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Generation and rescue of a murine model of platelet dysfunction: the Bernard-Soulier syndrome.

ABSTRACT: The human Bernard-Soulier syndrome is an autosomal recessive disorder of platelet dysfunction presenting with mild thrombocytopenia, circulating "giant" platelets and a bleeding phenotype. The bleeding in patients with the Bernard-Soulier syndrome is disproportionately more severe than suggested by the reduced platelet count and is explained by a defect in primary hemostasis owing to the absence of the platelet glycoprotein (GP) Ib-IX-V membrane receptor. However, the molecular basis for the giant platelet phenotype and thrombocytopenia have remained unresolved but assumed to be linked to an absent receptor complex. We have disrupted the gene encoding the alpha-subunit of mouse GP Ib-IX-V (GP Ibalpha) and describe a murine model recapitulating the hallmark characteristics of the human Bernard-Soulier syndrome. The results demonstrate a direct link between expression of a GP Ib-IX-V complex and normal megakaryocytopoiesis and platelet morphogenesis. Moreover, using transgenic technology the murine Bernard-Soulier phenotype was rescued by expression of a human GP Ibalpha subunit on the surface of circulating mouse platelets. Thus, an in vivo model is defined for analysis of the human GP Ib-IX-V receptor and its role in the processes performed exclusively by megakaryocytes and platelets.

SUBMITTER: Ware J

PROVIDER: S-EPMC16010 | biostudies-literature | 2000 Mar

REPOSITORIES: biostudies-literature

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Generation and rescue of a murine model of platelet dysfunction: the Bernard-Soulier syndrome.

Ware J J Russell S S Ruggeri Z M ZM

Proceedings of the National Academy of Sciences of the United States of America 20000301 6

The human Bernard-Soulier syndrome is an autosomal recessive disorder of platelet dysfunction presenting with mild thrombocytopenia, circulating "giant" platelets and a bleeding phenotype. The bleeding in patients with the Bernard-Soulier syndrome is disproportionately more severe than suggested by the reduced platelet count and is explained by a defect in primary hemostasis owing to the absence of the platelet glycoprotein (GP) Ib-IX-V membrane receptor. However, the molecular basis for the gia ...[more]

PMID: 10706630

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Project description:BackgroundBernard-Soulier syndrome is a severe bleeding disease due to a defect of GPIb/IX/V, a platelet complex that binds the von Willebrand factor. Due to the rarity of the disease, there are reports only on a few cases compromising any attempt to establish correlations between genotype and phenotype. In order to identify any associations, we describe the largest case series ever reported, which was evaluated systematically at the same center.Design and methodsThirteen patients with the disease and seven obligate carriers were enrolled. We collected clinical aspects and determined platelet features, including number and size, expression of membrane glycoproteins, and ristocetin induced platelet aggregation. Mutations were identified by direct sequencing of the GP1BA, GP1BB, and GP9 genes and their effect was shown by molecular modeling analyses.ResultsPatients all had a moderate thrombocytopenia with giant platelets and a bleeding tendency whose severity varied among individuals. Consistent with expression levels of GPIbα always lower than 10% of control values, platelet aggregation was absent or severely reduced. Homozygous mutations were identified in the GP1BA, GP1BB and GP9 genes; six were novel alterations expected to destabilize the conformation of the respective protein. Except for obligate carriers of a GP9 mutation with a reduced GPIb/IX/V expression and defective aggregation, all the other carriers had no obvious anomalies.ConclusionsRegardless of mutations identified, the patients' bleeding diathesis did not correlate with thrombocytopenia, which was always moderate, and platelet GPIbα expression, which was always severely impaired. Obligate carriers had features similar to controls though their GPIb/IX/V expression showed discrepancies. Aware of the limitations of our cohort, we cannot define any correlations. However, further investigations should be encouraged to better understand the causes of this rare and underestimated disease.

Project description:BackgroundGiant platelets and thrombocytopenia are invariable defects in the Bernard-Soulier syndrome caused by deficiency of the GPIb-V-IX complex, a receptor for von Willebrand factor supporting platelet adhesion to the damaged arterial wall. Various properties of this receptor may be considered potential determinants of the macrothrombocytopenia.Design and methodsTo explore the underlying mechanisms of the disease, megakaryopoiesis was studied in a mouse model deficient in GPIbbeta. Megakaryocytes were initially characterized in situ in the bone marrow of adult mice, after which their capacity to differentiate into proplatelet-bearing cells was evaluated in cultured fetal liver cells.ResultsThe number of megakaryocyte progenitors, their differentiation and progressive maturation into distinct classes and their level of endoreplication were normal in GPIbbeta(-/-) bone marrow. However, the more mature cells exhibited ultrastructural anomalies with a thicker peripheral zone and a less well developed demarcation membrane system. GPIbbeta(-/-) megakaryocytes could be differentiated in culture from Lin(-) fetal liver cells in normal amounts but the proportion of cells able to extend proplatelets was decreased by 41%. Moreover, the GPIbbeta(-/-) cells extending proplatelets displayed an abnormal morphology characterized by fewer pseudopodial extensions with thicker shaft sections and an increased diameter of the terminal coiled elements. GPIbbeta(-/-) released platelets were larger but retained a typical discoid shape. Proplatelet formation was similarly affected in bone marrow explants from adult mice examined by videomicroscopy. The marginal microtubular ring contained twice as many tubulin fibers in GPIbbeta(-/-) proplatelet buds in cultured and circulating platelets.ConclusionsAltogether, these findings point to a role of the GPIb-V-IX complex intrinsic to megakaryocytes at the stage of proplatelet formation and suggest a functional link with the underlying microtubular cytoskeleton in platelet biogenesis.

Dataset Information

Generation and rescue of a murine model of platelet dysfunction: the Bernard-Soulier syndrome.

Publications

Generation and rescue of a murine model of platelet dysfunction: the Bernard-Soulier syndrome.

Similar Datasets

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