VEGF-A recruits a proangiogenic MMP-9–delivering neutrophil subset that induces angiogenesis in transplanted hypoxic tissue

Abstract

Recruitment and retention of leukocytes at a site of blood vessel growth are crucial for proper angiogenesis and subsequent tissue perfusion. Although critical for many aspects of regenerative medicine, the mechanisms of leukocyte recruitment to and actions at sites of angiogenesis are not fully understood. In this study, we investigated the signals attracting leukocytes to avascular transplanted pancreatic islets and leukocyte actions at the engraftment site. Expression of the angiogenic stimulus VEGF-A by mouse pancreatic islets was elevated shortly after syngeneic transplantation to muscle. High levels of leukocytes, predominantly CD11b ؉ /Gr-1 ؉ /CXCR4 hi neutrophils, were observed at the site of engraftment, whereas VEGF-A-deficient islets recruited only half of the amount of leukocytes when transplanted. Acute VEGF-A exposure of muscle increased leukocyte extravasation but not the levels of SDF-1␣. VEGF-A-recruited neutrophils expressed 10 times higher amounts of MMP-9 than neutrophils recruited to an inflammatory stimulus. Revascularization of islets transplanted to MMP-9-deficient mice was impaired because blood vessels initially failed to penetrate grafts, and after 2 weeks vascularity was still disturbed. This study demonstrates that VEGF-A recruits a proangiogenic circulating subset of CD11b ؉ /Gr-1 ؉ neutrophils that are CXCR4 hi and deliver large amounts of the effector protein MMP-9, required for islet revascularization and functional integration after transplantation. (Blood. 2012; 120(23):4653-4662)

Identification and characterization of VEGF-A–responsive neutrophils expressing CD49d, VEGFR1, and CXCR4 in mice and humans

“…This finding contrasts to what is reported for neutrophil recruitment to an inflammatory stimulus, which completely depends on LFA-1 (integrin a L b 2 [CD11a/CD18]) and Mac-1 (integrin a M b 2 [CD11b/CD18]). 8,9,30 In murine models however, myeloid cell trafficking into tumors has been reported to rely on VLA-4 after activation by PI3-kinase p110g. 46 Only a small population of circulating neutrophils expressed CD49d in this study, which is in accordance with the prevailing view.…”

“…[2][3][4][5] Macrophages, monocytes, and neutrophils can stimulate angiogenesis by delivering proangiogenic growth factors (eg, vascular endothelial growth factor A [VEGF-A] and VEGF-C) as well as by the release of proteinases (eg, matrix metalloproteinase 9 ) that digest extracellular matrix and thereby release matrixbound growth factors and allow for vessel sprouting. [6][7][8] Neutrophils represent the major leukocyte subset in blood. Their recruitment from circulation to inflammatory foci has been extensively studied and is the result of sequential steps of the recruitment cascade.…”

“…6,11 In addition, we have previously demonstrated that VEGF-A production by intramuscularly transplanted pancreatic islets is crucial for recruitment of a neutrophil subset that delivers high concentrations of MMP-9 and thereby induces revascularization of the hypoxic grafts. 8 VEGF-A expression is upregulated by hypoxia and transmits its proangiogenic effects by binding receptors on endothelial cells. Endothelial activation by VEGF-A predominantly occurs after ligation of VEGF receptor 2 (VEGFR2; also known as kinase insert domain receptor [KDR] or fetal liver kinase 1 [Flk1]), but lower levels of VEGF receptor 1 (VEGFR1; also known as fms-like tyrosine kinase-1 [Flt-1]) with uncertain signaling properties are also detected on endothelium.…”

Nitric Oxide-Donating Statins Upgrade the Benefits of Lipid-Lowering in Vascular Inflammation by Desensitizing Neutrophil Activation

“…In line, mice that obtained stents coated with cathelicidin displayed significantly reduced in-stent stenosis. Similarly, evidence for an angiogenic, tissueregenerating effect of neutrophils is accumulating [28]. Hence, in such conditions reduction of neutrophil activation may prove counterproductive.…”

Contribution of complement anaphylatoxin receptors to melanoma growth: potential therapeutic targets

“…The recruitment of neutrophils into the inflammatory site is mediated by chemokines, complement fragment C5a, platelet activating factor and lipid mediators. Upon activation, neutrophils release a range of chemokines as well as toxic contents, such as reactive oxygen species (ROS) and the matrix metalloproteinase (MMP)-9 which contribute to tissue damage and remodelling by degrading extracellular matrix components (Christoffersson et al, 2012). MMP-9 also regulates leukocytosis (Opdenakker et al, 1998) and activates bound growth factors such as vascular endothelial growth factor-A (VEGF-A), a key mediator of angiogenesis (Van den Steen et al, 2002).…”