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Karema-Jokinen V, Koskela A, Hytti M, Hongisto H, Viheriälä T, Liukkonen M, Torsti T, Skottman H, Kauppinen A, Nymark S, Kaarniranta K. Crosstalk of protein clearance, inflammasome, and Ca 2+ channels in retinal pigment epithelium derived from age-related macular degeneration patients. J Biol Chem 2023:104770. [PMID: 37137441 DOI: 10.1016/j.jbc.2023.104770] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2022] [Revised: 04/21/2023] [Accepted: 04/23/2023] [Indexed: 05/05/2023] Open
Abstract
Degeneration and/or dysfunction of retinal pigment epithelium (RPE) is generally detected as the formation of intra- and extracellular protein aggregates, called lipofuscin and drusen, respectively, in patients with age-related macular degeneration (AMD), the leading cause of blindness in the elderly population. These clinical hallmarks are linked to dysfunctional protein homeostasis and inflammation, and furthermore, are both regulated by changes in intracellular Ca2+ concentration. While many other cellular mechanisms have been considered in the investigations of AMD-RPE, there has been relatively little work on understanding the interactions of protein clearance, inflammation, and Ca2+ dynamics in disease pathogenesis. Here we established induced pluripotent stem cell-derived RPE from two patients with advanced AMD and from an age- and gender-matched control subject. We studied autophagy and inflammasome activation under disturbed proteostasis in these cell lines and investigated changes in their intracellular Ca2+ concentration and L-type voltage-gated Ca2+ channels. Our work demonstrated dysregulated autophagy and inflammasome activation in AMD-RPE accompanied by reduced intracellular free Ca2+ levels. Interestingly, we found currents through L-type voltage-gated Ca2+ channels to be diminished and showed these channels to be significantly localized to intracellular compartments in AMD-RPE. Taken together, the alterations in Ca2+ dynamics in AMD-RPE together with dysregulated autophagy and inflammasome activation indicate an important role for Ca2+ signaling in AMD pathogenesis, providing new avenues for the development of therapeutic approaches.
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Affiliation(s)
| | - Ali Koskela
- Department of Ophthalmology, University of Eastern Finland, Kuopio, Finland
| | - Maria Hytti
- School of Pharmacy, Faculty of Health Sciences, University of Eastern Finland, Kuopio, Finland
| | - Heidi Hongisto
- Faculty of Medicine and Health Technology, Tampere University, Tampere, Finland; Department of Ophthalmology, University of Eastern Finland, Kuopio, Finland
| | - Taina Viheriälä
- Faculty of Medicine and Health Technology, Tampere University, Tampere, Finland
| | - Mikko Liukkonen
- Department of Ophthalmology, University of Eastern Finland, Kuopio, Finland
| | - Tommi Torsti
- School of Pharmacy, Faculty of Health Sciences, University of Eastern Finland, Kuopio, Finland
| | - Heli Skottman
- Faculty of Medicine and Health Technology, Tampere University, Tampere, Finland
| | - Anu Kauppinen
- School of Pharmacy, Faculty of Health Sciences, University of Eastern Finland, Kuopio, Finland
| | - Soile Nymark
- Faculty of Medicine and Health Technology, Tampere University, Tampere, Finland.
| | - Kai Kaarniranta
- Department of Ophthalmology, University of Eastern Finland, Kuopio, Finland; Department of Ophthalmology, Kuopio University Hospital, Finland, Immuno-Ophthalmology, School of Pharmacy, University of Eastern Finland, Kuopio, Finland; Department of Molecular Genetics, University of Lodz, Lodz, Poland.
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Mamaeva D, Jazouli Z, DiFrancesco ML, Erkilic N, Dubois G, Hilaire C, Meunier I, Boukhaddaoui H, Kalatzis V. Novel roles for voltage-gated T-type Ca 2+ and ClC-2 channels in phagocytosis and angiogenic factor balance identified in human iPSC-derived RPE. FASEB J 2021; 35:e21406. [PMID: 33724552 DOI: 10.1096/fj.202002754r] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2020] [Revised: 01/13/2021] [Accepted: 01/19/2021] [Indexed: 01/26/2023]
Abstract
Human-induced pluripotent stem cell (hiPSC)-derived retinal pigment epithelium (RPE) is a powerful tool for pathophysiological studies and preclinical therapeutic screening, as well as a source for clinical cell transplantation. Thus, it must be validated for maturity and functionality to ensure correct data readouts and clinical safety. Previous studies have validated hiPSC-derived RPE as morphologically characteristic of the tissue in the human eye. However, information concerning the expression and functionality of ion channels is still limited. We screened hiPSC-derived RPE for the polarized expression of a panel of L-type (CaV 1.1, CaV 1.3) and T-type (CaV 3.1, CaV 3.3) Ca2+ channels, K+ channels (Maxi-K, Kir4.1, Kir7.1), and the Cl- channel ClC-2 known to be expressed in native RPE. We also tested the roles of these channels in key RPE functions using specific inhibitors. In addition to confirming the native expression profiles and function of certain channels, such as L-type Ca2+ channels, we show for the first time that T-type Ca2+ channels play a role in both phagocytosis and vascular endothelial growth factor (VEGF) secretion. Moreover, we demonstrate that Maxi-K and Kir7.1 channels are involved in the polarized secretion of VEGF and pigment epithelium-derived factor (PEDF). Furthermore, we show a novel localization for ClC-2 channel on the apical side of hiPSC-derived RPE, with an overexpression at the level of fluid-filled domes, and demonstrate that it plays an important role in phagocytosis, as well as VEGF and PEDF secretion. Taken together, hiPSC-derived RPE is a powerful model for advancing fundamental knowledge of RPE functions.
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Affiliation(s)
- Daria Mamaeva
- Institute for Neurosciences of Montpellier, Inserm, Montpellier University, Montpellier, France
| | - Zhour Jazouli
- Institute for Neurosciences of Montpellier, Inserm, Montpellier University, Montpellier, France
| | - Mattia L DiFrancesco
- Institute for Neurosciences of Montpellier, Inserm, Montpellier University, Montpellier, France
| | - Nejla Erkilic
- Institute for Neurosciences of Montpellier, Inserm, Montpellier University, Montpellier, France.,National Reference Centre for Inherited Sensory Diseases, Montpellier University, CHU, Montpellier, France
| | - Gregor Dubois
- Institute for Neurosciences of Montpellier, Inserm, Montpellier University, Montpellier, France
| | - Cecile Hilaire
- Institute for Neurosciences of Montpellier, Inserm, Montpellier University, Montpellier, France
| | - Isabelle Meunier
- Institute for Neurosciences of Montpellier, Inserm, Montpellier University, Montpellier, France.,National Reference Centre for Inherited Sensory Diseases, Montpellier University, CHU, Montpellier, France
| | - Hassan Boukhaddaoui
- Institute for Neurosciences of Montpellier, Inserm, Montpellier University, Montpellier, France
| | - Vasiliki Kalatzis
- Institute for Neurosciences of Montpellier, Inserm, Montpellier University, Montpellier, France
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Lee-Rivera I, López E, Alvarez-Arce A, López-Colomé AM. The PKC-ζ pseudosubstrate peptide induces glutamate release from retinal pigment epithelium cells through kinase- independent activation of Best1. Life Sci 2020; 265:118860. [PMID: 33301813 DOI: 10.1016/j.lfs.2020.118860] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2020] [Revised: 11/19/2020] [Accepted: 12/01/2020] [Indexed: 10/22/2022]
Abstract
AIMS The retinal pigment epithelium (RPE) is a highly specialized cell monolayer, that plays a key role in the maintenance of photoreceptor function and the blood-retina barrier (BRB). In this study, we found that a myristoylated pseudosubstrate of PKC-ζ (PKCζ PS), considered as a PKC-ζ inhibitor, plays a distinct role in RPE. MAIN METHODS We demonstrated that PKCζ PS stimulates the release of Glutamate (Glu) using in vitro3H-Glutamate release experiments. By western blot, kinase assays, and Fluoresence Ca+2 Concentration Measurements, we determined the cellular mechanisms involved in such release. KEY FINDINGS Surprisingly, PKCζ PS has no effect on either phosphorylation of T560, essential for catalytic activity, nor it has an effect on kinase activity. It induces the dose-dependent release of Glu by increasing intracellular Ca+2 levels. Interestingly, this release was not observed upon stimulation by other non-competitive PKC-ζ inhibitors. We here demonstrated that the PKCζ PS stimulates the release of Glutamate from RPE by activating the Ca2+-dependent Cl channel Bestrophin 1 (Best1). SIGNIFICANCE These results question PKCζ PS specificity as an inhibitor of this enzyme. Furthermore, the present results underline the relevance of clarifying the molecular mechanisms involved in glutamate release from the retina under conditions derived from excitotoxic stimuli.
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Affiliation(s)
- Irene Lee-Rivera
- Department of Molecular Neuropathology, Instituto de Fisiología Celular, UNAM, Apartado Postal 70-253, Ciudad Universitaria, México City, CdMx, Mexico
| | - Edith López
- Department of Molecular Neuropathology, Instituto de Fisiología Celular, UNAM, Apartado Postal 70-253, Ciudad Universitaria, México City, CdMx, Mexico
| | - Alejandro Alvarez-Arce
- Department of Molecular Neuropathology, Instituto de Fisiología Celular, UNAM, Apartado Postal 70-253, Ciudad Universitaria, México City, CdMx, Mexico
| | - Ana María López-Colomé
- Department of Molecular Neuropathology, Instituto de Fisiología Celular, UNAM, Apartado Postal 70-253, Ciudad Universitaria, México City, CdMx, Mexico.
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Giblin JP, Comes N, Strauss O, Gasull X. Ion Channels in the Eye: Involvement in Ocular Pathologies. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2015; 104:157-231. [PMID: 27038375 DOI: 10.1016/bs.apcsb.2015.11.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The eye is the sensory organ of vision. There, the retina transforms photons into electrical signals that are sent to higher brain areas to produce visual sensations. In the light path to the retina, different types of cells and tissues are involved in maintaining the transparency of avascular structures like the cornea or lens, while others, like the retinal pigment epithelium, have a critical role in the maintenance of photoreceptor function by regenerating the visual pigment. Here, we have reviewed the roles of different ion channels expressed in ocular tissues (cornea, conjunctiva and neurons innervating the ocular surface, lens, retina, retinal pigment epithelium, and the inflow and outflow systems of the aqueous humor) that are involved in ocular disease pathophysiologies and those whose deletion or pharmacological modulation leads to specific diseases of the eye. These include pathologies such as retinitis pigmentosa, macular degeneration, achromatopsia, glaucoma, cataracts, dry eye, or keratoconjunctivitis among others. Several disease-associated ion channels are potential targets for pharmacological intervention or other therapeutic approaches, thus highlighting the importance of these channels in ocular physiology and pathophysiology.
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Affiliation(s)
- Jonathan P Giblin
- Universitat de Barcelona, Barcelona, Spain; Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain
| | - Nuria Comes
- Universitat de Barcelona, Barcelona, Spain; Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain
| | | | - Xavier Gasull
- Universitat de Barcelona, Barcelona, Spain; Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain.
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Zhao PY, Gan G, Peng S, Wang SB, Chen B, Adelman RA, Rizzolo LJ. TRP Channels Localize to Subdomains of the Apical Plasma Membrane in Human Fetal Retinal Pigment Epithelium. Invest Ophthalmol Vis Sci 2015; 56:1916-23. [PMID: 25736794 DOI: 10.1167/iovs.14-15738] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
PURPOSE Calcium regulates many functions of the RPE. Its concentration in the subretinal space and RPE cytoplasm is closely regulated. Transient receptor potential (TRP) channels are a superfamily of ion channels that are moderately calcium-selective. This study investigates the subcellular localization and potential functions of TRP channels in a first-passage culture model of human fetal RPE (hfRPE). METHODS The RPE isolated from 15- to 16-week gestation fetuses were maintained in serum-free media. Cultures were treated with barium chloride (BaCl2) in the absence and presence of TRP channel inhibitors and monitored by the transepithelial electrical resistance (TER). The expression of TRP channels was determined using quantitative RT-PCR, immunoblotting, and immunofluorescence confocal microscopy. RESULTS Barium chloride substantially decreased TER and disrupted cell-cell contacts when added to the apical surface of RPE, but not when added to the basolateral surface. The effect could be partially blocked by the general TRP inhibitor, lanthanum chloride (LaCl3, ~75%), or an inhibitor of calpain (~25%). Family member-specific inhibitors, ML204 (TRPC4) and HC-067047 (TRPV4), had no effect on basal channel activity. Expression of TRPC4, TRPM1, TRPM3, TRPM7, and TRPV4 was detected by RT-PCR and immunoblotting. The TRPM3 localized to the base of the primary cilium, and TRPC4 and TRPM3 localized to apical tight junctions. The TRPV4 localized to apical microvilli in a small subset of cells. CONCLUSIONS The TRP channels localized to subdomains of the apical membrane, and BaCl2 was only able to dissociate tight junctions when presented to the apical membrane. The data suggest a potential role for TRP channels as sensors of [Ca(2+)] in the subretinal space.
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Affiliation(s)
- Peter Y Zhao
- Department of Surgery, Yale University, New Haven, Connecticut, United States
| | - Geliang Gan
- Department of Surgery, Yale University, New Haven, Connecticut, United States
| | - Shaomin Peng
- Department of Surgery, Yale University, New Haven, Connecticut, United States
| | - Shao-Bin Wang
- Department of Surgery, Yale University, New Haven, Connecticut, United States Department of Ophthalmology & Visual Science, Yale University, New Haven, Connecticut, United States
| | - Bo Chen
- Department of Ophthalmology & Visual Science, Yale University, New Haven, Connecticut, United States
| | - Ron A Adelman
- Department of Ophthalmology & Visual Science, Yale University, New Haven, Connecticut, United States
| | - Lawrence J Rizzolo
- Department of Surgery, Yale University, New Haven, Connecticut, United States Department of Ophthalmology & Visual Science, Yale University, New Haven, Connecticut, United States
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Activation of endogenously expressed ion channels by active complement in the retinal pigment epithelium. Pflugers Arch 2014; 467:2179-91. [PMID: 25427445 DOI: 10.1007/s00424-014-1656-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2014] [Revised: 11/07/2014] [Accepted: 11/13/2014] [Indexed: 10/24/2022]
Abstract
Defective regulation of the alternative pathway of the complement system is believed to contribute to damage of retinal pigment epithelial (RPE) cells in age-related macular degeneration. Thus we investigated the effect of complement activation on the RPE cell membrane by analyzing changes in membrane conductance via patch-clamp techniques and Ca(2+) imaging. Exposure of human ARPE-19 cells to complement-sufficient normal human serum (NHS) (25 %) resulted in a biphasic increase in intracellular free Ca(2+) ([Ca(2+)]i); an initial peak followed by sustained Ca(2+) increase. C5- or C7-depleted sera did not fully reproduce the signal generated by NHS. The initial peak of the Ca(2+) response was reduced by sarcoplasmic Ca(2+)-ATPase inhibitor thapsigargin, L-type channel blockers (R)-(+)-BayK8644 and isradipine, transient-receptor-potential (TRP) channel blocker ruthenium-red and ryanodine receptor blocker dantrolene. The sustained phase was carried by CaV1.3 L-type channels via tyrosine-phosphorylation. Changes in [Ca(2+)]I were accompanied by an abrupt hyperpolarization, resulting from a transient increase in membrane conductance, which was absent under extracellular Ca(2+)- or K(+)-free conditions and blocked by (R)-(+)-BayK8644 or paxilline, a maxiK channel inhibitor. Single-channel recordings confirmed the contribution of maxiK channels. Primary porcine RPE cells responded to NHS in a comparable manner. Pre-incubation with NHS reduced H2O2-induced cell death. In summary, in a concerted manner, C3a, C5a and sC5b-9 increased [Ca(2+)]i by ryanodine-receptor-dependent activation of L-type channels in addition to maxi-K channels and TRP channels absent from any insertion of a lytic pore.
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7
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Ion channels and transporters of the retinal pigment epithelium. Exp Eye Res 2014; 126:27-37. [DOI: 10.1016/j.exer.2014.05.005] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2013] [Revised: 05/02/2014] [Accepted: 05/12/2014] [Indexed: 12/19/2022]
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8
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Gómez NM, Tamm ER, Strauβ O. Role of bestrophin-1 in store-operated calcium entry in retinal pigment epithelium. Pflugers Arch 2012. [PMID: 23207577 DOI: 10.1007/s00424-012-1181-0] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The retinal pigment epithelium (RPE) expresses bestrophin-1 where mutant bestrophin cause retinal degenerations. Overexpression of bestrophin-1 demonstrated Ca(2+)-dependent Cl(-) channel function, whereas the RPE in bestrophin-1 knockout or mutant bestrophin-1 knock-in mice showed no change in Cl(-) conductance. To account for these apparently mutually exclusive findings, we investigated the function of endogenously expressed bestrophin-1 in a short-time RPE cell culture system by means of immunocytochemistry, Ca(2+) imaging, and siRNA knockdown. Immunocytochemical quantification of bestrophin-1 localization demonstrated 2.5 times higher co-localization with the endoplasmic reticulum (ER) Ca(2+)-sensor protein, Stim-1, than with the membrane protein β-catenin, implicating it in store-operated Ca(2+) entry (SOCE). Ca(2+) release from ER stores under extracellular Ca(2+)-free conditions using thapsigargin (1 μM) to inhibit endoplasmic Ca(2+) ATPase (SERCA) followed by re-adjustment of extracellular Ca(2+) to physiological levels activated SOCE, which was insensitive to the blocker of numerous transient receptor potential channels and voltage-dependent Ca(2+) channels SKF96563 (1 μM). SOCE was augmented at 5 μM and inhibited at 75 μM by 2-aminoethoxydiphenyl borate which indicates the involvement Orai-1 channels. In confirmation, SOCE was decreased by siRNA knockdown of Orai-1 expression. SOCE amplitude was strongly reduced by siRNA knockdown of bestrophin-1 expression, which was due to neither changes in Stim-1/Orai-1 expression nor Stim-1/bestrophin-1 interaction. The amount of Ca(2+) released by SERCA inhibition was reduced after siRNA knockdown of bestrophin-1, but not of Orai-1. In conclusion we found that a proportion of bestrophin-1 is functionally localized to ER Ca(2+) stores where it influences the amount of Ca(2+) and therefore Ca(2+) signals which result from activation of Orai-1 via Stim-1.
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Affiliation(s)
- Néstor Más Gómez
- Experimental Ophthalmology, Eye Hospital, University Medical Center Regensburg, Franz-Josef-Strauss-Allee 11, 93053, Regensburg, Germany
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Large RJ, Hollywood MA, Sergeant GP, Thornbury KD, Bourke S, Levick JR, McHale NG. Ionic currents in intimal cultured synoviocytes from the rabbit. Am J Physiol Cell Physiol 2010; 299:C1180-94. [PMID: 20720182 PMCID: PMC2980311 DOI: 10.1152/ajpcell.00028.2010] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Hyaluronan, a joint lubricant and regulator of synovial fluid content, is secreted by fibroblast-like synoviocytes lining the joint cavity, and secretion is greatly stimulated by Ca2+-dependent protein kinase C. This study aimed to define synoviocyte membrane currents and channels that may influence synoviocyte Ca2+ dynamics. Resting membrane potential ranged from −30 mV to −66 mV (mean −45 ± 8.60 mV, n = 40). Input resistance ranged from 0.54 GΩ to 2.6 GΩ (mean 1.28 ± 0.57 GΩ; ν = 33). Cell capacitance averaged 97.97 ± 5.93 pF. Voltage clamp using Cs+ pipette solution yielded a transient inward current that disappeared in Ca2+-free solutions and was blocked by 1 μM nifedipine, indicating an L-type calcium current. The current was increased fourfold by the calcium channel activator FPL 64176 (300 nM). Using K+ pipette solution, depolarizing steps positive to −40 mV evoked an outward current that showed kinetics and voltage dependence of activation and inactivation typical of the delayed rectifier potassium current. This was blocked by the nonspecific delayed rectifier blocker 4-aminopyridine. The synoviocytes expressed mRNA for four Kv1 subtypes (Kv1.1, Kv1.4, Kv1.5, and Kv1.6). Correolide (1 μM), margatoxin (100 nM), and α-dendrotoxin block these Kv1 subtypes, and all of these drugs significantly reduced synoviocyte outward current. The current was blocked most effectively by 50 nM κ-dendrotoxin, which is specific for channels containing a Kv1.1 subunit, indicating that Kv1.1 is critical, either as a homomultimeric channel or as a component of a heteromultimeric Kv1 channel. When 50 nM κ-dendrotoxin was added to current-clamped synoviocytes, the cells depolarized by >20 mV and this was accompanied by an increase in intracellular calcium concentration. Similarly, depolarization of the cells with high external potassium solution caused an increase in intracellular calcium, and this effect was greatly reduced by 1 μM nifedipine. In conclusion, fibroblast-like synoviocytes cultured from the inner synovium of the rabbit exhibit voltage-dependent inward and outward currents, including Ca2+ currents. They thus express ion channels regulating membrane Ca2+ permeability and electrochemical gradient. Since Ca2+-dependent kinases are major regulators of synovial hyaluronan secretion, the synoviocyte ion channels are likely to be important in the regulation of hyaluronan secretion.
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Affiliation(s)
- R J Large
- Smooth Muscle Research Centre, Dundalk Institute of Technology, Dundalk, Ireland
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Peltonen LM, Mänttäri S. Is there life in the horny layer? Dihydropyridine and ryanodine receptors in the skin of female and male chickens (Gallus domesticus). J Exp Biol 2008; 211:1394-401. [PMID: 18424673 DOI: 10.1242/jeb.014282] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Previous findings in pigeons and chickens show that Ca(2+) may be accumulated inside the cornified skin cells and that Ca(2+) microenvironments with a lower- or higher-than-blood concentration may exist in the skin. It has been suggested that the skin may function as a secretory pathway or a reservoir for Ca(2+) recycling. To test this hypothesis, we studied the dermis and epidermis of female and male chickens in vivo to find out whether cellular mechanisms exist for the accumulation, recycling or secretion of Ca(2+). For calcium influx and intracellular Ca(2+) release, respectively, the density of dihydropyridine receptors (DHPRs) and ryanodine receptors (RyRs) was examined, using high-affinity (-)-enantiomers of dihydropyridine and ryanodine labelled with fluorophores. To investigate Ca(2+) utilization in the skin, the systemic and local activity of the enzyme alkaline phosphatase (ALP) and the concentration of ionic Ca(2+) were measured in plasma and in cutaneous extracellular fluid, collected by suction blister technique. We found that both DHPRs and RyRs were present in all skin layers from dermis to horny layer. However, receptor densities were highest in the surface layers. With a basic calcium-rich diet, receptor densities were higher in males, particularly in the dermis and mid-epidermis. After a reduction in the nutritional Ca(2+) input, receptor densities in males decreased to the same level as in females, in which the receptor densities were not affected by the amount of Ca(2+) in the diet or that resulting from coming out of lay. The extracellular concentration of ionic Ca(2+) per se was not found to affect the density of DHPRs and RyRs in the skin. Spatially, RyRs seem to be located in the periphery of the sebokeratinocyte. ALP activity was shown to be lower in the extracellular fluid than in the plasma in both sexes. However, activity in both extracellular domains increased significantly in females that had come out of lay. This was probably connected with the increased osteoblast activity related to the reformation of structural bone. In conclusion, voltage-sensitive L-type Ca(2+) channels for ion influx and RyRs for Ca(2+) release are present in the cells of the skin of female and male chickens. Higher densities in the males receiving excessive Ca(2+) imply an increased capacity for Ca(2+) influx and intracellular processing. Even though the functional interactions between DHPRs and RyRs in the sebokeratinocytes could not be demonstrated, peripheral colocation and high receptor densities at the level of exocytosis of the lamellar bodies point to their role as part of a signalling pathway for secretion. The finding that DHPRs and RyRs are present in the horny layer implies that the function of the outermost skin might be more active than had been previously thought and that this function might be both secretory and sensory.
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Affiliation(s)
- Liisa M Peltonen
- Department of Biomedicine/Physiology, Biomedicum Helsinki, PO Box 63, 00014 University of Helsinki, Finland
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11
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Wimmers S, Coeppicus L, Rosenthal R, Strauß O. Expression profile of voltage-dependent Ca2+ channel subunits in the human retinal pigment epithelium. Graefes Arch Clin Exp Ophthalmol 2008; 246:685-92. [DOI: 10.1007/s00417-008-0778-7] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2007] [Revised: 01/14/2008] [Accepted: 01/18/2008] [Indexed: 11/30/2022] Open
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Kunzelmann K, Milenkovic VM, Spitzner M, Soria RB, Schreiber R. Calcium-dependent chloride conductance in epithelia: is there a contribution by Bestrophin? Pflugers Arch 2007; 454:879-89. [PMID: 17361457 DOI: 10.1007/s00424-007-0245-z] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2007] [Accepted: 02/26/2007] [Indexed: 01/09/2023]
Abstract
Although known for more than 20 years, the molecular identity of epithelial Ca(2+)-activated Cl(-) channels remains obscure. Previous candidate proteins did not hold initial promises, and thus, new hope is put into the recently identified family of bestrophin proteins, as they reflect many of the properties found for native channels. Mutations in the bestrophin gene cause an autosomal form of macular dystrophy of the retina. Bestrophin 1 is assumed to form the basolateral Ca(2+)-activated Cl(-) channel in the retinal pigment epithelium of the eye. Other data suggest that bestrophin is a regulator of voltage gated Ca(2+) channels. Structural information on bestrophins is available and a Cl(-) selective filter has been localized to the second transmembrane domain of bestrophin. It is possible that bestrophins function as physiologically regulated Cl(-) channels only in association with additional subunits and auxiliary proteins. Little is known about expression of bestrophin in gland acinar cells, which show a pronounced Ca(2+)-activated Cl(-) secretion. In airways and intestinal epithelia, bestrophins could be particularly important in diseases such as cystic fibrosis and secretory diarrhea.
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Affiliation(s)
- Karl Kunzelmann
- Institut für Physiologie, Universität Regensburg, Universitätsstrasse 31, 93053, Regensburg, Germany.
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Mergler S, Pleyer U. The human corneal endothelium: new insights into electrophysiology and ion channels. Prog Retin Eye Res 2007; 26:359-78. [PMID: 17446115 DOI: 10.1016/j.preteyeres.2007.02.001] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The corneal endothelium is a monolayer that mediates the flux of solutes and water across the posterior corneal surface. Thereby, it plays an essential role to maintain the transparency of the cornea. Unlike the epithelium, the human endothelium is an amitotic cell layer with a critical cell density and the risk of corneal decompensation. The number of endothelial cells subsequently decreases with age. Moreover, the endothelial cell loss is accelerated after various impairments such as surgical trauma (e.g. cataract extraction) and following corneal transplantation. This cell loss is associated with programmed cell death (apoptosis) and changed ion channel activity. However, little is known about the electrophysiology and ion channel expression (in particular Ca2+ channels) in corneal endothelial cells. This article reviews our current knowledge about the electrophysiology of the corneal endothelium. It highlights ion channel expression, which may have a major role in corneal cell physiology and pathological events. A better understanding of the (electro)physiological function of the cornea may lead to the development of clinical relevant new therapeutic and preventive measures.
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Affiliation(s)
- Stefan Mergler
- Department of Ophthalmology, Charité-University Medicine Berlin, Campus Virchow-Clinic, Augustenburger Platz 1, 13353 Berlin, Germany.
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Marmorstein LY, Wu J, McLaughlin P, Yocom J, Karl MO, Neussert R, Wimmers S, Stanton JB, Gregg RG, Strauss O, Peachey NS, Marmorstein AD. The light peak of the electroretinogram is dependent on voltage-gated calcium channels and antagonized by bestrophin (best-1). ACTA ACUST UNITED AC 2006; 127:577-89. [PMID: 16636205 PMCID: PMC2151522 DOI: 10.1085/jgp.200509473] [Citation(s) in RCA: 139] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Mutations in VMD2, encoding bestrophin (best-1), cause Best vitelliform macular dystrophy (BMD), adult-onset vitelliform macular dystrophy (AVMD), and autosomal dominant vitreoretinochoroidopathy (ADVIRC). BMD is distinguished from AVMD by a diminished electrooculogram light peak (LP) in the absence of changes in the flash electroretinogram. Although the LP is thought to be generated by best-1, we find enhanced LP luminance responsiveness with normal amplitude in Vmd2-/- mice and no differences in cellular Cl- currents in comparison to Vmd2+/+ littermates. The putative Ca2+ sensitivity of best-1, and our recent observation that best-1 alters the kinetics of voltage-dependent Ca2+ channels (VDCC), led us to examine the role of VDCCs in the LP. Nimodipine diminished the LP, leading us to survey VDCC beta-subunit mutant mice. Lethargic mice, which harbor a loss of function mutation in the beta4 subunit of VDCCs, exhibited a significant shift in LP luminance response, establishing a role for Ca2+ in LP generation. When stimulated with ATP, which increases [Ca++]I, retinal pigment epithelial cells derived from Vmd2-/- mice exhibited a fivefold greater response than Vmd2+/+ littermates, indicating that best-1 can suppress the rise in [Ca2+]I associated with the LP. We conclude that VDCCs regulated by a beta4 subunit are required to generate the LP and that best-1 antagonizes the LP luminance response potentially via its ability to modulate VDCC function. Furthermore, we suggest that the loss of vision associated with BMD is not caused by the same pathologic process as the diminished LP, but rather is caused by as yet unidentified effects of best-1 on other cellular processes.
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Affiliation(s)
- Lihua Y Marmorstein
- Department of Ophthalmology and Vision Science, University of Arizona, Tucson 85711, USA
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15
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Rosenthal R, Bakall B, Kinnick T, Peachey N, Wimmers S, Wadelius C, Marmorstein A, Strauss O. Expression of bestrophin‐1, the product of the VMD2 gene, modulates voltage‐dependent Ca
2+
channels in retinal pigment epithelial cells. FASEB J 2006; 20:178-80. [PMID: 16282372 DOI: 10.1096/fj.05-4495fje] [Citation(s) in RCA: 148] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Mutations in the VMD2 gene cause Best's disease, an inherited form of macular degeneration. The reduction in the light-peak amplitude in the patient's electro-oculogram suggests that bestrophin-1 influences the membrane conductance of the retinal pigment epithelium (RPE). Systemic application of the L-type Ca2+ channel blocker nimodipine reduced the light-peak amplitude in the rat electroretinogram but not a- and b-waves. Expression of bestrophin-1 in a RPE cell line (RPE-J) led to changes in L-type channel properties. Wild-type bestrophin-1 induced an acceleration of activation kinetics of Ba2+ currents through L-type Ca2+ channels and a shift of the voltage-dependent activation to more negative values, closer to the resting potential of RPE cells. Expression of bestrophin-1 with Best disease-causing mutations led to comparable shifts in voltage-dependent activation but different effects on activation and inactivation kinetics. Bestrophin W93C exhibited slowed activation and inactivation, and bestrophin R218C accelerated the activation and inactivation. Thus, transfection of RPE cells with bestrophin-1 distinctively changed L-type Ca2+ channel kinetics and voltage-dependence. On the basis of these data, we propose that presence of bestrophin-1 influences kinetics and voltage-dependence of voltage-dependent Ca2+ channels and that these effects might open new ways to understand the mechanisms leading to retinal degeneration in Best's disease.
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Affiliation(s)
- Rita Rosenthal
- Augenklinik, Charité-Universitaetsmedizin Berlin, Campus Benjamin Franklin, Berlin, Germany
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16
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Rosenthal R, Malek G, Salomon N, Peill-Meininghaus M, Coeppicus L, Wohlleben H, Wimmers S, Bowes Rickman C, Strauss O. The fibroblast growth factor receptors, FGFR-1 and FGFR-2, mediate two independent signalling pathways in human retinal pigment epithelial cells. Biochem Biophys Res Commun 2005; 337:241-7. [PMID: 16188231 DOI: 10.1016/j.bbrc.2005.09.028] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2005] [Accepted: 09/01/2005] [Indexed: 11/16/2022]
Abstract
To examine the effects and potential implications for the expression of the two basic fibroblast growth factor (bFGF) receptors, FGFR-1 and FGFR-2, in retinal pigment epithelial (RPE) cells, bFGF-dependent changes in gene expression and RPE cell function were studied. bFGF increased L-type Ca2+ channel activity of RPE cells, which in turn resulted in an increase of vascular endothelial growth factor A (VEGF-A) secretion from RPE cells. Also, both bFGF and direct stimulation of L-type Ca2+ channels by BayK8644 increased the expression of c-fos in RPE cells, to the same extent. bFGF-induced-c-fos expression was reduced by inhibition of FGFR-1, but not by L-type Ca2+ channel inhibition, demonstrating that stimulation of FGFR-1 results in a Ca2+ channel-independent change of gene expression. In contrast, stimulation of FGFR-2 results in a Ca2+ channel-dependent stimulation of VEGF secretion. Furthermore, immunohistological investigation of neovascular tissues obtained from patients with age-related macular degeneration (AMD) revealed FGFR-1 and FGFR-2 expression in the RPE of the diseased tissue. Our findings support the hypothesis that there are two different FGFR-1- and FGFR-2-dependent pathways that modulate the role of bFGF in induction of neovascularisation in AMD.
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Affiliation(s)
- Rita Rosenthal
- Augenklinik und Hochschulambulanz, Charité-Universitätsmedizin, Berlin Campus Benjamin Franklin, Berlin, Germany.
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17
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Abstract
Located between vessels of the choriocapillaris and light-sensitive outer segments of the photoreceptors, the retinal pigment epithelium (RPE) closely interacts with photoreceptors in the maintenance of visual function. Increasing knowledge of the multiple functions performed by the RPE improved the understanding of many diseases leading to blindness. This review summarizes the current knowledge of RPE functions and describes how failure of these functions causes loss of visual function. Mutations in genes that are expressed in the RPE can lead to photoreceptor degeneration. On the other hand, mutations in genes expressed in photoreceptors can lead to degenerations of the RPE. Thus both tissues can be regarded as a functional unit where both interacting partners depend on each other.
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Affiliation(s)
- Olaf Strauss
- Bereich Experimentelle Ophthalmologie, Klinik und Poliklinik fuer Augenheilkunde, Universitaetsklinikum Hamburg-Eppendorf, Martinistrasse 52, 20246 Hamburg, Germany.
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18
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Gao Q, Ge J. The Inhibition of Ca 2+ Influx Induced by Hypericin in Cultured Human Retinal Pigment Epithelial Cells Analyzed by Confocal Imaging. Ophthalmic Res 2005; 37:128-35. [PMID: 15821349 DOI: 10.1159/000084999] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2004] [Accepted: 08/11/2004] [Indexed: 12/23/2022]
Abstract
PURPOSE Hypericin, a specific inhibitor of protein kinase C, has been reported to have potential as a therapeutic drug for proliferative vitreoretinopathy (PVR) in vitro and in vivo. In the present studies, we analyzed the dynamic changes in Ca2+ influx and free intracellular Ca2+ concentration ([Ca2+]i) of cultured human retinal pigment epithelial (RPE) cells after stimulation with hypericin in an attempt to elucidate its mechanism as a therapeutic drug for PVR. METHODS RPE cells were plated in a special plastic dish and then stimulated with 100 nM phorbol-12-myristate-13-acetate (PMA) and/or 6 hypericin concentrations (0.5, 1, 2, 3, 4 and 5 microM), after which Ca2+ influx and [Ca2+]i were determined using the fluorescence Ca2+ dye fluo-3 AM and laser scanning confocal microscopy. RESULTS The fluorescence in resting RPE cells was strong and distributed throughout the cells. The nucleus appeared more fluorescent than the cytoplasm. After stimulation with 0.5 microM hypericin, no obvious change of Ca2+ influx and [Ca2+]i was observed. In contrast, stimulation with higher concentrations of hypericin (1-5 microM) led to a rapid decrease in Ca2+ influx and [Ca2+]i, which was significantly different from those detected without hypericin (control experiments). In addition, no significant differences in [Ca2+]i were found between 1 and 5 microM hypericin used. Stimulation with hypericin, which was applied immediately after preincubation with PMA for 24 h did not further change Ca2+ influx and [Ca2+]i. CONCLUSION In RPE cells, high concentrations of hypericin (1-5 microM) significantly inhibit Ca2+ influx and induce a decrease in [Ca2+]i. Therefore, hypericin has potential as a therapeutic drug for PVR maybe through its inhibition of the Ca2+ influx pathway.
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Affiliation(s)
- QianYing Gao
- Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China
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Abstract
Clarification of the function of bestrophin, the gene product of VMD2, establishes a basis for the understanding of the pathomechanisms leading to Best's vitelliform macular degeneration. Studies of heterologously expressed bestrophin showed that bestrophin can function as a Cl(-) channel. All four known bestrophins were found to display Cl(-) channel activity. A loss in Cl(-) channel function would elegantly explain the development of the leading symptom for Best's disease, the reduction of the light peak amplitude in the patient's electro-oculogram. However, there are still gaps in the chain of evidence demonstrating that bestrophin is a Cl(-) channel, and this hypothesis is inconsistent with newly published follow-up observations. In an alternative hypothesis bestrophin appears as a regulator of voltage-dependent Ca(2+) channels assuming an indirect involvement of bestrophin in the generation of the light peak. Further studies on either bestrophin-deficient mice or transgenic mice will show that either one of the hypotheses is right or maybe both will be proven correct, showing bestrophin as a Cl(-) channel and Ca(2+) channel regulator.
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Affiliation(s)
- O Strauss
- Abteilung für Experimentelle Ophthalmologie, Klinik und Poliklinik für Augenheilkunde des Universitätsklinikums Hamburg-Eppendorf, Hamburg.
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Mergler S, Dannowski H, Bednarz J, Engelmann K, Hartmann C, Pleyer U. Calcium influx induced by activation of receptor tyrosine kinases in SV40-transfected human corneal endothelial cells. Exp Eye Res 2003; 77:485-95. [PMID: 12957147 DOI: 10.1016/s0014-4835(03)00154-4] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
This study was undertaken to investigate electrophysiological properties of immortalized SV40-transfected human corneal endothelial cells (HCEC-SV40) combined with the analysis of intracellular Ca(2+) responses mediated by ligands for receptor tyrosine kinases (RTK). In addition, the effects of several tyrosine kinase inhibitors were tested on Ca(2+) inflow mediated by induction of capacitative calcium entry (CCE). Patch-clamp techniques and measurements of the intracellular free Ca(2+) ([Ca(2+)](i)) by fura-2 were performed using HCEC-SV40. Stimulation of fibroblast growth factor receptors (FGFR) (e.g. by basic-FGF) (10 ng ml(-1)) elicited activation of Ca(2+) permeable channels and a subsequent increase of cytosolic free Ca(2+) in HCEC-SV40. This effect could be disrupted by the L-type Ca(2+) channel blocker nifedipine (5 microM). In addition, nifedipine significantly reduced the magnitude of CCE. Inhibition of protein tyrosine kinases (PTKs) by genistein, lavendustin A, or tyrphostin 51 (all 5 microM) also led to a reduction of CCE in HCEC-SV40. This study demonstrates for the first time that L-type Ca(2+) channel activity in HCEC-SV40 is linked to the activity of FGF receptor tyrosine kinases. These data regarding Ca(2+) inflow through Ca(2+) channels could be useful for investigation of culture and vitality conditions of HCEC.
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Affiliation(s)
- Stefan Mergler
- Medizinische Klinik m. S. Hepatologie und Gastroenterologie, Universitätsklinikum Charité der Humboldt-Universität zu Berlin, Campus Virchow-Klinikum, Augustenburger Platz 1, D-13353 Berlin, Germany.
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