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Biomedical subjects

D Zipori

Publications and source records attributed to D Zipori.

At least 55 records · Page 3Linked to original sources
PubMed1992

The renewal and differentiation of hemopoietic stem cells.

Blood-forming tissues are organized in well-defined microenvironments composed of hemopoietic cells and a supportive stroma of connective tissue and endothelium. Hemopoietic cells segregate to various lineages, all derived from a small population of pluripotent stem cells residing in the bone marrow. Regulation of growth and differentiation, particularly under conditions of perturbations, damage, and disease, is mediated by inducer colony-stimulating factors and interleukins counteracted by inhibitory cytokines. Whereas much is known about the mode of induction of differentiation, insufficient information is available to explain the process of stem cell renewal that is crucial for the longevity of the hemopoietic system. It is also only partially known how inhibition of hemopoietic processes occurs, and what molecules in blood-forming tissues signal organization into discrete patterns. This paper reviews recent progress that has opened new avenues to a better understanding of this highly complex issue.

Animals↗
PubMed1992

Absence of negative growth regulation in three new murine radiation-induced myeloid leukemia cell lines with deletion of chromosome 2.

Murine radiation-induced acute myeloid leukemia (RI-AML) may be considered as the experimental counterpart of human secondary leukemia. Three new myelomonocytic cell lines derived from RI-AML and carrying a partially deleted chromosome 2 are described. The RI-AML cells responded with increased proliferation after being incubated with the hemopoietic growth factors rG-CSF, rGM-CSF and IL-3. Increased proliferation of the same extent without any effect in differentiation, was also demonstrated in the RI-AML cells after incubation with IL-6 and with mouse lung conditioned medium (CM) and Krebs ascites tumor cells CM which induce differentiation in normal and most leukemic myeloid cells. Down-regulation of the c-myc gene and induction of (2'-5') oligo-adenylate synthetase (reflecting autocrine interferon secretion), two essential mechanisms operating during arrest of growth and concomitant differentiation, were demonstrated to be absent in RI-AML cells. In contrast, the M1 cells responded to the above differentiating factors with growth arrest and differentiation and with appropriate c-myc down-regulation and synthetase induction. The genetic basis for the distinct RI-AML cells' behavior may be connected with the loss or structural and/or functional abnormalities of DNA sequences located in the deleted part of chromosome 2 or in the respective allele. The presently described new RI-AML cell lines may be used for studies concerning myeloid leukemogenesis in general and secondary leukemia in particular.

2',5'-Oligoadenylate Synthetase↗
PubMed1991

Expression of alpha-smooth muscle actin in murine bone marrow stromal cells.

Human fibrotic bone marrow (BM) stroma has been shown to contain alpha-smooth muscle actin (alpha-SMA)-positive cells. These closely resemble myofibroblasts that were described in other fibrotic tissues. We studied the expression of alpha-SMA in a series of murine BM-derived stromal cell lines to investigate the cellular origin and functional significance of myofibroblast-like cells in hematopoietic tissues. Although these cell lines differed in their biologic properties, most of them expressed alpha-SMA under certain conditions. Cells expressing alpha-SMA constituted a minor population in post-confluent, growth-arrested cultures. However, the incidence of cells expressing alpha-SMA increased significantly when cultures were transferred to nonconfluent conditions. A similar increase in alpha-SMA-positive cells occurred after a strip of cells was scraped away from the confluent cell layer; the cells of the affected area acquired alpha-SMA-positive contractile phenotype. The relationship between alpha-SMA expression and hematopoietic activity was studied using a cloned cell line of BM origin (14F1.1). The ability of these endothelial-adipocyte cells to support hematopoiesis in vitro was maximal under confluent conditions, whereas their expression of alpha-SMA under such conditions was residual. Moreover, in long-term BM cultures supported by confluent 14F1.1 cells, stromal areas associated with proliferating hematopoietic precursors, known as "cobblestone areas," were devoid of alpha-SMA-positive cells. These observations suggest that the expression of alpha-SMA is reversible and inversely related to hematopoietic activity.

Actins↗
PubMed1991

Subpopulations of marrow stromal cells share a variety of osteoblastic markers.

A series of stromal cell lines derived from mouse bone marrow, representing subpopulations of putative stromal cell types, were examined for the expression of osteoblastic properties. The effects of dexamethasone and specific inhibitors on alkaline phosphatase activity, cAMP response to bone-seeking hormones, and the ability to mineralize extracellular matrix in vitro as well as collagen typing were used as osteoblastic markers. We found that all stromal cell types examined possess some osteoblastic features but differ in the degree of expression. The data provide support to the hypothesis of a common stem cell for marrow stromal cells.

Alkaline Phosphatase↗
PubMed1991

Restrictin-P: the first member of a putative family of novel inhibitors.

MBA-2.1 cells produce an activity, designated restrictin-P, which is specifically inhibitory to the growth of plasmacytomas and mature B cell lymphomas. We examined whether the activity of this stromally derived glycoprotein could be attributed to a well-characterized growth factor. Restrictin-P-producing cells were therefore screened for the expression of transcripts of a variety of growth suppressors. With the exception of TGF-beta 1, none was produced in detectable amounts by these cells. Furthermore, recombinant forms of the inhibitory molecules tested did not exert a biological effect similar to that of restrictin-P. Restrictin-P was shown to elicit a G0/G1 arrest in the cell cycle of its target cells, as soon as 24 h after their exposure to the inhibitor. This effect could not be mimicked by TGF-beta 1. We suggest that restrictin-P is part of a novel family of inhibitors which are required for the maintenance of cell-type specificities in the hematopoietic microenvironment.

Animals↗
PubMed1990

A periodicity in the response of SJL/J thymocytes to isoproterenol. Simulation by cell lines.

Thymocytes from SJL/J mice exhibit a periodicity in their response to hormonal stimulation with isoproterenol. This periodicity (5-9 days) is expressed in large changes in the intensity of the response (peak levels of intracellular cAMP which vary approximately 6-fold), and in the response pattern, i.e., in the occurrence or non-occurrence of an immediate hormone-induced desensitization. In contrast, C57BL/6 thymocytes have a homogeneous response pattern (in all cases there was an immediate desensitization). Their response does change with the same periodicity, but these changes are restricted to the intensity of response (the peak of cAMP levels varies only approximately 2-fold). Using T, B and pre-B shown that these periodic changes may be due to fluctuations in T cell subpopulations in the thymus and possibly also the infiltration of B cells into it. These observations provide a useful system for studying at the cellular and molecular level the known correlation between endocrine disorders and neoplasia in mice. On the other hand, the set of cell lines with such different response patterns to a single hormone may be used for the identification and isolation of additional cellular constituents involved in the cellular response to hormones and its immediate desensitization.

Animals↗
PubMed1990

Detection of interleukin-3 in the serum of mice infected with Mycobacterium lepraemurium.

Infection of mice by Mycobacterium lepraemurium is accompanied by ablation of erythropoiesis in the bone marrow and gross enlargement of the spleen. This, together with increased monocytopoiesis and the earlier demonstration of macrophage colony-stimulating factor in the serum of infected mice, suggested the activity of additional cytokines. Eight weeks after infection of mice by M. lepraemurium, interleukin-3 (IL-3) activity was demonstrated in the serum (titer, 1:3200). The serum titer of IL-3 activity was maximal after 13 weeks (greater than 1:6400) and was slightly reduced after 18 weeks (1:6400). That the IL-3 activity detected in the serum of the M. lepraemurium-infected mice reflected the presence of IL-3 itself was confirmed by a neutralization assay using anti-murine IL-3 antibodies; IL-3 activity in the serum of mice 13 weeks after infection was completely abolished by the anti-IL-3 antibodies. Finally, a 1-kb signal of IL-3 RNA was detected in the spleens of M. lepraemurium-infected mice 13 weeks after infection.

Animals↗
PubMed1990

Selective accumulation of lymphocyte precursor cells mediated by stromal cells of hemopoietic origin.

Thymocytes were propagated in long-term cultures supported by stromal cells of both bone marrow and thymus origin. Interleukin 2 (IL-2) supplementation augmented the cell yield and allowed detailed phenotype analysis. Within 2-3 months of culture a cell population was selected in which the expression of Thy-1 antigen persisted, CD4 and CD8 antigens gradually declined, and Pgp-1 antigen, found on less than 5% of fresh thymocytes, was strongly increased. This cultured cell population (Thy-1.2 origin) contained no detectable spleen colony-forming units (CFU-S) but efficiently repopulated the thymus of Thy-1.1-irradiated congenic mice, indicating the precursor T-cell nature of the population. Upon removal from the stroma, the T cells exhibited poor cytotoxicity towards syngeneic tumor cells. Further propagation with IL-2 in the absence of stroma resulted in the acquisition of cytotoxic ability. Replacement of the horse serum used in the above experiments with fetal calf serum resulted in accumulation of cells expressing B220 antigen. This experimental model provides the means to maintain lymphocyte precursor cells in long-term culture and to further study their differentiation in the absence of stroma, both in vitro and in vivo.

Animals↗
PubMed1990

Regulation of hemopoiesis by cytokines that restrict options for growth and differentiation.

Regulators of hemopoiesis are traditionally classified as belonging to two groups having antagonistic activities, that is, stimulators versus inhibitors. The majority of the so-called "inhibitory" molecules do not differ from stimulators in their biological activity since both are inducers of differentiation and consequent cell death. It is hypothesized that these cytokines operate during emergency situations (such as bacterial infections) in peripheral organs and bloodstream. Conversely, steady-state hemopoiesis in blood-forming organs is regulated by stromal factors that support stem cell renewal and direct cell positioning. Some of these stromal cell factors are lineage-specific inhibitors. It is proposed that hemopoietically active cytokines be called restrictions, since their function is to minimize the options available for the cell and thereby determine its growth and differentiation pathway.

Animals↗
PubMed1989

Bone marrow-derived stromal cell line expressing osteoblastic phenotype in vitro and osteogenic capacity in vivo.

Marrow stroma has been shown to have osteogenic potential. Here we report the characterization of a unique stromal cell line derived from mouse bone marrow (MBA-15), which expresses osteoblastic phenotype in vitro and forms bone in vivo. More than 70% of cells in culture were histochemically positive for alkaline phosphatase. The enzyme levels were enhanced threefold when cultures were treated with dexamethasone. Gel electrophoresis of [3H]-proline-labeled cultures showed that MBA-15 cells produced only type I collagen. These cells were responsive to PTH, as indicated by a 50-fold increase in intracellular cAMP. Prostaglandin E2, but not calcitonin, stimulated cAMP up to 70-fold. When cultures were grown to confluence and fed daily with ascorbic acid and beta-glycerophosphate, the cells formed a Von Kossa positive, thick extracellular matrix, shown to contain hydroxyapatite crystals. MBA-15 cells produced mineralized bone when implanted in diffusion chambers. These results indicate that the MBA-15 cell line possesses osteoblastic features in vitro and osteogenic capacity in vivo.

Alkaline Phosphatase↗
PubMed1989

Stromal cells of hemopoietic origin.

Hemopoiesis is a multistep process involving stem cell renewal, commitment, differentiation, maturation and consequent positioning of the cells within the tissue. Stromal cells are a major component of the hemopoietic microenvironment. The in vitro culture of cloned stromal cells has enabled detailed analysis of their functions and has provided answers relating to the contribution of stromal cells to the control of hemopoiesis. Cultured stromal cells were found to support the renewal of stem cells through a mechanism that did not seem to involve already known cytokines. Cloned stromal cells from both marrow and thymus supported the in vitro accumulation of myeloid as well as T and B lymphoid cells. Thus, cloned stromal cells had the ability to induce multilineage hemopoiesis, irrespective of the organ from which they were derived. Invariably, stromal cells tended to select in culture for hemopoietic cells at early differentiation stages and restricted the accumulation of mature cells. These functions may be part of the mechanism that protects the stem cell pool from excess differentiation.

Animals↗
PubMed1989

Multilineage hemopoiesis induced by cloned stromal cells.

Long-term hemopoiesis in culture depends upon the presence of an adherent layer composed of a variety of stromal cells. A subtype of endothelial-adipocytes from the bone marrow stroma (clone 14F1.1) was previously shown to induce long-term myelopoiesis and renewal of pluripotent stem cells. One of a series of stromal cell lines and clones from mouse thymus stroma (STAC-1.2) has now been found to support long-term hemopoiesis. These marrow- and thymus-derived stromal cell clones also have lymphopoietic activities: precursor T cells, or pre-B cells accumulated in co-cultures of thymus cells and the stromal clones, as indicated by cell surface markers, T cell receptor and immunoglobulin gene rearrangements. The predominance of a cell type in these cultures depended upon the serum used to supplement the medium. Recombinant interleukin 2 (IL-2) and the 14F1.1 clone synergistically promoted the proliferation of thymocytes, while a thymus hormone, THF-gamma 2, shifted the population to a relatively mature phenotype. It is proposed that one major function of stromal cells, whether from the bone marrow or thymus, is to restrain the maturation flow and preferentially support the accumulation of cells at early differentiation stages.

Animals↗
PubMed1989

Age related changes in hemopoietic capacity of bone marrow cells.

The effect of aging on the hemopoietic capacity of bone marrow (BM) cells was investigated. No difference was found in the incidence of colony forming units-spleen (CFU-S) and granulocyte-macrophage colony forming cells (GM-CFC) present in the BM of young (2-4 months) or old (24-30 months) mice. However, increased proliferation (x3) of the old BM cells was observed when cultured in the presence of L-cell conditioned medium. The cells were also cultivated over an adherent layer of a BM stroma cell line (14F1.1, endothelial-adipocytes) and the non-adherent cells removed and tested weekly. Cells originating from the old BM proliferated to a greater extent and produced more GM-CFC than those from the young. Differentiation into T-cells after colonizing fetal thymus explants was also measured and found to be reduced in both groups, though to a greater extent in the old. Thus, under the present experimental conditions, myeloid progenitors in the old BM manifest a more pronounced self renewal and differentiation capacity than the young while for the T-cell progenitors the situation is reversed.

Aging↗
PubMed1989

Long-term proliferation of human leukemia cells induced by mouse stroma.

Acute lymphocytic leukemias (ALL) of infants and children were found to preferentially survive in coculture with a cloned cell line of endothelial adipose cells (14F1.1) from mouse bone marrow. One of these ALLs expressed a phenotype compatible with an early stage of differentiation (HLA-DR+, CD19+, and CD34+) and exhibited extensive growth in the presence of the mouse stromal cells during a period greater than 25 weeks following seeding. These ALL cells were strictly dependent upon the mouse stromal clone 14F1.1 and failed to proliferate in the absence of the endothelial adipocytes or with a variety of "feeder cells." Throughout the culture period the cells died if removed from the stroma. No similarly proliferative cell population with strict dependence upon stromal cells was found among a variety of other leukemias including hairy cell, acute myeloid, and chronic lymphocytic leukemia. The 14F1.1 clone has been previously found to promote the renewal of mouse and human stem cells. It is therefore possible that leukemias with a stem cell-like phenotype depend upon stromal cell factors similar to those affecting the growth of normal stem cells. These factors appear to operate across genetic barriers.

Antibodies, Monoclonal↗
PubMed1988

Modulation of hemopoiesis by novel stromal cell factors.

The microenvironment of the bone marrow in mammals is a crucial site for the maintenance of a pluripotent hemopoietic stem cell pool. Our previous studies and present findings support the notion that both this function and the fine architecture of hemopoietic organs, i.e., the spatial arrangement of blood cells within the tissue, may be directed by stromal cells. Despite the ability of cloned stromal cells to support prolonged hempoiesis and maintenance in vitro of stem cells with high radioprotective ability, they are a poor source of colony stimulating factor-1 (CSF-1) and do not secrete the other species of CSF. Furthermore, cultured stromal cells antagonize the activity of CSF. It is proposed that stromal cell factors distinct from known CSFs, regulate stem cell renewal. An additional phenomenon that is mediated by stromal cells and can not be attributed to CSF, is their ability to specifically inhibit the accumulation of cells of particular lineage and stage of differentiation. A glycoprotein that inhibits the growth of plasmacytomas but not a variety of other cell types was isolated from one type of cloned stromal cells. Such specific inhibitors may account for the control of cell localization in the hemopoietic system.

Adipose Tissue↗