The vascular endothelium has a well-established function in nutrient and gaseous exchange between tissues and blood. It also involved in organogenesis, but the importance of signaling between the endothelium and surrounding cells has been unclear. In the February 7 Science, Jennifer LeCouter and colleagues from Genentech Inc, South San Francisco, USA, show that VEGFR-1 triggers liver endothelial cells to communicate with neighboring hepatocytes by promoting secretion of growth and survival factors (Science, 299: 890-893, February 7, 2003).

LeCouter et al. studied the effects of vascular endothelial growth factor (VEGF) receptor activation on mouse hepatocyte growth. They observed that delivery of VEGF-A increased liver mass in mice but did not stimulate growth of hepatocytes in vitro, unless liver sinusoidal endothelial cells (LSECs) were also present in the culture. Hepatocyte growth factor (HGF) was identified as one of the LSEC-derived paracrine mediators promoting hepatocyte growth. In addition, they...

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