Dataset Information

Megakaryocyte-derived microparticles: direct visualization and distinction from platelet-derived microparticles.

ABSTRACT: Platelet microparticles are a normal constituent of circulating blood. Several studies have demonstrated positive correlations between thrombotic states and platelet microparticle levels. Yet little is known about the processes by which platelet microparticles are generated in vivo. We now characterize microparticles derived directly from megakaryocytes. Video microscopy of live mouse megakaryocytes demonstrated that microparticles form as submicron beads along the lengths of slender, unbranched micropodia. These microparticles are CD41(+), CD42b(+), and express surface phosphatidylserine. Megakaryocyte microparticle generation is resistant to inhibition of microtubule assembly, which is critical to platelet formation, and augmented by inhibition of actin polymerization. To determine whether circulating microparticles are derived primarily from activated platelets or megakaryocytes, we identified markers that distinguish between these 2 populations. CD62P and LAMP-1 were found only on mouse microparticles from activated platelets. In contrast, full-length filamin A was found in megakaryocyte-derived microparticles, but not microparticles from activated platelets. Circulating microparticles isolated from mice were CD62P(-), LAMP-1(-) and expressed full-length filamin A, indicating a megakaryocytic origin. Similarly, circulating microparticles isolated from healthy volunteers were CD62P(-) and expressed full-length filamin A. Cultured human megakaryocytes elaborated microparticles that were CD41(+), CD42b(+), and express surface phosphatidylserine. These results indicate that direct production by megakaryocytes represents a physiologic means to generate circulating platelet microparticles.

SUBMITTER: Flaumenhaft R

PROVIDER: S-EPMC2635076 | biostudies-literature | 2009 Jan

REPOSITORIES: biostudies-literature

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Megakaryocyte-derived microparticles: direct visualization and distinction from platelet-derived microparticles.

Flaumenhaft Robert R Dilks James R JR Richardson Jennifer J Alden Eva E Patel-Hett Sunita R SR Battinelli Elisabeth E Klement Giannoula L GL Sola-Visner Martha M Italiano Joseph E JE

Blood 20080918 5

Platelet microparticles are a normal constituent of circulating blood. Several studies have demonstrated positive correlations between thrombotic states and platelet microparticle levels. Yet little is known about the processes by which platelet microparticles are generated in vivo. We now characterize microparticles derived directly from megakaryocytes. Video microscopy of live mouse megakaryocytes demonstrated that microparticles form as submicron beads along the lengths of slender, unbranched ...[more]

PMID: 18802008

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Project description:Essentials Platelet microparticles play a major role in pathologies, including hemostasis and thrombosis. Platelet microparticles have been analyzed and classified based on their ultrastructure. The structure and intracellular origin of microparticles depend on the cell-activating stimulus. Thrombin-treated platelets fall apart and form microparticles that contain cellular organelles.SummaryBackground Platelet-derived microparticles comprise the major population of circulating blood microparticles that play an important role in hemostasis and thrombosis. Despite numerous studies on the (patho)physiological roles of platelet-derived microparticles, mechanisms of their formation and structural details remain largely unknown. Objectives Here we studied the formation, ultrastructure and composition of platelet-derived microparticles from isolated human platelets, either quiescent or stimulated with one of the following activators: arachidonic acid, ADP, collagen, thrombin or calcium ionophore A23187. Methods Using flow cytometry, transmission and scanning electron microscopy, we analyzed the intracellular origin, structural diversity and size distributions of the subcellular particles released from platelets. Results The structure, dimensions and intracellular origin of microparticles depend on the cell-activating stimulus. The main structural groups include a vesicle surrounded by one thin membrane or multivesicular structures. Thrombin, unlike other stimuli, induced formation of microparticles not only from the platelet plasma membrane and cytoplasm but also from intracellular structures. A fraction of these vesicular particles having an intracellular origin contained organelles, such as mitochondria, glycogen granules and vacuoles. The size of platelet-derived microparticles depended on the nature of the cell-activating stimulus. Conclusion The results obtained provide a structural basis for the qualitative differences of various platelet activators, for specific physiological and pathological effects of microparticles, and for development of advanced assays.

Project description:BackgroundIt is well established that inflammation and platelets promote multiple processes of cancer malignancy. Recently, platelets have received attention for their role in carcinogenesis through the production of microvesicles or platelet-derived microparticles (PMPs), which transfer their biological content to cancer cells. We have previously characterized a new subpopulation of these microparticles (termed mito-microparticles), which package functional mitochondria. The potential of mitochondria transfer to cancer cells is particularly impactful as many aspects of mitochondrial biology (i.e., cell growth, apoptosis inhibition, and drug resistance) coincide with cancer hallmarks and disease progression. These metabolic aspects are particularly notable in chronic lymphocytic leukemia (CLL), which is characterized by a relentless accumulation of proliferating, immunologically dysfunctional, mature B-lymphocytes that fail to undergo apoptosis. The present study aimed to investigate the role of PMPs on CLL metabolic plasticity leading to cancer cell phenotypic changes.MethodsCLL cell lines were co-incubated with different concentrations of human PMPs, and their impact on cell proliferation, mitochondrial DNA copy number, OCR level, ATP production, and ROS content was evaluated. Essential genes involved in metabolic-reprogramming were identified using the bioinformatics tools, examined between patients with early and advanced CLL stages, and then validated in PMP-recipient CLLs. Finally, the impact of the induced metabolic reprogramming on CLLs' growth, survival, mobility, and invasiveness was tested against anti-cancer drugs Cytarabine, Venetoclax, and Plumbagin.ResultsThe data demonstrated the potency of PMPs in inducing tumoral growth and invasiveness in CLLs through mitochondrial internalization and OXPHOS stimulation which was in line with metabolic shift reported in CLL patients from early to advanced stages. This metabolic rewiring also improved CLL cells' resistance to Cytarabine, Venetoclax, and Plumbagin chemo drugs.ConclusionAltogether, these findings depict a new platelet-mediated pathway of cancer pathogenesis. We also highlight the impact of PMPs in CLL metabolic reprogramming and disease progression.

Dataset Information

Megakaryocyte-derived microparticles: direct visualization and distinction from platelet-derived microparticles.

Publications

Megakaryocyte-derived microparticles: direct visualization and distinction from platelet-derived microparticles.

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