1. Neuro-vascular cross-talk and targeting of neuro-degenerative diseases:
The vascular network closely associates with the neuronal network throughout embryonic development, in adulthood and during tissue regeneration. Close association of vessels and nerves allows reciprocal cross-talk involving diffusible molecules, which is important for physiological functions in both domains. Arteries secrete factors that attract sympathetic axons, and adrenergic innervation of arteries allows the autonomic nervous system to control arterial tone and tissue perfusion. The nervous system on the other hand requires a specialized network of blood vessels for its development and survival. Metabolically active nerves rely on blood vessels to provide oxygen necessary for sustaining neuronal activity, and disturbances herein result in neuronal dysfunction. How nerves attract blood vessels is debated, but several studies addressing vascularization of the mouse embryonic nervous system suggest that the angiogenic cytokine VEGF-A is involved. In the mouse peripheral nervous system axons of sensory nerves innervating the embryonic skin trigger arteriogenesis involving VEGF-A - Neuropilin-1 (Nrp1) dependent signaling. While these studies provide evidence for the physical proximity and cooperative patterning of the developing nerves and vasculature, relatively little is known about mechanisms controlling VEGF-A signalling at the neurovascular interface. We are interested in the cellular and molecular mechanisms contributing to organo-typical vascularisation of the nervous system. As part of an effort to translate our experimental findings to the clinical setting, we furthermore explore how targeting neuronal vascular network structure can help to overcome neuro-degenerative processes and ischemic stroke.
2. Vascular remodelling - Angiogenesis and Arteriogenesis - in ischemic cardiovascular diseases:
The arterial vascular network distributes blood flow through the body, a process crucial for sustaining organ function and homeostasis. During embryonic development arterial networks enlarge and expand to meet the increasing metabolic demand of the growing and differentiating tissue. Also in ischemic cardiovascular diseases, revascularization, and regeneration of hypoperfused organs involve adaptations of the arterial system. Selective targeting of the arterial growth process, and in particular creating arteries with a structurally large diameter to enhance flow conductance and relief hypoxia, is considered therapeutically relevant for treating patients with ischemic cardiovascular diseases. The molecular and cellular mechanisms controlling arterial diameter are only partly understood but involve interactions between blood flow - hemodynamic factors - and endothelial cells, and BMP-Smad signaling controlling distinct endothelial cell behaviors during the vascular remodeling process. We are interested how blood vessels sense changes in tissue metabolism and how such information is processed into changes in vessel dimensions and network architecture. We are furthermore interested in the design of small molecules for tissue specific tailored revascularization strategies. In order to translate our experimental findings to the clinical setting we closely collaborate with experts in large animal models (mainly pigs) and clinical experts in angiology, and cardiology. We currently have several targets in the pipeline, at various stages of validation in (pre-)clinical-experimental settings.
3. Angiocrine control of tissue regeneration:
The microvascular circulation comprises a vast network of capillary endothelial cells that connects the arteries to veins. Besides transporting oxygen and nutrients, the microcirculation fulfils additional important physiological tasks: sustaining the homeostasis of resident stem cells and guiding the regeneration and repair of adult organs. Emerging evidence suggests that epithelial, haematopoietic, mesenchymal and neuronal cells — together with their corresponding repopulating stem and progenitor cells — reside in proximity to capillary ECs. Genetic and biochemical studies have shown that ECs serve as a fertile, instructive niche that has important roles in homeostasis, metabolism and directing organ regeneration in a perfusion-independent manner. Tissue-specific ECs regulate these complex tasks by supplying the repopulating cells with stimulatory and inhibitory growth factors, morphogens, extracellular matrix components and chemokines. These EC-derived paracrine factors are defined collectively as angiocrine factors (Rafii, Nature, 2016). Angiocrine factors comprise secreted and membrane-bound inhibitory and stimulatory growth factors, trophogens, chemokines, cytokines, extracellular matrix components, exosomes and other cellular products that are supplied by tissue-specific ECs to help regulate homeostatic and regenerative processes. Aberrant production of angiocrine factors could constitute the underlying pathogenesis of various conditions, such as cardiovascular or cerebrovascular diseases and the ageing process.Through single cell sequencing we recently identified several novel potential mediators of angiocrine signalling. To address their functional role in angiocrine signalling we are examining cardiac, neuronal and muscle repair in a series of zebrafish in which these potential mediators were genetically silenced or over expressed in an organ-context specific manner.
4. EC cell-type specific metabolic demands:
The main function of endothelial cells outlining our vasculature is to transport oxygen and reduced carbons to organs and tissues and to supply each and every cell of our body with oxygen and reduced carbons.
Angiogenic sprouts tackle distinct metabolic tasks. The tip cell of an outgrowing sprout explores its surrounding by massive outgrowth of filopodia, where the treadmilling process of actin polymerization consumes high amounts of cytoplasmic ATP. Thus, glycolysis is highly upregulated. Stalk cells, instead, are highly proliferative and thus use reduced carbons manly to produce new biomass. Roughly spoken, in tip cells anaerob catabolism dominates whereas in stalk cells anabolism dominates.
In this project we knock-down (morpholino) and knock out (Crispr/CAS) metabolic key enzymes including PFK2B3 and PEPCK as well as upstream transcription factors including c-myc and/or overexpress them in a cell-type specific manner. Furthermore, we combine these molecular approaches with the application of pharmacological inhibitors. Time-lapse imaging of the vasculature combined with qPCR will allow us to decipher specific aspects of sprouting angiogenesis depending on distinct metabolic pathways. This knowledge might help to support medical applications in the treatment of cardiovascular disorders.