Atypical Platelet Research Articles

Platelet vacuoles in a dog with severe nonregenerative anemia: evidence of platelet autophagy

A 13-year-old neutered male English Springer Spaniel was presented to The Ohio State University Veterinary Medical Center for evaluation of severe anemia. Upon blood smear review, approximately 50% of the platelets contained single to multiple variably sized clear vacuoles. Transmission electron microscopy of the platelets revealed hallmark features of autophagy, including membrane-lined vesicles and vacuoles containing membrane whorls and degrading organelles. While autophagy has been demonstrated in a wide range of eukaryotic cells for decades, reports of platelet autophagy are lacking. This case report illustrates atypical platelet vacuolation with electron microscopic features characteristic of autophagy.

Lipopolysaccharide Signaling without a Nucleus: Kinase Cascades Stimulate Platelet Shedding of Proinflammatory IL-1β–Rich Microparticles

Platelets contain unspliced heteronuclear IL-1β RNA, which is rapidly spliced and translated upon activation. LPS is a superior agonist for this atypical platelet response, but how LPS induces proinflammatory cytokine production in anucleate cells lacking NF-κB is unknown. Platelets express functional TLR4, and stimulation by LPS induced rapid splicing, translation, and secretion of mature IL-1β after caspase-1 processing. LPS stimulated microparticle shedding, and secreted IL-1β was exclusively present in these particles. Microparticles from LPS-stimulated platelets induced VCAM-1 production by cultured human endothelial cells, and blockade of endothelial IL-1β receptor with IL-1 receptor antagonist completely suppressed endothelial activation. Splicing was posttranscriptional as the SR kinase inhibitor TG003 blocked IL-1β RNA production by platelets, but not by monocytes, and was dependent on exogenous CD14--a property of platelets. We used a combination of small-molecule inhibitors, cell-penetrating chimeric peptide inhibitors, and gene-targeted animals to show splicing required MyD88 and TIRAP, and IRAK1/4, Akt, and JNK phosphorylation and activation. Traf6 couples MyD88 to the Akt pathway and, remarkably, a Traf6 interacting peptide-antennapedia chimera was more effective than LPS in stimulating IL-1β splicing. The Traf6 chimera did not, however, stimulate microparticle shedding, nor was IL-1β released. We conclude LPS-induced kinase cascades are sufficient to alter cellular responses, that three signals emanate from platelet TLR4, and that Akt and JNK activation are sufficient to initiate posttranscriptional splicing while another event couples microparticle shedding to TLR4 activation. Platelets contribute to the inflammatory response to LPS through production of microparticles that promote endothelial cell activation.

Proliferation of internal membranes in platelets from patients with Alzheimer's disease.

Platelets from six moderately demented patients with probable Alzheimer's disease (NINCDS-ADRDA criteria) and six neurologically healthy controls were examined by electron microscopy. While platelet preparations from the control group contained infrequent examples (4.6%) of platelets with an unusually abundant internal system of smooth membranes, the frequency of these atypical cells (15.5%) was over three times higher in the samples prepared from the demented patients (p = 2.2 X 10(-2)). Consistent with our previous reports, platelet membranes from the Alzheimer's disease group exhibited a significant increase in membrane fluidity, as reflected by the rotation rate and fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH) at 37 degrees C. Moreover, membrane fluidity was correlated with the frequency of atypical platelets visualized by electron microscopy. Since internal platelet membranes have been reported to be more fluid than external platelet membranes, these and other results presented suggest that the increase in platelet membrane fluidity associated with Alzheimer's disease may be the result of a dysregulation of platelet membrane biosynthesis.

Balloon-like platelets in myelodysplastic syndromes—a feature of dysmegakaryopoiesis?

Large bizarre platelets are a frequent finding in the peripheral blood of the myelodysplastic syndrome (MDS). In this study we describe a distinct subpopulation of platelets in MDS which by phase contrast microscopic examination seems to have a balloon-shaped bulge of the cell membrane. Increased numbers of these atypical platelets were found in 24 of 27 MDS patients (89%). Only 3 patients, all with ringsideroblastic anemia, had normal platelet morphology. The number of atypical platelets were negatively correlated ( r = 0.44; p = 0.021) to the peripheral platelet counts in MDS. Among 48 patients with acute leukemia, chronic lymphoproliferative or chronic myeloproliferative disorders, 13 (27%) had atypical platelets, Here, but not in the MDS group, atypical platelets seemed to be associated with recent chemotherapy. In a group of patients with benign hematological disorders abnormal platelet morphology was seen only occasionally. The described atypical platelets most likely reflect maturation disturbances of the megakaryopoiesis. An increased value (>1%) in a cytopenic patient would suggest a diagnosis of MDS, unless associated with recent cytotoxic therapy.

Freeze-fracture of the normal and pathological megakaryocyte lineage in chronic megakaryocytic-granulocytic myelosis

Freeze-fracture and thin sections were performed on human bone marrow of chronic megakaryocytic-granulocytic myelosis (CMGM) to study the three-dimensional fine structure and maturation of normal and atypical megakaryocytes and thrombocytes. In the many normally maturing megakaryocytes the development of the demarcation membrane system (DMS) was best investigated by comparison of thin sections with freeze-fracture replicas. The DMS shows no connections with the Golgi apparatus or rough-surfaced endoplasmic reticulum, but originates from tubular infoldings of the plasma membrane. These infoldings are always in continuity with the extracellular space and form an intracellular membranous pool by branching and coalescing of flattened tubules from which finally the perforated cisternae of the DMS arise. Freeze-fracture of the normal thrombocytes confirms earlier findings. The abnormal giant platelets seen in CMGM display extensive areas of smooth membranes of a spongy structure consisting of dense tubules surrounded by the labyrinth of the surface-connected system. Their physiological significance in these atypical platelets remains unsolved.

CHRONIC NONLEUKEMIC MYELOSIS

This report concerns a case in which were presented generalized diffuse osteosclerosis, generalized fibrosis of the bone marrow, an arresting erythroleukoblastic blood picture with numerous atypical platelets and primitive cells with megakaryocytoid characteristics and splenomegaly characterized by myeloid metaplasia in which megakaryocytes were numerous. This case is unique in presenting the association of such advanced changes in blood and bone. The French authors, Emil-Weil and Clerc, 1 in 1902, and Vaquez and Aubertin, 2 in 1904, first discussed a syndrome characterized by splenomegaly due to myeloid change and a leukemia-like blood picture, which they suggested showed clinical and pathologic differences from leukemia proper (leukemic myelosis). Since then the reports of approximately 70 cases have been contributed in which are recognized certain common characters of this polymorphic, leukemia-like syndrome. Usually there is hepatosplenomegaly due to myeloid metaplasia in which, in addition to leukoblastic cells, erythroblasts are constantly prominent and giant cells