title: Role of tumor associated macrophages in tumor angiogenesis and lymphangiogenesis.
abstract: Tumor angiogenesis is an essential process for supplying rapidly growing malignant tissues with essential nutrients and oxygen. An angiogenic switch allows tumor cells to survive and grow, and provides them access to vasculature resulting in metastatic disease. Monocyte-derived macrophages recruited and reprogrammed by tumor cells serve as a major source of angiogenic factors boosting the angiogenic switch. Tumor endothelium releases angiopoietin-2 and further facilitates recruitment of TIE2 receptor expressing monocytes (TEM) into tumor sites. Tumor-associated macrophages (TAM) sense hypoxia in avascular areas of tumors, and react by production of angiogenic factors such as VEGFA. VEGFA stimulates chemotaxis of endothelial cells (EC) and macrophages. In some tumors, TAM appeared to be a major source of MMP9. Elevated expression of MMP9 by TAM mediates extracellular matrix (ECM) degradation and the release of bioactive VEGFA. Other angiogenic factors released by TAM include basic fibroblast growth factor (bFGF), thymidine phosphorylase (TP), urokinase-type plasminogen activator (uPA), and adrenomedullin (ADM). The same factors used by macrophages for the induction of angiogenesis [like vascular endothelial growth factor A (VEGF-A) and MMP9] support lymphangiogenesis. TAM can express LYVE-1, one of the established markers of lymphatic endothelium. TAM support tumor lymphangiogenesis not only by secretion of pro-lymphangiogenic factors but also by trans-differentiation into lymphatic EC. New pro-angiogenic factor YKL-40 belongs to a family of mammalian chitinase-like proteins (CLP) that act as cytokines or growth factors. Human CLP family comprises YKL-40, YKL-39, and SI-CLP. Production of all three CLP in macrophages is antagonistically regulated by cytokines. It was recently established that YKL-40 induces angiogenesis in vitro and in animal tumor models. YKL-40-neutralizing monoclonal antibody blocks tumor angiogenesis and progression. The role of YKL-39 and SI-CLP in tumor angiogenesis and lymphangiogenesis remains to be investigated.
authors.affiliation: Department of Dermatology, University Medical Center and Medical Faculty Mannheim, Ruprecht-Karls University of Heidelberg Mannheim, Germany ; Department of Nanopathology, Institute of General Pathology and Pathophysiology, Russian Academy of Medical Sciences Moscow, Russia.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Riabov
authors.affiliation: Department of Dermatology, University Medical Center and Medical Faculty Mannheim, Ruprecht-Karls University of Heidelberg Mannheim, Germany ; Department of Innate Immunity and Tolerance, University Medical Center and Medical Faculty Mannheim, Institute of Transfusion Medicine and Immunology, Ruprecht-Karls University of Heidelberg Mannheim, Germany.
authors.forename: Alexandru
authors.initials: A
authors.lastname: Gudima
authors.affiliation: Department of Dermatology, University Medical Center and Medical Faculty Mannheim, Ruprecht-Karls University of Heidelberg Mannheim, Germany.
authors.forename: Nan
authors.initials: N
authors.lastname: Wang
authors.affiliation: Department of Dermatology, University Medical Center and Medical Faculty Mannheim, Ruprecht-Karls University of Heidelberg Mannheim, Germany ; Department of Innate Immunity and Tolerance, University Medical Center and Medical Faculty Mannheim, Institute of Transfusion Medicine and Immunology, Ruprecht-Karls University of Heidelberg Mannheim, Germany.
authors.forename: Amanda
authors.initials: A
authors.lastname: Mickley
authors.affiliation: Department of Nanopathology, Institute of General Pathology and Pathophysiology, Russian Academy of Medical Sciences Moscow, Russia.
authors.forename: Alexander
authors.initials: A
authors.lastname: Orekhov
authors.affiliation: Department of Dermatology, University Medical Center and Medical Faculty Mannheim, Ruprecht-Karls University of Heidelberg Mannheim, Germany ; Department of Nanopathology, Institute of General Pathology and Pathophysiology, Russian Academy of Medical Sciences Moscow, Russia ; Department of Innate Immunity and Tolerance, University Medical Center and Medical Faculty Mannheim, Institute of Transfusion Medicine and Immunology, Ruprecht-Karls University of Heidelberg Mannheim, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Kzhyshkowska
keywords: LYVE-1; TIE2 receptor; VEGF; chitinase-like protein; stabilin-1; tumor-associated macrophages