1
|
Chung DD, Chen AC, Choo CH, Zhang W, Williams D, Griffis CG, Bonezzi P, Jatavallabhula K, Sampath AP, Aldave AJ. Investigation of the functional impact of CHED- and FECD4-associated SLC4A11 mutations in human corneal endothelial cells. PLoS One 2024; 19:e0296928. [PMID: 38252645 PMCID: PMC10802951 DOI: 10.1371/journal.pone.0296928] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2023] [Accepted: 12/22/2023] [Indexed: 01/24/2024] Open
Abstract
Mutations in the solute linked carrier family 4 member 11 (SLC4A11) gene are associated with congenital hereditary endothelial dystrophy (CHED) and Fuchs corneal endothelial dystrophy type 4 (FECD4), both characterized by corneal endothelial cell (CEnC) dysfunction and/or cell loss leading to corneal edema and visual impairment. In this study, we characterize the impact of CHED-/FECD4-associated SLC4A11 mutations on CEnC function and SLC4A11 protein localization by generating and comparing human CEnC (hCEnC) lines expressing wild type SLC4A11 (SLC4A11WT) or mutant SLC4A11 harboring CHED-/FECD4-associated SLC4A11 mutations (SLC4A11MU). SLC4A11WT and SLC4A11MU hCEnC lines were generated to express either SLC4A11 variant 2 (V2WT and V2MU) or variant 3 (V3WT and V3MU), the two major variants expressed in ex vivo hCEnC. Functional assays were performed to assess cell barrier, proliferation, viability, migration, and NH3-induced membrane conductance. We demonstrate SLC4A11-/- and SLC4A11MU hCEnC lines exhibited increased migration rates, altered proliferation and decreased cell viability compared to SLC4A11WT hCEnC. Additionally, SLC4A11-/- hCEnC demonstrated decreased cell-substrate adhesion and membrane capacitances compared to SLC4A11WT hCEnC. Induction with 10mM NH4Cl led SLC4A11WT hCEnC to depolarize; conversely, SLC4A11-/- hCEnC hyperpolarized and the majority of SLC4A11MU hCEnC either hyperpolarized or had minimal membrane potential changes following NH4Cl induction. Immunostaining of primary hCEnC and SLC4A11WT hCEnC lines for SLC4A11 demonstrated predominately plasma membrane staining with poor or partial colocalization with mitochondrial marker COX4 within a subset of punctate subcellular structures. Overall, our findings suggest CHED-associated SLC4A11 mutations likely lead to hCEnC dysfunction, and ultimately CHED, by interfering with cell migration, proliferation, viability, membrane conductance, barrier function, and/or cell surface localization of the SLC4A11 protein in hCEnC. Additionally, based on their similar subcellular localization and exhibiting similar cell functional profiles, protein isoforms encoded by SLC4A11 variant 2 and variant 3 likely have highly overlapping functional roles in hCEnC.
Collapse
Affiliation(s)
- Doug D. Chung
- Department of Ophthalmology, Stein Eye Institute at UCLA, Los Angeles, California, United States of America
| | - Angela C. Chen
- Department of Ophthalmology, Stein Eye Institute at UCLA, Los Angeles, California, United States of America
| | - Charlene H. Choo
- Department of Ophthalmology, Stein Eye Institute at UCLA, Los Angeles, California, United States of America
| | - Wenlin Zhang
- Department of Ophthalmology, Stein Eye Institute at UCLA, Los Angeles, California, United States of America
| | - Dominic Williams
- Department of Ophthalmology, Stein Eye Institute at UCLA, Los Angeles, California, United States of America
| | - Christopher G. Griffis
- Department of Ophthalmology, Stein Eye Institute at UCLA, Los Angeles, California, United States of America
| | - Paul Bonezzi
- Department of Ophthalmology, Stein Eye Institute at UCLA, Los Angeles, California, United States of America
| | - Kavya Jatavallabhula
- Department of Ophthalmology, Stein Eye Institute at UCLA, Los Angeles, California, United States of America
| | - Alapakkam P. Sampath
- Department of Ophthalmology, Stein Eye Institute at UCLA, Los Angeles, California, United States of America
| | - Anthony J. Aldave
- Department of Ophthalmology, Stein Eye Institute at UCLA, Los Angeles, California, United States of America
| |
Collapse
|
2
|
Lu Y, Zuo P, Chen H, Shan H, Wang W, Dai Z, Xu H, Chen Y, Liang L, Ding D, Jin Y, Yin Y. Structural insights into the conformational changes of BTR1/SLC4A11 in complex with PIP 2. Nat Commun 2023; 14:6157. [PMID: 37788993 PMCID: PMC10547724 DOI: 10.1038/s41467-023-41924-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2023] [Accepted: 09/25/2023] [Indexed: 10/05/2023] Open
Abstract
BTR1 (SLC4A11) is a NH3 stimulated H+ (OH-) transporter belonging to the SLC4 family. Dysfunction of BTR1 leads to diseases such as congenital hereditary endothelial dystrophy (CHED) and Fuchs endothelial corneal dystrophy (FECD). However, the mechanistic basis of BTR1 activation by alkaline pH, transport activity regulation and pathogenic mutations remains elusive. Here, we present cryo-EM structures of human BTR1 in the outward-facing state in complex with its activating ligands PIP2 and the inward-facing state with the pathogenic R125H mutation. We reveal that PIP2 binds at the interface between the transmembrane domain and the N-terminal cytosolic domain of BTR1. Disruption of either the PIP2 binding site or protonation of PIP2 phosphate groups by acidic pH can transform BTR1 into an inward-facing conformation. Our results provide insights into the mechanisms of how the transport activity and conformation changes of BTR1 are regulated by PIP2 binding and interaction of TMD and NTD.
Collapse
Affiliation(s)
- Yishuo Lu
- Institute of Precision Medicine, Peking University Shenzhen Hospital, Shenzhen, 518036, China
- Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, 100871, China
| | - Peng Zuo
- Institute of Systems Biomedicine, Department of Pathology, Beijing Key Laboratory of Tumor Systems Biology, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, 100191, China
| | - Hongyi Chen
- Institute of Precision Medicine, Peking University Shenzhen Hospital, Shenzhen, 518036, China
- Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, 100871, China
| | - Hui Shan
- Institute of Precision Medicine, Peking University Shenzhen Hospital, Shenzhen, 518036, China
| | - Weize Wang
- Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, 100871, China
- Institute of Systems Biomedicine, Department of Pathology, Beijing Key Laboratory of Tumor Systems Biology, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, 100191, China
| | - Zonglin Dai
- Institute of Systems Biomedicine, Department of Pathology, Beijing Key Laboratory of Tumor Systems Biology, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, 100191, China
| | | | | | - Ling Liang
- Institute of Systems Biomedicine, Department of Pathology, Beijing Key Laboratory of Tumor Systems Biology, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, 100191, China
- Department of Biochemistry and Biophysics, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, 100191, China
| | - Dian Ding
- Institute of Precision Medicine, Peking University Shenzhen Hospital, Shenzhen, 518036, China
- Institute of Systems Biomedicine, Department of Pathology, Beijing Key Laboratory of Tumor Systems Biology, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, 100191, China
| | - Yan Jin
- Institute of Systems Biomedicine, Department of Pathology, Beijing Key Laboratory of Tumor Systems Biology, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, 100191, China
| | - Yuxin Yin
- Institute of Precision Medicine, Peking University Shenzhen Hospital, Shenzhen, 518036, China.
- Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, 100871, China.
- Institute of Systems Biomedicine, Department of Pathology, Beijing Key Laboratory of Tumor Systems Biology, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, 100191, China.
| |
Collapse
|
3
|
Mehta N, Verma A, Achanta DS, Kannabiran C, Roy S, Mishra DK, Chaurasia S, Edward DP, Ramappa M. Updates on congenital hereditary endothelial dystrophy. Taiwan J Ophthalmol 2023; 13:405-416. [PMID: 38249503 PMCID: PMC10798399 DOI: 10.4103/tjo.tjo-d-23-00135] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2023] [Revised: 10/08/2023] [Accepted: 10/09/2023] [Indexed: 01/23/2024] Open
Abstract
Congenital hereditary endothelial dystrophy (CHED) is a rare genetic corneal disorder causing progressive cornea clouding and significant visual impairment. CHED remains a leading indication for pediatric corneal transplantation despite its infrequency, particularly in regions with high consanguinity rates like Southeast Asia. Identifying the Solute Carrier Family 4 Member 11 (SLC4A11) gene as the genetic basis of CHED has led to the discovery of it's various genetic variations. However, a comprehensive understanding of its clinical-genetic correlation, pathophysiology, and optimal management is ongoing. This review aims to consolidate current knowledge about CHED, covering its genetic origins, pathophysiological mechanisms, clinical presentation, and management strategies. Surgical intervention, such as penetrating keratoplasty (PK), Descemet stripping automated endothelial keratoplasty (DSAEK), and Descemet membrane endothelial keratoplasty (DMEK), remains the primary treatment. DSAEK and DMEK offer advantages over PK, including quicker visual recovery, reduced complications, and longer graft survival, especially in the pediatric age group. The timing of surgical interventions depends on disease severity, age at presentation, comorbidities, and visual potential. Elevated oxidative stress in CHED corneal tissue suggests potential benefits from anti-inflammatory drugs to rescue mutated endothelial cells. Considering the limitations of corneal graft surgeries, exploring novel gene-based molecular therapies are essential for future management. Early diagnosis, appropriate surgical interventions, amblyopia control, and genetic counseling for predictive analysis are pivotal for optimizing CHED management. A multidisciplinary approach involving ophthalmologists, researchers, and genetic counselors is essential for precise diagnosis and optimal care for CHED patients.
Collapse
Affiliation(s)
- Neet Mehta
- Academy of Eye Care Education, L V Prasad Eye Institute, Hyderabad, Telangana, India
| | - Anshuman Verma
- Centre for Rare Eye Diseases and Ophthalmic Genetics, L V Prasad Eye Institute, Hyderabad, Telangana, India
- Prof. Brien Holden Eye Research Center, LV Prasad Eye Institute, Hyderabad, Telangana, India
| | - Divya Sree Achanta
- Centre for Rare Eye Diseases and Ophthalmic Genetics, L V Prasad Eye Institute, Hyderabad, Telangana, India
- The Cornea Institute, L V Prasad Eye Institute, Hyderabad, Telangana, India
- Jasti V Ramanamma Children’s Eye Care Center, L V Prasad Eye Institute, Hyderabad, Telangana, India
| | - Chitra Kannabiran
- Prof. Brien Holden Eye Research Center, LV Prasad Eye Institute, Hyderabad, Telangana, India
| | - Sanhita Roy
- Prof. Brien Holden Eye Research Center, LV Prasad Eye Institute, Hyderabad, Telangana, India
| | - Dilip Kumar Mishra
- Ophthalmic Pathology Services, L V Prasad Eye Institute, Hyderabad, Telangana, India
| | - Sunita Chaurasia
- The Cornea Institute, L V Prasad Eye Institute, Hyderabad, Telangana, India
| | - Deepak Paul Edward
- Department of Ophthalmology and Visual Sciences and Pathology, University of Illinois College of Medicine, Chicago, IL, USA
| | - Muralidhar Ramappa
- Centre for Rare Eye Diseases and Ophthalmic Genetics, L V Prasad Eye Institute, Hyderabad, Telangana, India
- The Cornea Institute, L V Prasad Eye Institute, Hyderabad, Telangana, India
- Jasti V Ramanamma Children’s Eye Care Center, L V Prasad Eye Institute, Hyderabad, Telangana, India
| |
Collapse
|
4
|
Shyam R, Ogando DG, Bonanno JA. Mitochondrial ROS in Slc4a11 KO Corneal Endothelial Cells Lead to ER Stress. Front Cell Dev Biol 2022; 10:878395. [PMID: 35557943 PMCID: PMC9086159 DOI: 10.3389/fcell.2022.878395] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2022] [Accepted: 03/30/2022] [Indexed: 11/13/2022] Open
Abstract
Recent studies from Slc4a11 -/- mice have identified glutamine-induced mitochondrial dysfunction as a significant contributor toward oxidative stress, impaired lysosomal function, aberrant autophagy, and cell death in this Congenital Hereditary Endothelial Dystrophy (CHED) model. Because lysosomes are derived from endoplasmic reticulum (ER)-Golgi, we asked whether ER function is affected by mitochondrial ROS in Slc4a11 KO corneal endothelial cells. In mouse Slc4a11 -/- corneal endothelial tissue, we observed the presence of dilated ER and elevated expression of ER stress markers BIP and CHOP. Slc4a11 KO mouse corneal endothelial cells incubated with glutamine showed increased aggresome formation, BIP and GADD153, as well as reduced ER Ca2+ release as compared to WT. Induction of mitoROS by ETC inhibition also led to ER stress in WT cells. Treatment with the mitochondrial ROS quencher MitoQ, restored ER Ca2+ release and relieved ER stress markers in Slc4a11 KO cells in vitro. Systemic MitoQ also reduced BIP expression in Slc4a11 KO endothelium. We conclude that mitochondrial ROS can induce ER stress in corneal endothelial cells.
Collapse
Affiliation(s)
- Rajalekshmy Shyam
- Vision Science Program, School of Optometry, Indiana University, Bloomington, IN, United States
| | | | | |
Collapse
|
5
|
Genetic profiles of non-syndromic severe-profound hearing loss in Chinese Hans by whole-exome sequencing. Gene 2022; 819:146258. [PMID: 35114279 DOI: 10.1016/j.gene.2022.146258] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2021] [Revised: 01/07/2022] [Accepted: 01/27/2022] [Indexed: 11/20/2022]
Abstract
Hereditary hearing loss is highly heterogeneous. Despite over 120 non-syndromic deafness genes have been identified, there are still some of novel genes and variants being explored. In the study, we investigated 105 Chinese Han children with non-syndromic, prelingual, severe-profound hearing loss by whole-exome sequencing on DNA samples. The most common deafness gene was GJB2, mainly in variant c.235delC (p.Leu79CysfsTer3). 14 children were identified with pathogenic mutations in three genes, GJB2, SLC26A4, and OTOF. Two mutations have been identified to be pathogenic and not recorded previously, including c.4691G > A (p.Trp1564Ter) and c.3928_3930dup (p.Lys1310dup) in OTOF. The rare variants c.1349G > A (p.Arg450His) and c.456 T > G (p.Asn152Lys) in GSDME, and c.1595G > T (p.Ser532Ile) in SLC26A4 were detected. The frequency of nonsense variant c.2359G > T (p.Glu787Ter) in OTOA was very high in 17 cases. Four of them were identified to be digenic inheritance, including GJB2 and COL4A4, GJB2 and EYA1, GJB2 and COL4A5, and GJB2 and DFNA5. The findings showed that a novel pathogenic variant and rare variants may be associated with severe and profound hearing loss.
Collapse
|
6
|
Bonanno JA, Shyam R, Choi M, Ogando DG. The H + Transporter SLC4A11: Roles in Metabolism, Oxidative Stress and Mitochondrial Uncoupling. Cells 2022; 11:197. [PMID: 35053313 PMCID: PMC8773465 DOI: 10.3390/cells11020197] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2021] [Revised: 01/03/2022] [Accepted: 01/05/2022] [Indexed: 12/23/2022] Open
Abstract
Solute-linked cotransporter, SLC4A11, a member of the bicarbonate transporter family, is an electrogenic H+ transporter activated by NH3 and alkaline pH. Although SLC4A11 does not transport bicarbonate, it shares many properties with other members of the SLC4 family. SLC4A11 mutations can lead to corneal endothelial dystrophy and hearing deficits that are recapitulated in SLC4A11 knock-out mice. SLC4A11, at the inner mitochondrial membrane, facilitates glutamine catabolism and suppresses the production of mitochondrial superoxide by providing ammonia-sensitive H+ uncoupling that reduces glutamine-driven mitochondrial membrane potential hyperpolarization. Mitochondrial oxidative stress in SLC4A11 KO also triggers dysfunctional autophagy and lysosomes, as well as ER stress. SLC4A11 expression is induced by oxidative stress through the transcription factor NRF2, the master regulator of antioxidant genes. Outside of the corneal endothelium, SLC4A11's function has been demonstrated in cochlear fibrocytes, salivary glands, and kidneys, but is largely unexplored overall. Increased SLC4A11 expression is a component of some "glutamine-addicted" cancers, and is possibly linked to cells and tissues that rely on glutamine catabolism.
Collapse
Affiliation(s)
- Joseph A. Bonanno
- Vision Science Program, School of Optometry, Indiana University, Bloomington, IN 47405, USA; (R.S.); (M.C.).; (D.G.O.)
| | | | | | | |
Collapse
|
7
|
Chibani Z, Abid IZ, Söderkvist P, Feki J, Aifa MH. Autosomal recessive congenital hereditary corneal dystrophy associated with a novel SLC4A11 mutation in two consanguineous Tunisian families. Br J Ophthalmol 2021; 106:281-287. [PMID: 33879471 DOI: 10.1136/bjophthalmol-2020-318204] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2020] [Revised: 02/11/2021] [Accepted: 03/20/2021] [Indexed: 11/03/2022]
Abstract
BACKGROUND Autosomal recessive congenital hereditary corneal dystrophy (CHED) is a rare isolated developmental anomaly of the eye characterised by diffuse bilateral corneal clouding that may lead to visual impairment requiring corneal transplantation. CHED is known to be caused by mutations in the solute carrier family 4 member 11 (SLC4A11) gene which encodes a membrane transporter protein (sodium bicarbonate transporter-like solute carrier family 4 member 11). METHODS To identify SLC4A11 gene mutations associated with CHED (OMIM: #217700), genomic DNA was extracted from whole blood and sequenced for all exons and intron-exon boundaries in two large Tunisian families. RESULTS A novel deletion SLC4A11 mutation (p. Leu479del; c.1434_1436del) is responsible for CHED in both analysed families. This non-frameshift mutation was found in a homozygous state in affected members and heterozygous in non-affected members. In silico analysis largely support the pathogenicity of this alteration that may leads to stromal oedema by disrupting the osmolarity balance. Being localised to a region of alpha-helical secondary structure, Leu479 deletion may induce protein-compromising structural rearrangements. CONCLUSION To the best of our knowledge, this is the first clinical and genetic study exploring CHED in Tunisia. The present work also expands the list of pathogenic genotypes in SLC4A11 gene and its associated clinical diagnosis giving more insights into genotype-phenotype correlations.
Collapse
Affiliation(s)
- Zohra Chibani
- Molecular and Functional Genetics Laboratory, University of Sfax, Faculty of Science of Sfax, Sfax, Tunisia
| | - Imen Zone Abid
- Department of Ophthalmology, Habib Bourguiba University Hospital, University of Sfax, Sfax, Tunisia
| | - Peter Söderkvist
- Department of Biomedical and Clinical Sciences, Linköping University, Linköping, Sweden
| | - Jamel Feki
- Department of Ophthalmology, Habib Bourguiba University Hospital, University of Sfax, Sfax, Tunisia
| | - Mounira Hmani Aifa
- Molecular and Functional Genetics Laboratory, University of Sfax, Faculty of Science of Sfax, Sfax, Tunisia
| |
Collapse
|
8
|
Zhang W, Frausto R, Chung DD, Griffis CG, Kao L, Chen A, Azimov R, Sampath AP, Kurtz I, Aldave AJ. Energy Shortage in Human and Mouse Models of SLC4A11-Associated Corneal Endothelial Dystrophies. Invest Ophthalmol Vis Sci 2021; 61:39. [PMID: 32721020 PMCID: PMC7425690 DOI: 10.1167/iovs.61.8.39] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Purpose To elucidate the molecular events in solute carrier family 4 member 11 (SLC4A11)-deficient corneal endothelium that lead to the endothelial dysfunction that characterizes the dystrophies associated with SLC4A11 mutations, congenital hereditary endothelial dystrophy (CHED) and Fuchs endothelial corneal dystrophy 4. Methods Comparative transcriptomic analysis (CTA) was performed in primary human corneal endothelial cells (pHCEnC) and murine corneal endothelial cells (MCEnC) with normal and reduced levels of SLC4A11 (SLC4A11 KD pHCEnC) and Slc4a11 (Slc4a11−/− MCEnC), respectively. Validation of differentially expressed genes was performed using immunofluorescence staining of CHED corneal endothelium, as well as western blot and quantitative PCR analysis of SLC4A11 KD pHCEnC and Slc4a11−/− MCEnC. Functional analyses were performed to investigate potential functional changes associated with the observed transcriptomic alterations. Results CTA revealed inhibition of cell metabolism and ion transport function as well as mitochondrial dysfunction, leading to reduced adenosine triphosphate (ATP) production, in SLC4A11 KD pHCEnC and Slc4a11−/− MCEnC. Co-localization of SNARE protein STX17 with mitochondria marker COX4 was observed in CHED corneal endothelium, as was activation of AMPK–p53/ULK1 in both SLC4A11 KD pHCEnC and Slc4a11−/− MCEnC, providing additional evidence of mitochondrial dysfunction and mitophagy. Reduced Na+-dependent HCO3− transport activity and altered NH4Cl-induced membrane potential changes were observed in Slc4a11−/− MCEnC. Conclusions Reduced steady-state ATP levels and subsequent activation of the AMPK–p53 pathway provide a link between the metabolic functional deficit and transcriptome alterations, as well as evidence of insufficient ATP to maintain the Na+/K+-ATPase corneal endothelial pump as the cause of the edema that characterizes SLC4A11-associated corneal endothelial dystrophies.
Collapse
|
9
|
Kao L, Azimov R, Shao XM, Abuladze N, Newman D, Zhekova H, Noskov S, Pushkin A, Kurtz I. SLC4A11 function: evidence for H +(OH -) and NH 3-H + transport. Am J Physiol Cell Physiol 2019; 318:C392-C405. [PMID: 31774702 PMCID: PMC7052617 DOI: 10.1152/ajpcell.00425.2019] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Whether SLC4A11 transports ammonia and its potential mode of ammonia transport (NH4+, NH3, or NH3-2H+ transport have been proposed) are controversial. In the absence of ammonia, whether SLC4A11 mediates significant conductive H+(OH-) transport is also controversial. The present study was performed to determine the mechanism of human SLC4A11 ammonia transport and whether the transporter mediates conductive H+(OH-) transport in the absence of ammonia. We quantitated H+ flux by monitoring changes in intracellular pH (pHi) and measured whole cell currents in patch-clamp studies of HEK293 cells expressing the transporter in the absence and presence of NH4Cl. Our results demonstrate that SLC4A11 mediated conductive H+(OH-) transport that was stimulated by raising the extracellular pH (pHe). Ammonia-induced HEK293 whole cell currents were also stimulated by an increase in pHe. In studies using increasing NH4Cl concentrations with equal NH4+ extracellular and intracellular concentrations, the shift in the reversal potential (Erev) due to the addition of ammonia was compatible with NH3-H+ transport competing with H+(OH-) rather than NH3-nH+ (n ≥ 2) transport. The increase in equivalent H+(OH-) flux observed in the presence of a transcellular H+ gradient was also compatible with SLC4A11-mediated NH3-H+ flux. The NH3 versus Erev data fit a theoretical model suggesting that NH3-H+ and H+(OH-) competitively interact with the transporter. Studies of mutant SLC4A11 constructs in the putative SLC4A11 ion coordination site showed that both H+(OH-) transport and ammonia-induced whole cell currents were blocked suggesting that the H+(OH-) and NH3-H+ transport processes share common features involving the SLC4A11 transport mechanism.
Collapse
Affiliation(s)
- Liyo Kao
- Department of Medicine, Division of Nephrology, David Geffen School of Medicine, University of California, Los Angeles, California
| | - Rustam Azimov
- Department of Medicine, Division of Nephrology, David Geffen School of Medicine, University of California, Los Angeles, California
| | - Xuesi M Shao
- Department of Neurobiology, University of California, Los Angeles, California
| | - Natalia Abuladze
- Department of Medicine, Division of Nephrology, David Geffen School of Medicine, University of California, Los Angeles, California
| | - Debra Newman
- Department of Medicine, Division of Nephrology, David Geffen School of Medicine, University of California, Los Angeles, California
| | - Hristina Zhekova
- Department of Biological Sciences, Centre for Molecular Simulation, University of Calgary, Calgary, Alberta, Canada
| | - Sergei Noskov
- Department of Biological Sciences, Centre for Molecular Simulation, University of Calgary, Calgary, Alberta, Canada
| | - Alexander Pushkin
- Department of Medicine, Division of Nephrology, David Geffen School of Medicine, University of California, Los Angeles, California
| | - Ira Kurtz
- Department of Medicine, Division of Nephrology, David Geffen School of Medicine, University of California, Los Angeles, California.,Brain Research Institute, University of California, Los Angeles, California
| |
Collapse
|
10
|
Malhotra D, Loganathan SK, Chiu AM, Lukowski CM, Casey JR. Human Corneal Expression of SLC4A11, a Gene Mutated in Endothelial Corneal Dystrophies. Sci Rep 2019; 9:9681. [PMID: 31273259 PMCID: PMC6609610 DOI: 10.1038/s41598-019-46094-y] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2019] [Accepted: 06/21/2019] [Indexed: 12/21/2022] Open
Abstract
Two blinding corneal dystrophies, pediatric-onset congenital hereditary endothelial dystrophy (CHED) and some cases of late-onset Fuchs endothelial corneal dystrophy (FECD), are caused by SLC4A11 mutations. Three N-terminal SLC4A11 variants: v1, v2 and v3 are expressed in humans. We set out to determine which of these transcripts and what translated products, are present in corneal endothelium as these would be most relevant for CHED and FECD studies. Reverse transcription PCR (RT-PCR) and quantitative RT-PCR revealed only v2 and v3 mRNA in human cornea, but v2 was most abundant. Immunoblots probed with variant-specific antibodies revealed that v2 protein is about four times more abundant than v3 in human corneal endothelium. Bioinformatics and protein analysis using variant-specific antibodies revealed that second methionine in the open reading frame (M36) acts as translation initiation site on SLC4A11 v2 in human cornea. The v2 variants starting at M1 (v2-M1) and M36 (v2-M36) were indistinguishable in their cell surface trafficking and transport function (water flux). Structural homology models of v2-M36 and v3 suggest structural differences but their significance remains unclear. A combination of bioinformatics, RNA quantification and isoform-specific antibodies allows us to conclude that SLC4A11 variant 2 with start site M36 is predominant in corneal endothelium.
Collapse
Affiliation(s)
- Darpan Malhotra
- Department of Biochemistry, Membrane Protein Disease Research Group, University of Alberta, Edmonton, Alberta, T6G 2H7, Canada
| | - Sampath K Loganathan
- Department of Biochemistry, Membrane Protein Disease Research Group, University of Alberta, Edmonton, Alberta, T6G 2H7, Canada.,Lunenfeld-Tanenbaum Research Institute, Toronto, Ontario, M5G 1X5, Canada
| | - Anthony M Chiu
- Department of Biochemistry, Membrane Protein Disease Research Group, University of Alberta, Edmonton, Alberta, T6G 2H7, Canada
| | - Chris M Lukowski
- Department of Biochemistry, Membrane Protein Disease Research Group, University of Alberta, Edmonton, Alberta, T6G 2H7, Canada
| | - Joseph R Casey
- Department of Biochemistry, Membrane Protein Disease Research Group, University of Alberta, Edmonton, Alberta, T6G 2H7, Canada.
| |
Collapse
|
11
|
Romero PT, Donoso R, López P, Miranda A, Rodríguez L, Chrzanowsky D, Asenjo MS, Burgos G, Villegas P, Desir J, Moya G, Herrera LM. Clinical features and possible founder mutation of the 8bp duplication mutation in the SLC4A11 gene causing corneal dystrophy and perceptive deafness in three South American families. Ophthalmic Genet 2019; 40:91-98. [PMID: 30856043 DOI: 10.1080/13816810.2019.1571615] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
BACKGROUND Corneal Dystrophy and Perceptive Deafness (CDPD) or Harboyan syndrome is an autosomal recessive rare disorder, characterized by congenital corneal opacities and progressive sensorineural hearing loss, which usually begins after the second decades of life. This study reports the ophthalmic, audiological and genetic features, in five CDPD affected patients from three Chilean families. MATERIALS AND METHODS Five individuals affected with CDPD from three unrelated Chilean families were clinically and genetically examined. To evaluate a putative founder mutation 7 SNPs were analyzed in the three families, an Argentinian patient (carrier of the same mutation previously reported) and 87 Chilean controls. RESULTS The ophthalmic symptoms in the five patients were bilateral and symmetric, starting before one year of age, and visual acuity varied from 0.1 to 0.3. In all cases, hearing loss began over 8 years old. The sequence of the 19 exons of SLC4A11 gene of all the affected patients exhibited homozygous eight nucleotide sequence duplication (c.2233_2240dup TATGACAC, p.(Ile748Metfs*5)) at the end of exon 16. All the affected patients of the three families were homozygous for a haplotype composed of five SNPs and covering 4,1 Mb. The same haplotype was present in one allele of the heterozygous Argentinean patient and has a frequency of 2.76% in Chilean population. CONCLUSIONS The five CDPD patients were homozygous for the same mutation in the SLC4A11 gene. Haplotype analysis of all the affected, including the case reported from Argentina was in accordance with a founder mutation.
Collapse
Affiliation(s)
- Pablo T Romero
- a Hospital Clínico Universidad de Chile José Joaquín Aguirre , Santiago , Chile
| | - Rodrigo Donoso
- b Servicio de Oftalmología , Hospital del Salvador , Santiago , Chile
| | - Pamela López
- c Programa de Genética Humana, ICBM, Facultad de Medicina , Universidad de Chile , Santiago , Chile
| | - Ana Miranda
- c Programa de Genética Humana, ICBM, Facultad de Medicina , Universidad de Chile , Santiago , Chile
| | - Leandro Rodríguez
- d Servicio de Otorrinolaringología , Hospital del Salvador , Santiago , Chile
| | - Dominique Chrzanowsky
- c Programa de Genética Humana, ICBM, Facultad de Medicina , Universidad de Chile , Santiago , Chile
| | - Maria S Asenjo
- c Programa de Genética Humana, ICBM, Facultad de Medicina , Universidad de Chile , Santiago , Chile
| | - Gonzalo Burgos
- c Programa de Genética Humana, ICBM, Facultad de Medicina , Universidad de Chile , Santiago , Chile
| | - Pablo Villegas
- e Servicio de Anatomía Patológica , Hospital del Salvador , Santiago , Chile
| | - Julie Desir
- f Department of Medical Genetics , Hôpital Erasme, ULB , Brussels , Belgium
| | | | - Luisa M Herrera
- c Programa de Genética Humana, ICBM, Facultad de Medicina , Universidad de Chile , Santiago , Chile
| |
Collapse
|
12
|
Alka K, Casey JR. Molecular phenotype of SLC4A11 missense mutants: Setting the stage for personalized medicine in corneal dystrophies. Hum Mutat 2018; 39:676-690. [PMID: 29327391 DOI: 10.1002/humu.23401] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2017] [Revised: 12/19/2017] [Accepted: 01/02/2018] [Indexed: 12/30/2022]
Abstract
SLC4A11 mutations cause cases of congenital hereditary endothelial dystrophy (CHED), Harboyan syndrome (HS), and Fuchs endothelial corneal dystrophy (FECD). Defective water reabsorption from corneal stroma by corneal endothelial cells (CECs) leads to these corneal dystrophies. SLC4A11, in the CEC basolateral membrane, facilitates transmembrane movement of H2 O, NH3 , and H+ -equivalents. Some SLC4A11 disease mutants have impaired folding, leading to a failure to move to the cell surface, which in some cases can be corrected by the drug, glafenine. To identify SLC4A11 mutants that are targets for folding-correction therapy, we examined 54 SLC4A11 missense mutants. Cell-surface trafficking was assessed on immunoblots, by the level of mature, high molecular weight, cell surface-associated form, and using a bioluminescence resonance energy transfer assay. Low level of cell surface trafficking was found in four out of 18 (20%) of FECD mutants, 19/ out of 31 (61%) of CHED mutants, and three out of five (60%) of HS mutants. Amongst ER-retained mutants, 16 showed increased plasma membrane trafficking when grown at 30°C, suggesting that their defect has potential for rescue. CHED-causing point mutations mostly resulted in folding defects, whereas the majority of FECD missense mutations did not affect trafficking, implying functional impairment. We identified mutations that make patients candidates for folding correction of their corneal dystrophy.
Collapse
Affiliation(s)
- Kumari Alka
- Department of Biochemistry, Membrane Protein Disease Research Group, University of Alberta, Edmonton, Alberta, Canada
| | - Joseph R Casey
- Department of Biochemistry, Membrane Protein Disease Research Group, University of Alberta, Edmonton, Alberta, Canada
| |
Collapse
|
13
|
Abeshi A, Fanelli F, Beccari T, Dundar M, Viola F, Colombo L, Bertelli M. Genetic testing for corneal dystrophies and other corneal Mendelian diseases. THE EUROBIOTECH JOURNAL 2017. [DOI: 10.24190/issn2564-615x/2017/s1.13] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Abstract
We studied the scientific literature and disease guidelines in order to summarize the clinical utility of the genetic test for corneal dystrophies and other Mendelian corneal diseases (CDs). CDs are mostly inherited in an autosomal dominant manner (autosomal recessive inheritance is rare). The overall prevalence is currently unknown. CDs are caused by mutations in the AGBL1, CHST6, COL8A2, DCN, GSN, KRT12, KRT3, NLRP1, PAX6, PIKFYVE, PRDM5, SLC4A11, TACSTD2, TCF4, TGFBI, UBIAD1, VSX1, ZEB1, and ZNF469 genes. Clinical diagnosis is based on clinical findings, ophthalmological examination, confocal microscopy and slit-lamp biomicroscopy. The genetic test is useful for confirming diagnosis and for differential diagnosis, couple risk assessment and access to clinical trials.
Collapse
Affiliation(s)
- Andi Abeshi
- MAGI Balkans, Tirana , Albania
- MAGI’S Lab, Rovereto , Italy
| | | | - Tommaso Beccari
- Department of Pharmaceutical Sciences, University of Perugia, Perugia , Italy
| | - Munis Dundar
- Department of Medical Genetics, Erciyes University Medical School, Kayseri , Turkey
| | - Francesco Viola
- Department of Clinical Sciences and Community Health, University of Milan, Ophthalmological Unit, IRCCS-Ca Granda Foundation-Ospedale Maggiore Policlinico, Milan , Italy
| | - Leonardo Colombo
- Department of Ophthalmology, ASST Santi Paolo e Carlo, University of Milan, Milan , Italy
| | | |
Collapse
|
14
|
Parents of Patients With Congenital Hereditary Endothelial Dystrophy Should Be Evaluated for Fuchs Endothelial Corneal Dystrophy. Cornea 2017; 36:e34-e35. [PMID: 28976417 DOI: 10.1097/ico.0000000000001397] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
|
15
|
Kumawat BL, Gupta R, Sharma A, Sen S, Gupta S, Tandon R. Delayed onset of congenital hereditary endothelial dystrophy due to compound heterozygous SLC4A11 mutations. Indian J Ophthalmol 2017; 64:492-5. [PMID: 27609159 PMCID: PMC5026072 DOI: 10.4103/0301-4738.190100] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Background: Congenital hereditary endothelial dystrophy (CHED) is an autosomal recessive disorder characterized by bilateral, symmetrical, noninflammatory corneal clouding (edema) present at birth or shortly thereafter. This study reports on an unusual delayed presentation of CHED with compound heterozygous SLC4A11 mutations. Materials and Methods: A 45-year-old female, presenting with bilateral decreased vision since childhood that deteriorated in the last 5 years, was evaluated to rule out trauma, viral illness, chemical injury, glaucoma, and corneal endothelial dystrophies. Tear sample was sent for herpes simplex viral (HSV) antigen testing. Genomic DNA from peripheral blood was screened for mutations in all exons of SLC4A11 by direct sequencing. Full-thickness penetrating keratoplasty was done and corneal button was sent for histopathological examination. Results: Slit-lamp findings revealed bilateral diffuse corneal edema and left eye spheroidal degeneration with scarring. Increased corneal thickness (762 μm and 854 μm in the right and left eyes, respectively), normal intraocular pressure (12 mmHg and 16 mmHg in the right and left eyes, respectively), inconclusive confocal scan, and specular microscopy, near normal tear film parameters, were the other clinical features. HSV-polymerase chain reaction was negative. Histopathological examination revealed markedly thickened Descemet's membrane with subepithelial spheroidal degeneration. SLC4A11 screening showed a novel variant p.Ser415Asn, reported mutation p.Cys386Arg and two polymorphisms, all in the heterozygous state and not identified in 100 controls. Conclusions: The study shows, for the first time, compound heterozygous SLC4A11 mutations impair protein function leading to delayed onset of the disease.
Collapse
Affiliation(s)
- Babu Lal Kumawat
- Dr. Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India
| | - Ranjan Gupta
- Department of Anatomy, Laboratory of Cyto-Molecular Genetics, All India Institute of Medical Sciences, New Delhi, India
| | - Arundhati Sharma
- Department of Anatomy, Laboratory of Cyto-Molecular Genetics, All India Institute of Medical Sciences, New Delhi, India
| | - Seema Sen
- Dr. Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India
| | - Shikha Gupta
- Dr. Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India
| | - Radhika Tandon
- Dr. Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India
| |
Collapse
|
16
|
Zhang W, Ogando DG, Kim ET, Choi MJ, Li H, Tenessen JM, Bonanno JA. Conditionally Immortal Slc4a11-/- Mouse Corneal Endothelial Cell Line Recapitulates Disrupted Glutaminolysis Seen in Slc4a11-/- Mouse Model. Invest Ophthalmol Vis Sci 2017; 58:3723-3731. [PMID: 28738416 PMCID: PMC5525555 DOI: 10.1167/iovs.17-21781] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Purpose To establish conditionally immortal mouse corneal endothelial cell lines with genetically matched Slc4a11+/+ and Slc4a11-/- mice as a model for investigating pathology and therapies for SLC4A11 associated congenital hereditary endothelial dystrophy (CHED) and Fuchs' endothelial corneal dystrophy. Methods We intercrossed H-2Kb-tsA58 mice (Immortomouse) expressing an IFN-γ dependent and temperature-sensitive mutant of the SV40 large T antigen (tsTAg) with Slc4a11+/+ and Slc4a11-/- C57BL/6 mice. The growth characteristics of the cell lines was assessed by doubling time. Ion transport activities (Na+/H+ exchange, bicarbonate, lactate, and Slc4a11 ammonia transport) were analyzed by intracellular pH measurement. The metabolic status of the cell lines was assessed by analyzing TCA cycle intermediates via gas chromatography mass spectrometry (GC-MS). Results The immortalized Slc4a11+/+ and Slc4a11-/- mouse corneal endothelial cells (MCECs) remained proliferative through passage 49 and maintained similar active ion transport activity. As expected, proliferation was temperature sensitive and IFN-γ dependent. Slc4a11-/- MCECs exhibited decreased proliferative capacity, reduced NH3:H+ transport, altered expression of glutaminolysis enzymes similar to the Slc4a11-/- mouse, and reduced proportion of TCA cycle intermediates derived from glutamine with compensatory increases in glucose flux compared with Slc4a11+/+ MCECs. Conclusions This is the first report of the immortalization of MCECs. Ion transport of the immortalized endothelial cells remains active, except for NH3:H+ transporter activity in Slc4a11-/- MCECs. Furthermore, Slc4a11-/- MCECs recapitulate the glutaminolysis defects observed in Slc4a11-/- mouse corneal endothelium, providing an excellent tool to study the pathogenesis of SLC4A11 mutations associated with corneal endothelial dystrophies and to screen potential therapeutic agents.
Collapse
Affiliation(s)
- Wenlin Zhang
- School of Optometry, Indiana University, Bloomington, Indiana, United States
| | - Diego G Ogando
- School of Optometry, Indiana University, Bloomington, Indiana, United States
| | - Edward T Kim
- School of Optometry, Indiana University, Bloomington, Indiana, United States
| | - Moon-Jung Choi
- School of Optometry, Indiana University, Bloomington, Indiana, United States
| | - Hongde Li
- Department of Biology, Indiana University, Bloomington, Indiana, United States
| | - Jason M Tenessen
- Department of Biology, Indiana University, Bloomington, Indiana, United States
| | - Joseph A Bonanno
- School of Optometry, Indiana University, Bloomington, Indiana, United States
| |
Collapse
|
17
|
Badior KE, Alka K, Casey JR. SLC4A11 Three-Dimensional Homology Model Rationalizes Corneal Dystrophy-Causing Mutations. Hum Mutat 2016; 38:279-288. [PMID: 27925686 DOI: 10.1002/humu.23152] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2016] [Accepted: 12/01/2016] [Indexed: 12/17/2022]
Abstract
We studied the structural effects of point mutations of a membrane protein that cause genetic disease. SLC4A11 is a membrane transport protein (OH- /H+ /NH3 /H2 O) of basolateral corneal endothelium, whose mutations cause some cases of congenital hereditary endothelial dystrophy and Fuchs endothelial corneal dystrophy. We created a three-dimensional homology model of SLC4A11 membrane domain, using Band 3 (SLC4A1) crystal structure as template. The homology model was assessed in silico and by analysis of mutants designed on the basis of the model. Catalytic pathway mutants p.Glu675Gln, p.His724Arg, and p.His724Ala impaired SLC4A11 transport. p.Ala720Leu, in a region of extended structure of the proposed translocation pore, failed to mature to the cell surface. p.Gly509Lys, located in an open region at the core domain/gate domain interface, had wild-type level of transport function. The molecular phenotype of 37 corneal dystrophy-causing point mutants was rationalized, based on their location in the homology model. Four map to the substrate translocation pathway, 25 to regions of close transmembrane helix packing, three to the dimeric interface, and five lie in extramembraneous loops. The model provides a view of the spectrum of effects of disease mutations on membrane protein structure and provides a tool to analyze pathogenicity of additional newly discovered SLC4A11 mutants.
Collapse
Affiliation(s)
- Katherine E Badior
- Department of Biochemistry, Membrane Protein Disease Research Group, University of Alberta, Edmonton, Alberta, Canada
| | - Kumari Alka
- Department of Biochemistry, Membrane Protein Disease Research Group, University of Alberta, Edmonton, Alberta, Canada
| | - Joseph R Casey
- Department of Biochemistry, Membrane Protein Disease Research Group, University of Alberta, Edmonton, Alberta, Canada
| |
Collapse
|
18
|
Kao L, Azimov R, Shao XM, Frausto RF, Abuladze N, Newman D, Aldave AJ, Kurtz I. Multifunctional ion transport properties of human SLC4A11: comparison of the SLC4A11-B and SLC4A11-C variants. Am J Physiol Cell Physiol 2016; 311:C820-C830. [PMID: 27581649 DOI: 10.1152/ajpcell.00233.2016] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2016] [Accepted: 08/30/2016] [Indexed: 12/13/2022]
Abstract
Congenital hereditary endothelial dystrophy (CHED), Harboyan syndrome (CHED with progressive sensorineural deafness), and potentially a subset of individuals with late-onset Fuchs' endothelial corneal dystrophy are caused by mutations in the SLC4A11 gene that results in corneal endothelial cell abnormalities. Originally classified as a borate transporter, the function of SLC4A11 as a transport protein remains poorly understood. Elucidating the transport function(s) of SLC4A11 is needed to better understand how its loss results in the aforementioned posterior corneal dystrophic disease processes. Quantitative PCR experiments demonstrated that, of the three known human NH2-terminal variants, SLC4A11-C is the major transcript expressed in human corneal endothelium. We studied the expression pattern of the three variants in mammalian HEK-293 cells and demonstrated that the SLC4A11-B and SLC4A11-C variants are plasma membrane proteins, whereas SLC4A11-A is localized intracellularly. SLC4A11-B and SLC4A11-C were shown to be multifunctional ion transporters capable of transporting H+ equivalents in both a Na+-independent and Na+-coupled mode. In both transport modes, SLC4A11-C H+ flux was significantly greater than SLC4A11-B. In the presence of ammonia, SLC4A11-B and SLC4A11-C generated inward currents that were comparable in magnitude. Chimera SLC4A11-C-NH2-terminus-SLC4A11-B experiments demonstrated that the SLC4A11-C NH2-terminus functions as an autoactivating domain, enhancing Na+-independent and Na+-coupled H+ flux without significantly affecting the electrogenic NH3-H(n)+ cotransport mode. All three modes of transport were significantly impaired in the presence of the CHED causing p.R109H (SLC4A11-C numbering) mutation. These complex ion transport properties need to be addressed in the context of corneal endothelial disease processes caused by mutations in SLC4A11.
Collapse
Affiliation(s)
- Liyo Kao
- Division of Nephrology.,David Geffen School of Medicine, University of California, Los Angeles, California
| | - Rustam Azimov
- Division of Nephrology.,David Geffen School of Medicine, University of California, Los Angeles, California
| | - Xuesi M Shao
- Department of Neurobiology.,David Geffen School of Medicine, University of California, Los Angeles, California
| | - Ricardo F Frausto
- Stein Eye Institute, and.,David Geffen School of Medicine, University of California, Los Angeles, California
| | - Natalia Abuladze
- Division of Nephrology.,David Geffen School of Medicine, University of California, Los Angeles, California
| | - Debra Newman
- Division of Nephrology.,David Geffen School of Medicine, University of California, Los Angeles, California
| | - Anthony J Aldave
- Stein Eye Institute, and.,David Geffen School of Medicine, University of California, Los Angeles, California
| | - Ira Kurtz
- Division of Nephrology, .,Brain Research Institute.,David Geffen School of Medicine, University of California, Los Angeles, California
| |
Collapse
|
19
|
Loganathan SK, Schneider HP, Morgan PE, Deitmer JW, Casey JR. Functional assessment of SLC4A11, an integral membrane protein mutated in corneal dystrophies. Am J Physiol Cell Physiol 2016; 311:C735-C748. [PMID: 27558157 DOI: 10.1152/ajpcell.00078.2016] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2016] [Accepted: 08/17/2016] [Indexed: 12/19/2022]
Abstract
SLC4A11, a member of the SLC4 family of bicarbonate transporters, is a widely expressed integral membrane protein, abundant in kidney and cornea. Mutations of SLC4A11 cause some cases of the blinding corneal dystrophies, congenital hereditary endothelial dystrophy, and Fuchs endothelial corneal dystrophy. These diseases are marked by fluid accumulation in the corneal stroma, secondary to defective fluid reabsorption by the corneal endothelium. The role of SLC4A11 in these corneal dystrophies is not firmly established, as SLC4A11 function remains unclear. To clarify the normal function(s) of SLC4A11, we characterized the protein following expression in the simple, low-background expression system Xenopus laevis oocytes. Since plant and fungal SLC4A11 orthologs transport borate, we measured cell swelling associated with accumulation of solute borate. The plant water/borate transporter NIP5;1 manifested borate transport, whereas human SLC4A11 did not. SLC4A11 supported osmotically driven water accumulation that was electroneutral and Na+ independent. Studies in oocytes and HEK293 cells could not detect Na+-coupled HCO3- transport or Cl-/HCO3- exchange by SLC4A11. SLC4A11 mediated electroneutral NH3 transport in oocytes. Voltage-dependent OH- or H+ movement was not measurable in SLC4A11-expressing oocytes, but SLC4A11-expressing HEK293 cells manifested low-level cytosolic acidification at baseline. In mammalian cells, but not oocytes, OH-/H+ conductance may arise when SLC4A11 activates another protein or itself is activated by another protein. These data argue against a role of human SLC4A11 in bicarbonate or borate transport. This work provides additional support for water and ammonia transport by SLC4A11. When expressed in oocytes, SLC4A11 transported NH3, not NH3/H.
Collapse
Affiliation(s)
- Sampath K Loganathan
- Department of Biochemistry, Membrane Protein Disease Research Group, University of Alberta, Edmonton, Alberta, Canada
| | - Hans-Peter Schneider
- Abteilung für Allgemeine Zoologie, Fachbereich Biologie, Technische Universtät Kaiserslautern, Kaiserslautern, Germany; and
| | - Patricio E Morgan
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, La Plata, Buenos Aires, Argentina
| | - Joachim W Deitmer
- Abteilung für Allgemeine Zoologie, Fachbereich Biologie, Technische Universtät Kaiserslautern, Kaiserslautern, Germany; and
| | - Joseph R Casey
- Department of Biochemistry, Membrane Protein Disease Research Group, University of Alberta, Edmonton, Alberta, Canada;
| |
Collapse
|
20
|
Hand CK, McGuire M, Parfrey NA, Murphy CC. Homozygous SLC4A11 mutation in a large Irish CHED2 pedigree. Ophthalmic Genet 2016; 38:148-151. [PMID: 27057589 DOI: 10.3109/13816810.2016.1151901] [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: 11/13/2022]
Abstract
BACKGROUND Congenital hereditary endothelial dystrophy (CHED) is a genetic disorder of corneal endothelial cells resulting in corneal clouding and visual impairment. Autosomal dominant (CHED1) and autosomal recessive (CHED2) forms have been reported and map to distinct loci on chromosome 20. CHED2 is caused by mutations in the SLC4A11 gene which encodes a membrane transporter protein. MATERIALS AND METHODS Members of a large CHED2 family were recruited for clinical and genetic studies. Genomic DNA was sequenced for the exons and intron-exon boundaries of the SLC4A11 gene. RESULTS Twelve family members were recruited, of which eight were diagnosed with CHED. A homozygous SLC4A11 mutation (Leu843Pro) was detected in the eight patients; a single copy of the mutation was present in three unaffected carriers. CONCLUSIONS A missense SLC4A11 mutation (Leu843Pro) is responsible for CHED2 in this family; this is the first report of this mutation in a homozygous state.
Collapse
Affiliation(s)
- Collette K Hand
- a Department of Pathology , University College Cork , Cork , Ireland
| | - Mairide McGuire
- b Department of Ophthalmology , Royal Victoria Eye and Ear Hospital , Dublin , Ireland
| | - Nollaig A Parfrey
- a Department of Pathology , University College Cork , Cork , Ireland
| | - Conor C Murphy
- b Department of Ophthalmology , Royal Victoria Eye and Ear Hospital , Dublin , Ireland.,c Department of Ophthalmology , Royal College of Surgeons in Ireland , Dublin , Ireland
| |
Collapse
|
21
|
Kim JH, Ko JM, Tchah H. Fuchs Endothelial Corneal Dystrophy in a Heterozygous Carrier of Congenital Hereditary Endothelial Dystrophy Type 2 with a Novel Mutation in SLC4A11. Ophthalmic Genet 2016; 36:284-6. [PMID: 24502824 DOI: 10.3109/13816810.2014.881510] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
PURPOSE Congenital hereditary endothelial dystrophy (CHED) is a rare genetic disorder caused by mutations in corneal endothelial cells. CHED can be divided into 2 types by the modes of inheritance; CHED type 1 (CHED1) with autosomal dominant inheritance and CHED type 2 (CHED2) with autosomal recessive inheritance. Mutations in the sodium bicarbonate transporter-like solute carrier family 4 member 11 (SLC4A11) gene result CHED2. METHODS A 37 years old female was clinically diagnosed as CHED2. Peripheral blood from the patient and her family members was obtained under informed consents. Genomic DNA was extracted in their WBCs, and whole exons and exon-intron boundaries of the SLC4A11 gene were amplified using polymerase chain reaction. The amplified materials were analyzed by direct sequencing method. RESULTS The sequencing results of the SLC4A11 gene showed a novel homozygous mutation in exon 9 (c.1158C > A, p.C386*) in the proband with CHED2 phenotype. Her father and sister showing normal cornea were heterozygous carriers of the mutation. Her mother showing late onset Fuchs endothelial corneal dystrophy (FECD) also had the same mutation heterozygously. DISCUSSION We report a novel nonsense mutation of the SLC4A11 gene in the patient with CHED2. In addition, one of heterozygous carriers in this family showed features of late onset FECD. Close clinical ocular examination for the heterozygous carriers should be performed to detect late onset FECD.
Collapse
Affiliation(s)
- Jae-hyung Kim
- a Department of Ophthalmology , College of Medicine, Chungbuk National University , Cheongju , Korea
| | | | | |
Collapse
|
22
|
Loganathan SK, Lukowski CM, Casey JR. The cytoplasmic domain is essential for transport function of the integral membrane transport protein SLC4A11. Am J Physiol Cell Physiol 2015; 310:C161-74. [PMID: 26582474 DOI: 10.1152/ajpcell.00246.2015] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2015] [Accepted: 11/11/2015] [Indexed: 12/21/2022]
Abstract
Large cytoplasmic domains (CD) are a common feature among integral membrane proteins. In virtually all cases, these CD have a function (e.g., binding cytoskeleton or regulatory factors) separate from that of the membrane domain (MD). Strong associations between CD and MD are rare. Here we studied SLC4A11, a membrane transport protein of corneal endothelial cells, the mutations of which cause genetic corneal blindness. SLC4A11 has a 41-kDa CD and a 57-kDa integral MD. One disease-causing mutation in the CD, R125H, manifests a catalytic defect, suggesting a role of the CD in transport function. Expressed in HEK-293 cells without the CD, MD-SLC4A11 is retained in the endoplasmic reticulum, indicating a folding defect. Replacement of CD-SLC4A11 with green fluorescent protein did not rescue MD-SLC4A11, suggesting some specific role of CD-SLC4A11. Homology modeling revealed that the structure of CD-SLC4A11 is similar to that of the Cl(-)/HCO3(-) exchange protein AE1 (SLC4A1) CD. Fusion to CD-AE1 partially rescued MD-SLC4A11 to the cell surface, suggesting that the structure of CD-AE1 is similar to that of CD-SLC4A11. The CD-AE1-MD-SLC4a11 chimera, however, had no functional activity. We conclude that CD-SLC4A11 has an indispensable role in the transport function of SLC4A11. CD-SLC4A11 forms insoluble precipitates when expressed in bacteria, suggesting that the domain cannot fold properly when expressed alone. Consistent with a strong association between CD-SLC4A11 and MD-SLC4A11, these domains specifically associate when coexpressed in HEK-293 cells. We conclude that SLC4A11 is a rare integral membrane protein in which the CD has strong associations with the integral MD, which contributes to membrane transport function.
Collapse
Affiliation(s)
- Sampath K Loganathan
- Membrane Protein Disease Research Group, Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada
| | - Chris M Lukowski
- Membrane Protein Disease Research Group, Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada
| | - Joseph R Casey
- Membrane Protein Disease Research Group, Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada
| |
Collapse
|
23
|
Sacchetti M, Macchi I, Tiezzi A, La Cava M, Massaro-Giordano G, Lambiase A. Pathophysiology of Corneal Dystrophies: From Cellular Genetic Alteration to Clinical Findings. J Cell Physiol 2015; 231:261-9. [DOI: 10.1002/jcp.25082] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2015] [Accepted: 06/19/2015] [Indexed: 02/04/2023]
Affiliation(s)
- Marta Sacchetti
- Cornea and Ocular Surface Unit; Ospedale San Raffaele, IRCCS-Milan; Milano Italy
| | - Ilaria Macchi
- Department of Ophthalmology; University of Rome “Campus Bio-Medico”; Rome Italy
| | - Alessandro Tiezzi
- Section of Ophthalmology, Department of Sense Organs; University of Rome “Sapienza”; Rome Italy
| | - Maurizio La Cava
- Section of Ophthalmology, Department of Sense Organs; University of Rome “Sapienza”; Rome Italy
| | | | - Alessandro Lambiase
- Section of Ophthalmology, Department of Sense Organs; University of Rome “Sapienza”; Rome Italy
| |
Collapse
|
24
|
SLC4A11 and the Pathophysiology of Congenital Hereditary Endothelial Dystrophy. BIOMED RESEARCH INTERNATIONAL 2015; 2015:475392. [PMID: 26451371 PMCID: PMC4588344 DOI: 10.1155/2015/475392] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/27/2015] [Accepted: 05/17/2015] [Indexed: 12/13/2022]
Abstract
Congenital hereditary endothelial dystrophy (CHED) is a rare autosomal recessive disorder of the corneal endothelium characterized by nonprogressive bilateral corneal edema and opacification present at birth. Here we review the current knowledge on the role of the SLC4A11 gene, protein, and its mutations in the pathophysiology and clinical presentation of CHED. Individuals with CHED have mutations in SLC4A11 which encodes a transmembrane protein in the SLC4 family of bicarbonate transporters. The expression of SLC4A11 in the corneal endothelium and inner ear patterns the deficits seen in CHED with corneal edema and hearing loss (Harboyan syndrome). slc4a11-null-mouse models recapitulate the CHED disease phenotype, thus establishing a functional role for SLC4A11 in CHED. However, the transport function of SLC4A11 remains unsettled. Some of the roles that have been attributed to SLC4A11 include H(+) and NH4 (+) permeation, electrogenic Na(+)-H(+) exchange, and water transport. Future studies of the consequences of SLC4A11 dysfunction as well as further understanding of corneal endothelial ion transport will help clarify the involvement of SLC4A11 in the pathophysiology of CHED.
Collapse
|
25
|
Siddiqui S, Zenteno JC, Rice A, Chacón-Camacho O, Naylor SG, Rivera-de la Parra D, Spokes DM, James N, Toomes C, Inglehearn CF, Ali M. Congenital hereditary endothelial dystrophy caused by SLC4A11 mutations progresses to Harboyan syndrome. Cornea 2014; 33:247-51. [PMID: 24351571 PMCID: PMC4195577 DOI: 10.1097/ico.0000000000000041] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Supplemental Digital Content is Available in the Text. Purpose: Homozygous mutations in SLC4A11 cause 2 rare recessive conditions: congenital hereditary endothelial dystrophy (CHED), affecting the cornea alone, and Harboyan syndrome consisting of corneal dystrophy and sensorineural hearing loss. In addition, adult-onset Fuchs endothelial corneal dystrophy (FECD) is associated with dominant mutations in SLC4A11. In this report, we investigate whether patients with CHED go on to develop hearing loss and whether their parents, who are carriers of an SLC4A11 mutation, show signs of having FECD. Methods: Patients with CHED were screened for mutations in the SLC4A11 gene and underwent audiometric testing. The patients and their parents underwent a clinical examination and specular microscopy. Results: Molecular analyses confirmed SLC4A11 mutations in 4 affected individuals from 3 families. All the patients were found to have varying degrees of sensorineural hearing loss at a higher frequency range. Guttate lesions were seen in 2 of the 4 parents who were available for examination. Conclusions: Our observations suggest that CHED caused by homozygous SLC4A11 mutations progresses to Harboyan syndrome, but the severity of this may vary considerably. Patients with CHED should therefore be monitored for progressive hearing loss. We could not determine conclusively whether the parents of the patients with CHED were at increased risk of developing late-onset FECD.
Collapse
Affiliation(s)
- Salina Siddiqui
- *Section of Ophthalmology and Neuroscience, Leeds Institute of Biomedical and Clinical Sciences, University of Leeds, Leeds, United Kingdom; †Department of Ophthalmology, St James's University Hospital, Leeds, United Kingdom; ‡Department of Biochemistry, Faculty of Medicine, National Autonomous University of Mexico (UNAM), Mexico City, Mexico; §Department of Genetics, Institute of Ophthalmology "Conde de Valenciana," Mexico City, Mexico; and ¶Department of Ophthalmology, Bradford Royal Infirmary, Bradford, United Kingdom
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
26
|
Biosynthetic and functional defects in newly identified SLC4A11 mutants and absence of COL8A2 mutations in Fuchs endothelial corneal dystrophy. J Hum Genet 2014; 59:444-53. [PMID: 25007886 DOI: 10.1038/jhg.2014.55] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2014] [Revised: 05/26/2014] [Accepted: 06/12/2014] [Indexed: 12/31/2022]
Abstract
Late-onset Fuchs endothelial corneal dystrophy (FECD) shows genetic heterogeneity. Identification of SLC4A11 as a candidate gene for congenital hereditary endothelial dystrophy with similar corneal endothelial defects as FECD and reduced mRNA expression of SLC4A11 in the endothelium of FECD cases suggested that this gene may also be involved in pathogenesis of FECD. Mutations in SLC4A11 give rise to SLC4A11 protein marked by retention in the endoplasmic reticulum as a result of mis-folding. We screened 45 sporadic late-onset, 4 early-onset FECD patients and an early-onset autosomal dominant FECD family. We identified three previously unreported missense mutations: c.719G>C (p.W240S), c.1519G>A (p.V507I) and c.1304C>T (p.T434I) in unrelated individuals. These SLC4A11 mutants, expressed in HEK293 cells, had defects in either their cell surface expression or functional activity (rate of osmotically driven water flux). SLC4A11 mutations contribute to 11% (5/45) of sporadic late-onset FECD in the cohort studied. COL8A2, which causes some cases of early-onset FECD, was also screened in this cohort. No mutations were identified in COL8A2, in neither the late-onset cohort nor the early-onset family, suggesting genetic heterogeneity in this FECD family.
Collapse
|
27
|
Romero MF, Chen AP, Parker MD, Boron WF. The SLC4 family of bicarbonate (HCO₃⁻) transporters. Mol Aspects Med 2013; 34:159-82. [PMID: 23506864 DOI: 10.1016/j.mam.2012.10.008] [Citation(s) in RCA: 236] [Impact Index Per Article: 21.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2012] [Accepted: 08/28/2012] [Indexed: 01/13/2023]
Abstract
The SLC4 family consists of 10 genes (SLC4A1-5; SLC4A7-11). All encode integral membrane proteins with very similar hydropathy plots-consistent with 10-14 transmembrane segments. Nine SLC4 members encode proteins that transport HCO3(-) (or a related species, such as CO3(2-)) across the plasma membrane. Functionally, eight of these proteins fall into two major groups: three Cl-HCO3 exchangers (AE1-3) and five Na(+)-coupled HCO3(-) transporters (NBCe1, NBCe2, NBCn1, NBCn2, NDCBE). Two of the Na(+)-coupled transporters (NBCe1, NBCe2) are electrogenic; the other three Na(+)-coupled HCO3(-) transporters and all three AEs are electroneutral. In addition, two other SLC4 members (AE4, SLC4A9 and BTR1, SLC4A11) do not yet have a firmly established function. Most, though not all, SLC4 members are functionally inhibited by 4,4'-diisothiocyanatostilbene-2,2'-disulfonate (DIDS). SLC4 proteins play important roles many modes of acid-base homeostasis: the carriage of CO2 by erythrocytes, the transport of H(+) or HCO3(-) by several epithelia, as well as the regulation of cell volume and intracellular pH.
Collapse
Affiliation(s)
- Michael F Romero
- Physiology & Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, MN 55905, USA.
| | | | | | | |
Collapse
|
28
|
Jalimarada SS, Ogando DG, Vithana EN, Bonanno JA. Ion transport function of SLC4A11 in corneal endothelium. Invest Ophthalmol Vis Sci 2013; 54:4330-40. [PMID: 23745003 DOI: 10.1167/iovs.13-11929] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
PURPOSE Mutations in SLC4A11, a member of the SLC4 superfamily of bicarbonate transporters, give rise to corneal endothelial cell dystrophies. SLC4A11 is a putative Na⁺ borate and Na⁺:OH⁻ transporter. Therefore we ask whether SLC4A11 in corneal endothelium transports borate (B[OH]₄⁻), bicarbonate (HCO3⁻), or hydroxyl (OH⁻) anions coupled to Na⁺. METHODS SLC4A11 expression in cultured primary bovine corneal endothelial cells (BCECs) was determined by semiquantitative PCR, SDS-PAGE/Western blotting, and immunofluorescence staining. Ion transport function was examined by measuring intracellular pH (pHi) or Na⁺ ([Na⁺](i)) in response to Ringer solutions with/without B(OH)₄⁻ or HCO₃⁻ after overexpressing or small interfering RNA (siRNA) silencing of SLC4A11. RESULTS SLC4A11 is localized to the basolateral membrane in BCEC. B(OH)₄⁻ (2.5-10 mM) in bicarbonate-free Ringer induced a rapid small acidification (0.01 pH unit) followed by alkalinization (0.05-0.1 pH unit), consistent with diffusion of boric acid into the cell followed by B(OH)₄⁻. However, the rate of B(OH)₄⁻-induced pHi change was unaffected by overexpression of SLC4A11. B(OH)₄⁻ did not induce significant changes in resting [Na⁺(i)] or the amplitude and rate of acidification caused by Na⁺ removal. siRNA-mediated knockdown of SLC4A11 (∼70%) did not alter pHi responses to CO₂/HCO₃⁻-rich Ringer, Na⁺-free induced acidification, or the rate of Na⁺ influx in the presence of bicarbonate. However, in the absence of bicarbonate, siSLC4A11 knockdown significantly decreased the rate (43%) and amplitude (48%) of acidification due to Na⁺ removal and recovery (53%) upon add-back. Additionally, the rate of acid recovery following NH₄⁺ prepulse was decreased significantly (27%) by SLC4A11 silencing. CONCLUSIONS In corneal endothelium, SLC4A11 displays robust Na⁺-coupled OH⁻ transport, but does not transport B(OH)₄⁻ or HCO₃⁻.
Collapse
|
29
|
Aldave AJ, Han J, Frausto RF. Genetics of the corneal endothelial dystrophies: an evidence-based review. Clin Genet 2013; 84:109-19. [PMID: 23662738 DOI: 10.1111/cge.12191] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2013] [Revised: 05/08/2013] [Accepted: 05/08/2013] [Indexed: 11/27/2022]
Abstract
The aim of this review was to provide an evidenced-based review of the genetic basis of the corneal endothelial dystrophies. A review of the English language peer-reviewed literature describing the molecular genetic basis of posterior polymorphous corneal dystrophy (PPCD), congenital hereditary endothelial dystrophy (CHED), Fuchs endothelial corneal dystrophy (FECD) and X-linked endothelial corneal dystrophy (XECD) was performed. Mutations in several genes have been implicated as playing a pathogenic role in the corneal endothelial dystrophies: VSX1 mutations in PPCD1; COL8A2 mutations in PPCD2 and FECD; ZEB1 mutations in PPCD3 and FECD; and SLC4A11 mutations in CHED2 and FECD. However, linkage, association and familial segregation analyses support a role of only one gene in each corneal endothelial dystrophy: ZEB1 in PPCD3, SLC4A11 in CHED2 and COL8A2 in FECD (early onset). In addition, insufficient evidence exists to consider the autosomal dominant form of CHED (CHED1) as distinct from PPCD. An accurate classification of the corneal endothelial dystrophies requires a critical review of the evidence to support the role of each suggested chromosomal locus, gene and genetic mutation associated with a corneal endothelial dystrophy. Only after the separation of evidence from opinion is performed can a critical examination of the molecular pathways that lead to endothelial dysfunction in each of these disorders be accurately performed.
Collapse
Key Words
- corneal dystrophy, Fuchs endothelial, 1
- corneal dystrophy, Fuchs endothelial, 2
- corneal dystrophy, Fuchs endothelial, early onset
- corneal dystrophy, Fuchs endothelial, late onset
- corneal dystrophy, posterior polymorphous, 1
- corneal dystrophy, posterior polymorphous, 2
- corneal dystrophy, posterior polymorphous, 3
- corneal endothelial dystrophy 1
- corneal endothelial dystrophy 2
Collapse
Affiliation(s)
- A J Aldave
- The Jules Stein Eye Institute, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095–7003, USA.
| | | | | |
Collapse
|
30
|
Parker MD, Boron WF. The divergence, actions, roles, and relatives of sodium-coupled bicarbonate transporters. Physiol Rev 2013; 93:803-959. [PMID: 23589833 PMCID: PMC3768104 DOI: 10.1152/physrev.00023.2012] [Citation(s) in RCA: 197] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The mammalian Slc4 (Solute carrier 4) family of transporters is a functionally diverse group of 10 multi-spanning membrane proteins that includes three Cl-HCO3 exchangers (AE1-3), five Na(+)-coupled HCO3(-) transporters (NCBTs), and two other unusual members (AE4, BTR1). In this review, we mainly focus on the five mammalian NCBTs-NBCe1, NBCe2, NBCn1, NDCBE, and NBCn2. Each plays a specialized role in maintaining intracellular pH and, by contributing to the movement of HCO3(-) across epithelia, in maintaining whole-body pH and otherwise contributing to epithelial transport. Disruptions involving NCBT genes are linked to blindness, deafness, proximal renal tubular acidosis, mental retardation, and epilepsy. We also review AE1-3, AE4, and BTR1, addressing their relevance to the study of NCBTs. This review draws together recent advances in our understanding of the phylogenetic origins and physiological relevance of NCBTs and their progenitors. Underlying these advances is progress in such diverse disciplines as physiology, molecular biology, genetics, immunocytochemistry, proteomics, and structural biology. This review highlights the key similarities and differences between individual NCBTs and the genes that encode them and also clarifies the sometimes confusing NCBT nomenclature.
Collapse
Affiliation(s)
- Mark D Parker
- Dept. of Physiology and Biophysics, Case Western Reserve University School of Medicine, 10900 Euclid Ave., Cleveland, OH 44106-4970, USA.
| | | |
Collapse
|
31
|
Liu J, Seet LF, Koh LW, Venkatraman A, Venkataraman D, Mohan RR, Praetorius J, Bonanno JA, Aung T, Vithana EN. Depletion of SLC4A11 causes cell death by apoptosis in an immortalized human corneal endothelial cell line. Invest Ophthalmol Vis Sci 2012; 53:3270-9. [PMID: 22447871 DOI: 10.1167/iovs.11-8724] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE To investigate the effects of SLC4A11 gene depletion in human corneal endothelial cells. METHODS To achieve stable downregulation of SLC4A11 gene expression in immortalized human corneal endothelial cells (HCECs), short-hairpin RNA (shRNA) targeted against SLC4A11 was used. Cell growth and viability were determined using the real-time cell analyzer and trypan blue staining respectively. Apoptosis was investigated by Annexin V and TUNEL assays. Alterations in apoptotic gene expression following SLC4A11 silencing were determined using the RT(2)Profiler PCR array for human apoptosis while activation of the apoptotic pathway was ascertained by western analysis. RESULTS SLC4A11 silencing in HCECs could be achieved by stable expression of shRNA targeted against SLC4A11. SLC4A11 knockdown suppressed HCEC growth and reduced HCEC viability compared to the control. This reduction in cell growth is associated with increased apoptosis in SLC4A11-silenced cells. CONCLUSIONS Our data suggest that the reduction of cell number with time in SLC4A11-depleted HCECs is due to an increase in cell death by apoptosis. This suggests that SLC4A11 is necessary for cell survival and may explain the pathologic corneal endothelial cell loss in endotheliopathies due to SLC4A11 mutations.
Collapse
Affiliation(s)
- Jun Liu
- Singapore Eye Research Institute, Singapore
| | | | | | | | | | | | | | | | | | | |
Collapse
|
32
|
Vilas GL, Loganathan SK, Quon A, Sundaresan P, Vithana EN, Casey J. Oligomerization of SLC4A11 protein and the severity of FECD and CHED2 corneal dystrophies caused by SLC4A11 mutations. Hum Mutat 2011; 33:419-28. [PMID: 22072594 DOI: 10.1002/humu.21655] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2011] [Accepted: 10/31/2011] [Indexed: 11/06/2022]
Abstract
Mutations in the SLC4A11 gene, which encodes a plasma membrane borate transporter, cause recessive congenital hereditary endothelial corneal dystrophy type 2 (CHED2), corneal dystrophy and perceptive deafness (Harboyan syndrome), and dominant late-onset Fuchs endothelial corneal dystrophy (FECD). We analyzed missense SLC4A11 mutations identified in FECD and CHED2 patients and expressed in transfected HEK 293 cells. Chemical cross-linking and migration in nondenaturing gels showed that SLC4A11 exists as a dimer. Furthermore, co-immunoprecipitation of epitope-tagged proteins revealed heteromeric interactions between wild-type (WT) and mutant SLC4A11 proteins. When expressed alone, FECD- and CHED2-causing mutant SLC4A11 proteins are primarily retained intracellularly. Co-expression with WT SLC4A11 partially rescued the cell surface trafficking of CHED2 mutants, but not FECD mutants. CHED2 alleles of SLC4A11 did not affect cell surface processing of WT SLC4A11. In contrast, FECD mutants reduced WT cell surface processing efficiency, consistent with dominant inheritance of FECD. The reduction in movement of WT protein to the cell surface caused by FECD SLC4A11 helps to explain the dominant inheritance of this disorder. Similarly, the failure of CHED2 mutant SLC4A11 to affect the processing of WT protein, explains the lack of symptoms found in CHED2 carriers and the recessive inheritance of the disorder.
Collapse
Affiliation(s)
- Gonzalo L Vilas
- Membrane Protein Disease Research Group, Department of Physiology, School of Molecular and Systems Medicine, University of Alberta, Edmonton, Canada
| | | | | | | | | | | |
Collapse
|
33
|
Schmedt T, Silva MM, Ziaei A, Jurkunas U. Molecular bases of corneal endothelial dystrophies. Exp Eye Res 2011; 95:24-34. [PMID: 21855542 DOI: 10.1016/j.exer.2011.08.002] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2011] [Revised: 07/18/2011] [Accepted: 08/03/2011] [Indexed: 01/12/2023]
Abstract
The phrase "corneal endothelial dystrophies" embraces a group of bilateral corneal conditions that are characterized by a non-inflammatory and progressive degradation of corneal endothelium. Corneal endothelial cells exhibit a high pump site density and, along with barrier function, are responsible for maintaining the cornea in its natural state of relative dehydration. Gradual loss of endothelial cells leads to an insufficient water outflow, resulting in corneal edema and loss of vision. Since the pathologic mechanisms remain largely unknown, the only current treatment option is surgical transplantation when vision is severely impaired. In the past decade, important steps have been taken to understand how endothelial degeneration progresses on the molecular level. Studies of affected multigenerational families and sporadic cases identified genes and chromosomal loci, and revealed either Mendelian or complex disorder inheritance patterns. Mutations have been detected in genes that carry important structural, metabolic, cytoprotective, and regulatory functions in corneal endothelium. In addition to genetic predisposition, environmental factors like oxidative stress were found to be involved in the pathogenesis of endotheliopathies. This review summarizes and crosslinks the recent progress on deciphering the molecular bases of corneal endothelial dystrophies.
Collapse
Affiliation(s)
- Thore Schmedt
- Schepens Eye Research Institute, Boston, MA 02114, USA
| | | | | | | |
Collapse
|
34
|
Vilas GL, Morgan PE, Loganathan SK, Quon A, Casey JR. A Biochemical Framework for SLC4A11, the Plasma Membrane Protein Defective in Corneal Dystrophies. Biochemistry 2011; 50:2157-69. [DOI: 10.1021/bi101887z] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Affiliation(s)
- Gonzalo L. Vilas
- Membrane Protein Disease Research Group, Department of Physiology, and Department of Biochemistry, School of Molecular and Systems Medicine, University of Alberta, Edmonton, Canada T6G 2H7
| | - Patricio E. Morgan
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, La Plata, Buenos Aires, Argentina CP1900
| | - Sampath K. Loganathan
- Membrane Protein Disease Research Group, Department of Physiology, and Department of Biochemistry, School of Molecular and Systems Medicine, University of Alberta, Edmonton, Canada T6G 2H7
| | - Anita Quon
- Membrane Protein Disease Research Group, Department of Physiology, and Department of Biochemistry, School of Molecular and Systems Medicine, University of Alberta, Edmonton, Canada T6G 2H7
| | - Joseph R. Casey
- Membrane Protein Disease Research Group, Department of Physiology, and Department of Biochemistry, School of Molecular and Systems Medicine, University of Alberta, Edmonton, Canada T6G 2H7
| |
Collapse
|
35
|
Molecular Genetics of Corneal Disease. Cornea 2011. [DOI: 10.1016/b978-0-323-06387-6.00019-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
|
36
|
Weisenthal RW, Streeten BW. Descemet's Membrane and Endothelial Dystrophies. Cornea 2011. [DOI: 10.1016/b978-0-323-06387-6.00080-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/22/2023]
|
37
|
Abstract
The corneal endothelium maintains the level of hydration in the cornea. Dysfunction of the endothelium results in excess accumulation of water in the corneal stroma, leading to swelling of the stroma and loss of transparency. There are four different corneal endothelial dystrophies that are hereditary, progressive, non-inflammatory disorders involving dysfunction of the corneal endothelium. Each of the endothelial dystrophies is genetically heterogeneous with different modes of transmission and/or different genes involved in each subtype. Genes responsible for disease have been identified for only a subset of corneal endothelial dystrophies. Knowledge of genes involved and their function in the corneal endothelium can aid understanding the pathogenesis of the disorder as well as reveal pathways that are important for normal functioning of the endothelium.
Collapse
|
38
|
Gröger N, Fröhlich H, Maier H, Olbrich A, Kostin S, Braun T, Boettger T. SLC4A11 prevents osmotic imbalance leading to corneal endothelial dystrophy, deafness, and polyuria. J Biol Chem 2010; 285:14467-74. [PMID: 20185830 DOI: 10.1074/jbc.m109.094680] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Maintenance of ion concentration gradients is essential for the function of many organs, including the kidney, the cornea, and the inner ear. Ion concentrations and fluid content in the cornea are regulated by endothelial cells that separate the collagenous avascular corneal stroma from the anterior eye chamber. Failure to maintain correct ion concentrations leads to swelling and destruction of the cornea. In the inner ear, the stria vascularis is responsible for generating proper ion concentrations in the endolymph, which is essential for hearing. Mutations of SLC4A11 in humans lead to syndromes associated with corneal dystrophy and perceptive deafness. The molecular mechanisms underlying these symptoms are poorly understood, impeding therapeutic interventions. The ion transporter SLC4A11 mediates sodium-dependent transport of borate as well as flux of sodium and hydroxyl ions in vitro. Here, we show that SLC4A11 is expressed in the endothelial cells of the cornea where it prevents severe morphological changes of the cornea caused by increased sodium chloride concentrations in the stroma. In the inner ear, SLC4A11 is located in fibrocytes underlying the stria vascularis. Loss of SLC4A11 leads to morphological changes in the fibrocytes and deafness. We demonstrate that SLC4A11 is essential for the generation of the endocochlear potential but not for regulation of potassium concentrations in the endolymph. In the kidney, SLC4A11 is expressed in the thin descending limb of Henle loop. SLC4A11 is essential for urinary concentration, suggesting that SLC4A11 participates in the countercurrent multiplication that concentrates urine in the kidney medulla.
Collapse
Affiliation(s)
- Nicole Gröger
- Max-Planck-Institut für Herz- und Lungenforschung, Parkstrasse 1, D-61231 Bad Nauheim, Germany
| | | | | | | | | | | | | |
Collapse
|
39
|
Lopez IA, Rosenblatt MI, Kim C, Galbraith GC, Jones SM, Kao L, Newman D, Liu W, Yeh S, Pushkin A, Abuladze N, Kurtz I. Slc4a11 gene disruption in mice: cellular targets of sensorineuronal abnormalities. J Biol Chem 2009; 284:26882-96. [PMID: 19586905 DOI: 10.1074/jbc.m109.008102] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
NaBC1 (the SLC4A11 gene) belongs to the SLC4 family of sodium-coupled bicarbonate (carbonate) transporter proteins and functions as an electrogenic sodium borate cotransporter. Mutations in SLC4A11 cause either corneal abnormalities (corneal hereditary dystrophy type 2) or a combined auditory and visual impairment (Harboyan syndrome). The role of NaBC1 in sensory systems is poorly understood, given the difficulty of studying patients with NaBC1 mutations. We report our findings in Slc4a11(-/-) mice generated to investigate the role of NaBC1 in sensorineural systems. In wild-type mice, specific NaBC1 immunoreactivity was detected in fibrocytes of the spiral ligament, from the basal to the apical portion of the cochlea. NaBC1 immunoreactivity was present in the vestibular labyrinth, in stromal cells underneath the non-immunoreactive sensory epithelia of the macula utricle, sacule, and crista ampullaris, and the membranous vestibular labyrinth was collapsed. Both auditory brain response and vestibular evoked potential waveforms were significantly abnormal in Slc4a11(-/-) mice. In the cornea, NaBC1 was highly expressed in the endothelial cell layer with less staining in epithelial cells. However, unlike humans, the corneal phenotype was mild with a normal slit lamp evaluation. Corneal endothelial cells were morphologically normal; however, both the absolute height of the corneal basal epithelial cells and the relative basal epithelial cell/total corneal thickness were significantly increased in Slc4a11(-/-) mice. Our results demonstrate for the first time the importance of NaBC1 in the audio-vestibular system and provide support for the hypothesis that SLC4A11 should be considered a potential candidate gene in patients with isolated sensorineural vestibular hearing abnormalities.
Collapse
Affiliation(s)
- Ivan A Lopez
- Division of Head and Neck, David Geffen School of Medicine at UCLA, Los Angeles, California 90095, USA
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
40
|
Abstract
The term corneal dystrophy embraces a heterogenous group of bilateral genetically determined non-inflammatory corneal diseases that are restricted to the cornea. The designation is imprecise but remains in vogue because of its clinical value. Clinically, the corneal dystrophies can be divided into three groups based on the sole or predominant anatomical location of the abnormalities. Some affect primarily the corneal epithelium and its basement membrane or Bowman layer and the superficial corneal stroma (anterior corneal dystrophies), the corneal stroma (stromal corneal dystrophies), or Descemet membrane and the corneal endothelium (posterior corneal dystrophies). Most corneal dystrophies have no systemic manifestations and present with variable shaped corneal opacities in a clear or cloudy cornea and they affect visual acuity to different degrees. Corneal dystrophies may have a simple autosomal dominant, autosomal recessive or X-linked recessive Mendelian mode of inheritance. Different corneal dystrophies are caused by mutations in the CHST6, KRT3, KRT12, PIP5K3, SLC4A11, TACSTD2, TGFBI, and UBIAD1 genes. Knowledge about the responsible genetic mutations responsible for these disorders has led to a better understanding of their basic defect and to molecular tests for their precise diagnosis. Genes for other corneal dystrophies have been mapped to specific chromosomal loci, but have not yet been identified. As clinical manifestations widely vary with the different entities, corneal dystrophies should be suspected when corneal transparency is lost or corneal opacities occur spontaneously, particularly in both corneas, and especially in the presence of a positive family history or in the offspring of consanguineous parents. Main differential diagnoses include various causes of monoclonal gammopathy, lecithin-cholesterol-acyltransferase deficiency, Fabry disease, cystinosis, tyrosine transaminase deficiency, systemic lysosomal storage diseases (mucopolysaccharidoses, lipidoses, mucolipidoses), and several skin diseases (X-linked ichthyosis, keratosis follicularis spinolosa decalvans). The management of the corneal dystrophies varies with the specific disease. Some are treated medically or with methods that excise or ablate the abnormal corneal tissue, such as deep lamellar endothelial keratoplasty (DLEK) and phototherapeutic keratectomy (PTK). Other less debilitating or asymptomatic dystrophies do not warrant treatment. The prognosis varies from minimal effect on the vision to corneal blindness, with marked phenotypic variability.
Collapse
Affiliation(s)
- Gordon K Klintworth
- Department of Ophthalmology, Duke University Medical Center, Durham, North Carolina, USA.
| |
Collapse
|
41
|
Weiss JS, Møller HU, Lisch W, Kinoshita S, Aldave AJ, Belin MW, Kivelä T, Busin M, Munier FL, Seitz B, Sutphin J, Bredrup C, Mannis MJ, Rapuano CJ, Van Rij G, Kim EK, Klintworth GK. The IC3D classification of the corneal dystrophies. Cornea 2008; 27 Suppl 2:S1-83. [PMID: 19337156 PMCID: PMC2866169 DOI: 10.1097/ico.0b013e31817780fb] [Citation(s) in RCA: 195] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
BACKGROUND The recent availability of genetic analyses has demonstrated the shortcomings of the current phenotypic method of corneal dystrophy classification. Abnormalities in different genes can cause a single phenotype, whereas different defects in a single gene can cause different phenotypes. Some disorders termed corneal dystrophies do not appear to have a genetic basis. PURPOSE The purpose of this study was to develop a new classification system for corneal dystrophies, integrating up-to-date information on phenotypic description, pathologic examination, and genetic analysis. METHODS The International Committee for Classification of Corneal Dystrophies (IC3D) was created to devise a current and accurate nomenclature. RESULTS This anatomic classification continues to organize dystrophies according to the level chiefly affected. Each dystrophy has a template summarizing genetic, clinical, and pathologic information. A category number from 1 through 4 is assigned, reflecting the level of evidence supporting the existence of a given dystrophy. The most defined dystrophies belong to category 1 (a well-defined corneal dystrophy in which a gene has been mapped and identified and specific mutations are known) and the least defined belong to category 4 (a suspected dystrophy where the clinical and genetic evidence is not yet convincing). The nomenclature may be updated over time as new information regarding the dystrophies becomes available. CONCLUSIONS The IC3D Classification of Corneal Dystrophies is a new classification system that incorporates many aspects of the traditional definitions of corneal dystrophies with new genetic, clinical, and pathologic information. Standardized templates provide key information that includes a level of evidence for there being a corneal dystrophy. The system is user-friendly and upgradeable and can be retrieved on the website www.corneasociety.org/ic3d.
Collapse
Affiliation(s)
- Jayne S Weiss
- Department of Ophthalmology, Kresge Eye Institute, Wayne State University School of Medicine, Detroit, MI 48201, USA.
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
42
|
Desir J, Abramowicz M. Congenital hereditary endothelial dystrophy with progressive sensorineural deafness (Harboyan syndrome). Orphanet J Rare Dis 2008; 3:28. [PMID: 18922146 PMCID: PMC2576053 DOI: 10.1186/1750-1172-3-28] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2008] [Accepted: 10/15/2008] [Indexed: 12/13/2022] Open
Abstract
Harboyan syndrome is a degenerative corneal disorder defined as congenital hereditary endothelial dystrophy (CHED) accompanied by progressive, postlingual sensorineural hearing loss. To date, 24 cases from 11 families of various origin (Asian Indian, South American Indian, Sephardi Jewish, Brazilian Portuguese, Dutch, Gypsy, Moroccan, Dominican) have been reported. More than 50% of the reported cases have been associated with parental consanguinity. The ocular manifestations in Harboyan syndrome include diffuse bilateral corneal edema occurring with severe corneal clouding, blurred vision, visual loss and nystagmus. They are apparent at birth or within the neonatal period and are indistinguishable from those characteristic of the autosomal recessive CHED (CHED2). Hearing deficit in Harboyan is slowly progressive and typically found in patients 10-25 years old. There are no reported cases with prelinglual deafness, however, a significant hearing loss in children as young as 4 years old has been detected by audiometry, suggesting that hearing may be affected earlier, even at birth. Harboyan syndrome is caused by mutations in the SLC4A11 gene located at the CHED2 locus on chromosome 20p13-p12, indicating that CHED2 and Harboyan syndrome are allelic disorders. A total of 62 different SLC4A11 mutations have been reported in 98 families (92 CHED2 and 6 Harboyan). All reported cases have been consistent with autosomal recessive transmission. Diagnosis is based on clinical criteria, detailed ophthalmological assessment and audiometry. A molecular confirmation of the clinical diagnosis is feasible. A variety of genetic, metabolic, developmental and acquired diseases presenting with clouding of the cornea should be considered in the differential diagnosis (Peters anomaly, sclerocornea, limbal dermoids, congenital glaucoma). Audiometry must be performed to differentiate Harboyan syndrome from CHED2. Autosomal recessive types of CHED (CHED2 and Harboyan syndrome) should carefully be distinguished from the less severe autosomal dominant type CHED1. The ocular abnormalities in patients with Harboyan syndrome may be treated with topical hyperosmolar solutions. However, corneal transplantation (penetrating keratoplasty) represents definitive treatment. Corneal transplantation produces a substantial visual gain and has a relatively good surgical prognosis. Audiometric monitoring should be offered to all patients with CHED2. Hearing aids may be necessary in adolescence.
Collapse
Affiliation(s)
- Julie Desir
- Department of Medical Genetics, Hôpital Erasme, ULB, Brussels, Belgium.
| | | |
Collapse
|
43
|
Kao L, Sassani P, Azimov R, Pushkin A, Abuladze N, Peti-Peterdi J, Liu W, Newman D, Kurtz I. Oligomeric structure and minimal functional unit of the electrogenic sodium bicarbonate cotransporter NBCe1-A. J Biol Chem 2008; 283:26782-94. [PMID: 18658147 DOI: 10.1074/jbc.m804006200] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
The electrogenic sodium bicarbonate cotransporter NBCe1-A mediates the basolateral absorption of sodium and bicarbonate in the proximal tubule. In this study the oligomeric state and minimal functional unit of NBCe1-A were investigated. Wild-type (wt) NBCe1-A isolated from mouse kidney or heterologously expressed in HEK293 cells was predominantly in a dimeric state as was shown using fluorescence energy transfer, pulldown, immunoprecipitation, cross-linking experiments, and nondenaturing perfluorooctanoate-PAGE. NBCe1-A monomers were found to be covalently linked by S-S bonds. When each of the 15 native cysteine residues were individually removed on a wt-NBCe1-A backbone, dimerization of the cotransporter was not affected. In experiments involving multiple native cysteine residue removal, both Cys(630) and Cys(642) in extracellular loop 3 were shown to mediate S-S bond formation between NBCe1-A monomers. When native NBCe1-A cysteine residues were individually reintroduced into a cysteineless NBCe1-A mutant backbone, the finding that a Cys(992) construct that lacked S-S bonds functioned normally indicated that stable covalent linkage of NBCe1-A monomers was not a necessary requirement for functional activity of the cotransporter. Studies using concatameric constructs of wt-NBCe1-A, whose activity is resistant to methanesulfonate reagents, and an NBCe1-A(T442C) mutant, whose activity is completely inhibited by methanesulfonate reagents, confirmed that NBCe1-A monomers are functional. Our results demonstrate that wt-NBCe1-A is predominantly a homodimer, dependent on S-S bond formation that is composed of functionally active monomers.
Collapse
Affiliation(s)
- Liyo Kao
- Division of Nephrology, David Geffen School Medicine, UCLA, Los Angeles, California 90095-1689, USA
| | | | | | | | | | | | | | | | | |
Collapse
|