Angiocrine factors from Akt-activated endothelial cells balance self-renewal and differentiation of haematopoietic stem cells. Nature - Cell Biology

Howard Hughes Medical Institute, Ansary Stem Cell Institute, Department of Genetic Medicine, Weill Cornell Medical College, New York, NY 10065, USA.
Nature Cell Biology (Impact Factor: 19.68). 10/2010; 12(11):1046-56. DOI: 10.1038/ncb2108
Source: PubMed


Endothelial cells establish an instructive vascular niche that reconstitutes haematopoietic stem and progenitor cells (HSPCs) through release of specific paracrine growth factors, known as angiocrine factors. However, the mechanism by which endothelial cells balance the rate of proliferation and lineage-specific differentiation of HSPCs is unknown. Here, we demonstrate that Akt activation in endothelial cells, through recruitment of mTOR, but not the FoxO pathway, upregulates specific angiocrine factors that support expansion of CD34(-)Flt3(-) KLS HSPCs with long-term haematopoietic stem cell (LT-HSC) repopulation capacity. Conversely, co-activation of Akt-stimulated endothelial cells with p42/44 MAPK shifts the balance towards maintenance and differentiation of the HSPCs. Selective activation of Akt1 in the endothelial cells of adult mice increased the number of colony forming units in the spleen and CD34(-)Flt3(-) KLS HSPCs with LT-HSC activity in the bone marrow, accelerating haematopoietic recovery. Therefore, the activation state of endothelial cells modulates reconstitution of HSPCs through the modulation of angiocrine factors, with Akt-mTOR-activated endothelial cells supporting the self-renewal of LT-HSCs and expansion of HSPCs, whereas MAPK co-activation favours maintenance and lineage-specific differentiation of HSPCs.

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Available from: Laura Elaine Benjamin, Sep 19, 2014
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    • "Within the perivascular niche, two different types of cell seem to display niche functions: CXC chemokine ligand 12 (CXCL-12)-abundant reticular cells (CAR cells) and Nestin + mesenchymal stem cells. CAR cells secrete stem cell factor (SCF) and CXCL12, also known as SDF-1 (stromal cellderived factor-1) (Salter et al., 2009; Butler et al., 2010; Kobayashi et al., 2010). Nestin + cells express high levels of genes involved in the regulation of HSCs, and acute depletion of these cells impairs HSC homing after irradiation (Méndez-Ferrer et al., 2010). "
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    ABSTRACT: The regulation of hematopoietic stem cells (HSCs) depends on the integration of the multiple signals received from the bone marrow niche. We show the relevance of the protein tyrosine phosphatase PTPN13 and β-catenin as intracellular signaling molecules to control HSCs adhesiveness, cell cycling, and quiescence. Lethally irradiated mice transplanted with Lin(-) bone marrow cells in which PTPN13 or β-catenin had been silenced showed a significant increase of long-term (LT) and short-term (ST) HSCs. A decrease in cycling cells was also found, together with an increase in quiescence. The decreased expression of PTPN13 or β-catenin was linked to the upregulation of several genes coding for integrins and several cadherins, explaining the higher cell adhesiveness. Our data are consistent with the notion that the levels of PTPN13 and β-catenin must be strictly regulated by extracellular signaling to regulate HSC attachment to the niche and the balance between proliferation and quiescence.
    Full-text · Article · Sep 2015 · Stem Cell Reports
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    • "Current data suggest that the effects of EPC-CM might go beyond survival of local endothelial cells. In fact it has been reported that AKT and ERK activated endothelial cells in bone marrow differently modulate hematopoietic stem cells self-renewal and differentiation [51]. It is thus possible that a bidirectional crosstalk between endothelial cells and EPC through soluble factors might take place also in the periphery of the circulatory system and have a relevant role in tissue homeostasis. "
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    ABSTRACT: Angiogenesis and vascular remodelling are crucial events in tissue repair mechanisms promoted by cell transplantation. Current evidence underscores the importance of the soluble factors secreted by stem cells in tissue regeneration. In the present study we investigated the effects of paracrine factors derived from cultured endothelial progenitor cells (EPC) on rat brain endothelial cell properties and addressed the signaling pathways involved. Endothelial cells derived from rat brain (rBCEC4) were incubated with EPC-derived conditioned medium (EPC-CM). The angiogenic response of rBCEC4 to EPC-CM was assessed as effect on cell number, migration and tubular network formation. In addition, we have compared the outcome of the in vitro experiments with the effects on capillary sprouting from rat aortic rings. The specific PI3K/AKT inhibitor LY294002 and the MEK/ERK inhibitor PD98059 were used to study the involvement of these two signaling pathways in the transduction of the angiogenic effects of EPC-CM. Viable cell number, migration and tubule network formation were significantly augmented upon incubation with EPC-CM. Similar findings were observed for aortic ring outgrowth with significantly longer sprouts. The EPC-CM-induced activities were significantly reduced by the blockage of the PI3K/AKT and MEK/ERK signaling pathways. Similarly to the outcome of the rBCEC4 experiments, inhibition of the PI3K/AKT and MEK/ERK pathways significantly interfered with capillary sprouting induced by EPC-CM. The present study demonstrates that EPC-derived paracrine factors substantially promote the angiogenic response of brain microvascular endothelial cells. In addition, our findings identified the PI3K/AKT and MEK/ERK pathways to play a central role in mediating these effects.
    Full-text · Article · Apr 2014 · PLoS ONE
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    • "Emerging evidence suggests the “vascular niche”, and bone marrow endothelial cells (BMEC) in particular, conveys signals to hematopoietic progenitor and stem cells, promoting BM recovery via instructive “angiocrine” signals that tightly regulate the hematopoietic differentiation process [3,4]. The coordinated production and release (in such cases) of instructive signals is crucial for adequate BM recovery and function; hematopoietic differentiation and exit into peripheral organs is tightly regulated by the instructive signals from the BM vascular niche [3,5]. In particular, the communication between BMEC and hematopoietic elements, namely the hematopoietic stem and progenitor cells, is crucial for normal BM function and for maintaining BM integrity following stress. "
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    ABSTRACT: Recent findings have shown that the blood vessels of different organs exert an active role in regulating organ function. In detail, the endothelium that aligns the vasculature of most organs is fundamental in maintaining organ homeostasis and in promoting organ recovery following injury. Mechanistically, endothelial cells (EC) of tissues such as the liver, lungs or the bone marrow (BM) have been shown to produce "angiocrine" factors that promote organ recovery and restore normal organ function. Controlled production of angiocrine factors following organ injury is therefore essential to promote organ regeneration and to restore organ function. However, the molecular mechanisms underlying the coordinated production and function of such "angiocrine" factors are largely undisclosed and were the subject of the present study. In detail, we identified for the first time a microRNA (miRNA) expressed by BM EC that regulates the expression of angiocrine genes involved in BM recovery following irradiation. Using a microarray-based approach, we identified several miRNA expressed by irradiated BMEC. After validating the variations in miRNA expression by semi-quantitative PCR, we chose to study further the ones showing consistent variations between experiments, and those predicted to regulate (directly or indirectly) angiogenic and angiocrine factors. Of the mi-RNA that were chosen, miR-363-5p (previously termed miR-363*) was subsequently shown to modulate the expression of numerous EC-specific genes including some angiocrine factors. By luciferase reporter assays, miR-363-5p is shown to regulate the expression of angiocrine factors tissue inhibitor of metalloproteinases-1 (Timp-1) and thrombospondin 3 (THBS3) at post-transcriptional level. Moreover, miR-363-5p reduction using anti-miR is shown to affect EC angiogenic properties (such as the response to angiogenic factors stimulation) and the interaction between EC and hematopoietic precursors (particularly relevant in a BM setting). miR-363-5p reduction resulted in a significant decrease in EC tube formation on matrigel, but increased hematopoietic precursor cells adhesion onto EC, a mechanism that is shown to involve kit ligand-mediated cell adhesion. Taken together, we have identified a miRNA induced by irradiation that regulates angiocrine factors expression on EC and as such modulates EC properties. Further studies on the importance of miR-363-5p on normal BM function and in disease are warranted.
    Full-text · Article · Nov 2013 · Journal of Hematology & Oncology
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