1
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Donaldson PJ, Petrova RS, Nair N, Chen Y, Schey KL. Regulation of water flow in the ocular lens: new roles for aquaporins. J Physiol 2024; 602:3041-3056. [PMID: 37843390 PMCID: PMC11018719 DOI: 10.1113/jp284102] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2023] [Accepted: 09/28/2023] [Indexed: 10/17/2023] Open
Abstract
The ocular lens is an important determinant of overall vision quality whose refractive and transparent properties change throughout life. The lens operates an internal microcirculation system that generates circulating fluxes of ions, water and nutrients that maintain the transparency and refractive properties of the lens. This flow of water generates a substantial hydrostatic pressure gradient which is regulated by a dual feedback system that uses the mechanosensitive channels TRPV1 and TRPV4 to sense decreases and increases, respectively, in the pressure gradient. This regulation of water flow (pressure) and hence overall lens water content, sets the two key parameters, lens geometry and the gradient of refractive index, which determine the refractive properties of the lens. Here we focus on the roles played by the aquaporin family of water channels in mediating lens water fluxes, with a specific focus on AQP5 as a regulated water channel in the lens. We show that in addition to regulating the activity of ion transporters, which generate local osmotic gradients that drive lens water flow, the TRPV1/4-mediated dual feedback system also modulates the membrane trafficking of AQP5 in the anterior influx pathway and equatorial efflux zone of the lens. Since both lens pressure and AQP5-mediated water permeability (P H 2 O ${P_{{{\mathrm{H}}_{\mathrm{2}}}{\mathrm{O}}}}$ ) can be altered by changes in the tension applied to the lens surface via modulating ciliary muscle contraction we propose extrinsic modulation of lens water flow as a potential mechanism to alter the refractive properties of the lens to ensure light remains focused on the retina throughout life.
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Affiliation(s)
- Paul J. Donaldson
- Department of Physiology, School of Medical Sciences, New Zealand National Eye Center, University of Auckland, Auckland, New Zealand
| | - Rosica S. Petrova
- Department of Physiology, School of Medical Sciences, New Zealand National Eye Center, University of Auckland, Auckland, New Zealand
| | - Nikhil Nair
- Department of Physiology, School of Medical Sciences, New Zealand National Eye Center, University of Auckland, Auckland, New Zealand
| | - Yadi Chen
- Department of Physiology, School of Medical Sciences, New Zealand National Eye Center, University of Auckland, Auckland, New Zealand
| | - Kevin L. Schey
- Department of Biochemistry, Vanderbilt University, Nashville, TN, USA
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2
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Suresh P, Sun X, Zhou Z, Zhang Q. Spatial Proteomics Reveals Alcohol-Induced Damages to the Crypts and Villi of the Mouse Small Intestine. J Proteome Res 2024; 23:1801-1809. [PMID: 38655769 PMCID: PMC11077582 DOI: 10.1021/acs.jproteome.4c00037] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2024] [Revised: 04/05/2024] [Accepted: 04/16/2024] [Indexed: 04/26/2024]
Abstract
Alcohol consumption perturbs the gut immune barrier and ultimately results in alcoholic liver diseases, but little is known about how immune-related cells in the gut are perturbed in this process. In this study, we employed laser capture microdissection and a label-free proteomics approach to investigate the consequences of alcohol exposure to the proteomes of crypts and villi in the proximal small intestine. Intestinal tissues from alcohol-fed and pair-fed mice were microdissected to selectively capture cells in the crypts and villi regions, followed by one-pot protein digestion and data-independent LC-MS/MS analysis. We successfully identified over 3000 proteins from each of the crypt or villi regions equivalent to ∼3000 cells. Analysis of alcohol-treated tissues indicated an enhanced alcohol metabolism and reduced levels of α-defensins in crypts, alongside increased lipid metabolism and apoptosis in villi. Immunofluorescence imaging further corroborated the proteomic findings. Our work provides a detailed profiling of the proteomic changes in the compartments of the mouse small intestine and aids in molecular-level understanding of alcohol-induced tissue damage.
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Affiliation(s)
- Patil
Shivprasad Suresh
- Center
for Translational Biomedical Research, University
of North Carolina at Greensboro, North Carolina Research Campus, Kannapolis, North Carolina 28081, United States
| | - Xinguo Sun
- Center
for Translational Biomedical Research, University
of North Carolina at Greensboro, North Carolina Research Campus, Kannapolis, North Carolina 28081, United States
| | - Zhanxiang Zhou
- Center
for Translational Biomedical Research, University
of North Carolina at Greensboro, North Carolina Research Campus, Kannapolis, North Carolina 28081, United States
- Department
of Nutrition, University of North Carolina
at Greensboro, Greensboro, North Carolina 27402, United States
| | - Qibin Zhang
- Center
for Translational Biomedical Research, University
of North Carolina at Greensboro, North Carolina Research Campus, Kannapolis, North Carolina 28081, United States
- Department
of Chemistry & Biochemistry, University
of North Carolina at Greensboro, Greensboro, North Carolina 27402, United States
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3
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Shaohua H, Yihui W, Kaier Z, Ying B, Xiaoyi W, Hui Z, Guohu D, Peng C. Aquaporin 5 maintains lens transparency by regulating the lysosomal pathway using circRNA. J Cell Mol Med 2023; 27:803-818. [PMID: 36824022 PMCID: PMC10002928 DOI: 10.1111/jcmm.17679] [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: 09/14/2022] [Revised: 01/01/2023] [Accepted: 01/06/2023] [Indexed: 02/25/2023] Open
Abstract
The lens is transparent, non-vascular, elastic and wrapped in a transparent capsule. The lens oppacity of AQP5-/- mice was increased more than that of wild-type (AQP5+/+ ) mice. In this study, we explored the potential functional role of circular RNAs (circRNAs) and transcription factor HSF4 in lens opacity in aquaporin 5 (AQP5) knockout (AQP5-/- ) mice. Autophagy was impaired in the lens tissues of AQP5-/- mice. Autophagic lysosomes in lens epithelial cells of AQP5-/- mice were increased compared with AQP5+/+ mice, based on analysis by transmission electron microscopy. The genetic information of the mice lens was obtained by high-throughput sequencing, and then the downstream genes were analysed. A circRNA-miRNA-mRNA network related to lysosomal pathway was constructed by the bioinformatics analysis of the differentially expressed circRNAs. Based on the prediction of the TargetScan website and the validation by dual luciferase reporter assay and RNA immunoprecipitation-qPCR, we found that circRNA (Chr16: 33421321-33468183+) inhibited the function of HSF4 by sponging microRNA (miR-149-5p), and it downregulated the normal expression of lysosome-related mRNAs. The accumulation of autophagic lysosome may be one of the reasons for the abnormal development of the lens in AQP5-/- mice.
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Affiliation(s)
- Hu Shaohua
- Department of Human Anatomy, Histology and Embryology, School of Basic Medicine, Qingdao University, Qingdao, China
| | - Wang Yihui
- Department of Human Anatomy, Histology and Embryology, School of Basic Medicine, Qingdao University, Qingdao, China
| | - Zhang Kaier
- Department of Human Anatomy, Histology and Embryology, School of Basic Medicine, Qingdao University, Qingdao, China
| | - Bai Ying
- Department of Human Anatomy, Histology and Embryology, School of Basic Medicine, Qingdao University, Qingdao, China
| | - Wang Xiaoyi
- Department of Human Anatomy, Histology and Embryology, School of Basic Medicine, Qingdao University, Qingdao, China
| | - Zhao Hui
- The 971 Hospital of the Chinese People's Liberation Army Navy, Qingdao, China
| | - Di Guohu
- Department of Human Anatomy, Histology and Embryology, School of Basic Medicine, Qingdao University, Qingdao, China
| | - Chen Peng
- Department of Human Anatomy, Histology and Embryology, School of Basic Medicine, Qingdao University, Qingdao, China.,Institute of Stem Cell Regeneration Medicine, School of Basic Medicine, Qingdao University, Qingdao, China
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4
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Aquaporins Display a Diversity in their Substrates. J Membr Biol 2023; 256:1-23. [PMID: 35986775 DOI: 10.1007/s00232-022-00257-7] [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: 12/29/2021] [Accepted: 07/13/2022] [Indexed: 02/07/2023]
Abstract
Aquaporins constitute a family of transmembrane proteins that function to transport water and other small solutes across the cell membrane. Aquaporins family members are found in diverse life forms. Aquaporins share the common structural fold consisting of six transmembrane alpha helices with a central water-transporting channel. Four such monomers assemble together to form tetramers as their biological unit. Initially, aquaporins were discovered as water-transporting channels, but several studies supported their involvement in mediating the facilitated diffusion of different solutes. The so-called water channel is able to transport a variety of substrates ranging from a neutral molecule to a charged molecule or a small molecule to a bulky molecule or even a gas molecule. This article gives an overview of a diverse range of substrates conducted by aquaporin family members. Prime focus is on human aquaporins where aquaporins show a wide tissue distribution and substrate specificity leading to various physiological functions. This review also highlights the structural mechanisms leading to the transport of water and glycerol. More research is needed to understand how one common fold enables the aquaporins to transport an array of solutes.
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5
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Gletten RB, Cantrell LS, Bhattacharya S, Schey KL. Lens Aquaporin-5 Inserts Into Bovine Fiber Cell Plasma Membranes Via Unconventional Protein Secretion. Invest Ophthalmol Vis Sci 2022; 63:5. [PMID: 35816045 PMCID: PMC9284464 DOI: 10.1167/iovs.63.8.5] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Purpose To spatially map aquaporin-5 (AQP5) expression in the bovine lens, molecularly characterize cytoplasmic AQP5-containing vesicles in the outer cortex, and elucidate AQP5 membrane trafficking mechanisms. Methods Immunofluorescence was performed on bovine lens cryosections using AQP5, TOMM20, COX IV, calnexin, LC3B, Sec22β, LIMP-2, and connexin 50 antibodies and the membrane dye CM-DiI. AQP5 plasma membrane insertion was defined via line expression profile analysis. Transmission electron microscopy (TEM) was performed on bovine lens sections to examine cytoplasmic organelle morphology and subcellular localization in cortical fiber cells. Bovine lenses were treated with 10-nM bafilomycin A1 or 0.1% dimethyl sulfoxide vehicle control for 24 hours in ex vivo culture to determine changes in AQP5 plasma membrane expression. Results Immunofluorescence analysis revealed cytoplasmic AQP5 expression in lens epithelial cells and differentiating fiber cells. In the lens cortex, complete AQP5 plasma membrane insertion occurs at r/a = 0.951 ± 0.005. AQP5-containing cytoplasmic vesicles are spheroidal in morphology with linear extensions, express TOMM20, and contain LC3B and LIMP-2, but not Sec22β, as fiber cells mature. TEM analysis revealed complex vesicular assemblies with congruent subcellular localization to AQP5-containing cytoplasmic vesicles. AQP5-containing cytoplasmic vesicles appear to dock with the plasma membrane. Bafilomycin A1 treatment reduced AQP5 plasma membrane expression by 27%. Conclusions AQP5 localizes to spheroidal, linear cytoplasmic vesicles in the differentiating bovine lens fiber cells. During fiber cell differentiation, these vesicles incorporate LC3B and presumably fuse with LIMP-2–positive lysosomes. Our data suggest that AQP5 to the plasma membrane through lysosome-associated unconventional protein secretion, a novel mechanism of AQP5 trafficking.
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Affiliation(s)
- Romell B Gletten
- Department of Biochemistry, Vanderbilt University, Nashville, Tennessee, United States
| | - Lee S Cantrell
- Department of Biochemistry, Vanderbilt University, Nashville, Tennessee, United States
| | - Sujoy Bhattacharya
- Department of Ophthalmology and Visual Sciences, Vanderbilt University, Nashville, Tennessee, United States
| | - Kevin L Schey
- Department of Biochemistry, Vanderbilt University, Nashville, Tennessee, United States
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6
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Chu H, Zheng H, Miao A, Deng C, Sun N. Probing region-resolved heterogeneity of phosphoproteome in human lens by hybrid metal organic frameworks. CHINESE CHEM LETT 2022. [DOI: 10.1016/j.cclet.2022.07.059] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
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7
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Zahraei A, Guo G, Varnava KG, Demarais NJ, Donaldson PJ, Grey AC. Mapping Glucose Uptake, Transport and Metabolism in the Bovine Lens Cortex. Front Physiol 2022; 13:901407. [PMID: 35711316 PMCID: PMC9194507 DOI: 10.3389/fphys.2022.901407] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2022] [Accepted: 05/04/2022] [Indexed: 11/13/2022] Open
Abstract
Purpose: To spatially correlate the pattern of glucose uptake to glucose transporter distributions in cultured lenses and map glucose metabolism in different lens regions. Methods: Ex vivo bovine lenses were incubated in artificial aqueous humour containing normoglycaemic stable isotopically-labelled (SIL) glucose (5 mM) for 5 min-20 h. Following incubations, lenses were frozen for subsequent matrix-assisted laser desorption/ionisation (MALDI) imaging mass spectrometry (IMS) analysis using high resolution mass spectrometry. Manually dissected, SIL-incubated lenses were subjected to gas chromatography-mass spectrometry (GC-MS) to verify the identity of metabolites detected by MALDI-IMS. Normal, unincubated lenses were manually dissected into epithelium flat mounts and fibre cell fractions and then subjected to either gel-based proteomic analysis (Gel-LC/MS) to detect facilitative glucose transporters (GLUTs) by liquid chromatography tandem mass spectrometry (LC-MS/MS). Indirect immunofluorescence and confocal microscopy of axial lens sections from unincubated fixed lenses labelled with primary antibodies specific for GLUT 1 or GLUT 3 were utilised for protein localisation. Results: SIL glucose uptake at 5 min was concentrated in the equatorial region of the lens. At later timepoints, glucose gradually distributed throughout the epithelium and the cortical lens fibres, and eventually the deeper lens nucleus. SIL glucose metabolites found in glycolysis, the sorbitol pathway, the pentose phosphate pathway, and UDP-glucose formation were mapped to specific lens regions, with distinct regional signal changes up to 20 h of incubation. Spatial proteomic analysis of the lens epithelium detected GLUT1 and GLUT3. GLUT3 was in higher abundance than GLUT1 throughout the epithelium, while GLUT1 was more abundant in lens fibre cells. Immunohistochemical mapping localised GLUT1 to epithelial and cortical fibre cell membranes. Conclusion: The major uptake site of glucose in the bovine lens has been mapped to the lens equator. SIL glucose is rapidly metabolised in epithelial and fibre cells to many metabolites, which are most abundant in the metabolically more active cortical fibre cells in comparison to central fibres, with low levels of metabolic activity observed in the nucleus.
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Affiliation(s)
- Ali Zahraei
- Department of Physiology in the School of Medical Sciences, Auckland, New Zealand
| | - George Guo
- Department of Physiology in the School of Medical Sciences, Auckland, New Zealand.,Mass Spectrometry Hub, Auckland, New Zealand
| | - Kyriakos G Varnava
- Department of Physiology in the School of Medical Sciences, Auckland, New Zealand.,Mass Spectrometry Hub, Auckland, New Zealand
| | - Nicholas J Demarais
- Mass Spectrometry Hub, Auckland, New Zealand.,School of Biological Sciences, University of Auckland, Auckland, New Zealand
| | - Paul J Donaldson
- Department of Physiology in the School of Medical Sciences, Auckland, New Zealand
| | - Angus C Grey
- Department of Physiology in the School of Medical Sciences, Auckland, New Zealand.,Mass Spectrometry Hub, Auckland, New Zealand
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8
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Schey KL, Gletten RB, O’Neale CVT, Wang Z, Petrova RS, Donaldson PJ. Lens Aquaporins in Health and Disease: Location is Everything! Front Physiol 2022; 13:882550. [PMID: 35514349 PMCID: PMC9062079 DOI: 10.3389/fphys.2022.882550] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2022] [Accepted: 03/23/2022] [Indexed: 01/07/2023] Open
Abstract
Cataract and presbyopia are the leading cause of vision loss and impaired vision, respectively, worldwide. Changes in lens biochemistry and physiology with age are responsible for vision impairment, yet the specific molecular changes that underpin such changes are not entirely understood. In order to preserve transparency over decades of life, the lens establishes and maintains a microcirculation system (MCS) that, through spatially localized ion pumps, induces circulation of water and nutrients into (influx) and metabolites out of (outflow and efflux) the lens. Aquaporins (AQPs) are predicted to play important roles in the establishment and maintenance of local and global water flow throughout the lens. This review discusses the structure and function of lens AQPs and, importantly, their spatial localization that is likely key to proper water flow through the MCS. Moreover, age-related changes are detailed and their predicted effects on the MCS are discussed leading to an updated MCS model. Lastly, the potential therapeutic targeting of AQPs for prevention or treatment of cataract and presbyopia is discussed.
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Affiliation(s)
- Kevin L. Schey
- Department of Biochemistry, School of Medicine, Vanderbilt University, Nashville, TN, United States,*Correspondence: Kevin L. Schey,
| | - Romell B. Gletten
- Department of Biochemistry, School of Medicine, Vanderbilt University, Nashville, TN, United States
| | - Carla V. T. O’Neale
- Department of Biochemistry, School of Medicine, Vanderbilt University, Nashville, TN, United States
| | - Zhen Wang
- Department of Biochemistry, School of Medicine, Vanderbilt University, Nashville, TN, United States
| | - Rosica S. Petrova
- Department of Physiology, School of Medical Sciences, University of Auckland, Auckland, New Zealand
| | - Paul J. Donaldson
- Department of Physiology, School of Medical Sciences, University of Auckland, Auckland, New Zealand
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9
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Cantrell LS, Schey KL. Proteomic characterization of the human lens and Cataractogenesis. Expert Rev Proteomics 2021; 18:119-135. [PMID: 33849365 DOI: 10.1080/14789450.2021.1913062] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
INTRODUCTION The goal of this review is to highlight the triumphs and frontiers in measurement of the lens proteome as it relates to onset of age-related nuclear cataract. As global life expectancy increases, so too does the frequency of age-related nuclear cataracts. Molecular therapeutics do not exist for delay or relief of cataract onset in humans. Since lens fiber cells are incapable of protein synthesis after initial maturation, age-related changes in proteome composition and post-translational modification accumulation can be measured with various techniques. Several of these modifications have been associated with cataract onset. AREAS COVERED We discuss the impact of long-lived proteins on the lens proteome and lens homeostasis as well as proteomic techniques that may be used to measure proteomes at various levels of proteomic specificity and spatial resolution. EXPERT OPINION There is clear evidence that several proteome modifications are correlated with cataract formation. Past studies should be enhanced with cutting-edge, spatially resolved mass spectrometry techniques to enhance the specificity and sensitivity of modification detection as it relates to cataract formation.
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Affiliation(s)
- Lee S Cantrell
- Department of Biochemistry, Vanderbilt University, Nashville, TN, United States
| | - Kevin L Schey
- Department of Biochemistry, Vanderbilt University, Nashville, TN, United States
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10
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Schey KL, Wang Z, Friedrich MG, Garland DL, Truscott RJW. Spatiotemporal changes in the human lens proteome: Critical insights into long-lived proteins. Prog Retin Eye Res 2019; 76:100802. [PMID: 31704338 DOI: 10.1016/j.preteyeres.2019.100802] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2019] [Revised: 10/24/2019] [Accepted: 10/30/2019] [Indexed: 12/15/2022]
Abstract
The ocular lens is a unique tissue that contains an age gradient of cells and proteins ranging from newly differentiated cells containing newly synthesized proteins to cells and proteins that are as old as the organism. Thus, the ocular lens is an excellent model for studying long-lived proteins (LLPs) and the effects of aging and post-translational modifications on protein structure and function. Given the architecture of the lens, with young fiber cells in the outer cortex and the oldest cells in the lens nucleus, spatially-resolved studies provide information on age-specific protein changes. In this review, experimental strategies and proteomic methods that have been used to examine age-related and cataract-specific changes to the human lens proteome are described. Measured spatio-temporal changes in the human lens proteome are summarized and reveal a highly consistent, time-dependent set of modifications observed in transparent human lenses. Such measurements have led to the discovery of cataract-specific modifications and the realization that many animal systems are unsuitable to study many of these modifications. Mechanisms of protein modifications such as deamidation, racemization, truncation, and protein-protein crosslinking are presented and the implications of such mechanisms for other long-lived proteins in other tissues are discussed in the context of age-related neurological diseases. A comprehensive understanding of LLP modifications will enhance our ability to develop new therapies for the delay, prevention or reversal of age-related diseases.
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Affiliation(s)
- Kevin L Schey
- Department of Biochemistry, Vanderbilt University, USA.
| | - Zhen Wang
- Department of Biochemistry, Vanderbilt University, USA
| | - Michael G Friedrich
- Illawarra Health and Medical Research Institute, University of Wollongong, Australia
| | | | - Roger J W Truscott
- Illawarra Health and Medical Research Institute, University of Wollongong, Australia
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11
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Demarais NJ, Donaldson PJ, Grey AC. Age-related spatial differences of human lens UV filters revealed by negative ion mode MALDI imaging mass spectrometry. Exp Eye Res 2019; 184:146-151. [PMID: 31004573 DOI: 10.1016/j.exer.2019.04.016] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Revised: 04/08/2019] [Accepted: 04/16/2019] [Indexed: 01/01/2023]
Abstract
Tryptophan-derived UV filters are predominantly found in the lenses of primates and humans. While protective against UV radiation, aging alters the complement and spatial distributions of human lens UV filters, and a role for UV filters has been suggested in age-related cataract formation. To establish how the spatial distributions of UV filters change in normal human lens aging, matrix assisted laser desorption/ionisation-imaging mass spectrometry (MALDI-IMS) was utilised to map the locations and relative abundance of multiple UV filters simultaneously. Frozen human lenses were cryosectioned axially, and the 20 μm-thick sections coated with MALDI matrix via robotic sprayer and analysed using negative ion mode MALDI-Fourier transform-ion cyclotron resonance MS. While signal for many UV filters was detected throughout the lenses, signal intensity was generally highest in the central (embryonic) nucleus and decreased uniformly in outer (foetal, juvenile, adult) nuclear and cortical regions, and many UV filter signals declined with age. In contrast, two antioxidant-conjugated UV filters (Cys-3-OHKG and GSH-3-OHKG) were restricted to the lens nucleus and their relative signal increased with increasing lens age. The enhanced spatial resolution of MALDI-IMS over manual trephine dissection techniques and its multiplex capability allowed the spatial relationships between lens UV filters to be established and explored in relation to aging. Together these results confirmed that the complement of UV filters in each lens is dynamic and undergoes significant age-related changes. In the future, this information could be used to compare with other lens biomolecule changes to better understand the lens aging process and age-related cataract formation.
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Affiliation(s)
- Nicholas J Demarais
- School of Biological Sciences, University of Auckland, Auckland, New Zealand
| | - Paul J Donaldson
- Department of Physiology, School of Medical Sciences, University of Auckland, Auckland, New Zealand
| | - Angus C Grey
- Department of Physiology, School of Medical Sciences, University of Auckland, Auckland, New Zealand.
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12
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Kumari SS, Varadaraj K. A predominant form of C-terminally end-cleaved AQP0 functions as an open water channel and an adhesion protein in AQP0 ΔC/ΔC mouse lens. Biochem Biophys Res Commun 2019; 511:626-630. [PMID: 30826060 DOI: 10.1016/j.bbrc.2019.02.098] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2019] [Accepted: 02/19/2019] [Indexed: 01/14/2023]
Abstract
The purpose of this investigation was to find out whether C-terminally end-cleaved aquaporin 0 (AQP0), that is present predominantly in the lens mature fiber cells of the WT, functions as a water channel and a cell-to-cell adhesion (CTCA) protein in a knockin (KI) mouse model (AQP0ΔC/ΔC) that does not express intact AQP0. A genetically engineered KI mouse model, AQP0ΔC/ΔC, expressing only end-cleaved AQP0 was developed. This model expresses 1-246 amino acids of AQP0, instead of the full length 1-263 amino acids. Lens transparency of postnatal day 10 (P10) was analyzed qualitatively by dark field imaging. WT, AQP0+/- and AQP0+/ΔC lenses were transparent; AQP0-/- and AQP0ΔC/ΔC mouse lenses displayed loss of transparency. Lens fiber cell membrane vesicles (FCMVs) were prepared from wild type (WT), AQP0 heterozygous (AQP0+/-), AQP0 knockout (AQP0-/-), AQP0+/ΔC and AQP0ΔC/ΔC; water permeability (Pf) was measured using the osmotic shrinking method. CTCA assay was performed using adhesion-deficient L-cells and FCMVs prepared from the abovementioned genotypes. FCMVs of AQP0+/- and AQP0-/- showed a statistically significant reduction (P < 0.001) in Pf and CTCA compared to those of WT. AQP0+/ΔC and AQP0ΔC/ΔC FCMVs exhibited no statistically significant alteration (P > 0.05) in Pf compared to those of WT. However, CTCA of AQP0+/ΔC AQP0ΔC/ΔC FCMVs was significantly higher (P < 0.001) than that of WT FCMVs. Our experiments clearly show that C-terminally end-cleaved AQP0 can function both as a water channel and a CTCA molecule in the lens fiber cell membranes. Also, end-truncation plays an important role in increasing the CTCA between fiber cells.
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Affiliation(s)
| | - Kulandaiappan Varadaraj
- Physiology and Biophysics, Stony Brook University, NY, USA; SUNY Eye Institute, Syracuse, NY, USA.
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13
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Schey KL, Petrova RS, Gletten RB, Donaldson PJ. The Role of Aquaporins in Ocular Lens Homeostasis. Int J Mol Sci 2017; 18:E2693. [PMID: 29231874 PMCID: PMC5751294 DOI: 10.3390/ijms18122693] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2017] [Revised: 12/08/2017] [Accepted: 12/08/2017] [Indexed: 12/13/2022] Open
Abstract
Abstract: Aquaporins (AQPs), by playing essential roles in the maintenance of ocular lens homeostasis, contribute to the establishment and maintenance of the overall optical properties of the lens over many decades of life. Three aquaporins, AQP0, AQP1 and AQP5, each with distinctly different functional properties, are abundantly and differentially expressed in the different regions of the ocular lens. Furthermore, the diversity of AQP functionality is increased in the absence of protein turnover by age-related modifications to lens AQPs that are proposed to alter AQP function in the different regions of the lens. These regional differences in AQP functionality are proposed to contribute to the generation and directionality of the lens internal microcirculation; a system of circulating ionic and fluid fluxes that delivers nutrients to and removes wastes from the lens faster than could be achieved by passive diffusion alone. In this review, we present how regional differences in lens AQP isoforms potentially contribute to this microcirculation system by highlighting current areas of investigation and emphasizing areas where future work is required.
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Affiliation(s)
- Kevin L Schey
- Department of Biochemistry, Vanderbilt University, Nashville, TN 37240, USA.
| | - Rosica S Petrova
- Department of Physiology, School of Medical Sciences, New Zealand National Eye Centre, University of Auckland, Auckland 1023, New Zealand.
| | - Romell B Gletten
- Department of Biochemistry, Vanderbilt University, Nashville, TN 37240, USA.
| | - Paul J Donaldson
- Department of Physiology, School of Medical Sciences, New Zealand National Eye Centre, University of Auckland, Auckland 1023, New Zealand.
- School of Optometry and Vison Sciences, New Zealand National Eye Centre, University of Auckland, Auckland 1023, New Zealand.
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14
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Petrova RS, Webb KF, Vaghefi E, Walker K, Schey KL, Donaldson PJ. Dynamic functional contribution of the water channel AQP5 to the water permeability of peripheral lens fiber cells. Am J Physiol Cell Physiol 2017; 314:C191-C201. [PMID: 29118028 DOI: 10.1152/ajpcell.00214.2017] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Although the functionality of the lens water channels aquaporin 1 (AQP1; epithelium) and AQP0 (fiber cells) is well established, less is known about the role of AQP5 in the lens. Since in other tissues AQP5 functions as a regulated water channel with a water permeability (PH2O) some 20 times higher than AQP0, AQP5 could function to modulate PH2O in lens fiber cells. To test this possibility, a fluorescence dye dilution assay was used to calculate the relative PH2O of epithelial cells and fiber membrane vesicles isolated from either the mouse or rat lens, in the absence and presence of HgCl2, an inhibitor of AQP1 and AQP5. Immunolabeling of lens sections and fiber membrane vesicles from mouse and rat lenses revealed differences in the subcellular distributions of AQP5 in the outer cortex between species, with AQP5 being predominantly membranous in the mouse but predominantly cytoplasmic in the rat. In contrast, AQP0 labeling was always membranous in both species. This species-specific heterogeneity in AQP5 membrane localization was mirrored in measurements of PH2O, with only fiber membrane vesicles isolated from the mouse lens, exhibiting a significant Hg2+-sensitive contribution to PH2O. When rat lenses were first organ cultured, immunolabeling revealed an insertion of AQP5 into cortical fiber cells, and a significant increase in Hg2+-sensitive PH2O was detected in membrane vesicles. Our results show that AQP5 forms functional water channels in the rodent lens, and they suggest that dynamic membrane insertion of AQP5 may regulate water fluxes in the lens by modulating PH2O in the outer cortex.
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Affiliation(s)
- Rosica S Petrova
- Department of Physiology, School of Medical Sciences, University of Auckland , Auckland , New Zealand
| | - Kevin F Webb
- Department of Physiology, School of Medical Sciences, University of Auckland , Auckland , New Zealand.,Optics and Photonics Research Group, Department of Electrical and Electronic Engineering, University of Nottingham , Nottingham , United Kingdom
| | - Ehsan Vaghefi
- School of Optometry and Vision Sciences, New Zealand National Eye Centre, University of Auckland , Auckland , New Zealand
| | - Kerry Walker
- Department of Physiology, School of Medical Sciences, University of Auckland , Auckland , New Zealand
| | - Kevin L Schey
- Department of Biochemistry, Vanderbilt University , Nashville, Tennessee
| | - Paul J Donaldson
- Department of Physiology, School of Medical Sciences, University of Auckland , Auckland , New Zealand.,School of Optometry and Vision Sciences, New Zealand National Eye Centre, University of Auckland , Auckland , New Zealand
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15
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Chen BJ, Lam TC, Liu LQ, To CH. Post-translational modifications and their applications in eye research (Review). Mol Med Rep 2017; 15:3923-3935. [PMID: 28487982 DOI: 10.3892/mmr.2017.6529] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2016] [Accepted: 02/22/2017] [Indexed: 02/05/2023] Open
Abstract
Gene expression is the process by which genetic information is used for the synthesis of a functional gene product, and ultimately regulates cell function. The increase of biological complexity from genome to proteome is vast, and the post-translational modification (PTM) of proteins contribute to this complexity. The study of protein expression and PTMs has attracted attention in the post‑genomic era. Due to the limited capability of conventional biochemical techniques in the past, large‑scale PTM studies were technically challenging. The introduction of effective protein separation methods, specific PTM purification strategies and advanced mass spectrometers has enabled the global profiling of PTMs and the identification of a targeted PTM within the proteome. The present review provides an overview of current proteomic technologies being applied in eye research, with a particular focus on studies of PTMs in ocular tissues and ocular diseases.
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Affiliation(s)
- Bing-Jie Chen
- Department of Optometry and Visual Science, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, P.R. China
| | - Thomas Chuen Lam
- Laboratory of Experimental Optometry, Centre for Myopia Research, School of Optometry, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, SAR, P.R. China
| | - Long-Qian Liu
- Department of Optometry and Visual Science, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, P.R. China
| | - Chi-Ho To
- Laboratory of Experimental Optometry, Centre for Myopia Research, School of Optometry, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, SAR, P.R. China
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16
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Abstract
The lens is an avascular organ composed of an anterior epithelial cell layer and fiber cells that form the bulk of the organ. The lens expresses connexin43 (Cx43), connexin46 (Cx46) and connexin50 (Cx50). Epithelial Cx50 has critical roles in cell proliferation and differentiation, likely involving growth factor-dependent signaling pathways. Both Cx46 and Cx50 are crucial for lens transparency; mutations in their genes have been linked to congenital and age-related cataracts. Congenital cataract-associated connexin mutants can affect protein trafficking, stability and/or function, and the functional effects may differ between gap junction channels and hemichannels. Dominantly inherited cataracts may result from effects of the connexin mutant on its wild type isotype, the other co-expressed wild type connexin and/or its interaction with other cellular components.
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Affiliation(s)
| | - Anaclet Ngezahayo
- Institute of Biophysics, Leibniz University Hannover, Hannover, Germany.
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17
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Nakazawa Y, Oka M, Funakoshi-Tago M, Tamura H, Takehana M. The Extracellular C-loop Domain Plays an Important Role in the Cell Adhesion Function of Aquaporin 0. Curr Eye Res 2016; 42:617-624. [PMID: 27754715 DOI: 10.1080/02713683.2016.1217547] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
PURPOSE Although aquaporin 0 (AQP0) is a member of the AQP family, it has limited water permeability compared with other members. AQP0 may also have cell adhesion-related functions, but the evidence is still limited. Here, we studied the relationship of AQP0 to cell adhesion and determined the region required for cell adhesion. METHODS L-cell fibroblasts stably expressing AQP0 or AQP1 (L-AQP0 or L-AQP1) were established. One group of cells was stained with CellTracker Red and cultured into a confluent monolayer, whereas the other group was loaded with CellTracker Blue and seeded over the monolayer. To study cell adhesion, the percentages of lower and upper layer cells were measured using flow cytometry. To determine the region of AQP0 required for adhesion, activity was done by pull-down assay using glutathione S-transferase fusion proteins. To study the water permeability, Xenopus laevis oocyte expressing AQP0 wild-type or AQP0 mutated in C-loop was transferred to a hypotonic solution and photographed, and the diameter was measured to calculate the volume. RESULTS More cells adhered to the lower cells in the L-AQP0 homotypic pair than other pairs such as L-AQP1 homotypic or L-AQP0/L-AQP1 heterotypic pairs. Pull-down assays revealed that AQP0 could bind to itself via the C-loop extracellular domain. Furthermore, we determined that 109Pro and 110Pro in the C-loop were important for cell adhesion. However, mutation of the C-loop in AQP0 did not affect its water permeability. CONCLUSIONS AQP0 is known to bind lipids in the opposing membrane. Our data suggest that this cell-to-cell adhesion occurs not only in the AQP0/liquids but also via AQP0/AQP0 interaction through the C-loop domain. Mutations in the C-loop amino acids did not affect the water permeability of AQP0 but did affect its cell adhesion function. These independent dual functions of AQP0 are important for lens transparency.
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Affiliation(s)
| | - Mikako Oka
- b Center for Pharmaceutical Education , Yokohama University of Pharmacy , Kanagawa , Japan
| | | | | | - Makoto Takehana
- a Faculty of Pharmacy , Keio University , Tokyo , Japan.,b Center for Pharmaceutical Education , Yokohama University of Pharmacy , Kanagawa , Japan
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18
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Slavi N, Wang Z, Harvey L, Schey KL, Srinivas M. Identification and Functional Assessment of Age-Dependent Truncations to Cx46 and Cx50 in the Human Lens. Invest Ophthalmol Vis Sci 2016; 57:5714-5722. [PMID: 27787559 PMCID: PMC5089213 DOI: 10.1167/iovs.16-19698] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2016] [Accepted: 08/21/2016] [Indexed: 11/24/2022] Open
Abstract
PURPOSE Many proteins in the lens undergo extensive posttranslational modifications (PTMs) with age, leading to alterations in their function. The extent to which lens gap junction proteins, Cx46 and Cx50, accumulate PTMs with aging is not known. In this study, we identified truncations in Cx46 and Cx50 in the human lens using mass spectrometry. We also examined the effect of truncations on channel function using electrophysiological measurements. METHODS Human lenses were dissected into cortex, outer nucleus, and nucleus regions, and fiber cell membranes were subjected to trypsin digestion. Tryptic peptides were analyzed by liquid chromatography (LC)-electrospray tandem mass spectrometry (ESI/MS/MS). Effects of truncations on channel conductance, permeability, and gating were assessed in transfected cells. RESULTS Cleavage sites were identified in the C-terminus, the cytoplasmic loop, and the N-terminus of Cx46 and Cx50. Levels of C-terminal truncations, which were found at residues 238 to 251 in Cx46 and at residues 238 to 253 and 274 to 284 in Cx50, were similar in different lens regions. In contrast, levels of truncations in cytoplasmic loop and N-terminal domains of Cx46 and Cx50 increased dramatically from outer cortex to nucleus. Most of the C-terminally truncated proteins were functional, whereas truncations in the cytoplasmic loop did not result in the formation of functional channels. CONCLUSIONS Accumulation of cytoplasmic loop and N-terminal truncations in the core might lead to decreases in coupling with age. This reduction is expected to lead to an increase in intracellular calcium and a decrease in levels of glutathione in the nucleus. These changes may ultimately lead to age-related nuclear cataracts.
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Affiliation(s)
- Nefeli Slavi
- Department of Biological and Vision Sciences and the Graduate Center for Vision Research, SUNY College of Optometry, New York, New York, United States
| | - Zhen Wang
- Department of Biochemistry and Mass Spectrometry Research Center Vanderbilt University School of Medicine, Nashville, Tennessee, United States
| | - Lucas Harvey
- Department of Biological and Vision Sciences and the Graduate Center for Vision Research, SUNY College of Optometry, New York, New York, United States
| | - Kevin L. Schey
- Department of Biochemistry and Mass Spectrometry Research Center Vanderbilt University School of Medicine, Nashville, Tennessee, United States
| | - Miduturu Srinivas
- Department of Biological and Vision Sciences and the Graduate Center for Vision Research, SUNY College of Optometry, New York, New York, United States
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19
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Wenke JL, McDonald WH, Schey KL. Spatially Directed Proteomics of the Human Lens Outer Cortex Reveals an Intermediate Filament Switch Associated With the Remodeling Zone. Invest Ophthalmol Vis Sci 2016; 57:4108-14. [PMID: 27537260 PMCID: PMC4991037 DOI: 10.1167/iovs.16-19791] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2016] [Accepted: 06/15/2016] [Indexed: 01/25/2023] Open
Abstract
PURPOSE To quantify protein changes in the morphologically distinct remodeling zone (RZ) and adjacent regions of the human lens outer cortex using spatially directed quantitative proteomics. METHODS Lightly fixed human lens sections were deparaffinized and membranes labeled with fluorescent wheat germ agglutinin (WGA-TRITC). Morphology directed laser capture microdissection (LCM) was used to isolate tissue from four distinct regions of human lens outer cortex: differentiating zone (DF), RZ, transition zone (TZ), and inner cortex (IC). Liquid chromatography-tandem mass spectrometry (LC-MS/MS) of the plasma membrane fraction from three lenses (21-, 22-, and 27-year) revealed changes in major cytoskeletal proteins including vimentin, filensin, and phakinin. Peptides from proteins of interest were quantified using multiple reaction monitoring (MRM) mass spectrometry and isotopically-labeled internal peptide standards. RESULTS Results revealed an intermediate filament switch from vimentin to beaded filament proteins filensin and phakinin that occurred at the RZ. Several other cytoskeletal proteins showed significant changes between regions, while most crystallins remained unchanged. Targeted proteomics provided accurate, absolute quantification of these proteins and confirmed vimentin, periplakin, and periaxin decrease from the DF to the IC, while filensin, phakinin, and brain acid soluble protein 1 (BASP1) increase significantly at the RZ. CONCLUSIONS Mass spectrometry-compatible fixation and morphology directed laser capture enabled proteomic analysis of narrow regions in the human lens outer cortex. Results reveal dramatic cytoskeletal protein changes associated with the RZ, suggesting that one role of these proteins is in membrane deformation and/or the establishment of ball and socket joints in the human RZ.
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20
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Petrova RS, Schey KL, Donaldson PJ, Grey AC. Spatial distributions of AQP5 and AQP0 in embryonic and postnatal mouse lens development. Exp Eye Res 2015; 132:124-35. [PMID: 25595964 DOI: 10.1016/j.exer.2015.01.011] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2014] [Revised: 12/19/2014] [Accepted: 01/12/2015] [Indexed: 12/11/2022]
Abstract
The expression of the water channel protein aquaporin (AQP)-5 in adult rodent and human lenses was recently reported using immunohistochemistry, molecular biology, and mass spectrometry techniques, confirming a second transmembrane water channel that is present in lens fibre cells in addition to the abundant AQP0 protein. Interestingly, the sub-cellular distribution and level of post-translational modification of both proteins changes with fibre cell differentiation and location in the adult rodent lens. This study compares the sub-cellular distribution of AQP0 and AQP5 during embryonic and postnatal fibre cell development in the mouse lens to understand how the immunolabelling patterns for both AQPs observed in adult lens are first established. Immunohistochemistry was used to map the cellular and sub-cellular distribution of AQP5 and AQP0 throughout the lens in cryosections from adult (6 weeks-8 months) and postnatal (0-2 weeks) mouse lenses and in sections from paraffin embedded mouse embryos (E10-E19). All sections were imaged by fluorescence confocal microscopy. Using antibodies directed against the C-terminus of each AQP, AQP5 was abundantly expressed early in development, being found in the cytoplasm of cells of the lens vesicle and surrounding tissues (E10), while AQP0 was detected later (E11), and only in the membranes of elongating primary fibre cells. During the course of subsequent embryonic and postnatal development the pattern of cytoplasmic AQP5 and membranous AQP0 labelling was maintained until postnatal day 6 (P6). From P6 AQP5 labelling became progressively more membranous initially in the lens nucleus and then later in all regions of the lens, while AQP0 labelling was abruptly lost in the lens nucleus due to C-terminal truncation. Our results show that the spatial distribution patterns of AQP0 and AQP5 observed in the adult lens are established during a narrow window of postnatal development (P6-P15) that precedes eye opening and coincides with regression of the hyaloid vascular system. Our results support the hypothesis that, in the older fibre cells, insertion of AQP5 into the fibre cell membrane may compensate for any change in the functionality of AQP0 induced by truncation of its C-terminal tail.
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Affiliation(s)
- Rosica S Petrova
- School of Medical Sciences, University of Auckland, Auckland, New Zealand
| | - Kevin L Schey
- Departments of Biochemistry and Ophthalmology, Vanderbilt University, Nashville, TN, USA
| | - Paul J Donaldson
- School of Medical Sciences, University of Auckland, Auckland, New Zealand
| | - Angus C Grey
- School of Medical Sciences, University of Auckland, Auckland, New Zealand.
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21
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Ye H, Mandal R, Catherman A, Thomas PM, Kelleher NL, Ikonomidou C, Li L. Top-down proteomics with mass spectrometry imaging: a pilot study towards discovery of biomarkers for neurodevelopmental disorders. PLoS One 2014; 9:e92831. [PMID: 24710523 PMCID: PMC3978070 DOI: 10.1371/journal.pone.0092831] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2013] [Accepted: 02/27/2014] [Indexed: 11/19/2022] Open
Abstract
In the developing mammalian brain, inhibition of NMDA receptor can induce widespread neuroapoptosis, inhibit neurogenesis and cause impairment of learning and memory. Although some mechanistic insights into adverse neurological actions of these NMDA receptor antagonists exist, our understanding of the full spectrum of developmental events affected by early exposure to these chemical agents in the brain is still limited. Here we attempt to gain insights into the impact of pharmacologically induced excitatory/inhibitory imbalance in infancy on the brain proteome using mass spectrometric imaging (MSI). Our goal was to study changes in protein expression in postnatal day 10 (P10) rat brains following neonatal exposure to the NMDA receptor antagonist dizocilpine (MK801). Analysis of rat brains exposed to vehicle or MK801 and comparison of their MALDI MS images revealed differential relative abundances of several proteins. We then identified these markers such as ubiquitin, purkinje cell protein 4 (PEP-19), cytochrome c oxidase subunits and calmodulin, by a combination of reversed-phase (RP) HPLC fractionation and top-down tandem MS platform. More in-depth large scale study along with validation experiments will be carried out in the future. Overall, our findings indicate that a brief neonatal exposure to a compound that alters excitatory/inhibitory balance in the brain has a long term effect on protein expression patterns during subsequent development, highlighting the utility of MALDI-MSI as a discovery tool for potential biomarkers.
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Affiliation(s)
- Hui Ye
- State Key Laboratory of Natural Medicines, Key Lab of Drug Metabolism and Pharmacokinetics, China Pharmaceutical University, Nanjing, PR China
- Department of Pharmaceutical Analysis, China Pharmaceutical University, Nanjing, PR China
- School of Pharmacy, University of Wisconsin Madison, Madison, Wisconsin, United States of America
| | - Rakesh Mandal
- Department of Neurology, University of Wisconsin Madison, Madison, Wisconsin, United States of America
| | - Adam Catherman
- Proteomics Center of Excellence, Northwestern University, Evanston, Illinois, United States of America
| | - Paul M. Thomas
- Proteomics Center of Excellence, Northwestern University, Evanston, Illinois, United States of America
| | - Neil L. Kelleher
- Proteomics Center of Excellence, Northwestern University, Evanston, Illinois, United States of America
| | - Chrysanthy Ikonomidou
- Department of Neurology, University of Wisconsin Madison, Madison, Wisconsin, United States of America
- * E-mail: (CI); (LL)
| | - Lingjun Li
- School of Pharmacy, University of Wisconsin Madison, Madison, Wisconsin, United States of America
- Department of Chemistry, University of Wisconsin Madison, Madison, Wisconsin, United States of America
- * E-mail: (CI); (LL)
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22
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Schey KL, Wang Z, L Wenke J, Qi Y. Aquaporins in the eye: expression, function, and roles in ocular disease. Biochim Biophys Acta Gen Subj 2013; 1840:1513-23. [PMID: 24184915 DOI: 10.1016/j.bbagen.2013.10.037] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2013] [Revised: 10/22/2013] [Accepted: 10/23/2013] [Indexed: 12/13/2022]
Abstract
BACKGROUND All thirteen known mammalian aquaporins have been detected in the eye. Moreover, aquaporins have been identified as playing essential roles in ocular functions ranging from maintenance of lens and corneal transparency to production of aqueous humor to maintenance of cellular homeostasis and regulation of signal transduction in the retina. SCOPE OF REVIEW This review summarizes the expression and known functions of ocular aquaporins and discusses their known and potential roles in ocular diseases. MAJOR CONCLUSIONS Aquaporins play essential roles in all ocular tissues. Remarkably, not all aquaporin function as a water permeable channel and the functions of many aquaporins in ocular tissues remain unknown. Given their vital roles in maintaining ocular function and their roles in disease, aquaporins represent potential targets for future therapeutic development. GENERAL SIGNIFICANCE Since aquaporins play key roles in ocular physiology, an understanding of these functions is important to improving ocular health and treating diseases of the eye. It is likely that future therapies for ocular diseases will rely on modulation of aquaporin expression and/or function. This article is part of a Special Issue entitled Aquaporins.
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Affiliation(s)
- Kevin L Schey
- Department of Biochemistry, Vanderbilt School of Medicine, Vanderbilt University, Nashville, TN 37232, USA.
| | - Zhen Wang
- Department of Biochemistry, Vanderbilt School of Medicine, Vanderbilt University, Nashville, TN 37232, USA
| | - Jamie L Wenke
- Department of Biochemistry, Vanderbilt School of Medicine, Vanderbilt University, Nashville, TN 37232, USA
| | - Ying Qi
- Department of Biochemistry, Vanderbilt School of Medicine, Vanderbilt University, Nashville, TN 37232, USA
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23
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Schey KL, Anderson DM, Rose KL. Spatially-directed protein identification from tissue sections by top-down LC-MS/MS with electron transfer dissociation. Anal Chem 2013; 85:6767-74. [PMID: 23718750 DOI: 10.1021/ac400832w] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
MALDI imaging mass spectrometry (MALDI-IMS) has become a powerful tool for localizing both small molecules and intact proteins in a wide variety of tissue samples in both normal and diseased states. Identification of imaged signals in MALDI-IMS remains a bottleneck in the analysis and limits the interpretation of underlying biology of tissue specimens. In this work, spatially directed tissue microextraction of intact proteins followed by LC-MS/MS with electron transfer dissociation (ETD) was used to identify proteins from specific locations in three tissue types; ocular lens, brain, and kidney. Detection limits were such that a 1 μL extraction volume was sufficient to deliver proteins to the LC-MS/MS instrumentation with sufficient sensitivity to detect 50-100 proteins in a single experiment. Additionally, multiple modified proteins were identified; including truncated lens proteins that would be difficult to assign to an imaged mass using a bottom-up approach. Protein separation and identification are expected to improve with advances in intact protein fractionation/chromatography and advances in interpretation algorithms leading to increased depth of proteome coverage from distinct tissue locations.
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Affiliation(s)
- Kevin L Schey
- Department of Biochemistry and Mass Spectrometry Research Center, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA.
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24
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Schey KL, Grey AC, Nicklay JJ. Mass spectrometry of membrane proteins: a focus on aquaporins. Biochemistry 2013; 52:3807-17. [PMID: 23394619 DOI: 10.1021/bi301604j] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Membrane proteins are abundant, critically important biomolecules that conduct essential functions in all cells and are the targets of a significant number of therapeutic drugs. However, the analysis of their expression, modification, protein-protein interactions, and structure by mass spectrometry has lagged behind similar studies of soluble proteins. Here we review the limitations to analysis of integral membrane and membrane-associated proteins and highlight advances in sample preparation and mass spectrometry methods that have led to the successful analysis of this protein class. Advances in the analysis of membrane protein posttranslational modification, protein-protein interaction, protein structure, and tissue distributions by imaging mass spectrometry are discussed. Furthermore, we focus our discussion on the application of mass spectrometry for the analysis of aquaporins as a prototypical integral membrane protein and how advances in analytical methods have revealed new biological insights into the structure and function of this family of proteins.
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Affiliation(s)
- Kevin L Schey
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, United States.
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25
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Grey AC, Walker KL, Petrova RS, Han J, Wilmarth PA, David LL, Donaldson PJ, Schey KL. Verification and spatial localization of aquaporin-5 in the ocular lens. Exp Eye Res 2013; 108:94-102. [PMID: 23313152 DOI: 10.1016/j.exer.2012.12.004] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2012] [Revised: 12/07/2012] [Accepted: 12/10/2012] [Indexed: 12/25/2022]
Abstract
Until recently, the lens was thought to express only two aquaporin (AQP) water channels, AQP1 and AQP0. In this study we confirm lenticular AQP5 protein expression by Western blotting and mass spectrometry in lenses from a variety of species. In addition, confocal microscopy was used to map cellular distributions of AQP5 in mouse, rat and human lenses. Tandem mass spectrometry of a human lens membrane preparation revealed extensive sequence coverage (56.2%) of AQP5. Western blotting performed on total fiber cell membranes from mouse, rat, bovine and human lenses confirmed AQP5 protein expression is conserved amongst species. Western blotting of dissected lens fractions suggests that AQP5 is processed in the lens core by C-terminal truncation. Immunohistochemistry showed that AQP5 signal was most abundant in the lens outer cortex and decreased in intensity in the lens core. Furthermore, AQP5 undergoes differentiation-dependent changes in subcellular location from an intracellular localization in differentiating fiber cells to the plasma membrane of mature fiber cells upon the loss of fiber cell nuclei. Our results show that AQP5 is a significant component of lens fiber cell membranes, representing the second most abundant water channel in these cells. Together, the changes to AQP5 distribution and structure are likely to modulate the functional role of AQP5 in different regions of the lens.
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Affiliation(s)
- Angus C Grey
- Department of Optometry and Vision Science, New Zealand National Eye Centre, University of Auckland, Auckland, New Zealand
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26
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Ye H, Gemperline E, Li L. A vision for better health: mass spectrometry imaging for clinical diagnostics. Clin Chim Acta 2012; 420:11-22. [PMID: 23078851 DOI: 10.1016/j.cca.2012.10.018] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2012] [Accepted: 10/09/2012] [Indexed: 12/13/2022]
Abstract
BACKGROUND Mass spectrometry imaging (MSI) is a powerful tool that grants the ability to investigate a broad mass range of molecules from small molecules to large proteins by creating detailed distribution maps of selected compounds. Its usefulness in biomarker discovery towards clinical applications has obtained success by correlating the molecular expression of tissues acquired from MSI with well-established histology. RESULTS To date, MSI has demonstrated its versatility in clinical applications, such as biomarker diagnostics of different diseases, prognostics of disease severities and metabolic response to drug treatment, etc. These studies have provided significant insight in clinical studies over the years and current technical advances are further facilitating the improvement of this field. Although the underlying concept is simple, factors such as choice of ionization method, sample preparation, instrumentation and data analysis must be taken into account for successful applications of MSI. Herein, we briefly reviewed these key elements yet focused on the clinical applications of MSI that cannot be addressed by other means. CONCLUSIONS Challenges and future perspectives in this field are also discussed to conclude that the ever-growing applications with continuous development of this powerful analytical tool will lead to a better understanding of the biology of diseases and improvements in clinical diagnostics.
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Affiliation(s)
- Hui Ye
- School of Pharmacy, University of Wisconsin-Madison, Madison, WI 53705-2222, USA
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27
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Kumari SS, Varadaraj M, Yerramilli VS, Menon AG, Varadaraj K. Spatial expression of aquaporin 5 in mammalian cornea and lens, and regulation of its localization by phosphokinase A. Mol Vis 2012; 18:957-67. [PMID: 22550388 PMCID: PMC3340213] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2012] [Accepted: 04/14/2012] [Indexed: 10/25/2022] Open
Abstract
PURPOSE Aquaporins (AQPs) play a significant role in the movement of water across the plasma membrane. In the eye, the cornea and lens are avascular with unique microcirculatory mechanisms to meet the metabolic demands. We have previously shown that AQP0 and AQP1 water channels participate in maintaining lens transparency and homeostasis. In the present investigation, we explored the expression and spatial distribution of AQP5 in the cornea and lens, and its regulation during membrane localization. METHODS AQP5 expression and cellular localization were investigated by reverse transcription polymerase chain reaction (RT-PCR) using gene-specific primers, and by western blot and immunocytochemistry analyses using specific antibodies. AQP5 phosphorylation was studied using calf intestinal alkaline phosphatase for dephosphorylation. Effects of phosphokinase A (PKA) agonist cyclic AMP (cAMP), and antagonist H-89 on AQP5 expression and localization were studied in vitro using MDCK (Madin-Darby Canine Kidney) cells, and ex vivo using isolated corneas from wild type mice. RESULTS RT-PCR revealed the presence of AQP5 transcripts in the cornea, lens epithelial cells and fiber cells. Western blotting identified the presence of both non-phosphorylated and phosphorylated forms of AQP5 protein. Immunostaining showed the distribution of AQP5 in the epithelial layer and stromal keratocytes of the cornea, and epithelial and fiber cells of the lens. In vitro and ex-vivo experiments revealed PKA-induced AQP5 internalization; PKA inhibition prevented such internalization. CONCLUSIONS This is the first report on the spatial expression of AQP5 in the corneal keratocytes and lens epithelial cells, as well as on the regulation of AQP5 localization by PKA in the corneal epithelial cells. PKA-mediated regulation of AQP5 holds promise for therapeutic intervention to control corneal and lens diseases.
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Affiliation(s)
- S. Sindhu Kumari
- Department of Physiology and Biophysics, State University of New York at Stony Brook, Stony Brook, NY
| | | | - Venkata S. Yerramilli
- Department of Physiology and Biophysics, State University of New York at Stony Brook, Stony Brook, NY
| | - Anil G. Menon
- Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, Cincinnati, OH
| | - Kulandaiappan Varadaraj
- Department of Physiology and Biophysics, State University of New York at Stony Brook, Stony Brook, NY,SUNY Eye Institute, New York, NY
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Wang Z, Schey KL. Aquaporin-0 interacts with the FERM domain of ezrin/radixin/moesin proteins in the ocular lens. Invest Ophthalmol Vis Sci 2011; 52:5079-87. [PMID: 21642618 DOI: 10.1167/iovs.10-6998] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
PURPOSE Aquaporin 0 (AQP0) is the major intrinsic protein in the lens and is essential for establishing proper fiber cell structure and organization. Cytoskeletal proteins that directly interact with the C terminus of AQP0 are identified herein. METHODS The water-insoluble fraction of lens fiber cells was chemically cross-linked, and cross-linked peptides with the C terminus of AQP0 were identified by mass spectrometry. Coimmunoprecipitation and AQP0 C-terminal peptide pulldown experiments were used to confirm the protein-protein interaction. RESULTS Unexpectedly, AQP0 was found to directly associate with ezrin/radixin/moesin (ERM) family members, proteins that are involved in linkage of actin filaments to the plasma membrane. Cross-linked peptides were detected between AQP0 and degenerate sequences of ezrin and radixin; however, AQP0 interaction with ezrin is believed to play a more significant function in the lens because of its higher level of expression and observed ezrin-specific cross-linking. The interaction was found to occur between the C terminus of AQP0 and subdomains F1 and F3 of ERM proteins. The interaction between AQP0 and ezrin was confirmed by coimmunoprecipitation and AQP0 C-terminal peptide pulldown experiments. CONCLUSIONS Considering the important known functions of the cellular actin cytoskeleton in fiber cell differentiation, the interaction of AQP0 and ERM proteins may play an important role in fiber cell morphology, elongation, and organization.
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Affiliation(s)
- Zhen Wang
- Mass Spectrometry Research Center and Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-8575, USA
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29
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Bassnett S, Shi Y, Vrensen GFJM. Biological glass: structural determinants of eye lens transparency. Philos Trans R Soc Lond B Biol Sci 2011; 366:1250-64. [PMID: 21402584 PMCID: PMC3061108 DOI: 10.1098/rstb.2010.0302] [Citation(s) in RCA: 231] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
The purpose of the lens is to project a sharply focused, undistorted image of the visual surround onto the neural retina. The first pre-requisite, therefore, is that the tissue should be transparent. Despite the presence of remarkably high levels of protein, the lens cytosol remains transparent as a result of short-range-order interactions between the proteins. At a cellular level, the programmed elimination of nuclei and other light-scattering organelles from cells located within the pupillary space contributes directly to tissue transparency. Scattering at the cell borders is minimized by the close apposition of lens fibre cells facilitated by a plethora of adhesive proteins, some expressed only in the lens. Similarly, refractive index matching between lens membranes and cytosol is believed to minimize scatter. Refractive index matching between the cytoplasm of adjacent cells is achieved through the formation of cellular fusions that allow the intermingling of proteins. Together, these structural adaptations serve to minimize light scatter and enable this living, cellular structure to function as 'biological glass'.
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Affiliation(s)
- Steven Bassnett
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St Louis, MO, USA
| | - Yanrong Shi
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St Louis, MO, USA
| | - Gijs F. J. M. Vrensen
- Department of Ophthalmology, Leiden University Medical Center, Leiden, The Netherlands
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30
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Unique and analogous functions of aquaporin 0 for fiber cell architecture and ocular lens transparency. Biochim Biophys Acta Mol Basis Dis 2011; 1812:1089-97. [PMID: 21511033 DOI: 10.1016/j.bbadis.2011.04.001] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2010] [Revised: 03/24/2011] [Accepted: 04/01/2011] [Indexed: 11/20/2022]
Abstract
Aquaporin (AQP) 1 and AQP0 water channels are expressed in lens epithelial and fiber cells, respectively, facilitating fluid circulation for nourishing the avascular lens to maintain transparency. Even though AQP0 water permeability is 40-fold less than AQP1, AQP0 is selectively expressed in the fibers. Delimited AQP0 fiber expression is attributed to a unique structural role as an adhesion protein. To validate this notion, we determined if wild type (WT) lens ultrastructure and fiber cell adhesion are different in AQP0(-/-), and TgAQP1(+/+)/AQP0(-/-) mice that transgenically express AQP1 (TgAQP1) in fiber cells without AQP0 (AQP0(-/-)). In WT, lenses were transparent with 'Y' sutures. Fibers contained opposite end curvature, lateral interdigitations, hexagonal shape, and were arranged as concentric growth shells. AQP0(-/-) lenses were cataractous, lacked 'Y' sutures, ordered packing and well-defined lateral interdigitations. TgAQP1(+/+)/AQP0(-/-) lenses showed improvement in transparency and lateral interdigitations in the outer cortex while inner cortex and nuclear fibers were severely disintegrated. Transmission electron micrographs exhibited tightly packed fiber cells in WT whereas AQP0(-/-) and TgAQP1(+/+)/AQP0(-/-) lenses had wide extracellular spaces. Fibers were easily separable by teasing in AQP0(-/-) and TgAQP1(+/+)/AQP0(-/-) lenses compared to WT. Our data suggest that the increased water permeability through AQP1 does not compensate for loss of AQP0 expression in TgAQP1(+/+)/AQP0(-/-) mice. Fiber cell AQP0 expression is required to maintain their organization, which is a requisite for lens transparency. AQP0 appears necessary for cell-to-cell adhesion and thereby to minimize light scattering since in the AQP0(-/-) and TgAQP1(+/+)/AQP0(-/-) lenses, fiber cell disorganization was evident.
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31
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Roulhac PL, Ward JM, Thompson JW, Soderblom EJ, Silva M, Moseley MA, Jarvis ED. Microproteomics: quantitative proteomic profiling of small numbers of laser-captured cells. Cold Spring Harb Protoc 2011; 2011:pdb.prot5573. [PMID: 21285273 DOI: 10.1101/pdb.prot5573] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Petra L Roulhac
- Department of Neurobiology, Howard Hughes Medical Institute, Duke University Medical Center, Durham, North Carolina 27710, USA.
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32
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Mathias RT, White TW, Gong X. Lens gap junctions in growth, differentiation, and homeostasis. Physiol Rev 2010; 90:179-206. [PMID: 20086076 DOI: 10.1152/physrev.00034.2009] [Citation(s) in RCA: 181] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The cells of most mammalian organs are connected by groups of cell-to-cell channels called gap junctions. Gap junction channels are made from the connexin (Cx) family of proteins. There are at least 20 isoforms of connexins, and most tissues express more than 1 isoform. The lens is no exception, as it expresses three isoforms: Cx43, Cx46, and Cx50. A common role for all gap junctions, regardless of their Cx composition, is to provide a conduit for ion flow between cells, thus creating a syncytial tissue with regard to intracellular voltage and ion concentrations. Given this rather simple role of gap junctions, a persistent question has been: Why are there so many Cx isoforms and why do tissues express more than one isoform? Recent studies of lens Cx knockout (KO) and knock in (KI) lenses have begun to answer these questions. To understand these roles, one must first understand the physiological requirements of the lens. We therefore first review the development and structure of the lens, its numerous transport systems, how these systems are integrated to generate the lens circulation, the roles of the circulation in lens homeostasis, and finally the roles of lens connexins in growth, development, and the lens circulation.
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Affiliation(s)
- Richard T Mathias
- Department of Physiology and Biophysics, SUNY at Stony Brook, Stony Brook, New York 11794-8661, USA.
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33
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Wang N, Xu M, Wang P, Li L. Development of Mass Spectrometry-Based Shotgun Method for Proteome Analysis of 500 to 5000 Cancer Cells. Anal Chem 2010; 82:2262-71. [DOI: 10.1021/ac9023022] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Affiliation(s)
- Nan Wang
- Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada
| | - Mingguo Xu
- Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada
| | - Peng Wang
- Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada
| | - Liang Li
- Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada
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Bassnett S, Wilmarth PA, David LL. The membrane proteome of the mouse lens fiber cell. Mol Vis 2009; 15:2448-63. [PMID: 19956408 PMCID: PMC2786885] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2009] [Accepted: 11/18/2009] [Indexed: 11/16/2022] Open
Abstract
PURPOSE Fiber cells of the ocular lens are bounded by a highly specialized plasma membrane. Despite the pivotal role that membrane proteins play in the physiology and pathophysiology of the lens, our knowledge of the structure and composition of the fiber cell plasma membrane remains fragmentary. In the current study, we utilized mass spectrometry-based shotgun proteomics to provide a comprehensive survey of the mouse lens fiber cell membrane proteome. METHODS Membranes were purified from young mouse lenses and subjected to MudPIT (Multidimensional protein identification technology) analysis. The resulting proteomic data were analyzed further by reference to publically available microarray databases. RESULTS More than 200 membrane proteins were identified by MudPIT, including Type I, Type II, Type III (multi-pass), lipid-anchored, and GPI-anchored membrane proteins, in addition to membrane-associated cytoskeletal elements and extracellular matrix components. The membrane proteins of highest apparent abundance included Mip, Lim2, and the lens-specific connexin proteins Gja3, Gja8, and Gje1. Significantly, many proteins previously unsuspected in the lens were also detected, including proteins with roles in cell adhesion, solute transport, and cell signaling. CONCLUSIONS The MudPIT technique constitutes a powerful technique for the analysis of the lens membrane proteome and provides valuable insights into the composition of the lens fiber cell unit membrane.
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Affiliation(s)
- Steven Bassnett
- Ophthalmology & Visual Sciences, Washington University School of Medicine, St. Louis, MO
| | - Phillip A. Wilmarth
- Biochemistry & Molecular Biology, Oregon Health & Science University, Portland, OR
| | - Larry L. David
- Biochemistry & Molecular Biology, Oregon Health & Science University, Portland, OR
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35
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Grey AC, Chaurand P, Caprioli RM, Schey KL. MALDI imaging mass spectrometry of integral membrane proteins from ocular lens and retinal tissue. J Proteome Res 2009; 8:3278-83. [PMID: 19326924 DOI: 10.1021/pr800956y] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
A tissue preparation protocol for MALDI (matrix-assisted laser desorption/ionization) imaging mass spectrometry of integral membrane proteins was developed using ocular lens and retinal tissues as model samples. Frozen bovine and human lenses were cryosectioned equatorially or axially at -20 degrees C into 20 mum-thick tissue sections. Lens sections were mounted onto gold-coated MALDI targets by methanol soft-landing to maintain tissue integrity. Tissue sections underwent extensive water washing to deplete the samples of highly abundant water-soluble proteins. Automated matrix deposition was achieved using an acoustic reagent multispotter, with sinapinic acid as matrix and high percentage acetonitrile as solvent, with a center-to-center spot spacing of 200-300 mum. Molecular images of full-length Aquaporin-0 (AQP0) and its most abundant truncation products were obtained from mass spectral data acquired across whole bovine and human lens sections. In equatorial and axial sections of bovine lenses, full-length AQP0 was detected throughout the lens. A truncation product corresponding to AQP0 (1-260) was detected in the bovine lens core at low abundance. In axial lens sections, no antero-posterior variation was detected. In 11 year-old human lens sections, full-length AQP0 was most abundant in the lens periphery, but was detected throughout the lens. The major truncation product, consisting of AQP0 residues 1-246, was absent from the lens periphery and increased in abundance in the lens core. This tissue preparation protocol was then applied to image the distribution of the G-protein coupled receptor, opsin, in the rabbit retina. This protocol has expanded the variety of target analytes which can be detected by MALDI imaging mass spectrometry to include intact integral membrane proteins.
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Affiliation(s)
- Angus C Grey
- Mass Spectrometry Research Center and Department of Biochemistry, Vanderbilt University Medical Center, Nashville, Tennessee 37232-8575, USA
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36
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Grey AC, Schey KL. Age-related changes in the spatial distribution of human lens alpha-crystallin products by MALDI imaging mass spectrometry. Invest Ophthalmol Vis Sci 2009; 50:4319-29. [PMID: 19387068 DOI: 10.1167/iovs.09-3522] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE To develop a protocol for MALDI (matrix-assisted laser desorption ionization) imaging mass spectrometry for mapping the distributions of alpha-crystallin and its modified forms in human lens tissue as a function of lens age and cataract. METHODS Frozen human lenses were cryosectioned equatorially and axially into 20-mum-thick sections, and the sections were mounted onto conductive glass slides by methanol soft-landing. An ethanol washing procedure facilitated uniform matrix crystal formation by a two-step matrix deposition procedure to produce high-quality mass spectral data. Molecular images of modified and unmodified alpha-crystallin subunits were obtained from mass spectral data acquired in 100-mum steps across normal and cataractous lens sections. Proteins extracted from the lens sections were digested with endoproteinase Glu-C and subjected to mass spectrometric analysis for identification of modifications. RESULTS Intact alpha-crystallin signals were detected primarily in the outer cortical fiber cells in lenses up to 29 years of age. Multiple truncation products were observed for alpha-crystallin that increased in abundance, both with distance into the lens and with lens age. Phosphorylated alphaB-crystallin forms were most abundant in the cortical region of older lenses. In axial sections, no significant anterior-posterior pole variation was observed. A previously unreported alphaA-crystallin mutation was detected in an age-matched cataractous human lens. CONCLUSIONS A method has been developed to spatially map the age-related changes of human lens alpha-crystallin by MALDI imaging mass spectrometry including a novel L52F alphaA-crystallin mutation in a cataractous lens. Application of this spatially resolved proteomic technique to lens biology enhances the understanding of alpha-crystallin protein processing in aging and diseased human lenses.
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Affiliation(s)
- Angus C Grey
- Department of Biochemistry, Mass Spectrometry Research Center, Vanderbilt University, Nashville, Tennessee 37232-8575, USA
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