THE major regulator of circulating platelet levels is believed to be a cytokine termed thrombopoietin1,2. It is thought to be a lineage-specific cytokine affecting the proliferation and maturation of committed cells resulting in the production of megakaryocytes and platelets. Despite considerable efforts by a number of laboratories, the unequivocal identification of thrombopoietin has proven elusive. Here we report the functional cloning of a murine complementary DNA encoding a ligand for the receptor encoded by the c-mpl proto-oncogene (c-Mpl) 3–5. The encoded polypeptide has a predicted molecular mass of 35,000 (M
r 35K). The protein has a novel two-domain structure with an amino-terminal domain homologous with erythropoietin and a carboxy-terminal domain rich in serine, threonine and proline residues and containing seven potential N-linked glycosylation sites. Intraperitoneal injections of mice with recombinant protein increase circulating platelet levels by greater than fourfold after 7 days. These results along with those presented in the accompanying report strongly suggest that the ligand for c-Mpl is thrombopoietin.
"In support of this possibility, we found that the mean platelet volume , which is a measurement of the average size of the platelets and gives information about platelet production, was significantly decreased by rapamycin in PPVL rats (p < 0.01; Fig. 7C). Furthermore, the expression of thrombopoietin and its cell surface receptor c-Mpl, which are the most important physiological regulators of platelet formation and are expressed in the spleen , was significantly down-regulated by rapamycin in PPVL rats (p < 0.01; Fig. 7D). Therefore, it is possible that a deficient production of thrombopoietin secondary to rapamycin treatment may well contribute to the drop in blood platelet count observed in PPVL rats. "
"Prior to the identification of TPO, the receptor for TPO, called c-Mpl, was discovered as the product of the c-mpl gene, the wild-type homolog of the v-mpl oncogene (Vigon et al., 1992). The use of c-Mpl was instrumental in purifying thrombopoietin as its ligand (Bartley et al., 1994; de Sauvage et al., 1994; Lok et al., 1994; Sohma et al., 1994; Wendling et al., 1994). Although TPO-independent mechanisms exist in thrombopoiesis (Bunting et al., 1997), TPO/Mpl signaling is essential for proliferation and differentiation of megakaryocytes and platelet production. "
"times above normal value (Lok et al. 1994; Harker et al. 1996) and ameliorates chemotherapy/radiation-induced thrombocytopenia (Hokom et al. 1995; Ulich et al. 1995). Erythropoietin (EPO), a glycoprotein primarily produced by cells in the kidney and liver, where its production is upregulated by hypoxia, is best known as the principal factor regulating erythropoiesis in mammals and promotes survival, proliferation, and differentiation of erythroid progenitor/ precursor cells (Elliott et al. 2008; Paschos et al. 2008). "
[Show abstract][Hide abstract] ABSTRACT: Nuclear accidents or terrorist attacks could expose large numbers of people to ionizing radiation. Early biomarkers of radiation injury will be critical for triage, treatment, and follow-up of such individuals. The authors evaluated the utility of multiple blood biomarkers for early-response assessment of radiation exposure using a murine (CD2F1, males) total-body irradiation (TBI) model exposed to Co γ rays (0.6 Gy min) over a broad dose range (0-14 Gy) and timepoints (4 h-5 d). Results demonstrate: 1) dose-dependent changes in hematopoietic cytokines: Flt-3 ligand (Flt3L), interleukin 6 (IL-6), granulocyte colony stimulating factor (G-CSF), thrombopoietin (TPO), erythropoietin (EPO), and acute phase protein serum amyloid A (SAA); 2) dose-dependent changes in blood cell counts: lymphocytes, neutrophils, platelets, and ratio of neutrophils to lymphocytes; 3) protein results coupled with peripheral blood cell counts established very successful separation of groups irradiated to different doses; and 4) enhanced separation of dose was observed as the number of biomarkers increased. Results show that the dynamic changes in the levels of SAA, IL-6, G-CSF, and Flt3L reflect the time course and severity of acute radiation syndrome (ARS) and may function as prognostic indicators of ARS outcome. These results also demonstrate proof-in-concept that plasma proteins show promise as a complimentary approach to conventional biodosimetry for early assessment of radiation exposures and, coupled with peripheral blood cell counts, provide early diagnostic information to manage radiation casualty incidents effectively, closing a gap in capabilities to rapidly and effectively assess radiation exposure early, especially needed in case of a mass-casualty radiological incident.
Health physics 06/2014; 106(6):772-86. DOI:10.1097/HP.0000000000000094 · 1.27 Impact Factor
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