scholarly journals Lin28b regulates age-dependent differences in murine platelet function

2019 ◽  
Vol 3 (1) ◽  
pp. 72-82 ◽  
Author(s):  
Massiel Chavez Stolla ◽  
Seana C. Catherman ◽  
Paul D. Kingsley ◽  
R. Grant Rowe ◽  
Anne D. Koniski ◽  
...  
Keyword(s):  
Platelet Function ◽  
Rna Binding ◽  
Developmental Regulation ◽  
Negative Regulator ◽  
Transcriptional Analysis ◽  
Hematopoietic Stem ◽  
Age Dependent ◽  
Low Levels

Abstract Platelets are essential for hemostasis; however, several studies have identified age-dependent differences in platelet function. To better understand the origins of fetal platelet function, we have evaluated the contribution of the fetal-specific RNA binding protein Lin28b in the megakaryocyte/platelet lineage. Because activated fetal platelets have very low levels of P-selectin, we hypothesized that the expression of platelet P-selectin is part of a fetal-specific hematopoietic program conferred by Lin28b. Using the mouse as a model, we find that activated fetal platelets have low levels of P-selectin and do not readily associate with granulocytes in vitro and in vivo, relative to adult controls. Transcriptional analysis revealed high levels of Lin28b and Hmga2 in fetal, but not adult, megakaryocytes. Overexpression of LIN28B in adult mice significantly reduces the expression of P-selectin in platelets, and therefore identifies Lin28b as a negative regulator of P-selectin expression. Transplantation of fetal hematopoietic progenitors resulted in the production of platelets with low levels of P-selectin, suggesting that the developmental regulation of P-selectin is intrinsic and independent of differences between fetal and adult microenvironments. Last, we observe that the upregulation of P-selectin expression occurs postnatally, and the temporal kinetics of this upregulation are recapitulated by transplantation of fetal hematopoietic stem and progenitor cells into adult recipients. Taken together, these studies identify Lin28b as a new intrinsic regulator of fetal platelet function.

scholarly journals Transcription factor Gfi-1 induced by G-CSF is a negative regulator of CXCR4 in myeloid cells

Blood ◽  
2007 ◽  
Vol 110 (7) ◽  
pp. 2276-2285 ◽  
Author(s):  
Maria De La Luz Sierra ◽  
Paola Gasperini ◽  
Peter J. McCormick ◽  
Jinfang Zhu ◽  
Giovanna Tosato
Keyword(s):  
Bone Marrow ◽  
Dna Sequences ◽  
Peripheral Blood ◽  
Cell Function ◽  
Myeloid Cell ◽  
Cxcr4 Expression ◽  
Negative Regulator ◽  
Hematopoietic Stem

The mechanisms underlying granulocyte-colony stimulating factor (G-CSF)–induced mobilization of granulocytic lineage cells from the bone marrow to the peripheral blood remain elusive. We provide evidence that the transcriptional repressor growth factor independence-1 (Gfi-1) is involved in G-CSF–induced mobilization of granulocytic lineage cells from the bone marrow to the peripheral blood. We show that in vitro and in vivo G-CSF promotes expression of Gfi-1 and down-regulates expression of CXCR4, a chemokine receptor essential for the retention of hematopoietic stem cells and granulocytic cells in the bone marrow. Gfi-1 binds to DNA sequences upstream of the CXCR4 gene and represses CXCR4 expression in myeloid lineage cells. As a consequence, myeloid cell responses to the CXCR4 unique ligand SDF-1 are reduced. Thus, Gfi-1 not only regulates hematopoietic stem cell function and myeloid cell development but also probably promotes the release of granulocytic lineage cells from the bone marrow to the peripheral blood by reducing CXCR4 expression and function.

Sqstm1 Is Required to Retain Hematopoietic Stem Cell/ Progenitors As a Negative Regulator of Macrophage-Dependent Inflammatory Signaling in the Bone Marrow Osteoblastic Niche

Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 350-350
Author(s):  
Kyung-Hee Chang ◽  
Amitava Sengupta ◽  
Ramesh C Nayak ◽  
Angeles Duran ◽  
Sang Jun Lee ◽  
...  
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Hematopoietic Stem Cells ◽  
Research Funding ◽  
Negative Regulator ◽  
Wild Type ◽  
Hematopoietic Stem ◽  
P Retention

Abstract In the bone marrow (BM), hematopoietic stem cells and progenitors (HSC/P) reside in specific anatomical niches. Among these niches, a functional osteoblast (Ob)-macrophage (MΦ) niche has been described where Ob and MΦ (so called "osteomacs") are in direct relationship. A connection between innate immunity surveillance and traffic of hematopoietic stem cells/progenitors (HSC/P) has been demonstrated but the regulatory signals that instruct immune regulation from MΦ and Ob on HSC/P circulation are unknown. The adaptor protein sequestosome 1 (Sqstm1), contains a Phox bemp1 (PB1) domain which regulates signal specificities through PB1-PB1 scaffolding and processes of autophagy. Using microenvironment and osteoblast-specific mice deficient in Sqstm1, we discovered that the deficiency of Sqstm1 results in macrophage contact-dependent activation of Ob IKK/NF-κB, in vitro and in vivo repression of Ccl4 (a CCR5 binding chemokine that has been shown to modulate microenvironment Cxcl12-mediated responses of HSC/P), HSC/P egress and deficient BM homing of wild-type HSC/P. Interestingly, while Ccl4 expression is practically undetectable in wild-type or Sqstm1-/- Ob, primary Ob co-cultured with wild-type BM-derived MΦ strongly upregulate Ccl4 expression, which returns to normal levels upon genetic deletion of Ob Sqstm1. We discovered that MΦ can activate an inflammatory pathway in wild-type Ob which include upregulation of activated focal adhesion kinase (p-FAK), IκB kinase (IKK), nuclear factor (NF)-κB and Ccl4 expression through direct cell-to-cell interaction. Sqstm1-/- Ob cocultured with MΦ strongly upregulated p-IKBα and NF-κB activity, downregulated Ccl4 expression and secretion and repressed osteogenesis. Forced expression of Sqstm1, but not of an oligomerization-deficient mutant, in Sqstm1-/- Ob restored normal levels of p-IKBα, NF-κB activity, Ccl4 expression and osteogenic differentiation, indicating that Sqstm1 dependent Ccl4 expression depends on localization to the autophagosome formation site. Finally, Ob Sqstm1 deficiency results in upregulation of Nbr1, a protein containing a PB1 interacting domain. Combined deficiency of Sqstm1 and Nbr1 rescues all in vivo and in vitro phenotypes of Sqstm1 deficiency related to osteogenesis and HSC/P egression in vivo. Together, this data indicated that Sqstm1 oligomerization and functional repression of its PB1 binding partner Nbr1 are required for Ob dependent Ccl4 production and HSC/P retention, resulting in a functional signaling network affecting at least three cell types. A functional ‘MΦ-Ob niche’ is required for HSC/P retention where Ob Sqstm1 is a negative regulator of MΦ dependent Ob NF-κB activation, Ob differentiation and BM HSC/P traffic to circulation. Disclosures Starczynowski: Celgene: Research Funding. Cancelas:Cerus Co: Research Funding; P2D Inc: Employment; Terumo BCT: Research Funding; Haemonetics Inc: Research Funding; MacoPharma LLC: Research Funding; Therapure Inc.: Consultancy, Research Funding; Biomedical Excellence for Safer Transfusion: Research Funding; New Health Sciences Inc: Consultancy.

scholarly journals HIF-1α is a negative regulator of plasmacytoid DC development in vitro and in vivo

Blood ◽  
2012 ◽  
Vol 120 (15) ◽  
pp. 3001-3006 ◽  
Author(s):  
Andreas Weigert ◽  
Benjamin Weichand ◽  
Divya Sekar ◽  
Weixiao Sha ◽  
Christina Hahn ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Cell Function ◽  
Bone Marrow Cells ◽  
Negative Regulator ◽  
Low Oxygen ◽  
Hematopoietic Stem ◽  
Lineage Differentiation ◽  
Marrow Cells

Abstract Hypoxia-inducible factors (HIFs) regulate hematopoiesis in the embryo and maintain hematopoietic stem cell function in the adult. How hypoxia and HIFs contribute to hematopoietic lineage differentiation in the adult is ill defined. Here we provide evidence that HIF-1 limits differentiation of precursors into plasmacytoid dendritic cells (pDCs). Low oxygen up-regulated inhibitor of DNA binding 2 (ID2) and suppressed Flt3-L–induced differentiation of bone marrow cells to pDCs in wild-type but not HIF-1αfl/fl LysM-Cre bone marrow cells. Moreover, pDC differentiated normally in hypoxic ID2−/− bone marrow cultures. Finally, we observed elevated pDC frequencies in bone marrow, blood, and spleen of HIF-1αfl/fl LysM-Cre and ID2−/−, but not HIF-2αfl/fl LysM-Cre mice. Our data indicate that the low oxygen content in the bone marrow might limit pDC development. This might be an environmental mechanism to restrict the numbers of these potentially autoreactive cells.

scholarly journals Aging of Hematopoietic Stem Cells Is Driven By Regional Specialization of Marrow Macrophages

Blood ◽  
2017 ◽  
Vol 130 (Suppl_1) ◽  
pp. 95-95
Author(s):  
Corey M Hoffman ◽  
Sarah E Latchney ◽  
Mark LaMere ◽  
Jason R Myers ◽  
John M Ashton ◽  
...  
Keyword(s):  
Stem Cells ◽  
Ex Vivo ◽  
Aging Effect ◽  
Transcriptional Analysis ◽  
Hematopoietic Stem ◽  
Regional Specialization ◽  
Aged Mice ◽  
Human Volunteers

Abstract While hematopoietic stem cells (HSCs)-intrinsic effects of aging have been explored, less is known about how HSC support is altered by the aged bone marrow microenvironment (BMME). To assess the role of the BMME in HSC aging, we compared the BMME in young (6-12 weeks) and aged (20-24 months) male mice and young (<50 years old; YO) and aged (>50 YO) human volunteers. Aged mice had remodeling of the BMME, with expansion of the marrow cavity and vascular volume compared to young mice. BMME constituents were redistributed within two distinct anatomic regions, namely endosteal bone-associated (BA) and marrow-associated (MA) cells. BA cells in aged mice contained fewer phenotypic mesenchymal/osteoblastic progenitors, with reduction in their ability to constitute colony forming units (CFUs). CFU loss was also observed in aged human volunteers. Aged murine MA had significant expansion of dysfunctional mesenchymal stem cells (MSCs) and activated macrophages (MΦ). Increased MΦ were also detected in aged human marrows. Following this in vivo characterization, we developed an ex vivo co-culture system to determine if aged murine BMME cells could impart aging characteristics to young HSCs. Young murine HSCs co-cultured with aged MA cells acquired phenotypic properties of aged HSCs, including increased CD41+ expression. Single cell RNA sequencing of Long Term-HSCs (LT-HSCs) from young and aged mice also identified upregulation of integrin-β3 (CD61) as a novel marker of aged LT-HSCs. Subsequent flow cytometry analysis confirmed the increase in CD61+ expression in vivo in aged HSCs. Importantly, aged MA - but not BA cells - also increased CD61+ expression in young HSCs ex vivo, highlighting the region-specific remodeling of the BMME that occurs with age. We then used a reductionist approach to identify targetable cellular and molecular regulators of the region-specific BMME-induced HSC aging. CD45+ and Ter119+ depletion in aged MA cells did not induce CD41+ expression in young HSCs, suggesting that a critical BMME component responsible for non-cell-autonomous HSC aging is present within the hematopoietic pool. Since marrow MΦ can regulate HSCs, we co-cultured aged MA MΦ with young MA and found that aged MΦ were sufficient to increase CD41+ expression in young HSCs. The addition of aged MΦ also expanded young MSCs, demonstrating that MΦ orchestrate both BMME remodeling and HSC aging. We next aimed to explore mechanisms by which aged MA MΦ impart aging characteristics to HSCs. Transcriptional analysis of murine MA MΦ demonstrated an increase in inflammatory activation in aged mice compared to young mice. This finding was also present in aged human MΦs. Among the inflammatory signals, interleukin-1β (IL-1β) was identified to be necessary and sufficient to mediate the aging effect of aged MA MΦ on young HSCs. Transcriptional analysis also revealed downregulation of phagocytic programs in aged MA MΦ compared to young MA MΦ. Supporting the transcriptional data, aged MA MΦs cultured in vitro demonstrated impaired ability to engulf senescent neutrophils compared to young MA MΦ. Bone marrow MΦ continuously remove large quantities of senescent neutrophils through phagocytosis, a process also known as efferocytosis. Complementing the in vitro findings, in vivo testing demonstrated that young MA MΦ are primarily responsible for engulfing senescent neutrophils and that aged MA MΦ had reduced engulfment of senescent neutrophils. No phagocytic defect was identified in aged BA MΦ, highlighting the regionalization of MΦ function within the BMME that is differentially impacted with age. Consistent with the systemic impact of the efferocytic defect of aged MA MΦ, aged mice had increased levels of circulating senescent neutrophils and. Moreover, neutrophils from aged mice had increased caspase-1 activity, a signal required for IL-1β activation. Together, these data provide evidence that aging differentially remodels two anatomically distinct BMMEs. Regional specialization of marrow MΦ was differentially impacted by aging and induced aging characteristics in HSCs. We propose that impaired removal of senescent neutrophils by aged MA MΦ increases IL-1β production, leading to local inflammation and disrupted BMME and HSC function in aged mice. Strategies aimed at restoring healthy efferocytic activity as well as diminishing IL-1β production or function could therefore reduce the aging effect on HSCs by rejuvenating the BMME. Disclosures Liesveld: Onconova: Honoraria; Seattle Genetics: Honoraria.

An In Vivo Functional Screen Identifies miRNA-150 As a Regulator of Hematopoietic Regeneration Post Chemotherapeutic Injury

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 2333-2333
Author(s):  
Brian D. Adams ◽  
Shangqin Guo ◽  
Haitao Bai ◽  
Changchun Xiao ◽  
E. Premkumar Reddy ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Conflicts Of Interest ◽  
Negative Regulator ◽  
Post Transplantation ◽  
Hematopoietic Stem ◽  
Hematopoietic Recovery ◽  
Expression Construct

Abstract Abstract 2333 . MicroRNAs are important regulators of many hematopoietic processes, yet little is known with regard to the role of microRNAs in controlling normal hematopoietic regeneration. The most common methodology for in vivo microRNA studies follows a hypothesis-driven candidate approach. Here, we report the establishment of an unbiased, in vivo, microRNA gain-of-function screen, and the identification of miR-150 as a negative regulator of hematopoietic recovery post chemotherapeutic challenge. Specifically, a retroviral-library consisting of 135 hematopoietic-expressed microRNAs was generated, with each expression construct containing a barcode sequence that can be specifically recognized using a novel bead-based platform. Hematopoietic-stem-and-progenitor-cell (HSPC)-enriched wild-type bone marrow was transduced with this library and transplanted into lethally-irradiated recipients. Analysis of peripheral blood samples from each recipient up to 11 weeks post transplantation revealed that 87% of the library barcodes are reliably detected. To identify microRNAs that regulate hematopoietic regeneration after chemotherapy-induced injury, we measured the change in barcode abundance for specific microRNA constructs after 5-fluorouracil (5-FU) challenge. Notably, a small number of barcodes were consistently depleted in multiple recipient mice after treatment. Among the top hits was the miR-150-associated barcode, which was selected for further experimentation. Indeed, overexpression of miR-150 in a competitive environment resulted in significantly lower recovery rates for peripheral myeloid and platelet populations after 5-FU treatment, whereas the effects on B- and T-cells were milder. Furthermore, full recovery of these cell populations did not occur until ∼12 weeks after treatment, suggesting the involvement of HSPCs and/or common lineage progenitors. Conversely, knocking out miR-150 led to an opposite phenotype, with platelets and myeloid cells displaying faster recovery in both competitive and non-competitive settings. Interestingly, we could not observe the described effects of miR-150 in bone marrow primary cell cultures, suggesting that such effects cannot be recapitulated in vitro. Overall, these data indicate that miR-150 is a novel regulator of hematopoietic recovery after chemotherapeutic-induced injury, and highlight the important role of microRNAs in the intrinsic wiring of the hematopoietic regeneration program. Our experiments also demonstrate the feasibility and power of functional in vivo screens for studying normal hematopoietic functions, which can become an important tool in the hematology field. Disclosures: No relevant conflicts of interest to declare.

Enhanced platelet MRP4 expression and correlation with platelet function in patients under chronic aspirin treatment

2016 ◽  
Vol 116 (12) ◽  
pp. 1100-1110 ◽  
Author(s):  
Isabella Massimi ◽  
Lavinia Lotti ◽  
Flavia Temperilli ◽  
Massimo Mancone ◽  
Gennaro Sardella ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Platelet Function ◽  
Platelet Reactivity ◽  
Thrombus Formation ◽  
Independent Mechanism ◽  
Mrna And Protein Expression ◽  
Low Levels ◽  
Cox 1

SummaryPlatelet multidrug resistance protein4 (MRP4)-overexpression has a role in reducing aspirin action. Aspirin in vivo treatment enhances platelet MRP4 expression and MRP4 mediated transport inhibition reduces platelet function and delays thrombus formation. The aim of our work was to verify whether MRP4 expression is enhanced in platelets obtained from patients under chronic aspirin treatment and whether it correlates with residual platelet reactivity. We evaluated changes on mRNA and protein-MRP4 expression and platelet aggregation in four populations: healthy volunteers (HV), aspirin-free control population (CTR), patients who started the treatment less than one month ago (ASA<1 month patients) and aspirinated patients who started the treatment more than two months ago (ASA>2 months patients). In platelets obtained from ASA>2 months patients, it was found a statistically significant MRP4 enhancement of both mRNA and protein expression compared to HV, CTR and ASA<1 month patients. Platelets obtained from ASA>2 months patients that present high levels of platelet MRP4, have higher serum TxB2 levels and collagen-induced platelet aggregation compared to patient with low levels of MRP4 in platelets. In addition collagen induced platelet aggregation is higher in in vitro aspirinated platelets obtained from patients with high levels of MRP4 patients compared to those obtained from patients with low MRP4 levels. We can assert that, in patients under chronic aspirin treatment, platelets that present high MRP4 levels have an increase of residual platelet reactivity, which is due in part to incomplete COX-1 inhibition, and in part to COX-1–independent mechanism.

TET Family Oncogene Fus Is Essential for the Maintenance of Self-Renewing Hematopoietic Stem Cells.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 2529-2529
Author(s):  
Takeaki Sugawara ◽  
Hideyuki Oguro ◽  
Atsushi Iwama
Keyword(s):  
Stem Cells ◽  
Hematopoietic Stem Cells ◽  
Transcriptional Repression ◽  
Cell Activation ◽  
B Lymphocyte ◽  
Rna Binding ◽  
Conflicts Of Interest ◽  
Hematopoietic Stem

Abstract Abstract 2529 Poster Board II-506 A Proto-oncogene FUS (fusion derived from malignant liposarcoma), also known as TLS (translocated in liposarcoma), was originally identified in chromosomal translocation of human soft tissue sarcoma. FUS is also known to be fused with an ETS family transcription factor ERG in human myeloid leukemia with t(16;21) which is associated with poor prognosis. Based on its protein structure, DNA- and RNA-binding activity and involvement in many human cancers as the fusion with various transcription factors, FUS is now grouped with EWS and TAFII68 into TET (FET) oncogene family. Multiple functions have been postulated for FUS, including non-coding-RNA-mediated transcriptional repression, posttranscriptional RNA processing and the maintenance of genomic integrity. Fus-deficient (Fus−/−) mice showed a non-cell-autonomous defect in B lymphocyte development, defective B cell activation and increased sensitivity to radiation in previous studies. However, its physiological function in hematopoiesis remains unknown. In this study we performed detailed analyses of Fus−/− hematopoietic stem cells (HSCs). Fus−/− fetal livers at embryonic day 14.5 exhibited a mild reduction in numbers of hematopoietic stem and progenitor cells compared with the wild type. Disruption of Fus, however, did not grossly affect proliferation or differentiation of hematopoietic progenitors. Of note, Fus−/− HSCs had significantly reduced repopulating activity of hematopoiesis in competitive repopulation assays, and did not repopulate hematopoiesis at all in tertiary recipients. Moreover, Fus−/− HSCs were highly sensitive to radiation both in vitro and in vivo and showed a drastic reduction in numbers in recipient mice after sublethal irradiation. All these findings implicate Fus in the maintenance and radioprotection of HSCs. Studies of chromosome stability, telomere length, apoptosis and levels of reactive oxigen species (ROS) appeared not accountable for the apparent defect of Fus−/− HSCs. However, gene expression profiling identified changes in expression of several genes in Fus−/− HSCs, and dysregulated expression of some of these genes might be responsible for the defective function of Fus−/− HSCs. Disclosures: No relevant conflicts of interest to declare.

The Bone Marrow "Mystery Population" of Stem Cells 20 Years Later - a Puzzle Solved?

Blood ◽  
2015 ◽  
Vol 126 (23) ◽  
pp. 2392-2392
Author(s):  
Malwina Suszynska ◽  
Daniel Pedziwiatr ◽  
Magdalena J Kucia ◽  
Mariusz Z Ratajczak ◽  
Janina Ratajczak
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Receptor Expression ◽  
Stem Cell Population ◽  
Hematopoietic Stem ◽  
Murine Bone Marrow ◽  
Low Levels

Abstract Background . Almost 20 years ago, a "mystery" population of small stem cells with many of the phenotypic characteristics attributed to resting hematopoietic stem cells was identified in murine bone marrow (BM) (Stem Cells 1998, 16, 38-48). These cells expressed high levels of Sca-1, H-2K, and CD38 and low levels of Thy-1.1; they expressed CD45 antigen but were lineage-negative (lin-) for other hematopoietic markers. These cells incorporated only low levels of Rh123 and were resistant to the cytotoxic effects of 5-fluorouracil. The only phenotypic characteristic that distinguishes these cells from Sca-1+, Lin-, CD45+ Thy-1.1low long-term-reconstituting hematopoietic stem cell population is the lack of c-kit expression. In sum, this "mystery" population of small Sca-1+, lin-, c-kit- but CD45+ stem cells do not respond to hematopoietic growth factors in vitro, form in vivo spleen colonies, or reconstitute lethally irradiated mice. With our discovery of Sca-1+ Lin- CD45- very small embryonic-like stem cells (VSELs) in murine bone marrow (BM) (Leukemia 2006, 20, 857-869), we became interested in this "mystery" population of stem cells. VSELs, like the "mystery" population, are c-kit - and, if freshly isolated from BM, do not show any hematopoietic activity in standard in vitro and in vivo assays. In order to become specified to hematopoiesis, they need to be expanded over an OP-9 stromal support (Exp Hematol 2011;39:225-237). Hypothesis. Since (1) very small CD45- VSELs can be specified in OP-9 co-cultures into long-term reconstituting CD45+ HSCs, (2) the size of the "mystery" population is intermediate between VSELs and HSCs, and (3) VSELs and HSCs differ in cell surface receptor expression, we hypothesized that the "mystery" population is a missing developmental intermediate between VSELs and HSCs. Materials and Methods . Multicolor FACS analysis was employed to compare size and expression of surface markers between murine BM HSCs, the unknown population of stem cells, and VSELs. Next, the populations of small Sca-1+ H2-K+ lin- c-kit+ CD38+/- CD45+ cells (HSCs), smaller Sca-1+ H-2K+ lin- c-kit- CD38+ CD45+ cells (the "mystery" population), and very small in size Sca-1+ H-2K+ lin- c-kit- CD38+/- CD45- cells (VSELs) were purified by FACS from BM (Figure 1) and tested for in vitro colony formation. All these cell populations were primed/expanded over OP-9 support and subsequently evaluated for their hematopoietic potential after passaging in consecutive methylocellulose cultures (passages 1-4). RQ-PCR analysis was employed for detection of pluripotency marker expression as well as hematopoietic gene expression. Results . We found that, in contrast to HSCs, neither freshly sorted stem cells from the "mystery" BM population nor, as expected, VSELs grew hematopoietic colonies in standard methylcellulose cultures. This was also an important step in excluding contamination of our sorted populations with clonogenic cells. We also found that, while VSELs highly expressed Oct-4, this transcription factor was expressed at very low levels in the "mystery" population and was not detectable in HSCs. The most important observation was that the "mystery" population of stem cells became specified in OP-9-supported cultures into clonogenic HSPCs, and this specification occurred faster than the delayed specification of VSELs. VSELs first became enriched for HSPCs after acquiring CD45 antigen expression. Conclusions . Based on the results presented, we propose that the "mystery" population in murine BM is a population of stem cells intermediate between the most primitive population of BM-residing stem cells (VSELs) and the population of stem cells already specified to lympho-hematopoietic development (HSCs). Disclosures No relevant conflicts of interest to declare.

scholarly journals Tsc1 Regulates the Proliferation Capacity of Bone-Marrow Derived Mesenchymal Stem Cells

Cells ◽  
2020 ◽  
Vol 9 (9) ◽  
pp. 2072 ◽  
Author(s):  
Maria V. Guijarro ◽  
Laura S. Danielson ◽  
Marta Cañamero ◽  
Akbar Nawab ◽  
Carolina Abrahan ◽  
...  
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Mesenchymal Stem Cells ◽  
Myogenic Differentiation ◽  
Negative Regulator ◽  
Benign Tumors ◽  
Hematopoietic Stem ◽  
The Impact

TSC1 is a tumor suppressor that inhibits cell growth via negative regulation of the mammalian target of rapamycin complex (mTORC1). TSC1 mutations are associated with Tuberous Sclerosis Complex (TSC), characterized by multiple benign tumors of mesenchymal and epithelial origin. TSC1 modulates self-renewal and differentiation in hematopoietic stem cells; however, its effects on mesenchymal stem cells (MSCs) are unknown. We investigated the impact of Tsc1 inactivation in murine bone marrow (BM)-MSCs, using tissue-specific, transgelin (Tagln)-mediated cre-recombination, targeting both BM-MSCs and smooth muscle cells. Tsc1 mutants were viable, but homozygous inactivation led to a dwarfed appearance with TSC-like pathologies in multiple organs and reduced survival. In young (28 day old) mice, Tsc1 deficiency-induced significant cell expansion of non-hematopoietic BM in vivo, and MSC colony-forming potential in vitro, that was normalized upon treatment with the mTOR inhibitor, everolimus. The hyperproliferative BM-MSC phenotype was lost in aged (1.5 yr) mice, and Tsc1 inactivation was also accompanied by elevated ROS and increased senescence. ShRNA-mediated knockdown of Tsc1 in BM-MSCs replicated the hyperproliferative BM-MSC phenotype and led to impaired adipogenic and myogenic differentiation. Our data show that Tsc1 is a negative regulator of BM-MSC proliferation and support a pivotal role for the Tsc1-mTOR axis in the maintenance of the mesenchymal progenitor pool.

GSK3β Is a Negative Regulator of Platelet Function In Vitro and In Vivo.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 395-395
Author(s):  
Donna S. Woulfe ◽  
Shelley August ◽  
Dongjun Li
Keyword(s):  
Platelet Aggregation ◽  
Platelet Function ◽  
Ferric Chloride ◽  
Arterial Thrombosis ◽  
Platelet Rich Plasma ◽  
Human Platelets ◽  
Negative Regulator ◽  
Response Curves

Abstract GSK3β is a ser-thr kinase that is itself phosphorylated on ser9 by the kinase Akt. Because Akt has recently been shown to regulate platelet aggregation and arterial thrombosis in mice, we sought to identify Akt substrates in platelets that may play important roles in platelet function. We show here that the Akt effector, GSK3β, is present in platelets and becomes phosphorylated after treatment of mouse or human platelets with ADP or thrombin receptor-activating peptides (TRAP). Agonist-dependent phosphorylation of GSK3β is reduced by pre-treatment of mouse or human platelets with the PI3K inhibitor LY294002 and is also reduced in platelets from Akt2−/−Akt1+/− mice relative to non-littermate controls, suggesting that agonist-induced GSK3β phosphorylation is partially PI3K- and Akt-dependent. To determine whether GSK3β plays a role in platelet function, aggregation and secretion of dense granule contents were evaluated in human platelets treated with the GSK3 inhibitors, LiCl or SB216763. The dose-response curves for agonist-induced platelet aggregation and secretion were left-shifted in the presence of either inhibitor compared to untreated control platelets, suggesting that GSK3 activity suppresses platelet aggregation. Comparative immunoblots suggest that GSK3β is more highly expressed in platelets than GSK3α. Therefore, to confirm that GSKβ plays a suppressive role in platelet function, the aggregation of platelet-rich plasma (PRP) from GSK3β+/− mice was compared to that of non-littermate controls (GSK3β −/− mice die in utero). PRP from GSK3β+/− mice showed enhanced aggregation and secretion in response to U46619 or TRAP compared to control PRP. TRAP-induced binding of AlexaFluor-fibrinogen to platelet surfaces was also enhanced in washed platelets from GSK3β+/− mice compared to control platelets. Finally, the effect of GSK3β on platelet function in vivo was evaluated using two thrombosis models: a ferric chloride injury model of arterial thrombosis and a collagen-induced model of disseminated thrombosis. In the arterial thrombosis model, all GSK3β+/− mice (n=5) formed stable occlusive thrombi after ferric chloride injury to the carotid artery, whereas the majority of wildtype mice (67%) formed no thrombi, 27% formed stable occlusive thrombi, and 7% formed unstable thrombi under the same conditions (n=15). In a model of disseminated thrombosis, injection of a combination of collagen (170 μg/kg) and epinephrine (350 μM/kg) resulted in reduced survival of GSK3β+/− mice 10 minutes post-injection relative to wildtype mice (20%, n=5 versus 83%, n=6, respectively). Histological examination of lung sections suggested that all mice that died did so due to pulmonary embolism. These data suggest that removal of a single allele of GSK3β in mice confers enhanced sensitivity to thrombotic insult. Taken together, these results suggest that GSK3β is a substrate of Akt-dependent phosphorylation in platelets and, in contrast to the function of Akt, acts as a negative regulator of platelet function in vitro and in vivo.

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