Progenitor cell mobilization by granulocyte colony-stimulating factor controlled by loci on chromosomes 2 and 11

Cobalt protoporphyrin IX increases endogenous G-CSF and mobilizes HSC and granulocytes to the blood

Granulocyte colony‐stimulating factor (G‐CSF) is used in clinical practice to mobilize cells from the bone marrow to the blood; however, it is not always effective. We show that cobalt protoporphyrin IX (CoPP) increases plasma concentrations of G‐CSF, IL‐6, and MCP‐1 in mice, triggering the mobilization of granulocytes and hematopoietic stem and progenitor cells (HSPC). Compared with recombinant G‐CSF, CoPP mobilizes higher number of HSPC and mature granulocytes. In contrast to G‐CSF, CoPP does not increase the number of circulating T cells. Transplantation of CoPP‐mobilized peripheral blood mononuclear cells (PBMC) results in higher chimerism and faster hematopoietic reconstitution than transplantation of PBMC mobilized by G‐CSF. Although CoPP is used to activate Nrf2/HO‐1 axis, the observed effects are Nrf2/HO‐1 independent. Concluding, CoPP increases expression of mobilization‐related cytokines and has superior mobilizing efficiency compared with recombinant G‐CSF. This observation could lead to the development of new strategies for the treatment of neutropenia and HSPC transplantation.

The abundance of cis-acting loci leading to differential allele expression in F1 mice and their relationship to loci harboring genes affecting complex traits

Background

Genome-wide surveys have detected cis-acting quantitative trait loci altering levels of RNA transcripts (RNA-eQTLs) by associating SNV alleles to transcript levels. However, the sensitivity and specificity of detection of cis- expression quantitative trait loci (eQTLs) by genetic approaches, reliant as it is on measurements of transcript levels in recombinant inbred strains or offspring from arranged crosses, is unknown, as is their relationship to QTL’s for complex phenotypes.

Results

We used transcriptome-wide differential allele expression (DAE) to detect cis-eQTLs in forebrain and kidney from reciprocal crosses between three mouse inbred strains, 129S1/SvlmJ, DBA/2J, and CAST/EiJ and C57BL/6 J. Two of these crosses were previously characterized for cis-eQTLs and QTLs for various complex phenotypes by genetic analysis of recombinant inbred (RI) strains. 5.4 %, 1.9 % and 1.5 % of genes assayed in forebrain of B6/129SF1, B6/DBAF1, and B6/CASTF1 mice, respectively, showed differential allelic expression, indicative of cis-acting alleles at these genes. Moreover, the majority of DAE QTLs were observed to be tissue-specific with only a small fraction showing cis-effects in both tissues. Comparing DAE QTLs in F1 mice to cis-eQTLs previously mapped in RI strains we observed that many of the cis-eQTLs were not confirmed by DAE. Additionally several novel DAE-QTLs not identified as cis-eQTLs were identified suggesting that there are differences in sensitivity and specificity for QTL detection between the two methodologies. Strain specific DAE QTLs in B6/DBAF1 mice were located in excess at candidate genes for alcohol use disorders, seizures, and angiogenesis previously implicated by genetic linkage in C57BL/6J × DBA/2JF2 mice or BXD RI strains.

Conclusions

Via a survey for differential allele expression in F1 mice, a substantial proportion of genes were found to have alleles altering expression in cis-acting fashion. Comparing forebrain and kidney, many or most of these alleles were tissue-specific in action. The identification of strain specific DAE QTLs, can assist in assessment of candidate genes located within the large intervals associated with trait QTLs.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2922-9) contains supplementary material, which is available to authorized users.

Quantitative trait gene Slit2 positively regulates murine hematopoietic stem cell numbers

Hematopoietic stem cells (HSC) demonstrate natural variation in number and function. The genetic factors responsible for the variations (or quantitative traits) are largely unknown. We previously identified a gene whose differential expression underlies the natural variation of HSC numbers in C57BL/6 (B6) and DBA/2 (D2) mice. We now report the finding of another gene, Slit2, on chromosome 5 that also accounts for variation in HSC number. In reciprocal chromosome 5 congenic mice, introgressed D2 alleles increased HSC numbers, whereas B6 alleles had the opposite effect. Using gene array and quantitative polymerase chain reaction, we identified Slit2 as a quantitative trait gene whose expression was positively correlated with the number of HSCs. Ectopic expression of Slit2 not only increased the number of the long-term colony forming HSCs, but also enhanced their repopulation capacity upon transplantation. Therefore, Slit2 is a novel quantitative trait gene and a positive regulator of the number and function of murine HSCs. This finding suggests that Slit2 may be a potential therapeutic target for the effective in vitro and in vivo expansion of HSCs without compromising normal hematopoiesis.

Pten loss in the bone marrow leads to G-CSF-mediated HSC mobilization

Loss of the phosphatase and tumor suppressor gene PTEN induces G-CSF production in myeloid and stromal cells, thereby promoting HSCs mobilization from the bone marrow to the spleen and the initiation of lethal leukemia.

The phosphatase and tumor suppressor PTEN inhibits the phosphoinositol-3-kinase (PI3K) signaling pathway and plays a key role in cell growth, proliferation, survival, and migration. Pten conditional deletion using MxCre or Scl-CreER^T leads to splenomegaly and leukemia formation, which occurs after the relocation of normal hematopoietic stem cells (HSCs) from the bone marrow to the spleen. Unexpectedly, dormant HSCs in the bone marrow do not enter the cell cycle upon Pten loss, they do not lose self-renewal activity, and they are not exhausted. Instead, Pten deficiency causes an up-regulation of the PI3K pathway in myeloid cells, but not in HSCs. Strikingly, myeloid cells secrete high levels of G-CSF upon Pten loss, leading to the mobilization of HSCs from the bone marrow and accumulation in the spleen. After deletion of Pten in mice lacking G-CSF, the splenomegaly, myeloproliferative disease, and splenic HSC accumulation are rescued. Our data show that although PTEN has little if any role in normal HSCs, it is essential to prevent overt G-CSF production by myeloid and stromal cells which otherwise causes HSCs to relocate to the spleen followed by lethal leukemia initiation.

Quantitative trait mapping reveals a regulatory axis involving peroxisome proliferator-activated receptors, PRDM16, transforming growth factor-β2 and FLT3 in hematopoiesis

Hematopoiesis is the process whereby BM HSCs renew to maintain their number or to differentiate into committed progenitors to generate all blood cells. One approach to gain mechanistic insight into this complex process is the investigation of quantitative genetic variation in hematopoietic function among inbred mouse strains. We previously showed that TGF-β2 is a genetically determined positive regulator of hematopoiesis. In the presence of unknown nonprotein serum factors TGF-β2, but not TGF-β1 or -β3, enhances progenitor proliferation in vitro, an effect that is subject to mouse strain-dependent variation mapping to a locus on chr.4, Tb2r1. TGF-β2-deficient mice show hematopoietic defects, demonstrating the physiologic role of this cytokine. Here, we show that TGF-β2 specifically and predominantly cell autonomously enhances signaling by FLT3 in vitro and in vivo. A coding polymorphism in Prdm16 (PR-domain-containing 16) underlies Tb2r1 and differentially regulates transcriptional activity of peroxisome proliferator-activated receptor-γ (PPARγ), identifying lipid PPAR ligands as the serum factors required for regulation of FLT3 signaling by TGF-β2. We furthermore show that PPARγ agonists play a FLT3-dependent role in stress responses of progenitor cells. These observations identify a novel regulatory axis that includes PPARs, Prdm16, and TGF-β2 in hematopoiesis.

Effective mobilization of hematopoietic progenitor cells in G-CSF mobilization defective CD26-/- mice through AMD3100-induced disruption of the CXCL12-CXCR4 axis

OBJECTIVE

We previously reported that inhibition or loss of CD26 (DPPIV/dipeptidylpeptidase IV) results in a defect in normal mobilization of hematopoietic stem and progenitor cells induced by granulocyte-colony stimulating factor (G-CSF). This suggests that CD26 is a necessary component of the mobilization pathway. Our goal in this study was to determine whether mobilization can be induced by the CXCR4 antagonist AMD3100 in mice lacking CD26 (CD26(-/-)).

MATERIALS AND METHODS

Ten week old CD26(-/-) and C57BL/6 mice received a subcutaneous injection of AMD3100. One hour post-injection the mice were euthanized and peripheral blood and bone marrow were collected and evaluated.

RESULTS

AMD3100 mobilizes hematopoietic progenitors into the peripheral blood of CD26(-/-) and mice.

CONCLUSIONS

Our finding that AMD3100 rapidly mobilizes hematopoietic progenitor cells from the bone marrow into the periphery in CD26-deficient transgenic mice that otherwise exhibit a mobilization defect in response to G-CSF suggests that: (1) CD26 is downstream of G-CSF but upstream of the CXCL12-CXCR4 axis and (2) AMD3100 can be used as a single agent to mobilize hematopoietic stem and progenitor cells in normal donors or patients that have an intrinsic defect in their response to G-CSF treatment. Stem cell transplants are often the only curative treatment in some cancer patients. The ability to perform the transplantation and its success is dependent on the ability to mobilize adequate numbers of hematopoietic progenitor cells. The use of AMD3100 as a single agent would give patients or donors an additional option for a successful stem cell transplant.

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

Mobilization of hematopoietic stem and progenitor cells (HSPCs) from bone marrow into peripheral blood by the cytokine granulocyte colony-stimulating factor (G-CSF) has become the preferred source of HSPCs for stem cell transplants. However, G-CSF fails to mobilize sufficient numbers of stem cells in up to 10% of donors, precluding autologous transplantation in those donors or substantially delaying transplant recovery time. Consequently, new regimens are needed to increase the number of stem cells in peripheral blood upon mobilization. Using a forward genetic approach in mice, we mapped the gene encoding the epidermal growth factor receptor (Egfr) to a genetic region modifying G-CSF-mediated HSPC mobilization. Amounts of EGFR in HSPCs inversely correlated with the cells' ability to be mobilized by G-CSF, implying a negative role for EGFR signaling in mobilization. In combination with G-CSF treatment, genetic reduction of EGFR activity in HSPCs (in waved-2 mutant mice) or treatment with the EGFR inhibitor erlotinib increased mobilization. Increased mobilization due to suppression of EGFR activity correlated with reduced activity of cell division control protein-42 (Cdc42), and genetic Cdc42 deficiency in vivo also enhanced G-CSF-induced mobilization. Our findings reveal a previously unknown signaling pathway regulating stem cell mobilization and provide a new pharmacological approach for improving HSPC mobilization and thereby transplantation outcomes.

A quantitative trait locus on chromosome 4 affects cycling of hematopoietic stem and progenitor cells through regulation of TGF-beta 2 responsiveness

The hematopoietic stem and progenitor cell (HSPC) compartment is subject to extensive quantitative genetic variation. We have previously shown that TGF-beta2 at low concentrations enhances flt3 ligand-induced growth of HSPCs, while it is potently antiproliferative at higher concentrations. This in vitro enhancing effect was subject to quantitative genetic variation, for which a quantitative trait locus (QTL) was tentatively mapped to chromosome 4 (chr.4). Tgfb2(+/-) mice have a smaller and more slowly cycling HSPC compartment, which has a decreased serial repopulation capacity, and are less susceptible to the lethal effect of high doses of 5-fluorouracil. To unequivocally demonstrate that these phenotypes can be attributed to the enhancing effect of TGF-beta2 on HSPC proliferation observed in vitro and are therefore subject to mouse strain-dependent variation as well, we generated congenic mice where the telomeric region of chr.4 was introgressed from DBA/2 into C57BL/6 mice. In these mice, the enhancing effect of TGF-beta2 on flt3 signaling, but not the generic antiproliferative effect of high concentrations of TGF-beta2, was abrogated, confirming the location of this QTL, which we named tb2r1, on chr.4. These mice shared a smaller and more slowly cycling HSPC compartment and increased 5-fluorouracil resistance but not a decreased serial repopulation capacity with Tgfb2(+/-) mice. The concordance of phenotypes between Tgfb2(+/-) and congenic mice indicates that HSPC frequency and cycling are regulated by tb2r1, while an additional QTL in the telomeric region of chr.4 may regulate the serial repopulation capacity of hematopoietic stem cells.

The use of experimental murine models to assess novel agents of hematopoietic stem and progenitor cell mobilization

The recent explosion in the understanding of the cellular and molecular mechanisms underlying hematopoietic stem and progenitor cell (HSPC) mobilization has facilitated development of novel therapeutic agents, targeted at improving mobilization kinetics as well as HSPC yield. With the development of new agents comes the challenge of choosing efficient and relevant preclinical studies for the testing of the HSPC mobilization efficacy of these agents. This article reviews the use of the mouse as a convenient small animal model of HSPC mobilization and transplantation, and outlines the range of murine assays that can be applied to assess novel HSPC mobilizing agents. Techniques to demonstrate murine HSPC mobilization are discussed, as well as the role of murine assays to confirm human HSPC mobilization, and techniques to investigate the biologic phenotype of HSPC mobilized by these novel agents. Technical aspects regarding mobilization regimens and control arms, and choice of experimental animals are also discussed.

Combining transcriptional profiling and genetic linkage analysis to uncover gene networks operating in hematopoietic stem cells and their progeny

Stem cells are unique in that they possess both the capacity to self-renew and thereby maintain their original pool as well as the capacity to differentiate into mature cells. In the past number of years, transcriptional profiling of enriched stem cell populations has been extensively performed in an attempt to identify a universal stem cell gene expression signature. While stem-cell-specific transcripts were identified in each case, this approach has thus far been insufficient to identify a universal group of core “stemness” genes ultimately responsible for self-renewal and multipotency. Similarly, in the hematopoietic system, comparisons of transcriptional profiles between different hematopoietic cell stages have had limited success in revealing core genes ultimately responsible for the initiation of differentiation and lineage specification. Here, we propose that the combined use of transcriptional profiling and genetic linkage analysis, an approach called “genetical genomics”, can be a valuable tool to assist in the identification of genes and gene networks that specify “stemness” and cell fate decisions. We review past studies of hematopoietic cells that utilized transcriptional profiling and/or genetic linkage analysis, and discuss several potential future applications of genetical genomics.

Donor demographic and laboratory predictors of allogeneic peripheral blood stem cell mobilization in an ethnically diverse population

A reliable estimate of peripheral blood stem cell (PBSC) mobilization response to granulocyte colony-stimulating factor (G-CSF) may identify donors at risk for poor mobilization and help optimize transplantation approaches. We studied 639 allogeneic PBSC collections performed in 412 white, 75 black, 116 Hispanic, and 36 Asian/Pacific adult donors who were prescribed G-CSF dosed at either 10 or 16 microg/kg per day for 5 days followed by large-volume leukapheresis (LVL). Additional LVL (mean, 11 L) to collect lymphocytes for donor lymphocyte infusion (DLI) and other therapies was performed before G-CSF administration in 299 of these donors. Day 5 preapheresis blood CD34(+) cell counts after mobilization were significantly lower in whites compared with blacks, Hispanics, and Asian/Pacific donors (79 vs 104, 94, and 101 cells/microL, P < .001). In addition, donors who underwent lymphapheresis before mobilization had higher CD34(+) cell counts than donors who did not (94 vs 79 cells/microL, P < .001). In multivariate analysis, higher post-G-CSF CD34(+) cell counts were most strongly associated with the total amount of G-CSF received, followed by the pre-G-CSF platelet count, pre-G-CSF mononuclear count, and performance of prior LVL for DLI collection. Age, white ethnicity, and female gender were associated with significantly lower post-G-CSF CD34(+) cell counts.

Identification of quantitative trait loci regulating haematopoietic parameters in B6AKRF2 mice

The haematopoietic system is a complex organised tissue with a hierarchical structure. Identification of organisational pathways within the haematopoietic system is relevant for a better understanding of haematopoiesis in health and disease. We have analysed numerous haematopoietic parameters in two panels of a total of 157 genetically distinct B6AKRF2 mice, derived from an intercross between AKR and C57Bl/6 mice, strains known to differ in various stem cell traits. The major objective of our study was to assess the extent to which various haematopoietic parameters, such as stem cell numbers, progenitor cell cycling, progenitor cell mobilisation and neutrophil numbers in blood and bone marrow are coregulated. The genotypes of these mice were used to search for genetic loci that regulate these parameters. We found significant quantitative trait loci (QTL) associated with the number of stem cells (CAFC-35) in the bone marrow and the number of neutrophils in the blood. However, most haematopoietic parameters appeared to be controlled by non-heritable (epigenetic) factors, or by multiple QTLs. Our study reveals striking differences in structure of the haematopoietic hierarchy between individual mice. Surprisingly, stem and progenitor cell pool size and proliferation rate, as well as peripheral blood cell counts are all independently regulated.

Genes and Susceptibility to Leishmaniasis

Leishmania are digenetic protozoa which inhabit two highly specific hosts, the sandfly where they grow as motile, flagellated promastigotes in the gut, and the mammalian macrophage where they grow intracellularly as non-flagellated amastigotes. Leishmaniasis is the outcome of an evolutionary 'arms race' between the host's immune system and the parasite's evasion mechanisms which ensure survival and transmission in the population. The spectrum of disease manifestations and severity reflects the interaction between the genome of the host and that of the parasite, and the pathology is caused by a combination of host and parasite molecules. This chapter examines the genetic basis of host susceptibility to disease in humans and animal models. It describes the genetic tools used to map and identify susceptibility genes, and the lessons learned from murine and human cutaneous leishmaniasis.

The Positive Regulatory Effect of TGF-β2 on Primitive Murine Hemopoietic Stem and Progenitor Cells Is Dependent on Age, Genetic Background, and Serum Factors

TGF-beta is considered a negative regulator of hemopoietic stem and progenitor cells. We have previously shown that one TGF-beta isoform, TGF-beta2, is, in fact, a positive regulator of murine hemopoietic stem cell function in vivo. In vitro, TGF-beta2, but not TGF-beta1 and TGF-beta3, had a biphasic dose response on the proliferation of purified lin-Sca1(++)kit(+) (LSK) cells, with a stimulatory effect at low concentrations, which was subject to mouse strain-dependent variation. In this study we report that the stimulatory effect of TGF-beta2 on the proliferation of LSK cells increases with age and after replicative stress in C57BL/6, but not in DBA/2, mice. The age-related changes in the TGF-beta2 effect correlated with life span in BXD recombinant strains. The stimulatory effect of TGF-beta2 on the proliferation of LSK cells requires one or more nonprotein, low m.w. factors present in fetal calf and mouse sera. The activity of this factor(s) in mouse serum increases with age. Taken together, our data suggest a role for TGF-beta2 and as yet unknown serum factors in the aging of the hemopoietic stem cell compartment and possibly in organismal aging.

The biology of hematopoietic stem cells

Rarely has so much interest from the lay public, government, biotechnology industry, and special interest groups been focused on the biology and clinical applications of a single type of human cell as is today on stem cells, the founder cells that sustain many, if not all, tissues and organs in the body. Granting organizations have increasingly targeted stem cells as high priority for funding, and it appears clear that the evolving field of tissue engineering and regenerative medicine will require as its underpinning a thorough understanding of the molecular regulation of stem cell proliferation, differentiation, self-renewal, and aging. Despite evidence suggesting that embryonic stem (ES) cells might represent a more potent regenerative reservoir than stem cells collected from adult tissues, ethical considerations have redirected attention upon primitive cells residing in the bone marrow, blood, brain, liver, muscle, and skin, from where they can be harvested with relative sociological impunity. Among these, it is arguably the stem and progenitor cells of the mammalian hematopoietic system that we know most about today, and their intense study in rodents and humans over the past 50 years has culminated in the identification of phenotypic and molecular genetic markers of lineage commitment and the development of functional assays that facilitate their quantitation and prospective isolation. This review focuses exclusively on the biology of hematopoietic stem cells (HSCs) and their immediate progeny. Nevertheless, many of the concepts established from their study can be considered fundamental tenets of an evolving stem cell paradigm applicable to many regenerating cellular systems.

Current mechanistic scenarios in hematopoietic stem/progenitor cell mobilization

Uncovering the molecular mechanisms governing the exit of stem/progenitor cells from bone marrow to peripheral blood at steady state or after their enforced migration has been an ongoing challenge. Recently, however, several new avenues or paradigms in mobilization have emerged from ever-expanding work in humans subjected to granulocyte colony-stimulating factor (G-CSF) mobilization, as well as from studies in normal and gene-deficient mouse models. Although these developments represent notable advances that met with considerable excitement, they have been quenched by surprising vacillations in subsequent research. This perspective highlights recent developments in mobilization along with their controversies. A full understanding of the directional cues that control the migratory behavior and the fate of stem/progenitor cells once they migrate out of bone marrow will await further experimentation, aiming to bridge our current gaps in knowledge.

Quantitative genetic variation in the hematopoietic stem cell and progenitor cell compartment and in lifespan are closely linked at multiple loci in BXD recombinant inbred mice

The number of bone marrow hematopoietic stem and progenitor cells as defined by the lineage(-), Sca1(++), c-kit(+) (LSK) phenotype and their proliferative capacity in vitro are subject to quantitative genetic variation, and several quantitative trait loci (QTL) have been identified in young mice. Because some traits affecting hematopoiesis also change with age in a mouse strain-dependent fashion, we performed quantitative trait analysis in aged BXD recombinant inbred (RI) mice for the number and frequency of LSK cells, and for their proliferative capacity in vitro. Several novel QTL were identified. The number and frequency of LSK cells in old mice correlated inversely with lifespan. Furthermore, 4 of 7 lifespan QTL overlap with QTL contributing to the number, frequency, or proliferative capacity of LSK cells in young or old mice. Taken together, these data establish a close genetic, and perhaps functional, link between genetic variation in lifespan and characteristics of stem and progenitor cells.

Genetic analysis of progenitor cell mobilization by granulocyte colony-stimulating factor: verification and mechanisms for loci on murine chromosomes 2 and 11

OBJECTIVE

It is notable that there is significant inter-individual variability in humans and inter-strain variability in mice in the ability to mobilize hematopoietic stem and progenitor cells, suggesting that there is genetic regulation of mobilization. In the murine system, loci on chromosomes 2 and 11 have been linked to an inter-strain variation in granulocyte colonystimulating factor (G-CSF)-induced stem cell mobilization proficiency. The aim of this study was to verify this linkage and to gain insight into the function of these loci.

METHODS

Animals congenic for the loci on chromosomes 2 and 11 were generated by a speed-congenic approach and the function of the loci were further analyzed in doubly congenic animals and with a competitive transplantation/mobilization protocol.

RESULTS

The analysis of congenic animals verified that both loci are linked to mobilization proficiency. Analysis of mobilization in doubly congenic animals suggested that both loci act in the same regulatory pathway. Mobilization experiments conducted with mice that had previously been competitively repopulated with congenic and parental-strain BM revealed that the locus on chromosome 11 operates via a progenitor cell-intrinsic mechanism.

CONCLUSION

We confirmed linkage of loci on chromosomes 2 and 11 to G-CSF-induced mobilization and thus validated their role as regulators of hematopoietic progenitor cell mobilization in mice. These findings will be useful for further studies directed at identifying genes that regulate mobilization proficiency.

A mouse-based strategy for cyclophosphamide pharmacogenomic discovery

Genome-wide mapping approaches are needed to more fully understand the genetic basis of chemotherapy response. Because of technical and ethical limitations, cancer pharmacogenomics has not yet benefited from traditional robust familial genetic strategies. We have therefore explored the use of the inbred mouse as a genetic model system in which to study response to the cytotoxic agent cyclophosphamide. Multiple phenotypes have been assessed in response to cyclophosphamide in up to 19 inbred mouse strains, including in vitro hematopoietic progenitor cell toxicity and the mobilization of hematopoietic progenitor cells into peripheral blood. Hematopoietic progenitor cell toxicity in vitro varied 2-fold among strains, whereas in vivo progenitor cell mobilization varied almost 75-fold among strains. Males mobilized more hematopoietic progenitor cells than did females, and the low-mobilization phenotype was dominant to the high-mobilization phenotype in F1 hybrid animals. In an initial attempt to analyze candidate genes, genetic variation was assessed in three cytochrome P-450 genes involved in the metabolism of cyclophosphamide. Resequencing of eight strains identified 26 polymorphisms in these genes that may influence response to cyclophosphamide. Distinct regions of high- and low-polymorphism rates were identified, and two common haplotypes were shared among the strains for each gene that exhibited variation. This phenotypic and genotypic variation among inbred strains provides a framework for cyclophosphamide pharmacogenomic discovery.

Cell surface peptidase CD26/DPPIV mediates G-CSF mobilization of mouse progenitor cells

CXC ligand 12 (CXCL12; also known as stromal cell-derived factor 1alpha/SDF-1alpha) chemoattracts hematopoietic stem and progenitor cells (HSCs/HPCs) and is thought to play a crucial role in the mobilization of HSCs/HPCs from the bone marrow. CD26 (dipeptidylpeptidase IV [DPPIV]) is a membrane-bound extracellular peptidase that cleaves dipeptides from the N-terminus of polypeptide chains. CD26 has the ability to cleave CXCL12 at its position-2 proline. We found by flow cytometry that CD26 is expressed on a subpopulation of normal Sca-1+c-kit+lin- hematopoietic cells isolated from mouse bone marrow, as well as Sca-1+c-kit-lin- cells, and that these cells possess CD26 peptidase activity. To test the functional role of CD26 in CXCL12-mediated normal HSC/HPC migration, chemotaxis assays were performed. The CD26 truncated CXCL12(3-68) showed an inability to induce the migration of sorted Sca-1+c-kit+lin- or Sca-1+c-kit-lin- mouse marrow cells compared with the normal CXCL12. In addition, CXCL12(3-68) acts as an antagonist, resulting in the reduction of migratory response to normal CXCL12. Treatment of Sca-1+c-kit+lin- mouse marrow cells, and myeloid progenitors within this population, or Sca-1+c-kit-lin- cells with a specific CD26 inhibitor, enhanced the migratory response of these cells to CXCL12. Finally, to test for potential in vivo relevance of these in vitro observations, mice were treated with CD26 inhibitors during granulocyte colony-stimulating factor (G-CSF)-induced mobilization. This treatment resulted in a reduction in the number of progenitor cells in the periphery as compared with the G-CSF regimen alone. This suggests that a mechanism of action of G-CSF mobilization involves CD26.

Genetically determined variation in the number of phenotypically defined hematopoietic progenitor and stem cells and in their response to early-acting cytokines

Quantitative trait analysis may shed light on mechanisms regulating hematopoiesis in vivo. Strain-dependent variation existed among C57BL/6 (B6), DBA/2, and BXD recombinant inbred mice in the responsiveness of primitive progenitor cells to the early-acting cytokines kit ligand, flt3 ligand, and thrombopoietin. A significant quantitative trait locus was found on chromosome 2 that could not be confirmed in congenic mice, however, probably because of epistasis. Because it has been shown that alleles of unknown X-linked genes confer a selective advantage to hematopoietic stem cells in vivo in humans and in cats, we also analyzed reciprocal male D2B6F1 and B6D2F1 mice, revealing an X-linked locus regulating the responsiveness of progenitor and stem cells to early-acting factors. Among DBA/2, B6, and BXD recombinant inbred mice, correlating genetic variation was found in the absolute number and frequency of Lin(-)Sca1(++)kit(+) cells, which are highly enriched in hematopoietic progenitor and stem cells, and in the number of Lin(-)Sca1(++)kit(-) cells, a population whose biologic significance is unknown, suggesting that both populations are functionally related. Suggestive quantitative trait loci (QTLs) for the number of Lin(-)Sca1(++) cells on chromosomes 2, 4, and 7 were confirmed in successive rounds of mapping. The locus on chromosome 2 was confirmed in congenic mice. We thus demonstrated genetic variation in the response to cytokines critical for hematopoiesis in vivo and in the pool size of cells belonging to a phenotype used to isolate essentially pure primitive progenitor and stem cells, and we identified loci that may be relevant to the regulation of hematopoiesis in steady state.

Stem cells from birth to death: The history and the future

The concept that adult stem cells, despite their impressive proliferative potential, are immortal has been challenged by experimental studies of hematopoietic stem cells. In this review, we discuss the properties that characterize a stem cell, the growing list of tissues in which stem cells are found, how they can be identified and isolated, how stem cells may transdifferentiate, and the findings that illustrate how age affects the hematopoietic stem cell population. We propose that an aging stem cell population affects tissue and organ homeostasis, particularly in response to environmental stresses, and we hypothesize that through this mechanism the functional status of stem cells affects the longevity of the organism.

Association between the SDF1-3'A allele and high levels of CD34(+) progenitor cells mobilized into peripheral blood in humans

Some patients unexpectedly fail to mobilize sufficient numbers of haematopoietic progenitor cells (HPCs) into the peripheral blood for autologous transplantation. Considering the important role of the chemokine stromal cell-derived factor 1 (SDF-1) in HPC homing, we investigated a possible relationship between SDF1 gene polymorphism and HPC mobilization capacity in 63 patients with malignancy. Some 67% of the good mobilizers (> or = 50 CD34(+) cells/microl) and only 36% of the intermediate/poor mobilizers were SDF1-3'A allele carriers (P = 0.032). In multivariate analysis, the presence of the SDF1-3'A allele was the only factor predictive of good CD34(+) cell mobilization (P = 0.025). This is the first report showing the involvement of genetic factors for HPC mobilization in humans and suggests a significant role for SDF-1 in this process.

Autonomous behavior of hematopoietic stem cells

Mechanisms that affect the function of primitive hematopoietic stem cells with long-term proliferative potential remain largely unknown. Here we assessed whether properties of stem cells are cell-extrinsically or cell-autonomously regulated. We developed a model in which two genetically and phenotypically distinct stem cell populations coexist in a single animal. Chimeric mice were produced by transplanting irradiated B6D2F1 (BDF1) recipients with mixtures of DBA/2 (D2) and C57BL/6 (B6) day-14 fetal liver cells. We determined the mobilization potential, proliferation, and frequency of D2 and B6 stem and progenitor cells in animals with chimeric hematopoiesis. After granulocyte colony-stimulating factor (G-CSF) administration, peripheral blood D2 colony-forming units granulocyte-macrophage were fourfold to eightfold more numerous than B6 progenitors. We determined that D2 and B6 progenitors maintained their genotype-specific cycling activity in BDF1 recipients. Chimeric marrow was harvested and D2 and B6 cell populations were separated by flow cytometry. Cobblestone area-forming cell (CAFC) analysis of sorted marrow showed that the number of late appearing CAFC subsets within the D2 cell population was approximately threefold higher than within the B6 fraction. We performed secondary transplantation using unfractionated chimeric marrow, which was given in limiting doses to lethally irradiated BDF1 recipients. Comparison of the proportion of animals possessing D2 and/or B6 leukocytes 5 months after transplant revealed that the frequency of D2 LTRA was approximately 10-fold higher than B6 LTRA numbers. Our data demonstrate that genetically distinct stem cell populations, coexisting in individual animals, independently maintain their parental phenotypes, indicating that stem cell properties are predominantly regulated cell-autonomously.

Efficient mobilization of haematopoietic progenitors after a single injection of pegylated recombinant human granulocyte colony-stimulating factor in mouse strains with distinct marrow-cell pool sizes

We have compared the efficacy of a single injection of SD/01, a newly engineered, pegylated form of recombinant human granulocyte colony stimulating factor (rhG-CSF), with a single injection of glycosylated rhG-CSF (Filgrastim). SD/01 was administered to regular and recombinant inbred strains of mice (AKR, C57L/J, DBA/2, C57BL/6, AKXL) known to have widely distinct marrow-cell pool sizes and proliferation kinetics. A single injection of G-CSF was unable to mobilize granulocyte-macrophage colony-forming units (CFU-GM). In sharp contrast, a single dose of SD/01 resulted in massive mobilization of progenitors and stem cells. Although all mice strains showed qualitatively similar mobilization responses, large interstrain differences remained. C57L and C57BL/6 mice mobilized relatively poorly, whereas AKR and DBA/2 mice showed threefold to tenfold superior responses. In order to explain these different phenotypes, we studied the effects of SD/01 in nine AKXL recombinant inbred strains, derived from well-responding AKR and poorly responding C57L parental strains. The best predictor for SD/01 responsiveness in these strains was marrow cellularity prior to mobilization. Comparison of the AKXL strain distribution pattern for marrow cellularity with loci previously mapped in these strains showed complete concordance with Aat, a serine protease inhibitor mapping to chromosome 12.