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Balboni N, Babini G, Poeta E, Protti M, Mercolini L, Magnifico MC, Barile SN, Massenzio F, Pignataro A, Giorgi FM, Lasorsa FM, Monti B. Transcriptional and metabolic effects of aspartate-glutamate carrier isoform 1 (AGC1) downregulation in mouse oligodendrocyte precursor cells (OPCs). Cell Mol Biol Lett 2024; 29:44. [PMID: 38553684 PMCID: PMC10979587 DOI: 10.1186/s11658-024-00563-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2023] [Accepted: 03/20/2024] [Indexed: 04/02/2024] Open
Abstract
Aspartate-glutamate carrier isoform 1 (AGC1) is a carrier responsible for the export of mitochondrial aspartate in exchange for cytosolic glutamate and is part of the malate-aspartate shuttle, essential for the balance of reducing equivalents in the cells. In the brain, mutations in SLC25A12 gene, encoding for AGC1, cause an ultra-rare genetic disease, reported as a neurodevelopmental encephalopathy, whose symptoms include global hypomyelination, arrested psychomotor development, hypotonia and seizures. Among the biological components most affected by AGC1 deficiency are oligodendrocytes, glial cells responsible for myelination processes, and their precursors [oligodendrocyte progenitor cells (OPCs)]. The AGC1 silencing in an in vitro model of OPCs was documented to cause defects of proliferation and differentiation, mediated by alterations of histone acetylation/deacetylation. Disrupting AGC1 activity could possibly reduce the availability of acetyl groups, leading to perturbation of many biological pathways, such as histone modifications and fatty acids formation for myelin production. Here, we explore the transcriptome of mouse OPCs partially silenced for AGC1, reporting results of canonical analyses (differential expression) and pathway enrichment analyses, which highlight a disruption in fatty acids synthesis from both a regulatory and enzymatic stand. We further investigate the cellular effects of AGC1 deficiency through the identification of most affected transcriptional networks and altered alternative splicing. Transcriptional data were integrated with differential metabolite abundance analysis, showing downregulation of several amino acids, including glutamine and aspartate. Taken together, our results provide a molecular foundation for the effects of AGC1 deficiency in OPCs, highlighting the molecular mechanisms affected and providing a list of actionable targets to mitigate the effects of this pathology.
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Affiliation(s)
- Nicola Balboni
- Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy
| | - Giorgia Babini
- Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy
| | - Eleonora Poeta
- Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy
| | - Michele Protti
- Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy
| | - Laura Mercolini
- Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy
| | - Maria Chiara Magnifico
- Department of Biosciences, Biotechnologies and Environment, University of Bari, Bari, Italy
| | - Simona Nicole Barile
- Department of Biosciences, Biotechnologies and Environment, University of Bari, Bari, Italy
| | - Francesca Massenzio
- Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy
| | - Antonella Pignataro
- Department of Biosciences, Biotechnologies and Environment, University of Bari, Bari, Italy
| | - Federico M Giorgi
- Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy.
| | | | - Barbara Monti
- Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy.
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Pardo B, Herrada-Soler E, Satrústegui J, Contreras L, del Arco A. AGC1 Deficiency: Pathology and Molecular and Cellular Mechanisms of the Disease. Int J Mol Sci 2022; 23:528. [PMID: 35008954 PMCID: PMC8745132 DOI: 10.3390/ijms23010528] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2021] [Revised: 12/23/2021] [Accepted: 12/24/2021] [Indexed: 02/01/2023] Open
Abstract
AGC1/Aralar/Slc25a12 is the mitochondrial carrier of aspartate-glutamate, the regulatory component of the NADH malate-aspartate shuttle (MAS) that transfers cytosolic redox power to neuronal mitochondria. The deficiency in AGC1/Aralar leads to the human rare disease named "early infantile epileptic encephalopathy 39" (EIEE 39, OMIM # 612949) characterized by epilepsy, hypotonia, arrested psychomotor neurodevelopment, hypo myelination and a drastic drop in brain aspartate (Asp) and N-acetylaspartate (NAA). Current evidence suggest that neurons are the main brain cell type expressing Aralar. However, paradoxically, glial functions such as myelin and Glutamine (Gln) synthesis are markedly impaired in AGC1 deficiency. Herein, we discuss the role of the AGC1/Aralar-MAS pathway in neuronal functions such as Asp and NAA synthesis, lactate use, respiration on glucose, glutamate (Glu) oxidation and other neurometabolic aspects. The possible mechanism triggering the pathophysiological findings in AGC1 deficiency, such as epilepsy and postnatal hypomyelination observed in humans and mice, are also included. Many of these mechanisms arise from findings in the aralar-KO mice model that extensively recapitulate the human disease including the astroglial failure to synthesize Gln and the dopamine (DA) mishandling in the nigrostriatal system. Epilepsy and DA mishandling are a direct consequence of the metabolic defect in neurons due to AGC1/Aralar deficiency. However, the deficits in myelin and Gln synthesis may be a consequence of neuronal affectation or a direct effect of AGC1/Aralar deficiency in glial cells. Further research is needed to clarify this question and delineate the transcellular metabolic fluxes that control brain functions. Finally, we discuss therapeutic approaches successfully used in AGC1-deficient patients and mice.
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Affiliation(s)
- Beatriz Pardo
- Departamento de Biología Molecular, Universidad Autónoma de Madrid, 28049 Madrid, Spain; (E.H.-S.); (J.S.); (L.C.)
- Centro de Biología Molecular Severo Ochoa, Universidad Autónoma de Madrid (UAM)-Consejo Superior de Investigaciones Científicas (CSIC), 28049 Madrid, Spain;
- Instituto de Investigaciones Sanitarias Fundación Jiménez Díaz (IIS-FJD), Universidad Autónoma de Madrid, 28049 Madrid, Spain
| | - Eduardo Herrada-Soler
- Departamento de Biología Molecular, Universidad Autónoma de Madrid, 28049 Madrid, Spain; (E.H.-S.); (J.S.); (L.C.)
- Centro de Biología Molecular Severo Ochoa, Universidad Autónoma de Madrid (UAM)-Consejo Superior de Investigaciones Científicas (CSIC), 28049 Madrid, Spain;
- Instituto de Investigaciones Sanitarias Fundación Jiménez Díaz (IIS-FJD), Universidad Autónoma de Madrid, 28049 Madrid, Spain
| | - Jorgina Satrústegui
- Departamento de Biología Molecular, Universidad Autónoma de Madrid, 28049 Madrid, Spain; (E.H.-S.); (J.S.); (L.C.)
- Centro de Biología Molecular Severo Ochoa, Universidad Autónoma de Madrid (UAM)-Consejo Superior de Investigaciones Científicas (CSIC), 28049 Madrid, Spain;
- Instituto de Investigaciones Sanitarias Fundación Jiménez Díaz (IIS-FJD), Universidad Autónoma de Madrid, 28049 Madrid, Spain
| | - Laura Contreras
- Departamento de Biología Molecular, Universidad Autónoma de Madrid, 28049 Madrid, Spain; (E.H.-S.); (J.S.); (L.C.)
- Centro de Biología Molecular Severo Ochoa, Universidad Autónoma de Madrid (UAM)-Consejo Superior de Investigaciones Científicas (CSIC), 28049 Madrid, Spain;
- Instituto de Investigaciones Sanitarias Fundación Jiménez Díaz (IIS-FJD), Universidad Autónoma de Madrid, 28049 Madrid, Spain
| | - Araceli del Arco
- Centro de Biología Molecular Severo Ochoa, Universidad Autónoma de Madrid (UAM)-Consejo Superior de Investigaciones Científicas (CSIC), 28049 Madrid, Spain;
- Instituto de Investigaciones Sanitarias Fundación Jiménez Díaz (IIS-FJD), Universidad Autónoma de Madrid, 28049 Madrid, Spain
- Centro Regional de Investigaciones Biomédicas, Facultad de Ciencias Ambientales y Bioquímica, Universidad de Castilla La Mancha, 45071 Toledo, Spain
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Kumar A, Priyamvada S, Ge Y, Jayawardena D, Singhal M, Anbazhagan AN, Chatterjee I, Dayal A, Patel M, Zadeh K, Saksena S, Alrefai WA, Gill RK, Zadeh M, Zhao N, Mohamadzadeh M, Dudeja PK. A Novel Role of SLC26A3 in the Maintenance of Intestinal Epithelial Barrier Integrity. Gastroenterology 2021; 160:1240-1255.e3. [PMID: 33189700 PMCID: PMC7956241 DOI: 10.1053/j.gastro.2020.11.008] [Citation(s) in RCA: 50] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/09/2019] [Revised: 11/02/2020] [Accepted: 11/03/2020] [Indexed: 02/08/2023]
Abstract
BACKGROUND & AIMS The down-regulated in adenoma (DRA) protein, encoded by SLC26A3, a key intestinal chloride anion exchanger, has recently been identified as a novel susceptibility gene for inflammatory bowel disease (IBD). However, the mechanisms underlying the increased susceptibility to inflammation induced by the loss of DRA remain elusive. Compromised barrier is a key event in IBD pathogenesis. The current studies were undertaken to elucidate the impact of DRA deficiency on epithelial barrier integrity and to define underlying mechanisms. METHODS Wild-type and DRA-knockout (KO) mice and crypt-derived colonoids were used as models for intestinal epithelial response. Paracellular permeability was measured by using fluorescein isothiocyanate-dextran flux. Immunoblotting, immunofluorescence, immunohistochemistry, and ribonucleoprotein immunoprecipitation assays were performed. Gut microbiome analysis was conducted to investigate the impact of DRA deficiency on gut microbial communities. RESULTS DRA-KO mice exhibited an increased colonic paracellular permeability with significantly decreased levels of tight junction/adherens junction proteins, including ZO-1, occludin, and E-cadherin. A similar expression pattern of occludin and E-cadherin was observed in colonoids derived from DRA-KO mice and short hairpin RNA-mediated DRA knockdown in Caco-2 cells. Microbial analysis showed gut dysbiosis in DRA-KO mice. However, cohousing studies showed that dysbiosis played only a partial role in maintaining tight junction protein expression. Furthermore, our results showed increased binding of RNA-binding protein CUGBP1 with occludin and E-cadherin genes in DRA-KO mouse colon, suggesting that posttranscriptional mechanisms play a key role in gut barrier dysfunction. CONCLUSIONS To our knowledge, our studies demonstrate a novel role of DRA in maintaining the intestinal epithelial barrier function and potential implications of its dysregulation in IBD pathogenesis.
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Affiliation(s)
- Anoop Kumar
- Jesse Brown Veterans Affairs Medical Center, Chicago, Illinois; Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
| | - Shubha Priyamvada
- Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
| | - Yong Ge
- Department of Infectious Diseases and Immunology and Division of Gastroenterology, Hepatology and Nutrition, Department of Medicine, University of Florida, Gainesville, Florida
| | - Dulari Jayawardena
- Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
| | - Megha Singhal
- Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
| | - Arivarasu N Anbazhagan
- Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
| | - Ishita Chatterjee
- Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
| | - Aneal Dayal
- Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
| | - Mitul Patel
- Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
| | - Kimia Zadeh
- Department of Infectious Diseases and Immunology and Division of Gastroenterology, Hepatology and Nutrition, Department of Medicine, University of Florida, Gainesville, Florida
| | - Seema Saksena
- Jesse Brown Veterans Affairs Medical Center, Chicago, Illinois; Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
| | - Waddah A Alrefai
- Jesse Brown Veterans Affairs Medical Center, Chicago, Illinois; Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
| | - Ravinder K Gill
- Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
| | - Mojgan Zadeh
- Department of Infectious Diseases and Immunology and Division of Gastroenterology, Hepatology and Nutrition, Department of Medicine, University of Florida, Gainesville, Florida
| | - Ni Zhao
- Department of Infectious Diseases and Immunology and Division of Gastroenterology, Hepatology and Nutrition, Department of Medicine, University of Florida, Gainesville, Florida
| | - Mansour Mohamadzadeh
- Department of Infectious Diseases and Immunology and Division of Gastroenterology, Hepatology and Nutrition, Department of Medicine, University of Florida, Gainesville, Florida
| | - Pradeep K Dudeja
- Jesse Brown Veterans Affairs Medical Center, Chicago, Illinois; Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois.
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4
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Munemasa T, Mukaibo T, Melvin JE. Slc26a6 is an apical membrane anion exchanger that drives HCO 3--dependent fluid secretion in murine pancreatic acinar cells. Am J Physiol Cell Physiol 2019; 317:C1153-C1160. [PMID: 31532720 PMCID: PMC6957380 DOI: 10.1152/ajpcell.00257.2019] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2019] [Revised: 09/10/2019] [Accepted: 09/10/2019] [Indexed: 11/22/2022]
Abstract
The nonselective anion exchanger Slc26a6, also known as putative anion transporter 1 and chloride/formate exchanger, is thought to play a major role in HCO 3 - transport in exocrine glands. In this study, Slc26a6 null mice were used to explore the function of Slc26a6 in the exocrine pancreas. Slc26a6 primarily localized to the apical membrane of pancreatic exocrine acinar cells. The volume of stimulated juice secretion by the ex vivo pancreas was significantly reduced ~35% in Slc26a6-/- mice, but no changes occurred in the gross structure or gland weights of Slc26a6 null mice. The secretion of pancreatic juice by Slc26a6+/+ mice was dependent on HCO 3 - while, in contrast, fluid secretion by Slc26a6-/- mice was independent of HCO 3 - , suggesting that Slc26a6 mediates the HCO 3 - -dependent component of fluid secretion. Consistent with these observations, disruption of Slc26a6 also significantly reduced HCO 3 - secretion by the pancreas ~35%. Taken together, these results demonstrate that the apical Slc26a6 anion exchanger in acinar cells is involved in HCO 3 - -dependent fluid secretion but that another major HCO 3 - -independent pathway is the primary driver of the fluid secretion process in the mouse pancreas.
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Affiliation(s)
- Takashi Munemasa
- Secretory Mechanisms and Dysfunctions Section, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland
- Division of Oral Reconstruction and Rehabilitation, Kyushu Dental University, Kitakyushu, Japan
| | - Taro Mukaibo
- Secretory Mechanisms and Dysfunctions Section, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland
- Division of Oral Reconstruction and Rehabilitation, Kyushu Dental University, Kitakyushu, Japan
| | - James E Melvin
- Secretory Mechanisms and Dysfunctions Section, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland
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5
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Petralla S, Peña-Altamira LE, Poeta E, Massenzio F, Virgili M, Barile SN, Sbano L, Profilo E, Corricelli M, Danese A, Giorgi C, Ostan R, Capri M, Pinton P, Palmieri F, Lasorsa FM, Monti B. Deficiency of Mitochondrial Aspartate-Glutamate Carrier 1 Leads to Oligodendrocyte Precursor Cell Proliferation Defects Both In Vitro and In Vivo. Int J Mol Sci 2019; 20:ijms20184486. [PMID: 31514314 PMCID: PMC6769484 DOI: 10.3390/ijms20184486] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2019] [Revised: 09/04/2019] [Accepted: 09/06/2019] [Indexed: 11/16/2022] Open
Abstract
Aspartate-Glutamate Carrier 1 (AGC1) deficiency is a rare neurological disease caused by mutations in the solute carrier family 25, member 12 (SLC25A12) gene, encoding for the mitochondrial aspartate-glutamate carrier isoform 1 (AGC1), a component of the malate-aspartate NADH shuttle (MAS), expressed in excitable tissues only. AGC1 deficiency patients are children showing severe hypotonia, arrested psychomotor development, seizures and global hypomyelination. While the effect of AGC1 deficiency in neurons and neuronal function has been deeply studied, little is known about oligodendrocytes and their precursors, the brain cells involved in myelination. Here we studied the effect of AGC1 down-regulation on oligodendrocyte precursor cells (OPCs), using both in vitro and in vivo mouse disease models. In the cell model, we showed that a reduced expression of AGC1 induces a deficit of OPC proliferation leading to their spontaneous and precocious differentiation into oligodendrocytes. Interestingly, this effect seems to be related to a dysregulation in the expression of trophic factors and receptors involved in OPC proliferation/differentiation, such as Platelet-Derived Growth Factor α (PDGFα) and Transforming Growth Factor βs (TGFβs). We also confirmed the OPC reduction in vivo in AGC1-deficent mice, as well as a proliferation deficit in neurospheres from the Subventricular Zone (SVZ) of these animals, thus indicating that AGC1 reduction could affect the proliferation of different brain precursor cells. These data clearly show that AGC1 impairment alters myelination not only by acting on N-acetyl-aspartate production in neurons but also on OPC proliferation and suggest new potential therapeutic targets for the treatment of AGC1 deficiency.
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Affiliation(s)
- Sabrina Petralla
- Department of Pharmacy and BioTechnology, University of Bologna, 40126 Bologna, Italy; (S.P.); (L.E.P.-A.); (E.P.); (F.M.); (M.V.)
| | - Luis Emiliano Peña-Altamira
- Department of Pharmacy and BioTechnology, University of Bologna, 40126 Bologna, Italy; (S.P.); (L.E.P.-A.); (E.P.); (F.M.); (M.V.)
| | - Eleonora Poeta
- Department of Pharmacy and BioTechnology, University of Bologna, 40126 Bologna, Italy; (S.P.); (L.E.P.-A.); (E.P.); (F.M.); (M.V.)
| | - Francesca Massenzio
- Department of Pharmacy and BioTechnology, University of Bologna, 40126 Bologna, Italy; (S.P.); (L.E.P.-A.); (E.P.); (F.M.); (M.V.)
| | - Marco Virgili
- Department of Pharmacy and BioTechnology, University of Bologna, 40126 Bologna, Italy; (S.P.); (L.E.P.-A.); (E.P.); (F.M.); (M.V.)
| | - Simona Nicole Barile
- Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari, 70121 Bari, Italy (E.P.); (F.P.)
| | - Luigi Sbano
- Department of Morphology, Surgery and Experimental Medicine, Section of Pathology, Oncology and Experimental Biology, Laboratory for Technologies of Advanced Therapies (LTTA), University of Ferrara, 44121 Ferrara, Italy; (L.S.); (M.C.); (A.D.); (C.G.); (P.P.)
| | - Emanuela Profilo
- Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari, 70121 Bari, Italy (E.P.); (F.P.)
| | - Mariangela Corricelli
- Department of Morphology, Surgery and Experimental Medicine, Section of Pathology, Oncology and Experimental Biology, Laboratory for Technologies of Advanced Therapies (LTTA), University of Ferrara, 44121 Ferrara, Italy; (L.S.); (M.C.); (A.D.); (C.G.); (P.P.)
| | - Alberto Danese
- Department of Morphology, Surgery and Experimental Medicine, Section of Pathology, Oncology and Experimental Biology, Laboratory for Technologies of Advanced Therapies (LTTA), University of Ferrara, 44121 Ferrara, Italy; (L.S.); (M.C.); (A.D.); (C.G.); (P.P.)
| | - Carlotta Giorgi
- Department of Morphology, Surgery and Experimental Medicine, Section of Pathology, Oncology and Experimental Biology, Laboratory for Technologies of Advanced Therapies (LTTA), University of Ferrara, 44121 Ferrara, Italy; (L.S.); (M.C.); (A.D.); (C.G.); (P.P.)
| | - Rita Ostan
- Department of Experimental, Diagnostic and Specialty Medicine (DIMES, Dipartimento di Medicina Specialistica Diagnostica e Sperimentale) and C.I.G. Interdepartmental Centre “L. Galvani”, University of Bologna, 40126 Bologna, Italy; (R.O.); (M.C.)
| | - Miriam Capri
- Department of Experimental, Diagnostic and Specialty Medicine (DIMES, Dipartimento di Medicina Specialistica Diagnostica e Sperimentale) and C.I.G. Interdepartmental Centre “L. Galvani”, University of Bologna, 40126 Bologna, Italy; (R.O.); (M.C.)
| | - Paolo Pinton
- Department of Morphology, Surgery and Experimental Medicine, Section of Pathology, Oncology and Experimental Biology, Laboratory for Technologies of Advanced Therapies (LTTA), University of Ferrara, 44121 Ferrara, Italy; (L.S.); (M.C.); (A.D.); (C.G.); (P.P.)
- Maria Cecilia Hospital, GVM Care & Research, Cotignola, 48010 Ravenna, Italy
| | - Ferdinando Palmieri
- Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari, 70121 Bari, Italy (E.P.); (F.P.)
- Institute of Biomembranes, Bioenergetics and Molecular Biotechnologies IBIOM, CNR, 70126 Bari, Italy
| | - Francesco Massimo Lasorsa
- Institute of Biomembranes, Bioenergetics and Molecular Biotechnologies IBIOM, CNR, 70126 Bari, Italy
- Correspondence: (F.M.L.); (B.M.); Tel.: +39-080-544-2772 (F.M.L.); +39-051-209-4134 (B.M.)
| | - Barbara Monti
- Department of Pharmacy and BioTechnology, University of Bologna, 40126 Bologna, Italy; (S.P.); (L.E.P.-A.); (E.P.); (F.M.); (M.V.)
- Correspondence: (F.M.L.); (B.M.); Tel.: +39-080-544-2772 (F.M.L.); +39-051-209-4134 (B.M.)
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Tochigi Y, Takamatsu Y, Nakane J, Nakai R, Katayama K, Suzuki H. Loss of Wwox Causes Defective Development of Cerebral Cortex with Hypomyelination in a Rat Model of Lethal Dwarfism with Epilepsy. Int J Mol Sci 2019; 20:ijms20143596. [PMID: 31340538 PMCID: PMC6678113 DOI: 10.3390/ijms20143596] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2019] [Revised: 07/20/2019] [Accepted: 07/22/2019] [Indexed: 12/20/2022] Open
Abstract
WW domain-containing oxidoreductase (Wwox) is a putative tumor suppressor. Several germline mutations of Wwox have been associated with infant neurological disorders characterized by epilepsy, growth retardation, and early death. Less is known, however, about the pathological link between Wwox mutations and these disorders or the physiological role of Wwox in brain development. In this study, we examined age-related expression and histological localization of Wwox in forebrains as well as the effects of loss of function mutations in the Wwox gene in the immature cortex of a rat model of lethal dwarfism with epilepsy (lde/lde). Immunostaining revealed that Wwox is expressed in neurons, astrocytes, and oligodendrocytes. lde/lde cortices were characterized by a reduction in neurite growth without a reduced number of neurons, severe reduction in myelination with a reduced number of mature oligodendrocytes, and a reduction in cell populations of astrocytes and microglia. These results indicate that Wwox is essential for normal development of neurons and glial cells in the cerebral cortex.
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Affiliation(s)
- Yuki Tochigi
- Laboratory of Veterinary Physiology, School of Veterinary Medicine, Faculty of Veterinary Science, Nippon Veterinary and Life Science University, Musashino-shi, Tokyo 180-8602, Japan
| | - Yutaka Takamatsu
- Laboratory of Veterinary Physiology, School of Veterinary Medicine, Faculty of Veterinary Science, Nippon Veterinary and Life Science University, Musashino-shi, Tokyo 180-8602, Japan
| | - Jun Nakane
- Laboratory of Veterinary Physiology, School of Veterinary Medicine, Faculty of Veterinary Science, Nippon Veterinary and Life Science University, Musashino-shi, Tokyo 180-8602, Japan
| | - Rika Nakai
- Laboratory of Veterinary Physiology, School of Veterinary Medicine, Faculty of Veterinary Science, Nippon Veterinary and Life Science University, Musashino-shi, Tokyo 180-8602, Japan
| | - Kentaro Katayama
- Laboratory of Veterinary Physiology, School of Veterinary Medicine, Faculty of Veterinary Science, Nippon Veterinary and Life Science University, Musashino-shi, Tokyo 180-8602, Japan
| | - Hiroetsu Suzuki
- Laboratory of Veterinary Physiology, School of Veterinary Medicine, Faculty of Veterinary Science, Nippon Veterinary and Life Science University, Musashino-shi, Tokyo 180-8602, Japan.
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7
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Snyder NA, Palmer MV, Reinhardt TA, Cunningham KW. Milk biosynthesis requires the Golgi cation exchanger TMEM165. J Biol Chem 2019; 294:3181-3191. [PMID: 30622138 PMCID: PMC6398142 DOI: 10.1074/jbc.ra118.006270] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2018] [Revised: 01/02/2019] [Indexed: 11/06/2022] Open
Abstract
Milk is a hallmark of mammals that is critical for normal growth and development of offspring. During biosynthesis of lactose in the Golgi complex, H+ is produced as a by-product, and there is no known mechanism for maintaining luminal pH within the physiological range. Here, using conditional, tissue-specific knockout mice, immunostaining, and biochemical assays, we test whether the putative H+/Ca2+/Mn2+ exchanger known as TMEM165 (transmembrane protein 165) participates in normal milk production. We find TMEM165 is crucial in the lactating mammary gland for normal biosynthesis of lactose and for normal growth rates of nursing pups. The milk of TMEM165-deficient mice contained elevated concentrations of fat, protein, iron, and zinc, which are likely caused by decreased osmosis-mediated dilution of the milk caused by the decreased biosynthesis of lactose. When normalized to total protein levels, only calcium and manganese levels were significantly lower in the milk from TMEM165-deficient dams than control dams. These findings suggest that TMEM165 supplies Ca2+ and Mn2+ to the Golgi complex in exchange for H+ to sustain the functions of lactose synthase and potentially other glycosyl-transferases. Our findings highlight the importance of cation and pH homeostasis in the Golgi complex of professional secretory cells and the critical role of TMEM165 in this process.
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Affiliation(s)
- Nathan A Snyder
- From the Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218 and
| | - Mitchell V Palmer
- the Bacterial Diseases of Livestock, Research Unit, United States Department of Agriculture/Agricultural Research Services, National Animal Disease Center, Ames, Iowa 50010
| | | | - Kyle W Cunningham
- From the Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218 and
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Raggi F, Pissavino AL, Resaz R, Segalerba D, Puglisi A, Vanni C, Antonini F, Del Zotto G, Gamberucci A, Marcolongo P, Bosco MC, Grillo F, Mastracci L, Eva A. Development and characterization of an inducible mouse model for glycogen storage disease type Ib. J Inherit Metab Dis 2018; 41:1015-1025. [PMID: 29967951 DOI: 10.1007/s10545-018-0211-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/30/2018] [Revised: 05/23/2018] [Accepted: 05/30/2018] [Indexed: 12/31/2022]
Abstract
BACKGROUND AND AIMS Glycogen storage disease type Ib (GSD1b) is a rare metabolic and immune disorder caused by a deficiency in the glucose-6-phosphate transporter (G6PT) and characterized by impaired glucose homeostasis, myeloid dysfunction, and long-term risk of hepatocellular adenomas. Despite maximal therapy, based on a strict diet and on granulocyte colony-stimulating factor treatment, long-term severe complications still develop. Understanding the pathophysiology of GSD1b is a prerequisite to develop new therapeutic strategies and depends on the availability of animal models. The G6PT-KO mouse mimics the human disease but is very fragile and rarely survives weaning. We generated a conditional G6PT-deficient mouse as an alternative model for studying the long-term pathophysiology of the disease. We utilized this conditional mouse to develop an inducible G6PT-KO model to allow temporally regulated G6PT deletion by the administration of tamoxifen (TM). METHODS We generated a conditional G6PT-deficient mouse utilizing the CRElox strategy. Histology, histochemistry, and phenotype analyses were performed at different times after TM-induced G6PT inactivation. Neutrophils and monocytes were isolated and analyzed for functional activity with standard techniques. RESULTS The G6PT-inducible KO mice display the expected disturbances of G6P metabolism and myeloid dysfunctions of the human disorder, even though with a milder intensity. CONCLUSIONS TM-induced inactivation of G6PT in these mice leads to a phenotype which mimics that of human GSD1b patients. The conditional mice we have generated represent an excellent tool to study the tissue-specific role of the G6PT gene and the mechanism of long-term complications in GSD1b.
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Affiliation(s)
- Federica Raggi
- Laboratory of Molecular Biology, Department of Translational Research, Laboratory Medicine, Diagnosis and Services, Istituto Giannina Gaslini, Largo Gaslini 5, 16147, Genoa, Italy
| | - Anna Livia Pissavino
- Laboratory of Molecular Biology, Department of Translational Research, Laboratory Medicine, Diagnosis and Services, Istituto Giannina Gaslini, Largo Gaslini 5, 16147, Genoa, Italy
| | - Roberta Resaz
- Laboratory of Molecular Biology, Department of Translational Research, Laboratory Medicine, Diagnosis and Services, Istituto Giannina Gaslini, Largo Gaslini 5, 16147, Genoa, Italy
| | - Daniela Segalerba
- Laboratory of Molecular Biology, Department of Translational Research, Laboratory Medicine, Diagnosis and Services, Istituto Giannina Gaslini, Largo Gaslini 5, 16147, Genoa, Italy
| | - Andrea Puglisi
- Laboratory of Molecular Biology, Department of Translational Research, Laboratory Medicine, Diagnosis and Services, Istituto Giannina Gaslini, Largo Gaslini 5, 16147, Genoa, Italy
| | - Cristina Vanni
- Laboratory of Molecular Biology, Department of Translational Research, Laboratory Medicine, Diagnosis and Services, Istituto Giannina Gaslini, Largo Gaslini 5, 16147, Genoa, Italy
| | - Francesca Antonini
- Core Facilities Laboratory, Department of Translational Research, Laboratory Medicine, Diagnosis and Services, Istituto Giannina Gaslini, Genoa, Italy
| | - Genny Del Zotto
- Core Facilities Laboratory, Department of Translational Research, Laboratory Medicine, Diagnosis and Services, Istituto Giannina Gaslini, Genoa, Italy
| | - Alessandra Gamberucci
- Department of Molecular and Developmental Medicine, University of Siena, Siena, Italy
| | - Paola Marcolongo
- Department of Molecular and Developmental Medicine, University of Siena, Siena, Italy
| | - Maria Carla Bosco
- Laboratory of Molecular Biology, Department of Translational Research, Laboratory Medicine, Diagnosis and Services, Istituto Giannina Gaslini, Largo Gaslini 5, 16147, Genoa, Italy
| | - Federica Grillo
- Pathology Unit, Department of Surgical Sciences and Integrated Diagnostics, University of Genova, Genoa, Italy
- IRCCS AOU San Martino IST Genova, Genoa, Italy
| | - Luca Mastracci
- Pathology Unit, Department of Surgical Sciences and Integrated Diagnostics, University of Genova, Genoa, Italy
- IRCCS AOU San Martino IST Genova, Genoa, Italy
| | - Alessandra Eva
- Laboratory of Molecular Biology, Department of Translational Research, Laboratory Medicine, Diagnosis and Services, Istituto Giannina Gaslini, Largo Gaslini 5, 16147, Genoa, Italy.
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Rodan LH, Qi W, Ducker GS, Demirbas D, Laine R, Yang E, Walker MA, Eichler F, Rabinowitz JD, Anselm I, Berry GT. 5,10-methenyltetrahydrofolate synthetase deficiency causes a neurometabolic disorder associated with microcephaly, epilepsy, and cerebral hypomyelination. Mol Genet Metab 2018; 125:118-126. [PMID: 30031689 PMCID: PMC6557438 DOI: 10.1016/j.ymgme.2018.06.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/20/2018] [Revised: 06/12/2018] [Accepted: 06/12/2018] [Indexed: 10/28/2022]
Abstract
Folate metabolism in the brain is critically important and serves a number of vital roles in nucleotide synthesis, single carbon metabolism/methylation, amino acid metabolism, and mitochondrial translation. Genetic defects in almost every enzyme of folate metabolism have been reported to date, and most have neurological sequelae. We report 2 patients presenting with a neurometabolic disorder associated with biallelic variants in the MTHFS gene, encoding 5,10-methenyltetrahydrofolate synthetase. Both patients presented with microcephaly, short stature, severe global developmental delay, progressive spasticity, epilepsy, and cerebral hypomyelination. Baseline CSF 5-methyltetrahydrolate (5-MTHF) levels were in the low-normal range. The first patient was treated with folinic acid, which resulted in worsening cerebral folate deficiency. Treatment in this patient with a combination of oral L-5-methyltetrahydrofolate and intramuscular methylcobalamin was able to increase CSF 5-MTHF levels, was well tolerated over a 4 month period, and resulted in subjective mild improvements in functioning. Measurement of MTHFS enzyme activity in fibroblasts confirmed reduced activity. The direct substrate of the MTHFS reaction, 5-formyl-THF, was elevated 30-fold in patient fibroblasts compared to control, supporting the hypothesis that the pathophysiology of this disorder is a manifestation of toxicity from this metabolite.
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Affiliation(s)
- Lance H Rodan
- Division of Genetics and Genomics, The Manton Center for Orphan Disease Research, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA; Department of Neurology, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA.
| | - Wanshu Qi
- Division of Genetics and Genomics, The Manton Center for Orphan Disease Research, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - Gregory S Ducker
- Lewis-Sigler Institute for Integrative Genomics, Department of Chemistry, Princeton University, Princeton, NJ, USA
| | - Didem Demirbas
- Division of Genetics and Genomics, The Manton Center for Orphan Disease Research, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - Regina Laine
- Department of Neurology, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - Edward Yang
- Department of Radiology, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - Melissa A Walker
- Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA
| | - Florian Eichler
- Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA
| | - Joshua D Rabinowitz
- Lewis-Sigler Institute for Integrative Genomics, Department of Chemistry, Princeton University, Princeton, NJ, USA
| | - Irina Anselm
- Department of Neurology, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - Gerard T Berry
- Division of Genetics and Genomics, The Manton Center for Orphan Disease Research, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA.
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10
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Nakayama T, Al-Maawali A, El-Quessny M, Rajab A, Khalil S, Stoler JM, Tan WH, Nasir R, Schmitz-Abe K, Hill RS, Partlow JN, Al-Saffar M, Servattalab S, LaCoursiere CM, Tambunan DE, Coulter ME, Elhosary PC, Gorski G, Barkovich AJ, Markianos K, Poduri A, Mochida GH. Mutations in PYCR2, Encoding Pyrroline-5-Carboxylate Reductase 2, Cause Microcephaly and Hypomyelination. Am J Hum Genet 2015; 96:709-19. [PMID: 25865492 PMCID: PMC4570282 DOI: 10.1016/j.ajhg.2015.03.003] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2014] [Accepted: 03/05/2015] [Indexed: 12/27/2022] Open
Abstract
Despite recent advances in understanding the genetic bases of microcephaly, a large number of cases of microcephaly remain unexplained, suggesting that many microcephaly syndromes and associated genes have yet to be identified. Here, we report mutations in PYCR2, which encodes an enzyme in the proline biosynthesis pathway, as the cause of a unique syndrome characterized by postnatal microcephaly, hypomyelination, and reduced cerebral white-matter volume. Linkage mapping and whole-exome sequencing identified homozygous mutations (c.355C>T [p.Arg119Cys] and c.751C>T [p.Arg251Cys]) in PYCR2 in the affected individuals of two consanguineous families. A lymphoblastoid cell line from one affected individual showed a strong reduction in the amount of PYCR2. When mutant cDNAs were transfected into HEK293FT cells, both variant proteins retained normal mitochondrial localization but had lower amounts than the wild-type protein, suggesting that the variant proteins were less stable. A PYCR2-deficient HEK293FT cell line generated by genome editing with the clustered regularly interspaced short palindromic repeat (CRISPR)-Cas9 system showed that PYCR2 loss of function led to decreased mitochondrial membrane potential and increased susceptibility to apoptosis under oxidative stress. Morpholino-based knockdown of a zebrafish PYCR2 ortholog, pycr1b, recapitulated the human microcephaly phenotype, which was rescued by wild-type human PYCR2 mRNA, but not by mutant mRNAs, further supporting the pathogenicity of the identified variants. Hypomyelination and the absence of lax, wrinkly skin distinguishes this condition from that caused by previously reported mutations in the gene encoding PYCR2's isozyme, PYCR1, suggesting a unique and indispensable role for PYCR2 in the human CNS during development.
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Affiliation(s)
- Tojo Nakayama
- Division of Genetics and Genomics, Department of Medicine, Boston Children's Hospital, Boston, MA 02115, USA; Manton Center for Orphan Disease Research, Boston Children's Hospital, Boston, MA 02115, USA; Department of Pediatrics, Harvard Medical School, Boston, MA 02115, USA
| | - Almundher Al-Maawali
- Division of Genetics and Genomics, Department of Medicine, Boston Children's Hospital, Boston, MA 02115, USA; Manton Center for Orphan Disease Research, Boston Children's Hospital, Boston, MA 02115, USA; Department of Genetics, College of Medicine and Health Science, Sultan Qaboos University, Muscat 123, Oman
| | - Malak El-Quessny
- Division of Genetics and Genomics, Department of Medicine, Boston Children's Hospital, Boston, MA 02115, USA; Manton Center for Orphan Disease Research, Boston Children's Hospital, Boston, MA 02115, USA
| | - Anna Rajab
- National Genetics Center, Directorate General of Health Affairs, Ministry of Health, Muscat 113, Oman
| | - Samir Khalil
- Department of Pediatrics, Al-Makassed Islamic Charitable Society Hospital, Jerusalem 91220; Faculty of Medicine, Al-Quds University, Jerusalem 90612
| | - Joan M Stoler
- Division of Genetics and Genomics, Department of Medicine, Boston Children's Hospital, Boston, MA 02115, USA; Department of Pediatrics, Harvard Medical School, Boston, MA 02115, USA
| | - Wen-Hann Tan
- Division of Genetics and Genomics, Department of Medicine, Boston Children's Hospital, Boston, MA 02115, USA; Department of Pediatrics, Harvard Medical School, Boston, MA 02115, USA
| | - Ramzi Nasir
- Department of Pediatrics, Harvard Medical School, Boston, MA 02115, USA; Division of Developmental Medicine, Department of Medicine, Boston Children's Hospital, Boston, MA 02115, USA
| | - Klaus Schmitz-Abe
- Division of Genetics and Genomics, Department of Medicine, Boston Children's Hospital, Boston, MA 02115, USA; Manton Center for Orphan Disease Research, Boston Children's Hospital, Boston, MA 02115, USA; Department of Pediatrics, Harvard Medical School, Boston, MA 02115, USA; Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA
| | - R Sean Hill
- Division of Genetics and Genomics, Department of Medicine, Boston Children's Hospital, Boston, MA 02115, USA; Manton Center for Orphan Disease Research, Boston Children's Hospital, Boston, MA 02115, USA; Howard Hughes Medical Institute, Boston Children's Hospital, Boston, MA 02115, USA
| | - Jennifer N Partlow
- Division of Genetics and Genomics, Department of Medicine, Boston Children's Hospital, Boston, MA 02115, USA; Manton Center for Orphan Disease Research, Boston Children's Hospital, Boston, MA 02115, USA; Howard Hughes Medical Institute, Boston Children's Hospital, Boston, MA 02115, USA
| | - Muna Al-Saffar
- Division of Genetics and Genomics, Department of Medicine, Boston Children's Hospital, Boston, MA 02115, USA; Manton Center for Orphan Disease Research, Boston Children's Hospital, Boston, MA 02115, USA; Howard Hughes Medical Institute, Boston Children's Hospital, Boston, MA 02115, USA; Department of Paediatrics, College of Medicine and Health Sciences, United Arab Emirates University, PO Box 17666, Al-Ain, United Arab Emirates
| | - Sarah Servattalab
- Division of Genetics and Genomics, Department of Medicine, Boston Children's Hospital, Boston, MA 02115, USA; Manton Center for Orphan Disease Research, Boston Children's Hospital, Boston, MA 02115, USA; Howard Hughes Medical Institute, Boston Children's Hospital, Boston, MA 02115, USA
| | | | - Dimira E Tambunan
- Department of Neurology, Boston Children's Hospital, Boston, MA 02115, USA
| | - Michael E Coulter
- Division of Genetics and Genomics, Department of Medicine, Boston Children's Hospital, Boston, MA 02115, USA; Manton Center for Orphan Disease Research, Boston Children's Hospital, Boston, MA 02115, USA; Howard Hughes Medical Institute, Boston Children's Hospital, Boston, MA 02115, USA; Harvard-MIT Division of Health Sciences and Technology, Cambridge, MA 02139, USA
| | - Princess C Elhosary
- Division of Genetics and Genomics, Department of Medicine, Boston Children's Hospital, Boston, MA 02115, USA; Manton Center for Orphan Disease Research, Boston Children's Hospital, Boston, MA 02115, USA; Howard Hughes Medical Institute, Boston Children's Hospital, Boston, MA 02115, USA; Department of Neurology, Boston Children's Hospital, Boston, MA 02115, USA
| | - Grzegorz Gorski
- Cellular Neuroscience Core, F.M. Kirby Neurobiology Center, Boston Children's Hospital, Boston, MA 02115, USA
| | - A James Barkovich
- Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA 94143, USA
| | - Kyriacos Markianos
- Division of Genetics and Genomics, Department of Medicine, Boston Children's Hospital, Boston, MA 02115, USA; Manton Center for Orphan Disease Research, Boston Children's Hospital, Boston, MA 02115, USA; Department of Pediatrics, Harvard Medical School, Boston, MA 02115, USA; Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA
| | - Annapurna Poduri
- Department of Neurology, Boston Children's Hospital, Boston, MA 02115, USA; Epilepsy Genetics Program, Boston Children's Hospital, Boston, MA 02115, USA; Department of Neurology, Harvard Medical School, Boston, MA 02115, USA
| | - Ganeshwaran H Mochida
- Division of Genetics and Genomics, Department of Medicine, Boston Children's Hospital, Boston, MA 02115, USA; Manton Center for Orphan Disease Research, Boston Children's Hospital, Boston, MA 02115, USA; Department of Pediatrics, Harvard Medical School, Boston, MA 02115, USA; Pediatric Neurology Unit, Department of Neurology, Massachusetts General Hospital, Boston, MA 02114, USA.
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Abstract
The SLC37 family consists of four sugar-phosphate exchangers, A1, A2, A3, and A4, which are anchored in the endoplasmic reticulum (ER) membrane. The best characterized family member is SLC37A4, better known as the glucose-6-phosphate (G6P) transporter (G6PT). SLC37A1, SLC37A2, and G6PT function as phosphate (Pi)-linked G6P antiporters catalyzing G6P:Pi and Pi:Pi exchanges. The activity of SLC37A3 is unknown. G6PT translocates G6P from the cytoplasm into the lumen of the ER where it couples with either glucose-6-phosphatase-α (G6Pase-α) or G6Pase-β to hydrolyze intraluminal G6P to glucose and Pi. The functional coupling of G6PT with G6Pase-α maintains interprandial glucose homeostasis and the functional coupling of G6PT with G6Pase-β maintains neutrophil energy homeostasis and functionality. A deficiency in G6PT causes glycogen storage disease type Ib, an autosomal recessive disorder characterized by impaired glucose homeostasis, neutropenia, and neutrophil dysfunction. Neither SLC37A1 nor SLC37A2 can functionally couple with G6Pase-α or G6Pase-β, and there are no known disease associations for them or SLC37A3. Since only G6PT matches the characteristics of the physiological ER G6P transporter involved in blood glucose homeostasis and neutrophil energy metabolism, the biological roles for the other SLC37 proteins remain to be determined.
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Affiliation(s)
- Janice Y Chou
- Section on Cellular Differentiation, Program on Developmental Endocrinology and Genetics, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
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12
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Wongkittichote P, Tungpradabkul S, Wattanasirichaigoon D, Jensen LT. Prediction of the functional effect of novel SLC25A13 variants using a S. cerevisiae model of AGC2 deficiency. J Inherit Metab Dis 2013; 36:821-30. [PMID: 23053473 DOI: 10.1007/s10545-012-9543-5] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/20/2012] [Revised: 09/05/2012] [Accepted: 09/12/2012] [Indexed: 01/31/2023]
Abstract
AGC2, a member of the mitochondrial carrier protein family, is as an aspartate-glutamate carrier and is important for urea synthesis and the maintenance of the malate-aspartate shuttle. Mutations in SLC25A13, the gene encoding AGC2, result in two age dependent disorders: neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) and type II citrullinemia (CTLN2). The clinical features of CTLN2 are very similar to those of other urea cycle disorders making a clear diagnosis difficult. Analysis of the SLC25A13 gene sequence can provide a definitive diagnosis, however the predictive value of DNA sequencing requires that the disease association of variants be characterized. We utilized the yeast Saccharomyces cerevisiae lacking AGC1 as a model system to study the effect on the function of AGC2 variants and confirmed that this system is capable of distinguishing between AGC2 variants with normal (p.Pro632Leu) or impaired function (p.Gly437Glu, p.Gly531Asp, p.Thr546Met, p.Leu598Arg and p.Glu601Lys). Three novel AGC2 genetic variants, p.Met1? (c.2T>C), p.Pro502Leu (c.1505C>T), and p.Arg605Gln (c.1814G>A) were investigated and our analysis revealed that p.Pro502Leu and p.Arg605Gln substitutions in the AGC2 protein were without effect and these variants were fully functional. The p.Met1? mutant is capable of expressing a truncated p.Met1_Phe34del AGC2 variant, however this protein is not functional due to disruptions in a calcium binding EF hand as well as incorrect intracellular localization. Our study demonstrates that the characterization of AGC2 expressed in yeast cells is a powerful technique to investigate AGC2 variants, and this analysis should aid in establishing the disease association of novel variants.
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Affiliation(s)
- Parith Wongkittichote
- Graduate Program in Molecular Medicine, Faculty of Science, Mahidol University, Bangkok, Thailand
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13
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Amlal H, Xu J, Barone S, Zahedi K, Soleimani M. The chloride channel/transporter Slc26a9 regulates the systemic arterial pressure and renal chloride excretion. J Mol Med (Berl) 2012; 91:561-72. [PMID: 23149824 DOI: 10.1007/s00109-012-0973-1] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2012] [Revised: 10/07/2012] [Accepted: 10/16/2012] [Indexed: 01/21/2023]
Abstract
Apical chloride secretory pathways in the kidney medullary collecting duct are thought to play an important role in the modulation of final urine composition and regulation of systemic vascular volume and/or blood pressure. However, the molecular identity of these molecules has largely remained unknown. Here, we demonstrate that Slc26a9, an electrogenic chloride channel/transporter, is localized on the apical membrane of principal cells in the kidney medullary collecting duct and mediates chloride secretion. Mice with the genetic deletion of Slc26a9 show significant reduction in renal chloride excretion when fed a diet high in salt or subjected to water deprivation. Arterial pressure measurements indicated that Slc26a9 knockout (Slc26a9(-/-)) mice are hypertensive under baseline conditions and increase their blood pressure further within 48 h of switching to a high-salt diet. These results suggest that Slc26a9 plays an important role in renal chloride/fluid excretion and arterial pressure regulation. We propose that impaired SLC26A9 activity in humans may interfere with the excretion of excess salt and result in hypertension.
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Affiliation(s)
- Hassane Amlal
- Research Services, Veterans Affairs Medical Center, Cincinnati, OH, USA
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14
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Visser G, de Jager W, Verhagen LP, Smit GPA, Wijburg FA, Prakken BJ, Coffer PJ, Buitenhuis M. Survival, but not maturation, is affected in neutrophil progenitors from GSD-1b patients. J Inherit Metab Dis 2012; 35:287-300. [PMID: 21863279 DOI: 10.1007/s10545-011-9379-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/11/2011] [Revised: 07/04/2011] [Accepted: 07/22/2011] [Indexed: 12/14/2022]
Abstract
Glycogen storage disease type 1b (GSD 1b) is caused by mutations in the Glucose-6-phosphate transporter and is characterized by impaired glucose homeostasis. In addition, GSD-1b is associated with chronic neutropenia resulting in recurrent infections and inflammatory bowel disease. It is unclear whether the neutropenia is solely due to enhanced apoptosis of mature neutrophils or whether aberrant neutrophil development may also contribute. Here we demonstrate that hematopoietic progenitors from GSD-1b patients are not impaired in their capacity to develop into mature neutrophils. However, optimal survival of neutrophil progenitors from GSD-1b patients requires high glucose levels (> 200 mg dl(-1)), suggesting that even under normoglycemic conditions these cells are more prone to apoptosis. Furthermore, analysis of cytokine levels in peripheral blood suggests an inflammatory state with an inverse correlation between the level of inflammation and the number of neutrophils. Finally, in some patients, with low numbers of peripheral blood neutrophils, high numbers of neutrophils were observed in the intestine. Together, these results suggest that the neutropenia observed in GSD-1b patients is not caused by impaired maturation, but may be caused by both increased levels of apoptosis and egress of neutrophils from the blood to the inflamed tissues.
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Affiliation(s)
- Gepke Visser
- Department of Metabolic Diseases, Wilhelmina Children's Hospital, University Medical Center Utrecht, Utrecht, The Netherlands
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Hofstetter W, Siegrist M, Simonin A, Bonny O, Fuster DG. Sodium/hydrogen exchanger NHA2 in osteoclasts: subcellular localization and role in vitro and in vivo. Bone 2010; 47:331-40. [PMID: 20441802 DOI: 10.1016/j.bone.2010.04.605] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/30/2010] [Revised: 04/26/2010] [Accepted: 04/26/2010] [Indexed: 11/29/2022]
Abstract
NHA2 was recently identified as a novel sodium/hydrogen exchanger which is strongly upregulated during RANKL-induced osteoclast differentiation. Previous in vitro studies suggested that NHA2 is a mitochondrial transporter required for osteoclast differentiation and bone resorption. Due to the lack of suitable antibodies, NHA2 was studied only on RNA level thus far. To define the protein's role in osteoclasts in vitro and in vivo, we generated NHA2-deficient mice and raised several specific NHA2 antibodies. By confocal microscopy and subcellular fractionation studies, NHA2 was found to co-localize with the late endosomal and lysosomal marker LAMP1 and the V-ATPase a3 subunit, but not with mitochondrial markers. Immunofluorescence studies and surface biotinylation experiments further revealed that NHA2 was highly enriched in the plasma membrane of osteoclasts, localizing to the basolateral membrane of polarized osteoclasts. Despite strong upregulation of NHA2 during RANKL-induced osteoclast differentiation, however, structural parameters of bone, quantified by high-resolution microcomputed tomography, were not different in NHA2-deficient mice compared to wild-type littermates. In addition, in vitro RANKL stimulation of bone marrow cells isolated from wild-type and NHA2-deficient mice yielded no differences in osteoclast development and activity. Taken together, we show that NHA2 is a RANKL-induced plasmalemmal sodium/hydrogen exchanger in osteoclasts. However, our data from NHA2-deficient mice suggest that NHA2 is dispensable for osteoclast differentiation and bone resorption both in vitro and in vivo.
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Affiliation(s)
- Willy Hofstetter
- Group for Bone Biology and Orthopaedic Research, Department of Clinical Research, University of Bern, Bern, Switzerland
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Wibom R, Lasorsa FM, Töhönen V, Barbaro M, Sterky FH, Kucinski T, Naess K, Jonsson M, Pierri CL, Palmieri F, Wedell A. AGC1 deficiency associated with global cerebral hypomyelination. N Engl J Med 2009; 361:489-95. [PMID: 19641205 DOI: 10.1056/nejmoa0900591] [Citation(s) in RCA: 123] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The mitochondrial aspartate-glutamate carrier isoform 1 (AGC1), specific to neurons and muscle, supplies aspartate to the cytosol and, as a component of the malate-aspartate shuttle, enables mitochondrial oxidation of cytosolic NADH, thought to be important in providing energy for neurons in the central nervous system. We describe AGC1 deficiency, a novel syndrome characterized by arrested psychomotor development, hypotonia, and seizures in a child with a homozygous missense mutation in the solute carrier family 25, member 12, gene SLC25A12, which encodes the AGC1 protein. Functional analysis of the mutant AGC1 protein showed abolished activity. The child had global hypomyelination in the cerebral hemispheres, suggesting that impaired efflux of aspartate from neuronal mitochondria prevents normal myelin formation.
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Affiliation(s)
- Rolf Wibom
- Center for Inherited Metabolic Diseases, Karolinska University Hospital, Stockholm, Sweden
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18
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Prasad V, Bodi I, Meyer JW, Wang Y, Ashraf M, Engle SJ, Doetschman T, Sisco K, Nieman ML, Miller ML, Lorenz JN, Shull GE. Impaired cardiac contractility in mice lacking both the AE3 Cl-/HCO3- exchanger and the NKCC1 Na+-K+-2Cl- cotransporter: effects on Ca2+ handling and protein phosphatases. J Biol Chem 2008; 283:31303-14. [PMID: 18779325 PMCID: PMC2581574 DOI: 10.1074/jbc.m803706200] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2008] [Revised: 08/27/2008] [Indexed: 12/27/2022] Open
Abstract
To analyze the cardiac functions of AE3, we disrupted its gene (Slc4a3) in mice. Cl(-)/HCO3(-) exchange coupled with Na+-dependent acid extrusion can mediate pH-neutral Na+ uptake, potentially affecting Ca2+ handling via effects on Na+/Ca2+ exchange. AE3 null mice appeared normal, however, and AE3 ablation had no effect on ischemia-reperfusion injury in isolated hearts or cardiac performance in vivo. The NKCC1 Na+-K+-2Cl(-) cotransporter also mediates Na+ uptake, and loss of NKCC1 alone does not impair contractility. To further stress the AE3-deficient myocardium, we combined the AE3 and NKCC1 knock-outs. Double knock-outs had impaired contraction and relaxation both in vivo and in isolated ventricular myocytes. Ca2+ transients revealed an apparent increase in Ca2+ clearance in double null cells. This was unlikely to result from increased Ca2+ sequestration, since the ratio of phosphorylated phospholamban to total phospholamban was sharply reduced in all three mutant hearts. Instead, Na+/Ca2+ exchanger activity was found to be enhanced in double null cells. Systolic Ca2+ was unaltered, however, suggesting more direct effects on the contractile apparatus of double null myocytes. Expression of the catalytic subunit of protein phosphatase 1 was increased in all mutant hearts. There was also a dramatic reversal, between single null and double null hearts, in the carboxymethylation and localization to the myofibrillar fraction, of the catalytic subunit of protein phosphatase 2A, which corresponded to the loss of normal contractility in double null hearts. These data show that AE3 and NKCC1 affect Ca2+ handling, PLN regulation, and expression and localization of major cardiac phosphatases and that their combined loss impairs cardiac function.
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Affiliation(s)
- Vikram Prasad
- Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0524, USA
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Singh AK, Sjöblom M, Zheng W, Krabbenhöft A, Riederer B, Rausch B, Manns MP, Soleimani M, Seidler U. CFTR and its key role in in vivo resting and luminal acid-induced duodenal HCO3- secretion. Acta Physiol (Oxf) 2008; 193:357-65. [PMID: 18363901 DOI: 10.1111/j.1748-1716.2008.01854.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
BACKGROUND AND AIMS We investigated the role of the recently discovered, villous-expressed anion exchanger Slc26a6 (PAT1) and the predominantly crypt-expressed cystic fibrosis transmembrane regulator (CFTR) in basal and acid-stimulated murine duodenal HCO(3)(-) secretion in vivo, and the influence of blood HCO(3)(-) concentration on both. METHODS The proximal duodenum of anaesthetized mice was perfused in situ, and HCO(3)(-) secretion was determined by back-titration. Duodenal mucosal permeability was assessed by determining (51)Cr-EDTA leakage from blood to lumen. RESULTS Compared with wild type (WT) littermates basal duodenal HCO(3)(-) secretory rates were slightly reduced in Slc26-deficient mice at low ( approximately 21 mm), and markedly reduced at high blood HCO(3)(-) concentration ( approximately 29 mm). In contrast, basal HCO(3)(-) secretion was markedly reduced in CFTR-deficient mice compared with WT littermates both at high and low blood HCO(3)(-) concentration. A short-term application of luminal acid increased duodenal HCO(3)(-) secretory rate in Slc26a6-deficient and WT mice to the same degree, but had no stimulatory effect in the absence of CFTR. Luminal acidification to pH 2.5 did not alter duodenal permeability. CONCLUSIONS The involvement of Slc26a6 in basal HCO(3)(-) secretion in murine duodenum in vivo is critically dependent on the systemic acid/base status, and this transporter is not involved in acid-stimulated HCO(3)(-) secretion. The presence of CFTR is essential for basal and acid-induced HCO(3)(-) secretion irrespective of acid/base status. This suggests a coupled action of Slc26a6 with CFTR for murine basal duodenal HCO(3)(-) secretion, but not acid-stimulated secretion, in vivo.
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Affiliation(s)
- A K Singh
- Department of Gastroenterology, Hepatology and Endocrinology, Hannover Medical School, Hannover, Germany
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20
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Salas JT, Banales JM, Sarvide S, Recalde S, Ferrer A, Uriarte I, Oude Elferink RPJ, Prieto J, Medina JF. Ae2a,b-deficient mice develop antimitochondrial antibodies and other features resembling primary biliary cirrhosis. Gastroenterology 2008; 134:1482-93. [PMID: 18471521 DOI: 10.1053/j.gastro.2008.02.020] [Citation(s) in RCA: 149] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/14/2007] [Accepted: 01/31/2008] [Indexed: 02/06/2023]
Abstract
BACKGROUND & AIMS Cl(-)/HCO(3)(-) anion exchanger 2 (AE2) is involved in intracellular pH (pH(i)) regulation and transepithelial acid-base transport, including secretin-stimulated biliary bicarbonate excretion. AE2 gene expression was found to be reduced in liver biopsy specimens and blood mononuclear cells from patients with primary biliary cirrhosis (PBC), a disease characterized by chronic nonsuppurative cholangitis associated with antimitochondrial antibodies (AMA) and other autoimmune phenomena. In mice with widespread Ae2 gene disruption, we previously reported altered spermiogenesis and reduced gastric acid secretion. We now describe the hepatobiliary and immunologic changes observed in these Ae2(a.b)-deficient mice. METHODS In this murine model, splenocyte pH(i) and T-cell populations were studied by flow cytometry. CD3-stimulated cytokine secretion was estimated using cytokine arrays. AMA were evaluated by immunoblotting and proteomics. Hepatobiliary changes were assessed by immunohistopathology, flow cytometry, and serum biochemistry. Cholangiocyte gene expression was analyzed by real-time polymerase chain reaction. RESULTS Ae2(a,b)(-/-) mice exhibit splenomegaly, elevated pH(i) in splenocytes, increased production of interleukin-12p70 and interferon gamma, expanded CD8(+) T-cell population, and under represented CD4(+)FoxP3(+)/regulatory T cells. Most Ae2(a,b)(-/-) mice tested positively for AMA, showing increased serum levels of immunoglobulin M and G, and liver-specific alkaline phosphatase. About one third of Ae2(a,b)(-/-) mice had extensive portal inflammation with CD8(+) and CD4(+) T lymphocytes surrounding damaged bile ducts. Cholangiocytes isolated from Ae2(a,b)(-/-) mice showed gene expression changes compatible with oxidative stress and increased antigen presentation. CONCLUSIONS Ae2 deficiency alters pH(i) homeostasis in immunocytes and gene expression profile in cholangiocytes, leading to immunologic and hepatobiliary changes that resemble PBC.
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Affiliation(s)
- January T Salas
- Division of Gene Therapy and Hepatology, CIMA, Clínica Universitaria and School of Medicine, University of Navarra, and CIBERehd, Pamplona, Spain
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22
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Meier S, Hübner CA, Groeben H, Peters J, Bingmann D, Wiemann M. Expression of anion exchanger 3 influences respiratory rate in awake and isoflurane anesthetized mice. J Physiol Pharmacol 2007; 58 Suppl 5:371-378. [PMID: 18204149] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
The anion exchanger 3 (AE3) is involved in neuronal pH regulation of which may include chemosensitive neurons. Here we examined the effect of AE3 expression on respiratory rate (RR) in vivo. AE3 knockout (KO, n=5) and wild type (WT, n=6) mice were subjected to body plethysmography, both while awake and during isoflurane anesthesia. RR was significantly lower in awake AE3 KO (162+/-7SE min(-1)) than in WT mice (212+/-20 min(-1), P=0.036). The same was found during isoflurane anesthesia at 0.5 MAC (KO: 123+/-9 min(-1), WT: 168+/-15 min(-1), P=0.026) and 1.0 MAC (KO: 51+/-6 min(-1), WT: 94+/-6 min(-1), P=0.001). Hypercapnia (5% CO2) increased RR in awake and decreased RR in nesthetized (1.0 MAC) mice, whereby relative changes were larger in AE3 KO mice. Recovery from isoflurane anesthesia in respect to RR regaining baseline values was more pronounced in AE3 KO. Results show that AE3 expression profoundly influences control of breathing in mice.
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Affiliation(s)
- S Meier
- Klinik für Anästhesiologie und Intensivmedizin, Universitätsklinikum Essen, Essen, Germany.
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23
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Seidler U, Rottinghaus I, Hillesheim J, Chen M, Riederer B, Krabbenhöft A, Engelhardt R, Wiemann M, Wang Z, Barone S, Manns MP, Soleimani M. Sodium and chloride absorptive defects in the small intestine in Slc26a6 null mice. Pflugers Arch 2007; 455:757-66. [PMID: 17763866 DOI: 10.1007/s00424-007-0318-z] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2007] [Revised: 06/04/2007] [Accepted: 07/03/2007] [Indexed: 12/19/2022]
Abstract
PAT1 (Slc26a6) is located on the apical membrane of the small intestinal villi, but its role for salt absorption has not been studied. To ascertain the role of Slc26a6 in jejunal sodium and chloride absorption, and its interplay with NHE3, muscle-stripped jejuna from Slc26a6+/+ and -/- and NHE3 +/+ and -/- mice were mounted in Ussing chambers and electrical parameters, and (36)Cl(-) and (22)Na(+) fluxes were measured. In parallel studies, expression of the apical Na(+)/H(+) exchanger (NHE3) was examined by immunofluorescence labeling and immunoblot analysis in brush border membrane (BBM). In the basal state, net Cl(-) and Na(+) fluxes were absorptive in Slc26a6-/- and +/+ jejuni, but significantly decreased in -/- animals. Upon forskolin addition, net Na(+) absorption decreased, Isc strongly increased, and net Cl(-) flux became secretory in Slc26a6-/- and +/+ jejuni. When luminal glucose was added to activate Na(+)/glucose cotransport, concomitant Cl(-) absorption was significantly reduced in Slc26a6 -/- jejuni, while Na(+) absorption increased to the same degree in Slc26a6 -/- and +/+ jejuni. Identical experiments in NHE3-deficient jejuni also showed reduced Na(+) and Cl(-) absorption. Results further demonstrated that the lack of NHE3 rendered Na(+) and Cl(-) absorption unresponsive to inhibition by cAMP, but did not affect glucose-driven Na(+) and Cl(-) absorption. Immunoblotting revealed comparable NHE3 abundance and distribution in apical membranes in Slc26a6-/- and +/+ mice. The data strongly suggests that Slc26a6 acts in concert with NHE3 in electroneutral salt absorption in the small intestine. Slc26a6 also serves to absorb Cl(-) during glucose-driven salt absorption.
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Affiliation(s)
- Ursula Seidler
- Department of Gastroenterology, Hepatology and Endocrinology, Hannover Medical School, Hannover, Germany.
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24
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Simpson JE, Schweinfest CW, Shull GE, Gawenis LR, Walker NM, Boyle KT, Soleimani M, Clarke LL. PAT-1 (Slc26a6) is the predominant apical membrane Cl-/HCO3- exchanger in the upper villous epithelium of the murine duodenum. Am J Physiol Gastrointest Liver Physiol 2007; 292:G1079-88. [PMID: 17170027 DOI: 10.1152/ajpgi.00354.2006] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Basal HCO(3)(-) secretion across the duodenum has been shown in several species to principally involve the activity of apical membrane Cl(-)/HCO(3)(-) exchanger(s). To investigate the identity of relevant anion exchanger(s), experiments were performed using wild-type (WT) mice and mice with gene-targeted deletion of the following Cl(-)/HCO(3)(-) exchangers localized to the apical membrane of murine duodenal villi: Slc26a3 [down-regulated in adenoma (DRA)], Slc26a6 [putative anion transporter 1 (PAT-1)], and Slc4a9 [anion exchanger 4 (AE4)]. RT-PCR of the isolated villous epithelium demonstrated PAT-1, DRA, and AE4 mRNA expression. Using the pH-sensitive dye BCECF, anion exchange rates were measured across the apical membrane of epithelial cells in the upper villus of the intact duodenal mucosa. Under basal conditions, Cl(-)/HCO(3)(-) exchange activity was reduced by 65-80% in the PAT-1(-) duodenum, 30-40% in the DRA(-) duodenum, and <5% in the AE4(-) duodenum compared with the WT duodenum. SO(4)(2-)/HCO(3)(-) exchange was eliminated in the PAT-1(-) duodenum but was not affected in the DRA(-) and AE4(-) duodenum relative to the WT duodenum. Intracellular pH (pH(i)) was reduced in the PAT-1(-) villous epithelium but increased to WT levels in the absence of CO(2)/HCO(3)(-) or during methazolamide treatment. Further experiments under physiological conditions indicated active pH(i) compensation in the PAT-1(-) villous epithelium by combined activities of Na(+)/H(+) exchanger 1 and Cl(-)-dependent transport processes at the basolateral membrane. We conclude that 1) PAT-1 is the major contributor to basal Cl(-)/HCO(3)(-) and SO(4)(2-)/HCO(3)(-) exchange across the apical membrane and 2) PAT-1 plays a role in pH(i) regulation in the upper villous epithelium of the murine duodenum.
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Affiliation(s)
- Janet E Simpson
- Department of Biomedical Sciences, University of Missouri, Columbia, MO, USA
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25
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Ishiguro H, Namkung W, Yamamoto A, Wang Z, Worrell RT, Xu J, Lee MG, Soleimani M. Effect of Slc26a6 deletion on apical Cl-/HCO3- exchanger activity and cAMP-stimulated bicarbonate secretion in pancreatic duct. Am J Physiol Gastrointest Liver Physiol 2007; 292:G447-55. [PMID: 16901991 DOI: 10.1152/ajpgi.00286.2006] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The role of Slc26a6 (PAT1) on apical Cl-/HCO3- exchange and bicarbonate secretion in pancreatic duct cells was investigated using Slc26a6 null and wild-type (WT) mice. Apical Cl-/HCO3- exchange activity was measured with the pH-sensitive dye BCECF in microperfused interlobular ducts. The HCO3(-)-influx mode of apical [Cl-]i/[HCO3-]o exchange (where brackets denote concentration and subscripts i and o denote intra- and extracellular, respectively) was dramatically upregulated in Slc26a6 null mice (P < 0.01 vs. WT), whereas the HCO3(-)-efflux mode of apical [Cl-]o/[HCO3-]i exchange was decreased in Slc26a6 null mice (P < 0.05 vs. WT), suggesting the unidirectionality of the Slc26a6-mediated HCO3- transport. Fluid secretory rate in interlobular ducts were comparable in WT and Slc26a6 null mice (P > 0.05). In addition, when pancreatic juice was collected from whole animal in basal and secretin-stimulated conditions, neither juice volume nor its pH showed differences between WT and Slc26a6 null mice. Semiquantitative RT-PCR demonstrated more than fivefold upregulation in Slc26a3 (DRA) expression in Slc26a6 knockout pancreas. In conclusion, these results point to the role of Slc26a6 in HCO3- efflux at the apical membrane and also suggest the presence of a robust Slc26a3 compensatory upregulation, which can replace the function of Slc26a6 in pancreatic ducts.
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Affiliation(s)
- Hiroshi Ishiguro
- Laboratory of Human Nutrition, Nagoya Univ. Graduate School of Medicine, Nagoya, Japan.
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26
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Wang Y, Soyombo AA, Shcheynikov N, Zeng W, Dorwart M, Marino CR, Thomas PJ, Muallem S. Slc26a6 regulates CFTR activity in vivo to determine pancreatic duct HCO3- secretion: relevance to cystic fibrosis. EMBO J 2006; 25:5049-57. [PMID: 17053783 PMCID: PMC1630422 DOI: 10.1038/sj.emboj.7601387] [Citation(s) in RCA: 121] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2006] [Accepted: 09/18/2006] [Indexed: 12/29/2022] Open
Abstract
Fluid and HCO(3)(-) secretion are vital functions of the pancreatic duct and other secretory epithelia. CFTR and Cl(-)/HCO(3)(-) exchange activity at the luminal membrane are required for these functions. The molecular identity of the Cl(-)/HCO(3)(-) exchangers and their relationship with CFTR in determining fluid and HCO(3)(-) secretion are not known. We show here that the Cl(-)/HCO(3)(-) exchanger slc26a6 controls CFTR activity and ductal fluid and HCO(3)(-) secretion. Unexpectedly, deletion of slc26a6 in mice and measurement of fluid and HCO(3)(-) secretion into sealed intralobular pancreatic ducts revealed that deletion of slc26a6 enhanced spontaneous and decreased stimulated secretion. Remarkably, inhibition of CFTR activity with CFTR(inh)-172, knock-down of CFTR by siRNA and measurement of CFTR current in WT and slc26a6(-/-) duct cells revealed that deletion of slc26a6 resulted in dis-regulation of CFTR activity by removal of tonic inhibition of CFTR by slc26a6. These findings reveal the intricate regulation of CFTR activity by slc26a6 in both the resting and stimulated states and the essential role of slc26a6 in pancreatic HCO(3)(-) secretion in vivo.
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Affiliation(s)
- Youxue Wang
- The Department of Physiology, The University of Texas Southwestern Medical Center at Dallas, Dallas, TX, USA
| | - Abigail A Soyombo
- The Department of Physiology, The University of Texas Southwestern Medical Center at Dallas, Dallas, TX, USA
| | - Nikolay Shcheynikov
- The Department of Physiology, The University of Texas Southwestern Medical Center at Dallas, Dallas, TX, USA
| | - Weizhong Zeng
- The Department of Physiology, The University of Texas Southwestern Medical Center at Dallas, Dallas, TX, USA
| | - Michael Dorwart
- The Department of Physiology, The University of Texas Southwestern Medical Center at Dallas, Dallas, TX, USA
| | | | - Philip J Thomas
- The Department of Physiology, The University of Texas Southwestern Medical Center at Dallas, Dallas, TX, USA
| | - Shmuel Muallem
- The Department of Physiology, The University of Texas Southwestern Medical Center at Dallas, Dallas, TX, USA
- The Department of Physiology, The University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, TX 75390-9040, USA. Tel.: +1 214 645 6008; Fax: +1 214 645 6089; E-mail:
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Schweinfest CW, Spyropoulos DD, Henderson KW, Kim JH, Chapman JM, Barone S, Worrell RT, Wang Z, Soleimani M. slc26a3 (dra)-deficient mice display chloride-losing diarrhea, enhanced colonic proliferation, and distinct up-regulation of ion transporters in the colon. J Biol Chem 2006; 281:37962-71. [PMID: 17001077 DOI: 10.1074/jbc.m607527200] [Citation(s) in RCA: 162] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mutations in the SLC26A3 (DRA (down-regulated in adenoma)) gene constitute the molecular etiology of congenital chloride-losing diarrhea in humans. To ascertain its role in intestinal physiology, gene targeting was used to prepare mice lacking slc26a3. slc26a3-deficient animals displayed postpartum lethality at low penetrance. Surviving dra-deficient mice exhibited high chloride content diarrhea, volume depletion, and growth retardation. In addition, the large intestinal loops were distended, with colonic mucosa exhibiting an aberrant growth pattern and the colonic crypt proliferative zone being greatly expanded in slc26a3-null mice. Apical membrane chloride/base exchange activity was sharply reduced, and luminal content was more acidic in slc26a3-null mouse colon. The epithelial cells in the colon displayed unique adaptive regulation of ion transporters; NHE3 expression was enhanced in the proximal and distal colon, whereas colonic H,K-ATPase and the epithelial sodium channel showed massive up-regulation in the distal colon. Plasma aldosterone was increased in slc26a3-null mice. We conclude that slc26a3 is the major apical chloride/base exchanger and is essential for the absorption of chloride in the colon. In addition, slc26a3 regulates colonic crypt proliferation. Deletion of slc26a3 results in chloride-rich diarrhea and is associated with compensatory adaptive up-regulation of ion-absorbing transporters.
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Affiliation(s)
- Clifford W Schweinfest
- Hollings Cancer Center and the Departments of Pathology and Laboratory Medicine and of Medicine, Medical University of South Carolina, Charleston, South Carolina 29425, USA
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Belkaid A, Copland IB, Massillon D, Annabi B. Silencing of the human microsomal glucose-6-phosphate translocase induces glioma cell death: Potential new anticancer target for curcumin. FEBS Lett 2006; 580:3746-52. [PMID: 16777101 DOI: 10.1016/j.febslet.2006.05.071] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2006] [Revised: 05/19/2006] [Accepted: 05/31/2006] [Indexed: 01/15/2023]
Abstract
G6P translocase (G6PT) is thought to play a crucial role in transducing intracellular signaling events in brain tumor-derived cancer cells. In this report, we investigated the contribution of G6PT to the control of U-87 brain tumor-derived glioma cell survival using small interfering RNA (siRNA)-mediated suppression of G6PT. Three siRNA constructs were generated and found to suppress up to 91% G6PT gene expression. Flow cytometry analysis of propidium iodide/annexin-V-stained cells indicated that silencing the G6PT gene induced necrosis and late apoptosis. The anticancer agent curcumin, also inhibited G6PT gene expression by more than 90% and triggered U-87 glioma cells death. Overexpression of recombinant G6PT rescued the cells from curcumin-induced cell death. Targeting G6PT expression may provide a new mechanistic rationale for the action of chemopreventive drugs and lead to the development of new anti-cancer strategies.
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Affiliation(s)
- Anissa Belkaid
- Laboratoire d'Oncologie Moléculaire, Département de Chimie, Centre BIOMED, Université du Québec à Montréal, C.P. 8888, Succ. Centre-ville, Montréal, Que., Canada H3C 3P8
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Pushkin A, Kurtz I. SLC4 base (HCO3 -, CO3 2-) transporters: classification, function, structure, genetic diseases, and knockout models. Am J Physiol Renal Physiol 2006; 290:F580-99. [PMID: 16461757 DOI: 10.1152/ajprenal.00252.2005] [Citation(s) in RCA: 116] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In prokaryotic and eukaryotic organisms, biochemical and physiological processes are sensitive to changes in H(+) activity. For these processes to function optimally, a variety of proteins have evolved that transport H(+)/base equivalents across cell and organelle membranes, thereby maintaining the pH of various intracellular and extracellular compartments within specific limits. The SLC4 family of base (HCO(3)(-), CO(3)(2(-))) transport proteins plays an essential role in mediating Na(+)- and/or Cl(-)-dependent base transport in various tissues and cell types in mammals. In addition to pH regulation, specific members of this family also contribute to vectorial transepithelial base transport in several organ systems including the kidney, pancreas, and eye. The importance of these transporters in mammalian cell biology is highlighted by the phenotypic abnormalities resulting from spontaneous SLC4 mutations in humans and targeted deletions in murine knockout models. This review focuses on recent advances in our understanding of the molecular organization and functional properties of SLC4 transporters and their role in disease.
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Affiliation(s)
- Alexander Pushkin
- Division of Nephrology, David Geffen School of Medicine at UCLA, University of California-Los Angeles, 10833 Le Conte Avenue, Rm. 7-155 Factor Bldg., Los Angeles, CA 90095, USA
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Abstract
Intestinal oxalate transport, mediated by anion exchange proteins, is important to oxalate homeostasis and consequently to calcium oxalate stone diseases. To assess the contribution of the putative anion transporter (PAT)1 (Slc26a6) to transepithelial oxalate transport, we compared the unidirectional and net fluxes of oxalate across isolated, short-circuited segments of the distal ileum of wild-type (WT) mice and Slc26a6 null mice [knockout (KO)]. Additionally, urinary oxalate excretion was measured in both groups. In WT mouse ileum, there was a small net secretion of oxalate (J(net)(Ox) = -5.0 +/-5.0 pmol.cm(-2).h(-1)), whereas in KO mice J(net)(Ox) was significantly absorptive (75 +/- 10 pmol.cm(-2)h.h(-1)), which was the result of a smaller serosal-to-mucosal oxalate flux (J(sm)(Ox)) and a larger mucosal-to-serosal oxalate flux (J(ms)(Ox)). Mucosal DIDS (200 microM) reduced J(sm)(Ox) in WT mice, leading to reversal of the direction of net oxalate transport from secretion to absorption (J(net)(Ox) = 15.0 +/- 5.0 pmol.cm(-2).h(-1)) , but DIDS had no significant effect on KO ileum. In WT mice in the absence of mucosal Cl(-), there were small increases in J(ms)(Ox) and decreases in J(sm)(Ox) that led to a small net oxalate absorption. In KO mice, J(net)(Ox) was 1.5-fold greater in the absence of mucosal Cl(-), due solely to an increase in J(ms)(Ox). Urinary oxalate excretion was about fourfold greater in KO mice compared with WT littermates. We conclude that PAT1 is DIDS sensitive and mediates a significant fraction of oxalate efflux across the apical membrane in exchange for Cl(-); as such, PAT1 represents a major apical membrane pathway mediating J(sm)(Ox).
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Affiliation(s)
- Robert W Freel
- Department of Pathology, Immunology, and Laboratory Medicine, College of Medicine, University of Florida, Gainesville, 32610-00275, USA.
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van Hall T, Wolpert EZ, van Veelen P, Laban S, van der Veer M, Roseboom M, Bres S, Grufman P, de Ru A, Meiring H, de Jong A, Franken K, Teixeira A, Valentijn R, Drijfhout JW, Koning F, Camps M, Ossendorp F, Kärre K, Ljunggren HG, Melief CJM, Offringa R. Selective cytotoxic T-lymphocyte targeting of tumor immune escape variants. Nat Med 2006; 12:417-24. [PMID: 16550190 DOI: 10.1038/nm1381] [Citation(s) in RCA: 121] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2005] [Accepted: 02/23/2006] [Indexed: 12/12/2022]
Abstract
Defects in major histocompatibility complex (MHC) class I-restricted antigen presentation are frequently observed in human cancers and result in escape of tumors from cytotoxic T lymphocyte (CTL) immune surveillance in mice. Here, we show the existence of a unique category of CTLs that can prevent this escape. The CTLs target an alternative repertoire of peptide epitopes that emerge in MHC class I at the surface of cells with impaired function of transporter associated with antigen processing (TAP), tapasin or the proteasome. These peptides, although derived from self antigens such as the commonly expressed Lass5 protein (also known as Trh4), are not presented by normal cells. This explains why they act as immunogenic neoantigens. The newly discovered epitopes can be exploited for immune intervention against processing-deficient tumors through adoptive T-cell transfer or peptide vaccination.
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MESH Headings
- Animals
- Antigen Presentation
- Antiporters/deficiency
- Antiporters/genetics
- Antiporters/physiology
- CD8-Positive T-Lymphocytes/immunology
- Cell Line, Transformed
- Cell Line, Tumor
- Cell Transformation, Neoplastic
- Cell Transformation, Viral
- Clone Cells
- Cytotoxicity Tests, Immunologic
- Epitopes
- Gene Targeting
- Genes, MHC Class I
- Genetic Variation
- Histocompatibility Antigens Class I/immunology
- Immunoglobulins/deficiency
- Immunoglobulins/genetics
- Immunoglobulins/physiology
- Immunologic Surveillance
- Immunotherapy
- Immunotherapy, Adoptive
- Membrane Transport Proteins
- Mice
- Mice, Inbred C57BL
- Mice, Inbred Strains
- Mice, Knockout
- Molecular Sequence Data
- T-Lymphocytes, Cytotoxic/immunology
- Tumor Escape
- Vaccines, Synthetic/therapeutic use
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Affiliation(s)
- Thorbald van Hall
- Department of Immunohematology and Blood Transfusion, Leiden University Medical Center, PO Box 9600, 2300 RC Leiden, The Netherlands.
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Tuo B, Riederer B, Wang Z, Colledge WH, Soleimani M, Seidler U. Involvement of the anion exchanger SLC26A6 in prostaglandin E2- but not forskolin-stimulated duodenal HCO3- secretion. Gastroenterology 2006; 130:349-58. [PMID: 16472591 DOI: 10.1053/j.gastro.2005.10.017] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/06/2005] [Accepted: 10/12/2005] [Indexed: 12/02/2022]
Abstract
BACKGROUND & AIMS SLC26A6 is a recently identified apical Cl(-)/HCO(3)(-) exchanger with strong expression in murine duodenum. The present study was designed to examine the role of SLC26A6 in prostaglandin E(2) (PGE(2))-, forskolin-, and carbachol-induced duodenal HCO(3)(-) secretion. METHODS Murine duodenal mucosal HCO(3)(-) secretion was examined in vitro in Ussing chambers and mucosal SLC26A6 expression levels were analyzed by semiquantitative reverse-transcription polymerase chain reaction. RESULTS Basal HCO(3)(-) secretion was diminished by 20%, PGE(2)-stimulated HCO(3)(-) secretory response by 59%, and carbachol-stimulated response was reduced by 35% in SLC26A6-/- compared with +/+ duodenal mucosa, whereas the forskolin-stimulated HCO(3)(-) secretory response was not different. In Cl(-)-free solutions, PGE(2)- and carbachol-stimulated HCO(3)(-) secretion was reduced by 81% and 44%, respectively, whereas forskolin-stimulated HCO(3)(-) secretion was not altered significantly. PGE(2) and carbachol, but not forskolin, were able to elicit a Cl(-)-dependent HCO(3)(-) secretory response in the absence of short-circuit current changes in cystic fibrosis transmembrane conductance regulator knockout mice. CONCLUSIONS In murine duodenum, PGE(2)-mediated HCO(3)(-) secretion is strongly SLC26A6 dependent and cystic fibrosis transmembrane conductance regulator independent, whereas forskolin-stimulated HCO(3)(-) secretion is completely SLC26A6 independent and cystic fibrosis transmembrane conductance regulator dependent. Carbachol-induced secretion is less pronounced, but occurs via both transport pathways. This suggests that PGE(2) and forskolin activate distinct HCO(3)(-) transport pathways in the murine duodenum.
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Affiliation(s)
- Biguang Tuo
- Department of Gastroenterology and Hepatology, Hannover Medical School, Germany
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Chen M, Tabaczewski P, Truscott SM, Van Kaer L, Stroynowski I. Hepatocytes express abundant surface class I MHC and efficiently use transporter associated with antigen processing, tapasin, and low molecular weight polypeptide proteasome subunit components of antigen processing and presentation pathway. J Immunol 2005; 175:1047-55. [PMID: 16002705 DOI: 10.4049/jimmunol.175.2.1047] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Hepatic expression levels of class I MHC Ags are generally regarded as very low. Because the status of these Ags and their ability to present peptides are important for the understanding of pathogen clearance and tolerogenic properties of the liver, we set out to identify the factors contributing to the reported phenotype. Unexpectedly, we found that the surface densities of K(b) and D(b) on C57BL/6 mouse hepatocytes are nearly as high as on splenocytes, as are the lysate concentrations of mRNA encoding H chain and beta(2)-microglobulin (beta(2)m). In contrast, the components of the peptide-loading pathway are reduced in hepatocytes. Despite the difference in the stoichiometric ratios of H chain/beta(2)m/peptide-loading machineries, both cell types express predominantly thermostable class I and are critically dependent on TAP and tapasin for display of surface Ags. Minor differences in the expression patterns in tapasin(-/-) background suggest cell specificity in class I assembly. Under immunostimulatory conditions, such as exposure to IFN-gamma or Listeria monocytogenes, hepatocytes respond with a vigorous mRNA synthesis of the components of the Ag presentation pathway (up to 10-fold enhancement) but up-regulate H chain and beta(2)m to a lesser degree (<2-fold). This type of response should promote rapid influx of newly generated peptides into the endoplasmic reticulum and preferential presentation of foreign/induced Ag by hepatic class I.
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Affiliation(s)
- Ming Chen
- Center for Immunology, Department of Internal Medicine, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA
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34
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Wang Z, Wang T, Petrovic S, Tuo B, Riederer B, Barone S, Lorenz JN, Seidler U, Aronson PS, Soleimani M. Renal and intestinal transport defects in Slc26a6-null mice. Am J Physiol Cell Physiol 2004; 288:C957-65. [PMID: 15574486 DOI: 10.1152/ajpcell.00505.2004] [Citation(s) in RCA: 150] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
SLC26A6 (PAT1, CFEX) is an anion exchanger that is expressed on the apical membrane of the kidney proximal tubule and the small intestine. Modes of transport mediated by SLC26A6 include Cl-/formate exchange, Cl-/HCO3- exchange, and Cl-/oxalate exchange. To study its role in kidney and intestinal physiology, gene targeting was used to prepare mice lacking Slc26a6. Homozygous mutant Slc26a6-/- mice appeared healthy and exhibited a normal blood pressure, kidney function, and plasma electrolyte profile. In proximal tubules microperfused with a low-HCO3-/high-Cl- solution, the baseline rate of fluid absorption (Jv), an index of NaCl transport under these conditions, was the same in wild-type and null mice. However, the stimulation of Jv by oxalate observed in wild-type mice was completely abolished in Slc26a6-null mice (P<0.05). Formate stimulation of Jv was partially reduced in null mice, but the difference from the response in wild-type mice did not reach statistical significance. Apical membrane Cl-/base exchange activity, assayed with the pH-sensitive dye BCPCF in microperfused proximal tubules, was decreased by 58% in Slc26a6-/- animals (P<0.001 vs. wild types). In the duodenum, the baseline rate of HCO3- secretion measured in mucosal tissue mounted in Ussing chambers was decreased by approximately 30% (P<0.03), whereas the forskolin-stimulated component of HCO3- secretion was the same in wild-type and Slc26a6-/- mice. We conclude that Slc26a6 mediates oxalate-stimulated NaCl absorption, contributes to apical membrane Cl-/base exchange in the kidney proximal tubule, and also plays an important role in HCO3- secretion in the duodenum.
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Affiliation(s)
- Zhaohui Wang
- Department of Internal Medicine, Division of Nephrology and Hypertension, Univ. of Cincinnati, 231 Albert Sabin Way, MSB 259G, Cincinnati OH 45267-0585, USA
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35
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Li L, Sullivan BA, Aldrich CJ, Soloski MJ, Forman J, Grandea AG, Jensen PE, Van Kaer L. Differential Requirement for Tapasin in the Presentation of Leader- and Insulin-Derived Peptide Antigens to Qa-1b-Restricted CTLs. J Immunol 2004; 173:3707-15. [PMID: 15356116 DOI: 10.4049/jimmunol.173.6.3707] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The loading of MHC class I molecules with peptides involves a variety of accessory proteins, including TAP-associated glycoprotein (tapasin), which tethers empty MHC class I molecules to the TAP peptide transporter. We have evaluated the role of tapasin for the assembly of peptides with the class Ib molecule Qa-1b. In normal cells, Qa-1b is predominantly bound by a peptide, the Qa-1 determinant modifier (Qdm), derived from the signal sequence of class Ia molecules. Our results show that tapasin links Qa-1b to the TAP peptide transporter, and that tapasin facilitates the delivery of Qa-1b molecules to the cell surface. Tapasin was also required for the presentation of endogenous Qdm peptides to Qdm-specific, Qa-1b-restricted CTLs. In sharp contrast, tapasin expression was dispensable for the presentation of an insulin peptide to insulin-specific, Qa-1b-restricted CTL isolated from TCR transgenic mice. However, tapasin deficiency significantly impaired the positive selection of these insulin-specific, Qa-1b-restricted transgenic CD8+ T cells. These findings reveal that tapasin plays a differential role in the loading of Qdm and insulin peptides onto Qa-1b molecules, and that tapasin is dispensable for retention of empty Qa-1b molecules in the endoplasmic reticulum, and are consistent with the proposed peptide-editing function of tapasin.
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Affiliation(s)
- LiQi Li
- Department of Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
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36
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Abstract
There are few reports of liver transplantation in glycogenosis type Ib (GSD Ib). We present two cases who had dramatic catch-up growth and reduced infections after transplantation, despite persistent neutropenia.
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Affiliation(s)
- N Bhattacharya
- Metabolic Unit, Great Ormond Street Hospital, London, UK.
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37
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Zarling AL, Luckey CJ, Marto JA, White FM, Brame CJ, Evans AM, Lehner PJ, Cresswell P, Shabanowitz J, Hunt DF, Engelhard VH. Tapasin Is a Facilitator, Not an Editor, of Class I MHC Peptide Binding. J Immunol 2003; 171:5287-95. [PMID: 14607930 DOI: 10.4049/jimmunol.171.10.5287] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Tapasin has been proposed to function as a peptide editor to displace lower affinity peptides and/or to favor the binding of high affinity peptides. Consistent with this, cell surface HLA-B8 molecules in tapasin-deficient cells were less stable and the peptide repertoire was substantially altered. However, the binding affinities of peptides expressed in the absence of tapasin were unexpectedly higher, not lower. The peptide repertoire from cells expressing soluble tapasin was similar in both appearance and affinity to that presented in the presence of full-length tapasin, but the HLA-B8 molecules showed altered cell surface stability characteristics. Similarly, the binding affinities of HLA-A*0201-associated peptides from tapasin(+) and tapasin(-) cells were equivalent, although steady state HLA-A*0201 cell surface expression was decreased and the molecules demonstrated reduced cell surface stability on tapasin(-) cells. These data are inconsistent with a role for tapasin as a peptide editor. Instead, we propose that tapasin acts as a peptide facilitator. In this role, it stabilizes the peptide-free conformation of class I MHC molecules in the endoplasmic reticulum and thus increases the number and variety of peptides bound to class I MHC. Full-length tapasin then confers additional stability on class I MHC molecules that are already associated with peptides.
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Affiliation(s)
- Angela L Zarling
- Carter Immunology Center and Department of Microbiology, University of Virginia, Charlottesville, VA 22908, USA
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38
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Ogino T, Wang X, Ferrone S. Modified flow cytometry and cell-ELISA methodology to detect HLA class I antigen processing machinery components in cytoplasm and endoplasmic reticulum. J Immunol Methods 2003; 278:33-44. [PMID: 12957394 DOI: 10.1016/s0022-1759(03)00224-2] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Flow cytometry and cell-enzyme linked immunosorbent assay (ELISA) are useful techniques for the quantitative analysis of cell surface antigen expression. Furthermore, flow cytometry can detect intracellular markers in cells permeabilized to facilitate the intracellular penetration of antibodies. However, to the best of our knowledge, neither method has been used to detect antigens located in the endoplasmic reticulum (ER) of cells. This limitation has a negative impact on the analysis of the expression of HLA class I antigen processing machinery components in cells. Therefore in this study, we show that markers located in cytoplasm and ER can be detected by flow cytometry and cell-ELISA in cells sequentially fixed with paraformaldehyde, heated in a microwave oven, permeabilized with saponin and reacted with monoclonal antibodies (mAb). Utilizing LMP10 as an intracytoplasmic marker and calreticulin and tapasin as ER luminal markers, we show that the modified flow cytometry and cell-ELISA are sensitive, simple and reproducible methods to detect HLA class I antigen processing machinery components in cells. Furthermore, testing of 10 human cell lines with HLA class I antigen processing machinery component-specific mAb has shown that the results obtained with the modified flow cytometry and cell-ELISA are significantly correlated. These results altogether indicate that the modified flow cytometry and cell-ELISA methods we have described will facilitate the analysis of the expression of HLA class I antigen processing machinery components in cells under physiological and pathological conditions. The resulting information will contribute to the characterization of the effect of changes in the expression of antigen processing machinery components on the recognition of cells by the host's immune system.
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Affiliation(s)
- Takeshi Ogino
- Department of Immunology, Roswell Park Cancer Institute, Elm and Carlton Streets, Buffalo, NY 14263, USA
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39
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Chen LY, Shieh JJ, Lin B, Pan CJ, Gao JL, Murphy PM, Roe TF, Moses S, Ward JM, Lee EJ, Westphal H, Mansfield BC, Chou JY. Impaired glucose homeostasis, neutrophil trafficking and function in mice lacking the glucose-6-phosphate transporter. Hum Mol Genet 2003; 12:2547-58. [PMID: 12925567 DOI: 10.1093/hmg/ddg263] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Glycogen storage disease type Ib (GSD-Ib) is caused by a deficiency in the glucose-6-phosphate transporter (G6PT). In addition to disrupted glucose homeostasis, GSD-Ib patients have unexplained and unexpected defects in neutrophil respiratory burst, chemotaxis and calcium flux, in response to the bacterial peptide f-Met-Leu-Phe, as well as intermittent neutropenia. We generated a G6PT knockout (G6PT-/-) mouse that mimics all known defects of the human disorder and used the model to further our understanding of the pathogenesis of GSD-Ib. We demonstrate that the neutropenia is caused directly by the loss of G6PT activity; that chemotaxis and calcium flux, induced by the chemokines KC and macrophage inflammatory protein-2, are defective in G6PT-/- neutrophils; and that local production of these chemokines and the resultant neutrophil trafficking in vivo are depressed in G6PT-/- ascites during an inflammatory response. The bone and spleen of G6PT-/- mice are developmentally delayed and accompanied by marked hypocellularity of the bone marrow, elevation of myeloid progenitor cell frequencies in both organs and a corresponding dramatic increase in granulocyte colony stimulating factor levels in both GSD-Ib mice and humans. So, in addition to transient neutropenia, a sustained defect in neutrophil trafficking due to both the resistance of neutrophils to chemotactic factors, and reduced local production of neutrophil-specific chemokines at sites of inflammation, may underlie the myeloid deficiency in GSD-Ib. These findings demonstrate that G6PT is not just a G6P transport protein but also an important immunomodulatory protein whose activities need to be addressed in treating the myeloid complications in GSD-Ib patients.
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Affiliation(s)
- Li-Yuan Chen
- Section on Cellular Differentiation, Heritable Disorders Branch, Natioanl Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-1830, USA
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40
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Chefalo PJ, Grandea AG, Van Kaer L, Harding CV. Tapasin-/- and TAP1-/- macrophages are deficient in vacuolar alternate class I MHC (MHC-I) processing due to decreased MHC-I stability at phagolysosomal pH. J Immunol 2003; 170:5825-33. [PMID: 12794107 DOI: 10.4049/jimmunol.170.12.5825] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Alternate class I MHC (MHC-I) Ag processing via cytosolic or vacuolar pathways leads to cross-presentation of exogenous Ag to CD8 T cells. Vacuolar alternate MHC-I processing involves phagolysosomal Ag proteolysis and peptide binding to MHC-I in post-Golgi compartments. We report the first study of alternate MHC-I Ag processing in tapasin(-/-) cells and experiments with tapasin(-/-) and TAP1(-/-) macrophages that characterize alternate MHC-I processing. Tapasin promotes retention of MHC-I in the endoplasmic reticulum (ER) for loading with high affinity peptides, whereas tapasin(-/-) cells allow poorly loaded MHC-I molecules to exit the ER. Hypothetically, we considered that a large proportion of post-Golgi MHC-I on tapasin(-/-) cells might be peptide-receptive, enhancing alternate MHC-I processing. In contrast, alternate MHC-I processing was diminished in both tapasin(-/-) and TAP1(-/-) macrophages. Nonetheless, these cells efficiently presented exogenous peptide, suggesting a loss of MHC-I stability or function specific to vacuolar processing compartments. Tapasin(-/-) and TAP1(-/-) macrophages had decreased MHC-I stability and increased susceptibility of MHC-I to inactivation by acidic conditions (correlating with vacuolar pH). Incubation of tapasin(-/-) or TAP1(-/-) cells at 26 degrees C decreased susceptibility of MHC-I to acid pH and reversed the deficiency in alternate MHC-I processing. Thus, tapasin and TAP are required for MHC-I to bind ER-derived stabilizing peptides to achieve the stability needed for alternate MHC-I processing via peptide exchange in acidic vacuolar processing compartments. Acidic pH destabilizes MHC-I, but also promotes peptide exchange, thereby enhancing alternate MHC-I Ag processing. These results are consistent with alternate MHC-I Ag processing mechanisms that involve binding of peptides to MHC-I within acidic vacuolar compartments.
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Affiliation(s)
- Peter J Chefalo
- Department of Pathology, Case Western Reserve University, Cleveland, OH 44106, USA
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41
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Abstract
BACKGROUND & AIMS The presence of glucose transporter 2 (GLUT2) molecules in the basolateral membrane of enterocytes has long been considered to be of major importance for intestinal glucose absorption. The aim of this study was to reevaluate the role of GLUT2 in a patient with congenital GLUT2 deficiency (Fanconi-Bickel syndrome, FBS). METHODS Oral mono- and disaccharide tolerance tests including gaschromatographic determination of breath hydrogen concentrations were performed in an FBS patient. For comparison, a patient with a microsomal carbohydrate transport defect, glucose-6-phosphate translocase 1 (G6PT1) deficiency, and a control individual were investigated. RESULTS No increase in breath hydrogen concentration was found in the GLUT2-deficient patient after a glucose load. In G6PT1 deficiency, basal hydrogen concentrations were repeatedly found to be elevated. CONCLUSIONS From the fact that a GLUT2-deficient patient does not show any impairment of intestinal monosaccharide transport measurable by the hydrogen breath test, we conclude that mechanisms other than facilitative glucose transport by GLUT2 must be involved in the transport of monosaccharides at the basolateral membrane of enterocytes. When relating this observation to the high intestinal expression of human hexokinase, G6PT1, and glucose-6-phosphatase and to our results of oral carbohydrate tolerance tests in a G6PT1-deficient patient, there is evidence that a microsomal membrane traffic-based transport pathway, as recently suggested for GLUT2-deficient animals, also plays a major role in transcellular monosaccharide transport of the human intestine.
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Affiliation(s)
- René Santer
- University Children's Hospital, Schwanenweg 20, D-24105 Kiel, Germany.
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42
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Abstract
Many viral proteins modulate class I expression, yet, in general, their mechanisms of specific class I recognition are poorly understood. The mK3 protein of gamma(2)-Herpesvirus 68 targets the degradation of nascent class I molecules via the ubiquitin/proteasome pathway. Here, we identify cellular components of the MHC class I assembly machinery, TAP and tapasin, that are required for mK3 function. mK3 failed to regulate class I in TAP- or tapasin-deficient cells, and mK3 interacted with TAP/tapasin, even in the absence of class I. Expression of mK3 resulted in the ubiquitination of TAP/tapasin-associated class I, and mutants of class I incapable of TAP/tapasin interaction were unaffected by mK3. Thus, mK3 subverts TAP/tapasin to specifically target class I molecules for destruction.
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Affiliation(s)
- Lonnie Lybarger
- Department of Genetics, Washington University School of Medicine, St. Louis, MO 63110, USA
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43
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Garbi N, Tiwari N, Momburg F, Hämmerling GJ. A major role for tapasin as a stabilizer of the TAP peptide transporter and consequences for MHC class I expression. Eur J Immunol 2003; 33:264-73. [PMID: 12594855 DOI: 10.1002/immu.200390029] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Tapasin is a member of the MHC class I loading complex where it bridges the TAP peptide transporter to class I molecules. The main role of tapasin is assumed to be the facilitation of peptide loading and optimization of the peptide cargo. Here, we describe another important function for tapasin. In tapasin-deficient (Tpn(-/-)) mice the absence of tapasin was found to have a dramatic effect on the stability of the TAP1/TAP2 heterodimeric peptide transporter. Steady-state expression of TAP protein was reduced more than 100-fold from about 3 x 10(4) TAP molecules per wild-type splenocyte to about 1 x 10(2) TAP per Tpn(-/-) splenocyte. Thus, a major function of murine tapasin appears to be the stabilization of TAP. The low amount of TAP moleculesin Tpn(-/-) lymphocytes is likely to contribute to the severe impairment of MHC class I expression. Surprisingly, activation of Tpn(-/-) lymphocytes yielded strongly enhanced class I expression comparable to wild-type levels, although TAP expression remained low and in the magnitude of several hundred molecules per cell. The high level of class I on activated Tpn(-/-) cells depended on peptides generated by the proteasome as indicated by blockade with the proteasome-specific inhibitor lactacystin. Lymphocyte activation induced an increase in ubiquitinated proteins that are cleaved into peptides by the proteasome. These findings suggest that in the presence of a large peptide pool in the cytosol, a small number of TAP transporters is sufficient to translocate enough peptides for high class I expression. However, these class I molecules were less stable than those of wild-type cells, indicating that tapasin is not only required for stabilization of TAP but also for optimization of the spectrum of bound peptides.
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Affiliation(s)
- Natalio Garbi
- Deutsches Krebsforschungszentrum Heidelberg, Abteilung Molekulare Immunologie, Heidelberg, Germany
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44
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Chen LY, Pan CJ, Shieh JJ, Chou JY. Structure-function analysis of the glucose-6-phosphate transporter deficient in glycogen storage disease type Ib. Hum Mol Genet 2002; 11:3199-207. [PMID: 12444104 DOI: 10.1093/hmg/11.25.3199] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Glycogen storage disease type Ib (GSD-Ib) is caused by a deficiency in the glucose-6-phosphate transporter (G6PT), a 10 transmembrane domain endoplasmic reticulum protein. To date, 69 G6PT mutations, including 28 missenses and 2 codon deletions, have been identified in GSD-Ib patients. We previously characterized 15 of the missense and one codon deletion mutations using a pSVL-based expression assay. A lack of sensitivity in this assay limited the discrimination between mutations that lead to loss of function and mutations that leave a low residual activity. We now report an improved G6PT assay, based on an adenoviral vector-mediated expression system and its use in the functional characterization of all 30 codon mutations found in GSD-Ib patients. Twenty of the naturally occurring mutations completely abolish microsomal G6P uptake activity while the other 10 mutations, including 5 previously characterized ones, partially inactivate the transporter. This information should greatly facilitate genotype-phenotype correlation. We also report a structure-function analysis of G6PT. In addition to the 3 destabilizing mutations reported previously, we now show that the G50R, C176R, V235del, G339C and G339D mutations also compromise the G6PT stability. Mutation analysis of the amino-terminal domain of G6PT shows that it is required for optimal G6P uptake activity. Finally, we show that degradation of both wild-type and mutant G6PT is inhibited by a potent proteasome inhibitor, lactacystin, demonstrating that G6PT is a substrate for proteasome-mediated degradation.
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Affiliation(s)
- Li-Yuan Chen
- Section on Cellular Differentiation, Heritable Disorders Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, 20892, USA
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45
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Yabe T, Kawamura S, Sato M, Kashiwase K, Tanaka H, Ishikawa Y, Asao Y, Oyama J, Tsuruta K, Tokunaga K, Tadokoro K, Juji T. A subject with a novel type I bare lymphocyte syndrome has tapasin deficiency due to deletion of 4 exons by Alu-mediated recombination. Blood 2002; 100:1496-8. [PMID: 12149238 DOI: 10.1182/blood-2001-12-0252] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
HLA class I expression depends on the formation of a peptide-loading complex composed of class I heavy chain; beta(2)-microglobulin; the transporter associated with antigen processing (TAP); and tapasin, which links TAP to the heavy chain. Defects in TAP result in a class I deficiency called the type I bare lymphocyte syndrome (BLS). In the present study, we examined a subject with a novel type I BLS who does not exhibit apparent TAP abnormalities but who has a tapasin defect. The subject's TAPASIN gene has a 7.4-kilobase deletion between introns 3 and 7; an Alu repeat-mediated unequal homologous recombination may be the cause of the deletion. No tapasin polypeptide was detected in the subject's cells. The cell surface class I expression level in tapasin-deficient cells was markedly reduced but the reduction was not as profound as in TAP-deficient cells. These results suggest that tapasin deficiency is another cause of type I BLS.
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Affiliation(s)
- Toshio Yabe
- Department of Research, Japanese Red Cross Central Blood Center, Tokyo, Japan.
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Affiliation(s)
- N Garbi
- Department of Molecular Immunology, German Cancer Research Center, Heidelberg, Germany
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Abstract
The stable assembly of Major Histocompatibility Complex (MHC) molecules with peptides is controlled by a number of cofactors, including proteins with general housekeeping functions and proteins with dedicated functions in MHC assembly. Recent work in my laboratory has focused on two chaperones, tapasin (tpn) and DM, that play critical roles in the loading of peptides onto MHC class I and MHC class II molecules, respectively. Tapasin is a transmembrane protein that tethers empty class I molecules in the endoplasmic reticulum to the transporter associated with antigen processing. DM is a peptide exchange factor that binds with empty and peptide-loaded class II molecules in endosomal and lysosomal compartments. Although a number of different functions for tapasin and DM have been proposed, emerging evidence suggests that both of these chaperones retain unstable MHC molecules in peptide-loading compartments until they bind with high-affinity peptides. These cofactors therefore promote the surface expression of long-lived MHC-peptide complexes.
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Affiliation(s)
- L Van Kaer
- Department of Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, TN 37232-0295, USA.
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Abstract
Effective immunity to infectious agents requires the initial recognition of antigen by specific receptors, which leads to the activation of immunocytes and the elicitation of an immune response. Because T cell antigen recognition and directed responses are complex processes, they are initiated and quelled in a highly regulated manner. Our laboratory has focused on defining the molecular processes that control T cell antigen presentation and recognition. Research in this area is focused on determining the chemical nature of antigens displayed by Major histocompatibility, complex (MHC)-encoded class I molecules and the nonclassical class I-like protein CD1d. Quantitative aspects of antigen presentation and recognition are also being studied to determine how these factors control the initiation of a T cell response. Our studies provide insights into the biochemical basis of T cell antigen recognition and response as well as the molecular processes underlying the initiation and regulation of immune responses by CD1d-restricted natural T lymphocytes.
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MESH Headings
- Amino Acid Sequence
- Animals
- Antigen Presentation
- Antigens, CD1/chemistry
- Antigens, CD1/immunology
- Antigens, CD1/metabolism
- Antigens, CD1d
- Antiporters/deficiency
- Antiporters/physiology
- Cytokines/physiology
- Endoplasmic Reticulum/metabolism
- Golgi Apparatus/metabolism
- H-2 Antigens/immunology
- Histocompatibility Antigens Class I/chemistry
- Histocompatibility Antigens Class I/immunology
- Humans
- Immune System/cytology
- Immune System/immunology
- Immunoglobulins/deficiency
- Immunoglobulins/physiology
- Killer Cells, Natural/immunology
- Ligands
- Lipids/immunology
- Lymphocyte Activation
- Membrane Transport Proteins
- Mice
- Mice, Knockout
- Models, Immunological
- Molecular Sequence Data
- Protein Conformation
- Protein Transport
- Receptors, Antigen, T-Cell/immunology
- Sequence Alignment
- Sequence Homology, Amino Acid
- T-Lymphocyte Subsets/immunology
- T-Lymphocytes, Cytotoxic/immunology
- Thymus Gland/cytology
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Affiliation(s)
- S Joyce
- Department of Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, TN, USA.
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Lybarger L, Yu YY, Chun T, Wang CR, Grandea AG, Van Kaer L, Hansen TH. Tapasin enhances peptide-induced expression of H2-M3 molecules, but is not required for the retention of open conformers. J Immunol 2001; 167:2097-105. [PMID: 11489993 DOI: 10.4049/jimmunol.167.4.2097] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
H2-M3 is a class Ib MHC molecule that binds a highly restricted pool of peptides, resulting in its intracellular retention under normal conditions. However, addition of exogenous M3 ligands induces its escape from the endoplasmic reticulum (ER) and, ultimately, its expression at the cell surface. These features of M3 make it a powerful and novel model system to study the potentially interrelated functions of the ER-resident class I chaperone tapasin. The functions ascribed to tapasin include: 1) ER retention of peptide-empty class I molecules, 2) TAP stabilization resulting in increased peptide transport, 3) direct facilitation of peptide binding by class I, and 4) peptide editing. We report in this study that M3 is associated with the peptide-loading complex and that incubation of live cells with M3 ligands dramatically decreased this association. Furthermore, high levels of open conformers of M3 were efficiently retained intracellularly in tapasin-deficient cells, and addition of exogenous M3 ligands resulted in substantial surface induction that was enhanced by coexpression of either membrane-bound or soluble tapasin. Thus, in the case of M3, tapasin directly facilitates intracellular peptide binding, but is not required for intracellular retention of open conformers. As an alternative approach to define unique aspects of M3 biosynthesis, M3 was expressed in human cell lines that lack an M3 ortholog, but support expression of murine class Ia molecules. Unexpectedly, peptide-induced surface expression of M3 was observed in only one of two cell lines. These results demonstrate that M3 expression is dependent on a unique factor compared with class Ia molecules.
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MESH Headings
- ATP Binding Cassette Transporter, Subfamily B, Member 2
- ATP Binding Cassette Transporter, Subfamily B, Member 3
- ATP-Binding Cassette Transporters/metabolism
- Adjuvants, Immunologic/deficiency
- Adjuvants, Immunologic/genetics
- Adjuvants, Immunologic/metabolism
- Adjuvants, Immunologic/physiology
- Animals
- Antiporters/deficiency
- Antiporters/genetics
- Antiporters/metabolism
- Antiporters/physiology
- Cell Line, Transformed
- Epitopes/chemistry
- Epitopes/genetics
- Epitopes/metabolism
- H-2 Antigens/metabolism
- HeLa Cells
- Histocompatibility Antigen H-2D
- Histocompatibility Antigens Class I/biosynthesis
- Histocompatibility Antigens Class I/chemistry
- Histocompatibility Antigens Class I/genetics
- Histocompatibility Antigens Class I/metabolism
- Humans
- Immunoglobulins/deficiency
- Immunoglobulins/genetics
- Immunoglobulins/metabolism
- Immunoglobulins/physiology
- L Cells
- Membrane Transport Proteins
- Mice
- Mutagenesis, Site-Directed
- Peptides/metabolism
- Peptides/pharmacology
- Protein Binding/genetics
- Protein Binding/immunology
- Protein Conformation
- Transfection
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Affiliation(s)
- L Lybarger
- Department of Genetics, Washington University School of Medicine, St. Louis, MO 63110, USA
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