Distinct c-Myb Regulation by HoxA9, Meis1 and Pbx1 in Haemopoietic and Leukaemic-Like Stem Cells.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 1431-1431
Author(s):  
Emilie Dassé ◽  
Giacomo Volpe ◽  
Walter del Pozzo ◽  
Jonathan Frampton ◽  
Stephanie Dumon
Keyword(s):  
Stem Cells ◽  
Transcription Factor ◽  
Stem Cell ◽  
Regulatory Elements ◽  
Proximal Promoter ◽  
Cell Leukaemia ◽  
Mouse Bone Marrow ◽  
First Intron ◽  
Hypersensitive Sites ◽  
Factor C

Abstract Abstract 1431 Poster Board I-454 The transcription factor c-Myb is an essential regulator of haemopoiesis and its expression is deregulated in several types of leukaemia. Although some c-Myb functions have been defined, the mechanisms involved in the control of its expression have yet to be elucidated. Previous studies have suggested that transcription initiation at the c-myb gene is constitutive, and that the level of mRNA is regulated by an elongation-blocking mechanism operating in its first intron. Here, we define and compare mechanisms influencing c-myb expression in haemopoietic stem cells (HSCs) versus leukaemic stem cell (LSC)-like cells. Using a nuclease sensitivity assay we have defined several potential regulatory elements in both HSC and LSC-like model cell lines. These hypersensitive sites are in the proximal promoter and the first intron, the latter correlating with the position of the putative transcription elongation regulatory region. Moreover, the hypersensitive sites are located in regions of sequence conservation and encompass a number of potential binding sites for homeodomain (HD)-containing proteins. In this study, we were able to demonstrate that the HD-containing transcription factors HoxA9 and Meis1, which are highly expressed in HSCs and whose co-expression in mouse bone marrow leads to rapid development of acute myeloid leukaemia (AML), are necessary but not sufficient for c-myb expression. In addition, we show that the pre-B-cell leukaemia transcription factor-1 (Pbx1), known to be a key binding partner of HD-containing factors, is indispensable in the regulation of c-myb expression. Comparing the effects of altered levels of HoxA9, Meis1 and Pbx1 in HSCs versus LSCs suggests that distinct mechanisms involving dimeric or trimeric complexes operate to regulate c-myb expression in these two stem cell types. Disclosures No relevant conflicts of interest to declare.

Transcriptional Regulation of the LMO2 T-Cell Leukaemia Oncogene.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 2728-2728
Author(s):  
Josette-Renée Landry ◽  
Sarah Kinston ◽  
Kathy Knezevic ◽  
Anthony R. Green ◽  
Berthold Göttgens
Keyword(s):  
Stem Cells ◽  
T Cell ◽  
Cell Lines ◽  
Molecular Mechanisms ◽  
Regulatory Elements ◽  
Proximal Promoter ◽  
Cell Leukaemia ◽  
Haematopoietic Stem Cells ◽  
Haematopoietic Cells

Abstract Transcriptional control has long been identified as a key mechanism regulating the formation and subsequent behaviour of haematopoietic stem cells. We have used a comparative genomics approach to identify transcriptional regulatory elements of the LMO2 gene, a transcriptional cofactor originally identified through its involvement in T-cell leukaemia and subsequently shown to be critical for the formation of haematopoietic stem cells and endothelial development. An initial stringent search for homology between evolutionary distant species demonstrated that, apart from the coding exons, high level of identity between mammalian, amphibian and fish sequences was restricted to the proximal promoter region of LMO2. Real-time RT-PCR expression analysis identified this promoter as the predominant source of transcription in haematopoietic tissue. Transient and stable transfections indicated that the proximal promoter was active in haematopoietic progenitor and endothelial cell lines and this activity was shown to depend on three conserved Ets sites which were bound in vivo by Elf1, Fli1 and Ets1. Transgenic analysis demonstrated that the LMO2 proximal promoter was sufficient for expression in endothelial cells in vivo. However, no haematopoietic expression was observed indicating that additional enhancers are required to mediate transcription from the proximal promoter in haematopoietic cells. To identify additional elements involved in haematopoietic expression of LMO2, we have performed a less restrictive search for conserved sequences by comparing the human, dog, rat and mouse LMO2 loci to the marsupial opossum LMO2 locus. The addition of the opossum locus, and removal of the more distant fish and amphibian sequences from the alignment, resulted in the discovery of eleven conserved regions. These sequences represent candidate haematopoietic regulatory regions as they contain conserved transcription factor binding sites (E boxes, Ets and Gata sites) previously shown to regulate several other haematopoietic genes. We will present results from a systematic analysis of these regions for enhancer activity in both haematopoietic cell lines and transgenic mice, which suggest that several of these elements indeed act as enhancers. Taken together, our experiments will provide a framework for the transcriptional hierarchies within which LMO2 exerts its function in normal haematopoietic cells. Moreover, the current studies will serve as a platform to examine potential molecular mechanisms that can cause ectopic expression of LMO2 in T-cell progenitors with the ultimate consequence of developing T-ALL.

scholarly journals Mitochondria regulate intestinal stem cell proliferation and epithelial homeostasis through FOXO

2020 ◽  
Vol 31 (14) ◽  
pp. 1538-1549
Author(s):  
Fan Zhang ◽  
Mehdi Pirooznia ◽  
Hong Xu
Keyword(s):  
Stem Cells ◽  
Cell Proliferation ◽  
Transcription Factor ◽  
Stem Cell ◽  
Electron Transport Chain ◽  
Intestinal Stem Cell ◽  
Stem Cell Proliferation ◽  
Epithelial Homeostasis ◽  
Chain Complexes ◽  
Transport Chain

Deficiencies in electron transport chain complexes increase the activity of FOXO transcription factor in Drosophila midgut stem cells, which impairs stem cell proliferation and enterocyte specification.

scholarly journals Dissecting Hes-centered transcriptional networks in neural stem cell maintenance and tumorigenesis in Drosophila

2020 ◽  
Author(s):  
Srivathsa S. Magadi ◽  
Chrysanthi Voutyraki ◽  
Gerasimos Anagnostopoulos ◽  
Evanthia Zacharioudaki ◽  
Ioanna K. Poutakidou ◽  
...  
Keyword(s):  
Stem Cells ◽  
Nervous System ◽  
Transcription Factor ◽  
Stem Cell ◽  
Neural Stem Cells ◽  
Cell Fate ◽  
Asymmetric Cell Division ◽  
Transcriptional Networks ◽  
Malignant Tumours ◽  
Stem Cell Maintenance

ABSTRACTNeural stem cells divide during embryogenesis and post embryonic development to generate the entire complement of neurons and glia in the nervous system of vertebrates and invertebrates. Studies of the mechanisms controlling the fine balance between neural stem cells and more differentiated progenitors have shown that in every asymmetric cell division progenitors send a Delta-Notch signal back to their sibling stem cells. Here we show that excessive activation of Notch or overexpression of its direct targets of the Hes family causes stem-cell hyperplasias in the Drosophila larval central nervous system, which can progress to malignant tumours after allografting to adult hosts. We combined transcriptomic data from these hyperplasias with chromatin occupancy data for Dpn, a Hes transcription factor, to identify genes regulated by Hes factors in this process. We show that the Notch/Hes axis represses a cohort of transcription factor genes. These are excluded from the stem cells and promote early differentiation steps, most likely by preventing the reversion of immature progenitors to a stem-cell fate. Our results suggest that Notch signalling sets up a network of mutually repressing stemness and anti-stemness transcription factors, which include Hes proteins and Zfh1, respectively. This mutual repression ensures robust transition to neuronal and glial differentiation and its perturbation can lead to malignant transformation.

scholarly journals Use of adipose-derived stem cells in lymphatic tissue engineering and regeneration

2021 ◽  
Vol 48 (5) ◽  
pp. 559-567
Author(s):  
Antonio Jorge Forte ◽  
Daniel Boczar ◽  
Rachel Sarabia-Estrada ◽  
Maria T. Huayllani ◽  
Francisco R. Avila ◽  
...  
Keyword(s):  
Breast Cancer ◽  
Systematic Review ◽  
Tissue Engineering ◽  
Stem Cells ◽  
Stem Cell ◽  
Growth Factor ◽  
Cochrane Central Register ◽  
Adipose Derived Stem Cells ◽  
Lymphatic Tissue ◽  
Factor C

The potential to differentiate into different cell lines, added to the easy and cost-effective method of extraction, makes adipose-derived stem cells (ADSCs) an object of interest in lymphedema treatment. Our study’s goal was to conduct a comprehensive systematic review of the use of ADSCs in lymphatic tissue engineering and regeneration. On July 23, 2019, using PubMed/MEDLINE, Cochrane Clinical Answers, Cochrane Central Register of Controlled Trials, and Embase databases, we conducted a systematic review of published literature on the use of ADSCs in lymphatic tissue engineering and regeneration. There were no language or time frame limitations, and the following search strategy was applied: ((Adipose stem cell) OR Adipose-derived stem cell)) AND ((Lymphedema) OR Breast Cancer Lymphedema). Only original research manuscripts were included. Fourteen studies fulfilled the inclusion criteria. Eleven studies were experimental (in vitro or in vivo in animals), and only three were clinical. Publications on the topic demonstrated that ADSCs promote lymphangiogenesis, and its effect could be enhanced by modulation of vascular endothelial growth factor-C, interleukin-7, prospero homeobox protein 1, and transforming growth factor-β1. Pilot clinical studies included 11 patients with breast cancer-related lymphedema, and no significant side effects were present at 12-month follow-up. Literature on the use of ADSCs in lymphatic tissue engineering and regeneration demonstrated promising data. Clinical evidence is still in its infancy, but the scientific community agrees that ADSCs can be useful in regenerative lymphangiogenesis. Data collected in this review indicate that unprecedented advances in lymphedema treatment can be anticipated in the upcoming years.

scholarly journals The Role of Transcription Factor PU.I in the Activity of the Intronic Enhancer of the Eosinophil-Derived Neurotoxin (RNS2) Gene

Blood ◽  
1998 ◽  
Vol 91 (6) ◽  
pp. 2126-2132 ◽  
Author(s):  
Thamar B. van Dijk ◽  
Eric Caldenhoven ◽  
Jan A.M. Raaijmakers ◽  
Jan-Willem J. Lammers ◽  
Leo Koenderman ◽  
...  
Keyword(s):  
Transcription Factor ◽  
Point Mutations ◽  
Proximal Promoter ◽  
Multiple Forms ◽  
Enhancer Activity ◽  
Promoter Sequences ◽  
Intronic Enhancer ◽  
First Intron ◽  
Shift Analysis

Eosinophil-derived neurotoxin (EDN) found in the granules of human eosinophils is a cationic ribonuclease toxin. Expression of the EDN gene (RNS2) in eosinophils is dependent on proximal promoter sequences in combination with an enhancer located in the first intron. We further define here the active region of the intron using transfections in differentiated eosinophilic HL60 cells. We show that a region containing a tandem PU.I binding site is important for intronic enhancer activity. This region binds multiple forms of transcription factor PU.I as judged by gel-shift analysis and DNA affinity precipitation. Importantly, introducing point mutations in the PU.I site drastically reduces the intronic enhancer activity, showing the importance of PU.I for expression of EDN in cells of the eosinophilic lineage.

Establishment of human OCT4 as a putative HSP90 client protein : a case for HSP90 chaperoning pluripotency

2015 ◽  
Author(s):  
◽  
Jason Neville Sterrenberg
Keyword(s):  
Stem Cells ◽  
Transcription Factor ◽  
Stem Cell ◽  
Cell Biology ◽  
Therapeutic Potential ◽  
Stem Cell Biology ◽  
Client Protein ◽  
Hsp90 Inhibition ◽  
Regulated Gene Expression ◽  
Hsp90 Client Protein

The therapeutic potential of stem cells is already being harnessed in clinical trails. Of even greater therapeutic potential has been the discovery of mechanisms to reprogram differentiated cells into a pluripotent stem cell-like state known as induced pluripotent stem cells (iPSCs). Stem cell nature is governed and maintained by a hierarchy of transcription factors, the apex of which is OCT4. Although much research has elucidated the transcriptional regulation of OCT4, OCT4 regulated gene expression profiles and OCT4 transcriptional activation mechanisms in both stem cell biology and cellular reprogramming to iPSCs, the fundamental biochemistry surrounding the OCT4 transcription factor remains largely unknown. In order to analyze the biochemical relationship between HSP90 and human OCT4 we developed an exogenous active human OCT4 expression model with human OCT4 under transcriptional control of a constitutive promoter. We identified the direct interaction between HSP90 and human OCT4 despite the fact that the proteins predominantly display differential subcellular localizations. We show that HSP90 inhibition resulted in degradation of human OCT4 via the ubiquitin proteasome degradation pathway. As human OCT4 and HSP90 did not interact in the nucleus, we suggest that HSP90 functions in the cytoplasmic stabilization of human OCT4. Our analysis suggests HSP90 inhibition inhibits the transcriptional activity of human OCT4 dimers without affecting monomeric OCT4 activity. Additionally our data suggests that the HSP90 and human OCT4 complex is modulated by phosphorylation events either promoting or abrogating the interaction between HSP90 and human OCT4. Our data suggest that human OCT4 displays the characteristics describing HSP90 client proteins, therefore we identify human OCT4 as a putative HSP90 client protein. The regulation of the transcription factor OCT4 by HSP90 provides fundamental insights into the complex biochemistry of stem cell biology. This may also be suggestive that HSP90 not only regulates stem cell biology by maintaining routine cellular homeostasis but additionally through the direct regulation of pluripotency factors.

Developing Lentiviral Vectors for Gene Therapy of Wiskott-Aldrich Syndrome.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 3170-3170
Author(s):  
Marguerite V. Evans-Galea ◽  
Matthew M. Wielgosz ◽  
Ted S. Strom ◽  
Hideki Hanawa ◽  
John M. Cunningham ◽  
...  
Keyword(s):  
Gene Expression ◽  
Stem Cells ◽  
Stem Cell ◽  
T Cell ◽  
Gene Transfer ◽  
Hela Cells ◽  
Lentiviral Vectors ◽  
Proximal Promoter ◽  
Wiskott Aldrich Syndrome ◽  
Wasp Gene

Abstract The Wiskott-Aldrich syndrome (WAS) is a rare X-linked recessive disorder caused by mutations in the WASP gene. WASP is an effector protein in the actin polymerization pathway. Characterized by immunodeficiency, micro-thrombocytopenia and eczema, untreated WAS patients may also suffer hemorrhages, recurring infections and potential malignancies. WAS can be cured by bone marrow (BM) transplant but because many patients lack a suitable donor, stem cell-targeted gene transfer is being developed as an alternative therapeutic approach. We have demonstrated correction of the T-cell proliferation defect in Wasp− mice using MSCV oncoretroviral vectors (Blood102:3108, 2003). However, our competitive repopulation studies in mice with both wild-type (WT) and gene-corrected Wasp− BM, demonstrated only a modest selective advantage for gene modified lymphocytes. Correction of the lymphocytopenia was observed only in animals having high proportions of transduced cells. In addition, variability in the level of gene expression among gene-corrected cells was associated with only partial correction of the T-cell cytokine secretory defects. Thus, the efficiency of stem cell-targeted gene transfer as well as the level and consistency of gene expression are likely to be key factors that determine success in any clinical application of gene transfer for the treatment of WAS. In attempting to improve vector design, we have used lentiviral vectors because of their greater efficiency in transducing repopulating stem cells as we recently demonstrated in a non-human primate model (Blood103:4062, 2004). The WASP gene is regulated by two promoter regions. The proximal promoter lies immediately adjacent to the translation start site with the distal promoter found 6 kb upstream, followed by an alternate first exon. We have developed a series of third generation, self-inactivating lentiviral vectors containing the MSCV, proximal or distal WASP promoters driving GFP in the reverse transcriptional orientation. The WASP promoters were active in lymphocytes but not HeLa cells in vitro. However, expression was low in lymphocytes and granulocytes in mice transplanted with genetically modified stem cells. In an effort to abrogate any position-effect variegation and enhance expression, we generated a new series of vectors with the transcriptional unit in the forward orientation that also contained the woodchuck post-transcriptional regulatory element, the chicken beta-globin 5′ DNase I hypersensitive site 4 (I) and human beta-interferon scaffold attachment region (S) insulator elements. Either GFP or murine Wasp cDNA were included for expression analysis. Despite the complexity of the SI-containing vectors, titers of concentrated preparations ranged from 9x106 TU/ml to 5x107 TU/ml and enabled transduction of both cell lines and murine hematopoietic stem cells. Low-level GFP expression from the proximal promoter was detected in HeLa cells with higher expression found in lymphocytes (NALM6 and Jurkat cells). Expression of GFP under the control of the proximal WASP promoter was detected in vivo in multiple hematopoietic lineages in mice transplanted with transduced stem cells. Future efforts will focus on further characterization and optimization of vector design with the goal of achieving consistent, high level expression.

Maintenance of Earlier Hematopoietic Stem Cell (HSC) Phenotype and Improved NOD/SCID Engraftment for UCB Expanded Short-Term in Cytokines over a Human Mesenchymal Stem Cell (huMSC) Platform.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 2846-2846
Author(s):  
M. Kozik ◽  
J. Banks ◽  
L. Fanning ◽  
M. Finney ◽  
Y. Huang ◽  
...  
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Stem Cell ◽  
Flow Analysis ◽  
Scid Mice ◽  
Mouse Bone Marrow ◽  
Short Term ◽  
Color Flow ◽  
Hematopoietic Stem ◽  
Cell Counts

Abstract Cytokine-based expansion of umbilical cord blood (UCB) in vitro prior to infusion has been pursued in an attempt to overcome the limited cellular content of a single UCB unit. Thus far, these attempts have not shown improvement in kinetics of donor-derived hematopoietic recovery. Our studies have incorporated UCB expanded over a feeder-layer of human mesenchymal stem cells (huMSC), known to inhibit the differentiation of hematopoietic stem cells (HSC) observed in expansion with cytokines alone. Expansion conditions included: UCB expanded over a huMSC monolayer with the addition of cytokines (IL-3, IL-6, G-CSF, SCF, FLT-3L, EPO) and UCB expanded in the same cytokines alone. Day 12 culture readouts included: viable cell counts, 4-color flow analysis, and rates of human engraftment in NOD/SCID mice. In the current study the fold expansion was 6.4 fold in the huMSC + cytokines condition and 7 fold in the cytokines alone condition. Flow cytometry surface marker analysis proportions (absolute numbers) were notable for higher proportions and numbers of early HSC expressing CD133 in cultures incorporating huMSC stromal layer: Unexpanded MSC+ cytokines Cytokines CD34 0.68 (.068M) 0.74 (3.63M) 1.94 (5.39M) CD133 5.69 (.569M) 2.56 (12.54M) 0.74 (2.06M) CD3 49.6 (4.96M) 2.2 (10.78M) 0.42 (1.17M) CD56 17.4 (1.74M) 2.71 (13.28M) 1.06 (2.95M) CD69 0.80 (7.28M) 7.28 (35.67M) 24.4 (67.8M) UCB graft T and NK populations were maintained in huMSC culture conditions and the observed difference in CD69 expression supports the hypothesis that huMSC may have an inhibitory effect on T cell activation during UCB ex vivo expansion. To assess the human engraftment potential of the cultures, cells from each culture condition were injected by tail vein into NOD/SCID mice (no CD34 selection was performed). Mice receiving unexpanded UCB received 10M mononuclear cells each. Mice receiving culture expanded cells received cell doses in proportion to the fold expansion over the number of cells at the initiation of the cultures. Engraftment was assessed by the percentage of human CD45+ (≥0.4%) cells found within the bone marrow of mice at seven weeks post infusion. Mice were injected as follows: 7 mice with unexpanded UCB (2 of which died within a month of transplant), 7 mice with UCB expanded in huMSC + cytokines, and 3 mice with UCB expanded in cytokines alone. Flow analysis of mouse bone marrow cells revealed average CD45+ percentages of 1.79% for mice injected with unexpanded UCB, 2.66% for mice injected with cytokine alone cells, and 5.94% for mice injected with huMSC + cytokine cells. Human cell subset analysis was performed for CD3, CD19, and CD56 content. The percentages of gated CD45+ co-expressing CD3+ were 10.3% in the unexpanded UCB, 16.6% in the cytokine alone condition and 10.4% in the huMSC + cytokine condition. Cells co-expressing CD19+ were 7.86% in the unexpanded UCB, 8.31% in the huMSC + cytokine condition and dropped to 1.43% in the cytokine alone condition. Gated CD45+ cells co-expressing CD56+ were 16.4% in the unexpanded UCB, 8.8% in the huMSC + cytokines condition, and dropped to 2.6% in the cytokines alone condition. In conclusion, UCB expanded short-term in cytokines demonstrates maintenance of earlier HSC phenotype and improved human engraftment in NOD/SCID in cultures incorporating a huMSC monolayer platform.

Bone Marrow-Derived Cells Regenerate Kit+ Cardiac Stem Cells (CSCs) in Damaged Heart.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 1681-1681
Author(s):  
Francesco Cerisoli ◽  
Lucio Barile ◽  
Roberto Gaetani ◽  
Letizia Cassinelli ◽  
Giacomo Frati ◽  
...  
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Stem Cell ◽  
Troponin I ◽  
Regulatory Elements ◽  
Cardiac Cells ◽  
Cardiac Differentiation ◽  
Pcr Analysis ◽  
Cardiac Stem Cells ◽  
Wild Type

Abstract A growing amount of data indicates that the heart harbours stem cells (CSCs) with regenerative potential, however the origin(s) of adult CSCs is still unknown. The expression of Kit a marker of several stem cell types, including hematopoietic and cardiac stem cells, suggests that Kit positive-CSCs may derive, at least in part, from extracardiac sources. In addition, it has been suggested that bone marrow (BM) cells may be mobilized, home into the heart and trans-differentiate into cardiomyocytes, following myocardial infarction. To investigate whether BM cells can contribute to repopulate the cardiac Kit+ stem cell pool, we transplanted BM cells from a mouse line expressing transgenic Green Fluorescent Protein (GFP) under the control of Kit regulatory elements, into wild type irradiated recipients. After hematological reconstution (4–5 months) and following cardiac infarction, cardiac cells were grown in vitro into typical “cardiospheres” (Messina et al., Circ. Res. 95,911;2004). The cardiospheres obtained, although not numerous, were all GFP fluorescent; this result was confirmed by PCR analysis of genomic DNA of individual CSs. At confocal microscopy, cells at the periphery of CSs showed coexistence of low GFP with cardiac markers, such as Troponin I and the transcription factor NKx2.5, consistent with the expected kit downregulation during cardiac differentiation. Our results show that cells of bone marrow origin can give rise, after homing into the heart, to cells with properties of Kit+ CSC. In contrast, CSCs isolated from kit/GFP transgenic mice are not able, upon transplantation, to repopulate the bone marrow of wild-type irradiated recipients. Thus, at least in pathological conditions, part of the Kit-positive CSCs population may be generated by BM-derived cells, capable of adopting in the heart the same function and features of cardiac stem cells.

Dipeptidyl Peptidase 4 (DPP4) Is Altered By, and Modulates Sensitivity to, Extra-Physiologic Oxygen Shock Stress (EPHOSS): Implications for Hematopoietic Stem Cell Transplantation

Blood ◽  
2015 ◽  
Vol 126 (23) ◽  
pp. 2361-2361
Author(s):  
Heather A. O'Leary ◽  
Thomas McNamara ◽  
Hal E. Broxmeyer
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Stem Cell ◽  
Ambient Air ◽  
Mouse Bone Marrow ◽  
Human Cord Blood ◽  
Hematopoietic Stem ◽  
Dipeptidyl Peptidase 4 ◽  
Expression Activity ◽  
Shock Stress

Abstract Hematopoietic stem cells (HSC) reside in hypoxic niches (~1-4% O2), however, HSC studies are consistently performed using cells isolated in ambient air (~20% O2), regardless of subsequent processing in low oxygen tension. We recently published that by collecting/processing stem cells in physiologically native conditions of hypoxia, with all procedures performed inside a hypoxic chamber (3% O2), we enhance the recovery of phenotypic, and functional, self-renewing long-term repopulating HSC (LT-HSC) with concomitantly decreasing numbers of progenitor cells. This occurs by inhibiting damage due to brief exposure of mouse bone marrow (BM) or human cord blood (CB) cells to ambient oxygen (a phenomenon we term Extra Physiologic Oxygen Shock/Stress (EPHOSS)) which we, in part, mechanistically linked to mitochondrial permeability transition pore (MPTP), Reactive Oxygen Species (ROS) and cyclophilin D. This data suggests that true numbers of HSCs, and the transplantation potency of BM and CB, have been consistently underestimated due to rapid differentiation of LT-HSCs in ambient air (EPHOSS), but the broad effects of EPHOSS on stem cell phenotype are unknown. We hypothesized that Dipeptidyl Peptidase 4 (DPP4) may be altered by EPHOSS and involved in the effects of EPHOSS on HSC. We showed that DPP4, a serine peptidase whose enzymatic activity leads to the N terminal cleavage of select penultimate amino acids of proteins, alters homing and engraftment of HSC and the number of cytokines, chemokines and growth factors that have putative DPP4 truncation sites have been dramatically underestimated. Functional and mechanistic roles of full length (FL) versus DPP4 truncated (T) factors, the ability of DPP4 T proteins to induce signaling that FL factors cannot, and the effects of EPHOSS on DPP4 expression/activity, and vice versa, have not been investigated and may have yet unappreciated clinical application. Here we present novel data demonstrating that mouse bone marrow harvested in air in the presence of Diprotin A, a DPP4 inhibitor, or from DPP4 K/O mice, results in a significant increase in the number of phenotypic LT-HSC (p=.017), suggesting that inhibition of DPP4 can diminish the loss of phenotypic LT-HSC due to EPHOSS. Further, the percentage of DPP4+ cells is significantly increased in primitive fractions of mouse bone marrow and human cord blood (LSK ~15% DPP4+, LSKCD150+ ~40%DPP4+, CD34+CD38- of CB ~10% DPP4+, CD34+CD38-CD45RA-CD90+CD49F+ ~40% DPP4+, p=.007), the numbers of DPP4+ cells are additionally enhanced 15- 20% when cells (BM and hCB) are isolated in hypoxia, especially in the LT-HSC fraction (Air 40% DPP4+ Hypoxia 60% DPP4+, p=.005). However, DPP4 activity on lineage- bone marrow harvested in hypoxia showed a 2 fold decrease (p=.005) compared to lineage- cells harvested in air. Interestingly, this increase in the number of DPP4+ cells in hypoxia is not recapitulated when mouse BM is harvested in the presence a Cyclosporin A, a cylophilin D inhibitor, (even though the increase in numbers of LT-HSC is preserved similarly to that in hypoxia) suggesting an alternative mechanism for modulation of DPP4 other than inhibition of mitochondrial ROS/MPTP. Unexpectedly, LT-HSC ROS levels (both mitochondrial and total) were not diminished in groups with decreased DPP4 activity (DPA or DPP4 K/O) harvested in air despite the blunting of EPHOSS leading to maintenance of the phenotypic LT-HSC increase over air harvest alone. These data suggest that pathways in addition to ROS, such as DPP4 expression/activity, may be influencing LT-HSC function after, and sensitivity to, EPHOSS as well as being modulated by EPHOSS. Further investigation of these collaborative pathways may facilitate increased HSC collections to enhance HSC transplantation. Disclosures No relevant conflicts of interest to declare.

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