The Experts below are selected from a list of 294 Experts worldwide ranked by ideXlab platform
Alan T. Nurden - One of the best experts on this subject based on the ideXlab platform.
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should any genetic defect affecting α granules in Platelets be classified as Gray Platelet Syndrome
American Journal of Hematology, 2016Co-Authors: Alan T. Nurden, Paquita NurdenAbstract:There is much current interest in the role of the Platelet storage pool of α-granule proteins both in hemostasis and non-hemostatic events. As well as in the arrest of bleeding, the secreted proteins participate in wound healing, inflammation, and innate immunity while in pathology they may be actors in arterial thrombosis and atherosclerosis as well as cancer and metastasis. For a long time, Gray Platelet Syndrome (GPS) has been regarded as the classic inherited Platelet disorder caused by an absence of α-granules and their contents. While NBEAL2 is the major source of mutations in GPS, other gene variants may give rise to significant α-granule deficiencies in Platelets. These include GATA1, VPS33B, or VIPAS39 in the arthrogryposis, renal dysfunction, and cholestasis (ARC) Syndrome and now GFI1B. Nevertheless, many phenotypic differences are associated with mutations in these genes. This critical review was aimed to assess genotype/phenotype variability in disorders of Platelet α-granule biogenesis and to urge caution in grouping all genetic defects of α-granules as GPS. Am. J. Hematol. 91:714-718, 2016. © 2016 Wiley Periodicals, Inc.
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Should any Genetic Defect Affecting α‐Granules in Platelets be Classified as Gray Platelet Syndrome?
American journal of hematology, 2016Co-Authors: Alan T. Nurden, Paquita NurdenAbstract:There is much current interest in the role of the Platelet storage pool of α-granule proteins both in hemostasis and non-hemostatic events. As well as in the arrest of bleeding, the secreted proteins participate in wound healing, inflammation, and innate immunity while in pathology they may be actors in arterial thrombosis and atherosclerosis as well as cancer and metastasis. For a long time, Gray Platelet Syndrome (GPS) has been regarded as the classic inherited Platelet disorder caused by an absence of α-granules and their contents. While NBEAL2 is the major source of mutations in GPS, other gene variants may give rise to significant α-granule deficiencies in Platelets. These include GATA1, VPS33B, or VIPAS39 in the arthrogryposis, renal dysfunction, and cholestasis (ARC) Syndrome and now GFI1B. Nevertheless, many phenotypic differences are associated with mutations in these genes. This critical review was aimed to assess genotype/phenotype variability in disorders of Platelet α-granule biogenesis and to urge caution in grouping all genetic defects of α-granules as GPS. Am. J. Hematol. 91:714-718, 2016. © 2016 Wiley Periodicals, Inc.
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The Nbeal2(-/-) mouse as a model for the Gray Platelet Syndrome.
Rare diseases (Austin Tex.), 2013Co-Authors: Carsten Deppermann, Alan T. Nurden, Paquita Nurden, Bernhard Nieswandt, David StegnerAbstract:The Gray Platelet Syndrome (GPS) is a rare, autosomal-recessive Platelet disorder characterized by thrombocytopenia, large Platelets lacking α-granules, and variable bleeding. GPS has been linked to mutations in the neurobeachin-like 2 gene (NBEAL2). We have recently characterized Nbeal2-deficient mice and shown that the absence of Nbeal2 results in defective protein sorting in megakaryocytes (MKs) and impaired α-granule biogenesis, a finding also seen for human MKs. In the mice, the lack of α-granules results in impaired aggregation, defective Platelet adhesion to collagen under flow and reduced pro-coagulant activity; findings that translate into defective hemostasis and thrombosis in vivo indicating that α-granule secretion is critical for Platelet plug stability. Furthermore, we revealed a role of α-granule proteins in ischemic stroke and wound healing. Thus, Nbeal2-deficient mice recapitulate the hallmarks of human GPS without showing its phenotypic heterogeneity and are a promising model to investigate the (patho-)physiological relevancy of α-granules.
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the nbeal2 mouse as a model for the Gray Platelet Syndrome
Rare diseases (Austin Tex.), 2013Co-Authors: Carsten Deppermann, Alan T. Nurden, Paquita Nurden, Bernhard Nieswandt, David StegnerAbstract:The Gray Platelet Syndrome (GPS) is a rare, autosomal-recessive Platelet disorder characterized by thrombocytopenia, large Platelets lacking α-granules, and variable bleeding. GPS has been linked to mutations in the neurobeachin-like 2 gene (NBEAL2). We have recently characterized Nbeal2-deficient mice and shown that the absence of Nbeal2 results in defective protein sorting in megakaryocytes (MKs) and impaired α-granule biogenesis, a finding also seen for human MKs. In the mice, the lack of α-granules results in impaired aggregation, defective Platelet adhesion to collagen under flow and reduced pro-coagulant activity; findings that translate into defective hemostasis and thrombosis in vivo indicating that α-granule secretion is critical for Platelet plug stability. Furthermore, we revealed a role of α-granule proteins in ischemic stroke and wound healing. Thus, Nbeal2-deficient mice recapitulate the hallmarks of human GPS without showing its phenotypic heterogeneity and are a promising model to investigate the (patho-)physiological relevancy of α-granules.
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Phenotypic heterogeneity in the Gray Platelet Syndrome extends to the expression of TREM family member, TLT-1
Thrombosis and haemostasis, 2008Co-Authors: Alan T. Nurden, Paquita Nurden, Robert Combrié, Emilse Bermejo, Daniel W. Mcvicar, A. Valance WashingtonAbstract:The Gray Platelet Syndrome (GPS) is a rare inherited disorder linked to undefined molecular abnormalities that prevent the formation and maturation of α-granules. Here, we report studies on two patients from unrelated families that confirm phenotypic heterogeneity in the disease. First we used immunoelectron microscopy (I-EM) to confirm that TREM-like transcript- 1 (TLT-1) is mostly localized to α-granule membranes of normal Platelets. Then we performed Western blotting (WB) and flow cytometry with permeabilized Platelets to show that TLT-1 is selectively reduced in the Platelets of patient 1, previously noted to be deficient in glycoprotein (GP)VI (Nurden et al., Blood 2004; 104: 107–114). Yet both TLT-1 and GPVI were normally expressed in Platelets of patient 2. Usual levels of JAM-C and claudin-5, also members of the immunoglobulin receptor family, were detected in Platelets of both patients. In contrast, P-selectin was markedly decreased for patient 1 but not patient 2. Two metalloproteases, MMP-2 and MMP-9 were normally present. As predicted, Platelets of patient 1 showed little labelling for TLT-1 in I-EM, whereas residual Fg was seen in small vesicular structures and P-selectin lining vacuoles or channels of what may be elements of the surface-connected canalicular system. Our results identify TLT-1 as a glycoprotein potentially targeted in Platelets of GPS patients, while decreases in at least three membrane glycoproteins suggest that an unidentified proteolytic activity may contribute to the phenotype in some patients with this rare disease.
Paquita Nurden - One of the best experts on this subject based on the ideXlab platform.
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should any genetic defect affecting α granules in Platelets be classified as Gray Platelet Syndrome
American Journal of Hematology, 2016Co-Authors: Alan T. Nurden, Paquita NurdenAbstract:There is much current interest in the role of the Platelet storage pool of α-granule proteins both in hemostasis and non-hemostatic events. As well as in the arrest of bleeding, the secreted proteins participate in wound healing, inflammation, and innate immunity while in pathology they may be actors in arterial thrombosis and atherosclerosis as well as cancer and metastasis. For a long time, Gray Platelet Syndrome (GPS) has been regarded as the classic inherited Platelet disorder caused by an absence of α-granules and their contents. While NBEAL2 is the major source of mutations in GPS, other gene variants may give rise to significant α-granule deficiencies in Platelets. These include GATA1, VPS33B, or VIPAS39 in the arthrogryposis, renal dysfunction, and cholestasis (ARC) Syndrome and now GFI1B. Nevertheless, many phenotypic differences are associated with mutations in these genes. This critical review was aimed to assess genotype/phenotype variability in disorders of Platelet α-granule biogenesis and to urge caution in grouping all genetic defects of α-granules as GPS. Am. J. Hematol. 91:714-718, 2016. © 2016 Wiley Periodicals, Inc.
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Should any Genetic Defect Affecting α‐Granules in Platelets be Classified as Gray Platelet Syndrome?
American journal of hematology, 2016Co-Authors: Alan T. Nurden, Paquita NurdenAbstract:There is much current interest in the role of the Platelet storage pool of α-granule proteins both in hemostasis and non-hemostatic events. As well as in the arrest of bleeding, the secreted proteins participate in wound healing, inflammation, and innate immunity while in pathology they may be actors in arterial thrombosis and atherosclerosis as well as cancer and metastasis. For a long time, Gray Platelet Syndrome (GPS) has been regarded as the classic inherited Platelet disorder caused by an absence of α-granules and their contents. While NBEAL2 is the major source of mutations in GPS, other gene variants may give rise to significant α-granule deficiencies in Platelets. These include GATA1, VPS33B, or VIPAS39 in the arthrogryposis, renal dysfunction, and cholestasis (ARC) Syndrome and now GFI1B. Nevertheless, many phenotypic differences are associated with mutations in these genes. This critical review was aimed to assess genotype/phenotype variability in disorders of Platelet α-granule biogenesis and to urge caution in grouping all genetic defects of α-granules as GPS. Am. J. Hematol. 91:714-718, 2016. © 2016 Wiley Periodicals, Inc.
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The Nbeal2(-/-) mouse as a model for the Gray Platelet Syndrome.
Rare diseases (Austin Tex.), 2013Co-Authors: Carsten Deppermann, Alan T. Nurden, Paquita Nurden, Bernhard Nieswandt, David StegnerAbstract:The Gray Platelet Syndrome (GPS) is a rare, autosomal-recessive Platelet disorder characterized by thrombocytopenia, large Platelets lacking α-granules, and variable bleeding. GPS has been linked to mutations in the neurobeachin-like 2 gene (NBEAL2). We have recently characterized Nbeal2-deficient mice and shown that the absence of Nbeal2 results in defective protein sorting in megakaryocytes (MKs) and impaired α-granule biogenesis, a finding also seen for human MKs. In the mice, the lack of α-granules results in impaired aggregation, defective Platelet adhesion to collagen under flow and reduced pro-coagulant activity; findings that translate into defective hemostasis and thrombosis in vivo indicating that α-granule secretion is critical for Platelet plug stability. Furthermore, we revealed a role of α-granule proteins in ischemic stroke and wound healing. Thus, Nbeal2-deficient mice recapitulate the hallmarks of human GPS without showing its phenotypic heterogeneity and are a promising model to investigate the (patho-)physiological relevancy of α-granules.
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the nbeal2 mouse as a model for the Gray Platelet Syndrome
Rare diseases (Austin Tex.), 2013Co-Authors: Carsten Deppermann, Alan T. Nurden, Paquita Nurden, Bernhard Nieswandt, David StegnerAbstract:The Gray Platelet Syndrome (GPS) is a rare, autosomal-recessive Platelet disorder characterized by thrombocytopenia, large Platelets lacking α-granules, and variable bleeding. GPS has been linked to mutations in the neurobeachin-like 2 gene (NBEAL2). We have recently characterized Nbeal2-deficient mice and shown that the absence of Nbeal2 results in defective protein sorting in megakaryocytes (MKs) and impaired α-granule biogenesis, a finding also seen for human MKs. In the mice, the lack of α-granules results in impaired aggregation, defective Platelet adhesion to collagen under flow and reduced pro-coagulant activity; findings that translate into defective hemostasis and thrombosis in vivo indicating that α-granule secretion is critical for Platelet plug stability. Furthermore, we revealed a role of α-granule proteins in ischemic stroke and wound healing. Thus, Nbeal2-deficient mice recapitulate the hallmarks of human GPS without showing its phenotypic heterogeneity and are a promising model to investigate the (patho-)physiological relevancy of α-granules.
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Gray Platelet Syndrome and defective thrombo-inflammation in Nbeal2-deficient mice
The Journal of clinical investigation, 2013Co-Authors: Carsten Deppermann, Paquita Nurden, Deya Cherpokova, Jan-niklas Schulz, Ina Thielmann, Peter Kraft, Timo Vögtle, Christoph Kleinschnitz, Sebastian Dütting, Georg KrohneAbstract:Platelets are anuclear organelle-rich cell fragments derived from bone marrow megakaryocytes (MKs) that safeguard vascular integrity. The major Platelet organelles, α-granules, release proteins that participate in thrombus formation and hemostasis. Proteins stored in α-granules are also thought to play a role in inflammation and wound healing, but their functional significance in vivo is unknown. Mutations in NBEAL2 have been linked to Gray Platelet Syndrome (GPS), a rare bleeding disorder characterized by macrothrombocytopenia, with Platelets lacking α-granules. Here we show that Nbeal2-knockout mice display the characteristics of human GPS, with defective α-granule biogenesis in MKs and their absence from Platelets. Nbeal2 deficiency did not affect MK differentiation and proPlatelet formation in vitro or Platelet life span in vivo. Nbeal2-deficient Platelets displayed impaired adhesion, aggregation, and coagulant activity ex vivo that translated into defective arterial thrombus formation and protection from thrombo-inflammatory brain infarction following focal cerebral ischemia. In a model of excisional skin wound repair, Nbeal2-deficient mice exhibited impaired development of functional granulation tissue due to severely reduced differentiation of myofibroblasts in the absence of α-granule secretion. This study demonstrates that Platelet α-granule constituents are critically required not only for hemostasis but also thrombosis, acute thrombo-inflammatory disease states, and tissue reconstitution after injury.
A. Valance Washington - One of the best experts on this subject based on the ideXlab platform.
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Phenotypic heterogeneity in the Gray Platelet Syndrome extends to the expression of TREM family member, TLT-1
Thrombosis and haemostasis, 2008Co-Authors: Alan T. Nurden, Paquita Nurden, Robert Combrié, Emilse Bermejo, Daniel W. Mcvicar, A. Valance WashingtonAbstract:The Gray Platelet Syndrome (GPS) is a rare inherited disorder linked to undefined molecular abnormalities that prevent the formation and maturation of α-granules. Here, we report studies on two patients from unrelated families that confirm phenotypic heterogeneity in the disease. First we used immunoelectron microscopy (I-EM) to confirm that TREM-like transcript- 1 (TLT-1) is mostly localized to α-granule membranes of normal Platelets. Then we performed Western blotting (WB) and flow cytometry with permeabilized Platelets to show that TLT-1 is selectively reduced in the Platelets of patient 1, previously noted to be deficient in glycoprotein (GP)VI (Nurden et al., Blood 2004; 104: 107–114). Yet both TLT-1 and GPVI were normally expressed in Platelets of patient 2. Usual levels of JAM-C and claudin-5, also members of the immunoglobulin receptor family, were detected in Platelets of both patients. In contrast, P-selectin was markedly decreased for patient 1 but not patient 2. Two metalloproteases, MMP-2 and MMP-9 were normally present. As predicted, Platelets of patient 1 showed little labelling for TLT-1 in I-EM, whereas residual Fg was seen in small vesicular structures and P-selectin lining vacuoles or channels of what may be elements of the surface-connected canalicular system. Our results identify TLT-1 as a glycoprotein potentially targeted in Platelets of GPS patients, while decreases in at least three membrane glycoproteins suggest that an unidentified proteolytic activity may contribute to the phenotype in some patients with this rare disease.
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Heterogeneity in the Gray Platelet Syndrome: Variable Expression of the TREM Family Member, TLT-1, in Platelets of Patients of Two Unrelated Families.
Blood, 2006Co-Authors: Alan T. Nurden, Paquita Nurden, Emilse Bermejo, A. Valance Washington, Daniel W. McvicarAbstract:The Gray Platelet Syndrome is a rare inherited disorder of Platelets linked to undefined molecular abnormalities that prevent the normal formation and maturation of alpha-granules. This leads to the spontaneous release of endogenously synthesized alpha-granule proteins from megakaryocytes into the marrow, a factor favouring the development of fibrosis. The Platelet functional response varies greatly in patients in the GPS. Here we examine patients from two unrelated families, patient 1 has Platelets that have a much reduced aggregation response to collagen, and patient 2 has a normal response. Both patients possess Platelets severely deficient in alpha-granules. Features of their internal stucture include numerous vacuoles, thin channels and a reduced surface-connected canalicular system (SCCS) and small vesicular structures (SVs) some of which are open to the surface and rapidly accessed by abciximab used as a probe for ligand trafficking in immunoelectron microscopy (I-EM). Residual amounts of fibrinogen, and VWF are often associated with the SVs, P-selectin delimits some elements of the SCCS and vacuoles while most internal and surface membranes are labelled for seven transmembrane receptors such as PAR-1 and TPalpha, Immunoblotting showed that unlike Platelets of patient 1 where GPVI was severely decreased (Nurden P et al, Blood 2004; 104:107–114), those of patient 2 normally expressed this collagen receptor. TREM-like transcript-1 (TLT-1), a membrane glycoprotein, has recently been predominantly localized to the alpha-granules of human Platelets on the basis of its codistribution with P-selectin. Using a rabbit antibody to a cytoplasmic domain sequence we have confirmed this distribution in normal Platelets. Significantly, we then further showed by Western blotting (WB) that TLT-1, like GPVI, is severely reduced in the Platelets of patient 1 but normally expressed in those of patient 2. Flow cytometry using permeabilized Platelets showed that this decrease was selective compared to normal levels of JAM-3 and claudin-5, also members of the immunoglobulin family. I-EM showed residual TLT-1 associated with both internal and external membranes. One possibility is that a pathology-related metalloprotease activity (MMP) leads to spontaneous cleavage of the extracellular domains of GPVI and TLT-1 in the Platelets of some patients. We therefore examined the Platelets of patient 1 to see if MMP-2 and MMP-9, two proteases expressed in normal Platelets, were present. I-EM first showed that while for normal Platelets both proteases were in their majority localized to alpha-granules, other pools were present in the cytoplasmic and surface-linked membrane systems. The latter were retained in the Platelets of patient 1 but flow cytometry with permeabilized Platelets failed to show over-expression. Our results identify TLT-1 as a new glycoprotein potentially cleaved in GPS Platelets and further show that so-far undefined protease activity contributes to phenotypic heterogeneity in this rare disease.
Rémi Favier - One of the best experts on this subject based on the ideXlab platform.
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Neutrophil specific granule and NETosis defects in Gray Platelet Syndrome.
Blood advances, 2021Co-Authors: Cathelijn E. M. Aarts, Rémi Favier, Marie Favier, Kate Downes, Arie J. Hoogendijk, Evelien G. G. Sprenkeler, Roel P. Gazendam, Anton T.j. Tool, John L. Van Hamme, Myrto KostadimaAbstract:Abstract Gray Platelet Syndrome (GPS) is an autosomal recessive bleeding disorder characterized by a lack of α-granules in Platelets and progressive myelofibrosis. Rare loss-of-function variants in neurobeachin-like 2 (NBEAL2), a member of the family of beige and Chediak-Higashi (BEACH) genes, are causal of GPS. It is suggested that BEACH domain containing proteins are involved in fusion, fission, and trafficking of vesicles and granules. Studies in knockout mice suggest that NBEAL2 may control the formation and retention of granules in neutrophils. We found that neutrophils obtained from the peripheral blood from 13 patients with GPS have a normal distribution of azurophilic granules but show a deficiency of specific granules (SGs), as confirmed by immunoelectron microscopy and mass spectrometry proteomics analyses. CD34+ hematopoietic stem cells (HSCs) from patients with GPS differentiated into mature neutrophils also lacked NBEAL2 expression but showed similar SG protein expression as control cells. This is indicative of normal granulopoiesis in GPS and identifies NBEAL2 as a potentially important regulator of granule release. Patient neutrophil functions, including production of reactive oxygen species, chemotaxis, and killing of bacteria and fungi, were intact. NETosis was absent in circulating GPS neutrophils. Lack of NETosis is suggested to be independent of NBEAL2 expression but associated with SG defects instead, as indicated by comparison with HSC-derived neutrophils. Since patients with GPS do not excessively suffer from infections, the consequence of the reduced SG content and lack of NETosis for innate immunity remains to be explored.
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Correction of Severe Myelofibrosis, Impaired Platelet Functions and Abnormalities in a Patient with Gray Platelet Syndrome Successfully Treated by Stem Cell Transplantation
Platelets, 2019Co-Authors: Rémi Favier, Xavier Roussel, Sylvain Audia, Jean Claude Bordet, Emmanuel De Maistre, Pierre Hirsch, Anne Neuhart, Isabelle Bedgedjian, Vasiliki Gkalea, Marie FavierAbstract:Gray Platelet Syndrome (GPS) is an inherited disorder. Patients harboring GPS have thrombocytopenia with large Platelets lacking α-granules. A long-term complication is myelofibrosis with pancytope...
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Exome sequencing identifies NBEAL2 as the causative gene for Gray Platelet Syndrome
2016Co-Authors: Cornelis A Albers, Ana Cvejic, Rémi Favier, Evelien E Bouwmans, Paul Bertone, Gregory Jordan, Ross N W Kettleborough, Myrto Kostadima, Christine Alessi, Y J ReadAbstract:Gray Platelet Syndrome (GPS) is a predominantly recessive Platelet disorder characterized by a mild thrombocytopenia with large Platelets and a paucity of α-granules; these abnormalities cause mostly moderate but in rare cases severe bleeding. We sequenced the exomes of four unrelated cases and identified as the causative gene NBEAL2, a gene with previously unknown function but a member of a gene family involved in granule development. Silencing of nbeal2 in zebrafish abrogated thrombocyte formation. Platelets are the second most abundant cell in the blood and maintain arterial vessel wall integrity. Formation of the Platelet plug at the site of vessel wall damage is a multi-step process of tethering and attachment followed by activation that causes the release of both the α- and δ-granules. Platelets are anucleate and formed in large numbers in the bone marrow Correspondence should be addressed to C.A.A
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Exome sequencing identifies NBEAL2 as the causative gene for Gray Platelet Syndrome
Nature Genetics, 2011Co-Authors: Cornelis A Albers, Ana Cvejic, Rémi Favier, Evelien E Bouwmans, Marie-christine Alessi, Paul Bertone, Gregory Jordan, Ross N W Kettleborough, Graham Kiddle, Myrto KostadimaAbstract:Gray Platelet Syndrome (GPS) is a predominantly recessive Platelet disorder that is characterized by mild thrombocytopenia with large Platelets and a paucity of α-granules; these abnormalities cause mostly moderate but in rare cases severe bleeding. We sequenced the exomes of four unrelated individuals and identified NBEAL2 as the causative gene; it has no previously known function but is a member of a gene family that is involved in granule development. Silencing of nbeal2 in zebrafish abrogated thrombocyte formation. Cornelis Albers and colleagues identify NBEAL2 as the causative gene for Gray Platelet Syndrome (GPS). Knockdown of this gene in zebrafish leads to spontaneous bleeding and defects in thrombocyte formation.
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Exome sequencing identifies NBEAL2 as the causative gene for Gray Platelet Syndrome
Nature genetics, 2011Co-Authors: Cornelis A Albers, Ana Cvejic, Rémi Favier, Evelien E Bouwmans, Marie-christine Alessi, Paul Bertone, Ross N W Kettleborough, Graham Kiddle, Gregory E. Jordan, Myrto KostadimaAbstract:Gray Platelet Syndrome (GPS) is a predominantly recessive Platelet disorder that is characterized by mild thrombocytopenia with large Platelets and a paucity of α-granules; these abnormalities cause mostly moderate but in rare cases severe bleeding. We sequenced the exomes of four unrelated individuals and identified NBEAL2 as the causative gene; it has no previously known function but is a member of a gene family that is involved in granule development. Silencing of nbeal2 in zebrafish abrogated thrombocyte formation.
Jorge Di Paola - One of the best experts on this subject based on the ideXlab platform.
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NBEAL2 mutations and bleeding in patients with Gray Platelet Syndrome.
Platelets, 2018Co-Authors: Fred G. Pluthero, Jorge Di Paola, Manuel Carcao, Walter H. A. KahrAbstract:Homozygosity/compound heterozygosity for loss of function mutations in neurobeachin-like 2 (NBEAL2) is causative for Gray Platelet Syndrome (GPS; MIM #139090), characterized by thrombocytopenia and...
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Novel Congenital Platelet Disorders
Blood, 2016Co-Authors: Jorge Di PaolaAbstract:The processes of megakaryocyte differentiation, proPlatelet formation, and the daily release of 1011 Platelets into the bloodstream are tightly regulated. Genetic disturbances can lead to a cascade of downstream molecular alterations that markedly affect the function of megakaryocytes and Platelets. Therefore, identifying new genes and their function in megakaryocytes and Platelets is critical for understanding how these unique cells contribute to health and disease. Over the last decade advances in genomics, specifically next generation sequencing, have allowed for the discovery of several mutations and genetic variants that cause disease or influence associated hematological traits. By performing Platelet RNA-Seq we were among the first to identify NBEAL2 as the causative gene for Gray Platelet Syndrome (GPS) and showed that NBEAL2 regulates megakaryocyte development and Platelet function.1-3 Mice carrying targeted Nbeal2 null alleles not only replicated the thrombocytopenia and lack of alpha granules observed in humans, but also provided new information about the role of Platelets in thromboinflammation, wound healing, myelofibrosis and metastasis dissemination.4-7 More recently, we and others found that germline mutations in ETV6 lead to thrombocytopenia, red cell macrocytosis, and predisposition to lymphoblastic leukemia.8,9ETV6 encodes an ETS family transcriptional repressor, which exerts its activity by binding a consensus sequence in the promoter regions of DNA. Mice with conditional Etv6 knockout in megakaryocytic-erythroid cells are thrombocytopenic indicating the involvement of Etv6 in thrombopoiesis.10 Several of the families recently described have a missense mutation in the central domain of ETV6 (p.P214L). This mutation results in aberrant cellular localization of ETV6, decreased transcriptional repression, and impaired megakaryocyte maturation. The bone marrow of individuals affected by this mutation show hyperplasia of immature megakaryocytes suggesting a differentiation arrest. Deep sequencing of the Platelet transcriptome also revealed significant differences in mRNA expression levels between patients with the ETV6 p.P214L mutation and non-affected family members, indicating that ETV6 is critically involved in defining the molecular phenotype and function of Platelets. Consistent with this notion, individuals with the ETV6 p.P214L mutation experience bleeding that is disproportionate to their mild thrombocytopenia. We have also used CRISPR/Cas9 technology to generate a mouse colony where the human p.P214L ETV6 mutation was inserted into the conserved site of Etv6. Mice with this mutation (Etv6H.P214L) have reduced Platelet counts. In summary, advances in human genetics that led to the discovery of novel congenital Platelet disorders coupled with relevant animal models will likely contribute to our understanding of megakaryopoiesis and Platelet function. References 1. Kahr WH, Hinckley J, Li L, et al. Mutations in NBEAL2, encoding a BEACH protein, cause Gray Platelet Syndrome. Nature genetics. 2011;43(8):738-740. 2. Gunay-Aygun M, Falik-Zaccai TC, Vilboux T, et al. NBEAL2 is mutated in Gray Platelet Syndrome and is required for biogenesis of Platelet alpha-granules. Nature genetics. 2011;43(8):732-734. 3. Albers CA, Cvejic A, Favier R, et al. Exome sequencing identifies NBEAL2 as the causative gene for Gray Platelet Syndrome. Nature genetics. 2011;43(8):735-737. 4. Deppermann C, Cherpokova D, Nurden P, et al. Gray Platelet Syndrome and defective thrombo-inflammation in Nbeal2-deficient mice. The Journal of clinical investigation. 2013. 5. Kahr WH, Lo RW, Li L, et al. Abnormal megakaryocyte development and Platelet function in Nbeal2(-/-) mice. Blood. 2013;122(19):3349-3358. 6. Guerrero JA, Bennett C, van der Weyden L, et al. Gray Platelet Syndrome: proinflammatory megakaryocytes and alpha-granule loss cause myelofibrosis and confer metastasis resistance in mice. Blood.2014;124(24):3624-3635. 7. Tomberg K, Khoriaty R, Westrick RJ, et al. Spontaneous 8bp Deletion in Nbeal2 Recapitulates the Gray Platelet Syndrome in Mice. PLoS One. 2016;11(3):e0150852. 8. Noetzli L, Lo RW, Lee-Sherick AB, et al. Germline mutations in ETV6 are associated with thrombocytopenia, red cell macrocytosis and predisposition to lymphoblastic leukemia. Nature Genetics. 2015;47(5):535-538. 9. Zhang MY, Churpek JE, Keel SB, et al. Germline ETV6 mutations in familial thrombocytopenia and hematologic malignancy. Nature genetics. 2015;47(2):180-185. 10. Wang LC, Swat W, Fujiwara Y, et al. The TEL/ETV6 gene is required specifically for hematopoiesis in the bone marrow. Genes & development. 1998;12(15):2392-2402. Disclosures Di Paola:CSL BEhring: Consultancy; Biogen: Consultancy.
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PlateletS AND THROMBOPOIESIS Brief report
2016Co-Authors: Thomas Bair, Brian Schutte, Jorge Di PaolaAbstract:Homozygosity mapping with SNP arrays confirms 3p21 as a recessive locus for Gray Platelet Syndrome and narrows the interval significantl
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Spontaneous 8bp Deletion in Nbeal2 Recapitulates the Gray Platelet Syndrome in Mice.
PloS one, 2016Co-Authors: Kärt Tomberg, Rami Khoriaty, Randal J. Westrick, Heather Fairfield, Laura G. Reinholdt, Gary Brodsky, Pavel Davizon-castillo, David Ginsburg, Jorge Di PaolaAbstract:During the analysis of a whole genome ENU mutagenesis screen for thrombosis modifiers, a spontaneous 8 base pair (bp) deletion causing a frameshift in exon 27 of the Nbeal2 gene was identified. Though initially considered as a plausible thrombosis modifier, this Nbeal2 mutation failed to suppress the synthetic lethal thrombosis on which the original ENU screen was based. Mutations in NBEAL2 cause Gray Platelet Syndrome (GPS), an autosomal recessive bleeding disorder characterized by macrothrombocytopenia and Gray-appearing Platelets due to lack of Platelet alpha granules. Mice homozygous for the Nbeal2 8 bp deletion (Nbeal2gps/gps) exhibit a phenotype similar to human GPS, with significantly reduced Platelet counts compared to littermate controls (p = 1.63 x 10-7). Nbeal2gps/gps mice also have markedly reduced numbers of Platelet alpha granules and an increased level of emperipolesis, consistent with previously characterized mice carrying targeted Nbeal2 null alleles. These findings confirm previous reports, provide an additional mouse model for GPS, and highlight the potentially confounding effect of background spontaneous mutation events in well-characterized mouse strains.
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Thrombocytopenias due to Gray Platelet Syndrome or THC2 mutations.
Seminars in thrombosis and hemostasis, 2011Co-Authors: Jorge Di Paola, Jan JohnsonAbstract:Over the last two decades the genetic causes of several Mendelian Platelet disorders have been elucidated, while the genetics of many other thrombocytopenic conditions are still unresolved. Among those are the Gray Platelet Syndrome (GPS) and the thrombocytopenia linked to the THC2 locus on human chromosome 10p11-12. GPS is an α-granule defect associated with the development of myelofibrosis and mild to moderate thrombocytopenia. Most forms of GPS are autosomal recessive, and recently, the recessive form of the disease was mapped to chromosome 3p21. THC2-linked thrombocytopenia is an autosomal dominant disorder in which affected family members have a mild reduction in Platelet counts and occasional bleeding. Platelets in THC2-linked thrombocytopenia appear to be normal in size and function although bone marrow morphology reveals a lack of mature, polyploid megakaryocytes. To date, mutations in three different genes within the THC2 locus have been associated with congenital thrombocytopenia, including a mutation in MASTL. In this article, we summarize the recent discoveries in these two forms of thrombocytopenia, including the functional data that support a role for MASTL kinase in thrombopoiesis.
