The extracellular matrix of the hematopoietic microenvironment

The bone marrow microenvironment plays an important role in promoting hematopoietic progenitor cell proliferation and differentiation and the controlled egress of these developing hematopoietic cells. The establishment of long-term bone marrow cultures, which are thought to mimic hematopoiesis in vitro, and various stromal cell lines has greatly facilitated the analysis of the functions of this microenvironment. Extracellular matrix (ECM) molecules of all three categories (collagens, proteoglycans and glycoproteins) have been identified as part of this microenvironment and have been shown to be involved in, different biological functions such as cell adhesion and anti-adhesion, binding and presentation of various cytokines and regulation of cell growth. It is suggested that these matrix molecules in combination with cytokines are crucial for compartmentalization of the bone marrow. Although many cell adhesion molecules have been characterized on the surface of hematopoietic progenitor cells, the nature of cellular receptors for the ECM components is less well defined. During leukemia, many immature blood cells are released from bone marrow, but it is not yet known whether these abnormalities in hematopoiesis are also caused by an altered microenvironment or altered composition of its extracellular matrix. The elucidation of the involvement of specific ECM-isoforms and as yet not characterized ECM components and their receptors in the bone marrow will certainly help towards a better understanding of these phenomena.     

De novo hem- and lymphangiogenesis by endothelial progenitor and mesenchymal stem cells in immunocompetent mice

Cellular pro-angiogenic therapies may be applicable for the treatment of peripheral vascular diseases. Interactions between mesenchymal stem cells (MSCs) and endothelial progenitor cells (EPCs) may provide such a treatment option. With the exception of some studies in man, experiments have only been performed in immunodeficient mice and rats. We studied an immunocompetent syngeneic mouse model. We isolated MSCs from bone marrow and EPCs from the lung of adult C57/Bl.6 mice and co-injected them in Matrigel subcutaneously in adult C57/Bl.6 mice. We demonstrate development of both blood vessels and lymphatics. Grafted EPCs integrated into the lining of the two vessel types, whereas MSCs usually did not incorporate into the vessel wall. Injections of each separate cell type did not, or hardly, reveal de novo angiogenesis. The release of VEGF-A by MSCs has been shown before, but its inhibitors, e.g., soluble VEGF receptors, have not been studied. We performed qualitative and quantitative studies of the proteins released by EPCs, MSCs, and cocultures of the cells. Despite the secretion of VEGF inhibitors (sVEGFR-1, sVEGFR-2) by EPCs, VEGF-A was secreted by MSCs at bioavailable amounts (350 pg/ml). We confirm the secretion of PlGF, FGF-1, MCP-1, and PDGFs by EPCs/MSCs and suggest functions for VEGF-B, amphiregulin, fractalkine, CXCL10, and CXCL16 during MSC-induced hem- and lymphangiogenesis. We assume that lymphangiogenesis is induced indirectly by growth factors from immigrating leukocytes, which we found in close association with the lymphatic networks. Inflammatory responses to the cellular markers GFP and cell-tracker red (CMPTX) used for tracing of EPCs or MSCs were not observed. Our studies demonstrate the feasibility of pro-angiogenic/lymphangiogenic therapies in immunocompetent animals and indicate new MSC/EPC-derived angiogenic factors.     

Ephrin ligands and Eph receptors contribution to hematopoiesis

Hematopoietic stem and progenitor cells reside predominantly in the bone marrow. They supply billions of mature blood cells every day during life through maturation into multilineage progenitors and self-renewal. Newly produced mature cells serve to replenish the pool of circulating blood cells at the end of their life-span. These mature blood cells and a few hematopoietic progenitors normally exit the bone marrow through the sinusoidal vessels, a specialized venous vascular system that spreads throughout the bone marrow. Many signals regulate the coordinated mobilization of hematopoietic cells from the bone marrow to the circulation. In this review, we present recent advances on hematopoiesis and hematopoietic cell mobilization with a focus on the role of Ephrin ligands and their Eph receptors. These constitute a large family of transmembrane ligands and receptors that play critical roles in development and postnatally. New insights point to distinct roles of ephrin and Eph in different aspects of hematopoiesis.     

Leukocyte mobilization by epinephrine and hydrocortisone in patients with chronic renal failure

Summary The mobilization of WBC from the bone marrow, as judged from hydrocortisone-induced leucocytosis, is markedly impaired in dialyzed and nondialyzed uremic patients. The release of WBC from the marginal pool by epinephrine was found to be normal.     

The interrelationship between bone and fat: from cellular see-saw to endocrine reciprocity

The number of mature osteoblasts and marrow adipocytes in bone is influenced by the differentiation of the common mesenchymal progenitor cell towards one phenotype and away from the other. Consequently, factors which promote adipogenesis not only lead to fatty marrow but also inhibit osteoblastogenesis, resulting in decreased osteoblast numbers, diminished bone formation and, potentially, inadequate bone mass and osteoporosis. In addition to osteoblast and bone adipocyte numbers being influenced by this skewing of progenitor cell differentiation towards one phenotype, mature osteoblasts and adipocytes secrete factors which may evoke changes in the cell fate and function of each other. This review examines the endogenous factors, such as PPAR-γ2, Wnt, IGF-1, GH, FGF-2, oestrogen, the GP130 signalling cytokines, vitamin D and glucocorticoids, which regulate the selection between osteoblastogenesis and adipogenesis and the interrelationship between fat and bone. The role of adipokines on bone, such as adiponectin and leptin, as well as adipose-derived oestrogen, is reviewed and the role of bone as an energy regulating endocrine organ is discussed.     

Stimulation of hematopoietic stem cells by antilymphocyte serum]

The physiopathogeny of aplastic anemia is still unknown, it can be related to a stem cell defect or a microenvironment disease. An autoimmune origin is suspected but not as yet proved. To demonstrate the autoimmune origin of some cases of aplastic anemia, we have studied the effect of antilymphocyte globulin (ALG) on the hematopoiesis of aplastic patients by serial hematological and bone marrow investigation including blood counts, bone marrow cellularity, scanning with indium and technetium and granulocytic colonies in agar, 8 out of 17 patients had a response to ALG as shown by a rise of granulocytes and reticulocytes counts, increase of bone marrow cellularity and number of granulocytic colonies. This study tends to show that ALG has a stimulating effect on hematopoiesis in some cases of severe aplastic anemia.     

Vascular stem/progenitor cells: functions and signaling pathways

Vascular stem/progenitor cells (VSCs) are an important source of all types of vascular cells needed to build, maintain, repair, and remodel blood vessels. VSCs, therefore, play critical roles in the development, normal physiology, and pathophysiology of numerous diseases. There are four major types of VSCs, including endothelial progenitor cells (EPCs), smooth muscle progenitor cells (SMPCs), pericytes, and mesenchymal stem cells (MSCs). VSCs can be found in bone marrow, circulating blood, vessel walls, and other extravascular tissues. During the past two decades, considerable progress has been achieved in the understanding of the derivation, surface markers, and differentiation of VSCs. Yet, the mechanisms regulating their functions and maintenance under normal and pathological conditions, such as in eye diseases, remain to be further elucidated. Owing to the essential roles of blood vessels in human tissues and organs, understanding the functional properties and the underlying molecular basis of VSCs is of critical importance for both basic and translational research.     

Granulocyte colony formation in vitro: Enhancement by human placental (umbilical cord) serum

Summary Addition of human placental umbilical cord serum to bone marrow cultures reproducibly increased the number of granulocyte colonies in vitro. This stimulatory effect was significantly greater than that of fetal calf serum which was seen in cultures of human bone marrow under the conditions described.This work was financed by grant FOR. No. 004.AK.71 (1) from the Swiss Cancer League.The authors wish to express their gratitute to colleagues from Maternity Ward, Frauenspital, Bern, and Department of Thoracic and Vascular Surgery, Inselspital, Bern, through whose kind assistance samples of umbilical blood and fragments of ribs removed at thotacotomies were obtained. MissJ. Blom provided excellent technical assistance.     

Regulation of phagocyte migration and recruitment by Src-family kinases

Src-family kinases (SFKs) regulate different granulocyte and monocyte/macrophage responses. Accumulating evidence suggests that members of this family are implicated in signal transduction pathways regulating phagocytic cell migration and recruitment into inflammatory sites. Macrophages with a genetic deficiency of SFKs display marked alterations in cytoskeleton dynamics, polarization and migration. This same phenotype is found in cells with either a lack of SFK substrates and/or interacting proteins such as Pyk2/FAK, c-Cbl and p190RhoGAP. Notably, SFKs and their downstream targets also regulate monocyte recruitment into inflammatory sites. Depending on the type of assay used, neutrophil migration in vitro may be either dependent on or independent of SFKs. Also neutrophil recruitment in in vivo models of inflammation may be regulated differently by SFKs depending on the tissue involved. In this review we will discuss possible mechanisms by which SFKs may regulate phagocytic cell migratory abilities.     

Carnosine levels in blood

Summary Carnosine levels were determined in chick erythrocytes (2510 nmoles/g cells) and plasma from chick (27 nmoles/ml), rat and rabbit. Carnosine was also measured in rabbit reticulocyte-rich blood (105 nmoles/g cells), normal blood (18 nmoles/g cells) and in bone marrow.This work was supported by grant NS-06137 of the National Institutes of Health.     

Cure of osteopetrosis by allogenic bone marrow injection in the double mutant "osteopetrosi-athymic" rat]

The cure of osteopetrosis by allogenic bone marrow injection has been obtained in homozygous rats for both mutations, osteopetrosis (op) and athymic nude (rnu). This new animal model will help in studying the eventual relationship between the bone resorption process and the immunological reconstitution.     

Cell proliferation in the bone marrow and thymus following partial bone marrow aspiration

Summary Aspiration of the one femoral bone marrow caused a significant rise of the cell population, arrested in colchicine-metaphase both of the bone marrow from the other femur and of the thymus.     

Colony promoting activity and its target 'pre-CFUc' in genetically anemic mice of W/Wv genotype

Incubation of bone marrow cells with supernatant from long-term cultures of bone marrow cells increases the number of granulocyte-macrophage progenitor cells. This study reveals the presence of target cells of the colony promoting activity (CPA) in W/Wv mouse marrow. It is also shown that CPA does not stimulate erythroid colony formation in vitro.     

TULA-2, a novel histidine phosphatase, regulates bone remodeling by modulating osteoclast function

Bone is a dynamic tissue that depends on the intricate relationship between protein tyrosine kinases (PTK) and protein tyrosine phosphatases (PTP) for maintaining homeostasis. PTKs and PTPs act like molecular on and off switches and help modulate differentiation and the attachment of osteoclasts to bone matrix regulating bone resorption. The protein T cell ubiquitin ligand-2 (TULA-2), which is abundantly expressed in osteoclasts, is a novel histidine phosphatase. Our results show that of the two family members, only TULA-2 is expressed in osteoclasts and that its expression is sustained throughout the course of osteoclast differentiation, suggesting that TULA-2 may play a role during early as well late stages of osteoclast differentiation. Skeletal analysis of mice that do not express TULA or TULA-2 proteins (DKO mice) revealed that there was a decrease in bone volume due to increased osteoclast numbers and function. Furthermore, in vitro experiments indicated that bone marrow precursor cells from DKO mice have an increased potential to form osteoclasts. At the molecular level, the absence of TULA-2 in osteoclasts results in increased Syk phosphorylation at the Y352 and Y525/526 residues and activation of phospholipase C gamma 2 (PLCγ2) upon engagement of immune-receptor-tyrosine-based-activation-motif (ITAM)—mediated signaling. Furthermore, expression of a phosphatase-dead TULA-2 leads to increased osteoclast function. Taken together, these results suggest that TULA-2 negatively regulates osteoclast differentiation and function.     

Relevance of specific activity in experimental erythrocytocide by 55Fe.

Iron loads between 0.20 microgram and 26 microgram, added to 5 mu Ci 59Fe, were followed for up to 150 days in mice. Relative organ uptake increased as a function of iron load in liver and kidneys while it decreased in bone marrow and blood. Several weeks after injection, all load-related differences disappeared.     

Collagen synthesis by human bone marrow fibroblasts

Collagen synthesis was measured in fibroblast cultures derived from normal and acute lymphoblastic leukemia (ALL) bone marrow. Collagen production was higher in normal than in ALL fibroblasts. These cells elaborate type I and type III procollagens in a ratio that depends on cell density and whether cells originate from normal or ALL bone marrow.     

Autophagy as a target for glucocorticoid-induced osteoporosis therapy

Autophagy takes part in regulating the eukaryotic cells function and the progression of numerous diseases, but its clinical utility has not been fully developed yet. Recently, mounting evidences highlight an important correlation between autophagy and bone homeostasis, mediated by osteoclasts, osteocytes, bone marrow mesenchymal stem cells, and osteoblasts, and autophagy plays a vital role in the pathogenesis of glucocorticoid-induced osteoporosis (GIOP). The combinations of autophagy activators/inhibitors with anti-GIOP first-line drugs or some new autophagy-based manipulators, such as regulation of B cell lymphoma 2 family proteins and caspase-dependent clearance of autophagy-related gene proteins, are likely to be the promising approaches for GIOP clinical treatments. In view of the important role of autophagy in the pathogenesis of GIOP, here we review the potential mechanisms about the impacts of autophagy in GIOP and its association with GIOP therapy.     

Preservation of hematopoietic stem cells by slow freezing and elimination of the heat of fusion]

Previous experiments, in dogs with fresh bone marrow or bone marrow frozen with a modified freezing system have demonstrated a 100% recovery of frozen stem cells, stored for periods up to 5 months. Five patients, three with drug resistant acute leukemia and two with metastic carcinomas, have been treated with a high dose combination chemotherapy regimen (TACC) followed by reinfusion of marrow cryopreserved with the same modified freezing system. Following the reinfusion of marrow, autologous engraftment was demonstrated on bone marrow aspiration between days 5 and 10.