The Experts below are selected from a list of 789 Experts worldwide ranked by ideXlab platform
Susanne Kohl - One of the best experts on this subject based on the ideXlab platform.
-
Safety and Vision Outcomes of Subretinal Gene Therapy Targeting Cone Photoreceptors in Achromatopsia: A Nonrandomized Controlled Trial.
JAMA ophthalmology, 2020Co-Authors: M. Dominik Fischer, Susanne Kohl, Stylianos Michalakis, Barbara Wilhelm, Ditta Zobor, Regine Muehlfriedel, Nicole Weisschuh, G. Alex Ochakovski, Reinhild Klein, Christian SchoenAbstract:Importance Achromatopsia linked to variations in theCNGA3gene is associated with day blindness, poor visual acuity, photophobia, and involuntary eye movements owing to lack of cone photoreceptor function. No treatment is currently available. Objective To assess safety and vision outcomes of supplemental gene therapy with adeno-associated virus (AAV) encodingCNGA3(AAV8.CNGA3) in patients withCNGA3-linked Achromatopsia. Design, Setting, and Participants This open-label, exploratory nonrandomized controlled trial tested safety and vision outcomes of gene therapy vector AAV8.CNGA3 administered by subretinal injection at a single center. Nine patients (3 per dose group) with a clinical diagnosis of Achromatopsia and confirmed biallelic disease-linked variants inCNGA3were enrolled between November 5, 2015, and September 22, 2016. Data analysis was performed from June 6, 2017, to March 12, 2018. Intervention Patients received a single unilateral injection of 1.0 × 1010, 5.0 × 1010, or 1.0 × 1011total vector genomes of AAV8.CNGA3 and were followed up for a period of 12 months (November 11, 2015, to October 10, 2017). Main Outcomes and Measures Safety as the primary end point was assessed by clinical examination of ocular inflammation. Systemic safety was assessed by vital signs, routine clinical chemistry testing, and full and differential blood cell counts. Secondary outcomes were change in visual function from baseline in terms of spatial and temporal resolution and chromatic, luminance, and contrast sensitivity throughout a period of 12 months after treatment. Results Nine patients (mean [SD] age, 39.6 [11.9] years; age range, 24-59 years; 8 [89%] male) were included in the study. Baseline visual acuity letter score (approximate Snellen equivalent) ranged from 34 (20/200) to 49 (20/100), whereas baseline contrast sensitivity log scores ranged from 0.1 to 0.9. All 9 patients underwent surgery and subretinal injection of AAV8.CNGA3 without complications. No substantial safety problems were observed during the 12-month follow-up period. Despite the congenital deprivation of cone photoreceptor–mediated vision in Achromatopsia, all 9 treated eyes demonstrated some level of improvement in secondary end points regarding cone function, including mean change in visual acuity of 2.9 letters (95% CI, 1.65-4.13;P = .006, 2-sidedttest paired samples). Contrast sensitivity improved by a mean of 0.33 log (95% CI, 0.14-0.51 log;P = .003, 2-sidedttest paired samples). Conclusions and Relevance Subretinal gene therapy with AAV8.CNGA3 was not associated with substantial safety problems and was associated with cone photoreceptor activation in adult patients, as reflected by visual acuity and contrast sensitivity gains. Trial Registration ClinicalTrials.gov Identifier:NCT02610582
-
ARTICLE
2016Co-Authors: Susanne Kohl, Britta Baumann, Thomas Rosenberg, Ulrich Kellner, Birgit Lorenz, Balazs Varsanyi, Gesine Abadin Antunes, Carel B, Roberto Salati, Bernhard JurkliesAbstract:CNGB3 mutations account for 50 % of all cases with autosomal recessive achromatopsi
-
spectral domain optical coherence tomography staging and autofluorescence imaging in Achromatopsia
JAMA Ophthalmology, 2014Co-Authors: Jonathan P Greenberg, Susanne Kohl, Royce W.s. Chen, Britta Baumann, Bernd Wissinger, J Sherman, Sandrine A Zweifel, Tobias Duncker, Lawrence A Yannuzzi, S TsangAbstract:IMPORTANCE Evidence is mounting that Achromatopsia is a progressive retinal degeneration, and treatments for this condition are on the horizon. OBJECTIVES To categorize Achromatopsia into clinically identifiable stages using spectral-domain optical coherence tomography and to describe fundus autofluorescence imaging in this condition. DESIGN, SETTING, AND PARTICIPANTS A prospective observational study was performed between 2010 and 2012 at the Edward S. Harkness Eye Institute, New York-Presbyterian Hospital. Participants included 17 patients (aged 10-62 years) with full-field electroretinography-confirmed Achromatopsia. MAIN OUTCOMES AND MEASURES Spectral-domain optical coherence tomography features and staging system, fundus autofluorescence and near-infrared reflectance features and their correlation to optical coherence tomography, and genetic mutations served as the outcomes and measures. RESULTS Achromatopsia was categorized into 5 stages on spectral-domain optical coherence tomography: stage 1 (2 patients [12%]), intact outer retina; stage 2 (2 patients [12%]), inner segment ellipsoid line disruption; stage 3 (5 patients [29%]), presence of an optically empty space; stage 4 (5 patients [29%]), optically empty space with partial retinal pigment epithelium disruption; and stage 5 (3 patients [18%]), complete retinal pigment epithelium disruption and/or loss of the outer nuclear layer. Stage 1 patients showed isolated hyperreflectivity of the external limiting membrane in the fovea, and the external limiting membrane was hyperreflective above each optically empty space. On near infrared reflectance imaging, the fovea was normal, hyporeflective, or showed both hyporeflective and hyperreflective features. All patients demonstrated autofluorescence abnormalities in the fovea and/or parafovea: 9 participants (53%) had reduced or absent autofluorescence surrounded by increased autofluorescence, 4 individuals (24%) showed only reduced or absent autofluorescence, 3 patients (18%) displayed only increased autofluorescence, and 1 individual (6%) exhibited decreased macular pigment contrast. Inner segment ellipsoid line loss generally correlated with the area of reduced autofluorescence, but hyperautofluorescence extended into this region in 2 patients (12%). Bilateral coloboma-like atrophic macular lesions were observed in 1 patient (6%). Five novel mutations were identified (4 in the CNGA3 gene and 1 in the CNGB3 gene). CONCLUSIONS AND RELEVANCE Achromatopsia often demonstrates hyperautofluorescence suggestive of progressive retinal degeneration. The proposed staging system facilitates classification of the disease into different phases of progression and may have therapeutic implications.
-
© 2008 Molecular Vision CNGA3 mutations in two United Arab Emirates families with Achromatopsia
2013Co-Authors: Yachna Ahuja, Susanne Kohl, Elias I. TraboulsiAbstract:Purpose: Achromatopsia results from mutations in one of three genes: cyclic nucleotide-gated channel, alpha-3 (CNGA3); cyclic nucleotide-gated channel, beta-3 (CNGB3); and guanine nucleotide-binding protein, alpha-transducing activity polypeptide 2 (GNAT2). We report the responsible mutations in two United Arab Emirates families who have this autosomal recessive disease. Methods: Clinical examinations were performed in seven patients from three nuclear families. Molecular genetic testing for common CNGA3 and CNGB3 mutations was undertaken using standard protocols. Results: All patients were extremely light sensitive and had reduced visual acuity and no color perception. Fundus examinations did not show any visible abnormalities. After further pedigree analysis, two of the families were found to be linked through the paternal line. Two mutations in CNGA3 were identified: Arg283Trp and Gly397Val. Family A, the larger pedigree, had one branch in which two sisters and one brother were homozygous for the Gly397Val mutation and another branch in which a brother and sister were compound heterozygous for both aforenamed mutations. Family B, however, only had two brothers who were homozygous for the Arg283Trp mutation. Conclusions: Achromatopsia in these two United Arab Emirates families results from two different mutations in CNGA3. Two branches of the same pedigree had individuals with both homozygous and compound heterozygous disease, demonstrating a complex molecular pathology in this large family
-
a nonsense mutation in pde6h causes autosomal recessive incomplete Achromatopsia
American Journal of Human Genetics, 2012Co-Authors: Susanne Kohl, Frauke Coppieters, Simone Schaich, Susanne Roosing, Christina Brennenstuhl, Sylvia Bolz, Maria M Van Genderen, Francoise Meire, F C C Riemslag, Robert LukowskiAbstract:Achromatopsia (ACHM) is an autosomal-recessive retinal dystrophy characterized by color blindness, photophobia, nystagmus, and severely reduced visual acuity. Its prevalence has been estimated to about 1 in 30,000 individuals. Four genes, GNAT2, PDE6C, CNGA3, and CNGB3, have been implicated in ACHM, and all encode functional components of the phototransduction cascade in cone photoreceptors. Applying a functional-candidate-gene approach that focused on screening additional genes involved in this process in a cohort of 611 index cases with ACHM or other cone photoreceptor disorders, we detected a homozygous single base change (c.35C>G) resulting in a nonsense mutation (p.Ser12∗) in PDE6H, encoding the inhibitory γ subunit of the cone photoreceptor cyclic guanosine monophosphate phosphodiesterase. The c.35C>G mutation was present in three individuals from two independent families with a clinical diagnosis of incomplete ACHM and preserved short-wavelength-sensitive cone function. Moreover, we show through immunohistochemical colocalization studies in mouse retina that Pde6h is evenly present in all retinal cone photoreceptors, a fact that had been under debate in the past. These findings add PDE6H to the set of genes involved in autosomal-recessive cone disorders and demonstrate the importance of the inhibitory γ subunit in cone phototransduction.
Xiqin Ding - One of the best experts on this subject based on the ideXlab platform.
-
endoplasmic reticulum er ca2 channel activity contributes to er stress and cone death in cyclic nucleotide gated channel deficiency
Journal of Biological Chemistry, 2017Co-Authors: Michael R Butler, Stylianos Michalakis, Fan Yang, Joshua Belcher, Katsuhiko Mikoshiba, Martin Biel, Anthony Iuso, David Križaj, Xiqin DingAbstract:Endoplasmic reticulum (ER) stress and mislocalization of improperly folded proteins have been shown to contribute to photoreceptor death in models of inherited retinal degenerative diseases. In particular, mice with cone cyclic nucleotide-gated (CNG) channel deficiency, a model for Achromatopsia, display both early-onset ER stress and opsin mistrafficking. By 2 weeks of age, these mice show elevated signaling from all three arms of the ER-stress pathway, and by 1 month, cone opsin is improperly distributed away from its normal outer segment location to other retinal layers. This work investigated the role of Ca2+ release channels in ER stress, protein mislocalization, and cone death in a mouse model of CNG-channel deficiency. We examined whether preservation of luminal Ca2+ stores through pharmacological and genetic suppression of ER Ca2+ efflux protects cones by attenuating ER stress. We demonstrated that the inhibition of ER Ca2+ -efflux channels reduced all three arms of ERstress signaling while improving opsin trafficking to cone outer segments and decreasing cone death by 20-35%. Cone-specific gene deletion of the inositol-1,4,5-trisphosphate receptor type I (IP3R1) also significantly increased cone density in the CNGchannel- deficient mice, suggesting that IP3R1 signaling contributes to Ca2+ homeostasis and cone survival. Consistent with the important contribution of organellar Ca2+ signaling in this Achromatopsia mouse model, significant differences in dynamic intraorganellar Ca2+ levels were detected in CNG-channel-deficient cones. These results thus identify a novel molecular link between Ca2+ homeostasis and cone degeneration, thereby revealing novel therapeutic targets to preserve cones in inherited retinal degenerative diseases.
-
suppressing thyroid hormone signaling preserves cone photoreceptors in mouse models of retinal degeneration
Proceedings of the National Academy of Sciences of the United States of America, 2014Co-Authors: Arjun Thapa, Lynsie Morris, Michael T Redmond, Wolfgang Baehr, Xiqin DingAbstract:Cone phototransduction and survival of cones in the human macula is essential for color vision and for visual acuity. Progressive cone degeneration in age-related macular degeneration, Stargardt disease, and recessive cone dystrophies is a major cause of blindness. Thyroid hormone (TH) signaling, which regulates cell proliferation, differentiation, and apoptosis, plays a central role in cone opsin expression and patterning in the retina. Here, we investigated whether TH signaling affects cone viability in inherited retinal degeneration mouse models. Retinol isomerase RPE65-deficient mice [a model of Leber congenital amaurosis (LCA) with rapid cone loss] and cone photoreceptor function loss type 1 mice (severe recessive Achromatopsia) were used to determine whether suppressing TH signaling with antithyroid treatment reduces cone death. Further, cone cyclic nucleotide-gated channel B subunit-deficient mice (moderate Achromatopsia) and guanylate cyclase 2e-deficient mice (LCA with slower cone loss) were used to determine whether triiodothyronine (T3) treatment (stimulating TH signaling) causes deterioration of cones. We found that cone density in retinol isomerase RPE65-deficient and cone photoreceptor function loss type 1 mice increased about sixfold following antithyroid treatment. Cone density in cone cyclic nucleotide-gated channel B subunit-deficient and guanylate cyclase 2e-deficient mice decreased about 40% following T3 treatment. The effect of TH signaling on cone viability appears to be independent of its regulation on cone opsin expression. This work demonstrates that suppressing TH signaling in retina dystrophy mouse models is protective of cones, providing insights into cone preservation and therapeutic interventions.
-
endoplasmic reticulum stress associated cone photoreceptor degeneration in cyclic nucleotide gated channel deficiency
Journal of Biological Chemistry, 2012Co-Authors: Arjun Thapa, Stylianos Michalakis, Martin Biel, Lynsie Morris, Xiqin DingAbstract:Cyclic nucleotide-gated (CNG) channels play a pivotal role in phototransduction. Mutations in the cone CNG channel subunits CNGA3 and CNGB3 account for >70% of all known cases of Achromatopsia. Cones degenerate in Achromatopsia patients and in CNGA3−/− and CNGB3−/− mice. This work investigates the molecular basis of cone degeneration in CNG channel deficiency. As cones comprise only 2–3% of the total photoreceptor population in the wild-type mouse retina, we generated mouse lines with CNG channel deficiency on a cone-dominant background, i.e. CNGA3−/−/Nrl−/− and CNGB3−/−/Nrl−/− mice. The retinal phenotype and potential cell death pathways were examined by functional, biochemical, and immunohistochemical approaches. CNGA3−/−/Nrl−/− and CNGB3−/−/Nrl−/− mice showed impaired cone function, opsin mislocalization, and cone degeneration similar to that in the single knock-out mice. The endoplasmic reticulum stress marker proteins, including Grp78/Bip, phospho-eIF2α, phospho-IP3R, and CCAAT/enhancer-binding protein homologous protein, were elevated significantly in CNGA3−/−/Nrl−/− and CNGB3−/−/Nrl−/− retinas, compared with the age-matched (postnatal 30 days) Nrl−/− controls. Along with these, up-regulation of the cysteine protease calpains and cleavage of caspase-12 and caspase-7 were found in the channel-deficient retinas, suggesting an endoplasmic reticulum stress-associated apoptosis. In addition, we observed a nuclear translocation of apoptosis-inducing factor (AIF) and endonuclease G in CNGA3−/−/Nrl−/− and CNGB3−/−/Nrl−/− retinas, implying a mitochondrial insult in the endoplasmic reticulum stress-activated cell death process. Taken together, our findings suggest a crucial role of endoplasmic reticulum stress in cone degeneration associated with CNG channel deficiency.
Bernd Wissinger - One of the best experts on this subject based on the ideXlab platform.
-
spectral domain optical coherence tomography staging and autofluorescence imaging in Achromatopsia
JAMA Ophthalmology, 2014Co-Authors: Jonathan P Greenberg, Susanne Kohl, Royce W.s. Chen, Britta Baumann, Bernd Wissinger, J Sherman, Sandrine A Zweifel, Tobias Duncker, Lawrence A Yannuzzi, S TsangAbstract:IMPORTANCE Evidence is mounting that Achromatopsia is a progressive retinal degeneration, and treatments for this condition are on the horizon. OBJECTIVES To categorize Achromatopsia into clinically identifiable stages using spectral-domain optical coherence tomography and to describe fundus autofluorescence imaging in this condition. DESIGN, SETTING, AND PARTICIPANTS A prospective observational study was performed between 2010 and 2012 at the Edward S. Harkness Eye Institute, New York-Presbyterian Hospital. Participants included 17 patients (aged 10-62 years) with full-field electroretinography-confirmed Achromatopsia. MAIN OUTCOMES AND MEASURES Spectral-domain optical coherence tomography features and staging system, fundus autofluorescence and near-infrared reflectance features and their correlation to optical coherence tomography, and genetic mutations served as the outcomes and measures. RESULTS Achromatopsia was categorized into 5 stages on spectral-domain optical coherence tomography: stage 1 (2 patients [12%]), intact outer retina; stage 2 (2 patients [12%]), inner segment ellipsoid line disruption; stage 3 (5 patients [29%]), presence of an optically empty space; stage 4 (5 patients [29%]), optically empty space with partial retinal pigment epithelium disruption; and stage 5 (3 patients [18%]), complete retinal pigment epithelium disruption and/or loss of the outer nuclear layer. Stage 1 patients showed isolated hyperreflectivity of the external limiting membrane in the fovea, and the external limiting membrane was hyperreflective above each optically empty space. On near infrared reflectance imaging, the fovea was normal, hyporeflective, or showed both hyporeflective and hyperreflective features. All patients demonstrated autofluorescence abnormalities in the fovea and/or parafovea: 9 participants (53%) had reduced or absent autofluorescence surrounded by increased autofluorescence, 4 individuals (24%) showed only reduced or absent autofluorescence, 3 patients (18%) displayed only increased autofluorescence, and 1 individual (6%) exhibited decreased macular pigment contrast. Inner segment ellipsoid line loss generally correlated with the area of reduced autofluorescence, but hyperautofluorescence extended into this region in 2 patients (12%). Bilateral coloboma-like atrophic macular lesions were observed in 1 patient (6%). Five novel mutations were identified (4 in the CNGA3 gene and 1 in the CNGB3 gene). CONCLUSIONS AND RELEVANCE Achromatopsia often demonstrates hyperautofluorescence suggestive of progressive retinal degeneration. The proposed staging system facilitates classification of the disease into different phases of progression and may have therapeutic implications.
-
oligocone trichromacy clinical and molecular genetic investigations
Investigative Ophthalmology & Visual Science, 2010Co-Authors: Mette K Andersen, Susanne Kohl, Bernd Wissinger, Nynne Christoffersen, Birgit Sander, Carsten Edmund, Michael Larsen, Tanja Grau, Thomas RosenbergAbstract:Purpose To describe the phenotype and genotype of patients with a diagnosis of oligocone trichromacy (OT). Methods Six unrelated patients had a detailed ophthalmic examination including color vision testing, a Goldmann visual field test, fundus photography, and full-field electroretinography (ffERG). Five patients also underwent multifocal (mf)ERG, autofluorescence recording, and optical coherence tomography (OCT). Genetic analysis included sequencing of all coding regions and flanking introns of CNGA3, CNGB3, GNAT2, KCNV2, and PDE6C. Results All patients had subnormal visual acuity, a history of congenital nystagmus, and subjectively normal or near-normal color vision; five patients reported photophobia. Clinical examinations revealed largely normal fundi, normal Goldmann visual field results with the IV/4e target, and normal color discrimination or mild color vision deficiency. Electrophysiological investigations showed either complete absence of recordable cone responses or severely reduced amplitudes. All retinal layers were identifiable by OCT, which also showed thinning of the peripheral retina. Genetic analysis revealed two causative CNGB3 mutations in one patient and single heterozygous mutations of unknown significance in CNGB3 and PDE6C in two other patients. Conclusions Oligocone trichromacy is a heterogeneous condition with respect to both phenotypic appearance and genetic background. The finding of mutations in genes known to be involved in complete and incomplete Achromatopsia supports the notion that some forms of OT is an extreme form of incomplete Achromatopsia with preferential loss of peripheral cones.
-
functional analysis of human cnga3 mutations associated with colour blindness suggests impaired surface expression of channel mutants a3r427c and a3r563c
European Journal of Neuroscience, 2008Co-Authors: Katja Koeppen, Susanne Kohl, Peggy Reuter, Britta Baumann, Thomas Ladewig, Bernd WissingerAbstract:Mutations in the CNGA3 gene have been associated with complete and incomplete forms of total colour blindness (Achromatopsia), a disorder characterized by reduced visual acuity, lack of colour discrimination, photophobia and nystagmus. CNGA3 encodes the A-subunit of the cone photoreceptor cyclic nucleotide-gated (CNG) channel, an essential component of the phototransduction cascade. Here we report the identification of three new CNGA3 mutations in patients with Achromatopsia. To assess the pathogenicity of these newly identified and four previously reported mutations, mutant CNGA3 channels were heterologously expressed in a human embryonic kidney cell line (HEK293 cells) and functionally analysed using calcium imaging. Channels with the mutations R427C and R563C showed a response in imaging experiments and were subsequently characterized in-depth with the patch-clamp technique. The mutant channels were analysed as homooligomers and also as heterooligomers with the wild-type B-subunit present in native channels. Overall, cyclic guanosine monophosphate (cGMP) maximum currents of mutant channels were profoundly reduced in homo- and heteromers. Treatment with the chemical chaperone glycerol effectively increased macroscopic currents, presumably by enhancing surface expression of mutant channels as confirmed by immunocytochemistry. These results suggest decreased channel density in the cell membrane due to impaired folding or trafficking of the channel protein as the main pathogenic effect of the mutations R427C and R563C. Moreover, A3(R427C) homomers showed distinctly increased cGMP and cyclic adenosine monophosphate (cAMP) sensitivities as well as cAMP fractional currents that were raised to over 90% of cGMP maximum currents. Co-expression of A3(R427C) with the B3 subunit compensated for most of these aberrant properties, apart from the reduced cGMP maximum currents.
-
mutations in the cone photoreceptor g protein α subunit gene gnat2 in patients with Achromatopsia
American Journal of Human Genetics, 2002Co-Authors: Susanne Kohl, Britta Baumann, Thomas Rosenberg, Ulrich Kellner, Birgit Lorenz, Maria Vadala, Samuel G Jacobson, Bernd WissingerAbstract:Achromatopsia is an autosomal recessively inherited visual disorder that is present from birth and that features the absence of color discrimination. We here report the identification of five independent families with Achromatopsia that segregate protein-truncation mutations in the GNAT2 gene, located on chromosome 1p13. GNAT2 encodes the cone photoreceptor–specific α-subunit of transducin, a G-protein of the phototransduction cascade, which couples to the visual pigment(s). Our results demonstrate that GNAT2 is the third gene implicated in Achromatopsia.
Joseph Carroll - One of the best experts on this subject based on the ideXlab platform.
-
rac cnn multimodal deep learning based automatic detection and classification of rod and cone photoreceptors in adaptive optics scanning light ophthalmoscope images
Biomedical Optics Express, 2019Co-Authors: David Cunefare, Emily J Patterson, Joseph Carroll, Alfredo Dubra, Alison L Huckenpahler, Sina FarsiuAbstract:Quantification of the human rod and cone photoreceptor mosaic in adaptive optics scanning light ophthalmoscope (AOSLO) images is useful for the study of various retinal pathologies. Subjective and time-consuming manual grading has remained the gold standard for evaluating these images, with no well validated automatic methods for detecting individual rods having been developed. We present a novel deep learning based automatic method, called the rod and cone CNN (RAC-CNN), for detecting and classifying rods and cones in multimodal AOSLO images. We test our method on images from healthy subjects as well as subjects with Achromatopsia over a range of retinal eccentricities. We show that our method is on par with human grading for detecting rods and cones.
-
deep learning based detection of cone photoreceptors with multimodal adaptive optics scanning light ophthalmoscope images of Achromatopsia
Biomedical Optics Express, 2018Co-Authors: David Cunefare, Emily J Patterson, Christopher S Langlo, Joseph Carroll, Alfredo Dubra, Sarah Blau, Sina FarsiuAbstract:Fast and reliable quantification of cone photoreceptors is a bottleneck in the clinical utilization of adaptive optics scanning light ophthalmoscope (AOSLO) systems for the study, diagnosis, and prognosis of retinal diseases. To-date, manual grading has been the sole reliable source of AOSLO quantification, as no automatic method has been reliably utilized for cone detection in real-world low-quality images of diseased retina. We present a novel deep learning based approach that combines information from both the confocal and non-confocal split detector AOSLO modalities to detect cones in subjects with Achromatopsia. Our dual-mode deep learning based approach outperforms the state-of-the-art automated techniques and is on a par with human grading.
-
in vivo imaging of human cone photoreceptor inner segments
Investigative Ophthalmology & Visual Science, 2014Co-Authors: Drew Scoles, Christine A Curcio, Gerald A Fishman, Christopher S Langlo, Yusufu N Sulai, Joseph Carroll, Alfredo DubraAbstract:Purpose An often overlooked prerequisite to cone photoreceptor gene therapy development is residual photoreceptor structure that can be rescued. While advances in adaptive optics (AO) retinal imaging have recently enabled direct visualization of individual cone and rod photoreceptors in the living human retina, these techniques largely detect strongly directionally-backscattered (waveguided) light from normal intact photoreceptors. This represents a major limitation in using existing AO imaging to quantify structure of remnant cones in degenerating retina. Methods Photoreceptor inner segment structure was assessed with a novel AO scanning light ophthalmoscopy (AOSLO) differential phase technique, that we termed nonconfocal split-detector, in two healthy subjects and four subjects with Achromatopsia. Ex vivo preparations of five healthy donor eyes were analyzed for comparison of inner segment diameter to that measured in vivo with split-detector AOSLO. Results Nonconfocal split-detector AOSLO reveals the photoreceptor inner segment with or without the presence of a waveguiding outer segment. The diameter of inner segments measured in vivo is in good agreement with histology. A substantial number of foveal and parafoveal cone photoreceptors with apparently intact inner segments were identified in patients with the inherited disease Achromatopsia. Conclusions The application of nonconfocal split-detector to emerging human gene therapy trials will improve the potential of therapeutic success, by identifying patients with sufficient retained photoreceptor structure to benefit the most from intervention. Additionally, split-detector imaging may be useful for studies of other retinal degenerations such as AMD, retinitis pigmentosa, and choroideremia where the outer segment is lost before the remainder of the photoreceptor cell.
-
photoreceptor structure and function in patients with congenital Achromatopsia
Investigative Ophthalmology & Visual Science, 2011Co-Authors: Mohamed A. Genead, Gerald A Fishman, Adam M Dubis, Alfredo Dubra, Jungtae Rha, Daniela Maria Oliveira Bonci, Edwin M Stone, Maureen Neitz, Joseph CarrollAbstract:Congenital Achromatopsia is a genetically heterogeneous, predominantly autosomal recessive, retinal disorder with a prevalence of approximately 1 in 30,000 in the general population.1 It is characterized by a lack of color discrimination, poor visual acuity, photophobia, pendular nystagmus, and abnormal photopic electroretinographic (ERG) recordings with preservation of the rod-mediated ERG. A prior report by Khan and colleagues2 showed that the rod ERG function can be modestly subnormal. The disease has been categorized into complete and incomplete Achromatopsia subtypes. The incomplete (atypical) form is defined as dyschromatopsia, in which the symptoms are similar to those of the complete Achromatopsia (typical) form but with less visual dysfunction.3 Patients with the complete form have nondetectable cone function on ERG testing, whereas those with the incomplete form retain some residual cone function on ERG, and often more preserved color vision and a higher level of visual acuity (up to 0.20).3–5 Funduscopy is usually normal in both forms, although not infrequently macular pigmentary mottling and even occasionally atrophic changes have been described.6 The known causes of congenital Achromatopsia are all due to malfunction of the retinal phototransduction pathway. Specifically, recessive forms of Achromatopsia result from the inability of cone photoreceptors to properly respond to a light stimulus by hyperpolarizing. To date, mutations in four genes have been identified to cause Achromatopsia in human patients, including the α- and β-subunits of the cone cyclic nucleotide-gated ion channels, CNGA3 (ACHM2, OMIM600053) and CNGB3 (ACHM3, OMIM605080), which are located in the plasma membrane of the cone outer segments, the α-subunit of the cone photoreceptor transducin, GNAT2 (ACHM4, OMIM139340), and the catalytic α-subunit of the cone cyclic nucleotide phosphodiesterase, PDE6C (OMIM600827). The vast majority of human cases of Achromatopsia are caused by mutations in either CNGA3 or CNGB3.7–11 Prior recent reports of animal studies showed that CNGB3, CNGA3, or GNAT2 knockout mice and naturally occurring dog models of Achromatopsia responded well to adenoassociated virus (AAV) gene therapy. In animal models of human Achromatopsia, cone ERG amplitudes recovered to nearly normal levels.12–14 These results from proof-of-principle experiments in animals with cone-directed gene therapy offer promise for eventual translation to human patients. Identifying and then targeting retinal locations with retained photoreceptors will be a prerequisite for successful gene therapy in Achromatopsia patients. Previous observations regarding photoreceptor structure in Achromatopsia have been limited primarily to histologic reports. In a previous report by Galezowski,15 the retinal cones were described as entirely absent. Larsen16 reported malformed foveal cones with normal cones in the peripheral retina, whereas Harrison et al.17 found misshaped and reduced numbers of retinal cones. In another report by Falls et al.,18 normal numbers of odd-shaped foveal cones and isolated numbers of cones in the peripheral retina were described. Glickstein and Heath19 found no evidence of foveal cones and reduced numbers of peripheral cones. Although genetic testing was not available at the time of these studies, they nevertheless highlight the fact that the picture of photoreceptor structure in Achromatopsia is likely to be complex. Some clarity on this issue has begun to come from the use of noninvasive imaging techniques to assess photoreceptor structure in patients with Achromatopsia. Optical coherence tomography (OCT), which provides excellent axial resolution, has been used to show a highly variable phenotype at the level of the photoreceptor inner segment (IS) and outer segment (OS),4,6,20,21 although the general interpretation has been that there is an absence or reduction of healthy cone structure. Adaptive optics (AO) provides high lateral resolution,22–24 and was used in a single case to examine photoreceptor structure on the single-cell level.25 The authors visualized a normal rod photoreceptor mosaic, but did not report any evidence of cone structure. These findings only confirm the complexity of the photoreceptor phenotype in Achromatopsia, thus warranting further investigation. Here we used noninvasive high-resolution imaging tools (spectral domain [SD]- OCT and AO scanning laser ophthalmoscopy [SLO]) together with functional measures of vision (ERG, microperimetry [MP], and color vision) to assess photoreceptor structure and function in patients with congenital Achromatopsia. We sought to correlate these findings with genetic information from the same subjects. Not only is this approach expected to provide a better understanding of the disease, but also should prove useful in identifying which patients may be most likely to benefit from participating in future gene-targeted treatment trials to rescue or restore cone photoreceptors in this group of patients. Moreover, the structural and functional assays used here would be useful for evaluating the therapeutic efficacy in patients who in fact go on to receive intervention.
Martin Biel - One of the best experts on this subject based on the ideXlab platform.
-
endoplasmic reticulum er ca2 channel activity contributes to er stress and cone death in cyclic nucleotide gated channel deficiency
Journal of Biological Chemistry, 2017Co-Authors: Michael R Butler, Stylianos Michalakis, Fan Yang, Joshua Belcher, Katsuhiko Mikoshiba, Martin Biel, Anthony Iuso, David Križaj, Xiqin DingAbstract:Endoplasmic reticulum (ER) stress and mislocalization of improperly folded proteins have been shown to contribute to photoreceptor death in models of inherited retinal degenerative diseases. In particular, mice with cone cyclic nucleotide-gated (CNG) channel deficiency, a model for Achromatopsia, display both early-onset ER stress and opsin mistrafficking. By 2 weeks of age, these mice show elevated signaling from all three arms of the ER-stress pathway, and by 1 month, cone opsin is improperly distributed away from its normal outer segment location to other retinal layers. This work investigated the role of Ca2+ release channels in ER stress, protein mislocalization, and cone death in a mouse model of CNG-channel deficiency. We examined whether preservation of luminal Ca2+ stores through pharmacological and genetic suppression of ER Ca2+ efflux protects cones by attenuating ER stress. We demonstrated that the inhibition of ER Ca2+ -efflux channels reduced all three arms of ERstress signaling while improving opsin trafficking to cone outer segments and decreasing cone death by 20-35%. Cone-specific gene deletion of the inositol-1,4,5-trisphosphate receptor type I (IP3R1) also significantly increased cone density in the CNGchannel- deficient mice, suggesting that IP3R1 signaling contributes to Ca2+ homeostasis and cone survival. Consistent with the important contribution of organellar Ca2+ signaling in this Achromatopsia mouse model, significant differences in dynamic intraorganellar Ca2+ levels were detected in CNG-channel-deficient cones. These results thus identify a novel molecular link between Ca2+ homeostasis and cone degeneration, thereby revealing novel therapeutic targets to preserve cones in inherited retinal degenerative diseases.
-
Loss of HCN1 enhances disease progression in mouse models of CNG channel-linked retinitis pigmentosa and Achromatopsia
Human molecular genetics, 2016Co-Authors: Christian Schön, Sabrina Asteriti, Susanne Koch, Vithiyanjali Sothilingam, Marina Garcia Garrido, Naoyuki Tanimoto, Jochen Herms, Mathias W. Seeliger, Lorenzo Cangiano, Martin BielAbstract:Most inherited blinding diseases are characterized by compromised retinal function and progressive degeneration of photoreceptors. However, the factors that affect the life span of photoreceptors in such degenerative retinal diseases are rather poorly understood. Here, we explore the role of hyperpolarization-activated cyclic nucleotide-gated channel 1 (HCN1) in this context. HCN1 is known to adjust retinal function under mesopic conditions, and although it is expressed at high levels in rod and cone photoreceptor inner segments, no association with any retinal disorder has yet been found. We investigated the effects of an additional genetic deletion of HCN1 on the function and survival of photoreceptors in a mouse model of CNGB1-linked retinitis pigmentosa (RP). We found that the absence of HCN1 in Cngb1 knockout (KO) mice exacerbated photoreceptor degeneration. The deleterious effect was reduced by expression of HCN1 using a viral vector. Moreover, pharmacological inhibition of HCN1 also enhanced rod degeneration in Cngb1 KO mice. Patch-clamp recordings revealed that the membrane potentials of Cngb1 KO and Cngb1/Hcn1 double-KO rods were both significantly depolarized. We also found evidence for altered calcium homeostasis and increased activation of the protease calpain in Cngb1/Hcn1 double-KO mice. Finally, the deletion of HCN1 also exacerbated degeneration of cone photoreceptors in a mouse model of CNGA3-linked Achromatopsia. Our results identify HCN1 as a major modifier of photoreceptor degeneration and suggest that pharmacological inhibition of HCN channels may enhance disease progression in RP and Achromatopsia patients.
-
endoplasmic reticulum stress associated cone photoreceptor degeneration in cyclic nucleotide gated channel deficiency
Journal of Biological Chemistry, 2012Co-Authors: Arjun Thapa, Stylianos Michalakis, Martin Biel, Lynsie Morris, Xiqin DingAbstract:Cyclic nucleotide-gated (CNG) channels play a pivotal role in phototransduction. Mutations in the cone CNG channel subunits CNGA3 and CNGB3 account for >70% of all known cases of Achromatopsia. Cones degenerate in Achromatopsia patients and in CNGA3−/− and CNGB3−/− mice. This work investigates the molecular basis of cone degeneration in CNG channel deficiency. As cones comprise only 2–3% of the total photoreceptor population in the wild-type mouse retina, we generated mouse lines with CNG channel deficiency on a cone-dominant background, i.e. CNGA3−/−/Nrl−/− and CNGB3−/−/Nrl−/− mice. The retinal phenotype and potential cell death pathways were examined by functional, biochemical, and immunohistochemical approaches. CNGA3−/−/Nrl−/− and CNGB3−/−/Nrl−/− mice showed impaired cone function, opsin mislocalization, and cone degeneration similar to that in the single knock-out mice. The endoplasmic reticulum stress marker proteins, including Grp78/Bip, phospho-eIF2α, phospho-IP3R, and CCAAT/enhancer-binding protein homologous protein, were elevated significantly in CNGA3−/−/Nrl−/− and CNGB3−/−/Nrl−/− retinas, compared with the age-matched (postnatal 30 days) Nrl−/− controls. Along with these, up-regulation of the cysteine protease calpains and cleavage of caspase-12 and caspase-7 were found in the channel-deficient retinas, suggesting an endoplasmic reticulum stress-associated apoptosis. In addition, we observed a nuclear translocation of apoptosis-inducing factor (AIF) and endonuclease G in CNGA3−/−/Nrl−/− and CNGB3−/−/Nrl−/− retinas, implying a mitochondrial insult in the endoplasmic reticulum stress-activated cell death process. Taken together, our findings suggest a crucial role of endoplasmic reticulum stress in cone degeneration associated with CNG channel deficiency.
