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Extracellular vesicles (EVs) released from healthy endothelial cells (ECs) have shown potential for promoting angiogenesis, but their therapeutic efficacy remains poorly understood. We have previously shown that transplantation of a human embryonic stem cell-derived endothelial cell product (hESC-ECP), promotes new vessel formation in acute ischemic disease in mice, likely via paracrine mechanism(s). Here, we demonstrated that EVs from hESC-ECPs (hESC-eEVs) significantly increased EC tube formation and wound closure in vitro at ultralow doses, whereas higher doses were ineffective. More important, EVs isolated from the mesodermal stage of the differentiation (hESC-mEVs) had no effect. Small RNA sequencing revealed that hESC-eEVs have a unique transcriptomic profile and are enriched in known proangiogenic microRNAs (miRNAs, miRs). Moreover, an in silico analysis identified three novel hESC-eEV-miRNAs with potential proangiogenic function. Differential expression analysis suggested that two of those, miR-4496 and miR-4691-5p, are highly enriched in hESC-eEVs. Overexpression of miR-4496 or miR-4691-5p resulted in increased EC tube formation and wound closure in vitro, validating the novel proangiogenic function of these miRNAs. In summary, we demonstrated that hESC-eEVs are potent inducers of EC angiogenic response at ultralow doses and contain a unique EV-associated miRNA repertoire, including miR-4496 and miR-4691-5p, with novel proangiogenic function., Competing Interests: Declaration of interests The authors declare the following financial interests/personal relationships which may be considered potential competing interests: D.K., J.C.M., M.B., A.B., and A.H.B. are named inventors on two patent application related to this work. The first patent was filed by the University Court of the University of Edinburgh (no. EP22386089.1) “Extracellular Vesicles That Promote Angiogenesis or Neovascularisation.” The second patent was filed by Mirabilis Therapeutics BV (no. EP22386090.9) “ANGIOGENIC MIRNAS.”, (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Aims: Coronary vasculature formation is a critical event during cardiac development, essential for heart function throughout perinatal and adult life. However, current understanding of coronary vascular development has largely been derived from transgenic mouse models. The aim of this study was to characterize the transcriptome of the human foetal cardiac endothelium using single-cell RNA sequencing (scRNA-seq) to provide critical new insights into the cellular heterogeneity and transcriptional dynamics that underpin endothelial specification within the vasculature of the developing heart., Methods and Results: We acquired scRNA-seq data of over 10 000 foetal cardiac endothelial cells (ECs), revealing divergent EC subtypes including endocardial, capillary, venous, arterial, and lymphatic populations. Gene regulatory network analyses predicted roles for SMAD1 and MECOM in determining the identity of capillary and arterial populations, respectively. Trajectory inference analysis suggested an endocardial contribution to the coronary vasculature and subsequent arterialization of capillary endothelium accompanied by increasing MECOM expression. Comparative analysis of equivalent data from murine cardiac development demonstrated that transcriptional signatures defining endothelial subpopulations are largely conserved between human and mouse. Comprehensive characterization of the transcriptional response to MECOM knockdown in human embryonic stem cell-derived EC (hESC-EC) demonstrated an increase in the expression of non-arterial markers, including those enriched in venous EC., Conclusions: scRNA-seq of the human foetal cardiac endothelium identified distinct EC populations. A predicted endocardial contribution to the developing coronary vasculature was identified, as well as subsequent arterial specification of capillary EC. Loss of MECOM in hESC-EC increased expression of non-arterial markers, suggesting a role in maintaining arterial EC identity., Competing Interests: Conflict of interest: none declared., (© The Author(s) 2022. Published by Oxford University Press on behalf of the European Society of Cardiology.)

Background: Mechanisms contributing to tissue remodeling of the infarcted heart following cell-based therapy remain elusive. While cell-based interventions have the potential to influence the cardiac healing process, there is little direct evidence of preservation of functional myocardium., Aim: The aim of the study was to investigate tissue remodeling in the infarcted heart following human embryonic stem cell-derived endothelial cell product (hESC-ECP) therapy., Materials and Methods: Following coronary artery ligation (CAL) to induce cardiac ischemia, we investigated infarct size at 1 day post-injection in media-injected controls (CALM, n = 11), hESC-ECP-injected mice (CALC, n = 10), and dead hESC-ECP-injected mice (CALD, n = 6); echocardiography-based functional outcomes 14 days post-injection in experimental (CALM, n = 13; CALC, n = 17) and SHAM surgical mice ( n = 4); and mature infarct size (CALM and CALC, both n = 6). We investigated ligand-receptor interactions (LRIs) in hESC-ECP cell populations, incorporating a publicly available C57BL/6J mouse cardiomyocyte-free scRNAseq dataset with naive, 1 day, and 3 days post-CAL hearts., Results: Human embryonic stem cell-derived endothelial cell product injection reduces the infarct area (CALM: 54.5 ± 5.0%, CALC: 21.3 ± 4.9%), and end-diastolic (CALM: 87.8 ± 8.9 uL, CALC: 63.3 ± 2.7 uL) and end-systolic ventricular volume (CALM: 56.4 ± 9.3 uL, CALC: 33.7 ± 2.6 uL). LRI analyses indicate an alternative immunomodulatory effect mediated via viable hESC-ECP-resident signaling., Conclusion: Delivery of the live hESC-ECP following CAL modulates the wound healing response during acute pathological remodeling, reducing infarct area, and preserving functional myocardium in this relatively acute model. Potential intrinsic myocardial cellular/hESC-ECP interactions indicate that discreet immunomodulation could provide novel therapeutic avenues to improve cardiac outcomes following myocardial infarction., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Spiroski, McCracken, Thomson, Magalhaes-Pinto, Lalwani, Newton, Miller, Bénézech, Hadoke, Brittan, Mountford, Beqqali, Gray and Baker.)

Background Aims: Cell-based therapies (CBTs) provide opportunities to treat rare and high-burden diseases. Manufacturing development of these innovative products is said to be complex and costly. However, little research is available providing insight into resource use and cost drivers. Therefore, this study aimed to assess the feasibility of estimating the cost of manufacturing development of two cell-based therapy case studies using a CBT cost framework specifically designed for small-scale cell-based therapies., Methods: A retrospective costing study was conducted in which the cost of developing an adoptive immunotherapy of Epstein-Barr virus-specific cytotoxic T lymphocytes (CTLs) and a pluripotent stem cell (PSC) master cell bank was estimated. Manufacturing development was defined as products advancing from technology readiness level 3 to 6. The study was conducted in a Scottish facility. Development steps were recreated via developer focus groups. Data were collected from facility administrative and financial records and developer interviews., Results: Application of the manufacturing cost framework to retrospectively estimate the manufacturing design cost of two case studies in one Scottish facility appeared feasible. Manufacturing development cost was estimated at £1,201,016 for CTLs and £494,456 for PSCs. Most costs were accrued in the facility domain (56% and 51%), followed by personnel (20% and 32%), materials (19% and 15%) and equipment (4% and 2%)., Conclusions: Based on this study, it seems feasible to retrospectively estimate resources consumed in manufacturing development of cell-based therapies. This fosters inclusion of cost in the formulation and dissemination of best practices to facilitate early and sustainable patient access and inform future cost-conscious manufacturing design decisions., (Copyright © 2021 International Society for Cell & Gene Therapy. Published by Elsevier Inc. All rights reserved.)

Many single nucleotide variants (SNVs) associated with human traits and genetic diseases are thought to alter the activity of existing regulatory elements. Some SNVs may also create entirely new regulatory elements which change gene expression, but the mechanism by which they do so is largely unknown. Here we show that a single base change in an otherwise unremarkable region of the human α-globin cluster creates an entirely new promoter and an associated unidirectional transcript. This SNV downregulates α-globin expression causing α-thalassaemia. Of note, the new promoter lying between the α-globin genes and their associated super-enhancer disrupts their interaction in an orientation-dependent manner. Together these observations show how both the order and orientation of the fundamental elements of the genome determine patterns of gene expression and support the concept that active genes may act to disrupt enhancer-promoter interactions in mammals as in Drosophila. Finally, these findings should prompt others to fully evaluate SNVs lying outside of known regulatory elements as causing changes in gene expression by creating new regulatory elements.

Background Aims: Mesenchymal stromal cells (MSCs) isolated from various tissues are under investigation as cellular therapeutics in a wide range of diseases. It is appreciated that the basic biological functions of MSCs vary depending on tissue source. However, in-depth comparative analyses between MSCs isolated from different tissue sources under Good Manufacturing Practice (GMP) conditions are lacking. Human clinical-grade low-purity islet (LPI) fractions are generated as a byproduct of islet isolation for transplantation. MSC isolates were derived from LPI fractions with the aim of performing a systematic, standardized comparative analysis of these cells with clinically relevant bone marrow-derived MSCs (BM MSCs)., Methods: MSC isolates were derived from LPI fractions and expanded in platelet lysate-supplemented medium or in commercially available xenogeneic-free medium. Doubling rate, phenotype, differentiation potential, gene expression, protein production and immunomodulatory capacity of LPIs were compared with those of BM MSCs., Results: MSCs can be readily derived in vitro from non-transplanted fractions resulting from islet cell processing (i.e., LPI MSCs). LPI MSCs grow stably in serum-free or platelet lysate-supplemented media and demonstrate in vitro self-renewal, as measured by colony-forming unit assay. LPI MSCs express patterns of chemokines and pro-regenerative factors similar to those of BM MSCs and, importantly, are equally able to attract immune cells in vitro and in vivo and suppress T-cell proliferation in vitro. Additionally, LPI MSCs can be expanded to therapeutically relevant doses at low passage under GMP conditions., Conclusions: LPI MSCs represent an alternative source of GMP MSCs with functions comparable to BM MSCs., (Copyright © 2020 International Society for Cell & Gene Therapy. Published by Elsevier Inc. All rights reserved.)

More than seven months into the coronavirus disease -19 (COVID-19) pandemic, infection from the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has led to over 21.2 million cases and resulted in over 760,000 deaths worldwide so far. As a result, COVID-19 has changed all our lives as we battle to curtail the spread of the infection in the absence of specific therapies against coronaviruses and in anticipation of a proven safe and efficacious vaccine. Common with previous outbreaks of coronavirus infections, SARS and Middle East respiratory syndrome, COVID-19 can lead to acute respiratory distress syndrome (ARDS) that arises due to an imbalanced immune response. While several repurposed antiviral and host-response drugs are under examination as potential treatments, other novel therapeutics are also being explored to alleviate the effects on critically ill patients. The use of mesenchymal stromal cells (MSCs) for COVID-19 has become an attractive avenue down which almost 70 different clinical trial teams have ventured. Successfully trialled for the treatment of other conditions such as multiple sclerosis, osteoarthritis and graft versus host disease, MSCs possess both regenerative and immunomodulatory properties, the latter of which can be harnessed to reduce the severity and longevity of ARDS in patients under intensive care due to SARS-CoV-2 infection.

Background Aims: Recent technical and clinical advances with cell-based therapies (CBTs) hold great promise in the treatment of patients with rare diseases and those with high unmet medical need. Currently the majority of CBTs are developed and manufactured in specialized academic facilities. Due to small scale, unique characteristics and specific supply chain, CBT manufacturing is considered costly compared to more conventional medicinal products. As a result, biomedical researchers and clinicians are increasingly faced with cost considerations in CBT development. The objective of this research was to develop a costing framework and methodology for academic and other small-scale facilities that manufacture cell-based therapies., Methods: We conducted an international multi-center costing study in four facilities in Europe using eight CBTs as case studies. This study includes costs from cell or tissue procurement to release of final product for clinical use. First, via interviews with research scientists, clinicians, biomedical scientists, pharmacists and technicians, we designed a high-level costing framework. Next, we developed a more detailed uniform methodology to allocate cost items. Costs were divided into steps (tissue procurement, manufacturing and fill-finish). The steps were each subdivided into cost categories (materials, equipment, personnel and facility), and each category was broken down into facility running (fixed) costs and operational (variable) costs. The methodology was tested via the case studies and validated in developer interviews. Costs are expressed in 2018 euros (€)., Results: The framework and methodology were applicable across facilities and proved sensitive to differences in product and facility characteristics. Case study cost estimates ranged between €23 033 and €190 799 Euros per batch, with batch yield varying between 1 and 88 doses. The cost estimations revealed hidden costs to developers and provided insights into cost drivers to help design manufacturing best practices., Conclusions: This framework and methodology provide step-by-step guidance to estimate manufacturing costs specifically for cell-based therapies manufactured in academic and other small-scale enterprises. The framework and methodology can be used to inform and plan cost-conscious strategies for CBTs., (Copyright © 2020 International Society for Cell and Gene Therapy. All rights reserved.)

Aims: Pluripotent stem cell-derived endothelial cell products possess therapeutic potential in ischaemic vascular disease. However, the factors that drive endothelial differentiation from pluripotency and cellular specification are largely unknown. The aims of this study were to use single-cell RNA sequencing (scRNA-seq) to map the transcriptional landscape and cellular dynamics of directed differentiation of human embryonic stem cell-derived endothelial cells (hESC-EC) and to compare these cells to mature endothelial cells from diverse vascular beds., Methods and Results: A highly efficient directed 8-day differentiation protocol was used to generate a hESC-derived endothelial cell product (hESC-ECP), in which 66% of cells co-expressed CD31 and CD144. We observed largely homogeneous hESC and mesodermal populations at Days 0 and 4, respectively, followed by a rapid emergence of distinct endothelial and mesenchymal populations. Pseudotime trajectory identified transcriptional signatures of endothelial commitment and maturation during the differentiation process. Concordance in transcriptional signatures was verified by scRNA-seq analysis using both a second hESC line RC11, and an alternative hESC-EC differentiation protocol. In total, 105 727 cells were subjected to scRNA-seq analysis. Global transcriptional comparison revealed a transcriptional architecture of hESC-EC that differs from freshly isolated and cultured human endothelial cells and from organ-specific endothelial cells., Conclusion: A transcriptional bifurcation into endothelial and mesenchymal lineages was identified, as well as novel transcriptional signatures underpinning commitment and maturation. The transcriptional architecture of hESC-ECP was distinct from mature and foetal human EC., (© The Author(s) 2019. Published by Oxford University Press on behalf of the European Society of Cardiology.)

Background: Pluripotent stem cells are attractive progenitor cells for the generation of erythroid cells in vitro as have expansive proliferative potential. However, although embryonic (ESC) and induced pluripotent (iPSC) stem cells can be induced to undergo erythroid differentiation, the majority of cells fail to enucleate and the molecular basis of this defect is unknown. One protein that has been associated with the initial phase of erythroid cell enucleation is the intermediate filament vimentin, with loss of vimentin potentially required for the process to proceed., Methods: In this study, we used our established erythroid culture system along with western blot, PCR and interegation of comparative proteomic data sets to analyse the temporal expression profile of vimentin in erythroid cells differentiated from adult peripheral blood stem cells, iPSC and ESC throughout erythropoiesis. Confocal microscopy was also used to examine the intracellular localisation of vimentin., Results: We show that expression of vimentin is turned off early during normal adult erythroid cell differentiation, with vimentin protein lost by the polychromatic erythroblast stage, just prior to enucleation. In contrast, in erythroid cells differentiated from iPSC and ESC, expression of vimentin persists, with high levels of both mRNA and protein even in orthochromatic erythroblasts. In the vimentin-positive iPSC orthochromatic erythroblasts, F-actin was localized around the cell periphery; however, in those rare cells captured undergoing enucleation, vimentin was absent and F-actin was re-localized to the enucleosome as found in normal adult orthrochromatic erythroblasts., Conclusion: As both embryonic and adult erythroid cells loose vimentin and enucleate, retention of vimentin by iPSC and ESC erythroid cells indicates an intrinsic defect. By analogy with avian erythrocytes which naturally retain vimentin and remain nucleated, retention in iPSC- and ESC-derived erythroid cells may impede enucleation. Our data also provide the first evidence that dysregulation of processes in these cells occurs from the early stages of differentiation, facilitating targeting of future studies.

Red blood cells mature within the erythroblastic island (EI) niche that consists of specialized macrophages surrounded by differentiating erythroblasts. Here we establish an in vitro system to model the human EI niche using macrophages that are derived from human induced pluripotent stem cells (iPSCs), and are also genetically programmed to an EI-like phenotype by inducible activation of the transcription factor, KLF1. These EI-like macrophages increase the production of mature, enucleated erythroid cells from umbilical cord blood derived CD34 + haematopoietic progenitor cells and iPSCs; this enhanced production is partially retained even when the contact between progenitor cells and macrophages is inhibited, suggesting that KLF1-induced secreted proteins may be involved in this enhancement. Lastly, we find that the addition of three secreted factors, ANGPTL7, IL-33 and SERPINB2, significantly enhances the production of mature enucleated red blood cells. Our study thus contributes to the ultimate goal of replacing blood transfusion with a manufactured product.

Use of clinical-grade human induced pluripotent stem cell (iPSC) lines as a starting material for the generation of cellular therapeutics requires demonstration of comparability of lines derived from different individuals and in different facilities. This requires agreement on the critical quality attributes of such lines and the assays that should be used. Working from established recommendations and guidance from the International Stem Cell Banking Initiative for human embryonic stem cell banking, and concentrating on those issues more relevant to iPSCs, a series of consensus workshops has made initial recommendations on the minimum dataset required to consider an iPSC line of clinical grade, which are outlined in this report. Continued evolution of this field will likely lead to revision of these guidelines on a regular basis.

Pluripotent stem cell-derived differentiated endothelial cells offer high potential in regenerative medicine in the cardiovascular system. With the aim of translating the use of a human stem cell-derived endothelial cell product (hESC-ECP) for treatment of critical limb ischemia (CLI) in man, we report a good manufacturing practice (GMP)-compatible protocol and detailed cell tracking and efficacy data in multiple preclinical models. The clinical-grade cell line RC11 was used to generate hESC-ECP, which was identified as mostly endothelial (60% CD31 + /CD144 + ), with the remainder of the subset expressing various pericyte/mesenchymal stem cell markers. Cell tracking using MRI, PET, and qPCR in a murine model of limb ischemia demonstrated that hESC-ECP was detectable up to day 7 following injection. Efficacy in several murine models of limb ischemia (immunocompromised/immunocompetent mice and mice with either type I/II diabetes mellitus) demonstrated significantly increased blood perfusion and capillary density. Overall, we demonstrate a GMP-compatible hESC-ECP that improved ischemic limb perfusion and increased local angiogenesis without engraftment, paving the way for translation of this therapy., (Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.)

Blood transfusion is widely used in the clinic but the source of red blood cells (RBCs) is dependent on donors, procedures are susceptible to transfusion-transmitted infections and complications can arise from immunological incompatibility. Clinically-compatible and scalable protocols that allow the production of RBCs from human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) have been described but progress to translation has been hampered by poor maturation and fragility of the resultant cells. Genetic programming using transcription factors has been used to drive lineage determination and differentiation so we used this approach to assess whether exogenous expression of the Erythroid Krüppel-like factor 1 (EKLF/KLF1) could augment the differentiation and stability of iPSC-derived RBCs. To activate KLF1 at defined time points during later stages of the differentiation process and to avoid transgene silencing that is commonly observed in differentiating pluripotent stem cells, we targeted a tamoxifen-inducible KLF1-ER T2 expression cassette into the AAVS1 locus. Activation of KLF1 at day 10 of the differentiation process when hematopoietic progenitor cells were present, enhanced erythroid commitment and differentiation. Continued culture resulted the appearance of more enucleated cells when KLF1 was activated which is possibly due to their more robust morphology. Globin profiling indicated that these conditions produced embryonic-like erythroid cells. This study demonstrates the successful use of an inducible genetic programing strategy that could be applied to the production of many other cell lineages from human induced pluripotent stem cells with the integration of programming factors into the AAVS1 locus providing a safer and more reproducible route to the clinic. Stem Cells 2017;35:886-897., (© 2016 The Authors STEM CELLS published by Wiley Periodicals, Inc. on behalf of AlphaMed Press.)

Assessing the retention of cell therapies following implantation is vital and often achieved by labelling cells with 2'-[ 18 F]-fluoro-2'-deoxy-D-glucose ( 18 F-FDG). However, this approach is limited by local retention of cell-effluxed radiotracer. Here, in a preclinical model of critical limb ischemia, we assessed a novel method of cell tracking using 3'-deoxy-3'-L-[ 18 F]-fluorothymidine ( 18 F-FLT); a clinically available radiotracer which we hypothesise will result in minimal local radiotracer reuptake and allow a more accurate estimation of cell retention. Human endothelial cells (HUVECs) were incubated with 18 F-FDG or 18 F-FLT and cell characteristics were evaluated. Dynamic positron emission tomography (PET) images were acquired post-injection of free 18 F-FDG/ 18 F-FLT or 18 F-FDG/ 18 F-FLT-labelled HUVECs, following the surgical induction of mouse hind-limb ischemia. In vitro, radiotracer incorporation and efflux was similar with no effect on cell viability, function or proliferation under optimised conditions (5 MBq/mL, 60 min). Injection of free radiotracer demonstrated a faster clearance of 18 F-FLT from the injection site vs. 18 F-FDG (p ≤ 0.001), indicating local cellular uptake. Using 18 F-FLT-labelling, estimation of HUVEC retention within the engraftment site 4 hr post-administration was 24.5 ± 3.2%. PET cell tracking using 18 F-FLT labelling is an improved approach vs. 18 F-FDG as it is not susceptible to local host cell reuptake, resulting in a more accurate estimation of cell retention.

: This article describes a good manufacturing practice (GMP)-compatible, feeder-free and serum-free method to produce large numbers of erythroid cells from human pluripotent stem cells (hPSCs), either embryonic or induced. This multistep protocol combines cytokines and small molecules to mimic and surpass the early stages of development. It produces, without any selection or sorting step, a population of cells in which 91.8% ± 5.4% express CD34 at day 7, 98.6% ± 1.3% express CD43 at day 10, and 99.1% ± 0.95% of cells are CD235a positive by day 31 of the differentiation process. Moreover, this differentiation protocol supports extensive expansion, with a single hPSC producing up to 150 hematopoietic progenitor cells by day 10 and 50,000-200,000 erythroid cells by day 31. The erythroid cells produced exhibit a definitive fetal hematopoietic type, with 90%-95% fetal globin and variable proportion of embryonic and adult globin at the protein level. The presence of small molecules during the differentiation protocol has quantitative and qualitative effects; it increases the proportion of adult globin and decreases the proportion of embryonic globin. Given its level of definition, this system provides a powerful tool for investigation of the mechanisms governing early hematopoiesis and erythropoiesis, including globin switching and enucleation. The early stages of the differentiation protocol could also serve as a starting point for the production of endothelial cells and other hematopoietic cells, or to investigate the production of long-term reconstituting hematopoietic stem cells from hPSCs., Significance: This differentiation protocol allows the production of a large amount of erythroid cells from pluripotent stem cells. Its efficiency is compatible with that of in vitro red blood cell production, and it can be a considerable asset for studying developmental erythropoiesis and red blood cell enucleation, thereby aiding both basic and translational research. In addition to red cells, the early stages of the protocol could also be used as a starting point for the large-scale production of other hematopoietic cell types, including the ultimate goal of generating long-term reconstituting hematopoietic stem cells., (©AlphaMed Press.)

Unlabelled: : We have developed a robust, Good Manufacturing Practice-compatible differentiation protocol capable of producing scalable quantities of red blood cells (RBCs) from human pluripotent stem cells (hPSCs). However, translation of this protocol to the clinic has been compromised because the RBCs produced are not fully mature; thus, they express embryonic and fetal, rather than adult globins, and they do not enucleate efficiently. Based on previous studies, we predicted that activation of exogenous HOXB4 would increase the production of hematopoietic progenitor cells (HPCs) from hPSCs and hypothesized that it might also promote the production of more mature, definitive RBCs. Using a tamoxifen-inducible HOXB4-ER(T2) expression system, we first demonstrated that activation of HOXB4 does increase the production of HPCs from hPSCs as determined by colony-forming unit culture activity and the presence of CD43(+)CD34(+) progenitors. Activation of HOXB4 caused a modest, but significant, increase in the proportion of immature CD235a(+)/CD71(+) erythroid cells. However, this did not result in a significant increase in more mature CD235a(+)/CD71(-) cells. RBCs produced in the presence of enhanced HOXB4 activity expressed embryonic (ε) and fetal (γ) but not adult (β) globins, and the proportion of enucleated cells was comparable to that of the control cultures. We conclude that programming with the transcription factor HOXB4 increases the production of hematopoietic progenitors and immature erythroid cells but does not resolve the inherent challenges associated with the production of mature adult-like enucleated RBCs., Significance: As worldwide blood donations decrease and transfusable transmitted infections increase, intense interest has ensued in deriving red blood cells (RBCs) in vitro from alternative sources such as pluripotent stem cells. A translatable protocol was developed to generate RBCs; however, these RBCs have an immature phenotype. It was hypothesized that the transcription factor HOXB4 could enhance their production and maturation. Although HOXB4 increased the production of erythroid progenitors, it did not promote their maturation. Despite the remaining challenges, a robust system has been established to test other candidates and add to the knowledge base in this field., (©AlphaMed Press.)

Despite the increasing importance of long noncoding RNA in physiology and disease, their role in endothelial biology remains poorly understood. Growing evidence has highlighted them to be essential regulators of human embryonic stem cell differentiation. SENCR, a vascular-enriched long noncoding RNA, overlaps the Friend Leukemia Integration virus 1 (FLI1) gene, a regulator of endothelial development. Therefore, we wanted to test the hypothesis that SENCR may contribute to mesodermal and endothelial commitment as well as in endothelial function. We thus developed new differentiation protocols allowing generation of endothelial cells from human embryonic stem cells using both directed and hemogenic routes. The expression of SENCR was markedly regulated during endothelial commitment using both protocols. SENCR did not control the pluripotency of pluripotent cells; however its overexpression significantly potentiated early mesodermal and endothelial commitment. In human umbilical endothelial cell (HUVEC), SENCR induced proliferation, migration, and angiogenesis. SENCR expression was altered in vascular tissue and cells derived from patients with critical limb ischemia and premature coronary artery disease compared to controls. Here, we showed that SENCR contributes to the regulation of endothelial differentiation from pluripotent cells and controls the angiogenic capacity of HUVEC. These data give novel insight into the regulatory processes involved in endothelial development and function.

In platelets, splicing and translation occur in the absence of a nucleus. However, the integrity and stability of mRNAs derived from megakaryocyte progenitor cells remain poorly quantified on a transcriptome-wide level. As circular RNAs (circRNAs) are resistant to degradation by exonucleases, their abundance relative to linear RNAs can be used as a surrogate marker for mRNA stability in the absence of transcription. Here we show that circRNAs are enriched in human platelets 17- to 188-fold relative to nucleated tissues and 14- to 26-fold relative to samples digested with RNAse R to selectively remove linear RNA. We compare RNAseq read depths inside and outside circRNAs to provide in silico evidence of transcript circularity, show that exons within circRNAs are enriched on average 12.7 times in platelets relative to nucleated tissues and identify 3162 genes significantly enriched for circRNAs, including some where all RNAseq reads appear to be derived from circular molecules. We also confirm that this is a feature of other anucleate cells through transcriptome sequencing of mature erythrocytes, demonstrate that circRNAs are not enriched in cultured megakaryocytes, and demonstrate that linear RNAs decay more rapidly than circRNAs in platelet preparations. Collectively, these results suggest that circulating platelets have lost >90% of their progenitor mRNAs and that translation in platelets occurs against the backdrop of a highly degraded transcriptome. Finally, we find that transcripts previously classified as products of reverse transcriptase template switching are both enriched in platelets and resistant to decay, countering the recent suggestion that up to 50% of rearranged RNAs are artifacts., (© 2016 by The American Society of Hematology.)

Previous work has shown that the protein kinase A (PKA)-regulated phosphodiesterase (PDE) 4D3 binds to A kinase-anchoring proteins (AKAPs). One such protein, AKAP9, localizes to the centrosome. In this paper, we investigate whether a PKA-PDE4D3-AKAP9 complex can generate spatial compartmentalization of cyclic adenosine monophosphate (cAMP) signaling at the centrosome. Real-time imaging of fluorescence resonance energy transfer reporters shows that centrosomal PDE4D3 modulated a dynamic microdomain within which cAMP concentration selectively changed over the cell cycle. AKAP9-anchored, centrosomal PKA showed a reduced activation threshold as a consequence of increased autophosphorylation of its regulatory subunit at S114. Finally, disruption of the centrosomal cAMP microdomain by local displacement of PDE4D3 impaired cell cycle progression as a result of accumulation of cells in prophase. Our findings describe a novel mechanism of PKA activity regulation that relies on binding to AKAPs and consequent modulation of the enzyme activation threshold rather than on overall changes in cAMP levels. Further, we provide for the first time direct evidence that control of cell cycle progression relies on unique regulation of centrosomal cAMP/PKA signals.

MicroRNAs (miRNAs) are short noncoding RNAs, which post-transcriptionally regulate gene expression. miRNAs are transcribed as precursors and matured to active forms by a series of enzymes, including Dicer. miRNAs are important in governing cell differentiation, development, and disease. We have recently developed a feeder- and serum-free protocol for direct derivation of endothelial cells (ECs) from human embryonic stem cells (hESCs) and provided evidence of increases in angiogenesis-associated miRNAs (miR-126 and -210) during the process. However, the functional role of miRNAs in hESC differentiation to vascular EC remains to be fully interrogated. Here, we show that the reduction of miRNA maturation induced by Dicer knockdown suppressed hES-EC differentiation. A miRNA microarray was performed to quantify hES-EC miRNA profiles during defined stages of endothelial differentiation. miR-99b, -181a, and -181b were identified as increasing in a time- and differentiation-dependent manner to peak in mature hESC-ECs and adult ECs. Augmentation of miR-99b, -181a, and -181b levels by lentiviral-mediated transfer potentiated the mRNA and protein expression of EC-specific markers, Pecam1 and VE Cadherin, increased nitric oxide production, and improved hES-EC-induced therapeutic neovascularization in vivo. Conversely, knockdown did not impact endothelial differentiation. Our results suggest that miR-99b, -181a, and -181b comprise a component of an endothelial-miRNA signature and are capable of potentiating EC differentiation from pluripotent hESCs., (Copyright © 2012 AlphaMed Press.)

Retroviral vectors remain the most efficient and widely applied system for induction of pluripotency. However, mutagenic effects have been documented in both laboratory and clinical gene therapy studies, principally as a result of dysregulated host gene expression in the proximity of defined integration sites. Here, we report that cells with characteristics of pluripotent stem cells can be produced from normal human fibroblasts in the absence of reprogramming transcription factors (TFs) during lentiviral (LV) vector-mediated gene transfer. This occurred via induced alterations in host gene and microRNA (miRNA) expression and detrimental changes in karyotype. These findings demonstrate that vector-induced genotoxicity may alone play a role in somatic cell reprogramming derivation and urges caution when using integrating vectors in this setting. Clearer understanding of this process may additionally reveal novel insights into reprogramming pathways.

Objective: To develop an embryoid body-free directed differentiation protocol for the rapid generation of functional vascular endothelial cells derived from human embryonic stem cells (hESCs) and to assess the system for microRNA regulation and angiogenesis., Methods and Results: The production of defined cell lineages from hESCs is a critical requirement for evaluating their potential in regenerative medicine. We developed a feeder- and serum-free protocol. Directed endothelial differentiation of hESCs revealed rapid loss of pluripotency markers and progressive induction of mRNA and protein expression of vascular markers (including CD31 and vascular endothelial [VE]-cadherin) and angiogenic growth factors (including vascular endothelial growth factor), increased expression of angiogenesis-associated microRNAs (including miR-126 and miR-210), and induction of endothelial cell morphological features. In vitro, differentiated cells produced nitric oxide, migrated across a wound, and formed tubular structures in both the absence and the presence of 3D matrices (Matrigel). In vivo, we showed that cells that differentiated for 10 days before implantation were efficient at the induction of therapeutic neovascularization and that hESC-derived cells were incorporated into the blood-perfused vasculature of recipient mice., Conclusions: The directed differentiation of hESCs is efficient and effective for the differentiation of functional endothelial cells from hESCs.

The use of donated red blood cells in transfusion is a well-established cellular therapy. However, problems including insufficient supply, transfusion-transmitted infections and the need for immunological matching hamper even in the best services. These issues may be eliminated by using pluripotent stem cells to generate universal donor group O, Rhesus D-negative red blood cells. Human embryonic stem cells can be maintained and expanded indefinitely and can, therefore, produce the very large cell numbers required for this application. Red blood cell production is also an attractive goal for pluripotent stem cell-derived therapeutics because it is a well-characterized single cell suspension, lacking nucleated cells and with a low expression of HLA molecules. Much progress has been made; however, a number of challenges remain including scale-up, clinical effectiveness and product safety.

Background: The majority of acute myeloid leukaemia (AML) patients are over sixty years of age. With current treatment regimens, survival rates amongst these, and also those younger patients who relapse, remain dismal and novel therapies are urgently required. In particular, therapies that have anti-leukaemic activity but that, unlike conventional chemotherapy, do not impair normal haemopoiesis., Principal Findings: Here we demonstrate the potent anti-leukaemic activity of the combination of the lipid-regulating drug bezafibrate (BEZ) and the sex hormone medroxyprogesterone acetate (MPA) against AML cell lines and primary AML cells. The combined activity of BEZ and MPA (B/M) converged upon the increased synthesis and reduced metabolism of prostaglandin D(2) (PGD(2)) resulting in elevated levels of the downstream highly bioactive, anti-neoplastic prostaglandin 15-deoxy Delta(12,14) PGJ(2) (15d-PGJ(2)). BEZ increased PGD(2) synthesis via the generation of reactive oxygen species (ROS) and activation of the lipid peroxidation pathway. MPA directed prostaglandin synthesis towards 15d-PGJ(2) by inhibiting the PGD(2) 11beta -ketoreductase activity of the aldo-keto reductase AKR1C3, which metabolises PGD(2) to 9alpha11beta-PGF(2alpha). B/M treatment resulted in growth arrest, apoptosis and cell differentiation in both AML cell lines and primary AML cells and these actions were recapitulated by treatment with 15d-PGJ(2). Importantly, the actions of B/M had little effect on the survival of normal adult myeloid progenitors., Significance: Collectively our data demonstrate that B/M treatment of AML cells elevated ROS and delivered the anti-neoplastic actions of 15d-PGJ(2). These observations provide the mechanistic rationale for the redeployment of B/M in elderly and relapsed AML.

Imatinib mesylate and nilotinib are highly effective at eradicating the majority of chronic myeloid leukemia (CML) cells; however, neither agent induces apoptosis of primitive CML CD34(+) cells. One possible explanation is that CD34(+) cells do not accumulate sufficient intracellular drug levels because of either inadequate active uptake or increased efflux. To determine the interaction of nilotinib with major clinically implicated drug transporters, we analyzed their interactions with MDR1 (ABCB1), MRP1 (ABCC1), ABCG2 (BCRP) and human organic cation transporter (hOCT)1 in CML cell lines and primitive (CD34(+)) primary CML cells. Nilotinib is neither dependent on active import by hOCT1, nor effluxed through the ATP-binding cassette transporters analyzed. Indeed, we found nilotinib to be an inhibitor of hOCT1, MDR1 and ABCG2. The efflux transporters MDR1, MRP1 and ABCG2 are expressed on CML CD34(+) cells at 13.5, 108 and 291% of control, respectively, although hOCT1 expression was absent; however, inhibition of efflux transporter activity did not potentiate the effect of nilotinib on apoptosis, Bcr-Abl inhibition or CML CD34(+) cell proliferation. Therefore, we have found no evidence for either active uptake of nilotinib through hOCT1 or efflux through MDR1, MRP1 or ABCG2, and it is therefore unlikely that these transporters will have any effect on the clinical response to this drug.

Objective: To investigate the interaction of imatinib mesylate (IM) with the clinically relevant adenosine triphosphate-binding cassette efflux transporter MDR1 (ABCB1) in cells from patients with chronic myeloid leukemia (CML) and to explore whether inhibition of this transporter would improve IM's efficacy in the elimination of CML CD34(+) cells by increasing cell-associated drug accumulation., Materials and Methods: Cells from newly diagnosed chronic-phase CML patients were harvested by leukapheresis and enriched to >95% CD34(+). Expression of the transporter gene MDR1 was performed by quantitative reverse transcription polymerase chain reaction. Interaction of IM with MDR1 was analyzed by substrate (rhodamine 123) displacement assay. Cell-associated levels of IM in CML CD34(+) cells were measured by high-pressure liquid chromatography. Intracellular phospho-CrkL levels, apoptosis in total CML CD34(+) cells and high-resolution tracking of cell division were assayed by flow cytometry., Results: Measurements of cell-associated IM uptake showed significantly lower drug levels in CD34(+) cells, particularly the CD38(-) subpopulation, as compared to IM-sensitive K562 cells. MDR1 was expressed at low level and dye efflux studies demonstrated very little MDR1 activity in CML CD34(+) cells. Furthermore, combination treatment of primitive CML cells with IM and the MDR1 inhibitor PSC833 did not result in elevated cell-associated IM levels. Although we observed slightly enhanced cytostasis with IM when combined with PSC833, this was independent of BCR-ABL inhibition because no associated decrease in phospho-CrkL was observed., Conclusions: Our findings demonstrate that inhibition of MDR1 neither enhances the effect of IM against BCR-ABL activity, nor significantly potentiates IM's efficiency in eliminating primitive CML cells.

Objective: This study investigated two approaches, short hairpin RNA (shRNA) and the potent ABL inhibitor, dasatinib, alone and together, to achieve complete inhibition of BCR-ABL activity in Philadelphia-positive (Ph(+)) cells., Materials and Methods: shRNA specific for BCR-ABL b3a2 were delivered, by lentiviral transduction or electroporation, to K562 cells, with or without dasatinib. mRNA and protein knockdown were measured by quantitative reverse transcriptase polymerase chain reaction, flow cytometry, and Western blotting. BCR-ABL activity was assessed by intracellular flow cytometry for pCrkL. Cell death and apoptosis were assayed using trypan blue exclusion, Annexin-V, and active caspase-3 staining., Results: Forty-eight hours after transduction or electroporation of shRNA, BCR-ABL mRNA, and protein were reduced by 75% and >90%, respectively, and sustained for 5 days. Lentiviral delivery and electroporation were equally effective. pCrkL was inhibited in association with cell death. By 5 days after transduction or electroporation, viable cells represented 50% of input, with a 12-fold reduction vs control, which expanded 6-fold. When shRNA, titrated by green fluorescent protein into low and high, was combined with dasatinib (concentration range, 0-10 nM), low shRNA was additive with low dasatinib (0.6 and 1 nM), leading to inhibition of pCrkL, induction of activated caspase-3, expression of Annexin-V, and marked reduction in viable cells., Conclusion: These results confirm that by lowering BCR-ABL levels with shRNA, complete inhibition of oncoprotein activity can be achieved with a lower concentration of dasatinib, thus providing a rationale for combining these approaches in the setting of high target expression, such as found in advanced phase disease and in the stem cell compartment.

Purpose: The HOX genes comprise a large family of homeodomain-containing transcription factors, present in four separate clusters, which are key regulators of embryonic development, hematopoietic differentiation, and leukemogenesis. We aimed to study the role of DNA methylation as an inducer of HOX gene silencing in leukemia., Experimental Design: Three hundred and seventy-eight samples of myeloid and lymphoid leukemia were quantitatively analyzed (by COBRA analysis and pyrosequencing of bisulfite-modified DNA) for methylation of eight HOXA and HOXB cluster genes. The biological significance of the methylation identified was studied by expression analysis and through re-expression of HOXA5 in a chronic myeloid leukemia (CML) blast crisis cell line model., Results: Here, we identify frequent hypermethylation and gene inactivation of HOXA and HOXB cluster genes in leukemia. In particular, hypermethylation of HOXA4 and HOXA5 was frequently observed (26-79%) in all types of leukemias studied. HOXA6 hypermethylation was predominantly restricted to lymphoid malignancies, whereas hypermethylation of other HOXA and HOXB genes was only observed in childhood leukemia. HOX gene methylation exhibited clear correlations with important clinical variables, most notably in CML, in which hypermethylation of both HOXA5 (P = 0.00002) and HOXA4 (P = 0.006) was strongly correlated with progression to blast crisis. Furthermore, re-expression of HOXA5 in CML blast crisis cells resulted in the induction of markers of granulocytic differentiation., Conclusion: We propose that in addition to the oncogenic role of some HOX family members, other HOX genes are frequent targets for gene inactivation and normally play suppressor roles in leukemia development.

Chronic myeloid leukemia (CML) stem and progenitor cells overexpress BcrAbl and are insensitive to imatinib mesylate (IM). We therefore investigated whether these cells were efficiently targeted by nilotinib. In K562, the inhibitory concentration (IC50) of nilotinib was 30 nM versus 600 nM for IM, consistent with its reported 20-fold-higher potency. However, in primary CD34(+) CML cells, nilotinib and IM were equipotent for inhibition of BcrAbl activity, producing equivalent but incomplete reduction in CrkL phosphorylation at 5 microM. CML CD34(+) cells were still able to expand over 72 hours with 5 microM of either drug, although there was a concentration-dependent restriction of amplification. As for IM, the most primitive cells (CFSE(max)) persisted and accumulated over 72 hours with nilotinib and remained caspase-3 negative. Furthermore, nilotinib with IM led to further accumulation of this population, suggesting at least additive antiproliferative effects. These results confirmed that, like IM, the predominant effect of nilotinib is antiproliferative rather than proapoptotic.

Imatinib mesylate (IM) therapy for chronic myeloid leukemia (CML) has transformed the treatment of this disease. However, the vast majority of patients, despite major responses, still harbor Philadelphia chromosome-positive (Ph(+)) cells. We have described a population of primitive Ph(+) cells that are insensitive to IM and may be a source of IM resistance. Cell line studies have suggested that the drug transporter ABCG2 may be a mediator of IM resistance, however there is considerable debate about whether IM is an ABCG2 substrate or inhibitor. We demonstrate here that primitive CML CD34(+) cells aberrantly overexpress functional ABCG2 but that cotreatment with IM and an ABCG2 inhibitor does not potentiate the effect of IM. We definitively show that IM is an inhibitor of, but not a substrate for, ABCG2 and that, therefore, ABCG2 does not modulate intracellular concentrations of IM in this clinically relevant cell population.

Dasatinib (BMS-354825), a novel dual SRC/BCR-ABL kinase inhibitor, exhibits greater potency than imatinib mesylate (IM) and inhibits the majority of kinase mutations in IM-resistant chronic myeloid leukemia (CML). We have previously demonstrated that IM reversibly blocks proliferation but does not induce apoptosis of primitive CML cells. Here, we have attempted to overcome this resistance with dasatinib. Primitive IM-resistant CML cells showed only single-copy BCR-ABL but expressed significantly higher BCR-ABL transcript levels and BCR-ABL protein compared with more mature CML cells (P = .031). In addition, CrKL phosphorylation was higher in the primitive CD34(+)CD38(-) than in the total CD34(+) population (P = .002). In total CD34(+) CML cells, IM inhibited phosphorylation of CrKL at 16 but not 72 hours, consistent with enrichment of an IM-resistant primitive population. CD34(+)CD38(-) CML cells proved resistant to IM-induced inhibition of CrKL phosphorylation and apoptosis, whereas dasatinib led to significant inhibition of CrKL phosphorylation. Kinase domain mutations were not detectable in either IM or dasatinib-resistant primitive CML cells. These data confirm that dasatinib is more effective than IM within the CML stem cell compartment; however, the most primitive quiescent CML cells appear to be inherently resistant to both drugs.

Objective: In chronic myeloid leukemia (CML), imatinib mesylate (IM; Gleevec, Glivec) induces a G0/G1 cell-cycle block in total CD34(+) cells without causing significant apoptosis. Bryostatin-1 (bryo), a protein kinase C (PKC) modulator, was investigated for its ability to increase IM-mediated apoptosis either through induction of cycling of G0/G1 Ph(+) cells or antagonism of the IM-induced cell-cycle block., Methods: The Ph(+) K562 cell line and primary CD34(+) CML cells were studied for cell-cycle progression (PI staining), proliferation ((3)H thymidine uptake), and survival (dye exclusion)., Results: Following 48 hours exposure to IM, on average more than 80% of surviving K562 cells were in G0/G1 as compared to approximately 50% for untreated control cultures (p < 0.001). After accounting for IM-induced cell kill, the absolute number of viable G0/G1 cells was significantly increased, confirming its anti-proliferative effect. However, pretreatment for 24 hours with bryo both increased K562 total cell kill and normalized the percentage of cells recovered in G0/G1, thus reducing their absolute number. For primary CML CD34(+) cells, pretreatment with bryo prior to IM significantly enhanced cell death of both total and, critically, G0/G1 populations., Conclusion: These results suggest that carefully scheduled drug combinations that include an agent to antagonize the anti-proliferative effect of IM may prove more efficacious within the Ph(+) stem cell compartment than IM monotherapy.

Recent studies indicate that a rare population of primitive quiescent BCR-ABL(+) cells are innately insensitive to imatinib mesylate (IM) and persist after IM therapy of patients with chronic myeloid leukemia (CML). New approaches to the eradication of these cells are therefore likely to be crucial to the development of curative therapies for CML. We have now found that Ara-C, LY294002 (a PI-3 (phosphatidylinositol-3' kinase) kinase inhibitor), 17AAG (a heat-shock protein (HSP)-90 antagonist) and lonafarnib (a farnesyltransfease inhibitor) all enhance the toxicity of IM on K562 cells and on the total CD34(+) leukemic cell population from chronic phase CML patients. However, for quiescent CD34(+) leukemic cells, this was achieved only by concomitant exposure of the cells to lonafarnib. Ara-C or LY294002 alone blocked the proliferation of these cells but did not kill them, and Ara-C, LY294002 or 17AAG in combination with IM enhanced the cytostatic effect of IM but did not prevent the subsequent regrowth of the surviving leukemic cells. These studies demonstrate the importance of in vitro testing of novel agents on the subset of primary leukemic cells most likely to determine long-term treatment outcomes in vivo.

Chronic myeloid leukemia (CML) is sustained by a rare population of primitive, quiescent, BCR-ABL+ cells and represents an excellent example of a malignancy in which tumor-initiating cells represent the key to disease eradication. CML is also the first malignancy for which targeted therapy has replaced conventional chemotherapy. Within a vast excess of proliferating progenitor cells that express breakpoint cluster region-abelson (BCR-ABL) and are exquisitely sensitive to the tyrosine kinase inhibitor imatinib mesylate (IM) resides a small population of quiescent leukemic cells that, despite higher levels of BCR-ABL transcripts, exhibits innate insensitivity to IM. These cells remain after IM therapy, even when apparently complete responses are achieved, and they probably explain molecular disease persistence. Although it can be argued that patients may survive for many years with low levels of leukemia still present, it is possible to achieve disease clearance at the molecular level following an allogeneic stem cell transplantation. The emergence of drug resistance with IM monotherapy also argues in favor of complete disease eradication that we believe should remain the ultimate therapeutic goal in CML. New approaches to the elimination of these primitive CML cells may thus be crucial to the development of curative strategies.

Treatment of MSCV-GFP-transduced HL60 promyelocytic cells with all-trans retinoic acid (ATRA) resulted in a significant increase in GFP expression. The increased GFP expression was observed by 16 hr and was dependent on de novo protein production. This effect was specific to ATRA and unrelated to cell differentiation because it was not induced by dimethyl sulfoxide. Furthermore, a similar increase in GFP expression was observed in MSCV-GFP-transfected K562 cells, which do not differentiate when exposed to ATRA. Significantly increased GFP expression was seen at doses as low as 0.5 nM ATRA and was abrogated by AGN193109, an antagonist of retinoid signaling. We therefore conclude that this increase in gene expression is mediated by retinoic acid receptors. The long terminal repeat (LTR) region of MSCV contains candidate retinoic acid response elements and response elements for the ATRA-inducible transcription factor C/EBPalpha. We suggest that the increase in GFP expression is driven by the action of ATRA-activated host cell transcription factors. These findings offer a method to increase the expression of retroviral transgenes either in vitro or in vivo by treatment with low doses of retinoic acid that are clinically achievable and well tolerated. This use of inducible host cell transcription factors offers an alternative to engineering novel LTR regulatory sequences in order to increase transgene expression.

We and others have demonstrated expression of the aldo-keto reductase AKR1C3 in myeloid leukemia cell lines and that inhibitors of the enzyme, including nonsteroidal anti-inflammatory drugs (NSAIDs), promote HL-60 differentiation in response to all-trans retinoic acid (ATRA) and 1alpha,25-dihydroxyvitamin D3 (D3). Here, we demonstrate that overexpression of AKR1C3 reciprocally desensitizes HL-60 cells to ATRA and D3, thus confirming the enzyme as a novel regulator of cell differentiation. AKR1C3 possesses marked 11-ketoreductase activity converting prostaglandin (PG) D2 to PGF2alpha. Supplementing HL-60 cultures with PGD2 mimicked treatment with AKR1C3-inhibitors by enhancing the differentiation of the cells in response to ATRA. However, PGD2 is chemically unstable, being converted first to PGJ2 and then stepwise to 15-deoxy-Delta(12,14)-prostaglandin J2(15Delta-PGJ2), a natural ligand for the peroxisome proliferator-activated receptor-gamma (PPARgamma). Consistent with this, PGD2 was rapidly converted to PGJ2 under normal tissue culture conditions but not in the presence of recombinant AKR1C3 when PGF2alpha was predominantly formed. In addition, PGJ2 but not PGF2alpha recapitulated the potentiation of HL-60 differentiation by PGD2 and AKR1C3 inhibitors. Furthermore, the capacity of all of these treatments to potentiate HL-60 cell differentiation was significantly reduced in the presence of the PPARgamma-antagonist GW 9662. We conclude that AKRIC3 protects HL-60 cells against ATRA and D3-induced cell differentiation by limiting the production of natural PPARgamma ligands via the diversion of PGD2 toward PGF2alpha and away from PGJ2. In addition, these observations identify AKR1C3 as plausible target for the non-cyclooxygenase-dependent antineoplastic actions of NSAIDs.

Collagen activates platelets through a tyrosine kinase-dependent pathway, involving phospholipase Cgamma2. Functional responses such as aggregation and secretion induced by collagen are potentiated by preincubation with thrombopoietin (TPO). In this study, we show that collagen and thrombopoietin activate the phosphatidylinositol 3-kinase (PI 3-kinase) pathway and that this contributes to their respective actions. The structurally distinct inhibitors of PI 3-kinase, wortmannin, and LY294002, completely inhibit formation of phosphatidylinositol 3,4,5-trisphosphate by collagen. This leads to a substantial reduction in the formation of inositol phosphates and phosphatidic acid, 2 indices of PLC activity, and the consequent inhibition of intracellular Ca(++) [Ca(++)](i), aggregation and secretion. Potentiation of the collagen response by TPO is prevented in the presence of wortmannin and LY294002. However, when the 2 PI 3-kinase inhibitors are given after the addition of TPO but before the collagen, recovery of potentiation is observed. This suggests that potentiation is mediated through activation of PI 3-kinase. TPO stimulates aggregation of platelets from a low percentage of donors and this is also blocked by wortmannin. These results suggest that the PI 3-kinase pathway plays an important role in signaling by collagen and in the priming action of TPO.

Hormones such as 1 alpha, 25-dihydroxy vitamin D3 (D3), all-trans retinoic acid, and 9-cis retinoic acid stimulate differentiation of myeloid progenitor cells via their interaction with specific hormone receptors. However, the sensitivity of cells to these agents is not merely governed by the expression of their receptors and the availability of ligand to bind them. Recent studies from our group suggested that the actions of D3 and retinoids on myelopoiesis also are influenced by endogenous mechanisms involving other steroid hormones. In this study we examined the influence of local estrogen metabolism on the differentiation of HL60 cells and normal primitive myeloid progenitor cells. Quantitative thin-layer chromatography (TLC) analyses showed that HL60 and normal cells are able to generate estrone (E1) from estradiol (E2). Neither cell population generated significant amounts of E2 from E1. Reverse transcriptase polymerase chain reaction and Northern analyses confirmed that normal and leukemic myeloid progenitor cells expressed mRNA for the type I and IV isoforms of 17 beta-hydroxysteroid dehydrogenase. Conversion of E2 to E1 was upregulated within 24 hours when HL60 cells were treated with either all-trans retinoic acid or D3 at doses that induce their differentiation toward neutrophils or monocytes, respectively. Similarly, D3-induced monocyte differentiation of normal myeloid progenitor cells was associated with increased capacity to generate E1 from E2. When HL60 cells or normal myeloid progenitor cells were exposed to exogenous E1 they became more sensitive to the differentiation-inducing effects of D3. Data presented provide further evidence for the local modulation of myelopoiesis by intracrine mechanisms. In particular, our findings suggest that local metabolism of steroids by normal as well as leukemic myeloid cells influences their responsiveness to D3 and retinoids.

We have compared the levels of inositol metabolites in three pairs of normal and transformed cells which have been matched with respect to their cell lineage, differentiation and proliferation status: (i) normal human myeloid blast cells and the human promyelocytic leukaemic cell line, HL60; (ii) human umbilical-cord T-helper cells and C8166 cells, a HTLV-1-transformed T-helper cell line; and (iii) an interleukin 3-dependent long-term culture of murine pro-B-cells (BAF3) and BAF3 cells transformed by transfection with the bcr-abl oncogene. Complex patterns of inositol metabolites were present in each of the cell populations. Although there were a number of differences in the levels of certain inositol metabolites between individual cell populations in the paired groups, we did not observe any consistent difference in the levels of inositol metabolites between the proliferating normal and transformed cells. In particular, our data do not support the reported correlation between elevated glycerophosphoinositol (GroPIns) levels and transformation of cells by membrane and cytoplasmic oncogenes which has been reported by other workers. All the cells contained high concentrations of Ins(1,3,4,5,6)P5 (between 12 and 55 microM) and InsP6 (between 37 and 105 microM). The HTLV1-transformed T-helper cells had particularly high levels of total inositol phosphates (predominantly GroPIns, an unidentified inositol bisphosphate and InsP6). The observations are discussed with reference to cell transformation and to the differentiation status of the paired populations.