness. To reduce
photophobia, currently available medical care is to limit light exposure using dark glasses. With the
development of adeno-associated virus (AAV) vectors as gene delivery tools for many recessively
inherited retinal diseases, several promising gene therapy projects have been initiated [2±9].
Recent preclinical trials have made significant progress in providing effective treatment for
achromatopsia. The first clinical trials of gene therapy are either underway or will be launched soon and
they are expected to contribute important data on the safety and efficacy of these treatments [
10
].
Thus far, six genes have been implicated in achromatopsia-associated mutations [11±15]:
cyclic nucleotide-gated channel alpha-3 (Cnga3) [
16,17
], cyclic nucleotide-gated channel
beta3 (Cngb3) [
18,19
], guanine nucleotide binding protein alpha transduction active peptide 2
(Gnat2) [
1,20
], phosphodiesterase 6C (Pde6c) [
21,22
], Pde6h [
12,13
], and cyclic
AMP-dependent activating transcription factor-6 alpha (Atf6) [
14,15
]. The proteins encoded by these
genes play vital roles in the phototransduction cascade of cone photoreceptors.
The Cnga3 gene encodes a member of the cyclic nucleotide-gated ion channel protein
family, which is critical for normal vision in cone photoreceptors [23]. As the first identified and
second most common cause of achromatopsia, Cnga3 mutations account for approximately
25% of all cases [
24,25
]. A cone photoreceptor function loss 5 (cpfl5) mouse strain, with a
naturally occurring Cnga3 mutation, was discovered at The Jackson Laboratory [11]. Due to a
single nucleotide A to G transition at position 492 of exon 5, the deficient mice exhibit selective
loss of cone-mediated electroretinogram (ERG) responses [
11
]. In addition, it has been shown
that loss of CNGA3 results in impaired expression and trafficking of cone opsins [
11,26
].
New generations of viral vectors have made it possible to deliver functional genes to retinal
cells [
27
]. Gene therapy, which can r (...truncated)