Identification of Bipotent Basophil/Mast Cell Progenitors in Adult Murine Hematopoiesis.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 633-633
Author(s):  
Yojiro Arinobu ◽  
Hiromi Iwasaki ◽  
Michael F. Gurish ◽  
Shinichi Mizuno ◽  
Hirokazu Shigematsu ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Mast Cell ◽  
Mast Cells ◽  
Cell Fate ◽  
Bone Marrow Cells ◽  
Cell Lineage ◽  
Primary Role ◽  
Peripheral Tissues ◽  
Fate Decision

Abstract Basophils and mast cells are multifunctional hematopoietic effectors that co-operate to mount a variety of allergic and innate immune responses. Their origin and developmental relationships, however, have not yet been resolved, and remain as one of the major issues in the biology of hematopoiesis. Here we report that progenitors bipotent for basophils and mast cells(basophil/mast cell progenitors: BMCPs) are prospectively isolatable within murine spleen. We have shown that the β7-integrin(β7) is an essential molecule for tissue-specific homing of putative precursors for intestinal mast cells (J Exp Med194:1243, 2001). To identify a candidate population that seeds intestinal progenitors for mast cells, we searched for β7+ cells in the bone marrow and the spleen. Lin−c-Kit+ spleen cells contained a fraction of cells expressing β7 at high levels. They also expressed FcγRII/III, but the majority of these cells did not express FcεRIα. These Lin−c-Kit+FcγRII/III+β7hiFcεRIα−/locells exclusively differentiated into mature mast cells and basophils. Strikingly, single Lin−c-Kit+FcγRII/III+β7hiFcεRIα−/locells formed colonies containing both basophils and mast cells as well as pure mast cell or basophil colonies. We thus named these cells as BMCPs. In 2-day cultures, purified BMCPs upregulated FcεRIα, giving rise to Lin−CD34+FcεRIαhic-Kit+ and Li− CD34+FcεRIαhic-Kit− blastic cell populations, and they differentiated exclusively into mast cells and basophils, respectively. Based on this phenotype, we searched for precursors committed to either lineage in vivo. The Lin−CD34+ bone marrow cells contained FcεRIαhic-Kit−cells, which differentiated exclusively into basophils. We named this population as basophil progenitors (BaPs). Since mast cell progenitors(MCPs) were not isolatable as a distinct population in the bone marrow or the spleen, we searched for MCPs in the intestine. We newly identified CD45+Li− CD34+β7hiFcεRIαlocells in the intestine, and these cells exclusively formed pure mast cell colonies, which were named as intestinal MCPs. Since the expression of C/EBPα was dramatically increased in BaPs but was downregulated in MCPs, we hypothesized that it plays a key role in the basophil versus the mast cell lineage commitment. To test this hypothesis, we disrupted or overexpressed C/EBPα at the BMCP stage. BMCPs disrupted with C/EBPα gave rise exclusively to mast cells, while, BMCPs overexpressing C/EBPα differentiated mainly into basophils, suggesting that C/EBPα plays a primary role in deciding the basophil vs. mast cell fate at the BMCP stage. Thus, differentiation of the BMCPs into committed progeny may lead to selective migration, BaPs to the bone marrow or MCPs to peripheral tissues, and this fate decision is controlled principally by C/EBPα. These newly identified progenitors should be useful to analyze the mechanism of commitment into each of these lineages, and could also be therapeutic targets for a variety of allergic and autoimmune disorders.

scholarly journals Leukotriene B4, an activation product of mast cells, is a chemoattractant for their progenitors

2005 ◽  
Vol 201 (12) ◽  
pp. 1961-1971 ◽  
Author(s):  
Charlotte L. Weller ◽  
Sarah J. Collington ◽  
Jeremy K. Brown ◽  
Hugh R.P. Miller ◽  
Adam Al-Kashi ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Mast Cell ◽  
Mast Cells ◽  
Bone Marrow Cells ◽  
Marrow Cell ◽  
The Body ◽  
Active Principle ◽  
Human Cord Blood ◽  
Hematopoietic Stem

Mast cells are tissue-resident cells with important functions in allergy and inflammation. Pluripotential hematopoietic stem cells in the bone marrow give rise to committed mast cell progenitors that transit via the blood to tissues throughout the body, where they mature. Knowledge is limited about the factors that release mast cell progenitors from the bone marrow or recruit them to remote tissues. Mouse femoral bone marrow cells were cultured with IL-3 for 2 wk and a range of chemotactic agents were tested on the c-kit+ population. Cells were remarkably refractory and no chemotaxis was induced by any chemokines tested. However, supernatants from activated mature mast cells induced pronounced chemotaxis, with the active principle identified as leukotriene (LT) B4. Other activation products were inactive. LTB4 was highly chemotactic for 2-wk-old cells, but not mature cells, correlating with a loss of mRNA for the LTB4 receptor, BLT1. Immature cells also accumulated in vivo in response to intradermally injected LTB4. Furthermore, LTB4 was highly potent in attracting mast cell progenitors from freshly isolated bone marrow cell suspensions. Finally, LTB4 was a potent chemoattractant for human cord blood–derived immature, but not mature, mast cells. These results suggest an autocrine role for LTB4 in regulating tissue mast cell numbers.

scholarly journals Distribution of mast-cell precursors in hematopoeitic and lymphopoietic tissues of mice.

1979 ◽  
Vol 150 (3) ◽  
pp. 482-490 ◽  
Author(s):  
Y Kitamura ◽  
M Shimada ◽  
S Go ◽  
H Matsuda ◽  
K Hatanaka ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Mast Cell ◽  
Mast Cells ◽  
Bone Marrow Cells ◽  
Cell Number ◽  
Precursor Cells ◽  
Lymphoid Cells ◽  
Experimental Systems ◽  
Chediak Higashi Syndrome

Two experimental systems were used to investigate the origin of precursor cells which differentiate into tissue mast cells in vivo. (a) Increase of mast cell number was examined in the skin, stomach, cecum, and mesentery of genetically mast cell-depleted WBB6F1 (WB X C57BL/6)-W/WV mice after the injection of various hematolymphoid cells of congenic +/+ mice. (b) Appearance of mast cells with giant granules was studied in irradiated C57BL/6-+/+ mice after the injection of lymphoid cells of C57BL/6-bgJ/bgJ (beige, Chediak-Higashi syndrome) mice. Concentrations of mast cell precursors in the thymus, lymph node and Peyer's patch were less than 0.1% of the concentration in the bone marrow. Neither treatment of donor bone marrow cells with anti-Thy-1.2 serum and complement nor thymectomy of the recipient mice affects the development of mast cells in the skin, stomach, cecum, and mesentery. Moreover, the number of mast cells increased to normal level when the skin of WBB6F1-W/WV mice was grafted on the back of nude athymic (BALB/c-nu/nu) mice. These results indicate that mast cell precursors are derived from hematopoietic tissues rather than lymphopoetic ones and that the differentiation of the precursor cells does not depend on T lymphocytes or the thymus.

scholarly journals Changes in numbers and types of mast cell colony-forming cells in the peritoneal cavity of mice after injection of distilled water: evidence that mast cells suppress differentiation of bone marrow-derived precursors

Blood ◽  
1988 ◽  
Vol 71 (3) ◽  
pp. 573-580 ◽  
Author(s):  
Y Kanakura ◽  
A Kuriu ◽  
N Waki ◽  
T Nakano ◽  
H Asai ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Mast Cell ◽  
Mast Cells ◽  
Peritoneal Cavity ◽  
Bone Marrow Cells ◽  
Water Injection ◽  
Lymphoid Cells ◽  
Distilled Water ◽  
Peritoneal Mast Cells ◽  
Chediak Higashi Syndrome

Abstract Two different types of cells in the peritoneal cavity of mice produce mast cell colonies in methylcellulose. “Large” mast cell colonies are produced by bone marrow-derived precursors resembling lymphoid cells by light microscopy (L-CFU-Mast), whereas “medium” and “small” mast cell colonies are produced by morphologically identifiable mast cells (M-CFU- Mast and S-CFU-Mast, respectively). In the present study we eradicated peritoneal mast cells by intraperitoneal (IP) injection of distilled water. The regeneration process was investigated to clarify the relationship between L-CFU-Mast, M-CFU-Mast, and S-CFU-Mast. After injection of distilled water, M-CFU-Mast and S-CFU-Mast disappeared, but L-CFU-Mast increased, and then M-CFU-Mast and S-CFU-Mast appeared, suggesting the presence of a hierarchic relationship. When purified peritoneal mast cells were injected two days after the water injection, the L-CFU-Mast did not increase. In the peritoneal cavity of WBB6F1-+/+ mice that had been lethally irradiated and rescued by bone marrow cells of C57BL/6-bgJ/bgJ (beige, Chediak-Higashi syndrome) mice, L-CFU-Mast were of bgJ/bgJ type, but M-CFU-Mast and S-CFU-Mast were of +/+ type. The injection of distilled water to the radiation chimeras resulted in the development of bgJ/bgJ-type M-CFU-Mast and then S-CFU-Mast. The presence of mast cells appeared to suppress the recruitment of L-CFU- Mast from the bloodstream and to inhibit the differentiation of L-CFU- Mast to M-CFU-Mast.

scholarly journals Rescue of W-associated mast cell defects in W/Wv bone marrow cells by ectopic expression of normal and mutant epidermal growth factor receptors

Blood ◽  
1993 ◽  
Vol 82 (5) ◽  
pp. 1463-1470
Author(s):  
T von Ruden ◽  
L Stingl ◽  
A Ullrich ◽  
EF Wagner
Keyword(s):  
Signal Transduction ◽  
Bone Marrow ◽  
Mast Cell ◽  
Growth Factor ◽  
Mast Cells ◽  
Epidermal Growth Factor ◽  
Bone Marrow Cells ◽  
Ectopic Expression ◽  
Tissue Type ◽  
Epidermal Growth

Abstract The normal human epidermal growth factor receptor (EGF-R) (HERc), a chimeric EGF-R/v-erbB (HERerbB) receptor, and the ligand-independent oncogenic EGF-R variant (v-erbB) were used to correct the mast cell defects in W/Wv bone marrow (BM) cells. In culture, all three receptor molecules transduced functional mitogenic signals in infected interleukin-3 (IL-3)-dependent bone marrow-derived mast cells (BMMCs) and enabled their differentiation into safranin-positive mast cells resembling connective tissue-type mast cells (CTMCs). Furthermore, expression of these receptors restored the capacity of W/Wv BMMCs to colonize the peritoneal cavity of mast cell-deficient W/Wv mice where they differentiated to safranin-positive cells with similar frequencies as wild-type BMMCs. These experiments show that expression of normal and mutant EGF-Rs in W/Wv BM cells is able to complement the function of the c-kit-encoded Steel factor receptor (SLF-R) in mast cell development. We conclude that signal transduction by normal and mutant EGF-Rs in murine hematopoietic cells apparently involves components also used by the SLF-R, which suggests that these receptors use overlapping pathways for signal transduction.

scholarly journals The Role of Prep1 in the Regulation of Mesenchymal Stromal Cells

2019 ◽  
Vol 20 (15) ◽  
pp. 3639 ◽  
Author(s):  
Giorgia Maroni ◽  
Daniele Panetta ◽  
Raffaele Luongo ◽  
Indira Krishnan ◽  
Federica La Rosa ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Cell Fate ◽  
Mesenchymal Stromal Cells ◽  
Stromal Cells ◽  
Molecular Mechanisms ◽  
Gene Dosage ◽  
Homeobox Gene ◽  
Fate Decision

Molecular mechanisms governing cell fate decision events in bone marrow mesenchymal stromal cells (MSC) are still poorly understood. Herein, we investigated the homeobox gene Prep1 as a candidate regulatory molecule, by adopting Prep1 hypomorphic mice as a model to investigate the effects of Prep1 downregulation, using in vitro and in vivo assays, including the innovative single cell RNA sequencing technology. Taken together, our findings indicate that low levels of Prep1 are associated to enhanced adipogenesis and a concomitant reduced osteogenesis in the bone marrow, suggesting Prep1 as a potential regulator of the adipo-osteogenic differentiation of mesenchymal stromal cells. Furthermore, our data suggest that in vivo decreased Prep1 gene dosage favors a pro-adipogenic phenotype and induces a “browning” effect in all fat tissues.

Thrombopoietin Regulates Proliferation and Maturation of Murine Mast Cells.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 1707-1707
Author(s):  
Giovanni Migliaccio ◽  
Barbara Ghinassi ◽  
Lucia Centurione ◽  
Maria Zingariello ◽  
Lucia Bianchi ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Mast Cell ◽  
Cell Differentiation ◽  
Growth Factor ◽  
Mast Cells ◽  
Wild Type ◽  
Connective Tissues ◽  
Immature Cells

Abstract Megakaryocytopoiesis is regulated by extrinsic (interaction of the growth factor thrombopoietin, TPO with its receptor Mpl) and intrinsic (interaction between the trascription factors GATA-1 and Fog-1) factors. The observation that mice impaired for GATA-1 expression (i.e. harbouring the GATA-1low mutation) are defective not only in megakaryocyte maturation but also in mast cell differentiation (Migliaccio et al. J Exp Med197:281, 2003), led us to investigate whether TPO might control mast cell differentiation as well. We first observed that mice genetically unable to responde to TPO (Mplnull mice) express in the connective tissues 5 times more mast cells than their normal littermates. Then, we analysed the effects on mast cell differentiation of in vivo treatment with TPO. Normal mice, and their GATA-1low littermates, were injected i.p. with TPO (100 μg/kg/day per 5 days, kindly provided by Kirin Brewery, Japan) and the number of immature (Toluidinepos) and mature (AlcianBlue/Saphraninepos) mast cells present in the connective tissues of the animals, as well as the frequency of GATA-1pos and TUNELpos mast cells, was evaluated 14 days after treatment. In wild-type animals, TPO reduced the presence of GATA-1 in mast cells (by immuno-histochemistry) and increased the number of immature cells (from 320±28 to 852±60) and of those undergoing apoptosis (from 16±1 to 600±43). In contrast, in GATA-1low animals, TPO-treatment induced the expression of GATA-1 in mast cells while decreased the number of immature cells (from 1100±72 to 427±29) as well as that of apoptotic cells (from 600±45 to 60±2). The role of TPO on mast cell differentiation were further confirmed by the analysis of the effects exerted by the growth factor on in vitro differentiation of bone marrow derived mast cells (BMMC). In these experiments, wild type bone marrow and spleen cells were cultured for 21 days with SCF and IL-3 with or without TPO and BMMC differentiation measured on the basis of the number of cells expressing the phenotype c-kithigh/CD34high and FcεRIpos. In cultures stimulated with SCF and IL-3, all the cells expressed the phenotype c-kithigh/CD34high and FcεRIpos. In contrast, in cultures supplemented also with SCF, IL-3 and TPO, only 25% of the cells were c-kithigh/CD34high and none of them was FcεRIpos. These results establish a role for TPO in the control of mast cell differentiation (possibly by modulating the GATA-1 content of the cells) and unveil further similarities between the mechanism(s) controlling megakaryocyte and mast cell differentiation.

Differential Role of Class 1A PI 3-Kinase Regulatory Subunits in Mast Cell Growth, Maturation and Survival.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 77-77
Author(s):  
Raghuveer Mali ◽  
Subha Krishnan ◽  
Ramdas Baskar ◽  
Veerendra Munugalavadla ◽  
Emily Sims ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Mast Cell ◽  
Mast Cells ◽  
Bone Marrow Cells ◽  
Full Length ◽  
Receptor Internalization ◽  
Regulatory Subunits ◽  
Growth And Survival ◽  
Cell Functions ◽  
Kit Receptor

Abstract Abstract 77 Stem cell factor (SCF) mediated c-Kit receptor activation plays a pivotal role in mast cell growth, maturation and survival. However, the signaling events downstream from c-Kit are poorly understood. Mast cells express multiple regulatory subunits of class 1A PI 3-kinase including p85α, p85β, p50α, and p55α. While it is known that PI 3-kinase plays an essential role in mast cells; the precise mechanism by which these regulatory subunits impact specific mast cell functions including maturation, growth, and survival are not known. Using mice deficient in the expression of p85α or p85β or combination of both p85α/p55α/p50α as well as all four subunits we have examined the role of these subunits in mast cell functions. We show that loss of p85α subunit alone results in impaired bone marrow derived mast cell (BMMC) maturation, growth, and survival compared to wild-type (WT) controls, in spite of the continuous expression of p85β, p55α, and p50α subunits in these cells. Restoring the expression of p85α in p85α deficient mast cells restores the maturation and growth defects. To assess the contribution of p50α and p55α subunits, we generated mice using the Cre lox system that were deficient in the expression of all three subunits (i.e. p85α/p55α/p50α). Deficiency of p85α/p55α/p50α subunits in bone marrow cells completely blocked mast cell maturation and growth, suggesting an essential role for the smaller subunits p50 and p55 in addition to the full length form of p85. Curiously, over-expression of p50α in p85α deficient BMMCs only marginally rescued mast cell maturation and growth, suggesting that the full length form of p85α functions with specificity in regulating mast cell functions. Since the major difference between the shorter isoforms and the full length form of p85α is the absence of the amino terminal SH3 and BH domains, we generated two mutants of p85α lacking either the SH3 or the BH domain and expressed them in p85α−/− BMMCs. While both these mutants completely restored the maturation defect associated with p85α deficiency and showed normal binding to the c-Kit receptor upon SCF stimulation as well as to the p110 catalytic subunits; none of these mutants completely rescued SCF induced proliferation (50% and 70% respectively, n=3, p<0.004). Biochemically, lack of SCF induced growth rescue in p85α−/− BMMCs expressing p85αΔSH3 and p85αΔBH mutants was associated with a lack of rescue in the activation of Akt and Erk, but complete rescue in the activation of JNK (n=3). Consistently, while transplantation of p85α deficient bone marrow cells transduced with p85α into mast cell deficient Wsh mice resulted in complete restoration of gastrointestinal mast cells as well as mast cells in the stomach and spleen, p85αΔSH3 and p85αΔBH mutants restored mast cells only partially. These results indicate that other domains (SH3 and BH) of p85α are required for mast cell growth. In contrast to p85α, deficiency of p85β alone resulted in increased BMMC maturation, growth and survival compared to controls (1.2 fold, n=3, p<0.003). Consistently, over-expression of p85β in WT bone marrow cells resulted in a profound reduction in the maturation of mast cells as well as proliferation. We studied whether reduced maturation and proliferation due to the loss or over-expression of p85β was a result of altered c-Kit receptor internalization and degradation. Our results revealed significantly more c-Kit receptor internalization and degradation in p85β expressing cells compared to p85α expressing cells (2 fold, n=5, p<0.001). Since Cbl family of ubiquitin ligases are involved in the down-regulation of tyrosine kinase receptors, we analyzed whether c-Cbl is involved in p85β mediated c-Kit receptor internalization and degradation. Phosphorylation of c-Cbl and ubiquitination of c-Kit receptor was more in p85β expressing cells compared to p85 expressing cells (n=3). In conclusion, while the current dogma in the field of PI3Kinase signaling suggests that all regulatory subunits of PI3Kinase function in a similar manner; we provide genetic and biochemical evidence to suggest that p85 regulatory subunits differentially regulate growth and maturation of mast cells. Disclosures: Munugalavadla: Genentech: Employment, Patents & Royalties.

Mucosal mast cells and nematode infection: strain-specific differences in mast cell precursor frequency revisited

2003 ◽  
Vol 77 (2) ◽  
pp. 155-161 ◽  
Author(s):  
J.K. Brown ◽  
S.H. Wright ◽  
H.R.P. Miller
Keyword(s):  
Bone Marrow ◽  
Mast Cell ◽  
Mast Cells ◽  
Transforming Growth Factor ◽  
Bone Marrow Cells ◽  
Trichinella Spiralis ◽  
Cell Precursor ◽  
Mucosal Mast Cells ◽  
Bone Marrow Cultures ◽  
Marrow Cultures

AbstractMucosal mast cells (MMC) play an important role in the immune response against selected species of intestinal nematode. The kinetics with which different strains of inbred mice resolve infection withTrichinella spiraliscorrelates with their ability to mount MMC responses in the intestinal mucosa. Homologues of MMC that express and constitutively secrete abundant amounts of the granule chymase, mouse mast cell protease-1 (mMCP-1), can be generatedin vitrofrom bone marrow cultures supplemented with interleukins-3 and -9, stem cell factor and transforming growth factor-β1. Using the enhanced growth characteristics of these MMC homologues, a novel limiting dilution assay for mast cell precursor (MCp) frequency has been developed. The assay is highly specific, in that cultures containing mast cells are identified with mMCP-1 specific antibody, and almost three-fold more sensitive than previously published systems. MCp frequencies were compared in BALB/c and C57/BL10 strains of mice that, respectively, respond rapidly and slowly to infection withT. spiralis. MCp frequency (1/378 bone marrow cells) was significantly greater (P<0.05) in BALB/c than C57/BL10 mice (frequency: 1/751). Similarly the rate of growth of MMC homologues and the production of mMCP-1 was significantly (P<0.05) greater in BALB/c than in C57/BL10 bone marrow cultures.

Notch Signaling-Dependant Expulsion of Parasites through Mast Cell-Mediated Immunity.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 1473-1473
Author(s):  
Mamiko Sakata-Yanagimoto ◽  
Etsuko Yamaguchi-Nakagami ◽  
Toru Sakai ◽  
Keiki Kumano ◽  
Atsushi Kunisato ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Mast Cell ◽  
Mast Cells ◽  
Notch Signaling ◽  
Cell Generation ◽  
Pre Treatment ◽  
And Function ◽  
Tgf Β1

Abstract [Background] Notch signaling is known to be important in hematopoiesis, but very little information is available about its significance in mast cells. Here we provide direct evidence that notch signaling is critical for both development and function of mast cells in vitro and in vivo. [Methods] A Lin− fraction of mouse bone marrow cells was cultured on immobilized Delta1 in the presence of SCF and IL-3, and emerging Lin−FcεRI+c-Kit+ mast cells were characterized. Next, production of mouse mast cell protease-1 (mMCP-1), which is specific for nematode infection through locally expressed TGF-β1 in vivo, by bone marrow-derived mast cells (BMMC) was analyzed after the stimulation with Delta1 in the presence of TGF-β1. Finally, mice were infected with Strongyloides venezuelensis after pre-treatment with Delta1, and expulsion of the worms was examined. [Results] Lin−FcεRI+c-Kit+ mast cells developed remarkably earlier if stimulated with Delta1 (at one week, 15% vs. 3%). DAPT, a γ-secretase inhibitor, blocked the Delta1 effect, while it did not affect the regular time-course mast cell generation by SCF and IL-3. SB431542, a selective inhibitor of TGF-β1 signaling, also blocked early mast cell generation by Delta1. Delta1 augmented mMCP-1 expression and secretion from BMMC by 50 fold. Both DAPT and SB431542 showed a dose-dependent inhibition of Delta1 effect on mMCP-1 expression and secretion. Pre-treatment of the hosts with Delta1 promoted the expulsion of S. venezuelensis, (left/inoculated ratios of worms, 3% vs. 40%) while Delta1 had no effect in the mast cell-deficient W/Wv mice. [Discussion] Our observations reveal that notch signaling regulates both development and function of mast cells in vitro in conjunction with TGF-β1 signaling. In vivo, it is also likely that Delta1 facilitates the functional maturation of intestinal mast cells to eradicate parasites. More precise mechanism of Delta1 action on mast cells in vivo is under a study.

CCR2 Mediates Hematopoietic Stem/Progenitor Cell Trafficking to Peripheral Tissues after Inflammation

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 472-472
Author(s):  
Yue Si ◽  
Chia-Lin Tsou ◽  
Israel Charo
Keyword(s):  
Bone Marrow ◽  
Chemokine Receptor ◽  
Bone Marrow Cells ◽  
Cell Trafficking ◽  
Aseptic Inflammation ◽  
Hematopoietic Stem ◽  
Peripheral Tissues ◽  
Marrow Cells

Abstract Hematopoietic stem cells (HSCs) are bone-marrow derived, self-renewing pluripotent cells that give rise to terminally differentiated circulating blood cells. HSCs have been implicated in parenchymal tissue repair in the setting of inflammation. In response to the antagonist of the chemokine receptor CXCR4, HSCs and their progenitors migrate from bone marrow to the blood. However, little is known about the signals that mediate their trafficking from the blood into peripheral tissues. Recently, we showed that mice genetically deficient in chemokine receptor CCR2 (CCR2−/− mice) have a marked decrease in the number of circulating “inflammatory” (7/4+, Ly6c+) monocytes, but no decrease in myeloid progenitor cells in the bone marrow (Tsou et al, J Clin Invest, 2007, 902). These data indicated that although CCR2 is not necessary for HSCs to differentiate into mature monocytes, it does play a role in monocyte egress from bone marrow to blood. In the current study, we extend this work and investigate the expression of CCR2 on HSCs, and tested the hypothesis that CCR2 is critical for the recruitment of circulating HSCs to sites of inflammation. We found that CCR2 was expressed on subsets of primitive HSCs and myeloid progenitors and mediated HSC movement in response to inflammation. Using traditional transwell chambers, we found that c-Kit+Lin− cells derived from bone marrow underwent chemotaxis in response to the CCR2 ligands MCP-1 (CCL2) and MCP- 3 (CCL7). To determine whether CCR2 mediates HSC movement in vivo, we treated wildtype mice with thioglycollate to induce aseptic inflammation. HSCs were actively recruited to the peritoneum, as shown by fluorescence-activated cell sorting and functional colony formation assays. In contrast, this response was profoundly impaired in CCR2−/− mice. To determine whether the clonogenic cells recruited to peritoneum were true HSCs, we performed competitive transplantation assays. Thioglycollate was instilled into wildtype CD45.2+ mice, and peritoneal Lin− cells were collected, purified, and infused, together with CD45.1+ bone marrow cells, into lethally irradiated CD45.1+ mice. Four months later, up to 12% of the leukocytes in the peripheral blood of these primary recipient mice were CD45.2+. At the time of sacrifice, bone marrow cells were collected from these mice and injected into lethally irradiated secondary CD45.1+ recipient mice. Two months following the transplantation, up to 9% of the blood leukocytes in these secondary recipient mice were CD45.2+, confirming that long-term repopulating HSCs were recruited to the inflamed peritoneum of the donor mice. These findings suggest a novel role for CCR2 in the recruitment of long-term repopulating HSCs to sites of inflammation and injury. We are currently investigating whether recruited HSCs and their progenitors hasten the resolution of the inflammatory response or promote the repair of injured tissue.

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