A flow cytometry investigation into the effect of Sema3a on the angiogenic signaling cascade of VEGF-A
- Thomas Vandergon, Professor of Biology, Pepperdine University
- Donna Nofziger Plank, Associate Professor of Biology, Pepperdine University
Vascular development during angiogenesis may be affected by the local composition of positive and negative growth factors. Semaphorin 3a (Sema3a), a signaling molecule known to stop vessel sprouting and cause leakiness, shares the co-receptor neuropilin-1 (NP-1) with vascular endothelial growth factor A (VEGF-A), a prominent inducer of vessel sprouting and growth. While these antagonists do not directly compete for a binding site on NP-1, each signal may induce an opposite endothelial cell behavior: growth (VEGF-A) or regression (Sema3a). In this study, the effect of Sema3a on the VEGF-A signaling cascade in human umbilical vascular endothelial cells (HUVECs) was investigated. We hypothesized that Sema3a would depress the response of the VEGF-A signal cascade. We used flow cytometry and fluorescent probes to measure delta-like ligand 4, VEGF receptor 2, and Notch1 response changes between these two signals. Sema3a, VEGF-A, or both were added to cultured HUVECs at equal concentrations. In general, Sema3a induced lower expression of the signal cascade than VEGF-A, which agrees with the established understanding of their competing effects. The combined Sema3a/VEGF-A treatment results were equivocal, meaning that some results appeared intermediate between the individual treatments whereas others appeared similar to the VEGF-A-only treatment. Similar results were found when we analyzed the median fluorescence values, which are a relative estimate of surface marker concentration. Given the protocol used, it may be that increased HUVEC sensitivity to VEGF-A versus Sema3a might explain the dual-signal results. Continued study of the interaction between semaphorin and VEGF signaling could potentially be used to optimize angiogenic therapy-based treatments of various cancers.