Roles of Exosomes in the Hematopoietic Stem Cell-Supporting Capacity of Stromal Cells

Abstract Hematopoietic stem cells (HSCs) are identified by their ability to self-renew and to differentiate into all blood cell lineages. In vivo, hematopoietic stem/progenitor cells (HSPCs) are in close association with stromal cells that constitute a supportive microenvironment also called niche. Recently, exosomes that are small microvesicles enclosed by a lipid bilayer and enriched in cytoplasmic proteins, mRNAs, microRNAs, have emerged as major communication mediators between cells. However, their implication in the cross-talk between HSCs and stromal cells is still largely unknown. This study aims to assess the existence and the functionality of stromal cell-derived exosomes in the HSPC support. To address this issue, we used two murine stromal cell lines derived from the fetal liver and with differing capacity to maintain HSPCs ex vivo as revealed by repopulation assay and long-term cultures. AFT024 (AFT) harbors a potent HSPC supporting capacity in vitro whereas BFC012 (BFC) is non supportive. For each cell line, the exosome fractions were isolated from culture supernatant by ultra-centrifugation. Electron microscopy, western blot, and flow cytometry analyses revealed that both AFT and BFC stromal cells secrete exosomes. Interestingly, using PKH67 stained exosomes, we demonstrated that bone marrow Lin-Sca-1+c-kit+ (LSK) cells preferentially uptake AFT-derived exosomes. This observation might be related to the different tetraspanin compositions of AFT and BFC derived exosomes as observed by flow cytometry. We then showed an increase in cell viability and clonogenic potential when LSK cells were exposed to AFT-derived exosomes for 96 hours in cytokine-free medium as compared to controls. Moreover, cultures with AFT-derived exosomes exhibited a 3.5 fold increase in the number of LSK cells as compared to untreated conditions. We then used high-throughput sequencing to explore the molecular signatures of AFT and BFC derived exosomes, as well as their cells of origin. We identified a list of 394 mRNAs and 6 microRNAs specifically expressed in exosomes and correlated to the HSPC support. Gene ontology analysis revealed that the apoptotic regulation, cell survival and proliferation pathways were significantly enriched in the AFT-derived exosomal signature. In addition, we showed the transfer of mRNAs involved in these pathways from the AFT-exosomes to the LSK recipient cells. Together with our observation of a decrease in the LSK apoptotic cells after co-culture with AFT-derived exosomes, these data suggest that exosomes released by AFT cells may protect HSPCs from apoptosis. Collectively, our results revealed an important role for exosomes in the HSPC supporting capacity of stromal cells. This work provides new insights in our understanding of the molecular and cellular mechanisms involved in the cross-talk between HSPCs and their niches. It may also have interesting applications in regenerative medicine, regarding the ex vivo manipulation of HSCs in stromal-free conditions for cell therapy. Disclosures No relevant conflicts of interest to declare.

Download Full-text

A secreted and LIF-mediated stromal cell–derived activity that promotes ex vivo expansion of human hematopoietic stem cells

Blood ◽

10.1182/blood.v95.6.1957 ◽

2000 ◽

Vol 95 (6) ◽

pp. 1957-1966 ◽

Cited By ~ 40

Author(s):

Chu-Chih Shih ◽

Mickey C.-T. Hu ◽

Jun Hu ◽

Yehua Weng ◽

Paul J. Yazaki ◽

...

Keyword(s):

Stem Cells ◽

Stem Cell ◽

Hematopoietic Stem Cells ◽

Stromal Cells ◽

Cell Expansion ◽

Culture System ◽

Stromal Cell ◽

Ex Vivo ◽

Hematopoietic Stem ◽

Stem Cell Expansion

Abstract The development of culture systems that facilitate ex vivo maintenance and expansion of transplantable hematopoietic stem cells (HSCs) is vital to stem cell research. Establishment of such culture systems will have significant impact on ex vivo manipulation and expansion of transplantable stem cells in clinical applications such as gene therapy, tumor cell purging, and stem cell transplantation. We have recently developed a stromal-based culture system that facilitates ex vivo expansion of transplantable human HSCs. In this stromal-based culture system, 2 major contributors to the ex vivo stem cell expansion are the addition of leukemia inhibitory factor (LIF) and the AC6.21 stromal cells. Because the action of LIF is indirect and mediated by stromal cells, we hypothesized that LIF binds to the LIF receptor on AC6.21 stromal cells, leading to up-regulated production of stem cell expansion promoting factor (SCEPF) and/or down-regulated production of stem cell expansion inhibitory factor (SCEIF). Here we demonstrate a secreted SCEPF activity in the conditioned media of LIF-treated AC6.21 stromal cell cultures (SCM-LIF). The magnitude of ex vivo stem cell expansion depends on the concentration of the secreted SCEPF activity in the SCM-LIF. Furthermore, we have ruled out the contribution of 6 known early-acting cytokines, including interleukin-3, interleukin-6, granulocyte macrophage colony-stimulating factor, stem cell factor, flt3 ligand, and thrombopoietin, to this SCEPF activity. Although further studies are required to characterize this secreted SCEPF activity and to determine whether this secreted SCEPF activity is mediated by a single factor or by multiple growth factors, our results demonstrate that stromal cells are not required for this secreted SCEPF activity to facilitate ex vivo stem cell expansion.

Download Full-text

RUNX1C-Mediated Reprogramming Of Human Bone Marrow Stromal Cells into Early Blood Progenitors

Blood ◽

10.1182/blood.v122.21.2463.2463 ◽

2013 ◽

Vol 122 (21) ◽

pp. 2463-2463

Author(s):

Weihong Yin ◽

Christopher D Porada ◽

Stephen Walker ◽

Colin Bishop ◽

Graca Almeida-Porada

Keyword(s):

Bone Marrow ◽

Flow Cytometry ◽

Conflicts Of Interest ◽

Ex Vivo ◽

Hematopoietic Cells ◽

Dermal Fibroblasts ◽

Hematopoietic Stem ◽

Surface Marker Expression ◽

Somatic Cell Reprogramming ◽

Hematopoietic Lineage

Abstract Somatic cell reprogramming to the hematopoietic lineage, either through a pluripotent state or directly, opens the possibility of production of a ready source of autologous hematopoietic stem cells (HSC) that can be used to treat/cure a wide variety of blood disorders. While it has previously been shown that dermal fibroblasts (HFF) can be directly reprogrammed to the hematopoietic lineage, the efficiency was relatively low and the resultant hematopoietic cells lacked multilineage differentiative potential. Stro1(+) isolated stromal progenitors (SIPs) can easily be isolated from the bone marrow (BM) and expanded ex-vivo to obtain clinically significant numbers of cells. In similarity to HSC, SIPs are derived from the mesoderm, and are intimately linked with HSC specification during ontogeny. As such, they are likely to be epigenetically closer to HSC than HFF, and therefore good candidates for reprogramming into hematopoietic cells. To verify the uniqueness of SIPs for reprogramming, we transduced SIPs and HFF with OCT4 and/or RUNX1C, a master transcription factor (TF) that triggers the developmental onset of definitive hematopoiesis, in the following combinations: 1) OCT4 alone; 2) RUNX1C alone; or 3) OCT4+RUNX1C. We then performed a timeline of gene/cell surface marker expression (using microarray, qRT-PCR, and flow cytometry) from day 3-16 post-transduction. Visual inspection of the cultures showed that, while reprogrammed colonies began to appear in SIPs cultures at day 9, no colonies were seen during this time period in HFF cultures. Flow cytometry and molecular analyses of colonies obtained from OCT4+RUNX1C combination demonstrated that expression of CD41, the earliest marker of commitment to the hematopoietic lineage, commenced within only 3-4 days and peaked at day 5-6, by which time ∼20% of SIPs expressed this marker. This peak in CD41 expression coincided with commencement of expression of CD34 and CD45, and maximal induction of several hematopoiesis-specific TFs and phenotypic markers such as PU.1, HOXB4, GATA2, MIXL, WNT3, KDR, CDX4, which occurred at 1-3 logs higher levels in SIPs than HFF. Further studies demonstrated that the chromatin remodeling function of OCT4 could be replaced with the histone methyltransferase inhibitor Bix-01294, with the combination of RUNX1C and Bix-01294 inducing levels of CD34 and CD41 expression by day 5 that were similar to those achieved with RUNX1C plus OCT4. The present studies thus take several important steps towards making the promise of producing autologous hematopoietic cells for transplantation via direct reprogramming a reality. Disclosures: No relevant conflicts of interest to declare.

Download Full-text

Deletion of Pleiotrophin in LepR+ Perivascular Cells Depletes Hematopoietic Stem Cells

Blood ◽

10.1182/blood.v128.22.1491.1491 ◽

2016 ◽

Vol 128 (22) ◽

pp. 1491-1491

Author(s):

Heather A Himburg ◽

Vivian Y. Chang ◽

Joshua Sasine ◽

Jenny Kan ◽

Liman Zhao ◽

...

Keyword(s):

Steady State ◽

Stromal Cells ◽

Leptin Receptor ◽

Conflicts Of Interest ◽

Ex Vivo ◽

Hematopoietic Cells ◽

Heparin Binding ◽

Perivascular Cells ◽

Hematopoietic Stem

Abstract Pleiotrophin (PTN) is a heparin binding growth factor which is expressed by bone marrow vascular endothelial cells (BM ECs) and perivascular stromal cells. Treatment of murine or human HSCs ex vivo promotes HSC expansion (Nat Med. 2010 Apr;16(4):475-82) and constitutive deletion of PTN depletes LT-HSCs in steady state and markedly impairs HSC regeneration following myeloablation (Cell Rep. 2012 Oct 25;2(4):964-75; JCI. 2014;18(7):1123-1129). Here, we sought to determine which BM microenvironment cell is responsible for PTN-mediated maintenance of the HSC pool. Utilizing the Cre-loxP system, we deleted PTN from VE-cadherin+ ECs, leptin receptor+ (lepR+) perivascular stromal cells, osteocalcin+ osteoblasts, and vav1+ hematopoietic cells and examined the effects on hematopoiesis. We observed no differences in steady state hematopoiesis or HSC content as measured by long-term competitive repopulation assays in mice lacking PTN expression in osteocalcin+ cells, vav1+ hematopoietic cells or VE-cadherin+ BM ECs. However, deletion of PTN from lepR+ BM perivascular cells caused a significant decrease in BM c-kit+sca-1+lin- cells (KSL cells) and BM SLAM+KSL HSCs, and colony forming cell (CFC) content compared to PTN+/+ controls (*p = 0.04, 0.04, and 0.001, respectively). Importantly, deletion of PTN in lepR+ cells, caused a significant reduction in long-term HSC content as measured by primary and secondary competitive repopulation assays (*P<0.01 for all time points through 20 weeks). These data suggest that LepR+ BM perivascular cells, rather than VE-cadherin+ ECs are the primary source of PTN in the BM niche which contributes to the maintenance of the HSC pool. Figure 1 Figure 1. Figure 2 Figure 2. Disclosures No relevant conflicts of interest to declare.

Download Full-text

CD166+CD34+ Cells Exhibit Marked Functional Differences During Fetal and Adult Life

Blood ◽

10.1182/blood.v122.21.2435.2435 ◽

2013 ◽

Vol 122 (21) ◽

pp. 2435-2435

Author(s):

Saloomeh Mokhtari ◽

Zanetta S. Lamar ◽

Chris Booth ◽

Frank Marini ◽

Christopher D Porada ◽

...

Keyword(s):

Flow Cytometry ◽

Growth Medium ◽

Stromal Cells ◽

Conflicts Of Interest ◽

Fetal Liver ◽

Flow Cytometric Analysis ◽

Adult Life ◽

Hematopoietic Stem ◽

Flow Cytometric ◽

Cd34 Cells

Abstract ALCAM/CD166 is expressed from the onset of hematopoiesis in the yolk sac and in a variety of hematopoietic tissues throughout ontogeny. Both hematopoietic and stromal cells in the AGM region, fetal liver, and fetal and adult marrow express this molecule. CD166 double knockout mice are viable and fertile, without any major blood defects, but their microenvironment and hematopoietic stem cells (HSC) exhibit deficiencies in their ability to support and engraft long-term, respectively. In order to further study the role of CD166 in hematopoiesis, we characterized, during ontogeny, the origin, function, and sub-populations of CD166+ cells in different hematopoietic organs. To this end, we used flow cytometry, confocal microscopy, and colony-forming assays to analyze human fetal liver (FL) at 18 and 20 gestational weeks (gw), bone marrow (BM) from 10 to 20gw, and adult BM. Flow cytometric analysis of FL at 18 and 20gw demonstrated that although 3±1% of liver cells at this age were CD166+, less than 1% were endothelial CD166+CD34+ cells, and no hematopoietic CD166+CD34+CD45+ cells were detected. In fetal BM, CD166+ cells emerged after 15gw, expressed Flk-1 and CD34, and their percentage increased progressively with gestational age. Flow cytometric analysis at 20gw showed that 1.5±1% of cells were CD166+CD34+, of which 93±0.5% were CD45+. Human adult BM contained 2±0.5% of CD166+CD34+ cells, of which only 66±0.6% were CD45+. In order to functionally characterize CD166+CD34+ cells from adult and fetal BM (20gw), we plated these cells in mesenchymal cell growth medium (MSCGM), endothelial growth medium (EGM-2), and complete methylcellulose (MC). MSCGM and EGM-2 did not support growth and expansion of fetal or adult CD166+CD34+ cells. Quantification of the hematopoietic colony-forming potential of these cells demonstrated that fetal CD166+CD34+ generated/1000 cells: 8±1 Blast; 27±2 CFU-Mix; 51±10 CFU-GM; and 0 BFU-E, while adult CD166+CD34+ gave rise to 7 Blast; 17 CFU-Mix; 36 CFU-GM; and 10 BFU, demonstrating differences in the hematopoietic potential of these cells. Furthermore, at day 12 of MC culture, adherent stromal cells were detected underneath MC, but only in cultures from fetal BM. Characterization of these cells by flow cytometry showed that more than 90±2% of these cells were CD166+CD9+, and 30±5% were CD146+. Furthermore, these stromal CD166+ cells did not express CD34, CD45, CD31, CD209, or CD6. Immunostaining demonstrated that the CD166+CD146+ cells expressed osteopontin and Stro-1. A CD41+CD68+ population of cells was also found. In conclusion, we found that, during ontogeny, expression of CD166 in FL is not associated with hematopoietic cells. In the BM, expression of CD166 is associated with CD34 and Flk2, and its expression on HSC commences later in gestation, suggesting that these cells either arise in the BM, or that CD166 expression is triggered at a certain time point in gestation, probably associated with rapid proliferation of HSC during this time period. Furthermore, we demonstrated that CD34+CD166+ cells from 20gw fetal BM contain hematopoietic and stromal cell populations, while adult BM-derived CD34+ CD166+ cells are exclusively hematopoietic. Disclosures: No relevant conflicts of interest to declare.

Download Full-text

Targeting Bone Marrow Mesenchymal Stromal Cells Using Cre-Recombinase Transgenes

Blood ◽

10.1182/blood.v126.23.2401.2401 ◽

2015 ◽

Vol 126 (23) ◽

pp. 2401-2401

Author(s):

Jingzhu Zhang ◽

Daniel C. Link

Keyword(s):

Bone Marrow ◽

Mesenchymal Stromal Cells ◽

Stromal Cells ◽

Stromal Cell ◽

Conflicts Of Interest ◽

Expression Profiles ◽

Sympathetic Nerves ◽

Cell Populations ◽

Hematopoietic Stem ◽

Lineage Mapping

The bone marrow microenvironment contains hematopoietic niches that regulate the proliferation, differentiation, and trafficking of hematopoietic stem/progenitors cells (HSPCs). These hematopoietic niches are comprised of a heterogeneous population of stromal cells that include, endothelial cells, osteoblasts, CXCL12-abundant reticular (CAR) cells, mesenchymal stem cells (MSCs), arteriolar pericytes, and sympathetic nerves. Emerging data suggest that specific stromal populations may regulate distinct types of HPSCs. Thus, it is important to have validated approaches to interrogate and target specific stromal cell populations. Prior studies have shown that Prx1-Cre, Osx-Cre, Lepr-Cre, and Nes-Cre broadly target mesenchymal stromal cells in the bone marrow. Here, we rigorously define the stromal cell populations targeted by two Cre-transgenes that are commonly used to target osteolineage cells (Ocn-Cre, and Dmp1-Cre) and introduce a new Cre-transgene (Tagln-Cre) that efficiently targets bone marrow pericytes. For each Cre-transgene, we performed lineage mapping using ROSA26Ai9/Ai9 mice, in which cells that have undergone Cre-mediated recombination express tdTomato. In some cases, we further crossed these mice to introduce the Cxcl12gfp transgene, which can be used to define GFP-bright CAR cells. Immunostaining of bone sections and flow cytometry were used to define the target stromal cell population(s) in these mice. Osteocalcin (Bglap, Ocn) is primarily expressed in mature osteoblasts. Accordingly, Ocn-Cre is widely used to specifically target osteoblasts. However, our lineage mapping studies show that Ocn-Cre targets not only all osteoblasts, but also 72 ± 4.0% of CAR cells. Ocn-Cre also targets a subset of NG2+ arteriolar pericytes. Dentin matrix acidic phosphoprotein 1 (Dmp1) is expressed primarily in osteocytes, and Dmp1-Cre has been widely used to specifically target osteocytes. However, we show that Dmp1-Cre also efficiently targets endosteal osteoblasts and approximately 40% of CAR cells. To target bone marrow pericytes, we tested several Cre-transgenes, ultimately focusing on Tagln-Cre. Transgelin (Tagln, SM22a) is broadly expressed in pericytes, smooth muscle cells, and cardiomyocytes. Lineage-mapping studies show that Tagln-Cre targets all arteriolar and venous sinusoidal pericytes in the bone marrow. It also targets osteoblasts and 75 ± 5.2% of CAR cells. There are several recent studies that have ascribed specific functions to osteoblasts or osteocytes based on targeting using Ocn-Cre or Dmp1-Cre, respectively. In light of our data, these conclusions need to be re-evaluated. Ocn-Cre, Dmp1-Cre, and Tagln-Cre each target a subset of CAR cells. Studies are underway to determine whether these CAR subsets have unique expression profiles and functions. Finally, Talgn-Cre represents a new tool for investigators in the field to efficiently target bone marrow pericytes. Disclosures No relevant conflicts of interest to declare.

Download Full-text

Residual HSPC in the Leukemia Microenvironment Are Reprogrammed Via Extracellular Vesicle Trafficking

Blood ◽

10.1182/blood.v128.22.888.888 ◽

2016 ◽

Vol 128 (22) ◽

pp. 888-888 ◽

Cited By ~ 1

Author(s):

Sherif Abdelhamed ◽

Noah I Hornick ◽

Peter Kurre

Keyword(s):

Cell Cycle ◽

Dna Methylation ◽

Dna Damage ◽

High Throughput Sequencing ◽

Conflicts Of Interest ◽

Ex Vivo ◽

Leukemic Cells ◽

Alternative Mechanism ◽

Proteomic Profiling ◽

Hematopoietic Stem

Several groups have shown that leukemic cells create a self-reinforcing bone marrow (BM) niche that functionally impairs normal hematopoietic stem and progenitor cells (HSPC) indirectly through stroma-secreted factors. We recently demonstrated an alternative mechanism whereby extracellular vesicles (EVs) from acute myeloid leukemia (AML) patients and cell lines, but not BM CD34 controls, suppress their clonogenicity through EV trafficking of microRNA that directly downregulate critical transcription factors (c-Myb and HoxA9). Here, we aimed to clarify the fate of residual HSPC in in vivo AML xenografts, as well as ex vivo intrafemural (IF) injection and in vitro exposure of EVs experiments. Among KSL cells we observed a significant increase in the frequency of the long-term hematopoietic stem cell (SLAM, CD150+CD48−) subpopulation, but not the multipotent progenitors even at low levels of AML infiltration or direct IF injection of EVs. The HSPC pool redistribution was accompanied by cell cycle alterations in residual HSPC that showed AML EVs consistently induced quiescence (G0) in KSL (cKit+Sca1+Lin−) HSPC populations. When we assessed their DNA damage, residual HSPC showed a distinct increase in the gH2AX foci relative to control non-engrafted mice as well as the transcriptional upregulation of Rad51 and P21 genes along with gains in phosphorylation of the tumor suppressor p53. Yet, the reprogrammed KSL showed no evidence of apoptosis indicated by the lack of upregulation of the p53 target, Puma, and Annexin V staining, nor evidence of senescence (P16 and Sparc transcripts). To gain additional insight, we performed a tandem mass tag (TMT) proteomic profiling of AML-EV exposed HSPC with or without exposure to EVs derived from AML cells. The results showed significant enrichment of DNA methylation regulatory pathway such as DNMT1, HELLS and UHRF1 as well as inflammatory pathways including IL1b, NOS, CEBPB and NFkB pathway-targets, confirmed by transcriptional profiling of KSL from xeno-transplanted mice. Based on our recent report that miR-1246 is one of the most highly enriched miRNA in AML derived EVs and proceeded to determine its target transcripts using an attenuated RISC complex (RISC-Trap), followed by high-throughput sequencing. Bioinformatics analysis identified a set of 27 miR-1246-specific targets relative to control microRNAs. Strikingly, the target set was selectively enriched for a panel of negative cell-cycle regulator genes (CDK1, CDK7, CDK11, CCNF, HDAC2 and GATA3) as well as the DNA methylation regulators (DNMT1 and HELLS).Collectively, our results demonstrated that residual HSPC in the AML BM are phenotypically reprogrammed and suppressed in their proliferation along with DNA damage accumulation via paracrine EV microRNA trafficking. Our study provides insight into HSPC fates in the AML niche and echoes observations of cell competition, as a mode of non-cell autonomous regulation where p53 activation in the reprogrammed cells leads to a progressive decline in proliferation and fitness. We propose that AML EV trafficking of miR-1246 specifically may contribute to the altered fate of residual HSPC via transcriptional regulation of proliferation-related genes. Disclosures No relevant conflicts of interest to declare.

Download Full-text

Bone Marrow Stromal Cell Remodeling Is a Common Feature of Diverse Fibrotic Myeloproliferative Neoplasm Models

Blood ◽

10.1182/blood.v128.22.25.25 ◽

2016 ◽

Vol 128 (22) ◽

pp. 25-25

Author(s):

Timothy B Campbell ◽

Si Yi Zhang ◽

Alexander Valencia ◽

Emmanuelle Passegue

Keyword(s):

Bone Marrow ◽

Stromal Cells ◽

Stromal Cell ◽

Conflicts Of Interest ◽

Myeloproliferative Neoplasms ◽

Critical Role ◽

Myeloproliferative Neoplasm ◽

Myelogenous Leukemia ◽

Hematopoietic Stem ◽

Cell Numbers

Abstract Myeloproliferative neoplasms (MPN) are blood cancers initiated by driver mutations that transform hematopoietic stem cells. MPN exhibit gross pathologic bone marrow (BM) stromal remodeling, including damaging myelofibrotic change that leads to dependence on extramedullary hematopoiesis and more severe clinical diseases. Therapies targeting fibrotic change would have broad appeal in the treatment of these diseases. We previously demonstrated a critical role for malignant myeloid cells in remodeling endosteal mesenchymal stromal cells (MSC) into myelofibrotic osteoblast-lineage cells (OBC) in a model of chronic myelogenous leukemia (CML) driven by BCR/ABL (Schepers et al., Cell Stem Cell, 2013). In a separate study in a fibrotic MPN model driven by Jak2V617F, neuropathy and nestin-positive MSC cell death were found critical to disease progression but their involvement in myelofibrosis was not investigated (Arranz et al. Nature. 2014). Our goal is to characterize the type of BM stromal remodeling occurring in non-CML MPN models driven by various mutations and representing a spectrum of disease severity and fibrosis. This includes a minimally fibrotic transgenic Jak2V617F alone model (Jak2V617F model, Xing et al., Blood, 2008) and more advanced fibrotic models driven by MPLW515L expression (MPLW515L model, Pikman et al., PLoS Med, 2006) or combined transgenic Jak2V617F expression with conditional deletion of the polycomb gene EZH2 (Jak2V617F/EZH2-/- model, Sashida et al., JEM, 2016). We found common blood and BM hematopoietic changes in all three models, including thrombocytosis and expansion of myeloid-biased multipotent progenitor BM cells and confirmed the degree of fibrosis using picrosirius red staining of bone sections. Both MPLW515L and Jak2V617F/EZH2-/- heavily fibrotic models demonstrated inhibition of total endosteal MSC, OBC and endothelial cell (EC) numbers during disease development - in most cohorts a greater than 50% decrease in absolute stromal cell numbers was found. In addition, we observed that whole BM cells from Jak2V617F/EZH2-/-mice contained a significantly lower number of totalfibroblast colony forming cells (CFU-F). In co-culture experiments designed to measure direct MSC remodeling induced by malignant cells, both MPLW515L and Jak2V617F/EZH2-/- BM cells inhibited healthy endosteal MSC colony formation over time. In contrast, we found no inhibition of stromal cell numbers or co-culture MSC growth in the minimal fibrotic Jak2V617F model. In initial experiments measuring rare central marrow perivascular MSC, we found reduced LepR+ MSC (Ding et al., Nature, 2012) in both MPLW515L and Jak2V617F/EZH2-/- long bone sections using immunofluorescence. Our results show that fibrotic development in non-CML MPN inhibits stromal cell numbers and function likely via direct effects of malignant hematopoietic cells. This is in contrast to fibrotic CML development where myelofibrotic endosteal stromal cells are expanded. This difference could be partly explained by the type and localization of fibrosis in these various models. The CML model has focal endosteal collagen-I fibrosis which is heavily reliant on osteoblast remodeling, while the MPLW515L and Jak2V617F/EZH2-/- models have more diffuse reticulin central marrow fibrosis which may be produced through a process of stromal cell senescence or differentiation. Overall, this study underscores that a “one size fits all“ approach to understanding myelofibrosis is insufficient. To tease out these differences, we are examining qualitative and quantitative changes in additional central marrow MSC populations, including PDGFR+, Sca-1+ and Gli-1+ MSC, during MPN development as well as assaying the molecular mediators of stromal remodeling. Our long-term goal is to identify therapies that can restore a more normal BM stroma and support healthy hematopoiesis in MPN. Disclosures No relevant conflicts of interest to declare.

Download Full-text

A Review of Evaluating Hematopoietic Stem Cells Derived from Umbilical Cord Blood's Expansion and Homing

Current Stem Cell Research & Therapy ◽

10.2174/1574888x15666200124115444 ◽

2020 ◽

Vol 15 (3) ◽

pp. 250-262

Author(s):

Maryam Islami ◽

Fatemeh Soleimanifar

Keyword(s):

Stem Cells ◽

Hematopoietic Stem Cells ◽

Umbilical Cord ◽

Stromal Cells ◽

Ex Vivo ◽

Hematologic Malignancies ◽

Future Directions ◽

Hematopoietic Stem ◽

Efficient Procedure ◽

Hematopoietic Recovery

Transplantation of hematopoietic stem cells (HSCs) derived from umbilical cord blood (UCB) has been taken into account as a therapeutic approach in patients with hematologic malignancies. Unfortunately, there are limitations concerning HSC transplantation (HSCT), including (a) low contents of UCB-HSCs in a single unit of UCB and (b) defects in UCB-HSC homing to their niche. Therefore, delays are observed in hematopoietic and immunologic recovery and homing. Among numerous strategies proposed, ex vivo expansion of UCB-HSCs to enhance UCB-HSC dose without any differentiation into mature cells is known as an efficient procedure that is able to alter clinical treatments through adjusting transplantation-related results and making them available. Accordingly, culture type, cytokine combinations, O2 level, co-culture with mesenchymal stromal cells (MSCs), as well as gene manipulation of UCB-HSCs can have effects on their expansion and growth. Besides, defects in homing can be resolved by exposing UCB-HSCs to compounds aimed at improving homing. Fucosylation of HSCs before expansion, CXCR4-SDF-1 axis partnership and homing gene involvement are among strategies that all depend on efficiency, reasonable costs, and confirmation of clinical trials. In general, the present study reviewed factors improving the expansion and homing of UCB-HSCs aimed at advancing hematopoietic recovery and expansion in clinical applications and future directions.

Download Full-text