Megakaryocyte Polyploidization and Proplatelet Formation in Low-Attachment Conditions

Transcription factor 3 is dysregulated in megakaryocytes in myelofibrosis

Transcription factor 3 (TCF3) is a DNA transcription factor that modulates megakaryocyte development. Although abnormal TCF3 expression has been identified in a range of hematological malignancies, to date, it has not been investigated in myelofibrosis (MF). MF is a Philadelphia-negative myeloproliferative neoplasm (MPN) that can arise de novo or progress from essential thrombocythemia [ET] and polycythemia vera [PV] and where dysfunctional megakaryocytes have a role in driving the fibrotic progression. We aimed to examine whether TCF3 is dysregulated in megakaryocytes in MPN, and specifically in MF. We first assessed TCF3 protein expression in megakaryocytes using an immunohistochemical approach analyses and showed that TCF3 was reduced in MF compared with ET and PV. Further, the TCF3-negative megakaryocytes were primarily located near trabecular bone and had the typical "MF-like" morphology as described by the WHO. Genomic analysis of isolated megakaryocytes showed three mutations, all predicted to result in a loss of function, in patients with MF; none were seen in megakaryocytes isolated from ET or PV marrow samples. We then progressed to transcriptomic sequencing of platelets which showed loss of TCF3 in MF. These proteomic, genomic and transcriptomic analyses appear to indicate that TCF3 is downregulated in megakaryocytes in MF. This infers aberrations in megakaryopoiesis occur in this progressive phase of MPN. Further exploration of this pathway could provide insights into TCF3 and the evolution of fibrosis and potentially lead to new preventative therapeutic targets.

Multiomic profiling reveals metabolic alterations mediating aberrant platelet activity and inflammation in myeloproliferative neoplasms

Platelets from patients with myeloproliferative neoplasms (MPNs) exhibit a hyperreactive phenotype. Here, we found elevated P-selectin exposure and platelet-leukocyte aggregates indicating activation of platelets from essential thrombocythemia (ET) patients. Single-cell RNA-seq analysis of primary samples revealed significant enrichment of transcripts related to platelet activation, mTOR, and oxidative phosphorylation in ET patient platelets. These observations were validated via proteomic profiling. Platelet metabolomics revealed distinct metabolic phenotypes consisting of elevated ATP generation accompanied by increases in the levels of multiple intermediates of the tricarboxylic acid cycle, but lower α-ketoglutarate (α-KG) in MPN patients. Inhibition of PI3K/AKT/mTOR signaling significantly reduced metabolic responses and hyperreactivity in MPN patient platelets, while α-KG supplementation markedly reduced oxygen consumption and ATP generation. Ex vivo incubation of platelets from both MPN patients and Jak2 V617F-knockin mice with α-KG supplementation significantly reduced platelet activation responses. Oral α-KG supplementation of Jak2 V617F mice decreased splenomegaly and reduced hematocrit, monocyte, and platelet counts. Finally, α-KG treatment significantly decreased proinflammatory cytokine secretion from MPN CD14+ monocytes. Our results reveal a previously unrecognized metabolic disorder in conjunction with aberrant PI3K/AKT/mTOR signaling that contributes to platelet hyperreactivity in MPN patients.

In vitro megakaryocyte culture from human bone marrow aspirates as a research and diagnostic tool

Megakaryocytes (MKs) are relatively rare in bone marrow, comprising <0.05% of the nucleated cells, which makes direct isolation from human bone marrow impractical. As such, in vitro expansion of primary MKs from patient samples offers exciting fundamental and clinical opportunities. As most of the developed ex vivo methods require a substantial volume of biomaterial, they are not widely performed on young patients. Here we propose a simple, robust, and adapted method of primary human MK culture from 1 mL of bone marrow aspirate. Our technique uses a small volume of bone marrow per culture, uses straightforward isolation methods, and generates approximately 6 × 10⁵ mature MKs per culture. The relative high cell purity and yield achieved by this technique, combined with efficient use of low volumes of bone marrow, make this approach suitable for diagnostic and basic research of human megakaryopoiesis.

Detection of abundant megakaryocytes in pulmonary artery blood in lung cancer patients using a microfluidic platform

OBJECTIVES

The lung was recently re-discovered as a hematopoietic organ for platelet production in mice. However, evidence for the role of the lung in thrombopoiesis in humans is still limited. In this study, we examined megakaryocytes in the pulmonary and systemic circulation, specifically in pulmonary arterial blood (PAB), venous blood (PVB) and peripheral blood using a newly developed microfluidic platform for rare cell isolation.

MATERIALS AND METHODS

We analyzed 23 lung cancer patients who underwent surgery in our institute. PAB and PVB were obtained from the resected lung immediately after surgery. Blood samples were size-selected using a filtration-based microfluidic device and enriched rare cells on glass slide specimens were stained with Papanicolaou (Pap), immunocytochemistry (ICC), and immunofluorescence (IF). Lung tissues were also analyzed by immunohistochemistry.

RESULTS

Pap/ICC/IF showed the presence of abundant CD61+/cytokeratin- giant cells with a megakaryocyte lineage in PAB, but only a few in PVB. These megakaryocytes were found to consist of CD61+/CD41+ immature megakaryocytes and CD61+/CD41- mature megakaryocytes with the potential to produce platelets. These findings were confirmed by the conventional hematological analysis of blood smears stained with Giemsa. In analysis of lung cancer, CD61+ megakaryocytes were observed exclusively in the capillaries of non-cancerous tissue, whereas platelets were selectively observed in the tumor blood vessels of cancerous tissue.

CONCLUSIONS

These results indicate that numerous megakaryocytes migrate from systemic bone marrows to accumulate in PAs and arrest of mature megakaryocytes in the capillaries of normal lung, suggesting the possibility that the lung plays a physiological role in the systemic thrombopoiesis in lung cancer patients.

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.