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Est CB, Murphy RM. An in vitro model for vitamin A transport across the human blood-brain barrier. eLife 2023; 12:RP87863. [PMID: 37934575 PMCID: PMC10629827 DOI: 10.7554/elife.87863] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2023] Open
Abstract
Vitamin A, supplied by the diet, is critical for brain health, but little is known about its delivery across the blood-brain barrier (BBB). Brain microvascular endothelial-like cells (BMECs) differentiated from human-derived induced pluripotent stem cells (iPSCs) form a tight barrier that recapitulates many of the properties of the human BBB. We paired iPSC-derived BMECs with recombinant vitamin A serum transport proteins, retinol-binding protein (RBP), and transthyretin (TTR), to create an in vitro model for the study of vitamin A (retinol) delivery across the human BBB. iPSC-derived BMECs display a strong barrier phenotype, express key vitamin A metabolism markers, and can be used for quantitative modeling of retinol accumulation and permeation. Manipulation of retinol, RBP, and TTR concentrations, and the use of mutant RBP and TTR, yielded novel insights into the patterns of retinol accumulation in, and permeation across, the BBB. The results described herein provide a platform for deeper exploration of the regulatory mechanisms of retinol trafficking to the human brain.
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Affiliation(s)
- Chandler B Est
- Department of Chemical and Biological Engineering, University of WisconsinMadisonUnited States
| | - Regina M Murphy
- Department of Chemical and Biological Engineering, University of WisconsinMadisonUnited States
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Est CB, Murphy RM. Retinol binding protein IV purified from Escherichia coli using intein-mediated cleavage as a suitable replacement for serum sources. Protein Expr Purif 2019; 167:105542. [PMID: 31756375 DOI: 10.1016/j.pep.2019.105542] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2019] [Revised: 10/22/2019] [Accepted: 11/18/2019] [Indexed: 12/27/2022]
Abstract
Retinol binding protein IV (RBP) functions as the principal carrier of retinol (Vitamin A) in the blood, where RBP circulates bound to another serum protein, transthyretin. Isolation of pure RBP from the transthyretin complex in human serum can be difficult, but expression of RBP in recombinant systems can circumvent these purification issues. Human recombinant RBP has previously been successfully expressed and purified from E. coli, but recovery of active protein typically requires extensive processing steps, such as denaturing and refolding, and complex purification steps, such as multi-modal chromatography. Furthermore, these methods produce recombinant proteins, often tagged, that display different functional and structural characteristics across systems. In this work, we optimized downstream processing by use of an intein-based expression system in E. coli to produce tag-free, human recombinant RBP (rRBP) with intact native amino termini at yields of up to ~15 mg/L off column. The novel method requires solubilization of inclusion bodies and subsequent oxidative refolding in the presence of retinol, but importantly allows for one-step chromatographic purification that yields high purity rRBP with no N-terminal Met or other tag. Previously reported purification methods typically require two or more chromatographic separation steps to recover tag-free rRBP. Given the interest in mechanistic understanding of RBP transport of retinol in health and disease, we characterized our purified product extensively to confirm rRBP is both structurally and functionally a suitable replacement for serum-derived RBP.
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Affiliation(s)
- Chandler B Est
- Department of Chemical and Biological Engineering, University of Wisconsin - Madison, 1415 Engineering Dr., Madison, WI, 53706, USA
| | - Regina M Murphy
- Department of Chemical and Biological Engineering, University of Wisconsin - Madison, 1415 Engineering Dr., Madison, WI, 53706, USA.
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Kaukonen M, Woods S, Ahonen S, Lemberg S, Hellman M, Hytönen MK, Permi P, Glaser T, Lohi H. Maternal Inheritance of a Recessive RBP4 Defect in Canine Congenital Eye Disease. Cell Rep 2019; 23:2643-2652. [PMID: 29847795 PMCID: PMC6546432 DOI: 10.1016/j.celrep.2018.04.118] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2017] [Revised: 04/16/2018] [Accepted: 04/26/2018] [Indexed: 01/20/2023] Open
Abstract
Maternally skewed transmission of traits has been associated with genomic imprinting and oocyte-derived mRNA. We report canine congenital eye malformations, caused by an amino acid deletion (K12del) near the N terminus of retinol-binding protein (RBP4). The disease is only expressed when both dam and offspring are deletion homozygotes. RBP carries vitamin A (retinol) from hepatic stores to peripheral tissues, including the placenta and developing eye, where it is required to synthesize retinoic acid. Gestational vitamin A deficiency is a known risk factor for ocular birth defects. The K12del mutation disrupts RBP folding in vivo, decreasing its secretion from hepatocytes to serum. The maternal penetrance effect arises from an impairment in the sequential transfer of retinol across the placenta, via RBP encoded by maternal and fetal genomes. Our results demonstrate a mode of recessive maternal inheritance, with a physiological basis, and they extend previous observations on dominant-negative RBP4 alleles in humans.
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Affiliation(s)
- Maria Kaukonen
- Department of Veterinary Biosciences, University of Helsinki, 00014 Helsinki, Finland; Research Programs Unit, Molecular Neurology, University of Helsinki, 00014 Helsinki, Finland; The Folkhälsan Institute of Genetics, 00290 Helsinki, Finland
| | - Sean Woods
- Department of Cell Biology and Human Anatomy, University of California, Davis School of Medicine, Davis, CA 95616, USA
| | - Saija Ahonen
- Department of Veterinary Biosciences, University of Helsinki, 00014 Helsinki, Finland; Research Programs Unit, Molecular Neurology, University of Helsinki, 00014 Helsinki, Finland; The Folkhälsan Institute of Genetics, 00290 Helsinki, Finland
| | - Seppo Lemberg
- Department of Eye Diseases, Helsinki University Hospital, 00029 The Hospital District of Helsinki and Uusimaa, Finland
| | - Maarit Hellman
- Department of Chemistry, Nanoscience Center, University of Jyväskylä, 40014 Jyväskylä, Finland
| | - Marjo K Hytönen
- Department of Veterinary Biosciences, University of Helsinki, 00014 Helsinki, Finland; Research Programs Unit, Molecular Neurology, University of Helsinki, 00014 Helsinki, Finland; The Folkhälsan Institute of Genetics, 00290 Helsinki, Finland
| | - Perttu Permi
- Department of Chemistry, Nanoscience Center, University of Jyväskylä, 40014 Jyväskylä, Finland; Department of Biological and Environmental Science, Nanoscience Center, University of Jyväskylä, 40014 Jyväskylä, Finland
| | - Tom Glaser
- Department of Cell Biology and Human Anatomy, University of California, Davis School of Medicine, Davis, CA 95616, USA.
| | - Hannes Lohi
- Department of Veterinary Biosciences, University of Helsinki, 00014 Helsinki, Finland; Research Programs Unit, Molecular Neurology, University of Helsinki, 00014 Helsinki, Finland; The Folkhälsan Institute of Genetics, 00290 Helsinki, Finland.
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Abstract
Multiple binding and transport proteins facilitate many aspects of retinoid biology through effects on retinoid transport, cellular uptake, metabolism, and nuclear delivery. These include the serum retinol binding protein sRBP (aka Rbp4), the plasma membrane sRBP receptor Stra6, and the intracellular retinoid binding-proteins such as cellular retinol-binding proteins (CRBP) and cellular retinoic acid binding-proteins (CRABP). sRBP transports the highly lipophilic retinol through an aqueous medium. The major intracellular retinol-binding protein, CRBP1, likely enhances efficient retinoid use by providing a sink to facilitate retinol uptake from sRBP through the plasma membrane or via Stra6, delivering retinol or retinal to select enzymes that generate retinyl esters or retinoic acid, and protecting retinol/retinal from excess catabolism or opportunistic metabolism. Intracellular retinoic acid binding-proteins (CRABP1 and 2, and FABP5) seem to have more diverse functions distinctive to each, such as directing retinoic acid to catabolism, delivering retinoic acid to specific nuclear receptors, and generating non-canonical actions. Gene ablation of intracellular retinoid binding-proteins does not cause embryonic lethality or gross morphological defects. Metabolic and functional defects manifested in knockouts of CRBP1, CRBP2 and CRBP3, however, illustrate their essentiality to health, and in the case of CRBP2, to survival during limited dietary vitamin A. Future studies should continue to address the specific molecular interactions that occur between retinoid binding-proteins and their targets and their precise physiologic contributions to retinoid homeostasis and function.
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Affiliation(s)
- Joseph L Napoli
- Graduate Program in Metabolic Biology, Department of Nutritional Sciences and Toxicology, University of California, 119 Morgan Hall, 94720, Berkeley, CA, USA.
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Zhong M, Kawaguchi R, Ter-Stepanian M, Kassai M, Sun H. Vitamin A transport and the transmembrane pore in the cell-surface receptor for plasma retinol binding protein. PLoS One 2013; 8:e73838. [PMID: 24223695 PMCID: PMC3815300 DOI: 10.1371/journal.pone.0073838] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2013] [Accepted: 07/25/2013] [Indexed: 11/18/2022] Open
Abstract
Vitamin A and its derivatives (retinoids) play diverse and crucial functions from embryogenesis to adulthood and are used as therapeutic agents in human medicine for eye and skin diseases, infections and cancer. Plasma retinol binding protein (RBP) is the principal and specific vitamin A carrier in the blood and binds vitamin A at 1∶1 ratio. STRA6 is the high-affinity membrane receptor for RBP and mediates cellular vitamin A uptake. STRA6 null mice have severely depleted vitamin A reserves for vision and consequently have vision loss, even under vitamin A sufficient conditions. STRA6 null humans have a wide range of severe pathological phenotypes in many organs including the eye, brain, heart and lung. Known membrane transport mechanisms involve transmembrane pores that regulate the transport of the substrate (e.g., the gating of ion channels). STRA6 represents a new type of membrane receptor. How this receptor interacts with its transport substrate vitamin A and the functions of its nine transmembrane domains are still completely unknown. These questions are critical to understanding the molecular basis of STRA6′s activities and its regulation. We employ acute chemical modification to introduce chemical side chains to STRA6 in a site-specific manner. We found that modifications with specific chemicals at specific positions in or near the transmembrane domains of this receptor can almost completely suppress its vitamin A transport activity. These experiments provide the first evidence for the existence of a transmembrane pore, analogous to the pore of ion channels, for this new type of cell-surface receptor.
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Affiliation(s)
- Ming Zhong
- Department of Physiology, Jules Stein Eye Institute, and Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
| | - Riki Kawaguchi
- Department of Physiology, Jules Stein Eye Institute, and Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
| | - Mariam Ter-Stepanian
- Department of Physiology, Jules Stein Eye Institute, and Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
| | - Miki Kassai
- Department of Physiology, Jules Stein Eye Institute, and Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
| | - Hui Sun
- Department of Physiology, Jules Stein Eye Institute, and Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
- * E-mail:
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Kawaguchi R, Zhong M, Kassai M, Ter-Stepanian M, Sun H. Differential and isomer-specific modulation of vitamin A transport and the catalytic activities of the RBP receptor by retinoids. J Membr Biol 2013; 246:647-660. [PMID: 23811822 DOI: 10.1007/s00232-013-9578-z] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2013] [Accepted: 06/12/2013] [Indexed: 12/20/2022]
Abstract
Retinoids are vitamin A derivatives with diverse biological functions. Both natural and artificial retinoids have been used as therapeutic reagents to treat human diseases, but not all retinoid actions are understood mechanistically. Plasma retinol binding protein (RBP) is the principal and specific carrier of vitamin A in the blood. STRA6 is the membrane receptor for RBP that mediates cellular vitamin A uptake. The effects of retinoids or related compounds on the receptor's vitamin A uptake activity and its catalytic activities are not well understood. In this study, we dissected the membrane receptor-mediated vitamin A uptake mechanism using various retinoids. We show that a subset of retinoids strongly stimulates STRA6-mediated vitamin A release from holo-RBP. STRA6 also catalyzes the exchange of retinol in RBP with certain retinoids. The effect of retinoids on STRA6 is highly isomer-specific. This study provides unique insights into the RBP receptor's mechanism and reveals that the vitamin A transport machinery can be a target of retinoid-based drugs.
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Affiliation(s)
- Riki Kawaguchi
- Department of Physiology, Jules Stein Eye Institute, and Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA
| | - Ming Zhong
- Department of Physiology, Jules Stein Eye Institute, and Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA
| | - Miki Kassai
- Department of Physiology, Jules Stein Eye Institute, and Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA
| | - Mariam Ter-Stepanian
- Department of Physiology, Jules Stein Eye Institute, and Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA
| | - Hui Sun
- Department of Physiology, Jules Stein Eye Institute, and Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA
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