Autosomal recessive retinitis pigmentosa E150K opsin mice exhibit photoreceptor disorganization
Ning Zhang, Alexander V. Kolesnikov, Beata Jastrzebska, Debarshi Mustafi, Osamu Sawada, Tadao Maeda, Christel Genoud, Andreas Engel, Vladimir J. Kefalov, Krzysztof Palczewski
Ning Zhang, Alexander V. Kolesnikov, Beata Jastrzebska, Debarshi Mustafi, Osamu Sawada, Tadao Maeda, Christel Genoud, Andreas Engel, Vladimir J. Kefalov, Krzysztof Palczewski
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Research Article Ophthalmology

Autosomal recessive retinitis pigmentosa E150K opsin mice exhibit photoreceptor disorganization

Abstract

The pathophysiology of the E150K mutation in the rod opsin gene associated with autosomal recessive retinitis pigmentosa (arRP) has yet to be determined. We generated knock-in mice carrying a single nucleotide change in exon 2 of the rod opsin gene resulting in the E150K mutation. This novel mouse model displayed severe retinal degeneration affecting rhodopsin’s stabilization of rod outer segments (ROS). Homozygous E150K (KK) mice exhibited early-onset retinal degeneration, with disorganized ROS structures, autofluorescent deposits in the subretinal space, and aberrant photoreceptor phagocytosis. Heterozygous (EK) mice displayed a delayed-onset milder retinal degeneration. Further, mutant receptors were mislocalized to the inner segments and perinuclear region. Though KK mouse rods displayed markedly decreased phototransduction, biochemical studies of the mutant rhodopsin revealed only minimally affected chromophore binding and G protein activation. Ablation of the chromophore by crossing KK mice with mice lacking the critical visual cycle protein LRAT slowed retinal degeneration, whereas blocking phototransduction by crossing KK mice with GNAT1-deficient mice slightly accelerated this process. This study highlights the importance of proper higher-order organization of rhodopsin in the native tissue and provides information about the signaling properties of this mutant rhodopsin. Additionally, these results suggest that patients heterozygous for the E150K mutation should be periodically reevaluated for delayed-onset retinal degeneration.

Authors

Ning Zhang, Alexander V. Kolesnikov, Beata Jastrzebska, Debarshi Mustafi, Osamu Sawada, Tadao Maeda, Christel Genoud, Andreas Engel, Vladimir J. Kefalov, Krzysztof Palczewski

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Figure 7

Photoreceptor and RPE structures in WT, EK, and KK mice.

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Photoreceptor and RPE structures in WT, EK, and KK mice. (A) Plastic sec...
(A) Plastic sections of P30 KK mouse retinas stained with toluidine blue show disorganized photoreceptor OS with dying photoreceptor cells (arrows). Scale bar: 20 μm. (B) TEM images depict disordered photoreceptor OS discs in P30 KK mouse retina but not in retinas from WT or EK littermates. In WT and EK retinas, higher-magnification images reveal normal ROS architecture, whereas in the KK retina, there is severe ROS disorganization characterized by ROS with loosened and irregular shaped discs together with inclusions (arrows). Scale bars: 1 μm. (C) Phagosomes in P14 WT, EK, and KK RPE. Normal phagosomes were observed in P14 WT and EK mouse RPE (boxes with dashed lines in the upper two rows; scale bar: 4 μm). Augmented phagosome images are shown in right panels. Scale bar, 1 μm. P14 KK mouse retinas display severe RPE pathology with undigested phagocytized discs (arrows, bottom panels) and even ingested discs show abnormal processing. (D) TEM images of retinas from 4-month-old WT, EK, and KK mice. Compared with WT retinas, EK retinas exhibit largely normal-appearing discs in most regions of the outer segment, with just a few abnormal deposits (*) in the subretinal space. KK mouse retinas completely lacked photoreceptor disc structures at this age (&) but pigmented deposits (#) are seen in their subretinal space. Scale bar: 5 μm. IS, photoreceptor inner segment.