miRNA调控骨髓增生异常综合征的发生发展

骨髓增生异常综合征(MDS)是一组起源于造血干细胞(HSC)的异质性克隆性疾患,以形态学改变(病态造血)和造血功能异常(无效造血)为主要特征,然而其发生、发展及白血病转化的分子机制尚不明确。MicroRNA(miRNA)是一类重要的非编码小分子RNA,在调控造血干细胞发育进程中起着重要作用,其在MDS的发生发展及白血病转化中的作用也逐渐被认识,以miRNA为分子靶点诊治造血干细胞受损疾患的研究具有广阔的应用前景。     

Damaged DNA binding protein 1 in Drosophila defense reactions

We have focused attention on functions of Drosophila damaged DNA binding protein 1 (D-DDB1) in Drosophila hematopoiesis and previously reported that its whole body dsRNA over-expression using a GAL4-UAS targeted expression system results in melanotic tumors and complete lethality. Since the lesions appear to arise as a normal and heritable response to abnormal development, forming groups of cells that are recognized by the immune system and encapsulated in melanized cuticle, D-DDB1 appears to be an essential development-associated factor in Drosophila. To probe the possibility that it contributes to hemocyte development, we used a collagen promoter-GAL4 strain to over-express dsRNA of D-DDB1 in Drosophila hemocytes. The D-DDB1 gene silencing caused melanotic tumors and mortality at the end of larval development. Similarly, it interfered with melanization and synthesis of antimicrobial peptides. Transgenic flies with D-DDB1 gene silencing were found to accumulate abnormal large blood cells, reminiscent of human leukemia, suggesting that D-DDB1 has functions in hemocyte development.     

The peripheral nervous system supports blood cell homing and survival in the Drosophila larva

Interactions of hematopoietic cells with their microenvironment control blood cell colonization, homing and hematopoiesis. Here, we introduce larval hematopoiesis as the first Drosophila model for hematopoietic colonization and the role of the peripheral nervous system (PNS) as a microenvironment in hematopoiesis. The Drosophila larval hematopoietic system is founded by differentiated hemocytes of the embryo, which colonize segmentally repeated epidermal-muscular pockets and proliferate in these locations. Importantly, we show that these resident hemocytes tightly colocalize with peripheral neurons and we demonstrate that larval hemocytes depend on the PNS as an attractive and trophic microenvironment. atonal (ato) mutant or genetically ablated larvae, which are deficient for subsets of peripheral neurons, show a progressive apoptotic decline in hemocytes and an incomplete resident hemocyte pattern, whereas supernumerary peripheral neurons induced by ectopic expression of the proneural gene scute (sc) misdirect hemocytes to these ectopic locations. This PNS-hematopoietic connection in Drosophila parallels the emerging role of the PNS in hematopoiesis and immune functions in vertebrates, and provides the basis for the systematic genetic dissection of the PNS-hematopoietic axis in the future.     

The peptide network regulated by angiotensin converting enzyme (ACE) in hematopoiesis

The concept of a local bone marrow renin-angiotensin system (RAS) has been introduced and accumulating evidence suggests that the local RAS is actively involved in hematopoiesis. Angiotensin converting enzyme (ACE) is a key player in the RAS and makes the final effector angiotensin II. Besides angiotensin II, ACE also regulates a panel of bioactive peptides, such as substance P, Ac-SDKP and angiotensin 1–7. These peptides have also been individually reported in the regulation of pathways of hematopoiesis. In this setting, an ACE-regulated peptide network orchestrating hematopoiesis has emerged. Here, we focus on this peptide network and discuss the roles of ACE and its peptides in aspects of hematopoiesis. Special attention is given to the recent revelation that ACE is a bona fide marker of hematopoietic stem cells.Key words: hematopoiesis, myelopoiesis, angiotensin converting enzyme (ACE), angiotensin II, AT1 receptor, renin-angiotensin system (RAS), substance P, Ac-SDKP, angiotensin 1–7     

The peptide network regulated by angiotensin converting enzyme (ACE) in hematopoiesis

The concept of a local bone marrow renin-angiotensin system (RAS) has been introduced and accumulating evidence suggests that the local RAS is actively involved in hematopoiesis. Angiotensin converting enzyme (ACE) is a key player in the RAS and makes the final effector angiotensin II. Besides angiotensin II, ACE also regulates a panel of bioactive peptides, such as substance P, Ac-SDKP and angiotensin 1-7. These peptides have also been individually reported in the regulation of pathways of hematopoiesis. In this setting, an ACE-regulated peptide network orchestrating hematopoiesis has emerged. Here, we focus on this peptide network and discuss the roles of ACE and its peptides in aspects of hematopoiesis. Special attention is given to the recent revelation that ACE is a bona fide marker of hematopoietic stem cells.     

Pericarditis as a manifestation of essential thrombocythemia.

A 58-year-old woman presented with pericarditis and pericardial effusion. Investigation revealed that she was suffering from a thrombocythemic myeloproliferative disorder; she died of massive pulmonary embolism 10 days after admission. Histologic study verified epicardial and pericardial trilineage hematopoiesis. Pericarditis is an unusual feature of essential thrombocythemia and it may occur in direct relation to the abnormal cellular proliferation.     

Hematopoiesis sculpted by pathogens: Toll-like receptors and inflammatory mediators directly activate stem cells

Hematopoietic stem cells (HSCs) repopulate the immune system during normal replenishment as well as under the burden of pathogen stress, but the respective outcomes of differentiation are not the same. Under homeostatic conditions such as those which accompany turnover of immune cell subsets, HSCs appear to co-equally prime genes associated with the major downstream lineages: lymphoid, myeloid, and megakaryocyte/erythroid. Recent studies reveal, however, that during pathogen exposure, hematopoiesis may yield progeny in proportions different than those produced under homeostasis. At least some of these effects may be due to pathogen engagement of Toll-like receptors (TLRs) expressed on HSCs. HSCs are also responsive to inflammatory cytokines that are produced in response to pathogen burden and are present in the bone marrow microenvironment. Thus, hematopoiesis is not a formulaic process that produces the same, predictable outcome regardless of the specific environmental context. Rather, hematopoiesis represents a dynamic biological system that can be appreciably responsive to environmental factors, an influence that extends to the level of the HSC itself. Knowledge of functional consequences of TLR ligation on HSCs may be therapeutically exploited and applied to treatment of hematopoietic insufficiency in the setting of infection and disease.     

Lysophosphatidic acid acts as a nutrient‐derived developmental cue to regulate early hematopoiesis

Primitive hematopoiesis occurs in the yolk sac blood islands during vertebrate embryogenesis, where abundant phosphatidylcholines (PC) are available as important nutrients for the developing embryo. However, whether these phospholipids also generate developmental cues to promote hematopoiesis is largely unknown. Here, we show that lysophosphatidic acid (LPA), a signaling molecule derived from PC, regulated hemangioblast formation and primitive hematopoiesis. Pharmacological and genetic blockage of LPA receptor 1 (LPAR1) or autotoxin (ATX), a secretory lysophospholipase that catalyzes LPA production, inhibited hematopoietic differentiation of mouse embryonic stem cells and impaired the formation of hemangioblasts. Mechanistic experiments revealed that the regulatory effect of ATX‐LPA signaling was mediated by PI3K/Akt‐Smad pathway. Furthermore, during in vivo embryogenesis in zebrafish, LPA functioned as a developmental cue for hemangioblast formation and primitive hematopoiesis. Taken together, we identified LPA as an important nutrient‐derived developmental cue for primitive hematopoiesis as well as a novel mechanism of hemangioblast regulation.     

Zebrafish mll gene is essential for hematopoiesis

Studies implicate an important role for the mixed lineage leukemia (Mll) gene in hematopoiesis, mainly through maintaining Hox gene expression. However, the mechanisms underlying Mll-mediated hematopoiesis during embryogenesis remain largely unclear. Here, we investigate the role of mll during zebrafish embryogenesis, particularly hematopoiesis. Mll depletion caused severe defects in hematopoiesis as indicated by a lack of blood flow and mature blood cells as well as a significant reduction in expression of hematopoietic progenitor and mature blood cell markers. Furthermore, mll depletion prevented the differentiation of hematopoietic progenitors. In addition, we identified the N-terminal mini-peptide of Mll that acted as a dominant negative form to disrupt normal function of mll during embryogenesis. As expected, mll knockdown altered the expression of a subset of Hox genes. However, overexpression of these down-regulated Hox genes only partially rescued the blood deficiency, suggesting that mll may target additional genes to regulate hematopoiesis. In the mll morphants, microarray analysis revealed a dramatic up-regulation of gadd45αa. Multiple assays indicate that mll inhibited gadd45αa expression and that overexpression of gadd45αa mRNA led to a phenotype similar to the one seen in the mll morphants. Taken together, these findings demonstrate that zebrafish mll plays essential roles in hematopoiesis and that gadd45αa may serve as a potential downstream target for mediating the function of mll in hematopoiesis.     

9.1C3 is identical to LAIR-1, which is expressed on hematopoietic progenitors

The leukocyte-associated Ig-like receptor-1 (LAIR-1) is a negative regulator of natural killer (NK) cells, its encoding gene belonging to the leukocyte receptor complex (LRC). Antibody to LAIR-1 can inhibit Ab-induced redirected lysis and TNF-alpha release of effector cells. LAIR-1 contains 2 immunoreceptor tyrosine-based inhibitory motifs (ITIM) in its cytoplasmic region that have been shown to bind constitutively and presumably regulate the tyrosine phosphatase SHP-1 in hematopoietic cells. SHP-1 mutation in mice results in abnormal lymphoproliferation, suggesting that LAIR-1 may also be implicated in regulating hematopoiesis. Here we investigated a monoclonal antibody, 9.1C3, against a NK cell antigen previously described as inducing increased colony formation in in vitro assays of human bone marrow cells. We found that 9.1C3 was expressed on CD34 positive hematopoietic progenitors for the first time. In functional assays, 9.1C3 MAb was able to inhibit Ab-induced redirected lysis and TNF-alpha secretion of NK cells. We proved that 9.1C3 is identical to LAIR-1, based on the fact that not only the antigen precipitated by 9.1C3 MAb was of 40kDa but also 9.1C3 MAb bound specifically to LAIR-1 cDNA transfected COS7 cells as well as recognized LAIR-1 fusion protein in ELISA. This finding provided the first evidence that LAIR-1 expresses on hematopoietic progenitor, implicating its role in the regulation of hematopoiesis at early stage.     

Hematopoiesis

Enormous numbers of adult blood cells are constantly regenerated throughout life from hematopoietic stem cells through a series of progenitor stages. Accessibility, robust functional assays, well-established prospective isolation, and successful clinical application made hematopoiesis the classical mammalian stem cell system. Most of the basic concepts of stem cell biology have been defined in this system. At the same time, many long-standing disputes in hematopoiesis research illustrate our still limited understanding. Here we discuss the embryonic development and lifelong maintenance of the hematopoietic system, its cellular components, and some of the hypotheses about the molecular mechanisms involved in controlling hematopoietic cell fates.     

Bef medaka mutant reveals the essential role of c-myb in both primitive and definitive hematopoiesis

Vertebrate hematopoiesis is characterized by two evolutionally conserved phases of development, i.e., primitive hematopoiesis, which is a transient phenomenon in the early embryo, and definitive hematopoiesis, which takes place in the later stages. Beni fuji (bef) was originally isolated as a medaka mutant that has an apparently reduced number of erythrocytes in its peripheral blood. Positional cloning revealed that the bef mutant has a nonsense mutation in the c-myb gene. Previous studies have shown that c-myb is essential for definitive hematopoiesis, and c-myb is now widely used as a marker gene for the onset of definitive hematopoiesis. To analyze the phenotypes of the bef mutant, we performed whole-mount in situ hybridization with gene markers of hematopoietic cells. The bef embryos showed decreased expression of α-globin and l-plastin, and a complete loss of mpo1 and rag1 expression, suggesting that the bef embryos had defects not only in erythrocytes but also in other myeloid cells, which indicates that their definitive hematopoiesis was aberrant. Interestingly, we observed a diminution in the number of primitive erythrocytes and a delay in the emergence of primitive macrophages in the bef embryos. These results suggest that c-myb also functions in the primitive hematopoiesis, potentially demonstrating a link between primitive and definitive hematopoiesis.     

Optimal protocols of hematopoietic stem cell expansion in vitro

Hematopoietic stem cells (HSCs) effectively and continuously replenish the full range of blood-cell populations. Bone-marrow and umbilical-cord blood stem-cell transplantation (SCT) restore hematopoiesis when used in various hematological and oncohematological disorders in adults and children. However, wider clinical application of effective SCT-based approaches is limited by the low number of primitive HSCs in the available biospecimens. Development of effective protocols of HSC expansion in vitro is therefore necessary. In this review, the notion of bone marrow hematopoiesis is discussed as a complex cellular system and a comparative analysis of various methods for HSC expansion in vitro is provided. The review is illustrated by our own data supporting application of various feeder-cell types for human HSC expansion in vitro.     

一个造血模型的全局吸引性和周期解相交

本文将Mackey和Glass提出的一个造血模型推广到具有周期系数和无穷时滞的情形．研究该模型的全局吸引性和周期解相交,并相应地得到两个充分条件.