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Mbiandjeu S, Balduini A, Malara A. Megakaryocyte Cytoskeletal Proteins in Platelet Biogenesis and Diseases. Thromb Haemost 2021; 122:666-678. [PMID: 34218430 DOI: 10.1055/s-0041-1731717] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
Thrombopoiesis governs the formation of blood platelets in bone marrow by converting megakaryocytes into long, branched proplatelets on which individual platelets are assembled. The megakaryocyte cytoskeleton responds to multiple microenvironmental cues, including chemical and mechanical stimuli, sustaining the platelet shedding. During the megakaryocyte's life cycle, cytoskeletal networks organize cell shape and content, connect them physically and biochemically to the bone marrow vascular niche, and enable the release of platelets into the bloodstream. While the basic building blocks of the cytoskeleton have been studied extensively, new sets of cytoskeleton regulators have emerged as critical components of the dynamic protein network that supports platelet production. Understanding how the interaction of individual molecules of the cytoskeleton governs megakaryocyte behavior is essential to improve knowledge of platelet biogenesis and develop new therapeutic strategies for inherited thrombocytopenias caused by alterations in the cytoskeletal genes.
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Affiliation(s)
- Serge Mbiandjeu
- Department of Molecular Medicine, University of Pavia, Pavia, Italy
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Zuidscherwoude M, Haining EJ, Simms VA, Watson S, Grygielska B, Hardy AT, Bacon A, Watson SP, Thomas SG. Loss of mDia1 and Fhod1 impacts platelet formation but not platelet function. Platelets 2020; 32:1051-1062. [PMID: 32981398 PMCID: PMC8635707 DOI: 10.1080/09537104.2020.1822522] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022]
Abstract
An organized and dynamic cytoskeleton is required for platelet formation and function. Formins are a large family of actin regulatory proteins which are also able to regulate microtubule dynamics. There are four formin family members expressed in human and mouse megakaryocytes and platelets. We have previously shown that the actin polymerization activity of formin proteins is required for cytoskeletal dynamics and platelet spreading using a small molecule inhibitor. In the current study, we analyze transgenic mouse models deficient in two of these proteins, mDia1 and Fhod1, along with a model lacking both proteins. We demonstrate that double knockout mice display macrothrombocytopenia which is due to aberrant megakaryocyte function and a small decrease in platelet lifespan. Platelet function is unaffected by the loss of these proteins. This data indicates a critical role for formins in platelet and megakaryocyte function.
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Affiliation(s)
- Malou Zuidscherwoude
- Institute of Cardiovascular Sciences, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK
- Centre of Membrane Proteins and Receptors (COMPARE), University of Birmingham and University of Nottingham, Midlands, UK
| | - Elizabeth J. Haining
- Institute of Cardiovascular Sciences, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK
| | - Victoria A. Simms
- Institute of Cardiovascular Sciences, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK
| | - Stephanie Watson
- Institute of Cardiovascular Sciences, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK
| | - Beata Grygielska
- Institute of Cardiovascular Sciences, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK
| | - Alex T. Hardy
- Institute of Cardiovascular Sciences, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK
| | - Andrea Bacon
- Genome Editing Facility, Technology Hub, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK
| | - Stephen P. Watson
- Institute of Cardiovascular Sciences, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK
- Centre of Membrane Proteins and Receptors (COMPARE), University of Birmingham and University of Nottingham, Midlands, UK
| | - Steven G. Thomas
- Institute of Cardiovascular Sciences, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK
- Centre of Membrane Proteins and Receptors (COMPARE), University of Birmingham and University of Nottingham, Midlands, UK
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Green HLH, Zuidscherwoude M, Alenazy F, Smith CW, Bender M, Thomas SG. SMIFH2 inhibition of platelets demonstrates a critical role for formin proteins in platelet cytoskeletal dynamics. J Thromb Haemost 2020; 18:955-967. [PMID: 31930764 PMCID: PMC7186844 DOI: 10.1111/jth.14735] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2019] [Accepted: 01/07/2020] [Indexed: 12/24/2022]
Abstract
BACKGROUND Reorganization of the actin cytoskeleton is required for proper functioning of platelets following activation in response to vascular damage. Formins are a family of proteins that regulate actin polymerization and cytoskeletal organization via a number of domains including the FH2 domain. However, the role of formins in platelet spreading has not been studied in detail. OBJECTIVES Several formin proteins are expressed in platelets so we used an inhibitor of FH2 domains (SMIFH2) to uncover the role of these proteins in platelet spreading and in maintenance of resting platelet shape. METHODS Washed human and mouse platelets were treated with various concentrations of SMIFH2 and the effects on platelet spreading, platelet size, platelet cytoskeletal dynamics, and organization were analyzed using fluorescence and electron microscopy. RESULTS Pretreatment with SMIFH2 completely blocks platelet spreading in both mouse and human platelets through effects on the organization and dynamics of actin and microtubules. However, platelet aggregation and secretion are unaffected. SMIFH2 also caused a decrease in resting platelet size and disrupted the balance of tubulin post-translational modification. CONCLUSIONS These data therefore demonstrated an important role for formin-mediated actin polymerization in platelet spreading and highlighted the importance of formins in cross-talk between the actin and tubulin cytoskeletons.
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Affiliation(s)
- Hannah L. H. Green
- Institute of Cardiovascular SciencesUniversity of BirminghamBirminghamUK
- Present address:
School of Cardiovascular Medicine & SciencesBHF Centre of Research ExcellenceKing's College LondonLondonUK
| | - Malou Zuidscherwoude
- Institute of Cardiovascular SciencesUniversity of BirminghamBirminghamUK
- Centre of Membrane Proteins and Receptors (COMPARE)University of Birmingham and University of NottinghamMidlandsUK
| | - Fawaz Alenazy
- Institute of Cardiovascular SciencesUniversity of BirminghamBirminghamUK
| | | | - Markus Bender
- Institute of Experimental Biomedicine – Chair IUniversity Hospital and Rudolf Virchow CenterWürzburgGermany
| | - Steven G. Thomas
- Institute of Cardiovascular SciencesUniversity of BirminghamBirminghamUK
- Centre of Membrane Proteins and Receptors (COMPARE)University of Birmingham and University of NottinghamMidlandsUK
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Schurr Y, Spindler M, Kurz H, Bender M. The cytoskeletal crosslinking protein MACF1 is dispensable for thrombus formation and hemostasis. Sci Rep 2019; 9:7726. [PMID: 31118482 PMCID: PMC6531446 DOI: 10.1038/s41598-019-44183-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2019] [Accepted: 04/27/2019] [Indexed: 12/15/2022] Open
Abstract
Coordinated reorganization of cytoskeletal structures is critical for key aspects of platelet physiology. While several studies have addressed the role of microtubules and filamentous actin in platelet production and function, the significance of their crosstalk in these processes has been poorly investigated. The microtubule-actin cross-linking factor 1 (MACF1; synonym: Actin cross-linking factor 7, ACF7) is a member of the spectraplakin family, and one of the few proteins expressed in platelets, which possess actin and microtubule binding domains thereby facilitating actin-microtubule interaction and regulation. We used megakaryocyte- and platelet-specific Macf1 knockout (Macf1fl/fl, Pf4-Cre) mice to study the role of MACF1 in platelet production and function. MACF1 deficient mice displayed comparable platelet counts to control mice. Analysis of the platelet cytoskeletal ultrastructure revealed a normal marginal band and actin network. Platelet spreading on fibrinogen was slightly delayed but platelet activation and clot traction was unaffected. Ex vivo thrombus formation and mouse tail bleeding responses were similar between control and mutant mice. These results suggest that MACF1 is dispensable for thrombopoiesis, platelet activation, thrombus formation and the hemostatic function in mice.
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Affiliation(s)
- Yvonne Schurr
- Institute of Experimental Biomedicine - Chair I, University Hospital and Rudolf Virchow Center, Würzburg, Germany
| | - Markus Spindler
- Institute of Experimental Biomedicine - Chair I, University Hospital and Rudolf Virchow Center, Würzburg, Germany
| | - Hendrikje Kurz
- Institute of Experimental Biomedicine - Chair I, University Hospital and Rudolf Virchow Center, Würzburg, Germany
| | - Markus Bender
- Institute of Experimental Biomedicine - Chair I, University Hospital and Rudolf Virchow Center, Würzburg, Germany.
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Ward LSC, Sheriff L, Marshall JL, Manning JE, Brill A, Nash GB, McGettrick HM. Podoplanin regulates the migration of mesenchymal stromal cells and their interaction with platelets. J Cell Sci 2019; 132:jcs.222067. [PMID: 30745334 PMCID: PMC6432720 DOI: 10.1242/jcs.222067] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2018] [Accepted: 01/24/2019] [Indexed: 12/18/2022] Open
Abstract
Mesenchymal stromal cells (MSCs) upregulate podoplanin at sites of infection, chronic inflammation and cancer. Here, we investigated the functional consequences of podoplanin expression on the migratory potential of MSCs and their interactions with circulating platelets. Expression of podoplanin significantly enhanced the migration of MSCs compared to MSCs lacking podoplanin. Rac-1 inhibition altered the membrane localisation of podoplanin and in turn significantly reduced MSC migration. Blocking Rac-1 activity had no effect on the migration of MSCs lacking podoplanin, indicating that it was responsible for regulation of migration through podoplanin. When podoplanin-expressing MSCs were seeded on the basal surface of a porous filter, they were able to capture platelets perfused over the uncoated apical surface and induce platelet aggregation. Similar microthrombi were observed when endothelial cells (ECs) were co-cultured on the apical surface. Confocal imaging shows podoplanin-expressing MSCs extending processes into the EC layer, and these processes could interact with circulating platelets. In both models, platelet aggregation induced by podoplanin-expressing MSCs was inhibited by treatment with recombinant soluble C-type lectin-like receptor 2 (CLEC-2; encoded by the gene Clec1b). Thus, podoplanin may enhance the migratory capacity of tissue-resident MSCs and enable novel interactions with cells expressing CLEC-2. Summary: Podoplanin enhances the migration of mesenchymal stromal cells in a Rac-1-dependent manner, enabling direct interactions of subendothelial stroma with circulating platelets.
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Affiliation(s)
- Lewis S C Ward
- Institute of Inflammation and Ageing, University of Birmingham, Birmingham B15 2TT, UK
| | - Lozan Sheriff
- Institute of Cardiovascular Sciences, College of Medical and Dental Sciences, University of Birmingham, Birmingham B15 2TT, UK
| | - Jennifer L Marshall
- Institute of Inflammation and Ageing, University of Birmingham, Birmingham B15 2TT, UK
| | - Julia E Manning
- Institute of Inflammation and Ageing, University of Birmingham, Birmingham B15 2TT, UK
| | - Alexander Brill
- Institute of Cardiovascular Sciences, College of Medical and Dental Sciences, University of Birmingham, Birmingham B15 2TT, UK.,Centre of Membrane and Protein and Receptors (COMPARE), Institute for Biomedical Research, The Medical School, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK.,Department of Pathophysiology, Sechenov First Moscow State Medical University, Moscow 119048, Russia
| | - Gerard B Nash
- Institute of Cardiovascular Sciences, College of Medical and Dental Sciences, University of Birmingham, Birmingham B15 2TT, UK
| | - Helen M McGettrick
- Institute of Inflammation and Ageing, University of Birmingham, Birmingham B15 2TT, UK
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7
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Zuidscherwoude M, Green HLH, Thomas SG. Formin proteins in megakaryocytes and platelets: regulation of actin and microtubule dynamics. Platelets 2018; 30:23-30. [PMID: 29913076 PMCID: PMC6406210 DOI: 10.1080/09537104.2018.1481937] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The platelet and megakaryocyte cytoskeletons are essential for formation and function of these cells. A dynamic, properly organised tubulin and actin cytoskeleton is critical for the development of the megakaryocyte and the extension of proplatelets. Tubulin in particular plays a pivotal role in the extension of these proplatelets and the release of platelets from them. Tubulin is further required for the maintenance of platelet size, and actin is the driving force for shape change, spreading and platelet contraction during platelet activation. Whilst several key proteins which regulate these cytoskeletons have been described in detail, the formin family of proteins has received less attention. Formins are intriguing as, although they were initially believed to simply be a nucleator of actin polymerisation, increasing evidence shows they are important regulators of the crosstalk between the actin and microtubule cytoskeletons. In this review, we will introduce the formin proteins and consider the recent evidence that they play an important role in platelets and megakaryocytes in mediating both the actin and tubulin cytoskeletons.
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Affiliation(s)
- Malou Zuidscherwoude
- a Institute of Cardiovascular Sciences , University of Birmingham , Birmingham , UK.,b Centre of Membrane Proteins and Receptors (COMPARE) , University of Birmingham and University of Nottingham , Midlands , UK
| | - Hannah L H Green
- a Institute of Cardiovascular Sciences , University of Birmingham , Birmingham , UK
| | - Steven G Thomas
- a Institute of Cardiovascular Sciences , University of Birmingham , Birmingham , UK.,b Centre of Membrane Proteins and Receptors (COMPARE) , University of Birmingham and University of Nottingham , Midlands , UK
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8
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Léon C, Dupuis A, Gachet C, Lanza F. The contribution of mouse models to the understanding of constitutional thrombocytopenia. Haematologica 2017; 101:896-908. [PMID: 27478199 DOI: 10.3324/haematol.2015.139394] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2016] [Accepted: 05/04/2016] [Indexed: 11/09/2022] Open
Abstract
Constitutional thrombocytopenias result from platelet production abnormalities of hereditary origin. Long misdiagnosed and poorly studied, knowledge about these rare diseases has increased considerably over the last twenty years due to improved technology for the identification of mutations, as well as an improvement in obtaining megakaryocyte culture from patient hematopoietic stem cells. Simultaneously, the manipulation of mouse genes (transgenesis, total or conditional inactivation, introduction of point mutations, random chemical mutagenesis) have helped to generate disease models that have contributed greatly to deciphering patient clinical and laboratory features. Most of the thrombocytopenias for which the mutated genes have been identified now have a murine model counterpart. This review focuses on the contribution that these mouse models have brought to the understanding of hereditary thrombocytopenias with respect to what was known in humans. Animal models have either i) provided novel information on the molecular and cellular pathways that were missing from the patient studies; ii) improved our understanding of the mechanisms of thrombocytopoiesis; iii) been instrumental in structure-function studies of the mutated gene products; and iv) been an invaluable tool as preclinical models to test new drugs or develop gene therapies. At present, the genetic determinants of thrombocytopenia remain unknown in almost half of all cases. Currently available high-speed sequencing techniques will identify new candidate genes, which will in turn allow the generation of murine models to confirm and further study the abnormal phenotype. In a complementary manner, programs of random mutagenesis in mice should also identify new candidate genes involved in thrombocytopenia.
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Affiliation(s)
- Catherine Léon
- UMR_S949, INSERM, Strasbourg, France Etablissement Français du Sang-Alsace (EFS-Alsace), Strasbourg, France Université de Strasbourg, France Fédération de Médecine Translationnelle de Strasbourg (FMTS), France
| | - Arnaud Dupuis
- UMR_S949, INSERM, Strasbourg, France Etablissement Français du Sang-Alsace (EFS-Alsace), Strasbourg, France Université de Strasbourg, France Fédération de Médecine Translationnelle de Strasbourg (FMTS), France
| | - Christian Gachet
- UMR_S949, INSERM, Strasbourg, France Etablissement Français du Sang-Alsace (EFS-Alsace), Strasbourg, France Université de Strasbourg, France Fédération de Médecine Translationnelle de Strasbourg (FMTS), France
| | - François Lanza
- UMR_S949, INSERM, Strasbourg, France Etablissement Français du Sang-Alsace (EFS-Alsace), Strasbourg, France Université de Strasbourg, France Fédération de Médecine Translationnelle de Strasbourg (FMTS), France
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9
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Poulter NS, Thomas SG. Cytoskeletal regulation of platelet formation: Coordination of F-actin and microtubules. Int J Biochem Cell Biol 2015. [PMID: 26210823 DOI: 10.1016/j.biocel.2015.07.008] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Platelets are small, anucleate blood cells which play an important role in haemostasis. Thrombocytopenia is a condition where the platelet count falls below 150×10(9)/l and patients suffering from severe forms of this condition can experience life-threatening bleeds requiring platelet transfusions. Platelets are produced from large progenitor cells called megakaryocytes which are found in the bone marrow. The process of megakaryocyte maturation and the formation of proplatelets are essential steps in the production of mature platelets and both depend heavily on the actin and microtubule cytoskeletons. Understanding these processes is important for the development of in vitro platelet production which will help to treat thrombocytopenia as well as produce model systems for studying platelet-associated disorders. This review will highlight some of the recent advances in our understanding of the role of the cytoskeleton in platelet production, especially the key molecules and signalling pathways that regulate actin and microtubule crosstalk.
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Affiliation(s)
- Natalie S Poulter
- Centre for Cardiovascular Sciences, College of Medical and Dental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
| | - Steven G Thomas
- Centre for Cardiovascular Sciences, College of Medical and Dental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
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10
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Abstract
Rho GTPases are critical for platelet function. Although the roles of RhoA, Rac and Cdc42 are characterized, platelets express other Rho GTPases, whose activities are less well understood. This review summarizes our understanding of the roles of platelet Rho GTPases and focuses particularly on the functions of Rif and RhoG. In human platelets, Rif interacts with cytoskeleton regulators including formins mDia1 and mDia3, whereas RhoG binds SNARE-complex proteins and cytoskeletal regulators ELMO and DOCK1. Knockout mouse studies suggest that Rif plays no critical functions in platelets, likely due to functional overlap with other Rho GTPases. In contrast, RhoG is essential for normal granule secretion downstream of the collagen receptor GPVI. The central defect in RhoG-/- platelets is reduced dense granule secretion, which impedes integrin activation and aggregation and limits platelet recruitment to growing thrombi under shear, translating into reduced thrombus formation in vivo. Potential avenues for future work on Rho GTPases in platelets are also highlighted, including identification of the key regulator for platelet filopodia formation and investigation of the role of the many Rho GTPase regulators in platelet function in both health and disease.
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The formin DIAPH1 (mDia1) regulates megakaryocyte proplatelet formation by remodeling the actin and microtubule cytoskeletons. Blood 2014; 124:3967-77. [PMID: 25298036 DOI: 10.1182/blood-2013-12-544924] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Megakaryocytes are highly specialized precursor cells that produce platelets via cytoplasmic extensions called proplatelets. Proplatelet formation (PPF) requires profound changes in microtubule and actin organization. In this work, we demonstrated that DIAPH1 (mDia1), a mammalian homolog of Drosophila diaphanous that works as an effector of the small GTPase Rho, negatively regulates PPF by controlling the dynamics of the actin and microtubule cytoskeletons. Moreover, we showed that inhibition of both DIAPH1 and the Rho-associated protein kinase (Rock)/myosin pathway increased PPF via coordination of both cytoskeletons. We provide evidence that 2 major effectors of the Rho GTPase pathway (DIAPH1 and Rock/myosin II) are involved not only in Rho-mediated stress fibers assembly, but also in the regulation of microtubule stability and dynamics during PPF.
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12
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Iskratsch T, Yu CH, Mathur A, Liu S, Stévenin V, Dwyer J, Hone J, Ehler E, Sheetz M. FHOD1 is needed for directed forces and adhesion maturation during cell spreading and migration. Dev Cell 2014; 27:545-59. [PMID: 24331927 DOI: 10.1016/j.devcel.2013.11.003] [Citation(s) in RCA: 80] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2013] [Revised: 10/19/2013] [Accepted: 11/04/2013] [Indexed: 01/13/2023]
Abstract
Matrix adhesions provide critical signals for cell growth or differentiation. They form through a number of distinct steps that follow integrin binding to matrix ligands. In an early step, integrins form clusters that support actin polymerization by an unknown mechanism. This raises the question of how actin polymerization occurs at the integrin clusters. We report here that a major formin in mouse fibroblasts, FHOD1, is recruited to integrin clusters, resulting in actin assembly. Using cell-spreading assays on lipid bilayers, solid substrates, and high-resolution force-sensing pillar arrays, we find that knockdown of FHOD1 impairs spreading, coordinated application of adhesive force, and adhesion maturation. Finally, we show that targeting of FHOD1 to the integrin sites depends on the direct interaction with Src family kinases and is upstream of the activation by Rho kinase. Thus, our findings provide insights into the mechanisms of cell migration with implications for development and disease.
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Affiliation(s)
- Thomas Iskratsch
- Department of Biological Sciences, Columbia University, New York, NY 10027, USA.
| | - Cheng-Han Yu
- Mechanobiology Institute, National University of Singapore, Singapore 117411, Singapore
| | - Anurag Mathur
- Department of Mechanical Engineering, Columbia University, New York, NY 10027, USA
| | - Shuaimin Liu
- Department of Mechanical Engineering, Columbia University, New York, NY 10027, USA
| | - Virginie Stévenin
- Department of Biological Sciences, Columbia University, New York, NY 10027, USA
| | - Joseph Dwyer
- Randall Division of Cell and Molecular Biophysics and Cardiovascular Division, King's College London, London SE1 1UL, UK
| | - James Hone
- Department of Mechanical Engineering, Columbia University, New York, NY 10027, USA
| | - Elisabeth Ehler
- Randall Division of Cell and Molecular Biophysics and Cardiovascular Division, King's College London, London SE1 1UL, UK
| | - Michael Sheetz
- Department of Biological Sciences, Columbia University, New York, NY 10027, USA; Mechanobiology Institute, National University of Singapore, Singapore 117411, Singapore.
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Goggs R, Savage JS, Mellor H, Poole AW. The small GTPase Rif is dispensable for platelet filopodia generation in mice. PLoS One 2013; 8:e54663. [PMID: 23359340 PMCID: PMC3554654 DOI: 10.1371/journal.pone.0054663] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2012] [Accepted: 12/13/2012] [Indexed: 11/18/2022] Open
Abstract
Background Formation of filopodia and other shape change events are vital for platelet hemostatic function. The mechanisms regulating filopodia formation by platelets are incompletely understood however. In particular the small GTPase responsible for initiating filopodia formation by platelets remains elusive. The canonical pathway involving Cdc42 is not essential for filopodia formation in mouse platelets. The small GTPase Rif (RhoF) provides an alternative route to filopodia generation in other cell types and is expressed in both human and mouse platelets. Hypothesis/Objective We hypothesized that Rif might be responsible for generating filopodia by platelets and generated a novel knockout mouse model to investigate the functional role of Rif in platelets. Methodology/Principal Findings Constitutive RhoF−/− mice are viable and have normal platelet, leukocyte and erythrocyte counts and indices. RhoF−/− platelets form filopodia and spread normally on various agonist surfaces in static conditions and under arterial shear. In addition, RhoF−/− platelets have normal actin dynamics, are able to activate and aggregate normally and secrete from alpha and dense granules in response to collagen related peptide and thrombin stimulation. Conclusions The small GTPase Rif does not appear to be critical for platelet function in mice. Functional overlap between Rif and other small GTPases may be responsible for the non-essential role of Rif in platelets.
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Affiliation(s)
- Robert Goggs
- School of Physiology and Pharmacology, University of Bristol, Bristol, United Kingdom
| | - Joshua S. Savage
- School of Physiology and Pharmacology, University of Bristol, Bristol, United Kingdom
| | - Harry Mellor
- School of Biochemistry, University of Bristol, Bristol, United Kingdom
| | - Alastair W. Poole
- School of Physiology and Pharmacology, University of Bristol, Bristol, United Kingdom
- * E-mail:
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Severin S, Gaits-Iacovoni F, Allart S, Gratacap MP, Payrastre B. A confocal-based morphometric analysis shows a functional crosstalk between the actin filament system and microtubules in thrombin-stimulated platelets. J Thromb Haemost 2013; 11:183-6. [PMID: 23122006 DOI: 10.1111/jth.12053] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Affiliation(s)
- S Severin
- Inserm, U1048 and Université Toulouse 3, I2MC, Toulouse Cedex, France.
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15
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Abstract
The Rho family of GTP binding proteins, also commonly referred to as the Rho GTPases, are master regulators of the platelet cytoskeleton and platelet function. These low-molecular-weight or 'small' GTPases act as signaling switches in the spatial and temporal transduction, and amplification of signals from platelet cell surface receptors to the intracellular signaling pathways that drive platelet function. The Rho GTPase family members RhoA, Cdc42 and Rac1 have emerged as key regulators in the dynamics of the actin cytoskeleton in platelets and play key roles in platelet aggregation, secretion, spreading and thrombus formation. Rho GTPase regulators, including GEFs and GAPs and downstream effectors, such as the WASPs, formins and PAKs, may also regulate platelet activation and function. In this review, we provide an overview of Rho GTPase signaling in platelet physiology. Previous studies of Rho GTPases and platelets have had a shared history, as platelets have served as an ideal, non-transformed cellular model to characterize Rho function. Likewise, recent studies of the cell biology of Rho GTPase family members have helped to build an understanding of the molecular regulation of platelet function and will continue to do so through the further characterization of Rho GTPases as well as Rho GAPs, GEFs, RhoGDIs and Rho effectors in actin reorganization and other Rho-driven cellular processes.
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Affiliation(s)
- J E Aslan
- Department of Biomedical Engineering and Cell & Developmental Biology, School of Medicine, Oregon Health & Science University, Portland, OR 97239, USA.
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Steele BM, Harper MT, Smolenski AP, Alkazemi N, Poole AW, Fitzgerald DJ, Maguire PB. WNT-3a modulates platelet function by regulating small GTPase activity. FEBS Lett 2012; 586:2267-72. [PMID: 22705156 DOI: 10.1016/j.febslet.2012.05.060] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2012] [Revised: 05/04/2012] [Accepted: 05/23/2012] [Indexed: 12/13/2022]
Abstract
Here we provide evidence that WNT-3a modulates platelet function by regulating the activity of four key GTPase proteins: Rap1, Cdc42, Rac1 and RhoA. We observe WNT-3a to differentially regulate small GTPase activity in platelets, promoting the GDP-bound form of Rap1b to inhibit integrin-α(IIb)β(3) adhesion, while concomitantly increasing Cdc42 and Rac1-GTP levels thereby disrupting normal platelet spreading. We demonstrate that Daam-1 interacts with Dishevelled upon platelet activation, which correlates with increased RhoA-GTP levels. Upon pre-treatment with WNT-3a, this complex disassociates, concurrent with a reduction in RhoA-GTP. Together these data implicate WNT-3a as a novel upstream regulator of small GTPase activity in platelets.
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Affiliation(s)
- Brian M Steele
- UCD Conway Institute, University College Dublin, Belfield, Dublin D4, Ireland.
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