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M Tavassoli

Publications and source records attributed to M Tavassoli.

At least 19 recordsLinked to original sources
PubMed1992

Expression of chondroitin sulfate as a unique type of proteoglycan on the cell membrane of multipotential and committed hemopoietic progenitor cells.

Proteoglycans are increasingly implicated as a major factor in the regulation of hemopoiesis. They are generally synthesized by stromal cells and released to the extracellular matrix. More recently the ability of hemopoietic progenitor cells to synthesize proteoglycans has come into focus. In the present study we maintained 3 cloned factor-dependent hemopoietic progenitor cells (B6 and F-mix which are multipotential and F-2 which is bipotential) in liquid culture. The cells were pulse-labeled with 35SO4 which becomes incorporated into the glycan side-chains of proteoglycans. We then studied subcellular distribution and chemical characterization of the newly synthesized proteoglycans. All 3 cell lines synthesized chondroitin sulfate as a unique type of proteoglycan as identified by gel filtration on a Sepharose CL-4B column followed by chondroitinase ABC cleavage of its glycosaminoglycan. This single type of proteoglycan was compartmentalized into intracellular, membrane-associated and extracellular pools. Its density on the membrane appeared to be a function of the differentiation state of the cell. The functional significance of membrane-associated proteoglycan in hemopoietic progenitor cells appears to be underestimated and requires further investigation.

Animals↗
PubMed1992

Ex vivo incubation with growth factors enhances the engraftment of fetal hematopoietic cells transplanted in sheep fetuses.

Hematopoietic stem cells (HSC) transplanted in utero are in competition with endogenous HSC; thus, ultimately the graft constitutes a relatively small fraction of total HSC pool. To enhance the engraftment of donor cells in sheep fetuses, we preincubated these cells, ex vivo, for 16 hours at 37 degrees C with the conditioned medium from phytohemagglutinin-stimulated lymphocytes (PHA-LCM) before in utero transplantation. PHA-LCM is a rich source of hematopoietic growth factors in sheep. Subsequent engraftment was significantly higher in cells preincubated with PHA-LCM compared with fresh cells or those incubated with control medium only. This was reflected in all markers of the donor cells (hemoglobin type, karyotype, and progenitor cell assays). Brief ex vivo incubation with PHA-LCM also increased viability of all marrow cells as well as total numbers of progenitors. Similar enhancement of engraftment was also noted in monkeys after a brief preincubation of donor cells with interleukin-3 (IL-3) and granulocyte-macrophage colony-stimulating factor (GM-CSF). We conclude that brief (16 hours) ex vivo incubation of donor cells with a source of such growth factors as IL-3 and GM-CSF enhances the subsequent engraftment of transplanted cells.

Animals↗
PubMed1992

Plasminogen activator inhibitor-1 messenger RNA expression is induced in rat hepatocytes in vivo by dexamethasone.

Plasminogen activator inhibitor-1 (PAI-1), the major physiologic inhibitor of tissue plasminogen activator (tPA), plays a crucial role in the regulation of fibrinolysis. Both hepatocytes and endothelial cells have been implicated as major sources of plasma PAI-1. To study the relative contribution of these cell types to hepatic PAI-1 production, we have separated hepatocytes and hepatic sinusoidal endothelial cells by fractionation of freshly isolated rat livers using metrizamide density gradients and centrifugal elutriation. In untreated animals, PAI-1 messenger RNA (mRNA) was detected only in the purified endothelial cell fraction, and not in the hepatocyte fraction or in unfractionated liver. However, when the animals were treated with dexamethasone, PAI-1 mRNA expression was transiently induced in the liver. This induction paralleled the appearance of PAI-1 mRNA in purified hepatocytes, while PAI-1 expression in sinusoidal endothelial cells was unchanged. Four hours after dexamethasone treatment, plasma PAI-1 levels were increased approximately twofold over levels measured in animals treated with the diluent alone. These data suggest that PAI-1 production by hepatocytes may contribute to elevated plasma PAI-1 levels in the setting of acute injury and stress.

Animals↗
PubMed1992

Membrane-associated chondroitin sulfate proteoglycan and fibronectin mediate the binding of hemopoietic progenitor cells to stromal cells.

The initial step in hemopoiesis is the binding of progenitor cells to stroma. What mediates this binding at the molecular level is not entirely clear. We have previously reported that the cell line FDCP-1, a factor-dependent hemopoietic progenitor cell, actively synthesizes a membrane-associated chondroitin sulfate (CS) proteoglycan (MA-PG) which is unstable. After the binding of the progenitor cell to stromal, the stability of the MA-PG is enhanced, suggesting its involvement in the binding of progenitor cells to the stroma. Since stromal cells possess pericellular fibronectin (FN), we examined the possibility that binding to stromal cells may involve interactions between MA-PG of FDCP-1 on the one side and pericellular FN in stromal cells on the other side. To examine this hypothesis, we developed a cell adherence assay to measure the binding of FDCP-1 cells to a monolayer of stromal cells or to FN-coated dishes. Cell binding was inhibited by a monoclonal antibody against CS as well as by free CS and heparin, suggesting the involvement of MA-PG in the binding. Pretreatment of FDCP-1 cells with chondroitinase ABC, which selectively removes the CS portion of the MA-PG, also affects binding to the stromal cells. The binding was also inhibited by a pentapeptide (GRGDS) which competes with the cell-binding domain of FN as well as by a monoclonal antibody anti-FN. We conclude that interactions between MA-PG and a putative integrin-like molecule in FDCP-1 and the heparin and the cell binding domains in pericellular FN in the stromal cells contribute to the stabilization of progenitor-stromal cell binding which originally comes about by homing receptors of progenitor cells.

Amino Acid Sequence↗
PubMed1992

Laboratory markers of ethanol intake and abuse: a critical appraisal.

Laboratory markers for ethanol intake and abuse and chronic alcoholism currently in use have been critically reviewed. The merits and pitfalls of each test have been evaluated. The clinical use of the new test of carbohydrate-deficient transferrin has been particularly emphasized. Carbohydrate-deficient transferrin currently provides the highest specificity and sensitivity of all commonly used markers of alcoholism.

Alcoholism↗
PubMed1992

Endothelial transcytosis of iron-transferrin in the liver does not involve endosomal traffic.

Through a process resembling receptor-mediated internalization, liver endothelium binds and internalizes iron-transferrin (Fe-Tf) complexes, transporting them from the luminal to abluminal side. Since in most systems, the path of receptor-mediated endocytosis leads to the endosomal compartment where the medium is acidified, it is expected that Fe and Tf become dissociated in this acidified medium. However, experiments with double labeling (59Fe, 125I-Tf) indicate that these remain associated. To determine whether the endosomal pathway is used in the course of transendothelial transport of Fe-Tf, experiments were done by incubating purified liver endothelium with radiolabeled Fe-Tf in the presence and absence of endosomal inhibitors, NH4Cl, ethylamine and monensin. The discharge of radiolabeled protein was measured as a function of time. While there was an early phase inhibition in the presence of endosomal inhibitors, the discharge of Tf by endothelium in the presence of inhibitors, reached a plateau comparable to control cells after 4 h, indicating that endosomal inhibition does not inhibit transendothelial transport of Tf and, thus, the transport does not involve endosomal traffic.

Ammonium Chloride↗
PubMed1992

Engraftment and long-term expression of human fetal hemopoietic stem cells in sheep following transplantation in utero.

Hemopoietic stem cells from human fetal liver were transplanted in utero into preimmune fetal sheep (48-54 days of gestation). The fate of donor cells was followed using karyotype analysis, by immunofluorescence labeling with anti-CD antibodies, and by fluorescent in situ hybridization using human-specific DNA probes. Engraftment occurred in 13 of 33 recipients. Of five live born sheep that exhibited chimerism, all expressed human cells in the marrow, whereas three expressed them in blood as well. Engraftment was multilineage (erythroid, myeloid, and lymphoid) and human hemopoietic progenitors (multipotent colony-forming units, colony-forming units-granulocyte, macrophage, and erythroid burst-forming units) capable of forming colonies in vitro were detected in all five lambs for greater than 2 yr. These progenitors responded to human-specific growth factors both in vitro and in vivo. Thus the administration of recombinant human IL-3 and granulocyte macrophage-colony-stimulating factor to chimeric sheep resulted in a 2.1-3.4-fold increase in the relative expression of donor (human) cells. These results demonstrate that the permissive environment of the preimmune fetal sheep provides suitable conditions for the engraftment and long-term multilineage expression of human hemopoietic stem cells in a large animal model. In this model, donor human cells appear to retain certain phenotypic and functional characteristics that can be used to manipulate the size of donor cell pool.

Animals↗
PubMed1992

Effect of erythropoietic stress on donor hematopoietic cell expression in chimeric rhesus monkeys transplanted in utero.

We have previously reported the successful development of hematopoietic chimerism after the in utero transplantation of fetal hematopoietic stem cells (HSC) in rhesus monkeys (Macaca mulatta). These animals exhibit sustained engraftment without immunosuppression or graft-versus-host disease (GVHD). To assess the functional response of the donor-derived erythropoietic population, we assayed the relative expression of donor and recipient hematopoietic progenitors in chimeric monkeys before and after anemic stress. Anemia in our chimeric animals resulted in increased erythropoietin (EPO) production comparable to controls. This was accompanied by changes in erythroid progenitor profiles, again similar to controls. Chimeric animals demonstrated normal reticulocytosis and reconstituted their hematocrit after hemorrhage at the same rate as controls. The donor-derived erythropoietic population exhibited normal responses to recipient regulatory signals and did not seem to expand at the expense of other hematopoietic lineages. Thus the proportions of engraftment for the myeloid and erythroid precursors in bone marrow and for blood lymphocytes remained stable. Our results demonstrate that the in utero transplantation of fetal HSC results in stable engraftment of donor erythropoietic progenitors, which appear to be fully integrated within the recipient's regulatory system. The abnormalities reported in the postnatal transplantation setting can then be attributed to immunologic reactions requiring conditioning myeloablative regimens. Fetal transplantation bypasses all these factors.

Anemia↗
PubMed1992

Human-ovine xenogenic transplantation of stem cells in utero.

The preimmune status of the early gestational age fetus provides a permissive environment that bypasses the immunological barrier and permits the engraftment and expression of hemopoietic stem cells (HSC). We used in utero approach to establish long term (greater than 2 years) engraftment and expression of human fetal liver HSC in sheep. Engraftment occurred in 40% (13 of 33) of the recipients. Of 5 live born sheep, all were chimeric. Engraftment was multilineage, involving lymphoid, myeloid and erythroid donor (human) cells. Interestingly, these progenitors have continued to exhibit responsiveness to human specific growth factors both in vitro and in vivo. Therefore, the integration of human HSC into the hemopoietic framework of the host appeared to be incomplete, with donor progenitors retaining certain phenotypic characteristics that may be exploited to preferentially manipulate the donor (human) cell population in these animals. Donor HSC primarily seeded the host bone marrow. Since the donor cells were of liver origin and the host liver at the time of transplantation was the major hemopoietic organ, this near exclusive seeding to the marrow indicates the greater affinity of marrow for the homing HSC. Nonetheless, no cells of donor origin appeared in the host circulation until the perinatal period, suggesting that donor HSC expand with the developing marrow spaces, but do not undergo terminal differentiation. The absence of a significant immunological barrier and the availability of expanding marrow homing sites render the fetus an excellent host (and donor) for HSC transplantation.

Animals↗
PubMed1992

The fetus as an optimal donor and recipient of hemopoietic stem cells.

In the present work we used allogeneic in utero transplantation of fetal stem cells in sheep and monkeys. Thus, both the donor and recipient cells had preimmune status. We showed engraftment of allogeneic stem cells in the tolerant environment of the host. The engrafted cells showed trilineage (lymphoid, erythroid and myeloid) expression of differentiation. Long term maintenance of these engrafted cells was observed. We also demonstrated that ex vivo incubation of donor cells with growth factor can enhance the engraftment. Moreover, we have shown that the engrafted cells respond to phlebotomy in the same manner as endogenous cells. We, therefore, conclude that (a) Preimmune fetuses are highly suitable for stem cell transplantation both as donors and recipients. (b) Engraftment can be modulated by brief maneuvers such as ex vivo manipulation. (c) Functionally, the engrafted cells can respond to hemopoietic stimuli in a similar manner as the endogenous cells. Implications of this transplantation system in clinical medicine is discussed. Everyone who is involved in organ transplantation must, sooner or later, come to grips with immunological barriers which establishes the individuality of each organism by recognizing "self" from "non-self". Transplanters must overcome this barrier, if allogeneic organ transplantation is to be successful. In the case of hemopoietic stem cells (HSC), where immunocompetent cells are transplanted, graft-vs-host disease (GVHD) may also be expected. Tolerance can be expected when the recipient is genetically immunodeficient, thus being unable to mount an immunological barrier.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Alterations of bone marrow sinus endothelium induced by ionizing irradiation: implications in the homing of intravenously transplanted marrow cells.

The endothelium of bone marrow sinuses is a continuous layer which is selective in its cellular transport. It is not known how selective and massive seeding of hemopoietic progenitor cells after intravenous transplantation of marrow cells occurs. We postulate that the conditioning irradiation could disrupt the endothelial barrier, thus permitting the "homing" of progenitor cells to occur. To demonstrate this phenomenon, we irradiated mice with doses ranging from 100-2000 cGy-total body and studied perfusion-fixed marrow by transmission electron microscopy. The major finding was sloughing and denudation of plasma membrane, particularly on the luminal side of endothelium. Membrane vesiculation was also frequently seen in this border. Moreover, dilatation of the perinuclear space and rough endoplasmic reticulum was commonplace and testified to instability and fragility of the membrane system. Focal cytoplasmic swelling of endothelium was seen reflecting increased permissiveness of the endothelial barrier. Endocytosis and phagocytosis were increased in the marrow; and the endothelium, normally quiescent with regard to phagocytosis, was now overtly phagocytic. A dipogenecity of the adventitial layer was increased as hemopoietic function of marrow decreased. The end result of membrane alterations in the endothelium was the appearance of discontinuities in these cells, which form the essential element of bone marrow-blood barrier. Consequent to these discontinuities, the permissiveness of the endothelial barrier was enhanced and those cellular elements, such as mature, nonreticulated erythrocytes that are normally confined to the vascular space, now appeared in large number in the hemopoietic compartment. With low doses, these findings were transient and repair set in by 1-2 weeks. With higher doses, total disruption of marrow-blood barrier occurred and the process did not seem to be repairable. We conclude that the conditioning irradiation before bone marrow transplantation is essential in disrupting the endothelial barrier and permitting large-scale entry of transplanted cells into the hemopoietic compartment.

Animals↗
PubMed1992

Homing of liver-derived hemopoietic stem cells to fetal bone marrow.

Tissue distribution of HSC in fetal sheep was studied by in utero transplantation during the period when a switch in the site of hemopoiesis occurs from liver/spleen to the bone marrow. At day 50 of gestation, transplanted cells exclusively homed to the liver/spleen. By day 60, some HSC also homed to the marrow and, between days 60-80, their proportion in the marrow increased. By day 100 almost all engrafted donor HSC homed to the marrow. Nonetheless, expression of these stem cells did not occur in the blood until birth (day 145) when marrow assumed the function of hemopoiesis from liver/spleen. During this latter part of gestation, although homing sites in the marrow are available to transplanted HSC, the marrow does not contribute to the function of hemopoiesis. The significance of these observations in the context of in utero gene therapy via stem cell transplantation is discussed.

Animals↗
PubMed1992

The role of conditioning regimens in homing of transplanted hemopoietic cells.

Evidence is reviewed to indicate that the conditioning regimens given to prepare the patient for bone marrow transplantation have two unintended but desirable consequences: (a) they eliminate endogenous progenitor cells that may otherwise be in competition with grafted hemopoietic progenitor cells, leaving all homing sites open for transplanted cells, and (b) they induce membrane alterations in marrow endothelium, thus effectively removing the endothelial barrier which otherwise the grafted cells must negotiate to enter the hemopoietic compartment of the marrow. Hence the conditioning regimens may also facilitate the homing of transplanted cells.

Animals↗
PubMed1992

Induction of upmodulation of homing receptors in cloned hemopoietic progenitors by growth factors.

Recognition and selective seeding of hemopoietic cells to the marrow after intravenous transplantation is a function of membrane protein known as homing receptor (HR), which is a lectin with galactosyl and mannosyl specificities. We have previously shown that ex vivo incubation of marrow cells with IL-3 or GM-CSF enhances the seeding efficiency and that this enhancement may be the result of upmodulation of homing receptors. In the present work, we have shown that incubation of two cloned progenitor cell lines, FDCP-1 and FDCP-mix, with IL-3 or GM-CSF resulted in a dose-dependent increase in the number of HR per cell. Interferon-gamma did not have such an effect. The upmodulation of receptors was the result of enhanced de novo synthesis and transport of the protein as it was ablated by cyclohexamide, monensin or NH4Cl. On the other hand, degradation of the protein was not affected by the growth factors. The possible mechanisms whereby a brief exposure to growth factor ex vivo could lead to enhancement of homing efficiency are discussed. Induction of upmodulation of HR by ex vivo incubation of donor cells with certain hemopoietic growth factors, could be a useful strategy for enhancing marrow reconstitution after bone marrow transplantation. This could reduce the cost and prevent the side effects of in vivo growth factor therapy.

Ammonium Chloride↗