Deciphering the role of Apelin signaling in the development of the lymphatic system

• Applicant: Professor Dr. Christian Helker
• Subject Area: Developmental Biology
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 506858860

The formation of a functional lymphatic system is essential for the drainage of interstitial fluid and immune cell trafficking. Moreover, recent work has shown that lymphatic vessels modulate organ homeostasis and regeneration in different organ-specific environments in adults. Therefore, understanding the developmental pathways leading up to the formation of the lymphatic system is a key to identify therapeutic targets to modulate lymphatic vessel growth during physiological and pathophysiological conditions. During embryonic development, venous endothelial cells are stimulated by growth factors to specify into lymphatic endothelial cell (LEC) cell fate. Subsequently, LECs adapt a highly migratory and proliferative phenotype in response to growth factors to form new lymphatic vessels (lymphangiogenesis). So far, most identified growth factors regulating lymphangiogenesis activate enzyme-coupled receptors, such as receptor tyrosine kinases. However, far less is known about the function of G protein-coupled receptors (GPCRs), the most successful class of druggable targets in the human genome, during lymphangiogenesis.In this project, we will analyze the function of Apelin receptor signaling, a class A GPCR, during lymphangiogenesis in developing and adult zebrafish. We observed that apelin mutant zebrafish larvae display a complete lack of lymphatic vessels in specific anatomical regions. In order to analyze the expression, as well as the function of Apelin ligands and receptors during lymphangiogenesis, we generated a set of novel transgenic reporters, mutants and overexpression fish lines for the Apelin signaling pathway. To gain insights into the integration of Apelin signaling into the network of pro-lymphangiogenic pathways, we set up a fast and reliable genetic interaction assay. Using this assay, we could identify Vascular endothelial growth factor C signaling, a well-known pro-lymphangiogenic pathway, as an Apelin interacting pathway. In preliminary in vitro experiments, we generated a map of the phosphoproteome downstream of Apelin signaling, which we will use, in combination with RNA-sequencing, to identify the key downstream targets of Apelin signaling in LECs. Overall this project will provide new insights into the fundamental principles of lymphatic vessel formation and Apelin signaling, enabling a better understanding of lymphatic vessels growth in health and disease.

• DFG Programme: Research Grants