Role Of The Rna Modification N6-Methyladenosine In Normal Hematopoiesis & Disease

N6-methyladenosine (m6A) is the most abundant modified nucleotide occurring in mRNA, with key roles in RNA metabolism and regulation of gene expression. Proposed effects of m6A modification of RNA transcripts include effects on transcript half-life, translation efficiency, splicing and miRNA biogenesis. Importantly, m6A is the only known dynamic RNA modification, with deposition mediated by the “writer” METTL3, and demethylation carried out by the “erasers” ALKBH5 and FTO. We hypothesized a role for m6A in hematopoiesis, with potential disease relevance in myeloid malignancies. To gain an understanding of the effects of m6A on normal hematopoiesis and myeloid malignancies such as the myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML), we developed conditional knockout mice for the m6A writer METTL3, and the eraser ALKBH5. We find that deletion of METTL3 results in embryonic lethality, with an accumulation of dysfunctional hematopoietic stem cells (HSCs) that are incompetent in hematopoietic rescue assays. We further characterize disturbances in myeloid & lymphoid lineage differentiation. Deletion of ALKBH5 does not result in steady-state hematopoietic dysfunction, but results in hematopoietic stem cell deficiencies in competitive transplant assays. We propose that deletion of METTL3 locks HSCs in a naïve multipotent state, and hypothesize that ALKBH5 exerts effects on HSC function that are yet to be characterized

Computer simulation of gamma irradiation energy deposition in MOSFET dosimeters

The application of MOSFETs as detectors or device components in pulse power technique requires an investigation of their characteristics in radiation fields. Computing possibilities of the renowned programs FOTELP and PENELOPE for determining the energy deposited in MOISFET structure and dose distribution within microscopic dimensions of the dosimeter sensitive volume were presented in this paper. Based on the obtained results, qualitative conclusions were drawn about the values of energy deposited in different material zones having various dimensions. The difference between the two codes used for calculations in materials physics and semiconductor technics, basically originates from the different physical models for numerical simulation of photon, positron, and electron transport through various materials.15th IEEE International Pulsed Power Conference, 2005, Monterey, C

Distinctive Mesenchymal-Parenchymal Cell Pairings Govern B Cell Differentiation in the Bone Marrow

Summary Bone marrow niches for hematopoietic progenitor cells are not well defined despite their critical role in blood homeostasis. We previously found that cells expressing osteocalcin, a marker of mature osteolineage cells, regulate the production of thymic-seeding T lymphoid progenitors. Here, using a selective cell deletion strategy, we demonstrate that a subset of mesenchymal cells expressing osterix, a marker of bone precursors in the adult, serve to regulate the maturation of early B lymphoid precursors by promoting pro-B to pre-B cell transition through insulin-like growth factor 1 (IGF-1) production. Loss of Osx+ cells or Osx-specific deletion of IGF-1 led to a failure of B cell maturation and the impaired adaptive immune response. These data highlight the notion that bone marrow is a composite of specialized niches formed by pairings of specific mesenchymal cells with parenchymal stem or lineage committed progenitor cells, thereby providing distinctive functional units to regulate hematopoiesis

ALKBH5 modulates hematopoietic stem and progenitor cell energy metabolism through m6A modification-mediated RNA stability control

Summary: N6-methyladenosine (m6A) RNA modification controls numerous cellular processes. To what extent these post-transcriptional regulatory mechanisms play a role in hematopoiesis has not been fully elucidated. We here show that the m6A demethylase alkB homolog 5 (ALKBH5) controls mitochondrial ATP production and modulates hematopoietic stem and progenitor cell (HSPC) fitness in an m6A-dependent manner. Loss of ALKBH5 results in increased RNA methylation and instability of oxoglutarate-dehydrogenase (Ogdh) messenger RNA and reduction of OGDH protein levels. Limited OGDH availability slows the tricarboxylic acid (TCA) cycle with accumulation of α-ketoglutarate (α-KG) and conversion of α-KG into L-2-hydroxyglutarate (L-2-HG). L-2-HG inhibits energy production in both murine and human hematopoietic cells in vitro. Impaired mitochondrial energy production confers competitive disadvantage to HSPCs and limits clonogenicity of Mll-AF9-induced leukemia. Our study uncovers a mechanism whereby the RNA m6A demethylase ALKBH5 regulates the stability of metabolic enzyme transcripts, thereby controlling energy metabolism in hematopoiesis and leukemia

Inhibiting stromal cell heparan sulfate synthesis improves stem cell mobilization and enables engraftment without cytotoxic conditioning

The glycosyltransferase gene, Ext1, is essential for heparan sulfate production. Induced deletion of Ext1 selectively in Mx1-expressing bone marrow (BM) stromal cells, a known population of skeletal stem/progenitor cells, in adult mice resulted in marked changes in hematopoietic stemand progenitor cell (HSPC) localization.HSPCegressed fromBMto spleen after Ext1 deletion. This was associated with altered signaling in the stromal cells and with reduced vascular cell adhesion molecule 1 production by them. Further, pharmacologic inhibition of heparan sulfate mobilized qualitatively more potent and quantitatively more HSPC from the BM than granulocyte colony-stimulating factor alone, including in a setting of granulocyte colony-stimulating factor resistance. The reduced presence of endogenous HSPC after Ext1 deletion was associated with engraftment of transfused HSPC without any toxic conditioning of the host. Therefore, inhibiting heparan sulfate production may provide a means for avoiding the toxicities of radiation or chemotherapy in HSPC transplantation for nonmalignant conditions. (Blood. 2014;124(19):2937-2947).Stem Cell and Regenerative Biolog