1,721,127 research outputs found
Autophagy-dependent generation of free fatty acids is essential for normal neutrophil differentiation by guiding an energy-metabolic switch
Get PDFNeutrophils are critical and short lived mediators of innate immunity that require constant replenishment. Their differentiation in the bone marrow requires extensive cytoplasmic and nuclear remodeling, but the processes governing these energy-consuming changes are unknown. While previous studies show that autophagy is required for differentiation of other blood cell lineages, its function during granulopoiesis has remained elusive. Autophagy was described as a critical process in HSC differentiation and in memory- and regulatory T cells, where it prevents excessive glycolysis and maintains lipid metabolic homeostasis. In the myeloid lineage, an essential role for autophagy is to prevent pro-inflammatory macrophage polarization and to limit glycolytic metabolism of acute myeloid leukemia. While these studies provide robust in vivo evidence for the relevance of autophagy in the differentiation of hematopoietic and immune cells, the targets and mechanisms of autophagy remain elusive. Here, we show that metabolism and autophagy are developmentally programmed and essential for neutrophil differentiation in vivo. Atg7 -deficient neutrophil precursors had increased glycolytic activity but impaired mitochondrial respiration, decreased ATP production and accumulated lipid droplets. Inhibiting autophagy-mediated lipid degradation or fatty acid oxidation alone was sufficient to cause defective differentiation, while administration of fatty acids or pyruvate for mitochondrial respiration rescued differentiation in autophagy deficient neutrophil precursors. Together, we show that autophagy-mediated lipolysis provides free fatty acids to support a mitochondrial respiration pathway essential to neutrophil differentiation. Evidence presented here also contributed to studies on autophagy-mediated metabolic homeostasis in HSCs, Treg cells and myeloid leukemia, suggesting that this pathway may act broadly during differentiation.</p
The role of Notch and GATA3 in postnatal and adult haematopoiesis
Get PDFThe role of Notch in cell fate determination and lineage restriction in the bone marrow (BM) is controversial in the field. Recent studies have convincingly shown that Notch is dispensable for haematopoietic stem cell (HSC) regulation in adult haematopoiesis (Maillard et al., 2008). In contrast, Notch signaling has been proposed to be of importance in the regulation of BM megakaryocyte progenitor differentiation, based on dominant negative genetic approaches, identifying a potentially distinct role for Notch in adult BM haematopoiesis (Mercher et al., 2008). Here, I found that by selectively ablating the gene coding the transcription factor recombination signal-binding protein J kappa (RBP-Jk), to which all canonical Notch signaling converges, canonical Notch signaling does not mediate HSC maintenance, neither in steady state nor in conditions of stress. Furthermore, I propose, in contrast with previous studies (Mercher et al., 2008), that canonical Notch signaling plays no role in myeloerythropoiesis cell lineage commitment in the BM. My data also show that key Notch target genes are suppressed by RBP-Jk, as their expression is unaffected in Notch1-deficient BM progenitors, while target genes are upregulated in Rbp-Jk-deleted megakaryocyte and erythroid progenitors. This establishes for the first time in mammalian cells in vivo, that Notch target genes are kept in a suppressed state by RBP-Jk, potentially restricting T cell commitment to the thymus and not to the BM, at the expense of myeloerythropoiesis.Notch signaling and GATA3 are two master regulators in T cell commitment (Han et al., 2002; Ho et al., 2009; Pui et al., 1999; Radtke et al., 1999; Zhu et al., 2004). However, although very well established as being involved in the thymic stages of T cell restriction, there is little evidence of Notch and GATA3 being involved in the migration of a thymus settling progenitor (TSP) from the BM to the thymus or in the establishment of the earliest thymic progenitor (ETP) in the thymus. From this thesis work, I conclude that Notch signaling is essential for the emergence of ETPs in the thymus in a NOTCH1-independent manner. Moreover, I demonstrate, as supported by a very recent published study (Hosoya et al., 2009), that GATA3 is important for the development of the earliest T cell progenitor.GATA1 and GATA2 mediate haematopoietic stem cell maintenance in the BM. GATA1 is required for erythropoiesis, megakaryocytes and eosinophils while GATA2 is important for the proliferation and survival of HSCs. In contrast, a role for GATA3 in the BM has never been established. By using a Gata3-conditional knockout mouse model, I demonstrate that GATA3 is dispensable for HSC maintenance in steady state and following active haematopoietic regeneration as well as for HSC self-renewal in the BM
Interleukin-3 supports expansion of long-term multilineage repopulating activity after multiple stem cell divisions in vitro
No full textAlthough long-term repopulating hematopoietic stem cells (HSC) can self-renew and expand extensively in vivo, most efforts at expanding HSC in vitro have proved unsuccessful and have frequently resulted in compromised rather than improved HSC grafts. This has triggered the search for the optimal combination of cytokines for HSC expansion. Through such studies, c-kit ligand (KL), flt3 ligand (FL), thrombopoietin, and IL-11 have emerged as likely positive regulators of HSC self-renewal. In contrast, numerous studies have implicated a unique and potent negative regulatory role of IL-3, suggesting perhaps distinct regulation of HSC fate by different cytokines. However, the interpretations of these findings are complicated by the fact that different cytokines might target distinct subpopulations within the HSC compartment and by the lack of evidence for HSC undergoing self-renewal. Here, in the presence of KL+FL+megakaryocyte growth and development factor (MGDF), which recruits virtually all Lin(-)Sca-1(+)kit(+) bone marrow cells into proliferation and promotes their self-renewal under serum-free conditions, IL-3 and IL-11 revealed an indistinguishable ability to further enhance proliferation. Surprisingly, and similar to IL-11, IL-3 supported KL+FL+MGDF-induced expansion of multilineage, long-term reconstituting activity in primary and secondary recipients. Furthermore, high-resolution cell division tracking demonstrated that all HSC underwent a minimum of 5 cell divisions, suggesting that long-term repopulating HSC are not compromised by IL-3 stimulation after multiple cell divisions. In striking contrast, the ex vivo expansion of murine HSC in fetal calf serum-containing medium resulted in extensive loss of reconstituting activity, an effect further facilitated by the presence of IL-3. (Blood. 2000;96:1748-1755
The role of Notch and GATA3 in postnatal and adult haematopoiesis
No full textThe role of Notch in cell fate determination and lineage restriction in the bone marrow (BM) is controversial in the field. Recent studies have convincingly shown that Notch is dispensable for haematopoietic stem cell (HSC) regulation in adult haematopoiesis (Maillard et al., 2008). In contrast, Notch signaling has been proposed to be of importance in the regulation of BM megakaryocyte progenitor differentiation, based on dominant negative genetic approaches, identifying a potentially distinct role for Notch in adult BM haematopoiesis (Mercher et al., 2008). Here, I found that by selectively ablating the gene coding the transcription factor recombination signal-binding protein J kappa (RBP-Jk), to which all canonical Notch signaling converges, canonical Notch signaling does not mediate HSC maintenance, neither in steady state nor in conditions of stress. Furthermore, I propose, in contrast with previous studies (Mercher et al., 2008), that canonical Notch signaling plays no role in myeloerythropoiesis cell lineage commitment in the BM. My data also show that key Notch target genes are suppressed by RBP-Jk, as their expression is unaffected in Notch1-deficient BM progenitors, while target genes are upregulated in Rbp-Jk-deleted megakaryocyte and erythroid progenitors. This establishes for the first time in mammalian cells in vivo, that Notch target genes are kept in a suppressed state by RBP-Jk, potentially restricting T cell commitment to the thymus and not to the BM, at the expense of myeloerythropoiesis.Notch signaling and GATA3 are two master regulators in T cell commitment (Han et al., 2002; Ho et al., 2009; Pui et al., 1999; Radtke et al., 1999; Zhu et al., 2004). However, although very well established as being involved in the thymic stages of T cell restriction, there is little evidence of Notch and GATA3 being involved in the migration of a thymus settling progenitor (TSP) from the BM to the thymus or in the establishment of the earliest thymic progenitor (ETP) in the thymus. From this thesis work, I conclude that Notch signaling is essential for the emergence of ETPs in the thymus in a NOTCH1-independent manner. Moreover, I demonstrate, as supported by a very recent published study (Hosoya et al., 2009), that GATA3 is important for the development of the earliest T cell progenitor.GATA1 and GATA2 mediate haematopoietic stem cell maintenance in the BM. GATA1 is required for erythropoiesis, megakaryocytes and eosinophils while GATA2 is important for the proliferation and survival of HSCs. In contrast, a role for GATA3 in the BM has never been established. By using a Gata3-conditional knockout mouse model, I demonstrate that GATA3 is dispensable for HSC maintenance in steady state and following active haematopoietic regeneration as well as for HSC self-renewal in the BM.This thesis is not currently available via ORA. Work described in chapter 4: This research was originally published in Blood. Buza-Vidas N, Duarte S, Luc S, Bouriez-Jones T, Woll PS, Jacobsen SE. GATA3 is redundant for maintenance and self-renewal of hematopoietic stem cells. Blood. 2011;118(5):1291-3. © the American Society of Hematology
- …
