Essential thrombocythemia: Impaired regulation of megakaryocyte progenitors

Abstract

In this paper, the in vitro growth of bone marrow early (megakaryocyte burst-forming units, BFU-meg) and late (megakaryocyte colony-forming units, CFU-meg) progenitors was evaluated in 18 essential thrombocythemia (ET) patients and 22 normal control subjects. BFU-meg clonality was demonstrated both in normal and ET bone marrows, cultivating these primitive progenitors at limiting dilutions in plasma clot assay: 1 to 7 BFU-meg/2.5 x 10(4) mononuclear non-adherent cells were observed, with a strong correlation in ET [r = 0.955 stimulated by recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) plus recombinant human interleukin (rhIL) 3], as well as in normal controls (r = 0.969). In order to clearly elucidate the in vitro response of ET megakaryocyte (meg) progenitors to recombinant growth factors, the interference of accessory cells (i.e., monocytes, T lymphocytes, and natural killer cells) and human serum were avoided by performing experiments on CD34+ cells in a serum-free fibrin clot assay. The number of both early and late meg progenitors in ET was significantly increased in response to rhIL-3, rhIL-3 plus rhIL-6, and rhIL-3 plus rhGM-CSF, but not in response to rhGM-CSF alone. Furthermore, both meg progenitors were investigated for their response to rh transfer growth factor (TGF)-beta 1, tested at concentrations from 0.01 to 10 ng/ml. rhTGF-beta 1 was able to inhibit CFU-meg and BFU-meg in a dose-response manner normal, whereas ET CFU-meg appeared less sensitive to the lower doses investigated (p less than 0.05) and ET BFU-meg were slightly reduced in number only at the higher concentrations of rhTGF-beta 1 (p less than 0.01). Our data suggest that the increased thrombopoiesis in ET may depend on an increased sensitivity of meg progenitors to some of the physiological growth factors and to a disrupted sensitivity to at least one negative regulator of megakaryocytopoiesis. Since these abnormalities involve both meg progenitors, this can be considered a demonstration that the neoplastic event hits the most primitive hemopoietic progenitors.

Polycythemia vera megakaryocytes but not megakaryocytes from normal controls and patients with smokers polyglobuly spontaneously express IL-6 and IL-6R and secrete IL-6

“…35 Other experimental studies repeatedly pointed out that megakaryocyte progenitors in CMPDs were hypersensitive to rhIL-3, rhIL-6 and rhGM-CSF. 2,36,37 In previous studies, we found that megakaryocytic IL-6 production can be induced by IL-3 stimulation.…”

Reduced responsiveness of bone marrow megakaryocyte progenitors to platelet‐derived transforming growth factor β1, produced in normal amount, in patients with essential thrombocythaemia

“…Several groups of investigators have described alterations that characterize the in vitro growth of haematopoietic progenitors in ET (Kamostsu et at, 1986;Juvonen et al, 1987: Kimura et nl, 1987Mazur et al, 1988;Han et al, 1989) and MMM (Hibbin et al 1984;Battegay et al, 1989;Visani et al, 1990). Moreover, we have previously demonstrated that ET bone marrow megakaryocyte progenitors show an increased sensitivity to suboptimal concentrations of recombinant growth factors, such as granulocyte/macrophage-colony stimulating factor (rGM-CSF) and interleukin 3 (rIL-3) (Gugliotta et al, 1989: Zauli et al 1991.…”

“…Megakaryocyte and erythroid progenitor cell assays. The in vitro growth of haematopoietic progenitors was studied in a serum-free fibrin clot assay, performed as previously described (Dainiak et al 1985;Zauli et al, 1991), to avoid the interference of serum with the activity of TGF-pl contained in platelet lysate. 5 x lo4 CD34+ cells were seeded in 1 ml of IMDM, supplemented with 300 pg/ml iron saturated transferrin (Sigma, St Louis, Mis., U.S.A.), 3 mg bovine serum albumin (BSA, fraction V Chon, Sigma), 280 pg/ml CaCI2; 1 x lo' M L-asparagine; 0.1 ml of 0.2% (wt/vol) purified fibrinogen (Kabi, Stockholm, Sweden) resuspended in PBS and 0.1 ml of 0.2 U/ml purified human thrombin (95%) (Sigma) in PBS.…”

Combined Exercise and Insulin-Like Growth Factor-1 Supplementation Induces Neurogenesis in Old Rats, but Do Not Attenuate Age-Associated DNA Damage

“…However, a recent report has challenged this finding, because the data from this study showed that exercise was able to improve results on the Morris water maze test, even with inhibition of neurogenesis. 64 Most studies on neurogenesis have used voluntary running, 65,66 but studies using enforced running 37,67 have shown similar results. However, the data from these studies further suggest that voluntary and treadmill running have different effects on brain plasticity in different regions of the brain.…”