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Myeloproliferative Neoplasms
Platelet-derived growth factor receptor b activation and regulation in murine myelofibrosis
Ferrata Storti Foundation
Haematologica 2020 Volume 105(8):2083-2094
Frederike Kramer,1,2 Jens Dernedde,1 Artur Mezheyeuski,3 Rudolf Tauber,1 Patrick Micke3 and Kai Kappert1,2,4
1Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Institute of Laboratory Medicine, Clinical Chemistry and Pathobiochemistry, Berlin, Germany; 2Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt- Universität zu Berlin, and Berlin Institute of Health, Center for Cardiovascular Research (CCR), Berlin, Germany; 3Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden and 4DZHK (German Centre for Cardiovascular Research), partner site Berlin, Berlin, Germany
ABSTRACT
There is prevailing evidence to suggest a decisive role for platelet- derived growth factors (PDGF) and their receptors in primary myelofibrosis. While PDGF receptor b (PDGFRb) expression is increased in bone marrow stromal cells of patients correlating with the grade of myelofibrosis, knowledge on the precise role of PDGFRb signaling in myelofibrosis is sparse. Using the Gata-1low mouse model for myelofibro- sis, we applied RNA sequencing, protein expression analyses, multispectral imaging and, as a novel approach in bone marrow tissue, an in situ proxim- ity ligation assay to provide a detailed characterization of PDGFRb signal- ing and regulation during development of myelofibrosis. We observed an increase in PDGFRb and PDGF-B protein expression in overt fibrotic bone marrow, along with an increase in PDGFRb–PDGF-B interaction, analyzed by proximity ligation assay. However, PDGFRb tyrosine phosphorylation levels were not increased. We therefore focused on regulation of PDGFRb by protein tyrosine phosphatases as endogenous PDGFRb antagonists. Gene expression analyses showed distinct expression dynamics among PDGFRb-targeting phosphatases. In particular, we observed enhanced T- cell protein tyrosine phosphatase protein expression and PDGFRb–T-cell protein tyrosine phosphatase interaction in early and overt fibrotic bone marrow of Gata-1low mice. In vitro, T-cell protein tyrosine phosphatase (Ptpn2) knockdown increased PDGFRb phosphorylation at Y751 and Y1021, leading to enhanced downstream signaling in fibroblasts. Furthermore, Ptpn2 knockdown cells showed increased growth rates when exposed to low-serum growth medium. Taken together, PDGF signaling is differential- ly regulated during myelofibrosis. Protein tyrosine phosphatases, which have so far not been examined during disease progression, are novel and hitherto unrecognized components in myelofibrosis.
Introduction
Primary myelofibrosis (PMF) is a malignant hematologic disorder characterized by the clonal proliferation of hematopoietic stem cells (HSC) in the bone marrow. Patients display symptoms of ineffective hematopoiesis such as anemia, thrombo- cytopenia and related extramedullary hematopoiesis resulting in splenomegaly. The bone marrow of PMF patients shows dysplastic megakaryocytes, neoangio- genesis and, as a central pathological feature, progressive fibrosis.1 The develop- ment of myelofibrosis is mainly ascribed to the overproduction of pro-fibrotic cytokines and growth factors by malignant immature cells of the megakaryocytic lineage. As a consequence, fibroblasts proliferate and produce extensive amounts of extracellular matrix (ECM) components, leading to impaired hematopoietic function of the bone marrow.2
Correspondence:
KAI KAPPERT
kai.kappert@charite.de
Received: May 14, 2019. Accepted: October 29, 2019. Pre-published: October 31, 2019.
doi:10.3324/haematol.2019.226332
Check the online version for the most updated information on this article, online supplements, and information on authorship & disclosures: www.haematologica.org/content/105/8/2083
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