The regulation of proplatelet production

Geddis, Amy E.

doi:10.3324/haematol.2009.006577

Cited by 20 publications

(11 citation statements)

References 35 publications

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“…In particular, megakaryoctyes, following polyploidization and prior to platelet release, form elongated cellular processes called proplatelets (proPLT). 1 Perturbations in proPLT formation lead to alterations in platelet morphology and thrombocytopenia, 2,3 emphasizing the importance of this step. The marginal microtubule band, actin-based cytoskeleton, and spectrin-based membrane skeleton are all prominent components of the cytoskeletal remodeling that occurs during platelet formation.…”

Section: Introductionmentioning

confidence: 99%

Proplatelet generation in the mouse requires PKCε-dependent RhoA inhibition

Gobbi

Mirandola

Carubbi

et al. 2013

Blood

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• PKCe, regulating RhoA activity, is a critical mediator of proplatelet formation. • PKCe shut down results inRhoA expression levels that are incompatible with normal platelet generation.During thrombopoiesis, megakaroycytes undergo extensive cytoskeletal remodeling to form proplatelet extensions that eventually produce mature platelets. Proplatelet formation is a tightly orchestrated process that depends on dynamic regulation of both tubulin reorganization and Rho-associated, coiled-coil containing protein kinase/RhoA activity. A disruption in tubulin dynamics or RhoA activity impairs proplatelet formation and alters platelet morphology. We previously observed that protein kinase Cepsilon (PKC«), a member of the protein kinase C family of serine/threonine-kinases, expression varies during human megakaryocyte differentiation and modulates megakaryocyte maturation and platelet release. Here we used an in vitro model of murine platelet production to investigate a potential role for PKC« in proplatelet formation. By immunofluorescence we observed that PKC« colocalizes with a/b-tubulin in specific areas of the marginal tubular-coil in proplatelets. Moreover, we found that PKC« expression escalates during megakarocyte differentiation and remains elevated in proplatelets, whereas the active form of RhoA is substantially downregulated in proplatelets. PKC« inhibition resulted in lower proplatelet numbers and larger diameter platelets in culture as well as persistent RhoA activation. Finally, we demonstrate that pharmacological inhibition of RhoA is capable of reversing the proplatelet defects mediated by PKC« inhibition. Collectively, these data indicate that by regulating RhoA activity, PKC« is a critical mediator of mouse proplatelet formation in vitro. (Blood. 2013;122(7):1305-1311) IntroductionDefective platelet numbers can compromise proper wound healing and cause bleeding, whereas excessive platelet production or activation can lead to thrombosis. As a result, platelet homeostasis is a tightly regulated process. The process of generating thousands of platelets from a single megakaryocyte is characterized by several morphologically distinct stages that involve extensive cytoskeletal remodeling. In particular, megakaryoctyes, following polyploidization and prior to platelet release, form elongated cellular processes called proplatelets (proPLT).1 Perturbations in proPLT formation lead to alterations in platelet morphology and thrombocytopenia, 2,3 emphasizing the importance of this step. The marginal microtubule band, actin-based cytoskeleton, and spectrin-based membrane skeleton are all prominent components of the cytoskeletal remodeling that occurs during platelet formation. 4 Specifically, dynamic tubulin polymerization is required for the proper platelet morphology, assembly of the marginal microtubule coil, proPLT extensions and microtubule band formation.4-8 Various mutations in genes that regulate actin polymerization and turnover cause thrombocytopenia due to altered formation and morphology of proPLT exten...

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Section: Introductionmentioning

confidence: 99%

Proplatelet generation in the mouse requires PKCε-dependent RhoA inhibition

Gobbi

Mirandola

Carubbi

et al. 2013

Blood

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“…51,52 Pecam1 was overexpressed in JAK2V617F MKs, and there is ample evidence that Pecam1 plays a role in fine-tuning megakaryopoiesis, in particular regulating MK migration. 32,53 Programmed cell death, or apoptosis, is a regulator of proplatelet formation (reviewed by Geddis 54 ) as well as platelet count by influencing platelet survival in circulation. 55 Several apoptosis-related genes were found to be less expressed in JAK2V617F MKs, among them Phlda3, a negative regulator of AKT signaling, a pathway now recognized as a therapeutic target in myeloproliferative disorders.…”

Section: Jak2v617f Makes Platelets Intrinsically Prothrombotic 3793mentioning

confidence: 99%

JAK2V617F leads to intrinsic changes in platelet formation and reactivity in a knock-in mouse model of essential thrombocythemia

Hobbs

Manning

Bennett

et al. 2013

Blood

122

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The principal morbidity and mortality in patients with essential thrombocythemia (ET) and polycythemia rubra vera (PV) stems from thrombotic events. Most patients with ET/PV harbor a JAK2V617F mutation, but its role in the thrombotic diathesis remains obscure. Platelet function studies in patients are difficult to interpret because of interindividual heterogeneity, reflecting variations in the proportion of platelets derived from the malignant clone, differences in the presence of additional mutations, and the effects of medical treatments. To circumvent these issues, we have studied a JAK2V617F knock-in mouse model of ET in which all megakaryocytes and platelets express JAK2V617F at a physiological level, equivalent to that present in human ET patients. We show that, in addition to increased differentiation, JAK2V617F-positive megakaryocytes display greater migratory ability and proplatelet formation. We demonstrate in a range of assays that platelet reactivity to agonists is enhanced, with a concomitant increase in platelet aggregation in vitro and a reduced duration of bleeding in vivo. These data suggest that JAK2V617F leads to intrinsic changes in both megakaryocyte and platelet biology beyond an increase in cell number. In support of this hypothesis, we identify multiple differentially expressed genes in JAK2V617F megakaryocytes that may underlie the observed biological differences.

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“…10 Several molecules, including transcription factors and their intermediates, have been found to be involved in the regulation of this process and the perturbation of the expression and activity of these proteins leads to alterations in platelet number, morphology or function. [11][12][13][14][15] Protein kinase C (PKC) is a family of serine-threonine kinase involved in many cellular functions, including cell death, proliferation, migration and differentiation. 16,17 Protein Kinase C epsilon (PKCε) and Protein Kinase C delta (PKCδ) are both members of the novel sub-family of PKCs, which can be considered as "yin and A deeper understanding of the molecular events driving megakaryocytopoiesis and thrombopoiesis is essential to regulate in vitro and in vivo platelet production for clinical applications.…”

Section: Introductionmentioning

confidence: 99%