VEGF-A isoforms differentially regulate ATF-2-dependent VCAM-1 gene expression and endothelial-leukocyte interactions

Vascular endothelial growth factor A (VEGF-A) regulates many aspects of vascular physiology. VEGF-A stimulates signal transduction pathways that modulate endothelial outputs such as cell migration, proliferation, tubulogenesis, and cell-cell interactions. Multiple VEGF-A isoforms exist, but the biological significance of this is unclear. Here we analyzed VEGF-A isoform-specific stimulation of VCAM-1 gene expression, which controls endothelial-leukocyte interactions, and show that this is dependent on both ERK1/2 and activating transcription factor-2 (ATF-2). VEGF-A isoforms showed differential ERK1/2 and p38 MAPK phosphorylation kinetics. A key feature of VEGF-A isoform-specific ERK1/2 activation and nuclear translocation was increased phosphorylation of ATF-2 on threonine residue 71 (T71). Using reverse genetics, we showed ATF-2 to be functionally required for VEGF-A-stimulated endothelial VCAM-1 gene expression. ATF-2 knockdown blocked VEGF-A-stimulated VCAM-1 expression and endothelial-leukocyte interactions. ATF-2 was also required for other endothelial cell outputs, such as cell migration and tubulogenesis. In contrast, VCAM-1 was essential only for promoting endothelial-leukocyte interactions. This work presents a new paradigm for understanding how soluble growth factor isoforms program complex cellular outputs and responses by modulating signal transduction pathways

Pharmacokinetics and efficacy of an ivermectin implant for long-term prevention of Dirofilaria immitis infection in dogs

An exploratory study was carried out to assess the in vivo efficacy of different prototypes of subcutaneous implants containing ivermectin (IVM) for the prevention of canine Dirofilaria immitis infection. The implants consisted of an ethylcellulose matrix containing IVM (3.0, 4.5, and 6.0 mg/implant; from 0.29 to 0.63 mg/kg bw) as active ingredient designed to release approximately 0.1 ng of IVM/mL in the plasma for at least 12 months. Six dogs were implanted on day -365. On day -12, three heartworm-free dogs were included in the study as a control group. All nine dogs were examined on day -7 and day 0 for circulating D. immitis microfilariae and by an antigen ELISA kit to confirm that the dogs were heartworm-free. The dogs were artificially infected with 75 D. immitis infective larvae (L3) each on day 0. Dogs in the control group were humanely euthanized on day 153 to verify the infectivity of the larvae, while implanted dogs were further examined for circulating D. immitis microfilariae and antigen on days 153, 195, and 246. The treated dogs were not necropsied. The pharmacokinetic profile of the IVM implant was assessed in plasma samples taken on day -364, then at different times until the infection day, and again on days, 15, 30, 60, 90, 120, and 153. Throughout the study, body weights were measured during clinical examination on days 0, 30, 60, 90, 120, and 153. At necropsy, all control dogs were found infected, each with 10-11 adult heartworms. Implanted dogs were negative at both microfilaria and D. immitis antigen examinations until day 246 (8 months from the infection). IVM plasma levels ranged 0.06-0.16 ng/mL on day 0 and remained stable until day 60, afterward they gradually decreased under the limit of quantification of the method. Throughout the study, no side effect was observed. On the basis of these results, it was possible to conclude that the different prototypes of implants were able to protect the dogs from D. immitis artificial infection for at least 12 months

VEGF-A Splice Variants: Do They Play a Role in Tumor Responses to Anti-Angiogenic Therapies?

International audienceIt has been known for two decades that VEGF-A encodes several VEGF-A splice variants, which are termed VEGFxxx, according to the total number of amino acids in the mature protein. To date, nine VEGFxxx isoforms have been described, displaying different biodistribution and pro-angiogenic activity. Adding another level of complexity to VEGF-A biology, a new family of VEGF-A isoforms, termed VEGFxxxb, which exert anti-angiogenic functions was discovered in 2002 and only differ from VEGFxxx polypeptides with regard to their C-terminal six amino acids. Therefore, reminiscent of what is observed, for instance, during apoptosis, the alternative splicing of VEGF-A pre-mRNA generates two types of isoforms with antagonistic biological functions. As anti-angiogenic therapies target both the VEGFxxx and VEGFxxxb families, VEGF-A pre-mRNA splicing may therefore impact tumor responses to these therapies. Consistently, recent clinical studies have highlighted VEGF-A splice variants as predictive biomarkers in response to bevacizumab. Hence, identification of the upstream signaling pathways that control VEGF-A pre-mRNA splicing, better characterization of the specific biological functions played by each VEGF-A splice variant, and/or analysis of the impact of anti-angiogenic therapies on VEGF-A pre-mRNA splicing are critical goals. The purpose of this chapter is to summarize the current knowledge in this field

Hypoxia and extracellular matrix remodeling

International audienceHypoxia regulates composition of both the vascular basement membrane (BM) and the extracellular matrix (ECM) by modulating deposition, cross-linking, posttranslational modifications, and rearrangement events but also degradation. Hypoxia-driven remodeling of the ECM includes highly temporally and spatially coordinated processes that eventually affect angiogenesis leading to blood vessel formation from existing blood vessels. Hypoxia thereby affects the mechanical properties of the vascular milieu as well as matricellular proteins expression and function and availability of angiogenesis-regulating growth factors such as vascular endothelial growth factor (VEGF). ECM composition and stiffness may be required for optimal VEGFR2 expression and vascular development in vitro and in vivo (Mammoto et al. Nature 2009), but how it might control signaling pathways such as VEGFR2 signaling is not fully appreciated yet. Thus, vascular BM and ECM composition affects vascular microenvironment architecture and interaction with angiogenic growth factors but also exerts mechanical forces controlled by physical interactions between vascular cells and the ECM that cooperate in regulating angiogenesis