In vitro imaging of angiogenesis using embryonic stem cell-derived endothelial cells
Angiogenesis is an important event during developmental processes, and it plays a key role in neovascularization. The development of an in vitro model that can be used for live imaging of vessel growth will facilitate the study of molecular and cellular mechanisms for the growth of blood vessels. Embryonic stem cells (ESCs) are considered to be a novel renewable source for the derivation of genetically manipulable endothelial cells (ECs). To derive green fluorescence protein (GFP)-expressing ECs, we used a transgenic ESC line in which a GFP reporter was driven by the endothelial-specific promoter fetal liver kinase 1. ESC-ECs were isolated from 11-day embryoid bodies by fluorescence-activated cell sorting. Embedding the aggregated ESC-ECs in a 3-dimensional collagen gel matrix resulted in ESC-EC migration out of the aggregates and coalescence into a capillary network. Time-lapse microscopy revealed EC migration, proliferation, lumen formation, and anastomosis to other capillary vessels during this process, which were reminiscent of angiogenic processes. Vascular endothelial growth factor plays major roles in the induction of ESC-EC angiogenesis in vitro. Blockage of the β1 integrin subunit severely impaired ESC-EC survival and migration. We demonstrate that our in vitro ESC-EC angiogenesis model represents a high-resolution dynamic video-image system for observing the cellular events underlying angiogenic cascades. We also consider this model as an image screening tool for the identification of pro-angiogenic and anti-angiogenic molecules.