Lineage-specific growth factors can compensate for stem and progenitor cell deficiencies at the postprogenitor cell level: an analysis of doubly TPO- and G-CSF receptor–deficient mice

Abstract

Multiple lines of evidence indicate that thrombopoietin (TPO) substantially impacts the number of hematopoietic stem cells and progenitors of all myeloid lineages. Nevertheless, tpo knock-out mice (T ؊ ) display thrombocytopenia only; blood erythroid and neutrophil levels are normal despite 60% to 85% reductions in stem and progenitor cells. The compensatory mechanism(s) for these deficiencies remains uncertain; lineage-specific cytokines such as erythropoietin or granulocyte colony-stimulating factor (G-CSF) have been postulated but never proven to be responsible. To directly test whether G-CSF can compensate for the myeloid progenitor cell reduction in the T ؊ model of hematopoietic deficiency, T ؊ and G-CSF-receptor knock-out (GR ؊ ) mice were crossed, and F1 animals bred to obtain doubly nullizygous mice (T ؊ GR ؊ ). This experiment also allowed us to test the hypothesis that G-CSF contributes to the residual platelet production in T ؊ mice. We found that T ؊ GR ؊ F2 mice displayed similar blood platelet levels as that seen in T ؊ mice, indicating that G-CSF does not account for the residual megakaryopoiesis in T ؊ mice. However, we also noted excessive perinatal mortality of T ؊ GR ؊ animals, caused by infection due to a profound and significant decrease in marrow and peripheral blood neutrophils, far greater than that seen in either T ؊ or GR ؊ mice. These data indicate that in the additional absence of GR, T ؊ mice cannot compensate for their 62% reduction in myeloid progenitors and become profoundly neutropenic, supporting the hypothesis that G-CSF can compensate for the myeloid effects of TPO deficiency by expanding the pool of cells between the granulocyte-macrophage colony-forming unit and mature neutrophil stages of granulopoiesis. IntroductionA major step in our understanding of the regulation of blood cell production came with the cloning and characterization of hematopoietic cytokines and their receptors. Based on their activities in various in vitro assays and administration in vivo, the lineage specificity of these glycoprotein hormones was quickly determined. At present, the hematopoietic cytokines can be broadly divided into those that primarily affect the early aspects of hematopoietic development, working on multiple cell types with multilineage potential, and a subfamily of lineage-dominant cytokines that work primarily on cells committed to a single hematopoietic lineage. 1 It is also clear that the most profound hematopoietic effects in vivo are exerted by the lineage-dominant cytokines erythropoietin (EPO), granulocyte colony-stimulating factor (G-CSF), and thrombopoietin (TPO).There is little doubt that G-CSF is the primary regulator of steady state and reactive neutrophil production. 2 The administration of the cytokine to normal animals leads to profound increases in neutrophil levels, and mice in which the G-CSF or G-CSFreceptor (G-CSF-R) genes have been genetically eliminated are reported to have neutrophil counts about 25% that of littermate controls. 3,4 Likewise, the use of TPO ...

Cytokine receptors and hematopoietic differentiation

“…Mice with deletion of two or more cytokine receptors and/or cytokines have also been generated. The outcome of these genetic crosses has yielded few surprises, with the phenotypes generally being additive (Liu et al, 1997;Seymour et al, 1997;Gainsford et al, 1999;Scott et al, 2000;Kaushansky et al, 2002). The phenotypes of mice bearing genetic deletion of cytokine receptors contrast with those in which transcription factors are deleted, such as stem cell leukemia (SCL) and GATA binding protein (GATA-1).…”

The Complex Role of Neutrophils in Tumor Angiogenesis and Metastasis

“…However, mice lacking both G-CSF (or its receptor) and GM-CSF (26), IL6 (29), or thrombopoietin (ref. 28; double knockout) display more severe neutropenia than mice lacking only G-CSF (or its receptor). It is noteworthy that mice lacking all three myeloid colony-stimulating factors (G-CSF, GM-CSF, and M-CSF) can still generate macrophages and granulocytes, albeit at substantially reduced levels (30).…”

“…Other factors, including GM-CSF, IL6, and thrombopoietin, can also contribute to granulopoiesis, although to a lesser extent than G-CSF. Knockout mice for GM-CSF (26), IL6 (27), or thrombopoietin (28) have been examined and, in contrast to G-CSF À/À (23) or G-CSFR À/À (24) mice, appear to have normal neutrophil numbers in the blood. However, mice lacking both G-CSF (or its receptor) and GM-CSF (26), IL6 (29), or thrombopoietin (ref.…”

Fine-tuning p53 activity through C-terminal modification significantly contributes to HSC homeostasis and mouse radiosensitivity

“…Importantly, responses measured by peripheral blood cell counts can underestimate a progenitor cell phenotype, as the post-progenitor cell hematopoietic compartment can hyperproliferate to compensate for profound deficiencies in marrow stem or progenitor cells (Kaushansky et al 2002). As such, we evaluated total BM counts before and after 5 Gy irradiation to further understand the factors involved in the increased radiosensitivity of p53 7KR mice.…”