Abstract
Purpose :
Inherited macular dystrophy shows bilateral visual loss caused by a progressive degeneration of photoreceptors in the macula. We have reported the association of a novel gene mutation, c.G1613A, p.C538Y, in the cytoplasmic region of LRRTM4 long isoform, with autosomal dominant macular dystrophy (adMD) in a Japanese family (Kawamura et al., J Hum Genet 2018). Since LRRTM4 is a post-synaptic protein, mechanisms to cause macular degeneration is still in question. In this study, we examined the effect of long-isoform specific mutation on protein function in vitro, and on the retinal structure using a genome-edited mutant mouse model.
Methods :
Expression of the long and short isoforms of Lrrtm4 in the mouse retina was tested by RT-PCR. Protein-protein interaction between the long and short isoforms of LRRTM4 was examined in vitro. Mouse carrying the Lrrtm4 (p.C538Y) mutation with the C57BL/6J background (C538Y mutant mouse) was generated by CRISPR/Cas9 system. The C538Y mutant mice and the wild type control mice were exposed to strong light illumination, and examined for their retinal layer structure with Optical Coherence Tomography (OCT). Expression and localization of the photoreceptor and ribbon synaptic markers were examined by immunohistochemistry.
Results :
Both the long- and short- isoforms of Lrrtm4 mRNA expressions were detected in the mouse retina. Long and short isoforms of LRRTM4 proteins interacted each other in vitro. Exposure to the white LED light (3,000 to 7,500 lux) caused degeneration of superior outer nuclear layer in C538Y heterozygous mutant mice, dependent on the light intensity and the duration of exposure time. On the other hand, normally maintained heterozygous and homozygous C538Y mutant mice did not show significant photoreceptor degeneration or structural abnormality in the retina. Outer segments of rod and cone photoreceptors were shortened in the degenerated retinal region.
Conclusions :
Model mouse carrying the same amino acid replacement to the human adMD patients, Lrrtm4 (p.C538Y), was generated. Light-induced photoreceptor degeneration was detected by OCT and immunohistochemistry in the C538Y mutant mouse retina.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.