Effect of Sugars on Photoreceptor Outer Segment Assembly

To determine the specific location of the initial lesion in acute retinal pigment epitheliitis. Four patients diagnosed with acute retinal pigment epitheliitis were studied. Fundus photographs, fluorescein angiography and indocyanine green angiography, and spectral-domain optical coherence tomography findings were reviewed. Four healthy young patients presented with acute onset of unilateral decreased vision. Ophthalmoscopy showed macular pigment mottling with surrounding yellow hypopigmented areas at the level of the retinal pigment epithelium (RPE). Fluorescein angiography revealed transmission hyperfluorescence. Early-phase and midphase indocyanine green angiography images showed a patchy macular hyperfluorescence. At late phase of indocyanine green angiography, a hyperfluorescent halo with a cockadelike appearance of the macular area was observed. Spectral-domain optical coherence tomography showed a disruption of the photoreceptors' inner segment and outer segment interface associated with a wider disruption of the RPE inner band. These disrupted lines were replaced by a dome-shaped highly reflective lesion involving the RPE inner layer, the photoreceptors' inner segment and outer segment layers, and, in two cases, the outer nuclear layer. With time, indocyanine green angiography showed resolution of the observed lesions. Spectral-domain optical coherence tomography showed restored and continuous inner segment and outer segment layers and RPE inner band. Spectral-domain optical coherence tomography findings suggest that the initial lesion in acute retinal pigment epitheliitis is located at the junction between the photoreceptor outer segments and the apical side of the RPE cells. Indocyanine green angiography and spectral-domain optical coherence tomography show that the RPE appears to be more widely involved than the neurosensory retina.

Macular telangiectasia Type 2 (MacTel 2) is a bilateral disease characterized by neurodegenerative and vascular changes affecting the fovea.1 The occurrence of subretinal neovascularization in MacTel 2 is rather rare but constitutes a vision-threatening complication.2 We describe longitudinal multimodal imaging features of a novel variant of bacillary layer detachment (BLD, outer retinal split at the level of the photoreceptor inner segment myoid)3 and termed “hemorrhagic BLD” in a case of subretinal neovascularization associated with MacTel 2. This report followed the tenets of the Declaration of Helsinki. A 55-year-old woman presented with proliferative MacTel 2. Fundus photography showed active yellowish neovascular membrane with subretinal hemorrhages (Figure 1A). Optical coherence tomography (OCT) angiography segmented at the level of the outer retina confirmed subretinal neovascularization (Figure 1B). Optical coherence tomography disclosed a parafoveal outer retinal cyst consistent with BLD and adjacent subretinal fluid (Figure 1, C–E). The higher optical intensity in the BLD compared with that of subretinal fluid and its colocalization with subretinal hemorrhage on fundus photography suggested heme accumulation in the BLD. Eye-tracked follow-up OCT performed one month after a single intravitreal injection of ranibizumab (0.5 mg/0.05 mL) demonstrated significant regression of the BLD (Figure 1, F and G). Persistent focal attenuations of the ellipsoid and interdigitation zones were noted.Fig. 1.: Multimodal imaging features of hemorrhagic bacillary layer detachment. A. Color fundus photography shows typical features of macular telangiectasia Type 2 including retinal graying, crystalline deposits, ectatic capillaries, and hyperpigmentation foci. There is an active yellowish neovascular membrane (white arrowhead) with subretinal hemorrhages. B. Optical coherence tomography angiography segmented from the outer retina to the choriocapillaris shows a subretinal neovascular membrane (white arrowhead). The inset shows segmentation lines of the en face optical coherence tomography angiography image with red flow signal overlay. C–E. The (C) is a magnified view of the BLD on OCT as illustrated in (E). The intraretinal split occurs at the level of the hyporeflective myoid zone (green arrowheads). The ellipsoid zone (orange arrowhead) of the attached retina is continuous with a faint hyperreflective line (orange arrowhead) that likely represents split photoreceptor inner segments and outer segments remaining adherent to the retinal pigment epithelium/Bruch membrane complex (yellow arrowhead). The external limiting membrane (blue arrowheads) is visible over the top of the BLD (withe arrowhead). Note the dense hyperreflective material within the BLD that corresponds to heme accumulation and may interfere with accurate delineation of the outer retinal layers. The (D) is the near infrared reflectance image with the green line indicating the position of the OCT scan. Vertical OCT scan (E) shows parafoveal outer retinal cyst consistent with BLD (white arrowhead) and adjacent subretinal fluid (asterisk). F and G. Eye-tracked follow-up near infrared reflectance image (F) and OCT scan (G) performed 1 month after an intravitreal injection of ranibizumab shows dramatic resolution of the BLD. The external limiting membrane is intact. Note the persistent focal attenuations of the ellipsoid and interdigitation zones (between red arrowheads).To the best of our knowledge, hemorrhagic BLD has not been associated with proliferative MacTel 2, although similar findings coined “atypical outer retinal fluid accumulation” have been reported in neovascular age-related macular degeneration.4 Intense leakage of fluid from the subretinal neovascularization and modulation of the adherence between photoreceptor outer segments and retinal pigment epithelium by the subretinal hemorrhage may have induced BLD development.5 In fact, fibrin interdigitation between photoreceptor outer segments has been documented after experimental subretinal hemorrhages and may explain the presumed photoreceptor fracture under hydrostatic pressure effect.

In humans, inositol polyphosphate-5-phosphatase E (INPP5E) mutations cause retinal degeneration as part of Joubert and MORM syndromes and can also cause non-syndromic blindness. In mice, mutations cause a spectrum of brain, kidney and other anomalies and prevent the formation of photoreceptor outer segments. To further explore the function of Inpp5e in photoreceptors, we generated conditional and inducible knockouts of mouse Inpp5e where the gene was deleted either during outer segment formation or after outer segments were fully formed. In both cases, the loss of Inpp5e led to severe defects in photoreceptor outer segment morphology and ultimately photoreceptor cell loss. The primary morphological defect consisted of outer segment shortening and reduction in the number of newly forming discs at the outer segment base. This was accompanied by structural abnormalities of the Golgi, mislocalized rhodopsin and an accumulation of extracellular vesicles. In addition, knockout cells showed disruption of the actin network. Together, these data demonstrate that Inpp5e plays a crucial role in maintaining the outer segment and the normal process of outer segment renewal depends on the activity of this enzyme.

Protein kinase C (PKC) has been implicated in regulating several proteins involved in phototransduction. This contribution characterizes the biochemical and immunological properties of PKC isozyme(s) in the photoreceptor outer segment. Activity measurements revealed that at least 85% of the PKC in this specialized compartment belongs to the subfamily of Ca2+-regulated (conventional) PKCs. Of the known Ca2+-dependent PKCs, only PKC alpha was immunodetected by western blot analysis of rod outer segment proteins. However, the ratio of immunoreactivity to enzyme activity for rod outer segment PKC was no more than 40% of that for brain PKC, using antibodies against conventional PKCs. Therefore, at least half the Ca2+/lipid-stimulated activity in rod outer segment preparations cannot be accounted for by the known isozymes, suggesting the presence of a previously uncharacterized isozyme. Despite extensive tests using a variety of antibodies against different domains of PKC alpha, PKC alpha could not be detected in rod outer segments by immunofluorescence of retinal sections. In summary, our data reveal that most of the PKC in photoreceptor outer segments is of the conventional type and that most, if not all, of this conventional PKC activity comes from a novel isozyme(s).

The aim of this study was to define landmarks to better characterize foveal microstructure in normal subjects and in preterms with or without signs of immaturity, and to report on thickness changes of outer foveal layers following analysis of optical coherence tomography (OCT) B-scan images. Selected eyes from eight young adults with a history of prematurity (24-33 weeks of gestation) and five controls were imaged using conventional and directional OCT. Retinal layer thickness analysis was performed at selected temporal eccentricities defined by the individual distance between two landmarks for each case, the foveal center and the foveal rim. The use of a foveal center and foveal rim landmark transformation enabled comparisons of interindividual B-scans at corresponding landmark positions in both controls and preterms. We found a 20% shorter foveal center to foveal rim distance in preterms with an immature fovea than in controls. Reflectometric and manual segmentation measurements showed increased thickness of inner retinal layers and photoreceptor cell body and outer plexiform layers centrally, but no observable change of photoreceptor inner and outer segment thickness. Our landmark-based analysis of OCT images using reflectometry and manual segmentation provides complementary findings in comparisons of normal and immature foveal structures. We show a central thickness increase in the outer nuclear layer, outer plexiform layer, and postreceptor layers in preterms with signs of arrested foveal development. We found no indication of abnormal photoreceptor inner or outer segment development in preterms.

Reduced birth weight is associated with an increased risk of visual impairments. This study was undertaken to determine whether prenatal exposure to a chronic compromise sufficient to cause fetal growth restriction (FGR) results in long-term alterations to the retina and optic nerve. FGR was induced by umbilicoplacental embolization (UPE) in two cohorts of pregnant ewes from (1) 120 days of gestation (dg) until 140 dg and (2) 120 dg until term ( approximately 147 dg). Control fetuses were not subjected to UPE. The structure and neurochemistry of the retina and number and structure of ganglion cell axons were assessed in near-term (140 dg) and adult animals (2.3 years). In near-term FGR fetuses compared with control fetuses there were significant reductions (P < 0.05) in the outer plexiform layer (OPL), the photoreceptor inner and outer segment layers, the inner nuclear layer (INL) in the central retina and the outer nuclear layer (ONL) in the peripheral retina, and the diameter of ganglion cell axons in the optic nerve, with a proportional reduction in the thickness of myelin sheaths. In FGR animals compared with the control at 2.3 years, there were significant reductions (P < 0.05) in the total thickness of the retina, the thickness of the photoreceptor outer segment layer and the INL and the number of tyrosine hydroxylase-immunoreactive (TH-IR) dopaminergic amacrine cells. Axonal diameter and myelin sheath thickness in the optic nerve were not different (P > 0.05) between groups. Chronic placental insufficiency in late gestation results in long-lasting effects on specific retinal components, including photoreceptor outer segments and TH-IR amacrine cells. Other alterations observed at term, including reductions in growth and myelination of optic nerve axons, do not persist, suggesting delayed rather than permanently compromised development. Alterations persisting into adulthood could affect visual function.

Актуальность. На сегодняшний день остается нерешенным вопрос подбора параметров лазерного излучения при проведении субпороговой лазерной коагуляции сетчатки без видимых офтальмоскопических изменений глазного дна. Цель. Изучить ультраструктурные изменения хориоретинального комплекса после воздействия лазерного излучения с длиной волны 577 нм в различных режимах. Материал и методы. Эксперимент проводился на 6 кроликах (12 глаз). Использовался лазер с длиной волны 577 нм. Лазерное воздействие выполнялось в различных режимах. Проводилось электронно-микроскопическое исследование глаз кроликов. Результаты. Лазерная коагуляция в классическом режиме повреждает клетки пигментного эпителия сетчатки, все отделы фоторецепторов и хориокапилляры, селективная лазерная коагуляция – клетки пигментного эпителия сетчатки, наружные и внутренние сегменты фоторецепторных клеток, микроимпульсная лазерная коагуляция с 50% мощности от порогового воздействия повреждает преимущественно апикальные отделы клеток пигментного эпителия сетчатки и наружные сегменты фоторецепторов. Вывод. Лазерное воздействие на структуры сетчатки излучением с длиной волны 577 нм в микроимпульсном режиме является наиболее щадящим для фоторецепторов и хориокапилляров в сравнении с классической и селективной лазерной коагуляцией и может быть использовано в клинике как наименее инвазивное лазерное воздействие на хориоретинальный комплекс.

PurposeThe determination of the molecular mechanism underlying retinal pathogenesis and visual dysfunction during innate inflammation, and the treatment effect of rapamycin thereon.MethodsThe endotoxin-induced uveitis and retinitis mouse model was established by injecting lipopolysaccharide. The mice were subsequently treated with rapamycin, a mammalian target of rapamycin (mTOR) inhibitor. The rhodopsin mRNA and protein expression level in the retina and the photoreceptor outer segment (OS) length in immunohistochemical stainings were measured, and visual function was recorded by electroretinography. Inflammatory cytokines, their related molecules, mTOR, and LC3 levels were measured by real-time PCR and/or immunoblotting. Leukocyte adhesion during inflammation was analyzed using concanavalin A lectin.ResultsThe post-transcriptional reduction in the visual pigment of rod photoreceptor cells, rhodopsin, OS shortening, and rod photoreceptor cell dysfunction during inflammation were suppressed by rapamycin. Activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and induction of inflammatory cytokines, such as interleukin-6 (IL-6) and monocyte chemoattractant protein-1 (MCP-1), and the activation of the downstream signaling protein, signal transducer and activator of transcription 3 (STAT3), which reduces rhodopsin in the retina during inflammation, were attenuated by rapamycin. Increased leukocyte adhesion was also attenuated by rapamycin. Interestingly, although mTOR activation was observed after NF-κB activation, mTOR inhibition suppressed NF-κB activation at the early phase, indicating that the basal level of activated mTOR was sufficient to activate NF-κB in the retina. In addition, the inhibition of NF-κB suppressed mTOR activation, suggesting a positive feedback loop of mTOR and NF-κB during inflammation. The ratio of LC3II to LC3I, which reflects autophagy induction, was not changed by inflammation but was increased by rapamycin.ConclusionsOur results propose the potential use of rapamycin as a neuroprotective therapy to suppress local activated mTOR levels, related inflammatory molecules, and the subsequent visual dysfunction during retinal inflammation.

The photoreceptor outer segment (OS) is a unique modification of the primary cilium, specialized for light perception. Being homologous organelles, the primary cilium and the OS share common building blocks and molecular machinery to construct and maintain them. The OS, however, has several unique structural features that are not seen in primary cilia. Although these unique features of the OS have been well documented, their implications in protein localization have been under-appreciated. In this review, we compare the structural properties of the primary cilium and the OS, and propose a hypothesis that the OS can act as a sink for membrane proteins. We further discuss the implications of this hypothesis in polarized protein localization in photoreceptors and mechanisms of photoreceptor degeneration in retinal ciliopathies.

It has been long speculated that specific signals are transmitted from photoreceptors to the retinal pigment epithelium (RPE). However, such signals have not been identified. In this study, we examined the retinal expression and localization of acetylcholine-related molecules as putative candidates for these signals. Previous reports revealed that α7 nicotinic acetylcholine receptors (nAChRs) are present in the microvilli of RPE cells that envelope the tips of photoreceptor outer segments (OS). Secreted mammalian leukocyte antigen 6/urokinase-type plasminogen activator receptor-related protein-1 (SLURP-1) is a positive allosteric modulator of the α7 nAChR. Therefore, we first focused on the expression of SLURP-1. SLURP-1 mRNA was expressed in the outer nuclear layer, which is comprised of photoreceptor cell bodies. SLURP-1 immunoreactivity co-localized with rhodopsin and S-opsin in photoreceptor OS, while choline acetyltransferase (ChAT) and high affinity choline transporter (CHT-1) were also expressed in photoreceptor OS. Immunoelectron microscopy identified that the majority of SLURP-1 was localized to the plasma membranes of photoreceptor OS. These results provide evidence that SLURP-1 is synthesized in photoreceptor cell bodies and transported to photoreceptor OS, where SLURP-1 may also be secreted. Our findings suggest that photoreceptor OS communicate via neurotransmitters such as ACh and SLURP-1, while RPE cells might receive these signals through α7 nAChRs in their microvilli.

Vitamin A immunoreactive sites were studied in the retina and pineal organ of the frog, Rana esculenta, by the peroxidase antiperoxidase, avidin-biotinperoxidase and immunogold methods. In dark-adapted material, strong immunoreaction was found in the outer and inner segments of the photoreceptor cells of both retina and pineal organ, as well as in the pigment epithelium, retinal Müller cells and pineal ependymal cells. In light-adapted retina, cones and green (blue-sensitive) rods were immunopositive. At the electron microscopic level, immunogold particles were found on the membranes of the photoreceptor outer segments as well as on the membranes of the endoplasmic reticulum and mitochondria. Individual retinal photorecptor cells exhibited strong immunoreaction in the distal portion of the inner segment, the ciliary connecting piece and the electron-dense material covering the outer segment. In the pigment epithelium, the immunolabeling varied in intensity in the basal and apical cytoplasm and phagocytosed outer segments. The immunocytochemical results indicate that retinoids (retinal, retinol and possibly retinoic acid) are present not only in the photoreceptor cells of the retina but also in those of the pineal organ. The light-dependent differences in the immunoreactivity of vitamin A underlines its essential role in the visual cycle of the photopigments. Our results suggest that the pineal ependyma plays a role comparable to that of the Müller cells and pigment epithelium of the retina with regard to the transport and storage of vitamin A. The presence of a retinoid in nuclei, mitochondria and cytoplasmic membranes suggests an additional role of vitamin A in other metabolic processes.

Photoreceptor Outer Segment Disc Morphogenesis

Prominin 1 (PROM1) is a pentaspan transmembrane glycoprotein localized on the nascent photoreceptor discs. Mutations in PROM1 are linked to various retinal diseases. In this study, we assessed the role of PROM1 in photoreceptor biology and physiology using the PROM1 knockout murine model (rd19). Our study found that PROM1 is essential for vision and photoreceptor development. We found an early reduction in photoreceptor response beginning at post-natal day 12 (P12) before eye opening in the absence of PROM1 with no apparent loss in photoreceptor cells. However, at this stage, we observed an increased glial cell activation, indicative of cell damage. Contrary to our expectations, dark rearing did not mitigate photoreceptor degeneration or vision loss in PROM1 knockout mice. In addition to physiological defects seen in PROM1 knockout mice, ultrastructural analysis revealed malformed outer segments characterized by whorl-like continuous membranes instead of stacked disks. In parallel to the reduced rod response at P12, proteomics revealed a significant reduction in the levels of protocadherin, a known interactor of PROM1, and rod photoreceptor outer segment proteins, including rhodopsin. Overall, our results underscore the indispensable role of PROM1 in photoreceptor development and maintenance of healthy vision.

The photoreceptor outer segment: Development and renewal.

Effects of antioxidant nutrient deficiency on the retina and retinal pigment epithelium of albino rats: a light and electron microscopic study