MicroRNAs in Normal and Malignant Myelopoiesis

__abstract__ Hematopoiesis is the lifelong continuous process in which hematopoietic stem and progenitor cells (HSPCs) proliferate and differentiate towards mature blood cells. Hematopoiesis is tightly controlled by a network of growth factors and the hematopoietic niche in the bone marrow (BM). This ensures the balanced blood cell production under homeostatic conditions and allows for transient elevation of specific blood cell types production in response to infections or bleeding 1. In mammalian organisms, long-term hematopoietic stem cells (LT-HSCs) reside in the BM and have self-renewal capacity over the lifespan of the organism 2,3. The estimated amount of LT-HSCs is approximately 0.007% of all hematopoietic cells in the BM 4. LT-HSCs give rise to short-term HSCs (ST-HSCs) and multipotent progenitors (MPPs) (Figure 1). These cells have the potential to differentiate into all the different hematopoietic cell types but have less self-renewal capacity 4. Together, LT-HCSs, ST-HCSs and MPPs constitute 0.05% of mouse BM cells 2. MPPs differentiate into common lymphoid progenitors (CLPs) and common myeloid progenitors (CMPs) (Figure 1). Subsequently, CLPs differentiate into B-cell and T-cell lineages. CMPs first develop into more specified myeloid progenitors, which are megakaryocyte/erythroid progenitors (MEPs) and granulocyte/monocyte progenitors (GMPs). Granulocytes, monocytes and macrophages arise from GMPs, whereas MEPs differentiate towards erythrocytes and thrombocytes (platelets) (Figure 1). The process of differentiation of HSPCs towards mature myeloid cells is referred as myelopoiesis. In adult mammalian organisms, myelopoiesis occurs in the BM. Disruption of the balance between cell proliferation, differentiation and cell death leads to different hematopoietic disorders, e.g., leukemia, characterized by proliferation of undifferentiated cells, or bone marrow failure (BMF), characterized by impaired hematopoiesis involving one or multiple hematopoietic lineages 5,6. Proliferation and differentiation of HSPCs are coordinated by gene expression programs driven by endogenous and exogenous factors. MicroRNAs (miRNAs) are a class of non-coding RNAs which function as regulators of gene expression. In the studies described in this thesis the role of miRNAs in normal myelopoiesis and their involvement in acute myeloid leukemia (AML) and Fanconi anemia (FA), the most frequent inherited form of BMF syndromes are investigated. AML, FA and miRNAs will be further introduced in the following sections

Stop the dicing in hematopoiesis: What have we learned?

MicroRNAs (miRNAs) belong to an abundant class of highly conserved small (22nt) non-coding RNAs. MiRNA profiling studies indicate that their expression is highly cell type-dependent. DICER1 is an essential RNase III endoribonuclease for miRNA processing. Hematopoietic cell type- and developmental stage-specific Dicer1 deletion models show that miRNAs are essential regulators of cellular survival, differentiation and function. For instance, miRNA deficiency in hematopoietic stem cells and progenitors of different origins results in decreased cell survival, dramatic developmental aberrations or dysfunctions in mice. We recently found that homozygous Dicer1 deletion in myeloid-committed progenitors results in an aberrant expression of stem cell genes and induces a regained self-renewal capacity. Moreover, Dicer1 deletion causes a block in macrophage development and myeloid dysplasia, a cellular condition that may be considered as a preleukemic state. However, Dicer1-null cells do not develop leukemia in mice, indicating that depletion of miRNAs is not enough for tumorigenesis. Surprisingly, we found that heterozygous Dicer1 deletion in myeloid-committed progenitors, but not Dicer1 knockout, collaborates with p53 deletion in leukemic progression and results in various types of leukemia. Our data indicate that Dicer1 is a haploinsufficient tumorsuppressor in hematopoietic neoplasms, which is consistent with the observed downregulation of miRNA expression in human leukemia samples. Here, we review the various hematopoietic specific Dicer1 deletion mouse models and the phenotypes observed within the different hematopoietic lineages and cell developmental stages. Finally, we discuss the role for DICER1 in mouse and human malignant hematopoiesis

The Ig heavy chain protein but not its message controls early B cell development

Development of progenitor B cells (ProB cells) into precursor B cells (PreB cells) is dictated by immunoglobulin heavy chain checkpoint (IgHCC), where the IgHC encoded by a productively rearranged Igh allele assembles into a PreB cell receptor complex (PreBCR) to generate signals to initiate this transition and suppressing antigen receptor gene recombination, ensuring that only one productive Igh allele is expressed, a phenomenon known as Igh allelic exclusion. In contrast to a productively rearranged Igh allele, the Igh messenger RNA (mRNA) (IgHR) from a nonproductively rearranged Igh allele is degraded by nonsense-mediated decay (NMD). This fact prohibited firm conclusions regarding the contribution of stable IgHR to the molecular and developmental changes associated with the IgHCC. This point was addressed by generating the Igh Ter5H∆TM mouse model from Igh Ter5H mice having a premature termination codon at position +5 in leader exon of Igh Ter5H allele. This prohibited NMD, and the lack of a transmembrane region (∆TM) prevented the formation of any signaling-competent PreBCR complexes that may arise as a result of read-through translation across premature Ter5 stop codon. A highly sensitive sandwich Western blot revealed read-through translation of Igh Ter5H message, indicating that previous conclusions regarding a role of IgHR in establishing allelic exclusion requires further exploration. As determined by RNA sequencing (RNA-Seq), this low amount of IgHC sufficed to initiate PreB cell markers normally associated with PreBCR signaling. In contrast, the Igh Ter5H∆TM knock-in allele, which generated stable IgHR but no detectable IgHC, failed to induce PreB development. Our data indicate that the IgHCC is controlled at the level of IgHC and not IgHR expression

Заболевание тазобедренного сустава у детей с наследственной предрасположенностью: концептуальная модель

На основе принципов интегративной медицины, системного подхода с использованием концептуально−логического моделирования разработана единая система представлений о заболеваниях тазобедренного сустава у детей с наследственной предрасположенностью. Показано, что предлагаемый интегративный подход может служить основой для разработки диагностических и прогностических критериев развития суставов и проведения патогенетического хирургического лечения, направленного на ликвидацию или существенное снижение частоты формирования диспластического коксартроза.Based on the principles of integrative medicine, systemic approach with the use of concept of logical modelling, a uniform system of concepts about the diseases of the hip joint in children with hereditary susceptibility was worked out. It was shown that the suggested integrative approach can be used for working out diagnostic and prognostic criteria of joint development and performing pathogenetic surgery aimed at elimination or reduction in the frequency of forming dysplastic coxarthrosis

Dicer1 deletion in myeloid-committed progenitors causes neutrophil dysplasia and blocks macrophage/dendritic cell development in mice

MicroRNAs (miRNAs) have the potential to regulate cellular differentiation programs; however, miRNA deficiency in primary hematopoietic stem cells (HSCs) results in HSC depletion in mice, leaving the question of whether miRNAs play a role in early-lineage decisions unanswered. To address this issue, we deleted Dicer1, which encodes an essential RNase III enzyme for miRNA biogenesis, in murine CCAAT/enhancer-binding protein α (C/EBPA)-positive myeloid-committed progenitors in vivo. In contrast to the results in HSCs, we found that miRNA depletion affected neither the number of myeloid progenitors nor the percentage of C/EBPA-positive progenitor cells. Analysis of gene-expression profiles from wild-type and Dicer1-deficient granulocyte-macrophage progenitors (GMPs) revealed that 20 miRNA families were active in GMPs. Of the derepressed miRNA targets in Dicer1-null GMPs, 27% are normally exclusively expressed in HSCs or are specific for multipotent progenitors and erythropoiesis, indicating an altered geneexpression landscape. Dicer1-deficient GMPs were defective in myeloid development in vitro and exhibited an increased replating capacity, indicating the regained self-renewal potential of these cells. In mice, Dicer1 deletion blocked monocytic differentiation, depleted macrophages, and caused myeloid dysplasia with morphologic features of Pelger-Huë t anomaly. These results provide evidence for a miRNA-controlled switch for a cellular program of self-renewal and expansion toward myeloid differentiation in GMPs