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

Histone methyltransferase DOT1L controls state-specific identity during B cell differentiation

Differentiation of naïve peripheral B cells into terminally differentiated plasma cells is characterized by epigenetic alterations, yet the epigenetic mechanisms that control B-cell fate remain unclear. Here, we identified a role for the histone H3K79 methyltransferase DOT1L in controlling B-cell differentiation. Mouse B cells lacking Dot1L failed to establish germinal centers (GC) and normal humoral immune responses in vivo. In vitro, activated B cells in which Dot1L was deleted showed aberrant differentiation and prematurely acquired plasma cell characteristics. Similar results were obtained when DOT1L was chemically inhibited in mature B cells in vitro. Mechanistically, combined epigenomics and transcriptomics analysis revealed that DOT1L promotes expression of a pro-proliferative, pro-GC program. In addition, DOT1L indirectly supports the repression of an anti-proliferative plasma cell differentiation program by maintaining the repression of Polycomb Repressor Complex 2 (PRC2) targets. Our findings show that DOT1L is a key modulator of the core transcriptional and epigenetic landscape in B cells, establishing an epigenetic barrier that warrants B-cell naivety and GC B-cell differentiation

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

MicroRNAs: key players of normal and malignant myelopoiesis

Purpose of review Recent data show that microRNAs play critical roles in the regulation of the developmental process of hematopoietic stem and progenitor cells toward mature myeloid cells. The main focus of the article is the function of some evolutionary conserved microRNAs that are abundantly expressed and tightly regulated during myelopoiesis. Recent findings Global microRNA depletion studies in hematopoietic stem cells have shown the importance of microRNA-controlled pathways for hematopoiesis. Recent insights from genetic mouse models and overexpression or deletion of microRNAs in developmental cell intermediates demonstrate strong evidence for evolutionary conserved microRNA-regulated pathways involved in tight control of cellular processes such as proliferation, differentiation and apoptosis at different stages of blood cell development. It is be Summary Despite the large number of articles describing differential microRNA expression during hematopoiesis, microRNA functions and their downstream pathways in myeloid lineage decisions and leukemia are only recently emerging. Here we discuss new findings concerning PU.1-controlled microRNAs and miR-125-regulated networks in normal and malignant myelopoiesis

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 alpha (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 gene-expression 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-Huet anomaly. These results provide evidence for a miRNA-controlled switch for a cellular program of self-renewal and expansion toward myeloid differentiation in GMPs. (Blood. 2012; 119(20):4723-4730

Towards an understanding of C9orf82 protein/CAAP1 function

Chemical Immunolog