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ROM1 contributes to phenotypic heterogeneity in PRPH2-associated retinal disease.

ABSTRACT: Peripherin 2 (PRPH2) is a retina-specific tetraspanin protein essential for the formation of rod and cone photoreceptor outer segments (OS). Patients with mutations in PRPH2 exhibit severe retinal degeneration characterized by vast inter- and intra-familial phenotypic heterogeneity. To help understand contributors to this within-mutation disease variability, we asked whether the PRPH2 binding partner rod OS membrane protein 1 (ROM1) could serve as a phenotypic modifier. We utilized knockin and transgenic mouse models to evaluate the structural, functional and biochemical effects of eliminating one allele of Rom1 (Rom1+/-) in three different Prph2 models which mimic human disease: C213Y Prph2 (Prph2C/+), K153Del Prph2 (Prph2K/+) and R172W (Prph2R172W). Reducing Rom1 in the absence of Prph2 mutations (Rom1+/-) had no effect on retinal structure or function. However, the effects of reducing Rom1 in the presence of Prph2 mutations were highly variable. Prph2K/+/Rom1+/- mice had improved rod and cone function compared with Prph2K/+ as well as amelioration of K153Del-associated defects in PRPH2/ROM1 oligomerization. In contrast, Prph2R172W/Rom1+/- animals had worsened rod and cone function and exacerbated retinal degeneration compared with Prph2R172W animals. Removing one allele of Rom1 had no effect in Prph2C/+. Combined, our findings support a role for non-pathogenic ROM1 null variants in contributing to phenotypic variability in mutant PRPH2-associated retinal degeneration. Since the effects of Rom1 reduction are variable, our data suggest that this contribution is specific to the type of Prph2 mutation.

SUBMITTER: Strayve D

PROVIDER: S-EPMC7530533 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Rom1 converts Y141C-Prph2-associated pattern dystrophy to retinitis pigmentosa.

Project description:Mutations in peripherin 2 (PRPH2), also known as retinal degeneration slow/RDS, lead to various retinal degenerations including retinitis pigmentosa (RP) and macular/pattern dystrophy (MD/PD). PRPH2-associated disease is often characterized by a phenotypic variability even within families carrying the same mutation, raising interest in potential modifiers. PRPH2 oligomerizes with its homologue rod outer segment (OS) membrane protein 1 (ROM1), and non-pathogenic PRPH2/ROM1 mutations, when present together, lead to digenic RP. We asked whether ROM1 could modify the phenotype of a PRPH2 mutation associated with a high degree of intrafamilial phenotypic heterogeneity: Y141C. In vitro, Y141C-Prph2 showed signs of retention in the endoplasmic reticulum (ER), however co-expression with Rom1 rescued this phenotype. In the heterozygous Y141C knockin mouse model (Prph2Y/+), Y141C-Prph2 and Rom1 formed abnormal complexes but were present at normal levels. Abnormal complexes were eliminated in the absence of Rom1 (Prph2Y/+/Rom1-/-) and total Prph2 levels were reduced to those found in the haploinsufficient Prph2+/- RP model. The biochemical changes had functional and structural consequences; while Prph2Y/+?animals exhibited a cone-rod electroretinogram defect, Prph2Y/+/Rom1-/- animals displayed a rod-dominant phenotype and OSs similar to those seen in the Prph2+/-. These data show that ablation of Rom1 results in the conversion of an MD/PD phenotype characterized by cone functional defects and the formation of abnormal Prph2/Rom1 complexes to an RP phenotype characterized by rod-dominant functional defects and reductions in total Prph2 protein. Thus one method by which ROM1 may act as a disease modifier is by contributing to the large variability in PRPH2-associated disease phenotypes.

| S-EPMC6075606 | biostudies-literature

Prph2 initiates outer segment morphogenesis but maturation requires Prph2/Rom1 oligomerization.

Project description:The retinal disease gene peripherin 2 (PRPH2) is essential for the formation of photoreceptor outer segments (OSs), where it functions in oligomers with and without its homologue ROM1. However, the precise role of these proteins in OS morphogenesis is not understood. By utilizing a knock-in mouse expressing a chimeric protein comprised of the body of Rom1 and the C-terminus of Prph2 (termed RRCT), we find that the Prph2 C-terminus is necessary and sufficient for the initiation of OSs, while OS maturation requires the body of Prph2 and associated large oligomers. Importantly, dominant-negative physiological and biochemical defects in RRCT heterozygous rods are rescued by removing Rom1, suggesting Rom1 is a regulator for OS formation. Our experiments evaluating Prph2 trafficking show that Rom1 is a key determinant of whether Prph2 complexes utilize conventional versus unconventional (Golgi bypass) secretory pathways to reach the OS. These findings significantly advance our understanding of the molecular underpinnings of OS morphogenesis and particularly the role of Rom1.

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Project description: Not available

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Genetic and Phenotypic Landscape of PRPH2-Associated Retinal Dystrophy in Japan.

Project description:Peripherin-2 (PRPH2) is one of the causative genes of inherited retinal dystrophy. While the gene is relatively common in Caucasians, reports from Asian ethnicities are limited. In the present study, we report 40 Japanese patients from 30 families with PRPH2-associated retinal dystrophy. We identified 17 distinct pathogenic or likely pathogenic variants using next-generation sequencing. Variants p.R142W and p.V200E were relatively common in the cohort. The age of onset was generally in the 40's; however, some patients had earlier onset (age: 5 years). Visual acuity of the patients ranged from hand motion to 1.5 (Snellen equivalent 20/13). The patients showed variable phenotypes such as retinitis pigmentosa, cone-rod dystrophy, and macular dystrophy. Additionally, intrafamilial phenotypic variability was observed. Choroidal neovascularization was observed in three eyes of two patients with retinitis pigmentosa. The results demonstrate the genotypic and phenotypic variations of the disease in the Asian cohort.

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Project description: Not available

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Oligomerization of Prph2 and Rom1 is essential for photoreceptor outer segment formation.

Project description:Mutations in peripherin 2 (PRPH2, also known as Rds), a tetraspanin protein found in photoreceptor outer segments (OSs), cause retinal degeneration ranging from rod-dominant retinitis pigmentosa (RP) to cone-dominant macular dystrophy (MD). Understanding why some Prph2 mutants affect rods while others affect cones remains a critical unanswered question. Prph2 is essential for OS structure and function and exhibits a very specific pattern of oligomerization with its homolog Rom1. Non-covalent Prph2/Rom1 homo- and hetero-tetramers assemble into higher-order covalently linked complexes held together by an intermolecular disulfide bond at Prph2-C150/Rom1-C153. Here we disrupt this crucial bond using a C150S-Prph2 knockin mouse line to study the role of Prph2 higher-order complex formation. We find that C150S-Prph2 traffics to the OS, interacts with Rom1 and forms non-covalent tetramers, but alone cannot support normal OS structure and function. However, C150S-Prph2 supports the initiation or elaboration of OS disc structures, and improves rod OS ultrastructure in the presence of wild-type (WT) Prph2 (i.e. Prph2C150S/+ versus Prph2+/-). Prph2C150S/+ animals exhibit haploinsufficiency in rods, but a dominant-negative phenotype in cones, suggesting cones have a different requirement for large Prph2 complexes than rods. Importantly, cone but not rod function can be improved by the addition of one Prph2Y141C allele, a mutation responsible for pattern dystrophy owing to the extra cysteine. Combined these findings show that covalently linked Prph2 complexes are essential for OS formation, but not for Prph2 targeting to the OS, and that cones are especially sensitive to having a broad distribution of Prph2 complex types (i.e. tetramers and large complexes).

| S-EPMC6168975 | biostudies-literature

ROM1 is redundant to PRPH2 as a molecular building block of photoreceptor disc rims.

Project description:Visual signal transduction takes place within a stack of flattened membranous 'discs' enclosed within the light-sensitive photoreceptor outer segment. The highly curved rims of these discs, formed in the process of disc enclosure, are fortified by large hetero-oligomeric complexes of two homologous tetraspanin proteins, PRPH2 (a.k.a. peripherin-2 or rds) and ROM1. While mutations in PRPH2 affect the formation of disc rims, the role of ROM1 remains poorly understood. In this study, we found that the knockout of ROM1 causes a compensatory increase in the disc content of PRPH2. Despite this increase, discs of ROM1 knockout mice displayed a delay in disc enclosure associated with a large diameter and lack of incisures in mature discs. Strikingly, further increasing the level of PRPH2 rescued these morphological defects. We next showed that disc rims are still formed in a knockin mouse in which the tetraspanin body of PRPH2 was replaced with that of ROM1. Together, these results demonstrate that, despite its contribution to the formation of disc rims, ROM1 can be replaced by an excess of PRPH2 for timely enclosure of newly forming discs and establishing normal outer segment structure.

| S-EPMC10665016 | biostudies-literature

Late-onset pattern macular dystrophy mimicking ABCA4 and PRPH2 disease is caused by a homozygous frameshift mutation in ROM1.

Project description:ROM1 (retinal outer segment membrane protein 1) is a 351-amino acid integral membrane protein on Chromosome 11q, with high structural similarity to PRPH2/RDS. Localized at the rims of photoreceptor outer segments (OSs), it is required for the maintenance of OS structure. Here, we describe a case with a phenotypic manifestation of a homozygous single-base pair deletion, c.712delC (p.Leu238Cysfs*78) in the ROM1 gene, resulting in early termination at exon 2. The variant was detected by whole-exome sequencing (WES) in a 63-yr-old Caucasian woman with late-onset pattern macular dystrophy. Notably, although the phenotype resembles those caused by pathogenic variants in ABCA4 or RDS/PRPH2, no pathogenic variants in these, or any other plausible candidate genes, were identified by WES. Clinical features include the presence of hyperautofluorescent flecks, relative sparing of the central macula, and preserved visual acuity. Reduced visual sensitivity was detected among flecked regions in the retina; however, full-field electroretinogram testing revealed no generalized cone dysfunction. The described first case of the complete loss of ROM1 protein function in the retina suggests its sufficiency for late-onset macular dystrophy. ROM1 and PRPH2 pattern macular dystrophies exhibit phenotype overlap, which may be attributable to their shared role in maintenance of the photoreceptor outer segment structure.

| S-EPMC6549556 | biostudies-literature

Quantitative Fundus Autofluorescence and Optical Coherence Tomography in PRPH2/RDS- and ABCA4-Associated Disease Exhibiting Phenotypic Overlap.

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| S-EPMC4451616 | biostudies-literature

Expanding the phenotypic spectrum in RDH12-associated retinal disease.

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| S-EPMC6996522 | biostudies-literature

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