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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.
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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
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Gour A, Garg A, Tibrewal S, Pegu J, Gupta S, Mathur U, Sangwan V. Corneal transplantation in children - when and how? EXPERT REVIEW OF OPHTHALMOLOGY 2023. [DOI: 10.1080/17469899.2023.2177153] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- Abha Gour
- Department of Cornea and Anterior Segment Services, Dr Shroffs Charity Eye Hospital, New Delhi
| | - Aastha Garg
- Department of Cornea and Anterior Segment Services, Dr Shroffs Charity Eye Hospital, New Delhi
| | - Shailja Tibrewal
- Department of Pediatric Ophthalmology, Strabismus and Neurophthamology, Dr Shroffs Charity Eye Hospital, New Delhi
| | - Julie Pegu
- Department of Glaucoma and Anterior Segment Services, Dr Shroffs Charity Eye Hospital, Dr Shroffs Charity Eye Hospital, New Delhi
| | - Sonal Gupta
- Department of Cornea and Anterior Segment Services, Dr Shroffs Charity Eye Hospital, New Delhi
| | - Umang Mathur
- Department of Cornea and Anterior Segment Services, Dr Shroffs Charity Eye Hospital, New Delhi
| | - Virender Sangwan
- Department of Cornea and Anterior Segment Services, Dr Shroffs Charity Eye Hospital, New Delhi
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Yousaf K, Naz S, Mushtaq A, Wohler E, Sobreira N, Ho BM, Chen LJ, Chu WK, Bashir R. Exome Sequencing Reveals SLC4A11 Variant Underlying Congenital Hereditary Endothelial Dystrophy (CHED2) Misdiagnosed as Congenital Glaucoma. Genes (Basel) 2023; 14:genes14020310. [PMID: 36833236 PMCID: PMC9956413 DOI: 10.3390/genes14020310] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2022] [Revised: 01/02/2023] [Accepted: 01/21/2023] [Indexed: 01/27/2023] Open
Abstract
Autosomal recessive congenital hereditary endothelial dystrophy (CHED2) may be misdiagnosed as primary congenital glaucoma (PCG) due to similar clinical phenotypes during early infancy. In this study, we identified a family with CHED2, which was previously misdiagnosed as having PCG, and followed up for 9 years. Linkage analysis was first completed in eight PCG-affected families, followed by whole-exome sequencing (WES) in family PKGM3. The following in silico tools were used to predict the pathogenic effects of identified variants: I-Mutant 2.0, SIFT, Polyphen-2, PROVEAN, mutation taster and PhD-SNP. After detecting an SLC4A11 variant in one family, detailed ophthalmic examinations were performed again to confirm the diagnosis. Six out of eight families had CYP1B1 gene variants responsible for PCG. However, in family PKGM3, no variants in the known PCG genes were identified. WES identified a homozygous missense variant c.2024A>C, p.(Glu675Ala) in SLC4A11. Based on the WES findings, the affected individuals underwent detailed ophthalmic examinations and were re-diagnosed with CHED2 leading to secondary glaucoma. Our results expand the genetic spectrum of CHED2. This is the first report from Pakistan of a Glu675Ala variant with CHED2 leading to secondary glaucoma. The p.Glu675Ala variant is likely a founder mutation in the Pakistani population. Our findings suggest that genome-wide neonatal screening is worthwhile to avoid the misdiagnosis of phenotypically similar diseases such as CHED2 and PCG.
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Affiliation(s)
- Khazeema Yousaf
- Department of Biotechnology, Lahore College for Women University, Lahore 54000, Pakistan
| | - Sadaf Naz
- School of Biological Sciences, University of the Punjab, Quaid-i-Azam Campus, Lahore 54590, Pakistan
| | - Asma Mushtaq
- Department of Ophthalmology, Children’s Hospital & the Institute of Child Health, Lahore 54000, Pakistan
- Hong Kong Hub of Paediatric Excellence, The Chinese University of Hong Kong, Hong Kong 999077, China
| | - Elizabeth Wohler
- McKusick-Nathans Department of Genetic Medicine, Baylor Hopkins Center for Mendelian Genomics, Baltimore, MD 21205, USA
| | - Nara Sobreira
- McKusick-Nathans Department of Genetic Medicine, Baylor Hopkins Center for Mendelian Genomics, Baltimore, MD 21205, USA
| | - Bo-Man Ho
- McKusick-Nathans Department of Genetic Medicine, Baylor Hopkins Center for Mendelian Genomics, Baltimore, MD 21205, USA
| | - Li-Jia Chen
- Hong Kong Hub of Paediatric Excellence, The Chinese University of Hong Kong, Hong Kong 999077, China
- Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong 999077, China
| | - Wai-Kit Chu
- Hong Kong Hub of Paediatric Excellence, The Chinese University of Hong Kong, Hong Kong 999077, China
- Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong 999077, China
- Correspondence: (W.-K.C.); (R.B.)
| | - Rasheeda Bashir
- Department of Biotechnology, Lahore College for Women University, Lahore 54000, Pakistan
- Correspondence: (W.-K.C.); (R.B.)
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Iqbal A, Naz S, Kaul H, Sharif S, Khushbakht A, Naeem MA, Iqtedar M, Kaleem A, Firasat S, Manzoor F. Mutational analysis in sodium-borate cotransporter SLC4A11 in consanguineous families from Punjab, Pakistan. PLoS One 2022; 17:e0273685. [PMID: 36037197 PMCID: PMC9423612 DOI: 10.1371/journal.pone.0273685] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2021] [Accepted: 08/12/2022] [Indexed: 12/02/2022] Open
Abstract
AIM To identify the molecular basis of Congenital Hereditary Endothelial Dystrophy CHED caused by mutations in SLC4A11, in the consanguineous Pakistani families. METHODS A total of 7 consanguineous families affected with Congenital Hereditary Endothelial Dystrophy were diagnosed and registered with the help of ophthalmologists. Blood samples were collected from affected and unaffected members of the enrolled families. Mutational analysis was carried out by DNA sequencing using both Sanger and Whole Exome Sequencing (WES). Probands of each pedigree from the 7 families were used for WES. Results were analyzed with the help of different bioinformatics tools. RESULTS The sequencing results demonstrated three known homozygous mutations in gene SLC4A11 in probands of 7 families. These mutations p.Glu675Ala, p.Val824Met, and p.Arg158fs include 2 missense and 1 frameshift mutation. The mutations result in amino acids that were highly conserved in SLC4A11 across different species. The mutations were segregated with the disease phenotype in the families. CONCLUSION This study reports 3 mutations in 7 families. One of the pathogenic mutations (p.R158fs) was identified for the first time in the Pakistani population. However, two mutations (p.Glu675Ala, p.Val824Met) were previously reported in two and one Pakistani family respectively. As these mutations segregate with the disease phenotype and bioinformatics tool also liable them as pathogenic, they are deemed as probable cause of underlying disease.
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Affiliation(s)
- Afia Iqbal
- Department of Zoology, Lahore College for Women University, Lahore, Pakista
| | - Shagufta Naz
- Department of Zoology, Lahore College for Women University, Lahore, Pakista
| | - Haiba Kaul
- Department of Animal Breeding and Genetics, Genetics Discipline, University of Veterinary and Animal Sciences, Lahore, Pakistan
| | - Saima Sharif
- Department of Zoology, Lahore College for Women University, Lahore, Pakista
| | - Aysha Khushbakht
- Department of Zoology, Lahore College for Women University, Lahore, Pakista
| | - Muhammad Asif Naeem
- Vision Impairment Lab of Genetic Diseases Group, Center of Excellence in Molecular Biology, Lahore, Pakistan
| | - Mehwish Iqtedar
- Department of Biotechnology, Lahore College for Women University, Lahore, Pakistan
| | - Afshan Kaleem
- Department of Biotechnology, Lahore College for Women University, Lahore, Pakistan
| | - Sabika Firasat
- Department of Biological Sciences, Quaid-e-Azam University, Islamabad, Pakistan
| | - Farkhanda Manzoor
- Department of Zoology, Lahore College for Women University, Lahore, Pakista
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SLC4A11 mutations causative of congenital hereditary endothelial dystrophy (CHED) progressing to Harboyan syndrome in consanguineous Pakistani families. Mol Biol Rep 2021; 48:7467-7476. [PMID: 34637099 DOI: 10.1007/s11033-021-06765-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2021] [Accepted: 08/17/2021] [Indexed: 10/20/2022]
Abstract
BACKGROUND Autosomal recessive corneal hereditary endothelial dystrophy (CHED) is a rare congenital disorder of cornea. Mutations in SLC4A11 gene are associated with CHED phenotype. CHED is also an early feature of Harboyan syndrome. The aim of the present study was to identify genetic mutations in the SLC4A11 gene in CHED cases belonging to inbred Pakistani families. Furthermore, all homozygous mutation carriers were investigated for hearing deficit. METHODS AND RESULTS This study included consanguineous CHED families presented at Al-Shifa Trust Eye Hospital, Rawalpindi, Pakistan from June 2018 to September 2018. DNA was extracted from blood samples. Direct sequencing of SLC4A11 gene was performed. All identified variants were evaluated by in silico programs i.e., SIFT, PolyPhen-2, and MutationTaster. Pathogenicity of the two identified splice site variants was analyzed by Human Splicing Finder and MaxEnt Scan. Screening of five CHED families revealed a total of three previously un reported (p.Arg128Gly, c.2241-2A > T and c.1898-2A > C in family CHED19, CHED22 and CHED26 respectively) and two already reported homozygous disease causing variants (p.Arg869Cys and p.Val824Met in family CHED24 and CHED25 respectively) as predicted by mutation taster. All of these variants segregated with disease phenotype and were not detected in controls. CONCLUSION Affected individuals of the five CHED families screened in this study had the disease due to SLC4A11 mutations and progressing to Harboyan syndrome. Identification of previously unreported mutations aid to heterogeneity of SLC4A11 and CHED pathogenesis as well as helped to provide genetic counseling to affected families.
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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.
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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
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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.
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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.
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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
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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.
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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
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Fine mapping of chromosome 9 locus associated with congenital cataract. Int Ophthalmol 2017; 38:1187-1192. [PMID: 28585112 DOI: 10.1007/s10792-017-0581-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2016] [Accepted: 05/31/2017] [Indexed: 10/19/2022]
Abstract
PURPOSE The purpose of this study was to study the molecular basis of inherited autosomal recessive cataracts in Pakistan population and to identify the molecular defect segregating with the disease phenotype. METHODS Families having two or more affected individuals were identified through hospital, blood samples were collected and DNA was extracted. We employed the traditional strategy of linkage analysis using M13-labeled primers to map the already known genes for autosomal recessive cataract. Statistically, the data were evaluated through LOD score. RESULTS Ten families affected with autosomal receive congenital cataract were enrolled for this study. Overall, three families were linked to reported loci for autosomal recessive congenital cataract. Out of these, one family Bl05 was linked to a cataract locus at 9q13. Fine mapping of the chromosome 9 locus considerably delimited the previously reported linkage interval from 13.99 to 7.99 cM in this study. CONCLUSION Our results reduced the linkage interval of previously reported cataract locus on chromosome 9, thus considerably reducing the number of candidate genes.
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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.
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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
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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.
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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;
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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.
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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
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