The role of blood stem cells in hematopoietic cell renewal

Diversity of Vascular Niches in Bones and Joints During Homeostasis, Ageing, and Diseases

The bones and joints in the skeletal system are composed of diverse cell types, including vascular niches, bone cells, connective tissue cells and mineral deposits and regulate whole-body homeostasis. The capacity of maintaining strength and generation of blood lineages lies within the skeletal system. Bone harbours blood and immune cells and their progenitors, and vascular cells provide several immune cell type niches. Blood vessels in bone are phenotypically and functionally diverse, with distinct capillary subtypes exhibiting striking changes with age. The bone vasculature has a special impact on osteogenesis and haematopoiesis, and dysregulation of the vasculature is associated with diverse blood and bone diseases. Ageing is associated with perturbed haematopoiesis, loss of osteogenesis, increased adipogenesis and diminished immune response and immune cell production. Endothelial and perivascular cells impact immune cell production and play a crucial role during inflammation. Here, we discuss normal and maladapted vascular niches in bone during development, homeostasis, ageing and bone diseases such as rheumatoid arthritis and osteoarthritis. Further, we discuss the role of vascular niches during bone malignancy.

Cellular kinetics of hematopoietic cells with Sfpi1 deletion are present at different frequencies in bone-marrow and spleen in X-irradiated mice

PURPOSE

Several past studies using a mouse model of radiation-induced AML (rAML) have shown that hemizygous deletion of the Sfpi1 gene (HDSG) is an initiating event for the development of rAML. In this study, we examined the difference in frequency of HDSG in hematopoietic stem cells (HSCs) Rich hematopoietic Cell population (HRCs) from bone marrow (BM) and spleen of C3H mice irradiated with 3 Gy X-rays.

MATERIALS AND METHODS

8-weeks old male C3H mice were irradiated 3Gy of whole body X-ray (1 Gy/min) and mice were sacrificed at 1, 4, 8, and 26 weeks. Then, HSPCs were isolated from BM of femur and spleen, the frequency of HRCs with Sfpi1 gene deletion was analyzed by fluorescence in situ hybridization (FISH).

RESULTS AND CONCLUSIONS

The frequency of HRCs with HDSG in both BM and spleen was increased 1 week after X-irradiation. Then, the frequency of HRCs with HDSG in BM showed a gradual decrease from 4 to 26 weeks, whereas HRCs with HDSG in spleen remained high, even at 26 weeks after X-irradiation. HDSG is less likely to be eliminated, particularly in the spleen, after X-irradiation. The spleen as well as BM of the femur may be major sites of rAML development.

The Impact of Mesenchymal Stem Cells on Differentiation of Hematopoietic Stem Cells

Bone marrow microenvironment contains cellular and acellular compartments. The cellular compartment includes hematopoietic stem cells, mesenchymal stem cells and some other stromal cell types, while the acellular compartment is composed of scaffold proteins known as the extra cellular matrix. Direct cell-cell contact as well as cytokines secreted by mesenchymal stem cells during coculture of hematopoietic stem cells and mesenchymal stem cells play a critical role in hematopoiesis, and determines the fate of hematopoietic stem cells. Several studies have demonstrated the impact of mesenchymal stem cells on self-renewal, expansion, proliferation and differentiation of hematopoietic stem cells in vitro, which have shown different and contradictory results. In this paper, we will investigate the effect of mesenchymal stem cells on differentiation of hematopoietic stem cells in vitro.

Quantitative analysis of glycans, related genes, and proteins in two human bone marrow stromal cell lines using an integrated strategy

Altered expression of glycans is associated with cell-cell signal transduction and regulation of cell functions in the bone marrow micro-environment. Studies of this micro-environment often use two human bone marrow stromal cell lines, HS5 and HS27a, co-cultured with myeloid cells. We hypothesized that differential protein glycosylation between these two cell lines may contribute to functional differences in in vitro co-culture models. In this study, we applied an integrated strategy using genomic, proteomic, and functional glycomic techniques for global expression profiling of N-glycans and their related genes and enzymes in HS5 cells versus HS27a cells. HS5 cells had significantly enhanced levels of bisecting N-glycans (catalyzed by MGAT3 [β-1,4-mannosyl-glycoprotein 4-β-N-acetylglucosaminyltransferase]), whereas HS27a cells had enhanced levels of Galβ1,4GlcNAc (catalyzed by β4GalT1 [β4-galactosyltransferase I]). This integrated strategy provides useful information regarding the functional roles of glycans and their related glycogenes and glycosyltransferases in the bone marrow microenvironment, and a basis for future studies of crosstalk among stromal cells and myeloma cells in co-culture.

Robust regeneration of adult zebrafish lateral line hair cells reflects continued precursor pool maintenance

We have examined lateral line hair cell and support cell maintenance in adult zebrafish when growth is largely complete. We demonstrate that adult zebrafish not only replenish hair cells after a single instance of hair cell damage, but also maintain hair cells and support cells after multiple rounds of damage and regeneration. We find that hair cells undergo continuous turnover in adult zebrafish in the absence of damage. We identify mitotically-distinct support cell populations and show that hair cells regenerate from underlying support cells in a region-specific manner. Our results demonstrate that there are two distinct support cell populations in the lateral line, which may help explain why zebrafish hair cell regeneration is extremely robust, retained throughout life, and potentially unlimited in regenerative capacity.

Fetal organ dosimetry for the Techa River and Ozyorsk Offspring Cohorts, part 2: radionuclide S values for fetal self-dose and maternal cross-dose

One of the many objectives of the European Union's SOLO (Epidemiological Studies of Exposed Southern Urals Populations) project is to quantify the radiation dose-response following chronic in utero exposures to ionizing radiation. The project is presently conducting a pooled analysis of two cohorts of individuals born to exposed mothers-the Techa River Offspring Cohort (TROC) and the Ozyorsk Offspring Cohort (OOC). The TROC includes the offspring of mothers with external exposures to contaminated riverbanks and internal ingestions of (89)Sr, (90)Sr/(90)Y, and (137)Cs/(137m)Ba, while the OOC includes the offspring of mothers with external exposures seen within the Mayak plutonium production facilities and internal inhalation of (239)Pu and possibly (131)I. In the present study, a newly created Urals-based series of fetal and maternal models is employed to assess S values for all seven radionuclides. Among all fetal ages, S values ranged in magnitude from 10(-14) to 10(-10) Gy per Bq-s for fetal source organs and from 10(-18) to 10(-14) Gy per Bq-s from maternal source organs, depending upon particle type, particle energy, and fetal age. For a given radionuclide and fetal age, S values for fetal source organs were approximately two orders of magnitude higher than for maternal source organs. Little variation in S values was observed among fetal source organs, while variations of over 100 % with respect to the mean were observed for maternal source organs near the fetus. S value variations from maternal cross-fire were highly dependent on fetal position and separation distance from the maternal source organ. These radionuclide S values have been coupled with biokinetic models for use in cohort dose assessment within the SOLO project.

Antineoplastic Agents and the Associated Myelosuppressive Effects

Bone marrow is a complex organ responsible for the regulation of hematopoietic cell distribution throughout the human body. Patients receiving antineoplastic agents as a therapeutic intervention for hematologic malignancy often experience varying degrees of myelotoxicity. Antineoplastic agents cause hypocellularity in marrow resulting in a reduction in hematopoietic tissue activity and a corresponding decline in cell production. Quantifying the adverse effects on hematopoiesis is based on the properties of a single agent, the use of individual drugs within a combination chemotherapy regimen, and the course, or courses, of chemotherapy designed to treat cancer. The direct or indirect suppression of erythrocytes, granulocytes, and megakaryocytes has potential for multiple negative clinical consequences ranging from increased monitoring of blood counts to life-threatening infection and death. This review will provide an overview of the structure and function of competent adult bone marrow, describe the process of hematopoiesis, and characterize the myelotoxicities associated with common antineoplastic agents currently used in the treatment of cancer.

Acute radiation syndrome caused by accidental radiation exposure - therapeutic principles

Fortunately radiation accidents are infrequent occurrences, but since they have the potential of large scale events like the nuclear accidents of Chernobyl and Fukushima, preparatory planning of the medical management of radiation accident victims is very important. Radiation accidents can result in different types of radiation exposure for which the diagnostic and therapeutic measures, as well as the outcomes, differ. The clinical course of acute radiation syndrome depends on the absorbed radiation dose and its distribution. Multi-organ-involvement and multi-organ-failure need be taken into account. The most vulnerable organ system to radiation exposure is the hematopoietic system. In addition to hematopoietic syndrome, radiation induced damage to the skin plays an important role in diagnostics and the treatment of radiation accident victims. The most important therapeutic principles with special reference to hematopoietic syndrome and cutaneous radiation syndrome are reviewed.

CXCR4-mediated bone marrow progenitor cell maintenance and mobilization are modulated by c-kit activity

RATIONALE

The mobilization of bone marrow (BM) progenitor cells (PCs) is largely governed by interactions between stromal cell-derived factor (SDF)-1 and CXC chemokine receptor (CXCR)4. Ischemic injury disrupts the SDF-1-CXCR4 interaction and releases BM PCs into the peripheral circulation, where the mobilized cells are recruited to the injured tissue and contribute to vessel growth. BM PCs can also be mobilized by the pharmacological CXCR4 antagonist AMD3100, but the other components of the SDF-1-CXCR4 signaling pathway are largely unknown. c-kit, a membrane-bound tyrosine kinase and the receptor for stem cell factor, has also been shown to play a critical role in BM PC mobilization and ischemic tissue repair.

OBJECTIVE

To investigate the functional interaction between SDF-1-CXCR4 signaling and c-kit activity in BM PC mobilization.

METHODS AND RESULTS

AMD3100 administration failed to mobilize BM PCs in mice defective in c-kit kinase activity or in mice transplanted with BM cells that expressed a constitutively active c-kit mutant. Furthermore, BM levels of phosphorylated (phospho)-c-kit declined after AMD3100 administration and after CXCR4 deletion. In cells adhering to culture plates coated with vascular cell adhesion molecule 1, SDF-1 and stem cell factor increased phospho-c-kit levels, and AMD3100 treatment suppressed SDF-1-induced, but not SCF-induced, c-kit phosphorylation. SDF-1-induced c-kit phosphorylation also required the activation of Src nonreceptor tyrosine kinase: pretreatment of cells with a selective Src inhibitor blocked both c-kit phosphorylation and the interaction between c-kit and phospho-Src.

CONCLUSIONS

These findings indicate that the regulation of BM PC trafficking by SDF-1 and CXCR4 is dependent on Src-mediated c-kit phosphorylation.

Bone and bone marrow: the same organ

Interplays between bone and bone marrow are not limited to merely anatomic and histological connections, but include a tight functional correlation. Bone marrow resides within the medullary cavity of the bones and the process of hematopoiesis is regulated, at least in part, by bone cells. Moreover, osteoclasts and osteoblasts derive from precursors of hematopoietic and mesenchymal origin, respectively, both residing within the bone marrow. Alterations in one of these components typically cause impairment in the other, so diseases of the bone marrow compartment often affect the bone and vice versa. All these findings could make us to speculate that bone and bone marrow are not two separate districts, but can be considered as the two elements of the same unique functional unit, the bone-bone marrow organ. Here we will describe histological and functional interplays between bone and bone marrow, and will illustrate some diseases in which this tight correlation is evident.

Stem-cell ecology and stem cells in motion

This review highlights major scientific developments over the past 50 years or so in concepts related to stem-cell ecology and to stem cells in motion. Many thorough and eloquent reviews have been presented in the last 5 years updating progress in these issues. Some paradigms have been challenged, others validated, or new ones brought to light. In the present review, we will confine our remarks to the historical development of progress. In doing so, we will refrain from a detailed analysis of controversial data, emphasizing instead widely accepted views and some challenging novel ones.

Pathophysiological principles underlying the blood cell concentration responses used to assess the severity of effect after accidental whole-body radiation exposure: an essential basis for an evidence-based clinical triage

OBJECTIVE

The objective of this review is to provide a scientific justification for using the pattern of changes of granulocytes, platelets, and lymphocytes within the first few days after an accidental whole-body exposure to ionizing radiation as a convincing indicator of the severity of its effect on the hematopoietic stem cell pool.

METHOD

The availability of the SEARCH database system (System for Evaluation and Archiving of Radiation Accidents based on Case Histories) allowed us to analyze the "early" blood cell changes after accidental whole-body radiation exposure in more than 100 patients and to assign them to severity of effect code H4 and H3, described in the METREPOL approach.

RESULTS

A specific pattern of blood cell changes (granulocytes, platelets, lymphocytes) within the first 5 to 8 days after exposure is compatible with the assumption of an irreversible damage of the stem cell pool distributed throughout the skeletal bone marrow designated as H4. Distinguishable from this pattern is a blood cell response pattern characterized by an "abortive recovery," which can be explained by the "injured cell hypothesis," allowing to assign these patients to a severity-of-effect-code H3, H2, or H1 compatible with the assumption of a "reversible" damage to the stem cell pool. Biomathematical models allow one to correlate the blood cell change patterns with the extent of damage to the stem cell pool.

CONCLUSION

Patterns of change in peripheral blood cell counts indicate the effect of radiation on the hematopoietic stem cell pool, and have the potential to predict autochthonous regeneration.

Radiation-induced leukemia at doses relevant to radiation therapy: modeling mechanisms and estimating risks

BACKGROUND

Because many cancer patients are diagnosed earlier and live longer than in the past, second cancers induced by radiation therapy have become a clinically significant issue. An earlier biologically based model that was designed to estimate risks of high-dose radiation-induced solid cancers included initiation of stem cells to a premalignant state, inactivation of stem cells at high radiation doses, and proliferation of stem cells during cellular repopulation after inactivation. This earlier model predicted the risks of solid tumors induced by radiation therapy but overestimated the corresponding leukemia risks.

METHODS

To extend the model to radiation-induced leukemias, we analyzed--in addition to cellular initiation, inactivation, and proliferation--a repopulation mechanism specific to the hematopoietic system: long-range migration through the blood stream of hematopoietic stem cells (HSCs) from distant locations. Parameters for the model were derived from HSC biologic data in the literature and from leukemia risks among atomic bomb survivors who were subjected to much lower radiation doses.

RESULTS

Proliferating HSCs that migrate from sites distant from the high-dose region include few preleukemic HSCs, thus decreasing the high-dose leukemia risk. The extended model for leukemia provides risk estimates that are consistent with epidemiologic data for leukemia risk associated with radiation therapy over a wide dose range. For example, when applied to an earlier case-control study of 110,000 women undergoing radiotherapy for uterine cancer, the model predicted an excess relative risk (ERR) of 1.9 for leukemia among women who received a large inhomogeneous fractionated external beam dose to the bone marrow (mean = 14.9 Gy), consistent with the measured ERR (2.0, 95% confidence interval [CI] = 0.2 to 6.4; from 3.6 cases expected and 11 cases observed). As a corresponding example for brachytherapy, the predicted ERR of 0.80 among women who received an inhomogeneous low-dose-rate dose to the bone marrow (mean = 2.5 Gy) was consistent with the measured ERR (0.62, 95% CI = -0.2 to 1.9).

CONCLUSIONS

An extended, biologically based model for leukemia that includes HSC initiation, inactivation, proliferation, and, uniquely for leukemia, long-range HSC migration predicts, with reasonable accuracy, risks for radiation-induced leukemia associated with exposure to therapeutic doses of radiation.

Nuclear terrorism: the role of hematology in coping with its health consequences

PURPOSE OF REVIEW

This review reports on a novel approach to use blood cell change patterns after accidental whole body radiation exposure (to be expected as a consequence of nuclear terrorism) as reliable indicators of effect and as an aid to plan therapeutic measures.

RECENT FINDINGS

There is growing concern about the potential of nuclear terrorism. Several scenarios are being discussed. In all of them one finds elements that mimic the experience gained in assessing and treating humans who were exposed to ionizing radiation in radiation accidents. This experience leads to diagnostic and therapeutic measures laid down in a recently published Manual on the Acute Radiation Syndrome. The European Bone Marrow Transplantation Group (EBMT) together with the Institut de Radioprotection et de Sûreté Nucléaire (IRSN) in Paris and the University of Ulm published a consensus paper to use 'response categories' based on organ-specific gradings of severity as indicators of the severity of health impairments.

SUMMARY

The implication of this review is obvious: the medical staff confronted suddenly with the challenge of clinically managing an irradiated person will find all scientifically based recommendations in order to cope with the evolving problems on a scientific-pathophysiology driven approach.

A multi-compartment cell repopulation model allowing for inter-compartmental migration following radiation exposure, applied to leukaemia

There is much uncertainty about cancer risks at the high radiation doses used in radiotherapy (RT). It has generally been assumed that cancer induction decreases rapidly at high doses due to cell killing. However, this is not seen in all RT groups, and a model recently developed by Sachs and Brenner [2005. Solid tumor risks after high doses of ionizing radiation. Proc. Natl Acad. Sci. USA 102, 13040-13045] proposed a mechanism for repopulation of cells after radiation exposure that explained why this might happen, at least for solid tumours. In this paper, this model is generalized to allow for heterogeneity in the dose received, and various alternate patterns of repopulation are also considered. The model is fitted to the Japanese atomic bomb survivor leukaemia incidence data, and data for various therapeutically irradiated groups. Two sets of parameters from these model fits are used to assess the sensitivity of model predictions. It is shown that in general allowing for heterogeneity in dose distribution and haematopoietic stem cell migration results in lower risks than the same average dose administered uniformly and without such migration, although this does not hold in the limiting case of complete stem cell repopulation between radiation dose fractions. We also investigate the difference made by assuming a compartmental repopulation signal, and a global repopulation signal. In general we show that in the absence of stochastic extinction, compartmental repopulation always predicts a larger number of mutated cells than global repopulation. However, in certain dose regimes stochastic extinction cannot be ignored, and in these cases the numbers of mutated cells predicted with global repopulation can exceed that for compartmental repopulation. In general, mutant cell numbers are highly overdispersed, with variance much greater than the mean.

The stem cell niches in bone

The stem cell niche is composed of a specialized population of cells that plays an essential role in regulating adult stem cell self-renewal and differentiation. In adults, osteoblasts, responsible for osteogenesis, and hematopoietic cells, responsible for hematopoiesis, are closely associated in the bone marrow, suggesting a reciprocal relationship between the two. It was recently discovered that a subset of osteoblasts functions as a key component of the HSC niche (namely, the osteoblastic niche), controlling HSC numbers. HSCs interact not only with osteoblasts but also with other stromal cells, including endothelial cells. Sinusoidal endothelial cells in bone marrow have been revealed as an alternative HSC niche called the vascular niche. In this Review we compare the architecture of these 2 HSC niches in bone marrow. We also highlight the function of osteoblasts in maintaining a quiescent HSC microenvironment and the likely role of the vascular niche in regulating stem cell proliferation, differentiation, and mobilization. In addition, we focus on studies of animal models and in vitro assays that have provided direct insights into the actions of these osteoblastic and vascular niches, revealing central roles for numerous signaling and adhesion molecules. Many of the discoveries described herein may contribute to future clinical treatments for hematopoietic and bone-related disorders, including cancer.

Human hematopoietic stem/progenitor-enriched CD34+ cells are mobilized into peripheral blood during stress related to ischemic stroke or acute myocardial infarction

The hematopoietic and non-hematopoietic stem/progenitor cells harvested directly from the bone marrow (BM) or G-CSF mobilized peripheral blood were demonstrated to play an important role in regeneration of damaged organs (1, 2). Here, we asked if the stroke- or acute heart infarct-related stress triggers mobilization of stem/progenitor-enriched CD34(+)cells from the BM into the peripheral blood, which subsequently could contribute to regeneration of damaged tissues. To address this question the peripheral blood samples were harvested from patients with ischemic stroke during the first 24 h of manifestation of symptoms and on the second and sixth day afterwards or during the first 24 h of acute cardiac pain as well as on the second and sixth day of infarct. We measured in these patients (i) percentage of circulating hematopoietic stem/progenitor-enriched CD34(+) cells in peripheral blood by employing fluorescence activated cell sorter (FACS) and (ii) number of hematopoietic progenitor cells for the granulocyte-monocytic colony-forming unit (CFU-GM) and erythoid burst-forming unit (BFU-E) lineages circulating in peripheral blood. We concluded that stress related to ischemic stroke or acute myocardial infarction triggers the mobilization of hematopoietic stem/progenitor-enriched CD34(+) cells from the BM into peripheral blood. These circulating stem/progenitor-enriched CD34(+) cells may contribute to the regeneration of ischemic tissues, however, this possibility requires further studies.

Bovine mammary progenitor cells: current concepts and future directions

Although cell number is positively correlated with milk production, much remains to be learned about the bovine mammary stem cell and progenitor cells. Bovine mammary development is driven by many of the same classic mammogenic hormones studied in murine models, yet histologic features of bovine mammary development differ from that of rodent models. Most notably, terminal end buds, as they have been described for murine models, do not exist in the bovine mammary gland. However, among the most important common features of mammary development in disparate species is the involvement of histologically distinct, lightly staining epithelial cells as putative stem and progenitor cells. Although stem cell research has often focused on mammary development, mammary stem cells seemingly provide the basis for mammary growth and cell turnover in the mature animal. These cells provide an obvious focus for research aimed at increasing the efficiency of milk production. This review addresses recent findings concerning the histology and molecular physiology of putative bovine mammary stem and progenitor cell populations, areas where more study is critically needed, and areas where studies of bovine mammary physiology may present a unique opportunity to better understand mammary physiology in many species.

Mathematical model of peripheral blood stem cell harvest kinetics

A mathematical model of peripheral blood stem cell harvests was developed, taking two new parameters R (number of recruited cells/minute) and E(f) (efficiency of collection) into consideration in addition to concentrations and collected amounts of cells. This model was tested on 241 harvest procedures in cancer patients (chemotherapy+G-CSF stimulation), donors of allogeneic PBSC, and platelet donors, using different collection procedures, with a Cobe Spectra Cell separator. The relationships between preapheresis concentrations, R, E(f) and harvested amounts of cells were complex, and different for different harvest procedures and populations of donors. However, invariably, recruitment played an important role and contributed significantly to the final harvest in all types of cells studied. For example, for the patient group, mean recruitment was 1.3 x 10(6) CD34+ cells/min and the amount of recruited cells corresponded to 65% of all collected cells. Recruitment was significantly influenced by pretreatment with chemo-therapy and/or radiotherapy. The mean recruitment values for the subgroups with limited, moderate, and extensive pretreatment were 1.65 x 10(6), 0.87 x 10(6), and 0.32 x 10(6) CD34+ cells released per minute, respectively. The finding of a quick and massive recruitment phenomenon may stimulate further research into hematopoiesis in order to maximize harvested cells.

Spontaneous circulation of myeloid-lymphoid-initiating cells and SCID-repopulating cells in sickle cell crisis

The only curative therapy for sickle cell disease (SCD) is allogeneic hematopoietic stem cell (HSC) transplantation. Gene therapy approaches for autologous HSC transplantation are being developed. Although earlier engraftment is seen when cells from GCSF-mobilized blood are transplanted than when bone marrow is transplanted, administration of GCSF to patients with SCD can cause significant morbidity. We tested whether primitive hematopoietic progenitors are spontaneously mobilized in the blood of patients with SCD during acute crisis (AC-SCD patients). The frequency of myeloid-lymphoid-initiating cells (ML-ICs) and SCID-repopulating cells (SRCs) was significantly higher in blood from AC-SCD patients than in blood from patients with steady-state SCD or from normal donors. The presence of SRCs in peripheral blood was not associated with detection of long-term culture-initiating cells, consistent with the notion that SRCs are more primitive than long-term culture-initiating cells. As ML-ICs and SRCs were both detected in blood of AC-SCD patients only, these assays may both measure primitive progenitors. The frequency of ML-ICs also correlated with increases in stem cell factor, GCSF, and IL-8 levels in AC-SCD compared with steady-state SCD and normal-donor sera. Because significant numbers of ML-ICs and SRCs are mobilized in the blood without exogenous cytokine treatment during acute crisis of SCD, collection of peripheral blood progenitors during crisis may yield a source of autologous HSCs suitable for ex-vivo correction by gene therapy approaches and subsequent transplantation.

Pathologic thrombopoiesis of rheumatoid arthritis

Rheumatoid arthritis (RA) is frequently complicated by thrombocytosis correlated with disease activity. The exact pathogenetic mechanism(s) that cause increased platelet counts in RA are still unknown. Recent investigations indicate that proinflammatory pleiotropic cytokines of RA also have megakaryocytopoietic/thrombopoietic properties. Moreover, several lineage-dominant hematopoietic cytokines can also act as acute phase responders and contribute to the inflammation. This review focuses on the current literature and our experience regarding the dual relationships of the pathologic thrombopoiesis of RA. Growth factors contributing to it, namely interleukin (IL)-6, IL-11, stem cell factor, leukemia inhibitory factor, granulocyte colony stimulating factor, thrombopoietin (TPO), and the regulation of megakaryocytopoiesis during the inflammatory cascade are reviewed. Some data indicate that thrombopoietin could contribute to the reactive thrombocytosis of RA. In the non-lineage-specific gp130 cytokine family, IL-6 appears to predominate for the induction of megakaryopoiesis. However, other cytokines and growth factors may also contribute to the pathologic megakaryocytopoiesis of RA. Those pleiotropic mediators seem to act in concert to regulate this enigmatic process. Clarification of the pathobiologic basis of thrombopoiesis in RA may improve understanding of the disease pathogenesis and management of the inflammatory thrombocytosis.

Induction of hypoxia-inducible factor-1alpha and activation of caspase-3 in hypoxia-reoxygenated bone marrow stroma is negatively regulated by the delayed production of substance P

The bone marrow (BM), which is the major site of immune cell development in the adult, responds to different stimuli such as inflammation and hemorrhagic shock. Substance P (SP) is the major peptide encoded by the immune/hemopoietic modulator gene, preprotachykinin-1 (PPT-I). Differential gene expression using a microarray showed that SP reduced hypoxia-inducible factor-1alpha (HIF-1alpha) mRNA levels in BM stroma. Because long-term hypoxia induced the expression of PPT-I in BM mononuclear cells, we used timeline studies to determine whether PPT-I is central to the biologic responses of BM stroma subjected to 30-min hypoxia (pO(2) = 35 mm Hg) followed by reoxygenation. HIF-1alpha mRNA and protein levels were increased up to 12 h. At this time, beta-PPT-I mRNA was detected with the release of SP at 16 h. SP release correlated with down-regulation of HIF-1alpha to baseline. A direct role for SP in HIF-1alpha expression was demonstrated as follows: 1) transient knockout of beta-PPT-I showed an increase in HIF-1alpha expression up to 48 h of reoxygenation; and 2) HIF-1alpha expression remained baseline during reoxygenation when stroma was subjected to hypoxia in the presence of SP. Reoxygenation activated the PPT-I promoter with concomitant nuclear translocation of HIF-1alpha that can bind to the respective consensus sequences within the PPT-I promoter. SP reversed active caspase-3, an indicator of apoptosis and erythropoiesis, to homeostasis level after reoxygenation of hypoxic stroma. The results show that during reoxgenation the PPT-I gene acts as a negative regulator on the expression of HIF-1alpha and active caspase-3 in BM stroma subjected to reoxygenation.

The skeletal muscle satellite cell: stem cell or son of stem cell?

The concept of the adult tissue stem cell is fundamental to models of persistent renewal in functionally post-mitotic tissues. Although relatively ignored by stem cell biology, skeletal muscle is a prime example of an adult tissue that can generate terminally differentiated cells uniquely specialized to carry out tissue-specific functions. This capacity is attributed to satellite cells, a population of undifferentiated, quiescent precursors that become activated to divide and differentiate in response to the demands of growth or damage. The aim of this review is to discuss the role of the satellite cell as an adult tissue-specific stem cell. We examine evidence for the presence of behaviourally and phenotypically distinct subpopulations of precursor within the satellite cell pool. Further, we speculate on the possible identity, origins and relevance of multipotent muscle stem cells, a population with both myogenic and hematopoietic potentials that has been isolated from whole muscle. Taken together, current evidence suggests the possibility that the regenerative compartment of adult skeletal muscle may conform to an archetypal stem cell-based hierarchy, maintained within a stem cell niche. It therefore remains to be seen whether all satellite cells are skeletal muscle-specific stem cells, or whether some or all are the progeny of an as yet unidentified muscle stem cell.

Hypermethylation of E-cadherin in leukemia

E-cadherin gene is often termed a “metastasis suppressor” gene because the E-cadherin protein can suppress tumor cell invasion and metastasis. Inactivation of the E-cadherin gene occurs in undifferentiated solid tumors by both genetic and epigenetic mechanisms; however, the role of E-cadherin in hematologic malignancies is only now being recognized. E-cadherin expression is essential for erythroblast and normoblast maturation, yet expression is reduced or absent in leukemic blast cells. This study examined the messenger RNA (mRNA) and protein expression of the E-cadherin gene in bone marrow and blood samples from normal donors and patients with leukemia. We found that all normal donor samples expressed E-cadherin mRNA, whereas both samples of acute myelogenous leukemia and chronic lymphocytic leukemia had a significant reduction or absence of expression. However, normal blast counterparts expressed only a low level of E-cadherin surface protein. Sodium bisulphite genomic sequencing was used to fully characterize the methylation patterns of the CpG island associated with the E-cadherin gene promoter in those samples with matched DNA. All of the normal control samples were essentially unmethylated; however, 14 of 18 (78%) of the leukemia samples had abnormal hypermethylation of the E-cadherin CpG island. In fact both alleles of the E-cadherin gene were often hypermethylated. We conclude the E-cadherin gene is a common target for hypermethylation in hematologic malignancies.

Hypermethylation of E-cadherin in leukemia

E-cadherin gene is often termed a “metastasis suppressor” gene because the E-cadherin protein can suppress tumor cell invasion and metastasis. Inactivation of the E-cadherin gene occurs in undifferentiated solid tumors by both genetic and epigenetic mechanisms; however, the role of E-cadherin in hematologic malignancies is only now being recognized. E-cadherin expression is essential for erythroblast and normoblast maturation, yet expression is reduced or absent in leukemic blast cells. This study examined the messenger RNA (mRNA) and protein expression of the E-cadherin gene in bone marrow and blood samples from normal donors and patients with leukemia. We found that all normal donor samples expressed E-cadherin mRNA, whereas both samples of acute myelogenous leukemia and chronic lymphocytic leukemia had a significant reduction or absence of expression. However, normal blast counterparts expressed only a low level of E-cadherin surface protein. Sodium bisulphite genomic sequencing was used to fully characterize the methylation patterns of the CpG island associated with the E-cadherin gene promoter in those samples with matched DNA. All of the normal control samples were essentially unmethylated; however, 14 of 18 (78%) of the leukemia samples had abnormal hypermethylation of the E-cadherin CpG island. In fact both alleles of the E-cadherin gene were often hypermethylated. We conclude the E-cadherin gene is a common target for hypermethylation in hematologic malignancies.