Effects of a 2-step culture with cytokine combinations on megakaryocytopoiesis and thrombopoiesis from carbon-ion beam-irradiated human hematopoietic stem/progenitor cells

Regulation of the genetic code in megakaryocytes and platelets

Platelets are generated from nucleated precursors referred to as megakaryocytes. The formation of platelets is one of the most elegant and unique developmental processes in eukaryotes. Because they enter the circulation without nuclei, platelets are often considered simple, non-complex cells that have limited functions beyond halting blood flow. However, emerging evidence over the past decade demonstrates that platelets are more sophisticated than previously considered. Platelets carry a rich repertoire of messenger RNAs (mRNAs), microRNAs (miRNAs), and proteins that contribute to primary (adhesion, aggregation, secretion) and alternative (immune regulation, RNA transfer, translation) functions. It is also becoming increasingly clear that the 'genetic code' of platelets changes with race, genetic disorders, or disease. Changes in the 'genetic code' can occur at multiple points including megakaryocyte development, platelet formation, or in circulating platelets. This review focuses on regulation of the 'genetic code' in megakaryocytes and platelets and its potential contribution to health and disease.

Separation of in-vitro-derived megakaryocytes and platelets using spinning-membrane filtration

In-vitro-derived platelets (PLTs) could potentially overcome problems associated with donated PLTs, including contamination and alloimmunization. Although several groups have produced functional PLTs from stem cells in vitro, the challenge of developing this technology to yield transfusable PLT units has yet to be addressed. The asynchronous nature of in vitro PLT generation makes a single harvest point infeasible for collecting PLTs as soon as they are formed. The current standard of performing manual centrifugations to separate PLTs from nucleated cells at multiple points during culture is labor-intensive, imprecise, and difficult to standardize in accordance with current Good Manufacturing Practices (cGMP). In an effort to develop a more effective method, we adapted a commercially-available, spinning-membrane filtration device to separate in-vitro-derived PLTs from nucleated cells and recover immature megakaryocytes (MKs), the precursor cells to PLTs, for continued culture. Processing a mixture of in-vitro-derived MKs and PLTs on the adapted device yielded a pure PLT population and did not induce PLT pre-activation. MKs recovered from the separation process were unaffected with respect to viability and ploidy, and were able to generate PLTs after reseeding in culture. Being able to efficiently harvest in-vitro-derived PLTs brings this technology one step closer to clinical relevance.

Radiation sensitivities in the terminal stages of megakaryocytic maturation and platelet production

These studies examined the effects of X radiation and interleukin 3 (IL-3), which is an effective cytokine for the generation of megakaryocytopoiesis from X-irradiated hematopoietic stem/progenitor cells, on the terminal process of human megakaryocytopoiesis and thrombopoiesis. Mature megakaryocytes were induced by culturing CD34(+) cells from normal human peripheral blood in a serum-free liquid culture stimulated with thrombopoietin. The experiments contained the following groups: control cultures with nonirradiated cells incubated for 15 days; cultures treated with IL-3 on day 7 or day 11, cultures irradiated with 2 Gy on day 7 or day 11, and cultures treated with IL-3 immediately after X irradiation. The nonirradiated control cultures produced megakaryocytes from day 7, and both the megakaryocyte and platelet generation reached a peak on day 12-13. When X irradiation was performed on day 7, both the megakaryocyte and platelet numbers decreased remarkably, while no significant effect was observed on those numbers when cultures were X-irradiated on day 11. IL-3 showed neither protective nor promoting effects on the terminal stages of megakaryocytic maturation and platelet production. The results demonstrated that mature megakaryocytes are radiosensitive but that the radiosensitivity decreased with the terminal stages of megakaryocytic maturation, especially for the megakaryocytes entering into proplatelet formation.

Heavy ion beam irradiation regulates the mRNA expression in megakaryocytopoiesis from human hematopoietic stem/progenitor cells

Heavy ion beams are a high-LET radiation that has greater biological effect than electron beams or X-rays. However, little is known about the effect of heavy ion beams on the proliferation and differentiation of human hematopoietic stem/progenitor cells (HSPCs). The present study examined the effect of heavy ion beams on gene expression in human HSPCs, especially during early stage of megakaryocytopoiesis. Human CD34+ cells were exposed to monoenergetic carbon-ion beams (290 MeV/nucleon, LET = 50 KeV/m) that were generated by an accelerator (Heavy Ion Medical Accelerator in Chiba). The expression of various genes related to early hematopoiesis, megakaryocytopoiesis/erythropoiesis, cytokine receptors and oxidative stress were analyzed by real-time RT-PCR. Friend leukemia virus integration 1, an early hematopoiesis-related gene, showed significantly higher mRNA expression than the control at 6 hr after irradiation. In contrast, no significant differences were observed in almost all of the other early hematopoiesis-related genes, cytokine receptor-coded genes and megakaryocytopoiesis/erythropoiesis-differentiation pathway-related genes, respectively. An analysis of the response of the genes to oxidative stress revealed the expression of heme oxygenase 1 to show a 1.5-fold and 11.9-fold increase from the day 0 control at 24 hr after 0.5 Gy and 2 Gy irradiation, respectively. Similarly, the NAD(P)H dehydrogenase-quinone 1 expression also showed a 22.0-fold and a 21.8-fold increase at 6 hr in comparison to the initial control. These results showed that the heavy ion beams affect megakaryocytopoiesis/ erythropoiesis differentiation of human HSPCs on the gene expression level.

Ion beam radiobiology and cancer: time to update ourselves

High-energy protons and carbon ions exhibit an inverse dose profile allowing for increased energy deposition with penetration depth. Additionally, heavier ions like carbon beams have the advantage of a markedly increased biological effectiveness characterized by enhanced ionization density in the individual tracks of the heavy particles, where DNA damage becomes clustered and therefore more difficult to repair, but is restricted to the end of their range. These superior biophysical and biological profiles of particle beams over conventional radiotherapy permit more precise dose localization and make them highly attractive for treating anatomically complex and radioresistant malignant tumors but without increasing the severe side effects in the normal tissue. More than half a century since Wilson proposed their use in cancer therapy, the effects of particle beams have been extensively investigated and the biological complexity of particle beam irradiation begins to unfold itself. The goal of this review is to provide an as comprehensive and up-to-date summary as possible of the different radiobiological aspects of particle beams for effective application in cancer treatment.