Megakaryocytic cell lines

Craniofacial Bone Tissue Engineering: Current Approaches and Potential Therapy

Craniofacial bone defects can result from various disorders, including congenital malformations, tumor resection, infection, severe trauma, and accidents. Successfully regenerating cranial defects is an integral step to restore craniofacial function. However, challenges managing and controlling new bone tissue formation remain. Current advances in tissue engineering and regenerative medicine use innovative techniques to address these challenges. The use of biomaterials, stromal cells, and growth factors have demonstrated promising outcomes in vitro and in vivo. Natural and synthetic bone grafts combined with Mesenchymal Stromal Cells (MSCs) and growth factors have shown encouraging results in regenerating critical-size cranial defects. One of prevalent growth factors is Bone Morphogenetic Protein-2 (BMP-2). BMP-2 is defined as a gold standard growth factor that enhances new bone formation in vitro and in vivo. Recently, emerging evidence suggested that Megakaryocytes (MKs), induced by Thrombopoietin (TPO), show an increase in osteoblast proliferation in vitro and bone mass in vivo. Furthermore, a co-culture study shows mature MKs enhance MSC survival rate while maintaining their phenotype. Therefore, MKs can provide an insight as a potential therapy offering a safe and effective approach to regenerating critical-size cranial defects.

Dengue viruses infect human megakaryocytes, with probable clinical consequences

One of the most important clinical signs of dengue virus infection is the reduction of white blood cells and platelets in human peripheral blood (leukopenia and thrombocytopenia, respectively), which may significantly impair the clearance of dengue virus by the immune system. The cause of thrombocytopenia and leukopenia during dengue infection is still unknown, but may be related to severe suppression of bone marrow populations including hematopoietic stem cells and megakaryocytes, the progenitors of white blood cells and platelets respectively. Here, we explored the possibility that bone marrow suppression, including ablation of megakaryocyte populations, is caused by dengue virus infection of megakaryocytes. We used three different models to measure dengue virus infection and replication: in vitro, in a human megakaryocyte cell line with viral receptors, ex vivo, in primary human megakaryocytes, and in vivo, in humanized mice. All three systems support dengue virus infection and replication, including virus strains from serotypes 1, 2, and 3, and clinical signs, in vivo; all assays showed viral RNA and/or infectious viruses 7–14 days post-infection. Although we saw no significant decrease in cell viability in vitro, there was significant depletion of mature megakaryocytes in vivo. We conclude that megakaryocytes can produce dengue viruses in the bone marrow niche, and a reduction of cell numbers may affect bone marrow homeostasis.

Dengue virus is the most common cause of viral hemorrhagic fever in humans. Over half of the world’s population lives in an at risk area for dengue virus infection, and this number will continue to grow as climate change allows the mosquito vectors of dengue virus to expand their breeding ranges to more temperate climates. Currently, there are no specific treatments for dengue virus infection. Understanding how dengue virus causes hemorrhagic fever could inform the development of these much needed treatments. Populations of important immune system mediators, such as white blood cells and platelets, are significantly dysregulated during dengue virus infection. These cells originate in the bone marrow, which experiences significant suppression, including a complete ablation of megakaryocytes (platelet progenitor cells), during DENV infection. Here, we add to the knowledge on how dengue virus induces bone marrow suppression by investigating whether dengue virus infects human megakaryocytes. We discovered that dengue virus infects human megakaryocytes in vitro, ex vivo, and in vivo models of dengue virus infection; however, dengue virus infection does not appear to directly affect viability of human megakaryocytes. Future studies will investigate whether infected megakaryocytes are still able to perform their functions of producing platelets and maintaining bone marrow homeostasis.

Large-scale culture of a megakaryocytic progenitor cell line with a single-use bioreactor system

The increasing application of regenerative medicine has generated a growing demand for stem cells and their derivatives. Single-use bioreactors offer an attractive platform for stem cell expansion owing to their scalability for large-scale production and feasibility of meeting clinical-grade standards. The current work evaluated the capacity of a single-use bioreactor system (1 L working volume) for expanding Meg01 cells, a megakaryocytic (MK) progenitor cell line. Oxygen supply was provided by surface aeration to minimize foaming and orbital shaking was used to promote oxygen transfer. Oxygen transfer rates (k_L a) of shaking speeds 50, 100, and 125 rpm were estimated to be 0.39, 1.12, and 10.45 h^-1 , respectively. Shaking speed was a critical factor for optimizing cell growth. At 50 rpm, Meg01 cells exhibited restricted growth due to insufficient mixing. A negative effect occurred when the shaking speed was increased to 125 rpm, likely caused by high hydrodynamic shear stress. The bioreactor culture achieved the highest growth profile when shaken at 100 rpm, achieving a total expansion rate up to 5.7-fold with a total cell number of 1.2 ± 0.2 × 10⁹ cells L^-1 . In addition, cells expanded using the bioreactor system could maintain their potency to differentiate following the MK lineage, as analyzed from specific surface protein and morphological similarity with the cells grown in the conventional culturing system. Our study reports the impact of operational variables such as shaking speed for growth profile and MK differentiation potential of a progenitor cell line in a single-use bioreactor. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:362-369, 2018.

Recent developments in ex vivo platelet production

The platelet is a component of blood that functions to initiate blood clotting. Abnormal platelet count and function can lead to a life-threatening condition caused by excessive bleeding. At present, platelet supply for transfusion can be obtained only from platelet donation. However, platelets cannot be stored for longer than 7 days, meaning that routine isolation is required to maintain platelet supply for transfusion. To mitigate for potential platelet shortages, several strategies have been proposed to generate platelets ex vivo. By employing both of natural and artificial approaches, several researchers have successfully generated biomaterials with characteristics similar to human-derived platelets. Their reports indicated that the biomaterials could mimic the aggregation of human-isolated platelets, further suggesting the possibility to substitute or complement human-isolated platelets. The current review summarizes the progress in ex vivo platelet production and gives a prospect for the possible approaches to achieving a feasible platelet factory, based on the Good Manufacturing Practice standards.

Artificial MiRNA Knockdown of Platelet Glycoprotein lbα: A Tool for Platelet Gene Silencing

In recent years, candidate genes and proteins implicated in platelet function have been identified by various genomic approaches. To elucidate their exact role, we aimed to develop a method to apply miRNA interference in platelet progenitor cells by using GPIbα as a proof-of-concept target protein. After in silico and in vitro screening of siRNAs targeting GPIbα (siGPIBAs), we developed artificial miRNAs (miGPIBAs), which were tested in CHO cells stably expressing GPIb-IX complex and megakaryoblastic DAMI cells. Introduction of siGPIBAs in CHO GPIb-IX cells resulted in 44 to 75% and up to 80% knockdown of GPIbα expression using single or combined siRNAs, respectively. Conversion of siGPIBAs to miGPIBAs resulted in reduced silencing efficiency, which could however be circumvented by tandem integration of two hairpins targeting different regions of GPIBA mRNA where 72% GPIbα knockdown was achieved. CHO GPIb-IX cells transfected with the miGPIBA construct displayed a significant decrease in their ability to aggregate characterized by lower aggregate numbers and size compared to control CHO GPIb-IX cells. More importantly, we successfully silenced GPIbα in differentiating megakaryoblastic DAMI cells that exhibited morphological changes associated with actin organization. In conclusion, we here report the successful use of miRNA technology to silence a platelet protein in megakaryoblastic cells and demonstrate its usefulness in functional assays. Hence, we believe that artificial miRNAs are suitable tools to unravel the role of a protein of interest in stem cells, megakaryocytes and platelets, thereby expanding their application to novel fields of basic and translational research.

BMS-777607 promotes megakaryocytic differentiation and induces polyploidization in the CHRF-288-11 cells

Introduction of a polyploidy inducer is a promising strategy to achieve a high level of polyploidization during megakaryocytic (MK) differentiation. Here, we report that a multi-kinase inhibitor, BMS-777607, is a potent polyploidy inducer for elevating high ploidy cell formation in the MK-differentiated CHRF-288-11 (CHRF) cells. Our result showed that BMS-777607 strongly inhibited cell division without affecting cell viability when detected at day 1 after treatment. As a consequence, the high ploidy (≥8N) cells were accumulated in culture for 8 days, with an increase from 16.2 to 75.2 % of the total cell population. The elevated polyploidization was accompanied by the increased expression level of MK marker, CD41 (platelet glycoprotein IIb/IIIa, GPIIb/IIIa), suggesting that BMS-777607 promoted both polyploidization and commitment of MK-differentiated CHRF cells. Platelet-like fragments (PFs) were released by mature CHRF cells. Based on a flow cytometry assay, it was found that the PFs produced from BMS-777607-treated cells tended to have larger size and higher expression of GPIIb/IIIa, a receptor for platelet adhesion. Taken together, these results suggested that BMS-777607 promoted MK differentiation of CHRF cells and increased the functional property of platelet-like fragments.

Unique in vitro and in vivo thrombopoietic activities of ingenol 3,20 dibenzoate, a Ca(++)-independent protein kinase C isoform agonist

Thrombopoiesis following severe bone marrow injury frequently is delayed, thereby resulting in life-threatening thrombocytopenia for which there are limited treatment options. The reasons for these delays in recovery are not well understood. Protein kinase C (PKC) agonists promote megakaryocyte differentiation in leukemia cell lines and primary cells. However, little is known about the megakaryopoietic effects of PKC agonists on primary CD34+ cells grown in culture or in vivo. Here we present evidence that the novel PKC isoform-selective agonist 3,20 ingenol dibenzoate (IDB) potently stimulates early megakaryopoiesis of human CD34+ cells. In contrast, broad spectrum PKC agonists failed to do so. In vivo, a single intraperitoneal injection of IDB selectively increased platelets in mice without affecting hemoglobin or white counts. Finally, IDB strongly mitigated radiation-induced thrombocytopenia, even when administered 24 hours after irradiation. Our data demonstrate that novel PKC isoform agonists such as IDB may represent a unique therapeutic strategy for accelerating the recovery of platelet counts following severe marrow injury.

Establishment of an ES cell-derived murine megakaryocytic cell line, MKD1, with features of primary megakaryocyte progenitors

Because of the scarcity of megakaryocytes in hematopoietic tissues, studying megakaryopoiesis heavily relies on the availability of appropriate cellular models. Here, we report the establishment of a new mouse embryonic stem (ES) cell-derived megakaryocytic cell line, MKD1. The cells are factor-dependent, their cell surface immunophenotype and gene expression profile closely resemble that of primary megakaryocyte progenitors (MkPs) and they further differentiate along the megakaryocyte lineage upon valproic acid treatment. At a functional level, we show that ablation of SCL expression, a transcription factor critical for MkP maturation, leads to gene expression alterations similar to that observed in primary, Scl-excised MkPs. Moreover, the cell line is amenable to biochemical and transcriptional analyses, as we report for GpVI, a direct target of SCL. Thus, the MKD1 cell line offers a pertinent experimental model to study the cellular and molecular mechanisms underlying MkP biology and more broadly megakaryopoiesis.

Switch to high-level virus replication and HLA class I upregulation in differentiating megakaryocytic cells after infection with pathogenic hantavirus

Hantaan virus (HTNV), the prototype member of the Hantavirus genus in the family Bunyaviridae, causes hemorrhagic fever with renal syndrome (HFRS) in humans. Hemorrhage is due to endothelial barrier damage and a sharp decrease in platelet counts. The mechanisms underlying HTNV-associated acute thrombocytopenia have not been elucidated so far. Platelets are produced by mature megakaryocytes that develop during megakaryopoiesis. In this study, we show that HTNV targets megakaryocytic cells whereas rather non-pathogenic hantaviruses did not infect this cell type. After induction of differentiation megakaryocytic cells switched from low-level to high-level HTNV production without reduction in cell survival or alteration in differentiation. However, increased HTNV replication resulted in strong upregulation of HLA class I molecules although HTNV escaped type I interferon (IFN)-associated innate responses. Taken together, HTNV efficiently replicates in differentiating megakaryocytic cells resulting in upregulation of HLA class I molecules, the target structures for cytotoxic T cells (CTLs).

Methods for genetic modification of megakaryocytes and platelets

During recent decades there have been major advances in the fields of thrombosis and haemostasis, in part through development of powerful molecular and genetic technologies. Nevertheless, genetic modification of megakaryocytes and generation of mutant platelets in vitro remains a highly specialized area of research. Developments are hampered by the low frequency of megakaryocytes and their progenitors, a poor efficiency of transfection and a lack of understanding with regard to the mechanism by which megakaryocytes release platelets. Current methods used in the generation of genetically modified megakaryocytes and platelets include mutant mouse models, cell line studies and use of viruses to transform primary megakaryocytes or haematopoietic precursor cells. This review summarizes the advantages, limitations and technical challenges of such methods, with a particular focus on recent successes and advances in this rapidly progressing field including the potential for use in gene therapy for treatment of patients with platelet disorders.

Thrombopoietin Enhances Rapid Current Responses Mediated by P2X1 Receptors on Megakaryocytic Cells in Culture

The effect of thrombopoietin (TPO), a magakaryocytopoietic cytokine, on the functional maturation of megakaryocytes was studied by using cell culture and patch-clamp techniques focusing on purinergic 2X(1) (P2X(1))-receptors, which are expressed specifically on platelets and their progenitors. Meg-01 cells, one of the typical human megakaryocytic cell lines, were cultured and studied by using a whole-cell patch electrode. In control cells cultured in RPMI1640 medium, an application of adenosine nucleotide (ADP, 40 microM) evoked transient inward currents with amplitudes of 45 +/- 19 pA (at -43 mV). Based on kinetic, ionic, and pharmacological properties as well as on previously reported findings, these currents were thought to be mediated by P2X(1) receptors. When Meg-01 cells were cultured for 7-9 d in a medium to which the differentiation-inducing agent phorbol ester (PMA; 10 nM) or TPO (100 ng/ml) had been added, the responses of the cells to ADP increased to about 150% of the control with PMA and to about 200% of the control value with TPO. A combination of the two agents enhanced the response of the cells to ADP to about 570% of the control value. These results suggest that phorbol ester and TPO cause cellular differentiation of Meg-01 cells and enhance the level of expression of P2X(1)-receptors on cell membranes in a synergetic manner. The effect of TPO on the induction of P2X(1)-receptors on mouse megakaryocytes in culture was more obvious.

Recombinant Semliki Forest virus enhanced plasminogen activator inhibitor 1 expression and storage in the megakaryocytic cell line MEG-01

Platelet plasminogen activator inhibitor I (PAI-1), a trace alpha-granule protein, is a key physiological regulator of fibrinolysis. Because information on the packaging of PAI-1 into alpha-granules during megakaryocytopoiesis may reveal novel approaches for controlling hemostasis, this study investigated basal, plasmid-mediated, and alphavirus-mediated PAI-1 packaging into alpha-granules-like structures in the megakaryocytic cell line MEG-01. Differentiation of MEG-01 cells with phorbol myristate acetate (PMA) was observed to result in a four-fold increase in both secreted and cell-associated PAI-1 antigen over a four day period. Subcellular fractionation of PMA-treated MEG-01 cells on 45% self-forming Percoll gradients was employed to separate low density membrane and Golgi-rich fractions from a high density granule-containing region. A subsequent 30-60% pre-formed Percoll gradient was employed to remove contaminating lysosomes from the PAI-1/glycoprotein IIbIIIa-containing granules. Electron microscopy showed that these MEG-01 granules share a similar size distribution (350-600 nm) and morphology to platelet alpha-granules. PAI-1 (40 ng/mg protein) in isolated MEG-01 storage granules was approximately 10% of the levels present in isolated platelet alpha-granules. To elevate PAI-1 production/storage, two expression systems were investigated. Experiments with plasmids encoding PAI-1 and beta-galactosidase resulted in low transfection efficiency (0.001%). In contrast, Semliki Forest virus (SFV)-mediated gene transfer increased cellular PAI-1 by 31-fold (1,200 ng/10(6) cells at 10 MOI) in comparison to mock-infected cells. Pulse-chase experiments demonstrated that SFV/PAI-1 mediated gene expression could enhance PAI-1 storage 6-9-fold, reaching levels present within platelets. To document the ability of PAI-1 to be stored in a rapidly releasable form in MEG-01 cells, we isolated platelet-like particles from the media conditioned by the cells and examined secretagogue-induced release of PAI-1. Particles from SFV/PAI-1 infected cells display a 5-fold enhanced secretion of PAI-1 following treatment with ADP in comparison to particles incubated in the absence of secretagogue. These results suggest that SFV mediated gene expression in MEG-01 cells provides a useful framework for analyzing the production and storage of alpha-granule proteins.

Overexpression of GATA-2 inhibits erythroid and promotes megakaryocyte differentiation

GATA-1 and GATA-2 transcription factors are required for effective hematopoiesis. These regulatory proteins present overlapping yet distinct patterns of expression in hematopoietic cells. Absence of GATA-2 leads to defective hematopoiesis and an embryonic lethal phenotype. Disruption of GATA-1 results in a compensatory increase in GATA-2 in early erythroid cells and incomplete erythropoiesis with embryos dying at 11.5 days. We examine the specific role of GATA-2 later in hematopoiesis, during erythroid differentiation. Stable K562 cell lines expressing various levels of GATA-2 were generated using a GATA-2 expression plasmid. Overexpression of GATA-2 transcripts was determined by quantitative polymerase chain reaction (PCR). Cytospin smears, growth curve analysis, PCR, and flow cytometry were used to examine the effects of increased levels of GATA-2 in altering cell phenotype and activation of megakaryocytic markers. Human progenitor erythroid cells also were transfected with a GATA-2 expression vector. Growth curve analysis, benzidine staining, and high-performance liquid chromatographic analysis were used to study the effects of GATA-2 on erythroid maturation and proliferation.K562/GATA-2 cell lines expressing high levels of GATA-2 mRNA showed a marked decrease in proliferation and a shift in phenotype toward the megakaryocyte lineage. Ploidy analyses showed that these cell lines developed a multinuclear phenotype, including tetraploids and octaploids. PCR analysis showed activation of megakaryocyte-specific genes including thrombopoietin receptor (c-mpl). Surface expression of platelet glycoprotein receptors Ib/IX (CD42b/CD42a) and IIb/IIIa (CD41/CD61) also was demonstrated by flow cytometry. In primary human adult erythroid cultures transfected with a GATA-2 expression vector, production of total hemoglobin and cell proliferation decreased in a dose-dependent manner.GATA-2 plays an important role in deciding cell lineage throughout hematopoiesis, and increased expression of GATA-2 determines megakaryocytic differentiation. Downregulation of GATA-2 is required for erythroid differentiation.