Doctoral School

The VRC provides basic research training for students in biology, chemistry, bio-engineering, pharmacy, veterinary science and medicine. Research performed by graduate students is situated within the context of ongoing projects supervised by one of the staff scientists, and offers the opportunity of creative and independent but interactive research.

Degree:

Ph.D. in Medical Sciences (Doctor in de Medische Wetenschappen)
Faculty of Medicine, K.U.Leuven

Graduate students are funded through individual fellowships or grants, or by support secured by senior scientists. Research towards a Ph.D. degree consists of one or more original scientific contributions published in peer-reviewed international journals.

Graduate students participate in all research-related activities (unit meetings, weekly lab-meetings, weekly in-house seminars, invited seminars or lectures within the Department), for which English is the standard language. In addition to these activities, a graduate student shall comply with the Ph.D. in Medical Sciences study credit program, as determined by the Faculty of Medicine, K.U.Leuven.

Eligible students are invited to request additional information on our graduate training program, providing their undergraduate scores and degrees were on average at least A (onderscheiding). Graduate students will be expected to compete for fellowship support at institutions such as FWO, IWT, etc.

Genetic analysis of the molecular basis of angiogenesis and the neurovascular link in health and disease

The formation of new blood vessels (angiogenesis) is important in health and disease (1,2). Blood vessels grow actively in the embryo, but also in numerous malignant, ischemic and inflammatory disorders (3). Our own genetic and pharmacological studies have identified the VEGF homologue PlGF as an attractive target for anti-angiogenic therapy, currently being evaluated in clinical trials (4,5). Recent studies now also indicate an exciting link between the vascular and nervous system, with angiogenic factors regulating nervous system development and disease, and, conversely, neuronal signals regulating vessel guidance (6,7). We discovered that low VEGF levels cause motor neurodegeneration (amyotrophic lateral sclerosis, ALS) in mice and humans, and showed that VEGF treatment ameliorates motoneuron survival in preclinical ALS models (8-10); clinical VEGF trials in ALS humans are underway. Understanding the molecular basis of angiogenesis and the neurovascular link thus offers novel therapeutic opportunities to treat disorders, ranging from cancer to ischemia, and neurodegeneration.

Using various genetic animal models (zebrafish, frogs and mice), our laboratory is interested in dissecting the molecular basis of angiogenesis and the neurovascular link, and use these genetic insights to develop novel therapeutic strategies. In particular, we focus on the following topics: (i) which signals determine and what is the molecular signature of endothelial cell fate (tip versus stalk cell; we recently identified a novel “phalanx” endothelial cell fate (Mazzone et al, Cell, in revision); arterial, venous versus lymphatic) 4,11; (ii) which signals determine vessel navigation and guidance (focussing on neuronal axon guidance cues as possible candidates) (6,12,13); (iii) how do oxygen and metabolism, and their sensors, regulate angiogenesis and neurovascular processes (including neurodegeneration) (14,15); and (iv) how do angiogenic factors, and in particular VEGF, regulate neuronal wiring, axon guidance, circuitry formation, synapse formation, synaptic plasticity, and neurodegeneration (Meissirel et al, Science, under review) (6,12,13).

1. Carmeliet, P. Mechanisms of angiogenesis and arteriogenesis. Nat Med 6, 389-95 (2000).
2. Carmeliet, P. Angiogenesis in health and disease. Nat Med 9, 653-60 (2003).
3. Carmeliet, P. et al. Abnormal blood vessel development and lethality in embryos lacking a single VEGF allele. Nature 380, 435-9 (1996). Carmeliet, P. et al. Synergism between vascular endothelial growth factor and placental growth factor contributes to angiogenesis and plasma extravasation in pathological conditions. Nat Med 7, 575-83 (2001).
4. Fischer, C. et al. Anti-PlGF inhibits growth of VEGF(R)-inhibitor-resistant tumors without affecting healthy vessels. Cell 131, 463-75 (2007).
5. Carmeliet, P. & Tessier-Lavigne, M. Common mechanisms of nerve and blood vessel wiring. Nature 436, 193-200 (2005).
6. Zacchigna, S., Lambrechts, D. & Carmeliet, P. Neurovascular signalling defects in neurodegeneration. Nat Rev Neurosci 9, 169-81 (2008).
7. Oosthuyse, B. et al. Deletion of the hypoxia-response element in the vascular endothelial growth factor promoter causes motor neuron degeneration. Nat Genet 28, 131-8 (2001).
8. Lambrechts, D. et al. VEGF is a modifier of amyotrophic lateral sclerosis in mice and humans and protects motoneurons against ischemic death. Nat Genet 34, 383-94 (2003).
9. Storkebaum, E. et al. Treatment of motoneuron degeneration by intracerebroventricular delivery of VEGF in a rat model of ALS. Nat Neurosci 8, 85-92 (2005).
10. Ny, A. et al. A genetic Xenopus laevis tadpole model to study lymphangiogenesis. Nat Med 11, 998-1004 (2005).
11. Lu, X. et al. The netrin receptor UNC5B mediates guidance events controlling morphogenesis of the vascular system. Nature 432, 179-86 (2004).
12. Carmeliet, P. Blood vessels and nerves: common signals, pathways and diseases. Nat Rev Genet 4, 710-20 (2003).
13. Carmeliet, P. et al. Role of HIF-1alpha in hypoxia-mediated apoptosis, cell proliferation and tumour angiogenesis. Nature 394, 485-90 (1998).
14. Aragones, J. et al. Deficiency or inhibition of oxygen sensor Phd1 induces hypoxia tolerance by reprogramming basal metabolism. Nat Genet 40, 170-80 (2008).

The endothelial phalanx cell: at the crossroad between anti-angiogenic therapy and therapeutic angiogenesis

In contrast to our increasing understanding of how vessels sprout, little is known about how vessels regulate their shape and morphogenesis. Unraveling the mechanisms underlying these processes is important, since vessel shape regulates its primary function, i.e. to supply oxygen to distant cells. In addition, in pathological conditions such as cancer and ischemic diseases, vessels are abnormal and dysfunctional, which impairs perfusion and oxygenation. The resultant hypoxia in tumors alters the cell metabolism (Warburg effect), and promotes invasion and metastasis, all together favoring a shift to malignancy (1-4), while, on the other side, therapeutic angiogenesis of ischemic organs has been challenging since new vessels are often disorganized, tortuous and hypoperfused, and unable to restore tissue oxygenation and nutrient delivery5. In a recent genetic study, we found evidence that a specific type of endothelial cells, which we named the “phalanx” cell, participates in the normalization of the endothelial cell layer, that allows vessels to readjust their shape, not numbers, to optimize oxygen supply when the latter is insufficient (Mazzone et al, Cell, in revision)(6). Directing the endothelial cell, therefore, towards a phalanx fate might represent a novel therapeutic strategy to combat cancer and promote revascularization of ischemic tissues. Our research aims to i) identify the genetic signature and the molecular basis of phalanx cells; ii) generate mice with overexpressed or silenced phalanx genes in the endothelium; iii) to functionally characterize phalanx genes during development, health and disease; and iv) to generate and characterize phalanx cell-reporter lines in mouse and zebrafish. Such insights might offer novel therapeutic opportunities to improve anti-cancer therapy as well as therapeutic angiogenesis for revascularization of ischemic tissues, largely unmet medical problems to date (3,5,7).

1. Fischer, C. et al. Anti-PlGF inhibits growth of VEGF(R)-inhibitor-resistant tumors without affecting healthy vessels. Cell 131, 463-75 (2007).
2. Mazzone, M. et al. An uncleavable form of pro-scatter factor suppresses tumor growth and dissemination in mice. J Clin Invest 114, 1418-32 (2004).
3. Mazzone, M. & Comoglio, P.M. The Met pathway: master switch and drug target in cancer progression. Faseb J 20, 1611-21 (2006).
4. Michieli, P. et al. Targeting the tumor and its microenvironment by a dual-function decoy Met receptor. Cancer Cell 6, 61-73 (2004).
5. Mazzone, M. & Carmeliet, P. Drug discovery: a lifeline for suffocating tissues. Nature 453, 1194-5 (2008).
6. Mazzone M et al. Endothelial haploinsufficiency of the oxygen sensor PHD2 inhibits metastasis by inducing endothelial normalization to a “phalanx” fate. Cell (in revision).
7. Aragones, J. et al. Deficiency or inhibition of oxygen sensor Phd1 induces hypoxia tolerance by reprogramming basal metabolism.[see comment]. Nature Genetics 40, 170-80 (2008).

Significance of Ig-receptor diversity in the innate immune system of insects

The Drosophila receptor Dscam it is a bi-functional Ig-recptor receptor essential for the formation of proper connectivity in the fly nervous system (Schmucker et al. 2000) and involved in innate immune responses (Watson et al. 2005). Dscam is a member of the immunoglobulin superfamily and is highly related to the human pro¬tein “Down syndrome cell adhesion molecule” (DSCAM; Yamakawa et al. 1998).

The Drosophila Dscam gene is extraordinarily complex and can generate some 38,000-protein iso¬forms through alternative splicing.  Dscam is expressed in hemocytes and fat body, which together constitute the primary cell types of the fly immune system. Variable Dscam receptors are also secreted into the hemolymph. In addition, efficient phagocytosis of bacteria depends on Dscam. Dscam can bind directly to surface epitopes of bacteria and this binding requires a variable binding domain (Meijers et al. 2006). This is particularly intriguing as this suggests the possibility that Dscam provides a surprising source of receptor diversity (i.e. thousands of immunoglobulin receptors) for the innate immunity of insects, which was thought to require only a small number of pattern recognition receptors.

Goal of this project is to examine the role of Dscam in innate immunity of insects, and in a general context the significance of receptor diversity in recognition specificity.

1. Schmucker D, Clemens JC, Shu H, Worby CA, Xiao J, Muda M, Dixon JE and Zipursky SL. Drosophila Dscam is an axon guidance receptor exhibiting extraordinary molecular diversity. Cell. 2000; 101: 671-84.
2. Watson FL, Püttmann-Holgado R, Thomas F, Lamar DL, Hughes M, Kondo M, Rebel VI and Schmucker D. Extensive diversity of Ig-superfamily proteins in the immune system of insects. Science. 2005; 309: 1874-8.
3. Chen BE, Kondo M, Garnier A, Watson FL, Püttmann-Holgado R, Lamar D and Schmucker D. The molecular diversity of Dscam is functionally required for neuronal wiring specificity in Drosophila. Cell. 2006; 125: 607-20.
4. Hughes E M, Bortnik R. Tsubouchi, A. Bäumer P, Kondo M, Uemura, T. Schmucker D. Homotypic Dscam-Dscam interactions control complex dendrite morphogenesis. Neuron2007; 54, 417-427.
5. Meijers, R, Püttmann-Holgado R, Skiniotis G, Liu J-H, Walz, T, Wang J-H, Schmucker D, Structural Basis of Dscam Isoform specificity. (Epub ahead of print, Aug. 26th); Nature. 2007; 449:487-91

Molecular, genetic and imaging approaches to synaptic connectivity in the CNS

The elucidation of molecular mechanisms that control neuron specific and spatially selective synapse formation is one of the key questions in developmental neuroscience yet remains technically a very challenging problem. Synapse formation in the central nervous system (CNS) is especially difficult for in vivo analysis. Despite the many experimental tools and forward genetic screens available in model organisms, the mechanisms underlying formation of synapses in the CNS especially the precise spatiotemporal control matching pre and postsynaptic contacts is essentially unknown.

Projects will therefore focus on generating transgenic animals for visualization of a small set of synapses within the CNS of the model organisms Drosophila and Xenopus tropicalis. Goal will be to improve protein-tagging and labeling for visualization of proteins at single specific synaptic sites within the developing and adult fly CNS.

We expect that this will help us to better analyze neural circuits using the following approaches:

• Time lapse and high-resolution analysis of axon branching, synaptic target site selection and synaptogenesis.
• Monitoring spatial and temporal specificity of synapse formation within the complex CNS
• Localization and tracking of synapse-forming proteins
• Exploring the possibility of screening for postsynaptic target sites and promoter elements that drive expression in postsynaptic target cells
• Screening and identifying novel factors involved either in spatially defined axonal branching or selection of specific synaptic target sites as well as synaptogenesis.

Dr Schmucker will be affiliated to the Faculty of Medicine of the University of Leuven from March 2009.

1. Schmucker D, Clemens JC, Shu H, Worby CA, Xiao J, Muda M, Dixon JE and Zipursky SL. Drosophila Dscam is an axon guidance receptor exhibiting extraordinary molecular d iversity. Cell. 2000; 101: 671-84.
2. Watson FL, Püttmann-Holgado R, Thomas F, Lamar DL, Hughes M, Kondo M, Rebel VIand Schmucker D. Extensive diversity of Ig-superfamily proteins in the immune system of insects. Science. 2005; 309: 1874-8.
3. Chen BE, Kondo M, Garnier A, Watson FL, Püttmann-Holgado R, Lamar D and Schmucker D. The molecular diversity of Dscam is functionally required for neuronal wiring specificity in Drosophila. Cell. 2006; 125: 607-20.
4. Hughes E M, Bortnik R. Tsubouchi, A. Bäumer P, Kondo M, Uemura, T. Schmucker D. Homotypic Dscam-Dscam interactions control complex dendrite morphogenesis. Neuron 2007; 54, 417-427.
5. Meijers, R, Püttmann-Holgado R, Skiniotis G, Liu J-H, Walz, T, Wang J-H, Schmucker D, Structural Basis of Dscam Isoform specificity. (Epub ahead of print, Aug. 26th); Nature. 2007; 449:487-91

The VRC participates in the Doctoral School Programme Emerging concepts of Cardiovascular Medicine of the Leuven International Doctoral School Biomedical Scienes