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Cavanaugh BL, Milstein ML, Boucher RC, Tan SX, Hanna MW, Seidel A, Frederiksen R, Saunders TL, Sampath AP, Mitton KP, Zhang DQ, Goldberg AFX. A new mouse model for PRPH2 pattern dystrophy exhibits functional compensation prior and subsequent to retinal degeneration. Hum Mol Genet 2024:ddae128. [PMID: 39231530 DOI: 10.1093/hmg/ddae128] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2024] [Revised: 07/19/2024] [Accepted: 08/21/2024] [Indexed: 09/06/2024] Open
Abstract
Mutations in PRPH2 are a relatively common cause of sight-robbing inherited retinal degenerations (IRDs). Peripherin-2 (PRPH2) is a photoreceptor-specific tetraspanin protein that structures the disk rim membranes of rod and cone outer segment (OS) organelles, and is required for OS morphogenesis. PRPH2 is noteworthy for its broad spectrum of disease phenotypes; both inter- and intra-familial heterogeneity have been widely observed and this variability in disease expression and penetrance confounds efforts to understand genotype-phenotype correlations and pathophysiology. Here we report the generation and initial characterization of a gene-edited animal model for PRPH2 disease associated with a nonsense mutation (c.1095:C>A, p.Y285X), which is predicted to truncate the peripherin-2 C-terminal domain. Young (P21) Prph2Y285X/WT mice developed near-normal photoreceptor numbers; however, OS membrane architecture was disrupted, OS protein levels were reduced, and in vivo and ex vivo electroretinography (ERG) analyses found that rod and cone photoreceptor function were each severely reduced. Interestingly, ERG studies also revealed that rod-mediated downstream signaling (b-waves) were functionally compensated in the young animals. This resiliency in retinal function was retained at P90, by which time substantial IRD-related photoreceptor loss had occurred. Altogether, the current studies validate a new mouse model for investigating PRPH2 disease pathophysiology, and demonstrate that rod and cone photoreceptor function and structure are each directly and substantially impaired by the Y285X mutation. They also reveal that Prph2 mutations can induce a functional compensation that resembles homeostatic plasticity, which can stabilize rod-derived signaling, and potentially dampen retinal dysfunction during some PRPH2-associated IRDs.
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Affiliation(s)
| | - Michelle L Milstein
- Eye Research Institute, Oakland University, Rochester, MI 48309, United States
| | - R Casey Boucher
- Eye Research Institute, Oakland University, Rochester, MI 48309, United States
| | - Sharon X Tan
- Eye Research Institute, Oakland University, Rochester, MI 48309, United States
| | - Mario W Hanna
- Eye Research Institute, Oakland University, Rochester, MI 48309, United States
| | - Adam Seidel
- Eye Research Institute, Oakland University, Rochester, MI 48309, United States
| | - Rikard Frederiksen
- Stein Eye Institute, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA 90095-7000, United States
| | - Thomas L Saunders
- Trangsgenic Animal Model Core, Biomedical Research Core Facilities, Division of Genetic Medicine, University of Michigan, Ann Arbor, MI 41809, United States
| | - Alapakkam P Sampath
- Stein Eye Institute, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA 90095-7000, United States
| | - Kenneth P Mitton
- Eye Research Institute, Oakland University, Rochester, MI 48309, United States
- Department of Foundational Medical Studies, Oakland University William Beaumont School of Medicine, Rochester, MI 48309, United States
| | - Dao-Qi Zhang
- Eye Research Institute, Oakland University, Rochester, MI 48309, United States
- Department of Foundational Medical Studies, Oakland University William Beaumont School of Medicine, Rochester, MI 48309, United States
| | - Andrew F X Goldberg
- Eye Research Institute, Oakland University, Rochester, MI 48309, United States
- Department of Foundational Medical Studies, Oakland University William Beaumont School of Medicine, Rochester, MI 48309, United States
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Bonezzi PJ, Tarchick MJ, Moore BD, Renna JM. Light drives the developmental progression of outer retinal function. J Gen Physiol 2023; 155:e202213262. [PMID: 37432412 PMCID: PMC10336150 DOI: 10.1085/jgp.202213262] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2022] [Revised: 02/24/2023] [Accepted: 06/08/2023] [Indexed: 07/12/2023] Open
Abstract
The complex nature of rod and cone photoreceptors and the light-evoked responsivity of bipolar cells in the mature rodent retina have been well characterized. However, little is known about the emergent light-evoked response properties of the mouse retina and the role light plays in shaping these emergent responses. We have previously demonstrated that the outer retina is responsive to green light as early as postnatal day 8 (P8). Here, we characterize the progression of both photoreceptors (rods and cones) and bipolar cell responses during development and into adulthood using ex vivo electroretinogram recordings. Our data show that the majority of photoreceptor response at P8 originates from cones and that these outputs drive second-order bipolar cell responses as early as P9. We find that the magnitude of the photoresponse increases concurrently with each passing day of postnatal development and that many functional properties of these responses, as well as the relative rod/cone contributions to the total light-evoked response, are age dependent. We compare these responses at eye opening and maturity to age-matched animals raised in darkness and found that the absence of light diminishes emergent and mature cone-to-bipolar cell signaling. Furthermore, we found cone-evoked responses to be significantly slower in dark-reared retinas. Together, this work characterizes the developmental photoresponsivity of the mouse retina while highlighting the importance of properly timed sensory input for the maturation of the first visual system synapse.
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Affiliation(s)
- Paul J. Bonezzi
- Department of Biology, The University of Akron, Akron, OH, USA
| | | | | | - Jordan M. Renna
- Department of Biology, The University of Akron, Akron, OH, USA
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Cangiano L, Asteriti S. An Ex Vivo Electroretinographic Apparatus for the mL-Scale Testing of Drugs to One Day and Beyond. Int J Mol Sci 2023; 24:11346. [PMID: 37511106 PMCID: PMC10380068 DOI: 10.3390/ijms241411346] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2023] [Revised: 07/09/2023] [Accepted: 07/10/2023] [Indexed: 07/30/2023] Open
Abstract
When screening new drugs to treat retinal diseases, ex vivo electroretinography (ERG) potentially combines the experimental throughput of its traditional in vivo counterpart, with greater mechanistic insight and reproducible delivery. To date, this technique was used in experiments with open loop superfusion and lasting up to a few hours. Here, we present a compact apparatus that provides continuous and simultaneous recordings of the scotopic a-waves from four mouse retinas for much longer durations. Crucially, each retina can be incubated at 37 °C in only 2 mL of static medium, enabling the testing of very expensive drugs or nano devices. Light sensitivity and response kinetics of these preparations remain in the physiological range throughout incubation, displaying only very slow drifts. As an example application, we showed that barium, a potassium channel blocker used to abolish the glial component of the ERG, displayed no overt side effects on photoreceptors over several hours. In another example, we fully regenerated a partially bleached retina using a minimal quantity of 9-cis-retinal. Finally, we demonstrated that including antibiotic in the incubation medium extends physiological light responses to over one day. This system represents a necessary stepping stone towards the goal of combining ERG recordings with organotypically cultured retinas.
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Affiliation(s)
- Lorenzo Cangiano
- Department of Translational Research, University of Pisa, 56123 Pisa, Italy
| | - Sabrina Asteriti
- Department of Translational Research, University of Pisa, 56123 Pisa, Italy
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, 37134 Verona, Italy
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Leinonen H, Cheng C, Pitkänen M, Sander CL, Zhang J, Saeid S, Turunen T, Shmara A, Weiss L, Ta L, Ton T, Koskelainen A, Vargas JD, Kimonis V, Palczewski K. A p97/Valosin-Containing Protein Inhibitor Drug CB-5083 Has a Potent but Reversible Off-Target Effect on Phosphodiesterase-6. J Pharmacol Exp Ther 2021; 378:31-41. [PMID: 33931547 DOI: 10.1124/jpet.120.000486] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2020] [Accepted: 04/29/2021] [Indexed: 12/16/2022] Open
Abstract
CB-5083 is an inhibitor of p97/valosin-containing protein (VCP), for which phase I trials for cancer were terminated because of adverse effects on vision, such as photophobia and dyschromatopsia. Lower dose CB-5083 could combat inclusion body myopathy with early-onset Paget disease and frontotemporal dementia or multisystem proteinopathy caused by gain-of-function mutations in VCP. We hypothesized that the visual impairment in the cancer trial was due to CB-5083's inhibition of phosphodiesterase (PDE)-6, which mediates signal transduction in photoreceptors. To test our hypothesis, we used in vivo and ex vivo electroretinography (ERG) in mice and a PDE6 activity assay of bovine rod outer segment (ROS) extracts. Additionally, histology and optical coherence tomography were used to assess CB-5083's long-term ocular toxicity. A single administration of CB-5083 led to robust ERG signal deterioration, specifically in photoresponse kinetics. Similar recordings with known PDE inhibitors sildenafil, tadalafil, vardenafil, and zaprinast showed that only vardenafil had as strong an effect on the ERG signal in vivo as did CB-5083. In the biochemical assay, CB-5083 inhibited PDE6 activity with a potency higher than sildenafil but lower than that of vardenafil. Ex vivo ERG revealed a PDE6 inhibition constant of 80 nM for CB-5083, which is 7-fold smaller than that for sildenafil. Finally, we showed that the inhibitory effect of CB-5083 on visual function is reversible, and its chronic administration does not cause permanent retinal anomalies in aged VCP-disease model mice. Our results warrant re-evaluation of CB-5083 as a clinical therapeutic agent. We recommend preclinical ERG recordings as a routine drug safety screen. SIGNIFICANCE STATEMENT: This report supports the use of a valosin-containing protein (VCP) inhibitor drug, CB-5083, for the treatment of neuromuscular VCP disease despite CB-5083's initial clinical failure for cancer treatment due to side effects on vision. The data show that CB-5083 displays a dose-dependent but reversible inhibitory action on phosphodiesterase-6, an essential enzyme in retinal photoreceptor function, but no long-term consequences on retinal function or structure.
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Affiliation(s)
- Henri Leinonen
- Gavin Herbert Eye Institute, Department of Ophthalmology (H.L., C.L.S., J.Z., K.P.), Department of Physiology & Biophysics (K.P.), Department of Chemistry (K.P.), and Division of Genetics and Genomic Medicine, Department of Pediatrics (C.C., A.S., L.W., L.T., T.T., V.K.), University of California Irvine, Irvine, California; Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio (C.L.S.); Department of Neuroscience and Biomedical Engineering, Aalto University, Espoo, Finland (M.P., S.S., T.T., A.K.); and Cleave Therapeutics, Inc., San Francisco, California (J.D.V.)
| | - Cheng Cheng
- Gavin Herbert Eye Institute, Department of Ophthalmology (H.L., C.L.S., J.Z., K.P.), Department of Physiology & Biophysics (K.P.), Department of Chemistry (K.P.), and Division of Genetics and Genomic Medicine, Department of Pediatrics (C.C., A.S., L.W., L.T., T.T., V.K.), University of California Irvine, Irvine, California; Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio (C.L.S.); Department of Neuroscience and Biomedical Engineering, Aalto University, Espoo, Finland (M.P., S.S., T.T., A.K.); and Cleave Therapeutics, Inc., San Francisco, California (J.D.V.)
| | - Marja Pitkänen
- Gavin Herbert Eye Institute, Department of Ophthalmology (H.L., C.L.S., J.Z., K.P.), Department of Physiology & Biophysics (K.P.), Department of Chemistry (K.P.), and Division of Genetics and Genomic Medicine, Department of Pediatrics (C.C., A.S., L.W., L.T., T.T., V.K.), University of California Irvine, Irvine, California; Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio (C.L.S.); Department of Neuroscience and Biomedical Engineering, Aalto University, Espoo, Finland (M.P., S.S., T.T., A.K.); and Cleave Therapeutics, Inc., San Francisco, California (J.D.V.)
| | - Christopher L Sander
- Gavin Herbert Eye Institute, Department of Ophthalmology (H.L., C.L.S., J.Z., K.P.), Department of Physiology & Biophysics (K.P.), Department of Chemistry (K.P.), and Division of Genetics and Genomic Medicine, Department of Pediatrics (C.C., A.S., L.W., L.T., T.T., V.K.), University of California Irvine, Irvine, California; Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio (C.L.S.); Department of Neuroscience and Biomedical Engineering, Aalto University, Espoo, Finland (M.P., S.S., T.T., A.K.); and Cleave Therapeutics, Inc., San Francisco, California (J.D.V.)
| | - Jianye Zhang
- Gavin Herbert Eye Institute, Department of Ophthalmology (H.L., C.L.S., J.Z., K.P.), Department of Physiology & Biophysics (K.P.), Department of Chemistry (K.P.), and Division of Genetics and Genomic Medicine, Department of Pediatrics (C.C., A.S., L.W., L.T., T.T., V.K.), University of California Irvine, Irvine, California; Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio (C.L.S.); Department of Neuroscience and Biomedical Engineering, Aalto University, Espoo, Finland (M.P., S.S., T.T., A.K.); and Cleave Therapeutics, Inc., San Francisco, California (J.D.V.)
| | - Sama Saeid
- Gavin Herbert Eye Institute, Department of Ophthalmology (H.L., C.L.S., J.Z., K.P.), Department of Physiology & Biophysics (K.P.), Department of Chemistry (K.P.), and Division of Genetics and Genomic Medicine, Department of Pediatrics (C.C., A.S., L.W., L.T., T.T., V.K.), University of California Irvine, Irvine, California; Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio (C.L.S.); Department of Neuroscience and Biomedical Engineering, Aalto University, Espoo, Finland (M.P., S.S., T.T., A.K.); and Cleave Therapeutics, Inc., San Francisco, California (J.D.V.)
| | - Teemu Turunen
- Gavin Herbert Eye Institute, Department of Ophthalmology (H.L., C.L.S., J.Z., K.P.), Department of Physiology & Biophysics (K.P.), Department of Chemistry (K.P.), and Division of Genetics and Genomic Medicine, Department of Pediatrics (C.C., A.S., L.W., L.T., T.T., V.K.), University of California Irvine, Irvine, California; Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio (C.L.S.); Department of Neuroscience and Biomedical Engineering, Aalto University, Espoo, Finland (M.P., S.S., T.T., A.K.); and Cleave Therapeutics, Inc., San Francisco, California (J.D.V.)
| | - Alyaa Shmara
- Gavin Herbert Eye Institute, Department of Ophthalmology (H.L., C.L.S., J.Z., K.P.), Department of Physiology & Biophysics (K.P.), Department of Chemistry (K.P.), and Division of Genetics and Genomic Medicine, Department of Pediatrics (C.C., A.S., L.W., L.T., T.T., V.K.), University of California Irvine, Irvine, California; Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio (C.L.S.); Department of Neuroscience and Biomedical Engineering, Aalto University, Espoo, Finland (M.P., S.S., T.T., A.K.); and Cleave Therapeutics, Inc., San Francisco, California (J.D.V.)
| | - Lan Weiss
- Gavin Herbert Eye Institute, Department of Ophthalmology (H.L., C.L.S., J.Z., K.P.), Department of Physiology & Biophysics (K.P.), Department of Chemistry (K.P.), and Division of Genetics and Genomic Medicine, Department of Pediatrics (C.C., A.S., L.W., L.T., T.T., V.K.), University of California Irvine, Irvine, California; Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio (C.L.S.); Department of Neuroscience and Biomedical Engineering, Aalto University, Espoo, Finland (M.P., S.S., T.T., A.K.); and Cleave Therapeutics, Inc., San Francisco, California (J.D.V.)
| | - Lac Ta
- Gavin Herbert Eye Institute, Department of Ophthalmology (H.L., C.L.S., J.Z., K.P.), Department of Physiology & Biophysics (K.P.), Department of Chemistry (K.P.), and Division of Genetics and Genomic Medicine, Department of Pediatrics (C.C., A.S., L.W., L.T., T.T., V.K.), University of California Irvine, Irvine, California; Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio (C.L.S.); Department of Neuroscience and Biomedical Engineering, Aalto University, Espoo, Finland (M.P., S.S., T.T., A.K.); and Cleave Therapeutics, Inc., San Francisco, California (J.D.V.)
| | - Timothy Ton
- Gavin Herbert Eye Institute, Department of Ophthalmology (H.L., C.L.S., J.Z., K.P.), Department of Physiology & Biophysics (K.P.), Department of Chemistry (K.P.), and Division of Genetics and Genomic Medicine, Department of Pediatrics (C.C., A.S., L.W., L.T., T.T., V.K.), University of California Irvine, Irvine, California; Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio (C.L.S.); Department of Neuroscience and Biomedical Engineering, Aalto University, Espoo, Finland (M.P., S.S., T.T., A.K.); and Cleave Therapeutics, Inc., San Francisco, California (J.D.V.)
| | - Ari Koskelainen
- Gavin Herbert Eye Institute, Department of Ophthalmology (H.L., C.L.S., J.Z., K.P.), Department of Physiology & Biophysics (K.P.), Department of Chemistry (K.P.), and Division of Genetics and Genomic Medicine, Department of Pediatrics (C.C., A.S., L.W., L.T., T.T., V.K.), University of California Irvine, Irvine, California; Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio (C.L.S.); Department of Neuroscience and Biomedical Engineering, Aalto University, Espoo, Finland (M.P., S.S., T.T., A.K.); and Cleave Therapeutics, Inc., San Francisco, California (J.D.V.)
| | - Jesse D Vargas
- Gavin Herbert Eye Institute, Department of Ophthalmology (H.L., C.L.S., J.Z., K.P.), Department of Physiology & Biophysics (K.P.), Department of Chemistry (K.P.), and Division of Genetics and Genomic Medicine, Department of Pediatrics (C.C., A.S., L.W., L.T., T.T., V.K.), University of California Irvine, Irvine, California; Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio (C.L.S.); Department of Neuroscience and Biomedical Engineering, Aalto University, Espoo, Finland (M.P., S.S., T.T., A.K.); and Cleave Therapeutics, Inc., San Francisco, California (J.D.V.)
| | - Virginia Kimonis
- Gavin Herbert Eye Institute, Department of Ophthalmology (H.L., C.L.S., J.Z., K.P.), Department of Physiology & Biophysics (K.P.), Department of Chemistry (K.P.), and Division of Genetics and Genomic Medicine, Department of Pediatrics (C.C., A.S., L.W., L.T., T.T., V.K.), University of California Irvine, Irvine, California; Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio (C.L.S.); Department of Neuroscience and Biomedical Engineering, Aalto University, Espoo, Finland (M.P., S.S., T.T., A.K.); and Cleave Therapeutics, Inc., San Francisco, California (J.D.V.)
| | - Krzysztof Palczewski
- Gavin Herbert Eye Institute, Department of Ophthalmology (H.L., C.L.S., J.Z., K.P.), Department of Physiology & Biophysics (K.P.), Department of Chemistry (K.P.), and Division of Genetics and Genomic Medicine, Department of Pediatrics (C.C., A.S., L.W., L.T., T.T., V.K.), University of California Irvine, Irvine, California; Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio (C.L.S.); Department of Neuroscience and Biomedical Engineering, Aalto University, Espoo, Finland (M.P., S.S., T.T., A.K.); and Cleave Therapeutics, Inc., San Francisco, California (J.D.V.)
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Functional modulation of phosphodiesterase-6 by calcium in mouse rod photoreceptors. Sci Rep 2021; 11:8938. [PMID: 33903621 PMCID: PMC8076185 DOI: 10.1038/s41598-021-88140-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2021] [Accepted: 04/07/2021] [Indexed: 02/02/2023] Open
Abstract
Phosphodiesterase-6 (PDE6) is a key protein in the G-protein cascade converting photon information to bioelectrical signals in vertebrate photoreceptor cells. Here, we demonstrate that PDE6 is regulated by calcium, contrary to the common view that PDE1 is the unique PDE class whose activity is modulated by intracellular Ca2+. To broaden the operating range of photoreceptors, mammalian rod photoresponse recovery is accelerated mainly by two calcium sensor proteins: recoverin, modulating the lifetime of activated rhodopsin, and guanylate cyclase-activating proteins (GCAPs), regulating the cGMP synthesis. We found that decreasing rod intracellular Ca2+ concentration accelerates the flash response recovery and increases the basal PDE6 activity (βdark) maximally by ~ 30% when recording local electroretinography across the rod outer segment layer from GCAPs-/- recoverin-/- mice. Our modeling shows that a similar elevation in βdark can fully explain the observed acceleration of flash response recovery in low Ca2+. Additionally, a reduction of the free Ca2+ in GCAPs-/- recoverin-/- rods shifted the inhibition constants of competitive PDE inhibitor 3-isobutyl-1-methylxanthine (IBMX) against the thermally activated and light-activated forms of PDE6 to opposite directions, indicating a complex interaction between IBMX, PDE6, and calcium. The discovered regulation of PDE6 is a previously unknown mechanism in the Ca2+-mediated modulation of rod light sensitivity.
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Bonezzi PJ, Tarchick MJ, Renna JM. Ex vivo electroretinograms made easy: performing ERGs using 3D printed components. J Physiol 2020; 598:4821-4842. [PMID: 32886799 DOI: 10.1113/jp280014] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2020] [Accepted: 09/02/2020] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Rod and cone photoreceptors convert light into electrochemical signals that are transferred to second order cells, initiating image-forming visual processing. Electroretinograms (ERGs) can detect the associated light-induced extracellular transretinal events, allowing for physiological assessment of cellular activity from morphologically intact retinas. We outline a method for economically configuring a traditional patch-clamp rig for performing high signal-to-noise ex vivo ERGs. We accomplish this by incorporating various 3D printed components and by modifying existing light pathways in a typical patch-clamp rig. This methodology provides an additional set of tools to labs interested in studying the physiological function of neuronal populations in isolated retinal tissue. ABSTRACT Rod and cone photoreceptors of the retina are responsible for the initial stages in vision and convey sensory information regarding our visual world across a wide range of lighting conditions. These photoreceptors hyperpolarize in the presence of light and subsequently transmit signals to second-order bipolar and horizontal cells. The electrical components of these events are experimentally detectable, and in conjunction with pharmacological agents, can be further separated into their respective cellular contributions using electroretinograms (ERGs). Extracellular activity from populations of rods and cones generate the negative-going a-wave, while ON-bipolar cells generate positive-going b-waves. ERGs can be performed in vivo or alternatively using an ex vivo configuration, where retinas are isolated and transretinal photovoltages are recorded at high signal-to-noise ratios. However, most ERG set-ups require their own unique set of tools. We demonstrate how, at low cost, to reconfigure a typical patch-clamp rig for ERG recordings. The bulk of these modifications require implementation of various 3D printed components, which can alternatively aid in generating a stand-alone ERG set-up without a patch-rig. Further, we discuss how to configure an ERG system without a patch-clamp rig. Compared to in vivo ERGs, these are superior when measuring small responses, such as those that are cone-evoked or those from immature mouse retinae. This recording configuration provides high signal-to-noise detection of a-waves (300-600 µV) and b-waves (1-3 mV), and is ultimately capable of discerning small (1-2 µV) photovoltages from noise. These quick and economical modifications allow researchers to equip their technical arsenal with an interchangeable patch-clamp/ERG system.
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Vinberg F, Palczewska G, Zhang J, Komar K, Wojtkowski M, Kefalov VJ, Palczewski K. Sensitivity of Mammalian Cone Photoreceptors to Infrared Light. Neuroscience 2019; 416:100-108. [PMID: 31400484 PMCID: PMC6815255 DOI: 10.1016/j.neuroscience.2019.07.047] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2019] [Revised: 07/19/2019] [Accepted: 07/29/2019] [Indexed: 11/26/2022]
Abstract
Two-photon vision arises from the perception of pulsed infrared (IR) laser light as color corresponding to approximately half of the laser wavelength. The physical process responsible for two-photon vision in rods has been delineated and verified experimentally only recently. Here, we sought to determine whether IR light can also be perceived by mammalian cone photoreceptors via a similar activation mechanism. To investigate selectively mammalian cone signaling in mice, we used animals with disabled rod signal transduction. We found that, contrary to the expected progressive sensitivity decrease based on the one-photon cone visual pigment spectral template, the sensitivity of mouse cone photoreceptors decreases only up to 800 nm and then increases at 900 nm and 1000 nm. Similarly, in experiments with the parafoveal region of macaque retinas, we found that the spectral sensitivity of primate cones diverged above the predicted one-photon spectral sensitivity template beyond 800 nm. In both cases, efficient detection of IR light was dependent on minimizing the dispersion of the ultrashort light pulses, indicating a non-linear two-photon activation process. Together, our studies demonstrate that mammalian cones can be activated by near IR light by a nonlinear two-photon excitation. Our results pave the way for the creation of a two-photon IR-based ophthalmoscope for the simultaneous imaging and functional testing of human retinas as a novel tool for the diagnosis and treatment of a wide range of visual disorders.
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Affiliation(s)
- Frans Vinberg
- John A. Moran Eye Center, University of Utah, 65 Mario Capecchi Drive, Salt Lake City, UT 84132, USA
| | - Grazyna Palczewska
- Polgenix, Inc., Department of Medical Devices, 5171 California Ave., Suite 150, Irvine, CA, USA 92617
| | - Jianye Zhang
- Gavin Herbert Eye Institute, Department of Ophthalmology, University of California, Irvine, CA, USA 92697
| | - Katarzyna Komar
- Institute of Physics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University in Torun, Grudziadzka 5, 87-100, Torun, Poland; Baltic Institute of Technology, Al. Zwyciestwa 96/98, 81-451, Gdynia, Poland
| | - Maciej Wojtkowski
- Baltic Institute of Technology, Al. Zwyciestwa 96/98, 81-451, Gdynia, Poland; Department of Physical Chemistry of Biological Systems, Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka Str. 44/52, 01-224, Warsaw, Poland
| | - Vladimir J Kefalov
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, 660 S. Euclid Avenue, Saint Louis, MO 63110, USA
| | - Krzysztof Palczewski
- Gavin Herbert Eye Institute, Department of Ophthalmology, University of California, Irvine, CA, USA 92697.
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Determination of basal phosphodiesterase activity in mouse rod photoreceptors with cGMP clamp. Sci Rep 2019; 9:1183. [PMID: 30718640 PMCID: PMC6362171 DOI: 10.1038/s41598-018-37661-w] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2018] [Accepted: 12/11/2018] [Indexed: 12/26/2022] Open
Abstract
Light regulates cGMP concentration in the photoreceptor cytoplasm by activating phosphodiesterase (PDE) molecules through a G-protein signalling cascade. Spontaneous PDE activity is present in rod outer segments even in darkness. This basal PDE activity (βdark) has not been determined in wild type mammalian photoreceptor cells although it plays a key role in setting the sensitivity and recovery kinetics of rod responses. We present a novel method for determination of βdark using local electroretinography (LERG) from isolated mouse retinas. The method is based on the ability of PDE inhibitors to decrease βdark, which can be counterbalanced by increasing PDE activity with light. This procedure clamps cytoplasmic cGMP to its dark value. βdark can be calculated based on the amount of light needed for the "cGMP clamp" and information extracted from the registered rod photoresponses. Here we apply this method to determine βdark values for the first time in the mammalian rods and obtain the following estimates for different mouse models: 3.9 s-1 for wild type, 4.5 s-1 for guanylate cyclase activating proteins (GCAPs) knockout, and 4.4 s-1 for GCAPs and recoverin double knockout mice. Our results suggest that depletion of GCAPs or recoverin do not affect βdark.
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Schwarz C, Sharma R, Cheong SK, Keller M, Williams DR, Hunter JJ. Selective S Cone Damage and Retinal Remodeling Following Intense Ultrashort Pulse Laser Exposures in the Near-Infrared. Invest Ophthalmol Vis Sci 2018; 59:5973-5984. [PMID: 30556839 PMCID: PMC6298064 DOI: 10.1167/iovs.18-25383] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2018] [Accepted: 10/30/2018] [Indexed: 02/06/2023] Open
Abstract
Purpose Infrared ultrashort pulse lasers are becoming increasingly popular for applications in the living eye. However, safety standards are not yet well established. Here we investigate retinal damage close to threshold for this pulse regime in the living macaque eye. Methods Retinal radiant exposures between 214 and 856 J/cm2 were delivered to the photoreceptor layer with an ultrashort pulse laser (730 nm, 55 fs, 80 MHz) through a two-photon adaptive optics scanning light ophthalmoscope. Retinal exposures were followed up immediately after and over several weeks with high-resolution reflectance and two-photon excited fluorescence ophthalmoscopy, providing structural and functional information. Results Retinal radiant exposures of 856 J/cm2 resulted in permanent S cone damage. Immediately after the exposure, the affected cones emitted about 2.6 times less two-photon excited fluorescence (TPEF) and showed an altered TPEF time course. Several weeks after the initial exposure, S cone outer and inner segments had disappeared. The space was filled by rods in the peripheral retina and cones near the fovea. Conclusion Interestingly, S cones are the receptor class with the lowest sensitivity in the near-infrared but are known to be particularly susceptible to ultraviolet and blue light. This effect of selective S cone damage after intense infrared ultrashort pulse laser exposure may be due to nonlinear absorption and distinct from pure thermal and mechanical mechanisms often associated with ultrashort pulse lasers.
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Affiliation(s)
- Christina Schwarz
- Center for Visual Science, University of Rochester, Rochester, New York, United States
| | - Robin Sharma
- Facebook Reality Labs, Redmond, Washington, United States
| | - Soon Keen Cheong
- Center for Visual Science, University of Rochester, Rochester, New York, United States
| | - Matthew Keller
- Center for Visual Science, University of Rochester, Rochester, New York, United States
- College of Natural Science, Michigan State University, East Lansing, Michigan, United States
| | - David R. Williams
- Center for Visual Science, University of Rochester, Rochester, New York, United States
- The Institute of Optics, University of Rochester, Rochester, New York, United States
- Flaum Eye Institute, University of Rochester, Rochester, New York, United States
| | - Jennifer J. Hunter
- Center for Visual Science, University of Rochester, Rochester, New York, United States
- The Institute of Optics, University of Rochester, Rochester, New York, United States
- Flaum Eye Institute, University of Rochester, Rochester, New York, United States
- Department of Biomedical Engineering, University of Rochester, Rochester, New York, United States
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10
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Electrophysiological determination of phosphodiesterase-6 inhibitor inhibition constants in intact mouse retina. Toxicol Appl Pharmacol 2018. [DOI: 10.1016/j.taap.2018.03.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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11
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Bonezzi PJ, Stabio ME, Renna JM. The Development of Mid-Wavelength Photoresponsivity in the Mouse Retina. Curr Eye Res 2018; 43:666-673. [PMID: 29447486 DOI: 10.1080/02713683.2018.1433859] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
PURPOSE Photoreceptors in the mouse retina express much of the molecular machinery necessary for phototransduction and glutamatergic transmission prior to eye opening at postnatal day 13 (P13). Light responses have been observed collectively from rod and cone photoreceptors via electroretinogram recordings as early as P13 in mouse, and the responses are known to become more robust with maturation, reaching a mature state by P30. Photocurrents from single rod outer segments have been recorded at P12, but no earlier, and similar studies on cone photoreceptors have been done, but only in the adult mouse retina. In this study, we wanted to document the earliest time point in which outer retinal photoreceptors in the mouse retina begin to respond to mid-wavelength light. METHODS Ex-vivo electroretinogram recordings were made from isolated mouse retinae at P7, P8, P9, P10, and P30 at seven different flash energies (561 nm). The a-wave was pharmacologically isolated and measured at each developmental time point across all flash energies. RESULTS Outer-retinal photoreceptors generated a detectable response to mid-wavelength light as early as P8, but only at photopic flash energies. a-wave intensity response curves and kinetic response properties are similar to the mature retina as early as P10. CONCLUSION These data represent the earliest recorded outer retinal light responses in the rodent. Photoreceptors are electrically functional and photoresponsive prior to eye opening, and much earlier than previously thought. Prior to eye opening, critical developmental processes occur that have been thought to be independent of outer retinal photic modulation. However, these data suggest light acting through outer-retinal photoreceptors has the potential to shape these critical developmental processes.
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Affiliation(s)
- Paul J Bonezzi
- a Department of Biology , The University of Akron , Akron , Ohio , USA
| | - Maureen E Stabio
- b Department of Cell and Developmental Biology , University of Colorado School of Medicine , Aurora , CO , USA
| | - Jordan M Renna
- a Department of Biology , The University of Akron , Akron , Ohio , USA
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12
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Abstract
This study introduces a novel retinal temperature determination method based on the temperature dependent properties of photoresponses recorded by electroretinography (ERG). The kinetics and amplitudes of ERG photoresponses depend on retinal temperature. Additionally, raising retinal temperature increases the probability of long-wavelength photon absorption, which manifests as temperature dependence of photoreceptor sensitivity. In this study we extract a number of features that represent these properties from the a- and b-waves of mouse ex vivo ERG flash responses and construct three multivariable regression models between temperature and the selected features. The performance of these models was evaluated against a separate test dataset and for two of the models, an RMS temperature determination error of less than 0.50 °C could be reached. Our results demonstrate that the method can be successfully used for reliable retinal temperature determination ex vivo. The method, reflecting the temperature of distal retina, can be applied also in the estimation of retinal pigment epithelium temperature.
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Zhou Z, Vinberg F, Schottler F, Doggett TA, Kefalov VJ, Ferguson TA. Autophagy supports color vision. Autophagy 2016; 11:1821-32. [PMID: 26292183 DOI: 10.1080/15548627.2015.1084456] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Cones comprise only a small portion of the photoreceptors in mammalian retinas. However, cones are vital for color vision and visual perception, and their loss severely diminishes the quality of life for patients with retinal degenerative diseases. Cones function in bright light and have higher demand for energy than rods; yet, the mechanisms that support the energy requirements of cones are poorly understood. One such pathway that potentially could sustain cones under basal and stress conditions is macroautophagy. We addressed the role of macroautophagy in cones by examining how the genetic block of this pathway affects the structural integrity, survival, and function of these neurons. We found that macroautophagy was not detectable in cones under normal conditions but was readily observed following 24 h of fasting. Consistent with this, starvation induced phosphorylation of AMPK specifically in cones indicating cellular starvation. Inhibiting macroautophagy in cones by deleting the essential macroautophagy gene Atg5 led to reduced cone function following starvation suggesting that cones are sensitive to systemic changes in nutrients and activate macroautophagy to maintain their function. ATG5-deficiency rendered cones susceptible to light-induced damage and caused accumulation of damaged mitochondria in the inner segments, shortening of the outer segments, and degeneration of all cone types, revealing the importance of mitophagy in supporting cone metabolic needs. Our results demonstrate that macroautophagy supports the function and long-term survival of cones providing for their unique metabolic requirements and resistance to stress. Targeting macroautophagy has the potential to preserve cone-mediated vision during retinal degenerative diseases.
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Affiliation(s)
- Zhenqing Zhou
- a Department of Ophthalmology and Visual Sciences, Washington University in St. Louis; School of Medicine ; St. Louis , MO USA
| | - Frans Vinberg
- a Department of Ophthalmology and Visual Sciences, Washington University in St. Louis; School of Medicine ; St. Louis , MO USA
| | - Frank Schottler
- a Department of Ophthalmology and Visual Sciences, Washington University in St. Louis; School of Medicine ; St. Louis , MO USA
| | - Teresa A Doggett
- a Department of Ophthalmology and Visual Sciences, Washington University in St. Louis; School of Medicine ; St. Louis , MO USA
| | - Vladimir J Kefalov
- a Department of Ophthalmology and Visual Sciences, Washington University in St. Louis; School of Medicine ; St. Louis , MO USA
| | - Thomas A Ferguson
- a Department of Ophthalmology and Visual Sciences, Washington University in St. Louis; School of Medicine ; St. Louis , MO USA
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14
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Sakurai K, Vinberg F, Wang T, Chen J, Kefalov VJ. The Na(+)/Ca(2+), K(+) exchanger 2 modulates mammalian cone phototransduction. Sci Rep 2016; 6:32521. [PMID: 27580676 PMCID: PMC5007492 DOI: 10.1038/srep32521] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2016] [Accepted: 08/04/2016] [Indexed: 12/15/2022] Open
Abstract
Calcium ions (Ca2+) modulate the phototransduction cascade of vertebrate cone photoreceptors to tune gain, inactivation, and light adaptation. In darkness, the continuous current entering the cone outer segment through cGMP-gated (CNG) channels is carried in part by Ca2+, which is then extruded back to the extracellular space. The mechanism of Ca2+ extrusion from mammalian cones is not understood. The dominant view has been that the cone-specific isoform of the Na+/Ca2+, K+ exchanger, NCKX2, is responsible for removing Ca2+ from their outer segments. However, indirect evaluation of cone function in NCKX2-deficient (Nckx2−/−) mice by electroretinogram recordings revealed normal photopic b-wave responses. This unexpected result suggested that NCKX2 may not be involved in the Ca2+ homeostasis of mammalian cones. To address this controversy, we examined the expression of NCKX2 in mouse cones and performed transretinal recordings from Nckx2−/− mice to determine the effect of NCKX2 deletion on cone function directly. We found that Nckx2−/− cones exhibit compromised phototransduction inactivation, slower response recovery and delayed background adaptation. We conclude that NCKX2 is required for the maintenance of efficient Ca2+ extrusion from mouse cones. However, surprisingly, Nckx2−/− cones adapted normally in steady background light, indicating the existence of additional Ca2+-extruding mechanisms in mammalian cones.
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Affiliation(s)
- Keisuke Sakurai
- Department of Ophthalmology and Visual Sciences, Washington University, Saint Louis, MO 63110, USA
| | - Frans Vinberg
- Department of Ophthalmology and Visual Sciences, Washington University, Saint Louis, MO 63110, USA
| | - Tian Wang
- Zilkha Neurogenetic Institute, Department of Cell and Neurobiology &Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA
| | - Jeannie Chen
- Zilkha Neurogenetic Institute, Department of Cell and Neurobiology &Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA
| | - Vladimir J Kefalov
- Department of Ophthalmology and Visual Sciences, Washington University, Saint Louis, MO 63110, USA
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15
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Adhikari P, Feigl B, Zele AJ. Rhodopsin and Melanopsin Contributions to the Early Redilation Phase of the Post-Illumination Pupil Response (PIPR). PLoS One 2016; 11:e0161175. [PMID: 27548480 PMCID: PMC4993463 DOI: 10.1371/journal.pone.0161175] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2016] [Accepted: 08/01/2016] [Indexed: 12/03/2022] Open
Abstract
Melanopsin expressing intrinsically photosensitive Retinal Ganglion Cells (ipRGCs) entirely control the post-illumination pupil response (PIPR) from 6 s post-stimulus to the plateau during redilation after light offset. However, the photoreceptor contributions to the early redilation phase of the PIPR (< 6 s post-stimulus) have not been reported. Here, we evaluated the photoreceptor contributions to the early phase PIPR (0.6 s to 5.0 s) by measuring the spectral sensitivity of the criterion PIPR amplitude in response to 1 s light pulses at five narrowband stimulus wavelengths (409, 464, 508, 531 and 592 nm). The retinal irradiance producing a criterion PIPR was normalised to the peak and fitted by either a single photopigment nomogram or the combined melanopsin and rhodopsin spectral nomograms with the +L+M cone photopic luminous efficiency (Vλ) function. We show that the PIPR spectral sensitivity at times ≥ 1.7 s after light offset is best described by the melanopsin nomogram. At times < 1.7 s, the peak PIPR sensitivity shifts to longer wavelengths (range: 482 to 498 nm) and is best described by the combined photoreceptor nomogram, with major contributions from melanopsin and rhodopsin. This first report of melanopsin and rhodopsin contributions to the early phase PIPR is in line with the electrophysiological findings of ipRGC and rod signalling after the cessation of light stimuli and provides a cut-off time for isolating photoreceptor specific function in healthy and diseased eyes.
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Affiliation(s)
- Prakash Adhikari
- Visual Science and Medical Retina Laboratories, Institute of Health and Biomedical Innovation, Queensland University of Technology (QUT), Brisbane, Queensland, Australia
- School of Optometry and Vision Science, Queensland University of Technology (QUT), Brisbane, Queensland, Australia
| | - Beatrix Feigl
- Visual Science and Medical Retina Laboratories, Institute of Health and Biomedical Innovation, Queensland University of Technology (QUT), Brisbane, Queensland, Australia
- School of Biomedical Sciences, Queensland University of Technology (QUT), Brisbane, Queensland, Australia
- Queensland Eye Institute, Brisbane, Queensland, Australia
| | - Andrew J. Zele
- Visual Science and Medical Retina Laboratories, Institute of Health and Biomedical Innovation, Queensland University of Technology (QUT), Brisbane, Queensland, Australia
- School of Optometry and Vision Science, Queensland University of Technology (QUT), Brisbane, Queensland, Australia
- * E-mail:
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16
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Leinonen H, Rossi M, Salo AM, Tiainen P, Hyvärinen J, Pitkänen M, Sormunen R, Miinalainen I, Zhang C, Soininen R, Kivirikko KI, Koskelainen A, Tanila H, Myllyharju J, Koivunen P. Lack of P4H-TM in mice results in age-related retinal and renal alterations. Hum Mol Genet 2016; 25:3810-3823. [DOI: 10.1093/hmg/ddw228] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2016] [Revised: 07/01/2016] [Accepted: 07/01/2016] [Indexed: 01/15/2023] Open
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17
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Vinberg F, Turunen TT, Heikkinen H, Pitkänen M, Koskelainen A. A novel Ca2+-feedback mechanism extends the operating range of mammalian rods to brighter light. ACTA ACUST UNITED AC 2016; 146:307-21. [PMID: 26415569 PMCID: PMC4586592 DOI: 10.1085/jgp.201511412] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
A previously unidentified calcium-dependent mechanism contributes to light adaptation in mammalian rods. Sensory cells adjust their sensitivity to incoming signals, such as odor or light, in response to changes in background stimulation, thereby extending the range over which they operate. For instance, rod photoreceptors are extremely sensitive in darkness, so that they are able to detect individual photons, but remain responsive to visual stimuli under conditions of bright ambient light, which would be expected to saturate their response given the high gain of the rod transduction cascade in darkness. These photoreceptors regulate their sensitivity to light rapidly and reversibly in response to changes in ambient illumination, thereby avoiding saturation. Calcium ions (Ca2+) play a major role in mediating the rapid, subsecond adaptation to light, and the Ca2+-binding proteins GCAP1 and GCAP2 (or guanylyl cyclase–activating proteins [GCAPs]) have been identified as important mediators of the photoreceptor response to changes in intracellular Ca2+. However, mouse rods lacking both GCAP1 and GCAP2 (GCAP−/−) still show substantial light adaptation. Here, we determined the Ca2+ dependency of this residual light adaptation and, by combining pharmacological, genetic, and electrophysiological tools, showed that an unknown Ca2+-dependent mechanism contributes to light adaptation in GCAP−/− mouse rods. We found that mimicking the light-induced decrease in intracellular [Ca2+] accelerated recovery of the response to visual stimuli and caused a fourfold decrease of sensitivity in GCAP−/− rods. About half of this Ca2+-dependent regulation of sensitivity could be attributed to the recoverin-mediated pathway, whereas half of it was caused by the unknown mechanism. Furthermore, our data demonstrate that the feedback mechanisms regulating the sensitivity of mammalian rods on the second and subsecond time scales are all Ca2+ dependent and that, unlike salamander rods, Ca2+-independent background-induced acceleration of flash response kinetics is rather weak in mouse rods.
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Affiliation(s)
- Frans Vinberg
- Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, FI-00076 Aalto, Finland Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, MO 63110
| | - Teemu T Turunen
- Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, FI-00076 Aalto, Finland
| | - Hanna Heikkinen
- Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, FI-00076 Aalto, Finland
| | - Marja Pitkänen
- Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, FI-00076 Aalto, Finland
| | - Ari Koskelainen
- Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, FI-00076 Aalto, Finland
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18
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Vinberg F, Wang T, Molday RS, Chen J, Kefalov VJ. A new mouse model for stationary night blindness with mutant Slc24a1 explains the pathophysiology of the associated human disease. Hum Mol Genet 2015; 24:5915-29. [PMID: 26246500 DOI: 10.1093/hmg/ddv319] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2015] [Accepted: 07/31/2015] [Indexed: 11/12/2022] Open
Abstract
Mutations that affect calcium homeostasis (Ca(2+)) in rod photoreceptors are linked to retinal degeneration and visual disorders such as retinitis pigmentosa and congenital stationary night blindness (CSNB). It is thought that the concentration of Ca(2+) in rod outer segments is controlled by a dynamic balance between influx via cGMP-gated (CNG) channels and extrusion via Na(+)/Ca(2+), K(+) exchangers (NCKX1). The extrusion-driven lowering of rod [Ca(2+)]i following light exposure controls their light adaptation and response termination. Mutant NCKX1 has been linked to autosomal-recessive stationary night blindness. However, whether NCKX1 contributes to light adaptation has not been directly tested and the mechanisms by which human NCKX1 mutations cause night blindness are not understood. Here, we report that the deletion of NCKX1 in mice results in malformed outer segment disks, suppressed expression and function of rod CNG channels and a subsequent 100-fold reduction in rod responses, while preserving normal cone responses. The compensating loss of CNG channel function in the absence of NCKX1-mediated Ca(2+) extrusion may prevent toxic Ca(2+) buildup and provides an explanation for the stationary nature of the associated disorder in humans. Surprisingly, the lack of NCKX1 did not compromise rod background light adaptation, suggesting additional Ca(2+)-extruding mechanisms exist in these cells.
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Affiliation(s)
- Frans Vinberg
- Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, MO, USA
| | - Tian Wang
- Cell and Neurobiology, Zilkha Neurogenetic Institute, University of Southern California, Los Angeles, CA, USA and
| | - Robert S Molday
- Biochemistry/Molecular Biology, University of British Columbia, Vancouver, Canada
| | - Jeannie Chen
- Cell and Neurobiology, Zilkha Neurogenetic Institute, University of Southern California, Los Angeles, CA, USA and
| | - Vladimir J Kefalov
- Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, MO, USA,
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Vinberg F, Kefalov V. Simultaneous ex vivo functional testing of two retinas by in vivo electroretinogram system. J Vis Exp 2015:e52855. [PMID: 25992809 DOI: 10.3791/52855] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
An In vivo electroretinogram (ERG) signal is composed of several overlapping components originating from different retinal cell types, as well as noise from extra-retinal sources. Ex vivo ERG provides an efficient method to dissect the function of retinal cells directly from an intact isolated retina of animals or donor eyes. In addition, ex vivo ERG can be used to test the efficacy and safety of potential therapeutic agents on retina tissue from animals or humans. We show here how commercially available in vivo ERG systems can be used to conduct ex vivo ERG recordings from isolated mouse retinas. We combine the light stimulation, electronic and heating units of a standard in vivo system with custom-designed specimen holder, gravity-controlled perfusion system and electromagnetic noise shielding to record low-noise ex vivo ERG signals simultaneously from two retinas with the acquisition software included in commercial in vivo systems. Further, we demonstrate how to use this method in combination with pharmacological treatments that remove specific ERG components in order to dissect the function of certain retinal cell types.
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Affiliation(s)
- Frans Vinberg
- Department of Ophthalmology and Visual Sciences, Washington University in St. Louis;
| | - Vladimir Kefalov
- Department of Ophthalmology and Visual Sciences, Washington University in St. Louis
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20
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Human infrared vision is triggered by two-photon chromophore isomerization. Proc Natl Acad Sci U S A 2014; 111:E5445-54. [PMID: 25453064 DOI: 10.1073/pnas.1410162111] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Vision relies on photoactivation of visual pigments in rod and cone photoreceptor cells of the retina. The human eye structure and the absorption spectra of pigments limit our visual perception of light. Our visual perception is most responsive to stimulating light in the 400- to 720-nm (visible) range. First, we demonstrate by psychophysical experiments that humans can perceive infrared laser emission as visible light. Moreover, we show that mammalian photoreceptors can be directly activated by near infrared light with a sensitivity that paradoxically increases at wavelengths above 900 nm, and display quadratic dependence on laser power, indicating a nonlinear optical process. Biochemical experiments with rhodopsin, cone visual pigments, and a chromophore model compound 11-cis-retinyl-propylamine Schiff base demonstrate the direct isomerization of visual chromophore by a two-photon chromophore isomerization. Indeed, quantum mechanics modeling indicates the feasibility of this mechanism. Together, these findings clearly show that human visual perception of near infrared light occurs by two-photon isomerization of visual pigments.
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Ex vivo ERG analysis of photoreceptors using an in vivo ERG system. Vision Res 2014; 101:108-17. [PMID: 24959652 DOI: 10.1016/j.visres.2014.06.003] [Citation(s) in RCA: 54] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2014] [Revised: 06/09/2014] [Accepted: 06/12/2014] [Indexed: 11/21/2022]
Abstract
The Function of the retina and effects of drugs on it can be assessed by recording transretinal voltage across isolated retina that is perfused with physiological medium. However, building ex vivo ERG apparatus requires substantial amount of time, resources and expertise. Here we adapted a commercial in vivo ERG system for transretinal ERG recordings from rod and cone photoreceptors and compared rod and cone signaling between ex vivo and in vivo environments. We found that the rod and cone a- and b-waves recorded with the transretinal ERG adapter and a standard in vivo ERG system are comparable to those obtained from live anesthetized animals. However, ex vivo responses are somewhat slower and their oscillatory potentials are suppressed as compared to those recorded in vivo. We found that rod amplification constant (A) was comparable between ex vivo and in vivo conditions, ∼10-30s(-2) depending on the choice of response normalization. We estimate that the A in cones is between 3 and 6s(-2) in ex vivo conditions and by assuming equal A in vivo we arrive to light funnelling factor of 3 for cones in the mouse retina. The ex vivo ERG adapter provides a simple and affordable alternative to designing a custom-built transretinal recordings setup for the study of photoreceptors. Our results provide a roadmap to the rigorous quantitative analysis of rod and cone responses made possible with such a system.
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22
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Sundermeier TR, Zhang N, Vinberg F, Mustafi D, Kohno H, Golczak M, Bai X, Maeda A, Kefalov VJ, Palczewski K. DICER1 is essential for survival of postmitotic rod photoreceptor cells in mice. FASEB J 2014; 28:3780-91. [PMID: 24812086 DOI: 10.1096/fj.14-254292] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Photoreceptor cell death is the proximal cause of blindness in many retinal degenerative disorders; hence, understanding the gene regulatory networks that promote photoreceptor survival is at the forefront of efforts to combat blindness. Down-regulation of the microRNA (miRNA)-processing enzyme DICER1 in the retinal pigmented epithelium has been implicated in geographic atrophy, an advanced form of age-related macular degeneration (AMD). However, little is known about the function of DICER1 in mature rod photoreceptor cells, another retinal cell type that is severely affected in AMD. Using a conditional-knockout (cKO) mouse model, we report that loss of DICER1 in mature postmitotic rods leads to robust retinal degeneration accompanied by loss of visual function. At 14 wk of age, cKO mice exhibit a 90% reduction in photoreceptor nuclei and a 97% reduction in visual chromophore compared with those in control littermates. Before degeneration, cKO mice do not exhibit significant defects in either phototransduction or the visual cycle, suggesting that miRNAs play a primary role in rod photoreceptor survival. Using comparative small RNA sequencing analysis, we identified rod photoreceptor miRNAs of the miR-22, miR-26, miR-30, miR-92, miR-124, and let-7 families as potential factors involved in regulating the survival of rods.
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Affiliation(s)
| | | | - Frans Vinberg
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, Saint Louis, Missouri, USA
| | | | | | | | | | - Akiko Maeda
- Department of Pharmacology, Department of Ophthalmology and Visual Sciences, Case Western Reserve University, School of Medicine, Cleveland, Ohio, USA; and
| | - Vladimir J Kefalov
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, Saint Louis, Missouri, USA
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Sundermeier TR, Vinberg F, Mustafi D, Bai X, Kefalov VJ, Palczewski K. R9AP overexpression alters phototransduction kinetics in iCre75 mice. Invest Ophthalmol Vis Sci 2014; 55:1339-47. [PMID: 24526444 DOI: 10.1167/iovs.13-13564] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
PURPOSE Determine the impact of rod photoreceptor-specific expression of Cre recombinase on the kinetics of phototransduction in the mouse eye and identify changes in gene expression that underlie any observed phenotypic differences. METHODS Transretinal ERG and single-cell suction electrode recordings were used to measure the kinetics of phototransduction in a mouse line exhibiting rod photoreceptor-specific Cre recombinase expression, and the results were compared with those from control non-Cre-expressing littermates. Gene expression changes were evaluated using RNA sequencing transcriptome analysis. The pattern of expression of Rgs9bp was determined by mapping sequencing reads to the mouse genome and performing 3'-rapid amplification of cDNA ends (3'-RACE). RESULTS Expression of the rod-specific iCre75 transgene was accompanied by accelerated phototransduction inactivation, likely due to overexpression of the Rgs9bp gene, which encodes the Rgs9 anchor protein (R9AP). R9AP upregulation stabilized the RGS9 GAP complex, altering phototransduction kinetics. 3'-Race identified an abundant, unexpected Rgs9bp-Prm1 fusion mRNA in Cre-expressing mouse retinas, which was determined to be derived from a second transgene present in the iCre75 line. CONCLUSIONS Here we report the presence of a second, R9AP-expressing transgene in the iCre75 mouse line, leading to altered kinetics of phototransduction. These results highlight an important caveat that must be considered when utilizing this mouse line for rod photoreceptor-specific gene loss of function studies.
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Reprogramming of adult rod photoreceptors prevents retinal degeneration. Proc Natl Acad Sci U S A 2013; 110:1732-7. [PMID: 23319618 DOI: 10.1073/pnas.1214387110] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
A prime goal of regenerative medicine is to direct cell fates in a therapeutically useful manner. Retinitis pigmentosa is one of the most common degenerative diseases of the eye and is associated with early rod photoreceptor death followed by secondary cone degeneration. We hypothesized that converting adult rods into cones, via knockdown of the rod photoreceptor determinant Nrl, could make the cells resistant to the effects of mutations in rod-specific genes, thereby preventing secondary cone loss. To test this idea, we engineered a tamoxifen-inducible allele of Nrl to acutely inactivate the gene in adult rods. This manipulation resulted in reprogramming of rods into cells with a variety of cone-like molecular, histologic, and functional properties. Moreover, reprogramming of adult rods achieved cellular and functional rescue of retinal degeneration in a mouse model of retinitis pigmentosa. These findings suggest that elimination of Nrl in adult rods may represent a unique therapy for retinal degeneration.
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Form and function of the M4 cell, an intrinsically photosensitive retinal ganglion cell type contributing to geniculocortical vision. J Neurosci 2012; 32:13608-20. [PMID: 23015450 DOI: 10.1523/jneurosci.1422-12.2012] [Citation(s) in RCA: 172] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The photopigment melanopsin confers photosensitivity upon a minority of retinal output neurons. These intrinsically photosensitive retinal ganglion cells (ipRGCs) are more diverse than once believed, comprising five morphologically distinct types, M1 through M5. Here, in mouse retina, we provide the first in-depth characterization of M4 cells, including their structure, function, and central projections. M4 cells apparently correspond to ON α cells of earlier reports, and are easily distinguished from other ipRGCs by their very large somata. Their dendritic arbors are more radiate and highly branched than those of M1, M2, or M3 cells. The melanopsin-based intrinsic photocurrents of M4 cells are smaller than those of M1 and M2 cells, presumably because melanopsin is more weakly expressed; we can detect it immunohistochemically only with strong amplification. Like M2 cells, M4 cells exhibit robust, sustained, synaptically driven ON responses and dendritic stratification in the ON sublamina of the inner plexiform layer. However, their stratification patterns are subtly different, with M4 dendrites positioned just distal to those of M2 cells and just proximal to the ON cholinergic band. M4 receptive fields are large, with an ON center, antagonistic OFF surround and nonlinear spatial summation. Their synaptically driven photoresponses lack direction selectivity and show higher ultraviolet sensitivity in the ventral retina than in the dorsal retina, echoing the topographic gradient in S- and M-cone opsin expression. M4 cells are readily labeled by retrograde transport from the dorsal lateral geniculate nucleus and thus likely contribute to the pattern vision that persists in mice lacking functional rods and cones.
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Cangiano L, Asteriti S, Cervetto L, Gargini C. The photovoltage of rods and cones in the dark-adapted mouse retina. J Physiol 2012; 590:3841-55. [PMID: 22641773 DOI: 10.1113/jphysiol.2011.226878] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Research on photoreceptors has led to important insights into how light signals are detected and processed in the outer retina. Most information about photoreceptor function, however, comes from lower vertebrates. The large majority of mammalian studies are based on suction pipette recordings of outer segment currents, a technique that doesn't allow examination of phenomena occurring downstream of phototransduction. Only a small number of whole-cell recordings have been made, mainly in the macaque. Due to the growing importance of the mouse in vision research, we have optimized a retinal slice preparation that allows the reliable collection of perforated-patch recordings from light responding rods and cones. Unexpectedly, the frequency of cone recordings was much higher than their numeric proportion of ∼3%. This allowed us to obtain direct functional evidence suggestive of rod–cone coupling in the mouse. Moreover, rods had considerably larger single photon responses than previously published for mammals (3.44 mV, SD 1.37, n = 19 at 24°C; 2.46 mV, SD 1.08, n = 10 at 36°C), and a relatively high signal/noise ratio (6.4, SD 1.8 at 24°C; 6.8, SD 2.8 at 36°C). Both findings imply a more favourable transmission at the rod–rod bipolar cell synapse. Accordingly, relatively few photoisomerizations were sufficient to elicit a half-maximal response (6.7, SD 2.7, n = 5 at 24°C; 10.6, SD 1.7, n = 3 at 36°C), leading to a narrow linear response range. Our study demonstrates new features of mammalian photoreceptors and opens the way for further investigations into photoreceptor function using retinas from mutant mouse models.
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Affiliation(s)
- Lorenzo Cangiano
- Department of Physiological Sciences, University of Pisa, Via San Zeno 31, I-56123 Pisa, Italy.
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Kolesnikov AV, Kefalov VJ. Transretinal ERG recordings from mouse retina: rod and cone photoresponses. J Vis Exp 2012:3424. [PMID: 22453300 DOI: 10.3791/3424] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
There are two distinct classes of image-forming photoreceptors in the vertebrate retina: rods and cones. Rods are able to detect single photons of light whereas cones operate continuously under rapidly changing bright light conditions. Absorption of light by rod- and cone-specific visual pigments in the outer segments of photoreceptors triggers a phototransduction cascade that eventually leads to closure of cyclic nucleotide-gated channels on the plasma membrane and cell hyperpolarization. This light-induced change in membrane current and potential can be registered as a photoresponse, by either classical suction electrode recording technique or by transretinal electroretinogram recordings (ERG) from isolated retinas with pharmacologically blocked postsynaptic response components. The latter method allows drug-accessible long-lasting recordings from mouse photoreceptors and is particularly useful for obtaining stable photoresponses from the scarce and fragile mouse cones. In the case of cones, such experiments can be performed both in dark-adapted conditions and following intense illumination that bleaches essentially all visual pigment, to monitor the process of cone photosensitivity recovery during dark adaptation. In this video, we will show how to perform rod- and M/L-cone-driven transretinal recordings from dark-adapted mouse retina. Rod recordings will be carried out using retina of wild type (C57Bl/6) mice. For simplicity, cone recordings will be obtained from genetically modified rod transducin α-subunit knockout (Tα(-/-)) mice which lack rod signaling(8).
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Affiliation(s)
- Alexander V Kolesnikov
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, Washington, USA.
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Reuter T. Fifty years of dark adaptation 1961–2011. Vision Res 2011; 51:2243-62. [DOI: 10.1016/j.visres.2011.08.021] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2010] [Revised: 08/24/2011] [Accepted: 08/24/2011] [Indexed: 02/07/2023]
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Abstract
A negative phototransduction feedback in rods and cones is critical for the timely termination of their light responses and for extending their function to a wide range of light intensities. The calcium feedback mechanisms that modulate phototransduction in rods have been studied extensively. However, the corresponding modulation mechanisms that enable cones to terminate rapidly their light responses and to adapt in bright light, properties critical for our daytime vision, are still not understood. In cones, calcium feedback to guanylyl cyclase is potentially a key step in phototransduction modulation. The guanylyl cyclase activity is modulated by the calcium-binding guanylyl cyclase activating proteins (GCAP1 and GCAP2). Here, we used single-cell and transretinal recordings from mouse to determine how GCAPs modulate dark-adapted responses as well as light adaptation in mammalian cones. Deletion of GCAPs increased threefold the amplitude and dramatically prolonged the light responses in dark-adapted mouse cones. It also reduced the operating range of mouse cones in background illumination and severely impaired their light adaptation. Thus, GCAPs exert powerful modulation on the mammalian cone phototransduction cascade and play an important role in setting the functional properties of cones in darkness and during light adaptation. Surprisingly, despite their better adaptation capacity and wider calcium dynamic range, mammalian cones were modulated by GCAPs to a lesser extent than mammalian rods. We conclude that a disparity in the strength of GCAP modulation cannot explain the differences in the dark-adapted properties or in the operating ranges of mammalian rods and cones.
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Heikkinen H, Vinberg F, Nymark S, Koskelainen A. Mesopic background lights enhance dark-adapted cone ERG flash responses in the intact mouse retina: a possible role for gap junctional decoupling. J Neurophysiol 2011; 105:2309-18. [PMID: 21389302 DOI: 10.1152/jn.00536.2010] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The cone-driven flash responses of mouse electroretinogram (ERG) increase as much as twofold over the course of several minutes during adaptation to a rod-compressing background light. The origins of this phenomenon were investigated in the present work by recording preflash-isolated (M-)cone flash responses ex vivo in darkness and during application of various steady background lights. In this protocol, the cone stimulating flash was preceded by a preflash that maintains rods under saturation (hyperpolarized) to allow selective stimulation of the cones at varying background light levels. The light-induced growth was found to represent true enhancement of cone flash responses with respect to their dark-adapted state. It developed within minutes, and its overall magnitude was a graded function of the background light intensity. The threshold intensity of cone response growth was observed with lights in the low mesopic luminance region, at which rod responses are partly compressed. Maximal effect was reached at intensities sufficient to suppress ∼ 90% of the rod responses. Light-induced enhancement of the cone photoresponses was not sensitive to antagonists and agonists of glutamatergic transmission. However, applying gap junction blockers to the dark-adapted retina produced qualitatively similar changes in the cone flash responses as did background light and prevented further growth during subsequent light-adaptation. These results are consistent with the idea that cone ERG photoresponses are suppressed in the dark-adapted mouse retina by gap junctional coupling between rods and cones. This coupling would then be gradually and reversibly removed by mesopic background lights, allowing larger functional range for the cone light responses.
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Affiliation(s)
- H Heikkinen
- Aalto University School of Science, Department of Biomedical Engineering and Computational Science, PO Box 12200, FI-00076 Aalto, Finland.
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Vinberg F, Koskelainen A. Calcium sets the physiological value of the dominant time constant of saturated mouse rod photoresponse recovery. PLoS One 2010; 5:e13025. [PMID: 20885958 PMCID: PMC2946398 DOI: 10.1371/journal.pone.0013025] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2010] [Accepted: 09/03/2010] [Indexed: 11/19/2022] Open
Abstract
Background The rate-limiting step that determines the dominant time constant (τD) of mammalian rod photoresponse recovery is the deactivation of the active phosphodiesterase (PDE6). Physiologically relevant Ca2+-dependent mechanisms that would affect the PDE inactivation have not been identified. However, recently it has been shown that τD is modulated by background light in mouse rods. Methodology/Principal Findings We used ex vivo ERG technique to record pharmacologically isolated photoreceptor responses (fast PIII component). We show a novel static effect of calcium on mouse rod phototransduction: Ca2+ shortens the dominant time constant (τD) of saturated photoresponse recovery, i.e., when extracellular free Ca2+ is decreased from 1 mM to ∼25 nM, the τD is reversibly increased ∼1.5–2-fold. Conclusions We conclude that the increase in τD during low Ca2+ treatment is not due to increased [cGMP], increased [Na+] or decreased [ATP] in rod outer segment (ROS). Also it cannot be due to protein translocation mechanisms. We suggest that a Ca2+-dependent mechanism controls the life time of active PDE.
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Affiliation(s)
- Frans Vinberg
- Department of Biomedical Engineering and Computational Science (BECS), Aalto University School of Science and Technology, Espoo, Finland
| | - Ari Koskelainen
- Department of Biomedical Engineering and Computational Science (BECS), Aalto University School of Science and Technology, Espoo, Finland
- * E-mail:
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Kefalov VJ, Cornwall MC, Fain GL. Physiological studies of the interaction between opsin and chromophore in rod and cone visual pigments. Methods Mol Biol 2010; 652:95-114. [PMID: 20552424 DOI: 10.1007/978-1-60327-325-1_5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The visual pigment in vertebrate photoreceptors is a G protein-coupled receptor that consists of a protein, opsin, covalently attached to a chromophore, 11-cis-retinal. Activation of the visual pigment by light triggers a transduction cascade that produces experimentally measurable electrical responses in photoreceptors. The interactions between opsin and chromophore can be investigated with electrophysiologial recordings in intact amphibian and mouse rod and cone photoreceptor cells. Here we describe methods for substituting the native chromophore with various chromophore analogs to investigate how specific parts of the chromophore affect the signaling properties of the visual pigment and the function of photoreceptors. We also describe methods for genetically substituting the native rod opsin gene with cone opsins or with mutant rod opsins to investigate and compare their signaling properties. These methods are useful not only for understanding the relation between the properties of visual pigments and the function of photoreceptors but also for understanding the mechanisms by which mutations in rod opsin produce night blindness and other visual disorders.
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Affiliation(s)
- Vladimir J Kefalov
- Department of Ophthalmology and Visual Sciences and Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, MO, USA
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Wang JS, Kefalov VJ. An alternative pathway mediates the mouse and human cone visual cycle. Curr Biol 2009; 19:1665-9. [PMID: 19781940 DOI: 10.1016/j.cub.2009.07.054] [Citation(s) in RCA: 102] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2009] [Revised: 07/17/2009] [Accepted: 07/20/2009] [Indexed: 10/20/2022]
Abstract
One of the fundamental mysteries of the human visual system is the continuous function of cone photoreceptors in bright daylight. As visual pigment is destroyed, or bleached, by light, cones require its rapid regeneration, which in turn involves rapid recycling of the pigment's chromophore. The canonical visual cycle for rod and cone pigments involves recycling of their chromophore from all-trans retinol to 11-cis retinal in the pigment epithelium, adjacent to photoreceptors. However, shortcomings of this pathway indicate the function of a second, cone-specific, mechanism for chromophore recycling. Indeed, biochemical and physiological studies on lower species have described a cone-specific visual cycle in addition to the long-known pigment epithelium pathway. Two important questions remain, however: what is the role of this pathway in the function of mammalian cones, and is it present in higher mammals, including humans? Here, we show that mouse, primate, and human neural retinas promote pigment regeneration and dark adaptation selectively in cones, but not in rods. This pathway supports rapid dark adaptation of mammalian cones and extends their dynamic range in background light independently of the pigment epithelium. This pigment-regeneration mechanism is essential for our daytime vision and appears to be evolutionarily conserved.
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Affiliation(s)
- Jin-Shan Wang
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, MO 63110, USA
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