Interleukin-34 (IL-34) was recently characterized as the M-CSF "twin" cytokine, regulating the proliferation/differentiation/survival of myeloid cells. The implication of M-CSF in oncology was initially suspected by the reduced metastatic dissemination in knock-out mice, due to angiogenesis impairment. Based on this observation, our work studied the involvement of IL-34 in the pathogenesis of osteosarcoma. The in vivo effects of IL-34 were assessed on tissue vasculature and macrophage infiltration in a murine preclinical model based on a paratibial inoculation of human osteosarcoma cells overexpressing or not IL-34 or M-CSF. In vitro investigations using endothelial cell precursors and mature HUVEC cells were performed to analyse the involvement of IL-34 in angiogenesis and myeloid cell adhesion. The data revealed that IL-34 overexpression was associated with the progression of osteosarcoma (tumor growth, lung metastases) and an increase of neo-angiogenesis. In vitro analyses demonstrated that IL-34 stimulated endothelial cell proliferation and vascular cord formation. Pre-treatment of endothelial cells by chondroitinases/heparinases reduced the formation of vascular tubes and abolished the associated cell signalling. In addition, IL-34 increased the in vivo recruitment of M2 tumor-associated macrophages into the tumor tissue. IL-34 increased in vitro monocyte/CD34 1 cell adhesion to activated HUVEC monolayers under physiological shear stress conditions. This work also demonstrates that IL-34 is expressed by osteosarcoma cells, is regulated by TNF-a, IL-1b, and contributes to osteosarcoma growth by increasing the neo-angiogenesis and the recruitment of M2 macrophages. By promoting new vessel formation and extravasation of immune cells, IL-34 may play a key role in tumor development and inflammatory diseases.Angiogenesis and vasculogenesis are central events during embryogenesis and growth.

Objective-We examined whether plasma levels of angiogenic factors are altered in plasma of patients with peripheral arterial disease (PAD) and whether these factors affect endothelial progenitor cell-induced angiogenesis. Methods and Results-Plasma was collected from 184 patients with PAD and 330 age-matched healthy controls. Vascular endothelial growth factor and placental growth factor concentrations did not differ between the groups, whereas we found a linear correlation between PAD disease and thrombospondin (TSP)-1 plasma level. TSP-1 was expressed in newly formed vessels in PAD patients having received local injections of bone marrow mononuclear cells. To analyze the functional role of TSP-1 during neoangiogenesis, we used a Matrigel-plug assay and showed that vascularization of implanted Matrigel-plugs was increased in TSP-1 Ϫ/Ϫ mice. Moreover, injections of TSP-1 in C57Bl6/J mice after hindlimb ischemia induced a significant decrease of blood flow recovery. To investigate the effects of TSP-1 on human endothelial colony-forming cell (ECFC) angiogenic potential, recombinant human TSP-1 and a small interfering RNA were used. In vitro, TSP-1 N-terminal part significantly enhanced ECFC adhesion, whereas recombinant human TSP-1 had a negative effect on ECFC angiogenic potential. This effect, mediated by CD47 binding, modulated stromal cell-derived factor 1/CXC chemokine receptor 4 pathway. Key Words: angiogenesis Ⅲ arterial thrombosis Ⅲ endothelial progenitor cells P eripheral arterial disease (PAD), characterized by atherosclerosis of the lower extremities, affects up to 15% of people older than 55 years. 1 The main clinical manifestations of PAD are intermittent claudication and critical limb ischemia (CLI). Intermittent claudication is characterized by reproducible pain on exertion that is relieved by rest. CLI is the most severe form of PAD and is characterized by the inability of arterial blood flow to meet the metabolic demands of resting muscle or tissue, resulting in rest pain and/or tissue necrosis and frequently necessitating amputation. Currently, PAD diagnosis is based on the ankle-brachial systolic pressure index (ABI), but the ABI is a poor marker of PAD severity. There are no other reliable diagnostic tests for PAD, and new biomarkers would therefore be useful. Conclusion-TSP-1 is a potential biomarker of PAD and ECFC-induced angiogenesisAtherosclerosis induces occlusion of the arterial tree and tissue hypoxia, which is a strong stimulus for angiogenesis. Collateral vessels develop physiologically in patients with CLI, mainly driven by an enhanced angiogenic response. 2 However, the capacity of this compensatory mechanism is rapidly exceeded, and normal flow is not restored. Autologous endothelial progenitor cells (EPCs) are candidates for angiogenic therapy. Because of their scarcity in human samples, EPCs have been characterized by culture methods. At least 2 populations of EPCs have been described. 3 "Early" EPCs appear within 4 to 7 days of culture, whereas "late" EPCs, also called endothe...