ERK1 Regulates the Hematopoietic Stem Cell Niches

The mitogen-activated protein kinases (MAPK) ERK1 and ERK2 are among the major signal transduction molecules but little is known about their specific functions in vivo. ERK activity is provided by two isoforms, ERK1 and ERK2, which are ubiquitously expressed and share activators and substrates. However, there are not in vivo studies which have reported a role for ERK1 or ERK2 in HSCs and the bone marrow microenvironment. The present study shows that the ERK1-deficient mice present a mild osteopetrosis phenotype. The lodging and the homing abilities of the ERK1−/− HSC are impaired, suggesting that the ERK1−/−-defective environment may affect the engrafment of HSCs. Serial transplantations demonstrate that ERK1 is involved in the maintenance of an appropriate medullar microenvironment, but that the intrinsic properties of HSCs are not altered by the ERK1−/− defective microenvironment. Deletion of ERK1 impaired in vitro and in vivo osteoclastogenesis while osteoblasts were unaffected. As osteoclasts derive from precursors of the monocyte/macrophage lineage, investigation of the monocytic compartment was performed. In vivo analysis of the myeloid lineage progenitors revealed that the frequency of CMPs increased by approximately 1.3-fold, while the frequency of GMPs significantly decreased by almost 2-fold, compared with the respective WT compartments. The overall mononuclear-phagocyte lineage development was compromised in these mice due to a reduced expression of the M-CSF receptor on myeloid progenitors. These results show that the cellular targets of ERK1 are M-CSFR-responsive cells, upstream to osteoclasts. While ERK1 is well known to be activated by M-CSF, the present results are the first to point out an ERK1-dependent M-CSFR regulation on hematopoietic progenitors. This study reinforces the hypothesis of an active cross-talk between HSCs, their progeny and bone cells in the maintenance of the homeostasis of these compartments

The MAPK ERK1 is a negative regulator of the adult steady-state splenic erythropoiesis.

International audienceThe mitogen-activated protein kinases (MAPKs) extracellular signal-regulated kinase 1 (ERK1) and ERK2 are among the main signal transduction molecules, but little is known about their isoform-specific functions in vivo. We have examined the role of ERK1 in adult hematopoiesis with ERK1(-/-) mice. Loss of ERK1 resulted in an enhanced splenic erythropoiesis, characterized by an accumulation of erythroid progenitors in the spleen, without any effect on the other lineages or on bone marrow erythropoiesis. This result suggests that the ablation of ERK1 induces a splenic stress erythropoiesis phenotype. However, the mice display no anemia. Deletion of ERK1 did not affect erythropoietin (EPO) serum levels or EPO/EPO receptor signaling and was not compensated by ERK2. Splenic stress erythropoiesis response has been shown to require bone morphogenetic protein 4 (BMP4)-dependent signaling in vivo and to rely on the expansion of a resident specialized population of erythroid progenitors, termed stress erythroid burst-forming units (BFU-Es). A great expansion of stress BFU-Es and increased levels of BMP4 mRNA were found in ERK1(-/-) spleens. The ERK1(-/-) phenotype can be transferred by bone marrow cells. These findings show that ERK1 controls a BMP4-dependent step, regulating the steady state of splenic erythropoiesis

Flow cytometry to estimate leukemia stem cells in primary acute myeloid leukemia and in patient-derived-xenografts, at diagnosis and follow up

Acute myeloid leukemia (AML) is a heterogeneous, and if not treated, fatal disease. It is the most common cause of leukemia-associated mortality in adults. Initially, AML is a disease of hematopoietic stem cells (HSC) characterized by arrest of differentiation, subsequent accumulation of leukemia blast cells, and reduced production of functional hematopoietic elements. Heterogeneity extends to the presence of leukemia stem cells (LSC), with this dynamic cell compartment evolving to overcome various selection pressures imposed upon during leukemia progression and treatment. To further define the LSC population, the addition of CD90 and CD45RA allows the discrimination of normal HSCs and multipotent progenitors within the CD34+CD38- cell compartment. Here, we outline a protocol to detect simultaneous expression of several putative LSC markers (CD34, CD38, CD45RA, CD90) on primary blast cells of human AML by multiparametric flow cytometry. Furthermore, we show how to quantify three progenitor populations and a putative LSC population with increasing degree of maturation. We confirmed the presence of these populations in corresponding patient-derived-xenografts. This method of detection and quantification of putative LSC may be used for clinical follow-up of chemotherapy response (i.e., minimal residual disease), as residual LSC may cause AML relapse

Maintenance of red blood cell integrity by AMP-activated protein kinase α1 catalytic subunit

AMP-activated protein kinase (AMPK) plays a pivotal role in regulating cellular energy metabolism. We previously showed that AMPKα1-/- mice develop moderate anemia associated with splenomegaly and high reticulocytosis. Here, we report that splenectomy of AMPKα1-/- mice worsened anemia supporting evidence that AMPKα1-/- mice developed a compensatory response through extramedullary erythropoiesis in the spleen. Transplantation of bone marrow from AMPKα1-/- mice into wild-type recipients recapitulated the hematologic phenotype. Further, AMPKα1-/- red blood cells (RBC) showed less deformability in response to shear stress limiting their membrane flexibility. Thus, our results highlight the crucial role of AMPK to preserve RBC integrity. © 2010 Federation of European Biochemical Societies.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Genetic polymorphisms in ARID5B, CEBPE, IKZF1 and CDKN2A in relation with risk of acute lymphoblastic leukaemia in adults: a Group for Research on Adult Acute Lymphoblastic Leukaemia (GRAALL) study.

International audienc

ERK1 deficiency impairs osteoclastogenesis.

<p>(A) Total number of osteoclasts per well following 5 days of culture under osteoclastogenic condition (n = 3) (B) Representative picture of TRAP-positive multinucleated osteoclasts generated from BMNCs of WT and ERK1^−/− mice. (C) Relative expression of cathepsin K (CTSK), calcitonin receptor (CaR), and receptor activator of nuclear factor <i>kappa</i> B (RANK) in WT and ERK1^−/− osteoclasts. (D) Representative pictures of the bone resorption pits formed by WT and ERK1^−/− derived osteoclasts. (E) Bar graph representing the quantification of the resorptive area per dentin slice for WT and ERK1^−/− osteoclasts (n = 3). Data represent the mean± SEM. The <i>t</i>-test was used to calculate the <i>P</i> value.</p

ERK1^−/− microenvironment alters the lodging and the homing efficiencies of BM cells.

<p>Lodging of the bone marrow cells into a non irradiated host were quantified 3 h (A) and 24 h (B) after injection. Homing of the bone marrow cells into a lethally irradiated host were quantified 3 h (C) and 24 h (D) after injection. Results are presented as scatter plots showing the percentage of recovered CFSE⁺ cells in the BM 3 and 24 hours after transplantation. The non parametric Mann-Whiney test was used to calculate the <i>P</i> value. Horizontal bars show the mean values.</p

ERK1 loss alters the bone architecture.

<p>Cortical and trabecular parameters in WT and ERK1^−/− mice (n = 5 for each group). (A) midshaft diaphysis cortical thickness, (B) bone volume/tissue volume (% BV/TV), (C) trabecular thickness (Tb.Th), (D) trabecular number (Tb.N), (E) trabecular separation (Tb.S). The non parametric Mann-Whiney test was used to calculate the <i>P</i> value. Horizontal bars show the mean values.</p

ERK1^−/− mice have a reduced fraction of bone marrow monocytes.

<p>(A) Representative FACS plot of BM monocytes defined as Gr1⁺CD115⁺ cells. (B) Proportion of monocytes as described above in the total BM in WT (n = 11) and ERK1^−/− (n = 12). Data represent the mean±SEM. The <i>t</i>-test was used to calculate the <i>P</i> value.</p

ERK1^−/− microenvironment induces a defect in WT HSC activity.

<p>(A) Scheme of transplantation assay. (B) Analysis of WT donor cells engraftment in WT (n = 10) and ERK1^−/− mice (n = 10) primary recipient 24 weeks after transplantation. (C) Analysis of WT donor cells engraftment in WT (n = 9 per group) and ERK1^−/− mice (n = 16) secondary recipient 24 weeks after transplantation. In panels B and C, total donor cells are shown as a percentage of live cells. Individual lineages are shown as a percentage of donor-derived cells. Data represent the mean±SEM, the <i>t</i>-test was used to calculate the <i>P</i> value.</p