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The retinal pigmentation pathway in human albinism: Not so black and white. Prog Retin Eye Res 2022; 91:101091. [PMID: 35729001 DOI: 10.1016/j.preteyeres.2022.101091] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Revised: 05/24/2022] [Accepted: 05/26/2022] [Indexed: 12/16/2022]
Abstract
Albinism is a pigment disorder affecting eye, skin and/or hair. Patients usually have decreased melanin in affected tissues and suffer from severe visual abnormalities, including foveal hypoplasia and chiasmal misrouting. Combining our data with those of the literature, we propose a single functional genetic retinal signalling pathway that includes all 22 currently known human albinism disease genes. We hypothesise that defects affecting the genesis or function of different intra-cellular organelles, including melanosomes, cause syndromic forms of albinism (Hermansky-Pudlak (HPS) and Chediak-Higashi syndrome (CHS)). We put forward that specific melanosome impairments cause different forms of oculocutaneous albinism (OCA1-8). Further, we incorporate GPR143 that has been implicated in ocular albinism (OA1), characterised by a phenotype limited to the eye. Finally, we include the SLC38A8-associated disorder FHONDA that causes an even more restricted "albinism-related" ocular phenotype with foveal hypoplasia and chiasmal misrouting but without pigmentation defects. We propose the following retinal pigmentation pathway, with increasingly specific genetic and cellular defects causing an increasingly specific ocular phenotype: (HPS1-11/CHS: syndromic forms of albinism)-(OCA1-8: OCA)-(GPR143: OA1)-(SLC38A8: FHONDA). Beyond disease genes involvement, we also evaluate a range of (candidate) regulatory and signalling mechanisms affecting the activity of the pathway in retinal development, retinal pigmentation and albinism. We further suggest that the proposed pigmentation pathway is also involved in other retinal disorders, such as age-related macular degeneration. The hypotheses put forward in this report provide a framework for further systematic studies in albinism and melanin pigmentation disorders.
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Tingaud-Sequeira A, Mercier E, Michaud V, Pinson B, Gazova I, Gontier E, Decoeur F, McKie L, Jackson IJ, Arveiler B, Javerzat S. The Dct−/− Mouse Model to Unravel Retinogenesis Misregulation in Patients with Albinism. Genes (Basel) 2022; 13:genes13071164. [PMID: 35885947 PMCID: PMC9324463 DOI: 10.3390/genes13071164] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2022] [Revised: 06/21/2022] [Accepted: 06/24/2022] [Indexed: 11/16/2022] Open
Abstract
We have recently identified DCT encoding dopachrome tautomerase (DCT) as the eighth gene for oculocutaneous albinism (OCA). Patients with loss of function of DCT suffer from eye hypopigmentation and retinal dystrophy. Here we investigate the eye phenotype in Dct−/− mice. We show that their retinal pigmented epithelium (RPE) is severely hypopigmented from early stages, contrasting with the darker melanocytic tissues. Multimodal imaging reveals specific RPE cellular defects. Melanosomes are fewer with correct subcellular localization but disrupted melanization. RPE cell size is globally increased and heterogeneous. P-cadherin labeling of Dct−/− newborn RPE reveals a defect in adherens junctions similar to what has been described in tyrosinase-deficient Tyrc/c embryos. The first intermediate of melanin biosynthesis, dihydroxyphenylalanine (L-Dopa), which is thought to control retinogenesis, is detected in substantial yet significantly reduced amounts in Dct−/− postnatal mouse eyecups. L-Dopa synthesis in the RPE alone remains to be evaluated during the critical period of retinogenesis. The Dct−/− mouse should prove useful in understanding the molecular regulation of retinal development and aging of the hypopigmented eye. This may guide therapeutic strategies to prevent vision deficits in patients with albinism.
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Affiliation(s)
- Angèle Tingaud-Sequeira
- Rare Diseases Genetics and Metabolism, INSERM U1211, SBM Department, University of Bordeaux, F-33076 Bordeaux, France; (A.T.-S.); (E.M.); (V.M.); (B.A.)
| | - Elina Mercier
- Rare Diseases Genetics and Metabolism, INSERM U1211, SBM Department, University of Bordeaux, F-33076 Bordeaux, France; (A.T.-S.); (E.M.); (V.M.); (B.A.)
| | - Vincent Michaud
- Rare Diseases Genetics and Metabolism, INSERM U1211, SBM Department, University of Bordeaux, F-33076 Bordeaux, France; (A.T.-S.); (E.M.); (V.M.); (B.A.)
- Molecular Genetics Laboratory, Bordeaux University Hospital, F-33076 Bordeaux, France
| | - Benoît Pinson
- SAM, TBMcore, CNRS UAR 3427, INSERM US005, Université Bordeaux, F-33076 Bordeaux, France;
| | - Ivet Gazova
- MRC Human Genetics Unit, University of Edinburgh, Edinburgh EH4 2XU, UK; (I.G.); (L.M.); (I.J.J.)
| | - Etienne Gontier
- Bordeaux Imaging Center, CNRS, INSERM, BIC, UMS 3420, US 4, University Bordeaux, F-33076 Bordeaux, France; (E.G.); (F.D.)
| | - Fanny Decoeur
- Bordeaux Imaging Center, CNRS, INSERM, BIC, UMS 3420, US 4, University Bordeaux, F-33076 Bordeaux, France; (E.G.); (F.D.)
| | - Lisa McKie
- MRC Human Genetics Unit, University of Edinburgh, Edinburgh EH4 2XU, UK; (I.G.); (L.M.); (I.J.J.)
| | - Ian J. Jackson
- MRC Human Genetics Unit, University of Edinburgh, Edinburgh EH4 2XU, UK; (I.G.); (L.M.); (I.J.J.)
| | - Benoît Arveiler
- Rare Diseases Genetics and Metabolism, INSERM U1211, SBM Department, University of Bordeaux, F-33076 Bordeaux, France; (A.T.-S.); (E.M.); (V.M.); (B.A.)
- Molecular Genetics Laboratory, Bordeaux University Hospital, F-33076 Bordeaux, France
| | - Sophie Javerzat
- Rare Diseases Genetics and Metabolism, INSERM U1211, SBM Department, University of Bordeaux, F-33076 Bordeaux, France; (A.T.-S.); (E.M.); (V.M.); (B.A.)
- Correspondence:
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3
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Abstract
Binocular vision depends on retinal ganglion cell (RGC) axon projection either to the same side or to the opposite side of the brain. In this article, we review the molecular mechanisms for decussation of RGC axons, with a focus on axon guidance signaling at the optic chiasm and ipsi- and contralateral axon organization in the optic tract prior to and during targeting. The spatial and temporal features of RGC neurogenesis that give rise to ipsilateral and contralateral identity are described. The albino visual system is highlighted as an apt comparative model for understanding RGC decussation, as albinos have a reduced ipsilateral projection and altered RGC neurogenesis associated with perturbed melanogenesis in the retinal pigment epithelium. Understanding the steps for RGC specification into ipsi- and contralateral subtypes will facilitate differentiation of stem cells into RGCs with proper navigational abilities for effective axon regeneration and correct targeting of higher-order visual centers.
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Affiliation(s)
- Carol Mason
- Department of Pathology and Cell Biology, Columbia University, New York, NY 10027, USA; .,Department of Neuroscience, Columbia University, New York, NY 10027, USA.,Department of Ophthalmology, Columbia University, New York, NY 10027, USA.,Mortimer B. Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY 10027, USA;
| | - Nefeli Slavi
- Mortimer B. Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY 10027, USA;
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Mason C, Guillery R. Conversations with Ray Guillery on albinism: linking Siamese cat visual pathway connectivity to mouse retinal development. Eur J Neurosci 2019; 49:913-927. [PMID: 30801828 DOI: 10.1111/ejn.14396] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2018] [Revised: 01/23/2019] [Accepted: 02/12/2019] [Indexed: 02/06/2023]
Abstract
In albinism of all species, perturbed melanin biosynthesis in the eye leads to foveal hypoplasia, retinal ganglion cell misrouting, and, consequently, altered binocular vision. Here, written before he died, Ray Guillery chronicles his discovery of the aberrant circuitry from eye to brain in the Siamese cat. Ray's characterization of visual pathway anomalies in this temperature sensitive mutation of tyrosinase and thus melanin synthesis in domestic cats opened the exploration of albinism and simultaneously, a genetic approach to the organization of neural circuitry. I follow this account with a remembrance of Ray's influence on my work. Beginning with my postdoc research with Ray on the cat visual pathway, through my own work on the mechanisms of retinal axon guidance in the developing mouse, Ray and I had a continuous and rich dialogue about the albino visual pathway. I will present the questions Ray posed and clues we have to date on the still-elusive link between eye pigment and the proper balance of ipsilateral and contralateral retinal ganglion cell projections to the brain.
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Affiliation(s)
- Carol Mason
- Departments of Pathology and Cell Biology, Neuroscience, and Ophthalmology, Mortimer B. Zuckerman Mind Brain Behavior Institute, Columbia University, Jerome L. Greene Science Center, 3227 Broadway, Room L3-043, Quad 3C, New York, NY, 10027, USA
| | - Ray Guillery
- Departments of Pathology and Cell Biology, Neuroscience, and Ophthalmology, Mortimer B. Zuckerman Mind Brain Behavior Institute, Columbia University, Jerome L. Greene Science Center, 3227 Broadway, Room L3-043, Quad 3C, New York, NY, 10027, USA
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5
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Stofkova A, Kamimura D, Ohki T, Ota M, Arima Y, Murakami M. Photopic light-mediated down-regulation of local α 1A-adrenergic signaling protects blood-retina barrier in experimental autoimmune uveoretinitis. Sci Rep 2019; 9:2353. [PMID: 30787395 PMCID: PMC6382936 DOI: 10.1038/s41598-019-38895-y] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2018] [Accepted: 01/04/2019] [Indexed: 01/15/2023] Open
Abstract
We have reported the gateway reflex, which describes specific neural activations that regulate immune cell gateways at specific blood vessels in the central nervous system (CNS). Four types of gateway reflexes exist, all of which induce alterations in endothelial cells at specific vessels of the blood-brain barrier followed by inflammation in the CNS in the presence of CNS-autoreactive T cells. Here we report a new gateway reflex that suppresses the development of retinal inflammation by using an autoreactive T cell-mediated ocular inflammation model. Exposure to photopic light down-regulated the adrenoceptor pathway to attenuate ocular inflammation by suppressing breaching of the blood-retina barrier. Mechanistic analysis showed that exposure to photopic light down-regulates the expression of α1A-adrenoceptor (α1AAR) due to high levels of norepinephrine and epinephrine, subsequently suppressing inflammation. Surgical ablation of the superior cervical ganglion (SCG) did not negate the protective effect of photopic light, suggesting the involvement of retinal noradrenergic neurons rather than sympathetic neurons from the SCG. Blockade of α1AAR signaling under mesopic light recapitulated the protective effect of photopic light. Thus, targeting regional adrenoceptor signaling might represent a novel therapeutic strategy for autoimmune diseases including those that affect organs separated by barriers such as the CNS and eyes.
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Affiliation(s)
- Andrea Stofkova
- Division of Molecular Psychoimmunology, Institute for Genetic Medicine and Graduate School of Medicine, Hokkaido University, Sapporo, 060-0815, Japan. .,Department of Physiology, Third Faculty of Medicine, Charles University, Prague, Czech Republic.
| | - Daisuke Kamimura
- Division of Molecular Psychoimmunology, Institute for Genetic Medicine and Graduate School of Medicine, Hokkaido University, Sapporo, 060-0815, Japan
| | - Takuto Ohki
- Division of Molecular Psychoimmunology, Institute for Genetic Medicine and Graduate School of Medicine, Hokkaido University, Sapporo, 060-0815, Japan
| | - Mitsutoshi Ota
- Division of Molecular Psychoimmunology, Institute for Genetic Medicine and Graduate School of Medicine, Hokkaido University, Sapporo, 060-0815, Japan
| | - Yasunobu Arima
- Division of Molecular Psychoimmunology, Institute for Genetic Medicine and Graduate School of Medicine, Hokkaido University, Sapporo, 060-0815, Japan
| | - Masaaki Murakami
- Division of Molecular Psychoimmunology, Institute for Genetic Medicine and Graduate School of Medicine, Hokkaido University, Sapporo, 060-0815, Japan.
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Ather S, Proudlock FA, Welton T, Morgan PS, Sheth V, Gottlob I, Dineen RA. Aberrant visual pathway development in albinism: From retina to cortex. Hum Brain Mapp 2019; 40:777-788. [PMID: 30511784 PMCID: PMC6865554 DOI: 10.1002/hbm.24411] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2018] [Revised: 09/08/2018] [Accepted: 09/18/2018] [Indexed: 12/27/2022] Open
Abstract
Albinism refers to a group of genetic abnormalities in melanogenesis that are associated neuronal misrouting through the optic chiasm. We perform quantitative assessment of visual pathway structure and function in 23 persons with albinism (PWA) and 20 matched controls using optical coherence tomography (OCT), volumetric magnetic resonance imaging (MRI), diffusion tensor imaging and visual evoked potentials (VEP). PWA had a higher streamline decussation index (percentage of total tractography streamlines decussating at the chiasm) compared with controls (Z = -2.24, p = .025), and streamline decussation index correlated weakly with inter-hemispheric asymmetry measured using VEP (r = .484, p = .042). For PWA, a significant correlation was found between foveal development index and total number of streamlines (r = .662, p < .001). Significant positive correlations were found between peri-papillary retinal nerve fibre layer thickness and optic nerve (r = .642, p < .001) and tract (r = .663, p < .001) width. Occipital pole cortical thickness was 6.88% higher (Z = -4.10, p < .001) in PWA and was related to anterior visual pathway structures including foveal retinal pigment epithelium complex thickness (r = -.579, p = .005), optic disc (r = .478, p = .021) and rim areas (r = .597, p = .003). We were unable to demonstrate a significant relationship between OCT-derived foveal or optic nerve measures and MRI-derived chiasm size or streamline decussation index. Our novel tractographic demonstration of altered chiasmatic decussation in PWA corresponds to VEP measured cortical asymmetry and is consistent with chiasmatic misrouting in albinism. We also demonstrate a significant relationship between retinal pigment epithelium and visual cortex thickness indicating that retinal pigmentation defects in albinism lead to downstream structural reorganisation of the visual cortex.
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Affiliation(s)
- Sarim Ather
- Nuffield Department of Surgical SciencesUniversity of OxfordOxfordUnited Kingdom
| | - Frank Anthony Proudlock
- University of Leicester Ulverscroft Eye UnitRobert Kilpatrick Clinical Sciences BuildingLeicesterUnited Kingdom
| | - Thomas Welton
- Radiological Sciences, Division of Clinical NeuroscienceUniversity of Nottingham, Queen's Medical CentreNottinghamUnited Kingdom
- Sir Peter Mansfield Imaging Centre, University of NottinghamQueen's Medical CentreNottinghamUnited Kingdom
| | - Paul S. Morgan
- Sir Peter Mansfield Imaging Centre, University of NottinghamQueen's Medical CentreNottinghamUnited Kingdom
- Medical Physics and Clinical Engineering, Nottingham University Hospitals NHS TrustQueen's Medical CentreNottinghamUnited Kingdom
| | - Viral Sheth
- University of Leicester Ulverscroft Eye UnitRobert Kilpatrick Clinical Sciences BuildingLeicesterUnited Kingdom
| | - Irene Gottlob
- University of Leicester Ulverscroft Eye UnitRobert Kilpatrick Clinical Sciences BuildingLeicesterUnited Kingdom
| | - Rob A. Dineen
- Radiological Sciences, Division of Clinical NeuroscienceUniversity of Nottingham, Queen's Medical CentreNottinghamUnited Kingdom
- Sir Peter Mansfield Imaging Centre, University of NottinghamQueen's Medical CentreNottinghamUnited Kingdom
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McKay BS. Pigmentation and vision: Is GPR143 in control? J Neurosci Res 2019; 97:77-87. [PMID: 29761529 PMCID: PMC6235735 DOI: 10.1002/jnr.24246] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2017] [Revised: 02/21/2018] [Accepted: 03/21/2018] [Indexed: 12/30/2022]
Abstract
Albinism, typically characterized by decreased melanin synthesis, is associated with significant visual deficits owing to developmental changes during neurosensory retina development. All albinism is caused by genetic mutations in a group of diverse genes including enzymes, transporters, G-protein coupled receptor. Interestingly, these genes are not expressed in the neurosensory retina. Further, regardless of cause of albinism, all forms of albinism have the same retinal pathology, the extent of which is variable. In this review, we explore the possibility that this similarity in retinal phenotype is because all forms of albinism funnel through the same final common pathway. There are currently seven known genes linked to the seven forms of ocular cutaneous albinism. These types of albinism are the most common, and result in changes to all pigmented tissues (hair, skin, eyes). We will discuss the incidence and mechanism, where known, to develop a picture as to how the mutations cause albinism. Next, we will examine the one form of albinism which causes tissue-specific pathology, ocular albinism, where the eye exhibits the retinal albinism phenotype despite near normal melanin synthesis. We will discuss a potential way to treat the disease and restore normal retinal development. Finally, we will briefly discuss the possibility that this same pathway may intersect with the most common cause of permanent vision loss in the elderly.
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Affiliation(s)
- Brian S McKay
- Department of Ophthalmology and Vision Science, University of Arizona, Tucson, Arizona
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Lahne M, Piekos SM, O'Neill J, Ackerman KM, Hyde DR. Photo-regulation of rod precursor cell proliferation. Exp Eye Res 2018; 178:148-159. [PMID: 30267656 DOI: 10.1016/j.exer.2018.09.015] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2018] [Revised: 09/18/2018] [Accepted: 09/26/2018] [Indexed: 11/29/2022]
Abstract
Teleosts are unique in their ability to undergo persistent neurogenesis and to regenerate damaged and lost retinal neurons in adults. This contrasts with the human retina, which is incapable of replacing lost retinal neurons causing vision loss/blindness in the affected individuals. Two cell populations within the adult teleost retina generate new retinal neurons throughout life. Stem cells within the ciliary marginal zone give rise to all retinal cell types except for rod photoreceptors, which are produced by the resident Müller glia that are located within the inner nuclear layer of the entire retina. Understanding the mechanisms that regulate the generation of photoreceptors in the adult teleost retina may ultimately aid developing strategies to overcome vision loss in diseases such as retinitis pigmentosa. Here, we investigated whether photic deprivation alters the proliferative capacity of rod precursor cells, which are generated from Müller glia. In dark-adapted retinas, rod precursor cell proliferation increased, while the number of proliferating Müller glia and their derived olig2:EGFP-positive neuronal progenitor cells was not significantly changed. Cell death of rod photoreceptors was excluded as the inducer of rod precursor cell proliferation, as the number of TUNEL-positive cells and l-plastin-positive microglia in both the outer (ONL) and inner nuclear layer (INL) remained at a similar level throughout the dark-adaptation timecourse. Rod precursor cell proliferation in response to dark-adaptation was characterized by an increased number of EdU-positive cells, i.e. cells that were undergoing DNA replication. These proliferating rod precursor cells in dark-adapted zebrafish differentiated into rod photoreceptors at a comparable percentage and in a similar time frame as those maintained under standard light conditions suggesting that the cell cycle did not stall in dark-adapted retinas. Inhibition of IGF1-receptor signaling reduced the dark-adaptation-mediated proliferation response; however, caloric restriction which has been suggested to be integrated by the IGF1/growth hormone signaling axis did not influence rod precursor cell proliferation in dark-adapted retinas, as similar numbers were observed in starved and normal fed zebrafish. In summary, photic deprivation induces cell cycle entry of rod precursor cells via IGF1-receptor signaling independent of Müller glia proliferation.
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Affiliation(s)
- Manuela Lahne
- Department of Biological Sciences, The Center for Stem Cells and Regenerative Medicine and The Center for Zebrafish Research, Galvin Life Sciences Building, University of Notre Dame, Notre Dame, IN, 46556, USA
| | - Samantha M Piekos
- Department of Biological Sciences, The Center for Stem Cells and Regenerative Medicine and The Center for Zebrafish Research, Galvin Life Sciences Building, University of Notre Dame, Notre Dame, IN, 46556, USA
| | - John O'Neill
- Department of Biological Sciences, The Center for Stem Cells and Regenerative Medicine and The Center for Zebrafish Research, Galvin Life Sciences Building, University of Notre Dame, Notre Dame, IN, 46556, USA
| | - Kristin M Ackerman
- Department of Biological Sciences, The Center for Stem Cells and Regenerative Medicine and The Center for Zebrafish Research, Galvin Life Sciences Building, University of Notre Dame, Notre Dame, IN, 46556, USA
| | - David R Hyde
- Department of Biological Sciences, The Center for Stem Cells and Regenerative Medicine and The Center for Zebrafish Research, Galvin Life Sciences Building, University of Notre Dame, Notre Dame, IN, 46556, USA.
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Felfeli T, Mandelcorn MS, Yan P, Jeffery G, Mandelcorn ED. Failed Pneumatic Retinopexy for Rhegmatogenous Retinal Detachment Repair in Ocular Albinism: Clues to the Role of Melanin in Retinal Pigment Epithelium Pump Function. Ophthalmic Surg Lasers Imaging Retina 2017; 48:1016-1020. [DOI: 10.3928/23258160-20171130-10] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2017] [Accepted: 06/02/2017] [Indexed: 11/20/2022]
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Dopamine signaling regulates the projection patterns in the mouse chiasm. Brain Res 2015; 1625:324-36. [PMID: 26363092 DOI: 10.1016/j.brainres.2015.08.026] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2014] [Revised: 08/10/2015] [Accepted: 08/22/2015] [Indexed: 11/22/2022]
Abstract
Ocular albinism (OA) is characterized by inadequate L-3, 4-dihydroxyphenylalanine (L-DOPA) and dopamine (DA) in the eyes. This study investigated DA-related signaling pathways in mouse chiasm projection patterns and the potential role of ocular albinism type 1 (OA1) and dopamine 1A (D1A) receptors in the optic pathway. In embryonic day (E) E13-E15 retina, most L-DOPA and OA1-positive cells were distributed among Müller glial cells on E13 and retinal ganglion cells (RGC) on E14. In the ventral diencephalon, OA1 and L-DOPA were strongly expressed on the optic chiasm (OC) and optic tract (OT), respectively, but weak on the optic stalk (OS). At E13-E15, DA and D1A staining was predominately expressed in radially arranged cells with a neuronal expression pattern. In the ventral diencephalon, DA and D1A were strongly expressed on the OC, OT and OS. Furthermore, L-DOPA significantly inhibited retinal axon outgrowth in both the dorsal nasal (DN) and ventral temporal (VT) groups. DA inhibited retinal axon outgrowth, which was abolished by the D1A antagonist SCH23390. Brain slice cultures indicated that L-DOPA inhibited axons that crossed at the OC of E13 embryos, which was not abolished by DA. L-DOPA also inhibited axons that crossed at the OC of albino mice. Albino mice exhibited reduced ipsilateral retinal projections compared with C57 pigmented mice. No significant difference was identified in the uncrossed projections of albino mice following L-DOPA and DA expression. Furthermore, transcription factor Zic family member 2 (Zic2) upregulated OA1 mRNA expression. Our findings provide critical insights into DA-related signaling in retinal development.
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Abstract
Physical challenges, emotional arousal, increased physical activity, or changes in the environment can evoke stress, requiring altered activity of visceral organs, glands, and smooth muscles. These alterations are necessary for the organism to function appropriately under these abnormal conditions and to restore homeostasis. These changes in activity comprise the "fight-or-flight" response and must occur rapidly or the organism may not survive. The rapid responses are mediated primarily via the catecholamines, epinephrine, and norepinephrine, secreted from the adrenal medulla. The catecholamine neurohormones interact with adrenergic receptors present on cell membranes of all visceral organs and smooth muscles, leading to activation of signaling pathways and consequent alterations in organ function and smooth muscle tone. During the "fight-or-flight response," the rise in circulating epinephrine and norepinephrine from the adrenal medulla and norepinephrine secreted from sympathetic nerve terminals cause increased blood pressure and cardiac output, relaxation of bronchial, intestinal and many other smooth muscles, mydriasis, and metabolic changes that increase levels of blood glucose and free fatty acids. Circulating catecholamines can also alter memory via effects on afferent sensory nerves impacting central nervous system function. While these rapid responses may be necessary for survival, sustained elevation of circulating catecholamines for prolonged periods of time can also produce pathological conditions, such as cardiac hypertrophy and heart failure, hypertension, and posttraumatic stress disorder. In this review, we discuss the present knowledge of the effects of circulating catecholamines on peripheral organs and tissues, as well as on memory in the brain.
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Affiliation(s)
- A William Tank
- Department of Pharmacology & Physiology, University of Rochester Medical Center, Rochester, NY, USA
| | - Dona Lee Wong
- Department of Psychiatry, Harvard Medical School, McLean Hospital, Belmont, MA, USA
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Jayakody SA, Gonzalez-Cordero A, Ali RR, Pearson RA. Cellular strategies for retinal repair by photoreceptor replacement. Prog Retin Eye Res 2015; 46:31-66. [PMID: 25660226 DOI: 10.1016/j.preteyeres.2015.01.003] [Citation(s) in RCA: 78] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2014] [Revised: 01/13/2015] [Accepted: 01/19/2015] [Indexed: 02/08/2023]
Abstract
Loss of photoreceptors due to retinal degeneration is a major cause of blindness in the developed world. While no effective treatment is currently available, cell replacement therapy, using pluripotent stem cell-derived photoreceptor precursor cells, may be a feasible future treatment. Recent reports have demonstrated rescue of visual function following the transplantation of immature photoreceptors and we have seen major advances in our ability to generate transplantation-competent donor cells from stem cell sources. Moreover, we are beginning to realise the possibilities of using endogenous populations of cells from within the retina itself to mediate retinal repair. Here, we present a review of our current understanding of endogenous repair mechanisms together with recent progress in the use of both ocular and pluripotent stem cells for the treatment of photoreceptor loss. We consider how our understanding of retinal development has underpinned many of the recent major advances in translation and moved us closer to the goal of restoring vision by cellular means.
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Affiliation(s)
- Sujatha A Jayakody
- Gene and Cell Therapy Group, Department of Genetics, UCL Institute of Ophthalmology, 11-43 Bath St, London EC1V 9EL, UK
| | - Anai Gonzalez-Cordero
- Gene and Cell Therapy Group, Department of Genetics, UCL Institute of Ophthalmology, 11-43 Bath St, London EC1V 9EL, UK
| | - Robin R Ali
- Gene and Cell Therapy Group, Department of Genetics, UCL Institute of Ophthalmology, 11-43 Bath St, London EC1V 9EL, UK; NIHR Biomedical Research Centre at Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, City Road, London EC1V 2PD, UK
| | - Rachael A Pearson
- Gene and Cell Therapy Group, Department of Genetics, UCL Institute of Ophthalmology, 11-43 Bath St, London EC1V 9EL, UK.
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Abstract
The visual system is beautifully crafted to transmit information of the external world to visual processing and cognitive centers in the brain. For visual information to be relayed to the brain, a series of axon pathfinding events must take place to ensure that the axons of retinal ganglion cells, the only neuronal cell type in the retina that sends axons out of the retina, find their way out of the eye to connect with targets in the brain. In the past few decades, the power of molecular and genetic tools, including the generation of genetically manipulated mouse lines, have multiplied our knowledge about the molecular mechanisms involved in the sculpting of the visual system. Here, we review major advances in our understanding of the mechanisms controlling the differentiation of RGCs, guidance of their axons from the retina to the primary visual centers, and the refinement processes essential for the establishment of topographic maps and eye-specific axon segregation. Human disorders, such as albinism and achiasmia, that impair RGC axon growth and guidance and, thus, the establishment of a fully functioning visual system will also be discussed.
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Affiliation(s)
- Lynda Erskine
- School of Medical Sciences, Institute of Medical Sciences, University of Aberdeen, Scotland, UK
| | - Eloisa Herrera
- Instituto de Neurosciencias de Alicante, CSIC-UMH, San Juan de Alicante, Spain
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Roffler-Tarlov S, Liu JH, Naumova EN, Bernal-Ayala MM, Mason CA. L-Dopa and the albino riddle: content of L-Dopa in the developing retina of pigmented and albino mice. PLoS One 2013; 8:e57184. [PMID: 23526936 PMCID: PMC3602463 DOI: 10.1371/journal.pone.0057184] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2012] [Accepted: 01/18/2013] [Indexed: 01/11/2023] Open
Abstract
Background The absence or deficiency of melanin as in albinos, has detrimental effects on retinal development that include aberrant axonal projections from eye to brain and impaired vision. In pigmented retinal pigment epithelium (RPE), dihydroxyphenalanine (L-Dopa), an intermediate in the synthetic path for melanin, has been hypothesized to regulate the tempo of neurogenesis. The time course of expression of retinal L-Dopa, whether it is harbored exclusively in the RPE, the extent of deficiency in albinos compared to isogenic controls, and whether L-Dopa can be restored if exogenously delivered to the albino have been unknown. Methodology/Principal Findings L-Dopa and catecholamines including dopamine extracted from retinas of pigmented (C57BL/6J) and congenic albino (C57BL/6J-tyrc2j) mice, were measured throughout development beginning at E10.5 and at maturity. L-Dopa, but not dopamine nor any other catecholamine, appears in pigmented retina as soon as tyrosinase is expressed in RPE at E10.5. In pigmented retina, L-Dopa content increases throughout pre- and postnatal development until the end of the first postnatal month after which it declines sharply. This time course reflects the onset and completion of retinal development. L-Dopa is absent from embryonic albino retina and is greatly reduced in postnatal albino retina compared to pigmented retina. Dopamine is undetectable in both albino and pigmented retinas until after the postnatal expression of the neuronal enzyme tyrosine hydroxylase. If provided to pregnant albino mothers, L-Dopa accumulates in the RPE of the fetuses. Conclusions L-Dopa in pigmented RPE is most abundant during development after which content declines. This L-Dopa is not converted to dopamine. L-Dopa is absent or at low levels in albino retina and can be restored to the RPE by administration in utero. These findings further implicate L-Dopa as a factor in the RPE that could influence development, and demonstrate that administration of L-Dopa could be a means to rescue developmental abnormalities characteristic of albinos.
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Affiliation(s)
- Suzanne Roffler-Tarlov
- Department of Neuroscience, Tufts University School of Medicine, Boston, Massachusetts, United States of America.
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15
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El-Sayyad HIH, El-Sherbiny MA, Sobh MA, Abou-El-Naga AM, Ibrahim MAN, Mousa SA. Protective effects of Morus alba leaves extract on ocular functions of pups from diabetic and hypercholesterolemic mother rats. Int J Biol Sci 2011; 7:715-28. [PMID: 21697998 PMCID: PMC3119844 DOI: 10.7150/ijbs.7.715] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2010] [Accepted: 05/18/2011] [Indexed: 01/21/2023] Open
Abstract
Phytotherapy is frequently considered to be less toxic and free from side effects than synthetic drugs. Hence, the present study was designed to investigate the protective use of crude water extract of Morus alba leaves on ocular functions including cataractogenesis, biochemical diabetic and hypercholesterolemic markers, retinal neurotransmitters and retinopathy of rat pups maternally subjected to either diabetes and/or hypercholesterolemia. Application of crude water extract of Morus alba resulted in amelioration of the alterations of maternal serum glucose, LDL, HDL, total cholesterol and creatine phosphokinase activity as well as retinal neurotransmitters including acetylcholine (ACE), adrenaline (AD), nor-adrenaline (NAD), serotonin (5-HT), histamine (HS), dopamine (DA) and gamma amino butyric acid (GABA). The retina of pups of either diabetic and/or hypercholesterolemia mothers exhibited massive alterations of retinal neurotransmitters. The alterations of retinal neurotransmitters were correlated with the observed pathological alterations of retinal pigmented epithelium, photoreceptor inner segment and ganglion cells and increased incidence of DNA fragmentation and apoptosis cell death. However, protection with Morus alba extract led to amelioration of the pathological alterations of retinal neurons and estimated neurotransmitters. Furthermore, a striking incidence of cataract was detected in pups of either diabetic and/or hypercholesterolemic mothers. Highest cataractogenesis was observed in pups of combined -treated groups. Our data indicate that experimental maternal diabetes alone or in combination with hypercholesterolemia led to alteration in the ocular structures of their pups, with an increasing incidence of cataract and retinopathy, and the effects of the extract might be attributed to the hypoglycaemic, antihypercholesterolemic and anti-oxidative potential of flavonoids, the major components of the plant extract.
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Affiliation(s)
- H I H El-Sayyad
- Laboratory of Experimental Embryology, Zoology Department, Mansoura University, Egypt & El-Kuwait.
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16
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Differential immunodetection of
l
‐DOPA decarboxylase and tyrosine hydroxylase in the vertebrate retina. Int J Dev Neurosci 2009; 27:469-76. [DOI: 10.1016/j.ijdevneu.2009.05.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2009] [Revised: 04/23/2009] [Accepted: 05/06/2009] [Indexed: 11/19/2022] Open
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Fox DA, Kala SV, Hamilton WR, Johnson JE, O'Callaghan JP. Low-level human equivalent gestational lead exposure produces supernormal scotopic electroretinograms, increased retinal neurogenesis, and decreased retinal dopamine utilization in rats. ENVIRONMENTAL HEALTH PERSPECTIVES 2008; 116:618-25. [PMID: 18470321 PMCID: PMC2367685 DOI: 10.1289/ehp.11268] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/15/2008] [Accepted: 02/21/2008] [Indexed: 05/18/2023]
Abstract
BACKGROUND Postnatal lead exposure in children and animals produces alterations in the visual system primarily characterized by decreases in the rod-mediated (scotopic) electroretinogram (ERG) amplitude (subnormality). In contrast, low-level gestational Pb exposure (GLE) increases the amplitude of scotopic ERGs in children (supernormality). OBJECTIVES The goal of this study was to establish a rat model of human equivalent GLE and to determine dose-response effects on scotopic ERGs and on retinal morphology, biochemistry, and dopamine metabolism in adult offspring. METHODS We exposed female Long-Evans hooded rats to water containing 0, 27 (low), 55 (moderate), or 109 (high) ppm of Pb beginning 2 weeks before mating, throughout gestation, and until postnatal day (PND) 10. We measured maternal and litter indices, blood Pb concentrations (BPb), retinal Pb concentrations, zinc concentrations, and body weights. On PND90, we performed the retinal experiments. RESULTS Peak BPb concentrations were < 1, 12, 24, and 46 microg/dL in control, low-, moderate- and high-level GLE groups, respectively, at PNDs 0-10. ERG supernormality and an increased rod photoreceptor and rod bipolar cell neurogenesis occurred with low- and moderate-level GLE. In contrast, high-level GLE produced ERG subnormality, rod cell loss, and decreased retinal Zn levels. GLE produced dose-dependent decreases in dopamine and its utilization. CONCLUSIONS Low- and moderate-level GLE produced persistent scotopic ERG supernormality due to an increased neurogenesis of cells in the rod signaling pathway and/or decreased dopamine utilization, whereas high-level GLE produced rod-selective toxicity characterized by ERG subnormality. The ERG is a differential and noninvasive biomarker of GLE. The inverted U-shaped dose-response curves reveal the sensitivity and vulnerability of the developing retina to GLE.
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Affiliation(s)
- Donald A Fox
- College of Optometry, University of Houston, 4901 Calhoun Rd., Houston, TX 77204-2020, USA.
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18
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Vugler A, Lawrence J, Walsh J, Carr A, Gias C, Semo M, Ahmado A, da Cruz L, Andrews P, Coffey P. Embryonic stem cells and retinal repair. Mech Dev 2007; 124:807-29. [PMID: 17881192 DOI: 10.1016/j.mod.2007.08.002] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2007] [Revised: 08/07/2007] [Accepted: 08/07/2007] [Indexed: 12/11/2022]
Abstract
In this review we examine the potential of embryonic stem cells (ESCs) for use in the treatment of retinal diseases involving photoreceptors and retinal pigment epithelium (RPE). We outline the ontogenesis of target retinal cell types (RPE, rods and cones) and discuss how an understanding of developmental processes can inform our manipulation of ESCs in vitro. Due to their potential for cellular therapy, special emphasis is placed upon the derivation and culture of human embryonic stem cells (HESCs) and their differentiation towards a retinal phenotype. In terms of achieving this goal, we suggest that much of the success to date reflects permissive in vitro environments provided by established protocols for HESC derivation, propagation and neural differentiation. In addition, we summarise key factors that may be important for enhancing efficiency of retinal cell-type derivation from HESCs. The retina is an amenable component of the central nervous system (CNS) and as such, diseases of this structure provide a realistic target for the application of HESC-derived cellular therapy to the CNS. In order to further this goal, the second component of our review focuses on the cellular and molecular cues within retinal environments that may influence the survival and behaviour of transplanted cells. Our analysis considers both the potential barriers to transplant integration in the retina itself together with the remodelling in host visual centres that is known to accompany retinal dystrophy.
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Affiliation(s)
- Anthony Vugler
- Institute of Ophthalmology, University College London, 11-43 Bath Street, London EC1V9EL, UK.
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19
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Martins RAP, Pearson RA. Control of cell proliferation by neurotransmitters in the developing vertebrate retina. Brain Res 2007; 1192:37-60. [PMID: 17597590 DOI: 10.1016/j.brainres.2007.04.076] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2007] [Revised: 04/04/2007] [Accepted: 04/20/2007] [Indexed: 01/24/2023]
Abstract
In the developing vertebrate retina, precise coordination of retinal progenitor cell proliferation and cell-cycle exit is essential for the formation of a functionally mature retina. Unregulated or disrupted cell proliferation may lead to dysplasia, retinal degeneration or retinoblastoma. Both cell-intrinsic and -extrinsic factors regulate the proliferation of progenitor cells during CNS development. There is now growing evidence that in the developing vertebrate retina, both slow and fast neurotransmitter systems modulate the proliferation of retinal progenitor cells. Classic neurotransmitters, such as GABA (gamma-amino butyric acid), glycine, glutamate, ACh (acetylcholine) and ATP (adenosine triphosphate) are released, via vesicular or non-vesicular mechanisms, into the immature retinal environment. Furthermore, these neurotransmitters signal through functional receptors even before synapses are formed. Recent evidence indicates that the activation of purinergic and muscarinic receptors may regulate the cell-cycle machinery and consequently the expansion of the retinal progenitor pool. Interestingly, GABA and glutamate appear to have opposing roles, inducing retinal progenitor cell-cycle exit. In this review, we present recent findings that begin to elucidate the roles of neurotransmitters as regulators of progenitor cell proliferation at early stages of retinal development. These studies also raise several new questions, including how these neurotransmitters regulate specific cell-cycle pathways and the mechanisms by which retinal progenitor cells integrate the signals from neurotransmitters and other exogenous factors during vertebrate retina development.
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Affiliation(s)
- Rodrigo A P Martins
- Department of Developmental Neurobiology, St. Jude Children's Research Hospital, MS323, Memphis, TN 38105, USA.
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Reis RAM, Ventura ALM, Kubrusly RCC, de Mello MCF, de Mello FG. Dopaminergic signaling in the developing retina. ACTA ACUST UNITED AC 2007; 54:181-8. [PMID: 17292477 DOI: 10.1016/j.brainresrev.2007.01.001] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2006] [Revised: 01/03/2007] [Accepted: 01/09/2007] [Indexed: 11/16/2022]
Abstract
The role of dopamine in the retina has been studied for the last 30 years and there is now increasing evidence that dopamine is used as a developmental signal in the embryonic retina. Dopamine is the main catecholamine found in the retina of most species, being synthesized from the L-amino acid tyrosine. Its effects are mediated by G protein coupled receptors constituting the D(1) (D(1) and D(5)) and D(2) (D(2), D(3) and D(4)) receptor subfamilies that can be coupled to adenylyl cyclase in opposite manners. Dopamine-mediated cyclic AMP (cAMP) accumulation, via D(1)-like receptors, is observed very early during retina ontogeny, before synaptogenesis and, in some species, before the expression of tyrosine hydroxylase (TH), the enzyme that characterizes the neuronal dopaminergic phenotype. D(2)-like receptors appear in the tissue days after D(1)-like activity is detected. In the embryonic avian retina, before the tissue is capable of synthesizing its own dopamine via TH, dopamine synthesis is observed from L-DOPA supplied to the neuroretina from retina pigmented epithelium which results in dopaminergic communication in the embryonic tissue before TH expression. Müller cells, the main glia type found in the retina, seem to actively contribute to dopaminergic activity in the retinal tissue. Understanding the dopaminergic role during retina development may contribute to novel strategies approaching certain visual dysfunctions such as those found in ocular albinism.
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Affiliation(s)
- Ricardo A M Reis
- Lab. Neurochemistry, Program in Neurobiology IBCCF, UFRJ, Rio de Janeiro, Brazil.
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Tibber MS, Becker D, Jeffery G. Levels of transient gap junctions between the retinal pigment epithelium and the neuroblastic retina are influenced by catecholamines and correlate with patterns of cell production. J Comp Neurol 2007; 503:128-34. [PMID: 17480016 DOI: 10.1002/cne.21388] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Retinal mitosis takes place at the interface between the retinal pigment epithelium (RPE) and the neural retina. Multiple studies have highlighted the essential role that gap junction-mediated communication plays in the regulation of retinal organogenesis. Here, the localization pattern and function of the gap junction protein connexin 43 were examined in vivo in the rat at the interface between the retina and RPE during the main phases of retinal cell production. Connexin 43 was expressed at this site from E15 onward, and levels were subsequently temporally regulated. When Cx43 protein levels were reduced experimentally, by using antisense oligodeoxynucleotides, mitotic activity in the retina decreased significantly. Conversely, in the hypopigmented eye elevated mitotic levels were associated with a significant increase of connexin 43. Both excess protein levels and elevated mitosis were corrected by the in vivo administration of L-DOPA (a dopamine precursor and intermediary compound in the melanin synthesis pathway). These findings suggest that connexin 43-mediated communication between the retina and RPE is essential for the correct pacing of retinal organogenesis. Furthermore, this pathway may be gated by levels of ocular catecholamines.
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Affiliation(s)
- Marc S Tibber
- Institute of Ophthalmology, University College London, London, UK
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Kubrusly RCC, Ventura ALM, de Melo Reis RA, Serra GCF, Yamasaki EN, Gardino PF, de Mello MCF, de Mello FG. Norepinephrine acts as D1-dopaminergic agonist in the embryonic avian retina: late expression of beta1-adrenergic receptor shifts norepinephrine specificity in the adult tissue. Neurochem Int 2006; 50:211-8. [PMID: 17014930 DOI: 10.1016/j.neuint.2006.08.004] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2006] [Revised: 08/01/2006] [Accepted: 08/15/2006] [Indexed: 10/24/2022]
Abstract
Dopamine is the main catecholamine found in the chick retina whereas norepinephrine is only found in trace amounts. We compared the effectiveness of dopamine and norepinephrine in promoting cyclic AMP accumulation in retinas at embryonic day 13 (E13) and from post-hatched chicken (P15). Dopamine (EC(50)=10microM) and norepinephrine (EC(50)=30microM), but not the beta(1)-adrenergic agonist isoproterenol, stimulated over seven-fold the production of cyclic AMP in E13 retina. The cyclic AMP accumulation induced by both catecholamines in embryonic tissue was entirely blocked by 2microM SCH23390, a D(1) receptor antagonist, but not by alprenolol (beta-adrenoceptor antagonist). In P15 retinas, 100microM isoproterenol stimulated five-fold the accumulation of cAMP. This effect was blocked by propanolol (10microM), but not by 2microM SCH23390. Embryonic and adult retina display beta(1) adrenergic receptor mRNA as detected by RT-PCR, but the beta(1) adrenergic receptor protein was detected only in post-hatched tissue. We conclude that norepinephrine cross-reacts with D(1) dopaminergic receptor with affinity similar to that of dopamine in the embryonic retina. In the mature retina, however, D(1) receptors become restricted to activation by dopamine. Moreover, as opposed to the embryonic tissue, norepinephrine seems to stimulate cAMP accumulation via beta(1)-like adrenergic receptors in the mature tissue.
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Lavado A, Jeffery G, Tovar V, de la Villa P, Montoliu L. Ectopic expression of tyrosine hydroxylase in the pigmented epithelium rescues the retinal abnormalities and visual function common in albinos in the absence of melanin. J Neurochem 2006; 96:1201-11. [PMID: 16445854 DOI: 10.1111/j.1471-4159.2006.03657.x] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Albino mammals have profound retinal abnormalities, including photoreceptor deficits and misrouted hemispheric pathways into the brain, demonstrating that melanin or its precursors are required for normal retinal development. Tyrosinase, the primary enzyme in melanin synthesis commonly mutated in albinism, oxidizes l-tyrosine to l-dopaquinone using l-3,4-dihydroxyphenylalanine (L-DOPA) as an intermediate product. L-DOPA is known to signal cell cycle exit during retinal development and plays an important role in the regulation of retinal development. Here, we have mimicked L-DOPA production by ectopically expressing tyrosine hydroxylase in mouse albino retinal pigment epithelium cells. Tyrosine hydroxylase can only oxidize l-tyrosine to L-DOPA without further progression towards melanin. The resulting transgenic animals remain phenotypically albino, but their visual abnormalities are corrected, with normal photoreceptor numbers and hemispheric pathways and improved visual function, assessed by an increase of spatial acuity. Our results demonstrate definitively that only early melanin precursors, L-DOPA or its metabolic derivatives, are vital in the appropriate development of mammalian retinae. They further highlight the value of substituting independent but biochemically related enzymes to overcome developmental abnormalities.
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Affiliation(s)
- Alfonso Lavado
- Centro Nacional de Biotecnología (CNB-CSIC), Department of Molecular and Cellular Biology, Campus de Cantoblanco, Madrid, Spain
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