Disease-causing mutations in the CLRN1 gene alter normal CLRN1 protein trafficking to the plasma membrane

PurposeMutations of clarin 1 (CLRN1) cause Usher syndrome type 3 (USH3). To determine the effects of USH3 mutations on CLRN1 function, we examined the cellular distribution and stability of both normal and mutant CLRN1 in vitro. We also searched for novel disease-causing mutations in a cohort of 59 unrelated Canadian and Finnish USH patients.MethodsMutation screening was performed by DNA sequencing. For the functional studies, wild-type (WT) and mutant CLRN1 genes were expressed as hemagglutinin (HA) tagged fusion proteins by transient transfection of BHK-21 cells. Subcellular localization of CLRN1-HA was examined by confocal microscopy. The N-glycosylation status of CLRN1 was studied by using the N-glycosidase F (PNGase F) enzyme and western blotting. Cycloheximide treatment was used to assess the stability of CLRN1 protein.ResultsWe found three previously reported pathogenic mutations, p.A123D, p.N48K, and p.Y176X, and a novel sequence variant, p.L54P, from the studied USH patients. The WT HA-tagged CLRN1 was correctly trafficked to the plasma membrane, whereas mutant CLRN1-HA proteins were mislocalized and retained in the endoplasmic reticulum. PNGase F treatment of CLRN1-HA resulted in an electrophoretic mobility shift consistent with sugar residue cleavage in WT and in all CLRN1 mutants except in p.N48K mutated CLRN1, in which the mutation abolishes the glycosylation site. Inhibition of protein expression with cycloheximide indicated that WT CLRN1-HA remained stable. In contrast, the CLRN1 mutants showed reduced stability.ConclusionsWT CLRN1 is a glycoprotein localized to the plasma membrane in transfected BHK-21 cells. Mutant CLRN1 proteins are mislocalized. We suggest that part of the pathogenesis of USH3 may be associated with defective intracellular trafficking as well as decreased stability of mutant CLRN1 proteins

Involvement of glutaredoxin-1 and thioredoxin-1 in -amyloid toxicity and Alzheimer's disease

25 páginas, 10 figuras.Strong evidence indicates oxidative stress in the pathogenesis of Alzheimer's disease (AD). Amyloid (A) has been implicated in both oxidative stress mechanisms and in neuronal apoptosis. Glutaredoxin-1 (GRX1) and thioredoxin-1 (TRX1) are antioxidants that can inhibit apoptosis signal-regulating kinase (ASK1). We examined levels of GRX1 and TRX1 in AD brain as well as their effects on A neurotoxicity. We show an increase in GRX1 and a decrease in neuronal TRX1 in AD brains. Using SH-SY5Y cells, we demonstrate that A causes an oxidation of both GRX1 and TRX1, and nuclear export of Daxx, a protein downstream of ASK1. Atoxicity was inhibited by insulin-like growth factor-I (IGF-I) and by overexpressing GRX1 or TRX1. Thus, A neurotoxicity might be mediated by oxidation of GRX1 or TRX1 and subsequent activation of the ASK1 cascade. Deregulation of GRX1 and TRX1 antioxidant systems could be important events in AD pathogenesis.This research was supported by grants from the following Swedish foundations: Hjärnfonden (Swedish Brain Foundation), Gun och Bertil Stohnes Stiftelse, Karolinska Institutets Foundation for geriatric research, Loo and Hans Ostermans Foundation, Åke Wiberg Foundation, Svenska Lundbeck-stiftelsen, Demensförbundet, Alzheimer Foundation; Sweden, Lars Hiertas minnesstiftelse, Gamla Tjänarinnor foundation, Insamlingsstiftelsen för Alzheimer och demenforskning (SADF) and Swedish Brain Power project. AM-V was supported by Swedish Medical Research Council (Projects 03P-14096, 03X-14041, and 13X-10370). AJ was supported by a postdoctoral fellowship EX2003-0390 from the Spanish Ministerio de Educacion, Cultura y Deporte.Peer reviewe

Natural history and biomarkers of retinal dystrophy caused by the biallelic TULP1 variant c.148delG

Purpose To report clinical features and potential disease markers of inherited retinal dystrophy (IRD) caused by the biallelic c.148delG variant in the tubby-like protein 1 (TULP1) gene. Methods A retrospective observational study of 16 IRD patients carrying a homozygous pathogenic TULP1 c.148delG variant. Clinical data including fundus spectral-domain optical coherence tomography (SD-OCT) were assessed. A meta-analysis of visual acuity of previously reported other pathogenic TULP1 variants was performed for reference. Results The biallelic TULP1 variant c.148delG was associated with infantile and early childhood onset IRD. Retinal ophthalmoscopy was primarily normal converting to peripheral pigmentary retinopathy and maculopathy characterized by progressive extra-foveal loss of the ellipsoid zone (EZ), the outer plexiform layer (OPL), and the outer nuclear layer (ONL) bands in the SD-OCT images. The horizontal width of the foveal EZ showed significant regression with the best-corrected visual acuity (BCVA) of the eye (p < 0.0001, R-2 = 0.541, F = 26.0), the age of the patient (p < 0.0001, R-2 = 0.433, F = 16.8), and mild correlation with the foveal OPL-ONL thickness (p = 0.014, R-2 = 0.245, F = 7.2). Modelling of the BCVA data suggested a mean annual loss of logMAR 0.027. The level of visual loss was similar to that previously reported in patients carrying other truncating TULP1 variants. Conclusions This study describes the progression of TULP1 IRD suggesting a potential time window for therapeutic interventions. The width of the foveal EZ and the thickness of the foveal OPL-ONL layers could serve as biomarkers of the disease stage.Peer reviewe

USH3A transcripts encode clarin-1, a four-transmembrane-domain protein with a possible role in sensory synapses

[EN] Usher syndrome type 3 (USH3) is an autosomal recessive disorder characterised by the association of post-lingual progressive hearing loss, progressive visual loss due to retinitis pigmentosa and variable presence of vestibular dysfunction. Because the previously defined transcripts do not account for all USH3 cases, we performed further analysis and revealed the presence of additional exons embedded in longer human and mouse USH3A transcripts and three novel USH3A mutations. Expression of Ush3a transcripts was localised by whole mount in situ hybridisation to cochlear hair cells and spiral ganglion cells. The full length USH3A transcript encodes clarin-1, a four-transmembrane-domain protein, which defines a novel vertebrate-specific family of three paralogues. Limited sequence homology to stargazin, a cerebellar synapse four-transmembrane-domain protein, suggests a role for clarin-1 in hair cell and photoreceptor cell synapses, as well as a common pathophysiological pathway for different Usher syndromes.We are grateful to all patients and their family members who participated in this study. We would also like to thank Ronna Hertzano for the preparation of the mouse inner ear cDNA. This work was funded by an Infrastructure grant of the Israeli Ministry of Science Culture and Sports, the Crown Human Genome Center at The Weizmann Institute of Science, the Alfried Krupp Foundation and by the Finnish Eye and Tissue Bank Foundation, the Finnish Eye Foundation, the Maud Kuistila Memorial Foundation, the Oskar Oflund Foundation, Finnish State grant TYH9235, the European Commission (QLG2-CT-1999-00988) (KB Araham) and by the Foundation Fighting Blindness. JS Beckman holds the, Hermann Mayer professorial chair and D Lancet holds the Ralf and Lois Silver professorial chair.Adato, A.; Vreugde, S.; Joensuu, T.; Avidan, N.; Hamalainen, R.; Belenkiy, O.; Olender, T.... (2002). USH3A transcripts encode clarin-1, a four-transmembrane-domain protein with a possible role in sensory synapses. European Journal of Human Genetics. 10(6):339-350. https://doi.org/10.1038/sj.ejhg.520083133935010

CLRN1 Is Nonessential in the Mouse Retina but Is Required for Cochlear Hair Cell Development

Mutations in the CLRN1 gene cause Usher syndrome type 3 (USH3), a human disease characterized by progressive blindness and deafness. Clarin 1, the protein product of CLRN1, is a four-transmembrane protein predicted to be associated with ribbon synapses of photoreceptors and cochlear hair cells, and recently demonstrated to be associated with the cytoskeleton. To study Clrn1, we created a Clrn1 knockout (KO) mouse and characterized the histological and functional consequences of Clrn1 deletion in the retina and cochlea. Clrn1 KO mice do not develop a retinal degeneration phenotype, but exhibit progressive loss of sensory hair cells in the cochlea and deterioration of the organ of Corti by 4 months. Hair cell stereocilia in KO animals were longer and disorganized by 4 months, and some Clrn1 KO mice exhibited circling behavior by 5–6 months of age. Clrn1 mRNA expression was localized in the retina using in situ hybridization (ISH), laser capture microdissection (LCM), and RT–PCR. Retinal Clrn1 transcripts were found throughout development and adulthood by RT–PCR, although expression peaked at P7 and declined to undetectable levels in adult retina by ISH. LCM localized Clrn1 transcripts to the retinas inner nuclear layer, and WT levels of retinal Clrn1 expression were observed in photoreceptor-less retinas. Examination of Clrn1 KO mice suggests that CLRN1 is unnecessary in the murine retina but essential for normal cochlear development and function. This may reflect a redundancy in the mouse retina not present in human retina. In contrast to mouse KO models of USH1 and USH2, our data indicate that Clrn1 expression in the retina is restricted to the Müller glia. This is a novel finding, as most retinal degeneration associated proteins are expressed in photoreceptors, not in glia. If CLRN1 expression in humans is comparable to the expression pattern observed in mice, this is the first report of an inner retinal protein that, when mutated, causes retinal degeneration

Prevalence of RPGR-Mediated Retinal Dystrophy in an Unselected Cohort of Over 5000 Patients

Purpose: Comprehensive genetic testing for inherited retinal dystrophy (IRD) is challenged by difficult-to-sequence genomic regions, which are often mutational hotspots, such as RPGR ORF15. The purpose of this study was to evaluate the diagnostic contribution of RPGR variants in an unselected IRD patient cohort referred for testing in a clinical diagnostic laboratory. Methods: A total of 5201 consecutive patients were analyzed with a clinically validated next-generation sequencing (NGS)-based assay, including the difficult-to-sequence RPGR ORF15 region. Copy number variant (CNV) detection from NGS data was included. Variant interpretation was performed per the American College of Medical Genetics and Genomics guidelines. Results: A confirmed molecular diagnosis in RPGR was found in 4.5% of patients, 24.0% of whom were females. Variants in ORF15 accounted for 74% of the diagnoses; 29% of the diagnostic variants were in the most difficult-to-sequence central region of ORF15 (c.2470-3230). Truncating variants made up the majority (91%) of the diagnostic variants. CNVs explained 2% of the diagnostic cases, of which 80% were one- or two-exon deletions outside of ORF15. Conclusions: Our findings indicate that high-throughput, clinically validated NGS-based testing covering the difficult-to-sequence region of ORF15, in combination with high-resolution CNV detection, can help to maximize the diagnostic yield for patients with IRD. Translational Relevance: These results demonstrate an accurate and scalable method for the detection of RPGR-related variants, including the difficult-to-sequence ORF15 hotspot, which is relevant given current and emerging therapeutic opportunities.Peer reviewe

Measurement and Reproducibility of Preserved Ellipsoid Zone Area and Preserved Retinal Pigment Epithelium Area in Eyes With Choroideremia

PURPOSE: To identify valid and reproducible methods for quantifying anatomic outcome measures for eyes with choroideremia (CHM) in clinical trials. DESIGN: Reliability analysis study. METHODS: In this multicenter study, patients with confirmed genetic diagnosis of CHM were enrolled. All cases underwent spectral-domain optical coherence tomography (SDOCT) and fundus autofluorescence (FAF) imaging. Two graders independently delineated boundaries of preserved autofluorescence (PAF) and pre-served ellipsoid zone (EZ) on FAF and OCT images, respectively. The results of the 2 independent gradings of both FAF and OCT images were compared to assess the reproducibility of the grading methods. RESULTS: A total of 148 eyes from 75 cases were included. In 21% of eyes PAF and in 43% of eyes preserved EZ had extended beyond the image capture area. After exclusion of these eyes and low-quality images, 114 FAF and 77 OCT images were graded. The mean PAF areas from 2 independent gradings were 3.720 +/- 3.340 mm(2) and 3.692 +/- 3.253 mm2, respectively. Intraclass correlation coefficient (ICC) for these gradings was 0.996. The mean preserved EZ areas from 2 independent gradings were 2.746 +/- 2.319 mm2 and 2.858 2.446 mm2, respectively. ICC for these gradings was 0.991. CONCLUSIONS: Quantifying preserved retinal pigment epithelium and EZ areas on FAF and OCT images, respectively, in CHM patients is highly reproducible. These variables would be potential anatomic outcome measures for CHM clinical trials and could be studied and tracked longitudinally in choroideremia. (C) 2017 Elsevier Inc. All rights reserved.Peer reviewe

Cone Structure in Patients With Usher Syndrome Type III and Mutations in the Clarin 1 Gene

ObjectiveTo study macular structure and function in patients with Usher syndrome type III (USH3) caused by mutations in the Clarin 1 gene (CLRN1).MethodsHigh-resolution macular images were obtained by adaptive optics scanning laser ophthalmoscopy and spectral domain optical coherence tomography in 3 patients with USH3 and were compared with those of age-similar control subjects. Vision function measures included best-corrected visual acuity, kinetic and static perimetry, and full-field electroretinography. Coding regions of the CLRN1 gene were sequenced.ResultsCLRN1 mutations were present in all the patients; a 20-year-old man showed compound heterozygous mutations (p.N48K and p.S188X), and 2 unrelated women aged 25 and 32 years had homozygous mutations (p.N48K). Best-corrected visual acuity ranged from 20/16 to 20/40, with scotomas beginning at 3° eccentricity. The inner segment-outer segment junction or the inner segment ellipsoid band was disrupted within 1° to 4° of the fovea, and the foveal inner and outer segment layers were significantly thinner than normal. Cones near the fovea in patients 1 and 2 showed normal spacing, and the preserved region ended abruptly. Retinal pigment epithelial cells were visible in patient 3 where cones were lost.ConclusionsCones were observed centrally but not in regions with scotomas, and retinal pigment epithelial cells were visible in regions without cones in patients with CLRN1 mutations. High-resolution measures of retinal structure demonstrate patterns of cone loss associated with CLRN1 mutations.Clinical relevanceThese findings provide insight into the effect of CLRN1 mutations on macular cone structure, which has implications for the development of treatments for USH3.Trial registrationclinicaltrials.gov Identifier: NCT00254605

Cone Structure in Patients With Usher Syndrome Type III and Mutations in the Clarin 1 Gene

OBJECTIVE: To study macular structure and function in patients with Usher syndrome type III (USH3) caused by mutations in the Clarin 1 gene (CLRN1). METHODS: High-resolution macular images were obtained by adaptive optics scanning laser ophthalmoscopy and spectral domain optical coherence tomography in 3 patients with USH3 and were compared with those of age-similar control subjects. Vision function measures included best-corrected visual acuity, kinetic and static perimetry, and full-field electroretinography. Coding regions of the CLRN1 gene were sequenced. RESULTS: CLRN1 mutations were present in all the patients; a 20-year-old man showed compound heterozygous mutations (p.N48K and p.S188X), and 2 unrelated women aged 25 and 32 years had homozygous mutations (p.N48K). Best-corrected visual acuity ranged from 20/16 to 20/40, with scotomas beginning at 3° eccentricity. The inner segment-outer segment junction or the inner segment ellipsoid band was disrupted within 1° to 4° of the fovea, and the foveal inner and outer segment layers were significantly thinner than normal. Cones near the fovea in patients 1 and 2 showed normal spacing, and the preserved region ended abruptly. Retinal pigment epithelial cells were visible in patient 3 where cones were lost. CONCLUSIONS: Cones were observed centrally but not in regions with scotomas, and retinal pigment epithelial cells were visible in regions without cones in patients with CLRN1 mutations. High-resolution measures of retinal structure demonstrate patterns of cone loss associated with CLRN1 mutations. CLINICAL RELEVANCE: These findings provide insight into the effect of CLRN1 mutations on macular cone structure, which has implications for the development of treatments for USH3. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT0025460