Biomedical subjects

F Wendling

Publications and source records attributed to F Wendling.

At least 37 records · Page 2Linked to original sources

PubMed2000

Three-dimensional computer morphometry of the maxilla and face in infants with Pierre Robin sequence--a comparative study.

OBJECTIVE: To analyze the morphology of the maxillary crest in infants with Pierre Robin sequence using an anthropometric coordinate system and to compare the data with those of healthy infants. SETTING: The study was performed at a craniofacial center servicing a large geographic area. PARTICIPANTS: The study involved eight infants aged 1-28 days (average, 7 days) with an established diagnosis of Pierre Robin sequence and six healthy infants aged 1-43 days (average, 22 days). MAIN OUTCOME MEASURES: Physical models of the maxilla and face obtained by alginate replication were analyzed by computer morphometry yielding the three-dimensional topology of the maxillary crest. RESULTS: The maxillary crest of children with Pierre Robin sequence shows an increased inclination relative to the transverse plane (30 +/- 3.9 degrees) as compared with that of healthy infants (20 +/- 2.9 degrees). The maxillary crest of the patients is shortened in the sagittal direction by comparison with healthy controls. CONCLUSIONS: The increased inclination of the maxilla in infants with Pierre Robin sequence may aggravate the retroposition of the mandible and may thus be a pathogenetic factor contributing to the severe respiratory problems.

Alginates↗

PubMed1999

High-level expression of Mpl in platelets and megakaryocytes is independent of thrombopoietin.

Thrombopoietin (TPO) is a hematopoietic growth factor that regulates megakaryocytopoiesis and platelet production through binding to its receptor, Mpl, encoded by the c-mpl proto-oncogene. Circulating levels of TPO are regulated by receptor-mediated uptake and degradation. To better understand this mode of TPO regulation, we examined whether expression of Mpl was regulated by its ligand. Using RNase protection analysis, we found no differences in the levels of c-mpl transcripts in megakaryocytes (MKs) produced in vitro either in the presence or absence of TPO and in platelets (PLTs) obtained from mice hyperstimulated in vivo by ectopic secretion of TPO. Similarly, Western blot analysis of MKs produced in the presence or absence of TPO showed no difference in Mpl levels. Levels of Mpl, GpIIb, or P-selectin were virtually identical in platelet lysates obtained from normal, TPO knockout and mildly TPO-stimulated mice. In contrast, the expression of Mpl was significantly reduced in PLTs from severely thrombocythemic mice. These results show that TPO does not have a major effect on the transcription or translation of Mpl. However, they do suggest that an excess of circulating TPO can lead to the disappearance of Mpl from PLTs via catabolism.

Animals↗

PubMed1999

Autonomous megakaryocyte growth in essential thrombocythemia and idiopathic myelofibrosis is not related to a c-mpl mutation or to an autocrine stimulation by Mpl-L.

Essential thrombocythemia (ET) and idiopathic myelofibrosis (PMF) are two myeloproliferative diseases characterized by a marked megakaryocytic (MK) involvement. The pathogenesis of these two diseases is unknown. Recently it has been shown that overexpression of Mpl-ligand (Mpl-L) in mice induces thrombocytosis and myelofibrosis. In this study, we investigated whether Mpl-L was responsible for the pathogenesis of ET and PMF. Using in vitro cultures of blood or marrow CD34(+) cells, we investigated whether MK growth was abnormal in these two diseases. Spontaneous MK growth involving only a fraction (20%) of the MK progenitors, as compared with growth in the presence of pegylated recombinant human megakaryocyte growth and development factor (PEG-rhuMGDF), was found in both diseases (21ET and 14PMF) using serum-free semisolid and liquid cultures, including cultures at one cell per well. We first searched for a c-mpl mutation/deletion by sequencing the entire coding region of the gene by polymerase chain reaction (PCR) in nine ET patients and five PMF patients, but no mutation was found. We subsequently investigated whether an autocrine stimulation by Mpl-L could explain the autonomous MK growth. Addition of different preparations of soluble Mpl receptor (sMpl) containing a Fc domain of IgG1 (sMpl-Fc) markedly inhibited MK spontaneous growth in both ET and PMF patients. This effect was specific for sMpl because a control soluble receptor (s4-1BB-Fc) had no inhibitory effect and an sMpl devoid of the Fc fragment had the same inhibitory efficacy as the sMpl-Fc. This inhibition was reversed by addition of PEG-rhuMGDF or a combination of cytokines. The sMpl-Fc markedly altered the entry into cell cycle of the CD34(+) cells and increased the apoptosis that occurs in most patient CD34(+) cells in the absence of exogenous cytokine, suggesting an autocrine stimulation. In contrast, a neutralizing antibody against Mpl-L did not alter the spontaneous MK growth, whereas it totally abolished the effects of 10 ng/mL PEG-rhuMGDF on patient or normal CD34(+) cells. Mpl-L transcripts were detected at a very low level in the patient CD34(+)cells and MK and only when a highly sensitive fluorescent PCR technique was used. By quantitative reverse-transcription (RT)-PCR, the number of Mpl-L transcripts per actin transcripts was lower than detected in human Mpl-L-dependent cell lines, suggesting that this synthesis of Mpl-L was not biologically significant. In favor of this hypothesis, the Mpl-L protein was not detected in culture supernatants using either an enzyme-linked immunosorbent assay (ELISA) or a biological (Ba/F3hu c-mpl) assay, except in one PMF patient. Investigation of Mpl-L signaling showed an absence of constitutive activation of STATs in spontaneously growing patient MKs. Addition of PEG-rhuMGDF to these MKs activated STATs 3 and 5. This result further suggests that spontaneous growth is neither related to a stimulation by Mpl-L nor to a c-mpl mutation. In conclusion, our results show that Mpl-L or Mpl are not directly implicated in the abnormal proliferation of MK cells from ET and PMF. The mechanisms by which the sMpl mediates a growth inhibition will require further experiments.

Adult↗

PubMed1999

Seizures of temporal lobe epilepsy: identification of subtypes by coherence analysis using stereo-electro-encephalography.

OBJECTIVES: Two subtypes of temporal lobe epilepsy (TLE) according to the structures initially involved during seizures are currently recognized: medial TLE (MTLE) and lateral (or neocortical) TLE (LTLE). A few reports have suggested that the classification of TLE subtypes might be larger according to variations in the interactions between medial structures and the neocortex. In this study, we analyzed these interactions using coherence analysis of stereo-encephalographic (SEEG) signals during spontaneous seizures. METHODS: Twenty-seven patients with drug-resistant TLE, diagnosed from ictal SEEG recordings obtained during pre-surgical evaluation, were studied. Orthogonally implanted depth electrodes with multiple leads according to Talairach's method were used to sample medial and neocortical structures. Coherence analysis of ictal discharges was performed between two SEEG bipolar signals from adjacent leads located either in medial structures (amygdala and hippocampus) or in neocortical regions of the temporal lobe. A new algorithm, which was designed to reduce the bias inherent in coherence estimation, was used to compute the coherence. RESULTS: We were able to classify TLE seizures (TLES) into 4 distinct categories: (1) 'medial' TLES, characterized by medial onset with later involvement of the neocortex in the form of a 'phasic' discharge. High ictal coherence values were observed between medial structures; (2) 'medial-lateral' TLES which started in medial structures with a fast low-voltage discharge (FLVD) which rapidly affects the neocortex (< or = 3 s). High coherence values were observed between medial and lateral structures; (3) 'lateral-medial' TLES, which are different from medial-lateral TLES in that the FLVD starts in the lateral neocortex and involves the amygdala and/or hippocampus almost immediately after; (4) 'lateral' TLES: characterized by a neocortical onset, a delayed involvement of medial structures (when present), and high coherence values between neocortical structures. CONCLUSIONS: These results demonstrate the existence of numerous interactions between medial limbic structures and the neocortex during TLE seizures. Such findings could have implications for surgical strategies and the prognosis of epilepsy surgery, particularly when limited resection is indicated.

Adolescent↗

PubMed1999

Time-frequency matching of warped depth-EEG seizure observations.

A methodology of comparing depth-EEG seizure recordings is presented. The approach is based on an extension of Wagner and Fischer's algorithm to N x 2-dimensional sets, allowing a confrontation of nonequal duration observations characterized by their time-frequency distributions. It proceeds by time and frequency warping on the first observation to match the second, under cost constraints. Preliminary results show that relevant signatures can be extracted from recordings.

Algorithms↗

PubMed1999

Computer-supported collaborative work (CSCW) in biomedical signal visualization and processing.

A collaborative extension to a platform dedicated to signal visualization and processing is presented. The platform now allows geographically distant users to work together, in real-time, on the same data (electroencephalographic signals). The extension is based on a client-server collaborative architecture using remote procedure call programming. Through this first implementation, general issues of computer-supported collaborative work are presented.

Computer Systems↗

PubMed1999

Thrombopoietin: its role from early hematopoiesis to platelet production.

BACKGROUND AND OBJECTIVE: Thrombopoietin (TPO), also referred to as MpI ligand, is the most potent cytokine that physiologically regulates platelet production. With the availability of sufficient amounts of recombinant forms of the protein, the biological in vitro and in vivo activities of this cytokine have been extensively studied. The objective of this review is to summarize the published data focusing on TPO production and regulation and to discuss the pleiotropic biological action of this hormone. The review also highlights the results so far obtained in preclinical and clinical trials. EVIDENCE AND INFORMATION SOURCES: The material examined in this review includes data published by the author and articles or abstracts published in Journals covered by Medline. The author has contributed to the isolation of TPO, has been working in the field for several years and has contributed original papers on the TPO/MpI system in normal and pathologic situations. STATE OF THE ART: TPO is a hormone constitutively produced by the liver and kidneys. Plasma levels of TPO are regulated through receptor-mediated uptake, internalization and catabolism. First thought to be a lineage dominant factor promoting megakaryocytopoiesis, several lines of evidence indicate that TPO has pleiotropic effects on hematopoiesis. In vitro studies show that TPO alone, or in combination with early acting cytokines, stimulates the proliferation and enhances the expansion of primitive CD34+ CD38- hematopoietic progenitor cells. In vivo studies with c-mpl- and TPO-null mice reveal that the molecule sustains the survival and proliferation of early committed progenitor cells of various type. Preclinical and clinical trials indicate that recombinant TPO molecules increase platelet counts and megakaryocyte numbers in normal or mildly thrombocytopenic states. However, no significant effects of TPO administration on platelet recovery have so far been reported in patients subjected to intensive chemotherapy regimens. Recombinant molecules appear to be safe to administer and very little toxicity is reported. TPO augments the number of erythroid and myeloid committed progenitor cells in marrow, and mobilized stem cells in peripheral blood. PERSPECTIVES: The potential clinical use of TPO is still unclear. With the increased knowledge of the multiple effects of TPO on hematopoiesis, it is expected that future carefully monitored clinical trials will provide more information regarding the eventual benefits of this cytokine in the treatment of thrombocytopenia. At present, one successful application of TPO appears to be its addition in cytokine cocktails used to expand hematopoietic stem cells ex vivo.

Animals↗

PubMed1999

Preferential liver irradiation enhances hematopoiesis through a thrombopoietin-independent mechanism.

Liver synthesizes thrombopoietin, which is a major cytokine involved in the production of hematopoietic cells. The purpose of this study was to examine the effects of preferential liver irradiation on expression of thrombopoietin and production of hematopoietic cells. About 70% of the liver of C57BL6/J mice was irradiated with 20 Gy of gamma rays. Exposure to ionizing radiation enhanced hematopoietic progenitors and megakaryocyte frequency in bone marrow and induced a transient increase in platelet and neutrophil counts that peaked 14 days after irradiation. The concentration of thrombopoietin was increased in serum as early as 5 h after liver irradiation and was still elevated at day 14. By using Northern blot analysis and an RNase protection assay, we showed that thrombopoietin mRNA was increased in the irradiated liver. To determine whether thrombopoietin was involved in the stimulation of hematopoiesis, we irradiated mice in which thrombopoietin deficiency had been induced by homologous recombination. Platelet levels were increased in both heterozygous and homozygous thrombopoietin-deficient mice with a magnitude similar to that obtained in normal mice. In summary, our data demonstrate that local irradiation of the abdomen encompassing the liver leads to stimulation of hematopoiesis through a thrombopoietin-independent mechanism.

Animals↗

PubMed1998

[Thrombopoietin and megakaryocyte differentiation].

Regulation of megakaryocytopoiesis and platelet production is a complex phenomenon. It has been demonstrated that numerous pleiotropic cytokines act in vivo and in vitro on megakaryocytopoiesis. Historically, studies on the regulation of megakaryocytopoiesis were largely dominated by the concept of humoral regulation. Despite 35 years of work, the factor responsible for these effects (thrombopoietin, TPO) could not be purified to homogeneity. The proto-oncogene c-mpl has been demonstrated to encode a protein which is the receptor for a humoral cytokine regulating megakaryocytopoiesis. Its ligand was isolated by three independent groups. The purified protein was termed Mpl-L (Mpl-Ligand), thrombopoietin (TPO), or megakaryocyte growth and development factor (MGDF). Strong evidence that Mpl-L is the homeostatic regulator of platelet production has been provided by c-mpl or Mpl-L knock-out mice which have a severe but not lethal thrombocytopenia. In vitro experiments have indicated that the Mpl-L acts both as a proliferative and differentiative factor as many other CSF. At the unicellular level, Mpl-L acts on MK progenitors inducing their proliferation. Mpl-L induces polyploidisation of the MKs and cytoplasmic maturation leading to an in vitro platelet production. As a single cytokine Mpl-L is the most potent growth factor for the MK lineage in vitro. However, a combination of cytokines can totally replace the effects of Mpl-L both on proliferation of MK progenitors and their maturation. In addition, Mpl-L has a major effect on primitive hematopoietic progenitors.

Animals↗

PubMed1998

Spi-1 transgenic mice develop a clonal erythroleukemia which does not depend on p53 mutation.

Spi-1 transcriptional activation and wild-type p53 extinction are two oncogenic alterations involved in the malignant transformation of erythroblasts during the Friend acute erythroleukemia. To dissect the contribution of these alterations in the deregulation of the differentiation and proliferation of erythroblasts, we generated spi-1 transgenic mice. Analysis of these animals revealed that Spi-1 overexpression was directly involved in the block of proerythroblast differentiation. However, the erythroleukemia that develops in these animals evolved in two steps. During the early step (HS1 step), non tumorigenic proerythroblasts remained strictly dependent upon erythropoietin (Epo) for their survival and proliferation. Later on, Epo-independent and tumorigenic proerythroblasts emerged (HS2 step) suggesting that other oncogenes cooperate with Spi-1 to lead to a fully malignant phenotype. By provirus tagging, we demonstrate that the HS1 step was clonal indicating that a cell selection must occur in vivo. Analysis of the nature of p53 in both the in vivo HS1 and HS2 proerythroblasts and in cultured erythroblastic cell lines showed that--p53 was normal in the HS1 primary tissues but was mutated in the HS1 cultured cell lines--p53 was frequently altered in HS2 primary tissues but was found normal in some mice. These data indicate that (i) the blockage of the erythroblast differentiation by Spi-1 occurs independently of p53 alteration (ii) p53 alteration is not necessary to confer Epo independence and tumorigenicity to spi-1 transgenic proerythroblasts.

Animals↗

PubMed1998

Thrombopoietin (TPO) knockout phenotype induced by cross-reactive antibodies against TPO following injection of mice with recombinant adenovirus encoding human TPO.

Adenovirus vectors have emerged as potent agents for gene transfer. Immune response against the vector and the encoded protein is one of the major factors in the transient expression following in vivo gene transfer. A single injection of an adenovirus encoding human thrombopoietin (TPO) into mice induced transient thrombocytosis, followed by a chronic immune thrombocytopenia. Thrombocytopenic mice had anti-human TPO Abs of the IgG2a and IgG1 isotypes. Thrombocytopenic mice sera neutralized more efficiently human than murine TPO, and exhibited no detectable anti-murine TPO Abs. Despite their low affinity for murine TPO, anti-TPO Abs induced a TPO knockout-like phenotype, i.e., low number of marrow megakaryocytes and of all kinds of hemopoietic progenitors. Hybridomas derived from a thrombocytopenic mouse revealed cross-reactivity of all of the secreted anti-TPO Ab isotypes. Mice subjected to myelosuppression after virus injection showed that anti-human TPO of IgG1 and IgG2a isotypes disappeared. Thus, sustained human TPO production was responsible for platelet elevation for at least 5 mo. Compelling results showed that elevated IgG2a/IgG2b ratios are always associated with thrombocytopenia, whereas low ratios are associated with tolerance or normal platelet counts. Finally, we hypothesize that in humans some chronic thrombocytopenia associated with a low TPO plasma level are due to anti-TPO Abs.

Adenoviridae↗

PubMed1998

Compared effects of Mpl ligand and other cytokines on human MK differentiation.

The discovery of the Mpl ligand (Mpl-L), also called thrombopoietin (TPO), has facilitated in vitro investigation of human megakaryocytopoiesis. By confocal microscopy, endomitosis appeared as abortive mitosis skipping late stages of mitosis. No telophase and cytokinesis were observed. A spherical multipolar spindle which limits chromatid segregation was observed. The nuclear envelope subsequently reformed isolating all chromatids in a single nucleus. Platelet shedding was ultrastructurally studied. Platelet release occurred after formation of long cytoplasmic extensions (proplatelet formation), constriction areas delineating platelet territories. Heterogeneity in platelet size may be determined by the length of these extensions. Pegylated-recombinant human megakaryocyte growth and development factor, a truncated form of Mpl-L, was the most efficient cytokine to produce proplatelet-bearing megakaryocytes (MKs) and platelets in vitro. However, functional platelets with a normal ultrastructure could be produced in the presence of a combination of other cytokines. Finally, we investigated whether the induction of MK differentiation by the MS-5 stromal cell lines is due to Mpl-L. MS-5 cells synthesized Mpl-L transcripts and a biologically active protein. When human CD34+ cells were grown in contact or noncontact cultures with MS-5 cells, MK differentiation was observed. Soluble Mpl receptor (sMpl-Fc) addition inhibited MK growth, suggesting that the MK-promoting activity was due to Mpl-L production. Marrow stromal cell lines derived from TPO-/- mice were also able to sustain MK growth. Despite the absence of any production of Mpl-L, the sMpl-Fc continued to inhibit MK differentiation. This result suggests that the sMpl has a direct inhibitory effect and may explain the divergent results in the literature concerning the precise role of Mpl-L on the MK terminal differentiation.

Animals↗

PubMed1998

Myelofibrosis: experimental models and human studies.

Thrombopoietin (TPO) is the central regulator of megakaryocytopoiesis and thrombocytopoiesis. Preclinical data and human studies have so far shown that the recombinant molecule is safe to administer and associated with very little toxicity. Nevertheless, different experimental animal models have revealed that a chronic exposure to very high doses of TPO could result in myeloproliferative syndromes with a spectrum of pathological features in common with human idiopathic myelofibrosis (PMF). A number of investigators have researched whether TPO or its receptor Mpl were involved in the pathogenesis of human myeloproliferative syndromes which are also characterized by a predominant megakaryocytic involvement, in PMF and primitive essential thrombocythemia. In both diseases, megakaryocyte (MK) progenitors develop autonomously in serum-deprived cultures. This spontaneous MK development is also observed at limiting dilution demonstrating that MK escape the normal regulatory controls. Furthermore, this abnormal MK proliferation and maturation is neither due to an autocrine stimulation by TPO nor by point mutation or deletion in the coding region of the c-mpl gene. This paper will review the data that have been reported to date on the effects of an overexpression of Mpl ligand and related molecules on the induction of experimental myelofibrosis and highlight recent insights into the pathogenesis of PMF.

Animals↗

PubMed1998

Mpl ligand or thrombopoietin: biological activities.

Thrombopoietin (TPO) or Mpl ligand is the primary physiological regulator of platelet production. This cytokine is the most potent stimulator of the proliferation and differentiation of MK progenitor and precursor cells in vitro. It also acts additively or synergistically with several cytokines on progenitor cells from various hematopoietic lineages, including the primitive stem cells. The factor is an extremely potent thrombocytopoietic agent when administrated to normal animals, and it accelerates platelet and erythropoietic recovery in several models of myelosuppression. Phase I/II clinical trials are ongoing with no detectable adverse effects. Mpl ligand does not induce platelet aggregation, but it lowers the platelet sensitivity to physiological dose of agonists. In experimental mouse models, high and chronic dose of Mpl ligand results in myelofibrosis. TPO is constantly produced by the liver and the kidney; its plasmatic clearance occurs by binding to its receptor expressed on megakaryocytes and platelets. However, the full spectrum of the biological effects of this new cytokine is not fully understood, in particular its the role in the terminal stage of platelet production. In the near future, it is likely that new insights will be obtained in the physiopathological mechanisms underlying abnormal platelet production in human.

Animals↗

PubMed1998

Major effects of TPO delivered by a single injection of a recombinant adenovirus on prevention of septicemia and anemia associated with myelosuppression in mice: risk of sustained expression inducing myelofibrosis due to immunosuppression.

Adenoviral vectors may be useful tools to deliver a cytokine in vivo. A single intravenous injection of an adenovirus vector containing the human thrombopoietin (TPO) cDNA (AdRSVhuTPO) was able to induce a thrombocytosis for more than 6 weeks in SCID mice, associated with a megakaryocyte (MK) hyperplasia in different organs. A marrow and spleen fibrosis was observed at 6 weeks. In immunocompetent mice, a single AdRSVhuTPO injection led to a moderate and transient thrombocytosis without myelofibrosis. To evaluate the usefulness of TPO for the prevention of secondary side-effects during an aplastic period, mice were subjected to a myeloablative regimen 7 days after the intravenous AdRSVhuTPO injection. In this setting, TPO prevented mortality by accelerating hematological recovery. Survival was essentially related to an improvement in the leukopenia since all control mice died from septicemia. However, the effects of TPO may be potentiated by the release of inflammatory cytokines following the adenovirus infection; AdRSV beta galactosidase injected-mice had higher numbers of BFU-E and CFU-GM in the marrow than PBS-injected mice. Myelosuppression induced transient immunosuppression responsible for a sustained expression and elevation of platelet numbers for at least 5 months. These results further suggest that TPO may be an effective therapy in diminishing hematological complications related to myeloablative regimens, but emphasize that immunosuppression secondary to myelosuppression may lead to sustained expression associated with a risk of thrombosis and myelofibrosis when delivered by adenovirus vectors.

Adenoviridae↗

PubMed1998

Thrombopoietin and its receptor.

Thrombopoietin (TPO), the primary physiological regulator of platelet production, was initially thought to be a lineage-specific factor acting predominantly on megakaryocytopoiesis. Detailed studies establish that this cytokine mediates biological effects on a broad spectrum of hematopoietic progenitor cells, including stem cells. TPO is a hormone constitutively produced mainly by the liver and kidney. Plasma TPO levels are regulated by the platelet and megakaryocyte mass through Mpl receptor binding, internalization and degradation. The Mpl receptor is a member of the hematopoietin receptor superfamily lacking intrinsic kinase activity. Upon ligand-induced Mpl homodimerization, the major signaling events for proliferation are mediated through the JAK2/STAT5 pathway, while differentiation might occur through a prolonged activation of the MAPK pathway. Preclinical and clinical studies demonstrate the potential use of TPO in a variety of contexts, but it is too early to evaluate its benefit in reducing platelet transfusion.

Animals↗

PubMed1997

High thrombopoietin production by hematopoietic cells induces a fatal myeloproliferative syndrome in mice.

To evaluate the effects of long-term, high-dose exposure to thrombopoietin (TPO), lethally irradiated mice were grafted with bone marrow cells infected with a retrovirus carrying the murine TPO cDNA. Mice were studied for 10 months after transplantation. In plasma, TPO levels were highly elevated (10(4) U/mL) throughout the course of the study. All mice developed a lethal myeloproliferative disorder evolving in two successive phases. During the first phase (7-9 weeks posttransplant), platelet and white blood cell (WBC) counts rose four- and ten-fold, respectively, whereas hematocrits decreased slightly to 29% +/- 3%. The WBC were mainly mature granulocytes, but myeloid precursor cells were invariably observed as well as giant platelets with an irregular granule distribution. The striking features were a massive hyperplasia of megakaryocytes and granulocytes in the spleen and bone marrow and a hypoplasia of erythroblasts in bone marrow. Total numbers of megakaryocyte colony-forming cell, burst-forming unit-erythroid, and granulocyte macrophage colony-forming cells were increased but colony-forming unit-erythroid numbers decreased. From 10 weeks posttransplant and thereafter, WBC, platelets, and red blood cell numbers declined dramatically. The absolute numbers of progenitor cells were very low in the spleen and bone marrow, but sharply increased in the blood and peritoneal cavity. Extramedullary hematopoiesis was observed in several organs. Histologic sections of the spleen and bones revealed severe fibrosis and osteosclerosis. The mean survival time was 7 months posttransplant and mice died with severe pancytopenia. Notably, two mice died between 3 and 4 months posttransplant with a leukemic transformation. This disorder was transplantable into secondary recipients who developed an attenuated form of the disease similar to the one previously described (Yan et al, Blood 86:4025, 1995). Taken together, our data show that high and persistent TPO production by transduced hematopoietic cells in mice results in a fatal myeloproliferative disorder that has a number of features in common with human idiopathic myelofibrosis.

Animals↗

PubMed1997

Thrombopoietin does not induce lineage-restricted commitment of Mpl-R expressing pluripotent progenitors but permits their complete erythroid and megakaryocytic differentiation.

In this study, we examined the in vitro and in vivo effects of forced expression of Mpl-R (the thrombopoietin receptor) on the progeny of murine hematopoietic stem cells. Bone marrow cells from 5-FU-treated mice were transduced with retroviral vectors containing the human Mpl-R cDNA, or the neomycine gene as a control. After 7 days cocultivation on virus-producer cells, GpE86-Mpl-R or Gp86-Neo, the types of hematopoietic progenitor cells responding to thrombopoietin (TPO) were studied by clonogenic assays. Mpl-R-infected cells gave rise to CFU-GEMM, BFU-E, CFU-MK, but not CFU-GM while Neo-infected cells produced only megakaryocytic colonies. In addition, when nonadherent cells from GpE86-Mpl-R cocultures were grown with TPO as the only stimulus for 7 days, a marked expansion of CFU-GEMM, BFU-E, and CFU-MK was observed, while no change in CFU-GM number was seen. Erythroid and megakaryocytic maturation occurred in the presence of TPO while a block in granulocytic differentiation was observed at the myeloblast stage. The direct effects of TPO on Mpl-R-transduced progenitor cells were demonstrated by single cell cloning experiments. To analyze the effects of the constitutive expression of Mpl-R on the determination of multipotent progenitors (CFU-S) and long-term repopulating stem cells, Mpl-R- or Neo-infected cells were injected into lethally irradiated recipient mice. No difference was seen in (1) the number of committed progenitor cells contained in individual CFU-S12 whether colonies arose from noninfected or Mpl-R-infected CFU-S; (2) the mean numbers of progenitor cells per leg or spleen of mice reconstituted with Mpl-R- or Neo-infected cells, 1 or 7 months after the graft; and (3) the blood parameters of the two groups of animals, with the exception of a 50% reduction in circulating platelet counts after 7 months in mice repopulated with Mpl-R-infected bone marrow cells. These results indicate that retrovirus-mediated expression of Mpl-R in murine stem cells does not modify their ability to reconstitute all myeloid lineages of differentiation and does not result in a preferential commitment toward the megakaryocytic lineage.

Animals↗