Pharmacological inhibition of EGFR signaling enhances G-CSF-induced hematopoietic stem cell mobilization

Hematopoietic stem cells and betaherpesvirus latency

The human betaherpesviruses including human cytomegalovirus (HCMV), human herpesvirus (HHV)-6a and HHV-6b, and HHV-7 infect and establish latency in CD34+ hematopoietic stem and progenitor cells (HPCs). The diverse repertoire of HPCs in humans and the complex interactions between these viruses and host HPCs regulate the viral lifecycle, including latency. Precise manipulation of host and viral factors contribute to preferential maintenance of the viral genome, increased host cell survival, and specific manipulation of the cellular environment including suppression of neighboring cells and immune control. The dynamic control of these processes by the virus regulate inter- and intra-host signals critical to the establishment of chronic infection. Regulation occurs through direct viral protein interactions and cellular signaling, miRNA regulation, and viral mimics of cellular receptors and ligands, all leading to control of cell proliferation, survival, and differentiation. Hematopoietic stem cells have unique biological properties and the tandem control of virus and host make this a unique environment for chronic herpesvirus infection in the bone marrow. This review highlights the elegant complexities of the betaherpesvirus latency and HPC virus-host interactions.

pH regulates hematopoietic stem cell potential via polyamines

Upon ex vivo culture, hematopoietic stem cells (HSCs) quickly lose potential and differentiate into progenitors. The identification of culture conditions that maintain the potential of HSCs ex vivo is therefore of high clinical interest. Here, we demonstrate that the potential of murine and human HSCs is maintained when cultivated for 2 days ex vivo at a pH of 6.9, in contrast to cultivation at the commonly used pH of 7.4. When cultivated at a pH of 6.9, HSCs remain smaller, less metabolically active, less proliferative and show enhanced reconstitution ability upon transplantation compared to HSC cultivated at pH 7.4. HSCs kept at pH 6.9 show an attenuated polyamine pathway. Pharmacological inhibition of the polyamine pathway in HSCs cultivated at pH 7.4 with DFMO mimics phenotypes and potential of HSCs cultivated at pH 6.9. Ex vivo exposure to a pH of 6.9 is therefore a positive regulator of HSC function by reducing polyamines. These findings might improve HSC short-term cultivation protocols for transplantation and gene therapy interventions.

Hematopoietic stem and progenitors cells gene editing: Beyond blood disorders

Lessons learned from decades-long practice in the transplantation of hematopoietic stem and progenitor cells (HSPCs) to treat severe inherited disorders or cancer, have set the stage for the current ex vivo gene therapies using autologous gene-modified hematopoietic stem and progenitor cells that have treated so far, hundreds of patients with monogenic disorders. With increased knowledge of hematopoietic stem and progenitor cell biology, improved modalities for patient conditioning and with the emergence of new gene editing technologies, a new era of hematopoietic stem and progenitor cell-based gene therapies is poised to emerge. Gene editing has the potential to restore physiological expression of a mutated gene, or to insert a functional gene in a precise locus with reduced off-target activity and toxicity. Advances in patient conditioning has reduced treatment toxicities and may improve the engraftment of gene-modified cells and specific progeny. Thanks to these improvements, new potential treatments of various blood- or immune disorders as well as other inherited diseases will continue to emerge. In the present review, the most recent advances in hematopoietic stem and progenitor cell gene editing will be reported, with a focus on how this approach could be a promising solution to treat non-blood-related inherited disorders and the mechanisms behind the therapeutic actions discussed.

The biology of hematopoietic stem cells and its clinical implications

Hematopoietic stem cells (HSCs) give rise to all types of blood cells and self-renew their own population. The regeneration potential of HSCs has already been successfully translated into clinical applications. However, recent studies on the biology of HSCs may further extend their clinical use in future. The roles of HSCs in native hematopoiesis and in transplantation settings may differ. Furthermore, the heterogenic pool of HSCs dynamically changes during aging. These changes also involve the complex interactions of HSCs with the bone marrow niche. Here, we review the opportunities and challenges of these findings to improve the clinical use of HSCs. We describe new methods of HSCs mobilization and conditioning for the transplantation of HSCs. Finally, we highlight the research findings that may lead to overcoming the current limitations of HSC transplantation and broaden the patient group that can benefit from the clinical potential of HSCs.

Comparison of the efficacy of hematopoietic stem cell mobilization regimens: a systematic review and network meta-analysis of preclinical studies

BACKGROUND

Mobilization failure may occur when the conventional hematopoietic stem cells (HSCs) mobilization agent granulocyte colony-stimulating factor (G-CSF) is used alone, new regimens were developed to improve mobilization efficacy. Multiple studies have been performed to investigate the efficacy of these regimens via animal models, but the results are inconsistent. We aim to compare the efficacy of different HSC mobilization regimens and identify new promising regimens with a network meta-analysis of preclinical studies.

METHODS

We searched Medline and Embase databases for the eligible animal studies that compared the efficacy of different HSC mobilization regimens. Primary outcome is the number of total colony-forming cells (CFCs) in per milliliter of peripheral blood (/ml PB), and the secondary outcome is the number of Lin^- Sca1⁺ Kit⁺ (LSK) cells/ml PB. Bayesian network meta-analyses were performed following the guidelines of the National Institute for Health and Care Excellence Decision Support Unit (NICE DSU) with WinBUGS version 1.4.3. G-CSF-based regimens were classified into the SD (standard dose, 200-250 μg/kg/day) group and the LD (low dose, 100-150 μg/kg/day) group based on doses, and were classified into the short-term (2-3 days) group and the long-term (4-5 days) group based on administration duration. Long-term SD G-CSF was chosen as the reference treatment. Results are presented as the mean differences (MD) with the associated 95% credibility interval (95% CrI) for each regimen.

RESULTS

We included 95 eligible studies and reviewed the efficacy of 94 mobilization agents. Then 21 studies using the poor mobilizer mice model (C57BL/6 mice) to investigate the efficacy of different mobilization regimens were included for network meta-analysis. Network meta-analyses indicated that compared with long-term SD G-CSF alone, 14 regimens including long-term SD G-CSF + Me6, long-term SD G-CSF + AMD3100 + EP80031, long-term SD G-CSF + AMD3100 + FG-4497, long-term SD G-CSF + ML141, long-term SD G-CSF + desipramine, AMD3100 + meloxicam, long-term SD G-CSF + reboxetine, AMD3100 + VPC01091, long-term SD G-CSF + FG-4497, Me6, long-term SD G-CSF + EP80031, POL5551, long-term SD G-CSF + AMD3100, AMD1300 + EP80031 and long-term LD G-CSF + meloxicam significantly increased the collections of total CFCs. G-CSF + Me6 ranked first among these regimens in consideration of the number of harvested CFCs/ml PB (MD 2168.0, 95% CrI 2062.0-2272.0). In addition, 7 regimens including long-term SD G-CSF + AMD3100, AMD3100 + EP80031, long-term SD G-CSF + EP80031, short-term SD G-CSF + AMD3100 + IL-33, long-term SD G-CSF + ML141, short-term LD G-CSF + ARL67156, and long-term LD G-CSF + meloxicam significantly increased the collections of LSK cells compared with G-CSF alone. Long-term SD G-CSF + AMD3100 ranked first among these regimens in consideration of the number of harvested LSK cells/ml PB (MD 2577.0, 95% CrI 2422.0-2733.0).

CONCLUSIONS

Considering the number of CFC and LSK cells in PB as outcomes, G-CSF plus AMD3100, Me6, EP80031, ML141, FG-4497, IL-33, ARL67156, meloxicam, desipramine, and reboxetine are all promising mobilizing regimens for future investigation.

EGFR inhibitors, MHC expression and immune responses : Can EGFR inhibitors be used as immune response modifiers?

A recent study from our laboratory demonstrated that epidermal growth factor receptor (EGFR) inhibitors (EGFRIs) augment the expression of class I and class II MHC molecules. This finding provides an additional mechanism through which EGFRIs may exert anti-tumor effects and supports the notion that EGFRIs may influence adaptive immune responses by altering immune gene expression.

Dysregulated megakaryocyte distribution associated with nestin+ mesenchymal stem cells in immune thrombocytopenia

Impaired megakaryocyte (MK) maturation and reduced platelet production are important causes of immune thrombocytopenia (ITP). However, MK distribution and bone marrow (BM) niche alteration in ITP are unclear. To investigate the maturation and distribution of MKs in the BM niche and examine the components of BM niche regulation of MK migration, BM and peripheral blood were obtained from 30 ITP patients and 28 healthy donors. Nestin⁺ mesenchymal stem cells (MSCs) and CD41⁺ MKs were sorted by fluorescence-activated cell sorting. The components of the BM niche and related signaling were analyzed via immunofluorescence, flow cytometry, enzyme-linked immunosorbent assay, reverse transcription polymerase chain reaction, and western blot analysis. The number of MKs in the BM vascular niche was reduced in ITP. Moreover, the concentrations of CXCL12 and CXCR4⁺ MKs in the BM were decreased in ITP. Further investigation demonstrated that nestin⁺ MSCs and CXCL12 messenger RNA (mRNA) in nestin⁺ MSCs were both reduced whereas the apoptosis of nestin⁺ MSCs was significantly increased in ITP. Sympathetic nerves, Schwann cells, the proportion of β3-adrenoreceptor (β3-AR)⁺ nestin⁺ MSCs, and β3-AR mRNA in nestin⁺ MSCs were all markedly reduced in ITP. Moreover, matrix metalloproteinase 9, vascular endothelial growth factor (VEGF), and VEGF receptor 1 were significantly reduced in ITP. Our data show that impaired MK distribution mediated by an abnormal CXCL12/CXCR4 axis is partially involved in reduced platelet production in ITP. Moreover, sympathetic neuropathy and nestin⁺ MSC apoptosis may have an effect on the alterations of BM CXCL12 in ITP.

Mobilized peripheral blood: an updated perspective

Enforced egress of hematopoietic stem cells (HSCs) out of the bone marrow (BM) into the peripheral circulation, termed mobilization, has come a long way since its discovery over four decades ago. Mobilization research continues to be driven by the need to optimize the regimen currently available in the clinic with regard to pharmacokinetic and pharmacodynamic profile, costs, and donor convenience. In this review, we describe the most recent findings in the field and how we anticipate them to affect the development of mobilization strategies in the future. Furthermore, the significance of mobilization beyond HSC collection, i.e. for chemosensitization, conditioning, and gene therapy as well as a means to study the interactions between HSCs and their BM microenvironment, is reviewed. Open questions, controversies, and the potential impact of recent technical progress on mobilization research are also highlighted.

Aging alters the epigenetic asymmetry of HSC division

Hematopoietic stem cells (HSCs) balance self-renewal and differentiation to maintain homeostasis. With aging, the frequency of polar HSCs decreases. Cell polarity in HSCs is controlled by the activity of the small RhoGTPase cell division control protein 42 (Cdc42). Here we demonstrate—using a comprehensive set of paired daughter cell analyses that include single-cell 3D confocal imaging, single-cell transplants, single-cell RNA-seq, and single-cell transposase-accessible chromatin sequencing (ATAC-seq)—that the outcome of HSC divisions is strongly linked to the polarity status before mitosis, which is in turn determined by the level of the activity Cdc42 in stem cells. Aged apolar HSCs undergo preferentially self-renewing symmetric divisions, resulting in daughter stem cells with reduced regenerative capacity and lymphoid potential, while young polar HSCs undergo preferentially asymmetric divisions. Mathematical modeling in combination with experimental data implies a mechanistic role of the asymmetric sorting of Cdc42 in determining the potential of daughter cells via epigenetic mechanisms. Therefore, molecules that control HSC polarity might serve as modulators of the mode of stem cell division regulating the potential of daughter cells.

Stem cells are unique cells that can differentiate to produce more stem cells or other types of cells and can divide both symmetrically (to produce daughter cells with the same fate) and asymmetrically (to produce one daughter cell that retains stem cell potential and one that differentiates). The mechanisms that control the outcome of stem cell divisions have been the focus of many studies; however, they remain mainly unknown. Here, we have analyzed these mechanisms in murine hematopoietic stem cells (HSCs) by directly comparing the epigenetic signature, the transcriptome, and the function of the two daughter cells stemming from the first division of either a young or an aged HSC. We observe that, while young HSCs divide mainly asymmetrically, aged HSCs divide primarily symmetrically. We find that the mode of division is tightly linked to stem cell polarity and is regulated by the activity level of the small RhoGTPase cell division control protein 42 (Cdc42). In addition, we show that the potential of daughter cells is further linked to the amount of the epigenetic mark H4K16ac and also to the amount of open chromatin allocated to a daughter cell, but it is not linked to its transcriptome. In summary, our study suggests that HSC polarity linked to Cdc42 activity drives the mode of division, while epigenetic mechanisms determine the functional outcome of the stem cell division.

Nur77 variants solely comprising the amino-terminal domain activate hypoxia-inducible factor-1α and affect bone marrow homeostasis in mice and humans

Gene targeting via homologous recombination can occasionally result in incomplete disruption of the targeted gene. Here, we show that a widely used Nur77-deficient transgenic mouse model expresses a truncated protein encoding for part of the N-terminal domain of nuclear receptor Nur77. This truncated Nur77 protein is absent in a newly developed Nur77-deficient mouse strain generated using Cre-Lox recombination. Comparison of these two mouse strains using immunohistochemistry, flow cytometry, and colony-forming assays shows that homologous recombination-derived Nur77-deficient mice, but not WT or Cre-Lox-derived Nur77-deficient mice, suffer from liver immune cell infiltrates, loss of splenic architecture, and increased numbers of bone marrow hematopoietic stem cells and splenic colony-forming cells with age. Mechanistically, we demonstrate that the truncated Nur77 N-terminal domain protein maintains the stability and activity of hypoxia-inducible factor (HIF)-1, a transcription factor known to regulate bone marrow homeostasis. Additionally, a previously discovered, but uncharacterized, human Nur77 transcript variant that encodes solely for its N-terminal domain, designated TR3β, can also stabilize and activate HIF-1α. Meta-analysis of publicly available microarray data sets shows that TR3β is highly expressed in human bone marrow cells and acute myeloid leukemia samples. In conclusion, our study provides evidence that a transgenic mouse model commonly used to study the biological function of Nur77 has several major drawbacks, while simultaneously identifying the importance of nongenomic Nur77 activity in the regulation of bone marrow homeostasis.

Spleen Regulates Hematopoietic Stem/Progenitor Cell Functions Through Regulation of EGF in Cirrhotic Hypersplenism

BACKGROUND

Hematopoietic abnormality is a common cause of cirrhotic hypersplenism (CH) complications and death; it causes serious adverse effects and is associated with bleeding, anemia, infection in CH patients. However, the underlying mechanism is unclear.

AIMS

We aimed to investigate the effects of the spleen on hematopoiesis and hematopoietic stem/progenitor cells (HSPCs) in CH patients.

METHODS

Eleven CH patients were enrolled to assess the effects of the spleen on HSPC functions. Hematopoietic changes were examined by flow cytometry analysis. HSPC functions were detected with colony-forming assays and in vitro cell cultures. Enzyme-linked immunosorbent assay (ELISA) was used to test the concentration of epithelial growth factor (EGF).

RESULTS

The number of HSPCs was decreased in CH patients and was rescued after splenectomy. Serum from CH patients dysregulated HSPCs function, and serum from splenectomy patients restored the dysregulated HSPC function in vitro. The concentration of EGF was decreased in CH patients and was restored to normal level after splenectomy. EGF rescued the dysregulated HSPCs function in vitro.

CONCLUSIONS

The spleen can regulate the functions of HSPCs in CH patients by regulating EGF signaling. EGF may be a therapeutic target for CH treatment.

Inhibition of the RhoGTPase Cdc42 by ML141 enhances hepatocyte differentiation from human adipose-derived mesenchymal stem cells via the Wnt5a/PI3K/miR-122 pathway: impact of the age of the donor

Background

Human adipose-derived mesenchymal stem cells (hADSCs) are promising cells that may promote hepatocyte differentiation (Hep-Dif) and improve liver function, but the involvement of Cdc42, a key small RhoGTPase which plays a crucial role in aging, is still not well established. We hypothesized that the inhibition of Cdc42 may rescue the hepatogenic potential of hADSCs derived from aged donors.

Methods

hADSCs isolated from 61 women of different ages were cultured for evaluation of the proliferation of cells, adherence, apoptosis, immunomodulation, immunophenotyping, multipotency, gene expression, and cell function during Hep-Dif. Inhibition of Cdc42 by ML141 was realized during two phases: initiation (days –2 to 14 (D–2/14)) from undifferentiated to hepatoblast-like cells, or maturation (days 14 to 28 (D14/28)) from undifferentiated to hepatocyte-like cells. Mechanistic insights of the Wnt(s)/MAPK/PI3K/miR-122 pathways were studied.

Results

Cdc42 activity in undifferentiated hADSCs showed an age-dependent significant increase in Cdc42-GTP correlated to a decrease in Cdc42GAP; the low potentials of cell proliferation, doubling, adherence, and immunomodulatory ability (proinflammatory over anti-inflammatory) contrary to the apoptotic index of the aged group were significantly reversed by ML141. Aged donor cells showed a decreased potential for Hep-Dif which was rescued by ML141 treatment, giving rise to mature and functional hepatocyte-like cells as assessed by hepatic gene expression, cytochrome activity, urea and albumin production, low-density lipoprotein (LDL) uptake, and glycogen storage. ML141-induced Hep-Dif showed an improvement in mesenchymal-epithelial transition, a switch from Wtn-3a/β-catenin to Wnt5a signaling, involvement of PI3K/PKB but not the MAPK (ERK/JNK/p38) pathway, induction of miR-122 expression, reinforcing the exosomes release and the production of albumin, and epigenetic changes. Inhibition of PI3K and miR-122 abolished completely the effects of ML141 indicating that inhibition of Cdc42 promotes the Hep-Dif through a Wnt5a/PI3K/miR-122/HNF4α/albumin/E-cadherin-positive action. The ML141(D–2/14) protocol had more pronounced effects when compared with ML141(D14/28); inhibition of DNA methylation in combination with ML141(D–2/14) showed more efficacy in rescuing the Hep-Dif of aged hADSCs. In addition to Hep-Dif, the multipotency of aged hADSC-treated ML141 was observed by rescuing the adipocyte and neural differentiation by inducing PPARγ/FABP4 and NeuN/O4 but inhibiting Pref-1 and GFAP, respectively.

Conclusion

ML141 has the potential to reverse the age-related aberrations in aged stem cells and promotes their hepatogenic differentiation. Selective inhibition of Cdc42 could be a potential target of drug therapy for aging and may give new insights on the improvement of Hep-Dif.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0910-5) contains supplementary material, which is available to authorized users.

CRISPR-Mediated Integration of Large Gene Cassettes Using AAV Donor Vectors

The CRISPR/Cas9 system has recently been shown to facilitate high levels of precise genome editing using adeno-associated viral (AAV) vectors to serve as donor template DNA during homologous recombination (HR). However, the maximum AAV packaging capacity of ∼4.5 kb limits the donor size. Here, we overcome this constraint by showing that two co-transduced AAV vectors can serve as donors during consecutive HR events for the integration of large transgenes. Importantly, the method involves a single-step procedure applicable to primary cells with relevance to therapeutic genome editing. We use the methodology in primary human T cells and CD34⁺ hematopoietic stem and progenitor cells to site-specifically integrate an expression cassette that, as a single donor vector, would otherwise amount to a total of 6.5 kb. This approach now provides an efficient way to integrate large transgene cassettes into the genomes of primary human cells using HR-mediated genome editing with AAV vectors.

Cutting Edge: Check Your Mice-A Point Mutation in the Ncr1 Locus Identified in CD45.1 Congenic Mice with Consequences in Mouse Susceptibility to Infection

B6.SJL-Ptprc^a Pepc^b /Boy (CD45.1) mice have been used in hundreds of congenic competitive transplants, with the presumption that they differ from C57BL/6 mice only at the CD45 locus. In this study, we describe a point mutation in the natural cytotoxicity receptor 1 (Ncr1) locus fortuitously identified in the CD45.1 strain. This point mutation was mapped at the 40th nucleotide of the Ncr1 locus causing a single amino acid mutation from cysteine to arginine at position 14 from the start codon, resulting in loss of NCR1 expression. We found that these mice were more resistant to CMV due to a hyper innate IFN-γ response in the absence of NCR1. In contrast, loss of NCR1 increased susceptibility to influenza virus, a result that is consistent with the role of NCR1 in the recognition of influenza Ag, hemagglutinin. This work sheds light on potential confounding experimental interpretation when this congenic strain is used as a tool for tracking lymphocyte development.

Epidermal Growth Factor and Granulocyte Colony Stimulating Factor Signaling Are Synergistic for Hematopoietic Regeneration

Hematopoietic regeneration following chemotherapy may be distinct from regeneration following radiation. While we have shown that epidermal growth factor (EGF) accelerates regeneration following radiation, its role following chemotherapy is currently unknown. We sought to identify EGF as a hematopoietic growth factor for chemotherapy-induced myelosuppression. Following 5-fluorouracil (5-FU), EGF accelerated hematopoietic stem cell regeneration and prolonged survival compared with saline-treated mice. To mitigate chemotherapy-induced injury to endothelial cells in vivo, we deleted Bax in VEcadherin⁺ cells (VEcadherinCre;Bax^FL/FL mice). Following 5-FU, VEcadherinCre;Bax^FL/FL mice displayed preserved hematopoietic stem/progenitor content compared with littermate controls. 5-FU and EGF treatment resulted in increased cellular proliferation, decreased apoptosis, and increased DNA double-strand break repair by non-homologous end-joining recombination compared with saline-treated control mice. When granulocyte colony stimulating factor (G-CSF) is given with EGF, this combination was synergistic for regeneration compared with either G-CSF or EGF alone. EGF increased G-CSF receptor (G-CSFR) expression following 5-FU. Conversely, G-CSF treatment increased both EGF receptor (EGFR) and phosphorylation of EGFR in hematopoietic stem/progenitor cells. In humans, the expression of EGFR is increased in patients with colorectal cancer treated with 5-FU compared with cancer patients not on 5-FU. Similarly, EGFR signaling is responsive to G-CSF in humans in vivo with both increased EGFR and phospho-EGFR in healthy human donors following G-CSF treatment compared with donors who did not receive G-CSF. These data identify EGF as a hematopoietic growth factor following myelosuppressive chemotherapy and that dual therapy with EGF and G-CSF may be an effective method to accelerate hematopoietic regeneration. Stem Cells 2018;36:252-264.

Current Developments in Mobilization of Hematopoietic Stem and Progenitor Cells and Their Interaction with Niches in Bone Marrow

The clinical application of hematopoietic stem and progenitor cells (HSPCs) has evolved from a highly experimental stage in the 1980s to a currently clinically established treatment for more than 20,000 patients annually who suffer from hematological malignancies and other severe diseases. Studies in numerous murine models have demonstrated that HSPCs reside in distinct niches within the bone marrow environment. Whereas transplanted HSPCs travel through the bloodstream and home to sites of hematopoiesis, HSPCs can be mobilized from these niches into the blood either physiologically or induced by pharmaceutical drugs. Firstly, this review aims to give a synopsis of milestones defining niches and mobilization pathways for HSPCs, including the identification of several cell types involved such as osteoblasts, adventitial reticular cells, endothelial cells, monocytic cells, and granulocytic cells. The main factors that anchor HSPCs in the niche, and/or induce their quiescence are vascular cell adhesion molecule(VCAM)-1, CD44, hematopoietic growth factors, e.g. stem cell factor (SCF) and FLT3 Ligand, chemokines including CXCL12, growth-regulated protein beta and IL-8, proteases, peptides, and other chemical transmitters such as nucleotides. In the second part of the review, we revise the current understanding of HSPC mobilization. Here, we discuss which mechanisms found to be active in HSPC mobilization correspond to the mechanisms relevant for HSPC interaction with niche cells, but also deal with other mediators and signals that target individual cell types and receptors to mobilize HSPCs. A multitude of questions remain to be addressed for a better understanding of HSPC biology and its implications for therapy, including more comprehensive concepts for regulatory circuits such as calcium homeostasis and parathormone, metabolic regulation such as by leptin, the significance of autonomic nervous system, the consequences of alteration of niches in aged patients, or the identification of more easily accessible markers to better predict the efficiency of HSPC mobilization.

Mobilization of hematopoietic stem cells with the novel CXCR4 antagonist POL6326 (balixafortide) in healthy volunteers-results of a dose escalation trial

BACKGROUND

Certain disadvantages of the standard hematopoietic stem and progenitor cell (HSPC) mobilizing agent G-CSF fuel the quest for alternatives. We herein report results of a Phase I dose escalation trial comparing mobilization with a peptidic CXCR4 antagonist POL6326 (balixafortide) vs. G-CSF.

METHODS

Healthy male volunteer donors with a documented average mobilization response to G-CSF received, following ≥6 weeks wash-out, a 1-2 h infusion of 500-2500 µg/kg of balixafortide. Safety, tolerability, pharmacokinetics and pharmacodynamics were assessed.

RESULTS

Balixafortide was well tolerated and rated favorably over G-CSF by subjects. At all doses tested balixafortide mobilized HSPC. In the dose range between 1500 and 2500 µg/kg mobilization was similar, reaching 38.2 ± 2.8 CD34 + cells/µL (mean ± SEM). Balixafortide caused mixed leukocytosis in the mid-20 K/µL range. B-lymphocytosis was more pronounced, whereas neutrophilia and monocytosis were markedly less accentuated with balixafortide compared to G-CSF. At the 24 h time point, leukocytes had largely normalized.

CONCLUSIONS

Balixafortide is safe, well tolerated, and induces efficient mobilization of HSPCs in healthy male volunteers. Based on experience with current apheresis technology, the observed mobilization at doses ≥1500 µg/kg of balixafortide is predicted to yield in a single apheresis a standard dose of 4× 10E6 CD34+ cells/kg from most individuals donating for an approximately weight-matched recipient. Exploration of alternative dosing regimens may provide even higher mobilization responses. Trial Registration European Medicines Agency (EudraCT-Nr. 2011-003316-23) and clinicaltrials.gov (NCT01841476).

EGFR-Stat3 signalling in nerve glial cells modifies neurofibroma initiation

Neurofibromatosis type 1 (NF1) is an inherited disease in which affected patients are predisposed to develop benign Schwann cell (SC) tumours called neurofibromas. In the mouse, loss of Nf1 in the SC lineage causes neurofibroma formation. The tyrosine kinase receptor EGFR is expressed in Schwann cell precursors (SCP), which have been implicated in plexiform neurofibroma initiation. To test if EGFR activity affects neurofibroma initiation, size, and/or number, we studied mice expressing human EGFR in SCs and SCP in the context of mice that form neurofibromas. Neurofibroma number increased in homozygous CNP-hEGFR mice versus heterozygous littermates, and neurofibroma number and size increased when CNP-hEGFR was crossed to Nf1^fl/fl;DhhCre mice. Conversely, diminished EGFR signalling in Nf1^fl/fl;DhhCre;Wa2/+ mice decreased neurofibroma number. In vivo transplantation verified the correlation between EGFR activity and neurofibroma formation. Mechanistically, expression of CNP-hEGFR increased SCP/neurofibroma-initiating cell self-renewal, a surrogate for tumour initiation, and activated P-Stat3. Further, Il-6 reinforced Jak2/Stat3 activation in SCPs and SCs. These gain- and loss-of function assays show that levels of tyrosine kinase expression in SCPs modify neurofibroma initiation.

Chemical Modulation of Cell Fate in Stem Cell Therapeutics and Regenerative Medicine

Regenerative medicine aims to repair and regenerate injured tissues and restore their impaired functions. Recent developments in stem cell biology have attracted significant interest in their applications in regenerative medicine. Chemical approaches using small molecules have yielded exciting results in induction and differentiation of pluripotent stem cells, lineage conversion of somatic cells, and ex vivo as well as in vivo modulation of adult stem cells. In this review, we discuss recent progress, new insights, and future challenges of the chemical approaches in stem cell biology and regenerative medicine.

Discovery and characterization of an endogenous CXCR4 antagonist

CXCL12-CXCR4 signaling controls multiple physiological processes and its dysregulation is associated with cancers and inflammatory diseases. To discover as-yet-unknown endogenous ligands of CXCR4, we screened a blood-derived peptide library for inhibitors of CXCR4-tropic HIV-1 strains. This approach identified a 16 amino acid fragment of serum albumin as an effective and highly specific CXCR4 antagonist. The endogenous peptide, termed EPI-X4, is evolutionarily conserved and generated from the highly abundant albumin precursor by pH-regulated proteases. EPI-X4 forms an unusual lasso-like structure and antagonizes CXCL12-induced tumor cell migration, mobilizes stem cells, and suppresses inflammatory responses in mice. Furthermore, the peptide is abundant in the urine of patients with inflammatory kidney diseases and may serve as a biomarker. Our results identify EPI-X4 as a key regulator of CXCR4 signaling and introduce proteolysis of an abundant precursor protein as an alternative concept for chemokine receptor regulation.

Effect of crossing C57BL/6 and FVB mouse strains on basal cytokine expression

C57BL/6 is the most often used laboratory mouse strain. However, sometimes it is beneficial to cross the transgenic mice on the C57BL/6 background to the other strain, such as FVB. Although this is a common strategy, the influence of crossing these different strains on homeostatic expression of cytokines is not known. Here we have investigated the differences in the expression of selected cytokines between C57BL/6J and C57BL/6JxFVB mice in serum and skeletal muscle. We have found that only few cytokines were altered by crossing of the strains. Concentrations of IL5, IL7, LIF, MIP-2, and IP-10 were higher in serum of C57BL/6J mice than in C57BL/6JxFVB mice, whereas concentration of G-CSF was lower in C57BL/6J. In the skeletal muscle only the concentration of VEGF was higher in C57BL/6J mice than in C57BL/6JxFVB mice. Concluding, the differences in cytokine expression upon crossing C57BL/6 and FVB strain in basal conditions are not profound.

Cdc42 inhibitor ML141 enhances G-CSF-induced hematopoietic stem and progenitor cell mobilization

G-CSF is the most often used agent in clinical hematopoietic stem and progenitor cell (HSPC) mobilization. However, in about 10 % of patients, G-CSF does not efficiently mobilize HSPC in clinically sufficient amounts. Cdc42 activity is involved in HSPC mobilization. In the present study, we explore the impact of Cdc42 inhibitor ML141 on G-CSF-mediated HSPC mobilization in mice. We found that the use of ML141 alone only triggered modest HSPC mobilization effect in mice. However, combination of G-CSF and ML141 significantly promoted HPSC counts and colony forming units in peripheral blood, as compared to mice treated with G-CSF alone. ML141 did not significantly alter the levels of SDF-1 and MMP-9 in the bone marrow, when used alone or in combination with G-CSF. We also found that G-CSF administration significantly increases the level of GTP-bound Cdc42, but does not alter the expression of Cdc42 in the bone marrow. Our data indicate that the Cdc42 signal is a negative regulator in G-CSF-mediated HSPC mobilization, and that inhibition of the Cdc42 signal efficiently improves mobilization efficiency. These findings may provide a new strategy for efficient HSPC mobilization, especially in patients with poor G-CSF response.

VEGFR2-mediated vascular dilation as a mechanism of VEGF-induced anemia and bone marrow cell mobilization

Molecular mechanisms underlying tumor VEGF-induced host anemia and bone marrow cell (BMC) mobilization remain unknown. Here, we report that tumor VEGF markedly induced sinusoidal vasculature dilation in bone marrow (BM) and BMC mobilization to tumors and peripheral tissues in mouse and human tumor models. Unexpectedly, anti-VEGFR2, but not anti-VEGFR1, treatment completely blocked VEGF-induced anemia and BMC mobilization. Genetic deletion of Vegfr2 in endothelial cells markedly ablated VEGF-stimulated BMC mobilization. Conversely, deletion of the tyrosine kinase domain from Vegfr1 gene (Vegfr1(TK-/-)) did not affect VEGF-induced BMC mobilization. Analysis of VEGFR1(+)/VEGFR2(+) populations in peripheral blood and BM showed no significant ratio difference between VEGF- and control tumor-bearing animals. These findings demonstrate that vascular dilation through the VEGFR2 signaling is the mechanism underlying VEGF-induced BM mobilization and anemia. Thus, our data provide mechanistic insights on VEGF-induced BMC mobilization in tumors and have therapeutic implications by targeting VEGFR2 for cancer therapy.

A phase I/II trial of Erlotinib in higher risk myelodysplastic syndromes and acute myeloid leukemia after azacitidine failure

Survival after azacitidine (AZA) failure in higher-risk myelodysplastic syndromes (MDS) is poor and new treatment options are needed. Erlotinib, an oral inhibitor of the epidermal-growth-factor-receptor (EGFR), has shown in preclinical models some efficacy in higher risk MDS and acute myeloid leukemia (AML). In this phase I/II trial, 30 patients received 100mg/day (n=5) or 150mg/day (n=25) of Erlotinib orally after primary or secondary resistance to AZA treatment. Eighteen MDS and 12 AML patients were treated. This outpatient treatment was well tolerated with limited grade III-IV extra hematological toxicities (skin (n=1), and diarrhea (n=3). Response was observed in 6 patients (20%) including 1 complete remission (CR), 1 marrow CR and 4 hematological improvement (2 erythroid and 2 on platelets). Median duration of response was 5 months. Erlotinib appears to induce a significant number of responses in higher risk MDS/AML having failed AZA treatment. Given the good safety profile of Erlotinib, its combination with other drugs could be tested in the future in MDS and AML.

A novel role for bioactive lipids in stem cell mobilization during cardiac ischemia: new paradigms in thrombosis: novel mediators and biomarkers

Despite major advances in pharmacological and reperfusion therapies, regenerating and/or replacing the infarcted myocardial tissue is an enormous challenge and therefore ischemic heart disease (IHD) remains a major cause of mortality and morbidity worldwide. Adult bone marrow is home for a variety of hematopoietic and non-hematopoietic stem cells including a small subset of primitive cells that carry a promising regenerative potential. It is now well established that myocardial ischemia (MI) induces mobilization of bone marrow-derived cells including differentiated lineage as well as undifferentiated stem cells. While the numbers of stem cells carrying pluripotent features among the mobilized stem cells is small, their regenerative capacity appears immense. Therapies aimed at selective mobilization of these pluripotent stem cells during myocardial ischemia have a promising potential to regenerate the injured myocardium. Emerging evidence suggest that bioactive sphingolipids such as sphingosine-1-phosphate and ceramide-1-phosphate hold a great promise in selective mobilization of pluripotent stem cells to the infarcted region during MI. This review highlights the recent advances in the mechanisms of stem cell mobilization and provides newer evidence in support of bioactive lipids as potential therapeutic agents in the treatment of ischemic heart disease.

Rho GTPases control specific cytoskeleton-dependent functions of hematopoietic stem cells

The Rho family of guanosine triphosphatases (GTPases) is composed of members of the Ras superfamily of proteins. They are GTP-bound molecules with a modest intrinsic GTPase activity that can be accelerated upon activation/localization of specialized guanine nucleotide exchange factors. Members of this family act as molecular switches and are required for coordinated cytoskeletal rearrangements that are crucial in a set of specialized functions of mammalian stem cells. These functions include self-renewal, adhesion, and migration. Mouse gene-targeting studies have provided convincing evidence of the indispensable and dispensable roles of individual members of the Rho GTPase family and the putative upstream and downstream mediators in stem cell-specific functions. The role of Rho GTPases and related signaling pathways previously seen in other cell types and organisms have been confirmed in mammalian hematopoietic stem cells (HSCs), and new signaling pathways and unexpected functions unique to HSCs have been identified and dissected. This review summarizes our current understanding of the role of Rho family of GTPases on HSC and progenitor activity through cytoskeleton-mediated signaling pathways, providing insight about relevant signaling pathways that regulate mammalian stem cell self-renewal, adhesion, and migration.

Chemical approaches to stem cell biology and therapeutics

Small molecules that modulate stem cell fate and function offer significant opportunities that will allow the full realization of the therapeutic potential of stem cells. Rational design and screening for small molecules have identified useful compounds to probe fundamental mechanisms of stem cell self-renewal, differentiation, and reprogramming and have facilitated the development of cell-based therapies and therapeutic drugs targeting endogenous stem and progenitor cells for repair and regeneration. Here, we will discuss recent scientific and therapeutic progress, as well as new perspectives and future challenges for using chemical approaches in stem cell biology and regenerative medicine.

Transcription factor SCL/TAL1 mediates the phosphorylation of MEK/ERK pathway in umbilical cord blood CD34⁺ stem cells during hematopoietic differentiation

Transcription factor stem cell leukemia (SCL), also known as the T-cell acute lymphocytic leukemia 1 (TAL1), plays a key role in the regulation of hematopoiesis, but the molecular mechanisms are not well understood. The aim of the present study is to elucidate the effects of the epidermal growth factor receptor (EGFR) signal pathways underlying the biologic activity of SCL/TAL1 on normal hematopoietic development. Lentiviral vectors with up or down-regulation of SCL/TAL1 were transfected into umbilical cord blood CD34 stem cells. EGFR signaling pathways (including MEK/ERK and Akt/mTOR) and surface hematopoietic markers were analyzed in the process of hematopoietic differentiation. The data revealed that up or down-regulation of SCL/TAL1 gene was accompanied positively by the expressions of p-MEK and p-ERK1/2 protein, but the changes of Akt/mTOR were unobvious. MEK/ERK inhibitor U0126 and SCL/TAL1 down-regulation showed similar inhibitory effects on erythroid, myeloid, and megakaryoid differentiation. However, Akt/mTOR pathway altered insignificantly. MEK/ERK inhibitor U0126 could not affect the expression of SCL/TAL1 mRNA or protein. Taken together, these findings fully illustrated that SCL/TAL1 is located in the up-stream of MEK/ERK pathway and partially regulates hematopoiesis by modulating the phosphorylation level of the key proteins in MEK/ERK pathway.

The role of bioactive lipids in stem cell mobilization and homing: novel therapeutics for myocardial ischemia

Despite significant advances in medical therapy and interventional strategies, the prognosis of millions of patients with acute myocardial infarction (AMI) and ischemic heart disease (IHD) remains poor. Currently, short of heart transplantation with all of its inherit limitations, there are no available treatment strategies that replace the infarcted myocardium. It is now well established that cardiomyocytes undergo continuous renewal, with contribution from bone marrow (BM)-derived stem/progenitor cells (SPCs). This phenomenon is upregulated during AMI by initiating multiple innate reparatory mechanisms through which BMSPCs are mobilized towards the ischemic myocardium and contribute to myocardial regeneration. While a role for the SDF-1/CXCR4 axis in retention of BMSPCs in bone marrow is undisputed, its exclusive role in their mobilization and homing to a highly proteolytic microenvironment, such as the ischemic/infarcted myocardium, is currently being challenged. Recent evidence suggests a pivotal role for bioactive lipids in the mobilization of BMSPCs at the early stages following AMI and their homing towards ischemic myocardium. This review highlights the recent advances in our understanding of the mechanisms of stem cell mobilization, provides newer evidence implicating bioactive lipids in BMSPC mobilization and differentiation, and discusses their potential as therapeutic agents in the treatment of IHD.

The novel CXCR4 antagonist POL5551 mobilizes hematopoietic stem and progenitor cells with greater efficiency than Plerixafor

Mobilized blood has supplanted bone marrow (BM) as the primary source of hematopoietic stem cells for autologous and allogeneic stem cell transplantation. Pharmacologically enforced egress of hematopoietic stem cells from BM, or mobilization, has been achieved by directly or indirectly targeting the CXCL12/CXCR4 axis. Shortcomings of the standard mobilizing agent, granulocyte colony-stimulating factor (G-CSF), administered alone or in combination with the only approved CXCR4 antagonist, Plerixafor, continue to fuel the quest for new mobilizing agents. Using Protein Epitope Mimetics technology, a novel peptidic CXCR4 antagonist, POL5551, was developed. In vitro data presented herein indicate high affinity to and specificity for CXCR4. POL5551 exhibited rapid mobilization kinetics and unprecedented efficiency in C57BL/6 mice, exceeding that of Plerixafor and at higher doses also of G-CSF. POL5551-mobilized stem cells demonstrated adequate transplantation properties. In contrast to G-CSF, POL5551 did not induce major morphological changes in the BM of mice. Moreover, we provide evidence of direct POL5551 binding to hematopoietic stem and progenitor cells (HSPCs) in vivo, strengthening the hypothesis that CXCR4 antagonists mediate mobilization by direct targeting of HSPCs. In summary, POL5551 is a potent mobilizing agent for HSPCs in mice with promising therapeutic potential if these data can be corroborated in humans.

The effects of p38 MAPK inhibition combined with G-CSF administration on the hematoimmune system in mice with irradiation injury

The acute and residual (or long-term) bone marrow (BM) injury induced by ionizing radiation (IR) is a major clinic concern for patients receiving conventional radiotherapy and victims accidentally exposed to a moderate-to-high dose of IR. In this study, we investigated the effects of the treatment with the p38 inhibitor SB203580 (SB) and/or granulocyte colony-stimulating factor (G-CSF) on the hematoimmune damage induced by IR in a mouse model. Specifically, C57BL/6 mice were exposed to a sublethal dose (6 Gy) of total body irradiation (TBI) and then treated with vehicle, G-CSF, SB, and G-CSF plus SB. G-CSF (1 µg/mouse) was administrated to mice by intraperitoneal (ip) injection twice a day for six successive days; SB (15 mg/kg) by ip injection every other day for 10 days. It was found that the treatment with SB and/or G-CSF significantly enhanced the recovery of various peripheral blood cell counts and the number of BM mononuclear cells 10 and 30 days after the mice were exposed to TBI compared with vehicle treatment. Moreover, SB and/or G-CSF treatment also increased the clonogenic function of BM hematopoietic progenitor cells (HPCs) and the frequency of BM lineage⁻Sca1⁺c-kit⁺ cells (LSK cells) and short-term and long term hematopoietic stem cells (HSCs) 30 days after TBI, in comparison with vehicle treated controls. However, the recovery of peripheral blood B cells and CD4⁺ and CD8⁺ T cells was not significantly affected by SB and/or G-CSF treatment. These results suggest that the treatment with SB and/or G-CSF can reduce IR-induced BM injury probably in part via promoting HSC and HPC regeneration.

Epidermal growth factor regulates hematopoietic regeneration after radiation injury

The mechanisms which regulate HSC regeneration following myelosuppressive injury are not well understood. We identified epidermal growth factor (EGF) to be highly enriched in the bone marrow (BM) serum of mice bearing deletion of Bak and Bax in Tie2⁺ cells (Tie2Cre;Bak1^−/−;Bax^fl/− mice), which displayed radioprotection of the HSC pool and 100% survival following lethal dose total body irradiation (TBI). BM HSCs from wild type mice expressed functional EGFR and systemic administration of EGF promoted the recovery of the HSC pool in vivo and the improved survival of mice following TBI. Conversely, administration of erlotinib, an EGFR antagonist, significantly decreased both HSC regeneration and mice survival following TBI. VavCre;EGFR^fl/+ mice also demonstrated delayed recovery of BM stem/progenitor cells following TBI compared to VavCre;EGFR^+/+ mice. Mechanistically, EGF reduced radiation-induced apoptosis of HSCs and mediated this effect via repression of the proapoptotic protein, PUMA. EGFR signaling regulates HSC regeneration following myelosuppressive injury.

Amphiregulin-EGFR signaling mediates the migration of bone marrow mesenchymal progenitors toward PTH-stimulated osteoblasts and osteocytes

Intermittent administration of parathyroid hormone (PTH) dramatically increases bone mass and currently is one of the most effective treatments for osteoporosis. However, the detailed mechanisms are still largely unknown. Here we demonstrate that conditioned media from PTH-treated osteoblastic and osteocytic cells contain soluble chemotactic factors for bone marrow mesenchymal progenitors, which express a low amount of PTH receptor (PTH1R) and do not respond to PTH stimulation by increasing cAMP production or migrating toward PTH alone. Conditioned media from PTH-treated osteoblasts elevated phosphorylated Akt and p38MAPK amounts in mesenchymal progenitors and inhibition of these pathways blocked the migration of these progenitors toward conditioned media. Our previous and current studies revealed that PTH stimulates the expression of amphiregulin, an epidermal growth factor (EGF)-like ligand that signals through the EGF receptor (EGFR), in both osteoblasts and osteocytes. Interestingly, conditioned media from PTH-treated osteoblasts increased EGFR phosphorylation in mesenchymal progenitors. Using several different approaches, including inhibitor, neutralizing antibody, and siRNA, we demonstrate that PTH increases the release of amphiregulin from osteoblastic cells, which acts on the EGFRs expressed on mesenchymal progenitors to stimulate the Akt and p38MAPK pathways and subsequently promote their migration in vitro. Furthermore, inactivation of EGFR signaling specifically in osteoprogenitors/osteoblasts attenuated the anabolic actions of PTH on bone formation. Taken together, these results suggest a novel mechanism for the therapeutic effect of PTH on osteoporosis and an important role of EGFR signaling in mediating PTH's anabolic actions on bone.

At the crossroads: EGFR and PTHrP signaling in cancer-mediated diseases of bone

The epidermal growth factor receptor is a well-established cancer therapeutic target due to its stimulation of proliferation, motility, and resistance to apoptosis. Recently, additional roles for the receptor have been identified in growth of metastases. Similar to development, metastatic spread requires signaling interactions between epithelial-derived tumor cells and mesenchymal derivatives of the microenvironment. This necessitates reactivation of developmental signaling molecules, including the hypercalcemia factor parathyroid hormone-related protein. This review covers the variations of epidermal growth factor receptor signaling in cancers that produce bone metastases, regulation of parathyroid hormone-related protein, and evidence that the two molecules drive cancer-mediated diseases of bone.

Connexin-43 in the osteogenic BM niche regulates its cellular composition and the bidirectional traffic of hematopoietic stem cells and progenitors

Connexin-43 (Cx43), a gap junction protein involved in control of cell proliferation, differentiation and migration, has been suggested to have a role in hematopoiesis. Cx43 is highly expressed in osteoblasts and osteogenic progenitors (OB/P). To elucidate the biologic function of Cx43 in the hematopoietic microenvironment (HM) and its influence in hematopoietic stem cell (HSC) activity, we studied the hematopoietic function in an in vivo model of constitutive deficiency of Cx43 in OB/P. The deficiency of Cx43 in OB/P cells does not impair the steady state hematopoiesis, but disrupts the directional trafficking of HSC/progenitors (Ps) between the bone marrow (BM) and peripheral blood (PB). OB/P Cx43 is a crucial positive regulator of transstromal migration and homing of both HSCs and progenitors in an irradiated microenvironment. However, OB/P Cx43 deficiency in nonmyeloablated animals does not result in a homing defect but induces increased endosteal lodging and decreased mobilization of HSC/Ps associated with proliferation and expansion of Cxcl12-secreting mesenchymal/osteolineage cells in the BM HM in vivo. Cx43 controls the cellular content of the BM osteogenic microenvironment and is required for homing of HSC/Ps in myeloablated animals.

MicroRNA126 contributes to granulocyte colony-stimulating factor-induced hematopoietic progenitor cell mobilization by reducing the expression of vascular cell adhesion molecule 1

BACKGROUND

Mobilization of hematopoietic stem/progenitor cells from the bone marrow to the peripheral blood by granulocyte colony-stimulating factor is the primary means to acquire stem cell grafts for hematopoietic cell transplantation. Since hematopoietic stem/progenitor cells represent a minority of all blood cells mobilized by granulocyte colony-stimulating factor, the underlying mechanisms need to be understood in order to develop selective drugs.

DESIGN AND METHODS

We analyzed phenotypic, biochemical and genetic changes in bone marrow cell populations from granulocyte colony-stimulating factor-mobilized and control mice, and linked such changes to effective mobilization of hematopoietic stem/progenitor cells.

RESULTS

We show that granulocyte colony-stimulating factor indirectly reduces expression of surface vascular cell adhesion molecule 1 on bone marrow hematopoietic stem/progenitor cells, stromal cells and endothelial cells by promoting the accumulation of microRNA-126 (miR126)-containing microvescicles in the bone marrow extracellular compartment. We found that hematopoietic stem/progenitor cells, stromal cells and endothelial cells readily incorporate these miR126-loaded microvescicles, and that miR126 represses vascular cell adhesion molecule 1 expression on bone marrow hematopoietic stem/progenitor cells, stromal cells and endothelial cells. In line with this, miR126-null mice displayed a reduced mobilization response to granulocyte colony-stimulating factor.

CONCLUSIONS

Our results implicate miR126 in the regulation of hematopoietic stem/progenitor cell trafficking between the bone marrow and peripheral sites, clarify the role of vascular cell adhesion molecule 1 in granulocyte colony-stimulating factor-mediated mobilization, and have important implications for improved approaches to selective mobilization of hematopoietic stem/progenitor cells.

Decreased autocrine EGFR signaling in metastatic breast cancer cells inhibits tumor growth in bone and mammary fat pad

Breast cancer metastasis to bone triggers a vicious cycle of tumor growth linked to osteolysis. Breast cancer cells and osteoblasts express the epidermal growth factor receptor (EGFR) and produce ErbB family ligands, suggesting participation of these growth factors in autocrine and paracrine signaling within the bone microenvironment. EGFR ligand expression was profiled in the bone metastatic MDA-MB-231 cells (MDA-231), and agonist-induced signaling was examined in both breast cancer and osteoblast-like cells. Both paracrine and autocrine EGFR signaling were inhibited with a neutralizing amphiregulin antibody, PAR34, whereas shRNA to the EGFR was used to specifically block autocrine signaling in MDA-231 cells. The impact of these was evaluated with proliferation, migration and gene expression assays. Breast cancer metastasis to bone was modeled in female athymic nude mice with intratibial inoculation of MDA-231 cells, and cancer cell-bone marrow co-cultures. EGFR knockdown, but not PAR34 treatment, decreased osteoclasts formed in vitro (p<0.01), reduced osteolytic lesion tumor volume (p<0.01), increased survivorship in vivo (p<0.001), and resulted in decreased MDA-231 growth in the fat pad (p<0.01). Fat pad shEGFR-MDA-231 tumors produced in nude mice had increased necrotic areas and decreased CD31-positive vasculature. shEGFR-MDA-231 cells also produced decreased levels of the proangiogenic molecules macrophage colony stimulating factor-1 (MCSF-1) and matrix metalloproteinase 9 (MMP9), both of which were decreased by EGFR inhibitors in a panel of EGFR-positive breast cancer cells. Thus, inhibiting autocrine EGFR signaling in breast cancer cells may provide a means for reducing paracrine factor production that facilitates microenvironment support in the bone and mammary gland.

The hematopoietic stem cell niche

Hematopoietic stem cells (HSCs) possess the ability to self-renew and to differentiate to mature progeny along multiple different hematopoietic lineages. The function of HSCs depends upon the signals from surrounding cells found within the highly specialized microenvironment termed the hematopoietic stem cell niche. Understanding and exploiting the HSC niche is a goal of basic scientists and clinicians alike. Recent studies have focused on defining the cellular components and molecular factors critical to this microenvironment. Here we review recent findings, discuss unresolved questions, and examine the clinical implications of our current knowledge of the HSC niche.

Regression of cardiac hypertrophy by granulocyte colony-stimulating factor-stimulated interleukin-1β synthesis

AIMS

Aortic stenosis causes cardiac hypertrophy and fibrosis, which often persists despite pressure unloading after aortic valve replacement. The persistence of myocardial fibrosis in particular leads to impaired cardiac function and increased mortality. We investigated whether granulocyte colony-stimulating factor (G-CSF) beneficially influences cardiac remodelling after pressure unloading.

METHODS AND RESULTS

Left ventricular hypertrophy was induced by transverse aortic constriction in C57bl6 mice followed by debanding after 8 weeks. This model closely mimics aortic stenosis and subsequent aortic valve replacement. After debanding, mice were treated with either G-CSF or saline injection. Granulocyte colony-stimulating factor treatment significantly improved systolic (ejection fraction 70.48 ± 1.17 vs. 58.41 ± 1.56%, P < 0.001) and diastolic (E/E' 26.0 ± 1.0 vs. 32.6 ± 0.8, P < 0.05) function. Furthermore, cardiac fibrosis was significantly reduced in G-CSF-treated mice (collagen-I area fraction 7.96 ± 0.47 vs. 11.64 ± 1.22%, P < 0.05; collagen-III area fraction 10.73 ± 0.99 vs. 18.46 ± 0.71%, P < 0.001). Direct effects of G-CSF on cardiac fibroblasts or a relevant transdifferentiation of mobilized bone marrow cells could be excluded. However, a considerable infiltration of neutrophils was observed in G-CSF-treated mice. This sterile inflammation was accompanied by a selective release of interleukin-1 β (IL-1β) in the absence of other proinflammatory cytokines. In vitro experiments confirmed an increased expression of IL-1β in neutrophils after G-CSF treatment. Interleukin-1β directly induced the expression of the gelatinases matrix metalloproteinase-2 (MMP-2) and MMP-9 in cardiac fibroblasts thereby providing the regression of cardiac fibrosis.

CONCLUSION

Granulocyte colony-stimulating factor treatment improves the cardiac function and leads to the regression of myocardial fibrosis after pressure unloading. These findings reveal a previously unknown mechanism of fibrosis regression. Granulocyte colony-stimulating factor might be a potential pharmacological treatment approach for patients suffering from congestive heart failure after aortic valve replacement, although further basic research and clinical trials are required in order to prove beneficial effects of G-CSF in the human organism.

How I treat patients who mobilize hematopoietic stem cells poorly

Transplantation with 2-5 × 106 mobilized CD34+cells/kg body weight lowers transplantation costs and mortality. Mobilization is most commonly performed with recombinant human G-CSF with or without chemotherapy, but a proportion of patients/donors fail to mobilize sufficient cells. BM disease, prior treatment, and age are factors influencing mobilization, but genetics also contributes. Mobilization may fail because of the changes affecting the HSC/progenitor cell/BM niche integrity and chemotaxis. Poor mobilization affects patient outcome and increases resource use. Until recently increasing G-CSF dose and adding SCF have been used in poor mobilizers with limited success. However, plerixafor through its rapid direct blockage of the CXCR4/CXCL12 chemotaxis pathway and synergy with G-CSF and chemotherapy has become a new and important agent for mobilization. Its efficacy in upfront and failed mobilizers is well established. To maximize HSC harvest in poor mobilizers the clinician needs to optimize current mobilization protocols and to integrate novel agents such as plerixafor. These include when to mobilize in relation to chemotherapy, how to schedule and perform apheresis, how to identify poor mobilizers, and what are the criteria for preemptive and immediate salvage use of plerixafor.

Epidermal growth factor receptor expression in acute myelogenous leukaemia is associated with clinical prognosis

The epidermal growth factor receptor (EGFR) family belongs to type I receptor tyrosine kinases. Overexpression or mutation of EGFR/ErbB1 gene has been detected in a large number of human solid tumours. According to some previous report, this gene is not expressed in hematological malignancies. However, two recent clinical case reports showed that erlotinib caused complete remission of acute myeloid leukaemia (AML)-M1 in patients who had both AML-M1 and non-small-cell lung cancer. These results are supported by preclinical studies in which EGFR tyrosine kinase inhibitors have anti-proliferative effects on AML. These findings prompted us to determine whether EGFR is expressed in human AML, through a large-scale screening of both leukaemic cell lines and clinical samples. Our results show that EGFR is expressed by about 33% of human AML (containing M1 to M7 subtypes) and by some human leukaemia cell lines (K562, MEG-01, CEM and SKO-007). Its expression is not limited to certain AML types but has been detected in many leukaemic cells. In addition, EGFR expression was intimately associated with the poor clinical outcomes. Finally, we find that only EGFR-positive leukaemic cells respond to antibody-dependent cellular cytotoxicity of cetuximab, the monoclonal antibodies against EGFR.

R-Ras and Rac GTPase cross-talk regulates hematopoietic progenitor cell migration, homing, and mobilization

Adult hematopoietic progenitor cells (HPCs) are maintained by highly coordinated signals in the bone marrow. The molecular mechanisms linking intracellular signaling network of HPCs with their microenvironment remain poorly defined. The Rho family GTPase Rac1/Rac2 has previously been implicated in cell functions involved in HPC maintenance, including adhesion, migration, homing, and mobilization. In the present studies we have identified R-Ras, a member of the Ras family, as a key signal mediator required for Rac1/Rac2 activation. We found that whereas Rac1 activity is up-regulated upon stem cell factor, integrin, or CXCL12 stimulation, R-Ras activity is inversely up-regulated. Expression of a constitutively active R-Ras mutant resulted in down-regulation of Rac1-activity whereas deletion of R-Ras led to an increase in Rac1/Rac2 activity and signaling. R-Ras(-/-) HPCs displayed a constitutively assembled cortical actin structure and showed increased directional migration. Rac1/Rac2 inhibition reversed the migration phenotype of R-Ras(-/-) HPCs, similar to that by expressing an R-Ras active mutant. Furthermore, R-Ras(-/-) mice showed enhanced responsiveness to G-CSF for HPC mobilization and exhibited decreased bone marrow homing. Transplantation experiments indicate that the R-Ras deficiency-induced HPC mobilization is a HPC intrinsic property. These results indicate that R-Ras is a critical regulator of Rac signaling required for HPC migration, homing, and mobilization.

Targeting the hematopoietic system for the treatment of Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent cause of dementia in humans. This disease is characterized by the presence of amyloid beta (Ab) deposits in the parenchyma (also known as amyloid plaques or senile plaques) and in the cerebral vasculature. Though Ab formation and deposits are strongly correlated with cognitive impairment, the mechanisms responsible for the synaptic dysfunctions and loss of neurons in AD remain largely unknown. Many studies have provided evidence that microglial cells are attracted to amyloid deposits both in human samples and in rodent transgenic models that develop this disease. We have recently found that blood-derived microglia and not their resident counterparts have the ability to eliminate amyloid deposits by a cell-specific phagocytic mechanism. These bone marrow-derived microglia have consequently a great therapeutic potential for AD patients. Molecular strategies aiming to improve their recruitment could lead to a new powerful tool for the elimination of toxic Ab and improve cognitive functions. However, numerous limitations have to be taken into consideration before recommending such a cellular therapy and these are discussed in the present review.

G-CSF downregulates natural killer cell-mediated cytotoxicity in donors for hematopoietic SCT

In G-CSF-mobilized hematopoietic SCT (HSCT), natural killer (NK) cells have a critical role in GVHD and GVL effects. However, regulation of NK cell response to G-CSF remains unclear. This study assayed G-CSF effects in both HSCT donors and NK-92MI cells. The donors who received G-CSF had significantly decreased NK cell cytotoxicity. Levels of phosphatidylinositol 3-kinase (PI3K) and phosphorylated (p)-Akt, but not mammalian target of rapamycin (mTOR), were downregulated in NK cells from G-CSF-injected donors. G-CSF also decreased cytotoxicity without affecting viability and NF-κB of NK-92MI cells. PI3K and p-ERK expression were also decreased in G-CSF-treated NK-92MI cells, and their inhibitors, wortmannin and PD98059, respectively, both enhanced the downregulation of cytotoxicity. These effects were accompanied by decreased expression of a cytotoxicity-related gene, triosephosphate isomerase (TPI). Wortmannin, but not PD98059, enhanced the downregulation of TPI in G-CSF-treated NK-92MI cells, indicating a correlation between PI3K and TPI. We conclude that G-CSF-impaired NK cell cytotoxicity may accompany PI3K/Akt signaling. The effect is transient and NK cells may recover after G-CSF clearance, suggesting that G-CSF-mobilized HSCT may benefit both acute GVHD prevention and late-phase GVL promotion in HSCT recipients.

Vagrant stem cells draft their gene companions

In a recent issue of Nature Medicine, Ryan et al. (2010) uncover genetic modifiers of G-CSF responses by hematopoietic progenitors. The authors document a negative role of EGFR signaling and, provided an analogous pathway functions in humans, propose a potential new angle to promote clinical blood stem cell mobilization.