Abstract 12680: Id1 May Spatiotemporally Regulate Endothelial Cell Movements Driving Angiogenesis
Id1, an HLH transcriptional factor, has emerged as a potent contributor of angiogenesis, however the underlying mechanisms remain unknown in detail. To dissect the issue, we first examined the expression of Id1 in endothelial cells (ECs) during in vivo and ex vivo angiogenesis. We identified a mosaic pattern of Id1 expression, composed of ECs with different Id1expression levels, in an angiogenic sprout in mouse embryonic brain and postnatal retina, and in aortic ring assay. Interestingly, total levels of Id1 appeared to oscillate periodically in confluent HUVECs independently of cell cycle, possibly explaining the mosaic expression pattern during angiogenesis. Next, we addressed how Id1 contributes to angiogenesis. Because Id1-knockdown reduced VEGF-induced HUVECs motility, we hypothesized that Id1 might affect collective ECs movement in angiogenesis. To validate the possibility, we have established a time-lapse imaging and computer-assisted analyzing system which visualized and characterized the dynamic behavior of ECs driving an ex vivo angiogenesis with a nuclear tracking. In addition, we analyzed the individual behavior in more detail by visualizing cell shape with adenovirus-mediated EGFP signal (mosaic analysis). These analyses showed that sprouting angiogenesis was driven via complex and heterogeneous EC movement, where individual ECs moved fast or slow, overtaking each other, and as a result, relative positional relationship was dramatically and dynamically changed (“Cell-mixing”), even at the tip. In mosaic analysis, we observed that highly motile ECs display forward-rear cell polarity whereas less motile ECs were spindle-shaped without cell polarity, and individual ECs switch the two motile modes dynamically. Furthermore, an in vivo EC-tracking analysis revealed evidences for cell mixing in murine developing retinal vessels. Considering the dynamic and heterogeneous EC movements, we propose a possible mechanistic model, in which Id1 might spatiotemporally control EC movement driving angiogenesis partially via oscillation of the expression level. We are now examining how Id1 links to EC movements driving sprouting angiogenesis using the time-lapse imaging system.
- © 2011 by American Heart Association, Inc.