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Schijven JF, van Veen T, Delmaar C, Kos J, Vermeulen L, Roosien R, Verhoeven F, Schipper M, Peerlings B, Duizer E, Derei J, Lammen W, Bartels O, van der Ven H, Maas R, de Roda Husman AM. Quantitative Microbial Risk Assessment of Contracting COVID-19 Derived from Measured and Simulated Aerosol Particle Transmission in Aircraft Cabins. Environ Health Perspect 2023; 131:87011. [PMID: 37589660 PMCID: PMC10434022 DOI: 10.1289/ehp11495] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/27/2022] [Revised: 07/13/2023] [Accepted: 07/13/2023] [Indexed: 08/18/2023]
Abstract
BACKGROUND SARS-CoV-2 can be effectively transmitted between individuals located in close proximity to each other for extended durations. Aircraft provide such conditions. Although high attack rates during flights were reported, little was known about the risk levels of aerosol transmission of SARS-CoV-2 in aircraft cabins. OBJECTIVES The major objective was to estimate the risk of contracting COVID-19 from transmission of aerosol particles in aircraft cabins. METHODS In two single-aisle and one twin-aisle aircraft, dispersion of generated aerosol particles over a seven-row economy class cabin section was measured under cruise and taxi conditions and simulated with a computational fluid dynamic model under cruise conditions. Using the aerosol particle dispersion data, a quantitative microbial risk assessment was conducted for scenarios with an asymptomatic infectious person expelling aerosol particles by breathing and speaking. Effects of flight conditions were evaluated using generalized additive mixed models. RESULTS Aerosol particle concentration decreased with increasing distance from the infectious person, and this decrease varied with direction. On a typical flight with an average shedder, estimated mean risk of contracting COVID-19 ranged from 1.3 × 10 - 3 to 9.0 × 10 - 2 . Risk increased to 7.7 × 10 - 2 with a super shedder (< 3 % of cases) on a long flight. Risks increased with increasing flight duration: 2-23 cruise flights of typical duration and 2-10 flights of longer duration resulted in at least 1 case of COVID-19 due to onboard aerosol transmission by one average shedder, and in the case of one super shedder, at least 1 case in 1-3 flights of typical duration cruise and 1 flight of longer duration. DISCUSSION Our findings indicate that the risk of contracting COVID-19 by aerosol transmission in an aircraft cabin is low, but it will not be zero. Testing before boarding may help reduce the chance of a (super)shedder boarding an aircraft and mask use further reduces aerosol transmission in the aircraft cabin. https://doi.org/10.1289/EHP11495.
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Affiliation(s)
- Jack F. Schijven
- Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, the Netherlands
- Department of Earth Sciences, Utrecht University, Utrecht, the Netherlands
| | - Theo van Veen
- Royal Netherlands Aerospace Centre, Amsterdam, the Netherlands
| | - Christiaan Delmaar
- Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, the Netherlands
| | - Johan Kos
- Royal Netherlands Aerospace Centre, Amsterdam, the Netherlands
| | - Lucie Vermeulen
- Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, the Netherlands
| | - Rui Roosien
- Royal Netherlands Aerospace Centre, Amsterdam, the Netherlands
| | | | - Maarten Schipper
- Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, the Netherlands
| | - Bram Peerlings
- Royal Netherlands Aerospace Centre, Amsterdam, the Netherlands
| | - Erwin Duizer
- Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, the Netherlands
| | - Jonathan Derei
- Royal Netherlands Aerospace Centre, Amsterdam, the Netherlands
| | - Wim Lammen
- Royal Netherlands Aerospace Centre, Amsterdam, the Netherlands
| | - Onno Bartels
- Royal Netherlands Aerospace Centre, Amsterdam, the Netherlands
| | | | - Robert Maas
- Royal Netherlands Aerospace Centre, Amsterdam, the Netherlands
| | - Ana Maria de Roda Husman
- Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, the Netherlands
- Institute for Risk Assessment Sciences, Utrecht University, Utrecht, the Netherlands
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Kaur J, Mencl S, Sahaboglu A, Farinelli P, van Veen T, Zrenner E, Ekström P, Paquet-Durand F, Arango-Gonzalez B. Calpain and PARP activation during photoreceptor cell death in P23H and S334ter rhodopsin mutant rats. PLoS One 2011; 6:e22181. [PMID: 21765948 PMCID: PMC3134478 DOI: 10.1371/journal.pone.0022181] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2011] [Accepted: 06/20/2011] [Indexed: 11/18/2022] Open
Abstract
Retinitis pigmentosa (RP) is a heterogeneous group of inherited neurodegenerative diseases affecting photoreceptors and causing blindness. Many human cases are caused by mutations in the rhodopsin gene. An important question regarding RP pathology is whether different genetic defects trigger the same or different cell death mechanisms. To answer this question, we analysed photoreceptor degeneration in P23H and S334ter transgenic rats carrying rhodopsin mutations that affect protein folding and sorting respectively. We found strong activation of calpain and poly(ADP-ribose) polymerase (PARP) in both mutants, concomitant with calpastatin down-regulation, increased oxidative DNA damage and accumulation of PAR polymers. These parameters were strictly correlated with the temporal progression of photoreceptor degeneration, mirroring earlier findings in the phosphodiesterase-6 mutant rd1 mouse, and suggesting execution of non-apoptotic cell death mechanisms. Interestingly, activation of caspases-3 and -9 and cytochrome c leakage-key events in apoptotic cell death--were observed only in the S334ter mutant, which also showed increased expression of PARP-1. The identification of the same metabolic markers triggered by different mutations in two different species suggests the existence of common cell death mechanisms, which is a major consideration for any mutation independent treatment.
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Affiliation(s)
- Jasvir Kaur
- Institute for Ophthalmic Research, Centre for Ophthalmology, University of Tübingen, Tübingen, Germany
| | - Stine Mencl
- Institute for Ophthalmic Research, Centre for Ophthalmology, University of Tübingen, Tübingen, Germany
| | - Ayse Sahaboglu
- Institute for Ophthalmic Research, Centre for Ophthalmology, University of Tübingen, Tübingen, Germany
| | - Pietro Farinelli
- Institute for Ophthalmic Research, Centre for Ophthalmology, University of Tübingen, Tübingen, Germany
- Department of Ophthalmology, Clinical Sciences Lund, University of Lund, Lund, Sweden
| | - Theo van Veen
- Institute for Ophthalmic Research, Centre for Ophthalmology, University of Tübingen, Tübingen, Germany
- Department of Ophthalmology, Clinical Sciences Lund, University of Lund, Lund, Sweden
| | - Eberhart Zrenner
- Institute for Ophthalmic Research, Centre for Ophthalmology, University of Tübingen, Tübingen, Germany
| | - Per Ekström
- Department of Ophthalmology, Clinical Sciences Lund, University of Lund, Lund, Sweden
| | - François Paquet-Durand
- Institute for Ophthalmic Research, Centre for Ophthalmology, University of Tübingen, Tübingen, Germany
| | - Blanca Arango-Gonzalez
- Institute for Ophthalmic Research, Centre for Ophthalmology, University of Tübingen, Tübingen, Germany
- * E-mail:
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3
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Paquet-Durand F, Beck S, Michalakis S, Goldmann T, Huber G, Mühlfriedel R, Trifunović D, Fischer MD, Fahl E, Duetsch G, Becirovic E, Wolfrum U, van Veen T, Biel M, Tanimoto N, Seeliger MW. A key role for cyclic nucleotide gated (CNG) channels in cGMP-related retinitis pigmentosa. Hum Mol Genet 2010; 20:941-7. [PMID: 21149284 DOI: 10.1093/hmg/ddq539] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The rd1 natural mutant is one of the first and probably the most commonly studied mouse model for retinitis pigmentosa (RP), a severe and frequently blinding human retinal degeneration. In several decades of research, the link between the increase in photoreceptor cGMP levels and the extremely rapid cell death gave rise to a number of hypotheses. Here, we provide clear evidence that the presence of cyclic nucleotide gated (CNG) channels in the outer segment membrane is the key to rod photoreceptor loss. In Cngb1(-/-) × rd1 double mutants devoid of regular CNG channels, cGMP levels are still pathologically high, but rod photoreceptor viability and outer segment morphology are greatly improved. Importantly, cone photoreceptors, the basis for high-resolution daylight and colour vision, survived and remained functional for extended periods of time. These findings strongly support the hypothesis of deleterious calcium (Ca(2+))-influx as the cause of rapid rod cell death and highlight the importance of CNG channels in this process. Furthermore, our findings suggest that targeting rod CNG channels, rather than general Ca(2+)-channel blockade, is a most promising symptomatic approach to treat otherwise incurable forms of cGMP-related RP.
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Affiliation(s)
- François Paquet-Durand
- Division of Experimental Ophthalmology, Institute for Ophthalmic Research, University of Tübingen, Röntgenweg 11, 72076 Tübingen, Germany.
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4
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Paquet-Durand F, Sanges D, McCall J, Silva J, van Veen T, Marigo V, Ekström P. Photoreceptor rescue and toxicity induced by different calpain inhibitors. J Neurochem 2010; 115:930-40. [PMID: 20807308 DOI: 10.1111/j.1471-4159.2010.06983.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Photoreceptor degeneration is the hallmark of a group of inherited blinding diseases collectively termed retinitis pigmentosa (RP); a major cause of blindness in humans. RP is at present untreatable and the underlying neurodegenerative mechanisms are largely unknown, even though the genetic causes are often established. The activation of calpain-type proteases may play an important role in cell death in various neuronal tissues, including the retina. We therefore tested the efficacy of two different calpain inhibitors in preventing cell death in the retinal degeneration (rd1) human homologous mouse model for RP. Pharmacological inhibition of calpain activity in rd1 organotypic retinal explants had ambiguous effects on photoreceptor viability. Calpain inhibitor XI had protective effects when applied for short periods of time (16 h) but demonstrated substantial levels of toxicity in both wild-type and rd1 retina when used over several days. In contrast, the highly specific calpain inhibitor calpastatin peptide reduced photoreceptor cell death in vitro after both short and prolonged exposure, an effect that was also evident after in vivo application via intravitreal injection. These findings highlight the importance of calpain activation for photoreceptor cell death but also for photoreceptor survival and propose the use of highly specific calpain inhibitors to prevent or delay RP.
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Affiliation(s)
- François Paquet-Durand
- Division of Experimental Ophthalmology, Institute for Ophthalmic Research, University of Tübingen, Tübingen, Germany.
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Miranda M, Arnal E, Ahuja S, Alvarez-Nölting R, López-Pedrajas R, Ekström P, Bosch-Morell F, van Veen T, Romero FJ. Antioxidants rescue photoreceptors in rd1 mice: Relationship with thiol metabolism. Free Radic Biol Med 2010; 48:216-22. [PMID: 19854264 DOI: 10.1016/j.freeradbiomed.2009.10.042] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/07/2009] [Revised: 09/18/2009] [Accepted: 10/18/2009] [Indexed: 10/20/2022]
Abstract
We have previously shown that the use of a combination of antioxidants delayed the degeneration process in rd1 mouse retina. In an effort to understand the mechanism of action of these substances (zeaxanthin, lutein, alpha-lipoic acid, glutathione, and Lycium barbarum extract) the changes in the levels of several proteins and oxidative stress markers in the rd1 retina have been studied. The treatment increased glutathione peroxidase activity and glutathione levels and decreased cystine concentrations in rd1 retinas. Considering all the results obtained from treated and untreated animals, a high correlation was present between glutathione concentration and glutathione peroxidase activity, and there was a negative correlation between glutathione retinal concentration and number of TUNEL-positive cells. No difference was observed between the numbers of nNOS- and NADPH-diaphorase-positive cells in treated and untreated rd1 mice. Thiol contents and thiol-dependent peroxide metabolism seem to be directly related to the survival of photoreceptors in rd1 mouse retina.
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Affiliation(s)
- María Miranda
- Department of Physiology, University CEU-Cardenal Herrera, 46113 Moncada, Valencia, Spain
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6
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Bujakowska K, Maubaret C, Chakarova CF, Tanimoto N, Beck SC, Fahl E, Humphries MM, Kenna PF, Makarov E, Makarova O, Paquet-Durand F, Ekström PA, van Veen T, Leveillard T, Humphries P, Seeliger MW, Bhattacharya SS. Study of gene-targeted mouse models of splicing factor gene Prpf31 implicated in human autosomal dominant retinitis pigmentosa (RP). Invest Ophthalmol Vis Sci 2009; 50:5927-33. [PMID: 19578015 DOI: 10.1167/iovs.08-3275] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE Pre-mRNA processing factor 31 (PRPF31) is a ubiquitous protein needed for the assembly of the pre-mRNA splicing machinery. It has been shown that mutations in this gene cause autosomal dominant retinitis pigmentosa 11 (RP11), which is characterized by rod-cell degeneration. Interestingly, mutations in this ubiquitously expressed gene do not lead to phenotypes other than retinal malfunction. Furthermore, the dominant inheritance pattern has shown incomplete penetrance, which poses interesting questions about the disease mechanism of RP11. METHODS To characterize PRPF31 function in the rod cells, two animal models have been generated. One was a heterozygous knock-in mouse (Prpf31(A216P/+)) carrying a point mutation p.A216P, which has previously been identified in RP11 patients. The second was a heterozygous knockout mouse (Prpf31(+/-)). Retinal degeneration in RP11 mouse models was monitored by electroretinography and histology. RESULTS Generation of the mouse models is presented, as are results of ERGs and retinal morphology. No degenerative phenotype on fundus examination was found in Prpf31(A216P/+) and Prpf31(+/-) mice. Prpf31(A216P/A216P) and Prpf31(-/-) genotypes were embryonic lethal. CONCLUSIONS The results imply that Prpf31 is necessary for survival, and there is no compensation mechanism in mouse for the lack of this splicing factor. The authors suggest that p.A216P mutation in Prpf31 does not exert a dominant negative effect and that one Prpf31 wild-type allele is sufficient for maintenance of the healthy retina in mice.
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Affiliation(s)
- Kinga Bujakowska
- Institute of Ophthalmology, University College London, London, United Kingdom
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Abstract
Photoreceptor degeneration in retinitis pigmentosa is one of the leading causes of hereditary blindness in the developed world. Although causative genetic mutations have been elucidated in many cases, the underlying neuronal degeneration mechanisms are still unknown. Here, we show that activation of cGMP-dependent protein kinase (PKG) hallmarks photoreceptor degeneration in rd1 and rd2 human homologous mouse models. When induced in wild-type retinae, PKG activity was both necessary and sufficient to trigger cGMP-mediated photoreceptor cell death. Target-specific, pharmacological inhibition of PKG activity in both rd1 and rd2 retinae strongly reduced photoreceptor cell death in organotypic retinal explants. Likewise, inhibition of PKG in vivo, using three different application paradigms, resulted in robust photoreceptor protection in the rd1 retina. These findings suggest a pivotal role for PKG activity in cGMP-mediated photoreceptor degeneration mechanisms and highlight the importance of PKG as a novel target for the pharmacological intervention in RP.
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Affiliation(s)
- François Paquet-Durand
- University of Tübingen, Centre for Ophthalmology, Institute for Ophthalmic Research, Division of Experimental Ophthalmology, Röntgenweg 11, Tübingen, Germany.
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8
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Sancho-Pelluz J, Wunderlich KA, Rauch U, Romero FJ, van Veen T, Limb GA, Crocker PR, Perez MT. Sialoadhesin Expression in Intact Degenerating Retinas and Following Transplantation. ACTA ACUST UNITED AC 2008; 49:5602-10. [DOI: 10.1167/iovs.08-2117] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Affiliation(s)
- Javier Sancho-Pelluz
- From the Department of Ophthalmology and2Fundacio´n Oftalmolo´gica del Mediterra´neo (FOM) and Universidad Cardenal Herrera-CEU, Valencia, Spain;3Experimental Ophthalmology, University Eye Hospital, Tu¨bingen, Germany; the Divisions of
| | | | - Uwe Rauch
- Vessel Wall Biology Group, Lund University, Lund, Sweden; the
| | - F. Javier Romero
- Fundacio´n Oftalmolo´gica del Mediterra´neo (FOM) and Universidad Cardenal Herrera-CEU, Valencia, Spain
| | - Theo van Veen
- From the Department of Ophthalmology and3Experimental Ophthalmology, University Eye Hospital, Tu¨bingen, Germany; the Divisions of
| | - G. Astrid Limb
- Pathology and6Cell Biology, UCL Institute of Ophthalmology, London, United Kingdom; the
| | - Paul R. Crocker
- Wellcome Trust Biocentre, University of Dundee, Dundee, United Kingdom; and the
| | - Maria-Thereza Perez
- From the Department of Ophthalmology and8Department of Ophthalmology, University of Copenhagen, Glostrup Hospital, Glostrup, Denmark
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Sancho-Pelluz J, Arango-Gonzalez B, Kustermann S, Romero FJ, van Veen T, Zrenner E, Ekström P, Paquet-Durand F. Photoreceptor cell death mechanisms in inherited retinal degeneration. Mol Neurobiol 2008; 38:253-69. [PMID: 18982459 DOI: 10.1007/s12035-008-8045-9] [Citation(s) in RCA: 205] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2008] [Accepted: 10/16/2008] [Indexed: 02/24/2023]
Abstract
Photoreceptor cell death is the major hallmark of a group of human inherited retinal degenerations commonly referred to as retinitis pigmentosa (RP). Although the causative genetic mutations are often known, the mechanisms leading to photoreceptor degeneration remain poorly defined. Previous research work has focused on apoptosis, but recent evidence suggests that photoreceptor cell death may result primarily from non-apoptotic mechanisms independently of AP1 or p53 transcription factor activity, Bcl proteins, caspases, or cytochrome c release. This review briefly describes some animal models used for studies of retinal degeneration, with particular focus on the rd1 mouse. After outlining the major features of different cell death mechanisms in general, we then compare them with results obtained in retinal degeneration models, where photoreceptor cell death appears to be governed by, among other things, changes in cyclic nucleotide metabolism, downregulation of the transcription factor CREB, and excessive activation of calpain and PARP. Based on recent experimental evidence, we propose a putative non-apoptotic molecular pathway for photoreceptor cell death in the rd1 retina. The notion that inherited photoreceptor cell death is driven by non-apoptotic mechanisms may provide new ideas for future treatment of RP.
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Affiliation(s)
- Javier Sancho-Pelluz
- Institute for Ophthalmic Research, University of Tübingen, Centre for Ophthalmology, Röntgenweg 11, 72076, Tübingen, Germany
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Ahuja S, Ahuja-Jensen P, Johnson LE, Caffé AR, Abrahamson M, Ekström PAR, van Veen T. rd1 Mouse retina shows an imbalance in the activity of cysteine protease cathepsins and their endogenous inhibitor cystatin C. Invest Ophthalmol Vis Sci 2008; 49:1089-96. [PMID: 18326735 DOI: 10.1167/iovs.07-0549] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE To compare in vivo levels, spatial localization, and in vitro secretion of cysteine protease cathepsins and cystatin C (cysC) in the retinal degeneration 1 (rd1) mouse model of retinitis pigmentosa and control (wt) mouse retinas. METHODS The spatial localization, protein contents, cysC levels and cathepsin-B, -S, and -L activities in wt and rd1 retinas at postnatal (PN) days 2, 7, 14, 21, and 28 were analyzed by immunostaining, spectrophotometry, ELISA, and fluorescence spectrophotometry. The in vitro secretion of cysC and cysteine proteases by PN7 retinal explants into the conditioned medium (RCM) was quantified. RESULTS The pigment epithelium, photoreceptors, and inner retinal and ganglion cell layers of both wt and rd1 retinas showed cysC and cathepsin-B labeling. CysC immunostaining was extensive in the optic nerve head fibers. The rd1 explants secreted higher amounts of cysteine protease into the RCM. The protein content in wt and rd1 retinal extracts increased up to PN14, then decreased in rd1 but not in wt. In rd1 extracts at PN14 to -28, cathepsin activity was higher and increased with age, but the cysC level was higher and constant. The ratios of cathepsin activity to cysC (cathepsin-L at PN2 and total, -B, and -L at PN14 to -28) were higher in rd1 extracts. CONCLUSIONS Similar localization of both cathepsin-B and cysC in wt and rd1 retinas along with lower proteins and higher cathepsin activity in rd1 retinal extracts and RCM are consistent with their localization in extracellular matrix and a role in physiopathologic remodeling in wt and rd1 retinas.
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Affiliation(s)
- Satpal Ahuja
- Department of Ophthalmology Research, Biomedical Centre B-13, Lund University, Lund, Sweden.
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11
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Paquet-Durand F, Silva J, Talukdar T, Johnson LE, Azadi S, van Veen T, Ueffing M, Hauck SM, Ekström PAR. Excessive activation of poly(ADP-ribose) polymerase contributes to inherited photoreceptor degeneration in the retinal degeneration 1 mouse. J Neurosci 2007; 27:10311-9. [PMID: 17881537 PMCID: PMC6672664 DOI: 10.1523/jneurosci.1514-07.2007] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Retinitis pigmentosa (RP) is an inherited blinding disease for which there is no treatment available. It is characterized by a progressive and neurodegenerative loss of photoreceptors but the underlying mechanisms are poorly understood. Excessive activation of the enzyme poly(ADP-ribose) polymerase (PARP) has recently been shown to be involved in several neuropathologies. To investigate the possible role of PARP in retinal photoreceptor degeneration, we used the retinal degeneration 1 (rd1) mouse RP model to study PARP expression, PARP activity, and to test the effects of PARP inhibition on photoreceptor viability. PARP expression was found to be equal between rd1 and wild-type counterpart retinas. In contrast to this, a dramatic increase in both PARP activity per se and PARP product formation was detected by in situ assays in rd1 photoreceptors actively undergoing cell death. Furthermore, PARP activity colabeled with oxidatively damaged DNA and nuclear translocation of AIF (apoptosis-inducing factor), suggesting activation of PARP as a bridge between these events in the degenerating photoreceptors. The PARP-specific inhibitor PJ34 [N-(6-oxo-5,6-dihydrophenanthridin-2-yl)-N,N-dimethylacetamide x HCl[ reduced the number of cells exhibiting death markers in a short-term retinal culture paradigm, a protective effect that was translated into an increased number of surviving photoreceptors when the inhibitor was used in a long-term culture setting. Our results thus demonstrate an involvement of PARP activity in rd1 photoreceptor cell death, which could have a bearing on the understanding of neurodegenerations as such. The findings also suggest that the therapeutical possibilities of PARP inhibition should include retinal diseases like RP.
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Ahuja-Jensen P, Johnsen-Soriano S, Ahuja S, Bosch-Morell F, Sancho-Tello M, Romero FJ, Abrahamson M, van Veen T. Low glutathione peroxidase in rd1 mouse retina increases oxidative stress and proteases. Neuroreport 2007; 18:797-801. [PMID: 17471069 DOI: 10.1097/wnr.0b013e3280c1e344] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Malondialdehyde, reduced glutathione, glutathione peroxidase, glutathione reductase and cysteine protease cathepsins at postnatal (PN) days 2, 7, 14, 21 and 28 in controls (wt) and the retinal degeneration 1 (rd1) mouse model for retinitis pigmentosa retinas were measured to determine oxidative stress. In PN28 wt and PN2 rd1 retinas, elevated malondialdehyde and low glutathione peroxidase activity indicate higher oxidative load, despite higher reduced glutathione in PN2 rd1 retinas. This is due to physiological exposure to light and retinal vascular/neural restructuring, respectively. Compared with wt retinas, relatively high malondialdehyde at PN2 and cathepsin levels at PN14, 21 and 28 in rd1 retinas indicate that cells of the residual inner retina also contribute to the oxidative stress and retinal degeneration.
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Azadi S, Johnson LE, Paquet-Durand F, Perez MTR, Zhang Y, Ekström PAR, van Veen T. CNTF+BDNF treatment and neuroprotective pathways in the rd1 mouse retina. Brain Res 2007; 1129:116-29. [PMID: 17156753 DOI: 10.1016/j.brainres.2006.10.031] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2006] [Revised: 10/05/2006] [Accepted: 10/06/2006] [Indexed: 11/22/2022]
Abstract
The rd1 mouse is a relevant model for studying the mechanisms of photoreceptor degeneration in retinitis pigmentosa. Treatment with ciliary neurotrophic factor (CNTF) in combination with brain derived neurotrophic factor (BDNF) is known to rescue photoreceptors in cultured rd1 retinal explants. To shed light on the underlying mechanisms, we studied the effects of 9 days (starting at postnatal day 2) in vitro CNTF+BDNF treatment on the endogenous production of CNTF, BDNF, fibroblast growth factor 2 (FGF2), or the activation of extracellular signal-regulated kinase (ERK), Akt and cAMP-response-element-binding protein (CREB) in retinal explants. In rd1 explants, CNTF+BDNF decreased the number of TUNEL-positive photoreceptors. The treatment also increased endogenous rd1 levels of CNTF and BDNF, but lowered the level of FGF2 expression in rd1 explants. When wild-type explants were treated, endogenous CNTF was similarly increased, while BDNF and FGF2 levels remained unaffected. In addition, treatment of rd1 retinas strongly increased the phosphorylation of ERK, Akt and CREB. In treated wild-type explants, the same parameters were either unchanged (ERK) or decreased (Akt and CREB). The results suggest a role for Akt, ERK and CREB in conveying the neuroprotective effect of CNTF+BDNF treatment in rd1 retinal explants.
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Affiliation(s)
- Seifollah Azadi
- Department of Ophthalmology, University of Lund, BMC-B13, SE-221 84 LUND, Sweden
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14
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Azadi S, Paquet-Durand F, Medstrand P, van Veen T, Ekström PAR. Up-regulation and increased phosphorylation of protein kinase C (PKC) delta, mu and theta in the degenerating rd1 mouse retina. Mol Cell Neurosci 2006; 31:759-73. [PMID: 16503160 DOI: 10.1016/j.mcn.2006.01.001] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2005] [Revised: 12/16/2005] [Accepted: 01/06/2006] [Indexed: 11/18/2022] Open
Abstract
The rd1 mouse serves as a model for inherited photoreceptor degeneration: retinitis pigmentosa. Microarray techniques were employed to compare the transcriptomes of rd1 and congenic wild-type retinas at postnatal day 11, when degenerative processes have started but most photoreceptors are still present. Of the several genes that were differentially expressed, focus was put on those associated with the protein kinase C (PKC) signaling pathway, in particular PKCdelta, mu and theta. Microarray identified these as being up-regulated in the rd1 retina, which was confirmed by QRT-PCR. Western blotting and immunostaining, using antibodies against either total or phosphorylated variants of the PKC isoforms, revealed increased expression and phosphorylation of PKCdelta, mu and theta in the rd1 retina at the protein level as well. Our results suggest that these PKC isoforms are involved in rd1 degeneration.
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Affiliation(s)
- Seifollah Azadi
- Department of Ophthalmology, Lund University, BMC-B13, SE-221 84 Lund, Sweden
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15
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Abstract
The retinal degeneration (rd)1 mouse displays an inherited retinal degeneration and therefore allows studies of the molecular mechanisms behind the blinding disease retinitis pigmentosa. Activation of the calcium-dependent protease calpain has been suggested to play an important role in cell death in various tissues, but little is known about the expression and activity of calpain during inherited retinal degeneration. Using microarray techniques, transcript levels of cyclic AMP response element-binding protein (CREB)-1, calpastatin and of various calpain genes were analysed in the rd1 mouse compared with its wild-type control. Expression of distinct calpain isoforms and calpastatin was investigated using immunofluorescence and immunoblotting. Gene transcription and protein expression levels were compared with calpain activity using an enzymatic assay that allowed monitoring of calpain activity at the cellular level. We found that CREB-1 and calpastatin expression was reduced in rd1 retinas, whereas calpain activity was substantially increased in rd1 photoreceptors. Calpain activity peaked at postnatal day 13, together with rd1 photoreceptor cell death. Calpain-specific inhibitors decreased calpain activity in situ. These results indicate that activation of calpains correlates with rd1 photoreceptor cell death, which raises the possibility of using calpain inhibitors to prevent or delay photoreceptor degeneration.
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Ahuja S, Ahuja P, Caffé AR, Ekstrom P, Abrahamson M, van Veen T. rd1 mouse retina shows imbalance in cellular distribution and levels of TIMP-1/MMP-9, TIMP-2/MMP-2 and sulfated glycosaminoglycans. Ophthalmic Res 2005; 38:125-36. [PMID: 16374054 DOI: 10.1159/000090533] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2004] [Accepted: 09/06/2005] [Indexed: 12/29/2022]
Abstract
BACKGROUND The rd1 mouse retina displays fast degeneration of photoreceptors resulting in a depletion of almost all rod photoreceptors by postnatal day 21 (PN21). To evaluate the role of proteinases in the pathophysiology of this animal model of retinitis pigmentosa, C3H rd1 and congenic wild-type (wt) mice retinas were analyzed. MATERIAL AND METHODS The cellular localization and levels of proteins, matrix metalloproteinases (MMPs), their endogenous inhibitors (TIMPs), total sulfated glycosaminoglycans (sGAG) and nature of saccharides in rd1 and wt retinal extracts were compared. RESULTS MMP-2/TIMP-2 and MMP-9/TIMP-1 were predominantly localized in the interphotoreceptor matrix (IPM) of both genotypes, but MMP-2/TIMP-2 also appeared in the Muller cell fibers of rd1 retina. In rd1 retinal extracts the levels of total proteins were lower and those of active MMP-9, MMP-2, TIMP-1 and total sGAG were higher than those of wt extracts. Despite an increase in TIMP-1, active MMP-9/MMP-2 were disproportionately elevated in rd1 compared to wt retina. With increasing age, MMPs in wt retinas were decreased but were increased in rd1. The sialylation of proteoglycans in PN2 and PN7 rd1 retinas was lower, and galactosylation was higher than that in wt retinas. CONCLUSIONS MMP-9/MMP-2 and TIMP-1/TIMP-2 are associated with IPM, possibly after secretion by retinal pigmented epithelial cells. In degenerating rd1 retina, MMP-2/TIMP-2 are associated with the Muller cell fibers, which apparently play a central role in modifying the balance between MMPs and TIMPs. Elevated sGAG and proteolysis due to an imbalance in the levels of TIMPs and active MMP-9/MMP-2 in rd1 retina possibly contribute to retinal degeneration in the rd1 mouse.
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Affiliation(s)
- Satpal Ahuja
- Department of Ophthalmology, Wallenberg Retina Center, BMC, B-13, Lund University, Lund, Sweden.
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17
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Hauck SM, Ekström PAR, Ahuja-Jensen P, Suppmann S, Paquet-Durand F, van Veen T, Ueffing M. Differential modification of phosducin protein in degenerating rd1 retina is associated with constitutively active Ca2+/calmodulin kinase II in rod outer segments. Mol Cell Proteomics 2005; 5:324-36. [PMID: 16253986 DOI: 10.1074/mcp.m500217-mcp200] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Retinitis pigmentosa comprises a heterogeneous group of incurable progressive blinding diseases with unknown pathogenic mechanisms. The retinal degeneration 1 (rd1) mouse is a retinitis pigmentosa model that carries a mutation in a rod photoreceptor-specific phosphodiesterase gene, leading to rapid degeneration of these cells. Elucidation of the molecular differences between rd1 and healthy retinae is crucial for explaining this degeneration and could assist in suggesting novel therapies. Here we used high resolution proteomics to compare the proteomes of the rd1 mouse retina and its congenic, wild-type counterpart at postnatal day 11 when photoreceptor death is profound. Over 3000 protein spots were consistently resolved by two-dimensional gel electrophoresis and subjected to a rigorous filtering procedure involving computer-based spot analyses. Five proteins were accepted as being differentially expressed in the rd1 model and subsequently identified by mass spectrometry. The difference in one such protein, phosducin, related to an altered modification pattern in the rd1 retina rather than to changed expression levels. Additional experiments showed phosducin in healthy retinae to be highly phosphorylated in the dark- but not in the light-adapted phase. In contrast, rd1 phosducin was highly phosphorylated irrespective of light status, indicating a dysfunctional rd1 light/dark response. The increased rd1 phosducin phosphorylation coincided with increased activation of calcium/calmodulin-activated protein kinase II, which is known to utilize phosducin as a substrate. Given the increased rod calcium levels present in the rd1 mutation, calcium-evoked overactivation of this kinase may be an early and long sought for step in events leading to photoreceptor degeneration in the rd1 mouse.
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Affiliation(s)
- Stefanie M Hauck
- GSF-National Research Centre for Environment and Health, Institute of Human Genetics, Neuherberg 85764, Germany
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18
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Johnson LE, van Veen T, Ekström PAR. Differential Akt activation in the photoreceptors of normal and rd1 mice. Cell Tissue Res 2005; 320:213-22. [PMID: 15789220 DOI: 10.1007/s00441-004-1046-8] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2004] [Accepted: 11/03/2004] [Indexed: 10/25/2022]
Abstract
Retinitis pigmentosa is a blinding disease in which unknown mechanisms cause the degeneration of retinal photoreceptors. The retinal degeneration (rd1) mouse is a relevant model for this condition, since it carries a mutation also found in some forms of retinitis pigmentosa. To understand the degenerative process in the rd1 mouse, we must identify the survival and apoptosis-related signaling pathways in its photoreceptors and determine whether signaling differs from that in normal mice. The phosphatidylinositol 3-kinase/Akt kinase pathway promotes survival in several different cell types. The purpose of the present study has been to compare Akt activity in retinal cells of normal and rd1 mice. We have found that, in normal mice, Akt becomes activated in the retina in a developmentally regulated and cell-type-specific fashion, encompassing essentially all retinal cells. In most cell types, once Akt activation has begun, it remains in this state throughout life. An exception is seen in the rod photoreceptors, in which Akt is activated only transiently during their development. The rd1 retina behaves identically in all but one respect, namely that the activation of Akt in rod photoreceptors persists until these cells undergo apoptosis. Thus, Akt may participate in constitutive survival processes in retinal neurons, except in rod photoreceptors in which the role of this pathway may be restricted to the developmental period. However, Akt activation in the rods may be part of a defense mechanism initiated in response to insults, such as the retinal degeneration seen in the rd1 mouse.
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Affiliation(s)
- Leif E Johnson
- Department of Ophthalmology, Wallenberg Retina Center, Lund University, Sweden.
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19
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Zhang Y, Kardaszewska AK, van Veen T, Rauch U, Perez MTR. Integration between abutting retinas: role of glial structures and associated molecules at the interface. Invest Ophthalmol Vis Sci 2005; 45:4440-9. [PMID: 15557453 DOI: 10.1167/iovs.04-0165] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE Integration between subretinal grafts and the host retina is limited in part by the presence of a barrier at the graft-host interface. This study was conducted to identify factors that may contribute to this barrier, by examining the distribution of glial structures and associated molecules in different setups of overlapping retinal pieces. METHODS Neuroretinal tissue derived from mice that express green fluorescent protein (GFP) was fragmented and transplanted into the subretinal space of adult rd1 mice. In an in vitro system, two retinal pieces, derived from GFP and rd1 mice, respectively, were placed overlapping each other and forming either laminar-laminar pairs or fragment-laminar pairs. The glia-associated markers analyzed included glial fibrillary acidic protein (GFAP), cellular retinaldehyde-binding protein (CRALBP), and two molecules known to inhibit neurite outgrowth: CD44 and neurocan. Bridging fibers and migrated cells were visualized with GFP fluorescence and retinal cell markers. RESULTS A thick CRALBP-immunolabeled band was observed in the interface in cultured laminar-laminar pairs, whereas a thinner band was seen in cultured fragment-laminar pairs and in transplants. Accumulation of CD44 and neurocan was also observed in the interface between abutting retinal pieces in all setups. GFP(+) bridging fibers and GFP(+) cells (some of which coexpressed neuronal markers) were observed within the abutting rd1 retina in some areas. However, such integration occurred exclusively where CRALBP, CD44, and neurocan immunolabeling appeared disrupted in the interface, but coincided with high GFAP expression within the rd1 retina. CONCLUSIONS The results demonstrate that, on the one hand, an accumulation of glial-associated inhibitory molecules in the interface correlates with limited integration between overlapping retinal pieces. On the other hand, glial reactivity within the rd1 retina does not appear to be incompatible with integration.
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Affiliation(s)
- Yiqin Zhang
- Department of Ophthalmology, Lund University, Klinikgatan 26, S-221 84, Lund, Sweden
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20
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Archer SN, Ahuja P, Caffé R, Mikol C, Foster RG, van Veen T, von Schantz M. Absence of phosphoglucose isomerase-1 in retinal photoreceptor, pigment epithelium and Muller cells. Eur J Neurosci 2004; 19:2923-30. [PMID: 15182299 DOI: 10.1111/j.0953-816x.2004.03417.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Macroarray analysis was used to compare equal amounts of cDNA from wild-type and rd/rd (retinal degeneration) mice, collected at P90 when photoreceptor degeneration is virtually complete. A stronger signal for the glycolytic enzyme phosphoglucose isomerase (Gpi1) was observed in the rd/rd sample. Extracellularly, Gpi1 may act as a cytokine, independently described as neuroleukin and autocrine motility factor. Retinal Gpi1 expression was investigated by Northern and Western blot analysis and immunohistochemistry. Double-labelling was performed with antibodies against Gpi1 and calbindin-D, glutamine synthetase, RPE65, calretinin and ultraviolet opsin in order to provide positive cell type identification. Northern and Western blots showed double expression levels per microgram of RNA and protein, respectively, in the rd/rd retina compared with wild-type. However, the total amount of Gpi1 protein per retina was indistinguishable. Gpi1 immunoreactivity was found in ganglion, amacrine, horizontal and bipolar cells, but not in rods, cones, pigment epithelium and Muller cells. This distribution explains why the absolute amounts of Gpi1 protein were not appreciably different between wild-type and the rd/rd phenotype, where rods and cones are absent, whilst the relative contribution of Gpi1 to the total protein and RNA pools differed. Some extracellular immunoreactivity was observed in the photoreceptor matrix around cones in freshly fixed tissue only, which could possibly reflect a role as a cytokine. We propose that glycolysis in Gpi1-negative cells proceeds entirely through the pentose phosphate pathway, creating NADPH at the cost of organic carbon. We hypothesize that the unique metabolic needs of photoreceptors justify this trade-off.
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Affiliation(s)
- Simon N Archer
- School of Biomedical and Molecular Sciences, University of Surrey, Guildford GU2 7XH, UK
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21
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Abstract
AIM: To investigate the association of FAS gene polymorphism with coeliac disease (CD) development.
METHODS: FAS-G670A gene polymorphism, located in a gamma interferon activation site, was studied in 146 unrelated CD patients and 203 healthy ethnically matched controls. The restriction fragment length polymorphism (RFLP) method was used to identify FAS-G670A gene polymorphism.
RESULTS: No significant difference was found in genotype frequency between CD cases and controls. In controls, however, the frequency of the GG genotype was significantly higher in women (26.5%) than in men (12.8%) (OR = 2.44, 95%CI 1.15-5.20, P = 0.020) and it was also higher in men with CD than controls (OR = 2.60, 95%CI 0.96-7.05, P = 0.061). The GG genotype frequency was significantly higher in patients with most severe villous atrophy (Marsh IIIc lesions) (OR = 3.74, 95%CI 1.19-11.82, P = 0.025). A significantly less proportion of men suffered from Marsh IIIc lesions than women (OR = 0.20, 95%CI 0.06-0.68, P = 0.01). The risk of having severe villous atrophy increased with the additive effect of the G allele in women (P = 0.027 for trend, age and gender adjusted).
CONCLUSION: FAS-G670A gene polymorphism is associated with the severity of villous atrophy in CD. Female gender is also associated with the severity of villous atrophy.
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Affiliation(s)
- Jing Wu
- VU University Medical Centre, Department of Gastroenterology, Laboratory of Immunogenetics, P.O. Box 7057, 1007 MB Amsterdam, The Netherlands
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22
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Abstract
PURPOSE Limited integration is consistently observed between subretinal transplants and host retinas. In the current study, an in vitro model system for studying connections forming between two abutting retinas was developed. METHODS Neuroretinas were dissected from normal wild-type (WT) mice and green fluorescent protein (GFP) transgenic mice (obtained at postnatal days [P]0, P5, or P60), as well as from adult rd mice. Pieces from two different retinas (WT-WT, GFP-WT, GFP-rd) were placed side-by-side (contacting each other at the margins) or overlapping each other in organ cultures for 7 or 12 days. The abutting retinal pieces derived from animals of the same age (P5-P5; P60-P60) or of different ages (P0-P60; P5-P60). Retinal cells and fibers were visualized in wholemount preparations and in cross sections by immunocytochemistry using antibodies against neurofilament (NF+), neuronal nitric oxide synthase (NOS+), and protein kinase C (PKC+) and by GFP fluorescence (GFP+). RESULTS In side-by-side pairs (WT-WT, GFP-WT), numerous horizontal cell fibers (NF+) and amacrine cell fibers (NOS+) crossed the interface between the two pieces, forming continuous plexiform layers. In overlapping pairs, NF+, NOS+, and PKC+ fibers displayed parallel plexiform layers, and no crossover of fibers was observed in any of the pair combinations examined (WT-WT, GFP-WT, GFP-rd). Some integration was seen only in small areas where the structure of both retinal pieces was disrupted at the interface. CONCLUSIONS The results demonstrate the ability of neurites to extend between abutting retinas and to make appropriate target choices when they are placed side-by-side. However, this ability is limited when they overlap each other, similar to that observed in subretinal transplantation.
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Affiliation(s)
- Yiqin Zhang
- Wallenberg Retina Center, Department of Ophthalmology, Lund University, Lund, Sweden
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Narfström K, Bragadóttir R, Redmond TM, Rakoczy PE, van Veen T, Bruun A. Functional and structural evaluation after AAV.RPE65 gene transfer in the canine model of Leber's congenital amaurosis. Adv Exp Med Biol 2003; 533:423-30. [PMID: 15180294 DOI: 10.1007/978-1-4615-0067-4_54] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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25
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van Veen T, Andersson M, Nilsson DE. Diel Rhythm in the Elver, Anguilla Anguilla: Testing a Computerized System for Recording Biorhythmics. OIKOS 1981. [DOI: 10.2307/3544074] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Eriksson LO, Veen TV. Circadian rhythms in the brown bullhead, Ictalurus nebulosus (Teleostei). Evidence for an endogenous rhythm in feeding, locomotor, and reaction time behaviour. CAN J ZOOL 1980. [DOI: 10.1139/z80-259] [Citation(s) in RCA: 40] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Locomotor and feeding activity was investigated under(1) 12 h light(L): 12 h dark(D)and 16 h L: 8 h D, (2) 24 h D and 24 h L, and (3) dark pulses (0.75 h L: 0.25 h D), in the brown bullhead (Ictalurus nebulosus). In addition to locomotor and feeding activity, reaction time (latency time on lights-off and lights-on) was also measured.Fish subjected to a light–dark regime showed nocturnal behaviour, in many cases with a positive phase angle difference (i.e., the animals ceased their activity several hours before lights-on). Further, the actograms showed, as expected, a distinct 24 h rhythm. Only 2 brown bullheads out of 15, subjected to constant conditions, showed a circadian component in the locomotor activity, which could only be detected by frequency analysis.Nine out of 12 animals subjected to dark pulses (0.75 h L: 0.25 h D) showed a free-running circadian rhythm (approximately 23 h) in locomotor activity and 2 out of 3 showed such a rhythm in feeding activity. Observations and measurements of reaction time on leaving and re-entering the shelter after lights-off and lights-on (0.75 h L: 0.25 h D) showed also that this parameter has a circadian course. Measurements performed a fortnight later showed a similar, but less pronounced, pattern of behaviour.Dark pulses are thought to prevent rapid dissociation of a flexible multioscillatory circadian system in the brown bullhead.
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