High Thrombopoietin Production by Hematopoietic Cells Induces a Fatal Myeloproliferative Syndrome in Mice

Abstract

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 (104 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 granulocytemacrophage 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.

Interpreting the developmental dance of the megakaryocyte: a review of the cellular and molecular processes mediating platelet formation

“…Likewise, inhibition of c‐Mpl‐dependent MK migration and function results in significantly decreased donor stem cell engraftment in murine transplantation assays (Olson et al , ). This is consistent with older data showing that TPO‐overexpressing mice develop a myeloproliferative phenotype similar to idiopathic myelofibrosis described in humans, with symptoms including thrombocytosis, leucocytosis and bone marrow myelofibrosis (Yan et al , ; Villeval et al , ). Together, these studies demonstrate that TPO not only drives proliferation and maturation of MKs but also other bone marrow‐derived progenitor cells.…”

Pyk2 and Megakaryocytes Regulate Osteoblast Differentiation and Migration Via Distinct and Overlapping Mechanisms

“…). We demonstrated that mice deficient in the MK transcription factor, GATA‐1, exhibit a profound increase in bone marrow MKs and exhibit a marked increase in osteoblast number and bone mass [Drachman et al, ; Villeval et al, ; Kacena et al, , , ]. Our current studies provide a potential Pyk2‐regulated mechanism for the MK‐mediated decrease in ALP.…”

“…Briefly, embryonic E13‐15 fetuses were dissected from pregnant WT mice, fetal livers were removed and single cell suspensions were generated. Cells were washed and then seeded in 100 ml culture dishes in Dulbecco modified eagle medium (DMEM) supplemented with 10% FCS and 1% murine thrombopoietin [Villeval et al, ]. MKs were isolated 5–7 days later by separating them from the lymphocytes and other cells using a one‐step albumin gradient to obtain a 90–95% pure MK population [Drachman et al, ].…”

Circulating levels of MCP‐1, sIL‐2R, IL‐15, and IL‐8 predict anemia response to pomalidomide therapy in myelofibrosis

“…Current dogma holds that bone marrow collagen fibrosis and osteosclerosis in the aforementioned conditions reflect a cytokine‐mediated secondary inflammatory response that is triggered by the abnormal interaction between clonal myeloid cells and polyclonal bone marrow stromal cells [2]. Various studies utilizing either tissue specimens from MPN patients or murine models that develop myelofibrosis have implicated either megakaryocytes/platelets [3–5] or monocyte/macrophage lineage cells [6, 7] as the key source for abnormal cytokine synthesis.…”