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Mansour R, El-Orfali Y, Saber A, Noun D, Youssef N, Youssef Y, Hanna-Wakim R, Dbaibo G, Abboud M, Massaad MJ. Wiskott-Aldrich Syndrome in four male siblings from a consanguineous family from Lebanon. Clin Immunol 2020; 219:108573. [PMID: 32814211 DOI: 10.1016/j.clim.2020.108573] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2020] [Revised: 08/07/2020] [Accepted: 08/12/2020] [Indexed: 01/29/2023]
Abstract
BACKGROUND Wiskott-Aldrich syndrome (WAS) is a rare X-linked primary immunodeficiency disorder (PID) characterized by microthrombocytopenia, bloody diarrhea, eczema, recurrent infections, and a high incidence of autoimmunity and malignancy. OBJECTIVE To investigate the mechanism of thrombocytopenia and infections in four boys of consanguineous parents from Lebanon. METHODS Patient gDNA was studied using Next Generation Sequencing and Sanger Sequencing. Protein expression was determined by immunoblotting, and mRNA expression by semi-quantitative RT-PCR. F-actin polymerization and cellular proliferation were assayed by flow cytometry. RESULTS We identified a threonine to a methionine change at position 45 (T45M) of the WAS protein (WASp) that abolished protein expression and disturbed F-actin polymerization and T cell proliferation, but not B cell proliferation. In addition, the levels of the WAS-interacting protein (WIP) were significantly decreased in the patients. CONCLUSION The mutation identified severely destabilizes WASp and affects the downstream signaling events important for T cell function, but not B cell function. It was previously known that the stability of WASp depends on WIP. In this manuscript, we report that the stability of WIP also depends on WASp. Finally, it is important to suspect X-linked PIDs even in consanguineous families. CLINICAL IMPLICATIONS The patients are above the optimal age for transplant in WAS, and it is difficult to identify one or more donors for four patients, therefore, they represent ideal candidates for gene therapy or interleukin-2 therapy.
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Affiliation(s)
- Rana Mansour
- Department of Experimental Pathology, Immunology, and Microbiology, Faculty of Medicine, American University of Beirut, Beirut, Lebanon
| | - Youmna El-Orfali
- Department of Experimental Pathology, Immunology, and Microbiology, Faculty of Medicine, American University of Beirut, Beirut, Lebanon
| | - Antoine Saber
- Department of Experimental Pathology, Immunology, and Microbiology, Faculty of Medicine, American University of Beirut, Beirut, Lebanon
| | - Dolly Noun
- Division of Pediatric Hematology Oncology, Department of Pediatrics and Adolescent Medicine, Beirut, Lebanon; Children's Cancer Center of Lebanon, American University of Beirut Medical Center, Beirut, Lebanon
| | - Nour Youssef
- Division of Pediatric Infectious Diseases, Department of Pediatrics and Adolescent Medicine, American University of Beirut Medical Center, Beirut, Lebanon
| | - Yolla Youssef
- Division of Pediatric Infectious Diseases, Department of Pediatrics and Adolescent Medicine, American University of Beirut Medical Center, Beirut, Lebanon
| | - Rima Hanna-Wakim
- Division of Pediatric Infectious Diseases, Department of Pediatrics and Adolescent Medicine, American University of Beirut Medical Center, Beirut, Lebanon; Center for Infectious Diseases Research, American University of Beirut, Beirut, Lebanon
| | - Ghassan Dbaibo
- Division of Pediatric Infectious Diseases, Department of Pediatrics and Adolescent Medicine, American University of Beirut Medical Center, Beirut, Lebanon; Center for Infectious Diseases Research, American University of Beirut, Beirut, Lebanon; Department of Biochemistry, Faculty of Medicine, American University of Beirut, Beirut, Lebanon
| | - Miguel Abboud
- Division of Pediatric Hematology Oncology, Department of Pediatrics and Adolescent Medicine, Beirut, Lebanon; Children's Cancer Center of Lebanon, American University of Beirut Medical Center, Beirut, Lebanon
| | - Michel J Massaad
- Department of Experimental Pathology, Immunology, and Microbiology, Faculty of Medicine, American University of Beirut, Beirut, Lebanon; Division of Pediatric Infectious Diseases, Department of Pediatrics and Adolescent Medicine, American University of Beirut Medical Center, Beirut, Lebanon; Center for Infectious Diseases Research, American University of Beirut, Beirut, Lebanon.
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Pleines I, Cherpokova D, Bender M. Rho GTPases and their downstream effectors in megakaryocyte biology. Platelets 2018; 30:9-16. [DOI: 10.1080/09537104.2018.1478071] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- Irina Pleines
- Institute of Experimental Biomedicine I, University Hospital and Rudolf Virchow Center, University of Würzburg, Würzburg, Germany
| | - Deya Cherpokova
- Program in Cellular and Molecular Medicine, Boston Children’s Hospital, and Department of Pediatrics, Harvard Medical School, Boston, MA, USA
| | - Markus Bender
- Institute of Experimental Biomedicine I, University Hospital and Rudolf Virchow Center, University of Würzburg, Würzburg, Germany
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FlnA binding to PACSIN2 F-BAR domain regulates membrane tubulation in megakaryocytes and platelets. Blood 2015; 126:80-8. [PMID: 25838348 DOI: 10.1182/blood-2014-07-587600] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2014] [Accepted: 03/30/2015] [Indexed: 11/20/2022] Open
Abstract
Bin-Amphiphysin-Rvs (BAR) and Fes-CIP4 homology BAR (F-BAR) proteins generate tubular membrane invaginations reminiscent of the megakaryocyte (MK) demarcation membrane system (DMS), which provides membranes necessary for future platelets. The F-BAR protein PACSIN2 is one of the most abundant BAR/F-BAR proteins in platelets and the only one reported to interact with the cytoskeletal and scaffold protein filamin A (FlnA), an essential regulator of platelet formation and function. The FlnA-PACSIN2 interaction was therefore investigated in MKs and platelets. PACSIN2 associated with FlnA in human platelets. The interaction required FlnA immunoglobulin-like repeat 20 and the tip of PACSIN2 F-BAR domain and enhanced PACSIN2 F-BAR domain membrane tubulation in vitro. Most human and wild-type mouse platelets had 1 to 2 distinct PACSIN2 foci associated with cell membrane GPIbα, whereas Flna-null platelets had 0 to 4 or more foci. Endogenous PACSIN2 and transfected enhanced green fluorescent protein-PACSIN2 were concentrated in midstage wild-type mouse MKs in a well-defined invagination of the plasma membrane reminiscent of the initiating DMS and dispersed in the absence of FlnA binding. The DMS appeared less well defined, and platelet territories were not readily visualized in Flna-null MKs. We conclude that the FlnA-PACSIN2 interaction regulates membrane tubulation in MKs and platelets and likely contributes to DMS formation.
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Duerschmied D, Bode C, Ahrens I. Immune functions of platelets. Thromb Haemost 2014; 112:678-91. [PMID: 25209670 DOI: 10.1160/th14-02-0146] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2014] [Accepted: 09/03/2014] [Indexed: 01/12/2023]
Abstract
This review collects evidence about immune and inflammatory functions of platelets from a clinician's point of view. A focus on clinically relevant immune functions aims at stimulating further research, because the complexity of platelet immunity is incompletely understood and not yet translated into patient care. Platelets promote chronic inflammatory reactions (e.g. in atherosclerosis), modulate acute inflammatory disorders such as sepsis and other infections (participating in the host defense against pathogens), and contribute to exacerbations of autoimmune conditions (like asthma or arthritis). It would hence be obsolete to restrict a description of platelet functions to thrombosis and haemostasis--platelets clearly are the most abundant cells with immune functions in the circulation.
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Affiliation(s)
- Daniel Duerschmied
- Daniel Duerschmied, MD, Department of Cardiology and Angiology I, Heart Center, University of Freiburg, Hugstetter Str. 55, 79106 Freiburg, Germany, Tel.: +49 761 207 34410, Fax: +49 761 270 37855, E-mail:
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Abstract
WIP plays an important role in the remodeling of the actin cytoskeleton, which controls cellular activation, proliferation, and function. WIP regulates actin polymerization by linking the actin machinery to signaling cascades. WIP binding to WASp and to its homolog, N-WASp, which are central activators of the actin-nucleating complex Arp2/3, regulates their cellular distribution, function, and stability. By binding to WASp, WIP protects it from degradation and thus, is crucial for WASp retention. Indeed, most mutations that result in WAS, an X-linked immunodeficiency caused by defective/absent WASp activity, are located in the WIP-binding region of WASp. In addition, by binding directly to actin, WIP promotes the formation and stabilization of actin filaments. WASp-independent activities of WIP constitute a new research frontier and are discussed extensively in this article. Here, we review the current information on WIP in human and mouse systems, focusing on its associated proteins, its molecular-regulatory mechanisms, and its role as a key regulator of actin-based processes in the immune system.
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Affiliation(s)
- Sophia Fried
- The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel
| | - Omri Matalon
- The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel
| | - Elad Noy
- The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel
| | - Mira Barda-Saad
- The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel
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Megakaryocyte-specific Profilin1-deficiency alters microtubule stability and causes a Wiskott–Aldrich syndrome-like platelet defect. Nat Commun 2014; 5:4746. [DOI: 10.1038/ncomms5746] [Citation(s) in RCA: 72] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2014] [Accepted: 07/20/2014] [Indexed: 11/08/2022] Open
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Kim H, Falet H, Hoffmeister KM, Hartwig JH. Wiskott-Aldrich syndrome protein (WASp) controls the delivery of platelet transforming growth factor-β1. J Biol Chem 2013; 288:34352-63. [PMID: 24133214 DOI: 10.1074/jbc.m113.459750] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Platelets are immunologically competent cells containing cytokines such as TGF-β1 that regulate cell-mediated immunity. However, the mechanisms underlying cytokine secretion from platelets are undefined. The Wiskott-Aldrich syndrome protein (WASp) regulates actin polymerization in nucleated hematopoietic cells but has other role(s) in platelets. WASp-null (WASp(-/-)) platelets stimulated with a PAR-4 receptor agonist had increased TGF-β1 release compared with WT platelets; inhibiting WASp function with wiskostatin augmented TRAP-induced TGF-β1 release in human platelets. TGF-β1 release is dissociated from α-granule secretion (P-selectin up-regulation) and occurs more gradually, with ∼10-15% released after 30-60 min. Blockade of Src family kinase-mediated WASp Tyr-291/Tyr-293 phosphorylation increased TGF-β1 release, with no additive effect in WASp(-/-) platelets, signifying that phosphorylation is critical for WASp-limited TGF-β1 secretion. Inhibiting F-actin assembly with cytochalasin D enhanced secretion in WT platelets and further increased TGF-β1 release in WASp(-/-) platelets, indicating that WASp and actin assembly independently regulate TGF-β1 release. A permeabilized platelet model was used to test the role of upstream small GTPases in TGF-β1 release. N17Cdc42, but not Rac1 mutants, increased TGF-β1 secretion and abrogated WASp phosphorylation. We conclude that WASp function restricts TGF-β1 secretion in a Cdc42- and Src family kinase-dependent manner and independently of actin assembly.
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Affiliation(s)
- Hugh Kim
- From the Division of Translational Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts 02115
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Massaad MJ, Ramesh N, Geha RS. Wiskott-Aldrich syndrome: a comprehensive review. Ann N Y Acad Sci 2013; 1285:26-43. [DOI: 10.1111/nyas.12049] [Citation(s) in RCA: 229] [Impact Index Per Article: 20.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
- Michel J. Massaad
- Division of Immunology, Boston Children's Hospital, and Department of Pediatrics; Harvard Medical School; Boston; Massachusetts
| | - Narayanaswamy Ramesh
- Division of Immunology, Boston Children's Hospital, and Department of Pediatrics; Harvard Medical School; Boston; Massachusetts
| | - Raif S. Geha
- Division of Immunology, Boston Children's Hospital, and Department of Pediatrics; Harvard Medical School; Boston; Massachusetts
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Strom TS. A numerical analysis model for the interpretation of in vivo platelet consumption data. PLoS One 2013; 8:e55087. [PMID: 23383066 PMCID: PMC3557263 DOI: 10.1371/journal.pone.0055087] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2012] [Accepted: 12/21/2012] [Indexed: 12/18/2022] Open
Abstract
Unlike anemias, most thrombocytopenias cannot be separated into those due to impaired production and those due to accelerated consumption. While rapid clearance of labeled platelets from the bloodstream can be followed in thrombocytopenic individuals, no model exists for quantitatively inferring from autologous or allogeneic platelet consumption data what changes in random consumption, lifespan dependent consumption, and platelet production rate may have caused the thrombocytopenia. Here we describe a numerical analysis model which resolves these issues. The model applies three parameter values (a random consumption rate constant, a lognormally-distributed platelet lifespan, and the standard deviation of the latter) to a matrix comprising a series of platelet cohorts which are sequentially produced and fractionally consumed in a series of time intervals. The cohort platelet counts achieved after equilibration of production and consumption both enumerate the population age distribution and sum to the population platelet count. Continued platelet consumption after production is halted then serves to model in vivo platelet consumption data, with consumption rate in the first such interval defining the equilibrium platelet production rate. We use a least squares fitting procedure to find parameter values which best fit observed platelet consumption data obtained in WT and thrombocytopenic WASP(-) mice. Equilibrium platelet age distributions are then ‘grafted’ into the matrix to allow modeling of the consumption of WT platelets in WASP(-) recipients, and vice versa. The optimal parameter values obtained indicate that random WT platelet consumption accounts for a larger fraction of platelet turnover than was previously suspected. Platelet WASP deficiency accelerates random consumption, and a trans effect of recipient WASP deficiency contributes to this. Application of the model to clinical data will allow distinctions to be made between thrombocytopenias due primarily to impaired platelet production and those due to acceleration of random or lifespan-dependent platelet consumption.
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Affiliation(s)
- Ted S Strom
- Department of Pathology and Laboratory Medicine, Memphis Veterans Administration Medical Center, Memphis, TN, USA.
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Mazharian A, Wang YJ, Mori J, Bem D, Finney B, Heising S, Gissen P, White JG, Berndt MC, Gardiner EE, Nieswandt B, Douglas MR, Campbell RD, Watson SP, Senis YA. Mice lacking the ITIM-containing receptor G6b-B exhibit macrothrombocytopenia and aberrant platelet function. Sci Signal 2012; 5:ra78. [PMID: 23112346 PMCID: PMC4973664 DOI: 10.1126/scisignal.2002936] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Platelets are highly reactive cell fragments that adhere to exposed extracellular matrix (ECM) and prevent excessive blood loss by forming clots. Paradoxically, megakaryocytes, which produce platelets in the bone marrow, remain relatively refractory to the ECM-rich environment of the bone marrow despite having the same repertoire of receptors as platelets. These include the ITAM (immunoreceptor tyrosine-based activation motif)-containing collagen receptor complex, which consists of glycoprotein VI (GPVI) and the Fc receptor γ-chain, and the ITIM (immunoreceptor tyrosine-based inhibition motif)-containing receptor G6b-B. We showed that mice lacking G6b-B exhibited macrothrombocytopenia (reduced platelet numbers and the presence of enlarged platelets) and a susceptibility to bleeding as a result of aberrant platelet production and function. Platelet numbers were markedly reduced in G6b-B-deficient mice compared to those in wild-type mice because of increased platelet turnover. Furthermore, megakaryocytes in G6b-B-deficient mice showed enhanced metalloproteinase production, which led to increased shedding of cell-surface receptors, including GPVI and GPIbα. In addition, G6b-B-deficient megakaryocytes exhibited reduced integrin-mediated functions and defective formation of proplatelets, the long filamentous projections from which platelets bud off. Together, these findings establish G6b-B as a major inhibitory receptor regulating megakaryocyte activation, function, and platelet production.
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Affiliation(s)
- Alexandra Mazharian
- Centre of Cardiovascular Sciences, Institute of Biomedical Research, School of Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, Birmingham B15 2TT, UK
| | - Ying-Jie Wang
- Centre of Cardiovascular Sciences, Institute of Biomedical Research, School of Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, Birmingham B15 2TT, UK
| | - Jun Mori
- Centre of Cardiovascular Sciences, Institute of Biomedical Research, School of Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, Birmingham B15 2TT, UK
| | - Danai Bem
- Centre of Cardiovascular Sciences, Institute of Biomedical Research, School of Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, Birmingham B15 2TT, UK
| | - Brenda Finney
- Centre of Cardiovascular Sciences, Institute of Biomedical Research, School of Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, Birmingham B15 2TT, UK
| | - Silke Heising
- Centre of Cardiovascular Sciences, Institute of Biomedical Research, School of Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, Birmingham B15 2TT, UK
| | - Paul Gissen
- Department of Medical and Molecular Genetics, School of Clinical and Experimental Medicine, University of Birmingham, Birmingham B15 2TT, UK
| | - James G. White
- Department of Laboratory Medicine and Pathology, University of Minnesota, Minneapolis, MN 55455, USA
| | - Michael C. Berndt
- Biomedical Diagnostics Institute, Dublin City University and Royal College of Surgeons in Ireland, Glasnevin, Dublin 9, Ireland
| | - Elizabeth E. Gardiner
- Australian Centre for Blood Diseases, Monash University, Alfred Medical Research and Education Precinct, Melbourne, Victoria 3004, Australia
| | - Bernhard Nieswandt
- University Hospital and Rudolf Virchow Center, DFG Research Center for Experimental Biomedicine, University of Würzburg, Würzburg 97080, Germany
| | - Michael R. Douglas
- Neuropharmacology and Neurobiology Section, School of Clinical and Experimental Medicine, University of Birmingham, Birmingham B15 2TT, UK
- Department of Neurology, Dudley Group of Hospitals NHS Foundation Trust, Dudley DY1 2HQ, UK
| | - Robert D. Campbell
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford OX1 3QX, UK
| | - Steve P. Watson
- Centre of Cardiovascular Sciences, Institute of Biomedical Research, School of Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, Birmingham B15 2TT, UK
| | - Yotis A. Senis
- Centre of Cardiovascular Sciences, Institute of Biomedical Research, School of Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, Birmingham B15 2TT, UK
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Chen Y, Aardema J, Misra A, Corey SJ. BAR proteins in cancer and blood disorders. INTERNATIONAL JOURNAL OF BIOCHEMISTRY AND MOLECULAR BIOLOGY 2012; 3:198-208. [PMID: 22773959 PMCID: PMC3388730] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Subscribe] [Scholar Register] [Received: 04/13/2012] [Accepted: 04/18/2012] [Indexed: 06/01/2023]
Abstract
Remodeling of the membrane and cytoskeleton is involved in a wide range of normal and pathologic cellular function. These are complex, highly-coordinated biochemical and biophysical processes involving dozens of proteins. Serving as a scaffold for a variety of proteins and possessing a domain that interacts with plasma membranes, the BAR family of proteins contribute to a range of cellular functions characterized by membrane and cytoskeletal remodeling. There are several subgroups of BAR proteins: BAR, N-BAR, I-BAR, and F-BAR. They differ in their ability to induce angles of membrane curvature and in their recruitment of effector proteins. Evidence is accumulating that BAR proteins contribute to cancer cell invasion, T cell trafficking, phagocytosis, and platelet production. In this review, we discuss the physiological function of BAR proteins and discuss how they contribute to blood and cancer disorders.
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Affiliation(s)
- Yolande Chen
- Departments of Pediatrics and Cell & Molecular Biology, Children’s Memorial Hospital, Robert H. Lurie Comprehensive Cancer Center, Northwestern University Feinberg School of MedicineChicago, IL
| | - Jorie Aardema
- Departments of Pediatrics and Cell & Molecular Biology, Children’s Memorial Hospital, Robert H. Lurie Comprehensive Cancer Center, Northwestern University Feinberg School of MedicineChicago, IL
| | - Ashish Misra
- Division of Cardiology, Department of Medicine, Yale University School of MedicineNew Haven, CT, USA
| | - Seth J Corey
- Departments of Pediatrics and Cell & Molecular Biology, Children’s Memorial Hospital, Robert H. Lurie Comprehensive Cancer Center, Northwestern University Feinberg School of MedicineChicago, IL
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FlnA-null megakaryocytes prematurely release large and fragile platelets that circulate poorly. Blood 2011; 118:2285-95. [PMID: 21652675 DOI: 10.1182/blood-2011-04-348482] [Citation(s) in RCA: 80] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Filamin A (FlnA) is a large cytoplasmic protein that crosslinks actin filaments and anchors membrane receptors and signaling intermediates. FlnA(loxP) PF4-Cre mice that lack FlnA in the megakaryocyte (MK) lineage have a severe macrothrombocytopenia because of accelerated platelet clearance. Macrophage ablation by injection of clodronate-encapsulated liposomes increases blood platelet counts in FlnA(loxP) PF4-Cre mice and reveals the desintegration of FlnA-null platelets into microvesicles, a process that occurs spontaneously during storage. FlnA(loxP) PF4-Cre bone marrows and spleens have a 2.5- to 5-fold increase in MK numbers, indicating increased thrombopoiesis in vivo. Analysis of platelet production in vitro reveals that FlnA-null MKs prematurely convert their cytoplasm into large CD61(+) platelet-sized particles, reminiscent of the large platelets observed in vivo. FlnA stabilizes the platelet von Willebrand factor receptor, as surface expression of von Willebrand factor receptor components is normal on FlnA-null MKs but decreased on FlnA-null platelets. Further, FlnA-null platelets contain multiple GPIbα degradation products and have increased expression of the ADAM17 and MMP9 metalloproteinases. Together, the findings indicate that FlnA-null MKs prematurely release large and fragile platelets that are removed rapidly from the circulation by macrophages.
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Abstract
PURPOSE OF REVIEW Blood platelets are involved in primary and secondary hemostasis and thus maintain the integrity of the vasculature. They circulate with an average lifespan of 5-9 days in humans. Thus, the body must generate and clear platelets daily to maintain normal physiological blood platelet counts. Known platelet clearance mechanisms include antibody-mediated clearance by spleen macrophages, as in immune thrombocytopenia, and platelet consumption due to massive blood loss. RECENT FINDINGS New concepts in the clearance mechanisms of platelets have recently emerged. New evidence shows that platelets desialyted due to chilling or sepsis are cleared in the liver by macrophages, that is Kupffer cells, as well as hepatocytes, through lectin-mediated recognition of platelet glycans. On the contrary, platelet-associated antibodies normalize the clearance of platelets in a mouse model for Wiskott-Aldrich syndrome. SUMMARY The goal of this review is to summarize the latest findings in platelet clearance mechanisms with a focus on lectin-mediated recognition of platelet glycans. Transfusion medicine and treatments of hematopoietic disorders associated with severe thrombocytopenia may benefit from a better understanding of these mechanisms.
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Falet H, Pollitt AY, Begonja AJ, Weber SE, Duerschmied D, Wagner DD, Watson SP, Hartwig JH. A novel interaction between FlnA and Syk regulates platelet ITAM-mediated receptor signaling and function. ACTA ACUST UNITED AC 2010; 207:1967-79. [PMID: 20713593 PMCID: PMC2931168 DOI: 10.1084/jem.20100222] [Citation(s) in RCA: 94] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Filamin A (FlnA) cross-links actin filaments and connects the Von Willebrand factor receptor GPIb-IX-V to the underlying cytoskeleton in platelets. Because FlnA deficiency is embryonic lethal, mice lacking FlnA in platelets were generated by breeding FlnAloxP/loxP females with GATA1-Cre males. FlnAloxP/y GATA1-Cre males have a macrothrombocytopenia and increased tail bleeding times. FlnA-null platelets have decreased expression and altered surface distribution of GPIbα because they lack the normal cytoskeletal linkage of GPIbα to underlying actin filaments. This results in ∼70% less platelet coverage on collagen-coated surfaces at shear rates of 1,500/s, compared with wild-type platelets. Unexpectedly, however, immunoreceptor tyrosine-based activation motif (ITAM)- and ITAM-like–mediated signals are severely compromised in FlnA-null platelets. FlnA-null platelets fail to spread and have decreased α-granule secretion, integrin αIIbβ3 activation, and protein tyrosine phosphorylation, particularly that of the protein tyrosine kinase Syk and phospholipase C–γ2, in response to stimulation through the collagen receptor GPVI and the C-type lectin-like receptor 2. This signaling defect was traced to the loss of a novel FlnA–Syk interaction, as Syk binds to FlnA at immunoglobulin-like repeat 5. Our findings reveal that the interaction between FlnA and Syk regulates ITAM- and ITAM-like–containing receptor signaling and platelet function.
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Affiliation(s)
- Hervé Falet
- Division of Translational Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA.
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Cracking the platelet WIP. Blood 2009; 114:4611-2. [DOI: 10.1182/blood-2009-09-239905] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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