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Kingma SDK, Neven J, Bael A, Meuwissen MEC, van den Akker M. Imerslund-Gräsbeck syndrome: a comprehensive review of reported cases. Orphanet J Rare Dis 2023; 18:291. [PMID: 37710296 PMCID: PMC10500774 DOI: 10.1186/s13023-023-02889-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2023] [Accepted: 08/25/2023] [Indexed: 09/16/2023] Open
Abstract
Imerslund-Gräsbeck syndrome (IGS) is a rare autosomal recessive disorder characterized by vitamin B12 malabsorption. Most patients present with non-specific symptoms attributed to vitamin B12 deficiency, and proteinuria. Patients may if untreated, develop severe neurocognitive manifestations. If recognized and treated with sufficient doses of vitamin B12, patients recover completely. We provide, for the first time, an overview of all previously reported cases of IGS. In addition, we provide a complete review of IGS and describe two new patients.
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Affiliation(s)
- Sandra D K Kingma
- Centre for Metabolic Diseases, University Hospital Antwerp, University of Antwerp, Drie Eikenstraat 655, Edegem, Antwerp, 2650, Belgium
- Department of Pediatrics, University Hospital Antwerp, University of Antwerp, Drie Eikenstraat 655, Edegem, 2650, Belgium
- Faculty of medicine and health sciences, University of Antwerp, Antwerp, Belgium
| | - Julie Neven
- Department of Pediatrics, University Hospital Antwerp, University of Antwerp, Drie Eikenstraat 655, Edegem, 2650, Belgium
| | - An Bael
- Faculty of medicine and health sciences, University of Antwerp, Antwerp, Belgium
- Department of Pediatric Nephrology, ZNA Queen Paola Children's Hospital, Lindendreef 1, Antwerp, 2020, Belgium
| | - Marije E C Meuwissen
- Center of Medical Genetics, University Hospital Antwerp, Drie Eikenstraat 655, Edegem, 2650, Belgium
| | - Machiel van den Akker
- Department of Pediatrics, University Hospital Antwerp, University of Antwerp, Drie Eikenstraat 655, Edegem, 2650, Belgium.
- Faculty of medicine and health sciences, University of Antwerp, Antwerp, Belgium.
- Department of Pediatrics, ZNA Queen Paola Children's Hospital, Lindendreef 1, Antwerp, 2020, Belgium.
- Pediatric Hematology and Oncology, Department of Pediatrics, University Hospital Antwerp, Drie Eikenstraat 655, Edegem, Antwerp, 2650, Belgium.
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2
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Kulkarni K, Patel S, Ali R, Hussain T. Angiotensin II type 2 receptor activation preserves megalin in the kidney and prevents proteinuria in high salt diet fed rats. Sci Rep 2023; 13:4277. [PMID: 36922642 PMCID: PMC10017765 DOI: 10.1038/s41598-023-31454-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2022] [Accepted: 03/12/2023] [Indexed: 03/18/2023] Open
Abstract
Proteinuria is a risk factor for and consequence of kidney injury. Angiotensin II type 2 receptor (AT2R) is an emerging reno-protective target and is anti-proteinuric under pathological conditions, including high salt-fed obese animals. However, the mechanisms remain unknown, particularly whether the anti-proteinuric activity of AT2R is independent of its anti-hypertensive and anti-inflammatory effects. In the present study, obese Zucker rats were fed high sodium (4%) diet (HSD) for 48 h, a time in which blood pressure does not change. HSD caused proteinuria without affecting glomerular slit diaphragm proteins (nephrin and podocin), glomerular filtration rate, inflammatory and fibrotic markers (TNFα, IL-6, and TGF-β), ruling out glomerular injury, inflammation and fibrosis but indicating tubular mechanisms of proteinuria. At cellular and molecular levels, we observed a glycogen synthase kinase (GSK)-3β-mediated megalin phosphorylation, and its subsequent endocytosis and lysosomal degradation in HSD-fed rat kidneys. Megalin is a major proximal tubular endocytic protein transporter. The AT2R agonist C21 (0.3 mg/kg/day, i.p.) administration prevented proteinuria and rescued megalin surface expression potentially by activating Akt-mediated phosphorylation and inactivation of GSK-3β in HSD-fed rat kidneys. Overall, AT2R has a direct anti-proteinuric activity, potentially via megalin regulation, and is suggested as a novel target to limit kidney injury.
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Affiliation(s)
- Kalyani Kulkarni
- Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, University of Houston, Health 2, 4349 Martin Luther King Boulevard, Houston, TX, 77204-5037, USA
| | - Sanket Patel
- Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, University of Houston, Health 2, 4349 Martin Luther King Boulevard, Houston, TX, 77204-5037, USA
| | - Riyasat Ali
- Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, University of Houston, Health 2, 4349 Martin Luther King Boulevard, Houston, TX, 77204-5037, USA
| | - Tahir Hussain
- Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, University of Houston, Health 2, 4349 Martin Luther King Boulevard, Houston, TX, 77204-5037, USA.
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3
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McCorvie TJ, Ferreira D, Yue WW, Froese DS. The complex machinery of human cobalamin metabolism. J Inherit Metab Dis 2023; 46:406-420. [PMID: 36680553 DOI: 10.1002/jimd.12593] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/03/2022] [Revised: 01/17/2023] [Accepted: 01/19/2023] [Indexed: 01/22/2023]
Abstract
Vitamin B12 (cobalamin, Cbl) is required as a cofactor by two human enzymes, 5-methyltetrahydrofolate-homocysteine methyltransferase (MTR) and methylmalonyl-CoA mutase (MMUT). Within the body, a vast array of transporters, enzymes and chaperones are required for the generation and delivery of these cofactor forms. How they perform these functions is dictated by the structure and interactions of the proteins involved, the molecular bases of which are only now being elucidated. In this review, we highlight recent insights into human Cbl metabolism and address open questions in the field by employing a protein structure and interactome based perspective. We discuss how three very similar proteins-haptocorrin, intrinsic factor and transcobalamin-exploit slight structural differences and unique ligand receptor interactions to effect selective Cbl absorption and internalisation. We describe recent advances in the understanding of how endocytosed Cbl is transported across the lysosomal membrane and the implications of the recently solved ABCD4 structure. We detail how MMACHC and MMADHC cooperate to modify and target cytosolic Cbl to the client enzymes MTR and MMUT using ingenious modifications to an ancient nitroreductase fold, and how MTR and MMUT link with their accessory enzymes to sustainably harness the supernucleophilic potential of Cbl. Finally, we provide an outlook on how future studies may combine structural and interactome based approaches and incorporate knowledge of post-translational modifications to bring further insights.
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Affiliation(s)
- Thomas J McCorvie
- Biosciences Institute, The Medical School, Newcastle University, Newcastle upon Tyne, UK
| | - Douglas Ferreira
- Biosciences Institute, The Medical School, Newcastle University, Newcastle upon Tyne, UK
- Centre for Medicines Discovery, Nuffield Department of Medicine, University of Oxford, Oxford, UK
| | - Wyatt W Yue
- Biosciences Institute, The Medical School, Newcastle University, Newcastle upon Tyne, UK
| | - D Sean Froese
- Division of Metabolism and Children's Research Center, University Children's Hospital Zürich, University of Zürich, Zürich, Switzerland
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4
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Erban T, Sopko B, Bodrinova M, Talacko P, Chalupnikova J, Markovic M, Kamler M. Proteomic insight into the interaction of Paenibacillus larvae with honey bee larvae before capping collected from an American foulbrood outbreak: Pathogen proteins within the host, lysis signatures and interaction markers. Proteomics 2023; 23:e2200146. [PMID: 35946602 DOI: 10.1002/pmic.202200146] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2022] [Revised: 07/17/2022] [Accepted: 07/25/2022] [Indexed: 01/05/2023]
Abstract
American foulbrood (AFB) is a devastating disease of honey bees. There remains a gap in the understanding of the interactions between the causative agent and host, so we used shotgun proteomics to gain new insights. Nano-LC-MS/MS analysis preceded visual description and Paenibacillus larvae identification in the same individual sample. A further critical part of our methodology was that larvae before capping were used as the model stage. The identification of the virulence factors SplA, PlCBP49, enolase, and DnaK in all P. larvae-positive samples was consistent with previous studies. Furthermore, the results were consistent with the array of virulence factors identified in an in vitro study of P. larvae exoprotein fractions. Although an S-layer protein and a putative bacteriocin were highlighted as important, the microbial collagenase ColA and InhA were not found in our samples. The most important virulence factor identified was isoform of neutral metalloproteinase (UniProt: V9WB82), a major protein marker responsible for the shift in the PCA biplot. This protein is associated with larval decay and together with other virulence factors (bacteriocin) can play a key role in protection against secondary invaders. Overall, this study provides new knowledge on host-pathogen interactions and a new methodical approach to study the disease.
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Affiliation(s)
- Tomas Erban
- Proteomics and Metabolomics Laboratory, Crop Research Institute, Prague, Czechia
| | - Bruno Sopko
- Proteomics and Metabolomics Laboratory, Crop Research Institute, Prague, Czechia
| | - Miroslava Bodrinova
- Proteomics and Metabolomics Laboratory, Crop Research Institute, Prague, Czechia
| | - Pavel Talacko
- Proteomics Core Facility, Faculty of Science, Charles University, Prague, Czechia
| | - Julie Chalupnikova
- Proteomics and Metabolomics Laboratory, Crop Research Institute, Prague, Czechia
| | - Martin Markovic
- Proteomics and Metabolomics Laboratory, Crop Research Institute, Prague, Czechia
| | - Martin Kamler
- Bee Research Institute at Dol, Libcice nad Vltavou, Czechia
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5
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Li H, Dai W, Liu Z, He L. Renal Proximal Tubular Cells: A New Site for Targeted Delivery Therapy of Diabetic Kidney Disease. Pharmaceuticals (Basel) 2022; 15:ph15121494. [PMID: 36558944 PMCID: PMC9786989 DOI: 10.3390/ph15121494] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2022] [Revised: 11/28/2022] [Accepted: 11/29/2022] [Indexed: 12/04/2022] Open
Abstract
Diabetic kidney disease (DKD) is a major complication of diabetes mellitus (DM) and the leading cause of end-stage kidney disease (ESKD) worldwide. A significant number of drugs have been clinically investigated for the treatment of DKD. However, a large proportion of patients still develop end-stage kidney disease unstoppably. As a result, new effective therapies are urgently needed to slow down the progression of DKD. Recently, there is increasing evidence that targeted drug delivery strategies such as large molecule carriers, small molecule prodrugs, and nanoparticles can improve drug efficacy and reduce adverse side effects. There is no doubt that targeted drug delivery strategies have epoch-making significance and great application prospects for the treatment of DKD. In addition, the proximal tubule plays a very critical role in the progression of DKD. Consequently, the purpose of this paper is to summarize the current understanding of proximal tubule cell-targeted therapy, screen for optimal targeting strategies, and find new therapeutic approaches for the treatment of DKD.
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Affiliation(s)
| | | | | | - Liyu He
- Correspondence: ; Tel.: +86-731-8529-2064
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6
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Yadav SPS, Yu A, Zhao J, Singh J, Kakkar S, Chakraborty S, Mechref Y, Molitoris B, Wagner MC. Glycosylation of a key cubilin Asn residue results in reduced binding to albumin. J Biol Chem 2022; 298:102371. [PMID: 35970386 PMCID: PMC9485058 DOI: 10.1016/j.jbc.2022.102371] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2022] [Revised: 08/09/2022] [Accepted: 08/10/2022] [Indexed: 10/28/2022] Open
Abstract
Kidney disease often manifests with an increase in proteinuria, which can result from both glomerular and/or proximal tubule injury. The proximal tubules are the major site of protein and peptide endocytosis of the glomerular filtrate, and cubilin is the proximal tubule brush border membrane glycoprotein receptor that binds filtered albumin and initiates its processing in proximal tubules. Albumin also undergoes multiple modifications depending upon the physiologic state. We previously documented that carbamylated albumin had reduced cubilin binding, but the effects of cubilin modifications on binding albumin remain unclear. Here, we investigate the cubilin-albumin binding interaction to define the impact of cubilin glycosylation and map the key glycosylation sites while also targeting specific changes in a rat model of proteinuria. We identified a key Asn residue, N1285, that when glycosylated reduced albumin binding. In addition, we found a pH-induced conformation change may contribute to ligand release. To further define the albumin-cubilin binding site, we determined the solution structure of cubilin's albumin-binding domain, CUB7,8, using small-angle X-ray scattering and molecular modeling. We combined this information with mass spectrometry crosslinking experiments of CUB7,8 and albumin that provides a model of the key amino acids required for cubilin-albumin binding. Together, our data supports an important role for glycosylation in regulating the cubilin interaction with albumin, which is altered in proteinuria and provides new insight into the binding interface necessary for the cubilin-albumin interaction.
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Affiliation(s)
- Shiv Pratap Singh Yadav
- Nephrology Division, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, USA
| | - Aiying Yu
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas, USA
| | - Jingfu Zhao
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas, USA
| | - Jasdeep Singh
- Department of Biochemical Engineering and Biotechnology, Indian Institute of Technology Delhi, New Delhi, India
| | - Saloni Kakkar
- CSIR-Institute of Microbial Technology, Chandigarh, India
| | | | - Yehia Mechref
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas, USA
| | - Bruce Molitoris
- Nephrology Division, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, USA; Department of Cellular & Integrative Physiology, Indiana University School of Medicine, Indianapolis, Indiana, USA
| | - Mark C Wagner
- Nephrology Division, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, USA.
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7
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Megalin and Vitamin D Metabolism—Implications in Non-Renal Tissues and Kidney Disease. Nutrients 2022; 14:nu14183690. [PMID: 36145066 PMCID: PMC9506339 DOI: 10.3390/nu14183690] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2022] [Revised: 09/02/2022] [Accepted: 09/06/2022] [Indexed: 11/17/2022] Open
Abstract
Megalin is an endocytic receptor abundantly expressed in proximal tubular epithelial cells and other calciotropic extrarenal cells expressing vitamin D metabolizing enzymes, such as bone and parathyroid cells. The receptor functions in the uptake of the vitamin D-binding protein (DBP) complexed to 25 hydroxyvitamin D3 (25(OH)D3), facilitating the intracellular conversion of precursor 25(OH)D3 to the active 1,25 dihydroxyvitamin D3 (1,25(OH)2D3). The significance of renal megalin-mediated reabsorption of 25(OH)D3 and 1,25(OH)2D3 has been well established experimentally, and other studies have demonstrated relevant roles of extrarenal megalin in regulating vitamin D homeostasis in mammary cells, fat, muscle, bone, and mesenchymal stem cells. Parathyroid gland megalin may regulate calcium signaling, suggesting intriguing possibilities for megalin-mediated cross-talk between calcium and vitamin D regulation in the parathyroid; however, parathyroid megalin functionality has not been assessed in the context of vitamin D. Within various models of chronic kidney disease (CKD), megalin expression appears to be downregulated; however, contradictory results have been observed between human and rodent models. This review aims to provide an overview of the current knowledge of megalin function in the context of vitamin D metabolism, with an emphasis on extrarenal megalin, an area that clearly requires further investigation.
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8
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Molitoris BA, Sandoval RM, Yadav SPS, Wagner MC. Albumin Uptake and Processing by the Proximal Tubule: Physiologic, Pathologic and Therapeutic Implications. Physiol Rev 2022; 102:1625-1667. [PMID: 35378997 PMCID: PMC9255719 DOI: 10.1152/physrev.00014.2021] [Citation(s) in RCA: 46] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
For nearly 50 years the proximal tubule (PT) has been known to reabsorb, process, and either catabolize or transcytose albumin from the glomerular filtrate. Innovative techniques and approaches have provided insights into these processes. Several genetic diseases, nonselective PT cell defects, chronic kidney disease (CKD), and acute PT injury lead to significant albuminuria, reaching nephrotic range. Albumin is also known to stimulate PT injury cascades. Thus, the mechanisms of albumin reabsorption, catabolism, and transcytosis are being reexamined with the use of techniques that allow for novel molecular and cellular discoveries. Megalin, a scavenger receptor, cubilin, amnionless, and Dab2 form a nonselective multireceptor complex that mediates albumin binding and uptake and directs proteins for lysosomal degradation after endocytosis. Albumin transcytosis is mediated by a pH-dependent binding affinity to the neonatal Fc receptor (FcRn) in the endosomal compartments. This reclamation pathway rescues albumin from urinary losses and cellular catabolism, extending its serum half-life. Albumin that has been altered by oxidation, glycation, or carbamylation or because of other bound ligands that do not bind to FcRn traffics to the lysosome. This molecular sorting mechanism reclaims physiological albumin and eliminates potentially toxic albumin. The clinical importance of PT albumin metabolism has also increased as albumin is now being used to bind therapeutic agents to extend their half-life and minimize filtration and kidney injury. The purpose of this review is to update and integrate evolving information regarding the reabsorption and processing of albumin by proximal tubule cells including discussion of genetic disorders and therapeutic considerations.
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Affiliation(s)
- Bruce A. Molitoris
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, United States
- Dept.of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, Indiana, United States
| | - Ruben M. Sandoval
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, United States
| | - Shiv Pratap S. Yadav
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, United States
| | - Mark C. Wagner
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, United States
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9
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Kozyraki R, Verroust P, Cases O. Cubilin, the intrinsic factor-vitamin B12 receptor. VITAMINS AND HORMONES 2022; 119:65-119. [PMID: 35337634 DOI: 10.1016/bs.vh.2022.01.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Cubilin (CUBN), the intrinsic factor-vitamin B12 receptor is a large endocytic protein involved in various physiological functions: vitamin B12 uptake in the gut; reabsorption of albumin and maturation of vitamin D in the kidney; nutrient delivery during embryonic development. Cubilin is an atypical receptor, peripherally associated to the plasma membrane. The transmembrane proteins amnionless (AMN) and Lrp2/Megalin are the currently known molecular partners contributing to plasma membrane transport and internalization of Cubilin. The role of Cubilin/Amn complex in the handling of vitamin B12 in health and disease has extensively been studied and so is the role of the Cubilin-Lrp2 tandem in renal pathophysiology. Accumulating evidence strongly supports a role of Cubilin in some developmental defects including impaired closure of the neural tube. Are these defects primarily caused by the dysfunction of a specific Cubilin ligand or are they secondary to impaired vitamin B12 or protein uptake? We will present the established Cubilin functions, discuss the developmental data and provide an overview of the emerging implications of Cubilin in the field of cardiovascular disease and cancer pathogenesis.
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Affiliation(s)
- Renata Kozyraki
- Centre de Recherche des Cordeliers, Sorbonne Université, INSERM, Université de Paris, Paris, France.
| | - Pierre Verroust
- Centre de Recherche des Cordeliers, Sorbonne Université, INSERM, Université de Paris, Paris, France
| | - Olivier Cases
- Centre de Recherche des Cordeliers, Sorbonne Université, INSERM, Université de Paris, Paris, France
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Atienza-Manuel A, Castillo-Mancho V, De Renzis S, Culi J, Ruiz-Gómez M. Endocytosis mediated by an atypical CUBAM complex modulates slit diaphragm dynamics in nephrocytes. Development 2021; 148:272711. [PMID: 34738617 PMCID: PMC8710305 DOI: 10.1242/dev.199894] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2021] [Accepted: 10/22/2021] [Indexed: 01/14/2023]
Abstract
The vertebrate endocytic receptor CUBAM, consisting of three cubilin monomers complexed with a single amnionless molecule, plays a major role in protein reabsorption in the renal proximal tubule. Here, we show that Drosophila CUBAM is a tripartite complex composed of Amnionless and two cubilin paralogues, Cubilin and Cubilin2, and that it is required for nephrocyte slit diaphragm (SD) dynamics. Loss of CUBAM-mediated endocytosis induces dramatic morphological changes in nephrocytes and promotes enlarged ingressions of the external membrane and SD mislocalisation. These phenotypes result in part from an imbalance between endocytosis, which is strongly impaired in CUBAM mutants, and exocytosis in these highly active cells. Of note, rescuing receptor-mediated endocytosis by Megalin/LRP2 or Rab5 expression only partially restores SD positioning in CUBAM mutants, suggesting a specific requirement of CUBAM in SD degradation and/or recycling. This finding and the reported expression of CUBAM in podocytes suggest a possible unexpected conserved role for this endocytic receptor in vertebrate SD remodelling. Summary: A genetic study revealing that endocytosis mediated by an atypical CUBAM endocytic receptor, composed of Amnionless and two Cubilin paralogues, regulates slit diaphragm remodelling in Drosophila nephrocytes.
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Affiliation(s)
- Alexandra Atienza-Manuel
- Centro de Biología Molecular Severo Ochoa, CSIC and UAM, Nicolás Cabrera 1, Cantoblanco 28049, Madrid, Spain
| | - Vicente Castillo-Mancho
- Centro de Biología Molecular Severo Ochoa, CSIC and UAM, Nicolás Cabrera 1, Cantoblanco 28049, Madrid, Spain
| | - Stefano De Renzis
- European Molecular Biology Laboratory (EMBL), Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Joaquim Culi
- Centro de Biología Molecular Severo Ochoa, CSIC and UAM, Nicolás Cabrera 1, Cantoblanco 28049, Madrid, Spain
| | - Mar Ruiz-Gómez
- Centro de Biología Molecular Severo Ochoa, CSIC and UAM, Nicolás Cabrera 1, Cantoblanco 28049, Madrid, Spain
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11
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Weisz OA. Endocytic adaptation to functional demand by the kidney proximal tubule. J Physiol 2021; 599:3437-3446. [PMID: 34036593 DOI: 10.1113/jp281599] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2021] [Accepted: 05/06/2021] [Indexed: 12/28/2022] Open
Abstract
The kidney proximal tubule (PT) efficiently recovers the low level of albumin and other proteins that normally escape the glomerular filtration barrier. Two large receptors, megalin and cubilin/amnionless (CUBAM), bind to and efficiently retrieve these predominantly low molecular-weight proteins via clathrin-mediated endocytosis. Studies in cell culture models suggest that PT cells may sense changes in shear stress to modulate recovery of filtered proteins in response to normal variations in filtration rate. Impairments in PT endocytic function lead to the excretion of filtered proteins into the urine (tubular proteinuria). Remarkably, when the glomerular filtration barrier is breached, the PT is able to recover excess albumin with a capacity that is orders of magnitude higher than normal. What mediates this excess capacity for albumin uptake under nephrotic conditions, and why doesn't it compensate to prevent tubular proteinuria? Here we propose an integrated new working model to describe the PT recovery of filtered proteins under normal and nephrotic states. We hypothesize that uptake via the fluid phase provides excess capacity to recover high concentrations of filtered proteins under nephrotic conditions. Further, concentration of tubular fluid along the tubule axis will enhance the efficiency of uptake in more distal regions of the PT. By contrast to cells where fluid phase and receptor-mediated uptake are independent pathways, expression of megalin is required to maintain apical endocytic pathway integrity and is essential for both uptake mechanisms. This model accounts for both the high-affinity and the high-capacity responses to filtration load in physiological and pathological states.
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Affiliation(s)
- Ora A Weisz
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA, 15261, USA
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12
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Gburek J, Konopska B, Gołąb K. Renal Handling of Albumin-From Early Findings to Current Concepts. Int J Mol Sci 2021; 22:ijms22115809. [PMID: 34071680 PMCID: PMC8199105 DOI: 10.3390/ijms22115809] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2021] [Revised: 05/20/2021] [Accepted: 05/25/2021] [Indexed: 12/29/2022] Open
Abstract
Albumin is the main protein of blood plasma, lymph, cerebrospinal and interstitial fluid. The protein participates in a variety of important biological functions, such as maintenance of proper colloidal osmotic pressure, transport of important metabolites and antioxidant action. Synthesis of albumin takes place mainly in the liver, and its catabolism occurs mostly in vascular endothelium of muscle, skin and liver, as well as in the kidney tubular epithelium. Long-lasting investigation in this area has delineated the principal route of its catabolism involving glomerular filtration, tubular endocytic uptake via the multiligand scavenger receptor tandem—megalin and cubilin-amnionless complex, as well as lysosomal degradation to amino acids. However, the research of the last few decades indicates that also additional mechanisms may operate in this process to some extent. Direct uptake of albumin in glomerular podocytes via receptor for crystallizable region of immunoglobulins (neonatal FC receptor) was demonstrated. Additionally, luminal recycling of short peptides into the bloodstream and/or back into tubular lumen or transcytosis of whole molecules was suggested. The article discusses the molecular aspects of these processes and presents the major findings and controversies arising in the light of the research concerning the last decade. Their better characterization is essential for further research into pathophysiology of proteinuric renal failure and development of effective therapeutic strategies.
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13
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Bryniarski MA, Zhao B, Chaves LD, Mikkelsen JH, Yee BM, Yacoub R, Shen S, Madsen M, Morris ME. Immunoglobulin G Is a Novel Substrate for the Endocytic Protein Megalin. AAPS JOURNAL 2021; 23:40. [PMID: 33677748 DOI: 10.1208/s12248-021-00557-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2020] [Accepted: 01/07/2021] [Indexed: 11/30/2022]
Abstract
Therapeutic immunoglobulin G (IgG) antibodies comprise the largest class of protein therapeutics. Several factors that influence their overall disposition have been well-characterized, including target-mediated mechanics and convective flow. What remains poorly defined is the potential for non-targeted entry into various tissues or cell types by means of uptake via cell surface receptors at those sites. Megalin and cubilin are large endocytic receptors whose cooperative function plays important physiological roles at the tissues in which they are expressed. One such example is the kidney, where loss of either results in significant declines in proximal tubule protein reabsorption. Due to their diverse ligand profile and broad tissue expression, megalin and cubilin represent potential candidates for receptor-mediated uptake of IgG into various epithelia. Therefore, the objective of the current work was to determine if IgG was a novel ligand of megalin and/or cubilin. Direct binding was measured for human IgG with both megalin and the cubilin/amnionless complex. Additional work focusing on the megalin-IgG interaction was then conducted to build upon these findings. Cell uptake studies using megalin ligands for competitive inhibition or proximal tubule cells stably transduced with megalin-targeted shRNA constructs supported a role for megalin in the endocytosis of human IgG. Furthermore, a pharmacokinetic study using transgenic mice with a kidney-specific mosaic knockout of megalin demonstrated increased urinary excretion of human IgG in megalin knockout mice when compared to wild-type controls. These findings indicate that megalin is capable of binding and internalizing IgG via a high affinity interaction.
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Affiliation(s)
- Mark A Bryniarski
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, University at Buffalo, 445 Pharmacy Building, Buffalo, New York, 14214-8033, USA
| | - Bei Zhao
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, University at Buffalo, 445 Pharmacy Building, Buffalo, New York, 14214-8033, USA
| | - Lee D Chaves
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, University at Buffalo, 445 Pharmacy Building, Buffalo, New York, 14214-8033, USA.,Department of Internal Medicine, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, Buffalo, New York, USA
| | | | - Benjamin M Yee
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, University at Buffalo, 445 Pharmacy Building, Buffalo, New York, 14214-8033, USA
| | - Rabi Yacoub
- Department of Internal Medicine, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, Buffalo, New York, USA
| | - Shichen Shen
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, University at Buffalo, 445 Pharmacy Building, Buffalo, New York, 14214-8033, USA
| | - Mette Madsen
- Department of Biomedicine, Aarhus University, 8000, Aarhus C., Denmark
| | - Marilyn E Morris
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, University at Buffalo, 445 Pharmacy Building, Buffalo, New York, 14214-8033, USA.
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14
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Huang LM, Mao JH. Glomerular podocyte dysfunction in inherited renal tubular disease. World J Pediatr 2021; 17:227-233. [PMID: 33625696 PMCID: PMC8253710 DOI: 10.1007/s12519-021-00417-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/08/2020] [Accepted: 01/20/2021] [Indexed: 11/26/2022]
Abstract
BACKGROUND Hereditary renal tubular disease can cause hypercalciuria, acid-base imbalance, hypokalemia, hypomagnesemia, rickets, kidney stones, etc. If these diseases are not diagnosed or treated in time, they can cause kidney damage and electrolyte disturbances, which can be detrimental to the maturation and development of the child. Glomerular involvement in renal tubular disease patients has only been considered recently. METHODS We screened 71 papers (including experimental research, clinical research, etc.) about Dent's disease, Gitelman syndrome, and cystinosis from PubMed, and made reference. RESULTS Glomerular disease was initially underestimated among the clinical signs of renal tubular disease or was treated merely as a consequence of the tubular damage. Renal tubular diseases affect glomerular podocytes through certain mechanisms resulting in functional damage, morphological changes, and glomerular lesions. CONCLUSIONS This article focuses on the progress of changes in glomerular podocyte function in Dent disease, Gitelman syndrome, and cystinosis for the purposes of facilitating clinically accurate diagnosis and scientific treatment and improving prognosis.
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Affiliation(s)
- Li-Min Huang
- Department of Nephrology, National Clinical Research Center for Child Health, The Children's Hospital, Zhejiang University School of Medicine, #57 Zhugan Lane, Hangzhou 310006, China
| | - Jian-Hua Mao
- Department of Nephrology, National Clinical Research Center for Child Health, The Children's Hospital, Zhejiang University School of Medicine, #57 Zhugan Lane, Hangzhou 310006, China.
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15
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Festa BP, Berquez M, Nieri D, Luciani A. Endolysosomal Disorders Affecting the Proximal Tubule of the Kidney: New Mechanistic Insights and Therapeutics. Rev Physiol Biochem Pharmacol 2021; 185:233-257. [PMID: 33649992 DOI: 10.1007/112_2020_57] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Epithelial cells that line the proximal tubule of the kidney rely on an intertwined ecosystem of vesicular membrane trafficking pathways to ensure the reabsorption of essential nutrients. To function effectively and to achieve homeostasis, these specialized cells require the sorting and recycling of a wide array of cell surface proteins within the endolysosomal network, including signaling receptors, nutrient transporters, ion channels, and polarity markers. The dysregulation of the endolysosomal system can lead to a generalized proximal tubule dysfunction, ultimately causing severe metabolic complications and kidney disease.In this chapter, we highlight the biological functions of the genes that code endolysosomal proteins from the perspective of understanding - and potentially reversing - the pathophysiology of endolysosomal disorders affecting the proximal tubule of the kidney. These insights might ultimately lead to potential treatments for currently intractable diseases and transform our ability to regulate kidney homeostasis and health.
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Affiliation(s)
- Beatrice Paola Festa
- Institute of Physiology, Mechanisms of Inherited Kidney Disorders Group, University of Zurich, Zurich, Switzerland
| | - Marine Berquez
- Institute of Physiology, Mechanisms of Inherited Kidney Disorders Group, University of Zurich, Zurich, Switzerland
| | - Daniela Nieri
- Institute of Physiology, Mechanisms of Inherited Kidney Disorders Group, University of Zurich, Zurich, Switzerland
| | - Alessandro Luciani
- Institute of Physiology, Mechanisms of Inherited Kidney Disorders Group, University of Zurich, Zurich, Switzerland.
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16
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Zhao J, Lei T, Zhang XJ, Yin TY, Wang XW, Liu SS. A vector whitefly endocytic receptor facilitates the entry of begomoviruses into its midgut cells via binding to virion capsid proteins. PLoS Pathog 2020; 16:e1009053. [PMID: 33270808 PMCID: PMC7714154 DOI: 10.1371/journal.ppat.1009053] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2020] [Accepted: 10/07/2020] [Indexed: 12/20/2022] Open
Abstract
Many circulative plant viruses transmitted by insect vectors are devastating to agriculture worldwide. The midgut wall of vector insects represents a major barrier and at the same time the key gate a circulative plant virus must cross for productive transmission. However, how these viruses enter insect midgut cells remains poorly understood. Here, we identified an endocytic receptor complex for begomoviruses in the midgut cells of their whitefly vector. Our results show that two whitefly proteins, BtCUBN and BtAMN, compose a receptor complex BtCubam, for which BtCUBN contributes a viral-binding region and BtAMN contributes to membrane anchorage. Begomoviruses appear to be internalized together with BtCubam via its interaction with the 12–19 CUB domains of BtCUBN via clathrin-dependent endocytosis. Functional analysis indicates that interruption of BtCUBN and BtAMN lead to reduction of virus acquisition and transmission by whitefly. In contrast, CUBN-begomovirus interaction was not observed in two non-competent whitefly-begomovirus combinations. These observations suggest a major role of the specific endocytic receptor in facilitating viral entry into vector midgut cells. Many viruses depend on insect vectors for transmission and spread. Following ingestion by insect vectors, many viruses need to circulate in the vector via a sequential path of stylet-midgut-haemolymph-salivary glands and are finally inoculated into plants with saliva secretion. To complete this journey, virions have to cross many physical/physiological barriers, of which the insect midgut wall represents the first and one of the major challenges. While this route of virus circulation has been known for a long time, the physiological and molecular mechanisms underlying the crossing of these barriers by viruses are poorly understood. Working with begomoviruses, a group of plant viruses of economic significance worldwide, and their insect vectors, the whiteflies of the Bemisia tabaci complex, we found that upon virus infection, two vector proteins, cubilin (CUBN) and amnionless (AMN), form a virus receptor complex to uptake the virions and assist them to move through the apical membrane of whitefly midgut cells via clathrin-dependent endocytosis. These novel findings contribute to a better understanding on the molecular mechanisms of insect transmission of circulative viruses.
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Affiliation(s)
- Jing Zhao
- Ministry of Agriculture Key Laboratory of Molecular Biology of Crop Pathogens and Insects, Institute of Insect Sciences, Zhejiang University, Hangzhou, China
| | - Teng Lei
- Ministry of Agriculture Key Laboratory of Molecular Biology of Crop Pathogens and Insects, Institute of Insect Sciences, Zhejiang University, Hangzhou, China
| | - Xin-Jia Zhang
- Ministry of Agriculture Key Laboratory of Molecular Biology of Crop Pathogens and Insects, Institute of Insect Sciences, Zhejiang University, Hangzhou, China
| | - Tian-Yan Yin
- Ministry of Agriculture Key Laboratory of Molecular Biology of Crop Pathogens and Insects, Institute of Insect Sciences, Zhejiang University, Hangzhou, China
| | - Xiao-Wei Wang
- Ministry of Agriculture Key Laboratory of Molecular Biology of Crop Pathogens and Insects, Institute of Insect Sciences, Zhejiang University, Hangzhou, China
| | - Shu-Sheng Liu
- Ministry of Agriculture Key Laboratory of Molecular Biology of Crop Pathogens and Insects, Institute of Insect Sciences, Zhejiang University, Hangzhou, China
- * E-mail:
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17
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Shipman KE, Weisz OA. Making a Dent in Dent Disease. FUNCTION (OXFORD, ENGLAND) 2020; 1:zqaa017. [PMID: 33015630 PMCID: PMC7519470 DOI: 10.1093/function/zqaa017] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/14/2020] [Revised: 09/04/2020] [Accepted: 09/09/2020] [Indexed: 01/06/2023]
Abstract
Dent disease (DD) is a rare kidney disorder caused by mutations in the Cl-/H+ exchanger ClC-5. Extensive physiologic characterization of the transporter has begun to illuminate its role in endosomal ion homeostasis. Nevertheless, we have yet to understand how loss of ClC-5 function in the kidney proximal tubule impairs membrane traffic of megalin and cubilin receptors to cause the low molecular weight proteinuria characteristic of DD. This review identifies open questions that remain to be answered, evaluates the current literature addressing these questions, and suggests new testable models that may link loss of ClC-5 function to tubular proteinuria in DD.
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Affiliation(s)
- Katherine E Shipman
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
| | - Ora A Weisz
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA,Address correspondence to O.A.W. (e-mail: )
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18
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Bryniarski MA, Yee BM, Chaves LD, Stahura CM, Yacoub R, Morris ME. Megalin-mediated albumin endocytosis in cultured murine mesangial cells. Biochem Biophys Res Commun 2020; 529:740-746. [PMID: 32736701 DOI: 10.1016/j.bbrc.2020.05.166] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2020] [Accepted: 05/22/2020] [Indexed: 12/25/2022]
Abstract
Endocytosis by podocytes is gaining increased attention as a biologic means of removing large proteins such as serum albumin from the glomerular barrier. Some of this function has been attributed to the megalin/cubilin (Lrp2/Cubn) receptor complex and the albumin recycling protein FcRn (Fcgrt). However, whether other glomerular cells possess the potential to perform this same phenomenon or express these proteins remains uncharacterized. Mesangial cells are uniquely positioned in glomeruli and represent a cell type capable of performing several diverse functions. Here, the expression of megalin and FcRn in murine mesangial cells along with the megalin adaptor protein Dab-2 (Dab2) was shown for the first time. Cubilin mRNA expression was detected, but the absence of the cubilin partner amnionless (Amn) suggested that cubilin is minimally functional, if at all, in these cells. Mesangial cell endocytosis of albumin was characterized and shown to involve a receptor-mediated process. Albumin endocytosis was significantly impaired (p < 0.01) under inducible megalin knockdown conditions in stably transduced mesangial cells. The current work provides both the novel identification of megalin and FcRn in mesangial cells and the functional demonstration of megalin-mediated albumin endocytosis.
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Affiliation(s)
- Mark A Bryniarski
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, University at Buffalo, 303 Pharmacy Building, Buffalo, NY, 14214, USA
| | - Benjamin M Yee
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, University at Buffalo, 303 Pharmacy Building, Buffalo, NY, 14214, USA
| | - Lee D Chaves
- Department of Internal Medicine, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, 875 Ellicott St, Buffalo, NY, 14214, USA
| | - Corrine M Stahura
- Department of Internal Medicine, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, 875 Ellicott St, Buffalo, NY, 14214, USA
| | - Rabi Yacoub
- Department of Internal Medicine, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, 875 Ellicott St, Buffalo, NY, 14214, USA
| | - Marilyn E Morris
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, University at Buffalo, 303 Pharmacy Building, Buffalo, NY, 14214, USA.
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19
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Urae S, Harita Y, Udagawa T, Ode KL, Nagahama M, Kajiho Y, Kanda S, Saito A, Ueda HR, Nangaku M, Oka A. A cellular model of albumin endocytosis uncovers a link between membrane and nuclear proteins. J Cell Sci 2020; 133:jcs242859. [PMID: 32482797 DOI: 10.1242/jcs.242859] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2019] [Accepted: 05/20/2020] [Indexed: 12/21/2022] Open
Abstract
Cubilin (CUBN) and amnionless (AMN), expressed in kidney and intestine, form a multiligand receptor complex called CUBAM that plays a crucial role in albumin absorption. To date, the mechanism of albumin endocytosis mediated by CUBAM remains to be elucidated. Here, we describe a quantitative assay to evaluate albumin uptake by CUBAM using cells expressing full-length CUBN and elucidate the crucial roles of the C-terminal part of CUBN and the endocytosis signal motifs of AMN in albumin endocytosis. We also demonstrate that nuclear valosin-containing protein-like 2 (NVL2), an interacting protein of AMN, is involved in this process. Although NVL2 was mainly localized in the nucleolus in cells without AMN expression, it was translocated to the extranuclear compartment when coexpressed with AMN. NVL2 knockdown significantly impaired internalization of the CUBN-albumin complex in cultured cells, demonstrating an involvement of NVL2 in endocytic regulation. These findings uncover a link between membrane and nucleolar proteins that is involved in endocytic processes.
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Affiliation(s)
- Seiya Urae
- Department of Pediatrics, Graduate School of Medicine, The University of Tokyo, Bunkyo-ku, Tokyo 113-8655, Japan
- Division of Nephrology and Endocrinology, The University of Tokyo, Bunkyo-ku, Tokyo 113-8655, Japan
| | - Yutaka Harita
- Department of Pediatrics, Graduate School of Medicine, The University of Tokyo, Bunkyo-ku, Tokyo 113-8655, Japan
| | - Tomohiro Udagawa
- Department of Pediatrics and Developmental Biology, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Bunkyo-ku, Tokyo 113-8510, Japan
| | - Koji L Ode
- Department of Systems Pharmacology, Graduate School of Medicine, The University of Tokyo, Bunkyo-ku, Tokyo 113-8654, Japan
| | - Masami Nagahama
- Laboratory of Molecular and Cellular Biochemistry, Meiji Pharmaceutical University, Kiyose-shi, Tokyo 204-8588, Japan
| | - Yuko Kajiho
- Department of Pediatrics, Graduate School of Medicine, The University of Tokyo, Bunkyo-ku, Tokyo 113-8655, Japan
| | - Shoichiro Kanda
- Department of Pediatrics, Graduate School of Medicine, The University of Tokyo, Bunkyo-ku, Tokyo 113-8655, Japan
| | - Akihiko Saito
- Department of Applied Molecular Medicine, Niigata University Graduate School of Medical and Dental Sciences, Niigata-shi, Niigata 951-8510, Japan
| | - Hiroki R Ueda
- Department of Systems Pharmacology, Graduate School of Medicine, The University of Tokyo, Bunkyo-ku, Tokyo 113-8654, Japan
- Laboratory for Synthetic Biology, RIKEN Center for Biosystems Dynamics Research, Wako-shi, Saitama 351-0198, Japan
| | - Masaomi Nangaku
- Division of Nephrology and Endocrinology, The University of Tokyo, Bunkyo-ku, Tokyo 113-8655, Japan
| | - Akira Oka
- Department of Pediatrics, Graduate School of Medicine, The University of Tokyo, Bunkyo-ku, Tokyo 113-8655, Japan
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20
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Ren Q, Weyer K, Rbaibi Y, Long KR, Tan RJ, Nielsen R, Christensen EI, Baty CJ, Kashlan OB, Weisz OA. Distinct functions of megalin and cubilin receptors in recovery of normal and nephrotic levels of filtered albumin. Am J Physiol Renal Physiol 2020; 318:F1284-F1294. [PMID: 32200668 DOI: 10.1152/ajprenal.00030.2020] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Proximal tubule (PT) cells express a single saturable albumin-binding site whose affinity matches the estimated tubular concentration of albumin; however, albumin uptake capacity is greatly increased under nephrotic conditions. Deciphering the individual contributions of megalin and cubilin to the uptake of normal and nephrotic levels of albumin is impossible in vivo, as knockout of megalin in mice globally disrupts PT endocytic uptake. We quantified concentration-dependent albumin uptake in an optimized opossum kidney cell culture model and fit the kinetic profiles to identify albumin-binding affinities and uptake capacities. Mathematical deconvolution fit best to a three-component model that included saturable high- and low-affinity uptake sites for albumin and underlying nonsaturable uptake consistent with passive uptake of albumin in the fluid phase. Knockdown of cubilin or its chaperone amnionless selectively reduced the binding capacity of the high-affinity site, whereas knockdown of megalin impacted the low-affinity site. Knockdown of disabled-2 decreased the capacities of both binding sites. Additionally, knockdown of megalin or disabled-2 profoundly inhibited the uptake of a fluid phase marker, with cubilin knockdown having a more modest effect. We propose a novel model for albumin retrieval along the PT in which cubilin and megalin receptors have different functions in recovering filtered albumin in proximal tubule cells. Cubilin binding to albumin is tuned to capture normally filtered levels of the protein. In contrast, megalin binding to albumin is of lower affinity, and its expression is also essential for enabling the recovery of high concentrations of albumin in the fluid phase.
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Affiliation(s)
- Qidong Ren
- School of Medicine, Tsinghua University, Beijing, China.,Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Kathrin Weyer
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
| | - Youssef Rbaibi
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Kimberly R Long
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Roderick J Tan
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Rikke Nielsen
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
| | | | - Catherine J Baty
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Ossama B Kashlan
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Ora A Weisz
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
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21
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Protective Role of Vitamin D in Renal Tubulopathies. Metabolites 2020; 10:metabo10030115. [PMID: 32204545 PMCID: PMC7142711 DOI: 10.3390/metabo10030115] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2020] [Revised: 03/13/2020] [Accepted: 03/17/2020] [Indexed: 02/06/2023] Open
Abstract
Vitamin D is tightly linked with renal tubular homeostasis: the mitochondria of proximal convoluted tubule cells are the production site of 1α,25-dihydroxyvitamin D3. Patients with renal impairment or tubular injury often suffer from chronic inflammation. This alteration comes from oxidative stress, acidosis, decreased clearance of inflammatory cytokines and stimulation of inflammatory factors. The challenge is to find the right formula for each patient to correctly modulate the landscape of treatment and preserve the essential functions of the organism without perturbating its homeostasis. The complexity of the counter-regulation mechanisms and the different axis involved in the Vitamin D equilibrium pose a major issue on Vitamin D as a potential effective anti-inflammatory drug. The therapeutic use of this compound should be able to inhibit the development of inflammation without interfering with normal homeostasis. Megalin-Cubilin-Amnionless and the FGF23-Klotho axis represent two Vitamin D-linked mechanisms that could modulate and ameliorate the damage response at the renal tubular level, balancing Vitamin D therapy with an effect potent enough to contrast the inflammatory cascades, but which avoids potential severe side effects.
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22
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van der Wijst J, Belge H, Bindels RJM, Devuyst O. Learning Physiology From Inherited Kidney Disorders. Physiol Rev 2019; 99:1575-1653. [PMID: 31215303 DOI: 10.1152/physrev.00008.2018] [Citation(s) in RCA: 56] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The identification of genes causing inherited kidney diseases yielded crucial insights in the molecular basis of disease and improved our understanding of physiological processes that operate in the kidney. Monogenic kidney disorders are caused by mutations in genes coding for a large variety of proteins including receptors, channels and transporters, enzymes, transcription factors, and structural components, operating in specialized cell types that perform highly regulated homeostatic functions. Common variants in some of these genes are also associated with complex traits, as evidenced by genome-wide association studies in the general population. In this review, we discuss how the molecular genetics of inherited disorders affecting different tubular segments of the nephron improved our understanding of various transport processes and of their involvement in homeostasis, while providing novel therapeutic targets. These include inherited disorders causing a dysfunction of the proximal tubule (renal Fanconi syndrome), with emphasis on epithelial differentiation and receptor-mediated endocytosis, or affecting the reabsorption of glucose, the handling of uric acid, and the reabsorption of sodium, calcium, and magnesium along the kidney tubule.
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Affiliation(s)
- Jenny van der Wijst
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center , Nijmegen , The Netherlands ; Institute of Physiology, University of Zurich , Zurich , Switzerland ; and Division of Nephrology, Institute of Experimental and Clinical Research (IREC), Medical School, Université catholique de Louvain, Brussels, Belgium
| | - Hendrica Belge
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center , Nijmegen , The Netherlands ; Institute of Physiology, University of Zurich , Zurich , Switzerland ; and Division of Nephrology, Institute of Experimental and Clinical Research (IREC), Medical School, Université catholique de Louvain, Brussels, Belgium
| | - René J M Bindels
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center , Nijmegen , The Netherlands ; Institute of Physiology, University of Zurich , Zurich , Switzerland ; and Division of Nephrology, Institute of Experimental and Clinical Research (IREC), Medical School, Université catholique de Louvain, Brussels, Belgium
| | - Olivier Devuyst
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center , Nijmegen , The Netherlands ; Institute of Physiology, University of Zurich , Zurich , Switzerland ; and Division of Nephrology, Institute of Experimental and Clinical Research (IREC), Medical School, Université catholique de Louvain, Brussels, Belgium
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23
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Perea-Gomez A, Cases O, Lelièvre V, Pulina MV, Collignon J, Hadjantonakis AK, Kozyraki R. Loss of Cubilin, the intrinsic factor-vitamin B12 receptor, impairs visceral endoderm endocytosis and endodermal patterning in the mouse. Sci Rep 2019; 9:10168. [PMID: 31308417 PMCID: PMC6629654 DOI: 10.1038/s41598-019-46559-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2019] [Accepted: 06/26/2019] [Indexed: 11/17/2022] Open
Abstract
The visceral endoderm is a polarized epithelial monolayer necessary for early embryonic development in rodents. A key feature of this epithelium is an active endocytosis and degradation of maternal nutrients, in addition to being the source of various signaling molecules or inhibitors required for the differentiation and patterning of adjacent embryonic tissues. Endocytosis across the visceral endoderm epithelium involves specific cell surface receptors and an extensive sub-membrane vesicular system with numerous apical vacuoles/lysosomes. We previously reported that Cubilin, the endocytic receptor for intrinsic factor-vitamin B12, albumin and apolipoproteinA-I/HDL allows maternal nutrient uptake by the visceral endoderm. In the present study, we show that the germline ablation of Cubilin impairs endodermal and mesodermal patterning, and results in developmental arrest at gastrulation. Notably, visceral endoderm dispersal is impeded in Cubilin null embryos. We further confirm the essential role of Cubilin in nutrient internalization by the early visceral endoderm and highlight its involvement in the formation of apical vacuoles. Our results reveal essential roles for Cubilin in early embryonic development, and suggest that in addition to its nutritive function, Cubilin sustains signaling pathways involved in embryonic differentiation and patterning.
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Affiliation(s)
- Aitana Perea-Gomez
- Institut Jacques Monod, Université de Paris, CNRS, Paris, F-75013, France.,Université Côte d'Azur, CNRS, Inserm, iBV, France
| | - Olivier Cases
- Centre de Recherche des Cordeliers, INSERM, UMRS-1138, Université de Paris, Paris, F-75006, France
| | - Vincent Lelièvre
- CNRS UPR 3212, INCI, 5 rue Blaise Pascal, F-67084, Strasbourg, France
| | - Maria V Pulina
- Developmental Biology Program, Sloan Kettering Institute, Memorial Sloan Kettering Cancer Center, New York, USA.,The Rockefeller University, New York, USA
| | - Jérôme Collignon
- Institut Jacques Monod, Université de Paris, CNRS, Paris, F-75013, France
| | - Anna-Katerina Hadjantonakis
- Developmental Biology Program, Sloan Kettering Institute, Memorial Sloan Kettering Cancer Center, New York, USA
| | - Renata Kozyraki
- Centre de Recherche des Cordeliers, INSERM, UMRS-1138, Université de Paris, Paris, F-75006, France.
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24
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Structural assembly of the megadalton-sized receptor for intestinal vitamin B 12 uptake and kidney protein reabsorption. Nat Commun 2018; 9:5204. [PMID: 30523278 PMCID: PMC6283879 DOI: 10.1038/s41467-018-07468-4] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2018] [Accepted: 11/01/2018] [Indexed: 11/08/2022] Open
Abstract
The endocytic receptor cubam formed by the 460-kDa protein cubilin and the 45-kDa transmembrane protein amnionless (AMN), is essential for intestinal vitamin B12 (B12) uptake and for protein (e.g. albumin) reabsorption from the kidney filtrate. Loss of function of any of the two components ultimately leads to serious B12 deficiency and urinary protein loss in humans (Imerslund-Gräsbeck’s syndrome, IGS). Here, we present the crystal structure of AMN in complex with the amino-terminal region of cubilin, revealing a sophisticated assembly of three cubilin subunits combining into a single intertwined β-helix domain that docks to a corresponding three-faced β-helix domain in AMN. This β-helix-β-helix association thereby anchors three ligand-binding cubilin subunits to the transmembrane AMN. Electron microscopy of full-length cubam reveals a 700–800 Å long tree-like structure with the potential of dimerization into an even larger complex. Furthermore, effects of known human mutations causing IGS are explained by the structural information. Cubilin and the transmembrane protein amnionless (AMN) form the endocytic receptor cubam that is essential for intestinal vitamin B12 uptake. Here the authors present the 2.3 Å crystal structure of AMN in complex with the amino-terminal region of cubilin and discuss cubam architecture and disease causing mutations.
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25
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Abstract
Phosphoinositides (PIs) play pivotal roles in the regulation of many biological processes. The quality and quantity of PIs is regulated in time and space by the activity of PI kinases and PI phosphatases. The number of PI-metabolizing enzymes exceeds the number of PIs with, in many cases, more than one enzyme controlling the same biochemical step. This would suggest that the PI system has an intrinsic ability to buffer and compensate for the absence of a specific enzymatic activity. However, there are several examples of severe inherited human diseases caused by mutations in one of the PI enzymes, although other enzymes with the same activity are fully functional. The kidney depends strictly on PIs for physiological processes, such as cell polarization, filtration, solute reabsorption, and signal transduction. Indeed, alteration of the PI system in the kidney very often results in pathological conditions, both inherited and acquired. Most of the knowledge of the roles that PIs play in the kidney comes from the study of KO animal models for genes encoding PI enzymes and from the study of human genetic diseases, such as Lowe syndrome/Dent disease 2 and Joubert syndrome, caused by mutations in the genes encoding the PI phosphatases, OCRL and INPP5E, respectively.
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Affiliation(s)
- Leopoldo Staiano
- Telethon Institute of Genetics and Medicine, 80078 Pozzuoli, Italy
| | - Maria Antonietta De Matteis
- Telethon Institute of Genetics and Medicine, 80078 Pozzuoli, Italy .,University of Naples Federico II, 80131 Naples, Italy
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26
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Kozyraki R, Cases O. Cubilin, the Intrinsic Factor-Vitamin B12 Receptor in Development and Disease. Curr Med Chem 2018; 27:3123-3150. [PMID: 30295181 DOI: 10.2174/0929867325666181008143945] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2018] [Revised: 08/11/2018] [Accepted: 08/21/2018] [Indexed: 12/29/2022]
Abstract
Gp280/Intrinsic factor-vitamin B12 receptor/Cubilin (CUBN) is a large endocytic receptor serving multiple functions in vitamin B12 homeostasis, renal reabsorption of protein or toxic substances including albumin, vitamin D-binding protein or cadmium. Cubilin is a peripheral membrane protein consisting of 8 Epidermal Growth Factor (EGF)-like repeats and 27 CUB (defined as Complement C1r/C1s, Uegf, BMP1) domains. This structurally unique protein interacts with at least two molecular partners, Amnionless (AMN) and Lrp2/Megalin. AMN is involved in appropriate plasma membrane transport of Cubilin whereas Lrp2 is essential for efficient internalization of Cubilin and its ligands. Observations gleaned from animal models with Cubn deficiency or human diseases demonstrate the importance of this protein. In this review addressed to basic research and medical scientists, we summarize currently available data on Cubilin and its implication in renal and intestinal biology. We also discuss the role of Cubilin as a modulator of Fgf8 signaling during embryonic development and propose that the Cubilin-Fgf8 interaction may be relevant in human pathology, including in cancer progression, heart or neural tube defects. We finally provide experimental elements suggesting that some aspects of Cubilin physiology might be relevant in drug design.
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Affiliation(s)
- Renata Kozyraki
- INSERM UMRS 1138, Centre de Recherche des Cordeliers, Paris-Diderot University, Paris, France
| | - Olivier Cases
- INSERM UMRS 1138, Centre de Recherche des Cordeliers, Paris-Diderot University, Paris, France
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27
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Amnionless-mediated glycosylation is crucial for cell surface targeting of cubilin in renal and intestinal cells. Sci Rep 2018; 8:2351. [PMID: 29402915 PMCID: PMC5799345 DOI: 10.1038/s41598-018-20731-4] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2017] [Accepted: 01/23/2018] [Indexed: 11/10/2022] Open
Abstract
Mutations in either cubilin (CUBN) or amnionless (AMN) genes cause Imerslund–Gräsbeck syndrome (IGS), a hereditary disease characterised by anaemia attributed to selective intestinal malabsorption of cobalamin and low-molecular weight proteinuria. Although cubilin protein does not have a transmembrane segment, it functions as a multi-ligand receptor by binding to the transmembrane protein, amnionless. We established a system to quantitatively analyse membrane targeting of the protein complex in cultured renal and intestinal cells and analysed the pathogenic mechanisms of mutations found in IGS patients. A novel CUBN mutation, several previously reported CUBN missense mutations and all previously reported AMN missense mutations resulted in endoplasmic reticulum (ER) retention and completely inhibited amnionless-dependent plasma membrane expression of cubilin. The ER retention of cubilin and amnionless was confirmed in renal proximal tubular cells of a patient with IGS. Notably, the interaction between cubilin and amnionless was not sufficient, but amnionless-mediated glycosylation of cubilin was necessary for their surface expression. Quantitative mass spectrometry and mutagenesis demonstrated that N-linked glycosylation of at least 4 residues of cubilin protein was required for its surface targeting. These results delineated the molecular mechanisms of membrane trafficking of cubilin in renal and intestinal cells.
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Zeng B, Chen GL, Garcia-Vaz E, Bhandari S, Daskoulidou N, Berglund LM, Jiang H, Hallett T, Zhou LP, Huang L, Xu ZH, Nair V, Nelson RG, Ju W, Kretzler M, Atkin SL, Gomez MF, Xu SZ. ORAI channels are critical for receptor-mediated endocytosis of albumin. Nat Commun 2017; 8:1920. [PMID: 29203863 PMCID: PMC5714946 DOI: 10.1038/s41467-017-02094-y] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2016] [Accepted: 11/06/2017] [Indexed: 01/15/2023] Open
Abstract
Impaired albumin reabsorption by proximal tubular epithelial cells (PTECs) has been highlighted in diabetic nephropathy (DN), but little is known about the underlying molecular mechanisms. Here we find that ORAI1-3, are preferentially expressed in PTECs and downregulated in patients with DN. Hyperglycemia or blockade of insulin signaling reduces the expression of ORAI1-3. Inhibition of ORAI channels by BTP2 and diethylstilbestrol or silencing of ORAI expression impairs albumin uptake. Transgenic mice expressing a dominant-negative Orai1 mutant (E108Q) increases albuminuria, and in vivo injection of BTP2 exacerbates albuminuria in streptozotocin-induced and Akita diabetic mice. The albumin endocytosis is Ca2+-dependent and accompanied by ORAI1 internalization. Amnionless (AMN) associates with ORAIs and forms STIM/ORAI/AMN complexes after Ca2+ store depletion. STIM1/ORAI1 colocalizes with clathrin, but not with caveolin, at the apical membrane of PTECs, which determines clathrin-mediated endocytosis. These findings provide insights into the mechanisms of protein reabsorption and potential targets for treating diabetic proteinuria. Patients with diabetic nephropathy suffer from impaired albumin reabsorption by proximal tubular epithelial cells. Here authors use diabetic and transgenic mouse models and in vitro models to show the cause for this lies in the down regulation and internalization of the ion channels, ORAI1-3.
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Affiliation(s)
- Bo Zeng
- Centre for Cardiovascular and Metabolic Research, Hull York Medical School, University of Hull, Hull, HU6 7RX, UK. .,Key Laboratory of Medical Electrophysiology, Ministry of Education, and Institute of Cardiovascular Research, Southwest Medical University, Luzhou, 646000, China.
| | - Gui-Lan Chen
- Centre for Cardiovascular and Metabolic Research, Hull York Medical School, University of Hull, Hull, HU6 7RX, UK.,Key Laboratory of Medical Electrophysiology, Ministry of Education, and Institute of Cardiovascular Research, Southwest Medical University, Luzhou, 646000, China
| | - Eliana Garcia-Vaz
- Department of Clinical Sciences in Malmö, Lund University Diabetes Centre, Lund University, Malmö, 214 28 Malmö, Sweden
| | - Sunil Bhandari
- Department of Renal Medicine and Hull York Medical School, Hull Royal Infirmary, Hull and East Yorkshire Hospitals NHS Trust, Hull, HU3 2JZ, UK
| | - Nikoleta Daskoulidou
- Centre for Cardiovascular and Metabolic Research, Hull York Medical School, University of Hull, Hull, HU6 7RX, UK
| | - Lisa M Berglund
- Department of Clinical Sciences in Malmö, Lund University Diabetes Centre, Lund University, Malmö, 214 28 Malmö, Sweden
| | - Hongni Jiang
- Centre for Cardiovascular and Metabolic Research, Hull York Medical School, University of Hull, Hull, HU6 7RX, UK
| | - Thomas Hallett
- Centre for Cardiovascular and Metabolic Research, Hull York Medical School, University of Hull, Hull, HU6 7RX, UK
| | - Lu-Ping Zhou
- Key Laboratory of Medical Electrophysiology, Ministry of Education, and Institute of Cardiovascular Research, Southwest Medical University, Luzhou, 646000, China
| | - Li Huang
- Key Laboratory of Medical Electrophysiology, Ministry of Education, and Institute of Cardiovascular Research, Southwest Medical University, Luzhou, 646000, China
| | - Zi-Hao Xu
- Key Laboratory of Medical Electrophysiology, Ministry of Education, and Institute of Cardiovascular Research, Southwest Medical University, Luzhou, 646000, China
| | - Viji Nair
- Department of Internal Medicine & Department of Computational Medicine and Bioinformatics, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Robert G Nelson
- Chronic Kidney Disease Section, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Phoenix, AZ, 85014, USA
| | - Wenjun Ju
- Department of Internal Medicine & Department of Computational Medicine and Bioinformatics, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Matthias Kretzler
- Department of Internal Medicine & Department of Computational Medicine and Bioinformatics, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Stephen L Atkin
- Centre for Cardiovascular and Metabolic Research, Hull York Medical School, University of Hull, Hull, HU6 7RX, UK.,Weill Cornell Medical College Qatar, PO Box, 24144, Doha, Qatar
| | - Maria F Gomez
- Department of Clinical Sciences in Malmö, Lund University Diabetes Centre, Lund University, Malmö, 214 28 Malmö, Sweden
| | - Shang-Zhong Xu
- Centre for Cardiovascular and Metabolic Research, Hull York Medical School, University of Hull, Hull, HU6 7RX, UK.
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29
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Fatah H, Benfaed N, Chana RS, Chunara MH, Barratt J, Baines RJ, Brunskill NJ. Reduced proximal tubular expression of protein endocytic receptors in proteinuria is associated with urinary receptor shedding. Nephrol Dial Transplant 2017; 33:934-943. [DOI: 10.1093/ndt/gfx321] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2017] [Accepted: 10/01/2017] [Indexed: 02/06/2023] Open
Affiliation(s)
- Hiwa Fatah
- Department of Infection Immunity and Inflammation, University of Leicester, Leicester, UK
| | - Nura Benfaed
- Department of Infection Immunity and Inflammation, University of Leicester, Leicester, UK
| | - Ravinder S Chana
- Department of Infection Immunity and Inflammation, University of Leicester, Leicester, UK
| | - Mohamed H Chunara
- Department of Infection Immunity and Inflammation, University of Leicester, Leicester, UK
| | - Jonathan Barratt
- Department of Infection Immunity and Inflammation, University of Leicester, Leicester, UK
- Department of Nephrology, Leicester General Hospital, Leicester, UK
| | - Richard J Baines
- Department of Infection Immunity and Inflammation, University of Leicester, Leicester, UK
- Department of Nephrology, Leicester General Hospital, Leicester, UK
| | - Nigel J Brunskill
- Department of Infection Immunity and Inflammation, University of Leicester, Leicester, UK
- Department of Nephrology, Leicester General Hospital, Leicester, UK
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30
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Gianesello L, Priante G, Ceol M, Radu CM, Saleem MA, Simioni P, Terrin L, Anglani F, Del Prete D. Albumin uptake in human podocytes: a possible role for the cubilin-amnionless (CUBAM) complex. Sci Rep 2017; 7:13705. [PMID: 29057905 PMCID: PMC5651885 DOI: 10.1038/s41598-017-13789-z] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2017] [Accepted: 10/02/2017] [Indexed: 12/23/2022] Open
Abstract
Albumin re-uptake is a receptor-mediated pathway located in renal proximal tubuli. There is increasing evidence of glomerular protein handling by podocytes, but little is known about the mechanism behind this process. In this study, we found that human podocytes in vitro are committed to internalizing albumin through a receptor-mediated mechanism even after exposure to low doses of albumin. We show that these cells express cubilin, megalin, ClC-5, amnionless and Dab2, which are partners in the tubular machinery. Exposing human podocytes to albumin overload prompted an increase in CUBILIN, AMNIONLESS and CLCN5 gene expression. Inhibiting cubilin led to a reduction in albumin uptake, highlighting its importance in this mechanism. We demonstrated that human podocytes are committed to performing endocytosis via a receptor-mediated mechanism even in the presence of low doses of albumin. We also disclosed that protein overload first acts on the expression of the cubilin-amnionless (CUBAM) complex in these cells, then involves the ClC-5 channel, providing the first evidence for a possible role of the CUBAM complex in albumin endocytosis in human podocytes.
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Affiliation(s)
- Lisa Gianesello
- Clinical Nephrology, Department of Medicine - DIMED, University of Padua, 35129, Padua, Italy
| | - Giovanna Priante
- Clinical Nephrology, Department of Medicine - DIMED, University of Padua, 35129, Padua, Italy
| | - Monica Ceol
- Clinical Nephrology, Department of Medicine - DIMED, University of Padua, 35129, Padua, Italy
| | - Claudia M Radu
- Thrombotic and Hemorrhagic Diseases Unit, Department of Medicine - DIMED, University of Padua, 35129, Padua, Italy
| | - Moin A Saleem
- Academic and Children's Renal Unit, Dorothy Hodgkin Building, BS8 1TH, Bristol, United Kingdom
| | - Paolo Simioni
- Thrombotic and Hemorrhagic Diseases Unit, Department of Medicine - DIMED, University of Padua, 35129, Padua, Italy
| | - Liliana Terrin
- Clinical Nephrology, Department of Medicine - DIMED, University of Padua, 35129, Padua, Italy
| | - Franca Anglani
- Clinical Nephrology, Department of Medicine - DIMED, University of Padua, 35129, Padua, Italy
| | - Dorella Del Prete
- Clinical Nephrology, Department of Medicine - DIMED, University of Padua, 35129, Padua, Italy.
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31
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Seliverstova EV, Prutskova NP. Tubular protein uptake pattern in the frog model (Rana temporaria): The effect of previous protein loading. J EVOL BIOCHEM PHYS+ 2017. [DOI: 10.1134/s0022093017030061] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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32
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Abstract
Lowe syndrome is an X-linked disease that is characterized by congenital cataracts, central hypotonia, intellectual disability and renal Fanconi syndrome. The disease is caused by mutations in OCRL, which encodes an inositol polyphosphate 5-phosphatase (OCRL) that acts on phosphoinositides - quantitatively minor constituents of cell membranes that are nonetheless pivotal regulators of intracellular trafficking. In this Review we summarize the considerable progress made over the past decade in understanding the cellular roles of OCRL in regulating phosphoinositide balance along the endolysosomal pathway, a fundamental system for the reabsorption of proteins and solutes by proximal tubular cells. We discuss how studies of OCRL have led to important discoveries about the basic mechanisms of membrane trafficking and describe the key features and limitations of the currently available animal models of Lowe syndrome. Mutations in OCRL can also give rise to a milder pathology, Dent disease 2, which is characterized by renal Fanconi syndrome in the absence of extrarenal pathologies. Understanding how mutations in OCRL give rise to two clinical entities with differing extrarenal manifestations represents an opportunity to identify molecular pathways that could be targeted to develop treatments for these conditions.
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33
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Nielsen R, Christensen EI, Birn H. Megalin and cubilin in proximal tubule protein reabsorption: from experimental models to human disease. Kidney Int 2017; 89:58-67. [PMID: 26759048 DOI: 10.1016/j.kint.2015.11.007] [Citation(s) in RCA: 298] [Impact Index Per Article: 42.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2015] [Revised: 08/17/2015] [Accepted: 08/19/2015] [Indexed: 01/19/2023]
Abstract
Proximal tubule protein uptake is mediated by 2 receptors, megalin and cubilin. These receptors rescue a variety of filtered ligands, including biomarkers, essential vitamins, and hormones. Receptor gene knockout animal models have identified important functions of the receptors and have established their essential role in modulating urinary protein excretion. Rare genetic syndromes associated with dysfunction of these receptors have been identified and characterized, providing additional information on the importance of these receptors in humans. Using various disease models in combination with receptor gene knockout, the implications of receptor dysfunction in acute and chronic kidney injury have been explored and have pointed to potential new roles of these receptors. Based on data from animal models, this paper will review current knowledge on proximal tubule endocytic receptor function and regulation, and their role in renal development, protein reabsorption, albumin uptake, and normal renal physiology. These findings have implications for the pathophysiology and diagnosis of proteinuric renal diseases. We will examine the limitations of the different models and compare the findings to phenotypic observations in inherited human disorders associated with receptor dysfunction. Furthermore, evidence from receptor knockout mouse models as well as human observations suggesting a role of protein receptors for renal disease will be discussed in light of conditions such as chronic kidney disease, diabetes, and hypertension.
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Affiliation(s)
- Rikke Nielsen
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
| | | | - Henrik Birn
- Department of Biomedicine, Aarhus University, Aarhus, Denmark; Department of Renal Medicine, Aarhus University Hospital, Aarhus, Denmark.
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34
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Prutskova NP, Seliverstova EV. Effect of different proteins on reabsorption of yellow fluorescent protein in the kidney of the brown frog Rana temporaria. J EVOL BIOCHEM PHYS+ 2016. [DOI: 10.1134/s0022093016030078] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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35
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Schneider WJ. Lipid transport to avian oocytes and to the developing embryo. J Biomed Res 2015; 30:174-80. [PMID: 26585559 PMCID: PMC4885163 DOI: 10.7555/jbr.30.20150048] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2015] [Revised: 05/12/2015] [Accepted: 07/03/2015] [Indexed: 11/25/2022] Open
Abstract
Studies of receptor-mediated lipoprotein metabolic pathways in avian species have revealed that physiological intricacies of specific cell types are highly analogous to those in mammals. A prime example for the power of comparative studies across different animal kingdoms, elucidated in the chicken, is that the expression of different lipoprotein receptors in somatic cells and oocytes are the key to oocyte growth. In avian species, yolk precursor transport from the hen's liver to rapidly growing oocytes and the subsequent transfer of yolk nutrients via the yolk sac to the developing embryo are highly efficient processes. Oocytes grow from a diameter of 5 mm to 2.5-3 cm in only 7 days, and the yolk sac transfers nutrients from the yolk stored in the mature oocyte to the embryo within just 2 weeks. The underlying key transport mechanism is receptor-mediated endocytosis of macromolecules, i.e., of hepatically synthesized yolk precursors for oocyte growth, and of mature yolk components for embryo nutrition, respectively. Recently, the receptors involved, as well as the role of lipoprotein synthesis in the yolk sac have been identified. As outlined here, lipoprotein degradation/resynthesis cycles and the expression of lipoprotein receptors are not only coordinated with the establishment of the follicular architecture embedding the oocyte, but also with the generation of the yolk sac vasculature essential for nutrient transfer to the embryo.
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Affiliation(s)
- Wolfgang J Schneider
- Department of Medical Biochemistry, Max F. Perutz Laboratories, Medical University and Biocenter Vienna, Austria.
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36
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Wagner MC, Campos-Bilderback SB, Chowdhury M, Flores B, Lai X, Myslinski J, Pandit S, Sandoval RM, Wean SE, Wei Y, Satlin LM, Wiggins RC, Witzmann FA, Molitoris BA. Proximal Tubules Have the Capacity to Regulate Uptake of Albumin. J Am Soc Nephrol 2015; 27:482-94. [PMID: 26054544 DOI: 10.1681/asn.2014111107] [Citation(s) in RCA: 59] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2014] [Accepted: 05/04/2015] [Indexed: 12/26/2022] Open
Abstract
Evidence from multiple studies supports the concept that both glomerular filtration and proximal tubule (PT) reclamation affect urinary albumin excretion rate. To better understand these roles of glomerular filtration and PT uptake, we investigated these processes in two distinct animal models. In a rat model of acute exogenous albumin overload, we quantified glomerular sieving coefficients (GSC) and PT uptake of Texas Red-labeled rat serum albumin using two-photon intravital microscopy. No change in GSC was observed, but a significant decrease in PT albumin uptake was quantified. In a second model, loss of endogenous albumin was induced in rats by podocyte-specific transgenic expression of diphtheria toxin receptor. In these albumin-deficient rats, exposure to diphtheria toxin induced an increase in albumin GSC and albumin filtration, resulting in increased exposure of the PTs to endogenous albumin. In this case, PT albumin reabsorption was markedly increased. Analysis of known albumin receptors and assessment of cortical protein expression in the albumin overload model, conducted to identify potential proteins and pathways affected by acute protein overload, revealed changes in the expression levels of calreticulin, disabled homolog 2, NRF2, angiopoietin-2, and proteins involved in ATP synthesis. Taken together, these results suggest that a regulated PT cell albumin uptake system can respond rapidly to different physiologic conditions to minimize alterations in serum albumin level.
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Affiliation(s)
- Mark C Wagner
- Indiana University School of Medicine, The Roudebush Veterans Affair Medical Center, Indiana Center for Biological Microscopy, Indianapolis, Indiana
| | - Silvia B Campos-Bilderback
- Indiana University School of Medicine, The Roudebush Veterans Affair Medical Center, Indiana Center for Biological Microscopy, Indianapolis, Indiana
| | - Mahboob Chowdhury
- Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan
| | - Brittany Flores
- Indiana University School of Medicine, The Roudebush Veterans Affair Medical Center, Indiana Center for Biological Microscopy, Indianapolis, Indiana
| | - Xianyin Lai
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana; and
| | - Jered Myslinski
- Indiana University School of Medicine, The Roudebush Veterans Affair Medical Center, Indiana Center for Biological Microscopy, Indianapolis, Indiana
| | - Sweekar Pandit
- Indiana University School of Medicine, The Roudebush Veterans Affair Medical Center, Indiana Center for Biological Microscopy, Indianapolis, Indiana
| | - Ruben M Sandoval
- Indiana University School of Medicine, The Roudebush Veterans Affair Medical Center, Indiana Center for Biological Microscopy, Indianapolis, Indiana
| | - Sarah E Wean
- Indiana University School of Medicine, The Roudebush Veterans Affair Medical Center, Indiana Center for Biological Microscopy, Indianapolis, Indiana
| | - Yuan Wei
- Department of Pediatrics, The Icahn School of Medicine at Mount Sinai, New York
| | - Lisa M Satlin
- Department of Pediatrics, The Icahn School of Medicine at Mount Sinai, New York
| | - Roger C Wiggins
- Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan
| | - Frank A Witzmann
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, Indiana
| | - Bruce A Molitoris
- Indiana University School of Medicine, The Roudebush Veterans Affair Medical Center, Indiana Center for Biological Microscopy, Indianapolis, Indiana; Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, Indiana
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37
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Devuyst O, Luciani A. Chloride transporters and receptor-mediated endocytosis in the renal proximal tubule. J Physiol 2015; 593:4151-64. [PMID: 25820368 DOI: 10.1113/jp270087] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Accepted: 03/16/2015] [Indexed: 01/09/2023] Open
Abstract
KEY POINTS The reabsorptive activity of renal proximal tubule cells is mediated by receptor-mediated endocytosis and polarized transport systems that reflect final cell differentiation. Loss-of-function mutations of the endosomal chloride-proton exchanger ClC-5 (Dent's disease) cause a major trafficking defect in proximal tubule cells, associated with lysosomal dysfunction, oxidative stress and dedifferentiation/proliferation. A similar but milder defect is associated with mutations in CFTR (cystic fibrosis transmembrane conductance regulator). Vesicular chloride transport appears to be important for the integrity of the endolysosomal pathway in epithelial cells. ABSTRACT The epithelial cells lining the proximal tubules of the kidney reabsorb a large amount of filtered ions and solutes owing to receptor-mediated endocytosis and polarized transport systems that reflect final cell differentiation. Dedifferentiation of proximal tubule cells and dysfunction of receptor-mediated endocytosis characterize Dent's disease, a rare disorder caused by inactivating mutations in the CLCN5 gene that encodes the endosomal chloride-proton exchanger, ClC-5. The disease is characterized by a massive urinary loss of solutes (renal Fanconi syndrome), with severe metabolic complications and progressive renal failure. Investigations of mutations affecting the gating of ClC-5 revealed that the proximal tubule dysfunction may occur despite normal endosomal acidification. In addition to defective endocytosis, proximal tubule cells lacking ClC-5 show a trafficking defect in apical receptors and transporters, as well as lysosomal dysfunction and typical features of dedifferentiation, proliferation and oxidative stress. A similar but milder defect is observed in mouse models with defective CFTR, a chloride channel that is also expressed in the endosomes of proximal tubule cells. These data suggest a major role for endosomal chloride transport in the maintenance of epithelial differentiation and reabsorption capacity of the renal proximal tubule.
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Affiliation(s)
- Olivier Devuyst
- Institute of Physiology, Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland
| | - Alessandro Luciani
- Institute of Physiology, Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland
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38
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Seliverstova EV, Prutskova NP. Receptor-mediated endocytosis of lysozyme in renal proximal tubules of the frog Rana temporaria. Eur J Histochem 2015; 59:2482. [PMID: 26150156 PMCID: PMC4503969 DOI: 10.4081/ejh.2015.2482] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2015] [Revised: 02/18/2015] [Accepted: 02/24/2015] [Indexed: 12/23/2022] Open
Abstract
The mechanism of protein reabsorption in the kidney of lower vertebrates remains insufficiently investigated in spite of raising interest to the amphibian and fish kidneys as a useful model for physiological and pathophysiological examinations. In the present study, we examined the renal tubular uptake and the internalization rote of lysozyme after its intravenous injection in the wintering frog Rana temporaria using immunohisto- and immunocytochemistry and specific markers for some endocytic compartments. The distinct expression of megalin and cubilin in the proximal tubule cells of lysozyme-injected frogs was revealed whereas kidney tissue of control animals showed no positive immunoreactivity. Lysozyme was detected in the apical endocytic compartment of the tubular cells and colocalized with clathrin 10 min after injection. After 20 min, lysozyme was located in the subapical compartment negative to clathrin (endo-somes), and intracellular trafficking of lysozyme was coincided with the distribution of megalin and cubilin. However, internalized protein was retained in the endosomes and did not reach lysosomes within 30 min after treatment that may indicate the inhibition of intra-cellular trafficking in hibernating frogs. For the first time, we provided the evidence that lysozyme is filtered through the glomeruli and absorbed by receptor-mediated clathrin-dependent endocytosis in the frog proximal tubule cells. Thus, the protein uptake in the amphibian mesonephros is mediated by megalin and cubilin that confirms a critical role of endocytic receptors in the renal reabsorption of proteins in amphibians as in mammals.
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Affiliation(s)
- E V Seliverstova
- Sechenov Institute of Evolutionary Physiology and Biochemistry of the Russian Academy of Sciences.
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39
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Jensen LL, Andersen RK, Hager H, Madsen M. Lack of megalin expression in adult human terminal ileum suggests megalin-independent cubilin/amnionless activity during vitamin B12 absorption. Physiol Rep 2014; 2:2/7/e12086. [PMID: 25052491 PMCID: PMC4187553 DOI: 10.14814/phy2.12086] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Cubilin plays an essential role in terminal ileum and renal proximal tubules during absorption of vitamin B12 and ligands from the glomerular ultrafiltrate. Cubilin is coexpressed with amnionless, and cubilin and amnionless are mutually dependent on each other for correct processing to the plasma membrane upon synthesis. Patients with defects in either protein suffer from vitamin B12‐malabsorption and in some cases proteinuria. Cubilin lacks a transmembrane region and signals for endocytosis and is dependent on a transmembrane coreceptor during internalization. Amnionless has been shown to be able to mediate internalization of cubilin in a cell‐based model system. Cubilin has additionally been suggested to function together with megalin, and a recent study of megalin‐deficient patients indicates that uptake of cubilin ligands in the kidney is critically dependent on megalin. To further investigate the potential role of amnionless and megalin in relation to cubilin function in terminal ileum and vitamin B12 uptake, we initiated a study of CUBN/cubilin, AMN/amnionless, and LRP2/megalin expression in adult human terminal ileum. Our study is the first to reveal the expression pattern of cubilin, amnionless, and megalin in adult human terminal ileum, where cubilin and amnionless localize to the epithelial cells. Surprisingly, we did not detect any megalin protein in adult terminal ileum and consistently, only extremely low amounts of LRP2 mRNA. Our data therefore advocate that cubilin and amnionless act independently of megalin in adult terminal ileum and that the cubilin‐megalin interdependency accordingly should be considered as tissue and ligand specific. e12086 Studies of human terminal ileum samples demonstrate lack of LRP2/megalin expression in adult terminal ileum and point to a megalin‐independent cubilin‐amnionless‐driven uptake mechanism for vitamin B12.
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Affiliation(s)
- Louise L Jensen
- Department of Biomedicine, University of Aarhus, 8000 Aarhus C., Denmark
| | - Rikke K Andersen
- Department of Biomedicine, University of Aarhus, 8000 Aarhus C., Denmark
| | - Henrik Hager
- Department of Pathology, Aarhus University Hospital, 8000 Aarhus C., Denmark
| | - Mette Madsen
- Department of Biomedicine, University of Aarhus, 8000 Aarhus C., Denmark
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De S, Kuwahara S, Saito A. The endocytic receptor megalin and its associated proteins in proximal tubule epithelial cells. MEMBRANES 2014; 4:333-55. [PMID: 25019425 PMCID: PMC4194038 DOI: 10.3390/membranes4030333] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/31/2014] [Revised: 06/23/2014] [Accepted: 07/01/2014] [Indexed: 02/08/2023]
Abstract
Receptor-mediated endocytosis in renal proximal tubule epithelial cells (PTECs) is important for the reabsorption and metabolization of proteins and other substances, including carrier-bound vitamins and trace elements, in glomerular filtrates. Impairment of this endocytic process results in the loss of such substances and development of proteinuria, which is an important clinical indicator of kidney diseases and is also a risk marker for cardiovascular disease. Megalin, a member of the low-density lipoprotein receptor gene family, is a multiligand receptor expressed in the apical membrane of PTECs and plays a central role in the endocytic process. Megalin interacts with various intracellular adaptor proteins for intracellular trafficking and cooperatively functions with other membrane molecules, including the cubilin-amnionless complex. Evidence suggests that megalin and the cubilin-amnionless complex are involved in the uptake of toxic substances into PTECs, which leads to the development of kidney disease. Studies of megalin and its associated molecules will be useful for future development of novel strategies for the diagnosis and treatment of kidney diseases.
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Affiliation(s)
- Shankhajit De
- Division of Clinical Nephrology and Rheumatology, Niigata University Graduate School of Medical and Dental Sciences, 1-757 Asahimachi-dori, Chuo-ku, Niigata 951-8510, Japan.
| | - Shoji Kuwahara
- Department of Applied Molecular Medicine, Niigata University Graduate School of Medical and Dental Sciences, 1-757 Asahimachi-dori, Chuo-ku, Niigata 951-8510, Japan.
| | - Akihiko Saito
- Department of Applied Molecular Medicine, Niigata University Graduate School of Medical and Dental Sciences, 1-757 Asahimachi-dori, Chuo-ku, Niigata 951-8510, Japan.
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Sah BR, Schibli R, Waibel R, von Boehmer L, Bläuenstein P, Nexo E, Johayem A, Fischer E, Müller E, Soyka JD, Knuth AK, Haerle SK, Schubiger PA, Schaefer NG, Burger IA. Tumor Imaging in Patients with Advanced Tumors Using a New 99mTc-Radiolabeled Vitamin B12 Derivative. J Nucl Med 2013; 55:43-9. [DOI: 10.2967/jnumed.113.122499] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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Christensen EI, Wagner CA, Kaissling B. Uriniferous tubule: structural and functional organization. Compr Physiol 2013; 2:805-61. [PMID: 23961562 DOI: 10.1002/cphy.c100073] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The uriniferous tubule is divided into the proximal tubule, the intermediate (thin) tubule, the distal tubule and the collecting duct. The present chapter is based on the chapters by Maunsbach and Christensen on the proximal tubule, and by Kaissling and Kriz on the distal tubule and collecting duct in the 1992 edition of the Handbook of Physiology, Renal Physiology. It describes the fine structure (light and electron microscopy) of the entire mammalian uriniferous tubule, mainly in rats, mice, and rabbits. The structural data are complemented by recent data on the location of the major transport- and transport-regulating proteins, revealed by morphological means(immunohistochemistry, immunofluorescence, and/or mRNA in situ hybridization). The structural differences along the uriniferous tubule strictly coincide with the distribution of the major luminal and basolateral transport proteins and receptors and both together provide the basis for the subdivision of the uriniferous tubule into functional subunits. Data on structural adaptation to defined functional changes in vivo and to genetical alterations of specified proteins involved in transepithelial transport importantly deepen our comprehension of the correlation of structure and function in the kidney, of the role of each segment or cell type in the overall renal function,and our understanding of renal pathophysiology.
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Storm T, Zeitz C, Cases O, Amsellem S, Verroust PJ, Madsen M, Benoist JF, Passemard S, Lebon S, Jønsson IM, Emma F, Koldsø H, Hertz JM, Nielsen R, Christensen EI, Kozyraki R. Detailed investigations of proximal tubular function in Imerslund-Gräsbeck syndrome. BMC MEDICAL GENETICS 2013; 14:111. [PMID: 24156255 PMCID: PMC3826550 DOI: 10.1186/1471-2350-14-111] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/16/2012] [Accepted: 10/18/2013] [Indexed: 11/10/2022]
Abstract
BACKGROUND Imerslund-Gräsbeck Syndrome (IGS) is a rare genetic disorder characterised by juvenile megaloblastic anaemia. IGS is caused by mutations in either of the genes encoding the intestinal intrinsic factor-vitamin B12 receptor complex, cubam. The cubam receptor proteins cubilin and amnionless are both expressed in the small intestine as well as the proximal tubules of the kidney and exhibit an interdependent relationship for post-translational processing and trafficking. In the proximal tubules cubilin is involved in the reabsorption of several filtered plasma proteins including vitamin carriers and lipoproteins. Consistent with this, low-molecular-weight proteinuria has been observed in most patients with IGS. The aim of this study was to characterise novel disease-causing mutations and correlate novel and previously reported mutations with the presence of low-molecular-weight proteinuria. METHODS Genetic screening was performed by direct sequencing of the CUBN and AMN genes and novel identified mutations were characterised by in silico and/or in vitro investigations. Urinary protein excretion was analysed by immunoblotting and high-resolution gel electrophoresis of collected urines from patients and healthy controls to determine renal phenotype. RESULTS Genetic characterisation of nine IGS patients identified two novel AMN frameshift mutations alongside a frequently reported AMN splice site mutation and two CUBN missense mutations; one novel and one previously reported in Finnish patients. The novel AMN mutations were predicted to result in functionally null AMN alleles with no cell-surface expression of cubilin. Also, the novel CUBN missense mutation was predicted to affect structural integrity of the IF-B12 binding site of cubilin and hereby most likely cubilin cell-surface expression. Analysis of urinary protein excretion in the patients and 20 healthy controls revealed increased urinary excretion of cubilin ligands including apolipoprotein A-I, transferrin, vitamin D-binding protein, and albumin. This was, however, only observed in patients where plasma membrane expression of cubilin was predicted to be perturbed. CONCLUSIONS In the present study, mutational characterisation of nine IGS patients coupled with analyses of urinary protein excretion provide additional evidence for a correlation between mutation type and presence of the characteristic low-molecular-weight proteinuria.
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Aseem O, Barth JL, Klatt SC, Smith BT, Argraves WS. Cubilin expression is monoallelic and epigenetically augmented via PPARs. BMC Genomics 2013; 14:405. [PMID: 23773363 PMCID: PMC3706236 DOI: 10.1186/1471-2164-14-405] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2012] [Accepted: 05/30/2013] [Indexed: 01/04/2023] Open
Abstract
Background Cubilin is an endocytic receptor that is necessary for renal and intestinal absorption of a range of ligands. Endocytosis mediated by cubilin and its co-receptor megalin is the principal mechanism for proximal tubule reabsorption of proteins from the glomerular filtrate. Cubilin is also required for intestinal endocytosis of intrinsic factor-vitamin B12 complex. Despite its importance, little is known about the regulation of cubilin expression. Results Here we show that cubilin expression is under epigenetic regulation by at least two processes. The first process involves inactivation of expression of one of the cubilin alleles. This monoallelic expression state could not be transformed to biallelic by inhibiting DNA methylation or histone deacetylation. The second process involves transcriptional regulation of cubilin by peroxisome proliferator-activated receptor (PPAR) transcription factors that are themselves regulated by DNA methylation and histone deacetylation. This is supported by findings that inhibitors of DNA methylation and histone deacetylation, 5Aza and TSA, increase cubilin mRNA and protein in renal and intestinal cell lines. Not only was the expression of PPARα and γ inducible by 5Aza and TSA, but the positive effects of TSA and 5Aza on cubilin expression were also dependent on both increased PPAR transcription and activation. Additionally, 5Aza and TSA had similar effects on the expression of the cubilin co-receptor, megalin. Conclusions Together, these findings reveal that cubilin and megalin mRNA expression is under epigenetic control and thus point to new avenues for overcoming pathological suppression of these genes through targeting of epigenetic regulatory processes.
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Affiliation(s)
- Obaidullah Aseem
- Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, SC 29425, USA
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Christensen EI, Nielsen R, Birn H. From bowel to kidneys: the role of cubilin in physiology and disease. Nephrol Dial Transplant 2013; 28:274-81. [DOI: 10.1093/ndt/gfs565] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Zhang F, Zhao Y, Chao Y, Muir K, Han Z. Cubilin and amnionless mediate protein reabsorption in Drosophila nephrocytes. J Am Soc Nephrol 2012; 24:209-16. [PMID: 23264686 DOI: 10.1681/asn.2012080795] [Citation(s) in RCA: 80] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
The insect nephrocyte and the mammalian glomerular podocyte are similar with regard to filtration, but it remains unclear whether there is an organ or cell type in flies that reabsorbs proteins. Here, we show that the Drosophila nephrocyte has molecular, structural, and functional similarities to the renal proximal tubule cell. We screened for genes required for nephrocyte function and identified two Drosophila genes encoding orthologs of mammalian cubilin and amnionless (AMN), two major receptors for protein reabsorption in the proximal tubule. In Drosophila, expression of dCubilin and dAMN is specific to nephrocytes, where they function as co-receptors for protein uptake. Targeted expression of human AMN in Drosophila nephrocytes was sufficient to rescue defective protein uptake induced by dAMN knockdown, suggesting evolutionary conservation of Cubilin/AMN co-receptors function from flies to humans. Furthermore, we found that Cubilin/AMN-mediated protein reabsorption is required for the maintenance of nephrocyte ultrastructure and fly survival under conditions of toxic stress. In conclusion, the insect nephrocyte combines filtration with protein reabsorption, using evolutionarily conserved genes and subcellular structures, suggesting that it can serve as a simplified model for both podocytes and the renal proximal tubule.
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Affiliation(s)
- Fujian Zhang
- Department of Internal Medicine, Division of Molecular Medicine and Genetics, University of Michigan Medical School, Ann Arbor, MI 48109, USA
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Bauer R, Plieschnig JA, Finkes T, Riegler B, Hermann M, Schneider WJ. The developing chicken yolk sac acquires nutrient transport competence by an orchestrated differentiation process of its endodermal epithelial cells. J Biol Chem 2012; 288:1088-98. [PMID: 23209291 DOI: 10.1074/jbc.m112.393090] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
During chicken yolk sac (YS) growth, mesodermal cells in the area vasculosa follow the migrating endodermal epithelial cell (EEC) layer in the area vitellina. Ultimately, these cells form the vascularized YS that functions in nutrient transfer to the embryo. How and when EECs, with their apical aspect directly contacting the oocytic yolk, acquire the ability to take up yolk macromolecules during the vitellina-to-vasculosa transition has not been investigated. In addressing these questions, we found that with progressive vascularization, the expression level in EECs of the nutrient receptor triad, LRP2-cubilin-amnionless, changes significantly. The receptor complex, competent for uptake of yolk proteins, is produced by EECs in the area vasculosa but not in the area vitellina. Yolk components endocytosed by LRP2-cubilin-amnionless, preformed and newly formed lipid droplets, and yolk-derived very low density lipoprotein, shown to be efficiently endocytosed and lysosomally processed by EECs, probably provide substrates for resynthesis and secretion of nutrients, such as lipoproteins. In fact, as directly demonstrated by pulse-chase experiments, EECs in the vascularized, but not in the avascular, region efficiently produce and secrete lipoproteins containing apolipoprotein A-I (apoA-I), apoB, and/or apoA-V. In contrast, perilipin 2, a lipid droplet-stabilizing protein, is produced exclusively by the EECs of the area vitellina. These data suggest a differentiation process that orchestrates the vascularization of the developing YS with the induction of yolk uptake and lipoprotein secretion by EECs to ensure embryo nutrition.
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Affiliation(s)
- Raimund Bauer
- Department of Medical Biochemistry, Medical University of Vienna, Max F. Perutz Laboratories, Dr. Bohr Gasse 9/2, 1030 Vienna, Austria
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Abstract
BACKGROUND Vitamin B12 (cobalamin) is a cobalt-containing compound synthesized by bacteria and an essential nutrient in mammals, which take it up from diet. The absorption and distribution of dietary vitamin B12 to the organism is a complex process involving several gene products including carrier proteins, plasma membrane receptors and transporters. Disturbed cellular entry, transit or egress of vitamin B12 may lead to low vitamin B12 status or deficiency and eventually hematological and neurological disorders. OBJECTIVE The aim of this review is to summarize the causes leading to vitamin B12 deficiency including decreased intake, impaired absorption and increased requirements. Under physiological conditions, vitamin B12 bound to the gastric intrinsic factor is internalized in the ileum by a highly specific receptor complex composed by Cubilin (Cubn) and Amnionless (Amn). Following exit of vitamin B12 from the ileum, general cellular uptake from the circulation requires the transcobalamin receptor CD320 whereas kidney reabsorption of cobalamin depends on Megalin (Lrp2). Whereas malabsorption of vitamin B12 is most commonly seen in the elderly, selective pediatric, nondietary-induced B12 deficiency is generally due to inherited disorders including the Imerslund-Gräsbeck syndrome and the much rarer intrinsic factor deficiency. Biochemical, clinical and genetic research on these disorders considerably improved our knowledge of vitamin B12 absorption. This review describes basic and recent findings on the intestinal handling of vitamin B12 and its importance in health and disease.
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Christensen EI, Birn H, Storm T, Weyer K, Nielsen R. Endocytic Receptors in the Renal Proximal Tubule. Physiology (Bethesda) 2012; 27:223-36. [DOI: 10.1152/physiol.00022.2012] [Citation(s) in RCA: 170] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Protein reabsorption is a predominant feature of the renal proximal tubule. Animal studies show that the ability to rescue plasma proteins relies on the endocytic receptors megalin and cubilin. Recently, studies of patients with syndromes caused by dysfunctional receptors have supported the importance of these for protein clearance of human ultrafiltrate. This review focuses on the molecular biology and physiology of the receptors and their involvement in renal pathological conditions.
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Affiliation(s)
- Erik I. Christensen
- Department of Biomedicine, Faculty of Health Sciences, Aarhus University, Aarhus, Denmark
| | - Henrik Birn
- Department of Biomedicine, Faculty of Health Sciences, Aarhus University, Aarhus, Denmark
| | - Tina Storm
- Department of Biomedicine, Faculty of Health Sciences, Aarhus University, Aarhus, Denmark
| | - Kathrin Weyer
- Department of Biomedicine, Faculty of Health Sciences, Aarhus University, Aarhus, Denmark
| | - Rikke Nielsen
- Department of Biomedicine, Faculty of Health Sciences, Aarhus University, Aarhus, Denmark
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Abstract
Vitamin B(12) (B(12); also known as cobalamin) is a cofactor in many metabolic processes; deficiency of this vitamin is associated with megaloblastic anaemia and various neurological disorders. In contrast to many prokaryotes, humans and other mammals are unable to synthesize B(12). Instead, a sophisticated pathway for specific uptake and transport of this molecule has evolved. Failure in the gastrointestinal part of this pathway is the most common cause of nondietary-induced B(12) deficiency disease. However, although less frequent, defects in cellular processing and further downstream steps in the transport pathway are also known culprits of functional B(12) deficiency. Biochemical and genetic approaches have identified novel proteins in the B(12) transport pathway--now known to involve more than 15 gene products--delineating a coherent pathway for B(12) trafficking from food to the body's cells. Some of these gene products are specifically dedicated to B(12) transport, whereas others embrace additional roles, which explains the heterogeneity in the clinical picture of the many genetic disorders causing B(12) deficiency. This Review describes basic and clinical features of this multistep pathway with emphasis on gastrointestinal transport of B(12) and its importance in clinical medicine.
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