CD9 and megakaryocyte differentiation

Prognostic value and multifaceted roles of tetraspanin CD9 in cancer

CD9 is a crucial regulator of cell adhesion in the immune system and plays important physiological roles in hematopoiesis, blood coagulation or viral and bacterial infections. It is involved in the transendothelial migration of leukocytes which might also be hijacked by cancer cells during their invasion and metastasis. CD9 is found at the cell surface and the membrane of exosomes affecting cancer progression and therapy resistance. High expression of CD9 is mostly associated with good patients outcome, with a few exceptions. Discordant findings have been reported for breast, ovarian, melanoma, pancreatic and esophageal cancer, which might be related to using different antibodies or inherent cancer heterogeneity. According to in vitro and in vivo studies, tetraspanin CD9 is not clearly associated with either tumor suppression or promotion. Further mechanistic experiments will elucidate the role of CD9 in particular cancer types and specific conditions.

Targeting TLR2/Rac1/cdc42/JNK Pathway to Reveal That Ruxolitinib Promotes Thrombocytopoiesis

BACKGROUND

Thrombocytopenia has long been considered an important complication of chemotherapy and radiotherapy, which severely limits the effectiveness of cancer treatment and the overall survival of patients. However, clinical treatment options are extremely limited so far. Ruxolitinib is a potential candidate.

METHODS

The impact of ruxolitinib on the differentiation and maturation of K562 and Meg-01 cells megakaryocytes (MKs) was examined by flow cytometry, Giemsa and Phalloidin staining. A mouse model of radiation-injured thrombocytopenia (RIT) was employed to evaluate the action of ruxolitinib on thrombocytopoiesis. Network pharmacology, molecular docking, drug affinity responsive target stability assay (DARTS), RNA sequencing, protein blotting and immunofluorescence analysis were applied to explore the targets and mechanisms of action of ruxolitinib.

RESULTS

Ruxolitinib can stimulate MK differentiation and maturation in a dose-dependent manner and accelerates recovery of MKs and thrombocytopoiesis in RIT mice. Biological targeting analysis showed that ruxolitinib binds directly to Toll Like Receptor 2 (TLR2) to activate Rac1/cdc42/JNK, and this action was shown to be blocked by C29, a specific inhibitor of TLR2.

CONCLUSIONS

Ruxolitinib was first identified to facilitate MK differentiation and thrombocytopoiesis, which may alleviate RIT. The potential mechanism of ruxolitinib was to promote MK differentiation via activating the Rac1/cdc42/JNK pathway through binding to TLR2.

Deciphering transcriptome alterations in bone marrow hematopoiesis at single-cell resolution in immune thrombocytopenia

Immune thrombocytopenia (ITP) is an autoimmune disorder, in which megakaryocyte dysfunction caused by an autoimmune reaction can lead to thrombocytopenia, although the underlying mechanisms remain unclear. Here, we performed single-cell transcriptome profiling of bone marrow CD34+ hematopoietic stem and progenitor cells (HSPCs) to determine defects in megakaryopoiesis in ITP. Gene expression, cell-cell interactions, and transcriptional regulatory networks varied in HSPCs of ITP, particularly in immune cell progenitors. Differentially expressed gene (DEG) analysis indicated that there was an impaired megakaryopoiesis of ITP. Flow cytometry confirmed that the number of CD9+ and HES1+ cells from Lin-CD34+CD45RA- HSPCs decreased in ITP. Liquid culture assays demonstrated that CD9+Lin-CD34+CD45RA- HSPCs tended to differentiate into megakaryocytes; however, this tendency was not observed in ITP patients and more erythrocytes were produced. The percentage of megakaryocytes differentiated from CD9+Lin-CD34+CD45RA- HSPCs was 3-fold higher than that of the CD9- counterparts from healthy controls (HCs), whereas, in ITP patients, the percentage decreased to only 1/4th of that in the HCs and was comparable to that from the CD9- HSPCs. Additionally, when co-cultured with pre-B cells from ITP patients, the differentiation of CD9+Lin-CD34+CD45RA- HSPCs toward the megakaryopoietic lineage was impaired. Further analysis revealed that megakaryocytic progenitors (MkP) can be divided into seven subclusters with different gene expression patterns and functions. The ITP-associated DEGs were MkP subtype-specific, with most DEGs concentrated in the subcluster possessing dual functions of immunomodulation and platelet generation. This study comprehensively dissects defective hematopoiesis and provides novel insights regarding the pathogenesis of ITP.

Single-cell multi-omics of human clonal hematopoiesis reveals that DNMT3A R882 mutations perturb early progenitor states through selective hypomethylation

Somatic mutations in cancer genes have been detected in clonal expansions across healthy human tissue, including in clonal hematopoiesis. However, because mutated and wild-type cells are admixed, we have limited ability to link genotypes with phenotypes. To overcome this limitation, we leveraged multi-modality single-cell sequencing, capturing genotype, transcriptomes and methylomes in progenitors from individuals with DNMT3A R882 mutated clonal hematopoiesis. DNMT3A mutations result in myeloid over lymphoid bias, and an expansion of immature myeloid progenitors primed toward megakaryocytic-erythroid fate, with dysregulated expression of lineage and leukemia stem cell markers. Mutated DNMT3A leads to preferential hypomethylation of polycomb repressive complex 2 targets and a specific CpG flanking motif. Notably, the hypomethylation motif is enriched in binding motifs of key hematopoietic transcription factors, serving as a potential mechanistic link between DNMT3A mutations and aberrant transcriptional phenotypes. Thus, single-cell multi-omics paves the road to defining the downstream consequences of mutations that drive clonal mosaicism.

The characterization of an agranulocyte-specific marker (CgCD9) in the Pacific oyster Crassostrea gigas

The agranulocytes in the Pacific oyster Crassostrea gigas are a group of haemocytes that are significantly different from semi-granulocytes and granulocytes on the morphology. Agranulocytes are the smallest haemocytes characterized by a spherical shape, the largest ratio of nucleus to cytoplasm, and no granules in the cytoplasm. The lack of unique cell surface markers impedes the isolation of agranulocytes from total haemocytes. Previous transcriptome sequencing analysis of three subpopulations of haemocytes revealed that a homologue of CD9 (designed as CgCD9) was highly expressed in agranulocytes of oyster C. gigas (data not shown). In the present study, CgCD9 was identified to share a similarity of 60% with other vertebrates CD9s, and it harbored a typical four transmembrane domain and a conserved Cys-Cys-Gly (CCG) motif. The mRNA transcript of CgCD9 was found to be highly expressed in agranulocytes, which was 6.63-fold (p < 0.05) and 3.68-fold (p < 0.05) of that in granulocytes and semi-granulocytes, respectively. A specific monoclonal antibody of CgCD9 (named 3D8) was successfully prepared by traditional hybridoma technology, and a single positive band at 25.2 kDa was detected in the haemocyte proteins by Western Blotting, indicating that this monoclonal antibody exhibited high specificity and sensitivity to CgCD9 protein. The ELISA positive value of 3D8 monoclonal antibody to recognize agranulocytes, semi-granulocytes and granulocytes was 17.35, 4.48 and 1.55, respectively, indicating that monoclonal antibody was specific to agranulocytes. Immunocytochemistry assay revealed that CgCD9 was specifically distributed on the membrane of agranulocytes. Using immunomagnetic beads coated with 3D8 monoclonal antibody, CgCD9⁺cells with a purity of 94.53 ± 5.60% were successfully isolated with a smaller diameter, a larger N:C ratio and no granules in cytoplasm, and could be primary culture in the modified L-15 medium in vitro. Collectively, these results suggested that CgCD9 was a specific cell surface marker for agranulocytes, which offered a tool for high-purity capture of agranulocytes from total haemocytes in C. gigas.

Investigating the genetic architecture of disease resilience in pigs by genome-wide association studies of complete blood count traits collected from a natural disease challenge model

Background

Genetic improvement for disease resilience is anticipated to be a practical method to improve efficiency and profitability of the pig industry, as resilient pigs maintain a relatively undepressed level of performance in the face of infection. However, multiple biological functions are known to be involved in disease resilience and this complexity means that the genetic architecture of disease resilience remains largely unknown. Here, we conducted genome-wide association studies (GWAS) of 465,910 autosomal SNPs for complete blood count (CBC) traits that are important in an animal’s disease response. The aim was to identify the genetic control of disease resilience.

Results

Univariate and multivariate single-step GWAS were performed on 15 CBC traits measured from the blood samples of 2743 crossbred (Landrace × Yorkshire) barrows drawn at 2-weeks before, and at 2 and 6-weeks after exposure to a polymicrobial infectious challenge. Overall, at a genome-wise false discovery rate of 0.05, five genomic regions located on Sus scrofa chromosome (SSC) 2, SSC4, SSC9, SSC10, and SSC12, were significantly associated with white blood cell traits in response to the polymicrobial challenge, and nine genomic regions on multiple chromosomes (SSC1, SSC4, SSC5, SSC6, SSC8, SSC9, SSC11, SSC12, SSC17) were significantly associated with red blood cell and platelet traits collected before and after exposure to the challenge. By functional enrichment analyses using Ingenuity Pathway Analysis (IPA) and literature review of previous CBC studies, candidate genes located nearby significant single-nucleotide polymorphisms were found to be involved in immune response, hematopoiesis, red blood cell morphology, and platelet aggregation.

Conclusions

This study helps to improve our understanding of the genetic basis of CBC traits collected before and after exposure to a polymicrobial infectious challenge and provides a step forward to improve disease resilience.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07835-4.

Transfer to the clinic: refining forward programming of hPSCs to megakaryocytes for platelet production in bioreactors

The production of in vitro-derived platelets has great potential for transfusion medicine. Here, we build on our experience in the forward programming (FoP) of human pluripotent stem cells (hPSCs) to megakaryocytes (MKs) and address several aspects of the complex challenges to bring this technology to the bedside. We first identify clinical-grade hPSC lines that generate MKs efficiently. We design a bespoke media to maximize both production and maturity of MKs and improve platelet output. Crucially, we transition the lentiviral-based FoP of hPSCs to a nonviral inducible system. We also show how small molecules promote a definitive hematopoiesis phenotype during the differentiation process, thereby increasing the quality of the final product. Finally, we generate platelets using a bioreactor designed to reproduce the physical cues that promote platelet production in the bone marrow. We show that these platelets are able to contribute to both thrombus formation in vitro and have a hemostatic effect in thrombocytopenic mice in vivo.

AHR:IKAROS Interaction Promotes Platelet Biogenesis in Response to SR1

In vitro, the differentiation of megakaryocytes (MKs) is improved by aryl-hydrocarbon receptor (AHR) antagonists such as StemRegenin 1 (SR1), an effect physiologically recapitulated by the presence of stromal mesenchymal cells (MSC). This inhibition promotes the amplification of a CD34+CD41low population able to mature as MKs with a high capacity for platelet production. In this short report, we showed that the emergence of the thrombocytogenic precursors and the enhancement of platelet production triggered by SR1 involved IKAROS. The downregulation/inhibition of IKAROS (shRNA or lenalidomide) significantly reduced the emergence of SR1-induced thrombocytogenic population, suggesting a crosstalk between AHR and IKAROS. Interestingly, using a proximity ligation assay, we could demonstrate a physical interaction between AHR and IKAROS. This interaction was also observed in the megakaryocytic cells differentiated in the presence of MSCs. In conclusion, our study revealed a previously unknown AHR/ IKAROS -dependent pathway which prompted the expansion of the thrombocytogenic precursors. This AHR- IKAROS dependent checkpoint controlling MK maturation opens new perspectives to platelet production engineering.

Decoding Human Megakaryocyte Development

Despite our growing understanding of embryonic immune development, rare early megakaryocytes (MKs) remain relatively understudied. Here we used single-cell RNA sequencing of human MKs from embryonic yolk sac (YS) and fetal liver (FL) to characterize the transcriptome, cellular heterogeneity, and developmental trajectories of early megakaryopoiesis. In the YS and FL, we found heterogeneous MK subpopulations with distinct developmental routes and patterns of gene expression that could reflect early functional specialization. Intriguingly, we identified a subpopulation of CD42b⁺CD14⁺ MKs in vivo that exhibit high expression of genes associated with immune responses and can also be derived from human embryonic stem cells (hESCs) in vitro. Furthermore, we identified THBS1 as an early marker for MK-biased embryonic endothelial cells. Overall, we provide important insights and invaluable resources for dissection of the molecular and cellular programs underlying early human megakaryopoiesis.

Single-cell analyses and machine learning define hematopoietic progenitor and HSC-like cells derived from human PSCs

Hematopoietic stem and progenitor cells (HSPCs) develop in distinct waves at various anatomical sites during embryonic development. The in vitro differentiation of human pluripotent stem cells (hPSCs) recapitulates some of these processes; however, it has proven difficult to generate functional hematopoietic stem cells (HSCs). To define the dynamics and heterogeneity of HSPCs that can be generated in vitro from hPSCs, we explored single-cell RNA sequencing (scRNAseq) in combination with single-cell protein expression analysis. Bioinformatics analyses and functional validation defined the transcriptomes of naïve progenitors and erythroid-, megakaryocyte-, and leukocyte-committed progenitors, and we identified CD44, CD326, ICAM2/CD9, and CD18, respectively, as markers of these progenitors. Using an artificial neural network that we trained on scRNAseq derived from human fetal liver, we identified a wide range of hPSC-derived HSPCs phenotypes, including a small group classified as HSCs. This transient HSC-like population decreased as differentiation proceeded, and was completely missing in the data set that had been generated using cells selected on the basis of CD43 expression. By comparing the single-cell transcriptome of in vitro-generated HSC-like cells with those generated within the fetal liver, we identified transcription factors and molecular pathways that can be explored in the future to improve the in vitro production of HSCs.

Tetraspanin Scaffold Proteins Function as Key Regulators of Hematopoietic Stem Cells

Hematopoietic stem and progenitor cells (HSPCs) are responsible for the development, maintenance, and regeneration of all the blood forming cells in the body, and as such, are critical for a number of patient therapies. For successful HSPC transplantation, stem cells must traffic through the blood and home to the bone marrow (BM) microenvironment or “niche,” which is composed of soluble factors, matrix proteins, and supportive cells. HSPC adhesion to, and signaling with, cellular and extracellular components of the niche provide instructional cues to balance stem cell self-renewal and differentiation. In this review, we will explore the regulation of these stem cell properties with a focus on the tetraspanin family of membrane proteins. Tetraspanins are molecular scaffolds that uniquely function to distribute proteins into highly organized microdomains comprising adhesion, signaling, and adaptor proteins. As such, tetraspanins contribute to many aspects of cell physiology as mediators of cell adhesion, trafficking, and signaling. We will summarize the many reports that identify tetraspanins as markers of specific HSPC populations. Moreover, we will discuss the various studies establishing the functional importance of tetraspanins in the regulation of essential HSPC processes including quiescence, migration, and niche adhesion. When taken together, studies outlined in this review suggest that several tetraspanins may serve as potential targets to modulate HSPC interactions with the BM niche, ultimately impacting future HSPC therapies.

Tspan8 and Tspan8/CD151 knockout mice unravel the contribution of tumor and host exosomes to tumor progression

BACKGROUND

The tetraspanins Tspan8 and CD151 promote metastasis, exosomes (Exo) being suggested to be important in the crosstalk between tumor and host. The contribution of Tspan8 and CD151 to host versus tumor-derived exosome (TEX) activities being not defined, we approached the questions using 3-methylcholanthrene-induced (MCA) tumors from wt, Tspan8ko, CD151ko and Tspan8/CD151 (db)ko mice, implanted into tetraspanin-competent and deficient hosts.

METHODS

Tumor growth and dissemination, hematopoiesis and angiogenesis were surveyed in wild type (wt), Tspan8ko, CD151ko and dbko mice bearing tetraspanin-competent and -deficient MCA tumors. In vitro studies using tumor cells, bone marrow cells (BMC) and endothelial cells (EC) elaborated the mechanism of serum (s)Exo- and TEX-induced target modulation.

RESULTS

Tumors grew in autochthonous and syngeneic hosts differing in Tspan8- and/or CD151-competence. However, Tspan8ko- and/or CD151ko-tumor cell dissemination and settlement in metastatic organs was significantly reduced in the autochthonous host, and less severely in the wt-host. Impaired wt-MCA tumor dissemination in the ko-host confirmed a contribution of host- and tumor-Tspan8/-CD151 to tumor cell dissemination, delivery of sExo and TEX being severely impaired by a Tspan8ko/CD151ko. Coculturing tumor cells, BMC and EC with sExo and TEX revealed minor defects in epithelial mesenchymal transition and apoptosis resistance of ko tumors. Strongly reduced migratory and invasive capacity of Tspan8ko/CD151ko-MCA relies on distorted associations with integrins and CAM and missing Tspan8/CD151-promoted recruitment of proteases. The defects, differing between Tspan8ko- and CD151ko-MCA, were rescued by wt-TEX and, less efficiently Tspan8ko- and CD151ko-TEX. Minor defects in hematopoietic progenitor maturation were based on the missing association of hematopoietic growth factors /- receptors with CD151 and, less pronounced, Tspan8. Rescue of impaired angiogenesis in ko mice by wt-sExo and promotion of angiogenesis by TEX depended on the association of Tspan8 and CD151 with GPCR and RTK in EC and tumor cells.

CONCLUSIONS

Tspan8-/CD151-TEX play central roles in tumor progression. Tspan8-/CD151-sExo and TEX contribute by stimulating angiogenesis. Tspan8 and CD151 fulfill these tasks by associating with function-relevant proteins, the additive impact of Tspan8 and CD151 relying on differences in preferred associations. The distinct Tspan8 and CD151 contributions suggest a blockade of TEX-Tspan8 and -CD151 promising for therapeutic intervention.

CD9 Tetraspanin: A New Pathway for the Regulation of Inflammation?

CD9 belongs to the tetraspanin superfamily. Depending on the cell type and associated molecules, CD9 has a wide variety of biological activities such as cell adhesion, motility, metastasis, growth, signal transduction, differentiation, and sperm-egg fusion. This review focuses on CD9 expression by hematopoietic cells and its role in modulating cellular processes involved in the regulation of inflammation. CD9 is functionally very important in many diseases and is involved either in the regulation or in the mediation of the disease. The role of CD9 in various diseases, such as viral and bacterial infections, cancer and chronic lung allograft dysfunction, is discussed. This review focuses also on its interest as a biomarker in diseases. Indeed CD9 is primarily known as a specific exosome marker however, its expression is now recognized as an anti-inflammatory marker of monocytes and macrophages. It was also described as a marker of murine IL-10-competent Breg cells and IL-10-secreting CD9⁺ B cells were associated with better allograft outcome in lung transplant patients, and identified as a new predictive biomarker of long-term survival. In the field of cancer, CD9 was both identified as a favorable prognostic marker or as a predictor of metastatic potential depending on cancer types. Finally, this review discusses strategies to target CD9 as a therapeutic tool. Because CD9 can have opposite effects depending on the situation, the environment and the pathology, modulating CD9 expression or blocking its effects seem to be a new promising therapeutic strategy.

Calreticulin Affects Hematopoietic Stem/Progenitor Cell Fate by Impacting Erythroid and Megakaryocytic Differentiation

Calreticulin (CALR) is a chaperone protein that localizes primarily to the endoplasmic reticulum (ER) lumen where it is responsible for the control of proper folding of neo-synthesized glycoproteins and the retention of calcium. Recently, mutations affecting exon 9 of the CALR gene have been described in approximately 40% of patients with myeloproliferative neoplasms (MPNs). Although the role of mutated CALR in the development of MPNs has begun to be clarified, there are still no data available on the function of wild-type (WT) CALR during physiological hematopoiesis. To shed light on the role of WT CALR during normal hematopoiesis, we performed gene silencing and overexpression experiments in hematopoietic stem progenitor cells (HSPCs). Our results showed that CALR overexpression is able to affect physiological hematopoiesis by enhancing both erythroid and megakaryocytic (MK) differentiation. In agreement with overexpression data, CALR silencing caused a significant decrease in both erythroid and MK differentiation of human HSPCs. Gene expression profiling (GEP) analysis showed that CALR is able to affect the expression of several genes involved in HSPC differentiation toward both the erythroid and MK lineages. Moreover, GEP data also highlighted the modulation of several genes involved in ER stress response, unfolded protein response (UPR), and DNA repair, and of several genes already described to play a role in MPN development, such as proinflammatory cytokines and hematological neoplasm-related markers. Altogether, our data unraveled a new and unexpected role for CALR in the regulation of normal hematopoietic differentiation. Moreover, by showing the impact of CALR on the expression of genes involved in several biological processes already described in cellular transformation, our data strongly suggest a more complex role for CALR in MPN development that goes beyond the activation of the THPO receptor and involves ER stress response, UPR, and DNA repair.

Gfi1b controls integrin signaling-dependent cytoskeleton dynamics and organization in megakaryocytes

Mutations in GFI1B are associated with inherited bleeding disorders called GFI1B-related thrombocytopenias. We show here that mice with a megakaryocyte-specific Gfi1b deletion exhibit a macrothrombocytopenic phenotype along a megakaryocytic dysplasia reminiscent of GFI1B-related thrombocytopenia. GFI1B deficiency increases megakaryocyte proliferation and affects their ploidy, but also abrogates their responsiveness towards integrin signaling and their ability to spread and reorganize their cytoskeleton. Gfi1b-null megakaryocytes are also unable to form proplatelets, a process independent of integrin signaling. GFI1B-deficient megakaryocytes exhibit aberrant expression of several components of both the actin and microtubule cytoskeleton, with a dramatic reduction of α-tubulin. Inhibition of FAK or ROCK, both important for actin cytoskeleton organization and integrin signaling, only partially restored their response to integrin ligands, but the inhibition of PAK, a regulator of the actin cytoskeleton, completely rescued the responsiveness of Gfi1b-null megakaryocytes to ligands, but not their ability to form proplatelets. We conclude that Gfi1b controls major functions of megakaryocytes such as integrin-dependent cytoskeleton organization, spreading and migration through the regulation of PAK activity whereas the proplatelet formation defect in GFI1B-deficient megakaryocytes is due, at least partially, to an insufficient α-tubulin content.

Single-Cell RNA-Sequencing Reveals a Continuous Spectrum of Differentiation in Hematopoietic Cells

The transcriptional programs that govern hematopoiesis have been investigated primarily by population-level analysis of hematopoietic stem and progenitor cells, which cannot reveal the continuous nature of the differentiation process. Here we applied single-cell RNA-sequencing to a population of hematopoietic cells in zebrafish as they undergo thrombocyte lineage commitment. By reconstructing their developmental chronology computationally, we were able to place each cell along a continuum from stem cell to mature cell, refining the traditional lineage tree. The progression of cells along this continuum is characterized by a highly coordinated transcriptional program, displaying simultaneous suppression of genes involved in cell proliferation and ribosomal biogenesis as the expression of lineage specific genes increases. Within this program, there is substantial heterogeneity in the expression of the key lineage regulators. Overall, the total number of genes expressed, as well as the total mRNA content of the cell, decreases as the cells undergo lineage commitment.

Prospective isolation of human erythroid lineage-committed progenitors

Determining the developmental pathway leading to erythrocytes and being able to isolate their progenitors are crucial to understanding and treating disorders of red cell imbalance such as anemia, myelodysplastic syndrome, and polycythemia vera. Here we show that the human erythrocyte progenitor (hEP) can be prospectively isolated from adult bone marrow. We found three subfractions that possessed different expression patterns of CD105 and CD71 within the previously defined human megakaryocyte/erythrocyte progenitor (hMEP; Lineage(-) CD34(+) CD38(+) IL-3Rα(-) CD45RA(-)) population. Both CD71(-) CD105(-) and CD71(+) CD105(-) MEPs, at least in vitro, still retained bipotency for the megakaryocyte (MegK) and erythrocyte (E) lineages, although the latter subpopulation is skewed in differentiation toward the erythroid lineage. Notably, the proliferative and differentiation output of the CD71(intermediate(int)/+) CD105(+) subset of cells within the MEP population was completely restricted to the erythroid lineage with the loss of MegK potential. CD71(+) CD105(-) MEPs are erythrocyte-biased MEPs (E-MEPs) and CD71(int/+) CD105(+) cells are EPs. These previously unclassified populations may facilitate further understanding of the molecular mechanisms governing human erythroid development and serve as potential therapeutic targets in disorders of the erythroid lineage.

Tetraspanin CD9 participates in dysmegakaryopoiesis and stromal interactions in primary myelofibrosis

Primary myelofibrosis is characterized by clonal myeloproliferation, dysmegakaryopoiesis, extramedullary hematopoiesis associated with myelofibrosis and altered stroma in the bone marrow and spleen. The expression of CD9, a tetraspanin known to participate in megakaryopoiesis, platelet formation, cell migration and interaction with stroma, is deregulated in patients with primary myelofibrosis and is correlated with stage of myelofibrosis. We investigated whether CD9 participates in the dysmegakaryopoiesis observed in patients and whether it is involved in the altered interplay between megakaryocytes and stromal cells. We found that CD9 expression was modulated during megakaryocyte differentiation in primary myelofibrosis and that cell surface CD9 engagement by antibody ligation improved the dysmegakaryopoiesis by restoring the balance of MAPK and PI3K signaling. When co-cultured on bone marrow mesenchymal stromal cells from patients, megakaryocytes from patients with primary myelofibrosis displayed modified behaviors in terms of adhesion, cell survival and proliferation as compared to megakaryocytes from healthy donors. These modifications were reversed after antibody ligation of cell surface CD9, suggesting the participation of CD9 in the abnormal interplay between primary myelofibrosis megakaryocytes and stroma. Furthermore, silencing of CD9 reduced CXCL12 and CXCR4 expression in primary myelofibrosis megakaryocytes as well as their CXCL12-dependent migration. Collectively, our results indicate that CD9 plays a role in the dysmegakaryopoiesis that occurs in primary myelofibrosis and affects interactions between megakaryocytes and bone marrow stromal cells. These results strengthen the "bad seed in bad soil" hypothesis that we have previously proposed, in which alterations of reciprocal interactions between hematopoietic and stromal cells participate in the pathogenesis of primary myelofibrosis.

Improved quantitative analysis of primary bone marrow megakaryocytes utilizing imaging flow cytometry

Life-threatening thrombocytopenia can develop following bone marrow injury due to decreased platelet production from megakaryocytes (MKs). However, the study of primary MKs has been complicated by their low frequency in the bone marrow and by technical challenges presented by their unique maturation properties. More accurate and efficient methods for the analysis of in vivo MKs are needed to enhance our understanding of megakaryopoiesis and ultimately develop new therapeutic strategies for thrombocytopenia. Imaging flow cytometry (IFC) combines the morphometric capabilities of microscopy with the high-throughput analyses of flow cytometry (FC). Here, we investigate the application of IFC on the ImageStream(X) platform to the analysis of primary MKs isolated from murine bone marrow. Our data highlight and address technical challenges for conventional FC posed by the wide range of cellular size within the MK lineage as well as the shared surface phenotype with abundant platelet progeny. We further demonstrate that IFC can be used to reproducibly and efficiently quantify the frequency of primary murine MKs in the marrow, both at steady-state and in the setting of radiation-induced bone marrow injury, as well as assess their ploidy distribution. The ability to accurately analyze the full spectrum of maturing MKs in the bone marrow now allows for many possible applications of IFC to enhance our understanding of megakaryopoiesis and platelet production.

The calcineurin-NFAT pathway negatively regulates megakaryopoiesis

The calcium regulated calcineurin-nuclear factor of activated T cells (NFAT) pathway modulates the physiology of numerous cell types, including hematopoietic. Upon activation, calcineurin dephosphorylates NFAT family transcription factors, triggering their nuclear entry and activation or repression of target genes. NFATc1 and c2 isoforms are expressed in megakaryocytes. Moreover, human chromosome 21 (Hsa21) encodes several negative regulators of calcineurin-NFAT, candidates in the pathogenesis of Down syndrome (trisomy 21)-associated transient myeloproliferative disorder and acute megakaryoblastic leukemia. To investigate the role of calcineurin-NFAT in megakaryopoiesis, we examined wild-type mice treated with the calcineurin inhibitor cyclosporin A and transgenic mice expressing a targeted single extra copy of Dscr1, an Hsa21-encoded calcineurin inhibitor. Both murine models exhibited thrombocytosis with increased megakaryocytes and megakaryocyte progenitors. Pharmacological or genetic inhibition of calcineurin in mice caused accumulation of megakaryocytes exhibiting enhanced 5-bromo-2'-deoxyuridine uptake and increased expression of messenger RNAs encoding CDK4 and G1 cyclins, which promote cell division. Additionally, human megakaryocytes with trisomy 21 show increased proliferation and decreased NFAT activation compared with euploid controls. Our data indicate that inhibition of calcineurin-NFAT drives proliferation of megakaryocyte precursors by de-repressing genes that drive cell division, providing insights into mechanisms of normal megakaryopoiesis and megakaryocytic abnormalities that accompany Down syndrome.

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.

Valproic acid triggers erythro/megakaryocyte lineage decision through induction of GFI1B and MLLT3 expression

Histone deacetylase inhibitors represent a family of targeted anticancer compounds that are widely used against hematological malignancies. So far little is known about their effects on normal myelopoiesis. Therefore, in order to investigate the effect of histone deacetylase inhibitors on the myeloid commitment of hematopoietic stem/progenitor cells, we treated CD34(+) cells with valproic acid (VPA). Our results demonstrate that VPA treatment induces H4 histone acetylation and hampers cell cycle progression in CD34(+) cells sustaining high levels of CD34 protein expression. In addition, our data show that VPA treatment promotes erythrocyte and megakaryocyte differentiation. In fact, we demonstrate that VPA treatment is able to induce the expression of growth factor-independent protein 1B (GFI1B) and of mixed-lineage leukemia translocated to chromosome 3 protein (MLLT3), which are crucial regulators of erythrocyte and megakaryocyte differentiation, and that the up-regulation of these genes is mediated by the histone hyperacetylation at their promoter sites. Finally, we show that GFI1B inhibition impairs erythroid and megakaryocyte differentiation induced by VPA, while MLLT3 silencing inhibits megakaryocyte commitment only. As a whole, our data suggest that VPA sustains the expression of stemness-related markers in hematopoietic stem/progenitor cells and is able to interfere with hematopoietic lineage commitment by enhancing erythrocyte and megakaryocyte differentiation and by inhibiting the granulocyte and mono-macrophage maturation.

Medical countermeasures for platelet regeneration after radiation exposure. Report of a workshop and guided discussion sponsored by the National Institute of Allergy and Infectious Diseases, Bethesda, MD, March 22–23, 2010

The events of September 11, 2001 and their aftermath increased awareness of the need to develop medical countermeasures (MCMs) to treat potential health consequences of a radiation accident or deliberate attack. The medical effects of lethal exposures to ionizing radiation have been well described and affect multiple organ systems. To date, much of the research to develop treatments for mitigation of radiation-induced hematopoietic damage has focused on amelioration of radiation-induced neutropenia, which has long been considered to be the primary factor in determining survival after an unintentional radiation exposure. Consistent with historical data, recent studies have highlighted the role that radiation-induced thrombocytopenia plays in radiation mortality, yet development of MCMs to mitigate radiation damage to the megakaryocyte lineage has lagged behind anti-neutropenia approaches. To address this gap and to foster research in the area of platelet regeneration after radiation exposure, the National Institute of Allergy and Infectious Diseases (NIAID) sponsored a workshop on March 22-23, 2010 to encourage collaborations between NIAID program awardees and companies developing pro-platelet approaches. NIAID also organized an informal, open discussion between academic investigators, product development contractors, and representatives from the U.S. Food and Drug Administration (FDA) and other relevant government agencies about drug development toward FDA licensure of products for an acute radiation syndrome indication. Specific emphasis was placed on the challenges of product licensure for radiation/nuclear MCMs using current FDA regulations (21 CFR Parts 314 and 601) and on the importance of animal efficacy model development, design of pivotal protocols, and standardization of irradiation and animal supportive care.

The tetraspanin CD9 regulates migration, adhesion, and homing of human cord blood CD34+ hematopoietic stem and progenitor cells

The stromal cell-derived factor-1 (SDF-1)/chemokine C-X-C receptor 4 (CXCR4) axis plays a critical role in homing and engraftment of hematopoietic stem/progenitor cells (HSCs) during bone marrow transplantation. To investigate the transcriptional regulation provided by this axis, we performed the first differential transcriptome profiling of human cord blood CD34(+) cells in response to short-term exposure to SDF-1 and identified a panel of genes with putative homing functions. We demonstrated that CD9, a member of the tetraspanin family of proteins, was expressed in CD34(+)CD38(-/lo) and CD34(+)CD38(+) cells. CD9 levels were enhanced by SDF-1, which simultaneously down-regulated CXCR4 membrane expression. Using specific inhibitors and activators, we demonstrated that CD9 expression was modulated via CXCR4, G-protein, protein kinase C, phospholipase C, extracellular signal-regulated kinase, and Janus kinase 2 signals. Pretreatment of CD34(+) cells with the anti-CD9 monoclonal antibody ALB6 significantly inhibited SDF-1-mediated transendothelial migration and calcium mobilization, whereas adhesion to fibronectin and endothelial cells was enhanced. Pretreatment of CD34(+) cells with ALB6 significantly impaired their homing to bone marrow and spleen of sublethally irradiated NOD/SCID (nonobese diabetic/severe combined immune-deficient) mice. Sorted CD34(+)CD9(-) cells displayed lower bone marrow homing capacity compared with that of total CD34(+) cells. CD9 expression on homed CD34(+) cells was significantly up-regulated in vivo. Our results indicate that CD9 might possess specific functions in HSC homing.

Tetraspanin CD9 is required for microparticle release from coated-platelets

CD9, a member of the tetraspanin superfamily, is the third most abundant protein on the platelet surface, but its function remains unknown. In this report, we demonstrate that CD9 is required for the release of microparticles from coated-platelets. Coated-platelets are formed as a result of dual agonist activation with collagen and thrombin, and each coated-platelet releases 15-25 microparticles averaging 0.4 microm in diameter. We report here that four separate monoclonal antibodies against CD9 inhibited microparticle release from coated-platelets by 72-102% with an IC(50) of approximately 500 ng/mL for ALB6 and SN4. In addition, the anti-alpha(IIb)beta(3) monoclonal antibody AP2 also inhibited microparticle release although additional anti-alpha(IIb)beta(3) monoclonals did not. These data support participation of the tetraspanin CD9, together with the integrin alpha(IIb)beta(3), in the membrane vesiculation process associated with platelet microparticle release.

Chromosome wide analysis of CUGBP1 binding sites identifies the tetraspanin CD9 mRNA as a target for CUGBP1-mediated down-regulation

CUGBP1 is an RNA-binding protein controlling alternative splicing, mRNA translation and stability. In this work we used a motif scoring approach to identify putative CUGBP1 binding sites for genes located on the human chromosome 12. This allowed us to identify the gene CD9 as a presumptive target for CUGBP1-mediated regulation. In a number of cancers, the tetraspanin CD9 is down-regulated, an event correlated with a bad prognostic. Using a combination of biochemical approaches and CUGBP1 knockdown, we showed that CUGBP1 directly controls CD9 expression.

Identification of new target molecules PTK2, TGFBR2 and CD9 overexpressed during advanced bone marrow remodelling in primary myelofibrosis

Primary myelofibrosis (PMF) is a myeloproliferative neoplasm characterized by remodelling of the bone marrow, including progressive myelofibrosis and exaggerated angiogenesis. Advanced PMF frequently shows a full-blown fibre meshwork, which avoids aspiration of cells, and the expression profile of genes related to stroma pathology at this stage remains largely undetermined. We investigated bone marrow core biopsies in PMF showing various degrees of myelofibrosis by custom-made low density arrays (LDA) representing target genes with designated roles in synthesis of extracellular matrix, matrix remodelling, cellular adhesion and motility. Among a set of 11 genes up-regulated in advanced stages of PMF (P < or = 0.01) three candidates, PTK2 protein tyrosine kinase 2 (PTK2), transforming growth factor beta type II receptor (TGFBR2) and motility-related protein-1 (CD9 molecule, CD9), were investigated in more detail. PTK2, TGFBR2 and CD9 were significantly overexpressed in larger series of advanced PMF stages (P < or = 0.01 respectively). Endothelial cells of the increased microvessel network in PMF could be identified as a predominant source for PTK2, TGFBR2 and CD9. CD9 also strongly identified activated fibroblasts in advanced myelofibrosis. We conclude that PTK2, TGFBR2 and CD9 represent new target molecules involved in bone marrow remodelling of PMF and warrant further investigation for potential targeted therapy.

Restoration and reversible expansion of the osteoblastic hematopoietic stem cell niche after marrow radioablation

Adequate recovery of hematopoietic stem cell (HSC) niches after cytotoxic conditioning regimens is essential to successful bone marrow transplantation. Yet, very little is known about the mechanisms that drive the restoration of these niches after bone marrow injury. Here we describe a profound disruption of the marrow microenvironment after lethal total body irradiation of mice that leads to the generation of osteoblasts restoring the HSC niche, followed by a transient, reversible expansion of this niche. Within 48 hours after irradiation, surviving host megakaryocytes were observed close to the endosteal surface of trabecular bone rather than in their normal parasinusoidal site concomitant with an increased stromal-derived factor-1 level. A subsequent increase in 2 megakaryocyte-derived growth factors, platelet-derived growth factor-beta and basic fibroblast growth factor, induces a 2-fold expansion of the population of N-cadherin-/osteopontin-positive osteoblasts, relative to the homeostatic osteoblast population, and hence, increases the number of potential niches for HSC engraftment. After donor cell engraftment, this expanded microenvironment reverts to its homeostatic state. Our results demonstrate the rapid recovery of osteoblastic stem cell niches after marrow radioablation, provide critical insights into the associated mechanisms, and suggest novel means to manipulate the bone marrow microenvironment to promote HSC engraftment.

Role of CD34 antigen in myeloid differentiation of human hematopoietic progenitor cells

CD34 is a transmembrane protein that is strongly expressed on hematopoietic stem/progenitor cells (HSCs); despite its importance as a marker of HSCs, its function is still poorly understood, although a role in cell adhesion has been demonstrated. To characterize the function of CD34 antigen on human HSCs, we examined, by both inhibition and overexpression, the role of CD34 in the regulation of HSC lineage differentiation. Our results demonstrate that CD34 silencing enhances HSC granulocyte and megakaryocyte differentiation and reduces erythroid maturation. In agreement with these results, the gene expression profile of these cells reveals the upregulation of genes involved in granulocyte and megakaryocyte differentiation and the downregulation of erythroid genes. Consistently, retroviral-mediated CD34 overexpression leads to a remarkable increase in erythroid progenitors and a dramatic decrease in granulocyte progenitors, as evaluated by clonogenic assay. Together, these data indicate that the CD34 molecule promotes the differentiation of CD34+ hematopoietic progenitors toward the erythroid lineage, which is achieved, at least in part, at the expense of granulocyte and megakaryocyte lineages.

CD41+/CD45+Cells Without Acetylcholinesterase Activity Are Immature and a Major Megakaryocytic Population in Murine Bone Marrow

Murine megakaryocytes (MKs) are defined by CD41/CD61 expression and acetylcholinesterase (AChE) activity; however, their stages of differentiation in bone marrow (BM) have not been fully elucidated. In murine lineage-negative (Lin(-))/CD45(+) BM cells, we found CD41(+) MKs without AChE activity (AChE(-)) except for CD41(++) MKs with AChE activity (AChE(+)), in which CD61 expression was similar to their CD41 level. Lin(-)/CD41(+)/CD45(+)/AChE(-) MKs could differentiate into AChE(+), with an accompanying increase in CD41/CD61 during in vitro culture. Both proplatelet formation (PPF) and platelet (PLT) production for Lin(-)/CD41(+)/CD45(+)/AChE(-) MKs were observed later than for Lin(-)/CD41(++)/CD45(+)/AChE(+) MKs, whereas MK progenitors were scarcely detected in both subpopulations. GeneChip and semiquantitative polymerase chain reaction analyses revealed that the Lin(-)/CD41(+)/CD45(+)/AChE(-) MKs are assigned at the stage between the progenitor and PPF preparation phases in respect to the many MK/PLT-specific gene expressions, including beta1-tubulin. In normal mice, the number of Lin(-)/CD41(+)/CD45(+)/AChE(-) MKs was 100 times higher than that of AChE(+) MKs in BM. When MK destruction and consequent thrombocytopenia were caused by an antitumor agent, mitomycin-C, Lin(-)/CD41(+)/CD45(+)/AChE(-) MKs led to an increase in AChE(+) MKs and subsequent PLT recovery with interleukin-11 administration. It was concluded that MKs in murine BM at least in part consist of immature Lin(-)/CD41(+)/CD45(+)/AChE(-) MKs and more differentiated Lin(-)/CD41(++)/CD45(+)/AChE(+) MKs. Immature Lin(-)/CD41(+)/CD45(+)/AChE(-) MKs are a major MK population compared with AChE(+) MKs in BM and play an important role in rapid PLT recovery in vivo.

The expression of CD9 in the peri-implantation mouse uterus is upregulated in an ovarian steroid hormone-dependent manner

OBJECTIVE

To examine the spatiotemporal expression of CD9 protein in the peri-implantation mouse uterus as well as the effects of ovarian steroid hormones on CD9.

DESIGN

Experimental animal study.

SETTING

Reproductive biological center of Chinese Academy of Sciences.

ANIMAL(S)

Female Kunming white strain mice (6-8 weeks old).

INTERVENTION(S)

Subcutaneous injection of P(4)/E(2); uterine tissues were collected at different times after injection.

MAIN OUTCOME MEASURE(S)

The levels of protein and mRNA were detected in mouse uterus during peri-implantation and after steroid hormones treatment.

RESULT(S)

CD9 protein was expressed intensely in the stromal cells on days 1 and 2 of pregnancy. On days 3 and 4, the glandular and luminal epithelial cells exhibited accumulation of CD9 protein. After the initial attachment reaction on day 5, luminal epithelial and stromal cells immediately surrounding the blastocysts exhibited distinct accumulation of CD9. On days 6-8, the accumulation of CD9 occurred in decidual cells. Using ovariectomized mice, we also observed that both progesterone and estrogen upregulated uterine CD9 expression.

CONCLUSION(S)

The results of the current investigation showed that CD9 was differentially expressed in the uterus depending on the stage of implantation and was upregulated in ovarian steroid hormone-dependent manner, implicating multiple roles of CD9 in the regulation of embryo implantation during the peri-implantation period.

Molecular Profiling of CD34+Cells in Idiopathic Myelofibrosis Identifies a Set of Disease-Associated Genes and Reveals the Clinical Significance of Wilms' Tumor Gene 1 (WT1)

This study was aimed at the characterization of a gene expression signature of the pluripotent hematopoietic CD34(+) stem cell in idiopathic myelofibrosis (IM), which would eventually provide novel pathogenetic insights and/or diagnostic/prognostic information. Aberrantly regulated genes were revealed by transcriptome comparative microarray analysis of normal and IM CD34(+) cells; selected genes were also assayed in granulocytes. One-hundred seventy four differentially expressed genes were identified and in part validated by quantitative polymerase chain reaction. Altered gene expression was corroborated by the detection of abnormally high CD9 or CD164, and low CXCR4, membrane protein expression in IM CD34(+) cells. According to class prediction analysis, a set of eight genes (CD9, GAS2, DLK1, CDH1, WT1, NFE2, HMGA2, and CXCR4) properly recognized IM from normal CD34(+) cells. These genes were aberrantly regulated also in IM granulocytes that could be reliably differentiated from control polycythemia vera and essential thrombocythemia granulocytes in 100% and 81% of cases, respectively. Abnormal expression of HMGA2 and CXCR4 in IM granulocytes was dependent on the presence and the mutational status of JAK2(V617F) mutation. The expression levels of both CD9 and DLK1 were associated with the platelet count, whereas higher WT1 expression levels identified IM patients with more active disease, as revealed by elevated CD34(+) cell count and higher severity score. In conclusion, molecular profiling of IM CD34(+) cells uncovered a limited number of genes with altered expression that, beyond their putative role in disease pathogenesis, are associated with patients' clinical characteristics and may have potential prognostic application.

Characterization of primitive marrow CD34+ cells that persist after a sublethal dose of total body irradiation

Knowledge of the molecular events that occur during hematopoietic stem/progenitor cell (HSPC) development is vital to our understanding of blood cell production. To study the functional groups of genes characteristic of HSPCs we isolated a subpopulation of CD34+ bone marrow (BM) cells from nonhuman primates that persisted in vivo after a sublethal dose of total body irradiation (TBI). CD34+ cells isolated during the phase of maximal hematopoietic suppression show a transcriptional profile characteristic of metabolically inactive cells, with strong coordinate downregulation of a large number of genes required for protein production and processing. Consistent with this profile, these CD34+ cells were not able to generate hematopoietic colonies. Transcriptional profiling of these CD34+ cells in conjunction with a pathway analysis method reveals several classes of functionally related genes that are upregulated in comparison to the CD34+ cells obtained prior to TBI. These families included genes known to be associated with self-renewal and maintenance of HSPCs (including bone morphogenetic proteins), resistance to apoptosis (Bcl-2) as well as genes characteristic of a variety of nonhematopoietic tissues (gamma-aminobutyric acid/glycine receptor, complement receptor C1qRp). In contrast, during the period of hematopoietic recovery, the CD34+ cells expressed higher level of genes encoding factors regulating maturation and differentiation of HSPCs. Our data indicate that the primitive BM CD34+ cell population that persists after radiation possesses a transcriptional profile suggestive of pluripotency.

[Inflammatory reactions in the wear particle induced and infectious periprosthetic membrane of loosened hip- and knee endoprostheses: pathogenetic relevance of differentially expressed genes cd9, cd11b, cd18, cd52 and pdgfrbeta]

BACKGROUND

A previous cDNA-microarray analysis described constantly differentially expressed genes in wear particle induced and infectious SLIM (synovial-like interface membrane). This study aims to validate the cDNA microarray data in order to approve differences of the gene expression profiles of RNA and proteins.

METHODS

Tissue from 16 wear particle induced and 20 infectious periprosthetic membranes were analyzed by RT-PCR and immunohistology with regard to the expression of inflammatoric associated genes.

RESULTS

RT-PCR showed the genes cd9, cd11b, cd18, cd52 as well as pdgfrbeta in interface membranes. In the wear particle induced membrane the immunohistochemical analysis showed a significantly weaker gene expression of PDGFRbeta, whereas the differential overexpression of CD9, CD11b and CD52 was confirmed. For CD18, there was no difference in expression between wear induced and infectious periprosthetic tissue.

CONCLUSION

Different pathomechanisms, which are reflected by different gene expression profiles, might produce different types of periprosthetic membranes. By RT-PCR and immunohistochemical analysis the micro array data of the genes cd9, cd11b, cd52 and pdgfrbeta could be validated. Identifying the gene products of cd9, cd11b and cd52 in blood or tissue may help to differentiate between wear induced and infectious loosening.

Role of beta(1)-integrins and their associated tetraspanin molecules in fibronectin-enhanced megakaryopoiesis

BACKGROUND

We have shown previously that fibronectin (FN) together with megakaryocyte (Mk) growth and development factor (MGDF) enhanced generation of Mk progenitors determined by colony-forming unit (CFU)-Mk assay. MGDF can activate beta(1)-integrins on progenitor cells and increase binding to FN. We studied the role of beta(1)-integrin-tetraspanin complexes by which FN may enhance megakaryopoiesis.

METHODS

Cord blood CD34(+) cells were cultured for up to 8 days in serum-free medium containing IL-3, IL-6 and SCF with or without MGDF in the presence or absence of FN. Immunofluorescence flow cytometry was used to monitor changes in beta(1)-integrin-tetraspanin complexes. CFU-Mk assay was used to assess Mk commitment.

RESULTS

The cocktail of cytokines irrespective of the presence of MGDF altered the percentage expression of beta(1)-integrins CD49d and CD49e on CD34(+) cells. CD49d expression fell initially (98% to 15%) and then rose to 75%, whereas CD49e progressively increased over the 8 days of culture, from 5.4% to 22%. However, with the addition of FN, similar changes in the expression of beta(1)-integrins were observed but the expression was maintained at a higher level. MGDF and FN increased expression of tetraspanin molecules, CD63 and CD151, as well as their co-expression with the beta(1)-integrins on both the CD34(+) and CD34(-) cells (e.g. and increase from 0% to 80% co-expression of CD49d and CD151 on CD34(+)). Blocking of beta(1)-integrins or the tetraspanin CD151 with the respective MAb reduced Mk progenitor generation in a stromal cell model.

DISCUSSION

FN enhanced Mk progenitor generation through modulation of beta(1)-integrin-tetraspanin complexes, such as CD151/CD49d.

N-Ras–Induced Growth Suppression of Myeloid Cells Is Mediated by IRF-1

Activating mutations in ras oncogenes occur at high frequency in human malignancies and expression of activated ras in immortalized cells lines is generally transforming. However, somewhat paradoxically, ectopic expression of ras in some myeloid cell lines has been shown to induce growth suppression associated with up-regulation of the cyclin-dependent kinase inhibitor p21CIP1/WAF1 in a p16INK4a, p15INK4b, and p53 independent fashion. We have used cDNA array technology to compare the expression profile induced by activated N-ras (N-rasG13R) in growth-suppressed myeloid cells with that induced in myeloid cells, which are transformed by N-rasG13R. The expression profile induced in growth suppressed cells was consistent with differentiation and included the up-regulation of the transcription factor IFN regulatory factor-1 (IRF-1), a known transcriptional activator of p21CIP/WAF1 expression and a target of oncogenic mutations associated with myeloid leukemia. Antisense suppression of IRF-1 prevented N-rasG13R–associated growth arrest and up-regulation of p21CIP1/WAF1. These results define a novel tumor suppressive response to oncogenic signaling and provide a mechanistic link between growth suppression and differentiation in myeloid cells.

IL-8 and its CXCR1 and CXCR2 receptors participate in the control of megakaryocytic proliferation, differentiation, and ploidy in myeloid metaplasia with myelofibrosis

Myeloproliferation, myelofibrosis, and neoangiogenesis are the 3 major intrinsic pathophysiologic features of myeloid metaplasia with myelofibrosis (MMM). The myeloproliferation is characterized by an increased number of circulating CD34+ progenitors with the prominent amplification of dystrophic megakaryocytic (MK) cells and myeloid metaplasia in the spleen and liver. The various biologic activities of interleukin 8 (IL-8) in hematopoietic progenitor proliferation and mobilization as well as in neoangiogenesis prompted us to analyze its potential role in MMM. We showed that the level of IL-8 chemokine is significantly increased in the serum of patients and that various hematopoietic cells, including platelets, participate in its production. In vitro inhibition of autocrine IL-8 expressed by CD34+ cells with either a neutralizing or an antisense anti-IL-8 treatment increases the proliferation of MMM CD34(+)-derived cells and stimulates their MK differentiation. Moreover, addition of neutralizing anti-IL-8 receptor (CXC chemokine receptor 1 [CXCR1] or 2 [CXCR2]) antibodies to MMM CD34+ cells cultured under MK liquid culture conditions increases the proliferation and differentiation of MMM CD41+ MK cells and restores their polyploidization. Our results suggest that IL-8 and its receptors participate in the altered MK growth that features MMM and open new therapeutic prospects for this still incurable disease.

Gene expression profiling of normal and malignant CD34-derived megakaryocytic cells

Gene expression profiles of bone marrow (BM) CD34-derived megakaryocytic cells (MKs) were compared in patients with essential thrombocythemia (ET) and healthy subjects using oligonucleotide microarray analysis to identify differentially expressed genes and disease-specific transcripts. We found that proapoptotic genes such as BAX, BNIP3, and BNIP3L were down-regulated in ET MKs together with genes that are components of the mitochondrial permeability transition pore complex, a system with a pivotal role in apoptosis. Conversely, antiapoptotic genes such as IGF1-R and CFLAR were up-regulated in the malignant cells, as was the SDF1 gene, which favors cell survival. On the basis of the array results, we characterized apoptosis of normal and ET MKs by time-course evaluation of annexin-V and sub-G1 peak DNA stainings of immature and mature MKs after culture in serum-free medium with an optimal thrombopoietin concentration, and annexin-V-positive MKs only, with decreasing thrombopoietin concentrations. ET MKs were more resistant to apoptosis than their normal counterparts. We conclude that imbalance between proliferation and apoptosis seems to be an important step in malignant ET megakaryocytopoiesis.

NMDA receptor-mediated regulation of human megakaryocytopoiesis

Identification of the regulatory inputs that direct megakaryocytopoiesis and platelet production is essential for the development of novel therapeutic strategies for the treatment of thrombosis and related hematologic disorders. We have previously shown that primary human megakaryocytes express the N-methyl-d-aspartate acid (NMDA) receptor 1 (NR1) subunit of NMDA-type glutamate receptors, which appear to be pharmacologically similar to those identified at neuronal synapses, responsible for mediating excitatory neurotransmission in the central nervous system. However, the functional role of NMDA receptor signaling in megakaryocytopoiesis remains unclear. Here we provide evidence that demonstrates the fundamental importance of this signaling pathway during human megakaryocyte maturation in vitro. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of RNA extracted from CD34+-derived megakaryocytes identified expression of NR2A and NR2D receptor subunits in these cells, as well as the NMDA receptor accessory proteins, Yotiao and postsynaptic density protein 95 (PSD-95). In functional studies, addition of a selective NMDA receptor antagonist, MK-801 inhibited proplatelet formation, without affecting proliferation or apoptosis. Exposure of CD34+ cells to MK-801 cultured for 14 days in the presence of thrombopoietin induced a decrease in expression of the megakaryocyte cell surface markers CD61, CD41a, and CD42a compared with controls. At an ultrastructural level, MK-801-treated cells lacked alpha-granules, demarcated membranes, and multilobed nuclei, which were prominent in untreated mature megakaryocyte controls. Using immunohistochemistry on sections of whole tibiae from c-Mpl knockout mice we demonstrated that megakaryocytic NMDA receptor expression was maintained following c-Mpl ablation. These data support a fundamental role for glutamate signaling in megakaryocytopoiesis and platelet production, which is likely to be independent of thrombopoietin-mediated effects.

Characterization of mouse clonogenic megakaryocyte progenitors

Although it has been shown that unfractionated bone marrow, hematopoietic stem cells, common myeloid progenitors, and bipotent megakaryocyteerythrocyte progenitors can give rise to megakaryocyte colonies in culture, monopotent megakaryocyte-committed progenitors (MKP) have never been prospectively isolated from the bone marrow of adult mice. Here, we use a monoclonal antibody to the megakaryocyte-associated surface protein, CD9, to purify MKPs from the c-kit(+)Sca-1(-)IL7Ralpha(-)Thy1.1(-)Lin(-) fraction of adult C57BLKa-Thy1.1 bone marrow. The CD9(+) fraction contained a subset of CD41(+)FcgammaR(lo)CD34(+)CD38(+) cells that represent approximately 0.01% of the total nucleated bone marrow cells. They give rise mainly to colony-forming unit-megakaryocytes and occasionally burst-forming unit-megakaryocytes, with a plating efficiency >60% at the single-cell level. In vivo, MKPs do not have spleen colony-forming activity nor do they contribute to long-term multilineage hematopoiesis; they give rise only to platelets for approximately 3 weeks. Common myeloid progenitors and megakaryocyteerythrocyte progenitors can differentiate into MKPs after 72 h in stromal cultures, indicating that MKPs are downstream of these two progenitors. These isolatable MKPs will be very useful for further studies of megakaryopoiesis as well as the elucidation of their gene expression patterns.

Prospective isolation of human clonogenic common myeloid progenitors

The hierarchical development from hematopoietic stem cells to mature cells of the hematolymphoid system involves progressive loss of self-renewal capacity, proliferation ability, and lineage potentials. Here we show the prospective isolation of early developmental intermediates, the human clonogenic common myeloid progenitors and their downstream progeny, the granulocyte/macrophage and megakaryocyte/erythrocyte progenitors. All three populations reside in the lineage-negative (lin(-)) CD34(+)CD38(+) fraction of adult bone marrow as well as in cord blood. They are distinguishable by the expression of the IL-3R alpha chain, the receptor of an early-acting hematopoietic cytokine, and CD45RA, an isoform of a phosphotyrosine phosphatase involved in negative regulation of cytokine signaling. Multipotent progenitors, early lymphoid progenitors, and the here-defined myeloid progenitors express distinct profiles of hematopoiesis-affiliated genes. The isolation of highly purified hematopoietic intermediates provides tools to better understand developmental programs underlying normal and leukemic hematopoiesis.

The absence of Tssc6, a member of the tetraspanin superfamily, does not affect lymphoid development but enhances in vitro T-cell proliferative responses

The tetraspanins are a family of integral membrane proteins with four transmembrane domains. These molecules form multimolecular networks on the surfaces of many different cell types. Gene-targeting studies have revealed a role for tetraspanins in B- and T-lymphocyte function. We have isolated and deleted a novel tetraspanin, Tssc6, which is expressed exclusively in hematopoietic and lymphoid organs. Using a gene-trapping strategy, we generated an embryonic stem (ES) cell line with an insertion in the Tssc6 locus. Mice were derived from these ES cells and, using RNase protection and reverse transcription-PCR, we demonstrated that the insertion resulted in a null mutation of the Tssc6 allele. Mice homozygous for the gene trap insertion (Tssc6(gt/gt) mice) were viable and fertile, with normal steady-state hematopoiesis. Furthermore, responses to hemolysis and granulocyte colony-stimulating factor-induced granulopoiesis were equivalent to those of wild-type mice. Lymphoid development was normal in Tssc6(gt/gt) mice. Whereas Tssc6(gt/gt) B cells responded normally to lipopolysaccharide, anti-CD40, and anti-immunoglobulin M stimulation, Tssc6(gt/gt) T cells showed enhanced responses to concanavalin A, anti-CD3, and anti-CD28. This increased proliferation by Tssc6-deleted T lymphocytes was due to increased interleukin 2 production following T-cell receptor stimulation. These results demonstrate that Tssc6 is not required for normal development of the hematopoietic system but may play a role in the negative regulation of peripheral T-lymphocyte proliferation.

Histone deacetylase inhibition results in decreased macrophage CD9 expression

Histone deacetylase (HDAC) inhibitors have been demonstrated to regulate myeloid cell differentiation. In the present study the effects of the HDAC inhibitor trichostatin A (TSA) on the tetraspanin cell surface antigen CD9 were determined in primary murine macrophages. TSA inhibited CD9 protein and message expression and was optimal by 48 h. TSA did not induce similar effects on other surface markers and resulted in a modest increase or no effect on CD54 and CD11b, respectively. These effects were concentration dependent and concomitant with increased histone H4 acetylation. While interferon-gamma (IFN-gamma) and TSA had similar effects on CD9 expression, transcriptional profiling demonstrated significant differences in the genes activated by these stimuli. Notably CD14 message was down-regulated by IFN-gamma while increased by TSA. These results demonstrate that HDAC inhibition may modulate macrophage function in part through changes in the expression of membrane proteins associated with matrix interactions.

Flt3/Flk-2-ligand in synergy with thrombopoietin delays megakaryocyte development and increases the numbers of megakaryocyte progenitor cells in serum-free cultures initiated with CD34+ cells

Megakaryocytopoiesis involves proliferation and maturation of committed precursors that increase their size by polyploidy, a process that is believed to be critical for the efficient production and release of platelets. Thrombopoietin has been shown to act on proliferation, maturation, and survival pathways in megakaryocytopoiesis. Less is known about the role of Flt3/Flk-2-ligand in this development. Apoptosis has an important role in hematopoiesis in general. It has been shown to have an effect on senescent megakaryocytes but not megakaryocyte progenitor cells. In this study, a serum-free culture model was developed, differentiating bone marrow CD34(+) hematopoietic stem cells into megakaryocytes, using thrombopoietin and Flt3/Flk-2-ligand. The model was used to study the effect of these growth factors on expansion of megakaryocyte progenitor cells, differentiation of megakaryocytes, and ploidy. Our results demonstrate that bone marrow CD34(+) cells cultured with thrombopoietin and Flt3/Flk-2-ligand show a lower developmental rate into MK cells compared to cells cultured with thrombopoietin alone. Cells cultured with thrombopoietin and Flt3/Flk-2-ligand expressed less CD41, the ploidy level was lower, and they appeared less mature. On the other hand, the cells showed up to 10-fold increase in cell numbers compared to five-fold increase when cultured with thrombopoietin alone. These results suggest that Flt3/Flk-2-ligand in synergy with thrombopoietin may slow down megakaryocyte development by causing increased proliferation of megakaryocyte progenitor cells.