Analysis of Notch signalling pathway activation in controlling artery formation during sprouting angiogenesis
Cell Biology
Final Report Abstract
The aim of this proposal was to determine Notch pathway activation in newly growing blood vessel sprouts and how this pathway might interact with the transforming growth factor beta/bone morphogenetic protein (TGFb/BMP) signaling pathway in regulating blood vessel morphogenesis through influencing gene expression patterns. We first performed live imaging of Notch signaling in endothelial cells by making use of a transgenic Notch indicator line. These results showed that Notch signaling was first activated in leading tip cells of nascent blood vessel sprouts, followed by pathway activation in trailing cells. This activation was preceded by expression of the main Notch ligand in the vasculature, dll4. Through cell transplantation experiments we showed that Notch pathway activation occurred in trans from follower cells to the leading tip cell. When analyzing mutants for the BMP receptor alk1, we found that these cells preferentially contributed to tip cell positions within blood vessel sprouts, similar to Notch deficient cells. We further found that alk1 signaling repressed cxcr4a expression. Thus, increases in cxcr4a expression might account for the overrepresentation of alk1 mutant cells within tip positions. Interestingly, this increase in cxcr4a expression was opposite of what we observed in Notch signaling mutants, where cxcr4a expression was initially downregulated, but only at later stages showed increased expression. We are currently investigating the reason for this difference. Finally, we show that in a setting of blood vessel growth, in which venous cells exclusively generate veins, Notch signaling is dispensable for blood vessel morphogenesis. Together, our results suggest that Notch signaling is solely important to regulate blood vessel sprouting in settings where arteries need to be generated and that one important aspect of both Notch and TGFb/BMP signaling is the regulation of cxcr4a expression. We are currently analyzing the downstream factors through which Notch and TGFb/BMP influence cxcr4a expression and plan to examine possible crosstalk between these factors.
Publications
- (2017) Endothelial Notch signalling limits angiogenesis via control of artery formation, Nature cell biology, 19(8):928-940
Hasan, S. S., Tsaryk, R., Lange, M., Wisniewski, L., Moore, J. C., Lawson, N. D., Wojciechowska, K., Schnittler, H. and Siekmann, A. F.
(See online at https://doi.org/10.1038/ncb3574) - (2019) Veins and Arteries build Hierarchical branching patterns differently: Bottom-Up versus Top-Down, Bioessays, 41(3):e1800198
Red-Horse, K., Siekmann A. F.
