The regulation of megakaryocyte and platelet production

Drop-shaped microgrooves guide unidirectional cell migration for enhanced endothelialization

Atrial fibrillation (AF) significantly increases the risk of ischemic stroke, and in non-valvular AF, 90% of stroke-causing thrombi arise from the left atrial appendage (LAA). Percutaneous LAA occlusion using an occluder is a crucial clinical intervention. However, occluder materials could provoke thrombi, termed device-related thrombosis (DRT), leading to treatment failure. Rapid endothelialization is essential to address the DRT but the occluder's large surface area and irregular cell migration on the surface impede this process. Here, we report a continuous drop-shaped microgroove, which has a drop-shaped unit structure similar to endothelial cells. The microgrooves polarize the cytoskeleton, guiding cell unidirectional migration within the grooves, and increase cell migration efficiency. We show that drop-shaped microgrooves accelerate wound healing in a rat model, and that occluder discs with drop-shaped microgrooves promote endothelialization in a canine model. Together, our results show that integrating microgrooves with medical devices is a promising approach for addressing DRT.

Controlling Surface-Induced Platelet Activation by Agarose and Gelatin-Based Hydrogel Films

Platelet-surface interaction is of paramount importance in biomedical applications as well as in vitro studies. However, controlling platelet-surface activation is challenging and still requires more effort as they activate immediately when contacting with any nonphysiological surface. As hydrogels are highly biocompatible, in this study, we developed agarose and gelatin-based hydrogel films to inhibit platelet-surface adhesion. We found promising agarose films that exhibit higher surface wettability, better controlled-swelling properties, and greater stiffness compared to gelatin, resulting in a strong reduction of platelet adhesion. Mechanical properties and surface wettability of the hydrogel films were varied by adding magnetite (Fe3O4) nanoparticles. While all of the films prevented platelet spreading, films formed by agarose and its nanocomposite repelled platelets and inhibited platelet adhesion and activation stronger than those of gelatin. Our results showed that platelet-surface activation is modulated by controlling the properties of the films underneath platelets and that the bioinert agarose can be potentially translated to the development of platelet storage and other medical applications.

Modulation of Platelet-Surface Activation: Current State and Future Perspectives

Modulation of platelet-surface activation is important for many biomedical applications such as in vivo performance, platelet storage, and acceptance of an implant. Reducing platelet-surface activation is challenging because they become activated immediately after short contact with nonphysiological surfaces. To date, controversies and open questions in the field of platelet-surface activation still remain. Here, we review state-of-the-art approaches in inhibiting platelet-surface activation, mainly focusing on modification, patterning, and methodologies for characterization of the surfaces. As a future perspective, we discuss how the combination of biochemical and physiochemical strategies together with the topographical modulations would assist in the search for an ideal nonthrombogenic surface.

Effect of IFN-alpha on normal human hematopoiesis: an immunohistochemical and morphometric study on trephine biopsy specimens

To elucidate the effects of interferon-alpha (IFN-alpha) on normal human bone marrow in vivo, an immunomorphometric study was performed using trephine biopsy specimens without hematopoietic pathology. Samples were derived from patients with mycosis fungoides but no marrow involvement, who were undergoing low-dose IFN-alpha treatment. Parameters included density of reticulin (argyrophilic) fibers, CD61+ megakaryocytes, PGM1+ macrophages, the GSA-I lectin-expressing (activated) macrophage subpopulation, proliferative activity (PCNA staining), and apoptosis. Following IFN-alpha therapy (3 x 3 x 10(6) U/week between 6 and 21 months), morphometric evaluation of sequential bone marrow examinations revealed a significant increase in the number of megakaryocytes and the amount of reticulin fibers. Additionally, there was an overall decrease in PCNA+ cells, accompanied by a reduction in the incidence of apoptotic bodies. On the other hand, total number of macrophages and their activated subfraction remained unchanged. Opposed to in vitro findings, a fibrogenetic capacity of IFN-alpha associated with megakaryocyte growth was detectable. Moreover, contrasting with effects of IFN-alpha treatment in chronic myelogenous leukemia, the incidence of apoptosis was significantly reduced. This feature was assumed to contribute to a maintenance of steady-state hematopoiesis expressed by a nonaltered bone marrow cellularity in our specimens.

Regulation of hematopoiesis by microvascular endothelium

The bone marrow microenvironment is a complex three dimensional structure where hematopoietic stem cells proliferate, mature, migrate into the sinusoidal space, and enter the circulation in an exquisitely regulated fashion. Stromal cells within the BM microenvironment provide a suitable environment for self-renewal, proliferation and differentiation of hematopoietic stem cells. Within the hematopoietic microenvironment, whether it is embryonic yolk sac, fetal liver, or adult bone marrow, microvascular endothelium not only acts as a gatekeeper controlling the trafficking and homing of hematopoietic progenitors, but also provides cellular contact and secretes cytokines that allows for the preservation of the steady state hematopoiesis. Recently, homogenous monolayers of bone marrow endothelial cells (BMEC) have been isolated and cultivated in tissue culture. Long-term coculture studies have shown that BMEC monolayers are unique type of endothelium and can support long-term proliferation of hematopoietic progenitor cells particularly megakaryocytic and myeloid progenitor cells by constitutive elaboration of lineage-specific cytokines such as G-CSF, GM-CSF, M-CSF, Kit-ligand, IL6, FLK-2 ligand, and leukemia inhibitory factor. Direct cellular contact between hematopoietic progenitor cells and BMEC monolayers through specific adhesion molecules including beta1, beta2 integrins and selectins play a critical role in trafficking and possibly proliferation of hematopoietic stem cells. Dysfunction of microvascular endothelial cells within the hematopoietic microenvironment may result in stem cell disorders and progression to aplastic anemias, and contribute to graft failure during bone marrow transplantation. Further studies on the role of microvascular endothelium in the regulation of hematopoietic stem cell homing and proliferation may enhance our understanding of the pathophysiology of stem cell and leukemic disorders.

Platelet transfusion and alternatives to transfusion in patients with malignancy

Platelet transfusions have long had an important role in the treatment of patients with thrombocytopenia due to disease or myelotoxic treatment or in patients with reduced platelet function. However, platelet transfusions are associated with numerous risks, both immunologic (e.g., transfusion reactions, alloimmunization, immunosuppression) and infectious (e.g., viral, bacterial). In addition, several laboratory and clinical factors can influence post-transfusion platelet recovery. Recent technological advances have introduced the potential for using alternatives to platelet transfusions, such as cytokines or platelet substitutes, which may avoid the risks of transfusion. Platelet development from megakaryocytes is a process that is highly regulated by cytokines and animal research suggests that selected cytokines involved in this process may be useful in the treatment of thrombocytopenia. Newer developments, including the utilization of recombinant cytokines with relatively selective stimulation of platelet production (e.g., interleukin 6 [IL-6]) and the recent discovery of a megakaryocyte colony stimulating factor (thrombopoietin), represent major therapeutic opportunities in the treatment of thrombocytopenia. Platelet substitutes, e.g., thromboerythrocytes, also show promise in the management of platelet deficiencies.

Carbohydrate antigens of human megakaryocytes and platelet glycoproteins: a comparative study

Until now, carbohydrate antigens of human megakaryocytes have not been studied very extensively. For this reason, we investigated the staining pattern of 25 lectins and carbohydrate-specific monoclonal antibodies on paraffin-embedded trephine biopsies and acetone-fixed smears from patients with reactive and neoplastic bone marrow lesions. A biotin-streptavidin-alkaline phosphatase assay was used to visualize the binding of lectins or antibodies. Ulex europaeus agglutinin I (UEA-I) stained megakaryocytes in all cases tested. Monoclonal antibodies detecting fucosylated Lewis type 2 chain antigens (19-OLE, 12-4LE and LeuM1) were also reactive. Several lectins detecting backbone and core oligosaccharides [Helix pomatia agglutinin (HPA), peanut agglutinin (PNA), Erythrina cristagalli agglutinin (ECA), soybean agglutinin (SBA)] bound to megakaryocytes only after neuraminidase digestion. Moreover, we investigated human platelet lysates to gain some information about the carbohydrate residues of platelet glycoproteins which are synthesized by megakaryocytes. The carbohydrate expression of platelets showed striking similarities to that of megakaryocytes. Immunoblotting experiments revealed a strong binding of UEA-I, 19-OLE and 12-4LE to a band isographic to glycoprotein (gp) Ib. After desialylation of glycoproteins transblotted to nitrocellulose, ECA and PNA also reacted with a band of this molecular weight. Gp Ib is known to contain a mucin-like peptide core with a great number of potential O-glycosylation sites. Therefore, it is tempting to speculate that carbohydrate residues characterized in this study are involved in the complex biological interactions of gp Ib.

Ki-S1 and PCNA expression in erythroid precursors and megakaryocytes--a comparative study on proliferative and endoreduplicative activity in reactive and neoplastic bone marrow lesions

The monoclonal antibody Ki-S1 reacts with a cell proliferation-associated nuclear antigen which is expressed in the G1 through G2/M phases of the cell cycle and is resistant to formalin fixation. We have studied Ki-S1 and PCNA (PC10) immunostaining of erythroid precursors (proliferative activity) and megakaryocytes (endoreduplicative activity) in bone marrow trephine biopsies in a variety of reactive and neoplastic lesions using double immunohistochemistry to identify both cell lineages. A significant increase in Ki-S1 labelling compared with PCNA positivity was found in all conditions studied. In particular, specimens derived from secondary polycythaemia (SP), polycythaemia vera (P. vera), and primary osteomyelofibrosis (OMF), and from splenic tissue with myeloid metaplasia (MM), revealed a disproportionally high labelling index of erythropoiesis, which was not present in chronic myelogenous leukaemia (CML), AIDS, and autoimmune (idiopathic) thrombocytopenia (ITP). Enhancement of Ki-S1 (PCNA) staining in SP and P. vera is in keeping with the relevant increase in erythroid precursor proliferation, but in OMF and MM there is overexpression of both proliferation markers, possibly due to secondary folic acid deficiency, which is known to cause a block in the S-phase of the cell cycle. A significant correlation was observed between the sizes of megakaryocytes and their nuclei with Ki-S1 (and also PCNA) staining. Ki-S1 (and PCNA) labelling of predominantly smaller elements of this lineage supports a hypothesis that the phases of the cell cycle have different durations in the various steps of polyploidization, with a prolongation of G1/G2 at higher ploidy levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Proliferating cell nuclear antigen (PCNA) expression of megakaryocytopoiesis in normal human bone marrow and reactive lesions with special emphasis on HIV-myelopathy

A morphometric analysis was performed on bone marrow trephine biopsies using sequential double-immunostaining, to evaluate endoreduplicative activity of megakaryocytopoiesis. A total of 104 marrow specimens were studied with employment of monoclonal antibodies PC10 (anti-proliferating cell nuclear antigen-PCNA) and Y2/51-CD61 (anti-platelet glycoprotein IIIa). In addition to the control group patients included non-specific inflammatory changes, HIV-myelopathy with normal or decreased platelet counts, idiopathic thrombocytopenic purpura (ITP), and finally reactive thrombocytosis (TH). To exclude an undue overexpression of PCNA, in a comparative pilot study we also applied MIB1 (Ki-67 antigen) on normal bone marrow specimens. In accordance with the various modalities of cell-cycle marker expression, no significantly different findings were disclosed. PCNA-labelling index was relatively low, ranging from 0.8 to 1.7% of the total megakaryocytopoiesis (promegakaryoblasts to mature platelet-shedding megakaryocytes). A significant relationship between megakaryocyte size and PCNA-expression was determinable. This implies that some of the cases with a prevalence of small megakaryocytes, like ITP, have the tendency to show a higher proportion of positively-stained cells. Moreover, this feature confirms a hypothesis postulating a decrease in the time for DNA-synthesis (S-phase) and a relative prolongation of the G1/G2-phases of the cell-cycle at higher ploidy levels (large-sized megakaryocytes). On the other hand, it may be speculated that some of the hyperpolyploid giant megakaryocytes may have reached their endstage of endoreduplication and enter into G0-phase. In comparison with the control group and the other entities under study, a significant reduction of PCNA-reactivity was recognizable in HIV-myelopathy accompanied by thrombocytopenia.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of recombinant human interleukin-11 on rat megakaryopoiesis and thrombopoiesis in vivo: comparative study with interleukin-6

The ability of recombinant human interleukin-11 (IL-11) to stimulate rat megakaryopoiesis and thrombopoiesis in vivo was investigated. Once daily subcutaneous injections of IL-11 at doses of 2, 8 and 20 micrograms/rat for 5 d caused dose-dependent increases in platelet counts. The chronic administration of 20 micrograms/rat/d for 14 d resulted in biphasic increases in platelet counts with peaks at days 8 and 15 of up to 30% over the control, continuing for more than 5 d after cessation of IL-11 injections. Moreover, a striking increase in megakaryocytic size and ploidy in bone marrow in response to IL-11 was elicited. IL-11 induced a dose-dependent elevation in bone marrow cell numbers but not in splenic weight and cell numbers. Modifications of these parameters were noted as soon as 24 h after the first IL-11 injections. IL-11 had a same potency of thrombopoietic effect in rats as compared with IL-6. However, elevation of acute phase protein such as immunosuppressive acidic protein was 2.2-fold in rats given 20 micrograms/d of IL-6 over those receiving a same dose of IL-11 (470 v 210 micrograms/ml). In addition, the rate of body-weight increase in rats receiving IL-11 for 5 d as well as 14 d did not differ from that in control animals. In IL-6 treated rats, the increase in body weight was significantly slower than the controls, which was observed even in the group given 8 micrograms/d of IL-6. These results suggest that IL-11 may be an effective strategy for the treatment of thrombocytopenia.

Growth factors produced by human embryonic kidney cells that influence megakaryopoiesis include erythropoietin, interleukin 6, and transforming growth factor-beta

Partially purified protein preparations containing megakaryocyte growth factor activity were prepared from human embryonic kidney (HEK) cell conditioned medium using ammonium sulfate precipitation, Cibicron blue affinity chromatography, and wheatgerm lectin affinity chromatography. Treatment of these preparations with neutralizing antibodies directed against erythropoietin (EPO) and interleukin 6 (IL6) resulted in a dramatic reduction in their capacity to stimulate megakaryocyte maturation in vitro. The presence of EPO in these preparations was confirmed by both immunoblotting and use of a mouse spleen erythroid progenitor cell proliferation assay routinely used to quantitate EPO activity in vitro. Northern blot analysis of HEK cell-derived mRNA with IL6 DNA probes revealed the presence of an IL6 transcript with a molecular size of 1.3 kb. Analysis of the HEK cell-derived preparation by ELISA confirmed the presence of immunologically reactive IL6. In addition, it was shown that purified recombinant human EPO and IL6 stimulated megakaryocyte maturation in the in vitro assay used in this study. These data indicate that the activity in HEK cell conditioned medium that stimulates megakaryocyte maturation in vitro is predominantly due to the presence of IL6 and EPO. Immunoneutralization studies of another HEK cell-derived preparation, which was inhibitory in the megakaryocyte maturation assay, demonstrated that it contained transforming growth factor beta (TGF beta), a potent inhibitor of megakaryocyte maturation. Taken together, these studies indicate that HEK cell conditioned medium, which has previously been reported to contain megakaryocyte growth factor activity, is comprised of a complex mixture of growth and differentiation factors, some of which promote and others that inhibit the process of megakaryopoiesis.

Dysmegakaryopoiesis in myelodysplastic syndromes (MDS): an immunomorphometric study of bone marrow trephine biopsy specimens

An immunohistochemical and morphometric analysis was performed on trephine biopsy specimens of the bone marrow in 40 patients (23 men and 17 women, mean age 62 years) with different subtypes of myelodysplastic syndromes (MDS) to determine dysmegakaryopoiesis, but particularly precursor cells--that is, pro- and megakaryoblasts. In 31 of the 40 patients the numbers of megakaryocytes were increased which was associated with a predominance of smaller cell forms (micromegakaryocytes). Compared with periodic acid Schiff, immunostaining with a formalin resistant monoclonal antibody against glycoprotein IIIa (Y2/51(CD61) showed a clinically important proportion of immature elements. These could be designated pro- and megakaryoblasts by taking morphometric measurements on smears and bone marrow sections. There was a relevant increase in the number of promegakaryoblasts in 32 patients, consistent with uncontrolled expansion of the precursor pool. Seventeen repeated bone marrow biopsy specimens taken after chemotherapy largely showed a decrease in the numbers of megakaryocytes including the precursor cell population. Moreover, morphometric evaluation disclosed that micromegakaryocytes in MDS differ significantly from those in chronic myeloid leukaemia (CML) due to distinctive nuclear features and a disturbed nuclear:cytoplasmic ratio. These changes generate a more pleomorphic or atypical appearance of this cell population in MDS, compared with micromegakaryocytes in CML. It is concluded that the disproportionate increase in megakaryocyte precursors and the grossly abnormal aspects of micromegakaryocytes in MDS are characteristics of the severe defect involving haematopoiesis in this disorder.

The clinical spectrum of thrombocytosis and thrombocythemia

Platelet production is the result of a highly ordered maturation of a developmental hierarchy of megakaryocytic progenitor cells regulated by a variety of cytokines. GM-CSF, II-3 and II-6 have a stimulatory effect and several cytokines (TGF-beta, platelet released glycoprotein, platelet factor 4 and interferons) have inhibitory effects down regulating platelet production perhaps as part of an autocrine control loop. Excess platelet production can be clinically characterized as pseudothrombocytosis, thrombocytosis or thrombocythemia; the clinical features and criteria for each are defined. The term thrombocytosis infers its reactive nature and, in the absence of arterial disease or prolonged immobility, it poses little risk regardless of platelet numbers. By contrast, in thrombocythemia, whether primary or associated with other myeloproliferative lesions, significant thrombohemorrhagic events occur. The natural history, rationale, and approach to platelet reduction and control of clinical sequela are reviewed. Clinical therapeutic options include a new agent, Anagrelide.

Partial purification and characterization of human megakaryocyte colony-stimulating factor (Meg-CSF)

Megakaryocyte colony-stimulating factor (Meg-CSF) in urinary extracts from patients with aplastic anemia was partially characterized and purified. Using Meg-CSF-enriched fractions, we established that the moiety has the following characteristics: 1) portions of the molecules having Meg-CSF activity have sialic acid, probably with a biantennary structure, and beta-galactose residues as the terminal and penultimate sugars; 2) disulfide residues are an essential chemical group of the molecule and are located on its surface; and 3) Meg-CSF activity is stable in n-propanol, but not in acetonitrile with trifluoroacetic acid. Partial purification of Meg-CSF by a four-step procedure of ethanol precipitation, CM Affi-Gel Blue chromatography, wheat germ agglutinin-sepharose chromatography, and high-resolution hydroxyapatite chromatography, yielded a concentrate with a 430- to 630-fold increase in specific activity. The partially purified Meg-CSF fractions stimulated both human and murine megakaryocytopoiesis in vitro (CFU-meg). When analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under nonreduced conditions, Meg-CSF activity was recovered in the 29-34 kDa molecular weight fractions. We have also shown that Meg-CSF, purified from the urine of aplastic anemia patients, stimulated murine megakaryocytopoiesis and platelet production in vivo. Final purification of human urinary Meg-CSF is currently in progress.