Impairment of Hematopoietic Stem Cell (HSC) Niche by G-CSF Is Associated with Rapid Mobilization of Serially Reconstituting HSC and Reduced Competitive Repopulation of Mobilized Bone Marrow

Abstract Abstract 1889 We have previously shown that G-CSF administration impairs HSC niches in the mobilized bone marrow (BM). G-CSF causes rapid suppression (within 2 days) of endosteal osteoblasts and bone formation with concomitant down-regulation of Kit ligand, CXCL12 and angiopoietin-1. This effect is mediated by the depletion of specific populations of BM macrophages1. Considering the very rapid impairment of HSC niches in response to G-CSF, we hypothesized that 1) the most primitive HSC should also mobilize at this very early stage within the first 48 hours of G-CSF treatment, and 2) that down-regulation of HSC niche function should also alter the number or function of HSC remaining in the mobilized BM. To test this, 125μg/kg rhuG-CSF was injected twice daily to C57BL/6 mice; blood and BM harvested at days 2 and 5 of G-CSF treatment to be transplanted into congenic recipients in a long-term competitive repopulation assay (LT-CR). Transplantation of 25μL blood showed a gradual increase in the number of LT-CR cells mobilized in response to G-CSF as measured by donor chimerism in myeloid and B lineages at 16 weeks post-transplant. Expectedly repopulating units (RU) per mL blood progressively increased from 0.2 ± 0.0 (n=6) in steady-state to 2.9 ± 1.6 (n=9) and 82.6 ± 40.4 (n=9) at days 2 and 5 of G-CSF treatment respectively. At 16 weeks post-transplant, BM from primary recipients were transplanted into secondary recipients. Surprisingly, secondary recipients of blood samples collected after 2 and 5 days of G-CSF treatment had equivalent levels of donor chimerism (37.2% ± 6.6% for 2 days G-CSF and 47.1% ± 7.8% for 5 days G-CSF, n = 8 per group). Therefore, although the absolute number of RU mobilized at day 2 of G-CSF was 28-fold lower than at day 5 of G-CSF administration, more primitive serially reconstituting HSC were mobilized at equivalent levels at days 2 and 5 of G-CSF treatment. This supports our hypothesis that most potent serially reconstituting HSC are mobilized as early as day 2 of G-CSF treatment consistent with the disappearance of osteoblasts1. To test the potential of HSC remaining in the BM, BM cells from G-CSF mobilized mice were transplanted in competition with BM cells from congenic mice in steady-state. Donor chimerism at 16 weeks post-transplant showed that competitive repopulation of BM cells was severely impaired at day 5 of G-CSF treatment with the number of RU per 200,000 BM cells decreasing from 4.1 ± 1.4 in steady-state and 5.2 ± 1.6 at day 2 of G-CSF treatment, to only 0.14 ± 0.05 at day 5 of G-CSF treatment. To test whether this 29-fold decrease in competitive repopulation was due to increased HSC proliferation, we measured BrdU incorporation for the last 2.5 days prior to BM harvest as well as cell cycle analysis with Ki67 and Hoechst33342. The proportion of quiescent Lin- Sca1+ Kit+ CD48- phenotypic HSC in G0 phase decreased from 62.8 ±4.0% in steady-state to 43.5±8.2% at day 2 of G-CSF, but surged back to 80.5±1.9% and 75.1±3.5% at days 3.5 and 5 of G-CSF treatment. The proportion of HSC in G1 and S/G2/M phases followed the opposite pattern, up at day 2, down at days 3.5 and 5. This was confirmed by BrdU incorporation for 2.5 days with the number of BrdU+ cells among Lin- Sca1+ KIT+ CD48- cells rising from 35.1±4.0% in steady-state, to 51.2±4.5% at day 2 of G-CSF and going down to 18.1±1.9% at day 3.5 and 23.3±5.5% at day 5 of G-CSF. Therefore, G-CSF recruits phenotypic HSC into cell cycle within the first 2 days of administration, but HSC return to quiescence despite continuing G-CSF. Therefore decreased repopulation potential at day5 of G-CSF is not due to increased cycling. Finally, we noted that the number of Lin-Sca1+KIT+CD48-CD150+ HSC and Lin-Sca1+KIT+CD48-CD150- multipotent progenitors were reduced 2.4- and 2.8-fold respectively (p<.05) in G-CSF-mobilized BM. In conclusion, administration of G-CSF rapidly disrupts HSC niches resulting in rapid mobilization of serially-reconstituting LT-CRC as early as day 2 of G-CSF administration. Secondly, the marked reduction of competitive reconstitution potential of mobilized BM was not due to increased HSC cycling but rather to decreased number of HSC remaining in mobilized BM. Disclosures: No relevant conflicts of interest to declare.

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Candidemia-Induced Emergency Granulopoiesis Consists of Successive Dual Waves Triggered by the Shift From C/EBPalpha to C/EBPbeta Dependency.

Blood ◽

10.1182/blood.v116.21.3778.3778 ◽

2010 ◽

Vol 116 (21) ◽

pp. 3778-3778

Author(s):

Sakiko Satake ◽

Hideyo Hirai ◽

Nobuaki Shime ◽

Rina Nagao ◽

Ruriko Tanaka ◽

...

Keyword(s):

Cell Cycle ◽

Bone Marrow ◽

Steady State ◽

Early Phase ◽

Cathepsin G ◽

Brdu Incorporation ◽

Mouse Bone Marrow ◽

Granulocytic Differentiation ◽

Hematopoietic Stem ◽

Factor C

Abstract Abstract 3778 Introduction: Granulocyte is a major cellular component in the front line of host defense. The number of granulocytes must be tightly tuned to meet the demand, because both the shortage and the excess of granulocytes can be harmful to the host. During emergency situations such as infections, granulocytes are replenished from peripheral pools and bone marrow production. As the half-life of granulocytes is quite short, granulopoiesis, de novo production of granulocytes in bone marrow, plays an important role during emergency. We have previously shown that granulopoiesis at steady state is largely dependent on a transcription factor, C/EBPalpha, whereas emergency granulopoiesis is dependent on C/EBPbeta (Hirai H, et al. Nature Immunol., 2006). However, the precise developmental stage where the shift from C/EBPalpha dependency to C/EBPbeta dependency takes place is almost unknown. The aim of this study is to dissect the process of granulopoiesis by a novel flow cytometric method and to elucidate the molecular mechanisms involved in the regulation of emergency granulopoiesis. Methods: 4 ≂ 106 cfu Candida albicans were intravenously injected to induce emergency granulopoiesis. Mouse bone marrow cells were harvested and stained with a combination of fluorescent-conjugated antibodies including anti-c-kit, anti-CD34, anti-Ly6G antibodies and markers for other lineages. Then the stained cells were analyzed or sorted by flow cytometry. After eliminating the cells which lost potential to give rise to granulocytes, the remaining cells were dissected into five subpopulations (#1≂ #5) according to the expression levels of c-kit and Ly6G. #1 is c-kithigh Ly6Glow cells, @ #2: c-kitint Ly6Glow, #5: c-kitlow Ly6Ghigh, and the cells residing between #2 and #5 are divided into #3 and #4. Cell number, gene expressions and cell cycle status of each population were analyzed before and after inducing emergency granulopoiesis. @ Results and Discussions: Wright-Giemsa staining and qRT-PCR for granule proteins (cathepsin G, myeloperoxidase, neutrophil elastase2, lactoferrin and MMP9) in each population indicated that lower c-kit expression and higher Ly6G expression correlated well with granulocytic differentiation and that the granulopoiesis progresses from # 1 to #5 in this order both at steady state and during emergencies (Figure 1). Then we applied this method to candidemia-induced emergency granulopoiesis. In vivo BrdU incorporation analysis showed immediate acceleration of the cell cycle in the most immature population (#1) and in one of the intermediate populations (#2). Chronological monitoring of each population after inducing candidemia revealed that rapid increase in mature granulocytes (#5) preceded the replenishment from the most immature population (#1). These results suggested that there are two distinct gwavesh in granulopoiesis at the early phase of infection, a rapid supply (first gwaveh) of granulocytes from relatively mature population (#2≂ #4), and a further and sustained supply (second gwaveh) originated from more immature populations (#1) including hematopoietic stem/progenitor cells (Figure 1). Transcripts of C/EBPalpha were significantly downregulated in #1≂ #4 at the early phase of infection, while those of C/EBPbeta were maintained in all the subpopulation (Figure 2), suggesting that shift from C/EBPalpha dependency to C/EBPbeta dependency took place at multiple developmental steps in granulopoiesis. C/EBPbeta has less inhibitory effects on cell cycle than C/EBPalpha while their abilities to induce granulocytic differentiation are similar (Hirai H, et al. Nature Immunol., 2006). The shift toward C/EBPbeta dependency may trigger the dual waves in emergency granulopoiesis, which demands both differentiation and proliferation of granulocytic precursors. Disclosures: No relevant conflicts of interest to declare.

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Novel Role for Host-Derived Megakaryocytes In Facilitating Stem Cell Engraftment through Enhancement of Osteoblastic Niche Restoration Following Radioablation

Blood ◽

10.1182/blood.v116.21.558.558 ◽

2010 ◽

Vol 116 (21) ◽

pp. 558-558

Author(s):

Timothy S. Olson ◽

Anna Caselli ◽

Satoru Otsuru ◽

Ted Hofmann ◽

Edwin M. Horwitz

Keyword(s):

Bone Marrow ◽

Stem Cell ◽

B Lymphocyte ◽

Conflicts Of Interest ◽

Brdu Incorporation ◽

Hematopoietic Stem ◽

Endosteal Surface ◽

Post Transplant ◽

Cell Engraftment ◽

Donor Cells

Abstract Abstract 558 The osteoblastic niche is a critical site of engraftment following stem cell transplantation. We have previously demonstrated that the osteoblastic niche expands within the first 48 hours following marrow radioablation. This expansion is accompanied by relocalization of megakaryocytes from their homeostatic location within the central marrow space to the endosteal surface at sites of osteoblast expansion, suggesting that these relocalized megakaryocytes may play a key role in reconstitution of the niche. To determine whether megakaryocytes contribute to the radioablation-induced osteoblast expansion and consequently assist in facilitating engraftment, we have examined osteoblast expansion and stem cell engraftment in wildtype (WT) mice, thrombopoietin receptor (c-Mpl) deficient mice (mpl−/−) that have less than 20% of normal megakaryocyte numbers, and in mice treated with an anti-CD41 blocking antibody (MWREG30). BrdU incorporation and TUNEL assays demonstrated that megakaryocyte relocalization following radioablation occurs through active migration of viable megakaryocytes. mpl−/− mice or anti-CD41 treated WT mice developed less than 20% of the megakaryocyte endosteal migration seen in untreated WT mice 48 hours after radioablation (*P<0.001), and anti-CD41 treatment of irradiated mpl−/− mice reduced endosteal megakaryocytes to baseline pre-radiation numbers. Moreover, mpl−/− mice developed less than 50% of the osteoblast expansion seen in WT mice following irradiation; thus, abrogating megakaryocyte activity blocks critical signals required for osteoblast expansion. Bone marrow expression of IGF-1, a recognized osteoblast growth factor, increased 5-fold within 48 hours after radiation relative to pre-radiation levels in WT mice, but this IGF-1 spike is completely blocked by c-Mpl deficiency, suggesting that megakaryocytes may induce osteoblast expansion through a pathway in which c-Mpl signaling leads to IGF-1 expression. To test the functional significance of radiation-induced megakaryocyte migration and osteoblast expansion, we transplanted lethally irradiated WT or mpl−/− mice with or without anti-CD41 treatment using bone marrow from GFP-transgenic mice. Initial bone marrow engraftment of WT GFP+ donor cells within 24h of transplantation was significantly reduced (*P<0.01 for all groups) in anti-CD41 treated WT (51% of engraftment seen in untreated wildtype recipients), untreated mpl−/− (45%), and anti-CD41 treated mpl−/− (35%) recipients. Expansion of engrafted WT GFP+ donor cells at 3, 5 and 7 days post-transplant was also significantly reduced in untreated mpl−/− recipients (36%, 53%, 63% of untreated WT recipients at 3, 5, and 7 days, respectively, *P<0.05) and anti-CD41 treated mpl−/− recipients (25%, 33%, and 30% at 3, 5, and 7 days, respectively, *P<0.05), with prominent deficits specifically in the reconstitution of the B lymphocyte lineage. Bone marrow cellularity remained significantly reduced in anti-CD41 treated WT and untreated or anti-CD41 treated mpl−/− recipients by 35–45% relative to untreated WT recipients at least out to 3 weeks post-transplant (*P<0.01). Using competitive repopulation secondary transplantation assays performed with marrow harvested from primary recipients at 24h after primary transplantation, we showed that progenitor and short term hematopoietic stem cell (HSC) engraftment was significantly decreased in mpl−/− versus WT primary recipients (*P<0.05). Secondary transplant assays performed with marrow harvested from primary recipients 3 weeks after initial transplantation demonstrated that engraftment and expansion of long term-HSC (*P <0.05) and B cell reconstitution (*P<0.005) are significantly impaired in anti-CD41 treated mpl−/− versus untreated WT recipients. Taken together, our findings demonstrate that host megakaryocytes migrate to the endosteal surface following marrow radioablation where, through the enhancement of osteoblast niche expansion and potential osteoblast-independent effects, they play a pivotal role in facilitating efficient HSC engraftment following transplantation. Further understanding of these stem cell niche restoration pathways may reveal novel therapeutic targets to improve engraftment efficiency in the clinical setting. Disclosures: No relevant conflicts of interest to declare.

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Bone Marrow Arteriolar Niches Maintain Hematopoietic Stem Cell Quiescence

Blood ◽

10.1182/blood.v120.21.638.638 ◽

2012 ◽

Vol 120 (21) ◽

pp. 638-638

Author(s):

Yuya Kunisaki ◽

Ingmar Bruns ◽

Christoph Scheiermann ◽

Sandra Pinho ◽

Dachuan Zhang ◽

...

Keyword(s):

Cell Cycle ◽

Stem Cells ◽

Bone Marrow ◽

Stem Cell ◽

Conflicts Of Interest ◽

3D Structure ◽

Hematopoietic Stem ◽

Hsc Niche ◽

Whole Mount ◽

Vascular Structures

Abstract Abstract 638 A prevailing idea suggests that quiescent hematopoietic stem cells (HSCs) reside near osteoblasts in the bone marrow (BM) whereas actively cycling HSCs are found near sinusoids. However, this idea is not been proven experimentally. Our recent studies have identified Nestin+ perivascular cells containing all BM mesenchymal stem cell activity as a candidate HSC niche cell (Nature 2010;466:829). To gain more insight in the 3-dimensional (3D) structure of the HSC niche, we have established a novel whole-mount immunofluorescence imaging technique in which the 3D spatial relationships between vascular structures and endogenous CD150+CD48−CD41−Lineage− HSCs in the sternal or femoral BM can be precisely determined. Our imaging analyses in both bone types revealed a prominent sinusoidal network interrupted by rare small caliber (∼10μm) arterioles whose identity was confirmed by staining with artery-specific Alexa Fluor 633 (Nat Methods 2012;9:273) or Sca-1 (Cell Stem Cell 2009;4:263). 3D analyses using Nes-GFP transgenic mice showed two distinct types of Nestin+ cells associated with distinct vascular structures: Nes-GFPbright cells exhibiting a pericyte-like morphology were tightly associated with arterioles (referred to as periarteriolar Nestin (Nesperi) cells) whereas more abundant Nes-GFPdim cells exhibiting a reticular shape (Nesretic cells) were largely associated with sinusoids. We sorted Nesperi and Nesretic cells based on GFP expression and cell size for further characterization. Nesperi cells were very rare (∼0.002% of BM) and expressed ∼3-fold and 10–50-fold higher levels of genes associated with HSC maintenance and retention (Cxcl12, Kitl, Angpt1, Vcam1) compared to Nesretic cells and Nes-GFPneg CD45−CD31−Ter119− stromal cells, respectively. These factors were down-regulated after G-CSF stimulation in Nesperi cells but not in Nesretic cells, which led us to hypothesize that Nesperi cells played an important role in HSC maintenance. We examined the spatial correlation between endogenous HSCs and Nesperi cells by whole-mount immunostaining and found that 38.6 ± 2.9% and 54.9 ± 6.8% of HSCs were localized within 20μm and 40μm distance from Nesperi cells, respectively. After G-CSF treatment, HSCs entered cell cycle (control/G-CSF; 86.8 ± 2.6%/52.2 ± 3.8% in G0, as defined by Ki67 and Hoechst 33342 staining, p=0.002) and expanded around Nesperi cells (control/G-CSF; 34.3 ± 1.0%/48.2 ± 1.6% in 0–20μm proximity, p<0.0001), suggesting that Nesperi cells may regulate cell cycle of HSCs by expression of HSC retention factors. Cell cycle quiescence is a hallmark of stem cells and protecting them from exogenous insults. We thus analyzed the cell cycle status and distribution of HSCs using Ki67 staining. Ki67+ cycling HSCs were distributed significantly further away from Nesperi cells than Ki67− non-cycling cells (Ki67+/Ki67−; 8.3 ± 8.3%/36.8 ± 4.7% in 0–20 μm proximity, p<0.05, 53.4 ± 7.0%/24.6 ± 7.0% > 80μm distance, p<0.05). We evaluated a genetic model (mice deficient in promyelocytic leukemia protein, Pml−/−) that leads to a loss of HSC quiescence in a cell autonomous manner (Nature 2008;453:1072). In Pml−/− BM, HSCs were distributed significantly further away from arterioles compared to wild-type mice (WT/Pml−/−; 34.2 ± 3.9%/9.4 ± 5.1% in 0–20μm proximity, p<0.05, 9.2 ± 4.7%/59.0 ± 12.7% >80μm distance, p<0.05). These data indicate that proximity to arterioles surrounded by Nesperi cells is critical for HSC behavior. Interestingly, we found that Nesperi cells themselves were more quiescent than Nesretic cells (88.7 ± 4.6%/64.2 ± 5.5% in G0, p=0.01). To test the relevance of this quiescent niche, we challenged mice with 5-fluorouracil (5FU). After 5FU administration, the number of Nesperi cells was largely preserved compared to Nesretic cells (63.4 ± 17.1%/13.8 ± 2.9% of untreated control, p=0.01). In addition, the vast majority of HSCs were closely associated with Nesperi cells on day 7 (Control/Day 7 5FU; 34.4 ± 1.0%/70.6 ± 4.0% in 0–20μm, p<0.0001) and returned to baseline levels on day 21 (Day 21 5FU; 36.0 ± 11.4% in 0–20μm), indicating that both HSCs and the niche cells are quiescent and thus resistant to myeloablation. These results indicate that bone marrow arterioles comprise a specialized microenvironment that promotes quiescence of both Nesperi niche cells and the HSCs. Understanding its regulation will have important implications in healthy and cancerous hematopoiesis. Disclosures: No relevant conflicts of interest to declare.

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Multifunctional Role of Caspase-3 in Regulating Hematopoietic Stem Cells.

Blood ◽

10.1182/blood.v108.11.861.861 ◽

2006 ◽

Vol 108 (11) ◽

pp. 861-861 ◽

Cited By ~ 1

Author(s):

Viktor Janzen ◽

Heather E. Fleming ◽

Michael T. Waring ◽

Craig D. Milne ◽

David T. Scadden

Keyword(s):

Cell Cycle ◽

Stem Cells ◽

Bone Marrow ◽

Stem Cell ◽

Hematopoietic Stem Cells ◽

Peripheral Blood ◽

Caspase 3 ◽

Brdu Incorporation ◽

Hematopoietic Stem ◽

Regulatory Pathways

Abstract The processes of cell cycle control, differentiation and apoptosis are closely intertwined in controlling cell fate during development and in adult homeostasis. Molecular pathways connecting these events in stem cells are poorly defined and we were particularly interested in the cysteine-aspartic acid protease, Caspase-3, an ‘executioner’ caspase also implicated in the regulation of the cyclin dependent kinase inhibitors, p21Cip1 and p27Kip1. These latter proteins are known to participate in primitive hematopoietic cell cycling and self-renewal. We demonstrated high levels of Caspase-3 mRNA and protein in immunophenotypically defined mouse hematopoietic stem cells (HSC). Using mice engineered to be deficient in Caspase-3, we observed a consistent reduction of lymphocytes in peripheral blood counts and a slight reduction in bone marrow cellularity. Notably, knockout animals had an increase in the stem cell enriched Lin−cKit+Sca1+Flk2low (LKSFlk2lo) cell fraction. The apoptotic rates of LKS cells under homeostatic conditions as assayed by the Annexin V assay were not significantly different from controls. However, in-vitro analysis of sorted LKS cells revealed a reduced sensitivity to apoptotic cell death in absence of Caspase-3 under conditions of stress (cytokine withdrawal or gamma irradiation). Primitive hematopoietic cells displayed a higher proliferation rate as demonstrated by BrdU incorporation and a significant reduction in the percentage of cells in the quiescent stage of the cell cycle assessed by the Pyronin-Y/Hoechst staining. Upon transplantation, Caspase-3−/− stem cells demonstrated marked differentiation abnormalities with significantly reduced ability to differentiate into multiple hematopoietic lineages while maintaining an increased number of primitive cells. In a competitive bone marrow transplant using congenic mouse stains Capase-3 deficient HSC out-competed WT cells at the stem cell level, while giving rise to comparable number of peripheral blood cells as the WT controls. Transplant of WT BM cells into Caspase-3 deficient mice revealed no difference in reconstitution ability, suggesting negligible effect of the Caspase-3−/− niche microenvironment to stem cell function. These data indicate that Caspase-3 is involved in the regulation of differentiation and proliferation of HSC as a cell autonomous process. The molecular bases for these effects remain to be determined, but the multi-faceted nature of the changes seen suggest that Caspase-3 is central to multiple regulatory pathways in the stem cell compartment.

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Prostaglandin E2 (PGE2) Treatment Rapidly Increases the Fraction of Non-Dividing Hematopoietic Stem Cells (HSCs)

Blood ◽

10.1182/blood.v112.11.73.73 ◽

2008 ◽

Vol 112 (11) ◽

pp. 73-73

Author(s):

Rebecca L Porter ◽

Benjamin J Frisch ◽

Regis J O’Keefe ◽

Laura M Calvi

Keyword(s):

Cell Cycle ◽

Bone Marrow ◽

Prostaglandin E2 ◽

Flow Cytometric Analysis ◽

Brdu Incorporation ◽

Hematopoietic Stem ◽

Hematopoietic System ◽

Cell Fate Decisions ◽

Flow Cytometric ◽

Incorporated Brdu

Abstract HSCs are pluripotent cells responsible for the establishment and renewal of the entire hematopoietic system. Our group and others have established that osteoblastic cells in the bone marrow microenvironment regulate HSC cell fate decisions. Specifically, Parathyroid hormone (PTH) expands HSCs by activating osteoblasts in the HSC niche. However, the molecular mechanisms for this increase are unknown. PTH increases local production of prostaglandin E2 (PGE2) in osteoblasts by stimulating cyclo-oxygenase 2 (Cox-2). We also recently found that treatment of osteoblastic MC3T3 cells with PTH (10−7 M) rapidly induces PGE2 Synthase expression. Therefore, we hypothesized that PGE2 may act as a mediator of the PTH effect on HSCs. We have shown that in vivo PGE2 treatment caused a 2.75-fold increase in lineage− Sca-1+ c-kit+ (LSK) cells within the bone marrow compared with vehicle treated mice (p=0.0061, n=8/group). Bone marrow mononuclear cells (BMMC) from mice treated with PGE2 also demonstrated superior lymphomyeloid reconstitution in competitive repopulation analyses, suggesting that HSCs are being expanded or modulated to more efficiently reconstitute the hematopoietic system in the recipients. It is known that HSCs that reside in the G0 phase of the cell cycle have increased ability to reconstitute myeloablated recipient mice. Since PGE2 treatment resulted in superior reconstitution, we hypothesized that PGE2 may increase the percentage of HSCs residing in G0. To test this hypothesis, we treated BMMC from male C57b/6 mice with 10−6 M PGE2 or vehicle for 90 minutes. The percentage of cells in G0 vs. G1 was determined by flow-cytometric analysis using the RNA and DNA dyes, Pyronin-Y and Hoechst 33342 respectively. As we predicted, PGE2 treatment increased the percentage of wild-type LSK cells in G0 1.85 fold over vehicle-treated LSK cells (23.63% in vehicle-treated, n=4 vs. 43.7% in PGE2-treated, n=6). Since the PTH-dependent increase in HSCs is Protein Kinase A (PKA) mediated and the PGE2 receptors EP2 and EP4 signal via PKA, we assayed the effect of PGE2 on the percentage of cells in G0 in mice lacking the EP2 receptor (EP2−/− mice). Interestingly, there was no enrichment for HSC in G0 when BMMC from EP2−/− mice were treated with PGE2 (55.25% in vehicle-treated, n=4 vs. 56.06% in PGE2-treated, n=5). These findings suggest that PGE2-dependent regulation of HSC activity may involve increasing the percentage of HSCs that reside in G0 by activation of EP2, thereby augmenting their ability to reconstitute the hematopoietic system of a myeloablated recipient. 5-bromo-2-deoxyuridine (BrdU) incorporation was also used to investigate the effect of PGE2 on cell cycling of HSCs. Male 6–8 week old C57b/6 mice were injected intraperitoneally with 1 mg BrdU and PGE2 (6 mg/kg) or vehicle. After 30, 60, 90 or 120 minutes, mice were sacrificed and BMMC were subjected to flow cytometric analysis for incorporation of BrdU and DNA content in HSCs. As expected for the highly quiescent HSC population, only a small fraction of HSCs incorporated BrdU. After 30 and 60 minutes of treatment, there was no difference in the percentage of cells that incorporated BrdU between vehicle and PGE2-treated mice. However, at the 90 and 120 minute time points, there were significantly less HSCs cycling in the bone marrow from the PGE2 treated mice (12.1% vs. 5.3% at 90 min, n=2 per group; 11.1% vs. 1.8% at 120 min, n=5 per group, p=0.0060), suggesting that fewer PGE2-treated cells were synthesizing DNA. Taken together, the increase in the percentage of HSCs in G0 and the decrease in cycling HSCs after PGE2 treatment indicate that PGE2 could improve engraftment and reconstitution of the hematopoietic system by enriching for HSCs in G0. These results suggest that PGE2 may exert its beneficial effect on bone marrow reconstitution by altering cell cycle dynamics in HSCs. Identification of the molecular events mediating this novel PGE2 action on HSC could provide additional targets for HSC manipulation in clinical situations requiring rapid and efficient bone marrow reconstitution, such as recovery from iatrogenic or pathologic myeloablative injury.

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Poly I:C Stimulates Sca-1 Expression in Murine Bone Marrow and Increases the Number of Phenotypic Hematopoietic Stem Cells.

Blood ◽

10.1182/blood.v114.22.2504.2504 ◽

2009 ◽

Vol 114 (22) ◽

pp. 2504-2504

Author(s):

Russell Garrett ◽

Gerd Bungartz ◽

Alevtina Domashenko ◽

Stephen G. Emerson

Keyword(s):

Cell Cycle ◽

Stem Cells ◽

Bone Marrow ◽

Hematopoietic Stem Cells ◽

Conflicts Of Interest ◽

Hematopoietic Cells ◽

Poly I:C ◽

Hematopoietic Stem ◽

Marrow Cells ◽

Myeloid Progenitors

Abstract Abstract 2504 Poster Board II-481 Polyinosinic:polycytidlyic acid (poly I:C) is a synthetic double-stranded RNA used to mimic viral infections in order to study immune responses and to activate gene deletion in lox-p systems employing a Cre gene responsive to an Mx-1 promoter. Recent observations made by us and others have suggested hematopoietic stem cells, responding to either poly I:C administration or interferon directly, enter cell cycle. Twenty-two hours following a single 100mg intraperitoneal injection of poly I:C into 10-12 week old male C57Bl/6 mice, the mice were injected with a single pulse of BrdU. Two hours later, bone marrow was harvested from legs and stained for Lineage, Sca-1, ckit, CD48, IL7R, and BrdU. In two independent experiments, each with n = 4, 41 and 33% of Lin- Sca-1+ cKit+ (LSK) IL-7R- CD48- cells from poly I:C-treated mice had incorporated BrdU, compared to 7 and 10% in cells from PBS-treated mice. These data support recently published reports. Total bone marrow cellularity was reduced to 45 and 57% in the two experiments, indicating either a rapid death and/or mobilization of marrow cells. Despite this dramatic loss of hematopoietic cells from the bone marrow of poly I:C treated mice, the number of IL-7R- CD48- LSK cells increased 145 and 308% in the two independent experiments. Importantly, the level of Sca-1 expression increased dramatically in the bone marrow of poly I:C-treated mice. Both the percent of Sca-1+ cells and the expression level of Sca-1 on a per cell basis increased after twenty-four hours of poly I:C, with some cells acquiring levels of Sca-1 that are missing from control bone marrow. These data were duplicated in vitro. When total marrow cells were cultured overnight in media containing either PBS or 25mg/mL poly I:C, percent of Sca-1+ cells increased from 23.6 to 43.7%. Within the Sca-1+ fraction of poly I:C-treated cultures, 16.7% had acquired very high levels of Sca-1, compared to only 1.75% in control cultures. Quantitative RT-PCR was employed to measure a greater than 2-fold increase in the amount of Sca-1 mRNA in poly I:C-treated cultures. Whereas the numbers of LSK cells increased in vivo, CD150+/− CD48- IL-7R- Lin- Sca-1- cKit+ myeloid progenitors almost completely disappeared following poly I:C treatment, dropping to 18.59% of control marrow, a reduction that is disproportionately large compared to the overall loss of hematopoietic cells in the marrow. These cells are normally proliferative, with 77.1 and 70.53% accumulating BrdU during the 2-hour pulse in PBS and poly I:C-treated mice, respectively. Interestingly, when Sca-1 is excluded from the analysis, the percent of Lin- IL7R- CD48- cKit+ cells incorporating BrdU decreases following poly I:C treatment, in keeping with interferon's published role as a cell cycle repressor. One possible interpretation of these data is that the increased proliferation of LSK cells noted by us and others is actually the result of Sca-1 acquisition by normally proliferating Sca-1- myeloid progenitors. This new hypothesis is currently being investigated. Disclosures: No relevant conflicts of interest to declare.

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RhoA Is An Essential Regulator of Mitosis and Survival During Hematopoietic Stem Cell Differentiation to Multipotent Progenitors

Blood ◽

10.1182/blood.v118.21.1273.1273 ◽

2011 ◽

Vol 118 (21) ◽

pp. 1273-1273

Author(s):

Xuan Zhou ◽

Jaime Meléndez ◽

Yuxin Feng ◽

Richard Lang ◽

Yi Zheng

Keyword(s):

Cell Cycle ◽

Bone Marrow ◽

Intracellular Signaling ◽

Conflicts Of Interest ◽

Stem Cell Differentiation ◽

Conditional Knockout ◽

Hematopoietic Progenitors ◽

Hematopoietic Stem ◽

Differentiated Cells ◽

Multipotent Progenitors

Abstract Abstract 1273 The maintenance and differentiation of hematopoietic stem cells (HSC) are critical for blood cell homeostasis, which is tightly regulated by a variety of factors. In spite of extensive investigation of HSC biology, however, the mechanism of regulation of HSC and progenitor cell division, particularly the unique molecular events controlling the mitosis process during HSC differentiation, remains unclear. RhoA GTPase is a critical intracellular signaling nodal that has been implicated in signal transduction from cytokines, chemokines, wnt/notch/shh, and adhesion molecules to impact on cell adhesion, migration, cell cycle progression, survival and gene expression. Recent mouse genetic studies in keratinocytes and embryonic fibroblast cells showed that RhoA is a key regulator of mitosis. By using an interferon-inducible RhoA conditional knockout mouse model (Mx-cre;RhoAlox/lox), we have made the discovery that RhoA plays an indispensible role in primitive hematopoietic progenitor differentiation through the regulation of mitosis and survival. RhoA deficient mice die at ∼10 days because of hematopoietic failure, as evidenced by a loss of bone marrow, splenocyte and PB blood cells. Syngenic as well as reverse transplant experiments demonstrate that these effects are intrinsic to the hematopoietic compartment. RhoA loss results in pancytopenia associated with a rapid exhaustion of the lin−c-kit+ (LK) phenotypic progenitor population (within 4 days after two polyI:C injections). Meanwhile, the lin−c-kit+sca1+ (LSK) primitive cell compartment is transiently increased in BM after RhoA deletion due to a compensatory loss of quiescence and increased cell cycle. Interestingly, we find that within the LSK population, there is a significant accumulation of LSKCD34+Flt2− short-term HSCs (ST-HSC) and a corresponding decrease in frequency of LSKCD34+Flt2+ multipotent progenitors (MPPs). Consistent with these phenotypes, the LK and more differentiated hematopoietic cell populations of RhoA knockout mice show an increased apoptosis while the survival activities of LSK and more primitive compartments of WT and RhoA KO mice remain comparable. These data suggest that RhoA plays an indispensible role in the step of ST-HSCs differentiation to MPP cells, possibly through the regulation of MPP cell survival. This hypothesis is further supported by a competitive transplantation experiment. Deletion of RhoA in a competitive transplantation model causes an extinction of donor derived (CD45.2+) differentiated cells (myeloid, erythroid, T and B cells) in the peripheral blood. Interestingly, bone marrow CD45.2+ LSK cells are only marginally affected by deletion of RhoA and RhoA−/− LSK cells are able to engraft into 2nd recipient, whereas CD45.2+ LK and more differentiated cells are mostly eliminated after RhoA deletion. This effect is associated with a decrease in the survival of CD45.2+ RhoA−/− LK, but not LSK cells. Further in vitro culture of isolated lin− progenitors demonstrates that RhoA deficiency results in a failure of cytokinesis, causing an accumulation of multinucleated cells, further suggesting that RhoA is essential for the cytokinesis of hematopoietic progenitors. Surprisingly, the well-defined Rho downstream target, actomyosin machinery, does not appear to be affected by RhoA knockout. We are further exploring the mechanism of RhoA contribution to the differentiation of HSCs by dissecting the signaling and functional relationship of RhoA regulated survival activity and cell cycle mitosis in early hematopoietic progenitors. Disclosures: No relevant conflicts of interest to declare.

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Metabolic Regulation of Hematopoietic Stem Cells During Stress

Blood ◽

10.1182/blood.v120.21.sci-42.sci-42 ◽

2012 ◽

Vol 120 (21) ◽

pp. SCI-42-SCI-42

Author(s):

Toshio Suda

Keyword(s):

Cell Cycle ◽

Stem Cells ◽

Bone Marrow ◽

Stem Cell ◽

Hematopoietic Stem Cells ◽

Metabolic Regulation ◽

Conflicts Of Interest ◽

Hypoxia Inducible Factor ◽

Ros Generation ◽

Hematopoietic Stem

Abstract Abstract SCI-42 Tissue homeostasis over the life of an organism relies on both self-renewal and multipotent differentiation of stem cells. Hematopoietic stem cells (HSCs) are sustained in a specific microenvironment known as the stem cell niche. Adult HSCs are kept quiescent during the cell cycle in the endosteal niche of the bone marrow. Normal HSCs maintain intracellular hypoxia, stabilize the hypoxia-inducible factor-1a (HIF-1a) protein, and generate ATP by anaerobic metabolism. In HIF-1a deficiency, HSCs became metabolically aerobic, lost cell cycle quiescence, and finally became exhausted. An increased dose of HIF-1a protein in VHL-mutated HSCs and their progenitors induced cell cycle quiescence and accumulation of HSCs in the bone marrow (BM), which were not transplantable. This metabolic balance promotes HSC maintenance by limiting the production of reactive oxygen species (ROS), but leaves HSCs susceptible to changes in redox status (1). We have performed the metabolomic analysis in HSCs. Upregulation of pyruvate dehydrogenase kinases enhanced the glycolytic pathway, cell cycle quiescence, and stem cell capacity. Thus, HSCs directly utilize the hypoxic microenvironment to maintain their slow cell cycle by HIF-1a-dependent metabolism. Downregulation of mitochondrial metabolism might be reasonable, since it reduces ROS generation. On the other hand, at the time of BM transplantation, HSCs activate oxidative phosphorylation to acquire more ATP for proliferation. Autophagy also energizes HSCs by providing amino acids during transplantation. ATG (autophagy-related) 7 is essential for transplantation and metabolic homeostasis. The relationship between mitochondrial heat shock protein, mortalin, and metabolism in HSCs will also be discussed. Disclosures: No relevant conflicts of interest to declare.

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Periostin Acts As An Important Cell Cycle Regulator Of Adult Hematopoietic Stem Cells Via Binding To Integrin-αvβ3

Blood ◽

10.1182/blood.v122.21.341.341 ◽

2013 ◽

Vol 122 (21) ◽

pp. 341-341 ◽

Cited By ~ 2

Author(s):

Satish Khurana ◽

Catherine M. Verfaillie

Keyword(s):

Cell Cycle ◽

Stem Cells ◽

Hematopoietic Stem Cells ◽

Conflicts Of Interest ◽

Integrin Αvβ3 ◽

Brdu Incorporation ◽

Hematopoietic Stem ◽

Hematopoietic System ◽

Cell Cycle Regulator ◽

Blocking Antibodies

Osteoblasts are one of the important cellular components of the niche for hematopoietic stem cells (HSCs) in mammalian bone marrow (BM). Integrin receptors not only play a key role in HSC adhesion within the BM niche but also transfer regulatory signals from the microenvironment to HSCs. Periostin (Postn or osteoblast specific factor-1; OSF-1) is expressed in osteoblasts in addition to many other tissues, and acts as a ligand for Integrin-αvβ3 (ITGAV-B3). We identified POSTN as an important regulator of the cell cycle in adult murine HSCs. POSTN inhibited culture induced proliferation of HSCs thereby decreasing the total number of cells following 2-5 day culture of primitive HSCs, identified as CD150+CD48-Lin-Sca-1+c-kit+ (CD150 KLS) cells with SCF and TPO, while increasing the proportion of long-term (LT-) HSCs. Culture for 5 days with POSTN decreased the short-term (ST-) engraftment of progeny of 200 CD150 KLS cells, while significantly increasing LT- engraftment of the donor derived cells. A significant fraction of CD150 KLS cells expressed ITGAV as well as ITGB3. POSTN did not affect proliferation of HSCs in vitro following blocking of ITGAV with neutralizing antibodies. Among the important cell cycle regulators, we found an increase in p27kip1 expression in HSCs. Preliminary studies on possible signaling mechanisms involved, showed that POSTN inhibits Akt phosphorylation, known to mediate inhibition of both expression and activation of p27Kip1. Intravenous infusion of recombinant POSTN protein significantly decreased proliferation of hematopoietic progenitors as shown by Brdu incorporation and Hoechst/Pyronin staining. Interestingly, POSTN infusion also led to an increase in the number of KLS as well as CD150 KLS cells in the BM. Studies on characterization of the hematopoietic system of Postn-/- mice are underway. To further determine the role of ITGAV in HSCs, we used blocking antibodies against ITGAV and performed homing and engraftment studies. No effect on either homing potential or engraftment of ST- and LT- engraftment was seen. However, the competitive repopulation of ITGAV- CD150 KLS cells was significantly lower that that of ITGAV+ CD150 KLS cells (isolated using non-blocking antibodies). Therefore, our studies confirm the importance of ITGAV expression on primitive HSCs as well as presents POSTN as an important cell cycle regulator in the hematopoietic system. Disclosures: No relevant conflicts of interest to declare.

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Favorable Results of Allo-HSCT from MRD in Patients with Myelofibrosis

Blood ◽

10.1182/blood.v124.21.5934.5934 ◽

2014 ◽

Vol 124 (21) ◽

pp. 5934-5934

Author(s):

Miroslaw Markiewicz ◽

Monika Dzierzak-Mietla ◽

Patrycja Zielinska ◽

Agata Wieczorkiewicz-Kabut ◽

Sylwia Mizia ◽

...

Keyword(s):

Bone Marrow ◽

Collagen Type ◽

Conflicts Of Interest ◽

Chronic Gvhd ◽

Graft Loss ◽

Chronic Phase ◽

Curative Treatment ◽

Unrelated Donor ◽

Hematopoietic Stem ◽

Post Transplant

Abstract Introduction: Myelofibrosis (MF), chronic myeloid malignancy associated with shortened survival, in majority of patients develops de novo as Primary MF, but also polycythemia vera (PV) or essential thrombocythemia (ET) may progress into post-PV or post-ET MF. Although management of MF includes several treatment options, the only potentially curative treatment approach in MF is allogeneic hematopoietic stem cell transplantation (allo-HSCT). Aim of this study was to evaluate the results of allo-HSCT in patients with MF treated in Katowice, Poland. Material and Methods: 27 pts (14 male and 13 female) with median age 51 years (range 21–63) were treated with allo-HCT due to PMF (20), post-PV (4) or post-ET (3) MF. 11,7,11,26 and 41% of pts had DIPSS 0,1,2,3 and 4, respectively. Median bone marrow cellularity was 70% (10-100%), fibrosis was collagen-type (14 pts including 2 with osteosclerosis), reticulin (10) or it was not specified (3). Splenomegaly was present in all pts: 13-20 cm (14 pts), > 20 cm (13 pts). JAK2V617F point mutation was present in 18 pts. Karyotype was available in 14 pts: in 9 normal, in 5 with variable abnormalities. Median time from diagnosis to allo-HCT was 1.5 (0.4–9.5) years. 16 pts (59.3%) received cells from HLA-matched related donor (MRD), 11 pts (40.7%) from unrelated donor: 10/10 (9) or 9/10 (2) HLA-A,B,C,DR,DQ alleles matched. Reduced intensity conditioning (RIC) was used in 26 pts, 1 patient received myeloablative conditioning (MC). Sources of stem cells were: peripheral blood (21), bone marrow (4) and both (2). All pts but one had chronic phase of MF at time of transplantation. Results: 14/27 (52%) pts are alive at median 3.4 (0.4-5.4) years after allo-HSCT: 11/16(69%) from MRD and 3/11(27%) from MUD, p=0.032. Graft failure, graft loss or PRCA were observed in 3, 5 and 1 pt, respectively. Absolute neutrophil count >0.5×109/L and platelet count >50×109/L were achieved at median 16 and 28 days, respectively. 12/27 (44%) pts reached complete blood count of Hb>10 g/dl, Plt>100 G/l and WBC>3.5 G/l; 11 of them (92%) are alive. 6/27 (22%) pts remained either RBC or PLT transfusions dependent post-transplant; 3 of them (50%) died. 9/27 (33%) pts remained both RBC and PLT transfusion dependent and all of them died. JAK2V617F mutation was completely eradicated in 11/16 evaluated previously positive patients (69%), decreased in 4 (25%) and stable in 1(6%) pt. Acute graft-versus-host disease (aGVHD) III-IV developed in 5/27 (19%) and extensive chronic GVHD in 5/19 (26%) pts. Relapse occurred in 4 pts and was treated with subsequent second transplant (in 1 pt thereafter by 3-rd allo-HSCT). Spleen length decreased at median by 5 (0.3-9.2) cm. Out of 7 pts with initial collagen fibrosis who were evaluated post-transplant, 1 had no fibrosis, 5 reticulin type and only in 1 pt collagen fibrosis was stable. Out of 3 pts with initial reticulin fibrosis it disappeared in 2 and progressed to collagen type in 1. Causes of death were GVHD (5 pts: 3 aGVHD, 2 cGVHD) and pancytopenia with either infection (7 pts) or CNS hemorrhage (1 pt). Conclusions: Allo-HSCT, the only curative treatment of myelofibrosis, provides chance of long survival, regression of the disease (lower stage of fibrosis, JAK2V617F eradication) and improved quality of life (transfusion independency, decreased splenomegaly). Transfusion independency may indicate good outcome. Favorable results are observed after allo-HSCT from MRD. Disclosures No relevant conflicts of interest to declare.

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