NBEAL2 is mutated in gray platelet syndrome and is required for biogenesis of platelet ?-granules.
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ABSTRACT:
SUBMITTER: Gunay-Aygun M
PROVIDER: S-EPMC3154019 | biostudies-literature | 2011 Jul
REPOSITORIES: biostudies-literature
Publications
NBEAL2 is mutated in gray platelet syndrome and is required for biogenesis of platelet α-granules.
Gunay-Aygun Meral M Falik-Zaccai Tzipora C TC Vilboux Thierry T Zivony-Elboum Yifat Y Gumruk Fatma F Cetin Mualla M Khayat Morad M Boerkoel Cornelius F CF Kfir Nehama N Huang Yan Y Maynard Dawn D Dorward Heidi H Berger Katherine K Kleta Robert R Anikster Yair Y Arat Mutlu M Freiberg Andrew S AS Kehrel Beate E BE Jurk Kerstin K Cruz Pedro P Mullikin Jim C JC White James G JG Huizing Marjan M Gahl William A WA
Nature genetics 20110717 8
Gray platelet syndrome (GPS) is an autosomal recessive bleeding disorder that is characterized by large platelets that lack α-granules. Here we show that mutations in NBEAL2 (neurobeachin-like 2), which encodes a BEACH/ARM/WD40 domain protein, cause GPS and that megakaryocytes and platelets from individuals with GPS express a unique combination of NBEAL2 transcripts. Proteomic analysis of sucrose-gradient subcellular fractions of platelets indicated that NBEAL2 localizes to the dense tubular sys ...[more]
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Project description:Next-generation RNA sequence analysis of platelets from an individual with autosomal recessive gray platelet syndrome (GPS, MIM139090) detected abnormal transcript reads, including intron retention, mapping to NBEAL2 (encoding neurobeachin-like 2). Genomic DNA sequencing confirmed mutations in NBEAL2 as the genetic cause of GPS. NBEAL2 encodes a protein containing a BEACH domain that is predicted to be involved in vesicular trafficking and may be critical for the development of platelet ?-granules.
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Project description: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.
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Project description:Gray platelet syndrome (GPS) is a predominantly recessive platelet disorder that is characterized by mild thrombocytopenia with large platelets and a paucity of ?-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.
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Project description: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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Project description:BACKGROUND:Deficiencies in granule-bound substances in platelets cause congenital bleeding disorders known as storage pool deficiencies. For disorders such as gray platelet syndrome (GPS), in which thrombocytopenia, enlarged platelets and a paucity of ?-granules are observed, only the clinical and histologic states have been defined. OBJECTIVES:In order to understand the molecular defect in GPS, the ?-granule fraction protein composition from a normal individual was compared with that of a GPS patient by mass spectrometry (MS). METHODS:Platelet organelles were separated by sucrose gradient ultracentrifugation. Proteins from sedimented fractions were separated by sodium dodecylsulfate polyacrylamide gel electrophoresis, reduced, alkylated, and digested with trypsin. Peptides were analyzed by liquid chromatography-tandem MS. Mascot was used for peptide/protein identification and to determine peptide false-positive rates. MassSieve was used to generate and compare parsimonious lists of proteins. RESULTS:As compared with control, the normalized peptide hits (NPHs) from soluble, biosynthetic ?-granule proteins were markedly decreased or undetected in GPS platelets, whereas the NPHs from soluble, endocytosed ?-granule proteins were only moderately affected. The NPHs from membrane-bound ?-granule proteins were similar in normal platelets and GPS platelets, although P-selectin and Glut3 were slightly decreased, consistent with immunoelectron microscopy findings in resting platelets. We also identified proteins not previously known to be decreased in GPS, including latent transforming growth factor-?-binding protein 1(LTBP1), a component of the transforming growth factor-? (TGF-?) complex. CONCLUSIONS:Our results support the existence of 'ghost granules' in GPS, point to the basic defect in GPS as failure to incorporate endogenously synthesized megakaryocytic proteins into ?-granules, and identify specific new proteins as ?-granule inhabitants.
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Project description:Gray platelet syndrome is a rare hereditary autosomal recessive condition distinguished by a mild to moderate propensity toward bleeding, moderate reduction in platelet count, and a significant decrease or complete absence of platelet alpha granules. VACTERL association is a condition of specific birth defects affecting multiple organ systems, with an unknown etiology. The acronym stands for vertebral anomalies (V), anal anomalies (A), cardiac anomalies (C), tracheoesophageal fistula (TE), renal anomalies or radial bone anomalies (R), and limb defects (L). To diagnose the VACTERL association, at least three of the aforementioned abnormalities should be present. This case report concerns a neonate born with a left absent thumb, a hypoplastic right thumb, an imperforate anus, and an atrial septal defect. During postoperative investigations, after addressing an anorectal malformation, the patient was found to have moderate thrombocytopenia and large gray platelets upon examination of a peripheral blood smear. A genetic analysis validated the pathogenic homozygous mutation c.5257C>T in the NBEAL2 gene, which corresponds to gray platelet syndrome.
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Project description:Gray platelet syndrome (GPS) is an inherited bleeding disorder associated with macrothrombocytopenia and α-granule-deficient platelets. GPS has been linked to loss of function mutations in NEABL2 (neurobeachin-like 2), and we describe here a murine GPS model, the Nbeal2(-/-) mouse. As in GPS, Nbeal2(-/-) mice exhibit splenomegaly, macrothrombocytopenia, and a deficiency of platelet α-granules and their cargo, including von Willebrand factor (VWF), thrombospondin-1, and platelet factor 4. The platelet α-granule membrane protein P-selectin is expressed at 48% of wild-type levels and externalized upon platelet activation. The presence of P-selectin and normal levels of VPS33B and VPS16B in Nbeal2(-/-) platelets suggests that NBEAL2 acts independently of VPS33B/VPS16B at a later stage of α-granule biogenesis. Impaired Nbeal2(-/-) platelet function was shown by flow cytometry, platelet aggregometry, bleeding assays, and intravital imaging of laser-induced arterial thrombus formation. Microscopic analysis detected marked abnormalities in Nbeal2(-/-) bone marrow megakaryocytes, which when cultured showed delayed maturation, decreased survival, decreased ploidy, and developmental abnormalities, including abnormal extracellular distribution of VWF. Our results confirm that α-granule secretion plays a significant role in platelet function, and they also indicate that abnormal α-granule formation in Nbeal2(-/-) mice has deleterious effects on megakaryocyte survival, development, and platelet production.
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Project description: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 NBEAL2, a member of the family of BEACH genes, are causal of GPS. The gene is involved in fusion, fission and trafficking of vesicles and granules. Whether NBEAL2 controls the ontogeny of granules of myeloid cells remains disputed. We found that neutrophils obtained from the peripheral blood from GPS patients have a normal distribution of azurophilic granules, but show a deficiency of specific granules, as confirmed by immuno-electron microscopy and mass spectrometry proteomics analyses. In cultures from peripheral CD34+ hematopoietic stem cells (HSCs) into mature neutrophils, the time dynamics showed concordance of NBEAL2 and specific granule protein expression at transcriptional and protein level, which were discordant in neutrophils obtained GPS-HSCs. This is indicative of normal granulopoiesis in GPS and identifies NBEAL2 as an important regulator of granule release (similar to platelets) which is suggested to occur upon egress into the blood stream. Patient neutrophil functions, including production of reactive oxygen species, chemotaxis and killing of bacteria and fungi were intact. Since GPS patients do not excessively suffer from infections, the consequence of the reduced specific granule content and lack of NET formation for innate immunity remains to be explored.
2021-01-28 | PXD017784 | Pride
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Project description:Gray platelet syndrome (GPS) is an autosomal recessive bleeding disorder characterized by a lack of ?-granules in platelets and progressive myelofibrosis. Rare loss-of-function variants in neurobeachin-like 2 (NBEAL2), a member of the family of beige and Chédiak-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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