Abstract
Purpose :
Leber congenital amaurosis type 4 (LCA4), a severe form of inherited retinal dystrophy, is an autosomal recessive disorder caused by mutations in aryl hydrocarbon receptor interacting protein-like 1 (AIPL1). AIPL1 is a photoreceptor-specific co-chaperone that is crucial for the correct folding and assembly of the cGMP phosphodiesterase PDE6 complex. AIPL1 is highly heterogeneous, but W278X -which encodes a premature stop codon in the last exon of the AIPL1 transcript- is the most common (50-65% frequency) LCA4 pathogenic allele. The position of the W278X mutation renders it potentially amenable to translation readthrough inducing drug (TRID) therapy, which aims to override the premature stop codon with the incorporation of near-cognate tRNA amino acids.
Methods :
In order to test TRID therapy as a potential treatment for LCA4, induced pluripotent stem cells (iPSC) were derived from 4 different LCA4 patients, comprising one W278X homozygote and 3 W278X compound heterozygotes. Retinal organoids (ROs) were differentiated and extensively characterised. 10ug/ml PTC124 was tested on patient ROs from D120 onwards, when AIPL1 expression is observed in developing photoreceptor cells.
Results :
LCA4-ROs were indistinguishable from control in terms of organoid structure, retinal cell development and differentiation kinetics. Both control and LCA4-ROs generated the full complement of retinal cell types, with an outer nuclear layer (ONL) comprised of photoreceptors with presumptive inner/outer segment structures. However, LCA4-ROs lack detectable AIPL1 protein in the ONL, and PDE6A and PDE6B are absent, recapitulating key aspects of LCA4. PTC124-treated W278X+/+ and +/- LCA4-ROs displayed partial rescue of AIPL1 protein, proving that PTC124 is indeed able to drive readthrough of the W278X allele. Moreover, low-level restoration of PDE6B was seen in W278X+/+ LCA4-ROs.
Conclusions :
Patient-derived LCA4 ROs recapitulate the key molecular features of LCA4, validating it as a useful in vitro system in which to interrogate novel therapies. Excitingly, PTC124 was able to partially restore AIPL1 protein in W278X-/+ and +/+ LCA4-RO photoreceptors with limited rescue of PDE6B in W279X+/+ RO, potentially due to the increased amount of W278X transcript in these ROs. These results demonstrate that translational readthrough therapy might be a promising approach to LCA4 treatment.
This is a 2021 ARVO Annual Meeting abstract.