Projects
Project 1. Tip Cell biology and Vessel Guidance
Recent studies of vascular network development in the embryo identified several novel aspects of angiogenesis crucial to generate a functional and stable branched vascular network.
These aspects include:
1) the specification of arterial and venous identity in vessels
2) the differentiation and guidance of endothelial tip cells in angiogenic vessels
3) the formation of branches and network patterning
Based on transcriptional profiling we identified several novel candidate molecules involved in endothelial tip cell differentiation and vessel guidance events. At present we are validating these candidates. We therefore perform loss and gain of function experiments in zebrafish and mouse models to elucidate the mechanism of action of these molecules. Our candidates appear to directly affect tip cell differentiation from endothelial cells and coordination of their movement in the extracellular matrix.
For analysis of vascular function in vivo, we established state of the art imaging techniques using two-photon microscopy imaging in transgenic zebrafish and mice with fluorescent reporters in relevant cardiovascular compartments (vessels, heart). This technique allows 3D time-lapse imaging. Other techniques used include micro-array and deep sequencing analysis, generating transgenics and (conditional) mutants in zebrafish or mouse, as well as routine molecular biological techniques (Western- and Northern blot, in situ hybridization, in vitro angiogenesis and cell migration assays, interfering RNA, promoter-reporter assays).
Project 2. Mechanosensing, Arteriogenesis and Ischemic Diseases
Arteriogenesis, the outward remodeling of pre-existing small collateral arterial networks, occurs as a response to vascular occlusion or stenosis and importantly determines the clinical outcome of ischemic cardiovascular disease. Release of vasodilators and activation of inflammatory pathways allowing influx of monocytes may result in revascularization and restoration of blood flow into the hypoperfused ischemic area. Therapeutic arteriogenesis is considered of major clinical importance to treat the increasing population with complex occlusive artery diseases. Distinct differences exist between animal strains and patients with regard to collateral development and response to angiogenic growth factors. We aim at understanding the molecular mechanism accounting for such differences. In particular we focus on the formation of native collaterals and efficiency of collateral recruitment and maintenance. Hemodynamic forces exerted by flowing blood and neural guidance molecules (neuropilins-VEGFR2; Notch-delta ligands, ephrins and downstream targets) play a critical role in initiation and maintenance of the arteriogenesis response. We are interested in how biophysical signals exerted by flowing blood activate specific genetic programs essential for arterial differentiation. The role of neural guidance molecules in the arteriogenesis is studied in conditional mutant mice exposed to ischemic vascular stress (femoral artery occludion, cardiac infarct, stroke models). We examine adaptive recovery from such pathological insults using laser-doppler flow, perfusion-microspheres, imaging including standard angiography, MRI and micro CT. In addition, we perform extensive molecular and histological analysis of target organs. In collaboration with clinical research partners we are evaluating novel strategies and compounds to stimulate arteriogenesis in patients suffering from vascular occlusive disease.